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Won't sonic booms prevent Space X's BFR intercity transport plan from being acceptable? Considering that Space X have just announced that their BFR can take anyone anywhere in the world in under 1 hour, that would be enormous speed, does this rocket not produce sonic boom? If not is it because of its shape and that it does not have wings? Will it ever be allowed to fly across the US above the oceans and anywhere at those speeds considering again sonic boom? <Q> The only way to get anything that far that quickly is to send it into space, and that's exactly what Musk is suggesting. <S> The BFR will launch a passenger carrying spacecraft out of the atmosphere and into a sub-orbital path, it will re-enter the atmosphere close to its destination. <S> Rockets launch pretty much straight up and a sonic boom would have to compete with the rocket itself on noise. <S> Once above the atmosphere there is no sonic boom because there is no air. <S> On re-entry all spacecraft create a sonic boom, for most of the re-entry this is inaudible from the ground because the air is extremely thin, once in the lower atmosphere it gets louder. <S> By the time the spacecraft gets low enough to create a really big sonic boom <S> it's usually at a subsonic speed and would not make any boom at all. <S> The shuttle and Apollo spacecraft both created sonic booms on re-entry, that's covered in this Space SE Question . <S> So, are sonic booms a problem in this idea? <S> It depends, the space shuttle re-entered <S> over the continental US many times <S> and it never bothered anyone, but if it was happening a few times a day it might be a problem. <S> You could get around that for the most part by re-entering over sparsely populated areas or the ocean. <S> More likely it's not the sonic booms that people won't want from a noise perspective, but the launches. <A> As pointed by @DeltaLima in the comments, a lot of satellites are crossing the sky above us at this very moment. <S> Since there is no air in space, no sound can be heard, especially from that distance. <S> The only noisy parts will be the takeoff and landing, but with carefully selected location, this shouldn't be a problem. <A> I doubt it. <S> Sonic boom/s may well occur but likely (or could be specifically planned by routing etc) to occur in upper atmosphere/away from population centers. <S> The rocket seems planned to take off from an island or floating structure (judging by the graphics, which showed a ferry to the launch site), which could easily be tens of miles away from land if that were an issue. <S> That distance might be enough to mitigate a lot of the launch noise. <S> As for landing, it's probably possible to come into landing along such a trajectory as to not be near a city when excessive noise will be produced, either by coming in over the ocean (in the graphic's example) or even by 's'turning around populated areas, shedding speed in the same trajectory (the space shuttle bled off speed this way, I believe). <S> Note that military craft produce booms frequently (although AFAIK they try to limit proximity to populated areas), as does any orbital (and most suborbital, although not so many of those fly these days) rocket, and Concorde produced booms. <S> So: Will it ever be allowed to fly across the US above the oceans and anywhere at those speeds I don't see potential booms impacting whether it is allowed at all. <S> Where it is permitted to be routed/produce booms, and how frequently, are open questions.
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Since the rocket will be traveling through space, there will be no noise on the ground during cruise.
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Were WW2 American fighters designed to operate from dirt airstrips? Fighter or fighter-bomber planes built in America during WW2, such as the P-36 , P-39 , P-47 , P-51 . Were these designed to takeoff and land on dirt airstrips? My impression, and correct me if I'm wrong, is the following: Most airbases inside USA/Canada at this time had paved runways. At least half the fighters were designed to takeoff and land on carriers. Also, I think every single photo in wikipedia I've seen of these planes on the ground, is on a paved runway. Now there is of course the Western Front in Europe, and some American aircraft did get sent to the USSR in lend-lease. I do not know if Britain and France had the luxury of paved runways at the time, but in Russia, most certainly did not. So you would think at least some of them had to had the strong undercarriage required for dirt airstrips. But I am not sure if they came that way or had to be modified after arriving in Europe. One way to investigate this is to start looking at the airfields America had during WW2. Wikipedia has a giant category page for this, but even tho most of those pages have a history section, sadly I could find nothing about paved/unpaved. However, this photo from Midway shows paved runways, and I'm pretty sure Wheeler Airfield during Pearl Harbor had a paved runway too. If they were doing that in the middle of the Pacific, my guess is that most airbases in the 48 states and east/west coast mainland also had paved runways. The reason I ask is because a stronger undercarriage requires more weight. Dirt landings require bigger wheels which take up room in the fuselage that could otherwise be used for fuel or bombs. Therefore, if paved surfaces are available, it makes sense to take advantage of it in your design. But as I said above, I can't be sure if paved surfaces would be available everywhere they intended to use them. <Q> ( Source ) <S> Opening theaters in the Pacific, for example, using fighters/bombers fitted with bush tires would not have been a good choice indeed. <S> Maybe one pilot can pull it off. <S> But not all, and certainly not the damaged planes. <S> As planes got heavier before WWII, and especially during WWII due to the massive engines and the all-metal construction, came the need for inflated tires, paved runways, hydraulic brakes... ... and the need for the Marston Mat . <S> By using perforated steel planks, a runway can be built almost anywhere in a relatively short time ( source ). <S> ( Source ) <S> Above shows a North American P-51 taking off from Iwo Jima. <S> Note the pattern on the ground. <S> From far away in other B&W images the pattern does not become clear and the planes look as if they're using pure dirt runways. <S> Marston Mats were among the most important inventions of World War II ( airspacemag.com ). <S> As seen in your other question, How are modern jets modified to takeoff/land on a dirt runway? , Russian fighters are built with unpaved runways in mind. <S> As are modern military transports. <S> Transports have the luxury of space for many tires. <S> But for jet fighters, it was the advances in tire manufacturing, which itself was due to the jet age that brought the swept wings and consequently the faster takeoff and landing speeds. <S> ( Source ) <S> Of course a humid tropical rainy island is different from a bone dry desert. <S> The different soils and the water content affect their bearing and shear strengths. <S> In North Africa, you may not need special reinforcements for the soil where its strength can be 4 times as high (think dry lakebeds ). <A> Early in the war, the RAF was using grass strips. <S> In the UK, there were special runway teams, that would re-concrete a runway in sections, using fast curing concrete. <S> For more remote locations, the allies also had Marston Mat, a brilliant invention, the perforated steel planks used to cover dirt runways. <S> Compact for transport, and assembly was very quick with a minimum of tools and equipment needed. <S> However, in very remote locations where supply wasn't so plentiful, dirt, crushed coral, or grass runways were used. <S> This includes recently captured island bases, and China, which had a difficult supply situation when the Japanese closed the Ledo road, and supplies had to be flown in. <S> My father told me stories about landing on hand built Chinese dirt runways in a P61 Black Widow, which touched down at around 110 kts. <S> A bit bumpy. <S> Aside from being smoother, easing the load on the landing gear, prepared runways keep the dust and dirt down, which increases engine life. <S> No air filters on those aircraft engines, so the less dust and debris that got sucked in, the longer the engine stayed in service. <A> At more sophisticated airbases, yes. <S> However plenty of bases used grass fields or strips as well as dirt strips plowed flat with a dozer blade. <A> In 1939 most military airfields were grass strips, since there were no four-engined bombers, and most warplanes were capable of landing on roads or meadows in emergency (as instructors say, "You can land anywhere -once.") <S> With the outbreak of war, aircraft designers needed more powerful engines (with larger, more sensitive air intakes) and longer take-off distances (obviously concrete, being smoother than grass. <S> works better here). <S> Commanders were also less keen on their air support taking a day off because it was raining. <S> So suddenly, all over Europe and other combat areas, new airfields were being built, and old ones refitted, with concrete runways; these were often called "all-weather airfields" and could be strategic objectives ( this Wikipedia page refers to a unit being sent to capture the only all-weather airfield in Burma). <S> Though the military had construction units (the British Pioneer Corps and the US Corps of Engineers ), they were often overstretched, and cililian contractors had to be used. <S> One airfield near where I live, RAF Beaulieu , was built by local labourers. <S> Having left school at 14, too young to be called up, they did their bit by joining construction companies for a few years, and indeed the airfield opened on time in 1941. <S> They were, however, obviously inexperienced (both the young workers and the managers who might have never seen a concrete runway, let alone built one), and working under a lot of pressure for both time and cost. <S> Interestingly, though the RAF squadrons who used the airfield made no complaint, the USAAF pilots found that it was not up to the standards they were used to (and it rained a lot more than back home, which also degraded performance). <S> They did not receive much sympathy from the builders who had dodged machine-gun fire. <S> (Some memoirs have been published, but not on the internet; a few of them are still around and telling stories in the pub). <A> http://warbirdsnews.com/warbirds-news/poor-lambs-corsairs-baa-baa-blacksheep.html I enjoyed watching this show as a youngster, with Corsairs flying out of what looked like a dirt airstrip in the Channel Isands. <S> Filming apparently took place at Indian Dunes Airfield in CA.Pictures of the set at the bottom of the site sure seem to show a dirt strip. <S> Other links about Indian Dunes Airfield discuss it being turned into farmland, I don't think that would have been done if it was paved. <S> Of course, if the land was worth enough, anything goes I guess.
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Later in the war, the Allies tended to have prepared runways because they had much better supply and field engineering support than the Axis powers.
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What prevents companies like Cessna and Piper from connecting multiple alternators to a single engine? Firstly, I'm not even sure if there's only one alternator connected to the engine in a C172-like aircraft. But if that is true, then why don't manufacturers connect multiple alternators to a single? What are the draw-backs of doing so, other than a waste of generated power? I just want to know whether it is possible - and preferably without any major draw-backs. Without too much increase in weight and complexity, one more alternator could together produce twice the electricity - this might actually be primarily useful for large air-liners relying more on electricity than hydraulics, like the A380 and the 787 Dreamliner. So, again, why not? <Q> You almost answered the question yourself. <S> Alternators scale really good so that a bigger alternator generates more electric power then two smaller of the same weight. <S> So the only reason to do that on a smaller air plane is to have a backup if one of them fails. <S> This brings up two questions: <S> How often do alternators fail? <S> what are the consequences of a failed alternator? <S> For the first question I have a (non representative) experience: <S> At my airfield 6 SEP plane are are posted. <S> In 25 years I'm flying there we had 1 failed alternator. <S> For the second question we have to look in the flight instructions and the planes manuals. <S> For smaller planes like those you mentioned they state that you should turn off some electric devices and land on the next reachable airfield. <S> That means there is no immediate risk when an alternator fails. <S> The conclusion is that we simply don't need more than one alternator in a SEP plane. <A> It is possible and I have done it, with payloads which draw more than the aircraft can provide. <S> Need an STC, and in my case about $12K engineering costs, for a Cessna 210. <S> I have also stuck extra starter/generators on aircraft like the Caravan 208B, and in that case there was some concern with the torque on the accessory drive for the 300A SG with a second 200A SG. <S> The additional power was needed for payloads which were active sensors and had fairly high power needs for both the sensors and the targeting and processing equipment. <A> Point to add, backup alternators (smaller units)on cirrus aircraft are required to provide backup power to display systems since engine indications on the later generation aircraft are only on electronic displays (although the displays have compacted views on remaining units in the event of failure of the display) <S> meaning it does not constitute a dire emergency if the main alternator goes belly up (rare but still happens). <A> Definitely possible. <S> Here is one that is offered <S> http://www.bandc.aero/pdfs/quickfacts_bc410-h.pdf <S> Measuring 4.6" wide and 6 <S> " deep, and weighing only 5.75 lbs. <S> , the BC410-H will clear the tachometer cable and oil filter on stock Lycoming engines. <S> http://www.bandc.aero/alternator20ampshomebuilt1-1-1.aspx <S> The bottom of the page discusses how it is spline driven (vs a belt) and fits on a vacuum pad. <S> I only see it listed for Experimental/Homebuilt aircraft, so that could be an issue getting it approved for a Certificated C-172. <S> Some of us have pulled their entire vacuum system and gone to battery backed electronic Attitude Indicator/Direction Gyro, such as a pair of Garmin G5s; 4 hours should be enough time to get clear of clouds and make a VFR landing somewhere.
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Having more than one alternator would introduce more complexity not only mechanically but also in the electric system (even if they work correctly).
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What are the main differences between Flares and Chaff? Over the years I've heard the two used almost interchangeably but after watching some videos it would seem that they each have specific and particular functions. <Q> Both chaff and flares are defensive countermeasures deployed by military aircraft. <S> The purpose is to confuse radar-guided or infrared-guided anti-aircraft missiles fired so that they can divert. <S> A good definition about them is here : <S> Chaff is composed of millions of tiny aluminum or zinc coated fibers stored on-board the aircraft in tubes. <S> When an aircraft isthreatened by radar tracking missiles, chaff is ejected into theturbulent wake of air behind the plane. <S> Flares are used to distract heat-seeking missiles. <S> Most are magnesium pellets ejected from tubes to ignite in the wake behind theaircraft. <S> These flares burn at temperatures above 2,000 degreesFahrenheit, hotter than the jet engine nozzles or exhaust and exhibitlarge amounts of infrared light. <A> Flare Flares are <S> a, let's call it "passive defense system". <S> They are used for misleading rockets fired on an aircraft. <S> Many missiles are following a heat source to hit their target. <S> In case of an aircraft, it's the engine. <S> If such a missile is on the way, the pilot fires those flares. <S> They burn really hot and the missile will fly into the flare instead of the aircraft. <S> Source Chaff <S> Chaff is also spread out by aircraft. <S> There are used for, what can be called "electronic war". <S> As you know, a radar sends out electromagnetic signals. <S> If they are being reflected to the radar, there is a dot visible on the radar. <S> This can be an aircraft but also lots of birds. <S> Now, chaff is made of aluminium or metallized glass fibre or plastic. <S> So, when the aircraft spreads a big cloud of that chaff, it is visible on the radar. <S> And this can work like a curtain. <S> There is a wall of chaff sprayed out. <S> Behind that wall, every aircraft is invisible and operations can be accomplished secretly. <S> But chaff can also be used as "flare" but for radar-assisted systems. <S> Like radar-lead missiles or radar-targeting systems by fighters. <S> Source <A> They both belong in the category of countermeasures, but let's say that they... target different audience. <S> Chaff is used to spoof radar guided (active or semi active) missiles. <S> Chaff pods contain several small metallic parts of similar size and shape and their aim is to create false returns to the radar beaming the targeted aircraft. <S> The sized and shape depends on the radar wavelength they try to spoof <S> but I am unaware of the exact relationship. <S> Flare on the other hand targets heat seeking missiles. <S> As user3528438 mentioned in their comment, they are "fireworks" that aim to create a brighter thermal image and drive the missile away of the aircraft's thermal trail. <S> The tricky part for the pilots (and perhaps the modern warplane designers) is to distinguish between the type of the homing missile, so that they use the right countermeasure for each threat without wasting consumables. <S> That's probably the reason you've heard them as chaff <S> /flare like there is no difference. <A> There are two ways for an anti-air missile to "see" its target: <S> Radar signature : <S> the missile is fitted with a radar receiver, so when the launching plane illuminates his target with his radar, the missile get the signature and can go to the target. <S> (Some more advanced missiles even have their own little radar emitter and receptor for the last part of their guidance.) <S> Heat signature : <S> the missile is fitted with a heat seeker, and will follow the eat source he was assigned by the launching plane before firing. <S> Chaffs are designed to defeat the first category, flares the second : <S> Chaffs are small pieces of material that will reflect radar waves in different directions. <S> Their goal is to disrupt attacker's radar so he can not guide his missile or will guide it on the chaffs, not the defending plane. <S> They do not produce any smoke and are really difficult to see visually. <S> Flares are small pieces of material that will produce a lot of heat, trying to blind / confuse the enemy eat seeking missile, making him think one of the flare is in fact the planes engine. <A> Flares are normally pyrotechnic devices designed to create a large IR signature to capture IR targeting on missiles. <S> There are two common types of chaff. <S> The most common is metal based and is reflective, designed to create a field of reflections and capture the radar receiver. <S> They are not necessarily foolproof. <S> For example, their velocity drops to the ambient wind velocity within a few seconds, were as an aircraft will continue to depart at a flight velocity. <S> Also, metastatic radar and other techniques may see around / through them. <S> There is also IR chaff (also a pyrotechnic measure) which is designed to create a field of temperature, reducing the signal to noise of the targeted aircraft (or other target) and decreasing the capture and hold on that target. <S> The effectiveness of IR chaff is similar to RF chaff as reported by several sources.
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Flare is used to spoof heat seeking (passive) missiles. In both cases they are employed to try to divert a missile from his target.
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Is it correct to say "the up-elevator position decreases the camber of the elevator"? Aft movement of the control column deflects the trailing edge of the elevator surface up. This is usually referred to as the up-elevator position. The up-elevator position decreases the camber of the elevator (my emphasis) and creates a downward aerodynamic force, which is greater than the normal tail-down force that exists in straight-andlevel flight. The overall effect causes the tail of the aircraft to move down and the nose to pitch up. PHAK 6-5 This is an excerpt from PHAK on the elevator. Do you agree with the statement "the up-elevator position decreases the camber of the elevator"? I've always thought the camber of control surfaces indicates their curvature, which is designed by aircraft designers or controlled by pilots using high-lift devices, and it is the angle of attack that that changes when pilots give control inputs. So isn't it more correct to say "The up-elevator position decreases the angle of attack of the elevator"? <Q> The camber of the horizontail tail is changed by deflecting the elevator, not the camber of the elevator itself. <S> And yes the local angle of attack changes when the elevator deflects, resulting in an aerodynamic moment. <A> Both of the approaches are correct. <S> The camber is a basic geometric concept, useful for understanding flow around airfoils. <S> The airfoil can be the wing, and the deflected trailing edge can be the aileron, flap, elevator, or rudder, etc. <S> The angle of attack description, that the aoa decreases with up elevator, is also correct. <S> In fact, many basic calculations and preliminary aircraft sizing includes empirical correlations of Deflection to AoA ratio. <S> Deflection of a trailing edge surface, effectively (though not physically) alters the flow such that the AOA of the undeflected airfoil is increased or decreased, somewhat proportionally. <S> DATCOM and ESDU are some resources that include empirical approaches to these approaches. <A> However, you're talking about the stabiliser/elevator, which is an INVERTED airfoil. <S> So elevator-up INCREASES the camber of the airfoil, which generates more (inverted) lift, and forces the tail downwards.
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You're absolutely correct, camber equals curvature.
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How dissimilar are redundant flight control computers? Facts On Airbus aircraft there are computers to secure the flight envelope, or to move the control surfaces. FADECs totally control the engines. Computers take decisions in place of the pilots, or even against their commands. Boeing aircraft have similar computers, even if the crew has more authority. A330 electronic bay, source , photo by 'swiss_a320' Safety implications Being critical, systems are redundant and supervise each other to detect possible failures and isolate failed components. However a computer can still be developed from faulty specifications, or be wrongly manufactured, and a program can contains bugs. If the same defect is present on all computers on the production line, the purpose of redundancy may be defeated, as they wouldn't be able to detect erroneous behavior. This is better stated in this article : Because of the severe consequences resulting from a single point of failure, hardware redundancy is critical in DAL A systems. But if the aircraft uses a redundant architecture built with similar channels, that system will still be susceptible to common mode failures that can cause all channels to fail in the same way. Question What are the principles used in aviation to reduce the possibility for redundant computers to fail or to make the same errors at the same time? <Q> As far as Airbus is concerned: Each unit is composed of two dissimilar boards, one driving the output and the other checking it. <S> Dissimilar means both different CPUs and chipsets (A320 uses i386 (Intel) and m68k (Motorola); newer models use different combinations, basically whatever was widely used at the time they were designed) and software written by two independent teams. <S> There are fail-overs, two or three depending on the system (IIRC the unit reading the side-sticks is the only one with four copies). <S> The two main axes, pitch and roll, are controlled by two different systems. <S> ELAC controls elevator and ailerons, SEC controls horizontal stabilizer and spoilers. <S> This is two completely independent chains including different actual control surfaces except for the side-sticks. <S> A320 has (hydro)mechanical backup for pitch via the trim wheel and yaw via the pedals, utilizing yaw-roll coupling for roll. <S> This works even with complete electrical failure. <S> IIRC the backups on newer models don't though (because complete electrical failure has never happened). <A> Redundancy is not only achieved by multiplying the computers, but also by diversifying them. <S> To cite from chapter 12 of The Avionics Handbook : <S> Despite the nonrecurring costs induced by dissimilarity, it is fundamental that the five computers all be of different natures to avoid common mode failures. <S> These failures could lead to the total loss of the electrical flight control system. <S> Consequently, two types of computers may be distinguished: 2 ELAC (elevator and aileron computers) and 3 SEC (spoiler and elevator computers) on A320/A321 and, 3 FCPC (flight control primary computers) and 2 FCSC (flight control secondary computers) on A330/A340. <S> Taking the 320 as an example, the ELACs are produced by Thomson-CSF around 68010 microprocessors and the SECs are produced in cooperation by SFENA/Aerospatiale with a hardware based on the 80186 microprocessor. <S> We therefore have two different design and manufacturing teams with different microprocessors (and associated circuits), different computer architectures, and different functional specifications. <S> At the software level, the architecture of the system leads to the use of four software packages (ELAC control channel, ELAC monitor channel, SEC control channel, and SEC monitor channel) <S> when, functionally, one would suffice. <A> In general, software isn't manufactured wrong. <S> When the software is created (programmed), defects can be introduced as you described by either faulty implementations or by bad specifications. <S> Faulty implementations are detected by testing the software. <S> Testing takes many forms; unit testing is one of the more basic forms, where individual functions of the underlying programming code is tested to see if it is implemented correctly. <S> This can scale upwards when doing system and integration testing where larger pieces of the software is coupled together to see how it performs as a whole. <S> But simply testing the code at this level doesn't catch everything. <S> Writing a program is rarely about getting it to do what you want it to do, it's mostly about handling all the strange edge-cases and failure scenarios. <S> And this is where most software fail. <S> To guard against such cases, you can run through audits, simulations, static code analysis and lots of other forms of inspections and testing. <S> Faulty specifications is a different beast, where you have to rely on documentation. <S> In a perfect world each requirement must be documented to a level describing why the requirement exists, and any input and output that should result from it if applicable. <S> Specifications are developed by multiple people to guard against one person forgetting something, or wrongly interpreting something, but this doesn't catch everything either. <S> To add another level of protection against software defects, you add multiple instances of the system, and you also have a team create their own version of the systems, preferably on different hardware. <S> You can then divide responsibility of certain subsystems and spread it out among the various computers running the system, adding another level of redundancy as well as to lessen the computational load on each computer, and the risk that any parts of the system interact in unforeseen ways. <S> The Fast Company had an excellent writeup on the process of writing software for the space shuttle. <S> Although it isn't directly related to neither Airbus or Boeing, it gives an insight into how the process worked and what it resulted in.
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On Airbus airliners, two different computers are used (one with Intel chips, the other with Motorola chips in case of the A320) and software is written twice, one for control, the other for monitoring, by two teams which are not allowed to interact.
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Why would one wing stall before the other? Reading about the Douglas C-133 , I see this: The second issue discovered was stall characteristics gave very little warning to the crew. The left wing was found to stall before the right wing. The fix was simple, a small strip of metal was attached to the right wing causing it to stall at the same time the left wing would stall. The issue affects the whole type. What would cause one wing to reliably stall before the other? <Q> In general, aircraft aerodynamics can be affected from manufacturing tolerances or consistent asymmetries. <S> The reason can be due to any asymmetry in the wings or fuselage shapes, or wing-to-fuselage fixtures. <A> For any design, a skidded turn stall is an example of one wing stalling before the other. <S> This would be characteristic of a handling error rather than a design issue. <S> In an aircraft not in balanced flight, particularly in a skid (nose inside the radius of turn) <S> the fuselage will somewhat mask the airflow on one wing causing it to stall before the other. <S> We used to teach these to instructors at altitude when I was a standardization pilot in the Navy, for the T-34C, to illustrate the disorienting rolling moment that occurs when one wing stalls. <S> Close to the ground this kind of stall could be lethal <S> (Please view the whole video, the narration by the instructor is very good). <S> The video example shows a rapid loss of about 700' with an instructor knowing it was coming. <S> He calls it a "base to final skidded stall" that he describes as causing "an incipient spin." <S> This is a form of a cross control departure . <S> A college classmate of mine died in a cross control departure in the landing pattern, in a T-2 over 30 years ago during flight training. <S> (I just discovered that the Navy now prohibits cross control departure training in the T-45C jet trainer <S> which IIRC was part of the OCF syllabus in the T-2. <S> I also found it missing from the T-6B syllabus, which I must say surprises me). <A> In a non-design respect, sharp yawing pressure during a stall can result in one wing stalling more than the other. <S> That causes a spin. <S> If you're looking for a design that can do it, a square of metal near the top of the camber can increase the turbulent airflow to match or exceed the other wings'.
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Any difference of the wing shape, airfoil size, or airfoil shape between one wing and the other can also result in one wing stalling more easily than the other.
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Why stall on 2D faster than 3D? why cl on 2D is better than 3D. and why cl 2D stall faster than 3D? what happens when CP continues to move forward on the wing. and what happens when CP continues to move forward on the elevator. <Q> This explains the stall at higher AoA because the additional airflow over the wing surface "energises" the air. <S> Flow seperation happens when the kinetic energy is equal to the pressure differential that the airstream flows into, so if you can increase the kinetic energy, you can decrease the tendency of the airstream to separate. <A> You could phrase the question differently: why does a wing with low aspect ratio need a higher Angle of Attack to provide the same lift, and why is maximum lift lower? <S> Because the pressure can escape over the wing tip. <S> The larger the wing tip, the larger the effect. <S> Yes a low AR wing can reach a higher AoA than a high AR wing, but only because it produces less pressure differential, therefore less lift. <A> Stall happens because the flow cannot follow the airfoil. <S> If you have a 3d wing, the pressure difference between the pressure side (below the wing) and the suction side (above the wing) can be reduced due to wing tip vortices —> less lift —> <S> smaller <S> $c_L$. They are generated because of the pressure difference. <S> This will reduce the adverse pressure gradient above the airfoil and hence reduce flow separation. <S> These vortices additionally inject energy into the boundary layer (pushing the air toward the airfoil) such that the flow can better follow the air foil despite the adverse pressure gradient. <S> Hence, stall is later for 3d wings.
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The 3D-wing allows for air to flow over the wingtip into the low pressure zone over the wing, thus reducing the overall pressure differential and reducing overall lift.
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Is a destination airport necessary for cross-country VFR departure clearance? New flyer here. When you’re requesting departure clearance for a cross-country VFR, do you have to specify the destination airport to the controller, or can you just specify a direction (eg. “VFR to the south”)? <Q> Just say direction of flight. <S> If they need more info, they'll ask: N12345: Say destination. <S> I've almost never heard that, except if they think you might be headed towards weather or a TFR. <S> Examples: <S> Understand you're headed to the south. <S> Be aware of Stadium TFR in effect. <S> or Understand you're headed to the south; have had reports of severe weather in that direction. <A> Furthermore, filing a flight plan is always a smart and safe thing to do -- these certainly require destinations, among other details. <A> For VFR flight at least in the US, you don't need departure clearance. <S> You can choose to get flight following though for safer flight, and in that case you're supposed to give ATC basic information including your callsign, altitude, and destination.
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If you request flight following when you call Clearance, they will generally want to know which direction you're heading.
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Why are airplanes sometimes led by a vehicle? Airplanes are sometimes led by a vehicle on taxiways until they reach the runway or stand, why is this? <Q> "Follow-me cars", as they are known, make it easier for pilots to get to the correct spot by the correct route. <S> This could be the runway before take-off, or the final stand after landing. <S> They're useful at airports with complex routes and relieve the pilots of some additional navigation burden; their function is one both of safety and convenience. <S> However, the presence of cars around aircraft and runways is not without its own risks, and follow-me cars in fact add an extra layer of complication to airfield management. <S> (And sometimes, they have a rather odd marketing role... <S> at Bologna (BLQ) one of the follow-me cars is a Lamborghini. <S> Make of that what you will.) <A> In addition to the reasons given by @Daniele, there are two others that I can think of: security and lack of visibility. <S> At Amsterdam Schipol for a time at least in the 1990s there were two airlines, El Al and Tower that were escorted from the gate to the runway and from the runway to the gate because there was a concern about what we would now call terrorist activity. <S> They used a follow-me car in front and, as I remember, a light armored vehicle (wheeled, not tracked) at each wing and a following vehicle. <S> There are occasions, especially in 747s where the pilot eye level is high, that after landing in minimum conditions on a well lit runway (think centerline lighting, etc.) <S> you turn off the runway only to find that you can't see the taxiway edges all that well. <S> The solution is to call for a follow-me car. <S> Once after landing on 22R at KJFK with the barest of minimums, we asked for a follow-me when we were concerned about being able to keep to the taxiway. <A> It may be required by the airport authority for large aircraft. <S> For example, at LAX, there's a detailed operations plan (no clue if that's the most recent version) for how FAA group VI aircraft (such as the A380 and 747-8) move around the airport. <S> The plan requires airport personnel to escort and monitor large aircraft since many taxi routes may cause the wings to encroach on the normal safety clearances. <S> These aircraft are large enough to pose a hazard to service roads around the airport, and airport staff need to block traffic temporarily to accommodate movements. <S> Of course, having a follow-me car doesn't eliminate all risk of incidents .
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They might be used as a rule at a particular airport, or on request (if perhaps the pilot is unfamiliar with the taxiways, or there's an urgent need to get to a gate very quickly), or because of local conditions (signage or lighting problems, re-routing because of ground maintenance work).
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Can I take the FAA CFI knowledge exam(s) based on my EASA ATPL knowledge? One of the requirements to be a flight instructor in the USA is FAA theoretical exams. Can I sit those exams with EASA ATPL theory basis? Also, do I have the right to sit those exams without completing an official FAA theory exam preparation process? <Q> There is no official theory exam preparation process that is required to be able to take the test, you can do all preparation on your own. <S> If you are asking if having passed the EASA ATP theory exam means you don't have to take the FAA CFI then <S> I think what you're asking is if the material in the EASA ATP is the same in the FAA CFI and you don't need to study. <S> While the material is very similar and there will be a lot of overlap the two are not the same, there will be questions which ask specifically about FAA regulations, testing standards and student training which are not obvious and you are not likely to pass without knowing the material. <A> You are going to have to be a little bit more clear with your question. <S> I don't know exactly what you are asking. <S> With that said, for the CFI-Airplane initial practical test, you will have to have taken the CFI Aeronautical Knowledge Test (I hope I have the current wording correctly). <S> As far as I know, there are no substitutions, and you must take that test. <S> Additionally, you will need to take a Fundamentals of Instruction test, unless you already have a Ground Instructor certificate or you are an accredited teacher. <S> Around here if one is "licensed" to teach K or 1st grade, that is considered adequate to waive the FOI test. <S> The knowledge for a CFI is quite different from the knowledge needed for an ATP (while ATPs may teach in their work). <S> Furthermore, the expectations and rules for CFIs vary between countries. <S> I know Canadian CFIs who have had to struggle with the US CFI coursework, despite their obvious competence and excellent track record in Canada. <S> One more item worth mentioning: The ability to answer as well as ask questions in a clear and unambiguous manner is an expectation of CFI's in the US. <S> So you will want to hone your skills a bit, based upon the clarity of the question you asked. <A> The testing requirements are spelled out in 14 CFR §61.183(d)(e)(f), which require you to received a logbook endorsement from an authorized instructor to take the fundamentals of instruction knowledge exam. <S> These requirements can be waived if you are currently employed as a teacher in junior high or high school or are a college professor. <S> The only other requirement is that you pass an aeronautical knowledge exam appropriate to the category and class of aircraft you are applying for on a flight instructor’s certificate. <S> (d) Receive a logbook endorsement from an authorized instructor on the fundamentals of instructing listed in §61.185 of this part appropriate to the required knowledge test; (e) Pass a knowledge test on the areas listed in §61.185(a)(1) of this part, unless the applicant: (1) Holds a flight instructor certificate or ground instructor certificate issued under this part; (2) Holds a teacher’s certificate issued by a State, county, city, or municipality that authorizes the person to teach at an educational level of the 7th grade or higher; or (3) Is employed as a teacher at an accredited college or university. <S> (f) Pass a knowledge test on the aeronautical knowledge areas listed in §61.185(a)(2) and (a)(3) of this part that are appropriate to the flight instructor rating sought; <S> As to specific preparation for the flight instructor aeronautical knowledge exam, there is no special requirement for this <S> and It does not require a formal ground school or home study course nor an instructor endorsement to take it. <S> You will be required to receive an instructor sign off to take the fundamentals of instruction exam, and a formal study course is recommended as preparation for this. <S> I’d also recommend a formal ground school with experienced instructors for preparation to obtain an instructor rating. <S> Having the knowledge of how to fly and airplane is one thing. <S> Being able to teach another person how to fly is an entirely different animal. <S> Some formative tutelage by an experienced instructor on all the knowledge and practical nuances required for an instructor certificate can go a long way. <S> The FI and CFI airplane knowledge exams aren’t bad, but the CFI practical test is going to be pretty grueling. <S> Mine was 10 hours long - 7.5 oral, 2.5 flying - and probably the most difficult exam I ever had in my life.
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the answer is no, you definitely would have to take the exam, although I don't think that's your question.
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Why is Python used on aircraft although it may not be certifiable? I recently had a discussion with people who were active in the aviation industry and told me that one of the main languages/tools they use is Python. On the other hand I have always known that people avoid C++ or eg Linux due to certification reasons for avionics. Certification is also one of the reasons you don't see AI and computer vision in C++ on aircraft. Yet, those people use Python all the time. I didn't have (and never will have) the opportunity to ask why and for what they used it. Could someone explain why and for what people would still use Python although it may be very difficult to get it certified? <Q> Just because aviation developers use Python, does not mean that Python actually goes flying. <S> Lots of aviation development is about testing, stressing, validating, analyzing, and documenting the code that does go flying. <A> As a software engineer who works at a defence company that develops and sells mission critical (but not safety critical) <S> systems <S> , I can confirm that there's a pretty even split between development in Ada (95) for our legacy products and various flavours of C/C++ for our new products. <S> Development in both is of course done to the appropriate standards. <S> Python is largely limited to plugins for our IDEs or validation and verification activities (being used by both software and systems engineers). <A> There are three basic areas of coding for aviation engineers. <S> Software code that runs on flight computers and other avionics equipment, software that formally verifies and creates that code, and scripting to automate informal work tasks. <S> Python has different use cases in all of them. <S> First, for actual on-airplane software. <S> There are different safety levels here and different required levels of testing. <S> Python would be a nightmare to certify for a critical display, autopilot, or ground-proximity warning unit. <S> C's lack of object-oriented programming and complaints when you abuse variable types may be annoying, but they also lead to easy verification that the software isn't doing something wrong behind your back. <S> On the other hand, I've heard of noncritical systems like in-flight entertainment and maintenance even using systems like Windows NT. <S> Code generation and formal verification ( <S> the kind that's documented to prove to certification authorities that you won't, well, kill anyone), do have to be formally qualified sometimes. <S> You can't just write a Python script to test all your software by simulation, formal methods, etc, then say to certification authorities that your Python script showed no problems. <S> To be more specific, DO-330 provides guidance that if you're using a tool to replace DO-178 processes (like testing, code generation, or configuration control), then that tool needs to either be formally qualified or its output needs to be checked (yes, even if the output is more fool-proof then a human doing the same analysis). <S> Finally, a lot of engineers' jobs involve scripting, and there are few langugages more popoular right now for scripting than python. <S> By scripting I mean solving problems like: <S> What issues am I working on in this area? <S> How do I add a description to a hundred files at once? <S> Is this criteria statistically different from that criteria? <S> How can I pull hundreds of lines of data from our database and dump it into a spreadsheet for my project engineer? <S> How can I email my boss every day asking for a promotion? <S> In these non-critical but quotidian affairs, python scripting can help wrangle lots of complex or repetitive tasks and make them manageable.
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Python is an excellent language for all that validation work, even though it stays on the ground.
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Is a license required to transmit in the designated aviation band? Is an FCC license required for people to operate a radio in the aviation band? <Q> These are covered in Part 87 of the FCC regulations. <S> Travel outside the US requires a station license, and I believe HF transmissions require a license. <S> Similarly the operator (pilot) needs a permit when traveling outside the US, but does not need the permit within the US, to answer your question about the operator. <A> Within the Continental US, no, VHF air band comms do not require a license. <S> You are required to possess a restricted radiotelephone operator’s permit ($80 and some online paperwork with the FCC) when using command over international waters and while flying in foreign nations. <A> When you are the PIC (Pilot in Command) you of course are granted permission to operate those systems as needed as it’s required to properly and in most airspace classes legally fly the craft. <S> If you own <S> /volunteer/operate at an FBO with it’s own FCC assigned frequency and/or your airport has no control tower and is assigned a ‘Unicom’ frequency (e.g. 122.80 MHz) <S> then you can transmit as needed to dispatch WX info, conditions, etc. <S> If you have nothing to do with this field or are an avid flight simmer heh.. <S> (yes <S> I am too despite flying in real life), then it is illegal to TRANSMIT IN ANYWAY on aviation frequencies (VHF or HF). <S> A license to purchase one is NOT required however. <S> NOTE: <S> Some sellers will not sell you an aviation radio (transceiver) without you showing them your license or other authorized certification). <S> That is up to the dealer and is perfectly okay. <S> The FAA & FCC DOES require you to be Certified (authorized anotherwords) to modify, install, remove, calibrate and ‘sign off’on any piece of avionics equipment involving communications and among other equipment, navigation equipment. <S> Obtaining certification(s) <S> to install, repair, fix & calibrate 2-way comms (handheld, FBO or in the plane) for aviation can be obtained by attending a certified school or company that offers training & certification. <S> There are several different types of certifications offered depending on the scope of what you want to do. <S> The basic ‘technician’ can remove/replace in dash comm systems, however, CANNOT by law troubleshoot it beyond that of the most obvious of adjustments on the front panel switches/options, etc. <S> Another type of certification is required to actually open it up and bench test it, replace components and calibrate it. <S> It then requires someone to ‘sign off’ on the repairs made and certify it to be ‘air worthy’ so to speak so it can be re-installed. <S> It yet again needs to be signed off on post installation. <S> Tim Dickerson, CEM, FCC/FAA ACC. <S> ARS N9NUWoodlake Landing <S> (Sandwich, IL)Unicom: 122.80. <S> ICAO: IS65 Commercial License <S> -135 <S> Endorsed
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The FCC does not presently require a license for Aviation Radio installations in aircraft, where those are VHF and UHF (as I recall).
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Do helicopters fly holding patterns under IFR? If a helicopter is flying an IFR flight plan, and the airspace around the destination is busy, will controllers tell them to fly holding patterns just like planes do? Or will they hover at the holding fix? Or something else entirely? <Q> just like airplanes. <S> Hovering at a fix is not practical, as they do not really have the nav capability to perform that, and it is contrary to normal ATC procedures. <A> Indeed helicopters can be put on holding during IFR. <S> ICAO <S> DOC 8168 VOL II (PANS-OPS) has helicopter specifics in Section 4 Chapter 1 HOLDING CRITERIA : <S> 1.3.2.2.2 Helicopter timing. <S> The outbound timing should be: a) <S> one minute up to and including 1 830 m (6 000 ft); and b) <S> Category A fixed-wing aeroplane criteria above 1 830 m (6 000 ft). <S> Also Table II-4-1-2. <S> Airspeeds for holding area construction specifies that for Helicopters up to 1 830 <S> m(6 000 ft) <S> inclusive airspeed is <S> 185 km/h (100 kt) <S> under normal (non turbulent) conditions. <S> From the above, we can conclude that timing and airspeed <S> equals flying the pattern and not hover the point. <A> A. <S> A helicopter uses a LOT more fuel hovering than it does in forward flight. <S> B. ATC are used to seeing their radar blips moving, so having the helicopter keep on moving complies with radar's expectations.
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In short, yes, helicopters fly procedure turns, hold, etc.
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When using the phonetic alphabet, for airways, should we say Uniform or Upper? Listening some RTs, I heard ATCos reporting airways, for example: UL65, UPPER LIMA 65. But the phonetic alphabet says UNIFORM. Why do they say like this, please? Is there any manual in which we can study these differences? <Q> ICAO ICAO Annex 11 and Doc 4444 confirm the usage of Upper. <S> Airways are four groups per ICAO, the older group is A, B, G, and R . <S> Those stand for Amber, Blue, Green, and Red. <S> There are three other groups. <S> So an airway named UG1 will be called Upper Green (not Golf) <S> One on the radio. <S> Example they give in Doc 4444: N0450F310 L9 <S> UL9 <S> STU285036/ <S> M082F310 <S> UL9 LIMRI <S> (...) the flight will proceed on Airways Lima 9 and Upper Lima 9 to a point bearing 285 degrees magnetic and 36 NM from the Strumble VOR. <S> From this (...) <S> Jeppesen Airway Manual also confirms it, check page 251: <S> FAA (for airways only) <S> Q is called Q (kyo͞o) on the radio ( not Quebec ), J is called J, not Juliet or Jet <S> (Jet is what it means). <S> See FAA JO 7110.65X 2−5−1 AIR TRAFFIC SERVICE (ATS) ROUTES. <S> VOR/VORTAC/TACAN airways or jet routes. <S> State the word “Victor” or the letter “J” followed by the number of the airway or route in group form. <S> EXAMPLE− <S> “Victor Twelve.” <S> “J Five Thirty−Three.” <S> The FAA is similar in using the color code for the aforementioned group: <S> Colored/L/MF airways. <S> State the color of the airway followed by the number in group form. <S> EXAMPLE− <S> “Blue Eighty−One.” <S> Also check the FAA Instrument Procedures Handbook , page 2-24 of Chapter 2 , here are two examples they give: UR5—Upper Romeo Five UW456—Upper <S> Whiskey Four Fifty Six <S> Yes the FAA handbook does not agree with their ATC Job Order regarding R being Red (this will be for the old airway system such as those still in Alaska). <S> Note: <S> the question asks about airways, the information here is not for tail numbers, navaids, etc., only airways. <S> See here for how the FAA decides on the designations: <S> How are Victor airways defined and numbered? <A> @JimyPP is correct on the use of Uniform. <S> In this case (I assume you are listening in Europe) <S> there is such thing as an Upper airway . <S> So the controller was correct in his phraseology <S> All airspace above FL195 is class C controlled airspace, the equivalent to airways being called Upper Air Routes and having designators prefixed with the letter "U" . <S> If an upper air route follows the same track as an airway, its designator is the letter "U" prefix and the designator of the underlying airway. <A> I'm not really sure what <S> the controller meant by "Upper". <S> The "U" in UL65 might already stand for the word Upper, so he used the entire word instead of the one letter abbreviation. <S> There is no reference to the word "Upper" and only "Uniform" is correct. <A> It is important to understand the reason for the phonetic alphabet. <S> It is not intended that plain language words should be abbreviated <S> , then re-expanded using a phonetically pronounced first letter as a code word substitution for the original word. <S> Rather it provides a means to spell out a word in cases where communication is difficult. <S> If a controller couldn't hear well and misunderstood the word "upper", saying "uniform" by itself would probably not help unless the context was very clear. <S> For example, an exchange where the phonetic alphabet is useful might go something like this: <S> Controller: "Say again, <S> did you mean 'udder' like the udder of a cow? <S> " <S> You: <S> "Negative, I spell - Uniform, Papa, Papa, Echo, Romeo." <S> Whenever a plain language word exists you should generally use it first, but spell phonetically as necessary to clear up any miscommunication. <S> The caveat to this is when the phonetic version is in more common use. <S> I am not actually familiar with the term "upper" as it pertains to an airway, but in the US the low altitude airways are referred to as "victor" airways. <S> I am guessing that originally the "V" may have been for VFR, but nobody seems to know or care, or to call them anything else. <S> If the convention is to say "uniform" instead of "upper" (even if that is what it originally meant...) <S> it is generally easier to follow convention to avoid confusion. <S> In the case cited in the question though, it seems that the plain language word is being used.
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The phraseology for the letter U is indeed " Uniform " as you can see on the specification of the NATO phonetic alphabet .
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Who activates the fasten seat belt warning on commercial flights? Who activates (and de-activates) the "fasten seat belt" warning on commercial flights? I would guess it is either the pilot in command (normally the captain) or the first officer (co-pilot). If the answer is airline specific, then answer for American Airlines. <Q> It's P1's decision, and P2's hand that moves the switch. <S> But, there's a really nice position of the switch, "Auto", which switches them on/off automatically based on some rules (which are usually passing through 10,000ft). <S> Using the "Auto" position means that you can't forget them! <A> Sometimes, the switch can be set to 'Auto' -if applicable-, which turns the Fasten Seatbelts sign off, once the flaps are set to the position 0 (Boeing Aircraft). <A> I believe it's the pilot monitoring...
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Depending to the Standard Operating Procedures of each airline, the Pilot Flying or the Pilot in Command will switch on the Fasten Seatbelts Sign, on takeoff, landing and when required mid-flight at their own discretion.
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Was the "Air Berlin" lap of honor over Düsseldorf problematic? A few days ago, flight AB 7001 (Air Berlin, New York - Düsseldorf) went for a "lap of honor" around the airport. One video can be found here . No emergency or technical issue, it just was that airlines last ever flight on that route (they're bankrupt), and the pilot wanted to give a nice gooodbye. Now, of course comment-sections on news regarding this are full of "experts" saying if it was ok or not. Here the question for the ACTUAL experts I can reach: Did the pilot do anything "bad" or even dangerous, or should a quick circling of the airport be just fine as long as the pilot can actually, well, fly his airplane properly? UPDATE:The Bundesaufsichtsamt für Flugsicherung (BAF) (German bureau for flight-safety) agrees with this page, the manoeuvre was ruled to have been legal and safe. <Q> The maneuver was safe. <S> A spokesperson of the DFS (German Air Traffic Control) told the Berliner Morgenpost that the pilot requested and was given clearance to fly a left curve in case of a go-around. <S> The necessary distance to other aircraft was ensured and a specific height for the maneuver was not determined. <S> The spokesperson also said that the DFS believes that this maneuver was safe. <S> However the LBA (Federal Aviation Office) started examining the case and requested Air Berlin to submit a statement which provides a reason for the go-around. <S> The editorial staff of that newspaper believes this to be a routine procedure. <S> source (in German) <S> A rough translation of the relevant part in english: Christian Hoppe, spokesperson of the German Air Traffic Control confirmed that: "The pilot previously requested if he is allowed to fly a left-curve in case of a go-around and was given clearance. <S> " The necessary distance to other aircraft was ensured, the specific height of the maneuver was not determined. " <S> From the DSF's point of view the maneuver was safe." <S> The Federal Office for Air Navigation corrected earlier information, which claimed that the pilot had reported problems with the landing-gear. <S> "That was our assumption." <S> The Federal Aviation Office will nonetheless examine the case, Air Berlin should submit a statement on the reason of the go-around. <S> Our editorial staff believes, after multiple requests, that this is most likely routine operation. <A> This can happen if the previous jet to land failed to exit the runway in time. <S> Some might call this bad because it delays the landing, it burns extra fuel, and it might conceivably interrupt traffic flow <S> (are there other aircraft behind this one waiting to land?) <S> I choose to believe that the pilot was well aware of traffic, fuel requirements, etc. <S> and did a good job in a safe manner. <S> Another thing to consider - <S> even if the airline isn't flying any more, it's very likely that the pilots will. <A> Since the Air Berlin flight got clearance from controllers before performing this maneuver, it should be legal. <S> The only legality is whether the flight declared a missed approach only to justify the pass. <S> If so, the now defunct airline <S> and it's now unemployed pilot might have some questions to answer. <S> There is a sad story about the last Pan Am flight . <S> Upon arriving at Miami, being the last Pan Am aircraft still flying, the controllers actually requested that the plane make a slow pass over the field before landing, to honor the passing of a landmark airline.
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It looks to me to be a simple "go-around" - a maneuver the pilots would be expected to execute if the runway were to become unavailable shortly before landing. Doing something dramatic and unsafe makes it very difficult to continue in their career.
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Why are most runways laid out in a generally East-West direction? Runways are named by a number between 01 and 36, which is generally the magnetic azimuth of the runway's heading in decadegrees. From what I have read, most airport runways are aligned along an East-West corridor. Why is the North-South direction rarely used? <Q> While there are many exceptions to east-west runways, generally speaking prevailing winds (which blow from a single direction) blow east-west rather than north-south. <S> It happens because of Earth's rotation generates Coriolis effect . <S> There are other wind patterns besides prevailing winds. <S> Trade winds occur near the equator and flow from either the north or south towards the equator. <S> They curve towards the west due to the spin of the Earth. <S> Polar easterlies blow close to the north and south poles. <S> They blow away from the poles and curve east to west. <S> Hence, most of the runways are Eastish-Westish (not exactly East-West). <A> Runway directions are largely chosen both for geographic land features of the site of the airport as well as the average local wind directions. <S> There are some sections of central Kansas and Oklahoma which have runways predominately oriented to in north south heading due to the winds blowing largely in a latitude parallel or approximately thereof in that region. <A> I haven't seen the East/West bias that you reference, runways are typically built where they make the most sense. <S> If there are prominent geological features such as mountain ranges or hills that could affect the approach, the designers may decide to construct the runway so that approaches and departures are not near the obstacles. <S> Populated areas are another concern, if an airport is near a town, the designers may direct the departures and arrivals away from the town in order to limit the noise.
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As most winds blow from West to east in the continental United States, most runways will be oriented approximately in that direction.
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Has anyone been able to verify ADS-B works without radar? I know that one of the biggest advantages of ADS-B is "supposed" to be that it will directly communicate between equipped aircraft without ground support. Has anyone actually seen that in action? That is, seeing another aircraft on an ADS-B display where radar coverage is impossible, say, a remote valley surrounded by mountains with no radar station near. Obviously both aircraft would need to be ADS-B equipped for this to work. <Q> I can confirm that ADS-B works without radar. <S> I have been involved in several ADS-B trials in areas where there was no or only partial radar coverage. <S> It works. <S> No surprise, it has been designed that way. <A> Ah, a trick question. <S> You ask about a remote valley surrounded by mountains with no radar ADS-B radio station near. <S> Let's make it worse, the valley walls are high enough to also make communicating with the GNSS constellation difficult, further losing one's own location. <S> For those, you need Wide Area Multilateration (WAM). <S> A new surveillance system introduced, called multilateration or Wide Area Multilateration (WAM), is now allowing air traffic controllers to track aircraft along the difficult approach to Juneau, Alaska—a mountainous area where radar was not possible <S> ( FAA ). <S> ADS-B is not a magic bullet for those very unique locations. <S> See: <S> What is the purpose of wide area multilateration (WAM)? <S> Like Secondary Surveillance Radar (SSR) <S> it is classified as a cooperative independent surveillance system; the aircraft has to cooperate (i.e. an active transponder) but position is determined independent from data sent from the aircraft (unlike e.g. ADS-B). <A> The purpose of ADS-B In is to detect and display the ADS-B Out aircraft and related information. <S> However, since not all aircraft are or will be equipped with <S> ADS-B Out, in the US, a service called Traffic Information Service-Broadcast (TIS-B) is provided. <S> TIS-B depends upon the presence of radar and proximity to an ADS-B (ground) radio station. <S> A transponder only aircraft (no ADS-B Out) is detected by radar. <S> The track information on that aircraft is broadcast to properly equipped ADS-B Out & In aircraft in that proximity. <S> So in a remote valley (or any area with no radar), the ADS-B In aircraft would have to capable of detecting an ADS-B Out aircraft directly on the correct link (1090Mhz or 978Mhz).
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Radar is not a component of ADS-B; so by definition it can operate in the absence of radar.
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Can lift be created without air downwash? I was looking at the great site code7700.com , but I don't really understand their explanation of lift and drag: The so-called infinite wing displaces air for a while, but the air particles return to their original positions along the relative wind. The relative wind experience up wash as it approaches the airfoil and down wash as it leaves the airfoil. But the up wash and down wash are equal so the net effect is cancelled. Because of this, the aerodynamic force occurs perpendicular to the relative wind and their is no induced drag. In other words, all of the aerodynamic force is producing lift, none of it is pulling the wing backwards. Source It seems this is a big confusion. Could someone just confirm that lift is created solely by the downwash and Newton's 3rd law of motion ? (Why air is deflected is not part of the question.) <Q> If no downward acceleration occurs, there can be no lift. <S> However, a wing of infinite span will use an infinite amount of air for lift production, so an infinitely small amount of downward acceleration already suffices to produce lift. <S> Clearly, this is a thought experiment that cannot realistically be reproduced in reality. <A> Sorry but this source is pretty bad. <S> The explanation is clearly wrong. <S> You should download a basics aerodynamic book... <S> Here's what happen in a finite (real world) wing, the lifting of the wing generates a pressure field which induces vortices running from the lower surface to the upper, these vortices generate the downwash which is explicitly related to induced drag by a simple equation. <S> The strength of the downwash is mainly depended on the lift coefficient and the aspect ratio of the wing, and in the limiting case of infinite wing (which is a theoretical aerodynamic's term) <S> the wing's induced downwash doesn't exist and induced drag is zero. <S> So, downwash or upwash would depend on the wing geometry and lift, it's lift tha generates the upwash/downwash and also affected by it since it modifies the local angle of attack on each wing's section. <S> If you're considering the full airplane, the upwash/downwash of wing is also affected by the fuselage near the root. <S> This picture you posted is very wrong and confusing, because even in 2D flow, you have a cambering of the flow behind the airfoil (of course flow isn't just going flat after trailing edge). <S> The flow then re-alignes with the freestream direction. <S> This picture. <S> taken by a Stanford's Aerodynamic's lecture course, perfectly answers your question The Kutta-Jukowski theorem for lift states that lift is proportional to density, freestream velocity and circulation $\Gamma$ by the equation $L=\rho V_{\infty <S> } \Gamma$. <S> For a 2D airfoil <S> the circulation is as depicted in the far upper sketch and will produce an upwash in leading edge region and a downwash in the trailing edge region <S> , then in the second sketch you see the downwash induced by the wing's free vortices. <S> Lastly, you see the combined induced flowfield. <A> To complete some of the other explanations here, lift is produced (at least the most part, there are other mechanisms by which lift is produced in real aircraft, such as engine mount angle) by downwash. <S> By deflecting air downward, even if the velocity field at infinity is strictly unaffected by the immediate downwash of the wing, it still creates a slight deviation of the airflow close to the wing. <S> This is translated to a pressure field, which combined with Bernouilli's theorem, gives rise to lift. <S> Basically, pressure lift can be explained by downwash and vice-versa.
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Most if not all phenomenons producing lift can by explained by or can be linked to downwash.
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What do pilots do on a windshear alert after V1? What is a pilot taught to do, when a windshear is detected and the planes speed is above V1 and before Vr? I can't think of what is safer. Rejecting, with the risk of overshooting the runway. Taking off, with the risk of the windshear stalling the plane and dropping it on the ground. If the height of the aircraft was low it probably would just overshoot the runway. If the aircraft already gained some altitude, it could crash. As well, are there any differences in procedures if the alert occured After V1 but before Vr After Vr <Q> V1 is the calculated decision point at which <S> takeoff must continue. <S> The danger when taking off during windshear is the sudden lost of airspeed may result in the airplane settling back on the ground after it has become airborne. <S> The technique, therefore, is aimed at gaining ground clearance in the shortest amount of time possible. <S> In general, this involves: Apply max thrust Delay rotation <S> Once rotation is initiated, quickly pitch up to gain altitude <S> Below is an extract from the Boeing 777 FCOM about taking off when windshear is suspected (my emphasis): Takeoff with less than full rated thrust is not recommended (...) <S> Use the longest suitable runway (...) <S> Consider increasing Vr speed to the performance limited gross weight rotation speed. <S> (...) If windshear is encountered at or beyond <S> the actual gross weight Vr, do not attempt to accelerate to the increased Vr, but rotate without hesitation . <S> (...) Minimize reductions from the initial climb pitch attitude until terrain and obstruction clearance is assured, unless stick shaker activates. <S> (...) <S> Stick shaker must be respected at all times. <A> What pilots are taught is that V1 is the go/ <S> no-go decision point. <S> So after V1 they will continue with the take off, but the PIC is the final authority as to the operation of the flight and may take an action that he or she determines is best depending on the specific scenario. <S> Regarding Vr: pilots are trained to do thorough pre-flight planning and become familiar with the flight plan and weather conditions at the point of departure, route of flight, and destination at the calculated time of arrival. <S> The pilots should know if there are windy weather conditions, an approaching front, or storm so that they can delay or cancel the flight or increase the Vr speed for takeoff from the standard Vr speed and have some extra buffer. <S> That way if there is windshear they have a higher safety margin between their climb speed and stall speed. <A> What I would do is to keep full throttle, and try to hold the plane in ground effect until reaching a fairly high speed. <S> Then, start increasing altitude slowly and carefully... <A> Windshear alert will not occur while on the ground on Airbuses; you will only get the alert once airborne, after Vr. <S> I suspect most manufacturers have implemented a similar feature, perhaps, in order to prevent pilots from rejecting after V1. <S> What to do is usually a precise and exact procedure. <S> While it does vary from type to type the main items are in common: <S> Use full available power <S> pitch up for a max rate of climb maintain a/c configuration (no gear or flaps retract) <A> In case of an engine failure, the total available thrust to the aircraft be reduced by 50% and it will lose at least 80% of the available climb thrust. <S> Suffer wind shear in these conditions, the airplane may not be able to sustain a positive rate of climb on one engine, making it very dangerous at low levels. <S> If low level wind shear conditions are anticipated at or in the vicinity of the airport, the pilot should consider this as part of the pre-takeoff briefing or postpone flight operations until conditions subside. <S> Have a plan based upon the procedures listed in the AFM and stick with it. <S> If an LLWAS alert is heard or if wind shear is encountered past V1, in general you’re past the point of no return and the airplane is going flying - unless you’re absolutely certain you can still stop it with the remaining runway available at your current takeoff weight, but that’s up to the captain to make that call. <S> Most jets have a considerably higher OEI performance margin than do light or medium twins and would take a pretty strong wind shear in order to threaten climbout on OEI. <S> Some things a pilot might do in those circumstances. <S> Advance both thrust levers to maximum. <S> Delay rotation or remain in ground effect until V2 has been attained. <S> Accept additional touchdown on runway of airplane cannot sustain a climb until V2 is reached. <S> Select a Vr with an appropriate wind <S> shear margin added on.
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Unless the aircraft is suffering a catastrophic failure, the pilot should not abort takeoff after V1. If sustained positive rate of climb is possible and attained, retract the gear to remove parasite drag.
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What is the difference between a go-around and a missed approach? What is the difference between a go-around and a missed approach? What are the steps involved in each of the procedures? <Q> Approach, missed approach, departure & holding Approach, missed approach, departure and holding are published instrument procedures. <S> They are characterised by waypoints, alitudes, headings, climb-, and descend profiles. <S> An approach procedure tells you how to get from cruise to short final, from a holding to short final, or from cruise into a holding. <S> A departure procedure tells you how to get from climb out to cruise flight. <S> Takeoff, landing, go around & touch and go <S> Landing is the process of getting an aircraft from short final to a full stop on the runway. <S> Takeoff is the process of getting an aircraft from a full stop to climb out. <S> A go around takes an aircraft from short final to climb out directly, not touching the runway. <S> A touch and go takes the aircraft from short final to climb out, touching the runway in the process. <S> Relationships <S> The procedures listed above can be combined arbitrarily. <S> Even though a missed approach is often flown after a go around, they are not synonymous. <S> Missed approaches can also be (and are) flown after a touch and go, or, for training purposes, after a takeoff. <S> Also, a missed approach is not the only thing you can follow after a go around: Sometimes, you want to perform a departure and continue toward your alternate destination. <A> If a pilot is approaching the runway to land and decides that conditions are not conducive to a safe landing, he can opt to “go around”. <S> This can be for a wide variety of reasons including the pilot or aircraft <S> being unprepared for the landing, the descent to landing being performed poorly, or even animals/FOD on the runway. <S> In a go around, the pilot will first apply power, then “clean up” by retracting flaps/gear as necessary to reduce drag (down to 20 degrees in a C172). <S> Once a positive rate of climb has been established, the pilot will remove the remaining flaps and radio that he is going around. <S> Generally the pilot will re-enter the traffic pattern and attempt to land again. <S> A missed approach is terminology used exclusively with instrument approaches . <S> Instrument approaches always have a missed approach procedure in case the pilot is unable to complete the approach. <S> This most often happens when cloud cover and visibility are poorer than allowed by the approach. <S> If a pilot descends to a certain altitude and is unable to see the landing environment or at least the airport lights, he will “clean up” similarly to the go around procedure discussed above, tell ATC that they have “gone missed” and then follow the steps outlined on the instrument approach plate. <S> These steps generally involve the aircraft climbing to a safe altitude and entering a hold. <S> At this point the pilot can choose what their next course of action is. <S> Missed approaches can also be used if the pilot decides that he isn’t well prepared for the approach, and the missed approach procedure must be initiated if the pilot doesn’t stick to the approach closely enough. <A> "Go Around" is the ATC instruction used in any circumstances, IFR or VFR, where it is necessary to execute a Missed Approach. <S> There is no instruction such as "make Missed Approach", the instruction is "Go Around".
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A go around is terminology generally used during VFR flight . A missed approach procedure tells you how to get from climb out into a holding or to another point from where you can commence a new approach.
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Where could I find a MATLAB implementation of TCAS algorithms? Where could I find a MATLAB implementation of TCAS algorithms and simulation? My research work deals with collision avoidance of a multi-UAV scenario in a small airspace. <Q> I doubt they will release it, but it's worth trying to start there . <S> Otherwise, they did release quite a bit of details in reports . <S> You'll probably end up rebuilding it from their logic. <A> If you are planning to build your own implementation and you are looking for the pseudo code of TCAS then buy a copy of the TCAS II MOPS. <S> It includes the algorithm description. <S> You can find it as RTCA document DO-185B , Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance Systems II (TCAS II). <A> If the size of the airspace is small and you're just looking for collision avoidance between UAV's you <S> 'd probably be better off using FLARM, which is used by gliders. <S> There is a variant of it called "UAS Electronic ID" . <S> The standard is open and available on request.
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MIT LL did indeed build a TCAS model in Simulink/Matlab which was used to validate the algorithms.
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Why do control towers have tilted glass panels? Almost all control towers I've seen have tilted glass panels: Amsterdam-Schiphol tower (EHAM), source . What is the reason behind this choice? How is the tilt angle determined? <Q> I'm pretty sure that has to do with reflections especially at night. <S> If you have ever stood between two mirriors you will understand the infinity mirror. <S> Light bounces back and forwards between the mirrors so when you look into them it appears like the scene goes on forever. <S> In a control tower, where windows are all around you, if the surfaces of the windows are parallel you get that infinite mirror effect. <S> During daylight hours this can be seen as glare, but at night when you are trying to see that navigation light on Flight 594 amid a sea of runway and taxi-way lights, having your vision further confused by a myriad of reflections from the back window would be a bad thing. <S> Further, since the room is a glass box, light can bounce all the way round the room. <S> It would be quite possible to look off to your right and think so you see an unidentified aircraft approaching, but be actually seeing some truck's lights on the hill a couple of miles away over your right shoulder. <S> Tilting the windows outwards means the reflection angle is towards the ceiling, which is generally painted black, and the effect goes away. <S> Further, tilting out means you can no longer see your own reflection, or reflections from other lit workstations in the window. <S> Ever tried looking out of a window at night into the dark and only see your own ugly mug staring back at you, then tried to move your head to the side to see around yourself. <S> LOL <S> Of course, for all this to work, the ceiling should be dark. <S> A few other reasons include, less affected by rain, fewer refraction effects, and external reflections. <S> Bonus feature, less greenhouse effect and AC bills. <S> Downside... darn hard to clean. <A> As FAA ( Order 6480.7D ) used to put it: <S> Positive tilt outward eliminates reflections from consoles and provides shading at high sun angles. <S> Another reason for tilting the Visual Control Room (VCR) windows is less deposits and less need for cleaning. <S> This is particularly important to avoid rain impacting on the controller's ability to see from the tower. <S> In fact, many other typical planning and design requirements for control towers (and for airports in general) are based on visibility, such as the use of dark ceiling tiles in the VCR, restricting the use of solar farms in and around airports, or the highly controllable VCR room and desk lighting, among others. <S> The tilt angle is determined by the appropriate authority, which depends on the country but in the USA is the FAA. <S> From my experience, tilt angle is usually set between 15 degrees and 20 degrees. <S> Another fun fact is that the increased sun shading provided by the window tilt helps keep the VCR cool. <S> Keep in mind the VCR is essentially a greenhouse! <A> The glass is the most transparent and easiest to view through when it is strictly perpendicular to the line of view. <S> Otherwise it scatters the passing light, adding "fog" that makes remote objects more difficult to see and identify. <S> Following Lambert's cosine law , radiant intensity observed from an diffusely reflecting surface is directly proportional to the cosine of the angle θ between the direction of the incident light and the surface normal". <S> At the right angle, cos(90) = 0, so. <S> This should be much more noticeable when the glass is not perfectly clean (see also here ). <S> If this assumption is true, the slanting angle should be such that the glass is perpendicular to the most usual line of sight into the ground from above. <S> As other answer suggests, avoidance of the direct reflection (this is is not a diffused scattering) may be another reason. <S> Railway control towers, where present, also have the similarly slanted windows.
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Window glass reflects a certain amount of light, like a mirror.
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Is it possible to accurately measure airspeed without pitot tube? This is a follow-up to my previous question: How does this IMU work and how to convert its output into meaningful information? for which many people asserted that I need a pitot tube and a static port in order to calculate airspeed and pressure altitude respectively, and errors will build up if I just integrate the accelerometer values from the IMU. I'd like to know whether it is possible to measure airspeed without a pitot tube, accurately ? Is there any electronic sensor that can be used for this purpose? Also are there any airplanes around the world, Airliners, GA, Military, or even Experimental, that operate without any pitot tubes? <Q> Technically speaking, inertial measurements are not sufficient to derive airspeed. <S> You need pressure measurement (or airspeed measurement, see LIDAR). <S> Pitot-static probes are the most usual and conventional devices to measure pressure. <S> However, several researches have been conducted, to replace pitot-static tubes with different technologies. <S> These technologies are mainly based on measuring surface pressure on a part of the fuselage. <S> Of course the measurements (not a single value but several values from various locations) have to be calibrated via flight tests. <S> With the current popularity of machine learning I think the calibration algorithms will not be the main problem. <S> Some other technology being investigated <S> there's also ongoing research and trials about using LIDAR todirectly measure airspeed. <S> Which won't need pressure measurement. <S> ultrasonic devices are also able to measure airspeed directly,however their real flight usage is unknown (to the author). <A> Airspeed - not reliably under all circumstances. <S> You need to feel that wind somewhere in order to get a direct and accurate measure of the speed of it, and the pitot tube is an accurate and proven instrument to measure total pressure. <S> Other possible methods: Laser based(LIDAR). <S> A 20 year old NASA report can be found here . <S> It mentions at the end that the method was not always accurate: An inherent source of error in the system is noise generated by ambient or background illumination. <S> The most intense source during daylight hours is, of course, the sun. <S> As a consequence, the smallest detect- able scattered light signal is a strong function of the angle between the optical axis and the direct line to the sun. <S> On some occasions, velocity measurements with the sheet-pairs system were impossible when this angle was less than about 30° Pressure measurement from the skin of the aircraft. <S> Problem is that the stagnation point moves as the aircraft angle of attack changes, the pitot tube front opening always hits the stagnation point. <S> But yeah you could indeed stick a whole lot of static pressure ports on the aircraft and calibrate them with a proper towed flying pitot. <S> For ground speed and navigation it is a different matter, GPS makes nulling the integration errors for ground speed very simple. <A> It is possible to think devices that could potentially replace Pitot tubes, while it is not very obvious how good they would operate under conditions of the real flight, for instance: <S> Compare temperature of the heated wire cooled by the air flow with the temperature of the similar wire that is in the same air but shielded from the flow. <S> Measure the time sound (or ultrasound) takes to travel between two points within the air flow. <S> The travel speed should be the speed of sound in the air plus the speed the air itself is moving, carrying the propagating sound wave. <S> If there are some particles (snow, hail, etc) in the air, it may be possible to measure the speed of these particles in the air flow. <S> The first two types of devices seem exist, but I found no information on using them as Pitot tube replacements. <A> OP question answer: <S> Yes, it is possible to much more accurately measure airspeed with Doppler lidar, than it is with a pitot /static system. <S> Discussion below:I have used particle scattering and Geiger mode lidar for velocity and flow measurements, particularly (no pun intended) when a tempo/spatial map of the flow is desired. <S> In atmospheric air, there are always some particles! <S> Here is an example of recent work in creating a lidar based sensor for aircraft velocity measurements: https://hal.archives-ouvertes.fr/hal-01111306/document <S> This device provides TAS, angle of slip and AOA. <S> Here is a device which utilizes Doppler velocimetry. <S> While the article suggests that the technique used is not lidar, there are several lidar techniques which perform analogous functions. <S> http://optics.org/news/5/12/35 <S> Here is a BAE concept which has been demoed at airshows, and utilizes Doppler lidar processing, utilizing a UV laser. <S> http://www.baesystems.com/en/article/bae-systems-develops-laser-airspeed-sensor-for-aircraft <S> Here is a Doppler sensor for air data patent, which is 6 years old. <S> https://www.google.com/patents/US8434358 <S> Quoting this press release: " <S> Airbus Group has completed successful flight tests on a fiber-optic, eye-safe, laser-based sensor system that delivers accurate airspeed information in the three axis at low and even negative airspeed. <S> This range of capability is not possible with pitot tubes, the longstanding industry standard for airspeed sensors." <S> http://www.marketwired.com/press-release/airbus-group-completes-successful-flight-tests-of-laser-based-airspeed-sensor-system-1978428.htm <S> A pitot tube / static port is a rather simple and inexpensive device. <S> IMUs and GPS proposed solutions are misplaced and will have a phenomenal error budget and do not accurately measure airflow. <S> NASA promoted a Rayleigh scattering lidar device a couple of years ago (2015?) <S> , so there are new developments. <S> A couple of decades ago the Navy was promoting an ultrasound doppler device. <S> While there are many ways of replacing the functionality of a pitot / static airspeed sensor, all are more expensive than a pitot system. <S> However, the most likely technology to emerge with a reasonable sensor cost will be a Doppler lidar variant. <A> If my understanding is correct, all the solutions mentioned in the answers so far would provide true airspeed, not indicated airspeed. <S> True airspeed is useful for navigation, but not for flight to determine critical speeds. <A> A wind anemometer could provide an indication of relative airflow: Or a metal plate with a spring <S> The front of the plate is receiving a dynamic pressure, while the rear of the plate is an approximation of static pressure. <S> Neither of them would handle icing well without heating. <S> Also are there any airplanes around the world, Airliners, GA, Military, or even Experimental, that operate without any pitot tubes? <S> An aircraft at very high speed relative to the wind, was well above stall speed, and well below any never exceed speed wouldn't need air data until it slowed down (e.g. Space shuttle's deploy-able probes).
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A pitot static system measures indicated airspeed which is the best indicator of things like when a stall will occur (at the slow end) and when the tail will rip off (at the fast end).
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How serious is an impact like the 10/2017 Delta Airlines suspected bird strike? Recently, there was an incident where a Delta Airlines charter flight carrying the Oklahoma City Thunder basketball team was struck by an "unidentified object". Delta's official statement claims that Delta flight 8935, operating from Minneapolis to Chicago-Midway as a charter flight for the Oklahoma City Thunder, likely encountered a bird while on descent into Chicago. The aircraft, a Boeing 757-200, landed safely without incident; customers have since deplaned and maintenance teams are evaluating. While I do not agree with the UFO label that this story seems to have run with, I am shocked that a bird (especially at such an altitude) could cause such severe damage to the nose cone (even at such speeds). Is this characteristic of a bird strike and how severe would this incident have been had the collision been with the windshield? <Q> Bird strike happens all the time - almost on a daily basis. <S> See avherald : there are 9 instances of bird strike in the past 7 days at the time this answer is written. <S> Usually it is ingested into the engine (which usually turns out to be a non-issue ), other times it impacts the cone or leading edge of the wings or knocks off a pitot tube. <S> How severe if it collided with the windshield? <S> The windshield is tested against this type of impact during certification. <S> At worst the outer layers will crack, and the pilot will execute the landing using the "cracked windshield" procedure ( <S> Yes there is a procedure written for this scenario). <S> A note about the UFO: technically it is an UFO, an Unidentified Flying Object. <S> It could be a bird, a drone, weather balloon etc. <S> Examination of the impact area might reveal what the object was. <A> If you observe the photos of the incident, you will find that the dent was in the radar dome in the nose, which is not nearly as strong as the windshield. <S> Doesn't need to be, it isn't part of the pressurized section. <S> Note also that the dome was not punctured, so whatever hit it was fairly blunt, like a large bird. <S> The absence of blood on the dome is a bit curious, though... maybe the photo just doesn't show it. <S> Note also that the radar dome didn't fracture apart <S> , it just buckled but remained intact and remained in position. <S> It did what it was designed <S> to do - take an unexpected hit and not shatter or dislodge and possibly FOD the engines. <S> Modern airliners have been tested extensively for bird strikes, especially on the windshield, as a breakage or intrusion at speed there could be catastrophic to the aircraft, as in rendering the pilots blind or unconscious. <S> This isn't a very serious incident. <S> The radar dome was buckled, but that's about all that happened. <S> Radar domes on airliners have suffered similar damage in flight from large hailstones, without seriously impacting the aircraft's ability to fly. <S> As it is, the flight crew responded exactly as they should have, and the flight landed without further problems. <S> Had the bird hit the angled and much stronger windshield, and not the blunt, forward facing radar dome, it would most likely have just glanced off, maybe leaving a nasty blood smear. <A> There are a couple of assumptions that need to be cleared up. <S> While I do not agree with the UFO <S> But the official word was not UFOs... <S> It was labelled a likely bird strike. <S> especially at such an altitude <S> This question address the fact that birds can fly very high and there was a confirmed bird strike upwards of 37500 ft. <S> could cause such severe damage to the nose cone (even at such speeds). <S> You're really underestimating the forces here. <S> The bird metioned in the last question could have weighed upwards of 20 lbs. <S> That's 20 lbs, mach 0.8, hitting a thin composite radome. <S> Is this characteristic of a bird strike <S> YES. <S> Here is an AV Herald search result for bird strikes. <S> They happen all the time. <S> If you randomly click through the search results you will see either pictures or descriptions of bent radomes, broken props and struts, or engine flamouts. <S> The beauty of it all is these planes all landed relatively safe (even the miracle on the hudson!) <S> how severe would this incident have been had the collision been with the windshield? <S> It depends. <S> If the pilots are both still conscious and can see they can fly the plane. <S> In theory they could even "fly blind" like they were flying IFR (landing would be tricky depending on the runway equipment). <S> Heck <S> a pilot got half sucked out of a plane due to a faulty window and even he lived <S> Planes are like cars. <S> They balance functionality with sturdiness. <S> The vehicle has done its job if you can walk away from an accident.
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While a few incidents make it to mainstream news from time to time, bird strikes are a common occurrence in the aviation industry. It is an unusual situation, but not a dangerous situation if the pilots handle it properly.
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What is the exact definition of Taxi Time? I found some definitions on the web, but they weren't same. Some resources mentioned it is sum of the times the aircraft is moving on the ground with its own engines. Some defined it as the time between chocks-on and take-off. <Q> As always, the definition depends on the context. <S> That is why official documents always included the definitions of important terms used in the text. <S> For Collaborative Decision Making (CDM) as defined by EUROCONTROL in the latest CMD manual (2017) , taxi time is divided in taxi-out time and taxi-in time. <S> 3.4.2 Definition of Taxi Time For Airport CDM purposes, taxi time is considered to be: For arriving flights: <S> the Actual taXi-In Time (AXIT) is the period between the Actual Landing Time (ALDT) and the ActualIn-Block Time (AIBT) For departing flights: the Actual taXi-Out Time <S> (AXOT) is the period between the Actual Off-Block Time (AOBT) and the ActualTake Off Time (ATOT). <S> For calculation purposes within the CDM Platform, taxi timeswill be referred to as estimated taxi-in (EXIT) and estimated taxi-out(EXOT) as there is no requirement for a scheduled, actual or targettaxi time. <S> Now that in itself doesn't help if you don't know how the ALDT, AIBT, AOBT and ATOT are defined. <S> The ALDT is the same as the ATC Actual Time of Arrival, which is the time the aircraft touches down. <S> The AIBT is the actual time when the parking brakes have been engaged at the parking position. <S> ( source ) <S> The AOBT is the time the aircraft pushes back <S> / vacates the parking position. <S> ( source ) <S> The ATOT is the same as the ATC Actual Time of Departure, which is the time the aircraft lifts of from the runway. <S> Now Taxi time defined as above is used in Airport management, Air Traffic Management. <S> It may be different in other areas. <S> Some observations that I want to make given the above definition: <S> De-icing on-stand is excluded from the taxi-time. <S> De-icing on a remote de-icing pad is included in the taxi-time. <S> The take-off run is included in the taxi-time. <S> The landing run is included in the taxi-time. <S> Taxiing between stands or to/from maintenance is not defined. <A> Time from the start of motion of an aircraft, under engine power, until the cessation of motion at the completion of a flight, minus flight time. <S> Addendum <S> #1Block time, an industry term in the US, refers to the time the aircraft departs the blocks initiating a flight, until it returns to the blocks at the completion of the flight. <S> Block time may be dichotomized into flight time and taxi time. <S> Flight time strict definitions vary, but the general industry term is from the initiation of the take off roll, to the stopping of the aircraft after landing, or the departure of the aircraft from the landing runway, which ever comes first. <S> While the above is generally practiced industry definitions, there are notable variations, as there is no absolute terminology agreement between the various industry segments in aviation and the regulatory segments. <S> For example, in the US, 14 CFR 1.1 provides a definition of "flight time" which is analogous to "block time" in the industry. <S> However, in Europe, JAR 1.1 defines "flight time" as airborne time. <S> Even that definition varies from the industry common practice of the time from initiation of take off roll until the stopping of the aircraft or clearing the runway. <S> In the US, block time (aka 14 CFR 1.1 "flight time") is normally logged for pilot experience purposes, and includes taxi time associated with movement of the aircraft to/from the runway and the ramp. <S> ICAO Annex 1 is slightly different from the US FAA definition. <S> Since the OP asked for a definition of taxi time, I answered this question with the generally, although not 100% universally, industry defacto terms. <A> From the Pilot Controller Glossary TAXI− <S> The movement of an airplane under its own power on the surface of an airport (14 CFR Section 135.100 [Note]). <S> Also, it describes the surface movement of helicopters equipped with wheels. <S> §135.100 Flight crewmember duties. <S> (c) <S> For the purposes of this section, critical phases of flight includes all ground operations involving taxi, takeoff and landing, and all other flight operations conducted below 10,000 feet, except cruise flight. <S> Note: <S> Taxi is defined as “movement of an airplane under its own power on the surface of an airport.”
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Taxi time is the time the aircraft spends in movement or holds on the surface of the airport, prior and subsequent to flight.
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Is it allowed to launch powered paragliders from national parks? I'm new to the sport and can't find a written answer. I've been told by local PPG pilots that it is illegal to launch from state/federal parks. I live near Johnson's Beach, Gulf Islands National Seashore and was told by the officer at the gate entrance: Yeah, go ahead, use the parking area and beach to the west, we have guys that fly out of there regularly. <Q> FAA has the following informational web page for Alaska National Parks: https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/systemops/fs/alaskan/advisories/parks/ <S> Which has contact information for parks where flight operations are periodically done. <S> Several of my pilot friends have used park and forest service airstrips with permission, so it is worth asking. <S> In Alaska, the parks are generally more open to aircraft, than in the lower 48. <S> There is also an advisory circular, 91-36C. https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/systemops/fs/alaskan/advisories/parks/media/ac91-36c.pdf <S> Some of the lower 48 have strips where permission may be granted, plus <S> forest service has some strips (usually gravel) which permission may be granted to use. <S> Again, contact the park in question, because they often have local rules which are permissive. <S> State parks vary. <S> Some states prohibit aircraft of any kind, others permit operations, usually situationally. <S> Paragliders are just one class of airman who are impacted by park policies. <S> sUAS pilots are also impacted. <S> Regardless of what you are told verbally, I would only consider ops in a Congress Designated Wilderness with written permission. <S> Those areas have a prohibition of mechanized devices, and that includes hang glider and sUAS activities. <A> No. <S> According to FAA handbook (page 8-6) : Pilots are requested to maintain a minimum altitude of 2,000 feet above the surface of the following: National Parks, Monuments, Seashores, Lakeshores, Recreation Areas <S> USPPA's information brochure also mentioned this : Most state and national parks are off-limits to launch but do allow overflight. <A> That's up to the landowner, and any local/state/federal land use laws that apply. <S> 36 CFR 2.17 governs aircraft use in national parks, and it says: §2.17 Aircraft and air delivery. <S> (a) <S> The following are prohibited: (1) Operating or using aircraft on lands or waters other than at locations designated pursuant to special regulations. <S> In other words, you can't take off or land without permission. <S> I couldn't find any information source that lists the permissions (if any) for each park, so unless someone else can find one then you'll just have to ask at each one, as you did. <S> ( This question is closely related.)
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The general rule in the US is that the FAA regulates where you can fly, but not where you can land or take off.
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What are the names of the vehicles to provide assistance to aircraft during the turnaround? During the turnaround many vehicles support the aircraft on the gate. What are the name of those "vehicles"and their purpose? <Q> The most common vehicle seen is the tug . <S> source source <S> Tugs are multipurpose tractors that are used to tow around all sorts of things. <S> Several types of equipment are shown in this diagram: <S> source <S> The tow vehicle at the nose is more commonly referred to as a pushback tug . <S> They come in different sizes. <S> Here is an example: source <S> The GPU is most often a unit that is towed behind a tug. <S> source <S> Belt loaders usually can be driven on their own: <S> source <S> The wide loader is used to put cargo containers in the hold: source <S> The cabin cleaning truck and galley service truck often have a lift built in: source <S> Luggage can be brought in baggage carts source or in cargo containers which are brought to the aircraft on dollies source <S> Another vehicle often seen is the people mover: source <A> In general, you could refer to most of the vehicles and their attachments/trailers as ground support equipment (GSE) <A>
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The vehicle is usually called a ground tug.
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What would be a technical or slang term for 'in the air'? I'm writing a sci-fi story involving aircraft and space craft. I'm struggling to get the terminology right for referring to a pilot being 'in the air' either on a mission or a training exercise. I have a feeling there is a phrase for this but I'm struggling to think of it. The context would be military, as in the following sentence: She kept the Squadron Leader updated as much as she needed to, but she preferred to keep comms chatter to a minimum when she was in the air. <Q> She kept the Squadron Leader updated as much as she needed to, but she preferred to keep comms chatter to a minimum when she was... <S> Military-related terms: ... on patrol ... on station ...on a sortie ... <S> on a shout <S> [ British English, specifically used for search and rescue ] ... on recce/on recon [ British and American English, respectively ] <S> General terms: ... <S> in the air ... <S> airborne ...at the controls ...flying ...in flight ... <S> on a mission ...doing (her) rounds ... <S> aloft <S> There might be other, more technical terms in use in the military for specific operations or missions <S> but I have no experience there. <A> In your example, it will appear as: ... <S> she preferred to keep comms chatter to a minimum when she was in the air ... <A> I've used the term "wheels up" before. <A> Since you've had many in-atmosphere answers, here are a few for not-in-atmosphere flight: <S> In / <S> On orbit Weightless <S> Parabolic (Usually used to say that something is above the Karman line but has not achieved orbital velocity) <S> Off-planet <A> Here is one more that might help... aloft <A> Another option not yet mentioned, from U.S. military jargon, is in country , though this carries some contextual baggage. <S> It's similar to in enemy territory and might be used by, for example, a carrier pilot while in an assigned combat or patrol area. <S> It might contextually suggest to the reader that radio silence or strict concentration is important to the specific mission at hand. <S> It would be less fitting if you want to suggest to the reader that this pilot's general, personal preference is simply to avoid chit-chat in the cockpit. <S> There's also the phrase <S> sterile cockpit <S> which just means a policy of avoiding distractions in the cockpit. <S> This is a common phrase among pilots and would be used as in "She preferred to keep a sterile cockpit." <S> (Of course, these nuances will only matter to readers familiar with the jargon. <S> There's always a balance to be struck between impressing those who know the jargon and alienating those who don't. <S> Everyone understands " ... while airborne " and pilots won't look at you funny for saying it.)
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Mostly when a pilot is busy in flying, the phrase used it in the air .
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How to slow down a seaplane on water? A seaplane cannot use brakes to slow down, like a land-based aircraft. So how does one slow it down? I am asking this in the context of landing, taxiing, aborted takeoff etc., as long as the plane is on the surface of water. I imagine a few possibilities: Land on a really long "strip" to ensure that water friction slows the aircraft down enough, then remember to not taxi too fast because you cannot slow down If the plane has a variable pitch propeller, probably you can go to beta range to produce reverse thrust (what to do if the plane has a fixed pitch propeller?) Steer left and right repeatedly (but wouldn't this cause stress on the airframe / chance to flip the plane?) <Q> Unless you're planning on trucking a seaplane out of where you have landed it, you usually don't need to worry about slowing down on landing since you can land in a far shorter distance than you can take off. <S> In other words, the landing water run is far shorter than the takeoff water run. <S> If you do want to shorten the water run or reduce your taxi speed, holding up elevator will do that. <S> A few seconds after touching the water and at idle power, you can use full up elevator without fear of the aircraft lifting off again, and it will add the drag of the elevator plus change the attitude of the floats or hull to a high-drag, plowing attitude. <S> I used to do that if where I wanted to dock was aft of the touchdown point <S> and I wanted to quickly slow to a safe turning speed. <S> Most constant speed props (variable pitch) on reciprocating engines don't have a reversible pitch or beta, but that can be purchased as a modification on some. <S> The major use of such is as an aid in docking, and for that it's really useful. <S> Steering left and right repeatedly doesn't impress me as a very good idea, but I suppose it would help a little, but very little since it wouldn't be advisable to do it until you're well off the step. <S> Deploying the water rudder adds a little additional drag. <S> Depending on the wind conditions, putting in a little rudder to match cross-controlled ailerons also adds drag, but that's not generally used to slow down as I remember. <S> It is used, though, when sailing the aircraft, for which it's standard procedure. <S> See also Chapter 4 of the FAA Seaplane Handbook . <A> Your first flight in a seaplane will impress you as to how much drag is offered by the floats / hull during water operations. <S> In general, seaplane pilots have three modalities of water operations. <S> Idling position. <S> In this position, the floats / hull have a similar displacement as when the plane is at rest in the water. <S> Low power is used, as on many planes it is possible kick up water which substantially erodes propellers. <S> Ploughing position. <S> The aircraft is nose high, and the floats have less displacement than at rest, causing less drag. <S> Generally ploughing is utilized when on rough water, as it helps keep the propeller out of water spray, reducing erosion and probability of damage. <S> Planing or on the step. <S> The aircraft is nose high, and the speed is greater, permitting take off. <S> Water rudders are retracted, and as float/hull displacement becomes less, the drag from water displacement and surface tension becomes less. <S> When landing, water displacement causes substantial drag and there is no need for brakes as might be needed on a land plane with a hard surface runway. <S> Beta is available on some seaplanes, but they are normally larger planes, which sit higher, and most frequently have turbine engines. <S> Even in a Cessna Caravan with floats, use of beta on the water is discouraged as it can increase prop erosion. <S> Again, it is not necessary for slowing the plane in normal operations. <A> As already mentioned, decelerating from flying speed to a slow taxi speed occurs naturally at a much higher rate than when touching wheels down on a runway. <S> But there are tricks to minimize forward motion with the engine running when that matters (e.g. approaching a dock). <S> One method is to switch off one magneto, which decreases RPM and thus thrust (if you use this make it a habit to verify both mags are on right before EVERY takeoff). <S> Another is to head into the wind as much as possible and for maximum effect open one or both doors fully. <A> A floatplane landing on water will experience much more drag than a normal plane on a runway as the water wraps around the underside of the floats, due to its surface-tension. <S> This, combined with the vastly higher area of contact between the float and the water (which is much more than the area of contact between a tyre and a solid runway), means that the drag experienced by floatplanes skimming around on water is several times higher than the drag experienced by planes that land on a solid strip of asphalt. <S> Deploying water rudders also increases the drag to a noticeable effect. <S> Please do comment if you find any discrepancies in my answer.
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In order to slow down the airplane even faster, you can perform aerodynamic braking , by using your elevators to disrupt the flow of air and hence increase drag in a controlled manner to slow the airplane down.
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What was the first flight instrument ever used in an airplane? It's not magnetic compass, turn coordinator, stopwatch, wind meter, VVI, and airspeed indicator.I want to know what is the first flight instrument. <Q> It's the yaw string : <S> Picture: Source <A> The Wright Flyer , arguably the first controllable aircraft, had three instruments: A stopwatch to measure air time. <S> A crude tachometer to gauge engine speed And an anemometer, to make an estimate of distance traveled by measuring airflow. <A> I believe the correct answer (and the answer that you looking for) would be the forerunner of the of an artificial horizon, the yaw string. <S> The tendency of airplanes (particularly pioneer aircraft) to roll needed to correct in a timely manner, and the visual earth horizon reference was not an effective means of detecting slip or skid in the necessary timely manner. <S> Consisting of a suspended short piece string or yarn, often weighted the bottom give the pilot a quick measure of the side slip angle of the craft. <S> However, the magnetic compass in my opinion would be the first true instrument. <S> Of the seven standard flight instruments, the altimeter, attitude indicator (artificial horizon), airspeed indicator, magnetic compass, heading indicator, turn and band indicator, and vertical speed indicator, the magnetic compass was not only an existing instrument, but would have become a natural necessity as flying evolved from the day-light, good weather over ground with recognizable landmarks, to night time, over water or monotonous terrain, or limited visibility, etc. <S> The ability to maintain a constant and correct direction of travel is essential to dead reckoning. <S> A magnetic compass would have been the logical first step. <S> However, the earth magnetic fluctuations, mistaken speed of travel, and travel heading deviation (the sidewards travel of a vessel as the result of forces (such as wind, currents, etc.) makes dead reckoning as means navigation by any means of transportation, well, dicey. <S> Consider 50 mile due south flight over water with no visual references, if a easterly cross wind deviates the flight path <S> one half mile laterally for every ten miles of flights, then, even with a correct speed in relation to ground, the pilot could of the mark by two and half miles. <S> Thus many other flight instruments had to be developed to bring aviation to where it's at today. <S> Known as Gyro, Lawrence B. Sperry, a well known for many innovative flight instruments he constantly conceived, developed and personally tested. <S> Gyro was one the first to fly at night, regularly army night flights in 1916. <S> Todays modern aircraft still equipped with the basic flight instruments the Sperry developed.
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The yaw string dates from the earliest days of aviation, and actually was the first flight instrument. Early flight in conditions that disallowed landmark and horizon earth reference often used dead reckoning as a means of navigation.
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4 Boeing 707 for $50,000. Is that possible? I'm helping a friend with an article on some issues in my country, mostly related to corruption. His English isn't very good, so here I go One of the cases he's analyzing is the sale of 4 Boeing-707 airplanes for $50,000 . These airplanes couldn't fly but according to public information, they had their avionics, each of them has 4 working (not suitable for flying) Pratt & Whitney JT3D engines and one of them had a working intelligence/surveillance system (this was a very complex subject and now government says they'll try to keep this for training). Airplanes were for military use, both passengers and cargo. Even considering selling them for scrap or replacement parts, is $50,000 a realistic price? For example, is there a place I can find prices for the parts, eg engines, landing gear and such? EDIT: this is in Argentina, newspaper article (in Spanish) . Some data translated from article: Approximate cruising speed: 977 km / h Service ceiling: 11,000 meters Approximate range: 8690 km Empty weight: 62,500 kg Load capacity: 94,000 pounds Maximum operating weight: 335,600 pounds It could carry up to 180 passengers They are four-engine jet aircraft, Boeing brand. Primary function: Transport of passengers and cargo, as the case may be. Wing type: low implantation. Undercarriage: type retractable tricycle with 10 armed wheels. They have four Pratt & Whitney engines (turbines). Length: 44 meters. Span: 47 meters. Tail height: 13 meters. 3 of the airplanes were bought by an US company specialized in airplanes' instrumental and parts, 1 was bought by a local party. <Q> Its surely possibly and there are a few things I can think of off hand, Missing Log Books : generally speaking if an aircraft is missing its log books you need to do quite a bit of tear down and rework on it to make it airworthy once again. <S> In many cases the cost of this far out weighs the cost of a logbook/airworth plane so not always done. <S> As such this can severely drive down the price of the aircraft making it close to worthless. <S> In line with this, without the log books you can not sell any of the parts for replacement either. <S> With out the ability to properly tag the part <S> they are only worth their weight in scrap. <S> Considering they seem unflyable and are fairly large to chop up and ship scrapping it can also become a costly maneuver. <S> The tax man... : <S> Airplanes (and all manner of vehicles) often change hands for strange dollar amounts due to various tax regulations. <S> That does not look like the case here <S> but it does happen. <S> Simply Outdated : <S> keep in mind the 707 is a fairly old plane by anyones standards these days. <S> While it may have avionics chances are they are no newer than when it was parked there to collect dust, like it or not the best LORAN C unit in the world may have cost a fortune to install back then but is worth next to nothing now. <S> These things dont exactly go up for sale all that often <S> but here is a pretty nice one listed for 6.2 Million and here is reference to one listed for only 700K . <S> Please keep in mind that there are countless variables for this kind of thing that could drive the price both up and down drastically. <A> Actually $50,000 is a good price, at least for scrap. <S> If the empty weight of each jet is approx 130,000lbs and aluminum sells for roughly 25 cents on the pound of scrap, that gives a scrap value for each jet at roughly 32,500 USD or about 130,000 USD for all four aircraft, netting you a profit of 80,000 USD on the sale. <S> DO NOT BUY THE AIRCRAFT FOR FLIGHT USE; my guess is they’re worn out airframes and engines and would cost in the millions to refurbish them for that role. <A> According to the article, they were classified as unrecoverable, damaged, had missing parts, didn't fly since 2006, and the EW system dated back from 1984. <S> Since the buyer is normally also responsible for getting it out of the field to wherever they want it, their actual costs are a lot higher than $12,500 per aircraft. <S> There's certainly more parts (in however little demand, as these are outdated) and scrap value in the planes, but cutting them up, finding the few parts worth something, taking them out, and disposing of what remains also takes money. <S> Disposal also has a cost to the seller, so sometimes they're willing to let what amounts to scrap for them to go for free, just to be rid of it. <S> In that light, $50,000 is more than nothing. <A> Although the previous answers definitely provide accurate information in terms of the possibility that this is either for scrap airframes or a fraud deal, I would like to open your perspective to one more type. <S> For certain countries and corporations, trades and sales between two groups that are at least friendly in relations can take part in certain limited "donations" in which a country (say the US) "sells" a set amount of old or outdated military hardware to an allied country with very limited offensive or usually defensive capabilities (think Western-aligned African and South American countries). <S> This is more commonly done with naval or disposable hardware as they are more difficult for these friendly countries to develop/obtain otherwise, and are sold for a symbolic price, even something as low as $1.00 as to make the transfer an official sale. <S> I understand that your friend is investigating something FROM a smaller country (Argentina by no means is needy in the military hardware category) but still country-to-corp transfers like these are not uncommon. <S> The case I wish to point out is the sale of 23 Mig-29's from the recently reunited German Luftwaffe to Poland's air force for a symbolic price of 1 Euro. <S> This is a great example of politically passable and legal transfers for what would seem like criminally low prices.
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Old aircraft (and other large hardware, like ships) get auctioned off all the time.
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What is the purpose of blades on a compressor? What is the point of having blades on a compressor. I heard on NASA that it alters the flow but how would this help. As the flow of a fluid increases, the pressure decreases, and vice versa. The rotors increase the speed of the air and descreases the pressure and the stators decrease the speed of the air and increase the pressure. How would this help create higher pressure. Why not just have the rotors? I know that the ducts this whole thing goes in gets smaller as it goes on, does this play a role? Don't get all complicated here on me, I'm still learning about airplanes and flying. Try to be as simple as possible, thank you. <Q> The statement about the rotor blades ("the rotors increase the speed of the air and descrease the pressure") is not correct, because Bernoulli's Equation does not apply in this situation. <S> Hence, the statement "as the flow of a fluid increases, the pressure decreases, and vice versa" isn't appropriate for the rotating compresser blades. <S> Bernouilli's equation (below) assumes no energy is being added or removed from the fluid. <S> This is true when the fluid is flowing through the stationary stator vanes, but not the rotating blades. <S> This energy (or power) comes from the turbine. <S> When no energy is being added to the fluid: $$total\space pressure = <S> static\space pressure + <S> 1/2 \rho <S> v^2$$ <S> where$\rho$ is the density and $v$ is the velocity. <S> This is the mathematical equivalent of your statement "as the flow of the fluid increase, the static pressure decreases". <S> But, the rotating blades add total energy. <S> So this equation does not apply, so as the velocity increases, static pressure <S> does not go down. <S> But, total energy has increased, by the mechanical work done by the blades. <S> So the value on the left of the equation goes up as the fluid flows through the rotating blades. <S> Next, the fluid flows through the stationary stator vanes. <S> Because they are static, they add no energy, so Bernoulli's equation now does apply. <S> Hence, as the velocity is decreased, the static pressure goes up <S> (i.e. there is no change in total pressure). <S> If you just have the rotor blades, and no stator vanes, the compressor would just make the fluid move (i.e an increase in the total pressure) but with no increase in static pressure. <S> The stator vanes slow the fluid down, and convert the velocity into an increase in static pressure. <S> You need to understand the difference between total and static pressures. <A> You're talking about an engine . <S> Bernouilli is valid for free flow when no energy is added to the airflow, and adding energy to the airflow is exactly what a jet engine does. <S> Inside an engine, it is perfectly possible to increase both pressure and speed. <S> It is not done that way because higher pressure is what is required, but it is possible. <S> This energy added to the airflow is applied by the rotors, in the same way that a propeller does. <S> In doing so, they also make the airflow swirl around a bit, and the stators twist the flow back. <S> That is all they do, make life easier for the next rotor stage to do their work. <S> Stators don't impart any energy on the flow. <A> In simple terms, the compressor blades (both the fixed stator blades and the rotating "fan" blades) in the front of the engine are an air pump: the rotating blades actively draw air into the engine and squeeze it, raising its pressure. <S> the work required to compress the air is large, and comes from the power-extraction turbine at the back end of the engine. <S> Many rotor/stator pairs are present in the compressor side of the engine; each one squeezes the air further and further, raising its pressure further and further. <S> At the end of the process, the air exits the compressor and is sent on to the combustors.
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The rotating blades increase the velocity, but do not decrease the static pressure, becuase they are adding mechanical work (energy) to the fluid.
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How does a combat aircraft handle the recoil force of a mounted gun? How is the recoil momentum distributed or countered for smaller aircraft or drones while using a mounted gun? Is there any hydraulic mechanism to counter it and how it is distributed across the entire body of an aircraft? <Q> In this case, the large aircraft mass acts to reduce the effects, though if the gun has too much recoil, it can cause damage to the aircraft. <S> For example , The MiG-27's GSh-6-30 cannon didn't prove particularly useful in practice. <S> It was an impressive weapon in principle, ..., but the recoil -- about 5.5 tonnes (6.05 tons) -- still had a tendency to inflict damage on the aircraft. ... <S> Landing lights almost always broke after firing, <S> In case of smaller aircraft or drones, you can chose a gun with lesser recoil. <S> Or the drone (for example) could be programmed to fly back to its original position as a way of 'absorbing' the recoil. <S> Another way is to mount the gun on stabilization platform, which makes sense only if the gun is quite small. <S> A few such systems exist , which usually use robotic stabilizers to reduce the effects of the recoil due to the gun. <A> The force of the recoil is distributed into the airframe in the same way that engine thrust is. <S> Recoil is nothing but impulse thrust, like what happens inside a piston engine which is exploding gas propelling a piston mass as well. <S> So structurally, there is no special wizardry required, everything just needs to be strong enough. <S> The main issue here is making sure that the aircraft can still be flown while the gun is doing its job, and that the aircraft is still pointed more or less in the intended direction, as this answer addresses. <A> The firing of a forward firing cannon can generate thousands of pounds of reverse thrust. <S> The use of shock absorbers in the gun mounting has the effect of reducing the peak recoil forces which might damage the airframe, but it does not reduce the average recoil force/thrust or the total impulse imparted to the aircraft over the time the gun is firing. <S> If the weapon aiming system in a drone or UCAV is capable of improved accuracy relative to a manned aircraft then a high rate of fire might be rendered unnecessary, which would reduce the impact on the aircraft's flight performance and would also mean that the gun itself could be lighter for a given calibre.
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In case of combat aircraft, the guns are hard mounted on the fuselage (or wings, for that matter) so that the recoil force is distributed throughout the body.
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Is the Airbus A380 a viable shorthaul airliner? What is the technical, mechanical and economic feasibility of using the Airbus A380 for short haul flights of under 4 hours in its 800 plus seat configuration? I'm talking about cost and economies of scale, frequency of repairs and service etc. <Q> I can't say if anyone has looked at a short-haul version of the A380, but we can look to the Boeing 747-400D for comparison. <S> In addition to removing the wingtip extensions and winglets as described in the Wikipedia article, a friend at Boeing described to me other changes needed. <S> Boeing beefed up the wing box due to the increased landing cycles. <S> There were also some changes to the brakes to improve cooling as the short flights didn't provide adequate time to cool the brakes passively. <S> It should be noted that ANA was the only customer with 19 aircraft built. <S> They retired the last of them 3 years ago. <S> So it would appear that there isn't much of a market for a short haul jumbo. <A> Last year, Emirates started a flight between Dubai and Doha, only 235 miles (378 km) apart and the flight lasted 40 minutes. <S> The flight is cancelled now, because of rather political reasons. <S> The fuel efficiency of B787 is 102 mpg per seat, compared to A380 is 74 mpg per seat. <S> The maximum seats Emirates offer on A380 is 615. <S> At present, Emirates does not have a B787, but B787's seating capacity is around 300, when classes are implemented. <S> Taking the example of people traveling between UAE (Abu Dhabi and Dubai) and Doha, there is a very high demand. <S> A single flight of A380 is more fuel efficient than two flights of B787, when a single A380 is carrying almost twice as many passengers as B787. <S> If there is a demand, economy is better. <S> When a single aircraft flies instead of two, it will also decrease congestion, at the airports, and in the airspace. <S> However, when A380 is used on smaller routes as opposed to longer ones, it will increase its cycles faster. <S> Simply comparing fuel efficiency can be flawed (noted in this answer ) as different phases of a flight cost different. <S> Emirates also operates other smaller routes besides Doha. <A> Sure can. <S> There are number of airlines on the Pacific rim areas which use 747s as puddle jumpers, making multiple short hop flights and the jet, simply because there is so much passenger travel between destinations there that an airplane like a 747 <S> all of a sudden becomes useful for that purpose. <S> It’s not unreasonable to think that in the near future past your demands in that region could potential he make an A380 configured for 700-800 seat cabin arrangements a feasible option here. <S> I don’t know if structural reinforcement here would be needed as the above poster stated, primarily because the aircraft would take off with only a fraction of the fuel on board that without an intercontinental flight. <S> 30,000 to 40,000 pounds of fuel would be useful on such routes, not the 380,000 to 400,000 pounds of fuel typically carried on a long transcontinental route.
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Compared to several other airliners (Boeing 787 ), A380 is less fuel efficient.
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Why does ADS-B broadcast velocity? I just read on opensky-network (scroll down to the section "facts") that ADS-B transmits roughly as many velocity as position messages. Since the velocity of an aircraft can be computed from two successive position broadcasts, why is the velocity transmitted directly? <Q> The "position" and "velocity" include more than what the title would suggest. <S> Airborne position gives you: <S> Latitude/longitude Altitude <S> Airborne velocity gives you: Horizontal ground speed vector Vertical rate Air speed (when ground speed not available, can be true or indicated) Heading (when ground speed is not available) <S> Together these two message types give you all the basic information you need about an aircraft's location and velocity. <S> You are correct that given two lat/lon/altitude points, you can calculate the average horizontal speed, heading, and vertical rate. <S> Keep in mind that ADS-B is already using the Compact Position Reporting format which calculates position with either two sequential messages or a reference position. <S> ADS-B broadcasts a "Navigation Integrity Category" or NIC, which expresses the accuracy of the GPS position. <S> In terminal airspace, ADS-B is required to have about +/-300 feet in positional accuracy. <S> While this is sufficient for giving general position and providing separation, it would create a lot of error in computing velocity. <S> In reality the positions are fairly consistent but data errors still happen . <A> GPS receivers can get very accurate velocity vector information. <S> It is part of the receiver architecture, and does not require a separate processing of prior positions. <S> So the velocity information is "free" and actually is much more accurate than the position information. <S> From a global architecture standpoint, it is far preferable to provide the velocity vector than it is to defer the calculation to a ground station, and because of the accuracy, it is desirable to use the velocity vector from the receiver rather than to rely of historical points to calculate that velcity vector value. <S> Those are factors in the architecture of ADS-B and the data fields. <S> Addendum <S> #1: <S> The OP asks, "Since the velocity of an aircraft can be computed from two successive position broadcasts, why is the velocity transmitted directly?" <S> There are two parts of the answer. <S> The OP surmises that successive position estimates can be used for a velocity estimation, but a velocity estimate determined that way will have substantial error, and latency. <S> The second is that the standard says that velocity information will be transmitted. <S> Of course it was designed that way because the continuous, low latency and high accuracy velocity information was available from the GPS (utilizing the Doppler of each SA L1 carrier against the local clock or other method). <A> It sounds logical to have the velocity (speed) data in the ADS-B messages rather than computing it. <S> One of the reasons is the computational cost on the receiver side. <S> In order to calculate the speed of a broadcaster from position data, the receiver must first translate(convert) <S> the difference of consecutive positions into a distance unit (meters?). <S> Then it must divide that value to the time-difference between two messages. <S> It's totally unnecessary if the broadcaster is not a concern at all. <S> However, if the speed is high enough, you'd have to mark it as a potential threat (for collision). <S> Now, suppose that you're receiving signals from 1000 broadcasters simultaneously, you'd have to 1000 computations simultaneously and continuously. <S> This is a problem of scales. <S> On the broadcaster side, speed is a readily available value, and it takes little effort to broadcast it.
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The first is that the velocity information is available from the GPS receiver and is magnitudes more accurate than the position estimation, and happens at a much higher rate than the position estimations needed for a velocity estimation. In addition to the additional computation cost, the measurement accuracy also needs to be considered.
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Do airline transport pilot trainees ever fly a passenger-less aircraft? Do airline transport pilot (ATP) trainees ever fly an empty aircraft? Consider the example where a pilot is under training to operate a 777 . Would the pilot ever fly the real aircraft without any passengers? Or is training only limited to simulation? <Q> When pilots are trained for flying in an aircraft type they have not flown in before, they go through type rating, then line training. <S> During the type rating, they learn where all the instruments and buttons are, what starts which system, how the plane behaves, how to land and auto-land etc. <S> During line training, they spend time in the cockpit together with an instructor pilot, usually a senior captain. <S> Most airlines have a 3-person crew in the cockpit when a new F/O is receiving line training. <S> This training is about the airline specific bit of flying, company procedures etc. <S> Note that before going to type rating, the pilot already has at least a commercial flying license: they can fly already. <S> Depending on the country, the type rating can take place in a Level D simulator for 100%. <S> Some countries still require a couple of actual flights in an aircraft, but there is an increasing trend to use Level D simulators only, for two reasons: <S> Back when the airlines paid and arranged for type ratings, it was relatively simple for them to arrange for an aircraft for a training flight, empty or not. <S> But now a majority of type ratings is self funded, how does a student find the finance to charter an empty aircraft? <S> The realism of Level D simulators is incredible. <S> My office used to be not far from the simulators - every once in a while I would hear the siren for the sim coming down at an unscheduled time, for an unscheduled break: the stress level inside is real, you reckon that you are really 30,000 feet up with an engine on fire, alarms sounding, actual (non-toxic) <S> smoke entering the cockpit, etc. <S> After clearing the emergency, some students needed time to reflect. <S> Boeing predicts that we need 30,000 new pilots every year for the next 20 years. <S> How do we streamline it such that all competent persons can become pilots, not only people with enough money to charter a plane? <S> As @user71659 points out, at airlines that only fly widebodies, standard entry position is a second officer/relief first officer/cruise pilot on a long haul plane like the 777. <S> (Cathay Pacific, Singapore Airlines, Emirates, for example). <A> The answer depends on which country you are in. <S> Under FAA regulations (and those countries that generally follow FAA rules), there is no requirement for you to actually fly the actual aircraft before taking passengers on a trip. <S> Under EU/EASA regulations, there is a default requirement, which is flown on a aircraft with instructors and fellow student pilots. <S> This is called "base training". <S> AMC2 ORA.ATO.125(k)(1) <S> states <S> With the exception of courses approved for ZFTT, certain training exercises normally involving take-off and landing in various configurations should be completed in the aeroplane rather than an FFS. <S> For MPAs where the student pilot has more than 500 hours of MPA experience in aeroplanes of similar size and performance, these should include at least four landings of which at least one should be a full-stop landing , unless otherwise specified in the OSD established in accordance with Regulation (EC) 1702/2003, when available. <S> In all other cases the student should complete at least six landings . <S> European airlines want to follow the US model since the actual flight time is expensive, hence the Zero Flight Time Training. <S> If the specific airline has a ZFTT approved course with a Level D full flight simulator, a pilot with at least 500 hours of multi-pilot aeroplane experience can skip the actual flight if their first four flights are also done under a specially approved program. <A> The other answers describe the use of simulators, and I don't dispute that. <S> So it likely depends on each airline's policies. <S> For a slightly less clear example, this post by Air Canada implies that the new B737MAX is being used for training this weekend. <A> All type rating training would be done in full motion simulators. <S> The problem with doing it in the real thing is that it is prohibitively expensive. <S> Also sims allow pilots to run through emergency scenarios - and sometimes allow them to fail and crash - in order to teach key points and reinforce training. <S> Large commercial airplanes are rarely flown empty; the only examples I can think of are test flights after maintenance has been performed or on ferry flights to a departure city. <S> When I interned at Boeing as an engineer in 2000, the only empty flights once the airplane was purchased were short ferry hops. <S> One airline bought a 777-200, thence flew it form KPAE 50 nm south to KSEA, where, within an hour, it was fully fueled, catered, loaded with passengers and flight crew and departed on a polar flight to Moscow, Russia.
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But, earlier this year, there was a documentary by EasyJet, where they showed how their new pilots trained, and they had to go through a couple of touch and go in an empty aircraft before they started flying with passengers.
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If my parachute fails to open, why should I aim for land rather than water? I was watching these 'what if' parachute failure videos on YouTube and everywhere they say do not choose water over land. Why should we not choose water and what happens if we land in water? One such video: <Q> A partial failure of a chute is much more survivable. <S> You will be coming down much faster than you would with a good chute, and you are going to get injured, probably badly. <S> Think broken legs and arms with neck or back trauma. <S> You may sustain a concussion as well, and you will certainly go into shock. <S> If you come down in the water you will be injured and unable to keep yourself afloat, and it will be much harder to rescue you. <S> On land help will be much closer and, and as @RonBeyer says in comments , you can't drown on land. <S> Land has features which may help you survive: trees, vegetation, hay bales, crops, snow, and many other things may cushion your impact enough to make the difference between life and death. <S> Water is the same wherever you go, and doesn't have nearly enough give to cushion an impact. <A> From a jump instructor, whose chute failed: You landed in a blackberry bush, right? <S> Yeah, it was less than a meter high and it wasn't super dense <S> but it was better than hitting than the hard floor or hitting the lake. <S> If I'd landed in the water I would have been knocked out just the same and broken the exact same bones. <S> But my lungs would have collapsed and I would have drowned, because I was unconscious. <S> So this instructor had studied the problem enough to know that he didn't want to land in the water. <S> He is not alone. <S> How to fall 15,000 feet, hit the ground, and survive (2016) <S> Also, years ago, I remember meeting a woman who was in the Army, doing a jump in North Carolina, and her chutes failed to open. <S> She targeted a pile of hay, and survived. <S> The terminal velocity of the human body is about 120 MPH, and may be less if the jumper can increase their drag. <S> Picking the right landing spot, such as soft vegetation, appears to increase survivability. <S> Landing in water seems to cause complications with breathing and also with the ability to swim if limbs are broken or consciousness is lost. <S> A co-worker was a base commander when a F-4 went down and the pilot's chute failed to deploy in the North Sea at night. <S> The pilot survived, and his injuries were limited to compressed discs and hypothermia. <S> It took them about 70 minutes to fish out the pilot. <S> I do not know what the statistics are for water landings vs land landings, but it is generally recognized that a land touchdown provides more opportunity to steer to favorable soft targets. <A> An impact on land has a small chance of survival, an impact on unbroken water has none. <S> Falling from thousands of feet without a parachute is very likely a death sentence, but there are a handful of cases in which people have survived. <S> In nearly all of them, it is because the person landed in particularly hospitable terrain, like hitting a number of branches on the way down to slow their fall, or rolling down a steep hill. <S> All of these stories have one thing in common: slowly breaking your fall <S> What kills you isn't really the impact, it's the deceleration of the impact. <S> You could be slowly lowered from 10,000 feet by a crane <S> and you'd be just fine. <S> But when you fall from great height, you build up a lot of speed as energy that has to be dissipated upon impact, and if it can't be dissipated into your environment it gets dissipated into you . <S> Your body can absorb reasonable impacts from reasonable heights, but it has limits. <S> When you slowly break your fall, you're essentially splitting one unsurvivable impact into many smaller survivable ones. <S> What does this all have to do with land versus water? <S> Land has terrain. <S> Water doesn't. <S> If you hit the side of a grassy hill and roll down hundreds of feet before finally stopping, you've dissipated all this energy into the hill, while splitting up all the impact on your body. <S> It's going to be a very, very hard impact, and it's going to be head-on, because water is always level to gravity, so <S> no hills or angles to dissipate energy. <S> Water's very high surface tension means that at speed, the surface of water behaves much like the surface of a brick. <S> In Short: Avoid water if you're falling without a parachute. <S> Aim for trees. <S> Or hills. <S> Or peat bogs. <S> Or giant trampolines. <S> Or something that isn't flat and uniform like water. <A> At a freefall speed of 120MPH, water would provide a drag of about 1000 Gs which would be the same as hitting the ground and stopping in 6 inches (15cm). <S> Better than concrete but still not survivable.
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If your parachute fails to open entirely you are almost certainly extremely dead no matter where you land, however occasionally people do survive. If you hit the water, it really doesn't matter whether it's hot water, cold water, saltwater, freshwater, mineral water, branded water.
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What is the largest taildragger in history? Large, modern multi-engine airplanes do mostly have the 'tricycle' landing gear type. But it hasn't always be the norm. I remember at least one big plane with 'conventional landing gear', the German four-engined FW 200 'Condor'... But, was it the largest of them all...? <Q> If you are going by MTOW, I believe that would be the Junkers Ju 390 , which had a maximum takeoff weight of 75,500 kg. <S> Junkers Ju 390, By Bundesarchiv, Bild 141-0072 / <S> CC-BY-SA 3.0, CC BY-SA <S> 3.0 de , Link <S> Sadly, only a couple of these were built. <S> 'Maksim Gorki', which had a wingspan of 63m ANT-20, <S> By Unknown - http://www.dkvnukovo.ru/photos/museum/photos/35.jpg , Public Domain, Link <A> I nominate the Tupolev ANT-20 , with a wing span of 63.00 m (206 ft 8¼ in), an empty weight of 28,500 kg (62,700 lb), and a MTOW of 53,000 kg (116,600 lb). <S> 2 were built, first flight was 1934. <S> ( tupolev.ru ) Note the two engines above the fuselage. <A> I nominate the XB-15 heavy bomber prototype. <S> Wing span 45.43 m Max. <S> TO weight 32,139 kg
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If you are going by the wingspan, that would be the Tupolev ANT-20
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Why do many stealth aircraft have a similar shape and design? I have been playing around on a bunch of programs with stealth planes and their general shape. I know that they are required to be flat and have some sort of special material/paint on to 'absorb' the radio waves. But I have been pondering about the required shape of these aircraft and why the flying wing shape is so widely used (excluding its lift efficiency). Why not some other shape, like a tilted square, triangle, or even a sphere? What makes the general shape of the B-2 and F-117 so common in the design of stealth aircraft? <Q> First of all, the general idea is to avoid reflection of radar energy back to its source. <S> Next, you want to direct the reflected energy into as few directions as possible in order to dazzle any observer with a momentary bright beam , surrounded by as little reflection as possible. <S> That is the reason for the aligned edges and serrated patterns on stealth designs. <S> Next, there is quite some variety. <S> How about this one ( Northrop Battlefield Surveillance Aircraft eXperimental (BSAX), or Tacit Blue ; source ): Or this ( <S> McDonnell-Douglas Bird of Prey stealth demonstrator ; source <S> ): <S> Or this ( BAE Taranis UCAV demonstrator; source ): <S> If you think that all stealth airplanes look the same, maybe you are only looking at those which were designed for the same purpose ? <A> That is a compromise between low observable requirements and traditional aerodynamics. <S> Actually a B-2 and an F-117 are quite different in terms of configuration. <S> One is flying wing and the other is not. <S> Flying wings have historically been very popular for low observable use as the absence of a fuselage, empennage, and other structural features decreases the aircraft’s radar signature. <S> Most low observable UAV aircraft, such as the X-47 and the RQ-175 also use the flying wing configuration in them. <A> This is achieved in two ways; firstly, the aircraft's shape is designed to reflect the radar energy, which is electromagnetic radiation, away from the radar. <S> This is what gives stealth aircraft their distinctive "look". <S> Secondly, the aircraft's structure is designed to absorb radar energy rather than reflecting it as far as possible. <S> This applies to the aircraft's external "skin" and also to the internal structural components. <S> The use of composite materials rather than metal has benefits in this respect.
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Briefly, the design of stealth aircraft aims to reflect the minimum possible amount of radar energy back towards the radar.
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Why don't we see business jets with wingtip fuel tanks anymore? There is something I miss from the Learjet 35 (one from FS95/98) that I don't see any more:Fuel tanks on the wingtips!What happened to the wingtip integrated fuel tanks in the business jet industry? <Q> One of the main reasons wing tip tanks were used was to counteract some of the forces of wing bending by adding mass to the end of the wings. <S> As time has progressed and our understanding of materials has grown as well as our ability to design structures better the need for tricks like this has gone away. <S> As our general understanding of aerodynamics has gotten better so has the understanding of the impact of wing tip shape on reducing drag . <S> As such wing tip tanks have been traded out for wing tip devices. <S> In some cases the tip tanks are an option available as a later add-on or at purchase time. <S> Generally this increases the range of the aircraft at the cost of useful load. <S> As such, it may just be that most people who order planes these days prefer the higher useful load and the reduced range, rather than the extended range flying with a lighter load. <S> You can find some more discussion on it here . <A> More modern engines need less fuel for the same thrust, so the fuel volume needed for an acceptable range has shrunk over the last five decades. <S> Wing volume alone is now more than sufficient. <S> While a typical 1950s era jet engine would consume 1 pound of fuel for every hour and pound of thrust <S> (= 28 g/kN·s), <S> comparable engines of recent design consume less than half of that <S> (0.44 lb/lb-f·h in case of the PW500). <S> Note that even entry-level business jets have a range in excess of 2000 km, without tip tanks. <A> The Lears with tip tanks were the 23-25 and the 35. <S> They had laminar profiles with 9% wing thickness, the thin profile was to not have to apply wing sweep. <S> The Lear 23 was developed form <S> a Swiss fighter design, Bill Lear Sr. sold his electronics company, bought the design, and founded his bizjet corp. Hail Bill! <S> Story of Bill Internal fuel volume of a thin wing is a limiting factor. <S> Storing fuel at the wing tip is a very good idea that is still carried out in all aircraft : internal fuel at the tip is used last as well. <S> The external fuel tank further doubled as an aerodynamic barrier device, like a wingtip. <S> However, tip tanks increase drag and therefore if at all possible to provide the range, will be stored inside the wing.
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The use of supercritical airfoil s, which allow thicker wings for the same drag divergence Mach number , helped as well to make tip tanks superfluous.
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Do the wheels of taxi-capable helicopters have power? There are many big helicopters which seem to taxi just as good as any fixed wing aircraft, for example CH-47. Do their landing gear wheels have power or they also taxi using thrust like their fixed wing counterparts? If they do have power, are the taxi controls different from the standard controls? <Q> Taxiing is achieved by adding just enough collective so that the helicopter starts moving, but not enough to lift it off the ground. <S> A little forward cyclic also help. <S> To slow down, the main wheels have brakes, like fixed-wing aircraft. <A> Helicopter wheels do not have power. <S> Taxiing is accomplished by using the thrust from rotors- for example, in case of CH-47, with rotors at normal rpm, the helicopter will have some forward speed (5-6 kt) with controls at neutral and thrust control rod at ground detent. <S> Steering is usually using pedals (some helicopters have hydraulic steering) and there are, of course brakes (which are used to control taxi using differential braking in some cases). <S> As you mentioned CH-47, it is interesting to know that there are different ways to taxi the helicopter under different conditions. <S> For example, according to the operator's manual , Taxiing with two aft gear on the Ground ... <S> Displace the cyclic stick aft approximately 2 inches and increase the thrust till the forward landing gear is off the ground the helicopter begins to move. <S> Maintain directional control with the directional pedals. <S> and Taxiing with power steering ... <S> After the helicopter has started to roll, the thrust control rod should be lowered to the ground detent. <S> This amount of thrust and braking will maintain a moderate taxi speed. <S> ... <S> Turns are initiated by slowly rotating the control knob a small amount and then gradually increasing the knob rotation until the desired turn is reached. <S> There are separate procedures for hover taxiing and water taxiing, though they don't make use of wheels. <A> MI-17s have wheel capability, but only utilizing thrust. <S> No other system used for taxing. <S> It uses main rotor to taxi ahead and tail rotor to turn left and right. <S> Pneumatic available for braking. <A> The helicopter can taxi on them, similar to fixed wing aircraft, or they can hover taxi, as most helicopters do. <S> The primary usefulness in wheeled landing gear is to make it easier to tow and maneuver for parking, hangar storage, etc, while the engines are shut down. <S> Virtually all large helicopters use this kind of landing gear for these reasons.
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Helicopters using wheeled landing gear do not have a drivetrain providing power to the wheels, though they are equipped with brakes. The wheels do not have power - there is no propulsion system linked to the wheels, they just spin freely. Control taxi by adjusting the thrust control rod.
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What is the purpose of extending one degree of flaps (perhaps with spoilers)? What would be the use of one degree of flaps? And is there any reason to use both flaps and spoilers combined? <Q> Normally, one degree of flaps in fact only translates to an extension of the leading edge devices (e.g. slats), trailing edge flaps remain fully retracted. <S> On some aircraft this configuration can be used for take-off. <S> Combination of flaps and spoiler is for example used in slow flight on steep descends. <A> Setting your flaps to 1 degree increases lift slightly, but also doesn't cause too much drag because its only set to 1 degree. <S> The flaps and the spoilers are used for landing. <S> The design of the flap is too increase lift but also increase drag. <S> So it comes in nice and slow, but has plently of lift. <S> The spoilers are used for when the plane touches the runway. <S> They flip up to cause drag which helps slow down the plane. <S> Spoilers can also be used if the plane is going to fast in midair, which I have seen pilots flip up the spoilers because the approach was a little bit too quick. <S> Both are used during landing. <A> As mentioned in other answer, you use the flaps to put the wings in a configuration where, at the cost of more drag, they increase lift; this allows the aircraft to fly a bit slower. <S> The spoilers, on the other hand, are used as a temporary measure to decrease lift and increase descent. <S> So, basically, in approach you would have your flaps in a fixed position, and eventually would use the spoilers for a short time to adjust the glide path (i.e, "I'm coming too high").
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The flaps ensure that the wing doesn't stall, the spoilers dump part of the lift and act as airbrakes to keep the speed under control.
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Who decided which airspaces not to fly through and how? I was looking at some flight paths, and I noticed that while some airspaces are ignored by planes for "obvious" reasons, like the Ukraine - Russian border airspace. For example, this flight seems to purposely ignore the Ukraine airspace. But on the other hand, I found some flight which are not ignoring airspaces which should probably be ignored. Like planes flying over Syrian airspace or over Yemen. These places too are war zones and might have militant groups capable of repeating something like MH-17. This made me wonder as to who decides what airspaces to not fly over, and what are the criteria to do so? <Q> One major driving factor is whether a permit is required. <S> Many countries in the world require a permit even for overflight . <S> ( source ) <S> Depending on country to country, airline to country and general relations it may be more advantageous for a carrier to get permits in one country than it would be in a close neighbor. <S> Going a bit out of the way (burning extra fuel ultimately) may be less costly than delays related to permit issues, etc. <S> In some cases there are also prohibited airspaces within a country. <S> This is simply airspace you cant fly over for regulatory reasons (generally security). <S> While some of these airspaces are small, some areas can be quite large in size. <S> While increasingly a smaller case not all aircraft are equipped to fly through all airspaces. <S> Different regulating bodies may require different gear on board for a given flight. <S> Aircraft may be prevented from entering a given airspace if not properly equipped or certified. <S> On any given day routes may be amended for weather or potential weather hazards. <S> As @mins notes in the comments, this answer covers areas avoided for safety reasons. <A> If there is a large sporting event, or festival, they will limit air traffic around that area. <S> They do this for safety in case an aircraft attempts. <S> A government based aviation regulatory agency would determine where to fly and not fly. <S> If you are flying over a war zone, that would be up to the management of the airline to determine that. <S> Let me know if you want me to add on. <S> Hope this helps, Charlie :) <A> Conversrly, some countries dont allow their own planes to overfly certain other countries, even if those countries are okay with it. <S> Some countries may allow aircraft to overfly but not land, even in an emergency, which is also problematic since it may be impossible to reach a safe country depending on the emergency. <S> All of those are very common in the Middle East, even absent an actual war. <S> War zones are generally unsafe for anyone to fly in, though that doesn't stop some carriers from doing it anyway--and occasionally getting shot down. <S> Besides safety, there is also the issue of fees. <S> Many countries gouge airlines to the point <S> it's cheaper to take a longer route around them or at least minimize the time/distance over them. <S> For instance, US domestic routes are adjusted south to only overfly southern Ontario rather than take the great circle route that would spend more (very expensive) time over Canada.
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In addition to permits, some countries simply don't allow planes registered in certain other countries to overfly them, period.
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Why do we seldom see small unmanned aircraft with gasoline engines? Most commercially available FLYING WINGS (RC aircraft or UAVs) are battery powered. Why aren't there more with with gasoline engines? PS: Sorry I edited. The question is specific about flying wings configuration. <Q> Because electric is the best propulsion method available for small commercial UAVs and <S> their mission profiles: -Significantly <S> quieter -No smells involved <S> -No flammable liquid involved -Way easier to operate: properly tuning an RC gas engine is not for everybody <S> -Much lower vibration and on frequencies easier to filter out -More controllability, <S> a BLDC (brushless DC) motor has near-instant response to the throttle and thus enables the actual, simple building scheme of quadcopters <A> Not so long ago, internal combustion engines were the standard for R/C aircraft. <S> They had some big drawbacks though: these engines used nitromethane fuel, which is a solvent that attacks many common materials used in RC aircraft, and leaves everything covered in a smelly film <S> they are loud and run at high temperatures they need to be fiddled with to get them to run well if you have multiple engines, you have the extra problem of having to match their power output <S> When electric motors + battery packs reached the point where their power/weight ratio was high enough for use in RC aircraft, many hobbyists switched to this (more convenient) option. <S> So large UAVs will have internal combustion engines. <A> Many UAVs do used internal combustion 2 or 4 stroke engines. <S> Examples include the Scan Eagle, Integrator and RQ-21 Blackjack from Insitu/Boeing. <S> The Scan Eagle has demonstrated flight of 29 hours nonstop. <S> Electric motors are limited by their battery weight and size; internal combustion fuel has far more energy per unit weight or volume. <S> Of course, these have weights of 30 to 140 pounds (15 to 60 kg) and only need one motor each. <S> For quadrotors and such, the complexity of getting the engine rotation to the multiple rotors and controlling same isn't worth the trouble for most realistic designs.
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A large variety of R/C engines is still available, from single-cylinder two-stroke glowplug engines with less than 1 cm 3 displacement, to 4-strokes, multi-cylinder engines, mini turbines, up to a 1/4 scale Rolls Royce Merlin. For larger aircraft, the square/cube law means higher demands on power/weight ratio, and electric systems still lag behind gas engines in this regard.
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What types of fuel quantity sensors are used in an aircraft? How do they work? Can you explain the different types of fuel quantity sensors used in most recent aircraft? Are ultrasonic tank sensors used these days? How does an ultrasonic sensor work? <Q> From this PPRune forum thread , the Boeing 777 does use ultrasonic sensors (some 20 per tank) <S> This airplane has some 20 sensors per tank. <S> Each of these is effectively a "radio doppler" and works on the same principle. <S> The sensor calculates the height of fluid by measuring the difference in the speed of the sonic signal sent out thru one sensor to another,as against the ACTUAL local speed of sound (which is a preset value) thru standard temp air. <S> This difference is then converted very accurately into height in the tank in mm. <S> Which translates into quantity of fuel AT <S> THAT sensor given the actual specific gravity of fuel at that point. <S> - King on a Wing <A> In small aircraft, fuel is measured simply with a floating fuel gauge. <S> In large commercial aircraft, this is accomplished by measuring the capacitance of the fuel. <A> Ultrasonic fuel sensors use a transmitter/receiver to transmit a sonic pulse inside a pipe filled with fuel. <S> The pulse is reflected back to the transmitter/receiver by the fuel surface and the time taken by the pulse is the measurement of fuel height which is then converted to fuel quantity using the fuel density and specific gravity.
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Ultrasonic fuel sensors seem to be prevalent in stationery ground fuel tanks, not in aircraft.
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What is the difference between MIL-H-5606 and MIL-PRF-5606 hydraulic fluid? what is the meaning of PRF here and can you differentiate them visually ? <Q> About 25 years ago, there was a major effort to revise MIL standards and specifications. <S> The biggest change in MIL specs was to move away from a design or manufacture spec to a performance spec. <S> The downside of the old specs were that they didn't allow for an improved product without getting the spec revised. <S> By switching to performance spec (what it must do as opposed to how to make it), improvements can be made without spec revisions and contract revisions (that call out the specs) ultimately saving everyone time and money while delivering products that use up to date technology. <S> The H is taken from the primary application, in this case "Hydraulics". <S> The current spec is MIL-PRF-5606. <S> PRF is used to indicate a 'performance' specification. <S> 'MIL-PRF' and other abbreviations are defined within DoD 4120.24-M, [2], Defense Standardization Program (DSP) Policies and Procedures, March 2000, OUSD (Acquisition, Technology and Logistics). <A> MIL-H-5606 and MIL-PRF-5606 are US specifications for hydraulic fluid based on mineral oil. <S> They are used in US military 3000 PSI hydraulic systems. <S> The biggest draw back is their flammability, which is why their use in new commercial aircraft designs has been eliminated. <S> However, many piston general aviation aircraft still depend on -5606 hydraulic fluid. <S> MIL-H-5606 is obsolete and superseded by MIL-PRF-5606. <A> Commonly MIL-H-5606 is replaced with the compatible MIL-H-83282 or now PRF due to its increased flammability resistance. <S> As long as the operating temp range stays above -40. <S> It also is not restricted to piston engine aircraft, Beechcraft King Air with a PT-6 as well as many turbine commercial helicopters use one or both of these fluids. <S> Sikorsky, Bell and Airbus helicopters to name a few. <A> See MIL-PRF . <S> From AeroShell handbook on hydraulic fluids... <S> Although the military did not move to phosphate ester type fluids they did identify the need for a more fire resistant fluid as a direct replacement for MIL-H-5606. <S> As a result a synthetic hydrocarbon-based fluid, MIL-H-83282 was developed. <S> This fluid is completely compatible with MIL-H-5606 fluids and MIL-H-5606 hydraulic system materials. <S> All physical properties of MIL-H-83282 (now MIL-PRF-83282) were equivalent to or superior to those of MIL-H-5606 (now MIL-PRF-5606) except for low temperature viscosity. <S> In particular all fire resistant properties of MIL-PRF-83282 are superior to those of MIL-PRF-5606. <S> More recently MIL-PRF-87257 was introduced in order to address the concerns over the low temperature viscosity of MIL-PRF-83282. <S> Visually, there is no distinctive difference between the old 5606 and the replacement variants of 83282. <S> My take is that we should all be moving to 83282. <S> Another part number to remember...
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In your case, MIL-H-5606 is the 'old' spec. PRF is from the MIL-PRF portion of the Performance Specification and is not specific to this item number.
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What's the difference between orientation and position? In INS (Inertial navigation system) sensors, is there a distinction between the following? Orientation (heading, pitch and roll) Position (latitude, longitude and altitude) Is the orientation relative to a specific axis while the position is absolute? If yes, what is the axis? <Q> Yes there is a distinction, pitch, roll and heading are angles [unit = radian] and <S> latitude, longitude and altitude are linear distances [unit = meter]. <S> Together, these six parameters define the six Degrees of Freedom that define the momentary state of a rigid object with reference to the earth. <S> All six are defined relative to earth axes. <S> For the linear dimensions this is clear, we just need to define a suitable zero point. <S> For the angles: Pitch is the nose up/down angle relative to the gravity field of the earth. <S> Roll is the wingtip up/down angle relative to the gravity field of the earth. <S> Conversion of aircraft axes into earth axes is a non-trivial matter and the cause of much confusion, for instance in questions comparing lift to weight: lift is always coupled to aircraft axes, weight to earth axes. <S> The axes sets are defined as follows: Aircraft axes <S> Origin: Centre of Gravity of aircraft <S> X-axis: in the symmetry plane of the aircraft, + = forward to the aircraft nose Y-axis: <S> in the span wise direction of the aircraft, + = to the right wingtip <S> Z-axis <S> : perpendicular to the XOY-plane, + = down into the floor. <S> Earth axes <S> Origin: Centre of Gravity at the start of the response <S> X-axis: In the horizontal plane (relative to gravity), + = pointing north. <S> Y-axis: <S> Perpendicular to XOZ-plane, + = pointing east. <S> Z-axis: <S> Pointing to the centre of the earth = + Edit <S> Yes navigation lat/lon is given in [degrees] - the INS sensor ultimately converts displacement into proper navigational definitions of course. <S> But for measuring 3-D aircraft inertial effects the SI system is used, and displacement is internally treated as a linear motion, units [metres]. <A> Position is where you are; orientation is which way you're pointing (including any roll). <A> "position" is absolute. <S> You can think of it as the x, y, z coordinates of the aircraft in the 3D space. <S> "orientation" is the state of the aircraft relative to its own axes: <S> Image from https://en.wikipedia.org/wiki/Aircraft_principal_axes "position" (coordinates) - https://en.wikipedia.org/wiki/Geographic_coordinate_system orientation - https://en.wikipedia.org/wiki/Aircraft_principal_axes
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Heading is the angle relative to a suitable earth reference, usually magnetic north or geographical north.
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How do commercial pilots keep situational awareness of their current call sign? Air transport pilots operate flights with a variety of flight numbers, often with multiple flights in the same day. This means, as a result, the callsign that they are using changes as well. Also, according to this answer , sometimes the callsign is completely different from the flight number. Given that, how do pilots maintain keep track of what callsign that they are listening for at a given point in time? Are there conventions for posting the callsign somewhere in the cockpit? <Q> Some modern airliners have a place where the flight number can be displayed on the cockpit displays. <S> This information can be entered off the dispatch paperwork when setting up the flight plan, and is displayed throughout the flight for easy reference. <S> For example, you can make out "DLH463" on the screen at the bottom right of <S> this Lufthansa A380 cockpit photo , corresponding to Lufthansa flight 463. <S> The Boeing 787 has a similar feature : <S> The two outboard displays are a fixed format that provides primary flight display information combined with an “auxiliary” display that consolidates frequently referenced information for the crew, such as flight number , each pilot’s microphone-selected radio and its frequency, and transponder code. <S> You can see this on this 787 cockpit photo at the top of the leftmost monitor: "FLT - <S> > <S> BAW787" (Photos not embedded due to licensing restrictions.) <A> Changing call signs (or tail numbers) is fairly common from even early training. <S> Its something that many pilots are accustomed to even before they get to the big operations. <S> As a student pilot its quite possible your flight school will have a few airframes usually of a given make. <S> You may not always fly the same airframe and will get accustomed to rotating tail numbers. <S> I did all my training in one of 3 Piper Warriors all outfitted the same. <S> From there many who plan to go to the airlines get their commercial ticket and instruct first to build their hours. <S> While students will only fly a given type of airframe instructors may fly all the various makes the flight school owns. <S> The last instructor I was flying with in any given day usually flys one of two Archers, An Arrow, one of 3 172's and a 150 all with different tail numbers. <S> Some pros may go on to fly 135 charts if they are lucky. <S> Often times smaller chart outfits will have a variety of small aircraft that are constantly flying short hops and rotating crews allowing plenty of practice at hopping call signs/tail numbers <S> Once at the ATP level you already have a lot of hours flying a variety of planes, often all in one day. <S> ( source ) <A> The 737 has it on the yoke where the right hand would rest. <S> It doesn't affect any systems but you can turn the numbers to represent a 3 digit integer. <S> You can also see the callsign you entered when filling out the flightplan page in the fmc when pressing the "PROG" button on the fmc <A> The first time I saw a post-it was in the cockpit of a Flying Tigers 747 in the early 80s, stuck next to the standby altimeter with the flight number on it (ie FT66 or similar). <A> I fly several different types of aircraft, in varied missions. <S> So I can keep track of it, without making a radio fool of myself, I carry pink Post-its, and throw the callsign I am to use on my kneeboard or on the yoke. <S> Experience has taught me to avoid posting it on the panel, as the vertical position, plus sometimes high airflow can cause "callsign loss" which is on par with the embarrassment of "callsign error." <S> Also, I used to use any color of Post-it, but experienced "callsign obscurity", and found that uniquely using a deep and bold pink reduced my radio stress. <S> As for others? <S> I preach conversion, but there are few adopters and multitudes of critics. <S> Look and see how many pilots carry a short stack of small pink Post-its on their kneeboard.
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Many smaller aircraft have a placard with the tail number affixed to the panel somewhere (like in this citation cockpit).
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Is there a system where plane/heli auto adjusts prop pitch/mixture? This one is simple: is there a system that automatically adjusts things such as: Mixture (I Am bored of listening for engine sounds) Prop Pitch (I Hate auto adjusting "gears") So I can only spend time adjusting throttle ? <Q> There sure is but it is generally independent of what is traditionally considered a "glass cockpit" and is often wrapped up under the FADEC system . <S> One of the earlier production designs for this found its way into the Mooney M20PFM which was a Porsche Powered Mooney that had an <S> electronically inject 3.2L Porsche car motor in it. <S> Most importantly it had "single lever operation" where the throttle, prop, and mixture were all wrapped into one lever. <S> For a variety of reasons the plane was ultimately a failure and I do not belive any are still flying with the Porsche motor. <S> As Ron mentions in the comments some of the Diamond's like the DA42 are set up this way. <S> So I can only spend time adjusting throttle? <S> This is perhaps the more important part of the question. <S> Perhaps one of the main reasons that planes are set up with the throttle, prop and mixture adjusts is to allow for fine control. <S> Automatic control systems generally operate in the most "efficient" range but as a pilot you may wish to operate in other ranges, run lean of peak or cruise at a very slow but efficient burn. <S> Your POH will give you all the relevant information to operate your plane in all sorts of ways. <A> It was designed by Heinrich Leibach and so complex that it was said only a handful of experts truly understood how it worked. <S> It was called Kommandogerät and <S> Wikipedia writes it could be considered to be a precursor to the engine control units used for many vehicles' internal combustion engines of the late 20th and early 21st centuries. <S> BMW Kommandogerät (picture source ) <S> Internal workings of the Kommandogerät ( source ): <S> This should illustrate that it was indeed possible since 1940 to allow single-lever control of an aero engine, but doing so before electronic computers became cheap and reliable enough involved a very complex device. <S> All other engine designers concluded that separate levers for prop pitch and mixture would be better, pilot workload be damned. <S> The almost non-existent technological progress in aero piston engines in the last 60 years means that only spillover developments from the car industry would introduce electronic engine control systems into aviation use, such as the PFM 3200 in the 1980s and Thielert (now Continental) Diesel engines more recently. <A> Our company, Flight Enhancements, has an STC for a semi-automatic, add on mixture control device called Auto-Lean. <S> It is STCd for many single engine general aviation aircraft. <S> It allows the pilot to select their preferred mixture setting for phase of flight and flight profile (ie. climb, best power, efficiency, descent, LOP, ROP) while doing the actual setting automatically. <S> It can also hold the setting and warn of any problems. <S> See www.flightenhancements.com for details.
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The BMW 801 had such a thing, essentially a mechanical/hydraulic analog computer which allowed to automatically adjust prop pitch, mixture, supercharger settings and ignition timing, all with a single lever in the cockpit.
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How does the nitrogen generation system in a Boeing 777 work? How does the nitrogen generation system in a B777 work and how does it differ from that used in a B787? Any diagrams will be appreciated. <Q> The 777 system <S> As RAC points out , "nitrogen-generation system" is somewhat of a misnomer. <S> All the system does is remove oxygen from the ambient air and blow the rest into the center fuel tank; there is no chemically "new" nitrogen created. <S> For example, here is an Airbus schematic: <S> Parker has a breakdown of the major components. <S> Summarizing it and filling in some gaps, we have: Ozone (O 3 ) <S> converter: <S> Basically a catalytic converter that converts triatomic oxygen (ozone) to biatomic ("regular") oxygen to protect other elements in the system from oxidation. <S> Heat exchanger: <S> Cools the bleed air (which is really hot when it comes off the engine), again to protect other elements of the system and increase their effectiveness. <S> Air separation module: <S> Physically removes almost everything but the dinitrogen (N 2 ) in the air. <S> This separation is accomplished by running the air through semipermeable fibrous tubes ; because almost all the non-N 2 molecules present are smaller than the N 2 molecules, those smaller molecules pass through the membranes and are exhausted overboard, leaving only the nitrogen to exit into the fuel tank. <S> Other: <S> There are various filters to protect components from particulate matter, valves to control the timing and rate of flows, controllers to control the valves, and sensors to inform the controllers. <S> The 787 system <S> The 787 is a no-bleed airplane, which means that instead there is an electric-driven compressor to supply the NGS rather than bleed air. <S> This setup requires a slightly different heat-exchanging architecture, but the overall function and operation of the primary system components are similar. <A> The NGS uses proprietary tech to separate nitrogen enriched air from bleed air. <S> Diagram attached. <A> On the 787 it's NOT a nitrogen generation system, it's an oxygen depletion system. <S> If the air starts at 77% N2 and 21% O2, and you take half the oxygen out, you end up with 87% N2 and 11% O2. <S> The whole idea is to reduce the balance of fuel fumes v oxygen above the fuel, so that it won't burn. <S> On the 787, air from the Cargo Heat system is passed through a catalytic convertor (like your car), which takes out some of the oxygen. <S> The reduced-oxygen/enriched-nitrogen is then fed to the fuel tanks like a vent system.
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The 777 architecture is basically the same as the schematic that mike provides ; in fact, all bleed-air aircraft use pretty much the same system.
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What is the smallest manned jet aircraft? In the movie Spy Kids (2001) , there is a scene where the characters board a small jet aircraft "built for one passenger". The aircraft is about 2 meters tall with a 3 meters wingspan, and features a single jet engine, air intake located below the canopy, and tricycle landing gear. Which got me wondering: what is the smallest fixed-wing jet-powered aircraft to date? Some clarifications: The aircraft must be able to takeoff and land under its own power (i.e. aircraft launched mid-air does not count). The aircraft is propelled by one or more turbojet or turbofan engine(s) (i.e. no propellers, no rockets). "Smallest" is measured by wing span. The aircraft must be pilot operated (i.e. RC aircraft does not count). This is not a question about whether an aircraft that small is possible, since there is already another very similar question . Rather, this question is about the smallest aircraft successfully flown in history to date. <Q> (the BD-5A is smaller than the Cri-Cri but prop powered) <S> making it the smallest. <S> Although I will admit it is predicated on a lose definition of "wing" and is rocket (not jet) powered. <S> Although if you broaden your definition of "aircraft" Yves Rossy's jet wing backpack is the smallest coming in at a wingspan of 7.9 ft. <S> It is still piloted, jet powered although I do not think it can take off under its own power. <A> I don't have a definitive answer, but the jet variant of the Colomban Cri-cri will probably be tough to beat. <S> According to Wikipedia, its wingspan is 4.9 m (16 ft 1 in). <A> The Bede BD-5J is smallest according to Guinness. <A> Probably the best answer? <S> The Bell Rocket Belt. <S> Developed in the late 1960s, it used a Williams jet engine and could provide up to 20 minutes of flight at speeds as high as 85 mph. <S> The Army has evaluated it but eventually declined to purchase it and the project was dropped.
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The BD-5J is what guinness world records claims to be the smallest but it is larger than the Cri-Cri in its jet implementation If you want to count really experimental stuff the Martin Marietta X-24A lifting body has a wingspan of only 11 ft 6in.
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How does the lift coefficient of an A380 change when flaps are extended? I would like to know the lift coefficient with 10 degrees of flaps extended. <Q> As mostly when questions are vague, the answer is: It depends. <S> If nothing else changes, the nominal lift coefficient stays the same. <S> A coefficient is referenced to an area, and for aircraft this is the reference area which is derived from the wing area. <S> Regardless of flap settings, the reference area stays fixed, and so does the lift coefficient because neither the mass nor the speed of the aircraft have changed when flaps have been set. <S> In reality, the aircraft will slow down when flaps are extended, and it can afford to do so because drag is increased and stall speed lowered. <S> Now, with the lower flight speed, the lift coefficient will go up in proportion to the ratio of the speeds before and after squared:$$c_{L_{flaps}} = <S> c_{L_{clean}}\cdot\frac{v_{clean}^2}{v_{flaps}^2}$$Again <S> , this assumes the same reference area. <S> $$c_{L_{flaps}} = <S> c_{L_{clean}}+ (\alpha_{0_{clean}} - \alpha_{0_{flaps}})\cdot <S> c_{L_{\alpha}}$$ <S> Note that the lift curve slope increases when setting flaps increases the effective wing area. <S> Again, all is referenced to the unchanged reference area. <A> With extended flaps, the chord length of the airfoil increases, increasing area of the wing itself. <S> This would decrease the lift coefficient of the wing, thanks to this formula from NASA : Cl <S> = L / <S> (A <S> * .5 <S> * r <S> * V^2) <S> Hope I could help, at least partially. <A> When an aircraft flap is deployed, it increases the effective camber of the wing airfoil. <S> Thus, the zero lift angle, i.e., AoA at zero lift decreases as a result the cl-a curve shifts to the left. . <S> As you would know, a cambered airfoil has higher cl than a symmetric airfoil. <S> It is the same concept here. <S> As the camber increases, so does the cl. <S> To calculate the change wrt flap deflection you need more information. <S> Either you could do this physically on a model of A380 or you could try to plot the curve if you have aircraft aerodynamic data.
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In a wind tunnel where the aircraft model is fixed to a sting and the angle of attack is controlled, setting flaps will increase the lift coefficient by the difference in zero-lift angles of the aircraft with and without flaps, multiplied by the lift curve slope of the aircraft.
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Is there a website with a list of all commercial airline incidents? I am looking for a website that contains a listing of all commercial airline incidents (under a sufficiently large definition of "incident"), by airline company. I assume that incidents that happen are logged automatically somewhere, and I presume that this information may be further relayed to a public website. Here's my finding so far: I know of the ASRS database, https://asrs.arc.nasa.gov/search/dbol/strategies.html , but this doesn't list airline names, as far as I could see (and is also tricky to navigate). The 3 other more usable website, that don't report just accidents, but also incidents (whatever they define as "incident"... meaning sites like http://aviation.globalincidentmap.com/ are excluded) are https://aviation-safety.net/ http://avherald.com/ https://www.aeroinside.com/ Are these sources credible? E.g. http://avherald.com/ states in their FAQ that they compile their report based on "own sources". https://www.aeroinside.com/ says, after some looking, that it's information is compiled from multiple other databases, but doesn't specify which. https://aviation-safety.net/ seems the most legit of these (excepting ASRS), but again, official assurances are missing. I'm asking this, because I'd like to compile for myself some flights statistics (I'm a statistician by profession) and I'd like some site sthat are easier to navigate than ASRS (recompiling their data in a form amenable to statistics would be very time-consuming). <Q> under a sufficiently large definition of "incident" <S> Although somewhat vague, ICAO and most national regulatory agencies do have an actual definition for the term "Incident". <S> First, however, you need to start with the term, "Accident", which can get very specific... down to the number of days someone was hospitalized, or a certain monetary damage amount, for example. <S> Then, the definition of incident becomes, essentially, "anything that does not meet the definition of an accident, but which the safety of operations was or could have been affected." <S> Source: ICAO Annex 13; US NTSB Part 830.2 <S> I assume that incidents that happen are logged automatically somewhere <S> Although I can only speak for the US, Part 830 defines what an incident is and which ones must be reported, by whom, and when. <S> These incidents are recorded in the online NTSB database, and can be retrieved in several formats conducive to statistical analysis (xml, csv, etc.). <S> https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx <S> There are non-US accidents/incidents also in this database if US parts or aircraft were involved (a Boeing 737, an engine part manufactured in the US, etc.); however, these aren't as readily formatted for statistical analysis - but they do point to the foreign nation's investigative board's information. <A> Each jurisdiction or organization will have its own reporting system, not all will provide that information to the public. <S> News, social media, and websites provide information but more research is required to determine which parts are accurate. <S> https://aviation-safety.net/ <S> The Aviation Safety Network is probably your best bet for both completeness and accuracy. <S> The database is fairly comprehensive, contains events as far back as 1919, and lists sources. <S> You can browse by date, location, and aircraft type. <S> http://avherald.com/ <S> Avherald strives for accuracy but is far from complete. <S> Information is not reported without reasonable verification, sources are provided when possible. <S> The team sometimes even has access to the radar data to provide more insight. <S> Many news outlets use this as a source. <S> This will make any statistical analysis hard. <S> https://www.aeroinside.com/ AeroInside appears to just copy from Avherald and put the entries in a fancier format with ads and make them a bit more searchable. <A> There is also JACDEC <S> (Jet Airliner Crash Data Evaluation Centre). <S> JADEC provide, for each airline listed, a "safety index". <S> The Index is the result of a complex formular containing multiple factors such as accidents and serious incidents, revenue passenger numbers, Safety Audits, etc. <S> Unfortunately, if you want the report that comes up with that assessment, I believe you have to pay for it. <S> Also, a subtle point, JADEC is NOT a list of airlines in order of safety. <S> Its a list of the 60 biggest airlines (in terms of revenue), in order of safety. <S> The Safety Index is calculated from a number of factors. <S> They say: We believe the operational environment is a crucial factor for an airline´s safety performance. <S> One lesson of our now decade-long experience in aviation safety analysis is the following: There is a direct correlation between the safety of a airline and the competence and transparency of the controlling authorities. <S> Therefore we use for years the results of the so-called USOAP , this abbreviation stands for Universal Safety Oversight Audit Programme . <S> In this global program, guided by all ICAO member, the whole civil aviation system is undergoing a voluntary audit. <S> In particular it is investigated how a country is able to meet and maintain defined standards on aviation safety. <S> Furthermore, we looked at the level of trancparency an governing authority has. <S> We ask: Are there all relevant occurences laid on the table, or not ? <S> Compared to earlier years, 2013 gave us some encouraging results, but many important players like China, Turkey or Mexico failed to open their accident investigations to a wider audience. <S> It's prehaps not what your loking for, because you want the raw data to make your own assessments/analysis, rather than <S> someone elses's that includes non-statistical factors, but it seems to be quite a reputable and robust / professional assessment.
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The Wikibase allows users to add incidents, providing coverage of many more small aircraft incidents but may be less accurate. The safety index for each airline they cover is shown on their website. Entries go as far back as 1999, but the items are intended to provide information on accidents and an overview of the types of incidents occurring worldwide.
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Are there any models for planning aircraft placement in hangars? I work alone at night doing line operations (fueling, tugging/towing, etc.) and emergency services (police, fire and EMS) at my airport. When a pilot/customer comes in and wants to know if we have hangar space available for their aircraft, it would be nice when planning aircraft placement in those hangars to have figures to scale of various aircraft. That way you can see whether or not a specific aircraft can indeed fit, and in what configuration, before trying as I rarely (if ever) have a "spotter" or a wing-walker. Or perhaps even software or a computer program. Put in the hangar dimensions and which aircraft are to be placed. <Q> I’ve not heard of software programs to do this, but the Navy has made use of a relatively low tech solution to address this problem for decades aboard their aircraft carriers. <S> Known simply as the Ouija Board, the aircraft handler and his crew utilize a scaled physical map of both the carrier flight deck and hangar deck along with appropriately scaled footprint models of aircraft in order to track and plan aircraft movements. <S> I’d guess a similar scheme could be employed to solve your problems. <A> There’s at least one software solution that can be used to address this for a wide range of aircraft types. <S> The same or similar software products are also used for airport design. <S> They would, as far as I can see, very well allow to simulate hangar occupancy as well. <A> We solved a similar problem of optimization for a customer once which is an analog of this. <S> The exact algorithm used was simulated annealing. <S> If the same problem were presented today, there would be many competing alternative algorithms, generally in the class of genetic algorithms. <S> The problem of optimization presents itself in many aviation related activities, from packing aircraft, to routing aircraft, and in a recent instance, to optimizing dynamically flights in a battlefield, to factor in new situations, and adjust the costs and risks depending upon the rules established by command. <S> The interested person might start with an analog of the problem, which is the traveling salesman problem. <S> One might also consider watching: "The Secret Rules of Modern Living: Algorithms," a one hour movie on similar topics, where air traffic sequencing is discussed. <S> In short, the problem is trivial with a handful of planes to fit in a hangar, and grows rapidly as the numbers increase. <S> So much so that it rapidly becomes seemingly unsolvable. <S> Optimization algorithms generally do not find perfect solutions, but find approximations, which are practically close enough. <A> There is a program called Stax that runs on Mac, Windows, and iPad that probably does what you're looking for.
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In my old company, we have used a software called PathPlanner and looked at another one called Aeroturn to simulate aircraft ground manoeuvring.
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How much computing power is needed to keep commercial and military planes flying? I've always wondered, what sort of computing power is needed to keep modern commercial and military planes in the air? There are many systems of a modern commercial plane (e.g an Airbus A350), that would need to be automated and controlled by computer, one example that springs to mind is autopilot, another is flight instruments. Similarly I'm assuming that there'd be many systems (e.g fly-by-wire) that need to be controlled by computer in a modern military jet (e.g F-22 Raptor). What sort of computing power is needed to run commercial planes and military jets, and how do they compare to each other, and how does their computing power compare to the computing power of modern commercial CPU's? (Could my 2nd-gen Intel i7 CPU, with the appropriate hardware to make it into a PC, hypothetically be able to control all the automated systems on a modern commercial plane or military jet?) <Q> For commercial airliners: the computing power is set during development and certification of the type. <S> The A320 was developed in the 1980s and still uses Intel 80186 and Motorola 68020 processors. <S> Your i7 CPU would be able to run rings around anything on board of the average airliner. <S> But processing capacity is of secondary importance to airliners, safety and redundancy are in the limelight. <S> Image source Military planes are different, in that the requirements are more pressing and the accepted risks are higher. <S> Yes modern fly-by-wire planes use digital systems, however when the F-16 first came out with a fly-by-wire control system, it was a quadruple redundant analog system, with a digital processing requirement of zero. <S> These were upgraded to digital fly-by-wire in the block 40/42 upgrade in the early 90s, so again the fly-by-wire used pretty primitive processors by today's standards. <S> Generalising, the long development and certification/ready-for-mission time of aircraft systems means that any system on board uses processing power that is behind the latest-to-market specs. <A> Flight code is generally not cleverly designed to be efficient, but rather clear and simple, so an optimization rewrite can save some CPU time. <S> If you only have 1 processor, then you have no redundancy to worry about, no need to log faults or data redording since only one thing that can fail, only I/ <S> O needed would be directly from sensors and to controls/displays. <S> Leaves you with only the core functions to process. <S> This slims the processor load down by at least half. <S> Get rid of partitioned OS, TAWS, synthetic vision, controls channel b, assume external sensors and controls never fail <S> and maybe, just maybe, you (not me) could fly on a single multi core i7, for some peiod of time. <A> With a current processor power, Flight Management would be more than possible. <S> The mathematical operations in an automatic flight control system are quite simple (matrix multiplication, some transfer functions, some filters) for a cpu of today’s standards. <S> The trick would be to have a robust operating system (real time maybe), and to handle the <S> I/O <S> within the time window required for the control. <S> This answer assumes GPS and INS data are fused in a separate device, and actuator commands are driven through servo actuators. <S> Especially In military aircraft, and also in commercial aircraft several high frequency filters need to be included into the controller, to decouple it from structural modes. <S> This brings in more computational requirements, but would be easily handled by the processor, as long as the necessary data I/ <S> O does not choke the processor.
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Any processor capacity that can do the job is good enough, and is only the start of all the aspects that go into certifying an airliner including its systems.
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When a typical commercial airliner flies overhead, what is the actual noise we are hearing? We're all familiar of the sound planes flying quite high overhead and you hear a faint drone, even when planes are lower to the ground you hear them scream at a slightly higher pitch, but what exactly are you hearing? I would guess it's either the sound of the fan blades spinning extremely fast or the noise of the air (thrust) being forced out the rear of the engine? <Q> It depends on the type of operation: Approach (close to airport): <S> Much aerodynamic broadband noise from the air-frame Modern turbofan engines are less noisy than the air frame during approach. <S> But engines emit most of the tonal components in the sound. <S> Depending on the type of aircraft and angle of descent the pilot might need to use air-brakes to reduce speed. <S> That will cause turbulence and noise. <S> On some Airbuses you hear a typical high pitch annoying sound that is caused by air flowing across cavities under the wing (Fuel Over Pressure Protector to be exact, not from the engine). <S> Departure (close to airport): <S> Pretty much all the noise you hear comes from the engines, such as the buzzsaw noise generated when the tips of the fan blades reach supersonic speeds. <S> Hot high speed gases causes turbulence and that creates low frequency noise, especially behind the aircraft. <S> Overflight at 35.000-40.000 ft: <S> All the high and medium frequencies are gone because the air between aircraft and ground absorbs much of the sound. <S> The sound will also fluctuate due to differences in wind speed, humidity and temperature, along with the flight path and along the sound propagation path. <S> Further reading / sources 1. <S> Conference lecture by Prof. Dr. Ing. J. Delfs,Head of Technical Acoustics, German Aerospace Center 2. <S> ECAC doc 29 <S> (Technical documentation) 3. <S> An Overview of Aircraft NoiseReduction Technologies <A> Here's NASA Glenn's breakdown of the noise emitted by a typical commercial airliner with 1992-level technology. <S> Image <S> source <A> There are many great YouTube videos on aircraft noise reduction such as this NASA noise reduction program <S> It won't surprise anyone, the majority of noise during takeoff is the engines. <S> What is interesting is the engines are now quite enough that during landing, most of the noise comes from the wheels and flaps whistling and rumbling!
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What you hear is low-frequency broad band noise that originates from turbulence behind the engines.
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Why isn't the APU a standard diesel generator? Why isn't the APU a standard diesel generator? Jet-A and diesel are interchangeable (with the addition of a lubricant). So why not use a cheaper piston engine as opposed to a jet turbine? V.S. <Q> Weight. <S> Piston APUs for trucks are designed for frugal and quiet operation. <S> This one produces 5.2 kW electrical power and weighs 375 lbs. <S> The APU for the A320 and B737 is a noisy screaming unit that produces 90 kW electrical power, <S> 445 shaft kW. <S> It weighs 375 lbs as well. <S> The main difference is in the weight of the engine itself. <S> The turbine engine of the A320/B737 APU produces 445 shaft kW and weighs 145 kg. <S> This diesel engine also produces 450 shaft kW and weighs 1542 kg. <S> Power-to-weight ratios: <S> The turbine produces 3.1 kW/kg engine weight. <S> The diesel engine produces 0.3 kW/kg engine weight, it is a standard industrial machine and not optimised for weight. <S> The Rolls Royce Merlin was very much optimised for weight, it used aviation fuel (gasoline) and produced 1.58 kW/kg <A> Three words: <S> They’re much heavier. <S> Gas turbines have a very high power to weight ratio As opposed to reciprocating diesel engines. <S> So for the needs of an airplane which requires large amounts of electrical and hydraulic power in order to operate, a gas turbine makes a lot of sense for use as an APU. <A> You need to look at the overall picture. <S> Yes, a diesel is cheaper, but it will weigh more and be less reliable. <S> Also, the operating time of an APU is rather a small fraction of total airframe operating time, so it will mostly be a dead weight. <S> To arrive at a number representative of overall cost, add to the acquisition cost all the maintenance and all the fuel needed, not only for operation, but also for lugging the APU around. <S> If you need a handle on the weight-induced amount of fuel, use the Breguet equation. <S> Here is an answer where it is used to calculate the extra fuel needed to have windows in the fuselage, and here it is used for a partially loaded A320 . <A> A primary reason, aside from weight considerations, is that a gas turbine APU has a built in air compressor - the compressor stage of the turbine. <S> As such, it can supply air under pressure, or bleed air, just as the main engines can. <S> Bleed air is used for several purposes on an airliner. <S> It is used not only to pressurize the cabin while in flight, but also serves as an air conditioner or heater, as the climate dictates. <S> The APU can operate the climate control system on the airliner when the main engines aren't running. <S> Bleed air is also used to start the main engines. <S> One running engine can start all of the others - the main engines have a small turbine that uses the pressurized bleed air to spin the main turbine up to starting speed. <S> Or... the APU can also supply that bleed air. <S> It is not uncommon to use bleed air from the APU to start the main engines, such as when an airliner has shut down its engines while waiting on the taxiway due to extended delays. <S> In some cases, APU bleed air may be the only option: BA flight 9 used APU bleed air to restart its engines, when all four had been disabled by volcanic ash. <S> So one reason gas turbine APUs are used on airliners <S> is that they can supply the bleed air that is used for several purposes on the airliner, when the main engines are not running.
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A diesel generator would have to power a separate air compressor to do the same, and that's more weight, and another thing to break or need service.
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Why can a plane land in zero visibility conditions but not take off in zero visibility? After waiting hours for a flight departure delayed because of heavy fog, I wonder why planes can perform an instrument landing with no visibility, but cannot take off without a minimum visibility. <Q> Using a HUD, an airliner can take off with visibility as low as 300’, and land with visibility as low as 600’. <S> Without a HUD, you need 500’ (and appropriate runway lights/markings, plus regulatory approval) for takeoff, and whatever your autopilot Cat III autoland system (along with the landing runway) is approved to for landing. <S> (Or 1800’ for cases of no Cat II / Cat III capability.) <S> As noted, a pure “zero visibility” landing (a Cat IIIc) doesn’t yet exist, because while the autopilot can bring the aircraft to a stop on the runway, some visibility (300’) is still required to taxi clear and get to the parking spot. <S> Thankfully, visibilities below 500-600’ are pretty rare in most places. <S> That is an airport limitation, not an aircraft limit. <S> Talking about so many feet of lateral visibility, the actual nomenclature is Runway Visual Range, or RVR. <S> That is reported in feet in the U.S., and often in meters elsewhere. <A> Though your question does not explicitly say so, it implies that you're talking about flights that are carrying passengers or cargo for hire, and other answers address that. <S> However, taking your question as explicitly stated, in other words not just air carrier operations, and applying it to U.S. operations, the phrase: cannot take off without a minimum visibility is not always correct. <S> There is no takeoff minimum required for Part 91 operations (private aircraft if you will). <S> In the 2017 edition of https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/instrument_procedures_handbook/media/FAA-H-8083-16B.pdf , you will find on page 1-8 the following: <S> Aircraft operating under 14 CFR Part 91 are not required to comply with established takeoff minimums. <S> Legally, a zero/ zero departure may be made, but it is never advisable. <S> Takeoffs by corporate and personal aircraft without established takeoff minimums were common, though not frequent, in the rainy and foggy U.S. Pacific Northwest weather prior to my retirement, and I have no doubt Part 91 <S> operators still take advantage of that regulatory flexibility. <S> I made many such takeoffs without incident as did fellow corporate and personal pilots at my home field. <S> By the way, while everyone I think understands what they're saying when they say zero visibility, you can always see something, especially if you're sitting down low in a small aircraft. <A> They can take off at very limited visibility, and they do. <S> Key is then of course to make sure that no other aircraft are on the runway, and this is in fact how the deadliest crash in aviation history happened: the collision between two B747s at Tenerife Airport in 1977. <S> The accident was not caused by the reduced visibility alone, but as usual by a long chain of individual factors. <S> If all proper infrastructure and procedures are in place, take-off can take place in very low visibility. <A> When an aircraft lands in near zero visibility, it is a fully automated process that is actually done without input from the pilot. <S> The pilots are only needed to taxi off the runway and park the aircraft. <S> It is called "Autoland" and many of today's aircraft have it. <S> As of today no manufacturer has designed an aircraft with "Auto Takeoff" but I suppose it is not impossible. <A> I have departed in zero-zero conditions (twice.) <S> In both cases, there was another airport very nearby without this problem <S> and I was operating under Part 91. <S> The biggest danger in a zero-zero takeoff, after unseen planes/objects on the runway, is what are you going to do if the aircraft decides to malfunction on liftoff? <S> Lose and engine (or the only engine.) <S> Commercial operations have limits for this, and other, reasons. <A> Under Part 91 operations an aircraft can takeoff with zero visibility (however dangerous that might be). <A> Aircraft can, under certain circumstances, land in zero visibility conditions. <S> But this requires both the aircraft be equipped to fly a Cat IIIc ILS, approach. <S> The aircrew must have undergone specific training and certification to fly Cat IIIc instrument approaches, and the airport must be equipped with the infrastructure on the ground to support a Cat IIIc ILS approach. <S> As for conducting a zero zero take off, for revenue carrying commercial and charter flights conducted under parts 121 and 135, this is not allowed; minimum visibilities are 1 sm with 2 or less engines and 1/2 sm with more than 2 engines. <S> You may, however, conduct zero zero departures while operating under Part 91 regulations. <S> Zero zero instrument landings are flown by specifically designed auto pilot for this purpose.
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It all depends upon the equipment the aircraft has board, the infrastructure at the airport that is landing on, and the regulations under which the flight is being conducted under. Not all airports have the taxiway lighting required for low-visibility (typically, below 1200’ lateral visibility) taxi operations.
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Would an aircraft with no ailerons, no elevators and no rudders be safely flyable? With contrarotative propeller (or not, if twin engine), cyclic and collective blade control. Would such an aircraft be safely flyable, and how efficient would it be, assuming it can have perfectly smooth wings (and tailplane)? In case of engine stop (allowing axle free spin and control on blades), could it control its glide and land on the runway, with the propeller's blades in an almost feathered autorotation configuration, allowing attitude control and minimum disk drag? (like autorotating one reversed Kamov on its rotor-head, in a skydiving wind tunnel blowing a bit slower than terminal velocity) Edit: If it goes twin engine and tailless (and still controlesurfaceless) how active cyclic pitch control would be necessary to allow use of non-reflex wing's airfoil? Edit2:Switch from thrust + attitude control mode, to no-thrust + attitude control "reversed autorotation" mode.Reversed rotation allows most efficient use of blade's airfoil camber. <Q> An interesting thought. <S> Control the aeroplane through its propeller(s), like a helicopter does. <S> Propeller torque differential would control roll Propeller cyclic would control both pitch and yaw Propeller collective would control engine thrust, like already done in constant speed propellers. <S> The thing that immediately comes to mind is moment arm for pitch and yaw. <S> Helicopter blades are relatively long, and the rotor is mounted about halfway along the fuselage. <S> The prop is limited in its blade length due to ground clearance. <S> With a configuration like above, longer propeller blades can be mounted so the pitch and yaw moment arms can be extended. <S> As @Sanchises points out, placing of the propeller like this creates a coupling between pitch and thrust - not a bad thing, increasing pitch controllability by controlling thrust. <S> A strong nose wheel might be required for take-off. <S> It would be a bit draggy though, with the drag comparable with a parachute of the same diameter as the propeller. <S> Autorotation works best with a large blade moment of inertia, and the propeller would definitely not have the optimal blade length for that. <A> This will work as long as the propellers produce enough thrust and blade pitch can be adjusted fast enough to outrun all eigenmodes. <S> As soon as you need to throttle back (and eventually you must, to come down again), the control effectivity of the propellers will be greatly reduced . <S> Granted, you can float down in autorotation like an autogyro, but the landing will be more a crash than anything else. <S> Note that the Boeing V-22 Osprey is not capable of power-off <S> landings because the propeller inertia is too small to support the landing deceleration. <S> It can glide down in autorotation but cannot perform a soft landing. <S> Your configuration looks quite similar and will similarly not be capable of autorotation landings. <S> If you want to control the plane with propeller forces, the propeller must spin at high speed all the times to have sufficient thrust potential available when it is needed for stabilization. <S> For artificial stability you have no time to spin up the prop first! <S> Thrust is controlled by pitch only, but the higher-than-normal prop speed will cause its own inefficiency. <A> from an engineering design standpoint, the performance of (for example) a small aircraft like the seaplane pictured above is not in any practical sense limited by the presence of an empennage carrying an elevator and rudder. <S> For this reason, alternatives like cyclic pitch changes on the propulsion propellors have not been actively researched for pitch and yaw control.
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Not sure about your reference to the skydiving Kamov, but the aircraft could glide down after engine failure while keeping enough RPM to control cyclic.
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Why do some aircraft have symmetrical tip airfoils while others do not? On some aircraft, the tip airfoil is symmetrical, while others carry their root foil all the way through the tip. It would seem an aerodynamic disadvantage to have a non-symmetric airfoil at the tip since it is not making much (any?) lift. It doesn't seem to be simply for manufacturing purposes since it is on planes with tapered wings as well as straight wings. Why is it incorporated into wing design? <Q> Camber shifts the airfoil's section of lowest drag of the drag polar to higher lift coefficients. <S> In order to create the least amount of drag in level flight, an airplane wing benefits from moderate camber. <S> Most of the lift is created in the mid section, but enough lift is left towards the tips to justify camber there, too. <S> In case of elliptical or tapered wings, the design lift coefficient for lowest drag at a given lift will be equal over the whole span (elliptic wing) or <S> even peak near the tip (highly tapered and untwisted wing with no regard given to stall behavior or spar mass). <S> Normally the tips carry less load than the inner wing, details depending on wing taper and twist. <S> This helps to prevent the tip section stalling first at high angle of attack. <S> One example would be the Me-262 . <S> When Ludwig Bölkow designed the wingtip , very little was known about transsonic effects and a thin, symmetric airfoil with an elliptic nose was chosen because it showed a late onset of transsonic effects in wind tunnel tests. <S> When North American later designed the F-86 , the outer wing design of the 262 was copied over because it had worked well in the German design. <S> Many Horten flying wings used symmetric tip airfoils because the bell-shaped lift distribution needed for stability resulted in a slightly negative lift at the tips at low angle of attack and very little positive lift at high angle of attack. <S> With some designs <S> I a sceptical that a symmetric airfoil has been used even if it is claimed so in David Lednicer's outstanding collection . <S> The Lockheed P-3 is there listed with NACA 0014 at the root and NACA 0012 at the tip - no, <S> the Lockheed engineers 60 years ago knew better than that! <A> Generally you want a slightly less effective AOA at the tip to keep the ailerons working near stall. <S> A symmetrical section would do this if the root were flat bottomed. <S> You wouldn’t lose as much cruise speed compared to washout. <A> Symmetrical airfoils do not cause lift at all, because there is no pressure difference. <S> They lift just because of the angle of attack. <S> They are profitable on private jets because there is enough speed and the weight isn't large, so, symmetrical airfoils is enough. <S> That's maybe not right, but it's my opinion.
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Good aileron effectiveness also requires an airfoil which equally produces positive and negative lift at low drag.
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What is the "on condition" concept of aircraft maintenance? "On-condition" appears to mean that a component should be "fit until failure" or that the maintenance should only be performed upon failure of the component. This seems problematic. Can someone help me to understand why some components are handled this way and not as part of a regular inspection schedule of some kind? <Q> I'm not a maintenance guy, but you may be mixing 'inspection' and 'maintenance' together here. <S> An inspection helps you decide if maintenance is needed or not. <S> For example, inspecting the tire tread before every flight, or checking the cylinder compressions every 100hrs. <S> If the inspection shows that the condition of the item is still within acceptable limits, then you don't need any maintenance yet. <S> This is the 'on condition' or 'condition-based' approach , at least as I understand it. <S> Another approach is to do planned maintenance at fixed time intervals whether it's 'necessary' or not. <S> For example, replacing engine oil every 50hrs, or replacing the entire engine every 2000hrs. <S> In this case it doesn't matter what the item's physical condition is, you perform the maintenance even if everything looks good. <S> FWIW, some people strongly prefer the 'on condition' approach, especially for piston engines (see this book , for example). <S> But even they probably replace their oil at more or less fixed intervals. <S> If you want something more official, I found an FAA definition : <S> On Condition Item (Oc) <S> A primary maintenance process requiring repetitive inspection or test to determine the condition of units, systems or portions of structure to assure continued serviceability. <S> Corrective action is taken when required by item condition as determined by analysis of inspection and/or test results. <S> The key point as I understand it is that you base the decision to do maintenance (or not) on the physical condition of the item. <A> "On-condition" appears to mean that a component should be "fit until failure" or that the maintenance should only be performed upon failure of the component. <S> This seems problematic. <S> Only if there isn't a second unit of equal capability which can take over. <S> This is called redundancy and is the guiding principle in aircraft design. <S> You will not find an airliner with fewer than two engines or two tires per landing gear leg . <S> If one of them fails, the other is capable of maintaining the core functionality of both to bring the craft to a safe landing. <S> In case of single-unit designs (most GA aircraft use only one engine, after all), the safety concept is a low wing loading and minimum speed of 61 knots or less so an emergency landing can be performed easily. <S> In systems design, the goal is to have a gradual failure (" graceful degradation ") <S> so the flight can be continued even if that means temporarily a higher pilot workload or less than ideal flight characteristics. <S> The philosophy of aviation certification is to prove that fatal consequences occur less than once per 10⁵ flight hours to persons directly involved with control of the aircraft (pilots, in other words), 10⁷ flight hours to persons accepting the risk of flight travel but not directly involved with control of the aircraft (passengers, in other words) and 10⁹ flight hours to innocent bystanders (occupants of the house the aircraft is crashing into, for example). <S> If you can prove that on-condition maintenance will keep you above those numbers, the procedure is fine with the authorities. <S> You keep the unit running and monitor its condition in regular intervals. <S> The intervals are chosen such that the probability of deadly consequences due to the failure of both parts of any redundant system will be lower than the numbers cited above, and in case of single-component systems that the probability of failure with deadly consequences for one airplane relative to the flying hours of the whole fleet is lower than the numbers above. <S> The accident tolerance has been higher in the past for some aviation organisations, but in general we have managed quite well lately to surpass the required minimum level of safety. <A> On Condition are those items which, maintenance depends on certain Conditions being met. <S> The maintenance required can be determined based on the conditions being met, for eg. <S> If a part is being lubricated regularly, there would be less wear, and hence less replacement. <S> On the other hand, Condition Monitored items are those, on which we cant do any inspection to determine if it is wearing down or not. <S> Hence we monitor them for failures, and get them replaced when failed. <S> Thus called fit until failure items. <S> Common eg are avionics items. <A> An "On-condition" inspection is a non technical term, in other words it is not defined under definitions by the FAA in FAR 1.1 (Federal Regulations). <S> However, FAR part 147 Appendix A Par(a)(1) defines non description "inspection" ( <S> on-condition is a inspection) as "to examine by sight and touch" . <S> By exclusion from other types of inspection such as "destructive", "magnetic resonance", etc - "On-condition" is an inspection able to be accomplished by an A&P using their "sight and touch". <S> [jz pilot/A&P] <A> Maintenance tasks (inspections/checks) used to detect potential failures, and consequently to avoid a total functional failure, are called on-condition inspection in maintenance. <S> This is because machine are left in service on the condition that they continue to meet a desired physical condition and performance standards. <S> At specific periods, the condition of technical judgement to determine failure of the item will not occur prior to the next scheduled inspection.
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In simple terms, maintenance depends on the condition of the item, which can be determined by regular inspections, hence the 'On-Condition' term.
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How come nobody survived Air Moorea 1121, yet other people have survived crashes from altitudes more than 90x higher? Air Moorea 1121 crashed from no more than 400 feet, yet people have survived far more awful disasters, such as UA232 or JAL123. <Q> I'm guessing you consider your examples to be crashes from "90x higher" because the initiating events happened at high altitude. <S> This extra altitude was actually a good thing in these cases, because while the pilots lost most control of the aircraft, they were still left with partial control. <S> The extra altitude gave them plenty of room to figure out what was wrong with the airplane and how to control it with what was still working. <S> This allowed them to end up in more of a crash landing rather than just a crash. <S> United 232 was more of a crash landing. <S> Although the hydraulic systems were lost, the plane was still trimmed for level flight and the pilots could use the remaining engines to control the plane. <S> They had plenty of altitude and airspeed at the time of the engine failure to get the plane under control and figure this out. <S> This resulted in the crash landing where about 2/3 of the people on board survived. <S> Japan Air 123 was similar in that the aircraft lost hydraulics but they also lost most of the vertical stabilizer. <S> Again, this happened at a higher altitude which gave the pilots room to react to the issue. <S> The pilots still managed to fly the plane for a while but ended up crashing into the mountains. <S> The survival rate was less than 1% though this was partially due to delay in the rescue operation. <S> Air Moorea Flight 1121 lost its elevator control cable. <S> While the pilot could have used trim to control the aircraft's pitch, the airplane initially entered a dive and 400 feet was much too low to recover from this. <S> If the cable had broken at a much higher altitude it's possible the pilot could have regained control. <S> Another point to remember is that in a large airliner like the DC-10, the passengers have a lot around them to cushion the impact. <S> In a small plane like the DHC-6 <S> this isn't the case. <S> A crash into the water also results in a much higher impact, and any survivors would have to be able to swim free to the surface. <A> From 400 feet or 40000 feet the most important factors in surviving a crash are how fast you are going and how sudden the stop is. <S> In Morea 1121 the elevator cable snapped and the airplane became uncontrollable, pitching down and impacting terrain at high speed, the airplane came to a very sudden stop. <S> In UA232 the airplane was still controllable to a degree, the pilots were able to get the airplane close to the ground and when it crashed the energy was dissipated over a longer period of time. <S> The fuselage of UA232 was able to absorb some of the energy and protect some of the people on board. <A> The aircraft nosed over and dived into the ocean at full power. <S> The loss of pitch control was caused by a snapped elevator cable. <S> If the cable had snapped at a higher altitude, the pilot may have had time to use the elevator trim tab to regain partial pitch control and not crash with such severity. <S> Those other accidents you mention were very different. <S> In both cases the loss of control started at high altitude and the pilots had enough time to establish partial or limited control. <S> They were able to maintain some control up until the time of impact. <A> There's a simple physics principle you need to keep in mind <S> Increase the distance, decrease the force <S> The aircraft in question cruises at about 200MPH . <S> It nosedived into water (which probably accelerated it some). <S> At that speed, water acts like a solid A good way to think about high-velocity impacts is not in terms of things (like water) acting more solid, but in terms of things (like people, rocks, Fabergé eggs) acting more fluid. <S> The more energy that’s involved in a collision, the less important the binding energy (the energy required to pull a thing apart) is. <S> A general, hand-wavy rule of thumb is: if the random kinetic energy of a piece of material is greater than the binding energy, then the material will behave like a fluid. <S> A bit more energy, and it will fly apart. <S> So, when you fall from a great height and land in water there’s a bunch of kinetic energy going every which way. <S> The water continues to behave like water, but since the kinetic energy in different parts of your body are greater than the binding energy keeping them connected, then the body as a whole will act more like a fluid. <S> That is; it’ll “splash” (in the grossest sense). <S> In other words, the impact victims took the brunt of the impact energy themselves, thus destroying their bodies (i.e. they died). <S> Had the pilot leveled off before hitting the water, the water would have absorbed far more of the aircraft's energy. <S> This is why, for instance, United 1549 had no fatalities. <S> In this recreation (relevant portion starts about 3:00) you can see the aircraft enter the water parallel to the water and slow down.
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In airliners that really do crash from higher altitudes, there are no survivors. Air Moorea 1121 was unsurvivable due to the high G forces of the impact with the water. The impact G forces were therefore far less and were survivable for many of the passengers.
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Can a small GA plane maintain level flight with a significant nose-down attitude? Consider a small, one- or two-seater motor GA aircraft, something like a Cessna 152 or similar, designed for level flight at roughly neutral pitch. It's certainly possible to fly such an aircraft in a nose-high attitude while maintaining altitude, by careful use of pitch and thrust. I'm not sure I'd want to do that for any significant length of time, but as long as the angle of attack is kept below the critical angle for the current aircraft configuration, I can see no aerodynamic reason why it can't be done even in the general case. But is it possible to fly it in a significant nose-down (say, several degrees or more) attitude while maintaining altitude ? My gut feeling says no; no matter what else you do with the aircraft in such a nose-down attitude, you're going to be losing altitude. But I've been surprised before, so: is there a way? <Q> I may have misunderstood the question <S> but I think the answer may be... <S> flaps . <S> Wing flaps will increase the lifting ability of the wing and at a constant airspeed the nose will need to be lowered to maintain a particular altitude. <A> Beyond a very small angle, a nose-down attitude means a negative AoA, and lift will be negative. <S> A nose-high attitude is different, because lift will be always positive, even beyond the critical stall angle, and for some airfoils, that lift may be quite significant... <A> It depends on the angle of the wing chord line relative to the fuselage and also on the current vertical component of the wind. <S> and/or if the mass of air through which the aircraft is flying is rising. <S> As user2209250's answer alludes to, dropping the flaps is one way to increase the pitch of the wing chord line relative to the fuselage, possibly allowing the wings to have a positive AoA even while flying level with a nose-down attitude. <S> Especially for larger flap extensions, many airplanes will likely require a nose-down pitch in order to maintain level flight with a full thrust setting. <S> Of course, most airplanes are designed such that you will not be able to maintain a positive angle of attack with a very steep nose-down attitude in level flight in a non-rising mass of air, but shallow nose-down attitudes are certainly possible. <A> As long as the wing (the whole aircraft) has lift, theoretically, with higher speeds the pitch should go lower and lower. <S> This means with full thrust, keeping the altitude constant, time will show how nose-down the aircraft can go.
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A normal light GA airplane will not be able to fly level with a negative angle of attack , but it can fly level with a nose-down attitude if the wings themselves are pitched upwards relative to the aircraft fuselage
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What is the maximum G load a 747 can withstand during an emergency course reversal? In an emergency course reversal, passenger safety first priority, to avoid say, a column of ash from a new volcano, what it the most G a 747 can withstand with an average passenger complement? <Q> It depends on how you define :withstand". <S> China Airlines flight 006 experienced vertical load factors of up to 5.1 g on 19 February 1985. <S> The aircraft could be landed safely and there were no fatalities, but there was considerable damage: Image source From the NTSB incident report: <S> The wings were bent or set permanently 2 to 3 inches upward at the wingtips; however, the set was within the manufacturer's allowable tolerances. <S> The left aileron's upper surface panel was broken and the trailing edge wedge was cracked in several places. <S> The maximum load factor an aircraft can be subjected to is a function of time. <S> Two cases are determined for civil aircraft: <S> Limit load factor. <S> For transport aircraft weighing more than 50,000 lb(22,680 kg) <S> this load factor is equal to 2.5, while for lighter aircraft it is a function of the weight. <S> Ultimate load factor = 1.5 times limit load factor, is the higher of the gust and the manoeuvre load factor. <S> The load factors are determined in accordance with the airworthiness regulations 14 CFR part 23.341 and 14 CFR Part 25.341. <S> Damage tolerance of the airframe and the consequences of metal fatigue are stated in 14 CFR part 25.571 . <S> The B747SP of the incident is an aeroplane that was designed and constructed in the 60s/70s, before Computer Aided Design and engineering were wide-spread, and the structures were designed with analytical mathematics and knowledge from experience, then tested for limit loads and ultimate loads. <S> The more the design stresses can be modelled on a computer screen, the closer the wing ultimate load can be to 150% of limit load. <S> Older aeroplanes did not have these modelling tools, and wings could end up to be stronger and heavier than they needed to be. <S> Something that everybody applauds, but nobody wants to pay for with a higher ticket price. <S> A video of the B777 shows how the static testing for ultimate load is done: an actual wing is bent until it breaks. <S> It is not a test of wing flex, it is a test of static strength. <S> The particular 747 of the incident had a wing designed for an MTOW of 378,000 kg, while actual MTOW of the 747SP was 320,000 kg: an extra load factor of 1.18. <S> Fuel in the wing tanks provides extra bending relief, not for the ailerons though.. <A> Googling EASA CS25 should show this for European-certified aircraft. <S> The same design requirements furthermore specify that the structure must withstand loads in excess of these, but I am not quite sure as to the actual factors. <A> In clean configuration, as has already been said, it's +2.5 / -1g, this is called limit load. <S> Then you add on a 50% factor to yield the 'proof load', or ultimate fail load, which is proven in destructive testing. <S> But it's important to remember though, bits break by force, not G. G is just acceleration. <S> So you have to multiply it by the aircraft weight to yield the shear force that breaks the wing root, spar, or whatever. <S> That's why the limit load is applicable at <S> Max Take Off weight. <S> And also why a glider or aerobatic aeroplane can pull more G, because multiplied by the mass, the ultimate force applied to the components is lower.
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Civil aircraft certification requirements for airliners demand normal operations be possible up to 2.5g and down to -1g in clean configuration up to design manoeuvring speed, reducing above that speed. There have been accidents where design operational loads were exceeded which still ended with a safe landing.
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What is the purpose exactly of a ‘Control Check’? I recently watched an Air Crash Investigation episode where Qantas flight 32 lost an engine shortly after takeoff. It was revealed that a stud pipe in a Rolls-Royce engine was made incorrectly, causing the pipe to snap and burst through the engine and the aircraft's wing, severing major hydraulic systems, and causing the ECAM to display pages and pages of errors. On the final approach, the captain announced he wished to perform a ‘control check’. He said (and this is approximate): When the aircraft is damaged, you have to certify it is safe to land before you try to land. I assume this is so that the captain can make the necessary preparations if he feels his aircraft is not safe to land. On flight 32 this was done by moving the stick left and right to simulate lining up with the runway. Perhaps a better question is back to the post's title. What are the purposes of in-flight Control Checks? In my example of Qantas Flight 32, the stick was moved left and right on final approach to simulate lining up with the runway. This was only small left and right control deflections. The flight deck had only minutes until landing. What was the captain expecting to see, or not to see? Can the captain after that brief manoeuvre be aware of his aircraft enough to make a decision? Does this mean then that a Control Check only comes, or should only be done, if you are worried that the aircraft cannot land ? Can it be done at any other time? In other words: is an in-flight control check only done for landing? SOURCES: Wikipedia Flight 32: https://en.m.wikipedia.org/wiki/Qantas_Flight_32 <Q> Technically speaking, a control check is part of any pre-flight. <S> In the case of Qantas 32, one engine had exploded, punching holes in the wing and setting off a host of warnings, so there was a reasonable expectation that some of the controls might also have been damaged. <S> What the pilot did was put the plane through some basic maneuvers to see how the controls responded in their now potentially damaged form. <S> And found that roll rate had been affected, something he factored in on the subsequent landing. <S> He also found that pitch control had not been affected, which meant he could make a reasonably conventional approach to the runway. <S> Better to find out how much the controls had been affected when there is time and altitude to recover from an unexpected response, than to find out on final approach, where the margin for recovery is very slim to none at all. <S> During flight, this is not normal. <S> It is prudent if an inflight incident may have damaged some of the controls, so that the pilot knows the level of controllability they have to work with. <A> Why controllability checks matter <S> The procedure you're referring to from the QF32 mishap is called a "controllability check". <S> The controllability check is different from an ordinary control check in that while a control check is looking only for flight control motion, range of motion, binding, or free-play, a controllability check evaluates the airframe's response to control inputs in-flight at various speeds, typically from a stable clean speed at 10,000' down to a normal landing Vref if all is functional. <S> Flap and gear extension will also be tested if possible as part of this exercise due to their impact on aerodynamics. <S> Of course, if the controls start getting too close to full deflection during what basically is a mock landing approach, the pilots will knock it off and accelerate back to a safer speed, cleaning up the airplane if possible. <S> As a result of this, the pilots could determine what impact the damage had on airplane handling. <S> For instance, damage to a wing or wing control surfaces could have an impact in roll, while damaged or missing engines can be problematic at low speeds in roll and/or yaw. <S> Tail damage will often manifest itself as pitch control issues, but sometimes can be a yaw problem instead. <S> A load shift or other C.G. issue will also show up as pitch control trouble at low speeds. <S> A good example of a flight where one should have been performed was El Al 1862. <S> Had they performed a controllability check, they'd have noticed that the departure of engines #3 and #4 from the aircraft, as well as the loss of the right outboard aileron and right leading edge devices, had effectively jacked their Vmca up sky-high. <S> With this knowledge in hand, the crew could have recalibrated their expectations, shooting a partial flap approach at a much higher Vref speed to a choice of runway that gave them more favorable winds as they could still maintain flight at this higher speed and would need the headwind to help slow down after landing. <A> Aircraft control their flight using movable portions of the wing and tail called control surfaces; a control check is a check performed to make sure that they're capable of moving through the range of motion that they're expected to be capable of moving through. <S> In the case of small airplanes, they're connected to the control column directly through the use of small cables, but in large airplanes, they use electrical sensors in the avionics to create electrical signals that then control hydraulics in the wings and tail that move the control surfaces. <S> In the case of the Qantas plane, the damaged engine might have damaged the control surfaces or the fluid lines that power the hydraulics, so they carried out the check to figure out how much functionality they had so that they could get an idea of how damaged the plane was, and how it would control as they came in for an emergency landing.
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While a standard control check is done as part of a ground preflight to make sure that the flight controls work well enough to fly, a controllability check is an in-flight operation, performed either as part of a functional check flight or, more importantly, after the aircraft has sustained damage .
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Why do airplanes use MAYDAY when in danger but ships send SOS? I thought SOS means "save our souls", but apparently it doesn't. But ships send SOS when in danger and they used Morse code. Why do airplanes use MAYDAY? <Q> The difference here isn't between ships and aircraft: it's between Morse code and voice. <S> The SOS signal is only for Morse code. <S> It's short, easy to send, and easy to recognise. <S> But it's not as convenient to say. <S> It doesn't actually mean "save our souls". <S> The letters were chosen just to form the simple Morse pattern, and "save our souls" is a backformation : it was made up by sailors later, partly as a joke, partly as a mnemonic. <S> "Mayday" is an English-looking spelling of French m'aidez , "help me". <S> It doesn't have any sounds that some nationalities can't say (such as r , th , or v ). <S> It's a good signal to use as voice, but would be much worse as Morse code, because it's too long. <S> Back in the days when aircraft were equipped with Morse code transmitters, they would have sent SOS as a distress call, just like a ship. <S> And a ship with voice radio would send "Mayday" instead of SOS. <S> Now that Morse code has fallen out of use, SOS is also disused. <S> You only hear it in movie plots where the plucky hero doesn't have a working radio but can somehow improvise a way of signalling Morse code (usually by holding two wires together on a broken radio). <A> Ships use Mayday. <S> This is the transcript of M/S Estonia disaster from 1994, a major passenger ferry sunk. <S> 01:23.11Estonia> Europa, Estonia. <S> 01:23.15Estonia <S> > <S> Silja Europa, Estonia. <S> 01:23.19Europa <S> > <S> Estonia, this is Silja Europa replying on channel 16. <S> 01:23.27Estonia <S> > <S> Silja Europa <S> * 01:23.34Europa <S> > <S> Estonia, this is Silja Europa on channel 16. <S> 01:23.55Estonia <S> > <S> Silja Europa, Viking, Estonia. <S> 01:23.59Mariella <S> > <S> Estonia Estonia. <S> 01:24.02Estonia <S> > <S> MAYDAY MAYDAY. <S> 01:24.07Estonia <S> > <S> Silja Europa, Estonia. <S> 01:24.10Europa <S> > <S> Estonia, Silja Europa. <S> Are you replying— calling Mayday? <S> Source: <S> http://oona.windytan.com/estonia/ <S> You can also listen the same in Youtube: SOS is for morse code, Mayday for voice. <A> Merely being a ham operator for 58 years, this is my understanding. <S> "SOS" means nothing. <S> It's easily sent and easily copied (understood), and it follows "CQD" which was also used on the Titanic. <S> CQD is most aptly "COME QUICKLY DISTRESS" (the D has various meanings / uses). <S> The senior radioman on the Titanic told the jr. to go ahead and try the new call. <S> As an aside; a young Welsh lad, about 15 being a young ham, heard the Titanic's distress call, sic (ITS A CQD DE MGY CQD DE MGY SOS AM SINKING HAVE STRUCK A BERG). <S> ("DE" means <S> from,- <S> MGY is the TITANIC'S <S> Marconi owned wireless station call letters). <S> He copied the text and went to the local police. <S> When he told them, they laughed at him saying sic. <S> ("the Titanic is unsinkable, go home"). <S> They were surprised the next morning to hear / read the news. <S> MAYDAY is from a French word "French "m'aidez", "mayDAY," [one word], and means in actuality - "help me". <S> It is a short form of venez m'aider - come and help me'. <S> This first URL is a simulated spark gap transmission. <S> The second is an exchange between the Titanic and the Carpathia.
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Spoken out loud, it's short, easy to send, and easy to recognise.
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Who checks that pilots have their licenses? One weird thing came to my head In the ground, Every time you drive an 91 CRX SIR/Civic Si EM1 or ride an Honda Dirtbike There is an possibility of getting busted by the cops waiting in the temporary checkpoints But what about the air? Who will check (Non existent) licenses of DC-3/Bell 47GH pilots? Who will check (Non existent) licenses of C208B Grand Caravan Amphibian pilots on the sea? Who will check people that flies alone in a Learjet 35 during IFR conditions? (I know, there are countries that you can do IFR flights alone) Do you tell your license information to the ATC before the takeoff or there is an another way like authorities requesting flight logs of an C208B etc? <Q> Just as people can go for quite a while driving without a license before they get caught, there is no certain way to catch somebody who goes flying without a license. <S> There are various ways that it can happen, but none of them are certain. <S> There was a quip quoted elsewhere referring to the high proportion of unlicensed pilots in Alaska, that supposedly the FAA had a goal of getting at least half of them licensed. <S> I have no idea how much, if any, truth is behind that statement. <S> On the other hand, just as having a license can make various things you might do with a car easier or possible, there are plenty of instances where having a pilot license is necessary: Renting a plane <S> Buying insurance for a plane you own (without a convincing story of who else would be flying it, at least) A "ramp check" by an FAA inspector Getting a job (from a reputable company, at least) as a pilot If you file a flight plan for your flight (required for IFR -- mostly, not required but very highly recommended for VFR), part of that is to provide a name for the pilot. <S> But that's it, just a name, not a license number. <S> (Phone number, yes <S> -- so they have somebody to call in case <S> you're overdue so they can see if you simply forgot to close your flight plan.) <S> I don't know how often that info would be checked against any database of current pilots, but the potential would be there. <S> But the ways the FBI would find people in an investigation is wildly different from what's routinely done by Flight Service. <S> So if Farmer Joe (licensed) owns an airplane & his (unlicensed) brother <S> Fred flies it every now and <S> then from their private dirt strip, the chances of Fred getting caught are probably pretty slight, unless something goes pretty badly wrong. <S> And, depending on Joe and Fred's tolerance for risk, they might be entirely okay with that scenario. <S> Me personally, there's no *% <S> # <S> @ing way <S> I'd be party to any such arrangement, but I'm probably more cautious than some Alaska bush pilots that way! <S> This thread discusses the consequences for flying without a license. <A> I've heard of the FAA conducting ramp checks but never experienced it myself. <S> Licensing is for knowledge, knowledge leads to safety for you, your passengers and those on the ground and their property. <S> Small craft that don't do much damage don't require the license, part 103 for example <A> it depends on whether or not your plane carries hull insurance. <S> No insurance underwriter is going to knowingly insure an aircraft given that its owner is unlicensed and pilots the craft. <S> This means that the FAA might not care whether or not you have a license, but your insurance agent almost certainly will.
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I've only experienced being checked when there was an accident, and FAA was investigating I've asked this same question of pilots in the past and gotten rather comical responses, like "as long as you don't crash the faa doesn't care" and things of that sort.
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Is it possible for a civilian to use a VORTAC station? Suppose you have a Cessna 208 Grand Caravan Amphibian and you want to use VORTAC stations on military bases (or somewhere else). Is it possible? Is it legal? <Q> Totally legal to tune it up & use it. <S> If it is a VORTAC, it will work just like every other VORTAC out there. <S> If it is a TACAN, you may be able to get DME from it, but you won”t get bearing from it without a TACAN receiver. <S> Many, perhaps most VOR’s out there are in fact VORTAC’s <S> — the TACAN station is colocated with the VOR. <S> It is possible to have a VOR-DME station, which gives a civillian user everything a VORTAC does, but no bearing info to TACAN-only military aircraft. <S> And you can have a VOR station with no associated DME at all. <S> But you won’t find any rule prohibiting you from tuning up any of the above - doesn’t exist (at least in the U.S., nor anywhere else I’ve ever heard of). <S> If the military wanted a NAVAID they could use that you couldn’t, they could put up a TACAN using a channel that civillian DME receivers can’t pair with (ex ch 16X “pairs” to 135.9 - not a frequency in the range civil VOR receivers can tune to) and not publish it. <S> But realistically, they’d probably just use a GPS coordinate & call it good. <S> (Edit: as @UnrecognizedFallingObject mentioned, it is not the “Y” TACAN channels that conventional VOR receivers can’t pair with, but there are some channels you can’t get DME from using normal VOR tuning — see this chart .) <S> Flying over that navaid on a military base may entail issues with the airspace involved, but that is its own issue, unrelated to using or not using the navaid. <A> Absolutely. <S> A VORTAC is nothing more than a VOR colocated with a TACAN. <S> Most VOR-DMEs in the US are VORTACs. <A> Short answer : <S> A VORTAC station combines a VOR-DME and a TACAN. <S> It is the result of a cooperation between civil and military worlds to share the same DME (and the navaid place). <S> Civil aircraft use includes accessing the VOR part (civil), the DME part (civil and military), but not the TACAN bearing transponder, said otherwise they access the VOR-DME equivalent, or for what civilians are concerned, a VORTAC is a VOR-DME. <S> They are not equipped for receiving the TACAN bearing equipment, though nothing prevent them to be equipped with the related UHF receiver. <S> More details : <S> A VORTAC station is composed of three signal generators: A VOR (VHF) signal used for civil bearing determination. <S> A DME (UHF) signal used for range determination <S> An UHF signal used for military bearing determination, in theory 9 times more accurate than a VOR. <S> DME and UHF bearing station components are interrogated by the aircraft, contrary to the VOR which broadcasts continuously. <S> When civilians use a VORTAC, they actually use the two first signals (VOR-DME). <S> Military use the two last signals (TACAN) and the VOR as a backup if they are equipped, which is normally the case. <S> Pure TACAN have only the UHF bearing determination signal and the DME signal. <S> Source <S> Their little size, compared to a VOR-DME , allow them to be used on ships. <S> More: Wikipedia article on TACAN , and How does Tactical Air Navigation work?
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If there happens to be one located on a base you are certainly still able to use it.
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Is it legal to fly under the Golden Gate Bridge? I recently had the opportunity to rent a plane and fly in the San Francisco Bay Area. While flying in the HWD/OAK/SFO area is challenging enough, when I spoke of my adventures of flying above Alcatraz and the Golden Gate Bridge, some of my fellow pilots asked me if I flew UNDER the Golden Gate Bridge and voiced their desire to do so. As a relatively new pilot (3 months), while flying is definitely an adventure for me, flying under a suspension bridge is pushing my minimum safety limits and just does not seem lawful. Others have told me that they have seen GA aircraft fly under the bridge. While I'm sure pilots have done it...I don't see how this can be legal. According to sources on the internet the bridge is only suspended 270' above the bay. It doesn't seem enough space to fly through legally. According to 91.119 Except for takeoff or landing, no person may operate an aircraft below the following altitudes; a. Anywhere . An altitude allowing, if power unit fails, an emergency landing without undue hazard to persons or property on the ground. c. Over other than congested areas . An altitude of 500' feet above the surface, except over open water or sparsely populated areas . In those areas the aircraft may not be operated closer than 500' to any person, vessel, vehicle, or structure. To me, 270' does not meet the legal requirements set in 91.119(c) I don't consider the SF Bay or water under the bridge to be "open". So, is it legal to fly under a suspension bridge like the Golden Gate or Verrazano-Narrows Bridges? <Q> No, it would violate regulations unless it was to meet the needs of an emergency. <S> Don't forget the catch-all regulation about reckless operation; many regulations may be interpreted very subjectively, and I feel that it is safe to say that flying under the Golden Gate bridge would attract a lot of negative publicity and would ultimately be considered something that the pilot of a fixed-wing aircraft would certainly be reprimanded for. <S> That's not even considering whether the bridge is 500 feet high, boats that may or may not be passing under the bridge, and your question completely truncated the 91.119(b) <S> that lists information for congested areas, which I am almost certain <S> the Golden Gate bridge would be subjectively qualified as. <A> like that would yank your license in a heartbeat. <S> §91.13 <S> Careless or reckless operation. <S> (a) Aircraft operations for the purpose of air navigation. <S> No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another. <S> (b) Aircraft operations other than for the purpose of air navigation. <S> No person may operate an aircraft, other than for the purpose of air navigation, on any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo), in a careless or reckless manner so as to endanger the life or property of another. <S> They are all experienced aerobatic pilots with thousands of flight hours doing low altitude demonstration flying under their belts and have specific permits issued by the FAA in order to make these kinds of demonstration flights. <S> THEY ALSO UNDERSTAND THAT THIS KIND OF FLYING IS INHERENTLY RISKY, HAVE CAREFULLY PLANNED THE STUNT IN ADVANCE <S> PRIOR TO EXECUTING IT <S> AND ARE WILLING TO ACCEPT THESE RISKS <S> AS PART OF THE PERFORMANCE. <S> If your attempt results in an accident causing loss of life you can face severe civil and criminal penalties for wrongful death and manslaughter. <S> If your friends are suggesting you do it, they’re idiots. <S> Don’t try it. <A> It is not illegal, but it is a violation of FAA regulations, which could result in various civil penalties. <S> You quoted the violation yourself: you are not supposed to fly closer than 500 feet to any building or structure, unless engaged in specific activities, like crop dusting. <S> The deck of the bridge is about 250 feet above the water, so you would definitely be too close.
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If you are found to have done this you will be sanctioned and potentially lose your license. It’s illegal under 91.13 and any FSDO inspector who found out you did a damn fool stunt On rare occasions pilots have flown under bridges and other structures as part of demonstration flying.
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How to perform a "first principle" performance calculation? I am a PhD student on flight dynamics and control. This week I was given an assignment to do some research on methods of aircraft performance calculation. After some search on the Internet, I found that traditional methods depended on tabulated data on the airplane flight manual (APM), and about a decade ago, both Boeing and Airbus started to do performance calculation using "first principle" method. I read on an Advisory Circular document that provides a definiton of this method: A calculation using basic parameters such as lift, drag, power or thrust, etc. with the equations of motion. ( AC No: 25.1581-1, Change 1. ) And an Airbus document gives some explanation on this method: The next step in the performance calculation process, referred to as OCTOPUS (Operational and Certified Takeoff and landing Universal Software), not only offers the same advantages as TLC but also drastically changes the performance calculation method. It is no longer based on pre-computed data, but uses the “first principle” mode that allows a real on-time computation to benefit from a higher takeoff weight. Instead of smoothed pre-computed performance results, the OCTOPUS performance database contains all the airplane and engine characteristics, enabling performance computation based on physics equations. In addition, OCTOPUS introduces a new and improved takeoff chart format, with its use of multi-configurations and influences. (" Getting to Grips with Aircraft Performance ", Airbus) However, I have not found any paper or report on this topic. Is there anybody out there who could help by offering some details of this method, or, providing some references? <Q> The equations of motion are the easy part. <S> In essence, you look at all forces affecting the aircraft (lift, thrust, drag, weight) and balance them with proper control settings (elevator, throttle) and accelerations ( <S> if thrust <S> > drag, the forward acceleration is (thrust - drag)/mass). <S> This you repeat over and over, one timestep at a time. <S> The next timestep sees the aircraft at a new speed, which you get by multiplying the forward acceleration with time, and altitude if the climb speed is nonzero. <S> The new, changed mass is the old mass minus the fuel consumed during the last timestep. <S> And so on. <S> This involves coordinate translations as some forces are defined in the aerodynamic and others in the airplane coordinate system. <S> NASA Langley has published an open source software which does exactly that ( LaRCsim ). <S> For very high precision you can even model the inertias and calculate which aileron deflection is needed to arrive at a desired roll rate in the next timestep, but even without that you will get very precise data if the forces are correct. <S> The hard part is to arrive at the correct forces. <S> We have had several questions here asking for the aerodynamic data of modern airliners, and every time the answer was: They are kept secret. <S> You need to do your own analysis, and it is the same with engine data. <S> Older methods relied on tabulated data, but in order to calculate conditions outside of the validity of the table they need to calculate the forces analytically. <S> To get an idea what parameters need to be considered, look at this answer about the Boeing SCAP module . <S> However, even some crude assumptions can get you very close to the real result. <A> It's the aerodynamic and inertial data also used in Full Flight Simulators (FFS). <S> Both Airbus and Boeing provide the data package for Level D FFS, where at the beginning of the flight the instructor enters payload, CoG, fuel load etc and the resulting aircraft dynamics are used for simulating flight. <S> Simplified and not certified of course <S> so no reference to actual fidelity, but they should get a reasonable result if the simulated dynamics are in the ballpark. <A> Unfortunately this requires a lot of information on aircraft characteristics (e.g. drag data or engine parameters) that generally aren’t published for most aircraft due to their business sensitivity. <S> Sidenote: Estimates can get you pretty far! <S> Manufacturer provided software like OCTOPUS (Airbus) or BPS (Boeing) contains a method of numerically evaluating the (often simplified) equations of motion and the required aircraft databases but aren’t publicly available to the best of my knowledge.
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You could have a look in open source PC flight simulator software such as FlightGear, which has aerodynamics and flight dynamics models for both A320 and B737. The only way to properly do a „first principle“ calculation is by (numerically) evaluating the basic equations of motion found in flight mechanics text books.
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Could a golf ball damage an airliner? Question Would a golf ball ingested into an engine, or impacting a windshield cause meaningful damage to a commercial airplane? The scenario below outlines that this is possible, but the principle question is: would it actually matter, as in, would it cause the same level of damage as, say, a strike from a single bird? Plausible Scenario At McCarran airport in Las Vegas (KLAS), runway 1R is situated just across the street from a driving range. Several years ago, I was hitting balls on this range when a 747 landed on 1R. It seemed impossibly low; many people on the range stopped hitting to point and take pictures. For context, here's a video (not mine) taken from nearly the exact same spot, with an approach to the same runway. At the time, I remember thinking "That plane is very low... what if it got hit?" Appearances are often deceiving, so my initial assumption was that it must be higher than I thought, so a did a bit of basic trig to find out: The touchdown markers on 1R are about 4,250 feet (red line in picture below) from the top-level hitting stations. With a 3 deg. glide slope, the plane would have been roughly 225 feet above the ground when passing over the driving range (slightly lower down range when balls that have been hit are at their highest point). (Image: Google Earth; own drawing) With a 21-degree 7-wood which I hit about 200 yards, the ball would reach an apex of around 230 feet. So, wind, timing, and the quality of golf shot actually struck notwithstanding, it seems at least possible that a ball hit from off that range could hit an airplane. In other words, the "bounding box" of the plane at least theoretically intersects a line representing the maximum height of a shot from the driving range. Thus, it seems unsafe, even if the chance is 1:1,000,000 (or greater). I have to assume that since KLAS is one of the busiest airports in the U.S., that this is not actually an issue, otherwise changes would already have been made. However, if an impact or ingestion were to occur, are there circumstances where it would be a "significant" event? Notes No one, esp. myself, was trying to hit the plane. Despite #1, there are at least 50 hitting stations, which means lots of shots in the air as the plane is passing over the range. This is Vegas, and alcohol is served at that range. People do try, sometimes, to hit the guy in the little range car. I doubt that would ever carry over to a plane, but it can't be logically ruled out. My concern is that even without anyone trying, a ball could still impact the plane. But would it matter? <Q> Turbofans on commercial airliners are tested against hail, up to 'golf ball size', and ice is harder than a golf ball. <S> Think back to Taca 110, that lost both engines while descending through a hailstorm reported to be up to golf ball size. <S> What killed the engines wasn't the impact of the hail, but the amount of water ingested into the engines. <S> It seems that the engines had been tested for water and hail ingestion at cruising speed... not at near idle, which was the power setting during a descent. <S> Once identified, that problem was rectified quickly with mods to the engines. <S> Nor does the golf ball have the sheer mass of a goose, such as the flock of geese that took out both engines of USAir 1549. <S> Most likely, a golf ball striking a running turbofan would be sliced up by the front fan, and centrifugal force would tend to fling the fragments outward where they would exit via the bypass, and not through the turbine engine. <S> The greatest problem from a golf ball being ingested by a turbine, is figuring out what rule of golf applies... <S> how do you mark your card? <S> (WTF probably doesn't meet approved guidelines) <A> Is there a risk? <S> Possible <S> but I'd say negligible. <S> A typical champion golfer can drive a golf ball with a departure velocity of about 150 mph or so from the tee. <S> That's <S> fast but atmospheric drag quickly slows the ball down to around 50 mph or so by the time of impact back on the turf. <S> Golfball drives from even the best athletes only gain about 90 feet of altitude during a typical drive, making it highly unlikely that that a drive could launch a ball to even the ILS decision altitude of 200 feet AGL. <S> With a typical jetliner flying an approach at 140 knots (161 mph), it's highly unlikely that a golfball could catch up to the aircraft in flight as well. <S> But even if you cold drive a golf ball with a herculean effort, as any anti aircraft artillery gunner will tell you, <S> it's extremely difficult to hit a moving aircraft using unguided fusillades. <S> Golfers have enough trouble aiming for a putting green, taking into account position, obstacles, winds, etc. <S> to have to add in the additional difficulty of hitting an airborne and fast moving object as well. <S> Now should a golf ball hit an airplane, <S> yes there is a change to damage it similar to an errant drive hitting a car. <S> Superficial dents or scuffs would be anticipated. <S> It might damage an aircraft window, though I highly doubt it would shatter, particularly windows on pressurized aircraft. <S> Golf balls ingested into engine intakes and or propeller arcs would be pretty hazardous for the aircraft as well. <S> So who knows, maybe someone here can dig up a wild story from the past where a golfer nailed a low flying 707 with a drive and took out an engine, but I highly doubt it's possible and <S> really not even a risk at that distance from the airport. <S> Now a pilot with an engine failure shortly after takeoff and makes a forced landing onto a golf course, only to have an ill tempered golfer fire a drive at his airplane out of ire, that's another possibility. <A> This is an answer to a slightly different question: Could a golf ball damage an aircraft? <S> The answer is yes, at least indirectly, as it has happened in 1987 in Benin. <S> Basically, this golfer hit a bird with the golf ball. <S> The bird fell into a fighter on takeoff with the canopy open (or hit the windshield, unclear). <S> The pilot lost control of the aircraft and subsequently collided and destroyed several other planes on the apron. <S> Refs: <S> PPrune <S> Google <S> Book: The Golf Hall of Shame
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So I'd have to say, very unlikely, only to allow for the chance in a billion that the sliced up fragments of a golf ball might actually enter the compressor stage and cause a problem in one engine.
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Why do aircraft piston engines consume so much oil? This question is related to single/twin piston engine aircraft. After flying in a Cessna 152 and a Piper Dakota I have noticed that they both consume a lot of oil. Oil check is an integral part of the checklist. Pilots carry extra bottles of oil in the back. Why is this so? Especially compared to car engines that are 'similar' and do not require such regular top offs? <Q> Automobile engines are not similar. <S> They are liquid-cooled and therefore can be built to much tighter tolerances with regard to thermal expansion and contraction. <S> Air-cooled aircraft engines must deal with a large range of operating temperatures and oil is consumed due to the relatively looser fit of the piston rings. <A> As I think most folks here tend to be A&P's I'll add this. <S> Aircraft horizontally opposed four cylinder engines also use specifically "asheless dispersant" oil because the oil is pumped to lubricate the top of the cylinder and a decent bit is burned in combustion. <S> So yes, there is a line that can be considered "excessive" and that has a lot to do with wisdom in a small piston engine as opposed, to a jet where there is generally a one pint per hour limit, or something to that affect, where anything more than than that would require an oil consumption run. <S> Cheers ! <A> 'Air cooled engines' is a popular misnomer... <S> oil does the primary cooling, with the fins on the cylinders only dispersing part of the heat. <S> The oil, in addition to lubricating, draws heat away from high temperature points, like the cylinder heads, bearing surfaces on the crankshaft, and to a degree, the cylinder walls when oil splashes on them. <S> For a variety of reasons, oil/air cooled engines tend to consume more oil than water cooled engines, from the wider temperature range the engines experience, to the oil doing double duty. <S> In addition, the flat cylinder layout can result in some oil loss on startup, from oil pooling in the cylinders when not running, which doesn't happen in vertical or V cylinder arrangements that are typically used in automobiles. <S> This is especially true of radial engines, which have some cylinders inverted, letting oil pool on the pistons when not running, leaking past and getting into the combustion chambers. <S> That's why radial engines tend to expel huge clouds of smoke when started, as that oil burns off. <S> This is also true of automotive oil/air cooled engines, such as the flat four used in Volkswagen vehicles of the 1950's - 1980's, and the flat six in Porsche 911's until the wide temperature range of such engines ran up against tighter emissions controls. <S> Those engines were also noted for their higher oil consumption.
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But as far as aircraft piston engines go, they do burn oil because they lubricate differently than an automobile engine.
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Are engines automatically stopped in an emergency landing? This answer made me wonder if engines are stopped automatically after an emergency landing as soon as one of the exit doors are opened. (...) if the engine is still running, you're about to run forward into the area where you're at risk of being sucked into the running engine. I'm not sure how high the risk would be to be sucked in or being blasted away by the jet-blast, I guess a lot of the emergency landings are because of engine failure so they aren't running anymore. Maybe as an added extra - how long does it take for an engine to spin down to a safe RPM (so that it won't suck in people or blast them away)? <Q> There is no automatic shutdown. <S> However, shutting down the engines is part of the evacuation checklist done by the flight crew. <S> It's happened before that the controls link was severed and an engine could not be shutdown, such as in Qantas Flight 32 . <S> Upon landing, the crew were unable to shut down the No. 1 engine, which had to be doused by emergency crews until flameout was achieved. <S> Normally the captain would then instruct the cabin crew to not use that side of the plane. <S> Same thing happens when there is a fire on one side, in that case the captain would also steer the plane so that the good side is upwind . <S> Aircraft are tested to ensure all occupants can evacuate with 50% of the emergency exits not working <S> (glass half-full: 50% of the doors working). <S> See: <S> How are evacuation tests made as realistic as possible? <S> About how long it takes for the engine to stop producing thrust, it's about 5 seconds. <S> If there is no or little thrust, there is no suction to worry about. <S> Also note that figure is for a spool down from full thrust (not from idle thrust, which is to be expected after landing). <S> (Source: Jet Transport Performance Methods) <A> I guess a lot of the emergency landings are because of engine failure <S> so they aren't running anymore. <S> That is not correct - there are many types of emergency landings: inoperative or stuck control surfaces , landing gear problems , bird strike , explosive decompression , etc. <S> Engine failure is one of the failures people talk more about because it is easy to practice. <S> In an emergency, obviously some system is not working. <S> Therefore there is no automatic mechanism to shut down the engines - the pilots may need them running in a scenario that is not accounted for by the engineers. <S> The timing of that action is determined by the pilots. <S> Even in the event of an engine fire, the pilots have the option to continue running the engine). <S> How long does it take for an engine to slow down its RPM? <S> Around 20 seconds seems enough. <S> I have no data to support this though. <A> There have been incidents, like Continental flight 426 in 1975 <S> (DEN, cause was a microburst) in which the engines continued to run after the crash. <S> Fortunately from the NTSB report it seems like the running engines didn't prevent passenger egress.
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(Actually there is never a mechanism to auto shut down the engines - emergency or not.
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Why do most radial engines use an odd number of cylinders? To help suppress vibration, most 'V' and 'horizontal' engines use an even number of cylinders as closely opposed as possible. Radial engines are well known for excessive vibration. For some reason they nearly always use a staggered odd number of cylinders that would seem to promote vibration, why? <Q> To keep the design simple and lightweight, a single-bank radial airplane engine has one crank, which means that the pistons must reach the top of their travel in rotation order. <S> But the four-stroke cycle requires that a piston must reach the top of its travel twice for each power stroke. <S> The only way to promote evenly timed power strokes is to fire every other cylinder in rotation order. <S> With an even number of cylinders this would require a hesitation or skip in the firing sequence on every rotation as the engine switched between the odd and even cylinders. <S> With an odd number of cylinders the timing is quite naturally smooth. <S> For example, the firing order of a nine-cylinder radial is 1 - 3 - 5 - 7 - 9 - 2 - 4 - 6 - 8. <S> If you could watch a radial airplane engine in slow motion you would see that when a cylinder is in its compression stroke, the cylinders on either side of it are in their exhaust strokes, and when a cylinder is beginning its power stroke, the cylinders on either side of it are near to beginning their intake strokes. <S> Two-stroke radial engines do not need to have an odd number of cylinders. <A> Surely a 1, 3, 2, 4 firing order (just like an inline-4) seems possible in theory, but [one of] <S> the issues is the ring camshaft. <S> (...) unless there is an odd number of cylinders, the ring cam around the nose of the engine would be unable to provide the inlet valve open - exhaust valve open sequence required by the four-stroke cycle. <S> Watch the animation here: https://en.wikipedia.org/wiki/File:Radial_engine_timing-small.gif <S> (too big to upload here). <S> Notice <S> the two rings, each with two opposite steps (lobes). <S> As one step pushes a rod, the opposite step does the same two cylinders down with a delay. <S> If they were an even number, the ring cam would be operating two opposite cylinders simultaneously due to the shared crankshaft mounting. <S> In other words, the ring cam would be letting in the air/fuel mixture with one of the pistons (in a pair) going up, not down. <A> Look at valve timing figures for a average four stroke and bearing loads this will give a clue as to the firing order and to make sure that only one cylinder would fire at a time and avoid bearing overload. <S> As to vibration you have to have equal reciprocating forces in opposite directions but in the radial this cannot be achieved without some sort of balancing shaft this would take valuable power and increase weight obviously <A> first of all not all V engines have even number of cylinders. <S> Honda RC211V uses a v5 (yepp, 3 cyl on one bank and 2 on the other) engine. <S> i just do not have enough rep yet to answer there.now, odd number of cylinders in a radial engine is required for 4 stroke engines only.it was well described why. <S> but 2 stroke ones may not have odd numbers. <S> allso if double ended pistons are used (rare engine concept) then it would be possible to fire 2 pistons at the same time.
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An odd number of cylinders is required by the combination of the single-crank radial design, the four-stroke (Otto) work cycle, and the desire to keep the power strokes evenly spaced in time.
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Does engine failure shut off the auto-pilot? After answering this question it got me wondering whether there can be a situation where a complete flameout of engines could cause a serious loss of control if the auto-pilot were to continue to try to maintain altitude despite the loss of power. If it did, presumably by raising the nose and losing air-speed, eventually the aircraft would enter a stall. Which raises the question, does the auto-pilot automatically shut off in the event of engine failure? Though I suppose it depends on the auto-pilot and the aircraft model. I do realize the pilot and co-pilot should be very aware something is awry, but I can also see them being rather busy trying to figure out what all the alarms are telling them, and or trying to restart the engines and not notice the AP is setting them up for disaster. <Q> No, there is no necessary connection between the autopilot and an engine failing on any aircraft that I'm aware of -- which is far from all of them! <S> Also, once you have everything trimmed up (i.e. rudder trim in to balance the asymmetric thrust), it's nice to put the autopilot on to let it keep the wings level & hold altitude for you while the pilots sort out everything that comes next -- checklists, ATC coordination, choosing where you'll land, etc. <S> What DOES come off almost immediately after engine failure, at least on the 737, is the Autothrottle. <S> It will sense that the thrust and throttle position are mismatched, and rather than moving the good throttle around when you may not be ready to compensate with the rudder, it disengages. <S> I'm not certain if that is universally true; the 777 computers are crazy smart, and they may actually leave the A/T engaged in that sort of a scenario (while the A/P flies the rudder for you). <S> The basic challenge that you mention, an autopilot that will hold altitude even when the thrust is insufficient to maintain airspeed, is a scenario that's not limited to an engine failure. <S> The automation will have some set of rules as far as when to hold, when to go into reversion modes, and so forth. <S> And if you get caught in the wrong spot, the automation can bite you. <S> In the 737, for instance, if you're in altitude hold or glideslope capture, the autopilot will hold that no matter how badly the speed decays. <S> (Stall while on glide path, or follow the speed cursor into the dirt short of the runway... damned if you do, damned if you don't!) <S> On the other hand, if you're in a vertical speed mode or a VNAV climb or descent, there are speed reversions that will change your flightpath rather than accepting a speed above or below safe limits. <S> If everything has been set up correctly and the Autothrottle is engaged (or the pilot is setting the power appropriately), then everything works really well. <S> But if enough things go wrong and you aren't paying attention... <S> well, that's when bad things can happen. <A> I can't find a link to an article from the 90s, but there was an article where a Bonanza pilot died in flight (due to health issues), his plane came smoothly down in a field somewhere due to the autopilot keeping the wings level after it ran out of gas. <S> So as long as the plane has electric power, many autopilots will function when the engine stops. <A> On most modern aircraft thrust asymmetry is compensated by the FBW irrespective of the autopilot in the following phases: takeoff(obviously since A/P is not engaged), climb, cruise, and descent; in these phases one active autopilot is managing the vertical and the lateral path, and it will keep engaged. <S> Another situation occurs in land mode where in most modern aircrafts we have triple redundancy(Boeing has 3 APFD computers, Airbus has 2 doubled computers), and the active computers(left and <S> right in Boeing case)will manage the rudder too. <S> Normally in land mode every AP computer has its own power supply <S> , that is they are electrically totally separated, if the engine failure occurs while the APU is off, the A/P mode could get degraded because of lack of separate power supply but will not disconnect, however if the APU is running, the electrical reconfiguration will prevent the degraded mode. <S> With respect to old generation aircraft like the B737, I can’t answer.
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If you're in an idle descent, one motor failing wouldn't really change the flight characteristics of the aircraft, so in that case there's no great need to get rid of the autopilot.
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What is the physical meaning of circulation found in Kutta condition? The Kutta–Joukowski theorem is applicable for 2D lift calculation as soon as the Kutta condition is verified. When this is the case, there is a circulation $\small \Gamma$ around the airfoil . My question is related to this circulation: What is the physical meaning of the circulation $\small \Gamma$, often represented like this ( example 1 , example 2 , example 3 ): (Own work) I'm interested in a simple explanation of the circulation (is air moving around the airfoil? for dummies) and how does this circulation relate to a view of the airflow in a wind tunnel, where there is no apparent air flowing clockwise around the airfoil: Source: Youtube The rest of this post is a presentation of the circulation theory which motivates my question, and as I understand it, but is not part of the question. The Kutta condition is linked to stagnation points, the points where air tubes separate to flow on a given side of the airfoil, and where they join again behind the airfoil. The Kutta condition stipulates the latter point coincides with the airfoil trailing edge: Wikipedia : A body with a sharp trailing edge which is moving through a fluid will create about itself a circulation of sufficient strength to hold the rear stagnation point at the trailing edge. (Own work) According to theory, when the airfoil moves through air, the circulation moves the rear stagnation point to the trailing edge, and then maintains it at this position. When at this position, the circulation is finite and can be used to compute lift with Kutta–Joukowski theorem : Wikipedia : The theorem relates the lift generated by an airfoil to the speed of the airfoil through the fluid, the density of the fluid and the circulation around the airfoil. [...] The lift per unit span $L^{\prime}$ of the airfoil is given by: $$L^{\prime} = −\rho_{\infty} V_{\infty} \Gamma$$ where $\small \rho_{\infty}$ and $\small V_{\infty}$ are the fluid density and the fluid velocity far upstream of the airfoil, and and $\small \Gamma$ is the circulation defined as the line integral $$\Gamma = \oint _{C}V \cdot d \mathbf {s}$$ around a closed contour $C$ enclosing the airfoil and followed in the positive (anti-clockwise) direction. <Q> Circulation of a fluid around an object by itself will produce no lift. <S> The classic example of this is the spinning cylinder with no other airflow. <S> Viscosity will cause the fluid near a cylinder rotating clockwise to circulate in a clockwise direction around the cylinder. <S> If a left to right horizontal flow is introduced there will be a vector sum of the two flows. <S> This results in the stagnation points near 8 o'clock and 4 o'clock (as opposed to the cylinder with no rotation in the left to right flow having the stagnation points at 9 and 3 o'clock.) <S> The net result of this is the Magnus effect where lift is generated in the 12 o'clock direction. <S> In your first diagram (typical inviscid flow) there is no circulation. <S> The shape of the airfoil in viscid flow causes the trailing stagnation point to move to the trailing edge (second image -- the Kutta condition). <S> This has the same effect on the airflow as the spinning of the cylinder, in that it creates a clockwise circulation about the airfoil. <S> The line integral describes, for an arbitrary closed contour around the object, the dot product of the fluid flow velocity vector with the vector path moving around the contour. <S> The simplest contour to analyze is created by following flow streamlines above and below the airfoil and connecting them before and after the airfoil with lines perpendicular to the streamlines. <S> Since the dot product of perpendicular vectors is 0, the integral along perpendicular portions of the contour are 0. <S> The dot product of parallel vectors is just the multiplication of the scalar values, and since the direction of the contour is reversed between the upper and lower streamline the effect is adding one and subtracting the other. <S> Due to differences in lengths and the different flow speeds (Bernoulli...) along the contour, the integral is non-zero. <S> This number represents the net effective circulation about the airfoil (total flow minus the horizontal flow.) <S> The interesting thing is that if you extend the contour behind the airfoil far enough to enclose the wake of the airfoil from the beginning of movement, the circulation will be zero as the circulation of total wake is the vector opposite of the circulation about the airfoil. <A> There is no molecule in the air which actually revolves around the airfoil in the way you would normally think of it. <S> Circulation is a mathematical concept used to explain the motion of air from a frame of reference bound to the wing. <S> It is useful in understanding relative motion above and below the wing. <S> A similar situation might be a person walking toward the back of a train. <S> The person can walk at 2mph and the train runs at 80mph, so is the person going forward or backward? <S> The answer depends on your frame of reference: backward if you are on the train, forward if you standing by the tracks. <S> Don't even ask about the direction from space.) <S> The cause is immaterial. <S> For illustration assume a mach <S> .8 aircraft has mach .88 <S> airflow above its wing and mach .72 below. <S> All molecules move to the trailing edge. <S> If you want to compare these two flows, it is useful to subtract out the aircraft forward speed of .8 leaving mach +0.08 above the wing and -0.08 below, which defines the circulation. <S> The negative speed (forward) below the wing only exists mathematically. <A> I very much like @Gerry's answer. <S> It illustrates the principle of lift through potential theory very well. <S> I would like to add that circulation <S> doesn't mean that fluid particles are rotating around the airfoil. <S> In fact, even a simple rotating cylinder in an inviscid/irrotational flow would have well-defined streamlines flowing from upstream to downstream. <S> Rather, the integral definition of circulation in the OP is defined on a closed contour around the velocity vector field , not on a trajectory of any fluid particle. <S> Intuitively, then, circulation illustrates how much a uniform flow has turned. <S> From Wolfram
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The simplest way to think of it is that airfow above the wing is moving faster than that below the wing, which gives the wing its lift.
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What is this cutout in the Spitfire cockpit glass? This is a still from the film Dunkirk. I realise this is not a historical document, but I have also found a similar feature in photos of real Spitfires . What is the purpose of this? <Q> According to flight manuals, this allows the pilot to maintain a view on the outside if the windscreen becomes obscured: Source: Aircraft manual <S> This manual locates the panel on the right side. <S> Online forums see this as a typographer mistake, but @TomMcW has found some aircraft had it indeed on the right side: Source <S> On the reason for mist apparition: <S> Source: <S> Flight Journal <S> (pg 28) <A> Mins is right, but it's a more general thing: Glider planes have them too, or at least those built in the 80s that I flew in the 90s. <S> One of their effects is that they whistle in the (self-made) wind. <S> Basically any deceleration is immediately noticeable in the note of the whistle going down (helps avoid stalling)... <S> Relevant for a glider, but probably inaudible over a Spitfire's noise! <A> The ORIGINAL Spitfire I Pilot's Notes (as opposed to the concocted and suspect "1940 Spitfire Manual", whatever THAT means, quoted above) clearly state that the panel is for "Emergency use" and on the PORT side. <S> " <S> Port" is bolded in the text. <S> The real para number is 45 in the Spitfire I and 37 in the Spitfire II Notes. <S> The panel allows airflow <S> which may (or may not) clear the fogging of the front panel/hood and also could provide some perspective on landing to maintain the "triangle" of the runway edge and nose, <S> should the hood be jammed. <S> It also releases pressure aiding in getting the hood open in an emergency, necessary for vision or for bailing out... <S> these early hood not having the Martin Baker quick release system. <S> The knock out panel was always on port (the photo above actually shows this but because of the thickness of both layers of glass, only the studs can be seen. <S> If it were in fact on the starboard side, the outline of the panel could be seen. <S> The knockout was dispensed with from Mk V onwards. <S> Some later manufacture Spitfire <S> I's also lacked it, I believe, after the MB gear was introduced but have not been able to definitively confirm that.
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Note the punch-out panel on the canopy cover, an early solution to the new problem of canopy misting caused by the rapid altitude changes possible in the Spitfire.
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How did ww1 pilots handle G-forces? The wikipedia page on G-forces, https://en.wikipedia.org/wiki/G-force , lists that WW1 aircraft encountered 4.5-7g during dogfights. This made me wonder, how did pilots in the early days of aviation handle the g-forces? G-suits were not invented until 1940s. <Q> This interesting British document on the G loads sustainable by German WW1 fighters <S> pegs the highest G factor for a British fighter at 5.5G for reference, with the SE5. <S> German fighters examined and tested by the British after the war didn't fare quite as well, with max G tending to be in the 2-3 G range, beyond which the rear wing spar would fail. <S> What is also important to consider is that WW1 aircraft on both sides were not capable of sustaining those G's for very long, due to the low airspeed and rather underpowered engines of that day. <S> An aircraft sustaining very high G's bleeds off quite a bit of speed in the process, due to the increased drag. <S> A WW2 fighter capable of 300-350 knots with a 1500-2000 hp engine, can pull a lot of g's for a long time, before scrubbing off enough speed to be in danger. <S> A WW1 fighter at 80 knots, with a 150-200 hp engine, would only be able to sustain high G's for a few seconds, before they lost enough airspeed to risk stalling. <S> The few motion pictures of dogfights of that era, presumably re-enacted, tend to reinforce this: the planes appear to make a series of brief sharp turns interspersed with returns to level or near level flight, sort of a jerky movement as opposed to the long high G turns of WW2 fighters. <S> Finally, there were techniques some pilots used to avoid blacking out. <S> Major Greg Boyington, who had been a boxer before the war, reported withstanding more G's longer by tightening his neck muscles up. <A> Typically the human heart can produce enough head to keep the blood flowing to around +5g. <S> So sustained maneuvering at those limits should not pose a problem. <S> Remember, at their best an anti g garment will only offer an extra g or so of enhanced tolerance. <S> There is also the issue of instantaneous vs sustained load factors while maneuvering. <S> While a WWI fighter might be capable of pulling 4-7g instantaneously, sustained loading were probably more in the area of 2-3g - early engines just didn’t produce enough power to allow for hard sustained maneuvering. <S> So risk of s G-LOC was minimal in early fighters. <A> The phenomenon was first observed in WWI but was poorly understood. <S> The most likely flew up to their personal limits using their body as a queue. <S> G-LOC of pilots, then called "fainting in the air," first occurred in World War I and may-have been, the cause of some military aircraft accidents Head, H, The sense of stability and balance in the air, Chapter 11. <S> In The medical problems of flying. <S> H. Milford (ed.). <S> London: <S> Oxford U-siversity Press, 1920. <S> They may have just passed out and recovered... <S> According to this account, the pilot passed out in one dog fight although in this case it may have been from either the spin or blood loss in the leg. <S> ... <S> but succeeded in driving down two of the enemy in a spin. <S> He lost consciousness after this , and his machine fell out of control. <S> On recovery he found himself being again attacked heavily by a large formation, and singling out one machine, he deliberately charged and drove it down in flames. <S> This article would make it seem like red-out may have occurred in some maneuvers but due to a lack of understanding of what was actually happening they just flew through it. <S> This aircraft was designed to undertake a controlled bunt, with structural limits of -5G! <S> Those pilots surely would have had “Red out” during those -Gz maneuvers. <S> It could perform a U-Turn in less than 200 yards of air space, clocking up almost 8 G in the process. <S> Since those brave hearts did not know anything about G-LOC, neither were there any anti-G suits designed then, so they flew on <S> A type of AGSM useful in flight was first the discovered as a method to increase G tolerance by Stainforth of England in 1933. <S> He found that straining the abdominal muscles increased G tolerances 2 G, from 4 to 6 G. <A> The same article cites: A typical person can handle about 5 g0 (49 m/s2) (meaning some people might pass out when riding a higher-g roller coaster, which in some cases exceeds this point) before losing consciousness... <S> So they could just pull g's until their personal limit of consciousness - natural selection would then weed out the pilots with the lowest tolerance.
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It seems that little was done (or at least little was documented) during the first world war on this front as the first actual technique for G tolerance increase was not used until 1933 . Proper breathing, body position and flexure of the skeletal muscles in the legs and stomach combined with physical conditioning with weightlifting and experience can allow a pilot to pull sustained loads in excess of +10g without the use of anti g suits.
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What fighters have both 1 & 2 engine versions? Northrop originally built the F-5 "Freedom Fighter" (and T-38 "Talon") with two engines. Later it was re-fitted with a single F404 engine from the F/A-18, re-designating it the F-20 "Tigershark" to avoid confusion. The first F-5A and T-38 flights took place in 1959. [Addendum: There is no real contradiction, the T-38 "Talon" was a two place trainer version of the F-5 "Freedom Fighter". Most aircraft don't re-designate between one and two seat versions, but Northrop or the military did in this case. ] See the history of the F-5 YouTube Video "Though the USAF had no acknowledged need for a light fighter, it did procure roughly 1,200 Northrop T-38 Talon trainer aircraft, which were directly based on the F-5A." https://en.wikipedia.org/wiki/Northrop_F-5 "The F-5G was an advanced single-engined variant later renamed the F-20 Tigershark ." https://en.wikipedia.org/wiki/Northrop_T-38_Talon Have any other fighters (world wide) offered a fighter with one and two engine models? Twin engine F-5 "Freedom Fighter". Single engine F-20 (F-5G) "Tigershark". Wikipedia <Q> Its mutant offspring, the Republic XF-84H "Thunderscreech" was a experimental turboprop fighter, powered by an experimental Allison T40 engine, which consisted of two Allison T38 engines, joined through a common gearbox. <S> This was a twin-engine aircraft from the maintenance point of view, since there were two sets of turbo-machinery to go wrong. <S> It looked like a single-engine aircraft, and flew like nothing on earth, owing to the strange effects of two sets of supersonic shockwaves from the contra-rotating propellers hitting the wings several times per second. <S> Its first test pilot refused to have anything more to do with it after the first flight; the second test pilot flew it eleven times, but Republic did not submit the aircraft for USAF trials. <S> Edit: The reason for doing this was that early jet engines were very fuel-thirsty, while turboprops got much better mileage. <S> The propeller was supersonic because that was necessary to absorb the power in a small enough propeller to fit within the aircraft's ground clearance. <S> It wasn't remotely a good idea, but it may have shown the USAF that jet-age aircraft development was harder than it had been in the piston-engine era. <A> Well, the F-20 is a different airplane from the F-5, albeit an evolution of the original Northrop <S> N-156 design which developed into both the F-5 and F-18 families of airplanes <S> , so no aircraft model was ever offered with the option of having one or two engines. <S> Ideally fighters are more suited toward the single engine configuration as powering one with multiple engines invariably adds more complexity, systems to manage and weight. <S> The only justification for which is an increased thrust to weight ratio on a larger, heavier airframe. <S> I’d guess Northrop would have dearly loved to have the F-5 powered by a single GE J-79 turbojet given its for the time supreme thrust to weight ratio, but I don’t know if the engine was available for export back at that time. <S> The F-5 was also an export fighter derivative of the T-38 airplane which was currently powered by a pair of GE J-85 turbojets, originally designed for expendable use powering cruise missiles, which offered the Talon good performance and were available to sell to other nations. <S> Twenty years of both fighter aircraft and engine development provided the F-20 design team with the new GE F-404 engine, comparable in performance with the J-79 but with 6000 fewer parts and greater thrust to weight ratio, highly resistant to compressor stalls, and greater reliability than the older J-79. <S> This along with the availability for export made the F404 the preferred choice on the F-20; there was never any attempt to make a multi engine variant of the F-20. <A> Technically, several single-engine aircraft has been either designed or modified to utilize a second rocket engine at some point during their lives. <S> For one example, see the Lockheed NF-104A <S> The Soviet WWII era <S> Su-6 <S> and Su-7 <S> would examples of a piston engine single (the Su-6) being re-equipped with a hybrid piston and rocket propulsion system. <S> It could also be argued that the Mirage IV fits this criteria, as its design was derived from the existing Mirage IIIA.
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The Republic F-84F Thunderstreak was a fairly normal early jet fighter, powered by a single Wright J65 turbojet engine.
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How do I know my AGL altitude while in flight? I am about to start my PPL, still flying in my FSX. I have a question, let's say I am flying from airport A to airport B. Both airports are in G airspace and I would like to stay in G airspace and don't go over 1200' AGL to class E. Let's say I would like to fly at 1100' AGL and keep this altitude from A to B. And let's assume we are in un-congested area, so we do not violate minimum safe altitude rule. But I do not understand if terrain in uneven, I mean its elevation is constantly changing, how do I keep my altitude 1100' AGL. I don't have radio altimeter like in Boeing. I understand that at the airport you can get your elevation, also you can have minimum safe altitude from sectional chart and also you can find any obstructions, but how do I know in a middle of my flight (if I need to). If this question sound stupid and pilot don't fly in G airspace please let me know. <Q> You can't know with 100% accuracy, even radio altimeters have limitations , and if you're flying on a PPL the aircraft probably wouldn't have one anyway. <S> The VFR pilot flies with a map which shows the height of the highest terrain and noteworthy landmarks, but unless you are directly over one of these it is a matter of your experience in judging vertical distances. <S> I'm not sure if it's different wherever you come from, but where I fly in Australia, all airspace is measured in sea level altitudes or flight levels, never in reference to ground height, so we would never encounter your situation. <S> Trying to stick to one height AGL might sound like a fun challenge to some but to me <S> it sounds like less time to save my life when the engine quits. <A> I bumped into this thread and was disappointed to see that no one was able to actually answer your question. <S> Why you are avoiding Class E, whether 1200' AGL is unsafe, and the ins and outs of your flight planning are all subjective. <S> After 19 months I figure you probably know the answer yourself, but I wanted to post a solution for anyone who might run into this same issue while learning to fly. <S> Subtract the AGL altitude from the MSL altitude of the obstacle and this will give you the MSL altitude at the ground at that location. <S> Add to that MSL <S> altitude your desired AGL elevation and the answer is the MSL altitude you need to be at a specific AGL altitude over that point. <S> This method does require you to have a VFR sectional, have a generally good idea of your location (the need for accuracy of your location depends on the type of terrain you're flying over), and a bit of mental math. <S> You also need a current altimeter setting for improved accuracy. <S> Anyhow, I hope this helps, for anyone in the future who might have this question and can't find the answer. <A> As a practical matter, sans radio altimetry or synthetic vision, you don't have any way to determine your AGL en route accurately. <S> Why do you want to use Class E for en route flying? <S> In the U.S. neither Class E nor G require an ATC clearance, but both require adherence to VFR flight rules. <S> However, the VFR daytime flight visibility for Class G is only 1 mile versus 3 miles for Class E. <S> There's a nice table showing that at the beginning of Chapter 15 of the FAA's Pilots Handbook of Aeronautical Knowledge .
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The best way that I know of to determine your en-route AGL altitude with no GPS, albeit not the most accurate, is by finding obstacles along/near your route of flight which have an MSL and AGL altitude posted on VFR sectionals.
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Do airline pilots increase thrust when ordered to increase altitude by traffic controllers? Do airline pilots increase thrust when ordered to increase altitude by traffic controllers? Do they simply use flaps, the yoke (or joystick in the case of airbus) and the stabilizers without any increase in thrust. What is the altitude increase sequence or procedure . Do they simply rely on auto pilot and if so does it increase thrust too? <Q> Do airline pilots increase thrust when ordered to increase altitude by traffic controllers <S> Yes, without increasing thrust <S> the act of ascending would reduce speed. <S> Do they simply use flaps <S> No, flaps are not used to climb. <S> They are used to increase the surface area of the wing in order to allow the aircraft to fly at slower speeds (for example, during approach & landing). <S> What is the altitude increase sequence or procedure Generally, and put simply <S> , it is increase thrust then raise the nose. <S> Do they simply rely on auto pilot and if so does it increase thrust too? <S> They may well use the autopilot to do it all, but some autopilots do not control the throttle so that would be done manually by the pilot while the autopilot controls the rate of climb. <A> I’ll try my hand at a more ‘scholastic’-aviation approach: <S> The normal procedure taught in flight school for initiating a climb is P-A-T . <S> That is Power-Attitude-Trim . <S> You increase power on the engine(s) first. <S> If left alone, the plane will settle (very slowly, google phugoid) into a climb eventually Because we do not want to wait the few mins or so it takes for the plane to settle into the climb, we use the elevator (via yoke or sidestick) to settle the attitude of the plane directly into a climb position (ie. point the nose higher up). <S> A good pilot will do this without letting the speed climb or drop. <S> ‘Call it pitch-for-speed. <S> Now the plane is in a different power/attitude and even though the plane is (or should be) at the same speed, a little bit of trimming is required to null the forces on the yoke. <S> now you can sit back and enjoy the climb. <S> Leveling off after the climb is a A-P-T.... <S> you guessed: <S> Attitude-Power-Trim. <S> The reasoning for the change of order is that you want to prevent the plane from a nose-up, low-power situation, with speed decaying quickly. <S> Mind you <S> , in a modern airliner most of these things can be automated via an autopilot/autothrust as described in the other answers. <A> Most airliners today use auto pilot and auto thrust when flying in level flight or climbing and descending. <S> In any aircraft thrust is usually increased for a climb and decreased for a descent. <S> The Auto-thrust will adjust automatically in most modes to maintain a desired speed and rate of climb. <S> The autopilot adjusts the elevator or stabilizer to climb or descend to the set altitude.
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The normal sequence for a climb is to enter a new altitude in the flight computer and then engage a climb mode on the autopilot.
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Why do all airliners have life jackets? According to this question, life jackets are not mandatory in planes that do not fly over large bodies of water. However, I have never been on an airline flight without life jackets (and the corresponding safety demonstration). Why do airlines not remove the life jackets from planes that fly over land? The plane would be lighter and the safety demonstration shorter. Moreover, it can not be hard to dedicate different planes to different routes and avoid returning the life jackets each time the plane has to fly over water. <Q> The plane would be lighter. <S> Not by much. <S> It cannot be hard to dedicate different planes to different routes. <S> This adds to the logistics difficulties in scheduling the airframes. <S> It's MUCH easier if all the airframes can be used on all the routes. <S> Returning the life jackets each time the plane has to fly over water. <S> This involves extra down-time/logistics before the airframe can fly the next trip. <S> You've used the phrase, "large bodies of water"; think about if the airplane needed to ditch in a "small body of water". <S> It would be preferrable that all people had life jackets and thus a chance to live. <A> Why do airlines not remove the life jackets from planes that fly over land? <S> They do, at least some of them. <S> I fly on intra-European routes regularly (mainly Eurowings) and have never seen life jackets on flights that don't cross the Mediterranean. <S> Obviously, the safety instructions don't include the life jacket demonstration either. <S> I would guess that especially for low-cost carriers, the weight advantage makes a difference. <A> Because this can still happen. <S> That’s US Airways Flight 1549 on the Hudson River. <S> They made a movie about it starring Tom Hanks. <S> There’s no way to predict disasters, and had the plane been “efficient” having no life jackets, I suspect it could have meant a lot of people drowning. <S> [But see comments.] <S> So it’s better to plan for contingencies, especially when it’s a cheap solution (Like life jackets or floating seats). <S> In other words, planning for anything and everything going wrong is just something pilots and aerospace engineers (and lawyers) are in the habit of doing, ideally. <A> Why do airlines not remove the life jackets from planes that fly over land? <S> The plane would be lighter and the safety demonstration shorter. <S> Some do. <S> As a specific example, if you fly Delta from Minneapolis to Lincoln, Nebraska, you'll be on a Canadair RJ-something (actually run by Sky West) that will only have a couple of infant lifejackets on board. <S> Everyone else can use their seat bottom cushion to help float – there are straps on the bottom to help you hold onto it. <S> However, it only makes sense to do this on planes that won't be used over any significant body of water. <S> For example, the lack of lifejackets prevents Sky West using those particular planes for something like a Minneapolis–Detroit flight, which would either pass over Lake Michigan or take an uncompetitive detour to the south. <S> They probably couldn't be used on Minneapolis–Chicago flights, even, since those can be routed out over the lake to approach O'Hare from the east. <S> Similarly, a European carrier that decided not to carry lifejackets would be unable to fly that plane to the UK without spending the time to put the lifejackets back and replace all the safety cards. <A> The Airbus A380 seats around 850 passengers 4 . <S> American Airlines has a fleet of about 950 aircraft of various models 2 . <S> The Cadillac of Wal-mart life-vests, purchased individually, costs \$30 1 . <S> Outfitting a fleet of 950 A380s with life-vests purchased individually at Wal-mart comes in a $24,225,000 USD. <S> Even though I outfitted one of the largest fleets consisting of the largest aircraft with the life vests purchased using idiotically low business-sense, if I managed the rest of the business with some sense then the cost is (optimistically) about a day's worth of profits (American Airlines had a net profit of \$7.6B in 2015, though 2016 was a little slower at \$2.7B 3 ) for a once-in-an-aircraft's-liftime purchase (though there's no reason to retire them with the aircraft). <S> Regardless, your question was "why", not "why not"; what incentives are there for doing having life vests? <S> Maybe airports such as New York require life vests because it's so close to a large body of water that traveling over it is practically unavoidable? <S> Maybe it's economically advantageous to be able to re-route aircraft without the luxury of predictability. <S> Still I apologize I still have not fed you with any true answers, only supposition. <S> Maybe there is a regulation... <S> Otherwise, maybe the CEO of American Airlines will respond and tell us why the hell he blankets the life vests. <S> (Edited for coherence). <S> Mins raised a point about cost of maintenance being a significant cost (possibly larger than the cost to supply). <S> So maybe the there isn't much strength in the "why not" court. <S> References:
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One possible incentive for airliners to go ahead and equip all aircraft with them is to take out any restrictions on the aircraft's serviceable zone that would be in-place if not equipped with life vests.
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What is the lightest weight operational jet/turboprop fighter ever deployed in combat? Since the beginning of WWII there was been a trend towards larger fighter aircraft. In about 1960 the United States continued with larger fighters (F4, F100, F111, F15) but also started a branch of very small light weight fighters (F105, F16, Tucano, etc). What is the lightest weight jet/turboprop fighter any nation has ever deployed in actual combat? Epilogue: I learned more from this discussion than I expected. As I recall, at least one South American country used the BD5J but it never saw combat. That's why I included the combat stipulation. - Thanks for the answers... <Q> The A-37 Dragonfly is the smallest production combat aircraft <S> I'm aware of. <S> Empty weight of 6,211 lb (2,817 kg). <S> Max takeoff weight of 14,000 lb (6,350 kg). <A> I would think the Folland Gnat F.1 is hard to beat in this context, with an empty weight of 4,800lbs (2,175 kg) and a loaded weight of 6,250 lb (2,835 kg). <S> It is credited with a number of victories over the Pakistan Air Force in the Indo-Pakistani War of 1965, principally against the F-86 Sabre . <A> I'm surprised that nobody so far mentioned the Heinkel He-162 A-2 . <S> This was powered by a single BMW 003 turbojet and had a maximum take-off mass of 2805 kg, a tad below that of the Folland Gnat. <S> Its empty weight of 1660 kg (3660 lbs) places it clearly below all other contenders. <S> Note that the A-1 variant used heavier armament (2 MK 108 30mm guns), which produced excessive vibrations, so the A-2 version used the lighter MG 151 (20 mm caliber). <S> And, yes, it was operational , even if only for a few weeks in 1945. <S> He-162 <S> during post-war evaluation (picture source ) <S> Contrary to contemporary propaganda which claimed that it had been developed in only three months <S> , Heinkel had been working on this configuration for almost a year when the proposal for a cheap, single-engine jet was issued on September 8, 1944. <S> Basically, Heinkel only needed to scale down their design (which was based on a bigger Heinkel engine) and get the prototype into the air. <S> The drooped wingtips were no winglets but served to reduce the dihedral effect and were added when early flight testing revealed dynamic instabilities. <A> Similar too is the Messerschmitt 262 with an empty weight of 8,366lbs and a max takeoff weight of 14,272lbs. <S> Supersonic aircraft are a bit heavier. <S> Certainly the MiG-21 is a good contender with an empty weight 12,000 lbs of and a max TO weight of 21,600. <S> So, too the Lockheed F-104 <S> at 14,000lbs empty and just shy of 30,000lbs <S> at gross takeoff weight. <S> Perhaps the smallest jet fighter ever conceived, but never put into production <S> is the McDonnell XF-85 Goblin. <S> Designed as a parasite fighter to be carried aloft by a B-36 bomber, it measures just 14ft in length, with a wingspan of 21ft and a gross takeoff weight of just lbs 5600 lbs!! <A> F-5 also a contender. <S> 8085 lbs empty weight, 11,477 lbs combat weight, 13,400 gross takeoff weight, although Max takeoff weight was near 20,000.
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The MiG-15 is a good contender having an empty weight of 8,113 lbs and a maximum takeoff weight of 14,458lbs.
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Is repeatedly pitching an aircraft up and down to help it lose its energy quicker a viable landing technique? Say a pilot "bobs" his aircraft's nose up and down. The rapidly changing AOA should generate more drag than if the aircraft were to fly straight at a constant pitch where the AOA shouldn't be significantly large, right? Is the extra drag significant enough for this technique to be used in a practical landing approach? <Q> No, that kind of landing technique is too risky and dangerous. <S> You’re most likely to just exchange kinetic energy for potential energy, gain altitude, then slam into the ground with the aircraft exhausted of airspeed. <S> Also it’s superfluous, considering that a properly managed approach on glide path and airspeed will accomplish pretty much what you intended to do with your proposed landing technique. <S> A stabilized approach and entry into the roundout will result in the aircraft exhausted of energy and settling onto the runway once the power is pulled to idle, with little float. <A> Landing is pretty tricky: it can only be done in certain areas with a suitable landing strip; contact point with the ground should be at the start of the runway; vertical speed should be kept to a minimum; the speed vector must be aligned with the runway; lower horizontal speed is convenient for correcting wind gusts etc. <S> So the aircraft speed must be low, while the speed vector must remain carefully pointed at a specific point on earth. <S> Both these requirements are equally important for a successful landing, and voluntarily varying one for improving the other is not a good idea. <S> Which is what you would do if you would be pumping the stick forward & aft. <S> In order to reduce airspeed, the drag of the aeroplane must be increased - this can be done significantly by increasing Angle of Attack or sideslip, where AoA variations also change direction of the speed vector. <S> The change in pitch attitude (a rotational velocity) contributes very little to drag: rotation axis is the wing centreline, so only an extra speed around the horizontal tail surface is gained. <S> Nothing compared to what happens with the wing and fuselage surfaces. <S> Repeatedly stalling and recovering the aircraft could be a way to quickly lose energy. <S> Still at the cost of the vertical speed which will not be constant. <S> As @Ryan Mortensen points out in a comment, a much more controlled way of losing airspeed is by slipping: the sideslip angle increases drag while leaving the lift vector alone. <S> Much easier to hit that suitable spot on the landing strip. <A> In R/C model aviation beginners sometimes do inadvertently <S> try this technique. <S> While they are on the final they keep working the elevator up and down up and down because they can't really judge a good glide slope at that stage of their learning cycle. <S> So when they do this on approach, it also happens after touch down. <S> You have a bumpy ride going down to the landing strip you are going to have a bumpy landing and more often than not a broken prop and a nose wheel. <S> Why does it happen? <S> Because the very basic premise is incorrect. <S> Final approach is a very stable glide slope. <S> If you try anything fancy there you can’t expect a great landing. <S> Also, when you are coming in like that and touch down you will have a natural tendency to overcorrect the pitch on the first bump and it then becomes a catch 22 <A> No. <S> This would be the direct opposite of a stabilized approach, moreso it would be opening the possibility to cause an accelerated stall. <S> As has been mentioned, it would be an affront to the aircraft and to the humans aboard this aircraft. <S> Trying this is a sure sign of a bad approach, and would be better replaced with a go around and a better controlled second attempt. <A> Keeping on your glideslope is already tricky enough at times; trying to follow the glideslope while deliberately wavering up and down would be very difficult indeed - and when you start getting close to the ground, obviously the pitching risks bumping into the ground earlier than you planned, and at a flatter angle, which risks hitting the ground with something other than your landing gear (depending on your aircraft's configuration and how sharply you pitch down). <S> On top of that, landing brings you close to stall speed, and rapid changes to your AoA will therefore risk stalling the aircraft, and given that you're getting quite close to the ground during landing, you may not have the altitude to spare when recovering from that stall, which would result in a hard landing or crash somewhere short of the runway. <S> The principle, however, is sound. <S> Repetitive use of maneuvers that increase drag in order to reduce the aircraft's speed is the idea behind "fishtailing", which is basically the horizontal equivalent of what you describe. <S> Basically, a fishtail maneuver involves pushing the rudder over to one side or other while keeping the wings level, resulting in a slip. <S> Ordinarily you'd push it to one side for a moment, then let it come back and do the same thing the other way, resulting in a motion not unlike a fish swimming, hence the name. <S> This reduces your speed whilst having very little impact on your overall rate of descent (aside from the effects of your reduced speed), making it easier to achieve safely. <S> All the same, I probably wouldn't advise fishtailing as a deliberate intention unless you absolutely must land first try, for whatever reason. <S> If you feel you're coming in too fast <S> and you're not sure you can slow it down in time <S> , you're probably better off going around and having another try at getting it right. <A> You can do side slip if you want to loose energy which is much more easy to do and probably more effective. <S> Also fighter pilots can bank hard if the want to loose excessive speed on base turning final.
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The issue you face here is that pitching will affect your rate of descent rather strongly, which is exactly what you don't want while you're trying to land.
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What is the meaning of nose-art on the Tu-160 bomber? The BBC reports another Tu-160 interception on 15 Jan 2018 and it's clear that there is a large message painted on the side of the bomber. Looking at the Wikipedia page , it seems this style of nose-art is common among the Tu-160 community; the style is similar, but whatever it says, they're all different. It would be interesting to know what's being said here, and who is making the choices. Official propaganda, or personal messages? (source: BBC ) <Q> ( wikimedia.org ) <S> Most of the Tu-160 in service are named, much like the B-2 bombers are . <S> The one in the image is S/N: 7-02 <S> "Василий Решетников / Vasily Reshetnikov " named after a WW2 pilot. <S> You can find the names of the other ones on the Russian Wikipedia . <A> Most Tu-160's are named after notable Soviet military pilots. <S> English Wikipedia doesn't have a complete list; here's a link to the Russian version . <S> Out of 16 currently active Tu-160's, 9 are named after military or test pilots and 4 after aircraft designers (including famous helicopter designer Igor Sikorsky). <S> The rest, for some reason, bear the names of a famous Russian general , a Soviet wrestler champion and a Russian folk hero (though it may be a reference to WW1 Russian bombers of the same name). <S> The names are official. <S> This one is named after Vasily Reshetnikov , a WW2 bomber pilot who later became head of Soviet Long Range Air Force <S> (Link to the Russian Wikipedia article ). <S> The nose colors are from the Russian Air Force or Soviet Air Forces flag: <A> Both messages are Russian names: Vasily Reshetnikov (flew 307 missions in WWII mainly as a pilot for a long-range bomber, Hero of the Soviet Union) in this picture and Alexander Novikov <S> (Chief marshal of the aviation for the Soviet Air Force, involved in nearly all exploits of the air force during WWII, twice a Hero of the Soviet Union) in Wikipedia. <S> They are different for different planes.
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Probably these texts are the names of persons notable in Russian aviation (not necessary pilots).
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Why don't modern heavy bombers have gun turrets? I know that for a period of time the B-52 had a tailgunner, but nowadays many heavy bombers lack any turret defense.Why? <Q> There are really two reasons. <S> Fighter tactics Fighters used to depend (heavily) upon getting fairly close to an enemy, and shooting it down with a machine gun. <S> Over the years, guns have become less and less dominant, and instead fighters tend to use missiles from outside a machine gun's effective range. <S> Role Change <S> The B-52 was designed from the beginning to carry nuclear weapons. <S> Nonetheless, it's never been used to actually bomb an enemy with a nuclear weapon. <S> Early in its life, the B-52 was used to drop conventional bombs on enemies though. <S> During the Vietnam conflict (in particular) B-52s were used to drop thousands of conventional 500 pound bombs on various targets. <S> The Linebacker II campaign was, perhaps, especially notable. <S> During Linebacker II, 15 B-52s were lost--all of them to surface to air missiles (SAMs) not enemy fighters. <S> Linebacker II did see some limited success from tail guns as well: two B-52s shot down two MiGs. <S> No <S> B-52 (nor any other aircraft of similar size) has shot down an enemy fighter since. <S> Now, B-52s act as an aerial platform for launching stand-off weapons. <S> Its normal operation is to fly in low (where it's difficult to detect on radar), and launch from a substantial distance from the target. <S> Since it can be a substantial distance from the target, an enemy would need to defend a much larger perimeter (e.g., a large number of fighters basically blanketing a large area) to stand a decent chance of intercepting it. <S> Even if we assume an enemy fighter were to intercept the B-52, we get back to the situation with fighter tactics outlined above--they'd be unlikely to get within range of its tail gun anyway. <A> I was in the United States Air Force (USAF) working <S> B-52's when the tail gunner position was retired. <S> The reason was that it was deemed ineffective. <S> As the answers here point out, fighter aircraft evolved such that medium and long range air-to-air missiles were the primary weapons. <S> This kept fighters out far enough that the tail gun cannot hit. <S> But another very important reason was that the electronic countermeasures on the B-52s evolved such that it became the primary defense and was very effective. <S> Another major factor was that the fire control system was dependent on a radar transmitter/receiver. <S> That in itself is a problem, because the radar signal could be detected and identified. <S> When you are flying into enemy territory, you really don't want to do it with a radar transmission signal that says "BUFF OVER HERE WITH LARGE PAYLOAD <S> THAT WILL DO MASSIVE STRATEGIC DAMAGE IF WE GET THROUGH". <S> It needed to be re-engineered to be more stealth, and the USAF didn't assess the time and cost to do that would pay off. <A> Flexible gunnery is useless against surface-to-air and air-to-air missiles. <S> Which is the backbone of today's air defense systems. <S> Instead bombers have other means to distract said missiles. <S> ( Source ) <S> Flares and such. <A> Because the defending nations stopped sending fighter planes at them to shoot them down at close range (where those guns were effective) and instead launched Ground to Air or Air to Air missiles at them from a larger distance. <S> This meant that it's more important to defend against missiles than against fighters. <A> Gun turrets are for defending against aircraft that are within gun range. <S> However, modern fighters will usually lock on and fire missiles long before the fighter is within the range of a gun turret. <A> Nowadays, you can lock onto planes that you can barely see or even not see at all. <S> On the other hand, you have a very limited effective range with machineguns. <S> Also, keep in mind that shooting down a plane from another plane is very hard (check videos on gunner training in WWII). <S> Now imagine trying to do so on very fast planes like nowadays fighter jets. <S> To sum things up, most of the time, you won't even be in range to be able to use your machine guns and, even if you were, it would probably be really hard to defend yourself effectively. <S> Keep in mind that adding these machineguns weights down the aircraft and might even hinder the installation of more important equipment like flares or jammers. <S> There was a tailgunner on the B-52 because the use of canons by jet fighters back in the Vietnam war was more common than nowadays. <A> At least one North Vietnamese fighter was shot down by a B52D's rear gun armament during the Vietnam War, however.
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Modern fighters are usually armed with missiles, with which they can engage from far beyond the range of guns. First, fighter tactics have evolved over time, and second, the role of the B-52 has evolved over time.
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What is the real impact of biofuels on aviation? I have seen tons of initiatives about using biofuels (like the ASTM D7566), but it is operative at large scale?, there is background info about demonstrative flights, but I don’t see a manufacturer or airline that is making use of the biofuel in regular basis. It is a viable way of operate or it is a nonviable idea? <Q> When they burn, they produce exactly the same amount of CO2 as fossil fuels, but , all this CO2 came from CO2 that was already in the atmosphere. <S> So it's only putting back what was already there: <S> From the standpoint of human-released carbon dioxide, other greenhouse gas emissions, and contributions to climate change biofuels have one large advantage over gasoline, diesel and other fossil fuels: The feedstocks for biofuels are part of the above-ground carbon cycle. <S> Unlike petroleum or coal, the soybeans, corn, switchgrass and other biological materials that are made into biofuels are not dug up from underground, nor do they release long-stored carbon as carbon dioxide into the atmosphere when burned. <S> Instead, when biofuels are burned, carbon dioxide they recently captured is release back into the atmosphere. <S> This is sometimes claimed to mean biofuels are carbon neutral. <S> For example, it's claimed here a 95% reduction occurs . <S> But it's a bit more complex than that: Producing biofuel with crops like corn often requires converting land from food to fuel production or destroying natural ecosystems that provide valuable services, including carbon sequestration. <S> Crops also require fertilizers, pesticides and large amounts of water, as well as machinery for planting, growing, harvesting, transporting and processing. <S> If forests are cleared for fuel crops and if the entire lifecycle of the fuels is taken into account, biofuels don't always reduce overall greenhouse gas emissions. <S> Palm oil, used for biodiesel, is especially bad, because valuable carbon sinks like peat bogs and rain forests are often destroyed to grow palms. <A> As noted by Wikipedia , bio-fuel remains more expensive than traditional fuels. <S> A medium sized airline such as Jet Blue spends something like \$1 billion per year on fuel. <S> So if bio-fuel is a mere 1% more expensive (i.e. a few cents as mentioned by Ron), that costs them an extra \$10 million per year. <A> Yes it is viable, but like all new processes will need to go through the cycle of R&D, then scaling up production and distribution, then obtaining economy of scale. <S> Cost is always a driving factor in the succes of a product, both for businesses and consumers. <S> The traditional oil refining industry has a lead and experience of over a century in tackling and solving the problems associated with large scale logistics: there is a lot of aviation fuel that needs to be shipped and trucked around the world. <S> They could start this in a time when they could focus only on economical problems, not environmental ones. <S> Shell sold its refinery in the Netherlands Antilles in the 1980s: it was set up in the 1910s, supplied the majority of aviation fuel to the allied air forces in WW2, and was very much up for a total rebuild to comply with present day duty of care. <S> A sale of the refinery for one dollar to the Venezuelan state oil company PDVSA was deemed the best solution at the time. <S> So biofuel logistics needs to tackle the same logistical problems that conventional logistics has a century old headstart in, using technologies untried at this scale, and will have much higher production costs than traditional processes. <S> In countries where a large part of fuel cost is made up by taxes, the government can play a beneficial role here.
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The "real" (or at least ideal) impact of biofuels in aviation is a reduction in CO2 emissions.
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What kind of delay does the A320's fly-by-wire system add? More precisely, I am wondering if there is any kind of data on how long it takes between moving the sidestick and observing a reaction on the ailerons or elevator. I know that the physical control surfaces take time to move and, thus, I am only wondering about the actual latency added by the fly-by-wire (FBW) system. My naive assumption is that the A320 runs a fixed control loop with precise timings. So, every $n$ milliseconds it samples the sidestick, calculates the necessary control surface deflections and then sends that via some bus which runs at $m$ Hertz. So, on average there is an expected delay of $x$ milliseconds between input and the control surfaces starting to respond to the input. Also, is the delay noticeable by pilots? <Q> I've seen position control loops run successfully and stable at a couple of hundred Hz for simulator motion systems, and the time delay is just one iteration frame = less than 10 msec. <S> And as @ymb1 correctly points out, if we deflect any control surface the end position is subject to actuation forces, aerodynamic pushback forces, inertia of the surface, cable stretch and -friction, aero damping, maximum flow velocity through the servo valve etc etc. <S> The total transfer function of stick input = <S> > surface position is such that an extra time delay of 10 msec in the total loop is not really noticeable. <S> And control position is only the input of the aircraft response, with aircraft inertia playing a large role. <S> So my answer would be: a tiny time delay that can be totally disregarded. <A> I don't have an answer for the timings (I personally don't think that's publicly available information), but I can answer this <S> is the delay noticeable by pilots? <S> as I have some direct experience, and I can affirm that no, the pilot does not perceive a delay between a stick deflection and the aircraft reaction. <A> No, no, you can move a side stick much, much more quickly than moving the conventional controls. <S> Side stick inputs to the computers are updated every 10 ms which is extremely fast, this corresponds to 100hz update; compared to most television pictures update, FBW is twice as fast. <S> for very small displacement of conventional flight control, you have no flight control effect because of the system <S> Backlash <S> For very fast and large inputs in FBW, the order is voluntarily dampened to protect the aircraft structure, in conventional flight controls there is no protection <S> , you may damage the structure, mainly when the rudder is concerned even though the range is mechanically limited while in full FBW RUDDER, pedals EFFECT is voluntarily dampened when it gets dangerous to the structure <S> As a summary no ADDITIONAL delay with FBW
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Yes there will be a delay, but the delay caused by the control loop is really tiny.
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Do fighter jets use elevators as ailerons? I saw jets in game using elevators to roll right and left, but I never saw them doing in real life. I was wondering if fighter jets actually use elevator to roll like they do in game. <Q> Yes. <S> The airplane’s flight control computer can command a roll using all primary and secondary control surfaces, including differential actuation of the tailplane as Blue Angels #6 demonstrates during a preflight check. <A> Yes that exists, the combined elevator/ailerons are called elevons . <S> Particularly delta wing aircraft have them, because the space at the trailing edge of the wing is at a premium. <S> Image source Swing wing designs use elevons as well: <S> the F-14 Tomcat rolled through elevon and spoiler deflection. <S> This incident report mentions the elevon of the Panavia Tornado being damaged from a panel coming off. <A> This was the cause of many aircraft accidents. <S> The F-100 for example was infamous for something called the Sabre-Dance , where a pilot, by attempting to roll the aircraft using ailerons at high AOA on short final for landing, would induce a roll in the opposite direction, and put the aircraft out of control at very low altitude. <S> The F-4 also had this problem, although by the mid 60s, it was understood well enough that F-4 pilots were trained to use the rudder to roll the aircraft at higher AOA. <S> Instructors, training new pilots, were themselves trained to emphasize this flight characteristic, and, whenever at high AOA, to keep our knees in the back seat right up against the control stick to inhibit new pilots from introducing any aileron. <S> Before Fly-By-Wire was introduced, this tendency was addressed by having the stabilator, (Horizonal stabilizer and elevator), surface be differentially controllable, and mechanize it so that the fore and aft position of the control stick controlled the degree to which left/right deflection of the control stick would cause aileron deflection vs. differential stabilator deflection. <S> At low AOA (where control stick was forward), left right motion caused only aileron deflection. <S> At very high AOA (where control stick was aft), left/right deflection would cause mostly differential stabilator. <S> ( I think the first aircraft to use this technique was F-15, where it was implemented using mechanical linkages in the flight controls). <S> Later of course, once Fly By Wire (FBW) was introduced, this was all done by the computer, and it was determined directly from measured AOA, and not just from stick position.
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Yes, high performance aircraft prior to the F-15/F-16 era (1970) or so, had a real problem in that attempting to roll the aircraft using ailerons, when at higher angle of attack(AOA) would, because of Adverse Yaw , produce a yaw in the opposite direction, (Stick to the left would produce right Yaw), which, because of the wing sweep, would create a roll opposite the intended direction. The F-117 had elevons as well, as did Concorde.
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Why are the character keys on the Flight Management Computer in alphabetical order? Regardless of which aircraft type and manufacturer, the character keys on any Flight Management Computer are always in alphabetical order, see image: From a human factors view, this is sub-optimal, so why? Where does this order come from? From chats with pilots I learned that you get used to it easily and can type quite fast with this alphabetical layout, but still, we are all used to the QWERTY or QWERTZ layout... <Q> "we are all used to the QWERTY or QWERTZ layout..." or AZERTY. <S> But which one? <S> Universally there is no one standard, so whichever of these 3 (and others) is chosen, it will be wrong for some users. <S> So the only standard left is simple alphabetic. <S> Another thing to consider is that the QWERTY-types of layout were chosen to deliberately slow down typists on mechanical typewriters. <S> This slow-down is not necessary on an electronic piece of kit, so the pure-alph format is quite fast once you're used to it. <A> To touch type as professionally trained, a keyboard must be in front of the typist, equally accessible with both hands, with limited number of rows <S> (palms must stay close to the "standard position"). <S> The keys should not make vertical rows, keys in adjacent horizontal rows must be slightly shifted, the key size is dictated by finger size and cannot be too small. <S> The standard key placement is helpful, but also other can be learned as long other requirements are met (which, for these keyboards, are not). <S> Just putting letters in QWERTY order is not helpful. <S> Probably nobody writes novels, computer software or E-mails to multiple customers on this keyboard, so limited typing speed is not much a problem. <A> we are all used to the QWERTY or QWERTZ layout... <S> Now we all have computers and most of them come with QWERTY keyboard. <S> However in 70's when the early FMS were designed, computers were mainly in research institutions and big companies and most pilots would never use one (though their dispatch might have had some by that point). <S> So most people would only see the layout on a typewriter and average pilot didn't need that either. <S> So most pilots probably were not used to the layout back when it was created. <S> And since then, since some pilots were already used to the previous design, it was always more useful to stick with that design.
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The placement and form factor of these keyboards is not suitable for applying a classic touch-typing technique.
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Do wingtip vortices really only form when airplane wheels are separated from the ground? My GA theory textbook (which covers fixed wing up to and including EASA PPL) has some suggestions on taking off and landing light aircraft soon after large aircraft (besides avoiding it, if possible), intended to reduce the risk from wingtip vortices. These suggestions are to, when taking off ...after a heavy aircraft taking off , to lift off at a point on the runway before the heavier aircraft lifted off ...after a heavy aircraft landing , to lift off at a point on the runway later than where the heavier aircraft's nose wheel touched the runway when landing ...after a heavy aircraft taking off , to land as early as possible on the runway ...after a heavy aircraft landing , to land ahead of the point on the runway where the large aircraft touched down When I asked about the why of these suggestions, the answer was that wingtip vortices form because the wings are generating lift, and when the aircraft's wheels are on the ground, the wings don't generate (or aren't generating) lift so no wingtip vortices form. While that might be true in a "rule of thumb" sense, and a good generalization of these rules to serve as a memory aid, I want a bit more than that. The way I understand it, Any airfoil will generate some amount of lift as long as there is ambient air movement around it; "lift" (as opposed to net positive vertical lift , which isn't being generated when landing anyway because the aircraft is descending) isn't something that suddenly starts being generated when one or more of the aircraft's wheels are separated from the ground An aircraft can move at significant speed relative to the surrounding air even when all of its wheels are on the ground, causing likewise significant speed of movement of the wings through the ambient air It appears to me that wingtip vortices should form at any time the aircraft (or rather its wings) is moving relative to the surrounding air; whether that's because the aircraft is standing still and there's a wind, or because there's no ambient air movement and the aircraft is moving, or a combination of the two. It also appears to me that the strength of the vortices should be in some way proportional to the amount of lift being generated. Consquently, it seems to me that wingtip vortices should form at every point during the takeoff or landing roll (as well as taxiing and other movement on the ground) at which the aircraft is moving relative to the surrounding air, and increase in strength with (but not necessarily linearly with) the indicated airspeed of the aircraft. It seems weird that the air flowing near the wingtips would somehow "know" anything about the position of the aircraft's wheels with respect to the ground, let alone that of any specific wheel (such as the nose wheel). All that just as the lead-in to my question: am I missing something, or is this a case of the textbook (and teacher) presenting the simple case so as to not overwhelm students? <Q> You are absolutely right. <S> The vortices form whenever the wings produce lift. <S> Even if the lift is not enough to let the aircraft fly. <S> Of course it is necessary to have a flow across the wing, and with very low speeds (like taxiing) <S> the vortex is likely to be very small. <S> But, it seems your textbook is trying to establish a save way to avoid the vortices of previous aircrafts. <S> And since the strength of the vortex is related to the lift which is related to the air-speed and angle-of-attack this rule of thumb is quite practical. <S> Especially since landing is a highly transient process which is very likely to result in a significant reduction of vortex strength. <A> You are correct, but your textbook is more correct. <S> Here's why <S> : Your reasoning is that lift is a function of airspeed , which is true. <S> However lift is also a function of angle of attack . <S> This is why large aircrafts take off the way they do: they accelerate on the ground with a very small AoA, hence little lift. <S> Since lift increases with drag, by accelerating when producing minimum lift, drag is reduced, and the acceleration to takeoff speed can be achieved on a shorter runway length. <S> By pitching up at the right moment, lift is dramatically increased, and lift off is accomplished. <S> The reverse is true when landing. <S> The purpose of the landing rollout is to absorb the kinetic energy of the plane in the brakes. <S> Having the wings create lift reduces the friction between the tires and the ground, which does no good at all. <S> Therefore lift is dumped as soon as practical during the landing rollout. <S> It should be noted that, one technique to achieve a short field takeoff in a light aircraft is to accelerate with no flaps. <S> Then, when the takeoff speed is reached, quickly apply a notch of flaps and the plane will lift off the ground. <S> This technique is usually not taught to new pilots because it requires skillful coordination, but it illustrates that lift is suddenly increased at the point of lift off. <S> Another way to phrase it would be: when the wheels are on the ground, the amount of lift generated is small and usually within the tolerances of a light aircraft. <S> But you are correct in saying that lift is still generated as long as there is relative movement between the wing and air. <A> When the aircraft is on the ground, the wheels are supporting it. <S> When it is in the air, the wings are generating the upward force necessary for lifting it. <S> So at take-off, there is a sudden transition from wheels to wings in the lifting function. <S> Any airfoil will generate some amount of lift as long as there is ambient air movement around it; That depends on the angle of attack: <S> symmetrical airfoils generate zero lift at zero AoA; a-symmetrical airfoils generate zero lift at a slightly negative AoA; airliner wings have wing twist: the area near the tip can have negative AoA when on ground; the overall AoA of aircraft wings with short nose gear is negative when on ground. <S> Iron birds at an aircraft factory that go through their fatigue cycles simulate the starting cycle by actuating the wing up/down during taxiing (from bumping on the taxiway), then during the takeoff run the bumping intensifies, then at the take-off nose-up motion the wings bend upwards <S> dramatically - one can hear them groan and creak while they bend. <S> "lift" (as opposed to net positive vertical lift, which isn't being generated when landing anyway because the aircraft is descending) isn't something that suddenly starts being generated when one or more of the aircraft's wheels are separated from the ground.
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Strictly speaking there will be some downward force generated by the wings, but the transition from wheels to wings is so dramatic that for practical purposes we can indeed state that wingtip vortices are only significant with the wheels off of the ground.
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Do some right-handed pilots fail to use the left stick of an Airbus? After years of flying left-hand throttle and right-hand yoke (in the right seat), are there ever first officers who simply cannot transition to the opposite due to particular hand-dominance? As a corollary, are there any pilots who simply cannot acquire the left-hand dexterity/sensitivity to use the Airbus joystick when transitioning to captain? And in all cases, are there ever trainees who cannot get used to yoking or throttling with a non-dominant? <Q> In a study titled ' Role of handedness in flying performance ', the author notes: <S> [Leon had reported] that movements in one limb were not affected by actions in the other limb. <S> It may be for similar reasons that in multi-crew cockpits of transport and passenger aircraft, pilots have not reported any difficulty in operating controls at either the left or right seat even though the layout of the controls is a "mirror image". <S> From an observation that may or may not have been studied, operating controls is not like handwriting—handwriting requires major shifts in body position to use the other hand. <S> The human brain is really good at ordering one hand to mirror or follow the path of the other hand. <S> If you think of the yoke as a steering wheel, then when switching from right to left seat, the left hand follows the circular path of the now free hand. <S> It takes getting used to, but unlike handwriting, it's very quick. <S> I've done this experiment years ago. <S> If you have a flight simulator, setup the plane on approach and switch the joystick from your preferred side to the other. <S> In my case, just like the study above, I did not find any difficulty. <S> https://commons.wikimedia.org/wiki/File:Patria_pilot_training_OH-GSC_Malmi_3.JPG <S> Above is the cockpit of a Cirrus aircraft , it's often remarked that the stick resembles half a yoke, and would be operated much like any yoke. <S> The same is said about the Airbus stick. <S> But Airbus also has an armrest, which is very beneficial as the precision increases when the arm is rested, see here: <S> Why don't we fly helicopters with yokes? <A> Part a pilot's career is transitioning between the left and right seats (single pilot, captain, first officer, flight instructor, etc). <S> By the time a pilot gets to fly airliners they are accustomed to flying in both seats. <A> To be honest, it takes all of about 10 minutes to transition between a control yoke and a stick. <S> The more strained process is learning the systems, performance numbers and procedures. <S> Most certified aircraft have docile handling characteristics and good handling qualities and the kinesthetics feel of the stick quickly becomes accustomed to during the transition process. <S> Another factor is that many professional pilots are also certified flight instructors and have developed a familiarity with transitioning into new aircraft from both the left and the right seat. <S> Now some people who learned how to fly one type of plane only and have a lot of hours in it, then attempt to switch to another <S> have problems doing so, mainly due to handling qualities between the two aircraft. <S> I once saw a guy who recently bought a SR-22 after logging 800 or so hours in a PA-28R Arrow IV. <S> He seemingly could not land the new Cirrus no matter how hard he tried. <S> Again with limited flight time in different types and develop habits around the handling of one platform, it becomes harder and harder to change between types regardless of whether they use yokes, sticks, ram’s horns, etc.
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The more varied and different types of aircraft a pilot has flown, the easier this process is.
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What experimental techniques should one employ during cruise flight to determine correct airspeed to fly for max range in a headwind or tailwind? Theory demonstrates that one ought to increase speed in an headwind, and decrease speed in a tailwind to achieve maximum range. A lengthy discussion on the theoretical solution was answered, though not clearly, here . It is unlikely that a pilot will have the Thrust Required chart on which to draw a tangent line through the x-axis intercept at the given wind speed. What simple techniques should the pilot employ to determine the best speed to fly given specific environmental conditions (fixed headwind or tailwind)? <Q> An old technique is "Half the Headwind, all the Tailwind". <S> So if you're flying into a headwind of 20kts, increase your cruise speed by 10kts. <S> If it's a 20kt tailwind, decrease your Cruise Speed by 20kts (but only as far as BestEnduranceSpeed). <A> Since speed is increased in headwind, and decreased in tailwind, that's a good starting point. <S> Let's assume it's a headwind. <S> Increase the speed in increments, and calculate the range using the fuel flow figures and ground speed. <S> Some engine trend monitors are capable of doing that. <S> Keep increasing until the range starts going down, and go back one step. <S> Full disclosure: I'm not a test pilot. <A> In a good day, with no wind, you can make trial glides and note down the values of the variometer and of the anemometer. <S> Four or five points are enough to draw a best-fit parabola. <S> Once you have it, you find the best range speed for any wind condition by tracing a tangent to the parabola that starts at the value of the wind. <S> You note down the airspeed given by the tangent, and that's the best range speed for that wind condition. <A> Best Endurance Vg plus headwind <S> componentOR minus tailwind component Or Carson Number(Cost = 16% increase in fuel consumption)Carson = <S> Vg x 0.32Headwind = Carson + (Headwind/3)Tailwind = <S> Carson - (Headwind/3)
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You may make a list of winds and the corresponding best range speeds and have that list handy at the cockpit.
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How do elevons work to roll a flying wing? I have an RC Flying Wing that uses elevons for control. To go up both elevons move upwards and the wing pitches up. Both go down and the wing pitches down. I’m OK with this. However, if I want to roll right, looking from the rear of the wing, the left hand elevon goes down and the right hand one goes up. I can see this when I fly it that it rolls right but don’t understand why? If an upward pitch angle produces lift to go up, (like when the elevons act as elevators) then why doesn’t the right wing produce more lift and thus the wing roll left? Either a flap produces lift or doesn’t? <Q> Good question! <S> There's a bit of a misconception: when the elevon moves up, it actually decreases lift. <S> It pushes air up which pushes the wing down. <S> This explains the roll behaviour, but how does decreasing the lift make the plane go up? <S> The key here is that the lift is reduced only at the rear of the plane. <S> In other words, the rear of the plane is pushed down, but only the rear. <S> This makes the nose point up (just put the plane on the floor and push down on the tail, the nose will be up). <S> In this new orientation, the angle of attack (the angle of the wing relative to the airflow) is increased, and consequently the lift increases (the little bit of downforce at the rear of the wing doesn't really make a big difference). <S> The plane will start to climb, which will reduce the angle of attack (the wing will be pointed the same way as the direction of travel), until the plane is in a steady climb. <A> A somewhat simplified answer. <S> When both elevons go up, they will push the back of the plane down. <S> This makes the nose start to point upwards, or, as we say, the plane pitches up. <S> This increases lift, and so the plane goes up. <S> So the sequence really is: elevons up -- <S> > <S> back end pushed down = pitch up -- <S> > <S> increased lift -- <S> > increasing height. <S> roll towards the elevon going up. <A> A downward deflected elevon creates an upward force, an upward deflected elevon creates a downward force. <S> This pair of forces thus produce a rolling moment, making the aircraft start to roll.
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If one elevon goes up, and one down: the one going up will create a pressure downwards, the one going down will create a pressure upwards -->
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Does the FAA maintain pilot records from before 1998? I have held a PPL with an instrument rating since 1999, and I am desperate to continue, but I lost my logbook. Is there any way to get records from the FAA about my total flying time? I contacted my flight school, but they say they don't have a record of me, so they asked me to start over from 0 hours. What can I do? <Q> If you took a checkride the FAA has your 8710 <S> (form you would have filled out) which will have your flight times and can be used as proof of time. <S> Follow <S> these steps to get your records. <S> You can search the airman database . <S> My father's and grandfather's records are in there from the 1970s and 1980s. <S> This just lists certificates though, no times. <S> You can also request a replacement certificate . <S> If you are a PPL then they will send you one. <S> You'll need to do this anyway to get the new plastic card. <S> Also, no times...just a certificate... <S> which prove that you have at least the minimum flight time required to hold the certificate. <S> Good luck. <A> If you hold a PPL and an instrument rating, then those are locked in by virtue of having earned them. <S> If by chance they do, they do not have records of your individual flights, so the evidence of what you would be reporting is lost. <S> You will likely have to start over with <S> 0 hours logged as a pilot with a PPL and instrument rating. <S> You may want to look into an electronic logbook service to prevent this from happening in the future. <A> At least since the 1970's (when I received my PPL), the FAA has had all pilot information stored and available on micro-fiche. <S> I would expect the FAA has transferred, or at least be in the process of transferring the micro-fiche information to digital storage. <S> I would assume a request for a complete set of records includes print-outs of any remaining micro-fiche files and all digital storage in more recent years. <S> The FAA has a fee and specific form that needs to be filled out, the form is AC_8060-68 <S> The fee is 2 dollars for each search of records, .10 cents per printed page and an optional $10 for Certification of the record.
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Surely the FAA has records confirming that you are a pilot with an instrument rating, but they may not have your total times from 20 years ago.
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What's the appropriate course of action if an airliner bounces 5-10 feet on touchdown? I regularly fly in a PC flight simulator, and I'm currently trying to refine landings in medium-to-large airliners in various weather conditions. A problem I've faced in some conditions while flying the 737-800 has been bouncing on touchdown, where I lose just enough lift in the last few feet of my approach to touch down firmly on the main gear only, before bouncing back up 5-10 feet. While I'm already looking into avoiding this kind of bounce whenever possible, I'd like to know what common procedures are in this situation assuming the gear is left intact and there's no urgent failures or factors (such as a fuel emergency) which would time-constrain a landing. Specifically; would a real-world flight in this situation go around, adjust thrust, adjust flare, or do something else entirely? <Q> Well, "5 to 10 feet" is not "slightly." <S> One or two feet is "slightly," and in that case you can maintain your landing attitude or pitch very slightly nose-down -- really a matter of the slightest change in pressure, not really a perceptible change in pitch -- and you'll land soon after that. <S> However, for a larger bounce, the concern, especially on the longer 737's, the -800 and -900 and -900ER, is a tail-strike. <S> The tail skid protects the tail from a strike on takeoff, but on landing the geometry is different and the skid won't be what contacts the runway; it will be the fuselage. <S> And while tail strikes on takeoff are more common, it's the tail strikes on landing that are far more damaging & expensive. <S> So avoiding one of those is a major concern. <S> Thus, the usual guidance in the event of a bounced landing in the 737-800 is not to attempt to salvage the landing, but rather to go around. <S> One thing that complicates recovering from a bounce is the fact that your spoilers may have extended when you touched down the first time -- and the last ten feet to the runway with spoilers fully extended & power already at idle, won't look nearly the same as the usual last ten feet to the runway, with power coming off & no spoilers. <S> You'll settle fast, and hard, and you won't have the elevator authority you're used to for adjusting the sink rate. <S> You can pull back, but the change in attitude probably won't arrest the sink rate the way you think it will -- you'll just hit harder & in a more nose-high attitude. <S> Thus the increased risk of hitting the tail. <S> On a shorter aircraft without the tail-strike concerns (say a 737-200, -300, -500, -600, or -700), it might be possible to salvage the bounced landing, <S> although 10 feet up is a pretty high bounce -- even if you had a lot of airspeed to play with and runway ahead of you, I'm not sure it would be wise trying to sort that situation out -- go around & try again. <A> Your first reaction should be to advance the throttles. <S> Not all the way, but to around 40%. <S> This keeps the plane flying and avoid it sinking onto the ground in an impact that might collapse the landing gear. <S> Your second instinct would be to avoid large or abrupt pitch changes. <S> If you attempt to chase it, you might end up in pilot-induced oscillations. <S> Forget about the VSI and radar altimeter, fly the AI. <S> Pitch to about 2~3 degrees up. <S> That is why you always have one hand on the throttles and the other hand on the yoke while landing. <S> Now that you have accomplished all that, you can evaluate your options. <S> What is the condition that caused the bounce? <S> Is there a strong and gusty crosswind? <S> Poor height judgment? <S> Excessive airspeed? <S> How likely is it that you can land it on the remaining runway? <S> Are you trying to land on a 13,000 feet runway on a calm day, or 7,500 feet runway on a rainy night? <S> You need to make a decision quickly. <S> Ralph J has already stated the things that can go wrong when you try to salvage a bounced landing, which I will not repeat here. <S> Also, as stated, a bounce to 10 feet in real life is a very hard bounce, and more than a few passengers will certainly be upset. <S> Unless there is an emergency or fuel situation, a go-around is always an option. <S> And the reason why pilots have license is to ensure they won't end up going-around every time until they run out of fuel. <A> I <S> that case, you just have to keep the nose up at the same angle and you don't touch anything... <S> Just wait to be back on the ground. <S> This is the safest way because : if you put more engine power at this particular moment you will perform a very long landing <S> and it's not safe at all. <S> If you try to pull the nose up, you"ll risk to touch the tail. <S> To avoid to rebound, try to wait until 10 to 20 feet on a 737 (30 to 40 feet on a B777) on the radio altimeter and just retain a little bit (few degrees) <S> the pitch command back with a firm and quite fast move and block the position of the pitch <S> ( do not try to continue the backward movement ) <S> On real airliner that's what we do <S> and then the ground effect will normally play its role and you'll make a very soft landing.
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You may touch down again during the go-around, and that's okay, but you're better off aborting the landing & taking it around to try again, than to risk damaging the aircraft by trying to recover from a high bounce.
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Would removing heat from the compressor and adding heat to the turbine increase a gas turbine's efficiency? Since a compressor compresses air, the air temperature increases due to P1/T1=P2/T2. When the temperature is increased it would be harder to compress - so would removing the heat from the air inside the compressor reduce the energy required by the compressor, and increase the efficiency of the engine? Also, since the turbine accepts hot air and uses the expansion of the gas to do work, would adding the heat extracted from the compressor to the turbine area increase efficiency even further? <Q> Heat removal like that is sometimes done in gas turbine engines, not by cooling the compressor during operation, but by the use of an isobaric intercooler between the low and high pressure compressors. <S> These kinds of configurations are common in industrial gas turbines used for electric power generation, marine propulsion and other applications where extra weight is not as large of an issue as is with aviation gas turbines. <S> As far as adding this extracted heat energy back into the gas flow through the turbine section, this would not be possible as compressor outlet temps are in the neighborhood of 450 <S> °F where exhaust gases exit at around 1000 <S> °F, preventing a return of the compressor heat to the turbine section for extra power. <S> Typically intercooler exhaust is simply vented into the atmosphere. <S> More commonly, gas turbines are used in combined cycle powerplants which make use of the gas turbine exhaust heat to power a water boiler driving a steam turbine and secondary generator. <S> Some of the thermodynamic cycles used in these systems can be quite elaborate and can achieve an exergetic efficiency of over 60%, making them the most efficient heat engines on the planet. <A> TL;DR: <S> You are absolutely right! <S> your basic considerations are correct. <S> The obstacles are in the engineering and commercial field. <S> Engineering: Designing heat-exchangers which are small, light, and low-loss. <S> Commercial: <S> Reduce cost. <S> I am currently only aware of one european research program ( NEWAC to overcome these obstacles <S> but I am sure there are others. <S> The following illustration is from NEWAC’s homepage: <A> It is possible to increase efficiency of a gas turbine in two ways: by cooling air before it enters a compressor, or by heating air after it leaves a compressor. <S> It is therefore possible with an internal heat exchanger - if the heat flows opposite to what is posed in the OP: from the hot exhaust gases to the air delivered by the compressor. <S> From the Wikipedia article for Brayton cycle (which is what takes place inside a gas turbine): <S> Recuperator[14] – If the Brayton cycle is run at a low pressure ratio and a high temperature increase in the combustion chamber, the exhaust gas (after the last turbine stage) might still be hotter than the compressed inlet gas (after the last compression stage but before the combustor). <S> In that case, a heat exchanger can be used to transfer thermal energy from the exhaust to the already compressed gas, before it enters the combustion chamber. <S> The thermal energy transferred is effectively reused, thus increasing efficiency as well. <S> Note that the heat must be added after the compressor/before the combustion chamber. <S> From the same article: Transferring heat from the outlet (after the last turbine) to the inlet (before the first compressor stage) would reduce efficiency, as hotter inlet air means more volume, thus more work for the compressor. <S> In that light, cooling air before it enters a compressor increases efficiency. <S> Adding heat after the turbine decreases efficiency but does increase thrust, as afterburners demonstrate.
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There can be a thermodynamic advantage (inter)cooling the compressor and pre-/re-heating the turbine.
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Why does the B-52 outboard engine nacelle have a sharp change in shape? The outboard engine nacelle of a B-52 appears to have a change of shape too extreme for just blending to the center-line of the engine pod. Why is the B-52 outboard engine nacelle shaped the way it is? <Q> The B-52 was build in different versions (A-H) and <S> the engines and their installation differ between these version 1 . <S> The image in the question most likely shows the engine configuration of a B-52 H . <S> The following drawings suggest that this also changed the inlet design 2 . <S> There seem to be different engine-designations depending on the application. <S> For the B-52H, JT3Ds (TF33-P-3) were used 3 . <S> Pictures of the TF33-P-3 inlet show they are symmetrical. <S> (While the question is focused at the outboard engine-inlet, this question can only be answered taking the other engine and the placement relative to the wing into account as well). <S> At the symmetry-plane the TF33-P-3 inlet-section extends further than the rest of the inlet-lip. <S> I would guess that there are multiple reasons and considerations which led to this design. <S> Three of which will most likely have been: Basic aerodynamic considerations like stagnation-point and pressure distribution will prefer a sharp/point nose over a flat area. <S> Especially since the air needs to be diverted from the engine-pylon. <S> The cruise speed of the B-52H is Mach <S> 0.91 4 which means the nose could also be some kind of anti-shock-body reducing wave-drag by applying the area-rule . <S> The nose between the two engines prevents aerodynamic interaction of the two engines, for example during cross-wind operation. <S> The negative aspects of placing two jet-engines close to each other were also discussed in another SE-question with respect to commercial airliners. <S> [1]: <S> www.airpowerstrategy.com/ [2]: http://www.afwing.com/ [3]: en.wikipedia.org/wiki/Pratt_%26_Whitney_JT3D [4]: www.globalsecurity.org/wmd/systems/b-52.htm <A> A lot of pictures of this intake make it quite hard to determine what is the exact geometry. <S> But the one below is by far the best - thank you @ymb1. <S> http://www.af.mil/News/Photos/igphoto/2001513002/ <S> Before, it was hard to tell exactly what's happening. <S> In some pictures, it looked like the inboard engine was slightly further forward of the outboard engine. <S> But that is now shown to be incorrect. <S> The above picture shows where the two intakes touch, the duct protrudes further forward, with a sort of "nose". <S> This can be clearly seen from the parts of the inlet lit by the sun, and the bump in the shadow of the engine on the ground. <S> I would strongly expect this is to keep the airflow smooth, and reduce aerodynamic interference between the two inlets, and avoid turbulence that would cause inlet pressure distortion. <S> This is, to avoid a difference in total pressure for each engine, between the side that is adjacent to the other engine, and the side that isn't. <S> Uneven total pressure, or inlet distortion, can cause compressor stalls. <A> That looks like an optical illusion due to the angle to me. <S> A photo on this site shows a more frontal view of the outboard engines, with just the equal centre division between the two engines appearing. <S> Close-up underneath. <A> Why does the B-52 outboard engine nacelle have a sharp change in shape? <S> Not just the outboard, but all 8 engines on a B-52 have the same inlet design. <S> The original engines had a smaller fan diameter and symmetrical round inlets. <S> I suspect going to a larger fan diameter <S> created flow problems <S> which the engineers solved by modifying the inlets. <A> This inlet design was already used on the Convair B-36 D , which had twin turbojets added on the outer wing to give it a higher top speed when penetrating enemy airspace. <S> During cruise, only the six piston engines would run and the jet engine inlets were plugged to reduce their aerodynamic drag. <S> This plugged state is shown in the picture below (picture source ): <S> Since the B-36 was a purely subsonic design, any intention of area ruling in this design can be confidently ruled out (pun intended). <S> The same engine was used on the Boeing B-47 , but here the twin intakes of the inner nacelle show no such protruding center (below, picture source ): <S> Seems the Convair engineers knew something that the Boeing engineers didn't. <S> But in Seattle they caught up eventually, and the larger airflow of the P&W TF-33 turbofans made them use the same trick from the Boeing B-52 H on. <S> All versions before used the J57 turbojet and the simple B-47 style nacelle shape (B-52 F below, picture source ): <S> By pulling the divider forward in the center of the nacelle, any spillage will occur away from the running engine, ensuring symmetric intake flow there.
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The reason is the distorted airflow from spillage if one engine of a pair has to be shut down.
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