source
stringlengths 620
29.3k
| target
stringlengths 12
1.24k
|
|---|---|
Why are airports in Greece blurred and low res in Google Maps? Why are airports in Greece blurred and low res in Google Maps? <Q> The short answer seems to be that some countries have persuaded Google to blur out specific areas for "national security" reasons. <S> Wikipedia has an article on it with some more (limited!) information. <S> Interestingly, I couldn't find any official Google article on blurring in Maps, apart from some general references to Street View. <S> And, as it turns out, Street View at ATH works as normal. <S> FWIW, it seems that Greece didn't persuade Microsoft to play along, because Bing Maps has much better images . <S> That strongly suggests that the blurring is mostly security theater . <S> (By the way, I'm not saying that there are no security/privacy risks with Google Maps, Bing or other tools; it's just that some risks are more credible than others. <S> security. <S> SE would be a good place to ask more about that.) <A> Most other countries have entirely separate military bases. <S> With Greek geography being so fragmented by mountains and islands though, and with such a shortage of flat land where runways can be built, it simply isn't practical for every island and every major area of habitation to have separate air force bases and civilian airports. <S> Combining the two makes absolute sense; but it does have the knock-on effect of requiring precautions to be taken for the civilian airport which would normally only apply to a military establishment. <S> Most Western countries wouldn't consider this level of military infrastructure to be necessary. <S> After the Turkish invasion of Cyprus in 1974 though, Greece is very aware of the vulnerability of its territory and the need to be able to rapidly deploy troops to defend that territory. <S> This is a major factor in Greece still requiring its young people to carry out national service. <S> The military are regularly visible in a way which might be normal for people in Northern Ireland or Israel, but not for people in much of the rest of the world. <A> This blurring or pixellation is quite common on military airfields in France, and I've even seen a few military airfields in the Netherlands pixellated. <S> Ironically, the fact that the area is pixellated is a huge red flag to 'there's something interesting here'! <S> It's not just airfields <S> ... in France there is a place to the north of Paris which is pixellated, but it's in the suburbs (no airfield anywhere near!) <S> see N 49.032600 <S> E2.221700 <S> ... <S> it's a place called Tavernay. <A> I was once getting a flight home from a small airport on the Greek mainland. <S> We boarded the plane but take off was delayed for a long time. <S> The pilot got on the intercom and apologised for the delay which was 'due to congestion in the Athens airspace'. <S> We then saw a Nato AWACS take off from the runway we were waiting to use. <S> Shortly after that two very smartly-dressed Greek Air Force officers walked out of the flight deck, got in a car and drove away. <S> Short answer: many Greek civilian airports have a military role as well.
|
In Greece, many domestic airports are (or were) either officially military airports, or they have an air force base attached which uses the airport.
|
Why does this 757 have a propeller engine attached to the fuselage? I saw the following photo of a Honeywell Aviation Services Boeing 757-225 : If it's not a fake, the airplane has a propeller mounted on a pylon on one side. What's the purpose of such strange design? Why does it need a propeller engine, if it already has two jet engines? Or is it a permanently deployed RAT ? <Q> From the description below the image you linked: The Honeywell, Boeing 757 test bed appeared on static display for a few days before departing half way through the event. <S> A testbed aircraft is an aircraft used for flight research or testing new equipment such as engines. <S> You can see other photos without engine or with a jet engine instead of a propeller one. <S> The engine is not needed to fly, but is being tested, and apparently that position has been deemed a good solution to the problem "where do we attach an extra engine we need to do tests on?". <A> The airplane doesn't "need" that engine. <S> Obviously, you don't want to rely on the engine you're testing <S> , in case something goes wrong! <S> So the plane flies with 2 large turbofan engines, while the engineers are testing the smaller engine mounted up front. <S> If you look closely, you can even see the airplane is labeled "Flight Test". <A> Testing a new engine design can only go so far on the ground. <S> At some point, it has to be tested in conditions representative of actual use - in other words, in flight. <S> You don't want to be dependent on an untested engine to get you airborne and back on the ground safely. <S> The solution to this problem is to mount the test article on an aircraft that is entirely airworthy regardless of the operational state of the engine under test. <S> That way the test engine can be put through its paces without compromising the safety of the test crew.
|
It is a test platform for testing the engine during flight.
|
How many parts does the latest-generation 737 share with the original 737? There is an old paradox which states that if a boat sails round the world replacing worn out parts as it goes, once it has replaced all of itself is it still the same boat? I choose the 737 because it's been around for over 50 years. Specifically, is there anything from the original tooling for the 737-100 that would be a straight out replacement for a 737-MAX? 737-100 source 737-MAX-7 source <Q> The cross section and cabin pressure have remained the same. <S> From what I can tell virtually every part is different. <S> Even parts that might have been able to retain the same shape/loading have gotten improved materials and/or corrosion treatments. <S> I am still looking to see whether any window panels could be common as the holes into which they go have remained the same. <S> Looking at a couple of generations shows major differences, allowing elimination of whole sections of the aircraft. <S> Wings, tail, engines, pylons, landing gear, fuselage center sections, APU, interior and flight deck have all surely changed. <S> Originally conceived as a 60 seat jet, the first production model was designed for 100 seats . <S> The Max10 now goes to 230. <S> The Max also had major improvements to the the cockpit. <S> Even the throttle levers changed. <S> Here is a photo comparison to the original -100 flight deck. <S> b737-100 <S> b737-max <S> NG changes , both structural and cosmetic. <S> larger wing with new flaps slats larger tail with improved rudder and elevator <S> simplified higher capacity landing gear engines new AC electrical system new corrosion resistant materials and treatments throughout the plane new interior seats, panels, bins, coverings improved avionics <A> My first guess might be the wet compass, or the galley coffee pot. <S> The TCAS control head wasn't original in the -200, but the ones installed in those aircraft might still work in a NG; not sure if a Max needs a different one or not. <S> Some other obscure part might fit the bill, but I don't know what. <S> Roller for the toilet paper holder, maybe? <S> Plastic guards on the guarded switches? <S> Individual switches for things like generators and hydraulic pumps, perhaps. <S> The commonality is less from the -100/-200 to the Max, as it is from the -100/-200 to the "Classic" series (-300 thru -500) to the NG and then to the Max. <S> For each step, it was a common type rating and fairly quick "differences training". <S> For instance, the Max still uses a Master Caution system, rather than an EICAS. <S> Reason? <S> To maintain backward compatibility to the Next Gen aircraft, which didn't have an EICAS in order to maximize compatibility with the Classics. <S> Likewise, much of the overhead panel would be recognizable to a 737-200 pilot, and nearly identical to a Classic overhead. <S> Not "same part number" identical, but very, very close. <S> A pilot who has flown both pointed out that the 737 NG is a newer design than the 777, even though the latter when it rolled out 20+ years ago <S> was far more automated than the Max is today! <S> Certainly not simply a marketing device but very real similarities and roots to the past. <S> I doubt many parts from a 50 year old Corvette would fit a brand new one, either, but that doesn't deny the lineage dating back to the original! <A> By the numbers, this is the most I could find. <S> The 737 Original shared 60% of the trijet 727. <S> In fact the 737 had a 60% parts commonality with the 727 which included the doors, leading edge devices, nacelles, cockpit layout, avionics, components and other fittings. <S> One of the objectives was to have a high degree of commonality with the 737-200, the achieved figure was 67% by part count. <S> And the NG uses 33% fewer parts (in total ~600,000) compared to the Classic. <S> The NG's have 33% fewer parts than the Classics which reduces production time. <S> I could not find figures for the MAX. <S> But cockpit, winglets, landing gear, and engines aside, it's still an NG at heart. <S> Quotations source: b737.org.uk <S> Commentary: <S> Considering the JT8D engine , one could say the Original has more in common with the 727 than it does with the MAX.
|
The Max has plenty of switches and conventions that are very close to the -200, just not quite identical. The Classic series shared 67% of the parts of the Original. Only a mechanic with the list of part numbers could tell for sure.
|
What is this airport video? I was in a car dealership waiting room and saw this video of an airport that was slowly scrolling down the screen (like River Raid). The video is in motion - the cars on the street are moving and the 2 planes on the left were taxiing. The scrolling is very smooth - as if it's a satellite or maybe blimp. Is this real video or just CGI? What airport is it? How did they get the video while it was obviously in use? Wouldn't the airspace above the airport be restricted? <Q> [WARNING: high-def video link, ~267MB] [ alternate YouTube version , thanks to Mark]). <S> It's not CGI. <S> Apple used a variety of drones and helicopters to shoot the footage. <S> While the airspace around the airport is generally controlled (not restricted), there are a number of VFR flight routes that cross the airport . <S> These can be seen on the Los Angeles Terminal Area Chart . <S> In the case of this specific video, permission was presumably coordinated with ATC. <S> As the video was taken down the middle of the airport, between the sets of runways, it's likely that taking it didn't interfere with air traffic; traffic arriving/ <S> departing LAX won't be flying there. <S> This tweet (with photos) just crossed my feed. <S> @ethanklapper <S> : Today was special. <S> Chartered a helicopter and flew above LAX at 2,500 feet. <S> Took 500 pictures in an hour. <S> Can’t wait to share more! <S> I imagine a similar process was used for this video. <A> Plane Spotting is done regularly over LAX. <S> In fact there are a number of helicopter tour companies that will fly you over LAX often with open door. <S> Here is one tour company that has a map of the areas they can fly over. <S> Also in the Sept. edition of Airliner World they talk about the process in more details. <A> This is the Tom Bradley International Terminal (TBIT) at LAX. <S> Though I'm not sure how they filmed it. <S> If it's moving in real time I don't think it's satellite. <S> Drone seems like it may make the most sense, but it seems like it would be a huge pain to get permission to fly a drone right there, even though planes are not (hopefully) flying that low over the terminals. <S> Maybe another poster can chime in.
|
Specifically, the video is one of the Apple TV's screensaver images, taken at LAX ( this one in particular
|
Where in the FAR or AIM is a high speed taxi defined? While monitoring coms I recently heard a Cessna Centurion that had just cleared the runway request a "high speed taxi", which was approved by the tower. I'm assuming that means he wants to taxi at a faster than normal rate to his FBO of choice. Are high speed taxis defined somewhere as something you can request of ground control? <Q> There's no definition in the AIM or regulations, as far as I know, but there is one in <S> the P/CG , sort of (emphasis mine): <S> HIGH SPEED TAXIWAY− <S> A long radius taxiway designed and provided with lighting or marking to define the path of aircraft, traveling at high speed (up to 60 knots) , from the runway center to a point on the center of a taxiway. <S> Also referred to as long radius exit or turn-off taxiway. <S> The high speed taxiway is designed to expedite aircraft turning off the runway after landing, thus reducing runway occupancy time <S> So at least as far as the FAA is concerned, a high-speed taxi may be up to 60kts. <S> As for requesting it, you can request more or less anything. <S> There's an active EAA chapter at my local airport and pilots who are in the process of building and testing aircraft sometimes request a high-speed taxi on the runway. <S> The controllers don't question it or set any speed restrictions, it's all on the pilot. <S> I suppose if things were busy they might deny the request, but the pilots know to do these things at quiet times anyway. <A> He was likely asking for approval to use the runway for a simulated take off without actually departing. <S> Usually testing engine performance after modifications. <A> Normal SOP's are 30kts max with 10kts preferred. <S> The rule I have seen for most flight training schools is "no more than a fast walk" . <S> While not specific to the FAA's FAR or AIM, this FAA video describes the design and requirements of high speed taxies and refers technical specifications to AC 150-5300-13A-chg1 . <S> They define a high speed taxi as having no more than 30deg <S> and nor more turn radius than <S> 1500ft . <S> The exact dimension depends on aircraft category, IFR minimums, whether a reverse turn is needed, etc. <S> No speed requirements are required, they define the accommodation for speed as "higher than normal taxi speed" . <A> Taking a "High Speed Taxi" refers to using a specific taxiway designed to exit the runway at a high speed after landing. <S> The term does NOT refer to using ANY taxiway at a high speed. <S> Larger busier class D, C, and B airports have these highspeed taxiways. <S> An example of this is Taxiway Hotel at Van Nuys off of 16R. Thus the pilot you mentioned was requesting "the highspeed" taxiway to exit after landing. <S> Whether he did that at a slow rate or fast rate was up to him. <S> I frequently use the above taxiway at VNY because instead of taking the other taxiways at a 90 degree angle (which requires slowing down to almost a crawl to exit the runway), the highspeed is at a 30 degree angle to the runway which allows aircraft to exit the runway much faster than conventional taxiways. <S> Busier airports want to get planes on and off the runway as fast as safely possible to help the flow of traffic. <S> Highspeed taxiways help this process.
|
The FAA does not provide a taxi speed limit but most airlines require observance of SOP "standard operating procedures" as part of their certification process.
|
Do swept back wings affect the moment of inertia of an aircraft enough to be relevant for the roll response? I have studied that swept back wings help in delaying the shock waves formed on the wing, but also to my understanding I feel swept back wings reduce the moment of inertia (like for example a ballerina dancer where she spins so easily when she keeps her hands close to her body). This in turn helps in improving the roll response which is an advantage to a fighter jet. So is my understanding correct? <Q> A wing has three basic design parameters—span, chord and sweep—which are all independent of each other. <S> Span is always measured along the perpendicular axis of the whole aircraft and chord is always measured along the longitudinal axis. <S> So pivoting the wing around its root will change all three parameters and affect the properties that depend on them. <S> When designing the aircraft, you choose area (span times chord) to give you the needed amount of lift, then span to give you the desired minimum lift-to-drag speed and sweep for transsonic capability and/or stability. <S> So you should be comparing swept and unswept wing of the same span and area, and those somewhat obviously have the same moment of inertia in roll. <A> Yes, for a low-speed aircraft, swept wings are useful to avoid problems with the center of gravity, to move the wing spar into a more convenient location, or to improve the sideways view from the pilot's position. <S> This increases the longitudinal static stability of the aircraft as done by Anglo-Irish engineer John William Dunne. <S> The slight rearward shift of the aircraft center of gravity is caused by the rearward shift of the wing weight. <S> Indicated by the cross-hatching is the distance between the center of gravity and the center of lift. <S> Another issue with variable swept wings is reduced pitch stability due to additional lift and fuse interference. <S> They tend to suffer from lower yaw stability. <S> Also one should note that the mechanism for variable swept wing increases weight of the aircraft. <S> You also have to keep in mind that variable swept wing aircrafts were designed in an era that focused more on speed rather than maneuverability. <S> The ideology changed after realising the data that showed how much time these aircraft spend in supersonic speeds and hence the focus shifted from speedy to more agile aircrafts. <A> The Bell Airacobra was designed with the ballerina or ice skater analogy in mind by centering the weight as much as possible. <S> Amazingly, the Dunne swept wingbiplane (with rudders at the wing tips too) wasrejected as being TOO STABLE for military use! <S> Sweeping the wing was originally used for issuessuch as adjusting center of lift. <S> The B17 production design, with its huge new tail and lots of weight aftcompared to the prototypes, may have benefited from alittle sweep. <S> Adding the chin turret on the G modelmay have helped with weight balance considerably. <S> Swept wings can be also found in the Tiger Moth biplane. <S> It was serendipitously discovered that sweep also helps delay the onset of shock waves as one approachesMach 1 and became very popular at the dawn of thesupersonic age. <S> This is a famous story. <S> Not as often told, but equally true <S> , is making thewings THINNER, as on the Spitfire, also helped a lot. <S> But as far as ballerinas, it turns out that roll rateis generally improved with shorter wings as on the F16, but weight distribution remains important. <S> PS Birds do pull the inside wing in while turning, which also helps them slip-turn with their tails. <A> I feel swept back wings reduce the moment of inertia (like for example a ballerina dancer where she spins so easily when she keeps her hands close to her body). <S> If you take a straight wing and sweep it back, yes the moment of inertia is lowered. <S> This in turn helps in improving the roll response which is an advantage to a fighter jet. <S> So is my understanding correct? <S> No, it is not an advantage to a fighter jet, because planes place aileron control surfaces outboard from the fuselage (closer to the wing tips), as you sweep the wing back, the arm from the aileron to the fuselage gets smaller, resulting in a smaller moment being applied. <S> As a result, your roll response will be smaller if you swept the wing back, despite the lower moment of inertia. <S> The moment of inertia doesn't get much smaller - fuel tanks are located either in the fuselage or inboard in the wings, so most of the mass stays pretty much where it was before, as the outboard wing sections are empty and light. <S> The F-14 deployed straight wings during dogfights for better maneuverability, sacrificing top speed. <A> There is more than just the moment of inertia involved in the roll response, and the response itself is more than just one figure. <S> Let's consider something like a swing-wing airplane, where nothing changes except for the sweep angle. <S> Furthermore, we'll assume standard ailerons control, which rarely happens on the actual swing-wing aircraft. <S> The difference in inertia will be noticeable but not that great: most of the mass is still in the fuselage. <S> (Especially this applies to real swing-wings, where it is difficult to carry the fuel and ordinance under the wing). <S> That said, the contribution of the wingtips will reduce as a square of the reduction of the wingspan. <S> But there are also forces involved. <S> The most significant ones will be the ailerons (control) moment and the roll damping. <S> If we have ailerons near the wing tips, the moment from them will reduce linearly with the wingspan. <S> At the same time, roll damping depends on the square of wingspan and so will reduce more. <S> Damping reduction is the most drastic effect: the wing is almost exclusively responsible for it. <S> This fundamentally differs airplanes with the proverbial ice-skaters and ballerinas. <S> Overall, in a typical case, with a longer wingspan you may get faster initial response (ignoring aeroelastic effects, which may reverse the trend even here), but significantly slower sustained roll rate. <S> Aircraft with short stubby wings may get in trouble due to their fast roll rate, even if (and partly because) their ailerons do not seem that efficient: see inertia coupling .
|
A small amount of longitudinal stability is highly desirable, but the large increases with sweep angle can cause reductions in aircraft maneuverability and large increases in trim drag .
|
Can an APU be designed to also provide emergency thrust in the event of a double engine failure? Commercial airliners seem to be moving towards twin jets with incredibly powerful 100,000+ lb thrust engines becoming available for use. Would it be possible to design the APU to provide enough thrust to push an aircraft to a nearby runway in the event theyboth fail as a safety measure? <Q> No, it would not be possible with current technology. <S> To scale the APU to an engine that provides thrust, you would basically have to turn it into another engine, with significant weight penalty. <S> The position of the APU inlet and outlet would have to be re-designed, not to mention mechanisms that allow it to produce variable thrust. <S> In short, it would be turning the plane into a tri-jet. <S> Furthermore, the chance of a double independent engine failure are slim. <S> If a condition would lead to both engines fail, it would very likely lead to failure of any remaining engines. <S> Perhaps decades later, we can produce a powerful jet engine using lightweight materials. <A> Keep in mind that the APU is a turboshaft engine, not connected to a prop but a generator. <S> Therefore, any exhaust exiting the APU will have lost most of its thrust to the shaft turbines, or to bleed air used to power any aircraft systems that would normally be powered by main engine bleed air. <S> Sure, you could enlarge the APU to the point where it could supply thrust, but... <S> it would be very inefficient as an APU (gas turbines don't run at low power settings very efficiently), it would add substantially to both weight and drag when it wasn't in use, and it would be essentially another main engine. <S> The whole point of an APU is to supply power and bleed air efficiently to an aircraft when the main engines aren't running... <S> when it's parked on the ground. <S> Typically, on an airliner, the APU also supplies bleed air to start the main engines if ground based bleed air isn't available. <S> And typically the APU is small so it can be started by the aircraft's battery. <S> The keyword being efficient... for which it must be as small and light as possible, and consume as little fuel as possible. <S> Given the very high reliability in today's gas turbines, an APU that can also supply sufficient thrust to keep the aircraft flying wouldn't be necessary, and would make for a fuel hungry aircraft. <A> Quote from Jane's Aero Engines 2017-2018: <S> APU: auxiliary power unit. <S> An easily started gas turbine, usually forming a self-contained package inside the aircraft, which, either on the ground or following main-engine failure, can suply some of the following: shaft power, hydraulic power, electrical power, high-pressure aire, and (in a few recent cases, mounted in the tail) emergency propulsive thrust .
|
Converting the APU into a thrust producing device would be a complex engineering exercise with little to no benefit in risk reduction.
|
Is it okay to take off with weight more than the POH max gross weight? I wonder if I could take off with weight more than the gross weight stated in the POH of my aircraft as long as I take off with a higher speed? I think I have done it once by mistake. <Q> Can you take off over gross weight? <S> It's very easy to go above gross in a Cessna 152 with full fuel and 2 passengers, and probably happens more often than people realize or own up to. <S> That doesn't make it a good idea, which is why pilots are trained to do weight and balance plus performance calculations before every flight. <S> If there was an incident your insurance may not cover damage or litigation costs. <A> Are you a qualified Test Pilot with insurance covering you for crashing this aircraft? <S> The Max Gross Weight quoted in the POH tells you how far the factory Test Pilots have taken the airplane - any further and you are doing the experimenting. <S> (An obvious concern is that with too much weight, the wings will fold in flight. <S> But there are other concerns.) <S> There are margins, but you don't know what they are. <S> So you might already have been flying within those margins, and thus got away with it. <S> But if you don't know what the margins are then you can't guarantee to stay within them. <A> One thing that hasn't been mentioned yet is CG. <S> Often CG is what will get you. <S> On many aircraft the places that you are putting the weight has considerable arm from CG. <S> This means that you are also shifting the CG. <S> I have seen for instance <S> Cessna 402 loaded amazingly over gross with the load as far to the front as possible. <S> However Google Aaliya death and you will see what happens when the CG is too far aft. <S> All in all it's a bad idea to fly over gross, and it is death to fly out of CG especially aft. <A> Physically, yes the aircraft can take off at or above MTOW - and depending on the aircraft and ambient atmospheric conditions, can takeoff and fly at a considerably greater weight than MTOW. <S> The problem becomes that the values for MTOW were decided upon during design and flight test, taking into consideration a wide range of operating conditions plus design structural static and maneuvering loads on the airframe and landing gear. <S> Unless you are very familiar with these numbers, you can risk structural damage to the aircraft during ground roll, stability during ground movement operations, maneuvering and landing the airplane. <S> In addition, you have no known values for performance data on the airplane in terms of length of ground roll, takeoff distance to clear obstacles, maneuvering load limits, rates of climb and and climbing distances, stall recovery characteristics, etc. <S> Therefore, in loading an airplane beyond what the manufacturer states for an acceptable weight and balance envelope, you are now swimming in unknown and potentially very dangerous, waters. <S> Otherwise smart and rational people die all the time doing stupid things like this in airplanes. <S> Additionally, intentionally operating an airplane outside of its weight and balance envelope is illegal, as it violates §§91.9(a), <S> No person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft flight manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry. <S> Overloading also could easily be cited as a violation of §§91.13 Careless and Reckless Operation and §§91.7 Civil Aircraft Airworthiness. <S> The bottom line: <S> Don't try it. <S> You don't want to break the law or worse, find out the hard way that your guestimates on the plane's performance were incorrect. <A> This is a bad idea for a host of reasons, but structural failure is one of the worst. <S> Sensitivity to gust load is increased when overweight, reducing the designers G load margin. <S> source from Mountain Flying <S> Consider an airplane that has a maximum allowable gross weight of 3,000 pounds. <S> If it encounters a +30 fps gust that results in an additional 2-g load factor, the airplane experiences a total of 3 Gs load factor. <S> Multiply the 3-g load factor by 3,000 pounds and the wings are supporting 9,000 pounds. <S> Assume the airplane is loaded to 1,500 pounds and that it is subjected to the same gust. <S> With half the inertia, the gust acceleration is doubled, causing the airplane to experience a 5-g load factor (4-g force plus 1-g level flight). <S> Multiply 1,500 pounds by 5 gs and the wings are supporting 7,500 pounds. <S> The lightly loaded airplane is subjected to 1,500 pounds less load when encountering the same gust. <S> Even though the heavy airplane realizes less load factor, it incurs more strain. <S> The pilot recognizes load factor; the airplane recognizes load.
|
Yes, it's possible on any airplane, dependent on how far over the weight limit you are, the density altitude, how much runway you have, what obstacles are in the area and other factors. Besides the safety angle, taking off over gross weight could land you in trouble with the FAA even if nothing goes wrong, you can lose your ticket for that.
|
Why is the A380 a double-decker rather than a longer airplane? It seems like making the A380 a double-decker increases the cross-sectional area of the fuselage, thereby increasing drag on the airplane. Wouldn't it be more efficient to fit so many seats in a longer airplane rather than a wider airplane? So, is the A380 a double-decker because there is a limit to how long an airplane can be, would it be impractical to make a longer airplane, am I wrong about the cross-sectional area/length trade off when it comes to drag, or is there some other reason? <Q> That's right, having a longer plane would reduce drag by lowering the cross section <S> (altho there is also drag linked to the surface area of the plane). <S> There is a few reasons why you don't want to do it: <S> Cylinders don't scale this way: <S> Take a cylinder with a radius of 1 and a height of 10. <S> Volume is ≈31.41 <S> Double the height, volume is ≈62.83 <S> Double the radius, volume is ≈125.66 Increasing the length scale linearly and increasing the volume scales at π <S> * n * n <S> You will need a stronger structure to support the additional length and surface area of your pressure vessel, oscillations during turbulences, takeoff rotation, ... <S> All your cables, hydraulics, fuselage, will have to be stretched <S> Passengers will take forever to reach the back of the plane when boarding <S> Maneuvering in the airport will be impossible, you will need new airports (credit apple maps) <A> If they made it longer or gave it a wider wingspan airports would have to be redesigned to serve it, for instance gates would have to be spaced farther apart, taxiways would have to be changed to give clearance and accommodate a wider turning radius, These costs would have been prohibitive and the airplane would not have found customers. <S> Given the footprint constraints a double deck concept was the only workable solution for the number of passengers they wanted to fit. <A> Your assumption that a longer fuselage has lower drag is incorrect. <S> Optimal pressure drag (form or diameter driven) vs skin friction drag (surface area driven) can be determined using fineness ratio. <S> From Roskam and considering subsonic aerodynamics only, the optimal ratio is 6:1. <S> Including other factors such as ease of use or manufacture, the ratio can go higher. <S> The A380 fuselage at 7.15m wide and <S> 8.4m tall is 7.77m average diameter. <S> It is 72.7m long so even as a double decker it is more than 9:1, higher than optimal. <S> The curve is very flat beyond 4:1, so the length of the A380 is driven by considerations other than fuselage aerodynamics which mildly argue for an even fatter fuselage.
|
When designing the A380 Airbus made the decision that it would have to be able to use existing airport infrastructure, so the footprint could not be much larger than that of a Boeing 747.
|
Why aren't passengers trained and evaluated for operating emergency exits in commercial aircraft? The passengers sitting on the overwing exit doors are expected to operate the doors in times of emergency, with only a verbal instruction. Is that enough? Q. Why can't we have a designated area in the airport where a setup of emergency doors are kept and the passengers are trained and evaluated there before being alloted the seats on the emergency row. It can be short 2 min course, where passenger actually opens the door and puts it aside. There have been instances which highlight that proper training is required for passengers Soource : Passengers will frequently open an exit as soon as evacuation begins which may result in them evacuating into danger. This occurred in the Ryanair engine fire in Stansted Airport in 2002, where passengers evacuated themselves onto a burning wing, despite airport fire services personnel shouting at them to return inside the aircraft and evacuate via a usable exit. Source Another hazard in the use of overwing exits is them being improperly opened (usually a result of passengers in these seats not paying attention to the verbal briefing provided pre-departure, or not observing the opening instructions on the safety card and on the exit). The majority of overwing exits involve the passenger physically removing the hatch from its frame and disposing of it outside on the wing without blocking the exit. Research conducted at the Cranfield Institute in the UK Source Above situations taken from Wikipedia https://en.wikipedia.org/wiki/Overwing_exits#Hazards <Q> Former TWA here. <S> Emergency exit seats used to only be given to passengers who are ready, willing and able to assist in case of an evacuation. <S> They could not be assigned in advance, the passenger had to be asked and evaluated in person by the boarding agents, who would have been held responsible if a not-able passenger was to be seated in any of those rows/seats. <S> This used to be the rule, it was deemed that safety was more important than selling seats. <S> Maybe the rules have changed since? <A> In short because accidents do not happen . <S> It's easy to overestimate the number of accidents by looking at news articles about a crash. <S> But look at the following picture: You can hardly see Europe. <S> There's a bit less in USA, as it's night there at the moment this screenshot was taken. <S> But in short: none of these flights crashed. <S> It's thousands of flights per day, and accidents typically happens once or twice a year. <S> Training for it doesn't make any sense. <S> Training for how to get out of your car after an accident would make much more sense - yet very few do it... <A> How much training, for how long, would you require? <S> Do you realise how many different door designs there are, there are hundreds? <S> The facility would have to be massive. <S> And who'd pay for it? <S> Another $100 surcharge on every ticket just to pay for the facility and instructors would probably be called for. <S> I'm sure there are more reasons why this is not a good idea.
|
Airline accidents are incredibly rare, so training the average passenger for them simply does not make sense.
|
Why does load shedding still occur in jetliners (e.g., 787) when there is so much power available? I had a few questions about how electrical generator works on an aircraft, the 787 to be specific although I know it is similar for all aircraft. So the 787 engines have 2 VFSG each which are rated at 250 KW each which is 1000 KW -> 1 MW which is said to power a 2000 population town. Since the power is generated using the rotation of the engine, im assuming it does not always produce 1 MW , only at peak rotations? What on earth in the plane sucks that much energy, I know the 787 is a more electric aircraft, but still how much power does it really take? If the total power output of the plane is 1.45 MW, I'm assuming the APU Gens are able to provide 0.45 MW in total to the airplane. If there is so much power available, why does load shedding still occur in aircraft? <Q> Load shedding always occurs during engine start, according to the FCOM of the B789. <S> Both engines are allowed to start simultaneously. <S> The B789 engines are started using both VFSGs of each engine, which are mechanically connected to the N2 shaft via the accessory gearbox. <S> So, the VFSGs are using power instead of delivering during engine start. <S> The APU cannot provide enough power to prevent load shedding. <S> If the engines are started using external power, at least two 90 kVA external power sources are required. <S> Optimal start performance is achieved using 3 external power sources (2 on the left forward fuselage and 1 behind the left wing on the fuselage). <S> If only 2 external power sources are used, significant load shedding can occur (e.g. First Officers displays blanks and even the audio control panel receive and trasmit selections may be lost). <S> The APU is normally switched off during flight, unless e.g. one VFSG is U/S. Load shedding should normally not occur when both engines are running and all VFSGs are operational <S> (I haven’t experienced load shedding during flight). <A> First of all, I am not familiar with the electrical system on the 787. <S> What will normally be shedded is IFE and galley equipment (ovens, coffee makers, etc.). <S> Should this happen, a checklist will direct flight crew to start the APU in order to establish normal power supply for all the equipment of the aircraft. <S> If APU starts, the flight can continue normally. <S> If APU is unable to start for some reason (flight could be dispatched with APU INOP, or APU generator INOP), then the crew will likely have to land at the nearest suitable airport, as the electrical reduncancy is lost. <S> So, in case 1 when generator fails and crew successfully starts APU, the IFE and galley equipment will not be powered for perhaps 5 minutes or so. <S> No big deal to be honest. <S> In case 2, where the APU is not available, the flight will have to divert to an airport, so no real need for ovens or IFE anyway. <S> Now, of course the manufacturers could design electrical systems that would handle this kind of failure, but the cost/benefit just doesn't support it. <S> The generators would have to be more powerful, which would in turn lead to increased weight, wires would have to be thicker, other electrical elements would have to be designed to take the increased current/load, etc. <S> All this, just so passengers could enjoy IFE and a hot meal during their short diversion to a nearby airfield. <A> Technically the VFSG are 250kVA (kilo VoltAmps). <S> VoltAmps and Watts are only equal assuming a perfect power factor. <S> The various systems are largely motors and controllers and do not have a particularly good power factor, so there is some losses there. <S> As you noted, the VFSGs are direct coupled to the engines, so they vary in rotational speed based on engine speed, so there are some engine speeds where peak power may not be available. <S> I don't have wattage numbers for the various systems, but on the 787 everything is electrical, so there are a lot of loads you might not think of. <S> Some of the larger loads: <S> Wing Anti-ice Backup hydraulic pumps for both left and right systems, and both primary and backup pumps for the center system Pressurization and ECS (climate control) <S> Nitrogen Inerting system Fuel pumps Cargo heaters Galley systems. <S> The generators are also used for starting the engines, so if a engine fails in flight the generators on the other side may be called upon to provide power to restart the opposite side while at the same time providing power to the dead engine's hydraulic system, the center system and all the loads above.
|
In a modern twinjet airliners, if one engine-driven generator fails, load shedding is activate to protect the electrical system.
|
Why is best angle/rate of climb indicated in airspeed? I understand the difference between best angle of climb $V_{x}$ and best rate of climb $V_{y}$ . When I take off I would aim to maintain one speed or another depending on what I want. But I don't understand why it's measured in airspeed, instead of pitch angle, which would seem more intuitive. <Q> Because determining Vx and Vy has to do with the specific aircraft, specific power output of the engine, thrust from the propeller, etc, which is often a function of pressure altitude and airspeed. <S> Remember that Vx represents a situation where the aircraft has the MAXIMUM EXCESS THRUST meaning a situation where the difference between the maximum thrust available and and the thrust required to neutralize drag force and maintain straight and level flight is the greatest. <S> Images courtesy of BoldMethod Vy on the other hand is the point where the aircraft has the MAXIMUM EXCESS POWER available to it, translating into the greatest change in altitude for a given period of time by simple conservation of energy considerations. <S> Images courtesy of BoldMethod <S> The airspeed where Vx occurs increases as the pressure altitude increases. <S> Conversely Vy decreases as pressure altitude increases. <S> This is due changes in power and thrust outputs with increasing pressure altitudes. <S> Vx and Vy eventually equal each other at the aircraft’s absolute ceiling, since there is neither any more excess thrust or power available here for climbing. <A> This useful information is in the POH to be used by people who are quite busy at the moment, there for it is expressed in a user friendly form. <S> Climb angle, as a matter of interest, could be studiedfor a variety of engine, prop, weight, flap setting,etc., <S> but what the pilot needs on the spot is V at full throttle climb. <A> Let’s say you have an engine problem, or it’s hot and your performance is negatively effected. <S> The angle of attack will be very different to get best climb, but the airspeed will be the same as if you have lots of power. <A> Pitch angle only corresponds to an angle or rate of climb at a particular excess thrust. <S> Consider the typical stall exercise: you pull the engine to idle, then apply more and more elevator to try to maintain altitude, thereby pitching up and simultaneously reducing airspeed. <S> At one point, airspeed drops to the point where you lose lift, and you fall out of the sky, despite the fact that you are nose high. <S> Once you apply power and push the nose down a little, it again becomes easy to establish a climb to regain any altitude lost. <S> Heck, consider how you slow an airplane down in the air, by raising the nose without having excess thrust. <S> If rate of climb (expressed as either best angle or best rate) related only to pitch angle or angle of attack, then instead of slowing down, you'd start to climb and maintain that climb as long as the pitch angle is unchanged, no matter the power setting. <S> That's clearly not happening, at least not for long, so there must be something else to determine whether the airplane actually climbs or descends. <S> That factor, as already mentioned, is (excess) thrust. <S> Therefore, expressing V x or V <S> y <S> in terms of pitch angle would require taking into account the amount of excess thrust available. <S> Accurately estimating that directly is non-trivial, at least without specific instrumentation, and would also likely require the pilot to memorize a whole table, rather than a single (or two) indicated airspeed(s). <S> During a high-workload phase of flight, including take-off and initial climb-out, every little bit that adds to the mental workload of the pilot risks increasing the workload beyond the pilot's capabilities. <S> If instead you aim to maintain a given indicated airspeed, you will be at a point of the power curve where all the factors line up for that airspeed, regardless of the external conditions (pressure altitude, wind, etc.). <S> If airspeed drops for any reason, you pitch down slightly to pick up more speed and maintain the climb; if airspeed rises, you pull the nose up instead to slow down (trading airspeed for climb angle). <S> You're using the pitch angle to maintain an airspeed, and the only instrument you need to pay very close attention to is the airspeed indicator.
|
A very simple practical reason is that Vx and Vy speeds can be easily monitored as the pilot is climbing away and controlled with the elevator.
|
How is it possible for supersonic aircraft to push air out of the way? If the force (pressure) can be transferred/propagated only at the speed of sound, how are supersonic aircraft able to move air out of their way/do work on the air? It seems that they must transfer the force faster than the speed of sound or else they would intersect with the air. Does the speed of sound increase at the shock to allow it? <Q> The idea that force can only be transferred/propagated at the speed of sound is a simplification. <S> It's a very reasonable simplification, which works in a very wide array of cases, but it's a simplification. <S> A fundamental concept in gas mechanics is the "mean free path length." <S> This is how far a molecule can travel on average before it collides with another. <S> This is on the order of hundreds of nanometers for pressures you'd see at reasonable altitudes (68 nm at STP). <S> If you are looking at processes that occur at scales much larger than this, it is very reasonable to model their behaviors as transmitting things at the speed of sound, because these statistical effects lead to a very natural expected speed of propagation. <S> It can be seen as a result of the central limit theorem applied to a very large number of molecular collisions where the drift velocity (average movement of particles) is relatively smooth. <S> As you push things, this nice model breaks down. <S> As you approach the sound barrier, you get pressure gradients that get shorter and shorter. <S> Near the speed of sound, these gradients start to get into the single-digit-multiples of this mean path length. <S> At this point, we can no longer assume that we can just model everything with the nice clean statistical models we had earlier. <S> What actually ends up happening in most situations is that you get a "shock." <S> Far from the flying body, the air transmits force at the speed of sound with respect to the unmoving air (or slowly moving, if there's a wind). <S> Right up against the flying body, the air transmits force at the speed of sound with respect to the flying body. <S> At "reasonable" speeds, there's a smooth shift from one to the other, where the pressure gradients aren't so steep that we can't call them pressure gradients. <S> At supersonic speeds, that smooths shift doesn't happen. <S> Instead, we end up with a thin shock region (on the order of 1 μm or thinner) where it's not reasonable to model the air as having a "pressure." <S> It acts more like a bunch of billiard balls being flung along. <S> This region, a few mean free path lengths wide, is where the usual rules we're used to, break down enough to resolve the physics. <S> On each side of the shock, "normal" speed-of-sound behaviors occur. <S> Inside the shock, it's messy. <A> It is only the pressure <S> wave that can propagate at the speed of sound. <S> This means that a molecule of "air" that is ahead of a subsonic aircraft can get pushed out of the way without hitting that aircraft. <S> It gets a push from another molecule, which is pushed by chain of molecules until it get to the one which is the one that hit the aircraft. <S> The aircraft only transfers energy to the molecules that it actually hits. <S> The aircraft knocks them out of the way at whatever speed it is traveling, and the energy transferred to the whole volume of molecules is the source of the drag rise when speeds approach supersonic. <A> Supersonic aircraft do not push the air out of the way in front of the aircraft . <S> They only push it sideways out of the way after the aircraft has passed the air (for the air beside the aircraft), or at the very moment the air meets the aircraft (for the air directly in front of the very centre of the aircraft, i.e. directly in front of the nose spike). <S> That’s why a shock cone extends from the nose backwards , at an angle. <S> The faster the aircraft, the smaller the angle. <S> The formula relating mach to the shock cone angle can be found here, at NASA's website. <S> It's no more complex than that.
|
A supersonic aircraft winds up directly knocking all the molecules ahead of it out of its way, in the form of a shock wave.
|
Why do suborbital planes feature H-tail and/or large wingtips? Spaceplanes that are suborbital are mostly supersonic and feature H-tail or rather large wingtips. This looks to be similar to a H-tail configuration but I'm unsure abut how it works, which is why I say large wing tips. They focus on a delta wing and elevon for the pitch and roll and yaw seems to be controlled using this.For example look at the following spaceplanes. References: 1. https://www.virgingalactic.com/articles/VSS-Unity-First-Powered-Flight/ 2. https://www.sncorp.com/what-we-do/dream-chaser-space-vehicle/ 3. https://www.flyfighterjet.com/xcor-lynx-space-flight <Q> Dreamchaser isn't intended to be suborbital. <S> Don't know about your 3rd picture, but the Spaceship 1 & 2 were designed by the same person/company, <S> so it's not surprising they use the same design elements. <S> The designs of Dreamchaser vs Spaceship N address two different problems. <S> An orbital vehicle has to decelerate from ~17,000 mph, while a suborbital vehicle on a ballistic trajectory (simplistically straight up and straight down) starts from zero speed at its high point, and needs to keep from gaining too much speed. <S> That wouldn't be practical for an orbital reentry vehicle due to heating & aerodynamic forces. <A> At extreme speed, the more symmetry you have, the better your chances are of staying straight. <S> This is especially of concern at very high altitudes, whereaerodynamic forces (indicated airspeed) are small. <S> X15 is good example of this. <S> Also, H type tail helpskeep control surfaces away from the rocket nozzle. <S> Shuttle type vehicles also emphasize roll and pitch stability in re-entry. <S> Very interesting to note the humble capsule has 360 degrees of roll stability (there for also pitch). <S> The Soviets liked the ball, with the weight set a little low, for the same reason. <S> Space ship 2 has the (shuttle cock) feathered configuration. <S> Dream Chaser (and the Air Force)has <S> strong dihedral. <S> These just want to come in upright and land safely. <A> Most spaceplanes are aerodynamically just hypersonic airplanes. <S> The tailless delta wing with directional stabilising fins on the tips is an optimal solution, especially if you do not want a fin on the fuselage. <S> Directional stability can be elusive and highly non-linear, so types designed before the days of high-speed digital control systems often resorted to extra-large surfaces. <S> During re-entry a spaceplane cannot nosedive or it would overheat and melt or tear itself to bits. <S> It has to kind of pancake down on its underside, keeping just enough forward speed to maintain aerodynamic control (An orbital craft needs hi-tech heat insulation even for this but for suborbital craft <S> it is unlikely to be needed). <S> The safe angle for this manoeuvre is really quite small with little room for error, just a few degrees either way. <S> It was an acceptable risk for the Space Shuttle but may not be for commercial passenger flights. <S> SpaceShipOne and Two are a unique solution to the problem of safe re-entry. <S> The tail configuration is known as the outboard tail or outboard horizontal stabilizer (OHS). <S> It has been studied from time to time but never really flown (a German research prototype was built in WWII but it is unclear whether it ever flew). <S> It was adopted for the SpaceShip series for the obvious reason that it gets the stabilizer out of the way of the rocket exhaust. <S> It also eased the mechanical solution to their other big aerodynamic innovation, the variable-geometry "weathercock" tail. <S> By swinging the tail up for re-entry, it stabilises the spaceplane as it pancakes back down, hugely increasing the safe zone and making re-entry almost trivially safe. <S> Passengers returning from actual orbit present a far greater challenge, as yet unsolved.
|
So if I'm not mistaken, a main function of the H-tail is to allow the entire vehicle to act as a drag device.
|
Freezing cold cabin housing just under a window I flew on a Boeing 737 plane yesterday and was sitting next to 2 windows. When I tried to rest my arm on the inner housing of the cabin during the flight, I noticed that the inner cabin housing just below one of the two windows was very cold. It was almost like touching a surface in your freezer. I was under the impression that it is not a common thing and that it could only result from outside air being in contact with the inner cabin housing which I believe is not supposed to happen. I spoke to a flight attendant about it and he came check the window, but I feel like his feeling all in all was that I was worried for nothing, and I’m not sure he actually shared the information with anyone - and he did not thank me in anyway for reporting a potential issue. I’m curious of anyone views on this issue. My uneducated guess was that it was maybe not a critical issue now, but a defect that should be known by maintenance teams as it could be tied to a structural issue of the outside window. <Q> It's not a structural problem, and nothing to worry about. <S> The cabin of an airliner is a pressure vessel, the pressure outside of the airplane is far lower, if there was a leak air would be going out, not in. <S> The air outside is very cold, which makes the skin of the airplane cold, there's insulation between the skin and the cabin fixtures but if that comes off a bit you get cold spots. <S> By all means tell the cabin crew so they can log it for the next time <S> the airplane's in for maintenance, it's important for passenger comfort. <A> The air-conditioning packs are located under the floor, between the wings ahead of the landing-gear bays. <S> There is a duct which carries cold air to the crown of the fuselage <S> and it is then distributed fore and aft. <S> If I remember correctly, its usually located where the leading edge of the wing joins the fuselage. <S> If you were seated around this area this duct could be the reason for the cold surface. <S> Also the ducts are assembled using clamps and one could have come loose. <S> Both these conditions could result in cold area leaking out and cooling the interior panels. <A> I had a similar situation. <S> It was during a flight from KTW to MIR. <S> There was actually more or less 15 cm diameter and a couple of mm thick ice layer under my window inside the cabin. <S> While I see that other answers seem to suggest ignoring it, please read until the end of the story. <S> I'm a frequent flyer (used to have Platinum Topbonus membership when AirBerlin was still alive) <S> and I've never encountered ice inside the cabin and a stream of really cold air right under the window before. <S> I've decided to call a flight attendant. <S> As you could expect she told me initially with a very nice smile that ice on the window is completely normal. <S> Same reaction as in other answers here - no offense. <S> But when I finger-pointed the ice and said that I'd be fine with some ice on the window but not quite a chunk of ice under the window... <S> her smile disappeared instantly - "Thank you sir, I will tell the pilots". <S> Less than 30 seconds later the captain came to check it. <S> After a while of looking and touching he told me exactly this - "Thank you for reporting it. <S> This is a problem for sure but don't worry - we definitely don't have a big breach in the fuselage <S> and we are about to start the approach in 5 minutes so diverting to a different airport <S> is not necessary. <S> I will report it after landing - it has to be fixed before the next flight. <S> You can change your seat if you don't feel comfortable here." <S> Don't be afraid to ask stupid question or report anything you find unusual during the flight. <S> It's about the safety of you and other people on board. <S> Just be polite, patient, cooperative and don't call them every 5 minutes :)
|
There is usually insulation around the duct as mentioned by GdD and this could have been dislodged.
|
What is the correct procedure in case of vertical stabilizer failure? What is the correct procedure in case of vertical stabilizer failure in cruise? Am I correct in guessing that one should descend to a lower altitude and decrease speed? <Q> There is no procedure, generally a vertical stabilizer failure makes an airplane uncontrollable, meaning everyone dies. <S> There have been examples where vertical stabilizers failed and people survived, see this question for details. <S> A pilot local to me cut 2/3 of his vertical stabilizer on high tension power wires while scud running and still landed safely. <S> When there's any control surface failure pilots will have to learn how to fly the airplane and control it using whatever means possible. <S> Differential thrust and speed brakes have been used to control lateral movement (yaw), trim can be used if controls are seized, etc. <S> Reducing speed may not be a good idea, or at least not all at once, if the vertical stabilizer fails airflow over whatever stump remains may be the only think keeping it straight. <S> If the control is stuck then reducing speed would make sense, it all depends on the nature of the failure. <S> , you'd want to work the problem and find out what the new parameters are, then gingerly work your way down. <A> Am <S> I correct in guessing that one should descend to a lower altitude and decrease speed? <S> Yes, if you fly an aircraft with a backward swept wing. <S> Otherways, losing the fin will be impossible to compensate. <S> This answer explains how a backward swept wing will aid in directional stability, and this help increases with angle of attack. <S> Therefore, flying slow is the most important step in order to restore directional stability. <S> Flying low increases aerodynamic damping, so low and slow is the best choice in this case. <S> @Carlo mentions <S> B-52H 61-023 which lost most of its vertical on January 10, 1964. <S> This aircraft survived, but a number of them who suffered the same fate crashed. <S> There were several factors which helped: Just enough of the tail was left to keep the aircraft flying. <S> Later simulations showed that a full loss of the vertical would had been impossible to compensate. <S> The crew lowered the rear landing gear, so the gear doors helped by doubling as ventral fins. <S> Every bit counted on that occasion! <S> Also, the loss of mass from the lost tail portion shifted the center of gravity forward, which is another way to improve directional stability. <S> The crew did all they could to get the center of gravity forward, and again, without that the aircraft would had lost directional stability. <S> What is the correct abnormal procedure in case of vertical stabilizer failure in cruise? <S> My advice: Don't count on being as lucky as B-52H 61-023, but bail out as long as you can! <A> Depends on the aircraft. <S> Generally structural failure results in departure from controlled flight, though there are a few exceptions such as this USAF B-52H which lost its vertical fin over Colorado on Jan 10, 1964. <S> Oddly enough, the loss of a vertical fin is probably the least riskiest form of structural failure. <S> An airplane can still maintain approximate directional control from the longitudinal center of pressure from the tailboom of the airplane well behind the center of mass, provided all other systems remain functional. <S> The airplane can still be turned using aileron input, though slipping and skidding from adverse yaw and other factors are going to be much more pronounced demanding greater care in handling at lower speeds. <S> Multiengine aircraft will most likely depart from controlled flight here in the event of an engine failure. <S> Again the severity of the loss of control here will depend on the amount of structure lost and it’s <S> effect on directional control.
|
Descending is absolutely a requirement, you have to land somewhere after all, but unless you've depressurized there's no need to rush it
|
If cleared to cross a runway and expedite but are slow to get away, are you obliged to stop? Suppose ATC says "Big Jet, cleared to cross runway 36, expedite" and you acknowledge "Cross runway 36, wilco, Big Jet". As you start to move forward you immediately realize that you are unable to go as quickly as you expected (perhaps there's an incline or a gust of wind -- I'm not sure what's plausible). At the point you realize this, you can still hold short the runway. Are you obliged to stop and reply 'unable' or is that ill-advised? <Q> Remember: you are pilot in command; you are the final authority on the operation of that aircraft. <S> So the scenario might play out as: ATC: “Bigjet, cleared to cross Runway 36. <S> Expedite crossing and report clear.” <S> Bigjet: “Cross runway 36 and report clear, Bigjet.” <S> Bigjet: “ <S> So-And-So Ground, Bigjet, Unable. <S> I’ve got a problem here.” <S> ATC: <S> “Bigjet roger hold short of Runway 36 for arriving traffic. <S> Will you be able to taxi after traffic clears the active?” <A> Per Part 91, You are cleared to cross until/unless another clearance is obtained. <S> https://www.law.cornell.edu/cfr/text/14/91.123 <A> If you don't think you can safely comply with an instruction, don't comply with it. <S> If you can remain short of the "hold short" line, stop there and inform ATC. <S> If you have already crossed the line call tower and say "crossed hold short, unable to expedite" or something to that effect so they can have landing traffic go around. <S> Its been said quite a few times, the pilot is in control of the plane, not ATC. <S> You can agree to something and then later realize you can't comply, that is fine, as long as you communicate with ATC.
|
If you feel you cannot safely comply with any ATC instruction, you can simply reply “Unable” and the controllers will amend your clearance.
|
What is the vocabulary used by fighter pilots used to communicate? As far as I understand, fighter pilots or more general military aircrews will use a dedicated phraseology to communicate with each other, which is different to communicating to ATC.Is this phraseology standardized across different air-forces or even within NATO?Are there any public documents on this phraseology? <Q> There are NATO standard terms. <S> For example the MiG-29 is known as a "Fulcrum. <S> " That's not the Russian name for it but the "NATO reporting name" which you can look up on Wikipedia. <S> There are also some standard (but not codified) terms such as "angels" meaning "thousands of feet." <S> And there are some standard terms such as "bent" meaning "inoperative" <S> but I don't know how much those are used any more. <S> Within a certain operating area or task force, there may be specific code words used that may change from day to day. <S> These would not be known to anyone outside that area or task force. <A> When I read this question, I think of the chit chat which goes on during sorties. <S> It IS non-standard, and varies by location and service. <S> On youtube there is a recording of a F-4D pilot who went into the drink at night in the North Sea. <S> Listen to that (long) recording. <S> The dialog is quite similar to the dialog used, for example, by pilots in Vietnam. <S> (A buddy of mine was base commander of the affected pilots.) <S> You may find more current examples from more current conflicts where there are videos with radio audio. <S> An example of terminology which is rather universal but perhaps not standardized, might be the term "feet wet" which means the flight has crossed the shoreline and is over water. <A> They use brevity codes. <S> They are used to quickly convey information on the radio. <S> Like all things military, they are standardized but they do have some variation between services. <S> You can find a list of US/NATO multi-service codes on Wikipedia .
|
Much of the terminology is not standardized, but there are certainly components which are.
|
What do flight attendants do if a passenger asks what is going on in case of a potential emergency? This is related to, but not the same as, another question I asked on Interpersonal Skills . I was on a flight last year, on a route I fly on a fairly frequent basis. Shortly after takeoff, I heard the three double chime signal, which is commonly used by airlines to indicate to the crew of a potential problem. The crew quickly marched up to the front of the passenger cabin and was briefed by the pilots. I also noticed that the plane was going off course. Some time later, I used the onboard Wi-Fi service to query an online flight tracker about the flight I was on, and it said we were diverting back to our origin airport. Throughout the whole incident, all the crew kept quiet about the whole thing, and didn't let passengers know about the diversion until just a few minutes before landing back at the origin airport. Before the announcement, while the seat belt sign was turned off and while the crew weren't making any emergency preparations of any sort (just casually chatting with other passengers), I got up and asked the crew what was going on, and they said "nothing". I then showed them the tracker page which indicated the diversion, and they just asked me to return to my seat. What's the general protocol for cabin crew, when asked by passengers who notice potential issues like this and get curious? Is it common for them to simply say that "nothing" is going on until the flight deck makes an announcement? What if a passenger really insists on knowing what's going on? (As an aviation enthusiast, I feel more comfortable if told about the issue; not knowing about it can make me feel tensed.) <Q> What's the general protocol for cabin crew, when asked by passengers who notice potential issues like this and get curious? <S> The flight crew and pilots are under no obligation to inform the passengers about non critical issues and broadly speaking it's often better to provide only needed information so as not cause some kind of panic. <S> In the vast majority of situations on an aircraft there is nothing the passenger can do other than evacuate when told to do so. <S> Turning an aircraft around and heading back to the point of origin is not necessarily an emergency although it can be there is nothing to say it is or is not from a passenger point of view. <S> Even if a passenger insists the cabin crew will likely ask them to take their seats, buckle up and await any further instructions. <S> It's possible that the cabin crew is not even informed of anything as the pilots try and work the problem. <S> The later part of your question is answered here and the general answer is, unless you are a trained pilot it's hard to actually know if something is going wrong. <S> There is a very interesting example of this from the Air Florida Flight 90 incident which is the only incident I know of where a non flying pilot spotted an issue and took action, this would be a fairly rare case; Survivors of the crash indicated the trip over the runway was extremely rough, with survivor Joe Stiley – a businessman and private pilot – saying that he believed that they would not get airborne and would "fall off the end of the runway". <S> When the plane became airborne, Stiley told his co-worker (and survivor) <S> Nikki Felch to assume the crash position, with some nearby passengers following their example. <A> What if a passenger really insists on knowing what's going on? <S> As always, it depends. <S> Let's briefly summarize the possibilities here: <S> Passenger spotted an issue which the crew is unaware of. <S> Passenger spotted an issue which the crew is aware of. <S> Passenger is behaving in a rude manner. <S> And let's go over the actions the flight crew can possibly take, without matching the above conditions: <S> Inform other cabin crew members. <S> Explain to the passenger what the issue is. <S> Warn the passenger to stop the behavior. <S> Ignore the issue altogether. <S> Now let's go over the scenario. <S> The flight deck called for a briefing, so it is obvious that the pilots know what is going on. <S> Every crew member was briefed as well. <S> So that means scenario #2 on our first list, and we've ruled out #1 and #2 on the second list. <S> They knew the plane is diverting, and they saw what they expected. <S> Action #3 is unlikely to end up well. <S> When only individual passengers are informed about an abnormal situation, rumors would spread in the cabin, causing panic. <S> It is even worse when the passenger thinks he is an "expert" when in reality he is spreading disinformation. <S> Furthermore the flight attendants may not have complete information, they are only briefed by the pilots about the severity of the situation and what to do / not to do. <S> Beyond that, action #4 may be necessary. <S> Cabin crew are trained for this, and there are procedures about how to deal with a passenger whose behavior is judged as unacceptable in flight. <S> So that leaves, #5. <S> The pilots may make a PA explaining they have a technical issue and they are turning around. <S> Or they may not, depending on the workload in the cockpit, severity of the situation etc. <S> The senior flight attendant may, at their discretion, make an announcement informing the passengers they are going to divert. <S> Or they may not. <S> What the pilots and cabin crew did, was kept the passengers calm, worked the checklists, and landed the airplane without incident. <S> That's their job. <A> Flight crew are the two in the cockpit. <S> They would Aviate, Navigate and Communicate in that order. <S> In large commercial plane they are separate from passenger by a cockpit door <S> so they won’t know about your curiousity. <S> Anyway their priority is the safety of flight, not to answer your question. <S> The cabin crew, on the other hand, may not know about what happen. <S> They just know something is happening. <S> Their job is to maintain order in the cabin. <S> If they feel your action is against their job they may treat you as another problem and that is not a good thing.
|
If the passenger really insists, perhaps a brief "The pilot is aware of the situation, please take your seat" would be the simplest reply. Inform the pilots immediately.
|
Why would a pilot on final to a towered airport not speak up when ATC clears another aircraft to land on the same runway, without mentioning them? Every time I watch AOPA's Accident Case Study video Communication Breakdown , I'm left wondering. Here's an aircraft (in this case, '1DA) on final approach for landing on a towered airport, when another aircraft ('4SR) is cleared to enter the traffic pattern, and gets cleared to land before they turn base, without ATC mentioning the aircraft already on final. One could make an argument that the pilot of '4SR should be aware of '1DA, but somehow, they apparently weren't. Once the pilot of '4SR is made aware of the traffic already on final, they make what I can only describe as a hasty attempt at an evasive maneuver which results in '4SR crashing into the ground, killing everyone aboard '4SR. Yes, this is a towered, controlled airport; ATC should be the one to inform the incoming aircraft about the one on final. But for some (here unimportant) reason, ATC fails to do so. To make matters worse, '1DA is flown by a student pilot and instructor, so there's two people there, either of whom (and certainly the instructor) can use the radio. In such a situation, why wouldn't the pilot of '1DA speak up? '1DA was still some distance out from the airport. It seems to me that besides the obvious of maintaining situational awareness, there were several rather obvious options available here: No later than when the pilot reported being on base, ATC could (maybe should) have instructed the pilot of '4SR to make a right turn to re-enter the downwind leg, and to then extend downwind and land behind '1DA. Yes, reentering the downwind leg from the inside would be unusual, but it seems as though it would have kept them well out of the path of '1DA on final. ATC could have told '1DA to go around when the controller realized that '4SR was unaware of '1DA, allowing '4SR to land ahead of '1DA; things could be sorted out once both where on the ground (the video mentions this possibility). The pilot of '1DA could have made a position report specifying being number one on final for the same runway, when ATC didn't mention them to '4SR. The pilot of '1DA could have aborted their landing and executed a missed approach, announcing this, effectively letting '4SR land ahead of them. Any of those (and probably a few other) options seem like it could have prevented the accident altogether, at the cost of a relatively minor inconvenience to either '4SR or '1DA. So why would no one do anything until it was (obviously in retrospect in this particular example case) too late? <Q> why wouldn't the pilot of '1DA speak up? <S> The simple answer is that you are not trained to "speak up" at a towered airport, you are trained to follow instructions from the tower and there is an assumption the tower will provide separation and appropriate clearances. <S> As an ultimate fall back you are always supposed to "see and avoid". <S> For the official report you should reference the NTSB report <S> but if you listen to the ATC audio in the linked video as well as their explanation of the link the pilots had no reason to think there was an issue and the clearances given were rushed but explicit. <S> As I note above AOPA also notes " <S> it is a pilots responsibility to visually confirm final approach <S> " You can also hear that the pilot of '4SR was giving confusing instructions about base extension and clearance to land. <S> The pilots was not incorrect in his approach actions but made a critical go-around error and may have been a low altitude, dirty config, stall. <S> Ultimately the lower aircraft on approach had the right of way <S> so '1DA had no reason to speak up as they were in the right. <S> AOPA states that the pilots may have thought "he was overtaking the aircraft from above" which is incorrect, or at least procedurally incorrect as '4SR would have had to yield to '1DA anyway. <S> In the end the controller should have simply issued '4SR <S> Go Around <S> Any time, you as a pilot hear that you should build the habit to just go around. <S> As PIC you can ALWAYS execute a go around, controllers should be prepared for it and <S> more importantly you as the PIC should be prepared for it. <A> The pilot of 1DA didn't speak up because there was no reason to at that point; he didn't know of 4SR's intentions and probably thought that 4SR was going to fly a normal pattern just like the controller did. <S> When he saw that 4SR was cutting the corner (obviously in a hurry, never a good thing) in front of him the instructor pilot of 1DA took control from the student and started a go around. <S> Going around is a busy time, you have to change pitch and power while maintaining airspeed and keeping the airplane in balance. <S> The rule is Aviate, Navigate, Communicate, you don't make any radio communications until you have an established and controlled climb. <S> 1DA would have made a going around call once that was done, but in any case the controller was, as the NTSB report says, "yelling" at 4SR <S> so he wouldn't have been able to report anyway. <S> 1DA wouldn't have reported number 1 because it's up to ATC to say who's #1, #2, etc. <S> 4SR had multiple risk factors. <S> According to the NTSB report it was 22 pounds under the weight limit (which incidentally meant it would have been over the limit on departure), and probably loaded with a C of G at or behind the rear limit. <S> The pilot had elected to do a "slam dunk", close in approach rather than the normal pattern (probably intending to land long <S> so there was less of a roll-out), was at a high approach speed and likely in a rush, with get-there-itis. <S> The high weight would have increased stall speed and a rearward center of gravity would have decreased stability and control authority. <S> The pilot jammed full throttle on quickly when at the limits of performance and couldn't maintain control. <A> It was reasonable for 1DA to assume 4SR would fly a standard pattern, but Tower not explicitly telling 4SR <S> they were #2 <S> and/or confirming they had traffic in sight would have made me nervous enough to say something. <S> Perhaps that's because my home airport is very busy and Tower <S> always does both: they will not clear you to land until you report all preceding traffic in sight OR they call your base on extended downwind (the norm) when you pass abreast of the plane ahead of you on final. <S> This sort of accident is exactly why they do that even though VFR rules don't require it.
|
It's the controller's responsibility to issue instructions and a pilot's responsibility to follow them unless doing so is unsafe.
|
How to land using horizon? source I recently heard pilots discussing a landing technique that some instructors are now teaching. To assist new pilots in flaring, they instruct the pilot to adjust their attention toward the far end of the runway or horizon. There was some discussion that it won't work for a pilot short in height. As they look toward the end of the runway or horizon they are suppose to use some type of reference, such as "the horizon expanding" . What is this technique for landing and how is it suppose to help? Update: According to the "Rod Machado" YouTube video provided below, it is the runway width that is the primary reference, not the horizon or end of the runway. The pilot is viewing the end of the runway for peripheral vision of the width. <Q> I think the GIST here is: Look far ahead. <S> Don't look at whatever is directly in front of you. <S> It's the same as driving. <S> If one looks at the piece of concrete just meters ahead, then the barricade will "pop out in front suddenly" or the bumper of the car is "in your face out of nowhere". <S> Our peripheral vision will guide us to wherever we want. <S> It is natural and in-born, biologically. <S> You just need to know where to look. <A> This is how I was taught to land and perhaps the broader way to put it is, Look out at the end of the runway or horizon and keep that sight picture in your head <S> when landing As noted in the comments seats are often adjustable or you can use a thin cushion to add some height if you need it. <S> But even at that everyone will have a slightly different sight picture when landing and its important to keep that consistent. <S> A point like the far threshold or horizon (if your airport is in a generally level area) provides a nice reference for you to keep your flair pitch consistent and repeatable. <A> It depends on the student. <S> That guidance is used to teach students the art of flying the roundout in order to better teach the how to evaluate their height above the surface. <S> Care must be taken there as excess focus at the far end of the runway can result in a high round out resulting in a very firm touchdown or worse. <S> The actual technique of evaluating your height above the runway just comes with experience and several hundred landings and can be altered by different visual perceptions like runway width, grade, etc. <S> I personally find that it is useful to focus about 200 ft down the unwary in front of you while evaluating your height based on this as well as the end of the runway and the sides using your peripheral vision. <S> It can help to then shift focus to the end of the runway during the roundout <S> as most of your field of vision will be blocked during the roundout, particularly in 3-point landings in tailwheel airplanes. <S> Again sight picture depends on the aircraft, runway and several other factors. <S> Using this method can be a big help during your formative training, as you develop a good sight picture which can aid you in future landings in other types of airplanes. <A> Here's how my flight instructor explained it to me. <S> Human depth perception, beyond a very short distance, is very poor. <S> If you are looking at the runway directly ahead of your plane, it is difficult to judge your height, or changes in your height, with enough precision to make a good landing. <S> However, your ability to judge angles is very sensitive. <S> If you are looking down the runway, then you can see both the horizon and the runway edges. <S> The runway edges and the horizon have angular relationships that vary depending upon your height. <S> This angle, and changes to it, are easy to see. <S> Therefore, by focusing down the runway, you are exchanging a poor mechanism for judging height--depth perception--for a better mechanism--angle perception. <A> In addition to Dave's correct answer about holding a consistent pitch attitude through touchdown, it also helps new pilots to notice and eliminate drift. <S> Once you have a few thousand hours you don't even realize you're doing it, but for a beginning pilot it's hard to make the correct inputs of aileron to correct sideslip and rudder to align the longitudinal axis of the airplane with the centerline of the runway simultaneously (heck, it's even hard to type!). <S> By looking out at the far end of the runway a beginning pilot gets a better idea of how much rudder and aileron input is required.
|
Longtime CFI Rod Machado developed a really good method for new pilots to evaluate flare height based upon runway geometry that works very well for light aircraft.
|
In an articulated hub rotor craft, what could cause the blade to flap negatively? For example in forward flight what could cause the blade to flap lower than parallel to the CF at the front of the aircraft ? <Q> The first thing that comes to mind does not occur in forward flight. <S> That would be a hard landing. <S> Depending on the rotor design and the amount of articulation and the landing gear type, a hard landing can result in some serious problems, notably, Ground Resonance. <S> In-flight, it may be possible to achieve with a rapid unloading of the rotor (Zero - G) plus cyclic input. <S> Usually, if not always fatal. <S> Mast bumping takes a specific set of conditions and control inputs, to take place. <S> It is typically occurs with 2 bladed teetering rotor systems at zero G. <A> First, why does the blade need to flap "negatively"? <S> In forward flight the rotor disk must be tilted forward to produce the thrust required to overcome drag. <S> In order to tilt the rotor disk forward the rotor blade must be at the lowest point in its range of flapping when it is over the nose (12 o'clock), and at the highest point in its range of flapping when it is over the tail (6 o'clock). <S> For the above to occur the blade must also be at the neutral point (exactly halfway between the highest and lowest points) at the 3 and 9 o'clock positions. <S> Therefore the blade must be flapping "negatively" when it is between 3 o'clock and 9 o'clock. <S> The flapping of the rotor blades in forward flight is primarily controlled by cyclic feathering --- in other words, the pilot must hold forward cyclic to maintain forward airspeed. <S> I don't believe that mast bumping is a concern with fully-articulated rotors. <A> High forward speed at low weight could cause this. <S> A fully articulated rotor has a coning angle, which is a function of weight and centrifugal forces due to angular velocity. <S> In order to gain forward velocity, the disk tilts forward - at speed, there is usually collective-lateral coupling that tilts the disk sideways, for compensating tail rotor thrust. <S> With such a rotor head, low flapping angles will occur at high tilt and low coning angle due to weight. <S> The drawing in OP seems not to be a fully articulate rotor head, but a teetering rotor without pre-coning. <S> Such a rotor will have low flapping angles at forward tilt, period.
|
One adverse condition which causes negative flapping is Mast Bumping.
|
Does the required torque to spin a propeller increase with RPM? I‘ve currently been experimenting with different propellers: 12x12 prop, 16x12 prop (both two blades) and a 22x14 (6 blades) prop. They were propelled by a 2.4 kW electric motor with 260 kV on a 6S/5200mAh/12C battery setup. The 12x12 prop produced 2 kg of thrust at full throttle, the 16x12 produced 4.5 kg of thrust. So I thought the 22x14 would produce around 6 kg because its bigger blade area would be more efficient. However, I got only 0.8 kg of thrust and recognized that the motor would slow down at a certain RPM. I have to say the big prop is pretty heavy so could it be that the motor would have enough power to spin the prop faster but it lacks enough torque to get it there? <Q> Of course. <S> More and bigger blades is more drag. <S> Drag is also proportional to the velocity squared. <S> Even maintaining the RPM, a bigger propeller (diameter) will have the additional diameter flying faster. <S> Place the propeller in vacuum, and the engine will have no trouble with the propeller apart from any loads on the shaft (but there won't be any thrust). <A> Mechanical power is always the product of an effort (torque) times a flow (RPM) variable. <S> Similarly, electrical power is always the product of an effort (voltage) times a flow (current) variable. <S> The design problem of optimizing a motor-and-propeller combination for maximum power then always boils down to this: 1) determining the RPM at which the motor produces peak power (torque x RPM), 2) knowing the voltage and current required to produce that power, and 3) specifying the propeller which can absorb that amount of power at that specific RPM. <S> The analysis is complicated by the fact that from a dynamical systems modeling standpoint, a DC motor is a gyrator , in which the input effort variable (voltage) is proportional to the output flow variable (RPM). <A> If the other factors remain constant, the torque required to rotate a propellor will increase with RPM. <S> The power requirement is a function of torque and RPM. <A> Yes the required torque increases with RPM. <S> With simple impulse theory, the torque Q on a rotor or propeller is: $$Q = C_Q \cdot <S> \rho <S> \cdot <S> A <S> \cdot \Omega^2 \cdot <S> R^3$$ <S> Where $\Omega$ is the angular velocity <S> = RPM. <S> So the torque required goes up with the square of RPM, and since power = <S> $Q \cdot \Omega$ , the power increases with RPM $^3 <S> $ . <S> All other factors remaining as they were of course. <S> That is simple impulse theory however, which does not consider disk solidity and blade profile drag. <S> For a given thrust and blade radius, torque and power increase with number of blades since there is more blade profile drag to overcome. <A> Firstly, take the six blade and throw it away. <S> 2 blades are best until the arc hits the ground in front of your plane, then go with 3. <S> Curious as to the application here, is it a microlight? <S> Might help also to consider pitch too, but you are definitely on the right track with the 16x12.If <S> I am not mistaken, it is longer than the 12x12 with the same pitch. <S> You can get a rpm measuring device from a hobby shop to measure peak rpms, but as you are already measuring thrust it is not absolutely needed. <S> Now you can try 15x12, 17x12, maybe 18x10(longer with less pitch) until you get it perfect. <S> Pitch is just like gears on a car, lower means better acceleration from standstill and better at climbing, higher will give lower rpms at cruising. <S> I would keep trying, and make sure the battery/engine can handle the load withoutgoing up in flames. <S> Definitely check with an expert as you have some serious prop there.
|
To maintain a higher RPM (or to use a bigger prop) the force to cancel the increased drag is higher, and thus the torque (force times distance) that drives the propeller.
|
Can a controller be tasked to provide more than one ATC service at a time? During a visit to one of the ATC Facility I found out that the Aerodrome Controller was also providing procedural approach control service along with aerodrome control service. Similarly, Area Radar Controller of the same facility was also permitted to assume the responsibility of Procedural (Non Radar) controller (who acts as a backup to the Radar Controller) in the absence of Non Radar controller to provide relief to him. I find both of these arrangements a violation of safety. I tried to find some reference to support my idea about this in the ICAO DOC 9426 (ATS Planing Manual) and Human factors Training in ATM, but could not find out anything that specifically prevents or allows this particular arrangement. Can these services be combined? Any reference to the ICAO doc or some regulation would be a great help. <Q> Since you've asked for a document, check ICAO Doc 4444 : 3.1.3.1 Where traffic demand varies significantly on a daily or periodic basis, facilities and procedures should be implemented to vary the number of operational sectors or working positions to meet the prevailing and anticipated demand. <S> Applicable procedures should be contained in local instructions. <S> The local instructions of the airport you visited will contain the details you need. <A> JScarry is right. <S> Workload dependent, its completely acceptable for an ATC employee to provide multiple services. <S> No need to have 1 on Clearance, 1 on Ground, and 1 on Tower if you service 5 aircraft an hour. <A> It is a routine occurrence at ATC facilities to combine separate functions(e.g. <S> Radar Controller, Hand-Off Controller) as well as different positions or sectors as the traffic conditions warrant.
|
The ATS authority can indeed vary the number of working positions based on demand.
|
How fuselage creates lifting force when plane flying on a side? On a question "How plane able to fly on a side" people answer that it's because fuselage shape crate lifting force and plane should have enough thrust.But that seems vague to me.How fuselage creates lift ? Wing shaped that way that more air goes under it, so there more pressure below wing than above it. But fuselage is the same from both sides, so how it able to create lift after rotated on side ? <Q> The photo that you posted already gives quite a few hints on how this can be possible: <S> The aircraft is flying at a sideslip angle (the nose pointed slightly up), so a part of the thrust vector is counteracting the weight. <S> It seems like the aircraft is not exactly perpendicular to the surface, so a part of the lift vector is still counteracting the weight. <S> The vertical stabilizers produce some "lift" in this situation due to the sideslip angle mentioned in 1. <S> Note that these typically have symmetrical airfoils, so without the sideslip angle, these would not create any force. <S> The aircraft might be descending in a controlled way. <S> In that case, not all of the weight must be carried. <S> As an example, look at the high sideslip angle here: . <S> There you can also see the rudder being deflected for trimming. <A> Aircraft have multiple surfaces that move, in a maneuver like the one you posted a picture of, the aircraft will be relying on multiple surfaces to maintain altitude, this is a combination of the ailerons, the rudders, and elevators. <S> Objects in motion will stay in motion until they hit something. <S> Also, the forces of flight don't necessarily mean straight up and down, those axis's can move relative to the aircraft. <S> Source- Pilot for years. <A> With proper attitude control and enough thrust, a washing machine or a refrigerator can fly. <S> Angle of attack and lift are not something exclusive of wings... <A> If you want an object to generate lift, the object doesn't need to be any particular shape. <S> You only need two things: <S> The object's cross section should be long and skinny. <S> The object should be at an angle relative to the oncoming air. <S> Fuselages are long and thin, and during knife-edge (sideways) flight, they're at an angle relative to the oncoming air. <S> Therefore, they generate lift. <S> See also: <S> How do symmetrical airfoils generate lift?
|
Wings and fuselages both produce lift in the same way: they change the direction of the oncoming air.
|
Can time spent in consumer flight simulators increase the safety of flying light sports aircraft for licensed pilots? I've asked this question to my flight instructor, who believes flight simulators do a very poor job of modelling flight physics for very light airplanes, which makes them useless for preventing accidents. Considering most accidents are caused by loss of control this explanation does make sense. On the other hand, flight sims might help in dealing with engine failures. I intend to fly in a plane derived from Zenair CH-701. <Q> Perhaps yes, but it's not easy to qualify objectively . <S> Simulating a light airplane may require a different approach in some areas, but it's not inherently difficult compared to 'heavy' ones. <S> However, the truth is, nobody cares that much, so there is much less investment in such simulators. <S> A decent FTD (flight training device, something a step lower than what is legally called a 'simulator' (FFS)) will cost easily several times more than an ultralight, while the risk benefit is arguably lower (compared to real flight). <S> Secondly, type-rated simulators are rarity even on the 'proper' GA market; typically FTDs are 'generics' that aim to simulate a representative 'class' of aircraft. <S> This makes fair comparison difficult, especially by real pilots who have most experience on a single/few real types. <S> Then, there are technical features that are even more important for light (and GA) airplanes than for big ones. <S> One is a good visual system: in real visual flying, you obviously use it more, and having a single monitor stuck in front of you will hamper you more than you might think. <S> Second is control loading: on light airplanes you get airspeed and trim feedback right at your fingertips. <S> There are no cheap solutions to this. <S> You may argue this is not 'physics', but it actually is, this is all part of a feedback between the airplane and you being the part of control system. <S> Lack or poor quality of these things (which is more than common on the simulators used for light planes) will substantially affect subjective and objective qualification of the flying qualities/handling of the simulator. <S> There are areas where even expensive FFS suffer. <S> A typical example is ground handling. <S> Or, speaking about 'loss of control', many regimes that result from it, notably stall and spin, are actually difficult to simulate well, and are often not required for certification. <S> That all said, it's an overstatement to say that simulators are 'useless for preventing accidents'. <S> Flying is more about thinking ahead, planning and situation awareness than any specific piloting skills, and even a game simulator can teach you some of that. <A> They do a good job modeling the majority of the flight physics for airplanes with a few exceptions such as edge of envelope flight characteristics and some power plant characteristics. <S> Eg FSX does not model stall/spin characteristics well or turboprop characteristics well or autorotation characteristics for helicopters well. <S> X-Plane 11 is purported to have good flight physics models in them and they can be more custom tailored to specific aircraft than FSX or Prepar3d <S> can. <S> That being said, some of the aircraft handling actions are not quite the same as the real thing. <S> In the end desktop sims are not airplanes; they are just mathematical algorithms that closely match how an airplane flies. <S> It’s similar to saying that a synthesized violin sounds pretty good - <S> but it’s never gonna be a hand made <S> 1727 Stradivarius. <S> That being said those same desktop sims are good enough that the same mistakes I make in the sims, I will make in the real aircraft. <S> One thing anything short of a dedicated Level D full motion sim just can’t do is simulate the kinesthetic feel of an airplane. <S> That’s something you just don’t get sitting in an office chair with a joystick and staring at a 20” 2-D screen. <S> While VR sets can simulate what you see out of an airplane, it’s still not quite the same thing. <A> in the limit of aircraft so light that their weight is of order ~ the weight of the air they displace, the usual and customary rules of aerodynamics i.e., vehicle responses to control inputs goes out the window and the dynamical analysis gets a lot more complicated. <S> For example, in the case of macready's gossamer condor, deflecting the right aileron down did not roll the vehicle to the left; instead it skidded the vehicle to the right. <S> So it does not surprise me that consumer-grade flight simulation packages might do a poor job with predicting the response of ultra-ultralights. <A> I am in solid agreement with two statements made above: <S> Sims are good for practicing the patience part of flying, especially setting up for the pattern and landings, and instrument approaches and flying the procedure. <S> Without the feedback of the plane moving with you, and just having the screen view tilt in front of you, the visual part quickly becomes unrealistic as you make maneuvers. <S> Especially simulating the wind - the screen jumps and bounces around, but sitting in your chair <S> it just becomes annoying. <S> And depending on the plane you are flying, the joystick/mouse on your computer will allow full range of unlimited movement, while depending on the phase of flight the plane may require increasing amounts of force to actually move the stick in full range, and if not properly trimmed may require a lot of pressure. <S> For example, I was trying out a simulator at a training school. <S> Took off okay in a Beech Baron or something like that, but the trim was set wrong, so I had to really fight the pitch pressure while I searched for the elevator trim to keep from climbing up into a stall.
|
Flying is more about thinking ahead, planning and situation awareness than any specific piloting skills, One thing anything short of a dedicated Level D full motion sim just can’t do is simulate the kinesthetic feel of an airplane.
|
What are the rules of airfoil thickness from root to tip on tapered wings? I'm doing some research on wings and airfoils used in the 30s and 40s, and I'm trying to understand the rules about airfoil proportional thickness changes across the wing (root to tip) on tapered wings. Many planes of that time used airfoils with thickness ranging from 15% to 9% (root to tip). (Source: https://m-selig.ae.illinois.edu/ads/aircraft.html ) So the question is: what are the rules for dimensioning airfoil thickness from root to tip? <Q> Also, you want to create most lift at the wing root, that is why chord, thickness and incidence angle are all highest there. <S> All three tapering down towards the tip for structural reasons. <S> There is a bit more info in this answer. <A> There are no clear rules; choosing wing thickness was no rigid science. <S> However, some rules did exist: <S> Root thickness goes up with aspect ratio. <S> While "regular" wings (aspect ratio between 5 and 8) had a root thickness between 14% and 18%, the high aspect ratio Davis wing <S> (AR 11) needed a 21% root airfoil. <S> Tip thickness was chosen for maximum section lift in order to add stall margin and aileron authority. <S> This means thickness here <S> is between 9% and 12% . <S> Camber also reduces from root to tip proportional to the lift per area ratio. <S> While the inner wing should produce the highest lift per area, the outer wing reduces this for stall margin and better aileron authority with upwards deflected ailerons. <S> In the early jet age, high speed required thinner wings because this delays the onset of Mach effects. <S> The symmetrical tip airfoil of the Me-262 had 9% thickness and supersonic aircraft reduced wing thickness to 6% to 4%, the thickness of the Bell X-1E wing . <A> The term for the draftsman's job of airfoil depiction in the, 30's and 40's, was called "Lofting". <S> Maybe the term is still in use, today. <S> Airfoils camber would be defined as a percentage of the chordline dimension, either above or below the chordline. <S> In the day, a table of points along the chordline would have corresponding (+%) or (-%) values to be plotted and then connected via a draftsman's French curve template. <S> When making the drawings for the tapered wing's ribs, the camber diminishes proportionally with the length of the chord.
|
Airfoil thickness at the root was chosen to obtain a good cantilever ratio: the bending moment is highest there, and you need to give it structural height.
|
Do different planes (category) aim differently in the 'final stages before flaring'? ( youtube.com ) Do different planes (categories A through D) aim differently in the final stages before flaring? I'm asking about precision runways. The reasons I ask: An ILS' glide slope is not coincident with the PAPI for example (when does the shift from G/S to PAPI occur?) There may be differences in the touchdown zone markings Airplanes come in different cockpit heights and approach speeds. By 'final stages before flaring', I mean when the landing is manually flown in VMC, when the shift from looking down to up occurs. Example: you may be on the G/S but off the PAPI when you look up, which one do you follow based on the category? There is plenty of anecdotal information all over the internet, so I'm looking for as factual an answer(s) as possible based on experience. This post for example (pprune.org) offers contradicting advice, one quotes a document saying, "PAPI provides guidance down to flare initiation," and mostly others saying to ignore the PAPI. <Q> Because of the downrange offset between the PAPI and the GS antenna, only a P3 (jumbo jet size) PAPI (14 meters eye to wheels) gives a more or less parallel path between the ILS glide slope and the pilot's eye so that they are both aligned on short final. <S> The other PAPI categories all have a deviation between the ILS slope angle and the PAPI slope angle, so that if you stay on the ILS glideslope all the way down, at some point the eye height becomes too high for the PAPI and you will see three whites even though you are right on the ILS. <S> You take this into account in training to learn to resist the urge to dive to correct because the last thing you want is to increase sink rate close to the ground. <S> So really, once you are really close in, inside the airport boundary, you don't rely on the PAPI lights. <S> If you were on-slope in a stabilized approach configuration at Vref at decision altitude, you just have to hold the pitch attitude and speed with maybe a few small pitch tweaks based on the runway sight picture and you will cross more or less at a wheel height of 50 ft. <S> The goal is to hear "50" from the GPWS just as the threshold is passing below, and the speed tape pointer is right at Vref. <S> From there the touchdown point takes care of itself using the normal flare/thrust reduction procedure you use for that airplane. <S> This Transport Canada Staff Instruction regarding the design of PAPI installations and issues with harmonizing them with ILS approaches gives some useful background: https://www.tc.gc.ca/media/documents/ca-opssvs/AC_302-009.pdf <A> I think there is some confusion in the question <S> An ILS' glide slope is not coincident with the PAPI for example (when does the shift from G/S to PAPI occur?) <S> Example: you may be on the G/S but off the PAPI when you look up, which one do you follow based on the category? <S> According to this answer broadly speaking, the PAPI and Glide Slope should line up as much as possible so that if you fly the approach right on slope when you look out the front you should be on the PAPI correctly. <S> If for some reason they dont align it should be noted on the approach plate and you will need to fly the various parts of the approach according to the conditions, if you are coming in visually under VMC <S> then you should use your visual references if you are coming in under instruments you fly the approach and keep your eyes on the panel. <S> You should be able to follow either right down to the runway <S> but once you are below the clouds and inbound on a visual approach (the last segment of any instrument approach) you will use what ever visual references the airport has available to you no matter your category. <S> There are lots of ways to judge the flair and <S> cockpit height is simply a factor that gets addressed in type training. <S> Category also does not affect approach path, it will dictate approach speeds and potentially minimums but the glide slope is the glide slope <S> no matter what you fly. <S> In my experience classes are sometimes crossed when flying. <S> Generally this applies to smaller GA planes coming into larger Class C and Class B airports and <S> ATC asks you to keep your speed up. <S> To keep traffic flowing and provided the aircraft is capable its not unheard of to have GA planes that typically approach ~90Kts <S> come in much faster. <S> I flew a Saratoga into KPIT @ ~125Kts (close to the max gear speed) which puts it well into Category B. <S> Meanwhile I have flown the same plane into other fields at the more resonable ~90Kt approach speed, well in category A. <A> As to the approach itself, you’ll fly that according to the published procedure. <S> One major difference is that in slower aircraft, you’ll have considerably more time available from the DA/MAP to the beginning of the roundout where as in category D and E aircraft, the transition to the roundout is almost immediate. <S> Landing techniques vary based on the kind of airframe, wing configuration and approach speeds, but for most large jets, it’s a process of arresting their descent rate around 10 or so feet above the runway and assuming a nose high attitude with a gentle descent rate to the ground until the mains contact. <S> It’s not a full stall type of landing like a light GA airplane and more like a soft field technique. <S> The throttles are retarded to idle about 20-30ft AGL to rapidly drain off airspeed during the roundout. <S> Exactly when to do this is a matter of kinesthetics - pilot just feels their way down based on their judgment of height, etc. <S> It’s a skill that takes roughly 100 hours or so of flight time to fully perfect and passed down from captains to FOs during type rating and transition experience. <S> In regards to using visual glideslope aids as opposed to instrument glideslope aids, in the event they are not aligned, passed the DA or MAP, that’s up to the pic and their judgment as to how to place the airplane onto the runway, obstacle clearance, etc. <S> Both methods are fine though only instruments should be used on an approach prior to reaching the DA or MAP/DH. <A> I fly in small planes, Category A. <S> We fly the Localizer/Glide Slope needles (i.e. the ILS) at about 100 mph, keeping the needles centered, until 200 feet above the runway, and if the runway is not seen at 200 feet above the runway power is applied and we go around. <S> When the runway is seen, power is reduced and a normal visual landing is made.
|
The answer to that is a combination of the specific approach procedure being flown, the aircraft approach category, the specific aircraft type, weather, winds, etc.
|
Can I rent a Cessna for a week with my GF with a PPL? I want to do a 45 hour course to obtain a PPL. The course only includes 10 solo hours but states that it is enough to hire light aircraft. So could I rent a Cessna after this and take a passenger? <Q> Most people do not take 45 hours to get a PPL, the national average is closer to 70. <S> Do not fall for the "get your license in 45 hours" gimicks. <S> They will give you 45 hours of instruction (and you will probably need more), you also then need to book the examiner and pay for that. <S> 45 hours is difficult to do in short periods of time as well, for example I got my license in 47 hours, way below national average, and it took me 7 months (weather/work/instructor availability/aircraft availability/etc). <S> So theoretically yes, you can, if you are renting from the same place that you took your training. <S> If not, then you will probably have to pass a check-out which will include about half an hour of ground and an hour or so of air with the company renting the aircraft. <S> You may also not be allowed to rent overnight unless you have X number of hours, again this is up to the rental company. <S> You also need to have insurance which meets the rental company's requirements. <S> For example, a local company will rent one of the 172's for up to 4 days. <S> The regular rental rate is \$125/hr and overnights are charged $375 for each day. <A> The privileges of that license cover 95% of the flying that private pilots do anyway, which is flying around VFR during the day alone or with one passenger. <S> Probably less than half the cost. <S> Those licenses are a bit less than what the 35 hour Private Pilot course was like 43 years ago <S> when I learned to fly, which cost me $1100 1975 dollars or about 5 grand today. <A> Absolutely, if you indeed get your PPL.
|
Some rental companies won't rent aircraft overnight, so you need to check that, and if they rent for longer periods of time you will end up paying extra even while the aircraft sits on the ground. If you just want to be able to take people for rides, just do an NPPL, roughly equivalent to Sport Pilot in the US or Recreational Pilot in Canada/Aus.
|
Finding the center of gravity/centroid of an airfoil? I'm in the process of building myself a wing frame out of balsa wood. However, as a high school student that's just started aerospace engineering, I'm not really sure how to go about it in some ways. What I'm looking for is the center of my ribs so that I can find the best point to put my main spars in. The ribs themselves are full flat-bottoms if that helps any. Is there a go to equation for something like this? <Q> In addition to checking out wing frame structures on the internet, why not go down to the hobby shop and get a balsa plane kit? <S> Airplane building is a hobby you will have all your life. <S> Generally, in balsa, you have a top and bottom spar, a leading edge, and a trailing edge to attach the aileron <S> (get lots of sand paper and CA glue). <S> As mentioned, put you spars at around 25 - 33 % from leading edge, around the highest part of the rib. <S> You may also have good luck strengthening your wing by covering it with 1/16 sheet balsa, others use heat shrink monocoat. <S> But you must also stiffen the wing <S> so it can not twist when you use the ailerons. <S> So you may wish to add balsa between the ribs connecting the top and bottom spars, creating a box structure. <S> A lot of ways here, and you can't read too much about it. <S> Please let us know how you are doing with it. <S> Check out RC Groups website as well. <A> If you are looking for a suitable position to build a flyable model I would suggest locating them approximately 1/4 of the chord length from the leading edge. <S> The rest of the airframe would need to be factored into computing the aircraft center of gravity and its relationship to your spar, but generally 25% LEMAC, (Leading Edge of the Mean Aerodynamic Chord) is a good starting point. <S> As a point of reference, the acceptable CG range of the C-130 Hercules is 15 to 30% LEMAC. <S> The center of pressure or lift of the airfoil will change somewhat with AOA, but I'm afraid that I can't help you with calculating it. <A> Structurally, depending on how many spars you want to use, there are positions based on experience. <S> For a single spar D nose construction 25-40% is a good idea. <S> If you are calculating stability, about 25% for aerodynamic center is a good estimate
|
If you want to find the centroid, I recommend you get some CAD software and draw it, and let the software find it for you, at least that way you can print out templates straight away.
|
Which is safer? The Piper Tomahawk or the Cessna 152? I have booked my first flying lesson for 2 weeks time, in my first step to obtain a PPL or LAPL. I had done all of my research on the Cessna family, assuming that is what I would learn in. I was satisfied by the safety and glowing reviews by students and instructors alike. Anyway, my local school has since told me that they don't have the 152 anymore, so I will be learning in a Piper Tomahawk. Some quick reading here states: The PA38 accident rate ranged from 0.336 to 0.751 fatal stall/spin accidents per 100,000 flight hours, compared to 0.098 to 0.134 for the 150/152. and There was always a concern about the stall and spin characteristics of the Tomahawk. The old adage “be careful what you wish for” applies because an overwhelming majority of the PA38 survey respondents requested an aircraft that would stall with more authority than the 152. And they got it. You’ll hear many people talk about the stall characteristics of the PA38 like they’re referring to a demon, but it should be remembered that this was essentially a design feature to teach better pilots. Unfortunately, this led to a higher than average stall/spin accident rate that earned the PA38 a less than admirable reputation quite quickly (thus the nickname Traumahawk and Terrorhawk). This isn't as comforting. So taking into account engine reliability, stall issues, etc. - which aircraft really is safer? <Q> From the Wikipedia article on the Tomahawk: Safety record: <S> According to the Aircraft Owners and Pilots Association Air Safety Foundation, which published a Safety Highlight report on the Piper Tomahawk, the Piper Tomahawk has a one-third lower accident rate per flying hour than the comparable Cessna 150/152 series of two-place benchmark trainers. <S> The Tomahawk has a higher rate of fatal spin accidents per flying hour. <S> The National Transportation Safety Board (NTSB) estimated that the Tomahawk's stall/spin accident rate was three to five times that of the Cessna 150/152. <S> [2] <S> Earlier in the article it was stated: <S> Before designing the aircraft, Piper widely surveyed flight instructors for their input into the design. <S> Instructors requested a more spinnable aircraft for training purposes, since other two-place trainers such as the Cessna 150 and 152 were designed to spontaneously fly out of a spin. <S> The Tomahawk's NASA [1] GA(W)-1 Whitcomb airfoil addresses this requirement by making specific pilot input necessary in recovering from spins, thus allowing pilots to develop proficiency in dealing with spin recovery. <S> So what this means is that the Tomahawk was intentionally designed to be easy to spin so that instructors could teach students how to recover from a spin. <S> Other aircraft, like the Piper Cherokee, are almost impossible to spin so instructors cannot really teach spin recovery in those aircraft. <S> To answer your question on how this relates to safety that depends on how you look at it. <S> I would argue that a pilot who knows how to recover from a spin is a safer pilot than one who doesn't. <S> Aircraft like the Cessna 152 or Piper Cherokee have design features that can "cover up" a pilots mistakes because they are difficult to spin or stall, but if you plan on flying aircraft that are not so hard to stall then not knowing the proper recovery procedures can get you killed. <S> The main factor in safety is not usually the safety of the plane but the safety of the pilot. <S> The vast majority of accidents are caused by pilot error. <S> I would worry more about evaluating yourself as a pilot and understanding if you have the right mindset to be a safe pilot. <A> They both crash if you fly them badly. <S> Stall/spin crashes generally happen while in the circuit, usually turning to final, and both airplanes will oblige if you mishandle them. <S> The 152's more passive spin recovery characteristics will do you absolutely no good at 500 ft AGL, so the discussion of spin recovery characteristics of the two airplanes is largely irrelevant. <S> Cloud, knowledge is power and all that, but be careful about taking some of this stuff to obsessive levels, which is going to work against you as you progress through this journey. <S> You won't be able to enjoy yourself and will probably start to drive your instructor(s) bonkers. <S> Anyway, I would be more concerned with the condition of the school fleet and whether the school appears to maintain them well. <S> Like, are the trainers kept clean, does everything work, are airplanes grounded a lot, is the maintenance shop a disorganized dump, that sort of thing. <A> Basically, as the flight school still has the plane flying the design is safe enough to be used for school usage. <S> They do not wish to hurt either the student or the flight instructor. <S> And they have done this quite a while: you are not their first student. <S> You will train in how to safely fly the plane under the guidance of an instructor. <S> You will learn a lot about procedures and limitations and how to react in various situations. <S> You can get into serious trouble in any airplane type — the instructor is there to teach you how to avoid it. <S> Which of the generally available plane types is used is the last thing to worry about.
|
However since the Tomahawk is actually made to spin, there is the potential for increased spin/stall accidents if the pilot messes up.
|
How did the 9/11 hijackers find their way to New York City? It is quite well known that the airplane hijackers on 9/11 were not professional pilots. So, my question is how some people who didn't have any experience of navigating the airplanes could find their way, for example from Boston to New York City? I read somewhere that some natural signs like the Hudson River (for example) helped them to find their way through New York City. But I'm still looking to find a more convincing answer if it is available. <Q> Several of the hijackers, including Mohamed Atta , held at least private pilot certificates and had undergone ATP level jet training in DC9 and 737 full motion simulators in December of 2000. <S> Atta himself held a commercial license with instrument and multi engine ratings. <S> They were well versed in aerial navigation techniques and more than capable of navigating the aircraft in question back to New York City and Washington DC after it was hijacked and secured. <S> A basic scenario that any private or commercial pilot could have done <S> : the hijackers knew the flights they were booked on and the rough routes they would take to their destinations. <S> A little basic planning amongst themselves would have produced the approximate position the aircraft would be at at the time it was hijacked. <S> Once seized and the flight crew liquidated, they could quickly determine their positions either from their headings and next waypoints or with a simple VOR fix (any competent private pilot can do this). <S> The autopilots could quickly be disengaged and the airplanes hand flown using basic pilotage (good weather prevailed over the east coast that morning) or radio navaids to return to their targets. <S> The navigation and flying they did that day was relatively simple. <S> As an update, I know these kinds of questions float around with “9/11 truthers” and other conspiracy fanatics as some sort of proof that the official explanation is incorrect. <S> Quite often they cherry pick quotes and ignore any other evidence that won’t fit their narrative. <S> Combine that with the public that’s largely ignorant about aviation, it allows these kinds of ideas to fester very well without challenge. <A> All of the hijacked flights were going in different directions and had to be piloted to a different destination. <S> The hijacker pilots had different degrees of success in doing this. <S> The flight paths they took are shown in this map published by the FBI : <S> Marwan al-Shehhi trained with Atta and received similar simulator training for 737s. <S> Even so, al-Shehhi apparently missed Manhatten on his first pass, although he may have just been reconnoitering his approach. <S> The pilot of flight 77, Hani Hanjour, was also a licensed commercial pilot who had knowledge of how to operate and navigate a 737. <S> So, in summary, all of the hijacker pilots were trained in the basic operation of a 737 and knew how to do aeronautical navigation. <A> The 9/11 Commission Report goes into some detail on the hijackers' planning and preparation, including a (not entirely successful) attempt to obtain aviation GPS units: <S> Moussaoui <S> also purchased two knives and inquired of two manufacturers of GPS equipment whether their products could be converted for aeronautical use [...] <S> On August 22, moreover, Jarrah attempted to purchase four GPS units from a pilot shop in Miami. <S> He was able to buy only one unit, which he picked up a few days later when he also purchased three aeronautical charts (page 247-249) <S> The report doesn't detail whether there's any indication that unit was actually used. <S> However, during their flight training, two of the hijackers also took a number of practice flights that would have familiarized themselves with the areas around New York and DC, which could have helped them with visual landmarks: <S> Jarrah and Hanjour also received additional training and practice flights in the early summer. <S> A few days before departing on his cross-country test flight, Jarrah flew from Fort Lauderdale to Philadelphia, where he trained at Hortman Aviation and asked to fly the Hudson Corridor, a low-altitude “hallway” along the Hudson River that passes New York landmarks like the World Trade Center. <S> Heavy traffic in the area can make the corridor a dangerous route for an inexperienced pilot. <S> Because Hortman deemed Jarrah unfit to fly solo, he could fly this route only with an instructor. <S> Hanjour, too, requested to fly the Hudson Corridor about this same time, at Air Fleet Training Systems in Teterboro, New Jersey, where he started receiving ground instruction soon after settling in the area with Hazmi. <S> Hanjour flew the Hudson Corridor, but his instructor declined a second request because of what he considered Hanjour’s poor piloting skills. <S> Shortly thereafter, Hanjour switched to Caldwell Flight Academy in Fairfield, New Jersey, where he rented small aircraft on several occasions during June and July. <S> In one such instance on July 20, Hanjour—likely accompanied by Hazmi—rented a plane from Caldwell and took a practice flight from Fairfield to Gaithersburg, Maryland, a route that would have allowed them to fly near Washington, D.C. (page 242) <S> The report also says that several of the hijackers also had access to flight simulator software and/or simulator time at flight schools, which would have given them further opportunities to practice navigation. <A> The Hudson River will take you straight to Manhattan. <S> On a clear day, such as September 11 was, you could see the WTC for 100 miles or more (I had seen it from 160 miles away at Montauk Point on clear days, but you had to know where to look). <S> AA77 would have had a problem navigating eastbound with such an amateur as Hani (who most likely never had the certificates reported). <S> Since there aren't any prominent landmarks going east from Falmouth VOR.
|
Mohamed Atta, the ringleader of the effort, was a licensed commercial pilot received significant simulator training for large jets and the Boeing 737 in particular.
|
Is the aircraft neutral point a function of the tail incidence angle? While using XFLR v5 for a basic analysis I am facing this issue. For a fixed configuration I varied the tail incidence angle and XFLR is displaying a change in the Neutral point location. But as per theory neutral point location is not dependent on the tail incidence angle at all. I was hoping if someone could help me with this issue. <Q> I have done some homework and I will explain why the Neutral point does not vary with the tail incidence angle. <S> The above equation is the fundamental equation defining the location of the neutral point. <S> We can see that the Neutral point is a function of the following factors only, Aerodynamic centre Tail volume (Horizontal tail sizing and Arm length) Tail efficiency factor (Ratio of dynamic pressure at the tail and at the wing), Lift curve slope for the wing and HT (CLalpha - which is fixed and not dependent on the tail incidence), Downwash effect Fuselage moment contribution <S> So none of these factors are dependent on the tail incidence angle and hence there musnt be a change at all. <S> What shocked me the most is the fact that errors in variable quantites can be accounted for but errors in quantities that shouldnt vary is very confusing. <S> It is a very standard statement that '' Static margin or ultimately the Cmalpha shouldnt get affected by the change in tail incidence''This <S> is the information I could get about it. <A> The calculation of the neutral point of an aircraft is about moments, not aerodynamics. <S> The tail incidence angle has nothing to do with the neutral point, just as it also has nothing to do with the calculation of the CG. <A> I'm not that familiar with XFLR, so I'll answer with the general knowledge. <S> The neutral point (aka aerodynamic centre, AC) <S> does change with the tail incidence. <S> Why shouldn't it? <S> The peculiarity (and intention) of AC is that it doesn't move with the angle of attack (AoA) only. <S> If you balance your airplane at AC, by locating CG there or by hinging (and weight balancing) <S> the model in a wind tunnel, the airplane will be neutral with respect to AoA changes. <S> It won't 'weathervane'. <S> But this doesn't mean AC won't move with configuration. <S> If you pull the elevator/stab up, this will redistribute the moments such that the neutral point moved farther back. <S> Think this way: AC, by definition, is the point about which the added moments due to increase of AoA from the wing, stab and everything else, balance each other out. <S> Or, in other words, where we can think the added lift occurs. <S> When you reduce the stab incidence (with respect to the wing), you make it to contribute more to the moment balance (again, the balance due to changes of AoA and nothing else, it's boring to repeat <S> but it's important to understand. <S> We are not talking about the absolute balance). <S> But what can you do with that? <S> Your stab now produces a pitch-up moment. <S> Yes, the airplane actually became a bit more stable, but it will start doing loops. <S> If we want to restore neutrality, we'd need to move CG back, to the new AC - which would only make things worse. <S> The only way we can balance the situation(*) is to move CG forward , until it compensates the added pitch-up. <S> Which again increases static stability. <S> (In practice, of course, the opposite happens: when CG is forward, we make the tail to provide pitch-up). <S> So, in reality, we can't simply choose tail incidence as an independent variable. <S> It is needed to trim the airplane as much as to provide stability. <S> But, indeed, any aerodynamic configuration changes may shift the AC and affect stability. <S> (*) We can also tilt the thrust to provide the required moment, but this would be double waste: the tail works against the engine. <S> Nevertheless, technically, this way it is possible to make a statically neutral airplane with any desired tail incidence. <A> As you suggested, neutral point does not change with changes in decalage (tail incidence). <S> For more explanation, see these links from a model airplane forum-- <S> https://www.rcgroups.com/forums/showpost.php?p=24692807&postcount=3 <S> https://www.rcgroups.com/forums/showpost.php?p=24694083&postcount=7 <S> https://www.rcgroups.com/forums/showpost.php?p=24694082&postcount=6 <S> https://www.rcgroups.com/forums/showpost.php?p=24694515&postcount=9 <S> The links are more focussed on "static margin" than "neutral point", but implicit in the idea that the "static margin" is not changing if the decalage is changed, is the idea that the "neutral point" is not changing either. <S> Maybe someone can add to this answer to address the issue you are having with XFLR v5. <A> This may be a good time to dig into the formulas your software uses and try doing them manually. <S> It seems XFLR v5 is doing a few steps at a time. <S> Changing tail incidence indirectly affects the static stability nuetral point by assuming CG will move to new center (of lift) pressure. <S> Moving CG changes the torque arms of the stabilizing and destabilizing forces, which will change the static stability of the aircraft. <S> For example, is one reduces downforce of tail, center of pressure (of entire plane) moves back, matching CG moves back, now there is more area ahead of the CG. <S> One cannot ignore the CG when considering the effects of aerodynamic forces on an aircraft. <S> This net aerodynamic center still needs to be behind the center of gravity for positive stability. <S> More good info in this answer .
|
If one defines "nuetral point" as the aerodynamic center of the entire aircraft, where a change in pitch does not create a pitching moment, then a change in tail incidence should only slightly affect its location.
|
Can a Rutan Quickie be made into a legal Part 103 Ultralight? I was was thinking about buying a 80s rutan quickie q-1, it has a 18 hp motor. I want to get a ultralight but I like this one because it is fast. Can I get a motor that would be within the requirements? I don't know how I would be able to make this an ultralight. Iwas wondering if a Rutan 277 engine would work well in it and if this would be in the requirements <Q> Limiting fuel capacity is easy, and the 18 HP original engine worked well enough on the Q1 -- but it was a lot faster than 55 kt (close to double, as I recall). <S> From comments (thanks, Gerry) <S> I understand the Q1 has a stall speed of 42 kt -- fairly reasonable for a light aircraft, but well above Part 103 maximum of 24 kt. <S> You might be able to slow down enough by installing a flatter-pitch propeller, but that would have other effects (overspeeding the engine, for instance) that would need to be addressed, and then you'd be trying to fly with almost no speed range -- <S> 42 to 55 kts isn't, IMO, a safe performance envelope (and yes, the Q1 would still go faster than 55 kt in a dive, but the level flight and climb performance are where the safety issues lie in this case). <A> If it had a lighter engine, the wing loading would be slightly smaller. <S> If it could be rewinged (longer chord and more camber?) <S> , then it might work. <S> You could get enough lift at a slower speed. <S> A bigger wing would weigh more, but perhaps that would be offset by the lighter engine. <S> Of course, the CG would change and the wings would need to account for the shift in cg. <A> Speed is not just about the engine. <S> The reason the Q1 is so fast on an 18HP engine was that it had high wing loading, to put it a simple way it has to fly faster for the wings to produce enough lift. <S> Its stall speed is about 41 knots, which is a characteristic of the wing shape and area, if you put a smaller engine on it you won't change the characteristics of the wing.
|
I doubt the Quickie would fly well enough at very slow speeds to meet the rest of the Part 103 requirements -- specifically, the limit on maximum level flight speed.
|
In general, how do aircraft handle differently in inverted flight versus in upright flight? Inverted flight is flight with a roll angle between 90° and 270° (although it classically referred specifically to flight with a roll angle of 180° - i.e., upside-down). In what ways, in general, does aircraft handling in inverted flight differ from aircraft handling in upright (non-inverted) flight? Partially inspired by reading about the crash of Alaska Airlines Flight 261 , including how the pilots apparently tried (albeit unsuccessfully) to recover their airplane from its final dive by rolling it inverted. <Q> Typically, unless the CG is quite far aft (as is often the case with aircraft designed for aerobatics), lots of forward stick or yoke will be needed to keep the nose high enough for sustained inverted flight. <S> With inadequate forward yoke or stick input, the airspeed may increase very quickly as the flight path curves earthward and altitude is rapidly lost. <S> This orange radio-controlled model glider doesn't even have ailerons, and it has a flat-bottomed airfoil, yet it may be flown in sustained inverted flight. <S> (Roll control is challenging-- inverted, the ample dihedral is very destabilizing.) <S> With the right technique, nearly any aircraft would likely be controllable in sustained inverted flight. <S> Getting there safely from upright flight, and getting back safely to upright flight afterwards, may be another matter, especially if the roll rate is sluggish. <S> Obviously, whether or not the engines will receive adequate fuel and lubrication to keep running during sustained negative-G flight, and what will happen to the flight controls if they do not, will vary from one aircraft to another. <A> One factor in any type of flying is airspeed. <S> 250 knots indicated would be an EF 5 tornado. <S> Most objects that are not attached to earth will fly in any configuration, upright, inverted, even on their sides. <S> The original X1 that broke the sound barrier had (by today's standards) amazingly glider-like wings. <S> Reducing them allowed for even higher speeds. <S> Inverted flight limitations and concerns are mainly pilot training, fuel flow, trim, and objects falling to the ceiling. <S> Notice that weight forward and elevator "up" will cause a rapid descent when inverted, which is corrected by trimming elevator "down" (is the new up). <S> The aircraft, retrimmed, will fly, although less efficiently. <S> A fully symmetrical airfoil (common on aerobatic aircraft) minimizes these differences. <S> Stall speeds will vary with aircraft in inverted flight, but can be avoided. <S> The aircraft, even Flight 261, would have a workable flight envelope. <S> Sadly, in the case of Flight 261, they were dealing with a jammed and then completely detached horizontal stabilizer (allegedly poor design and improperly maintained) and simply had no chance once it broke free. <S> Had the plane been in proper working order, I would not doubt those 2 experienced pilots, with permission, could have flown inverted quite easily. <S> One would expect less roll stability from the anhedral, but more from the fuselage and tail <S> (weight) being below the wing. <S> Shame they could not save it. <A> Another aspect, not mentioned so far is that, because you effectively hold "bottom half" of the stick now (relative to the direction of aerodynamic forces) <S> , it is not only pitch but also roll control, which is in a sense inverted. <S> But pedals and rudder stays the same, so in order to make coordinated turn you need to move the stick in opposite direction then the pedal you push on. <S> Or, in other words, you need to roll your head outside the turn, not inside, when flying inverted. <S> Depending on how your brain works when flying an airplane, this can be quite a difference for some. <A> Among other things, this means that stall characteristics could be much different (presumably worse) for an airplane in inverted flight. <S> I can't find it now, but I recently saw a video of two similar biplanes flying straight and level, one flying inverted directly above the other. <S> The upper one suddenly dropped, striking the other, and I believe both crashed. <S> Although I can't prove this to be the case <S> (and I haven't heard the results of an official investigation), it seems plausible to me that the pilot of the upper airplane was unaware of the possibility of a significant increase in stall speed associated with inverted flight.
|
Most airplanes have asymmetric airfoils optimized for non-inverted flight.
|
Who else is using electro-thermal wing anti-/de-icing apart from the 787? I am researching into deicing technologies for the future, but apart from Boeing with Ultra/GKN, no one seems to be picking this technology up and being competitive. Any one know why this is? Is it an expensive development? Risky? Is it on any aircraft manufacturer's roadmaps? <Q> I fail to see what is exactly new in the B787 de-icing system, except for the way it is manufactured (spraying metallic layers onto the composite structure). <S> Electric heating is the most obvious and straightforward method of de-icing, and the least energetically efficient at that. <S> It is much more efficient to break <S> the ice rather than to melt it - in terms of the energy required. <S> Even B787 with its sheer electric supply can't afford anti-icing (that is, constant heating to prevent ice formation), and de-icing power consumption is 45-75 kW. <S> Perhaps most Russian (larger) aircraft had electrical wing de-icing system: from Tu-95 (1952) to <S> Il-18 (1957) to Tu-154 (1968) <S> (I could give specific links but they are in Russian). <S> Typically, they work in sections to reduce power demand, and consist of heating wires (rather than layers like on 787) that melt the ice. <S> Later aircraft such as Il-86 (1976) and -96 had a more advanced electric impulse system, which creates mechanical impulse on the leading edge with induction coils. <S> This deforms the skin for a very brief moment to break the accumulated ice. <A> The F-35 and V-22 also use the same kind of blended electric heating pads as an anti/deice method. <S> According to this article the conductive material that is used to make the heating units is applied during layup of the composite material for the wing. <S> Thus it might not work on metal wing aircraft as most modern airliners are. <S> There is also the consideration of certification, which in aviation is a very important factor. <S> Also as noted in this question , the 787 lacks the bleed air system needed to drive a classical anti-ice system so another solution is needed. <S> But it still uses engine bleed for engine cowl and nacelle anti-ice. <A> Apparently electrothermal anti-ice systems are more energy efficient – about 35% better efficiency – than using HP compressor bleed air channeled through pipes to the leading edges of the lifting surfaces. <S> See this article. <S> https://www.aviationpros.com/article/12414609/electrification-and-e-flight-part-4-boeing-is-on-the-way-to-a-more-electric-future <S> I was not aware that Boeing was using electrothermal anti-ice systems on the 787. <S> They have been common in general aviation for sometime. <S> Some examples are the Kelley ThermaWing used on some singles and light twins. <S> But yeah <S> that’s the first time I’ve ever heard of such a system being used on an application that large. <S> This <S> I believe goes back to the use of a uniform electrification in the aircraft. <S> Just about everything on the airplane is powered by its generators, including the flight controls hydraulics and other systems. <S> If you start off with that plan for an aircraft like that it would make more sense to install electrothermal anti-ice systems on the wings as opposed to a separate, and dedicated bleed air system. <A> Fokker 28 <S> MK 100 has leading edge electrical anti ice system.
|
Once an airframe is certified in a given configuration it may not be financially logical to certify some new part for a system that is already well in place and working.
|
For what program was this Cessna 182 fitted with canards? I want to see if anyone knows what the heck is going on here. I was doing a flight out in Palo Alto California recently, and during the run up this Cessna 182 pulled in next to us. It appears to have a canard foreplanes attached near the firewall of the airplane, and it appears to have a movable control surface on it as well. No this is not a Photoshopped image, this is an actual airplane that was sitting right next to us. I’m just curious if anyone here knows of any program using this aircraft and the purpose of the canard foreplanes. Thanks. <Q> From https://www.avweb.com/ownership/king-katmai-mod-safe-stol/ <S> The full King Katmai modification consists of the canard, 300-HP IO-550, choice of 82- or 86-inch, three-blade prop, speed mods/drag reduction fairings, wing extension, increased gross weight, heavy-duty landing gear, which includes Cleveland brakes, stainless steel leading edges on the gear legs, brake lines faired in behind the main gear legs and routed so they are unlikely to be snagged during rough field operations, heavy-duty Airglas nose strut and oversize tires. <S> It brings the stall speed down to 31 knots. <S> 3100 <S> lb gross weight takeoff distance of 290 feet from a hard surface runway. <A> Terry got it right! <S> It’s a King Katmai STOL Kit. <S> You can practically squeeze that thing into a parking lot! <A> For those who do not know -- the difference between a King Katmai and a Kenai is whether or not the plane includes the Wing-X STOL wing extensions, which add about 3' to the wingspan. <S> AFAIK, everything else is configurable. <S> I cannot tell from the picture whether or not the plane has the wing extensions, so the picture shows either a King Katmai with small wheels (a bit unusual) or else a Kenai . <S> Note that the video's performance figures are for a King Katmai with its usual tires (29" Bushwheels), not the smaller tires with wheel pants shown in the picture. <S> (The above assumes it had the 300HP IO550. <S> If not, there is one more choice -- a 260SE. <S> Think of that as a Kenai with a 260HP engine.) <S> As to price -- it can go up to the mid-$400 <S> K's -- depends on things like the avionics requested, how fancy a custom interior you have installed, and how fancy a paint job you have done.
|
It's a King Katmai STOL mod for a Cessna 182.
|
How can pilots minimize parasite drag? What can pilots do to minimize parasite drag? As far as I know the effect of parasite drag really depends on the manufacturer of the airplane, but can pilots do anything about it? <Q> Parasite drag is for the most part out of a pilot's hands, as it's a combination of: Form drag: drag from an airplane's general shape Interference drag: drag from airflow mixing around parts of the aircraft structure Skin friction drag <S> cause friction, removing them reduces friction. <S> You can also make sure all the little doors are flush. <S> Other than that you can't do much without making changes to the airplane itself, for instance: <S> Flush fuel caps Wheel spats <S> : these aren't decorative, they reduce the wheels' drag by providing an aerodynamic cover Seal kits: these reduce interference drag by smoothing <S> airflow Cowling replacements Fairing replacement <S> Whether these are worth the cost depends on the airplane, Cessna 152/172s are very draggy to begin with because of their rivets and wing struts, you could dump thousands into additions for very little benefit. <S> Other airplanes get measurable improvements in speed from a few seals here and there. <A> Pilots can help keep parasitic drag to a minimum by: closing all doors, hatches and windows retracting the landing gear ;-) keeping seatbelts from hanging outside of the aircraft during flight not adding GoPro cameras to the outside of the aircraft <A> Some competitors at the National Championship Air races in Reno, Nevada, depending on class, will tape-over wing and fuselage seams and gaps. <S> This is commonly seen in the Sport Class where general aviation, kit based, planes compete.
|
You can reduce skin friction drag by keeping the airplane clean, dirt and smashed bugs
|
Are there different symbols or graphics to identify different types of GA fuels? Are there different symbols to identify the different types of fuels used for general aviation aircraft? <Q> As Walker notes in his answer AvGas is typically noted by color when talking about telling it apart. <S> In terms of aircraft markings for fuel this is governed by FAA FAR 23.1557 Miscellaneous markings and placards. <S> and some more notes in this AC , (c)Fuel, oil, and coolant filler openings. <S> The following apply: (1) Fuel filler openings must be marked at or near the filler cover with- <S> (i) <S> For reciprocating engine-powered airplanes - (A) <S> The word “Avgas”; and (B) <S> The minimum fuel grade. <S> These are fairly simple regulations to comply with so there is a wide variety of markings available, but the end results tends to be a decal looking something like this: ( source ) Above ground storage tanks will also have to comply with local state regulations on petroleum storage, here are the New Hampshire regulations as an example . <S> Generally this will require an NFPA style decal but pilots dont really use those to identify anything. <S> this is common on tanks, and trucks alike, <S> ( source ) <S> ( source ) <S> Its also important that you as the pilot are present for fueling both to verify type and quantity. <S> If there is any doubt about what is in a truck or at a pump some should be pumped into a canister and verified by color before fueling an aircraft. <A> There is 87 Mogas, 100 Low Lead (100LL), and 130.100LL is pretty common for the 4 and 6 cylinder general aviation aircraft (single and 2, 4, 6 seaters with one and two engines). <S> 87 and 130 are getting less and less common. <S> I don't think I've ever seen 130, altho my plane is placarded to use 100LL or 130. <S> Larger planes than that <S> and you start seeing Jet A fuel used in single engine and twin turboprops, turbine, and turbofan equipped planes. <S> For example, in western NY, you can see prices in the Buffalo area for Jet A, 100LL, and Mogas: <S> http://www.airnav.com/fuel/local.html enter BUF or KBUF. <S> You can try other areas also, such as LAX (Los Angeles), FTW (Fort Worth), JFK, STL (St Louis). <A> Aviation Fuels are dyed different colors. <S> Jet A = Straw or Clear 82 Un-Leaded = <S> Purple <S> 100 Low Lead = <S> Blue 100/130 = <S> Green <S> When there were more grades containing lead there was Red and Orange. <S> Purple was 115/145 used in high power and military applications.
|
The typical signage for 100LL is a red back, white fount, all caps AVGAS 100LL
|
What measures prevent a military aircraft's weapons from being fired on the ground? Recently the 20mm cannon of an F-16 was accidentally fired on the ground by maintenance personnel at Florennes Air Base in Belgium, resulting the the destruction of another F-16 and damage to a third. https://theaviationist.com/2018/10/14/f-16-completely-destroyed-by-another-f-16-after-mechanic-accidentally-fires-cannon-on-the-ground-in-belgium/ What measures do military aircraft have to prevent their weapons from being fired while the plane is on ground? <Q> Normally with aircraft there is a sensor called a weight on wheels switch. <S> This tells the computer that the aircraft is on the ground. <S> The computer (or a system of relays for older air frames) will prevent any system that was designated by the owner, or required by regulations, from activating while in the ground. <S> Also as a secondary preventative measure certain mechanical systems are also pinned in place after landing to help prevent ground actuation. <S> However if it happened during maintenance it is very likely these systems were disabled to perform system maintenance on the cannon. <A> The article quoted implies that there is a sensor in the F16 to detect when the undercarriage is lowered, which functions as a a gun safety switch, but there is presumably provision for overriding this in order to perform gun testing. <S> A variety of technical and procedural measures are designed to ensure safety with aircraft gun armament, the details varying with the specific type of weapon. <S> The M61 20mm cannon will not function without electrical power, it is electrically rotated (when internally mounted) and fires electrically primed ammunition, so switching off the power should prevent accidental firing with this gun. <S> Other types of cannon with reciprocating mechanisms, such as the 30mm DEFA 550 series have to be cocked or armed before they will fire, a common procedure is to prohibit pilots from doing this until the aircraft is airborne. <A> Still present on modern armed aircraft. <S> On the F16, a switch on the joystick controls selection of missiles or gun. <S> One of it's positions is 'safe'. <S> Obviously, that switch on the Belgian F16 wasn't in the safe position. <S> During WW2, there was a real problem with aircraft landing on a carrier, and the guns being discharged accidentally when the jolt of the landing and arresting caused the pilot's hand to hit the trigger on the joystick. <S> Consequently, landing on a carrier with the gun switch not in the safe position was a serious transgression that would land a pilot in real trouble... <S> you could kill a lot of deck crew if you discharged six .50 cal machine guns across the deck. <S> Even so, accidents can happen. <S> On July 29, 1967, the USS Forrestal was seriously damaged when a Zuni air to ground missile was accidentally discharged from an F4 Phantom, striking an A4 Skyhawk waiting to take off. <S> Piloting that Skyhawk was a young navy <S> Lt, John S McCain. <S> While the missile didn't detonate, it did tear open the Skyhawk's fuel tanks, starting a major fire, which led to a 1000 pound bomb detonating. <S> 134 sailors died as a result, and hundreds were injured. <S> It is believed that a short circuit of the firing mechanism led to the missile being discharged. <S> Aircraft carriers in particular can be quite dangerous. <S> They combine high performance aircraft, high speed takeoffs and landings, plus all the fuel and munitions that the aircraft will carry, in a fairly small space. <S> The fact that aircraft carriers don't blow up more often is a testament to the quality and discipline of it's crew. <S> Since the Forrestal incident, there have been no repeats of missiles <S> being accidentally discharged on a carrier deck. <S> Whatever measures were put in place after that, appear to have been effective. <A> According to the article you linked: the use of the onboard weapons (including the gun) is usually blocked by a fail-safe switch when the aircraft has the gear down with the purpose of preventing similar accidents. <S> It seems it isn't quite so "fail" or "safe", at least in this instance. <A> A lot of fighters have some kind of a "Master Arm" switch that brings the weapons live as well as activates some other related functionality. <S> As discussed by this former F-15 pilot in the podcast 224 – Flying the F-15 Eagle its flown in the off position 99% of the time . <S> There is also some discussion about HUD functionality related to the master arm options in this thread (but its Reddit so take it with a grain of salt). <S> In this article about refueling the F-15 <S> As the fighters approach, they will be asked to “check nose cold andswitches safe.” <S> That simply means that all emitters are off, toinclude the IFF system, any ECM pods, and the radar is placed instandby mode. <S> If the approaching receivers were in a fight prior tothe rejoin, it’s <S> critical for them to have their Master Arm switch tothe OFF position and thereby safing any remaining stores aboard . <S> Depending on the airframe, they may slo simply unload the ordinance to prevent accidental discharge.
|
There are also physical safety switches, that date back to when weapons were first mounted on aircraft.
|
What runway materials reduce skidding in wet conditions? What are the possible materials that can be used on a runway, so as to reduce the plane speed and certainly stop the plane while preventing skidding when the runway is wet? <Q> This question has kept industry awake at night for ages now. <S> A good start is here . <S> TL <S> ; DR: <S> In addition to grooving, some runways (e.g. London City) apply a special surface material that is called a Porous Friction Course. <S> An alternative to grooving as a means of facilitating surface water dispersal is the laying of a Porous Friction Course (PFC) which allows water to pass vertically through the surface layer and then move horizontally clear of the runway beneath, but essentially parallel to the surface. <S> The trouble with all that is that if you test it, build it and then calculate performance taking credit for it, if it doesn’t work for real for whatever unknown unknown, you are likely to find out by having to remove an aircraft from the Thames river which is kind of frowned upon by most. <S> You want to be a bit conservative with runway friction. <A> In fact many Alaskan pilots prefer landing on gravel runways even in good conditions because they don't like the fact that tires tend to skid when they first make contact with a hard surface runway. <S> That being said gravel runways don't tend to work as well for nose gear or heavy aircraft. <S> The bouncy nature of the gravel runway is bad for the nose gear and could result in a prop strike. <S> Also Alaskan planes will usually be equipped with larger wheel base tires that are designed for bush flying and work well for gravel runways. <A> I believe the most that is done is to have grooves on the runway surface to help with water runoff. <S> Airports also use vehicles with large brushes to help keep the runways clean. <S> Plane tires do not have sipes (the cuts that go across the tire tread) to disperse water out to the sides that car tires have to help with hydroplaning.
|
In Alaska where most GA pilots fly tail wheel bush planes, many airports have gravel runways because they work better in the snow and ice.
|
Does shrouding a propeller minimize induced drag by equalizing the downwash velocity along its blades? EDIT: It's not a duplicate of Are ducted fans more efficient? That question and the answers doesn't address the reason for the higher theoretical efficiency, it is more about efficiency in practice (drag on the duct, weight, etc) and hence why they aren't used despite the higher theoretical efficiency I was told shrouded propellers are more efficient becuase tip vorticies are eliminated by the wall which would imply no induced drag but apparently that is wrong Do ducted fans eliminate induced drag? therefore I've been trying to figure out why they are still more efficient than an open propeller despite still having induced drag. It must have less induced drag. The vortex around an unshrouded propeller: At first I thought the wall somehow increases the effective wingspan, moving the vorticies to the top of the wall much like winglets do and thus reducing the induced drag that way However unlike winglets the walls don't have a pressure difference on either side (it's not an airfoil) therefore the vortex can't be there. So the vortex must be around the whole wall because above the wall the pressure is low and below it the pressure is high. But this doesn't change the effective wingspan so why does it have less induced drag? My explanation is that the existence of the wall causes the inside of the vortex to "straighten out" with the flow through the duct which makes the downwash velocity constant along the length of the blades (since the flow is irrotational). This means that this condition is satisfied: from page 7 of http://naca.central.cranfield.ac.uk/reports/1923/naca-report-121.pdf Therefore induced drag is minimized. Is this correct? <Q> Basically, yes. <S> The difference between shrouded and unshrouded propeller is that the shrouded one can produce uniform thrust across the diameter, while for the unshrouded one the thrust decreases near the tips. <S> That way a shrouded propeller accelerates more air than an unshrouded one of the same diameter . <S> This air therefore needs to be accelerated to lower speed, and therefore carries away less kinetic energy, requiring less induced power¹. <S> However, diameter can be varied, so the efficiency comparison is not that straightforward. <S> When the propeller spins relatively slowly, making it larger is better, similarly to how increasing wing span is better, aerodynamically, than adding winglets. <S> However increasing the speed of the tips increases parasite drag, especially if it becomes supersonic. <S> And since increasing size while maintaining angular speed increases the orbital speed of the tips, increasing size only helps to a certain point. <S> That's when shrouds become useful. <S> ¹ <S> In propellers and rotors it is called induced power rather than induced drag, because it counts directly against the engine power. <S> It also describes the physics better, since in both cases it is the work that is done on the air by the reaction to the generated lift/thrust. <A> I suppose the confusion may be due to different sources using different definitions of induced drag. <S> As used most commonly in my experience induced drag is the energy wasted as non-useful work in the creation of turbulence directly attributable to the generation of lift. <S> Most noticeably in the wingtip vortex. <S> In other words imparting flow in directions other than the ideal direction; in keeping with the photo-quote, an infinitely long completely uniform wing would have on lateral pressure gradient and thus no sidewards flow, nor the vortex formed from sideways flow.(It is not the vortex that causes drag, the vortex is just a symptom of the lateral pressure gradient.) <S> A close shroud, possibly even attached to propeller tips, of sufficient width will stop these vortex. <S> However it may not stop all lateral flow because of the helical flow of the propwash. <S> The helical flow can be reduced with static blades much like those used in axial flow compressors on gas-turbine engines. <S> The shroud does increase add parasitic and form drag <S> but it most definitely does reduce induced drag. <S> The first drawing in the Question with the un-shrouded prop, has the wrong perspective or axis so the vortex is in the wrong spacial plane; the second drawing has the vortex flowing through a solid wall and the prop again has the wrong axis. <S> The third drawing is not a vortex <S> it is the bulk flow encountered with a stationary fan in an enclosed room.(and <S> the prop has the wrong rotational axis) <A> What if there's no "outside" at all to your setup? <S> Imagine a theoretical scenario where the entire space outside the duct is solid to <S> $\infty$ . <S> Where are the vortices now? <S> They could only be within the tip clearance. <S> I just realized this paper from another question <S> is the perfect answer to this question. <S> And your assumption of shroud somehow making the downwash uniform is also wrong. <S> Note that although the drawing in the statement of the problem or this paper is for a two-blade shrouded fan, even a fan with a very high solidity factor, e.g. 0.8~0.9, as used in high bypass-ratio turbofans, does not equalize fan wake, and that equalization happens only due to shear friction between the infinitesimal pockets of air themselves. <S> Found this CFD of a turbofan's fan.
|
No, the vortices are trapped in the tip clearance .
|
What light signals or visual markings indicate that turns should be made to the right at class G airports? FAR 91.126 states: §91.126 Operating on or in the vicinity of an airport in Class G airspace. (a) General. Unless otherwise authorized or required, each person operating an aircraft on or in the vicinity of an airport in a Class G airspace area must comply with the requirements of this section. (b) Direction of turns. When approaching to land at an airport without an operating control tower in Class G airspace— (1) Each pilot of an airplane must make all turns of that airplane to the left unless the airport displays approved light signals or visual markings indicating that turns should be made to the right, in which case the pilot must make all turns to the right; and [...] Are there examples of "approved light signals or visual markings indicating that turns should be made to the right"? <Q> Here's the example from the FAA's Airplane Flying Handbook (chapter 7): <S> If there are no other aircraft present, the pilot should check traffic indicators on the ground and wind indicators to determine which runway and traffic pattern direction to use. <S> [Figure 7-2] <S> Many airports have L-shaped traffic pattern indicators displayed with a segmented circle adjacent to the runway. <S> The short member of the L shows the direction in which the traffic pattern turns are made when using the runway parallel to the long member. <S> The pilot should check the indicators from a distance or altitude well away from any other airplanes that may be flying in the traffic pattern. <S> Here's what it looks like at Huntsville Executive (KMDQ) , which has a right-hand pattern for runway 36: <A> 4.2.6 Right-hand traffic When displayed in a signal area, or horizontally at the end of the runway or strip in use, a right-hand arrow of conspicuous colour (Figure A1-9) indicates that turns are to be made to the right before landing and after take-off. <S> Figure A1-9 <S> Source: <S> ICAO Annex 2, Rules of the Air <A> The "L"-shaped marks near the tetrahedron or wind tee — adjoining the "segmented circle" — show the traffic pattern direction. <S> Intended to be viewed from above, not from ground level. <S> http://www.flightlearnings.com/2011/12/16/wind-direction-indicators/ <S> The figure above indicates "left traffic" (left turns) when taking off or landing to the north, right traffic when taking off or landing to the south, left traffic when taking off or landing to the east, and right traffic when taking off or landing to the west. <S> Typically we'd see this situation if there were some noise-sensitive area, obstacle, etc southwest of the airport. <S> Or as depicted in the FAA's "Airplane Flying Handbook" as noted in another answer: <S> This indication is a little more confusing than the one in the first diagram. <S> To interpret this indication we can imagine that there is a miniature runway running through the tetrahedron or wind sock. <S> The key point is that the "L" shape we need to pay attention to is the one at the approach end of that imaginary miniature runway, not the departure end, in relation to our planned take-off or landing. <S> For aircraft taking off or landing to the southwest, "left traffic" is indicated by the "L" shape on the upper right of the circle.
|
For aircraft taking off or landing to the northeast, "left traffic" is indicated by the "L" shape on the lower right of the circle.
|
Must quadcopters have the same propeller sizes? I was flying quads today and it just suddenly popped up into my mind — do the propellers all have to be the same size in quadcopters? Mine are, but What if two propellers were larger and the other two smaller? The drone would still be symmetrical, but would it have any effect on the performance of the drone? Could you explain the physics behind your answer? <Q> The main point of a quadcopter is that it can be controlled by engine power using much simpler fixed-pitch rotors¹. Assuming this construction, you need to be able to separately adjust power of forward and rear set of propellers for pitch control, left and right set of propellers for roll control and <S> clockwise and counterclockwise -rotating set of propeller for yaw control. <S> If you had two bigger and two smaller rotors, then one of the combinations would have the two bigger ones in one of the sets and the two smaller ones in the other. <S> That would make it really, really hard to balance all the parameters to maintain appropriate controlability. <S> I think it might not be completely impossible, but it certainly makes no sense. <S> ¹ <S> Of course once you add cyclic and collective control, you can fly with one rotor only (well, two, or one with anti-torque rotor or jet) as most full-scale helicopters do, but then you've lost the simplicity of fixed propellers. <A> No, they don't have to be the same size. <S> You could even fly with just two rotors - the Chinook does - the other pair would be needed for control only. <A> No, you can fly a quadcopter using different rotor sizes. <S> The smaller rotors would have to have a longer moment arm relative to the Centre of Gravity, and as @JanHudec points out the total rotational impulse in yaw direction must zero out as well. <S> So two pairs of counter-rotating rotors, correctly placed relative to CoG, would work.
|
But having them all comparable makes it easier to design the quadcopter and keeps it generally more maneuverable.
|
What is the difference between a Mechanic and a Repairman? In reviewing some of the data published by the FAA, I noticed that they make a distinction between a mechanic certificate and a repairman certificate. What is the difference? <Q> The full details are in 14 CFR 65 Subpart D (mechanics) and Subpart E (repairmen). <S> Here are the basic privileges for each one (emphasis mine): <S> A certificated mechanic may perform or supervise the maintenance, preventive maintenance or alteration of an aircraft or appliance, or a part thereof, for which he is rated (but excluding major repairs to, and major alterations of, propellers, and any repair to, or alteration of, instruments), and may perform additional duties in accordance with §§65.85, 65.87, and 65.95. <S> And: A certificated repairman may perform or supervise the maintenance, preventive maintenance, or alteration of aircraft or aircraft components appropriate to the job for which the repairman was employed and certificated, but only in connection with duties for the certificate holder by whom the repairman was employed and recommended . <S> "Repairman" also applies to experimental and light sport aircraft owners. <S> If you build your own aircraft you have repairman privileges to maintain it, but you can't use those privileges to work on other aircraft, per 65.104(b) <S> (emphasis mine): <S> The holder of a repairman certificate (experimental aircraft builder) may perform condition inspections on the aircraft constructed by the holder in accordance with the operating limitations of that aircraft. <A> This page from the FAA discusses both https://www.faa.gov/mechanics/become/basic/ <S> I'm a US Citizen. <S> What requirements must I meet to get a mechanic's certificate? <S> You must be at least 18 years old; able to read, write, speak, and understand English. <S> You must get 18 months of practical experience with either power plants or airframes, or 30 months of practical experience working on both at the same time. <S> As an alternative to this experience requirement, you can graduate from an FAA-Approved Aviation Maintenance Technician School. <S> You must pass three types of tests; a written examination an oral test a practical test <S> How do I get a repairman's certificate? <S> To get a repairman's certificate, you must be recommended by a repair station, commercial operator, or air carrier. <S> You must be at least 18 years old; be able to read, write, speak, and understand English be qualified to perform maintenance on aircraft or components be employed or a specific job requiring special qualifications by an FAA-certified Repair Station, commercial operator, or air carrier. <S> be recommended for the repairman certificate by your employer have either 18 months practical experience in the specific job or complete a formal training course acceptable to FAA. <S> So they look similar, with one having testing to go with it. <A> Also with an A&P license, once you have it, you do not have to get retested nor does it expire. <S> The only way to loose the license is if you personally give up it. <S> However it can be revoked. <S> A repairman looses their certificate once they leave the repair station.
|
The basic difference is that a mechanic can perform maintenance on any aircraft; a repairman can perform maintenance only on aircraft for their employer, or that they own.
|
Why did this 737 not take off on first attempt? This video shows a 737 'near miss' takeoff. I'm curious as to why the aircraft did not take off as expected, i.e. is there anything obvious from the video? I'm assuming the speed and payload would have been within the expected limits, so wondering if someone can explain what happened. <Q> With the help of the clearly visible livery (Royal Air Maroc), registration (CN-RNV) and approximate time (before August 2016, probably not by too much), I managed to find the specific Incident: Royal Maroc B737 at Frankfurt on Jul 23rd 2016, three takeoffs for the price of one on The Aviation Herald . <S> It even links to the very same video that you do. <S> Unfortunately: <S> On Aug 30th 2016 the BFU responded to an inquiry by The Aviation Herald of Aug 25th 2016 stating, the BFU had neither received any notification by the crew, airline or airport involved nor by the person taking the video (see below) and became aware of the occurrence only through the release of the video into the public more than a months after the occurrence. <S> The BFU argued that as result it will not be possible to establish sufficient facts and evidence needed for a detailed investigation, <S> hence the BFU decided to refrain from initiating an investigation. <S> So we won't have anything better than guesses anyway. <S> The article does speculate that the wake turbulence of the landing aircraft crossing above the runway just before might have affected it, but it was too close to the starting point and is unlikely to have this effect, so what remains is that the pilot flying started to rotate too early. <S> There may be basically two reasons for that: <S> The take-off procedure with the speed call-outs made by the pilot not flying is the same for every take-off, so the second reason seems more likely. <S> The rotation speed depends on weight, density altitude and flap setting. <S> Inserting wrong weight is probably most common reason for this type of incident, but calculating for higher flap setting than they used is a believable option here too as they used rather low setting for the actual take-off. <S> It should be noted that the pilot realised their mistake and handled it correctly by lowering the nose back to let the aircraft gain enough speed first. <A> It looks to me like a too-early rotation (lifting the nose off of the runway). <S> This may have happened as a result of a miscalculation of the rotation speed (known as Vr speed). <S> A miscalculation of the Vr speed, for example, can happen if you derive this speed using a lower than actual aircraft takeoff weight in your performance calculation. <S> This would lead to a calculated Vr speed that was less than was required. <S> If this was the case, as the pilot rotated the aircraft into the liftoff attitude there would not enough speed to allow the aircraft to climb out. <S> Instead the aircraft would stay on the ground (or in ground effect) until it accelerated to the proper lift off speed. <S> The crew could also have miscalculated the power setting necessary for takeoff by using an incorrect temperature, or physically failing to advance the thrust levers to the correct position. <S> Since the B737 in the video was a later model it likely had a Flight Management System (FMS) that would have calculated the takeoff thrust setting based on keyboard entries made by the crew. <S> Also, it's common for the takeoff thrust to be set, based on the FMS calculated values, using the auto-throttle function (sometimes takeoff thrust is manually set by the crew using the calculation provided by the FMS[or similar]). <S> In other words, after initially moving the thrust levers forward a bit, the pilot would just push a button on the mode control panel and the throttles would automatically move to the proper takeoff setting. <S> Again, this would depend on the proper information being loaded into the FMS/FMC so that proper calculations for Vr speed, thrust setting, etc. would be utilized. <S> There are many variables depending on what procedures the crew used and the pilot technique, but the video shows the airplane rotating and not lifting off, and just my opinion, but this was likely because the rotation was started at a lower speed than was appropriate. <S> Here is a link to a incident involving a B737 that appears to have some similar circumstances. <S> B737 tail strike <A> It looks like a case of the flight crew using an incorrect flap setting for the takeoff and calculated Vr. <S> Looking at the video, there was very little flap deployed though the LE flaps and slats were extended. <S> The airplane struggles to become airborne then settles back down on the runway after attempting to exit ground effect. <S> The crew apparently realized the airplane wouldn’t fly, so the allowed to to remain on the runway, gain additional airspeed, then rotate and fly off when there was no alternative left. <S> Major safety violation there and could have caused an accident. <S> Fortunately there was ample runway to do so on.
|
The pilot flying started rotating before appropriate speed was reached, or they calculated lower rotation speed (Vr) than they actually needed.
|
Is fuel balancing done automatically? Is the balacing of the fuel in the wings of an aircraft like A320 done automatically or does it have to be done manually by the pilot. If it is done manually does the pilot eyeball the balancing ? <Q> The A320 has an auto mode that will do the following: <S> Center tank will empty first. <S> The inner wing tanks will empty until they reach 750 kg in each. <S> The outer tank transfer valves will open and remain open allowing fuel to flow to the inner tanks. <S> The center tank pump will stop 5 minutes after low level is reached and remain stopped until the inner wing tank reaches the underfill sensor (approx. <S> 500 kg) <S> at which point it will restart. <S> The wing tanks can be turned off manually. <S> The cross feed valve is also operated manually. <S> source: <S> A320 FCOM <A> During refueling, it is generally automatic. <S> The fuel handler will just set the amount of fuel to pump in and the pipes will distribute it to the tanks as appropriate. <S> In flight, there is a schedule which tanks are used first, which is automatic (see TomMcW's answer), but this is not balancing— <S> the left wing tanks only feed engines on the left wing and <S> the right wing tanks only feed engines on the right wing. <S> If an imbalance appears, meaning the amount of fuel in the left and right wing tanks is significantly different, a warning is generated. <S> There is a cross-feed valve that the pilots can open to let all engines use the fuller tank, but it is not automatic, because unless one engine was shut down in flight (which in twins calls for landing as soon as possible anyway), it usually means the fuel is leaking somewhere and leaving the cross-feed valve open would lead to repeating of the incident of Air Transat flight 236 . <A> On multi-engine jets there is not so much of a need to balance fuel as there is on single-piston aircraft. <S> All the engines burn fuel at the same rate, so there is no cause fo a Fuel Imbalance. <S> In fact, a Fuel Imbalance is usually seen as the first symptom of a Fuel leak.
|
The aircraft tends to fly in balance all the time, so there is no differential feed of fuel. The center tank pumps can be switched to manual mode.
|
Why do stealth aircraft generally lose in maneuverability? Whilst stealthy built aircraft have (or claim to have) many anti-detection systems, they seem to have to compromise on less maneuverability features, and even have to keep their missiles inside, not on the outside. Why is it so these days? Based on the above what could be the tendency for the future military aircraft (the jet fighters in particular)? <Q> Radar stealth is achieved by carefully designing the aircraft to reflect radar waves in specific directions. <S> It helps to keep the aircraft shape as simple as possible. <S> External weapons make this more complex: each missile adds a large number of surfaces that can reflect radar. <S> The missile can also interact with the airplane fuselage to reflect radar waves several times. <S> And once the missile has been launched it leaves an empty pylon behind with yet more surfaces capable of reflection. <S> Some aircraft (e.g. the F-117) also try to achieve IR stealth by hiding the exhaust, mixing the exhaust gases with air etc. <S> This is difficult to combine with vectored thrust. <S> Still, an aircraft like the F-22 has pretty good maneuverability, thanks to good aerodynamics and huge amounts of engine power. <S> The Su-37 uses vectored thrust and canards (again, extra reflection surfaces) to achieve high maneuverability. <S> So, there's a tradeoff going on. <S> Do you want to blow your enemy out of the sky before he's seen you (which requires stealth)? <S> Or do you focus on close combat (where maneuverability is most important)? <A> Short answer: <S> There is no reason that a low observable aircraft should suffer in maneuverability, if properly designed, and <S> the F-22 and YF-23 are proof of concept. <S> LO does favor specific shapes which both minimize the amount of radar energy reflected back to a transceiver as well as provide good aerodynamic qualities. <S> Weapons carriage must be done internally in order to prevent compromising this shape and increasing the aircraft's RCS. <S> LO aircraft also possess an additional advantage over existing airframes with external weapons carriage in that internal stores carriage creates far less parasite drag than external carriage does, providing more excess thrust for maneuvering and accelerating at any given airspeed. <S> Again, if an aircraft is properly designed for a particular role and maintains strict design discipline and focus on the goals for the program, there is no reason a stealth airplane cannot possess good fighter qualities with low observable features included. <S> F-117 and B-2 are not terribly good comparisons on this issue as both were designed as bombers, though a B-2 does demonstrate stellar aerodynamics blended with LO features, having an Mmo of Mach 0.95, which is unheard of in the civilian world. <S> F-35 was a bloated compromise between three variants with cripples it in terms of traditional fighter metrics and is proof not that LO aircraft don't make good fighters but that multirole aircraft are not going to be stellar in any specific mission role. <A> The answer may lie in change of tactics. <S> Stealth aircraft are all about one of the oldest rules of gaining advantage: don't be seen first. <S> This is combined with the modern: <S> a 9g plane can not evade a 25 g missile. <S> They want the other plane trying to evade your missile. <S> The compromises in aircraft performance are understandably lamentable, but being "not seen first" remains the key to survival. <S> However, technology and tactics are always changing, and it may be wise to remember that many our Air Force's greatest successes came from teamwork of different types of aircraft working together, rather than putting everything into one plane. <S> Once a slower stealth is located, it then becomes a plane v plane situation.
|
It's much easier to maintain stealth if the missiles are stored inside the aircraft.
|
Why does the Ikarus C42 pitch down when stalled? Apparently, the C42 nose pitches down shortly after stall, like in this video . I know part of the video might be pilot input to recover from the stall, but I've read on various flying forums that this will happen naturally without input anyway. Why is this? <Q> Most aeroplanes are designed with the Centre of Gravity being ahead of Centre of Lift , so when the aeroplane's wing cannot produce sufficient lift anymore -- due to a high Angle of Attack , the nose will drop, therefore, it will decrease the AoA and as the gravity pulls the aeroplane towards earth, the speed will increase which in combination with the lower AoA will hopefully produce enough lift to keep the aeroplane flying again. <S> In some cases when the CG is not forward of CoL -- e.g. mostly in transport category aeroplanes, the horizontal stabiliser is set/installed on the neutral nose-down Angle of Incidence , which makes the aeroplane fly in a more stable manner and will help the stall recovery by pushing to nose-down. <S> Generally flying in any type of aeroplane with CG aft of CoL is considered a no-no, for the reasons explained above: 1) Flight instability and 2) possibly unrecoverable from a stall -- which in fact is likely to happen because of the displaced CG will tend to increase the AoA which will decrease the speed, until stall happens. <A> Most (if not all) longitudinally stable aircraft will pitch nose down after a stall. <S> This is because the forward flying surface (regardless of conventional or canard layout) -- or forward portion of the wing, in the case of tailless designs -- must fly at a higher loading and coefficient of lift than the rear in order to maintain stability, so when lift is lost, it will be lost first at the higher-loaded and higher-coefficient surface, which will then start to drop before the lower-loaded or lower-coefficient surface. <A> The Ikarus C42 is very similar to the Cessna 152 in design and power (but around 500 lbs lighter!). <S> This is a classic high wing design that is one of the safest aircraft one can fly. <S> Rock stable on all three axes and very forgiving. <S> These are a lot of fun to slip, as you will not see a lot of roll coupling with yaw (rudder) input. <S> As far as the video, this is a fairly normal stall recovery. <S> As with anything, practice makes perfect. <S> Properly weighted, this type of plane will not need a hugely aggressive push forward for stall recovery. <S> Just hold the nose straight with the rudder. <S> There are really 2 lines of defense in stall recovery with an aircraft properly balanced. <S> The first is a natural nose down with loss of speed caused by positioning CG ahead of center of lift from wing and trimming with downforce on tail (elevator up). <S> Because the trim torque is aerodynamic, it has less force when the plane slows down and the nose drops. <S> Planes set up this way will gently drop out of stall simply by relaxing the elevator. <S> The second line of defense comes from the surface area of the horizontal stabilizer (as seen from underneath the plane). <S> If the plane starts sinking in a nose up or level position, vertical motion will help flip the nose down sharply. <S> This is assisted with down elevator (stick forward). <S> The key is to hold the nose straight with the rudder. <S> Do not use the ailerons. <S> With the Ikarus, simply letting go of the stick should be enough to recover, but it would be highly recommended to take a lesson and learn the limitations and behavior of that plane. <A> As a stall is approached, the center of lift moves slowly forward. <S> The pilot will compensate for this with either back-pressure on the stick/yoke or by trimming the aircraft. <S> When the stall occurs the center of lift suddenly and rapidly moves towards the rear of the aircraft. <S> Since the aircraft was balanced before, moving the force of lift backwards will cause the rear of the aircraft to rotate upwards, and the nose to drop. <S> In a traditional aircraft configuration, the wing will stall before the horizontal stabilizer. <S> Canard configurations achieve the same effect by having the horizontal stabilizer produce positive lift and stall before the wing.
|
The horizontal stabilizer normally produces lift in the downwards direction just incase it does stall, that way the nose would automatically drop.
|
Navigate to the final approach course after radio failure under IFR What would ATC expect the pilot to do if, at the position marked below by the red X, the aircraft lost radio communication and was on a radar vector heading 250 degrees at/assigned 3000 msl and the pilot was told to expect the ILS approach to Runway 7 Right? Assume the IFR aircraft did not have DME, RNAV or GPS equipment and the weather was IMC. <Q> First, squawk 7600 to let ATC know you have lost two way radio communications and to clear traffic out of your way. <S> Then, from the AIM, Section 4. <S> Two-way Radio Communication Failure Section 6-4-1.c. <S> includes: 1. <S> General. <S> Unless otherwise authorized by ATC, each pilot who has two-way radio communications failure when operating under IFR must comply with the rules of this section. <S> and 2. <S> VFR conditions. <S> If the failure occurs in VFR conditions, or if VFR conditions are encountered after the failure, each pilot must continue the flight under VFR and land as soon as practicable. <S> This is the preferable solution, but the question said to assume the conditions are IFR. <S> Which leads to (displaying only applicable sections): 3. <S> IFR conditions. <S> If the failure occurs in IFR conditions, or if subparagraph 2 above cannot be complied with, each pilot must continue the flight according to the following: (a) Route. <S> ... <S> (2) <S> If being radar vectored, by the direct route from the point of radio failure to the fix, route, or airway specified in the vector clearance; (c) Leave clearance limit. <S> (1) <S> When the clearance limit is a fix from which an approach begins, commence descent or descent and approach as close as possible to the expect further clearance time if one has been received, or if one has not been received, as close as possible to the Estimated Time of Arrival (ETA) as calculated from the filed or amended (with ATC) Estimated Time En Route (ETE). <S> It would be a challenge to fly it without DME, but not impossible from the starting point. <S> Radar or DME (or GPS) is needed to get to the IAF. <S> If the pilot had a good estimate of his location when comm was lost, it would be to fly outbound for about 1 minute and <S> then a right 180 deg turn to intercept the localizer. <S> Once the glideslope is intercepted, being on GS plus altitude allows to to estimate passage of TIMSE and FUMBL. <S> The rest of the approach can be timed. <A> Squawk 7600 and fly the ILS RW 7 approach he was told to expect in a further clearance. <A> I'm not sure you could / would want to land here if you were in IMC. <S> The MSA is 4200 ft and you are at 3000 ft. <S> If you don't have any VFR charts on board, you don't know where those obstacles are. <S> I would climb to 4200 so you are not going to hit anything and find somewhere else to land that's VMC.
|
So the expectation of ATC would be that the crew would fly outbound, make a right turn and intercept the localizer and fly the approach.
|
Does Wing Area vary with angle ot attack? For a very basic airplane, say like Cessna 150 is built with Wing Area (S)=15 meter squared (say it 15m*1m). In another part said that the Lift (L)=0.5*rho*(V)^2*Cl*S. Mean, Lift is affected by the wing area. Yes, it is clear. My question, should I consider the wing area as fix area during the take off, cruise, and during landing? If angle of attack of the wing is 15 degree during take off, what is the wing area? From the Lift formula above that is written here , S (wing area) is planform (projected). Where it to be projected? If like above, if during the take off the Angle Of Attack is 15 degree, what is the wing area? Very appreciate if explanation provided with reference. <Q> Wing area does not change with angle of attack. <S> The only way wing area can change in flight is if there are devices on the wing that can extend and retract, making the wing longer, shorter or wider. <A> Simple answer: <S> the surface area is the area of the wing when you look at it straight down. <S> The question then of course is, why? <S> The answer is quite trivial: because it's easier that way. <S> In a way, your idea that the lift is dependent on the wing area projected in the direction of the incoming wind seems quite reasonable (surely, this is what the incoming air "sees"). <S> This projected area equals $$S_p= <S> S\sin(\alpha)$$ <S> A good reason not to use $S_p$ is that we like the equation to contain real geometric parameters, so that we can easily scale our equation up and down. <S> So, why not define the lift equation as $$L=\frac{1}{2}\rho <S> c_l S\sin(\alpha) <S> v^2$$ <S> This looks nice right? <S> Everything is in there, even the angle of attack! <S> Sadly, curve of the lift versus the angle of attack does not follow a nice $\sin(\alpha)$ curve. <S> This equation is thus sadly not only misleading, but you would have to divide all existing lift curves by $\sin(\alpha)$ , which would make them erratic (especially around $\alpha=0$ ) and much less insightful. <S> So, lumping the angle of attack into the lift coefficient is in the end the best way to go. <A> Here is the 150M planform, you can see the flaps from the fuselage out, a foot or so wider than the elevator. <S> The 150 uses Fowler flaps, described in Wikipedia: <S> Fowler flap A split flap that slides backwards, before hinging downward, thereby increasing first chord, then camber.[13] <S> The flap may form part of the upper surface of the wing, like a plain flap, or it may not, like a split flap, but it must slide rearward before lowering. <S> As a defining feature - distinguishing it from the Gouge Flap - it always provides a slot effect. <S> [14] Invented by Harlan D. Fowler in 1924, and tested by Fred Weick at NACA in 1932. <S> They were first used on the Martin 146 prototype in 1935, and in production on the 1937 Lockheed Super Electra,[15] and are still in widespread use on modern aircraft, often with multiple slots. <S> https://en.wikipedia.org/wiki/Flap_(aeronautics)#/media/File:Airfoil_lift_improvement_devices_(flaps).png <S> I can't find numbers on how much the chord/camber is changed on a 150. <S> Here's a great discussion of the Fowler flap from 1942 https://www.flightglobal.com/pdfarchive/view/1942/1942%20-%200783.html <A> An analysis of the variables shows Coefficent of Lift, C L , varies with change in angle of attack. <S> ρ is air density. <S> So, check your AoA/C L graph. <S> L = <S> 0.5 <S> * ρ * V 2 <S> * C L <S> * S Post Script: this equation may be of value if one wanted to swap airfoils in a design. <S> For AOA comparison of lift, one might make a giant constant out of the entire equation (L) and the run various AOA off the AOA/Cl graph. <S> Although laborious by hand, this would be tailor made for a spreadsheet and would make a nice presentation with graphics. <S> Also, if anyone knew if coefficient of lift for an airfoil was done at a specific AOA by convention, this would be extremely good information. <S> I would imagine it may be done at AoA for best lift/drag ratio.
|
Area should be constant.
|
In a part 91 formation flight within a mode C veil, are all the aircraft required to have their transponders on? Two aircraft are planning on conducting a standard formation flight (aircraft remaining within 1 mile of each other) as follows in the U.S.: Maintaining VFR below 10,000 MSL; Remaining outside/clear of Class B/C/D airspace; The route will be totally within the 30 mile mode-C veil of an airport listed in appendix D to Part 91, for example - Houston or Atlanta; ( FAR 91.215 ) FAR 91.111 will be complied with: see below: §91.111 Operating near other aircraft . (a) No person may operate an aircraft so close to another aircraft as to create a collision hazard. (b) No person may operate an aircraft in formation flight except by arrangement with the pilot in command of each aircraft in the formation. (c) No person may operate an aircraft, carrying passengers for hire, in formation flight. No flight plan will be filed; No communication with ATC will be established. (takeoff/landing will be at non-towered, uncontrolled airports in Class G airspace); Both aircraft will be equipped with a properly certified operable (4096 3/A, w/Mode C) transponder in accordance with FAR 91.215; Question: Is it legal for only the agreed upon formation leader to have his/her transponder on with the other aircraft'stansponder set to "standby?" Or do both airplanes have to have their transponders on? <Q> Yes, it is legal. <S> The FAA's guidance document for formation flight (short document, easy read) mentions standard formations, and it states: c. <S> After join-up, aircraft beacon code assignment will be determined by formation type. <S> For a standard formation only the aircraft acting as the lead will squawk an ATC assigned beacon code. <S> Ensure all other aircraft squawk standby. <S> There is also FAA Order JO 7610.4 regarding special operations, on which the guidance is based, but that document is only available internally from within the FAA network. <S> If you intend to fly within Class C airspace or within 30 nm of any airport in 91.215 Appendix D, you have to contact ATC (as you would to ask for flight following) to deviate from the requirement that all pilots squawk VFR. <S> Arbitrarily deviating from the transponder rule without getting permission from ATC would likely be judged in violation of rule. <A> The way 91.215 is written, you must operate your mode C transponder in rule <S> airspace unless ATC tells you not to. <S> The reason ATC tells you not to squawk in the case of a formation flight is to avoid triggering a constant stream of Collision Alerts between members of the formation, which is useless, annoying and may distract them from an actual problem elsewhere. <S> However, the CA is suppressed if all the aircraft involved are squawking 1200 (VFR) <S> because there's no point warning the controller about a possible collision between multiple aircraft they're not talking to. <A> (VFR/IFR/formation/flight plan or not/flight following or not). <S> On January 1, 2020 the new requirement for all aircraft to enter any Mode C veil is an operable transponder with AD-SB Out capability. <S> If you are leading a formation flight or part of a formation flight, each Aircraft PIC is required to comply with the current FAR. <S> Any deviation requires approval from ATC. <S> Supposedly, "on frequency" requests and approval in regards to the AD-SB out requirement is not going to be allowed. <S> All aircraft in formation entering the "rule" airspace should be equipped with AD-SB Out in the event that the formation breaks up. <S> If an aircraft loses the formation or breaks away and is not equipped while inside "rule" airspace, there is a good possibility of a violation occurring, unless an emergency is declared. <S> Using the 24 hour written pre-approval process, the formation flight could occur as described with proper planning and ATC approval. <S> Without any coordination or approval from ATC, I would be careful not to enter any "rule" airspace, including penetrating any Mode C veil around Class B airports unless your aircraft is properly equipped.
|
IMHO, I offer the following, the current FAR requires an operable transponder to enter any Mode C veil, regardless of your flight circumstances...
|
Is there any effect that contributes to roll stability even in the absence of sideslip? Is there any physical dynamic-- involving high wing placement, "pendulum" effect of CG far below wing, or anything else-- that contributes to roll stability in a way that is NOT dependent upon the aerodynamic forces generated by sideslip? For the purposes of this question, "roll stability" is defined as a tendency to roll towards wings-level, or a reduced tendency to roll toward a steeper bank angle. Perhaps a better term might be "spiral stability". <Q> Buoyancy is one such effect! <S> Or more specifically, a buoyant force acting above the aircraft CG. <S> Think hot-air balloon, <S> dirigible, blimp. <S> I think I've also thought of one such effect involving conventional winged airplanes but will mull it over some more before answering. <A> Roll stability, as in an opposing aerodynamic moment caused by a roll attitude of an aeroplane: no there is not. <S> These stabilising roll torques are a result of indirect state variables: <S> Sideslip angle, excluded for this question. <S> Damping forces due to roll velocity. <A> Yes but the effect is very weak or negligible on a high wing aircraft. <S> Like a lot of things, the effect is easiest to visualize by taking it to the extreme. <S> Like with paramotors, which get just about all their roll stability, as well as their ability to bank into turns by skidding, from pendulum effect. <A> Wing flex contributes to better spiral stability as far as my simulations shows. <S> But I guess this comes down to dihedral and sideslip again as well as the "pendulum effect". <S> Just imagine how much harder it becomes to roll an aircraft that flexes the wings like that <A> Imagine "outriggers" that are inverted airfoils, mounted far outboard of each wingtip. <S> In general, if an aircraft is banked, it will turn, which will mean that the outboard wingtip is moving faster than the inboard wingtip. <S> In this case the "outrigger" on the outside of the turn will generate more downward lift than the "outrigger" on the inside of the turn, creating a roll torque toward wings-level. <S> This dynamic seems to play a key roll in explaining why hang gliders and "trikes" tend to experience increased roll stability (or decreased roll instability) in flight at low angles-of-attack (high airspeed), despite the fact that at low angles-of-attack, the dihedral-like "downwind" roll torque contributed by the swept or delta shape of the wing in the presence of sideslip, is much less than at higher angles-of-attack. <S> By "increased roll stability (or decreased roll instability) <S> " I'm referring to an increased tendency to roll toward wings-level or a decreased tendency to roll toward a steeper bank angle. <S> This is static stability, not dynamic stability. <S> Note that these aircraft have lots of "washout" and the wingtips are generating downward lift during flight at low angle-of-attack (high airspeed). <S> In some cases the "outrigger" effect described above appears to contribute to a dynamic yaw-roll oscillation in these aircraft. <S> This oscillation may be fundamentally different from the well-known "Dutch Roll" oscillation that swept-wing aircraft are sometimes subject to, typically during flight at high angles-of-attack. <S> For example the timing of the point of maximum sideslip, in relation to the point of maximum bank angle, may be very different in the hang glider/ trike case and the classic "Dutch Roll" case. <S> For related content on stability and control in hang gliders and "trikes", but not dealing with the washout / "outrigger" effect, see this answer to the related question Does "pendulum effect" apply to hang gliders or any aircraft?
|
Differential air velocities over the inner and outer wing in a turn. In some cases the lower "flying wires" can observed to be slack.
|
What prevents Low Cost Carriers (LCCs) from cutting cost that compromise safety? I was reading an article about LCCs and here is an excerpt that got me thinking. While budget airlines cut other corners to keep fares low, they do not — actually cannot — compromise the safety of their passengers in the process. What prevents low-cost carriers from cutting corners that might compromise the safety of their passengers? <Q> There are two main factors. <S> The law One, as other answers have mentioned, is the law . <S> There are strict regulations that cover everything in aviation, from the way people speak to the training they must have and the specifications and audit trails of almost every piece of equipment they use. <S> Now it's true that people, especially unscrupulous ones who are keen to save money and might be willing to take a few risks in order to do that, don't always obey they law or follow regulations to the letter. <S> And after all, there are laws against murder with much more significant penalties than for (for example) flying with a bit less fuel than the regulations say you should, and yet people persist in murdering. <S> The culture <S> However, the other factor is the culture . <S> A low-cost airline exists in the culture of aviation, not independently, and the culture puts safety first. <S> Each person working for the airline will have trained and may have worked outside the airline, and will already have acquired attitudes and ways of thinking that prioritise safety and adherence to regulation. <S> Each person working for the airline will be working with and encountering aviation industry individuals from outside the airline, on a daily basis - if they didn't share similar attitudes and ways of thinking, they'd stand out a mile, and so would a corporate culture that similarly failed to embrace the industry's culture of safety. <A> Why can't low-cost carriers compromise for the safety of their passengers? <S> Because there are laws and regulations which keep passengers safe, and low-cost carriers are not exempt from those regulations. <A> <A> An airline will need to have an 'Air Operator Certificate' (AOC) or something similar issued by the state. <S> In order to have such a certificate it has to show that its operations are in compliance with the national laws of the country. <S> There is also an 'Operations Specification' which details the type of operations the airline can carry out. <S> The respective manuals will need to be checked by the authorities and the actual operation will be audited. <S> For operations into other countries, the other country may require you to undergo a 'foreign operator air license' which will require a check of the manuals and possibly an audit. <S> The list of checks is endless and usually in the long run it is easier to follow than try to cut costs related to safety and security. <S> The airline can have its AOC suspended for unsafe operations until they fix the operations. <S> Other countries can ban certain countries from operating in their airspace if there are security concerns. <S> The EU, for instance, maintains a blacklist of airlines banned from entering their airspace. <A> Along with being illegal and potentially looking bad, generally, people's lives are in the balance but historically this has not always stopped the more unscrupulous airlines in the past. <S> Arguably Alaska Airlines cut corners that ultimately lead to the fatal crash and deaths of 58 people on flight 261 . <S> From the NTSB report: Alaska Airlines' maintenance and inspection of its horizontal stabilizer activation system was poorly conceived and woefully executed. <S> The failure was compounded by poor oversight... <S> Had any of the managers, mechanics, inspectors, supervisors or FAA overseers <S> whose job it was to protect this mechanism done their job <S> conscientiously, this accident cannot happen Cutting corners on training, improper cargo loading and generally poor handling of hazardous materials also lead to the fatal crash of ValuJet Flight 592 killing 110 people. <S> There is some interesting info on it in this paper from the FAA <S> There has been push from various low cost carriers to introduce what is effectively standing room only aircraft or sections of aircraft for an even lower fare. <S> However this does not pass the seating requirements that the FAA/EASA generally have so no one has yet to actually bring it to market. <S> It will be interesting to see if they can ever push the regulation through. <A> What prevents low-cost carriers from cutting corners that might compromise the safety of their passengers? <S> Airlines are required by the International Civil Aviation Organization (ICAO) to implement formal aviation safety management systems (SMS) . <S> This mandate came from November 2006. <S> It is up to each member state's civil aviation authority (FAA, Transport Canada, CASA, EASA, etc.) to provide oversight of all airlines' SMS. <S> Oversight is provided by audits that follow an industry-accepted SMS audit checklist . <S> When there are audit findings coming from their civil aviation authority (CAA), the airline has a limited number of days to return to compliance else their operating certificate may be revoked. <S> Fines may also be employed to urge the airline toward compliance and to reduce the chances that the operator will return to non-compliant behavior. <A> While not technically an answer: I just want to point out that (most) LCCs do not have the financial means and public image credit to survive even a single minor incident or crash. <S> A simple runway overrun or engine fire might be enough to literally bankrupt the company within days, and (most) LCC managers are painfully aware of that. <S> The incentive is therefore quite high to avoid any incidents and keep safety levels way above the minimum required by law.
|
Beside all the regulations that require certain maintenance action to be done on aircraft in order for the aircraft to remain air worthy, the simple answer is if LCC compromise safety in order to cut cost no one will want to fly with them and they will lose business.
|
Are there any 100% renewable energy aircraft in development? There seem to be several options for aircraft R&D regarding cleaner fuels for the time when fossil fuels are no longer economically viable. Some of these include: Algae. A drop-in fuel. These fuels are being used and developed in co-operation with the USAF. They have had several successful test flights. Batteries. Doesn't seem viable at this stage. Nuclear reactor on board. Doesn't sound safe. Hydrogen. This wiki page says they could be built by 2020. That's only a year away now... I've found a few examples of test prototypes & flights using fuel mixtures that improve emissions and gasoline consumption, but are there any commercial aircraft in development, with an expected launch date that utilize 100% renewable energy? <Q> This includes both fixed-wing conventional types with single or multiple electric powered propellers, and "drone" style craft using what amounts to thrust hover with electric powered propellers. <S> Flight time is limited, but better with the fixed wing types -- enough so that I'd call an electric motor glider a very feasible design. <S> Hydrogen has limited usefulness, for the same reasons it doesn't work well for cars: it's technologically difficult to store enough for reasonable range. <S> Either extreme pressure, extreme cold, or a chemical storage method that limits the rate at which you can draw fuel are reqired. <S> A submarine type nuclear reactor was operated aboard a modified B36 in the 1950s -- the project, intended to lead to a strategic bomber with a flight time of weeks or months, was dropped due to lack of need as well as cost and safety concerns (most of the safety concerns, such as "roll-up" explosions, were later resolved or found to be overblown). <S> This kind of power isn't "fully renewable" anyway <S> -- fission fuel must be mined, it isn't grown. <A> Yes, there are projects <S> to power the jet engines by oil from plants: <S> canola (rapeseed), coconuts and soybeans. <S> This fuel is also cleaner (less sulfur) and even freezing point (-47 degrees C) is acceptable. <S> While not an immediate certified replacement, these oils can work as jet fuel without radically re-designing the engine. <S> Some refining technology and suitable engines are under development. <S> Planes with piston diesel engines could also probably run on this fuel. <A> Batteries are indeed more feasible then you give them credit for. <S> For short hop flights they are actually within reason: https://arstechnica.com/tech-policy/2018/10/scotlands-orkney-islands-may-see-electric-plane-service-by-2021/ ... <S> the added benefit of electrifying the Orkney Islands flights is that there's an abundance of renewable energy, especially wind energy, already on the grid in the area. <S> Though replacing the jet fuel burned by small island-hopping planes in a remote part of the world may seem like a drop in the bucket in efforts to reduce emissions, starting small is often a path to thinking big. <S> If the shortest flights in the world can be flown successfully, gradually longer and longer commercial electric flights may someday be attempted. <S> Norway is also setting a goal of entirely electric-powered short-haul flights by 2040: http://www.bbc.com/future/story/20180814-norways-plan-for-a-fleet-of-electric-planes
|
Contrary to one clause of your question, there are a number of battery-electric light aircraft (or what the USA calls "light sport" class) in development, with prototypes flying. Algae fuels, as drop-in replacements for kerosene, may have some usefulness, but there are storage issues (hard to stockpile something that can mold or rot) -- as you note, however, testing is in progress, and we'll know in a few years.
|
Does the pressure at the static ports drop as the aircraft's speed increases? This answer by Tyler Durden explains what static ports are and how they work: The "static ports" allow air into the instrument to provide the input for the air pressure on the side of the aircraft. They are called "static" ports because in general they take in air at the ambient pressure which does not change very much [...] Currently, the answer has a comment by Zeiss Ikon which states: In fact, the pressure at the static ports will drop as the aircraft's speed increases (Bernoulli principle) [...] Is this true? If I'm flying at a constant altitude, will the pressure at the static ports decrease as I speed up and increase as I slow down? If so, does the altimeter have a mechanism for compensating for this? <Q> The comment: In fact, the pressure at the static ports will drop as the aircraft's speed increases (Bernoulli principle) is not exactly accurate. <S> The aircraft is a complex aerodynamic shape and static pressure distribution across the fuselage is not linear. <S> An example is provided by the following figure from NASA Technical Memorandum 104316 : [Source: NASA] <S> If you look at the graphical part of the above figure, you'll see areas where the pressure is above (>0) and below (<0) <S> the reference pressure. <S> As the airspeed increases, the tendency will be for the positive values to get bigger and the negative values to get lower (more negative). <S> So along the line between points 2 and 3, and also between 4 and 5 (over the wing), the pressure will drop as speed increases. <S> Between 1 and 2 (the nose), and between 3 and 4 (just in front of the wing), the pressures will rise with speed. <S> From the same report: Zero static pressure error on the fuselage exists at locations 2 through 5. <S> One of these locations is chosen for the static port. <S> To keep pneumatic lag small, the static port is normally located as near the airdata instruments as possible (or the other way around). <S> (To determine this location precisely, several static ports are made in this area. <S> The optimum location is then selected as a result of comparing the various ports with a reference source, such as a trailing cone.) <S> This pressure distribution changes with flight condition, so a calibration over the flight envelope may still be necessary. <S> ... <S> Even with the selection of the best static port position, some pressure errors will remain, and these errors must be determined in flight. <S> The difference between the locally measured static pressure and the ambient static pressure, which is dependent upon angle of attack, airspeed, and aircraft configuration, is called position error. <S> Based on the measured position error, a Static Source Error Correction (SSEC) table is developed. <S> The SSEC is loaded into the air data system when it is installed in the aircraft so that it can make the necessary corrections. <A> For a basic shape, such as a sphere, the pressure on the side of the object would indeed decrease due to Bernoulli's principle. <S> However, as Gerry's answer points out, a plane is much more complex aerodynamically. <S> The graph in Gerry's answer shows how pressure decreases at some points, increases at others and is unchanged in some. <S> For indicated airspeed, a small error could be adjusted out easily enough. <S> After all, the pressure difference would still be mostly linear in relation to air speed, so just calibrating the scale on the airspeed indicator would suffice. <S> But the static ports are also used for the altimeter. <S> For this reason there is a strong incentive to find a location that minimizes the so called position error in the static pressure measurement. <S> Otherwise when indicated airspeed changes, the indicated altitude could also change, which would be much more difficult to compensate for. <S> So in summary: no, for a well-designed plane, the speed-induced pressure change at static ports will be minimal. <A> This is called Position Error. <S> The placement of the static port is at the spot where the Position Error is the smallest through the airplane's normal operating attitudes. <S> Position Error has to be small enough to keep the measured pressure altitude within 30 feet of true pressure altitude, and an error of not more than 3% or +/- <S> 5kt on airspeed.
|
There is a difference between the true static pressure and the measured static pressure, which varies with angle of attack, but it is generally quite small.
|
Best way of learning the aviation alphabet? I want to learn the aviation alphabet , and when searching the Internet on how to, I see a plethora of approaches, so I thought of asking here! If it's primarily opinion based, let me know. <Q> Presuming you're referring to the ICAO Alphabet <S> * , (alpha, bravo, charlie, delta, echo, etc.) <S> the easiest way (in my experience, from learning it as a disambiguator for phone work) is repetition, same way you learned the alphabet as a child, or the same way you'd memorize a poem. <S> Get a written list of the letter names, read them through several times a day, and over time, start reciting without reading. <S> Do this several times a day for a week, you'll be close if not there. <S> A second week <S> and you should start to think in phonetic alphabet. <S> A third week and you'll wonder why everyone doesn't think in phonetic alphabet. <S> *corrected from comments, originally International Phonetic Alphabet, which is a whole different thing. <A> Study like it's schoolwork! <S> I've found that quizzing yourself in a similar way to studying for a test is the best way to learn. <S> I've had to learn a few different alphabets for different reasons, but there's always good resources online. <S> I'd recommend two tests that I always give to beginners. <S> Beginner Quiz: https://www.sporcle.com/games/g/alpha_en <S> Intermediate Quiz: https://abg.ninja/alphabet <S> Ignoring the childish UI, these are actually great ways. <S> Begin with the first link, and type in all of the letters that you know. <S> This will very quickly show you which ones you know, and which you don't. <S> Rinse and repeat until you've memorized it fully, and can do it an hour after looking at the chart (so the information isn't remembered solely for being fresh in your mind). <S> After you've done this, use the second link I sent you to improve your usage, and to string multiple letters together. <S> Continue until you're comfortable. <S> It's incredibly helpful to read the letters out loud while doing these tests. <A> You might have to use your imagination for find a suitable image for each letter, but once you do, the memorization efficiency goes way up. <S> Another option is to make flash cards with the letter and its phonetic word in a huge font so it takes up an entire page. <S> You will find you are able to recall the "image" of the word more easily than just the information itself. <S> I use that method for memorizing operating limitations where it's just a numerical value you have to store in your head. <A> I can recommend the (free) site http://radioalphabet.com/ , specifically the Flash Cards tab. <S> It provides you with a word, listed vertically with an input box besides each letter, and requires you to write the second and third letter of the word for each letter (which are unique amongst the words). <S> It then automatically jumps to the next box, allowing you to practice quickly recalling the words for each letter. <S> After you have used it for a little, the Statistics tab provides you with hit and miss rates for each letter, so you can know which ones to focus on memorizing. <S> I personally schedule repetitions in my calendar, using the principle of spaced repetition learning mentioned in insysions answer, so I increase the time until next repetition if I get everything right. <A> Make drawings (it doesn't matter how good you can draw). <S> Use whatever comes to your mind first. <S> For example: for Charly I think of Charly Brown. <S> For Mike its another comic figure called Mike, but unlike Charly he is very tall, so these two side by side look very funny. <S> They together (funny view remember) are visiting Quebec in November... ... where they meet Romeo and Juliet who are dancing Tango. <S> Take just a few at a time. <S> Make each of them tell a little story. <S> Stick them where you can see them several times a day. <S> Bathroom for example. <S> If your brain has something to visualize its more likely that you will remember. <A> I had the same problem. <S> The easiest way to me to remember all the letters is with the car plates. <S> It's fun and also keeps you practice the alphabet without a specific order, that's important too.
|
Once you've figured out the ones you don't know, check a chart, attempt to memorize them, and try the test again. My favorite method for memorizing that kind of stuff is to create flash cards with a picture that can be associated with the word.
|
Do military bases still employ wheel watchers? When I was in the air wing in the '70s, I had the unpleasant opportunity of pulling wheel watch. The unfortunate individual sat in a small shack (maybe 3 x 6 ft.) with a pair of high-powered binoculars ensuring that each and every aircraft on final had their gears down. If not, there were two flare guns pointed at opposite right angles to the runway that had to be fired to warn the pilot off. I know I had to use them on more than one occasion. I think it was a thirty-day hitch. It seems like such a primitive way to ensure the gears were down, and I wonder if it's still being used today? <Q> No They do not continue this practice anymore. <S> This is likely because landing gear are more reliable now than they were in the 70's. <S> There is also the practice of Air Traffic Control prompting military pilots to check their gear is down, by verbally adding "Check Gear Down" to their landing clearance. <S> Source: <S> Checked in with some of the Air Force / Air National Guard pilots in the office. <S> They're not aware of any such practice and decided it must have been before their time. <S> Oldest pilot started in the 90's, so that leaves you with a 20 year gap where they abolished the practice. <A> In the early 1990s the Navy used to deploy instructor and student pilots to perform wheels watch at outlying fields that were NOT tower controlled, and where student solo pilots would practice landings during primary flight training in the T-34C. Without an instructor or tower this practice made sense. <S> I cannot speak to whether or not it is on-going. <S> Once complete with primary training, any landing practice at non-tower controlled outlying fields would be done with a carrier Landing Signals Officer on station. <S> The LSO would note trends, grade all landings and also function as a wheels watch, although wheels watch wasn't the primary purpose. <S> During 20 years spanning the mid 1980s to early 2000s I was never aware of any wheels watch at a tower controlled military airfield, but that's not to say it didn't happen somewhere. <A> I remember the AF still had the runway supervisory unit (RSU) when I was still on active duty in the '89-'92 time frame. <S> I wasn't an AF pilot, but I was a private pilot flying with the Aero Club at the time. <S> I'm pretty sure the RSU wasn't staffed full time. <S> It may have been limited to periods of high op tempo when the consequences of a gear up landing would be more severe. <S> I don't remember seeing an RSU in the years since then. <S> Edit: <S> I was reminded that the field got a new control tower shortly after I left. <S> I believe the RSU was removed at that time as it was no longer needed. <S> The new tower provided much better visibility to that runway end than the old tower. <S> We did have the 'check gear down' calls from the tower in those days. <S> I think the RSU became redundant to the ATC call/Pilot confirmation. <S> For a/c with 2 crew, you had a backup check on board. <S> Most of the fighters by that time had the landing lights on the gear, so in addition to the ATC call, the tower could just look for the landing lights. <S> As for the reason for the calls, it's not just about the potential loss of the a/c. <S> In a combat environment, the runway is a critical asset. <S> A gear up landing would render the runway unusable for a time preventing other a/c from landing or taking off. <S> That can seriously impact the mission. <S> Similarly, the Navy has been known to push an a/c overboard to clear the deck of a carrier. <S> The second factor is the culture. <S> In the civil world ATC has their job and pilots have theirs. <S> They don't want to cross that boundary. <S> In the military, everyone is part of the team and they work together to help ensure mission success. <A> To speak to the operational necessity of this safety measure, T-6B's still manage to have gear up landings at OLFs, so when you have an excess of warm bodies to throw at a problem you are inclined to keep using them.
|
As a current student naval aviator, I can tell you that Wheels Watch (who is a student assisting the Runway Duty Officer) is something that is still alive and well for the Navy Outlying Fields that we train at in addition to home field (North Whiting KNSE), which has a controlling tower.
|
In the US, is there a way for a pilot to legally "maneuver at will" in actual IMC? In the US, is there a way for a pilot to legally "maneuver at will" in actual IMC? Let's say you want to practice a series of reversing 360-degree turns and not have to communicate every change in heading to a controller or follow a controller's step-by-step instructions. For example, is there such a thing as an IMC "practice area" where only one aircraft at a time is allowed to operate under IFR? Also, is there a distinction between controlled and uncontrolled airspace in this regard? <Q> You don't have to have permission to fly in IMC in uncontrolled, class G, airspace. <S> However, you must have an instrument rating and be in an IFR-certified aircraft. <S> It's a very good idea to get flight following in order to receive traffic warnings from ATC if you decide to fly within IMC in uncontrolled, class G, airspace. <S> You do need to get permission to fly in controlled airspace (all classes except for G) if you are operating under IFR , regardless of actual meteorological conditions. <S> Note: <S> Classes A-D require permission under both IFR and VFR; classes E and G do not require permission under VFR. <S> If ATC has the space and the time, they may give you a clearance for a specific area and perhaps a block altitude if you want to climb and descend. <S> There aren't officially designated areas for practice, but if you ask local instructors, they will tell you where they usually go. <S> Most of the time, the preference is to get out of controlled airspace if possible; it's just easier. <A> Yes. <S> You can requests a local IFR, or quadrant clearance and then receive a clearance for a region, such as: CLEARED TO FLY (general direction from NAVAID) <S> OF (NAVAID name and type) <S> BETWEEN <S> (specified) <S> COURSES TO/BEARINGS FROM/RADIALS <S> (NAVAID name when a NDB) <S> WITHIN (number of miles) <S> MILE RADIUS, And an example: “ <S> Cleared to fly east of Allentown VORTAC between the zero four five and the one three five radials within four zero mile radius.” <S> Both are from FAA Order JO 7110.65W 4-1-1 <A> "Maneuvering at will" within a particular area is called "work". <S> This is particularly common for news/police helicopters, which often need to wander around above some event in class B/C airspace. <S> I've only heard it done as VFR, but I don't see a reason why ATC wouldn't allow it for IFR if there's nobody else around. <S> Be clear about the horizontal and vertical boundaries you want in your request, and let them know when you're done working and want to resume normal control. <S> You may want to call the relevant ATC unit ahead of time to see when/where will give you the best chance of approval and what exactly to put on your flight plan since this is obviously not a standard request. <A> You might have better luck working with a controller at a Class D tower near you, or maybe Class C. Find an intersection or something identifiable from an approach plate that's in their airspace, request the maneuvers you want. <S> They can have you report in as you maneuver, and yet still have control if they need room for some one actually landing, or keep you clear of transiting traffice, etc. <A> I have done this while operating under IFR in IMC several times. <S> Just ask for a block airspace and tell them what you want. <S> I've found ATC to be very accommodating.
|
If you want to practice in IMC within controlled airspace, you must explain your mission to ATC and obtain a clearance to operate under IFR. In uncontrolled airspace, you may fly into IMC as you like and perform whatever maneuvers you want.
|
What is the non-projected cross-hair for on the F-18 HUD? Top right, there's a little cross-hair - it looks like it's for lining something up, since on the second pane there's a little dot. I haven't seen this on any other HUDs. Appears to be present on all variants including Super Hornet. source simulated - source <Q> The reticle is fixed at a 15-mil depression angle from the gun boresight. <S> If the HUD fails, the HUD symbology is available by selecting HUD via the menu on the left or right DDI [Digital Display Indicator]. <S> To perform a HUD designation in the NAV or A/G [Air/Ground] mode when the HUD is inoperative, the pilot first places TDC [Target Designator Control] priority to the HUD (either by placing the sensor switch to the normal HUD position, or to the left or right DDI displaying the HUD symbology). <S> The mission computer slaves the radar in AGR mode to the LOS [line of sight] of the HUD standby reticle. <S> The pilot maneuvers the aircraft to position the standby reticle over the aim point and actuates the TDC to perform the designation. <S> The aim point position at the LOS of the standby reticle is computed. <S> The pilot may use the HUD display on the left or right DDI to null the steering error when automatic weapon delivery is being conducted. <S> Source: <S> ED Forums <S> The standby reticle is used when the HUD fails for designating targets. <S> The pilot must lean to the right and line up the cross-hairs with the dot so that the bore-sight is accurate. <A> It is technically the standby reticle as mentioned above but in house it is known more as the seat height marker due to that being the most common use for it. <S> As soon as you apply battery power the pilot will adjust their seat height lining this up. <S> Short guys and girls need not lower the seat. <S> Taller people lowed the seat quite a bit. <S> You must always check the leg restraint line anchor points are flush with the floor so they don't pierce the rocket motor of the ejection seat. <S> The HUD is not a display that fails that often <S> so not many people know what this thing is for. <S> The fact that you can just bring up the HUD page on any of the other displays when it fails and beyond visual range weapons being the default way with regards to tactics means it is seldom used. <S> Can't give any references as the publications are restricted, but I was a maintainer on this aircraft for over 10 years. <A> That point and the dot is to know the correct position of the seat height, you must regulate the seat height until you visually match the Cross and the point.
|
It is a "Standby Reticle": A fixed standby reticle (Figure 7–151) is available in the upper right side of the HUD for use in performing visual designations in the event of a HUD failure.
|
Do you need strong muscles as far as applying the yoke is concerned, in order to be able to deal with some emergencies? In some of the plane accidents, the pilot had to use all his might to apply the yoke in certain direction to save the plane from imminent crash; in some cases even crew members had to help with the force. So it seems certain degree of physical strength is needed to be a pilot in view of possible emergencies, though it doesn't seem to be explicitly required? <Q> For the Airbus it is not actually require any strength, all the technology is fly by wire, this means that the actual control (Side stick) is not directly connected to any cable, so been this said, there is no actual force to fly any airbus plane. <S> For the Boeing plane, at least for the 737, that's the one I know, when it loses all the hydraulic systems, the aircraft will become on a manual reversion mode and it will need strength from the pilot to move the aircraft controls that are linked to the surfaces by cables, but this is a remote possibility to happen, and if it is the case both pilots can apply force to the control column <A> Most transport category jets have hydraulic flight controls where the forces the pilot acts on are through bungee spring devices (a pitch feel unit) in the control cable circuit. <S> For certification, pitch feel units normally limit the force required to move the column to full travel to 50 lbs at high speeds and less than that, say around 30lbs, at low speeds (they are intended to simulate the increase/decrease in control resistance with speed that is felt with manual controls). <S> But, there's someone beside to help. <A> This question really is way too generic to be easy to universally answer. <S> The amount of force required to operate the controls of different aircraft under identical conditions is different, varying from very little to requiring some serious muscle. <S> Now apply that to a wide range of potential emergency scenarios. <S> At the one end we have emergencies where no amount of force will change the outcome either because the relevant controls are no longer there (ripped off vertical stab anyone?) <S> or because their use is irrelevant to the emergency <S> (landing gear not extending on approach for example).On the other end <S> we have emergencies where the controls are jammed but can be moved manually if only enough force is applied to them (e.g. the hydraulics failed, leaving the controls stuck in a high deflection position but they can still be moved if you are strong enough). <S> THAT would require a serious amount of muscle most likely. <S> But it all depends on the aircraft, the emergency in question, and the flight regime in which the aircraft finds itself when considering whether any amount of input at all will save the day, let alone brute force.
|
Most pilots, even small framed males and females, can pull 50 lbs, although sustaining that for more than a few seconds can be a problem.
|
How can drag induced by the landing gear be reduced? What are some of the methods used to reduce the drag caused by the landing gear for aircraft with non-retractable landing gear? <Q> The Pilot's Manual: <S> Ground School has a nice diagram that explains it pretty well. <S> It's all about streamlining. <S> Airplane designers add landing gear fairings (I've heard them call "wheel pants") over top of the wheels and also on the landing gear strut. <S> Beyond this, there isn't much else to do. <S> The fairings could be made out of single pieces of material to limit the parasite drag introduced by rivets, etc. <S> There can be different variations on the fairing, but it pretty much comes down to fairings to reduce the drag: <S> NACA (precursor to NASA) details more in REPORT <S> No. <S> 518 <S> THE DRAG OF AIRPLANE WHEELS, WHEEL FAIRINGS AND LANDING GEARS II-NONRETRACTABLE AND PARTLY RETRACTABLE LANDING GEARS <S> They also looked at wheel shape, but it primarily comes down to creating some sort of streamlined fairing to reduce the amount of eddying. <A> <A> Paulo Iscold gave a presentation at our EAA meeting last month where he talked about all the ways he investigated to break speed records for piston airplanes. <S> One of the more interesting things that hasn’t yet made into a flying aircraft is to mount electric turbines on the fairings. <A> Here is one way-- no longer in fashion-- <S> I believe these are called "spats" http://www.airminded.net/alpha/gamma_skch_flt.jpg from-- and see here for more-- http://www.airminded.net/alpha/gamma.html
|
One common way is to use wheel fairings: From wikipedia: wheel fairing
|
Can multiple aircraft share the same logbook? If a private pilot owns 3 planes can he use 1 logbook for all 3 or does he need to use 3 logbooks? Would the answer change if he also owns a helicopter? <Q> For pilot logbooks, the requirements of " what " needs to be logged to meet training time and aeronautical experience is specified in FAR 61.51 . <S> As long as you record all of the information required by FAR 61.51 (e.g., date, total time, day/night etc.) <S> " where " you place the information is up to you. <S> A single conventional logbook works fine, or you can use a spreadsheet, digital device, or any type of similar recording method you choose. <S> Keep in mind that you must present your logbook (in what ever form that you use to record your flight time) for inspection (upon a reasonable request from persons specified in FAR 61.51 (i)) <S> and, if you are a student pilot on a solo cross country flight, you must carry your logbook with you <S> (proof that you have the required instructor endorsements, etc.). <S> So, it's a good idea to record your flight time in a method that is easy for you to access. <S> For this, a conventional logbook works well. <A> Assuming that you are talking about the pilot logbook and not maintenance logs, he can use one logbook for all three aircraft. <S> There is a column for aircraft type and registration number, so clearly the intent is to allow a pilot to document time flown in more than one specific aircraft. <A> If you are asking about airframe/engine/prop records, you should keep separate logs but strictly speaking you may not have to. <S> It would be foolish to combine the records since in the event of a sale of one of the aircraft <S> the records must be passed a long, a complex task if they are all lines in the same log book. <S> The FAA governs log keeping for aircraft under §91.417 <S> Maintenance records. <S> which tells us what we need to log but does not really tell us how we need to log it in depth. <S> They cover acceptable methods for logging in <S> AC 43-9C - Maintenance Records <S> which interestingly states Section 91.417(a)(1). <S> Requires a record of maintenance for each aircraft (including the airframe) and each engine, propeller, rotor, and appliance of an aircraft. <S> This does not require separate or individual records for each of these items. <S> It does require the information specified in § 91.417(a)(1) through 91.417(a)(2)(vi) to be kept for each item as appropriate. <S> As a practical matter, many owners and operators find it advantageous to keep separate or individual records since it facilitates transfer of the record with the item when ownership changes . <S> Section 91.417(a)(1) has no counterpart in § 43.9 or § 43.11. <S> this chunk largely applies to keeping separate airframe/prop/engine log books (which most owners do) <S> but technically does not prevent nor explicitly rule out keeping multiple aircraft records in one book.
|
Separate logbooks for each airplane is not required.
|
What are these windows/portholes on the English Electric Canberra bomber? This may be an obvious question, but I don't know, which is why I'm asking here. I've searched "Canberra canopy porthole" and "window", but didn't get any information. There is a porthole of sorts on the left side of the canopy of this bomber, I'm wondering what it's for. Photo source. Here is a view from inside the cockpit: Photo source. There also appears to be a similar thing on the bottom of the nose of the aircraft, offset to its right. The following is a screenshot from a video game, as I wasn't to find a photo of this. I'm tempted to say that this second one is to do with bomb sighting, however if it weren't there, the bomber would have just as good a view, wouldn't they? <Q> It's called a "Direct Vision" (DV) window. <S> The canopies are sealed shut, so the small DV window is provided as a way to open a small hole if required. <S> For example, to communicate on the ground or in the event of icing or other canopy issues. <S> Edit: I wasn't able to find a formal source, but this page is fairly authoritative: http://alverstokeaviation.blogspot.com/2016/08/english-electric-canberra-technical-tour.html <A> Re the upper "porthole"-- <S> it sure looks like a heated panel for clear vision in extreme icing. <S> Note the resemblance to a "hot plate" in King Air etc. <S> Note that there is one on each side, and this aircraft has side-by-side seating in the cockpit. <S> As has been noted in another answer, it appears to have a hinge and a thumbscrew latch, so it could be opened if needed (e.g., a/c is heavily iced up and electrical power has been lost or can't keep up with the icing-- or just to talk to someone on the ground.) <S> Your question also references the flat panel on the transparency on the lower part of the nose. <S> It is not clear from the photos whether this is heated or not; it's almost certain that this larger flat panel could NOT be opened. <S> However you'll note that it is very common for aircraft to include a flat glass panel for aiming a bombsight or as a window for a camera in the case of a reconnaissance aircraft. <S> The curved perspex of the rest of the transparency will always have some optical distortion. <S> Note that until fairly recently, many fighter aircraft had a flat windscreen in front of the pilot. <S> Again part of the reason for this was to prevent optical distortion as the pilot looked through the gunsight. <S> If this weren't an issue, the thick armored flat glass of the windscreen could have been "faired" more smoothly by an additional curved piece of perspex in front of it, but this was only rarely done. <A> I was a Canberra pilot back in the day. <S> In fact I never had to use it. <A> The panel in the nose cone was a piece of optically flat glass to avoid distortion which would affect the bomb site, and/or to give a camera a clear view forward. <A> the DV window was used by aircrew , open the dv and stick your hand out, to indicate to the ground crew that the aircraft in now depressureised and that it was safe to open the side door (strike wing RAF Akrotiri)
|
It is undoubtedly glass and can be heated by a heating element (note the wires) to much higher temperatures than the perspex canopy could tolerate. The porthole in the canopy was simply a way for the pilot to see his way if the canopy misted or iced up, simple as that.
|
Why is 0 ft a valid target altitude for an autopilot? Inspired by this story ; The pilot of a Flybe plane that dropped 500 ft (152m) in 18 seconds had selected the wrong autopilot setting shortly after take-off, an inquiry has found... ...The plane climbed to 1,500 ft, but then pitched and "descended rapidly" because the autopilot was set with a target altitude of 0 ft. Why is 0 ft a valid target value for the autopilot? Is there any practical use for being able to set it so low and are there safety features that would prevent the plane just hitting the deck? <Q> Quite simply, it's because sometimes you fly below sea level. <S> There's a couple stories out there of aircraft navigation systems acting a bit odd due to their flight below sea level. <S> For example, there is this one, which involves a C-130 landing on an airfield that is 1,210 feet below sea level . <S> There are numerous areas in the world that are below sea level. <S> For example, flying at sealevel above Laguna Salada, Mexico means you are still 30 feet above the ground! <S> It's added as an additional option to cover a small set of scenarios. <S> A pilot is certainly not expected to select the incorrect altitude setting, as this is something that you should always doublecheck. <S> Beyond that, he should not have enabled his autopilot so soon after takeoff (unless 1,500 was his cruising altitude). <A> You would normally set the initial level off altitude provided in your departure clearance, or an initial level off altitude indicated in the SID, or you might set a level off altitude that you have decided to use as a level off for the single engine profile in the event of engine failure, based on the terrain around the airport. <S> All would be at least a 1000 ft above the airport at minimum. <S> You dial up that altitude in the AP's altitude preselect window, usually during the configuration setup during or after the crew departure briefing. <S> When you are airborne, you will normally select the autopilot's speed hold mode (on the -8 AP it's called IAS mode) which makes the flight director command a pitch attitude to hold bug speed, then when you pass 400 feet or above, you engage A/P in IAS mode and it will pitch the plane to hold the bug speed you select during the departure. <S> In IAS mode, whether you climb or descend depends on the power setting, so when you are climbing and descending in IAS mode you regulate the climb/descent with power while the AP pitches to hold the speed. <S> You can also use VS mode, or vertical speed mode, and the AP will now pitch to a preset vertical climb or descent rate. <S> With those two vertical modes, the incident description doesn't make a lot of sense as they would have had to have selected VS mode and dialed in a descent rate, or been in IAS mode and cut the power. <S> However... <S> The -8 400 has coupled VNAV, which adds an extra wrinkle. <S> With VNAV engaged, the autopilot will pitch to climb or descend to an altitude preselect independently of IAS or VS mode, instead of just hold an airspeed or vertical speed, until a preselect altitude is captured. <S> Coupled VNAV can also follow step climbs in a SID or step descents in a STAR if that is programmed into the FMS. <S> So my guess here is that they forgot to set the altitude preselect for their planned departure level off altitude, then engaged the autopilot in VNAV mode during the climbout, which caused the plane to dive to the existing altitude preselect of 0 feet, upon which hilarity ensued. <A> Besides flying below sea level, a situation for low and negative altimeter readings is use of QFE altimetry. <S> (see also <S> What is wrong about this interpretation of QFE and QNH? ) <S> QFE altimetry which was used by some airlines (gone by now), and is still in use in Russia (undergoing phase-out), is where you set the altimeter's reference pressure so that it reads zero at some ground reference point, typically the runway threshold. <S> So if the runway is above you, on terrain, you will fly at a negative height and your altimeters will show as such.
|
The answer is no you would never depart with the altitude preselect at 0.
|
Are there any specific weight or structural reasons to choose low vs. high wings for a cargo aircraft? I have a large cargo aircraft concept and I am debating between a high or low wing. It seems like both are viable, but intuitively it seems structurally harder to support a high wing. Alternatively though I like the idea of a high wing to raise the engines and provide better field landing abilities. Can anyone comment on the weight penalties associated with one concept or the other? Is there a structural advantage to one configuration? <Q> @Ron Beyer has pointed you in the right direction. <S> Study existing designs going all the way back to the Gigant. <S> The wing is by far the strongest part of the aircraft as it must carry leveraged aerodynamic loads and the weight of the aircraft while flying. <S> A low wing may be slightly stronger to positive G loads as the fuselage forms an arch over the middle of the wing. <S> However, for cargo transport the high wing offers the advantage of a lower set, roll through cargo bay and more stability in flight. <S> As far as landing gear, the low wing offers placementof gear on wings for wider track. <S> High wings mount theirs in the fuselage, but the high wing offers the opportunity for greater ground clearance of obstacles on "unfinished" landing strips. <S> As you can see both are made and both are in service worldwide. <S> Commercial freight would favor the 747 type, military the C-17. <S> And let's not forget turboprops for fuel efficiency! <S> Both high and low wings will fulfill the requirements for cargo hauling, what about both on one plane to get wingspan back under 150 feet!. <A> I checked Howe's conceptual design book and high or low wing doesn't seem to affect the structural mass. <S> Packaging the landing gear and its difference in length can change the mass, also if any aerodynamic fairings are required it can increase drag and result in fuel penalty. <A> As already pointed out, the best thing you can do at this stage is to study existing designs. <S> There are plenty of them. <S> You will notice that nearly all aircraft that have a ramp and are designed to carry self-loading cargo (like vehicles) are high-wing design. <S> (Most of them are military). <S> So, there must be a good reason for it, even if it has some penalties. <S> And the reason is simple: the ramp slope can't be too steep, and you don't want the ramp to be too long; thus you want the cargo deck to be as low as possible. <S> This is only achievable with a high-wing design, with its low ground clearance. <S> Some of such aircraft, like An-124 and <S> C-5 , can even 'kneel' the nose gear to provide even lower deck height. <S> By contrast, most commercial cargo aircraft are loaded at well-equipped airports, mostly with containers, and don't need a ramp. <S> They typically are converted passenger aircraft, which are predominantly low-wing. <S> There are 'objective' advantages and disadvantages to each design. <S> Briefly, the high-wing design is better aerodynamically (has less drag, other things being equal), but presents more structural challenges. <S> Smaller aircraft, e.g. Dash-8 , can afford to run the main landing gear up to the wing, where you really want to mount them. <S> But otherwise you need serious strengthening of the fuselage between the wing and the landing gear mount. <S> Presence of a ramp, and thus a big cut-out in the fuselage, is another headache. <S> Nevertheless, the respective advantages and problems are not fundamental, and practical considerations outweigh them, as you can see from the study of existing examples.
|
They usually have high wings for practical reasons, it's a lot easier to load the cargo, than to a a low winged aircraft where the fuselage is higher to give enough clearance. In terms of structural weight, there is probably little difference.
|
What does "out of trim" mean? Our flight was delayed from takeoff because the captain reported it to be "out of trim". What does this mean? <Q> In this context, it would mean the aircraft is loaded in such a way that the Center of Gravity is too far forward or aft. <S> That's actually not the way we usually use the word "trim" in aviation <S> but it's what it means in this case. <A> For example, if the aircraft is pitching up a bit by default, you can trim down in order to counteract it. <S> "Out of trim" would mean that the Aircraft has either been improperly trimmed, or is operating outside of the range trim can be applied. <S> (If the aircraft is pulling down hard, you can only trim up so much.) <S> This can be due to a mechanical defect, improper weight and balance, or other issues. <S> He may not be able to safely guarantee the aircraft is trimmed in such conditions. <S> There is a related question here that explains it in further detail: What is an out-of-trim condition and how is it detected? <A> If the center of gravity was out of limits <S> it is unlikely the crew would use the term "trim" to describe it. <S> Also, if passengers needed to be moved to correct the condition you would see this happening. <S> More likely the fuel control unit was out of trim and needed to be adjusted. <S> It is a fairly common procedure if an engine parameter is a little bit off from normal. <S> From Flight-Mechanic.com: <S> The field repair of the turbine engine fuel control is very limited. <S> The only repairs permitted in the field are the replacement of the control and adjustments afterwards. <S> These adjustments are limited to the idle rpm and the maximum speed adjustment, commonly called trimming the engine. <S> Both adjustments are made in the normal range of operation. <S> During engine trimming, the fuel control is checked for idle rpm, maximum rpm, acceleration, and deceleration. <S> The procedures used to check the fuel control vary depending on the aircraft and engine installation. <S> The engine is trimmed in accordance with the procedures in the maintenance or overhaul manual for a particular engine. <S> In general, the procedure consists of obtaining the ambient air temperature and the field barometric pressure (not sea level) immediately preceding the trimming of the engine. <S> Care must be taken to obtain a true temperature reading comparable to that of the air that enters the engine. <S> Using these readings, the desired turbine discharge pressure or EPR (engine pressure ratio) reading is computed from charts published in the maintenance manual.
|
"Trim" is the ability to correct for deviations in flight controls by prepositioning the flight surfaces for a particular direction.
|
Where do extra planes come from? Last night, I had to change planes at LAX because the United Airlines B737 that I was flying on had radio problems and thus could not fly over the ocean. One of the hi-frequency radios had problems, and the pilot said that both radios must function in order for the plane to fly over the ocean. So I flew on another B737 and arrived at Honolulu almost two hours late. Do airlines keep "spare" planes at major airports in case problems with planes that are scheduled to fly happen? What is the procedure for getting a replacement plane? A plane could not be flown in at a moment's notice, obviously, because it could take hours for it to arrive. <Q> In my experience, having permanent airplanes standing by as spares does not really happen. <S> Based on historical data potential realtime spares, airplanes with potential availability on any given day, can be pinpointed for reschedule or delayed maintenance, should the need arise. <S> At some airline "hub" locations, maintenance is being performed on aircraft and those aircraft can be used as spares, assuming the checks or maintenance is complete or can be delayed. <S> Two important points though: It is extremely costly to have "extra" airplanes standing by to replace an aircraft that may go out of service. <S> Swapping aircraft is sometimes quite difficult because the type aircraft scheduled may not be available. <S> An alternate aircraft (different type) poses difficulty because the crew that was going to fly the B737 you were scheduled on, could not fly a substitute Airbus, for example (they either would not be qualified or not current/legal to fly the different type at a moments notice). <S> The airline's SOC (Systems Operations Control) or similar has a difficult challenge on most occasions dealing with maintenance delays or cancellations. <S> It is not uncommon for the flight to just be cancelled and have the passengers put on later flights. <S> However, the airline's Operational management people are experienced at minimizing actual delays and maximizing aircraft utilization. <A> This is touched on a bit in this travel.se question . <S> Strictly speaking they don't really keep "spares" per se. <S> It's just too expensive. <S> There are a lot of factors to this and flight planning has gotten much better over the past few decades so planes are rarely flown empty, moved for no reason, or just sitting around any more like they did in the past. <S> The prevailing mentality is that an aircraft is only making money when it's flying, so keep it in the air as much as possible. <S> However the reality of airline operations requires aircraft to come in and out of service every so often for maintenance and routine checks . <S> This creates a bit of wiggle room in the fleet, so while there are no spare aircraft per se, a fleet of sufficient size may have excess resources. <S> The chances of getting a replacement aircraft are greatly increased if you are at an airport the airline considers a hub or an airport that has large maintenance facilities. <S> Ultimately the demand is not always there to keep all planes in the air all the time so spare capacity is sometime driven by the nature of the business. <S> In your particular case it's also possible another aircraft was swapped in with the assumption the HF would be fixed fairly fast and thus capable of being dispatched for a flight in fairly short order filling the void it created. <S> A plane could not be flown in at a moment's notice, obviously, because it could take hours for it to arrive. <S> That depends on where the other plane is sitting. <S> Sometimes an aircraft can be flown in if it's sitting at a nearby airfield. <S> These days it's often cheaper for an airline to cancel the flight, put everyone up in a hotel and book them on the next available flights to the destination. <S> This will obviously be weighed by the airline prior to doing so, but it's a risk they know they have <S> and one they are typically fairly prepared for. <S> The only operation that I know of, that keeps a full spare on hand 100% of the time, every time, is Air Force One . <A> HF radios are only used on transoceanic flights, so in that specific case, all the airline had to do was swap your plane for another one at LAX that had a working one but didn't need it, i.e. a continental flight. <S> Ideally, that plane would be on the ground at LAX long enough for them to replace the radio there, but if not, they could prearrange to have it replaced later somewhere else, probably overnight. <S> More generally, as others have noted, airlines don't really keep spare planes around. <S> However, many of the planes out of service for maintenance could be pressed into service if needed without too much hassle, especially at hubs like LAX, so there is some slack in practice. <A> My experience is on the Regional side but in that business spare aircraft are common with operators that have large fleets. <S> There are two important metrics: Dispatch Reliability and Schedule Completion Rate. <S> DR is % of aircraft leaving the gate within 15 minutes. <S> The industry standard is 99% or better, meaning airplanes leave with a delay of over 15 minutes not more than once every 100 departures. <S> SCR is flights that were completed one way or another, as opposed to being cancelled. <S> SCR should be above 99.5%. <S> An airline can have a fleet with at DR that is below 99%, sometimes well below, but by having spares they can achieve SCRs close to 100%, which is the critical metric overall. <S> In many cases, especially if the fleet is large and well ammortized, it's worth the cost to keep spares.
|
In reality, often the "spare" as you called it, is an airplane that can be pulled from another trip with a subsequent replacement available causing less delay than the flight generating the need for the spare in the first place.
|
How many Airbus planes have been destroyed in flight by severe turbulence? Since a brand new A350 has literally the exact same design specifications / G limits as an airliner built in the fifties does (A 1955 F27 Fellowship will break up at 2.5 G-3.75G, same as a modern Airbus jet - anymore than 2.5 G it will start to break up), and there were quite a few airliners from the 50's and 60's era losing wings or being destroyed completely as a result of turbulence. Are there any Airbus planes that have broke up due to turbulence or accidents that were likely due to turbulence, but covered up? Do Airbus planes have systems to avoid Clear Air Turbulence, and avoid flying over mountains, since most turbulence related inflight breakups occurred due to mountain wave activity? (BOAC Flight 911 for instance was flying over the top of a mountain - it experienced G forces of +9 and -4, and broke apart and crashed). https://en.wikipedia.org/wiki/Wien_Consolidated_Airlines_Flight_55 https://en.wikipedia.org/wiki/BOAC_Flight_911 https://en.wikipedia.org/wiki/Braniff_Flight_250 https://ral.ucar.edu/aap/turbulence (scroll down the last link for photos of the DC-8 jet with half its wing and engine torn off due to turbulence while flying at 31,000 feet over the Colorado mountains) <Q> None are on Airbus aircraft. <S> The most recent in flight breakup of a transport aircraft listed was in 1993. <S> All of the aircraft in your examples are fairly old designs, dating back to the 60's or earlier. <S> Your statement that the A350 has the exact same design requirements as an F-27 is inaccurate. <S> While the load factors required for certification may have remained constant, the actual loads aircraft must be designed to survive have changed over time. <S> As an example, for transport aircraft, the FAA regulation on gust and turbulence loads is 14 CFR 25.341 , which has been updated 3 times since it was originally introduced in 1965. <S> Maintenance has been improved since then, as has the durability of aircraft designs. <S> As accidents happen and the industry learns from experience, designs improve to better anticipate the conditions that aircraft will actually experience. <S> Other than the DC-8 in your last link, all of the occurrences happened in the 60's. <S> Apart from the design of the aircraft, a lot has changed operationally since then. <S> Weather radars have improved dramatically, both on the ground and on the aircraft. <S> Modern radars have a much better ability to detect turbulence , even clear air turbulence to a degree. <S> They have also become much less prone to operator error. <S> Weather satellites now provide information on weather even in remote areas. <S> Forecasts have improved as well, providing pilots and dispatchers a better idea of areas that should be avoided . <S> Below is an example of the kind of information that modern radar systems can provide to pilots about weather conditions in their path. <S> Source <A> TLDR: <S> As near as I can tell, probably none with the past few decades <S> I went to the NTSB's accident database https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx <S> This contains information since 1962. <S> It does contain information from foreign sources, although I do not know if 100% of foreign accidents are reported here. <S> I searched for Make: <S> Airbus, Damage:Destroyed, Injury Severity:Fatal, and keyword "turbulence" within the summary. <S> There was only one result, American Airlines flight 587 November 12, 2001. <S> However, if you read the report, you'll see that the turbulence was not severe (0.3g versus the 2.5+ mentioned in the question). <S> The summary text said The National Transportation Safety Board determines the probable cause(s) of this accident to be: the in-flight separation of the vertical stabilizer as a result of the loads beyond ultimate design that were created by the first officer's unnecessary and excessive rudder pedal inputs. <A> Aircraft design specification have changed significantly since the fifties of the last century. <S> Your claim that the: <S> a brand new A350 has literally the exact same design specifications / G limits as an airliner built in the fifties does is just false. <S> See for yourself at the FAA website . <S> For large aeroplanes, the applicable regulation is FAR 25.
|
The Aviation Safety database lists 91 accidents due to turbulence as of writing. For the F-27 incident in Alaska, one of the factors noted was cracks in the wings from a lack of maintenance.
|
Why was Concorde never sold as a private business jet? Airliners like Boeing 747 and even Airbus 380 are at times considered as personal jets for extremely wealthy people. Looking from the side, Concorde was ideal for this role: while not very big, it probably could provide luxury transportation for ten VIPs or thereabout, adding to that something that looks more valuable and more exceptional than just a "flying palace" - speed like no other. New supersonic aircraft like Aerion AS2 are often seen in this role. However, it looks like rich individuals only bought various bones of Concorde after retirement. The fate of F-BVFD looks especially strange. As I understand, it has been retired very early, in airworthy condition, just for being a surplus aircraft. After standing for many years in the open air, it deteriorated and then has been scrapped. I cannot imagine it to cost a lot during these years of standing. Why did nobody try it for personal use? Also, some pre-production aircraft have been retired after logging not so many hours and were airworthy. Surely, Concorde uses lots of fuel, but probably the A380 burns no much less if per flight (not per passenger). And it only could fly supersonic over sea, but was surely capable of the fastest possible subsonic flight over the land. <Q> Private business jets have a few requirements: <S> Operational costs must be within budget. <S> The concorde is pretty expensive to run as demonstrated by the high ticketprices you had to pay for a trip on one of them. <S> Fuel is only part of that costs; maintenance is a pretty big part of that as well. <S> Be able to land and take off close to where the CEO has his meeting. <S> This means making use of small airfields with their short runways and noise restrictions. <S> Account for airfields sometimes not having fuel available or the fuel being too expensive. <S> This may mean doing the roundtrip on a single tank or doing another short hop to an airfield with fuel. <S> Business jets would also mostly operate on a domestic scale. <S> Doing mostly short hops where the concorde would not even reach supersonic cruise altitude before it's over the destination. <S> While plenty of business jets can easily do 0.75 mach which is already 3/4 the speed of sound. <A> While it was never explicitly sold as such (although BAE would have happily delivered it as such) it was operated in such a manner on many occasions. <S> As detailed by this former pilot of the Concorde , the plane regularly flew as a charter with small passenger loads of VIPs often. <S> So even though no one ever owned it specifically for private business it served that purpose quite well. <S> There was also not a huge reason to own it privately for business as that was to be its main market. <S> Glitz and glam aside, the Concorde was a serious way for American and European based entities to have a face-to-face meeting on either turf and still be home for dinner. <S> Offloading the maintenance and ownership to an airline was a nice plus. <S> Some people also speculate that the ultimately canceled Iranian order by the then Shah was perhaps for his personal use : <S> I can’t blame Iran for canceling their orders, as like most airlines at the time <S> , Iran Air was more a symbol of national identity, and the Concorde’s were most certainly toys for the Shah rather than aircraft for his people. <S> Still, it’s a pity nonetherless. <S> Although they never bought the whole aircraft, Pepsi did buy the rights to paint one of the Concordes . <S> Commercial flying was still a fancier affair than it is now and lots of business individuals flew commercial. <S> Keep in mind the Lear 23 had also just come out and the whole space of business/private jets was quite literally in the process of being defined. <S> It would not be until 1972 that we would even start to see rock stars toted around in private jets. <S> The late 1960s and early 1970s were pretty much considered the haydays of general aviation as post-war pilots were in a position to buy planes. <S> The focus in the private market was heavily on selling single-engine piston planes. <A> At the time the jet was in production private jets were still in their infancy. <S> The largest purpose built one was the Grumman Gulfstream II. <S> I have a feeling the Concorde was a bit out of the reach of all firms at the time. <S> In addition by the time the SST had gone into full production, it had largely fallen out of favor for noise and environmental reasons. <S> Concorde was also, dimensionally a big airplane with a length over 200 ft, making it awkward and unruly to maneuver at many smaller airports. <S> It also had a gross takeoff weight of over 400,000 lbs, again limiting what runways it can fly from. <S> Supersonic aircraft also don’t typically feature good short field capabilities which limits the airports you could fly a Concorde into and out of. <S> SUD/BAC quoted a balanced field length at STP for the Concorde of 9400 ft. <S> That really limits where where you can fly from. <S> So unpopular was the SST by 1980 that SUD/BAC had only produced a total of 14 production Concordes, all earmarked for either British Airways or Air France. <S> Most likely all of these factors combined together deterred even the most rabid buyer. <A> Another factor to consider: Aircraft require a lot of support. <S> It's not enough to just sell a few aircraft. <S> There's support that must be factored in - spare parts, training of maintenance crews, etc.
|
Concorde needed a lot of runway and was not a quiet plane. Smaller private planes lived more in the propeller-driven space than the jet space. It's also worth noting that Concordes sales occurred mostly in the mid 1960s (approximately 24 minutes in) a time in which business aircraft were different than what we currently think of.
|
Why hasn't anyone tried making two propellers facing upwards and the other two facing downwards? Within a quadcopter, I know usually it's all the propellers facing upwards or all of them facing downwards. Why hasn't anyone tried making two propellers facing upwards and the other two facing downwards? Do some forces cancel out and renders that method ineffective? <Q> People have done that. <S> And it works. <S> They do it because it's one of the logical configuration for a quadcopter based VTOL plane. <S> Example: <A> The elegance and simplicity of a quad-copter design lies in how it achieves control in all axis with simple variation of engine power (and thus speed) using just simple fixed-pitch rotors: varying power to the forward pair of rotors compared to the aft pair controls pitch varying power to the left pair of rotors compared to the right pair control <S> roll varying power to the clockwise spinning pair compared to the counter-clockwise spinning pair control yaw (this means the rotors placed diagonally spin in the same direction) <S> These commands work independently if all the rotors generate the same lift and torque for the same power. <S> They also need to be laid out in a square or not too narrow rectangle. <S> And the easiest way to achieve that is if both the rotors and their mounts are all identical (except for mirroring for counter-rotation). <A> Does not really matter if they are facing up or down, it matters how they are pitched and what direction they are spinning. <S> This is common on twin engine aircraft. <S> How ever, notice in a helicopter <S> the tail rotor is tilted 90 degrees out of plane with the main rotor to control yaw torque from the main rotor. <S> And there is nothing to say you can not have more than 4 rotors, if you find an application where more is better. <S> Really a matter of matching (any) available technology that can be practically applied to the idea. <S> There might be slight differences in performance up vs down due to air circulation interferences near the prop, so the safer bet is to keep the design consistant, but 2 up and 2 down is not outside the realm of possible.
|
All 4 with the same orientation is a good common sense approach to a quadcopter, though you can have opposite spinning pairs to cancel torque.
|
Why don’t large aircraft (larger than ~737-size) have even partial manual-reversion capability? Essentially all large aircraft 1 have flight control surfaces powered, either directly or indirectly, by hydraulic actuators, as do most medium-sized and some small aircraft. Small- to medium-sized aircraft with hydraulically-actuated flight controls essentially always have some form of manual reversion capability, where the primary flight control surfaces (always the elevator and ailerons, and sometimes the rudder as well) are operated manually by the pilots, usually by control cables attached to the pilots’ yokes and pulling (depending on the aircraft) either on the control surfaces directly or on servo tabs which then generate aerodynamic forces which move the control surfaces. This allows the flight control surfaces to remain operational in the event of a total failure of the aircraft’s hydraulic systems, albeit requiring the pilots to exert a (sometimes considerably) greater force on the controls to operate them. Large aircraft, on the other hand, generally have no manual-reversion capability at all. This is ostensibly due to the greater aerodynamic forces acting on their flight control surfaces at cruising speeds , which would require superhuman strength to completely overcome (despite the fact that, before hydraulic flight control boosting came into wide use, many, many large and fast aircraft were successfully flown with purely manual controls through the use of a number of force-reducing tricks ). However, in a no-hydraulics situation, having any manual control capability at all, even with a significantly- to considerably-reduced control authority and range of movement compared with hydraulically-boosted operation, would be an extremely-useful adjunct to throttle pitch control and steering ( which – especially throttle steering – are difficult, sluggish, clunky, and only really usable for coarse altitude and flightpath adjustments ). So why don’t large aircraft have at least partial manual-reversion capability, despite even a little flight control authority being far, far better than nothing at all? 1 I'm using "large" here to mean "larger than a 737 MAX 10". <Q> Adding in manual control mechanics for a large aircraft has serious drawbacks: <S> Weight: For a large aircraft, the weight of pulleys, cables, etc., will add up quickly. <S> This costs money in fuel and by reducing the useful load of the aircraft. <S> Complexity: The manual system would have to be routed through the entire aircraft, including passing through pressure bulkheads and other structure. <S> This takes a lot of time to design, install, and maintain. <S> While there are certainly ways to deal with the high forces involved, that just adds more complexity. <S> Vulnerability: There have been multiple accidents in which manual control systems were improperly set up or jammed. <S> The manual system would have to be designed so that fly-by-wire system would still work even if the manual system develops an issue. <S> The alternative is to design a hydraulic system that can match or exceed the reliability of a manual system. <S> Of course this is not without its own complexities and issues, but virtually all modern airliners have gone this route. <S> The weight and complexity of a manual system are not worth the remote probability that such a system would be both necessary and useful. <A> You can't look at it and say that some worst case is theoretically possible and you have to design for that. <S> The industry uses a failure analysis and risk probability approach for failures, with 4 main risk categories; Minor (not too big a deal, just extra workload - probability of 1:1000), Major (Significant increase in workload or difficulty for crew - 1:10,000), Hazardous (Someone gets hurt - 1:10,000,000), and Catastrophic (loss of the airframe) <S> (1:1000,000,000). <S> So for Catastrophic events, the probability of a single component failure that causes loss of an airframe has to be better than one in a billion, and if not you have to add a backup to get it below that. <S> One in a billion is pretty unlikely, but not impossible, and outlier failures happen from time to time, and sometimes it's because the system safety analysis itself was flawed (that happens in a lot of cases). <S> What it means is that if the fully hydraulic controls are designed with sufficient damage tolerance and redundancy to keep potential failures within that risk profile, no further backup is required, and such additional equipment is effectively considered "ballast" from a design for risk perspective. <S> It's a cold hearted numbers game on the surface, but you have to create some kind of arbitrary mathematical model to go from or none of it would work because airplanes would have to be overdesigned to death to cater to every possible eventuality. <S> Great fodder for trial lawyers though. <A> Boeing aircraft, such as the B737 can be flown with manual reversion for ailerons and elevator following complete hydraulic failure/loss. <S> Other large aircraft also can be flown using manual reversion (e.g. MD 80, etc.). <S> Plenty of references available. <S> Here is some info from page 16 of an NTSB accident report for a B737: <S> link <S> From page 16 of the accident report identified by the link above :
|
For aircraft that don't have manual control capability, the required redundancy is built into the system design with redundant hydraulic actuators powered by redundant hydraulic systems. If an event is catastrophic enough to cripple all of the hydraulic/electrical systems, there's a good chance a manual system would be disabled as well.
|
Can someone explain this glideslope question? The glideslope deviation bar is covering the second upper dot. The required action to meet glideslope beam is to: What does this question mean? <Q> While on the glide slope, pitch controls airspeed and power controls altitude, so you will need to add a bit of power. <S> For small very small deviations caused by turbulence, just let the airspeed vary and use pitch for a short while. <S> For larger deviations you won’t be able to capture the glide slope without adding power. <S> The amount of correction depends on how far away you are from the glide slope transmitter. <S> Figure 139 from the Instrument Knowledge Test Supplement give you an idea of the amount of correction you need depending on how far away from the runway you are. <S> So if you are near the outer marker, 2 dots would mean that you definitely need to add power, level off and intercept the glide slope. <S> Near the runway 2 dots is less than 100' so a slight adjustment with pitch would be fine, presuming you were holding the glide slope until then. <A> You’re low. <S> Add power, tweak the nose up a bit. <S> Watch rated of descent decrease a couple hundred FPM. <S> The glideslope bar will move down slowly. <S> As it approaches center, reverse the correction by decreasing power and dropping the nose a little. <S> Rate of descent will settle back down to your target. <S> Add about half the power you just reduced to hold it there. <S> By this time it’ll be time for a new correction. <A> It's referring to the dots for the glideslope on the Horizontal Situation Indicator. <S> (Shown on the left side of the diagram below) <S> source <S> The dots above center indicate the plane is below the glide slope so rate of descent needs to be reduced.
|
If you are answering an FAA Knowledge Test question, the correct answer is to level off and intercept the glide slope.
|
Reasons for significantly lower than normal approach Not sure if this is going to be answerable to be honest, as I'm sort of asking for a bit of retroactive mind-reading! But here goes anyway! I was driving along Clifton Drive North, Lytham Saint Annes, England on 17/11/18 (~3:30 pm if that matters) and I saw a plane approaching the adjacent Blackpool Airport at an exceptionally low altitude (not sure on model but looked like it might have been a Cessna 400-series). It's always hard to estimate altitude accurately (particularly given I was also driving at the time) but somewhere in the order of 200-300ft at the point it crossed over the road and descending (suffice it to say I was at least half expecting a crash!) It was highly unusual - I've lived in the area for 5+ years, and travel that road frequently (typically at least 1-2 times a day and have been using the airport for even longer) and I've never seen a plane take that approach before. Here's the aerodrome chart for BPL: Pretty much every plane I've ever been on (either flying or being flown) has approached and landed on runway 28 - even when coming from the west (e.g. coming from IOM) the approach has always been from the SW, bearing around 50° and then turning right to about 270-280° before descending to runway 28 to land. As far as my limited knowledge allows I believe standard altitude for approach to BPL for this is 2000ft and there is not a cat in hell's chance that this plane was anywhere near that! I think it is possible to land on runway 10 - but that the approach path for doing that is to be coming in from the east at 1600ft bearing 256-281° and flying over before turning right to 92° and descending. The OCA for this path is 450-1000 depending on aircraft category, it's distinctly possible that the plane was at 450 (as I mention above my altitude as estimate was based off Mk 1 eyeball from a moving car so unlikely to be especially accurate!) but curiously I'm 95% certain that the aircraft didn't pass over coming from the east, I had been on the road for a good few minutes and there's nothing that would have obscured my view of them doing so - and I must admit I'd been watching the sky quite closely as I'd spent a large amount of the drive musing that conditions were fantastic and wishing I'd booked myself a lesson for that afternoon! The plot thickens in that probably less than a minute after the plane passed over a helicopter (reasonably large - probably a offshore-rig transport) flew over on roughly the same path, but if anything even lower! So I was wondering whether there was some circumstance causing ATC to advise a different approach from typical and what that might be? As I mention above conditions were fantastic wind was very slight (unusually so for Blackpool at this time of year!), visibility was great - sunny with light hazy cloud that was well above (would probably have said 10,000-12,000ft +). Could operations at WRT (~6 NMi to the SSE) have had an influence? <Q> The winds were coming from dead East 090°: <S> See METAR , at >15kts. <S> This strongly favours a landing on runway 10. <S> The predominant winds in Blackpool are from the West , which may be why this is unusual to you. <S> The approach you mention is just one of the possibilities. <S> The charts also give the option to approach directly from the West . <S> Outside of the published approaches, one could imagine that ATC vectored the Cessna in on a quicker path to beat the incoming helicopter. <A> The low approach was likely due to the layout of the airfield, which has all the parking, pumps, on the north west corner of it. <S> Also, once you're halfway down the runway there's no taxiways from the east half of the runway. <S> 28/10 is 1870 meters (6135 feet) long and a light single probably needs 300-400 meters of it to stop. <S> If the pilot landed 1/3 down the runway and then took 400 meters to stop they would have to backtrack to get back to the taxiway. <S> If the pilot put it on the numbers then they might turn off on taxiway delta, or echo at the longest, clearing the runway sooner and having less taxi time. <S> Conversely, if you are in a light single on approach to 28 you'd want to aim for a 1/3 of the way, putting it down on the numbers means ages taxiing down the runway to the first turn-off point, all the while hearing the calls of those on late final having to go around because you're trundling down to Echo. <A> I would agree with the previous posts that prevailing winds from the East is the likely solution, but you mentioned that this was significantly lower than most approaches. <S> I can't speak for a Cessna 400 series, but the flaps on high wing light Cessna aircraft are controlled electronically. <S> Should one lose their electrical system, they would land without flaps, at a higher rate of speed, and at a reduced angle of approach. <S> This is something that should be practiced from time to time.
|
One reason that one may fly a lower than normal approach is for a "no flap" landing.
|
Why cycle the magnetos before engine shutdown? Inspired by this question asking about shutting down a light aircraft engine I realised there is another ritual which I do, but have long forgotten the reason why. Having parked a light aircraft, and switched off the electrics, with the engine still running I always check left and right magnetos, similar to the magneto drop check done as pre-flight checks. I don't really pay much attention to the RPM, I do it because I've always done it. It's not (as far as I remember) on my shutdown checklist - and I'm starting to wonder why I do it. Is this necessary? Something in the back of my mind is saying "prevents mag fouling". What is the real reason to cycle Left & Right mag pre-shutdown? <Q> This is a hot-mag check to verify that when you shut the engine down, you are really putting it in a safe(r) state. <S> Think about how the mag-switch works, when you switch to R or L, it grounds the P-Lead on the other side (so switching to R grounds the P-Lead on the Left side). <S> If you don't see the RPM drop, you may have a hot mag on that side. <S> An un-grounded mag is a dangerous situation in that it can cause the aircraft engine to turn over if you accidentally (or intentionally) move the prop when you are parking the aircraft, or when somebody walks by and runs into your prop. <S> So during this mag check you are only looking for an RPM drop or a change that tells you that the mag is shut off. <A> You are doing it wrong if you are just cycling left <S> /right/both. <S> It is a hot mag check, not a mag function check like on a runup. <S> You are supposed to cycle them to OFF and then back on to BOTH before shutdown and listen for the sound of combustion stopping in the exhaust. <S> You do it after the engine has had time to cool down and while the engine is at idle to avoid backfires. <S> Remember that magnetos are disabled (shut off) by grounding out the primary circuit. <S> If the P lead, the ground out wire, to the ignition switch breaks, the mag is prevented from turning off and remains live. <S> You are making sure they are grounding out and really shutting off <S> so you don't have an undetetected live mag after shutdown. <S> You have to do this because shutdown is done with the mixture cutoff and if the one mag is live after being turned off you won't know it, and <S> a surprise could occur if the prop is moved later and the mag fires with residual fuel mixture in the cylinders. <A> This is going to give the same reason as Ron Beyer's answer. <S> I'm only writing another because I found his a little hard to follow <S> and I'm going to try to explain it differently. <S> It's nothing to do with mag fouling at all. <S> The magnetos are wired up so that a failure of the switch or wiring leaves them live (on), unlike most electrical devices which are wired to be off if they fail. <S> This is normally what you want because if the wiring fails in-flight, you'd like the magnetos to keep working. <S> But it can cause a dangerous state, where the magnetos are stuck on when you think they're off. <S> If you swung the prop in that condition, it could fire when you're not expecting it. <S> So one at a time, we switch a magneto off, and check that the RPM appears to drop, and that the engine sound changes. <S> The sound is more important - as John K says, the drop is small at the kind of RPM you do your mag drop test, and hard to see unambiguously on the gauge. <S> It's not so much for your benefit as whoever will touch or fly the aircraft next. <S> Even so, you should always treat a propeller as live. <S> If you have to swing it (e.g. to inspect it), do so as if you were hand-cranking the engine, keeping well clear and making sure your arm comes out of its path.
|
This way, you know that switching it off really does isolate the magneto, so you know that when you turn both off after stopping the engine, the propeller is safe.
|
Are you required to disclose medical conditions to your flight instructor? When talking with a local flight school about my interest in starting training, I started asking questions about how the AME process works. The flight instructor then asked me if I had any specific medical issues. Are you required to disclose any health information to your flight instructor? What about if the issue(s) could be disqualifying? Would you get in trouble for lying to the instructor (to avoid judgement or maintain privacy) but NOT lying during the AME? <Q> When it comes to the AME, you must disclose everything fully and completely. <S> Failure to do so may void any license and insurance and expose you to extraordinary civil and criminal risk. <S> When it comes to your flight instructor, who is not a medical professional, you do not need to disclose the specifics of your situation. <S> Saying, "I have concerns about passing a Class III Medical Exam due to certain conditions" is sufficient, and is not the same thing as lying. <S> Do not claim you are healthy when you know you are not. <S> Your instructor may decide not to continue training until a physical is passed, or he may decide just to be a little extra vigilant during training, and delay certain elements or maneuvers depending on the information you choose to provide. <S> For example: If you choose to disclose vertigo problems, he may avoid steep turns until medical clearance. <S> If you choose to disclose vision issues, he may avoid night-flight. <S> Regardless, you will need a medical before your first solo flight. <S> Do not lie to your instructor, but that is not the same thing as disclosing full details of your health with a non-medic. <A> There's no legal or regulatory obligation to tell your instructor about medical conditions as others have said. <S> There may be rare cases where there are insurance considerations the flight school must take into account, in which case they should explain that. <S> The more the instructor knows about you the more they can look out for the specific issues a medical issue may raise - Training works better if there is a rapport and trust between the instructor and student. <S> Lying to an instructor is a breach of trust, and could damage the relationship. <S> Think of it this way <S> : how would you like it <S> if you were an instructor and found out a student wasn't telling you he/ <S> she was prone to panic attacks? <S> And you found out on final approach when the student suddenly went rigid, or worse pulled back on the controls and put you both in a life threatening situation? <S> You'd want to know <S> so you could make an informed choice on whether to take that student on, and if you did you'd probably elect a different training regime, one with more gradual steps. <A> There is no obligation to disclose anything to your CFI, just your AME. <S> That said, your CFI may have useful advice about common problems, if you're willing to talk about them, and they may suggest delaying relevant parts of your training until thosr problems are resolved by your AME. <S> If a CFI (or anyone besides your AME) asks a question you don't want to answer, then tell them that , rather than evading the question or lying (even if only by omission), and they should respect your privacy. <S> Just knowing there's something they don't know is good enough. <S> If your flight school requires medical forms, then IMHO, find a new one. <S> All they need to know is whether or not you have your medical certificate. <A> At this stage, when you are just talking about maybe starting to learn to fly, this person is not acting as your flight instructor. <S> He's just a person giving you information about a process. <S> On the other hand, flight instructors often have a decent knowledge of the medical requirements to fly, and might have been able to give you a good opinion on whether any particular condition is disqualifying. <S> At a later stage, when you are actually taking instruction, it's probably a bad idea to withhold useful information from your instructor. <S> It is likely that a flight school will make you fill in a form which asks about medical conditions, and lying on that would be a very bad idea. <A> The reason he asked that is because he thinks you asked an XY question, and thinks the "X" is "I have a medical problem that I fear might fail me on my medical ". <S> So he is asking only to answer your query , and he's not wasting time on the Y, and taking the shorter path to X. Not his first rodeo... <S> As such, he's listening for relevant medical concerns likely to fail you, i.e. That could affect your safety to fly. <S> It would be an "overshare" to mention your excema, HIV status, enlarged prostate, well-managed cancer, eidetic memory, gluten allergy, or need for Viagra. <S> So answer the X: <S> say why you think you'd have trouble with the medical. <S> You can always trot out the old "asking for a friend"... <S> But then, expect to have an instructor who takes precautions against you having that problem in flight with him. <S> Really, a lying relationship is not one you want to have in the cockpit of a plane.
|
There's good reasons to be open, however: - Not disclosing a medical condition could increase the risk to both you and your instructor, depending on what that is. You aren't under any legal obligation to disclose anything to him.
|
How can we avoid running out of airport abbreviations? As far as I know, airport name abbreviations are a 3 letter name. For example: MEL for Melbourne/Australia airport LAX for Los Angeles/USA airport YYZ for Toronto/Canada airport And that means all the options we have for naming are 26 * 26 * 26 = 17,576 Sometimes these match the IATA code, but not always. IATA codes are also 3-letter codes, but are not assigned to every airport as shown in this answer . But what about all of the other airports in the world? Will the world ever run out of "regular" airport codes? A simple Google search about the number of the airports worldwide shows there are 17,678 airports. So are they going to extend airport codes to 4 letters or use numbers 0,1,2,...9? Even by starting to use numbers they may reach a point where they run out of options. What is the approach to fix that ? <Q> Only major airports get all Letters. <S> Many of the smaller airports also incorporate numbers. <S> Here are some examples: Osage City: 53K <S> Cle Elum: <S> S93 <S> De Vere: 2W1 <S> And many, many, many more... <S> Once you add in letters and numbers, you'll find plenty of combinations. <A> There are multiple airport code systems. <S> The one you seem to be asking about is the 3-letter IATA code, which is mostly assigned to airports with scheduled commercial service--and even some railway stations; they're nowhere near running out. <S> 4-letter ICAO codes are assigned to far more airports, and we're nowhere near running out of those globally either, though since countries are allocated 1- or 2-letter prefixes, it's rather uneven. <S> Some airports have only a three- or four-letter national code; this is particularly common for heliports and private fields, and one or more of the letters is often a number <S> so they aren't confused with IATA or ICAO codes. <A> These are called Airport Identification Codes. <S> The same ID code might exist in different countries, so it's not really possible to limit your 17,576 total combinations to all airports in the world. <S> Additionally, some countries will use a combination of letters and numbers. <S> There are three main conventions for determining an Airport ID code: <S> Each country has their own national authority, which assigns IDs to airports in that country ICAO - The ICAO organization has a process for each country to assign an ICAO ID to airports within that country. <S> IATA - The IATA organization has a process for each country to assign an IATA ID to airprots within that country. <S> National Authority: <S> For example, in the USA, the FAA assigns either 3- or 4-letter codes to its airports. <S> There is more information on FAA-specific codes at this ASE page . <S> The busier airports in the USA will get a 3-letter ID. <S> These IDs will usually match the IATA code. <S> And, within the 48-contiguous states, the 3-letter ID will be prefaced with the ICAO-designated letter "K". <S> International Civil Aviation Organization (ICAO) . <S> This body assigns a prefix designator letter to geographical regions and (if necessary) a second letter to individual countries within that region. <S> Some examples: <S> Northern European airports all start with E, and then the UK starts with G and Germany starts with D. <S> From there, the national authority selects the final two letters. <S> Thus, London Heathrow's ICAO Code is: EGLL. <S> International Air Transport Association (IATA) <S> IATA is not driven by the local authority, but rather by the Association itself, in cooperation with the member airlines. <S> IATA assigns a 3-letter code to airports which receive service by IATA-member airlines. <S> And to get even more complicated, the same airport might have three different ID Codes, one of each. <S> Related reading: <S> Can two airports have a different ICAO code but share the same IATA code? <S> When do we use IATA codes and when do we use ICAO codes? <A> as far as i know airport names abbreviation is a 3 letters name <S> There are multiple lists of airports that use abbreviations and none of them are completely comprehensive. <S> The major lists you will see for airports around the world will be IATA and ICAO. <S> The FAA has a separate list that is only for US airports. <S> The three-letter abbreviations you show are from the IATA list. <S> Many smaller airports do not get an IATA designation. <S> Checking a recent version of the data shows only a little over 9000 entries. <S> So unless the allocation rate is high (which seems unlikely), there's no immediate fear of running out. <S> See also: Can two airports have a different ICAO code but share the same IATA code? <S> and Where can I find a free list of ICAO and IATA airport identifiers?
|
Within each country, the national aviation authority assigns Airport IDs to all airports within its jurisdiction.
|
What would be a simple aerodynamics simulation software for a student? I have a project due 2 weeks from now that demands we make a glider using Styrofoam. I'd like to simulate the results as I plan my glider before I build it. Which simple software, which allows importing a 3D model to do the testing on, can give me data on CG, CL, lift, drag and reach based on initial velocity, etc.? <Q> If you have only two weeks it may be best not to go running into a maze, but you may wish to have simple and complex approaches running side by side. <S> As others have said, it would be helpful to know the parameters of your assignment. <S> Are they interested in the theory, or do they want to see something flying? <S> The most important thing will be the airfoil shape as far as lift and drag, but glider airfoils are easily obtained on the Net (airfoil tools). <S> Next would be wing loading, which can be obtained from existing models and data from birds. <S> Design can be your choice, but starting from scratch, a standard sailplane planform will serve well. <S> Remember to have your CG near your Clift, slightly forward, and your elevator trim slightly up. <S> For an indoor free flight glider a high aspect wing with some dihedral and an upright vertical stabilizer will help make it fly straight. <S> Although the theory behind gliders is well known, getting one to fly right will be a learning curve from scratch. <S> Leave at least 2 days for test flights, and plan on extra Styrofoam and glue for repairs. <S> Good luck! <A> Based on the original and a bit too-broad question: Look into XFLR5 , a basic design program that does airfoil design and analysis, and can do some more advanced computations such as stability and eigenvalues. <S> It is mostly useful for glider model design, but can be generalized if you know what you are doing. <A> There are many ways to approach this. <S> In 2004 I used the model for the Caravan (208) and built some good models very quickly. <S> Simulink runs with MATLAB. <S> The Simulink toolkit which the DHC-2 and Cessna 208 models are built upon, handles flight dynamics and control . <S> Since 2004, my usage of the above has only been situational and sporadic, but you may find a user group or some such group which can help you kickstart your design effort. <A> From weight and performance sizing to aerodynamics and stability and control analysis, you can monitor all aspects of the design every step of the way. <S> What you seem to want to do is analyze an airplane before you actually designed it though.
|
A professional software is this: http://darcorp.com/Software/AAA/ From the website: Advanced Aircraft Analysis (AAA) is a comprehensive airplane design program that gives its users full authority over the entire preliminary design process. For the bounding I suspect you want, one might try Simulink, which has a model for the DHC-2 and the Cessna 208.
|
Is it possible to know why an airline operates specific equipment on certain routes? I've spent far too long staring at flight tracking sites, and occasionally I think I'll notice some pattern in what types of aircraft a given airline uses for certain scenarios/routes. For example, Delta seems to operate a lot of MD-88's on short-haul routes that other airlines would likely use ERJs or CRJs on. They also seem to use 757s on quite short hops (ATL to southeastern cities ~1hr away). Another example would be why British Airways operates 747s to some cities, and 777s to others, and exactly how they decide where to use which aircraft. Is there a good reference for figuring out the reasoning behind why airlines use a given aircraft for a given route? Or are there too many different factors and too much corporate secrecy to really know for sure? <Q> There are many factors, but you can often predict what class of plane will be used for a particular route by the distance and demand. <S> For smaller cities, they want to fill the planes, but they also need several flights per day to cover the fixed costs of serving that airport (and make things convenient for customers), so it's often better to have a commuter jet bouncing to the nearest hub and back several times per day day than one large plane that carries an entire day's worth of passengers in one shot. <S> For larger non-hub cities, they'll do roughly the same thing but with mid-size planes. <S> Between hubs, they'll run the largest narrow-bodies to connect all the various small cities not served by a common hubs, plus hubs themselves tend to be large cities with plenty of native demand too. <S> For international, they'll run wide-bodies because they need higher fuel capacity, and there's rarely a convenient time for customers due to the long flight times combined with crossing several time zones, so you might as well pack them into as few planes as possible. <S> Notably, some carriers fly several different types, each optimized for specific route types, while others fly just a few types (or even just one) because that makes maintenance, pilot training and fleet scheduling easier--but may limit what kinds of routes they can fly profitably. <S> When airlines merge, they'll usually have similar fleets--and in cases where they don't, they'll quickly start dumping types they don't like and replacing them with types they do. <A> Every airline has their own recipe and priorities in this regard and it’s <S> unlikely you will find any open accessible references to this. <S> An aircraft with some inoperative equipment might still be legal and dispatched for a short haul flight but not ETOPs operations. <S> It can go down to small details like customer profile and preferences as well as configuration of the aircrafts interior (eg. <S> newly upgraded seats) and the availability of service and maintenance facilities. <A> You also get the occasional really big planes on routes that wouldn't seem to necessarily make sense for the distance. <S> This can happen when there's a big out and back that brings the plane back to the hub with some "downtime". <S> For example, out of SFO, a large plane may fly a 8 hour leg out to a far point, and then come back. <S> Adding time in for servicing etc, the plane would arrive back at the hub site around 18 hours after it left. <S> It could serve the same route and just sit on the ground for 6 hours waiting, but why not send it back and forth to DEN for example, which it could do in that downtime. <S> Or maybe the timing works to have the plane go to the east coast and then do a long trip out of there.
|
Apart from the obvious demand, availability and costs of aircraft and business they do take in consideration the wear and tear (and maintenance cycles) of the aircraft (how long to go before what maintenance) as well as a balance of long and short haul operations and the specifics of each particular aircraft and its parts.
|
Are there any airlines that fly a route that has an arrival time earlier than its departure time? Imagine the scenario where an airline flys a short 30 minute route which crosses a timezone going west. They could theoretically leave at 00:15 (local) and arrive at 23:45 local the previous day. I'm wondering if there are any airlines which fly such a route. P.S. I'm specifically interested in how the airline allows booking such a flight and the UI that is presented, but am leaving this question more general for any flights that do this. P.P.S. If someone could help with the tags for this question, it'd be much appreciated. <Q> I found such a route for you. <S> KATL (Atlanta) to KHSV (Huntsville, AL) is a 57 minute hop from the Eastern time zone to the Central time zone. <S> It appears how you would expect: <A> Back when Concorde was still a thing, British Airways' motto was 'Arrive before you leave', illustrating how you could arrive in North America sooner (in local time) than when you left Europe. <A> UA892 leaves ICN at 6PM <S> Friday (KT) and arrives at SFO at 11:30AM Friday (ET). <S> There's dozens of flights that leave Korea/Japan/etc and go to the US West Coast that arrive "before" they take off. <S> I'm not able to find a flight in these circumstances that leaves in the early AM from the west side of the Pacific, because that would seem to meet your criteria of arriving the previous day. <S> The same flight leaving at 6AM Friday would arrive 11:30PM Thursday. <A> My personal most frequent return flight - Atlanta to Nashville - is a good example. <S> It's 35-40 minutes flying time, but moves from the Eastern time zone to Central, thus landing 20-25 minutes before it took off. <S> Much more extreme examples happen when you cross the International Date Line going East. <S> For example, I've flown from Seoul (Incheon,) South Korea to San Francisco in about 10.5 hours. <S> However, Seoul's time zone is 17 hours ahead of San Francisco's, so, despite the flight being 10.5 hours in duration, it landed 6.5 hours before it took off in local time. <S> Even flights with 14+ hour duration from East Asia to the U.S. mainland frequently land earlier than they take off. <S> The most extreme examples would be from an airport just on the Western side of the International Date Line to one just on the East side. <S> These can land almost a full day before their departure in local time. <S> In some cases, it's even possible to land slightly more than a full day before their departure, such as flights from the Line Islands of Kiribati (UTC+14) to, say, American Samoa (UTC-11). <S> And this is why aviation always uses Zulu time (UTC) , not local time. <A> Yes, being a pretty frequent traveler between the US and Australia <S> I've very often technically 'arrived' before I left. <S> I tend to book through Orbitz and while the trip to Australia is often marked with a +2 to show that crossing the date line adds another day to your trip (ie, you leave on Monday and get there on Wednesday even though the flight is only 13 hours), when you return it's common to find flights that look like this one below. <S> Where you leave Australia at 9:35am, fly for over 13 hours, and arrive three hours earlier : <S> Personally, I'm not a big fan of how Orbitz doesn't show the actual dates with the times. <S> It'd help clear up confusion here.
|
Yes, there are loads of these.
|
How to find black boxes underwater absent any pinger signals? If CVR/FDR cannot be seen visually on the seafloor (because covered by a thick layer of mud/sediments) and no pinger signals are detected, how can they be found? Metal detectors? Any other methods? case in point: The FDR of crashed Lion Air flight 610 was recovered on 1 Nov 2018, but 2 months later now the CVR still has not been found (while the pinger batteries are rated for 30 days only): « The search for the CVR is hampered by thick mud. The signal source is difficult to ascertain its position considering the sea floor is mud with a depth of more than 1 meter. The ping signal from the CVR has not been received for 2 days now (5 Nov). There are other means to find the CVR however. » ( source ) Which "other means" are this ? update 18 Dec 2018: Lion Air contracts MCS to locate and recover the CVR of the 737MAX . update 21 Dec 2018: an expert answered the question for me. I'll paraphrase his explanation as an answer below. <Q> The CVR on a Boeing 737 is located in the aft cargo compartment. <S> The CVR itself is not built of the same materials as the aircraft, which is mostly aluminium and composites. <S> By mapping the location of other components of the aircraft found in the sea bottom it should be possible to make an educated guess of the general location of the CVR (assuming the aircraft did not disintegrate, sending everything in different directions). <S> The problem is that something as small as a CVR will only be detectable up to about 20' under the ocean floor. <S> If it is buried deeper than that it will be difficult to find. <S> That's why they have pingers, but those stop working when the battery runs out. <A> I don't know the details, but since there is still no good answer, I'll wager an educated guess. <S> Metal detectors do work under water, but I believe sonar can also scan through a layer of mud and can work from larger distance, so it can scan the debris field more effectively. <S> Then the mud will be sucked or blown away and the items identified visually. <S> Usually this is done using an remotely operated submersible vehicle. <A> When the underwater wreckage site has already been found, but CVR/FDR are still missing, at first hydrophones are use to listen for the black box acoustic pinger signals. <S> Absent these signals (or when they have stopped emitting after the batteries have died down), in the second stage another method is used: Sub-bottom <S> Profiling "High Penetration Sub-bottom Profiler" <S> : "The systems generate high-resolution images of the sub-bottom stratigraphy in oceans, lakes, and rivers." <S> ( source ) "Sub-bottom profilers work by transmitting sound energy in the form of a short pulse towards the seabed. <S> This sound energy is reflected from the seabed and the sub-surface sediment layers. <S> The reflected energy intensity depends on the different densities of the sediments, the denser (harder) <S> the sediments, the stronger the reflected signal. <S> The reflected signal then travels back through the water to the receiver (either a towed hydrophone or transducer). <S> The received signals are then amplified, processed and displayed in the acquisition system." <S> ( source ) Deployment of Various Shallow-Water Sub-bottom Profiling Systems <S> In the case of JT610 a ROV is also used: « <S> The recovery team is set to utilize an ROV equipped with the needed features to search for the missing CVR that is believed to be buried under the seabed. <S> “The device that we prepared is able to detect objects buried 4-meters under the bottom of the ocean.” <S> » <S> ( source )
|
One common way of tracking down the CVR is by using an underwater magnetometer to detect ferrous metal objects.
|
I wonder if it's possible to make a "compressed air" turbine engine I wonder if it's possible to make an efficient turbine engine that uses only hot compressed air to move but only that, meaning there is no ignition involved. To put it simple can we use compressors like turbo or superchargers to make a small turbine engine that will be able to move (not lift) 100+ kilos at high speed, well lets say around 40km/h (25 m/h)? I've studied it a bit and to actually know i need to make it but before that i thought to ask people that know certainly more than i do. Also if you can think of a way to do it i'd love to hear it cause iv'e thought of something but it might not work (i guess that's the fun of it tho doing tests and rebuilding and stuff). Ok, in addition to all that let's say that power for this comes from batteries and it's meant to work for short periods of time. <Q> Well, ships have been using turbine engines powered by super-heated water since the late 19th century. <S> But you still have to have an energy source to heat the steam. <S> And it's no good for a "jet" engine since the whole point is thrust by accelerating air through the engine, where the turbine and compressor are there just to keep the cycle going. <S> It would only work for a turbo-prop or turbo-shaft where the turbine's job is to produce torque for doing the work. <S> Theoretically, you could have a turboprop powered with a steam turbine, or some other heated gas, but you still have to have an energy source. <S> Maybe some kind of weird and wonderful battery powered water heater, or a tiny nuclear reactor? <S> Then you also need a huge supply of water or other fluid or gas to heat up. <S> It is possible however to have a closed system that recycles the water used for the steam. <S> You then have pretty much a small nuclear power plant or nuclear sub. <S> It's theoretically possible though, to have a nuclear powered turboprop that could fly for months. <S> If it works for subs and aircraft carriers, why not, if you could make the whole thing light enough. <S> Actually, none of that stuff is really new. <S> There were nuclear powered aircraft concepts in the 50s, that weren't really practical. <S> The thing about turbine engines powered by kerosene is that it's still the most efficient way to convert potential energy to kinetic energy in a light weight and trouble free package. <S> 50 years from now? <S> Who knows. <A> The idea falls foul of the law of thermodynamics. <S> The chief problem is that you seem to convert electricity (from the battery) via thermal energy (heat) to mechanical energy. <S> This cannot be efficient. <S> The amount of thermal energy that you can convert back to other forms of energy is limited by the [Carnot efficiency] <S> ( https://www.e-education.psu.edu/egee102/node/19420 . <S> As @jamesqf points out in the comments, you can skip the whole thermal step and just have an electrically driven propeller. <S> By not heating the air, you avoid the inefficiency. <S> Now turbine engines running on kerosene are also limited by this same Carnot efficiency. <S> I just told you it's bad, but why then do planes still burn kerosene? <S> It turns out that kerosene has a much higher energy density than batteries. <S> This means the plane can be much lighter at take-off, which compensates for the thermal inefficiency. <A> As I understand it you want to have a compressor creating compressed air that exits in a high-speed jet, thus causing thrust, <S> but you want the jet to be comprised only of air, not of combustion products. <S> That describes the air that is accelerated by the fan in a fanjet engine, which provides a substantial portion of the total thrust in such an engine. <S> Or if you prefer, rather than powering the fan by a turbine, you could power the fan or compressor by a piston engine. <S> The "motorjet" concept (see https://en.wikipedia.org/wiki/Motorjet ) used in the The Caproni Campini N.1 -- ( see https://en.wikipedia.org/wiki/Caproni_Campini_N.1 ) might seem to approximate this idea, but in the "motorjet" concept the compressed air IS mixed with fuel and ignited after compression, to provide more thrust than would be provided simply by allowing the compressed air to exit the nozzle without ignition. <S> This plane apparently never flew, but a similar engine was used to drive a snow sledge. <S> That seems to be a good match to what you are envisioning. <A> @jamesqf gave the correct answer in his comment. <S> Let me elaborate on why it would be inefficient. <S> Typical turbofan engine energy path is like this chemical energy (fuel) -> thermal energy (burning fuel) -> mechanical energy (low pressure turbine shaft rotating = fan blades rotating) -> mechanical energy (large volume of air accelerated out the back of the nozzle). <S> So 3 different conversion steps. <S> Each step is not 100% efficient. <S> You lose a decent amount of energy at every step. <S> So the more steps there are the worse. <S> Your proposed situation is something like: chemical energy (batteries) -> electrical energy -> thermal energy (heating the air) -> mechanical energy (low pressure turbine shaft rotating = fan blades rotating) -> mechanical energy ( <S> large volume of air accelerated out the back of the nozzle). <S> This has more conversion steps than a typical jet engine. <S> It will be less efficient. <S> The alternative path proposed by @jamesqf is chemical energy (batteries) - <S> > <S> electrical energy -> mechanical energy (propeller rotating) - <S> > mechanical energy (large volume of air accelerated past the propeller). <S> Do you see how this has one less conversion step? <S> you just go straight from electrical to mechanical energy with no thermal step in between. <S> Less conversion steps is better. <A> A turbojet with 'no ignition involved' is in principle possible, and it has been put into practice in the 1950s, in working prototypes of nuclear powered propulsion units. <S> https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19640019868.pdf https://en.wikipedia.org/wiki/General_Electric_J87
|
There was at least one piston-driven "jet" engine concept in which the air was NOT ignited after compression -- see for example the Coanda-1910 (see https://en.wikipedia.org/wiki/Coand%C4%83-1910 ).
|
What does the "DO NOT USE FOR NAVIGATION" indication mean? Sometimes when I'm browsing IAC charts online I find a "DO NOT USE FOR NAVIGATION" notice printed on the chart. Not always though. For example, have a look at the chart for Queenstown RNAV (RNP) Y RWY 05 .See the notice there? I have always wondered why do procedure designers put these notices on their charts. I find it almost contradictory, since I think these charts are the best source of information that an aircrew can have to navigate/maneuver. Isn't it ironic? I'm sure I must be missing something. Can anybody shed some light on this? PS: These are not SIM charts. These are real charts from the AIP. <Q> Unless it's an obsoleted procedure chart, it usually means that it's not complete. <S> The example you show has only the features pertinent to that approach, and its missing (for clarity) <S> the features needed for any other aviation in that area. <S> You must use a sufficiently complete chart for navigation; the approach diagram is supplementary to your navigation chart. <A> When an aviation chart is marked with "DO NOT USE FOR NAVIGATION", it means that ... umm ... <S> it should not be used for navigation. <S> The question is why it should not be, because it appears that the chart/map is very accurate and hence it is thought that it can provide details for navigation. <S> There are several reasons: <S> A newer version might be available and hence making older versions obsolete. <S> It may not be according to scale and can cause confusion. <S> It may not show air routes. <S> On the contrary, a chart can be used for navigation when it has the following (yes, AOPA said it) : topographic features hazards and obstructions navigation routes and aids <S> airspace airports <A> In some countries, administrative and legal reasons require that label, because maps officially usable for navigation may need process used for completion including various warranties, for example: <S> included map layers collected from their respective sources can be no more than 3 months old <S> the map got reviews and approvals prescribed by the process – all documented, with clear responsibilities by adhering with the process, the map received official certification and then catalogization etc. <S> The same company can produce ad-hoc maps from similar sources, of similar quality which still did not go through the entire (quite expensive) process and therefore they are mandatorily marked as "DO NOT USE FOR NAVIGATION" which is also connected to various legal implications. <S> So such a label might not inevitably mean that the map is missing something. <S> Even after closer look, it can appear 100% complete. <S> But it should not be used as official navigation aid. <S> For example, if an insurance event will occur where navigation can be at least slightly involved (or even theoretically), finding out that such a map was used for navigating will give aces into hands of the insurance company. <A> I do not believe the reasons stated in other answers. <S> The only difference between this approach plate http://www.aip.net.nz/pdf/NZQN_45.1_45.2.pdf and other approach plates for the very same aerodrome in the same AIP like http://www.aip.net.nz/pdf/NZQN_43.1_43.2.pdf or http://www.aip.net.nz/pdf/NZQN_45.3_45.4.pdf (also RNAV, but RNAV GNSS, not RNP) is the type of the approach. <S> The level of details of the map, for example, is exactly the same. <S> One needs special equipment and a special approval for this approach and cannot just fly it according to the map or select it in a normal Garmin. <S> The plate misses something important and it is NOT the details of the map. <S> These are the actual minima to be used for the approach (I do not get what other navigation some suggest other than the approach for which the map only exists...). <S> Notice the important notice: Minima figures are indicative only. <S> See CAANZ RNP-AR operator approval for specific procedure minima. <S> So this approach plate is not enough, more information is needed to properly perform the approach. <S> Not to do other unspecified navigation, no-one would do that, but to fly the approach (or the associated missed approach procedure). <A> In addition to the other excellent answers, because the publisher expects to be compensated for creating the charts. <S> In other words, they don't want you downloading free stuff, they want to sell you approach plates needed for actual flight. <S> They put this tag on any print or electronic version promulgated for training or general reference. <A> The simple answer is that the chart is or will become outdated. <S> As a pilot you need to have current charts when flying. <S> The marking shows that the publisher does not take any responsibility for the currency or accuracy of the free chart found on internet or in training material. <S> You can buy sets of current charts and subscribe to updates to always have a current set. <S> Not to promote this here, but one example of company selling charts is Jeppesen. <S> http://ww1.jeppesen.com/documents/aviation/business/ifr-paper-services/glossary-legends.pdf <A> That could be because it is missing features for clarity, is a training tool, or, as is this case for Queenstown, because pilots must have additional certifications in advance. <S> It is very rarely because a chart is out-of-date since why would anyone update a chart that is out of date? <S> Whatever the reason for the warning, a chart with this prohibition on it is intended to be used to assist a pilot who already knows whatever it is they need to know (as highlighted on this one with the text boxes in the lower left corner), but can not be used safely by anybody who does not already know how to navigate here.
|
The really simple answer is that the chart does not contain everything a pilot needs to know to navigate safely.
|
Fine for operating not single-pilot certified jet with one pilot Are there any clear-cut fines for flying an aircraft like a Global 5000 which is not single-pilot certified by a single pilot? And what would be the probability of being caught and how would they catch you? <Q> According to FAA Order 2150-3B in Appendix B <S> That is what I would expect would happen in real life if the FAA investigator thought that the pilot had no good reason for operating without a co-pilot. <S> I disagree with the other answers that claim it would be quickly reported. <S> Unless an informed passenger noticed it and reported it, I doubt it would get reported by anyone else. <S> The fuel guys have no idea what operating limitations are or who is operating the plane. <S> In many cases, crew and passengers are long gone by the time the fuel truck pulls up. <S> For the fuel truck to deal with just one guy or to fuel an unoccupied aircraft is commonplace. <S> For all the fuel truck guy knows, there could be crew inside the aircraft doing stuff. <S> He has absolutely no idea what the operating situation of the aircraft is. <A> FAA Order 2150-3B outlines the enforcement actions that the FAA may take. <S> Here are a few: <S> Civil penalties (cash fines) of up to \$50,000 for individuals and small businesses and up to $400,000 for larger businesses Suspension or revocation of your license Seizure of the aircraft Lien on the aircraft up to the amount of the civil penalty Medical denials <S> What exactly the FAA decides to do when it finds out is up to the FAA and subject to the surrounding circumstances. <S> If you moved the airplane from Podunk A 10 miles to Podunk B, or if you decided to buzz the Whitehouse and wave to the President, these would be evaluated differently. <S> At the very least your license would probably be revoked or suspended, the FAA doesn't take that very lightly (it is not done often). <S> Most likely you would not be given jail time, as this particular violation doesn't fall under one of the criminal violations (see page 4-39 in linked document). <S> As far as probability, it would be high, as John K says, you need to be around a lot of ground people (fueling, movement, etc). <S> They would catch you by noticing that you are the only pilot in the cockpit when the aircraft starts moving. <S> Not to mention that the aircraft is not single-pilot certified for a reason, it would be difficult to fly it by yourself (not necessarily impossible, but you will probably be noticed by ATC as you try to do a lot more workload than your resources allow). <A> But you could probably get away with it a few times. <S> Penalty for that kind of thing would depend on the circumstances and motivations. <S> At minimum a fine of a couple grand and a license suspension for a number of months. <S> A professional pilot who depends on his/her license would be insane to do it unless it was for life and death reasons (like escaping from some dangerous place). <S> Possibly jail time. <S> Authorities in the 80s and 90s started to revise regulations to add the option of criminal liability for certain violations on top of administrative punishments, to give the rules more bite.
|
If there was some good reason and the pilot's record was clean otherwise, they might change it to a warning. The probability of getting caught would be pretty high because you would be around ramp crew all the time and somebody would notice there's only one pilot aboard when there are normally always 2. (penalty guidelines) the recommended penalty for "Failure to comply with operating limitation" is a 30 to 90 day license suspension.
|
Between a helicopter and an airplane, which requires more power to fly, for a given TOW? For the given same mass (say it 400kgs), which one requires more power (in HP) between helicopter and airplane? Say that both are designed maximum (the required material are considered during design) to minimize the required power. Edit : Question should be like this: Which one is requires more power to lift a helicopter (to make it hover) and to make a fixed wing airplane fly? Not to make them move at the same speed. <Q> Airplanes fly by creating lift from their wings. <S> This causes some drag, but good wings have lift/drag ratio's in the range 15-20. <S> That means the lift-dependent drag is only 5% of the lift. <S> Helicopters on the other hand generate lift directly from trust; there is no multiplier involved. <S> E.g. a 4000 kg plane will have a weight of 40.000 Newton, so the drag incurred will be 2000-3000 Newton. <S> A 4000 kg helicopter will need to produce 40.000 Newton of lift just to hover. <S> Of course, planes and helicopters both have additional drag from forwards airspeed, and for planes this is obviously unavoidable to prevent stalls. <A> Let's look at this in an extremely simplified fashion. <S> An aircraft with mass $m_{ac}$ stays up in the air by pushing air downwards, or specifically, by giving a mass flow <S> $\dot{m}_A$ <S> [kg/s] of air a certain speed downwards <S> $v_A$ <S> [m/s]. <S> This gives a momentum 'flow' $\dot{m}v$ <S> [kg m/s²] which is the lift force <S> $F_{lift}$ <S> [N] $$F_g = <S> F_{lift}$$ $$ <S> m_{ac}g = <S> \dot{m}_A\cdot v_A$$ <S> The power required for this comes from having to give the air flow a kinetic energy flow $$ <S> P_{lift}=\dot{m}_A{v_A}^2$$ <S> This is purely the power required for lift generation (power required to overcome induced drag, specifically). <S> One can see that by making $\dot{m}_A$ arbitrarily large and $v_A$ arbitrarily small (while keeping their product constant), the power requirement can be made arbitrarily small. <S> This can for example be done by making the wings or rotors longer so that they affect a larger air volume (and thus air mass), or by flying faster (so they move through more air, again increasing the mass flow). <S> However, this assumes perfect efficiency. <S> In reality, wings will experience drag even if no lift is being generated, and the same goes for the fuselage. <S> You will often find a minimum of total power required at some speed such that the induced drag is quite small but the friction drag is not quite as large. <S> This goes for both fixed and rotary wing aircraft. <S> These factors are a result of the aircraft's practical design, not of theoretical considerations. <S> So, there is no theoretical answer to this question. <S> There is only a practical answer, which is that hovering in a helicopter is very inefficient and requires a lot of power (because it can only affect a small mass of air since it is not allowed to move), so given the constraints in your question (a hovering helo vs a fixed wing at 100kts), the fixed wing is probably more efficient in practice. <A> Helicopter rotors need to provide enough thrust to compensate the weight of the helicopter: $T_H = W$ . <S> Fixed wing aeroplanes need to provide enough thrust to overcome drag, while the wing lift compensates for weight. <S> As @MSalters correctly states, the wing provides much more lift than drag, plus there is a fuselage & tail as well. <S> Torenbeek Synthesis of Subsonic Airplane Design gives some L/W ratios of complete aeroplanes, a medium size turboprop such as the F-27 is listed as having an L/D of 13.8 during takeoff, since aspect ratio A = 12. <S> So this fixed wing aeroplane would have to provide 1/14 of the thrust of a helicopter of the same T/O weight: $T_F = W/14 <S> $ <S> Simple impulse theory gives the following relation between thrust T and power P: <S> $$ T = C_T \cdot <S> \rho <S> A { <S> (\Omega R)}^2$$ $$ P = <S> C_P <S> \cdot <S> \rho <S> A {(\Omega R)}^3$$ <S> And therefore at constant disk area and <S> tip speed: $$C_P = \frac{{C_T}^{3/2}}{\sqrt{2}} = <S> > P_F = <S> (P_H/14)^{3/2} = 0.1$$ <S> Tip speeds <S> $ <S> (\Omega R)$ of propellers and helicopter rotors are comparable, disk area of a fixed wing <S> is lower. <S> So the required power at constant weight for a fixed wing is at least an order of magnitude lower than for a helicopter. <A> Of course you can make the airplane draggy enough that it can require more power than the helicopter to go 100kt if you want, and there are plenty of those, but I assume we're talking about optimized craft here. <A> the helicopter's "wings" (its main rotor blades) are moving through the air at something like 400 MPH at their tips even while the helo itself is sitting in ground effect and not traveling through the air at all. <S> This requires work, and to fly forward, the engine has to overcome the main rotor drag at the same time it has to overcome the fuselage drag. <S> So: more drag for the helo, less for the Cessna 150.
|
If you mean for a 400kg helicopter and 400kg fixed wing airplane to move at 100kt, it's generally going to be the helicopter that requires more power since the whole egg beating thrashing mess is a lot less efficient at converting energy to forward speed.
|
DA40 fuselage static ports / G1000 not in AFM I’m a flight instructor who just switched from instructing in 172’s to flying the Diamond DA40 and am confused about a few things. Our DA40 has two static ports, one on either side of the fuselage. This doesn’t make sense to me because the AFM in the airplane says the static ports are on the left wing along with the pitot probe. I haven’t been able to find anything online about these static ports, and I’ve only seen one DA40 AFM. My second confusion is, the airplane is equipped with a G1000; however, the AFM in the airplane doesn’t say anything about the G1000, there is only a cockpit reference guide for it. Would this indicate an upgrade from original avionics? Would it be in the maintenance records? (Mx records was my next stop) <Q> I found the answer by further reading the AFM. <S> On DA40's with an auto pilot installed, optional static ports may be added to the fuselage. <A> My guess if you have an older airplane with a separate autopilot that is not integrated with the G1000. <S> If you have an autopilot with a separate static system, such as the KAP-140, there will be additional static ports. <S> They should be noted in the AFM, but in the supplement section referring to the KAP-140 autopilot. <S> In contrast an airplane with a G1000 integrated autopilot (GFC-700) <S> the autopilot will share airdata with the G1000, so it will not have an extra static port, but rather just a wire to get airdata from the GIA. <A> I'm doing my flight training on DA40NG. <S> Are you thinking about alternate static valve? <S> also stall warning port on left wing leading edge. <S> About G1000 shouldn't explain alot on AFM <S> but you should read more on G1000 manual. <S> I used to watch a video on youtube an hour long explained about G1000 all techincal stuff and more.
|
It's correct that there is static port on left and right side of fusalge more like rear and pitot tube on left wing,
|
What is the best design to stack wings of a triplane? I would like to design an ultralight airplane, which probably the total mass will be around 400kg. The speed should not exceed 200km/h. Forget about what the engine I will use. I intend it can land and take off in a small road and/or in a common road, which the road line not more than 2.5m each direction. If I have to occupy both direction, mean the road width is just around 5m , plus small space beside the road in both side. Beside the road, normally many electrical poles. So, not many space available. To tackle the situation, I need to change wings design without reduce the wing area (A in m2). Was discussed earlier here some of the triplanes that were used during the WWII. If they were used during the war, that mean that such design was safe enough. But, I have a bit confusion regarding how to place the wings' stack? Here are the three options design. The wings stack are lean to the tail. The wings are stacked exactly over another. The wings are lean to the nose. Another thing. We know that the closer wing to the ground will produce what is called earth deflection (CMIIW about the terminology) during take off. That will make the plane requires longer time to take off. In my opinion, the same effect will occur if we stack the wings too closed one to another, especially if the wings are stacked lean to the nose, the deflection will hit the lower trailing edge if there is no enough space. So what is the best design in this case? And what is the best space? <Q> Wing stagger was mostly chosen to improve pilot vision : In single-seaters, a positive stagger would allow to place the upper wing ahead of the pilot, improving the field of view. <S> Large bi- and triplanes had no stagger. <S> Here the pilot sits ahead of the wing and large aircraft fly mostly straight, reducing the need for the pilot to observe the airspace around him. <S> It had a wingspan of only 4 meters and a total weight of just 230 kg. <S> Emilio Pensuti, a test pilot with Caproni during WW I, designed it as an easy to fly aircraft for the common man. <S> Therefore, it is sometimes also called the Caproni-Pensuti triplane . <S> The first version was powered by a 35 HP Anzani engine while a later development, the Breda-Pensuti 2, used a 80 HP engine. <S> Of course, its wings had no stagger. <S> Drawing of the Pensuti triplane (picture source ). <S> Yes, it did fly! <S> Pensuti triplane in flight (picture source ) <S> If you build one, I would strongly suggest to change the wing airfoil to a thicker one with the same amount of camber. <A> Do note that total wing area of a multiplane (biplane or triplane) wing configuration does not give the same performance as that same area with a monoplane. <S> For a monoplane, all the wing deflects air downwards yielding lift. <S> For a bi- or tri-plane, the wings all deflect the air together, reducing the effect of each. <S> So a Cessna 152 with a 33 foot span would not fly if converted to a biplane with a 16.5 foot span or a triplane with an 11 foot span, to give an example. <S> Thus the concept of span loading. <S> All fixed wing aircraft get their lift by deflecting air down as they pass. <S> The amount of air they can deflect depends on their speed, their span and their weight. <S> For minimum airspeed, the use of high lift devices is more effective than adding multiple wing planes. <S> The main reason biplanes and triplanes were common in WW1 was for strength with the materials and understanding of aerodynamics at the time. <S> You might also note that many single place experimental aircraft designs have 5M spans already. <A> To answer your explicit question, I'll note that both the Sopwith Triplane and the Fokker Dr. <S> I are arranged in the 'lean towards nose' style. <S> However! <S> The Wainfan FMX-4 <S> Facetmobile might be of interest. <S> Wingspan: 15 ft (4.6 m) <S> Empty weight: 370 lb (168 kg) <S> Gross weight: 740 lb (336 kg)
|
However, if you look for a proven design of a very compact triplane, I would like to suggest the Italian Pensuti triplane .
|
How can the F-15 and Su-27 achieve a high top speed without variable wing geometry? I watched a documentary once that explained, I believe, how the Su-27 and similar aircraft such as the F-15, can achieve a high top speed without variable wing geometry. How does this work? How do they achieve high performance without swept wings in the F-15, Su-27, and similar aircraft? <Q> They simply have enough thrust to do so with their given wing. <S> There is no rule that high speeds are associated with variable sweep wings or that you need such a wing to go fast. <S> As a matter of fact many of the testbed super sonic aircraft as well as the really high speed stuff dont have swept wings. <S> Wing design can effect efficiency (which may or may not be a concern in fighters) and can limit top speeds but that simply means that for a fixed shape wing it must be optimized for a desired speed range. <A> Another signifficant factor is because the F-15 is an airforce aircraft. <S> So, it doesn’t have to land on a carrier. <S> Hence it can take plenty of runway length to land, which means it can touchdown at a higher speed. <S> So, its wings can be permanently swept at relatively high angle, because there is no need to have heavy wing pivots that enable them to sweep forward and allow lower speed flight for carrier landings. <S> In comparison, the F-111 had a variable geometry wing so it could fly slower, when the wings were swept forward, because it was intended as a joint aircraft, and so there was going to be a Navy version, that had to be capable of landing (and takeing off!) on carriers. <S> The F-111 wing sweep is from 16 to 72.5 degrees. <S> In comparison, the F-15 leading edge of 45 deg. <S> The wing angle is asignificant factor that helps define the mach number at which the shock cone from the nose will impinge the wing tips. <S> See below. <S> If the wing tips are outside the shock cone and in the sonic flow, the handling charteristics, as well as the increased drag, is likely to be very undesirable. <S> The formula linking mach number and shock angle is given here by NASA. <A> All sweep does is make the air think the wing's chord to thickness ratio is higher, or you could say thinner in relation to its chord than it really is, for a given wing area. <S> The benefit is mainly for wings with a fairly high aspect ratio, that is long with a narrow chord. <S> Fooling the air into thinking the wing is "finer" than it really is delays shock wave formation to a higher speed than if the same wing, with the same chord and length, was straight. <S> The F104 is the most extreme example of this. <S> Ultra low aspect ratio, thin biconvex supersonic airfoil, no sweep at all required because the benefit is negligible.
|
Airplanes like the F-15 with a low aspect ratio, fairly thin wing don't really need a lot of sweep because their airfoils are already really thin relative to their chord.
|
Do any aircraft have a "self-contained ILS"? The ILS is an invaluable aid to pilots, especially those operating to/from the many airports where poor weather is common (low-visibility operations would be completely impossible without an ILS); however, ILSs are expensive and maintenance-intensive, with the result that many smaller airports lack ILS capability. Also, the requirement for a considerable quantity of pre-emplaced infrastructure obviously precludes one from performing an off-airport instrument landing. On the other hand, the technology is available to guide an aircraft down to a precision landing at an arbitrary point on the ground, and much of this technology is already mandatory equipment on aircraft; GPS (which most if not all aircraft already have anyway) could be used for horizontal positioning and guidance and for plotting a landing route about the local terrain, the radar altimeter (also standard aircraft equipment) would provide vertical guidance, and a forward-looking radar system (also already standard, in the form of the aircraft's weather radar, which should only require an additional driver or two to add a terrain-sensing mode) would allow fine control of the aircraft's flightpath for the landing itself (where GPS, with its ~10m CEP, is insufficiently precise and accurate for a safe touchdown) and allow the aircraft to orient itself in space (as GPS tells the aircraft where it is, but not which direction it's pointing). Additional equipment that would be useful and could easily be added would be a second weather radar (to allow the pilots to continue to monitor the weather even with one radar in terrain-mapping mode), a Doppler radar system (to warn the pilots of dangerous windshear, microbursts, etc.), and a forward-looking lidar system (to provide advance warning of clear-air turbulence along the approach path). With the appropriate software, these instruments could be used to plot and fly a safe instrument landing at a noninstrumented airport, or even at a non-airport; this latter capability would be extremely useful for medevac and SAR pilots (whose duties, by their very nature, involve operations to and from off-airport locations, frequently in poor weather) and for military helicopter pilots (same reason). Are there any aircraft already equipped with such a "self-contained ILS"? <Q> Approaches guided by GPS are called RNAV; it can provide both lateral and vertical guidance, in some cases to the same precision as ILS Cat I, without need for a radar altimeter--which is not standard equipment. <S> (There are also non-GPS ways of using RNAV, which are mainly used by older airliners that haven't been upgraded yet.) <S> Note that standard GPS has accuracy of 100m; SBAS (aka WAAS) gets that down to 7.6m. <S> Both are standard in aviation GPS units these days, and GBAS (aka LAAS) will eventually get that down even further. <S> There are already three times as many RNAV approaches as there are ILS approaches with more appearing every day, and most aircraft are now equipped to use them or probably will be soon. <S> IOW, the essence of what you propose is already here. <S> Instrument approaches do have to be pre-planned to ensure obstacle and terrain clearance, so airplanes can generally only use them to land at airports. <S> (The rules are different for rotorcraft, and that's generally what you'd use for rescue, but I'll have to leave the specifics to someone else.) <S> Many large aircraft carry weather radar, but it's too heavy for light aircraft; both can use satellite weather data services, in addition to getting weather updates via radio the traditional way. <A> You don't need nearly all the equipment you mention. <S> I fly . <S> Units as small as a Garmin 430 are capable to providing all the facilities you need to fly GPS/RNAV approaches. <S> If your unit has WAAS capabilities <S> you can fly to even lower minimums. <A> This does exist, and is used by US military aircraft. <S> It's called a Self-contained Approach (SCA) or Independent Precision Radar Approach (IPRA). <S> The primary user of these approaches is Air Force Special Operations Command on aircraft like the MC-130 and AC-130. <S> Regulatory guidance is contained in the AFI 11-202v3 AFSOC Sup , section 7.4, and operational procedures would be governed by the applicable AFI 11-2MDS volume 3 or another MDS-specific publication, which may be a controlled item. <S> Shooting one of these approaches involves the flight crew looking for obstacles or obstructions; choosing the planned glideslope, and creating the plan, including update, missed approach, and descent points. <A> An ILS approach consists of a minimum of a localizer and glide slope transmitters. <S> Both transmitters are ground based, in a fixed location. <S> While the creation of some other reference point, using GNS or even inertial navigation might be possible, it does not directly emulate ILS. <S> Furthermore, if one were to recreate the references to a landing zone using some other form of navigation, it is likely that the exact emulation of a localizer and glide slope might not be exactly emulated. <S> Consider that MLS was intended to be an ILS substitute, and it offered a variety of localizer courses, and a variety of glide slope paths. <S> While it is true that self contained navigation systems, including INS, and even varied techniques such as radar mapping, or even IR lidar mapping, could be employed, it is unlikely and perhaps inefficient to have them emulate what an INS does. <S> Therefore the likelihood of a "self contained ILS" appears to be very close to zero. <S> While there are many systems and methods which will navigate to a given point, with the potential ability to align an aircraft for a landing, they do not match the essentials of an ILS, which is two ground based transmitters, one with lateral and the other with slope (vertical) guidance. <S> Finally, if one wants to consider self-contained navigation approaches, a study of missile guidance will yield scores of self-contained, and externally augmented approaches.
|
A great deal of aircraft are capable of flying GPS/RNAV approaches from big boys down to the little Piper Archer
|
Why can’t air traffic control radars determine the altitudes of primary targets? There are two types of returns that show up on an air traffic controller’s radar screen: Secondary returns are not, strictly-speaking, radar “returns” at all, but, rather, signals automatically broadcast from an aircraft’s transponder, containing encoded location, altitude, airspeed, identification, flightplan, aircraft type, etc., data retrieved from the aircraft’s onboard instruments. These are highly valuable, but, obviously, can only be used with aircraft equipped with a functional transponder which have said transponder turned on and transmitting non-bogus data. Primary returns , in contrast, are true radar returns – direct reflections of the radar’s beam from the surface of an aircraft, bird, cloud, piece of debris, missile, tree, UFO, balloon, hailstone, or whatever else happens to be in the air at that moment. As they merely require that an object be located where the radar beam can reach it, they are of great use in tracking aircraft with nonfunctional transponders (due to, for instance, a general electrical failure or simply a faulty transponder ), aircraft in combat zones (for whom broadcasting an identification signal would be a great way to get shot down), pieces of aircraft , flocks of birds, or whatever other non-transponder-equipped objects one has a desire to track. One common limitation given for primary radar returns is that they provide no altitude information, but only positional information. But this makes no sense, as determining the position of a target requires knowing its elevation angle, azimuth, and distance relative to the radar installation (without knowing the target’s distance, it could be located anywhere along a line extending from the radar’s location out to infinity; without knowing its elevation angle, it could be located [within the altitude limitations of the object generating the target] anywhere along a circular arc extending from the horizon to the zenith at the specified distance from the radar; without knowing its azimuth, it could be located anywhere along a horizontal circle centered in the sky directly above the radar), and, if the elevation angle, azimuth, and distance of the target are all known, that also pins down the target’s altitude – not just its location. Besides, military radars can and do provide altitude information for primary targets (they would be useless otherwise, as intercepting an enemy aircraft requires knowing both its position and its altitude, and enemy aircraft are unlikely to oblige a radar’s request to provide a transponder beacon signal that would aid immensely in shooting them down), which has proven valuable numerous times; for instance, the accident investigation that eventually produced the NTSB’s very first AAR used data from a military air-defence radar to determine that a 727 that crashed into Lake Michigan had descended steadily into the water without levelling off, instead of suffering an uncontrolled excursion from level flight, while, more recently, primary returns received at several military radar sites in Massachusetts showed that EgyptAir Flight 990 pulled out of its initial dive before making a second and final plunge. So what prevents civilian ATC radars from displaying altitude information for primary targets? <Q> without knowing its elevation angle, it could be located anywhere along a circular arc extending from the horizon to the zenith at the specified distance from the radar <S> Well, not quite. <S> Aircraft are generally much more restricted in their vertical positioning. <S> If there's a return from 30 miles away, that aircraft can't be overhead. <S> (And radars normally have a maximum elevation to the beam, often around 70 degrees). <S> This document suggests that (at least as of 1989) determining elevation angle was very difficult for ATC primary radar. <S> It was possible by cross-correlating information from multiple feeds, but that this was not routinely done. <S> The document focuses on how useful that would be for helping to remove ground clutter. <S> Even if some elevation information were available, that data might not be presented to controllers unless it were of a useful precision. <S> If the precision were worse than say 1500 feet, would that be useful? <S> Radartutorial suggests that vertical discrimination (or 3D radar) requires extra equipment and is therefore more expensive. <S> Since ATC can get this information by secondary radar, the expense of gathering it via a 3D primary system is avoided. <S> Besides cost, older 3D radar would scan a region more slowly than a 2D radar. <A> Primary (2D) <S> ATC radar provides azimuth and slant distance but not elevation. <S> If you use the slant distance as horizontal distance, it will be somewhat inaccurate, but since aircraft don't fly all that high (and shouldn't be above 10kft MSL at all without a working transponder), the error is minimal--and separation standards account for it. <S> Adding elevation scan (3D) would increase cost and slow scan rates yet add nothing when most aircraft have transponders anyway, so it's more efficient to live with the limitations. <A> The limitations of ATC radar are simple: they are not designed to provide more than distance and heading for primary returns. <S> PAR (precision approach radar) is an example of a radar system which provides altitude information, and is configured to allow the controller to provide vertical approach guidance information. <S> There are many radar systems which provide elevation information, for example on some SAM (surface to air missile) systems. <S> It's possible, but someone has not spent the additional taxpayer funds for ATC purposes. <A> The new types on the market can do this. <S> See for instance Thales STAR-NG (altimetry option), Hensoldt (previously Airbus) ASR-NG, ... <S> You can also upgrade existing radars, such as the FAA ASR-9, as you can for instance see on the website of Intersoft. <S> There are however a number of limitations in performance, and more importantly, civil ATC procedures are not designed to PSR derived altitudes. <S> But even if not used operationally, it still provides a benefit in tracking and clutter rejection. <A> Civilian Primary Surveillance Radar (PSR) does not provide elevation angle, and thus no altitude information can be displayed. <S> The location is therefor not accurate either, but that doesn't matter for ATC purposes. <S> Civil ATC does not need altitude or height information to provide traffic separation when using PSR. <S> They simple make sure the dots on the screen don't collide. <S> For traffic separation you don't need to know the exact position of the aircraft; as long as the plots are separated on the 2D screen, the will be separated in the 3D world. <S> Typical PSR displays are based on a flat world assumption; they only plot azimuth and range. <S> As long as the plots are separated by 5NM, no matter what the altitude difference between the aircraft is, they are safely separated for ATC purposes. <S> As you correctly observed, if you would want to determine the exact 3D position of the aircraft based on a primary radar, you need azimuth, range and elevation angle. <S> The PSRs used by civilian air traffic control don't measure the elevation angle, because this would require more sophisticated radar hardware and would therefore be more expensive. <S> The added value of the elevation angle is that the exact position including the height of the aircraft could be measured. <S> However, that is of limited value. <S> In air traffic control, vertical separation is not based on geometric altitude but on barometric altitude or flight level. <S> Using elevation angle, the primary radar would give the geometric height. <S> However, the barometric height showed in the cockpit to the pilot can easily be several hundreds or thousand feet off from the geometric height. <S> So for the communication between ATC and pilots, geometric height measured by primary radar is mostly useless. <S> Aircraft are vertically separated by putting them on different altitudes/ flight levels, based on the baro altimeter in the aircraft. <S> This altitude is transmitted to the secondary radar which allows display of that altitude and separation based on altitude difference. <S> This is the basis for communication of vertical position information between ATC and pilots. <S> In short, the costs of adding elevation angle measurement to civilian primary ATC radar outweighs the benefits.
|
Besides, military radars can and do provide altitude information for primary targets
|
When is aileron trim used? There is an aileron trimmer in some Boeings. When and why should it be used? P.S. I'm not a pilot, can you answer with less smart words? <Q> Given your request to "answer with less smart words," it's hard to know what knowledge can be assumed, but I'll give it a try. <S> Let's say you're hand-flying the airplane straight and level, and you find that the right wing keeps wanting to drop, which you prevent by using left-aileron pressure on the control yoke. <S> You can "trim out" the need for that left aileron pressure by rotating the aileron trim to the left (counter-clockwise). <S> In other words, you don't fuss with it unless you notice a need to fuss with it. <S> In 12 years on 727s and 747s, I think I used aileron trim less than a dozen times. <S> The reasons that I can think of offhand that would make you want to fuss with it include: <S> The trim wheel was inadvertently moved (or deliberately as a bit of a prank) by someone. <S> A fuel imbalance has occurred between the fuel in the left and right wings. <S> You're doing a 3-engine ferry on the 747 or continuing a flight after having lost an engine. <S> To the best of my knowledge, all Boeing aircraft have aileron trim capability, not just some. <S> Indeed, I would be surprised to find any transport category aircraft that does not have aileron trim capability. <S> Essentially, aileron trim can be used to to keep and airplane from responding to a situation where one side of an airplane is significantly heavier than the other side. <A> In short almost NEVER. <S> I have flown the A320/A330/A340 and they don’t have an option to trim the ailerons. <S> I am currently flying the 777, and when you feel that the aircraft is not flying straight we generally tend to use the rudder trim over the aileron trim. <A> Aileron trim is used in case of wings fuel assymetry, this is used until you correct the assymetry by providing the engines from a single wing.
|
Aileron trim is not often used for the simple reason that in normal aircraft operation, it's usually set where it should be from the previous flight.
|
How does an aircraft maintain level flight while accelerating? Let's assume a plane is initially moving at constant speed, level flight with a certain angle of attack. If the plane's thrust is increased, the plane's horizontal speed increases (at one point the drag force catches up and becomes again equal to thrust. The speed becomes constant at that point). But while the speed is increasing, the lift would increase and would the plane start climbing. How can we keep the plane in horizontal level flight while the speed is increasing? Does increasing the thrust need to be simultaneously complemented with controlling some of the rear lift surfaces to oppose the natural lift increase due to the wing? <Q> As the op points out, the increase in speed through the air increases lift, and the AOA (angle of attack) needs to be reduced. <S> This is normally done with stick (or yoke) input, followed by trim. <S> On most aircraft the lowering of the nose would be accomplished by lowering the elevator (and/or raising the trim tab) on the rear horizontal surfaces. <A> „Normal“ aircraft are statically stable in pitch, meaning that a disturbance in either speed or angle of attack will lead to a change in aerodynamic forces towards restoring the old state. <S> In your case, adding thrust will increase speed and hence lift, so the aircraft will naturally pitch up to restore its old speed and angle of attack (now in a climb due to added thrust). <S> To prevent this and keep level, angle of attack must be reduced to keep lift equal weight at the higher speed. <S> Note the stability in angle of attack and speed is a simplistic view - real life might be more complicated, as the aircraft will most certainly enter some form of oscillation before (again, on an aircraft of conventional design) settling into a new state. <S> Some electronic flight control systems are designed to pronounce this self-restoring tendency to the trimmed speed (e.g. that’s Boeing’s Fly-by-wire philosophy), some other flight control systems are designed to suppress it (e.g. on a Fly-by-wire Airbus). <S> Hence (and slightly on top of what was actually asked), on Fly-by-wire Boeings and conventional aircraft, the throttles are more or less „up/down“ controls and the yokes are more or less „fast/slow“ controls, while on an Airbus <S> it’s <S> vice versa (and sticks not yokes). <A> Trim for straight and level just as you normally would. <S> If you increase power you will need to retrim or apply nose down. <A> The increased airspeed, including the increased prop wash, also flows across the elevator (conventional aircraft), and for a typical (non-aerobatic) aircraft, the center of lift is a bit in front of the center of mass, and the elevator produces a bit of downforce to compensate, and the increased air speed over the elevator would also result in an aircraft pitching up. <S> For model aircraft, the prop axle is oriented a bit downwards (to reduce pitch reaction to increased thrust), and also a bit sideways (to reduce prop yaw effects). <S> I don't know if full scale aircraft do this. <A> Compensating for more lift does not require more down force ... <S> more lift while in stable flight WILL result in a climb, period. <S> The compensation is to reduce angle of attack for the purpose of maintaining the same lift at a higher air speed. <S> The horizontal stabilizer does not "push down" on the aircraft as a whole - <S> it pushes up or down on the tail to control this angle of attack. <A> Engines do not control speed in an aircraft. <S> Elevators control the speed. <S> Consider a glider (sailplane) which can control its speed quite happily without any engine thrust. <S> Engines control the rate at which total aircraft energy, kinetic plus potential, is gained or lost. <S> Looking at the exact wording of your question, 'how to maintain level flight while accelerating' ... <S> Accelerating means increasing speed. <S> To achieve this you push the stick forward. <S> The increased speed means increased kinetic energy, which has to come initially from potential energy, so there is an immediate loss of height. <S> The increased speed also means increased drag, so an increased rate of loss of energy and so height. <S> To maintain height, that is, level flight, you would increase engine power to match the increased drag, and accelerate sufficiently slowly that the engine would also provide the increased kinetic energy. <A> Yes, an increase in airspeed creates more lift which requires more down force from the tail to keep the airplane from climbing. <S> To maintain straight and level flight the total lift forces must equal total weight (1G). <S> In order to compensate for the increased lift more down force must be generated to balance out the increased lift. <S> So cruising at high speed puts more stress on the wings and horizontal stabilizer / elevator.
|
Simply put, in the scenario stated, to maintain level flight the appropriate amount of nose down input would be applied. Assuming a conventional, stable aircraft, most likely yes (unless the changed thrust moment around the centre of gravity balances the aircraft in trim in the new aerodynamic state).
|
Is the purpose of variable pitch propellers to maintain an optimal angle of attack? I recently had a discussion with an aviation expert, who works as a Flight Instructor, about constant speed propellers - variable pitch propellers - on light piston aircraft. I have always known that these kind of propellers are capable of changing their pitch angle in flight in order to keep propeller blades at their optimum angle of attack across a wide speed range, while maintaining constant RPM. Therefore, they are very efficient over a wider airspeed range compared to fixed pitch propellers. A change in TAS in flight, for example, would lead to a change in pitch, in order to restore the optimum angle of attack of the propeller blades. To my surprise, the instructor told me that what I knew about variable pitch propellers was not true: he explained to me that a change in TAS during the flight would lead to a change in the angle of attack of the blades, but that doesn’t mean that the resulting pitch change would lead to the optimum angle of attack. His answer really surprised me, so I am now wondering what is the purpose of variable pitch propellers then. I understand that there may be a point where the PCU and CSU won’t be able to adjust the pitch to the most optimum angle of attack, but I thought that during normal operating speeds the purpose of this kind of propellers was to provide the blades with the most efficient angle of attack. Am I wrong? <Q> What you know about variable pitch propellers is generally correct. <S> If you make a slight change, your flight instructor would not have had any reason to object: They keep propeller blades near their optimum angle of attack across a wide speed range. <S> As the distance from the hub increases, the blade section gains circumferential speed while being in the same forward speed as all other sections. <S> Therefore, the twist of the propeller blade should change linearly from the hub to the tip. <S> If you twist the full blade at its root, you add a constant change to each cross section, so at high speed the root of the blade sees too high an angle of attack and the tip has too little angle of attack. <S> Normally, the section at approximately 75% of propeller span is kept at its ideal angle for the best overall compromise. <S> That is good enough for practical use. <S> Ideally, the propeller would spin faster with increasing flight speed, but that would require a gearbox and switching gears with the limited speed ranges of combustion engines, would deliver little thrust at the beginning of the take-off run and at high speed you would run into compressibility problems at the tips much sooner - practical high speed propellers spin more slowly than typical low-speed propellers. <S> If you look at the efficiency chart of a three-bladed variable pitch propeller below, you will see that efficiency peaks for one speed (given as an advance ratio in the plot below) and one pitch angle. <S> This is when the full blade is flown at the optimum angle of attack for each section. <S> This optimum would shift to higher speeds for less twist and lower speeds for more twist. <S> Efficiency chart of a variable pitch propeller. <S> Source: <S> McCormick B.W. Aerodynamics, Aeronautics &Flight Mechanics. <S> John Wiley & Sons, Inc., 1979. <A> The purpose of a variable pitch prop is to allow is to allow the pilot to select where on the engine's power curve (s)he wishes to operate the engine. <S> When full power is needed, as for takeoff and initial climb, the throttle is fully opened and the pitch set as shallow as required so as to allow the engine to spool up to the peak of its rated power curve. <S> For economy cruise, the prop pitch is deepened to load the engine down to a lower rotating speed at which it produces less power and consumes less fuel. <S> In this regard, you can consider the pitch control on the prop as the analogue of the transmission in your car: <S> First gear = fine pitch, top gear/overdrive = coarse pitch. <S> Note here than this means a constant speed prop and engine combo to be the analogue of the cruise control system in your car. <A> There are two kind of propeller: Fix pitch propeller, which the pitch or we more familiar to say as the angle of attack (AoA) always same all the time, engine RPM is adjusted to meet requirement. <S> Constant speed propeller, which the engine RPM is variable due to the change in the pitch. <S> The first propeller is the old one, and cheaper. <S> No chance to change the pitch. <S> The pitch is normally low, around 5 degree (depend on the producer's design). <S> The latter one is more expensive and more suitable to be used in current flight. <S> A propeller with low pitch is suitable for take off, while high pitch is more suitable during cruise. <S> "High" here is depend on the producer, but will be around 15 degree, the maximum limit before it get stall, which mean the power from the engine is no more effective to move the airplane forward. <S> Low pitch with the fix pitch propeller <S> we can think like a car with low gear which is used to move a car from stop and then climbing a hiking road. <S> And after some distance, meet a flat and smooth toll road. <S> During climb, gear 1 (low pitch) is more suitable, but not while cruising in the flat and smooth toll road. <S> During cruising in that toll road is more suitable using gear 5 (high pitch). <S> The same thing is also apply to airplane. <S> During take off, airplane requires low pitch but high RPM. <S> That to allow the propeller to "bite" the air small by small, and slowly pull the airplane move forward, then take off, until it meet the cruise level. <S> After cruise level (which the airplane will force to be high speed), the propeller is adjusted with the suitable pitch to meet the suitable RPM , which is lower RPM but higher TAS or at least same TAS. <S> Lower RPM mean lower piston stroke per minute. <S> Lower piston's stroke per minute mean lower gas consumption. <S> So, the instructor word with " optimum " is mean " best gas consumption due to the lower RPM ". <S> Lower RPM will reduce the engine temperature, and finally will lengthen the engine life cycle.
|
Operating the propeller away from its design point incurs small losses since not all of the blade is exactly at its optimum angle of attack, but if you compare the overall efficiency with that of a single pitch setting, the advantage of variable pitch becomes obvious.
|
Is this Class G Airspace? So it's been about a decade since I got my private pilot cert and almost as long since I got to fly. My map reading is a little rusty. I'm trying to fly my drone at a local park and it's warning me that I'm in Class D airspace. I've marked on the map where the park is. If I'm reading this correctly, then I should be in Class G airspace up to 700ft AGL Am I missing something or is this probably just a bad GPS signal on start? I'm not getting repeated warnings so I think it's a bad signal but I figured a prudent pilot would check. <Q> Provided the drone is flying where the red dot is, you are correct and Class G extends from the surface to 700 ft AGL. <S> If you really wanted to play it safe, call the tower at KBKL to establish two way radio comms before flying there. <A> Yes you are in Class G at that location. <S> The shaded red band indicates the floor of Class E airspace extends down to 700 AGL at that location, and the floor of theshelf of Class B airspace is 1900 MSL above you. <S> The ground elevation is roughly 640 MSL according to the tower data nearby. <S> I agree that a call to the tower to verify would be prudent. <A> Yes, you're reading the chart correctly.
|
Either your drone's GPS is off by quite a bit, or it was deliberately designed to be overly sensitive so that you couldn't accidentally fly into nearby controlled airspace.
|
Do airplanes with fixed gear usually turn upside down during water landing? During discussion about emergency landing on water in this YouTube video (4:00) the flight instructor said: "...the problem with these airplanes with a fixed gear, you're usually going to be upside down". Is it really like this? If so, is there any water landing technique which could minimize the risk? <Q> Depends on the airplane. <S> I recall reading about a guy flying across from the Aleutians to Japan, in a Piper Super Cub of all things, and he had to ditch it for whatever reason, which he was able to do next to a freighter. <S> To his surprise, it didn't flip over but kind of submarined, stopped, then popped to the surface nose down but upright. <S> It's possible being a taildragger helped. <S> I think tricycle gear airplanes would be more prone to flipping right over because the pitching moment from water contact is a little stronger with 3 gears hanging down vs two. <S> I expect though, that if you surveyed ditchings you would find some do and some don't. <S> Pitching moment from water contact, elevator effectiveness in resisting the pitching, amount of up elevator at water contact, speed at water contact, maybe the surface contours of the fuselage could promote it or inhibit it, all kinds of variables. <S> As xxavier says, it would be prudent to assume you are going to flip over, and if you don't, bonus. <A> It is situational. <S> Locally there have been three Cessna ditchings that I have first hand knowledge of. <S> One of them resulted in an inversion. <S> The other two did not. <S> The general wisdom seems to be that high wing aircraft are more likely to upset than low wing aircraft. <S> I do not know what NSTB statistics are. <S> I am sure there are factors such as: vertical CG, AOA and or the attitide hitting the water, glassy water vs rough conditions, wind, gear dressings (tires, pants) etc. <S> At one time, probably 18 or so years ago, I saw a aeronautical engineering student's work on a simulation to model the likelihood of upsets using various commuter and short haul aircraft models, and what might happen in a ditching. <S> I have not seen anything more definitive since. <S> In the interim, if you plan on over water flights, the FAA safety seminar where one practices egress inverted and underwater, is a nice seminar. <S> I have taken it twice, and I learn as much the second time around as I did the first. <S> Fortunately, I have only had to demonstrate my skills in a high school swimming pool. <S> Not all water is as friendly as the Hudson during daylight hours. <A> The answer is in the torque created by protruding landing gear when they strike the water first with any forward motion relative to the landing surface. <S> Thus is why, if possible, water ditching is done gear up with the intent of "belly flopping" the aircraft onto the water. <S> Low wings and fuselage can absorb the impact over a greater area and will generally have a lower center of gravity, but GREAT CARE must be taken not to catch a wing tip first as this (also by torque) will cartwheel the aircraft. <S> High wings also stand a greater chance of remaining upright with gear up, if possible. <S> The best way is to reduce the ground (water) speed as much as possible by landing into the wind and holding the nose up as long as possible, applying full up elevator on contact. <S> Full flaps should be used for the lowest landing speed possible. <S> As @ <S> mongo said, training to escape an inverted aircraft in water is great life insurance, and would be worth the time in any type of aircraft. <A> In theory, for small airplanes with a very low stall speed, and with the help of a kind headwind, you may slow the plane down so much that the impact with the water may be almost vertical. <S> But that's the theory... <S> In practice, you should be ready to exit the cockpit inverted and underwater...
|
Water is much denser than air, so the drag created at the end of the lever arm of the landing gear easily flips the plane over.
|
Aviation theory for fighter pilots Background: I'm an 18-year-old Finn and so I'll be starting my military service next summer. I'm currently applying to the Air Force to become a fighter pilot, but I don't have any previous training in aviation. I have studied a bit of theory from the internet but I just want to ask what would be the most relevant information for someone trying to become a fighter pilot. So the quistion... What should someone, who's wanting to become a fighter pilot, try to learn and in what order? And what are good resources for learning those things? Thank you in advance! <Q> My experience is with US students who have joined the US Air Force, Navy or become Army Aviators. <S> My non-flight study guide includes: <S> Critical thinking Physics problem solving Math problem solving argumentation (related to critical thinking) <S> FAA Private Pilot and Instrument Pilot training material where possible visits to towers, TRACON, etc. <S> volunteering at: glider club, medvac company public speaking STEM college degree, not necessarily in aeronautical science <S> In college there will be more opportunities, and additional guidance. <S> Many high school students have learned to fly. <S> It's nice to have former students who are flying F-16s in various parts of the world. <S> Some who wanted to be fighter pilots ended up doing things like B-2s, tankers, etc. <S> Since most pilot jobs involve being an officer, leadership skills are important, and help differentiate applicants. <S> You will always have to somehow differentiate yourself, to be competitive. <S> Every former fighter pilot I know is very competitive. <S> Best. <A> I’d start with something similar to the USAF’s Pilot Aptitude Test or the RAF’s COMPASS test to first evaluate your ability to be a pilot. <S> If you like, pursue a pilot’s license in Finland or do glider training. <S> I would not go out and begin some military pilot training regiment recommended here as it’s probably wrong and will misguide you. <S> If you are accepted to undergo flight training in the Finnish Air Force, they will teach you all you need to know there. <S> Pursue extra curricular activities - aviation related, if possible. <S> Network with military pilots - find good people who will write letters of recommendation for you at some point Pursue leadership training and opportunities- military pilots are officers, which is the military equivalent of a manager in civilian life. <S> I also suggest doing team sports like football or similar to build hand eye coordination and working on a team. <S> Best of luck. <A> You may want to study basic aviation, but I advise you to avoid anything military or fighter pilot specific. <S> All armed forces spend substantial effort "untraining" recruits who picked up bad habits and mis-information before entering the service. <S> Military service involves absolute consistency and uniformity. <S> Anything you learn on your own that deviates from the service's SOP will have to be unlearned before you can make progress. <A> You can't go wrong by picking up a copy of "Aerodynamics for Naval Aviators" -- see for example <S> https://www.asa2fly.com/Aerodynamics-for-Naval-Aviators-P193.aspx <S> -- <S> It's certainly a few decades old by now, but full of excellent information. <S> Lots of interesting information about swept-wing flight dynamics and more--
|
Some basic recommendations: Get good grades - fighter pilot is s competitive job title.
|
Is the bleed air passengers breathe tapped from the engines before or after it comes in contact with fuel? And why? Isn't this unhealthy? Passengers are often surprised to hear that the air they breathe comes from inside the engines. This sounds unhealthy. Can you explain, why it is not ? Is bleed air tapped (for cabin pressurization) before or after it comes in contact with fuel inside turbofan engines on passenger airliners ? And what is the reason for either choice ? Specifically where is the location in this diagram ? (diagrams in answers would be very welcome) scope: This question is about the air breathed by humans inside the plane. Q11917 is about de-icing. Neither the question nor the answers in Q11917 deal with the aspect of whether the air would be safely breathable for passengers and crew. This aspect is very well dealt with in the comments and answers below. As such, these questions should remain separate. <Q> The bleed will be tapped from one or two of the 3rd, 4th, 5th or 6th High Pressure Compressor stages. <S> Usually there are two bleed ports. <S> The highest pressure port will supply really hot air for things like anti-icing. <S> The lower pressure port farther upstream will supply air for air conditioning/pressurization and other pneumatics. <S> Some systems combine the two ports into one system and draw from the low pressure or high pressure one as required. <S> The discharge in the last stages of the HP compressor can be upwards of 700-800F at takeoff thrust. <S> If the aircraft uses a high temperature "evaporative" anti-icing system, it will tap air from hotter stages of the compressor than if there is a non-evaporative system (Evaporative = anti-iced skin temperatures above the boiling point of water. <S> The leading edge will be over 100 C, like the surface of a steam iron.) <S> Even if it is taking "clean" air, the bleed flow will have all sorts of charred bits of things from the atmosphere in it; pollen, bits of bugs, that collect and get everything dirty in the ducting and components (at lower altitudes). <S> Combusted air would be ten times worse, not to mention the carbon monoxide poisoning the passengers and being way too hot to be usable in the first place. <A> I have found a diagram showing the location where the bleed air is tapped ( red arrow ). <S> As can be seen in the image, the location is upstream of the combustion chambers, which means that bleed air is tapped before it comes into contact with fuel: <A> To add to what John K already posted, cooling requirements prevent any bleed air being taken in the combustor and high pressure turbine sections. <S> In these sections, thin film cooling is preformed where a small amount of air is injected around the surfaces to prevent the hot combustion products from touching them. <S> Even if the bleed air was being taken for a non-human contact purpose such as active flow control, the air is simply too hot to handle at this point.
|
The air has to come from the compressor, not after combustion, mainly because it needs to be clean ambient air free of kerosene combustion byproducts, and it's plenty hot enough anyway and taking it from the turbine would be way too hot.
|
Are there any preventive measures against bird strikes while in flight? Most of the preventive measures for bird strikes are at/around the airport but what are some of the ways that can be used to prevent bird strikes on the plane as it is climbing or in flight? <Q> Airports engage in a number of strategies to reduce the number of birds nearby that might cause strikes. <S> This has been addressed in a previous question: <S> What are the ways to keep the birds away from airfields? <S> Properly designed and equipped avian radars can track thousands of birds simultaneously in real-time, night and day, through 360° of coverage, out to ranges of 10 km and beyond for flocks, updating every target's position (longitude, latitude, altitude), speed, heading, and size every 2–3 seconds. <S> Data from these systems can be used to generate information products ranging from real-time threat alerts to historical analyses of bird activity patterns in both time and space. <S> https://en.wikipedia.org/wiki/Bird_strike#Flight_path Installations include civil applications at New York/John F Kennedy International Airport, Chicago/O'Hare International Airport and Seattle-Tacoma although the majority of both deployment and development activity is still focussed (sic) on military air movements. <S> https://www.skybrary.aero/index.php/Detection_of_Bird_Activity_Using_Radar <S> MERLIN Avian Radar System technology...is used...to detect and monitor hazardous bird activity on and around airfields for bird-aircraft strike hazard management. <S> https://detect-inc.com/bird-control-radar-systems/ <A> In my Cessna 172 my eyes are the only advance warning system available. <S> I've used them a couple of times to avoid large birds, and not necessarily on approach. <S> I also know of several bird strikes in small planes that are just good stories after the clean up at the airport. <S> On the other hand, I also have heard of windscreens being shattered but the pilot still being able to maintain control and land the aircraft normally. <S> I suspect your question was written with airliners in mind, but bird strikes are not uncommon in small airplanes, and the results are mostly unremarkable. <A> See and avoid. <S> Avoid not always possible, especially when moving fast <S> and you don't see it/ <S> them coming, or are just not that maneuverable.
|
Avian Radar also exists: Avian radar[44] is an important tool for aiding in bird strike mitigation as part of overall safety management systems at civilian and military airfields.
|
Is it possible to make an analogy between a lever and an airplane wing in terms of force applied over distance? On most aircraft the engine force (thrust) is lower than the weight. Since wings therefore are always capable of generating greater force (lift) than the engine, there is an analogy between an airplane and a lever. Now, a lever produces greater force by doing the same work on a shorter path. How can we prove that wings enable the doing of work on a shorter path than the engine thrust? Is it reasonable to say the path on which the thrust does the work is the distance the aircraft needs to accelerate to takeoff speed, and the work/energy accumulated this way is used by the wings to exert greater force on a shorter path on the air? (And then this kinetic energy is constantly replenished by the engine keeping it constant, assuming no further acceleration?) Is this the right Newtonian explanation of flight? How can I find the distance on which the force is doing work on the air? <Q> Well, they call them air PLANES for some reason. <S> Maybe not a lever, how about a ramp? <S> How does 1/4th the thrust lift a given weight? <S> One consideration that is very important for aviators is to realize the best way to use thrust is to create speed. <S> Speed creates lift. <S> It is indeed a minor miracle that the airflow over a wing at flying speed creates so much upward force. <S> One way to see how this works is to look at the back of a boat while it is travelling slowly. <S> See the swirls and eddies of the water in the wake. <S> Now speed up and the water separates from the stern and forms a wave behind the boat. <S> The lack of water at the stern is the same as air being deflected away from the top of the wing at sufficient speed. <S> This area of lower pressure near the wing is lift. <S> How much to lift a one ton Cessna? <S> The wing is roughly 5 x 40 = 200 square feet. <S> 200 square feet x 144 <S> square inches/square feet = 28800 square inches. <S> 2000 pounds/28800 <S> square inches = 0.07 psi. <S> Not much, but it works! <S> Slow down and the wave collapses back to the boat. <S> This is a stall on a wing. <S> So lift is INDIRECTLY produced from thrust by forward motion (and angle of attack). <A> A lever is a very poor analogy to a wing. <S> And so is a ramp. <S> A lever used to lift a heavy load exchanges a small force over a large distance for a large force over a small distance. <S> In both cases the work done (force x distance) is the same. <S> Ignoring friction, a lever is 100% efficient, because the work out is the same as the work put in. <S> A ramp lifts a weight a short distance against gravity while moving it a large horizontal distance. <S> However the thing to note about a wing is that (at least in horizontal flight) it's doing no work against gravity at all - because the airplane isn't going up or down. <S> The wing is doing the same amount of work as my chair (as I sit in it) and a hook while it holds my coat off the floor, neither of which require any energy input - that is, zero work. <S> A wing is effective at providing a vertical FORCE in exchange for a horizontal amount of WORK. <S> Since no actual work is being done in the vertical direction in level flight the wing has an efficiency of zero %. <S> It would be nice to understand a wing as a kind of lever, but I'm afraid that's not what it is. <A> The airplane is applying force to a fluid (gas), which imparts a gazillion variables to an action/reaction situation. <S> On top of that, the airplane is accelerating a gas rearward to create the forward momentum, and then the wing is taking the same gas and accelerating it downward to create the lifting force, so you have a gazillion variables multiplied by a gazillion variables, which results, if my math is correct, in a jazillion variables. <S> You get the idea.
|
I don't think you can make a really useful comparison because the lever is applying force to one fixed object, pivoting around another fixed object, with a fixed mass and a fixed force and you can repeat the same result over and over.
|
Why don't airports have weigh stations to prevent overweight takeoffs? Currently, ensuring that an airplane isn't overweight when it takes off relies on the cargo handlers loading the aircraft properly and accurately documenting (on the weight-and-balance sheet) what with how much weight was placed where, and on the pilots properly reviewing the weight-and-balance sheet once the airplane is loaded. Even then, there are uncertainties (it is rarely possible to know exactly how much each passenger weighs, for instance). So why don't airports have weigh stations to weigh the planes as they taxi after being loaded, allowing any flights found to be overweight to be ordered back to the terminal to jettison the excess weight? <Q> Aircraft are heavy. <S> Really, quite heavy. <S> An Airbus A340 , depending on type, has a maximum takeoff weight (MTOW) of up to 380,000 kg. <S> A Boeing 747 , again depending on type, can have a maximum takeoff weight of a shade under 447,700 kg. <S> Measuring that kind of weight accurately is certainly not impossible, but it's not exactly easy either. <S> A bigger issue is that it's not as simple as saying that if the aircraft weighs more than some number of kilograms, then it's overweight, and if it weighs less, then all is fine. <S> The distribution of that weight within the aircraft – precisely that "weight and balance calculation" which you mention – matters, sometimes a great deal. <S> The aircraft could be putting an acceptable weight on the wheels, but if the weight is too far forward or too far aft, may still be outside of its controllability limits once it lifts off the ground. <S> Simply putting the aircraft on a scale and providing the pilots (somehow) with a weight-on-wheels readout as they taxi will catch the situation where the pilot can't add (as in, mathematically add up the weight components that make up the total aircraft weight), but it won't necessarily catch the situation where the load is improperly balanced. <S> So you'd be adding another fair bit of complexity (which can fail in various ways) to a currently relatively simple part of aviation (the taxiways or apron), possibly giving the pilots a false sense of security, and not solve the problem. <S> Someone would still need to do a weight and balance calculation, at which point the weight-on-wheels reading can, at best, provide a rough sanity check on the weight part of the weight and balance. <S> Seems easier to just try to figure out ways to make the weight and balance calculations easier to perform, and make random spot checks on weight and balance calculations done (and schedule followup training if the pilots, or ground crew, or whoever else, need it). <A> It's theoretically possible, but an airport would have to put in weighing pads for each landing gear, that can accommodate all sizes of airliners, and it would have to be in a specific spot for the purpose, which would require everybody to taxi to the same spot to get weighed causing a huge bottleneck (deicing pans are bad enough). <S> And the airport authority would have to pay for it, when there is nothing in it for them, and airlines wouldn't pay the weighing fees in the first place. <S> And the current methods work fine. <S> In essence it's a solution in search of a problem. <A> There is also economics to consider. <S> The number of airliner crashes that result from <S> overweight or weight imbalance takeoffs is very low, and almost always confined to marginal operators trying to pack in more paying customers, or not paying attention to weight balance. <S> Takeoff crashes most often occur when there is too much ice on the wings ( Air Florida 90 ), or the flaps aren't set correctly ( Northwest 255 ), or there is a problem with the landing gear dragging ( Lokomotiv Yaroslavl , Arrow Air ), none of which is directly related to overweight conditions. <S> A more efficient course to follow is to continue bearing down on marginal operators, and solve a lot of safety issues, overweight and otherwise, since the bulk of air crashes in general seem to originate with them. <S> More crashes will be averted for less money. <A> The OP needs to research AF90. <S> The problem was not too much ice on the wings! <S> It was iced over sensors in the engine. <S> The flight crew thought they had selected take-off thrust but instead had selected significantly less, and the plane with whatever ice load it did have couldn’t fly with that little thrust. <S> OP, you need to list crashes caused by overweight aircraft to convince us that there is a problem here... <S> nobody wants to pay for a solution in search of a problem. <S> Convince us, please, that there is a problem here. <S> And thanks in advance for your research on this matter.
|
Checking weight on every takeoff would be extremely expensive to implement, would impose additional delays on an industry already wrestling with delays, and wouldn't result in a big increase in safety, because very few airliners crash due to weight problems.
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.