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How to make ourselves more visible to other aircraft? What are the best practices in air to help others see our aircraft? <Q> Transponders, ADS-B (which, honestly, is pretty much just an outgrowth of transponders) and exterior lights have already been mentioned. <S> I'd like to add one more thing: speak up! <S> You've probably got a microphone right in front of your mouth, which is ultimately connected to a radio transmitter which is hopefully tuned to a frequency monitored by nearby aircraft. <S> To help make yourself more visible to other aircraft, press the transmit button and give your location and intentions, to let them know at least one place where they should look. <S> As a real-world example, another pilot did this the other day as I was in the air, saying something like " XX Radio , SE-XXX on downwind 21, for touch and go". <S> My instructor took the opportunity to quiz me about where they should be given that, and they were pretty much exactly where I expected them to be. <S> Not only did we now know where they were (position and, by inferrence, approximate altitude), which we could have known by looking for other traffic, but we also knew what they were planning to do . <S> In this case, there was no risk of a traffic conflict between us, but you never know who else is out there. <S> Unless the traffic situation is congested, or there's something like emergency traffic going on, the occasional radio call with your position and intentions can do little but help others. <A> Depends on the situation. <S> Night ops are much easier where one can use navigation and anti-collision lighting to readily be seen and identify other aircraft at a distance. <S> The Aircraft Owner’s and Pilot’s Association (AOPA), in conjunction with the FAA and other regulating bodies, instituted a safety improvement program called Lights On Look Out, which makes use of the aircraft landing lights when operating within Class B, C and D airspace at or below 10,000 ft ASL. <S> This is a very effective way to make the aircraft more visible to other pilots, provided the aircraft configuration can accommodate this. <S> Some aircraft actually make use of pulsing or strobing landing light modes intended for day use. <S> It is also extremely effective to make use of landing lights when maneuvering or flying in confined spaces like mountain valleys for easier identification and collision avoidance. <S> Another way to make ones self more readily visible is to be aware of blind spots which all aircraft have, depending on the configuration. <S> High wing aircraft block a great deal of the upper field of view just as low wing aircraft make it difficult for a pilot to see what’s under them. <S> Care therefore must be taken when turning or maneuvering to first clear blind spots around the aircraft by rolling slightly, scanning the airspace you are about to turn towards, then turning. <S> Aircraft therefore should exercise extra caution when descending to land for aircraft below them which may not be immediately visibile, yet in danger of overtaking and colliding with them. <S> Proper, established pattern entry techniques should be used when possible to allow other pilots in the pattern to easily identify aircraft entering or leaving the pattern and pilots should have descended to pattern altitude within 3 miles of the airport. <S> This is especially true during operations from untowered airports where all traffic may not be using or transmitting on the CTAF. <S> Proper radio calls should be used at said untowered airports to allow other traffic to more readily identify the block of airspace you are in and visually acquire you. <A> Have your lights on: Red beacon light on the fuselage or tail, white light on the tail, Red & Green <S> navigation lights on the wings, strobe lights on the wings, and your landing light(s). <A> Being equipped with ADS-B is also good. <S> Other aircraft with <S> ADS-B In will see you on their electronics and be looking for you.	For day operations, a minimum of an operational anti-collision light system must be used, but in general it is difficult to beacons or strobes in daylight prior to spotting the aircraft as a whole.
Has there ever been an uncommanded lowering of landing gear? Has there ever been an uncommanded lowering of the landing gear on a large commercial jet? I could not find any instance of it in a preliminary google search. Could a simple short-circuit cause such a thing? I think this would actually be pretty bad at cruising conditions, because the airplane is going much faster up there, than on approach. But the air is also much thinner so I can't be sure. <Q> The answer to your question is, in fact, "yes" - but the circumstances involved demonstrate just how difficult it is to make an aircraft's landing gear deploy without being commanded to do so. <S> In 1985, CI006 , a 747SP, experienced an uncommanded flameout of its #4 (right outboard) engine (something that particular engine was quite prone to doing) while cruising at FL410 en route from TPE to LAX. <S> An attempted relight failed, and a lack of corrective flight control inputs combined with a poorly-designed autopilot caused the airplane to decelerate and gradually roll into a steep bank despite the autopilot's attempts to counter the thrust asymmetry; the captain eventually noticed this and disconnected the autopilot, but made no flight control inputs of his own. <S> This, unsurprisingly, resulted in an immediate loss of control, and the aircraft rolled into a steep inverted dive, during which it exceeded mach 1 for an indeterminate period of time, plunging 30 kilofeet before the captain was able to orient himself when the aircraft broke out of the clouds at 11 kft and pull out of the dive, eventually levelling the aircraft at 9,600 feet. <S> During the dive and subsequent pullout, the aircraft was subjected to aerodynamic loads exceeding +5 <S> Gs, 1 which, in addition to causing severe structural damage to the aircraft (including tearing away large parts of the aircraft's horizontal tail), ripped off the body gear doors, broke the support brackets holding the body gear uplock hooks in place, and forced the aircraft's left and right body gear into the down-and-locked position. <S> (The added drag from the extended body gear [and from the aircraft's 29-kft maximum gear-down altitude] forced the flight to divert to SFO, having insufficient fuel to reach LAX with almost half of the aircraft's landing gear hanging out in the airstream.) <S> So, yes, it has happened... during an over-5-G pullout from a 30-kft supersonic dive in a 747. 1 : The highest normal acceleration recorded on the aircraft's FDR <S> was +5.1 Gs during the pullout from the dive; however, the absolute maximum G-forces encountered by the aircraft are unknown, as the extreme G-forces exerted on the aircraft, and the FDR, caused the latter to fail to record properly for large portions of the dive and pullout. <A> I found incidents where landing gear doors fell off jetliners , and only one incident where the gear uplock failed on an Airbus A320, but the door held it inside. <S> The crew had to slow down to a safe 'gear extended' speed. <S> A320 flight crew experiences a nose gear uplock failure climbing through FL200. <S> Nose gear doors remain closed but aircraft is slowed to 220 KTS to comply with overspeed warning and ECAM logic ( 37000feet.com ). <S> ' <S> L/G GEAR UPLOCK FAULT' is one of the abnormal procedures in the A320 flight crew operating manual. <S> The first two items is to keep the landing gear down and a max speed of 280/.67. <A> Only thing I can find is on the X-15 rocket plane . <S> Expansion of the airframe caused the nose gear to come unhooked and deploy at Mach 4.2. <S> The air friction tires and caused them to disintegrate on touchdown. <S> The pilot was still able to make a safe landing.	Typically it takes two points of failure for it to happen on a jetliner: the gear uplock to fail, and the door uplock to fail.
What is this transport aircraft, and why does it sometimes cary an air data boom when the Soviet Buran Space Shuttle is on top of it? This comment in chat points to a "google search of the day" which was for Buran the Soviet version of the Space Shuttle . Looking there I saw images of a large transport aircraft with the Buran shuttle on top. What caught my eye were some photos of the transport aircraft with what looks like a large, orange air data boom at the end. My understanding from Quora answers is that these are used for supersonic flight, and I wouldn't expect this shuttle to be transported supersonically. Question: What is this transport aircraft, and why does it sometimes cary an air data boom when the Buran shuttle is on top of it? According to this blog it is an Antonov AN-225 but I don't think that is a supersonic aircraft. above: From thelivingmoon.com . Click for full size views. below: I believe this is Buran itself , According to @Hobbes' correction/comment , this is the "OK-GLI: a Buran analog (shape is correct, systems are not identical to the orbital vehicle) with 4 jet engines that was used for flight testing in the atmosphere", also with an air data boom. I've kept this here because it's actually pretty cool. From pinterest . <Q> The only aircraft that ever had a shuttle on top of them is NASA's modified Boeing 747 and Russia's Myasishchev and the Antonov 225 . <S> All of them were subsonic. <S> The one in the picture is the high wing 6 engine Antonov 225. <S> The air data boom is likely to gather data for test flights for the shuttle. <S> Subsonic craft will affect the air in front of them (that's why you can hear them coming) <S> so putting the sensor on a boom will help put the sensors in clean air. <A> During flight testing, an aircraft's onboard instruments and sensors must be calibrated and validated. <S> Pitot-static systems located on the fuselage are affected by the air flow around the aircraft. <S> Some other measurement is needed to establish the relationship between actual atmospheric conditions and what the aircraft sensors measure. <S> One method is the boom extending from the nose. <S> This takes measurements far enough in front of the aircraft that the air is undisturbed by the aircraft itself. <S> Especially in larger aircraft this is an expensive installation, and would interfere with the weather radar in the nose. <S> Another method of measuring actual conditions is a trailing cone extended behind the aircraft. <S> This requires modification of the aircraft structure and is susceptible to damage. <S> The An-225 was built specifically to carry the Buran, so it makes sense that they would test it with the Buran on top. <S> It would also create an especially large wake that might make a trailing cone difficult. <A> A spike like this does not mean this aircraft is supersonic (as highlight by this question ). <S> It can also be to put sensors as far away from the disturbe airflow (du to the big flying machine carrying it) as possible. <S> I don't know if it is the case here, but some prototype tow such sensors to calibrate the onboard sensors as explained in this video (french). <A> Supplementary to @ratchetfreak's accepted answer <S> I'd like to include an image that demonstrates air data booms are used on sub-sonic aircraft as well. <S> From @fooot's comment linking to This Day in Aviation for 30 June 1968 , here are photos of a prototype Lockheed C-5A Galaxy <S> and it's first flight. <S> This amplifies the point that the air data boom is important to establish better measurements for new aircraft or those with unusual configurations. <S> above: <S> The prototype Lockheed C-5A Galaxy, 66-8303, at Marietta, Georgia, 30 June 1968. <S> (Bettmann/CORBIS) <S> From here . <S> below: Lockheed C-5A Galaxy 66-8303 during its first flight. <S> (Code One Magazine). <S> From here . <S> Click for full size.	Supersonic aircraft must use the boom method because the air flow behind the aircraft has been affected by the shockwaves created by the nose and other aircraft features. It is indeed an An-225 (the first and only one built).
What should I look for when choosing a kneeboard? There's a lot of variety in kneeboards. Some pilots fly with an improvised one: just a small clipboard with some scrap paper on, with a strap glued to the back. At the other extreme, fancy ones come with pen loops, pockets, and maybe even a fold-out area big enough to rest a map. I'm not looking for a specific recommendation: I'm looking for how to choose. If I decide to make something homebrew, what should I bear in mind? If I buy a commercial product, which features are actually useful and which are "box features"? <Q> You don't want something so big that it interferes with fully moving your control yoke/stick. <S> Decent width of velcro strap to go around your leg.Sportys.com has Aluminim VFR and IFR kneeboards, with good info printed right on it. <S> If you roll your own, they also have the same info available as a placard you could stick on. <S> The kneeboard and a few pieces of paper are all I've used. <S> I fly my own plane, so I can leave pens/pencils in places that are convenient for me. <S> If you are switching between planes, then maybe a kneeboard with holders for a pen or two would be handy also. <S> I also have a yoke mount clip that holds an approach chart. <S> I found that trying to read a chart on my leg under the yoke was too difficult. <S> I may change to an ipad holder on the yoke as that seems to be the trend now. <A> Compared to the cost of flying knee boards are pretty cheap to cycle through. <S> There are a few questions to answer that may be impacted by your training and the type of flying you are doing: <S> Am I an iPad Pilot? <S> These days many people use iPads in the cockpit to replace paper charts. <S> If this is the way you fly you will want something sturdy that can hold the iPad in place. <S> You may also want to consider a yoke mount . <S> Am I a paper pilot? <S> If you like sectionals and a note pad there are various clip style ones out there. <S> You can build one or buy it <S> but I like the ones from the various major aviation suppliers as they tend to have some useful aviation numbers like weather minimums and those pesky tower light signals printed on them for reference. <S> The military style ones tend to have a nice pen holder if thats what your after. <S> Do you want a side pocket? <S> Be it clip or iPad style <S> most knee boards I have seen are either single plate or dual in that they have a side pocket that hangs over (there are even some trifold ones out there <S> I belive). <S> The side is good for holding gum, extra headset batteries, a pen/stylus or an iPad cable (at least thats whats in mine). <A> Keep it small and simple. <S> Most are gimmicks and useless stuff. <S> Worse yet large awkward kneeboards or yoke mounts can interfere with one's ability to operate the flight controls effectively. <S> Just like gun aficionados will inevitably collect a drawer full of holsters, most pilots have a drawer full of old kneeboards with fancy features they saw in Sporty's and bought for 60 or so bucks but never quite worked as well as the basic $15 ASA kneeboard they inevitably ended up using. <S> My personal setup is a Hendrick's 9G Plus kneeboard which I use in conjunction with an iPad Mini 4 and ForeFlight. <S> It's <S> a compact, functional, and simple - if somewhat pricey - kneeboard. <S> The iPad is contained in a Urban Assault Gear hard rubber case which the kneeboard can clip on to hold it in place. <S> It's by far the cleanest solution for using a kneeboard in the cockpit combined with an EFB.	There are lots of options out there for iPad knee boards and with the scratch pad ability in most flying apps you can replace paper all together in the cockpit. People sell a lot of fancy kneeboards for use in cockpits and you'll quickly find that 90% of the features aren't going to be very helpful to you as a pilot. I have one that is about 1/2 sheet of paper in size (or about the size of an approach chart), that works good for me. You need to chose what works for you, and some trial and error may be pertinent here.
Why are turboprop intakes placed below the propeller? On many turboprop aircraft, such as the A400M and the ATR 72, it seems that the air intake tends to be placed below the propeller (images: Wikipedia): source source Given that mounting the intake in a higher location helps reduce the risk of foreign object damage from ingesting debris into the core, why are the intakes still mounted below the propeller? Are the wings and engines already mounted high enough that the intake location doesn't matter when it comes to FOD, or does another issue (maybe accessibility for ground crews?) outweigh the risk of FOD? <Q> Inertial separators are augmented by gravity when located under the engine. <S> Inertia keeps solid matter low at the indicated point while air makes the turn into the engine. <S> C130 Nacelle <A> ( wikimedia.org ) British Aerospace Jetstream <S> You're right, it's the wing placement. <S> For low-wing aircraft you find inlets above the prop, and sometimes circular inlets around the prop. <S> The same engine shown above has different inlets depending on the plane, where you'd find an under-prop inlet in high-wing aircraft . <S> ( norebbo.com ) <S> But having the inlet above in low-wing is not a fixed rule , because a benefit of the under placement is that more air affects the wing's upper (suction) side. <S> Inlets above the prop hub would take from that air : <S> Low pressure on the upper surface of the wing is really the major source of lift. <A> I believe the main reason is simply mechanical practicalities. <S> The bulk of the engine core is mounted overlapping the structural members of the wing, either below or above the wing spars. <S> The propellor is driven through a speed-reduction gearbox, which usually also offsets the propellor shaft from the turbine centreline. <S> That in turn means the most direct air intake path to the turbine is the opposite side of the core to the propellor & gearbox. <S> See the photos below:	It is easier to discharge ingested ice and debris downward, rather than some other direction, so that is where they go if possible. That offset is used to place the propellor nearer the centreline of the wing to optimise airflow.
Has this Google Maps imagery of 4 planes on a runway been tampered with? The image below is of Google Maps (30 May 2018) of Amsterdam Schiphol's Aalsmeerbaan (36R). It shows 4 planes on the runway and a fifth that's about to land. When you zoom in, all planes seem identical. Has this image been tampered with or could there be an explanation for this? <Q> Google Maps and Google Earth are made by stitching together many different images to create the illusion of a single massive picture of the globe. <S> In multiple snapshots, it captured the same plane on final, touching down, rolling out and stopping. <S> The images were assembled together to line up the ground and all static elements. <S> But items that are moving appear multiple times in different images. <A> This is a common occurrence with airplanes on Google maps. <S> Google overlays multiple scans taken seconds apart from satellite imagery to get the best image quality. <S> This works very well for stationary objects, such as buildings and land structures but results in multiple images of high speed objects, such as airplanes. <S> Sometimes this effect is visible even with cars on a highway. <A> What looks like tampering is actually multiple exposures, plus cross-channel rolling shutter (the color fringes). <S> If you measure the spacing of the aircraft images and the size of the fringes, you can infer that it's one aircraft slowing down after touchdown. <S> You can even see the puffs of smoke that show the main gear touching down before the nose wheel. <S> Here's a careful analysis .	The image you are seeing was almost certainly made by an aerial photography plane passing overhead of another plane landing.
What is this abandoned airport between Montague and Rothbury, Michigan? It appears to have had two intersecting paved runways, each very roughly 2000 feet long (give or take); the one that runs closer to north-south is still legibly numbered as runway 17/35, but the other runway is in much worse condition (suggesting that it was closed some time before runway 17/35), and its pavement is too broken up for me to make out the numbering. Runway 17/35 has considerably larger turnaround areas at both ends than the other runway does. There is a cleared strip extending for approximately 400 feet past the southern end of runway 17/35. West of the intersection of the two runways, there appears to be a dilapidated apron, with taxiways connecting it to both runways; immediately north of the apron, there is what could be the remnants of a collapsed hangar, or could be something else entirely (there is another area of junk just to the southwest of the apron). Google Maps link to location of the former airport here . Google Maps screenshot showing the mystery ex-airport: <Q> The airport is Ottiger Airport (2MI6) which is closed indefinitely. <S> I cannot find any information on when it was closed or for what reason. <S> The last update date that I can find for the charts is August of 2006, which is probably when the airport was closed. <S> Apparently there is one person who is trying to revive the airport for private use according to this post on Facebook . <A> That is Ottiger Airport. <S> I flew out of there for 10 years. <S> It is situated between Fuitvale Drive on the South and Sikinga Road on the North. <S> There was one paved runway that was 2000 ft. long and one shorter runway about 1800. <S> There were two hangers and a gas pump. <S> during the 60s & 70 there were about 7 planes there year round and many visitors during the summer from everwhere <S> even a Dornier from Germany one summer, I knew Mr. Ottiger very well as he also was one of my fishing partners. <S> The shorter runway was made of oiled gravel and there was only one paved runway which was done by the army at Camp Claybanks approx. <S> 5 miles north of there. <A> Normally with these kinds of airports they should show up on aeronautical charts as closed or abandoned to avoid any confusion with other airports (this way a pilot doesn't accidentally land on the wrong runway) <S> but this one doesn't show on this online Aeronautical Chart SkyVector . <S> Presumably because there aren't any other airports near 2MI6. <A> 2MI6, Ottiger Airport, is currently under rehab for private use. <S> The Michigan airport inspector shared his past inspection reports, which have been posted on Facebook- Ottiger Field since 1950. <S> The license was not renewed due to deterioration of the runway surface, lack of Displaced Threshold (DT) markings, and refusal to remove a majestic oak tree. <S> Note that private use has a lower threshold of setbacks, etc. <S> It seems the field was operated with commercial activity (instruction and fuel sales) for some time. <S> Absentee owner left it to users to maintain, which seemed to decline and eventually stop about 2004. <S> Expect it to be listed for sale shortly.	It looks to be Ottiger Airport 2MI6
What does it mean when ATC says "altitude indicates"? I've noticed that ATC sometimes calls out traffic (a traffic advisory?) to aircraft using the "altitude indicates" phraseology, and sometimes a specific altitude is given without the phrase "altitude indicates". Is there a specific reason for when they use one over the other? <Q> "Altitude indicates" means that the aircraft has a Mode C transponder but it isn't receiving radar service, i.e. it's VFR and not on flight following. <S> In other words, the transponder is reporting an altitude, but because the aircraft isn't in contact with ATC, they can't be sure about its altimeter's integrity or the pilot's intentions. <S> See the ATC orders 2-1-21 : <S> For aircraft displaying Mode C, not radar identified, issue indicated altitude <A> There's 2 types of radar in ATC, there's Primary Radar which gives bearing and distance, but it can't give altitude, which is why there is Secondary Surveillance Radar (SSR) which interrogates airplane transponders. <S> When a transponder is on and set to mode C or S <S> the controller will see flight level on their screen. <S> Flight level is altitude adjusted to standard pressure (1013hPa): <S> When a controller gives a traffic report and they haven't had a reported altitude from the aircraft they'll either report the aircraft's transponder reported flight level or altitude in feet which is the transponder reported flight level adjusted for local pressure. <S> A controller may also use the transponder reading if the airplane has changed altitude since its last report, say because they are maneuvering, doing practice forced landings, etc. <A> ATC is looking at the altitude reported by the aircraft's mode C transponder. <S> They have to talk to that aircraft and verify that the altitude is correct before they can trust that information. <S> This is part of "radar identifying" a target. <S> If a target is not radar identified, they just say "altitude indicates." <A> the Mode C encoded altitude readout showing on the display. <S> If that phrase is not used, the controller is likely referring to an aircraft flying an altitude associated with a clearance as confirmed by the pilot (and backed up by the encoded altitude displayed for that target also).	"Altitude indicates" means it is a random target and the controller is going by the only information available,
In a pusher configuration with turboprop(s), how is the superhot exhaust avoided? I actually looked around for turboprops in a pusher configuration, and so far I only found one: P180 Avanti . You can see the propellers are behind the turbine, and in fact it looks like two exhaust ports lead right into the propellers. How is this possible? Turbine exhaust is very, very hot. "Superheated steam" is actually a technically accurate term. Won't this disturb the propellers and cause them to fail or else need huge maintenance? Is there some elegant way to avoid this geometry in a pusher configuration? <Q> Because the blade is moving in and out of the exhaust stream at high velocity, and the exhaust stream is perhaps 20% of the total exposure, the heat transfer to the blades is negligible from the standpoint of heating up aluminum enough to affect its heat treat, or heating epoxy to its transition temperature. <S> Meanwhile there are the anti-icing benefits. <S> There is an issue with the exhaust impinging on the prop on the Avanti, and there is a Hartzel Service Bulletin <S> http://hartzellprop.com/wp-content/uploads/SB181A-R06-W.pdf <S> that covers it. <S> The carbon and heat from the exhaust attacks the aluminum of the blade and the problem is blade corrosion once the paint finish starts to erode. <S> The SB is to inspect, clean up, and repaint the blades from this damage. <S> (Carbon and aluminum are at opposite ends of the galvanic scale and don't like to live together; this caused much grief on the CRJ program when someone who evidently missed their corrosion module in university decided to put carbon floor panels on aluminum support beams without an adequate barrier, with unfortunate results and driving a switch to titanium beams). <S> Really though, with the Avanti the biggest problem is the prop directly behind the gear acting like a FOD catcher for stuff thrown up by the tires. <S> You wouldn't want to try to fly an Avanti off a gravel strip, that's for sure. <A> But then again the benefits would have to outweigh the drawbacks of such a design. <S> Adding additional exhaust routing would solve the problems of structural damage due to heating, But it’s also bulkier, heavier and imposes additional design requirements for heat shielding the aircraft structure, preventing exhaust gas leaks and designing an exhaust outlet installation to vent the exhaust gases away from the airframe somewhere else on the aircraft. <S> And that’s not really necessary if the temperature from the exhaust gases around the propeller blades is sufficiently cool enough to not cause structural damage the blades. <S> A PT6 usually has a maximum Inter-turbine temperature (ITT) around 750° C but the temperature of the exhaust gases exiting the exhaust stubs Is going to be lower-probably only order of 400°C or so. <S> Add intermixing with outside air flow and the temperature of the exhaust gases may be down as low as 250 to 300 <S> °C by the time it passes through the propeller arc. <S> This is going to be far from hot enough to damage the propeller blades provided their manufactured out of the right material to the right specifications. <S> It has an additional bonus and that the hot exhaust gases can serve as a means to prevent ice accumulation on the propeller blades during flight, thereby forgoing a requirement for hot props or another kind of prop anti ice solution <A> It actually serves to heat the props and help in a de-icing situation <S> so it appears to be quite deliberate and heat the props by design. <S> Propwash does not interfere with laminar flow over the wing and turbine exhaust gas heats the propeller blades, eliminating the need for de-icing. <S> However it does add to the exterior noise of the aircraft <S> The exterior noise level and its higher pitched sound has been exposed and p resented to be the result primarily of the interaction of the turbine engine exhaust flows and the five-bladed pusher propellers.	I suppose one could route an exhaust stack from the engine installation to a location away from the engine or propellers.
How common is it for military jets to use civilian airports? Today my wife witnessed 3 fighter jets taking off from Teterboro Airport in NJ. She even took a video. How common is it for military jets to use civilian airports? <Q> What your wife may have seen may have been related to the VIP TFR's that usually pop up in the summer due to the president (or first family) heading back to their home on weekends. <S> I fly out of KDYL which is fairly close (in aviation terms) and my local FBO has been warning everyone that the Secret Service has instructed them <S> the VIP TFR is going to be common on weekends this summer. <S> You can find a map of current TFR's here. <A> Some airports are shared with the military. <S> For example, Portland International in Oregon has the Portland Air National Guard Base, and Charleston International is shared with Joint Base Charleston. <S> Airports such as these will have frequent military traffic. <S> Even airports with no permanent military presence may see occasional military traffic. <S> Aircraft may do touch-and-gos there for training. <S> It's less likely for them to stay very long, as there could be special security and ground support requirements, especially with fighter jets. <S> You can look at statistics for US airports on AirNav. <S> KPDX sees military operations as 2% of its operations, while KCHS sees 20%. <S> KTEB shows <1% of its operations are military. <S> This is the lowest value they report but that could still be up to almost 5 per day on average. <A> There are many, many Air National Guard Bases at Regional and Municipal airports. <S> The ANGB planes typically have their own ramp area and hangars for repair, and have security systems around them. <S> Wikipedia has a list of ANGB locations Those Not at an Air Force Base are generally sharing civil airports. <A> Night and day, seven days per week at KABI. <S> This full time-use of a regional airport began early 2018. <S> Remember the song, "Abilene - Abilene... <S> prettiest town I've ever seen... <S> " <S> They should make a new song, "Loudest town I've ever seen..."	Fighter jets may fly into local fields for airshows, to re-fuel or for needed maintenance in route etc.
What is the effect of fuselage weight on a model glider? I've built a model glider and wanted to see the effect the weight of the fuselage had on its performance. It flew the further with more weight which seems counter intuitive. I can exert more force into the glider with more weight which results in greater airspeed, would this be the reason for the increased glide ratio? How does this compare to real life gliders? Thanks. <Q> Variations in aircraft weight do not affect the glide <S> angle provided that the correct airspeed is flown. <S> The glide ratio is based only on the relationship of the aerodynamic forces acting on the aircraft. <S> The only effect weight has is to vary the time the aircraft will glide for. <S> The heavier the aircraft is, the higher the airspeed must be to obtain the same glide ratio. <S> If two aircraft have the same L/D ratio but different weights and start a glide from the same altitude, the heavier aircraft gliding at a higher airspeed will arrive at the same touchdown point in a shorter time. <S> Both aircraft will cover the same distance but the lighter one will take a longer time to do so. <A> Real-life gliders require some minimum payload to have their C.G. within limits; without this they can't hit their performance numbers. <S> For this reason it is common to ballast a 2-seat glider with a sandbag if it is operated by a single occupant: the glider pilots say that if underweight, the glider "penetrates" poorly i.e., it cannot be trimmed into a minimum sink rate state that also is comfortably above the stall. <S> When underweight, the glider mushes along at low airspeed in a poorly-controllable state. <S> In my experience with model gliders, they too will fly poorly without ballast: hand-launching <S> an underweight glider causes it to pitch up, then quickly lose airspeed and descend more like a parachute than like a glider. <A> Even if your ballast doesn't change the CG location, there's a "sweet spot" airspeed at which the wing is most efficient (L/D ratio is highest), and this is always faster than minimum sink speed. <S> It's usually possible to trim a glider to fly at best L/D without ballast, but this requires nosing down, which increases sink more than adding correctly located ballast.	Since it is the lift over drag (L/D) ratio that determines the gliding range, weight will not affect it.
Were my airplane's wheels under-inflated? I recently took a flight on a (Lufthansa) Bombardier CRJ900 aircraft. As I was about to embark, my eyes caught this image: And the aircraft wasn't even loaded with the passengers yet. If I saw this in a car, I would assume a flat tire or other loss of air pressure...were these wheels under-inflated? <Q> It's absolutely normal. <S> Above is how the manufacturer even depicts the nose tire in the airport planning manual <S> (.pdf, page 42). <S> The pressures are checked by line engineers typically before leaving the hub, as well as an inspection by a flight crew member before every flight. <S> While not available on the CRJ900, there are many jetliners that have tire pressure sensors. <S> See: <S> Do airliners or business jets have brake temperature sensors? <S> (image of such cockpit display) <S> How do tyre pressure sensors in aircraft work? <S> (how they work) <A> High tire pressure means less rolling resistance at least on a good road. <S> However it also reduces grip that makes braking less efficient ( source ). <S> Hence high pressure may make sense for a bicycle but not for a plane where the power is more than abundant. <A> If you can think of a scientific argument why they should be, post it. <S> It's very common knowledge that inflating tires to maximum pressure reduces sidewall effectiveness and overall tire performance.	Neither car nor aircraft tires are supposed to be inflated to the point where only a small percentage of the tire is in contact with the ground.
Is it possible for ATC to see who’s transmitting on the radio on their radar? I don’t think ATC currently has the capability of seeing who’s actually transmitting on the frequency. If technology permits (probably by making a connection between the radios and the transponder), would it be helpful for controllers to be able to know the actual aircraft that’s transmitting on the frequency through their radar? Does it also have the possibility of eliminating the requirement of saying the callsign after each transmission (might help in extremely busy airspaces)? The visual aspect would be similar to how the “ident” feature works (like seeing a little “ TX ” when someone is transmitting). <Q> A version of this has been implemented in some areas, such as the Maastricht Upper Area Control Centre , using radio direction finding equipment. <S> The EUROCONTROL website provides an explanation of the system , including an image of how it appears on radar displays : <S> Using triangulation software, the Radio Direction Finder, recently deployed throughout MUAC’s international airspace (the upper airspace of Belgium, the Netherlands, Luxembourg and north-west Germany) calculates accurately an aircraft’s position on the basis of its radio transmissions. <S> This is particularly useful in MUAC’s sectors where controllers handle up to 25 aircraft at any one time, and is a prerequisite for the implementation of the free route airspace, planned at the end of the year. <S> The origin of a voice transmission appears clearly on the controller’s integrated Human Machine Interface and is totally independent of conventional radar- and GPS-based aircraft localising techniques; this feature contributes to reducing call sign confusion, read-backs from wrong aircraft or crossed transmissions. <A> As you state correctly, they can’t see who is transmitting. <S> Despite that the functionality is not build into the radios currently installed in thousands of planes, that would also mean you would have to register a hand radio a specific plane. <S> In theory you could use analog technology to transmit short data pieces with every PTT. <S> There is a good reason why aviation is still analog though. <S> Analoge signals can still be understand, even if connection is really bad. <S> It will be a lot more noisy and the pilot might not be understandable crystal clear, but the message will arrive. <S> While in a digital environment you will get what you have on your mobile. <S> If you take bad connections in consideration, you would need to send the data signal several times to be correct and display the right call sign. <S> That would probably take more time and block the frequency. <A> Mostly No, as normally configured. <S> Slow traffic or particular positions may be identified by ATC listening on two radios simultaneously i. e. <S> a BUEC, RCAG or portable radios especially, could identify how far away you are by precisely setting the squelch on a PET-2000 or other portable radio. <S> The antennas for such facilities are at different locations which affects where transmitted signals will be received. <S> It would be fairly easy with slow traffic and particular locations given multiple or lengthy transmissions. <A> Military transponders had, or possibly still have, a switch that, if selected, will cause an IDENT during every radio transmission. <S> This would have been very useful on radar displays with no target datablocks. <A> As David pointed out, they do not have any way to know where or who you are by com radio. <S> In the United States the FSS use to have directional steering capability for lost airplanes (and be able to locate the aircraft transmitting), but even that was done away with outside Alaska in 2007 , then in Alaska in 2013. <S> You would ask for a "directional steer" and they would ask estimated ground speed and would have you do a couple turns over a 3-5min period to identify your location by triangulation.	In densely occupied airspace, the Radio Direction Finder assists the controllers in rapidly identifying which aircraft is transmitting on the frequency.
Do any gliders carry GPWS? Do any gliders come with a ground proximity warning system (GPWS)? I realise that, for a glider, a GPWS probably wouldn't be able to help quite as much as in a powered aircraft, since a glider, by definition, doesn't have any engines which it can apply TOGA power on (unless, of course, it's a motorglider), but it could still warn the pilot if they were descending too rapidly for their altitude or were about to land with the glider in an unsafe configuration, thus allowing the pilot to take the necessary actions for avoiding a crash (for instance, by pulling back on the yoke, jettisoning ballast, lowering the flaps and landing gear if the glider in question is so equipped, etc.). <Q> GPWS is mostly useful for aircraft flying in instrument conditions or at night when there is low visibility preventing a good view of the ground. <S> Gliders aren't designed to fly in these conditions and they don't have the required instruments. <S> They should be able to see the ground and avoid it without GPWS. <A> This is not quite a GPWS but is cheaper and uses a lot less power (glider pilots rely on batteries for their electrical system). <S> Most GA aircraft don't have a GPWS either and usually rely on the GPS solution. <S> ForeFlight has a nice feature called Synthetic Vision which can allow you to see terrain in IMC conditions and is much cheaper than a GPWS. <A> I found this video of a glider equipped with GPWS , however, I doubt that such a system is very useful in glider <S> , that isn't very complex and would consider it a gimmick. <S> Also because the sounds in the video are Boeing GPWS sounds, so <S> it's probably self-built for fun. <S> So, to summarize: There surely are some self-built systems for fun and coolness, but I don't think there would be enough demand and need for a commercial system. <A> A glider will be usually flown according to VFR. <S> So it is basically the task of the pilot to maintain adeqaute distance to terrain. <S> The distance can be rather low, flying in mountains. <S> As already mentioned, current onboard flight computers include terrain databases, that will provide you with AGL. <S> Software like <S> XCSoar will perform a final glide calculation taking terrain into account, telling the pilot if glide path will be in conflict with terrain. <S> More important than GPWS is obstacle collision avoidance, as obstacles like power lines or cablecars in mountains are hard to see. <S> The popular traffic awareness system Flarm can optionally host a obstacle database and then will provide apropriate warnings.	Many glider pilots have a GPS flight computer that usually has terrain loaded in its database and can alert a glider pilot of terrain.
How do aerobatic aircraft land? The aerobatic aircraft I've seen don't have any flaps or air-brakes, besides they're taildraggers so I guess they usually have to do stall landing or three point landing but I don't understand how the pilot controls the approach speed or just how they slow down. <Q> The same as any other powered aircraft would - controlling their descent with a combination of pitch and power. <S> Most small GA type aircraft don't have air brakes, spoilers etc anyway, so that's fairly immaterial. <S> The only difference is a slightly faster approach and more nose high attitude. <A> You can land all planes without flaps etc.. <S> It's just the question, if it is a landing or an arrival <S> In crosswind situations, a lot of pilots prefer to do little to none flaps set, as the plane stays more controllable. <S> Btw. <S> you can slow down the plane by pulling the nose up. <S> Putting the nose down increases the speed. <S> This helps to adjust the speed. <A> The plane slows down from aerodynamic drag. <S> Level off above the runway ( also referred to as the "flare"), and wait - <S> the plane will slow down by itself, as it does the wing creates less left, and the plane will settle down to the runway. <S> Holding the nose up as that happens helps to create drag and slow it down.	I'd imagine almost any civil aircraft can be landed quite safely without flaps - it certainly forms part of the standard training syllabus for the PPL and you'd likely be expected to demonstrate a flapless landing on your skills test.
What are the disadvantages of having vortex generators? I know the advantages of vortex generators (VGs): lower stall speed, lower landing and takeoff speed according to www.stolspeed.com. So what are the major reasons most GA planes and low speed ultralights don't have VGs on their wings? <Q> Cost. <S> A set of Micro AeroDynamics VGs can run around $1500 plus installation cost. <S> On my plane they are installed on the top of the wing, the sides of the vertical stabilizer (fin), and the bottom of the stabilator. <S> I wasn't aware there were other suppliers of STC'd VGs for certificated planes. <S> I installed mine in early 2000s, price may have gone up some since then. <S> They do work well, lowering stall speed while allowing the controls to be effective the same as at higher speeds. <S> No noticeable loss of airspeed at higher power. <A> I've been thinking of putting them on my plane (a homebuilt). <S> I can make them myself, but would have to figure out the proper chord wise location. <S> I think the biggest negative to them is the care required to avoid knocking them off. <A> Since they consume energy all the time, most manufacturers have done just that.	The most important reason by far is that if you design your wing (or other surface) correctly they aren't needed.
What is the aerodynamic motivation behind vortex generators? An airplane's wing creates lift efficiently when the airflow is parallel to the chord of the wing. Vortex generators twist the airstream on the wing surface. Doesn't this kind of twisted airflow cause lift inefficiency? <Q> You are correct that vortex generators create drag, so a successful installation depends on reducing some other drag even more. <S> Airflow separation causes significant drag that vortex generators can reduce. <S> The energy consumed by vortex generators making drag is injected into the boundary layer, delaying airflow separation and the eventual stall, which might be of even more value. <S> Correcting poor flight characteristics on an existing design is often where they are used. <S> The illustration of a wing stalling is easy to understand but may not be the best use of VGs since few wings fly continuously on the brink of separation. <A> No. <S> The vortex helps keep the boundary layer attached so lift is created for a longer time as the plane slows and the wing is tilting up & back for landing. <S> Image <S> source <A> They only twist the flow in a little region just above the wing surface, whereas a substantial part of the overall lift is actually being produced by a huge package of air well above the wing being induced to move downward. <S> You could say they have a kind of catalytic beneficial effect much larger than their cost. <S> Yes there is energy consumed in making the vortex but that is usually offset by the drag reduction of the overall flow improvement achieved (they may be spinning, but the spinning air is a lot more orderly than random turbulence). <S> Usually VGs are used in local areas to help re-attach detached flow, but the best example of this is the popularity of VGs used as a "poor man's slat" along wing leading edges. <S> When aircraft have VG kits installed on the leading edges, it raises the stalling AOA somewhat less than half of what you get with a slat or slot, not bad for a row of little metal tabs. <S> From about 14-16 degrees for most airfoils to maybe 19-21 degrees (ballpark numbers for illustration). <S> On many light aircraft this is good for about 4-6 mph reduction in indicated stall speed. <S> On light twins VGs can also lower the minimum control speed to close to or even below the stall, a huge safety feature. <S> They also tend to drastically improve stall behaviour. <S> You would think leading edge VGs would come with quite a cruise speed penalty, but usually the penalty is negligible if at all, because there is a small drag reduction from the reduction of flow separated turbulence at cruise that offsets the energy used to create the vortices. <S> In a worst case, maybe a light twin with VGs will see a 3 mph hit on cruise speed, but the safety benefits are too massive for this to matter. <A> I am going to complement previous answers about VGs. <S> All previous three answers are showing a fact: <S> Your reasoning is right, a VG is introducing drag and, for a given angle of attack a less aerodynamically efficient wing. <S> However, let's take the problem from a different perspective. <S> I have an airplane that I am desiging <S> and I have several design parameters, imagine that one of the constrains of design is that, for example, we need to be able to be able to lift the aircraft with a given weight, but that point is not the nominal point, is just one design point in the envelop you shall design for. <S> Essentially, at design level, you will see what is the maximum ever lift you can generate and multiply by the surface and the dynamic pressure. <S> Dynamic pressure will be given by the design point, and your designing parameters will be surface of the wing and maximum lift. <S> So... you are interested in optimizing the cruise condition... <S> obviously you will try to make that wing, for the given lift of the cruise condition, having the less drag possible. <S> This is bringing you to a trade off, what will providing less drag, an extra surface or a set of VGs? <S> Given this trade-off, you've got the installation or not of VGs. <S> Essentially you will be using the energizing capabilities of VGs when there is a trade off in an specific condition. <S> I have described you a condition that is sizing the size of a wing (typical from tail plane) but you can also take a look to this question where another specific condition is discussed related to the engine nacelle.	Given a designed wing the stall angle can be reduced and also the maximum lift can be increased. The actual motivation to use VGs is the overall most efficient solution.
Is wing sweep needed on supersonic aircraft? Area rule states that bodies with the same crossectional area distribution have the same drag. Does that mean I could use a straight wing on mach 1.2 aircraft with performance as high as sweep winged plane as long as they have the same area distribution? <Q> Just witness the length to which aircraft manufacturers went to sweep wings for Mach 2+ flight . <S> However, sweep comes with its own set of problems . <A> A little more on the F104 vs sweept wings. <S> In order to optimize a design for a given mach number greater than 1.0, the wing needs to be entirely enveloped within the mach pressure wave cone. <S> Hence, large area with sweep or small area short and straight. <S> Conversely, a long straight wing would be partially inside the mach cone and partially outside (not optimum). <A> Wing sweep is not required on supersonic aircraft. <S> The F104 was a mach 2 interceptor with a straight, but tapered wing. <S> It wasn't a well respected aircraft. <S> The Lockheed tests, however, determined that the most efficient shape for high-speed supersonic flight was a very small, straight, mid-mounted, trapezoidal wing. <A> You will generally want to have a Swept Wing for supersonic aircraft as the swept wing delays the formation of shock waves. <S> The type of drag that a swept wing prevents is Wave Drag and would be a major source of drag at supersonic speeds. <S> I believe that the "Area rule" that you are quoting refers only to parasitic drag. <S> You may want to read this Wikipedia article on swept wings to learn more about their benefit. <S> The main downside of using swept wings is wing tip stall but that can usually be overcome with a Washout design. <A> Another example of a supersonic aircraft that did not have swept wings is the Bell X1 , the first aircraft to achieve supersonic speeds (and survive the experience). <S> Given that the aircraft was pushing the unknown, the fuselage was shaped like a .50 caliber bullet, an object known to go supersonic smoothly... <S> trial and error was a factor in pre computer aircraft design. <S> Note, though, that like the F104, the X1's wings are fairly short and set back on the fuselage, so that they are inside the shock wave cone coming off of the nose at supersonic speeds. <S> As the X1 could barely go beyond Mach 1, its wings weren't as narrow as the F104, whose top speed was Mach 2.	Sweep is not strictly required, but helpful to increase supersonic L/D .
stall with max power I saw a video of a test flight of a GA plane and it stalled with max power and with a moderate AOA (angle of attack). How can a plane stall with max power (with the wings flying below the critical angle of attack)? <Q> Airplanes stalling only below a specified airspeed is a common misconception largely due to the fact planes are usually listed with a “ stall speed ” below which the aircraft will generally stall in most situations. <S> However if the critical angle of attack is exceeded at a higher speed a stall can also occur. <S> The only way to know the critical angle of attack is from an angle of attack measurement device installed on the airframe <S> it is inherently somewhat different than the aircrafts attitude. <A> If it stalled, by definition, it did exceed the critical angle of attack. <S> Most GA aircraft have a critical AOA between 12-18°. <S> Pretty shallow compared with aircraft equipped with LE and TE high lift devices. <A> If you are wondering how an airplane can stall in straight and level flight with the engine running at full power, the answer has to do with the power curve . <S> However, by definition it cannot stall "with the wings flying below the critical angle of attack stall". <S> The only reason it might appear to do so while in a straight and level flight would be due to heavy icing or some other factor that reduces the critical angle of attack. <A> You're probably referring to a power-on stall. <S> This type of stall is the result of climbing more steeply than the engine can provide power for. <S> From AOPA <S> Pilots can become distracted or disoriented after takeoff and climb too steeply. <S> The airplane slows, the wing angle of attack increases, and an unintentional stall (and potential spin) is the result.	A plane (airfoil) can stall at any airspeed and/or power setting so long as the critical angle of attack is exceeded.
Why is it necessary for pilots to have trim controls on fly-by-wire aircraft? On Airbus family airliners why is it necessary for the pilots to have the facility to trim when there is no aerodynamic feedback through the flight controls? <Q> Airbus FBW aircraft have an Autotrim system, so the trim wheel is only there as a backup. <S> In normal law, the trim system is invisible to the pilot. <S> The sidestick pitch inputs control load factor , unlike in a yoke aircraft where it controls elevator deflection. <S> This means that that the farther you move the stick forward and back the faster it pitches, but at center it is a zero load factor , so it stays at its current pitch angle. <S> As an example of the difference, if you want to pitch up 10° in a yoke aircraft you pull back on the yoke until it reaches 10° and hold it there . <S> If you let the pressure off it will return to 0° unless you retrim for 10°. <S> Whereas in Airbus normal law, to pitch to 10° you pull on the sidestick until it reaches 10 <S> ° then let go. <S> The FBW system automatically maintains the new pitch angle. <S> If you don’t do anything else the FBW system will automatically trim the stabilizer to the new pitch angle. <S> There is no feedback as to elevator deflection because it’s not directly controlling the elevator. <S> Pilot misunderstanding of the Autotrim function was a factor in the crash of XL Airways flight 888T. <S> When the AoA vanes froze, the computer switched to Alternate 2 law, which does not have the Autotrim function. <S> Due to the AoA fault, the autopilot had trimmed the aircraft full nose up. <S> When the AP disconnected and control law degraded it remained there and notified the pilot that he needed to trim manually. <S> The PF did not realize this, so never moved the trim wheel. <S> With the stabilizer in full nose up trim he didn’t have enough elevator authority to prevent a stall and crashed into the ocean. <A> Note that on any aircraft the trim control system is fundamentally a speed selector. <S> Also, airliners with hydraulic controls and moving stabilizers have no aerodynamic feedback (and the neutral position of the column doesn't change with trim changes) and you are just pulling and pushing against springs when you move the stick. <S> Trimming these airplanes is quite different to trimming an airplane with an elevator <S> trim tab. <S> Trimming to a new speed requires that the column be displaced to pitch the airplane up or down and held there, then a trim input to move the stabilizer, then release some or all of the elevator input to see the result, then another trim input, release etc until the airplane is stabilized at the new trim speed with the control column at neutral. <S> It's a rapid tug/blip-the-trim/release/tug/blip/release/tug/blip/release process that becomes second nature once you figure it out (watch any cockpit video when the pilot is hand flying and slowing down during an approach). <S> A FBW system will mimic the same responses using software moving the elevator and stab so that the same instinctive pilot inputs will work and trim inputs change trim speed the same way. <S> Not sure about Airbus, but on the FBW C Series there is actually a trim speed bug on the primary flight display that tells you what your new trim speed will be when you make a trim input, taking away the guesswork zeroing in process when slowing down or speeding up. <A> The trimmed position of the flight controls has different meanings for different control systems: <S> For manually controlled flight control surfaces, the flight controls trimmed position is the stick equivalent position that the control surface returns to when it is released, no hand or feet on the controls. <S> The surface position where aerodynamic hinge moments are zero. <S> For hydraulically operated irreversible control surfaces, the stick trim position is an offset to the artificial feel spring - <S> the position that the stick feel spring returns to when released. <S> Notice that some irreversible systems have Q-feel: <S> feel springs that change their spring stiffness as a function of dynamic pressure. <S> The B737 has such a system. <S> In both cases, whether the aeroplane remains in a trimmed state of flight (no heading or altitude change) once the stick is released depends on where the zero force position is located. <S> This location needs to be set by the pilot, via the trim switches or trim wheels, which set the position of the trim tabs or stabilisers. <S> In the A320, there is an artificial feel spring loading the stick as well. <S> The only difference with the artificial feel spring system of an irreversible hydraulic actuation system, is that the zero force position never changes, and that in normal mode this is also the aeroplane trimmed position. <S> In degraded modes there is no automatic trimming of the flight state, and the pilot needs to operate the trim wheel in order to set the stabiliser angle. <S> This is also the backup pitch control mechanism for when all hydraulics are off.	It's because on FBW aircraft the software is designed to mimic the behaviour of a mechanical system so that the instinctive pilot inputs will have a similar result.
Are there regulations for water skiing in a ASEL aircraft? What are the regulations regarding water skiing with ASEL aircraft, as in touching your tires down in a particular body of water such as a lake or river? Sometimes referred to hydroplaning. <Q> ( bush-air.com ) <S> But the closest thing to an official mention of it I found was in a 2009 piece on Anchorage Daily News , where an unlicensed pilot water skied, hit a sandbar, and it didn't end nicely for his Super Cub. <S> The FAA regional counsel said: The practice is called water-skiing, and it is not encouraged. <S> It was developed for landing in tight quarters, like sand bars where space is short, but doing it wrong can be disastrous. <A> No regs against it but is strongly discouraged. <S> If an accident did occur, you’re likely to be cited under 14 CFR 91.13 Careless and Reckless Operation and the incident will probably be used as evidence in a Wrongful Injury/Death lawsuit. <A> It's very common in Alaska and was supposedly started (~1930-1935) by bush pilot <S> "Bob Reeves" delivering freight with skis from Valdez Alaska mud flats to higher snow covered altitudes and glaciers. <S> It's now common among J3 Cubs with balloon tires (often Goodyear Blimp tires). <S> Youtube clip of Bob Reeves landing on mud flats in 1938. <S> While most of use know the rating as a "Float Rating" , the FAA officially designates the privilege as a "Seaplane Rating" . <S> Therefore the aircraft must be in a "seaplane" configuration in-order to require a special license. <S> Amazingly, the FAA does not require a sign-off or special training for skis - despite the fact there can be as much or more of a difference in technique compared to the mandatory tail wheel sign-off! <A> The original useful purpose for skimming was to allow landing by bush planes in tight areas near water. <S> This is what is meant by skimming: Youtube <S> and there are no specific regulations against doing it. <A> Like a lot of things where there are no legal prohibitions, the real issue is if you have in-motion hull insurance or not. <S> If you don't have in-motion hull, knock yourself out. <S> If you do, better make sure its covered, otherwise you'll be in for a surprise if you mess up.	I couldn't find any regulations for it. No "hydroplaning" with tires or "skimming" with skis is not illegal.
What exactly are "clipped" wings? What exactly does "clipped wing" mean? Been having a rather heated debate. My understanding is that clipped means the tips were removed after manufacture. The other party claims that if it was designed squared off and built that way, it is called clipped. <Q> As far as I can find you may both be correct. <S> The term originally was used to describe a stock aircraft having it's wings shortened after-market. <S> Here is a reproduction of the December, 1970 issue of SPORT AVIATION Magazine article comparing stock vs clipped http://home.xcountry.tv/~dann/id72.htm <S> This modification has become well known and the clipped wing design sought after that there are planes (at least kits) being manufactured with "clipped" wings. <S> http://www.monocoupe.com/ <S> Hopefully that will give you some more points to debate over! ~Hoff <A> The term clipped wings can mean many things. <S> As @Fodder Hoff said, sometimes aircraft have their wings clipped after manufacture, but sometimes variants of certain aircraft are manufactured with clipped wings. <S> A common example of this is the supermarine spitfire. <S> The first Spitfire models had beautiful elliptical wings that were not clipped. <S> Then, starting with the Spitfire Mk. <S> V (Mark 5), some had their wings clipped to increase the roll rate and low altitude performance of the fighter. <S> This was done because the Focke-Wulf-190 outperformed the Spitfire in those two aspects. <A> The term "clipped" far pre-dates 1970 and generally--as in the Spitfire context-- means a design modification that created a wingspan shorter than the original design. <S> It generally does not mean that someone came along with a chainsaw and shortened the wings after the aircraft was already built-- although in the context of modern civil aviation, occasionally that is exactly what it means.	It appears that whether is was done 'aftermarket' or manufactured that way, clipped wings are those that have been shortened from original design to improve aerobatic capabilities.
Why was a Lockheed L-1011 chosen by Orbital ATK for its Pegasus launches? Not sure whether this fits better here in Aviation, or would be better suited for Space, but since the question is about a terrestrial aircraft, I'll start it out here. The topic of my question is why was the Lockheed L-1011 chosen by Orbital ATK as its aircraft launch platform for its Pegasus spacecraft launches? On the surface, choosing an L-1011 seems odd because it's no longer being manufactured (not a big deal, probably), but also with so few airworthy L-1011 aircraft still in existence, it seems like an odd choice, being such an unusual aircraft from a maintenance and spare-parts standpoint. Is there some performance reason that they chose to use an L-1011 that makes it a better aircraft for their launch purposes than other aircraft of similar size that have higher numbers of still-flying airframes? <Q> This allowed them more clearance than other aircraft although the L-1011 still have to be jacked up to mate the Pegasus. <S> Second, while the L-1011 is no longer manufactured, there are enough of them still sitting around that getting parts was still an option, and in fact, sometimes entire aircraft were available for purchase. <S> Third, they were able to acquire their own L-1011 simulator from Delta <S> and they operate it on a regular basis to maintain their flight currency. <S> Since they own it they can make modifications to it to allow them to not only simulate their training environment but also their launch environment. <S> And lastly (although may not have been a consideration) <S> some of the pilots of the Stargazer were Lockheed test pilots. <S> For more information, you should watch this short video: NASA Edge Program - OrbitalATK <S> ICON Program <A> ( Source ) <S> The initial carrier was NASA's DFRF B-52-008 – aka Balls 8 . <S> A detailed study considered the B-52G, 747, DC-10, and L-1011. <S> A study was initiated in late 1991 to identify the optimum carrier aircraft for long term Pegasus launch operations. <S> Some of the aircraft considered included the B-52G, Boeing 747, DC-10, and Lockheed L-1011. <S> Some of the factors considered included performance capability (altitude and speed capability for launch), aircraft range (both ferry and launch), modification complexity and cost, aircraft availability, acquisition cost and operational costs. <S> Following a detailed trade study, the Lockheed L-1011 was selected for conversion to serve as a Pegasus carrier aircraft. <S> Orbital Sciences acquired a L-1011 aircraft in May 1992, modifications to carry Pegasus are complete, and the aircraft is currently undergoing certification testing. <S> The L-1011 is scheduled to be operational in the Fall of 1993. <S> Source: <S> Pegasus XL Development and L-1011 Pegasus Carrier Aircraft - by Marty Mosier and Ed Rutkowski <S> - Orbital Sciences Corporation - 1993. <S> Is there some performance reason? <S> For a fixed payload, nothing stands out in the L-1011 that a 747 or DC-10 can't do. <S> " <S> The aforementioned detailed study is not in the public domain as far as I have looked, but that particular L-1011 has been with Air Canada since 1974. <S> The L-1011 was also not in great demand by the airlines – its slow initial sales due to development delays gave the DC-10 the upper edge – so it would not have been expensive to acquire. <A> It needed ground clearance for the rocket limiting the choice to the largest of the widebodies. <S> At the time of selection (mid 1990s) <S> the L1011 was already out of production and much cheaper to purchase than a 747 or MD11. <S> Operating cost was immaterial due to infrequent use. <S> You can see here that even with size, they still had to jack up <S> the aircraft to get the rocket underneath. <S> Given the age of the L1011 <S> launcher, an agreement was made in 2016 between Orbital and Stratolaunch to use the larger carrier aircraft for up to three rockets at a time. <S> Few details were made public. <A> They're not the only ones turning to used aircraft to do this. <S> Virgin Orbit is refurbishing a 747-400 from Virgin Airways . <S> The benefits are It's used. <S> They can own it for far less than a new aircraft and retrofit as needed Parts will be available from boneyards since similar aircraft are nearing retirement <S> It meets the need for hoisting heavier payloads. <S> The maximum take-off weight of a L1011 is 510,000 pounds. <S> That's a lot for an out-of-service aircraft. <A> Mighty Planes (Season 4, Episode 2) shows an animated view of the interior of the L-1011, with two keels spaced far enough apart for the Pegasus fin to insert into the fuselage. <S> That's the reason they give. <S> They claim it is (or was) <S> the only wide-body with two parallel keel beams.	One reason the L-1011 was chosen was that the keel beams on the L-1011 are spaced such that they could create an opening inside the aircraft for the verticle tailfin of the Pegasus when mated to the bottom of the aircraft and do so without jeopardizing the structural integrity of the airframe. So the reason would have been likely to do with the "modification complexity and cost, aircraft availability, acquisition cost and operational costs. As the rocket increased in size and weight, Orbital needed a more capable carrier.
What to look for when purchasing a headset I'm currently a student pilot, and I'm starting at an aviation university this fall to major in commercial aviation. Needless to say, I will be flying a lot. I'm looking to upgrade to a nice headset from the pretty basic one I have now, and I'm looking for a bit of guidance. I'm 6'3, so I wouldn't say I have a small head, and I've had problems in the past with headphones feeling cramped on my ears, which I don't want to be the case with my headset. I plan on having this headset for a while, at least all the way through college and hopefully several years after that. First of all, is noice-cancelling actually that important(in terms of health and comfort)? I know there are a few decent headsets are out there w/o noice cancelling, and they are quite a bit cheaper than noice cancelling headsets. I've been told about a couple commonly used expensive headsets that are pretty widely used across the industry. However, these headsets are $850+. At this price level, does the price of the headset accurately reflect quality, or is everything more personal preference? What are some of the pros and cons of the more popular headsets, and what should I look for when purchasing one? <Q> I've had problems in the past with headphones feeling <S> cramped on my ears, which I don't want to be the case with my headset <S> Some pilot shops will let you put them on your head and if you are nice to the people that lurk around the airport they may lend you one for a flight to try out. <S> I find that the Zulu's have bigger ear cups than the Bose <S> but I don't have any hard numbers on size <S> this is personal experience wearing them. <S> First of all, is noice-cancelling actually that important(in terms of health and comfort) <S> Yes, just ask any one that flew in the pre-headset days. <S> I personally find that I can comfortably fly for longer times with an ANR headset. <S> Another thing to note is that the ANR head sets tend to not squeeze your head quite like the passive headsets I find this to be the real gain in comfort. <S> One of the big functional differences is that some of the LightSpeed headsets do not cary a TSO, I belive all of the Bose do. <S> This may impact your ability to use them for commercial purposes in the future. <S> You can find a discussion on it here. <A> While "comfort" may seem like a luxury, it's no fun to fly around with a headache. <S> Give them a good try and look for minimal "squeezing" pressure. <S> Also see other answers and comments re taking hearing protection seriously. <S> Also if you routinely wear glasses (including sunglasses) be sure to test while wearing them-- they may break the earcup seal in a way that lets more noise in, or they may cause uncomfortable pressure points. <A> Good headsets are expensive, but an investment as they aren’t something you purchase every few months, you keep them for years - which makes the decision all that much more tricky. <S> Factors to consider: ANR vs PNR <S> It is significantly quieter, giving you clarity in busy airspace calls and obviously, and most importantly they mitigate damage to your hearing - cockpits are loud, especially helicopters. <S> Be weary though, their battery’s last only about 40 hours and although they will still work when this happens <S> you won’t have ANR and it is much worse than passive headsets at this point, almost unbearable to fly with. <S> PNR don’t need batteries, only advantage. <S> Impedance, high or low. <S> Without getting too technical, civilian aircraft use high impedance electet microphones and <S> military/ex military aircraft use low impedance microphone. <S> You most likely will fly Pipers/Cessnas/Robinsons, so get high impedance. <S> Plugs <S> a. <S> Dual Male Plugs - Fixed Wingb. <S> Single Male Plug - Helicopterc. <S> Bluetooth <S> It’s maybe an extra $100, <S> but it’s already so expensive don’t regret not having spent extra cash early on. <S> What will you connect it to? <S> Music, maybe. <S> Modernised instrument panels or iPads with aural flight information, yes, and it lets you make a phone call, <S> although it’s not permitted in flight - it doesn’t stop many pilots, it may just come in handy. <S> Brand <S> New contenders may have joined the game and are owed a consideration as well. <S> Consider a high impedance <S> Bose A20 lemo with the appropriate fixed with and/or helicopter adapters and Bluetooth. <S> Most adaptable option with excellent after market service. <S> This is what I have experience with. <S> The Lightspeeds are really nice <S> but I have no experience. <S> The David Clarks are my favourite PNR headsets.	With regards to active noise reduction in a headset, it makes a huge difference. Do your best to test them out before you buy. Panel Powered plugs - Here are various types but the most applicable to your case would be lemo - most newer aircraft have these plugs and allow you to use your ANR headset without batteries. The competition gaps have closed but the biggest international brands with good after purchase service are David Clark, Bose and Lightspeed.
When flying VFR without GPS, how do pilots know if they are inside controlled airspace or not? How do VFR pilots know whether or not they are inside controlled airspace if they don't have GPS onboard? <Q> VFR aviation maps called "sectionals" (and now GPS map displays) depict the types of airspace through borders with different colors and dashed lines . <S> You can buy or download the maps for free from this FAA site . <S> It is always the responsibility of a pilot to know where they are and follow all applicable laws. <S> In the US, a pilot that breaks a rule because they didn't check NOTAM's can expect certificate action. <S> NOTAM's will inform the pilot of TFR's, "hot" military zones, and other important regional and local (i.e. airport) regulatory information. <S> I got my PPL in 1975 and still carry maps with me. <S> I plot an "X" along my route every 10min of flight time (20-30mi). <S> As I reach each checkpoint, I follow a very old axiom, " <S> Never.. <S> Ever.. EVER! <S> .. <S> proceed to the next checkpoint until you identify where you are and what corrections are needed for the next checkpoint" . <S> In this manner, you can never be further than 1 or 2min and 1-2 mi from where you should be. <S> Even when sightseeing with no particular route, I routinely mark a map about every 10min with my location. <S> In my 2500hrs of flying, the most I have ever been off in my navigation <S> was 10mi (even when flying 1500mi x-country). <S> So, knowing where you are is not difficult if you practice the skill. <S> The front of the map has a legend to remind pilots what the coloring stands for. <S> Sectional map ( <S> US Gov public domain) <S> Front map legend ( <S> US Gov public domain) <A> Use of a sectional chart and pilotage. <S> You will have to be aware of where you are using ground references while cross referencing where the boundaries of controlled airspace lies in relation to those references. <S> For example if you’re flying around to the west of John Tune (KJWN) airport in Nashville, TN and will notice the river bends near the airport. <S> Anything to the east of them lies in the Nashville Class C shelf between 2400 and 4600 ft MSL. <S> A similar process can be used to assess your position relative to the surface area of the Class C airspace. <S> You can also pinpoint your location if your aircraft has two NAV radios and OBS heads using the intersection of two VOR radials or one NAV radio and a DME by locating you polar position relative to the VOR. <A> Other answers give great examples of this already, I don't have to repeat it. <S> But I thought I could add some real life experience here: 1) <S> Memorizing the Area <S> Glider pilots, especially trainees, often fly without maps and GPS. <S> As they tend to stay close to their departure airfield, they can be sure to not get into controlled airspace. <S> Trainees generally memorize beforehand where such airspace begins, for example at my old aviation club <S> we knew we had to contact a nearby airfield when going above a certain altitude, and going past the nearby city to the north <S> would also lead into that airspace. <S> This of course restricts these pilots to only flying within this well-known area, as anything beyond could or could not be controlled. <S> 2) Planning a Route Ahead of Time <S> I have flown cross country without any GPS for training purposes when I was a student pilot. <S> My trainer and <S> I plotted our route using the map before even going to the airport. <S> We planned to fly along highways and other highly visible landmarks in order to keep our orientation and avoid controlled airspace. <S> This way we barely ever needed the map while flying and still knew where to go.	Generally: By Using a (Physical) Map Aviation charts have landmarks and airspaces on them, which you can use to estimate where you're at.
Can ATC provide VFR flight following to a VFR aircraft in class E airspace? Just wondering if ATC can do this or not. I'd also appreciate input on whether it's useful or a good idea, and how it looks in the real world. <Q> They can. <S> I often pick it up here in the Northeast since the airspace is fairly busy. <S> Generally it helps to improve your radio skills and may reduce your work load ultimately. <S> As for who to contact, that can change. <S> I had this very question during my training (asked here) <S> and you can find the answer here. <S> If you are departing from a controlled field you can sometimes ask the tower to set it up which they may or may not do. <S> The Airport Facility Directory will have an "approach" and/or "departure" frequency listed for most fields which is generally who you call. <S> If you are in the wrong area they generally send you over to the right controller. <A> Yes, you can request VFR flight following in Class E airspace and 90% of the time you will be flying in Class E airspace. <S> There’s nothing unusual or difficult about it; you simply request flight following and ATC will usually approve it unless traffic congestion, emergencies, etc consume all available ATC resources for this. <A> Yes, as far as I know the entire US Airspace is covered by one center or another. <S> It is the centers which provide flight following. <S> For example on a recent flight from CYKZ ( Toronto Buttonville ) to KFRG (Farmingdale Republic on Long Island , NY), I asked CYKZ controller for flight following ( on the ground ) and she handed me off to Toronto Center. <S> I again requested flight following and the request was granted. <S> Toronto Center handed me off to Buffalo Center, then to Rochester center, Binghamton Center, Wilkes Barre Center, Boston Center, New York Center and finally to KFRG Tower. <S> I believe if I didn't pick up flight following with Toronto, then I could have picked it up with any of the other centers mentioned above. <S> In the JFK area I have picked up flight following with New York approach <S> ( there are different frequencies depending upon whether you are going East or not). <S> On a recent approach NY approach frequency was very busy and I ended up picking up flight following from Albany approach on my way to Montreal. <S> These rules apply in US only. <S> Canadian rules are different and I am still trying to figure them out.	Generally speaking I was taught that flight following is always a good idea. It is a useful tool to you in the cockpit and can provide advisories of fast moving hard to see aircraft as well as those that may be approaching to overtake you.
What does the "T" on sectional charts mean in reference to airspace altitude? These are present in the San Francisco class bravo / Oakland class charlie and O'Hare class bravo / Midway class charlie. <Q> T is used to signify that the top of Class C airspace that lies under Class B is the bottom surface of that airspace. <S> This is important when the Class C segment lies under multiple layers of Class B, where no single top altitude applies. <A> You can start many "what does this thing on an FAA chart mean" questions with the FAA's Aeronautical Chart User's Guide . <S> It doesn't go into a deep explanation, but does show it as an example in this case. <S> The symbol can be found on page 17 of the 2018 guide. <S> The figure at left identifies a sector that extends from the surface to the base of the Class B. <A>	Since the Class C airspace is sandwiched between the surface and the shelves of the nearby Class B airspace, the T indicates that the upper limit of the ClassC surface area is on the bottom of the overhead Class B shelf.
Are there any passenger aircraft with no cabin access to/from the cockpit? Most passenger aircraft (airliners and business aircraft) have an internal door or doorway connecting the cockpit area to the main cabin; are there passenger aircraft where there is a solid partition isolating the cockpit from the passenger cabin, and passing between the two requires exiting the aircraft? Yes, I know that many early passenger aircraft had enclosed cabins with separate, open cockpits; I'm wondering about aircraft with an enclosed cockpit and a separate, enclosed cabin. <Q> The only one I can think of is the Junkers F13. <S> It has an open cockpit and an enclosed 6 passenger cabin. <S> There's no access between the two areas; only a small window. <S> Credit: <S> THOMAS LÜTHI / RIMOWA 2016 <S> The CEO of Remowa is having recreations made of the aircraft which first flew in 1919. <S> It was (according to Rimowa) <S> the world’s first all-metal commercial aircraft. <A> Some DH.83 <S> Fox Moth had an enclosed cockpit (not all, some had open cockpits).Several examples are still flying, including one in Ottawa. <S> It has a cabin for three passengers with an entry door, and behind and above that a cockpit with (in some aircraft) <S> a sliding glass canopy Flying example from Vintage Wings of Canada Wikipedia page <A> Okay, I may have found one; the Bristol Wayfarer (a passenger version of the Bristol Freighter ) had a passenger cabin in the main fuselage, with an enclosed cockpit perched on top. <S> The aircraft's arrangement makes me suspect that the cockpit was isolated from the main passenger cabin, but I can't confirm yet whether or not that was actually the case. <S> As @jwenting's comment points out, the Freighter must have had some internal access between the cockpit and cabin, as it doesn't appear to have had any external cockpit access doors (except for a roof escape hatch which was probably not routinely used for non-emergency crew ingress and egress). <S> There's also the Tu-116 , a modified Tu-95 bomber with two passenger cabins mounted in its fuselage where the bomb bay had previously gone, with no internal access between these and the cockpit; two, originally meant to carry Nikita Khrushchev to other countries (although, as it turned out, they never actually carried the Comrade General Secretary), were built, but served only as military transports (so, partial example?). <A> as far as I know, there is no such aircraft. <S> Simply because it would be very hard to realize. <S> The cockpit is at the very front of the aircraft. <S> Followed by the cabin. <S> Even large modern cockpits are comparably small and don't offer a lot of space. <S> These doors are also used for the flight crew, to get aboard the plane, passing then through the cockpit door. <S> Meaning not to have a cockpit door, would mean that the cockpit would have to had its own door, which could only be used by the flight crew to get inside and outside. <S> This would mean a way larger cockpit and would probably not make a lot of sense, given that most aircraft are already pretty scarce when it comes to free space. <S> The cockpit door of all modern aircraft however, is locked from unauthorized access. <S> We have a switch in the cockpit, where we can put the door into auto, unlocked or locked mode. <S> If unlocked, the door is open. <S> If locked, the door is closed and cannot be opened by anyone. <S> In standard, auto-mode, doors are locked but can be opened by cabin crew, usually by entering a key combination. <S> Also the side cockpit windows can be removed in case of emergency and serve an an emergency exit for the pilots, which is used only by them. <S> To leave the aircraft this way, a rope is needed. <S> One of these ropes is part of the emergency equipment of both, the PIC and the PNF/FO and is found in a storage located on the upper side to of the cockpit to the left and right. <S> Smaller aircraft and general aviation planes usually don't employ a separate cockpit. <S> Cabin and cockpit are just one big space. <S> Cheers	All modern passenger aircraft are designed in such a way that the front door or doors (if one on each side) are located right BEHIND the cockpit.
Could an aircraft be tied down, then throttle up and release for takeoff in order to use a shorter runway? Could airplanes, in theory, be designed to takeoff by first tying the tail to a post, throttling the motors to full power, and then letting loose? Could it even take off while tied, if the cable is attached to a point that's higher than the tail of the aircraft? <Q> This is typically done by moving the wing, and thus also the fuselage it is attached to, forward. <S> There is, of course, another way to look at that: aircraft can take off without moving relative to the ground, if exposed to a strong enough wind from the front of the aircraft. <S> That said, keeping the aircraft stationary, "throttling the motors full power, and then letting lose" is a very common short-field take-off technique at least for propeller aircraft; there's nothing theoretical about that. <S> The aircraft is, however, typically kept stationary by applying full brakes while applying full engine power, rather than by using an external tie-down. <S> The tail likely isn't designed to take the force of holding the aircraft stationary while the engine is running at full whallop, although there's no reason why such an anchor point <S> couldn't in theory be installed (see motor aircraft towing gliders to altitude, scale up somewhat, and you're close). <S> Since the brakes are already there and need to be powerful enough to at the very least hold the aircraft stationary during the engine run-up prior to take-off, which happens at a significant fraction of full power and can quite well happen at a hold short point <S> just before the runway, there's no reason to spend weight on reinforcing the tail section to that point. <S> Instead, just use the brakes for the few seconds needed. <A> No, an airplane cannot takeoff while tied to a post. <S> What creates lift is the speed of the wings through the air. <S> (or the alternate frame of reference view: <S> The speed of air over the wings.) <S> If the plane is tied to a fixed point, like a post, it is not moving in the air, and the wings will not have any lift. <A> Well that’s part of a catapult launch from a carrier. <S> The aircraft is held motionless on the cat by a holdback bar attached to the nosewheel or a holdback bridle which is also attached to an anchor point on the flight deck. <S> The link between the bar or bridle and the aircraft is a frangible metal link, sometimes called the ‘dog bone’ because it is shaped something like a dog biscuit. <S> It is strong enough to hold the aircraft still, even under full power but fractures when the force of the catapult or EMALS is applied to the airframe during the launch stroke. <S> For terrestrial takeoffs, I suppose one could do something like that <S> but it is much simpler to just hold the brakes, run up to full power, then release the brakes and perform the takeoff roll. <S> This is the preferred method of takeoff for light twins and turboprops, as it minimizes the length of the takeoff roll.	As already mentioned, aircraft cannot take off without moving through the air, because it is the airflow around the wing that generates the lift required for take-off, and the only practical way of generating sufficient airflow around the wing is to move the wing through the air.
What are the disadvantages of using just rudder to roll an airplane? Ultralights with slight dihedral will roll and yaw on rudder input (e.g the Bloop 3 , Maxair Hummer ) so some don't have ailerons for the sake of simplicity. Is this kind of control input advisable, or are there disadvantages? <Q> It works in a half-assed way but the key word is half-assed. <S> You'll always be skidding around the sky since sideslip is required to obtain and maintain any rolling moment. <S> Control response can be somewhat laggy, since you have to induce a skid and wait for the roll, depending on how much dihedral you have. <S> So to have something approaching snappy control response, you need way more dihedral than is necessary for normal lateral stability. <S> The inability to cross control limits the ability to handle crosswinds and prevents you from using sideslip to increase descent rate. <S> So it works after a fashion, but will never be as good as full 3 axis. <S> The thing with ultralights is that because of the really low mass/large surface area, they are really strongly affected by turbulence, and when close to the ground, half-assed control authority is the LAST thing you want. <S> Control authority is not a place I would cut corners in the interest of simplicity. <S> I think that the attraction of 2 axis control for ultralight designers was in the idea that non-pilots getting into ULs would think "Hey that must be only 2/3rds as difficult to learn as 3 axis. <S> Must be better." <A> Rudder only limits banking as described very well by John K , and might be a distorted view of increased safety by helping the pilot to not become disorientated. <S> After considering John K's comment it appears to me this is more a marketing or cost savings stunt, then a safety consideration. <S> A stall in a skid or slip is all that is necessary to enter a spin! <S> So, essentially you are trading a less hazardous situation (disorientation) for the biggest pilot killer on the planet! <S> (spin) <S> source <A> I have some tens of hours flight experience with radio control aircraft that fly this way -- throttle, elevator, and rudder. <S> How well it works depends very much on how much rudder authority you have, and how much dihedral. <S> I have seen and flown aerobatics with these no-aileron aircraft, including prolonged, controlled inverted flight (tricky, because yaw-roll coupling reverses when inverted), outside snap rolls (again, roll is reversed relative to rudder and the aircraft may tumble if the wing unstalls before rudder is neutralized), as well as more conventional slow rolls, chandelles, Immelman turns, etc. <S> I wouldn't expect an ultralight to be flown through any of these maneuvers (at the least, you'd need full aerobatic stress limits), but I would expect one to fly well in normal operation if the rudder authority and dihedral are correctly balanced. <S> If you're interested in building one and don't want to follow an existing design, I'd very strongly recommend building a radio control test model to verify the setup (tail moment, surface deflection, CG position, thrust axis, etc.) <S> before cutting any tubing or fabric.	It may also be an attempt to not over stress the structure or prevent a stall in a high G turn.
How can larger wingspan decrease the strength of wingtip vortices? In the last paragraph from the link below, it states that Vortex Strength is inversely proportional to Wingspan. Why is this? http://avstop.com/ac/flighttrainghandbook/wingtipvortices.html EDIT: From https://howthingsfly.si.edu/aerodynamics/vortex-drag : "The farther a vortex is from the main body of the wing, the less influence it has on the wing." Again: why? <Q> The strength of the wing tip vortices depends upon the pressure differential between the top surface and the bottom surface. <S> In general larger heavier planes produce stronger vortices. <S> Now consider two planes with the same weight but one with shorter wing span and one with longer wing span. <S> The pressure differential between the top and bottom surfaces of the wing for the plane with the longer wingspan will be less ( pressure=force/area). <S> Thus the strength of the wing tip vortices for the plane with the longer wingspan will also be less. <A> Wingtip vortices, as from the wake rolling up at the wingtips, become larger with increasing lift and decreasing aspect ratio. <S> At equal wing area, the low aspect wing must deflect the airflow to a higher angle, relative to the free air stream. <A> For a useful comparison, we need to ensure each wing has the same lift coefficient $C_L$ . <S> As span increases, assuming chord is constant, then the wing area and aspect ratio ( $A$ ) also increases proportionally. <S> Since wingtip vortex strength is related to the induced drag, you may have seen this relationship: $$C_{D_i}=\frac{C_L^2}{\pi e A}$$ <S> The larger the span, or aspect ratio, the smaller the induced drag (i.e. wingtip vortex) for the same lift coefficient. <S> But why? <S> From the circulation theory of lift, any change in the circulation along the span will shed trailing vortices. <S> In turn, these trailing vortices will induce downwash on the wing span. <S> At the wingtip, the downwash rolls over and creates the wingtip vortex. <S> Now if the span is short, the change of circulation will be larger, thereby inducing higher downwash all along the span, and the rollover at the tip will be stronger. <S> If the span is longer, the change is circulation is gentler and less downwash/wingtip vortex is induced. <S> In the limit where the span becomes infinite, assuming the same $C_L$ for the whole wing, the circulation distribution is stretched to a constant value, such that the change in circulation along the span is zero, then no trailing vortex exists and the induced drag becomes zero as well. <A> Best way to visualize it is to take it to the extreme; look at a sailplane wing, where the area of the wing tip is a pretty small area in relation to the total area, so the leakage and resulting vortice is much smaller relative to the overall package of air displaced by the wing. <S> In other words, more span takes you a little bit closer to the theoretical infinite span wing that has no vortices at all because there is no tip. <S> Of course, adding span without reducing chord adds wing area. <S> If you want to compare tip losses of two wings with the same area, they should really be talking about aspect ratio.	It's because the "leakage zone", where air is flowing around the tip, is smaller relative to the total wing area if you add more span without increasing chord.
Is VOR identification automated in modern avionics? Is the VOR identification via audible Morse code automated in modern autopilots / avionics? Or does a pilot in an A380 still sits in there, listens and compares the .-. .. -.. to her charts? <Q> Modern air transport and bizjet avionics do decode the audio ID and provide it digitally on the data output bus. <S> This data is displayed on the Nav display or RMI (depending on Mode) along with the frequency. <S> It's not as common for general aviation radios to have this capability. <S> VORs that comply with ARINC Characteristic 711, VOR MB Receiver, output the ground station ID in two ARINC 429 Labels. <S> The first and second characters will be in Label 242. <S> The third and fourth (if there is a fourth) characters will be in Label 244. <S> Characters are coded in ISO 5 format. <S> Since all modern radios are DSP based, detecting and decoding the audio tones is a fairly straightforward process. <S> The radios also provide an analog audio output, so the crew can select the VOR radio on the audio panel and listen to the Morse code if they desire. <S> (I'd be surprised if you found a pilot that did that routinely.) <S> ILS is similar. <S> The ILS ID is contained in Labels 263 and 264. <A> Even small planes have radios that can decode & display identifiers. <S> The Avidyne IFD540 is one such example. <A> This is how it looks on the G1000 PFD/MFD (in the top left corner of the screen; taken from the Garmin manual):	As everyone said, modern avionics is capable to decode the audio code of the station, even on small GA airplanes.
How are leaks in door rubber seals detected? There are few reported incident where the rubber seal on the door was damaged and it took numerous hours to find the cause and then find the location of the damage. I want to know the ways to detect the leaks mostly for the big passenger jets. I am not sure if this can be detected during maintenance checks or even aircraft is in air. <Q> Testing the doors (and windows) by pressurizing the cabin eats into the aircraft's pressurization cycles. <S> Instead vacuum is used to simulate the in-flight conditions. <S> A special fabric and a sheet with attachments to hoses are attached to the outside where the door/windows are to be tested. <S> Vacuum is created between the fabric and fuselage, thereby locally simulating an in-flight differential pressure. <S> If the vacuum doesn't hold, it means there is a leak, which can be pinpointed from the inside with sensitive equipment. <S> Image and reference: Lufthansa Technik AG <A> Pressurized aircraft often leak like sieves once they get older. <S> It's difficult to set limits unless an OEM provides a specific procedure, and an OEM procedure may be designed for new a/c as a quality control measure without any latitude for service deterioration. <S> There isn't really any guidance on leak rates in the FARs for cert purposes. <S> There is only language limiting exposure time for passengers to low cabin pressures for emergency descents, which has an indirect impact on leak rates. <S> Beyond <S> that it's just the ability of the bleed sources to keep the cabin pressurized. <S> An airline may do a fuselage leak check on a heavy check interval like C Check (typically 5000 hrs) where they will pressurize the fuselage in the hangar (or use a vacuum system as ymb1 mentioned) and go around listening and spraying with a soap bottle. <S> It'll depend on their maintenance program. <S> If there are no service limits for leak rates however, they probably wouldn't do that kind of test if there are no pass/fail limits and will only do it as a troubleshooting exercise. <A> One common way to detect door seal leaks (in aircraft, cars, refrigeration, and so forth) is to (slightly) pressurize the cabin or storage space with a tracer gas and use a detector to look for locations where the gas passes the seal. <S> Obviously, this is easier with a smaller space an/or shorter total seal length, but if the gas is something common and cheap like carbon dioxide, it may be practical for even a full size airliner cabin.	From an operational standpoint, a leak will get looked at either when there are pressurization irregularities like a crew writing up a "slow to pressurize" snag of some kind, or when there are complaints about noise or drafts from door seals.
If a pilot ejects, what is the autopilot programmed to do? If a pilot uses his ejector seat during flight, what is the autopilot programmed to do? As a developer myself, I would want to build in a way for the plane to try and save itself if possible (to save money) by auto-landing, or at the very least, calculate the nearest least-populated area for a crash-landing. So I'm wondering if anything like this is even written into the software. <Q> I would want to build in a way for the plane to try and save itself if possible (to save money) by auto-landing <S> Had the situation allowed saving the airplane the human pilot would definitely have tried that first. <S> The fact that a trained fighter jet pilot decided to eject from an aircraft knowing that the ejection was a last resort and could be deadly, signifies that the plane was not able to be flown safely anymore. <S> On top of numerous irrecoverable problems at that point, one of the most significant issues is the fact that ejection destabilizes the flight path and the increased drag (because there is no longer a canopy on top) makes it even harder to safely glide that jet, let alone land it somewhere. <S> There is nothing much autopilot can do at that point. <S> There have been two famous incidents that are related to your question but afaik neither of them involve Auto Pilot. <S> 1989 <S> Belgian MiG-23 crash Cornfield Bomber <S> It's just like saying <S> I know the airplane can be saved <S> but my computer will take care of it, I'm outta here. <S> See you at the Court Martial. <S> Some commentators have noted that I did not answer one basic question: Don't forget to answer the question "If a pilot ejects, what is the autopilot programmed to do?", even if the question seems moot <S> This question is too broad: there are numerous models of fighter jets all around the world, built by a number of manufactures and internal details of which are closely guarded secrets. <S> You are not going to generally find out a manual on the web listing all the actions that the autopilot software will perform after a bail out. <S> If the OP can narrow down the question to a certain model one can research and try to find something <S> but I don't believe its going to be an easy find. <S> Hence I'm sorry <S> I don't have an answer to that question. <S> I hope someone more knowledgeable goes ahead and posts an answer to that. <A> To add some context to the other answers... <S> Ejection is not a safe thing to do. <S> The two most popular ejection systems today, the ACES II and Martin-Baker, have around a 90-92% success rate... <S> the definition of success being the person lived. <S> Most ejections result in some injury to the person, as it is a fairly violent activity, with a brief 20g impact when the seat fires. <S> Almost all ejection occupants will suffer some form of spinal compression, typically they'll lose half an inch of height. <S> If the person doesn't follow protocol exactly, they may lose an arm on the way out. <S> If the head isn't perfectly in line with the spine, the neck can be broken. <S> Ejection is a measure of last resort, to be used only if the only other option is certain death. <S> So it's pretty much a given if the crew member fires the ejection seat, there is no other viable option, and the aircraft is uncontrollable, or will very soon be uncontrollable, by a pilot or an autopilot. <S> Also, if the aircraft is gyrating wildly, the seat can malfunction, or the occupant can be struck by parts of the aircraft, <S> so waiting until the aircraft is completely out of control isn't a wise move, either. <A> Whatever it was programmed to do at the moment the pilot ejected. <S> Ejection seats are complex enough without integrating special processing of the event into the autopilot. <S> Some ejections are indeed performed from aircraft that could potentially be saved, and have been landed with similar damage. <S> It's a matter of avoiding excessive risks from a gamble for an 80% chance of a safe landing and 20% a violent crash that sets the deck park on fire. <S> For certain historical reasons, many navies maintain an understandable bias against fires on the deck, and would prefer just ditching one plane. <S> On dry land, there's more latitude for crash landings. <S> As for preventing (or causing) <S> collateral damage on the ground, the only way is for the pilot to point their plane somewhere and pray. <S> The autopilot is a reactive system - it doesn't concern itself with what's wrong or model the aircraft, just corrects what happens, so, possibly counterintuitively, it's often not too bad at controlling a damaged plane. <S> Since fighter control surfaces are large enough to counteract a lot of damage-induced drag, a working autopilot has a chance to maintain its last heading even with a damaged craft. <S> And that's as good as you could get with the current level of flight automation. <A> It generally does nothing. <S> When a pilot ejects from the plane, that bird is screwed beyond saving. <S> There is no autopilot in the world which is sophisticated enough to fly a military plane even when it's fully intact, let alone when it's on fire and going down. <S> However, as I heard, there was a Su-27 model (or some descendant of the Flanker, maybe just a prototype?) <S> which had a peculiar easter egg: after ejection the onboard voice announcement system (the female voice which warns the pilot to certain things) talked for the last time: "Good bye, and thank you on behalf of the fleet. <S> " There was nobody to hear it, and the pilot's helmet has already been disconnected by this time, so it was really just some engineer's idea of a joke. <S> I don't know if it's an actual feature in current Russian naval Flankers. <A> I imagine there's probably a switch such that over enemy or unknown territory the plane self-destructs. <S> But you don't want this over your own training areas such that some kind of controlled landing may be programmed in when in training mode.	Since the autopilot can't land even an intact plane on its own, there's nothing it could do to save the plane.
Why do I get a severe headache just before landing? I had severe painful headaches two times in my entire lifetime and both times I was in flight. I see some common factors in this two occurrences which I thought could be some known pattern so I would like to know if we can take precautions to avoid a headache. The first time it happened to me in June 2007 while I was traveling from San Francisco to Newark. I clearly remember that I was in deep sleep and the crew member woke me up and asked me to open the blind as we were going to land soon. After opening the blind I was exposed to the sunlight and immediately I got a severe headache. It got settled just before the flight landed. I initially thought it could be due to tiredness, insufficient sleep and sudden exposure to sunlight from dark until a similar thing happened to me after 11 years. The second time it happened to me was during my return flight last week (Jun 2018) from US to India; it was a connecting flight from Phoenix to London. Just a few (10-15) minutes before landing, the pilot started his announcement about the landing; I got this headache for a few minutes and it settled after a few minutes. Trust me, when it happened the first time it was such a pain I never felt before in my lifetime and I got so scared that something bad is going to happen to me. The second time it was only a little better but very similar. Though I had traveled more than a couple of dozen times in between these two events, I experienced this only twice and I remember common factors in this two events Traveling from East-West. Moving to different timezone and at the destination it was dawning. Pilot announcement. Window seat. Are there any patterns to it and can we take precautions? <Q> The air in your sinuses escapes much easier than it goes back in <S> so the problem is always after a descent. <S> Feels like someone trying to drive a nail into your skull between your eyes. <S> Plug your nose with your fingers with your mouth closed and blow GENTLY and you will feel the air enter your sinuses and relieve the pressure. <S> Good idea to take a sinus medication like Otrivin with your travel kit if you are having that problem regularly. <A> All in all, sounds like an equalization issue. <S> Descending in an aircraft the whole way is about equivalent to diving 10 feet. <S> That's not a lot, but it's enough that you'd equalize once or twice. <S> When you feel the characteristic pressure difference (a dull feeling in your head), equalize, either with a nose pinch or with Valsalva (similar to swallowing with your mouth closed). <A> One's head is packed full of nerves, all running close to each other and to parts of the head, face and neck that deal with, and are affected by, changes in pressure (as noted in other answers). <S> Nervous pathways are involved in the phenomenon of referred pain , in which the site of pain-causing activity is different from but related to the site at which pain is experienced. <S> I don't know enough however to know whether the sinuses or ears can cause a headache in this way <S> - normally, pressure changes cause splitting pains localised in the front of the head or the ears, rather than what would normally be described as a headache, which is usually a more generalised pain than "a pain in the head". <S> I once, as a teenager, had the experience of descending through indescribably beautiful cities and canyons of sunlit clouds on a summer evening over Rome. <S> I was transfixed with emotion at the heavenly magnificence that was unfolding itself through my window. <S> The next thing I knew, without any warning or preamble, was the sensation of someone inserting a hot soldering iron into the root of one my upper teeth. <S> The pain was excruciating, I have not experienced anything like it before or since. <S> It endured for hours, but by the following morning had faded. <S> The teeth are very sensitive to emotion, apparently (according to dentists). <S> But, this could also have been an effect of changing pressure on the nerves in the face and head.	Your sinus passages were obstructed and it was atmospheric pressure squeezing your skull as the increasing pressure on the descent tried to equalize the pressure.
What are the drawbacks for manufacturing a large airliner capable of water landing? Emergencies are rare but still occur. Apart from weight and extra fuel costs, What are the drawbacks for manufacturing a large airliner capable of water landing in case of an emergency? Assuming the extra weight problem could be mitigated through design and cost cutting techniques and advances in material science would this be feasible for airliners? <Q> Maintenance. <S> Ditching survivability calls for overwing engines, as underwing ones act as scoops and torque the aircraft. <S> But underwing engines are quieter for the pax and much easier to access. <S> Plus, you'll need to make most of the openings airtight, and regularly inspect and replace the seals. <S> But of course weight, drag and extra fuel are a big deal - with better materials you'll still be picking between better reducing fuel usage or improving ditching survivability. <S> The latter is also only helpful in controlled ditchings, which are mostly being prevented through engine reliability. <S> That said, airliner design has shifted from "don't crash" to considering crashworthiness at every stage. <S> So it's possible that ditch-worthiness might become a larger factor in design. <S> But it's going to take a couple high-profile high-fatality controlled ditchings for the authorities to make the call to sacrifice fuel efficiency for it, which is currently a big deal due to rising oil costs and AGW concerns. <A> Airliners are already designed to survivably land on water in an emergency. <S> You usually can't reuse the aircraft after you do, but it is a certification requirement. <S> See 14 CFR 25.801 <S> (b) Each practicable design measure, compatible with the general characteristics of the airplane, must be taken to minimize the probability that in an emergency landing on water, the behavior of the airplane would cause immediate injury to the occupants or would make it impossible for them to escape. <S> If aircraft were not designed to reasonably land on water, then they wouldn't bother putting in rafts and the lifejackets under your seat. <A> The last major examples of large flying boats for passenger or cargo use were the Martin S2B SeaMaster and the Hughes H-4 Hercules (better known as the Spruce Goose). <S> Both aircraft never progressed passed the flight test stage due to the global proliferation of terrestrial runways in the PostWar era and no military usefulness once the German U-Boat threat disappeared from the Atlantic. <S> And there’s <S> really no valid reason to design an airplane that way in the era of highly reliable engines and multiple system redundancy.	If you are talking about seaplanes, or designing an amphibious airliner, this biggest drawback would be excess drag from such a configuration, a less than optimal aircraft configuration to accommodate seaplane characteristics, adding to weight, increased costs due to maintenance, passenger discomfort from landing on rough seas.
Can I get a medical after having had a seizure eight years ago? In 2010 I had a seizure (as of this writing that would be 8 years ago.) I was a CFI/Commercial Multi pilot, and the FAA took away my medical. I have never piloted since, though I've missed it tremendously. At the time I was told that I could not obtain a medical again unless it was after 6 years being seizure free with 2 off medication. I have been off medication for 1 year and have had no problems. I recently got a battery of tests (EKG, MRI, CAT Scan/CT Scan) etc and found no seizure activity. Have the rules changed in nearly a decade for this? Should I see an AME or would it be a waste of time? I know there is a pilot shortage now, so I'm wondering if it has gotten more lenient. <Q> This is something <S> only an authorized AME can answer for you and it there is no harm in talking to one or two of them. <S> You can find a little bit of info here and a copy of the seizure questionnaire here but that appears to be something an AME would fill out so its contents are not really useful on its own. <S> At the time I was told that I could not obtain a medical again unless it was after 6 years being seizure free with 2 off medication. <S> I have been off medication for 1 year and have had no problems. <S> If you were explicitly told this when the FAA pulled your medical then you still have another year to go at which time you can reapply for a medical. <S> In terms of regulations <S> In short the regulation reads, if you can show that you are fit to fly and we agree we can issue a medical as we see fit. <S> What has changed quite a bit is the big overhaul that included the Basic Med requirements which do include some notes on special issuance cases that you may be able to operate under. <S> For you it also depends on what kind of operations you want to do since you are a CFI/Commercial. <S> If you just want to get back in the air it may be a bit easier to do that. <S> From what I can tell it looks like you can get it back <S> but you will need to talk to an AME. <A> Check your seizure from here : https://www.icao.int/publications/Documents/8984_cons_en.pdf <S> It will at least give you an idea about your situation. <S> I guess that your seizure is caused by your heart (According to the scans they have asked). <S> If it is neurological, situation changes completely. <A> Seizures doesn't appear in the FAA list of special issuance conditions for Cat 1 <S> so you may be out of luck. <S> https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/special_iss/all_classes/ <S> But I would write to an AME anyway. <S> Nothing to lose. <S> In Canada the authorities seem to be somewhat more lenient on medical conditioins. <S> Transport Canada has recently issued Cat 1s to a few airline pilots with Type 1 insulin dependent diabetes (albiet with tight restrictions and monitoring requirements). <A> I’d suggest you talk that one over with an AME <S> and we <S> what they have to say. <S> It may be a lengthy process but it can be done. <S> I’d also suggest, if you can, make contact with John King of King Schools in San Diego. <S> He had his medical temporarily revoked but managed to get it reinstated after having a seizure. <S> He could also shed some light on the process you’ll face.	§67.401 Special issuance of medical certificates allows the FAA to issue medical certificates to airmen who can demonstrate "a Statement of Demonstrated Ability (SODA)" which is at the discretion of the flight surgeon.
What is this F-18 Hornet "air intake" for? I think I read once that they served to cool the on-board computer systems, but I'm not sure. <Q> It's for keeping the boundary layer flow from entering the intake, it's called a splitter plate . <S> I think it's done to prevent turbulence inside the turbine (prevent compressor stall) and to make sure the intake doesn't ingest slow air, to maximize efficiency. <A> EDIT: <S> I'd just finished writing out my own answer when I stumbled across this answer to a different question, which nevertheless explains the function of the small intake in greater detail. <S> I've included my answer below anyway. <S> A couple of people have mentioned the splitter plate, but failed to address the smaller intake set between it and the fuselage. <S> It's very difficult to find any references to this in particular, but my first instinct was that it's probably to do with either engine cooling (Concorde has additional intakes beneath the engines for this purpose) or engine bleed air. <S> After a bit of reading I resorted to Wikipedia, and found the passage below: ... <S> the Hornet uses bleed-air vents on the inboard surface of the engine air intake ducts to slow and reduce the amount of air reaching the engine. <S> Incidentally, this bleed air is redirected to a slots just above over the wing, to improve the performance of the aircraft. <A> The intake is for the primary heat exchanger. <S> secondary is on the other side, Same location. <S> The ambient air flows across a large rectangular heat exchanger. <S> Air conditioning, <S> Wave guide pressurization, cabin pressure, avionics cooling, Gun,Etc. <S> It cuts the air temperature in half and water is sprayed on the face of the heat exchangers that is extracted in the cooling process. <S> Aids in cooling especially while sitting on the deck at idle. <S> Otherwise you get a AVAIR hot code. <S> The ACACS system has a water separator in it. <S> That's where the water comes from. <S> The Spent air and water exits on top of the aircraft. <S> Basically without this system the Bird wont fly! <S> If you ever see a F/A-18C throttle up on the deck you will see the water exit on top. <S> It appears to be smoke but it is a water mist. <S> I hope that answers some of the questions. <A> The rectangle in the center is the housing for the primary heat exchange. <S> There is another heat exchange on the right side. <S> The two "ramps" on top and bottom is to bleed off air during transonic/ supersonic flight. <A> If I remember correctly, bleed air from those tiny intakes is used for defogging the cockpit, blowing air across the front of the canopy to increase visibility under heavy rain, and pressurising the external fuel tanks. <A> As suggested above it not an intake but rather a aerodynamic plate that keeps the boundary layer out of the engine. <S> This is normally required for supersonic flight since the engines have to carefully manage the shock waves entering the engine. <S> Most engine designs are not capable of operating under supersonic conditions and require that the inlet is carefully designed to create a series of shockwaves that slow down the air to an appropriate Mach number before it reaches the compressor.	So it seems to be a simple intake for bleed air which has the additional effect of slowing the air entering into the main intake. Basically a air to air radiator for the Bleed air system used for most functions on the F/A-18.
What is this INOP instrument and when is it safe to fly with INOP instruments? I flew ZRH->LHR on BA0711 today on G-EUOG. I noticed through the cabin door one of the instruments had a yellow INOP sticker across it (see photo). Which instrument was it? I am presuming the instrument has a backup, and the backup was operative, but I had thought the purpose of an backup was so that it could be used if the primary failed in flight ? Or is the instrument just 'not important'? What are the rules re flying with INOP instruments? <Q> It is a standby display, specifically a DDRMI (Digital Distance Radio Magnetic Indicator). <S> The aircraft can be dispatched with inoperative equipment. <S> The process is controlled by a Minimum Equipment List (MEL). <S> The operator will have an MEL for each type of aircraft in their fleet. <S> The MEL is approved by the regulatory authority (FAA, CAA, etc.) and specifies what may be inop and associated restrictions. <S> I don't know what the BA MEL for the A319 is, but here's a snip from the FAA's Master MEL (MMEL), which is the guidance for each operator to use when creating their MEL. <S> Following this guidance, the MEL would say you can dispatch with the DDRMI INOP if the FAR equipment minimums are met. <S> That (at least in the US) is along the lines of "navigational equipment necessary for the planned flight". <A> I am presuming the instrument has a backup, and the backup was operative <S> The "INOP" instrument itself is a backup. <S> This backup instrument is an analog version which runs on 70s tech. <S> It is rarely (if ever) needed, only intending to be used when all cockpit computers fail, which is exceptionally rare. <S> The modern version uses computers and the results are displayed on the screens you see. <S> What are the rules re flying with INOP instruments? <S> As others have stated, the "Minimum Equipment List" is a document that lists what equipment is essential for an aircraft to be dispatched. <S> Besides safety, dispatch rate is another reason why there is redundancy in an airliner cockpit. <S> With systems as complex as this (the manual of a modern airliner is thousands of pages long), failures are not unusual. <S> It is more economical to design an aircraft that can still fly with some instruments / systems inoperative rather one which requires everything to be 100% working. <A> The instrument is a backup VOR gauge. <S> It's there in case manual radio navigation is needed (hardly in a modern airliner) AND the displays are not working. <S> As it's not an instrument that's vital for getting the aircraft on the ground safely, it's no problem if it's declared INOP <S> (there is probably a maximum time period for it to be marked as such before repairs are required). <A> Every aircraft has a MMEL (Master Minimum Equipment List) and a MEL (Minimum Equipment List).While the MMELs are published by the producer of the aircraft, MELs are generated by the companies flying these airplanes. <S> Every company may have different MEL for the same aircraft. <S> This MELs cannot be shorter than the MMEL.If that malfunctioning or inoperative equipment is in the MEL that aircraft cannot fly without special permissions. <S> This is the basic information. <S> For more information you can read Wikipedia or FAA, JAR or EU OPS publications.	It is a navigation instrument which combines a compass, VOR needles and ADF needles.
Is this photo showing dozens of airliners in close proximity real, or even plausible? CNN has an article about Heathrow that's accompanied by the following photo: Is this photo depicting an actual event? If not, would it even be possible/plausible to fly this many airliners this closely together or would wake turbulence and similar factors make this basically impossible? It looks like several of the planes may be in the process of either stowing or deploying their landing gear, and also have their flaps deployed. Does this indicate that maybe someone has photoshopped together a bunch of photos of planes landing to produce this image? <Q> The image is a composite image of 42 planes taking off from Heathrow over a one-hour period on November 2, 2016. <S> Here it is on Getty Images if you want to license it for your own purposes; it is credited to Dan Kitwood. <A> To answer the question, no, there was no single event with all of these aircraft flying in close proximity like this where a single photograph of the group could be taken. <A> It's a photoshop done for artistic purposes. <A> The paths are not parallel, all tracing back to a shared vanishing point. <S> They are on a collision path. <S> The perspective geometry is not right, meaning an object depending on the distance and position in a camera field distorts in a way that the points and lines closer to camera get blown up in scale and the lines and geometry further back gets flatten a bit. <S> This is the reason faces get distorted in selfies with nose getting out of proportion. <S> Even in the event of an aerobatic airshow where the planes trajectory explodes open to a flower pattern or spills into a cascading dive these perspective rules are valid and in fact taken advantage in photos and videos of the event.	It’s a composite shot of multiple departures from an airport. It is a Photoshop image and not done too skillfully at that, may be on purpose.
What time zone is used for operating an airplane? This might be a silly question but my thinking was the following: There has to be a definition of time in an airplane for the logging of data and so on, but what definition would that be assuming a flight goes across timezones? Would it be the local time at the airport of departure ? Or at that of arrival ? or maybe even a third, commonly agreed upon time (e.g., GMT)? The idea came from a story of a friend that was traveling with the ship from Italy (GMT+1) to Greece (GMT+2). The cafeteria on board had a sign saying that it opens at 14:00, but on 14:20 local Italy time, while the ship was anchored in Italy, he was denied service by the crew saying that the sign was referring to Greece local time; where the ship "belongs". <Q> The pilot (and the ATC) use the UTC <S> (Coordinated Universal Time). <S> The flight's departure and arrival are in terms of the local times at the respective airports. <S> As for data logging, the FDR/CVR usually records in UTC (preferred) or the relative time count (usually count increments each 4 seconds of system operation). <S> See Appendix M to Part 121 - Airplane Flight Recorder Specifications , for example. <A> ICAO SARPs Annex 2 <S> (Rules of the Air) states: 3.5 Time 3.5.1 Coordinated Universal Time (UTC) shall be used and shall be expressed in hours and minutes and, when required, seconds of the 24-hour day beginning at midnight. <S> 3.5.2 <S> A time check shall be obtained prior to operating a controlled flight and at such other times during the flight as may be necessary. <S> Note. <S> — Such time check is normally obtained from an air traffic services unit unless other arrangements have been made by the operator or by the appropriate ATS authority. <S> 3.5.3 <S> Wherever time is utilized in the application of data link communications, it shall be accurate to within 1 second of UTC. <S> The above should apply to almost every country when it comes to international civil aviation. <S> Militaries and uncontrolled flights are not covered by the above. <A> The same as ATC. <A> Let me add that pilots, ATC, and others use UTC, (not GMT) <S> but it's common for customer-facing times to be in the time zone of the event. <S> For example, a Flight from Florida to Alabama may land before it departs on the ticket. <S> Usually, ticket times are listed in local time. <S> So Departing 1:00 pm Arriving 12:48 pm could actually appear on a ticket.	The planes use UTC time.
What drives the shape of an engine's intake on a fighter jet? Rectangular intakes have more corners which might increase subsonic pressure losses and would weigh larger than a pitot (Semi-circular) type intake. Are the designer drivers solely based on supersonic pressure loss improvement? Or for area-ruling? Am I missing something here? F 16 has a pitot (Semi-circular) type intake whereas JAS 39 Gripen has a rectangular one. I wonder why. Edit: The question is in reference to a fighter aircraft intake which employ fuselage buried engine configuration in-contrast to wing mounted or externally integrated engines.Fighter aircraft intakes are more complex when compared to simple cowl-lip configurations designed for larger commercial engines.Intake shape,size,location are function of wide variety of parameters, so something must be influencing the intake entry cross section of a fighter aircraft configuration. <Q> Are the design drivers solely based on supersonic pressure loss improvement? <S> Yes. <S> And sometimes a few more considerations need to be taken into account. <S> We have covered the reason for intake shapes well on this site, but the details must be collected from several answers. <S> In a nutshell: Higher flight Mach numbers need more elaborate and heavier intakes in order to convert the kinetic energy of the flow into pressure. <S> A pitot intake is light and simple, but a poor choice for speeds in excess of Mach 1.6 . <S> Rectangular intakes are normally chosen in order to make internal, moveable ramps possible which create a cascade of shocks in order to slow down the flow as efficiently as possible. <S> Such designs are typical for Mach 2 aircraft (think Concorde, F-14, F-15, XB-70). <S> Another way would be a central intake with a moveable spike , but those had to make way for big radar arrays in more modern designs. <S> The JAS-39 intake is a little special: It sits next to the fully moveable canards, and those need a vertical wall in order to minimise the gap between canard root and fuselage/intake structure. <S> Yes, a round intake would be slightly lighter, but is impossible due to the situation of the canards. <S> Detail of JAS-39 canard, taken from this picture . <A> Another reason is stealth - the shapes can be selected to minimize radar return. <S> See the F22 and F35 leading edge shapes for example. <A> There are some aircraft such as the MiG-21 and SR-71 which use adjustable inlet cones in order to be able to cruise at higher speeds without significant performance losses. <S> According to Wikipedia, the MiG-21's inlet cone allows the creation of two shock waves, both of which are aimed at the inlet lips. <S> As for the F-16's semi-circular inlet, I'm not sure why that is the case. <S> I couldn't quite find any helpful info. <A> You have the right idea when you discuss area rule (Coke bottle) shape and pressure/compressibility. <S> A classic example of the area rule shape for supersonic flight is the T-38/AT-38 <S> and it's big brother the F-5. <S> A large part of the limitation on the T-38's flight envelope is the air entering the engine. <S> I have flown it up to Mach 1.3 which it can do reliably, however to go beyond that up to M 1.5 <S> requires a very narrow range of temperature and pressure altitude due to the susceptibility to engine compressor stall and flameouts above 1.3 , due in large part to the supersonic airflow entering the intakes. <S> The F-16, mentioned above, not only has a semi-circular (shark's mouth) intake, but also a large curve inside the intake (like a slide at a kid's park, slopes up as you enter the intake) and there are actually two flavors of intake for the Viper depending on the engine (the smallmouth and largemouth intake), the very long version of which is here: https://arc.aiaa.org/doi/abs/10.2514/3.22758?journalCode=jpp	From what I could find, the rectangular geometry of fighter aircraft intakes is due to the fact that the intakes incorporate sharper inlet lips in order to decelerate airflow to subsonic speeds to avoid supersonic performance losses from shock waves.
Why, until recently, were smooth nose sections not popular? Why, until recently, were smooth nose sections not popular? By smooth I mean without a break between the nose and windshield. (The question focuses on airliners.) Seeing the Starliner (left) and DC-7 (middle), which were vying for the transatlantic market, with their almost perpendicular windshields, I wonder if they were more slanted and followed the nose -- like the Commando (right), for example, which proves it was possible -- enough drag reduction would have helped their payloads on windy days. The Commando style windshields only made a comeback with the 787 and A350 -- the 747 gets close, but like the 75/76/777, there is still a break. Manufacturing difficulty: I don't think that's the reason (unless proven otherwise), because the noses are already smooth. The nose could start from the top surface of the fuselage, and cut-outs to be made where the windshield panels would go. Windshield materials: Plexiglas was used early on and on wartime aircraft with complex curvatures . Image sources: - https://imgur.com/iA7tbFV - https://airandspace.si.edu/multimedia-gallery/dc-7jpg - http://www.historynet.com/going-commando.htm <Q> Because it's bloody difficult to make the curved shapes out of the materials used until recently, with the technology available at the time. <S> The few aircraft that had it in the past generally were very expensive and labour intensive to build, compared to competitors, and therefore not economically successful. <S> Now, with improved manufacturing techniques and materials, plus the rising cost of fuel, it's becoming ever more viable and more such are appearing. <A> First, the Commando wasn't unique in having a 'stepless' cockpit design- <S> the Boeing 307 Stratoliner , for example had them. <S> Other military aircraft too had them, due to a few reasons like pressurization and the excellent visibility (He 111, Ju 388, B-29 Superfortress, the list goes on... <S> etc) they offered. <S> While it's true that having this design improves the aerodynamics of the aircraft, there are other things to consider. <S> Aircraft design, then as is now is a trade-off. <S> The designer has to select a nose design based on trade-offs between various factors like aerodynamics, ease of manufacture, location of LRUs etc. <S> In fact, during original design of Lockheed constellation, multiple nose configurations were considered, which included completely faired nose (along with 'bug-eye' types). <S> That the conventional arrangement was finally selected indicates that the designers decided that the drag reduction offered wasn't worthwhile. <S> Another problem with curved windshields is that presence of relective and refractive errors. <S> While I'm not sure if this problem was encountered in C-46, the assertion by Willis L Wells, Chief Engineer, Airplane Division, St. Louis Plant, Curtiss-Wright Corp <S> that, In order to achieve ideal visibility characteristics for the pilot, the entire nose and cockpit of the CW-20E was redesigned to incorporate a flat glass windshield with negligible refractive and reflective errors. <S> At the same time, the field of vision was increased. <S> indicates that this was definitely a consideration. <S> The present scenario is different- <S> better materials and manufacturing techniques are available- not only for the windshields reducing errors and quality issues but also the fuselage shell, enabling optimizing structures for better aerodynamics. <S> I believe the Commando erred on the side of the aerodynamics- <S> it had fairings between the top and bottom fuselage halves, which were later deleted, as flight tests showed they provided no improvement in performance. <S> According to George A Page, Chief Engineer St Louis Airplane Division of Curtiss-Wright Corporation , the C-46 had not only stepless cockpit, but also 'tunnel type' cowlings to reduce drag. <A> Blow-molded canopies (like the acrylic one on the P-51D) were relatively expensive in the late WWII and early post-War periods when the early-modern airliners were designed. <S> Cost is an important factor in airliner design, and was even in 1950. <S> Further, molding these materials in compound curves had a high drop-out rate due to distortions forming in the sheet material during heat forming. <S> Add to the above the need for very large panes to achieve required levels of visibility when the pilot is looking through at a sharp angle, and the difficulty of controlling reflections with strong sunlight falling on the (otherwise useless) panel area under the extended windscreen area, and you have a serious practicality issue with the sharply angles windscreens required for a Commando style. <A> A new Bendix or RCA weather radar could be installed in the nose, which changed the nosecone shape. <A> Bulky' windshields are easier to operate than curved ones. <S> Also, as pointed out in the blog post below [1], airliner front windows were also used for emergency escape purposes, as on China Airlines flight 120 incident [2]. <S> A350, that has curved windshield, includes an additional escape hatch for pilots. <S> The windshield itself is too small to be used as an escape route. <S> Small surface area is preferred to mitigate damage to the windshield. <S> [1] <S> http://bloga350.blogspot.com/2012/12/a350-xwb-first-curved-windows-airbus-is.html <S> [2] https://en.wikipedia.org/wiki/China_Airlines_Flight_120	Aircraft windshields usually need to be serviced more often than other parts of the nose, because any debris (hail, birds etc) might cause scratch marks or fractures that obstruct the view and might cause a decompression. ' Additional cost factors (contributing to the high cost of deeply or compound curved windshields) are that the materials (acrylic, aka Plexiglas or, by preference for its impact resistance, polycarbonate aka Lexan) were new, cutting edge materials in the early 1950s. More complex a shape, more difficult is it to manufacture usually (which increases cost). Part of the reason for the nose shape was a radar dish being installed there.
What is a biplane propeller and how efficient is it? Lazair ultralight series II used biplane props to absorb more power from the engine....so my question is what really is a biplane propeller and are they efficient in comparison to a four bladed prop? <Q> It is essentially two propellers stack on top of each other. <S> You can see it in this picture of a Lazair . <S> As for why they were chosen for the Lazair , Many have asked why Ultraflight opted for double propellers stacked in a biplane fashion. <S> This is a very unique setup and draws lots of attention. <S> Apparently when Ultraflight changed over to the Rotax 185 they tried several different propellers. <S> The problem was the 185’s had a woodruff key slot in the crankshaft and would snap the crank <S> whenever the engine coughed or kicked back on start up. <S> This was quite a serious problem. <S> After much deliberation it was determined that the rotational inertia of the propellers was too much for the crank to handle. <S> Dale could not locate a two bladed prop light enough to fit the need. <S> However, since they had been producing a lot of the early lazairs with Pioneer engines fitted with a single plastic prop, he had a ton left over that fit the pioneers. <S> He found that these could be “doubled up” and help to produce the extra thrust that the Rotax 185 was capable of producing over the 5.5 hp Pioneer engines. <S> It appears to be a quick way to gain more thrust from the props without increasing prop mass too much. <A> The interference between blades causes additional drag (which absorbs power without creating additional thrust), but the turbulence from each blade affects the following one in a conventional four-blade design, with similar effects, especially in a flatter-pitch design or at low airspeed. <S> The potential advantage of the biplane propeller is that, presuming the hubs have six or eight torque transmission bolts (or even four, though that arrangement is less versatile), the blades may be arranged with the forward propeller directly ahead of the aft (true biplane propeller), or one or two holes leading or trailing in rotation. <S> Without wind tunnel testing, it's impossible to be certain, but I'd expect an arrangement with the forward propeller trailing the aft by a fraction of a revolution to be most free of interference effects and hence most efficient, quite possibly more efficient than a four blade design with the same diameter, pitch, and blade area. <A> A biplane propeller is one prop stacked above another, similar to a biplane wing. <S> This looks to be very inefficient. <S> The gap between stacked blades looks like about one chord at the tip and a quarter chord at the root. <S> This should cause problems with the high pressure under the upper blade interfering with the low pressure above the lower blade. <S> At minimum the blades should be spaced farther apart. <S> Here is an analysis of biplane wing efficiency relative to separation as a percent of chord. <S> Efficiency is 10.5% higher when the gap/chord is 1.5 as compared to 0.75. <S> It doesn't go to 0.25 but it seems that would be much worse as the 1.5-1.25 gap drop in lift/drag <S> is 3% and the 1-0.75 drop is 4.2% at 4%. <S> This configuration is likely losing 6%-18% compared to a gap at 1.5 chord. <S> The .075 gap/chord entry in the table looks like a typo. <S> The reference shows biplane efficiency is lower than a similar monoplane, though not completely clear if wing area, span or chord are held constant for that comparison. <S> It also states that positive stagger (upper wing ahead of lower) by 0.4 chord gives 5% better efficiency, so rotating the upper prop <S> 0.4 chord would be beneficial compared to the vertical stacking shown.	Depending on the pitch and blade airfoil, a biplane propeller as used on the Lazair might be more or less efficient than a conventional four-blade propeller the same diameter.
Can you disengage A320 autopilot with stick pressure? I was recently reading that in most military jets, auto-pilot can disengaged without hitting the button, by applying 5lbs of pressure to sticks. Does this work in commercial airliners such as the A320? <Q> Yes. <S> I’m not sure of the amount of force, but from the A320 FCOM: <S> AP DISENGAGEMENT AP1 or 2 disengages when: The pilot presses the takeover pushbutton on the sidestick. <S> The pilot presses the corresponding AP pushbutton on the FCU. <S> The pilot pushes on the sidestick harder than a certain threshold or moves on the rudder pedals above a threshold. <S> The pilot moves the pitch trim wheel beyond a certain threshold. <S> The other AP is engaged, except when localizer/glideslope modes are armed or engaged, or when the rollout or go-around mode is engaged. <S> Both thrust levers are set above the MCT detent and the aircraft is on the ground. <S> The aircraft reaches the MDA-50 feet (MDH-50 feet), or 400 feet AGL if no MDA/MDH, with APPR mode engaged and a non-lLS approach is selected. <S> One of the engagement conditions is lost. <S> Furthermore, in normal law with all protections available, the AP will disconnect if: High speed protection is active; Angle-of-attack protection is active ( <S> α prot + 1° is reached); Pitch attitude exceeds 25° up, or 13° down, or bank angle exceeds 45°; A rudder pedal deflection is more than 10° out of trim. <S> The standard way for the flight crew to disengage the AP is to press the takeover pushbutton on the sidestick. <S> When the AP is OFF, the associated FCU pushbutton goes off. <S> and "APl" (or AP2) disappears from the PFD’s FMA. <S> *emphasis mine <A> While not an A320 per the OP's question, the case of Aeroflot Flight 593 in 1994 details a case where the partial disengagement of the autopilot on an A310 by means of continued pressure on the controls contributed to the crash. <S> ( massive oversimplification, look at the Wikipedia page linked above for more details ) <S> The circumstances that led to the crash of Aeroflot 593 were addressed in later revisions of Airbus aircraft to the point where you would know it if the autopilot disengaged due to conflicting control stick inputs . <A> The autopilot can also be disengaged by moving the control stick though this is not usually recommended as it can cause the aircraft to roll suddenly. <S> Airbus aircraft have an autopilot panel such as this one below that controls the autopilot: <S> https://en.wikipedia.org/wiki/Autopilot#/media/File:A340_FCU.jpg <S> Places <S> I got my info from: quora.com/How-do-you-disconnect-the-autopilot-in-airliners <S> aviation.stackexchange.com/questions/149/what-are-the-main-differences-piloting-boeing-vs-airbus-aircraft <S> Hope <S> this helps. <S> And if anyone feels like I stole your info, I apologize.	From what I could gather, airliners such as the Airbus A320 have a red button on the sidestick that will disengage the autopilot should you press it.
Is a 61.31 solo endorsement a one-time thing, or does it need to be repeated? The FAR 61.31(d)(2) reads that a person can act as pilot in command if they: Have received training required by this part that is appropriate to the pilot certification level, aircraft category, class, and type rating (if a class or type rating is required) for the aircraft to be flown, and have received an endorsement for solo flight in that aircraft from an authorized instructor. Is this endorsement a one-time thing, or does it need to be "renewed"? I met an glider instructor who claimed that my glider solo endorsement is no longer valid because my power license lapsed. <Q> You didn't say which certificates and ratings you hold, but since you mention 61.31 I assume you're already a certificated pilot in a non-glider category/class (ASEL?) <S> and you're receiving glider training. <S> Including an expiration date is optional, not required; see the Bennett interpretation : <S> The regulations of 14 C.F.R., however, do not prohibit an instructor from placing limitations, including an expiration date, in a § 61.31(d) solo endorsement. <S> See 14 CFR § 61.195(d) <S> (prescribing flight instructor limitations on endorsements). <S> AC 61-65 is the reference for endorsements, and it has this language for a 61.31 solo endorsement (note the "optional" limitations section at the end): A.71 <S> To act as pilot in command of an aircraft in solo operations when the pilot does not hold an appropriate category/class rating: § 61.31(d)(2). <S> I certify that [First name, MI, Last name] has received the training as required by § 61.31(d)(2) to serve as a pilot in command in a [specific category and class of aircraft]. <S> I have determined that [he or she] is prepared to solo that [M/M] aircraft. <S> Limitations: [optional]. <S> Therefore, whether your 61.31 solo endorsement expires or not is determined by the wording of the endorsement itself. <S> But as always, even if your endorsement is valid from the FAA's point of view, the glider school/club and their insurance company may have their own, additional requirements before letting you solo. <S> I don't understand the second part of your question: "my glider solo endorsement is no longer valid because my power license lapsed". <S> FAA certificates never expire so I have no idea <S> what you mean by "lapsed" <S> (maybe this scenario ?). <S> In any case, I suspect that it might be better to ask that as another question; if you do, please tell us exactly which certificates and ratings you have. <A> Logbook endorsements for solo flight do expire - or no longer authorize solo flight - on after 90 days since the CFI endorsed tour logbook for solo flight. <S> See 61.87(n). <S> Also solo endorsements authorize solo flight only to the specific make and model of aircraft listed in the solo endorsement and cannot be applied to conduct solo flight by a student pilot other types of aircraft. <A> Despite a low gross weight of only 5,520 lb the Eclipse 500 requires a type rating. <S> The OP should have warned this is not a "general" question, it is for special circumstances. <S> FAR 61.31 would normally be for an already rated pilot that does not hold a endorsement for a "TYPE" certificate necessary for a special type of aircraft. <S> FAR 61.31 Is for approval to act as PIC of aircraft that require a "TYPE" , rating commonly called "large", "turbojet", or "special" purpose aircraft (i.e. warbirds). <S> So, if a person already has a pilot's license , then FAR 61.31 is a lifetime endorsement. <S> A new FAR in 2017 (FAR 61.87(n)) places a 90day limit on student solos . <S> I doubt any instructors would approve a student pilot to fly solo in a aircraft that requires a TYPE rating such as the Eclipse 500. <S> However, if the person were a student pilot , then the endorsement would be for only 90days per the limitation placed on student pilots in FAR 61.87(n).	The short answer is that a 61.31 solo endorsement expires only if the instructor added an expiration date as a limitation.
Do floatplanes land on rivers? I'm sitting here in a coffee shop on the local river and I noticed it was just wide enough to facilitate a landing. There is no chop on the river, but it does move pretty switfly, and there are bridges and whatnot that would quickly come into play. However, there are some pretty slow-moving, unobstructed rivers out there. Does anyone land floatplanes on rivers for reasons other than emergencies? <Q> Yes, here is a river landing . <S> and another , even tighter. <S> This might technically be a beaver dam pond in a river. <S> and another , prettier. <S> I'd back this one up and watch the approach. <A> Float planes are used world wide on rivers. <S> Cessna 206 delivering supplies to a fishing camp along the Yukon River (Alaska). <S> Sightseeing along the Amazon River. <S> Wind River (Canada) tour map <A> They absolutely can and do on a regular basis. <S> River currents will play a significant role in takeoff and landing considerations as well as during displacement taxiing, casting off, docking and mooring of the airplane. <S> But it does happen on a regular basis.	In Alaska and Canada the primary use is fishing, hunting, sightseeing, lodging, supplies...
Why do we not see propellers on swept wings or jet engines on straight wings? Why are these configurations not observed often? The only time I see propellers are on straight wings or on the nose, while jet engines are always on swept wings or the tail. Why? <Q> You can find propellers on swept wing aircraft, such as the TU-95 , or more recently, <S> the Airbus A400M . <S> One turbofan powered aircraft that has straight wings is the Cessna Citation <S> No, it's not common, due largely to the speed at which the aircraft normally operates. <S> Turboprops tend to operate at a lower speed than turbojets or turbofans, where the benefits of swept wings (better performance when approaching Mach 1) aren't evident, while the benefits of straight wings (better performance at lower speeds) comes in handy on the shorter airfields that smaller turboprops operate from. <S> Bump the cruising speed up to Mach <S> .8 <S> +, and the swept wing is the optimal design. <S> In the case of both the TU95 and A400M, they cruise at higher speeds than most turboprop aircraft, hence the employment of a sweep to the wings. <A> "You always see" is perhaps due to you not seeing a wide enough variety of airplanes. <S> For instance, here's an example of a plane that has both props and jets on a moderately-swept wing: https://en.wikipedia.org/wiki/Convair_B-36_Peacemaker <S> Here are a couple of other examples (of many) of jets with straight wings: https://theaviationist.com/2014/06/17/scorpion-new-livery/ https://en.wikipedia.org/wiki/Lockheed_F-104_Starfighter <S> @John K's answer covers the technical reasons for swept wings. <S> There's also another factor that I'd think is pretty obvious: <S> if you put props on steeply-swept wings, you need to get the prop far enough out in front of the wing so that it doesn't hit it, which creates structural problem. <S> But here's an example of a single-engine propellor plane with swept wings: <S> http://thanlont.blogspot.com/2011/04/bell-l-39-wing-sweep-evaluation.html <S> Then there's the Beechcraft Starship, which has part of the wing swept: https://en.wikipedia.org/wiki/Beechcraft_Starship <S> (Note the pusher propellors: it's hard to see how tractor props could be mounted on the same wing.) <S> Many more examples of both sorts can be found by spending a few minutes with a search engine. <A> Swept wings are for cruising close to the speed of sound (all the sweep does is make the effective chord of the airfoil longer <S> so it's ratio of chord to thickness <S> is higher - a finer profile you might say - and this delays the shock wave formation a little bit). <S> The Russians did the sweep+propellers thing with airplanes like the TU-95, but in the West it wasn't considered worth the trouble. <S> So in a nutshell: Tubojets/turbofans go on the wings and tail/fuselage because that's the most efficient place for them, and they're associated with swept wings because they can operate fast enough to benefit from sweep; propellers are on the wings and nose because that's the most efficient place for them, and the wings are straight because there's no point in sweeping them (and dealing with the downsides of sweep) when the prop can't go fast enough for it to be worthwhile. <A> Propellers are more efficient, but they only work well when their tip speed is still subsonic, which limits the maximum speed of propeller-driven planes. <S> Jet engines on the other hand are inefficient at low speed, but their efficiency increases at higher speeds, and they can be designed for much higher flight speeds. <S> Straight wing is more efficient, but once the flow over it exceeds speed of sound—and the increase in speed over the wing means it happens about M0.70–0.75 (70–75% of speed of sound)—its drag increases significantly. <S> Swept wing delays this effect, because only the component of airflow velocity perpendicular to the wing causes it. <S> That way swept wings remain efficient near, and if sufficiently swept even above, speed of sound. <S> Therefore the slower aircraft have propellers and straight wings and the faster ones have jet engines and swept wings, while the other two combinations don't make much sense. <S> Note that there are a few aircraft with jet engines and straight wings, <S> either because they are not yet fast enough to need swept wings (e.g. the Cessna Citation <S> I and II or the early fighters) <S> or because they have supersonic wings (e.g. the F-104 ). <S> And the fastest propeller-driven planes do have (moderately) swept wings (e.g. the Tu-95 ).	Propeller tips become supersonic way below the speed that wings start to become transonic, limiting the forward speed the propeller can operate at, so you simply can't go fast enough with a propeller to enjoy a significant benefit from wing sweep.
How the fuel in the wings is managed in case of an engine failure? Consider an aircraft has fuel tanks only in wings (No central tank). Will the fuel for the respective engines will be consumed from the respective wings? In case of a single engine failure, if the fuel is keep on consumed by the active engine, whereas not consumed in the inactive/damaged engine, will this affect the aerodynamic property of aircraft? <Q> That’s a pretty broad topic and depends on the aircraft in question and the fuel systems which it uses. <S> Large airplanes like jetliners have complex fuel management systems which feed fuel from the main tanks into feeder tanks which the engines can “drink” from. <S> The process is automated in modern aircraft - around the same time that the Flight Engineer went the way of the dinosaur - so little, if any, input from the crew is required in the process. <S> On smaller twins, say, for example, a Cessna 310, fuel is provided to the engines via a dedicated main fuel tank and optional aux tanks for each engine. <A> While a tank generally provides fuel to the engines on that wing, an engine can also use fuel from the tank on the opposite side, if the crossfeed valve is opened by the setting in the control panel. <S> While the question itself may not be a duplicate, this answer likely explains enough. <A> 14 CFR § 25.1001 Fuel jettisoning system. <S> (a) <S> A fuel jettisoning system must be installed on each airplane unless it is shown that the airplane meets the climb requirements of §§ 25.119 and 25.121(d) at maximum takeoff weight, less the actual or computed weight of fuel necessary for a 15-minute flight comprised of a takeoff, go-around, and landing at the airport of departure with the airplane configuration, speed, power, and thrust the same as that used in meeting the applicable takeoff, approach, and landing climb performance requirements of this part. <S> 14 CFR <S> § 25.121 Climb: <S> One-engine-inoperative. <S> (d) <S> Approach. <S> In a configuration corresponding to the normal all-engines-operating procedure in which VSR for this configuration does not exceed 110 percent of the VSR for the related all-engines-operating landing configuration: (1) The steady gradient of climb may not be less than 2.1 percent for two-engine airplanes, 2.4 percent for three-engine airplanes, and 2.7 percent for four-engine airplanes, with - (i) <S> The critical engine inoperative, the remaining engines at the go-around power or thrust setting; (ii) <S> The maximum landing weight; (iii) <S> A climb speed established in connection with normal landing procedures, but not exceeding 1.4 VSR; and (iv) <S> Landing gear retracted. <S> (2) <S> The requirements of paragraph (d)(1) of this section must be met: (i) <S> In non-icing conditions; and (ii) <S> In icing conditions with the most critical of the approach ice accretion(s) defined in Appendices C and O of this part, as applicable, in accordance with § 25.21(g). <S> The climb speed selected for non-icing conditions may be used if the climb speed for icing conditions, computed in accordance with paragraph (d)(1)(iii) of this section, does not exceed that for non-icing conditions by more than the greater of 3 knots CAS or 3 percent. <S> In short - in case of an engine failure, fuel may be dumped to achieve acceptable handling characteristics for approach. <S> Furthermore, I would add that based on many articles I've read about engine failure involving fire, it's not uncommon for nearly all fuel to be dumped before landing, to avoid a fireball on the ground. <S> I will attempt to find some references for this.	In the event of an engine failure, the pilot can select the ability to cross feed the good engine on the fuel system for the bad engine in order to prevent a fuel imbalance.
Why is extreme cold weather a challenge at airports, since jets operate at extreme cold conditions in flight? Wondering what specifically the issues are. Obviously, taking off and landing have more 'moving parts' but more curious about the actual extreme cold. I assume the operating temperatures at cruise are much lower than ground temps. <Q> For example so long as the weather is good and the aircraft are equipped, there are plenty of airports in Antarctica <S> When extreme cold is accompanied by precipitation you can get ice build up on the runway which is quite dangerous. <S> Most airports that are in an area of regular cold weather are equipped in some way to handle this. <S> Extreme cold temperature that comes with/because of frontal movement may also come with very high winds that can exceed aircraft limits. <S> But high winds can come with warm weather as well <S> so this is not exclusive to the cold. <S> For piston engines you have an issue of thick oil. <S> Piston engines in commercial operations are much less common than they once were <S> so this is less of an issue. <S> However the general aviation fleet is still pretty effected by this issue. <S> Jet engines do have cold start procedures just like piston engines, there is a good discussion on that here . <S> You can see a neat video of an A320 starting up in -28C conditions here so cold weather starts are not a huge issue. <S> Most airports have some form of ground crew that operate in the elements. <S> Crew like baggage handlers , aircraft marshaller , and even mechanics may work out on the ramp to get an aircraft loaded and ready to go. <S> This is one instance where sheer cold can be a factor although weather can also make working conditions very tough, even if proper protective gear is available. <A> At cruise levels, the air holds nearly no water vapor and therefore the problems of icing & snow are less likely to occur than on ground. <S> Also, with already running engines, there is heat available to keep even with low outside temperature parts of the aircraft heated, e.g. the wing edges as anti-ice measures. <S> I don't know the details about jet engines enough, but it might be, that they have a narrower temperature range for startup than for cruise settings. <S> So it might be okay to run an engine at -20°C but not to start it at this temperature - but that's something hopefully others will know better and write a more detailed answer about that. <A> On the design side, transport aircraft are certified for a minimum operating temperature, typically -40C, sometimes -45 or maybe -50, and this will be a basic operating limitation, but only for departure purposes as it will regularly see -70 at high altitudes in the winter in the north. <S> This means that an airplane certified to -40 will not be able to legally depart an airport with an SAT of -45 and will have to wait around for the temperature to warm up. <S> This happens in the arctic quite a bit. <S> Operating components are also certified to the airplane's minimum temperature limitation and will have to perform to the required standard in endurance and qualification testing only to that minimum temperature, not the temperature it might be exposed to at altitude. <S> This can cause problems for mechanical non-hydraulic components away from the fuselage, like screwjack flap actuators(hydraulic components get warmed by the fluid and never really get cold soaked). <S> In theory, if you tried to deploy flaps at 35000 ft at -65, chances are they won't come out because the grease or oil in the gearbox is congealing. <S> However, this isn't the problem it seems because when the flaps are called for, the airplane is back down to somewhere around 3000 ft agl and components have warmed up at least to their min cert temp and can be expected to work.	The extreme cold is not an issue so much as the weather that typically accompanies it and the fact that planes are not always designed to be started in extreme cold with out some assistance even if they can run in it. When the temperature drops the oil thickens and it becomes hard to start the engine as well as running the risk of engine damage.
Why would a flight from Frankfurt to Madrid fly over London? While enjoying the sunshine at the bank of the river Main in Frankfurt (Germany) this evening, I saw a LATAM B787-9 depart over the city center towards the north. This was slightly surprising, as the only LATAM flight from Frankfurt is LAN705 to Madrid (Spain) (and then to Santigo, Chile) which is to the southwest. I have taken this flight quite a few times before and I don't remember it ever flew a northerly departure. Even more surprising was that continued for a while to north, until I lost sight of it and had to take out the Flight Radar 24 App to track it. The flight continued towards the northwest, into the Netherlands and across the North Sea towards the UK. By now I highly doubted the flight was going to Madrid. The only reason I could think of for this routing is that either LATAM changed their flight schedule and flies via another city to Chile or the aircraft was being ferried to Boeing in the US for maintenance (LATAM has many problems with the B789 Rolls Royce engines ). Coming back home, I just checked again where the flight was (fully expecting it to be mid-Atlantic) and I see this: source: Flight Radar 24 source: Flight Aware The flight departed Frankfurt, turn north, then northeast over Belgium and the Netherlands, into the UK. Then went over London, west-southwest over Lands-end, then over the Celtic sea it finally turns southbound toward Spain. It now entered Spain and seems to be heading to Madrid, but the flight will be over 2500 km, while a straight line between Frankfurt and Madrid airports is about 1420 km. What is going on? What is the reason for flying over 2500 kilometers, while it could be only 1500? <Q> I can't be completely sure but the most likely reason is a planned strike by ATC in south-east France. <S> It was planned from the 30th of June to the 1st or 2nd (depending on the source) of July, meaning that ATC services would be unavailable or at least seriously reduced in that area, presumably with knock-on effects in other parts of the country. <S> Some airlines had cancelled flights completely although in the end it looks like the strike was called off . <S> Strikes are notoriously common in France (there's even a website dedicated to tracking them all ) and especially in the summer, so an airline might just plan to avoid French airspace altogether to avoid the uncertainty. <S> Of course that costs more money, as you said, but a missed connection to Chile and stranded passengers in Madrid would also cost money. <A> Not having been there I can't tell for sure, but I would guess congestion. <S> For safety reasons, the number of flights handled by one controller, and thus flying through their sector, in an hour is limited (to 35 IIRC). <S> If there are more flight plans filed though it than the capacity, the flow management, handled in Europe by the Network Manager Operations Centre , will start to issue delays. <S> If the airline dispatcher does not like this—probably because the delay would cause problems with connections somewhere down the line—they can try to negotiate different route that avoids the congested area. <S> As mentioned in <S> Why do airlines follow these routes between between Barcelona and Düsseldorf? <S> , France has quite many restricted areas, which makes it more likely to get congested. <A> ATC charges by the mile multiplied by a factor for the size of the plane. <S> However out in the Bay of Biscay ATC is pretty much free. <S> See this article on the BBC for more details. <S> Here is a table comparing the costs.	In addition to the other reasons, it might simply be a matter of avoiding ATC charges.
How did this F/A-18's execute a "low-boom maneuver"? The Engadget article NASA will publicly test quiet supersonic technology in November says: The administration plans to conduct a series of public tests around the coastal city of Galveston in November. The F/A-18 Hornet aircraft at the heart of the tests will perform dive maneuvers that produce louder sonic booms out at sea, while quieter sonic "thumps" will take place over Galveston proper. After that, "at least" 500 local volunteers will provide feedback on what they heard, while audio sensors will provide more definitive noise readings. and links to the NASA YouTube video NASA Social: Low-Boom Maneuver : This footage is from a NASA Social event at Armstrong Flight Research Center during which the F/A-18 was flown to produce a regular sonic boom and then a low “boom” by performing the dive maneuver described in this story. The normal sonic double boom occurs at 0:43. The low “boom” occurs at 02:34. The rest of the footage includes a flyby, planes on the ground with NASA Social participants, a visit to the Ikhana UAS and a pilot signing. Question: What would be a simple way to understand what a "low-boom maneuver" is, and how would an F/A-18 execute it? In this case would it require any modification of the Hornet's configuration? Is producing the boom during a dive of particular relevance to the reduction in sound level, or is this just a convenient way to do this particular experiment? Since the sound level as well as the reduction of the level for the low-boom maneuver at ground level may have a directional dependence, I'm wondering if the direction of the dive needed to be carefully planned to be representative of how the reduction would work for civilian air travel boom reduction, where dives are (thankfully) less frequent. <Q> I did some reading and this is what I could find out so far: https://www.nasa.gov/aero/nasa-prepares-to-go-public-with-quiet-supersonic-tech <S> This article is similar to the Engagdet one but goes into slightly more detail(though not enough for a proper explanation) about the dive maneuver. <S> However, Lockheed Martin is in the process of designing and building a low sonic boom demonstrator , slated to fly in 2021. <S> The wikipedia page says that to prevent sonic booms from building up, the aircraft will have a long slender body and canards (thought the Concorde had these as well, so I'm not sure what the difference is). <S> They will probably add canards to the F/A-18. <S> The dive maneuver happens in such a way that while the sonic booms directly underneath the aircraft are strengthened, there is a secondary pair of sonic booms created further ahead that are weaker, giving quiet thumps instead. <S> Hope this helps. <A> I was doing some research when I came across this question and thought that maybe someone still cares about an answer. <S> In fact both answers given so far are almost right but lack some background. <S> To elicit low sonic booms, commonly also described as sonic thumps, the F-18 first ascents to a height of a couple of thousand feet (40-50k). <S> Once the height is reached the plane turns upside down and falls to a much lower height (15-20k ft), while breaking the mach border. <S> The overall procedure is somewhat accurately depicted on the QSF 18 (Quite Sonic Flights) research crew patch from NASA: <S> https://www.google.com/url?sa=i&url=https%3A%2F%2Fnews.psu.edu%2Fstory%2F546964%2F2018%2F11%2F08%2Fresearch%2Fnasa-penn-state-survey-reactions-sonic-thumps&psig=AOvVaw2bFvYl9dBQZkQphIwsfwzs&ust=1586263795917000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCOi_vKHr0-gCFQAAAAAdAAAAABAr <S> The sound signature of a conventional sonic boom on the ground roughly looks like the letter "N") to the ground (compare figure). <S> https://www.google.com/url?sa=i&url=https%3A%2F%2Fvibrationdata.wordpress.com%2F2017%2F02%2F02%2Fquieter-supersonic-passenger-jets%2F&psig=AOvVaw36SVi23jWSoygdQMinXdiy&ust=1586264669269000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCPjr88Hu0-gCFQAAAAAdAAAAABAO <S> The pull up manoeuvre observed wasn't the actual supersonic transistion, but the exit from the manoeuvre alltogether. <S> You can find a detailled description of the whole procedure in Sullivan et al.'s paper "Human Response to Low-Intensity Sonic Booms Heard Indoors and Outdoors". <S> I hope that helps. <S> Kind regards and stay healthy <A> By flying straight up before exceeding Mach 1, to spread the boom more widely. <S> The commentary says: at 2:10, "pull up" and the smoke trail suddenly points upwards; "[2:16] subsonic below thirty thousand feet," "point zero nine Mach [for?]ty thousand [feet?], thump, copy one point <S> zero nine Mach, more thumps, [2:39] one point zero eight Mach. <S> " <S> In the dive at 2:02 he's "supersonic" already before "he's pulling up." <S> The dive is only to build up enough speed so that the subsequent climb starts fast enough to eventually exceed Mach 1. <S> Heard from the ground, what are the thumps at 2:30? <S> Forty thousand feet up is eight miles, roughly 45 degrees above the horizon; so as many miles horizontal <S> , say twelve miles total. <S> The speed of sound is 4.5 seconds per mile, so the lag from video to audio is 54 seconds. <S> 2:05 is when the dive is "supersonic right now. <S> " The thump at 1:36 shows that the horizontal approach to the dive was supersonic. <S> Faint thumps are at 3:01 and 3:15, thus generated at 2:07 and 2:21. <S> 2:07 is just after ascent starts: maybe parts of the airframe exceeded Mach 1 in that high-G maneuver. <S> 2:21 is mid-ascent, thus the cause of the intended low-boom maneuver , between the radio chatter that says subsonic at 2:16 and supersonic at 2:39.	I think that turning the plane around on it's way to the ground achieves the rear fins of the plane distorting the soundwaves on their way to the ground (in contrast to a flat belly of the usual plane, which reflects "hard" N-Waves (
Did WW2-era aircraft have constant-speed or variable-pitch props? This is slightly related to my other question on variable-pitch controls. I want to know if WW2-era aircraft typically had variable-pitch or constant-speed propellers. Variable-pitch lets the pilot adjust the propeller blade pitch. "Constant speed" is the same as variable-pitch, but the engine does it automatically to keep the best performance at various airspeeds. This also lets the engine keep a constant RPM so it can always run at its optimal RPM, also increasing efficiency. Anyway, were such things seen in WW2? Were they the norm, or the exception? Did single-engine aircraft have them, or were they more common on multi-engines? I'm interested in all the nations who made aircraft, especially USA, UK, USSR, Germany, and Japan. And I'm interested specifically in the combat aircraft , like fighters and bombers, not necessarily the civilian transports of the era. This will give us a good idea if the extra complexity and weight was acceptable for combat aircraft of the era. <Q> Variable pitch (with feathering) was virtually universal on (at least American) multi-engine fighters, bombers, and transport aircraft even early in the war: the DC-2 had feathering variable pitch, and it entered service in 1934. <S> The P-38 had feathering and variable pitch, and was in service before the US entered the war. <S> Constant speed propellers were also found on many single engine combat aircraft -- one was the Hellcat, which entered service in 1943, though it's very possible the technology was introduced earlier. <S> The P-47 Thunderbolt also had this feature. <S> When you're talking about aircraft that weigh several tons and need to deliver thousands of horsepower through a propeller, especially for combat operations, the weight and cost of variable or constant-speed propellers became negligible by comparison to the cost of the aircraft or the cost of fielding a losing design. <A> Most WW II era military aircraft had constant speed propellers. <S> People often confuse variable pitch, controllable pitch, and constant speed. <S> In general practice they are all the same thing as all constant speed propellers are just the most common form of a variable pitch propeller. <S> A few aircraft also had propellers that were only adjustable on the ground. <S> Most aircraft made since early WW II either had a fixed pitch, or constant speed propeller. <S> “Constant speed” means the pilot controls engine RPM through either a hydraulically, or electrically, operated control system. <S> It really is a type of RPM governor. <S> Some notable exceptions were the early Hurricane and Spitfire fighter aircraft that initially had wooden, 2 bladed, fixed pitch propellers because they were lighter than metal constant speed propellers. <S> There were performance penalties though so these were soon replaced with metal 3 bladed, 2 position "controllable" propellers, with course and fine pitch settings. <S> By 1940, they were all updated to metal constant speed propellers. <A> A constant speed propellor is a variable pitch propellor, the idea is that the pitch is adjusted automatically so that engine rpm remains constant with varying altitude and power settings. <S> The answer is yes, they were used in World War Two, although some light aircraft and older types used in the early war years had fixed pitch propellors.	There were very few aircraft where the pilot only had a simple control to just vary the pitch of the propeller.
Has an airplane ever been launched from a submarine? Airplanes are routinely launched from ocean going vessels , namely carriers. Missiles are routinely launched from submarines . Has an airplane ever been launched from a submarine? From questions about what qualifies: Manned or unmanned is ok, but payload mass has to approximate a least a small person One way trip is ok Airboat dropped in the water is ok Airbreathing primary propulsion required, rocket assist for takeoff is ok Wings for lift are required, control fins alone do not qualify <Q> Yes, The HMS M2 had a single seaplane aboard that it was capable of launching. <S> Her 12-inch gun was removed, replaced by a small aircraft hangar, the work being completed in 1927. <S> This could carry a small Parnall Peto seaplane, specially designed for the M2, which, once its wings had been unfolded, could be lowered onto the sea alongside by a derrick for take off. <S> On landing, the aircraft was hoisted back onto the deck and replaced into the hangar. <S> ... <S> In October 1928, a hydraulic aircraft catapult was fitted, to enable the seaplane to take off directly from the deck. <S> The I-400 class submarine was also capable of aircraft launches . <S> The type name was shortened to Toku-gata Sensuikan (特型潜水艦 Special Type Submarine). <S> They were submarine aircraft carriers able to carry three Aichi M6A Seiran aircraft underwater to their destinations. <S> They were designed to surface, launch their planes, then quickly dive again before they were discovered. <S> There are some more info blurbs here worth checking out about various submarine/aircraft creations. <A> Probably the most advanced aircraft carrying submarines ever built. <S> They entered service too late to have any meaningful impact, but the engineering that went into them was amazing for its time. <S> Just designing a submarine that could carry a watertight aircraft hangar without the topside weight capsizing the submarine was no simple feat. <S> They built preheaters for the aircraft engines into the submarine, so the submarine didn't have to linger on the surface while the aircraft warmed their engines. <S> There was a plan to attack the Panama Canal locks with torpedos launched from the Serian aircraft, but it was never carried out. <A> If you allow "airplane" = "unmanned aircraft"...then, jets! <S> There was Regulus 1 <S> Submarine testing was performed from 1947 to 1953 at the Navy's facility at Naval Air Station Point Mugu, with USS Cusk (SS-348) and USS Carbonero (SS-337) converted as test platforms, initially carrying the missile unprotected, thus unable to submerge until after launch. <S> And Regulus II ... <S> the only submarine launch was carried out from USS Grayback in September 1958 <S> The air inlet on Regulus II always makes me think it's laughing for joy to be launched. <A> If a kite rather than an aircraft qualifies: German U-boats used a towed autogyro to lift a lookout/pilot to a more advantageous altitude (about 120 m). <S> https://en.wikipedia.org/wiki/Focke-Achgelis_Fa_330 . <S> The strategy increased the visible range from 5 nautical miles to 25 nautical miles. <S> There is one recorded instance of a submarine detecting, attacking and sinking the Greek steamer Efthalia Mari on 6 August 1943. <S> If a hostile vessel was seen, If the U-boat captain were forced to abandon it on the surface, the tether would be released and the Fa 330 descend slowly to the water. <S> I believe this might discourage reports of enemy warships by the pilot/observer. <A> (Wikipedia)I got beat to mentioning Regulus, but the Tomahawk cruise missile has been launched from a submerged sub. <S> A rocket is used to initially launch the missile. <S> ( reference ) <A> Yes. <S> Here is a wikipedia article about many of the designs: https://en.wikipedia.org/wiki/Submarine_aircraft_carrier <S> Most seem to have gone out of service before the end of WWII, but a German submarine, the Type 212, is being designed to launch UAVs out of its mast: <S> https://en.wikipedia.org/wiki/Type_212_submarine <S> (see the last paragraph in the "Weapons" section).	Also consider the Japanese I-400 class submarine, that carried three Aichi M6A Serian bombers.
How much water does a passenger airliner carry? How is the amount of water for (a) toilet and (b) drinking to be carried by a flight calculated in the industry? Is there any formula or thumb rule using which we can roughly estimate the amount of water required for toilet and for drinking calculated if the aircraft type $A$ is known and the flight has $P$ passengers on board and is scheduled to fly for $H$ before its next landing? <Q> It is going to vary according to flight mission, passenger count, season, or what part of the world the flight takes place. <S> Here are the capacities from a company document. <S> MD88/90 47USG ( <S> 177.9L)MD11 250USG (946.4L) <S> Estimated732/733 40USG ( <S> 151.2L)737 60USG (226.8L)747 3x 110USG = <S> 330USG757 66USG <S> (249.8L)-Fill valve closes automatically at 50USG <S> (189.3L)762/763 120USG <S> (453.6L)-Fill valve closes automatically at 102USG <S> (385.5L)763ER 160USG (600.6L)764ER 224USG (847.9L)772ER 300USG <S> (1135.6L)CRJ 200/700 31.5USG (galley 8USG/30L, lavatory 5USG/19L, toilet 18.5USG/70L) <S> As mentioned, the term "potable" water seems to be a minor overstatement. <S> Some companies warn employees to not uplift any potable water overseas (which means not outside the US, Canada, or UK). <S> But based on what I've heard, I wouldn't drink it wherever it came from . <S> Why You Should Think Twice Before Drinking Tap Water Why you should never drink water on a plane, according to a flight attendant <S> Airline's drinking water fails hygiene tests <S> The "potable" water is usually chlorinated water, but you´ll never know about the truck or tank service overseas. <S> Usually the galleys contain an anti-biological filter (silver ions) for the taps and coffee makers, which get changed regularly. <S> Also the tanks will be disinfected every few weeks, normally during an A-check. <S> Part of a C-check is to remove and test them. <S> On a B737 , the potable water tank is in the aft cargo pit behind the last wall under the aft galley just right in front of the pressurized bulkhead. <S> The tank itself is made out of composite materials and fiberglass. <S> The tank is about 4 feet long and 2 feet tall. <S> The 737s only have one potable water tank. <S> The water is moved from the tanks by pressurized air. <S> This pressure is provided by electrically driven air compressors mounted next to the tanks. <S> Not all operators use all three tanks and some have deleted some tanks. <S> 747 AMM, 38-11-00, page 1, pg 2. <S> Passenger <S> MD-11 hold up to four 63USG tanks, the freighter usually has all removed except for one. <S> This water also serves for flushing the vacuum toilets if installed. <S> The tanks sit in the utility tunnels (behind the sidewall) of the forward cargo compartment. <A> I used to work with the B747-400 when I was with Lufthansa. <S> From what I can remember it had water tanks which could hold 1500kgs of water. <S> On a long-haul flight from KUL to FRA we would generally uplift 75% so that would be 1125kgs. <S> The selector for water quantity is on the panel next to the door 2L. On water-source. <S> We were required to get an external laboratory to do a water test. <S> This involved bringing a technician to the water source at the airside where he would take a sample from each outlet and each water truck. <S> The lab report was relayed to HQ. <S> When we stopped passenger flights to KUL, we still had freighters operating to KUL but these planes usually did not require water <S> so we did not keep up our status as a water re-supply station. <S> On one occasion a plane came in with empty water tanks and the outgoing crew insisted on uplift of water. <S> This was not permitted because if any water from a 'non-certified' source was uplifted the tanks would need to be flushed and chemically treated when it went back to FRA base. <S> In this case we loaded a few cartons of mineral water and the crew was happy. <S> Anilv <A> It depends. <S> Airlines have an office that is constantly looking for ways to reduce weight as every pound of reduction can save thousands in fuel costs over the year. <S> The goal is to carry enough with a small margin over the predicted maximum need.	The B747 has three 110 gallon filament-wound fiberglass tanks attached to the forward side of the center section front spar (rear bulkhead of the forward baggage compartment). When it comes to water (and pretty much everything else that's not mandated) they look at historical use by route, season, load factors, and service locations to predict needed quantities and set the amount to be loaded.
How much water is produced in jet exhaust? If a jet has typical combustion efficiency, what equivilent amount of liquid water will be created per gallon of jet or kerosene fuel. An acceptable answer can be a ratio in weight or volume to the original unburned fuel. For example an answer might be 1 part in 50 by volume or 1/4oz per pound is converted to water. An answer in "water vapor" volume should be avoided because gas volume changes dramatically with altitude (pressure) and temperature. If you are also able to show a comparison for gasoline, that would be even better. <Q> According to Wikipedia Kerosene consists of molecules containing 10..16 C-atoms. <S> Assuming that the molecules are mainly Alkanes with formula <S> $C_nH_{2n+2}$: <S> $C_{10}H_{22}$: <S> 10 <S> * 12g + 22g = <S> 142 <S> g Alkane contains 22g H which burns to 22g + 11 <S> * 16g = 198g $H_2O$ Ratio Water/Kerosene <S> = <S> 198/142 = <S> ca. <S> 1.39 <S> $C_{16}H_{34}$: <S> 16 <S> * 12g + 34g = <S> 226 <S> g Alkane contains 34g H which burns to 34g + 17 <S> * 16g = <S> 306g <S> $H_2O$ Ratio Water/Kerosene = <S> 306/226 = ca. <S> 1.35 <S> I.e. <S> you get something between 1.35g and 1.39g Water per 1g Kerosene. <S> Comparison to Gasoline:Main difference of Gasoline is that molecule chains are shorter (4-12 C-atoms).I.e. <S> H/C-ratio will be higher, i.e. Gasoline will yield more water per fuel than Kerosene. <A> Typical fuels consist mainly of carbon (C) and hydrogen (H). <S> The amount of water that will be produced from combustion is dependent on the ratio of carbon to hydrogen. <S> Taking a general fuel with a hydrogen to carbon atom ratio (H/C ratio) of $r$ , the combustion looks like $$ CH_r + \left(1+\frac{r}{4}\right)O_2 \rightarrow CO_2+\frac{r}{2}H_2O$$ For gasoline fuels, the H/C ratio seems to be around 1.8 ; for kerosene fuels, around 1.9 . <S> Based on this data, kerosene fuels produce a bit more water than gasoline fuels, in molar quantities. <S> We can convert this to weight by using the molar weights of carbon, hydrogen and oxygen, which are approximately 12, 1 and 16 gram per mol respectively. <S> We can then find out that we will have $$ m_\textrm{fuel} = <S> 12+r \\m_\textrm{water}=\frac{r}{2}\cdot(2+16)$$ <S> or, a water-to-fuel mass ratio of $$\frac{m_\textrm{water}}{m_\textrm{fuel}} = <S> \frac{9\cdot <S> r}{r+12}$$ <S> For gasoline, this would be about 1.17 kg water per kg of fuel. <S> Side note: <S> I found very different H/C ratios for gasolines, ranging anywhere from 1.3 to 2.1. <S> I do not know if this based on actual variations (e.g., benzene has a H/C of 1, but hexane 2.33, despite having the same carbon chain length of 6) or if my quick literature search yielded bogus results. <S> The value for kerosenes (and related diesel fuels) seems to be pretty steady around or slightly above 1.9. <A> There are slight variables making the calculation a little inexact, but this illustration shows a 1:1.24 ratio.	For kerosene, it is about 1.23 kg water per kg of fuel.
Distance of downwind leg from runway in glider landing pattern? Is there guidance from the FAA or AGA on the distance of the runway from the downwind leg of a landing pattern for a glider? For powered aircraft, the FAA recommends in its flying handbook (FAA-H-8083-3B) that the downwind leg be flown from 2500 to 5000 feet out from the runway, a pretty wide variance. <Q> I was taught (by various publications and compenent CFIs) that angles are a better thing to focus on than distances. <S> For example, this publication suggests: You should turn from your crosswind leg (or from your 45 entry) onto your downwind leg when the runway centerline, or an extension of it, is 25-30 <S> ° below the horizon. <S> Using angles automatically compensates for variations in altitude. <S> For me, this makes sense for several reasons: <S> Judging angles is much easier than judging distances. <S> The AGL pattern altitude might differ depending on the airport/field you are landing at. <S> If you are landing out, you should ALWAYS fly a normal pattern if possible. <S> This may force you to fly an abbreviated pattern closer to the ground. <S> Obvously, adjustments to this will need to be made for a crosswind. <A> According to the FAA's Glider Flying Handbook (chapter 7): The distance for a normal pattern from downwind leg to the landing area should be approximately one quarter to one half of a mile. <S> Of course, this depends on current conditions and the type of glider. <S> This varies at different locations. <A> You may wish to start with the safe envelope parameters of your glider for turning in a landing pattern, in other words, speed and bank angle. <S> A glider turning a half circle at 50 knots (V 1.2 stall) will be much closer to the runway on downwind than a glider turning at150 knots (V 1.2 stall). <S> Of course, you can come in a little higher (and a little farther away) and "square it off" into a downwind, 1/4 turn, base leg, 1/4 turn, and final. <S> But the safe turn is the key. <S> Too slow or too tight could lead to a bad situation near the ground. <S> Not a good time to stall. <S> Hopefully your airport is "glider friendly" and <S> a suitable landing pattern can be worked out.	From the diameter of your safe 1/2 circle glide (and altitude loss),you determine your safe minimum distance from runway on downwind.
Is there a difference between a chart and map? Does the use or meaning of "chart" or "map" vary worldwide? Is there a difference between a chart and map? <Q> Colloquially, I would say not really, by definition <S> yes. <S> I think the simplest way to put is is: <S> All charts are maps but not all maps are charts. <S> Websters defines a chart as : map: such as a : <S> an outline map exhibiting something (such asclimatic or magnetic variations) in its geographical aspects <S> b : a map for the use of navigators while they define a map as <S> a : a representation usually on a flat surface of the whole or a partof an area b : a representation of the celestial sphere or a part of it c : a diagram or other visual representation that shows therelative position of the parts of something <S> In other words, maps are outlines of part or all of something while charts contain potentially more information like that needed to navigate or identify airspace. <S> Interestingly according to the definition, if used for navigation its a chart. <A> I was taught that charts give information on three dimensions of space while maps only represent two dimensional information. <S> For example, In the VFR sectional chart above, the altitude of various air-spaces, airports and key landmarks are indicated. <S> For nautical charts, the depth of the water is indicated. <A> Mathematically, (and technically), a Map is any one-to-one or one-to-many association between the items in one set (or list) and the items in another set or list. <S> You can have a map between the items on the surface of the earth and the points on a chart, but you can also have a map between the cities in the country and the individuals who are the mayors of those cities, or between dates, and the events that took place on those dates, or between the colors in the spectrum, and the frequency of the light that generates the color, etc. <S> etc. <S> Check out This Wikipedia article about "Mapping".	In general, the result of any "Mapping" is a "Map" but only those maps that relate geographic or spatial (2D or 3D) points in space to a visual representation of those points are "charts".
Does bypass air produce thrust? How does bypass air exiting the bypass nozzle produce thrust in a turbofan engine? I thought that thrust was produced by air reacting with the fans. So if thrust happens when there is an action-reaction pair with the air and fan blades, is there additional thrust provided when the mass of air pushed back by the fan blades exits the back of the engine? <Q> You can model the fan disc driving the bypass air flow as a well-shrouded propeller inside a short duct. <A> Yes a lot of the thrust is from the discharge of the fan being crammed into the convergent nozzle and forced to accelerate. <S> Similar to a regular jet engine where most of thrust is coming from the air coming out of the turbine being forced to accelerate by the convergent nozzle of the tail pipe. <S> Best way to envision it is to look at a balloon that you blow up and let go. <S> In that case all of thrust is coming from static air being forced to accelerate out the neck of the balloon by the rubber compressing it. <A> So if thrust happens when there is an action-reaction pair with the air and fan blades, is there additional thrust provided when the mass of air pushed back by the fan blades exits the back of the engine? <S> The thrust provided by the action of the fan blades against the air is the same thrust as the thrust provided by the air exiting the back of the engine. <S> If an engine is producing 200 kN of thrust, then you will see 200 kN of force exerted by the fan blades against the air, and you will see 200 kN of exhaust (measured by its mass flow rate times its speed) exiting the back of the engine.	It does indeed generate thrust which, as in the general case of a propeller, is transmitted to the engine case via a thrust bearing that supports the fan disc and thence to the airframe via the engine mounts.
Why do most biplanes have their top wing slightly forward of the lower wing? In most of the biplanes, the top wing is located a little forward of the lower wing. What is the use of this? Also, how does this affect stability of the aircraft. <Q> Placing the top wing ahead of the bottom wing in biplanes is called (positive) stagger. <S> It is mostly used in small biplanes and improves pilot vision. <S> In order to accommodate a variation of pilot weights and to reduce accelerations in maneuvers, it is advisable to place the pilot very close to the center of gravity. <S> If the upper wing were in the same lengthwise location, it would obstruct the forward and upward vision of the pilot. <S> Why is upward vision so important? <S> Because of the bank angle, in turns you need to look up in order to see what is ahead. <S> A high mounted wing right at the center of gravity would rob the pilot of forward vision in turns. <S> Therefore, in small biplanes the top wing is moved forward while the bottom wing is moved back correspondingly, so lift is created close to the center of gravity, but the top wing is out of the way. <S> Large biplanes do not need this arrangement because the pilot sits ahead of the wing. <S> The Antonov 2 below is an example ( source ): <S> In many designs, the center wing has a cutout at the rear in order to give the pilot a better field of view. <S> Even more interesting is what had to be done to improve pilot vision in parasol monoplanes. <S> The Focke-Wulf 56 used slight wing sweep in combination with a reduced root chord in order to reduce the obstruction to the pilot's field of view of the rear wing center (picture source ). <A> It's called a staggered wing and is done to reduce aerodynamic interference between wings in certain circumstances. <A> Wing efficiency. <S> Here is an analysis of biplane wing efficiency relative to separation as a percent of chord. <S> The reference states that positive stagger (upper wing ahead of lower) by 0.4 chord gives 5% better efficiency, so advancing the upper wing 0.4 chord would be beneficial compared to the vertical stacking shown. <A> In the case of the agricultural plane, pictured, the stagger increases the nominal CG range, a bit. <S> Finally, the upper wing will have a slightly greater angle of incidence, enhancing its stall and stall recovery characteristics. <A> Remember that a wing works by having high pressure below it and low pressure above it. <S> So, looking at the top wing, it has low pressure above it - OK. <S> And it has high pressure below it, <S> BUT... that high pressure is then affected by the low pressure of the bottom wing. <S> Now looking at the bottom wing: it has high pressure below it - OK. <S> It has low pressure above it, but that is affected by the high pressure below the upper wing. <S> So the high/low pressure areas of the two wings interfere with each other if they're mounted vertically above each other. <S> But if you move one wing foreward or aft of the vertical, then the high/low pressure areas affect each other less. <S> You can move the top wing forward, which is normal. <S> Or you can move the top wing backwards as on the Beech Staggerwing. <S> Either way works.	A wing with positive (forward) stagger is most common because it improves both downward visibility and ease of cockpit access for open cockpit biplanes.
Could modern military aircraft be retrofitted to work with alternative fuels instead of kerosene? I am geologist and I have heard in 50 years petroleum will be nearly gone. I know for commercial planes there are working projects with clean energy.I can be wrong, but I think military systems would fail with no kerosene maybe in 30-40 years, as petroleum is becoming much more expensive to extract and its quality is falling. So I wonder what's the sense of buying military appliances at 2018.I don't know if kerosene is being stored by the armies, but I wonder if it is just a madness to give the reason for increasing military budget. I am asking also what is the future for fighter planes etc. When petroleum is finished, is there any possibility to create technology that works with nuclear energy or so or this is the end of war? <Q> Petroleum isn't going to be finished for a very long time. <S> We keep discovering and accepting trickier, dirtier, and/or costlier ways to get more oil - shale is just the last step in a long chain. <S> It has been done . <S> This will require changes to the fuel system, to handle such considerably more contaminated fuel, increased fuel heating, possibly combustor alterations. <S> However, on a practical basis, it only makes sense to start replacing aviation fuels en masse once most road vehicles have switched to a different fuel. <S> Also, aviation's safety and maintenance requirements call for cleaner and more consistent fuels than acceptable on the road. <S> For the military, fuel consumption and costs have traditionally been considered less important. <S> It's going to get the fuel its jets need, since there will be plenty available for the foreseeable future. <A> In the 1950s, the US military were very interested in using high energy synthetic ethyl borane fuels, collectively known as "zip fuel", in aviation turbine engines. <S> The XB70 Valkyrie was intended to burn "zip fuel" in it's afterburners during supersonic cruising flight. <S> The cancellation of the USAF's HEF (High Energy Fuel) project in 1959 contributed to the cancellation of the XB70 because it effectively reduced the aircraft's operating range from 7,700 nm to 5,500, so that it could no longer attack targets in the Soviet Union without inflight refuelling. <S> Synthetic borane fuels offer much higher specific energies than kerosene, but there are also significant disadvantages such as a tendency to spontaneous ignition in the presence of air, and the buildup of solid combustion products on turbine blades, leading eventually to engine failure. <S> The fuels are also toxic as are the combustion products. <A> Let's not forget that electric airplanes are starting to make headway also, along with electric cars. <S> In 50 years, maybe a lot of small, private aviation will have switched to all electric. <S> Not sure that's viable for large commercial aviation or the military (assuming no world peace by then). <S> Here's an article with some under the hood shots of the electric motor <S> Siemens says electric will become an industry standard by 2050 with a move to electrification already moving along much faster than the company expected. <S> “We might have a market ramp-up to a certified electric system by 2021, possibly before the end of 2020. <S> We’ll be partnering with OEMs to help them integrate and maintain these electric systems,” Hamlin said. <S> The Chicago event also focused on how Siemens is currently working to bring electric aircraft to the marketplace, beginning with small aircraft like the Magnus and the Extra 330LE. <S> Siemens used the Extra in 2017 to set a world speed and climb record in electric airplanes. <S> The electrically powered Extra achieved a top speed of 211 mph and a climb record to 9,800 feet in four minutes 22 seconds. <S> Siemens is also blending the cyber and the physical worlds into its production process to reduce time to market for new products like a bearing shield displayed in Chicago. <S> The shield is used in the Extra 330LE’s electric motor. <S> When the original bearing shield was created, Siemens team created a digital twin that allowed them to continue redesigning, testing and optimizing a new version in a virtual reality world. <S> Results were impressive as the original part was reduced in weight from 25 pounds to just 9 pounds. <S> The Extra 330 <S> I believe normally flies with a 540 cubic inch flat 6 airpowered engine with 300+ horsepower. <S> If I could fit a same-weight engine in place of my 360 cubic inch/180 HP and get 5 hour endurance, I could see switching over when my current engine was due for a major overhaul or replacement (a 25K USD to 50K USD <S> effort).(how <S> do we get dollar signs to appear here without messing up the following font?) <A> There is a modified F-18 that runs on a 50% biofuel that the navy dubbed the green hornet <S> The military has been experimenting with biofuels and other alternative sources of energy for a while. <S> Here is a basic demonstration model of a saltwater converter which made fuel to power a drone . <S> The article linked mentions there are downsides that would have to be adressed like protecting surface organisms like Plankton from being sucked in.	Yes, planes could be altered to use other fuels such as biodiesel. Aviation is weight-critical and an energy-dense fuel matters; it's also a smaller consumer than road vehicles.
Are there any mandatory announcements that a captain has to make? Are there any announcements that a captain of an aircraft must make that is reinforced by law or a rule? (This is concerning all countries ) <Q> The US does have specific regulations that require the pilot to ensure that passengers are briefed on certain safety issues, although there's no requirement that the pilot must do it personally. <S> Here are two regulations from the part 91 (all flights) and part 121 (scheduled airline flights) regulations. <S> There may be others. <S> 14 CFR 91.107(a)(2) : <S> No pilot may cause to be moved on the surface, take off, or land a U.S.-registered civil aircraft [...] unless the pilot in command of that aircraft ensures that each person on board has been notified to fasten his or her safety belt <S> and, if installed, his or her shoulder harness. <S> 14 CFR 121.571 : <S> Each certificate holder operating a passenger-carrying airplane <S> shall insure that all passengers are orally briefed by the appropriate crewmember as follows [...] <S> I guess that other countries have similar regulations, but it would be difficult to list them all, so hopefully this example is helpful for you. <A> ICAO Annex 6 covers the necessary content on briefings for international flights, and most countries have regulations that mirror those rules for flights within that country. <S> The pilot-in-command (what airlines call the captain ) is responsible for briefing all passengers on where to find and how to use: the emergency exits, the oxygen equipment and life jackets, if they're required for the flight (which they are on airline flights), the safety belts or harnesses, and passenger briefing cards, if carried; and for ensuring that all passengers are familiar with the location and use of emergency equipment carried for collective use, for example life rafts or escape slides. <S> That's all that's required worldwide. <S> Although it's the PIC's responsibility, there's nothing wrong with them delegating to other crew, and this is common practice on airline flights. <S> The airline will also have a standard operating procedure (SOP), and this may specify additional things the PIC has to say to passengers. <S> Although the SOP isn't a law or regulation, if there's an accident in the flight, and it is found to have been caused by the PIC not following the SOP, the PIC will likely be blamed and this will probably cause them legal problems afterwards. <A> Of course, a pilot may choose not to tell the passengers. <S> All other announcements are up to the captain. <S> Airlines request that welcome announcements be made, but it remains up to the captain.(source: <S> USA - Today - Travel )	Only if there is an emergency condition and the captain must tell the flight attendants and passengers to “Brace!”
Why Airbus A220 if A320 already exists? Airbus just presented its new A220 aircraft, formerly the "old" Bombardier CSeries , that is re-branded after a 50.01% acquistion of Bombardier by Airbus. It's an aircraft very similar in target and characteristics to its own A320neo Family , so my question is simple... why? If they would cover different market segments this could be a logical choice but in this case, is there not the risk of creating internal competition ? <Q> The A320-318/319 or the improved A320neo-319 share the market area around 107 - 160 passengers with the CSeries (now A220), two main differences are: <S> The CSeries is designed generally for carrying less passengers than the basic A320-family. <S> The fuselage of the A320-family is stretchted or compressed, exemption is the A320-318, which has also smaller wings, but at some point strechting/compressing the fuselage becomes inefficient. <S> The CSeries is an entirley new plane, while the A320neo seems to be more some kind of improvment with new engines and some(?) modifications to the airframe. <S> Basically, the airframe, fuselage and engines should fit together, to make an efficient plane. <S> The CSeries should be therefore more efficient with small numbers of passengers. <S> The A320-318 will be not available as neo <S> and the A320neo-319 seems to be <S> market for special long-distance and hot-and-high (engines produce more thrust and consume more fuel) situations. <A> There will be A220 stretches to take it directly into competition with the larger products, which are rapidly ageing designs, and that's the thing. <S> The 320 is 30 years old, and the 737 is a 50+ year old design. <S> Sooner or later airlines are going to want something more up to date and the C is state of the art if slightly more conservative than the 787 <S> (aluminum alloy for the fuse, and they wisely decided to stick with NiCad batteries). <S> If design age wasn't an issue they'd still be building 707s and DC8s. <S> One key example of the benefit of state of the art design is maintenance. <S> The C's maintenance program requires a fraction of the labour hours of previous generation airliners. <S> It's too bad. <S> The financial strain of the C was on the verge of bringing the whole company down when Airbus stepped in to take it on for free. <S> The experience has left Bombardier Aerospace quietly backing out of the commercial aircraft industry (it is seeking to offload the turboprop program and RJ production will slowly peter out) and in 5-10 years will be a bizjet only operation. <A> You say "It's an aircraft very similar in target and characteristics", but this is not really true. <S> I made a quick comparison of typical number of passengers and MTOW (based on data from Wikipedia): <A> So, I dug around and this is what I could find: Airbus and Boeing <S> both cover mainline (130-240 pax upto 3300 nm) <S> with their A320neo and 737 MAX lines respectively. <S> For regional travel, which is less than 130 passengers, there is the A220-100 and -300. <S> Airbus now covers this section thanks to their acquisition of a majority stake in the CSeries line from Bombardier. <S> So the new A220 variants don't quite compete with the A320neo (especially since the A319 hasn't been doing so great in terms of sales) <S> This article explains it in greater detail. <S> Here is more about the CSeries/A220	You can see that the A220 is significantly smaller and lighter than the A320 and A321, more similar to the now discontinued A318 (and maybe A319).
Is it true that a soda can or a bag of chips will pop in a plane at high altitude? I've heard some conspiracy theorists claim that if you were to bring a soda can or a bad of chips onto an airplane, they would pop? Is this true? If so, why? <Q> Not likely. <S> Consider how food products normally make it to you. <S> Any competent US maker of soda or chips will design their product to be shipped on Interstate 70 or 80, via Sherman Summit (8650') or the Eisenhower Tunnel (11,158') <S> or more likely by rail , <S> via again Sherman Summit (8015') or Moffat Tunnel (9239'). <S> * Aircraft are pressurized to a pressure altitude of 8000' typically, so Sherman Summit (rail). <S> If a food manufacturer were to botch their packaging, they wouldn't have your problem of a soda can bursting, they'd have an entire container load of sodas or chips burst and ruined for sale. <S> That is simply unacceptable, so manufacturers have a big incentive to get this right. <S> Other markets will have similar issues - the EU has the Alps, and China and India have the Himalaya. <S> It does not apply to regional sellers in flatland areas, so a regional/indie Florida chipmaker, all bets are off. <S> It does, however, apply to soda manufacturers, whose cans must endure extreme temperature (e.g. solar loads in a car) also in high places. <S> * Tennessee Pass (10221') doesn't count, it is weedgrown, rusty and cut in several places, being held for future capacity needs. <A> I can confirm that bagged snacks can pop from the pressure difference. <S> Climbing through 7,000 feet (on our way up to 9,000) in an unpressurized PA32 we heard a quite loud POP. <S> In and out of clouds at the time we were busy in the front seat, didn't observe any flight control or systems issues. <S> Fortunately had a person in the back that looked around there for us. <S> After trying to look outside at airplane surfaces for awhile she turned her attention inside and found a bag of popcorn (the already popped, snack style) had exploded... <A> Sitting very close to the bag, I thought the sound was quite loud. <S> Nobody else noticed it. <S> Results may vary from bag to bag. <S> Chip bags are pressurised relative to the atmosphere. <S> As the plane climbs, the pressure in the cabin drops, which increases the pressure difference. <S> This pressure difference may exceed the strength of the bag, causing it to break. <A> Soda cans are designed to withstand much larger amounts of pressure from the inside. <S> Ever tried to squeeze a soda can that has just been shaken? <S> Taking away outside pressure can only increase the inside pressure by 1atm - and that would mean placing the can in a vacuum. <S> Simply shaking a can will increase the inside pressure much more than that and a can is supposed to survive even more than just shaking. <S> Bags of chips are not designed to withstand large amounts of inside pressure because chips to not generate any pressure like a carbonated liquid does. <S> Depending on the pressure at the time of packaging and the packaging itself, they usually do "inflate" a bit on a flying aircraft and in rare circumstances they may even burst. <S> [edit]I decided to dig out some numbers, so here we go: <S> https://hypertextbook.com/facts/2000/SeemaMeraj.shtml <S> A cooled soda can have an internal pressure as low as 1atm (~100kPa) up to more than 2atm. <S> At room temperature this goes up to around 4atm. <S> So taking a can out of the refrigerator and putting it on the table increases the pressure more than placing a (cooled) <S> can inside a vacuum . <S> As has been pointed out in the comment, shaking may not significantly increase pressure. <S> (I was expecting a more than minor increase because a bottle that has recently been shaken certainly feels "harder", but OTOH you need to be really careful when it comes to "feeling" things like pressure!) <S> Temperature, however, does increase pressure significantly and I would expect a soda can to be designed to withstand the pressure of a hot summer day in the shade - <S> i.e. 40 <S> ° <S> C/100°F. <S> (It's not trivial to predict the pressure at that temperature, so I'm not trying.)[/edit] <A> I have never had a bag of chips pop in a commercial flight (although I've had bags that seemed to be right on the verge). <S> On the other hand, in a single engine non pressurized Beechcraft Bonanza <S> we had a bag of chips explode in the cabin as we were climbing to our cruising altitude. <S> It's been too long for me to remember our altitude, but it can and does happen. <S> Scared the crap out of me as it was near me when it happened <S> and it was quite loud. <S> Can of soda? <S> Haven't had one explode in the air. <S> I have had cans of soda explode due to heat though in the summer in the trunk of my car, on several occasions. <S> Luckily in my case they were all seltzer water. <A> The only reason it might pop is if the cabin pressure were to suddenly disappear. <S> That's explosive decompression and if it happens you've more serious problems than having some soda or crisps soil your clothes or <S> whatever is in the bag it popped in. <S> I did once get the advise to open any cans or bottles containing carbonated drinks I was planning to consume during a flight before takeoff, but that was on board an old Soviet era aircraft with a faulty pressure cabin. <S> In such cases the sudden release of pressure can cause the liquid to spill out, similar to shaking a bottle of soda violently before opening the lid would do on the ground (or, as my aunt once did mistakenly, freeze cans of soda <S> so they'd be nice and cold for next day's road trip, then leaving them out in a hot car where they built up so much pressure they ruptured). <A> Definitely. <S> I have seen it on older aircraft at medium altitude chips bags <S> can pop easily. <S> Altitude at which no cabin pressure is even required.	You can make a soda can burst by heating it up, but that'll require quite a bit of heat. I brought a bag of chips on a Quantas A380 flight recently and it ruptured during ascent.
How to correct a roll due to turbulence? I fly a Piper Cherokee 180 (PA-28-180) in an area that has frequent turbulence. When turbulence causes the aircraft to roll to one side I usually try to correct by using aileron and rudder in the opposite direction of the roll. However my flight instructor says that I should use rudder only to correct for the roll. I can get the wings level by using only rudder but it seems to me that using aileron and rudder would be the most effective method. Can someone please explain to me why I should use only rudder in this instance? <Q> Your instructor needs some... instruction. <S> Inducing roll using rudder alone is something you do when you are right on the edge of a stall because a downgoing aileron can potentially induce a stall when right on the edge. <S> In a normal climb, using rudder alone is totally nuts. <S> If you needed all the roll power you can possibly get, you would apply full aileron and full rudder to use the resulting skidding to increase the roll rate. <A> I'm not sure I would agree with the advise of your instructor, but this is perhaps what he wants you to learn. <S> The Piper Cherokee has a small amount of dihedral built into it's wings. <S> This dihedral angle is used to "self right" the aircraft in the event of a roll. <S> The way it works is when an airplane starts to roll it loses altitude parallel to the slip direction: <S> So with a dihedral angle the wing facing the slip direction now produces more lift: <S> With enough time dihedral wings will right themselves, or as your instructor is telling you, you can make this faster with the rudder by turning the lower wing into the relative wind speed making it produce even more lift. <S> Why your instructor is preventing you from using any ailerons I'm not sure, but perhaps he has reasons you should ask him about. <S> This might not be the best example, but I have something personal that probably relates to what your instructor's getting at. <S> I ride horses quite a bit, and we have something called "no stirrup Thursday". <S> It's as the name sounds, when you ride on Thursday the stirrups stay in the barn. <S> Stirrups help you balance your weight so by spending a day without them <S> we force ourselves to learn to balance better and ultimately stay on the horse given a situation when our feet slip out of the stirrup. <S> It's not unheard of <S> that control sticks break and all your left with is the rudder pedals. <S> It's also not uncommon for new pilots to use the ailerons too much to correct roll and this causes the plane to roll the other direction, which they then switch the ailerons back again to try and correct it. <S> But I'm really just speculating at this point <S> , you should ask your instructor directly why he is preventing you from using the ailerons. <A> I'd urge you to exercise caution using this technique. <S> After all, this is how American Airlines 587 got down. <S> The pilot used rudder aggressively in an attempt to get the plane out of a jet wash - so aggressively that his rudder input caused structural failure and the entire vertical stabilizer snapped. <S> In post-crash interviews with other pilots who have flown with the accident pilot, others stated he like to use very large rudder inputs even in minor turbulence. <S> When questioned about this technique, he said he was taught to use the rudder this way. <S> Further investigations revealed that many pilots in the airline have a wrong concept of flying an airplane, namely using the rudder way too aggressively to correct the airplane's attitude. <S> Using the rudder is a very effective way to correct an upset situation. <S> Say I find myself in a left bank 135 degrees <S> (so I'm upside down) and nose down attitude. <S> Full right aileron and full right rudder would be my input. <S> My rudder input has two purpose. <S> First, the roll-yaw coupling (on most planes) means my right rudder with cause induced right roll. <S> Second, once the plane is at the vertical (90 degrees roll), the rudder pushes the nose up instantly. <S> As I transition to upward flight, somewhere between 60 degrees to 45 degrees of bank perhaps, I'd slowly let go of rudder input and at the same time gradually pull the stick/yoke aft, careful not to stall or cause abrupt input, depending on airspeed. <S> But that's more of an extreme situation. <S> Another use case, told to me by a Boeing 737 training captain: in case of complete hydraulic failure, a slight pedal input will bank the plane in the desired direction. <S> Again, this is an emergency situation, not normal flying. <S> Like others here, I do not agree with your instructor, or at least not in your presentation <S> (you may have misunderstood him, which led to the rest of us misunderstanding him as well). <S> For small attitude deviations, use the most direct method to correct. <S> Use rudder to keep the balls centered. <S> For larger deviations, aileron + rudder would be the most effective method. <S> Again, we cannot judge how big those deviations are here. <S> All I can say is - if you're dancing on the rudder pedals, it is definitely a wrong technique. <A> Not necessarily the best technique, but, in practice, say on a long cross country flight, use of rudder-only allows for the use of your hands to manipulate charts, plotters, portable electronics, etc. <S> I have found myself doing this many times over the years. <S> Just a thought. <A> Perhaps this is of some use. <S> AOPA put out a video recently about using rudder to correct for some turbulence. <S> I can't re-watch it just now, but as I recall it doesn't recommend always using rudder instead of aileron. <S> Rather, it talks about recognizing when bank is induced by crosswind gusts and using the rudder appropriately.	Apply only the rudder required to keep the ball centered with the application of whatever aileron is necessary.
What twinjet with rear-mounted engines and swept wings did I see in Savannah, GA? I saw this flying in Savannah, GA and need help identifying it. It looks like something military due to the color and lack of markings. Can anyone help? <Q> Gulfstream G500. <S> The G600 is longer. <S> The angle is close, but look at the window just ahead of the wing fairing. <S> The original is faint but clearly ahead of the fairing curve. <S> The G600 window is in the middle of the curve. <S> The G600 has a bigger wing. <S> G500 pinterest G600 wikipedia <A> It looks like a green Gulfstream G-650, which makes sense since Savannah is where they are made. <S> "Green" means unpainted (just in epoxy primer or bare metal in spots) and with no interior. <S> That's how corporate airplanes usually leave the factory. <S> Finish paint and interiors are normally custom done at completion centers selected by the purchaser. <S> There is a completion center across the ramp from Gulfstream, Midcoast Aviation, that probably does some of them, although as I said that's the buyer's choice. <S> Corporate manufacturers usually leave the completions to outside companies because the artisan level of work required doesn't dovetail well with normal production processes. <S> You have to have an interior with pretty much perfect joins and seams or the customer <S> will reject it. <S> Bombardier starting doing Global completions in house <S> and it was a disaster for quite a while, with customers forcing complete interior re-dos. <A> It’s a G600 test article (slightly longer fuselage than a G500) undergoing a test flight in the airspace near Hilton Head Intl (KSAV) where Gulfstream’s main factory and flight test center are. <S> They often fly them south from KSAV to Brunswick (KBQK) for flight testing. <S> The aircraft is not yet certified for production, nor is the G500 either. <A> It doesn't have its final paint job yet, hence the lack of markings.	That's a Gulfstream G500 or G600 (someone who knows the differences better can tell us which), probably a new one arriving to Hilton Head International for finishing at the Gulfstream service center there.
How do hot air balloons navigate? Hot air balloons are quite obviously carried along with the wind, so how can they be navigated? Choosing the correct launch point relative to the desired landing point would seem to play a major part of this, but logic states that it is not always possible to choose the best possible launch and landing points. Can a hot air balloon be "steered" by increasing or decreasing altitude, hence selecting just which wind it will be subject to? Does the direction of the wind vary with altitude, and if so, how much? How do balloon pilots know how the wind will vary at altitude if that is the case? <Q> That is exactly how balloons “steer” - they pick an altitude where the winds aloft are going the way the pilot wants to - assuming winds at an available altitude exist where the wind is what the pilot wants. <S> Many balloonists use Ryan Carlton <S> ’s wind tool found here to get a good idea of local winds: http://ryancarlton.com <S> NOAA has a website called RUC soundings that presents actual wind and temperature aloft data from balloon launch sites and then interpolates for locations in between: https://rucsoundings.noaa.gov/ While the pilot can plan a flight and do amazingly well to get near to where they wanted to go, at the end of the day, a balloon, as an unpowered aircraft, is at the mercy of the winds. <A> They use the fact that the wind veers when going up, that is, changes direction clockwise, and backs, changes direction counterclockwise, when going down. <S> This is largely (there are a lot of other factors but this is the one we are interested in) due to the tendency of air in the atmosphere to spiral away from high pressure toward low pressure (spiraling because of Coriolis effect; what makes draining water swirl - clockwise away from high pressure in the north, counterclockwise in the south). <S> Away from surface influence, the air spirals nearly perpendicular to the "slope" of the high pressure <S> (think of it as a mound of air that wants to flow toward and fill in adjacent low spots but Coriolis effect makes it swirl as it does so). <S> Closer to the surface, friction effects inhibit some of the Coriolis effect make air flow a bit more directly "downhill" toward the Low you might say, the more the lower you get. <S> For a high pressure area in the northern hemisphere where there is clockwise circulation as air flows away from the centre, this means the wind is more directly away from the center of the high at the surface than when higher up, where Coriolis effect is stronger and it "swirls" more. <S> As a result the wind direction will change clockwise as you go up. <S> And vise versa going down. <S> In the southern hemisphere where the circulation patterns are reversed, it'll be the opposite; veering going down and backing going up. <S> This gives the balloonist some control over ground track by choosing a specific altitude that gives the desired track. <S> Obviously, the amount of veering and backing being fairly small between the surface and 5000 ft, maybe 10-30 degrees, means the balloonist still has to pick a launch site that is upwind of destination. <S> A launch site that is directly upwind based on the wind direction at, say, 2000 ft will give some left and right directional control by going higher to change track to the right, and lower to go left. <S> The balloonist also has to account for wind backing during the descent to landing and allow for that in the "cruise" portion of the flight to get the best position for the final approach. <S> Beyond that, it's control the altitude with the burner and hope for the best. <A> Before launch, the balloonist will release a small helium balloon and note which direction it drifts as it ascends. <S> After launch, the balloonist will work up a goodly gob of spit and discharge it overboard from time to time, noting which way it drifts as it descends. <S> Such measures are limited in accuracy and in the presence of a strong wind, the balloonist has not much choice about where to go. <S> The ground crew in the chase truck follows the flight and knowing the flight's intended duration, will find a convenient location along the balloon's track and park there- <S> thereby defining the balloon's "destination".	Balloonists use spit and little balloons to track the variations of wind direction with altitude.
What is the true top speed of the SR-71? By "true" top speed I mean the absolute fastest horizontal airspeed the aircraft can achieve if damage to the engines is disregarded (similar to how the MiG-25 apparently can reach mach 3.2 but may damage its engines beyond repair). Catastrophic structural failure (of anything beyond the engines) is not permissible in this scenario. In "The Untouchables" Brian Shul claims that he reached mach 3.5 while evading a missile. This is also stated in the Wikipedia article on the SR-71 with a citation to the same book. Are there any other sources than his own book that can confirm or reject this claim? Can it be argued for or against this top speed claim on technical merit or physical limitations? On Wikipedia it is also stated "Maximum flight speed was limited by the temperature of the air entering the engine compressor, which was not certified for temperatures above 800 °F (430 °C).[57]" However, it is not clear how much abuse beyond this the compressor could take. It is possible to give some estimate or educated guess based on the materials used? <Q> Based on the SR-71A operational envelope , the top Mach number was Mach 3.3 when authorized by the commander and Mach 3.2 otherwise. <S> The top airspeed was 400 kts equivalent airspeed when supersonic and 450 kts equivalent airspeed when subsonic. <A> The SR-71 Pilot's Operating Handbook has been declassified and is available online . <S> The operating limitations section states that Mach 3.17 is the recommended maximum cruise speed for normal operations. <S> So while it might be possible to exceed the maximum Mach, doing so probably carried with it the risk of Bad Things(TM) happening. <A> The USAF never did release just how fast an SR-71 CAN fly, preferring to state that it DID fly at certain speeds on certain dates and set certain records. <S> Shul made references to the jet attaining Mach 3.5+ during flights he flew in his books. <S> I believe him. <S> There are also credible rumors that a Blackbird was capable of Mach 4 in ideal atmosphereic conditions. <S> If USAF or CIA Sled Drivers did attain that high of a speed on certain occasions, they’re not confirming it. <S> Shul liked to say that the muzzle velocity of a high powered rifle bullet was about 3000 ft/s. <S> A Sled comfortably cruised at 3,300 ft/s and the Pilot still had a couple of inches of throttle left in case he REALLY needed to haul ass!	Speeds of up to Mach 3.3 could be authorised by the commander as long as the maximum CIT (compressor inlet temperature) of 427 degrees C was not exceeded. Most Blackbird pilots were pretty coy about a top speed.
What does it mean when your destination airport is currently "below IFR minimums"? Does it mean that absolutely nobody can land there until conditions improve? Can ATC still give you an IFR clearance to your destination airport in this case? <Q> It would be very helpful to know where you read or heard the phrase, to get some context. <S> But, it likely means that weather conditions at the airport are below the IFR takeoff minimums in 14 CFR 91.175 : (f) <S> Civil airport takeoff minimums. <S> This paragraph applies to persons operating an aircraft under part 121, 125, 129, or 135 of this chapter. <S> (1) Unless otherwise authorized by the FAA, no pilot may takeoff from a civil airport under IFR unless the weather conditions at time of takeoff are at or above the weather minimums for IFR takeoff prescribed for that airport under part 97 of this chapter. <S> (2) <S> If takeoff weather minimums are not prescribed under part 97 of this chapter for a particular airport, the following weather minimums apply to takeoffs under IFR: (i) <S> For aircraft, other than helicopters, having two engines or less—1 statute mile visibility. <S> (ii) <S> For aircraft having more than two engines— 1⁄2 statute mile visibility. <S> (iii) <S> For helicopters— 1⁄2 statute mile visibility. <S> Landing minimums are per-approach <S> so it wouldn't make sense to say that the whole airport is below IFR minimums based on landing criteria. <S> However, without reading or hearing the phrase in context, I may be wrong. <S> As for landing there anyway, even in zero visibility a private pilot operating under part 91 is free to take off, or to start an instrument approach. <S> You can't legally land if visibility is below the approach requirements, but you can still fly the approach to 'take a look'. <S> It might not always be smart, but it's legal. <S> On the other hand, commercial flights under part 135 or 121 can't even start an approach unless conditions are above certain minimums (e.g. see 135.225(a) ). <S> Those minimums are usually just the ones required for the particular approach, but they can also have operator-specific requirements. <S> Of course, many commercial aircraft have crew and technical capabilities that light aircraft don't (like shooting a CAT III ILS ), so they might still have a better chance of landing in marginal conditions . <A> I think they are referring to the minimum visibility and ceiling that is required. <S> There are two cases. <S> Actually landing at an airport and filing an IFR flight plan. <S> Per §91.175 Takeoff and landing under IFR. <S> (c) Operation below DA/DH or MDA. <S> Except as provided in §91.176 of this chapter, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless— (2) <S> The flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and Part 91 aircraft may attempt an approach if visibility is reported to be below minimums, but Part 121 and 135 may not begin the approach if reported visibility is below minimums. <S> Effectively, the airport is closed to them. <S> You may file to an airport that is expected to be below minimums at the time of arrival, but you must file an alternate that is above IFR minimums. <S> §91.169 <S> IFR flight plan: Information required. <S> has details. <S> (c) IFR alternate airport weather minima. <S> Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima: (A) <S> For a precision approach procedure. <S> Ceiling 600 feet and visibility 2 statute miles. <S> (B) <S> For a nonprecision approach procedure. <S> Ceiling 800 feet and visibility 2 statute miles. <A> You can still get clearance to the destination, at your discretion. <S> It's not unheard of for weather conditions to be below minimums now and quite acceptable a few hours later after all. <S> Think Milan Linate, an airport plagued by early morning fog. <S> A flight taking off from say Amsterdam to Milan may take off with the airport covered in dense fog that would make it impossible to land legally, and by the time it gets there it's a clear morning with no fog or clouds. <S> Of course as always you, the pilot, are responsible for your actions and if you take off knowing your destination is currently closed for you <S> you'd better have a viable alternate plotted just in case the expected improvement in conditions doesn't happen.	So yes, ATC can give you a clearance to an airport that is below IFR minimums.
Was ATC overstepping its boundaries when advising a pilot to ignore a cell warning? I found a clip on YouTube (via an article on Jalopnik ) of an Aer Lingus pilot departing from JFK. Due to a weather cell showing up on his instruments, he can not make the left ATC asks him to make. ATC advises him that the weather is not as bad as the pilot makes it out to be. ATC: "Shamrock 104 heavy, it's light. I have 6 categories of weather here, it's the lightest category. I've had no adverse ride reports south of the airport by 10 miles." He then is put in a holding pattern (while departing ) until the situation is resolved. He is then told that the last 6 craft departing had no problem following that heading. ATC: "Shamrock 104 heavy, you're gonna go the way the last 6 GREKIs went while you did this overhead Kennedy." Was ATC overstepping its boundaries advising a pilot to ignore a weather warning? <Q> Shamrock demanded something that's extreme for the NYC airspace: runway heading for 15 miles. <S> Usually asking for right or left deviation is sufficient, and that appears to be what the previous Delta departure did. <S> Once Shamrock declined an easterly heading, the controller had no choice but to vector them in a temporary hold. <S> The controller was frustrated because the previous departures had been accepting turns to the east and his radar didn't show signs of significant precipitation. <S> He also astutely pointed out that this weather was 5 miles from the runway departure end. <S> Aer Lingus should have been able to paint that on their radar or see it with their eyes before they departed. <S> Their clearance was to the GREKI fix <S> so they knew they'd be heading that way after departure. <S> That doesn't mean Shamrock was wrong. <S> After all, they are flying in actual, and the controller is sitting in a room at zero knots, but in the incredibly dense NYC airspace, it can create an emergency if you have to deviate that much. <S> The controller was harsh and made his frustration evident in the way he chose his words. <S> The pilot stroked his ego by saying his boss would call the controller's boss. <S> Once you strip away the emotions, the pilot and controller did their jobs. <S> The pilot kept his airplane clear of weather that he determined to be dangerous. <S> The controller did the only thing he could to keep the Aer Lingus flight out of that weather and away from conflicting traffic. <A> The controller didn't overstep their boundary but used poor judgment in using "another aircraft just did it..." as justification. <S> That is almost always the last words of a crash as unforeseen weather tempted an aircrew to sneak in one more landing or takeoff. <S> Fast cold fronts travel 1/2mi a minute and what the previous aircraft encountered has nothing to do with what is about to happen. <S> In the Pan Am Flight 759 with 153 people killed during takoff , The weather chart reported. <S> "No fronts or low pressure areas were within 100 nm of the airport, and there were no severe weather warnings for the time and area of the accident " <S> The lemming principle of the guy in front of me seems to have lived <S> , why not do it <S> too - costs many lives. <S> Good pilots don't wait until things are proven bad before they don't do them, they wisely refuse if it may be bad. <S> The pilot only had seconds after takeoff to assess the request. <S> His assessment may or may not have been correct <S> but he did not have the luxury of sitting at a desk for the last hour watching it evolve. <S> The previous Delta departure also saw something they did not like. <S> The situation easily fits what may have appeared like (or even been) <S> a micro burst forming. <S> Something that could be new, it would not have effected the previous aircraft, and may not have been apparent to the controller, but would legitimately put safety in jeopardy. <A> PIC is the ultimate authority and can either accept or reject ATC instructions if unable to comply. <S> ATC was not wrong in that their job is traffic separation <S> but they also pass on pilot reports to other aircraft operating in the area, so I can understand what they were trying to relay to the crew. <S> "However", with statement #1 above in mind, I would not let ATC vector me into a cell, having personally experienced a CB from the inside due to the under-whelming performance of a very old monochrome green weather radar unit and a captain who believed far too much in the radar's capabilities. <S> The pilot in the Aer Lingus example can try for a wider block of airspace and altitude to maneuver, but pretty unlikely near JFK <S> (but you can still ask).	The controller didn't overstep his boundaries, and he didn't tell the pilot to ignore a weather warning.
Where can I find runway usage statistics of USA airports? Ok I’m looking for stats and data of planes arriving at various airports and what runways they use most. I need to know the most used runways for arrivals in airports here in the States. Can anyone point me in a direction where I can easily find this info? <Q> Like @CrossRoads said in his answer, there is no data available on which runways are used most. <S> You will need to listen to LiveATC on several days and keep track of the winds to get a rough estimate. <S> For example, from listening to the tower at KSFO <S> I gather that they usually land on 1L and 1R and take off on 10L and 10R. <S> However, when the winds are too strong out of the east they use 10L and 10R for landing. <S> Likewise, if you listen to the tower at KJFK you can tell which runways are in use on any given day. <S> There appears to be more variability there because the winds are much less consistent. <S> And then there are airports like KOAK and KSJC that have one runway or set of runways that GA aircraft use and one for the big guys. <S> The airports might keep that kind of information <S> so a call to a few of them might give you some answers, but I am not aware of it being published anywhere. <A> One can also review the data provided by the airlines at the big airports. <S> For example, Boston-Logan has data by month of the year going back to 1999. <S> The statistics included below are compiled by Massport from information provided by the airlines. <S> You won't find data for the 5,000+ non-towered that is much different than what airnav.com reports. <S> My home airport's "operations center" where we pay for gas & stuff is mostly not-manned, and for certain not between ~4PM and 8 or 9AM. <S> I've left plenty of time before 8 and after 5 with no one to see me come & go. <S> And if I didn't buy fuel, they'd have no record of my plane having moved at all. <S> Have tried the FAA's Aviation Data & Statistics page? <A> Please reach out if you're still interested in this: https://flightaware.com/commercial/customreports/	FlightAware.com can compile runway usage information, based on flight track positions near the airport.
What plane is this? This aircraft was parked at the very back of the McCarran airport, and I was absolutely fascinated by it. It has a propeller on the back of the fuselage as well, though not very well shown in the picture. What is its name or model? <Q> Googling the plane's registration number (this one is N6361F ) is almost always enough to identify the plane. <S> In this case, FlightAware is high on the list of hits and says that the plane is a Cessna 337A, built in 1966. <S> Searching for "Cessna 337A" then leads to Wikipedia for more information. <A> That's a Cessna 337 Skymaster . <S> They were built from the early 1960s to the early 1980s. <S> Because the two engines are both on the fuselage centerline, the Skymaster is more controllable than a conventional twin engine aircraft in the event that an engine fails. <A> The 337 uses a push/pull design which is rarely encountered, but gives you the advantage of centerline thrust in the event of an engine failure (but the disadvantage of a noisier cockpit). <S> You can see the military variant in the 1988 film Bat 21 with Gene Hackman and Danny Glover, some great aerial footage regarding the power and maneuverability of the aircraft. <S> Because of the push/pull prop design, some nicknamed it the "Mixmaster", but if you watch the movie Bat 21 , you will see what a great aircraft it is despite the blender reference.	Cessna 337 Skymaster and/or the O-2.
Have there been any incidents caused by an inability to shut down an engine? I read many items on the avherald.com site where it says "engine shut down during flight" or words to similar effect. I'm wondering if there are any instances where an engine could not be shut down or the pilots had trouble shutting down the engine when commanded. What sort of backup systems are in place to avoid this kind of scenario? <Q> The shrapnel of the explosion destroyed many systems, including a hydraulic system, the anti-lock braking system, flaps and electronic controls. <S> After emergency landing, the pilots were unable to stop engine number 1, because the controls had been destroyed by shrapnel. <S> Emergency services had to douse the engine until flameout was achieved. <S> Source <A> Cathay Pacific flight 780 on 13 Apr 2010 Fuel contaminated by super absorbent polymer jammed fuel valves caused engine control problems. <S> The aircraft eventually landed with one engine at about 70% N1 at significantly higher than normal airspeed, burst some tires from the increased braking necessary and was evacuated. <A> Etihad Airbus A340-600 <S> This famous crash happened on the acceptance engine run-up test. <S> The causes were unrelated to engine problems, but after the crash, due to damages, two engines couldn't be shut down. <S> One of them ran for 9 hours (!) <S> after the incident, until it ran out of fuel, creating obvious hazard for the emergency crew. <S> (Luckily, there were no passengers to evacuate). <A> There is this business jet with two engines that didn't quit for 20min after it overran the runway and splashed around in a Bay. <S> Investigators found it attempted the landing with a 10kt tailwind on too short of field and the touchdown too far beyond the threshold. <S> May 15, 2005, in Atlantic City, NJ , USA <A> Air France 72.12 <S> Sept 1993. <S> Aircraft (747-400) went off the runway in Papeete. <S> Due to electrical damage (aircraft nose was in the water) <S> the engine could not be shut down from the cockpit and AFRS had to 'drown' the engine by hosing a lot of water into the inlet. <S> My understanding is that the failure mode of engines is to be fail-safe, ie to minimise the impact of failure. <S> With FADEC (full authority digital engine control) the problem is what would be the best action if signal were to be lost from the control box to the engine? <S> It was explained to me that the lesser of two evils will be to have the engine running rather than shutting down so the protocols were designed accordingly. <S> While this does not answer your question on backup.. <S> It is more sense if you look at it from a different angle.. <S> "what is the backup in case control of engines is lost". <S> In this case the backup would be the engine would continue to run rather than shut down.. <S> If this happenned in the air you would be better off with a working (albeit uncontrollable) engine rather than a dead one. <A> What sort of backup systems are in place to avoid this kind of scenario? <S> As I understand it airliners normally have a "fire handle" for each engine which is independent from the normal engine controls. <S> This handle can be used to cut off fuel to the engine and optionally discharge the fire extinguishers. <S> I can't seem to find an official source but from what I can gather the fire handle did not work in the Quantas case, likely due to the severe damage from the uncontained failure of the other engine on the wing. <A> In addition to the posts above, it is worth pointing out that this exact scenario is part of the flight testing of any new aircraft. <S> If you can find it, there is a whole episode of the PBS show on the B777 that shows this test being carried out. <S> It was an especially odd one, because the aircraft had P&W engines and brakes designed to handle that, but they wanted to test the performance as if it was equipped with the more powerful RR engines. <S> The chief pilot originally said no, but as the engineers at the various companies said ok, he relented. <S> The test required the aircraft to go to maximum power, in this case higher than the official rating so they could test the RR case. <S> After it reached a certain speed, they put on full brakes, with the engines still at max power. <S> When it finally came to a stop, the brakes were bright yellow. <S> It then had to sit for a time (5 minutes IIRC) to simulate the emergency vehicles arriving, which then sprayed the brakes with water. <S> It was quite impressive. <S> As they were careful to say, the idea of the test is not to pass some requirement, but to simply give future pilots an understanding of what to expect in the case it happened.	Qantas Flight 32 Enroute to Sydney, Engine Number 2 of the A380 disintegrated explosively.
Why would a flight from North America to Asia sometimes fly over the Atlantic? I am going to take AC031 from Toronto to Beijing in a couple of weeks, I searched its flight path, most of the time it will fly westbound after taking off from Toronto and continue west across the north pole area and land in Beijing, but yesterday it flew eastbound, across the Atlantic, this is very strange since the distance is a little bit more than flying westbound. Why? <Q> Those routes are extremely similar. <S> They're basically two almost-a-straight-line routes over the arctic ocean, except that the second one has deviated a bit to the right, so that it's gone just on the right of the North Pole instead of passing by the left. <S> At the pole itself, there's no such thing as "East" or "West", and if you pass very close to it, there is a discontinuous jump between passing it "going East" and "going West". <S> You can see this explicitly by going to FlightAware, asking to View track log , and downloading the flight tracking data to be viewed on Google Earth: Actual tracking data in white. <S> Interpolations for the missing-data parts in green. <S> As you can see, there is indeed a nontrivial deviation of what's probably several hundred kilometers in clipping Nunavut vs the northeast corner of Greenland, but that deviation is within the normal ranges of what you'd get in your standard transatlantic flight, say. <S> The only change here is that the variation now includes the North Pole itself. <A> I took Hewgill's picture and added the routes in the OP (I just eyeballed this, so I won't guarantee accuracy). <S> With the FlightAware maps it looks like drastically different routes, but from this angle you can see that both routes are not that far off the ideal route. <A> The direct route from YYZ to PEK flies almost over the north pole : <S> If your route from YYZ needs to deviate a bit to the right, then it will cross over to the other side of the north pole (which is the very centre of the map above), and your projected map from Flightaware would show it flying "over" the Atlantic. <S> But really, it's just gone slightly to the right of the pole. <A> The flight did not fly across the Atlantic. <S> Rather, you're seeing the results of stereographic projection . <S> More specifically, the Earth is Spherical. <S> Navigation needs to be thought of on the basis of a sphere. <S> It is 3-dimensional, and if you have studied sphere geometry, you will know that it defies the rules of geometry we know in 2D - for example it is possible to construct a triangle with three 90-degree angles. <S> The problem is that 3-dimensional objects cannot be displayed on a map, which is 2-dimensional. <S> Therefore a mathematical formula is used to make a sphere look like a rectangle. <S> The conversion is really skewed for regions near the poles. <S> As a result, you cannot compare distances by measuring them on the projected map. <S> The route merely deviated slightly to the left in the second picture. <S> However it is still flying over the North Pole, not the Atlantic. <S> The deviation may be due to changes in winds aloft and/or traffic. <A> ALL flight paths on the earth are curved, cause the earth is a sphere! <S> Which way that curve appears depends on which side of the curve you are observing it from. <S> If you observe it frm south of the flight path it will appear to curve northwards and then south. <S> If you observe it from East of the flight path it will appear to curve West and then East, etc.	Sometimes, routes need to deviate a bit from the "direct" route, due to prevailing winds or other traffic.
Are all tires on an aircraft replaced at the same time? On cars, it is often to replace all four tires at the same time. Is this true also for aircraft? I imagine the nose gear and main gear probably can be replaced at different intervals. However, are tires within the same gear assembly replaced together? What about left and right gears? For example, is it ok to replace all tires on the left gear only while keeping old tires on the right? <Q> Nope.. they are replaced 'on condition'. <S> Exception is when one tyre has deflated before landing (cockpit indication and later confirmed) then the good tyre on the same axle has to be replaced irrespective of condition. <S> Tyres have a hard life and get damaged by rubbish on the runway and stand. <S> Also airplanes don't always hit the ground straight .. when they come in at an angle <S> it wears the side of the thread more on that tyre. <A> On small planes, tires & inner tubes are used, not like cars which use tubeless tires. <S> Tires are also different sizes & plys. <S> For example, my POH (Pilot Operating Handbook) calls for 4 ply 5"x5 nose wheel and 6 ply 6"x6 main gear. <S> I recently had a pinhole wear thru on a main gear tire, so it went flat after 2-3 days, requiring a tube change. <S> The tire itself was fine. <S> So changing the parts that are worn is the norm. <A> There is no regulatory limit, at least in North America, on the number of times a tire can be recapped if the carcass is serviceable.	Airline tires are replaced on-condition and are generally recapped until the tire carcass condition deteriorates or is damaged to the point recapping is no longer viable.
Why does the ICAO alphabet use "Charlie" for C? Why does the ICAO alphabet use "Charlie" for C? Specifically, why choose "Charlie", which has a "Ch" sound, rather than a word with the hard "C" such as "Carl"? A cursory Googling turns up nothing. <Q> Hard C sounds too much like K. Ch (Charlie) will not be confused with K (Kilo). <S> And soft C sounds too much like S (Sierra). <A> ICAO is a phonetic alphabet, so it's all about sounds. <S> You're proposing "Carl", but it's pronounced kɑɹl̩ - with K . <S> Other option would be "cent", but this one is pronounced sɛnt - with S . <S> "Ch" as in Charlie (ˈtʃɑːli) is the only C that sounds (tʃ) <S> distinctively and can be recognized as "C" without any doubt. <S> The fact that's not a singular C but a part of digraph is not relevant. <S> The clarity of the message is. <A> For the same reason we use niner for nine . <S> The phonetic alphabet took a lot into consideration when they were choosing words including how words are pronounced with different accents. " <S> Charlie" like all the other words was likely chosen due to its unique pronunciation across dialects. <S> It is also a nice short two syllable word.	English language doesn't have a distinct sound for singular letter "C".
Why do budget airlines not use the jetbridge that's right there? Related to Who decides whether an airline docks at a jetbridge or parks at a remote stand? , but I'm not asking about remote stands. I recently took an easyJet flight (A319/320) from London Gatwick (LGW) to Malaga (AGP), and once through the gate, we walked down some stairs adjacent to the jetbridge and out to the plane. We didn't use a bus. But the airbridge was right there . Why not use it? <Q> The answer to the question you link explain many of the reasons. <S> But aside from them, all valid, the main point is that the use of jet bridges is charged an extra fee from the airport. <S> Some airport charges for use, some charges for time, so <S> a low cost company which is trying to save money is going to save on the jetbridge too. <A> It is not always about the extra fees. <S> Boarding and de-boarding via the jetbridge is a lot slower than using two stairs. <S> You are using a single door instead of two, the people walk slower, there is a complex balance procedure to prevent the plane from tipping, etc, it just takes longer time. <A> As Radu094 has already mentioned, minimizing the gate turnaround time is usually the number one goal for budget airlines. <S> It is thus crucial to use both doors to board/deplane passengers, as that can obviously almost halve the necessary time. <S> In my experience (about 100 flights in Europe a year, maybe half of that with EasyJet), this is the norm and boarding only via the front door happens very rarely. <S> I have never seen a budget airline use one of the posh dual-jetbridge gates to board an A320, so that inevitably sends some passengers to the tarmac. <S> On some airports, the design of the gates makes it possible to use both the jetbridge and the stairs at the same time (the front half of the aircraft boards via the jetbridge, the other half is sent to take the stairs). <S> If this is not possible for some reason, then the jetbridge simply won't be used. <S> In fact, at some airports (for example PRG), there's usually a gate agent standing at the junction of the stairs and the jetbridge, checking everyone's boarding passes and sending them the right way. <S> Other airports rely on information screens or instructions on the boarding pass like "rows 1-15 via the front door, rows 16-30 via the rear door", but that's much less efficient as there are always some folks taking the front stairs even though they're seated in row 28, which .	Many low-costs operators are sporting 30 or 25 mins turn-arrounds, so losing 5 or 10 extra minutes during boarding (and then having to pay extra for the priviledge) is not something budget airlines are keen on.
Has any passenger airliner ever offered forward-facing windows? The empty, dolphin-like, forehead of the A380 seems like it would be an amazing place for the first and/or business class bar, especially if it had forward-facing windows. I realize in the A380's case there are crew rest and storage compartments in that space, but wondered if there have ever been any passenger planes outfitted with forward-facing windows to enjoy the view? Image source: lufthansa.com <Q> We could start with the Tupolev ANT-20 with its rather daring forward-facing passenger gallery. <S> [edit - the prime seat right at the front in the gallery was for the navigator and his equipment.] <S> source <S> Like the Tupolev, most examples are inter-war. <S> Here is the moderately successful Latécoère 521 being assembled showing its gallery beneath the cockpit [edit - seems this was only for the navigator, not for passengers] : source ... and <S> the more esoteric Caproni Ca.60 <S> which would have made for an interesting journey <S> had it entered service - source -- EDIT - one special mention for the Junkers <S> G.38 which also had a sizable glazed area in the wings. <S> Unfortunately as far as I can tell (and despite what Wikipedia says) neither the nose nor wings were accessible by the passengers, but rather used by the navigators and engineers, which seems like a missed opportunity. <S> [ed. <S> the wing area was indeed intended for passenger, see comments] source <A> Boeing 747 <S> I'm a little surprised to not already see the Queen of the Skies here. <S> If 'partially forward' counts, <S> the first several windows on each side of the lower deck of the 747 are angled partially forward. <S> The angle is enough that passengers seated in the first row or so can indeed see directly in front of the aircraft. <S> KLM 747-400 Front View - Image Source: <S> Wikipedia <S> Many 747 operators choose to install First or Business class seats in the forward part of the lower deck. <S> Especially with some of the " reverse herringbone " style business class configurations, where the seats are angled relative to the cabin wall, this can result in the first row or two facing more-or-less straight forward with a window in front of them. <S> This was the case with Delta's 747-400 configuration, for example. <S> Of course, there aren't any windows facing directly forward on the lower deck, as that would require placing them on the front of the nose itself, where the radome is. <A> That would definitely be an appealing feature for passengers but the airframe of the A380 at its forehead is too curved to be able to fit a viewing area for passengers. <S> Furthermore, the design and operational (aerodynamic) costs associated with structuring an aircraft to be able to fit a cockpit and a forward viewing area, along with the cost of another set of cockpit-spec windows has economically ruled out such a feature for modern airlines competing in a market where ticket price rules all. <S> I would imagine airlines would opt to install remote viewing stations connected to external cameras before creating a space with forward facing windows. <S> In fact, some airlines have already started to do just that -- Etihad's First Class "Apartment" seats have monitors that are connected to cameras with different viewing angles outside of the plane. <S> Many Soviet passenger aircraft did in fact have viewing areas in the nose of the aircraft aside from the cockpit. <S> Unfortunately for travelers, these areas were designated for navigators, not passengers. <S> Some examples: Tu-104: <S> Tu-134: <S> An-12: <A> Another two examples from the Farman Aviation Works , purveyors of the world's ugliest aircraft. <S> Unlike the ANT-20 (the gallery primarily for the navigator), the Caproni (never operational) and the Junkers (where the wing pods are separate from the passenger compartment), the Farman F.120 and the F.60 <S> "Goliath" were designed with the full gallery experience in mind. <S> The forward view in the Goliath was interrupted on the left hand side of the fuselage by the walkway up to the exposed cockpit on top. <S> However, the F.120 had, I think, exactly what is being asked for - uninterrupted forward view for the passengers . <S> F.120 interior source F.120 in flight (also known variously and confusingly as the F.3X and F.4X) source <S> "This unidentified horse accompanied Miss Betty Rand and the Hamm brothers from London to Paris aboard the Farman F.60 Normandie in 1922." <S> source	The 747 is notable as one of the few, if not the only, modern airliner to offer such a view to passengers through an actual window (as opposed to camera views on the IFE screens.)
Is it OK to greet ATC? My instructor told me that courtesies are forbidden in radio communication, however, we usually start conversation as "Turany Ground, OK-ABC, good morning, (... request)". I find it natural. Is that acceptable violation of the rules, or could it cause some troubles? <Q> It is not part of the standard phraseology by any means, but it is fairly common, as is a very quick pleasantry when changing frequency. <S> [station name], <S> Good morning, G-ABCD, [request] and G-ABCD, changing to [other station] thanks for your service. <S> The thing to remember is to not choke up a busy station with overuse of non-standard comms, and therefore to remember when it might be inappropriate to stray from the standards. <A> Technically you are not suppose to and for the greatest safety, internationally recognized vocabulary should always be used. <S> However, I have noticed most heavy pilots and many controllers do a greeting. <S> That is the difference between the ideal world and the real world. <S> I doubt being the 65th pilot to say "good morning" improves your handling or makes the controllers day any brighter. <S> With so many pilots and controllers doing it, it really has become a matter of personal preference. <S> One advantage to doing a greeting is it gives the controller a one second warning to prepare for a communication. <S> Some aircraft are equipped with VOX (voice actuated transmission) circuity that tends to cutoff the first syllable of a transmission and <S> a greeting gets the VOX turned on. <S> I believe disingenuous <S> "thank you's" and " <S> I love you's" dilute the meaning and sincerity of the words. <S> If a controller really does something special (I have had two occasions my life was saved), then I use sincerity, "thanks that may have saved my life..." , or "your professionalism is appreciated..." . <S> I learned to fly from the US's second busiest airport <S> so being brief and concise was a safety survival tactic on Saturday mornings <S> - most pilots learn to fly from a much more relaxed environment. <A> Most times common pleasantries are inert and generally either go unnoticed or mutually exchanged by the aircrews and ATC. <S> Flying an aircraft into Oshkosh, WI for the annual EAA Expo is an excellent example. <S> Here you may not even be identified by your tail number and given very brusque instructions and expected to comply with a minimum of chatter. <S> Eg <S> “Blue and white Cessna, land on the thousand footers. <S> Rock wings. <S> Red Cherokee, follow the Cessna on final, land on the numbers. <S> White experimental, turn base now....”	They are not “forbidden” but it’s not standard phraseology. There are instances, particularly in high density airspace where it can impeded communications and it’s not appreciated.
Have bi-wings been used without creating more drag? As I understand from answers I've read here 1 , 2 , 3 , biplanes create more lift with less wing span when compared to single wing aircraft, because the combined wings have greater surface area overall. However this is usually at the expense of added drag as both wings are accelerating the same air downwards causing interference and creating inefficiencies. Also the wings commonly have supporting wires/structures between them causing more drag. With that said biplanes do have some desirable characteristics like shorter roll response. I also realize when looking at how nasa calculates for the drag coefficient, wing aspect ratio is a major factor in their equation: With this information it would seem to me if you could separate the wings of a biplane far enough apart that they don't cause much interference, you could possibly get a better performing aircraft with the same wingspan. I almost imagine it being as simple as making the tail a full sized wing and giving each wing a thinner aspect ratio. However I've never seen this done before or even attempted. Is there a reason for this? Would the wings still interfere too much with each-other. <Q> Moving the wings vertically apart would mean more and heavier supporting structure, but also a higher pitch moment of inertia. <S> Since this grows with the square of the vertical expansion, a biplane with a lot of distance between both wings will be hard to control and very sluggish. <S> When cross-bracing enables the top wing to work as the compression member and the bottom wing to work as the tension member of a truss, a very lightweight structure becomes possible, especially when the size of the aircraft grows . <S> If all you have to power your airplane is a heavy, inefficient piston engine like those at the beginning of the last century, and you can tolerate that your aircraft won't fly fast or far, a biplane is indeed the lowest-drag solution. <A> As for "making the tail a full sized wing", this is a reasonable idea and it has been tried on quite a few designs. <S> Such configuration is called tandem wing . <S> Perhaps the best known example is Quickie : <S> Wikimedia <S> Purely aerodynamically, tandem is better than biplane, due to both the wing-wing interference and the lack of horizontal tail. <S> However, tandem doesn't have the structural benefits of the biplane (see Peter's answer) and so must be heavier. <S> In which conditions it may be preferential to the classical design deserves a separate analysis, but given the scarcity of such airplanes, they must be quite narrow. <A> Your question of "better performance" can be yes or a no, depending on what you're after. <S> Engineering is a management of compromises. <S> Understanding the pros and cons of a biplane design will prove that the disadvantages usually outweigh the advantages, but perhaps not- <S> again it depends on what you're after. <S> Engineers have learned things over the last 100+ years- <S> Stacked wings will not generate twice the lift of a single wing, their aerodynamics interfere with each other <S> BUT you will absolutely get more lift than a single wing of the same span. <S> Remember wingtip vortices kill lift, and you'll have four wingtips. <S> Stacked wings always add drag. <S> If you have two cantilever wings you could reduce the drag from whatever struts and wires you eliminate over the older designs, but it will still have more drag of all sorts than a monoplane. <S> You might like simpler wing design as biplanes have greater STOL performance without flaps <S> , The compromise here- <S> you'll have a tougher time handling that much wing in a crosswind. <S> Flaps give you flexibility of higher lift and a lower stall without so much wing area. <S> Plus you'll really need to slam the stick forward if you have an engine failure, these planes really slow down fast. <S> Back in the day biplanes were hard to beat. <S> The first monoplanes had just as many wires, the first cantilever wings were poorly made and killed a few people, which made pilots deathly afraid of them. <S> Change is hard to push onto people when the tried and true works so well like good lift and high strength, but the solutions are so well understood today the biplane's only advantages are maybe some margin of higher strength, Easy inexpensive strength, greater lift in a given span, short wings roll faster and an awesome look and experience. <S> Novelty can be fun, and you do gain some things with trade offs. <S> I'd say don't quit if you like the idea, do it. <S> They certainly do fly and can fly well, and you could improve on it. <S> If you just want to fly Cable trussed biplanes give you inexpensive, easier to design strength. <S> You might have a lot of fun- <S> but you won't improve fuel economy, safer ground handling, speed or a longer glide.	The real advantage of a biplane is reduced induced drag because less structure needs to be lifted.
What constrains a paraglider vertically? I recently flew on a tandem paraglider for the first time. Since then I keep asking myself a question I have no clear answers to. While flying I clearly perceived the lift generated by the airfoil, but the strongest feeling I had was as if the paraglider hung to a rail, like a suspension railway, or to a cable, like a cable-car. In other words, I perceived a very strong vertical constraint. I know the airfoil generates lift, but I understand the amount of lift is not enough to give you a stability feeling like when driving a truck! To be similar to the constraint produced by a rail, this vertical constraint should be in the order of thousands of kg, IMHO. Any suggestions on how to estimate this amount, and its origins? <Q> To be similar to the constraint produced by a rail, this vertical constraint should be in the order of thousands of kg, IMHO. <S> Any suggestions on how to estimate this amount, and its origins? <S> The thing is that the constraint is something you "perceived": I perceived a very strong vertical constraint <S> not that was actually there. <S> And the lift is easily estimated, as it is roughly equal to the weight of the passengers and the aircraft summed up and being this a paraglider, definitely not in the range of the thousands of kg. <S> Having this been your first experience, the sensation can easily be explained by your lack of familiarity with the transportation method. <A> What you perceive as "motion" is acceleration. <S> No acceleration, and you feel no "motion" -- your kinesic sense and inner ear will tell your brain you're sitting still on a solid surface. <S> What you experienced as "vertical constraint" was nothing more or less than the result of flying in a very stable manner relative to pitch -- no pitching, up or down, means no change in vertical acceleration (which ought to be exactly 1 G at all times, if you're to feel "still"), and no sensation of motion. <A> Fundamentally, the "constrained" feeling comes from the steepness of the lift coefficient vs angle of attack curve. <S> The angle of attack is the angle at which the air approaches the wing. <S> In level flight, this has a certain value, let's say around 5°. <S> Now let's say you encounter a rising pocket of air. <S> Instantaneously, the angle of attack increases. <S> This directly increases the lift coefficient. <S> As a result, the aircraft starts accelerating upwards, until it is ascending as fast as the rising pocket of air, at which point as far as the aircraft is concerned it is in level flight again (while it is in fact rising along with the air pocket). <S> The "sharpness" at which this happens is your "rail-like" feeling of "vertical constraint" as you call it. <S> For thin airfoils, the lift coefficient is approximately $2\pi \alpha$ with $\alpha$ the angle of attack. <S> That means that if we were in level flight at $\alpha=5°$, we would be accelerating upwards at $1g$ if the angle of attack increased to just 10°. <S> I can promise you that you can't tell such a minute change in the angle of the incoming wind. <S> Therefore, as far as you are concerned, the wind is always coming head on and you feel like you are flying "on rails". <S> By the way, "thousands of kilos" of lift for a tandem paraglider of let's say 250kg would mean over $4g$ of acceleration which would be enough to knock you unconscious if sustained for any amount of time.	Only gravity, lift, and drag (and thrust, if powered) are acting on the paraglider, nothing else.
Why not a second airbridge at the back? Airbridges slow boarding and disembarking because (normally) there's only one door in use. But... why? Now the most obvious reason would be that it's very easy to have the aircraft pull forward until its door is roughly in line with the bridge, while it's not possible to do that at the back as well, given the differences in fuselage length. Sure, but I suspect that 90% of all aircraft could be serviced from a set of two possible bridge locations and the existing bridge movement range. And then one notes that the wing would be an issue, but that's only true if the bridge is in the air. One could just as easily build a "bridge" on the surface, or even underground (I saw a cross-section of the ramp at Pearson, it was like swiss cheese). Of course that would mean walking down stairs, which is one of the reasons you use a bridge in the first place, but it would mean that anyone with normal capabilities could use it without exiting outside (did that at Pearson too, in the middle of winter). Such a system would have the added advantage of allowing the Spanish Solution, with three waves, the middle being the cleaning crew. <Q> It was tested at Denver airport by United for a few years ultimately the project was scraped due to jet bridge malfunction that lead to wing damage. <S> The deciding factor arose out of an incident where one of the bridges malfunctioned and damaged the wing of Boeing 757, as ANN reported in March. <S> United removed the section that failed, and stopped using the over-the-wing part on the other four bridges. <S> ( source ) <S> Side parked dual jet bridge terminals did exist in the early jet age but don't appear to be a great use of space <S> and I cant find any evidence they allowed faster board speeds back then. <S> Taxi in and out would always require quite a bit of bridge retraction and a careful tight turn. <S> ( source ) <S> ( source ) <S> As you note you could always go under the wing and come back up. <S> In areas where inclement weather is common you would need the ability to keep the whole jetway enclosed. <S> This could get in the way of the wing unless it was either very low or underground, you would then need some form of retractable stair on the end. <S> All in all it could be built but thats a lot of complexity to add into an airport ramp. <S> This means down time for the gate and money lost for the airport. <S> Depending on arrangement the tunnel may also need to be strong enough to support what ever is above it (vehicles, aircraft etc). <A> Some airlines do this all the time, as in the picture below. <S> The front boarding may be a jetway, or may also be stairs, depending on where the aircraft is parked. <S> The passengers in the front half of the aircraft board at the front, and the passengers in the back half board at the back. <S> Boarding at the back involves going down stairs, walking on the tarmac, and climbing the stairs pictured here, so they will seat passengers who can't do those things by themselves in the front half of the plane. <A> Back when Mirabel airport in Montreal (YMX) was still used for international passenger flights, they used "Passenger Transfer Vehicles" (PTVs - like at Dulles) instead of airbridges. <S> It wasn't unusual to see two of them latched to the sides of a large aircraft. <S> I've also seen two airbridges attached to two front doors of wide body jets. <S> The front-most one serving first-class and the far aisle of the plane, and the other the close aisle.	In a lot of cases the rear of the aircraft is used to load on the new food and remove old garbage blocking the rear with exiting and entering passengers could get in the way of the operations during fast turn arounds.
What is the identity of this abandoned, wrecked Sudan Airways airliner? The other day, I was browsing Twitter, when I came across this picture of an airliner posted by a Sudanese local (thought it was a Boeing 737, but a friend of mine pointed out that it was an Airbus A300). I tried Google Image Searching it, but couldn't find any more details about how it got to be wrecked in this condition ...Could anybody shed a light on this? <Q> It looks to me more like an abandoned plane (that's fallen apart) rather than a crashed/wrecked one. <S> A Sudanese A310 crashed at Khartoum in 2008 - but it caught fire and was destroyed, which clearly hasn't happened here unless someone came and repainted it afterwards. <S> This list gives ten A300s which have previously been owned by Sudan Airways; TC-OYC is stored at Istanbul (and this doesn't look like Istanbul), ST-ATA is stored location unknown, and ST-ASS was scrapped while last owned by Sudan. <S> Of their A310s , ST-AST, is stored (location unclear); ST-ATN was destroyed by fire after a crash. <S> So that's three A300/310s which might plausibly be lying derelict at a Sudanese airport. <S> For an alternative count, this thread lists <S> four <S> A300s "stored" at Khartoum, ST-ATA, ST-ATB, ST-ASS & ST-AST; all put up for sale as parts/scrap a few years back but never sold. <S> No pictures <S> but it's clear they're not in a great state. <A> According to this person <S> the photo is of an Airbus A300B4-620, ST-ASS (Ex F-WZLR, F-ODTK) that is being scrapped at Khartoum Airport. <S> In his photo the cut in the fuselage closest to the cockpit has been made, but the one further aft has not yet. <S> You can see by the shape of the first cut that it is the same aircraft. <A> This is an Airbus A300.	Sudan Airways has not had an accident with this type of aircraft and as such it must be a retired plane.
How much physical strength is required to control a Cessna 172? I have heard a number of folks tell me that one needs a certain amount of physical strength to be able to control the Cessna 172. Is that true? I'm flying sims now, just wanted to know. <Q> I will take this from a more general perspective. <S> A Cessna 172 is part of the CS-23 category (in EASA land, see the equivalent Part 23 for FAA land). <S> In the relevant document , point CS 23.143, we find the maximum forces a pilot might be required to exert on the control columns so that the aircraft can be certified. <S> As the Cessna 172 is certified, we then know that it respects these requirements, so the maximum forces required to pilot a <S> Cessna 172 (and any other CS-23 aircraft) are: \begin{array}{l\|c\|c\|c\|}\textrm{Values in Newton applied} & & & \\\textrm{to the relevant control} & \textrm{Pitch} & \textrm{Roll} & \textrm{Yaw}\\\hline\ <S> \ \ \ <S> \textrm{For temporary application –} & & & \\\textrm{Stick} & 267 \textrm{ <S> N} & 133 \textrm <S> { N} & \\\textrm{Wheel (two hands on rim)} & 334 \textrm <S> { N} & 222 \textrm <S> { N} & \\\textrm{Wheel (one hand on rim)} & 222 <S> \textrm{ N} & 111 <S> \textrm <S> { N} & \\\textrm{Rudder pedal} & & & 667 \textrm <S> { N} \\\hline\ \ <S> \ \ <S> \textrm{For prolonged application –} & 44.5\textrm{ N} & 22\textrm <S> { N} & 89\textrm{ N} \\\end{array} <A> It depends on what you mean by "strength". <S> In general, it is "not much". <S> I've flown a lot of sims and also flown a real Cessna 172. <S> It is true that most sim controllers (especially joysticks) require almost no effort to move at all. <S> In that perspective, then yes, flying a real airplane takes some strength, especially if you compare the force required to achieve max deflection (not recommend in flight!!!). <S> The flight controls of a light aircraft are still light enough that a healthy adult can manipulate them very easily. <S> In fact, the correct technique is to use two or three fingers on the yoke. <S> Most first-time students grab the yoke firmly in their hands, this is wrong because you cannot feel the airplane. <S> If one has the strength to drive a modern-day road car, one can certainly fly a light airplane. <S> I have also spent some time in a B737 training simulator (not PC simulators - I mean the real sims used for training). <S> I was surprised to find the controls much heavier. <S> I would describe the feeling as solid and fluid. <S> They are still easy enough to manipulate such that my mind can focus on elsewhere instead of the physical movements of the control. <A> I've never flown a 172, but I fly a Piper Warrior which is in the same ballpark. <S> You definitely need to apply a lot more force than with a flight sim yoke and provide positive pressure (Remember, you're fighting the airflow ultimately), but you don't need to be "strong". <S> I'd imagine anyone who can drive a car would have the strength to fly a plane. <S> Remember, most flying is one handed and most pilots will use their less-dominant hand (Left hand) <S> so it can't be that bad! <S> I do find the Warrior needs a lot of backpressure to rotate and flare. <S> I've struggled to find any mathematics to add to this, but I've found a few quotes which imply you need approximately 1lb of backpressure to hold the plane level for every 6kts without trim <S> (The whole point of trim is to avoid this and make life easier) <S> So, at 100kts that's 16lbs / 7kgs. <A> I taught people of all sizes to fly for about 30 years. <S> I taught my commercial students how to take off and land without even touching the yoke. <S> Just rudder, throttle and trim. <S> So by the use of proper trim use, one can control the aircraft using the yoke with only ounces of force. <S> Don't let people discourage you. <A> I have several hundred hours in a 172, while it's a bit heavier on the controls than a 152 <S> it isn't much. <S> If you have normal movement then you can likely fly a 172. <S> A benefit to control force in real aircraft vs Sims is the feedback you get through the controls with renders Sims largely ineffective in many cases. <S> OK for some stuff mostly instrument related <S> but it will never replace actual flying. <S> The 172 was a lot easier to fly than the turbine modified Grumman Goose <S> I flew, that thing was like trying to fly a dump truck with manual steering. <A> The amount of physical exertion required while flying a 172 depends largely on what you're trying to accomplish; for example, cruising in a trimmed attitude requires almost no effort whatsoever. <S> However, purposely inducing an aggravated stall/spin action then recovering requires considerably more effort. <S> Since recovering from all situations is important while flying as a PIC, one should give it a try before pursuing training in earnest. <S> Personally, the most exertion required is climbing up to manually check the fuel levels in the wing tanks. <S> But once I got the hang of it, it became quite easy. <A> I fly both Cessna and piper aircraft. <S> The flight controls on a 172 require a lot less force. <S> The flight controls on a piper feel much heaver.. <S> you feel like your flying a much bigger airplane.	So to answer your question it does not take a lot of strength to fly one. So it is possible to control a c- 172 with no yoke force whatsoever.
Can a zero hour pilot actually launch a Bombardier Q400 with only simulator experience? The thief of the Bombardier Q400 at SEATAC stated that he had a lot of simulator flying (I'm guessing like Flight Simulator for the PC?) Some "experts" stated that he must have had more than that to get the Bombardier off of the ground and flying 'stunts' like loops and rolls. Can a zero hour pilot pull off what apparently did happen or did the thief have to have had much more knowledge? I assume that just starting up the plane to taxi would be a complex procedure, is this easily learned in a PC Game? <Q> You don't even need your own simulator. <S> Here is a good video of how to start a Q400 (taken from a sim game) and here is one from a tech going through an actual cockpit . <S> There is even a chance there were checklists in the aircraft when he arrived. <S> To get off the ground he really just needed to know how to gun the throttles and roughly when to pull back on the yoke to get airborne. <S> These numbers can be found pretty readily around the web. <S> Considering his fuel and cargo load and depending on the trim of the aircraft it may have even started flying with almost no control inputs. <S> Whats important to understand about some of the maneuvers he did was the fact that the aircraft was empty and flying on a partial fuel load which will make it easier to do some of those things. <S> I will refrain from diving deep here until the NTSB report is out but at full throttle planes are capable of quite a bit. <S> Rolling an airliner is not out of the question in the right scenario. <A> Operating an aircraft is (simplified) only about pressing the right switches at the right time and monitoring the aircraft data. <S> Richard Russel probably didn't do the latter, because the probability that something does not work is low firstly and secondly it wasn't his goal to take care of the plane. <S> So, it's indeed easily possible to learn how to make this aircraft ready for takeoff, especially if your goal is just to get the engines running. <S> The hand-flying part is something else. <S> But yeah, nobody says what he did was good flying. <S> It sufficed for what he has done. <S> Also note: He has just done the very basics to get the plane up and fly it. <S> In his conversation with ATC, he asks about how to pressurize the plane and how to operate the autopilot, so he lacks some "deeper" understanding and knowledge of the aircraft. <S> In the background of his transmissions, there also is the master warning audible sometimes. <S> To summarize: Yes, a home simulator completely suffices for what Richard Russel wanted to accomplish. <A> Can a zero hour pilot pull off what apparently did happen ... ? <S> Yes, absolutely. <S> The hard part about flying isn't the actual mid-flight control, so much as it's getting into the air, getting back on the ground, and dealing with emergencies. <S> You can learn the first part and the basic flight controls in a simulator. <S> In Russel's case, the latter two parts were greatly simplified: he created an emergency, and he didn't need to get back in one piece. <S> It's actually possible to learn far more than he did in a sim. <S> The complex part of modern aircraft is the systems, and MSFS X with custom planes is a powerful learning tool. <S> If you haven't "played" it, it's not like a normal game at all. <S> Most of MSFS is looking at the instruments and flipping switches that model the systems as closely as the creators could. <S> Air maneuvering requires flight time to perform safely , with minimum risk to the aircraft - one has to learn to trust their instruments, deal with their senses, and respect the envelope.	Doing it with only sim training is simply dangerous, not impossible. It is possible to learn and study everything in a (home) simulator except for hand-flying.
Are the ICAO phonetic numbers used anywhere? I ran across a table of ICAO (NATO) approved phonetic number pronunciations. As early as I can remember (50+yrs) in the United States "nin-er" is the only one I ever remember hearing in aviation and I don't recall hearing it in the last 30yrs. I recall hearing "Fife" but I don't remember where - perhaps ham radio operators. I have never heard "tree" (three), "Tousand" (thousand), or "Fower" (four). If I heard ATC say, "maintain 'climb to nin-er humndred'", I would be very surprised. And if they said, "maintain 'tree tousand'", I would think they needed retesting for ICAO English language requirements. Is there any country, military, or agency that regularly uses the full ICAO (NATO) approved phonetic number pronunciations? Is it taught to any pilots? source <Q> Is there any country, military, or agency that regularly uses the full ICAO (NATO) approved phonetic number pronunciations? <S> Is it taught to any pilots? <S> Yes, pretty much every country in the world. <S> As you mostly have experience flying in the USA, where the native language is English, you may not be used to hearing these pronunciations so much. <S> In most of the world, however, English is by no means the native language, so controllers and pilots alike will use the pronunciation guidelines created by ICAO to ease understanding across multiple dialects and accents. <S> As an example, the Danish aviation regulations has an exact copy of the table you present in your question, and it is used by everyone. <A> Aside from NIN-ER, all of these phonetics just simplify the standard English pronunciation to something easier for people who don't speak English fluently. <S> For instance, many other languages don't have a TH sound, yet AFAIK all have a T sound. <S> In practice, fluent speakers will generally use the standard pronunciation out of habit, or they speak so quickly <S> you can't tell either way <S> so it doesn't matter. <S> I have noticed that, at least in the US, ATC will ofter mirror incorrect phonetics. <S> I slipped one time and checked in as NINE AIT NIN-ER, and they actually replied with that. <S> Another (old-timer) pilot always checked in as FOUR TWO SUGAR (rather than SIERRA) and they'd go with it every time. <S> I think I've heard them mirror FOX (no TROT) and POP (vs PAPA) too. <S> I wouldn't recommend that sort of thing for non-fluent speakers, though. <A> Anecdotally:I have personally heard and used every phonetic pronouncition on that list with the exception of 'TOUSAND'. <S> I have been flying professionally for the past 20+ years in North and Central America as well as the Atlantic and Caribbean. <S> So, is it still being used among ATC and pilots?. <S> Yes. <S> Is it widespread? <S> That has not been my experience operating primarily near the United States. <S> A sidenote on ZERO, I frequently hear 'ZE-RA' over the midwest U.S. <A> The FAA publishes the Pilot's Handbook of Aeronautical Knowledge to provide a guide for pilots. <S> In Chapter 14 (Airport Operations) it says: ICAO has adopted a phonetic alphabet that should be used in radio communications. <S> When communicating with ATC, pilots should use this alphabet to identify their aircraft. <S> The table you posted, along with the pronunciation of the phonetic alphabet, is included for reference, except the hundred and thousand entries. <S> FAA JO 7110.65 provides the requirements for air traffic controllers, which includes the same table. <S> 2−4−16. <S> ICAO PHONETICS Use the ICAO pronunciation of numbers and individual letters.	People whose native language is English tend to pronounce words [and numbers] as they would in normal speech.
Why do airliners have to park so accurately? I was watching some airport documentary and I noticed that the planes always had to park precisely. I honestly didn't think so much of it before, but in the documentary, an aircraft parked badly because the VDGS couldn't detect it correctly due to fog, so it had to be pushed back to park again with the help of a marshaller. The only two reasons for this I could come up with are the following: Jetways: I figured it's because of the jetways, but they can move about so as to adapt to where the plane is. Plus, when parking on stands, the accuracy is the same and there is no jetway. Aesthetics: I also thought it could be about aesthetics, but the systems used to help the pilot park (a marshaller or VDGS) can be expensive so business-wise, it wouldn't make sense to be so strict on parking if it's just for the looks. <Q> This is to ensure that there is space for all equipment around the aircraft. <S> It's not critical to the centimeter, but if it's off by a meter or more there may be problems. <S> For example, the tail may stick out into the taxiway behind or the nose may stick into the service road in front of the aircraft. <S> While most aircraft stop with the nose wheel on or very near the stop-mark, the main wheels can be off by a few feet, depending on how early/late the pilot turns into the stand. <S> Modern aerobridges have a wide range of movement to cater to various aircraft types, but nowadays there is a lot of equipment buried in the ground. <S> You might see ground power and air conditioning hoses which plug into the ground next to the aircraft nosewheel area. <S> If the aircraft is off by a few feet the hose/wires may cause obstruction to the ground crew. <S> The hydrants for fuel also need to be near the fuelling ports - too far and the hoses might not reach. <A> I worked for 3 years as a ramp agent and there are two reasons: Jet bridges and safety. <S> Jet bridges have plenty of leeway, but not a lot. <S> This gets worse in winter because those things hardly move at all with ice. <S> The painting on the ground tells the marshaller where to park the aircraft. <S> By putting the forward landing gear on the right spot, you ensure that the jet bridge will reach the door and line up. <S> Furthermore, it increases efficiency because the operator won't have to do as much adjusting to get the bridge into place, allowing for a smoother transfer of crew and passengers. <S> The bigger reason is safety. <S> The painting on the ground determines where suction and jetblast are dangerous. <S> Of course it isn't so bad as "a milimeter" off. <S> You can miss the marker by 1 or 2 feet and still be fine in most cases <S> (of course, your fellow ramp agents will make fun of you the rest of the day, but that's besides the point.) <A> To add to Anilv's answer, here's a prime example of what happens when a jet isn't positioned correctly on a jetway (it's not parked, but the same principle applies) <S> Or this Royal Jordanian clipping a parked jet <S> The 'fender bender' happened when the Royal Jordanian Boeing aircraft's nose and wing hit the tail of the ChautauquaAirlines flight which was parked at a gate. <A> In addition to all of the reasons already mentioned (jet bridge alignment, alignment with safety markings on the ground, positioning relative to ground equipment, and staying out of taxi lanes,) another important reason for jets to be parked accurately (laterally) is keeping their wings in the proper bounds. <S> Jet airliners tend to have rather long wings. <S> When you're parking a bunch of said jet airliners in a row, you need to make sure that each of their wings will stay within the proper bounds so that they don't clip either ground equipment or the wingtip of one of the adjacently-parked aircraft . <S> Each parking stand is designed for aircraft up to a certain wingspan, so, as long as the aircraft are parked correctly, an aircraft within the size limits for its stand is guaranteed not to clip wings with the adjacent aircraft if it is parked correctly. <S> If it is not parked correctly, all bets are off. <A> In addition to all the answers stated here, even in airfields where there are no fixed ground equipment, the reason the aircrafts must park accurately is to get the best use of the available space. <S> If the airfield is crowded, each extra parking spot or free taxiway is a bonus. <S> If everyone park their aircraft like some people park their cars however they want, the amount of aircrafts an airfield can receive will decrease.	By keeping the plane aligned with the markings, you keep your fellow ramp agents safe while they wait for the aircraft to park and turn the engines off. But the primary reasons are jet bridge limitations and safety. Some jet bridges are poorly engineered, some are old.
What does the extending the flaps do (or any high lift device) to the Rate-Of-Descent of an airplane? I know that deploying flaps will increase both drag and lift, thus increasing L/D ratio. But how exactly does that correlate with the increase/decrease of the rate-of-descent? <Q> According to the FAA , lowering or extending flaps allows one to increase drag without an increase in speed. <S> This increases descent rate for a given speed. <S> One must be careful to consider what factors are held constant to evaluate the effect. <S> For example, one can lower flaps during level flight. <S> This will result in a lower pitch attitude--since they produce more lift, less angle of attack is required. <S> If power/thrust is not increased, speed will decrease due to increased drag. <A> Flaps reduce L/D. <S> The lift increase is not as much as the drag increase, and ratio of lift over drag goes down. <S> So if L/D flaps up is 12 and I am descending in a glide at X knots with a vertical speed of Y (Y being 1/12th of my forward speed), and I deploy flaps and L/D is now 8, and I'm still at X knots, vertical speed will be higher, with the glide angle now much steeper at 8:1 vs 12:1 <S> (vertical speed will have increased from 1/12th to 1/8th of my forward speed). <S> I can reduce the descent rate, but for that I have to slow the airplane down but the new vertical descent rate rate will still be 1/8th of my reduced forward speed, which will generally still be higher than it was flaps up. <A> If your hold your Speed and Angle of Attack constant and deploy your flaps, you will gain Altitude. <S> That means, that you can reduce your Speed OR your Angle of attack (or both), while maintaining your altitude constant. <S> So depending on what situation, Flaps does not have to increase/ <S> decrease your rate-of-descent. <S> It is more an interaction between Flaps, angle of Attack and Speed.	However, an aircraft flying at a constant speed will descend faster (higher rate of descent) if the flaps are extended compared to when they are not.
Who controls airspace and time in my area on helicopters? I live in Newport Beach which is located in Orange County, California. I recently moved to an area where helicopters fly once in a while at 2-3 am above my house. Since I live on a hill, the sound is pretty loud and it wakes me up at night. I was wondering where can I find more information about who controls the airspace in my area in regards to helicopters and how I look up the rules. I've googled a few things but can't find any answers. I'm not sure if it is the FAA or the county or the city or the state. Any pointers in the right direction would be appreciated. <Q> Like others said, if it's military you're probably out of luck. <S> If it's police, they don't fall under federal jurisdiction, so it'd be up to whatever department is operating the helicopter, city, county, etc. <S> At 2am it's unlikely to be civil aircraft, but if it is <S> and they are operating out of John Wayne Airport, their noise abatement rules are published here . <A> Given that you're near a couple military bases, there's every likelihood (especially if the choppers you hear are heavy models like Chinooks or Apaches) that they're from one of those bases. <S> There is little chance <S> a complaint will change anything if that's the case; training exercises that don't cause a hazard to civilians are pretty well immune to civilian comment. <S> To start, you'd have to be able to positively identify the craft type (likely to be very difficult in the dead of night) and give exact time and location. <S> If they're non-military, you'd have to determine if they were in violation of FAA altitude, noise abatement, or restricted airspace limitations, or flying unsafely before a complaint to FAA authorities would stick -- once again, difficult to manage at that time of night. <S> Sorry to say, this might be why your new home was for sale. <A> The military ones don't show up, but if military there is little you can do anyway. <S> If it is civil you will see where it came from and where it is going. <S> That might give you the airport to which you can complain. <A> These 2 sites may be able to help you track them: https://planefinder.net/ <S> https://global.adsbexchange.com/VirtualRadar/desktop.html <S> Many here in New York and Long Island are faced with constant commuter helicopters. <S> They seem to have all the freedom to destroy the public's quality of life. <S> Over 80 000 complaints have been filed to our local officials, yet they have not done anything to re-route them! <A> Looks like SOCAL Approach. <S> I don't see a phone # on the chart tho. <S> https://skyvector.com/ <S> Click on World VFR, then pan around to Los Angeles. <S> Try <S> https://www.faa.gov/ for a phone number. <S> If you click on LA East Heli, you will also see quite a few H in a circle, those are heliports. <S> I see several for Police or Emergency use <S> , I doubt you'll have much luck getting those curtailed. <S> And would you want to? <S> What if you needed that service some day?	You can use a service like FlightRadar24.com to see whether the flight is civilian or military.
Why are fighter jets equipped with dorsal fin? I don't really get whats the purpose of dorsal fins and what they do with the flow over the vertical stabilizer. I noticed on most single tail configured aircrafts are equipped with a dorsal fin like the f 16. <Q> There are two features that you may be referring to. <S> A) Is an antenna that is shaped to provide low drag. <S> Not all F16 have this. <S> B) <S> many aircraft use this as a convenient air intake for equipment or auxiliary cooling. <S> source <A> If you are asking about the aerodynamic purpose of a dorsal fin, then dorsal fin actually increases the angle of side slip to get maximum side force. <S> At high side slip angles, it produces stable vortices along the surface of the vertical tail which produces higher suction force over vertical tail, thus increasing the side force. <S> So in absence of the dorsal fin at high side slip angle, aircraft would have stalled i.e. just as jwzumwalt said, it provides stability along the vertical axis. <S> According to me as F-16 is a fighter aircraft which requires high maneuverability, it would require a dorsal fin to stabilize at high side slip angles. <A> The fin acts as a directional stabiliser, but not all aircraft or fighters have them. <S> The Horten IX <S> (Gotha Go 229) <S> was a notable flying wing fighter design that didn't have a fin.	The true dorsal "fin": increases structural strength decreases drag by providing a fillet for the vertical stabilizer, improves stability about the vertical axis, and specifically in the case of the f16 (when installed) aerodynamically blends the drag chute pack (box at base of Rudder)
What is the maximum rate of descent in an instrument approach? What is the maximum rate of descent approved in an instrument approach procedure non-precision? Basically what is the maximum rate of descent (Fpm) that I use during the approach? <Q> ICAO Doc 8168 stipulates that for a non-CDFA non-precision approach, the aircraft should not exceed 15% gradient when descending from FAF to MDA. <S> 1.7.4 Stepdown descent <S> The third technique involves an expeditious descent and is described as “descend immediately to not below the minimum stepdown fix altitude/height or MDA/H, as appropriate”. <S> This technique is acceptable as long as the achieved descent gradient remains less than 15 per cent and the missed approach is initiated at or before the MAPt. <S> Careful attention to altitude control is required with this technique due to the high rates of descent before reaching the MDA/H and, thereafter, because of the increased time of exposure to obstacles at the minimum descent altitude. <A> There cannot possibly be a maximum descent rate because the rate depends on the ground speed. <S> Instrument approaches are based on a fixed glide path with a typical slope of $ 3^\circ $ (but can be higher). <S> E.g. flying at $ 150 \ <S> , \mathrm{kt} $ ground speed down a $ 3^\circ <S> $ glide slope will result in $$\tan(3^\circ) <S> \cdot 150 \, <S> \mathrm{kt} <S> \approx 796 \frac{\mathrm{ft}}{\mathrm{min}}$$ <S> Non-precision approaches may not have any vertical guidance available, but the chart should still specify the gradient and target altitudes at various points. <S> When flying this approach at a given true airspeed, the descent rate will still vary with the wind because the gradient is fixed with respect to the ground, e.g. adding $ 10 \, \mathrm{kt} <S> $ of headwind to the example above will result in $$\tan(3^\circ) <S> \cdot 140 \, \mathrm{kt} \approx 743 \frac{\mathrm{ft}}{\mathrm{min}}$$ <S> The maximum descent rate will therefore depend on the airspeed you want to fly at during approach, the glide slope angle and the wind speed. <A> Basically you should not exceed 1000 feet per minute after you have passed the initial approach fix. <S> The actual rate of descent will vary with speed, the approach angle and type of approach as well as met conditions. <S> Please see this article . <A> There is no "approved" legal maximum. <S> As a general rule of thumb, 500 fpm is the target rate you should use for IFR descents on non-precision approaches. <A> The standard descent angle is three degrees. <S> Assuming no wind, your sink rate is given by airspeed * sin 3 degrees, and it works out to about 5 ft/min/knot. <S> For a Cessna on final at 60 knots, the sink rate will be about 300 ft/min. <S> For a 737 on final at 150 knots or so (I'm used to seeing Vref30 + 5 = 148 knots in the simulator), you're looking at about 750 ft/min. <S> With wind, you'll have to calculate your along-track groundspeed component, and use tan 3 degrees instead of <S> sin 3 degrees. <S> However, tan(3 degrees) and sin(3 <S> degrees) are just about equal, and more than close enough for this particular flavor of government work. <S> According to a convenient calculator, sin 3 degrees = 0.0523, and tan 3 degrees = 0.0524. <S> That's close enough... <S> Incidentally, you CAN work this all the way through on an E6B computer. <A> Decent angles are fixed to the ground and not aircraft vertical or horizontal airspeeds or relative airflow angle. <S> Each segment of an approach has different slope and clearance requirements as they expect different aircraft configuration and technique in addition to local hazards(including odd wind patterns) and political rubbish like noise limitations. <S> The details of a modern approach are calculated by computer due to the number of variables and the details of the formulas take up <S> at least three 500 page FAA orders.(8260.3D, 8260.19H, TI8200.52, along with several other miscellaneous rules.) <S> There are maximum design descent angles but these depend on the approach segment, approach type, and aircraft category. <S> For example a non-precision final approach segment for straight in landings with category A aircraft at 80knots or less can be up to 6.4degrees, while the slope is limited to 3.5 degrees for approaches that allow category D aircraft. <S> The minimum decent angle is 2.75 degrees and 3.0 is preferred, but the angle should also be within 0.2 degrees of the visual slope indicator (ie. <S> papi, vasi)(FAA order 8260.3D section 2-6)	Your descent rate will depend on the ground speed during the approach. In the USA the maximum rate would only be that considered safe and in control for the equipment, crew training, and conditions.
How does Air Traffic Control know a flight's route and destination? I am trying to find out in layman's terms how does ATC determine the direction a flight has to take after takeoff, or when should it start descending for the destination airport. I understand it has to do with the flight plan but Googling revealed lot of technical stuff that I couldn't understand. In my limited experience of listening to LiveATC and YouTube video, ATC never inquired about the destination - it felt like they already knew. Is destination information always available on the screen to ATC or does the flight crew request changes based on their flight plan? How does it work when you cross international boundaries? Is the same flight plan available to ATC in all the countries the flight will be flying through? For example, a flight taking off from SFO could be northbound towards Seattle or southbound to LA or eastbound. ATC has to make room for the proper direction of the flight and hence needs to know the destination. To complicate matters, I have seen flights taking different routes while the destination is same e.g. one SFO-FRA flight hugged the west coast (magnificent views of the coastline) up to Canada before making a right turn, whereas other times - but with the same flight number - it kind of crosses the continental United States diagonally. So I feel it's not just about the destination, there are other factors involved. <Q> Under instrument flight rules (which all scheduled passenger flights operate under), the pilot will file a flight plan with the local air traffic control authority (in the US, that is the FAA). <S> This flight plan describes in fairly specific terms where the pilot intends to fly, by going from point to point. <S> You can see flight plans on a site like https://flightaware.com . <S> These flight plans are entered (electronically, in most cases, but sometimes typed in) into the air traffic control system. <S> So each controller who handles the flight knows where it is supposed to go next. <S> The details of the start and end of the flight isn't determined by the pilot, but by ATC when they set up the departure or arrival. <S> These are done using instructions called SID (Standard Instrument Departure) and STAR (Standard Terminal Arrival Route) . <S> Depending on the traffic patterns around each airport, ATC may assign a particular SID or STAR. <S> These instructions are like "fly at this altitude until this point, turn right, descend to this other altitude, fly until you get to this other point", and so on. <S> For international flights, the flight plans are transmitted from one country to another using AFTN (Aeronautical Fixed Telecommunications Network) . <S> So each country that the flight flies over knows where it is supposed to be going. <S> Other factors which can influence the actual route a flight takes can include: Weather Other air traffic Military operations International agreements (or more specifically, disagreements) <A> For example a flight taking off from SFO could be north bound towards Seattle or South bound to LA or east bound. <S> ATC has to make the room for the proper direction of the flight and hence need to know the destination. <S> All airplanes wanting to fly IFR have to put in a IFR flight request. <S> This will necessarily have the origin and destination as well as the approximate departure time. <S> But the request will also have a path between (by specifying intermediate waypoints and/or airways) and a cruising altitude. <S> Before takeoff, ATC will then clear the airplane for a particular path (which may be somewhat different from that initially filed). <S> (If you listen to "clearance delivery" frequencies, you can hear these being used). <S> Assuming the pilot accepts the clearance, ATC and pilots now agree on the path that will be flown. <S> Once in the air (assuming no emergencies) pilots will need to request if they want any changes to the flight plan (perhaps to detour around weather, or to find a more comfortable cruising altitude). <A> VFR flight (non-airlines): <S> Often times, we just tell ATC, no flight plan required; flight following can be requested while enroute. <S> For example, I have flown from my home airport west of the Boston Class B southeasterly down to Cape Cod (Nantucket Island in this case). <S> I took off, contacted Boston Approach while climbing, and requested flight following. <S> They ID'd me via radar/ADB-S, gave me a squawk code, and noted the altitude I was climbing to. <S> Several miles later, we were handed off to a different sector, then a 3rd, maybe even a fourth. <S> As I changed frequencies for each, I checked in, told them the altitude I was at, and that I was landing Nantucket. <S> Eventually I was handed off to Nantucket tower about 10 miles out. <S> Other times, we have depart from a towered airport. <S> Before taking the runway, you contact the tower and let them know your desired route of flight and altitude after takeoff. <S> Tower will tell you the direction to turn after takeoff to work you into any other traffic in the area if needed, otherwise straight out, or left or right turns away from the airport are approved, and any restrictions needed to keep you away from other aircraft if needed. <A> For IFR, the desired route is in the flight plan, which is almost always filed ahead of time. <S> As they move from one controller to the next, that all gets passed along. <S> Occasionally the squawk will change as they move (there are only 4096 codes, so <S> the code you get here may already be in use over there), but the new one is then linked to the callsign and therefore your flight plan. <S> For VFR, flight following is (basically) when you get a squawk from ATC without a flight plan, so you're responsible for your own navigation. <S> That still gets you the benefit of traffic advisories, but more importantly, if you run into trouble, they already know who and where you are so they can help you a lot faster than some random callsign <S> they know nothing about. <S> (You can file a VFR flight plan, but ATC won't use it; it's just a hint where to look for wreckage if you don't arrive at the destination, which doesn't seem all that useful to the pilot. <S> Prepare one for your own planning on long trips, sure, but instead of filing it just get flight following.)	When an aircraft is ready for departure, ATC assigns them a transponder code (squawk) that is linked to their call sign, which is in turn linked to their flight plan.
Is the 737's autopilot part of the FMS or is it a separate entity? I was watching a tutorial about the FMS and the autopilot in the 737, and I am consfused. I come from a Cessna background, where there is no FMS, there is only the AP (autopilot). So, is the AP a separate entity being fed info by the FMS and easily overridden by the values you input into the AP (heading, V/S, altitude)? Or is the AP under the FMS, and the FMS has full authority over the AP? <Q> In Boeing terminology, the FMS, Flight Management System , is comprised of: Flight Management Computer System (FMCS, which is essentially two FMC's, at least on the 737... other jets may have one FMC, or three) Autopilot AFDS (Autopilot/Flight Director System - includes the Mode Control Panel used to select autopilot modes, heading, speed, altitude, etc) <S> Autothrottle GPS(s) <S> Inertial Reference Systems (IRS) <S> Two (in the 737, three in some other jets) CDU's, which are the "Control and Display Units" with a small screen display and alphanumeric keyboards, used by pilots to view, enter, and edit things such as flight routes & performance data. <S> Many such units are now "Multifunction CDU's", or MCDU's, adding ACARS and/or CPDLC capability. <S> So in their terminology, the FMS is very broad and includes plenty of things, including the autopilot . <S> The FMC , on the other hand, is the computer that stores your route, calculates the aircraft's position (based on inputs from the GPS receiver(s) + the IRS + possibly other sensors), and does all the navigation tasks. <S> One can couple the autopilot to the FMC guidance - select LNAV and/or VNAV - or not. <S> The FMS (the system) includes the FMC (the computer) and the autopilot; the autopilot can be coupled to the FMC, but it is always a component of the FMS. <S> Sometimes you'll see a CDU referred to as "the FMC (or FMS)" since the CDU is the pilot's main interface with the FMC. <S> But they are separate things; you can have a CDU failure with all FMC's still working, and vice versa. <S> Clear as mud? <A> For lateral navigation, the autopilot can be set to follow a heading, or a VOR/LOC. <S> It can also be set in LNAV mode, which receives guidance from the FMC. <S> For vertical navigation, the autopilot can be set to hold an altitude, LVL CHG based on the set speed, or follow the glideslope in APP mode. <S> It can also be set in VNAV mode, which receives guidance from the FMC. <A> They are two different systems. <S> The autopilot receives selected inputs from the pilots, or managed inputs from the FMS. <S> Total failure of the FMS has no impact on the autopilot which keeps following selected inputs . <S> Total failure of the autopilot has no impacts on FMS which keeps computing the numerous data he is supposed to do such as time of arrival, fuel at destination, also the navigation data such as point to point required track, heading, optimum altitude for least fuel consumption.... <S> As a summary they are just complementary systems. <A> The FMS can be thought of as an electronic equivalent to a human Navigator. <S> The AutoPilot is an electronic equivalent to a human Pilot. <S> The human Pilot can listen to, or not, the human Navigator. <S> The human Pilot can listen to, or not, the electronic Navigator. <S> And the electronic pilot can listen to (call L/VNav), or not (called Hdg) the electronic Navigator. <S> Your flight, your choice.	They are separate systems, but the autopilot can be set to get guidance from the FMC (Flight Management Computer). It's not uncommon to hear or read "FMC" and "FMS" used interchangably, but they are in fact two separate things.
Do high-wingers have dihedral? I know that high wingers have an inherent dihedral effect. Are there any examples of high wing aircrafts with a dihedral?If so, what is the reason behind it? <Q> High wing planes typically have less dihedral than an otherwise comparable low wing design, because of keel effect: they have more righting moment for a given dihedral angle because the fuselage hanging below the wing increases pressure near the wing root on the low side when a bank induces slip. <S> The value of the dihedral can be low enough that the wing may look flat (Piper Cubs and Taylorcraft look flat, to me), but if you build a high wing airplane with genuinely zero dihedral, the wing will appear to droop (take a look at period photos of Lindbergh's Spirit of Saint Louis ). <S> Dihedral is present in nearly all high wing aircraft, for the same reason it's present in nearly all low wingers -- because it tends to support or raise the low wing when a bank without coordinated rudder causes side slip. <S> This produces lateral stability, which in turn makes the airplane easier to fly. <A> Yes, look at any Cessna 150, 172, 177, 180. <S> All have dihedral. <S> It helps the plane return to a wings level state after a disturbance. <A> Yes, many if not most high wing aircraft (general aviation at least) have dihedral. <S> The reason is the same as for low wing aircraft--to improve stability. <S> I had a remote controlled high wing slope soarer glider that I built which had 0 dihedral. <S> It was very maneuverable, wings tended to stay banked, unlike other aircraft with more dihedral that have stronger tendency to level out. <S> The dihedral on a high wing aircraft, be it positive, <S> none, or negative (as illustrated below) will depend on the engineering and performance goals of the aircraft being designed. <S> If you want maneuverability then it will have less. <S> In the case of the Harrier below, I imagine there were performance and engineering reasons for the extreme anhedral. <S> Here is a high wing airplane (Harrier), and it actually has a negative dihedral (i.e. anhedral). <S> Wikipedia <A> Depends mainly on the shape and size of the fuselage. <S> The high wing aeroplane has a wing/fuselage interference effect that tends to roll the aeroplane away from the sideslip direction, the low wing aeroplane wants to roll into the sideslip direction. <S> With high wingers, at larger fuselage diameters <S> the stabilising effect from interference can be excessively high, and then anhedral must be applied. <S> Image source <S> Other high-wingers do benefit from dihedral. <S> Image source	Dihedral (positive V-shape) provides a positive roll-sideslip stability, required on low wing aeroplanes. If you're building a primary trainer its going to have a lot of dihedral, even if its a high wing.
Can a door be shut while in flight? What is the best way to shut a door that has popped open in flight? I had a door on a Cessna 172 pop open shortly after takeoff and was unable to get it closed, but I was fortunate enough to be able to quickly circle around and land. I tried reaching across with my right hand, but I was unable to push the door open enough to pull it quickly enough to latch. Is there a way to shut a door? Source In this accident of a Cirrus SR22 the pilot became disorientated by an open door and crashed. What procedure should be used for an open door? <Q> I've had this happen a few times on aging C152's and in all cases I have been able to simply push it against the airflow enough to pull it closed. <S> On a PA28 with the door the other side of the cabin from the pilot seat, this wouldnt be possible. <S> Not that I have experienced it in a PA28, but I might ask a passenger to attempt the same (hard push followed by a hard pull). <S> Some things to note: <S> There's no massive danger of a door slightly ajar, so waiting until out of a critical phase of flight is advisable (ie, climbed to cruise, clear of any ATZ) <S> In all but one time I had another competent pilot sitting next to me who can keep an eye out and even hold the controls for a few seconds. <S> Just one reason flying with other pilots is nicer than flying alone. <S> However, I would suggest that every situation is different. <S> The most important thing is, as always, Aviate first. <S> A light aircraft is unlikely to be critically unable to continue flying with a door ajar. <S> Don't get distracted by something like an ajar door - fly the aircraft. <S> If in any doubt, land as soon as possible and fix the problem. <S> It would, I think, be acceptable to call "Pan Pan <S> " if you feel you need to expedite a landing. <A> Do whatever it says in the POH for your aircraft. <S> This is from the C172S POH, for example: <S> Accidental opening of a cabin door in flight due to improper closing does not constitute a need to land the airplane. <S> A C182RG <S> POH says exactly the same thing, but at 80 KIAS instead of 75. <A> If lower airspeed and the push/pull technique don't get the door closed, I have always had great success opening a window and trying again, especially in Cessnas (check your POH and observe max window open speeds). <S> This helps equalize the pressure between inside and out and makes the door close much more easily. <S> The windows are usually very easy to open and close by hand in light planes. <S> Again, as in the other answers, I emphasize to fly the plane first, and only try to close the door at a safe altitude, during trimmed, safe stable flight conditions. <A> A few points: The trick of pushing the door farther open then slamming it shut doesn't work as well as on a car as the door is generally much lighter weight than a car's, reducing its inertia that helps it slam shut. <S> And the force of the airflow over it prevents it from opening much farther anyway. <S> A sideslip in the direction of the open door can help a lot, though. <S> But besides the sudden wind noise and potential wind in the cockpit blowing loose items around, it is not an emergency. <S> I've flown (and been flown in) <S> a Cessna 152 when we had removed the passenger door altogether to allow air to air photography. <S> No problem. <S> Just be sure to be buckled in first! <A> While I was banking a Cessna 152 45 degrees left a few years back, the pilot-side door popped open. <S> That was exciting. <S> As I recall, closing it took a hard push into the windstream, then a pull as it bounced back. <S> Otherwise, it was just re-closing a car door. <S> The instructor didn't even have me level out first.	The best procedure is to set up the airplane in a trimmed condition at approximately 75 KIAS, momentarily shove the door outward slightly, and forcefully close and lock the door.
USA: Why don't airports raise landing fees to make up for low passenger fees? A question from travel.stackexchange.com about luggage carts prompted a discussion on the economics of airports. The gist was: American airports have much lower passenger service fees which are capped at USD4.50 per FAA rules than foreign airports, which can easily be USD20-50 per person. This results in much lower number of amenities at American airports compared to other international airports. You’d think they’d try to make it back with landing fees. But Tokyo Narita airport’s landing fee is JPY1550-2000 yen per tonne. A 787-8 has a weight of 172 t so the fee would be ¥258,000 - ¥344,000 or so or roughly USD2300 - USD3100. San Francisco SFO’s landing fee is USD5.54 per thousand pounds. A 787-8 landing weight is 379,200 pounds so the landing fee is around USD2100. There doesn’t appear to be a significant delta here to account for the difference in passenger fees. My question is: Why don't airports simply increase the landing fees to compensate for the lower per-passenger fees? <Q> This depends on where you are in the country and more specifically who controls the airport. <S> A lot of airports in the US are owned by cities (or local governments) in some capacity. <S> As such changing the landing fees often requires a legislative change which is not always easy. <S> For example here is the legislation that covers the landing fees at both major airports Philadelphia Controls Changing these requires a policy change at the government level and it takes a long time to get just about anything through the Philadelphia government. <S> In many cases these fees are paid to the municipality anyway and the airport never sees any of the money so the fees don't (directly) help the airport. <S> In a lot of cases the fees do (or at least are presumed) to go back to the maintenance and upkeep of the airport. <S> Private airports (generally smaller GA ones) can levy fees as they see fit and sometimes do to help with the upkeep of the field. <S> What airports or more specifically <S> FBO's and other on field operators do is raise operational costs to use their facilities. <S> Rising FBO fees have been of concern lately and sometimes there is no way to escape them if someone has what amounts to all the parking space on the field. <S> It may only cost $5 to land somewhere but keeping your plane there for a while, getting a pre-heat, maybe even using a terminal is by no means cheap. <A> Fee setting is complicated. <S> First, it should be noted the $4.50 per flight segment PFC charge is not intended to provide for terminal amenity improvements. <S> As described by the FAA, the stated purpose of the Passenger Facility Charge (PFC) Program is: Airports use these fees to fund FAA-approved projects that enhance safety, security, or capacity; reduce noise; or increase air carrier competition. <S> In addition, the structure of how landing fees are imposed varies. <S> This article provides a good overview of how US airports set fees. <S> This guidance can also be found directly from the FAA . <S> h. Airfield Revenue. <S> Unless users agree otherwise, airfield fees generally may not exceed the airfield capital and operating costs of existing airfield facilities and services. <S> Why don't airport simply raise landing fees? <S> Airports do impose fees, just not through the landing fee mechanism. <S> Looking at the Port of Seattle's Schedule of Fees , we can see the other fees the airport collects from airlines. <A> I think it's simply because passengers don't want to pay for free carts. <S> Ultimately, all costs are going back to the customer via fares. <S> It's similar to raising ticket prices and bringing back "free" food or check-ins or extra legroom; certain people in certain situations will go for it, first class or business travel, but the market has shown that most will instead choose the option with lower fares. <S> Instead of the airport forcing everybody to pay for it, airlines are free to offer it themselves. <S> In fact, airlines will have somebody carry your luggage from your house to check-in, if you buy the right ticket .	Airports set the landing fee based on airfield costs.
Are NDBs and VORs dying as a navigational method? I am new to aviation, so bear with me on this question: I have read in multiple places that the VOR/NDB navigational aids are dying out to GPS. Is this true? Are more modern aircraft being built with glass, digital instrument readouts that capitalize on GPS services instead of the traditional vacuum tube ADF and VOR Indicators? <Q> Yes, without a shadow of a doubt. <S> Many airports now publish GNSS (Generic term for all types of satellite navigation) approaches, completly negating the need for those aids even during complex, critical phases such as approach and landing and take off and departure. <S> Modern GNSS systems are capable of utilising synthetic VORs where even when doing something such as flying a particular radial, the aircraft actually uses it's GNSS data to do so. <S> And, if you needed outright evidence, how about this quote from the UK National Air Navigation provider (NATS): <S> Commercial aviation – which has always funded the upkeep of the VOR beacons – now almost exclusively relies on the use of satellite navigation (read last week’s post on EGNOS for an example), making the majority of beacons an expensive and unnecessary financial burden. <S> As such by 2020 we will be reducing their number from 44 down to 19. <S> Source: https://nats.aero/blog/2015/05/has-gps-killed-off-the-vor/ <A> This FAA page has more info. <S> The Very High Frequency Omni-directional Range (VOR) <S> MinimumOperational Network (MON) provides a conventional navigation backupservice in the event of a loss of Global Positioning System (GPS)signal. <S> The MON includes the minimum number of geographically situatedVORs in the contiguous United States (CONUS) necessary to providecoverage at and above 5,000 feet above ground level. <S> Additionally, theMON supports International Oceanic Arrival Routes and mission criticalmilitary use. <S> From the Federal Radionavigation Plan the Gerry references in the comments: ILS ILS is the standard precision approach system in the U.S. and abroad. <S> FAA operates more than 1,200 ILS systems of which approximately 150are CAT II or CAT III systems. <S> In addition, DoD operates approximately160 ILS facilities in the U.S. Non-Federal sponsors operate fewer than200 ILS facilities in the U.S. <S> As the GPS-based augmentation systems(WAAS and GBAS) are integrated into the NAS, and user equipage andacceptance grows, the number of CAT I ILSs may be reduced. <S> FAA doesnot anticipate phasing out any CAT II or III ILS systems. <S> The NAS includes more than 1,300 NDBs. <S> Fewer than 300 are owned by theFederal Government; the rest are non-Federal facilities ownedpredominately by state, municipal, and airport authorities. <S> NDBs used as compass locators, or as other required fixes for ILSapproaches (e.g., initial approach fix, missed approach <S> holding),where no equivalent ground-based means are available, may need to bemaintained until the underlying ILS is phased out. <S> Some NDBs may alsoneed to be maintained to facilitate training and proficiencyrequirements. <S> Most NDBs that define low-frequency airways in Alaska orserve international gateways and certain offshore areas like the Gulfof Mexico will be retained. <A> In the case of VORs, maybe as a primary means of navigation it is dying out, but I honestly do not see them being phased out completely within the next decade or so. <S> Most ANSPs prefer keeping them as a secondary means of navigation given that GNSS still relies on GPS developed by the US military. <S> As for NDBs, I think I've seen only one or two that are still in existence, <S> so yeah they're definitely out.	NDBs FAA has begun decommissioning stand-alone NDBs as users equip withGPS. Yes, it is true.
Why are helicopters less efficient than planes? At higher speeds, advancing helicopter blades will operate at velocities approaching mach 1, reducing efficiency. But what about lower speeds? A helicopter is basically a wingless plane with a giant propeller. Why is it more efficient to move around using propellers to provide forward trust while using separate fixed wings to provide lift? <Q> The answer lies in the difference between energy and momentum. <S> Both have to be maintained, but energy goes up as the square of velocity, while momentum goes up linearly. <S> To impart a given momentum, you can either move a lot of air slowly, or a little air quickly -- but as you move the air more quickly, it requires disproportionately more energy. <S> In other words, the bigger the wing, the more efficient (from an energy/momentum perspective, anyway). <S> That means it has to touch less air, but move it more -- which requires more energy. <S> There's more detail at this question on Physics StackExchange (disclaimer <S> : I wrote that question). <A> A helicopter is not exactly wingless - the rotor is the helicopter's wings. <S> A wing's drag is proportional to $W\cdot(L/D)$, where $W$ is weight and <S> $L/D$ is lift/drag. <S> The energy spent overcoming this drag each second is $V_{wing}\cdot W\cdot(L/D)$, where $V_{wing}$ is the wing's airspeed. <S> The amount of fuel required to travel distance $S$ is then $SFOC\cdot S/ <S> V_{aircraft}\cdot V_{wing}\cdot W\cdot(L/D)$, where $V_{aircraft}$ is the aircraft's ground speed, where $SFOC$ is specific fuel consumption. <S> For a fixed wing, $V_{wing}$ and $V_{aircraft}$, ignoring wind, are the same. <S> In a rotary wing (helicopter), $V_{wing}$ is higher than $V_{aircraft}$ - <S> the wing travels a longer path through the air, with rotation. <S> For this reason, a helicopter will always be less efficient than a fixed wing aircraft with the same lift/drag ratio. <S> If the ratio is 3x, that's 3 times more fuel for the same distance. <S> This is of course a vast simplification, ignoring all the details and just describing the principle. <S> To put it in even simpler terms, a helicopter is like a plane with its wings flying a path full of loops. <A> the wing on a small plane moves through the air at around 100MPH, whereas the main rotor blade on a small helo moves through the air at around 400MPH. <S> the blade is smaller than the wing to be sure, but the drag forces acting at 400MPH are still big, and soak up a lot of horsepower. <S> Try this comparison: imagine a Cessna 150 with two people in it at cruise conditions and compare it with a Robison R22 with two people in it, same altitude, etc. <A> As pointed out in this answer: <S> More interference drag A circular shape of the rotor disk <S> - it can be considered to be a wing in forward flight, but a circular wing is much less efficient than a long slender wing. <S> The picture from J. Gordon Leishman, Principles of Helicopter Aerodynamics, illustrates the complexity of the multitude of aerodynamic drags that can be found in a helicopter, and that decrease efficiency.	A rotor's size is limited, both because its fast rotation means it needs to be light (and thus can't be very reinforced, etc) and because the larger its radius, the faster the end spins. Look at their respective fuel burn rates.
What is the pivot point of pitch change on an aircraft? I was wondering if there is a way to determine the pivot point when an aircraft changes pitch, assuming a standard slightly nose heavy and back elevator trimmed Cessna 172. Will it pivot around the CG, the Center of lift, or somewhere in between. Logically, I would think it would be "from where it is held up", but some writers stress CG. Can you help me understand? <Q> Using anything else as a pivot (e.g. Aerodynamic Center) involves a combination of momentum and translation (linear movement) of the CG and will quickly get you into mathematical problems once you start combining the forces acting on the object. <S> Make no mistake, an object only rotates around its CG. <S> If this is just a mental visualisation exercise, you can 'imagine' the pivot point to be at the center of pressure (i.e. the famous plane suspended by strings at the wings), and as the plane is already flying at a few hundred knots in + <S> x, <S> the little +y acceleration error will not make much of a difference as a mental exercise, but the error is there mathematically. <S> Later edit:if you still have problems visualising it, place your aircraft in outerspace where there is no air or gravity. <S> Put some big thrusters on the wing and smaller thrusters on the tail. <S> CG (center of mass) is very much forward of the wing. <S> Now fire the thrusters. <A> You have not specified a frame of reference, so I will look at the two most common choices. <S> Body-fixed frame of reference <S> This is the frame that moves with the aircraft. <S> By definition, any rotation happens w.r.t. <S> the origin point of such frame. <S> By standard practice, the origin is the center of gravity (the equations are much simpler). <S> Thus in this case Radu094's answer applies. <S> Earth-fixed frame of reference <S> In this frame, not only you are pitching, but you are also moving forward (in the case of fixed wing aircraft; if you are in a hovering helicopter, then it is still the Center of Gravity). <S> This forward motion completely changes the position of the "pivot point", that will end up being outside the aircraft. <S> Assuming a vertical load $n$, and a forward velocity $V$, your aircraft will pull up around a point placed $R$ meters above the aircraft when the aircraft started pulling up: $$R = <S> \frac{V^2}{g <S> \cdot <S> (n -1)}$$ <A> The pivot point is whatever you choose! <S> However, choosing the centre of gravity makes any analysis simplest. <S> A motion of a free moving body (e.g. an airplane) can be described as combination of motion of an arbitrary reference point and rotation around that point. <S> As far as describing the path taken by the body, any reference point will do. <S> However, for dynamic analysis, that is understanding the relation between the forces acting on the body and its movement, using centre of mass (a.k.a. centre of gravity) is the only reasonable option. <S> That is because both the Newton's Second Law of Motion, $$ a = \frac{F}{m}, $$ and its rotational version, $$ \alpha = \frac{\tau}{I} $$ ( <S> $a$ is acceleration, <S> $F$ is force, <S> $m$ is mass, $\alpha$ is angular acceleration, $\tau$ is torque and $I$ is moment of inertia), only work in these simple forms for the centre of mass (you can verify that by doing the integration over the mass of the body). <S> Alternatively in some cases you might want to chose the pivot point so that it is not accelerating, but depending on the path taken, that may not be possible. <S> For example when the pilot pulls on the control column, an downward force will be generated at the tail. <S> Its moment will cause upward angular acceleration in pitch, but it is still an unbalanced force, so it will cause a downward acceleration of the centre of gravity first. <S> This combination means a non-accelerating pivot lies somewhere far ahead of the plane. <S> But as the attitude and path change, the angle of attack will increase and the wings will build up an upward force that eventually balances, and exceeds, the downward force at the tail and the plane will accelerate upward. <S> At which point, a non-accelerating pivot lies somewhere far above the plane (see the diagram in Frederico's answer). <S> So in case of an airplane, looking for a non-accelerated pivot is futile. <S> It rarely works in situations other than where the pivot actually has a solid support, so it can't accelerate.	By the very definition, a free-flying object can only pivot around its CG. It depends on your frame of reference
Bed sheet as wing skin? https://en.m.wikipedia.org/wiki/Aircraft_fabric_covering This article states several early aircrafts that successfully used cotton as wing skin including Wright flyer. "Colditz Cock" glider had its wingskin made from bedsheets plus this guys used bedsheets to make their wingskin and the plane kinda took for like 2 seconds.Can a good,strong bedsheet successfully replace tedlar in an airplane without any problem? <Q> Absolutely you can use a fabric for covering and airframe. <S> I used to build large scale R/C aircraft much like they used to build real world aircraft. <S> I used fine silk to cover the wings, elevator, tail, and fuselage. <S> I used epoxy to adhere it to the wooden airframe and then later apply some kind of lacquer, which serves to shrink and pull tight the silk and also makes it airtight. <S> This can then be painted or not. <S> Silk is a very strong lightweight material. <S> The performance is actually probably better than many modern materials, but probably would not hold up to the elements as well over time. <A> As an example : Piper PA–18s, for example, emerged from the factory wearing Grade A cotton fabric tested to withstand a minimum of 80 pounds per square inch. <S> This super cub cruised at 130mph with a wing loading of about 10lb/sqft. <S> Fabric wings, particularly cotton, are often also "doped", meaning they are painted with a material that shrinks, preserves and makes the fabric less permeable to air. <S> Classic and antique aircraft got coats of plasticized lacquer called dope, a flammable material that served to tighten the fabric and provide some protection from the elements; paint was applied over the dope. <S> Some ultralights with UV resistant nylon coverings do not take this extra step. <S> If your aircraft is only to be used a couple of times, preservation is less important. <A> The earliest covering systems were actually bedsheets... <S> well not literally bedsheets, but the fabric was linen. <S> The Wrights used muslin, a tightly woven cotton used for womens' unmentionables. <S> Grade A cotton came later after linen, then polyester after WW2. <S> I'd say the cheapest alternative to Tedlar might be to use commercial grade polyester fabric of a suitable weight that can be heat shrunk and use premium exterior latex house paint as the filler system. <S> and I don't think latex paint will have the same shrinking effect. <S> Instead of aluminum powder added to the dope for UV protection as is done for normal airplanes, for latex you add carbon black to the base coats. <S> Anyway, I'm not making this up. <S> http://www.flysquirrel.net/piets/paint/paint.html . <S> I've seen that Peitenpol in the article at Oshkosh <S> and it looked pretty good. <S> The article notes that the latex finishing system was actually lighter than an actual aircraft finishing system like Polyfibre.	Fabric coverings need to be strong enough to handle the load to which they are subjected. Latex paint has been used on homebuilt aircraft with success You'd have to use polyester instead of cotton or linen because on those fabrics it's the dope coating that shrinks the fabric to make it taught

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