What is the typical pilot to aircraft ratio in military squadrons? On aviation.SE, we already find this question addressing the pilot to aircraft ratio in airlines. It states that typical big airlines have roughly between 15 and 20 pilots per aircraft.

Military aircraft may require less pilots per aircraft:

airliners are in flight almost all day long every day
a typical airliner flight requires between 2 and 3 pilots (the 3rd one for very long steps or as an instructer)
a typical fighter is a one-seater
a fighter flight less time than an airliner
military cargo may flight more than fighters, but I hardly see a cargo used as much as a passenger aircraft (I may be mistaken)
HALE UAV may require several crew per flights but I don't know how long are those flight neither how many UAV can be operated simultaneously by one crew

When searching the number of each type of pilots (fighters, cargo/airliners, UAV) per air force (whatever the country), it is easy to come across recruiting websites (with requirement to become a military pilot and salary) but I fail to find anything about the number of pilot an air force has.

My question is : What is a typical ratio of pilots to aircraft in a typical military squadron? Does it differ between fighter squadron, transport squadron and UAV squadron?

As has been said, there is no one exact rule, but a broad estimate can be easily produced.

There are 12,500 active duty pilots in the USAF, and the service counts just over 5,000 manned aircraft. This will give an overall, rough, ballpark figure of 2.5 pilots per aircraft across the entire force.

Counting aircraft types by pilot seats, one can calculate the total number of pilot seats at around 8,350. About a thousand comes from training aircraft, however.

This gives an overall approximate figure of 1.5 pilots per seat, across the entire USAF.

This is not distributed equally. As mentioned in the comments above, combat units tend to run relatively low ratios. With the recent shortage of pilots, especially ones rated for combat aircraft, it has sometimes fallen below 1:1 in some units. For transport and utility aircraft, there are more crews.

The pilot-to-aircraft ratio depends mostly on the aircraft type the squadron flies. For example, a fighter squadron might have far more aircraft in its fleet than an airlift or reconnaissance squadron. There is no fixed number.


What would happen if one of the engines failed during takeoff and other engine is on full power? Assume the left engine failed and the right engine is at full power. The pilot has pulled his nose up and turned towards left. Is it possible for him to land the plane on a runway to his left? The plane is an ATR-72 turboprop design

No, no, by all means don't turn left. See also Why should you not turn in the direction of an inoperative engine?.

Transport category aircraft are capable of climbing out on one engine. It is a certification requirement for them. So if the left engine failed after rotation, the first thing the pilot has to concentrate on is to keep the plane flying and under control. That means ease the pull on the stick a bit to avoid stalling as the plane is not able to climb as fast and push the right rudder pedal to keep the plane flying straight¹.

Once the plane is in straight climb at $V_2$ speed, it's time to deal with the engine. First both pilots cross-check the instruments and the rudder position to determine it was the left engine that failed. Then they feather the propeller (auto-feather might have done it already) and cut fuel to the failed engine. If the engine fire warning is on and did not extinguish when fuel was cut, they discharge fire extinguisher.

These things are done according to standard emergency procedure that the pilots have to remember and train in simulator. I don't know the specifics for ATR-72, but in all aircraft it is roughly like above.

Meanwhile the aircraft climbs to safe altitude and then they should level off and let it accelerate a bit to get some safety margin for manoeuvring.

The plane is now in relatively safe condition. Even if engine was on fire, it is unlikely to spread while the aircraft is flying. So the pilots now have time to declare emergency and ask the controller for what options they have for landing. Whether they do a complete circuit and land back on the same runway or turn around and land in opposite direction or land on some other runway then depends on wind and where they are relative to the runways at the time.

There were many accidents where plane crashed after one engine failure during take-off because pilots started manoeuvring before they attained sufficient altitude and safe speed. It is better not to hurry, engine failure does not require it.

¹ Of course provided there are no obstacles in the way. For example if you were taking off from VQPR runway 33 and your right engine quit, you'd still have to do a right turn rather early to avoid the Mr. Smith's house right in the axis of the runway and quite a bit above it. But for any airport that require such avoidance (and there is quite a few of them in various mountains), the pilots are specifically briefed and trained for that airport which includes instructions on how to best handle engine failure during take-off and during approach and viability of the procedure is verified in simulator and with a test flight. The above answer just outlines the generic procedure.

The PIC has the authority to do whatever he/she deems necessary to control the situation. Landing on another runway on the same airport is one of several choices. Not all airports have multiple runways, and if they do, not all are suitable for an immediate landing, but if the runway layout allows for it, then yes, landing on another runway is a viable option. But only one of many. I always impart in my ME students to consider landing on another runway in case of an engine failure upon take-off, IF (and only if) the runway layout is suitable for that. On most airports, landing on another runway is not an option.


To what extent (if any) is it possible or desirable for the pilot of a large airliner to "fly by the seat of the pants"? I recall that some years ago the pilot of the A340'S first flight described its handling as "like riding a bicycle" (to me this would mean that as he went past his favourite bar he saw his friends inside so he propped it up against the wall to have a drink with them).

I can believe that despite its size and weight a large airliner would respond precisely to commands, but does the concept "flying by the seat of the pants" apply to such an aircraft?

Obviously experience and training will build up a great deal of intuition (visual, vestibular, etc) - what sort of bodily connection does an airline pilot experience with the aircraft? Is it markedly different from that of the pilot of a small plane?

I can believe that despite its size and weight a large airliner would respond precisely to commands, but does the concept "flying by the seat of the pants" apply to such an aircraft?

The phrase "flying by the seat of the pants" is an imprecise term, and I don't have an answer for that. However, if you allow it to mean operating an aircraft in the absence of instrumentation or other capability that is normally used, or using techniques not normally used, whether you're forced to because of failure(s) or because you prefer not to use them, then here is an observation.

In the early 1990s I was flying 747-100/200 freighters. The carrier had a contract with Japan Air Lines to haul freight between Tokyo Narita and KJFK, with a crew change and refueling at Anchorage. We used a JAL call sign. JAL had their own 747-200 freighters on the route as well, more of them than our small number of aircraft. Many of their flights would have an American flight engineer who would handle the radio going into U.S. airports. Thus, the Anchorage controllers could not tell from the radio communication whether the flight had American or Japanese pilots.

One summer Anchorage took the ILS down for extended maintenance. One severe clear day during this period we were on our descent but still well out when Anchorage approach cleared us for a VOR approach. We immediately called the airport in sight and requested a visual approach, which was granted.

Curious, when we were down I called approach control on a land line and asked why we were first assigned a VOR approach. They explained that, believing our flight probably had Japanese pilots, and having had those pilots always refuse the offer of a visual approach and request a VOR approach (in spite of the additional 10 minutes of flying), approach control had simply assigned the VOR approach.

As part of our contract, we occasionally had a Japanese check captain observe us, and the next time this happened, I brought up the subject with him. He explained that their pilots were never taught to simply look at a runway and land without reference to navigational instruments, and, lacking a robust general aviation segment, their pilots simply never had experience with doing that. He added that from their standpoint, we were a bunch of cowboys. Not the exact "flying by the seat of the pants" wording, but the same sentiment.

  Obviously experience and training will build up a great deal of intuition (visual, vestibular, etc) - what sort of bodily connection does an airline pilot experience with the aircraft? Is it markedly different from that of the pilot of a small plane?

When you're flying the same airplane type day in and day out, you internalize what that aircraft can do and how it will respond. You get used to its noises and even to its vibrations if you will. And regardless of how small or how large it is, it becomes the right size, neither little nor big, especially once you're in the air. When you change airplanes, and especially if it involves a significant change in size, there is a difference.

For example, I spent the last 10 years of my career on 747-100/200 aircraft. Fifteen years after retiring, and not having been in a cockpit during that time, I went out to a local airport to check out in a Cessna 172. I knew I would have trouble with flaring too high, and I warned the instructor. My first landing was a real lesson, actually to both of us. When I said to him, "I think I should flare," he said, "you're way to high." When I said, "I've got to flare,: he said, "still too high." When I said, "I'm flaring," with the sense that if I didn't I would prang the airplane, he said, "you're still a little high, but go ahead." It took me 5 hours to check out in the airplane, most of that time for landings.

Ask Captain Al Haynes and Captain Chesley Sullenberger.

Do not ask the Asiana crew who landed short at SFO.

So the answer is:  It depends on the individual crew members and their level and quality of experience.


Is there any mechanism in engine mount to prevent shock loads on engine while landing? How engine is mounted in wing is restricting motion in any direction but is it still resistant to shock loads, or is there any mechanism inside engine associated to bearings that will absorb shock loads that occur in spools?

"Shock" loads on landing can be transmitted to engine components.  The original poster appears to be asking about turbine engines specifically.  The significance of a hard landing on the engine spools themselves will be shaft flex and case flex, and the possibility of blade rubbing (and erosion).  This is a concern with a hard landing, and something that must be considered.  There are not "shock absorbing" features or capabilities built into bearings in engine spools; these are intended to have minimal friction in rotation, but no concentric movement about their axis.  It is possible in severe turbulence, and in a hard landing, to experience case or blade damage or wear, and there are inspections prescribed for certain components in certain engines to address this.

There are no mechanically significant shock loads on an airplane engine in normal operation.


Do the compressors and turbine rotate at the same speed? Since the turbine and the compressors are connected to each other via a common shaft, do they both rotate at the same speed. Because I've read that in some jet engines (single spool engines) they don't rotate at the same speed:

  Single spool jet engine. These are those jet engines who have one shaft inside them. The compressors and turbines rotate on a same shaft. The speed of compressors and turbines decreases half way down the compressor stages, that is why they can’t match the local airflow. The various turbines and compressors is forced to rotate at same speed which lead to their inefficiencies.

(quora.com)

Is this true?

That's one badly-worded quote:

  Single spool jet engine. These are those jet engines who have one shaft inside them. The compressors and turbines rotate on a same shaft.

Correct. In a single-spool engine, all of the compressor and turbine stages rotate at the same speed because they're attached rigidly to the shaft.

  The speed of compressors and turbines decreases half way down the compressor stages, that is why they can’t match the local airflow.

No, the speed of the compressors and turbines doesn't change. It's the airflow that changes, and causes a mismatch.

Your question answers itself. If they have a single shaft and no gear box, then they rotate at the same speed. If there is a gearbox then that gearbox gives you the speed difference.


How can I tell apart an Airbus from a Boeing? When looking at an airplane, what are the main external features I should look at if I want to determine if it is an Airbus or a Boeing (shape of the tail, fuselage, winglets, wings, etc.)? Same questions from a passenger point of view, quietly seated inside?

I like to train being able to determine the precise model of an aircraft.
I first try to tell if it's a Boeing or Airbus, and then I look at other details to determine the model.

The idea is to learn several differences :

cockpit windows shape (Boeing has an very specific angle) ;
nose shape (pointy nose on Boeing, "fat nose" on Airbus) ;
wingtips (winglets Boeing, fence Airbus) ;
number of engines (A340, B747, A380 have 4 engines, all others have 2) ;
gear.

Since there are already nice answers describing most of these points with pictures, I will focus on the gear to add a new item to the list.

Landing Gear

Looking at the gear adds a new hint. Some landing gears are unique, which means that only looking at them will be enough to determine the precise aircraft type. These very specific gears are :

B777
B747
A340 (2 different kinds for this aircraft only)
A380

It's not worth to look at the nose wheels, because there are always 2. But the main landing gear is helpful.

I made a gear cheat sheet to help me learning them.

Once these differences have been learned, the key is to use several of them to crosscheck and ease and speed up the recognition.
For example if I see the gear

   2
2*2 2*2

I will then check the cockpit windows to determine whether Boeing or Airbus.
If it's Airbus, I will know it's very likely to be an A330! If it's Boeing, it will be harder since there are still 3 different aircrafts. If I want to be able to distinguish between them, I can learn new specific hints for this purpose.

Easiest is internal. Look at overhead luggage compartments. If they raise up to close giving a sloping roof over the seats it is a Boeing. If the shutter comes from top and the roof over the seat is horizontal and immobile, it is an Airbus.


Why does the Beech Staggerwing have its low wing ahead of the high wing? Why does the Beech Staggerwing have its low wing in ahead of the high wing? What are the aerodynamic ideas behind this? Other biplanes of the era had the opposite, low wing behind the high one.

Notice the retractable landing gear? With a tail-wheel design, the main gear work best at or ahead of the center of gravity. The Staggerwing has a neat and efficient retractable main gear, that folds onto the lower wing. But the lower wing has to be farther forward than usual for this to work.

The two wings on a biplane interfere with each other, but the biplane structure is very strong and stiff for its weight. So the Staggerwing's design gives up some wing efficiency for strength and light weight. Then it gives-up a little more for the reverse stagger that puts the downwash of the lower wing right under what should be the high pressure under the upper wing.

However, the design gets good speed from the retractable gear reducing drag. And both wings, upper and lower, join the fuselage at 90 degrees, with no struts or other sources of drag. Aerodynamically, a very clean design. the Beech Bonanza looked more modern, but the Staggerwing had the same cruising speed, 176 knots, 202 mph. It also had a 450 hp P&W Wasp Junior, while the Bonanza got along with a 300 hp Continental.

Ted Wells did this just for visibility. It turned out that is was also good for flight characteristics as the bottom wing would stall first causing the airplane to pitch forward thus preventing the top wing from stalling. It also provided the ability to retract the gear into the wing.


Why would a flight from North America to Asia sometimes fly over the Atlantic? I am going to take AC031 from Toronto to Beijing in a couple of weeks, I searched its flight path, most of the time it will fly westbound after taking off from Toronto and continue west across the north pole area and land in Beijing, but yesterday it flew eastbound, across the Atlantic, this is very strange since the distance is a little bit more than flying westbound.

Why?

Those routes are extremely similar.

They're basically two almost-a-straight-line routes over the arctic ocean, except that the second one has deviated a bit to the right, so that it's gone just on the right of the North Pole instead of passing by the left. At the pole itself, there's no such thing as "East" or "West", and if you pass very close to it, there is a discontinuous jump between passing it "going East" and "going West".

You can see this explicitly by going to FlightAware, asking to View track log, and downloading the flight tracking data to be viewed on Google Earth:

 Actual tracking data in white. Interpolations for the missing-data parts in green.

As you can see, there is indeed a nontrivial deviation of what's probably several hundred kilometers in clipping Nunavut vs the northeast corner of Greenland, but that deviation is within the normal ranges of what you'd get in your standard transatlantic flight, say. The only change here is that the variation now includes the North Pole itself.

ALL flight paths on the earth are curved, cause the earth is a sphere! Which way that curve appears depends on which side of the curve you are observing it from. If you observe it frm south of the flight path it will appear to curve northwards and then south. If you observe it from East of the flight path it will appear to curve West and then East, etc.


Why don't flights fly towards their landing approach path sooner? For example shown here, the flight is heading to the centre of the airport, until it gets close when it then moves into it's landing path. This is an inefficient use of time, fuel and emmissions, why can't the airport tell the aeroplane exactly which runway and direction it will land earlier so it can more efficiently head towards the approach.

In general, IFR flights through controlled airspace use airways (highways in the sky) to fly between waypoints. The particular flight you show looks like it arrived via the N774 airway to a waypoint MARLN:

(skyvector.com)
The traffic flow around busy airports like Kingsford Smith (YSSY) in Sydney is usually structured using Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs). Your example was probably on the MARLN5 RNAV STAR:

(from the Jeppesen chart for MARLN5 at YSSY)
From somewhere after the JAKLN waypoint, the air traffic controller (ATC) would have instructed the flight to turn right to intercept their final approach path (probably to runway 34R).
All of this structure (airways and procedures around busy airports) exists to allow for an efficient flow of traffic that can be easily managed by ATC. There are many things to consider when these paths are designed:

avoiding conflicts between aircraft (e.g. between departing and arriving aircraft or between flights from different airports in the area)
restricted airspace (e.g. airspace reserved for the military or avoiding flights near sensitive areas, like nuclear power plants)
noise abatement (especially near large cities you want to avoid overflying the city center at low altitudes)
terrain (not really relevant for Sydney)

Nonetheless, one can deviate from these fixed routes. ATC might clear an aircraft on a more direct route if traffic and restricted airspace allows this (very common right now due to the pandemic). Some countries have even removed all high altitude airways and replaced it with Free Route Airspace.
The problem with setting an aircraft on a direct route for final approach interception is that this would have to be done far away from the airport. The aircraft needs time to descend and slow down (usually more than 100 NM). At this point they are typically not handled by the approach controller for the airport they are landing at, but still by the Area Control Center (ACC). This would require significantly more coordination between various controllers and is probably not very efficient in busy airspace. During the current pandemic with significantly less traffic, you might see it though.

ATC isn't incentivized to reduce CO2 emissions. To do so would require re-architectiing their whole SIDs and STARs (to make them dynamic based on AC type, weather, traffic, and other factors). I vaguely recall reading about a (US) FAA initiative to modernize the vector airways to optimize for descent rates, etc but that will take years. Ultimately, it's the airline who bears responsibility to minimize fuel consumption and government who is responsible for separation.
I'm not myself an aviator, but I imagine that the downwind, crosswind leg, and final also give the crew a good feel of the surface meteorological conditions.
My final $0.02: ultimately the best way to minimize CO2 is to not fly for leisure. Look at youtube for all the frivolous flights of people globe trotting just because they can. It's simply un-sustainable.


Is an ultralight aircraft allowed to fly near Class B airspace? May an ultralight vehicle operating under FAR part 103 operate within Class G and E airspace while within the mode C veil surrounding a Class B airport?

Quoting directly from Title 14 CFR 91.1 Applicability

  FAR 91.1(e) This part does not apply to any aircraft or vehicle governed by part 103 of this chapter, or subparts B, C, or D of part 101 of this chapter.

Part 103 addresses airspace in this way
103.17 Operations in certain airspace

  No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

Where can I find a restriction that applies to ultralight operation within the mode C veil but still in Class E or G airspace?

Yes, an ultralight aircraft operated under 14 CFR 103 can be operated within the "Mode C Veil" within the limitations of §103.

As you note, 14 CFR 91—including §91.215, ATC transponder and altitude reporting equipment and use—does not apply to ultralights governed by §103.

The limitations of §103 do generally prohibit: operations over congested areas; operations in certain types of airspace; operations in certain types of airspace.

  §103.15   Operations over congested areas.

  No person may operate an ultralight vehicle over any congested area of a city, town, or settlement, or over any open air assembly of persons.

  §103.17   Operations in certain airspace.
  No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

  §103.19   Operations in prohibited or restricted areas.
  No person may operate an ultralight vehicle in prohibited or restricted areas unless that person has permission from the using or controlling agency, as appropriate.

Let's look at an example, the MSP Class B area:

Point A, near A R S Sports Strip (7Y7), would be an area where operations under §103 would be allowable. It is not a congested area, and is not a type of airspace for which operations under §103 are prohibited.

Points B, C, and D, however, would be areas where operations under §103 are generally prohibited. Point B is arguably over congested areas, and by that determination would therefore be prohibited under §103.15. Points C and D are in Class D and B airspace, respectively, and are therefore prohibited under §103.17. The exception would be where the operation has received prior authorization as specified in §103.17 above.

For what it is worth, I have personally witnessed ultralight type aircraft flying in the area of Point A.

Let's make it simple if your ultra light does not have an electrical system like an alternator or generator you did not have to have a transponder. If you're flying into a mode C Veil The only reason why there is a mode C Veil is because there's going to be a class Bravo airport in the middle of it.

Obviously you have to stay out of class Bravo airspace. One of the examples previous to my post there was a listing for Zone B and Zone C, you could fly in that area as long as you remained under the class Bravo Shelf! You might be flying under part 103 but the rules of far 91 and 61 still apply to you.

If you're flying under part 103 which means you're doing a VFR flight that means you do not have to have communications which means obviously you would not be able to call the controller to request a deviation. Nor could you provide any radio discreet code given to you.  You would not need to do that because one you're not answering their class Bravo airspace that they're controlling and two part 91 specifically exempts you from requiring to have a transponder since you have no electrical driven system.

So yes you can fly in the mode C Veil, as long as you stay out of the class Bravo airspace, with no transponder ( as long as you have no electrical system) and you need not call anyone.

Additionally the air map above is not considered a congested area simply because it's yellow. The purpose of the yellow on an air chart is for when you're flying at night to help you identify a congested area that would be illuminated with a lot of lights. It does not necessary mean it's congested and you can't fly above that area for example if you flew above a railroad track going through a major city the railroad track would not be congested with people.


What is the difference between centripetal and centrifugal force? In a homework problem I was asked:  In a balanced banked turn an increase in angle of attack will :?

Answers are :
1/ reduce indused drag.
2/ increase centripetal force .
3/ increase centrifugal force .
4/ have no effect on the turn.

Obviously answer 1 and 4 are wrong but what about centripetal vs centrifugal force?  What is the difference between the two?

Two of the given answers - choices (2) and (3) - are correct in different reference systems. It depends on the reference system of the observer:

In a non-accelerated reference system, centrifugal forces do not exist. Increasing angle of attack increases the centripetal force, that increases the turn rate. The reaction force of the centripetal force is the innate force of the plane.
A passenger in the plane observes the scenario from within an accelerated reference system. The plane is turning without obvious reason. The passenger's body wants to move in a straight line and seems to exert a force on the seat. This virtual force is called centrifugal. The seat seems to react by supporting the body with the same amount of force. When the pilot increases the angle of attack of the balanced turn, the centrifugal force will increase. The observer inside the rotating system is not aware of the centripetal force. The centripetal force does not exist for him.

Centripetal and centrifugal forces never co-exist in the same reference system! Even though they might appear like counter forces to each other, they should not be understood like that.

Centrifugal force is a construct to explain our perception and sometimes to simplify calculations in rotating reference systems.

Between the two, centripetal force is the more fundamental notion. It really describes what is going on, therefore (2) is the better answer from a scientific point of view. Nevertheless, (3) centrifugal force is a valid answer if the reference to a rotating system is established. That seems to be the case in the question. The centrifugal force describes what an occupant feels who is not aware of the rotation.

Centripetal force is the answer.  Hopefully you can see that options 1 and 4 are wrong without me having to explain.  I will elaborate instead on the difference between Centripetal force and Centrifugal force.

First Centrifugal force is not really a force at all but really a perceived force due to the inertia of an object to resist a turning tendency.  In a coordinated/normal 1G turn you should not feel any Centrifugal force.

Centripetal force is a force that makes a body follow a curved path.  When the angle of attack is increased more lift is generated and hence there is more force to execute the turn.  Since the wings are banked the increase in lift causes the airplane to turn more so Centripetal force would be the correct answer.

EDIT:  Due to some comments about my answer I decided to clarify a few things.  First of all where there is Centripetal force there is centrifugal force with centrifugal opposing Centripetal force.  However in an airplane there are many forces at play.  In a coordinated 1G turn, the horizontal lift component matches the centrifugal force (but in opposite direction) as shown in the diagram below.    Therefore the horizontal lift cancels out the centrifugal force so you don't feel the centrifugal force but it doesn't mean the centrifugal force isn't there.  Forces in an airplane can be deceiving that is why pilots sometimes get disoriented when there is no horizon for a reference.


How do you hold at a non-towered airport? Let's say, hypothetically, that you enter the pattern for a small, non-towered airport (my local one, 3DW, may be a good example.)  But as you get into the pattern you find out that the runway is occupied by another craft and, for whatever reason the runway will probably be occupied for another 20 minutes, much longer than it will take you to complete the pattern.  So you'll have to delay landing.

But you've already entered the pattern, so what should you do?  Is there a standard holding pattern for small airports that incorporates parts of the pattern (maybe some little loop where the base leg and downwind meet)?  Or do you just fly away form the airport a bit and make up your own holding pattern?

There's no "standard holding pattern" at any airport, towered or not. If the runway is occupied or temporarily closed for some reason, you might was well leave the traffic pattern and go putt around for a while someplace where there are fewer aircraft. At a towered airport, the controller will likely tell you what to do - but again, you can make both his life and yours easier by just leaving the pattern and going somewhere else until the situation is resolved.

A holding pattern just means circling the airport. If you had to wait there, that is what you would do, circle the airport. If there are so many aircraft, that the pattern altitude is full, then you start stacking 2000 feet, 3000 feet, 4000 feet, etc.


Is lift in fact a kind of drag? Given the similarities between Lift and drag and their very similar relationships to the density, surface area, and airflow velocity, could one, in theory, describe aerodynamic lift as a kind of drag where most of the force from lift is just directed in the vertical direction where this vertical component of the force opposes gravity?

An 'aerodynamic force' (just one force...) appears when a body is immersed in a fluid stream. By convention, two components are chosen, one of them parallel to the stream direction, called 'drag', and the other one, perpendicular to that 'drag' is termed 'lift'.

I think that's the wrong way to look at it.  The lift force is 90 degrees to the airstream.  When you're gliding, the lift force is producing thrust, not drag, or else you would stop dead and fall from the sky.

I think of the lift-related drag component as the energy consumed in inducing the air to move from point A to point B, creating the pressure differentials and down thrust from action/reaction, as the wing passes through it.


Why don’t airplanes use turn signals? Why don’t airplanes use turn signals like cars do? Would this improve safety for ground operations at uncontrolled airports? Could a similar concept be used to indicate in air maneuvers?
For example: a specific color could denote a right turn, a left turn, a climb or a descent.

At uncontrolled airports, there is rarely enough traffic for signals to be needed, and pilots should (though are not required to) communicate with each other on CTAF—an option that cars do not have.
In the air, if you're close enough to see a turn signal, you are way too close and need to immediately follow the collision avoidance procedure.
More generally, aircraft are a lot more like boats than cars, and boats don't have turn signals either.

Although all of these answers are very good (and correct), they are missing an important fact: planes try to go on the most direct routes (unless mountains, or other landmarks that affect flight, are in the way). This means that most planes will be traveling in a straight path, so turns aren't applicable. That too planes are given routes that do not travel close to the same point at the same time (to prevent a collision). This means that contact (besides at airports) is rare.


Do cargo operators need an AOC? Is it just commercial operating aircraft flying paying passengers that require an air operators certificate (AOC) or do cargo operators require one also?

An aircraft doesn't need an AOC    Operating the aircraft for anything other than for private purposes is why you need one.


When the winds aloft are light and variable, what wind direction and speed should I use for flight planning? What do you input in a navlog for wind direction and velocity, when the wind and temp forecast says 9900+18? I know 9900 means light and variable winds less than 5kts but how do I determine the average wind direction to use for my navlog?

Light and variable means there's no meaningful windspeed or direction, so you can just ignore it. For planning purposes, you can simply plan as if the wind was calm.

But, it's very possible that the winds will actually be stronger and more directional than forecast. You should check your actual track and times against what you planned, and adjust your navlog in flight as needed. That's one of the cross-country navigation skills that pilots are expected to learn.

The best technique when planning your flight is to assume a 15knot headwind ALL the time. This allows for climbs, descents, and delays, and works quite nicely.


What is the meaning of these slang terms used in ATC? I have heard some slang terms used mainly by ATCs:

follow the black holes
taxi not too deep
how is your ride

What do they actually mean and are there others?

Follow the black holes

I have no idea about this one. I looked at the airport diagrams and arrival/departure procedures for MIA, MCO and ORL and I couldn't see anything that seems like it could be confused with the words "black hole". So, I have two guesses:

It's the code name for a set of local taxi instructions
As you suggested, it's the controller's slang for "the twin-engine aircraft in front of you", i.e. the black holes are the exhausts

I think the second possibility is very unlikely, though. A controller at a major international airport - which implies many pilots with English as a second language - is unlikely to use non-standard phrasing for a critical instruction like which aircraft to follow.

Taxi not too deep

This one is a lot clearer from the updated comment you gave: "CLEARED PUSHBACK, NOT TOO DEEP, THERE IS A TRAFFIC PASSING BEHIND YOU". That's exactly what it sounds like: the aircraft was cleared to push back from the gate, but the ground controller was warning the pilot not to push back too far ("too deep") because of another aircraft passing behind.

How is your ride?

This one is ATC asking a pilot for a PIREP. That could be because another aircraft nearby is in turbulence and trying to find a smoother altitude, so the controller asks other aircraft about the ride at their flight levels. Or, since you heard this in the US, it could be for this reason, from the AIM section 7-1-20:

  FAA air traffic facilities are required to solicit PIREPs when the
  following conditions are reported or forecast: ceilings at or below
  5,000 feet; visibility at or below 5 miles (surface or aloft);
  thunderstorms and related phenomena; icing of light degree or greater;
  turbulence of moderate degree or greater; wind shear and reported or
  forecast volcanic ash clouds.

Are there other examples of slang?

I'm sure there are, although slang in general is discouraged because of the potential for misunderstandings. The FAA has a pilot/controller glossary to make sure that everyone is using the same words and phrases as far as possible (ICAO provides one too), but that doesn't mean that people always stick to it 100% of the time. Ex-military pilots - and controllers - in particular sometimes use some military terminology (e.g. bingo fuel) out of habit (presumably) even though they really shouldn't in a civilian setting.

"Follow the black holes" doesn't sound like a good thing. A "black hole approach" is an optical illusion during night approaches when there isn't any light between you and the approach array. You tend to and up flying too low and crash short of the runway. So, "following the black hole" sounds to me like ATC is telling you to believe the illusion.

"Taxi not too deep" sounds like alternate phraseology for "land as short as possible and exit quickly". ATC will give this instruction when something bigger or faster is coming in behind you.


What advantage(s) are there for the HondaJet's engine mount position? The HondaJet has over wing mounted engines as can be seen here:

Image from LuxuryLaunches.com
The advantages v drawbacks of the over wing mount have been discussed here and here. The over wing mount on the HondaJet could take advantage of the Coandă effect, except that they're not in front of the wing, as can be seen (above), but more clearly here:

Sourced from HondaJet.com themselves.
In fact, the placement looks like the typical rear fuselage mount, except they're not mounted to the fuselage. The rear fuselage mount is quite common in the small private/luxury jet market:

Gulfstream G550 hosted by Gulfstream

Learjet 45 image from Aviation-Times.aero
This seems to combine all the disadvantages of an over wing mount with the disadvantages of a rear fuselage mount, and neither of those positions seem to have a huge amount of advantages.
What are the advantages of a high, over/behind wing engine mounting position as seen in the HondaJet?

Probably the reasons are similiar to the reasons which lead to the same mounting on the VFW-Fokker 614.

  This arrangement was used to avoid the structural weight penalties of rear mounted engines and the potential ingestion problems of engines mounted under the wings. This allowed a short and sturdy undercarriage, specially suited for operations from poorly prepared runways.

// Update

The space in the cabin should be the actual reason in this case.

  “I had the idea around 1996,” says Fujino. “The cost of a business jet is very high. To reduce the cost, you have to reduce the size of the aircraft, but then you sacrifice comfort. I wanted to make the aircraft smaller, but not sacrifice the cabin.” Most business jets have the engines mounted on the rear
  fuselage, and moving the structure and systems to support the engines out of the fuselage would maximise space inside the cabin without increasing the size of the aircraft, he believed.

As always, there are pro and cons:

  The problem with an overwing engine is
  that interference between the nacelle and
  wing can accelerate the airflow and cause
  a strong shockwave, reducing the drag
  rise Mach number – the airspeed at which
  shockwaves form and drag begins to rise
  rapidly. Fujino says computational analysis
  and windtunnel testing enabled Honda to
  find a “sweet spot”, an overwing engine
  location that minimises the shockwave.
  The result, he says, is a 5% better lift-to-
  drag ratio – aerodynamic efficiency – in the
  cruise than a rear-engined aircraft.

One major advantage of the engine mount on the wing as opposed to the empanada One major advantage to the engine mount on the wing as opposed to the  Tailcone of the aircraft was mentioned in an air and space article written by Bill Sweetman, when called How The 747 Got Its Hump. In the article, he talks about mounting an engine on the wing of an aircraft indirectly  reduces the bending moment on the spars and in the wingbox during flight  due to the weight of the engines helping to counteract the bending moment generated by lift in the structural components. As such there's a weight saving since these parts can be made thinner but still be able to take the loads needed.


Would it be more effective to increase the length or chord of a rotor blade for better performance? Would it be more effective to increase the length or chord of a helicopter rotor blade for better performance? (Say, 10%?)

It's not so easy. The blade length, chord and engine power are connected in complex ways, and for each desired performance there is an optimal combination of those parameters.

Rotors (and wings) generate lift by accelerating air downwards. The lift is proportional to the rate of change of inertia of the air. This, however, also changes kinetic energy of the air and therefore requires power. This is called induced drag.

Since inertia is proportional to velocity, but kinetic energy is proportional to the square of velocity, it is more efficient to accelerate a larger amount of air to a lower speed.

The amount of air affected is proportional to the area of the rotor disk (the whole area in which the blades move) and that is simply ($\pi\times$) square of blade length. So in a sense the answer is easy: only blade length has effect, blade chord does not.

However, increasing the blade length also increases the form and skin drag of the blades, so beyond some point the form drag will exceed the induced drag and any additional increase in blade length won't improve efficiency further.

Even more importantly, a longer blade will be heavier and therefore will have to be stronger to withstand the centrifugal force when turning, and stiffer so it does not bend too much when not. But that will make it even heavier and you'll reach a point where you simply exceed the capabilities of the material. And of course higher weight also means more lift is required. These effects will further reduce the optimal length of the blades.

The blade chord is then a secondary parameter governed by two concerns: the chord has to be long enough so the blades can generate the necessary lift without stalling and they have to be strong enough, strength being proportional to chord times thickness.

So if you want to improve load, you can try to improve efficiency, which you could do by making the blades longer, but you need to find a material with higher specific strength, otherwise the increased weight will outweigh the improved aerodynamic efficiency.

If you don't have that, you will primarily have to increase power of the engines. The optimal blade length may then be longer too, but you will be hitting the limits of the material quickly; that's why there are multi-rotor helicopters.

If you instead meant speed, that's a completely different issue and neither blade length nor chord play a significant role there. In forward motion, the speed of a helicopter is limited by two constraints: sufficient portion of the retreating blade has to move aft relative to the airflow and the tip of advancing blade must not exceed speed of sound (actually, critical Mach number, which is somewhat lower). The first requirement means the tip speed must be around three times higher than the maximum forward speed, otherwise the retreating side of the rotor won't be able to generate enough lift and the aircraft will roll to that side. Together with the second parameter, it limits the speed to about a quarter of the critical Mach. There are some experimental twin rotor (intermeshing, side-by-side) helicopters that don't mind the lift asymmetry and can fly somewhat faster. But it has nothing to do with blade length; blades of larger rotor spin at lower rpm to maintain similar tip speed.

I assume you are specifically asking about increase in lift.  There are a lot of other constraints and problems that come into play when designing an airfoil, but here is the short answer.

Keep in mind the main limiting factor is going to be the drag on the airfoil.  There are two primary kinds of drag: form drag and surface drag.  Form drag is the drag caused by the area and shape of an object moving through the air - think of this as holding your hand out the window of your car with the palm facing forward.  The other kind of drag is surface drag, this is the drag caused by the surface area parallel to the airflow - think of this as holding your hand out the window with your thumb forward.

Lift is proportional to surface area of the airfoil.  Increasing the size of the airfoil is going to increase the surface drag regardless of weather you increase the length or width.  However, increasing the length of an airfoil is going to introduce more form drag, while increasing the chord is "only" going to increase the surface drag.

So the short answer to your question is: increasing the chord is more efficient than increasing the length.  However, there is obviously a lot more at play, or else helo rotors would be short and stubby!


Why does a stall decrease lift, rather than increasing it? A stall occurs when the angle of attack of a wing or other airfoil becomes so high that the airflow over the upper surface of the wing separates from the wing, rather than remaining attached to it; this causes the wing to produce less lift and more drag, making it harder to maintain level flight and more sluggish to respond to control inputs.

However, shouldn't the airflow separating from the wing's upper surface result in a large area of low pressure above the wing, and, thus, greatly increase lift?  What am I missing?

For a parcel of air to generate a lift force as it flows over the wing requires the wing to tip that air parcel's momentum vector downwards slightly; the reaction force that the wing experiences as it does this is what we measure as lift.

In the case where the airflow over the top of the wing separates from it, the parcels of air flowing by do not get their momentum vectors redirected downwards anymore and the wing hence "stops flying".

Meanwhile, the region of separated flow constitutes a zone of turbulent air which forms a stirred-up wake in the rear-facing "shadow" of the wing at its high angle of attack and the only work performed by the wing in this case is to stir up that wake- and that constitutes lots of drag.

Starting off with a little physics: An airfoil (wing) generates lift due to pressure variations created by the shape of the wing.  Bernoulli's equation which models the laminate flow of a fluid (or in this case a gas) though a restriction is: P+(rho*V^2)/2 = n  (Pressure + (density x Velocity squared) divided by 2 = some constant.  I'll spare you the entire derivation but the end result is the equation for lift which is:

Lift = CI * (rho*V^2)/2 * A

Where:

CI = Coefficient of lift
rho = Air density
V = Air Velocity
A = Area of the wing

In essence this shows that the faster air is forced over the top of the wing, the lower the air pressure becomes above the wing.  Since the air pressure under the wing remains high due to a relatively flat surface, and that nature will look to fill a void, the wing is sucked up into the low pressure (or, if it is easier to wrap your head around the high pressure below the wing pushes it up into the low pressure above the wing (Newtonian view)) thus, we have lift.

(By the way, the Newtonian view and the Bernoulli's view are not mutually exclusive, they are two different approaches that show the same thing... but I digress and that is a whole other ball of wax)

Now, to the meat of your question:  As we increase the angle of attack(AOA), lift increases due to a higher coefficient of lift.  This would seem to suggest that your initial supposition is correct after all, higher AOA mean greater coefficient of lift but if we look back at our equation we see that the velocity of the airflow over the wing is critical to lift.  If we take an idealized look at the airflow as it separates from the wing(Critical Angle of Attack), the air velocity over the wing drops to zero which means we have: Lift = CI((rho*0.0)/2)*A = 0.0, no lift which causes a stall.

As to the second part of your question, why does the drag increase?  A fairly straight forward application of Newton's laws tells us what is going on.  As the AOA increases and increasing large surface area of the wing is exposed to the relative wind.  Combine that with increasing vorticities behind the trailing edge of your wing, creating a low pressure area, and you have increasing drag.

Hope that helps and best of luck in your flying.


Do twin engine airplanes have increased roll stability? Do twin engine airplanes with counter rotating props have increased roll stability?
Imagine a gust of wind hitting the airplane from the front right quarter.
The gust hitting the front of the plane first would yaw the plane to the left, before the rear vertical stabilizer can counter the yaw, the airplane will then roll to the left as the right wing sees more lift.
With a twin engined aircraft, the left engine would counter that yaw.
If less yaw, would that mean less roll, and therefore more roll stability?
Is this correct thinking?
If not, what can be done to increase roll stability besides using a maximum dihedral of about 6 deg and the addition of ventral fins, and wing sweep?

You're imagining the wind coming from the right, pushing the nose to the left. That doesn't happen. In fact, this is much more likely to push the nose to the right, because the vertical stabilizer, being a large panel that's far from the center of mass, creates a larger torque. This phenomenon is called "weathervaning", and is a huge concern for tailwheel planes and seaplanes particularly.
But, to get to the actual question: You are correct in thinking that, if a plane is yawing to the left, the outside wing is going to generate more lift, causing it to roll left. But, no, having multiple engines on an airplane will not stabilize it in either roll or yaw. For all the thrust from the left engine is doing to counter the yaw, the right engine's thrust is balancing it out, so a twin engine will not be any more stable than a single engine, all else being equal.

Yes, twin engines will have increased roll stability compared to a single engine, all other things being equal.
As others have mentioned in comments, roll stability is directly impacted by moment of inertia. To be specific, it is determined by roll moment of inertia. For a derivation of the relationship see sections 4.3 (Representation of Aerodynamic Forces and Moments) and 4.3.1 (Longitudinal Stability Derivatives) of this publication. Moment of inertia is a product of mass and the square of its distance from the axis of rotation. Increase in mass or distance increases the moment and thus the stability.

Suppose we have two airplanes that are identical apart from the placement of the engines. Assume the mass, aerodynamics, and mass distribution (apart from engine) are identical. Let the engines of the first plane be very far from the longitudinal axis and the engines of the second plane very close to the longitudinal axis.
The equations indicate that the first plane will have a higher roll moment of inertia and higher roll stability than the second plane. Consider a force acting on the plane that causes some amount of roll. How much force would be required to rotate each plane by angle θ? While both planes would rotate by the same angle, the engines would move different distances, resulting in different amounts of work required. To move the first plane the same as the second, you need either an increase in force or time.

With respect to the relationship between yaw and roll, I can't speak to it but check out this paper on Longitudinal Static Stability. As best I can tell, it seems to me that there is a positive relationship between roll and yaw as described by "roll-yaw inertial coupling".

Any tendency for divergence in pitch is resisted by the much larger longitudinal static stability. This form of inertial coupling is known as ‘roll-yaw inertial coupling’.


Can I get an EASA Class 1 medical if I have monocular vision? I have monocular vision (amblyopia). In the USA I can get an FAA first class medical via a SODA waiver. Can I get an EASA Class 1 Medical issued with the same monocular problem? I would be applying for a medical in Ireland.

If I absolutely can’t get an EASA Class 1 medical, then will European airlines hire ATPs with a US FAA first class medical, or do EU airlines all require EASA Class 1 Medicals?

The Irish Aviation Authority's aeromedical site directs you to the underlying EU regulations (Part-Med), which say:

  Applicants for a Class 1 medical certificate shall be required to have
  normal fields of vision and normal binocular  function.

That seems to rule out monocular vision completely, which is very strange (to me) considering that the FAA is very clear that binocular vision isn't needed to fly safely. But medical issues are complicated, so I would definitely consult an aviation medical specialist in Ireland before making any decisions.

As for using an FAA medical certificate instead of an EASA one, that should really be a separate question. However, it's highly unlikely to be possible: generally speaking, your pilot's license/certificate and medical have to come from the same country.

The answer to your question is... maybe! It really depends on the specifics of your situation, visual acuity wise etc. I'm also in your position. I have amblyopia and will be looking to take my initial EASA class 1 in the UK around May this year. I've researched this an awful lot and have had good success with vision therapy so far - no doubt you will have heard many doctors telling you it's too late to do anything. Not so!


Identify canard, low-wing, single pusher-prop plane over Upstate NY Yesterday, August 11, at around 3:30 pm, I saw an unusual-looking plane flying over Ithaca, NY. It seemed fairly small -- approximately business jet sized. Unfortunately, I didn't have time to get a picture, but I remember several distinctive aspects of its appearance:

Canard and seemingly no conventional tailplane
Single pusher propellor
Low, swept wing with winglets. Pretty sure it was tapered.

I only saw the plane from below, so I don't know anything about design aspects on the top side of the plane. I checked on FlightAware and FlightRadar24, and didn't see any obviously-matching flights, but I may have missed something. Based on some googling, what I saw seems pretty close in appearance to the AASI Jetcruzer (picture below), but apparently only five of these were ever registered, all in California. According to that same page, only one remains registered, most recently in Washington. The most recent flight recorded with its tail number (N200JC) by FlightAware is from 2014.

AASI Jetcruzer

Additionally, the wing profile doesn't look quite right to me. Another somewhat similar-looking plane that has a more correct-looking wing is the Beechcraft Starship (picture below). However, I'm quite sure that what I saw only had a single propellor. According to the same website, only one specimen of this aircraft remains registered, and similarly its last flight recorded by FlightAware was in 2011.

Beechcraft Starship

Are there any more likely possibilities for the aircraft I saw than one of these rare and seemingly seldom-flown planes?

There are a number of near-copies of the Long EZ, with nearly identical wing and canard shape; they differ in number of seats, performance, range, and, yes, several of them have retractable gear.  I think there's at least one that's pressurized.

Without a high quality photo (possibly even with one, if shot from the ground), it may be impossible to determine what you actually saw -- but a single pusher propeller, low mounted cranked/swept wing with tip fins, and swept canard originated with the Long EZ (before that, there was the Vari-EZ with unswept canard, and the Vari-Viggen with a different wing sweep profile).

The Adam A500 would be the right size. Wikipedia has more info.  It is a twin but it has a pusher prop and a canard. There were only five made and two flying:  N510AX and N510AX have recent flights in Pennsylvania, so it’s possible you saw them in New York.


What would happen if a pilot were to use the parking brakes after touchdown in order to slow down? The situation that I came up with is merely hypothetical. Say a pilot was unable to land right after the runway threshold, for whatever reason it may be - a crosswind, etc - but was determined to land the aircraft.

I understand that most pilots would abort the landing and go around but say this one decides to land. However, it is too close to the end of the runway to stop just by using brakes, spoilers, and the thrust reversers. Could this type of landing (in an emergency) be achieved and by using the parking brakes what would happen if a pilot actually used the parking brakes to slow down?

This question appears to have an implicit assumption: that the parking brake would provide more deceleration than is available from normal braking. This is not generally the case.

A much greater worry for pilots than insufficient braking is actually excessive braking - to the point that the wheel locks up and skids. A skidding tire provides much less braking than a rolling one, and also quickly acquires a flat spot. Even on dry pavement, maximum braking would require an anti-skid system to remain effective; consider a 757 and a Mig-29, each of which blew out their tires when their anti-skid systems failed.

Note also that in small planes without complex braking systems, the parking brake merely maintains the pressure that is in the brake lines at the time it's applied. The parking brake would have no effect if the pilot were not already on the brakes, and would not be able to add any additional braking than the pilot could otherwise apply.

Actual RTO (rejected take off) is a certification test that airplane manufacturer must perform succesfully.

In this test the airplane must reach decision speed and abort take-off. When aborting take-off, the pilot should stop the airplane without using the thrust reverses and fire should not be extended to the airplane within 5 minutes (enough for passenguers to evacuate). This test shall be performed using the airplane at MTOW

So, your question addresses a lighter airplane (MLW < MTOW) and thrust reverses can be used. So the answer is yes, it can use the breaks and will work.

I provide you here the video showing the actual test performed by the A340.


Can I fly with an airband receiver in the United States? I'm flying with American Airlines on a cross-country flight soon and was thinking about bringing along my airband receiver/scanner since it'd be fun to listen to ATC.

It looks like I'd be unable to use it during the flight since any type of radio isn't allowed. I don't see any TSA restrictions on them. Am I safe in assuming that I can bring it along and listen to it in the airport terminal without any trouble with security?

This is probably more a travel question than an aviation one, but I did some Googling of various aviation and travel sites and the consensus seems to be this:

You can carry the scanner with you, but if you're unlucky and encounter the wrong TSA agent on the wrong day then you may be asked a lot of questions at security (the TSA's "Can I Bring..." tool seems to consider scanners to be generic electronic items)
Using the scanner while sitting in the airport is fine, but if you attract attention to yourself then you may be questioned by the police or airport security
You may not use a two-way radio on board the aircraft, because they're specifically required to be off at all times (this is in every airline's safety instructions that I've seen); that shouldn't apply to a radio that only receives but the cabin crew might ask you to turn it off anyway if they're not sure about it
Even if you did operate the scanner in the air, the reception is terrible and you'll probably hear only the aircraft's crew, not ATC

Note that this information is for the USA only, many other countries are very strict about possession and use of scanners or two-way radios and in the UK (for example) just listening to ATC is actually illegal.

The problem is... if you are asked/told to turn it off, whether it's an airband radio or a passive device then you HAVE to turn it off. Cabin crew don't want you listening to the pilot's radio traffic particularly if any kind of emergency arises or flight detour. Think about it!


How do airlines handle SIGMETS? In general, what is the action taken by airlines when presented with a SIGMET in the projected route. Will they go around it, cancel the flight prior to takeoff, or simply fly thought it anyway?

As an example, there is a large SIGMET over the Sierra Nevada mountains right now due to high winds causing wind shear and moderate to severe turbulence. Knowing that severe turbulence can be a serious issue, would airlines, in general, cancel the flight, go around the area or simply fly anyway?

WSUS06 KKCI 250040
WS6N
SFON WS 250040
SIGMET NOVEMBER 2 VALID UNTIL 250440
CA NV
FROM 80N FMG TO 30ESE OAL TO 60NE EHF TO 50ESE RBL TO 80N FMG
OCNL SEV TURB BTN FL280 AND FL410. DUE TO WNDSHR ASSOCD WITH JTST
AND MTN WV ACT. RPTD BY ACFT. REPLACES NOVEMBER 1. CONDS CONTG
BYD 0440Z.

Source: aviationweather.gov

Your options, as you pointed out, are either to climb over this area, To go around it, to go under it, or wait until the segment expires or is expected to subside.

Another option available would be taken by this information with PIREPS.  What are pilots reporting happened to them in this air space at this time?   The SIGMET noted that there was occasional severe turbulence expected in that area which is pretty vague.  If there are a very large number of PIREPS widespread throughout that block of airspace, it’s a good bet that it is very turbulent throughout and may not be a good idea to penetrate it.  If the PIREPS are few and don’t repeat much turbulence in that airspace, then it may be advisable to fly through.  Just keep the speed at that recommend by the manufacturer for penetrating turbulence and keep the fasten seat belt signs on.

The chart you linked is not a SIGMET, it is a prognostic chart.

To answer your question, it depends on the nature and location of the weather. In the case of the example, nothing shown would stop a flight because the weather top is low enough that they fly over it. Also, the ceiling is high enough that they can easily land.

Normally, flights are only cancelled if visibility is zero or there is a storm right over the airport. On a prog, you look for stuff like this:

If this is right over the airport, then that is bad. If there is a storm on the flight path, then they just go around it.


What is 2D and 3D thrust vectoring? How do we define 2D and 3D thrust vectoring?
What are the differences between the two?
Is there anything called 1 D thrust vectoring?

As previously seen in a comment section, there are two main schools of thought:

The dimensionality indicates the actuation Degree of Freedom (1D has
1 DoF per exhaust vector, 2D has 2).
The dimensionality indicates the aircraft attitudes that can be affected (2 exhaust vectors with 1 DoF each can affect pitch and roll, hence this would be a 2D thrust vectoring, 2 exhausts with 2 DoFs can affect all 3 attitude angles, hence 3D)

Using the definitions of these two approaches, to make a couple of examples, the F22 thrust vectoring is 1D for the first group and 2D for the second, while the Su30 is 2D and 3D respectively.

From Aircraft Wiki:

  A plane has got thrust vectoring when it is able to direct its engine
  thrust in another direction to give it better maneuverability. If the
  plane is able to direct the thrust only in one direction it has 2D
  thrust vectoring control. If it's able to direct the thrust in all
  directions, (pitch,yaw and roll) it has 3D thrust vectoring.


Why are passenger required to put their phones in Airplane Mode during taxi to gate? Why do airlines require that phones remain in airplane mode during the final taxi to the gate after landing? As far as I can tell, it does not affect the airplane or anything else negatively or at all. Is this true? If so, then what is the point in keeping the phone in airplane mode until the cabin doors open? Is it just for the sake of convention?

Thanks a lot in advance for any responses!

In general, they don't. U.S. airlines generally allow you to use your phones as soon as the plane lands.
Southwest:

Effective today, Southwest Customers with cell phones onboard may begin using them after the flight attendant gives permission to do so upon landing at the destination and taxi to the airport gate.

Source: Southwest Press Release from Sept 2, 2003
Delta:

Use of cellular devices prior to takeoff is not allowed per Delta policy so that flight attendants may properly prepare the cabin for departure and conduct safety demonstrations uninterrupted. Cellular devices may be used upon landing as instructed by the cabin crew.

Source: Everything You Need to Know About Using Devices on U.S. Airlines

Perhaps of interest, the rule against using cell phone during flight in the U.S. is not an FAA Federal Aviation Regulation. It is instead an FCC (Federal Communications Commission) regulation designed to prevent interference to the cell network as a result of thousands of phones flying around at 600 mph hitting hundreds of cell stations at once. In general, the FCC acknowledges that this rule is outdated and that this is no longer an issue for the current cell network. As such, the FCC has issued a proposal to remove this regulation. However, some airlines (including Delta and Southwest) have publicly stated that they will continue to not allow cell phone use for voice calls during flight even if it is legal, as the majority of their customers have indicated that they don't want to listen to their neighbors chatting on a cell phone for hours on end.

Delta will not allow cellular calls or internet-based voice communications onboard Delta or Delta Connection flights. Our customer research and direct feedback tell us that our frequent flyers believe voice calls in the cabin would be a disruption to the travel experience.
In fact, a clear majority of customers who responded to a 2012 survey said they felt the ability to make voice calls onboard would detract from – not enhance – their experience. Delta employees, particularly our in-flight crews, have told us definitively that they are not in favor of voice calls onboard.
-Delta CEO Richard Anderson

Though all systems are gone through series of electro magnetic Tests in the Lab. The mobile phone signal may contribute enough electro magnetic interference in the real world. Due to this electro magnetic interference the systems may start behaving differently and erroneously. Take off and Landing are the crucial stages of flight phases, it is always better to avoid the chances of taking risks. If 1 mobile phone can produce this, you could just imagine about the all passengers turning on their mobile phones and contribute the interference.


What are the Area Control Center (ACC) frequencies for Germany? I'm looking for the frequencies of all Area Control Centers (ACC) in Germany. What are they, or where are they published?

The radio frequencies used by German ACC sectors are listed in AIP Germany ENR 2.1 (page 36 onward). This is the standard place to find ACC frequencies for any country in the world.

There are too many frequencies to list here, but you can find the full document here. Below is a screenshot of page 36. Column 1 contains the sector name and dimension, column 4 contains the frequency(ies) used by that sector.

Okey I found it out.
The map of Germany ACC sectors you can find here:
https://www.eurocontrol.int/sites/default/files/content/documents/nm/cartography/erc09l-23may2019.pdf
If you have your airway and name of sectors, then you are able to find the frequency on this site:
http://www.aviascan.de/downloads/Sector%20Information%20Manual%20Germany.pdf


Why are empty pylons weighed down? (airplane-pictures.net) Airbus A330 no engine option.

Why are empty pylons weighed down?

The plausible answer is to maintain the correct center of gravity. But why not just load ballast pallets in the forward cargo compartment, like those used on tail heavy planes on ferry flights?
On airliners.net there is a theory (plus debate) that states another reason is to relieve the load on the wingbox, which I would imagine would also decompress the landing gear (I don't see how).
Lastly, I remember on a TV documentary it was stated that the reason is so the wing would not deform upwards (again I don't see how).

Your reason 1 is correct. Without the ballast the aircraft would become a taildragger.

Why not pallets? This would produce the same center of gravity location, but a different mass distribution. Clearing this configuration even for being loaded and pushed around is more effort than simply placing the ballast where the mass of the engines would go. Now all clearances are valid and the aircraft can be handled much as one with the engines in place.

Next, engines are only installed shortly before delivery or first flight. The cost of capital is too high to install them any sooner.

(airbus.com) Example of clearances that would be affected by non-standard mass distribution.

That is to keep the center of gravity sufficiently forward of the main gear to prevent the aircraft leaning backward on its tail while the weight of installed engines is not present.


Does a plane have more lift while flying in a cloud? (All other things equal...) Inside a cloud, the plane flies in a medium (air + water droplets) with a higher density than 'normal' air. If airspeed and AoA are the same, lift should be higher. It is really so...?

No, higher humidity air is less dense than lower humidity air.  This is because water molecules are lighter than the nitrogen and oxygen they would replace in an airmass.

https://science.howstuffworks.com/nature/climate-weather/atmospheric/is-humid-air-heavier-than-dry-air.htm

  any water vapor that gets added replaces either nitrogen or oxygen in our free-moving air. Nitrogen and oxygen make up the majority of our atmosphere, and they're displaced -- or evaporated -- when water takes their place in the air. And water vapor molecules are lighter than both nitrogen and oxygen. In other words, humid air is going to have less heavy nitrogen and oxygen -- and lighter hydrogen and oxygen -- in its place. Remember that they have the same number of molecules, but the air with water vapor is simply less dense

Humidity, therefore, is also an important factor in density altitude calculations.

No, or at least not lift due to the airfoil (see below). The difference between the air inside of a cloud and that directly adjoining it will be relatively small. Also, the air inside a cloud is less dense in most cases than the surrounding air because it is warmer. The following diagram illustrates the effect:

The air outside the cloud is cooler and more dense. The air inside of a cloud, therefore rises, and outside of it, the air sinks. Any glider pilot experiences when passing beneath a cloud: the glider rises as it travels under the cloud, but as soon as it exits the area under the cloud, the glider sinks.

An aircraft will experience lift inside of a cloud, but this is due to rising thermal air currents, not lift granted by the wing's airfoil.


What are the advantages and disadvantages of the MiG-29's horizontal stabilizers (not what do they do)? The MiG-29's tail axes are located fairly close to the leading edge, and rotate along an axis oblique to the chord. What are the possible consequences to this arrangement (e.g. actuator torque, flutter potential)?

There is nothing too special about the MiG-29 stabilator.
The "slanted" (swept) axis of rotation is fairly common: as far as I remember, all MiGs that had a stabilator had this arrangement.
This has primarily structural advantages: it is easier to integrate the shaft (or axle) along the structural elements of the stabiliser, making it lighter. Also, the hinge moments are more consistent along the shaft. (For the straight shaft on a swept stabiliser, there will invariably be twisting forces that must be absorbed by the structure. Say, the root section may experience positive moment with respect to the shaft while the end section may have negative moment).
Also, as Charles already noted, a swept axis may allow to move the stabilator a bit further back (while keeping the same overall hinge moment), increasing its lever arm and thus efficiency. This is because the attachment point at the root can be closer to the leading edge. But this is only a gain when the actuator cannot be moved further back for some design reasons (like on MiG-29).
On the other hand, the leading edge may interfere with the fuselage when deflected, necessitating a "stump" at the root (which you can also see on most jet MiGs). At the same time, you need larger deflection in order to achieve the same aerodynamic effect (see also this answer).
The perception that the shaft is too close to the leading edge is a bit of an illusion. In fact, it is just a bit forward of the 1/4-chord line: exactly where it should be, as can be seen in these diagrams.

This arrangement is for a better fulcrum (not pun intended here) in pitching. Advantage is that they hide the plum of exhaust heat at some angle of view form the enemie aircraft


What are the mechanical deflection angles for Airbus side-stick controllers? Does anyone know the angular deflection limits of the longitudinal (pitch) and lateral (roll) axis of Airbus's side-stick?

From this site:

So max deflection in pitch is +/- 16 deg, in roll it is +/- 20 deg

There is a rather quick YouTube video by a gentleman called Capt. Joe which can partially answer your question.

The limits of the effective deflection of the sidestick is presented on the PFD, which that also changes with many variable factors to allow the aircraft to operate within its approved and safe performance envelope.


What causes descending aircraft to make a noise like a giant blown bottle? I've lived for years about eight miles NW of Boston's Logan Airport. Although I can't say we get a lot of aircraft noise, once in a while, due to winds or air traffic, there will be a long line of planes traveling right over my house, perhaps 6000-8000 feet up, descending into Logan. At night you can sometimes see three in a row, with a fourth one turning on its landing lights.

Most of the time the overhead planes sound mostly like a roar with some jet whine. However, once in a while a plane will suddenly start making a very strange sound like an enormous blown Coke bottle. Often the pitch will descend during a half dozen seconds, stay constant for a dozen seconds, and then rise again until the sound disappears.

My best guess is that the sound is caused by the pilot lowering the wheels during their descent, and that it only happens on certain models of aircraft. As the wheel well covers open, the air blowing across the wells sounds like that giant Coke bottle, with the pitch decreasing as the opening increases. On certain models, the covers will then close once the wheels are down, causing the pitch to go back up.

(Edit: it's been pointed out that gear isn't dropped until 2000-3000 feet, so in my case that isn't the sound. So, I've removed all those videos, cool though they may be.)

Is my guess right? What model/manufacturer of large jet would make this sound?

Short Answer:

The sound is caused by airflow across holes on the underside of the wings of certain aircraft.

Long Answer:

I too have noted the sound phenomenon that you describe. This video has a great example between 0:26-52 (link starts playback at 0:26 where the noise starts):

I will readily admit that this answer is mostly just a compilation of what I have learned researching this. Your question intrigued me and I've enjoyed learning about it!

As I discovered as I started researching this, many others are familiar with the noise as well. This article on Airliners.net had a lot of discussion about it, starting with a lot of interesting—but ultimately flawed—theories.

But, that thread led me to the answer to your question, which is: the sound is caused by the "circular opening used to equalise the pressure in wing fuel tanks", according to Euractiv.com

This article on AirportWatch further explains:

  The Airbus 320 series of aircraft, [...] have been known for many years
  [...] to have a particularly irritating high pitched
  whine. This is caused by air rushing across the under-surface of the
  wing, where there are Fuel Over Pressure Protector (FOPP) cavities.
  This generates noise, in the same way as blowing air over the mouth of
  a bottle. Every A320 series aircraft emits a signature howling noise
  while approaching to land. It is heard most when the plane is
  travelling at around 160 knots, and the frequency is around 500-600Hz,
  which is close to peak sensitivity of the  human ear.

That being said, there is apparently a fix to that problem, as both the aforementioned links describe. As Euractiv.com explains, the fix is a vortex generator:

  a 5-cm triangular piece of aluminium sheet metal upstream of the two
  vents on each wing, in order to divert the air flow and stop the
  whistle. A decade of research went into the vortex generator, which
  stems from efforts to mask a similar whistle produced when air blows
  over the gun ports of warplanes.

This image shows both the FOPP hole, and the VG that softens the sound:

[Image Courtesy of Lufthansa]

Read the articles linked, interesting stuff therein!

My best guess is that the sound is caused by the pilot lowering the wheels during their descent

This was what I was going to say immediately. I lived about the same distance from the south runway at Pearson and wondered what this was until I saw a 737 drop gear right above me.

I would describe the sound as a sort of "pfff-ewwwww" over the first second, and dropping in pitch until it ends in a constant low rumble after perhaps 5 seconds. Is that it?


Even after years of research, why are planes unable to keep passengers alive in case of a fiery crash? Aviation dates back to the 18th century, and since then tremendous research has been put into making aircraft safer and more efficient. Though these efforts have resulted in better aircraft, why are they still not strong enough to keep the passengers alive in case of a fiery crash?

In recent times, especially, it's a rare incident that a plane crashed and even some of its passengers survived. So, why has this issue not yet been resolved?

Short answer

The kinetic energy involved in a plane crash is inhumanely high.

Slightly longer answer

We can built bombs which will go through concrete roofs and ceilings of a bunker, counting the number of floors they crash through while descending so they can explode at the level where the bad guys sit and not where the widows and orphans are kept. We could equally well build a plane with this kind of strength, so the fuselage stays intact even when it crashes into a mountainside. That's not the problem.

Limits of the human body

The problem will be that rescuers will only find dead bodies inside. The human body was "designed" to endure things like running into a tree, but not being hurled around at Mach 0.85 and then being stopped almost instantly. Thanks to years of research we now have quite a good idea where the limits are. Martin Eiband collected a lot of data on this, if you want to know more, google for "Eiband diagrams". If you want the full picture, read the Army Aircraft Crash Survival Guide. It comes in five volumes, and volume 1 covers the design criteria. The Eiband diagram below is lifted from this source.

Note the time scale: A deceleration with 40 g can only be tolerated for a duration of 0.1 seconds; if the deceleration takes more than 1 second, the limit is only 10 g. Now let's see what deceleration distance is required to stop a human with an average deceleration of 10 g. The energy $E$ of a body of the mass $m$ increases with the square of speed $v$:
$$E = m\cdot\frac{v^2}{2} = m\cdot a\cdot s$$
At $a = 98.0665$ m/s², the stopping distance $s$ from an initial speed $v$ is $\frac{v^2}{2\cdot a}$:

Car crash at 30 m/s: This needs 4.6 m and good restraints, but is generally survivable.
Free fall at 60 m/s terminal velocity: 18.4 m. A few humans have indeed survived this by falling into soft ground like a snow-covered conifer forest. This is also the typical approach speed of airliners, and the 18.4 m is the fuselage ahead of you. That is the reason why a crash is more survivable for the occupants in the rear seat rows.
Propeller airplane flies into mountain (120 m/s): 73.42 m. This kind of crumple zone is simply not available, and nobody has survived such an impact.
Airliner flies into a mountain (240 m/s): 293.7 m. To make such a crash survivable, every airliner would need to carry a 300 m boom of stiff material around which would be needed as a crumple zone in an accident. Just think what kind of aft fuselage and tail this would require.
And to top it: Astronaut on a space walk collides with a satellite in an opposing orbit (16,000 m/s): 1305.23 km. Note that I had to switch units to keep the number manageable.

Please consider lower deceleration limits for elderly and untrained persons; the limit in the Eiband diagram was established using healthy young pilots (and hogs, chimps and corpses for the higher limits. A lot of blood was spilled to arrive at these numbers).

The problem is not the aircraft structure, it is the fact that humans like to go fast but are not built to stop quickly.

As for your answering the question about a 'fiery crash', NASA performed a test in the 1970s using a 720 filled with fuel formulated to reduce the chance of causing a fire. I recall seeing the footage on science programs. Unfortunately the fuel did ignite.

To quote the referenced Wikipedia article "The test resulted in a finding that the antimisting kerosene test fuel was insufficiently beneficial, and that several changes to equipment in the passenger compartment of aircraft were needed"


Airliner headlights flashing alternately I live in Portland,Oregon.  I watched a large jetliner coming into the airspace heading to the airport.  The red,green and tail lights were normal. But the headlights were blinking alternately.  I have never seen that in all my years watching the sky. Is there a reason for the alternate blinking?Emergency onboard?

Some modern landing lights have a pulsating or alternating mode. It's just for being recognized more easily, has nothing to do with an emergency.

A constant white light heading right for you over a city full of lights doesn't get as much attention as a pulsating light which gets bigger each time as you get closer :)

Here is one example: https://www.preciseflight.com/pulselite-pulsing-aircraft-lights/

and their video:

What you were likely seeing is the wingtip strobes which are white and flash alternatively. Aircraft don't have "headlights" per-say but they do have landing lights which do not flash by design but can be flashed manually.


What is a "frozen ATPL"? I've heard the term "frozen ATPL" and it seems to be some kind of limited EASA ATP certificate. What exactly is a frozen ATPL? What privileges does it give the holder? How is it unfrozen to become - presumably - a regular ATPL?

A frozen ATPL holder is somebody who has passed all the required (14) exams for the issue of an ATPL but does not have the required flying hours. Strictly speaking, there is no such thing as a 'frozen' ATPL, though a number of training schools do use the term:

A Frozen ATPL holder refers to somebody who has passed all the required theoretical exams but does not qualify him to be issued with a full ATPL until he has logged a total of 1500 hours.
A student from a flying school will normally graduate with a CPL (Commercial Pilot Licence) and IR (Instrumental Rating) (CPL+IR). This Licence is known as the Frozen ATPL.

In order to 'unfreeze' the ATPL, the candidate has to complete a flight time of 1500 hours subject to certain conditions:

... ATPL will remain frozen until you have reached 1500 hours of flying time, which is made up of the following criteria:

500 hrs multi-pilot in transport or commuter aircraft
250 hrs PIC (or 100 Pilot in Command and 150 PIC under supervision)*
200 hrs cross country flights (100 as Pilot in Command)
75 hrs instrument time
100 hrs night flight as PIC or co-pilot

A 'Frozen' Airline Transport Pilot Licence (ATPL) is the name given to the qualification of a pilot who holds passes in all 14 ATPL theoretical exams. The ATPL would become un-frozen when the flight experience requirements are met.

from: Asian Academy of Aeronautics


When a plane flies faster than the speed of sound, does the distance between plane and sound increase? I had this discussion with my dad about a question he had asked. Basically he said:

  If a plane flies faster than the speed of sound, will he be able to overtake his own sound and hear itself?

(let's leave behind the fact that he can run out of fuel or that the sound finishes before he hears it)

I disagreed because it seemed illogical to me, but we never actually found hard evidence to determine if the statement is true or false.

Can a plane actually do this?

I think you are missing some physics knowledge, so let's start from here:

  If a plane flies faster than the speed of sound

Sound is a compression wave that travels through air. Given a certain air temperature, the sound will travel at different speeds through the air.

If a plane flies faster than the speed of sound means that the compression waves it is generating will remain behind the aircraft:

image from here

  will he be able to overtake his own sound and hear itself?

As you can see on the right picture, if the aircraft is travelling faster that the speed of sound, the compression waves it generated in the past will remain behind. If it would stop/slow down, the waves would then catch up with the plane and a person on board would be theoretically capable of hearing them.

Sound does not travel in a straight line.  It radiates evenly in all directions.  Therefore, even if your moving super fast, and I mean fast, you would not be able to catch it. I know you're trying to think if you made a really quick lap around the planet could you catch it, you would simply blow through the place it was made. But there are echoes that you could hit if you moved fast enough but even then it would not be the sound itself but a vibration left on the surrounding matter.


What is the wing angle of attack of a Boeing 737 in cruise? I would like to know the angle of attack that a 737 flies at during cruise. I am specifically interested in the wing angle of attack (if you know the cruise nose-up attitude and the wing incidence angle, that would be good too).

First, let's assume that all lift is created by the wing, and that the plane is flying in ideal conditions, where fuel flow per distance flown is minimal. This point is given by $$c_L = \sqrt{\frac{1-n_v}{3+n_v}\cdot c_{D0} \cdot \pi \cdot AR \cdot \epsilon}$$ Please see this post for more background on this formula.

Nomenclature:
    $c_L \:\:\:$ lift coefficient
    $n_v \:\:\:$  thrust exponent, as in $T \sim v^{n_v} $
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing
    $\epsilon \:\:\:\:\:$  the wing's Oswald factor
    $c_{D0} \:$  zero-lift drag coefficient

The $n_v$ I would estimate to be -0.4, the $c_{D0}$ is somewhere around 0.016, the aspect ratio can be taken from this source and the Oswald factor is 0.8. This gives you an optimum lift coefficient of 0.445. Now we need to know what angle of attack is needed for this lift coefficient. If we look at the midspan airfoil of the 737, this angle of attack is around 2.8 degree.

This source is for model airplanes, so their Mach and Reynolds numbers are much too low for the real thing, and we need corrections for both. Using the Prantdl-Glauert rule for Mach effects, we need to correct by dividing with $\sqrt{(1-Ma^2) \cdot (1 + tan\varphi)}$ = 0.693 at Mach 0.82. Please note that this increment must be applied to the zero-lift angle of attack, which is -1°. Now our angle of attack is only 1.63°. The flight Reynolds number of the 737's MAC is 22 million, so the angle of attack is even less, maybe 1.5°. Now we need a correction for the 737 wing sweep of 25 degree, which is computed by dividing the angle of attack by 0.9, the cosine of the quarter chord sweep angle. This gives about 1.8° as the corrected value.

So my quick-and-dirty answer is 1.8 degrees. Other sections of the wing have slightly different values, according to the wing's twist. Please note that the wing area of the 737 is roughly constant since the Sixties, while the mass has increased considerably. It is safe to assume that it is operating at higher angles of attack than the optimum for best range.

The angle of attack on a 737 in cruise at 41000 is about 8 degrees on average.  A heavier plane will need a degree more.  A light one, about a degree less.  Keep in mind that airliners have a significant amount of wing twist, so I am only referring to the average angle of attack, not the AOA of the wing root or wing tip.


Can I work on my own airplane without formal mechanic's training? Suppose I am not planning to be a career A&P mechanics, but would like to get some hands-on skills for airplane maintenance, for reasons of both cost and hobby. Say my basic goal is to perform tasks from as simple as tire replacement, instrument replacement to avionics installation and troubleshooting. My goals may be progressive. The aircraft for maintenance is self-owned or owned by share. The ownership and operation of the aircraft is within US.

Can I work on my own airplane? Since I'm not certified for mechanics work would it be OK that a certified A&P endorse my work is standard-compliant?

FAR Part 43 contains the information of what you can and cannot do to an aircraft and what requirements you must have.

If you are a certificated Private Pilot (as in not a sport pilot), there are quite a few things you can do to an aircraft you own, that is not used for commercial purposes. Like:

Replace wheel bearings
Remove/repair/reinstall wheels
Replace safety wiring and cotter keys
Service landing gear struts by adding oil/air
Lubrication not requiring disassembly of non-structural items like cover plates, cowlings, and fairings
Simple fabric patches not requiring rib stitching or removing structural parts or control surfaces
Replenishing hydraulic fluid
Refinishing decorative coating of fuselage and other parts
Repairing upholstery without disassembly
Simple repairs to fairings, etc
Replacing side windows
Replacing safety belts
Replacing seats or seat parts with approved replacements
Troubleshooting and repairing broken circuits in landing light wing circuits
Replacing bulbs, reflectors, and lenses of position and landing lights
Replacing wheels and skis where no weight and balance computation is required
Replacing cowling not requiring removing the propeller or disconnecting flight controls
Replacing or cleaning spark plugs and setting gap clearance
Replacing any hose connection except hydraulic connections
Replacing prefabricated fuel lines
Cleaning or replacing fuel and oil strainers or filter elements
Replacing and servicing batteries

And others Source

However, note that it has to be your airplane, and it can't be used commercially (which I think includes offering it for rent). There is very little you can do in the way of avionics (read #31 and #32 in the reference I gave).

The fun thing to note is that although a PPL is required, the PPL training does not give any special attention to any of these items, and therefore really somebody off the street is technically just as qualified as a private pilot, but the private pilot is the only one authorized to do the work (provided they own the plane). When I got my PPL, nobody walked me through replacing cotter pins or anti-back-out devices...

Edit
These rules though may be different when you get into experimental category aircraft but I can't source it now and will do more research and edit when I can clarify.

Keep in mind you can work on your plane you own it and bought. It's yours, you can take cylinders off, poor sand down them, do whatever you want, it's your plane. HOWEVER, it's not airworthy once you do so, unless you are a certified mechanic or the work you are doing complies with what is allowed under preventive maintenance.
Do whatever you want if you own it, just remember it's not legal or airworthy to fly after your done until an authorized person releases it back into service.


Why tap the brakes on take-off in fixed gear aircraft? The Socata TB10 checklist indicates that you should touch the brakes after lift-off. I assume this is to stop the wheels from turning, but why?

In a retractable gear aircraft this would make sense to avoid using anything in the wheel-well to stop the wheels and potentially causing damage or generate heat (as a side note, I think some airliners actually have brake-pads in the wheel wells for this purpose). However, the TB10 is not equipped with retractable gear.

The TB10 and TB20 are very similar, and it might be a case of copy & paste between the two POHs (the TB10 POH also lists V-speeds for "flaps and landing gear retracted").

Do spinning wheels have an adverse effect on aerodynamics (or handling in general)? I would assume, if anything, they'd produce less drag. And as a cherry on top, I'd also assume they'd start spinning again fairly quickly, as only the lower part of the wheels are protruding out in to the air flow.

This answer to another question has a link suggesting that the spinning wheels may be sufficiently large gyroscopes to affect handling of the aircraft. That was however on a larger aircraft and higher speed (Lockheed Constellation). I don't know whether that effect would be observable on TB10.

I was told to do the same thing.
They said that once the wheels started spinning (from take-off) they often didn't stop: the air flow tends to keep them going once they are spinning. It has a slight effect on bearing wear.

I just thought a 2nd reason now: when you land if they are already spinning, then when you land, they don't need anymore energy to get up to speed. But you'd rather they DID require some energy, that would help you slow down. Might be quite small though, I haven't calculated it.

But I doubt that it's a big deal either way.