What is the effect of wingspan on wing stiffness?

Limit cycle oscillation is a fancy term for flutter with constant amplitude. The limit cycle is an attractor, meaning that the frequencies and amplitudes of a range of oscillations will converge to the limit cycle oscillation as time progresses. One example can be witnessed in this video.

By removing the wingtip, GE could raise the bending eigenfrequency of the wing, like you make a pendulum swing faster if you shorten it. Adding a heavier engine before certainly reduced the eigenfrequency, so the shortening was a way of compensating for the changed dynamic characteristics of the modified wing-engine combination.

Wingtip removal does not make the wing stiffer, only larger spar caps, a thicker spar or employing a stiffer spar material would. Stiffening the wing spar would raise its bending eigenfrequencies, and removal of the wing tip would do the same by different means. I guess the author wanted to express that bending frequencies were raised but picked the wrong explanation.


How big a risk is to abort take-off before V1 with uncontained engine fire and side-wind?

If it happens at a slower speed as you ask, then maneuvering the plane on the runway as it stops would help, even if it's only a 45-degree turn. You might wonder why not do a complete 180 if the runway width allows; that turn is slow and takes valuable time, while a fully loaded plane can theoretically be evacuated in under 90 seconds with only half the exits. It's a smaller risk considering the low-energy abort. A high-energy abort adds the risk of the brakes starting another fire.
As to Flight 1504, there's no need for opinions, as the final report did not fault the commander's decision:

The management of the failure by the flight crew was carried out professionally and in compliance with the established procedures. The same applies to the air traffic controllers, who assisted the aircraft with professionalism and providing maximum cooperation. The commander decided not to interrupt the take-off run despite the right engine fire warning having intervened a few knots before V1, thus exercising the expected discretion and taking into consideration all the available elements that favored this decision. [translated from Italian; emphasis added]

Speaking of Go shortly before V1, it is advisable for tire failures due to the compromised braking:

Source: Pilot Guide to Takeoff Safety - FAA (PDF)


Which aerobatic manuvers should I restrict myself to if I wear glasses?

If you're talking about what they call Gentleman's aerobatics - that is only controlled positive G maneuvers like aileron rolls, barrel rolls, Immelmanns, inside loops, split-S, Cuban Eights, etc. there shouldn't be a problem here as the loading will hold your glasses on your face.  For additional support you might consider a blackstrap for your eyewear, similar to what basketball players wear.

More extreme aerobatics involving negative G flight, tumbling, gyroscopic maneuvers, etc would not be recommended using free fitting corrective eyewear as they will probably come lose and can become a FOD hazard in the cockpit, in addition to losing your myopia correction.  Goggles with corrective lenses would be recommended here as well as contact lenses.


What are some specific benefits of cryogenic wind tunnels?

Short answer:
A cryogenic tunnel works by taking advantage of the different properties of nitrogen gas at cryogenic temperatures as compared to the properties of air at normal ambient conditions (speed of sound, density and viscosity). This allows testing at an order of magnitude higher Reynolds numbers over non-cryogenic tunnels. Being able to achieve full-scale values of Reynolds numbers removes a significant source of error in the wind-tunnel test results.
Long citation from https://cryogenicsociety.org/resources/cryo_central/wind_tunnels/:

Dr. Robert Kilgore

The development of the cryogenic wind tunnel is one of many significant breakthroughs in both cryogenics and wind-tunnel technology made during the past millennium. Interest in the development of high-speed commercial and military aircraft resulted in a review of problems of flow simulation in transonic wind tunnels during the 1950s and 60s. One of the more serious problems was the inability to test sub-scale models at Reynolds numbers sufficiently near flight values to ensure the usefulness of the wind-tunnel data. Typically, values of test Reynolds number were too low by a factor of 10 or more.

The search for a way to test at full-scale Reynolds number began soon after Wenham built the first wind tunnel in 1870. Margoulis proposed using a heavy gas or cooling the test gas as early as 1920. Margoulis reasoned that a heavy gas, such as carbon dioxide, when cooled to 253 K would increase Reynolds number and reduce drive power requirements for fan-driven wind tunnels. Margoulis and others of his time concluded the moderate benefits resulting from cooling only to 253 K were not worth the effort.

The idea of cooling the test gas lay dormant until 1945 when Smelt studied ways of reducing the size and power requirements of high Reynolds number high-speed tunnels. Smelt’s theoretical study again noted the advantages of using heavy gases and reducing temperatures. The study by Smelt was presumably a case of independent re-invention of a good idea since Smelt did not cite Margoulis.

Cooling of the test gas was again rejected in the 1940s. This time it was rejected because there did not appear to be a practical way to cool a reasonable size wind tunnel and there were some concerns about finding suitable materials for the tunnel structure.

The concept again lay essentially dormant until 1971. We needed a way to increase the Reynolds number capability of the small wind tunnels equipped with magnetic suspension and balance systems. Dr. M. J. Goodyer was working at the NASA Langley Research Center at the time. Goodyer studied the problem and, again independently, suggested the use of either air or nitrogen at cryogenic temperatures. Goodyer and a small group of researchers at NASA Langley quickly recognized several additional advantages of the cryogenic wind tunnel concept. We immediately set out to develop a practical approach to its application. We quickly built and successfully used a small low-speed atmospheric cryogenic tunnel. It first operated at cryogenic temperatures in January of 1972. We used this tunnel, which had a test section of 18 x 28 cm (7 x 11 in.), to prove the validity of the concept as well as to develop the method of cooling the tunnel by the direct injection of liquid nitrogen into the stream.

We then decided to build a relatively small fan-driven transonic cryogenic pressure tunnel. In its original configuration (since changed), the Pilot Transonic Cryogenic Tunnel had a test section of 34 x 34 cm (13.5 x 13.5 in.) and could operate at pressures up to 500 kPa (5 atm). This extended our cryogenic tunnel experience to the pressure and speeds needed for a large high Reynolds number tunnel. The design of the Pilot Transonic Cryogenic Tunnel began in December of 1973. Initial operation was in August 1993. Again, success led to greater things; this time to the decision to build a large cryogenic wind tunnel to meet the testing needs of the United States. The tunnel would be known as the US National Transonic Facility (NTF) and would be built at the NASA Langley Research Center in Hampton VA. Construction of the NTF began in 1975. It became operational in 1982. It has a test section of 2.5 x 2.5 m (8.2 x 8.2 ft) and operates from ambient to cryogenic temperatures at pressures up to 890 kPa (8.8 atm) at Mach numbers up to about 1.2. Cooling of the test gas is by the direct injection of liquid nitrogen into the tunnel circuit at rates up to 1000 pounds per second.

By taking full advantage of the cryogenic concept, the NTF can test at Reynolds numbers of 120 million. This is an order of magnitude increase in Reynolds number capability over non-cryogenic tunnels. Being able to achieve full-scale values of Reynolds number removes a significant source of error in the wind-tunnel test results. The net result is that commercial airplanes are more efficient and combat aircraft are more maneuverable.

We routinely use cryogenic wind tunnels to test at full-scale conditions (including some scaling parameters other than Reynolds number) for such diverse things as solar towers and submarines. Around the world we now have three large Cryogenic Wind Tunnels used for a variety of aerodynamic testing and fundamental research. These include the US NTF, the European Transonic Windtunnel (ETW) and the Kryo Kanal Köln, both located in Köln, Germany. In addition, there are another 20 or so smaller cryogenic wind tunnels used for a wide variety of purposes in nine countries.

The use of cryogenics in wind tunnels may be unique among the various uses of cryogenics. Most people use cryogenic temperatures because they want to take advantage in the change of some property of a material. For example, they want to turn an ordinary conductor into a superconductor. However, a cryogenic tunnel works by taking advantage of the different properties of the nitrogen gas itself at cryogenic temperatures as compared to the properties at normal ambient conditions (speed of sound, density and viscosity).

As used in cryogenic wind tunnels, cryogenic technology is making a major contribution to experimental aerodynamics.

“It is easy to invent a flying machine; more difficult to build one; to make it fly is everything.” — Otto Lilienthal, Pioneer Glider Pilot


What are the requirements of ferrying a spare engine?

It's a manufacturer option on some larger planes - basically adding a bit of structure and some attachment points. And it's expensive enough that airlines think about it.

Today's engines are much, much more reliable than the ones used in the 1960s so the need to move engines around by bolting them on to the next thing going that way is not what it once was. There is also a larger air cargo market, and it's likely cheaper in general to put the replacement on a pallet rather than under a wing.


What is the difference between types of propeller?

There should be two parameters you should know about:

Blade loading: The amount of force per unit of area a blade is creating. Like with a wing, you can formulate a lift coefficient, a dimensionless number which removes the influence of size, air density and speed. Ideally, this number should be between 0.5 and 0.7, so the propeller makes best use of its blade area.
Advance ratio, which is the ratio between the circumference of the propeller disc and the height it would screw itself up into the air in one rotation. Increasing the blade angle would directly increase this advance ratio, for example.

Now you should be able to guess the answers to your questions:

Adding more propellers: Will distribute the load over more propellers and helps if blade loading was too high, but makes matters worse if blade loading was low already.
Adding more blades: See 1.
Replacing blades with wider blades: See 1.
Making the angle of all blades steeper: If you run the prop at a lower speed, your blade loading will go up and thrust will be the same (if you don't mess up the flow over the blades by changing the angle). If you run the prop at a higher speed, blade loading will go up; again until the flow cannot cope with the angle anymore. This is similar to stalling a wing. Changing the blade angle is the preferred means of adjusting the prop to different flight speeds in airplanes.
Adding a second, contra-rotating prop is like adding another sets of props (see 1), but helps to reduce swirl losses. If blade loading was at a proper value before, halving blade loading will create more losses than reducing swirl losses. You add contra-rotating props only if your blade loading was high already.
Spinning propellers faster will create more thrust but also more losses. If your thrust is not sufficient, it is better to increase prop diameter (a parameter you forgot to include).


Why can’t electric motors be used in aviation

Electric motors can be and are used in aviation - there's hundreds of them on any airliner you fly on.

As for using them for main propulsion, let's first look at the power/weight ratios. The highest number for Tesla's car motors is 8.5 kW/kg. The electric-aircraft-specific Emrax 268 delivers about 12 kW/kg.

In comparison, the Trent XWB delivers 430 kN of thrust at 300m/s flow rate, which equates to 64.5 MW of power, in a 7,550 kg package - a power/weight ratio of 8.5 kW/kg. However this isn't apples to oranges: this ratio is for the whole package, engine and fan, and measures useful output, like wheel power for a car.

In short, turbine engines are still lighter than electric motors, but the difference is not dramatic.
Where all-electric powerplants fail to stack up is range. I've elaborated on it in response to another question - Are there any hybrid electric planes?. The short version is that the maximum possible range of an electric aircraft is 10 nmi for every % of its weight dedicated to the battery. This limits the range of electric aircraft to 300-450 nmi, if sticking with the fuel fractions of known airliners.

But there are aviation applications where this is enough. The most important non-renewable resource consumed by modern aviation - the supply of 1960s Cessnas and Pipers, without which no one could afford to become a pilot - will not last forever. Should authorities permit it, mass-produced Tesla powerplants could power trainers and GA planes at a fraction of the ownership cost of a certified avgas engine.


Why does XKCD say that autogyros will crash if the pilot reacts to a stall as in a normal airplane?

That one thing is to unload the rotor too much (i.e. "push on the stick"):
From explainxkcd:

... Unfortunately, as soon as the rotor stops spinning, the whole aircraft falls like a brick and the rotor may be impossible to restart in flight. This is a situation that should be avoided at all costs.
Normally it is not a problem since the weight of the aircraft keeps the rotor spinning. However, if the weight becomes too low or even negative, the angle of attack will become negative, and the rotor will slow down and eventually stop. It can happen when the pilot "pushes on the stick" and dives.
Unfortunately, "pushing on the stick" is also how you escape a stall in a fixed wing (normal) airplane as it is a way to regain airspeed. This is actually a counter-intuitive maneuver but because a stall is an emergency, pilots are trained to do it instinctively. It can trick a pilot trained in fixed wing aircraft into doing the one thing that shouldn't be done on a gyro.


How can I politely remind ATC that I'm waiting for instructions or clearance?

There's lots of advice I can give you here, but the answer is really that the degree of communication tower wants/needs depends on your local tower (and to some degree the individual controllers).

Perhaps the most universal piece of advice I can give you is to think like a controller.  Listen to the frequency and get a picture of what's going on in the airspace before you call them, and when you get good at it you'll also get good at knowing what kind of a situation you're flying in to (Is the airspace empty, or are there 4 planes in the pattern for landings, 3 in the opposite downwind shooting touch-and-gos, and a jet arrival on an instrument approach that just got dumped on the tower inside 7 miles barreling in & messing everything up?)

Also remember that from a controller's perspective of priorities ("Safe, Orderly, Expedient") speed doesn't count for much when compared to the other two requirements of the job (and aircraft on the ground are inherently Safe and Orderly unless they do something stupid like go charging across the hold-short line). Unfortunately for us pilots delaying the plane on the ground (that isn't moving, and is thus unlikely to hit anything) is generally preferable to trying to maneuver and delay the ones in the air (that can't stop moving unless they hit something, which is generally considered to be a Bad Thing).

For a masters class in "thinking like a controller" call your local tower and ask to arrange a tour / shadow a controller for an afternoon. Spending the day in the cab is a great way to get an appreciation for how crazy things can get up there.
You can usually Google up the phone number, or call Flight Service or your local FSDO and ask. For most towers it's relatively easy to set up a tour (they'll ask for a driver's license and possibly FAA certificate number to do a background check and make sure you're not completely insane).

The rest of this post is just my personal view on getting along with controllers based on doing most of my training & flying at a pretty busy towered field (According to the FAA's ATADS "Tower Operations" ranking KFRG was #42 in 2013).

On The Ground

When you're ready to go call tower and tell them - Something like Tower, Cessna 12345 number one runway 32, ready to go. is usually plenty (if your airport is configured such that there may be some question as to where you are specify which taxiway/intersection you're at).

After you call the tower and tell them you're ready my experience is you're not likely to be forgotten about. You may be sitting there for a while (my personal record is about a half hour at the hold-short line), but the tower can usually see you sitting there at the runway end waiting. They want to get rid of you, they just need a hole big enough that they can get you onto the runway and airborne without creating any conflicts.

If you are forgotten (it does happen sometimes - you'll see other aircraft being cleared for takeoff who called the tower to report ready after you, or the controller changes, or you've been listening and are pretty sure the airspace is clear but you're still waiting) a polite call to remind the tower you're ready to go isn't out of order. Just don't be That Guy calling every couple of minutes, and if the controller gets a little snippy just be the better person and shrug it off.

In The Air

In the air is a slightly different story.  Sometimes it can take me 3 or 4 calls to get tower to even acknowledge my existence on busy days (again, you don't want to be That Guy calling the tower every 10 seconds - you should have a picture of what's going on in the airspace, and if the controller is busy you may have to circle outside their airspace for a while).

Once you've made contact a good controller will communicate with you and tell you what they need you to do and where they want you to report, where to turn base, or who they want you to follow.

If you feel like you've been forgotten a well-timed position report is usually the best way to remind the tower you exist (and as a bonus it helps everyone else with their mental picture of the airspace too).
For example on an extended downwind for runway 01 at Republic you'll pass Sunrise Highway (a pretty easily identified road, and if you miss it you'll spot the train tracks right after it), the inner shore of Long Island, and the outer shore of the barrier beaches. Reporting each of those points while waiting for tower to call your base generally works (if they genuinely forgot about you they'll usually have an "Oh S%$^!" moment when you call them over the outer shoreline and turn you in for a 7-mile final).

One exception to my position reports technique is landing clearance -- I generally do something to remind myself if I've been cleared to land (fold a chart, turn my kneeboard, etc.) and if I don't recall being cleared I'll call somewhere between 500 feet and the threshold with something line Tower, confirm N12345 landing clearance? (Where depends on the conditions of the day - sometimes they crank out departures pretty tight & if someone's rolling waiting until they're airborne is usually a good idea).
Sometimes they cleared me and I missed it.
Sometimes they didn't clear me and they do.
Sometimes they have an "Oh S%$^!" moment (they forgot about me, have a conflict, and I go around).

All of those situations are generally preferable to landing on a runway someone else may have been told they can use.


Can a non FAA CFI (EASA for eg) sign off a high performance endorsement on an FAA PPL certificate?

No, the problem is that the endorsement must come from an "authorized instructor" which is defined in 61.1(b):

  Authorized instructor means -

  (i) A person who holds a ground instructor certificate issued under part 61 of this chapter and is in compliance with § 61.217, when conducting ground training in accordance with the privileges and limitations of his or her ground instructor certificate;

  (ii) A person who holds a flight instructor certificate issued under part 61 of this chapter and is in compliance with § 61.197, when conducting ground training or flight training in accordance with the privileges and limitations of his or her flight instructor certificate; or

  (iii) A person authorized by the Administrator to provide ground training or flight training under part 61, 121, 135, or 142 of this chapter when conducting ground training or flight training in accordance with that authority.

The requirement for an "authorized instructor" comes from 61.31:

  (f)Additional training required for operating high-performance airplanes.

  (1) Except as provided in paragraph (f)(2) of this section, no person may act as pilot in command of a high-performance airplane (an airplane with an engine of more than 200 horsepower), unless the person has -

  (i) Received and logged ground and flight training from an authorized instructor in a high-performance airplane, or in a flight simulator or flight training device that is representative of a high-performance airplane, and has been found proficient in the operation and systems of the airplane; and

  (ii) Received a one-time endorsement in the pilot's logbook from an authorized instructor who certifies the person is proficient to operate a high-performance airplane.

So you can't get an endorsement from a "CFI" who is not authorized under Part 61.


What are some first-order drag approximations for airframe/propwash interactions?

There is surprisingly little literature on that. This answer by @xxavier lead me to a very interesting paper in which the drag of a Luscombe 8b with and without thrust was compared. A very thoughtful way was used to arrive at zero-thrust numbers, and the result showed that the additional drag from the propeller effects was about 30% of the total zero-lift drag without thrust.

In the paper, the prop efficiency is 81% while the overall efficiency drops to 62% due to slipstream losses.


How can I use a magnetic declination chart to calculate true track, magnetic track and magnetic variation?

The chart shows you lines of equal declination $D$. You identify your location on the chart (which you have done and marked with an X in your second image). Then you determine on which line you are. It looks like the point is between the -26° line and the -28° line, so let's call it $D=-27^\circ$. That gives you a magnetic track of:

$$ \varphi_\text{mag} = \varphi_\text{true} - D = 70^\circ - (-27^\circ) = 97^\circ $$


How does one address a first officer in conversation?

Call the FO 'Captain' anyway.

Both crewmembers are equally rated in the aircraft.
The FO might have more time in the aircraft than the captain or even have been a captain at a previous airline, but is sitting in the right seat because of low seniority at this carrier.
Nobody minds being referred to by a higher title.
You're a passenger, no one expects you to be able to read the bars on their uniform anyway.


How are batteries cooled in passenger aircraft?

As far as I can tell, current aviation lithium batteries do not use active cooling.

I know the True Blue Power TB17 (Robinson R44 & R66, Bell 505 Jet Ranger X) and TB44 (Cessna Caravan, DHC-6, DHC-8) do not require active cooling.

I haven't seen any easily accessible info on the Saft batteries for the A350.


What are the pros and cons of high-wing compared to low-wing design?

This is actually a really hard question to answer, as there are a ton of factors. I'll try to cover a few.

Visibility is probably the reason you most hear when it comes to GA pilots.

High-wing aircraft offer better visibility below the aircraft, especially for passengers in 4-seat or larger aircraft, as the wing doesn't block it.
Low-wing aircraft can offer better visibility above the aircraft, as the wing remains mostly out of the field of view.
Note that a lot of midair collisions involve mixed types; low-wing aircraft descend into high-wing, or high-wing aircraft climb into low-wing.

Landing characteristics are different, as low-wing aircraft can incur more ground effect than high-wing.
Aerodynamic stability of the two designs differs a bit; the center of lift can be higher in a high-wing design, often offset with dihedral in low-wing aircraft.
Ground clearance (and debris protection), specifically in multi-engine aircraft, is going to be greater when engines are mounted on a high wing rather than a low wing. This is true of both propeller and jet engines, although propellers tend to have a larger radius for a given aircraft size.

There are a bunch more, but that ought to get the argument discussion going.


If we add a video recorder in the cockpit to complete FDR/CVR, will we add a blackbox?

Before answering, let's look at these terms:

FDR - Flight Data Recorder

FDRs record all flight data, every button pressed, every control input etc. They record throughout the duration of the flight.

CVR - Cockpit Voice Recorder

CVRs record all voice communications through the radios and the chat pilots have between themselves. They record only the last 30-120 minutes.

So what benefit will adding a camera bring?

After an accident (God forbid) the investigators are not interested to see what was the color of pilot's shirt or was he picking his nose before he pressed a button. In addition, you would need several cameras to record every single action of the pilots, and even then it would be hard to figure out as some buttons are placed very close to each other.

FDRs solve this problem as any input from the pilots are recorded. CVRs capture all communications so the motive or reason behind any input from pilots are be found out.

I suggest you to read some NSTB investigation reports (here or here) to get a detailed idea how in-depth knowledge the investigators can get by these two instruments.


How can an airline flight crew handle an in-flight oxygen system fire?

Opening the flight deck door may be sufficient in some minor cases at the expense of letting smoke and CO2 invading the cabin volume.

In serious cases: Protective breathing equipment is available in the aircraft:

Smoke hood demonstration video:

Portable oxygen cylinders and masks are also available, e.g. for A320 family:

(source)

The presence of this equipment is regulated, e.g. in US by 14 CFR 25.1439:

  at least one portable protective breathing equipment shall be located at or near the flight deck for use by a flight crewmember.

  In addition, portable
  protective breathing equipment must be installed for the use
  of appropriate crewmembers for fighting fires in compartments
  accessible in flight other than the flight deck. This includes
  isolated compartments and upper and lower lobe galleys, in which
  crewmember occupancy is permitted during flight. Equipment must be
  installed for the maximum number of crewmembers expected to be in the
  area during any operation.

The oxygen supply if for 15 minutes minimum:

  The equipment must supply protective oxygen of 15 minutes duration per
  crewmember at a pressure altitude of 8,000 feet with a respiratory
  minute volume of 30 liters per minute BTPD.

These systems are already necessary to the cabin crew to fight any fire or help passengers in case of cabin depressurization.

If a safe aircraft state cannot be restored within the 15 minutes, then the fire is already uncontrollable. Over the ocean and too remote from usable airports, the crew would have to resign and ditch the aircraft to evacuate it, a last resort and risky escape action.

In the accident you mention:

The oxygen system involvement/malfunction is suspected but not certain.
Considering the damages to the flight deck and panels (seen below), a problem for pilots would have been to be able to fly the aircraft with missing or failed instruments and controls, in a hot flight deck atmosphere. The passengers and crews seem to owe their lives to the accident occurring on the ground.

(avherald.com)


The plane would be lighter.

Not by much.

  It cannot be hard to dedicate different planes to different routes.

This adds to the logistics difficulties in scheduling the airframes. It's MUCH easier if all the airframes can be used on all the routes.

  Returning the life jackets each time the plane has to fly over water.

This involves extra down-time/logistics before the airframe can fly the next trip.

You've used the phrase, "large bodies of water"; think about if the airplane needed to ditch in a "small body of water". It would be preferrable that all people had life jackets and thus a chance to live.


Are records of certificate actions available?

Due to privacy concerns, certificate actions are not made publicly available without a formal request, and have to be made via an acceptable means.

The FAA has a document titled Information Provided by PRIA, FOIA, and the Privacy Act which goes into details about how information can be requested and what they will provide:

PRIA is basically a request made by a hiring air carrier, so you wouldn't be able to do that.
FOIA is the Freedom of Information Act, and the above document states:

  Through FOIA, ANY enforcement action, whether still open or fully
  adjudicated and closed, can be reported.

The Privacy Act allows you to request your own records, or a third party company may request records, so neither of these would apply in your case either.


Would an airliner fly more efficiently on a fatter wing at a low altitude?

Silly comments aside, "fat" wings, ones with greater camber, were all the rage 100 years ago when designers found they could eliminate draggy external bracing by building cantilever wings.  Hugo Junkers was one of these pioneers.
Wind tunnel testing also showed increased camber not only increased lifting efficiency, but also, combined with large, rounded leading edges, produced very benign stalling characteristics.  One result of this research, the Fokker D.VII., so terrified opposing pilots that it was specifically banned after the end of the "Great War".
Heavily cambered wing design such as the Davis wing lived on until aircraft began pushing the limits of the "sound barrier".  Aircraft fly higher to get more speed with the same amount of drag, and this works great until the wing approaches its critical Mach number.  Above this, drag greatly increases, ending the reign of the "fat wing".
Modern "super critical" wings, literally "surf" the slower bottom airflow, leaving the top of the wing as flat as possible.  This is what airliners use at 35,000 feet.
But at 1000 feet, where airspeed is limited to 250 knots, the "fat wing" makes a comeback by deploying slats and some flap.  For a given wing area and Angle of Attack, the "thin wing" is only more efficient when Critical Mach Number is approached.
This is why many airliners have a never exceed speed for lower altitudes, and a Mach limit for higher altitudes.


From this Goodyear document on aircraft tires, both types exist. For the 747, they are all tube-type.

  Tires are tube-type unless otherwise indicated.

The listed 747 civilian variants do not indicate otherwise (page 18).

(Source: wikimedia.org) Cross section of a 747 tire. Full resolution via link is a must see. You can make out the inner tube (flap) from this image.

But that document is from 2002, nowadays tubeless tires are also available for the 747 and many commercial types, for example the 49X19.0-20 Flight Leader by Goodyear (thanks @user71659).


I believe what you are referring to is an acceptance flight, rather than a certification flight. Certification flights (usually there many) are flights which the manufacturer demonstrates to aviation authorities that a new design of an aircraft is safe. However, just because a design has been tested, does not mean a new aircraft is produced exactly to the design. Acceptance flight is a test flight which make sure the aircraft has been manufactured up to standard.

Acceptance flights are also required after major maintenance work or avionics upgrades. Its purpose is to explore the entire flight envelope and ensure emergency / backup systems work as expected. During a normal flight, only a portion of the systems' functions are used. A test flight is a complete evaluation of all conditions, such that malfunctions or deviations will not go unnoticed.

Of course, the pilots will first examine critical systems (e.g. engines, flight controls) on the ground. Depending on the aircraft, the tests to be completed in the air include:

Engine shutdown and restarts
autopilot roll rates, flap extension speed, engine response etc.
Alternate gear extension
Fuel jettison
Over-speed warnings
Stall protection systems
Ground Proximity Warning System (GPWS)
Auxiliary Power Unit (APU) operation at high altitude
Cabin service systems


How can drag induced by the landing gear be reduced?

The Pilot's Manual: Ground School has a nice diagram that explains it pretty well. It's all about streamlining. Airplane designers add landing gear fairings (I've heard them call "wheel pants") over top of the wheels and also on the landing gear strut. Beyond this, there isn't much else to do. The fairings could be made out of single pieces of material to limit the parasite drag introduced by rivets, etc.

There can be different variations on the fairing, but it pretty much comes down to fairings to reduce the drag:

NACA (precursor to NASA) details more in REPORT No. 518 THE DRAG OF AIRPLANE WHEELS, WHEEL FAIRINGS AND LANDING GEARS II-NONRETRACTABLE AND PARTLY RETRACTABLE LANDING GEARS

They also looked at wheel shape, but it primarily comes down to creating some sort of streamlined fairing to reduce the amount of eddying.


Why is the A320neo considerably ahead of B737Max?

I certainly would not say that the 737 MAX is "losing heavily" to the A320neo. The A320neo is entering service in the next couple of months (October 2015.) The 737 MAX isn't entering service for another 2 years (2017.) I don't think many aircraft manufacturers would be upset with having 2,727 orders for an aircraft that is still 2 years from even entering service. It should further be noted that the A320neo was right around the same total when it was 2 years from entering service.

Some additional factors that come into play:

The A320 line tends to be more popular in the low-budget Asian market, which is growing significantly right now.
The U.S. Dollar is currently relatively strong compared to the Euro, due to lots of economic problems in the Eurozone. This means that products exported by European manufacturers are relatively cheaper than products exported by American manufacturers compared to their usual price difference. Obviously, that's an advantage for Airbus, as it means that it's cheaper than normal right now for customers to buy Airbus vs. buying Boeing. This is, again, especially important to the cost-sensitive low-budget markets.
Airbus' Chinese assembly line allows them to make A320s for the Asian market quite a bit cheaper than Boeing can make 737s for that market, due to the major differences in labor costs.


I don't have a proof for the thinking behind the rule making. But my understanding behind it is to prove that the brakes alone can do it in case the reversers are inop. But usually there are exceptions to rules:

dry runways
Dry runway takeoff data does not (with very few exceptions, such as the 737-300/-400/-500 certified to CAA rules) include credit for thrust reverse in the accelerate-stop calculations.
non-dry runways
Historically, Boeing has taken credit for reverse thrust when producing data for non-dry runways. This has been accepted by the FAA. The UKCAA rules, and now the JAA and European certification rules, also allow credit for reverse thrust under these conditions.

For the non-dry rule, Boeing uses half the engines, so for example a 747 would be based on two reversers, and a 737 on one.
Spoilers on the other hand are required so that the landing gears are compressed, if they weren't the tires will slip more. It is also true the heavier the aircraft, the better the brakes work up to their limit.

Quotation and image source: Jet Transport Performance Methods.


How can an aircraft not fall into the sea after the arresting cable snaps during a carrier landing?

The truth of the matter:  That E-2C pilot escaped crashing by a hair's breadth.  He was just very, very fortunate that the combination of holding full power, the position on the flight deck where the arrester pendant failed allowing for a small takeoff roll to accelerate, plus the 40+ ft drop off the deck of the ship to the waves combined with the ship steaming into the wind was enough to gain him the end airspeed he needed to fly again.  The flight crew received the Air Medal for their heroism in the face of that situation.  As an E-2 does not have crew stations equipped with ejection seats, there was no other option available to the flight crew than to attempt to gain airspeed and hope for the best.  That cross deck pendant failure could have easily resulted in disaster and most pilots in that situation don't live to tell the tale.

Although it is rare, cross deck pendant failures can and do happen and are extremely dangerous, both to the aircrew of the recovering aircraft and to nearby flight deck personnel; there have been cases where a failed cable has literally sliced a man in half.  As a precaution, each cross deck pendant has as pre-set service life of 100 traps, then it is removed from the purchase cables on the arresting gear and destroyed.

This video was shot by an sailor aboard the USS Ronald Reagan during sea trials in 2003.  The arresting gear failed, sending the aircraft over the edge of the deck.  The F-18 pilot ejected and survived.  Note the amount of damage which the end of the cross deck pendant does to equipment and personnel as it whips across the flight deck.


How do big planes like 737 manage fresh air for passengers during flight?

They bleed hot compressed air from inside the jet engines, cool it down and pass it into the cabin. There are outlet valves in the fuselage that allow stale air out and which control cabin pressure and air-refresh rates.

A few aircraft types, such as the 787, now use a compressor to take in air from under the aircraft. They do this because it can be more fuel-efficient (not for any other reason). It is arguable whether it creates an additional fire hazard.

See also

Why is the compressed air (from Engine Compressors) taken from High Pressure (HP) stage instead of Low Pressure (LP) stage
Can an aircraft re-pressurize at high altitude?
Is constant air pressure maintained inside the fuselage?


What is the difference between Part 135 and Part 129?

I'm not at all sure what you're asking, but maybe I can at least point you towards more information.

First, the parts you mentioned define operating rules for different flight types (I'm simplifying a bit here):

Part 91: rules for all flights in the US
Part 121: rules for flights by a US airline
Part 129: rules for flights by a foreign airline in the US
Part 135: rules for 'on demand' (usually charter) flights by a US operator

Any given flight will operate under one or more of those sets or rules, e.g. a US airline flight from New York to Los Angeles would follow the rules in parts 91 and 121; a foreign flight from London to New York would follow parts 91 and 129 (while in US airspace). Individual operators and airlines also have OpSpecs that are approved by the FAA and that can add more rules for specific situations.

And I'm not entirely sure, but it looks like 14 CFR 129.119(c) effectively applies part 121 to foreign airlines too, by requiring them to comply with the same rules as US airlines:

  (c) Each foreign air carrier shall conform to the practices,
  procedures, and other requirements prescribed by the Administrator for
  U.S. air carriers for the areas to be operated in.

Without knowing what your mysterious problem was (and I understand you can't share it), I don't think it's possible to say much more than that.

(By the way, "filing" is something different. Filing a flight plan is required for various reasons but they apply to all aircraft, even private flights. If I want to fly a C172 under IFR then I have to file essentially the same flight plan information that an A380 pilot will file.)


On how many routes an aircraft is used on a typical day?

Actually, a commercial airliner can do almost any set of legs, assuming those are technically possible (range/payload/laws like ETOPS...) But the main fact that make it possible is demand. If you run an airline, you won't make routes that don't have demand to make profit.

Aviation is a complex world. To make profit, you have to consider a massive load of parameters. You can't for example position complete set of crew in every city/airport hotel of your airline routes then decide to create fantasy flights "a la carte". Crews can't fly continuously aswell, so you can't put crew in a 737 and make them non-stop flights around the country an entire week.

One main thing you have to keep in mind : It's not one or several persons who decide "I want to build an airline with X aircraft on Y routes". It's one A-B route that decide how many passengers are available on, then, an airline has the opportunity to operate that route (and struggle to negociate all the authorizations)

Here are some hints about how airliners deals with their environment around the world :

What kind of flights does the airliner, and what airframes does it have in its fleet ?

An airliner can start with one single aircraft, says a DHC6 Twin Otter, and makes regular flights between two airports in the middle of the ocean. You can have 10, 15, maybe 20 round trip a day, some well after sunset.
An airliner can have half a dozen ATR or Dash 8, and a set of routes with the proper demand. You can have routes like hub-A-hub, hub-B-hub, when the demand is enough to make each flight profitable. Sometimes, you can't have enough passenger a day on each route, so the airliner makes hub-A-B-C-D-hub the day one, then hub-D-C-B-A-hub on day two, and cycle the sets...
An airliner with dozens of (the same) aircraft (737 or A32x) can either have the same round trip hub-X-hub destinations every day, several times a day, airlines like Air France, Southwest, Lufthansa, Air China... or the same fleet, but much more destinations operated two or three times a week : hub-A-B-hub, hub-C-D-E-hub, hub-F-G-H-nightstop-G-F-hub... like Angola Airlines (domestic and regional)
Long range flights (7 hours or more) requires the appropriate aircraft. If your airline can buy/lease such an airliner, the route hub-destination-hub can be operated in the limits of the demand. When the demand is enough to fill the plane along the week, then go ahead. Otherwise, the airline has to decide wether a) leave the plane on the tarmac, b) find a nearby complementary route : hub-A-B-hub, hub-B-A-hub, c) use a smaller and cheaper aircraft (if the crew is qualified on) d) combine destination A with a complementary destination B that fills schedules along the week (or bi-week) hub-A-hub-B-hub, e) replace the route with one better, f) negociate with one or several airliners to sell seats to them to fill the aircraft, g) negociate with one or several airliners operating on the destination airport to take advantage of the hubbing : make your airline land at the destination during rush hours.
Very long range flights can't be operated every day with one single aircraft. And very long range flights are a niche : the hours spent in that closed tube discourage passengers from taking such flights. And very long range flights are a hell to schedule : the aircraft does 3 or 4 flights a week, and stays on the tarmac the rest of the time.

The size of the airline :

If your airline is a big one, like British Airways or Japan Airlines or United, your reputation and historical operation is enough to get demand on most usual routes (and your staff has the expertise to select profitable ones) Most of your flights will be the type "hub-X-hub", either domestic, regional, or international.
If your airline is above average (like Kenya Airways, Aeromexico, Air India) you'll have a mix of "hub-X-hub" flights and some complementary legs to fix schedules and aircraft operation ratio : hub-A-B(-C)-Hub
If your airline is below average (Blue Panorama, Air Kazakstan, Belavia) chances are great to have charter flights, multiple flight shifts.. Timetables greatly vary from one year to another.
Small airlines like Air Austral, Republic Express (Indonesia), Insel Air will have historical regular flights, but most of them will be of type "hub-A-B-hub" and/or "hub-A-C-E-C-B-hub". Timetables also vary from one year to another, but at a less rate than above because the airline don't have enough aircraft to think of new or better routes to operate, as the ones available cannot be closed or replaced.

The region of operation - the airport statistics (passenger volume per year) :

There are regions of high frequency of flights : Western Europe, United States, Japan, South-East Asia, Eastern Australia, the Dubai-Europe axis... In those regions, you have several hundreds of round trip routes that can be operated ten times a day using a Boeing 747. Cheap flights, historical demand, dynamic business. You can operate flights of type "hub-destination-hub".
There are regions with much less traffic, but enought for one airline to operate the simpliest flights hub-dest-hub. However, once another airline or more decide to compete on the same route, everyone is forced to reconsider the way it operates their fleet.
You also have regions in the world, especially in Africa and some non-democratic countries out there, where only one airline is allowed to operate a given route. Usually, those airlines don't care about competition, as the state/country itself protect them. Ticket prices on those routes are unusually high, because they can. So the demand on those routes NEVER take off, thus, making the flights on them the same along the years. You'll have destinations operated once a week (if not once a month) You'll have very small airlines and you don't understand why, having the monopoly on the network, they are not able to grow, grow the traffic, and propose better schedules for custommers than the absurd routes and departure/arrival times. Simple : they simply don't care.

Night Flights - jet lag.

You can't just make an aircraft take off, and land when you want. A custommer usually don't want to land at an airport at 3AM.
An airline should avoid boarding passengers at 5:30AM, just because if you board at that time, you've waken up at 3:00AM, failed to take a breakfast, almost forgot your papers, arrives at the airport hungry and angry...
jet lag : If you take off from San Francisco at 09:00PM, going to New York, you'll land at 06:25AM. It's okay ! But if you take off at 05:15PM, you'll land at 03:40AM. You haven't slept well.. Perhaps at NY, it's okay to land so early in the morning, but try this in Charles de Gaulle and you'll see how boring (or expensive) it will be. Jet lag is an important factor for international flights. When the airline can't have the slots to land at a proper time at the destination airport, it should think of alternate flights to do, or negociate the opening of an intermediate destination of interest before operating the projected flight, this creating legs like "hub-alternal-hub-destination-hub" or "hub-alternate1-alternate2-destination-hub" or "hub-alternate-destination-alternate-hub". Airlines like Air Madagascar does this. Landing at an airport late in the night is another reason of nightstops. This is common with regional jets (737-ERJ-A32x...)

Aircraft operated by several airlines.

Sometimes, you'll have aircraft operated by the owner some days in a week, and by another operator the remaining time. Take for example InterAir of South Africa. The aircraft is based at Johannesburg, and operates InterAir flights from and to JNB. But on Wednesday and Friday morning, the aircraft takes off from JNB as an InterAir flight, to Cotonou, and from there, it operates for AeroBenin to several destination in central Africa. The aircraft returns from Cotonou the Thursday and Saturday afternoon as regular InterAir flight. So don't be surprised to find a flight from JNB to Cotonou Wed and Fri morning, and their returning legs on Thu and Sat afternoon. That's common in Africa, South America and Asia. Many airlines like Blue Panorama, Lot Polish, EgyptAir (...) lend some of their aircraft to smaller airlines in the world on a week basis like this. The smaller airlines operate them on routes like "hub-A-B-C-B-A-hub" to use the aircraft as long as possible in the few hours/days.

So, those are only hints to understand how routes as selected and arranged. To enumerate all possible schemes, even a book won't suffice.

It is possible to have much more aircraft than routes (when you have enough demand) or the inverse. An aircraft on the ground is an aircraft that costs money for nothing; so "hub-X-hub" flights are rarely the best way to operate an aircraft. Key words are "demand", "costs", "profit". To get factual datas to calculate those, you'll need parameters like aircraft performance, airframe availability, route statistics, crew/maintainance possibilities, security/safety, regulations/laws/authorizations... then compare and negociate the opening of the most profitable route with the less risks with the appropriate aircraft.

Side note : I'm no expert. I'm just an aviation enthusiast, mostly airliners of the 1960-today era.


Does the FAA allow a jet bridge to approach an aircraft that has engine #2 running?

On a two engine airplane, Engine #2 will be on the opposite side from the jetway, and keeping the engine running while the bridge is connected on the other side is not an issue.

(see related question: How are engines numbered?)

On a 4 engine airplane, Engine #2 will be directly behind the jet bridge, and should be shut down before the bridge is extended.  This is for the safety of the engine, to avoid ingesting any debris from the jet bridge, or debris dropped by people, rather than for the safety of the people (who are unlikely to be sucked in by an engine at low power).


How does an operator change the engine thrust rating?

Please refer to the following website, it explains the plug programming.:

http://nandang-smart.blogspot.com/2014/09/cfm56-7b-identification-plug.html

You may read:

  WHEN ENGINES ARE MOVED BETWEEN AIRCRAFT AND MAY REQUIRE A DIFFERENT THRUST INSTALLATION THIS N1 MODIFIER IS USED IN CALCULATIONS TO UPRATE OR DERATE A GIVEN ENGINE AT AN APPROPRIATE LEVEL.

You may also read

  THE THRUST LEVEL OF AN ENGINE IS CHANGED (PERHAPS MORE ACCURATELY "PROGRAMMED") BY INSTALLING A "ID PLUG" THAT SCREWS ONTO THE EEC AND CONVEYS PROGRAM INFORMATION THAT SETS THE ENGINE THRUST OUTPUT TO THE LEVEL DESIRED BY THE OPERATOR.

With respect to the thrust limit, you may display on the CDUs ( MCDUs) the FMS thrust limit page that allows the pilots to derate the TO thrust.

The following website shows for the B777 how to get access to the «  thrust limit » page:

So the pilot may change the thrust limit from the CDU, while the rating is changed by pin programming on the plug, the value entered in the CDU by the pilot is transmitted to the FMS which will ask the FADEC to reduce the thrust whatsoever below the rated value chosen by the operator by pin programming.


Does one have to practice engine failures in flight training?

From a general aviation standpoint here in the US, yes. Engine out landings and general procedures are practiced during your PPL training. No particular failure is trained for because there are really only 2 situations, the engine is running or the engine is not running. The procedures for different planes vary but generally you set for best glide, pick a touchdown point (airstrip if you can) and head for it. Once in route you can attempt a restart if you can identify the problem and solve it. on some planes you can feather the propellor and such.

That being said that generally applies to single engine planes, in a twin engine plane there are a few more situations depending on the design of the plane. In a twin you may have a "critical engine" as such engine outs are practiced with that in mind and the procedures are adjusted appropriately.

As for the why...

There are lots of things that can take out an engine like a bird strike, a mechanical failure, a fire etc. The fact of the matter is that it does happen  all be it not that often, you would be a fool not to prepare.

Anecdote:

When I started my training I got curious about piston engines cutting out so I began to ask around. Youtube videos aside, I was only able to actually find one guy who knew a guy that once lost an engine. Engine manufacturing has come a long way since the advent of airplanes and engines are simply more reliable than they once were. Here is a great article that touches on some of the twin engine points about reliability. While it does happen and you should never assume "this wont happen to me" engines are much better than they were 50 years ago when some of the requirements were made for the tests and training standards.


What is the maximum range of a BAe 146-300? Can auxiliary fuel tanks be added?

According to wikipedia it has a range of 2909 km and the distance is around 2500 km


What's a TRA and how does it differ from a TFR?

As the message says, a TRA has the same rules as an RA, just that it is temporary so it won't appear on charts. There may be expected times when the RA is in use but the actual times will be posted in a NOTAM.

It will be published in the Federal Register ahead of time
Using agency notifies controlling agency when airspace will be "hot"
NOTAMs describe when the airspace will be closed
When the airspace is open, ATC can clear flights (IFR or VFR) through

This is useful if the area is known ahead of time but times may be limited and variable. The using agency must also later submit a report detailing the actual usage of the area.

A TFR defines special flight rules that are applicable in specific circumstances. They are governed by different rules, and a NOTAM is published defining the airspace and times, as well as what restrictions are in effect. A TFR may be defined for the following reasons:

Disaster/hazard areas
Protecting the President, the Vice President, or other public figures
Space flight operations
High barometric pressure
Aerial demonstrations and major sporting events
Security requirements

Each of these categories has general rules for who is allowed to operate in the airspace, though each TFR may include more specific requirements. TFRs issued for disasters/hazards generally require aircraft that are not local flights or directly related to the event to be on an IFR flight plan. Other situations may just require permission from ATC, or effectively make the airspace Class C.


Are there regulations or adverse effects regarding Bluetooth in the cockpit?

There are multiple aviation headsets approved by the FAA that have built-in Bluetooth.

Based on that, I'm going to say that this has been tested and will not interfere with the aircraft avionics.  Radio/EMI testing is part of the testing that any device approved by the FAA for use in an airplane must go through.


What are the FAA requirements for an aircraft to be IFR certified?

As you say, the FAA certifies an aircraft for certain "kinds of operation".  For a normal category airplane certified under 14 CFR 23, it basically says that it must be "established appropriate to the installed equipment":

  §23.1525   Kinds of operation.
  The kinds of operation authorized (e.g. VFR, IFR, day or night) and the meteorological conditions (e.g.
  icing) to which the operation of the airplane is limited or from which
  it is prohibited, must be established appropriate to the installed
  equipment.

The installed equipment required for IFR flight (beyond that required for VFR flight)  is listed in 91.205(d) and is mostly equipment used to communicate with ATC and to maintain control of the airplane when flying without visual reference to the ground (so no navigation equipment is specified):

  §91.205   Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.

  ...

  (d) Instrument flight rules. For IFR flight, the following instruments
  and equipment are required:

  (1) Instruments and equipment specified in paragraph (b) of this
  section, and, for night flight, instruments and equipment specified in
  paragraph (c) of this section.

  (2) Two-way radio communication and navigation equipment suitable for
  the route to be flown.

  (3) Gyroscopic rate-of-turn indicator, except on the following
  aircraft:

  (i) Airplanes with a third attitude instrument system usable through
  flight attitudes of 360 degrees of pitch and roll and installed in
  accordance with the instrument requirements prescribed in §121.305(j)
  of this chapter; and

  (ii) Rotorcraft with a third attitude instrument system usable through
  flight attitudes of ±80 degrees of pitch and ±120 degrees of roll and
  installed in accordance with §29.1303(g) of this chapter.

  (4) Slip-skid indicator.

  (5) Sensitive altimeter adjustable for barometric pressure.

  (6) A clock displaying hours, minutes, and seconds with a sweep-second
  pointer or digital presentation.

  (7) Generator or alternator of adequate capacity.

  (8) Gyroscopic pitch and bank indicator (artificial horizon).

  (9) Gyroscopic direction indicator (directional gyro or equivalent).

As far as converting an airplane from VFR to IFR, the Type Certificate Data Sheet (TCDS) must specify that the airplane is designed for IFR flight, and then you could add the missing equipment to make it qualify.


What are the relative braking contributions from wheel brakes, spoilers and thrust reversers?

Your question shows that you understand the issue already very well, and more detailed fractions of the single components depend on the particular airframe and engine, so my answer will not add much insight.

The only detail I can add is a plot of tire friction coefficient over speed. Unfortunately, I do not know the source of it; I collected it sometime in the past and never found a reason to doubt its validity.

Also, this document might be helpful. Below I copied Figure 3 from it, because it comes closest to answering your question. But keep in mind that the details depend on the particular aircraft and its systems, as well as runway condition, wind speed, tire and brake condition.

Typical deceleration forces during landing roll, from this document. Note that the aerodynamic drag with spoilers plus reverse thrust at high speed produce already more deceleration than what is desired at low auto brake setting.

In order to find the overall contribution of each braking component, compare the areas under their respective plot lines.


Which company manufactures the air data system on the Boeing 787-9 'Dreamliner'

Boeing procured the avionics for the B787 in "packages". Air data was part of the "Navigation Package" which included in addition to air data, IRUs, nav radios, GPS sensors, and the FMS software.

Honeywell was selected as the supplier for the Nav package. So they provided the air data system.  I don't know what specific system they supplied.


Do I need FAA permission to install tundra tires on a Piper PA-28 Cherokee 140?

Any time you make a modification to a certificated aircraft you need FAA approval. Even what appear to be minor things, like replacing you sun visors with better ones requires an STC. Putting in shoulder harnesses requires and STC. I could go on forever, but you get the idea.

Putting tundra tires on your Cherokee is a major change. If you look in the parts manual, your Cherokee probably came with 4 ply 6.00x6 tires so to change them you need an STC. You would also need to get an STC for the wheels and brakes. You’d probably need a new nosewheel fork as well.

I have never heard of anyone putting tundra tires on a Cherokee, but stranger things have happened.


What is the typical touchdown vertical speed of a large airliner?

From an MIT ICAT paper:

  Today's commercial autoland systems utilize the ILS (...) At around 30 ft above the ground, the aircraft enters the flare mode, during which the aircraft pitches up to reduce the vertical speed from its current descent rate to 1-3 ft/s by touchdown.

Which means we're looking at 60-180 FPM touchdown rate.

Kiss landings (near 0 FPM) are undesirable, because they can't be achieved on regular basis without risking long landings. They can also break landing gears (more on that below).

I checked various Boeing/Airbus operating manuals, they do not state the target rate of the flare mode, but from the 747-400 flight crew training manual (page 6.11):

  Do not allow the airplane to float: fly the airplane onto the runway.
  Do not extend the flare by increasing pitch attitude in an attempt to achieve a perfectly smooth touchdown.

Left: a shimmy event "damaged the wheel, tire, and shimmy damper" (Boeing). Right: what a shimmy looks like (YouTube).

  Landing with extremely low sink rates is more likely to experience shimmy than a firmer landing because the torsion links remain in an extended vertical position, where the damper has less mechanical advantage for longer periods of time (Boeing).

Boeing commercial aircraft are designed for 600 FPM landings, with 360 FPM when above the maximum landing weight. Boeing also says pilots are the best evaluators of hard landings, "because of the difficulty in interpreting recorded acceleration values at the CG of the airplane."

Based on pilot reports and data, exceeding 240 FPM is a hard landing, which further confirms the 60-180 FPM to be an ideal firm value whether the landing is flown manually, or with the auto-land (Boeing).


What does the future of the weather radars look like?

In the USA, planes with ADS-B can receive FAA transmitted weather from ground stations for display in the cockpit. It can lag by several minutes.
https://www.faa.gov/nextgen/programs/adsb/pilot/

Planes with XM weather can receive more timely weather from satellite feed for display in the cockpit.

Airborne radar has the advantage of being the most immediate, but you may not be able to see much past what is immediately in front of you, so combining that with ground/satellite feed to give you a view of what is farther ahead would be the best of both.

I have ADS-B in my plane, but I don't do any extreme weather flying, just climbing thru cloud layers to get to nicer weather on top, or dropping thru a layer to land. I'm not out there trying to dodge thunderstorms and heavy rainstorms. If the weather is that bad, I can wait it out.


What was this helicopter photographed on a Chinese aircraft carrier?

Can't say for sure, but the size and shape (as far as can be determined from the picture) seems to match the Aerospatiale Super Frelon, which is built under license in China and is in use with the Chinese navy for shipboard operations under designation Z-8.

The image is of poor enough quality that a more precise determination isn't feasible, but the size and shape match the type and the type is in Chinese service (unlike similarly sized helicopters).


What is the meaning of flap detent names (e.g., 10 degrees)?

The "Degrees" of flap deployment generally refers to the deflection from the neutral (0° - flush with the rest of the wing) position of the flaps.

For most GA aircraft this is an actual angular measurement - 10° of flaps corresponds to the flaps lowering 10° from their neutral position, but the degree of travel can also be given as a percentage (0-100%). The aircraft's maintenance manual will specify the actual travel (and specify how it is to be measured), and if specific position detents are provided there will usually be "rigging limits" specified for where each position stop must be & how accurate the control position must be at each stop.


Is there still a minimum height required for becoming a Lufthansa pilot?

This page for pilot applications shows a 165cm number.
I didn't translate to see what it's for

https://career.be-lufthansa.com/index.php?ac=search_result&search_criterion_activity_level=107

4 pilot jobs listed, only the first 3 show the 165cm.


What is the Scaling Factor in ARINC 429?

In the example you pasted, the value $1.5_{10}$ is being sent, which has binary representation $1.1_{2}$. The data is sent as an unsigned integer so some kind of multiplier needs to be applied. The value occupies 19 bits, at offset 11 within the packet itself being bit 0 of the data. The default multiplier is such that the "units" bit (ie the one representing $1_{10}$) is in bit 26 in the packet, that is the bit 16 of the value. You can see that in the first example, the lefthand $1_{2}$ is in bit position 16 (counting from 0 from right).

This allows only values up to slightly short of 8. Various scalings are applied to values, depending on the label, as this may not be a convenient range for the data conveyed. If a label conveys data in the range 0-6, then it is fine as is. If 0-65 must be conveyed by a label, then the value is shifted right four places (to give more space for the larger numbers, but with less precision). Which scaling is applied is determined by the label. If a negative number is possible in a type, two's complement is applied. The label definition determines the range of its various words.

You can see this example effectively repeated immediately with value $1.25_{10}$, which is $1.01_{2}$.


How is a variable sweep wing constructed?

The easiest way to sweep a wing is an oblique flying wing. This is essentially a straight wing with pivoting rudders and engine pylons which flies at an increasing angle of sideslip where a swing wing aircraft would fold its wings back.

Oblique flying wing (picture source)

If you want to know more, I suggest to read this website. Excerpt:

  Although the oblique flying wing concept was described by Jones in
  1958 and a drawing by G. H. Lee was published in 1962, the concept
  received little attention until the 1990's when active digital flight
  control systems became more capable and widespread. The oblique
  all-wing configuration was studied in detail by researchers at NASA,
  Stanford University, McDonnell-Douglas, and Boeing in the 1990's as
  part of a NASA program.

If the wing is attached to a fuselage, only the wing should move. Again, this can be achieved by pivoting a straight wing, as done in the NASA AD-1 research aircraft, or by folding the wings back with a huge hinge at the wing root, as done on swing wing aircraft.

NASA AD-1 in flight (picture source)

The first aircraft with a variable wing sweep was the Messerschmitt P-1101 which was almost completed in 1945 when WW II ended. It was supposed to fly as a fighter-bomber with reduced wing sweep and as a pure fighter with increased wing sweep, and sweep could only be changed on the ground. On the basis of this design Bell built the X-5 research aircraft, the first to change sweep in flight.

P-1101 under construction (picture source)

The mechanics of a swing wing is rather straightforward: All you need is a big hinge connecting the wing spar at the root and a big hydraulic cylinder or spindle drive for adjusting the wing's sweep angle. And a flexible fairing at the wing root. And something to compensate for the shifting aerodynamic center.

Swing wing mechanism of the F-14 (picture source)


Where can I find information about Boeing delivery history?

Planespotters.net also has a nice list. It has a good layout, and has pictures.


Which Airbus models have exterior LED lights? (Taxi, Landing, Rotating Beacon)

The A320NEO has full LED lighting. Check out the below link.
http://utcaerospacesystems.com/cap/systems/Interiors%20Documents/Lighting%20Systems/06%20Anti-Collision%20Lights/06_0010%20LED%20Anti-Collision%20Lighting%20System%20A320.pdf


Where are the communications antennas normally located on general aviation aircraft?

Honestly? That AOPA article overstates the issue of airframe shadowing (at least for light GA singles): Both antennas will usually work fine on the ground, and will probably work without any issues in the air as well.

Airframe shadowing can cause issues, but if it were as big an issue as people like to make of it there would be no aircraft with single-radio installations (because they would either not be able to talk to people on the ground, or not be able to talk to people in the air).
There are plenty of aircraft flying around with only one radio.

If you're concerned about whether your transmissions are readable pick a nice quiet time of the day and ask the tower for a radio check on Com #1, then repeat the process on Com #2. (Because we're talking about AM radio the results of this test are valid for your aircraft's position and heading when you did the test, and in weather conditions similar to those the test was conducted.)

The general rule of thumb is that each radio will be connected to a separate antenna (this is necessary if you want them to work independently). Some avionics shops have a preference of which way they wire things, and I'm sure manufacturers have a standard they use in their shops (either the POH or the maintenance manual for your aircraft MAY tell you what the manufacturer's standard is; it may also be noted on the FAA Form 337 for the avionics installation if one was filed).

I've seen varying combinations of which radio is connected to which antenna ("Single radio - Antenna on top" ; "Single radio - Antenna on bottom" ; "#1 Left Wing, #2 Right Wing" ; "#1 Top-Front, #2 Top-Rear", "#1 Top/Ground, #2 Bottom/Air" ; "#1 Bottom/Air, #2 Top/Ground").


Vertical autorotation with passive rotor

There's some info on autorotation, including some references, in this answer. And also a pertinent question on Physics SE. Free body diagrams included.

In short:

Autorotation only works in a satisfactory way if the vehicle has forward velocity: in a vertical descent, in optimal circumstances, autorotation works as well as a leaky parachute does.
Getting the rotor to actually rotate from standstill is a hair raising kettle of fish, the first thing about autorotation that helicopter pilots learn is that they must maintain rotor rotation from when it was driven by an engine. During any time of rotor standstill the aircraft is simply falling, with no real means of aligning the rotor with the airflow.
Autogyro's start their flight by starting the rotor to rotate. Can be done on ground by driving fast and making use of the horizontal velocity, or by a flywheel mechanism attached to the propeller engine. Again, the first thing to do is to rotate the rotor.

The equations in OP are valid for fixed wing aeroplanes, and for the rotor blades. But since with rotor blades the velocity over the blade is a function of the blade radius, plus faster over the forward moving blade than over the retreating blade, they are not defined relative to airspeed V but to tip speed of the rotor blades $\Omega R$. Impulse theory using non dimensional coefficients, from Prouty Helicopter Performance, Stability and Control page 25:

$$ T = C_T \cdot \rho A (\Omega R)^2$$

with

T = rotor thrust
$\rho$ = air density
A = disk area
$\Omega R$ = tip speed

Note that Prouty uses the USA definition for $C_T$, which incorporates the factor ½ of the dynamic pressure $½ \rho V^2$ and is therefore twice as much as $C_T$ values used in Europe.

For the thrust to drive the rotor, analogous to aeroplane drag:

$$Q = C_Q \cdot \rho A (\Omega R)^2 R$$

And for the power:

$$P = C_P \cdot \rho A (\Omega R)^3$$

  Also will all kinds of foils work in this scenario? What is the important parameter in foils that will make it start spinning and descent with constant speed?

Airfoil shape is of much less importance than blade twist, solidity ratio and a whole lot more parameters, which would make the answer very broad. Best looked up in Prouty and Leishman.


Current FMS with COMM tunning function capability?

On Airbus/Boeing airliners, the Comms system is completely separate from the Nav system, so - no.

The 787 has the ability to pre-store lots of Comms frequencies, so that you've already got the numbers in the box. But it doesn't have the modern light aircraft capability to tell you that this frequency is this airport and that facility.


What airfoil design is needed for a 4 m wingspan soaring plane?

First for those who wonder what F3J is: This is the FAI model aircraft category for thermal soaring.

Quick answer: This answer describes what resources are available on the Net.

Your choice of airfoil depends on the wing loading and the size of the model, because those will determine the Reynolds number of the flow over the wings. Soaring flight requires high lift coefficients, but maybe you also want low drag for sprints between thermals or to avoid being blown away by strong winds.

The description of the NASA Autonomous Soaring Plane gives 15 pounds of mass and a wingspan of 170 in. It was based on a model glider by RnR Products, and there I found the aspect ratio of 19.8 and the wing area of 1545 sq.in. These numbers are not very consistent, but close enough to get an idea.

Thermals are strongest in their center, so it is desirable to fly as tight a circle as possible. Low wing loading $\frac{m}{S}$ and a high lift coefficient $c_{l_{max}}$ drive the minimum turning radius $r_{min}$ down (at a given density of air $\rho$), and the formula is:
$$r_{min} = \frac{\frac{n_{z_{max}}}{\sqrt{n_{z_{max}}^2 - 1}}}{c_{l_{max}}\cdot\frac{\rho}{2}\cdot \frac{S}{m}}$$

Here $n_{z_{max}}$ is the maximum load factor, and the picture below shows that little is gained by increasing $n_{z_{max}}$ beyond 3. The little DFS Habichts help to illustrate the bank angle.

With a wing loading of 6.8 $kg/m^2$ and a mean wing chord of just 23 cm the flight speed at a $c_l$ of 1.2 is 9.5 m/s. At sea level in a standard atmosphere the Reynolds number would be 150,000. The wingtip flies at a Reynolds number of below 100,000. In circling flight with a bank angle of 60° (equivalent to 2g, so you need twice the lift), the Reynolds number would increase to 212,000 for the mean chord and to 140,000 for the tip. If this sounds a lot to you, it isn't. This is a flow which needs highly specialized airfoils.

My recommendation is to try the UIUC airfoil database and select a specific model airfoil with low drag at high lift coefficients and Reynolds numbers down to 100.000. It should have high camber and a thickness of around 12% to keep wing weight down. If you have the lower range of Reynolds numbers covered, you need not to worry about the higher range. You might even consider to use different airfoils over the wingspan, depending on the minimum local Reynolds number. Ideally, you'll find a set of airfoils which have been optimized for exactly this purpose, like the DAE11 - DAE21 - DAE31 airfoils of the Dedalus human powered aircraft.


What's the possibility of a commercial airplane crashing due to a computer error?

First; let's be honest.  No one really knows what the exact probability is.

But we do have a design certification system that requires developers to apply various development assurance processes to meet specific safety standards for the design. The primary requirement is covered by §25.1309   Equipment, systems, and installations.

That has a lot of words about identifying potential faults and mitigating the associated hazards. But there are no numbers. As with most rules, the FAA conveniently provides an Advisory Circular to help you show compliance with the rule. In this case, its 25.1309-1A - System Design and Analysis.

The acceptable standard for critical faults (those with a potential catastrophic result) is found at the bottom of para 10.

  (3) Extremely Improbable failure conditions are those having a
  probability on the order of 1 X 10^-9 or less.

So, if the developers do their job to the standard and the standard (and the methods used to evaluate it) are accurate the answer to the question is:

The probability is less than once in every 1 billion hours of operation.

As a point of statistics, that number applies to the cumulative hours of all aircraft of that design.


Why don't hyperbolic navigation transmitters on the surface (e.g. Loran-C) allow altitude measurement?

You are correct, the time difference generates hyperboloids in 3D space and as such can be used to find the 3D position. However, if the transmitters are far apart and/or in the same plane, the geometry of the intersecting hyperboloids is such that the accuracy in the vertical axis is very poor.

When the receiver is in the same horizontal plane as the transmitters, all intersections almost form a vertical line. The slightest inaccuracy in time difference, would cause only a slight error in the horizontal position, but a significant error in the vertical position.

The concept is called Geometric Dilution of Precision (GDOP). A good start for more detail can be found on Wikipedia


What is involved in changing runway/taxiway/approach lighting?

To answer your two questions:

Unless the runway is a very busy one, or the failure is such that it can have an adverse effect on the safety of operations, runways are not closed to replace failed lamps.
Bulbs are not changed in the field, with rare exceptions such as PAPIs. Typically, the maintenance team will have hot spares ready to be installed of every kind of fitting. In the event of a failure, they will replace the whole fitting, which can be done in a few minutes, and replace the bulb at the workshop.

The replacement of a fitting typically involves the isolating of the circuits, untorqueing and disconnection of failed fitting from circuit, connection of new or serviced fitting, torqueing, and powering circuit again.

In the case of PAPIs, the bulbs are replaced on site. The replacement is done by opening the PAPI box, and replacing the halogen bulb.

By the way, bulb changing is becoming obsolete with the wide adoption of LED airfield lighting.


Is there a special way to calculate the (parasitic) drag produced by the propeller?

Not quite. The propeller accelerates air, and the cross section of the accelerated air is slightly smaller than the prop disc area. However, this jet of air will sweep surrounding air with it, so there is no clear boundary. Also, the fuselage or engine nacelle will displace the slip stream / propeller wake, so you need to check what cross section is needed to accommodate both. If you now look at the wetted area in the propeller's wake, you need to calculate two effects:

Increased dynamic pressure and surface speed with fully turbulent boundary layer, causing more friction and pressure drag, and
Propeller swirl, which creates additional lift / side force on the surfaces in the prop wake. Include trim drag to counteract the swirl effects.

Fist you calculate the drag without the propeller, and then with it. The difference is the contribution of the propeller wake. For simplicity, assume a constant speed over the cross section of the propeller wake and do not include the acceleration of surrounding air. For more precision, try to add the deflection of the propeller wake by the wing and consider that the acceleration of the air flowing through the propeller disc is normal to it while the airflow itself comes from a direction described by the angle of attack and the angle of sideslip. If these are not zero relative to the propeller, the propeller wake will have a different direction than the surrounding air flow.

If $\Omega$ is the angular velocity of the propeller, $v_{\infty}$ your flight speed and $\Delta v$ the speed increase due to the propeller of the diameter $d$, your swirl $\omega$ is $$\omega = \frac{2\cdot\Delta v\cdot(v_{\infty} + \frac{\Delta V}{2})}{d^2\cdot\Omega}$$
The speed increase in the propeller propeller wake for a given thrust $T$ is $$\Delta v = \sqrt{v_{\infty}^2 + \frac{4\cdot T}{\pi\cdot d^2\cdot\rho}} - v_{\infty}$$
in air of the density $\rho$. Thrust is engine shaft power times propeller efficiency, divided by flight speed.

This sketch shows the stream tube going through the propeller disc (light grey) and below the pressure profile in the stream tube. Air is sucked into the propeller and pushed out at the back, and the cross section of the stream tube is proportional to the inverse of the flow speed. In the propeller disc, just half of the speed increase $\Delta v$ has occurred (Froude's hypothesis).

EDIT:

This answer by @xxavier lead me to a very interesting paper in which the drag of a Luscombe 8b with and without thrust was compared. A very thoughtful way was used to arrive at zero-thrust numbers, and the result showed that the additional drag from the propeller effects was about 30% of the total zero-lift drag without thrust.


Relationship between wing aspect ratio and speed

It's really the other way around, speed of the aircraft affects aspect ratio.

Hawks fold their wings to dive at high speeds, and have them straight out for lower speeds.
At high speeds the main concern is drag.  The less drag, the faster you can go.  At lower speeds, the main concern is lift.  Here a higher aspect wing is more efficient.

  Why not use a smaller high aspect wing at higher speeds, and just vary the sweep?

This is done, but along with higher speed comes greater aerodynamic forces.  This is one reason why modern fighters feature low aspect wings and deltas.  These are simply much more able to withstand higher G forces.

The variable sweep wing concept was developed in the 1950s and 1960s, but generally carries a weight penalty.  Variable camber is widely seen in airliners today.
Some military aircraft, such as the B-1 bomber, use variable sweep to expand their useful
flight envelope, giving them the ability to "get low and fast".

Cruise missiles, optimized for one speed only with little abrupt maneuvering, can be found with very simple high aspect swept wings, which offer an improvement in drag over a lower aspect wing, thereby increasing fuel efficiency and extending range

There is no direct relationship with speed and aspect ratio, indeed, high subsonic aircraft such as airliners, that strive for maximum efficiency, are seen with increasingly higher aspect ratios in recent years.

Structural strength is the main limitation which continues to challenge engineers today.


How much physical strength is required to control a Cessna 172?

I will take this from a more general perspective.

A Cessna 172 is part of the CS-23 category (in EASA land, see the equivalent Part 23 for FAA land).

In the relevant document, point CS 23.143, we find the maximum forces a pilot might be required to exert on the control columns so that the aircraft can be certified.

As the Cessna 172 is certified, we then know that it respects these requirements, so the maximum forces required to pilot a Cessna 172 (and any other CS-23 aircraft) are:

\begin{array}{l|c|c|c|}
\textrm{Values in Newton applied} & & & \\
\textrm{to the relevant control} & \textrm{Pitch} & \textrm{Roll} & \textrm{Yaw}\\
\hline
\ \ \ \ \textrm{For temporary application –} & & & \\
\textrm{Stick} & 267 \textrm{ N} & 133 \textrm{ N} & \\
\textrm{Wheel (two hands on rim)} & 334 \textrm{ N} & 222 \textrm{ N} & \\
\textrm{Wheel (one hand on rim)} & 222 \textrm{ N} & 111 \textrm{ N} & \\
\textrm{Rudder pedal} & & & 667 \textrm{ N} \\
\hline
\ \ \ \ \textrm{For prolonged application –} & 44.5\textrm{ N} & 22\textrm{ N} & 89\textrm{ N} \\
\end{array}


Does the F-4 Phantom use (have) differential horizontal tail deflection?

No, the two sides of the Stabilator are connected to one another and move in unison.
The following is from the USAF F-4E flight manual, page 1-21.


As with most specific medical questions, the only real answer here is "talk to an experienced AME, preferably one who's handled similar cases before". Some standard advice is to schedule a consultation only first, to review your case. Once you have everything organized and documented properly and your AME is confident about your application, then you can do the actual medical exam.

Having said all that, as far as I know you don't request an SI directly. If the AME determines that he can't issue a medical certificate because of a condition you have, he should work with you and the FAA to put together whatever combination of test results, documentation and general information that the FAA wants in order to issue an SI. But all of that should happen before you do the actual medical exam, to avoid delays.

If you're an AOPA member they can help you with advice and information and they have more details about the SI process. (Their medical forum is very useful too).


Is Auto Pilot capable of performing TCAS resolution advisory?

Short answer is no.

First of all it is resolution advisory as you said. Its purpose, is to make the Pilots aware of an imminent danger/conflict. As with 'Terrain, Terrain', 'Pull up!, Pull up!', it is up to the pilots whether or not they will follow the instruction (normally they always do, but there are exceptions).

However when the pilots hear 'Climb, Climb' or 'Descent, Descent', or another TCAS alert, they should immediately initiate the required action. After all, these days there are top-notch ATC and confliction prevention systems, as well as high-tec TCAS systems on most of the commercial aircraft.


Where can I get a copy of my notice of disapproval from a failed checkride?

As far as I'm aware you can't pull the "completed" application from IACRA (with the examiner's notice of disapproval & failed areas on it). Much like with your knowledge test report you need to hang on to that original bit of paper.

I don't believe you NEED to bring the Notice Of Disapproval with you to a retest though.
61.43 says, in part:

  f) If a practical test is discontinued, the applicant is entitled credit for those areas of operation that were passed, but only if the applicant:
  (1) Passes the remainder of the practical test within the 60-day period after the date the practical test was discontinued;
  (2) Presents to the examiner for the retest the original notice of disapproval form or the letter of discontinuance form, as appropriate;
  (3) Satisfactorily accomplishes any additional training needed and obtains the appropriate instructor endorsements, if additional training is required; and
  (4) Presents to the examiner for the retest a properly completed and signed application.

So you only need it if you want to skip over the parts of the test you passed. If you don't have it, or your retest is more than 60 days after your original failed checkride, the examiner will have to give you a full exam, with no credit for the stuff you already completed.

Given that you failed the oral there's probably not much "credit for those areas of operation that were passed" you can claim, so it probably doesn't matter much that you lost the original notice of disapproval. You're almost certainly getting a "full checkride" anyway.


How does Mach number of Jet engine vary with respect to Compression Ratio?

The performance and exhaust Mach numbers depend on very many variables, to name a few:

Inlet shape.
Compression ratio.
Combustion inlet velocity of the airflow.
Throttle setting
Turbine entry temperature.
Exhaust shape.

A multi-dimensional matrix which to fully describe takes a book like this one. My edition has 491 pages, and the scope of the answer would be very broad indeed.

The exhaust Mach number however, is mainly determined by the shape of the exhaust. If the exhaust is convergent only, maximum Mach number of the exhaust stream is M = 1. In order to reach supersonic exhaust velocities, the shape must be converging then diverging. If converging only then depending on the operating state the exhaust can be choked, at a higher pressure than the environment. The higher pressure will still contribute to thrust.

Figure above shows an example for a supersonic exhaust for a low bypass engine.


How does the F-35B not flip over during transition?

To try and change lift by changing fan blade speed would be too slow to modify the lift for "tiny" and "delicate" changes in how the plane hovers.
Like a helicopter, the F-35 is able to maneuver in very small movements and change very fast (in fact likely better than a helicopter).
So the pilot can "nod" to you, and move around the front nose with tiny, delicate moves. So tiny movements by the F-35 and the flight stick are rapidly accepted by the flight computers.
Now a helicopter uses variable pitch blades to make rapid changes, which allows helicopters to achieve tiny, delicate, and fast "little" moves. So tiny fast changes in lift are required for these delicate moves.
Change of engine throttle to change fan lift would be far too slow (for the F-35, or for a helicopter).
To save weight, and complexity, the F-35 lift fans are counter rotating, and they are light weight carbon fiber.
So, to rapid change lift and have rapid tiny changes in lift, they simply change the area/size of the exit exhaust area of the lift fan.
Think of those "variable" nozzles much like a window shutter to let more or less light into a room.
The shutter looks like this:

So, you can open a bit more, or close a bit more.
However, when you close the shutter more, then where does the air go? It has to go somewhere! (remember, up to 20,000 lbs is created by that fan).
Well, there is a second set of doors that open right behind the one large fan lid.
That second set of doors can be seen here:

Those 2nd set of doors behind the big lift fan lid are to allow venting of the lift fan.
So you need a fast and delicate means to change lift fan output. So amazing and so tiny are these changes, that the pilot can "nod" the nose down a bit. Very tiny changes are achieved.
So to change the fan downforce you thus close or open the lift fan exit (exhaust) area doors. This can be closed or opened rather fast, and also by tiny amounts. This gives delicate control.
However, when you squeeze close this exit area, then the lift fan air has to go some place else, so it is vented out those doors right behind the big lift fan lid door.
So, if you close down the exit hole on the bottom of the F-35 fan, then that air takes another path – right out those 2nd set of doors.
9 out of 10 diagrams on the internet call that second set of doors an auxiliary inlet. However, that is NOT 100% correct. It should be called an auxiliary exhaust.
Now, to be fair, because the cold inlet turbine compressor is also exposed to that vent area, then no doubt that area likely remains "negative" pressure most of the time.
However, this is quite a brilliant design, since that lift fan exit area in general has some amount of "close" and thus "some" amounts of fan exit air is going to be vented (by-passed) right into that "box" behind the lift fan.
And that box just so happens to be right where the hungry for cold air turbine inlets of the massive F135 engine is. (What a nice design!)
So likely that area remains negative due to the compressor inlets. However, that area will go positive with most of the lift fan exhaust closed.
In this case, then those two doors are in fact a lift fan exhaust vent – not an intake vent!
I should also point out that due to vast amounts of cold air hitting the deck with this lift fan system, Lockheed engineers state that the overall deck temperatures are less than a Harrier when landing on the deck of a ship.
So while both Harrier and F-35 tend to heat up the decks on a vertical ship landing, the F-35 actually is less of a heating problem then is the Harrier for such vertical landings.
References to my statements:
From Lockheed:
https://www.lockheedmartin.com/content/dam/lockheed-martin/eo/documents/webt/F-35_Air_Vehicle_Technology_Overview.pdf
page 25:
quote:

With this system, nozzle thrust may be directed in an arc of 41.75-104
degrees (fore/aft aircraft coordinate system), at a rate of 40 degrees
per second.

Ok, so far, above ONLY talks about directing the down thrust.
But, we have this:

Independent control of the three VAVBN actuators provides the
capability to vary the nozzle throat area independent of the vector
angle

To save reading, we have:
VIGV = top intake part (variable )
VAVBN = bottom exit part (also variable).
So above states the VAVBN actuators (the EXIT PART OF THE FAN) can vary the nozzle throat area.
My claims:
Lift fan blades are NOT variable pitch.
There no evidence, no diagram, or ANY information of ANY kind in existence that CHANGES this claim of mine. I stand by this claim.
Lift exit fan can open/close or "vary" the fan output.
Again, the above document 100% supports and verifies my claim.
NOT verified:
My claim that when closing down the 20,000 lbs of fan vent flow, that flow HAS to go some other place, and I am claiming that flow goes to the air box behind. This is a SPECULATION on my part. I do believe this to be what occurs but I do NOT have a link or article that outright states this (some diagrams DO suggest this, but that would not be proof). So this claim of mine that fan air vents to the air box behind is NOT verified by me, and until I can provide solid evidence of this, then that claim should be taken with a grain of salt.
Edit 2
As for the speculation of air venting out of the fan box, this here is a photo.

It is "difficult" to tell if that is a vent door, but does seem to look like one. As noted - I am open to opinions on this - this right now thus is still a speculation on my part.


Joe Ayoob's world record throw of the John Collins designed paper airplane is worth watching over and over again.

Every time I throw the glider with my hand ...

This caused me to split my free flight hobby into throwing gliders and launching from a hill.
A thrown glider experiences a wide range of speeds in flight, therefor it cannot be set with a staticly stable "tail downforce/weight forward" arrangement.  This type of glider will loop if thrown hard, but will be fine if thrown off a hill.  Try to gently release it at its trim speed.  Moving the weight/changing tail decalage will produce the best glide.
But for throwing on flat ground for distance the glider must be slightly staticly unstable to keep flying as it slows down.  You want it to gradually pitch up (increasing AOA) as it loses speed to generate adequate lift for level flight.
The plane flies straight out until it stalls.  Notice on Joe's throw the glider went around 150 feet, from 40 mph to maybe 5 mph, stalled, then recovered from the dive, flying on to the world record.

Glider has asymmetric tail, which produce downforce, then glider is "tail heavy"

An asymmetric tail will produce pitching force aerodynamicly, not by weight.  This is why "classic" aircraft design has an "upright" vertical stabilizer (many glider designers also benefit by putting the horizontal stabilizer on top in "T" fashion, increasing pitch torque without adding drag).  The tail must produce a down pitching force to "set" wing AOA if CG is forward.
For "throwing" gliders, you need tail upforce, weight aft (while maintaining directional stability), and some luck to go 226 feet. If one can control the elevator (by R/C) in flight, then discus launched gliders (DLGs) are worth a look!


What is "required navigation performance" or "RNP"?

RNP (Required Navigation Performance) is a standard which avionics manufacturers may choose to design/certify their products for.  It guarantees a particular level of navigation performance that routes and procedures can be designed around, and not have to worry about how the navigation is being conducted, but only that it will meet requirements.

A particular product may be certified to various levels such as RNP10, RNP5, RNP2, RNP1, RNP0.3, etc. (accurate to within 10NM, 5NM, 2NM, 1NM, 0.3NM, etc.).

To see if a particular unit is certified for RNP, and to what level, you would need to look in the aircraft flight manual / supplement and see what it says (note that this is installation specific too, as it involves antennas and "full system" performance, not just the capability of one piece of the puzzle).

The FAA has an advisory circular caled AC 90-101A - Approval Guidance for Required Navigation Performance (RNP) Procedures with Authorization Required (AR) Including Change 1 if you want more technical information on it.


General usage
According to Etymology Online The term drone, meaning "pilotless aircraft" dates from 1946.
It evidently encompasses all types of aircraft where no onboard human pilot is needed, either because the human pilot operates the aircraft remotely (still true for most types of military "drone" aircraft I believe) or because the aircraft systems are capable of full autonomy during some of all of a flight.
The earliest uses were probably "target drones". Which is what Wikipedia suggests.
The term does seem to have supplanted "RC aircraft" for modern small RC aircraft, especially those which carry a camera and/or from which their operators derive some value other than simply from mastering the skill of flying the vehicle.
English language is defined by usage, not by edict. So this isn't subject to rulings or appeal.
Lawmakers or other bodies might define the term more narrowly but this doesn't affect other uses of the same word.
FAA definition
The FAA talks mainly about "model aircraft" and "unmanned model aircraft" (ref.) and about Unmanned Aircraft(UA)  or Unmanned Aerial Systems (UAS). (ref.)
They usually don't use the term drone or define it, but from their FAQ it seems they consider the terms drone and UAS to be equivalent

Myth #7:The FAA is lagging behind other countries in approving commercial drones.
Fact– This comparison is flawed.  The United States has the busiest, most complex airspace in the world, including many general aviation aircraft that we must consider when planning UAS integration, because those same airplanes and small UAS may occupy the same airspace.