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Can commercial airliners fly over hurricanes? When Patricia was making landfall yesterday I opened up Flight Radar 24 to see if there were any planes flying around or near it. As I had expected, there were a couple of storm watching planes near the hurricane, but what surprised me is that there were some commercial flights that seemed to be going over portions of the hurricane... So, I'm curious, can commercial aircraft go high enough to simply fly over a hurricane, assuming they take off and land at airports that are not effected by the storm? Or perhaps they can only safely fly over the fringes and need to stay away from the eye? Basically, can airliners fly over hurricanes, and if so can they fly over all of it, or just parts? <Q> In general, no- except in emergencies or 'small' hurricanes. <S> Commercial aircraft usually fly around bad weather (like hurricanes), not over it. <S> Some of the hurricanes can reach upto 50,000+ ft height, making it all but impossible for most modern commercial aircraft to fly over them (except maybe you're flying a Concorde). <S> Even for smaller storms, the convective process over the hurricane will cause severe turbulence, affecting overflying flights. <S> Even for hurricanes where the aircraft can fly over, there is the problem of safety- <S> What will happen is something happens (for example engine failure) and the aircraft has to descend to lower altitudes? <S> Obviously no one wants to descend into the storm. <S> There are some aircraft that do fly into hurricanes for scientific experiments. <S> These are crewed by trained (and experienced) specialists and involve a lot of detailed planning . <S> For example, the aircraft are equipped with radar that helps in avoiding the worst parts of the storm. <S> Still, it is risky and the aircraft is exposed to significant loads and vibrations not usually exposed in commercial service. <A> A hurricane can reach up into the tropopause at 50,000+ feet, making it impossible for a modern airliner to overfly it. <S> Even if you could overfly it, you're in a difficult situation where if anything goes wrong (i.e., requiring a descent), your options are much more limited since hurricanes are so large in area. <S> There are circumstances where you would fly near the edge of the hurricane in order to take off or land before the main part hits. <A> Can commercial airliners fly over hurricanes? <S> The critical point is crossing the edge of the hurricane eye. <S> However, an airplane can pass through that zone of high winds in minutes.
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They can fly through the top (or even the base) of the hurricane in an emergency situation and nothing will happen, see Flying through a hurricane (YouTube) , but it is not preferred to expose the plane to such vibrations if better options, like going around the hurricane, are available.
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Why is the rear seat ejected before the front one? On aircraft with 2 crew placed one in front of each other (tandem) equipped with ejection seats, the rear seat is ejected before the front one (described here for the F-14 ). Why is the rear seat ejected before the front one? Is an aircraft without ejection seat (e.g. glider) evacuated in the same order and why? <Q> If the front seat ejected first, the drag would probably bring him too close in the trajectory of the rear seat, thus making a collision of both probable. <S> Since the rear seat is ejected first, it experiences drag earlier than the front seat and will thus not have an increased probability of hitting it. <A> In general, in aircraft with tandem seating, the rear seat (having the Radar Officer) ejects first, followed by the forward (pilot) seat, after a delay of ~0.3 seconds. <S> In some aircraft, the pilot can eject only after the rear seat is ejected. <S> This is so that, in case the rear seat fails to eject, the pilot can still control the aircraft and 'pop out' the Radar officer's seat by maneuvering. <S> For example, the F-4 procedure called for the pilot to roll the aircraft inverted with a positive 'g' and then pop the radar officer with a negative 'g'. <S> In some cases like the (Mig-15 UTI), the rear seats were ejected first simply because the gas jets from the pilot seat ejection mechanism made ejecting from the rear compartment impossible. <A> I'd think the main reason would be to avoid cooking the rear seat crew while the rockets were firing as well as to avoid an accidental collision between the front seat and the rear seat crew. <S> After all - the jet is likely to be travelling forward at a relatively high velocity when the two are coming out of the plane (or what's left of it). <A> The pilot ejects last so that he/she can attempt to remain in control of the aircraft.
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This is done for a few reasons: If the pilot seat is ejected first (or both are ejected simultaneously), there is a possibility that the pilot seat may collide (as it will be dragged backwards due to wind force) with the copilot seat or damage the (rear) canopy during ejection.
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What was the first plane that allowed walking during flight? What was the first plane that allowed crew members and/or passengers to stand and walk during flight? P.S. I mean walking inside the cabin, as part of normal operation intended for by the plane designers, not walking outside the plane, on wings and other acrobatic activity. <Q> The first airplane with a cabin big enough for walking around was indeed a Sikorsky. <S> This was the Sikorsky Russky Vityas , also sometimes named "Le Grand", a name which was given to an earlier, two-engined version. <S> Oh, and the cabin included a washroom, too! <S> It was the first four-engined airplane in the world and the biggest airplane of its time. <S> It flew first on May 10 (or 13, depending on the source), 1913. <S> Quote from Wikipedia: After the Russky Vityaz's first test flights between 10 and 27 May 1913 (Old Style dates), it was established that a passenger could even walk around the cabins without causing any problems to stability. <S> Early Le Grand version with two engines ( source ) <A> Walking around was always allowed. <S> Allowing passengers to play tennis took more technology: <S> Meals and table service arrived around the same time, 1924, for this Curtiss JN-4: <A> In the early days (before we made people get up to keep the blood flowing) <S> the only real reason to get up on a plane would have been to go to the bathroom. <S> That being said the first plane with a bathroom was the Caproni <S> Ca.60 Transaereo <S> although it crashed on its second flight. <S> The Handley Page H.P.42 is considered the earliest plane to have a toilet built in 1928. <S> The other way to look at this would be to consider the first plane that allowed people to walk around if just to stretch. <A> What was the first plane that allowed crew members and/or passengers to stand and walk during flight? <S> What I know is that by 1913 people were already standing during flights (see the picture). <S> Russian plane Sikorsky Ilya Muromets ca. 1913
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Early airlines like the Short Empire 1936, or the Boeing 314 Clipper 1938, most likely saw regular walking around on their long flights but these still post date the HP42. Sikorsky Russky Vityas (picture source )
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Why don't helicopters prefer shorter rotors with more blades? My understanding of helicopters is that, despite theoretically increasing efficiency, longer blades are worse in practice than short ones in every respect (except, perhaps, cost): Longer blades are more prone to vibration and resonance dynamics, if for no reason other than that their rigidity is reduced by length, holding all else constant. Longer blades provide less operating clearance. Longer blades not only stall before shorter blades (retreating), but also hit the Critical Mach number at lower air speeds (advancing). Fewer blades require higher rotational speeds for a given "rotor disk" area, which is inefficient from not only an aerodynamics perspective but also, presumably, a transmission-and-control perspective. But all helicopters have few blades of significant length. So: What are the advantages of longer blades, or disadvantages of shorter blades, that lead to the rotor designs in common use? I would imagine that in the limit it would be optimal to run something more like a ducted turbine segment, where the swept area is virtually covered in blade surface (i.e., maximizing the number of blades over the swept disc). Noting that in practice blade size seems somewhat proportional to the body size of the aircraft, I'll deduce that in practice the bulk of the downforce needs to be generated some minimal distance away from the aircraft's body, though with some attention to the body's vertical aerodynamic aspect it seems like that could be reduced. I guess tilt-rotors could support this hypothesis since their rotors are positioned at a distance from the body and they use smaller rotors , although it seems like they still use blades as large as possible given the wing size and body configuration. <Q> The rotor works by accelerating air downwards, therefore creating an upward reaction force on the blades that lifts the craft. <S> The lift force is equal to $$ <S> L = <S> \dot{m}\Delta <S> v$$ <S> where $\dot{m}$ is mass flow rate through the rotor and $\Delta v$ is the change of speed of the air. <S> To accelerate the air to that speed, it has to give it kinetic energy. <S> This requires power $$D = <S> \frac12\dot{m}\Delta <S> v^2$$ <S> (the induced drag). <S> Now a rotor with smaller diameter will be able to affect less air, so the $\dot{m}$ will be lower. <S> To produce the same lift, it will need larger $\Delta v$ and therefore it will need more powerful engine (up to a point, because longer blades will have higher form drag that will eventually outweigh the reduction in induced drag) and, more importantly, burn more fuel . <S> The blades, like wings, affect air to a significant distance above and below them, so you don't need many blades to use all air within the rotor area. <S> But no matter how many blades you add, they will still only affect the air within the rotor area, so the efficiency won't change much. <S> As far as tiltrotors go, they have relatively small rotors and that makes them awfully inefficient in hover. <S> But they don't spend most of their time hovering, they spend most time flying somewhere and in the fixed-wing mode <S> they are faster and more efficient, which outweighs the worse efficiency during take-off and landing. <S> See also <S> : Is there any equation to bind velocity, thrust and power? <S> (via Energizer777's deleted answer). <A> The number of (main rotor) blades in a helicopter are dependent on a number of parameters; Usually there are some major issues with having a large number of blades in a helicopter though: <S> One main reason is efficiency- <S> akin to the bypass of turbofan engines). <S> In general, the performance of the helicopter rotor system is affected by solidity <S> (i.e the ratio of blade area to total disc area) rather than the number of blades. <S> As the number of blades increase, the interaction of subsequent blade with the advancing blade's vortex increase (i.e the blade flies into the preceding blade's wake), which affects the lift produced. <S> More blades means more complex rotor hub (more parts usually translate into more problems- maintenance and otherwise) and more interference in the inboard region of the blades. <S> Also, the rotor hub drag is increased. <S> One thing you're missing is that the blade velocity $V$ (in $L \ = \ \frac{1}{2} \ \rho \ <S> V^{2} \ S$ ) is in itself dependent on the blade length (and rotational speed, through $V \ <S> = \ R\omega$). <S> This means that as the blade length reduces, they have to rotate proportionally faster to produce the same lift- <S> thus in reality, the tip speeds of smaller blades will be more. <S> Usually, the inner third length of a rotor blade contributes very little to lift. <S> As far as vibration is concerned, (though it is better to have more blades) the whole rotor system has to be taken as a unit rather than as individual blades and the most important consideration is the rotor speed and its harmonics rather than the blade length. <A> The blades of a helicopter are long, narrow airfoils with a high aspect ratio, a shape that minimizes drag from tip vortices (see the wings of a glider for comparison). <S> They generally contain a degree of washout that reduces the lift generated at the tips, where the airflow is fastest and vortex generation would be a significant problem. <S> source: Wikipedia .
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In general, lesser the blades, more efficient the system- as it changes the momentum of more air mass i.e. accelerates more air by a lesser amount (
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Can you breathe with a drop down mask under water? Say a passenger jet lands in the ocean. Could the captain being the last person to get off the jet use the drop down dry chemical oxygen generators to breathe while checking for passengers? I know they are flimsier so depending on depth they would collapse. <Q> No, you cannot - at least not with the default masks. <S> In principle, the oxygen systems on board can all provide at least 15 mins. <S> of oxygen, in some of the worst conditions (indeed, that's what they're designed to do). <S> However, their sole purpose is to make high altitude air breathable. <S> The key principle here is partial pressure . <S> Basically, the partial pressure of a gas is the fraction of a certain gas in a gas mixture times the ambient pressure. <S> Since normal air consists of about 21% oxygen, the partial pressure of oxygen at sea level is 0.21 atm (atmosphere). <S> If the partial pressure of oxygen is too low, your lungs actually lose oxygen to the atmosphere when you breathe - much like a deflating balloon. <S> When the cabin pressure drops, the partial pressure of oxygen drops proportionally. <S> In that case, oxygen masks are provided. <S> They do not raise the pressure of the air you breathe in, but raise the partial pressure of oxygen by filling your mask with oxygen. <S> If the cabin pressure would drop to 0.2 atm, and you would be given 100% oxygen, the partial pressure of oxygen would be 0.2atm, which is about the same as at sea level - perfectly survivable. <S> The mask as such does not need to be airtight - it just needs to make sure that there's enough oxygen flowing into your mask to displace all the useless nitrogen in the air. <S> Indeed, the mask you will see on airplanes are generally flimsy, plastic masks. <S> Under water, these masks are not sufficient at all. <S> They will probably turn into a frothy, bubbly mess of a water/oxygen mixture, especially when the aircraft is filling up with water, due to strong currents. <S> So, you would have to wait for the currents to diminish, and then hold your oxygen mask in such a way that no water will enter it - <S> this probably means you will have to face upwards all the time. <S> Of course, you can get creative (pull the mask of and breathe from the tube), or luck out with a high quality mask that happens to work underwater. <S> But I'm afraid that as soon as your plane is sinking, it's too late to play the hero, and your best bet would be to get out and at least save your own life. <A> It is a chemical reaction. <S> However, it would not work for the reasons already mentioned in the comments and the infeasible logistics of a hollywood captain single-handedly saving his passengers at the last second ;-) <S> https://en.wikipedia.org/wiki/Emergency_oxygen_system#Mechanism <S> https://en.wikipedia.org/wiki/Chemical_oxygen_generator <A> It depends on how much oxygen is provided by the mask, i.e. what the flow rate is. <S> I guess masks for pilots should be independent from ambient air at any altitude for the case that there's smoke in the cockpit. <S> So yes, they would provide enough air for breathing at sea level, or even slightly under water. <S> But those masks are in the cockpit and not mobile. <S> Oxygen masks for passengers don't provide all the air they breathe, they just add some oxygen to the ambient air. <S> Have a look at this diagram, which shows which fraction of oxygen in air at certain altitudes correspond to which at sea level: <S> (This uses the given percentages and the simple common barometric formula, other sources may show other curves) <S> It would be fine if passengers are kept somewhere in the yellow region, as e.g. drowsiness wouldn't matter for them, just sitting around. <S> At an altitude of about 12km/ 40,000ft, the passengers should get air with maybe 50% oxygen, 20% from the ambient, 30% from the mask. <S> Now, imagine you are under water and try to breathe from the oxygen masks only. <S> You will have to cut off the mask and breathe from the tube. <S> The flow rate from this pipe is just 30% of the usual flow rate, so you have to breathe very slowly. <S> This will be a problem, though the amount of oxygen from the tube would be fine. <S> Physical stress like diving through the aircraft and pulling out passengers would increase the need for oxygen drastically and then, even the pure oxygen from the tubes would not be enough. <S> You may put several tubes into your mouth, if you manage to do that. <S> Finally, the gas flow from chemical oxygen generators decreases after activation, and comes to rest after a few minutes, so this wouldn't work if the masks were already deployed at high altitude. <S> I don't know about the mobile oxygen devices for the crew. <S> If they allow to breathe independent from ambient air, they would work under water. <S> But I guess, they also only enrich the air with oxygen, may be more than the passenger's masks. <A> In addition to the discussion of the physical ability to use the mask to deliver oxygen under water - it is worth noting that breathing pure oxygen in a high pressure environment results in oxygen toxicity . <S> In short, oxygen at high concentrations is increasingly poisonous to our nervous system and pulmonary system as atmospheric pressure increases. <S> This makes your example question an even more terrifying prospect if the aircraft is sinking rapidly. <S> Now, if faced with the choice of drowning or rolling the dice with toxicity, I guess I'd try the mask...
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So yes, if contained it could provide oxygen under water (provided the reaction did not react with the water).
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Can the V-22 autorotate? Can tilt-rotors like the V-22 execute an autorotation landing? If so, are the conditions under which that would be possible (and survivable) different from a helicopter? <Q> The V-22 rotor disks are much lighter than a helicopter's. <S> There's little energy available to use to cushion a landing, so although autorotation is theoretically possible, there's little point. <S> The Boeing <S> V-22 handbook has this to say (see page 26): <S> The wide separation of the engines and the ability to drive both rotors with one engine make a power-out landing extremely unlikely. <S> However, if required, the V-22 can glide for a predictable run-on landing in airplane mode, much like a turboprop <S> I've seen glide ratios of 2:1 and 4.5:1 quoted on the Internet, so it'll come down quite hard and destroy the rotors. <S> However, the design mitigates against this in various ways, or so the manufacturer claims. <S> In the survivability section of the same handbook they say <S> V-22 crashworthiness is a function of design. <S> Heavy components, <S> such as the engines and transmissions, are located away from the cabin and cockpit area. <S> The proprotors are designed to fray or “broomstraw” rather than splinter on impact with the ground. <S> The energy-absorbing landing gear system is designed to attenuate most of the energy for hard landings up to 24 fps. <S> The wing is constructed to fail outboard of the wing/fuselage attachment in a manner that absorbs kinetic energy and ensures the cabin area will not be crushed, thereby protecting the occupants. <S> An anti-plow bulkhead prevents the nose from digging in on impact, and the fuselage provides a reinforced shell that is designed to maintain 85% of its volume during a crash. <S> Aircrew and embarked troops receive additional protection from crashworthy seats that stroke vertically to absorb energy. <A> This seems to be a hot topic - in principle, the V-22 should be able to fly and land in autorotation, but tests so far did not demonstrate this. <S> What it comes down to is the inertia of the rotating parts relative to the aircraft's mass. <S> The requirement to fold the rotors put a limit on their diameter and consequently their inertia while increasing their disc loading. <S> The inertia is too low to reduce the rate of descent enough to enable a safe and soft landing. <S> Quote from Wikipedia : <S> While technically capable of autorotation if both engines fail in helicopter mode, a safe landing is difficult;[73] in 2005, a director of the Pentagon's testing office stated that in a loss of power while hovering below 1,600 feet (490 m), emergency landings "...are not likely to be survivable." <S> This is specific to the V-22 - other tiltrotors might well be able to land in autorotation if their rotor inertia and speed is high enough. <S> For all practical purposes, the V-22 can glide down in autorotation, but will not be able to perform a soft landing at the end of this glide. <A> There is nothing that prevents tilt rotors from performing an autorotational landing, in theory. <S> AugustaWestland AW 609 has already demonstrated this . <S> The Bell XV-3 also did this. <S> However, V22 has not demonstrated autorotation in any practical sense. <S> The descent rate is too high for safe landing. <S> The failure of V 22 to autorotate is due to the high wing loading (which is ~50% high compared to the AW609) and the low inertia of the blades. <S> The manufacturer/operator has instead claimed two things- <S> the requirement (of both engines failing together) is remote and that it can glide in any case. <S> At the end of the glide (which is pretty steep compared with 'normal' aircraft), the structure and seats are expected to absorb the impact. <A> I read there was nothing in the specs to require autorotation like a traditional helicopter. <S> I also read that the glide path to accomplish an auto would be too steep to go to a run on landing, which is recommended for single engine out procedures. <S> The only time there is not sufficient altitude for an auto <S> is when you are at a hover below 1800 feet, which is rediculously high to hover <S> and I am not sure what mission would require that task. <S> Even in a normal helicopter flying low over the trees does not allow much time to decelerate, speed up the rotor in time, and cushion landing with rotor inertia momentum. <S> Cushion is what the traditionalists are looking for. <S> Only the most superior pilot will stop all forward movement and not hit any obstacles when terminating at the ground without power. <S> The Osprey meets its specs. <S> And, all the other points are mute without the best pilot that exists at the controls, which is only the Senior Instructor Test Pilots or Acrobatic Pilots, which are not a part of the training. <S> Just stick with run on landings and avoid hard wood trees at the bottom. <S> There is no need to fuss over the Osprey ability to fully autorotate when landing.
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The V-22 is a tiltrotor and does not rely on autorotation for a survivable power-out landing. The manufacturer's position is that autorotation was never part of the specification.
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Are control inputs different during autorotation? My understanding is that during power-off autorotation the main rotor is still coupled to the tail rotor, and the flight controls execute the same functions as during power-on flight. Two questions: Do any (heavy) helicopters have power-assisted controls? If so are those difficult to handle in the event of total power failure? How is the input during autorotation different from the input for the same attitude under power? E.g., during a given glide and flare to land are the rotor blade angles of attack and swashplate orientation identical to when the a rotors are powered? <Q> Yes and yes. <S> A certification requirement of helicopters with powered controls is that they have a manual reversion so that control can be maintained in the event of a power failure. <S> However, the controls can be really heavy with no power and accidents have occurred when hydraulics have failed at critical moments or pilots have lifted off with hydraulics off and have been caught by suprise with the effort needed to maintain control. <S> The control inputs during autorotation are the same. <S> For any given glide, or flare, the lift required is the same powered or unpowered. <S> Lift is proportional to the speed of the blades, which is independent of powered or unpowered, and the angle of attack. <S> During autorotation, the energy (power) going into the rotors is derived from the airflow coming up through the disc. <S> In this sense, an autorotation is still powered but the power comes from the airflow rather than the engine. <S> During autorotation, since the airflow is from below, rather than above, the pitch required is lower for the same angle of attack to generate the same amount of lift. <S> So, the swashplate is lower in autorotation but lowering collective still decreases lift and raising it increases lift. <S> Lowering the collective has the opposite affect. <S> The cyclic control is the same in all respects (you tilt the rotor thrust in the direction you want to go) since it increases, or decreases the pitch, and therefore the angle of attack, cyclically. <S> The movement of the swashplate about the X and Y axis is independent of the position of the swashplate in the Z axis. <S> The pedals work in the same way too. <S> In summary, the only difference in the controls is the vertical position of the swashplate. <A> Heavy helicopters tend to be hydraulicly controlled to such an extent that there no longer is a physical link between the controls and the blades (like big jets). <S> You're just opening and closing hydraulic valves one way or another. <S> So... no hydraulics, no controls. <S> The hydraulic pumps are generally driven by the main gearbox so that you will always have hydraulic pressure (main and backup) as long as the rotors are turning faster than a minimum speed. <S> Usually you will fall out of the sky before that rotor speed falls below that threshold. <S> There is a rotor speed that if it falls below that rpm, you will have lost the ability to get it back up and will have lost the ability to auto rotate. <A> Image source <S> In heavy helicopters such as the CH-53E Super Stallion, the swash plate is actuated hydraulically only, there is no manual reversion and if all hydraulic power is off, the helicopter cannot be controlled. <S> That is why there are redundant hydraulic systems, powered by pumps mechanically connected to the rotor transmission: as long as the rotor turns, the pumps provide hydraulic power. <S> Loss of all hydraulic power is considered highly unlikely. <S> The main hydraulic actuation cylinders are located at the swash plate and at the tail rotor, and the cable run to the flight controls is of considerable length, creating some friction and lack of precision. <S> Also, there is a mechanical mixer installed which provides coupling between collective-pedals-cyclic: when collective is increased, the mixer provides extra tail rotor input without the pilot having to move the pedals. <S> Without any additional measures, the mechanical mixer also creates cross coupling between flight controls which would further complicate precision control: it is a big ship! <S> In order to make the stick forces simple and light, there is a second hydraulic actuator at each flight control, just behind the cockpit: they are irreversible, and the AFCS system can independently move these and add autopilot inputs. <S> The feel characteristics are as follows: <S> With AFCS ON, only artificial feel forces (including trim) are felt plus the friction of the short run to the AFCS system. <S> If the pilot moves a control, the mixer does its work without any other flight control being back driven. <S> With AFCS OFF, the higher friction of the run to the swash plate primary actuators is felt, plus back driving forces from the mechanical mixer. <S> However, there is considerable difference in the feel and in aircraft response with AFCS ON or OFF. <S> Both conditions are modelled in flight simulators and the pilots are experienced in controlling the ship in either condition.
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The primary difference is that rather than controlling lift and power, the collective controls rotor speed since increasing pitch increases the angle of attack which increases lift and therefore increases drag, slowing down the rotor. During autorotation, the coupling between the swash plate and the flight controls is exactly the same as when in powered flight.
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Why does the co-pilot sometimes keep a hand on the throttle as well as the pilot? In this YouTube video of a takeoff and landing in a Dash-8 , you can see the pilot, while landing, keeps his right hand on the throttle levers. The co-pilot keeps his left hand at the base of the throttle levers during this time. This happens at 3:38 in the video. I assume this is to ensure both pilot and co-pilot agree when lowering the throttle? I'm just guessing, though. Why is this, and are there other similar events that happen during a flight? <Q> The pilots were probably executing a Cat II coupled or monitored approach. <S> The PF is flying the plane (via autopilot, usually), while the PNF had his hands at the base of the throttle ready to take over to initiate a manual go around (or land in some cases, this varies from airline to airline). <S> There is a thread regarding this on this on airliners.net . <S> It gives one version of the procedure: <S> At my airline we use this procedure for Cat II approaches. <S> The FO always flies the approach... <S> well the autopilot flies it and the FO monitors the instruments, ready to perform a missed approach if the approach becomes unstable. <S> The Captain at the 500 to minimums call places their hand near the base of the thrust levers, under the FOs arm, and focuses outside looking for the runway. <S> If at any point prior to minimums the captain gets the runway in sight, they call "landing, my controls" and move their hand up to the thrust levers, bumping the FOs arm and hand up and off of the thrust levers. <S> If at minimums and the runway is not in sight the FO performs the missed approach. <A> We back up our PF on the throttles during takeoff and landing on the DHC-6 Twin Otter. <S> It's to ensure that the PF doesn't do anything goofy during an engine failure or other emergency (just a safeguard). <A> I agree. <S> Should there be any inadvertent throttle retard due to turbulence or runway surface ,the NFP can push them back up. <S> It's SOP in the Navy and Air Force in multiengine side by side cockpits.
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It also guards against inadvertent throttle retard due to failure of the seat adjustment slides during the catapult shot( S-3 Vikings,E2C Hawkeyes,C-2 Greyhounds,etc)
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What are the differences between air brakes, spoilers and lift dumpers? So many people use these words interchangeably, but after a little searching on Google, I found they are not quite the same thing. All the links I read explain things in a misleading way which pushed my confusion even further. I'm looking for a simple explanation on the effect of these parts on The Four Forces of Flight <Q> Air brakes increase drag with little change in lift. <S> The following image shows the air brake being used in BAe 146 <S> " Eurowings bae146-300 d-aewb arp " by Adrian Pingstone - Own work. <S> Licensed under Public Domain via Commons . <S> Spoilers both increase drag and reduce lift- basically, they change the lift-to-drag ratio. <S> Sometimes, they are also used as control surfaces in lieu of ailerons. <S> This image shows a Boeing 777 spoilers being used in flight. <S> Screengrab from youtube.com <S> The lift dumpers are basically ground spoilers that are used to 'dump' lift, especially immediately after landing, where you want rapid reduction in lift. <S> The following image shows lift dumpers being used in BAe 146. <A> In my mind these terms all refer to the same thing with 'Lift Dumper' being a more British/European term. <S> But to help illustrate the source of the confusion a quote from the A300 AMM <S> The lift dumping function is achieved by control surfaces on the uppersurface of each wing. <S> In flight, the speedbrake function is achieved on each wing by : <S> Two inner speedbrakes <S> Two outer speedbrakes <S> On the ground, the lift dumping function is achieved on each wing by : <S> The two inner speedbrakes <S> The two outer speedbrakes Three spoilers. <S> The spoilers are also used in roll control, when they complement the actionof the ailerons. <S> The A320 AMM <S> Five spoilers numbered 1 thru 5 inboard to outboard are provided on the rearupper surface of each wing. <S> The spoilers are used for: Roll function <S> Speedbrake function <S> Ground spoilers function <S> So really, the spoiler is the component, <S> while lift dump and speedbrake refer to function the spoiler is providing. <A> Speed brakes or air brakes is the same word and has the same meaning, mainly is used only in the air. <S> Once the pilot decide to use them 3 or 4 of the spoilers on the wing will deflect little bit but not fully extend. <S> purpose of using it is to 1. <S> Reduce the IAS ( indicated air speed ) 2. <S> To increase rate of descent beacause it will ad ( drag ) when you use them. <S> Spoiler of also called ground spoilers is only deployed and fully extended once the airplane weight is on the wheel which basically is on landing or when rejecting takeoff. <S> They work by deflecting all spoilers on the wing in an angle that kills lift thus having weight <S> and it helps the airplane decelerate cause you have the whole airplane weight on the wheels <A> I don't believe there is any industry standard term for these parts; they're often used interchangeably. <S> These are just speed brakes mounted on the upper wing surfaces, in general, about 1/2 to 2/3 the length of the chord line. <S> In addition to creating parasite drag, they induce flow separation over the top of the wing and, as mentioned above, greatly increasing induced drag in the process as the lift is 'dumped' off during deployment. <S> Large transports will use spoilers to increase braking effectiveness and decrease the length of the landing roll. <S> Another function of spoilers is roll authority, particularly in fly by wire aircraft, but sometimes seen in other types of mechanically controlled aircraft e.g MU-2, TBM, etc. <S> They will be used in conjunction with other control surfaces such as ailerons, all-moving tailplanes, etc.
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However in general: Airbrakes and speedbrakes are interchangeable terms; just large reinforced panels which can be extended out from the aerodynamic envelope, creating a lot of parasite drag. Spoilers and Lift Dumpers are, again, interchangeable terms.
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Why do police helicopters always fly in circles? Why do police helicopters always fly in circles while news helicopter hover in one spot? Is it to avoid criminals opening fire at them, or is it because there is a difference between the two types of helicopters? <Q> Police helicopters don't always fly in circles. <S> I've often seen my local police helicopter hovering. <S> There are a few reasons you might have seen police helicopters flying in circles:- <S> Not all types of helicopter can hover out of ground effect. <S> Helicopters are safer if they're moving forwards than hovering. <S> In the event of an engine failure, they can autorotate to land safely , but they need to have some airspeed to be able to do this. <S> The required airspeed depends on height (see the chart in the linked question), so if your news helicopters are usually operated higher up than police helicopters, they may be able to hover safely. <S> (This is quite likely, as police aircraft are exempt from the 500 ft rule and the 1000 ft rule, while news helicopters are not.) <S> Police helicopters often circle to search an area for a fugitive or casualty using thermal imaging cameras. <S> News helicopters tend to either follow a vehicle or hover to get a steady camera shot of a news event. <A> There is little difference between the helicopters used by news crews and police. <S> It is their operation that differs. <S> Flying instead of hovering helps minimize the chance of getting shot. <S> There has been incidents when law enforcement helicopters have been shot down . <S> Forward flight (at low speed) uses less power compared to hover. <S> This reduces the engine load and increases the time spent over target. <S> Police helicopters fly pretty low compared to the news helicopters. <S> Hovering for long periods can result in one settling in their own downwash. <S> In this case, the altitude can help news helicopters to gain forward momentum to get out of this. <S> As this option is not available to police helicopters, it is better for them to fly in circles. <A> Often the police helicopter is out looking for the target. <S> A circle is a search pattern. <S> News typically has a known target they just need a shot of.
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It might be that the police helicopters in your area can't hover at the heights they work at, with the weight of their usual equipment.
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What is the difference between a nacelle and a cowling? I see these terms used almost interchangeably. To my understanding they both refer to the covering of an engine. Is there a technical difference between the two? <Q> The definition of a nacelle refers to the housing of anything on the outside of an aircraft. <S> Engines are the most common thing in these housings. <S> a streamlined housing or tank for something on the outside of an aircraft or motor vehicle. <S> The definition of a cowling is specifically a removable cover of the engine. <S> the removable cover of a vehicle or aircraft engine. <S> The cowling would just be the removable part of this cover. <S> As Jan Hudec commented, engines mounted in the nose, as is typical in smaller aircraft, would have a cowling to allow access and cooling to the engine, but technically not a nacelle, since the covering would be part of the fuselage. <A> The nacelle is a housing that is separate from the fuselage, that holds something, usually engines or some other equipment in an aircraft. <S> The following figure shows some of the engine nacelles. <S> Source: <S> adg.stanford.edu <S> A cowl or cowling is any part of the aircraft (or engine nacelle) that can be opened or removed (for inspection etc.). <S> The following image shows cowlings in a nacelle. <S> Source: <S> compositesworld.com <S> These are maintenance cowlings. <S> Another type of cowlings (like NACA cowlings) serve to direct the airflow into the engine. <A> Nacelle comes from the french word "nacelle" which is the gondola or wicker basket suspended beneath a balloon. <S> So, by analogy, many things that are outside the body of an aircraft, like the compartments that house the engines, can be called nacelles. <S> A cowling is the covering of a vehicle's engine even if that motor is not inside a nacelle. <A> Nacelles usually have structural components like frames,formers and stringers due to there sizes, and are found mostly on turbine engines. <S> while Cowlings don't always have structural components and are usually smaller in size compare to Nacelles as seen on piston engine aircraft.
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So a nacelle refers to the whole covering of an engine that is outside the plane, typically on the wing.
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What is the ultraviolet signature, if any, of aircraft and jet engines? The Wikipedia article on the FIM-92 B variant of the Stinger Missile says: In this version, the infrared seeker head was replaced by a combined IR/UV seeker that utilized rosette scanning. This resulted in achieving significantly higher resistance to enemy countermeasures (Flares) and natural disturbances. Production ran from 1981 to 1987, a total of 600 missiles were produced. I'm assuming "IR/UV" means "infrared/ultraviolet." Do aircraft (or jet engines) really have a strong ultraviolet signature? If so, how is it formed? Is it only evident at high airspeeds? (Also, what on Earth could it be talking about by "natural disturbances"?) <Q> Your assumption is correct - it is indeed about infrared (wavelength between 750 nm and 10,000 nm) and ultraviolet <S> (wavelength between 100 nm and 400 nm) radiation. <S> The sensor detected two specific wavelengths, one from each range. <S> Every body has an electromagnetic radiation <S> which is consistent with its temperature. <S> This radiation has an intensity distribution which shifts to shorter wavelengths with temperature. <S> By comparing the intensity of the IR and UV parts of this radiation, the sensor can much better distinguish between radiation sources of different temperature. <S> Flares are normally hotter than engine exhausts, so by detecting an excess of UV radiation, the sensor can distinguish between flares and exhaust pipes. <S> "Wiens law" by 4C - Own work, based on JPG version . <S> Licensed under CC BY-SA 3.0 via Commons. <S> Natural disturbances means reflected sunlight off a polished aircraft surface or canopy, or off lakes or windows on the ground. <S> Even after filtering by the upper atmosphere, sunlight will contain much more UV radiation than your average exhaust pipe, and glares were a big distraction to early thermal seekers. <S> Sunlight would correspond to the green line in the diagram above, while the exhaust would be even below the dark red line. <S> Note that the absolute intensity also goes up with temperature, but would not help in identifying the temperature of a target if only one wavelength is observed. <S> A more distant, hotter target would cause the same intensity than a colder, closer one. <S> By sensing two wavelengths, the sensor could much better tell an exhaust pipe from other heat sources. <S> Lighting the afterburner will increase the UV radiation, but it will still be much less relative to the IR radiation that that of, say, burning magnesium . <A> What is the ultraviolet signature, if any, of aircraft and jet engines? <S> The exhaust plume of the jet engine that has radiation which flickers within the Ultraviolet Range and the ultraviolet light radiation that exists as a result of a pressure wave on the tip or leading edge of the aircraft that is moving fast enough to create a sonic pressure wave. <S> Several different constituents of a jet engine – accretion flow; stellar magnetosphere; winds and inner parts of the accretion disk radiate in the Ultraviolet spectrum. <S> I'm assuming "IR/UV" means "infrared/ultraviolet." <S> Correct <S> Also, what on Earth could it be talking about by "natural disturbances"? <S> In this context, what it means is that Infra-Red (IR) is the main method of tracking the target. <S> Ultraviolet(UV) is used in addition to discriminate the target from flares and "natural disturbances" like direct sunlight or sunlight reflecting from clouds as they usually have totally different amount of UV radiation compared to the target. <S> Basically they are referring to the Proportional Guidance system of the Stinger MANPAD. <S> Since the primary job of MANPADS like Stinger is to stay locked on, the heat seekers’ fields of view are usually small to prevent distraction from competing sources. <S> Seeker optics magnify IR/UV signatures emitted by distant aircraft,keeping track of the target aircraft is another matter altogether <A> In general, the aircraft (or its exhaust) does not have any appreciable UV emission. <S> MANPADS such as Stinger using a IR detector can be confused by launching flares that have the same (or similar) IR signature. <S> The reason the UV sensor was added was that that it can be used to discriminate the target by detecting the 'UV shadows' cast by an aircraft in a background sky radiance of atmospherically scattered solar UV. <S> These will be different for the actual aircraft and the flares. <S> Some Soviet missiles achieved the same effect by using IR sensors in two different wavelengths, while most modern missiles have sensors of sufficiently high resolution to discriminate the target. <A> Contrary to the suggestions in replies to this question the UV seeker of the FIM-92 Stinger looks for the "shadow" created by an aircraft against the relatively bright UV background of the sky. <S> The aiming and arming procedure of an FIM-92 with a dual-frequency seeker involves, amongst other things, aiming the seeker at a patch of empty sky for calibration purposes. <S> At night one imagines it reverts to the more basic modes alluded to above. <S> UV seeking mode mentioned here: https://bit.ly/2Hm59w5 <S> Still working on where I discovered the "point seeker at empty sky" calibration procedure.
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To answer the question directly: The UV signature of the aircraft itself is practically zero except for the reflection of the UV part of sunlight, and the active UV emission of a jet engine is extremely low and concentrated around its exhaust when seen from behind. You're correct that IR/UV means Infra red/Ultra Violet.
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Can any aircraft adjust the wing dihedral in flight? Are there any aircraft that can mechanically modify the dihedral angle of the wings whilst in flight? Would this solution give any advantage? <Q> There was one, and it did it to increase directional stability at supersonic speed. <S> I am talking of the North American XB-70 , of course. <S> There were three benefits to this configuration: Improved directional stability. <S> Without the effect of the folded-down wingtips, the XB-70 would had lost all directional stability upwards of Mach 2. <S> The wingtips folded down to 64.5° anhedral (or is it -64.5° dihedral?) <S> which effectively made them into ventral fins. <S> This answer explains how a ventral fin is especially helpful at supersonic speed, because it works in the compressed air below the aircraft. <S> Less shifting of the aerodynamic center. <S> Since the transition to supersonic flight will shift the aerodynamic center back, folding the wing tips down reduces lift in the aft section of the wing, thus reducing the aftward shift. <S> Better capture of the compressed lower wing flow for lift creation, which is called a waverider . <S> This increases the pressure on the lower side of the wing at high supersonic speed and allows to fly with a reduced angle of attack, thus reducing drag. <S> XB-70 landing with wingtips <S> straight (picture source ) <S> XB-70 in flight with wingtips down (picture source ) <S> The XB-70 is also one of only a few types where every aircraft ever built had different dihedral: <S> AV-1, the first prototype, had 0° while AV-2, the second prototype, had 5° dihedral over the whole wing to improve yaw and roll stability. <S> Only the dihedral of the outer panels could be adjusted in flight, however. <S> According to this source (PDF!) <S> they were the largest moveable aerodynamic device ever used on an airplane. <S> Other cases of variable dihedral were less intentional, though, and there was really no advantage to it: <S> Like on many Navy aircraft, the wings of the F-4 could be folded for stowage. <S> If the mechanism was not locked, the wings would fold up. <S> The F-4 was even powerful enough to be flyable this way. <S> When only one side folded up, the F-4 would crash , however. <A> Image from stackexchange.com <S> The North American XB-70 had a wing tip which was foldable in flight, which helped trap the shock wave under the wing between the downturned wing tips, creating compression lift, and also improved directional stability at high speeds by adding more vertical surface to the aircraft and reducing the rearward shift of aerodynamic center. <S> " <S> XB-70 final proposal " by NASA - NASA CR-115703, Volume 2, page 23.Transferred from <S> en.wikipedia to Commons by TheDJ using CommonsHelper.. <S> Licensed under Public Domain via Commons . <S> Ornithopters vary their dihedral all the time. <S> Ornithopter built by University of Toronto School of aerospace technologies; image from philschophoto.com <A> Hang-gliders are an obvious answer. <S> For over 30 years, all higher-performance hang-gliders have had a pull-cord <S> to tighten/loosen the sail, variously called "variable billow" or "variable geometry". <S> A sail which billows more in the middle will naturally give you higher dihedral. <S> The tradeoff of course is higher drag, which is why it's controllable - pilots pull on VB/VG for best performance in glides, and let it off for tight manoeuvring (e.g thermalling) or slow flying (e.g. takeoff/landing).
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In general, any aircraft will have its dihedral modified in flight due to the aerodynamic loads, though it is more pronounced in case of aircraft having high aspect ratio and slender wings like the Boeing 787.
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Can people who suffer from motion sickness become pilots? Suppose a person suffers from motion sickness when flying, but wishes to become a pilot (let us say, with the eventual goal of flying for a major commercial airline). Is this possible? Is motion sickness a medical disqualification for a pilot's license, in many or most jurisdictions? Most over-the-counter motion sickness medications cause drowsiness, so they are obviously not a good idea for a pilot to take. Do pilots have access to other effective treatments that are safe to use while operating an aircraft? Do pilots find that they get over motion sickness the more they fly, similar to the way sailors develop "sea legs"? Are pilots taught techniques to remain focused on flying even if they are experiencing motion sickness symptoms (nausea, vomiting, dizziness, etc)? <Q> The short answer is yes. <S> I can't answer all your questions in detail, but here's some US-based information. <S> First, is it disqualifying? <S> According to the FAA , if a candidate for a medical says he suffers from motion sickness then "a careful history" is required, and if the person requires medication then FAA approval (i.e. a special issuance ) is needed. <S> Motion sickness also seems to be fairly common in new pilots, by the way: Approximately 10% of all students taking flight training will become airsick at some point during their first 10 flights; 15-20% of these will have a severe enough form to interfere with their control of the aircraft. <S> Second, are there alternatives to medication? <S> The FAA has a video about motion sickness and how to deal with. <S> I haven't watched it <S> but the description implies <S> yes: <S> This video provides practical advice on diet, medications and other exercises to help cope with this potential problem <S> Wikipedia also mentions various treatments although some (like head-mounted displays) seem impractical for civil aviation at least. <S> Third, do pilots adjust over time? <S> Apparently, yes. <S> This FAA document says: The experienced or acrobatic pilot is conditioned to withstand abrupt attitude changes that a passenger or helicopter pilot might not have experienced. <S> [...] <S> Continued gradually escalating exposure is the most common process for facilitating adaptation. <S> Several days and repeated sessions of flying usually conditions the patient to the new environment. <S> That exposure would also be an alternative to medication, of course. <S> And Sami's answer has some interesting personal experiences. <S> Finally, are pilots taught techniques to stay focused on flying? <S> Instrument rated pilots are trained to ignore their physical sensations and focus fully on their instruments instead. <S> But that training has nothing to do with motion sickness as such, and I have no idea how pilots who do suffer from motion sickness are affected (or not) when flying on instruments. <A> I think there is no straight <S> yes or no answer to this question. <S> It all depends on the level of one's sickness. <S> "To suffer from motion sickness" is a relatively loose definition. <S> I would say everyone suffers from it, once the motion is rough enough. <S> The key is how much can one take and how much it affects one's ability to pilot the aircraft. <S> A pilot shouldn't get sick in normal operation. <S> Out of personal experience, I suffered from motion sickness during my initial training in air force. <S> I got nausious on aerobatic flights, and that prevented me from going beyond basic training. <S> However, I applied to a civil aviation academy and I'm currently employed as a commercial airline pilot, and have no problems with motion sickness in an airliner. <S> A commercial jet pilot doesn't experience aerobatics or rough maneuvres and therefore is less prone to nausea. <S> As of the sea legs , yes. <S> Experience most certainly helps, and one gets less and less nausious. <S> Simplified a little, motion sickness itself is caused by conflicting perceptions from your balance organs (sorry, don't know all the english terms) in your middle ear and from your secondary balance receptors, such as sight. <S> Meaning that if your inner ear organs feel that you're for example tilting your head to the right, but if you read a book and the book stays still, your sight is telling you that you're still. <S> Your brain can't decide which one is correct, and you get nausious. <S> During pilot training this is explained, but at least in my studies, the techniques to handle motion sickness was mostly up to me. <A> With regular practice, your body may become used to the motion so that motion sickness lessens or goes away (also going on roller coasters etc may help - although I personally don't like roller coasters and have never tried it). <S> You may find that being in the driving seat (i.e. doing the flying), lessens or removes motion sickness and you only feel it as a passenger when you are not looking at an horizon (real or artificial). <S> I can go up in the roughest weather when I'm doing the flying but don't like it too much when a passenger. <S> But if these (and other measures) don't work, ultimately it may well stop you if you have symptoms anything other than very minor, because motion sickness is so debilitating, it would prevent you from relaxing and stop you from thinking and functioning as a pilot.
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So it all depends on the person's individual situation, but it is definitely possible to get a medical, even if you require medication.
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Can an aeroplane ever be so far away from an airport that it cannot land? Hypothetically, if an aeroplane with two engines is flying over the ocean and is far away from land, is it not quite likely (but still not very likely at all), that one engine fails and it cannot get to an airport before fuel runs out? Are there any procedures/precautions that are specifically thought out for this scenario or is it just too unlikely to ever happen? <Q> Can a commercial airplane fly outside the safety area? <S> Yes, there is nothing physically stopping the plane from doing so. <S> Is it allowed to do so? <S> No, precisely for the event should an engine fail <S> then it will have enough range to get to the airport and make a safe landing. <S> Extending the allowable range of twin engine aircraft is what ETOPS (Extended-range Twin-engine Operational Performance Standards) <S> is about. <S> By default commercial airplanes with 2 engines must remain within 60 minutes flying time of an airport in case of engine failure. <S> This was decided at a time where engines were unreliable. <S> However as engine reliability increased airplanes could have that range increased with an ETOPS certificate. <A> It is against regulations not to have enough fuel reserve in case of engine failure to reach a diversion airport (for commercial flights at least). <S> So unless the airplane is breaking the regulations, it is not possible. <S> However, it is possible that both engines fail, or that a fuel leak/contamination could prevent an airplane from reaching his diversion airport. <A> There is never a situation that it cannot land - if the engines fail, the pilot has little choice than to terminate the flight. <S> Some aircraft are prepared for landing outside of airports. <S> The most obvious examples should be amphibians <S> which can use both conventional runways and water surfaces for take-off and landing. <S> In the first part of the last century the reliability of engines and the availability of airfields was low enough to make them and flying boats, which operated exclusively from water, a sensible choice for travel over long overwater routes. <S> Also, it was easier to open a staging post on a lake than building a long runway in a remote location, and the short range of early airliners forced airlines to fly long routes in many relatively short hops. <S> BOAC-operated Boeing 314 Clipper (picture source ) <S> Even today, ditching capacity is part of the design , and aircraft are able to float for some time if they are landed on water without structural damage. <S> One example is an A320 which flew into a flock of birds and had to land in the Hudson river. <S> US Airways Flight 1549 floating on the Hudson river ( source ). <S> Regulations ensure that the emergency slides can be used as rafts and the life vests do indeed help to stay afloat for a limited time, temperatures permitting. <S> However, a ditched aircraft will sink eventually, and without quick external help, ditching will quickly turn into a disaster. <S> If the ground is solid, flat and obstacle-free, even a modern airliner is able to land on unprepared ground . <S> Here is a video of an Illyushin 62 landing in a field . <S> Note that it was not anywhere near its maximum flight mass at this event. <S> It was the last flight of this bird; now it sits idle as a tourist attraction in the German countryside.
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Operating an aircraft carries a remote risk to land on unprepared ground.
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Is it possible for more than one airplane intercept the ILS at the same time? I was watching a timelapse video yesterday of the approaches on a busy airport (I don't remember which one), and I saw that about 3 or 4 planes were lined up and descending at the same time (they were far from each other) and that got me thinking: Is it possible (from a technical perspective) for more than one airplane to intercept the ILS signals (glideslope and localizer) at the same time? <Q> The ILS does not lock or tune onto one single aircraft, it continuously broadcasts the localizer and glidepath signal. <S> Since the localizer and glidepath antennas are located at the end of runway for the localizer and at the side of the runway for the glidepath, you will only need to worry about interference by aircraft on the ground, where they are close to the antennas and can deflect the signal due to proximity. <S> This is why there are protection areas and aircraft need to hold at certain holding points, e.g. CAT II holding points when CAT II approaches are in use. <S> Aircraft in the air can also interfere and deflect the signal, however the emitted signals spread in a cone, so other aircraft still can receive the correct signals. <S> To quote KeithS from one of the comments: <S> [...] basically, the localizer is projected from the far end of the runway, and the glideslope is projected from the side of the runway at or near the touchdown target. <S> Thus, aircraft in line to touch down on the ideal target will have good line-of-sight to both transmitter pairs (unless there's an aircraft in the ILS Critical Area) <S> (Image Source: www.aopa.org) <S> (Image Source: nustyR AirTeamImages <S> (found via LondonReconnections )) <S> (Image Source: <S> When is an aircraft cleared to land? ) <A> If you look at the following picture, you'll see that a typical Localizer can giving reliable signals up-to 18NM from its position. <S> On the other hand, a typical Glideslope can give reliable signals up-to 10NM. <S> That said, it is absolutely possible to have multiple-aircraft conducting the approach right behind each other as long as all aircraft receive positive guidance. <S> Needless to say, traffic separation has to be maintained according to the regulations. <A> An ILS is a beam of radio energy pointed down the approach path, there's no limit to how many aircraft can be using it from a technology point of view. <S> In practice you will only have a few descending on the ILS at the same time due to separation requirements. <S> As you could see the 4 airplanes on approach it means that conditions were visual, so the airplanes weren't necessarily using ILS for approach. <S> It's probable they were all approaching visually.
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Yes, since the ILS is just a set of radio signals emitted and received by aircraft, there can be more than one aircraft established on localizer and glidepath.
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Do commercial aeroplanes use ABS to brake? I have read that the wheel brakes on an aeroplane are by for the most efficient means of stopping it. I was wondering whether in low grip situations, such as in rain or snow, an ABS (Anti-lock Braking System) system is used to ensure the wheels do not lock. If not, why is this not necessary? <Q> Yes, they do. <S> They are called Anti-Skid and they go from Mark I of 1948, with simply an on-off switch triggered by wheel lock, till Mark V (or at least that's the last I've seen), with quite complex control systems and sensors behind. <S> The full details are a bit long to include them all here (there are entire book sections about them ). <S> For a brief overview, see this presentation from slide 12 till 18. <A> It is not called ABS but Anti-Skid, but the principle is similar. <S> All large aircraft have it. <S> The purpose is however slightly different. <S> In aircraft the nose wheel has relatively little weight on it and is usually not braked, so directional control, the main reason for ABS in cars, is possible¹ even without anti-skid. <S> However due to the higher speeds and weights involved, aircraft have much higher risk of skidding and hydro-planning and when either happens, it can severely damage the tires, so the anti-skid is to prevent that. <S> ¹ <S> To an extent. <S> Since the nose wheel has little weight on it, it also has limited authority, so if the braking force becomes too asymmetric, the nose wheel can't compensate for it. <A> The ABS systems in automobiles were based on the systems that had been in use in aircraft for decades. <S> Source: https://en.wikipedia.org/wiki/Anti-lock_braking_system#History <A> The first ABS system used in a car was the Dunlop Maxaret system, which was developed for aircraft (and used in a lot of British aircraft in the 1950s and 1960s). <S> It was used in the Jensen FF , introduced in 1966. <S> From 1971, car manufacturers introduced purpose-built automotive ABS.
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ABS was first developed for aircraft use in 1929 by the French automobile and aircraft pioneer Gabriel Voisin, as threshold braking on airplanes.
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Are “zero-bag fares” really profitable for airlines? Any extra weight costs the airline in fuel. So, if none of the passengers carry any extra luggage (be it checked in or cabin luggage), will it lead to lesser fuel for the airline, thus lesser expenses, which would justify the lower “zero-bag fares”. Or, do the airlines have to meet some minimum weight criteria anyway to make any feasible fuel savings. <Q> That's mostly a marketing ploy; people that don't have any bags are more likely to go with a airline that has a no-bag fare. <S> It also means that if you got lost and didn't make it to the gate in time they don't have to offload any luggage but can simply pushback as soon as the gate closes. <S> The freed-up space is then available for non-passenger cargo transport like mail. <A> One thing this does allow the airline to do is sell the space as freight space . <S> Since every plane out there has a maximum take off weight the airlines need to make sure they can fit People + Bags + Fuel on the plane before hand. <S> If they allow each passenger to bring a 50Lb bag then they need to make sure that they can take off assuming everyone on board brought a bag even if no one brings a bag. <S> If an airline can sell a no baggage ticket then they can turn around and guarantee that to freight hauling to make up the costs. <S> In some other cases it changes how people use the airline as a mode of transport. <S> A lot of people fly for business and generally would stay the night in their intended destination for what may only be one day of meetings. <S> If an airline offers cheap no bag fares <S> an individual may chose to fly out in the morning and back home in the evening after their business is done in which case they may not need to bring a bag. <S> This may help in having people fly both ways on the same airline (although most round trip tickets are booked on the same airline anyway). <S> It also opens up idea of "daily commuting" on a plane. <A> This is nothing to do with weight or costs. <S> Using a 'zero bag' price with a surcharge allows them to advertise a flight for less, and many people will take that flight over one for twenty dollars more, without checking or realizing that the 'more expensive' flight gives them a free bag and the 'cheap' one charges forty dollars for a bag. <S> It maximizes the chances that your flight shows up at the top when your flight is ordered by prices on the booking website.
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However not having any checked-in luggage means less overhead in terms of baggage handling as it's a bag less to load and keep track of.
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Jettison and Dump fuel - Do they have separate meanings? According to the definitions, is there any difference between Jettison and Dump fuel? Does one of them use a different procedure, or they are simply synonyms? <Q> In the linked image, the large tank below the main body is an external fuel pod that can be jettisoned . <S> Jet with external fuel tank <S> I believe in WWII that P51s would have drop tanks for escorts that would be jettisoned once an enemy encounter was expected. <S> Dumping fuel would simply mean that there is a type of valve located on the fuel tanks that can be actuated in some way such that the fuel can freely exit. <S> Jetliner dumping fuel To say differently, if one was holding water in a bucket, pouring the water on the ground would be 'dumping fuel' and simply dropping the bucket would be 'jettisoning fuel' Reviewing the wikipedia article on Fuel Dumping , the author(s) make no such distinction between dumping vs jettisoning and seem to use jettison solely. <S> In the context of ATP, after reading the wikipedia article on fuel dumping, I believe that they are considered synonyms. <S> I believe a non-pilot would go more along with my definition however. <S> I answered in this manner as I believe that the OP is not a native English speaker and that clarification was needed as to distinguishing the two as they seem very similar. <S> I am a native English speaker, but lay no claim to being a master of it. <A> Jettison means to throw or drop (something) from an aircraft. <S> Dumping fuel means the fuel (alone) is jettisoned. <S> One can jettison any item (removable in flight) from the aircraft. <S> For example, a combat aircraft jettisons its fuel tank, while a civil airliner dumps the fuel, not the tank. <A> Jettison means to 'throw something overboard' <S> , it isn't limited to fuel. <S> To take a practical example, if I experienced engine failure in a light aircraft and had to make an emergency landing (especially a ditching), I might jettison any large or heavy items in the cabin to avoid them causing injuries during the landing. <S> This appears in the ditching checklist for the C172, for example (my emphasis): DITCHING Radio -- <S> TRANSMIT MAYDAY on 121.5 MHz, giving location and intentions and SQUAWK 7700. <S> Heavy Objects (in baggage area) -- SECURE OR JETTISON <S> (if possible). <S> Therefore, dumping fuel is one specific type of jettisoning where only the fuel is jettisoned.
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In the context of fuel, jettisoning fuel would imply that the fuel is in a container that can be detached while in flight.
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Does landing in extreme weather conditions require any different or special training? Is there any special training, relating to land under extreme weather, such as snow storms, contaminated runways or ice conditions? <Q> On one hand there are physical limits to which a plane can be landed when it comes to wind both head on and cross winds. <S> Granted they are cases they may never or only rarely come up you may simply not be able to land the plane. <S> Assuming you have made it to the airport and are able to land... <S> There are some check lists and different procedures that me be executed for different weather. <S> Approaches are flown as published but changing winds and weather may cause the pilot to react differently or do different things to fly the approach. <S> For example if you compare a calm wind approach to a dry runway with a wind sheared approach to a wet runway you may see some differences. <S> The pilot may elect to come in a few knots over Vref and possibly with less flaps in a wind shear situation. <S> Again this is not special training as much as it is standard. <S> On a contaminated runway the pilot may chose to preform something like a short field landing so as not to potentially collapse the nose gear. <S> All pilots (even GA) are trained in this maneuver. <S> There are so many possible situations here it would be hard to train for ever one but some are trained for or a checklist exits. <S> Side Story : I was talking to a commercial pilot recently who flies the 777 <S> and he was telling me a story of a time during training in the sim where they gave them heavy rain and 40Kts of wind shear (no one could successfully land the plane that day in his group in the sim). <S> So they do at least throw situations like that at pilots in the sim, if they do it all the time I cant say. <A> As a pilot, you are trained for all eventual failures and conditions, but above all else your priority is the safe operation of the aircraft. <S> Therefore, landing during hazardous conditions is always avoided as a primary response. <S> There is nothing special (beyond training in the simulator) that is required to land aircraft in difficult conditions; because the mechanics of landing the aircraft do not change, just the variables you have to account for. <S> So, as common sense - during rain/sleet/snow/ice - a longer rollout is required to come to a stop. <S> You may also land with extra reserve power in case a takeoff/go-around is required (especially true in high wind / wind shear conditions). <S> Other than that, there is nothing special about landing in snow/sleet/rain vs. normal conditions. <A> In commercial pilot training, they have to go through training for all sorts special situations training. <S> So it probably is not "special" as requiring a whole new course or something like that although it might be "special conditions" inside the training programme. <S> However, as a comment above said, it would be safer to divert to an alternate airport if possible.
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Snow and wet runways in general may see a longer landing distance and roll out however this is not "special" training as landing distance should always be calculated based on conditions. In some regards there is but this depends on what you consider extreme weather . Every pilot must go through training for such situation.
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Why should a test flight be performed when the propellers are changed? From this question I've learned that after a propeller change the plane should go through a test flight. Why is this? <Q> The purpose of the test flight is for the safety of passengers. <S> For most maintenance, in a not-for-hire aircraft, a private pilot can perform the test flight and determine the aircraft is airworthy, but they must do it without passengers. <S> Title 14 chapter 91.407 <A> Often when people talk about propellers, they think of them as a solid piece of material attached to the crankshaft of an engine. <S> This is true for small planes, but absolutely untrue for larger aircraft. <S> On small aircraft, you might do a test flight to insure that the propeller functions properly in all flight modes. <S> Mostly you'd be looking to insure that replacing the prop actually fixed the problem your were having. <S> Defects in a fixed prop might make it vibrate due to not being properly balanced, which will show up on runup, or it might have an internal flaw that will only be apparent at particular flight modes, like ascending, descending or level flight and turns. <S> On larger aircraft, propellers are more sophisticated. <S> A reciprocating engine tends to develop maximum power in the 2200 to 2500 RPM range, so the engines are set to run in this range and the actual thrust is modified by changing the angle of attack of the propeller blades. <S> This is usually accomplished by either an electric motor or a hydraulic piston. <S> The motor or piston is in the hub and geared to the blades. <S> This makes the overall propeller system much more complex, and requires exercising it before certifying it flight ready even more important. <S> Adjustable propeller blades can be turned to a negative angle to allow engine braking on landing, and backing up on the ground. <S> It can also be 'feathered' if there is an engine failure, so that the engine will not continue to turn over if it is shut down in flight. <S> Additional notes: There are other adjustable propeller systems that use air pressure or mechanical gearing. <S> Gas turbine engines have an even narrower maximum power range, and require even more complex propeller systems. <S> They turn at around 10,000 RPM and use a gearbox to turn the props in the 2200 rpm range. <S> During my time in the Air Force, I changed propellers on C-124s, C-130s, C-133s, and a few other propeller driven aircraft. <S> None of these changes required an actual flight verification, but did require a runup with a checklist for specific verification. <S> Of course the pilots and flight engineer would be aware that the prop had been changed. <A>
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It is so that the props are tested to see if they have any defects or not as well as to make adjustments based on their behaviour.
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Do airlines employ FAs from their destination countries? I'm watching a documentary about daily business of an airport. There was a crew briefing for a Lufthansa flight from Germany to India, and as there was an Indian FA, the briefing was held in English (i.e. he didn't speak German). While it is advantageous to have an Hindi speaking FA on board of a flight to India, I wonder why he doesn't speak German.To me, it seems unusual to have an employee living here, but not speaking our language. (Though this is possible.) So, my question is:Do airlines employ people in their destination countries, for example to have FAs speaking the language of the destination country? Or is there some kind of exchange project? <Q> The 747 carrier I retired out of had FAs based in New York and Tel Aviv, and were residents of their respective countries. <S> The citizenship of the JFK FAs was not a factor insofar as I know as there were numerous green card holders. <S> Non-stop flights between JFK and Tel Aviv (and return, of course) were staffed by Israeli FAs. <S> All other flights were staffed by JFK FAs. <S> The primary reason for this arrangement was cultural. <S> For JFK/TLV the back quarter or so of the aircraft was allocated to Hasidics to attempt to satisfy their preferences. <S> For example, no movies were shown in the back because they were objectionable to the Hasidics. <S> The advantage of having Israeli FAs on the direct flights was that they knew how to handle the Hasidics. <S> Scheduling problems would occasionally result in JFK FAs operating a JFK/TLV flight. <S> It was not uncommon on such flights for the cabin crew to request a cockpit crew member to come back to help mediate a dispute. <S> I never received such a request from an Israeli cabin crew. <A> Airlines do employ people in their destination countries for a variety of tasks, both customer-oriented (such as gate agents and baggage handlers), as well as administrative and/or operational (such as station managers, maintenance staff, etc.). <S> Now, with respect to flight and cabin crew, things can get a bit more complex. <S> With respect to FAs, major carriers make an effort to staff their cabins with FAs that speak the local language when travelling to international destinations. <S> The FA might not have spoken German, but in addition to English, he might have also spoken Hindi, or any number of regional languages spoken in India, thus allowing the crew a greater probability of having someone who can can converse with any passenger on the flight. <A> Yes, Swiss does it for their Tokyo destination. <A> Yes they do. <S> My earlier flight this year on Hong Kong Airline from Hong Kong to Bangkok has FA who are Chinese and Thai. <S> Cabin announcements were made in 3 languages, Chinese, English and Thai.
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Generally speaking, crew are hired and certificated in the country where the carrier is based out of (and, incidentally, certificated to perform air transportation operations for hire), and would have to follow local employment and, potentially, immigration legislation should they wish to hire foreign nationals; certain countries may make exceptions to these rules for airlines and the transportation industry, making it easier to hire staff with the necessary language skills, but this is by no way a given.
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Is there any cockpit procedure used to avoid shutting the good engine, instead of the bad one (on fire, for example)? Reading some reports, about the failure of crew members to fully understand the fault on engines, rarely, but it happens, the crew can misjudge the engine on fire, shutting down the good one. On airlines where you fly, is there any standard procedure to avoid this event, I mean, shutting the good engine, instead of the bad one? <Q> Procedures exist If you read about the Kegworth crash <S> you will see that the pilot started to follow a procedure he has been trained on but was interrupted by an ATC call and failed to complete the procedure. <S> The procedure involves checking the engine vibration meters and reviewing decisions. <S> So, yes, procedures exist. <S> Procedures vary Procedures vary depending on exact aircraft model and on the airline operating the aircraft. <S> Some airlines use more memory checklists than other airlines. <S> So it isn't possible to list a specific procedure that is used by all pilots of multi-engined aircraft. <S> Identifying problems <S> Pilots don't start from the point <S> "we need to shut down engine <S> No 2" they start from some observable event like "smoke in the cockpit" (as in the example incident above) <S> There are instruments on the instrument panel that show engine temperatures, vibration and other parameters that should usually make it evident which engine is not performing normally. <S> Here's an example procedure - note that this isn't the one for the airline and plane model in the incident above <S> but it is probably similar <S> Note the points <S> Eliminates <S> No 2 engine as source ... ... <S> Eliminates <S> No 1 engine as source ... <A> The point is to be sure that the affected engine is shut down. <S> Boeing has inserted a recommendation for that in their Flight Crew Training Manual (FCTM), mentioning explicitly: <S> Mistakes were done in the past. <S> PF must coordinate with the PM in the procedure. <S> The procedure also includes to retard thrust on the affected engine slowly . <S> It gives time to feel something unexpected, like the aircraft loosing power on both engines (for a twin). <S> You can find such recommendation in the Boeing 737 NG FCTM and the 777 FCTM, like this one , page 308 (this is logical page 8-8 in both manuals). <S> Recommended technique for in-flight engine shutdown Extract for convenience: These FCTM are usually customized by operators / airlines before being used for crew training, so the recommendation may be improved or edited to better fit the company standards, but that's the idea. <S> The recommendation is not to be confused with the checklist for shutting down an engine, which depends on the cause of the problem. <S> The checklists are part of the non-normal checklists (referenced in the extract above as NNC ). <S> E.g. if there is a fire detected, the crew will apply the related NNC which is found in the Quick Reference Handbook (QRH), like this one , page 170. <S> Extract for convenience: While the NNC in the QRH just provides steps like: Thrust lever (affected side) . <S> . . . . . <S> Confirm. <S> . . . . . . . . . <S> Idle <S> the FCTM recommendation provides a way to train crews to ensure the affected side is properly identified. <A> The design of the cockpit itself shows that there is a procedure. <S> Beyond that, a common approach is asking the pilot monitoring for confirmation about which engine has problems before pressing the button. <S> Of course, to make it work, it has to be emphasized in the training process. <S> I have been a witness in a situation where the pilot asking for confirmation had already the finger on the switch... <S> if that is not corrected, you can be sure that, whatever the answer of the other pilot should be, he would press that button.
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If you look in places like Airliners.net the upper panel in an Airbus, you will find that the extinguishers have a cover to prevent the unintentional activation. Don't hurry in the engine shutdown.
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What does the term "tanker" mean when used in regards to a passenger airliner? In a comment on this answer : Airlines will tanker fuel if it's substantially cheaper at another airport I've wondered what that term meant before, and now this comment leads me to think that airliners will carry more fuel than what's required for a trip, because carrying the fuel might be cheaper than buying it at the next airport. Can someone provide more detail on why and when an airline might do this, the calculations that are involved, and any other interesting information on this topic? <Q> Since the 1960's and 1970's when political hijackings were a problem, airplanes started to only carry the fuel required for the flight. <S> This means a typical fuel load will be something on the order of: taxi fuel at the departure airport fuel to fly and land at the destination at a given altitude and forecast winds if an alternate is needed: fuel to fly to the alternate airport 45 minutes of reserve fuel perhaps a bit extra for contingency and to keep captains happy ( <S> e.g. 5-15 minutes worth of fuel). <S> For a normal flight this means you'll land with around 45-60 minutes of fuel on board, sometimes less. <S> You'll fill up for the next leg at this airport while you deplane and enplane passengers. <S> Fuel at the hub airports is sometimes a bit cheaper due to the fuel contracts the airline can secure when they order massive amounts of fuel every day. <S> Fuel at outstations that don't see a huge volume of fuel may be quite a bit more expensive. <S> In this case, and if your weights allow, the airline may elect to load extra fuel that isn't needed. <S> The purpose of this is so you do not need to buy as much fuel at higher prices at the outstation. <S> I only saw this happen operationally when we were going to be very light and the outstation fuel was very expensive. <S> Usually our loads were high enough that we were struggling to get all 50 passengers, bags, and especially jumpseaters on board with the required fuel load. <S> In that case it would not be economical to take more fuel because we'd have to take fewer passengers. <A> Tankering fuel means that an aircraft carries not only the fuel quantity required for the flight to the destination, but also the fuel, or a part of it, required for the next leg of the trip. <S> The aircraft is therefore its own tanker . <S> Tankering means reduced cost <S> This practice can be used when the difference in fuel price at departure and destination airports makes the operation less expensive than refueling at destination. <S> The time to refuel can be also a factor. <S> More: <S> The benefits of tankering considering cost index flying and optional refuelling stops . <S> From the previous article: Fuel expenses remain one of the major components of an airline operational cost, depending on the aircraft size, it may approach from20% up to 70% of its total flight cost. <S> Fuel tankering has been studied and applied by airlines at least since the oil crisis in the 1970 decade. <S> It has become an excellentfuel saving strategy for airliners proving costs reductions up to 10%. <S> Example of price difference in Europe: Difference in fuel prices in Europe, source Eurocontrol Example of savings by fuel tankering: Savings by fuel tankering for airports distant by 300 NM. <S> Eurocontrol <S> How to read: For a round trip between airports distant by 300 NM, if fuel is 20% cheaper at the departure airport, then by performing a full tankering, 45 kg of additional fuel will be needed, but this will save 196 € (8%) for the round trip. <S> From the study by Eurocontrol : <S> [...] it was estimated that fuel tankering could result in a netsaving of <S> 265M€ per year for <S> the airlines. <S> However, it wouldgenerate <S> 286,000 additional tonnes of fuel <S> burnt and 901,000tonnes of CO2 emissions at ECAC level per year. <S> This represents about 2,800 round-trips between Paris and New York orthe annual emissions of a European city of 100,000 inhabitants. <S> (ECAC is the European conference for civil aviation ) <S> Hence: <S> British Airways reviews 'fuel-tankering' over climate concerns <S> Thomsonfly reduces tankering and CO2 emissions ... <A> It basically means they will take on more fuel than necessary because the cost of doing so is cheaper than getting the fuel at the destination airport.
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Tankering means also more CO 2 Tankering means burning more fuel than strictly required, this can provide an economical advantage, but this operation is usually not neutral for our environment, depending on how fuel is delivered to airports.
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Do helicopters try to take off and land into the wind? When helicopters take off and land is it preferable to point the nose into the wind? Since a helicopter is providing its own lift does it matter which direction wind is coming from? <Q> Moving forward through the air helps to make the helicopter more efficient, and it does not matter if that movement comes from hovering in a headwind or from flying forward. <S> For the same reason, a helicopter will climb faster when flying in a spiral than when going straight up. <S> Technically, flying backwards or sideways will also improve the efficiency of the rotor, but in reverse the helicopter will become directionally unstable. <S> Moving the fuselage sideways will create much more drag, so flying forward is the better choice. <A> In general, helicopters require less power while flying forward (or backwards) compared to hover as translational lift (of Effective Translational Lift, ETL) is produced. <S> Even though the blades are providing lift by rotation, the airspeed experienced by the blades is different if wind is present. <S> For example, if there is headwind $v$, the advancing blades will have an airspeed of $r \omega + v$, while the retreating blade will have an airspeed of $r \omega - v$. <S> As lift is proportional to square of airspeed, the implications are obvious. <S> For this reason, it is preferable to take off into the wind, rather than take off vertically. <S> Note that the power required is same for headwind or tailwind. <S> However, tailwind landing (or takeoff) has some disadvantages from stability and power management point of view that is <S> it generally discouraged, like: <S> In case of landing in tail wind, it is very difficult to abort landing and re-gain forward airspeed. <S> Moving from negative speed to forward speed initially decreases the air speed the main rotor experiences, and the Power Curve shows an initial increase in Power Required. <S> As the helicopter accelerates from negative (ground) speed, the main rotor system loses translational lift before it goes through zero airspeed. <S> As a result, the power required increases, which requires increased pedal application and tail rotor power, precisely when the power requirement is high. <S> If there is a power failure, the chances of safe landing is reduced. <S> There is more risk of running out of directional control. <S> In case there is a tailwind, the helicopter vertical tail (and fuselage) may align try to align with the wind, resulting in uncommanded yaw. <S> If not corrected with proper pedal input, this may lead to loss of control. <S> In case of landing, the possibility of brownout or whiteout conditions is more in case of tailwind. <A> Here is something off an FAA document about helicopter performance. <S> https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/media/hfh_ch07.pdf <S> Winds <S> Translational lift occurs any time there isrelative airflow over the rotor disk. <S> This occurs whether therelative airflow is caused by helicopter movement or by thewind. <S> As wind speed increases, translational lift increases,resulting in less power required to hover. <S> The wind direction is also an important consideration. <S> Headwinds are the most desirable as they contribute to thegreatest increase in performance. <S> Strong crosswinds andtailwinds may require the use of more tail rotor thrust tomaintain directional control. <S> This increased tail rotor thrustabsorbs power from the engine, which means there is lesspower available to the main rotor for the production oflift. <S> Some helicopters even have a critical wind azimuth ormaximum safe relative wind chart. <S> Operating the helicopterbeyond these limits could cause loss of tail rotor effectiveness. <S> Takeoff and climb performance is greatly affected by wind. <S> When taking off into a headwind, effective translational liftis achieved earlier, resulting in more lift and a steeper climbangle. <S> When taking off with a tailwind, more distance isrequired to accelerate through translation lift. <A> Effective Translational Lift (ETL) is lift generated by airflow over the rotor, and increases the effectiveness of the airfoil by about 15%. <S> ETL is generated beginning about 15knots of airflow over the rotor. <S> Assuming the helicopter is landing with the nose pointed into the wind, a headwind decreases the ground speed at which ETL is generated. <S> So a helicopter landing into a 15 knot wind can maintain ETL all the way into a hover (when groundspeed is zero). <S> Maintaining ETL as long as possible into the landing is important for 2 different reasons: it requires less power to fly the approach, increasing the safety factor in the case of a go-around, or in high density altitude or high gross weight landings, the requirement to make a run-on landing by maintaining ETL, there is no chance of entering ring vortex state , which is nearly unrecoverable close to the ground, especially in steep approaches
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Wind direction and velocity also affect hovering, takeoff, andclimb performance.
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Is there a preferred turn direction for helicopters? If I have a requirement to fly a helicopter in a circle or racetrack over a point of interest that's stationary or moving relatively slowly, is there any reason to prefer left or right turns? I'm not concerned about visibility and I'm not asking about turns in a landing pattern: I'm asking if - all other things being equal - there's any mechanical, aerodynamic or procedural reason that pilots would prefer to turn in one direction over the other. <Q> Most helis make CW turns because the pilots sit on the right <S> and it is easier to judge position and drift when you can look out the window directly. <S> Turning CCW is no problem however but it takes a tad more concentration. <S> one drawback of CW turns from the right seat <S> is that the ALT and ASI would be out of your field of vision, so you'll have some head turning to peek at them. <S> In a CCW turn, its easy to glance at the instruments in the center console. <A> I am adding an answer as the outer 2 are incomplete. <S> [Simon obviously forgot to add his answer]. <S> I will attempt to explain the aerodynamic reason this only apply to very slow speeds or very sharp turns. <S> If the turn is to sharp and slow, the wrong way and the wind is in a dis-favorable direction, it is possible to "run out of" power peddle meaning there is not enough anti-torque force to stop the turn resulting in a spin and crash. <S> Most flight manuals recommend turns into the direction of the "power peddle" to avoid this. <S> Demonstration of a sharp turn power side vs non power side. <S> note how the first turn is a wide turn away from the [power peddle] and the second is almost a stationary spin [into the power peddle]. <A> Aerodynamically, if performing ground reference turns in a no-wind condition, there is no difference. <S> On the other hand, if in a moderate to high wind condition, Loss of Tail Rotor Effectiveness can be a real danger. <S> Many accidents have been attributed to LTE. <S> LTE can be encountered by way of several different mechanisms, one being turning (orbiting) in prevailing wind at lower speeds. <S> Effectively, main rotor vortices are blown toward the tail rotor at an angle which blanks the inflow to the tr, degrading its effectiveness, potentially to zero. <S> Pilots can mitigate the effect by turning in the direction of the rotor (as viewed from top looking down). <S> There are countless articles and video presentations on the www. <S> Search for Loss of Tail Rotor Effectiveness LTE.
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Vision is a valid reason, but only In confined areas [think valley or other aircraft]
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How is passenger baggage transferred, and how does it happen so quickly? I've always wondered how airlines transfer bags between connecting flights. At a hub, bags must be moved to any number of connecting flights throughout the airport - some with very short connecting times. Seems like sorting them would take a lot of time. How does this process happen? <Q> On big airliners, baggage is mostly stowed in containers, called Unit Load Device s. <S> They are packed at the departure airport and pre-sorted to minimize the amount of sorting at a hub, but normally need to be emptied after arrival so the baggage can be re-sorted. <S> On regional jets and older aircraft which don't take ULDs, bags are still loaded individually and transported to and from the aircraft on open carts which are assembled to small trains (see picture below). <S> Airport baggage transportation (picture source ) <S> Once the ULDs or the carts arrive inside the terminal, the bags are unloaded into the baggage handling system , a collection of conveyor belts, barcode readers and switch points. <S> Since every bag received a sticker with a big barcode upon check-in, the reader can report the barcode of the next bag to a computer wich sets the switch point accordingly. <S> Traditional systems employ humans with a portable barcode reader for putting the bags on the right belts. <S> Baggage tags (picture source ) <S> The most recent systems put the bags on plastic trays which have RFID tags attached, and the RFID information is used for switching the conveyor belts. <S> By loading the bags on standard size trays, the flow of bags is simplified. <S> However, a baggage handling system is a complex piece of machinery, and some new airport terminals were delayed because the system did not work initially, or opened with lots of mis-routed or even mangled bags in their first months of operation. <S> London's Terminal 5 and Denver airport , which went back to manual sorting after 10 painful years of trying to get their system working, come to mind. <S> When they are sorted, the bags are deposited either at a ULD packing station or an empty cart for transportation to their respective flight. <S> At the end of their journey, they are routed onto baggage carousel s for pick-up by their owners. <S> Baggage carousel (picture source ) <A> In case of connecting flights in same airline or between partner airliners which allow baggage transfer, the baggage is usually checked in for the duration of the journey i.e. from source to destination. <S> In case the time between interconnecting flight is short, someone (usually airline agent) picks up the luggage from the the aircraft and loads it into the connecting flight. <S> If I understand correctly, such cases are marked in their tags so as to allow for proper storage in cargo hold (for easy retrieval). <S> Transfer of luggage into a flight, from denverpost.com. <S> As this forum says, Most US airline tags will either be a 'city', 'hot' or 'cold'. <S> City is a bag going straight to where the flight is going. <S> Hot and cold are bags that are connecting onto another flight, depending on the amount of time between flights. <S> Hot bags are usually loaded separately and are the last ones loaded onto the flight so that they are the first ones off at the destination and they can make the connecting flights. <S> Source: australianfrequentflyer.com.au <S> For example, SWA put a single driver in charge of collecting all the baggage for a particular outbound flights from all the inbound ones . <S> In case there is sufficient time between connecting flights, the agent (who has a list of baggage to be transferred) unloads the baggage and loads it into the airport baggage control system, which then sorts it automatically into the correct aircraft. <S> Having the bags in ULD (unit load device) operates in the same way. <S> Each bag bar code tag triggers the opening/closing of a "door" on its way so <S> , after a few branchings it arrives into a "sorter" which sends it into a particular container. <S> Of course, this assumes that there is no security checks involved in the middle (like in international flights). <S> In that case, the system is similar, but involves screening. <A> Preamble I will keep it short and try to hit the point since I see some good answers here, please feel free to comment to get more detailed information <S> Answer <S> How does this process happen? <S> In about 15 minutes the baggage is automatically sorted, thanks to some sensors that scan the bag tag attached to your luggage. <S> In the meanwhile the baggage undergo X-Ray and potentially other security checks. <S> It finally gets to the dedicated " carousel " (similar to the one where you retrieve your baggage). <S> Here the operators put it in different ULD. <S> Transit baggage are usually kept in a different ULD so that they are the first to be unloaded from the aircraft and can be quickly sorted, and re-directed to the correct connection flight. <S> How is passenger baggage transferred? <S> There are three different technologies, and here <S> you can have a detailed look at them: <S> Tilt trays where each baggage has its own tray and the tray is moved around. <S> Convey belts, similar to the one you see in most airport <S> Operators: the baggage are moved by hand by an operator and a dolly
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In airport baggage is handled from the check-in desk to the Unit Load Device (ULD) via a Baggage Handling System .
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What do pilots actually see through the windows? As I have never flown inside a cockpit, but only played with simulators I find that the dashboard takes most of the field of view(or am I wrong?). So what actually can pilots see given good weather conditions, especially during critical parts of a flight, like take-offs and landings ? I'm generally interested in big airliners. P.S. I am not asking if they could takeoff/land without visual contact. <Q> This really depends on the type of aircraft and the seating position of the pilot. <S> In smaller aircraft, you will have a good view of the area around you, depending on the canopy. <S> In larger aircraft, the instrument panel and cockpit design can restrict your outside view a bit more. <S> Below you will find two pictures taken from the cockpit of a Super Dimona HK36, used for VFR general aviation flights. <S> Both are approximately at eye level. <S> (Source: Own Work - SentryRaven) <S> (Source: Own Work - SentryRaven) <A> In a document A319/A320/A321 Flight Deck and Systems Briefing for Pilots (can be found in many places on the net, e.g. on slideshare as presentation ), or page 16 Airbus shows following diagram of visibility from cockpit: 17 or 20 degrees below horizon is not that bad. <S> It is probably a little less than you see from a typical car , but not by much (of course since the pilots are sitting much higher, the nearest point on pavement is correspondingly further away). <S> Note, that whether the above is actually true depends on how the pilot adjusts their seat. <S> The recommended height for eyes is marked on the post between the forward windows. <A> According to Federal Aviation Regulations Part 225, Section 773- Pilot Compartment View , during non-precipitation conditions, Each pilot compartment must be arranged to give the pilots a sufficiently extensive, clear, and undistorted view, to enable them to safely perform any maneuvers within the operating limitations of the airplane, including taxiing takeoff, approach, and landing <S> The FAA advisory Circular 25.773-1 Pilot Compartment View design considerations gives certain guidelines for ensuring pilot visibility. <S> Pilot compartment view from FAA AC 25.773-1 Pilot Compartment View design considerations <S> The figure shows a pilot compartment view for optimum collision avoidancewhen seated in the left (port) seat. <S> For the starboard side, all left/right dimensions are reversed. <S> Usually, the aircrafts offer better visibility compared to the guidelines. <S> For example, the A330's visibility (from Flight deck and system's briefing ) is given here. <S> Image from A 330 Flight deck and system's briefing <S> The actual visibility of the pilots will vary according to the seat position For example, the following figure shows the variation in pilot visibility in Boeing 727 when seat position is adjusted. <S> Image from Airplane Design- Layout Design of Cockpit, Fuselage, Wing and Empennage by Jan Roskam <S> Of course, the pilots can see things which is normally not visible though the windows through cameras mounted on the outside, like on top of vertical tail in A380. <A> This might be a stupid answer, but you can see a lot of take-off, landing videos from cockpit in YouTube. <S> Here's one: <A> I'll illustrate some aspects which I think even the best flight simulation today cannot compensate: Peripheral vision <S> Telling distances and relative positions is much easier. <S> For example, you can tell a certain building is 1000 feet away. <S> When you are landing, you can take a quick glance to either side of the runway and judge whether it is time to flare. <S> Sitting in the cockpit of a 747 feels rather like standing on top of a 3-story building. <S> The best part is, this building moves! <S> It's truly amazing. <S> Detailed view <S> I know this sounds obvious, but I have to put it as number two. <S> Even when you are on final, you can see the little cars with people moving around the ramp and terminal. <S> The cockpit glass is just like the windshield in your car; if you can see something directly, you will see it in the cockpit. <S> You will also see the small cracks in the windshield, especially when sunlight is directly shinning at it. <S> This is a natural property of the material used. <S> If you're flying a single-engine propeller plane, your view will be slightly obstructed by the spinning propeller. <S> Other planes Spotting other planes in a real cockpit is a bit tricky. <S> If the plane is below you, and you're flying over residential areas with lot of houses, it can be hard to spot. <A> As stated in the comments, the view you get in a PC based flight simulator is not representative of the real thing. <S> To get a decent approximation of what you actually see from an airliner cockpit <S> you'd need at least 6 screens in 2 rows of 3 screens each. <S> This of course requires quite a bit of hardware to accomplish :( Using the virtual cockpit feature of some flight simulator software, and cranking up your viewpoint a bit from the default settings, you can get a much more authentic experience already <S> but it's still limited by the tiny viewport offered by even a larger widescreen computer monitor (let alone a 17" 4:3 display which is what many of them are programmed for as it's the smallest common denominator). <S> Of course that virtual cockpit has its own drawbacks in that the instruments are often a bit blurry and buttons and knobs less responsive than in the 2D view (let alone reality). <S> It's a set of compromises we have to live with as PC flyers, dictated by the limitations of our hardware and budgets.
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In general, the pilots are required to have good visibility to execute any maneuvers during normal operation of the aircraft.
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What lifting gas was used for barrage balloons during the world wars? During the world wars, various barrage balloons were used to protect targets from low-flying aircraft or similar threats (e.g. V-1 flying bombs), in particular by Britain. What lifting gas was used for such barrage balloons – the highly flammable hydrogen or the rare and expensive helium? <Q> <A> Hydrogen. <S> Helium was scarce or not available at all. <S> The only substantial source was in the United States, which had a capacity of 24 million cubic feet (680,000 m³) in 1940 . <S> Its commercial and military needs of that time were just a quarter of this amount. <S> If you look at this statistics of word helium production , you will notice that only from 1963 on did total world production of helium differ from the amount produced in the US. <S> You will also note that production shot up from 45 metric tons in 1940 to 608 metric tons (3.6 million m³) in 1944, which is most likely to cover the increased need for war. <S> Also, exports only started in the 1960s. <S> Sadly, the MYB statistics have no export data from earlier years. <S> This lets me conclude that only hydrogen was available in all other countries throughout the war, and only the US used helium. <S> The US production was needed to fill anti-submarine observation blimps. <S> One K-class blimp had a hull volume of 404,000 to 425,000 cubic feet (11,480 to 12,035 m³) and needed to be topped up every few weeks. <S> A total of 134 of that type were built, and just filling them once would already had consumed half of the helium produced in 1944, the most productive year. <S> US Navy K-class blimp in WW II (picture source ) <A> Hydrogen was used in Barrage Balloons flown by the British.
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According to a BBC article here , hydrogen was used, not helium. I understand that the US protected their supplies of the much safer Helium.
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Why does a hydraulic system failure increase the landing distance? Considering wide body aircraft, why do emergencies, related to hydraulic system failure, increase the landing distance? <Q> Any hydraulic failure will affect the landing distance as most of aircraft controls are operated by hydraulics. <S> Hydraulics are also used for operating a number of other systems like brakes, ground spoilers and thrust reversers. <S> Any degradation in their operation will increase landing distance. <A> Landing distance is a function of the formula Kinetic Energy = <S> 1/2 <S> * mass <S> * velocity² <S> Any change that will increase kinetic energy will require longer landing distances. <S> When we land, the kinetic energy needs to go somewhere. <S> It can be converted into heat with the brakes, opposed with drag from the thrust reversers or deployed spoilers <S> Higher landing speed will cause an increase kinetic energy that must be converted on landing and thus you will have a longer landing distance. <S> Braking, thrust reverser or spoiler issues will increase the landing distance because they will not be as effective (take more time) in converting kinetic energy. <S> In a hydraulic issue, most likely the manufacturer has chosen to fly the airplane at a speed greater than needed for a normal landing (VREF + 20) and will most likely not have the ability to use normal braking. <S> Most jets use hydraulic fluid to stop the brakes. <S> In the jets I fly, without normal braking means we use the emergency brakes which are not routed through the anti-skid system <S> so precaution must be taken to not skid the tires. <S> This all adds up to a substantial landing distance penalty. <S> Hare the landing distances for some airplanes. <S> Learjet family: Factor of 3.15 Learjet 45 family: Factor of 2.2 Challenger 604 family: Factor of 1.7 (braking) <S> times 1.8 (airspeed) for a total of 3.06 <A> In most wide body aircraft hydraulics are used to lower flaps, raise spoilers, and in some cases apply wheel brakes. <S> A flaps up landing is going to mean a higher landing speed, no spoilers will mean less drag to slow the aircraft, and not having wheel brakes will mean a much longer roll-out. <S> Also worth noting is that a hydraulic failure which will impact those systems will probably impact flight control surfaces as well, and landing gear extension, so a longer landing distance is the least of a pilot's worries in that situation.
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If the high lift devices (flaps) become inoperative (or become degraded) due to hydraulic failure, the aircraft will have a higher approach speed, which will increase the landing distance.
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How heading bug is calculated during cross wind and tail wind? From this question , it is been suggested to ask different question, rather than keep discussing it under comment section. How is the heading bug calculated and used for navigation when there is a cross wind? … when there is a tail wind? Will the heading bug matter for navigation when there is wind correction required? What role does the heading bug play in autopilot mode? <Q> First thing first, let's go over some concept: <S> heading is which way the plane's nose is pointing at, track is which way the plane is travelling on the ground. <S> E.g. if your heading is 360 (North), and the wind is blowing from 090 (blowing East to West), the plane's track may be 350 (slightly left of North). <S> With that in mind, it's not hard to deduce most of the time pilots want to fly track , rather than heading . <S> The purpose is to navigate from point A to point B on the ground. <S> In our example, you have to turn the plane slightly to the right to compensate for the crosswind. <S> To figure out exactly how many degrees to turn, you will first need to decide how fast you want to fly. <S> After that, it's simple geometry. <S> A mechanical flight computer can be used to calculate the drift angle easily. <S> Using it is a matter of marking dots on a transparent disc, then sliding and rotating it to the correct position and read off the pre-calculated figures below. <S> If you are flying manually, or flying a plane with an elementary autopilot, you will need to calculate the drift angle, then add (or minus) <S> that to your desired track to get the heading . <S> You will then set the heading bug to that value. <S> Theoretically, that heading should compensate just enough crosswind that you stay on your desired ground track. <S> In practice minor adjustments are often necessary. <S> Provided that the numbers you use are not awfully off, you should end up with an estimation good enough for the safety of your flight. <S> If you are flying a plane with an advanced flight computer which has the ability to detect winds aloft, your autopilot will fly the track you dial in and automatically compensate for crosswind. <S> It does not matter when you have an exact headwind or tailwind. <S> Heading bug denotes the desired heading, not track. <S> You always turn your plane towards the heading bug. <S> Advanced autopilot fly track, fundamental ones fly heading. <S> Some autopilots can read the heading bug position on the instrument, others must be set explicitly on another panel. <A> For cross-wind corrections: on the ground you can use a nice software or even an ol' CRP to compute a drift . <S> For setting the heading bug though, and for computing this in the cockpit, you need a quick way of doing it in your head: one great method involves the 'watch face' : <S> A) <S> Divide the wind speed (in knots) by your NPM( nautical miles per minute). <S> This is your Max Drift. <S> B) <S> Use the watch face to determine how much of that Max Drift you need to use: 15 is a quarter of an hour, so for 15 degrees you use 1/4, 30 degrees you use 1/2 of Max Drift, 45 deg 3/4 and for larger degrees use the hole Max Drift <S> eg. <S> wind 230/45 , your speed 180 kts (or 3 miles per minute), hdg 270 <S> Max Drift <S> = 45 / 3 = 15 degrees Angle between wind and me : 40 degrees, so <S> I use a little more than 1/2 and less than 3/4 (between 30 and 45 on the watch face) <S> Computed Drift <S> = 10 degrees <S> Set Hdg Bug to 260 to keep track 270 <S> Hdg bug will not be affected by tail wind, but your ground speed and ETA will be affected. <S> A CRP or an apropriate app sheet can tell you by how much. <S> It will matter if a) wind is very strong or b) your navigation leg is long enough (30+ mins) <S> Depending on the sophistication of the autopilot, most of them have a "keep heading mode" where the a/c will maintain the heading selected by the heading bug. <S> If operated in that mode, the pilot can turn the a/c by moving the hdg knob left or right. <A> To track a course in a crosswind using the bug, set the OBS to the waypoint you wish to fly to and use your normal crabbing skills to track the needle (025 below). <S> Once the needle is being tracked, you can set the heading bug to the current heading (015) and just fly that. <S> This works with or without an autopilot.
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So to answer your questions: You will use simple math or tools to compute the heading which will let you fly the desired track.
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Is there a standard for the trip paperwork packages that are used by the airlines? I have noticed that different airlines (like LIDO, Delta, AA, etc.) have different formats for their trip paperwork packages, containing pre-flight information that they give to their pilots. These packages contain things like their flight plan, NOTAM's, weather, weight & balance, etc. There is some overlap of course, but I was wondering if FAA/EASA has some standard or guideline for generating the package? <Q> For national flights, FAA prefers ICAO flight plan. <S> For international flights, ICAO format must be used, From FAA Flight Planning Information : <S> An ICAO format flight plan MUST be used when: The flight will enter international airspace, including oceanic airspace controlled by FAA facilities. <S> The flight expects routing or separation based on Performance Based Navigation (PBN), e.g. RNAV 1. <S> The flight will enter RVSM airspace. <S> The flight expects services based on ADS-B. EASA follows a format similar to ICAO. <S> The flight plan usually consists of the following: Aircraft type and identification. <S> Flight Rules. <S> Equipment. <S> Source, destination, departure time and (estimated) arrival time. <S> Route details. <S> among other things. <S> The following image shows the ICAO international flight plan Image from Form 7233-4 - Pre-Flight Pilot Checklist and International Flight Plan from faa.gov <S> The following shows the domestic flight plan from FAA. <S> Note that the ICAO format may be followed in domestic flights too. <S> Image from Form <S> 7233-1 - Flight Plan from faa.gov <A> The international standard is the ICAO flight plan. <S> For national flights different formats may be allowed. <S> See this article on SKYbrary for details on what the ICAO flight plan contains. <A> There are no guidelines by FAA/EASA for preparing flight plans. <S> As per FAA, criteria for International (ICAO) <S> Flight Plan Filing are: <S> The FAA prefers users to file ICAO format flight plans for all flights. <S> An ICAO format flight plan MUST be used when: The flight will enter international airspace, including oceanic airspace controlled by FAA facilities. <S> The flight expects routing or separation based on Performance Based Navigation (PBN), e.g. RNAV 1. <S> The flight will enter RVSM airspace. <S> The flight expects services based on ADS-B. <S> There is a form in Aeronautical Information Manual (AIM) Section 1, Paragraph 5-1-9 that need to be filled with all the required information. <S> Criteria for Domestic Flight Plan Filing are: Flights that remain wholly within domestic United States airspace, and do not meet any of the criteria requiring an ICAO format flight plan, may use an FAA domestic format flight plan. <S> There is a form in AIM Section 5-1-8 <S> (FAA Form 7233-1) that needs to be filled with all the required information. <S> File the Flight Plan by any of the following methods. <S> Submit a hard-copy flight plan form to your local flight servicestation. <S> Call Flight Services (1-800-WX-BRIEF or 1-800-992-7433) – The flight services specialist will file your flight plan. <S> Submit your plan online through one of the following free services: - Direct User Access Terminal (DUAT) - Direct User Access Terminal Service (DUATS) - Lockheed Martin Flight Services <S> Note: All the information is available in www.faa.gov
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The FAA prefers users to file ICAO format flight plans for all flights.
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Could a fighter aircraft be operated indefinitely? Is it possible for an air force to operate a fighter aircraft indefinitely? Suppose a country has some Mig-21s or Mirage-IIIs. Is it possible for them to operate those aircraft indefinitely by continuously overhauling and upgrading them? <Q> Yes and no. <S> In Cambridgeshire we still have some Spitfires and other Second World War aircraft which are still operated more than 60 years after being built. <S> The Shuttleworth Collection even flies some First World War and pre-war aircraft. <S> But that's not useful if the aircraft has no military value. <S> None of the examples I've mentioned are still operated as military aircraft : they're in civilian hands, performing for displays, mostly for their historic value (though many ex-military aircraft in civil use are performing other functions, such as air transport or crop spraying). <S> Aircraft get retired for two reasons. <S> The most obvious is that they're superseded by newer types, newer designs with better technologies and materials. <S> The first air force that tried to field one of these Spitfires in combat against modern jet fighters would quickly realise it had no military value whatsoever. <S> The second reason is that they get increasingly expensive to maintain. <S> Military aircraft especially can be very fussy about fuels and parts. <S> Maintenance might require special fabrication of small numbers of parts or tools, which gets more expensive when the rest of the industry has moved on. <S> (For example, the Tiger Moths I fly have one particular part that's impossible to obtain, because the alloy it's made of isn't produced any more.) <S> For this reason, although there are still surviving, operating aircraft from the earliest days of military aviation, it wouldn't be feasible or useful to continue operating them as combat aircraft. <A> In addition to the other answer: The magic number is the fatigue life of the aircraft. <S> This is the number of hours an aircraft can be flown before metal fatigue possibly sets in and the manufacturer can no longer guarantee the safety of the aircraft. <S> There have been cases (Vulcan and Victor in RAF service come to mind) where this limit was reached fairly quickly, and to keep the aircraft in service they would have had to replace the main wing spars, i.e. rebuild half the aircraft. <S> For complex aircraft like those, that's generally only possible with support from the manufacturer. <S> However, if you do have support, a lot is possible. <S> You can get avionics upgrades for the MiG-21 that allow it to fire modern weapons, for example. <A> An aircraft can be flown for as long as there is an operational demand for it. <S> Keep in mind that the aircraft will likely have been through multiple engines and subsystems <S> thereby "refreshing" the aircraft over time, but technically there is no reason it can't continue to fly as long as it continues to serve a purpose.
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It's demonstrably possible to keep operating a military aircraft for at least a century after it's built.
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Is there a tool to plot locations within X nm of a position? I'm looking for a tool to allow me to see what is within X nms or X hrs of my base airport. Is there such a thing? I remember a small airport I flew to once had a large map with a string attached to a pin located at the airports location on the map. There were concentric rings from the location stating 100/200/300....nm. I'm basically looking for something like that such that I could explore and look for locations that are off my normal radar of places I would typically visit. I typically use landings.com for baseline flight planning but you need an origin and destination. It doesn't look like it allows what I'm asking for. I'd even be happy if there was a hack for google maps etc. to do what I'm asking. <Q> You didn’t specify, so I will use mine: KHUA . <S> Using gcmap.com , search for near: <S> KHUA beyond:50nm <S> within:70nm <S> to get a list of airports in the specified range . <S> To plot some of them on a map, place a few of those in a comma-separated list, e.g., KHUA,KGAD,KBHM,KSYI,KBNA,KAYX,M22,TN50,KJFX,KMRC,KAPT,KPYP,1M4,M22 , and select the Map tool. <S> Plot range rings with one or more lines in the Ranges box under Map Controls . <S> I used 50nm@KHUA <S> 70nm@KHUA <S> Click the Draw Map button to update your map. <S> The final result will resemble the image below. <A> Google Earth probably has tools to do what you are looking for. <S> There's a lot of flexibility in that program to create overlays. <S> It can sometime take some knowledge of programming to do the more complex stuff <S> but it is a very powerful program. <A> gcmap.com allows drawing of range rings around airports. <S> I think it's more geared up around longer range travel rather than the $100 burger, though.
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At least a couple of tools exist to search for airports beyond a certain distance from your departure point.
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How do airlines provide crews for the return leg of a long-haul flight? In a video , a Swiss International Air Lines crew flies an Airbus A340-313 (flight LX38) from Zurich to San Francisco. Then, they can be seen ( I am not sure if this is on the very same day ) visiting downtown and the Golden Gate prior to getting back to the airport for the return flight (LX39), which is scheduled for departure around three hours later. The question here is: How do airlines handle crew turnovers in long-haul flights? Is it the same crew who is demanded to command the return flight? Or is there, oddly enough, a replacement crew in each destination airport? Or do they carry the crew for flight LX39 onboard flight LX38? <Q> You presume that they flew back the very same day... <S> but that is an incorrect presumption. <S> For long flights over about 8 hours, strict rest limits apply so they cannot fly again for 8-10 hours at a bare minimum. <S> Typically, a crew from a long-haul flight will stay in a hotel in the destination city for anywhere from 12 to 48 hours, depending on the flight length, timezone changes, airline schedules, union contracts, and so on. <S> Yes the hotels and travel bonuses costs the airline a pretty penny <S> but that's the cost of doing business. <S> So at this very moment there will be 1 or maybe 2 LX crews, resting (or touristing...) in San Francisco, waiting to fly a return service. <S> For more information you can google or ask a new question on Fatigue Risk Management Systems. <A> USA, EU, as well as other countries, have set law to regulate daily duty hour. <S> Both the actual flight time for pilots and time of gap between shift have been limited. <S> In USA,the rule has been tightened after Colgan Air Flight 3407 incident . <S> Usually the airlines will schedule the crew to service the return flight for next day. <S> The crew often receive extra bonus (in terms of local currency) from the airlines. <S> Special immigration policy are set for air crew, many countries are allowed to air crew entry with via crew certificate and on duty, regardless the general immigration and visa policy. <S> On the other hand, some countries have introduced Crew Visa System such as USA(C-1/D visa). <S> Sometimes the air crews, especially the pilot, are requested to travel to other destinations as passengers by another flight. <S> It depends on the airlines' schedules. <S> In such case the off-duty crews may also travel by freighters, like El Al Flight 1862 incident . <A> For long routes, quite often the crew of the outbound leg is not the same as the crew on the inbound leg. <S> For example the way KLM does it (or used to) to Curacao where there were 3 flights a week, they'd have the crew fly Amsterdam-Curacao, then have a few days off on the island before taking the next aircraft back, the crew of which would then have a few days off. <S> Depending on the destination city the route may be more or less desired by crews obviously, some places are much nicer to spend a few days on company time than others :)
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Most of the airlines rent hotel nearby the airport of long-haul destination for the cabin crew and pilot.
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Do any aircraft out there use negative lift? I think negative lift is where high pressure forms on the top of the wing instead of the bottom. I know that Indy cars use negative lift and some sports cars do, but do any aircraft exist that use negative lift and why do they use negative lift? <Q> A lot of aircraft generate negative lift- not in the wings, but in the tail plane. <S> This is used for stability. <S> Consider a trimmed aircraft as shown below: Image from grc.nasa.gov <S> On most aircraft, the center of gravity (through which weight acts) of the airplane is located near the center of pressure (through which lift acts) of the wing. <S> If the center of presure of the wing is aft of the center of gravity, its lift produces a counter-clockwise rotation about the cg. <S> A positive lift force from the tail produces a counter-clockwise rotation about the cg. <S> To trim the aircraft (i.e. no rotation about c.g), it is necessary to balance the torques produced by the wing and the tail. <S> But since both rotations are counter-clockwise, it is impossible to balance the two rotations to produce no rotation. <S> However, if the tail lift is negative it then produces a clockwise rotation about the cg which can balance the wing rotation. <S> For this reason, the tailplane is designed to produce a negative lift. <S> Text from Trimmed aircraft - slightly modified. <A> <A> Yes. <S> Most airplanes have the centre of mass forward of the centre of lift of the main wing(s). <S> This would make the airplane "tip over" forwards, so the tailplane is an upside-down wing, and provides negative lift sufficient to balance the airplane. <S> This is a conventional arrangement. <S> On some, the "car spoiler" shape of the tailplane, with the flat side on top and the cambered side underneath, is very obvious. <A> Short Answer: <S> Yes Long Answer: <S> Well, partially....You see, lift is generated not only at the wings but also at the tail. <S> The aircraft's tail has an elevator and a rudder (most single engine planes) by way of control structures. <S> The pitching motion of the airplane is caused by altering the elevator's shape. <S> The nose stays where it is (in the vertical plane) when the lift at the wings is balanced by that at the tail. <S> However, when the lift at the tail increases the nose starts dropping. <S> Similarly, when the lift at the tail decreases, the nose rises up. <S> You could call the increased downward at the tail 'negative-lift'. <S> I hope that answered your question. <S> If you are patient enough, try reading this chapter from the Pilot's Handbook of Aeronautical Knowledge. <S> It is the same book I used for my pilot's license.
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Yes . . . . . . . . .
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How can a military combat pilot indicate surrender? If a military pilot is captured by an enemy, how can he indicate that he has run out of ammunition to engage in combat or is not in a position to retaliate? Does he use lights, radio, and/or flares? <Q> There is no universally accepted means of surrendering an aircraft. <S> According to Humanitarian Policy and Conflict Research at Harvard University , Aircrews of a military aircraft wishing to surrender ought to do everything feasible to express clearly their intention to do so. <S> In particular, they ought to communicate their intention on a common radio channel such as a distress frequency. <S> They can do other things like rocking the wings, jettisoning the weapons, flashing navigational lights etc. <S> However, none of these are universally accepted or even have a clear meaning in the heat of combat. <S> So the best course of action will be to bail out. <S> If a pilot is captured by an enemy, there would be no need to surrender. <A> If the pilot engaged in combat, and simply ran out of ammunition, surrendering isn't something that has to be accepted by the opposing party. <S> The rule is, you need to surrender on first sight of the enemy. <S> Once you engage in combat all bets are off and you can be destroyed even if you release the canopy and throw up your hands (not recommended!) <S> See, people get a peculiar sentiment when you shoot at them. <S> They appreciate that you missed, but they don't take kindly that you offered surrender after you go winchester on the missiles and bullets. <S> Also, while you are surrendering. <S> For example, Viktor Belenko defected in a Mig-25 in 1976 by flying it to Japan. <S> This was a very valuable aircraft which he traded for a carton of American cigarettes and a million dollars. <S> (ok just kidding, but he did get a nice trust fund set up for him when President Ford accepted his asylum plea.) <A> Generally theres no surrender bail out, In the pacific theater during the Second World War there was no aircraft surrenders. <S> In fact even if the pilot chose to bail out of his aircraft (American Pilots) they would be strafed while in their parachute, and even if they had made it to the water. <S> ( Japan did not sign the Genova accord) <S> For this reason many American pilots returned the favor and would go so far continue shooting at the already critically damaged Japanese fighter. <A> In WW2, USAAF bombers would some times signify an intent of the aircrew to bail out of a shot up bomber, by dropping the landing gear. <S> The hope was that the attacking fighters would stop shooting, and not kill more of a crew that was just trying to get out and would be captured upon reaching the ground. <S> This was not official policy on either side, but it was occasionally done, and occasionally respected.
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Assuming you didn't engage in combat, consider learning the other side's language and make sure you surrender in a top of the line aircraft.
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Is an aircraft's maximum landing weight really weight, or is it mass? I'm calculating the lift of a Cessna 172 and I don't understand the numbers given for weight. The maximum landing weight is 2550 pounds which is nearly 1134kg. But does that mean 1134 Newtons (weight) or 1134 kilograms (mass)? Since weight = mass x gravity , I think the weight of the C172 is in Newtons even though it's written using a unit of mass. Am I correct? <Q> In general, the various 'weights' given for aircraft are masses, not weights. <S> i.e. they are in kilograms, not Newtons. <S> This is simply an extension of our everyday usage. <S> As @mins pointed out, if someone asks your weight, you tell your mass (70 kg or whatever), not the weight itself (~686N). <A> On Planet Earth, 1kg of mass exerts 9.81 Newtons of force (weight).Because this is true anywhere on planet Earth to within a tiny fraction of a percent, we use kg as a convenient measure of weight, even though pedantically it is a measure of mass. <S> If you are thinking of landing your C-172 on the Moon, Mars, or some other locale where G is different from 9.81 ms-2, then you'll have to convert kg to Newtons of weight. <S> Otherwise, you should consider kg a unit of both mass and weight. <A> Reiterating the point made by @aeroalias, the "weight" that FAA/manufacturer talks about is really "mass" in the pure physics world. <S> However, in the real world, imagine you have a big enough scale to hang the airplane to. <S> The MTOW or Max Take Off <S> Weight would be the reading on that scale. <S> So, if you are weighing your passengers' baggage, use a reliable scale. <S> You can then use it directly in your weight and balance calculations. <S> So, don't worry about conversions. <S> Just use the real world "weight" in Kgs or Lbs as the case may be as long you are flying on earth. <A> Aircraft are weighed on scales. <S> Attempting to measure the mass of a loaded aircraft isn't practical. <S> Clearly, the figure indicates weight.
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The maximum landing weight given here is actually the mass , not weight.
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Why are Airbus captain control sticks placed on the left when most people are right-handed? Why is it that control sticks for the captains on Airbus are placed on the left? Wouldn't it be uncomfortable considering that most of the people, and by consequence pilots, are right handed? To my opinion this would make flying more difficult as a right handed person would have less sensitivity on his left hand. ( airbus.com ) <Q> The Airbus is actually configured the same as the vast majority of other General Aviation and Civil Aviation aircraft. <S> It's something of a misconception to think that pilots spend much, if any, time with both hands on the control column. <S> The right hand is almost always somewhere else – configuring radios, squawks, navigation equipment, throttles and so on. <S> Watch this video of a Citation Jet – particularly during takeoff and landing. <S> The pilot on the left is using his control column in exactly the same way as he would on an Airbus. <S> You'll note that when his right hand is on the control column, it doesn't become dominant – it's just a resting position. <A> First, even if the aircraft is controlled using a yoke, the pilot is still controlling using his left hand (left hand on column, right hand on throttles/PCL). <S> This is not much different and almost all pilots switch from controlling using their right hand to left hand pretty easily (they'll usually do this while training itself as they switch seats). <S> The basic concept is same as say, a Boeing 737. <S> Boeing 737 cockpit, from gearthhacks.com <S> The basic control layout in airliners is that the pilot/copilot controls the yoke/sidestick with one hand and throttles/TCL (and flaps etc.) <S> with the other hand. <S> Having dissimilar layout for pilot/copilot has some advantages. <S> At the minimum, the throttles can be placed in the center. <S> If the pilot's sidestick is to (his) right, then the throttles have to be placed in the left, resulting in duplication. <S> This can be seen in the B1 Lancer, where the pilot's throttles are in the left (though the aircraft has a centre stick). <S> Image from left wingsovereurope.com <S> While this may be possible if only the throttles were to be duplicated, it is very difficult to do so with the whole center console. <S> Also, having the sidestick to the left side serves as a good hand(wrist) rest. <A> Please note the flying captain could be left seated or right seated, also the stick on Airbus needs no effort to move it, it is very soft to handle <S> it has a springy central positions. <S> In normal flight longitudinally once you reach the desired vertical speed you may leave the stick, similarly laterally once you get the desired bank angle you can leave it until you finish the turn, so no effort is applied to the stick. <S> What follows explains how this is possible: Indeed longitudinally it gives a LOAD FACTOR order(to simplify this is the ratio of lift to weight), when left in its neutral position it gives a load factor of (1)thus keeping the active path. <S> Laterally it gives a « rate of roll » order, that is when you get the bank angle you want you leave the stick in the neutral position; to get out of the bank, you move the stick in the opposite direction. <S> So it is a different technology you cannot compare it to a standard control column. <S> Whether right-handed or left-handed, whether the left seated or the right seated is flying it would make very little difference to operate this soft stick.
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The key factor is that the throttle is almost always the middle - meaning that as pilots get used to sitting in the left seat early on in their training, they become accustomed to using the throttle with their right hand and the control column in the left.
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What prevents a government from selling/leasing publicly owned airports? When an airport is open to the public, it is generally owned and operated by a government entity. If the local government leases or sells the airport, this would generate significant amounts of revenue. What are the legal impediments which discourage a local government (who owns a public airport) from leasing or selling their airport to a private entity? <Q> One possible impediment might be the grant assurances that come with accepting Federal aid to improve the airport. <S> In short, if the local airport accepts money from the Federal government to improve the airport, that money is often granted "with strings attached" - requirements that the airport remain open, etc. <A> Some places have land laws that protect public spaces as well as Privately Owned Public Spaces . <S> For example there are Privately Owned Public Use Airports in the US like T renton-Robbinsville N87 . <S> IN this case the government may not want to rent/sell it since it needs to remain a public entity anyway. <A> All US aircraft and airfields are subject to militarization on a moments notice. <S> It's an old Cold War law that's still on books. <S> In NATO planning, virtually the entire private airliner fleet was going to be militarized to form an airbridge if the Russkies invaded.(It was assumed that nuclear attack subs would be way worse on ocean shipping than German diesel-electric were in WWII.) <S> Some airports are designated emergency military landing zones. <S> Used to be this little grass <S> stripped airport outside of Bangs, <S> Tx that had to sweat to land an ultra-light but still had an official notice on the wall that it was expected to handle military aircraft during a designated emergency. <S> I finally figured out they meant helicopters from the nearby National Guard training ground.
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In some cases the laws may not prevent the rental to a private organization but may require that the airport remain in public use.
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Means of protection against hunter-killer UAVs I would like to know all existing technological means of defending an area against the MQ-9 Reaper or other hunter-killer unmanned aerial vehicles (UAVs) used by the United States in countries like Afghanistan, Syria, etc. Such means should either force the UAVs to leave the area or crash. <Q> By far the cheapest method for protecting a limited area would be to use an aerostat to carry aloft a jammer. <S> Vehicles like the Reaper rely on a satellite uplink to maintain their command and control. <S> As long as the aerostat is well above the altitude of the Reaper it can easily jam it. <S> The cost of this option might be around \$1 million with an annual operating cost of \$200,000 and an effective diameter of about 10-20 miles. <S> A more expensive, but more flexible response would be to just shoot it down. <S> To do this you would need an air surveillance radar, a high performance turboprop with machine guns like a Texan or Super Tucano, a pilot and a crew to operate the radar. <S> With this method you could deny a pretty large area, maybe 100 miles in diameter easily, possibly more. <S> The cost of this would be about \$3 to \$5 million plus annual operating costs of about $500,000. <S> If you want to spend a bit a more a Yak-130 would be an excellent light attack jet to consider for anti-drone work. <S> You might be able to find a used Yak for under \$10 million <S> and it is a bitchin aircraft that can go double the speed of a Predator plus it has its own radar. <S> Missile systems would not really work because the types you would need to reach the altitude a Reaper operates at, are very expensive and complex (which is exactly why the Reaper flies at those altitudes). <S> However if you could catch the Reaper while it was taking off or landing, a small missile like an RBS 70 would be even cheaper, assuming you could obtain that weapon. <A> A drone is practically a type of aircraft and can be shot down using the same means as shooting down aircraft, and then some, like missiles (surface to air or air to air). <S> If they are flying low, using guns in point or area defense weapons, There are some other defensive measures under development like laser and microwave . <S> In case of UAVs being controlled remotely (as most of them are), the signals can be jammed. <A> This is a Glock 19. <S> Cost: <S> $350 <S> This is a 9mm bullet. <S> The Glock holds 15 of them. <S> Cost: $12.99 for a box of 50 <S> This is the ground control station for a Predator drone. <S> And this is what it looks like on the inside. <S> Shoot everything . <S> Take control of the UAV . <S> Crash the UAV . <S> Total cost: $362.99
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The Cheapest Way To Bring Down A Hunter-Killer UAV Go to the ground control station .
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Why is Hydrazine used to power the F-16's EPU? Why does the military use hydrazine to power the F-16's Emergency Power Unit (EPU)? What is so unique about Hydrazine fuel that it's needed to power the EPU? Why not use a less volatile and less hazardous fuel? <Q> This energy is freed by letting the hydrazine stream over a catalyst , in case of the F-16 EPU that is iridium . <S> This breaks the chemical bond, producing ammonia, nitrogen gas, hydrogen gas and heat which converts the water into steam. <S> Heating increases the volume of the gasses and the steam so they pick up speed, just like the gasses in the combustion chamber of a jet engine . <S> In the catalyst chamber of the F-16's EPU the temperature reaches more than 800°C in just a couple of milliseconds, and no combustion is involved! <S> This high-pressure, high-speed gas flows through a small turbine which in turn drives a generator and supplies hydraulic pressure. <S> Compression is not needed because pressure is supplied from the bottle containing the hydrazine-water mixture. <S> Using a monopropellant also avoids any ignition problems and makes the setup very simple. <S> Since hydrazine is quite stable at high pressure and ambient temperature, the shelf life of a hydrazine engine is high, and the liquid state of the hydrazine-water mixture makes its storage very compact. <S> Just what you need in a fighter aircraft. <A> The EPU of F-16 is fueled with a monopropellant hydrazine mixture, H-70, which contains 70% hydrazine ($N_{2}H_{4}$) and 30% water, by weight. <S> The main requirements for the EPU are that it should be simple <S> , maintenance free, supply power immediately and consistently for the required time. <S> Use of Hydrazine assures this while requiring careful handling. <S> Basically, the catalytic decomposition of hydrazine produces ammonia, nitrogen and hydrogen. <S> Exhuast Gases from EPU Turbine contain 40% Ammonia, 17% Nitrogen, 15% Hydrogen and 28% Water. <S> $3N_{2}H_{4} <S> \rightarrow 4NH_{3} + N_{2}$ <S> $4NH_{3} \rightarrow 2N_{2} <S> + 6H_{2}$ $3N_{2}H_{4} <S> \rightarrow 4(1-x)NH_{3} + 6xH_{2} + (2x+1) N_{2}$ <S> where x is the fraction of the $NH_{3}$ disassociated. <S> The water modifies the decomposition temperature (the EPU reaches temperatures of ~870 $^{\circ}C$), preventing thermal damage to the catalyst bed and the turbine parts. <S> As the water removes heat, it is turned into steam which aids in powering the EPU. <S> The EPU, using hydrazine spins up to approximately 75,000 rpm in 2-3 seconds (The F-16 EPU starts within 2 sec.). <S> It would take a much greater time if another fuel, like JP-8 were used. <S> When required (EPU runs normally on engine bleed air), hydrazine is forced into decomposition chamber by nitrogen pressure , where the above reactions produce the gases to run the turbine/gearbox. <S> The decomposition of hydrazine produces enough pressure, eliminating the need for a compressor, thus saving weight and also eliminating the need for an igniter, reducing complexity. <S> For the given weight, it provides continuous operation for the required time. <S> In F-16, the EPU carries ~25l of hydrazine, which permits operation for about 10 minutes under normal load conditions and 15 minutes if the loads are less (i.e. in ground). <S> If any other form, (like battery or cartridge) were used, it would be difficult to have a long operational time without heavy increase in mass. <S> For a combat aircraft, RAT is not an option. <S> Also, a hydrazine powered EPU would work in any altitude or during maneuvering as it does not need an external oxidizer supply. <S> References: <S> Exhaust Gas Composition of the F-16 Emergency Power Unit by Harry J. Suggs et al. <S> Technical Order 00-105E-9, USAF AFR 110-14 USAF Aircraft Accident Investigation Report. <S> F-16 manual <S> Thanks to @Peter for pointing out errors. <A> Hydrazine use is related to aircraft stability. <S> Without power to the computers, the F-16's preferred flight attitude is flying tail first. <S> The basic aircraft design is aerodynamically unstable, intentionally, to achieve high performance. <S> The flight control computers maintain stability. <S> If electrical power goes down, the pilot suddenly needs wading boots. <S> To prevent such unfortunate circumstances, the APU was specified to be on-line at full power 0.25 seconds after power failure. <S> Apparently, in the late 60's to early 70's (design years) nothing else could meet the rapid start, weight, and power endurance requirements.
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To fill the voids in aeroalias' answer: Hydrazine is a monopropellant , something which does not need to be mixed and burned to free up the energy contained in its chemical bonds.
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Do unused parachutes need to be repacked? If so how often and why? I was reading some military fiction and saw a comment that army airborne operations were required to repack all parachutes every ninety days, allowing parachutes that were due to be repacked soon to be cheaply used for training. This got me thinking: do parachutes need to be repacked on a schedule? Is this uniform across all types of parachutes and use cases? (are there differences between military and civilian requirements?) How long is the repack cycle? Why is scheduled repacking needed? <Q> Yes, parachutes need to be repacked regularly. <S> The length of the interval depends on the material of the parachute and is between 60 and 180 days. <S> Every parachute should have a small pocket with a piece of paper which lists the most recent repack date and the name of the packer (who needs to comply with FAR part 65, subpart F ). <S> FAA part 91.307 says: (a) <S> No pilot of a civil aircraft may allow a parachute that is available for emergency use to be carried in that aircraft unless it is an approved type and has been packed by a certificated and appropriately rated parachute rigger— (1) <S> Within the preceding 180 days, if its canopy, shrouds, and harness are composed exclusively of nylon, rayon, or other similar synthetic fiber or materials that are substantially resistant to damage from mold, mildew, or other fungi and other rotting agents propagated in a moist environment; or (2) <S> Within the preceding 60 days, if any part of the parachute is composed of silk, pongee, or other natural fiber or materials not specified in paragraph (a)(1) of this section. <S> The reason should be clear from the regulation: If moisture is present, the growth of mold may prevent the parachute from unfolding easily. <S> For the T-10D parachute , which is the standard US Army parachute for airborne assault operations, the repack period is 120 days. <A> I'm adding this as an answer, because it is too long to be a comment, but it is meant as a supplement to the already accepted answer <S> As a skydiver of 13 years, and having been a member of two different national teams and three different national skydiving associations (US, NO, DK), I will add that repack cycles are in most countries <S> /states defined for reserve canopies. <S> Both main and reserve canopies have main control inspection intervals as well, where a repack also occurs, ofcourse. <S> The intervals I've come across differs. <S> Student gear have in most cases more frequent cycles, due to the fact that they land in trees and similar, more often than experienced skydivers. <S> Reserve canopies seems to have cycles that somewhat depends on climate, more specifically humidity. <S> Florida for instance has the most frequent reserve repack cycle I've come across. <S> I think it was three months. <S> In Norway however, it is 12 months. <S> I am not a rigger (an educated skydive-gear god), and I haven't checked this specifically, but my impression is that the opening functionality of a canopy might be compromised if it stays compressed for too long, and that humidity speeds up this process. <S> We like the opening sequence to be as predictable as possible, and even though it would probably work anyway, it is better to be on the safe side. <S> It is generally recommended to keep your main canopy unpacked if you are not going to use it for a while, as long as it is not exposed things that might compromise fabric or lines. <S> Military gear is sometimes round canopies, instead of the standard square sports-canopy. <S> I have no idea how the round ones needs to be packed, but from what I've seen of the military square-jumpers, I wouldn't be surprised if they have the same repack/control cycles as student canopies, and for the same reasons (trees). <A> When I started flying hang-gliders, there were a number of incidents (some fatal) where reserve chutes were thrown but did not deploy properly. <S> Competence at chute-packing was the main cause, but some came from chutes where the fabric was simply too stuck together. <S> Clubs started running chute repacking days in local halls or sports centres, sometimes with a zip-wire from the roof which would let you practise throwing your chute under realistic conditions. <S> For our reserves, we tended to reckon on repacking being a yearly activity, but then many people would go their whole flying career without ever throwing their reserve. <S> More frequent repacking was not justifiable given the odds of needing it. <S> If you're skydiving or doing military airdrops, using the chute is non-negotiable, and reducing risks by more regular repacking is very sensible. <A> If you go into a glider hangar, you'll find a bunch of club chutes, all of which have been repacked before the beginning of the season, and last 180 days. <S> Sometimes the chute has a pocket for the log, other times it's under one of the flaps. <S> I always wonder how much risk there would be flying in a glider with a slightly outdated chute at the end of the season.
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I normally repack my main canopy before jumping, if it has been more than 3 months in my container.
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Was there any progress in ramjet-powered helicopters after 1960? It seems in 1950's some countries investigated production of helicopters powered by ramjet engines on rotor tips - examples include American Hiller YH-32 Hornet or Polish JK-1 Trzmiel . The enthusiasm was short-lived - high fuel requirements, a significant load to the power transmission system, noise and high visibility on battlefield were significant disadvantages that ended the research programs which I know of. Still, that's over half a century ago, and the technology has progressed quite a bit since then so maybe some technical problems of that epoch are now past? - The ramjets are small, lightweight and quite simple in construction, so despite the disadvantages the technology doesn't seem like a total dead-end. Was this line of helicopter propulsion investigated further? Could someone provide a progress report - if there is anything to report? Or is this research branch still dead, with no attempts to revive it? <Q> Tip jet rotors are still being developed, none of them are ramjet powered as far as I know. <S> The Dragonfly DF1 is tip rocket powered, while the Pegasus uses air jets powered by a conventional engine. <S> Ramjet technology has not improved, so the cases for using them on rotor tips has not changed. <S> They are still too heavy, thirsty and noisy. <A> Short answer: <S> No. <S> Or at least, nothing that's been demonstrated that I'm aware of. <S> Whether there have been experimental R&D aircraft or developments, I'm not sure - but I can't find any. <S> "we know it works" product, unless there's a good reason to change. <S> It's not necessarily that tip-jet helicopters are a complete dead end in terms of development, just that we don't see any advantages to be gained from them. <A> I'm reading a book <S> right now that talks briefly about flight testing the Hiller. <S> As I recall, it was tough to get both engines started at the same time, and if one of them cut out, was a pretty violent affair. <S> It was also an environmental disaster, with horrible fumes and noise. <S> It was an interesting experiment, but it had no real world application at all. <S> There still doesn't appear to be one.
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The simplest reason is just because there's no need for them - they offer no real advantages over a conventional internal combustion or jet engine, so as with so much else in aviation we stick with the tried and tested
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What is the significance of Slip-Skid Indicator in PFD? Slip Skid Indicator as depicted in the picture below; What's the significance of Slip Skid Indicator? How Slip Skid Indicator is used in flying the aircraft? What are other performance/operations needs to be taken care while this exceeds its normal bound? Primary flight display with Slip Skid Indicator, Source - www.aboutflight.com <Q> The image below should clarify that. <S> Image from flightlearnings.com <S> The Slip/Skid Indicator (sometimes called turn-and-bank indicator) moves left and right relative to the roll pointer in proportion to lateral acceleration and helps the pilot correct for any deviations in a turn. <S> In a level flight, the indicator is centered. <S> Assume that the pilot is executing a left turn (the roll pointer would've moved left)- <S> if the indicator is in center, it means that the turn is coordinated i.e. the aircraft is not slipping or skidding. <S> If the indicator (bar) is moving right, it shows that the aircraft is skidding. <S> Movement in the opposite side (i.e. towards the left, same direction of turn) indicates that the aircraft is slipping. <S> This enables the pilot to take corrective action. <S> This is one of the necessary flight instruments. <A> OP asked what to do. <S> If indicator becomes unaligned with roll pointer, apply more rudder on the side where the indicator has moved. <S> It's called, "stepping on the ball." <S> So if the slip/skid is right of the roll pointer, apply right rudder. <S> If the indicator (a ball in the analog turn coordinator) is too far left, apply left rudder to force it back into alignment with the roll pointer. <S> This keeps the plane's nose pointing into the flight path, rather than to the inside or outside of the turn, which puts you at risk of stalling. <A> According to this page on using the G1000 : <S> Slip/Skid Indicator <S> The Slip/Skid Indicator is the small bar under the Roll Pointer. <S> It moves away from the Roll Pointer to indicate slip or skid, just like the ball on a traditional Turn Coordinator. <S> So it's used exactly the same as the analog ball. <S> If it's away from the roll pointer (out of center in analog), you're in a slip or a skid. <A> On the B777, the only time I use it is during engine out maneuvers in the simulator. <S> It helps determine how much rudder trim should be used while operating with one engine.
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The slip/skid indicator is the small bar under the roll pointer.
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Does tailless means no tail at all? When I was reading about the HAL Tejas I observed that it was described as a "tailless" plane. However I could see a tail in the picture . After careful reading I am assuming that being tailless means not having any tail planes a.k.a horizontal stabilizers. Does tailless means no tail at all? <Q> Tailless means no horizontal tail, but a vertical tail is still allowed. <S> Examples are the Convair F-102 or Convair B-58 . <S> Convair B-58 Hustler (picture source ) <S> Compare this to a flying wing: Here even the vertical tail is left off. <S> Since a classic delta would have too little lever arm for yaw control, this requires a higher aspect ratio wing. <S> An example is the Horten IX : <S> Horten IX V1 prototype aircraft (picture source ) <A> No, not at all - there are at least two Delta Wing aircraft that feature a conventional tail, and they are the Gloster Javelin and the Mig 21 https://en.wikipedia.org/wiki/Gloster_Javelin https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-21 <S> (Courtesy of http://airheadsfly.com/ ) <S> In addition (and I believe this is within the spirit of what you've asked) you then you have aircraft such as the Eurofighter Typhoon or Saab 37 Viggen which feature canards: <S> https://en.wikipedia.org/wiki/Eurofighter_Typhoon <S> https://en.wikipedia.org/wiki/Saab_37_Viggen <S> Ultimately, "Delta" only describes the wing shape - though there of course features of the shape that will lead to many designs appearing similar. <S> The Wikipedia article has a nice infographic showing the general variations of Delta Winged designs: https://en.wikipedia.org/wiki/Delta_wing <A> Until the postwar era it often also included planes with no tailplane but instead a "canard" foreplane in front of the wing, however we nowadays recognise the canard and tailless configurations as distinct, some even talk of the canard as "putting the tail in front of the wing". <S> One or two experimental types without a vertical tail fin have also been referred to publicly as "tailless" but this is technically incorrect.
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Tailless usually means no horizontal stabilizer (tailplane).
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Are there any manoeuvres that would be considered unrecoverable in a General Aviation / Training Aircraft? I'll try to make this question a little more manageable by applying the following constraints, though of course all answers would be welcome: By "General Aviation / Training" aircraft, I'm talking primarily about normal SEP's of the kind that we see daily and would require no more than a check-ride before hiring. No experimentals, warbirds, super rare aircraft etc - though MEP's and Complex Aircraft would count. I'm ignoring low level maneuvers. We all know a stall at 100ft is going to be tricky, though on the other hand, if something is going to require 5000' at a minimum to recover from then that's going to be fatal in most cases. Let's ignore mechanical and airframe failures that occur prior to the incident. I'm assuming Weight & Balance are within the normal category of the POH (As opposed to utility or aerobatic). Beyond that, the question is what it says on the tin. Is there anything stupid that I can do as a Pilot in a Single Engined Piston GA aircraft that I simply won't be able to recover from, even with a few thousand feet to do so? <Q> Yes, easily. <S> Just fly fast enough. <S> If you deflect a control surface fully at a speed above $v_A$, the risk of a structural failure is very real. <S> After all, at $v_D$ only a third of the mechanically possible deflection is allowed (see §23.441 for the rudder and §23.455 for the ailerons). <S> Even combining full deflections of more than one control surface at $v_A$ is not covered, as is a repeated deflection in sync with rigid body oscillations which can create excessive loads. <S> For a definition of the design speeds, see §23.335 . <S> The regulations require minimum control forces so the pilot feels when he/she overstresses the airframe, but they are still within the strength of a normal adult. <S> Also, if you fly too fast in gusty weather, you can overload the structure. <S> This is rare because the 25ft/s gusts which must be tolerated up to $v_D$ are quite uncomfortable to fly through. <A> I'm pretty sure this is not the kind of "maneuver" you're looking for, but it is something stupid that I can do as a Pilot in a Single Engined Piston GA aircraft that I simply won't be able to recover from. <S> CAPS deployment in an SR-20/22 is unrecoverable - once the chute is out, there's no putting it back in. <A> The two most common training aircraft out there are the Piper Cherokee (numerous variants) and the Cessna 172/152 (numerous variants as well) . <S> The cherokee is not spin certified and the 172 is only spin certified in the utility category <S> so I would not try spinning either frankly. <S> Even regular stalls put you at risk of entering a spin. <S> There are lots of maneuvers (aerobatic mainly) that would kill the engine on many common GA planes. <S> Generally speaking the oil systems are not built for inverted maneuvers or anything that would starve the oil pump. <S> The Cessna also has a gravity fed fuel system which would not do to well inverted. <S> In regards to stalling the engine and recovering while you may be able to glide down to a field if an engine is lost this is more in reference to losing an engine during a maneuver and having insufficient thrust to recover properly from the maneuver. <S> I would think that you might also be able to get the plane into an aggressive dive that might be hard to recover from for an untrained pilot. <S> At some point the recovery will exceed the load the wings can handle as well. <S> Here in the US the FAA requires knowledge of spin awareness and what may cause a plane to enter a spin but there is no requirement to demonstrate a spin for a basic private pilots license nor is there a requirement for them to be demonstrated to the student. <A> Yes indeed. <S> AD <S> 69-24-04 PIPER increases the Vmc speed of the Twin Comanche by 9 knots because the aircraft was discovered to enter an unrecoverable flat spin when stalled near Vmc. <S> Always a bummer when that happens. <A> Some bad ones: <S> Stalling while turning too abruptly at low speed and low alt < 500', but above ground effect height, cartwheeling to your death. <S> Ideally, a ballistic parachute system should optimize for this, but too much of a spin component may twist/collapse the chute of some designs from opening soon enough. <S> Losing power after takeoff but then trying an impossible 180° turn back when the safest plan is to dead-stick to anything remotely flat ahead. <S> Ripping wings off from too aggressive maneuvers plus repeated fatigue cycles of old/worn planes performing aerial firefighting without sufficiently-thorough metallurgical inspections (NDT). <S> There was that Herc that sadly bought it on viceo. <S> Far exceeding Vd and causing structural failure from control surface, harmonic resonant and/or structural overload. <S> Mach tuck on the early P-38, Hawker P.1081 and other late, fast WW2 aircraft. <S> Maybe they could sometimes recover with very careful dirty config and throttling back, but nosing over while transonic risks an unCFIT situation very quickly.
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Technically you may be able to recover from a spin with enough altitude and depending on the situation but a pilot could get them selves into a nasty situation by spinning either plane.
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On the F15-E, can the WSO take over if the pilot is incapacitated? The F15-E Strike Eagle features a two-man cockpit. The pilot in the front seat and the WSO (Weapons System Officer) in the back seat. If the jet is cruising straight and level is mechanically sound but the pilot becomes completely incapacitated (from a heart attack for example) can the WSO take over and land the aircraft? I could imagine that the correct procedure may be to just eject both the pilot and themselves. Do WSO's learn to fly the F15? The following image is the backseat cockpit area of a F-15 E where the WSO sits. Note the control stick and the throttle control I've highlighted with red arrows. Surely this means the WSO has the ability to take over control? source( http://i61.tinypic.com/dbqp2q.jpg ) <Q> Short answer, yes. <S> However, it is important to note that the WSO is not a pilot. <S> The WSO is trained to operate the weapons systems, not fly the aircraft, but does have basic flight controls including throttle, stick, rudder pedals, compass, HSI, etc. <S> He does not have good forward visibility and would likely have to be talked in on final approach by the tower, as his view is obstructed by the pilot's seat. <S> Although the F-15E was developed from the D-model used for pilot training, the airframe was significantly redesigned for it's new purpose, and the back seat of an E-model bears only a passing resemblance to the back seat of a D-model. <S> The WSO has a very specific and complex set of tasks which does not include flying the airplane, and his controls are designed around that purpose. <S> He has more screens than the pilot to look at, and two side-stick controllers (not part of the flight control system) that are used for controlling / selecting / guiding / programming / etc. <S> a large variety of weapons. <S> He also has primary control over the FLIR and laser pods used for target designation and tracking. <S> On a final note, it is not uncommon (although less common in these days of sequestration) for non-aircrew personnel to be given 'incentive rides' in the back seat of aircraft like the F-15D/E or F-16D, and during these rides control of the aircraft is invariably passed to the passenger. <S> I was privileged enough during my Air Force career to get a ride in the back seat of an F-15E (tail number 88-1671 at Seymour Johnson AFB, NC) and can say from personal experience that it is possible to fly an F-15E from the back seat. <S> It was the most exhilarating 5 minutes of my life. <S> Fortunately for both of us, the pilot didn't experience any problems during the flight... <A> Yes. <S> The F-15E is developed from F-15D , which is used for aircrew training, with the instructing pilot in the rear seat. <S> There is atleast one documented case where the WSO controlled the aircraft, albeit briefly. <S> On March 2012, a F-15E crashed, killing the pilot. <S> During the accident, as a result of pilot actions, the WSO decided that the pilot has suffered spatial disorientation and attempted to recover, before initiating the ejection sequence. <S> From USAF Accident Investigation Report : At that point, the MWSO believed that the MP did not know which way was up ... . <S> The MWSO grabbed the controls and rolled the MA left towards a near wings-level position... <S> The MWSO then pulled 11 g while rolling left to wings-level... <S> As the MWSO rolled the MA to nearly level flight, he initiated ejection for the MC... <A> The WSO can do everything from the back seat, but there is one thing he cannot do. <S> He can lower the landing gear, but he cannot raise it. <S> As far as ejecting, the WSO has the option of ejecting himself or both. <A> A pilot in my BCourse Gloc’d and the Instructor WSO recovered the aircraft and started the RTB process. <S> Student pilot came to later and took over to land. <S> The HUD repeater makes forward visibility problem somewhat of a no -factor. <S> 2000 <S> Hr strike eagleWSO <A> The WSO has an emergency landing gear handle that can be pulled in case of a loss of hydraulic pressure. <S> It gives just enough pressure to lower the gear and flaps once. <S> That's enough for the WSO to land the plane in an emergency and leaves space for systems that are more relevant to their job.
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They can fly the aircraft if required.
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Can someone/something other than the pilot trigger the ejection seat? Let's say there was a two-person jet (take the F-15 for example) that was involved in some sort of accident in the air that incapacitated the pilot (unconscious but still alive) and left the aircraft unflyable. Could the copilot eject his fellow pilot in an attempt to save his/her life from the inevitable crash that would eventually take place? Is there some sort of system in the aircraft that would do this automatically? Seems like an messy problem to have. On one hand you don't want to be blasted out the windshield accidentally by your copilot or faulty computer system but on the other hand it sure would be nice to survive in the off chance you are unable to exit the plane yourself. <Q> In a word, yes. <S> There is a switch which controls this and the default position is "both". <S> If any handle is pulled (pull down over the face or the one between your legs), then both seats fire. <S> If solo, the switch is turned to "solo" so that the rear seat is not ejected and the front seat gets to leave a little bit quicker. <S> If the switch is left on solo, and both seats are occupied, then each crew member can eject on their own. <S> You would also have if set to "solo" with an untrained passenger in the back. <S> You wouldn't want someone getting a bit excited and firing them both out of a perfectly working jet. <S> See this question about what happens, and this one to understand why you won't hit the canopy. <S> As far as I know, there is no computer controlled ejection system. <S> I don't think anyone would trust it to know better than the crew when it's time to bail out. <A> Yes. <S> In general, the Weapons System Officer (WSO) can initiate ejection sequence and usually has control over it (of course it varies from aircraft to aircraft). <S> From the interview of LCDR Joe "Smokin" Ruzicka , a F-14 Radar Intercept officer (RIO): Both crew member's [sic] relied on each other- even down to the RIO having control of the ejection sequence- <S> because conventional wisdom said the pilot would want to stay with the jet until it was too late. <S> Automatic ejection systems are rare, because you want the pilot to have control over when to eject (automatic ejection is considered a bad thing). <S> However, it is found in a few aircraft, like the Soviet Yak-38 , a VTOL aircraft. <S> Once the aircraft rolled past 60 degrees in case of engine failure, ejection sequence was initiated automatically. <A> Not really an answer to the text and intent of the question, but with regard to the question as asked in the title ("Can someone/something other than the pilot trigger the ejection seat?"), I'll share a story that a friend who flew AWACS told me: He was flying somewhere in the Middle East, and a Navy jet pulled up close enough to wave at the AWACS pilots, who weren't particularly amused. <S> Not knowing what frequency the Navy fighter was monitoring (if any), my friend in the left seat of the AWACS picks up his microphone, switches to Guard (which everybody monitors), and transmits something along the lines of, "Dude <S> , we're putting out enough RF energy to launch <S> your seat at that distance!" <S> The fighter peeled off in great haste. <S> I don't know how often this sort of thing has actually played out, but it has got to be an "oh <S> , ****" moment <S> if/when it ever did. <A> The question as to whether other crew members can trigger the ejection sequence has been answered. <S> The Yak-38 VTOL fighter of the Soviet navy <S> had just such a system and they were considered for other types as well (but afaik never installed for reasons that will become clear). <S> This system worked. <S> In fact it worked too good. <S> It had a tendency to eject the pilot even when there was nothing wrong with the aircraft, causing more than a few aircraft losses and injured pilots as a result. <S> A system like that monitors the aircraft parameters and systems and when they go out of normal operational ranges for a certain period triggers the ejection sequence. <S> With the Yak at least, it appears that putting the aircraft into a hover to land it would sometimes trigger the ejection, oops :) <A> Some thing — yes, albeit not intentionally in this case: There was an accident in Sweden some years ago, in which a Gripen pilot was blown out of his aircraft because his legs and flight suit, affected by some high-G turns, actioned the ejection handle. <S> See Wikipedia and the Official report from the Accident Investigation Authority (PDF in Swedish).
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So yes, something other than the pilot/s of the aircraft CAN potentially trigger the ejection seat. As to whether there can be automated systems that do it, the answer to that is a resounding "yes" as well.
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Which came to be first - bigger airplanes, or longer runways? I'm generally speaking about airports with runways long enough for airliners, be historic or still in use. In order not to turn this question to a chicken-egg discussion, here are my points: Would making an airport(s) before making the actual airplanes befeasible and cost-efficient ? Will new(and more runway-lengthdemanding) airplanes be able to take-off from shorter runways,because there are no other options ? I'm generally interested in historic terms, which came to be first - bigger airplanes, or longer runways ? <Q> It is the larger aircraft that came first. <S> Historically, the runway length (and design) of an airport has depended on the aircraft operating there (among other things), though this is changing. <S> For example, the Prague airport site : <S> The main runways – RWY 04/22 and RWY 13/31 – were continually lengthened during post WW II operations which kept them in line with the demands of the aviation industry until the mid 1960s... <S> The runway required for the aircraft depends on the take-off weight and the lesser runway length restricts the payload or range. <S> As a result, for economical operation, the runway needs to be longer. <S> However, there are other constraints to consider: <S> For large aircraft, the runway (and taxiway) width, apron and parking space are important considerations. <S> In most cases, lengthening the runway will be easier than taking care of these other constraints. <S> For major airports (like Heathrow, for example), the cost of runway expansion will run into the billions. <S> Unless the aircraft is going to be operated regularly (which depends on how many airports it can land), there is no point in lengthening the runway in an airport. <S> The economic operation of the aircraft has to be considered. <S> For example, the A380 was designed around a 80m 'box', which the airlines had decided is the maximum size they can operate economically. <S> A bigger aircraft does not mean more runway required. <S> For example, the A380 requires (slightly) lesser runway compared to 747-400. <S> If it comes to that, aircraft requiring more runway can takeoff from smaller ones. <S> For example, a Boeing Dreamlifter once took off from a 6000 ft runway (it normally requires > 9000ft). <S> The airports with longest runways have them for different reasons- <S> the Qamdo Bamda Airport (5500m runway) has a long runway due to its elevation (>4300m above MSL), while the Ramenskoye Airport as a long runway (5400m) due to the aircraft operated there; it was a test facility, for among other things, the Soviet Buran spacecraft. <A> The biggest airplanes first used water for taking off and landing, and only later were similarly sized land airplanes built. <S> Bigger airplanes tend to have a higher wing loading and so require longer runways. <S> The Caproni Ca.60 was the biggest aircraft of its time (1921) and is still bigger than a Jumbo Jet if you use wing area to measure size. <S> It could only be built as a flying boat. <S> Caproni Ca.60 (picture source ) <S> Another biggest aircraft of its time was the Dornier Do-X from 1929. <S> On one occasion it carried 169 people into the air, including one stowaway. <S> Its regular capacity of 60 to 100 passengers would only be surpassed in the jet age. <S> Dornier Do-X in flight (picture source ). <S> This one actually flew, but was hampered by the small aircraft engines which were available at its time. <S> Flying boats were also used on the first transatlantic and transpacific routes, and to connect the parts of the British Empire by air, Imperial Airways used a fleet of floatplanes and flying boats . <S> Routes were strung along lakes as staging points. <S> Short Empire as operated by Imperial Airways <S> (picture source ) <S> Long runways were only built during the second World War when the weight and speed advantage of land airplanes made them the preferred choice for bombers. <S> With the runways in place, flying boats soon disappeared. <A> The bigger airplanes came first. <S> A shortish runway length is not preventing bigger planes to operate, but it limits the take-off weight, especially in warm weather. <S> Since a lower take-off weight means less payload, the business case to extend runways became obvious. <S> So airports follow suit.
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In the end, airports have to weigh the benefits of letting heavier aircraft operate against the resources required for runway lengthening.
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Why is carburetor heat use discouraged on the ground? I've been reading my private pilot books for when I start in February and Carb Heat has me stuck in a rut. I feel like I need to have a very solid understanding of this being that I live in a very humid area. The book says do not use carb heat on the ground and on taxi because it will draw unfiltered air into the engine(air from exhaust)... But what is the difference between using it in the air vs on the ground and isn't the risk of icing just as equal in the air as on the ground? <Q> If you feel that you would need carb heat sitting on the ground, I'd recommend taxing back and waiting for conditions to improve. <S> If you are set on going, usually doing a run-up at the runway before take-off will tell you if you have carb ice or not. <S> The other answer gave good reasons, sucking in some FOD (foreign object debris), but there are some other things you would want to consider... <S> Forgetting to push the carb heat back in before takeoff - Especially important when taking off from short fields, you want all the power your engine has to offer, as carb heat robs your engine of some power. <S> 3/4 of the way down a 1200 foot runway is a bad time to realize the carb heat is still on, because it probably isn't on your takeoff checklist. <S> Carb heat is not very effective on a cold engine - <S> This is a real problem when you are at idle or especially gliding, the airflow over the engine components and the exhaust just doesn't create enough heat to melt the ice in the carb (at least not very quickly). <S> This is why you may be instructed to "clear" the engine periodically during low power operations. <S> This involves adding power and then carb heat to help melt any ice. <S> That all being said, its not so much a rule as a recommendation. <S> You'll probably find that during your flight training you'll end up leaving the carb heat on while on the ground for short periods. <S> This happens a lot during landing operations when you are instructed to have carb heat on (my instructor taught me mid-field downwind, "Seat Belts, Gear, Fuel Selector, Carb Heat , Mixture, Prop, Power"). <S> You'll end up leaving it on until you've cleared the runway (or set up for a touch-and-go) and are running your "after landing" checklists. <A> Several possible reasons. <S> While taxiing an engine failure is not as critical. <S> While in flight an aircraft is much less likely to ingest dirt, rocks, twigs, grass etc. <S> Finally, while at flying speed, the exhaust gases are carried "behind" the aircraft, while at slow taxi speed, there is less airflow to do that. <A> The Owner's Operation Handbook for the Luscombe recommends carb heat be ON during landing AND takeoff. <S> In the models where the fuel tank was in the fuselage, apparently there wasn't enough fuel head to get the fuel to the carb under full power climb (too steep an angle), but the handbook explicitly references icing as the reason for carb heat during takeoff.
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If you have carb ice, applying carb heat will cause your engine to make even less power (hot air is less dense than cold air).
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Can a helicopter operate continuously in a small, enclosed, sealed environment? Many years ago I had an interesting discussion with a friend (while drinking). We were discussing what would happen if a helicopter was placed into a sphere of some size (slightly larger than the helicopter, a few times larger than the helicopter, etc.). Assume the sphere is filled with air at standard temperature and pressure, and there is standard 1G gravity pulling in one direction. Can the helicopter maintain flight? I believe it might, for a very short time, until the air starts circulating in a (relatively) stable manner, causing the "natural flow" of air to be already descending when it encounters the rotor disc, therefore reducing lift to nearly nothing. I'm curious what an expert might think. If this is off-topic, mark it as such and I'll delete the question. Adding more useful tags I don't know about might also be helpful. :) <Q> A helicopter develops lift by accelerating air downwards through its rotors. <S> This relies on the air above the rotors being slow enough for the rotors to accelerate that air enough to provide sufficient lift. <S> When hovering in still air, the incoming air has zero velocity relative to the helicopter. <S> While of course the air is conserved, in a large volume of air, the downwash is able to diffuse much more, and much of it does not immediately circulate back up above the helicopter. <S> If the helicopter were enclosed in a sphere, the smaller the sphere, the less the air would be able to diffuse. <S> The downwash would circulate back to the top of the sphere, where the rotors would take that air in again. <S> The rotors would be less effective at accelerating the air that is coming in with significant velocity, just as a propeller develops less thrust with increasing forward speed. <S> Successful hover would depend on the helicopter being able to develop lift at a rate of circulation where the air can slow down enough for the rotors to be effective. <S> This seems like a experiment manageable enough that someone could try it at home... <A> A serious danger to helicopter flight is flying in a vortex ring state , causing a stall. <S> Essentially, the helicopter descends into its own downwash. <S> When the condition arises, increasing the rotor power merely feeds the vortex motion without generating additional lift Several helicopters have crashed as a result. <S> This state would be very quickly established for a helicopter in a confined container. <A> Indoor model helicopters would not be able to fly if the answer were no. <S> Of course it can, but the enclosure must be big or small enough to avoid a toroidal vortex from developing around the rotor. <S> To summarize my answer, three conditions make it possible: <S> A very big enclosure which allows enough forward speed <S> so the helicopter never flies in its own wake, a very low ceiling or a very narrow enclosure. <S> Case 1 is trivial, so I dwell here on case 2: <S> This is caused by the ground effect (or better ceiling effect in this case): The efficiency of the blades increases the closer they are to a horizontal surface and the helicopter needs less torque for the same lift. <S> Once the rotor head is touching the ceiling, you need to cut power almost to zero to free it again. <S> The same effect can now be used to fly in the constrained space because it will prevent the toroidal vortex of the vortex ring state from developing. <S> Now the explanation to case 3: If you insist on not touching any surface, the vortex will soon develop and reduce lift. <S> How long you can hover depends on the air volume, and there is a minimum when the diameter of the enclosure is approximately twice the rotor diameter. <S> Once the diameter becomes smaller, the vortex will again be inhibited, and when the enclosure is small enough the rotor will look like a fan in a duct. <S> Now again less energy is needed for lift - just enough to maintain the necessary pressure difference through the rotor disc. <S> I should add that this solution will best work with a co-axial rotor and no tail sticking out at one end. <A> In the movie 1982 Deadly Encounter, if my memory serves me correct, there is a scene where a Hugh 500 flies inside a large hangar. <S> No CGI in ‘82, don’t believe any special effects were used, so yes indoor flight possible. <S> My thought being the accelerated air above rotors would somewhat balanced by ground effect.
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If you have flown an indoor model helicopter, you probably know that it is not advisable to come too close to the ceiling: The helicopter will become unstable and will be sucked right into it.
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Is this the shortest route served by an Airbus A320? Is this the shortest route served by an Airbus A320? Port Louis to Saint-Denis, 231 km (144 mi). Air Mauritius flight MK248. <Q> This site seems to indicate that they had the shortest route using the A-320 family of aircraft at just over 70km. <S> The page also shows a list of flights, and it looks like one of them is listed at 58km. <S> Based on that list, it looks like your 231km flight wouldn't even break the top 10. <S> Its difficult to search based on the length of the route and the aircraft type. <S> As far as I can find though, 58km ACE->FUE shortest scheduled route for the A-320. <A> I don't think so. <S> Source here <A> The shortest A320 route I know of is from Dammam to Bahrain. <S> The flight duration is 15 minutes.
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The shortest route with an A319, which is an A320 family aircraft that I am aware of is Dar es Salaam - Zanzibar (HTDA, HTZA) which if I recall is roughly 73 kilometers (probably even less from airport to airport) operated by FastJet Tanzania.
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What is the true meaning of the word “wilco” when used on the radio? What is its origin? Pilots often learn to use the word "wilco" on the radio through contextual interpretation. During my experience as a pilot communicating on the radio I have often observed pilots using the word "wilco" improperly. What is the true meaning of the word "wilco" and what is its origin? <Q> "Wilco" is short for the phrase " will comply ," meaning that the speaker will follow the instructions to which they are replying. <S> Merriam-Webster places the origin at 1938, some time after the invention of radio, likely in military usage. <S> Although the phrase "roger wilco" is sometimes used, it is considered redundant since the "roger" ( meaning "received and understood" ) is implied. <A> In the US, the "official" meaning is in the Pilot/Controller Glossary : <S> WILCO <S> − <S> I have received your message, understand it, and will comply with it <S> (Note that this is slightly different from roger , which is just an acknowledgement and doesn't mean that you will comply with anything.) <S> The AIM 4-2-3 mentions using it to acknowledge instructions: Acknowledge with your aircraft identification, either at the beginning or at the end of your transmission, and one of the words “Wilco,” “Roger,” “Affirmative,” “Negative,” or other appropriate remarks <S> The problem I see with using wilco is that you're confirming that you'll comply with an instruction, but if you don't also read back the instruction <S> then the controller has no way to know what you're complying with. <S> You might have misheard or misunderstood it, so you should repeat it. <S> But if you repeat it, then wilco is unnecessary. <S> Outside the US, I was originally taught never to use roger or wilco for that reason: it leaves the controller wondering what you really heard and what you're going to do next. <S> But obviously as far as US aviation goes, both are completely acceptable. <S> And as for the etymology, that's already been covered in <S> another answer : <A> I have been a pilot for 47 years. <S> The use of the word WILCO vs. reading back a clearance is defined. <S> Keep in mind that early radios were not easy to understand and the phonetic alphabet was formed. <S> An ATC instruction "Plan on crossing XXXXX at FL280" can be addressed as WILCO as it is not a clearance. <S> "Cross XXXXX at FL280" is a clearance and must be read back. <A> As other answers have already mentioned, WILCO is a concatenation of Will Comply. <S> To provide a UK perspective, there are a number of ATC instructions that must be read back, however in other cases "Wilco" is preferred. <S> The CAA Radiotelephony Manual CAP 413 states (my emphasis): <S> "Instructions transmitted are to be complied with and, in most cases, should be read back to reduce the chance of any ambiguity or misunderstanding, e.g. ‘G-ABCD, taxi to the apron via taxiway Charlie’. <S> Chapter 2 specifies those instructions that are to be read back in full. <S> However, if the instruction is short, clear and unambiguous, acknowledgment of the instruction using standard phraseology such as ‘Roger’ (I have received all your last transmission) or Wilco’ (I understand your message and will comply with it) is preferred for the sake of brevity in the use of radiotelephony transmission time." <S> Based on the rather strong opinions of a CAA examiner, the following scenarios illustrate an example of acknowledging instructions to report position: <S> G-ABCD, report abeam Farmoor reservoir" <S> If a read-back is given in the response and it is clipped, the controller could hear "... <S> Abeam Farmoor reservoir G-ABCD", which could cause confusion. <S> Acknowledging with "Wilco G-ABCD", "Roger G-ABCD" or even just "G-ABCD" reduce the risk of confusion if the response is clipped, as well as providing brevity. <S> G-ABCD, number 2 in circuit, report final <S> In this scenario, again a clipped read-back could cause confusion ("... <S> Final G-ABCD"). <S> However, "Roger G-ABCD" (or just "G-ABCD") simply mean the transmission has been received. <S> This could refer to the traffic information, the instruction, or both. <S> The instruction could perhaps have been missed, especially as part of a more lengthy and complicated transmission. <S> In both scenarios, "Wilco" is the only response that unambiguously conveys that the instruction element of the transmission has been received and understood, and that it will be acted upon. <S> It is for this reason that it is preferred over "Roger" when a brief acknowledgement is desirable.
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"Wilco" is short for the phrase "will comply," meaning that the speaker will follow the instructions to which they are replying
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What happens if an aircraft declares an emergency while there is another aircraft ahead cleared to land? Lets assume this situation: In a controlled airport, two aircraft are approaching for landing. #1 is about to touch the runway (let's assume it is within 1~2 miles from touch zone). Then #2 declares a emergency. Is there any rule that require that the first airplane starts a go around, either by its decision or by controller's? Some assumptions: There is enough separation from #1 to #2. If #1 was allowed to land and it successfully does, that will not significantly interfere with #2 landing. Airfield has just one runway. I'm limiting this to a international accepted, US and/or Brazilian rule. My concern is that if some incident occurs with #1 on landing, like a gear collapsing, that may render the runway unsuable, causing trouble for the trailing aircraft in emergency. Speaking in other words: Is an aircraft cleared to land even if another is approaching in a emergency situation? <Q> No, the airport wouldn't be closed, and the #1 aircraft doesn't need to go around nor be sent around. <S> The risk of him shutting down the runway is very slight, and is probably of the same magnitude of risk that sending him around to hold until #2 has landed & the runway has been checked and reopened, would put him into a low-fuel emergency state. <S> The runway is often closed following an emergency landing until it can be checked by an airport vehicle, to ensure that it is clear of debris, spilled fuel/oil/hydraulic fluid/etc. <S> And if the emergency aircraft can't clear the runway under its own power, it takes time to get it towed off, possibly pinning the landing gear (to prevent unintended retraction) first. <S> Plus there may be an evacuation after the landing. <S> So closing the runway for some time after the emergency aircraft lands, is entirely possible. <S> But if the airport has planes in the pattern & the emergency aircraft is 50 miles out, it'd be better to let those who want/need to land, do so, rather than risk them running low on fuel airborne while awaiting the runway's reopening. <S> Same basic logic applies in the #1 / #2 scenario posed above. <S> If aircraft regularly had their gear collapse & shut down runways unexpectedly, that would be a different story. <S> But that's exceedingly rare, so that isn't the contingency that all planning is based on. <A> Your question is a little vague; depends on the nature of the emergency for aircraft #2. <S> Declaring an emergency provides the PIC with the power to obtain priority over any other aircraft. <S> If the PIC of aircraft #2 determined that they needed aircraft #1 to execute a go-around, then pilot of #1 aircraft would be expected to do that if able. <S> I will also add that this scenario is highly unlikely because required separation between the two aircraft would have already established enough time for #1 to land and clear the runway before #2 could get there - regardless of the situation. <A> It appears that the situation in your question is hypothetical. <S> There are several aspects missing about the nature of the emergency, condition of the airport etc. <S> A typical situation will require that the airport will be ready to deal with the emergency, and clear the intended runway where the aircraft declaring emergency can land without delays. <S> In clearing the runway, ATC can advise the #1 airplane to land and quickly clear the runway. <S> Again hypothetically speaking, after aircraft #2 has declared emergency, #1 can get into a situation where it would require more immediate assistance than #2.
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If they are both about the same distance (actually, time) away, then the emergency aircraft has priority (assuming that he doesn't decide to hold in order to troubleshoot, burn down fuel, prepare for the landing, etc), but essentially closing the airport from the time that the emergency has been declared until the emergency aircraft lands, isn't something I've ever seen or heard of.
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Why is radar required on some FAA instrument approaches? The ILS / LOC approach at KCXY states radar is required. I understand I can't fly the approach if not in radar contact. However, if flying the LOC approach I think I can identify both final and HORVI (for lower minimums) using HAR VOR. There's no reason I'd need the controller to call out a fix. If that is true, why is radar required? I think it would be more of a safety concern because of terrain and an adjacent airport (HAR Int)? <Q> Radar is most likely required in this case because there is no defined Initial Approach Fix (IAF). <S> Also note that in the profile view TIVNE and HORVI have the word RADAR underneath, which means that if you wanted to fly to either of those way points, including a course reversal in the hold, you would still need to be vectored by ATC via RADAR. <S> This means that ATC needs to give vectors to final or otherwise provide a specific clearance to establish an IFR aircraft on the approach. <S> There may be other considerations, but that is the main one that I see here. <A> As mentioned above, this approach has no IAF. <S> That's because the the VOR is at 1,301 MSL (note the height of the obstacle next to the VOR <S> is 1,410), and the segment from TIVNE to HORVI descends from 2,800 to 1,340 MSL, and will dip below the usable volume of a Low Altitude VOR. <S> According to AIM 1-1-8 , a low altitude VOR with a standard service volume cannot be received inside 10 miles and below 1,000 feet above the NAVAID. <A> Since most (almost all) instrument approach procedures are designed to allow a non-radar transition from the enroute phase of flight to the approach phase, any instrument approach that does not have published transitions requires "Radar." <S> Also, if there is a mandatory stepdown fix on the approach that cannot be identified by any other means (GPS/DME/VOR), the approach stipulates "Radar Required" (ref: FAA Oder 8260.19f) <A> From the FAA's hand book on IFR flying (page 4-17) . <S> It seems that it is the minimum equipment required to fly the approach. <S> In some cases, other types of navigation systems, including radar, are required to execute other portions of the approach or to navigate to the IAF (for example, an NDB procedure turn to an ILS, or an NDB in the missed approach, or radar required to join the procedure or identify a fix). <S> When ATC radar or other equipment is required for procedure entry from the en route environment, a note is charted in the plan view of the approach procedure chart (for example, RADAR REQUIRED or AUTOMATIC DIRECTION FINDER (ADF) REQUIRED). <S> When radar or other equipment is required on portions of the procedure outside the final approach segment, including the missed approach, a note is charted in the notes box of the pilot briefing portion of the approach chart (for example, RADAR REQUIRED or DISTANCE MEASURING EQUIPMENT (DME) REQUIRED). <S> Notes are not charted when VOR is required outside the final approach segment. <S> Pilots should ensure that the aircraft is equipped with the required NAVAIDs to execute the approach, including the missed approach. <S> Refer to the AIM paragraph 5-4-5 for additional options with regards to equipment requirements for IAPs. <S> Later on they talk about Radar Approaches (Page 4-71) <S> The two types of radar approaches available to pilots when operating in the NAS are precision approach radar (PAR) and airport surveillance radar (ASR). <S> Radar approaches may be given to any aircraft at the pilot’s request. <S> ATC may also offer radar approach options to aircraft in distress regardless of the weather conditions or as necessary to expedite traffic. <S> Despite the control exercised by ATC in a radar approach environment, it remains the pilot’s responsibility to ensure the approach and landing minimums listed for the approach are appropriate for the existing weather conditions considering personal approach criteria certification and company OpSpecs. <S> They can also be useful in helping disabled aircraft in (page 4-74). <S> Perhaps the greatest benefit of either type of radar approach is the ability to use radar to execute a no gyro approach. <S> Assuming standard rate turns, ATC can indicate when to begin and end turns. <S> If available, pilots should make use of this approach when the heading indicator has failed and partial panel instrument flying is required.
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Radar is required because there are no "published non-radar transitions" for this approach.
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Why do the RNAV (GPS) approaches to KAPC not use the same missed approach procedure as the ILS/LOC approach? While looking at the various instrument approaches for Napa Valley (KAPC), I noticed a discrepancy between the RNAV (GPS) Y/Z RWY36L missed approaches and the ILS/LOC RWY36L approach: Why is it that the ILS approach is able to use a turning missed approach to keep pilot and plane clear of the high ground to the north, but the RNAV approaches to the same runway force you to either have visual contact with the high ground early, or outclimb it? To me, it'd make more sense to have the RNAV procedures use a similar missed approach to the ILS, as then you could have an all-aircraft RNAV procedure with low minima, vs. one with high minima that works for everyone and one with low minima that requires a significant (more than twice the norm) missed approach climb rate. <Q> Specifically, I found the following (see chapters 7 and 15): <S> In RNAV missed approaches "turns shall not exceed 120°", but the ILS missed approach requires about a 180° turn. <S> There's some related information here about the FAA testing turns greater than 120° in RNAV instrument procedures, it looks like some avionics can't handle them properly. <S> RNAV missed approaches are made up of legs between waypoints, and the first leg after the MAP has a required minimum length "to allow the aircraft's stabilization on course immediately after the MAP". <S> Unfortunately I couldn't identify what that length is, because the FAA's PDF quality is abysmal and some information is unreadable, but the ILS missed approach requires a turn after a climb of less than 300' (from 214' to 500'), so the distance traveled in that time would presumably be quite small. <S> If the RNAV minimum leg length is significantly greater than that distance, then it might be necessary to continue straight ahead, as both RNAV approaches do. <S> I'm certainly not a TERPS expert and there may well be other reasons for not using the ILS missed approach, but those two points seem to show that the criteria for designing missed approaches is different enough between procedure types that you can't just 're-use' them freely. <A> Look at where the missed approach points are on each approach. <S> The ILS has you very low, and possibly unable to clear the terrain to the northeast, hence the turning procedure. <S> The RNAV has you going missed almost 1000 feet above the ILS, so terrain clearance would not be as much of a factor. <A> GPS approaches and missed approach routing are designed point to point to point, so "climb to XXX <S> then direct ABC" doesn't work -- there is no defined track to sequence to after the straight-ahead leg. <S> So the GPS approaches can't use the same procudure as the ILS does. <S> There does seem to be a terrain or obstacle issue somewhere on the missed approach routing of the GPS approaches. <S> So you can either fly the "Y" approach with a high MDA (so you start the missed approach higher, with less altitude needed to clear the obstacle), or you can fly the "Z" approach that takes you lower but requires a higher than standard missed approach climb gradient. <S> There is probably a reason that the approach designer didn't use a missed approach track that would look more like the ILS missed approach track (but done point to point to point), avoiding the obstacle even with a normal climb gradient, but we can't tell what that reason is. <S> A minimum length of each segment and similar TERPS criteria would be my guess, but that is only a guess. <A> Could it be because you are using two different navigation systems? <S> Yes, you might be on the RNAV/GPS for the approach and have the ILS on a second display. <S> But, why wouldn't you just use the lower DA on the ILS anyway?
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As best I can understand from the TERPS , it's because there are certain criteria for RNAV missed approaches that wouldn't be met by copying the ILS missed approach. For either ATC or convenience reasons they probably prefer you to go missed to the north east, hence they have the RNAV go that way.
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How does an airport catch up when it is behind on traffic? When airports fall behind traffic for some reason and delays piling up, how do they catch up? If flights need to be cancelled, who decides (and when) - ATC, airport management, or airlines themselves? As an illustration, here is a snapshot from this page (taken at approx. 2355 UTC 12/23/15): <Q> Most airports aren't at 100% capacity any of the time: they simply fit in a few extra flights for a couple of hours until they're back on track, causing relatively little delay. <S> Even those who are at 100% capacity sometimes, aren't usually at 100% capacity 24/7. <S> Heathrow runs at nearly 100% capacity (roughly 98%), and much of the "quiet" period is actually at the very start of the day which doesn't leave much slack. <S> However, there's some scope for "absorbing" flight delays: <S> at Heathrow, most aircraft will sit in a "hold" stack for a while before landing. <S> Aircraft join this stack as they arrive and wait their turn to land. <S> If one plane is a little late, another will simply take its place in the queue and everyone jumps "up" one space until the delayed flight. <S> As long as there are aircraft in the stack, short delays or aircraft arriving early don't really make things too chaotic - there are still 60 aircraft landing in the next hour <S> , it doesn't really matter what order they land in. <S> However if there's a bigger problem such as ice, which means the overall capacity is reduced, flights must be cancelled as they simply cannot all fit in. <S> In this case the airport will typically reduce capacity across the board and allow the airlines to choose which flights to cancel. <S> In the case of Heathrow, this will usually be the relatively local, high-frequency routes: eg the once-a-day flight to Sydney, Australia will still fly, but one of the once-per-hour Glasgow flights will be cancelled. <S> For the most part the number of cancelled flights is down to the airport/ATC, but the specific flights cancelled are up to the airlines. <A> Well, the delays usually pile up during the busy hours. <S> They manage to eliminate the delay times when the flights arrive or land at the non-busy hours which dissipates most of the delays. <S> One or two flight cancellations won't have much impact on the departure or arrival time during busy hours because the airport is packed. <S> This situation is very similar to rush hour traffic on roadways dissapating after those hours. <S> To answer your second question, it is mostly airlines that cancel their flights. <S> Airport management might cancel a flight if there is something really wrong with it. <S> and ATC might cancel if the weather or some other occasion warrants it. <A> To add to the other answers, one thing ATC will do is order ground stops. <S> Basically they stop the inbound flights at their origin until there is space to fit them in at the destination. <S> There's an excellent blog post on the whys of ground stops and why planes will leave the gate and sit on the ramp sometimes for hours. <S> When there's congestion or delays at the destination, ATC will often give them a narrow opening to get in the queue. <S> If they can't be in the air in so many minutes then someone else gets the spot. <S> It's a very informative read. <S> He's also got a post on how the "passenger bill of rights" throws a wrench into this.
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They can recover by delaying everyone a little for a few hours, with the delay slowly reducing as the airport gets quieter With a very busy airport (Heathrow is often quoted as an example), however, it's possible that the airport is at/near 100% capacity for long periods.
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Would an airliner be allowed to take off in snow? Im going to fly to Tucson tommorow. The weather is telling me its going to snow in Denver. So would snow cause a delay or are airliners allowed to take off in this kind of weather? <Q> Don't worry about it <S> While snow can sometimes cause a delay, airports are really good at snow removal. <S> (Especially airports like Denver that are used to getting a lot of snow.) <S> According to flydenver.com DIA has 500 trained snow removal people and 270 pieces of equipment to clear 12.2 million square feet of runway, taxiways, etc. <S> To put that in perspective, a typical highway (2 lanes each way, with shoulders) is around 38 feet wide each way, or 76 feet for both directions. <S> If I've done the math correctly, 12.2 million square feet is about 30 miles of road. <S> The state of Minnesota knows a thing or two about plowing snow . <S> They use about 1500 drivers and 839 plows to handle 12,000 miles of road. <S> To plow snow the way the Denver airport does it, they would need 200,000 drivers and 108,000 plows. <S> Here's a YouTube link that shows off some of Denver's bigger snow removal tools. <S> Chances are, if you can get to the airport you'll be able to fly (but perhaps not on time) <A> Yes There are two considerations in snow: Icing Visibility <S> Visibility is easily dealt with and most airlines have approved opspecs to takeoff in low visibility (e.g. down to 300 or 500 feet RVR). <S> Heavy snow can reduce visibilities to less than a quarter mile (e.g. less than 1200 feet RVR) <S> so there is quite a bit of margin between between typical snowfall and minimum visibility takeoffs. <S> Icing is a bit more of a challenge, but is a well defined problem with specific procedures. <S> In snow airplanes will be de-iced <S> with Type I fluid and then treated with an application of Type IV fluid for anti-ice protection. <S> This fluid has a holdover time that you can takeoff within without additional checks. <S> Some of these holdover times can be low (e.g. 5 minutes for specific conditions) but de-ice is usually where the takeoff bottleneck is and once you are treated you can generally take off without too much further delay. <S> Planes will be able to operate in snow, but departure rates will be less than they would be for a normal good weather day. <S> Winter ops are normal this time of year (northern hemisphere). <S> Continuous heavy snowfall can eventually close an airport if it becomes impossible to keep the runways clean, taxi routes become unusable due to drifting snow or snow transitions into sustained freezing rain (or runs out of de-ice fluid, yes IAH I'm looking at you). <S> This is a transient problem and the closure would end as soon as conditions ease and the facilities can keep up with it. <A> Yes, heavy snow delays departures from the Denver airport (based on personal experience). <S> Of course, nothing horrible <S> : the airport will be cleaned, the plane will be de-iced (twice if your are unlucky enough), and may even catch part of the lost time on the way to destination. <S> Still, it would be unwise to rely heavily on very on-time arrival. <S> If you need to change into another flight at your destination, and especially if you need to do anything else on time where the airline cannot help (change into unrelated train, or attend important meeting), I would advice to add a few extra hours for the possible delay. <A> I flew a few times out of some very cold places... on video shoots (I work in film/video). <S> Places like Albany NY, Buffalo, and Wyoming. <S> Those airports are pre-pared to deal with the snow, so what would fully shut down an airport like say Austin; its business as usual in Albany. <S> Being in a window seat, and watching a guy in a cherry picker with a fire hose outside your plane spraying down the entire aircraft with I assume a de-freezing chemical solution similar to whats in your windsheild wiper spray; was pretty scary the first time. <S> It was snowing hard. <S> Everything was covered. <S> But they sprayed us down; and off we went; in a 777 no less.
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Departure rates will be limited by runway condition (the airports ability to keep them treated and clean), the throughput of the de-ice facilities and to some degree the aircraft arrival rate (you don't have planes to fly out unless planes are making it in).
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How else can snowy/icy conditions disrupt airport operations? In casey's fabulous answer here , he identifies several ways snow/ice can disrupt airport operations: Continuous heavy snowfall can eventually close an airport if it becomes impossible to keep the runways clean, taxi routes become unusable due to drifting snow or snow transitions into sustained freezing rain (or runs out of de-ice fluid, yes IAH I'm looking at you). This is a transient problem and the closure would end as soon as conditions ease and the facilities can keep up with it. Are there other ways that heavy snow (or ice) can disrupt airport operations? Could it perhaps interfere with lighting or navaids? Are there other airport functions that stop or slow in snow and ice? <Q> There are multiple ways by which snow can affect the operation in an airport. <S> During landing, snow or slush in runway can reduce the deceleration rate by reducing friction coefficient, sometimes causing hydroplaning. <S> The runway length requirements in case of dry and wet conditions are different. <S> This means that some aircraft cannot use the available runway in case of snow/wet conditions. <S> The requirements to clean the runways (and taxiways) continuously means that the flights will be delayed. <S> The snow may reduce the visibility of runway and terminal visual markers. <S> Ramp operations may be affected due to snow/ice. <S> Beyond a certain level of snow, the airports have to be closed as the aircraft cannot takeoff/land. <S> Also, it will be snowing in areas around the airport too. <S> This means that there will be difficulty for people in reaching airport in the first place. <S> Also, see the FAA advisory circulars AC 150/5200-30C - Airport Winter Safety and Operations and AC 91-6A, Water, Slush, and Snow on the Runway <A> Airport workers often struggle to get to work. <S> This is generally OK for the first 12 hours or so but soon, people need to stop working and rest, especially those with safety critical roles which have legally mandated maximum working and rest periods. <A> There are various ways which heavy snow or ice can disrupt airport operations. <S> Visibility would certainly be an issue, as call tower operators would have trouble visually seeing aircraft and would be unable to accurately judge any distance between aircraft. <S> Additionally, ground crews and pilots would certainly have a tough time trying to navigate around the airport. <A> Well, snow and ice would stick on aircraft, causing a dangerous situation because of unsteady airflow over lift surfaces. <S> It would also decrease visibility, although it would not matter as much in an ILS except for seeing the runway at almost-touchdown altitudes. <S> If the snow or ice is too much, it could interfere with the radar systems of the airport.
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Snow (and ice) in runway can affect takeoff by absorbing energy and can impact the aircraft after being kicked up by tires.
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What are the ways to burn fuel faster in case of emergency without fuel dumping system? In many cases, the maximum landing weight of an aircraft is lower than the takeoff weight due to the amount of fuel it carries. While some aircraft have fuel dumping systems, others like the A320 family and Boeing 737 do not, and so have to cycle nearby until they have burned enough fuel. (And in case they have to land immediately, they will simply to, but need further inspection due to the high stress on brakes and landing gears) My question is: If an aircraft has to cycle to burn fuel, are there measures to burn fuel faster? Lower altitude requires more thrust and so needs more fuel, but are there more ways? Like a slight air brake setting? <Q> This question (sorry to say) is sort of moot because: if you have an urgency to land (e.g. cargo fire), you don't care if you are overweight <S> and you'd land anyway if you have time to dump fuel, the situation isn't as desperate, and you can easily wait just a bit longer. <S> The large jets (e.g. Airbus A380, Boeing 777) have a fuel dumping system because, with full fuel, these planes can travel up to 12 hours or more ! <S> That is to say, if you don't dump fuel, you might have to fly around all day to get down to your normal landing weight. <S> Airbus A320 and Boeing 737 are different: they usually fly 1~3 hours route, and may stretch to 6 hours on a full tank. <S> So, to begin with, you need less time to burn fuel. <S> Plus, these (relatively) small planes can land on shorter runways, which means your airport choice will not be as restricted as with a large jet. <S> Now, as to actually answering your question...... Flaps and gears have speed restrictions. <S> You cannot fly full throttle with these deployed. <S> That being said, if the pilots put the airplane in landing configuration (full flaps + gear down), drag will increase significantly and they will need more thrust to maintain altitude and airspeed. <S> You can technically achieve that with spoilers, but it's dangerous. <S> Spoilers destroy lift, so what you're really doing is reducing the effectiveness of your wings and compensate that by flying faster and/or increasing your angle of attack. <S> Then again, if you're desperate, just land right away...... <A> Fuel flow is proportional to air density, so it is advisable to stay low. <S> Since the propulsive power requirement scales with the cube of airspeed, flying faster is also advised. <S> However, when flying below 10.000 ft all civilian traffic has to obey a speed limit of 250 KIAS . <S> A Hapag-Lloyd A310 demonstrated in 2000 how much an extended gear will increase fuel consumption. <S> climb to an altitude just above FL100 and fly as fast as possible. <S> Depending on the aircraft, spoilers or speed brakes might still be used to increase drag, but the gear and high lift devices have to stay in. <S> fly a sawtooth pattern: Climb and descent in rapid succession, and use all drag-increasing means during descent, including sideslip. <S> Which version is best depends on the particular airframe. <S> My personal favorite is number three: Few maneuvers beat a proper sideslip for sheer fun. <A> This results in requirement of more thrust, which requires more fuel. <S> He can do it in lower altitudes, but the holding altitude has to be cleared by ATC, I guess. <S> Note that even jettisoning of fuel takes quite some time. <A> Another method - one employed by F-16 aircrews as the jet doesn't have a fuel dump vent - is 'burner and boards', that is selecting afterburning with the speedbrakes deployed. <A> Many times burning fuel off is not necessary. <S> However there are times when it is. <S> One pilot who flew for a company I worked for was ferrying a large Cessna from Kansas to Africa, with essentially a waterbed full of avgas. <S> He had a gear problem at takeoff. <S> The decision was to empty the bladder inside the cabin, prior to a landing with one gear down and one main someplace else. <S> Probably a good decision, but this type of situation is rather rare, thankfully. <S> One human factors consideration is that an extended burn or dump time can increase crew fatigue and stress. <S> That can increase risk.
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For increasing fuel burn, the pilot can simply increase drag by increasing the speed. My recommendation is to stay low and fly in approach configuration (gear, flaps and slats out) as close to 250 KIAS as the configuration allows.
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How do rocket engines produce more thrust than aircraft jet engines? I can't find the reason why rockets are able to produce so much thrust when compared to turbojets. I do know that the rockets carry their own own supply of oxygen since there is no oxygen in space or the upper region of our atmosphere. And that the upper stages use hydrogen for longer range. But given that RP-1 is kerosene basically. A highly refined form of kerosene that is used in jets but kerosene nevertheless. Is there something else that gives the first stage of the rocket it's unbelievable thrust or is it just all down to the RP-1 fuel? <Q> For one, don't only look at the engine, but at the whole propulsion system. <S> This includes tanks, piping, controls, pumps and the actual engine. <S> Now the rocket looks much less favorable, especially if you size the tanks for equal running times. <S> The rocket does not need any of the parts which are ahead of the combustion chamber of a jet and also does not need the turbine. <S> Also, being designed for full thrust only, it does not need an adjustable nozzle. <S> Please look below at the engine installation of a typical airliner (I tried but could not find a fitting cross section of a turbojet plus intake): Jet engine and nacelle cutaway drawing (picture source ). <S> As @Talisker correctly observed in the comments, the labels "high speed jet" and "low speed jet" have to be swapped in order to be correct. <S> Only the part labeled "combustor" and the section aft of the turbine are actually comparable to a rocket engine - all else is needed to condition and compress air or drive the turbo machinery in front. <S> A rocket enjoys the luxury of being fed propellant and oxidizer at just the right ratio, condition and at high pressure, and since the oxidizer is mostly pure liquid oxygen, the turbo pumps for compressing it can be much smaller than the turbo machinery of a jet which works with an 80% nitrogen - 20% oxygen mixture of gasses. <A> Seems as though everyone has missed the simple, obvious answer: the rate at which the engine burns fuel. <S> To take a concrete example, the Saturn V's first stage carried 205,400 gal/770,000l of kerosene fuel, which it burned in a bit less than 3 minutes: https://www.space.com/18422-apollo-saturn-v-moon-rocket-nasa-infographic.html <S> By contrast, a Boeing 747 carries about a quarter as much (48,445 gal/183,380 l), and burns it over perhaps 12 hours. <A> The rocket engine produces the same thrust regardless of the speed it moves. <S> Differently, the thrust of the jet engine depends on velocity and declines as velocity increases, because of the ram drag. <S> It is largely useless if the engine speed approaches the exhaust velocity. <S> The exact formula for efficiency can be found here : <S> $$ \eta_p = \frac{2}{1 <S> + \frac{v_e}{v}} <S> $$ <S> As a result, the rocket engine can produce significantly more thrust if the speed is really high. <A> The first, and most significant reason, is because more fuel is pumped in and burned. <S> Why does a car battery have more stored power than a AA battery? <S> Because, it is designed to be bigger, because that it necessary for the design requirements. <S> But, this is not always the case. <S> The mercury-redstone rocket, that carried Alan Shepard had 78,000 lbs of thrust, while the Boeing 777 can have up to 115,000 lbs of thrust per engine! <A> The answer is simpler than others mention here. <S> This translates to more thrust at the greater temperatures. <S> Turbine blades in turbojets would melt at such high temperatures. <S> Rockets cool the outer lining of the rocket combustion chamber. <S> This is done by using liquid hydrogen that is extremely cold in pipes encasing the hot combustion chamber. <S> The higher temperature in rockets gives more thrust. <A> A couple of reasons. <S> Atmospheric air is a relatively lousy oxidiser. <S> Firstly it's only 20% oxygen, secondly it's a gas <S> so you need to move huge volumes of it to the combustion chamber. <S> Thirdly the available pressure and volume varies with the flight regime. <S> Jet engines have a turbine downstream of the combustion chamber. <S> This limits the chamber temperatures that can be used (granted you can get around that by using an afterburner). <S> Orbital launch rockets use liquid oxygen fed by separately powered turbo pumps, so they don't have these issues. <S> Of course the trade-off is that rockets burn through a lot of fuel and oxidiser, so they can only sustain high thrust for a relatively short time. <S> For getting into orbit that is what you need, for flying a plane an engine with worse thrust to weight but lower thrust-specific fuel consumption is a better choice. <A> The thrust generated by a rocket can be related mathematically to the quantity and specific energy of the propellant or propellants and the burn time. <S> Unlike the thrust of a turbojet engine it is not limited by the mass of the air than can be compressed and mixed with fuel in a given time or by the concentration of oxygen in the atmosphere.
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It is simply that the rocket operates at much higher temperatures than gas turbines do.
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What is the aerodynamic effect of a panorama (skydeck) near the tail section of a commercial airline? A company called Windspeed Technologies posted the following concept video of a panorama seating option aboard a commercial plane. From the limited understanding I have of the phenomena called flow separation , such a structure on the fuselage may induce separation. The sphere example here is just an approximate representation for the semi-ellipsoid. The reason I am asking this question, is because the ellipsoid is relatively near the tail section of the plane. It does not seem like a good idea to have a turbulence inducing structure that close to the tail. How will this addition to the plane fuselage effect the air flow ? Worst case, can it cause navigation problems due to turbulence near the tail section ? <Q> You're correct that the structure may induce separation under some conditions. <S> However, the effects are unlikely to be significant given the (publicly) available data on the concept. <S> From the available images, the deck is quite small, with a seating capacity of only two. <S> Image from gizmag.com <S> Also, it is located at some distance in front of the vertical fin and appears shaped to reduce drag. <S> Image from technology.org <S> The company says that it has over come many design hurdles including ... <S> structural modification, structural integrity of the canopy to withstand a bird strike and flight loads, condensation, noise levels, UV protection, aerodynamic drag, potential disruption to the vertical tail's performance, safety, ingress and egress requirements per the FAA requirements. <S> Though this should be taken with a grain of salt (it from the company after all), there is nothing insurmountable in the engineering sense. <S> For example, the canopies of fighter jets are of similar size in smaller aircraft and they are operated without problems. <S> AWACS aircraft routinely carry huge antenna on top of their fuselages; they have no problem flying, albeit with reduced performance. <S> For example, the following image shows the E-767, <S> the AWACS version of Boeing 767 operated by the JASDF. <S> " <S> E-767 <S> Japan AWACS 112010 " by Jerry Gunner - AWACS Boeing E-767 of Hiko Keikai KanseitaUploaded by Altair78 . <S> Licensed under CC BY 2.0 via Commons . <S> However, it is another matter if this is going to enter into service. <S> My take would be that this is not going to happen in current time for a number of reasons including: <S> The cost quoted is pretty high and downtime, too long. <S> cutting up pressurized fuselage is not a good idea. <S> The concept is going to take up seats and increase weight for questionable benefits. <S> What are you going to see up there? <S> the same clouds that you are going to see from normal windows anyway. <A> Any kind of change to the aerodynamic envelope does have an effect on airflow over that section. <S> This would have been analyzed by engineering using competent CFD modelling and wind tunnel testing. <S> Second, the blister shape is mounted on the aft dorsal section of the fuselage, where we would already predict the boundary layer airflow to be turbulent, so flow separation is a minimal issue here. <S> Third, if the shape is sufficiently placed upstream of the control surfaces and the cross sectional area of the affected surface is limited (say, 5-10% of the total surface), the impact on flight control should be minimal and more than acceptable. <A> So, the "cupola" on top of the airplane is more of a teardrop shape than spheroid or ellipsoid. <S> Many of the control surfaces on aircraft use this shape, so the induced/pressure drag caused by it would not be much and since it is smaller than those surfaces, it would have less of that drag. <S> The addition of that surface adds more surfaces area, which creates more, though somewhat negligent, parasite drag. <S> Overall, the airworthiness of the airplane would not be affected much, although a Supplemental Type Certificate (STC) would be needed to add the structure on.
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The end result here is that the effect is probably minimal for several reasons: First, competent shaping of the protrusion should result in minimal disturbance to the airflow in that region.
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What is the rationale behind very short distance flights? I was impressed to read here that some passenger airline routes are even below 60 km in length. Even assuming that the passengers are already in the airport past the security check, probably a good bus could depart from the same gate and arrive to the destination gate in a very comparable time, as the plane still needs to taxi before and after the flight. Why these short haul flights are reasonable? <Q> Because air travel is the best option in those places. <S> The shortest commercial route in the world is between Westray and Papa Westray in the Orkney Islands, a distance of 1.7 miles. <S> If you see the list of short routes , almost all of them are between islands. <S> That instantly rules out buses and the like unless a bridge is built, which in most cases is not commercially viable. <S> One can use a boat or ferry, but in most cases, the sea may not be deep enough or calm enough. <A> Most very short distance flights are flown between Islands. <S> If you have a look at the list of such flight you can see they are places which are not or highly unlikely to be connected by a bridge which may be uneconomical. <S> Also the flights that are used on these routes are not the average airliners. <S> They are aircrafts like De Havilland Twin Otter and Cessna Caravan propeller planes which are very efficient at relatively slow speeds and low altitudes. <S> The ATR42 & ATR72 are examples of large propeller planes in service. <S> They are meant for short trips with the 72 having a max range of 1500km. <S> They are also able to land in very short distances. <S> Ideal for these island destinations <A> Fjords are also a reason these short routes exist, e.g. the trip from KKN to VDS takes less than 10 minutes, vs. driving 165 km (2h 16min according to Google: https://goo.gl/ev5dya ) <A> One point not yet mentioned is that most of these short flights are not just between islands, but in archipelagoes. <S> So an aircraft may be dearer to run than a ferry, but the aircraft can do six or seven journeys a day (e.g. Westray to Papa Westray and back, Westray to Mainland, Mainland to Hoy...) and save the costs of three or four ferries. <A> A few years ago it was possible to fly between Johnstown PA (JST) and Altoona PA (AOO); which are ~30 miles/60 minutes apart by road. <S> It wasn't because the airline expected significant amount of traffic between the two towns. <S> The main route was between Johnstown and Washington-Dulles Airport (IAD) which was flown <S> 3(?) times a day; one of those flights stopped in Altoona with the primary intent of offering a connection from it to DC. <S> This stop was cancelled in 2014, and only the direct flight is still offered. <S> Both airports are <S> very small rural locations and commercial traffic is partially funded with Federal Subsidies , so simple economics aren't the only consideration in the route planning.
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One other rational for unusually short overland flights is that the short hop is a layover to connect two small airports to a larger one.
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Why don't planes use pulsejets? According to my research, a pulsejet's thrust grows as the airspeed increases. Most pulsejets require no moving parts which makes it easier to manufacture them. They are also very lightweight which can have some great effects on aircraft. They are very slow at zero airspeed but very fast at high airspeeds. Therefore you could simply have a normal jet engine to power the take off and then switch after take off to the pulsejets. Here is an example where I've labelled a DC-10 of what a pulsejet with jet engine plane could look like: The plane would taxi onto the runway using the jet engine as power, it'd then line up on the runway. It'd then power its jet engine and take off. Shortly after take off it would switch to the pulse engines and optionally turn the jet engine off. So why don't planes use pulsejets? Surely they would allow planes to go faster and in turn allow them to reach destinations quicker. Also the pulsejets are easier and cheaper to produce than jet engines and there lighter than jet engines. <Q> 2 reasons really: Airplanes need most of their thrust right when their airspeed is low. <S> (to get more airspeed at takeoff and go-around). <S> The maximum airspeed in cruise is not dictated by how much thrust the engines can throw out. <S> Instead it's dictated by the aerodynamic forces on the airframe. <S> They cruise right below the speed of sound where the rules of aerodynamics change drastically. <S> Going too fast would rip an airplane apart. <A> In your proposed design an engine failure at low speed would result in essentially no thrust. <S> So, additionally you would need to carry a second gas turbine engine for redundancy. <S> Then, during cruise you would be carrying around these two extra engines that are not being used, so they are just dead weight. <S> Overall, airliner engine selection is driven largely by fuel efficiency. <S> Wikipedia reports that pulse jets have poor specific fuel consumption. <A> There are multiple reasons for pulsejets not being used in aircraft (or manned aircraft generally). <S> They are quite loud. <S> In fact most of the pulsejet aircraft are (in)famous for their noise. <S> One of the reasons for the US Army to reject the pulsejet powered XH-26 was the unacceptable noise. <S> " <S> XH-26 <S> Jet Jeep in flight " by <S> San Diego Air & Space Museum Archives - http://www.flickr.com/photos/sdasmarchives/4561399305/in/photostream/ . <S> Licensed under Public Domain via Commons . <S> The intermittent (combustion) operation means that vibration is a serious problem. <S> For aircraft engines this causes serious problem; especially for commercial airlines, such vibration levels would be unacceptable. <S> Though pulsejets can be operated in low (and even zero) airspeeds, it uses the dynamic pressure of air for compression. <S> Hence the engine will be producing little thrust in the most critical phases of operation (takeoff and climb). <S> Pulsejets' combustion chamber operates at high temperature and requires heat resistant materials. <S> Air cooling can improve this, but will complicate the engine. <S> There are other things here- having a dead engine (assuming that the turbofan is turned off at some point) simply increases drag and weight penalty.
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Also, pulse jets tend to be very loud, which can be a noise problem.
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Before a flight, what are the most important things to check in an aircraft (walkaround)? During the pre flight inspection, usually the copilot checks many parts of the aircraft. Which are the parts and Why do they check them? <Q> Many things are checked on a walkaround. <S> The pilot-in-command should do the walkaround, not the co-pilot. <S> no leaks ; hydraulic fluid, oil, fuel, and other critical liquids should not be leaking out of the aircraft chocks, control locks and covers removed ; all chocks, protective coverings and locks should be removed before flight and stowed correct tire inflation ; wear on the tires should not be excessive and the tires should be inflated properly fasteners present and correct ; all bolts, shims, nuts and other fasteners should be present, undamaged, and correctly installed hatches and fairings secure ; removable inspection plates and any other small doors, fairings and cowlings should be in place and secure. <S> lights ok ; the lights on the aircraft should operate correctly and their lenses should have no cracks or other defects <S> blades ok ; the propeller or turbine blades (as the case may be) should be perfect with no cracks or chips <S> Overlooking any of these sorts of items can cause (and has caused) serious accidents or incidents in flight or during takeoff and landing. <A> The following is an (incomplete) list of checks carried out: Engine - for any damage to blade (due to birdstrike etc.) <S> Tires - <S> Wings- <S> Leading and trailing edges and tips for any damage <S> Any oil leaks <S> APU Rear fuselage- <S> tail skid area Engine and <S> fuselage- <S> Any open cowling, exterior damage etc. <S> Probes- <S> Any damage, ice etc. <S> Any other suspected damage. <S> In case of helicopters, condition of rotors for any damage. <S> A more detailed list can be seen elsewhere for B737 and A320 . <A> The other answer gives what is checked, but doesn't really touch on the "why". <S> Here are a few examples: Birgenair 301 - Crashed shortly after take-off because it is believed a pitot tube was blocked by a wasps nest. <S> Aeroperu 603 <S> - Crashed shortly after take-off because some tape was covering the static ports left there because of maintenance work. <S> Gulfstream <S> IV - Crashed during take-off because the gust locks were not deactivated (Gulfstream had some role to play in this because the gust lock system is supposed to limit throttle movement but was not operating properly). <S> Twin Otter crashed just after take-off because the control lock was still in place. <S> Medical Flight crashed after take-off when it was refueled with JET-A instead of 100LL. <S> As a pilot, there is little you can do in the air when something goes really wrong, but there is a lot you can do on the ground to make sure that the aircraft is worthy to fly. <S> Preflight inspection is one step to a successful flight and preflight <S> doesn't just happen on the tarmac walking around the plane, there are also safety checks that happen inside the cockpit (like verifying the controls are free) and even more before you even see the plane (checking weather, routes, destination airports, NOTAMs, etc).
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The main classes of items are as follows: structural integrity ; the aircraft must be sound and undamaged and ready to fly sensors ; sensors such as antennas and gauges should be undamaged and not have anything blocking them or adhering to them clean flight surfaces ; the control surfaces and flight surfaces must be smooth and clean; for example, the wings must not have ice on them For any damage Oil level indicator
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Why are almost all STOL aircraft high-wing? Isn't ground effect a big factor in STOL operations? Don't low wings produce greater ground effect than high wings? Or is it a practical concern, that most real-world STOL operations are in unimproved or slightly-improved locations, and high wings are more likely to clear "runway" obstacles? <Q> You're correct that the low wings produce more ground effect compared to their high winged counterparts. <S> However, during takeoff and landing, it can result in undesirable handling qualities- <S> the aircraft can 'float' the runway; on contrary, the high wing design is more stable. <S> There are other reasons for STOL aircrafts to have high wing designs, most of which has to do with the location of their operation, as you noted: Most of them are operated from austere airfields. <S> The high wing location gives some protection from the debris (and obstacles). <S> For the same reason, engines mounted on the high wings have better protection compared to the low wing mounted ones from FOD ingestion. <S> Most STOL aircraft use large TE flaps. <S> In case a low wing is adopted (and also if propeller is used, like Twin Otter, for example), the required ground clearance will require long and consequently heavy landing gear. <S> This can be avoided in case of high wing design. <S> The visibility is better compared to low and mid wings. <S> Historically, STOL aircraft have been high wing. <S> Also, some of the STOL aircraft are (military) cargo aircraft- <S> the high wing means there is no wing spar across the cargo compartment; plus, the low fuselage means easier loading/unloading of cargo. <A> I suspect part of it is due to historical design: High-wing STOL worked in the past so why change it now? <S> That said, there are numerous reasons why high-wings are good for STOL: <S> Better visibility, no wings blocking the view below. <S> Helps the pilot see/avoid obstacles on the ground. <S> As you say, high wings also improve clearance over rough ground. <S> This is particularly important on grass strips. <S> The aircraft is more aerodynamically stable. <S> This can be of assistance when operating in difficult conditions and can, in some circumstances, mean that the aircraft is more resistant to crosswinds than it would be for a low-wing design. <S> You mention the ground effect: This is not necessarily a good thing. <S> -edit <S> -Oh, and one other thing (that's more of an opinion, though): High-wing aircraft are, in my experience, easier from a practical perspective. <S> STOL aircraft often operate in difficult environments and often carry cargo. <S> With high wings it's easier to get stuff into/out of the cabin. <A> High wing airplanes have their center of lift above the lateral center of rotation. <S> This means the majority of the mass of the aircraft is below the lifting surface. <S> This adds to longitudinal as well as lateral stability--especially at low speeds. <S> Sort of a pendulum effect. <S> Ground effect happens at less than one wingspan. <S> In small aircraft that's 25 to 40 feet. <S> This would also be reduced at the higher angle of climb that STOL aircraft exhibit. <S> The only way you could improve the stability of a low winged aircraft in that regard, one would have to drastically increase the wing's dihedral. <S> This would raise the stall speed slightly, reducing its lifting capacity. <S> Even though this effect would be very slight, the object of a STOL is to perform short takeoffs and landings. <A> I believe that the high wing with extended slotted flaps divides MORE prop blast UNDER the wing creating "blown flap" downwash & a slightly less turbulated flow over the top of the wing (from prop axis being below the wing). <S> I think this would keep a laminar flow on MORE of the inboard top TE section of the wing.. benefiting in MORE IMMEDIATE CONTROL of lift with power rather than lag of airspeed transition/top-blown. <S> I believe that the low wing with prop blast above the wing also creates plenty of lift effect on its own, but the underside of the flaps will receive less lift from lesser percentage of prop blast. <S> In the end the high wing is out of the way&offers unique handling & control benefits, while the low wing is less capable of "dumping" lift immediately when throttle is cut in ground effect. <S> Low wings may be beneficial with their intrinsic "float" deeper into full stall on SOFT fields where rollout distance is not a concern when landing, & possibly would be sooner to break ground on takeoff rollout, reducing ground drag sooner. <S> It really matters in the end what the primary purpose of the aircraft is to be.. a "burrow" that will get you in&out of anywhere, a Rolls Royce "highway traveler" or the addition of a STOL kit to an aircraft to ENHANCE (either for effect or safety. <S> or both) <S> its performance. <A> Looking @ some nose propped planes, the high wing ones seem to direct 2/3 or more prop blast into the high pressure area under the wing, forcing even higher air volume & density under the wing when in ground effect, giving more control over lift. <S> Low wing nose propped planes seem to direct 2/3 of prop blast OVER the wing, & the 1/3 that would pass under MAY <S> (?) be "deflected" off the ground laterally some & "split" over the wing, reducing the "blown" flap effect when at lowest points of ground effect prior to touchdown. <S> All said, high wings with flaps make for a good "solid-short arrival" & low wings with flaps make for some floaty- squeaky landings on that denser "air cushion"! <A> High wings allow for BIG balloon tundra tires to be supported by conventional gear (taildragger) readily with minimum modification, tricycle MAIN gear may allow the same, but NOSE gear tire size may be limited by origional equipment or available modifications
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High-wing designs are not as susceptible to the ground effect and therefore may have better landing performance (less float).
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Why do we lean the mixture when the air become less dense? In a carbureted engine at higher altitudes, less dense air means there is less air entering the engine. Wouldn't we want the mixture to be full rich to allow the maximum air into the engine? I understand that the engine will become rough if we don't lean the engine. I'm asking what is going on? It seems like a decrease in air means we would need to open the mixture not close it. <Q> The decrease in air means less oxygen. <S> If the fuel is burnt at "rich" there would not be enough oxygen in the air to burn some of the fuel, thus reducing efficiency, increasing the risk of carbon monoxide, and adding grime to the exhaust system. <S> That is why "lean" is used for high altitudes, to burn efficiently and safely. <A> Internal combustion gasoline engines need to have a constant air/fuel ratio of 14.7:1 for efficient combustion. <S> The air/fuel mixture by volume remains constant as we climb but <S> the air/fuel mixture by weight does not. <S> The carburetor only knows the volume of air passing through it, and because the weight of the air becomes less as we climb, the mixture becomes too rich at altitude. <S> THAT is why we have to lean the mixture as we climb <S> "Leaning" the mixture mixes less fuel with the air in order to keep the air/fuel ratio at a constant 14.7:1 ratio. <S> Even with a leaned mixture, as the air becomes less dense, less power is produced because less air and fuel enters the engine. <S> Forcing additional air into the engine with a mechanical driven compressor (supercharger), or <S> exhaust driven compressor(turbocharger), can restore normal sea level power to the engine. <S> At sea level, forcing additional air into the engine can also boost performance to more than is available in a "normally aspirated" engine. <A> Not only is a rich fuel mixture inefficient, if it is too rich there can be zero combustion. <S> A long time ago in auto shop, the shop teacher demonstrated the effect of too much gas and not enough oxygen. <S> He took a old coffee can and sprayed some gas in it, then covered it with the plastic lid, that had a small hole in it. <S> Placed a match at the hole and the resulting small fire was about the size of a small candle flame. <S> After some time (about a minute), the fire had burned enough fuel, the remaining fuel-air mixture was at the correct ratio, and they burned with a rapid little whoosh. <A> Airplanes with a Mixture control have internal combustion engines (like automobiles and lawnmowers, but not like jets). <S> An internal combustion engine runs on fuel (avgas, petrol, butane, alcohol, <S> whatever hydrocarbon you pick...) <S> mixed with air. <S> The ratio that the mixture of fuel and air is set to is important for several reasons: cost of fuel, engine cooling, avoiding carbon buildup in the engine, how smooth the engine runs, how much power the engine produces, etc. <S> The ratio is based on the number of molecules of fuel and the number of molecules of oxygen. <S> Air is approximately 20% oxygen no matter if at sea level or 30,000 feet. <S> But at sea level the air is compressed more than at 30,000 feet. <S> As the airplane, or you, go up in altitude the air gets "thinner", or less dense. <S> Less dense means that the air is not as compressed. <S> For some volume of air, 1 cubic foot for example, higher pressure air will have more air molecules than lower pressure air. <S> Since air is 20% oxygen, fewer air molecules also means fewer oxygen molecules. <S> The engine performs best when the air/fuel mixture ratio stays "in balance", or as close to ideal as possible. <S> As the engine is running is pulls air into the engine, but the amount of air is based on the volume of air, not the number of molecules of air. <S> As the pressure decreases, so do the number of molecules. <S> As the aircraft descends into "thicker" air, the number of oxygen molecules increase again, so the mixture must again be adjusted by increasing the number of fuel molecules to keep the air molecules and fuel molecules at the correct ratio.
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As the aircraft climbs into thinner and thinner air the mixture must be "leaned out", where the volume of fuel and the fuel molecules is reduced, to compensate for the fewer number of oxygen molecules being pulled into the engine.
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Why does rudder cause roll? In the few rudder incidents with the B737, rudder-freeze caused the airplane to roll. From what I know, the rudder causes yaw while the aileron causes roll. Why in the case of these accidents/incidents would the rudder cause a roll? <Q> There are many higher-order effects. <S> For example, yaw causes a slight increase in airspeed over the outer wing of the turn and a decrease in airspeed over the inner wing. <S> As a result, the outer wing will generate more lift than the other, introducing a rolling motion. <S> Yaw also causes side-slip which triggers several effects. <S> Further contributing to this roll is the outer wing having a higher angle of attack due to the dihedral effect ( visual explanation ). <S> Similar effects apply to other control surfaces. <S> It's not true that rudder only causes yaw and ailerons only cause roll. <S> Those are simplifications, even though aircraft are usually designed for these simplifications to hold fairly well. <S> There is also a direct effect. <S> The image below didn't show the center of mass; I drew in a guess as a yellow circle. <S> It's clearly below the rudder, which is true for most aircraft. <S> This means applying rudder introduces a rolling torque, roughly equal to the sideways component of the force on the control surface, multiplied by the distance between rudder and the longitudinal axis. <S> The magnitude of this product is visualised as the area of the red rectangle. <A> After stopping by at our physics friends, it's probably because of the swept wings (causing a lift differential) of the B737: [...] <S> if you introduce a yaw to the aircraft, one wing will extend out more directly into the wind-stream, while the other wing will be even more swept. <S> This effectively makes one wing longer, and the other wing shorter. <S> [...] The longer wing will generate more lift, and the shorter one will generate less lift. <S> And since there is unequal lift around the roll axis, the airplane will roll, and continue to roll. <S> The whole answer: <S> Physics: What causes an aircraft to roll when rudder is applied Note : Regarding the comments, this effect even occurs without swept wings. <S> Swept wings only amplify the effect. <A> The reasons can be split in two categories: Direct and indirect. <S> Direct reasons are rolling moments which are created directly due to the rudder deflection and the side force on the vertical tail: <S> Offset position of the vertical tail: Since the rudder is above the longitudinal axis of inertia, a side force will also cause a rolling moment. <S> This is the main reason for the anhedral of the Lockheed F-104 . <S> Once the yawing motion starts, the forward-moving wing experiences a slight increase in dynamic pressure, so lift is increased on the forward moving wing and vice versa. <S> This effect is inverse to flight speed and small in general. <S> Indirect reasons are caused by the resulting sideslip angle once the aircraft starts to yaw: <S> Dihedral: <S> Once the rudder-caused yaw produces a sideslip angle, the relative difference in angle of attack between both wings creates a rolling moment. <S> This is proportional to the dihedral angle in flight , so you need to add wing bending to a static view of the aircraft to get an idea of the effective dihedral angle. <S> Wing position: <S> On a high wing, the changed flow around the fuselage in sideslip will create a difference in angle of attack at the root of the wing. <S> This effect needs to be considered when selecting the proper dihedral angle; therefore high-wing aircraft have less dihedral than low-wing aircraft. <S> Wing sweep: <S> The reduced sweep angle of the windward wing will increase its lift curve slope, and the reverse happens on the opposite wing. <S> This creates a strong rolling moment which is proportional to the sweep angle. <S> Once the sideslip angle increases, the rudder-induced side force will decrease until the aircraft reaches the trim point where the sideslip angle fully cancels the rudder deflection. <S> But the aircraft is still yawing, so it will exceed the trim position and now the side force will act in the opposite direction. <S> Proportionally to the side force, the tail-induced rolling moment will also change due to the buildup in sideslip. <A> When an aircraft yaws, one wing travels faster than the other creating more lift on that side. <S> On a swept wing aircraft the lifting effect is even more pronounced. <S> The extra lift on one side will cause it to roll.
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Wings that are swept backwards, as on the B737, contribute to the roll towards the direction of the turn, because the outer wing gets effectively longer ( visual explanation ) and produces more lift.
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Why are some airplane wings not painted? Why is it that some wings are not painted on commercial jets? Couldn't they paint them the same color as the fuselage or would it be a waste of money? <Q> Fuselage present a large vertical surface with greater length than height. <S> Wings are a large horizontal surface that is shorter in the direction of travel. <S> So... <S> The fuselage paint job is clearly visible on the ground, painting on the wings only if you are above or below the plane. <S> This is probably the main reason. <S> Simple geometry. <S> It would be waste of money. <S> Sun will heat a large horizontal surface more than a large vertical surface, so making the wings white is more useful than making the fuselage white. <S> While I am not sure that wings would be structurally weaker if heated, the heat would cause thermal expansion, which would indirectly result in increased drag by making maintaining optimal shape more difficult. <S> Paint has significant effect on drag, more specifically it affects when the boundary layer transitions from laminar to turbulent. <S> In the very long fuselage the difference is probably insignificant and you can paint them as you wish, but for wings the paint should be as smooth as you can make it. <S> While I doubt white paint is smoother than paint of any other color, keeping it simple is probably a good idea. <A> A number of aircraft manufacturers do paint the wings; only that the color is more neutral (like white or gray) rather than the flashy aircraft liveries as found in the fuselage and vertical tail. <S> According to Boeing, the wings are indeed painted : Wing skins are made of bare aluminum and are protected by an impact-resistant paint system. <S> Modern wings are composite and are protected by paint anyway: <S> It appears that the wings of Airbus aircraft are also painted : <S> ... operate within the Airbus UK wing production facility, painting all narrow-body wing sets. <S> As for painting in airline livery, it would add another coat of paint, adding weight (For example, paint in A380 weighs half a ton already). <S> Not a lot of people is going to see the wing paint anyway. <A> American Airlines didn't paint many of their older aircraft, leaving them mostly bare metal, to save weight and thus fuel. <S> However, their newer aircraft are painted because it's required to protect composites. <S> Regarding colors of paint, most planes are mostly white because it absorbs the least heat <S> , doesn't fade and makes leaking fluids or corrosion more obvious. <S> Any other colors used are typically the minimum required for branding. <A> In some military aircraft, like the P-51 Mustang, the wings were often not painted. <S> This is because the rough camouflage paint made the P-51 Mustang go about 8 miles slower. <S> I don't know if this is the same reason for commercial planes, but it was for the P-51 Mustang and other military planes.
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Many commercial planes actually do have paint on the wings, but the paint is white, or light grey. Protective paint is used in certain areas to prevent corrosion, and it is used on all composites to prevent erosion and moisture ingress.
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Why do most commercial airplanes use hydraulics instead of electric/servo motors? I'm sure it's possible to use servo motors to get precise control of the ailerons, elevators or the rudder. But still, hydraulics are widely used instead. Hydraulics do have a disadvantage that a damage to the hydraulic pipes can cause loss of control. Even with redundancy, there are cases where all three hydraulic lines get damaged at the same time and there's complete loss of control (can't remember the example). I think in some smaller aircrafts servo motors are used. But why not in the larger ones. Is it because of the torque required? What are the issues with using electric motors?If used what are the safety concerns?In terms of safety, how different are they from hydraulics? <Q> I'm sure it's possible to use servo motors to get precise control of the ailerons, elevators or the rudder. <S> No, it isn't. <S> Primary flight control actuators require both rather high forces and quick response time. <S> Electric motors can provide either, but both at the same time is a problem. <S> Hydraulics is still better for that combination. <S> Note that other actuators that don't require the fast response time (like flaps, gear or horizontal stabilizer foreplane (elevator trim)) are electric in some aircraft. <A> As mentioned already, hydraulic systems are fast and powerful but you need to also consider how extremely efficient and simple they are. <S> Reducing complexity reduces maintenance costs which is a large factor. <S> Flaps, trim devices, and landing gear doors are the only good places to use motors. <S> I believe the specific example you're looking for was the Sioux City DC 10 accident in the 80's ( https://en.wikipedia.org/wiki/United_Airlines_Flight_232 ). <S> The DC10 had an achilles heel in that all of the hydraulic lines ran parallel to each other in one section of the tail. <S> When the tail engine suffered a catastrophic failure a fan blade struck through all 3 (?) <S> hydraulic lines which led to a complete hydraulic system loss. <S> Airplanes since then have been designed with the hydraulic lines running in separate places and further apart (i.e. different sides of the rudder) to prevent total flight control system failure. <A> Weight-to-power ratio of the actuators, but things are changing rapidly. <S> The main advantage of hydraulic vs. electrical actuation of flight controls is the easy way of distributing power of hydraulics. <S> One large pump can be mounted onto a motor or engine, and generate power for multiple small, light hydraulic actuators. <S> Hydraulics do have a disadvantage that a damage to the hydraulic pipes can cause loss of control. <S> True - however, this is more of a problem associated with the central/distributed architecture. <S> In existing aeroplanes, electrical is also generated by generators connected to the engine, then distributed via 400Hz power lines. <S> What are the issues with using electric motors? <S> If used what are the safety concerns? <S> In terms of safety, how different are they from hydraulics? <S> Electric actuators are still heavier than hydraulic ones: they require magnetic fields and metal in order to convert electrical into mechanical power, while the hydraulic actuator only requires a surface are for the oil to push onto. <S> But the power-to-weight ratios of electrical actuators are rapidly increasing. <S> The safety concerns: there are fewer for electrical actuation, since it is fail passive. <S> A hydraulic actuator can fail hard-over if the servo valve gets stuck, driving the actuator to one of its extremes. <S> Note that simulator motion used to be done with hydraulic actuators. <S> The hydraulic actuators would have an audible hiss, and maintenance requirements for preventing oil leaks. <S> The hydraulic fluid in these systems was petroleum based, that for aircraft is synthetic which is not flammable but very corrosive requiring specific anti-measures in aircraft. <S> Every engineer and technician is know who has worked with both hydraulic and electrical actuation <S> has been jubilant once <S> the transition hydraulic = <S> > <S> electric occurred, way easier to handle, tune and maintain. <A> Planes use hydraulics because of the immense pressures on the control surfaces during flight. <S> Hydraulic systems can deal with higher loads than motors of similar size. <S> An electric motor can get "stuck" when it encounters a load that is greater than it can move, possibly causing a crash if it happened in an airplane. <A> Electromechanical (EM) actuators can indeed replace conventional hydraulic actuators. <S> There is also a intermediate, the electrohydraulic actutator (EHA) which consists of a local electric pump and piston actuator. <S> Control is accomplished by servoing the motor rather than a hydraulic servovalve. <S> EHAs used as part of all primary surfaces on the Airbus A380 and A350. <S> The Boeing 787 uses EM actuators for stabilizer trim and midboard spoilers. <S> In an Airbus paper on the electrohydraulic architecture of the A380, they point out that their main concerns with electromechanical actuators are with the mechanical transmission between the motor and the surface. <S> In particular, they note that EM actuators require gear drives which are difficult to assess for the risk of jamming and failure. <S> Finally, they say that with EHAs, they can be made to operate as a damper for standby and failure mode operations, which makes it easier to integrate with existing hydraulic systems. <A> Electro-Mechanical Actuators are capable of performing as primary flight control actuation. <S> BLDC power density and modern controller power electronics may be well suited for the role, but hydraulic actuation has a significant head start in heritage. <S> I'm aware of an experiment a couple decades back that replaced hydraulic actuators on half of an F-18 to evaluate just this question: https://www.nasa.gov/centers/dryden/pdf/88699main_H-2425.pdf <S> That said, airplane builders are typically pretty conservative...
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As aircraft move toward "More Electric" architectures, there may be a greater drive toward EMAs throughout to minimize the required plumbing, maintenance, and system weight of hydraulics or EHAs. They also are concerned that when the gear train wears out, it will have slack, which may lead to limit cycle oscillations.
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Do I need to register my drone? Recently the FAA released some new regulations that require drone operators, including hobbyist, to register drones with the FAA. As I am a novice in both aviation and legalese, can someone please break down the regulations and give me a guideline in layman's terms for whether or not I need to register a drone? <Q> If: Your unmanned aircraft weighs between 250g and 25kg (including fuel and cargo), <S> You are not flying under the Special Rule for Model Aircraft , also known as section 336 <S> You intend to operate it outdoors, and You are operating it in the United States, <S> If your drone is heavier than 25kg, you need to go through the regular aircraft registration process . <S> If your drone is ligher than 250g, or you are only operating it indoors, you do not need to register it. <S> Additionally, if you are operating the drone for commercial purposes, you must have a remote pilot airman certificate . <S> (Note: if you are younger than 13 years old, someone who is 13 or older needs to register your drone for you.) <A> Well, everything in really basic terms can be found at the FAA Registration Site . <S> Everything is there on that page. <S> Owners must register their UAS online if it meets the following guidelines: <S> Weighs more than 0.55 lbs. <S> (250 g) and less than 55 lbs. <S> (25 kg). <S> Unmanned Aircraft weighing more than 55 lbs. <S> cannot use this registration process and must register using the Aircraft Registry process . <A> THE RULES HAVE CHANGED. <S> Part 101 recreational [aka Model] operators, flying sUAS, are no longer required to register most drones under 55 lbs. <S> This is because the FAA is not enforcing recreational sUAS registrations. <S> The FAA is working on a new rule to reflect this. <S> Part 107 operators, will continue to need to register <S> their sUAS. <S> This note: <S> Note: <S> Model aircraft operators that comply with all of these operational requirements during flight do not have to register their UAS with the FAA. <S> Is on this FAA website page: https://www.faa.gov/uas/getting_started/fly_for_fun/ <S> NB: <S> Probably this question should be deleted, and re-asked, given August 2016 FAA regulation changes, and the outcome of a subsequent court case , and yes, ultimately changes to the FAA regulations as a result of that case. <A> I would highly recommend following the AMA's guidance on this matter. <S> They've been doing this for many years now with safety as their primary mission before the FAA decided to stick their heavy hand into the matter after the increasing popularity of quad-rotor models led to several regrettable high-profile incidents by new flyers. <S> As of today (1/5/2016) <S> the AMA is currently in negotiations with the FAA to achieve at the very least an exemption for AMA members, and their current advice on the matter is <S> Don't register yet as the deadline has not passed and you are not breaking the law until it does. <S> Submit comments to the FAA expressing your opinion of the new legislation. <S> Additional information will no doubt be posted on their blog as the situation evolves. <A> As long as your drone is not on the list, you are exempted, if you are really worried about your drone <S> you might want to see the list here from this website http://smalldronesreview.com/2015/12/28/list-of-exempted-drones-for-registration-not-required/ <S> But lately there are moves about abolishing the regulations on registration of drone, but if you have one especially large drones, just to be safe register <S> it follow the law or be sorry
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you need to register your drone through the FAA's online registration system .
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Why shouldn't the pilot change the aircraft's configuration while avoiding windshear during landing? According to the procedures, when going around, due to windshear, pilots shouldn't change the aircraft's configuration, such as flaps position and landing gear extension. If changing, would the aircraft lose the lift? why? <Q> As far as landing is concerned, it is better to leave the landing gear down because if something goes down and the aircraft touches the ground, it is better to do so with the landing gear rather than the aircraft fuselage. <S> Also, the retraction process may increase drag, not what is desired. <S> During landing, the retraction of flaps (which may be already at their max) can cause loss of lift (as you noted). <S> Reduced airspeed due to windshear causes loss of lift; retracting the flaps in this condition is not desirable. <S> There is also the point that during the critical moments when the pilots are trying to pilot the aircraft during wind shear, their attention should be in flying the aircraft and not in fiddling with controls. <S> From FAA Advisory Circular 00-54 <S> Pilot Windshear Guide: <S> CONFIGURATION <S> Maintain flap and gear position until terrain clearance is assured. <S> Although a small performance increase is available after landing gear retraction, initial performance degradation may occur when landing gear doors open for retraction. <S> While extending flaps during a recovery after liftoff may result in a performance benefit, it is not a recommended technique because: 1) Accidentally retracting flaps (the usual direction of movement) has a large adverse impact on performance. <S> 2) <S> If landing gear retraction had been initiated prior to recognition of the encounter, extending flaps beyond a takeoff flap setting might result in a continuous warning horn which distracts the crew. <A> During extension and retraction the gear drag is substantially higher than in the extended position. <S> This has two reasons: <S> When the gear moves, the first thing to happen is that the big bay doors open. <S> They are also the last to close after the gear has reached its new position. <S> During that time, the large cavity of the gear bay will cause additional drag, sometimes as much as half of the drag of the extended gear. <S> When the wheels are close to the fuselage, their drag contribution is higher than when they are at some distance due to higher interference drag. <S> Figure 38 from S. Hoerner's Fluid Dynamic Drag , Chapter 13 page 14. <S> Note that after landing gear extension the biggest doors close again . <S> The time it takes to retract the gear is similar to that where windshear will cause the biggest airspeed loss. <S> Consequently, cycling the gear will increase drag over that of the extended configuration, and any improvement in aerodynamic quality due to a retracted gear can only be gained after the worst is over and the aircraft will speed up and climb anyway, regardless of gear position. <S> Also, changing the configuration will be distracting in a stressful situation, and the risk of a wrong configuration change is increased. <S> It is better to let the pilot focus on flying the plane than to burden her/him with additional work. <A> As usual, Peter's answer is correct. <S> However, I wanted to address the last part of the question regarding if lift would be lost, since I didn't see a direct answer to it in the other answers: <S> Yes, the aircraft will lose lift if you retract the flaps. <S> The whole purpose of flaps is to increase lift at low airspeeds in order to allow the aircraft to takeoff and land with lower airspeeds than it would be able to use if it had no flaps. <S> However, flaps also increase drag, which is why you retract them once the airspeed is high enough to not need them. <S> During a landing, flaps will normally be set at or near their maximum extension, which allows the aircraft to fly quite a bit slower than it would otherwise be able to fly. <S> Needless to say, that's not good on final approach, especially if you're trying to go around. <S> Note that flaps increase both lift and drag at any (positive) airspeed, so retracting them will always result in less lift, but also less drag.
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If you suddenly retract the flaps while flying at final approach speed, you will lose a lot of lift and potentially even stall the aircraft.
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What was the commercial speed of Concorde? I work on time-space cartography in a historical perspective and need to establish a commercial speed of Concorde aircraft flights based on timetable data. This issue differs from the issue of the maximum speed of planes , because in a time geography perspective I want to consider speed from the point of view of the user, the traveller, i.e timetable commercial speed, and not maximum aircraft speed. I found some indicative timetables of London-New York in 3,5 hours for 5 850 km which turns into an approximate value of 1 600 km/h. Could anyone confirm these data and this figure? A related problem is that time-tables are not symmetric, because of trade winds , so that transatlantic routes take longer from Europe to USA that the contrary. I want to use the longest value since it provides a consistent value for minimum time-distance. <Q> Concorde’s fastest transatlantic crossing was on 7 February 1996 when it completed the New York to London flight in 2 hours 52 minutes and 59 seconds . <S> When it flew the average flight time (was) around 3 hours 30 minutes , but can be slightly longer if the aircraft (needed) to hold before landing at the local airports. <S> Wind is a huge factor in flying. <S> A headwind or tail wind can mean a big difference in flight time. <S> The Concorde cruised at a significantly higher altitude than most airplanes <S> ~55,000Ft . <S> which means it was subject to very different wind than its sub sonic lower flying counterparts. <S> At that altitude winds in excess of 100Kt are common place. <S> So you could see a 200Kt difference in speed depending on direction. <S> Also of note the speed was often called out using Mach's Number <S> (the Concorde flew a bit over Mach 2). <S> However since Mach's number accounts for air density, Mach 1 at 55,000Ft. <S> is 660MPH which is significantly lower than the often quoted Mach 1 <S> = 760MPH <S> (which is the speed of sound at sea level). <S> One of the best sources of info on flying the Concorde is this podcast interviewing one of the pilots . <A> Well, this is very dependent on the windspeeds for a local area which changes day by day. <S> The official "Cruise speed" for Concorde is 2140 kph. <S> Other than that, your question is way too broad because the "relative airspeed" varies by day and time of day as well as location. <A> I want to measure a commercial speed for Concorde flights. <S> The answer was given by Andy in his comments providing links to websites that recorded past timetables for Concorde: forums.flightsimlabs.com and www.airliners.net Timetable schedule must take into account time difference between cities so that a British Airways Concorde flight JFK 12h15 to LHR 21h00 with -5 hours difference will give a 3h45 of commercial flight duration. <S> Surprisingly, to me at least, trade winds did not seem to play a significant role in this measurement because timetable on the reverse route exhibit similar duration. <S> Air France flights follow the same rationale. <S> The measurement indicate a general figure of 3h45 for transatlantic Concorde flights. <S> Next step is determining the kilometre distance. <S> As I want a geographical time-distance I care only about great circle distance and do not care about the exact path followed by the flight which would tell about aircraft/pilot/airline performance. <S> I used the flightaware.com website. <S> My only issue is measuring the performance (speed) of the transport system in getting from point A to point B. <S> So I finally have my figure: 5 850 km / 3h45 = <A> When I flew on it in 2000, the Mach meter at the front of the passenger cabin varied from 1.99 to 2.01
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The Concorde cruised at 1350mph (~Mach 2.05 at 55,000Ft.) 1 560 km/h was the commercial speed of Concorde (or 969 mph in non international units).
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What makes a visual approach quicker than an ILS approach? In the question What's the preferred approach for a passenger jet? it is mentioned that pilots prefer Visual Approaches over ILS Approaches, as they are a lot quicker. Why would a visual approach be quicker than an ILS approach? <Q> Visual approaches can be conducted from any point around the airport where the runway is in sight, e.g. if you are approaching from the north of the airport, you can be vectored to a position which is closer to the airport and be cleared for a visual approach from a position where you can turn visually and reach the runway threshold. <S> ILS approaches begin at the approach gate before the final approach fix (FAF) for the localizer and glidepath indications to be correctly used and the aircraft configured for the approach. <S> The FAF is at many airport around 10 NM from the runway threshold at 3.000ft AGL, thus placing the approach gate at around 12-14 NM. <S> A pilot on a forum has summed it up like this: Visual approaches are usually shorter than instrument approaches. <S> By that, I mean that the turn to final is accomplished closer to the runway when on a visual approach. <S> When traffic is heavier, or weather is around, or it's hazy, smoggy, etc, ATC will usually route everyone out for an ILS. <S> Many times, a pilot will call runway in sight, yet be sequenced behind someone who is on the ILS. <S> So, he'll get routed out for an ILS approach, even though he'll go visual within the cockpit. <S> Airport size doesn't have a whole lot to do with it. <S> Also, even though an aircraft may be on a visual approach, that does not absolve ATC of separation resposibility. <S> (Source: www.airliners.net - Author: Tom in NO) <S> Effectively, this means that visual approaches tend to be shorter and quicker than ILS approaches with vectors to the FAF/approach gate. <A> At the risk of just repeating information from the great answers that SentryRaven and casey already gave, here's a real example. <S> Last night I flew the ILS 22 into KLEX for practice, although conditions were perfectly clear and most aircraft were using a visual approach. <S> If it had been a 'real' flight and not practice I would certainly have taken the visual as well because it would have saved almost half an hour of flight time (and fuel): <S> I was inbound from the west and ATC started vectoring me when I was still more than 10 miles from KLEX to get me onto the ILS approach. <S> They sent me northeast, east then southeast to intercept the glideslope. <S> That means that instead of just flying 10 miles directly to join the pattern, I was vectored for almost 40 miles. <S> Normally, you just don't want to use up that much time and fuel if you don't have to. <S> Unfortunately I don't have track data from the flight but it looked roughly like this; even if you aren't familiar with the chart you can probably see how using the ILS required a huge diversion. <S> The pink line is my route and the red arrow shows where the vectors started: I was cleared for the ILS while about 10nm from the runway. <S> But the winds were very high, and instead of having a ground speed of 80 or 90 knots (in a C172), I had a ground speed of 50. <S> That meant I took about 12 minutes to land, which effectively blocked the final approach course for that amount of time. <S> A faster aircraft on a visual approach was turned in behind me and had to do S-turns on final to avoid getting too close. <S> If I had been on a visual approach instead, I would have been in the traffic pattern very close to the runway and would have spent just a minute or two on final. <S> You don't have to brief the approach, set up your nav equipment (and maybe autopilot) <S> etc. <S> ; instead, you just look outside and fly visually. <A> Visual approaches are preferred because it means you can potentially avoid being vectored out to intercept the final approach fix (FAF) which needs to be done for a an ILS approach. <S> If there is a long line of aircraft being vectored for the approach this may not yield any time savings as minimum spacing with the aircraft in front of you becomes a factor. <S> At an airport that isn't busy this can be the difference between flying a tight traffic pattern and landing quickly or a long vector 5+ miles past the airport to join the approach. <S> Also, being on a visual approach clearance with the aircraft in front of you in sight relieves the controller from providing normal spacing. <S> This means you can squeeze a bit closer to the airplane you are following <S> and you just have to make sure you are keeping far enough back that the runway will be clear when you get to it. <S> This can also help if the airplane in front of you slows down unexpectedly or too early, which if you are on an non-visual approach could result in S-turns for you or a missed approach. <S> In these cases the controller often asks if you can see the aircraft so you can be given the visual clearance and manage the spacing yourself and avoid going missed.
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It's also worth noting that apart from flight time, another reason to prefer visual approaches is that a pilot (a private one, anyway) has a much lower workload.
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Do airlines have to get permission from the FAA if they want to change their livery? Do airlines have to get permission from the FAA to change their livery? It would be great if someone can throw in some examples where this has happened. <Q> Not the FAA, but the manufacturer. <S> If the parts are composite, only a small range of colors may be approved, depending on the glass transition temperature of the resin matrix. <S> For gliders, only white is allowed for most of the surface area, and similarly composite parts of airliners must be painted in a light color <S> so they don't heat up too much in sunlight. <S> Curiously, the lower surface has the most restrictions, because here the reflected light from a concrete surface and the restricted ventilation create the highest surface temperatures. <S> Next, the UV absorption capability, moisture protection characteristics and the chemical stability of the paint when in contact with aviation fuel, hydraulic fluids, de-icing fluids and other solvents is important. <S> Composite gliders must use a special topcoat which is more brittle than the composite structure, so cracks will show up. <S> Airliners may use more flexible paints, but must then undergo regular inspections of their composite parts. <S> Metal surfaces are less demanding and can be painted in any color. <S> Only the area in front of the windshield should be dark enough to reduce glare and irritating reflections. <A> However, changing of aircraft liveries comes under refinishing of decorative coatings has to be done by certified personnel as it is considered major maintenance. <S> The materials used should comply to the applicable safety regulations. <A> A short answer, but: <S> No <S> They can paint their planes pretty much however they want. <S> I imagine various agencies and their customers would have something to say about it if they did something outrageous, but they can repaint their planes without asking permission or even informing the FAA.
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In general, the aircraft owners can paint the aircraft whichever the way they want.
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What liability concerns would drive an airplane homebuilder to scrap their plane? Via this post by Ron Rapp , I found this video of a plane owner and builder dismantling a GA plane and then scrapping the airframe. The video claims this is because after consulting with aviation attorneys and other experts regarding builder's liability, the owner concluded there was only one way out. However, I'm completely in the dark about - and rather baffled by - what this liability risk would be, and how it relates to the Van's Aircraft lawsuit . What liability would a builder pilot be under in the event of a crash that they would be able to avoid if the plane were factory-produced? <Q> I understand that the aircraft owner had sought for some time to donate the aircraft. <S> I would presume that he had come to a time in life where he was, or felt he was, no longer able to fly the aircraft, and so was seeking to rid himself of what may have become a burden <S> (hangar fees, etc.). <S> To quote liberally from the builder/destroyer's daughter who created and uploaded the YouTube video (this is quoted from what she wrote in the video description): <S> It took him two years to make this decision about his plane. <S> He did actually try to donate it to a couple of aviation schools in the area and the schools politely refused the offer. <S> He also tried to donate to a local museum and was also refused. <S> He knew when he built the plane he might face this decision one day, but he hoped some of the laws would have changed by that time. <S> [...] <S> Mr. Ron Rapp, author of the article “A Tragic Pile of Twisted Metal” and noted blogger on his website The House of Rapp., highlights many reasons my Dad made this decision among others. <S> A couple months before my dad made his final decision, a local fellow pilot was named in a lawsuit because he sold the plane he built to a man that later crashed and killed himself in the plane. <S> The spouse of the buyer filed the suit and also named other companies who made parts used to build the plane. <S> Many have commented that he should have used a limited liability entity, such as a LLC or a corporation to sell the plane. <S> However, because the plane was not, at the time of manufacturing, owned in a properly capitalized limited liability entity with a legitimate business purpose and was, in fact, used purely for personal reason, courts would in almost all cases “pierce the corporate veil.” <S> Therefore, this does not offer adequate (or any) protection. <S> I don't think I can add a whole lot to that. <S> Apparently, he had decided that he was unwilling to take on the liability of letting someone else fly what he had built. <S> In the absence of a party interested in the aircraft for anything other than flight, he chose to destroy it. <A> The USA has a culture of lawsuits, often frivolous. <S> When airplanes crash, people die and the estates of those people want someone to blame. <S> In the past they've tried to blame aircraft manufacturers and the resulting lawsuits were detrimental to general aviation. <S> It got to the point that congress had to step in and shield the industry from lawsuits (see: General Aviation Revitalization Act of 1994 ). <S> However, these protections don't apply to individuals. <S> Van's aircraft may get sued and if a judgement comes down the company will probably fold and cease to exist. <S> If you as an individual get slapped with a wrongful death lawsuit and a judgement is found against you, it will ruin you financially. <S> If you are getting to be old and retired, you may never recover from it. <S> The liability the builder shoulders is the accountability if anything ever goes wrong with the airplane, in perpetuity. <S> It'll be expensive to lose and nearly as expensive to win (lawyers are not cheap). <A> My father has built a small plane and talks about this problem (incidentally it is an RV through Van's too). <S> This is a very common understanding amongst the community involved in building RV's. <S> When you sell a plane, you are incurring significant liability. <S> A point not really mentioned in the other answers is that it takes a certain type of person to build a plane. <S> Many of those people are <S> ... let's say less than interested in someone else taking their money, especially through a lawsuit resulting from pilot error, which is probably immensely more likely than build defects. <S> Many homebuilders also are pretty financially well off, so they have a big target on their back in a litigious society. <S> Anecdotally I know of at least one RV that has an interesting post-flying life. <S> It currently is hanging over an office space for a startup company as a very interesting and expensive decoration. <S> The reason it is there, and not sold, is the same reason as the above.
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If that plane crashes some day and especially if it is fatal, someone is going see it is a homebuilt experimental and sue the guy who put it together, alleging they did something wrong.
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What are the physical/aerodynamic implications of designing a prop guard for multirotors? A number of drones these days like the one shown in the picture below have fully protected multi-rotor propeller guard system . These are lightweight, aerodynamic housing that keeps these spinning knife-blades away from people's fingers, trees etc. So,what are the physical/aerodynamic implications of designing a prop guard for a multirotor drone whose specs are as follows: All Up Weight with battery: 1050g Frame weight empty (no electronics, motors, or battery): 400g Flight time with 3s 2200mah lipo: 8 minutes Propeller size : 10" Skeletal Plastic Structure Source: Safe Flight Copters <Q> Aerodynamically, one can say that those prop guards create some kind of Fenestron (Like some tail rotors in helicopters), which will reduce the tip losses of the propeller. <S> On the other hand, they will increase drag in forward flight, reducing the UAV top horizontal speed. <S> If you take a look at the Aibotix X6 you see a one piece prop guard designed aerodynamically to reduce drag in forward flight. <S> In the particular case of your image, the black web also decreases the area of air flow into the propeller, certainly reducing its efficiency. <S> Another prop guards disadvantage is the weight they add. <S> Even though they might be made of lightweight material, they have to have some strength to resist any impact. <S> To sum up, with a prop guards like those, you should loose top speed and around 2 minutes of flight time. <S> One last tip: if you want to fly your UAV close to trees, forests or power lines, be careful with the prop guards because you might end with your UAV hanging on a tree branch 10m high... (happened to me :/) <A> Also, if the ducts are not designed properly, the flow entering the propellers may be affected, reducing the performance. <S> The main disadvantage is the weight- <S> the shroud and the support structure will affect the performance adversely (also, there is some increased drag) and is usually not recommended. <S> For an UAV having endurance of mere minutes, the effects can be substantial. <S> The main advantage is safety- <S> the propellers are safe from hitting the ground and getting damaged; so if you are reasonably confident of your flying abilities <S> it is better to go without a shroud, rather than with one. <S> Another thing is that the addition of aftermarket shrouds to UAVs have to be evaluated carefully- <S> the weight may alter the flying properties appreciably (for e.g. the descent rate), so one has to be careful. <A> Remember the drag contribution of a biplane's bracing wires? <S> Now this quadcopter has not one, but two screens in the flow path of the propellers. <S> Each thread of the mesh will act like a small bracing wire and reduce propeller efficiency considerably. <S> In comparison, the shroud has relatively little impact. <S> Tip clearances are too big and shroud size is too small to improve propeller efficiency measurably, the drag in forward flight should be manageable and the worst contribution of the shrouds is probably their added mass. <S> But it all pales in comparison to those two layers of mesh!
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In general, having a shroud (a duct actually) over the propeller reduces the tip losses; however, in an UAV, this effect is pretty small (and requires tight clearances) in order to have any practical effect.
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How should Isopropyl Alcohol be used as an AvGas Fuel System Icing Inhibitor? I understand that 100% Isopropyl Alcohol (IPA) is used as a Fuel System Icing Inhibitor (FSII) additive in aviation gasoline systems—including 87 through 100LL fuel types—for cold weather operations. I know that IPA is, or can be, included as part of AvGas formulation. However, I am referring to operational use of IPA as an additive when fueling the aircraft. Pure IPA is also known as anhydrous isopropanol. What documentation is available to support such use? What is a proper treatment ratio for using IPA as an FSII (or what is the concentration limit)? <Q> FAA Advisory Circular <S> AC <S> No: <S> 23.1521-1B deals with use of IPA for Part 23 aircraft. <S> It states: ASTM D 910, Standard Specification for Aviation Gasolines, allows the use of isopropyl alcohol conforming to the requirements of ASTM D 4171, specifications for Fuel System Icing Inhibitor, as a fuel system icing inhibitor. <S> Accordingly, isopropyl alcohol conforming to ASTM D 4171 may be used in concentrations up to 1 percent by volume, to benefit safety, as an icing inhibitor in automobile gasoline. <S> However, it is left to the aircraft manufacturers (according to ASTM 910 too) to determine whether or not to use IPA as an additive. <S> For example, in a letter regarding Lycoming engines in certain of their aircraft, Cessna says , Isopropyl alcohol in amounts not to exceed 1% by volume can be added only to aviation fuel (not automotive fuel) to prevent ice <S> formation in fuel <S> lines and tanks. <S> Note that Cessna allows the addition of IPA only to aviation fuel for the applicable aircraft. <S> In UK, the MoD Defense Standard 91-90 again leaves the matter to the individual manufacturers, saying, <S> The concentration of Isopropyl Alcohol shall be recommended by the aircraft manufacturer at the time of delivery to the purchaser and typically not exceeding 1% v/v. <S> Though almost all these cap the IPA at 1%, the best way is to refer to the individual aircraft's appropriate manual as it would have the necessary details. <S> But generally, I think that manufacturers (of large aircraft, atleast) prefer not using IPA these days due to environmental concerns. <A> It seems as though there was an accident involving a PA-23-180 a while back that lead to this advisory. <S> You can see the full report here (interestingly this was published by the NTSB not the FAA). <S> Require that Piper, Beech, and other airplane manufacturers who have not already done so issue service and operating information regarding the use of fuel additives in piston-powered airplanes for cold weather operation and incorporate this information in the pilot operating handbooks of all newly manufactured airplanes. <S> (Class 11, Priority Action) (A-85-79) <S> In terms of limits it looks like it might be in the POH and should be in the AFM for the aircraft or in a service bulletin like this one issued for MD helicopters . <S> The AFM for this 172S (page 4-23) notes the use of IPA and redirects to section 8 (page 8-17) which says a 1% by volume quantity should be used. <S> It also offers some steps on how to add it to the fuel and a nice chart on volume of additive vs volume of fuel. <A> I fly a PA-30 Twin Comanche regularly,and,since the POH does not discuss use of isopropyl alcohol or Prist,have contacted Piper repeatedly to seek approval. <S> No response has come from Piper. <S> AOPA and Int’l Comanche Society are equally silent on this topic. <S> I even requested that Air Safety Foundation look into it. <S> I consider this issue of great importance, as the PA-30 fuel system lacks individual drains for main & aux tanks, putting it at high risk for ice formation in its fuel system. <S> This system, along with its suboptimal procedure of draining the fuel bowl via the selector valve was the subject of criticism by NTSB in reviewing a Piper Apache fatal accident blamed on icing and obstruction of the fuel bowl. <S> This led to a Safety Recommendation, apparently ignored by Piper. <S> Beech & Cessna both had statements of approval in POH for use of IPA or Prist for my previous A36 & C310 aircraft. <S> Why is everyone so mute on this subject?Piper ought to be held accountable as irresponsible if preventable fuel system icing causes a future accident.
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Although approved for use in Lycoming engines, do not use isopropyl alcohol in the aircraft fuel systems unless approved by the aircraft manufacturer.
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What are good resources on causes of private aircraft crashes? I'm working on getting my PPL, and I would like to read more about the specific causes of small private aircraft (single or twin prop, primarily) crashing, especially those that were caused by pilot error. Are there any good books or other resources on this matter? A decent amount of searching hasn't turned up much -- it seems like the data from private charter jets is often combined with that of the aircraft I'm interested in. <Q> AOPA ASI Accident Analysis Page AOPA Accident Case Studies AOPA Real Pilot Stories <S> I do exactly what you are doing, during training and still after, <S> but I'd like to also say that you shouldn't narrow yourself to GA crashes, a lot of what happens commercially can be applied to GA, and usually with commercial accidents there is a lot more data and analysis available to work with. <S> In that regard, I like to watch shows on Youtube like "Air Crash Investigation" , or on TV like <S> "Why Planes Crash" (some available on Youtube) AOPA also has a lot of resources to view NTSB reports on individual crashes where you can search by certain criteria like aircraft type, states, type of flight, or even some specific keywords like "Vacuum Failure". <S> Just don't limit yourself to looking at things like "Pilot Error", pilot error is a broad category of crashes that is usually used to describe the pilot doing something wrong in the air , but a lot of crashes are "pilot error" in that the pilot could have broke the accident chain much earlier in the flight. <S> Read as many as you can, regardless of the cause. <S> For example an accident where the aircraft breaks up in flight may not be attributed to pilot error, but its good to know what lead to the break up and what could have been prevented. <A> The National Transportation Safety Board investigates vehicle-related accidents in the United States and publishes "accident reports" which includes details of the accidents and the findings of the investigators. <S> Go nuts. <A> Aviation Safety Network is another good place to look.
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The AOPA's Air Safety Institute has quite a few resources that I like to review from time to time, including some great videos with commentary on exceptional cases.
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What are the criteria that govern the choice between titanium, composites, and more common materials, like aluminum? In the newest large commercial jets, composite materials seem to be all the rage. The first thing I wanted to know is why composites were chosen instead of titanium? If I'm not mistaken, titanium has even more specific tensile strength. Let's also be clear about what exactly composites are. "Composite" just means a mix of two or more materials, and in aerospace, it is predominantly autoclave-cured carbon-epoxy. Ultimately, it would be good to understand the criteria that govern any choice among titanium, composites, and aluminum. Specifically, which areas of the plane are candidates for an advanced material? and why? What factors dictate the decision? <Q> What are the criteria that govern the choice between titanium, composites, and more common materials, like aluminum? <S> Three main criteria: cost, strength-to-weight ratio, and fatigue resistance. <S> Cost. <S> Of the three, aluminium used to be the clear winner, with composites having made large advances due to improved manufacturing processes. <S> Titanium is the most expensive and is difficult to machine. <S> Strength-to-weight. <S> Buckling . <S> Titanium alloys have higher strength-to-weight than aluminium <S> (this answer , more on temperature below), but aluminium is lighter and that gives it an advantage in structures loaded with compression stresses: buckling resistance is a function of cross sectional dimension as well. <S> For the wing upper surface aluminium would be lighter than titanium, despite the lower specific strength. <S> Composites have the highest specific strength of all. <S> Temperature . <S> The graph in the linked answer also shows the influence of temperature on the specific strength of materials: aluminium is first to drop, and at higher temps titanium is the best next choice, as from the comment by @PeterKämpf. <S> Fatigue resistance. <S> Titanium alloys, like steel allows, have a fatigue endurance limit. <S> If stresses remain below this limit, the construction can endure an endless number of cycles. <S> Aluminium does not have an endurance limit, and will eventually fail even from small stress amplitude cycles: aluminium constructions require careful monitoring and maintenance for prevention of fatigue failure. <S> Composites do not have an endurance limit, but fibre orientation and material choice can improve fatigue life. <S> Image source <A> "The application of aircraft" is extremely vague. <S> Modern aircraft use all of these materials in many different places , for many different reasons. <S> Each component will have different tradeoffs that depend on many factors. <S> The following is an extremely general overview. <S> Aluminum is a popular material in aircraft because it is relatively cheap and light, and has alloys with good material properties. <S> It is fairly easy to work with but must be protected from corrosion. <S> Light weight and low cost mean that it is used in large areas like fuselage and wing skin, and for a lot of the underlying structure. <S> Titanium is useful for its ability to withstand higher temperatures, while being stronger than aluminum but also heavier. <S> However, it is much more expensive than aluminum. <S> Composites are a large family of materials, with many different types and combinations possible. <S> Composites can be strong and light, but don't withstand high temperatures as well. <S> Although composites don't corrode like some metals, some situations such as carbon fiber contacting aluminum need to be avoided. <S> Exposure to UV light or moisture can also be an issue. <S> Manufacturing composites can become very expensive depending on the materials used. <S> Since composites are typically manufactured from multiple layers sandwiched together, they lend themselves more easily to applications with large and thin sections. <S> Larger and more complex parts are more difficult to make from composites. <S> Another important factor with aircraft is electrical conductivity. <S> While metal parts will naturally conduct electric charge between each other, composites will need special treatment to ensure conductivity for protection from lightning and static charges. <S> There are also many other considerations. <S> Besides yield strength, many materials on aircraft need to have good fatigue properties to withstand cyclic loading over time. <S> Material properties at high and/or low temperatures may also be important. <S> While metals tend to bend and dissipate energy before breaking, composites tend to suddenly snap . <S> Metals are also easier to inspect and repair, while composites can be much more complicated . <S> While a metal can be categorized fairly well by its type and dimensions, composites are more complex with their multiple plies. <S> This makes definition and analysis more complicated. <A> The first question is decently answerable. <S> Composites have the nice property that they are not homogeneous at a mesoscopic scale. <S> It's almost unavoidable that small cracks form in materials under stress. <S> This happens in aluminium, titanium and composites alike. <S> This is not dangerous if there's something to stop them from growing. <S> Within aerospace composites, the local material boundaries stop crack growth. <S> Practically speaking, for a laminar composite this means that one layer may develop a crack. <S> The two adjacent layers will stay glued to both sides of the crack, and keep the panel together. <S> This isn't impossible for titanium, but it is hugely expensive. <S> You have to grow and cut a single crystal of titanium. <S> In comparison, with a carbon composite it's just a matter of orienting the fiber layers.
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Composites are also easier to engineer for some specific purposes, such as having higher tensile strengths in critical directions.
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Would a chain strip built in the airport taxiways, help airlines in saving money and time during taxi? I am referring to the mechanism used in aircraft carriers, which help in catapulting fighter aircraft. What I had in mind is a milder version of the same concept. It would massively save cost, due to it being operated by electric power, save energy and time of the pilots, less exertion. Would such a system be feasible? <Q> Airports already have several ways to move aircraft along taxiways <S> Aircraft engines (least economical but always available) Tugs (often used for pushback from terminals) Aircraft wheel-motors (some makers are at least planning for electric taxi) <S> A system of fixed chains along a complex network of intersecting taxiways would be expensive to install and maintain and might be unreliable (e.g. icing up in cold weather). <S> See also <S> Does it make sense towing airplanes to the head of airstrip by external means? <A> An airport has taxiways that cross other taxiways and runways, so any chain system would require breaks in the chains at these points. <S> Airplanes would need some sort of motive power to cross these breaks, it's impractical and slow for an airplane to spin up its engines for 20 seconds to cross a break in the chain. <A> They don't do it for roughly the same reasons that they don't install such systems in roads. <S> Expensive modifications would be required to every aircraft of a vast array of aircraft types. <S> This alone would probably mean that you'd never recover the costs over the entire expected life of the system. <S> And getting modifications approved by the relevant regulatory agencies for airworthy aircraft designs is even more of a pain than getting them approved for road-worthy car designs. <S> The systems themselves would be quite expensive for initial install, especially if they were designed to operate in all weather conditions in which airports can currently operate. <S> Being able to drive where you want is much more flexible (which is somewhat less of a concern at an airport than on roads, but still a concern.) <S> Stopping or turning suddenly to avoid a collision (like when you're cleared to taxi across a runway and suddenly realize that there's a Learjet taking off on it ) might not be possible or would at least be slower. <S> In short, there are already cheaper alternatives that don't suffer these drawbacks, such as tugs (manual or automated,) electric motors on the gear, and, of course, aircraft engines, as mentioned in RedGrittyBrick's answer . <A> One point has been missed in the other fine answers. <S> On an aircraft carrier, the nose gear of each aircraft has a pull bar installed that links with the catapult sled. <S> This pull bar is manually engaged by a deck crew member for each aircraft that is to launch. <S> In order to do this at an airport, there would need to be a ground handler stationed at each runway turn-off point to engage the pull bar to get the aircraft moving. <S> I pity the poor souls who would have to stand next to a runway at KBOS or KJFK in the wonderful weather they are expecting this weekend. <S> It's possible that this system could be automated, but that's another very expensive design element that has to be brought into play, tested, and receive CAA certification. <A> In addition to all the 'minor' drawbacks already discussed, there is one huge, basic problem with this idea. <S> What has to be moved is an airplane, weighing less than about 600 tonnes, designed to move, with a manageable rolling resistance. <S> A chain or cable system extensive enough to take its payload everywhere <S> it should go adds many tonnes of metal to move with a lot of friction, that will only grow as water and dirt enter the trench. <S> The whole thing will need enormous horsepower just to get moving even without an aircraft attached. <S> Compared to a tug, or even compared to an aircraft taxiing under its own power, this will simply need too much energy to be feasible. <S> The only place where this system can make money is in some streets in San Francisco. <A> Also, note that the modifications to fighter planes (Air Force vs Navy) are fairly significant, as the forces on the plane (and humans inside) are significant when using the arrestor (sp?) <S> cables on aircraft carriers. <S> And yes, reducing the force is possible, but reducing it so that all existing planes flying could use it may (mostly) eliminate its benefit.
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A chain system would also be very expensive to install and run, probably more expensive than the fuel it takes to taxi the airplanes.
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Has anyone considered putting a hydrofoil on a sea plane? One of the main problems with water landings is that you need a bigger engine to counter the various drags caused by the pontoons. The specific case of "run[ing] across our own wake to be able to get up on the step on glassy water" brings some interesting thoughts. [B]asically a floatplane has to break the suction of the water - kind of like pulling your boot out of mud - and if the water isn't moving at all then it has to do that all by itself. If there are some waves, or a wake, or any kind of discontinuity in the water, then that gives the aircraft the momentary break it needs to overcome that initial suction. "The step" in this context refers to the step-up shape you see partway down the float (or hull); when you're "on the step" then you're using the part of the float forward of that step to hydroplane. It is well known that water's significantly higher density makes high speeds difficult. A solution to that problem is the hydrofoil - a small underwater wing that raises some or all of a boat's hull out of water to reduce friction and increase speed. So here is my dumb question: would placing a hydrofoil under a pontoon save fuel on takeoff? And how likely would the increased drag during flight cancel that advantage on a typical flight? <Q> Yes. <S> I mean, sort of. <S> Nobody's ever built a production hydrofoilplane. <S> It's not a bad idea, but seaplanes are a relatively niche product these days and there doesn't seem to be a lot of innovation in the field. <S> Back when there was, there was innovation everywhere <S> so the idea of hydrofoils didn't stick. <S> It was more or less awful compared to the crop of land-based aircraft coming along and after a prototype disintegrated they (probably wisely) chose to shut the program down. <S> There are some other prototype aircraft that used actual hydrofoils that I found after some quick googling . <S> A company called Lisa Airplanes seems to have an LSA - the Akoya - that's under development using tech similar to the Sea Dart. <S> The 1929 <S> Piaggio P.7 used hydrofoils, and was intended to compete for the Schneider Trophy, but never made it airborne. <S> Interestingly enough it had a screw (marine propeller) at the tail and a proper aviation propeller up front, and the pilot would've had to do some juggling between the two. <S> It's likely there were others, but I'm running low on sleep. <A> It could make sense for a seaplane/amphibious to use a retract or semi-retractable hydrofoil (or 2 or 3) instead of the specialized fast waterborne planing hull. <S> A simple barge-like hull (more aerodynamic, lighter/less robust since it's not hitting the water at 100+kts) would suffice up to maybe 15 kts. <S> Much beyond that <S> and the foil is starting to lift it. <S> By 25, the hull is almost completely out of the water, clean out at 30+.Starting at about 80, it's an ekranoplane, up to take-off speed. <S> The inflatable hydrofoils also are promising. <S> See the tests of a Goose with skis and with foils <A> https://en.wikipedia.org/wiki/Fairchild_C-123_Provider <S> "Pantobase" ski allows rough ground, or snow/ice, or water operation, if the plane has appropriate controls and can float. <S> As soon as it gets above ~30kts, it starts lifting, and the hull is effectively out of the water at anything above 50 <S> Lockheed looked at C-130 <S> seaplane adaptation, floats, boat hull, and skis were examined <S> https://www.g2mil.com/c130seaplane.htm Lockheed <S> (Secretprojects forum has an excellent thread) <A> Aeronautical engineer David Thurston experimented with hydrofoils on at least one of his designs <S> , I think it was the Colonial Skimmer. <S> He stated in one of his books, I think it was Design for Flying <S> that water is about 300 times the density of air, so a hydrofoil of very small size could lift an amphibious hull out of the water early in the takeoff run and significantly reduce overall drag. <S> It also helped in handling higher waves, as the hydrofoil was on strut some distance under the hull, and the strut and foil could slice through waves with less impact than a hull. <S> I have a Phantom ultralight aircraft, I would like to experiment with inflatable floats with retractable hydrofoils. <S> I believe the combination would be lower weight and drag than standard rigid floats. <S> The step built in to the bottom of standard floats (required to break hull suction during takeoff) creates significant drag throughout flight. <S> A retracting hydrofoil that is faired in flight should have less drag. <S> And inflatable fabric floats are very light weight, and only have to handle water loads up to the point where the hydrofoil(s) lift them out of the water. <S> And if I build the entire assembly of poured concrete it will be very safe, as it will never get off the ground. <S> Or water.
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The Convair F2Y Sea Dart , a 1950s prototype jet-powered fighter, used two 'hydro-skis' for takeoff and landing.
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Do any commercial airline models have a parachute at rear to help in landings? Some land-based fighter aircraft have a drogue-chute to help them slow down during landing. Do any current models of commercial aircraft have a similarmechanism? Secondly, would such a mechanism help aircraft in making a better landing and reduce landing related incidents/ accidents? <Q> It is called a drogue parachute <S> and I don't think that any of the present generation large commercial aircraft use them. <S> That said, a number of older commercial aircraft have used them, a good example being the Sud Caravelle. <S> Image from eu.airliners.net <S> There are some issues with using drogue chutes in a commercial airliner, which would limit their effectiveness. <S> Most commercial airliners have thrust reversers already. <S> For it to be effective, the parachute has to be quite huge. <S> For example, the Handley Page Victor, which had MTOW in the range of A320, had a drogue chute 48' (or 14.6m) in diameter. <S> The chute would occupy volume and increase weight. <S> If drogue chutes are used, they have to be packed before every flight, which will increase turnaround times. <S> Another option is to replace them at the end of every deployment, which would increase costs. <S> Deployment failure/partial deployment/Uncommanded deployment will affect the safety of the flight. <S> Aircraft dragging a huge chute during taxiing back to the ramp is not a good idea from FoD point of view. <A> The full list of airliners and business jets is: Sud Aviation Caravelle Tupolev <S> Tu-104 <S> Tupolev Tu-124 <S> Tupolev Tu-144 <S> Concorde prototypes <S> Learjet 25 <S> Learjet 35 Dassault Falcon 20 Concorde during brake tests <S> (picture source ) <S> Even some gliders used them (SHK, HKS, SB-5, Salto) <S> Hirth SHK with brake chute (picture source ) <S> Brake chutes increase drag and allow a steeper approach, which helps to control the touchdown point with great precision. <S> If the aircraft is too high, just push the stick forward - the drag of the chute prevents the aircraft from accelerating too much and the increased drag at higher speed gets rid of the excess height quickly. <S> On the ground the drag of the chute reduces the rollout distance which is especially helpful for aircraft with a high touchdown speed. <A> Nowadays the carbon brakes are the best brakes in the aviation market, together with auto brakes, reversers and speed brakes, most of the new generation aircrafts are landing much shorter compared with old generations, the reject takeoff is almost automatic and with the correct calculation the runway overrun accidents are decreasing considerably. <S> As the effectiveness of the thrust reversers are better at high speed, most of the airlines uses reverser thrust in idle, the pilots are suggested in case of using other than idle reversers, to apply reverser thrust until 80 knots or 60 kts after landing, auto brakes combined with Carbon Brakes and a speed brake, give to the aircraft shorter stop distance than before. <S> The brake temperature is much better in carbon brakes, hot temperatures are still a problem in case of reject takeoff but for long taxis is no longer a problem. <S> So parachutes are retired in commercial aviation. <S> Hope this explanation helps. <S> ;)
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The need to use a drogue chute can limit the crosswind landing of the airliner significantly. With the improvement of the brakes and reverse thrust, parachutes are no longer an option for airlines.
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What is the bypass air in a turbofan engine actually for? I'm planning on building a small model turbofan engine for a bit of fun but I thought I'd better get a better understanding of how they work first. I understand the majority of it at the moment but I'm struggling to see what the bypass air actually does, to my mind it seems like a waste of air and energy if its just going straight out of the engine without compression...could someone explain this to me? <Q> On modern turbojets the bypass air provides (at least) two things Thrust <S> The air does bypass the engine core, but it is accelerated by the N1 fan and provides thrust as it is expelled rearward out of the engine. <S> Thrust from the bypass air can contribute more than half of the total thrust produced by the engine (upwards of 80% of the total thrust for some engines in certain phases of flight). <S> Part of the reason the bypass air is <S> so efficient is that much energy is extracted from the core exhaust to spin the high and low pressure turbines (dual spool) that drive the N1 fan and the N2 compressor stages. <S> Engine cooling and noise reduction <S> Cool bypass air can be mixed with the hot air that went through the core at the rear of the engine. <S> This mixing cools the engine exhaust and reduces the jet engine noise resulting from the rapid expansion of that air once it leaves the engine. <S> The cool bypass air flowing around the engine core can also be used for general engine cooling. <A> An airplane engine provides thrust by accelerating air (plus some combustion products) backwards. <S> As air is accelerated backwards the plane is accelerated forward thanks to conservation of momentum. <S> Momentum is proportional to velocity but kinetic energy is proportional to velocity squared. <S> The result of this is that it is notionally more efficient to accelerate a larger amount of air to a low speed than a smaller amount to a higher speed. <S> In practice this is complicated by the fact that the air is already moving relative to the airplane. <S> It is difficult to efficently add a small ammount of extra speed to already fast-moving air. <S> So the best exhaust velocity depends on the speed at which the airplane will fly. <S> The exhaust velocity of a gas turbine core is higher than is desirable for most airplanes. <S> So a turbine and fan are used to capture energy from the exhaust gasses and use them to accelerate bypass air resulting in a turbofan. <S> For planes that spend a lot of time at low speeds, designers may use a gearbox and propeller instead of the fan resulting in a turboprop. <A> As the air enters the engine, some of it goes to the turbine core and runs the whole engine. <S> But most of the air goes through and is sped up by the large fan giving it the thrust. <S> Doing it this way increases the efficiency because the engine moves more air, although at a slightly lower velocity, than just a low-bypass engine which moves some air with high velocity. <A> Essentially, it is more efficient from a propulsion point of view. <S> Let me explain this with a very simple example. <S> Imagine that you are over a skateboard and you would like to propulse yourself using your hands to give yourself the boost. <S> You have 2 options, either you use your hands over another person over an skateboard or you impulse yourself using a heavy desk? <S> As you will imagine, if you use the other guy with the skateboard he will go in the other direction with a similar speed, and the desk will be moved slightly. <S> But... it is clear in your mind that is more efficient to use the desk, moreover, you will prefer to use a wall. <S> What is happening? <S> When you are trying to impulse yourself (third Newton's law) you create the same force on the other side, but when using a bigger and heavier body that body will go slower. <S> Essentially is more efficient to "propulse" using a heavier mass at lower speed that a lighter mass at higher speed. <S> Is exactly the same principle that you use in water, when you use diving fins you get faster speeds as you are moving your legs slower but moving a bigger amount of water, exactly like the skateboard. <S> The same principle applies to turbofans instead of water they use air. <S> Instead of diving fins they use blades. <S> By creating a bypass they use also the air going through the bypass to get propulsion. <S> Is more efficient than having a single core at very high speed. <A> Jet planes like fighter planes have their geometry designed for supersonic speed which is usually achieved with high velocity combusted jet exhaust from the jet engine. <S> This consumes a lot of fuels in the high pressure compressor section. <S> Passenger planes on other hand are not designed to fly at supersonic speed so high velocity jet exhaust with high fuel consumption rate are not desired. <S> The fuel optimal way to achieve this is to extract the kinetic energy from the combusted jet exhaust and transform it back into mechanical energy. <S> This energy is used to drive the turbo fan which only compresses bypass air through the bypass section of the engine to the exhaust to achieve all the benefits of bypass jet engine as described in many other comments or articles. <S> Note there is no fuel consumption here in the bypass section but only the excess kinetic energy of the hot exhaust is extracted and is used to run the bypass fan(s). <S> It is possible to design different engine mechanism to do the same thing as (high) bypass jet engine here, but it may be more complicated and has the penalty of heavier engine; therefore, less efficient than the current implementation.
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The bypass air is actually what gives the jet engine most of its thrust.
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Is it possible to tilt a propeller for attitude control, similarly to jet thrust vectoring? Are there examples of propellers tilted in a controlled way to help in attitude control for pitch and yaw, adding a torque component? Tilted propeller assumption This would be similar to thrust vectoring in jets. Vectored thrust principle Alternatively could a swashplate similar to the one used in helicopter main rotor be used to generate asymmetric thrust? (I think this excludes convertiplanes where the propellers are converted into rotors to take-off, land or move vertically.) <Q> Yes, on airships. <S> The Zeppelin NT can rotate its two forward and one rear propellers to create lift instead of thrust, a capability of particular value when the airship descends in an atmosphere with a strong temperature gradient. <S> From this page about the Zeppelin NT: The two forward propellors swivel to 120° and the aft one to 90°, and a fixed aft lateral propeller give a high level of manoeuverability, and enable smooth, quiet flight and impressive fuel economy. <S> Some of the unique flight characteristics come from the swivelling propellers, like vertical take offs, precise landings, hovering over exact locations, turns on its axis and flying backwards. <S> Tail propellers of the Zeppelin NT Airship. <S> While the sideways mounted propeller is fixed, the rear propeller can swivel through 90° (picture source ) <S> Front view of the Zeppelin NT with the forward propellers tilted up (picture source ) <S> Another example would be the V-22 Osprey , obviously, but you might prefer to call those whirly things rotors, not propellers. <A> While in case most VTOL aircraft, the rotors are tilted, one unique case is the Curtis Wright X-19 , which had what the company called tilt-propellers. <S> Curtis Wright at that point was a propeller manufacturer and its designers made the aircraft around the propeller. <S> Image from warbirdinformationexchange.org <S> This in turn, was developed from the X-100 Image from airandspace.si.edu <S> The designers used a property of the propeller called the radial lift force : ... <S> as a propeller is inclined towards the vertical from the horizontal, the resultant of the propeller's thrust and the pressure of the relative wind acting on the rotating disk is a force with an additional lift component in the vertical axis. ... <S> short propellers with wide blades magnified the radial force effect by increasing the surface area of the propeller disk without the compressibility issues of longer rotor blades. <S> This offered a potential advantage over other tilt-rotor models, such as the Bell XV-3, with longer and narrower blades that did not have sufficient surface area to take advantage of the phenomenon. <S> The added lift generated from the radial force permitted an aircraft built with the specially constructed lifting propellers to have smaller wings, which decreased weight and high-speed drag. <S> This resulted in the most aerodynamically efficient of all of the VTOL designs. <S> In hover, the roll control was provided by differential pitch of the propellers. <S> The aircraft basically behaved like a high-disc loading helicopter and was statically unstable in hover and in pitch and roll at low speed. <S> The aircraft crashed during its first transition flight in 1965, with the progra ending soon. <S> This method is also used in a number of small UAVs . <A> Yes, this is possible because many helicopters use this method to some of their control.
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There are also some aircraft like the V-22 Osprey which use some variation on this control method.
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Which Aircraft Models need a Tripod Jack for tail support at airport? Which are the aircraft models that need their tail to be supported by a jack when empty? Wikipedia says this: Aircraft Tripod Jack They are used to support a parked aircraft to prevent their tail from drooping or even falling to the ground. When the passengers in the front get off an aircraft, the aircraft becomes tail heavy and the tail will droop..... When needed, they are tugged to the tail and setup by manpower. Once setup, no supervision to the jack is needed until the aircraft is ready to leave. Are there even commercial airliners that need to be supported this way every time they load / unload? Sounded like a lot of work for ground staff. Was this a legacy equipment thing or still in use today? https://en.wikipedia.org/wiki/Ground_support_equipment <Q> A good example is the Boeing 747s. <S> Also used in DC10/MD11s used as freighters. <S> Image from reddit.com <S> Some 747-400 combis also use these, though it is mainly for cargo loading. <S> Photo: <S> Je89 W. / Source: PlanePictures. <S> Net <S> Some passenger airliners are prone to tipping ( 737-900 comes to mind ) and are usually supported by a pole rather than by a tail stand (same procedure is used in a KC-135 tanker too). <S> For example, a Boeing 737-932ER with tail support. <S> Image from <S> airliners.net <S> The tail supports are not strictly necessary and the loading can be carried out sequentially (from front to back) for safe operation, but are used as a precaution. <S> In some aircraft (like ATR-72 and Saab 340, called pogo sticks) small tubings are attached to the rear fuselage to prevent tipping over when loading/unloading. <S> Image from theflyingengineer.com <S> The nose can be tethered to prevent tipping during loading/unloading as done in this Korean Air 747F Image from koreanair.com <A> As I remember, if you loaded them properly the support wasn't needed, but people didn't always do that. <S> The cargo door was forward of the wing. <S> I've long since thrown out my DC-8 weight & balance manuals, but as best I remember, the proper protocol was to put the desired most forward ULDs in first and slide them to their positions forward of the door. <S> Next you would put in the rearmost ULD, but then move it just far enough aft to get the next ULD on, then move it and the previous one just enough aft to get the next one on, and so on. <S> At some point you had enough weight forward of the main gear to start moving pallets all the way to the rear. <S> If you miscalculated, the airplane would sit on the installed tail support. <S> This reportedly happened at Newark, as I remember, in the early 1990s, but they had neglected to put up the tail support. <S> The airplane sat on it's tail. <S> The same attention to balance was also needed when unloading. <S> Read this link for an unloading accident when the tail stand collapsed, causing one of the cargo pallets to roll down to the tail of the cargo compartment. <S> Three loaders were able to get out of the way of the runaway pallet, but the fourth got his foot caught, sustaining serious injury. <A> Back in the day I was weight and balance / loading qualified for all B747 types. <S> The tail-stand is promarily used for freighters. <S> If I'm doing a full load change (eg all off and reload) with a crew familiar with the aircraft .. <S> , then I wouldn't be too worried about tipping a freighter. <S> Especially for a transit flight where everything is happening all at once. <S> A fully loaded 747 combi and you have to have your wits about you when working around this aircraft. <S> The MD11 freighter was another aircraft you had to watch out for. <S> An empty plane will have its CG (centre of gravity) right up the back but once fully loaded the CG will be at the forward limits! <S> To get it in trim you have to load all the heavy stuff back in the rear of the aircraft <S> but this will require a careful loading sequence as the maindeck cargo door is in front.
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DC-8 freighters used tail supports as a safety precaution. Tripods are mostly found in cargo aircraft (and combis) as the cg shift is severe there (particularly for front loading). BUT for a 747 Combi I would say that a tail-stand is indispensable!
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What are "Alternate Minimums"? As I asked question about weather minimums yesterday, I've read some material including TERPs. And In the FAA 8260.3b, 'Taking and Landing Minimims' 3.1 there is one sentence "alternate minimims, when specified, must be stated as ceiling and visibility." But I don't know What alternate minimums exactly means because I am not native English speaker. I have used English dictionary to find exact meaning but failed. What is the difference between approach minimums and alternate minimums? <Q> FAR 91.169 states that IFR flight plans must include an alternate airport unless the weather is at least 2000 ft ceiling and 3 miles visibility, from one hour before to one hour afterwards ( 1-2-3 rule ). <S> The same regulation also states that the alternate airport must meet the following critera: (c) IFR alternate airport weather minima. <S> Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima: (1) <S> If an instrument approach procedure has been published in part 97 of this chapter, or a special instrument approach procedure has been issued by the Administrator to the operator, for that airport, the following minima: (i) <S> For aircraft other than helicopters: The alternate airport minima specified in that procedure, or if none are specified the following standard approach minima: (A) <S> For a precision approach procedure. <S> Ceiling 600 feet and visibility 2 statute miles. <S> (B) <S> For a non-precision approach procedure. <S> Ceiling 800 feet and visibility 2 statute miles. <A> The difference between APPROACH minimums, and ALTERNATE minimums: <S> APPROACH minimums are stated on each approach plate, for instance, 200 ft. ceiling with 3 mi. <S> visibility. <S> It's a real-time minimum, because it only affects whether or not you can begin that particular instrument approach. <S> On arrival, you check the airport's weather (METAR, for instance) and if the real weather is reported better than the required weather for a particular approach, then you can begin that approach. <S> Therefore, you need to take the destination weather forecast into account when planning. <S> ALTERNATE minimums affect your PLAN, even BEFORE you take off, and is not related to approach minimums. <S> An "alternate" refers to a second airport you identify in your planning that you can go to if the weather at the destination turns too bad to land. <S> The thinking is that, if the weather at the destination is FORECASTED to be good around your arrival time (an hour before til an hour after), then you shouldn't need to list an alternate airport in your flight plan. <S> The FORECASTED weather at the ALTERNATE airport has to be better than a certain ceiling / visibility, too. <S> You have to look at the approaches available at the alternate to know what the minimum requirements are there. <S> If the alternate airport has a "precision" approach (for instance, an ILS), the FORECASTED weather at the ALTERNATE has to be at least 600 ft. ceiling and at least 2 mi visibility, otherwise you can't list it as an alternate. <S> But airports with a non-precision approach (for example, a VOR-A approach) require better conditions with 800 ft. ceilings. <A> I found an excellent article about it at IFR Magazine . <S> Basically, to qualify as an alternate airport, the alternate must have certain forecast weather conditions (600-2 for precision approach, 800-2 for non-precision.) <S> These are the "alternate minimums". <S> However, those are just the default values. <S> Many airports have different values, in which case the alternate minimums will be published on the approach plate <S> (example: PAO VOR approach , top-left, next to the inverted 'A')
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Generally, the destination's weather has to be FORECASTED more than 2,000 ft. ceilings and 3 miles visibility, or if not, you have to IDENTIFY an alternate destination airport in your flight plan.
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Why is the take off speed and distance reduced by head winds? A headwind of 20 knots and a true airspeed for the take-off safety speed being 120 knots, the ground speed is only 100 knots. Getting to a true ground speed of only 100 knots will require less distance. Anyone can explain to me is that mean that the distance for take off will be less and also the take off speed will be less?� <Q> You're correct that a headwind will reduce the takeoff roll (takeoff distance). <S> As far as takeoff speed, the airspeed will remain same, but the ground speed will be reduced. <S> In the simplest sense, an aircraft rotates for takeoff when it generates enough lift (leaving aside other considerations). <S> This is dependent on the airspeed as the lift generated is propotional to the square of airspeed (provided the other factors like wing area and lift coeffecient are kept constant) at a density altitude. <S> As a result, it is the airspeed, not the groundspeed that matters. <S> If you have some headwind, the effective groundspeed is reduced by the same amount- resulting in reduced takeoff distance. <S> The effect of the wind on landing distance is similar to the takeoff distance. <S> You can see this in the following figure. <S> Image from <S> avstop.com <S> As it can be seen, the presence of winds can have a significant effect on the takeoff disantances required (note that the airspeed remains the same in all cases). <S> Due to this, the direction of prevailing winds can have a significant effect on determining the runway headings. <S> From Influences on Airport Layout : The weather patterns of an area, especially the prevailing winds, are a major factor in determining runway headings. <S> Prevailing winds are defined as the direction from which the winds blow most frequently. <S> Remember that airplanes take off and land into the wind. <S> Let's say that at a given airport the prevailing winds blow in from the west 65% of the year, while 30% of the year the wind blows in from the east, and the remaining 5% coming from the northwest. <S> It would be best then to orient the runway W (27) and E (9). <S> That would mean that approximately 95% of the year airplanes would be landing and taking off into the wind. <A> The takeoff indicated airspeed - shown on the ASI in the cockpit - will remain the same regardless of the wind. <S> The groundspeed required to takeoff however <S> , is greatly affected by the wind and ambient conditions. <S> At a very simplistic level, it helps to think of indicated airspeed as the speed of the air over the wings. <S> Therefore, if an aircraft is sitting still facing a 20kt wind, the speed of air over the wings - the indicated airspeed - is 20kt, yet the groundspeed (speed across the ground) is 0. <S> So if the aircraft needs to rotate at 120kt indicated airspeed, with a 20kt headwind the aircraft only needs to accelerate to 100kt of groundspeed, and thus requiring less takeoff distance. <S> But the ASI will still show 120kt at rotation speed. <A> The landing is also reduced for the same reason - less time is needed to come to a complete stop because the groundspeed is lower than the airspeed (also minus the time needed to shave off those 20 knots). <S> This is the main reason why runways are built in the prevailing wind directions and aircraft carriers steam into the wind when conducting flight operations.
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Yes, the distance will be less in both cases because the amount of time needed to reach the take-off speed is reduced because the necessary groundspeed is reduced (minus the time needed for 20 more knots in your case).
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Are aircraft capable of sustained inverted flight at constant altitude? Inverted flight as a part of manouveres, dogfights, acrobatics is fairly common but my question is: Are any aircraft capable of sustained inverted flight without losing altitude? e.g. Could you fly 10 mins inverted at the same flight level? To clarify: I'm not wondering about engines, fuel systems, air-frame strength etc. Fundamentally there's no reason why those systems cannot be engineered to be robust against inverted flight. What I'm curious about is specifically the aerofoil itself. i.e. As far as I can see, you'd need to balance the gravity vector with lift. Ergo, are aircraft wings generally capable of providing enough compensating lift in the "wrong" direction to balance gravity? Are all / most fighters / arerobatic certified craft capable of this? We'd need an aerofoil that can provide a lift vector pointed in the +z direction normally but changable to a large vector pointing in the -z direction in response to a flight surface deflection? <Q> Yes they are! <S> Aerobatic aircraft can have symmetrical wing to improve inverted performance. <S> So with these aircraft there is no any problem at all. <S> Other agile aircraft, gliders can fly inverted as well. <S> Of course is far from optimal but possible. <S> Don't forget that lift depends of angle of attack as well. <S> So if you fly inverted angle of attack and drag will be bigger to compensate for a "wrong" wing profile. <A> Most aircraft use a cambered airfoil. <S> Such an airfoil only gives you a higher stall speed, otherwise it will just cope fine with prolonged inverted flight. <S> The wing's twist will most likely increase the induced drag since the circulation distribution over span is designed for upright flight, and maybe the airfoil will operate outside of its laminar bucket (if its polar has one), so viscous drag will be higher. <S> If the wing uses a symmetric airfoil and has no washout, like in some aerobatic aircraft, the aircraft will perform identically in both attitudes. <S> The real limit to prolonged inverted operation is the fuel system and, on some engines, the lubrication. <S> If both are designed for prolonged inverted flight, only the fuel level and the physical condition of the pilot will limit the duration of inverted flight . <S> It is much more comfortable when your body weight is supported by a comfy seat than by two narrow straps running over your shoulders. <S> The higher stall speed will translate into a higher speed for the minimum power and minimum drag optima, so an aircraft which could keep its altitude in regular flight might have too little power for sustained inverted flight. <S> Also, the trim range of the elevator might be too small to trim the stick forces. <S> In inverted flight the sideslip-induced rolling moment will have the wrong sign, so sideslipping will make you roll into the wind. <S> But if you tolerate all this and engine power is sufficient (which should be true for all fighters since WW II), flying inverted at the same altitude is no particular problem. <A> I realize you explicitly stated: To clarify: I'm not wondering about engines, fuel systems, air-frame strength etc. <S> Fundamentally there's no reason why those systems cannot be engineered to be robust against inverted flight. <S> But I'm going to answer for part of this because it does seem to be the limiting factor of your question. <S> The main problem with inverted flight is not aerodynamic but propulsive. <S> Most aircraft fuel tanks require gravity to feed fuel to the engine. <S> However, there are usually very strict time restrictions. <S> For example, the B-1B bomber possesses only a single fuel tank able to operate under negative G maneuvers. <S> During normal flight fuel is pumped from gravity fed tanks into this special fuel tank. <S> Then during the negative G maneuvers only fuel from this special tank is available for continued engine operation. <S> What this means in practice is that aircraft performing any negative G maneuver starts a count-down clock. <S> When the clock reaches 0 its engine(s) die. <S> Which is a very bad thing during normally powered flight. <S> The amount of time any particular aircraft has is dependent upon its particular fuel tank design. <A> When at the top of a loop, you would normally still have positive g. <S> The issue here is to fly inverted sustainably at -1 g. <S> With a symmetric wing (most fighters and some aerobatic planes) this would be easier as it won't try to create lift towards the earth in that instance <A> Yes. <S> Modern high performance military and civilian aerobatic aircraft have dedicated inverted fuel and oil systems allowing them to operate in the negative G regimes of their flight envelope without airframe or engine damage.
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Military and high performance aircraft typically include some mechanisms for maintaining fuel flow during negative G maneuvers like inverted flight.
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Is there a benefit to a pilot/aviator having an FCC GROL license? I am an avionics technician (c-130) in the USAF and plan on learning to fly helicopters when I separate in about a year. I have debated whether or not to pursue a GROL or possibly A&P . From what I know, these are generally intended for maintainers/technicians rather than aviators. That said, would there be any benefit to having a GROL or related license for an aspiring helicopter pilot? <Q> There's no tangible benefit to having a GROL in getting a pilots license of any kind as getting the license generally confers the right to use aircraft radios. <S> In some places you need to get an RT license for aviation as a separate test, however that's pretty minimal. <S> A GROL is only good for repairing, maintaining, and running certain types of radio stations. <S> An A&P will let you work on airplanes, but it also does not help get a license. <S> An A&P will give you insights into how an airplane works, but you can get those insights without <S> an A&P. Having an A&P and a pilots license might be a different story if you plan to work in remote locations where being able to fix your aircraft when it breaks is useful. <S> It won't help you get a flying job in most places. <A> There is no test for the permit <S> but there is a fee. <S> You'll only need the permit if you intend to fly outside of the united states and communicate with foreign ATC. <A> From what I know, these are generally intended for maintainers/technicians rather than aviators. <S> Correct, an A&P will not help you get a pilots license (aside from maybe gaining a better understanding of how the internals work). <S> That said, would there be any benefit to having a GROL or related license for an aspiring helicopter pilot? <S> This is a bit of a different question, to which the answer may be yes, in the sense that an A&P cert can be useful if you are involved in aviation. <S> First off if you intend on owning a helicopter you will be able to undercut some of the costs by doing work yourself. <S> As mentioned if you intend on flying in remote places being able to work on your own bird can literally save your life. <S> If you are looking to fly professionally you can always make money on the side doing A&P work (its a pretty high paying profession). <S> I have no idea if it has any bearing <S> but there is a chance it will lower your insurance premiums as well ( <S> generally the more certifications you have <S> the lower your insurance
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An A&P could be very valuable to you as an aviator in general. The only FCC license that you might need is the restricted radiotelephone operator permit (RR) .
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Why is horizontal stabilizer set to 4° up in airbus aircraft for take off? Why is horizontal stabilizer set to 4° up ( or any other setting other than neutral) in airbus aircraft for take off? Why can't we keep the trim neutral? <Q> On landing, aircraft are configured for a stabilized approach , which means that the aircraft can be flown to the runway with a minimum of configuration changes to flaps/slats, trim, power, and drag devices. <S> On take-off, the aircraft is configured for take-off, and trim is set so as to provide a slight nose-up. <S> If the trim is set nose low, it requires a lot of pull to "unstick" the aircraft from the runway. <S> If the trim is set too nose high, then the aircraft will want to nose up before the aircraft may be ready to fly, and then to continue a nose-up attitude after rotation, requiring more than a minimal effort to keep the a proper departure attitude. <S> Nose-up trim can induce what is called a trim stall , which is when the trim is set so far back that the aircraft will exceed the critical angle on take-off: <S> ELEVATOR TRIM STALL <S> The elevator trim stall maneuver shows what can happen when full power is applied for a go-around and positive control of the airplane is not maintained. <S> [Figure 4-8] <S> Such a situation may occur during a go-around procedure from a normal landing approach or a simulated forced landing approach, or immediately after a takeoff. <S> The objective of the demonstration is to show the importance of making smooth power applications, overcoming strong trim forces and maintaining positive control of the airplane to hold safe flight attitudes, and using proper and timely trim techniques. <S> Source: Airplane Flying Handbook <S> p. 4-10 <A> Airbus WILL take off ~safely~ regardless of the pitch trim, as long as trim is in the t/o green range. <S> Adjusting the trim to the correct position, however, depending on the location of the CG for that flight, insures the aircraft handles similarly between takeoffs and rotation will be more or less standard between flights. <S> This means the pilot can make the same side-stick input on each takeoff and get the same 3deg/sec rotation. <S> If not properly trimmed, rotation would be faster/slower and the pilot would have to adjust for that at a critical phase of flight. <S> Not doing a good rotation will impact t/o performance significantly. <A> The idea is to trim the airplane for the initial climb phase, so it assumes the correct attitude and speed without further control input. <S> The exact value depends on CG location, weight, flap setting, temperature and more. <S> Consider you take off in IMC with nose-down trim and get the least bit distracted. <S> The aircraft is at a real risk to hit the ground .
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Both landing and take-off are critical phases of flight, and it is standard procedure to configure the aircraft for those phases to reduce the workload on the crew.
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What is the difference between a positioning flight and a ferry flight? What's the difference (for the purpose) between positioning and ferry flight? <Q> This is often done when the aircraft finishes its day in one city, but is needed in a different city the following day because another plane has broken down. <S> A positioning flight is technically a type of ferry flight, however the latter is a more broad term. <S> Examples of ferry flights include delivery from the manufacturer, or flying to a different city for heavy maintenance. <S> Both flights are generally conducted without fare-paying passengers on board, but sometimes extra airline staff are carried. <A> Ferry flight refers to flying the aircraft from the factory or flying of the aircraft to or from major maintenance (overhaul). <S> Positioning flight refers to the aircraft to some place(airport) from which it is operated. <S> For example, an aircraft may be positioned at an airport for normal operations from the next day. <S> Both are non revenue flights. <S> They are often used interchangeably. <S> NTSB, however, seems to consider ferry flights as a type of positioning flight. <S> Eurocontrol defines positioning flight as: A non-revenue flight carried out to position an aircraft for a scheduled or non-scheduled flight or service. <A> In a positioning flight the airplane could carry passengers, in a ferry flight usually not due to the condition of the airplane (mechanical problems, extra fuel tanks) or the ownership. <A> Positioning flights do not have to be approved, whereas ferry flights have to be approved by the FAA by permit or operations specifications. <S> Due to the nature of ferry flights only required crew and or mechanics my fly on the aircraft due to airworthiness limitations.
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A positioning flight is a flight for the sole purpose of positioning the aircraft to conduct another flight from another airport. There's no absolute accepted definition across the world, however generally it depends on whether passengers could be carried on the flight.
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When can a pilot disobey ATC commands? The title really asks it all: When can a pilot disobey ATC commands? . Of course, the pilot has the final decision, but when would the pilot really disobey someone in ATC with much more knowledge of planes and other potential hazards near by? <Q> In case of emergencies, yes. <S> The reasons for that and the results will decide the consequences. <S> From 14 CFR §91.123 Compliance with ATC clearances and instructions : (a) <S> When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists , or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. <S> (b) Except in an emergency , no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised. <S> From 14 CFR §121.557 <S> Emergencies: Domestic and flag operations : (a) <S> In an emergency situation that requires immediate decision and action the pilot in command may take any action that he considers necessary under the circumstances. <S> In such a case he may deviate from prescribed operations procedures and methods, weather minimums, and this chapter, to the extent required in the interests of safety. <S> Emphasis mine. <S> Obviously, it would be prudent for the the pilot (and required under FAR 91.123(c), as @Pondlife points out) to report the deviation to the ATC as soon as possible. <A> A pilot can break any rule in the book for the safety of the flight or those on the ground. <S> Ultimately the safety of the flight rests with the pilot in command of the aircraft and therefore not just the right but the duty to diverge from ATC instructions if the situation warrants. <S> Examples of this might be: A cabin depressurization or engine failure requiring an immediate descent <S> A change in course or altitude to avoid a collision with an aircraft or terrain Passenger illness <S> Unlawful interference <S> When intercepted by law enforcement or the military If complying with an instruction is hazardous, for instance putting the aircraft outside its flight envelope, into a possible collision Fuel emergencies Mechanical problems <S> In cases such as these pilots will take immediate action and inform ATC afterwards if they can. <A> To add one more case to what's been mentioned, if ATC tells you to climb to avoid a conflict and TCAS tells you to descend, pilots are required to follow the TCAS command rather than ATC's. <S> The reason behind this is that TCAS in the two aircraft can typically coordinate "behind the scenes" which aircraft will do what in order to avoid a collision, but there's no guarantee that both aircraft are hearing the same plan from ATC. <S> Maybe separate controllers both issue a "climb" command, or one aircraft is on the wrong frequency, or whatever. <S> But the TCAS-to-TCAS communication is sufficiently reliable that this is now a required (although extremely rare) case of disobeying ATC. <A> Others have talked about emergencies, which allows a pilot to take any action he sees fit. <S> This is correct, and you could even argue that it's not really disobeying, as in the moment the emergency was declared, all clearances sort of went out the window. <S> There's one important part missing and that's the option for a pilot to not accept a clearance or an amendment. <S> A clearance is not an instruction as much as it's a negotiation, and once established, is more or less valid until both pilot and controller can agree on something different. <S> If they can't agree, by either the pilot saying "unable" for whatever reason, or in the case where radio communication is lost and the pilot didn't actually hear anything, he is expected to carry on as previously cleared.
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The pilot in command has the final authority and responsibility for safety of the flight and can disobey ATC commands in case of emergencies.
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Why was the A380 built with a gull-wing design? I've noticed that the wings on the A380 are very curved in comparison to the 747. I mean the 747 has a lot of wing flex but the A380 has less wing flex and the wings are flexed down in comparison to the 747. Here there are two photos that might help you understand what I'm writing. So why are the A380 wings like that and what are the benefits? Source Source <Q> The wings are designed like that. <S> You can see them in the picture below. <S> Image from airliners.net <S> The A380 wings are designed to be the most efficient while still inside the 80m 'box' for efficient airport operations. <S> The result is a clean slate design which used CFD extensively to get the most efficient aerodynamic design possible. <S> The 'curve' near the root means that the landing gear in the wings could be as short as possible while being long enough to prevent a tail strike during rotation and allowing the spar to pass below the floor. <S> The shape also allows enough ground clearance for the inboard engines. <S> This assumes importance with the advent of engines with ever higher bypass ratios. <S> Of course, the use of modern composite materials means the the wing 'flexes' up to be more or less straight once the aircraft is airborne. <S> ( wikimedia.org ) <S> In-flight 'flex'. <A> The A380 has a gull-wing design. <A> Aeroalias answer already covers most points. <S> Still it may be worth to add that its not a clear gull wing, but more toward a dihedral setup with an increased volume at the front root part. <S> This is most obvious when looking at it from the back while flying. <S> There are not many pictures showing one flying and from behind but this (taken from Wikipedia ) <S> might give a hint: <S> Beside the already mentioned advantage of shorter and thus lighter landing gear and more room for engine mount <S> (much like the Ju87 inverted gull wind gid provide), a dihedral wing also increases lateral stability in flight. <S> Increased comfort was as well one of the ambitious design criteria for the A380. <S> Who ever had the chance to board one did enjoy the results. <S> So considering the many, often each other contradicting requirements for wing (and fuselage) design, this marks a sweet spot - at least when reaching a certain size :))
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This has some economic benefits, the main one being shorter landing gear while giving enough ground clearance for the engines.
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How do aircraft go off-course even with all their guidance technology? Pilots today have more than enough technology both in the cockpit and in the infrastructure that supports them to know with great precision where they are at any given time. How/why do they still sometimes go off-course? <Q> 2) Humans are fallible. <S> Now that aircraft have GPS receivers <S> it is rare for them to be off course by a considerable margin. <S> That said, technology can fail and there are cases where the GPS cannot, or should not, be used. <S> The crew can also make mistakes, either by incorrectly reading the navigation data or by incorrectly entering flight path details into the navigation system: An aircraft may actually be 'on course' based on what the crew told it to do, but they told it the wrong thing. <S> Depending on how data is entered into the system it's easy to add the wrong waypoint (some have very similar names, there's been a few cases of that happening) or to enter reciprocal bearings or lat/lon points. <A> The navigation data (angles, coordinates) are initially numbers and must be read by human first to use the navigation systems. <S> If the pilot misreads or wrongly interprets the initial data, the navigation tools cannot help. <S> This seems the reason of both Varig Flight 254 and TWA Flight 3 navigation mistakes. <S> In general cases seem rare as they require the navigators to stay disoriented for a long time, regardless of that they see, radio stations they hear, etc, etc. <A> My Dad was a fighter pilot in the Korean War. <S> He acidentally did something in the cockpit which effected his air mix. <S> Without sufficient oxygen, my Dad got lightheaded and started flying towards North Korea. <S> My Dad might well have died or become a POW except that members of his fighter group flew back to find him. <S> My Dad was sufficiently cognitively aware to recognize his comrades and use them as his "navigators" back to home base. <S> Things that can effect a pilot's cognitive state can still happen. <S> Look at naval and air force fighter crashes over the past handful of years. <S> As a chemist, I'd identify one likely culprit as new cockpit materials insufficiently tested for offgassing (changed chemical state) at critical state points. <S> I have one material, in particular, in mind. <A> A basic expansion of os1’s answer. <S> 1) broken or defective equipment. <S> 2) equipment that is not properly maintained or calibrated. <S> 3) improper use of equipment by flight crew. <S> 4) incorrectly interpretation of output data from equipment by flight crew. <S> 5) terrestrial or satellite navaids needed to operate equipment either down for maintenance or unavailable. <S> 6) incorrect procedures used by flight crew. <S> 7) Overconfidence in onboard systems causing negligence of basic airmanship and good risk management. <S> 8) <S> Confusion among duties for pilots in aircraft requiring more than one flight crewmember. <S> 9) saturation by existing cockpit tasks causing negligence in navigation. <S> 10) human frailty, fatigue and external pressures. <S> It can happen to anybody, in any kind of airplane, no matter how advanced the equipment on board is. <S> I wrote in a post about Instrument flying that modern integrated flightdecks i.e. glass cockpit have the capability to make a good pilot better and a poor pilot dangerous. <S> This still rings true today. <S> Smart people routinely do stupid things in aircraft and it can have tragic consequences. <S> This can be insidious if one is not careful.
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On top of that there's simple crew distraction - if they're manually flying then they may be focussing on something else and not notice that are off-course: As happened on the Sukhoi superjet demonstration flight a few years ago. 1) Technology is fallible.
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Do I have to declare an emergency if I cut into fuel reserves? In another question , I wrote You only need to plan for regulatory reserves. You don't actually have to land with them and @Jan replied: you have to declare emergency if you do cut into them though and that will quite probably get you an investigation I have never heard that you must declare an emergency if you cut into your reserves (regardless of the stage of flight), and I'm wondering if there is any regulation to back it up. The only reg that I could find that comes close is NTSB 830 , which lists a set of criteria for notifying the NTSB within 10 days: (a) An aircraft accident or any of the following listed serious incidents occur: (1) Flight control system malfunction or failure; (2) Inability of any required flight crew member to perform normal flight duties as a result of injury or illness; (3) Failure of any internal turbine engine component that results in the escape of debris other than out the exhaust path; (4) In-flight fire; (5) Aircraft collision in flight; (6) Damage to property, other than the aircraft, estimated to exceed $25,000 for repair (including materials and labor) or fair market value in the event of total loss, whichever is less. (7) For large multiengine aircraft (more than 12,500 pounds maximum certificated takeoff weight): (a bunch of other things) I'm interested in the answer for Parts 91, 135, and 121, under FAA regulations. <Q> There seems to be no regulations that require decleration of emergency in case of using reserve fuel. <S> US DoT InFO 8004 specifically discusses this: Emergency Fuel . <S> Although not defined in the AIM or Federal aviation regulations, the industry-wide connotation typically associated with the term “Fuel Emergency” is: The point at which, in the judgment of the pilot-in-command, it is necessary to proceed directly to the airport of in tended landing due to low fuel. <S> Declaration of a fuel emergency is an explicit statement that priority handling by ATC is both required and expected. <S> Noting that pilot declaring minimum fuel is not an emergency, <S> The act of using a portion of the reserve fuel assigned to a flight is not, in its self a cause to declare a minimum fuel state with the controlling agency. <S> Regulations require reserve fuel to enable aircraft to maneuver, due to unforeseen circumstances. <S> Many aircraft safely arrive at their destination having used a portion of the fuel designated as reserve. <S> There is no regulatory definition as to when, specifically, a pilot must declare “minimum fuel” or a fuel emergency . <S> Air carriers typically develop such guidance for their pilots and include it in their General Operations Manuals; such guidance generally falls along the following lines: •Declare “minimum fuel” when, in your best judgment, any additional delay will cause you to burn into your reserve fuel. <S> •Declare a fuel emergency at the point at which, in your judgment, it is necessary for you to proceed directly to the airport at which you intend to land. <S> Declaration of a fuel emergency is an explicit statement that priority handling by ATC is necessary and expected. <S> (Emphasis mine) <A> No, you don't, but per the AIM you should declare an emergency if you need priority for landing. <S> There may be some confusion here between declaring "minimum fuel" to ATC, and declaring an emergency. <S> The AIM 5-5-15 says: Advise ATC of your minimum fuel status when your fuel supply has reached a state where, upon reaching destination, you cannot accept any undue delay. <S> Be aware this is not an emergency situation, but merely an advisory that indicates an emergency situation is possible should any undue delay occur. <S> [...] If the remaining usable fuel supply suggests the need for traffic priority to ensure a safe landing, you should declare an emergency due to low fuel and report fuel remaining in minutes. <S> But in general there's no regulation or rule that I can find that says when a pilot must declare an emergency. <S> The general guidance from the AIM 6-1-2 is that pilots are expected to declare an emergency when a state of distress exists. <S> The ATC orders 10-1-1 are a little more specific: <S> A pilot who encounters a Distress condition should declare an emergency by beginning the initial communication with the word “Mayday,” preferably repeated three times. <S> For an Urgency condition, the word “Pan-Pan” should be used in the same manner. <S> As for what distress actually means, <S> the Pilot/Controller Glossary simply says: DISTRESS − <S> A condition of being threatened by serious and/or imminent danger and of requiring immediate assistance. <S> It's unlikely that cutting into fuel reserves by itself would constitute a "serious or imminent danger" (which is why "minimum fuel" isn't an emergency) but on the other hand if the pilot is also unsure of his position or has other issues to deal with, then it might still be the best thing to do. <A> One time after WX and extended vectors (over 50 minutes of additional delay), I was almost ready to cut into my night IFR with alternate reserves plus my modest buffer. <S> Not the legal minimum, but my minimum. <S> I told Baltimore Approach that I was declaring "MINIMUM FUEL. <S> " I was asked how much fuel I hand on board, which I provided in minutes. <S> I was also asked for souls on board. <S> They handed me to Dulles Approach, explaining that Dulles had better coverage for KGAI, even though KGAI was in their airspace (or sector). <S> My rules for the flight were that if I had any more delaying vectors I would have to divert, and given the WX, diversion would potentially be problematic. <S> I had been cleared to KGAI, but if I was delayed further I would have to land somewhere else. <S> To be clear, I did not intend to declare an emergency, but the controllers treated it that way. <S> Dulles gave me a dedicated controller and kid glove handling to KGAI, and cleared me for the NDB approach. <S> He also called the FBO to verify I made it in, I was told by the line guy. <S> The Dulles controller had asked me to call him when I landed, so I called Baltimore on Clearance Delivery, and asked them to tell Dulles I landed and appreciated the assistance. <S> It was raining hard, but I took the time to dip the tank, because I wanted to know exactly where I was fuel wise. <S> I was within 1 gal of my estimated fuel, which was 1:45 plus unusable, as I was at night, IFR, and <S> with weather that required an alternate. <S> There was never any paperwork. <S> The following week, when I got home, I sent both Baltimore and Dulles a thank you letter for their handling of things. <S> To this day I use this flight as an example to students of the power of "MINIMUM FUEL." <A> In Australia, the answer is <S> yes if you expect to land with less than the fixed fuel reserve. <S> CASA 29/18 – Civil Aviation (Fuel Requirements) <S> Instrument 2018 s7(5): <S> The pilot in command must declare an emergency fuel state by broadcasting MAYDAY, MAYDAY, MAYDAY FUEL. <S> https://www.legislation.gov.au/Details/F2018L00644/Html/Text#_Toc514142500
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The pilot in command must declare a situation of emergency fuel when the calculated usable fuel predicted to be available upon landing at the nearest aerodrome where a safe landing can be made is less than the fixed fuel reserve for the flight.
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Why do delta-wings perform so well on paper airplanes? Based on this question, it seems that delta-shaped wings do not perform well at low airspeeds. But why do paper airplanes, particularly the most well known one, fly well even though the airspeed they fly in is at most 15 knots on average? <Q> Your interpretation of the answer to that question is a bit wrong. <S> It would be an error to claim that delta wings don't perform well at low speed. <S> Delta wings perform exceptionally well at low speeds. <S> The correct interpretation is delta wings are not fuel efficient . <S> And this is true at low and high speeds. <S> There are advantages to delta wings at both high and low speeds. <S> The following list are some of the known advantages: <S> Improved handling at high Mach numbers due to swept leading edge (note: this is the same advantage as swept wings but with the down side of being draggy when performing manoeuvres - swept wing planes retain much more kinetic energy after a turn). <S> Intrinsically strong structurally <S> (it's a triangle!) <S> thus can be built much lighter. <S> Retains quite a lot of rudder effectiveness at low speeds and high angles of attack (this is unintuitive because you'd think the wing would block airflow to the rudder but <S> the strong vortex shedding on the leading edge maintains flow around the rudder). <S> Have very wide CG range compared to conventional aircraft. <S> This is especially useful in bombers. <S> Have very benign and gentle stall behaviour. <S> This is especially useful for paper airplanes since it can prolong flight at low speeds (paper airplanes simply dip their noses and regain speed instead of simply diving and crashing). <S> The major disadvantage is that it is draggy. <S> Thus not fuel efficient. <S> Thus in a business world where profit and cost matters delta wings are not attractive. <S> For supersonic flights the drag is apparently roughly on par with swept wings. <S> Except, as mentioned above, due to the geometry of the wing it can be built lighter thus save fuel - so it sort of cancels out. <S> For toy planes, where efficiency is not of great concern (fun and "cool" is more important) <S> delta wings are OK. <S> Still, if you use the same sheet of paper and built a long, narrow, cambered wing like this: .. you'll find that the long narrow winged plane flies much further than the delta wing paper airplane given the same launch speed. <A> The delta wings do have some disadvantages compared to the 'reguar' wings at low speeds. <S> I'm assuming that you're talking about paper aircraft like this: Image from secretprojects.co.uk <S> Delta wings have more friction drag, have difficulty in integrating high lift devices and have low AR etc. <S> (as already noted in that question); however, most of these disadvantages are marginal when it comes to the paper aircraft. <S> On the other hand, this kind of design offers some good advantages when you want it to just fly when thrown: <S> The delta wings still produce lift using a vortex, which means that they stall at much higher angles of attack. <S> At low Reynolds numbers, the max. <S> lift coeffecient is obtained at slightly higher AoA. <S> This helps in their flight. <S> The centerfold, in addition to helping in holding and throwing, also helps in lateral stability. <S> Also, the flow through that helps in reducing the pressure over the top surface of the paper craft, helping in increasing lift. <A> They don't perform well on paper airplanes as compared with custom engineered airplane's made from single or ply sheets of paper. <S> It's just that it's much easier to fold a sheet of paper into a delta wing shaped airplane; hence the reasons most paper airplane shoes have delta wings on them.
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Delta wings don't perform well at low speeds compared to other low speed wings such as straight ones.
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Why is pitch measured with respect to the horizon and not the ground? Why is the pitch measured with respect to the horizon and not the ground? How different are the angles between the ground and the horizon? Would it be possible to fly with an attitude indicator that indicated pitch with respect to ground rather than horizon? What does it mean when you have a 0 degree pitch with respect to the horizon? What, exactly, are you flying towards in that case? I've always had a hard time understanding this. Thanks for your time. <Q> Pitch is measured with respect to a plane orthogonal to the local weight¹ force, which is properly called the horizon tal . <S> That is used because: It is equipotential plane of the gravitational field. <S> Moving around it won't change your potential energy. <S> Is always well defined. <S> Is smooth and locally flat <S> (it is still a spherical surface globally, of course). <S> Can be measured by averaging inertial forces on board without external reference. <S> It is called simply horizon, presumably because looking at the horizon is the easiest way to find that plane by human senses. <S> Using ground, which is not flat, as reference wouldn't work. <S> Aircraft need to fly mostly along the equipotential plane, because climbing to a higher one requires adding more energy by the engines and descending below means the aircraft accelerates and needs to dissipate (= waste) the energy. <S> So following terrain would require quite a bit more energy than flying horizontal. <S> Plus it would be very complicated. <S> ¹ <S> By weight <S> I mean the sum of gravity and centrifugal force in the reference frame rotating with Earth . <A> If you used angle between the ground and the horizon then it would be constantly changing depending on your height and the elevation of the ground. <S> If the ground level ahead goes up then the angle between ground and horizon decreases, if the ground level stays the same and you increase altitude the angle increases. <S> If you see the angle diminish you would not know whether it was because of a change in attitude, altitude, or ground elevation. <A> Your question seems to boil down to the following: Assuming that the earth is a perfect sphere <S> , why does the virtual horizon (i.e., the pitch indicator) point to the horizon? <S> The answer is, it doesn't . <S> The virtual horizon you see on your pitch indicator is always at an angle of 90° (i.e., a straight angle) from that, and only points to the actual horizon in case you were exactly on the ground. <S> This difference is negligible for normal flight (which happens in the very lowest part of the atmosphere). <S> The following is only to demonstrate what is actually happening. <S> In the above picture, I drew an exaggerated version of what you mean. <S> The red line points to the center of the earth ( <S> so, where gravity points), and is the reference of your pitch indicator. <S> The green line is what you will see on your pitch indicator. <S> The blue line is where you actually see the horizon. <S> They don't match up, and that's fine . <S> A pilot really doesn't care where the horizon is. <S> He cares about maintaining altitude, ascending or descending. <S> Maintaining altitude is done by keeping the airplane level with respect to the center of the Earth, in which case he will make a complete circle around the earth since his velocity vector is always perpendicular to the center of the Earth. <S> Ascending and descending is done by having the pitch above or below this. <S> From the picture you can see that if the virtual horizon were to point to the actual horizon, you would eventually impact the ground - on a perfectly smooth sphere, it would be a smooth landing too. <S> I guess there's a reason they call it the virtual horizon, eh? <A> The "horizon" is a fixed reference that will be the same wherever you are flying. <S> It is fairly straightforward to create an instrument for the cockpit that illustrates pitch and roll with respect to this horizon. <S> It also relates to gravity, since gravity will be pointing straight down with respect to the horizon. <S> Pitching up means you are working against gravity, regardless of what the ground below you is like. <S> Humans have a natural sense of "up" and what is "level", which is based on our perception of gravity. <S> Showing pitch with respect to the ground would be much more chaotic. <S> You would need some way to know what the ground below the aircraft is doing, at any altitude. <S> The relationship of pitch and power would be even more confusing, as pitch would no longer consistently relate to gravity, and therefore no longer consistently relate to power. <S> Passengers typically like a smooth and level flight. <S> Airliners flying over mountains would have a wildly changing pitch indication, despite flying "straight and level. <S> " If an aircraft wanted to fly level with respect to the ground, it would require steep climbs and descents in these areas. <S> Since air density changes with height above sea level, not the ground, the aircraft's performance would continually change as it stays level with the ground. <S> If a pilot is concerned about hitting the ground, there are many better ways to avoid that . <S> Traditionally, charts and navigation will allow a pilot to avoid terrain. <S> Technology like radar altimeters have also helped, which shows the pilot how high they are above the ground. <S> Newer systems allow things like synthetic vision if the terrain is not clearly visible.
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Pitch is determined with gravity, which always 'points' to the center of the earth. An airplane needs to be oriented to a frame of reference which does not change depending on altitude or the elevation of the ground, this is so the pilot will be able to judge the angle of the wing through the air flow.
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What are the advantages of a Trimmable Horizontal Stabilizer? What are the advantages of a Trimmable Horizontal Stabilizer (THS)? For example, a THS is used on some Airbus and Embraer aircraft. What is the most important advantage, and why don't some other successful airliners have this type of horizontal stabilizer? Image used under CC BY-SA 3.0 ( Source ). Depicting the right side THS on an ERJ-170 Note: A Trimmable Horizontal Stabilizer (THS) differs both from a Stabilator and a horizontal stabilizer with a trimmable Elevator <Q> The main advantage is smaller elevator deflection angles. <S> This comes handy in two cases: <S> When high-lift devices are deployed, the center of pressure on the wing shifts backwards by up to a third of wing chord. <S> Fowler flaps add wing area aft of the trailing edge, and slotted flaps are able to generate high suction peaks. <S> The result is a massive change in trim, and the empennage now has to generate generous downforce. <S> Changing the lift on the empennage by elevator deflection alone will exceed the maximum practicable deflection angle and leave no margin for control. <S> By adjusting the stabilizer incidence, the elevator can be held near its neutral position and has reserves for control. <S> In transsonic flight the elevator might not always have a linear characteristic. <S> The contour break due to an elevator deflection induces shocks which in turn lead to flow separation which reduces the control effectivity and can even reverse the control characteristic. <S> Since the transition from subsonic to supersonic flight shifts the center of lift backwards, the empennage needs to add downforce when the aircraft accelerates in the transsonic speed range. <S> An elevator deflection might not be able to produce the desired lift change, and only adjusting the stabilizer such that the elevator can be held neutral can restore trim and control effectiveness. <S> Older airliners from the propeller age had lower wing loadings and less powerful flaps. <S> The center of lift on the wing changed less with flaps, so a fixed stabilizer was sufficient. <S> But once the wing loading goes up to jet levels, and the wing is fitted with slotted fowler flaps , a moveable stabilizer is unavoidable. <A> Trimmable horizontal stabilizers (THS) are found in majority of airliners and large transport aircraft (like C-17 globemaster III, for example). <S> They are usually part of the trimming system of the aircraft, unlike the elevators, which are controlled by conventional pilot inputs (like yoke etc.). <S> If the stabilizer is not trimmed, the (human or auto)pilot has to continuously adjust the controls to prevent the aircraft from pitching up or down more than required. <S> Aligning the elevator with the stabilizer reduces drag. <S> The decision to use a THS (or not) depends on the design. <S> For example, the BAe 146 had a fixed tail plane in order to reduce complexity (achieved in part by the elimination of leading edge slats). <S> The THS does add more complexity to the system and has been involved in a few accidents, like the Alaska Airlines Flight 261 and China Airlines Flight 140 . <S> The stabilator or all moving tailplane is entirely different (with no elevators) and is mostly used in supersonic aircraft. <S> It is used mainly to overcome the problem where elevator becomes unusable due to shockwaves produced by tailplane and the problem of Mach tuck . <S> Combat aircraft to use them as they create a large pitching moment for lesser control effort. <S> Also, they are used for roll control via differential movement. <S> In civil aircraft, Lockheed L-1011 Tristar used stabilators. <S> Image from tristar500.net <S> It is also used in some GA aircraft (like Piper Cherokee); the strong control response of the stabillator can result in overcorrection- <S> this is overcome in part by using an anti-servo tab. <A> There are 3 reasons for the existence of a THS. <S> The large speed range of jet airplanes. <S> The large range of CENTER of GRAVITY that is possible. <S> to reduce the drag produced by the tailplane especially during cruise, thus improving range significantly. <A> Some EASA questions for ATPL mention the fact that stabilizer trim is less sensitive to flutter when compared to elevator trim <A> There are two basic advantages to a trimmable stabilizer: greater trim range than other methods. <S> less drag than other methods. <S> These advantages are most significant in large airliners, supersonic planes and those rare tailless wings with washout which "put the tail at the ends of the wings". <S> Other answers expand on some of these applications. <S> The downside is increased structural weight, as the structure supporting the whole stabilizer is very small yet must be strong and rigid in two axes while pivoting about the third. <S> So airliners that can live without it <S> are usually happy to do so.
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The THS offers some important advantages like: The required elevator deflection angles are smaller in case of trimmed aircraft and the system has full elevator deflection angles at extreme trim angles. It allows for a wider range of c.g. movement compared to the elevator-trim tab system. The large trim changes with changes in the wing configuration, slats flaps etc.
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