What are the barriers to feasibility of stratospheric cruising for commercial air travel? (i.e. Concorde?)

I would argue that the Concorde was from the beginning economically unfeasible and instead served as a prestige technology for the British and French governments. Even the name Concorde, indicates that the two governments working together to produce the aircraft seemed the most important aspect of it.

Both British and France at the time had completely nationalized airlines and almost all their major aviation companies as well. Americans were going to the moon so Britain and France were looking around for a prestige technology of their own. Bigger and faster airplanes had been the rage for twenty years so the Concorde seemed like a cool thing to do. The Soviets came to the same conclusion.

In the US, civilian airline development was still wholly private so when when Boeing , Douglas et crunched the numbers they saw little value in supersonic transport with  it's non-linear cost. US supersonic transport never made it off the ground, but in Europe, the politically driven Concorde did because the people making the decisions weren't paying the bills.

As noted by others, the Concorde was essentially a military aircraft, produced by political compromise with the primary goal of expressing the technical powers of the governments involved. It was more an art project like building the Pyramids than it was a piece of mobile transportation infrastructure.

Edit: (May 14, 2014)

Some sources on the economics of the Concorde:

The Atlantic August 1977:

  Already Britain, and France spent £1.46 billion \$2.3 billion to reach this  (and a London political economist has recently argued that
  the true cost is roughly  three times this amount)...

  ...In May 1976, Professor David Henderson, newly appointed professor of political  economy at University College, London, argued
  that the government's figure of  £1.46 billion shared between Britain
  and France was a drastic underestimate.  It had been reached by adding
  the yearly expenditure on the project at the current prices.  If these
  were adjusted to 1975 prices, and interest charges of 10 percent
  added, then  the cost of Concorde was not £1.46 bilion but £4.26
  billion (\$6.82 billion at the  present exchange rate of \$1.60).

That would be $22 billion US (2014 dollars.) Just to get the thing into the air.

They built 26 of the aircraft, 20 of which that actually flew paid flights. So, around 1.1 billion per plane, roughly the cost of a B2 stealth bomber. I can't find any hard numbers on operating cost but with 1.1 billion per plane sunk capitial cost, it's clear it would never operate at a total profit.

I believe the plane only flew for 20+ years because the British government essentially gave it away, eating the billions of in development and deployment cost and leaving the plane to just have to cover operating cost. I'm not clear that it even really did that.

Considering how much money was thrown at the problem, not particularly elegant or interesting.

Edit 02:

In rereading the parent, I realized I didn't make my answer explicit to the original question. He wanted to know what it would take to bring a Concorde like plane back.

My answer was really just saying, "the Concorde itself had no economic foundation so firstly, you'd have to find an economic niche for SST."
There was never an economic demand for the Concorde's speed of travel and there doesn't seem to be one now, either.
Technologically, you'd probably need something hyper radical like a nuclear powered air spike so the plane wouldn't burn tons of fuel and could fly over land masses without sonic booms or destroying smaller aircraft. (Seriously, it would have to be that advanced.)
In our current luddite era, it would be saner to think about inventing anti-gravity drives than think that the political regulators would let that type of radical technology fly, even if it existed.


Why are some points shown on a STAR but not attached to the route?

Coming from Southern California, you'll often be filed to one of those points, and then on to SERFR for that arrival.  Putting those two points on the page gives perspective of what direction one is coming in from.

It's all RNAV stuff, so is having them on the chart strictly necessary in order to navigate? No.  But it gives a little bit of a picture of what you're expecting to see on the Navigation Display.

Also, as mentioned in the comment, if ATC needs to reroute somebody off of what they filed & over one of those points & then to SERFR, having the point on the page may reduce copying errors when the controller spells out "cleared direct MAKRS, Mike Alpha Kilo Romeo Sierra" -- it at least gives the pilot something to reference when that clearance is being read to him.  Things that reduce the frequency congestion ("Was that Mike Kilo Alpha Romeo Sierra? I don't have that in the database..." "No, it's Mike Alpha Kilo Romeo Sierra" "Oh, okay, Mike Alpha Kilo Romeo Sierra, we'll use that.") are beneficial.


Is it allowed to operate an aircraft when the Emergency Locator Transmitter has been removed?

Assuming that you are in the US, you need to comply with

§91.207   Emergency locator transmitters.

(2) … there must be attached to the airplane an approved personal type or an approved automatic type emergency locator transmitter that is in operable condition,

and

(ii) No person may operate the aircraft more than 90 days after the ELT is initially removed from the aircraft; and

So in the next 90 days you need to install an ELT. It must meet the TSO standards for ELTs.

The cheapest way to comply would be to purchase a used 121.5 MHz unit so you are legal and use a personal unit in case of an accident.

The newer 406MHz units require a GPS source and a panel switch. Installation costs can be more than the unit. However, since the previous owner removed the ELT, I would assume that the wiring is still intact so you can probably save money on the install.

Which type of attached transmitter you choose depends on your budget and the terrain over which you fly. On February 1, 2009, the international COSPAS-SARSAT satellite system discontinued satellite-based monitoring of the 121.5/243-MHz frequencies, in part because of a high number of false signals attributed with these frequencies. AOPA

They also frequently fail to activate and since they are only monitored by pilots who are following the AIM and monitoring 121.5 even if they do go off, they often are not heard. Not to mention the problem of triangulating the signal to find the source. If you fly over populated areas and are in contact with ATC via flight following or IFR flight plans, they are still adequate and most pilots I know have not upgraded to the 406 MHz units.

The newer 406 MHz are satellite monitored and because they transmit GPS location data it is easier to find a downed aircraft. They have an activation switch in the panel so that they can be activated before the pilot hits terrain which increases the odds of finding you. If I frequently flew over mountains, remote areas, or at night I would certainly install one of these.

Personal beacons have lots of advantages over installed ELTs. If you survive the landing, chances are that they will as well. They are also incredibly cheap and many of them have web-tracking or texting that can be used by those interested in tracking your progress. You can also take them with you if you leave the airplane.


landing with east to west wind on runway 11/29

if im correct to assume that with an east to west wind one should land from west to east meaning one would land on runway 11??

That is correct. The convention is that the runway number is the magnetic heading of the runway to the nearest 10 degrees, but with the low-order 0 removed. Thus, to the nearest 10 degrees, the magnetic heading of runway 11 is 110 degrees. That's the approximate heading the aircraft is going to have when they land on that runway. That would be a landing (or takeoff) to the east rather than the west. In other words, it's the heading of an aircraft using the runway as opposed to where the runway end is in a left-right sense when looking north.

Kolwezi Airport has only a 3° west magnetic variation. Thus, in your area magnetic heading and true heading are nearly the same.


Are there items bigger than an aircraft section transported by air today?

According to Wikipedia, the An-225 is the world's largest cargo aircraft and it's transported both the heaviest and longest items of cargo ever carried by air:

  On 11 August 2009, the heaviest single cargo item ever sent via air
  freight was loaded onto the Antonov 225. At 16.23 metres (53.2 ft)
  long and 4.27 metres (14.0 ft) wide, its consignment, a generator for
  a gas power plant in Armenia along with its loading frame, weighed in
  at a record 189 tonnes (417,000 lb)

  [...]

  On 11 June 2010, the An-225 carried the world's longest piece of air
  cargo, when it flew two new 42-meter test wind turbine blades from
  Tianjin, China

It's also carried the Buran spacecraft (the 'Soviet space shuttle'), which was actually what the aircraft was originally built for.

The An-225 is still in operation and the operator gives some examples of large cargo that can be carried:

  The aircraft has the spacious cargo compartment with length of 43.32
  m, width of 6.4 m and height of 4.4 m, that allows carrying a variety
  of cargoes inside. For instance,

  sixteen standard aeronautical containers of UAC−10 type;
  50 cars;
  single piece of cargoes up to 200 t (turbines, generators, dump trucks − Belaz, Kamatsu, Euclid, etc.).


How can I reduce the responsivness of my homebrew brake system?

the pressure to disk brake is too high?

That is sure, that is the only parameter that can influence how much braking authority you are using.

Given the schematic you posted, my otherwise uninformed opinion (as I don't have pressure measurements, or other data), is that you should investigate your brake valve.

It is probably not providing a sufficient pressure drop even when slightly open. This could be due to the valve model.

Yes, your suggestion to have a restrictor valve (or an O ring inside the pipes) should be a suitable approach, but it depends on the solution you are looking for.
The pressure will drop when the brake fluid is moving, but the equilibrium state will not change, if you keep your pedal slightly depressed your aircraft will still come to a complete stop, simply it will do so slightly later.

If your intention is to have the braking authority controlled by the pedal, what you really want is to change the pressure reaching the brake disk with the pedal.
No static solution is viable in that case: you will need a valve that lets you control the pressure received by the brake plate with the pedal deflection, i.e. you probably have to change your brake valve, or you have to install a system that dynamically adjusts the pressure downstream of the brake valve.


Do small business jets have HEPA filters?

Embraer's own website confirms that their business jets can recirculate or draw fresh air, but HEPA filters don't seem to be an option until you get into the Praetor size and above -

In addition, the now standard HEPA filter for the Praetor jets can
capture 99.97% of bacteria, viruses, and fungi — further providing
fresher, cleaner air inside the cabin. So when you fly on an Embraer
business jet, you can breathe easy.


I am not sure if I got your question completely.
As I am not entirely sure what you mean by leaving out Bernoulli.

Let's start with the lift issue:
Lift is created when the pressure (-forces) on the upper wing surface (suction side) and the pressure (-forces) on the lower surface do not cancel each other out. Usually this means that there is a net-force pointing upward (in level flight). Lift is therefore not directly connected to the ambient pressure. Does this answer the lift part of your question?
Image taken from wikipedia

Now let's focus on the bulged out surfaces:
I would guess there are at least two effects:

As you can see from the picture above the pressure is lower (than ambience) on
pressure and suction side (but since the pressure on the suction
side is lower than on on the pressure side, there is a net-force
(lift)).
Depending on the aircraft, it could be that the high-pressure in the stagnation point of the wing or aircraft pressurises the wing and cabin which would increase the effect from above. A bit like the canopy of a paraglider.


What is the purpose of the extremely high cabin altitudes in military aircraft?

Even the unmanned RQ-4 Global Hawk has a pressurized compartment. The low air density at altitude would not be sufficient to cool the electronics, so a pressurized electronics compartment had to be added.

I am not sure, but I expect the same reason required pressurization in the U-2 and the SR-71. The electronics were, besides the pilots, also an occupant of their pressurized cockpits.

At the pressure of 25.000 ft a human will not stay conscious, but will be able to survive. When the pressure drops below that of 30.000 ft, the breathing reflex will stop. If the pilot initiates a descent when his pressure suit starts to leak, he has a good chance of waking up at lower altitude before the aircraft hits the ground if the cabin can prevent the air pressure from falling to that of ambient air.


What do the different dates in a TCDS mean?

The Type Certificate document is just a kind of diploma so to speak, or, as it says in its name, a Certificate.  The real meat is in the TCDS, which describes the technical details, limitations etc., of the aircraft that are the basis of its Type Certificate and which set out the parameters that must be met to be in compliance.
When these details change or need to be corrected, they don't reissue the Type Certificate, they just revise and reissue the data sheet that is linked to the TC by its number, T00015W1.
In your example, Feb 5 is the date of issue of the revised Data Sheet at Rev 4, so there would be three other revisions, plus the original issue (which should have the same date as the TC itself), prior (Page 6 is still at Rev 3, and Rev 4 is Page 1-5, and revision bars show what was changed in Rev 4 on those pages).  That's why it's in the document identification block at the top right.  It's the issue date of that Data Sheet revision.
The TC approval date is just a reference to the original TC issue in Sept 2019, which doesn't normally change, being the fancy sheet of paper you frame and stick on the wall when you're the engineering VP who led the program.


What are differences between vortex, swirl, eddies and wake?

Wake is the general term for air disturbed by a passing aircraft, as might be guessed from the word's nautical origins.
Vortex (in aviation, usually a wingtip vortex) is a part of the wake that originates at the tip of a surface that has a pressure differential.  It's the preferred term in scholarly writing.
Eddy by now seems to be restricted to the name of a general model for turbulence, https://en.wikipedia.org/wiki/Large_eddy_simulation.
Swirl has a technical meaning that I can't quite fathom, but it seems to apply more to combustion in turbines than to airflow outside the aircraft.


How to read the propeller range chart for DHC-6 Twin Otter?

Most of high performance propeller aircraft use constant speed propellers, with variable pitch. The speed remains constant over (most of) the flight regime, while the propeller pitch is varied according to the requirement (by the Constant speed unit or CSU).
In case the propeller is stopped in flight (for example, due to engine failure), the propeller pitch is increased so that the propeller is basically parallel to the airflow, so as to minimise the drag. This marks the extreme value of feather angle 87$^{\circ}$ shown in the image.

Image from 12charlie.com
The propeller range used for forward  flight is usually called the $\alpha$ range, where the blade pitch has moderate values with constant speed, which is set by the propeller lever. Obviously, this speed is not constant over the entire range between engine start and shutdown. Usually around the idle, the rpm drops (this varies according to the design) and this gives the constant speed range limit.
Now, during landing, the aircraft speed is reduced usually using brakes etc. However, it is possible to do so using propeller itself- basically by turning it backwards. The $\beta$ range refers to the region where the propeller is producing zero or negative thrust.
From this article:

On PT6 powered aircrafts, the Bêta range is controlled by the PCL ( Power Control Lever ) which also directly control blade angle. Yeah, the governor is overriden and by moving the PCL past the idle gate ( you usually have to lift the PCL against that gate ) you directly schedule blade angle in correlation with Ng ( Gaz generator ) speed.

In the beta range, the aircraft can be slowed down by making the propeller pitch flat (0$^{\circ} 30'$ here) and creating drag. The reverse thrust starts after this, with the full reverse trust coming in at the limit -15$^{\circ}$.
I think there is some typo in the figure. From this answer(cleaned up):

Beta range in the Twin Otter is from 11° to -15°(reverse) propeller blade angle.
The Beta range lights will be lit when Your in the range from 9°to -15° propeller blade angle.


What is this on the starboard engine of the Dash 8?

It is the engine drain mast. From the Dash 8 Series 400 airport planning document - Chapter 2, Page 40:

Dash 8 engine drain; image from Dash 8 Series 400 airport planning document

Basically, the drain mast houses the drains that allow for the removal of the fluids (oil and fuel) that come out of the engine, due to seepage, leaks etc. For example, this incident report is a case where it was,

  ... observed ... fuel dripping from RH engine drain mast.


Does a RC aircraft require suspension in landing gears?

For one that size, you'll certainly need some spring in the landing gear, but it's likely that shock absorbers are still unneeded.  Most models use spring wire landing gear legs, at least up to around 5 kg weight.  As big as your model will be, you may need hinged gear legs with spring return, or something similar.

I'd suggest looking at the landing gear for smaller crewed aircraft (like a Cessna 152 or Piper Tomahawk).  The smaller Cessnas for certain have only spring legs for the main gear, though they use a shock strut for the nose.  Scale down from their practice and you should be good (though scaling down frequently means simplifying, as well as making smaller).


What do manufacturers do to reduce cabin noise?

it is being claimed by the Airbus that their new planes offer more sound proofing than those of Boeing

I guess you mean this sort of claim:

  No matter where they sit, all passengers benefit from the quiet A380 cabin with on average half the sound energy of other aircraft. Passengers' feedback confirms the extraordinary contribution to their general well-being due to the absence of background noise on the A380.

  In market research surveys the A320 is regularly rated higher than its rivals for the low level of noise in its cabin. Effective insulation in the cabin is one reason why passengers say they find the A320 a quiet aircraft in which to fly. The A320 cabin is the subject of continuous improvements and in its latest version, the noise has been reduced by a further 1dB.

  how do Airplane manufacturers tackle the problem of soundproofing the cabin

There are a variety of methods

soundproofing materials in the wall of the fuselage between inner and outer skins.
choice of interior materials and furnishings etc.
adjusting cabin interior contours to allow lower airflow velocity.
fuselage aerodynamics.
engine nacelle accoustic liners.
scalloped edges on engine exhaust nozzle.
larger slower engine fans.
sharklets.
etc

BBC report

  One of the main sources of noise is wind. So during the design phase of modern aircraft, computational tools model the aerodynamics of the aeroplane to highlight areas of high airflow that are likely to increase cabin noise. This allows engineers to reshape their designs, says Alan Pardoe, director of product marketing at Airbus. Such techniques, he says, helped the double-decker Airbus A380 plane to be recognised by the UK Noise Abatement Society as the quietest jet airliner on the market.

Airbus say

  When it comes to making the A380 one of the quietest aircraft in the sky, it's the small details that count... in fact, more than 3 million of them!

  This is the number of tiny perforations in acoustic linings on the large nacelles that surround and protect the A380’s jet engines.  The acoustic material helps dampen noise created by the airliner’s four turbofan powerplants, ensuring the A380 is a friendly neighbour wherever it operates in the world.
  The A380’s nacelles are supplied by Aircelle, which has worked closely with Airbus in minimising the jetliner’s noise output during takeoff and landing.  Acoustic panels are applied throughout the engine – from the air inlet to the exhaust nozzle.

  Each panel, which is produced from composite material or titanium, is designed to attenuate noise at different frequencies, further improving the soundproofing effect.  Noise-reducing innovations include Aircelle’s 2-degree-of-freedom acoustic panels, which use a stack of two honeycomb composite sandwich layers separated by a porous wall.

  These panels dampen high-frequency noise from the engine turbines.  With much of this noise source successfully dampened by the acoustic treatment, engineers and designers are now focusing their attention on treating other sources of aircraft noise, promising even quieter jetliners for the future.

and also this

  The Airbus-developed Zero-Splice engine nacelle liner was designed to reduce the noise generated by the jet engines’ large fan, which represents almost half the noise during both approach and take-off. Following extensive studies carried out by Airbus on how to reduce fan noise, it was found that splices used to join the engine nacelle inlet’s acoustic panels generated forward fan noise – which was counter-efficient to the liner’s acoustic treatment. Airbus therefore developed the Zero-Splice nacelle liner as a single 360 deg. piece of composite, which is comparable in size to the diameter of an A320 fuselage.

It is, I think, obvious that measures that reduce engine noise on the ground also reduce it in the cabin.

They also write about how wing sharklets reduce noise.

I'd guess there are many other measures and design choices that are introduced to reduce noise.

  What proportion of the total aircraft development cost ...

I'd be surprised if Airbus or Boeing make public any breakdown of their development costs.

You can find general breakdowns like the following but I havent found any that break out soundproofing development costs.


Polar curves for older airliners can be found in lecture notes or technical publications. The drag polars of the most recent ones, where no independent measurement is yet possible, are a closely guarded secret. If you see something, it will be restricted such that an important part of the puzzle is missing. For the polars to be meaningful, you need aircraft mass and flight conditions, air temperature and density and sometimes also engine thrust information to make any meaningful comparisons. Also be aware that the Airbus method to determine the reference area is different from Boeing's, but at least those methods are published. Full disclosure is only available to potential customers on the basis of an Non-Disclosure Agreement (NDA).


What is the function of the leading edge strip?

A wing's leading edge is a place where you really want to have a particular shape and a nice, smooth surface.  Stretched coverings (I've done this a fair amount with monokote and other heat-shrink coatings on model airplanes) suffer in this regard since, between ribs, the covering will bend inward and alter the shape of the leading edge (and, locally, the chord of the wing).  Also, since the covering is all one piece, the shape of the leading edge will also influence the shape of the rest airfoil as you go aft along the chord line.  Maintaining the shape that you actually want is really important (unless you want to make tubercule wings: https://secretofflight.wordpress.com/leading-edge-tubercles-2/) as that is the basis of your aircraft's performance and its ability to fly.  Having a solid leading edge strip does just this, ensuring that the leading edge of the wing has the desired shape and forms a smooth surface for the covering.

For a physical description of this, what we did (on model aircraft) to facilitate this was to take a very thin piece of balsa wood, maybe 1/32" thick, and gently bend it around the leading edge of our ribs.  As such, this sheet, which ran the length of the wing, would conform to the shape of the leading edge.  A picture of this from a wing I built is below (the leading edge is on the left hand side -- and just ignore the fact that the wing is twisted...).  We added some sheeting to the trailing edge of the wing for similar reasons (and to make it easier to cover).

The year prior to this, someone took a dowel and ran it the length of the wing at the leading edge instead of covering it with a sheet of balsa -- a little less effective at shaping the airfoil behind the leading edge, but much easier to implement.  However, a similar idea appears to have been implemented in the DH-60 Gipsy Moth.

In addition to aerodynamic shaping, the further you can extend a contiguous structure in the chordwise direction, the stronger your wing will be in torsion (generally speaking) -- this is a significant function of a "stressed skin" coating like you are talking about.  However, the addition of a structural element, such as a leading edge cap, that goes the length of the wing adds a non-negligible amount of torsional stiffness to the wing.

This part is more conjecture, but the leading edge of the wing will also receive a lot of wear, be it from FOD, bugs, or cleaning off bugs.  When I flew sailplanes, the leading edge of our wings would constantly be filled with bug carcasses and we'd be cleaning them off frequently.  To this end, I'd think that having a solid leading edge would be an easy way to preventing damage during the cleaning process.  However, sailplane pilots care about that more than powered aircraft, I think, so, unless you're looking at an old Schweizer 2-22 wing, this probably isn't too much of a concern.


What is the way to calculate the required twist of a flying wing?

Twist is closely coupled to the wing's sweep angle, airfoil camber, taper ratio and the desired level of static longitudinal stability. Other factors are the desired spanwise lift distribution and maneuverability. There is no simple, general formula: In the end twist, or, more precisely, local reflex camber, is the consequence of your selection of the parameters mentioned above.

Background

Static longitudinal stability means that the aircraft will return to the trimmed angle of attack after a disturbance. This is made possible by producing proportionally more lift in the forward part of the wing than in the rear part. Reflex airfoils do it all by themselves and unswept flying wings do not need washout, but a proper reflex airfoil.

The Horten flying wings had highly tapered wings and used a bell-shaped lift distribution over span which produced a small downforce at the tips. This helped a lot to reduce adverse yaw and allowed them to do away with a vertical tail. Also this made stall chararcteristics benign. This lift distribution was reached by extensive washout (as much as 8°).

If you add stability by computer control, washout will not be needed and you can use an elliptical planform for best performance. This will, however, have unfavorable stall characteristics and needs wing fences when the wing is swept. Moderate sweep adds stability and damping, but above a critical combination of aspect ratio and sweep angle it is hard to achieve satisfactory stall characteristics.

Critical angle of sweep for swept wings, from Chapter 16 of S. Hoerner's Fluid Dynamic Lift. Too much aspect ratio and sweep will result in a strong pitch-up when the wing stalls.

By adding some chord at the outer wing you can twist the local incidence by the amount of chord added. This will lower the local lift coefficient and produce reserves at stall which will improve stall characteristics a lot. Karl Nickel has published a method for calculating the optimum planform for a given static stability with nearly elliptic lift distribution over a wide range of speeds. The key is his insight that by trimming the wing for a particular angle of attack the pilot will adjust local washout by moving the elevons trailing edge up. Ideally, the wing uses several elevons with increasing trim deflection towards the wingtip. (By "trimming" I do not only mean the reduction of stick forces, but also the adjustment of local lift to cancel any pitching moments.)

Note that now the planform is tightly coupled to the static margin and, consequently, to the location of the center of gravity (cg). Flying with a more forward location of cg than ideal means more negative elevon deflection angles and lower local lift at the tips than ideal, and vice versa.

The SB-13 flying wing glider uses this technique and has a taper ratio (ratio of tip to root chord) of 0.8. It uses two elevons over the outer 50% of span, the inner of which travels 1/3 of the trim deflection of the outer elevon. Twist is zero for the inner half of the wing, changes from 0° to -1.5° over the 0.15 m section where the root airfoil (HQ 34 N) changes over to the tip airfoil (HQ 36 K) to adjust for their difference in zero-lift angle and increases again linearly towards the tip to +0.5° (I hope I got that detail right, typing all this from memory). The negative washout was chosen to allow the elevons to have 4° twist themselves, so in sum (fixed wing and elevons) the wing has increasing twist towards the tips. In flight, the elevons will always have a slightly negative deflection, so the effective washout is even stronger.

SB-13 in flight (picture source)

To answer your questions directly:

  Is (a) twist needed?

Not necessarily. An unswept flying wing does not benefit much from twist. It will only help to add some stall margin at the tips. A positively swept flying wing can also get away without twist if the airfoil is changed over span from positive camber at the root to negative camber at the tip. If the same airfoil is used over the whole span, twist/reflex camber is necessary and cannot be avoided as soon as the cg is ahead of the neutral point: It will result from trimming the wing for the desired angle of attack.

  How do I to calculate it?

Select your desired static margin.
Select your desired lift distribution over span. An elliptic distribution will result in the lowest induced drag, and a bell-shaped distribution will give better maneuverability.
Select the planform that results in the desired lift distribution when trim changes over speed are considered. Use several elevons over span to be able to adjust the local incidence independently.
Twist is then a necessary consequence of trimming the aircraft.


How do pilots in the US identify the circuit (pattern) height?

The Airport/Facility Directory (AFD) has that info. It lists the Traffic Pattern Altitude (TPA) in both MSL and AGL, as well as circuit direction.

QFE is not used in the US. So yes, you have to make the correction for field elevation. For example, an airport at 1200 MSL would have a pattern altitude of 2200 ft. (1000 AGL for props. 1500 AGL for Jets) and would be flown using that altitude on the altimeter.


Why do emergency exits over the wings have "step up and through motion" rather than having floor level exits?

(Image source)

The reason is the fillets (wing root fairings). They're curved as shown above.

You could have a plane without those fillets, but then there are two downsides:

Considerable increase in fuel consumption, and thus reduced range
Potential extra strengthening required for the fuselage/wing connections, as a direct floor-to-wing-top exit might change how the load transfers are distributed, resulting in increased aircraft weight.


How do passengers board the planes on this airport?

They are specially designed apron jet bridges. It looks like the normal gates but required to transfer passenger by bus.

A model shows how it runs (credit) :


Is the maximum lift-drag ratio found at minimum drag?

Well, for all L/D curves and D curves, the assumption is that the weight of the aircraft is constant and that there is no acceleration. Therefore the lift equals the weight (neglecting the small vertical component of thrust). So lift is a constant in these curves.

The rest is simple mathematics; the maximum of $\frac{1}{f(x)}$ occurs at the minimum of $f(x)$ (when $f(x) > 0$), so the maximum of $\frac{L}{D}$ coincides with the minimum of $D$.


Can a human be blown away by jet engines of an A380?

Absolutely. The jet engines used in airliners are quite powerful and can easily blow away human beings, vehicles and small aircraft. Other (large) airliners, not so much.
It depends on the aircraft's size, weight and distance from the engine actually. There are records of a F-16 being tipped over by a B-1B Lancer; as the thrust of an A380 engine is quite higher than that of the Lancer, the damage would be worse.
The minimum safe distance between the aircraft varies depending on the aircraft and engine type. For example, according to the Australian Civil Aviation Order 20.9 - Air service operations - Precautions in refuelling, engine and ground radar operations:

An aircraft engine shall not be started or operated:
...
(b)   within 8 metres (25 ft) of other aircraft;
... turbine engines, in addition, shall not be operated within the appropriate distance specified below of any other aircraft, fuelling equipment or exposed public areas which lie to the rear of and within a 15 degree arc either side of the exhaust outlet axis of that engine:

Minimum distance between aircraft for operation of engines; image from Civil Aviation Order 20.9 - Air service operations - Precautions in refuelling, engine and ground radar operations


There are two coefficients which determine the forces needed to deflect a control surface (besides the physical parameters like area and dynamic pressure):

Change in control surface hinge moment coefficient $c_r$ with angle of attack $\alpha$ : $c_{r\alpha}=\frac{\delta c_r}{\delta\alpha}$
Change in control surface hinge moment coefficient $c_r$ with control surface deflection $\eta$ : $c_{r\eta}=\frac{\delta c_r}{\delta\eta}$

By shifting the hinge line back, an overhanging nose of the control surface is created which reduces hinge moments because the forces here will counteract the forces on the rear part of the control surface. This overhanging nose will reduce both coefficients equally.
In contrast to that, the horn, while also creating counteracting forces, will affect $c_{r\alpha}$ more than $c_{r\eta}$. This allows the airplane designer to tailor the ratio between both coefficients. Why this is important becomes clear once you look at the floating angle of a control surface:
$$\eta_f = -\frac{c_{r0}+c_{r\alpha}\cdot\alpha}{c_{r\eta}}$$
Normally, both coefficients are negative and the absolute value of $c_{r\eta}$ is a bit higher than that of $c_{r\alpha}$. And that is good: A positive $c_{r\eta}$ means that propelling hinge moments will increase with flap deflection, making the flap unstable and run into its stops immediately. But a positive $c_{r\alpha}$ just means that the control surface will deflect into the airstream when angle of attack changes, increasing stick-free stability over stick-fixed stability. So it is desirable to make $c_{r\alpha}$ very small while keeping $c_{r\eta}$ decidedly negative. This can be accomplished with a horn on the control surface.


Why are longer wings with foldable wingtips used on the B777X instead of lighter ones with original size?

This explanation is given here :

The wing of the 777X is based upon the design of the 787’s wing. It
has less of the sweep of the 787 but 10% more surface area (increased
from 4,702 to 5,562 sq. ft.). The re-shaping has led to a higher
lift-to-drag ratio, which(and) in turn increases usable fuel bulk from
320,863 to 350,410 lb. As a result, the type will have a range of over
14,000 kilometers (8,699 miles).
Boeing’s motivation for its including folding wingtips within the
design was not wholly steered by fuel economy. With a fully-extended
wingspan of 71.8 meters, the new 777X falls within the ICAO’s
aerodrome Code F. But with raked and folded wings (and a span of 64.8
meters) the type can comfortably arrive at gates designed for Code E.
Aircraft in this group includes the current 777.

So not only are they looking for more surface area and aerodynamic efficiency, they need to house more fuel to give it an extended range.


What would the "wings level" button most likely do if activated in the event of a flat spin?

This video shows what happens in a spin.

The turn coordinator shows a left turn, and the slip indicator shows a skid (ball to the far left as well). To get out of it you'd want to push hard on the right rudder pedal.

The yaw damper doesn't allow full rudder deflection.

Also as the instructor shows, pushing the stick left and right does nothing.

The stall protection will push forward, again won't help.

The TBM 930 doesn't have an auto-throttle, so there is no engine control involved either.

The installed Electronic Stability and Protection (ESP) system doesn't handle developed spins—

Leveling at 4,500 feet, I performed a series of steep turns, slow flight, an imminent stall with gear and flaps down, and a power-on stall. As the stall approaches, the G3000’s Underspeed Protection (USP) feature, linked to the angle of attack computer, comes alive as it automatically commands the autopilot servos to lower the nose. ESP, meanwhile, will attempt to return the airplane to level flight if bank or pitch angle limits are exceeded.
— flyingmag.com

Summary:
The safety features on the TBM would alert and prevent getting into a stall or spin.


How is the control of airspace over disputed territories determined?

International air traffic control is divided into Flight Information Regions (FIR) by ICAO through international agreement. Normally this works fairly well. Even countries that are antagonistic to each other wish to maintain safe air traffic.

Currently there is one situation that causes some real consternation, though. That's the dispute between Greece and Turkey over northern Cyprus. ICAO officially assigns the region to Greek ATC, but the northern part of Cyprus, which aligns with Turkey feels that the airspace is theirs and operates a separate ATC that  is not in cooperation with the official ATC, causing confusion for pilots.

They often create long and ridiculous notams to state their point.


What do pilots landing on aircraft carriers do when the ship is not visible due to weather?

My experience is circa 1990s, but I can offer some perspective on US fixed wing operations.
Besides TACAN and ASR for non-precision approaches, there are (were) 3 precision instrument approach options available:  Precision Approach Radar (PAR), Instrument Landing System (ILS, or “Bullseye”) Automatic Carrier Landing System (ACLS).
PAR: This consists of both azimuth and glide slope radar that allows the controller to issue verbal advisories to “talk down” the pilot.  This is generally a back up for when the other systems might not be working.
ILS: Although it works on different frequencies than civilian ILS, functionally it is identical.  A passive signal is received by the approaching aircraft which powers azimuth and glide slope indicators in the cockpit.
ACLS: This is an active system that locks onto the aircraft and sends a discrete signal to drive the indicators.  For a pilot flying a Mode 2 approach the indications are identical to the ILS, but there is greater precision as well as the option to upgrade to a Mode 1.  In a Mode 1 ACLS approach the pilot can couple the autopilot to the signal to allow it to fly the approach hands-off.
All these options are similar to what civil airfields have available, with one notable exception:  The aircraft carrier has Landing Signal Officers (LSOs) on station.  These hardy souls man the flight deck during all recovery operations, in all kinds of weather, and are the final piece in helping a pilot get aboard when the weather is bad.  In very poor visibility LSOs can see the landing light before the pilot can see the carrier and can help talk them down on short final. (There are lots videos on YouTube of this...)
Because of the unique functionality of the Pilot/LSO team, the concept of “minimums” and “missed approach” don’t really apply at the ship.  At 3/4 mile from touchdown the pilot will be asked by the controller to “call the ball” in reference to seeing the glide slope indicator of the ship’s Optical Landing System.  The pilot will either call the ball in sight, or declare “Clara” which means he/she does not have the ball (ship) in sight.  On the call of Clara the LSO will take over issuing power and line up calls over the radio until touchdown, or instruct the pilot to wave off if a safe landing is not possible.
And finally, if the airplane is bingo fuel they would be expected to divert unless the ship is operating blue water, in which case they would go to the tanker.


I flew the wrong pattern at an uncontrolled airport... Should I be worried?

Don't worry about it too much.  Are you specifically asking what are the odds of getting a phone call about this?  I'm not sure this is a really good question for Stack Exchange.  If you are really worried about it, fill out one of those mistake-reporting forms just in case -- https://asrs.arc.nasa.gov/

Newish/ overloaded pilots at unfamiliar airports have been known to overfly the field, look at the wind sock, and then proceed to set up a landing in exactly the wrong direction.  It happens.  Try to be aware of when you are getting over-loaded and double-check yourself.

Live and learn-- you lived, so learn.


Which (if any) is the "most major" airport / field / strip on Antarctica?

You can find a full list of airports on the continent here, the majority are ice/snow runways with two gravel runways at Rothera Air Facility and TNM. Supported is a loose term down there, however Williams Field which services McMurdo Station is groomed and has fuel available. Phoenix Airfield which also serves McMurdo can accept wheeled landings and seems to be marked in some capacity. Marble Point (a helicopter landing site) is also operated by the US, has fuel available and is operable 24 hours a day in the summer and has weather reporting.

The full operations of the (US) bases can be found in this document which states

  Williams Field is serviced by MLS, TACAN, and RNAV (GPS) approaches.

  ...

  Phoenix Airfield is serviced by TACAN, MLS and RNAV approaches.

which is a solid set of approaches all things considered.

At least two fields have runway lighting

  Airfield lighting systems are established at Phoenix and Williams
  Fields. The NSF Prime Contractor maintains airfield markings and
  lighting systems in accordance with AFMAN 32-1076

McMurdo even offers ATC!

All that considered Williams/Phoenix are your best bets but if you are trying to fly there on your own keep in mind:

  All navigational and approach aids are intended strictly for use by
  USAP (United States Antarctic Program) approved aircraft only. The use of NAVAIDs by non-USAP aircraft
  are strictly at the pilot’s own risk.

All of the fields are "weather permitting" as are the flights so "open" all year is relative to weather conditions and other considerations.


What would cause an abrupt increase in engine noise after takeoff on the Boeing 737-800?

The buzzsaw sound is usually the fan blades breaking the sound barrier.

Could be the elevation change, temperature, and humidity caused the sound to be more pronounced at that time, or perhaps the pilots increased the thrust on that engine due to cross winds or for some other reason.

Here's a youtube video with a similar noise:


RNAV (RNP) Approach Height Loss Question?

The approach above appears to be associated with the Antonio Marino Airport, Colombia, South America: (I don't know if it is current or proposed)

Descent below the published DA/H is not permitted due to obstacle clearance requirements. Therefore, a "height loss" (amount of altitude expected to be lost during a go-around [missed approach]) is added to the minimums to account for this.

The first minimum on the chart is 6240 ft. with a 50 ft height loss added and assumes a missed approach climb gradient of 5%.  The second minimum is 6340 ft. with a 50 ft. height loss added and assumes a climb gradient of 4%.

The 50 ft. added for the height loss is based on the use of a "radio altimeter."

The third minimum on the chart is 6340 ft. with a 150 ft. height loss added and assumes a missed approach climb gradient of 5%. The other minimums, all with a 150 ft. height loss added, assume missed approach climb gradients as low as 2.5%.

The 150 ft. added for height loss is based on the use of a "pressure altimeter."

The chart below is from an advanced version of "Required Navigation Performance Authorization Required (RNP AR) Procedure Design Manual" ICAO Doc 9905-AN/471

NOTE: the added height loss for "radio altimeter" use (category C aircraft) shows 71 ft on the chart below.  The published height loss on the OPs IAP plate shows 50 ft.  I do not know why there is a difference unless the requirements are country localized or the ICAO document has been modified.


Why are "canard" not used on commercial aircraft?

Well the Tu-144 was one example of an airliner which made use of canards.  The design configuration has been proposed before for large transports such as Boeing's ill-fated Sonic Cruiser.

And I suppose if you consider other, smaller aircraft, like the Paiggio P.180 Avanti for use in Part 121 and Part 135 operations, the that configuration is used often.

Probably the biggest reason is there hasn't been a pressing need to do so or the costs to abandon all of the engineering knowledge base in favor of a brand new design does not outweigh its potential benefits.


Is there a standard text for parachute design?

Some useful texts are The Aerodynamics of Parachutes by Cockrell, Ram Air Parachute Design by Lingard, and the Parachute Recovery Systems Design Manual by Knacke.  The Lingard and Cockrell papers both have extensive references that are worth pursuing.  The Knacke manual is, as far as I know, only available in hardcopy.

It seems that the designers of modern sport ram-air parachutes and paragliders are more concerned with protecting trade secrets than they are in publishing research.  The paragliding side of the aisle is a bit more willing to share.  There is an online paraglider design handbook, and there are several open source paraglider CAD software packages available.


Do airline pilots ever risk not hearing communication directed to them specifically, from traffic controllers?

There is a ton of radio communication during the taxi, takeoff and departure phases, and then again during the arrival, landing and taxi phases. Pilots are generally very busy at these times and 100% focused. Airlines have two pilots, and one will be flying while the other works the radios and monitors various instruments.

Cruise is another matter. There generally isn't a lot to do other than keep an eye on the autopilot. The pilots will take turns eating, resting, going to the lav, etc. Radio work usually involves little more than getting handed from one frequency to the next. They may get rerouted due to traffic or weather, but it only takes a few seconds to update the autopilot.

Either way, pilots do occasionally miss radio calls. So does ATC for that matter. It's common enough that nobody gets worried about once or twice, though it's annoying. If it's a real radio problem, there are procedures for both sides to follow to keep everyone safe.

There (usually) isn't any sort of light or tone when someone is calling you. However, the standard format is "called station, calling station, message", so with a little training, your brain can quickly tell whether the message is for you. If so, it "tunes in" and you consciously hear the message; if not, it "tunes out" and the message is just background noise.


Is it possible to use US-made engines in Russian made air-frames?

Re-engine an existing airframe is such a complex undertaking, in a way that so much R&D is required that the entire aircraft ends up being reverse engineered to make it work. Or on some occasions, the airframe is first licensed or reverse engineered, after which, experience and expertise is gained to enable the re-engine effort.

China is notable in this area due their Russian lineage of airframes and a long lasting desire for western engines, and a mixed relationship with both. India is in a similar position but I'm not aware of any such attempts.

Notable examples:

Y-8-F600(Antonov An-12 clone) with PW engine, failed
Sabre II(Mig-21 derivative) with GE or PW engines), failed.
Shenyang J-11(license production Su-27 derivative) with Shenyang WS-10 engine (reverse engineered CFM56 derivative), successful.


What kind of filters are being used to filter the bleed air?

Although typical HEPA filters are what's used (speaking from Boeing experience only), it's important to understand how bleed air is used in a typical aircraft environmental control system (ECS). Bleed air is taken from the compressor section of the engine before the fuel is introduced, so it's still relatively clean ambient air. As such, special filtering is not really required, not any more than say a cabin air filter on a car.

Because taking bleed air from an engine robs it of power, commercial airliners will generally use a mix of engine bleed air and recirculated cabin air for the ECS. This reduces the amount of bleed air taken from the engines, and improves their efficiency.

Where the HEPA filters become important is for filtering of the recirculated cabin air. If you were to look under the floor of a commercial airliner that's been in service for a few years, there is a lot of collected dust, dirt, hair, and grime from all the people who've sat for hours on end. Since a significant amount of the air you're breathing onboard is recirculated, the HEPA filters are important for filtering out the typical air impurities you get from having a confined space with lots of people, not necessarily from the engine bleed air.


Could a plane land inside or on top of another plane in flight?

The airforce used to have Parasite Fighters that could be launched and then recovered by a larger aircraft.

Parasite Fighter

The Space Shuttle was routinely transported on the back of two specially equipped B747s.

Shuttle Carrier Aircraft


Under EASA regulations, what constitutes loggable flight time?

According to FCL.050(g):

  Flight time is recorded: (1) for aeroplanes, touring motor gliders and
  powered-lift aircraft, from the  moment an aircraft first moves to
  taking off until the moment it finally  comes to rest at the end of
  the flight;

That seems to be the same as the FAA regulation.


Whats the difference between a paragliding rescue chute and a parachute?

Drawbacks of a skydiving emergency reserve parachute compared to a paragliding emergency parachute would likely include excess bulk and weight, and possibly a longer time to complete the opening sequence-- though perhaps the latter point would not apply to a parachute intended for BASE jumping.  If one has room for the skydiving emergency reserve parachute in their harness, and one is engaged in a high-risk style of flying such as aerobatics, it might make some sense to consider flying with it rather than a purpose-designed paragliding emergency parachute.

For more see related answer Can a paraglider rescue chute and its pilot handle terminal velocity?

It sounds like you have a more than merely academic interest in this topic; if so I'm sure you'll do further research, and we'll look forward to seeing a detailed self-answer to one or both of these questions in the future.


At 0 G the plane does not need to generate any lift, therefore there is no critical angle past which the airfoil cannot generate the lift required.

In addition, a sustained 0 G maneuver is a parabolic arc, which means that in theory your flight path should keep your angle of attack at zero the entire time (in a theoretical, symmetrical airfoiled aicraft). You can't stall because your AoA is constantly 0 degrees and cannot exceed the critical angle.


Is it possible to reuse water extracted from the PACKs Water extractors?

Water comes from condensing water vapor present in the cabin, itself coming from human breathing and perspiration, and, for a small part, from atmosphere.

The question mentions an air generation unit which is an Airbus terminology, so let's go into the A380 air system:

A380 Engineering training, source (page 101)

The two green labels are my addition to show the extractor and a spray nozzle. Water separated by a cyclone in the extractor is sprayed into ram air just after the ram air inlet and before entering the heat exchangers of the air-cycle machines. Spraying water droplets creates evaporation, hence a temperature drop in the exchanger receiving fluid, increasing air exchanger capacity.

Bleed air from the engines/atmosphere is colder and dryer at high altitude. Air exchangers work better, but cabin atmosphere may be dry for human well being. A fraction of condensed water can be returned to conditioned air going to the cabin. This is done automatically by the air-conditioning system.

To answer your question: Water is already fully reused.


What is the ratio of Commercial + ATP pilots with employment as pilots in the US?

You can find the full database of FAA information at this link but more useful they offer some statistics here.

As of 2018 there are 162,145 individuals that carry an ATP level ticket and 99,880 Commercial tickets out there.

The Bureau of Labor Statistics provides some employment stats however their stuff only goes up to 2016. As of then they claim there are 124,800 jobs for the title "Airline and Commercial Pilots" If we look back at the FAA's 2016 data we will see that in 2016 there were 157,894 ATP tickets out there and 96,081 Commercial level tickets. Assuming that BLS rolls up quite a bit under "Airline and Commercial Pilots" including 135 ops, flight instructor and full on 121 jobs there are 124,800 jobs for 253,975 possibly qualified people.

So there are roughly 129,175 people with ATP or Commercial level tickets not working in ATP/Commercial Aviation jobs.

Note: This does not account for people over 65 (data that it does not appear is released) as well as people who may have lost their medical or otherwise cant fly. However the FAA uses the phrase "ESTIMATED ACTIVE"  which could mean they account for all the above noted things.


How can I stop being too high or low when on base and final?

I think one thing that does not get emphasized enough:
Pilots do not land airplanes!In fact, we try to keep the airplane flying as long as possible!  We systematically rob the airplane of energy (energy from engine power, energy from airspeed, energy from altitude) until the plane can no longer fly, and settles gently on the runway.

But even as the plane is landing, the pilot is still trying to coax it back into the air to remove as much energy as possible.  A big student mistake is to point the airplane at the runway, and try to force it to land there.  That leads to landings too fast, too high, big bounces, porpoising, and sometimes nose-in crashes.

So don't think about "how am I going to land this thing?"  Instead think about "How am I going to remove more energy from the equation to lose altitude and airspeed?"

A landing is a series of precise targets you are aiming to hit, each with less energy than the last one (but each one still with enough energy to keep flying and be safe)

Each target consists of Position (horizontal and altitude), airspeed, and descent rate.  You hit each of these targets at 3 different points on a square (abeam the numbers, downwind-to-base, and base-to-final) Hitting a target that consists of a position + airspeed + descent rate is not easy! But the more precisely you can hit each target, the easier the next part is.

Although I hope I'm repeating the same instructions you've already heard, for the sake of the Site, let me re-iterate the standard instructions for a C-172.

Be level at TPA (airport + 1000 feet), and at a cruise speed of approximately 100 kts.  The runway should be approx 3/4 of the way up your strut.
When you are abeam the numbers, Carb Heat (if applicable), throttle back to approx 1,600 RPM, and pull-back as necessary to maintain altitude (the consequence will be that you slow down).
Watch your speed, altitude and position.  Drop flaps 10° when speed allows, and aim to hit a speed of 85 kts, an altitude loss of 250 feet, and have the numbers at 45° behind you, all at the same time.
Turn the corner to base, using approximately 30° of bank angle.  Continue to reduce speed (by pulling back) to hit 75 kts, and drop altitude another 250 ft. (you're now 500 ft above the runway).  Add Flaps 20 when appropriate.
Turn the corner to final.  You can "oval" your turn if you are undershooting the centerline, but do NOT over-bank if you have overshot the centerline.
Aim for the centerline, acquire a PAPI/VASI, keep an eye on your airspeed relative to approach speed (68 kts).
Watch 3 and ONLY 3 things:

Airspeed (Slowing towards 68 kts)
Centerline (left? right? on target?)
Slope (PAPI/VASI? Light configuration).

Keep repeating "Airspeed, Centerline, Slope" out loud, describe if you're too far/too close on each one, and describe how you're going to correct.  For example:

"Airspeed: 75 kts; too fast; pulling back to slow down"
"Centerline: Left of center; coming slightly right"
"Slope: 3 red+1 white is too low; adding power to slow descent"
(repeat!)

When the runway is made, drop final flaps, engine to idle, and prepare to flare when you're about 10-15 feet, and hopefully right at the numbers.

Remember that your altitudes are 1000, 750, 500, touchdown.
And your airspeeds are 85, 75, 65.


How quickly should a maneuver be started when ATC gives new heading?

You are correct, you should turn to the assigned heading immediately unless you aren't sure of the instruction (was that 100 assignment a heading or a speed?).

When ATC gives you a change, it is based on a continuously changing environment and they want you comply right away, as long as it was clear. Usually, doing the wrong thing is worse than doing nothing at all.


Instrument approach DME VS instrument approch ILS DME

The name for each approach indicates what equipment is required, so DME, ILS/DME and LOC/DME would all be different--and some aircraft may be able to fly one but not another.  Generally, the better (i.e. more precise) the equipment available, the lower the minimums can be because the obstacle clearance area will be smaller.


Would there be any benefit in placing the aircraft engines on the elevator (end-tips)?

There are some issues with placing engines in the horizontal stabilizer tips (I'm assuming you mean putting the engines in stabilizer- elevators are the control surfaces):

The engines are heavy- putting them at the rear shifts the c.g aft. The associated change in the c.g requires a larger horizontal stabilizer.
Putting the engines in horizontal stabilizer tips mean that it has to be strengthened, increasing the weight
Also, the fuel lines etc. has to be routed through the elevator, which increases complexity and weight penalty (not to forget the control surfaces which have to be there, which places a lower limit on the horizontal stabilizer size).
Not only the engine weight has to considered, but also the fact that the thrust has to be transferred from the engine, which furthers the weight penalty.
Noise in the rear of the aircraft- though this can be reduced by placing them away from fuselage, this further increases the weight.
Another thing to consider is that the engine may be affected by the wing wake, especially at high angle of attack.


How large are the pilot rest areas of the A380 and B747-8?

The pilot crew rest areas are not as large as flight attendant rest areas as they only provide space for 2 occupants. A380 and B747-800 pilot rest areas will have 2 sleeping berths, and most airlines will also have 2 comfortable seats equipped with the same in-flight entertainment as the passengers. This gives the resting pilot the choice to sleep in a bed, or relax in a comfortable chair. Sometimes, instead of a chair in the crew rest area, a regular Business class seat will be blocked for the pilot's use.
Airbus A380
Airbus A380 Pilot Crew Rest Area Video

Boeing 747
The B747-800 Pilot Rest area is behind the flight deck. This photo shows 2 bunks with blue bedding. Crew rest seats may or may not be available depending on the airlines own specifications or requirements.


What happens at a ramp check when I forgot my license and medical?

If you get ramp checked in a country under EASA jurisdiction, they will follow the EASA ramp check SAFA procedures, which include 53 points of inspection, not all of which may be performed during a check. Licenses are part of the inspection. Medical certificates are not mentioned, but I assume they are as well. Discrepancies found can be minor, significant or major. As a former auditor myself, I am going to make an educated guess that not having your license in your possession is the same as not having a license at all and would be a major discrepancy, and might result in the inspector directing the facility not to allow you to depart in your aircraft until you go get your license. It is almost 100% certain that the discrepancy would also be reported to the FAA.
At what stage of the flight the ramp check is performed will also make a difference, of course. Getting ramp checked before you leave and not having your license may result in nothing more than a stern warning and being told to go get it. You will likely not get off as easily if you are ramp checked as you are arriving in your aircraft.
Solution: Follow your checklist and verify your documentation prior to even starting the engine.


When is the descent clearance requested from ATC?

Whether there are any formal policies for when to request descent will depend on the airline. However, I doubt formal procedures are established, since it should be pretty obvious to pilots when to request descent.

From a controller point of view, I will expect you to request descent when you are ready for it - so a minute or so before reaching your top of descent point. Controllers are able to estimate when you are going to request descent, based on experience, known level restrictions and typical aircraft performance. Controllers who have been working the same sector for a few years will be able to tell pretty much exactly when a certain flight is going to request descend, based on the current wind, runway in use, airline and aircraft type. What this means to you, as a pilot, is that you can expect the controller to be ready for your request; You can normally expect to receive a clearance for descent immediately after requesting it - so there is no reason to request it several minutes in advance.

Very few pilots will request descent several minutes before ToD. If they do, I can - if traffic flow permits - use the phrase "When ready descent to FL160". You are then free to start your descent when passing the ToD. Honestly though, if you call me up and say "Request descent in 5 minutes", I will most likely just reply with "Roger, call me back when ready for descent". The traffic situation can change significantly in 5 minutes, so I don't want to issue a clearance that may not fit into the future traffic picture. In the end, the early request just costs time on the frequency, which can be a scarce resource in a busy sector.

Moral of the story: as a controller, I know my airspace very well, and I have a pretty good idea of when you are going to be ready for descent. Because of this, there is no reason to request descent before you are ready for it. If you do, it will not matter at best, and be slightly annoying at worst.

ATC can of course also descend you before your ToD for various reasons, but that is another discussion.


Where could I find the FOD examples of C17?

You can search the National Traffic Safety Board here

https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx

as a starting point.

Under Aircraft:Category, select Airplane.

Under Model, Select C17.

Scroll down and select  Submit Query.

There are couple of hits on C17s on the first page of results, I didn't look at  further pages.

Try this stack exchange link also on the same occurrence, but not just limited to C17s.

How does this vortex form inside a jet engine?


What is the typical fatigue life of a helicopter airframe?

Typical helicopters do not have cycles or hours limits on the non-dynamic components.

Since they are not pressurised, there is no concept of "cycles" and the fuselage is neither stressed, nor subject to the same kinds of forces that airliners are.

They are inspected on fixed hours cycles and specific types might have areas which are subject to non-destructive testing in accordance with operator, manufacturer or regulatory instructions.  Some, most notably Robinsons, are rebuilt by the manufacturer on hours based cycles and return as new.  However, the fuselage and it's major components are not replaced.  They are inspected and refurbished.

The dynamic components are of course lifed but I see that you have a separate question for that.


Does the NTSB provide CVR audio recordings alongside transcripts in accident reports?

No. Federal law prohibits the NTSB from releasing any CVR recordings, and the NTSB notes that they are exempt from FOIA requests. The same law requires them to release a transcript, like the ones seen in accident reports, if the transcript is relevant to the accident or incident.

See 49 U.S.C. § 1114(c):

  (1) The Board may not disclose publicly any part of a cockpit voice or video recorder recording or transcript of oral communications by and between flight crew members and ground stations related to an accident or incident investigated by the Board. However, the Board shall make public any part of a transcript or any written depiction of visual information the Board decides is relevant to the accident or incident—

  (A) if the Board holds a public hearing on the accident or incident, at the time of the hearing; or

  (B) if the Board does not hold a public hearing, at the time a majority of the other factual reports on the accident or incident are placed in the public docket.


What is the regulation related to weather radar use?

The FAA has AC 20-68B, which limits ground operations to qualified personnel only.


Why would banking be a problem for passengers on the Flying-V aircraft?

There are two possible sources of discomfort for passengers sitting farther away from the aircraft's longitudinal axis during a roll manoeuvre:

At the start and end of the roll manoeuvre, the angular acceleration will be felt as a stronger vertical acceleration, as you pointed out (vertical as in perpendicular to the cabin's floor).
Between the start and the end, the aircraft will be rolling at constant angular speed (or roll rate), so the angular acceleration will be zero, but the passengers will still be moving along a circular trajectory (around the aircraft's longitudinal axis) and therefore will also be subject to a centrifugal force (parallel to the cabin's floor) that grows proportionally with the distance from the longitudinal axis.

The roll manoeuvre itself may only last a few seconds, but if the above effects are strong enough, it could be enough to make some passengers feel properly queasy, especially if it's repeated a few times as during departure and arrival procedures.

As you suggest, rolling more gently and more slowly would limit these effects. However, instrument flight procedures always involve standard rate turns, with turn radii expected to remain within certain limits, depending on the aircraft's speed. Rolling more slowly would increase the aircraft's overall turn radius and could make it harder or impossible to comply with currently published procedures.


Which is the technically correct term: Nose Gear or Nose Landing Gear?

Based on the ATA iSpec 2200, ATA Standard Numbering System, which provides a standard for structuring maintenance data by the manufacturers. The structure helps the airlines by providing a common structure regardless of manufacturer.  While voluntary, most aircraft manufacturers use it.

The spec is organized into chapters by aircraft system. ATA Chapter 32 is LANDING GEAR. Chapter subsections cover subsystems.  Subsection -10 is Main Gear and Doors and subsection -20 is Nose Gear and Doors.  So that's the 'common' terminology in the aircraft manufacturing and maintenance world.


How can best glide speed be lower than best rate of climb speed?

The best glide speed is the speed where tangent line from the origin (zero horizontal and vertical speed) touches power curve (for unpowered airplane).

Best rate of the climb is the highest point of the power curve.

When we start with unpowered airplane, the direct equivalent of best rate of climb is lowest rate of sink. The speed for lowest sink will be clearly lower than the best glide speed.

If we would assume that aircraft engine is a magical device, which simply adds some fixed amount of mechanical energy to the airplane regardless of what, then the "powered" power curve would be simply the "unpowered" one shifted up in the graph. Under such assumptions the speed for best climb would be the same as the speed for minimum sink and in both cases lower than best glide speed.

Nevertheless mentioned Cessna converts fuel to mechanical energy through not-so-magical fixed pitch propeller which pushes some amount of air around. Such propeller would be typically optimized for highest efficiency at the cruise speed, so with decreasing speed the amount of available mechanical energy dereases. Which results in changed shape of power curve and maximum point moves towards higher speeds compared to the "unpowered" power curve.

This shift can be high enough that Vy ends up higher than Vg.

The Vy is always higher than the speed for the best climb angle, because these two speeds are found on the same (max power) power curve. For the same reason best glide speed will be always higher than speed for minimum sink. But speeds for best rate of climb and for the least sink does not need to be the same because of effects of real propeller.

For related images and more information, have a look at great online text See How It Flies.


Icing conditions temperature range: SAT or TAT?

For the purpose of aircraft limitations, it's TAT for the upper limit of +10C.  SAT for the lower limit of -40C.

Generally once you are going faster (in the RJ, above 230kts) you only need to have cowls on for all visible moisture conditions, and wings only need to be on if actual icing is happening or indicated.  Ice can form on cowls from the temperature drop related to the inlet pressure drop, like carb ice, so the requirements are more conservative for the cowl A/I system.  Cowls are turned on and off way more frequently than wings.


There is no height at which ground effect is switched off. It just becomes less and less effective. There are two factors which determine how strong ground effect is.:

Height relative to wingspan: The downwash cannot move into the ground so the induced flow field around the wing is distorted. In a first order approximation, the wing affects mostly the air which flows through a stream tube with the diameter of the wing span. For an explanation see this answer. Once the height is above one semispan, the distortion of the flowfield comes to an end.
Trailing edge height relative to wing chord. For very small heights, the gap between trailing edge and ground becomes small enough to more or less block the proper exit of the flow below the wing. The result is an increase in ram pressure on the lower side and further distortion of the flow field such that the stagnation point moves down and the suction peak of the nose flow becomes stronger, adding nose thrust and reducing drag.

When moving up from zero height, ground effect diminishes rapidly because the gap between trailing edge and ground opens up and the ram effect vanishes. Moving up further will also weaken the first effect until at a height of one semispan the flow will be very similar to that of the airplane out of ground effect.

To illustrate how much happens on the last centimeters (or feet), look at the two pictures which I took from this YouTube video:

In the top picture the wing is clearly closer to the ground than its semispan, but the vortices from the flap edge trail straight behind the plane. Now move forward to the lower picture when the trailing edge is maybe half a chord above the ground. Now the trailing vortex is swept to the side because the flow, which is compressed below the wing, expands when it exits the gap between wing and ground. Additionally, the downwash becomes a sidewash, because it has no space below the wing left in which to drop.

This should demonstrate that most of the ground effect happens when the ram pressure below the wing builds up. Once the trailing edge is less than half the wing chord from the ground, this part of ground effect kicks in, and the aircraft sees a significant reduction in drag.


What flights were significantly affected by insects hitting the fuselage?

It is conceivable that an accumulation of bugs on the leading edge of an airfoil would affect its performance.  In fact, the in flight accumulation of bugs occurs at such a low rate, and only at low altitude, that it's not a problem.

Above a few thousand feet AGL, bug density is negligible.  A car, driving at night, or a small plane flying for hours at low altitude may accumulate a mess of bugs.  Even so, such change in airfoil shape and affect on drag is miniscule on powered aircraft that normally spend moments, not hours, at such low altitude, above which there is no bug density.

The common hazard of bugs hitting the fuselage is restriction to visibility through the windscreen.  Bugs on the windscreen can make it difficult to see other aircraft and creates a myopic focus point for the eyes.

Another conceivable problem is blockage of inlets and ports, through most certificated aircraft are designed with alternate systems, e.g. bypass and redundancies to deal with such emergency.  Flight into icing conditions, heavy rain and ash are of concerns here.


What is the largest (size) solid object ever dropped from an airplane to impact the ground in freefall?

I can't think of anything dropped from an aircraft larger than the US Space Shuttle when it was dropped from a specially modified 747 during the testing phases of development.


Which among the two contributes most of the lift, the upper or lower surface of the airfoil?

In subsonic flight, the majority of the lift is generated by the lower pressure (compared to ambient) at the upper surface of the airfoil, which produces a net suction. A portion of the lift is also provided by the lower surface that has higher pressure, but is much smaller in comparison.
The graph below shows experimentally derived data on a symmetric airfoil, which breaks down the pressure distribution between upper and lower surfaces. The vertical axis of the graphs shows difference between local static pressure and free-stream static pressure divided by dynamic pressure, which is also called pressure coefficient. Note that a negative number means lower pressure compared to free-stream static pressure, and is suction; a positive number means higher pressure, and is pushing.
As you can see, in the 9deg AOA case, the upper surface suction dwarfs the lower surface push force by observing that the area under the curve is much larger for the former.

Image ref: http://web.mit.edu/13.021/13021_2003/Lifting%20surfaces/lectureC.htm
The next two plots show the stall and post-stall. This airfoil stalls at leading edge, so the entire suction peak is removed once the flow is stalled.


Why do pilots' seat covers almost uniformly use sheepskin?

They aren't "almost uniformly sheepskin", but they are absolutely uniformly flame-resistant (or self-extinguishing) as required for aircraft certification.

Sheepskin (and other natural wool fabrics) are both flame resistant and self-extinguishing (which is why industrial fire blankets are often made of wool), and sheepskin tends to wear well, so it's a good choice for the two seats that will absolutely always be occupied when an aircraft is being operated.
In terms of comfort, sheepskin covers also breathe well (so the pilots aren't sweating profusely while operating the aircraft - one of the reasons they're popular accessories for cars).

Other popular fabric choices are natural leather, flame-resistant synthetic leather (vinyl), and various other textiles which pass the FAA "burn test" requirements (test procedures are described in Part 23 Appendix F for light aircraft, Part 25 appendix F for transport category aircraft).


What are the ejection injury and fatality rates?

Survival outcomes in low level ejections from high performance aircraft is a 2013 consolidation of ten separate studies of ejections from 1952-1997, focused on comparing low level to high level ejections. It doesn't state that these were military (though likely) and only considered those where altitude was known. From the abstract:

  There were 562 low-level ejections identified. Out of this number, there were 274 fatalities, giving a low-level ejection survival rate of 51.2%. There were 2607 ejections that occurred above 500 ft (152 m), with a survival rate of 91.4%. There was a significant difference between ejection survival rates below and above 500 ft (152 m). Low-level ejections have a significantly increased risk of a fatal outcome (Odds Ratio 10.07).

So overall the odds of surviving an ejection are 84%.


Why can US deny airspace to commercial flights?

Every country regulates its airspace. You will find the ones for the US airspace on the FAA website.

https://www.faa.gov/air_traffic/publications/us_restrictions/airspace/

What went wrong is speculation, but most probably had to do with Advance Passenger Information System (APIS). When filing a flightplan the passenger list is transmitted and the request for overflight was obviously denied.


How do you know what equipment code to put on a flight plan?

Basically you know what equipment is installed on the aircraft (and in working order), and that's what you enter on the form.

For FAA flight plans, there's a list in the AIM (It's table 5-1-3).
Generally for domestic flight plans you file the "best" equipment you have onboard in working order.

FAA "Domestic" flight plans are eventually going away though, and we'll be expected to use the ICAO flight plan format (including its equipment codes).
ICAO equipment codes are a little more complicated because the "Equipment" box lets you list a whole lot more stuff (and the more you enter the more ATC knows in the event of an emergency): Basically you list all the equipment you have in working order under the equipment box on the ICAO flight plan form.
Lists of ICAO equipment codes is available (the one on Wikipedia is pretty complete), and there are handy wizards floating around that let you check boxes and get the string you need to enter on the flight plan.

Look at two hypothetical aircraft, both identical Cessna 172s with different equipment to see how it works:

Aircraft #1 has a VHF Nav/Com (VOR only, no ILS), DME, GPS, and Mode C transponder.
This aircraft would file /G on a domestic flight plan, and DGOV/C on an ICAO flight plan (the ICAO flight plan may also include R and an appropriate PBN code for the GPS capability).
Aircraft #2 has a VHF Nav/Com with ILS capability, and a Mode C transponder.
This aircraft would file /U on a domestic flight plan, and SV/C on an ICAO flight plan.

Note that the ICAO flight plan gives ATC more information to work with:
If Aircraft #1 calls up and says their GPS died ATC knows they can assign them clearances that use VORs and DME for navigation, but that the aircraft cannot accept an ILS approach at their destination.
Conversely if working off a domestic flight plan ATC will have to ask the pilot what their navigation capabilities are (or they may assume "standard" equipment including an glideslope receiver and ILS capability and offer the pilot an ILS approach only to be told "Unable ILS" by the pilot).


Why did the Boeing 787 design change shape from the original renderings to the actual design?

According to this answer to the same question on Quora, it was changed in order to

  keep as many parts common with other Boeing products as possible so they could reuse old part designs, vendors and tools and let the economics of scale help bring down the costs of these parts and thus the entire airplane.

By maintaining a greater similarity to previous Boeing products, the altered designs made the plane easier to design, build and sell, for a few reasons:

Maintaining similarity with older models made the certification process much easier and faster.
Instead of having to revise, test, remodel, and debug an entirely new part, the revised design had a greater background for the engineers to work with.
Completely new parts would have required more work building the machines used to construct the aircraft. Using prior designs led to reduced costs and time required in manufacturing.

Overall, the revised design made the aircraft easier and quicker to design and build which,  considering the issues and delays suffered by even the revised model, was a necessity.


From which stages is the bleed air from a GE90?

The base engine (up -94B rating) has 10 stages HPC, the growth engine (up to -115B) has 9 (reference https://www.geaviation.com/commercial/engines/ge90-engine).

In both cases, the type certification is counting bleed starting from the first stage of the HPC (not the LPC).

The reference to "10th stage" bleed in the type certification is misleading.  There is no 10th stage bleed in either engine.  Rather it is "CDP" bleed.  "CDP" stands for "compressor discharge pressure", i.e. right after the last stage of the compressor.

So in the base engine, the last bleed is extracted immediately after the 10th stage, and on the growth engine it's extracted right after the 9th stage.

Below is a diagram showing the bleed air flow that may (hopefully) clarify.  The CDP bleed is in orange.

(image from this and this answer, original source)


Why does a steady-state non-zero body yaw and/ or roll rate induce side force?

Let's say we have a thin, straight and rigid stick traveling in a 2D circular path. We will attach our reference of frame to the CG of the stick, aligned with its natural forward. If it has a forward speed of $u$ and the circular path has a radius of curvature of $R$, then it has a yaw rate, $\dot{\psi}=u/R$, all of which are expressed in the said reference frame.

At locations forward or aft of the CG, different parts of the stick will experience different lateral speeds due to the yaw rate, when measured using our reference frame: $u(x) = \dot{\psi}x$. The intuition is that the stick is spinning, so top and bottom will experience the largest speed while the centre will have none.
If you had attached a fin near the of the stick, then it will experience a side airspeed, effectively giving it an aerodynamic incidence angle. As a result, there will be aerodynamic forces and moments, simply from the motion of rotation.
From an analysis perspective, we usually don't re-calculate the effects on every surface due to local speed changes. Instead, the stability derivatives are measured in the body axis (well, usually in the stability axis but easily transformed to the body axis). So we can easily lump the sum of the aerodynamic effects of the individual portions into a single derivative with respect to the rate of rotation about that axis.


What do winglets do to increase aircraft performance?

they reduce the wingtip vortex and the associated drag by deflecting the air that wants to escape over the tip back down

(source: wikipedia)


What is the origin of the "Pickle" switch for release of ordnance?

The accuracy of the Norden bombsight was often exaggerated, but it was never claimed it could put a bomb into a pickle jar. The exaggerated claim from the Norden Company was that a bombardier using it under "ideal" conditions could put a bomb into a pickle barrel from 20,000 feet AGL. In reality it could barely get within 100 ft of the target from 10,000 feet AGL. (AGL = Above Ground Level) Some sources claim that it's called a pickle switch because a control handle with many switches almost feels like a pickle with all its bumps, but that would imply the name was given considerably later than WW2.


What is the maximum wind speed a Boeing 737-800 can deal with during takeoff and landing?

As your source shows, the maximum tail wind is fixed and fairly simple.

Getting slightly more complex, there is technically no maximum headwind I'm aware of, although most airports will close when the wind gets much above 50 knots, and even with the wind coming almost straight down the runway, you still get some crosswind component, which factors in. Expect to see many pilots divert in winds much above 40 knots even if the airport is open, especially if gusting to above 50.

Crosswinds are a little different as they depend on the braking action - basically how grippy the runway is. Simplified, you can think of it as a scale from dry weather, through slightly and very wet, then slush and ice. The grippier the runway, the more the tyres will grip and the higher crosswind the aircraft can deal with. The higher numbers in the chart you show are for a dry runway (good on your chart) the lower numbers for wet or icy (poor on your chart) runways.

Although it's written in terms of 'braking action', it's really a measure of grippiness, and it's important both when braking, but also for the ability of the tyres to prevent the aircraft sliding laterally off the runway. This job doesn't solely come down to the tyres, but they're part of it. This is also a large part of the reason why landings and takeoff have different maximum crosswinds on some aircraft.


Is the Inspire 1 a good drone starter aircraft?

I'm not sure this question will remain open long but here's my $0.02:

You will definitely want to learn to fly a cheap quadcopter before going expensive. Quadcopters are not that easy to fly (there is a lot going on at the same time: 6 degrees of freedom being controlled in a changing frame of reference depending on orientation to a stationary pilot).

I crashed my cheap one a lot learning to fly it despite it being pretty stable, but it is robust and takes a good beating. A cheap one is a very low risk and pain compared to the one you're looking at: You're not going have to break a lot on the expensive one to recoup the investment of becoming acquainted to quadcopters before you started.

Quadcopters may become a little 'smarter' as you go more expensive and be more stable, but it still requires good piloting.


What happens when you apply full cyclic + collective?

Multiple questions here. Assuming by full cyclic you mean pushing the cyclic to a mechanical stop while pulling full collective to the mechanical stop, the answer is yes, at least for the Bell 206, a very common turbine helicopter in use worldwide. There are no restrictions with regards to full flight control inputs. At stabilized hover on a no wind day there is no appreciable dissymmetry of lift as aerodynamically, there is no advancing or retreating blade. If you push the cyclic straight and full forward, mechanically tilting the rotor disc, the instant you move forward you now have dissymmetry of lift between the advancing and retreating blades


The components needed for a databus depend on the specific bus standards chosen. The most common of the recent air transport (B787, B777X, A350XWB) aircraft use the ARINC 664 network standard.

These aircraft also use ARINC 653 IMA computing resources hosted in a cabinet. Within the cabinet will be ARINC 664 network switch modules. These connect the IMA modules via a backplane bus and also connect it to external systems via fiber optic or quadrax network cabling.

ARINC 664 is a switched Ethernet type of bus with each A664 end system connected directly to a network switch, so there is no contention for media access at the end system. All network access control is controlled within the switches.

Beyond the IMA switches, the network typically has 4 or 6 remote switches spread along the aircraft. Aircraft systems with A664 end systems can be connected directly to these switches, but many systems use legacy interfaces such ARINC 429, ARINC 825 (CAN), and even analog audio or differential voltage signals.

These other networks can be connected via generic programmable network bridge devices called Remote Data Interface Units (RDIU) or something similar. Specialized interfaces are typically identified as gateways (Audio Gateway unit or A825 Gateway). These have an A664 connection as well as a number of the legacy bus connections. These have internal software that translates the data between the bus types. The key benefit of this architecture is a significant reduction in network cabling.


I want to become a commercial pilot, can you do that through the RAF?

Yes, you can. It means giving a commitment for a fair number of years in service of your country, where you will be trained as a pilot (assuming you get on to that - there are more jobs in the RAF than just pilot!). After your service, one thing you can do with your military flying experience is become a commercial pilot.

When I was young enough to consider it, there were 3 ways to become a commercial pilot

Learn in the airforce
Pay your own way (PPL, CPL, ATPL etc)
Get a scholarship from a big carrier like BA. There were usually about 4-6 given per year to the highest achievers.


What happens if an aircraft's hydraulic system starts leaking during a flight?

That depends on the aeroplane. On the B737 for instance, there are three independent hydraulic systems: System A, System B, and Standby System. Normally Systems A and B are operating and Standy is off, only switched ON when necessary from a malfunction.

The flight systems are powered redundantly, with more than one hydraulic system powering the essential aircraft systems. The following systems are powered by the hydraulics:

The hydraulic systems are each redundantly powered as well. For instance hydraulic system A is powered by an engine driven pump and an electrical AC pump. System A is protected from leaks in the engine driven pump lines by a stand-pipe: should a leak occur there, fluid leaks away until the fluid level reaches the stand-pipe, at which point the fluid level is approx. 20% and the engine driven pump circuitry is empty. System pressure is then maintained by the electric pump. Should a leak develop in the electric pump circuitry, the fluid quantity in system A reser- voir, and therefore system pressure, steadily drop to zero.

System B has similar anti-leak features, with a stand-pipe that allows for the Power Transfer Unit (PTU) to operate on the remaining fluid. The PTU is a dual hydraulic pump/motor: one end is driven by System A, the other end can pressurise the fluid in System B.


What is the difference between "Type Certificate" and "Certificate of Airworthiness" for an aircraft?

A Type Certificate is a certificate that the FAA gives the manufacturer of an aircraft, certifying the design of the aircraft. So for instance, Cessna Aircraft Company of Wichita, KS holds a Type Certificate for the Cessna 172. Notice that the certificate specifies what components make a Cessna 172, what its limitations and performance specifications are, and so on. When Cessna makes a 172, that aircraft has to conform to this specification. Moreover, only aircraft that meet this specification are certified as a 172. Which is why, if you make a major modification to a certified aircraft, it requires an STC-- a "Supplemental Type Certificate," to confirm that with the new equipment, the aircraft design is still airworthy and the limitations are accurate. But there is only one Type Certificate for an unmodified Cessna, and it is issued to Cessna, Inc.

On the other hand, an Airworthiness Certificate is issued for each aircraft individually and certifies that this here particular airplane is airworthy. They can be revoked if the airplane undergoes, for instance, an accidental major airframe modification (or indeed, an uncertified major alteration of any kind or if for some reason the FAA has reason to believe the aircraft is no longer airworthy). Each aircraft has its own Airworthiness Certificate that is displayed in the passenger compartment, and thus there are as many Airworthiness Certificates for Cessna 172's as there are airworthy 172s.


Calculating the maximum altitude of a drone

In the US, drones are required to stay in visual range.  How far away can you see?
There is also a free AOPA app that you could look into to help keep you out of trouble (or form hurting me as I fly around in my airplane at 145 MPH trying to keep an eye out for smaller things like birds and drones):

B4UFLY is an easy-to-use smartphone app that helps unmanned aircraft operators determine whether there are any restrictions or requirements in effect at the location where they want to fly.
Key features of the B4UFLY app include:
clear "status" indicator that immediately informs the operator about the current or planned location. For example, it shows flying in the Special Flight Rules Area around Washington, D.C. is prohibited.
Information on the parameters that drive the status indicator
A "Planner Mode" for future flights in different locations
Informative, interactive maps with filtering options
Links to other FAA UAS resources and regulatory information


What do Fighter pilots' thumbs look like?

In some fighter aircraft there are several functional switches on the control stick--switching from guns to missles and vice-versa, aircraft trim, firing the weapon(s), etc. A fighter pilot's thumb can get a real workout and over time that could result in a very muscular thumb.


What would happen if a Russian TU-95 had an engine failure or other emergency close to the United States?

Losing an engine on a 4-engined aircraft is not overly dramatic. In fact the P3 Orion actually intentionally shuts off one engine in flight to conserve fuel- it's more efficient to run three of them at higher power setting.

I doubt that they would put their aircraft in a position that they could not withstand an engine failure. From Kamchatka to California is it around 6000km max one-way; The TU-95 has a range of 15,000km.

As for potential political mess, you can see what happened when a Chinese J-11 Fighter collided mid-air with a US Navy P3 Orion back in 2001 in what is known as the Hainan Island Incident.

A British Airways 747 lost one engine out of Los Angeles a few years ago, and almost made it all the way to London, but diverted to Manchester (although that event did cause a lot of controversy).