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Do pilots have to stop at the hold position of the takeoff runway? Or in other words, is the takeoff clearance ever given (implicitly or explicitly) before the aircraft reaches the hold position, so that the pilot can keep rolling through the hold line and to the takeoff roll? <Q> Typical clearances given before departure are: BigAir 123, hold short of runway 36. <S> BigAir 123, line up and wait runway 36. <S> Former phraseology in the US was "position and hold". <S> BigAir 123, behind landing A320, line up and wait runway 36, behind. <S> Note the word "behind" being repeated at the end of the clearance. <S> The interesting ones: <S> BigAir 123, are you ready for immediate departure? <S> It will be asked by the tower controller to assess if they can squeeze BigAir 123's departure between two landings, for example. <S> BigAir 123, cleared for takeoff runway 36. <S> It can be given to an aircraft still on the taxiway. <S> In such case, BigAir 123, who will have proceeded through checklists and briefings while taxiing, will turn into the runway and takeoff, without having to stop at any point. <S> It is possible that the crew actually needs to stop, to finish their preparations. <S> In such case, they will normally report not ready for departure, if asked. <S> The tower controller doesn't want aircraft making unexpected stops on the runway, especially in a single-runway airport, this can result in the following landing having to go-around. <S> Also note that the word "takeoff" is used only in the context of an actual takeoff clearance or its cancellation. <S> Otherwise the word "departure" is used, e.g., are you ready for departure? <S> Also see the Tenerife disaster . <A> No, it is not always mandatory to stop at the hold line. <S> Yes, the Tower controller can give you clearance to enter the runway (cross the hold line) before you actually stop at the hold line, in which case you're not required to stop there. <S> If the controller gives an aircraft the clearance: Runway XX, Clear for Takeoff <S> Then the aircraft may both cross the hold line to enter runway XX and proceed to take off on it. <S> Whether the aircraft stops after lining up at the end of the runway is up to the discretion of the Captain. <S> Some pilots will chose to come to a stop after lining up and then select takeoff power, while others will just keep rolling and select takeoff power once they're aligned with the runway. <S> The controller may also add "No Delay" to the clearance. <S> In that case, the pilot should not stop if it can be avoided or should at least keep the stop to an absolute minimum. <S> If the pilots are unable to do that, they should reject the clearance and not enter the runway. <S> If the controller gives an aircraft the clearance: <S> Runway XX, Line Up and Wait <S> Then the aircraft is clear to cross the hold line to enter runway XX, but, after lining up, should stop and wait for takeoff clearance before proceeding to initiate the takeoff run. <S> Either of these clearances can be given while the aircraft is still rolling on the taxiway and, in either case, the aircraft may cross the runway hold line to enter the runway without stopping. <A> While the above answers are technically correct--you can be given takeoff clearance while taxiing--this is rare. <S> The standard sequence is to receive a taxi clearance to the runway, where it is then mandatory to stop before the hold line. <S> Once there, you get your takeoff clearance, allowing you to enter the runway. <S> Disclaimer: this comes from the perspective of a piston-airplane pilot. <S> Because we have to do a run-up before takeoff, it is particularly true that we won't get clearance until we are ready at the line. <S> A jet, which does not have this requirement, might get an earlier clearance. <A> Two main instructions give a pilot clearance to cross a hold line: instructions to cross, and instructions for takeoff/line up. <S> Neither clearance requires the aircraft to actually stop at the hold line. <S> If the tower controller feels that clearance can be given early, they may do that. <S> This is particularly true if a runway is not active and would have no conflicts for crossing aircraft, or if there is no other traffic for the runway at the time. <A> Southwest 3828, Midway tower, runway 31C, line up and wait, don't plan on stopping . <S> That's in the audio but not in the subtitles, listen for it at 0:59. <S> ATC has a lot in motion, with Delta lining up on the cross runway and a short final approaching the other cross runway, and IIRC another flight on a 10-mile final on Southwest's runway. <S> Southwest has gotta go pretty much right now <S> or he'll lose the window of opportunity, <S> and so ATC is clearing him past every stop point before he can reach it. <S> ATC also cleared Delta to roll past the hold-short line, but did not clear him to takeoff. <S> If Delta had been paying more attention to chatter, he'd have the situational awareness to know what was going on. <S> Over in the railroad world, throwing clearances ahead of the train is SOP because of the high cost of restarting a train. <S> I once saw a beautifully written train order that is the old-school version of this same thing, giving statutory wait instructions you won't be using: <S> Extra 4419 East [a lowly switch job] move Echo to Alpha, take siding for Train 1. <S> Train 1 <S> [the late Presidential Limited] hold mainline and wait at Alpha until 7:00pm Bravo until 7:10pm Charley until 7:20pm Delta until 7:30pm for Extra 4419 East. <S> This schedule is impossible for Train 1, it can't get there at those times so it won't wait . <S> The order is for the benefit of X4419, who can now choose its meeting point with #1, without any further communication needed.
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You COULD request takeoff clearance as you are approaching the runway, obviating the need to come to a stop, but a towered airport is usually busy enough that the controller will want to see you at the line, ready to go, before giving you the runway. No, there is no mandatory stop.
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Do fighter jets have an auxiliary power unit? Do fighter jets have an auxiliary power unit? If they don't, then how does the propulsion/ignition process start in the engine? <Q> Most current fighters do. <S> A notable exception is the F-16. <S> The F-16 has a "jet fuel starter" (JFS), which is a small jet turbine started by a bottle of compressed air. <S> Unlike a normal APU, the JFS is linked directly to the main engine, so the only thing you can use it for is to start the main engine. <S> An APU can also provide backup electrical power. <S> Since the F-16 doesn't have one (and is a fly-by-wire aircraft, which requires electrical power for normal operation), it has an emergency power unit (EPU) instead. <S> The EPU uses a special fuel called H-70, which is 70% hydrazine, and 30% water. <S> Hydrazine (normally used as rocket propellant) doesn't require an external source of oxygen. <S> It carries its own oxygen supply; expose it to iridium and it immediately (well, within a couple milliseconds, anyway) starts to release large quantities of hot gas. <S> This runs a small turbine, which can restore power within about 2 seconds. <S> The main shortcoming is that hydrazine is quite hazardous (though the 30% water content of H-70 renders it substantially less hazardous than pure, anhydrous hydrazine). <A> To address the "how" part of the question <S> - non APU equipped <S> jets use some method to start the engine spinning to initiate airflow through the engine. <S> The JFS in the Viper powers the main gearbox, which is connected to (and spins) <S> the compressor core. <S> Same idea, different execution with jets that use a huffer cart. <S> A prime example is the T-38 with the J-85 engines. <S> The air cart spins drives compressed air through the core, spinning up the engine. <S> The igniters will initially be fired by the battery or by a generator. <A> Early fighter jets use pneumatic starters with air supplied by external start cart. <S> Larger, powerful, and modern jet fighters are usually equipped with some sort of gas turbine auxiliary power unit used for engine start in the event that external power sources, whether electric or pneumatic, are not available. <A> Yes, internal starting systems are found on most modern fighters, however be careful how you define 'modern'. <S> In my usage, 'modern' means anything designed and built in the 21st century, but many nations are using aircraft built decades ago, so a particular fighter may be very common and effective yet not technically 'modern' e.g. the F--15 and F-16 come to mind. <S> It dumps pressure into the jet fuel starter which in turn is used to start the engine. <S> If the accumulator loses its charge, the crew chief and/or a friend or two connect a 3-foot t-handle underneath the left main landing gear well and pump the accumulator back up to pressure to allow an engine start to be performed. <S> A detailed example of the start procedure is here: <S> https://www.quora.com/How-do-you-start-the-engine-on-an-F-16-Fighting-Falcon . <S> Certain fighters without an internal starting system can be started via an air-start system (like the T-38/F-5) connected externally by the ground crew or a cartridge start which is a chemical charge (think of a shotgun shell) to get the engine rotating, a whopping-great example of which follows here for a German F-4
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The F-16 starts the engine using the Jet Fuel Starter which receives its initial pressure to spin from the JFS/Brake Accumulator bottle which is a dual-purpose system as the name denotes. It all depends on the airframe you’re talking about.
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How is fuel planning done for a VFR flight that involves multiple full stops? Doing first cross country flight plan with several stops along the way. What is the general rule of thumb for calculating time, fuel, etc. for a mid trip landing? I've done conceptual flight plans with checkpoints etc, but not actual stops. In other words, I can calculate fuel burn, ground speed, course etc. for a point to point flight. Just not sure what to calculate in by adding a full stop in the middle of that same flight. While studying for the FAA knowledge exam it sometimes said calculate 3 minutes for take off and departure but curious if there is a generally accepted set of numbers. <Q> This may not be what your CFI is looking for, but I found the changes in fuel consumption during takeoff/landing to be negligible. <S> This is because the taxiing uses very little, the and extra fuel burn in the climb is largely compensated by the savings in the descent. <S> So, I just look at the distance between the airports, take winds aloft, calculate ETE and make sure it's acceptable in respect to fuel reserves. <S> Ditto for any foreseen diversions. <S> This may be less of a problem in North Carolina, but in New Mexico, you might need to return all the way. <S> A 30 minute VFR reserve isn't going to cut it. <A> We use a rule of thumb of +5 minutes at each startup/shutdown. <S> So a flight with two legs and a shutdown in the middle gets +20 min. <S> Obviously very conservative and used here in the context of helicopters. <A> I usually use a gallon (Piper Cherokee 180) for taxi, and my normal climb out and descents. <S> Assuming you’re calculating Top of Descent for the middle stop, and top of climb when leaving, <S> I’d just through those burns in there, plus, maybe, 3x your taxi requirements for parking, shutdown, startup, and taxi back.
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You have to have enough fuel on board to reach your planned reserve airport if you arrive at your destination and find that it's closed (e.g. because of an accident).
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What are the relations between stability, controllability and maneuverability? As preparation for my CFI checkride I have been trying to understand aerodynamics very well. One of the things I’m struggling with is stability If I have a stable aircraft, this means is less controllable and less maneuverable, right? Do this means an F-16 is poorly stable but very controllable and maneuverable? And a Cessna or a B737 are stable with less controllability and maneuverability? Thanks for your help guys <Q> a control system is "stable" if, upon a perturbation (like a gust or up/downdraft), the system will naturally return to its unperturbed state with your hands off the controls. <S> "negative" stability means the moment you take your hands off the controls, the plane will by itself pitch up or down, roll left or right, or skid one way or the other. <S> it cannot be flown hands-off unless it has an artificial stability augmentation system built into its control hardware. <S> A control system is "controllable" if pilot input is successful in recovering from a perturbation. <S> But without pilot inputs, a "controllable" system will not necessarily by itself recover from a perturbation. <S> Maneuverability refers to the airplane's overall sensitivity to control inputs from the pilot and the effectiveness of the control surfaces over their control range. <S> An airplane that is highly maneuverable MIGHT be unstable- <S> that is, it MIGHT not fly hands-off because of how sensitive it is to control inputs or gusts. <S> In general, a high degree of maneuverability usually is associated with marginal stability. <A> If I have a stable aircraft, this means is less controllable and less maneuverable, right? <S> Image source <S> Controllability : <S> Above depicts a ball in a cup: the centre situation is a statically stable equilibrium, you need to actively deflect the ball from equilibrium and it will want to return to the centre if released. <S> That is how you want the aircraft to be as well, statically stable. <S> When the ball is released it will eventually return to rest in the equilibrium state after some number of overshoots: it is dynamically stable as well. <S> If there was no friction and/or aerodynamic damping, the motion would continue forever: the system would be statically stable and dynamically neutral. <S> You definitely want a stable aircraft in order to be able to control it, an unstable aircraft is harder to control: the ball wants to roll away all the time, and you need to actively roll it back up the hill. <S> How hard to control, that is a function of the time period of the unstable motion. <S> In helicopters for instance, this is in order of 10 seconds: it is unstable in the hover, but the unstable motion is slow enough for humans to learn how to compensate for it. <S> An F-16 at cruise speed has artificial stability, it is aerodynamically unstable but an active control system provides stabilising inputs without the pilot noticing them. <S> So from the pilot's perspective, the aircraft is stable and relatively easy to control. <S> Manoeuvrability : <S> Responses to flight control inputs are indeed a function of how aerodynamically stable the aeroplane is, but also of the control volume: surface area times distance from Centre of Gravity. <S> Install a big enough elevator and a stable aeroplane will make lovely loopings. <S> Aerobatic aircraft are aerodynamically stable and very manoeuvrable. <A> This might help Stability - Imagine a stick hold it at the top and then displace it. <S> It swings and then hangs straight. <S> This is a dynamically stable system. <S> Now take the same stick and stand it on your hand, this is a dynamically unstable system and you have to make constant corrections to keep it standing. <S> (aeroplanes - Dynamically stable / Helicopters - Dynamically unstable) Control-ability - Capability of an aircraft to respond to the pilots control inputs. <S> If an aircraft fails to respond to a pilots inputs (or responds n the opposite manner), then it lacks control-ability. <S> Some examples are high speed control reversal, mach tuck, control lag through inertia, and control authority to dampen oscillations eg Dutch roll or spiral dive. <S> The ability to recover from a spin (A/B ratio) or a stall. <S> Manourverability - the ability for the aircraft to commence and sustain maneuvers, its responsiveness (eg control effectiveness) and its performance eg rate of roll, or turn and pitch rates(G load)
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a plane exhibits "neutral" stability if, upon a control input from the pilot or a gust perturbation, the plane will not right itself if the pilot takes his or her hands off the controls, but neither will it diverge and fly itself into a steeper turn, roll, or pitch attitude hands-off.
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Which manufacturer produced this fan blade? I acquired a fan blade a few years back, but have not had any luck finding out who manufactured it or what engine/aircraft it may have come from.The only data I can find on the blade is as follows: 4922T12P0199207 6018730P02KGA 65444GR.IN.15.620 65444 is hand engraved again in larger size above the data listed, which I assume is the serial number. The blade is about 15" from tip to root. I am curious about the root itself, as I have not seen other blades with a mount like this one. If anyone can help out it would be greatly appreciated. Images can be seen in full size by clicking on them <Q> GE Aviation <S> Clue 1. <S> Parts designed at the Lynn MA plant have part numbers of the form xxxxTxxPxx, where x is a digit. <S> 4922T12P01 fits that pattern. <S> The gr.in is another clue. <S> That refers to a weight that would be used in balancing the fan. <S> GE uses units of gr.in. <S> I'm fairly sure that Pratt uses oz.in, snecma uses gr.cm. <S> I'm not sure what RR uses. <S> But the definitive piece of information is 99207. <S> That is a CAGE code. <S> 99207 is registered to GE Aviation's lynn plant. <S> I looked it up here http://www.govcagecodes.com/ <A> That looks very much like a TF-34 fan blade. <S> The TF-34 is used on the A-10 Thunderbolt and S-3B Viking. <S> The root style is known as "pinned" or "clevis". <S> You can see a blade being pinned into the rotor hub in <S> this photo : <S> And there is a clear view of the blade root in this photo : U.S. Air Force Senior Airman Steven Valencia, 18th Component Maintenance Squadron aerospace propulsion journeyman, cleans and inspects fan blades of a TF-34 engine July 6, 2017, at Kadena Air Base, Japan. <S> The fan blades are used to generate approximately 85 percent of the thrust used by A-10 Thunderbolt II aircraft. <S> (U.S. Air Force photo by Senior Airman John Linzmeier) <A> This is a delayed reply. <S> Your fan blade is made of Ti 8-1-1. <S> The gage code is GE <S> however there are only two manufacturers for this fan blade since 1965. <S> The original manufacturer was Utica Drop Forge which became Kelsey Hayes and later became Utica Corporation and currently known as TECT Corporation. <S> The other manufacture was Sermatech Mexico for a very short period of time. <S> Sermatech struggled with holding the geometry of the Ti 8-1-1 material. <S> There are 28 fan blades per engine. <S> Besides the part number the only difference between the military version and the commercial version is the uncut in the platform. <S> This uncut (thinning) of the platform allows for the fan blade to be released on the military version Incase of a fan blade failure. <S> Without this thinning, multiple blades would fail in a domino effect. <S> The fan blade is precision forged from 2” diameter bar in a 8000 metric ton press (8800 US Tons). <S> After forging it is finished machined. <S> The manufacturer must retain records for 30 years. <S> GE would need to ask one of the manufacturers for the date of manufacture. <S> The fan blade is not a life limited component and no manufacturing date are applied to the part. <S> Cheers
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The serial number are sequential. Besides the TF34 this almost exact fan blade also goes on the CF34 (Canadair Regional Jet).
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Why does a Phugoid occur? How can it be eliminated? My model aircraft seems to do phugoid oscillations and I'm having trouble landing. It is around 2 kilos, very high mounted wing, so bad landing takes out the underbelly everytime. I'm wondering what's causing the phugoid, CG placement? The extremely high wing causing pitch oscillations due to inertia? Insufficient tail? How can I solve this? I cannot change the wing configuration, but I can change CG along the fuselage length / modify tail. Edit: More detail - design: <Q> Move the center of gravity forward <S> What you experience looks almost like a phygoid motion <S> (well, most of it is a phygoid), but involves stalling at the low-speed part of the cycle, so it is not the classical Eigenmode. <S> Rather, your aircraft's trim point is beyond its stall angle of attack. <S> It will, therefore, stall when not actively steered towards a lower angle of attack and then, when lift on the wing diminishes and its center moves backwards while lift on the tail is still linear, the aircraft will pitch down and pick up speed again. <S> Maybe it will be already enough to change the setting on your elevator to a few degrees more trailing-edge-down deflection. <S> From your sketch I would also guess that your tail volume * is on the low end. <S> * <S> This is the area of the horizontal tail surface, multiplied with it's lever arm (distance between center of gravity and the tail's quarter chord point). <A> The phugoid is an interchange between kinetic and potential energy. <S> Anything that dissipates energy in the process will add damping - more parasitic drag from a speed brake for instance when talking about the landing. <S> It's a bit of a dilemma, anything that is done to clean up the aerodynamic shape of the aircraft will decrease phugoid damping. <S> Control problems related to the phugoid are caused by the natural frequency being too high, this can be lowered by increasing horizontal tail size: a larger tail for a lower frequency, and more time to anticipate on the motion. <S> Helicopters have the phugoid behaviour exactly like fixed wing aircraft have, and the military have stability requirements for phugoid behaviour: from MIL-H-8501A $$\begin{array}{|c|c|c|} Period & Visual Flight & Instrument <S> Flight\\ \hline\text{< 5 sec} & \text{½ amplitude in 2 cycles} & \text{½ amplitude in 1 cycle} \\ \hline\text{5 - 10 sec} & \text{at least lightly damped} & \text{½ amplitude in 2 cycles} \\ \hline\text{10 - 20 sec} & \text{not double in 10 sec} & \text{at least lightly damped} \\ \hline\text{> 20 sec} & \text{no requirements} & \text{not double in 10 sec} \\ \hline\end{array}$$ <A> There can be two factors causing the landing mishaps mentioned: <S> Phugoid: the natural phenomenon of any aircraft. <S> Pilot Induced Oscillations: the pilot-in-the-loop oscillation of the aircraft while in control of a pilot. <S> To test the phugoid, trim the aircraft to a calm condition and do not touch the controls for several seconds. <S> For improving phugoid (long period) dynamics, especially if it is already causing troubles, a pitch-rate-gyro can assist in augmenting the stability. <S> A sample commercial product here. <S> The PIO is a far more important problem, and it's a combination of the pilot's behavior (his/her control dynamics) coupled with the airplane's dynamics. <S> During final approach and landing, pilots tend to be more stressed, and if the phugoid is not a lucky one, the touchdown may happen at not the best point. <S> The gyro would also help with the PIO problem, if any.
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Move the tail further back by lengthening the fuselage: This will increase stability and, especially, damping, so the pitch motion after stall becomes less violent. What certainly will help is to move the center of gravity forward because this will increase static stability and require more trailing-edge-up elevator deflection to maintain the same trim point.
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I have really intense ear pain during descent in commercial flights. Would it be better or worse if I was flying a small non-pressurized plane? Usually — but not always — after descending in a commercial jet airliner, my ears really hurt for several days, accompanied by minor hearing loss. Nonetheless, I am still in love with aviation. I am thinking of starting my lessons to become an ultralight (UL) pilot. Could flying a non-pressurized plane actually make these problems worse? <Q> Commercial airliners are generally pressurized to a cabin altitude of around 8000 feet when at high altitudes. <S> So it depends a bit on where you live. <S> If you live near sea level, you're feeling around 8000 feet of pressure change. <S> If you live somewhere higher like Denver, you're only feeling around 3000. <S> Small unpressurized planes, especially ultralights, will tend to fly at lower altitudes, usually within a few thousand feet from the ground. <S> If you live at a lower elevation, this will be much less pressure change than in an airliner. <S> If you live at a higher elevation, it would be more comparable. <S> That being said, it may only take a few hundred feet of elevation change for the pressure to noticeably change, and each person may react differently. <S> If you're worried about making commitments to flight training before you know how you'll handle it, you can go on a discovery flight, even just in a small Cessna. <A> It is not only the absolute pressure (aka cabin altitude , an altitude at which the standard ambient pressure is the same as in the cabin) <S> that counts, but the rate of change as well. <S> But the cabin climb rate , and especially the descent rate (which we tolerate worse), can be much higher. <S> The pressurisation systems are typically programmed such that the cabin altitude rates didn't exceed ±500 fpm in normal operation, regardless of what the aircraft is doing. <S> That is, even if the aircraft descends at -2000 fpm, the cabin altitude will 'descend' much slower. <S> In the end, it only needs to 'descend' from (typically) 8000 ft, rather than from the airliner's 30000 ft. <S> Conversely, in a non-pressurised aircraft you'll have the same rate of change as the aircraft's own climb/descent rate. <S> Touring GA aircraft typically descend at about -500 fpm, which is gentle enough. <S> Yet now it depends on the pilot's skill and the task at hand. <S> A fast descent even from a low altitude may hurt. <S> I don't have particular problems with altitude changes, but the most painful experience I ever had was similar to what @Andrius referred to: a very fast descent (or rather dive!) <S> after dropping parachutists from 800 m, so that we land before them. <S> Not only my ears, my eyes felt hurt! <S> In other words, if you are touring and not flying over mountains (above ~8000 ft), and have a minimally experienced pilot (or learn to fly yourself), you may feel better than in an airliner. <S> But many kinds of special airwork, or an emergency, may pose a greater problem. <A> False. <S> UL airplanes usually will not climb <S> very high(to avoid controlled airspace or other reasons) and climb rates are not so impressive either. <S> Cabin altitude is about 10000ft inside an airliner. <S> You can fly UL at 1000ft most of the time and enjoy the scenery unless you live somewhere in the mountains. <S> I am a glider tug pilot and usually I don't feel anything though I drop from 800m(2600ft) at a maximum rate plane can handle exceeding 2000ft/min. <S> I sometimes can feel the pressure difference in a commercial airplane. <S> Also you don't have to wait till you feel the pain. <S> Just hold your nose with the fingers, close the mouth and try to blow as soon as you start to feel anything. <S> It will release an inside pressure. <S> Do it many times during the altitude change. <S> If you wait to long if will be much harder or impossible to do that. <S> I towed gliders while sick and having running nose, cold, ect. <S> No problems at all.
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As other have said, the cabin altitude in typical non-pressurised GA airplanes will often be more favourable than in airliners, by the virtue of flying lower.
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Does the FAA issue multiple physical certificates for different aircraft categories and privileges? If one holds a private pilot certificate in both airplanes and gliders, does the FAA issue two plastic cards that one would have to carry? What if one has commercial privileges in airplanes, but private in gliders? What about being private in airplane, but sport in powered parachute? Some schools say that if one already has a private in airplane, then powered parachute at sport level would only be a logbook endorsement rather than a new piece of plastic. I was under the impression that logbook endorsements are generally things like the ability to fly a complex airplane, rather than being a sport level in a different category of aircraft. <Q> One certificate would be issued. <S> Your highest rating would be listed on the front and on the back any lower ratings would be outlined. <S> Before I had passed my rotorcraft ATP my certificate read: <S> Airline Transport Pilot Airplane Single and Multiengine Land <S> Commerical Privileges <S> Rotorcraft-Helicopter <A> My certificates, ATP MEL, Private SEL (VFR only), and Private Glider are all on one plastic card. <S> I think Ground Instructor certificates may be a second card, but I don't have any of those <S> so I can't tell you for certain about that. <A> There is a separate card issued for Flight Instructor and it may have a subset of privileges of those listed on your pilot certificate. <S> Foe example, you may be an instrument rated pilot but not an instrument flight instructor. <A> The highest level and all category/class ratings will be listed first, and then any category/class ratings not at the same level will be listed in the Limitations section. <S> For your first example, you would get a Commercial Pilot Certificate with ASEL and GLI ratings, and then the GLI rating would be limited to Private privileges. <S> The second example is weird since every Private pilot also has Sport privileges, which don't have category/class ratings. <S> As a Sport pilot, you just need a logbook endorsement from two different CFIs (rather than a checkride with a DPE) to fly a particular type of aircraft.
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The FAA only issues one "airman certificate" at a time.
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How could the Helios 522 passengers have survived so long without oxygen? I've noticed some strange inconsistencies regarding the documentation of Helios Airways Flight 522 . So first: Autopsies on the crash victims showed that all were alive at the time of impact But then: The emergency oxygen supply in the passenger cabin of this model of Boeing 737 is provided by chemical generators that provide enough oxygen, through breathing masks, to sustain consciousness for about 12 minutes So, the oxygen masks in the passenger cabin automatically deployed at 18,000 feet, probably around 09:20. The aircraft did not impact until 12:04. 2 hours, 44 minutes later. Obviously the oxygen masks didn't keep them alive for that long, so: How could they have survived so long? <Q> To add to Daniele's answer, from the final report : The forensic report concluded that the aircraft occupants <S> had heart function during the impact. <S> The report noted that this did <S> not necessarily imply <S> that they were alert. <S> The report further estimated that they were in deep non-reversible coma due to their prolonged exposure (over 2.5 h) to the high hypoxic environment. <S> So, again, saying that they were alive does not mean that they were well. <A> Consciousness requires quite a bit more oxygen than merely being alive. <S> And lack of oxygen will soon enough cause permanent damage. <S> The passengers may have been alive, even if they were not conscious, but they could have been anything from temporarily incapacitated to on the way to certain death by the oxygen starvation, even if they somehow had been rescued before the crash. <A> Here is a list of those people who survived as stowaway in the unpressurized and extremely cold wheel well . <S> On June 19, 2015 an unidentified male who was 24 years old survived 11(!!) <S> hours in the wheel weel of British Airways Flight 54 from Johannesburg to London. <S> As you also see, this is incredible because as you suggested most of the people simply die. <S> Another surviving victim without permanent damage was paraglider Ewa Wiśnierska , who survived half an hour long in a thunderstorm cloud at a height of nearly 10 000 m (33 000 feet). <S> You must also be aware that the passengers breathed pure oxygen allowing the oxygen supply to enter the blood and increase the level in the organs before they passed out, so the permanent effects of hypoxia may be delayed.
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Human beings can last remarkably long with very little oxygen, but not remain conscious.
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Why don't we treat all takeoffs as short field in GA? Depending on the airframe, there are a number of techniques to reduce the Take Off Distance required. For example, deploying flaps. What advantage is there to NOT using short field take offs, even when runway length is sufficient? Surely it's always advantageous to require the minimal amount of runway, thereby adding a larger margin for error? <Q> Short-field take-off techniques often achieve a shorter ground run by hurting climb performance. <S> While having more runway is great for safety, planning to use less of the runway is not a huge benefit: you always plan to have enough runway left if you need to abort during the take-off roll. <S> It's much better to have more height quickly in the climb-out: it gives you more margin against obstacles after the runway's protected area, and it gives you more height to land in case of an engine failure after take-off (EFATO). <S> The numbers for a normal take-off optimise for a good rate of climb, which has the greatest benefit to safety. <S> A short-field take-off gives you an extra option when the runway length is too short for that - at the cost of some margin if there's a problem in the climb-out. <A> First off as the pilot in command, you are free to do this if you feel it is the safe way to operate the aircraft in a given situation even if runway does not dictate it. <S> According to the FAA's handbook the short field take off requires a high degree of control of the aircraft, <S> The pilot should be aware that, in some airplanes, a deviation of 5 knots from the recommended speed may result in a significant reduction in climb performance; therefore, the pilot must maintain precise control of the airspeed to ensure the maneuver is executed safely and successfully. <S> While an experienced pilot may be ok with this student pilots and newly minted ticket holders may feel less comfortable and thus choose to only fly from runways where this is not required, although it should be noted this is part of the ACS and thus part of getting at least a PPL here in the US. <S> Due to the degree of precision the maneuver may be used less than a standard takeoff. <S> There is an interesting article here worth reading on the topic. <A> Short field takeoffs are more complicated than simple takeoffs. <S> That is why they are taught later, once you are familiar with normal takeoffs. <S> Depending upon the plane, there are several steps you need to take for a short field takeoff: <S> add flaps, line up before the piano, press brakes, full power, check engine gauges, release brakes, etc. <S> This is simply more complicated than full throttle/check engine gauges. <S> There are a thousand things that you need to keep in mind while flying. <S> It is best to keep simple things simple. <S> Of course you can always do short field takeoffs if it pleases you. <S> Most runways you will takeoff from will be long enough from a GA perspective. <S> In case the runway is short, you should of course use the short field technique. :) <A> As Dave and others have already mentioned, short-field takeoffs result in taking off with significantly less airspeed than usual. <S> Your goal in a short-field takeoff is essentially to fly the plane just slightly above the point where it is not flyable. <S> As a result of this, the margin for error in a short-field takeoff is considerably smaller than in a normal takeoff. <S> In addition to the relatively poor climb-out performance mentioned in Dan's answer, you're intentionally trying to fly just beyond stall speed. <S> Relatively small wind gusts can put you back on the ground in a hurry, as could momentarily pitching up too much. <S> You'll have less control authority and, <S> so, less ability to correct the plane's attitude in gusty conditions. <S> You'll have less airspeed and be more susceptible to stalling at low altitude (whether due to gusty winds, accidental excess pitch, or a combination of the two.) <S> You'll also be less able to climb clear of obstacles at the end of the runway. <S> The flaps will also be providing additional drag, so you'll use up more horizontal distance in order to get up to speed for the climb-out. <S> Your only real gain for all of these trade-offs is that the wheels will have a shorter roll across the ground, so it's just not worth it unless you really don't have the runway to spare. <A> I used to fly a 4-seater Rallye Minerva, and, if I recall correctly, the recommendedshort field take off involved putting on full flaps (30°) just before liftoffspeed (the flaps were operated by a handbrake sort of affair) and then basically flying level until an appropriate speed was attained. <S> While no takeoff was relaxing, this procedure was a little unnerving (it tookquite a bit of effort to latch the flaps in, and there wasn't always a secondchance), and certainly not one I would use on a regular basis. <S> A crosswind added tothe tension as the liftoff speed was fairly slow (something like 42KT). <S> This was a lot more work than I would want to do when operating from a busyairport, and generally reserved for shorter 'fields' (100m, <S> yep, you read thatright). <A> Furthermore, you want to minimize the time of full power to the engine to reduce the chance of its failing. <S> You also want to keep fuel burn down <S> so there's more reserve at the end - or less to be loaded to start, allowing more payload. <S> A "normal" takeoff improves all the above along with airspeed margins, visibility over the cowling, cooling airflow to the engine and more. <S> All of which are benefits it offers compared to a short (or soft) field takeoff.
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All-in-all the short-field takeoff is just a relatively more dangerous way to take off if you have sufficient runway for a normal takeoff.
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What exactly is the meaning of "detent" in aviation? I come across it in many different situations e.g. "settings changed to flight detent" or "landing altitude changes at first detent". There are other scenarios which I came across in the past, but I don't remember them. Could someone explain me all the different scenarios and what it really means? <Q> Image source <S> In the image above, the flap detents are clearly identifiable as the notches in the guide rail: in order to move the lever away from a notch, it needs to be lifted first and can only then be positioned in a different detent. <S> The flight control sticks often have a detent that indicates force trim position: on either side of stick travel is a preloaded spring, and the stick can only be moved once the breakout force is exceeded. <S> The rest of the stick travel will then simply increase force proportional with the spring gradient - if released to neutral, the force will gradually decrease until the stick falls into the breakout position. <A> An example most people would be familiar with is when shifting into reverse in a car with a manual transmission; normally there is a detent you need to "push through" to get into (and prevent accidental engagement of) reverse. <A> A detent can be simply a palpable change in operative force . <S> Take a wall dimmer: it has free movement in the dimming range. <S> At the lowest dim setting, if you continue, a significantly greater force will snap it past a detent and into "hard off", which causes a plain switch to de-energize the bulb <S> so you can change it. <S> At the other end is another detent to "hard on", where a plain switch bypasses the dimmer electronics entirely (so they will stop buzzing.) <S> E.G. <S> if you set throttles to full military, you don't need to release a latch to get it past TO/GA, just the extra force to push past the detent.
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A detent is usually a discontinuity in force at a certain position: the control likes to move into that position, and moving it away takes more than average force.
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Has there ever been an aircraft with three sets of flight controls? On every aircraft I know, there is either one set of flight controls if it is single-pilot operated, or two sets of flight controls allowing either the pilot or copilot full control. Has there ever been an aircraft that has three or more sets of flight controls? To clarify: "aircraft" includes fixed-wing, helicopter, powered lift etc. remotely operated aircraft do not count. A set of flight controls consists of yokes, pedals and/or sticks that allow the operator to manipulate the pitch, roll and yaw axes. <Q> Depends if you are asking about production or testbed stuff, <S> NASA had at least one test bed aircraft that looks to have had at least 4 sets of controls (also covered in this question ). <S> If you consider the space shuttle an aircraft, some of the thrusting capabilities (enough for pitch roll and <S> yaw I belive) were operable from the arm control position . <A> Dave's second reference ( here ) includes two helicopters with a third set of controls: The Boeing BV-347 ( link ) Sikorsky S-64 ( link ) <S> and it's predecessor the S-60 <A> Furthermore, if your restriction of "proper" flight controls were lifted we could consider a number of bombers which were "flown" by the bombardier, by redundant interfaces to the autopilot system. <S> There is also the unique situation of lifting bodies and attached gliders. <S> These were technically three or more people in control of two or more aircraft. <S> Given that the child aircraft would need to be trimmed in order to avoid upsetting flight, input to control surfaces by 3 or more people could influence the flight path of the agglomerated system. <S> The only "production" aircraft I can think of with more than two sets of flight controls is White Knight <S> Two which has a complete cockpit in each of its two fuselages. <S> Unfortunately I cannot find an indication as to whether all four sets of controls can assert authority at the same time. <S> If so, and if Space Ship Two's controls are not locked out <S> while it is being carried there would actually be six people influencing the flight of the aircraft in some way.
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There have been a number of one-off aircraft which attached one plane's cockpit to another aircraft for testing or training purposes.
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Rolling take off compared to take off from a standstill When ever I fly I choose flights with the most take off and landings. After going down the taxiway and turning onto the runway sometimes the flight crew ramp up the engines up while holding the airplane from moving with the brakes, then let off the brakes and the plane shoots down the runway like a rocket sled on on wheels. Other times the plane will go down the taxiway, turn onto the runway and without stopping ramp up the engines and head down the runway. What is the difference in these two techniques? Is it pilot choice? <Q> There are a few things that may be going on. <S> Generally the foot on the breaks, full throttle, spool up, release and roll is derivative of a short field takeoff. <S> In other words you need all available runway and all available power to get off the ground safely and clear your runway end obstacles. <S> This is dictated by airplane performance and runway conditions/length. <S> Roll on, roll into full throttle and go is more or less standard. <S> In some cases this may follow an ATC clearance like 123AB Cleared for takeoff 22 depart <S> no delay <S> This generally means there is either someone inbound for a landing <S> but theres time for you to go, or there is a long queue on the ground and the controller wants you to get going. <S> Stopping on the runway to spool up your engines takes time and at a busy field that can be in short supply. <S> Its important to note that in any case the pilot should line the aircraft up with centerline prior to applying full throttle. <S> The aircraft can also be instructed to, "line up and wait" in which case its cleared to enter the runway and wait on the numbers until cleared. <S> This may occur at an airport that offers parallel runway operations and the aircraft is waiting for a plane to land on a parallel runway. <S> EDIT: I found a possible dupe, noted in the comments. <S> Its a bit different so ill leave this answer here and let the community decide. <A> before takeoff, the pilot knows the handbook values for balanced runway length for any density altitude, the gross weight of the plane, and the runway length available. <S> If there is far more runway length available than the handbook requires, then upon being cleared the pilot may elect to roll on, start the run, and go to full power. <S> If not, the pilot should instead roll into position, stand on the brakes, spool up the engines, check gauges for full power, release brakes and roll. <S> Of course, ATC has the final say, and as pointed out by Dave, may specifically instruct the pilot to do one thing or the other depending on what's required. <A> Depends on the takeoff procedure being employed as well as the aircraft type. <S> Rolling takeoffs are a preferred procedure for soft field takeoffs on grass strips which may have high grass or wet sod and the aircraft is kept rolling to prevent the possibility of the landing gear becoming stuck in the muck. <S> This is done to miminimze the amount of runway needed to perform the takeoff roll on. <S> Multi engine airplanes will use the same technique in order to conform with manufacturer performance data on accelerate-stop and accelerate-go distances, which are a necessary performance metric to have established as part of the pre-takeoff brief for emergency contingencies in the event of an engine failure. <S> This is the standard takeoff procedure when flying multi engine aircraft. <S> In the case of most airliners and civil jets in general, they will usually hold brakes and establish 60% or so of the selected takeoff thrust in order to accomplish a final check on the engines, then release brakes and increase to takeoff thrust. <S> A pilot may opt to hold brakes and throttle to takeoff thrust first then begin the takeoff roll. <S> As for rolling takeoffs, one could argue it’s sloppy airmanship but <S> plenty of fleet pilots do it on a regular basis.
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Short field takeoffs involve lining the aircraft up on centerline as close to the threshold edge as possible, applying brake pressure while running the engines to full power, thence releasing the brakes and commence the takeoff roll.
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What design features or systems help to prevent a hard nose landing? Pilots perform perfect manual landings almost all the time with the nose wheel touching down softly and elegantly. When landing an aircraft of any size really more so for the jumbos and super jumbos, this seems like an incredible feat given their weight and the speed at touchdown. Apart from training, what design features or systems aid the pilot in achieving a soft nose wheel touchdown? Are there any features to help pilots in the event of an accidental abrupt push of the yoke during touchdown? <Q> The longitudinal stability of the aircraft. <S> Aircraft are designed so that at any given elevator position they maintain a corresponding angle of attack¹. <S> Any decrease in AoA creates pitch up moment to increase it and vice versa. <S> At touch down the pitching moments change a bit, but the general tendency remains, so without change in the elevator position, the plane will tend to keep the nose wheel off the ground. <S> The nose only touches down when the pilot eases the back pressure on the control column, or the plane slows down enough that the elevator efficiency decreases below what is needed to keep the attitude. <S> The pilot just has to ease the back pressure gently and not slam on the brakes until the nose wheel is on the ground, because brakes do generate significant downward pitching moment (this applies to all vehicles; you can feel it in a car quite well). <S> ¹ except modern fighters, <S> but there the control computer emulates that behaviour, otherwise they wouldn't be controllable. <A> <A> While Jan Hudec’s answer is certainly correct, I think some credit should be given to devices like flaps and vortices generators that improve flight characteristics with higher angles of attack. <S> Without them, pilots would have to land faster, with a more nose down attitude, which would make it more difficult to set the nose down softly.
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Having the airplane in proper (elevator) trim as the power is reduced prior to touchdown, flying the nose wheel onto the runway by relaxing the back pressure on the yoke while the elevator is still effective and practice.
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Why does the PA28 only have one door? I did the majority of my PPL training in a PA28 Warrior and I've recently started transitioning over to a C172 and one thing that amazes me is how convenient it is to have a door either side of the aircraft. My question is: Why does the PA28 only have one door on the passenger side of the aircraft? I've never seen the schematics of a PA28 but my assumption might be that there's equipment that runs down the left side of the fuselage preventing a door from being added. <Q> Having one door is just a design preference which makes the aircraft simpler, and lighter to build. <S> There are many other light aircraft with only one door. <S> Even the high wing Cessna 195, 206, P210, 337, and low wing Cessna 310 and 340 have only one door. <A> Later low wing aircraft like the Cirrus make use of an internal crash rollcage in the dorsal spins of the fuselage which adds extra strength to accommodate the second door. <S> Diamond uses a semi monocoque tub-like design with a single swing up canopy enclosure to facilitate ease of entrance and egress. <A> Piper's early low wing plane history, the best info I have found has been this: http://www.pilotfriend.com/aircraft%20performance/Piper/11.htm <S> In 1954, Bill Piper was looking for a design to compete with the Bonanza. <S> The engineers at Piper were busy with other projects at the time, so Bill Piper asked his friend Al Mooney if Piper could buy the new Mooney <S> MK-20 design that Mooney had not yet started producing. <S> Al wouldn't sell the design, so Bill Piper asked Al Mooney to come up with a totally new design. <S> Al submitted a design to Piper that was an all metal 4 place monocoque construction with retractable gear, a 180 HP Lycoming, and a stabilator in place of an elevator. <S> The stabilator was a new design, an all flying horizontal tail. <S> The cabin size of Al Mooney's design was a bit small, so the engineers at Piper increased the cabin size and the first Prototype PA-24, N2024P, was created in 1956. <S> As you can see in this photo, the trailing link landing gear on the prototype is not what we have on our Comanches. <S> It is suspected that Bill Piper decided that the trailing link landing gear would be too complex and expensive, and in an effort to undercut the cost of the Bonanza, he decided on the straight tube <S> oleo strut landing gear that all Comanches are equipped with. <S> Although it is much more difficult to make a good landing with the straight oleo strut landing gear than with the trailing link gear, that decision by Bill Piper is why Comanche Pilots have skills much more superior and a highly qualified group of Pilots than the Bonanza and Mooney bunch!! <S> The second prototype PA-24-180 flew in 1957. <S> The first production 180 was delivered in January of 1958. <S> It cost $14,500. <S> The 250 HP Lycoming was meanwhile being tested in the original prototype PA-24, and the first production 250 Comanche was delivered in April of 1958. <S> And from Wikipedia: <S> Piper PA-28 CherokeeI have <S> At the time of the Cherokee's introduction, Piper's primary single-engined, all-metal aircraft was the Piper PA-24 Comanche, a larger, faster aircraft with retractable landing gear and a constant-speed propeller. <S> Karl Bergey,[12] <S> Fred Weick and John Thorp designed the Cherokee as a less expensive alternative to the Comanche, with lower manufacturing and parts costs to compete with the Cessna 172, although some later Cherokees also featured retractable gear and constant-speed propellers.
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It reduces weight and increases the structural strength of the fuselage, particularly with the typical design of a low wing aircraft. Besides Piper, most Mooney, Beechcraft, and Bellanca aircraft only have one door.
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How is fuel weight calculated? I was having a conversation concerning airplanes and the calculated fuel. We were having a conversation about the Airbus A380. Based on this site: http://www.modernairliners.com/airbus-a380/airbus-a380-specs/ It shows a capacity of 320,000 Litres. After some conversion (I am in the US) 320,000 Litres = 84,535 gallons 84,535 gallons = 710,000 lbs Now that is based on water density. I've heard that jet fuel isn't exactly comparable to water? Is this true? I am trying to confirm because 700 thousand pounds of fuel sounds like a lot? Is there something I am missing? An average Olympic sized swimming pool carries about 660,430 gallons of water. How does this plane carry that much weight? And what would be the easiest way to explain this to a layman like myself? <Q> Fuel doesn't have the same density as water. <S> We're not planning a real flight, so a quick and dirty fuel density figure from Wikipedia tells us : <S> In performance calculations, airliner manufacturers use a density of jet fuel around 6.7 lb/USgal or 0.8 kg <S> /l. <S> So if we take your figure of 320,000 litres (it's a bit unclear quite how much of that is actually usable for flight, but that's a subject for another question) <S> , that's about 560,000lbs of fuel or around 254,000kgs. <S> Which, indeed, is a lot. <S> The fuel is spread throughout the wings (and the trim tank in the tail), which are designed to carry the weight. <S> If you look at What is the weight budget of a fully loaded A380? <S> , you'll see how the fuel capacity interacts with the other weight specifications for the aircraft: <S> The maximum fuel weight is the difference between maximum ramp weight and zero fuel weight (which is 562,000−361,000=201,000kg) <S> Max take-off weight is a bit less than maximum ramp weight, but we'll handwave over taxi fuel for simplicity. <S> The point here is that if you can fill the aircraft with cargo, it would be too heavy if you also filled it with fuel. <S> If you want to take a full load of fuel, you'd have to reduce your payload to keep the total weight low enough. <S> Working out the weight/fuel/range trade-offs for a given flight is what dispatchers and load planners do, using specialized software. <A> An aircraft is more interested in how much that is in kgs. <S> So the person in charge of the fuelling has to take into account the SG or specific gravity of the fuel on that day. <S> This varies according to the temperature. <S> In the tropics it is usually around 0.780. <S> This means if the fuel has a SG of .780 <S> it weighs 0.780 of 1 litre of of water @ <S> 4deg C (water is used as the reference unit). <S> As 1 Litre of water is equal to 1 kg, 1 Litre of Jetfuel at SG 0.780 is equal to 780grammes. <S> So if the bowser has metered out 100,000Litres of Jetfuel at SG 0.780, it will add 78,000kgs to the weight of the aircraft. <S> One flight I did was at maximum range of the B747-400. <S> The flight-planning was done in HKG and they needed to know the actual SG as this will give the actual maximum weight of the fual they could carry. <S> If I'm remember correctly the 747-400 can carry something like 170,000kgs of fuel but if the density is low you might not be able to fill it <S> max weight-wise. <S> I believe we uplifted around 167,000kgs that day. <S> There is another formula for gallons to Lbs <S> but I cant remember it as I've worked mostly with Metric. <A> Others have already addressed the issue of calculating fuel weight, but I'd like to take a moment to discuss what you wrote in a comment to the question. <S> 85,000lbs of a liquid would seem to take up a lot of space and my friend <S> and I were trying to figure out where all this liquid goes. <S> One of the beauties of the metric system is that one liter is exactly equal to one cubic decimeter (the latter, of course, being a cube of 10x10x10 cm <S> ; in US terms, that's a shade under 4x4x4 inches). <S> A liter, like a cubic decimeter, is a unit of volume, rather than a unit of mass. <S> 320,000 liters thus corresponds directly to 320,000 dm 3 . <S> In a more usable unit, this is 320 m 3 because 1 m 3 = 1,000 dm 3 . <S> Looking at Wikipedia , the wing area of the A380 is given as 845 m 2 . <S> If the entire wing area can be used for fuel tanks, which is not the case, and there are only fuel tanks in the wings, which is not the case, this means that the average height of the fuel tanks in the wings would need to be equal to 320 m 3 divided by 845 m 2 , or about 0.38 meters; a little thicker than the long side of a piece of A4 or Letter paper. <S> I haven't flown in an A380 recently, but I suspect that the wings are thicker than this. <S> The fuel also isn't kept only in the wings; while I don't know about the A380's configuration specifically, it's common for large aircraft to have both wing tanks, a center tank within the fuselage, and a trim tank farther back in the fuselage. <S> Bottom line here <S> , there's plenty of room for that amount of fuel.
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Fuel comes out of the bowser and is metered in Litres (at least where I come from!).
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Why didn't Air India always fly DEL-SFO over the Pacific? I read a 2016 article that said Air India broke a record for the longest flight (distance) by flying from New Delhi to San Francisco over the Pacific rather than a polar/Atlantic route. The total flight time was shorter because of the jet stream. Why didn't they always do this? <Q> (gcmap.com) <S> Great circle route. <S> The polar route is mostly over land and is in close proximity to airports and navigational aids. <S> Flying over long stretches over water requires (among other things) enhanced navigation, using specific communication protocols, and adhering to criteria set by the countries overseeing the region. <S> Picking the new Pacific route is not easy (authorization, training, and the associated costs). <S> The Pacific communication, navigation, and surveillance requirements also allow the utilization of flex routes to adapt to the changing jet stream, as the linked document below explains. <S> (The flight's history also shows the different routes.) <S> The relevant operational circular—Operational Authorization Process for Pacific Operations—can be found on the DGCA website (.pdf). <S> The document covers all the requirements, of which, the carrier seeking the authorization may need to demonstrate to the authorities a flight or more: (...) <S> the final step of the approval process may require a validation flight through Pacific airspace by a DGCA Flight Operations Inspector to verify that all relevant procedures are applied effectively. <S> It's like a pilot who has never flown over the Atlantic, <S> when that time comes, they undergo special training for it. <S> In this case, flying over the Pacific was new grounds for Air India. <S> The requirements (published August 2016) were put in place after Air India sought this route. <S> Air India has been undergoing major changes recently due to large amounts of debt , so they've been streamlining their operations. <S> Related (question about same flight) <S> : Could winds of up to 150 km/h impact <S> the structural loads on a Boeing 777? <A> In addition to the other answers, it's worth pointing out that the jet stream does not stay in a constant location above the Earth, but shifts and meanders over the course of weeks and months. <S> Here's a great video from NASA showing these shifts over a 30-day period: The Pacific route would only be advantageous if the jet stream was relatively far south in its meanderings. <A> The great circle (shortest path) between DEL and SFO goes nearly straight north then nearly straight south (slightly westerly). <S> It's super close to a route where you would go straight north, then straight south. <S> For instance, I plotted DEL to DEN (Denver-CO), and there we have a straight north route. <S> The fact is, often times the shorter distance (great circle) actually beats the Pacific route, and the jet stream isn't straight from the west to the east. <S> It does shift to the north and south in many places. <S> It might be just better to plot a DEL-SFO route where the aircraft goes mostly north but picks up a northeast jetstream in the beginning and then picks up a southeast jetstream in the end. <S> I've seen jets flying in the northern USA on a heading 040 (more north than south) with a 100+ knots tailwind. <A> The polar route is actually a shorter distance. <S> So, in the absence of winds (and in the absence of political conditions preventing you from overflying certain regions,) the polar route is faster. <S> The jet stream moves around and its average location and strength vary seasonally. <S> Even within a season, though, its position and strength can vary significantly even from one day to the next. <S> As such, it only makes sense to take that route when the jet stream is strong and located conveniently for where you're trying to go. <S> If the jet stream is weaker and/or heading the wrong way for your route, taking the polar route will be faster. <S> In the absence of wind, the only downside to taking the polar route over the Pacific route is that, if you have to divert mid-flight, you'll end up in some frozen wasteland in Russia, Canada, Svalbard, or Greenland, rather than some tropical island in the Pacific.
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Taking the Pacific route instead of the polar route adds quite a significant amount of distance to the DEL-SFO flight. In short, when an airline selects a new challenging route, it must prove it is prepared for it, and to set up new training procedures.
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Why not tow aircraft instead of single-engine taxi? To save costs, budget airlines could potentially eliminate the single-engine taxi that is standard. Companies are looking into things like electric motors on the wheels of airliners for taxi, which could be powered by the APU, using much less fuel than even a single-engine taxi. But why not just tow all of them using existing towing equipment? The related post ' Does it make sense towing airplanes to the head of airstrip by electric means? ' asks for electric technology (internal or external), this one asks about using existing technology. <Q> Single-engine taxi is used for taxiing out (to the runway) and taxiing in (after landing) when the aircraft/operator allows it . <S> It is usually done when the taxi time is big, which means at big and busy airports. <S> Use Google Earth to see how complicated big airports are in case you're not familiar with the airport layouts. <S> But for the purposes of your question, let's consider a simple airport. <S> ( wikimedia.org ) <S> As shown, there is a single runway and one major parallel taxiway. <S> Typically airplanes land and takeoff in the same direction. <S> First off too many tow trucks is too much traffic, too much money, and an increased chance of accidents on the ground. <S> Let's say in the above picture the plane is towed to where it says (11) for takeoff, the tow truck will detach, then what? <S> It will have to occupy the runway and exit (delaying departures and arrivals). <S> Same thing for arrivals, tow trucks will need to wait by the exits, and with the time it takes to attach, the exit will be occupied. <S> If not the exit but farther down, then you're already almost at the gate. <A> Towing is much slower than taxiing. <S> When taxiing, you have on the order of 25 MW available, and taxi speeds seem to be 55 km/h . <S> Towing vehicles have on the order of 500 kW , and towing speed about 5 km/h . <A> Its slow to tow. <S> Even with a towbarless (which can tow faster) it is not ideal. <S> Danger of miscommunication/slow communications. <S> Most airliners cannot be towed with 2 engines or more running as the idle thrust is high. <S> Therefore at least one may need to be started just before takeoff. <S> This is not good for engines going from cold to take-off thrust in a few minutes. <S> Also a no-start or fault on start will require a tow back to the gate. <S> A taxi to runway in a large airport would take half an hour to an hour. <S> A push-pack..? <S> 10-15 minutes at the most? <S> Towing to the take-off points will require a big increase in the number of pushback equipment. <S> Having said that there have been cases where aircraft have been towed into position on or near the entry point of the runway. <S> One case was United's first non-stop from New York <S> (or was it Newark) to Hong Kong back in the late 90s. <S> Aircraft was towed and I believed lined up with the runway to ensure the flight started off with max fuel. <S> Another scenario would be if the entry into the runway was not at the very start and the turning pan was either not existent or not suitable. <S> To get every inch of runway the aircraft may be towed onto and backed-up to the start of the runway.
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So the why not is basically: more traffic that doubles when the tow truck detaches, expenses (trucks, drivers, maintenance), reduced runway capacity, bigger chance for ground accidents, and a very complicated coordination task.
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Why does the radome on the AWACS rotate? I'm not sure I understand why the radome on the AWACS aircraft is so large, and could somebody explain the design and why it has to rotate? <Q> Basically, the radar antenna of the AWACS system is just like this ( source ): <S> Rotating waveguide antenna (picture source ) <S> The round shape is only an aerodynamic fairing. <S> Proof: <S> Boeing E-3A AWACS cutaway (picture source ) <S> A surveillance antenna can also be fixed. <S> Electronic beam steering helps to view a sector of approximately ±60°, but in order to get a 360° sweep the airplane needs to fly circles. <S> Beam steering is also used on the rotating antenna to rapidly switch between several targets, so this is not unique to a fixed antenna: <S> Pakistani AWACS based on EMB-145 <S> (picture source ) <A> The alternative would be to have a stationary dome with the radar rotating inside. <S> The Russians did that for their Il-76 AEW aircraft, this is the result: <S> This dome is noticeably thicker than that of the E-3 because there has to be space for the antenna inside the dome. <S> For the E-3, the outside surface of the antenna is also the outside surface of the dome (specifically, the white band of the dome), meaning the dome can be thinner. <S> The width of the dome is determined by the width of the antenna. <S> The wider the antenna, the higher the resolution, so you want the largest antenna you can install. <A> In short: because it covers a full 360 degree area. <S> Mounted atop the aircraft fuselage in a rotating dome, the AWACS S-band (E-F band) <S> surveillance radar is able to survey, in 10-second intervals, a volume of airspace covering more than 200,000 square miles (500,000 square km) around the AWACS, or greater than 250 miles (400 km) in all directions If the radome did not rotate it would only cover the area in the direction the array was pointed ( tangential to the stripe ). <S> Most similar radomes rotate , <S> although some are enclosed so you may not see the rotating device. <S> There are also ways to do it with out a rotating array. <A> Good answers above. <S> I just want to add <S> that the planar arrays do not need to fly in circles (or rotate) to provide 360 degree coverage. <S> The beams don't point solely perpendicularly from the radar on either the E-3 (rotating planar array) or E-7A (fixed planar array). <S> They're electronically scanned: A typical face will cover a 100-120 degree swath of the sky in front of it (a "two-sided" planar radar will cover 200-240 degrees). <S> For fixed/longitudinally installed radars, the main arrays face sideways, and the other 160-120 degrees are often (but not always) covered by smaller radars that face forward and/or aft. <S> These may have less power-range than the primary arrays. <S> [Boeing E-7 airborne early warning and control aircraft. <S> Credit: Boeing .] <S> Example: the <S> E-7 above has four main radars, two pointing left/right, two pointing fore/aft: <S> The 10.8 m long by 3.4 m high antenna assembly incorporates 7.3 m long by 2.7 m high Side-Emitting Electronic Manifold array, with the top hat supporting array providing 120° coverage on port and starboard side, while the top hat array itself provides 60° fore and aft, thus providing a complete 360° coverage. <S> [ Wiki . <S> Sorry, I couldn't find an illustration/cutaway.] <S> So fixed/longitudinal arrays do not necessarily need to fly in constant circles to provide 360 degree coverage. <S> (Note that this is different from saying that the quality/range of coverage is uniform for all bearings. <S> This also isn't saying that AEWC don't fly circuits. <S> The actual tracks can vary and take into account friendly forces and the anticipated threat direction to best situate/point the faces while minding your own security.) <A> The radome on the AWACS is NOT the black bit. <S> The radar is mounted on the long faces of the metal bit on the diameter, and 'sprays' radar out through the aerodynamic shaping of the black part.
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Since the radar beam is directional, like most radar beams, it has to be rotated to get 360d coverage.
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What biplane is this model modelled after? What biplane is this model modelled after? <Q> Look at the cutout of the wing above the pilot's seat. <S> It's rectangular as on the Snipe , not a semicircle as on the Camel . <S> The engine looks like a Camel's however. <S> So, this model is possibly a hybrid of two famous World War I British fighter planes. <S> It could also be a specially modified Camel according to @Michael Tracy (except the painting scheme <S> does not match the one on the picture he provides). <A> The plane is a Sopwith Camel . <S> It was a British fighter in service from 1917 to 1920. <S> There were 5490 built, of which only 8 survive, but many replicas are on static display and a few are even airworthy. <S> Source <A> Have a look at the 6th picture in this Camel link , you’ll see the exact same rectangular cut-out. <A> As for the specific plane it appears to be a rough approximation of a Sopwith Camel from No. 209 Squadron RAF–most likely Roy Brown's B7270 . <S> Source: <S> Valder137 CC BY 2.0 , via Wikimedia Commons <S> Capt. <S> Brown was officially credited by the RAF for shooting down Manfred von Richthofen, the "Red Baron", but modern historians suggest it was likely Australian anti-aircraft fire from the ground.
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The plane is probably modelled after both a Sopwith Snipe and a Sopwith Camel.
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Is a weather briefing required? Are pilots legally required to obtain a weather briefing prior to some or all flights? <Q> Yes, at least for flights that are not in the "vicinity" of the airport. <S> FAA CFR 91.103 <S> Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. <S> This information must include-- <S> (a) <S> If you do all flight services and happen to have an accident, then your accident will contain the details about your call. <A> No weather briefing is required. <S> According to the NTSB, the simple answer is NO (you aren't legally required to call the FSS). <S> The NTSB states... <S> Part 91 regulations do not specifically require the use of any particular sources of weather information for GA pilots, but do require that all pilots familiarize themselves with weather and weather forecast information before beginning a flight. <S> Source. <A> Most airlines nowadays only have briefings at their base/hubs. <S> On the line stations they would probably get handed a 'briefing package' consisting of an Operational flight plan, Weather, Notams (and company notams), charts (pressure and volcanic ash etc), this would be printed out by the station staff or handling agent. <S> The station staff will add more info like the special load notification, Dangerous goods notification. <S> In some cases like for short hops the station may print out the actual weather (METAR) at the destination and alternates.
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For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts , fuel requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which the pilot in command has been advised by ATC; You are not required to call Flight Services for a weather brief, but you are required to get the weather reports (which can be called a personal brief).
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Can I fly a UAS that weighs more than 55lbs if I'm on private property? Can I fly a UAS that weighs more than 55 pounds within my own private property if I stay below say, 200 feet? I do not have 333 exemption <Q> TL;DR <S> As far as I can tell, the rules don't specify zones or altitudes where the regulations aren't in effect, so I think it is highly advisable to register. <S> My personal rationale Being safe just in case is far better, at least in my mind, than choosing to avoid registration. <S> I know people in my RC Quadcopter possee that fly sUAS aircraft but don't have Part 107 licenses. <S> I have one, (I would rather be safe than sorry) <S> but I could see how as long as you are careful, flying a small sUAS without a Part 107 license isn't such a terrible option. <S> In my mind, UA aircraft are an entirely different story, as they are inherently significantly larger than sUAS aircraft, and if something does go wrong, damages would be more severe. <S> The risks (not to mention the responsibility) involved are far more substantial, and I would never consider flying a UA aircraft without a license even if I was only flying on my own property. <A> Flying over your own property doesn't matter. <S> As soon as you leave the blade of grass, whether at 1 inch or 1 mile, you are under FAA domain. <S> Therefore in your case, you would need to comply with appropriate regulations. <S> If you have a special application, or you are doing some specialized development, you might look in to a waiver. <S> But in general, expect that all the rules apply to you even if you are over your property. <S> This includes prohibitions about flying over people, night operations, etc. <A> Sure. <S> In the eyes of the FAA, a UAS over 55lbs is no different from any other aircraft operating in the national airspace system and subject to the regulations under Title 14 CFR.
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According to the FAA Part 333 rules , all UA aircraft (> 55 lbs) must register with the FAA with an N-number before flight.
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Do small aircraft have sockets for passenger headsets? I am currently training for my PPL. in the Cessna 182s we use I've only ever noticed two sets of ports for the headsets. If there were additional passengers in the back seats, how would they communicate? <Q> The rear seats of a Cessna 172 has headset jacks, I imagine the 182 has the same. <S> You can see them in this picture: <S> Image source <S> You might also find them over the shoulder of rear passengers - as can be seen in this image (copyright attached) <S> That links the rear-seat passengers to the same intercom you're used to from a front seat passenger. <A> Generally though the answer is yes. <S> Most modern general aviation airplanes include headset jacks at all passenger seats. <S> Cessna has them on the wall liners of the airplane. <S> Many modern airplanes also will sell active noise canceling headsets included with the aircraft for all passenger locations. <S> They provide active noise canceling to quiet the flight, intercom communications for all people on board the airplane and offer entertainment options such as Bluetooth connection with mobile devices and onboard XM radio. <A> While it's true that many "modern" aircraft designed for GA have passenger comm jacks, given that the average single engine GA plane is 40 years young, There are cases where they could be removed or INOP'd. <S> Assuming that in the 182 in question there really isn't a set of rear ports for passengers, they would need to use a portable intercom box. <S> These allow up to 6 occupants to communicate (pilot plus 5) and are often interfaced in some way with the aircraft communication system. <S> I've worked in the rear of a handful of PA-23s which had been "utility converted" (read been completely gutted rear of the pilot's seat.) <S> Since the trim panels had been pulled, the ports went with them. <S> We used an intercom box instead. <S> There are a handful of boxes available with varying degrees of sophistication. <S> Some for example, multiplex nicely with the airplane's com system to allow the pilot to make calls to tower while isolating passengers. <S> Other models are simply a vox-compatible signal splitter. <S> I haven't been able to confirm this <S> but I've been told that ultralights which take two occupants and glider trainers often use a comm box and portable transceiver to allow pilot/copilot/passenger to talk and be looped into ground comms without the need for any installed systems.
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Diamond aircraft have the plugs for all headset jacks on the aft section of the center console. It depends on the airplane and what year was manufactured in.
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What is a "flare-out" and why does auto-thrust reduce thrust during flare-out? The functions of auto-thrust include thrust reduction during a flare-out . What is flare out and why during flare out will the auto-thrust reduce thrust? <Q> The proper term is "flare" not "flare-out". <S> Whether the pilot, or Auto Thrust does it, a reduction of power to idle is needed in order to bleed off the excess speed that is used during the approach phase. <S> If the thrust is not reduced to idle, the aircraft will take longer to land, and use up more runway. <S> If you don't flare enough, the rate of descent will be too high and the aircraft will land hard. <S> Too much flare will make the aircraft climb back up. <A> The objective is to land smoothly, that is reducing the rate of descent which is still about 700 ft/min, 400 to 500 ft above ground. <S> Landing with this rate is quite hard, so we need to reduce this rate of descent before touch down. <S> The usual way is to lift the nose, thus increasing the AOA, therefore increasing the lift but not to a point of climbing, so a speed reduction would be simultaneously required. <S> Thus reducing the thrust is needed. <S> Happily this is very helpful if thrust reversers are used once on the runway, since reversing requires the transition through idle. <A> Are you talking about a "flare"? <S> Or a "flame-out"? <S> A flare is part of the landing sequence. <S> You raise the nose of the airplane so that you touch down gently on the main gear. <S> The engines need to be at idle (or at least, low thrust) at or before that point because the whole point of landing is to come to a stop. <S> A flame-out is what happens to a turbine (jet) engine when it doesn't get enough fuel to sustain combustion. <S> In this case, the thrust is lost because the engine is no longer running, not because of anything the autothrottle did.
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"Flare" is a term used to describe the act of raising the nose of an aircraft in order to increase lift and stop descending in order to land on a runway smoothly.
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What is it called when you roll without yawing or pitching? My instructor made me do an exercise that consists of banking the sailplane left and right around 30 degrees without moving from the axis. I need to aim for a specific point, and start with the exercise. This is a coordination exercise but does it have a name? It's like a dutch roll but I need to stay in the roll axis without moving. <Q> In the aerobatic community we would call that the beginning of an Aileron Roll . <S> It's harder than it looks. <A> You do a roll change maneuver. <S> In German it is a " Rollwechsel ", and the time it takes to do this from -45° bank to 45° bank is an important measure for the agility of a glider. <S> The maneuver is meant to teach you how to quickly change the direction of circling, and for most gliders it limits the minimum size of their vertical tail surface. <S> The European certification regulations for gliders demand in section CS 22.147: Using an appropriate combination of controls it must be possible to reverse the direction of a turn with a 45° bank in the opposite direction within b/3 seconds (b is the span in metres) when the turns are made at a speed of 1·4 V$_{S1}$ with wing-flaps in the most positive en-route position, air brakes and, where applicable, landing gear retracted and without significant slip or skid. <S> Note the speed (v$_{S1}$ is the stall speed): <S> The faster you fly, the easier it is. <S> Since induced drag is highest at low speed, <S> the adverse yaw resulting from the aileron deflection is impossible to overcome if you fly slowly. <S> Glider designers try to make the tail just big enough <S> so CS 22.147 can be fulfilled <S> (the condition "without significant slip or skid" is crucial here!). <S> If you want to start an aileron roll this way: Please don't! <S> It takes a little more to roll a glider properly. <A> <A> In Argentina we used to call it "coordinación" (coordination). <A> It sounds like the process of doing a slow roll, though the pilot usually does the role until they are at the 180 mark, that is inverted. <A> " <S> This is probably the most unambiguous description, as you are rolling the plane while using coordinated inputs to keep the heading constant.
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Here at the University we call it a "Perfect Roll", it is commonly used to assess the turning characteristics of an aircraft. In addition to being (mistakenly) called a Dutch roll, I hear that maneuver called "rolling on a point" or "rolling on a heading.
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What is the flight trajectory of a commercial airplane in regards to altitude v/s distance? So, my friend and I got into an argument regarding the flight trajectory of a plane. He said that for half the journey the plane is ascending and for the rest, it is descending and hence making a parabolic curve. I argued that it ascends and then stays at the same altitude for the journey before descending to make a trapezoidal curve. After some contemplation, I think that both of us are right just that the baseline reference is different where he took it as a straight line between the two places without the curvature of the earth and hence it would make it parabolic while I took the trapezoidal curve by accounting the curvature of the earth. We can also say it is from a different of view with him being in space while I am running on the ground to measure the altitude. So, can someone clarify and tell who is right and whether what I think is correct or not? It would be helpful if someone can actually plot the two graphs.Thank you. <Q> Your friend is not correct and you are somewhat correct. <S> For now I will consider long-haul flights as the effect is more visible. <S> As the aircraft takes off it climbs towards it cruising altitude, say 33,000ft. <S> Then during the cruise the airplane uses fuel meaning that the aircraft is effectively losing weight. <S> Since during a steady cruise, lift = weight the aircraft will have an excess lift if nothing but the weight changes. <S> This will make the aircraft climb to higher altitudes were the air is thinner and thus more lift is required. <S> Thus on some long-haul flights you can see that the flight ends at 38,000ft. <S> Then the pilot initiates the decent for landing. <S> Depending on ATC the aircraft is allowed to gradually climb during cruise to higher altitudes. <S> If that is not allowed the aircraft will climb once every hour or so to a higher flight level. <A> Normally, flight profiles (i.e. the altitude flown over the distance covered) are depicted assuming (yes I know this might be controversial... <S> oh dear ...) <S> a flat earth. <S> Constant altitude will then be represented by a straight horizontal line, so it is easy to see when the aircraft is in level flight and when it actually is climbing or descending: <S> Note, by the way, that some short flights will have virtually no level cruise phase: <S> Also, a flight with optimum efficiency (minimum fuel used to cover a given distance) will look roughly parabolic in this profile view. <S> Real life flights aren’t operated that way though, mainly due to constraints on airspace use. <S> Airspace constraints will also be the reason the descent phase in the second picture looks so stepped. <S> You could, as you say, instead of the profile view show a 2-dimensional view with the curvature of the earth shown and <S> the flight path plotted above it. <S> That would then look curved for most of the flight. <S> I don’t see much use in this representation for normal aircraft, though, unless we start to cover orbital operations... <S> Pictures are screenshots of historical commercial flights found in Flightradar24 app. <A> Each aircraft has an optimal service ceiling (or altitude so to speak), depending on type and usage (military vs passenger vs small piston plane). <S> As for passenger planes, airlines plan their routes the most optimal way: lateral and horizontally as well. <S> It's a combination of aircraft weight, upper winds, shortest way, time vs distance etc. <S> When you leave the the lateral options away and focus on the vertical options airline pilots mostly want to fly the optimal altitude to save fuel or time (or a combination of those two). <S> The optimal altitude increases for the duration of the flight: the lighter the plane, the higher is its optimal altitude - except if for some special wind situations. <S> Therefore a typical passenger plane climbs to a flight level (i.e. 35000ft) <S> and when the flight guidance computer shows a higher optimal altitude, the pilots ask for clearance and eventually can climb to the next level (i.e. 37000ft). <S> Roughly 30min before the landing the descend is initiated (can vary obviously) and can be a step descend (level to level) or a continious descend (the most economical way to descend). <A> What is the flight trajectory of a commercial airplane ... <S> Circular Arc <S> A flight from say, Aukland to Doha would follow a path through three-dimensional space that is approximately circular. <S> The great-circle distance along the track is 14,535 kilometres, <S> the vertical variation above the roughly spherical surface track is about 10 km - less than 0.07% - we can ignore that. <S> Google Earth showing shortest route from Aukland to Doha in red. <S> The thickness of the red line is about 22 times the cruising altitude of an airliner. <S> The difference between ground level and 35000 feet is maybe half a pixel. <S> Any graphs of long-distance flights that don't look circular are heavily distorted statistical deceptions designed to show only the insignificant† tiny variations from a perfectly smooth curve. <S> ... <S> in regards to altitude <S> v/s distance? <S> A Straight line See above. <S> † From a geometric perspective. <S> You pilots keep watching that altimeter!
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Both of you are somewhat right - in the way you mention.
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Can the FAA stop the municipality owned airport from closing down? I live in Wheeling IL . Our town owns the municipal airport there. Most of the residences here want to close down the airport. Can the FAA stop us from closing the airport? <Q> Frequently, municipal airports are created and/or operated with funds granted by the Federal Government that contain contractual obligations that the airport remain operating until a particular date or certain conditions. <S> I don't know about that particular airport. <S> Even if a municipality owns the airport free-and-clear without contractual obligations to operate it, the FAA does have a lengthy process for shutting down an airport. <S> Since you're in Wheeling, you may be familiar with Meigs Field , which was abruptly closed against FAA rules, leaving airplanes stranded, charts incorrect, and airplanes attempting to land at an airport that didn't even have a functional runway anymore! <A> Many airports receive federal grants which provide for portions of runway development and even snowplows to keep the runways clear in the winter. <S> However that grant money is restricted in how it, and things paid for with it, can be used. <S> So for example, a town owned airport which gets funds for a snowplow for the airport with federal monies <S> , cannot use that snowplow and truck in general highway service. <S> There are exceptions, for example, in disaster relief, and with FAA permission for certain circumstances. <S> A nearby privately owned airport, which received a large amount of federal aid, was discovered to have their airport equipment (trucks, excavators, bulldozers, etc.) parked at a family member's construction business, 35 miles away. <S> This put their federal funding in jeopardy and caused assessment of fines and sanctions by the FAA. <S> In the case of publicly owned, federally funded airports, there are often political forces at play, which can modify the outcome. <S> Similarly, well connected owners of an airport who use the airport facilities and equipment for non-aviation purposes (like federally funded hangers for storage of boats and RVs) may not suffer the expected sanctions and loss of federal funding. <S> Politics and business creates another vector force. <A> KPWK? <S> If the FAA has provided any funds to the airport, the closure may be impeded by the feds. <S> Of course that didn't stop the midnight closure of Meigs Field.
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Closures of airports are only impeded by the FAA (or other agencies) when there are contractual obligations.
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Why is the first turbine in a turboprop (or turboshaft) connected to the compressor? Typically the first turbine after the combustion chamber drives the compressor as shown in this picture. ( wikimedia.org ) This first turbine spins the fastest and harvests the most energy from the gas flow. This seems inefficient when you want to maximize power output from the power turbine. So why not have the power turbine the first to take advantage of the gas flow and then the compressor/gas producer turbine second? <Q> You can only use for shaft horse power what is available after the energy to drive the compressor is subtracted. <S> This subtraction is done by the high pressure turbine. <S> Any energy left in the exit flow after that can be extracted to drive a propeller, a fan or a generator. <S> What happens in your arrangement if the power turbine extracts too much energy to keep the core engine running? <S> No, clearly the priority has to go to keeping the core engine alive and to only use what is left. <A> A slower compressor will lower the compression ratio, and therefore will hurt the fuel economy of the engine. <S> A faster free turbine will require a much stronger and bigger reduction gearbox (remember the prop rotates much slower than the turbine). <S> There is no easy way to have the concentric (or otherwise) <S> shafts run the LPC (or prop) via the HPT (pictured above). <S> Assuming it can be done, adjusting the fuel flow will have a slower compressor response, resulting in overheating (not enough air) or choking of the turbine (too much air but not enough fuel). <S> In short, the gas flow is only strong because the compressor is run by the first stage(s) of the turbine. <A> The first turbine takes some of the energy from the combustion process and uses it to drive the compressor.
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The compressor obviously requires a power source, in order to do the work of compressing the air before it is mixed with the fuel.
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If both propellers and wings are airfoils, then why do propellers deflect air perpendicularly to the rotor, but wings not? Here is my dilemma. I have seen a lot of videos of airfoils in wind tunnels, and I've noticed how the airflow always moves away from the trailing edge parallel to the wing, or at a very small angle away from the wing (link to one of those videos ). I've also heard that propellers are nothing more than rotating wings (airfoils), producing lift sideways as opposed to upwards. What confuses me is that in the case of the propeller, the airflow leaves the propeller at a much higher angle, and not straight as is with the wing. In other words, the airflow is deflected backwards from the prop. I just can't understand how the wing and propeller, which are two very similar shapes (maybe not that similar, but they operate by the same principle), deflect air in two radically different directions. I have a few thoughts non why this happens, but I think it's better if someone tells my first. Thank you very much! <Q> Don't let wind tunnels fool with your perception of reality. <S> In the real world, it's the wing that moves while the air remains stationary. <S> Consider a video just like the one you posted, but filmed with a stationary camera. <S> (The one in your video is attached to the wing and moves along with it.) <S> You'd see the folowing scenes: <S> The field of view is filled with stationary air. <S> A wing quickly passes through the video from right to left. <S> The air now moves downward more or less vertically. <A> Expanding on @RainerP's answer, look more carefully at the wind tunnel footage. <S> The smoke streams are slightly lower behind the wing than they are in front of it. <S> This may look insignificant, but it isn't: the air in the tunnel is moving extremely quickly, and therefore only has a very short length of time to move vertically after it has left the wing before it is carried off camera by its horizontal motion... if we can see a 3m section of tunnel and the air is moving at 200mph, then it stays on camera for only around 30ms. <S> So if the air coming off the wing gains a vertical velocity of, say, 3 meters per second, you'd only expect to see a deflection of around 10cm by the time it reaches the edge of the frame. <A> The airflow behind an aerofoil (sorry, I'm English, I can't bring myself to write 'airfoil'!) <S> always moves downwards away from the trailing edge, if the aerofoil is generating lift. <S> This is Newton's Third Law in action: every action has an equal and opposite reaction. <S> It is not possible for the air to act on the aerofoil to generate lift without the aerofoil acting on the air to accelerate it downwards. <S> From Newton's Second Law, the force required to accelerate something is proportional to the mass of the thing and the amount by which it's accelerated ($F=m\times a$), so to generate the same amount of reaction force you can accelerate a small amount of air a lot, or a large amount of air a bit. <S> In a continuous process this force is also equal to the mass flow of the thing <S> being accelerated (the mass per unit time) multiplied by its ultimate change in velocity. <S> Wings are typically bigger than propeller blades, so the mass flow of air past them is higher for the same airspeed, and the required change in velocity is therefore lower for a given amount of lift. <S> (Side note: it might appear that propeller blades have a much higher airspeed than wings, but in flight they really don't. <S> The tips are almost always subsonic, and the linear speed of the blade decreases towards the hub too, so the speeds involved are loosely comparable to those of a wing.) <A> On a stationary aircraft the propeller keeps beating the air at the same spot. <S> That generates a horizontal column of air. <S> If you took wings lifted them more than 100 feet off the ground and kept beating the same spot you'd also get a column of air moving. <S> Actually that precisely describes what a helicopter does. <S> A helicopter has "wings" oriented horizontally and rotating fast. <S> It also has a tail rotor (wings) oriented vertically. <S> A wing does push air down but it doesn't generate a column of air moving simply because it always keeps moving on to a different air mass. <S> Same thing with a propeller moving fast forward. <S> It doesn't actually move the air backwards very much. <S> It also moves on to new air. <A> It sounds like you might be confusing the direction of airflow vs. the direction of lift : <S> As either a wing or a propeller moves through the air, the flow is approximately parallel to the airfoil. <S> In both cases, the air at the trailing edge of the airfoil is moving "downward" (relative to the airfoil) to some extent. <S> This is what produces lift (on a wing) and thrust (on a propeller), both of which are approximately perpendicular to the airfoil. <S> As an airplane moves through the air, its wings (hopefully) hold it the same distance off the ground. <S> As a propeller (on a moving airplane) moves through the air, the path it follows looks much like a screw, with each pass of the propeller being roughly the same distance from the previous path.
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For a given air-relative speed and airfoil shape, both a wing and a propeller will deflect the airflow the same amount: A propeller does not deflect the air perpendcular to the rotor, it provides thrust in that direction.
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Why B-52 engines produce lots of smoke only during take-off? During the flight it seems there is no smoke, it's only during takeoff. Here is an example This question explains that smoke is caused by unburnt fuel but why is there so much more during takeoff? <Q> There are a few reasons. <S> The first is that the engines run more efficiently when the aircraft is moving. <S> The second reason is even simpler: like most aircraft a B-52 only rarely runs at full throttle. <S> Most of the time that it's cruising, the throttles are backed off to just overcome the drag and maintain the current speed and altitude (though flying at terrain avoidance level is a rather different story). <S> The last reason is that the larger amount of smoke is largely an illusion. <S> When the aircraft is moving, it's actually still generating close to the same amount of smoke. <S> We're seeing the smoke from running the engines at full throttle for roughly a minute. <S> During one minute of normal flight, it would generate somewhere close to the same amount of smoke--but instead of being concentrated in the 1 mile or so that we see here, it would be spread across something like 10 miles of sky. <S> In addition, at altitude, you're a lot more likely to have much stronger winds, so exhaust from a minute ago will be relatively widely dispersed, rendering it much less visible than we see here (with air that looks like it's almost perfectly still). <A> This specific aircraft is a B-52H. <S> The engines are identifiable as TF-33's which means we can rule out water injection as the cause of the smoke. <S> Were this a G model or earlier it would be fitted with water injected J-57 engines and water injection would be the likely cause. <S> Since Water injection is not the cause I would suspect that you are looking at unburnt fuel. <S> Bear in mind that in aviation redesigning components is not done capriciously because changing even the smallest detail can be extremely costly or dangerous (the military gets to pick one of those, civilians can only choose costly.) <S> The TF-33 <S> in the B-52H is a verstion of the JT3D engine which started life in 1958 and was not changed very much to create the variant delivered for the B-52H in 1961 Consider how cleanly the engine in this vehicle burns: <A> All early generation jet engine smoke like this at take off. <S> This includes B707 and DC-8 and many other jet aircraft of the 1960's. <S> Most airliners today have more efficient engine that do not smoke. <S> All these older generation engines were designed when fuel was cheap. <S> They were far less fuel efficient and the black smoke you see is mostly un-burned fuel. <S> Just Google smoky jet engines at takeoff <S> and you will see what I mean.
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As the aircraft moves faster, it's easier for it to get more air into the engine, which helps it run more efficiently. The B-52 still uses older generation engines.
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Are private jets allowed to land at London Heathrow? Heathrow is among the worlds busiest airports, with traffic mostly (entirely?) from airliners. Are private/business jets (e.g. Gulfstream G650 or Cessna Citation X) allowed to land at Heathrow? If so, what are the landing fees and what criteria do they use in charging them? <Q> The answer appears to be "yes", but unless you're transferring directly from the private jet to/from an international flight in/out of Heathrow, it's a poor choice. <S> Fees are high and delays are common. <S> With no fewer than 13 other airports to choose from, chances are that one of the others will be a better choice. <S> Luton and Farnborough are the most popular choices for private jets. <S> Reference: <S> PrivateFly: <S> Inside London Airports - Private Jet & Helicopter charter <A> Charging is based, like many airports, on aircraft weight in the first instance, but also incurred are handling charges, parking charges, and extra charges for noise/emissions rating, as well as a different price for night landings. <S> Many airports use similar pricing structures. <S> Heathrow publishes their landing charges, so you can go and calculate the total cost for next time <S> you ask your Pilot to land you there! <A> The short answer is : You could. <S> But GA traffic is heavily discouraged both in terms of fees and policies. <S> Longer answer: <S> Most of the time, the only private jets you'll find at Heathrow are those operated by heads of state and their respective governments who, for whatever reason, feel they absolutely must land at Heathrow. <S> Most private private jet traffic that needs to be as close as humanly possible to Central London goes to RAF Northolt. <S> A military airfield that's (pretty much) the same distance to Central London as Heathrow. <S> But its far less busy than Heathrow (and probably cheaper too, I don't know the prices off the top of my head). <S> The added benefit of Northolt is that security is (obviously) MUCH higher than Heathrow. <S> Which makes the job of keeping your VIPs safe (and the paparazzi and unwashed masses away from them) much easier. <S> Military needs obviously take priority at RAF Northolt in terms of availability, but most of the time its not a problem. <S> The RAF do most of their stuff from bases outside London out of respect for the NIMBYs.
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Yes, Private jets can land at Heathrow.
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How long does it take to assemble an Airbus A380? How long does it take to assemble an Airbus A380? <Q> Airplanes are not built like cars where after completion, they are showcased at dealership to attract prospective buyers. <S> For larger commercial airplanes, airlines place an order first and then wait for the airplanes to be manufactured, custom modifications completed, inspected by the airline and then delivered. <S> It is a bit complicated process. <S> However, one of the A380s Emirates ordered, was manufactured and delivered in 80 days : <S> Emirates are celebrating having their fiftieth Airbus A380 in service with the release of footage showing how 800 workers across Europe came together to build the biggest passenger jet in the sky in just 80 days. <A> The timeline to build out each component of an Airbus A380 and the final assembly of the components are two different things. <S> I will focus on final assembly. <S> Once all the parts are available, the time it takes for the final assembly the fuselage, the wings and other components in the jig at Station 40 is about a week. <S> Add to that an additional month for testing the assembled components, customization and painting before delivering the plane to a customer. <S> In 2018, the assembly line is working at a significantly reduced output of 12 planes per year (1 per month) to keep the plane in production for as long as possible in hopes that additional orders will be placed to extend the life of the platform. <S> https://en.wikipedia.org/wiki/Airbus_A380 <S> https://www.cnet.com/news/building-the-a380-the-worlds-largest-passenger-plane/ <S> Good luck figuring out the timeline of how long it takes to assemble the individual components like the cockpit, the engines, the wings, 330 miles of wiring <S> , you get the idea. <S> The reason it's hard to determine things like the timeline for the wiring is that much of the wiring is done before the components are installed together into one physical unit. <A> Demand for the large airplanes can vary significantly month-to-month and year-to-year, and the manufacturers adjust their production rate to match demand. <S> Typical rates for the biggest airplanes are about 1 a month, while planes like the extremely popular Boeing 737 can be produced around 42-47 a month! <S> (Source: Boeing ) <S> Manufacturing large airplanes takes hundreds of people on the assembly line. <S> The variations in production rate are managed by changing the staffing levels on the assembly line. <S> When planes are in high demand, more people and more shifts are added to make planes faster. <S> When demand is low, shifts and individuals may be laid off to slow production. <S> Of course, no one wants to be constantly hiring and firing skilled assembly line workers, so carefully managing the backlog of orders, the expected rate of future orders, and the number of people working is crucial to keeping employment relatively stable. <S> Management wants to produce planes as fast as their customers need them, but not so fast that they have to layoff large numbers of people when a single airplane order is missed. <S> With a fully staffed line working fast, large planes can be produced, start-to-finish, in less than 2 months. <S> Typically, however, the biggest planes take around 6 months to make.
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When the assembly line is working at full speed, Airbus can deliver about 30 A380 planes a year, doing so in 2012 and 2014.
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Do Federal Regulations really require compliance with all crewmember instructions? On commercial flights, we're frequently told that all passengers are "required to comply with lighted signs and placards, and all crew member instructions". But when it comes to the CFRs, the closest I can find is 14 CFR 121.571 (a) Each certificate holder operating a passenger-carrying airplane shall insure that all passengers are orally briefed by the appropriate crewmember as follows: (1) Before each takeoff, on each of the following: (i)Smoking. Each passenger shall be briefed [...] This briefing shall include a statement that the Federal Aviation Regulations require passenger compliance with the lighted passenger information signs, posted placards, areas designated for safety purposes as no smoking areas, and crewmember instructions with regard to these items. (iii) The use of safety belts, [...] This briefing shall include a statement that the Federal Aviation Regulations require passenger compliance with lighted passenger information signs and crewmember instructions concerning the use of safety belts. These rules seem to say passengers only have to follow instructions regarding Smoking, and Seatbelts. Is there some specific , Federal Rule 1 , other than catch-all 91.3, that requires general compliance with all instructions? What if I want to leave my tray table down? Or keep my electronics on? Or put my feet in the aisle? 1 Not a contract of carriage with the airline <Q> I found an overview from a lawyer on what "interfering" actually means. <S> The short version is that there's no regulation or law that says "you must obey all instructions". <S> Instead, they say "you must not interfere" and that's interpreted very broadly. <S> She based the article on one regulation and one law: 14 CFR 121.580 (see also 91.11 and 135.120 ) <S> No person may assault, threaten, intimidate, or interfere with a crewmember in the performance of the crewmember's duties aboard an aircraft being operated under this part. <S> 49 <S> USC 46504 <S> An individual on an aircraft in the special aircraft jurisdiction of the United States who, by assaulting or intimidating a flight crew member or flight attendant of the aircraft, interferes with the performance of the duties of the member or attendant or lessens the ability of the member or attendant to perform those duties, or attempts or conspires to do such an act, shall be fined under title 18, imprisoned for not more than 20 years, or both. <S> However, if a dangerous weapon is used in assaulting or intimidating the member or attendant, the individual shall be imprisoned for any term of years or for life. <S> The lawyer's analysis is that not following an instruction would be a violation of the regulations (civil penalty). <S> If you go further and physically interfere with a crewmember that would be assault (criminal penalty). <S> When it comes to instructions specifically, she says that "interference" can be interpreted very broadly (emphasis mine): <S> Almost any offensive or disruptive behavior that distracts the crew can be considered interference, such as: [...] disobeying repeated requests to sit down, return to your seat, or turn off an electronic device <S> Her basic advice is to follow all instructions if possible and never touch a crewmember: <S> Any time you disobey a crewmember <S> ’s instructions, you run the risk of violating federal law. <S> But civil penalties and criminal prosecutions usually result only when passengers repeatedly ignore, argue with, or disobey flight attendants; or when they act out in a way that is dangerous. <S> You can see the FAA's enforcement statistics on this, by the way. <S> Interestingly, it seems that the number of cases fell sharply in 2005 and has been trending down since then. <A> §121.317 Passenger information requirements, smoking prohibitions, and additional seat belt requirements. <S> (emphasis is mine) <A> Title 49 U.S. Code Section 46504 states that interference with the duties of flight crew members and attendants can result in a fine and up to 20 years in prison. <S> This means anything that interferes, including refusal to stow a carry on, non compliance with safety briefing instructions, refusal to be seated when the seat belt sign is on, any disruptive behavior. <S> Nothing like this is tolerated and Will result in removal from the aircraft by the crew, customer service or armed airport security.
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For U.S. Air Carriers FAR Part 121 requires passenger compliance with specific instructions as specified in subparagraph (k) shown in the excerpt below: ( here is a link to the entire regulation shown below )
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Why do landing gear tires smoke upon touchdown? I have been observing several aircraft landings and have noticed that when the aircraft's landing gear touches down, it precipitates the rising of a cloud of smoke. Why is this? (Source: airliners.net ) <Q> Because the tires are momentarily skidding on the pavement as they rapidly spin up from standstill to the jet’s touchdown speed. <S> It’s just a puff of burnt rubber but the tire tread itself becomes quite warm, reaching 600-700°F for an instant. <S> It’s also the reason a pilot does not ride the brakes upon touchdown as this could cause a blowout as the tire is ground up rapidly. <A> Imagine yourself driving your car at a speed of 60mph (96 kmph) and suddenly you apply the brakes completely and notice that it produces smoke. <S> THIS IS FRICTION. <S> Now, when the aircraft lands at 180 knots (324 kmph) it creates friction too. <S> Exactly before the tyre touches the ground it is static. <S> As soon as it touches it takes that tiny bit of time to gain the relative speed with the airplane on the runway, but since it has already touched the rough surface. <S> It drags on it. <S> This is when the smoke appears. <S> After that it gains speed and the speed is gradually broken down by the speed brakes and it finally comes to a stop. <A> An example is a burnout, where the tire is spinning at high speed with a vehicle and road going 0 mph. <S> Roads generally go 0 mph . <S> Prior to aircraft touchdown, the tires are not turning, so the top and bottom of its tires are going at the same speed - aircraft ground speed, say 120 knots for a 737 in a bit of a headwind. <S> Not all runways have a ground speed of 0 knots, but the ones that land 737s do. <S> When the 120-knot tire bottom touches the 0-knot runway, that's a big difference, so as said, there'll be smoke. <S> This reveals drag on the tire, which will very quickly spin the tire up so its bottom is going 0 knots relative to the ground. <S> At that point the smoke will stop. <A> Planes land at somewhere in the ballpark of 150mph (230km/h). <S> At the moment when the plane lands, the wheels aren't spinning, and the only thing that can make them spin is the contact with the runway. <S> So, at the moment the plane lands, the wheels are skidding at 150mph, and they'll continue to partially skid until their rotation speed matches the speed of the plane. <S> And it takes a little while for that to happen, because aircraft wheels are pretty heavy: according to Lufthansa , a wheel and tyre on a 737 weighs about 112kg, and about 185kg on a 747. <S> So, the smoke you see is material being worn off the tyres as they skid up to speed. <S> They're designed to be used this way and are regularly inspected and replaced to ensure that not too much of the rubber is worn away. <A> It is kind of the reverse of burning tires on a car. <S> There is a limit to static friction and tires spin. <S> Even when they spin there is kinetic friction. <S> When the tires spin they get hot from friction and burn (more like the rubber vaporizes). <S> The tires have mass and it takes energy to spin them up the speed of the plane. <S> Initially the speed difference is so great they spin and smoke. <S> The kinetic friction quickly brings the tire up to the speed of the plane.
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Anytime a tire's bottom is moving at a significantly different speed than the roadway, it'll make smoke.
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Are steam gauges more reliable than glass panels? I have always had a deep appreciation for technology and the future and I encourage that technology should move us forward whether that be in aviation terms or otherwise but one question has been on my mind for a very long time and that is why we have computerized gauges and not the old fashioned ones with the gauge hand behind glass. In the event that a plane loses power, wouldn't it be better to have physical gauges because if the plane loses power, those critical gauges on a screen will disappear. Is it just me or does it not make a huge difference? I suppose an old-fashioned glass gauge will stop too, just the same as a glass cockpit gauge? Thanks. This is a question I have always wanted to ask someone who has the expertise to answer it. <Q> Most aircraft using electronic displays have double (and sometimes triple) redundant power supplies to keep the electronics alive in cases of power failure. <S> The mechanical gauge panels of the not so distant past did not have these same levels of redundancy built in. <S> Beyond power considerations, glass panels also contain features like weather radar, collision avoidance, and navigation that further increase the reliability and safety of the system as a whole. <S> That said, it's fair to say that glass panels are more reliable. <S> The funny thing is, critical mechanical gauges are still included on most panels as last resort backups. <A> Most integrated flight displays – the so-called glass cockpit – contain multiple redundancies both on the forms of computer power, and electrical power sources to keep them operating in the event of an emergency or other electrical problems. <S> As an example, I obtained my multi engine add-on in a Diamond DA-42 <S> TwinStar airplane equipped with a Garmin G1000 glass cockpit. <S> The aircraft’s electrical system uses a primary 24 V battery which is supplies power to all the electrical buses in the aircraft. <S> It is also charged by two 24V, 60 amp alternators, one on each engine, which supply power to their own electrical bus and the battery bus. <S> The main electrical busses supply power to the avionics power bus and both alternators can feed this bus as well. <S> In the event of a total electrical failure to both the battery and alternator power buses, there is an emergency battery available to power the avionics for at least 30 minutes of continued operation. <S> Many aircraft carry separate back up EFIS displays, each with its own emergency power supply for additional redundancy. <S> If you compare this with the typical systems an twin aircraft with a conventional cockpit, most of the gyroscopic instruments are powered by a pair of vacuum pumps, one on each engine. <S> The turn and bank indicator is powered by the aircraft’s electrical system. <S> Lose both of the vacuum pumps, and you’re on partial panel. <S> In comparing these two systems you would have to look at the probability of an all out failure for both systems. <S> The new glass cockpits have been just as reliable, if not more reliable, then conventional steam gauges and far more functional in the event of a failure. <A> When it comes to gauges, the most accurate and reliable ones are found in industrial applications like steam plants or ships because weight was not an important factor. <S> On an application like an airplane or a car, weight is an important consideration. <S> Obviously gauges on an airplane are accurate, but not nearly as accurate as they are in other applications. <S> A 50 year-old altimeter might be accurate within 10 feet, which is fine, just a little jarring when landing. <S> With the advancement of technology, glass panels have a definite weight advantage over gauges and can have a precision, accuracy and reliability beyond a need to display. <S> It depends on the sensor (does anyone need their air speed to the seventh decimal point?). <S> Glass panels can self-test to determine the accuracy of the readings and alert you to the need to replace a sensor, but a gauge cannot do that.
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Glass panels are more reliable and accurate in every way over steam gauges.
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Why are parking brakes not used for parking jetliners? From the question ' Do I Set the Parking Brake On the Ramp? ' it is concluded that you do not set the parking brake when parking the aircraft. The question concerns small aircraft which can be parked for a longer period of time. However, commercial jets (jetliners) are also parked at the gate without the parking brake engaged and rely on blocks/chocks placed around the wheels. Then why is it called the "parking brake" as it is not used while parking the aircraft? Other wheeled vehicles like cars, trucks and buses are always parked on the parking brake. <Q> The most common time for this to happen is during a lightning storm when ground crews are not allowed on the ramp. <S> Large airports like DFW have automatic parking lights that will guide the aircraft to the proper alignment and stopping point. <S> The crew will then set the parking brake before deplaning the passengers. <S> Some crews will also use the parking brake for ramp holds, de-icing, etc. <S> The reason why chocks are preferred over the parking brake, is due to the way parking brakes work on aircraft. <S> On commercial aircraft, the pilots apply the brake manually, then turn on the parking brake, which closes a hydraulic valve trapping the pressurized fluid in the brakes. <S> Due to internal leakage of the valve, the brake pressure will slowly bleed down over a few hours. <S> Therefore, after a few hours the brakes will no longer hold the aircraft. <S> Further, most aircraft ramps are slightly sloped away from the terminal, so the aircraft would end up rolling backwards. <S> Due to the bleed down issues, most airlines require pilots to stay in the cockpit ready to apply brakes until the wheel are chocked. <S> I have personally seen cases of large aircraft being parked with a parking brake, that rolled after the brake bleed down. <S> In one case, a 777 rolled backwards and the jet-bridge tore off its door. <S> Link to News Article Car parking brakes work differently. <S> Parking brakes in cars have a direct mechanical linkage (typically a cable) that is held in place. <S> Therefore, they do not have the bleed down issue and will maintain the same amount of braking force at all times. <A> I am going to answer you from an airline pilot point of view. <S> First of all, parking brakes in aircraft work pretty similar to the ones in a car or a truck. <S> And yes they are used to park the airplane by letting go off the toe brakes, which is again pretty similar to a road vehicle. <S> Once we are at the gate after a flight, we put on the parking brake and shut the aircraft down. <S> The ground engineer usually lets us know through the intercom once the chocks are in place. <S> This is a sort of 'okay' signal to release the parking brake. <S> The reason why we use chocks and keep the parking brake off is mainly to cool down the brakes. <S> Following a typical landing, and sometimes a long taxi to the gate, the brakes tend to heat up. <S> Because airplanes rarely stay on the ground, we need to cool the brakes down to ensure they remain efficient in a possible rejected take off that might occur in the next flight. <S> Keeping the parking brake off makes sure that the brake stators are released from the rotors, allowing better air flow circulation. <S> This ensures proper heat dissipation. <S> In some airplanes, we have brake fans, which helps to cool the brakes. <S> The fan is more effective with the parking brake off. <S> However, for the walkaround, we set the park brake on, even if the chocks are in place. <S> This is so that we can get a more accurate indication of the brake wear indicators. <S> When the airplane has to be parked at a place for a long period of time, the parking brake can be kept on. <S> But as the parking brake in most airplanes (when unpowered) is channeled through a pressurized hydraulic accumulator, it tends to slowly lose pressure. <S> For example, the A320 accumulator can hold the brakes in place for about 12 hours. <S> If you have to park it for more than 12 hours, you should place the chocks on the wheels to prevent it from moving and hitting something. <S> The A320 parking brake system. <S> It is powered by the yellow hydraulic system and by an accumulator when the aircraft is off power. <A> It’s so a linesman can tow your plane around if need be without you being there or needing to get into the plane.
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Parking brakes are used by commercial aircraft at the gate if the ground crew can not set the chocks.
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Why wasn't there a belly gunner on the B-25 Mitchell? The B-25 Mitchell doesn't have a belly gunner, which would seem quite dangerous. Why didn't it have one? <Q> The production B-25B, B-25C, B-25D, and some B-25G models did have retractable remote control belly turrets. <S> They were often removed in the field because they were ineffective and disliked by the crews. <S> The lower turret was officially deleted in the middle of the B-25G production run and continued with the B-25H and B-25J production. <S> More info on the B-25 here: B-25 History.org <A> My research has shown that the turret was operated through a panaflex prism periscope that caused such intense vertigo and nausea in its' user that is was rarely used and often removed. <A> My guess is that that conventional fighter aircraft couldn't attack from below (because they have forward-firing guns and can't fly vertically upwards) -- so belly-mounted guns are the only guns you don't need. <S> The Germans introduced upward-firing guns ( Schräge Musik ) so that they could attack from below (to take advantage of this undefended approach), but these didn't come into service until late in 1943, and (being on nightfighters) weren't discovered by the Allies for the next year or more.
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In the Pacific Southwest, the turrets were immediately removed and replaced with fuel tanks to increase range and also because monsoon rains turned airfields into mud which covered the gunsight on takeoff rendering the turret useless.
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If a circling airplane (AC-130) fires a bullet how does the plane's trajectory alter the shell's flight path? Background: An AC-130 is a military aircraft that has a cannon that fires out the side of its fuselage. If an AC-130 (or similar aircraft) is traveling in straight, level flight at a constant rate of speed calculating gun lead is straightforward. For example if the plane is traveling forward at 100 meters per second, the target is 1000 meters to the side and its cannon shell travels at 1000 meters per second simply fire 1 second or 100 meters early to score a hit. However what if the AC-130 is traveling in a circular orbit at 100 meters per second around its target instead of beside the target? I'm not sure how to calculate gun lead in that circumstance. Hopefully the image I attached below will help this make sense. Thanks so much in advance for any input! <Q> The bullet leaves the barrel with the combined velocity of barrel muzzle velocity plus the instantaneous aircraft true air speed velocity (actually, the instantaneous true air speed velocity of the tip of the muzzle). <S> That puts the velocity vector of the bullet ahead of the line of the barrel (ahead of the 90 degree wing line). <S> The fact that the barrel is rotating in inertial space is irrelevant. <S> Whether the aircraft is straight and level, turning towards the tank, or away from it, if, at the moment the bullet leaves the muzzle, it is traveling in inertial space towards the tank, (and sufficiently above it for gravity drop) it will hit it. <S> And since the bullet's velocity leaving the barrel is a simple vector sum of the muzzle velocity, and the aircraft's instantaneous velocity at that instant. <S> The velocity vector of the aircraft before, (or after), the bullet leaves the barrel is of no relevance. <S> So if the aircraft is moving due North at 100m/s and the muzzle velocity is 1000 <S> m/s <S> due East relative to the aircraft, the bullet is actually traveling SQR(100 <S> ^ <S> 2 + 1000^2) <S> = <S> 1004.98 <S> ~1005 <S> m/s in a direction <S> slightly North of due east by an amount equal to the arctangent of 100/1000 or ArcTan(0.1) <S> = <S> 6.345 degreesSo <S> the bullet is traveling 1004 m/s on a heading of 90-6.34 degrees = <S> 83.66 degrees true. <S> So, to hit the tank, the pilot has to fly so that the gun barrel is pointed behind the tank by 6.34 degrees (and above it by a sufficient amount to account for gravity drop) <A> In the case of the AC130, in which the weapons are mounted on the port side the deflection would be in a downward direction. <S> This occurs because the combination of the rotation of the projectile and the airflow causes a difference in air pressure between the upper and lower sides of the projectile. <S> Technically this is known as the Magnus Effect. <A> In the case of a gatling type weapon the detailed design of the gun and mounting and the rate of fire would all have to be taken into consideration as they would determine the direction and magnitude of the velocity vector imparted to the projectile by the rotation of the barrels while it was being loaded and fired, as well as the internal ballistics of the ammunition and the individual barrels. <S> AC130s were formerly armed with 7.62mm, 20mm and 25mm gatling guns, but now as I understand it these have all been replaced with 40mm single barreled guns.
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When a projectile is fired from a gun in a fixed wing aircraft or helicopter in a direction perpendicular to the direction of flight, the airflow across the muzzle has an effect on the trajectory which is known as "bullet jump", the deflection can be upwards or downwards depending on the direction of the rifling of the gun (normally right hand or clockwise) and the direction of the airflow.
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Can an airplane engine fire be extinguished without shutting down the engine? Airplane engines catch fire from time to time (and are falsely reported as being on fire even more often). In a modern airliner, the "fire handle" shuts down the engine, closes the fuel pipe, and discharges the fire extinguisher. Occasionally it's desirable to leave the burning engine running because you need the added thrust. For example during WWII B-29 engines had an unfortunate habit of catching fire on takeoff. Standard procedure was to leave the burning engine running until you got enough altitude to safely discard the bomb load and/or bail out. Is it possible to activate the fire extinguisher without shutting down the engine? <Q> In most modern jets (e.g. Boeing 757/767) when you pull the fire handle the engine shuts down (fuel, hydraulic, etc., are cutoff). <S> But pulling the fire handle only "arms" the extinguishing system. <S> You have to rotate the handle (left or right) to discharge a bottle. <S> (there are other bottle configurations based on the airplane type, but this is the general scheme) Usually, after pulling the fire handle (before rotating it left or right) <S> you wait momentarily to determine if the overheat or fire warning lights have extinguished. <S> If not, you rotate the handle to discharge the extinguisher. <S> , you can't discharge the extinguishing agent without shutting down the engine first. <S> I am not aware of a modern design that would allow the engine to continue operating after activating the fire extinguishing system. <A> I wanted to add to 757toga's answer. <S> In addition to being required to "pull" the fire handle before you can discharge the fire suppressant, which cuts off the fuel, hydraulics, electrical generation and pneumatic flow to and from the engine. <S> To the broader part of your question about an aircraft needing the extra thrust. <S> All multi-engine aircraft are certified to be able to complete a takeoff minus one engine from V1 (decision airspeed) . <S> V1 is the cross over speed at which the aircraft could safely reject a takeoff without overrunning the runway or can safely continue the takeoff minus one engine. <S> Therefore, there is no time that an aircraft HAS to have the extra thrust from one failed engine. <S> An interesting corollary from this requirement, is that the most overpowered aircraft will be twin jets (100% extra power at V1), while an aircraft like the B-52 with 8 engines has much lower power margins (14% extra power at V1). <A> The very nature of an engine fire suggests that either fuel or lubricating oil is going where it shouldn't be going. <S> Cutting off the source of fuel and the source of ignition is essential in extinguishing a fire. <S> An extinguishing bottle might put out the fire, but if the engine is still running, then it's getting fuel and producing heat... <S> it will probably just reignite. <S> The B29 engine fire situation was more a matter of desperation than anything. <S> My great uncle was a B29 pilot, killed when the plane crashed on takeoff due to engine failure. <S> The early B29's were prone to engine fires when the engine was under very heavy load, such as during takeoff. <S> If they were fully loaded with fuel and bombs, they couldn't climb or even remain airborne for long on three engines... <S> this was wartime and certain risks were justified to continue the war effort. <S> Modern airliners can climb after losing an engine, and the B29 could lose engines and remain in the air later in flight after it had burned off a good deal of it's fuel load, or better still, disposed of its bombs. <S> If a B29 engine caught fire on takeoff, it was kept running to try to gain enough altitude to bail out, only because the alternative was definitely to crash. <S> Typically, though, either the engine failed and the plane went down, or the fire weakened the wing and it came off. <S> The problem was finally solved when they replaced the carburetor on the R3350 engine with fuel injection, but they lost quite a few crews in the process. <A> My father was a crew chief on the UH-1H model Hueys <S> and I asked a similar question once. <S> I will give his answer, followed by my understanding. <S> Disclaimer <S> My dad had a habit of giving partly wrong answers on occasion. <S> His answer: <S> By throttling down to less than the ignition intake. <S> My understanding: Reducing fuel intake to less than what is necessary for ignition does not quite shut down all engines, some use batteries to keep the engine going and the fuel simply adds thrust. <S> In either case, extinguishing a fire will reduce the thrust available, however. <S> No way around that.
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Even aircraft that do not have fire suppression systems (such as the B-52), require the fire handle to be pulled if you have a fire indication, which shuts off the engine. So, if you are asking about modern jets, the answer would be no
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Is this XKCD comic list about autogyro features accurate? I recently came across this XKCD comic which gives you a number of facts about autogyros: Image is copyright XKCD, licensed under CC 2.5 BY-NC I'm not sure if this is satirical or really drawing attention to some very odd real-world facts, or a mix of the two. Statements: Looks like a helicopter, but is nothing like a helicopter Flies like a plane but is nothing like a plane Cheap Needs a runway to take off, but not a long one Can land vertically Cannot hover Big blade on top is not powered […] Never stalls Sort of like a powered parachute […] usually homemade. Common in Europe. (I'm fairly sure I've never seen one in the UK) Can often be flown without a licence Are these things all true? How do they actually work? <Q> Flies like a plane. <S> To a certain extent in that the controls are plane-like, you do not have helicopter controls (no cyclic, etc.), but you also do not have wing control surfaces, so in some respects like a plane, but not exactly. <S> Big blade on top is not powered. <S> True, the blades are unpowered; they rotate due to the wind. <S> Some autogyros use power to rotate the blade to speed before take off, but the power is removed for flight. <S> Never stalls. <S> You can put it into a stall attitude, but it self-corrects; it is basically a rotating parachute. <S> The fatal mistake that pilots made with early autogyros was that when they entered stall conditions they instinctively pushed forward on the stick which resulted in the 'fuselage' tipping forward and the blades chopping off the tail. <S> There have been a few fatalities this way. <S> Sort of like a powered parachute. <S> Fairly good description. <S> It is more like a powered paraglider than a helicopter or plane. <S> Common in Europe <S> (I'm fairly sure I've never seen one in the UK) <S> Maybe this should be more common in Europe. <S> They are still uncommon in Europe, but they are more common in Europe than the US. <S> Wallis Autogyros used to make them in the UK in the 1960s. <S> Check out the Bond film <S> "You Only Live Twice" for one in action (ignore the missiles, etc. <S> ; they are not standard fit on autogyros). <S> Can often be flown without a licence. <S> Not in anyplace I have flown in Europe. <S> The US may be different. <A> The "needs a runway to take off" statement is historically true of most autogyros, but many modern ones can take off vertically. <S> It's called a "jump takeoff." <S> It works by flattening the blade pitch <S> so no lift is generated, coupling the engine to the rotor, and spinning the rotor up to a higher-than-normal RPM. <S> Then the engine is decoupled, and at the same time the blades return to normal pitch. <S> This uses the stored energy in the rapidly-spinning rotor to pull the autogyro upward. <S> From there it transitions to forward flight before it has time to settle to the ground again. <A> All the more modern, useful ones that carry two people and have more powerful engines require a license. <S> Re the "safe unless..." piece, this is kinda true. <S> What Randall means is that most pilots, in situations where they are concerned about possible stalls, will push the stick forwards. <S> If you do this in a gyro, it can unweight the gyro to the point where air is no longer flowing up through the rotor, which will then slow down - quickly. <S> If it loses sufficient momentum (and this can happen very fast), it will stop AND IT WILL NOT START AGAIN. <S> This is because although you will be falling and air will start rushing up through it again, it doesn't happen in a way that allows the blade to start rotating correctly. <S> So gyro pilots have to learn not to do this. <S> I have 600 hrs in gyros (1200 total) <S> and when I take pilots up they always marvel at the gyro's ability to slow to zero airspeed and its incredible turning radius, but they're always nervous when I pitch up steeply <S> - always have to explain what I'm doing first!
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Re the "Can often be flown without a license" this is true in the US for certain types of gyro - small, one-person craft which are classed as part 103 aircraft.
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Does the speed of the air molecules matter in aircraft performance? Does the fact that air molecules move slower in cold weather and faster in hot weather also affect the aircraft's performance or no? So if its cold there is a higher chance or air molecules hitting the wing and engines because the air molecules are compacted and slow moving and in hot weather they are spread out and faster moving, so less of a chance of air molecules hitting the wings and going into the engine. So in cold weather the molecules move slow and in hot weather they move faster, does this also effect aircraft performance. I know that the fact that in cold air the air is more compacted and that increases aircraft performance but does the fact that it moves slow also have an effect on aircraft performance? Same with hot air, the air is more spread out which reduces aircraft performance but does the fact that the air molecules are moving fast have an effect on aircraft performance? <Q> In some sense, yes it does. <S> But we usually don't think about it in those terms. <S> You usually only need to think about individual air molecules when the object you are talking about is very small. <S> For example, if you are trying determine the aerodynamics of an airplane whose length is 1/100th diameter of a human hair, then you might start caring about individual air molecules. <S> For realistic sized planes, the planes are so big relative to the air molecules that we can just pretend that air is continuous. <S> So instead of thinking about the motion of individual air molecules, we think about continuous variables such as density and temperature. <S> i.e. when your air molecules "spread out and faster moving" we say that is a higher temperature with a corresponding lower density, and when they are "compacted and slow moving" <S> we say that is lower temperature and a higher density. <S> By doing that, we've taken the motion of a quadrillion individual air molecules and reduced it down to one single number. <S> And that one single number, density, does have an affect on aircraft performance. <S> For completeness, you also sometimes need to consider individual air molecules at very low pressures. <S> e.g. if your air pressure is a millionth of an atmosphere, then there are not many air molecules to go around and so each individual molecule's motion becomes more significant. <S> But airplanes generally do not fly at such low pressures. <S> Even at 40,000 ft, there's a lot more air pressure than that. <A> Nice, thick cold air is great for engine performance. <S> Especially for small single engine airplanes. <S> Hot, less dense air means less performance, making takeoff more of a problem, with longer takeoff rolls needed to get sufficient airspeed to liftoff. <A> Yes, of course, but not because of the average speed of the molecules. <S> Temperature affects density altitude. <S> Almost every performance metric for an aircraft is a function of density altitude, which increases as temperature increases, and decreases when it is colder. <S> Lift, drag, engine performance, all are affected by density altitude. <S> they are moving in all directions, both towards the airfoil, and away from it. <S> So any performance increase from additional relative speed of those air molecules moving towards the wing will be counterbalanced by the performance decrease from those air molecules moving in the same direction as the aircraft, which will be hitting the wing at an equivalently slower speed.
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Aircraft performance is dependent on density altitude, which considers not only the pressure altitude, (displayed on your altimeter), but air temperature as well. The fact that the air molecules are moving faster when it is hotter is irrelevant, because this speed is the average speed of the molecules.
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What does RPM mean in a propellor aircraft, compared to a jet aircraft? What is the practical significance of speed RPM in a propeller aircraft for a pilot? I am not able to correlate it with RPM in jet engines? <Q> RPM in a propeller aircraft is typically under 2400, as the prop spins at the engine RPM speed. <S> Above 2700 the tips of the propeller begin going supersonic and make more noise than anything. <S> Jets engine spin much faster, as discussed here Which are typical rpm values for aeronautical turbines? <A> in propeller aircraft, the practical significance of propeller RPM is it is one component of the equation that determines propulsive power, the other being shaft torque. <S> Controlling the power output of a turbine engine is a more complicated process, and depending on the type of engine and its application, the pilot may use pressure measurements in the different stages of the engine or ratios of those pressures or shaft RPM's expressed as percentages of full power to manage the power output of the engine. <A> There are three primary cases for use of RPM in aircraft that differ by engine type: piston, turboprop and turbofan. <S> In all three cases RPM refers mainly to two speeds, propulsor and engine. <S> They may be indicated in percent of maximum (usual for turbine) rather than as a specific speed (usual for piston). <S> Piston engine - the propulsor is the prop and the engine speed measured is the crankshaft. <S> Usually there is no gearing and both are the same, so there will only be one gauge in an aircraft. <S> Notable exceptions are warbirds with high power and correspondingly large props. <S> Turboprop - the propulsor is again <S> the prop and the engine speed being measured is the turbine output shaft, fixed to the low pressure compressor. <S> This is input to a gearbox since turbine speeds are too high to be useful in directly driving a prop. <S> There can be two speed gauges in the aircraft. <S> Turbofan - the propulsor is now the front fan and the engine speed being measured is usually the core, the high pressure compressor. <S> The front fan historically runs on the low pressure compressor shaft. <S> PW inserts a gearbox between the front fan and the output shaft, making the drivetrain resemble the turboprop configuration. <S> More complex engines may have three shafts, all running at different speeds.
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If the propeller has a fixed (nonadjustable) pitch, then the RPM of the propeller is a simple indication of the power output of the engine, and the pilot manages engine power by adjusting tachometer RPM with the throttle.
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How to select a SID during the planning stage? During the planning stage of an IFR flight how to choose the correct SID for your route in an airport with multiple runways and multiple SIDs? and how to predict the runway you will be going to use? <Q> "File what you want, fly what you get." <S> There's no way to know for sure what clearance ATC will give you until you actually call them. <S> If you're departing from an airport that you know well then you may be able to make an educated guess <S> but that won't help if the winds change, an incident closes a runway, or any number of other things happen to invalidate your assumptions. <S> For planning purposes, just use the SID that best fits your needs, based on all the information you have available: direction of departure, aircraft type, weather, local procedures etc. <S> But ultimately, you'll have to fly what you get (or what you can negotiate with ATC). <A> The runway(s) in use will depend primarily on the winds at the time, though there are other factors such as maximum arrival/departure rate that may take precedence, especially if the winds aren't very strong. <S> It's disruptive to traffic flow to change the active runway, so when the winds change, they will often wait until there's a natural lull in the traffic or a pilot rejects the assigned runway(s) because the crosswind or tailwind component exceeds their limitations (which varies by aircraft and pilot skill). <S> You can also request to use a specific runway. <S> For instance, pilots may accept a crosswind or even a tailwind to get a runway with the shortest taxi time to/from parking, or allows a straight in arrival or straight-out departure, or is longer than the one aligned with the winds to provide more safety margin, etc. <S> Whether ATC grants such a request will depend primarily on the manageability of potential conflicts with everyone else following the normal plan, which mostly boils down to how much traffic they're juggling at the moment. <S> Regarding the SID, usually there's either one generic SID for all departures, or there's a set of SIDs (or one set using VORs and another using RNAV) divided up by direction <S> so only one of them would makes sense for your flight. <A> That can be selected based on whether the SID is intended for use by your type of aircraft, as well as your aircraft’s performance capabilities and onboard avionics (eg an RNAV SID is useless unless your plane has RNAV equipment aboard or can’t meet the minimum required climb rates, etc.). <S> As stated above, depending on your aircraft type and airport, ATC may or may not clear you to fly that SID. <S> Also be aware of IFR Preferred Routes or TEC routes on the east and west coasts which will be often used by ATC and will influence what DPs you choose.
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EFB apps like ForeFlight do have the capability to show previously cleared routes so you can get a sense of how ATC likes to handle airplanes for those routes.
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Why would a stretch variant need a larger horizontal stabilizer? Update and accept reason The reason for asking why would as opposed to why does is I was not aware of any previous [jetliner] stretch requiring a larger horizontal stabilizer. For example, all the DC-8's from shortest to longest (almost the same stretch as the 787-10) retained the horizontal stabilizer throughout: ( Great Airliners ) Click to view. But then I finally recalled a situation where it has happened, the 737 Classic, and the reason given is the "fore-and-aft loading flexibility", in other words the cg range, and that's why I'm accepting @jwzumwalt's answer. With the 787-10 stretch, Vedad Mahmulyin (a Boeing engineer) saved the company millions by implementing a software solution that negated the need to enlarge the horizontal stabilizer.* When a plane is shrunk, that is usually the case because of the reduced moment arm. When it is stretched, the tail volume is retained if I understand this comment about the DC-10/MD-11 stretch correctly: Isn't the tail of the MD-11 smaller because it has a longer lever arm? The tail volume of both aircraft should be quite the same. Also, any FCS cannot help to trim the aircraft over a wide range of cg positions, and it is this trim range which drives tail surface volume. @PeterKämpf Why would a stretch variant need a larger horizontal stabilizer? From an interview with Mahmulyin: Mahmulyin figured out he could use software to tell the wings and the stabilizers how to fly together, "As opposed to having to produce all new horizontal and vertical stabilizers," he said. What does 'flying together' mean? (This is an optional question and does not involve proprietary information.) * Flight International (27 Mar 2018) confirms the horizontal stabilizer size issue: Software again proved useful with the sizing of the horizontal tails. As a stretch of the 787-9, textbook aircraft design would suggest the 787-10 would need larger horizontal stabilisers, offsetting the effect of the longer fuselage on pitch control. Instead, Boeing engineer Vedad Mahmulyin used software to increase the effectiveness of the existing stabilisers. Boeing gave Mahmulyin an internal engineering award for solving the problem. <Q> However, because the mass is distributed further away from the centre of gravity, the pitch moment of inertia increases too. <S> If the fuselage would be modelled as a uniform rod, the moment of inertia in pitch would be $\frac{1}{12}mL^2$, with mass $m$ and length <S> $L$. source: <S> hyperphysics.phy-astr.gsu.edu <S> You see that the moment of inertia increase with the square of the fuselage length, while the effectiveness of the elevator increase linearly with fuselage length. <S> The nett result is that the pitch response of a longer fuselage with the same horizontal stabiliser/elevator is reduced. <S> In addition to the change of inertia, the heavier aircraft needs more powerful flaps (double-slotter vs single slot before) <S> which causes a bigger pitch moment change. <S> Therefore a stretched aircraft needs a more effective elevator. <S> As for the meaning of "flying together" I assume that this means that the software solution for the 787-10 controls the pitch moment of the aircraft not only by changing the elevator angle, but also uses control surfaces on the wing. <A> The primary reason is probably because a larger tail increases the CG range . <S> It does not make sense to stretch an aircraft without increasing the CG range. <S> calculating tail volume <S> Often the horz stab is used for the extra fuel capacity neededfor stretch models (i.e MD11 and B747 ). <S> "...the tail fuel tank will provide added range and improve the aircraft’s performance" Part of the stretch is forward of the CG (and wings) and therefore counteract the tails effectiveness. <S> (float planes often suffer the same adverse weather cocking problem and so extra vertical surface is sometimes added below the fuslage.) <S> The stretch will have higher gross weight and the tail surfaces will have to overcome greater inertia. <S> Per @DeltaLima moment of inertia math shown below. <A> A stretch variant doesn't need a larger tail, due to increased arm. <S> If you want to muck with the CG or whatever that is independent of a stretch. <S> The classic counter example is the 747SP, a shorter variant with a gigantic tail, due to reduced arm.
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When the fuselage is stretched, the arm of the horizontal stabiliser is increased, and hence it's effectiveness increases linearly with the fuselage length.
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What is the difference between buffeting and fluttering? As I understand, both are dynamic effects of aeroelasticity - however, what is the exact difference between buffeting and flutter? <Q> The vernacular meaning is... 1) <S> Flutter is un-commanded self perpetuating (positive feedback) destructive & adverse cyclic movement of any part of an aircraft. <S> It most commonly occurs on a control surface but may be an entire wing, tail surface, or more rarely fuselage or other part or device. <S> Flutter may be induced either mechanically or aerodynamically and may be sustained mechanically (i.e. engine or prop, landing gear or ground resonance of a helicopter skid) or aerodynamically by self perpetuating (positive feedback) force. <S> Mechanical inception can be (but not limited to) brisk or pilot induced oscillation, weak, unsupported, or flimsy structures. <S> Aerodynamic inception can be (but not limited to) undesirable cg, or aerodynamic forces on parts. <S> Flutter is always undesirable, dangerous and a destructive force. <S> 2) Buffeting is a turbulent stream of air striking any part of the airframe. <S> The turbulent air may be completely external (weather) or created by the aircraft it self (prop, wing,etc). <S> The most common form of buffeting is turbulent airflow over a wing (i.e. during a stall or wind gusts) striking the wing or horizontal tail. <S> Buffeting is not usually considered self perpetuating with positive feedback, nor is it considered to be precisely cyclic or harmonic - though it may be repetitive. <A> Flutter is characterized by a frequency neighbourhood of a structural eigenmode and a cyclic aerodynamic load. <S> This causes their motions to be mutually reinforced. <S> Buffeting, on the other hand, is just the consequence of a cyclic aerodynamic load, such as an oscillating shock, or separated flow hitting another surface downstream. <A> The difference, I would say, is; <S> If the surface does not exhibit an increasing amplitude, as it is naturally damped at the frequency of the excitation force, it is called buffet . <S> Conversely, if the surface is not naturally damped at the frequency of the excitation force, its amplitude of oscillation will continue to grow, and likely structurally fail, catastrophically, it is called flutter . <S> In flutter, there is a coupling between the aerodynamic forces and structural response, that needs to be taken account of, in analysis of flutter, which is not required in buffet. <S> See the first paragraph of this technical paper. <S> The flutter analysis is generally conducted by complex eigenvalue analysis, whereas the buffeting response is typically estimated using a mode-by-mode approach that ignores the aerodynamic coupling among modes. <S> As examples of each, here is a video of flutter. <S> As can be seen, the amplitude of vibration starts to grow, and it wouldn't appear surprising if the tail plane failed very quickly. <S> In comparision, the F-18 has experienced tail buffet from vortices from the wing leading edge extensions. <S> As can be seen, the tails vibrate, but its a much smaller oscillation than the flutter example. <S> While it could cause cracking in the long term, it would not be expected to fail instantly.
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Both buffet and flutter is a vibration of a surface of the aircraft, such as a wing or tail, due to the air flowing over it (especially if the air is turbulent). Buffeting is usually considered undesirable but benign and not a destructive force.
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Do aircraft automatically send a message to the ground if there is a catastrophic failure? For example, if there is a engine failure, it will be displayed on EICAS as a CAS message. As per my knowledge, the pilot will initiate the contact with any ground station nearby for guidance to land safely. Iis there any equipment in the aircraft to send the distress automatically when there is any major failure? <Q> There is nothing formally standardized as far as I know however newer Rolls Royce jet engines (and presumably those from other major manufacturers) do have a continuous inflight data link that reports engine data in real time to their reporting centers. <S> You can read up on it here as well as this discussion with lots more info. <S> Aerospace Operations Centres are able to track the health of thousands of engines operating worldwide by using onboard sensors and live satellite feeds. <S> Rolls-Royce are world leaders at equipment health <S> management (EHM) <S> The centers are potentially able to detect certain emergencies remotely based on the parameters reported. <S> Since you note the pilot making contact presumably with the radio: Pilots can report an emergency without the use of a radio by Squawking 7700 on the transponder as well. <A> Most commercial aircraft have a system called ACARS <S> that can be used to transmit flight information and messages between the ground and the aircraft. <A> The only system that notifies anyone on the ground is the ACARS that the other answers mentioned. <S> There are all kinds of notifications to the pilots, and usually guidance to help them resolve it. <S> Look up EICAS. <S> There's not a notification to ATC or dispatchers, only maintenance. <S> If the pilots can't resolve the problem they will ask for whatever assistance they need. <S> In a complex aircraft there are lots of false alarms, sensor failures, momentary problems, etc. <S> that the pilots are able to work out without a problem. <S> It wouldn't be helpful to notify people on the ground for all these. <S> They can rarely do much to help anyway. <S> If the pilots need to divert or declare emergency then they will alert etc. <S> Sometimes they will confer with their dispatcher or maintenance personnel about what they need to do. <S> The ACARS messages can probably help with this. <S> They can discuss with dispatchers if they need to go to a specific terminal where there are personnel that can fix a specific problem and the dispatcher helps them determine if they have fuel to make it there. <S> The pilot is the one that's makes the decisions, so there's really no advantage to sending a distress signal to the ground since all they could really do is to contact the pilots.
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In many cases, the ACARS is configured to transmit flight data automatically (engine performance, airspeed, altitude, etc) that would include error messages/warnings from the various systems onboard.
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How are engines numbered? On a commercial aircraft, the number of engine is usually 2, 4 or 6. When the technician or LAE was given task to inspect an aircraft engine no 2 on a 4 engine aircraft. Which engine would they go to? 2 different lecturers of mine had 2 different answer for this and both have experience in working with aircraft engine. Lecturer A said: Lecturer B said: Which one is right? Requesting help from Technician or LAE. A brief explanation would be really helpful too. <Q> That corresponds to the second of your diagrams. <S> Twin engined aircraft have just engines 1 and 2 on the port and starboard wings respectively. <S> Three engined aircraft follow the same convention with the number 2 engine in the fuselage centre line. <S> Since this appears to be an arbitrary convention I'm not sure what more explanation you're expecting. <A> Aircraft engines are ALWAYS numbered from left to right when viewed from the pilot's seat. <S> Additionally, the start sequence is ALMOST ALWAYS number three, four, two, one. <S> There are several reasons for this sequence: <S> Number three engine starter distance from the battery(s) is the shortest The longer the distance the less amps delivered. <S> Jet aircraft like the B-707, DC-8 had the pneumatic air connection close to the Number 3 engine. <S> Once the number three engine was started it helped pressurize the pressure manifold for assisting the additional engine starts. <S> Remember, a low start pressure could result in a hot start. <S> Secondly, hydraulic pumps were located on the inboards #2 & #3 engines on the DC-4, DC-6, DC-7 & DC-8 as well as the B-707 (the B-747 had hydraulic pumps on all four engines plus an APU but the start sequence remains the same). <S> It's never a good idea to have an engine running without full hydraulic pressure available to the brakes. <S> Thirdly, passengers or cargo is loaded from the left side of the aircraft. <S> By starting #3 & #4 first, last minute changes could more easily be facilitated with #1 & #2 dead. <S> Boarding an aircraft behind an idling engine is always an interesting experience. <S> Starting the #2 next would give additional hydraulic back-up and then allow the fire guard to move to the #1 engine and exit to the left. <S> Lastly, by delaying the start of #1 & #2 engine, interior noise would be kept at a minimum for passengers and crew until all the cabin doors were closed. <A> 747 Thrust Levers, numbered by respective engine numbers.
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The Wikipedia article is clear: engines are numbered sequentially, left to right, as seen by the pilot facing forward.
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Is there any alternative to isolating the vibration of an ultralight engine other than using engine mounts? Is there any alternative to isolating the vibration of an ultralight engine other than using engine mounts? <Q> Similar in principle to Active Noise Reduction headsets that generate an inverse pressure wave to cancel sound, motion cancellation generates an inverse displacement of a mass to cancel vibrations. <S> Sensors determine the vector(s) required, and electronics control the mass actuator(s). <S> These can be added to any engine. <S> Predictable, repetitive vibrations are most successfully treated. <S> Actuators tend to be heavy, so better engine/prop balance and more effective isolators (mounts) are preferred. <A> As you've noted, engine mounts are used to isolate the vibration of the engine from the airframe. <S> Another technique is Dynamic <S> Prop Balancing - adding weights or washers to specific places on the propeller or spinner to eliminate the vibrations. <S> It's the same idea as is used to balance car tires. <A> Perhaps the choice of the engine helps, flat-six does vibrate less than in-line engines, also Wankel Rotary Combustion Engines have an intrinsic very low level of vibrations. <S> Some interesting approaches were proposed, as this patent from the extinct Barcelona Based motorcycle maker: 'Sanglas'. <S> They once prepared a working prototype for a single-cylinder, 4-valve, 750 cc engine.
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You can prevent engine vibrations from being transmitted to the airframe by motion cancellation techniques.
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What is the maximum altitude ATC would deal with? What's the maximum altitude ATC would deal with? Any example of jets service ceiling certified for above 45.000? Commercial & Business jets? <Q> There are many examples of aircraft with high service ceilings. <S> That being said, military jets can fly higher and will be talking to ATC while in their airspace. <S> Fighter jets are capable of high altitude flight, and planes like the <S> U-2 and Global Hawk still fly up there as well. <S> In the US, all aircraft from FL180 to FL600 must be in contact with ATC, but above this they are not required to. <S> ATC will still provide services when able though. <A> There is no maximum altitude for ATC service. <S> In the US, Class A airspace ends at FL600. <S> Meaning if you fly above 60,000 feet (pressure altitude), you are not required to contact ATC, because it is Class E airspace. <S> But that does not mean ATC will deny talking to aircraft at that altitude. <S> Practically speaking, very few aircraft (if any) can get above FL600. <S> Chances are if you can get there, you are in an experimental military aircraft or spaceship. <S> Flights above FL400 are common for private and business jets. <S> They are managed by ATC. <A> The other answer are correct that above FL600 you no longer need to be in contact however its worth noting there is some interesting historical implications to this. <S> The only civilian aircraft that routinely operated above the majority of other aircraft was the Concorde , which during its time cruised up around FL500. <S> In his interview on Omega Tau one of Concorde pilots discusses this very situation. <S> Essentially above ~FL450 they were allowed to transition altitudes as they saw fit and without contacting ATC essentially since they knew no one else was up there. <S> He mainly discusses it in the context of fuel burn and how as the aircraft burned fuel it had a tendency to slowly drift up. <S> ATC allowed them to do this (and not stick to an assigned altitude) as they could not really drift up into anyone.
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ATC will deal with anything that flies over their airspace. While most commercial aircraft have service ceilings of FL410 and rarely fly even that high, many business jets have a service ceiling of FL510, such as the Dassault Falcon 7X , Gulfstream G650 , and Bombardier Global Express .
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What is it called when an airplane has to circle because it can't land? Sometimes, a plane is required to circle around an airport repeatedly because for whatever reason, it is not able or permitted to land just yet. This state in which a plane is stuck in the air in this way has a name, what is it? <Q> <A> There is no generic name in aviation describing the state of an aircraft being hold up and unable to land. <S> The simplest term I have in mind is "circling the airport". <S> Note that these terms carry specific technical meaning in aviation, although they may be misused by journalists in news articles. <S> Holding Pattern is an race-course pattern flown over a specific radio station or waypoint at a constant altitude. <S> The outbound and inbound legs are 60 seconds and the turns are executed at Standard Rate Turn . <S> A Holding Pattern is flown under IFR . <S> Traffic Pattern is a rectangular pattern flown at a low altitude around a runway. <S> It consists of "upwind", "crosswind", "downwind" and "base" legs. <S> A Traffic Pattern is flown under VFR . <S> 360 is a circular pattern in which the aircraft maintains a constant rate of turn. <S> 360s are usually flown by small aircraft but rarely large airliners because small aircraft can maintain a small turn radius. <S> It may also be none of those: the controller may just issue heading instructions to direct the aircraft around terrain and other traffic as necessary. <A> Busy airports may have an established process for queuing arrivals so they can be spaced efficiently for landing. <S> In the UK these are known as "stacks" or "holding stacks", and aircraft in them are said to be in a "holding pattern". <S> See the Heathrow Airport website for examples of this phraseology. <S> Smaller airfields are unlikely to have designated stacks, but may advise aircraft to "orbit". <S> This advises the aircraft to fly in circles either a specific number of times, or until further instruction is received. <S> For example "G-ABCD, for spacing orbit once". <S> See the CAA Radiotelephony Manual for official guidance as to the use of this term. <S> An aircraft doing this could be said to be orbiting.
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Depending on the way the aircraft is circling the airspace, specific names can be used. It's called a holding pattern.
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What radio equipment do pilots use to communicate with ATC? I know of the transponders used for communication by Air Traffic Control, but apart from that, what radio equipment do pilots use to talk to ATC? What modulation method is used? <Q> https://en.wikipedia.org/wiki/Airband emphasis added As of 2012, most countries divide the upper 19 MHz into 760 channels for amplitude modulation voice transmissions, on frequencies from 118–136.975 MHz, in steps of 25 kHz. <S> A typical plane often has two communication radios, referred to as COM1 and COM2. <S> Each radio has an active and standby frequency. <S> The pilot can listen to either radio, or both radios at the same time, but can only broadcast on a single radio. <S> There are often 2 navigation radios as well, NAV1 and NAV2, which can be tuned to VORs or other radio beacons, and the pilot can listen on those radios (typically for Morse Code IDs, Recorded Voice broadcasts, and occasionally, Voice-over-VOR ATC) <A> In tran atlantic the voice comms are thru HF with SELCAL( selective call) which brings another communication tool more and more used : CPDLC( controller pilot datalink communications) <S> this one is not by voice. <S> Clearances or requests are given by this method certainly for transatlantic and more and more in land as well. <A> A short summary, specific to the US: VHF AM is the most common voice mode for communications with ATC. <S> UHF AM is also used for military and some government services, but generally just military, for communication with ATC. <S> HF radio is used for communications with ATC, and is most often used on oceanic routes. <S> It is not as "reliable" as VHF, but the signals will propagate farther. <S> Other enhancements and other modalities are available but they are not strictly voice communications. <S> 14 CFR 87 covers aviation services, and defines frequencies and modes as well as uses for aviation specific services. <S> https://www.law.cornell.edu/cfr/text/47/part-87
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The major communication tools are obviously Vhf radios for voice, another one is HF, particularly in remote place or oceanic.
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Does it help to climb in case of a partial engine failure? When the engines of a airplane show irregularities that do not reduce performance but indicate a possible failure of the engines, is it useful to climb to a higher level, to increase the glide length that is available in case the engines stop completely? The problem known in the cockpit is only that the engines do not run like they should. Say they make clearly unusual noises and slight vibration, but loose no performance. There is no indication whether the engines will fail, an in case the do fail, at which point in time that will happen. It's an emergency, without actual change in the planes performance. As example, I think of a small single propeller plane, and a situation where longer glide path could be useful. But I think the question applies to any plane that can glide without power. <Q> Agreeing with @Antzi, high engine speed when combined with some sort of small scale physical damage or corrosion is a typical failure mode for propeller engines. <S> Combining that logic with the fact that propeller engines run more efficiently at lower elevations (higher air density) I would recommend against climbing. <A> I recently saw a YouTube Video with this exact scenario in a single prop Cirrus plane. <S> He did not climb but rather turned back to the airport and maintained a higher altitude than normal for the approach for landing. <S> ATC was giving him clearance to descend for the landing but he rejected that clearance in order to give him some altitude in case his engine did fail. <A> Okay, as I understand your problem you have an engine that is suspect to possible failure. <S> So, you are asking, if it is a good idea to increase the stresses on the engine to climb by adding more power and possibly increase the chances of a potential failure. <S> Unless you are looking at an immediate confrontation with a object on the horizon that is higher than your current altitude, like a big rock, I would reduce power to a minimum and look for a place to land. <S> If you are in a four engine jet at, let's say FL 390, the last thing you would consider is climbing because, if you loose an engine at that altitude, decent will be mandatory immediately because three engines will not sustain flight at that altitude.
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In fact, lowering your elevation and speed will greatly reduce the stress/strain you are putting on the engine and will likely give you a better chance of making it safely to the closest airfield.
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How can a two-engine B787 create three contrails? Today I noticed overflying aircraft (over Sydney at FL400) which appeared to have three contrails. When I checked Flightradar24 app, I saw that this overflying aircraft is B787.What would be the reason for three contrails with only two engines? Could the third be caused by APU, or just by a wake turbulence, or anything else? I tried to take a photo using binoculars (sorry for the quality, I tried my best). And also a screenshot of the A/C from Flightradar24 app. <Q> When the 2 engines of the B787 blast their exhaust out, the high pressure of the exhaust temporarily causes the moisture to condense. <S> Two contrails are visible. <S> However, as the pressure waves from the 2 exhaust trails propagate through the open atmosphere, they interfere with each other. <S> This interference can also affect the pressure of the moist air between the 2 "primary" contrails, sometimes resulting in another, "secondary" contrail. <S> In fact, because of this, if there were enough moisture in the air, and the engines were powerful enough, there wouldn't actually be just 3 contrails. <S> Rather, the contrails would present themselves as the crests of a propagating wave much like the crests of water waves as a duck swims by. <S> In effect, we would see the 3 contrails separating, and between each of the 3 contrails, 2 more "tertiary" contrails would be visible. <S> Here on Earth though, the pressure variances and the density/moisture content of the air normalize far before any of that exotic pressure wave stuff could occur. <S> Except we <S> DO get that one in the middle! <A> Fascinating question. <S> Not being an expert in contrail aerodynamics <S> I'm forced to speculate, but I'm guessing <S> the apparent three trails is caused by the spreading of the trails by wingtip vortexes. <S> I find similar examples called hybrid contrails . <S> Here's one animation of a four-engine A340 from that article: <S> I think if you ignore the trails from the outer engines, this looks similar to your photograph. <S> Here, the inner trails are twisted and spread by the wingtip vortexes into a pair of semi-transparent "tubes" of condensation trailing the aircraft. <S> The apparent darkness of the tubes is thickest at the edges, since at these points we are looking through a greater thickness of vapor. <S> As the tubes expand they touch, leaving three areas at the red arrows where the trail appears darkest from below. <S> A similar formation can be seen in the first few seconds of this video . <S> It happens quickly, but paused at the right moment there appear to be three trails: <S> Within the next second the formation has spread enough it becomes an indistinguishable single trail again, but under conditions less favorable for persistent trails such as in your photograph, the trail may have dissipated by this time. <A> Those three contrails that formed are diverging, while maintaining some coherence. <S> It's hard to be sure, but the third one seems to appear when the diverging fan of the initial two reach the centre line of the airliner. <S> My guess is that they mark the vortices (vortexes) in the air shed by the tips of the flight surfaces. <S> There's a big one coming off the end of each wing, and a smaller one coming off the end of each horizontal stabilizer. <S> These latter are too close together and probably too much generally affected by turbulence generated by the fuselage to be seen as distinct. <S> So initally, two: one source of ice crystals emerging from each engine. <S> But these then get sucked into the vortices, and two transitions to what appears to be three. <S> The trailing vortices of a big airliner are huge. <S> They can cause serious turbulence for another airliner crossing the "wake" of a previous flight, and can cause damage or loss of control for a small aircraft. <S> They are one of the good reasons for a mandatory minimum separation between aircraft approaching an airport. <S> (ISTR, three miles). <A> I expect the earlier explanations are correct, but it also strikes me that there are more that two jet type engines on a 787 - the APU is right there in the middle and while its exhaust isn't nearly as strong as the main engines I can imagine that it might be strong enough to perturb the flow at the point where the main jet exhaust meets and have a visible effect on the main engine exhaust flow.
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Contrails are created due to variances in the pressure of the air, coupled with the amount of moisture in that air.
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Do Airbus aircraft have an "off" position for their landing gear? I know some Boeing aircraft feature an up, down, and "off" position for their landing gear lever. I know that some Boeing wide-body jets do not have a 3rd lever position, but still have an "automatic" "off" setting that takes effect after a time-delay (which begins when the gear comes up). Do airbus, bombardier, embraer, etc. have a 3rd gear lever position in any of their aircraft? If not, do they have an "automatic" off setting? <Q> I was working for Airbus before, never seen it on A300, A320, A330, A340, A380, A350 or A400M. <S> Only Gear Up or Gear Down position. <S> For confirmation on A320, here the FCOM section: NORMAL OPERATION <S> The flight crew normally operates the landing gear by means of the lever on the center instrument panel. <S> The LGCIUs control the sequencing of gear and doors electrically. <S> One LGCIU controls one complete gear cycle, then switches over automatically to the other LGCIU at the completion of the retraction cycle. <S> It also switches over in case of failure. <S> The green hydraulic system actuates all gear and doors. <S> When the aircraft is flying faster than 260 kt, a safety valve automatically cuts off hydraulic supply to the landing gear system. <S> Below 260 kt, the hydraulic supply remains cut off as long as the landing gear lever is up. <A> As Chris Lau's answer shows, this third position was removed on the A320 and all subsequent models. <S> Note however that there is no NEUTRAL label next to the lever (where Boeing would write OFF): (4) <S> Landing Gear Normal Lever: <S> UP: <S> The L/G lever electronically controls the Green hydraulic supply for the L/G operation. <S> The Green hydraulic system only is used for L/G retraction. <S> When the lever is UP, the main wheels are automatically braked, during the L/G doors opening, through the ANTI SKID system, (the ANTI SKID selector being in NORM position) and without action on the brake pedals. <S> L/G nose wheel is braked by a mechanical device. <S> NEUTRAL: <S> When L/G lever is in the Neutral position, ANTI SKID system is deactivated and the L/G hydraulic pressure is cut off. <S> Neutral position is normal flight position. <S> DOWN: <S> When L/G lever is at DOWN <S> the ANTI SKID system is operative. <S> Note: On ground, L/G lever can be moved from DOWN to Neutral position and vice versa, but interlocks prevent an inadvertent UP selection. <S> (Airbus A300 FCOM - Chapter 7 Landing Gear - Landing Gear Controls) (1) Landing Gear Control Lever: <S> UP: <S> The landing gear is retracted. <S> An interlock mechanism prevents unsafe retraction by locking the lever when gear position proximity detectors of selected SYS (1 or 2) are not in flight configuration: 3 shock absorbers extended nose wheel centered 2 bogie beams aligned. <S> During door opening only, anti skid is deactivated and main gear wheels are braked automatically. <S> At end of nose gear retraction travel, nose wheels are mechanically braked. <S> Neutral: Normal flight position. <S> Hydraulic pressure to landing gear circuit is cut off. <S> DOWN: <S> The landing gear is extended and the system remains pressurized. <S> ( Airbus A310 FCOM - Landing Gear <S> - Controls: <S> Landing Gear Lever Panel) <A> There are only two positions in the Embraer E-Jet family. <S> There is also a downlock release button (red) which mechanically bypasses the system protection logic. <S> It should be used only in the event of a landing gear control lever failure or when it is necessary to clear obstacles.
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Yes, Airbus aircraft used to have an OFF position (called NEUTRAL ) for the landing gear lever on the A300 and A310 .
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Do ATC displays show the target altitude that the pilot has set in the autopilot? When cleared to climb/descend to a level, the pilot enters that level in an altitude preset window, allowing the autopilot to climb/descend and level off at that level. Is this level, preset by the pilot, visible on an ATC radar screen? <Q> After issuing a climb/descend clearance and entering it into the sytem it would also warn us if the selected altitude is different from the cleared level. <A> If the ATC Automation System supports the Display of Mode S - Enhanced Surveillance Data, Then ATC Radar will display the Level Selected by Flight Crew <S> If the Aircraft is equipped with MOde S - EHS Transponder. <S> The method of showing the Selected Level varies from Automation System to Automation System. <S> The below image is an example for various data obtained from aircraft in an ATM Automation System. <A> No. <S> That information is contained within the automatic flight control system. <S> All altitude reporting to ATC comes from a radar transponder with an altitude reporting capability. <A> ATC only sees the altitude reported by the Transponder, which is provided by a seperate Altitude Encoder. <S> In the US by Jan 1 2020, all air vehicles operating in most US airspace where radios are required are required to have ADS-B <S> Out to report position & altitude over their transponder. <S> (Seems that airlines and the military will be late to the game, not having access to the same equipment that smaller planes are installing now or have already installed. <S> Panel mount and remote mount units are being installed for certificated planes that fly IFR, and other non-permanently installed units for experimental & VFR only craft are also being connected. <S> Also, ADS-B <S> In units for recieving other's position reports and displaying in iPad or similar are very popular. <S> My transponder has both and shows me traffic on my Moving Map GPS/Nav/Com unit.)
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Yes, our radar is indeed capable to display data of the Mode S Enhanced Surveillance Transponder like Selected altitude, IAS, Mach Number, Heading and more.
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Why do localizer/glideslopes use 90/150Hz specifically? Why is it that localizer and glideslope system are using 90 Hz and 150 Hz frequencies only, instead of some other LF such as 75 Hz? Part two of my question:How does the modulation depth differ for aircraft using localizer and GS receiver? <Q> Read through this Question and Answer . <S> As you can see in the description of the beam-forming, the width of the antenna array and the choice of the modulation signals (90 and 150 Hz) drive the ddm proportionally to the angle of approach to the antenna array. <S> There are also considerations tied to the broadcast signal. <S> Higher frequencies would require more bandwidth which would impact channel spacing. <S> Ultimately, the choice of the two frequencies is an optimization of a design for the approach guidance. <S> For any given runway the current system can be set to provide consistent guidance (+/- <S> 350 feet == <S> full scale deflection) at the runway threshold. <S> This is done by adjusting the distance between elements of the antenna array. <A> An AC motor in the USA will turn at 60 RPM and 90 is 3/2 and 150 is 5/2 of 60. <S> Both can be generated using a simple gear drive which would reduce the costs during development. <S> Similarly there are circuits to multiply or divide a driving frequency by whole numbers, with 60 hertz readily obtained. <S> Simple gear ratios could convert 50 hertz used elsewhere. <S> 90 is two digits and 150 is three digits. <S> Left is four characters and Right is five characters which makes for a handy memory aid, as the greater number of digits matches the longer word. <S> Similarly 180 hertz is commonly used to spin up X-ray tubes as a 60 rpm motor turns a generator via a 3:1 gear ratio. <S> Analog clocks are kept accurate by exact 60 hz power and is better regulated than that of a common occilator, especially during development. <S> Also the developers probably didn’t want to use 60 hz or a Harmonic of it to reduce noise from the power lines. <A> When ILS was developed, they actually used rotating capacitive plates with lobes. <S> The 90 had 3 lobes and the 150 had 5. <S> Easy way to modulate the RF with the phases locked. <S> The depth of modulation was adjusted with a fixed plate with a variable gap between it and the rotating plate.
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The frequencies are chosen to allow the system to produce a localizer and glideslope 'beam' that provides proportional guidance that can adequately guide an aircraft on the approach.
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What is the difference between axial compressor blades and centrifugal compressor blades? Is there a particular difference? The way they're overhauled is the same ? (I mean do we use the same overhauling methods ?) <Q> The blades are shaped completely differently. <S> Typically a centrifugal compressor is one solid piece that looks like a turbocharger and an axial compressor is a flat disk that looks like a fan with individually manufactured blades inserted, though axial compressor disks with integral blades "blisk" is starting to be used. <S> Here are compressor pics that show how they are used: Two stage radial/centrifugal compressor circled (with a three stage axial turbine following) Fifteen stage axial compressor A radial compressor can usually generate higher pressure in a single stage so it's usually simpler, while an axial compressor is easier to stack in multiple stages to get much higher pressure ratios. <A> The main difference is in how they operate, vs how they are maintained. <A> Axial blades are airfoils that compress air by forcing it aft into a converging space via downwash the same as a wing generates lift by downwash. <S> Efficient, but sensitive to angle of attack and aerodynamic stall, like a regular wing, so therefore sensitive to flow disruptions. <S> A centrifugal compressor is spinning duct that forces air into a converging space purely by centrifugal force imparted to air within it as it spins. <S> Less efficient, but relatively insensitive to flow disruptions and way easier to make.
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Flow through a centrifugal compressor is turned perpendicular to the axis of rotation, while air in an axial compressor flows parallel to the axis of rotation.
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During the holding procedure is it required that the pax must have the seat belt on? Imagine to have to hold at a busy airport before landing for a quite long time (let's say 20 plus minutes), does it requires that the pax must have the seat belt on during the whole holding procedure? Is it required by the Authority or just by the company? <Q> The plane is flying at a lower altitude, where it is more likely to encounter turbulence and other unstable weather conditions. <S> Up in FL330 it is usually clear skies all along. <S> The plane may need to get down quickly after an approach clearance is issued (after all, it is busy airspace). <S> From that point onward the pilots may deploy the spoilers to lose altitude (which shakes up the plane a little), turn towards the approach course and without you noticing, landing gear is down and locked already. <S> At the same time, we know it takes quite a few minutes after the seat belt sign has been turned on until everyone is seated (passengers won't just rush back to their seat after hearing the Ding Dong tune). <S> If the seat belt sign is not illuminated in this period, there may not be enough time for the cabin crew to prepare the cabin for landing. <S> It reminds the passengers that if they wish to get out of their seat for whatever reason, they should make it quick. <S> If the flight deck tells the passengers it is going to be a delay, the cabin crew is usually a bit relaxed at enforcing the seat belt sign. <S> E.g. if someone is going to the bathroom, they won't block unless that person is hanging around standing. <S> When the approach clearance is given, another announcement will be made, and the cabin crew will now make sure everyone is seated because landing will commence shortly. <A> There is no requirement for seatbelts during holding. <S> However, holding times are really hard to predict. <S> It is good to be prepared and to have the cabin ready for approach, so if an opportunity for a quick approach comes, it can be taken. <A> Seat belts are only required for ground movement, takeoff and landings. <S> For the US and presumably other countries too, the only requirement is given under FAR 91.107 which says, "(3) Except as provided in this paragraph, each person on board a U.S.-registered civil aircraft (except a free balloon that incorporates a basket or gondola or an airship type certificated before November 2, 1987) must occupy an approved seat or berth with a safety belt and, if installed, shoulder harness, properly secured about him or her during movement on the surface, takeoff, and landing."
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There are no regulations which require passengers to be seated when the plane is flying a holding pattern, but there are a few practical advantages to keep the seat belt sign on during this phase:
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Are there any regulations preventing one from converting an originally cargo aircraft to ferry passengers? Are there any regulations preventing one from converting the cargo version of the Airbus A380 for passenger use? <Q> Converting a freighter to an airliner would require lots of work: <S> you have to install an HVAC system capable of supporting hundreds of passengers, which means installing air ducts from the engines to the cabin, etc. <S> Major surgery to the wing and fuselage. <S> you have to install a sufficient number of doors and emergency exits (with associated systems). <S> Major surgery to the fuselage. <S> big changes to the electrical system to support e.g. entertainment for the passengers. <S> So the conversion would require taking most of the aircraft apart. <A> There is no cargo version of the A380, but for other types: There are no regulations prohibiting converting a cargo aircraft to a passenger one. <S> It will just need to meet all of the passenger certification requirements, such as evacuation times, seat and structure crashworthiness, oxygen systems, and so on. <S> I don't think this has ever been done because it is extraordinarily expensive. <S> It is cheaper to convert a passenger aircraft to cargo because for the most part you are removing items instead of installing them. <S> Passengers also prefer new aircraft, so after going through the cost of converting the aircraft you'll struggle to fill it with people. <S> Can cameras replace windows? <S> From a legal standpoint I'm not sure, I think yes as I recall a patent for it, but that would be an interesting question to ask here. <A> Normally the retrofitting path is from passenger service to freight service. <S> In my experience, many freight operations already have the necessary airpacs, as certain cargo (zoo animals, livestock, biologicals and chemicals) may require environmental control. <S> The cost comes in outfitting the aircraft for people, with the accouterments of modern air travel. <S> There are options for convertible interiors which will handle freight and can be rapidly converted to passenger use, and these are particularly popular with operators in under served areas which have lower volumes. <S> The convertible interiors can be switched out in very short times (less than 30 minutes) and are suited for operations where people are moved by day, and freight by night. <S> One larger effort will be in electrical needs for the cabin and associated lighting and electronics. <S> Without checking the US regulations, it is not clear to me that windows are a requirement, except for certain stations. <S> Some configurations, such as medvac, may use few windows. <S> Some prison transports are done with windowless (or nearly so) passenger aircraft. <S> Different freight has different risks. <S> For example one carrier found that giraffes tended to munch on cables and wiring in the ceiling, requiring protective coverings on subsequent carriage of those animals. <S> Those freight mitigations could increase some costs. <S> Generally, cargo aircraft have adequate doors, as well as larger doors to the upper decks. <S> The bulk of the retrofit is seating, bins, environmentals (lighting, O2, air distribution) and seat rails. <S> It will depend upon the aircraft, but the retrofits do not usually involve major airframe work, although the cost may be high.
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To answer the specifics on an A380 conversion, one would have to study the type certification and the delivery configuration of a given aircraft, and then analyze the requirements to move to dedicated passenger service.
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Which modern day prop (piston) engines allow for inverted flight? A buddy of mine is looking to buy an airplane with an old radial engine because he says radial engines can fly inverted in aerobatic flying. What modern day engines (engines that you can buy today), are capable of flying in inverted flight? <Q> The American Champion Citabria with the 7KCAB Inverted Fuel and Oil package along with the American Champion Decathlon are both "Modern Day" aircraft capable of sustained inverted flight. <S> The major differences between the7GCAA and 7KCAB were in the fuel system and the engine oil system. <S> The engine was replaced with a Lycoming IO-320-E2A of 150 horsepower (110 kW), while a header tank of 1.5 gallons—located beneath the instrument panel—was added to the fuel system. <S> In addition, the carburetor was replaced with a fuel injection system, and a Christen Industries inverted oil system was fitted to the engine. <S> All of these changes were made in order to allow for extended inverted flight, a mode not possible in the earlier models. <S> disciplesofflight.com/american-champion-decathlon/ <S> You can fly inverted continuously for about two minutes before the fuel in the header tank runs out and the engine falters. <S> Rolling upright will recharge a depleted header tank in about a minute while the faltering becomes a smooth running engine again <A> I fly competition aerobatics. <S> The only setup I've seen is some flavor of Lycoming engine with extra bits for fuel (flop tube in a header tank) and oil (Christen inverted oil system). <S> Your friend is correct that some (most? <S> all? <S> -- I don't know) <S> radials can handle inverted flight. <S> Make sure there's a way to ensure continuous fuel and oil delivery to all the moving parts. <S> I would ask a lot of questions before turning a Continental engine upside down. <S> I dimly recall some issue with oil getting past push rods that makes them unsuitable. <S> (Please note this is not a slam on Continental - they're great engines for upright flight, but I don't know if that fish will climb a tree very well) <A> Most engines can handle inverted flight just fine, but it is the fuel system (gravity-fed fuel and/or carburetor) that inhibits the airplane from doing so because of their need to maintain a positive G-force to enable operation.
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Any “modern day” piston engine can allow for inverted flight if it has the right equipment on it.
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Why not increase the number of Flight Data Recorders and add jettisoning capability? With some Flight Data Recorders gone unrecoverable during crashes , what's the argument for not changing their locations, like wings or engines? Given their utility after accidents, why not increase the redundancy even more by placing separate boxes in each engine for example. I understand that military aircraft have jettisoned Recorders that signal their location for recovery. Could this option be considered with Jettisoned Engines even before the crash in case of Extreme Load or excessive vibrations ? <Q> The simplest argument to me is that no location on the aircraft is particularly special when it comes to locating black boxes in this sense. <S> The recorders that aren't found are either in exceptionally remote locations or underwater - I don't see anything special about an engine that makes it more likely to be found than the wreckage of the fuselage. <S> No matter where you place them, there are going to be circumstances where they can't be found. <A> FDRs are already in the most survivable location, in the tail. <S> Look at any crash site and the tail cone is usually the only intact major component. <S> You don't want to jettison them because you need to record data right to the point of impact. <S> The jettisonable devices that are used today are crash locator beacons, not data recorders. <S> They've been around since the 70s. <S> Ultimately what will make <S> all this moot is that going forward all of the data that would be recorded by the FDR/CVR will be transmitted and recorded in real time via satellite... some day. <S> Hmmmm what about whoever is below this falling object the size of a single car garage, which may get discharged over populated areas with some regularity? <A> That is soon to be. <S> Starting in 2019 Airbus is equipping the A350 with redundant, floating, jettisoned recorders . <S> They will be in addition to the usual ones inside the aircraft. <S> None of the articles I've read indicate whether it's a standard feature or an option.
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In theory, it could be possible to jettison an engine on a wing mounted engine aircraft, because they have fallen off on their own and the airplane was still flyable because there was little CG shift.
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Clearance limit of VFR practice IFR approach? When a VFR aircraft has been approved by atc to perform a practice approach, is the aircraft also cleared for a published missed approach procedure? <Q> I'm assuming you're asking about the US, in which case the answer is no. <S> The AIM 4-3-1(e) <S> says: VFR aircraft practicing instrument approaches are not automatically authorized to execute the missed approach procedure. <S> This authorization must be specifically requested by the pilot and approved by the controller. <S> Separation will not be provided unless the missed approach has been approved by ATC. <A> If one asks for it. <S> When I was working on my instrument rating, we would often request a practice IFR approach using one of the various methods (ILS, Localizer, VOR, GPS, PAR, etc.) <S> with 'the option' - actually land, or fly the Missed approach. <S> Then the instructor could mix it up so you wouldn't get in the mindset that every approach would be successful. <S> You might be too off course, too high, too low too early, or he could say you were still in the clouds at the point where you had to decide to continue descending. <S> Sometimes we'd be cleared for the Miss as shown on the approach plate, other times we'd be given an alternate route to fly, perhaps to make way for a plane that would have conflicted: landing on intersecting runway, or taking off and climbing towards us; sometimes we'd practice the same approach from the same end a few times and basically just fly a closed pattern vs doing the whole climb out and procedure turn or hold, sometimes we'd do the approach from one end, then fly out and do the approach from the other end (say like ILS from one end and GPS from the other). <S> ATC at the smaller airports are generally friendly to work, and as long as you're flexible to accomodate planes that are actually landing, or departing, they have no problem working with you. <A> Terminology is important here. <S> You asked whether if under VFR, you were "cleared" to execute a missed approach. <S> There are two points worth mentioning: 1.) <S> Under VFR you are not actually cleared under the IFR definition of this term. <S> Your other wording was more correct, you are "approved" to execute the instrument procedure for practice under a different set of rules. <S> 2.) <S> (I will likely get some comments on this, but let me explain what I mean...) <S> Your IFR clearance includes your route of flight and altitudes up to and including your clearance limit. <S> Typically your intended point of landing is the termination of your flight, or your clearance limit. <S> The missed approach airspace will be protected for you under IFR, and you will have separation when <S> and if you execute the procedure, but you are technically not cleared for anything beyond your clearance limit. <S> That's why execution of a missed approach is an immediate mandatory radio call. <S> Think of the missed approach like an emergency procedure, because that is almost what it is. <S> And it is why they generally end in holding pattern so that you and ATC can sort out further clearance to your alternate. <S> In training and practice things are a bit different, but the important thing is clear communication of intent and understanding what ATC expects, or has cleared you to do. <S> (i.e. the "option" gives you wide latitude...)
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When you are IFR you are not technically cleared for the missed approach procedure either in accordance with the standard definition of the term.
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Are frisbees and boomerangs technically gliders? Frisbees and Boomerangs are heavier-than-air, unpowered, and fly through the air. So are they technically gliders? They also rotate, so I wonder if these are actually some kind of rotorcraft-type gliders. I looked up all types of rotorcraft on wikipedia, which listed 4 things: helicopters, auto-gyros, gyrodynes, and cyclocopters. All of them were powered, so none of them were rotor-gliders. But then, auto-rotation in a helicopter might be considered gliding (with a pretty bad glide ratio). One reason I ask is because I want to try to figure out the glide ratio or lift-to-drag ratio of these weird things. Not so easy to do empirically for a boomerang since it takes a weird ascending and descending path. How would you calculate that for a rotating assymetric airfoil? <Q> No, they are airfoils. <S> Airfoils are the contoured shape of the wings that give a boomerang the proper amount of lift as it's launched and spinning through the air. <S> They operate on the same principle as the wings and propellers of airplanes and helicopters. <S> You might even say that a boomerang is a combination of a wing and propeller. <S> Frisbees operate under two main physical concepts, aerodynamic lift and gyroscopic stability. <S> When flying through the air, a Frisbee can be viewed as a wing, with Bernoulli’s <S> Principle governing the magnitude of the lift force which keeps it aloft. <A> It sure seems like it, based on FAA definitions. <S> The FAA has also designated a paper airplane as a UAV ("drone"). <S> And they do define a UAV as an aircraft <S> It might also be a rotorcraft depending on whether a whole vehicle can also be a rotor. <A> No. <S> A glider is defined as an aircraft that is designed to fly long periods without an engine. <S> The word that eliminates boomerangs and frisbees from this definition is ‘aircraft’ as an aircraft is defined as a machine capable of flight. <S> Likewise, the phrase ‘for long periods’ also eliminates boomerangs and frisbees from the category ‘glider’ for obvious reasons. <S> Both a frisbee and a boomerang can be more closely defined as a wing (or airfoil). <S> When you look at the wing of an airplane or blade of a helicopter, those are what we call ‘airfoils’. <S> An airfoil is a design that’s shape gives an object a positive lift to drag ratio. <S> In the simplistic terms, the top of an airfoil is curved while the bottom is flat. <S> Using Bernoulli’s equation, this shape results in pressure differences over the top and bottom portion of the airfoil as air flows over it. <S> This is how a frisbee and a boomerang work. <S> If you look at each of them from the side, you will notice a flat bottom and a curved upper side which, as previously mentioned, is what causes lift as they move through the air.
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"The Federal Aviation Administration (FAA) defines a glider as a heavier-than-air aircraft that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose free flight does not depend principally on an engine. "
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Could a plane land on specialized vehicles if its landing gear failed? This (fake) video has stirred up a lot of questions online about whether such a scenario would be possible in reality - and the answer to those questions appears to be a resounding "No, that's very implausible." But most of those answers seem to focus on the specifics of the Nissan truck - it would exceed its rated weight tolerance, it probably wouldn't be able to match the plane's speed... What if an airport had specialized vehicles for this sort of thing, Thunderbirds-style ? Could such vehicles be built, or would the engineering challenges just be too great to overcome? <Q> Smaller planes can pull it off, here is video from a weekend airshow somewhere. <S> http://digg.com/video/plane-lands-on-truck <S> Bigger planes, that's a lot weight. <S> Even my Cessna Cardinal (4 passenger) could weigh close to 2500 lbs landing, basically a whole nother car on top of a truck. <S> Maybe a car carrier would be good, longer landing ramp, clear front to fly over if needed. <S> Jets, that's a lot more speed to match up with. <A> Yes, it potentially could, its a common air show stunt , but would it, most likely not. <S> There was a similar scenario where the gear failed in a similar way and the plane was simply landed delicately on the bad gear . <S> There were lots of sparks but everyone was ok. <S> Ultimately its not worth the risk of the truck driver (should the gear crush them) aircraft generally speaking can survive belly landings <S> should something go wrong with the gear. <A> I think for airliners it is perhaps borderline possible but highly impractical. <S> Lets assume a 737 and google around the internet for some rough figures. <S> A 737 apparently lands at 155 knots which translates to around 180 miles per hour and has a max landing weight of about 65 tonnes. <S> Apparent 4-20% of that can be on the nose gear. <S> So that is up to 13 tonnes on the nose gear and up to 31 tonnes on each main gear. <S> Dynamic loads can potentially be quite a bit higher than the static weight, even more so if the landing gear is damaged. <S> So you are looking at a vehicle with the speed of a supercar and the weight handling capacity of a large truck. <S> That is going to be a nontrivial engineering challenge. <S> Then you need some mechanism for the trucks to safely interface with the plane. <S> This is further complicated by the fact that the gear could be in almost any state. <S> Plus you need a runway with enough room for the trucks to accelerate, rendezvous with the plane and then slow down safely. <S> Probably at least double the length you need for a normal landing. <S> Plus the rendezvous itself isn't going to be an easy procedure. <S> And then finally you would have to convince the authorities that this hairbrained scheme is at least as safe as just landing the plane with broken gear.
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Sure stunt pilots can do similar things in small planes but those planes fly much slower and are much more manoeuvrable than an airliner.
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What is the difference in VTOL technology between British Aerospace Harrier II and F-35B? F-35B safer and looks more stable in terms of VTOL capability. What is the basic difference between Harrier II and F-35B's VTOL technology? <Q> the F35 has a ton of electronics that the Harrier could only dream about, but I will focus on propulsion differences. <S> The biggest is that the F35B uses a separate lift fan in front of the engine, oriented to provide vertical lift that balances the vectored thrust from the rear of the engine. <S> The lift fan is disconnected when flight speed is obtained and covers closed. <S> Roll control at low speed comes from bleed air from the front fan in the engine. <S> The Harrier uses a much larger version of a bleed system from a single engine to provide both forward located vertical lift/thrust and a similar total diversion system for rearward lift/thrust through four rotating nozzles. <S> All nozzles are working all the time and rotated to a lift/thrust position. <S> A separate bleed system provides roll and pitch control at low speed. <A> In the Harrier, the bypass air from the large diameter low pressure compressor of the Pegasus engine is ducted through the front pair of nozzles while the remaining gas output from the engine passes through the rear pair. <S> Rolls Royce designed the Pegasus engine with the main rotating components, the low and high pressure compressors and the corresponding high and low pressure turbines mounted on two concentric, counter-rotating shafts. <S> This minimises gyroscopic coupling effects and makes it possible to control the Harrier in hovering flight manually, without the aid of an automatic stabilisation system. <S> All four nozzles can be rotated through 98.5 degrees allowing for vertical takeoff and landing. <S> Thrust vectoring can also be used in combat to enhance manoeuverability, a technique pioneered by the USMC. <S> The F35B uses a separate engine driven fan in the forward fuselage in addition to thrust vectoring to provide vertical lift. <A> The F-35B can automatically do a VTOL landing while the Harrier is manual. <S> Also the F-35B has a more powerful engine that has an air opening on the top of the jet to increase air intake for VTOL operations. <S> The performance difference is that the F-35B can go faster than the speed of sound while the Harrier cannot. <S> Not to mention the F-35B has all the bells and whistles of a modern fighter.
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The Harrier system is much less complex mechanically and avoids the need for the lift fan which is only used for take off and landing and is dead weight the rest of the time, and which also takes up a lot of space in the F35B's forward fuselage.
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Is this a Hurricane or Spitfire? Can anyone identify the fighter here in this picture taken from a Dornier-do17? From: https://stukablr.tumblr.com/post/145040185970/a-pic-took-it-from-a-donier-do17-a-hurricane <Q> Relative thickness of the airfoil, thickness repartition over span, and low dihedral angle of the entire wing, tells it's a Hurricane. <A> In addition to @qq jkztd's very good answer, I'd like to add that the Spitfire never had a such a wide oil radiator under the fuselage. <S> That to me was the dead giveaway that it was a Hurricane. <S> Quite a durable but honestly lackluster fighter. <A> It's a Hurricane. <S> No Spitfire of any Mark had a radiator under the fuselage, whereas every Hurricane, from the prototype to the "Last of the Many" did. <S> And that is NOT a carburetor (carburettor in British English) air inlet. <S> Re the comment about the canopy, Mark I Spits had a narrow canopy. <S> No framed greenhouse, but not blown out at the sides either. <S> The earliest Mark I Spits had a canopy that effectively was just an extension of the windscreen. <S> Later ones had a bulged top for more head clearance, but still had flat sides. <S> Later Marks featured the "blown" canopy that was bulged on the sides as well. <A> It's a Hurricane. <S> On a Spitfire the radiator is on the right wing. <A> Agree with qq jkztd. <S> Also the canopy. <S> You can just about make out the lines (in profile, it looks like a greenhouse) plus it's narrower. <S> A Spit's is more bulbous.
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The radiator is on the fuselage, which means it is a Hurricane.
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Does a Tower controller need to see an aircraft on final to give landing clearance? If there is an IFR aircraft on approach that has already received an approach clearance, and he reports being at the final approach fix but the controller does not have him in sight yet, can the controller give the aircraft clearance to land at this point, or does he have to wait until he has the aircraft in sight (which may be on short final)? And what are the rules for (let's say) a VFR flight on final (maybe the controller can't see him due to rain over the field, etc.)? Also, are there any reference documents (ICAO/FAA/Eurocontrol) that have information on this? Here's a more specific IFR scenario: let's say the aircraft is making a CAT I ILS or maybe a VOR DME approach, in a non-radar environment. Does the tower need to see the aircraft before giving a landing clearance? The runway itself is clear from other vehicles or aircraft. Does the controller issue a "continue approach" instruction until he can see the aircraft and then clear it to land? O does he just issue the landing clearance at the final fix ( if the runway itself is clear)? <Q> The FAA's ATC orders cover this for the US. <S> Note that controllers can use radar instead of visual contact: 3−10−7. <S> LANDING CLEARANCE WITHOUT VISUAL OBSERVATION <S> When an arriving aircraft reports at a position where he/she should be seen but has not been visually observed, advise the aircraft as a part of the landing clearance that it is not in sight and restate the landing runway. <S> PHRASEOLOGY− <S> NOT IN SIGHT, RUNWAY (number) <S> CLEARED TO LAND. <S> NOTE− <S> Aircraft observance on the CTRD satisfies the visually observed requirement. <S> (A CTRD is a Certified Tower Radar Display.) <S> As others have said, operations in poor weather would be very difficult if controllers needed to see all aircraft before clearing them to land. <A> There may be some variations upon this basic rule depending on jurisdiction. <S> I am speaking from the context of FAA jurisdiction. <S> I fly in and out of multiple airports that are not radar equipped. <S> I routinely receive landing clearance before the tower has me in sight. <S> In cases of good weather (VFR), the controller will typically wait till he or she has us in sight before issuing the landing clearance. <S> This will often be preceded by an instruction for us to report over some point in order to facilitate that visual contact. <S> In cases of poor weather, the controller has little or no choice in issuing a landing clearance before establishing visual contact. <S> Just today, I was flying an ILS approach and the controller issued our landing clearance while we were still in the clouds. <S> We broke out of the clouds a few minutes later, at least five miles from the runway, so the controller could have waited, but did not need to. <S> In very poor weather, for example with visibility of half a mile, the controller would probably never see our aircraft at all while we were in the air. <S> At this airport the controller would only be able to see us as we rolled out on the runway after touching down. <A> In many cases, the controller has a radar set, and knows the positions of approaching aircraft that way. <S> It is not necessary for him to obtain visual confirmation in at least that case. <S> It is necessary for the controller to know that previous aircraft and/or vehicles have cleared the runway - <S> that is fundamentally what landing clearance is about. <S> He may be able to see that for himself (again possibly with radar assistance), or he may need to rely on reports of moving clear. <S> Another vital factor is that the pilot gains visibility of the field before reaching minimum descent altitude. <S> He has already gained landing clearance at that point, but as the tower tends to be in mid-field, the aircraft is not necessarily in sight from the tower! <S> On a Cat-III approach, minimums are at zero feet and suitably fitted aircraft can land in solid fog, unable to see the runway even after coming to a halt. <S> So this makes it obvious that the controller literally seeing the aircraft on approach is not necessary. <S> VFR is another matter, of course. <S> Often there is no tower at all at a VFR field, and everything is the pilots' responsibility. <A> One doesn't even need to be on final to get a landing clearance. <S> Depends what else is in the area. <S> I flew into Manchester, NH this weekend (called Manchester-Boston now it seems, but not in all places), http://www.airnav.com/airport/KMHT nice VFR day, was cleared to land while 3-4 miles south of the airport for Runway 24 on what turned out to be a very wide downwind leg (once I realized the airport was at my 9:00 - I had been looking at my 12:00 for it). <S> Good distance for the commercial jet traffic I guess, bit wide for a 4-seat prop plane.
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No, a tower controller does not need to have an aircraft in sight in order to issue a landing clearance.
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Which aircraft have fought against its own type in active combat? The criteria for this question are The aircraft has to be the same type (but not necessarily the same mark) The two opposing sides are actively hostile; but not restricted to nation states (so civil war a possibility) The aircraft treat each other as an active threat Cloned aircraft count, e.g. Tu-4 / B-29 or J8M / Me163 (neither of these occurred as far as I know) It's difficult to see circumstances in which it would happen; but in over 100 years of air combat I think it likely to have occurred at some point. <Q> Probably not the only situation, but in 1948 Israeli Spitfires faced Egyptian Spitfires, and just before the truce also faced a few RAF Spitfires that were too close to the combat area ( reference ) <A> Captured aircraft being used for evaluation is quite common, but I can only find one instance of them being redeployed actively: during the Spanish Civil War. <S> Among a number of aircraft that were captured by the Republicans was a squadron of Fiat CR.32: <S> During the war, the Republic captured at least 11 Fiat Cr.32; some of them were captured when the troops occupied anbandoned airfields, one more when its pilot deserted, three when italians pilots landed in enemy airfields and another one rebuilt at La Rabasa using wrecks... <S> The Cr.32 that stood [remained] in Spain were transfered to 71 Group, used to defend Alicante. <S> [source] <S> It's possible <S> they went head-to-head with the Aviación Legionaria CR.32s; I think it's safe to say that the opposing air forces were both using the same type of aircraft in active operation . <S> Here's Spanish Republican Air Force ace Manuel Aguirre López in front of his captured CR.32 - the printed caption says the aircraft is often flown by Aguirre himself <S> He's credited with shooting down a number of CR.32s himself, although none while flying his captured CR.32. <S> source source <A> They ended up crashing into each other (whether deliberately or not) in the Austrian airspace. <S> This might formally not qualify, but arguably the difference between MiG-15bis and MiG-17 is smaller than between, say, <S> F-15A and C, or even between <S> Tu-22M2 and Tu-22M3. <A> One story originally told by Martin Caidin in his book on the P38, was the tale of the phantom P38 , one that had been captured by the Italians and was flown in US colors by one of their pilots, Guido Rossi, to shoot down stragglers after coming in close under the guise of being an escort. <S> Supposedly, this morphed into a struggle between Rossi and one of his victims, Lt Harold Fischer, who survived the shoot down. <S> Fischer requested a YB40, a B17 with a lot of extra guns and ammunition, to go hunting Rossi. <S> Fischer went so far as to find Rossi's wife, who was living in Allied controlled territory, and paint her picture and name on the YB40 to draw Rossi in, and eventually shoot him down. <S> Both survived the war. <S> When Fischer died as the result of a crash during the Berlin airlift, Rossi was at his funeral. <S> The way the story is told has elements of 1940's fiction about it, so it may have 'grown in the telling'. <S> But, like a lot of wartime stories, it probably derives from an actual incident. <S> Interesting side story that came up while looking into this... the 500 round belts of ammunition for the M2 50 caliber machine guns on the B17 and B24 were 27 feet long. <S> Supposedly, the expression 'give them the whole nine yards' derived from a bomber gunner dumping an entire belt of ammunition at an attacker. <A> I recall that Hungarian and Romanian He 112's were active at the same time during their minor tiff over Transylvania, although I doubt they met in combat. <S> Various PZL designs ended up used throughout the area, so I would not be surprised if they were also operating against each other.
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There was an account of Soviet MiG-17s engaging in a fight with Hungarian MiG-15bis in 1956 (I could only find an archive quote now).
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Is it possible to build a flight-capable aircraft powered by compressed gas? I pray this isn't a physics SE question. A star engine can be considered "gas operated". So what if we power a star engine with unleashed, formerly compressed gas instead of... actual gas/aero-kerosene/etc...? So instead of fuel tank (oh the temptation to pun is so strong here) you use gas tank? Note that since nothing has to BURN, we can use lighter-than-metal material, as engines usually play a big part when it comes to weight of aircraft. Can you? And if that's a YES, can you estimate the flight time? <Q> In aircraft design, the main problem is energy density of the energy source. <S> Even with the phenomenally high energy density of kerosene fuels (>42 MJ/kg), the fuel still represents a sizable chunk of the weight of an aircraft. <S> For example, fueling an Airbus A330 will double its weight! <S> According to Wikipedia , compressed air has a practical energy density of about 0.1MJ/kg. <S> You would go from 110.000 kg of fuel to over 400 million kg of compressed air. <S> A more relatable example would be a Cessna 172. <S> It can carry 212 litres of fuel, or about 150kg. <S> On top of that, it can carry about 190kg of useful payload. <S> If we instead use compressed gas, we would need over 60.000kg of compressed gas to get the same range. <A> Yes Whereas it may not be feasible, as Sanchises explained, for large manned airplanes, on the scale of small models it is quite possible. <S> These are aircraft, too! <S> ( source ) <S> Such models were quite popular in the '60s and '80s: the engine is very simple indeed , and can be powered by the common CO 2 cartridge (as used for making fizzy water at home, which was also more popular at that time). <S> Nowadays, such engines are largely replaced by electric drive: also something not-yet-quite-working on a large scale, but excellent for small models. <A> If you allow to store the gas in liquefied form, the answer is a cautious <S> Yes. <S> But do not expect more than very brief flights. <S> Not compressed, but liquefied gas was used in the first attempts at powered flight. <S> Before internal combustion engines became light and fast enough for use in aircraft, carbonic acid engines were employed by several pioneers. <S> Otto Lilienthal , who built and flew the first man-carrying gliders, added carbonic acid engines of his own design to several of them. <S> They drove flapping wingtips which, according to his own description, clearly helped in stretching the glide, but were not powerful enough for sustained flight. <S> In 1905, the Romanian engineer Trajan Vuja used a carbonic acid engine to fly his high-wing monoplane. <S> It was powered by a 25 hp modified Serpollet engine which drove a tractor propeller. <S> It was capable of short hops only, even though Wikipedia reports that The fuel supply was enough for a running time of about five minutes at full power <S> In its "ten years ago" section, the October 19, 1916, issue of Flight International described the power plant of the Vuja machine as: <S> A peculiarity of the arrangement is that the motor is driven by liquid carbonic acid, a method of obtaining power which has not hitherto been conspicuous for its lightness.
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There is no way you can offset the enormous amount of compressed air required by downsizing your engines.
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What are the differences between the MiG-15 and MiG-17? Apart from the extra wing fence and angled leading edge of the MiG-17, what are the differences visually between the two aircraft? <Q> I'm surprised <S> no-one's mentioned the length - the MiG-15 has a much stubbier appearance than the MiG-17, because it was rather shorter (10.10m vs 11.26m) <S> The wings of the MiG-17 are angled at 45°, rather more than the MiG-15 (helpful to identify from above), and the tailplane is has a small amount of extra rake too. <S> Overall, the MiG-17 has a longer, sleeker profile than its older cousin. <S> Here's a comparison, 15 in blue, 17 in red. <A> In addition to the elements on the wing mentioned by @Jamiec , on the rear, there are some little differences close to the rear air brakes. <S> See the picture below of a Mig-15 : <S> The rear air brakes are in dark grey on this plane, the fuselage is smooth. <S> On a Mig-17, there is a small protruding part on the closed brakes; see this picture : I cannot find if this change on the mechanics of rear air brakes is on all versions of Mig-17. <A> Visually, the only differences are those you've mentioned - the extra wing fence and the angled vs straight leading edge. <S> But visually, they were very similar indeed. <A> In addition to the greater angle of wing sweep and the additional wing fences, the wing of the MiG 17 had a different, thinner profile with a thickness/chord ratio of 1 to 10 or 10%, down from the MiG 15's 11%. <S> This was still relatively much thicker than the 5% wing used on the supersonic McDonnell F4 Phantom. <S> The superior efficiency of the MiG 17's wing at subsonic speeds, coupled with the lower wing loading made it more maneuverable than the F4 in the horizontal plane. <S> The MiG 17 had increased power from a developed version of the Nene engine giving 7,450 lb thrust with afterburner. <S> Early MiG 17s had the MiG 15's armament of one N37 37mm cannon with 40 rounds and two 23mm NR23 with 80 rounds each, but many later aircraft substituted a third NR23 for the 37mm gun, giving a combined rate of fire of around 2,500 RPM with ammunition increased to 100 RPG. <A> Depends on the version of MiG 17, surely? <S> The MiG 17 PF had a completely different nose because of the Izumrud radar mounted on the intake splitter and the revised upper intake profile. !
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The MiG-17, being developed much later was meant to be a far more advanced aircraft compared to the MiG-15.
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How to find the flight paths of an airport? How can I find the flight paths near an airport (e.g., Heathrow or Pearson) including cruising altitude, descending speed (variations)? Specifically, I need a figure showing the height vs. speed of a plane as it's landing starting from the cruising altitude. <Q> You can find a great deal of approach path information here but that will only give you the path, and perhaps some intercept altitudes for a given approach it will not give you any speed information. <S> Cruising altitudes will also vary heavily by aircraft type. <S> Specifically, I need a figure showing the height vs. speed of a plane as it's landing starting from the cruising altitude. <S> This is broadly specific to each airframe as well as the loading of any given aircraft at a given time. <S> But you can find the information if you know the airframe in question <S> , there are also some limits depending on where you are in the world. <S> The FAA (and presumably most legal entities) cant have different rules for everyone so they broadly break down approach speeds into categories. <S> That should give you a fair idea of the approach speeds. <S> Keep in mind <S> these are airspeeds and local wind will alter ground speeds on an individual day basis. <S> If you start from the cruising altitude there will be a few phases of the decent that will see various speeds. <S> This depends on what ATC clears you for and what the local conditions call for more on that here . <A> Look at the Approach Charts for the airport of interest. <S> In the US, speeds are also limited to 250 knots below a certain altitude <S> and I think distance from an airport <S> (I never had to worry about that, my Vne (redline airspeed) doesn't go that high!). <S> I don't think you'll find speeds from cruising altitude as speeds are adjusted to match traffic flow. <S> And cruising speed varies by airplane type as well. <A> You might consider using a website such as Flightradar24 , which will show you real-world realtime flight paths (including vectors or holds that may be assigned by air traffic control, as opposed to ideal approaches). <S> You can click on a particular aircraft to see its track, then click "speed & altitude graph" on the detail pane to see speed and altitude at one-minute intervals. <S> There's also a speed/altitude graph for each flight tracked on FlightAware .
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If you check out a variety of flights into the same airport, you can see what approach paths are used by aircraft arriving from different directions for the current wind conditions.
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Why do simultaneous-ops parallel runways need to be so far apart? In the answers to this question about Denver's widely-scattered pinwheel of runways and this question about Schiphol's runway out in the middle of nowhere , it's mentioned that parallel runways are required, by both European and U.S. regulations to be over a kilometre apart in order to be able to have simultaneous departures or simultaneous arrivals on both runways. In contrast, if one runway is departing an aircraft while a parallel runway is landing an aircraft, the runways need only be a few hundred metres apart . Why is there such a large runway-separation requirement for simultaneous arrivals or simultaneous departures from parallel runways? It can't be for aircraft separation, since an aircraft is allowed to land on a runway quite close to a parallel runway that is simultaneously departing an aircraft, despite the possibility of this resulting in a head-on collision if one or both aircraft drift off track, so what, in fact, is the reason for this? <Q> The simple answer seems to be for wake turbulence. <S> This FAA document, ORDER JO 7110.308C , seems to say it is for wake turbulence reasons in para. <S> 9 <S> : <S> The geometry of the approach, as well as the lateral separation between the two approaches and prevailing local meteorological conditions, provide the wake turbulence avoidance necessary for reduced separation dependent approach operations. <S> Figure 3 shows the aircraft arriving in a staggered fashion, 1 nautical mile diagonal separation with runways 2500 ft apart (parallel runways separated by less than 2,500 feet, also referred to as, Closely Spaced Parallel Runways (CSPR)). <S> The text also describes how the lead aircraft follow a lower glide path than the following aircraft such that the lead's wake turbulence isn't a factor for the following aircraft. <A> ( YouTube ) Much closer than 1 km at SFO. <S> 1 km (~3,300') is not the minimum (see this illustration from the FAA AIM). <S> The centerline spacing for parallel approaches can go as low as 750' (~230 m), a prime example is San Francisco: (Google Earth) <S> Centerline spacing at SFO. <S> But getting very close like at SFO requires special training, procedures, charts, controllers, and ground equipment (namely the p recision r unway <S> m onitor system - PRM). <S> In lack of PRM and the associated items, the centerline separation allows sufficient reaction time against any transgression (e.g., pilot deviation). <S> Wake turbulence is a factor for the trailing plane whether on the same runway or a parallel one, but RECAT has helped reduce the over conservative separation ( ICAO ). <S> For your last point on departures and arrivals on parallel runways, a minimum centerline spacing is required: ( FAA ) <S> Further reading: Simultaneous Close Parallel PRM <S> Approaches (skybrary.aero) <A> See also Why is one of two parallel runways sometimes closed in foggy weather? <S> It can't be for aircraft separation, since an aircraft is allowed to land on a runway quite close to a parallel runway that is simultaneously departing an aircraft, despite the possibility of this resulting in a head-on collision if one or both aircraft drift off track <S> There can't be a head-on. <S> Unstated in that requirement is that both runways are used in the same direction. <S> If the arriving aircraft has perform a missed approach, it has procedures to direct it away from the other runway. <S> Also, the departing aircraft will be advised. <S> Under normal circumstances where the landings are executed, there's no overlap of tracks in the air, only on the runways.
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It is usually to guarantee sufficient aircraft separation when visual separation is not available (bad weather).
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How bad is the efficiency of jet engines under low loads? VTOL operations need 4-5 times more thrust than a conventional take-off of an aircraft. If you don't want to install additional lift-engines into a hypothetical aircraft and use thrust vectoring to turn the thrust towards the ground, you naturally end up with largely oversized engines for the cruise flight. But how bad does the fuel efficiency (thrust per amount of burned fuel) get, when the engines run at their minimal self-sustaining throttle setting during cruise? <Q> Current jet engines are actually not built for efficiency rather than performance. <S> If you consider efficiency, you don't build a VTOL aircraft. <S> This is why the F35 has multiple versions with and without VTOL capabilities. <S> Also, jet engines even during flight have to be able to sustain fast speed change, fast altitude increase and high load factors, all combined with lightweight designs. <S> Therefore, I wouldn't consider takeoff as the most demanding phase of flight for such engines, but I may be mistaken on that point. <S> All these conditions make it difficult to reach the efficiency of say turbofan or turboprop engines. <A> And because you need to lift the engine weight too, the thrust/weight ratio grows slower than the installed thrust. <S> The result significantly reduced payload fraction and payload fraction is the major factor in efficiency. <S> Now fighters normally do have thrust/weight around 1, but they are basically aerodynamic shells wrapped around the engines and some fuel tanks and almost nothing else. <S> Their payload is too small compared to transport aircraft to be practical. <S> Now vertical take-off is occasionally useful in civilian operations, but with all the airports already built not as often. <S> For the cases where it is we have the rotorcraft and the AugustaWestland AW609 tiltrotor. <S> Unlike jets, the large rotors have much lower induced power, so they can produce much more static thrust with the same power and thus support hover with reasonably small engines. <S> The price is that their thrust decreases faster with speed, so the top speed is lower. <A> Extensive research was done into civilian VTOL operations in the 1960s and 1970s. <S> Those projects were killed by several factors: high fuel cost (combined with the fuel crisis in the early 1970s) high capital cost (due to all the extra lift engines needed compared to regular aircraft, there were designs with dozens of lift engines). <S> noise. <S> The attraction of VTOL is being able to operate near a city center instad of having to drive to a remote airfield with a big runway. <S> But all that thrust necessary for VTOL results in an awesome racket (the Harrier is one of the loudest fighers ever, despite having much lower performance than its contemporaries). <S> Nobody is willing to have that much noise in an urban setting, making the whole exercise pointless.
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The main problem with installing bigger engines is that they are heavier.
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Is this statistic about the fatal accident rate correct? This link says that: fatal accidents occurred once every 200,000 flights in the 50s and 60s. Now, fatal accidents only occur once every two million flights While many sources, including this one , agree that the average number of commercial flights per day is around 100,000. If that is the case, then we should see a fatal accident every 20 days or so (2 million flights), but in 2017, there were no fatal incidents on commercial flight at all. What is the explanation for this? Is it just that the first link is plain wrong? <Q> The passage you're asking about is a paraphrase of something Boeing spokeswoman Julie O'Donnell said. <S> If you follow the citation in the article, you can see exactly what she said, and when she said it. <S> "During the 1950s and 1960s, fatal accidents occurred about once every 200,000 flights," says Julie O’Donnell, a spokeswoman for Boeing. <S> "Today, the worldwide safety record is more than 10 times better, with fatal accidents occurring less than once in every two million flights." <S> [Emphasis added.] <S> O'Donnell is being quoted in 2014. <S> According to the latest IATA safety fact sheet (published January 1, 2018), IATA measured a fatal accident rate of about one per 2.36 million flights in 2012, and one per 2.58 million flights in 2013. <S> If I were rounding that down for a reporter in 2014, "less than once in every two million flights" is exactly what I'd say. <S> IATA counted 15 and 14 fatal accidents in 2012 and 2013, respectively. <S> That's an average of one fatal accident every 25 days or so—just like you estimated. <S> As @fooot pointed out in their answer , we've seen fewer fatal accidents in more recent years: an average of one every 30 days, 90 days, 40 days, and 60 days or so in 2014, 2015, 2016, and 2017, respectively. <S> Statistical postscript <S> I agree with your gut feeling that, if fatal aircraft accidents were happening at an average rate of one every 20 days, I'd be very surprised to see no fatal accidents at all last year. <S> If fatal accidents were Poisson distributed in time, with a rate of one per 20 days, your chances of seeing no accidents in a year would be less than one in 80 million! <S> On the other hand, a year with no fatal large commercial passenger jet accidents is totally plausible, given the accident rate of one per 16 million flights that @fooot quotes. <S> In 2017, that comes out to an average accident rate of less than one every 140 days—maybe a lot less, if large commercial passenger jet flights make up only a small fraction of all flights. <S> If fatal accidents were Poisson distributed, with a rate of 1 per 140 days, your chances of seeing no fatal accidents in a year would be better than one in 14. <A> Per the Aviation Safety Network , there were 7 fatal incidents of commercial passenger aircraft in 2017. <S> It's true that none of these were in the US, and most of these were smaller aircraft that do not get widely reported. <S> If you only consider "large commercial passenger jets," the average is more like 1 in every 16 million flights. <S> However, 2017 was a bit of an outlier. <S> In 2018 there have been 4 so far. <S> Fatal incidents are fairly random and will not exactly follow a certain average rate, not even over the course of a year. <S> And with the total number being relatively low, it's even more prone to large fluctuations. <S> The total trend in the accident rate has also been downwards, so we would expect more recent periods to be below average. <A> The link is not wrong but your math is a bit misguided. <S> Just because an accident occurred on average every XXX,XXX flights does not mean that on flight XXX,XXX+1 there will be another accident, thats simply not how statistics work. <S> This also gets complicated due to the FAA's historical records and how the term accident has been used over the years. <S> As regulations have gotten stricter and reporting has gotten more verbose we now have much greater insight into accident information than we did even 25 years ago. <S> The FAA publishers a massive amount of info on the topic, you can find the real numbers for General Aviation here (for the last decade or so) and all accident reports are available here <A> One can also review the NTSB records to see what the rates were like for more recent years to date. <S> There is a 55MB file .XML <S> that can be downloaded (and opened with what? <S> I have no MS Office tools that will open it like an Excel spreadsheet or similar for sorting/manipulation). <S> I'm pretty sure it's a big table. <S> https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx <S> Here's a row for example: <S> ROW PublicationDate="05/02/2018 <S> " ReportStatus="Preliminary" BroadPhaseOfFlight="" WeatherCondition="VMC" TotalUninjured="2" TotalMinorInjuries="" TotalSeriousInjuries="" TotalFatalInjuries="" AirCarrier="" PurposeOfFlight="Personal" Schedule="" FARDescription="Part 91: General Aviation" EngineType="" NumberOfEngines="1" AmateurBuilt="Yes" Model="KIS" Make="SENO LOUIS C SR" <S> RegistrationNumber="N66SK <S> " AircraftCategory="Airplane" AircraftDamage="Substantial" InjurySeverity="Non-Fatal" AirportName="EAGLE LAKE" AirportCode="ELA" Longitude="-96.321945" Latitude="29.600556" Country="United States" <S> Location="Eagle Lake, TX" EventDate="04/29/2018" AccidentNumber="GAA18CA242" InvestigationType="Accident" EventId="20180430X21704" <S> The Table is accessible year by year and month by month here, seems a little easier to digest: https://www.ntsb.gov/_layouts/ntsb.aviation/month.aspx
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The statistic of 100,000 flights per day is a global one, and globally it is not true that there were no commercial airline fatalities in 2017. In 2016 there were 14 incidents, which is closer to the quoted average.
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Is it incorrect to refer to a C-130 as a jet? In this article by CNN, the C-130 involved in the unfortunate crash in Savannah, GA is referred to as a "jet." Is this considered proper usage? I'm not looking for public opinion here but official categorization, if one exists. Perhaps there is an USAF or FAA document I've not been able to find which delineates such things. I would imagine that there is also an engineering or academic definition of such things. The AV.SE description of the Turboprop tag states that it should be considered "as opposed to a jet engine." Wikipedia says that "Turboprop engines are jet engine derivatives." which really sort of muddies things but the actual turboprop article notes that "the exhaust jet typically produces around or less than 10% of the total thrust" It never occurred to me that the thrust produced by a turboprop engine is even measurable. Would this factor, then, be the delineation between jet and prop? Should it be a matter of whether the exhaust gasses or rotating components propel the aircraft? So to restate my question, Should a C-130 be called a jet even though a significant percentage of its propulsion is derived from a propeller? Note: Please consider JATO/RATO outside of scope of this question. <Q> CNN actually called it a jet with four turboprop engines, if you can believe that. <S> ICAO is probably as universal a source as you will find. <S> They list the C130 as turboprop/turboshaft. <S> Their table of aircraft type designators allows selection of engine types from this list: Jet, Turboprop/turboshaft, electric, piston and rocket. <S> There are no associated definitions. <A> No. <S> CNN incorrectly reported that is was a jet. <S> Most likely it was a staff writer with little background in aviation who posted the story in haste. <S> Contact them <S> and they’ll be happy to issue a correction. <S> The C-130 aircraft is a turboprop powered aircraft. <S> To be fair, sometimes turpopropeller engines are called ‘prop jets’ because they use a gas turbine engine similar to the gas generator core of a jet engine to drive the propeller. <S> While the gas core of a turboprop does produce some reactive thrust from the exhaust gases leaving the jet pipe or exhaust stubs, the vast majority of the engine power output is sent to the propeller gearbox and converted into thrust by the propeller. <A> According to the manufacturer, Lockheed Martin the C-130 is a turboprop multi-role aircraft powered by Four Rolls-Royce AE 2100D3 4691 shp turboprop engines. <S> Since the manufacturer itself classifies the 130 as a turboprop, I would tend to lean in that direction. <S> The dictionary.com definition of a turboprop is "an aircraft powered by one or more turbo-propeller engines". <S> Turbo-propeller engines are further defined as "a jet engine with a turbine driven propeller that produces the principal thrust, augmented by the thrust of the jet exhaust". <S> The major difference between turbofan engines and turboprop engines is that in the turboprop engine, the exhaust is routed across internal turbines connected to a shaft that then turns an externally mounted propeller from which most thrust is derived. <S> In a turbofan engine, that same exhaust is still routed across turbine blades attached to a shaft, but instead of spinning a propeller, the shaft spins a very large fan on the front of the engine and that is what produces the majority of thrust, at least in today's high bypass turbofan engines. <S> A great video can be found here <S> that does a good job of explaining <S> how a turbofan engine works and here is a good overview of the GE turboprop engine. <A> YES ! - <S> It is technically correct to call any axial or centrifugal combustion engine a "Jet". <S> The power originates from single cycle "jet" gas reaction but in the case of a turboprop or fan-jet is converted to other mechanical thrust. <S> TURBOPROP AIRCRAFT <S> − <S> An aircraft having a jet engine in <S> which the energy of the jet operates a turbine which drives the propeller . <S> Turboprop, turbofan, and turbojet refer to the manor in which the chemical energy is converted to mechanical thrust i.e fan, prop, or gas exhaust - not the combustion principle. <S> All three use intake, compression, power, exhaust in what is commonly called a single cycle or "jet" . <S> Therefore they are all "jets". <S> A pure jet (turbojet) derives all its thrust from exhaust reaction. <S> A turbo-prop or turbo fan translate the jet power to a prop or fan. <S> A typical modern Aerobus/Boeing turbo-fan engine only produce about 10% thrust from exhaust reaction and 90% thrust from prop or fan propulsion! <S> Mechanically a fan and a prop use the same mechanical principle for thrust, a prop has fewer wider blades that turn slower, while a fan has more thinner blades at a higher rpm. <S> A turbo-prop is a "jet" engine with a gearbox attached to a small number of blades (prop). <S> The aircraft is primarily driven by the reaction of air through the "prop". <S> The "jet" used on Aerobus and Boeing (i.e fan jet) is a a jet without a gearbox but has at least one auxiliary spool and bearing that "slips" in place of a gearbox and drives a many bladed prop (fan). <S> The power producing "jet" of a jet, turbo prop, turbo jet, and turbo fan, primarily differ in the bypass ratio and <S> rpm but <S> the power is produced by the same "jet" single cycle combustion principle . <S> A jet can be defined as a single cycle intake, compression, ignition, and expansion of combustible gas. <A> Is it incorrect to refer to a C-130 as a jet? <S> Yes, it is incorrect. <S> First things first, let's go over some terminology. <S> A "turbine" is a kind of engine used in aircraft. <S> There are 3 variations of the turbine engine: turboprop, turbofan, and turbojet. <S> In aviation, the term "jet" is used to refer to turbojet or turbofan engines.
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The FAA Pilot's Glossary defines a Turboprop... There is probably no official definition of this term, but this is how it is commonly used.
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How do I tell ATC that I don't have a transponder? If my plane doesn't have a transponder and ATC tells me to squawk some transponder code, how should I respond? Is it just as simple as "I don't have a transponder"? This is for the United States and for a plane with no electrical system, and obviously at a towered field where I would be communicating with ATC using a portable radio. No flight plans will be involved and I will generally be flying out of a class B field but within a class B umbrella. Flights will be VFR/daytime only. EDIT: Looks like I opened up quite a can o' worms, here. I didn't know it would be this complicated. Just found this, too, which adds some more info. Thanks for the lively debate and the good suggestions. https://www.aopa.org/training-and-safety/pic-archive/equipment/transponder-requirements Looks like it's getting more and more difficult to escape government control. I think I may have to get a transponder. Hmmm. <Q> From the AOPA : <S> Flying into a Mode C Veil Without a Transponder For flying into a Mode C veil without an operable transponder, the pilot needs to telephone the appropriate radar facility for the Class B airspace and ask for permission to make the flight. <S> Upon agreeing to conditions (including direction of flight and altitude), the pilot will be given a code number that he will mention to the controller upon initial radio contact. <S> This is the same procedure that a pilot with an inoperative transponder/encoder would use to fly in or out of the Mode C-veil airports for avionics repair. <S> The situation may be slightly different if the pilot is landing at a satellite Class D <S> (towered controlled) airport within the veil but <S> outside of Class B airspace. <S> The approval is still given by the controlling radar facility via telephone. <S> The radar facility may still issue the code number but may only require the pilot to contact the tower in the Class D airspace. <S> NOTE: <S> You should not expect approvals at the busiest of Class B airports during their peak times or under difficult weather conditions, but if this telephone procedure can expand the utilization of your aircraft occasionally, then by all means, phone to find if you can "fit into" the system. <A> @birdus 14 CFR 91.225 : (d) <S> After January 1, 2020, and unless otherwise authorized by ATC, no person may operate an aircraft in the following airspace unless the aircraft has equipment installed that meets the requirements in paragraph (b) of this section: (1) Class B and Class C airspace areas; (2) Except as provided for in paragraph (e) of this section, within 30 nautical miles of an airport listed in appendix D, section 1 to this part from the surface upward to 10,000 feet MSL; (3) Above the ceiling and within the lateral boundaries of a Class B or Class C airspace area designated for an airport upward to 10,000 feet MSL; (4) Except as provided in paragraph (e) of this section, Class E airspace within the 48 contiguous states and the District of Columbia at and above 10,000 feet MSL, excluding the airspace at and below 2,500 feet above the surface; and (5) <S> Class E airspace at and above 3,000 feet MSL over the Gulf of Mexico from the coastline of the United States out to 12 nautical miles. <S> (e) <S> The requirements of paragraph (b) of this section do not apply to any aircraft that was not originally certificated with an electrical system, or that has not subsequently been certified with such a system installed, including balloons and gliders. <S> These aircraft may conduct operations without ADS-B Out in the airspace specified in paragraphs (d)(2) and (d)(4) of this section. <S> Operations authorized by this section must be conducted— (1) Outside any Class B or Class C airspace area; and <S> (2) Below the altitude of the ceiling of a Class B or Class C airspace area designated for an airport, or 10,000 feet MSL, whichever is lower. <A> First I assume this is for VFR flights and I assume this is for flight following. <S> In this case you would tell ATC that you do not have a transponder <S> but if that were the case I would doubt the controller would want to do flight following as they won't have your altitude information. <S> You are not required to contact ATC if flying VFR in Class G and Class E airspace. <S> One exception to the transponder rule is that if you are flying an aircraft that was certified without an electrical system. <S> These are usually very old vintage aircraft and they literally have no electrical system and no radio either. <S> If that is the case you will have to pre-coordinate with ATC and the control towers of the departure and arrival airport to let them know you have no transponder or radio. <S> The tower can use light gun signals to let you know you have clearance to land. <S> If you do pick up a transponder for your plane be sure to install an ADS-B out transponder as these transponders will be required beginning January 1, 2020.
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In the US if you are flying in Class G airspace or Class E below 10,000 feet you are not required to have a transponder.
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Has there been an aircraft with multiple type of engines? Has there ever been an aircraft that can fly using at least two different type of engines? For example, a piston engine and a turbine engine, or a piston engine and a electric motor. To clarify the question: It is not necessary to operate both engines at the same time. However the pilot must have the ability to switch from one engine to another engine while in the air. The engines must generate power using completely different mechanisms. VTOL/STOL aircraft (e.g. V-22, F-35) does not quality because the aircraft is simply directing thrust from the same engine elsewhere. The question is not asking about variants of an aircraft model where each variant is fitted with a different kind of engine. Both engines has to be fitted on the same airframe and operable at the same time. <Q> The Convair B-36 <S> The turbojets were used during takeoff and shut down during flight. <S> image source Wikimedia Commons <A> Wikipedia lists 27 "mixed-power aircraft" . <S> Most were prototypes or were never even built, the only ones I can see that made it to double digits in their production runs were: <S> MiG I-250 <S> (piston/motorjet, 12 built) <S> Martin P4M Mercator (piston/turbojet, 21 built) Ryan FR Fireball <S> (piston/turbojet, 71 built) SNCASO Trident (rocket/turbjet, 12 built) <A> I would say that any aircraft equipped with JATO capabilities fits into your description. <S> The only point it may not subscribe to is the first one, the pilot can not really switch between power sources although they can ignite the JATO rockets on command. <S> The space shuttle <S> (if you want to include that as an aircraft) was powered by both liquid fuel rockets and solid fuel rockets. <A> The Screaming Sasquatch is a 1929 Taperwing (bi-plane) with a P&W 985 Radial Engine that they strapped a GE J85 with 3,000lb-thrust to the bottom of: Source: EAA Vintage.org <A> The B-36 Peacemaker quickly comes to mind, using 4 turbojet engines to augments it’s six diesel radial engines. <S> A number of proposed aircraft made use of multiple, different types of power plants. <S> The X-30 National Aerospace Plane, a reusable runway to orbit vehicle, used turbojet, scramjet and rocket engines at various stages of its proposed flight into space. <S> The new SR-72 hypersonic reconnaissance airplane is rumored to use a proprietary turbojet and scramjet powerplant built by Rocketdyne. <S> an experimental French fighter called the Nord 1500 Griffon , making use of a hybrid turbojet and ramjet for high speed flight. <S> Even business aircraft attempted with hybrid propulsion. <S> The ill fated Gulfstream American Hustler , used a PT-6 turboprop engine at low altitudes and a jet engine at high altitudes in an attempt to conserve fuel. <S> During the postwar era, hybrid turboprops and jets did make a debut, particularly as a solution for the problems early jet aircraft had recovering aboard aircraft carriers. <S> The Ryan Aircraft FR-1 <S> Some types of aircraft have used multiple types of jet engines. <S> This has been a popular solution for VTOL capable fixed wing aircraft. <S> The Yakolev Yak-38 Forger made use of a single R-28 engine for forward flight and combined that with a pair of RD-38 lift engines for VTOL operations. <S> Another impressive design was the Dornier DO 31 prototype V/STOL cargo aircraft which made use of a pair of Rolls Royce Pegasus turbofan engines combined with no less than eight Rolls Royce RB162-4D turbojets mounted in the twin wingtip pods for control during hover. <A> The engines must generate power using completely different mechanisms. <S> If you allow your two engines to be to be built stacked one after the other, then fast jets such as Lockheed SR-71 <S> Blackbird switch between the turbojet and afterburner as speed increases. <S> Either could be considered an engine in their own right - a turbojet and a ramjet.
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Fireball was a hybrid powered fighter, looking much like a conventional WWII era piston powered fighter but had an additional jet engine in the tail of the aircraft to be used in high speed flight. Peacemaker had six Pratt and Whitney radial piston engine propellers and four GE turbojets.
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Is it possible for a fighter jet to shoot itself down with an IR missile? In this answer , it's mentioned that However, IR missiles (AIM-9 Sidewinder, AA-11 Archer, MICA IR, ASRAAM) do not emit any EMR that indicates they're incoming; they use a passive FLIR sensor to identify and track the heat source they were told to kill (they don't even require a radar lock; the seeker can be cued to a pilot's helmet, or it can be "uncaged" and will lock on to the most significant heat source in front of it ). Emphasis added. Given this, is it possible, given some very bad luck, for a fighter jet to fire an IR missile, only for it to get turned around somehow (for instance, by some sort of momentary combustion instability in its rocket motor, or by some very bad turbulence) and end up locking onto and shooting down the jet that fired it? <Q> Not really, it would take any of these missiles so long to turn 235 degrees (way more than 6-10 secs), which is generally the maximum burn time of most of their rocket engines. <S> Plus, if it did somehow, get turned around 235 degrees, the energy (airspeed) bleed from such a large turn would leave it without any energy to intercept the launch aircraft even if by some miracle it acquired an IR lock <A> Unlikely but possible <S> It might be possible assuming that the missile does not read or request any IFF signals. <S> If the motor on a missile were to malfunction enough or the missile was to experience enough turbulence to turn it around then <S> it would probably destroy the missile or leave it having a hard time tracking a target. <S> Maybe if it was fired at an aircraft that the managed to get behind the firing aircraft this could happen. <S> There was a large number of similar events with the first homing torpedos, however sonar based homing has a larger angle of view that the sensor can pick up. <A> Stores separation can be an aerodynamically tricky business, and getting torched with rocket exhaust is a good way to find yourself on fire. <S> While an IR guided missile will have a smaller rocket motor than a big radar-guided missile like the AIM-7 <S> that did Pete and Tank's <S> test Tomcat in <S> , it's not beyond the realm of plausibility that an IR-guided missile could still cripple an aircraft simply by failing to separate from said aircraft correctly during the launch sequence. <A> Highly unlikely. <S> It is however easily possible for two aircraft armed with IR guided missiles, which can nowadays acquire targets in the head on aspect, to shoot each other down.
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Yes, but not in the way you're thinking As a general rule, a missile shouldn't get turned around like that -- if it did so as a sustained maneuver, it'd be vastly short on energy and thus easy to evade in addition to being well out in front of the launching aircraft, making a "circular running missile" self-shootdown scenario improbable. However , it's still possible to shoot yourself down with a missile, even if it never locks onto you , as Grumman test pilot Pete Purvis and his RIO "Tank" Sherman found out the hard way during testing of the F-14 Tomcat.
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What are the limitations to adding wings with engines to a helicopter? I've probably seen this in science fiction and cartoons but never in real life. Rotor wing aircraft (helicopters) have numerous advantages over their fixed wing counterparts, and vice versa. For example, helicopters can take off and land vertically and do this almost anywhere. But fixed wing aircraft can fly further, faster and are more fuel efficient than helicopters of similar weight. What are the limitations to adding folding wings to a helicopter, each equipped with a turboprop or turbofan whose shafts connects with the helicopter fan blade for vertical take off? Once enough speed is gained from the vertical takeoff helicopter phase, the gearbox connects the turboprop or turbofan, they power it enough for it to generate lift at the fixed wings and when the wings are generating lift, the gear box disconnects the helicopter blades and they fold and are housed in the fuselage (like landing gear) to reduce drag. The fixed wing part of the flight takes over for faster speed, more efficient cruise and better range. The same process applies for landing. I know there are turbofan aircraft that are a cross, their advantages of fixed wing over rotorwing are limited and their wings do not fold. <Q> A very promising British design from the 1950s used both, a rotor at low speed and a conventional wing at high speed for lift creation. <S> This was the Fairey Rotodyne , a prototype for a flying bus to connect remote locations with a VTOL aircraft. <S> Its rotor was tip-jet-powered and burned a mixture of fuel and compressed air bled from two wing-mounted Napier Eland turboprops. <S> After take-off, power was switched to the propellers and the rotor was unloaded to minimize its drag at high speed. <S> This way, both lift-creating means could be optimized for their speed domain. <S> You will notice that the wing is unusually small while the rotor is unusually large. <S> This allowed both to operate at higher efficiency than wings or rotors which are designed to work over the full speed range. <S> However, the combination of the two weighs more than either a rotor or a wing, which reduced the possible payload of the Rotodyne. <S> Neither was meant to fold away because that would had increased weight even more. <S> Fairey Rotodyne (picture source <S> Ed Coates collection) <S> In the end, it was wavering British government support rather than any technical issues which limited the Rotodyne to a single prototype. <S> Today, the most promising solution seems to be a coaxial rotor with a separate source of thrust; either a propeller or jet engines . <S> The coaxial rotor is slowed down at high flight speed in order to keep tip Mach numbers below 0.9 and the lift asymmetry of conventional helicopters is no problem for a coaxial rotor design, allowing much higher flight speeds. <S> Folding a wing would not help much: When the wing is not needed (which is at low speed), its friction drag is low. <S> Folding the rotor, on the other hand, makes more sense but so far is limited to a helicopter on the ground in order to reduce its storage space on aircraft carriers. <S> Illustration 1B from US patent application 2015/0474290 A1 by Bell Helicopter Textron Inc. <A> The V-22 Osprey is quite close to what you describe. <S> The connections from the rotors to the fuselage are in fact wings. <S> During takeoff, it's a rotorcraft, and during flight, it's a fixed wing aircraft. <S> Rather than a gearbox, they opted for rotating engines. <S> The project was plagued by cost overruns, Its [The V-22's] production costs are considerably greater than for helicopters with equivalent capability—specifically, about twice as great as for the CH-53E, which has a greater payload and an ability to carry heavy equipment <S> the V-22 cannot... an Osprey unit would cost around \$60 million to produce, and \$35 million for the helicopter equivalent. <S> — Michael E. O'Hanlon, 2002. <S> Another aircraft similar to your idea is the F-35B. <S> Rather than foldable rotors, it has a lift fan which connects to the main engine when needed. <S> This aircraft was also plagued by cost overruns. <S> The harsh reality in engineering is not that things are impossible, but that they are extremely expensive, and by combining multiple functions in a single airframe, you will always have to find a compromise between either function. <S> Both the F-35B and V-22 are very heavy aircraft due to the engineering complexity, and as such can carry less payload than more dedicated concepts. <S> However, this is deemed acceptable because the U.S. Navy likes their aircraft extremely versatile. <S> There is also the question of demand. <S> For decades, there has been the idea that aircraft need to be as versatile as possible, but whether this will be the case in the future, remains to be seen. <S> Finally a technical remark. <S> The most difficult part is transitioning from forward flight to hovering. <S> Rotor blades are very flappy, so how you will manage to deploy them during forward flight <S> (when centrifugal forces do not yet straighten them out, and when the lift vector may be in any direction unless you can carefully control their orientation) remains a large engineering challenge, especially if you want to keep the weight of the aircraft low. <A> the gear box disconnects the helicopter blades and they fold and are housed in the fuselage <S> Stopping the rotor is the hard part. <S> Rotor blades aren't terribly stiff and rely on centrifugal force to keep them straight in normal flight. <S> Most blades are hinged and free to flap up and own. <S> Just before the rotor stopped, there would be slow moving blades pointing forwards. <S> Unless it was perfectly aligned, the 100mph+ airflow would fold it back over the hub. <S> In tests where the rotor was merely slowed a little, this is seen as very large fluctuations in blade lift with angle of attack. <S> Quite a lot of research was done into stopped rotor designs, usually involving low aspect ratio rotors that looked more like wings, but I don't think they ever flew. <S> One hybrid <S> I quite like involved a wing on only the retreating blade side, and a lifting tail to counter the pitch-up with speed tendency of a flapping blade. <S> I'm not sure why that has never been used.
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Your concept may be capable of faster travelling and higher payloads than the V-22 (which rotors are too small for heavy lifting and too big for fast flying), but the real question is whether the added weight due to the complexity of this concept will offset the theoretical performance gain. Folding in flight has only been studied conceptually .
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Why was the Concorde painted white and not black? It's well-known that the stated reason the Concorde was painted predominantly white was to mitigate heating problems . However, given that the source of the Concorde's thermal woes wasn't excessive exposure to solar radiation, but, rather, direct conduction and convection of compression heat, I'm confused; in that case, shouldn't the Concorde have been painted black (or nearly black), like the SR-71 , to better radiate heat away? <Q> There is a discussion on it here <S> that's worth reading but in short the requirements were just different. <S> A few of the key points, The black color on the SR-71 offered some night camouflage in addition to its heat dissipation <S> The Concorde had an Aluminium airframe while the SR-71 had a primarily titanium airframe which could lead to different coating types. <S> The Concorde was a commercial aircraft many of which are often painted white thermal benefits aside they may have simply been keeping with what they usually did. <S> The SR-71 flew substantially faster than the Concorde and had different thermal requirements. <S> The hottest point on the Concorde was the nose 127°C which was actually cooled by fuel being pumped through as a coolant. <S> The hottest point on the SR-71 was the cockpit window which cooked in at 327° <S> C again, very different requirements thermally. <A> Concorde's average skin temperature was 92°C (365K). <S> Calculating the black body radiation using the Stefan Boltzmann law we get 1006W/m². <S> This the maximum heat flux possible with perfect radiation, and very similar to the heat flux of solar radiation, which is also about 1kW/m² at the earth's surface in the absence of clouds (and a bit higher at Concorde's typical cruising altitude.) <S> However, as others have pointed out, at these temperatures Concorde would radiate in the far infra red, and it is perfectly possible to have a selective paint that appears white in the visible region (reflecting much of the heat of sunlight) while also radiating in the infra red region. <A> The Blackbird was black so it could absorb radiation, not so it could emit radiation. <S> Look at the Blackbird's predecessor, the A-12, it is fairly easy to find pictures of the A-12 with polished or partially polished finish. <S> The Blackbird and A-12 moved to a radar absorbent black finish for reasons of observability, flying at the edge of space means a darker surrounding than lower in the atmosphere so the camouflage requirement is different than say a fighter jet. <S> Any thermal emissions that do occur do so well outside the visible spectrum. <S> To reach the point at which it is beneficial to thermally dissipation for the aircraft to be painted black is to reach the point that the aircraft emits more energy as radiation than it absorbs in the visible spectrum. <S> At that point the black aircraft would be brighter than a white aircraft. <A> Good question. <S> There are two main reasons for the Concorde's specific coloring: Heat absorption and heat emission. <S> The key to its color scheme is in the materials used in construction of each plane. <S> The Concorde was made of aluminum, which emits heat far more quickly and effectively than the SR-71's titanium skin. <S> Contrary to popular belief, the plane will become ductile and lose structural integrity at far lower temperatures than the metal's melting point, and preventing the metal from reaching these temperatures is a key reason for the paint colors of each aircraft. <S> Aluminum becomes ductile and unacceptably weak at higher temperatures, but would rarely reach them at the Concorde's cruise speed, as the metal reflects/releases sufficient heat so that the paint can can do a more proactive job of keeping heat absorption at a minimum. <S> If titanium had similarly good heat dissipation capabilities then I am confident that it too would have been white. <S> However, titanium at speeds around the Blackbird's cruise range would absorb far too much heat for it to release, so the black paint would actually be superior in terms of heat dissipation to compensate for titanium's natural characteristics. <S> The SR-71 however could not release heat as quickly as aluminum, so the paint was designed to aid it in that regard. <S> Hope this helps, sorry about the formatting I am in a rush so if there was anything conceptual <S> I left out then please comment. <A> Concorde was a civilian commercial vehicle. <S> It's mission is not 100% flying, but also embarking and disembarking of passengers, waiting for ATC permission, etc. <S> This means, it spend considerable time, on the ground, on low power, not heated by the airflow - but heated by the sun. <S> For this part of the mission, white paint is vastly superior. <S> SR-71 was a military aircraft and it was optimized for one thing only - the flight. <S> Sunbathing at the airport was not an issue, it was kept in a hangar for as long as possible anyway.
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Short answer shorter, the aluminum on the Concorde didn't get hot enough for the aluminum to lose integrity, so white was the better option in terms of preventing the metal from reaching those critical temperatures.
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Do modern aircraft require rudder input in order to perform a coordinated turn? With today's state-of-the-art electronic systems in modern aircraft, do aircraft equipped with autopilot systems, still require pilot rudder input to keep a turn coordinated? For the context, I'm assuming the pilot is hand-flying the aircraft so the autopilot must be at least partially disengaged to let the pilot manually initiate and perform the turn via the yoke/stick, but still make the rudder use unnecessary or optional. For example, would an F-16 pilot still need to apply the rudder during a turn? If the military case is not generic enough, how about an airliner pilot? Or a GA aircraft like the Cirrus SR22? <Q> Most transport aircraft use yaw damper systems to take care of minor rudder inputs. <S> Most autopilot systems are actually only 2-axis - pitch and roll since the rudder's job is only to keep the tail lined up behind the nose. <S> The yaw damper is a separate "autopilot" system and has limited authority, sufficient to deal with minor yaw disturbances, dampen dutch roll, and counter adverse yaw from the ailerons and is active all the time whether the autopilot is on or not. <S> Generally in a jet, once through the departure profile, feet are on the floor even when hand flying. <S> They are only on the pedals to steer the nosewheel during the takeoff and be ready in case an engine quits. <S> On a swept wing aircraft the yaw damper is essential; if the yaw damper is off and yaw disturbances occur, dutch roll motions can start and if the pilot tries to respond with rudder inputs he almost always can't stay in phase and things get exciting. <S> Because of this criticality the Y/D is usually dual channel. <S> One of the tests done on production aircraft is to induce a large yaw movement with both YD channels off to get a dutch roll going, then engage each YD channel and make sure it stops the dutch roll. <A> In my Cessna Cardinal, the rudder is cross coupled to the yoke through some kind of spring/bungey cord system (I don't have the manual handy), so I can fly with my feet off the pedals most of the time. <S> That's from a 1968 design, keeping turns coordinated with no autopilot needed. <A> At positive angles of attack, the down aileron is more in the relative wind than the Up aileron (due to blanking by the wing in front of the aileron). <S> An aircraft that is at zero AOA, (like a fighter unloaded, in a zero-G ballistic arc) requires no rudder. <S> To avoid this problem, in modern aircraft, like the F-15, for example, differential stabilator is used to mitigate this issue. <S> The stick is mechanized so that the further aft it is, the more any lateral motion is directed to generating asymmetrical stabilator deflection, rather than aileron deflection. <S> SO, at high AOA (assuming that stick position is an accurate indicator of AOA), when the pilot moves the stick to the side, the ailerons deflect very little or not at all, but the stabilators at the tail deflect asymmetrically. <S> The F-16 flight control surfaces are completely computer controlled, so pilot inputs are interpreted as commands for aircraft movement. <S> The computer then determines, based on all known factors (AOA, Airspeed, etc.) <S> what to do with all control surfaces (including the leading and trailing edge flaps) to get the airframe to move in the manner commanded by the flight control inputs. <S> I never flew the F-16, (perhaps someone who did can clarify), but my guess is that there is no need to depress the rudder pedal in the F-16 to coordinate a turn - that the computer automatically determines how much rudder, or differential stabilator, should be deflected to coordinate the requested roll rate. <A> I once spent a couple hours flying a full-motion 737 simulator with an instructor for that type. <S> My previous flight experience comprised entirely one hour at the controls of a Cessna 180 (cruise only) and hundreds of hours of Microsoft Flight Simulator with just a joystick, so I was pretty excited to show off that I knew, in theory, what a coordinated turn is. <S> The very first flight set us up in a situation necessitating a decisive turn to enter the traffic pattern correctly. <S> Being somewhat overwhelmed (hand-flying a 737 in a real sim is a fairly big leap from on a desktop computer), I of course completely forgot I had rudder pedals until halfway through the turn. <S> The moment I even brushed my foot onto one, the instructor said, and I remember this exactly, "woah there; we only use those if we want to make all the passengers sick!" <S> We continued the session hand-flying approaches in all kinds of weather in all kinds of places. <S> I never once needed to touch the rudder pedals again. <S> The modern Boeing jets all have the ability to use their yaw-damper systems to coordinate turns (although turn coordinating is physically not the same as yaw damping). <S> The details of the implementation depend on the model. <S> For example, 747s coordinate turns only with the flaps down, while 777s and C-17s always do.
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With a Y/D system the only time a pilot really needs to make a rudder input in flight is if an engine quits, because the yaw damper's authority is not sufficient to counter asymmetric thrust. The need for rudder to coordinate a turn is directly dependent on Angle of Attack (AOA).
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Why do narrowbodies have longer life than widebodies? Is it fair to say that narrowbody aircraft have a longer life than widebody aircraft? This is the conclusion drawn from a report written by Dick Forsburg from Avolon (.pdf), where he says that the average life of a narrowbody is 26.6 years, while the average life of a widebody is 24.6. Is it generally accepted that narrowbodies have a longer life than widebodies? If so, what are the reasons for narrowbodies having a longer life that widebodies? <Q> The author does a very good job explaining the jet market. <S> The key take-away is that it's all about economics. <S> Pressurization cycles are a big factor in structural fatigue. <S> But that's not the primary reason for retirements. <S> Profit is generically income minus costs. <S> Income for aircraft is maximized by flying as much as possible (high utilization) with the highest load factors possible. <S> Costs are primarily driven by capital depreciation, fuel, crew, and maintenance. <S> The shorter lifespan he identified for widebodies is driven by a few key factors: Widebodies are a smaller percentage of the total fleet, so that evena few "early" retirements will cause a larger shift in the average. <S> Widebodies are suited primarily for long-haul, high density routes. <S> So a shift in travel patterns can quickly leave a routeunprofitable. <S> Covering that reduced demand will often mean shiftingto a smaller aircraft to keep the load factors up. <S> Narrowbodies havemore inherent flexibility. <S> And what I would say is one of the most significant factors <S> is theshift of widebodies from 4 engines to 2 engines over the last 20-25years. <S> It's not a fast process as widebody construction is not veryhigh rate, but the cost benefit of 2 engine widebodies (B777, A330,A350) means a lot of 4 engine aircraft (B747, A340) have beenretired in the last 10-15 years. <A> The author has a masters degree in marketing, so please do not expect an expert in statistics. <S> Adding up some numbers without correcting for effects will lead to wrong conclusions. <S> When almost all 707s and DC-8s are retired already but one quarter of all DC-10s and half of all A300s are still in service, it is simply too early to give an "average" retirement age for wide bodies. <S> It would be better to only compare aircraft from a specific time period, like the 1980s, but to simply add all up will produce misleading results since wide bodies are not around long enough and have been introduced with high-bypass fan engines already, so they can still be operated profitably, if only as freighters. <A> Airframes are generally designed to be economical to operate to 80000 cycles, but often the airframes start to require patching and reinforcement of the structure at around 40-50000 cycles to avoid increasingly onerous inspection requirements. <S> Airframes get retired when the cost of incorporating the structural reinforcements exceeds the benefit. <S> Regional Jet aircraft that do a cycle every 1.2 hours suffer the most from this and many get retired after only 20 years of service because it's not worth patching them up. <S> In general, the longer the average cycle time, the more years that can be squeezed out of an airframe. <A> As stated in the comment above, if you mean economic life the reference you quote already proves the answer in the current environment. <S> The reason narrowbodies are currently kept in service longer than widebodies is due to the extraordinary demand for narrowbodies due to extreme growth of LCCs and competitors following a period of world wide deregulation. <S> If you can't get a new aircraft you keep using the old one, even if it is not as efficient as some newer unavailable model. <S> This environment may change at some point, and the answer will change with it. <S> If you mean design life, commercial aircraft are typically designed to last 30 years though this has been lower in the past. <S> A narrowbody's life is much tougher than a widebody's so they are built tougher; they have a higher cycle capacity built into them. <S> A typical widebody would wear out rapidly if exposed to typical narrowbody usage. <S> If you look at the 747D made for JAL/ANA to use on domestic routes, it not only was packed with a larger than normal number of seats, increased gross wt and reduced fuel capacity, it was also reinforced to endure the additional wear. <S> Its design cycle life was 52,000 compared to a standard 747 at 24,000. <S> It also had derated engines to lengthen their useful life.
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In many ways, narrowbodies may "wear out" faster as they typically fly shorter routes and accumulate more cycles in a shorter period of time. The cycle length is the biggest factor I think. Airplanes get retired when operating them is no longer profitable.
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What is this plane doing flying back and forth near Sydney at night? As I write this, a mystery plane is going back and forth over south Sydney, Australia: The plane took of at Bankstown, flies straight from West to East and back, with a distance between paths of about 600m. It maintains a steady height of ca. 4100ft at a speed 120kts. It is a Cessna 404, but flightradar24 provides no call sign or any other ID. I noticed the plane ca. 00:30 on 10 May 2018, as it was at its 8th "lap", and took the above screen shot. It may have gone on for a while, perhaps for an hour or more. As it's night, no markings on the plane are visible. It has the usual white flashers on the wing tips and the top of the rudder, and the red and green marker lights. The plane is quiet loud (prop), but that's most likely only because it's night and there's no other sound sources in my suburb. Does anyone have an idea what that plane could be, and what the purpose of such flights could be? Obviously, they (whoever they may be) waited until after the curfew of Kingsford Smith (23:00) to not get in the way of commercial traffic. Might be similar to this question , but I have no way of knowing whether it is the same. Italy and Australia are different countries. E.g., to my knowledge, Europe doesn't permit Police planes or helicopters above urban areas without reason. Australia does. <Q> With a path like that its most likely surveying something . <S> There are a handful of 404's registered in Australia for areal survey, you can find them on this list. <A> Sometimes planes are hired by the cell phone companies to scout good places to put a cell tower. <S> There could be any number of reasons that someone would fly parallel pattern route. <A> If the plane is operational at night it is a LiDAR capture. <S> There is a very limited scope for Thermal Infrared (TIR) and as such those captures are usually spot captures rather than swath <S> (BrEnglish swathe) capture you are seeing here. <S> Visible and Near IR (NIR) imagery must be captured during daytime whereas some TIR must be captured at night. <S> Although LiDAR can be operated any time the weather permits many crews opt for nighttime to avoid traffic, especially in congested airspace. <S> These sort of missions are flown daily all over the world. <S> In Australia there are dozens of planes engaged in aerial survey of all kinds, not including mineral exploration in WA. <S> In the USA and Europe aerial survey craft number into the hundred in the air each day. <S> While these missions occur all over the country, they will have a local transponder in controlled airspace for flight following. <S> Based on the line lengths and spacings as well as the aircraft altitude, I would speculate that this is a very high precision survey. <S> Data of this quality would be suitable for building mapping, very high resolution <S> DEMs and in cases where cutting edge technology is present, <S> infrastructure mapping <S> I'll get you some links on likely technologies and operators later.
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Flights that have that kind of pattern are usually doing some kind of aerial photography. Another possibility is that the plane could be collecting LIDAR data to get a 3D model of the city.
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When to switch from ground to tower frequencies at controlled airports in the US? I have heard that you can switch to the tower frequency once you are at the runway hold line and are ready for takeoff without getting permission from ground control to switch frequencies. Is this always true or does the procedure vary for different airports? <Q> While I acknowledge the answer by GdD to not change frequencies until instructed, that is at odds with my experience. <S> When I call Ground, then request and receive taxi-instructions, I stay with Ground to the runway hold short line. <S> I've never had Ground give me an explicit instruction to switch to Tower. <S> When I start my run-up checks, I switch to Tower (unprompted) to start hearing what is happening in the airspace. <S> When my run-up is complete, I call Tower with a "ready for takeoff" . <S> I've never had Ground, Tower, or any Instructor <S> tell me differently. <S> I've never observed another pilot wait for an explicit frequency change instruction from Ground, and I believe that is the way I was taught. <S> Note: <S> this only applies when you've taxied to the hold-short with Ground. <S> If Ground tells you to switch earlier, do it. <S> If you want to switch earlier, request it. <A> I have found this AIM 4-3-14a which I believe answers my question: AIM-4-3-14a: <S> Pilots of departing aircraft should communicate with the control tower on the appropriate ground control/clearance delivery frequency prior to starting engines to receive engine start time, taxi and/or clearance information. <S> Unless otherwise advised by the tower, remain on that frequency during taxiing and runup, then change to local control frequency when ready to request takeoff clearance <S> This seems to suggest that it is OK to switch to tower once you have completed the runup and are ready to takeoff at least in the US. <S> Also interesting here is that it says that you should contact clearance/ground prior to starting your engine. <S> I have never heard of that before. <A> If you are under control of ground you only switch to another frequency when directed, or are granted permission. <S> They'll tell you "Contact tower on xxx.yy", for example. <S> You may need to shut down your avionics to start up your engine, especially common in light singles, in which case you ask permission for that as well. <S> If ground goes off of the air or you have trouble contacting them you can change to a different frequency for a radio check, or if there's some sort of emergency requiring changing frequencies to resolve then do so, it's hard to think of a realistic case for that; if you have an emergency on the ground then ground is best placed to help you.
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You might ask to change, say you only have one radio and you want the latest ATIS, in which case you request to change, and wait until they give you positive indication that is okay.
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How do banner tow planes coordinate with air traffic control? I tried searching with terms I think were correct around the net, but no satisfying results. I have seem many times small planes circling around when there is some special event going on. They have advertising banners trailing behind them. For busy airspaces like the San Francisco bay area where you just have to glance up to spot a plane, how does this work with ATC? Do these planes have to stay under certain level that is not controlled by ATC or ATC just allocates them a block of area and declares it off limits for others? Do they have to declare their intention of circling special event areas given the security concerns and large gathering of people? <Q> An aircraft conducting a banner towing operation must have prior approval (written letters of authorization) from any ATC authority they will be conducting operations prior to the banner tow operation. <S> A copy of this letter must be carried on board the aircraft. <S> The local FSDO must also be involved (which will handle the 7711-2 application). <S> The first thing you need to do is to file Form 7711-2 <S> "Certificate of Waiver or Authorization Application" detailing all regulations which will be violated (minimum safe altitudes/separation, etc). <S> From the INFORMATION FOR BANNERTOW OPERATIONS FAA/FS <S> -I-8700-1 : <S> Conduct all banner tow operations in VFR weather conditions defined by Title 14 of the Code of Federal Regulations (14 CFR) <S> part 91, section 91.155. <S> Operations shall be conducted only between the hours of official sunrise and official sunset. <S> The certificate holder shall obtain the airport manager’s approval to conduct banner tow operations at each airport of intended operation. <S> ... <S> Operations outside the geographic area of the issuing FSDO will be coordinated with the appropriate jurisdictional FSDO in advance and the operator will comply with all special provisions imposed by that office. <A> They would coordinate with ATC beforehand to fly low & slow near congested areas. <S> For example, go to skyvector.com and enter KSFO and KOAK as a flight. <S> You can see all the controlled airspace, the levels it starts at and how high it goes. <S> I don't know where the area you are discussing is in relation to the controlled airspace <A> It depends what airspace they are in. <S> Typically most airports in major cities with class B and class C airspace have surface areas and then shelves extending out as far as 30 NM from the central airport. <S> Below these shelves is either Class E and Class G airspace which either will not require ATC clearance to operate in or is uncontrolled altogether. <S> Here, a banner tow aircraft can operate without a flight plan, or flight following with relative ease. <S> If you look at the airspace around San Francisco, you’ll notice that most of it are shelves, which banner tow aircraftcan fly under If banner tow ops are necessary within the surface areas, any licensed commercial pilot may operate in these areas with the appropriate ATC clearance and be equipped with a transponder with altitude reporting capability. <S> Some major airports may request you pre arrange this flight with ATC prior to flight to allow controllers to anticipate flight activity by a banner towing aircraft and route their traffic accordingly.
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Notify appropriate airport officials in advance when banner tow operations will be in close proximity to each non-towered airport.
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Will the steep beta descent mode become illegal for new aircraft? The PC6 is a popular skydiver carrier due to its ability to use steep nose down beta descent to get back to the ground quickly, even beating free falling skydivers. ( YouTube ) FAA AC25.1155x (I only saw the draft) proposes that a "means to prevent intentional or inadvertent selected of reverse thrust or propeller pitch below the flight regime" be required, which cannot be overridden. The intention is to prevent several accidents resulting from said deployment. The lockout means must not degrade landing performance, so the intent is not to eliminate beta entirely. Does this mean that no new aircraft can be certified that has a descent mode from altitude similar to the PC6? <Q> I wouldn't call it a "descent mode from altitude". <S> It's considered to be a dangerous and foolish practice to operate an engine in ground beta (generally coming back into DISCING - blades flat) while in flight to get steep descent rates. <S> If the prop doesn't want to come out of ground beta, you are dead meat. <S> When the Twin Otter was in production, it was an open secret that demo pilots were using DISCING to get crazy steep approaches to impress customers. <S> After a couple exciting events, flight ops finally put an end to it. <S> Some airplanes already have ground beta lockout systems. <S> Is this a proposal to mandate a system for the PC6 specifically? <A> I found this FAA Working Group paper on it <S> https://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/taepiht14-112699.pdf <S> (28 page paper, poorly scanned PDF, I am not copying any sections here.) <S> It looks to me under the Recommendation section that are proposing putting the plane into beta just be made a seperate distinct action such that the crew cannot accidentally go into beta. <S> They must go to Flight Idle, then beta could be allowed. <S> I am not seeing any follow up either, <S> so I don't know if the AC was published. <A> I just came across this . <S> AOPA is a reliable source but it is not a reference to a regulation. <S> Beta mode is only available for ground operations. <S> Many single-engine turboprops have low propeller ground clearances, so it is vital to minimize beta thrust in contaminated areas to avoid engine and prop damage from dirt and debris. <S> A few creative pilots have tried using beta thrust in flight to increase descent rates; however, some of those who have tried that trick wound up at the bottom of a smoking hole. <S> The use of reverse thrust in flight is strictly prohibited in virtually every type of aircraft. <S> That’s why most turboprop propeller controls have in-flight reverse-thrust lockout systems.
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Unless it’s approved for your aircraft, don’t even think about it.
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What is the correct ATC phraseology in the US for an immediate - no delay takeoff? Just wondering - what's the correct ATC phraseology for a takeoff where a plane does not stop first after lining up with the runway centerline before starting their takeoff roll? Redwood five-two-six-three, runway three-zero cleared for takeoff, no delay. Redwood five-two-six-three, runway three-zero cleared for immediate takeoff. <Q> The FAA AIM and ATC (7110.65) documents don't mention the ICAO equivalent. <S> But I found it in the US AIP : 34.1 (...) <S> At times a clearance may include the word “IMMEDIATE.” <S> For example: “ CLEARED FOR IMMEDIATE TAKEOFF. ” <S> In such cases “IMMEDIATE” is used for purposes of air traffic separation. <S> It is up to the pilot to refuse the clearance if, in the pilot’s opinion, compliance would adversely affect the operation. <A> Assuming US/FAA: <S> The Pilot/Controller Glossary only has one instance of "no delay": MINIMUM FUEL <S> − <S> Indicates that an aircraft’s fuel supply has reached a state where, upon reaching the destination, it can accept little or no delay. <S> This is not an emergency situation <S> but merely indicates an emergency situation <S> is possible <S> should any undue delay occur. <S> "Immediate takeoff" doesn't exist, either, but we do get <S> IMMEDIATELY <S> − Used by ATC or pilots when such action compliance is required to avoid an imminent situation. <S> We can cross-reference this with the Skybrary entry for Immediate Takeoff : <S> When given the instruction ‘cleared for immediate takeoff’, the pilot is expected to act as follows: <S> At the holding point: taxi immediately on to the runway and begin a rolling take off without stopping the aircraft. <S> If it is not possible to begin taxiing onto the runway at once or if take off performance calculations mean that a standing start is necessary, then the clearance must be declined If already lined-up on the runway: commence take-off without any delay. <S> If this is not possible for any reason, the pilot must advise the controller immediately. <S> So that suggests that "immediate takeoff" is more standard. <S> If the P/CG doesn't technically define either phrase then I can suppose that they use "no delays" to avoid the knee-jerk <S> "I must do something" to "immediately". <S> For "no delays" you can always easily respond "unable" and wait until the next plane lands. <A> According to the ICAO Doc <S> 4444 14th ed. <S> (Procedures forAir Navigation Services - Air Traffic Management ) <S> They mention a clearance for "immediate take-off" in section 7.8.3.4: <S> 7.8.3.4 <S> In the interest of expediting traffic, a clearancefor immediate take-off may be issued to an aircraft before itenters the runway. <S> On acceptance of such clearance the aircraftshall taxi out to the runway and take off in one continuousmovement. <S> I don't see any reference to "take-off, no delay" or "cleared for immediate take-off" in the FAA ORDER JO 7110.65W (air traffic control procedures and phraseology). <S> I believe both are correct with ATC opting to use "Cleared for take-off, no delay." to shorten their transmission to save time. <A> There's also the option of expedite . <S> https://www.faa.gov/air_traffic/publications/media/pcg_4-03-14.pdf <A> Here's one from the field , TOWER: <S> Southwest 3828, Midway tower, runway 31C, line up and wait. <S> Don't plan on stopping . <S> SWA3828: <S> 31C line up and wait, Southwest 3828. <S> TOWER: <S> Southwest 3828, traffic holding in position on the crossed runway, traffic on 3-mile final for the crossed runway, no delay please . <S> Turn left heading 250, Runway 31C, cleared for takeoff. <S> The wind 060 at 9. <S> SWA3828 and DELTA1328: <S> Heterodyne <S> What follows the heterodyne is what makes this one famous, but the answer to your question as plays out here, is the controller intentionally used informal language in his advisory "don't plan on stopping" and the admonishment "no delay please".
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EXPEDITE− Used by ATC when prompt compliance is required to avoid the development of an imminent situation. My experience has always had the clearance be "no delays".
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What is the average angle of attack of GA airplanes during takeoff? What is the average angle of attack of GA airplanes during takeoff? <Q> Depends on how slow you are going at rotation, and how aggressively you rotate. <S> Stalling AOA of most GA wings is somewhere in the region of 14-16 degrees and on takeoff it shouldn't get above 10ish to have adequate margin. <S> The issues over taking off with frost is due to the frost reducing stalling AOA to an unnaturally low angle, say 9 degrees, so that the pilot gets a surprise during a normal pitch up. <A> AOA is unknown for most GA airplanes. <S> The Icon A5 is <S> one of the few airplanes to have one <S> (video here ). <S> 5-10 degrees will be shown on the attitude indicator. <S> We go more by speed tho, Vx and Vy. <S> Values can be found in the Pilot Operating Handbook that will be in the plane. <S> In a Cessna Cardinal for example: Vy @ 6,000 ft / 2,500 lbs <S> 92 MPH IAS Vx @ <S> 6,000 ft / 2,500 lbs 69 MPH IAS <S> This page sums up the characteristics for a Cardinal nicely. <S> This chapter of an e-book, "See How if Flies" goes into Angle of Attack nicely, trimming the airplane for an AOA, and even has a chart with some typical AOA numbers vs other numbers. <S> From av8n.com : <A> Your question title says AOA during Climb , but your question says during takeoff . <S> In normal climb procedures published for all aircraft, including General Aviation (GA) aircraft, it is recommended that climbs be flown at the airspeed that produces or generates the maximum possible rate of climb, this is normally referred to as $V_X$. and it is calculated based on gross weight to put the aircraft at the angle of attack (AOA) that produces the maximum excess power. <S> This occurs at the point where the ratio of Lift to Drag is at a maximum $(L/D)_{Max}$ . <S> SO, the answer is <S> the AOA Is that AOA that produces maximum excess power or $ <S> (L/D)_{Max}$.
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About all that can be said about AOA during takeoff is that it starts out very low, (in tricycle aircraft anyway, in tail dragger it starts out high until the pilot pops the tail off the ground) then, at rotation, increases to something higher than climb AOA, but lower than stall AOA, then decreases as the aircraft accelerates towards climb speed. There is not an AOA indicator in most GA airplanes.
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Why would the Speedbrake be required for such a long time on approach? As far as I was aware, the Speedbrake is designed to slow the aircraft down. On landing, I do understand why they are required. Once the aircraft has hit the tarmac, they are deployed to 1) slow the aircraft and 2) prevent the aircraft from bouncing up and down. The airflow over the wing increases doesn’t it? To ‘push’ the aircraft down, as I say, preventing it from jumping up and down. I have (7 hours ago) just landed on a B757, but the Speedbrake was up pretty much for 70% of the descent and approach. Thinking back to my previous introductory paragraph, the reasoning must have been excessive speed, no? Or a need for the aircraft to slow down dramatically. Is this the case, or am I missing something obvious? I know Air France flight 447 considered deploying the Speedbrake when their Airbus gave them faulty warnings of speed and altitude; it was advised then that this would have been completely the wrong thing to do. I have never seen it before, as much as I did today on descent, and I wonder why the Speedbrake was required for near on 70% of our approach? <Q> There are two reasons I can think of off the bat: <S> Its possible the controller asked them to hold a slow speed due to increased traffic ahead. <S> The brakes may have been deployed to match the speed requested. <S> I have heard this called on occasion over the radio in the terminal area I fly. <S> The controller cleared them for a steeper decent than usual <S> this would cause them to potentially deploy the speedbrakes to make the descent rate. <S> This article discusses it in reference to small planes <S> but idea is the same. <S> And another article by a CFI here . <A> Those are spoilers...not speed brakes. <S> They do increase drag, but their primary function is that they kill lift. <S> They allow the aircraft to lose altitude rapidly without pointing the nose downhill and picking up speed. <S> You will also see them deploy upon touch down. <S> At high speeds they increase drag and thereby aid in deceleration, but again they kill lift making the weight on wheels higher allowing for much more effective wheel braking. <S> In the case you mention, the aircraft could have been held at a higher altitude longer than desired, and the pilot simply used them to get back on schedule. <S> Here is an example of a true speed brake. <S> The sole purpose being to increase drag. <A> This is especially true on final approaches, where the approach glide path may be steeper than the aircraft can descend with idle power and maintain a constant airspeed. <S> Another more legacy reason was in the early days of jet aircraft, centrifugal flow and early axial flow turbojet aircraft had poor fuel control systems and could not increase engine rpm very fast. <S> In some aircraft, it could take 20 to 30 seconds to accelerate the engine from idle to full power. <S> As a result, flying approaches in idle was very dangerous. <S> In these cases speed brakes were used to allow the aircraft to be flown on normal final approach glide path angles with the power set at higher, medium throttle positions so that unexpected power requirements (e.g., for go-arounds) could be satisfied in less time. <A> Those are "flight spoilers" which may be standalone or may be the landing lift dumpers doing double duty, or a combination thereof, and are used to increase sink rate, not as speed brakes as such. <S> They were being used there because the descent profile in the arrival clearance was steeper than an engines-idle glide. <S> There are times when you have to use them <S> but in general you try to avoid using them because when deployed you "wasting" energy and are below the most fuel efficient descent profile. <S> Some airlines discourage pilots from using them unless really necessary because they can alarm passengers. <S> You won't generally see them on final approach because the idle descent with gear and flaps down is more than steep enough so that some power is required, and on some jets there is a limitation that requires you to be somewhat above Vref (flaps down approach speed), say Vre +15 knots or something like that, to deploy them. <S> If you see flight spoilers being extended on final with gear and flaps down, somebody probably messed up.
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Speed brakes are often used on aircraft that are very clean (i.e., have very low drag), and, as a result cannot descend at a steep enough glide angle even with power at idle to satisfy minimum descent gradients for some specific phase of flight.
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Are there any data on the safety rate of gliders vs single-engine GA aircraft? Can anyone point me to statistics on the safety record of gliders vs. single engine general aviation aircraft? <Q> I had three days to burn so I took a look.) <S> Comparative data was very difficult to find beyond accident counts, so determining relative safety is problematic. <S> No one that I could find tracks or estimates the number of flights/hours for gliders, even the Soaring Society of America <S> , so this is all interesting but essentially meaningless. <S> Even if such data existed, the difference in use models would cause problems making a fair comparison. <S> So now that I've told you this was a waste of my time to compile <S> , I will make you waste your time to read. <S> If you could extrapolate single mode pilot certificate counts to a common usage basis, flying a glider is 2.5x safer than flying an airplane, but of course you can't. <S> NTSB accident count for 2017 shows 56x more airplane accidents and 90x more fatal airplane accidents than glider accidents. <S> 271 fatal and 972 non-fatal GA airplane accidents, total 1243 <S> 3 fatal and 19 non-fatal GA glider accidents, total 22 <S> US Civil Airmen Statistics shows 18x more airplane only pilots than glider only pilots, with 40-80% of both numbers muddied by multiple certificate pilots. <S> 14k registered glider only pilots 24k registered glider pilots with multiple certificates <S> 260k registered airplane <S> only pilots, excluding ATPs 190k registered airplane pilots with multiple certificates, excluding ATPs AOPA had a report for 2009 for all general aviation where the accident rate per 100k hrs is 7.2, and a fatal rate for the same of 1.33. <A> I looked at glider accidents for the last 18 years. <S> Tow accidents resulting in stalls or loss of control is another critical phase of flight it seems. <S> There are different tows like car, wench and of course tow plane. <S> (I am not a glider pilot but ATP, CFI fixed wing.) <S> One thing gliders have going for them is the slow stall and sink rate. <S> So even an off field landings should be survivable as the speeds are slow. <S> On the other hand there is not a lot of structure around you. <S> High performance gliders put the pilot stretched out in the very front of the air frame. <S> Fiberglass or Carbon fiber does not bend and absorb impact, it reaches it's limit and ruptures. <S> Aluminum airfares typical of powered fixed wings tend to bend and absorb some energy. <A> I found a blog post that answers the question by using commercial aviation as a metric. <S> General aviation (US) 1 death in 64,000 hours 156x as dangerous as commercial aviation <S> Flying sailplanes (Germany, France) 1 death in 50,000 hours 200x as dangerous as commercial aviation <S> The following graph shows the relative difference between sailplanes and powered planes: Charts and sources at this link .
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It is hard to compare because of hours flown... There are a lot of non fatal accidents. Fatal glider accidents (no particular order) seems to be in-flight break up, stalls and collision with ground (typically in mountainous terrain).
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Why is it 'aileron right and elevator up' with a front-right wind in a tailwheel airplane? Question: How should the flight controls be held while taxiing a tailwheel airplane into a right quartering headwind? Answer: When taxiing a tailwheel airplane into a right quartering headwind, use up aileron on the right hand wing and up elevator. My answer: put the control to the right should be enough, why bother the elevator? <Q> The wind could pick up the tail in tailwheel aircraft which is why they recommend elevator up to prevent that scenario. <S> If the wind is really bad <S> the tail could possibly get higher than the wings and flip the airplane over. <S> This will not be an issue for tricycle gear aircraft <S> so elevator doesn't matter in this case. <S> This will be tested on the FAA knowledge exam so you will want to remember this. <A> When taxiing into any headwind component (including a quartering wind) you should use up elevator on most general aviation aircraft. <S> On a tricycle aircraft it is less of an issue. <S> However, there is still some benefit in that it reduces the load on the front wheel/strut. <S> The pair of rear wheels/struts are usually stronger than the front (as the rear pair are designed to take landing impacts) and so it is preferable to distribute more load to them, particularly on uneven surfaces. <A> I'd also add that when there's a strong headwind your true airspeed goes up and you start producing lift, that lift transfers weight from the wheels to the wings, holding the elevator back raises the nose up a little putting more weight on the mains, increasing brake effectiveness.
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On a tailwheel aircraft, keeping load firmly on the rear wheel helps provide directional stability and reduces any tendency to pitch forward on braking or when negotiating uneven ground, which in severe cases could risk a prop strike.
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Is the increased humidity on modern jets artificial? Is the increased humidity on jets such as the 787 and A350 artificial? Or is it a direct result of a greater cabin pressure? <Q> A Reuters article confirms the humidity just comes from the passengers, on the 787 at anyway: <S> (...) the air is dry and moisture comes mostly from passengers. <S> And this Flight Global article : (...) <S> the system does not add moisture through active humidifiers. <S> This APEX article has no discussion of higher cabin pressure being an influence on humidity. <S> Lastly, this Business Insider article says Boeing indicates the higher pressure alleviates the feeling of mountain sickness that can come from being at 8,000 ft vs 6,000 ft. <S> [S]ince there isn't a perfect one-to-one correlation between altitude and jet lag, Boeing has taken additional measures to mitigate the symptoms. <S> These measures include an increase in cabin humidity as well as a new air-filtration system. <S> So, it's real humidity, and not really an effect of cabin pressure. <A> There may be two factors at work. <S> First, there may be less air exchange, which would leave more moisture in the aircraft from people. <S> Reducing air exchange reduces the power required to pressurize the aircraft. <S> As I recall the 787 is a no-bleed system, with electrical compressors utilized, resulting in a claimed 3% fuel efficiency. <S> Accordingly, I would expect that a system goal would be to minimize air exchange, which would in turn minimize power consumption. <S> This would result in more retained water vapor. <S> Secondly, atmospheric pressure impacts dew point, which relates to our sensation of humidity. <S> A psychometer reading is dependent upon atmospheric air pressure, and is often adjusted for ambient pressure at altitude (for example in cities at higher elevations). <S> I haven't worked out the numbers, so this is a matter of unsubstantiated but dangerously informed opinion. <A> I might expect higher differential to result in a higher leak rate, which would result in more inflow to compensate, which could reduce the humidity level some amount. <S> However, I suspect that this effect, from say going from 8 to 10 psi (or whatever the 787 uses), is pretty small and if the 787 is using a sophisticated control system that manages inflow/outflow to control humidity as well as pressure, the point is probably irrelevant.
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Coming with some ECS/Pressurization background in engineering tech support, the only factor I can think of where higher pressure differential would influence humidity, which is all coming from passengers, would be related to leak rate of the pressure hull (they all leak, mostly through door seals etc).
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Why ground a plane while fueling? Why does a plane need to be grounded while fueling, but we never ground our cars? Does the potential for a spark magically exist for an airborne vehicle but not for an earth bound one? <Q> On cars I think it's because static charges don't build up as much <S> but theoretically it's still possible for a spark to occur when the nozzle touches the tank inlet and provides a ground path. <S> On airplanes there are two issues: <S> Static charges built up in the airframe in flight. <S> For this it is essential to ground the aircraft before the fuel nozzle is brought to the tank inlet. <S> The risk is of a spark just before the nozzle touches the filler neck, the nozzle itself being grounded, which is right at the location where the air fuel ratio is favourable to ignition. <S> It's also a good idea to touch the nozzle to the fuel cap before you remove it in case the tank isn't adequately bonded to the rest of the airframe, but I don't think anybody does this. <S> The other one is static charges built up within the fuel tank by the shearing action of the incoming fuel column when adding fuel. <S> In a large refueling operation, the column of fuel builds huge static charges within the mass of fuel itself, which result in static discharges within the fuel (there are films that show this; a freakin' light show). <S> Most dangerous is fueling from a plastic can. <S> When I used to fuel my airplane from cans I made a grounding wire arrangement that bonded the fuel in the can, the fuel tank flange and the ground (using a nail on the end of the wire pushed into the dirt) together. <A> We do ground cars during fueling. <S> The biggest difference is probably just in the way the grounding is done. <S> Fueling Cars <S> Every car I've ever fueled in my life has a spring-loaded metal plate that touches the nozzle as the nozzle first begins to enter the fuel tank, before fueling would start. <S> Any sudden static discharge would happen then. <S> That metal remains in contact with the nozzle throughout the fueling process, keeping the car (or at least the part of it around the fuel) grounded throughout the entire fueling operation. <S> Fueling Light Airplanes <S> On the light airplanes I've fueled (Cherokees and the like,) there's a relatively large hole in the top of the wing through which the aircraft is fueled. <S> There's no spring-loaded metal plate or anything like that. <S> Just a hole that is significantly larger than the fuel nozzle with a cap that is unscrewed and completely removed before insertion of the nozzle. <S> It would, thus, be not only possible, but rather likely that contact would neither be made before fueling begins, nor maintained consistently throughout fueling. <S> Furthermore, even if contact is made before fueling begins, the fuel tank (which hopefully still has some fuel in it) is directly beneath the hole, so any spark that did form at first contact would already be dangerous. <S> With a car, that spark would form outside the fuel tank and would not enter the fuel tank. <S> On the light airplanes I've fueled, it would happen at the top of the fuel tank and fly into it, a much bigger problem. <S> So, in order to prevent sparks falling into the fuel tanks on a light airplane, we attach a separate cable to the airplane first (away from the fuel tank) <S> that grounds the entire (conveniently conductive) frame before we stick anything into the fuel tank that might have otherwise caused a spark. <A> EDIT: <S> Also, it's not "magically", but a plane can indeed build up a considerable charge while in the air, from flying through electrically-charged clouds and whatnot - something that is not usually an issue with groundbound vehicles (such as most cars).
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According to reddit , the amount of fuel transferred when refuelling a car is generally too small to generate a dangerous amount of static charge, and you actually do ground your car when you fill it, the action of touching the nozzle to the filler hole grounds it.
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Why is the 737 MAX 7 selling so poorly? The 737 MAX 7 is the smallest of the four major variants in Boeing's 737 MAX product line; it is intended as the successor to the highly-successful 737-700, and features a higher fuel efficiency, considerably greater capacity, and increased range compared to the 737-700. Yet it is selling very poorly, with only 58 orders so far - and 23 of those 58 orders, from MAX 7 launch customer Southwest Airlines, have been deferred until the mid-2020s, raising the possibility that Southwest might cancel those 23 orders entirely . Why are the airlines which enthusiastically jumped at the -700 balking at its successor, despite its being the longest-ranged 737 ever (the MAX 7 can fly for 7,130 kilometres before it needs to refuel), thanks to its increased fuel efficiency, and having a capacity of 138-172 passengers, as compared to the -700's 138-140 passengers? <Q> There are two reasons: the market changed, and seat economics favor larger aircraft. <S> The NG models were designed in the early 1990s, before much of the dramatic change in the air transport market wrought by deregulation and ascendancy of LCCs. <S> Southwest for example, was using high frequency of narrowbody aircraft to attack the network carriers and drove the extinction of widebodies in domestic US air travel. <S> Since the early nineties, airline traffic has more than doubled depending on how you count, and there is a maximum frequency that is appealing to travelers. <S> If you have four flights a day on a particular route and you double traffic, you might decide that six is enough and use larger aircraft. <S> This is what Southwest is now doing, replacing -700 aircraft with Max8s. <S> The Max8 acquisition and operating cost is only about 10% higher than the -700, but its passenger capacity is 25% greater. <S> The math makes the smaller aircraft unusable, given that market demand now supports the larger aircraft. <S> Ryanair came along later than Southwest and went straight to the lower seat cost of the larger aircraft. <S> This is why even smaller aircraft like the Cseries are in trouble, forcing Bombardier to sell half of the program to Airbus for nothing. <A> While Boeing has delivered over 1,000 of the -700 version, popularity has gone down more recently. <S> There were 101 delivered in 2007, and it declined sharply from there. <S> Only 18 have been delivered since 2015, compared to 1,300 of the -800. <S> So the recent sales performance of the two is not that different. <S> The direct competitor is the A319neo, which has a similarly low number of orders. <S> Although the Bombardier/Airbus and Embraer planes have fewer seats, they are newer designs and <S> the smaller size also helps to bring down the price and operating costs. <S> The 737-7 does have some advantages of being the smallest of the family including having the most range with standard fuel tanks. <S> Airlines using the 737-700 version for its extra range might find that the 737-8 has the range they need while also carrying more passengers. <S> Boeing also made the -7 a bit longer than the -700, so airlines might find that for the smaller difference they might as well just go with the larger version. <A> There is nothing wrong. <S> Boing is hedging its bets by offering 4 737-MAX variants . <S> Aircraft manufacturers doubtlessly ask their customers for their preferences, yet neither the manufacturers nor the airlines can gauge which aircraft will fit the market in 5 or 10 years. <S> There are also specific Airbus variants that sell poorly compared to their sibling-variants, e.g. the A-330 800/900 variants , which have 10 respectively 238 orders (by August 2019). <S> As long as an aircraft manufacturer offers a large enough variety of aircraft, either with distinct aircraft or aircraft variants, it will satisfy the needs of the airlines, which are hard to predict.
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The 737-7 is a smallest version of the family so some of the operating costs are fixed by the larger models. There is new competition from the Bombardier CS300 (now Airbus A220-300), which carries 130 seats in a 2-class configuration, and the Embraer E195-E2, which carries 120 in a 2-class configuration.
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Why wing ribs have diagonal struts Why do ribs have diagonal struts,why not vertical as seen in airfoils of Citabria airplane? <Q> The diagonal struts are best to transfer shear. <S> Imagine an upward pointing load at the nose. <S> In order to get that load transferred to the fuselage, it first needs to be transferred to the wing spar. <S> Imagine now that you hold the rib firmly in your right hand where the spar is and press the nose upward with your left hand. <S> With parallel struts, the rib will have much less stiffness and the nose load will deform the rib easily. <S> With the diagonal struts, the rib is much stiffer when that particular nose load is applied. <A> This isn't really aviation-specific <S> , it's just good structural engineering practice. <S> Triangles in structures are strong because they don't bend: <S> whichever way you apply load to the triangle, the load is along the members. <S> With a rectangle, any load that's not perfectly aligned to the structure will bend the joints and squash the rectangle into a diamond shape, which will then squash flat easily. <S> You don't want any rectangles in your structure anywhere. <A> It's a truss . <S> Ideally, all of the beam elements in a truss are in either tension or compression, without major bending loads. <S> This offers the lightest weight for given load. <S> This same design is commonly seen in the open in steel bridges, construction cranes, and spacecraft. <S> Triangles that a truss consist of cannot be bent without changing the elements' lengths. <S> If all of the struts were vertical, the structure would consist of rectangles, which can be easily deformed by bending the joints. <A> It's to make the wing stiff and strong in torsion. <S> For torsion stiffness, you want two things. <S> First and foremost, you want as much material on the outermost fibre as possible. <S> The further the material from the neutral axis, the more it contributes to torsion stiffness due to the moment arm from the neutral axis. <S> Secondly, you want the cross-section to remain undeformed. <S> Consider for example a matchbox 'shell', which is in theory very stiff for torsion. <S> However, if the forces do not enter the matchbox exactly right, the open ends will deform into a diamond shape and will twist easily. <S> This shearing into a diamond shape can be prevented by placing baffles in the matchbox. <S> This is in fact <S> the very reason wings have ribs: so that the wings maintain their cross-section by transferring shear loads due to torsion from and to the top and bottom skins of the airfoil. <S> In terms of stiffness, thin plates would be ideal, but these are prone to buckling so a strut structure is used instead. <S> The best way to transfer shear loads with struts is to use diagonals. <A> A top picture of number 2 might have been a bit better, but notice the "puny" cross struts run both ways, much like in the wing of an old time biplane. <S> Their function would be help prevent the wing fromcollapsing BACKWARDS as a result of excess airspeed.(spokes in wheel rims may also seem puny, but the rimcannot come out of round because the spokes, 90 degrees from the load, cannot be pulled apart). <S> This seems to be a bit of sensibly added insurance,but no, they probably would not add to the torsionalstiffness of the wing. <S> Regarding the design of the ribs themselves, as mentioned, 1 is a classic truss. <S> 2 has the center ofthe rectangular rib filled in with metal and the center circular portion and edges made as an I beam for strength. <S> 1 of wood, 2 of stamped metal. <S> As far as making a stiffer wing torsionally, might consider replacing aluminum skin with plywood or some type of composite material. <S> Others may know how better to do it within the wing.
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So, in short: the diagonal struts transfer shear loads to increase torsion strength and stiffness of the wing.
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Where does the Departure End of Runway (DER) exactly begin? I am having trouble understanding the concept of Departure End of Runway. Most sources state that DER is at the end of the portion of the runway that can be used for takeoff (which, as far as I can tell, excludes the threshold at the end of the runway). But from the official FAA's Aeronautical Information Manual one can clearly see that DER starts at the "utmost" end of the runway (including threshold). Many other sources seem to support this, like this picture . Could someone point me to the right direction? <Q> The picture you linked is from an FAA publication. <S> As pictured the threshold is the end of the runway pavement, it is a thin line that separates usable runway from either taxiway, blast pad, grass, or an emergency overrun area. <S> It is marked at night with a single row of green or red lights (depending on your direction). <S> It can be displaced or reloacated from the original pavment but in this case it will have noticeable markings that include a well defined line marking the exact end. <S> Some ends are usable for takeoff but not landing or vice versa <S> but that is down to individual runways. <S> The paint bars near the threshold of an instrument runway are simply for visual reference to help indicate the width and length of landing zone during approach, they have nothing to do with takeoff or departure. <S> VFR runways only have a number and dashed center line, no white bars at all. <S> To summarize: the threshold is a line not an area, it separates usable runway from non-runway, it may be marked with paint or lights but it can also simply be a change in surface such as tall grass to short grass. <S> Standard departure obstacle clearance climb gradients are calculated with the plane at 35feet above the ground, directly over the threshold at the departure end of the runway. <A> Just guessing out loud here, but if you go to airnav.com and look up any airfield, two points are given for opposite ends of the runway. <S> For MOR or Morristown, TN , Runway 5 <S> = <S> Latitude: <S> 36-10.456562N, <S> Longitude: 083-22.968408W, Elevation: 1312.9 ft. <S> and the other end, Runway 23 <S> = Latitude: <S> 36-11.069353N <S> , Longitude: 083-22.085700W, Elevation: 1274.4 ft. <S> As an Engineering Consultant, everything that is done on this runway is done considering these two points - measurements for placing markings, setting up the RSA and all Part 77 surfaces and safety lines, etc. <S> Approach surfaces, departure surfaces, everything is established off these two points, including length of runway, TODA, TORA ASDA, LDA, etc. <S> are all configured off these FAA established runway endpoints, whether there is any extra pavement beyond or not. <S> In my estimation, the DER is going to be the opposite end runway coordinate of the end you are rolling out on. <A> ICAO Doc 8168 defines the Departure End of the Runway as "the end of the area declared suitable for take-off (i.e. the end of the runway or clearway as appropriate.)" <A> The end of the runway opposite the landing threshold (see figure B-1). <A> Most sources state that DER is at the end of the portion of the runway that can be used for takeoff (which, as far as I can tell, excludes the threshold at the end of the runway). <S> The displaced threshold , marked with white arrows, can be used for take-off (and roll-out), so the departure end of runway is at the end of that if present. <S> Blast pad/overrun area, marked with yellow chevrons, and taxiway, marked with yellow edge and possibly centre line, cannot be used for take-off, so the DER is before they begin. <S> But from the official FAA's Aeronautical Information Manual one can clearly see that DER starts at the "utmost" end of the runway (including threshold). <S> Many other sources seem to support this, like this picture. <S> The pictures don't show any displaced threshold nor overrun areas, so they are not really indicative of anything.
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According to the FAA's Terminal Instrument Procedures (TERPS) , the definition is: Departure end of runway (DER).
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What was the value proposition of the 767-400ER over the 777? Aside from visible differences, what are some differences in the usage and design of the 767-400ER as compared to the 777-200/200ER (or 300/ER if you feel makes more sense)? What was the value proposition of the 767-400ER when compared to the 777, as both came into service within a decade of each other? <Q> The -400ER was a strategic response to the Airbus A330-200 ... <S> but it didn't have the range and ultimately didn't sell well. <S> But if you only have the bigger 777, the negotiations will be harder. <S> Flight noted the following in 1999 : <S> Anyone seeing the 61.4m (201ft)-long aircraft emerge for the first time could be forgiven for experiencing a certain deja vu. <S> Not only is the -400ER <S> a mere 3.6m shorter than the 777-200, but almost exactly 10 years ago, a similar "767-X" design was being proposed to airlines. <S> This soon evolved into the all-new 777, and for a while the stretched 767 plans were shelved. <S> (...) Delta's TriStar replacement competition therefore provided the expected battleground for yet another Airbus versus Boeing fight. <S> Airbus pushed hard to get Delta aboard the A330-200 as part of a wider fleet deal involving widebodies and narrowbodies. <S> Boeing was equally desperate for victory, as much to keep Airbus from gaining a foothold in Delta territory as to launch the strategically vital 767-400X. <S> I've also put together this derivative work showing the similar length noted by Flight above. <A> It's pretty clear that operators of the 767-400ER knew what they were doing when they selected that aircraft. <S> Only United and Delta bought them and they are still in service even as older 767 models are being retired. <S> The 764s have proven to be a good value proposition even though it did not sell well and is a unique bridge between smaller and older 767 models and the much larger 777s, especially when you examine passenger cost and revenue per mile. <S> They have been particularly useful for transatlantic service, and both United and Delta plan to fly them for at least ten more years -- and they've both decided to spend millions on them to upgrade their interiors to maintain parity with newer Airbus and Boeing products. <S> It appears that both airlines are planning to keep them going until Boeing introduces the NMA (797). <S> I hope that's what happens because there's no question that passengers greatly prefer two aisle aircraft over single aisle competition such as the A321LR or the A321XLR for seven to ten hour flights. <S> I still prefer the 777 over the 767-400 but can see why United and Delta continue to fly 764 over single aisle aircraft or a larger aircraft that does not sell out on the same length flights. <A> I take value proposition to mean criteria used by a purchaser to determine which aircraft to buy. <S> Excluding financing deals and fleet commonality, the main criteria used when purchasing an aircraft are capacity, range, and seat mile cost. <S> 3 class capacity of the 767-400 is 243 vs 301 in a 777-200er. <S> range is 5600kt vs 7000kt respectively. <S> seat mile cost is 7 cents vs 7.5-9 cents respectively. <S> source Seat mile cost is trickier as airlines do the reports and they use different criteria. <S> You would think that a larger plane would have lower seat mile costs, but configurations differ between aircraft, airlines, and trip length. <S> You are also looking at the largest model of one series, usually the most efficient, and comparing it to the smallest of another, usually the least efficient. <S> It's kind of a mess and the manufacturers argue about this all the time. <S> The upshot is that the 767-400 is better for thinner (lower passenger demand), shorter routes and the 777-200er is better for longer, thicker routes where the increased cost matters less, as the 767-400 can't do the job. <A> I think the only airlines which would have considered a 767-400 is one which already has 767s in the fleet. <S> And even then it would be a product at the end of its life-cycle so fleet renewal considerations would play a part.
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If you can get the customers who want to replace their DC-10s and L-1011s with the more comparable A330-200 (which entered service in 1998) in talks about the 767-400ER, you have a shot at selling the bigger 777 as well.
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Why aren't there aircraft with forward-mounted vertical stabilizers? Many aircraft have the horizontal stabilizers mounted in front of the main wings (this is called a canard configuration); however, to the best of my knowledge, there don't seem to be any aircraft with vertical stabilizers in front of the wings. Why is this? <Q> From the image you can see that a vertical stabilizer mounted behind the aircraft CG imparts a restoring moment to a yaw disturbance which increases as the yaw movement increases. <S> If the fin were placed on the nose of the aircraft, ahead of the CG, the moment would amplify the yaw disturbance, which is destabilizing. <S> An actively controlled rudder could be located ahead of the CG, but cost and complexity normally limit this to things like missiles. <A> Stabilizers create directional stability - they keep the pointy end pointed forward. <S> To do that, they must be mounted behind the rotational pivot point that the aircraft rotates about, the center of gravity. <S> So when a airfoil or control surface is mounted forward, in front of the center of gravity, (canard) <S> , it cannot, by itself, be functionating as a stabilizer, (even though we may refer to it as a stabilizer). <S> It is, in fact, only a horizontal or pitch control surface . <S> In this case, (a forward mounted canard), the canard is not creating directional stability, the rear-mounted main wing creates this directional stability (pitch stability) about the lateral axis. <S> The canard itself actually detracts from directional stability. <S> It is there to provide control about the lateral axis. <S> A vertical stabilizer is there to provide directional stability about the vertical axis (yaw or sideslip stability). <S> You can't mount a vertical stabilizer forward because there is no other vertical airfoil at the back providing directional stability about the vertical axis. <S> Or perhaps it might be more accurate to say you could, but only if there were a larger vertical stabilizer in the back. <S> In which case it would be pointless to put another one in the front. <S> that would be reducing stability and requiring the rear-mounted one to be bigger. <S> An example here to illustrate the point might be the AIM-7 sparrow missile. <S> It does have it's <S> horizontal and vertical control surfaces in the front. <S> It has fixed wings at the aft end of the missile (which are the stabilizing airfoils), and movable control surfaces somewhat forward of the C.G. <S> It maintains a constant* roll attitude and can maneuver in any direction (left <S> /right/up/down), without rolling or changing its bank angle. <S> It does this by deflecting the forward control surfaces as necessary to create lift in the desired direction. <S> So, it effectively does have it's horizontal and vertical "stabilizer" <S> (actually, control surfaces) <S> forward of its fixed stabilizing airfoils. <S> *NOTE. <S> although actually, in the F-4 at least, the AIM-7 was programmed to always initially roll and then maintain a roll attitude where its wings and control surfaces are oriented in an "X" configuration relative to the launch aircraft, not as a "+" the way you might imagine. <A> All the above answers are excellent, but I do need to post this: <S> This the famed HOTOL, SSTO spacecraft. <S> Note the forward vertical stabilizer! <S> In this case I believe the reason for this layout was that during the nose-high entry the rear of the fuselage had basically no airflow. <S> Why they didn't use two wing-tip mounted fins... <S> well you'll have to ask him. <A> Nature has done this kind of arrangement; birds with large beaks such as pelicans and the extinct Pteradactyl used their large heads as rudders during flight and rely on their central nervous system to provide an augmented control system.
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Because having the vertical fin fwd of the CG causes static and dynamic instability and requires an augmented flight control system in order to prevent the aircraft from spinning.
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Are piezoelectric energy harvesters too expensive to be used commercially as a power source in drones or small aircraft? Piezoelectric energy harvesters can draw energy from the mechanical loads and the vibrations in the fuselage/wings/blades of aircraft. What are the disadvantages of such a system being used as an auxiliary power source if not the main one? Is it not worth the money? <Q> What are the disadvantages of such a system being used as an auxiliary power source if not the main one? <S> Is it not worth the money? <S> It's not worth the weight. <S> The power that can be extracted from piezoelectronics is on the order of microwatts (100 uW in the above article). <S> In contrast, light aircraft have their power measured in kilowatts and commercial aircraft reach a megawatt of electrical power. <S> In other words, it would take 8-16 million of piezoelectronic harvesters to replace the alternator on a small aircraft, and 3-10 billion on a modern airliner. <S> Drones use more power than small aircraft as they've got a lot of electronics. <S> All aircraft, including drones, already have their own power source - the engine - with fuel tanks that get refilled each flight. <S> So power's cheap and available. <A> the quantity of power (volts times current) produced by flexure of piezoelectrics is very small. <A> Piezoelectric energy harvesters can draw energy from the mechanical loads and the vibrations in the fuselage/wings/blades of aircraft. <S> Ok, think about this: in a perfect airplane, there would be no vibration. <S> Every erg of energy being used would go into the propulsion. <S> Any vibrations are, by definition, wasted energy. <S> Think about a specific example. <S> You know the vibrations in a turboprop plane that make it sort of "buzz" inside the fuselage? <S> That's caused by air off the props that hits the fuselage. <S> That air is being pushed by the engine, yet it's not pushing the aircraft forward. <S> That is the definition of wasted energy. <S> Ok, so real aircraft waste some energy, big deal. <S> But how much? <S> Obviously, the thing is flying, right? <S> So it can't be that much. <S> I mean, if it was 50%, that would be 2000 hp of wind smacking into the fuse <S> - you'd need a parachute, not ear protection! <S> So we're talking about what, 1%? <S> 3% <S> So that's why we don't use piezos to recuperate. <S> You're trying to collect this tiny bit of power. <S> Even at 100% efficiency, and I'd say 10% is more likely, we're still talking about a tiny fraction of the power you need to do anything. <S> In fact, the only use of piezos in this role is the exact opposite. <S> The Q400 (and others <S> I assume) <S> power <S> a set of piezos on the fuselage that provide the opposite vibration to the air off the props, and thereby lower cabin noise.
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You would need a very large number of them to produce useful amounts of power from airframe vibrations. Piezo harvesting is being developed to power completely unattended tiny sensors that won't have access to any other power source for years.
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How does the nozzle diameter affect the thrust of a ducted propeller? I currently do some experiments with ducted propellers in which I try to figure out which effect a nozzle has on the thrust produced. My theory goes like this: If I reduce the exit diameter of the duct the pressure is going to decrease and the air velocity and thus the thrust is going to increase. Consequently, you would want a small exit diameter. However, in my experiments I measured the thrust of a 12x12 inch propeller at around 5500 rpm and got 20 N without a nozzle (just a constant diameter duct) and only 4 N with a nozzle reducing the exit diameter to 50 percent of the prop diameter. These results are contrary to my theory! Does anybody have an explanation for this ? And what should I change to actually increase the thrust compared to the prop without a nozzle ? Here are some pictures: <Q> Welcome. <S> I'm afraid your theory wasn't actually working. <S> Reducing the duct's exit diameter led to an increase in its internal pressure, increasing load on the propeller, and likely even causing some reverse flow. <S> Nozzle design is a complex subject. <S> I can't think of a way to condense it, even limited to one specific case, into a suitable answer; maybe I don't get it enough myself. <S> Keep that in mind; the below is just one small shard of the whole and by no means the full picture. <S> In general, the job of a nozzle is to match the pressure at jet engine exit to that outside it. <S> If the pressure is different, it gets matched outside the engine, where it doesn't produce thrust. <S> When the engine is a rocket, which creates high pressure, the nozzle needs to expand the gas, converting pressure to thrust through acting on the nozzle. <S> When the engine is a cold fan, which accelerates air, it's the opposite - the nozzle needs to compensate for the loss of pressure with a bit of compression, so that the air stream can exit without fighting the pressure of outside air at the back. <S> It's important for a convergent nozzle not to compress the exhaust to a higher pressure than the outside air, else it will destroy thrust. <S> That was your case, the nozzle was too narrow, so it compressed the air to above ambient - which caused it to try and blow back through the fan. <S> To give a practical answer, an optimal nozzle at these velocities would be very similar to a simple duct, narrowing just a percent or two at the end, with a smooth exit shape. <A> To add to @Therac's answer, you will probably add some drag on the outside of the nozzle by contracting it. <S> The air flowing around it will separate if the contraction angle is too steep. <S> A bit of contraction makes sense, as the accelerated flow aft of the propeller will need less cross section for the given mass flow. <S> You will also wish to make the capture area a bit larger than the cross section in the propeller plane. <S> Just calculate the speed increase through the propeller disc and assume that half of that is reached in the propeller plane. <S> This will ensure that pressure is about constant along the whole duct and losses are minimized. <A> This subject is one that the helicopter people have given a lot of thought. <S> From this figure from Leishman <S> we can see that the wake contracts by itself already. <S> The contracting shroud in your test setup has higher pressure just behind the propellor than at the shroud exhaust. <S> This static pressure gradient exerts a force on the shroud area, resulting in negative thrust. <S> Plus friction forces from the airstream in the duct. <S> The same book has a bit of a treatise on tail rotor fan-in-fin design based on momentum theory, which actually depicts a widening shape. <S> More details in the masters thesis report, mentioned in this answer . <A> The thrust equation gives us Thrust = <S> Mass <S> x Acceleration <S> You increased the airspeed but reduced the airflow. <A> This is great work, and you are off to a good start. <S> You may wish to review jet engine design. <S> What you are building seems to be the compressor half. <S> Forward motion created when applied to an aircraft will add to this affect. <S> This could be an air "scoop" for a piston engine! <S> The best way to test your designs might be full throttle in level flight, as this would also give you nacelle drag data. <S> Top speed comparisons will probably show by far a properly pitched prop with no duct will win the power to thrust efficiency test, but not without much being learned. <S> Ducted fans look great on scale model designs, but generally drain the batteries muchfaster than props. <S> They do have advantages at very low or hovering speeds, but props take over from around 50 to around 400 mph. <S> I would definitely continue this work for application of boosting power in piston engines. <S> Sports cars have air scoops on their hoods, this one might be better.
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Narrowing the "exhaust end" will increase pressure in the duct, which is what you want a compressor to do.
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