How does the radio altimeter reading change with the bank angle?

The Rad Alt will show the same value of 1000'.

The radio altimeter antennas provide a radiation pattern that covers at least +/- 15 deg in pitch and +/- 20 deg in roll, though most cover more - typically +/- 20 deg in pitch and +/- 30 deg in roll.

The transmitted signal fans out equally over the entire pattern area from the transmit antenna and is reflected back where it is received by the receive antenna. The returned signal is spread over a short period of time due to the varying distances the signal must cover. The closest point will be the first received. As the aircraft changes pitch or roll, the location of the closest point will move within the pattern, but the shortest distance will still be the same.

The DSP software also processes the signal to filter out smaller objects such as the approach lighting towers.


What's the difference between CPM and LDM?

Purpose of the LDM is for the load-planner on the next leg of a multi-sector flight knows the figures for the next leg.

Example.. if the flight is routed SIN-DXB-LHR, the LDM from SIN will be broken up into 2 parts, one for SIN-DXB and and one for SIN-LHR. The loadmaster in DXB will use the data in the SIN-LHR part of the LDM telex for his load-sheet and then add in the load joining from DXB.

The CPM is used for aircraft where ULDs are loaded. This will give the loaders info as to which containers are for which destination and also which ULDs contain bags and which contain cargo/mails etc.

A CPM is mandatory for all sectors of ULD equipped aircrafts. An LDM is required for all sectors on all aircraft types except the last sector for an aircraft with ULDs as the CPM is sufficient. As aircraft with only bulk does not have any CPM, the LDM, while not required by most airlines, is still a way to inform the next station of what to expect on the incoming flight.


If airplanes can't use reverse thrust in flight, what am I hearing?

It is normal for engines to spool up during the approach. The initial part of the approach, from cruise level down to approximately 10 miles from the airport, is flown at flight idle power. This is the most efficient way to get down. In the final part of the approach, flaps and landing gear add so much drag that the engines need to be well above idle power.

At low speeds required for landing, the wing of the aircraft will not produce enough lift to sustain flight. To compensate for the low speed, flaps are extended. They do not only increase the lift, they also increase the drag. When the flaps are extended, suddenly the drag increases, resulting in a deceleration. Extending the landing gear has a similar effect.

Normally the flight crew will limit the time that they fly at low speed and high drag. The first couple of degrees of flaps deployment are relatively efficient;they do not add a lot of drag but allow the aircraft to fly slower. When the aircraft is about 7 to 10 nautical miles from the runway, the crew will transition the aircraft to landing configuration for the final approach. Often there is a horizontal segment before the aircraft starts a 3 degree glide path down to the runway. The crew will ensure that enough flaps (drag) is added before they start this final segment, otherwise they have difficulty reducing speed (they usually try to prevent use of speed brakes in that part of the flight).
Often there is a sequence of flap and gear extension before the final descent segment starts. This causes the aircraft to decelerate from the efficient high speed configuration (flaps 2 or less on the B737) to the landing configuration. At the end of that configuration sequence the aircraft has a lot of drag and is decelerating rapidly towards the final approach speed. To stop the deceleration extra power is commanded which spools up the engines and stops the deceleration. To reduce the spool up time of the engines, the engine control system (FADEC) will give a short burst of power. This what you hear while still decelerating. When the engines are spooled up they start to produce thrust which is the end of your deceleration.

This youtube video shows how it happens. When at 28:20, the aircraft (Boeing 737) is flying horizontally, flaps 2, and is about to start decelerating and descending for landing. Keep a look at the thrust levers(right bottom corner of the screen) and the airspeed (on the left of the artificial horizon).

It begins at 28:28 when the captain ask for flaps 5, and reduces the thrust in order to reduce to final approach speed. 15 seconds later he asks for gear down and flaps 15. The speed is now reducing rapidly. Starting at 28:50 the thrust levers are moved forward, until they are reduced again at 29:08. This is the power boost you hear. In 40 seconds the aircraft is transformed from low drag / low thrust to landing configuration.


What would the pros and cons be of this 'zig-zagged' high-sweep wing planform?

That's called sweep variation along span. What you've done is combine an inner W wing with an outer M wing.

Both of which were never used.

  W-wing: A reversed M-wing. Proposed for the Blohm & Voss P.188 but studied even less than the M-wing and in the end never used.
  M-wing: the inner wing section sweeps forward, and the outer section sweeps backwards. Allows the wing to be highly swept while minimising the undesirable effects of aeroelastic bending. Periodically studied, but never used on an aircraft.

The chordwise flow would be something like this:

The blue area marks an area of very low-pressure and flow detachment. The outboard wing will experience high pressure due to converging flows1. The wing will want to bend up from the middle, and bend down from the tips, structurally that's a nightmare.

The M wing on the right does resemble birds, but birds had to retain their 'arm' joints from their ancestors, and they don't fly at Mach 0.8 speeds.

1 Answer is a wiki for a reason, this is a guess.


How are jet engine RPM cycles used to monitor LCF life?

"N1" is the low pressure shaft speed, and "N2" is the high pressure shaft speed. N1 and N2 throttle cycles are when the throttle is moved up-down-up (or vice-a-verse), which causes the N1 and N2 speeds to go up-down-up, and hence "around" like a "cycle".

However, you will not find an "exact" definition, because it varies from engine to engine, even for the same manufacturer. In addition, the exact numbers that define the rpm changes required are usually not publicly available, as they are probably commercially sensitive.

But you can find a general description of "throttle cycles". Low cycle fatigue (LCF), is monitored by counting stress cycles. LCF is what causes a wire to break by bending it back and forth, which is a much easier way to break it, than by pulling each end. Cycling the stress back and forth (up and down) fatigues the wire and it breaks. The same thing happens in gas turbine rotating parts. As they speed up and down (in RPM) the centrifugal stresses increase and decrease. This can cause the rotating parts to fail. So they all have a "hard life", which when reached, the part is thrown away, regardless of condition.

In old engines, that don't have a monitoring system, they don't actually count each time the speed goes up and down. Instead, the engine manufacturer analyses the typical flight, and works out how many cycles occur per hour, on average. This gives an exchange ratio between hours and throttle cycles. See page4.

In modern engines, they actually count the cycles that occur. This means, if they fly the plane slightly differently than intended, the life being consumed is correctly recorded, whereas the exchange ratio would be wrong. (Though the life limit still needs to be verified as correct for the different mission profile).

Typically, 1 cycle is from idle to max speed, and back to idle. 60% to max and back to 60% may be 0.5 cycles, and 75% to max and back to 75% 0.25 cycles, as an example. So, if you take-off, from idle, do a climb at max RPM, throttle back in cruise to 60%, return to max before landing, and then shutdown the engine, you have accumulated 1+0.5+0.25=1.75 cycles in the flight. (Recognising that when you go from 60 to max back to 60, you have meet the criteria for both the 0.5 and 0.25 cycles.)

e.g. Another example of throttle cycles:


How does increasing the RPM result in a higher AOA for the blades?

Prop blades from side view at two RPMs

Vector diagrams help with visualizing prop blades. Above the vertical vector lines are two RPMs, the horizontal vector lines are the forward velocity (the same for both), and the connecting orange vector lines are the resultant airflows. Note the AOA for the same blade pitch and how it is affected by the airflow at the two RPMs.

Note: that's also why slow/windmilling RPMs result in high drag (negative AOA; airflow hitting top side), and why dead engines are feathered if that's an option.


In UK Air Traffic Control, the term has particular meaning as per CAP 413 (The CAA Radiotelephony Manual):

  When receiving an ATS surveillance service, certain ex-military
  aircraft types have been granted a CAA exemption from the Air
  Navigation Order requirement to fly at an IAS less than 250 kt below
  Flight Level
  100. In order to alert the controller to this higher speed profile, pilots of exempted aircraft shall, on initial contact, prefix the
  aircraft callsign with ‘FASTJET’ or ‘FASTPROP’ (depending on
  propulsion type), e.g. “Kennington Radar, FASTJET G-ABCD request
  Deconfliction service”. Use of this prefix shall be confined to
  initial contact with ATC agencies for periods of flight during which
  operations at airspeeds in excess of 250 kt are intended. Once
  acknowledged, it will not normally be necessary for pilots to use the
  prefix in subsequent transmissions until making initial contact with
  other ATSUs.

In my experience, Fast Jet will generally be used to refer to pretty much any jet powered single or dual seat (i.e., non passenger carrying) aircraft


In the US, are inside loops permitted while flying a US- registered DG-1000S sailplane in the "utility" category?

Stuff you quoted in your question seems to provide the answer you're after:

2.6 Approved manoeuvres Category „Utility“: The glider is certified for normal gliding in the "Utility" category. Simple aerobatics are approved but only without waterballast and with the weight of the rear pilot compensated by ballast in the ballast box in the fin see section 6.8.7.
The following aerobatic manoeuvres are approved with all spans:
...
Inside loop


What is this light passenger prop airplane which crash landed in East Kalimantan, Borneo in 1983?

That registration looks like PK-DCR to me. It's a little bit blurry, but especially if you zoom in, it's fairly readable.

A quick web search for that registration and "airplane" brings me Wikipedia's page on Deraya Air Taxi, which indicates that

  On November 1982, Indonesian Aerospace 212-100 PK-DCR of Deraya Air Taxi and PT Pupuk Kaltim was damaged when it approaching Bontang. No fatalities in this accident.

The 212-100 brings us to the CASA C-212 Aviocar.

Looking at the pictures on Wikipedia, it's pretty close, so that's probably it. Note the pretty distinctive tail section, and the relative dimensions:

(source; photo by RuthAS, published under CC-BY-3.0)

(source; photo by John Wheatley, published under under GFDL-1.2)


Do airline dispatchers pre-block seats for weight and balance on large wide body aircraft?

Yes sometimes, because with most aircraft you can't fill all of the seats and all of the fuel tanks and stay under max gross weight, meaning the airplane can't achieve its potential maximum range with a full cabin and on long range city pairs some sort of passenger/fuel horse trading may have to go on.

So on flights where the airplane needs more range that it has with a full cabin, it may be forced to limit seats filled to accommodate the extra fuel, and it will distribute the empty seats throughout the loading zones to prevent load concentrations for balance reasons.

You will also see seats blocked off to accommodate dead heading crew, but if you see a significant number blocked off in each cabin loading zone, and the seats are still empty when you board and its a long flight, it was probably due to fuel requirements.


How many hours to remove and install a Cherokee 180 engine and prop

I once changed an engine in the bush when I was bush flying, helping the air service's mechanic.  It was a C-180 on floats (I had been forced down in it after the engine developed a loose cylinder from failed hold-down studs).

There was a rigid dock for us to work with at the remote lake we were at, and we used a bipod made of pine poles with a come-along to lift the engine and set it down on the dock (with the noses of the floats against the dock).

It took about 6-7 hours to have the engine and prop removed and ready to be loaded on the company Beaver when it showed up around 5 pm (loading it was the really entertaining part).

We went back in two weeks later with an overhauled engine and installed it, 2 mechanics and myself, and I flew it out that late afternoon around dinnertime.

So for a Cherokee sitting in a hangar with a lift handy, one mechanic with an assistant, about 4-6 hours to remove the engine, and about 6-8 hours to install it.  Certainly no more than two days at most.


Before COVID, what was the largest aviation crisis ever?

Crisis is somewhat hard to define explicitly but the September 11th Attacks had an enormous impact on the commercial aviation industry in perhaps more ways than the current Pandemic has.
It took nearly 3 years for aviation travel numbers to return after the attacks and arguably we are still seeing lasting impacts on changes to broad aviation travel procedures as a direct results of the attacks even 20 years later.


Do landing gear doors need repairs after a gear gravity deploy landing?

No, they do not get damaged.

The Main Landing Gear (MLG) or Gear Bay doors can and are regularly opened on ground for maintenance purposes. Even with fully compressed oleos the MLG doors are still off the runway surface. Have a look at this Air Canada A320. You can clearly see the doors being well above the bottom of the MLG.

If you came to your conclusion by watching the white puff of smoke coming from the area of the open MLG doors - that's actually the burning rubber from the nose gear touching down.


Why can't Norwegian's Boeing 787 operate from Vegas during hot weather?

Norwegian’s heat issues stem from an unusually high passenger capacity aboard the Boeing 787-8 jetliners that the carrier uses on its Las Vegas routes. Most airlines operate the plane with an average of 200 seats, but Norwegian puts 291 seats for sale on the 787-8 aircraft to keep costs down as part of its low-cost model.
Given the weight of those additional Norwegian passengers and all that accompanies them, the airline this summer found close to 300 people on board, including crew, and its planes’ ability to take-off during high-temperature periods was sometimes limited.
— reviewjournal.com

You see that Norwegian carries more people compared to other 787 operators. And they do indeed cite the passenger count as the reason.
Hot and high limitations are explained here, the biggest limitation for twin-jet planes such as the 787 is the ability to climb if an engine fails during takeoff.
The longest runway at Vegas' McCarran International Airport is 14,512 ft; the elevation is 2,181 ft.

From the 787 performance dispatch manual at 2000 ft pressure altitude and 42°C outside air temperature, we find the limiting factor is the climb limit weight, which is 195 tonnes (429,000 lbs).
The 787-8's maximum takeoff weight is 228 tonnes (502,500 lbs), that's a structural limit.
The 33-tonne difference is equivalent to 300 passengers (80 kg adult + 30 kg luggage and carry-on). Of course the plane won't be fully fueled, despite the huge distance, but you see how big the limitation is.
It gets even worse above 42°C. 30°C seems to be ideal. Vegas record high is 47°C, and the mean maximum in July is 44.7°C.
Why not depart from Vegas at night? Most probably due to slot restrictions. Waiting for the sun to go down means financial penalties, which is confirmed by the German news article.

Several times the airline had to move the flights to the cooler hours. It costs.— Google Translate

Vegas to Europe is a huge distance, and a direct-flight without a technical stop to refuel is Norwegian's only choice—evidently and understandably. Their low-cost model that favors filling all the seats over fuel is the limiting factor.

(gcmap.com) The four Norwegian routes, they range from 4,462 NM to 4,701 NM, London being ~4,600 NM.

(Source—PDF)
Fully loaded with payload, the range is limited to 2,700 NM for a takeoff from a 42°C Vegas.
18 tonnes are to be shed to make it to London, i.e., 163 seats will be empty, or 90 empty seats plus leaving behind 8 tonnes of freight—airlines do depend on freight for profit. So, the typical quoted 200 passenger capacity would work. But if Norwegian doesn't do freight, then they're not to blame for cancelling the four European routes during the summer heat.

Boeing PDF on how to read the payload/range chart.


Can you become a CFI with only a PPL (EASA)?

The EASA requirements for a CFI ticket are:

Over 18 yo
Hold a Commercial Pilot License or a Private Pilot License with the CPL theory done.
A minimum flight experience of 200 hours as a Pilot of which 150 will be as Pilot in Command
Hold a Medical Certificate Class I or II in accordance with
the license


What flying boat has the highest maximum takeoff/landing sea state?

The Grumman Albatross was capable of open sea operations and could operate in as high as ten foot seas, possibly higher with JATO rockets installed.

  The Albatross was capable of open-ocean landings (optimally in seas no
  higher than 10 feet) due to its deep-V hull cross-section and long
  keel length, although higher seas could be downright punishing on the
  aircraft and crew. HU-16s could utilize jet assisted takeoff (JATO)
  bottles to shorten takeoff runs in rougher seas.

This Albatross pilot offers some more specifics on the certifications and says

  Its certified for class 6 seas, which can be swells up to 10 ft. or waves up to 6 ft.

Although he says he would not really want to do it as his operation has no need but has landed in 4ft seas.

According to this source a Boeing 314 Clipper was successfully landed in 30 ft. seas but thats by no means regular operations.

  The weather was far from ideal, with a big storm blowing, and 30 foot
  seas running.  But the big Boeing was successfully landed without
  damage.  The seas were so high, it was almost impossible to transfer
  the occupants to the Cutter.

I don't think anything is certified for takeoff in hurricane conditions, seaplane or not.


What is this quad-jet plane at El Paso Airport?

It's the McDonnell 220, registration N4AZ.

(Source)

Wiki says

  The McDonnell 119/220 was an attempt at making a business jet by McDonnell Aircraft in the late-1950s. It had a configuration that was unique by bizjet standards, with four jet engines mounted in individual pods underneath a low wing; it could accommodate ten passengers in a luxury executive configuration but could carry as many as 26.

  ...

  The McDonnell Corporation used the airplane as a VIP transport for a few years before donating it to the Flight Safety Foundation's research facility in Phoenix, Arizona. As of 2020 the single prototype is still extant, registered as N4AZ and stored at El Paso International Airport.

Only one such plane exists. Its first flight was in 1959.

Here are some pictures.


Where can Cirrus Aircraft VisionJet Oleo Struts Material and Dimension Specifications be found?

You're after the landing gear oleo Source Control Drawings.  You need to contact Cirrus' tech support and request the drawings from their engineering organization via their support organization, who may or may not want to help you, or may charge for them if they do.

I expect they won't want to provide them because they'll suspect that it's for someone who wants to make a PMA (Parts Manufacturer Approval) copy. It's usually pretty tough to find source documentation like that for a product that is in current production.


Why is Emirates not considering buying or leasing used A380s?

(Source: IATA)
Used airplanes are costlier to operate and maintain. Take Ryanair for example, they have 420 Boeing 737's with an average young age of 6.8 years. That age is very important.
The graph above shows the direct maintenance cost of an A320 for the airframe, similar graphs are available for the other systems. Note when the first period ends.

First-Run is the initial operating years, often referred to as the honeymoon period and generally
considered the first 4-6 years of in-service operation. The structure, systems, and components
are new; and there is less non-routine maintenance and material scrap rate.

The following serves as both a proof and an answer: Airbus is buying back the older A380's in the new deal with Emirates for new A380's.

Airbus (AIR.PA) will have to buy back or find new homes for some of the older A380s currently operated by Dubai’s Emirates as it finalises a deal to sell new superjumbos to the Gulf carrier.
(...)
The decision by Airbus to buy back aircraft to facilitate the anticipated deal comes as the aviation market struggles to absorb some of the first A380s, which entered service a decade ago.

The Reuters article is from November 12, 2017. It's no wonder you see older Boeing 777's next to 727's:

Something Airbus is wary of, they don't want to see an A380 in the boneyard so soon.

Airbus is seen as keen to support the second-hand market to avoid having to break up one of the planes, a potential public relations setback as it tries to breathe new life into the iconic European programme following recent production cuts.


Can cabin pressure be lower than outside pressure?

Besides the sealing the aircraft would also need a vacuum pump that is able to pull air out of the cabin which means extra weight.

The way aircraft maintain cabin pressure is through a air cycle machine that pushes air into the aircraft and outflow valves. There is no facility to pull air out of the craft.

Any pressure drop you may experience on the ground is probably because the pilot increases air pressure on the ground slightly to test the seals and then releases it before takeoff.


Would a coaxial propeller with the second prop slower and larger improve speed?

I think what you'd ideally want to do is to have a fast-rotating "inner" propeller and a slower "outer" one, or actually a propeller whose RPM gradually decrease from the inside to the outside. Although that would look cool, it doesn't work with non-fluid materials for the rotor :o) So, the next best thing is to have two behind each other, where the downstream one spins a bit slower.

How I understand your proposition

Counter-rotating props do have the advantage that the second one can "straighten" out the flow from the first, effectively working similar to (but not entirely like) a rotor/stator couple in a turbojet. This means they can transfer more power per rotor area than single rotors. By putting the slower-spinning one behind, this couple will leave less swirl in the flow than the other way round, which sounds like a good idea to me.

Difficulties with regular counter-rotating rotors

In a counter-rotating rotor couple, the second rotor is exposed not just to the mean swirl coming from its upstream partner (for which it is designed, and which can increase its effectiveness), but also the pressure signatures and wakes coming off each blade. Every time a blade passes through one of these, the stagnation pressure at its leading edge goes down very sharply and the increases again. That makes a lot of noise, and also causes vibration in the blade, which then has to be made strong enough to deal with this. This is also the reason why most such rotors have swept blades like these:

This means that at no moment will the entire blade of the downstream rotor be in the wake of an upstream blade, but it will gradually pass through it. Still the blades have to be quite sturdy, which also prevents them from being very long. That, in turn, limits the ability to increase efficiency by making long, slender blades which produce less thrust per rotor area but make up for it in radius (like wind turbines, for example). That's one reason why most such configurations these days are seen in military airplanes where large elegant propellers would reduce maneuverability but lots of thrust is needed, pronto. Also, these machines are built very robustly anyway, so the added vibrations can be dealt with. In a passenger aircraft, the noise alone would be hard to sell to airlines, but developing the mechanical components would also not be easy. At the moment it seems that only Antonov has experience with large configurations of this type.

That said: These concepts keep cropping up, and it seems as if it should be possible and efficient to use counter-rotating rotors with strongly swept blades to replace turbofan engines at speeds that would seem a bit high for regular propellers (but maybe a bit low for turbofans).
Here are two sources I just found which give you some idea of what the flow looks like, and what types of aerodynamic and acoustic problems the designers have to content with:

A 2014 paper summarizing design and research activities
Slides from a 2010 presentation on simulating the flow, and on efficiency and acoustics -- very nice pictures, and a good way to get an idea of what propeller flow looks like.

The problem with having a larger downstream prop

You can also see in the references above that usually the downstream blades are actually shorter than the upstream blades. The reason is that otherwise the tip vortices from the upstream propeller would hit the downstream one, and that's acoustically, aerodynamically and structurally not nice. Even without those vortices, it would make sense because the downstream prop gets more vibrations either way, so it has to be sturdier (shorter, thicker blades will help!).
I think some of the existing configurations (the AN-70 above for example) do have equal blade lengths, but they are very much known for being loud, and any new civil application cannot have that.

This, by the way, is also why the configurations under discussions are rear-fuselage mounted rearward-facing rotors: That puts the source of the noise a good way downstream of the passenger cabin, instead of right next to their windows (which is loud enough with regular props already, as any passenger in a Saab 2000 can confirm). It also has the benefit of preventing accidents where a blade breaks off and hits the passenger cabin ...


Why does the Zapata Flyboard Air UL consume so much more fuel/hr than the Mosquito Air?

It's the difference between jet engines and propellers. It is a lot more efficient to accelerate more air to a low velocity, than it is to accelerate less air to a higher velocity. For fixed wings, the only reason to use jets is if propellers hit their speed limit, when the tips break the speed of sound.

Hovering flight is particularly demanding on fuel consumption. The Mosquito Air burns through its fuel a lot faster than 1 hour when it stays in hover all the time. Cruising in a helicopter makes the fuel consumption  a bit more similar to fixed wing: the rotor blades start to act more like wings and can use airspeed to reduce induced drag. Still less efficient than fixed wing cruise, but more efficient than helicopter hover.

The Zapata Air UL is always in a hover, and has no wings, and is a jet. It never gets the increased efficiency effect of forward flight that a rotor gets. And jets are really very inefficient at low speeds!


Given aircraft and runway characteristics, how do you compute the maximum temperature for take-off?

Well, there is some subjectivity here, but I consider the optimum temperature for takeoff to be 72-degrees Farenheit.

As far as the outside temperature is concerned, there is no specific optimum. In general, colder is better.


Why was there a rattling noise coming from the left engine of A319?

Yes indeed, the fan blades are loose and rattle in their sockets when the fan is freewheeling in the wind. Once the engine is running, centrifugal forces will make sure they do not rattle any longer.

The base of the fan blades have a shape like a fir tree, and they slide into sockets on the fan disk with a loose fit. When the fan is spinning slowly, they will sit on one side of the socket on the way up, and gravity will pull them into the opposite side on the way down. The rattling is caused by one blade after another falling into that opposite position once they rotate over the top.

Sorry for the bad picture (source) - I could not find a better one right now.

There are concepts to move to bladed disks ("blisks"), but while they are lighter and don't rattle, they are a headache once a single blade is damaged and needs to be replaced. Therefore, the single, easily removable fan blades are the solution of choice in all gas turbines.


12 point flange cap bolt/screw. For high torque applications, less likely to be accidentally rounded-off.
http://www.fbabolt.com.au/12-point-advantages.html


Because the AN-225 is not a military aircraft and Zeppelin will be winner, there is no one biggest plane.

C5 Galaxy = 76 meters long, 68 m wingspan, 20 m high, wing area:576 m2
An-124 = 69 meters long, 73 m wingspan, 21 m high, wing area: 628 m2
(Bonus:) Hughes H-4 Hercules (Spruce Goose on picture) = 66.55 meters long, 97,54 wingspan, 24 m high, wing area: 1 061,8 m2

See this :

Source:https://fr.m.wikipedia.org/wiki/Hughes_H-4_Hercules#/media/Fichier%3AGiant_planes_comparison.svg


To what degree do airline ops specs preclude hand flying?

There are no Ops Specs that preclude hand flying, however company policy and operational considerations do in specific situations:

Level flight within RVSM airspace
Cat III approaches (and I believe Cat II approaches)
High workload, critical phases of flight (company specific policies here)

The FAA even came out with a SAFO not too long ago recommending that pilots do more hand flying during periods of low workload (and during training) with the goal of maintaining hand flying proficiency.


Can you become a pilot with an Asperger syndrome diagnosis in Europe?

In order to fly commercial you will need a first class medical certificate, and getting that with aspergers is going to be tough. The first consideration is the safety or people in the air and on the ground, so the criteria is conservative. Getting a first class medical would mean lots of extra hoops, even if it is possible. If you did get a medical you would then be competing against candidates who are neuro-typical, and would have to convince the airlines that you would be able to perform your job as well as non-aspergers candidates. That's not to say it's impossible, you would want to talk to a few aviation medical examiners about it to see what they say. If you can get a medical then you've got a chance, and if you are motivated enough and willing to work for it then I believe where there's a will there's a way.

You need to consider your own temperament when going for a pilots license of any kind, whether aspergers or neuro-typical. Flying is not just about the technical details, you need to be able to work with people, first of all your instructor! In commercial flying you also need to cooperate with other pilots and work with passengers, ground crew, and cabin staff. The extreme focus on detail and depth of knowledge on aviation you might develop with aspergers can be a huge asset in some ways, however aspergers could make it very challenging to work cooperatively in the cockpit, deal with troublesome passengers, and make quick and effective decisions. Think about some scenarios:

You are FO on a flight, the captain makes a decision you do not agree with
A passenger is angry after the flight was delayed and is shouting abuse at you
You are the captain of a flight that is low on fuel and had developed an emergency. You need to very quickly opt for continuing to the destination airport or diverting, and there are problems with either choice

Do you think you would be able to successfully deal with these types of situations in the time frame you would have to work with? Not everyone is cut out for that sort of thing, whether aspergers or neuro-typical, these are scenarios all potential commercial pilots would need to be able to deal with.

I think first you should figure out whether you like flying airplanes or not as a love of aviation and airplanes does not automatically mean you will love being at the controls. Why not go for your private license and find out? It's the first step in getting an ATPL anyway, and you could probably get a third class medical. You can then build on that if you want a career in aviation, or keep flying privately if you don't.


Was differential thrust used in the P-38 to improve turn performance?

According to WW2 pilots, no. Aside from the dangers in adjusting 1600hp on one side of the aircraft on the fly in the midst of a dogfight... With the P38, they didn't need to. The P38 had an inherent advantage over single engine prop fighters of its era. Its engines (and propellers) rotated in opposite directions, canceling out any torque effect. The counter rotating engines and props were considered a big secret on the P38 when it was first designed. (as if anyone couldn't look at the angle of the props on each side and tell that.)

The pronounced torque of the 1600hp-2000hp single seat fighters played a major role in aircraft handling: both in takeoff and power on maneuvers, something WW2 flight simulators never seem to reproduce. Single engine fighters would roll left far quicker than they could roll right, due to the immense torque of the engine/prop combination, aiding in the left roll but inhibiting a roll to the right. This was most evident at lower altitudes, where the air is thicker and the torque effect more pronounced.

Not so with the P38 - contra rotating engines and props canceled the torque, and the P38 could roll right far quicker than any single engine fighter. While the P38 did have several issues at high altitude, WW2/Vietnam ace Robin Olds held that nothing could beat a P38... down low. (revisit the Dogfights/Air Ambush episode for that)

So, no, they didn't use asymmetrical engine power for maneuvering with the P38 - they didn't need to. Just roll right and turn - no single engine fighter of that day could stay with you.


How is altitude reached by aircraft flying above the stratosphere measured?

They used inertial altitude on the X-15 for high altitude measurements. This works just like an IRS (Inertial Reference System), which was used on airliners of that era: you can get the position (latitude and longitude) based on a manually entered (or GPS derived) start position by integrating rotations and accelerations over time. The principle also works in 3D, if you also enter the start altitude. Note however that inertial altitude (true altitude above mean sea level) is not equal to barometric altitude, which can deviate based on local environmental conditions.

On the instrument panel was an attitude indicator whose source was inertially derived. Also provided were inertial velocity, altitude, and rate-of-climb. Barometric instruments included an altimeter and a combined Mach-airspeed indicator; these instruments were usable only below about 75,000 feet and were used mainly in the traffic pattern. An angle of attack and a sideslip indicator were provided; the source of these two instruments was selectable, inertial for high altitude flight and barometric for the end of the mission.

(NASA - Dryden History - X-15 Lessons Learned, emphasis mine)
You can see both instruments in the following image:

(modified from source)


Is it necessary to have my full name (including middle name) on my student pilot license?

Alright so here is the outcome:

I called FSDO, spoke with a real nice guy who told me to give him a call if I couldn't handle this online.

Called a zillion bureaucracies, all telling me to call someone else.

Called the nice guy at FSDO, set up an appointment for a name correction not a name change. Went to the appointment and was in and out in under an hour.

If you're having the same issue, I would recommend bringing every official identification you've got: passport, birth certificate, drivers license, etc.

Tl;DR call FSDO and tell them you need a name correction. NOT a name change. Can't stress that enough.


How is propeller thrust vector accurately expressed for airplanes and multirotors?

The term
$$V_q\cdot{sin}\theta_t$$
is a speed, not a force, so it cannot be an accurate expression of the thrust vector.

Propellers accelerate the air flowing through the propeller disc in the direction of the propeller axis (or perpendicular to the propeller disc), so the force is only parallel to the propeller axis when the airspeed is aligned with the propeller axis. If the airspeed is at an angle to the propeller axis, the thrust vector is tilted towards the airspeed vector. The magnitude of this tilt depends on the speed increase of the propeller stream relative to airspeed.


At a constant power setting, does TAS change with altitude?

The answer to your question largely depends on what you mean by "constant throttle setting".

For propeller propulsion, if "constant throttle setting" means "constant power setting" as in a fixed output BHP, TAS will increase almost linearly with altitude (up to the altitude where constant power output can no longer be maintained).

For a normally aspirated reciprocating engine with a fixed pitch propeller, a constant throttle position will mean a decreased manifold pressure with increased altitude resulting in less power output, less thrust (T), and thus decreasing TAS (assuming the decrease in thrust is larger than the decrease in drag (D) resulting from the decreased density at higher altitude, this generally holds true). For a supercharged engine, depending on how the supercharger is controlled, "constant throttle setting" can have the charge control maintain a constant manifold pressure. In this case, the power setting will be maintained (up to the maximum altitude where the supercharger can maintain the manifold pressure), and TAS will increase.

For a jet propulsion engine, once again it depends on what is implied with "constant thrust setting". For example, for low/no bypass engines, a constant EPR should roughly correspond to constant T with altitude, hence with D decreasing with altitude, TAS will be higher before T = D. If "constant thrust" means "constant N1", thrust will actually decrease with altitude, how quickly it decreases with altitude will determine the effect on TAS (once again, where T = D).

If "constant throttle setting" simply implies "constant thrust". Resulting TAS will always be higher (as for a given TAS, T remains constant and D once again decreases).


Why are Airbus captain control sticks placed on the left when most people are right-handed?

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

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

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

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

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


How does a plane's weather radar ignore returns from other weather radars?

"Radar to radar interference" / "Mutual radar interference" is an ongoing research topic, though much of the current research (based on my cursory Googling) seems focused on interference between radars on self-driving cars.  That leads me to believe a certain degree of radar-to-radar interference is currently just tolerated.
The link shared by randomhead gives us some insight into how maritime radars mitigate mutual interference, both directly and indirectly.  The same techniques should be applicable to aircraft weather radars, which tend to also be X-Band and also be pulsing radars.
Directly

The interference rejection capability of the radar essentially relies on timing differences between the radars.  A pulse radar sends out many pulses, separated by around 1 millisecond.  Microsecond-resolution timing between the transmission of the pulse and the receipt of its echo is used to determine range to a target.
Interfering radar pulses will arrive somewhat randomly on that microsecond timescale, but actual target echoes (e.g. from weather) will be correlated across multiple pulses.  The radar can be made to only acknowledge a return as real if enough echoes arrive.  Related topics here seem like "m-out-of-n" detection, "binary integration", "coincidence detection", "dual threshold detection", and "double threshold detection".
Activating the "interference rejection" mode on a radar (or having it always on, which I suspect is the case on many aviation weather radars) will cause a radar to reject certain weak real returns (more false negatives).  Luckily, clouds full of precipitation tend to return radar fairly well.

Indirectly

A different section of the same link gives instructions for tuning radar.  This implies that there is room in the band for more than one transmitter to be operating simultaneously, though it may not be organized formally into channels.  This is reinforced later in the description of the Search and Rescue Transponder (SART) scanning the radar band for pulses to reply to, which wouldn't be necessary if they all operated on the same frequency.
So, automatically or manually, weather radars should also be able to deconflict by frequency separation.  This will, of course, run into limitations as the number of transmitters grows, but at least it reduces the amount of work the Interference Rejection mode has to do.

If the radar can change properties of its pulse, such as the pulse length or frequency modulation, it can potentially use those properties to distinguish between its pulses and pulses from other transmitters.  The link doesn't really support that being used to reduce interference in maritime navigation radar, though, and I kind of doubt it's used for such in aviation weather radar either.  I think I've heard of schemes like that being used for more warfare-oriented radars but that's even further outside my own expertise.


How much runway does an amphibious Cessna Caravan require for VFR part 135 operations?

The minimum required runway length for a Cessna Caravan is *762m/2500ft. Considering that the Caravan has a stall speed of 60 knots, and for a safety margin, you would approach at 70 knots, this makes sense. Assuming that it slows at a rate of around 1 knot/ 10m, You can do some basic calculations: 70/1, which is 70, resulting in a 700m long runway, plus 62m for a safety margin.

EDIT: But now we're talking about amphibious, so water could help the plane slow down, but at the same time a longer takeoff roll would be required. And it turned out that the website I used wasn't reliable. Sorry about that. Anyways, it is said that an amphibious Cessna Caravan needs a takeoff roll of 2,341 feet/714m. However, the actual requirements force a 3660ft/1116m runway. I didn't get the landing distance required, but I think it's safe to say that the landing would be shorter than the takeoff roll.

*the actual runway length required of a normal caravan is 2,055 feet/ 626m, and you can expect to rotate at 1,160 ft/ 354m.

*Some (incorrect) information was from: http://www.sgl.com/208.html
And more correct info from: https://cessna.txtav.com/en/turboprop/caravan

Please tell me if I should delete the first paragraph.


What are the rules for flying drones in National Recreation Areas?

The operation of UAS in these areas is regulated by the National Park Service, but, according to a 2014 memorandum, this authority has been delegated to the individual parks themselves.  You would have to check with the park itself.  Further information is available in an NPS article on the topic and in the NPS rules and regulations section.

For an example on the state level, the Pennsylvania Dept of Conservation and Natural Resources has designated flying sites in six flying sites at a selected number of state parks.  If I go to the website for the Allegheny Portage Railroad (a park managed by the NPS), they have a specific statement on UAS usage in their policy compendium.

Boats and such...that I'm less sure of.


What are the dimensions of the protected space provided by a holding pattern?

The exact answer to your question is found in a 500 page document titled "United States Standard for Terminal Instrument Procedures (TERPS)" that was revised and issued as Order 8260.3C on 03/14/2016. This is the answer to the part of your question about "where does the FAA define this."
As mentioned, the FAA uses templates. There used to be 31 templates of various sizes that are identified by pattern numbers 1 through 31. However, Patterns 1-3 are no longer in use. So there are now only 28 in use. Originally, these templates were literally plastic transparent templates. Now, most holding patterns are constructed using automation (i.e. computers). The following figure shows the exact proportions and geometry of every one of the 28 holding patterns in use today.

Point "L" (little orange circle) is the holding fix. This is a standard right hand holding pattern, (left hand holding patterns were drawn by flipping the plastic pattern over for a symmetrical left-handed pattern). The solid black line that runs from point "M" to point "L" is the holding course. All the straight line segments are defined by the definition of the respective Pattern Number as provided in the following chart.

Take a look at the dimensions of Pattern Number 4 on the chart above. Pattern 4 is the smallest holding pattern in use today. Specifically, see that the column M-E says 5.3 nautical Miles, and that column L-I/M-H reads 3.5 nautical Miles. Now look at the template in the figure above and find the line M-E. This is the protected distance from the holding course on the Holding Side of the pattern. Now, find the lines L-I and M-H. These represent the protected distance from the holding course on the Non-Holding side of the pattern. This is the answer to the part of your question about "what are the dimensions of the holding patterns and how does the FAA define it."
RANT:
Now my rant. I often hear pilots and even flight instructors talk about the "Protected Side" and the "Non-Protected Side" of the holding pattern. This is inaccurate. The FAA does not describe holding patterns in that way. There is either a Holding Side or a Non-Holding Side. BOTH sides are protected! Pattern #4, the smallest pattern in use in the USA, has 3.5 nautical miles of protection on the Non-Holding side. I plugged in all of the values in the chart above into Excel and calculated the ratio of Non-Holding Side protected area to Holding Side protected area, and all of the patterns had a protected area on the Non-Holding Side equal to approximately 2/3 or 67% of the Holding Side. That may not be as much protection as on the holding side, but it translates into multiple miles of protection.
Next time someone says Non-Protected Side of a holding pattern, take the time to explain to them that both sides are protected. Protection on the Non-Holding Side is necessary to protect aircraft entering a holding pattern using a parallel entry with a cross-wind that is pushing them away from the inbound course into the Non-Holding side during that initial 1 minute outbound entry.
End of RANT


It really depends on the aircraft. Some have plenty of rudder authority and sideslip very well, others are better at stall onset with still plenty of elevator and aileron authority.

Now first to the term "mushing glide": This happens at very low speed when the airplane flies far at the backside of its envelope. Flow on the inner wing is already partly separated which causes the high drag. The nose is up because of the extreme angle of attack and the stick is pulled back close to its rear stop.

Not every airplane will be pleasant to fly: Some will show abrupt stalling and cannot be held in this mushing glide. Others have less stall margin between inner and outer wing and the pilot risks an inadvertent roll when the outer wing has an airfoil with poor stall characteristics (think 5-digit NACA series) and one side stalls first.

But there are also many airplanes which can be held easily in this attitude and with responsive ailerons and elevator, too. Those are the ones which lend themselves to a mushing glide. I would only fly this after extensive stall testing at altitude, calm winds and when I know exactly how the airplane reacts to control inputs.

On the other hand, if there is plenty of rudder authority to achieve a substantial sideslip angle in a sideslip, I would't think twice and pick this approach. Ending it is possible with little to none altitude loss whereas a mushing glide needs to be ended at enough altitude to pick up some speed for the flare. Visibility is better and the risk of stalling a lot smaller.


Why do we calculate the pitching moment coefficient about quarter chord point?

Because the quarter chord point is the most meaningful point: the wing or surface lift vector can be found here. Like taking the CoG as reference point for gravity forces.

Theoretical and practical analysis have shown that if the moment and force reference point is taken at 25% of Mean Aerodynamic Cord (MAC), the magnitude of the aerodynamic moment remains nearly constant when the angle of attack changes. This location is called the wing's Aerodynamic Centre (AC).

The lift and moment system can be transferred to any convenient point, but that is the point of the quarter chord point :)


Are all student pilots required to have a TSA background check or just non-US Citizens?

This page on the FAA website has details on getting your student pilot certificate.

• Resident and US citizen student pilots follow Student Pilot’s
Certificate Requirements.
• Foreign student pilots (non-resident) follow the Alien Flight Student Program

It appears from your question that you should follow the same procedure as US citizens.
Refer to AC 61-141. Everyone must get a TSA screening before being issued a Student Pilot Certificate.

6.3 The Flight Instructor Verifies the Applicant’s Government-Issued Photo ID.
The flight instructor verifies the applicant’s identity and
enters information from the applicant’s ID. If the applicant cannot
present acceptable ID, discontinue the application process. Verify
that the applicant has entered a correct date of birth. IACRA will not
process an application unless the applicant is within 90 calendar-days
of his or her 14th birthday or older. If the applicant is not of
sufficient age, discontinue the application.
7.8 TSA Security Vetting and Temporary Certificate Availability of the Paper Method.
Provided the applicant is not deemed a security
risk and is at least 14 years of age, the Airmen Certification Branch
issues a permanent Student Pilot Certificate and mails it to the
applicant. Applicants must also wait to receive a permanent plastic
certificate in the mail.


A carrier aircraft launcher is called a "catapult", for good reason! It's job is to get an aircraft up to flying speed very quickly, which of course results in a very high acceleration for the plane and pilot. Sometimes as high as 4G.
On modern American aircraft carriers, the catapult is about 300 feet (90 metres) long, and can get a large plane up to flying speed, 140 knots, in about 2 seconds. By comparison, taking off on a conventional runway a plane might need 2 kilometres to get up to this speed.
As you can imagine this puts a lot of stress on the planes, carrier aircraft are built much more rugged than an aircraft that would only fly off normal runways.
Each catapult-launched aircraft has different procedures for launch. In the case of the F/A-18, the pilot keeps his hands off the control column during the actual launch, grabbing it as soon as the plane leaves the edge of the deck. This is not the case for other carrier aircraft, such as the C-2 Greyhound, nor is it the case when taking off the same aircraft from a runway.
I found this in the F/A-18E/F flight manual (PDF here):

Immediately after the end of the catapult stroke, the aircraft will rotate to capture the
12° reference AOA (hands-off). To avoid PIO with the FCS, do not restrain the stick during catapult
launch or make stick inputs immediately after catapult launch. The pilot should attempt to remain
out of the loop but should closely monitor the catapult sequence.

AOA = Angle of Attack, PIO = Pilot-induced oscillations, FCS = Flight Control System.
Which roughly translates as "The F-18 will fly itself and find the optimal climb angle without pilot input during the launch."  This is not the case though for other aircraft.


What are advantages and disadvantages of flaperons?

The main downside of flaperons is you can't lower them as much as a regular flap because it has to still do its aileron function when "flaps down".  This means the downgoing flaperon has to be limited to its "lift generation" range when the flaperon mixer is moving it to full down flap plus full down aileron, and can't exploit the "drag generation" range of a normal flap because the resulting adverse yaw is extreme and the roll rate drops.

At the same time, the inboard end of the flaperon contributes marginally to roll control, the roll arm being short.  And you are also limited to the use of differential aileron gearing as an adverse yaw reducer due to the need to keep the flap function reasonably symmetrical.

You end up with a flap with limited extension and therefore limited utility as a flap, and an aileron who's inboard end doesn't do much for roll control.  These issues limit their potential effectiveness to being marginally better than a well sized regular flap and aileron.

The principal advantage is you can get a lower overall stall speed because the early high lift range of flap travel is available across the entire span, and you have a much simplified control system since you are combining aileron and flap on one linkage, with some form of mechanical mixing device in the fuselage.

So, like so many things in aviation, they may seem like an ideal solution and have their place, but the limitations and disadvantages are significant enough that a majority of designers prefer to go with the separate flap/aileron.


What's the minimum legal height in Europe for a low pass at an airport?

Official Record Series 4 No 1174 General Permissions
Standardised European Rules of the Air – Exceptions to the Minimum Height Requirements
1) Definition
In these permissions:
a) ‘SERA’ means the Annex to Commission Implementing Regulation (EU) No. 923/2012 (‘the Standardised European Rules of the Air’ (and references to SERA followed by a number mean the corresponding provision of SERA)).
b) ‘licensed aerodrome’ means an aerodrome licensed under the Air Navigation Order 2009 or an aerodrome certificated under Commission Regulation (EU) No.139/2014 of 12 February 2014 and
c) ‘Government aerodrome’ means any aerodrome in the United Kingdom which is in the occupation of any Government Department or visiting force (as defined in article 255(1) of the Air Navigation Order 2009).
d) ‘notified’ has the same meaning as in article 255(1) of the Air Navigation Order 2009.
2) General (SERA.5005(f)(2))
a) The Civil Aviation Authority (CAA) permits, under SERA.3105 and SERA.5005(f), subject to the condition set out in subparagraph (b), an aircraft to fly elsewhere than as specified in SERA.5005(f)(1) at a height of:
i) less than 150 metres (500 feet) above the ground or water; or
ii) less than 150 metres (500) above the highest obstacle within a radius of 150 metres (500 feet) from
the aircraft.
b) The aircraft must not be flown closer than 150 metres (500 feet) to any person, vessel, vehicle or structure except with the permission of the CAA.
3) Approaches to Landing or Forced Landings
The Civil Aviation Authority permits, under SERA.3105, SERA.5005(f) and SERA.5015(b), an aircraft to fly below the heights specified in SERA.5005(f) and SERA.5015(b) if it is flying in accordance with normal aviation practice and:
a) practising approaches to land at or checking navigational aids or procedures at an aerodrome;
b) practising approaches to forced landings other than at an aerodrome if it is not flown closer than 150 metres (500 feet) to any person, vessel, vehicle or structure; or
c) flying in accordance with a notified procedure or when specifically authorised by the CAA in accordance with SERA.5015


Does an amended shortcut clearance change the clearance limit?

I assume that this question is about the US, based on your examples.

No, it doesn't change the clearance limit. For some reason I could only find the documentation in the ATC orders, not the AIM. Section 4-2-5 of the orders says:

  Issue a clearance “direct” to a point on the previously issued route.

  PHRASEOLOGY−
  CLEARED DIRECT (fix,waypoint).
  Or
  CLEARED DIRECT (destination) AIRPORT.

  NOTE− Clearances authorizing “direct” to a
  point on a previously issued route do not require the phrase “rest of
  route unchanged.” However, it must be understood where the previously
  cleared route is resumed. When necessary, “rest of route unchanged”
  may be used to clarify routing.

If the clearance limit changes, the controller will usually give you a completely new clearance to copy.


What is the typical voltage used on jet airliners?

You'll see all kinds of power on large aircraft - 28 VDC, 115 VAC 60 Hz (and likely 230 VAC 50 Hz), 115 VAC 400 Hz, 5 VDC (USB power in cockpic/pax seats), 230 VAC, and 270 VDC.

Here's a general idea of what the Boeing 787 Power Distribution System consists of:

(Source)


What PPL routes are available with gliding experience?

I have a partial answer after more research and some help on pprune.

A Bronze + XC can be used to get a gliding licence, which under the transitional arrangements can be used to obtain a LAPL(S).

In theory the route from there to a LAPL(S)+TMG  and on to a LAPL(A) TMG is feasible, however the BGA is not an ATO yet and there are very few instructors or examiners around.  This route may be problematic at the moment, but should become easier as time goes on.  There's no reason not to claim the LAPL(A) on the way to a PPL(A) if taking this route.

An alternative route is via an NPPL under the transitional arrangements.  After gaining the gliding certificate, a minimum of 10 hours under instruction is needed until reaching the standard for an NPPL SMLG.  After short conversion training, this can then be converted to an NPPL SSEA.  After 6 hours PIC this lot in turn can be traded in for a LAPL(A) SEP+TMG.  Complicated, but overall less hours and my much can be done at a BGA club with a motorglider and instructor.

Regarding the straight PPL(A) route with credit, given the statement

  If you hold a pilot’s licence for another type of aircraft, except
  balloons, you will be credited with 10% of your total flight time as
  PIC up to a maximum of 10 hours

it would seem clear that at that some form of licence is needed, and given the gliding licence qualifies for a LAPL(S) anyway, which one is moot.


Why do some helicopters have such complicated flight control mixers?

Flight dynamics of a helicopter are complicated indeed. Just to illustrate, consider a helicopter in a stable hover, with the pilot holding the collective, cyclic and pedals in the position that maintains attitude, altitude and heading.

They now want to gain altitude only, in a climbing hover. The sequence of events:

Pilot pulls on the collective, all rotor blades increase angle of attack and the rotor creates more lift. The helicopter climbs.
But because the AoA of the blades have changed, the engine must apply more torque to the rotor and the heading starts to change. So the pilot must apply pedal to change tail rotor thrust and compensate for the torque.
The increased thrust of the tail rotor causes lateral drift. So the pilot needs to input lateral cyclic in order to compensate.

To gain a pure vertical climb, the pilot needs to carry out simultaneous deflections of three flight controls! This collective-to-yaw and collective-to-lateral coupling not only occurs in the hover, but also in forward flight. When increasing speed, the pilot needs to:

deflect cyclic pitch forward;
increase collective for the additional required power;
deflect the pedal for the increase in rotor thrust - but at speed, the vertical fin and the tail rotor take over most or all of this;
deflect the cyclic to the side to compensate for the increased tail rotor thrust, or for the sideslip from the vertical tail stabilisation.

For small, simple and low cost helicopters, this is indeed the way they are flown. But for larger helicopters with a mission, some of the cross couplings are taken care of by the mechanical mixer: when increasing collective, a mechanical link automatically increases the inputs for the cross couplings. It does so in series with the flight controls, which do not move and retain their former selected position.

The drawing in the OP is of at the S-76, a medium sized helicopter, and we can find the following:

Collective/Roll mixer (lateral lead). Provides automatic rotor sideways deflection as a function of collective stick deflection.
Pitch bias actuator. Extends as a function of airspeed, so that the cyclic pitch stays near centre, for more comfort at high speed.
An unlabelled connection rod between collective and pedals.
Collective/Pitch mixer. This helicopter will start to pick up speed when collective is deflected, for a straight-up vertical speed, the pilot will need to deflect the stick backwards.

Also in the OP drawing: optional AFCS servos, which reduce control forces and provide the static stability that helicopter aerodynamics do not provide. Plus trim actuators, which change the neutral position of the feel springs or completely eliminates feel forces. And a yaw damper.

Very complicated indeed.


Did Airbus add an audible alert when the autopilot partially disengage after the crash of Aeroflot Flight 593?

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

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


May an airline replace an airliner's engines without the aircraft manufacturer's involvement?

If the airline owns their airplanes outright, then they don't need permission per-se from the manufacturer, but the new engine would have to be approved by the manufacturer for that type of plane. So the airline couldn't just pick some type of jet engine & decide that they're going to figure out how to mate it to their jets; if that combination hasn't already been tested & proven by the manufacturer, it would void the manufacturer's certifications and render the aircraft un-airworthy. So nobody goes that route.

On the other hand, if the airline leases their jets, they can only do what the owner approves.


What's with this non-exit Exit sign on Delta CRJs?

Normally there is some kind of barrier, a bulkhead or curtain, separating the business class and the common folk in steerage.  In such a case the sign is to indicate that there is an exit somewhere down yonder beyond the bulkhead.

In this case the curtain is not there so the sign kind of hangs there with its nonsensical implication that maybe there is an exit right next to it.  I'll go out on a limb and guess that the regs require the sign to be there between the two classes regardless of whether a visual divider is in place.


Do I need to be 'current' or hold a medical to become a Basic Ground Instructor?

You do not need a medical certificate.  It also does not matter that you have not flown in a long time.  You will need to study and take two separate tests to get you ground instructor certificate.

Fundamentals of Instruction (FOI) Test
Ground Instructor Test

The FOI information is covered extensively in the Aviation Instructor Handbook and is 50 questions (at least it once was).
The Flight Instructor test question bank is also used for the BGI (Basic Ground Instructor) and AGI (Advanced Ground Instructor) tests.  If I remember correctly, the BGI test is 80 questions and the AGI test is 100 questions.  The information on the test is covered in multiple FAA handbooks (not all inclusive):

Pilots Handbook of Aeronautical Knowledge
Airplane Flying Handbook
Rotorcraft Flying Handbook
Balloon Flying Handbook
Aviation Weather Services

One thing to notice is that the ground instructor test covers all aircraft and not just the "airplane category" as you can teach and sign off written tests for all aircraft.  Since the BGI and the AGI are the same test, I would suggest getting an AGI as you will be able to sign off all written tests and not just tests for sport, recreational or private pilots.


How do I know when to use flaps in glide approach or force landing?

This is not so much for normal power-on approaches, but the proper way to manage a forced landing approach is to use some way other than flaps to vary your sink rate as required.  Gliders do it with spoilers, which allows the glider's descent angle to be varied between maximum glide and nearly straight down at any time, which is why the one-shot landing aspect of gliders is really not such a big deal; it's easy to place it anywhere you want.

With power planes you use a forward slip as your variable drag tool.  As you are getting in close, a few hundred feet, you drop just takeoff flap to lower the stall speed and apply some forward slip, ideally roughly half of the maximum you can apply, to be about what seems to give you the correct descent path.

It's as if you had some power.  If you are overshooting, increase the slip angle to descend steeper like you were reducing power, if undershooting, decrease the slip to descend less steep like you were increasing power (a little bit).

Don't drop landing flap until you are down to the last hundred feet or so when making the field is assured.  Just about all aircraft can be slipped, but some may be restricted from slipping with full flap.

If you use and practice this method you will get good at placing the airplane precisely into a forced landing spot without power, and a forced approach will lose its terror as long as there is an open place to land.  I'd be disappointed with an instructor who wasn't teaching slipping to control descent rate in a power off emergency.


How the fuel in the wings is managed in case of an engine failure?

That’s a pretty broad topic and depends on the aircraft in question and the fuel systems which it uses.

Large airplanes like jetliners have complex fuel management systems which feed fuel from the main tanks into feeder tanks which the engines can “drink” from.  The process is automated in modern aircraft - around the same time that the Flight Engineer went the way of the dinosaur - so little, if any, input from the crew is required in the process.

On smaller twins, say, for example, a Cessna 310, fuel is provided to the engines via a dedicated main fuel tank and optional aux tanks for each engine.  In the event of an engine failure, the pilot can select the ability to cross feed the good engine on the fuel system for the bad engine in order to prevent a fuel imbalance.


To start: I flew gliders for 8 years at a field on the northern edge of KPHL's mode C veil and never saw a towplane (purposely) drop a rope for a non-emergency.  We operated out of a grass field surrounded by trees on most sides (maybe 10 miles south of KCKZ) and never had problems with towplanes landing with the rope attached.
There are some factors here that feed into this.  That particular field (http://www.pgcsoaring.com/) has generally well taken care of and is a completely turf field.  I think we added some lime markings to denote a landing box on our usual landing runway, but that's about it.  I have a picture of the runways used for normal operations below.  Takeoffs were started on the far right on runway 25 (picture has been rotated), and landings, typically, were facilitated on the runway marked by a dashed line.

Now, something that isn't quite clear from the overhead views are the trees.  At the far right hand side of 07-25, you have a stand of trees (and two hangers) that go up 40-50 feet.  Landing over these, particularly with a tow line, can put you out in the boonies if you want to make sure that the tow line isn't dragging through the trees.  The FAA Glider Flying Handbook (https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/glider_handbook/media/gfh_ch12.pdf) indicates that a 200 ft tow rope can "fly" about 130 ft below a towplane, so clearance in that dimension is critical.  The pictured field actually has 3 operating runways (07-25, 01-19, and 13-31) and, on the approach to each (save 25), there are no trees near the runway threshold or the runway is situated at the top of a significant hill.
Insofar as ground abrasion goes, I'd see wear and tear on a towline over time, but it was relatively slow accumulation.  Slow enough that you could track it by rope checks at the weak link (if in use) and tow hook prior to each flight...which you are probably doing anyhow.  We always had a spare rope spliced and on a reel so that an in-use line could be quickly replaced during normal operations (maybe a minute or less during a regular takeoff if it was coordinated well).  But that's more or less semantics: the point is, for the turf field we had, which was well-cleared of rocks, branches, or man-made debris, there were no problems with dragging a rope over the ground provided that pilots and line crew were doing the routine safety checks that they would be doing regardless.  Not dropping a tow line also kept down non-airplane vehicle traffic on the field during operations (i.e., it eliminated the need for another runner to get the tow line, especially when aircraft are anticipated to be landing).
The Glider Flying Handbook has this much more to say about landing with a tow rope (GFH 12-10):

Landing with the tow line attached is not prohibited by
regulation; however, the following points should be considered:

Obstructions are cleared by more than the tow line
length (altimeter lag considered).

The field is well turfed. It is simply inviting early
tow line failure from abrasion to land with the tow
line on hard ground or paved runways. Landing with
the tow line should never be attempted unless the
field has clear approaches and is at least 2,500 feet
in length.

Other situations require the tow line to be dropped, normally
in the glider launch area, during short approach to the
runway. If the tow line is to be dropped, the tow pilot must
be constantly aware of the launch area situation. The tow
line drop area must be defined and ground personnel must be
briefed and aware of the drop area. Ground personnel must
stay clear of the drop area, and the presence of an individual
in the drop area requires an immediate go-around by the pilot
of the tow plane without dropping the tow line.


Why should the leading edge be blunt on low-speed, subsonic airfoils?

When using an airfoil with a sharp leading edge in subsonic regime, you need to adapt the angle of attack so that the stagnation point occurs right on the sharp edge.

At every flight condition there should be an AoA which achieves this. Higher AoA, and the stagnation point is too low. To low AoA, and the stagnation point is too high. However flight conditions change frequently, so the required AoA changes dynamically as well. Since AoA also drives the lift and lift is the priority in a pilot's mind (he wants to keep flying after all), stagnation point will only occasionally match the leading edge.

During flight the AoA will often fail to match the stagnation point, let's say with too high AoA, separation would occur below the leading edge (on the "intrados").  This is the only good illustration I could find:

The stagnation point is at the tip of the only grey line that stops right on the black plate.
Basically all incoming flow between these leading edge and stagnation point  (unfortunately no line shows this on the picture) will follow this trajectory:

Incoming at high speed onto the airfoil, below leading edge, going towards the stagnation point, but aims just slightly higher up.
The stagnation point is the point of highest pressure, so the incoming flow slows down
Comes a point where the slowdown is sufficient to actually reverse the flow which now shoots up along the surface towards the leading edge, now driven by the pressure from stagnation point
Arriving at the leading edge from below the flow needs to do a U-turn around the leading edge to keep following the wing shape and flow towards the "extrados" and keep on with its life.

Therein lies the problem: when finally arriving at the leading edge, the air has non-zero speed (zero speed only occurs at stagnation point, of which there is only one), but must instantly reverse it. Physics says nope, and you get a large leading edge vortex to smooth the motion out. Unfortunately that is also called a flow separation bubble, which may became a stall.

This is:

bad for performance (drag)
bad for safety (stallable)
bad for comfort (vibration from the eddies)
bad for structure (vibration fatigue)

Why does it only happen in subsonic flight?

At supersonic speeds, information cannot travel back on the flow using the same pressure gradient trick, once the air is on the intrados/extrados, it stays there, and cannot back up the other way. So no 'adaptation' is possible, regardless of AoA.

Why use rounded leading edge to remedy this in subsonic?

With a rounded edge, the U-turn is not so sharp, it is actually manageable for the air. This means you'll not always have flow separation, so you're safe. The rounder, the easier larger the range of AoA stay "adapted". This animated gif shows really well how the stagnation point can move around the rounded tip thus avoiding separation:

Source: UNIVERSITY OF GENOA
FACULTY OF ENGINEERING
DEPARTMENT OF ENVIRONMENTAL ENGINEERING
IRROTATIONAL PLANE FLOWS OF AN INVISCID FLUID

TL;DR It's possible to fly subsonic with sharp leading edge, but less safe and lower performance. The key is AoA adaptation.


What is the procedure to fill/send/approve a flight plan to the ATS network from outside?

Using EUROCONTROLs „business-to-business web services“ you can file and manage flight Plans (including IFPS validation) as well as check details about the filed flights e.g. departure and arrival messages or where the aircraft is currently.

After a registration (you have to proof you are eligible to use the service) you do not need any ATFM connection at all - you implement the API features of B2B services into your app and that‘s it.

For more details and the conditions check: https://www.eurocontrol.int/service/network-manager-business-business-b2b-web-services


Is a Cessna 172S still airworthy if factory-installed instrumentation not required for day VFR flight is inoperative?

Part 91 does not require an EGT probe for any operations so the next thing to look at is your AFM.

Your C172S has an AFM that includes a Comprehensive Equipment List. It is probably similar to this one that indicates that the EGT probe is standard equipment—not required for certification, this airplane can fly with it placarded.


In order for a spin to develop, you need two things from the airplane:

it must be stalled
it must be yawing.

Since the airplane is not yawing while in a slip (it is actually flying straight ahead, although uncoordinated), the airplane simply won't spin.  Instead, when the stall occurs the higher wing (which has the higher angle of attack) will stall first, the wing will drop, and the wings will tend level.

That being said, it is still a stall and can be dangerous at low altitudes.  It can also turn into a spin if you leave the rudder applied as the wings level and you come out of the slip (and into a skid).

The best protection for all of this is to watch your airspeed and angle of attack to make sure that you always have sufficient airspeed so that you never stall in the first place.

Additional Information

Since this has generated some debate, here is additional information:

Spin

According to Wikipedia (emphasis added by me):

  Spins can be entered intentionally or unintentionally, from any flight
  attitude and from practically any airspeed—all that is required is
  sufficient yaw rate while an aircraft is stalled.

Yaw

So this brings us to Yaw - Wikipedia:

  The yaw axis is defined to be perpendicular to the body of the wings
  with its origin at the center of gravity and directed towards the
  bottom of the aircraft. A yaw motion is a movement of the nose of the
  aircraft from side to side.

Skid

Skid - Wikipedia actually covers this exact scenario:

  The skid is more dangerous than the slip if the airplane is close to a
  stall. In the slip, the raised wing — the left one if the airplane is
  turning to the right — will stall before the lowered one, and the
  airplane will reduce the bank angle, which prevents the stall. In the
  skid, the lowered wing will stall before the raised one, and the
  airplane will tighten the turn, and the stall can develop to a spin.

Slip

Slip - Wikipedia says:

  A slip is an aerodynamic state where an aircraft is moving somewhat
  sideways as well as forward relative to the oncoming airflow or
  relative wind. In other words, for a conventional aircraft, the nose
  will be pointing in the opposite direction to the bank of the wing(s).
  The aircraft is not in coordinated flight and therefore is flying
  inefficiently.

Note that the aircraft is moving sideways.  The nose of the aircraft is not moving, and it is therefore not yawing.  It also says:

  Often, if an airplane in a slip is made to stall, it displays very
  little of the yawing tendency that causes a skidding stall to develop
  into a spin. A stalling airplane in a slip may do little more than
  tend to roll into a wings level attitude. In fact, in some airplanes
  stall characteristics may even be improved.


How to determine the RPM of the rotating shaft of an A320 PTU?

If you are not allowed to attach the measuring device to it, the two unobtrusive methods are by sound or by video.
Measuring by video would require the device to be visible, have some surface features to determine some particular rotation and the possibility to make probably video recording while in operation. The recorded video can be split into individual frames in the simplest case just estimating the rotation visually, as the time interval between the frames would be known. Otherwise, tools like OpenCV or fast.ai may help to analyse the images automatically. But these methods are limited by the number of frames per second you can capture. Most of the cameras would only do 30 frames per second or about but much faster cameras are available if you look on purpose. But the method can also capture slow or irregular movements.
Another approach is by sound - record the sound and plot the windowed spectrogram of recording. This can be done with less access possible, and work with higher frequencies, as long as the rotation sound is loud enough. Of course it will be a strong band from the engines on the spectrogram but it may fall far outside the reasonable frequency range of this "barking dog".


When are aircraft required to dump fuel for emergency landings?

For many medium and large sized jets the maximum gross takeoff weight is higher than the maximum landing weight.  If the airplane has an emergency that requires an air return or other landing in the early part of flight, it is very likely overweight for landing.  The plane has 3 options at this point:

Land overweight
Dump fuel (if able)
Fly around at low altitude and high power to burn fuel

For some airplanes, option 2 is not available.  This includes airplanes that are not equipped to dump fuel (not all airplanes have this capability or have the capability under MEL) or are not approved to dump fuel at their current location and altitude.  For these airplanes, only option 1 and 3 are available.

The choice between option 1 and 2/3 comes down to what kind of emergency it is.  If you have to be on the ground now, you won't care about being overweight, and will just put it down.  If you have time and landing now isn't a priority, then you would choose to dump or burn fuel.

If an airplane chooses to dump, they will generally choose one of two values of remaining fuel:

fuel such that they land at the maximum landing weight
absolute minimum safe fuel to land

This choice comes down to how likely the landing will end in an accident.  If you are sure the landing will be a non-event (e.g. air return for anti-ice failure) then you'll likely just dump until landing wont be overweight.  Conversely, if you have a control issue or something that may end badly, you want minimum fuel to lessen the potential for fire.  In these cases the ARFF crew will spray the runway with foam to assist in reducing the fire potential.


Are General Aviation tires filled with Nitrogen?

Although I can’t speak for every GA pilot, the aircraft that I have flown have had their tires inflated from an ordinary air compressor. We have used handheld battery operated compressors, floor standing compressors, small-tank mobile compressors, and hand carried compressed air storage tanks.
The max speed that we actually use the tires is under 100 mph. The max weight that we carry on them is under 6000 pounds.


What are the checklist items for a runaway stab trim on a B737 MAX 8 and MAX 9?

Here is a screenshot of a B737 Max 8 Runaway Stabilizer Checklist.  There might be some small variations in the checklist when comparing each individual airline.

Additionally, here is the Boeing "Uncommanded Nose Down Stabilizer Trim" bulletin that was issued to all B737 Max 8 operators after the Lion Air crash.


Are control inputs different during autorotation?

Yes and yes.

A certification requirement of helicopters with powered controls is that they have a manual reversion so that control can be maintained in the event of a power failure.  However, the controls can be really heavy with no power and accidents have occurred when hydraulics have failed at critical moments or pilots have lifted off with hydraulics off and have been caught by suprise with the effort needed to maintain control.

The control inputs during autorotation are the same.  For any given glide, or flare, the lift required is the same powered or unpowered.  Lift is proportional to the speed of the blades, which is independent of powered or unpowered, and the angle of attack.

During autorotation, the energy (power) going into the rotors is derived from the airflow coming up through the disc. In this sense, an autorotation is still powered but the power comes from the airflow rather than the engine.

During autorotation, since the airflow is from below, rather than above, the pitch required is lower for the same angle of attack to generate the same amount of lift.  So, the swashplate is lower in autorotation but lowering collective still decreases lift and raising it increases lift.  The primary difference is that rather than controlling lift and power, the collective controls rotor speed since increasing pitch increases the angle of attack which increases lift and therefore increases drag, slowing down the rotor.  Lowering the collective has the opposite affect.

The cyclic control is the same in all respects (you tilt the rotor thrust in the direction you want to go) since it increases, or decreases the pitch, and therefore the angle of attack, cyclically.  The movement of the swashplate about the X and Y axis is independent of the position of the swashplate in the Z axis.

The pedals work in the same way too.

In summary, the only difference in the controls is the vertical position of the swashplate.


What are the disadvantages of a twin boom aircraft?

The main disadvantage is flutter. The booms add a mass behind the axis of elasticity which will twist the wing when it bends. This twisting will increase the local angle of attack when the wing bends upwards and increases the bending moment, and vice versa on downward deflection. Once the plane flies fast enough, flutter is hard to avoid. The main remedy is to make the inner wing stiffer in bending and torsion, so the flutter frequency is shifted outside of the flight envelope. This costs weight, though.


What are the reasons for the end of the dogfight era?

Primarily this was driven by the invention of the guided missile which can be deployed far outside the range of bullets (making them a standoff weapon) and which can actively track the target autonomously ("shoot and forget").
With these two features, it no longer became necessary to maneuver close enough to another plane to shoot it down with bullets and to accurately track the target aircraft with one's own aircraft while doing so- which made WWI and WWII dogfighting skills unnecessary.


You might have heard of the elliptical lift distribution which minimizes induced drag for a given span and a given lift. Area ruling is similar, but here it is about the lengthwise distribution of cross-sectional areas of a plane, and it minimizes wave drag at Mach 1.

The first picture is from a Junkers patent of 1944: Junkers found out in 1943 that transsonic drag can be minimized by shifting the parts of an airplane around. In this case it was the EF-122, a research project which became the Ju-287. The easiest bodies to shift were the engine nacelles, that is why the end product has such odd engine locations. The drawing shows several shaded cross sections along lines which carry Roman numerals: Plot the sum of all areas along each line over the aircraft's length coordinate, and you get a distribution which must be optimized such that it has the maximum area for the smallest gradients.

The next picture shows how those plots look like. This is from a different source, so it shows generic wing-body combinations. On the left is an airplane with a fuselage shaped like a Sears-Haak body. A Sears-Haak body is an optimum shape for the biggest volume with a given wave drag and was discovered by Wolfgang Haak in 1941 and again by William Sears in 1947. The wings come on top and mess up the area distribution by creating a bump in the middle.

The right plot shows what can be achieved by taking all parts of the airplane into account. The difference is shown in the small center plot.

How this is done: Take away from the fuselage what is added by the wings. The result is a fuselage wich looks like a coke bottle. You can also add Küchenmann bodies; older airliners have plenty of them. Look especially at fuselages like those of the Blackburn Buccaneer, or  T-tails like those of the Illjushin Il-62 or the Tupolev Tu-154. Today, things like engine pylons or flap track fairings are used as Küchemann bodies to smoothen out the lengthwise area distribution, and if you look carefully you will see the coke bottle technique on the fuselage around the horizontal tail of many airliners. They don't fly at Mach 1, but close enough that area ruling makes a difference already.

The dawing below shows the general concept and the magnitude of drag reduction achievable:


If I am transiting a class delta airspace on a VFR flight and am coming up to a class bravo boundary without a bravo clearance, what will happen?

Because you're in Delta space, you are necessarily talking with a Delta controller.They will likely do one of two things:

Either:

give you a vector to keep you clear of Bravo:
N45WTF:  Turn left 40 degrees
coordinate with the Bravo controller, and the Delta controller may give you clearance:
N45WTF:  Climb and maintain 3,500.  Squawk 3462, Cleared into the Bravo, contact Center on 118.9


Why stirring the cyclic helps in stuck left pedal?

The R22 has an anti-clockwise rotor. The more torque the rotor exerts, the higher the clockwise torque on the helicopter will be: nose right. With a stuck left pedal the nose wants to turn left, so we want the rotor to exert more torque.

On pumping the collective: there is an effect of how fast the collective pitch is raised, on the torque exerted. The figure below shows $C_T$ (a dimensionless measure of rotor torque) against time for a full sweep of the collective from full down to full up. Rapid deflection causes a torque overshoot, so a higher torque than a slow deflection.

So if the collective is raised fast and lowered more slowly, a net torque increase is generated while lowering the helicopter. Picture source: Helicopter Performance, Stability and Control by Raymond Prouty

On rotating the cyclic: cyclic pitch deflection causes angle-of-attack variation of the rotor blades, with an associated variation in blade drag, and therefore rotor torque. There is a section on this effect in the book Principles of Rotor Aerodynamics by J. Gordon Leishman (section 8.15.7 Unsteady Axial Force and Airfoil Drag). What I can distill from this chapter is that stirring the collective clockwise creates more airfoil drag, while keeping the net movements fwd/aft and left/right neutral. Unfortunately the section does not contain any helpful diagrams.


Can a company without an AOC hire out pilots to another company that does have one?

The simple answer to your question is "NO".
There are 4 different kinds of part 135 operating certificate, many of which have a limited number of pilot positions. These pilots must be listed on the paperwork for the certificate and must meet all training, experience and currency requirements as specified by the certificate.
On a Single Pilot Operator certificate, the holder is limited to using only one pilot for all part 135 operations. That specific pilot is listed by name and certificate number on the FAA issued Operations Specification (OpSpec) A040. The use of any pilot(s) other than the single pilot listed on OpSpec A040 is not authorized.
On a Single Pilot in Command certificate, the operator is limited to using only one PIC and up to a maximum of 3 Second In Command (SIC) pilots for all part 135 operations. The PIC and the SIC(s) are listed by name and certificate number on the FAA issued OpSpec A039. The certificate holder is only authorized to use those pilots in the specific duty positions listed in OpSpec A039. The certificate holder is not authorized to use any other pilots, nor are any pilots allowed to serve in a duty position (PIC or SIC), unless they are listed in that duty position in OpSpec A039.
On a 135 Basic, the operator is limited to a maximum of 5 pilots which includes SICs, but all 5 pilots may serve as PIC or SIC as required as long as they are all so qualified. However, they must still be listed ok the certificate as above and since this type of certificate requires the establishment of approved manuals and training programs, the pilots must also have completed the necessary training and comply with the standards set forth in all operation manuals.
On a 135 Standard, there is no pre-set limit to the size of the operation, but all pilots must be listed on the certificate as above and comply with all required training and manuals as above.
Basically, an operator can't just bring in a pilot to fill-in for a single mission. If their own pilots or aircraft are not available for the job, then their company is not available for the job. They would need to sub-out or recommend the client to another certificated operator whose plane and pilot(s) are available.


Wake turbulence: crossing under a final approach path VFR

Due to the nature of wake turbulence descending over time and weakening as time goes on, I would say that it's possible that you hit the wake of the 737, and just managed to avoid the A380's wake out of luck. It also depends on the wind direction as to the path of the wake, so it's hard to say in your specific case

Skybrary describes crossing wake turbulence as:

  A cross-track encounter en route is likely to lead to only one or two sharp 'jolts' as the vortices are crossed.

Which leads to me to believe you hit their wake, and not just some other form of turbulence.

In terms of wake avoidance the FAA says in 7.3.7(b).9:

  En route VFR (thousand-foot altitude plus 500 feet). Avoid flight below and behind a large aircraft's path. If a larger aircraft is observed above on the same track (meeting or overtaking) adjust your position laterally, preferably upwind.

And skybrary recommends:

  In the case of crossing tracks, it has been found that the time interval necessary to avoid creating a wake vortex hazard is 3 minutes.

In terms of a direction to cross the vortexes at this section of FAA 7.3.3(b).1 implies that you should do as you did and cross perpendicular to the path - as to avoid strong induced rolls:

  During inflight testing, aircraft intentionally flew directly up trailing vortex cores of larger aircraft. These tests demonstrated that the ability of aircraft to counteract the roll imposed by wake vortex depends primarily on the wingspan and counter-control responsiveness of the encountering aircraft. These tests also demonstrated the difficulty of an aircraft to remain within a wake vortex. The natural tendency is for the circulation to eject aircraft from the vortex.

To summarise those points in terms of enroute wake avoidance, and effect limitation:

Fly above their path
Position yourself upwind away from the wake path
Try to be at least 3 minutes behind the aircraft when crossing the path
And cross perpendicular to the wake path, to avoid inducing a roll

Sources: https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap7_section_3.html
https://www.skybrary.aero/index.php/En-route_Wake_Vortex_Hazard


Do most commercial jets have a negative lifting body?

You are right, the upsweep at the tailcone allows the pilot to rotate the aircraft during take-off and landing without touching the ground with the rear fuselage. When such a tail strike  happens, the aircraft needs to be inspected and repaired, and incorrect repairs after a tail strike have already caused loss of life.

While most Boeing fuselages show some downslope of the upper tailcone contour, this effect is even more pronounced with all Airbus aircraft except the A380. There the upper contour of the tailcone is straight. Military transports with a rear ramp show even more upsweep to keep the heavy ramp short, and most need additional strakes to limit the area of separated flow there at low speed.

This upsweep adds a small downforce and, since it happens away from the c.g., a pitch-up moment. First, at the transition from the cylindrical section to the tailcone you find a strong suction peak at the high curvature region on the lower fuselage. Also, the lower side of the tailcone has a lower pressure than the upper side. Both create the downforce and the pitch-up moment. However, a three-dimensional body of a very low aspect ratio like the fuselage has a very low lift curve slope, so even the strong upsweep creates a small moment when compared to the contribution of the horizontal tail surface.

The local flow at the tail is dominated by the wing wake. To create lift, the wing has to deflect the flow downwards, and this produces a local flow direction at the tailcone which aggravates the situation created by the upsweep. The best indication for the local direction of flow is the rain diverter above the rear fuselage door. See below the rear door of the A320: To create the lowest possible drag, the rain strip is aligned with the local direction of flow during cruise. When flying at lower speed, the downwash is even stronger.

A320 rear fuselage (own work, based on this source)


What are the unique sounds emitted by Embraer E190-E2 on final?

This was answered by an pilot acquaintance of mine:
The most recent generation of engines on the E2 comes with a geared turbofan. In the final stages of descent, the engines rotate at speeds which causes resonance in the combustion chamber. The distinct sound is that vibration.
This sound can also be heard when departing the gate, when the engine experiences similar rotational speeds.
Mitigation of this requires a redesign of the combustion chamber.


Why did the Flightaware groundspeed readout suddenly spike for this flight?

Looking into one set of data from the the popular Flightradar24 service it is not visible.
I think I found the data you're looking at. Since the heading also suddenly changed to (exactly) 360, I'm thinking this is just an invalid data point. Notice that the receiving station jumped between these measurements and something could have happened with the processing in between.
From the same site:

Aircraft with an ADS-B transponder broadcast their identification and this three dimensional position (latitude, longitude, altitude)

This simply implies that this service tries to interpolate the speed from the time between two positions. So say that the clock at the receiving station or something is off (for instance, just an idea), it will just screw up the reading. It comes with the disclaimer:

I believe I witnessed a traffic conflict, altitude deviation, or some other anomaly. Should I report it?
Please don't. Rather, read the terms of use and understand that this data is for casual observation only and not for any operational purpose. FlightAware technology was not designed with the intent to observe safety or regulation anomalies, so please do not try to use it for that purpose.