Do flight recorders float in water? In a recent BBC article regarding the disappearance of Malaysian Airlines Flight 370 (MH-370), the writer refers to a US Naval officer's statement:

Commander William Marks from the US Seventh Fleet, which is taking part in the search, says he expects the plane's flight recorders to be floating in the water.
"In calm seas, if there were a soccer ball [football] or a basketball floating in the water, the radar could pick it up. They [flight recorders] typically have a radio beacon and so for example our P3 [radar] - if they are flying within a certain range of that - will pick up that radio beacon. We have not yet picked up anything, but that's typically what those black boxes contain."

I was under the (potentially incorrect) impression that flight recorders, by nature of the materials needed to protect their contents in the event of a crash, are quite dense and unable to float in water. I base this impression on news reporting of other airliner crashes (such as Air France 447, which crashed in the Atlantic), where the recorders were found some time later on the ocean floor.
Additionally, it seems reasonable to me that one would want to have the recorders not float so that they would come to rest near the other debris on the ocean floor since the recorders are equipped with underwater locator beacons which would aid in locating not only the recorders themselves but also the debris of the plane. If the recorders floated then they could move significant distances from the crash site and other debris, complicating search efforts.
It seems that Commander Marks, the writer of the article, or I (or some combination thereof) misunderstand something about flight recorders and their behavior in water.
My questions are these:

Do flight recorders float on water? If so, why?
I know that flight recorders are equipped with underwater locator beacons. Are they also equipped with radio beacons (either an active transmitter or a some passive device like a corner reflector to make them easier to detect with radar)?

Edit: The article has been updated, with the section regarding floating data recorders now reading:

Commander William Marks from the US Seventh Fleet, which is taking part in the search, said he expected the plane's flight recorders to be floating in the water.
He said the recorders, also known as "black boxes", are fitted with radio beacons that can be picked up by radar.

You are correct in the assumption that the typical data recorders being used today are too heavy to float.   They are designed to withstand very high forces, extreme temperatures, and to withstand corrosive environments (like sea water) for long periods of time.

For example:

  A DFDR must obviously have a high degree of ‘crashworthiness.’ The
  first units were required to withstand a momentary shock force of
  1,000gs, the latest test standards now call for a test to 3,400gs for
  a duration of 6.5 milliseconds. The units also have to withstand a
  static crushing force at all of its six axis points of an applied load
  force of 5,000lbs for 5 minutes on each axis. Third, it must withstand
  a 500lbs piercing force test conducted by dropping it onto a ¼ inch
  steel pin from 10 feet. Lastly it must withstand a 1,100°C fire test
  for 60 minutes, and a 260°C oven test for 10 hours.

  It is also required that these units are mounted within the tail area
  of an aircraft, away from the potential crushing force of any engines
  mounted nearby. The DFDR must be watertight to a depth of 20,000 feet
  in sea water, and survive at this depth for 30 days - and it must be
  fitted with an underwater locator beacon which will act like a sonar
  transmitter, by ‘pinging’ a signal through the medium of water that it
  might be laying in.

Time has an article showing the Air France 447 flight data recorders resting on the bottom of the ocean (there are others there):

This particular FDR is pretty common, and weighs about 13.5 pounds1.

Without seeing the original interview, I suspect that the author of the article got confused during the interview and was told that radar could detect debris the size of a soccer ball that is floating in the water and at a different time mentioned that they would be looking for the radio signals emitted by the black box (which wouldn't even be detected by radar).

UPDATE:

That being said, there are black boxes that can float and even eject from the airplane when a crash is detected.  They seem to be more common in military aircraft, and there have been a few attempts to require them in the US (and even have the government pay the $60,000/airplane price) but the bills stalled in congress.  The lawmakers here have recently started discussing this again though.

Deployable Black Boxes have been around since the 60's and are a second set of black boxes meant to be a backup to the main ones.  They can be particularly useful when crashing into water or in the event of a major fire because they would not be within the main crash site.

Here are a couple of articles about them:

Lawmaker Calls for 'Black Boxes' that Eject from Planes
Canada’s ‘deployable recorder’ would have located missing airliner within minutes, experts say

1 See specifications on Honeywell's webpage and page 7 of their product description.


Is there a maximum airfield elevation in which a Cessna 172P can operate? The title says it all: is there a maximum airfield elevation in which a Cessna 172P can operate? Or a maximum density altitude at which take off shouldn't be considered?

You should look in the POH for your specific aircraft (because it may have had modifications to it which would make it different from a "standard" aircraft) and see what it says.

The 172P POH that I found online contains no maximum airport elevation for takeoff, and the Type Certificate Data Sheet (TCDS) doesn't either.

Therefore, you can only go by the performance charts in the POH.  According to the POH that I found above, assuming that you have enough runway available and can out climb any obstacles (big assumption, you need to make sure of this), you can takeoff at a pressure altitude of up to 8,000 ft. other than in cases where the airplane is very heavy and it is hot, in which case it will be restricted further.

This doesn't mean that the aircraft is not capable of taking off at a higher pressure/density altitude however, and if you have the need to do so then I would recommend contacting the manufacturer directly to see if they have any engineering data available for your situation (often they do but don't publish it; there may or may not be a fee).


Could one see stars from the Concorde in daytime? The Concorde flew to an altitude of 60,000 ft (18.3 km) where stars should be visible at noon, aren't they? This question asks on how high stars become visible, and it is said Blackbird pilots could see them at 80,000 ft. The Concorde flew at the Armstrong line when highest, above more than 90% of the atmosphere's mass. Are there reports of passengers and pilots on the Concorde seeing stars (other than the Sun) when at peak altitude? Also, did the Sun appear whiter due to the thinner atmosphere?

Yes, in at least one exceptional circumstance.
The book Racing the Moon’s Shadow with Concorde 001 describes a 1973 scientific flight that remained in the moon's umbra for more than an hour, in daytime.  As stars are quite visible from the ground during a solar eclipse's totality, they would have been even more visible from a 17 km altitude.


Which avionics suite does the 757 use? I am wondering who makes the 757 avionics? Is there a glass cockpit upgrade? What is the name of the avionics suite?

Thanks in advance

The original 757 cockpit was considered “glass.” It consisted of six screens: Pilot’s PFD and ND, Co-pilots PFD and ND, and an upper and lower EICAS screen.

Behind the scenes, there is a triple autopilot system (left, center and right), two flight management computers, three flight control computers, three display control units (think SGU or symbol generator), two to three air data computers depending on customer option, and two EICAS (Engine Indicating and Caution and Advisory System) computers. There are also a large number of card files that process various system discretes to provide aural warnings.

A more modern upgrade to this, called “IS&S” keeps the same “boxes” in the shelves, but changes the PFD/ND displays to 4 LCD displays. This also got rid of the standalone airspeed indicators and altimeters (save the standby) as well as VSI’s. It makes the aircraft “NextGen” compliant.


Will increasing the wing area result in higher aircraft range? Intuitively, it seems that a low loading (large area) wing will allow to climb higher from the start, thus increasing true air speed and range.
At the same time, a low loading wing also calls for a slightly lower cruising speeds due to higher lift produced, and has higher drag.
With all other things being equal (same fuselage, same amount of fuel, same engines) will increasing the wing area alone (by increasing the aspect ratio of example) result in higher aircraft range?

Up to a point.
There is an optimum for wing area that shifts with operational considerations and airfoil type.
Propeller aircraft benefit little from flying higher, and due to the high efficiency of piston engines, the highest wing loading possible with the desired take-off distance will give the best result. Aspect ratio should be as high as practical; past examples used values up to 14.5 for achieving high range.
Jets benefit more from altitude but need more fuel, so my main focus will be on jets. Now it helps to look at the Breguet range equation: $$R = \frac{v\cdot L/D}{g\cdot b_f} \cdot ln\left(\frac{m_1}{m_2}\right)$$
The indices denote the state at the beginning (1) and the end (2) of the flight. For a higher range $R$ it helps to increase

Fuel fraction $\frac{m_1}{m_2}$: The higher, the better. But note that doubling fuel will not double range. Bigger wings will allow to hold more fuel, so here wing size helps.
Flight speed $v$: This allows to cover more ground while in the air. However, flying faster will produce more drag and consume more fuel once you fly faster than at minimum drag.
Lift-to-drag ratio $L/D$: Obviously, producing less drag for the same lift is equally important. In order to shift the best L/D to higher speeds, a high wing loading helps because friction drag grows less than linearly with dynamic pressure.
Engine efficiency: Less fuel for the same thrust will let you fly longer. $b_F$ is the thrust-specific fuel consumption. Since this factor is independent of wing area, it can be disregarded for this answer. Indirectly, however, it helps to have more efficient engines because then the need for a high fuel fraction is less pressing. The inefficiency of their engines is the main reason for the low wing loading of the first generation of transatlantic jets.

An increase in wing area allows for a higher fuel fraction, as long as installed engine performance is sufficient to power the larger, heavier airplane. Both the higher mass and the higher wing area will increase drag, so the optimum range speed will decrease for increasing wing area. The tipping point where increasing area further will no longer yield an increase in range is reached when the fuel fraction is already so high that increasing it further buys too little range to make up for the lower cruise speed and the higher fuel flow enroute. For most configurations, the lower power loading of the larger, heavier airplane with the same engines will most likely set the upper limit of wing size.
The actual optimum shifts with details in the airplane's layout and operation. Supercritical airfoils with their higher relative thickness at transsonic speed and more efficient engines will directly help to increase range for the same wing area. The requirement for low altitude flight and not having to take off and land can also influence the result.
Don't neglect scale: Larger airplanes have disproportionally longer ranges than otherwise identical, smaller types.


Can you help me identifying an A-4 Skyhawk-like jet? I'm having trouble identifying a jet and am hoping someone can provide some help.  Here is the best picture I've been able to capture.

The closest similar jet I've been able to find is the A-4 Skyhawk, which shares many of its features, but even in looking through the variants, I can't find an exact match.

The next two pictures aren't as clear, but they show the profile and wing shape, respectively.

There are three features I've noticed which set it apart from the A-4 variants I've found.

Wing shape - It's very curvy, almost Concorde-like.
Vertical stabilizer - The forward section of the top of the vertical stabilizer is very sharp, whereas on the A-4's I've seen, this is curved.
Antennae - There are two antennae; one swept-back antenna directly behind the cockpit and a vertical antenna farther back where the vertical stabilizer begins.

I appreciate any guidance you can provide.  Thank you.

They are A-4 Skyhawks all right. They are operated by Draken International and provide adversary training for USAF (among others); here's a closeup photo of them.

Image from edwards.af.mil


Does the Airbus A350 have an Automatic Emergency Descent System? In 2009 Airbus went public with a new feature in the Airbus A350, an Automatic Emergency Descent (AED) System.

The system would detect a rapid depressurization and, after a defined waiting time, would initiate an automated descent if the pilots failed to respond to the respective alert (i.e. in case of pilot incapacitation).

I found some presentation slides from 2015 on the topic but haven't heard anything on that system since. Does anyone have additional information: is it a standard feature now on the A350, is it optional, or was it not pursued any further? If not, for what reasons?

Airbus will have it on the -1000, and will also introduce it on the -900.

A350 chief engineer Alain de Zotti says the -1000 will be able to "slightly deviate" from the flight plan, if the system is activated, and leave its cruise altitude.
As well as executing the high-speed manoeuvre the aircraft will automatically notify air traffic control of the action.

(flightglobal.com, Nov 2017)

The Falcon 7X already has it, they call it Automatic Descent Mode (ADM).

In case of a depressurization at high altitudes, the Autopilot and Auto throttle will guide the aircraft to safe altitude at maximum velocity. ADM is activated when Autopilot is engaged, the aircraft is above 30,000 ft., and the cabin altitude is 9,700 ft. or greater.

Further reading: Automatic Emergency Descent System (skybrary.aero)


Can someone identify if this is a Boeing or an Airbus? I would like to know if this is a Boeing or an Airbus. Maybe there is an Aviation Wizard out there. It's an EasyJet plane.

There's no need to be an aviation wizard - Easyjet only fly Airbus A319 and A320 aircraft.

Even if you didn't give the airline, I would guess that it is an A320. Comparing the size of the engine to the person suggests it is a narrow-body aircraft, and 737 engines have a distinctive, flattened lower surface, whereas the A320 series are more cylindrical.


Was the oxygen mask, on this flight, out of order? Recently I was on flight where the panel for the oxygen mask, above my seat, looked like on the picture: the "button" in the middle of the panel was extended, turned and was showing a red tag on the side.

I asked a member of the cabin crew if this indicated a problem and the response - after he had tried to turn and push it in - was "I don't know, I don't think so". The fact that he couldn't turn it, or push it back into the panel, makes me think that it is more than just a locking mechanism, that it might have indicated that the system was out of order and I should've moved to a different seat.

Was my hunch correct, does this indicate a faulty oxygen mask?

The plane was an Embraer 190.

According to this Airbus training manual, pages 10 and 11, that's the test door stop.

As you can see in the video you added, resetting the masks is a pain, so the little red stop is there to catch the door and stop it from fully opening.

  Manually operated doors stops are fitted on the container doors to allow an operational test of the mask release system.
  When set to test position the door stops will prevent doors from fully opening and masks from dropping out of the Container.


What is the correct name for this ILS Indicator? What is the correct terminology for the name of the aircraft instrument that looks like this?

That image is a basic representation of a course deviation indicator, as mentioned by Steve H. An actual gauge would look like this:

Image Source

In your image, it shows that the aircraft needs to correct to the left and a little upwards, so that it will be on the glideslope as shown here.


Is the term "guinea pig" defined in the Pilot/Controller Glossary? Is the term "guinea pig" now or was it previously defined in the Pilot/Controller Glossary?

If it's not defined in the Pilot/Controller Glossary, maybe it's in some other publication.

I was flying with a crew member who used it while querying ATC about threading a hole in a line of weather. It went something like, "has anyone else guinea pigged that hole?" He said it was an actual controller term in their documentation.

I can't find it, but I was wondering if there was some kernel of truth to the statement.

Being a "guinea pig" means to be the first to try out a (potentially dangerous) situation. There is no mention, past or current of the term "guinea pig" or any derivation of that.

Slang slips through on the radio, this is probably an instance of that. If the pilot or controller used that term the appropriate response would be "unclear, please say again".

There is also no mention of it in the AIM.


What is the difference between Boeing 73G, 73H and 737? I found a data source, where Boeing 737 could be encoded with the following values - 733, 734, 735, 738, 73G, and 73H; Boeing 767 with values 762, 763; Boeing 777 - 772, 773, 777.

Any idea why such coding is used? Is it some standard to encode them with such values? Can I get more details from such codes (for ex., full aircraft type incl. customer code like Boeing 737-808)?

There are two main systems of aircraft type designations: IATA and ICAO codes. The ones you mention are IATA codes (all 3-character) and are often used for shortened aircraft type designation in public information.

Both code types are listed here with the corresponding full aircraft types. As you can see, the IATA information covers the type and variant, including some features such as winglets, but not necessarily extended range models or sub-variants with different engines. It also differentiates between freighters and passenger versions.

Despite the additional digit, ICAO codes are less precise and often include several variants such as freighter as well as passenger variants of the same type.

The codes given in your question translate to:

733  - Boeing 737-300
734  - Boeing 737-400
735  - Boeing 737-500
738  - Boeing 737-800
73G  - Boeing 737-700 (7th letter of the alphabet)
73H  - Boeing 737-800 with winglets (8th letter of the alphabet)
762  - Boeing 767-200
763  - Boeing 767-300
772  - Boeing 777-200
773  - Boeing 777-300
777  - ambiguous 777 type

(all passenger aircraft)

Unfortunately, as @Ralph J mentions, it's not always clear which type of code is used. Mostly, a 4-digit-code will be an ICAO code and a 3-character-code will use the IATA system, but because some ICAO codes only contain 3 digits, this isn't always reliable. For example, if you read "DC6", it could be the IATA code and refer to the passenger version, or it could be the ICAO code and you wouldn't know if it refers to the passenger or the freighter version.


Why does the B737NG need electrical power for aircraft towing? I have read the AMM for towing and one of the mentioned steps is to supply electrical power. Is it because you need power to turn on the hydraulics in order to pressurize your brakes?

For B737NG

You need power for lighting, fans, intercom, and CVR/flight recorder, cameras; any and all of them are required for towing an aircraft, depending upon its size, and in the event of an accident.

See:

"Aircraft Towing":

Accidents and Incidents

  "B763, Luton UK, 2005 (On 16 February 2005, at Luton Airport, a Boeing B767-300 collided with the tug pulling it forward when the shear pin of the unserviceable tow bar being used to pull the aircraft broke. The aircraft ran onto the tug when the ground crew stopped the tug suddenly. As result of the collision with the tug the aircraft fuselage and landing gear was damaged.)"

  "JS41, Birmingham UK, 2007 (On 26 June 2007, at Birmingham Airport UK, a BAe Jetstream 41 started an engine running pushback without using intercom between ground crew and flight crew. The pushback could not be completed as the towbar could not be disconnected and confusion over a decision to return the aircraft to the gate resulted in an attempt to do so with the aircraft brakes selected which caused the aircraft nose landing gear to collapse.)"

"Pushback":

  "The responsibilities of the ground crew team carrying out a pushback include ensuring that no part of the aircraft structure will impact any fixed object or other aircraft and may include giving clearance to start one or more engines just before, during or immediately after a pushback. The number of people assigned to a ground crew team for a pushback may vary according to aircraft size, but in most cases will be at least three. One will be driving the pushback vehicle, one will be walking in the vicinity of one of the aircraft wingtips and looking beyond the aircraft tail and one will be in charge of the manoeuvre and in communication with the person with aircraft responsibility in the flight deck. Communication between the ground crew supervisor is usually by means of a plug in to an aircraft ground intercom circuit; if so, this is facilitated by a ground crew microphone which acquires the voice of the user whilst excluding background noise, which if the aircraft engines are running can be considerable. If only two ground crew are used for pushback of a smaller aircraft then it is important that the procedure takes full account of the roles of each ground crewmember and that the person in charge of ground crew communications on the flight deck is aware of the number of ground crew being used and the physical location of the supervisor. ...
  Observations of abnormal circumstances in connection with engine starts or any other matter affecting, or potentially affecting the safety of the aircraft during a pushback are of great importance to those on the flight deck but it is essential that any descriptions of external observations during engine starts are imparted accurately; this may sometimes be demanding using ground intercom but can be extremely difficult with only hand signals available.".

Accidents and Incidents

  "A332, Karachi Pakistan, 2014 (On 4 October 2014, the fracture of a hydraulic hose during an A330-200 pushback at night at Karachi was followed by dense fumes in the form of hydraulic fluid mist filling the aircraft cabin and flight deck. After some delay, during which a delay in isolating the APU air bleed exacerbated the ingress of fumes, the aircraft was towed back onto stand and an emergency evacuation completed. During the return to stand, a PBE unit malfunctioned and caught fire when one of the cabin crew attempted to use it which prevented use of the exit adjacent to it for evacuation.)
  ...

  "B738 / B738, Toronto Canada, 2018 (On 5 January 2018, an out of service Boeing 737-800 was pushed back at night into collision with an in-service Boeing 737-800 waiting on the taxiway for a marshaller to arrive and direct it onto the adjacent terminal gate. The first aircraft’s tail collided with the second aircraft’s right wing and a fire started. The evacuation of the second aircraft was delayed by non-availability of cabin emergency lighting. The Investigation attributed the collision to failure of the apron controller and pushback crew to follow documented procedures or take reasonable care to ensure that it was safe to begin the pushback.)"

There are additional examples available at those links which were not quoted. Sometimes there are external cameras which are useful to record towing operations in the event of an accident.


Why don't aircraft (commercial and military) use reflective visor windshields? Just like those used on an astronaut's helmet, these reflective visors can help in better visibility when facing the sun (or any bright light source). But the windshields of most aircraft (commercial and military) look transparent from both sides. The whole point behind the question is to find out if it was experimented and if yes, why was it dropped?

Reflective materials cut down the amount of light let into the cockpit, which is useful in very bright sunlight, but would be undesirable at night. At night these materials could potentially blind the pilot, so you would have to make these materials retractable somehow, which would add complexity and weight. Over time these coating would be damaged by airborne debris, smashed bugs, and regular wear and tear. Add this that these coatings are expensive - outfitting them would be a significant cost.

Add to this that ever pilot would have different tinting needs - some people with less sensitive eyesight would need less tinting and others more. It's far cheaper and more effective for people to simply buy sunglasses.


What is the difference between static and dynamic seals? What is the difference between static and dynamic seals and  How much leakage is allowed past each seal?

Generically speaking:

A static seal is a seal between two surfaces that don't move relative
to each other.
A dynamic seal is a seal between two surfaces that do move relative to
each other.

The amount of allowed leakage depends on the application.


EASA part 66 licence conversion to the Japanese version? I am looking at a job proposal in Japan. I need to transfer my EASA Part 66 engineers license to the Japanese version.

Can anybody offer any advice on how I would achieve this?

You'll probably need a letter from your part 66 licence holder's authority.
I know people who get equivalent between French and Australian.
The best approach is to contact the Japan's competent authority (JCAB-MLIT) for the application details.
Regards


Does 3D Thrust vectoring (TVC) provide improved maneuverability over 2D TVC? What are the additional capabilities that 3D thrust vectoring (TVC) provides over 2D thrust vectoring?

Thrust vectoring allows to control an aircraft when the airflow over its control surfaces has separated. Before thrust vectoring, the range of angles of attack in which an aircraft could be controlled was rather restricted.

With the X-31, it was for the first time possible to control a completely stalled aircraft, which enabled much quicker maneuvering in order to get the nose pointed at an adversary. This was powerfully demonstrated by mock air combats with an F-18. The X-31 used a rather simple arrangement with three paddles at the engine exhaust, and this allowed to create both pitch and yaw moments. This makes it what you call a 3D thrust vectoring aircraft.

Modern thrust vectoring nozzles are round and allow to deflect the thrust by up to 20° in both pitch and yaw, making them also what you call 3D. However, this geometry will scatter radar waves in all directions, which makes it unsuitable for stealth aircraft. Therefore, stealthy designs can use only two straight vanes above and below the jet exhaust, which will create only pitch moments. This is what you call 2D thrust vectoring. When two engines are installed, differential deflection will allow to create limited roll moments, but the powerful side forces which allowed the X-31 to rotate its nose (and radar) quickly into the path of its adversary will no longer be possible.

Stealthy thrust vectoring will still allow to control the aircraft at all angles of attack, but the yaw rates possible with a regular thrust vectoring nozzle are no longer achievable. This, and the structural mass of a rectangular exhaust, are the distinct disadvantages of stealthy nozzle designs.


What is the maximum safe bank angle of a 747? This question arose during the comments of another question, linked for the curious:
What does it take to turn a 747 around 180 degrees?

Because the discussion was interesting, (and to avoid congesting the comments of another user's question), I reposted it here.

Does anyone know the answer to this? Official sources/experience are preferred, but I'll take what I can get.

  If I was at altitude and suddenly realized we were about to cross into airspace that might get us shot down, I would, smoothly, do 3 things simultaneously: (1) start the nose down to around 25 degrees down, (2) start a roll to a bank angle of 60-80 degrees, and (3) start the power back to idle. At the same time, I'd ask the first officer to deploy the speed brakes, which would give me great roll response. –  Terry

To which I replied:

  80 degrees of bank would be a bit excessive no? 60 might be reasonable for an emergency turn, but certainly no more in a 747? (G-forces aside) –  HCBPshenanigans

Terry's reply:

  I was thinking of a range because, in an emergency turn, hitting an
  exact degree of bank would be hard. I would, however, not want to go
  beyond 90 degrees because of the possible disorienting nature for the
  flight crew. At 60 degrees, approximately 87% of the wings lift would
  be turning the airplane. At 80 degrees, about 98% of the lift would be
  turning the airplane, so the lesser bank would sacrifice 11% of the
  turning force. I would expect to lose a lot altitude in the turn. I
  can't think of a reason not use 80 degrees. Pax comfort would be a
  non-issue. –  Terry

My most recent response:

  Idk if you are a real 747 captain (there are quite a few on here), but
  iirc many 747 crashes have happened because when the aircraft banks so
  hard that it loses that much vertical lift, it is very difficult to
  recover from. In addition, some flight systems might malfunction under
  these rather extreme conditions. 60, hell even 70, is much steeper
  than it seems. I seem to remember seeing an episode of that old Air Disaster show about just this. –  HCBPshenanigans

Edit: What kind of difference would the difference between 60 and 70 or 80 degrees of roll make in time to turn 360 degrees?

The descent angle helps to reduce the lift that the wing needs to provide, in two ways. It leads the aircraft into higher density air, where more absolute lift is possible at the same Mach number. That takes a while, but a more immediate effect comes from pointing the aircraft's nose downwards. Then, part of the gravity-induced forces can be counteracted by drag (D in the sketch below). This is similar to a glider, only with much lower aerodynamic efficiency and steeper angles. Terry reduces thrust and opens the speed brakes to avoid overspeeding, so he can dive as steeply as possible, thus reducing lift requirements.

Now more of the wing's lift L can be employed for turning the aircraft around. If he wants to achieve a constant sink rate, he still has to produce enough lift to balance weight, but reduced by the cosine of the glide path compared to the level flight condition. At 25° nose down, this is a reduction by 10%.

Now you are concerned about his roll angle. Please note that he wants to create as much sideways component of lift as possible, which will look like gravity to all onboard. At 60° roll angle (I think his 80° are a bit extreme), this works out to twice the normal vertical acceleration, and with the dive actually just 1.8 g, so everyone will feel almost twice the force of normal gravity. With the 80° roll, this will not be a stationary turn and not enough lift will remain to counteract gravity, so the aircraft will accelerate downwards during the turn. It will actually fall out of the sky. When already at Mach 0.85, I would be more careful than Terry, because things get ugly very quickly when Mach goes further up.

The term $m\cdot\frac{v^2}{R}$ is the centrifugal force which can be afforded by the horizontal component of the lift and which needs to be as big as possible for tight turns (a smaller radius R helps). This is the lift component that Terry needs to pull the aircraft around.

If we stay with stationary turns (without the "falling out of the sky" part), the maximum bank angle is given by the maximum load factor of the 747. At 400 KEAS, this is just 1.5g, so even with the 25° nose down attitude the maximum bank angle would be 53°. If you fly slightly slower, the load factor goes to 2g (equals 63° in a 25° descent) and tops out at 2.5g at 310 KEAS (68.7° in a 25° descent). Flying at Mach 0.85 in 30.000 ft will produce an equivalent airspeed of 306 kt in normal atmospheric conditions. The precise value varies with the actual flight speed, and the maximum safe bank angle is in the region of 60° to 70°.

I expanded my answer to the original question, and I hope in combination with this I can cover your questions. If not, please keep asking!

EDIT: I see, now you want to know the time to turn around. All I can do is calculate it under the assumption that enough lift is available, regardless of buffeting. In reality, I doubt that even the 48° case will give you a pleasant ride. All results are for the 30.000 ft case, because at 36.000 ft those higher bank angles will not be cleanly flyable due to compressibility effects.

At 60° the airplane flies with 2g, and with 25° nose down still at 1.8g. The turn rate would be 3.77°/s and 180° would be completed after 48 s.

At 70° it flies with almost 3g, and with 25° nose down at 2.65 g which is a little outside of the g limits. The turn rate would be 5.98°/s and 180° would be completed after 30 s (plus the time to roll to 70°, which now starts to become important).

The 80° case becomes really hypothetical, because even with the 25° nose down attitude the load factor will be 5.2g if flown without sideslip and enough lift to prevent overspeeding. The 747 will be close to breaking apart, but maybe a future aerobatic version can fly this maneuver safely. It will result in a turn rate of 12.35° and need 14.6 s for a 180° turn. I would add at least 4 seconds to bank to 80°, but the turn can be completed within 20 s. Hypothetically.

What Terry hinted to when he said he would bank to 80° is not the clean turns I am calculating here, but a dynamic dive where the plane accelerates because not enough lift is left to keep it from falling. To compute this, I would need more aerodynamic data on the 747 and need to employ at least a finite difference algorithm or a lot of paper and pencils.

Just that much: If the 747 is rolled to 80° but the pilot pulls only as many gs as the aircraft can sustain (due to buffeting I doubt that even 2.5 g are possible), the lift will almost exclusively serve to fly a tight turn, but not enough will be left to counteract gravity. Therefore, the aircraft will slip sideways, and directional stability will turn the nose downwards. This will take a while (I am guessing maybe 12 seconds, really a guess), but the aircraft will pick up speed from the beginning of the maneuver. I am a little more scared of flying faster than Mach 0.85 than Terry is, and the various reports of 747s going up to Mach 0.98 support his view that a little overspeeding is OK. It is hard for me to guess how much time it needs to become uncomfortably fast, and then a lot of lift will be needed to pull out of the dive. On the other hand, when the airplane is diving, all it needs is a roll and a pull-out to come out at 180° to the previous course. The pull-out will be performed at a much lower altitude, and creating the gs there will not be a problem.


How to calculate "duty" when between flights in a 135 operation Here is the scenario ... at 6:00am pilot flies from Location A to Location B to drop off a customer.  Flight duration is 2hrs.  Pilot is then given the day to do with as they want to but must be ready for the return flight at 22:00 later that day.  The return flight is another 2hrs.

Question: Has the pilot exceeded their daily duty limit under part 135 rules?  Or is it reasonable to assume the interval between flights would constitute a 10hr rest period?

NOTE: between the time of 8:00 and 22:00, the pilot was not paid and able to do anything they wanted with their time.  They were not expected to wait at the airport and knew they would not be needed before 22:00.

I have not checked the latest regs, but the time beginning at the point where the pilot is done with all postflight duties until the time the preflight duties begin (ex. checking weather) is considered rest time ONLY IF the pilot is really off the clock.  If the company requires anything of the pilot (ex. "stay near the plane...just in case"), it is not rest time.


Why are general aviation avionics so expensive? I am quite sure that someone already asked this question, but I couldn't find it on this site.

Why are avionics for general aviation aircraft so expensive?

For example:

The Garmin® G5

$ 2,149.00

The mighty Garmin® G1000

$ ~ 50,000.00

Nobody can tell me, the hardware and development for a small screen costs more than 2,000 dollars. Or two screens with some knobs for the price of a middle-class car. (Of course, those avionics are not bad, they are worth every cent. But it still looks expensive for me.)

What causes this, quite high price?

I guess it's because of high licensing costs to license it for use in aircraft, or are the production costs really so high?

The cost of rigorous FAA certification versus number of units produced would be my subjective opinion.  Count on our little glass horizon not full up Galaxy 7 catching on fire or even just failing when needed.  That's one of several things we pay for, again: opinion without data.


Can a 16 year old student pilot "pre-take" the checkride? I am a student pilot, and I soloed about one month after my 16th birthday. I know I can't become a private pilot until I am 17, but I'm wondering if there is a way to take the check ride before you are 17, but be limited to the privileges of a student pilot until you are 17, at which point you can exercise the privileges of a private pilot? I doubt it, but its worth asking. I feel like I am pretty much ready to take the check ride, but I have to wait 8 more months. Thanks!

14 CFR Part 61.39 (a)(5) states that you can not take a checkride in the US until you are of age to hold the desired certificate.

(5) Meet the prescribed age requirement of this part for the issuance of the certificate or rating sought;

Sorry. I encourage you to take as many mock-checkrides as possible in the meantime.
Also, in addition to mock-checkrides. You can train for your instrument rating. 14 CFR Part 61.65 allows you to take a combined checkride or even back-to-back private and instrument checkrides.
§61.65 Instrument rating requirements.
(a) General. A person who applies for an instrument rating must:
(1) Hold at least a current private pilot certificate, or be concurrently applying for a private pilot certificate, with an airplane, helicopter, or powered-lift rating appropriate to the instrument rating sought;


What is a heat dissipater and how does it work? Wikipedia's Mi-24 Hind article (a Soviet helictoper) says:

  Heat dissipaters were also fitted to exhausts to decrease the Mi-24's heat signature.

There's no citation. What exactly is a heat dissipater and how does it work?

The heat dissipaters  are used to reduce the infra-red signature of the helicopter engine exhaust. They are also used in other helicopters, like the 'black hole ocarina' (BHO) infra-red suppression device used in AH-64 Apache.

Source: b-domke.de

The main purpose of the IR suppressors in use today is twofold:

Reduce the IR signature by reducing the exhaust temperature
'Shield' the hot engine from view.

The infra-red suppression systems in service today usually work by

'Bending' the exhaust, usually upwards, and shielding the exhaust from view by an insulating cowl. In these IR suppressors in Mi- 35 (export version of Mi-24), the exhaust is turned almost 90°.

Source: mamboccv.com

Mixing the hot engine exhausts with the cool air, effectively reducing the exhaust temperature. In the Black Hole IR suppression system, the exhaust temperature is reduced from ~600 °C to ~300 °C .
The RAH-66 Comanche had the infra-red suppression system integrated into the airframe (the exhaust was routed through the tail boom), though the principle is the same- mixing of engine exhaust with ambient cool air.

Source: sikorskyarchives.com

In some cases, the special high emissivity coatings are applied to the engine exhausts for reducing the IR signature.

Most of the present IR suppressors focus on achieving a thorough mix of the cool ambient air and the exhaust to reduce temperature and uneven mixing, in order to prevent 'hot spots'. Cooling of the exhaust pipe itself is achieved in some cases by using film cooling. In most helicopters, the infra red suppression system (IRSS) is optional and can be added separately.

The figure shows the schematic of the infrared suppression system used in AH- 64 Apache and the associated reduction in IR signature.

Image from Progress in helicopter infrared signature suppression by Jingzhou Zhang et al., Chinese Journal of Aeronautics, Volume 27, Issue 2


Why does adverse yaw exist? Why does the aileron deflected upwards, thereby reducing lift, not also reduce drag on that side?

Indeed, when an aileron moves upward, it locally generates less lift and less drag.

Assume we are talking about the aileron on the right wing.
The reduced lift drops that wing, rolling the aircraft right. But the reduced drag accelerates that wing, yawing the aircraft left.

On the left side the opposite happens, but it has the same effect. The aileron moves down, increasing lift to roll the aircraft right. But the added lift increases drag, decelerating the left wing to yaw the aircraft left.

That is the adverse yaw effect.


How does an Airbus pilot decide whether to use HDG-V/S or TRK/FPA guidance? The Flight Control Unit of modern Airbus aircraft has a pushbutton for selection of either

heading / vertical speed (HDG-V/S), or
track / flight path angle (TRK-FPA)

guidance for the Autopilot and Flight Director. I know in principle what these modes mean (i.e. difference of heading vs. track, or between vertical speed and flight path angle) and how the guidance on the Primary Flight Display changes from Pitch/Roll bars to the Flight Path Vector depending on the selected mode:

What I would like to ask is when is each mode used. How do pilots decide which guidance mode suits them most in a given situation? For example, is it related to

personal preference of the Pilot Flying?
specific flight phases or situation/circumstances?
procedures that require a certain selection?

It's mostly up to points 2 and 3 on your list rather than personal preference:
Note that most ATC instructions (beit on departure,cruise or initial approach) will ask of you to fly a specific heading and/or a specific climb rate (v/s). This makes the hdg/vs mode the 'standard' mode to be used durring flight. This is also the mode where the F/Ds provide an easy to use guidance for the pilots to follow.
The reason for this Hdg preference for ATC is beyond the scope of this question, and is quite a nice narative on how historically we arrived at using heading for separation, but I will say this much: imagine ATC software attempting to interpolate the track of two converging a/c , to determine minimum separation and/or collision conflicts. Now imagine there is (unkown to the atc) changing wind along route, and both a/c will change hdg to maintain proper ground track. The math required is mind-blowingly complicated...(because changing hdg will change time of arrival at intersection,etc )
Anyway, once you look at some final approaches you will see that there is usually a final approach Track and a (3deg usually) glide path angle posted on the chart. The reason is that being closer to the runway, you start to become a bit more interested in your path wrt to ground rather that wrt to other trafic.
TLDR
TRK-FPA, as part of normal operating procedures, is only used when flying the final part of a non-precision approach, and is usually engaged  about 1 NM before the FAF.
Mind you, it's use is not prohibited outside of that, just there is kinda little use for it.


Are artificial magnetic fields used or proposed to be used to shield high altitude pilots and astronauts from charged, high energy radiation? If not for the earth's magnetic field our atmosphere would be bombarded by high energy plasma (ionized gas) from the sun and other space sources.  At very high altitudes and orbital altitudes this protection is less and when space travel takes astronauts out of range of earth's magnetic field there is no protection.

Does the International Space Station or other craft have an artificial magnetic field to protect its astronauts?  If not are there plans for implementation?

This won't work.

What to shield

Most of the cosmic radiation has quite low energies and can easily be shielded by the hull of an aircraft, spaceship or spacesuit. This would also be shielded by the atmosphere, but it would also burn/blow it away over time due to the intensity of the radiation. For luck, the magnetic field of the earth shields us from this radiation before it reaches the atmosphere.

And then there is the nasty stuff. Particles with energies which can easily punch through several centimeters of iron, lead or whatever. This stuff can not really be shielded by the magnetic field of the earth, nor could it be by artificial fields. Even worse, when this stuff hits a nucleus in the hull of a spaceship, it would smash it into many pieces, which will then fly along the direction of the original particle. Yes, this means radiation can be even higher behind a too thin shield! And since this happens in the hull or in the spaceship, one can't shield that by fields outside the ship.

In fact, most of the radiation in aviation is not made of the primary particles from space, but of secondary particles created in collisions between the primary particles and atoms of the atmosphere.

Field strength

The most important factor of field strength of a magnetic dipole is

$$B(r) \sim m/r^3$$

(Yes, to the power of three)

$m$ is the magnetic dipole strength, which for a simple conductor loop is given by current times area enclosed by the conductor.

So, if we build a coil of several thousand windings, resulting in a total current of several thousands of amperes, and an area of some ten squaremeters, we end up with an $m$ of several 10000Am². In contrast, earths magnetic field has about $8\cdot10^{22}$Am², which is a totally different order of magnitude.

Earths field strength might not be high - only about 40µT at the surface, but it reaches far, far into space. So, the time / distance the field acts on a particle is quite long, an can deflect it easily. In contrast, a human-made field will decrease to near zero within just a very few meters, and that's not enough.


Does the A320 Trimmable Horizontal Stabilizer automatically reset after landing? Does the A320's Trimmable Horizontal Stabilizer (THS) automatically reset after landing? If so, is there any condition where it doesn't? And what about the rudder trim?

I'm asking because I'm studying from an old FCOM I found online and it doesn't state that any of those automatically reset but there are two questions in SmartCockpit that say otherwise (i.e. that both the THS and rudder trim reset after landing).

If the quiz you saw is the same as this one, then please double-check it, as the one I linked has 'THS only' as the correct answer...

  Q 31: Which of the following will automatically reset after landing?
  A: THS.
  B: Rudder trim.
  C: Both are correct.

... which is more inline with the manual.

THS -- yes

The THS resets to 0° after being on the ground for +5 seconds and with the pitch attitude less than +2.5°. This is when the pitch law reverts to 'ground mode'.

  Ground mode is a direct relationship between sidestick deflection and elevator deflection, without auto trim.
  It automatically sets the trimmable horizontal stabilizer (THS) at 0 ° (inside the green band).

  (A320 FCOM)

Also see: Why is it not recommended to hold the nose up on the A320 after touchdown?

Rudder -- no

There is no similar 'ground mode' for the rudder, and the manual does not mention an automatic rudder trim reset as far as I've checked.* I doubt one exists because in an engine-out landing, such reset would catch the pilot off balance. (The SOP calls for 5° trim towards the working engine when landing with an engine out.)

The SOP also calls for checking the rudder trim is zero after start, and resetting it if it is not.

* The manuals do not always tell the full story as Captain Sullenberger learned, so it goes without saying to not use the internet for flight.


Why are most cockpits gray? Russian cockpits were often painted turquoise to reduce pilot fatigue. So my question is why most non-Russian cockpits are painted gray, or in the 777's case, tan?

Basically, neutral mid-toned greys or tans are considered to be the best color to use, because they aren't any other color:

The base color shouldn't be confused for anything in an instrument display. This precludes using red, yellow, green, bright blues or brown, but also black and white as black is used to represent empty space in instrument displays while white is commonly text and also used for other display elements.
The color shouldn't cause glare. Too light a hue will increase sunlight scattering in the cockpit, reducing pilot visibility in high-sunlight situations.
The color shouldn't be too dark, as in those same situations a dark color will absorb the sunlight and become hot, increasing ambient temperature of the flight deck, requiring additional cooling system capacity for both pilots and instruments (many civvie aircraft have black instrument panels, but other elements of the design typically prevent the panel catching too much sunlight).
The color has to be relatively easy to find or make, allowing touch-ups. Brighter colors are harder to match exactly; neutral tones blend easier and aren't as distracting even if they are slightly mismatched. This is mainly a military concern, where crew chiefs do what they can with what's on hand; commercial airliners will have hundreds of gallons of their livery colors and other standard touch-ups including cockpit-approved colors available at maintenance hubs.
Western thought says the color should be visually uninteresting in order to provide the minimum distraction to the pilot from more important colors in the cockpit. This is where Western and Russian thought primarily differs; Russian designers favored a "mood color" over being completely nondescript, while Western designers favor the background color "disappearing" even if the net effect is depressing to a pilot sitting in it for several hours a day.

To be fair, Western cockpits are not always grey or tan, but really there are only a couple more common options. European Mirage, Rafale and Gripen fighters are commonly seen with a sky-ish blue interior, providing some of that mood color benefit while remaining nondescript. Aircraft cockpits in WWII, on all sides, were painted in whatever the crew chief had available, which usually amounted to land-based planes getting the same olive drab that coated every piece of metal the Army owned, while naval variants got one of the various blue-grays used on the ship itself.


Why do we see "page intentionally left blank" so often in aviation related documents? In aviation, we see the phrase "This page is intentionally left blank" quite often in documents like POHs, AIP etc. I can't remember seeing this in any other field. Why is that the case? Why do we see it that often in aviation related documents but nowhere else (anymore)?

There is a good answer to a general question about this phrase on UX.SE but I'm wondering specifically about its usage in aviation related contexts, especially in an age where the main distribution channel for documents is digital distribution and not paper anymore.

I've worked as a technical writer on flight and maintenance manuals in a previous life.  It's done with technical publications where there is a kind of quasi-legal status you might say, insofar as the information published is required for operation or maintenance, is invalid for use if not up to date, and where pages are revised, numbered and dated with a List of Effective Pages (LOEP) that goes at the front, that confirms the issue date of each page.

It provides a ready confirmation that a blank page is not a misprint (even as a PDF or other electronic format), saving the reader from having to check against the LOEP to make sure there isn't a missing page every time a blank page appears at the end of a section.


In which direction does air flow over a wing as observed from ground? A wing flies to the left in the air (no wind). Particles A and B moves to the right in relation to wing.

In which direction do particles A and B moves in relation to the ground?
What is velocity of particles in relation to the ground?
Don't forget, air is at rest (no wind) and the wing is moving, so why does particle C not move to the particle A, because the net pressure gradient is to the left and air always travels from high to low pressure?

(i think when observed from ground :

particle A moves up and left

particle B moves down and left

particle C moves down and left

and when wing pass all particles will move down and left)

particle A moves up and left

No, up and right

  particle B moves down and left

Yes

  particle C moves down and left

Yes

The low pressure region first pulls in the particle A, so it initially moves in the opposite direction of the wing, and then the adverse gradient over the rear part of the wing will gradually accelerate it so it ends up moving a little in the direction of the aircraft. It also ends up moving down much faster than forward, which is how the lift can be much more than the drag.

On highly cambered wings the pressure may be higher than ambient everywhere on the underside, but most wings are not cambered that much and there is some reduction of pressure under them as well, so even the particles moving under the wing accelerate a bit to the right, opposite of the wing, and only then change to moving left along the flight direction.


Can an IFR clearance be issued and flown through IMC in class G airspace? Let's say an IFR flight was planned to depart from a non-towered airport with class G airspace extending from the surface to 700 feet AGL. The flight visibility and ceiling both go down to 0. Can the pilot get an IFR clearance?

If the airport had class E airspace from the surface up it would be in controlled airspace from the ground and I'm positive that an IFR clearance could be issued allowing IFR flight in that class E airspace right from takeoff.

In the case of class G airspace from the ground, the airspace is uncontrolled. Could an IFR clearance be issued that allows IFR flight and waives the basic VFR weather minimums for class G airspace?

The key point is in your last sentence:

  In the case of class G airspace from the ground, the airspace is uncontrolled.

Uncontrolled airspace is, well, uncontrolled. An appropriately rated, current pilot, in an appropriately equipped aircraft, may fly IFR in class G airspace without either a clearance or a flight plan. There are no clearances to waive VFR minima in class G, because the flight is conducted under IFR.

If an entire flight is flown in class G airspace, a pilot does not need to talk to a controller at all. When class G airspace is overlaid by controlled airspace, like class E, the pilot will need a clearance before entering controlled airspace. The controller will provide a clearance (FAA Order  7110.65, p. 4-3-2):

  WHEN ENTERING CONTROLLED AIRSPACE (instruction), FLY HEADING (degrees) UNTIL REACHING (altitude, point, or fix) BEFORE PROCEEDING ON COURSE.

Once the pilot is released for departure, they would depart IFR in class G, where they would be responsible for their own terrain and traffic clearance (using tools like an Obstacle Departure Procedure). As soon as they climb into class E airspace, they receive the benefits and responsibilities of flying in the ATC system.

An interesting border case is raised by wbeard52. In this case, a pilot departed a class G airport with class E starting at 700 AGL, and broke out of the clouds before entering controlled airspace. The ruling basically said that taking off in this situation without a clearance is not explicitly illegal, but falls under "careless or reckless operation" prohibited by FAR 91.13.


Are Transponder Mode A and C still in use? Are the ATC transponder Mode A and Mode C still in use (according to ICAO or FAA rules)?

Yes. According to Title 14 CFR §91.215   ATC transponder and altitude reporting equipment and use.

Specifically:

  (a) All airspace: U.S.-registered civil aircraft. For operations not
  conducted under part  121 or 135 of this chapter, ATC transponder
  equipment installed must meet the performance and environmental
  requirements of any class of TSO-C74b (Mode A) or any class of
  TSO-C74c (Mode A with altitude reporting capability) as appropriate,
  or the appropriate class of TSO-C112 (Mode S).

the use of Mode A or Mode C (e.g.: Mode A with altitude reporting capability) is acceptable for flight under Part 91. That covers all of general aviation (GA), of which a large percentage use Mode A/C transponders.

With the upcoming ADS-B mandate, many GA operators are switching to Mode S to get the 1090 MHz ES ADS-B.  But others are keeping the Mode A/C and adding a 978 MHz UAT to meet the ADS-B requirement. In any case, there are still a large number of Mode A/C transponders in use and likely will be the case for quite a while.

Mode S is optional and only required for operations under Parts 121 (Air Carriers) and 135 (Air Taxi).

For Part 121, a Mode S transponder is required by §121.356   Collision avoidance system.

For Part 135, Mode S is required by §135.143   General requirements.


Why are Airbus captain control sticks placed on the left when most people are right-handed? Why is it that control sticks for the captains on Airbus are placed on the left? Wouldn't it be uncomfortable considering that most of the people, and by consequence pilots, are right handed?

To my opinion this would make flying more difficult as a right handed person would have less sensitivity on his left hand.

(airbus.com)

The Airbus is actually configured the same as the vast majority of other General Aviation and Civil Aviation aircraft.

The key factor is that the throttle is almost always the middle - meaning that  as pilots get used to sitting in the left seat early on in their training, they become accustomed to using the throttle with their right hand and the control column in the left.

It's something of a misconception to think that pilots spend much, if any, time with both hands on the control column. The right hand is almost always somewhere else – configuring radios, squawks, navigation equipment, throttles and so on.

Watch this video of a Citation Jet – particularly during takeoff and landing.

The pilot on the left is using his control column in exactly the same way as he would on an Airbus. You'll note that when his right hand is on the control column, it doesn't become dominant – it's just a resting position.


Can civil pilots *ever* fly military high-altitude penetration approach procedures? Let's say I'm flying some business types in a Gulfstream III (an approach category C aircraft) from Stockton to Palmdale to meet up with some USAF types there (new airplane deal, wooo!).  Can I accept/fly the HI-ILS approach to RWY 25 at KPMD:

or am I only allowed to accept a STAR or vectors to a standard ILS approach to KPMD?

As long as you can actually make the altitude restrictions, then yes, there's no reason why you cannot request to fly the approach.  However, as a general courtesy, you should also factor in your approach speed.  ATC might not appreciate a Cessna clobbering the approach 34 miles out.  These approaches are typically flown at 250+kts, so just keep that in mind.


What control inputs are required to perform a "turning-while-in-flight" maneuver in a helicopter? My question is relatively simple and has to do with the required control inputs to perform a simple turning maneuver over a large area.
Suppose a helicopter is traveling in forward flight, straight and level, and the pilot has to alter course to circle a large area. Now, suppose the helicopter begins a slight rightward turn, while continuing to fly 'forward', and ends up semi-circling over a broad area.
I want to make the point that the helicopter is not yawing/turning on its own axis, but rather performing a turn over a large area.
The resulting flight path, if viewed from above, would essentially be a semi-circle or horseshoe shape.
This would obviously involve some rightward banking. What I want to know is this: can this maneuver be performed with only cyclic inputs, or would there also have to be pedal inputs to complete such a turn? And if it can be performed only with cyclic inputs, what exactly would those inputs be apart from rightward cyclic? Thanks in advance!

Yes it's cyclic inputs only for banked turns because there is no adverse yaw due to ailerons to compensate for.  You will be working the pedals to keep the ball centered, but this is only in reaction to torque changes from increases in rotor pitch and power demands.
Note that the airplane isn't using rudder to turn either; only to correct for adverse yaw.  What brings the nose around in the turn is the vertical fin.  The banked wings creates a lateral force vector, moving the airplane sideways as it goes forward.  The sideway motion cause the airstream to strike the vertical fin from the side, and the airplane's inherent weathervaning tendency brings the nose around to keep it aligned with the arc of a turn.  If an airplane had no adverse yaw at all, you would not need to use any rudder to help with turns.
A helicopter is the same.  There is a small fin back there that gives it modest weathervaning tendency (the disk area of the tail rotor also contributes).  The pedals are just there to change tail rotor pitch to adjust for off-axis yawing motions induced by torque changes (which can be in either direction, depending on whether torque is going up or down); just as on the airplane the pedals are just there to compensate for adverse yaw due to aileron displacement. If the helicopter had some automated system to always compensate for torque changes, you would not need to touch the pedals to turn.
In practical terms, in both cases, when flying you simply do whatever you have to do with your feet to keep the skid ball centered; in the airplane you are generally reacting to aileron movements, and in the helicopter to torque/pitch changes.  The power plane pilot learning helicopters has to adjust to get out of the habit of squeezing a little into-turn rudder to anticipate adverse yaw, and has to instead anticipate the subtle yaw changes - in either direction - from the power and pitch changes the pilot may input during the turn.


What is the relation between airspeed and altitude at fixed throttle setting in a private jet? In the world of private jets, say a G-450, at a fixed throttle setting, does it simply go faster the higher it climbs/flies?

The basic principles needed for an answer are:

Thrust varies linearly with air density.
Lift at constant angle of attack (AoA) equally varies linearly with air density.
Increasing the angle of attack from a low value will improve the lift to drag ratio (L/D), while increasing it from a higher value than the AoA at optimum L/D will decrease it.
The aircraft will settle at the point where speed equals drag and lift equals weight. If the altitude change improves L/D, the aircraft has excess thrust to fly faster.
Due to the atmospheric lapse rate, the speed of sound decreases with altitude.
Above a certain Mach number ($M_{dd}$ = drag divergence Mach number), drag increases nonlinearly over dynamic pressure.

Now the answer depends on where you start:

Low altitude, moderate throttle setting: The aircraft will speed up, because it was flying at a low AoA in dense air. Climbing brings it closer to the polar point of optimum L/D.
Low altitude, high throttle setting: If the aircraft flew at close to its $M_{dd}$, climbing will put it in colder air where it needs to fly slower to maintain the same Mach number. Depending on the starting speed, the aircraft might slow down.
High altitude, moderate throttle setting: Now the thrust decrease with altitude will dominate the equation, because the aircraft will fly close to its optimum polar point. Once it flies above the AoA of minimum drag, climbing will slow it down.
High altitude, high throttle setting: If it flies above the tropopause and close to the polar point of minimum drag, the air temperature does not change with altitude, and climbing will not change flight speed. It will stay close to its $M_{dd}$. Once it flies above the polar point of minimum drag, however, climbing will again slow it down.


Does Part 135 allow single-engine night IFR operations in a turboprop? Do the Part 135 rules allow single-engine turboprop night IFR Part-135 operations? If not, then all the night activities of current popular (and expensive) single-engine turboprops are by private or corporate owners and there are no commercial operations...!!!

I understand certain single engine turboprops are allowed to fly IFR at night for hire in EU, but I am not sure about it. Your input is much appreciated.

Do the Part 135 rules allow single-engine turboprop night IFR Part-135 operations?

Yes, there is nothing preventing it provided the pilot is night current and the airports are suitable for night operation.

You can find the FAA's 135 general requirements here.


How can I use a window for an emergency exit? A survivor of US-Bangla Airlines Flight 211 crash reports exiting out of a broken window.

My question is, in case you need to break an airplane window, what is the best way to do that?

I personally would doubt the veracity of the quoted report, since they say

  I have no recollection after I got out of the plane

I would wager that their recollection of the moments just prior could be faulty.

Nevertheless, to try address your question, my answer is: you don't need to, and you better not try, you would be wasting time.

Aircraft are designed such that complete evacuation must be completed within 90 seconds using only half of the available doors. Trying to open a breach through a window would take much longer than that, would cause otherwise avoidable injuries, and in general would create an opening that is generally quite small for a person to go through.

Your time and efforts are much better spent in reaching a normal emergency exit.

The only situation where exiting through other passages could have sense, is when the impact has created breaches (large enough to pass through) in the hull for you, but the likelihood of you being conscious then is quite low.


Has a commercial or military jet bi-plane ever been manufactured? Are there any, or have there ever been any commercial/military jet bi-planes?
What would be some of the major advantages vs disadvantages if one was built?

Electric radio controlled ducted fan model.

University of Tokyo concept model.

Yes

I present to you, the Belphegor, a jet powered, crop-dusting, biplane. I think I need not say that this is a Soviet Bloc design, from Poland in particular.

Note the braces between the wings acted as tanks for whatever chemical agent it would be dispensing over the kolkhozy. It was not very successful due to a host of disadvantages, including:

Jet engines are not efficient at slow speeds, which are in turn required for crop dusting operations. The designers may have hoped to do away with this requirement by using it over the large collectivized farms of the USSR, but the straight wing attests to the top speed being low by design. The jet engine was apparently mandated by soviet planners wanting to simplify the logistics of fuel and maintenance by reusing the AI-25 engine.
Biplane configurations are less efficient than monowings of the same total area due to interference between both lifting surfaces.
For crop-dusting applications in particular, @Harper points out the fact that the shorter span of biplanes is detrimental to effective spraying, by limiting the width of the spray system, which needs to end short of the wingtips. Otherwise the agent will get picked up by the wingtip vortexes and spread in unintended directions.

On the other hand:

One advantage of biplanes is low roll inertia due to the shorter wings, which is mostly useful in dogfights and thus not highly-sought nowadays.
Another advantage of biplanes is the lower bending moment at the root of the individual wings, due to them being shorter. This allowed earlier designs to get into the air in spite of poor building materials and QA procedures; this solution was gradually abandoned as aircraft moved away from wood and fabric and towards aluminium alloys.
The lower span of biplanes might be useful in application that are span-limited, like modern airliners, which are limited by airport parking and runway restrictions. If you absolutely need to obtain more lift out of an airframe that is already at its maximum span, adding a second wing is not unreasonable.


Is it possible to integrate an AI CoPilot on existing planes? Or a new aircraft would have to be designed for such a thing? I have little knowledge of aviation, so please feel free to fill me in the required bits.

If an "AI Co-pilot" existed, it could likely be integrated on existing airplanes with an auto-pilot system.

Since your question is a little vague, I'm going to take a stab at some your hidden assumptions and go from there. I'm also making the assumption that you're talking about the enroute phase of flight, and leaving the taxiing, take-off and landing in the hands of the human pilot.

At the risk of (extreme) oversimplifying, an AI system is essentially something that takes in a lot of data, analyzes it (through different algorithms) and outputs data that can then be used to do something.

I'm going to assume that the AI algorithm is supervised and has been trained on a bunch of existing data, and it has been figured out what data is important to make high-probability inferences.

In-flight, there are multiple sources of data that could be fed to the AI algorithm for it to make probabilistic inferences on what it should do.  These data sources are things like:

Engine monitors (my EDM 700 I think logs 60 data points/second on things such as cylinder head temperature, exhaust gas temperature, RPM, location, power setting, etc.)
GPS Receivers (3D position)
AHRS (attitude information)
ADS-B (Traffic and Weather)
On-board Weather Radar
XM Satellite Weather

(As an aside, SavvyAnalysis already does a bit of this type of analysis using the data from your engine monitor).

So, provided that your "AI Co-pilot" has been properly trained in advance on the same type of data that you are able get from your airplane while in-flight, your AI Co-pilot could ingest the data, and output signals to the auto-pilot which would then fly the airplane. The autopilot controller is simply sending information to a particular servo for a particular control surface (aileron, elevator, etc.) and if your AI Co-pilot can output the same signal, then it could control the servos the same as the autopilot.

One of the (many) difficulties lies in designing the system to safely handle things that it hasn't seen in the training data.

But to answer your question, it wouldn't require the design of a new aircraft, but rather a new autopilot control system.

EDIT: Extra thoughts

After thinking about your question some more, I was thinking why you might want an AI Co-pilot? I'm thinking the answer to that might would be for it to either make decisions for you that you are unaware you should be making or to help you make better decisions.  There is existing software that does something like this, called Xavion, which continually figures out where you should land if your engine quits based on the current location and performance of your airplane. It's not hooked up to an autopilot, but it wouldn't be too far of a stretch to think that sometime in the future, something like this could be a part of the autopilot controller.

  Furthermore, Xavion is constantly running engine-out flight
  simulations behind-the-scenes as you fly. The app imagines an engine
  failure every single second, and it checks how your plane would do in
  a power-off glides to every runway at every airport in gliding range.

  For each of these simulated engine failures, Xavion estimates the
  likelihood of a successful landing based on the runway’s length,
  width, proximity to the aircraft, and glide path from your current
  location down to the threshold of that runway. When Xavion has found
  the runway that it believes is most likely to result in a safe
  engine-out landing, it builds a series of hoops from your current
  location to that runway—spiraling, circling, or extending as needed in
  order for the hoops to follow a constant descent angle that your
  airplane should be able to sustain without power.

When you start to think of something like this, you can start to imagine analyzing real-time weather data and having the system make (or help make) a decision to divert or land based on your performance and experience. However, this is all something that would happen in the auto-pilot controller, so retrofitting it to an airplane with an existing autopilot would be more of a software upgrade than a hardware redesign.

UPDATE:

Wired had a good article on this on 3/28/2017. It talks about all the different sources of data that could be used to make an AI learn about the airplane, figure out where the holes are in the data and who could fill them.  An interesting place for data that I didn't think about (because it's not data generated in flight), is maintenance and service logs.

Particularly relevant to the intent (I think) of your question might be this passage:

  Elsewhere, researchers are working to ensure AI can help pilots manage
  crises as they arise. At University College London, a team led by
  Haitham Baomar and Peter Bentley is developing a new autopilot system
  that learns how to manage emergencies by watching how well-trained
  pilots do so, and then behaving as they do in similar circumstances.

  “We want to increase safety by trying to tackle the human-error factor
  that might be caused by stress, information overload, and sometimes a
  lack of sufficient and up-to-date training,” Baomar says. “Modern
  autopilots, unfortunately, can’t handle challenging flight conditions
  such as severe weather conditions or system failures.”


What is this helicopter type at a U.S. military base? This helicopter is on a US military base, shown by Google Maps. I don't recognize the glass windows at the front top.

In addition to Peter Kämpf's comprehensive answer identifying the helicopter as part of the Mi-17 family, this aircraft is likely to be a Mi-171E, clandestinely operated by the United States government, specifically it is 15-5207. With respect to 15-5207, the pictured aircraft

is a similar colour to 15-5207
has a similar box in front of its engine intakes (possibly for infra-red reduction)
has the same black triangle design around its exhaust
and has a similar proliferation of aerials on its tail boom.

Mi-171E 15-5207 in Springerville AZ, 2016 (source)
15-5207 was photographed at Felker Army Airfield, Virginia USA in December 2017; the orignal picture from Google maps is also Felker (note the provided link does may not show the helicopter depending on where you are). Felker is part of Joint Base Langley–Eustis. This aircraft has been noted at -

Burbank, California 2016
Yuma 2016
Springerville, Arizona 2016
and in 2018 at Opa Locka, Florida.

Understandably, the American military and secret service use of Mi-171E is not widely publicised, although it's known that the CIA has used the Mi-17 in a number of theatres. This particular aircraft carries no identifying markings; it may be connected with the US Army's purchase of 30 Mi-17s in 2013.
The only comment I can find with regard to this particular aircraft is from the Dutch aviation Scramble magazine on social media -

There are rumors that the US Department of Defense are using Russian
build aircraft for Special Forces Operations in areas abroad where no
western type aircraft operate. Evidence of this is very hard to find.
...
It is known that the US Air Force has the 6th Special Operations
Squadron (SOS),based at Hurlburt Field (FL), which is specialized in
Foreign Internal Defense (FID) operations. The primary role of the 6th
SOS is to assess, train, advise and assist foreign aviation forces in
the use of their aircraft, but the squadron also carries out intra
theater support of special operations forces, flying clandestine
night-vision insertion and extraction, air land and air drop resupply
mission with the capability of operating from unimproved runways.

Mi-171E operated by the US Government (source)


What happens after a clearance or an instruction has been sent by ATC using CPDLC? With conventional ATC, an instruction or a clearance is broadcast using voice, in case of no response from the crew, it can be repeated, and if silence persists it can be discarded as if it was never transmitted by ATC.

For aircraft with appropriate equipment, ATC can use CPDLC (controller-pilot data link communication). The message is sent and can be displayed by the crew. Then the crew may accept it or reject it, which is equivalent to the voice protocol.

Source

However what happens in case:

The crew doesn't open the message.
The crew doesn't answer the message after opening it.

Will ATC use voice to ask the crew to expedite responding to CPDLC instruction?

For ATC, how long this message remains valid? Can a message already sent be cancelled?

Voice communication and CPDLC co-exist as means of ATS communication. CPDLC is considered a supplement to voice communication - even if that may change in the future.

CPDLC is only used for non-time-critical communications. This aspect is very important in the context of your question. A response to a message sent via CPDLC can be up to several minutes, whereas for a message sent via voice radio, a reply can be expected within seconds; pilots and controllers know this, and will only use CPDLC if a relatively long response time is acceptable.

Generally speaking, when communication is initiated via CPDLC, the response should be via CPDLC, and when communication is initiated via voice, the response should be via voice. However, there are situations where it is beneficial to revert to voice communication after a CPDLC message has been sent. One example is when it is necessary to ensure the timely execution of an instruction issued by CPDLC, another is when a system generates a time-out or error. There is no standard time limit for replying to a CPDLC message, but various systems probably have some sort of time limits in them.

Standard phraseology is established for situations where it is required to revert to voice communication. One example is:

  SAS123, disregard CPDLC climb message, break, climb FL330

In this case a CPDLC message to climb sent to SAS123 is no longer valid, and instead the crew should react to the voice instruction to climb to FL330.

If the sender of a CPDLC messages wants to cancel a previous message, this is indeed possible using CPDLC - but most of the time it is probably desirable to do so via voice, to make sure the message is conveyed immediately. The ICAO Standard CPDLC message for cancelling a previous message is UM168:

  DISREGARD

Answer largely based on Introduction to CPDLC Operations (SKYbrary) and PANS-ATM Appendix 5.


Can I do the EASA part 66 theory exams before starting practical training? Is it possible to do the EASA Part 66 B1.1 exam modules first and do the practical training afterwards? Also, is it possible do the exams and training in different European countries?

I know very little about EASA regulations, but it looks like your first question is answered in EASA's Part-66 FAQ:

  I have completed my EASA Part-66 modules for B1 and I have passed all the exams, but I still lack experience to get my licence. Is there
  a time limit to get the licence ? Will the certificate expire in a few
  years if I do not get the experience?

  According to Commission Regulation (EU) No 1149/2011 of 21 October
  2011 (amending Regulation (EC) No 2042/2003), the basic examinations
  shall be passed and experience shall be acquired within the ten years
  preceding the application for an aircraft basic licence. The new
  regulation also states that for the purpose of time limits related to
  basic knowledge examinations, basic experience acquired before the
  Regulation applies, the origin of time shall be the date by which this
  Regulation applies, which is 01/08/2012 (which means until
  31/07/2022).

I couldn't find any clear answer for your second question, but another FAQ item might be relevant:

  Where do I gain the required basic maintenance experience? Is it mandatory to gain the required maintenance experience in an EASA
  approved Part-145 organisation?

  According to the AMC 66.A.30(a)(4), aircraft maintenance experience
  gained within different types of maintenance organisations (under
  Part-145, M.A. Subpart F, FAR-145, etc.) or under the supervision of
  independent certifying staff may be accepted by the competent
  authorities. This means that the aircraft maintenance experience may
  be accepted by the competent authority when such maintenance is
  performed in a maintenance organisation which does not necessarily
  hold an EASA Part-145 approval. However, it is on the competent
  authority to evaluate whether this experience is acceptable.

  Consequently, please contact the competent authority where you intend
  to apply for a licence, in order to check whether the basic experience
  would be acceptable, with detailed information on the type of
  aircraft, its operation and the nature of the work.

In other words, ask the authority in your country.


What are the differences between each ILS category? I want to know the characteristics of the different categories of Instrument Landing System (ILS): CAT I, CAT II, CAT IIIa, CAT IIIb and CAT IIIc. What are the differences between them?

(This question only covers CAT III).

The category specs are easily found on Wikipedia. Here is a concise view of the ILS approach minimums, as far as the crew is concerned.

  Cat I

  DH: 200 ft (61 m) or more
  RVR: 1,800 ft (550 m); at some airports 1,210 ft (370 m) is approved. For single crew operations, increased to 2,600 ft (790 m)
  orVISIBILITY 800 m (2,600 ft)

  Cat II

  DH: less than 200 ft and more than 100 ft (30 m)
  RVR: 1,000 feet (300 m)

  Cat IIIa

  DH: less than 100 ft and more than 50 ft (15 m)
  RVR: 600 feet (180 m)

  Cat IIIb

  DH: less than 50 ft (15 m) or none
  RVR: 150 feet (46 m)

  Cat IIIc

  DH: No limitations
  RVR: None

They are based on decision height and RVR (or visibility for cat I).
Note that there are no public transport aircraft certified for Cat IIIc as there is no use for landing without visibility and then staying on the runway because you cannot visually taxi to the gate.

The requirement for equipment certification accuracy itself can be found here.


What are the regulations involved in aerial advertising? I often see small aircraft flying at a low altitude around beaches and the like with banner advertisements trailing behind them on a rope sort of structure. I have a few questions about them:

What sort of permissions does it require (FAA) ?
Is this hazardous in any way (I believe there would be some
restrictions on this type of flight but is there an inherent danger
involved in such flights) ?
Are there any limits as to what altitude they are allowed to reach and
any restricted air space that they are only allowed to fly in ?

The short answer is that you need to get an FAA waiver (special permission), as required by 14 CFR 91.311:

§91.311   Towing: Other than under §91.309.
No pilot of a civil
aircraft may tow anything with that aircraft (other than under
§91.309) except in accordance with the terms of a certificate of
waiver issued by the Administrator.

(91.309 is about towing gliders, so banner towing comes under 91.311.)
You need at least a private pilot certificate to tow banners - sport and recreational pilots aren't allowed to do it - but since most banner towing is paid work, in practice the pilot will usually have a commercial certificate (this is from the waiver instructions):

When banner tow operations are conducted for compensation or hire, the
pilot must have at least a limited commercial pilot certificate
(without an instrument rating) and at least a valid second class
medical certificate. An instrument rating is not a requirement for
this operation.

The FAA has a complete guide on banner towing and the waiver issue process has more administrative details. There don't seem to be many specific airspace requirements apart from the obvious, e.g. no towing in a TFR zone. But the FAA can impose more or less any conditions that they like as part of a waiver, and it will include the approved times and areas for operation.
(As an aside, it's widely believed in the pilot community that the permanent stadium and Disney TFRs are really there to prevent banner towing, not to increase security.)


What prevents a propeller from detaching completely from the engine body? How does a propeller remain attached to the engine? I know there is a gearbox and/or some other mechanism that transmit the movement but is there any security mechanism that avoids it from completely detaching from the main engine? There is a huge amount of forces acting on that tiny spot where the propeller is attached to the engine, especially on turboprops, and this is where my question comes from.

Nuts. Technically nuts and bolts.

If you look at pictures of propeller hubs (google "propeller hub") you'll see that the individual prop blades are held onto the prop hub by nuts and bolts holding the hub halves together. Or for wooden props they're bolted directly onto the hub.

If you then take the hub apart, you'll see that the hub is attached to the shaft using nuts and bolts.

I sometimes see people asking why aircraft engineers specify very expensive nuts and bolts for certain parts of the aircraft when a cheaper part can handle an equivalent load. Your question is exactly the reason - it's better to over-engineer certain parts like the prop assembly than have the prop accidentally fly off during flight.


Is a reversal of heading allowed in the NYC Hudson VFR corridor? The special rules chart indicates that northbound traffic should follow the eastern edge of the Hudson and southbound should follow the west one.

Suppose a pilot wanted to only go mid-way through the corridor and then turn back, would it be allowed to make a 180 turn, merge into the traffic along the opposite edge, and simply go back?

I've never flown the corridor myself but from what I can find online it looks like a U-turn would be a case of "legal but not safe". 14 CFR 93.350 defines two different types of traffic in the SFRA and the FAA's kneeboard guide has a 'plain English' summary:

  Fly in proper altitude range

  Transient operation* [1,000 ft up to, not including, 1,300 ft MSL]
  Local operation** [Surface up to, not including, 1,000 ft MSL]

It also explains what those operations are (emphasis mine):

  Transient operation: Aircraft transiting the Hudson River Exclusion from end to end without intending to signicantly [sic] change heading, altitude, or airspeed.
  Local operation: Any aircraft within the Hudson River Exclusion that is conducting an operation other than overflying.

Those definitions certainly seem to allow for turns and maneuvering as part of "local operations". However, as Dave pointed out, the corridor is very narrow and maneuvers in a fixed-wing aircraft might be risky. In fact, there's already been one high-profile accident in the East River corridor where the aircraft hit a building after trying to a make a tight U-turn in a strong wind. I suspect that most aircraft maneuvering actively in the SFRA are probably helicopters rather than fixed-wing airplanes.

If you search newsgroups and forums about this you'll find a lot of comments about helicopter traffic at very low altitudes, and many pilots say that turning in the Hudson River corridor isn't a great idea. This thread is a good example.

The FAA has a safety course for the SFRA, by the way. I haven't done it but it might have more information.


Why have helicopter top speeds not increased much over time? With advancements in technology why there isn't much increment in helicopter top speeds from what they were in the 1980s? We have newer designs like the Eurocopter X3 which is a hybrid, but the speed is still limited to 300+mph.

The underlying limit is that the forward-moving blade tip must remain subsonic, and the receding blade must not stall.  Hybrids do better than conventional or compound helicopters because the rotor can be slowed when the fixed wing picks up some of the lift load -- but this only solves the forward blade tip speed issue; unless the rotor can be operated at zero lift, receding blade stall is still a problem.

Some futuristic designs have proposed completely halting the rotor in forward flight (see the aircraft in the movie The Sixth Day with Arnold Schwarzenegger -- cheesy movie, but the aircraft were based on a real concept), using an airfoil shape for the rotor blades that can develop lift with either edge forward.  Others have proposed completely folding the rotor once forward speed is high enough for the fixed wing to support the craft -- but as far as I know, no flying example of either of these concepts has been built.  Until they are, the same speed limitations apply to helicopters and autogyros that were discovered in the 1930s, only partially mitigated by hybrid configurations.

Bottom line is, a helicopter's niche is in going slow, not going fast.  Other VTOL solutions exist for high speed (thrust-hover jets like the Super Harrier and F35 are supersonic).  Attack and high-rate maneuverability in hover are the special domain of choppers; high forward speed is not.


What are the maximum possible stabilizer and elevator deflections for the A320? For research purposes I would like to know the maximum deflection angles (in both positive and negative direction) of the A320-200's stabilizer and elevator.

I am trying to analyse what flight conditions are trimmable.  The outputs I get are deflection angles.  I need to know whether those angles are within the ranges of maximum deflection.

As per the A320 flight manual (§127.20 p3), the maximum permitted total pitch alteration in normal law depends upon speed, aircraft mass, CoG, and other factors:

Pitch Attitude Limitation:
Pitch attitude is limited to:

30º nose up in conf 0 to 3 (progressively reduced to 25º at low
speed)
25º nose up in conf FULL (progressively reduced to 20º at low speed)
15º nose down (indicated by green "=" symbols on the PFD's pitch scale)

The flight director bars disappear from the PFD when the pitch angle exceeds 25º up or 13º down. They return to the display when the pitch angle returns to the region 22º up to 10º down.

Likewise, the maximum physical elevator deflection is 30º nose up and 17º nose down. The maximum trimmable horizontal stabiliser deflection is separately 13.5º nose up to 4º nose down, but the plane will always fly within the total pitch limits specified above.
Good luck with your project!


What would happen if the Emergency Locator Transmitter was activated wrongly? Supposing, after a "bad" landing, performing a high vertical speeed, the crew, unintentionally, activates the ELT, sending the signs to the sattelites, warning the rescue and team about the "accident", that does not happen.
Would the fees for the services be payed?
Is there any penalty for the crew or company?

It happens ALL the time. I have been on many airport hunts looking for the airplane with a triggered ELT. You tale a handheld radio and walk through the ramp until you find it.


What is the effect of flying height on helicopter fuel consumption? Does the height at which a helicopter is flying affect its fuel consumption? Which factors are influencing its fuel consumption?

The lift equation shows that as air density decreases, as it does with altitude, in order to maintain lift, the speed of the blades must increase or, the coefficient of lift (CL) must increase.  Since the characteristics of the blades do not change, in order to increase the CL, the angle of attack must be increased.

Increasing either of these increases drag so, in order to prevent the blades from slowing down, the engine must produce more power to counteract the drag.

Most helicopters use constant speed rotors so in practice, the angle of attack (the pitch of the blades) is the only variable.  In order to maintain speed of the blades, the pilot, or a throttle governor, must increase power from the engine.

Therefore, a helicopter uses more fuel as it's altitude increases.


What is the relation between hinge moment at the control surface and servo torque? I am trying to estimate the required servo torque for my design using hinge moment at the elevator.

XFOIL results were as follows-

I am getting a Hinge moment of about 0.06-0.08 Nm. for the given deflection.
How can I relate this to the servo torque I require? Will they be equal?

The servo torque depends on the mechanism. If it has a gear ratio of 1, they will be equal. If the servo is driving larger angular deflections than its own, the servo torque will be higher.

Another important point is to consider the dynamic forces. XFOIL only computes results for steady conditions. Dynamically, the servo may have to bear even larger torques; due to acceleration or gravity.

Finally, unless you really trust your computations, some uncertainty factor can be used to reduce the risks of redesigning the control system solution.


Why do some airplanes have their winglets at different angles? While travelling recently a friend of mine noticed that the tips of the wings on some planes were at different angles on the left and the right hand sides of the plane.
Is this a thing and what is the reason for this?

Some googling and searching on this site did not reveal an answer.

Winglets are symmetric, meaning they are the same shape, size and angle on both sides of the airplane. Different shapes and/or angles would mean the wings would have different aerodynamic properties, i.e. they'd fly differently from one another, which is generally a bad thing. It's probably been done for testing purposes, but not in production aircraft.

It's possible that your friend noticed that different makes and models of airplane have different winglets. Some look like this:

Some look like this:

There's other shapes too. Viewed from different angles it's possible they may look like different shapes, but they're going to be the same even if it doesn't seem that way.


What is this old pusher propeller aircraft? I am researching the history of pusher aircraft and came across this photo. Any information or guesses as to its history? Country, designer, mfg, pilot, etc? It looks to me like perhaps a 1920's powered glider (looks like a wheel not a skid at the front but can't tell for sure) but that's a guess.

Update: I found another picture without comments of the same aircraft dated 1912 - so this is one of the very first attempts at flight. Which means it likely is not a glider but an experimentation with configuration. It does have a wheel at the front - not a skid.

I found two mentions of it, one was a design article written by Molt Taylor and his Aerocar...

"To our amazement, we found that a fellow by the name of Edson Gallaudet had built a shaft drive airplane way back in the 1910-1912 era which was twice as fast as contemporary airplanes! Gallaudet flew his Al and A2 Bullet models in the 120-130 mph speed range at a time when his fellow designers were happy to be able to fly 60 mph. And while they were still sitting out there on their wings with their pant legs fluttering in the breeze, Gallaudet was snug in a cockpit that enclosed all but his head."

"His landing gear was largely enclosed a within bullet shaped fuselage and his three bladed propeller was mounted on the tail. It was this latter feature that we were interested in, of course. We were fortunate in finding that a dear personal friend had actually seen the Gallaudet airplane fly and knew a lot about it. He had even flown in one of the later Gallaudet seaplanes. We were also curious to learn why Gallaudet had been able to make the long shaft to the tail propeller work so nicely, only to have the course of aviation progress move completely away from the concept when it was so obvious that the tail was where the propeller really should be mounted. Certainly, the performance of the Al and A2 proved that."

"As it turned out, the answer was quite simple — he had used a rotary engine, which served as a spinning flywheel that smoothed out the power pulses that can be so destructive to shaft drives. This "torsional resonance" was the problem that plagued the Waco Aristocraft, the Douglas Cloudmaster, the BD-5 and a number of others with shaft driven propellers. Some of the more sophisticated designs like the XB-42, P-39 and P-63 incorporated successful shaft drives, but only at the expense of heavy, costly, high maintenance vibration damper systems and' special operational techniques."

The second mention is at http://affordaplane.com/alumribs.html

"The first airplane to use aluminum tubing for ribs was this one, the Gallaudet A2 Bullet. Built in 1912, the tube ribs were flattened at the ends so rivets could attach them to the caps and spars."