Is it possible for ATC to see who’s transmitting on the radio on their radar? I don’t think ATC currently has the capability of seeing who’s actually transmitting on the frequency.

If technology permits (probably by making a connection between the radios and the transponder), would it be helpful for controllers to be able to know the actual aircraft that’s transmitting on the frequency through their radar?

Does it also have the possibility of eliminating the requirement of saying the callsign after each transmission (might help in extremely busy airspaces)?

The visual aspect would be similar to how the “ident” feature works (like seeing a little “TX” when someone is transmitting).

A version of this has been implemented in some areas, such as the Maastricht Upper Area Control Centre, using radio direction finding equipment.
The EUROCONTROL website provides an explanation of the system, including an image of how it appears on radar displays:

Using triangulation software, the Radio Direction Finder, recently deployed throughout MUAC’s international airspace (the upper airspace of Belgium, the Netherlands, Luxembourg and north-west Germany) calculates accurately an aircraft’s position on the basis of its radio transmissions.
In densely occupied airspace, the Radio Direction Finder assists the controllers in rapidly identifying which aircraft is transmitting on the frequency.  This is particularly useful in MUAC’s sectors where controllers handle up to 25 aircraft at any one time, and is a prerequisite for the implementation of the free route airspace, planned at the end of the year. The origin of a voice transmission appears clearly on the controller’s integrated Human Machine Interface and is totally independent of conventional radar- and GPS-based aircraft localising techniques; this feature contributes to reducing call sign confusion, read-backs from wrong aircraft or crossed transmissions.


How come nobody survived Air Moorea 1121, yet other people have survived crashes from altitudes more than 90x higher? Air Moorea 1121 crashed from no more than 400 feet, yet people have survived far more awful disasters, such as UA232 or JAL123.

I'm guessing you consider your examples to be crashes from "90x higher" because the initiating events happened at high altitude. This extra altitude was actually a good thing in these cases, because while the pilots lost most control of the aircraft, they were still left with partial control. The extra altitude gave them plenty of room to figure out what was wrong with the airplane and how to control it with what was still working. This allowed them to end up in more of a crash landing rather than just a crash. In airliners that really do crash from higher altitudes, there are no survivors.

United 232 was more of a crash landing. Although the hydraulic systems were lost, the plane was still trimmed for level flight and the pilots could use the remaining engines to control the plane. They had plenty of altitude and airspeed at the time of the engine failure to get the plane under control and figure this out. This resulted in the crash landing where about 2/3 of the people on board survived.

Japan Air 123 was similar in that the aircraft lost hydraulics but they also lost most of the vertical stabilizer. Again, this happened at a higher altitude which gave the pilots room to react to the issue. The pilots still managed to fly the plane for a while but ended up crashing into the mountains. The survival rate was less than 1% though this was partially due to delay in the rescue operation.

Air Moorea Flight 1121 lost its elevator control cable. While the pilot could have used trim to control the aircraft's pitch, the airplane initially entered a dive and 400 feet was much too low to recover from this. If the cable had broken at a much higher altitude it's possible the pilot could have regained control.

Another point to remember is that in a large airliner like the DC-10, the passengers have a lot around them to cushion the impact. In a small plane like the DHC-6 this isn't the case. A crash into the water also results in a much higher impact, and any survivors would have to be able to swim free to the surface.


Has there ever been an airliner design involving reducing generator load by installing solar panels? Has there ever been a trial/project/design, in which solar panels were incorporated in the design of a commerical airliner (e.g. on the wings), with the aim to reduce fuel consumption by lowering the generator workload?

If no, why not?

If no, why not?

While I can't say categorically that it's not happened, I'm pretty sure.

Solar radiance is approx. 1kW/m^2. A 737 has approximately 100m^2 wing area. Solar cells are approximately 20% effective.

If you covered the entire wings in solar panels, that would work out to 20kW of electrical power at best. At night, it would be close to zero extra power.

Jet fuel contains ~43MJ/kg of energy. 20kW is 20kJ/s. For a 2 hour flight, the total energy produced would be 144MJ, or comparable to energy in 3-4 kilograms of jet fuel.

Turbines is not 100% efficient, so let's say that with all losses in engine, 25% of the power in the fuel is available as electricity. That means you'd need 12kg of fuel to provide the same amount of electricity as the solar panels.

12kg of fuel. That's probably far less than the solar cells will weigh, probably by a factor of at least ten. In addition, the you don't have to carry around already burnt fuel, unlike solar cells, which you will have to carry around.

Edit: I found another answer on this site, that claims extra fuel use is on the order of 0.125kg/kWh. I don't know if that's correct or not, nor do I really care. It doesn't change the conclusion, it only makes jet fuel even more favorable.

In short the amount of power provided by solar cells is tiny compared to the energy contained in jet fuel. And that doesn't even touch on the mechanical requirements of a wing...


How are engines mounted onto wings? I've heard that the engines on a commercial air transports are typically mounted with 2 or 3 bolts. Is this true? If so, how big are these bolts and what are they made of?

I'm optimizing a bolted joint for my FEA class, and I'd like to check my results against reality.

PS: The Factor of Safety on such a bolt would be nice too!

On Sunday 4 October 1992, El Al Flight 1862 crashed into a suburb of Amsterdam after the right inboard engine separated from the wing and took part of the wing and the right outboard engine with it.

The separation was caused by fatigue fracture of the fuse-pins that connect the engine to the aircraft. The engines of the Boeing 747-200 are joined to the wing by four fuse-pins.

In the investigation report you can find detailed information about the construction that mounts the engine to the wing. Especially sections 1.6.3, 1.6.4 and 1.16 are of interest to you, although I recommend reading the entire report if you have the time.

Source: Raad voor de Luchtvaart, document AAR 92-11

Source: Raad voor de Luchtvaart, document AAR 92-11


Does an accelerating airplane also start climbing? Assume that an airplane is flying level. If I understood correctly in this situations there are four forces acting on it: weight, thrust, drag and lift.

Lift depends on air density, airspeed, wing area and lift coefficient. In the situation described above all of these parameters are constant with the exception of airspeed which can be changed by pilot. So when increasing airspeed lift increases too which makes sense because that seems to be how planes take off.

However when you watch footage of airplanes accelerating (for instance when a fighter turns the afterburners on) they seem to be able maintain altitude.

At this point I see three possibilities:

The airplane doesn't climb or climbs very little because the pilot simultaneously compensates.
I have the wrong impression and the airplane does climb.
My reasoning above was wrong and there's actually no reason for the airplane to climb further.

So which one is it?

You assume that three of the four forces are constant. This is not quite right: Only the mass is given, all the other forces are variable.

Thrust $T$: Changes with throttle setting. Also, thrust can vary with flight speed $v$ in a way that can be expressed as $T \propto v^{n_v}$.
Lift $L$: Depends on speed and on angle of attack $\alpha$, as in $L \propto v^2 \cdot (\alpha - \alpha_0)$. The accelerating airplane is held level by gradually reducing the angle of attack, such that lift exactly equals weight. The elevator is the instrument for controlling angle of attack.
Drag $D$: Like lift, drag depends also on speed and angle of attack: $D \propto v^2\cdot (\alpha - \alpha_0)^2$

Your option a is the correct one: The pilot compensates by adjusting the angle of attack by gradually pushing the stick forward. If he would keep the stick (and consequently the elevator) unchanged, the airplane would climb.

Now it might be opportune to introduce the concept of specific excess power ($SEP$). This is the extra power available to the pilot, related to the aircraft weight to make it comparable between airplanes. $$SEP = \frac{P_{eff}-D\cdot v}{m\cdot g}$$
where $P_{eff}$ is the effective power: $P_{eff} = T\cdot v$. When the pilot commands more thrust than needed for level flight, the excess thrust can be either converted into kinetic energy (speed) or potential energy (altitude). If you look at the units, $SEP$ is a speed. It tuns out that it is the possible climb speed available if flight speed stays constant: $$SEP = v_z$$
In reality, the practical climb speed is smaller because the airplane needs to speed up when climbing to compensate for the decreasing air density.

The possible acceleration is almost as easy to calculate from the specific excess power: $$\ddot x = SEP\cdot\frac{g}{v}$$

Of course, a mixture of both is also possible, as is trading in one for the other. By adjusting the elevator and with it the flight path, the pilot decides what happens.


What is the maximum weight on the main gear of a large aircraft at rotation and touchdown? For a large aircraft like a B747 or A380, how much does the weight on the main gear increase when the nose gear is in the air? I mean, in these two cases:

What is the maximum extra weight on the main wheels when rotating at maximum takeoff weight, with the nose wheel off the ground?
What is the maximum extra weight on the main wheels when touching down at maximum landing weight, with the nose wheel off the ground?

There's more weight on the main gear when the aircraft pushes back from the ramp and is taxiing than on the takeoff roll, due to the lift generated from the wings. When the aircraft rotates the higher angle of attack generates enough lift to 'offset' the aircrafts weight and it takes off.
The most weight a main gear set will take will be on a firm landing at max landing weights (or above in an emergency). On the 737 there is a 'hard landing' G limit of (i think) just over 2G. So in theory temporarily on touchdown the main gear between them are handling twice the aircrafts weight.

As an example for the 737:
MTOW 77 tons.
MLW 65 tons.
4 main gear wheels.

heavy take off = 77/4 tons when parked ready to push back, reducing to 0 on rotation.
ie roughly 20 tons per wheel and tyre.

adding in landing G forces...

firm landing (but in limits) = (65*2)/4 tons on touchdown, quickly reducing back to 65/4.
ie roughly 32 tons per wheel down to 16 when parked up.

emergency landing after take off at MTOW = (77*2)/4 tons at touchdown. 36 tons per wheel!


What does "traffic in position..." phrase mean? Recently heard the phrase "traffic in position..." issued by controller to one of the pilots, just wondering, what could it mean?

The phraseology in the question is incorrect.

If the planes on on the same runway without ASDE-X, the aircraft departing will be given:

  DELTA 2-7, RUNWAY 1, LINE UP AND WAIT, BOEING 7-2 6-MILE FINAL

The arriving aircraft will not be given a landing clearance until the holding aircraft has departed, but it will be told:

  AMERICAN 4-2-9, RUNWAY 1, CONTINUE, TRAFFIC HOLDING IN POSITION

If the planes are on different runways, it would be:

  DELTA 2-7, RUNWAY 1, LINE UP AND WAIT, TRAFFIC LANDING RUNWAY 19

and the other

  AMERICAN 4-2-9, RUNWAY 1-9, CLEARED TO LAND, TRAFFIC HOLDING IN POSTION RUNWAY 1

Source: Air Traffic Conrollers Handbook, Section 3−9−4. LINE UP AND WAIT (LUAW)


Why isn't cabin air quality in airliners directly monitored with sensors? Airliner air conditioning systems refresh the cabin air volume every couple of minutes. A portion of it is filtered and re-circulated into the cabin, however AFAIK there are no direct cabin air quality sensors on board, only pressure and temperature sensors. This question and this question on this site are related.

When researching for an answer to the oxygen question, I came across the surprising research result from this site: carbon dioxide levels in the first column are pretty reasonable, but oxygen content in the second column is around 12%,  a bit over half of the normal percentage.

A report on fumes and smoke events in Australia shows that these are rare, but that often there is not a direct cause found. Would the fumes be detected by human smell only?

  Many fumes/smoke notifications to the ATSB are followed up by a maintenance inspection that does not find a potential source or defect causing the fume/smoke, in which case an Service Difficulty Report would not be submitted to CASA.

Airliners do have smoke detectors on board. A Google search reveals that there are cheap key hangers for sale that detect carbon monoxide. Oxygen and carbon dioxide percentages can be easily monitored. My question is: why do aircraft not contain sensors for direct monitoring of the quality of the cabin air that passengers breathe?

There is no FAR or CS demanding that requirement.

I have worked on a system an "aeronose" to detect contaminants , and it worked,we did a trial I installation in an A320 but there was no legal requirement and therefore no airline interest.


Is there a practical carbon-free jet fuel? For example, when I want to use a small turbojet or low bypass turbofan as both the APU and bleed air supplier for blown flaps, ailerons, elevators, (like the ShinMaywa US-2 amphibious plane) and rudders, (and hot wing deicing) there's a lot of internal ducting, and a large number of them are quite narrow, so having soot in them is like having thrombus in capillaries, so it's best that it doesn't contain so much as a single carbon atom in it.

EDIT: OK, the small engine mentioned above is used as a gas generator, not for thrust, that's the main engines' job. For the sake of the argument, let us assume the main engines are not available for bleed air like in real-life large airliners because they are say mounted on gimbals in a tilt-turboprop. If this sounds artificial, how about having a complete set of blown surfaces so the tilt-turboprop can have control authorities in pitch, roll, and yaw at airspeed 0 knots, i.e. when it's taking off vertically. Being a tilt-turboprop means it can not have helicopter-like variable pitch propellers like the V22 Osprey and has to rely on external measures for attitude control.

EDIT: It doesn't matter how weak the alternative fuel is as long as it can support the small jet engine's N1 RPM. It is only for the small engine.

A different fuel is not necessary. Even the most extreme experiment in diverted jet engine output, the Hunting H.126 did not divert its exhaust flow, it just tapped off compressed air. Its takeoff speed was 52 km/h. All aircraft need forward thrust, and with modern high-bypass turbofans you can get massive amounts of compressed air that's more than enough for blowing any surface you want. The BAe Harrier is a good example; the front nozzles of the Pegasus blow compressed air and match the thrust of the jet exhaust in the rear nozzles.

Fuels roughly fall into 3 categories:

hydrocarbons (everything from methane to jet fuel and diesel). They all contain carbon. Some leave less soot than others: methane is relatively clean. But it's a gas at room temperature, which makes it difficult to store (you need heavy high-pressure tanks).
Hydrogen. Clean, but very difficult to store (needing even heavier high-pressure tanks than methane), and explosive in a wide range of circumstances.
Oddballs like hydrazine and hypergolics. They're all nasty, toxic fuels that require specialized handling which make them unsuitable for civilian use. Hypergolics are two-part fuels that spontaneously combust when in contact with their counterpart.

Some more details on hydrazine:

  Hydrazine is highly toxic and dangerously unstable

Anyone involved in fueling a hydrazine-powered vehicle has to wear a full Hazmat suit. That alone makes it difficult to use a hydrazine-powered aircraft on most airfields as it'd disrupt normal operations.

Hydrazine is also inefficient. For jet fuel, you can pull the oxidizer from the surrounding air. Hydrazine has a specific impulse of 220 s, while jet fuel has a specific impulse in the region of 350 s. So you have to carry 350/220 is 1.5 times more fuel to do the same work.

The exhaust products of hydrazine are extremely flammable (hydrogen). You could burn that in a jet engine, which would significantly increase the specific impulse. Hydrogen is a bit finicky, but hydrogen-fueled aircraft have been tested.


What is this intake bottom the wing of C-5 and why is it placed there? There are two intakes bottom the wings of C-5. What are those and why are they placed there?

This C-5 cutaway indicates it's a "Heat Exchanger Inlet (76)" or "Ground Cooling Fan (78)"
EDIT: Upon closer inspection of this higher-res image, it may be the intake for the Ground Cooling Fan.


Are nearest VOR stations always tuned to? I am flying under IFR.

My current leg route is Z401. I am between TIPRU and VOR VLM (VLASIM). I am on inbound radial 304° VLM:

This is an RNAV route. But let us imagine it is non-RNAV and I am flying a non-RNAV plane.

On the NAV1 receiver I tuned and checked I have VLM.

I have a spare NAV2 receiver. Should I tune on NAV2 the nearby VOR VOZ (VOZICE)? If yes, why?

I assume not, unless I am flying  RNAV plane which will utilize it as source of position. Even then I am not sure if I should tune it.

Your example is a bit confusing because it seems to be a GPS-based route, it may be better to a look at a more 'realistic' one, where you're using only VORs for navigation. The reason to tune a second VOR is to cross-check your position, either by crossing a specific radial or perhaps by using DME (for a VOR/DME or VORTAC). If that's useful to you then you should definitely tune it.

Here's a US example. Let's say I'm flying eastbound on V241 from the SJI VORTAC following the 081 radial outbound. I've tuned the SJI VORTAC on NAV1, but I have no DME or GPS:

ATC tells me to "report LOXLY", which is 29nm from SJI but I have no DME so I can't report based on that. However, LOXLY is at the intersection of the SJI 081 radial, the BFM 052 radial (BROOKLEY VORTAC) and the NUN VOR 305 radial. That means, on NAV2 I can tune either BFM 052 or NUN 305 and when both the NAV1 and NAV2 needles (as it were) are centered, I'm at LOXLY. You might also notice that the PENSI intersection to the east is defined not only by VOR radials but also by the localizer on runway 17 at KPNS.

In this example, two VOR radials are needed to identify the fix (assuming no DME and no GPS) but you could tune a second VOR even if it isn't required for a named fix, to manually check your progress along your route (see chapter 7 of the FAA Instrument Flying Handbook). You can also time how long it takes to cross two radials on the off-airway VOR and use that information to calculate the distance to it, as a sort of 'manual DME'.

Having said all that, if you don't need or want position information from the second VOR there's no reason to tune it. But especially if GPS is your primary navigation method it wouldn't hurt to stay familiar with them as a cross-check and even as a fallback in case GPS becomes unavailable (which is not unusual).

(As Carlo Felicione mentioned, you could use just one NAV radio and switch back and forth between two VOR frequencies, but that's rather awkward and not something that most people would want to do in normal circumstances.)


How to fill out IFR flight plan for manned helium balloon flight into class A airspace with no predetermined route or destination and less crew? Per FAA regulations, an IFR flight plan must be filed before going above 18,000 feet MSL as this is class A airspace.  How do we fill out the IFR flight plan if the destination landing site and the route taken of the lighter than air aircraft are unknown, and one of the crew members will be disembarking in flight and parachuting down?

Note: This operator does this on a regular basis.  They use manned helium lighter than air craft, not hot-air balloons as answered on previous questions so this question is not a duplicate.

I just helped a University launch of an unmanned balloon and I used an E-6B for completing the NOTAM for the launch.  GPS and tracking showed that the estimated path deviated from actual path by small numbers.

We were advised that no IFR FP was required for a small (~3kg payload) unmanned balloon, so none was filed.  We did advise center at launch, and with updates on the way up and down.

Addendum #1
After thinking about this, there are really two parts to this question. The part about route prediction I have addressed in part.  Keep in mind that gliders file IFR and they have little ability to climb higher on demand. The FP can provide an area, just like an IFR FP or and IFR clearance for aircraft can have block airspace, or even routing at pilot's discretion.

The other issue is whether a FP is needed. For manned balloons in controlled airspace, operating under IFR, the answer is clearly yes. But again, there is allot of latitude in what a FP can specify, and what clearance might be issued.

For unmanned balloons, which is where I have more experience, the rules are quite different.  And size is limited.

But again, the FAA can issue waivers, and they are done regularly for all kinds of flights. So just because the rules prohibit or do not allow, doesn't mean that a waiver could be issued to allow.


Do pilots get full credit hours when they fly double or augmented? In commercial airlines, in some very long flights as far as I know they require double cockpit crew sets (2 pilots, 2 co-pilots) to operate.

Do both crew sets get the full credit hours for these flights? Or do they get 50% only as they only operate half of the flight?

It would be nice if there's some sort of airline policy to back up the answer.

It really depends on the individual Air Regulations of each country, and the union contracts of each airline. Pilot union contracts are often more restrictive than the Air Regs of the country they operate in.

In my experience, North American airlines with "formula pay", both sets of pilots log the entire flight, because they are paid for the entire flight, even when they are sleeping in the bunk.

Other airlines who pay monthly salaries, with bonuses for extra overtime hours, do not credit the pilot for time in the bunk, and they tend not to log those hours either.


Are there runways that are numbered only on one side? For all runways I've known or seen, they're numbered on both sides, with the number on the opposite direction differ by 18.

Are there runways that are numbered only on one side? I.e. due to certain constrains, the runway can only be used in one direction and never the other.

EDIT: I'm looking for runways where the aircraft is always pointing at the same direction. E.g. only runway 9 is available, you can never use runway 27 for whatever reason.

A runway that is blocked on one end will still have two numbers, since you'd land at one direction and takeoff the other.

Yes, there are runways numbered on only one side.

For example, the third runway in the Frankfurt Airport (18, Runway west) is used only for takeoffs (to the south) and not for landings. Hence only number 18 is used. The other runways are used for both takeoffs and landings and are numbered 07C/25C, 07R/25L and 07L/25R.

Thomas Römer/OpenStreetMap data [CC BY-SA 2.0], via Wikimedia Commons

This restriction is due to the fact that it will interfere with the traffic in other runways.

Number 36 is not painted.


Is it possible to interchange different of fuels for turbine engines? There are a few types of fuel for turbine engines, for example Jet-A, Jet A-1 and Jet-B.

Is it safe / practical to interchange these types of fuel for a generic turbine engine?

If we are talking generic turbine engines then the answer is yes. Turbine engines will run on a wide range of fuels, I personally have flown a Military Helicopter, that normally runs on Jet A1 using AVGAS instead. The flight manual limited it to 10 hours of operation on AVGAS. Interestingly the same flight manual had other fuel types listed such as Deisel, and automotive gasoline.

The only difference I noticed on the different fuel was a slightly higher exhaust gas temperature for a given power setting.

Heavy duty industrial turbines are often run off crude oil!


How to calculate the drag on an airfoil from momentum equation (Fundamental of Aerodynamics 5th edition, J.D.Anderson)? If you got the book, please read 2.6 section (page 135). Here is my sumary of this section:

An airfoil in a wind tunnel (wingtips were butted against both sidewalls of wind tunnel). The control volume is 'abcdefghia', it has unit depth in the z direction (perpendicular to the page). Through some steps that you can read from pages, we got:
$$ Drag\space on \space the \space airfoil =  -\unicode{x222F}_{ai+bh}(\rho \vec V.\vec {ds})u $$

In experinment, how can we know where the line bh is, how long it is..?

In the picture above, can we move line bh backward (to the right) ?

How big is the wind tunnel or how far from top to bottom walls of the wind tunnels (with given airfoil)is in oder to have the lines ab and hi ?

Do you feel this method is very inaccurate with a lot of negligibly and pitot rake thing (page 141) ?

@Peter:
Thank you, nice to hear that !! . Actually, I thought I understood this section until I face the problem 2.2 at page 198 (by the end of chapter 2). I reviewed this section and a lot of questions arised. First, sorry because English is not my mother language.

1st question: I really have no idea where the line bh is (both in vertically and horizontally) and how is the length of bh ?.

2nd question: Suppose we already have the line bh located properly. My physical feel tell me that the line bh can move backward and the velocity gradinent $ u_2 $ = f(y) stay the same. But imagine in real life, if we move the line bh far enough, the velocity gradient $u_2$ will be uniform and equal the freestream velocity $u_1$ !!

About the third question, I think: we must have top and bottom walls of the wind tunnel that the pressure over them is equal to the free stream pressure, I mean: move them far from the airfoil in vertical direction so that the pressure over them is uniform and equal to freestream pressure.

4th question: I still had no idea because I never use my hands to do these kind of experiments, but my instinct tell me it will have a lot of errors.
My word maybe too dumb but I'd like to learn what people do in real experiment.

those are some great questions. I will try to be very concise.

Firstly, regarding to the line ‘bh’, there is no fixed length you can calculate. Ideally you want to make sure you get measurements of the entire region where there is a momentum loss. Therefore, you seek to take measurements until you reach a point far enough so $u_1=u_2$.

Note that this momentum loss is directly related to the size of the wake, thus the length of ‘bh’ would be determined by the Reynolds number, separation point, incidence, etc. One common problem, especially at high AoA, is that the rake is so large that the wake rake does not cover this ‘bh’ line. This would mean that the momentum loss measured, and therefore the drag, is smaller than it is physically.

With regards to the distance from the trailing edge: You must avoid being too close since phenomena like recirculation bubbles or the pressure difference between the upper and lower part of the aerofoil would basically ruin your measurements (the velocity is not normal to the probes , etc). On the other hand, the flow in the rake induces an additional momentum loss, thus if you take the measurements farther aft, you would be also measuring this contribution, apart from the drag of the aerofoil. In addition, the size of the wake increases, leading to the problems mentioned in the first question. Typically, a distance of approximately one chord is used for the experiments.

The next question is related to a different topic, wind tunnel corrections. From the picture, due to the momentum loss, using the equation of continuity, you will always have $ai<bh$. What is defined as ‘”streamlines far away from the body”, lines ab and hi, are assuming constant pressure and velocity. If you add the wind tunnel boundaries, imposing the streamlines to be parallel to the surface of the tunnel, there would be an acceleration of the flow, $u_1<u_2$, thus this p=p_infinity will no longer be achieved.

This change in the velocity profile will affect the measurements at the rake, therefore some corrections are needed. The bigger the wind tunnel is, the smaller the corrections are. In the book you will find a nice chapter about this.

Regarding to the last question, unfortunately I don’t have the book anymore… But this method has indeed some drawbacks (in addition to the ones aforementioned). Firstly, the pressure drag is almost neglected. Moreover, measuring the turbulent flow at the wake is difficult and leads to errors  if the velocity is not normal to the probe (this happens especially at high AoA).

Hope this has helped!


Did Airbus add an audible alert when the autopilot partially disengage after the crash of Aeroflot Flight 593? The major reason that lead Aeroflot Flight 593 to crash was the partial disengagement of the of autopilot (by the pilot's kid who was in the cockpit) which could have been avoided if the pilots were more familiar with the Airbus 310-100 or there was an audible alert.

Do new Airbus aircrafts have an audible alert in such cases now? were the old ones some how altered to implement this?

All Airbus aircraft from the A320 onwards currently do not have an method of disabling lateral or pitch control without the full disconnection of the autopilot. In the case that one of the controls fail, the autopilot will also disconnect.

In the case of the autopilot disconnecting fully, Airbus aircraft have an audible "cavalry charge" which sounds for 3 seconds if disconnected normally, and continuously (until cancelled) if due to a failure or a non-standard method of disconnecting the autopilot.


Why are many runways used just for departures/arrivals? At LAX and many other large airports they designate certain runways for landing or takeoffs Normally. Why is this? I think its inefficient use of available runways.

There are many constraints on runway usage, and sometimes it's not the runways themselves but the protected airspace for approaches that determines what "normal" is - as well as airport design, noise abatement, wind, aircraft type, taxiway configuration, departure routes in use, etc.  It is typically more efficient (= less delay) to run all of one type of operation on a runway: you can launch more departures faster if you're not trying to land other aircraft in between them, so if there is a major departure push on, the tower will try to dedicate at least one runway to departures only.  Same thing for arrivals: landing aircraft need to be spaced further apart if there are departures going out on the same runway, and if a departure can't roll as soon as expected (for example, if the last arrival doesn't clear the runway as quickly as possible), the next arrival may have to go around because the next departure is still sitting on the numbers.  Having said that, unless the airport management puts specific restrictions on runway usage, ATC is free to shuffle the deck any way they see fit and land/depart from any appropriate runway if operational needs require it.  Pilots also have the right to request a specific runway for THEIR operational needs, and ATC will accommodate the request even if it isn't exactly their current plan.

LAX generally lands on the outboard runways because the final approaches are further apart, and taxiing is less complex if the departures go off the inboard runways.  That doesn't mean they never do anything else, but that's kind of the "normal" case.


How will flying through mountains cause altimeter problems? There is an old warning on mountain flying that wind flowing through a narrow valley will cause Venturi effect, thus causing a drop in static pressure and making our little Cessna fly lower than indicated, possibly hitting some hidden mountain peak. I'm certain I know the answer to this one, but I'd like to hear someone explain it better, so here is my question:

  You fly a Cessna 172 level at FL50 (pressure altitude) with a huge
  40kts headwind. You need to traverse a narrow valley passing between
  two huge peaks on either side. Will your airplane fly at a constant
  true altitude in a straight line, or will the Venturi effect caused by
  the wind and the valley cause our aircraft to sink while passing
  through the valley?

.

You basically answered the question yourself already.
Venturi states: the sum of pressures in a system stays constant.
The system is the valley and the pressures are the air (static pressure) within the valley and the wind flowing through it (dynamic pressure).

Static Pressure + Dynamic Pressure = Total Pressure
If the wind flows faster, we got higher dynamic pressure. Since the sum stays constant the static pressure has to fall as a consequence.
Of course, then, all pressure levels shrink under lower static air pressure as they would do under cold temperatures. Flying at a constant pressure level results in following these shrinking levels and eventually end up at a lower true altitude.
That's the main reason why your true altitude is lower than your indicated.

If you knew the actual static pressure in the valley, you could adapt your altitude by the rule of thumb: per 1hPa: 30ft

So answering your question: if the venturi effect reduces static air pressure in the valley, the above stated applies.


For length in aircraft design, and in weight and balance manuals, what measurement unit does Airbus use? What length measurement unit does Airbus use for aircraft design and in their weight and balance manuals? Meters or centimeters?

Possibly they use both like Boeing does for, say, feet plus inches for overall length and wingspan but just inches for a position along the longitudinal axis for crew, pax, and cargo locations? For example 1821.0 inches for the lower hold aftmost ULD position on a 747.

Structures are soft metric. Airbus uses inch hardware so some measurements make sense in inches but are drawn with an ugly mm number. The coordinate system is in metric.

The rest of the aircraft is hard metric. For example, MTOW and fuel capacity is in a nice number of kg.

Documentation and instrumentation is localized according to the operator. Mass, as in fuel, can be switched between kg and lbs on ECAM, and all the manuals and W&B will follow.

There's a few units that aren't localized, most notably pressure is always in PSI and engine oil is always given in quarts (probably since it comes in quart cans).


Does taxiing time gets considered in a pilot's flying hours? Basically the title. This could be referenced to US or European rules.

In the US, taxi time can be logged. 14 CFR 61.51 says the pilot must log (emphasis mine):

  Total flight time or lesson time.

And 14 CFR 1.1 says (emphasis mine):

  Flight time means:

  (1) Pilot time that commences when an aircraft moves under its own
  power for the purpose of flight and ends when the aircraft comes to
  rest after landing; or

  (2) For a glider without self-launch capability, pilot time that
  commences when the glider is towed for the purpose of flight and ends
  when the glider comes to rest after landing.

Note that in reality, general aviation pilots (I don't know about airline pilots) usually just log whatever is on the Hobbs meter, which may include some time sitting still on the ramp doing post-startup checks, setting up avionics etc. That might not be strictly correct per the regulations, but absolutely no one cares.

This question is closely related.


Is flying bad for your health? I've always wondered if flying is bad for your health mainly because when you fly the air pressure changes a lot and i've always thought that, that can lead to negative side affects. So can someone please tell if there are any negatives to flying which may affect your health. And are there any reasons of why flying is good for your health??

There has been some reports which have noted a higher than average incidence of certain cancers in aircrew. The reports are somewhat inconclusive

  Overall, the reports suggest that pilots are at increased risk of malignant melanoma, non-melanoma skin cancer, and possibly acute myeloid leukemia, and that cabin crew are at increased risk for breast cancer and malignant melanoma. However, the question remains as to whether the observed excesses are due to occupational exposures or non-occupational factors, such as reproductive history and lifestyle

Source: British Medical Journal

Research is ongoing.


What position was this photo of a jet engine taken from? From that aviation photographer, I saw that beauty:

Having in mind the jet engine I would see, let's say as a normal passenger, I am not really able to understand from where I am looking at that engine. Do you?

Could it also be that I am looking in an inner part or something (which might explain the confusion)?

PS: I tried using the m character to medium-size the picture, but no luck.

Based on the Linkedin page, this is a portion of an IAE V2500 turbofan.  Looking at the following images of the engine (in modules and awaiting final assembly), I can pick out a view that is really similar to the image you have up, namely the module of the engine in the bottom right hand corner of the image or the one in the background, behind the fan section that is near the center of the image.

Looking at a cutaway of the V2500 (below), you can pick out similarities between this section and the engine if viewed from directly behind the fan.

Based on this, a schematic of the V2500 engine modules (below), and the insulation laid out in the bottom of the photo that you posted, I think that the picture you found is taken from inside of the engine, directly behind the fan section and looking aft.  The only things that I'm unsure about are background (appears solid?) and perspective (looks like the engine is in a tube--fan was removed, but the shroud is still on?).


What does a white over red VASI indicate? I have found the following mnemonic's to remember Visual Approach Slope Indicator combinations:

White over White, you're high as a kite. / you'll fly all night
Red over White, you're alright.
Red over Red, you're dead.
White over Red, unsaid / you're under head

What does White over Red exactly mean? Does you're under head mean your low? I can't seem to find it anywhere.

Mnemonic Src: https://en.wikipedia.org/wiki/Visual_approach_slope_indicator

"White over red" isn't actually possible unless the VASI installation is badly off, or else if you're upside down on final.  If the top lights are white, you're above their glidepath angle, and if the bottom lights are red, you're below theirs.  With a standard VASI installation done correctly, you can't be in both places at once -- if you're above the path for the upper lights, you're above the path for the lower lights as well, and vice versa.

The "white over red" is simply a nonsense answer thrown in to some test questions in order to see who understands what's going on with a VASI system.  Most folks will remember that when you're on the proper glidepath you'll have one set of red lights & one set of white lights, but which one should be where?  As long as you understand how the lights work, you can correctly answer that red above white = on glidepath.

My best guess at the mnemonic is that they're suggesting you're "standing on your head," or in other words upside down, in order to see the lights in that position.  I wouldn't get too wound up about the lame rhyme in the memory aid.  Just know that with all white, you're high; with all red, you're low, and with red over white, you're on path.


Is there a way to calculate the difference in pitch required to reach a certain vertical speed? I am programming an autopilot for a 787 flight sim software and I've been having a problem.
I'm trying to simulate a PID that controls the pitch of the aircraft In relation to the vertical speed selected. I'm not sure how to obtain the difference in pitch required to get to a certain vertical speed in fpm and keep it stable there. Any advice and input is appreciated.

Edit:
Posted updated question on a more suitable stackexchange forum:
https://robotics.stackexchange.com/questions/16249/needed-help-with-pid-for-an-airplane-autopilot-system

I'm surprised no-one has attempted to answer this question, as it is mostly a pilot's daily job to guess a pitch change that would give a certain rate of climb. :-)

This will not be a technical answer, but I suspect some of my attempts at controlling the rate can be ported to a PID algorithm.

Keeping math aside, if you draw the lift-drag-thrust-weight diagram, there is probably a tan(x) dependency there between pitch and rate. For the small angles of pitch we are talking here, a linear dependency is good enough on the assumption of tan(x) ~ x . So basically, if I want to half my climb rate, I start by reducing my pitch to half and then I take it from there.

Secondly, the larger planes will still fly by the numbers, so I have a pretty good idea of how 2.5 deg will give me level flight at 250kts, 5 deg will give me around 1000fpm at climb thrust ,etc. I initially pitch to the memorized pitch angle and then adjust as necessary.

Short answer:

Build a table of pitch vs speed vs climb rates with climb thrust, and a table of pitch vs speed vs descent rates at idle thrust.  Assume linear dependency between pitch and rate. Adjust PID from there. Voila'!


Can ATC decide whether or not to provide tower enroute services? Recently, when I requested tower enroute service from a Southern California airport with published TEC routes, I was told by the controller that, out of courtesy for him, I needed to prefile.

If I wanted to push the issue, would the regulations have been on his side, or mine? What good is TEC if it has to be prefiled?

According to the AIM, 4-1-19-c:

  There are no unique requirements upon pilots to use the TEC program. Normal flight plan filing procedures will ensure proper flight plan processing. Pilots should include the acronym “TEC” in the remarks section of the flight plan when requesting tower en route control.

Based on that, it would seem that the TEC request was essentially equivalent to that of getting a pop-up IFR clearance. If you pre-file, the controller has all the information necessary to enter you into the system rather than asking for it over the radio. It wouldn't be legally required, but neither would the controller be required to issue a clearance if workload doesn't permit.

When using a TEC route, there is still the benefit of only talking to local controllers, and using a known routing that you're less likely to have amended.


Are there cameras which can show external components of an airplane to help pilots determine a fault? Looking at this crash - wiki - my question came up - are there passanger planes, which have real time view of external components like engines, wings and so on, which can eventually help pilots understand what part malfunctioned ? If not what would be a good reason ?

Edit: Please note that I am not looking for planes with cameras used for manoeuvring, but for such pointed towards critical components e.g. engines, so if there is a visible fault (smoke coming out of the engine) the pilots would know the exact failed component/part of it.

External cameras for diagnosing aircraft issues are not used on any current aircraft. As mentioned in another answer and question, some aircraft do have external cameras, but these are more for maneuvering on the ground.

One reason for this is that cheap, high definition cameras that can stream directly to a monitor in the cockpit are a fairly recent invention. Previously, such an addition would have been fairly heavy and expensive to add to an aircraft. As mentioned, some newer aircraft that have digital cockpit displays do have external cameras for other purposes. However, even in aircraft with cameras, they are generally not used for diagnosing issues.

A lot of aircraft issues, especially with engines, are not readily visible from the outside. Internally placed sensors are still much better at detecting issues. Landing gear in particular may appear to be extended but not locked properly. Pilots are more concerned with how functional something is. Modern aircraft are equipped with hundreds of sensors and these are designed to give the pilots all the information they need about the functionality of the aircraft. These sensors are much more simple and precise than a camera. External cameras may give a misleading picture of the aircraft's state, and decisions lean towards an abundance of caution. Unless there is some extremely obvious discrepancy, it's unlikely that a camera will be trusted over the sensors.

Of course there are still incidents such as fuel leaks and fires that external cameras would help to identify. However, the aircraft sensors should be able to detect these issues once they are serious enough. Pilots also get information from passengers/crew in the cabin, and from external observers in other aircraft or air traffic control. Cameras are also limited in where they can be placed to provide a good view of things, and how well they will perform at night or in bad weather.

There may be a general case for cameras being helpful in identifying issues, but these situations are rare enough that is is hard to justify the expense. If something is enough of a risk that you need to point a camera at it, you're better off just fixing it so it's less of a risk.


How do PPL, CPL, and ATPL compare? What are hiding under these letters?
What do they stand for?
I have read many others, but I could never understand what they mean and the pilot's career on each of them.
If possible, can anyone post a brief list and their tasks and responsibilities, please?

PPL is Private Pilot License

May fly for pleasure or personal business. Private pilots cannot be paid, compensated to fly, or hired by any operator.

CPL is Commercial Pilot License

Can be paid, compensated to fly, or hired by operators and are required to have higher training standards than private or sport pilots.

ATPL is Airline Transport Pilot License

ATPs, as they are called, typically qualify to fly the major airliners. ATPs must qualify with a range of experience and training to be considered for this certificate.
— Wikipedia


Is it normal for a Boeing 757 engine to bounce under its fairing? Earlier this week I was on a 757 flight from SFO to JFK and the right engine was bouncing under the fairing under mild turbulence, and really moving 2+ cm under moderate turbulence. Is that in any way normal or cause for concern? Here's a video of the bounce with very mild turbulence. To see the bounce, zoom into the seam where the nacelle meets the fairing: https://drive.google.com/file/d/1QpegQ0FOUhJrp8vqMrshtCdBQDyJTWO0/view

Yes, it's normal. You will see engines bounce, yaw and shake, sometimes with apparently alarming ferocity, and you might wonder whether something is going to shake itself apart.

However, the fact is that the engines bounce because they can. Their mountings - which are extremely strong - are absorbing a lot of movement and energy safely. For example, they have to be able to handle the immense thrust that the engine puts out for the whole flight.

Another thing that you need to bear in mind is that many visible parts are themselves more flexibly attached to hidden and more stiffly mounted ones that are attached to each other. So you're not just seeing movement of structural parts, but that, plus the movement of the lighter, flexible coverings.

In short, there is nothing there to worry about, though it can be unsettling to see.


Why shouldn't variable pitch propellers be operated at low speed? Aircraft with variable pitch propellers usually have a red arc on the propeller speed gauge somewhere between about 500 and 1000 rpm, often accompanied by placard like "stabilized propeller operation between 500 rpm and 1000 rpm is prohibited" (the range is slightly different in different aircraft).

What is the reason for this restriction?

The specific reasons may be specific to each propeller/engine combination, but in general it seems to be related to stresses.

According to this King Air POH on page 2-2:

  Stabilized ground operation between 400 and 1,150 propeller RPM is prohibited. Operation between 0 and 400 propeller RPM is permissible only with propeller feathered.

  STABILIZED GROUND OPERATION WITHIN THE PROPELLER RESTRICTED RPM RANGE CAN GENERATE HIGH PROPELLER STRESSES AND RESULT IN PROPELLER FAILURE AND LOSS OF CONTROL OF THE AIRCRAFT.

This is probably due to the frequency of the aerodynamic forces at those RPM's resonating with the frequency of the propeller, and getting amplified to unsafe stress levels. This is called ground resonance and is also an issue with helicopters. In addition to over-stressing the propeller blades, it can also affect the fatigue life.

There is also a discussion in this thread, and it is mentioned in this guide.

As voretaq7 mentions, fixed-pitch propellers have similar restrictions for similar reasons. Some engines include a damper that removes this restriction by damping out the resonance.


Why did the L1011's direct lift control help make good landings? In landing configuration the 1011 had what was called “Direct Lift Control” or DLC. That feature was actually pretty cool. Once the airplane was in landing configuration the spoilers would come up to a neutral position of 7 degrees. If you moved the yoke forward, asking for an increased rate of descent, the spoilers would come up to a maximum of 14 deg but the pitch would not change. If you pulled the yoke back the spoilers would move toward 0 deg or stowed, thereby increasing lift and slowing descent. The DLC worked really well and made for super stable approaches with rock solid pitch attitude and rewarded you with “greaser” landings more often than other big jets I have flown.

Source
Why does altering sink rate without changing pitch make for a super stable approach and "greaser" landing? The explanation I can think of is that moving spoilers is faster than pitching, allowing faster reaction times to errors.
EDIT: B787 has something similar

John's fine answer is correct, but there is a bit more to it:
When increasing lift by pulling on the yoke, in most airplanes the elevator moves trailing edge up, decreasing lift initially. To look at the process in detail:

The yoke is pulled, the elevator moves trailing edge up
Downforce on the horizontal tail is increased without any lift change on the wing, so total lift is diminished. The sink rate increases slightly.
The lift imbalance adds a pitching moment, so the nose of the airplane rises.
Now the angle of attack on the wing increases with the pitch angle and lift increases. Only now will the desired reduction of the descent rate kick in.

This effect is especially pronounced in flying wings, but it also is noticeable in regular airplanes. Now compare that with partially deflected spoilers:

The yoke is pulled, the spoilers close.
Lift increases without a change in the elevator angle or the angle of attack. The desired reduction of the descent rate is immediate.

The effectiveness of spoilers is limited, so this technique will not allow you to fly aerobatic maneuvers, but for landing it is perfect. Drag is increased, so the engines will have to produce a bit more thrust than with spoilers fully closed, giving you more immediate engine response, too.


Would it be a good idea to use dihedral on a biplane? My engineering class uses model plane kits to build "frankenflyers" which use parts from multiple model planes to make one plane that will carry a maximum load (pennies). I was wondering what the best configuration would be. We have three wings and three bodies. I was thinking we should use a biplane for added lift, but I couldn't find much on dihedral wings being used on a biplane. Open to criticism and ideas.

If your aircraft is meant to be a "free flight" model, meaning that it flies without any guidance from any pilot, then generous dihedral will help keep the wings level.

Even if your aircraft is meant to fly under radio control, so long as the mission is load-carrying rather than aerobatics, some dihedral will help ease the pilot workload.  You may want to mix some rudder to your aileron channel to help it turn better, otherwise the dihedral will tend to create some resistance to aileron roll/turn inputs.  If you don't have a rudder, don't use very much dihedral.  If you have only a rudder and no ailerons, use lots of dihedral.

Many full-scale (piloted) biplanes do in fact have dihedral on one or both sets of wings.  Most typically the lower wing has dihedral while the upper wing is straight, because that helps improve ground clearance of the lower wingtips, but in some cases both sets of wings have equal or nearly equal dihedral.  (See for example this 3-view diagram of the "Bristol Fighter".  The combination of a straight lower wing and a dihedral upper wing has never been used before, to the best of my knowledge-- here's your chance to be the first!


Where is a missed approach point for circling while flying ILS? In my company we have a problem that we cannot understand completely, because we  cannot find the answer.

If I don't have the runway in sight at the circle minimum (MDA) on an ILS
approach, I must immediately execute a missed approach or can I level off and maintain the circle minimum (MDA) and continue inbound until reach the MAPt by DME or timing block (don't have DME) and missed approach?
If a RVR is published in the chart, normally it is RVR at MAPt right? For ILS (precision approach) it is clear that MAP is at the DA. LOC (Non-precision approach) uses MDA at MAPt by DME or timing but for circling where is a MAPt? Use same Non-precision or use circle minimum (MDA) on glide?
If we fly ILS for circling, is it a precision or non precision approach?

Circling approaches are non-precision, regardless of how you arrive at the MDA.  When circling you'll level off at the circling MDA and use the missed approach point depicted for the approach.

If you are looking at a Jeppesen approach plate there should be a level-off and 'M' depicted in the profile view.  If you are looking at government plates the level-off and MAP are not depicted in the profile view but are still specified elsewhere.  In any case, you'll fly the localizer to the MAP and then go missed.  You'll descend either via the GS or step down altitudes to the circling  MDA and stay there until either the MAP or you are able to further descend.

RVR probably won't be listed for circling minimums (it isn't published for the chart as a whole) as they will generally be at least 1 mile or more.  Whether the visibility requirement is specified in feet (RVR) or miles, this is the visibility you need to descend out of the circling MDA.  You have the further restriction that you may not descend out of MDA until you are in a position to land.  The same familiar rules in 91.175 still apply.

In summary, fly the approach like you normally would but level off at the non-precision circling MDA and go missed at the non-precision MAP if you have no visual contact with the runway.  You do not go missed exactly upon reaching the MDA, just as you wouldn't if you were flying a VOR or LOC approach.  You go missed at the missed approach point.


Are there any planes that have ramjet or scramjet engines? Are there any planes that have ramjet or scramjet engines? If so, how did they reach the required mach speed for the engines to start functioning?

Scramjets
There's only a couple flying examples. The early Soviet-born Kholod, the HyShot series, and the recent ISRO ATV all flew small scramjet engines, although none were designed for net thrust. By far the most [publicly] successful vehicles have been the X-43A and the X-51. Both were fully controllable, independent flight vehicles (rather than just engines hanging from rockets) that produced net thrust.
The NASA X-43A hypersonic research vehicle was dropped from a B-52, then boosted by a modified Pegasus booster, and briefly flew at Mach 9.6 with a hydrogen-fueled scramjet.

Credit: NASA

Credit: NASA
The Boeing X-51 Waverider hypersonic research vehicle was also dropped from a B-52, then boosted by a modified ATACMS (an Army surface-to-surface missile), and then flew at Mach 7 with a JP-7-fueled scramjet.

Credit: USAF
The DARPA Falcon program aimed to produce a hypersonic plane that could takeoff and land under its own power using a turbine-based combined cycle (TBCC) propulsion system (NASA TBCC overivew on NTRS). Two early designs, HTV-1 and HTV-2, were unpowered hypersonic gliders, the latter was launched by ICBMs (basically reentry vehicles, like the X-41 they were probably derived from). But the next two designs, HTV-3X Blackswift (YouTube) and the final Hypersonic Cruise Vehicle (HCV) (YouTube), would have been the first reusable, hypersonic CTOL aircraft. HCV would have been able to carry a few thousands pounds of payload (eg bombs, flight test equipment, cameras) very quickly across great distances. The [HTV-3X and HCV] program was eventually canceled, but other work continues on hypersonic weapons and vehicles.

Credit: DARPA
SR-72. Lockheed Martin is developing the SR-72, an unmanned Mach 6+ ISR (recon) platform. It's meant to fly completely under its own power using TBCC, taking off with turbines and transitioning to ramjet and finally scramjet operation. A key innovation was bridging the speed gap between where turbojets stop working well and where ramjets start working well, but LM declined to elaborate how they achieved that. Their design apparently builds upon their work on the Falcon program (see above). They said they'd fly a single-engined demo before moving to the twin-engined, full-scale vehicle.

Credit: Lockheed Martin
Other ambitious unflown designs include the LLNL Hypersoar and the X-30 National Aerospace Plane. Both were large (100-200 tonnes MTOW), hypersonic, intercontinental vehicles. The SSTO-capable X-30 could launch payloads to LEO as well as serve intercontinental passenger routes. Hypersoar was also envisioned to carry passengers in one variant, perform TSTO in another, and also perform global strike/recon in yet another.

X-30 NASP. Credit: Chad Slattery

Hypersoar. Source: FAS.
Ramjets
The Republic XF-103 Thunderwarrior was essentially an early attempt at TBCC in a manned interceptor. It was a very innovative design (Mach 3-5, no canopy, periscope, crew capsule, huge radar, and internal bays for 6 large missiles, precursors to the AIM-54) but never flew.

Source. Unknown.

Source with lots of great background.
There's a variety of ramjet powered missiles
Notable examples include...
... the Bomarc. Credit: Boeing.

... the GQM-163 Coyote, a notable supersonic, sea-skimming target. Credit: DR Kirk.

... the massive P-700 Granit Source and its relatives, the P-800 Oniks and the BrahMos.

... the RIM-8 Talos SAM. Credit: USN.

... and the Sea Dart, the Moskit, the Hughes/Raytheon AIM-152 (and related ACIMD), the Triple Target Terminator, and a bunch others. Some are antiship missiles (various trajectories), some are SAMs, and some are air to air missiles. All were rocket-boosted before the ramjet took over.
Obviously the most "terrifying" was the Supersonic Low Altitude Missile of Project Pluto fame, a nuclear-armed, nuclear-powered ramjet for the 100,000 mi cruise missile. Air was blown directly through the reactor, directly heating it for thrust. Its unshielded reactor would have propelled it to Mach 3+ at sea-level and irradiated targets below it before crashing into a final target, irradiating that as well. They successfully tested two engines before the program was cancelled in favor of ballistic missiles.
Here's a fun USAF-Convair vid from 1959 explaining the concept:

Credit: USG


Is this type of wing design structurally sound? Is the simple wings
frame(spar,ribs)of this maxair hummer structurally sound? I am asking because I'm considering using thesame wing design on my homebuilt ultralight.

The simple answer is yes. There are many examples of working tube and fabric aircraft, both ultralights and larger designs, that make use of wing designs similar to your example.

The more complex answer is that it depends on a lot of things:

Did the designer anticipate flight loads correctly?
Did the designer model flight loads correctly when validating the wing design?
Do the materials used to construct the wing have physical properties close enough to the model used during design?
Was the aircraft built correctly according to the design?
Was the aircraft damaged such that the structure was compromised?

I don't want to discourage you from designing and building your own aircraft--one of the most exciting things about ultralights is how accessible they are to people with little or no formal training. Before you build and fly though, you should either learn how to determine the safety of a wing design using analytical methods, or stick to copying proven designs exactly.


Is the 250kt limit below 10,000 feet MSL varied according to airfield height? FAR part 91 Sec 91.117 for example states that "unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots".  All of the major jurisdictions I can find reference to have the same rule.

I've highlighted MSL (mean sea level).  Why is MSL used?  What's the point of such a regulation when aircraft would be able to manoeuvre at high speed close to the surface of high elevation fields?

How, if at all, is this varied when operating to or from an airfield with a high elevation, for example Quito, Ecuador (SEQM) at 7,910 feet?

No, the 250 KIAS below 10000 MSL rule of 91.117(a) is not varied within FAA jurisdiction, including near airports with high field elevation.

The 200 KIAS near Class C and D airfields rule of 91.117(b) mitigates some of the risk you might perceive surrounding high elevation airports.

For example, Aspen (KASE) has a surveyed field elevation of 7838 ft and is within Class D airspace. Aircraft operating within 4 NM of Aspen would be speed limited to 200 KIAS up to 2500 AGL, which would equate to over 10000 MSL.

Other high elevation airfields in Class E or G airspace would presumably have less traffic, with the expected result that higher indicated airspeeds would pose less risk in the uncongested airspace..


How does a typical passenger jet come to a stop when it lands Do the pilots of the plane simply reverse thrust of the engines after touchdown or are there brakes on the landing wheels that slow the plane just like a car? Or a combination of both?

What about prop-planes?

The main components that stops the aircraft are the brakes and spoilers and secondary would be the reverse thrust and flaps.
When a airplane lands it still has some velocity and that velocity still creates lift.
When the spoiler goes up it stops the wing from create lift and sits the plane on the ground, so the brakes have more efficiency.
Some aircrafts would need twice or three times longer runways to stop with the spoiler inop.
As a secondary resource there are the reverse thrust and the flaps, witch when is full down creates more drag than lift and helps the aircraft to stop.


Why do airliners park with the nose facing the terminal? A few other questions have touched on why we don't board airliners from the front and back at the same time. My question is why is it that we choose to board at the front, rather than park the aircraft facing away from the terminal? This question shows that parking backward seems to be unusual. Why is this design not adopted widely?

I have two guesses:

Is it because of the jet blast? But this can be solved by towing the aircraft away from the terminal before using the jet engines.
Because it is difficult to attach the jet bridge without hitting the tail?

To park a passenger plane with its tail towards the terminal has several disadvantages:

it would require a pushback tractor (plus personnel) to do that. Thrust reversers in general are not meant for making the plane go backwards. If it was possible for the plane to go autonomously backwards, it would be extremely = too risky.
you would also need the pushback tracktor for leaving the gate, you couldn't use engines because of the jetblast hitting the terminal
you could not use the APU because it would scorch the terminal
the horizontal tail of some planes might have clearance issues with the jet bridge.
last but maybe not least: the upper class travelers. They sit at the front for a reason: they get on and off the plane first. Yes, the business and first class could be moved to the back. Now, I don't know if riding closer to the cockpit rather than the arse of the plane has some intrinsic value, but at least it is usually noisier at the back.
So customer satisfaction might take a hit there.

So: twice the hassle with pushback + other issues, with no benefits whatsoever.


Why are landing gear retraction mechanisms mostly based on the four bar system? I would like to know about the principles of landing gear retraction system and I struggle to find clear information about it.

It seems to be about a four bar systems in most cases. This seems more complicated than necessary at first glance, why is a design with a simple hinge with an actuator that pulls the strut in not sufficient?

Most retraction retraction mechanisms involve a lot of pieces with complicated motions. I would like to understand the kinematics that justify the use of more than one or two bars. Intuitively, one would only expect an actuator acting directly on the landing gear, holding it into position, but the reality always involves complex rotational kinematics.

This question would also apply to the kinematics of flap tracks, which seem to be fairly complex as well.

(wikimedia.org)

The schematic above (with four arcs that are easy to trace) will hopefully serve as a starting point. This is a rather simple mechanism, say compared to the A380's body landing gear.

The principle can be explained by trying the proposed solution, and see what problems we run into. If you place only one actuator to rotate the landing gear at the attachment point* to the airplane (magenta colored circle), you run into many problems:

No locking mechanism
Small lever arm
Bigger actuating force needed
Limited movement (no full retraction/extension possible), unless

Packaging the mechanism in a small volume is not required
More linkages are added.

End result: back to square one, the first 3 problems, and no space for it in the limited volume of wings/bellies.

* If you place the actuator in a more convenient place like near the wing root, then it won't be able to get out of the way to stow the landing gear, unless you have a very thick unrealistic wing.

Note from the above schematic that the hydraulic cylinder (1) needs to retract/expand only by a relatively short distance to accomplish the retraction/extension.

The flaps and slats are also complex, not only you need to turn something around an axis, you need to translate it as well, creating the gaps seen, and package it neatly in a small volume.

If this basic objective is clear now, the next step is to read more, and to build models and/or play with kinematic simulation software. Try to build the same mechanism with one link, and then try to solve the issues you run into.


How is it possible to perform a rapid climb / tight loop without stalling? I'm still trying to get my mind fully around "Angle of Attack". This makes sense to me in the most basic situations, but when I start throwing more dramatic situations at it, my understanding breaks down... which means I don't really understand it.

Take this video for example (at  0:17 and 1:32):

How is this possible? Is it due to the excess power of the aircraft allowing it to change its "flight path" constantly through the maneuver and thus keeping the flight path (relative wind) not far away from the Critical Angle of Attack?

Short answer:
The maximum angle of attack is never reached in this video, thus the aircraft is not stalled.
Longer answer:
Stall is a problem mainly occurring during low speed flight. Our angle of attack is always depending on our flight path.
Let's first assume, that are at cruising altitude in a level flight condition. In this case the pitch angle of the airplane equals our angle of attack. As generated lift is dependent on your airspeed and the lift coefficient (which is again dependent on your angle of attack), reducing airspeed in level flight while maintaining your altitude will force you to in increase the angle of attack. At some point a further increase will result in a too high angle of attack and thus stall the aircraft.
Now, let's look at your problem:

(source: aeroskytech.com)
The main difference is your speed, or so to say the excess power used for climbing. During climb, the trajectory of the plane is not equal the horizontal axis. Therefore, also your angle of attack is not equal to your pitch angle (the angle between the longitudinal axis of the plane an the horizontal axis), but to the angle between the trajectory and the longitudinal axis. During the loops showed in the video the airplane is not only changing its pitch angle but also its flight path, therefore it is not stalled.
An interesting example for maintaining your flight path while increasing are military aircraft in combat maneuvers, their pilots rapidly change their pitch angles while still flying in the same direction. This works as a decent speedbrake, allowing them to intercept other aircraft.


Is there a ceiling on weather patterns? I know there are winds and other effects at very high altitudes but how high can storms with lightning and rain be?

Bottom line, let's say you are flying a craft with the ceiling of a U-2, can't you fly over any storm?

Severe convection will have anvil tops at the tropopause and overshooting tops can penetrate much higher (severe thunderstorm warnings often use a value of 60,000 ft for threats to aircraft).  How high the overshooting tops can get is a balance of the positive buoyancy during parcel ascent against the negative buoyancy once it gets into the warming stratospheric air.

A U2 could overfly these storms, but most aircraft are not designed for stratospheric flight (due to the temperature increasing with height in the stratosphere) and any commercial aircraft will be unable to go over these storms.


How should a glider pilot handle inadvertently entering a foreign country? Typically, when an aircraft lands on a different country than its departure, it has to land on an international airport. There many services are provided like customs, passport control etc, to make the entrance to the country legal.

But what happens on an unpowered aircraft? (i.e. sailplane, paraglider, hangglider etc).

These aircraft may be forced to cross a border and not be able to return but to the country of origin. Landing at an airport (let alone international), may not be possible. As an example consider a paraglider that is blown back to the lee side of a mountain.

These aircraft usually don't file a flight plan, they are not equipped with a transponder, may not have radios to communicate with ATC, and possibly may not be detected by radars.

How can the pilot make their arrival formal, their stay legal and eventually return to the origin country with out problems? Is there any law protecting pilots in such cases, or will they be treated as illegal immigrants?

In general, if this ever happen to someone, what is the first action they have to take, and who shall they contact?

Consider crossing an "unfriendly" border. A EU citizen getting from an EU country to another obviously will not have any problems. But visiting a country that a visa is needed, or that in general you are not allowed entrance seems more troublesome.

How can the pilot make their arrival formal, their stay legal and eventually return to the origin country without problems?

Let others know your plans beforehand. If worst comes to worst you need someone on the other side to try and resolve the issue.

Is there any law protecting pilots in such cases?

Internationally agreed upon law? Not to my knowledge since laws are typically sovereign in nature. (Better ask on Law.SE; someone did ask a related but more specific question, but no answer as of yet.)

All I know is what ICAO recommends in SARPs Annex 9:

  3.72 Recommended Practice.— Contracting States should establish measures for authorizing temporary entry for a passenger or crew member who does not possess the required entry visa prior to arrival, due to diversion or delay of a flight for reasons of force majeure.

Also to my knowledge force majeure cases are few and far between, and handled according to the specific situation. You can't have a law that can be used as a loophole to fake a situation (ideally).

If such law existed, ICAO wouldn't have needed to make a recommendation to its member countries.

Or will they be treated as illegal immigrants?

Could be worse if the diplomatic relations of said two countries are not ideal. The pilot could be treated as a spy, hence, let others know of your flying plans.

I couldn't find a glider story, but balloons are similar, and 1995 saw a tragic incident:

  In an incident recalling the most violent excesses of the cold war, Belarussian combat aircraft have shot down a sport balloon that flew over the border from Poland while competing in a race.

Not just balloons, even jogging can land you in trouble:

  A visitor from France says she was jogging along the beach south of White Rock, B.C., when she crossed the U.S. border without realizing it. So began a two-week nightmare that landed her in a prison jumpsuit.


What is the height of the Boeing 747-8 landing gear? I can never find any information about the height of the landing gear on any airliner(can you put it into feet and inches).And Is the height of the 747-8 landing gear around the same height as the 737 or airbus a320.

In general, the landing gear height is defined as the distance between the ground and the conjunction between main gear strut and the aircraft structure (fuselage, wing, nacelles, etc.).

The landing gear height of any aircraft varies depending the loading conditions and where you measure it (nose or main landing gear). This info is from the 747-8 Airplane Characteristics for Airport Planning document by Boeing.

Image from 747-8 Airplane Characteristics for Airport Planning by Boeing

Here, 'E' gives the height of the (main) landing gear attached to the fuselage.


Fighter YO-YO counter measure? In a dogfight ("A" Scenario), aircraft "A" is being shot at by aircraft "B". In order to lead aircraft "A", "B" must turn inside "A" and will soon overshoot if "B" does not perform a defensive maneuver. "A" can force an overshoot and then turn into "B" for a shot.

("B" Scenario) To prevent "B" from overshooting, it is common practice for it to perform a YO-YO (quick climb then dive) which absorbs energy and increases the flight path which will help keep it behind "A".

In the second scenario, what options does the lead aircraft have to gain the advantage over an enemy behind it that likly is about to perform a YO-YO?

my artwork

Sort of amusing F-16s were used here, instead of older vintage aircraft.  One must realize those little turns would involve high Gs that may incapacitate the pilots.  Also, any "yo-yo" would bleed off a lot of energy and make B an easy target for wingman of A.

One "oldie but goodie" would be for A and its wingman (person) to weave and have B turn right into the wingman's line.  This is the value of teamwork.

However, these days, more realisticly, you need to dodge the opponents missile, which can be very tough.  Stealth and shoot now rule.  But old methods should still be studied.

In the second scenario, one on one, aircraft A would also try to "yo-yo", and they wind up in "a rolling scissors".  The aircraft with more power to weight and better turning rate prevails.  For identical aircraft, it would be pilot skill.  But for modern aircraft with missiles and partners, this type of turning engagement would be very rare.


Why does the second floor of the Boeing 747 occupy only part of the plane? Why does the second floor of the Boeing 747 occupy only part of the plane, while the second floor of the Airbus a380 occupies the entire space of the plane?

The basic design of the Boeing 747 was originally developed to for the US military's CX-HLS program for a large cargo aircraft. One of the main requirements of the program was for cargo to be loaded from the nose, and placing the cockpit above the main cabin made this possible. The Lockheed C-5 Galaxy was selected, but Boeing carried the same features over to the 747.

In the 1960s when the 747 was being developed, some believed that supersonic aircraft would be taking over the long-haul travel market. The relatively short "hump" was retained not for extra passenger capacity, but so that if the passenger market dried up, they could keep producing the aircraft for the cargo market.

Boeing did extend the "hump" further back to add capacity on passenger versions, first on the 747-300 (and later retrofitted to a few -100 and -200 planes), and again on the 747-8I. Extending the second deck all the way back would create too many major changes to the structure and aerodynamics of the airplane, essentially making it a completely new model. Boeing did study a full double-deck model to compete with the A380, but opted to focus on a smaller, more fuel-efficient market with the 787 instead.


What do the yellow lashes/wings on the B737 PFD indicate? When I was looking at a YouTube clip of a B737 doing a landing, I couldn't help but notice something on the PFD:

What do these yellow lashes/wings indicate on the artificial horizon?

Image Source (Added green arrows for question clarity)

They were on for the entire approach and remained on even after touchdown.

They display the maximum pitch that can be exercised with the current configuration of the aircraft.

Using data which is measured in modern airliners, a maximum pitch angle can be calculated and displayed to the pilot on the primary display. It is described fully on this page (h/t @mins)

  With airplane aerodynamic specific data and the angle of attack measurement, we can have an effective pitch limit indicator PLI. A pitch limit indicator informs the user about the current difference between $max(\alpha)$ and the current $\alpha$. In many commercial airplane the pitch limit indicator is integrated within the glass cockpit, as shown in Figure 3; with this setup the pilot has a real-time indication of how much can pull on the column.


Is flight training on Russian planes performed in Russian? When doing flight training in a Russian plane (e.g. Tupolev, Antonov, etc.), does the flight instructor speak Russian or English?

Kind of unclear, but this would be dependent upon the country in which the flight training is taking place. If the training is taking place in Russia, most likely the instructor would speak to the student in Russian. If in the United States, the instructor would speak to the student in English.  As for ATC  transmissions, the only time the flight crew would be required to speak in English would be on an IFR flight plan. Any other time, they would speak their native language on the radio.


What is this thing sticking out in front of wings? I was wondering what this little stick on the wing was. My best guesses are an antenna or some sort of air speed measuring tube?

You're correct. That is the pitot tube (head), placed  there so that it is in undisturbed airflow. This location of pitot tube is found in othe aircraft too, like the Messerschmitt  Bf 109 G-2  as shown below.

By Unknown - http://www.militaryimages.net/photopost/showphoto.php/photo/8212., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2278317


How am I supposed to track to KOSAX on the OLIVI 4W out of EDFM? The SID chart for Mannheim, Germany (EDFM) runway 27 has segments to OLIVI are not defined in terms of any navigational aids but simply specify a track.

How am I supposed to fly these accurately? And more to the point, how am I supposed to determine that I'm over KOSAX? Dead reckoning? You might think that the SID requires GPS or other RNAV equipment, but there is another chart for that (which is virtually identical, but uses GPS-fix symbols instead of intersections).

KOSAX is also not shown on the Lower Enroute chart, which might otherwise have helped to determine its location.

The textual description for OLIVI 4W is:

OLIVI FOUR WHISKEY
On track 256° to 6.0 DME MND; RT, on track 333° to KOSAX;
LT, on track 294° to OLIVI.
Climb with 7.9% (480 ft/NM) or more until passing 3000,
then climb with 6.4% (390 ft/NM) or more until passing 6000.

However, the remarks section holds the answer:

1. PDG 7.9% (480 ft/NM) due to obstacles.
   If unable to comply, request alternative instruction by ATC.
2. PDG 6.4% (390 ft/NM) due to airspace structure.
3. After 6.0 DME MND BRNAV equipment necessary.
4. During activity of ED-R 205 (TRA) MAX FL80.

Note "3. After 6.0 DME MND BRNAV equipment necessary."

BRNAV in this case means "Basic RNAV", which is essentially a form of RNAV equipment, but with less stringent certification requirements compared to normal IFR RNAV equipment.


Why did fly-by-wire systems take so long to implement? The first commercial FBW airplane was the Airbus A320, which was introduced in the late 1980s. This system only worked after decades of research by American and European aerospace companies. If FBW only converts mechanical motions from an airplane's control yoke into electrical signals (along with sensor feedback), which change the aircraft's control surfaces, what caused FBW to be implemented so late, besides the abundance of computers even before the A320? Can someone also check my understanding of FBW?

My understanding of FBW:

Aircraft manufacturers use rotary encoders and potentiometers to translate mechanical changes in the control yoke into electrical signals.
The FBW computer(s) use feedback from the aircraft's sensors, and compare it with the pilot's input. A derivative based FLL system is used, perhaps?
Hydraulic valves/servo motors are used by the FBW system to change the state of control surfaces.

Thank you.

A simple answer is that the aircraft control system has ultimate responsibility for survival of the aircraft. If it completely fails, you are as good as dead in most cases. Short of in-flight destruction, hardly anything can be worse.

Thus, full-authority (i.e. without mechanical backup) FBW gained acceptance only when the confidence in its overall reliability was sufficiently high. Naturally, it appeared on military airplanes first, where demands to reliability can be lower (the pilot can eject, after all), while demands to the control system sophistication are often higher.

(Others have already commented that A320 wasn't the first commercial airliner with FBW; Concorde had it much earlier. As for your understanding of FBW, it's basically correct. Sometimes, strain gauges rather than potentiometers are used as control stick sensors: force as the primary input is generally better than displacement).


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?

The 747 carrier I retired out of had FAs based in New York and Tel Aviv, and were residents of their respective countries. The citizenship of the JFK FAs was not a factor insofar as I know as there were numerous green card holders.

Non-stop flights between JFK and Tel Aviv (and return, of course) were staffed by Israeli FAs. All other flights were staffed by JFK FAs. The primary reason for this arrangement was cultural. For JFK/TLV the back quarter or so of the aircraft was allocated to Hasidics to attempt to satisfy their preferences. For example, no movies were shown in the back because they were objectionable to the Hasidics.

The advantage of having Israeli FAs on the direct flights was that they knew how to handle the Hasidics. Scheduling problems would occasionally result in JFK FAs operating a JFK/TLV flight. 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. I never received such a request from an Israeli cabin crew.


Does the canard config have radically different controls than classic config? Classic configuration is something like the A320: wings in the middle, horizontal stabilizers at the tail.

Canard configuration is something like the Beechcraft Starship: wings at the back and horizontal stabilizers at the front (canards).

I'm just wondering if the canard config has any radically different controls for pitch? Are the directions reversed for the yoke? Are there serious re-training requirements for pilots due to some major difference? Are there bad side-effects when pitching in either direction that must be compensated for?

Note, I'm interested in large commercial jets for subsonic speeds. I couldn't find any in the canard config, so the Beechcraft was the closest example I could find.

Also, I'm asking this with traditional controls in mind...hydraulics, not fly-by-wire. I want to know if there are any radically different pitch considerations, before they are compensated by a computer.

(A related question could be for supersonic deltas, because I know some of them have canards to help stability. But I wanted to focus on subsonic flight in this question.)

As far as in-cockpit controls, a canard has the same control setup as a conventional airplane.  Stick or yoke, throttle(s), rudder pedals.

All the differences are hidden in the linkages or hydraulics -- pulling the stick back lowers the elevator on the canard, instead of raising one on a rear stabilizer, but to the pilot it's the same.

There are some minor technique difference in actually flying a canard; stalls are very different (I've heard some canards referred to as "almost impossible to stall"), and trimming pitch is slightly different; correct CG location is very different (usually ahead of the leading edge of the wing or, at most rearward, roughly even with the leading edge of the root of a swept wing), and the engine or engines are almost always located in the rear -- but once again, the pilot manages the engines very nearly identically to a conventional airplane (with the exception that, in case of a failure, he can't just look out the window to see if an engine is on fire).


What are the different wing planforms? What are each's advantages? Where are they commonly used? I remember reading that there are four common wing planforms:

Rectangular
Eliptical
Tapered
Sweptback

I'm sure there are more. What are the different types of planform out there?

Each must have its own advantages and disadvantages. What are those?

What's a good example of each?

The wing planform (which is the shape and layout of wing) for each aircraft is mainly based on the aerodynamic requirements. There are other considerations like stealth, controllability etc. The basic terminology in the wing geometry is given in the figure below.

Source: grc.nasa.gov

Most of the wing platforms in use (or have been used) fall under one of these categories.

Elliptical Aerodynamically, the elliptical planform is the most efficient as elliptical spanwise lift distribution has the lowest possible induced drag (as given by thin airfoil theory). However, the most important disadvantage of the elliptical wing is that its manufacturability is poor.

Perhaps the most famous aircraft with elliptical planform is the Supermarine Spitfire, used in Battle of Britan.

"Spitfire mark19 ps853 planform arp" by Adrian Pingstone (Arpingstone) - Own work. Licensed under Public Domain via Commons.

Interestingly, the elliptical wing was not decided to minimize induced drag, but to house the retractable landing gear along with guns and ammunition inside a wing that had to be thin. As per designer Beverly Shenstone,

  The ellipse was simply the shape that allowed us the thinnest possible wing with room inside to carry the necessary structure and the things we wanted to cram in. And it looked nice.

Some aircraft like the Seversky P-35 had a semi elliptical wing, with only the leading or trailing edge elliptical.

"Seversky SEV-DS" by Unknown - http://www.flickr.com/photos/sdasmarchives/8392339249/in/set-72157631292290354. Licensed under CC0 via Commons.

Rectangular Arguably the simplest wing planform from a manufacturing point of view, the rectangular wing is a straight, untapered wing. A good example would be the light general aircraft like Piper PA 38.

"Piper pa-38-112 g-bppf arp". Licensed under Public Domain via Commons.

The main disadvantage of this wing is that it is aerodynamically inefficient.

Tapered Wing This is a modification of the rectangular wing where the chord is varied across the span to approximate the elliptical lift distribution. While not as efficient as the elliptical lift distribution, it offers a compromise between manufacturability and efficiency.

A very good example of aircraft using this type of wing is the North American P-51 Mustang, which became the premier USAAF escort fighter against the Luftwaffe.

"P51-d mustang 472216 arp". Licensed under Public Domain via Commons.

Constant Chord with Tapered Outer This is midway between the rectangular and the tapered wing, with the inner part having constant chord and the outer part having a taper.

A very good example of this type of wing is the English Electric Canberra.

Source:

Almost all of the wings seen so far are used in subsonic aircraft due to the large drag caused by them in the transonic regime. Most of the wings used in supersonic aircraft fall under one of the following categories.

Delta The delta is a very low aspect ratio wing used in supersonic aircraft, most notably in the European designs. The main advantages of the delta wing is that is efficient in all the flight regimes (subsonic, transonic and supersonic). Also, the wing offers a large wing area for the shape, reducing wing loading and improving maneuverability.

The delta wing design is also very strong structurally, offering large volume for internal fuel. The delta wings are also quite simple to build and maintain.

The main disadvantages are that they have high induced drag due to low aspect ratio and also that they should have high angle of attack at low speeds (takeoff and landing), mainly due to fact that at these speeds, lift is generated by vortices. To compensate for this, they have high stall angles.

A very good example for this wing is the Dassault Mirage 2000, which is an example of tailless delta i.e. without horizontal stabilizers.

Source: www.aircraftrecognition.co.uk

A variant of the delta wing used in some aircraft is the one with horizontal stabilizer (tailed delta), the most famous of them being the Russian Mikoyan-Gurevich MiG-21.

Source: hdwallpapers.cat

Another variant is the one used by the Eurofighter Typhoon, the so called cropped delta, where the tips of the delta are 'cut off' to reduce drag at high angles of attack.

"Eurofighter 9803 2" by Kogo - Own work. Licensed under GFDL via Commons.

Yet another variant of the delta wing (this planform is very popular in combat aircraft), is the so called double delta, where the leading edge angle is not constant, but has two different values. One good example of this is the Light Combat Aircraft 'Tejas' under development in India.

"LCA Tejas" by Rinju9 - Own work. Licensed under CC BY-SA 3.0 via Commons.

Trapezoidal The trapezoidal wing is a high performance configuration such that the leading edge sweeps back and the trailing edge sweeps forward. This is mostly found in combat aircraft from the US.

This wing configuration offers efficient supersonic flight and has very good stealth characteristics. However, the wing loading is quite high, resulting in reduced maneuverability, especially instantaneous turn rate.

This wing configuration is used most notably in the Lockheed Martin F-22 Raptor.

"F 22 raptor bomb bay display 2014 Reno Air Races photo D Ramey Logan" by WPPilot - Own work. Licensed under CC BY-SA 4.0 via Commons.

Ogive The Ogive is a type of supersonic wing used in high speed aircraft. This is a complex mathematical shape derived for minimizing drag, especially at supersonic speeds. They offer excellent supersonic performance, with minimal drag. However, they are extremely complex and manufacturing is difficult while their subsonic performance is poor in comparison.

The most important aircraft using this wing is the Aérospatiale-BAC Concorde, one of the two supersonic commercial aircraft.

Source: www.wired.com

The wing planforms can also be classified on their sweep and variability.

Swept Back wings The leading edges of these wings are swept back. This is done order to reduce drag in transonic speeds, which is determined by the velocity normal to the wing.

This planform is used in almost all high speed commercial airliners. A good example would be the Boeing 787 Dreamliner.

"Boeing 787-8 Dreamliner N787FT KBFI" by redlegsfan21 - Flickr: N787FT. Licensed under CC BY-SA 2.0 via Commons.

Swept Forward Wings One disadvantage of the swept back wings is that due to the flow characteristics, the ailerons stall before the flaps (i.e. outboard wings stall first), which can lead to controllability issues. In order to overcome this, swept forward wings were used  in a few (experimental) aircraft.

The man problem with swept forward wing is that it produces wing twisting as it bends under load, resulting in greater stress on the wing root than for a similar straight or swept back wing. One of the few aircraft to use this wing is the Sukoi Su-47 Berkut.

Source: tom-clancys-hawx.wikia.com

Variable Sweep Wings For high speeds (transonic and supersonic), the swept wing is most suitable while for low speed (subsonic) flight, unswept wings are better. Varaible sweep wings were used to optimize the wing planform over a wide range of speeds. The main problem with this type of wing is the mechanical complexity.

The first aircraft to enter service with the variable sweep wing was the General Dynamics F-111 Aardvak.

"F-111A Wing Sweep Sequence" by Unknown. - http://www.nationalmuseum.af.mil/factsheets/factsheet_media.asp?fsID=2321&page=3. Licensed under Public Domain via Wikipedia.

Though most of the aircraft have used these planform, a number of other wing shapes have also been tried.

For example, the Handley Page Victor used a Crescent shaped wing.

Source:

F-16 XL used a cranked-arrow double delta wing.

Source: www.nasa.gov

One point to note is that most of the aircraft in operation or development use wing planforms which are a combination of the above rather than any one of them.


What is the procedure to obtain an FAA ATP while in the United States for a holder of a CPL from Pakistan? I hold a CPL from Pakistan and currently fly an A320. I have accumulated over 4000 flight hours. If I visit the United States, what is the procedure to obtain a FAA ATP certificate?

There are many things that need to be accomplished.

Get a letter of authenticity from the FAA validating your license is valid and from an ICAO contracting country.
Study and pass the ATP multi-engine written test.  You may have to get a graduation certificate from a school offering the CTP course.
Apply for and receive TSA clearance.
https://www.flightschoolcandidates.gov/afsp2/?acct_type=c&section=WN
Take the FAA ATP practical test in an A320 airplane or FFS simulator.  It is best to contact a training center on what is required.


What is the cockpit shown in this picture? What is the cockpit shown in the picture below?

The cockpit shown in the photo is of a Boeing 747-400.
You can tell that it must be a 747 by the fact that it has 4 thrust levers (so 4 engines) in the typical Boeing design. The 6 screens with the EFIS controllers rule out anything older than the 747-400 (like a B707 or older B747 variants). The large gear lever with the 3 positions rules out the new 747-8 variant.
Here is a cockpit picture for comparison:

(image source: Wikimedia)