Is a golf ball surface a good idea for wings or fuselage?

Golf ball has dimples on its surface because we want a turbulent boundary layer. Golf ball is a bluff body (i.e. the drag is dominated by pressure drag). Hence, the drag on a sphere is dominated by the separation on the rear face. If we could minimize that, the drag would be reduced.

The following figure shows the variation of drag coeffecient of a sphere with Reynolds number.

Image from wfis.uni.lodz.pl, taken from (Hoerner 1965)

As can be seen, the drag reduces at the critical Reynolds number, which is the point where separation takes place. Because of separation, the wake in the rear of the sphere (or ball) is reduced, which reduces drag. So, if the boundary layer of a sphere can be made turbulent at a lower Reynolds number (by some means), then the drag should also go down at that Reynolds number, as a result of the reduced wake. This can be seen in the following picture, where the flow has been made turbulent using a trip wire.

Flow over a sphere: (a) Reynolds number = 15,000; (b) Reynolds number = 30,000, with trip wire. Image from princeton.edu

That is the purpose of having dimples in a golf ball- to reduce drag by inducing turbulence and delaying separation (this can be achieved by increasing the Reynolds number; but we are limited by the ball speed). The resulting wake is much smaller due to the delayed separation.

In case of a streamlined shape (like aircraft wing), the propotion of pressure drag is small, as can be seen below.

Image from pilotfriend.com

In case of streamlined shapes, the pressure drag is small because the wake is small. The net result is that 'tripping' the boundary layer as in bluff bodies is not a good idea (a laminar flow causes less friction drag than a turbulent one).

The aircrafts do use similiar devices, via the vortex generator, which are used mainly to delay flow separation.


Why are FDRs and CVRs still two separate physical devices?

You probably wouldn't believe the effort needed to certify anything that flies on an aircraft. This is a multi-year process, especially if it is so much security-related as the CVR and FDR. And it needs to be done with all national authorities of your intended customers.

This is a case of good-enough. The advantage from combining both is real, but so small, that nobody so far thought it worthwhile to go through the certification process. And regarding redundancy, transmitting the recorded data to some ground station would be even better than recording twice on the same aircraft. If that would have been installed in MH370, most of the search effort could have been saved.

I expect something to happen with the transmitting of data, and then both devices could conceivably merged into one.


How does a Hawk jet avoid pitching down when its air brake is applied

It did generate a nose down pitch moment, but the tail had enough control authority to deal with it in most cases. Airbrake extension at greater than 450kt produced an unacceptable trim change.

Efforts to increase control authority to counter "phantom dive" caused by tail stall during simultaneous flap and gear extension helped. The solution was to affix a leading edge extension to the tail, but since the tail was all moving it was felt that the structure would not be able to handle the extra load. Instead, the tail LEX was affixed to the fuselage and still gave acceptable results.

A later version, the Goshawk, developed as a military trainer for the US Navy had side mounted airbrakes, though this was done to facilitate the installation of an arrestor hook. This photo shows the LEX just above the side mounted airbrakes.

Hawk mk100 with ventral fins, center airbrake and tail canard LEX.


Why do fighter jets still have guns/cannons?

The idea that missiles will be all a fighter aircraft needs was prevalent in the late Fifties. The McDonnell-Douglas F-4 Phantom II carried initially only missiles, but at the start of the Vietnam war this turned out to be inadequate. The long-range missiles back then were rather unreliable, and in a real conflict things turn out always different than anticipated. As von Clausewitz said, the plan is the first casualty of war.

F-4s frequently found themselves in close-combat situations for which they were inadequately prepared. Even today, a gun gives the pilot a lot more options, and if the situation is unclear, close-up visual inspection before shooting is still vital to avoid politically embarrassing situations.

From the F-4C on, F-4s were equipped with a gun. First in external pods, from the F-4E as an internal gun. What also helped to make the F-4 more effective was better training for pilots and ground crew, so the missiles were in better shape and better applied.


Does too big an angle of decalage make the horizontal stabilizer to stall?

Declage controls the AOA to which the static stability forces will be focused with no control input; in other words, the hand's free AOA/speed.  A higher declage angle is the same as increasing elevator input and holding it there.
It changes the trim force balance (nose down pitching moment from the main wing, C of G relative to wing center of pressure, and other appendages that generate pitching moments, opposed by the nose up pitching moment from the tail) to occur at a higher AOA.  Airplanes with moveable horizontal stabilizers, like most jets and a lot of light planes like the Cessna 180/185 family, have what is in effect, adjustable declage as their method of changing trim.  What you are doing by sticking the tail surface in the different slot, they achieve by cranking a screw jack to move the front of the same surface up and down for the same result.
So the tail won't stall at the moderate angle variation there, it'll just drive the main wing to a higher AOA to achieve trim equilibrium, and your glider will trim to a slower speed. If designed properly, if you keep increasing the declage, the main wing will be driven to its stalling AOA, and the aft Center of Pressure shift that occurs at stall will cause the nose down pitching moment to overpower the tail's downward lifting force and the glider pitches over before the tail's airfoil itself stalls.
The result is, when you throw it with the tail stuck in the upper slot, it will pitch up harder for the same throwing velocity as it seeks its higher trim AOA/lower flying speed (if you throw it at exactly its trim speed, it's already in trim when you release it and will just glide straight without pitching).
So bottom line; the lower slot is a "fast slot" and the upper slot is a "slow slot".  The glider will trim to a lower AOA and a higher speed on the lower slot, and vice versa on the slow slot.  That's the practical result of the two options.


Is it true that cockpit doors are bulletproof?

For all air transport operating under 14 CFR 121, 121.313(f) requires a door to be installed between passenger compartment and cockpit.
14 CFR 25.795(a) outlines the relevant design requirements for such a door:

(a) Protection of flightcrew compartment. If a flightdeck door is required by operating rules:
(1) The bulkhead, door, and any other accessible boundary separating the flightcrew compartment from occupied areas must be designed to resist forcible intrusion by unauthorized persons and be capable of withstanding impacts of 300 joules (221.3 foot pounds).
(2) The bulkhead, door, and any other accessible boundary separating the flightcrew compartment from occupied areas must be designed to resist a constant 250 pound (1,113 Newtons) tensile load on accessible handholds, including the doorknob or handle.
(3) The bulkhead, door, and any other boundary separating the flightcrew compartment from any occupied areas must be designed to resist penetration by small arms fire and fragmentation devices to a level equivalent to level IIIa of the National Institute of Justice (NIJ) Standard 0101.04.

So to summarize, any airplane operating under 121 rules (i.e. scheduled air carrier operations) must have bullet-resistant cockpit door.


How much do the blades on the V22 or AW609 weigh?

" However, two Osprey 38-foot rotors weigh 4,654 lbs (JANE's, 1998-9, p. 557.)" this quote is from http://www.freepatentsonline.com/8382030.html

That would put the mass of a single V22 rotor at 1050 kg. The quoted source dates from 1998, so some improvements may have been made, but it is unclear to which parts of the rotor this refers, so it's only a guesstimate anyways.


During "partial panel" flying, in what ways is a turn rate indicator more useful than a turn coordinator?

A turn coordinator's axis of rotation is tilted around 30 degrees and rotates in the opposite direction. Because of this, looping errror is reversed and it under-reads at more than 1g. This makes it essentially useless when recovering from an unusual attitude on instruments, which is one situation in which you can easily find yourself when flying partial-panel.

With a turn rate indicator the instrument will over-read when the pilot is pulling excess G's in a turn; all the pilot has to do is relax the backpressure on the stick or yoke to correct.


How are aeronautical procedures created in the US?

does a worker go to an airport and monitors all information, and choose what kind of approach/departure (for example) will be? Or do airport workers advise regulators (charts creators)?

Yes. :)

Airport/airspace procedures are mainly created by a country's local aviation authority, so if you want an instrument approach to your private airstrip in the US you would contact AFS-420, the FAA's procedures branch, probably through someone at your local FSDO, and ask them to work with you to develop the procedure.
The Procedures people will survey the approach and design a procedure that makes sure you won't hit anything on the ground, and ensure that your procedure won't conflict with other existing procedures.

Once the procedure is designed they'll test-fly it - that's done by another group - and if everything checks out they'll publish charts for it.

Once published the FAA will periodically re-evaluate then procedure, both through flight checks and other feedback (if your new procedure is generating a lot of noise complaints for example the FAA will work with you to reduce the impact).


How do fighter jets stop pitching motion after a elevator deflection?

This depends on what level of realism you want.
If you want high, save yourself a lot of work by using an existing dynamics model like the JSBSim. There are model templates for it that have all the needed functions for reasonably realistic model are predefined and you just tweak the coefficients to get the performance you want.
If you want low, just make the surface deflection correspond to pitch/roll rate rather than acceleration, because that's what actually happens to a level of approximation that is perfectly fine for an arcade gamer.
What really happens is that when you deflect the control surface, the rotation will change the angle at which air hits the surface, and that will negate the effect of the control surface, so the aircraft settles at fixed rate of pitch/roll corresponding to the commanded displacement. And when the pilot centres the surface again, the aerodynamic force still exists that countered the deflection, which will now stop the rotation again.
This is fast enough that pilots normally don't need to stop the rotation with counter-movement of the controls except sometimes for fast rolls in aerobatics.
Regarding PID controller, a “position-integral-derivative” controller, the point is that the derivative term predicts the response delay, while the integral term compensates for any bias. The disadvantage is that if you tune it to have fast response, it always overshoots the target value, because the integral term will overestimate the bias. But it is simple to implement and does not require much modelling, just tweak the numbers until it works. The JSBSim provides PID controller (and some other simpler controllers) for the model definition.


How should time as safety pilot be logged?

The rules for safety pilots are spelled out in 91.109c but don't specifically state how the safety pilot should log the hours.

However, the common consensus I've heard from friends is that you can indeed log safety pilot time as PIC time. The August 2015 Flight Training magazine had an article about this actually. Here is what they said:

  What is implied but not specifically stated in the regulation is important. Because safety pilots are responsible for determining the safety of the flight, they can log their right-seat time when the left seat pilot is wearing a view-limiting device as PIC time. This transforms time spent serving as a safety pilot into a truly valuable educational experience that will also expand the flight time totals in your logbook

Edit: I did some more research into this.

PIC time is defined in Part 61.51(e). Safety pilots can qualify as PIC under bullet iii:

  (iii) When the pilot, except for a holder of a sport or recreational pilot certificate, acts as pilot in command of an aircraft for which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted

There are some other things to be aware of when logging PIC time as a safety pilot (in addition to the requirements of 91.109c):

The two pilots must agree that the safety pilot is the acting
PIC.
PIC time may be logged only while the other pilot is
"under-the-hood."
If something goes wrong you are the one that will be held responsible. I wouldnt take the responsibility lightly.
The pilot logging instrument time must record the safety pilots name in their logbook under 61.51(g)(3)


What are good alternatives to sunglasses for flying?

I've been flying for over twenty years. I've never once worn sunglasses or a hat in the cockpit, with exception of a view limiting device (i.e. hood). I understand why many pilots wear sun glasses and have nothing against it, but for me I feel like it hinders my vision more than helps.

You can fly just fine without sun glasses. One thing that might help, is to make sure you wipe down your windshield before flight to make sure its clean and clear, in order to reduce glare.

A baseball cap might be a good idea if your airplane doesn't have sun visors.

You should be totally fine. Flying without sunglasses is like flying without noise cancelling headsets. Its a creature comfort, but not absolutely necessary for safe operation.


What are the EU-equivalent terms of the FAA ATC tower, TRACON, and center in radio calls?

Area control centre   CONTROL

Approach control    APPROACH

Approach control radar arrivals ARRIVAL

Approach control radar departures   DEPARTURE

Aerodrome control   TOWER

Surface movement control     GROUND

Radar (in general)  RADAR

Precision approach radar   PRECISION

Direction- finding station HOMER

Flight information service INFORMATION

Clearance delivery DELIVERY

Apron service APRON

Company dispatch DISPATCH

Aeronautical station RADIO

Aerodrome Flight Information Service AFIS

Heliport Information Service HIS


What should a pilot do when facing a sudden tail, cross, or head wind?

Many people stress energy and airspeed management, this is a good example.

Sometimes a strong gust can reduce airspeed faster than your engine can increase it.
The sudden tail wind gust is very dangerous near the ground. Increase throttle and pitch down. Use your potential energy plus the engine thrust to maintain airspeed.  Wind conditions found in microbursts can create this effect.  Constantly check airspeed.

A strong headwind gust has the opposite effect, causing a momentary increase in airspeed, and increase in altitude.  Rarely a problem, keep an eye on airspeed as the gust passes, continue to use pitch and power to control airspeed and altitude as needed.

Side gust effect will affect your heading much more than speed and altitude, as it's velocity change does not add or subtract from airspeed.  Effects here could include a sharp roll initially away from the gust, and the nose being pushed into the wind from side force on the empennage. A stable plane should mostly self-recover without significant loss of altitude.

The mantra "the plane just moves with the air mass" does not apply to gusts.  This is why pilots generally approach at slightly higher airspeed under those conditions.


If an approach chart says "GPS required", do I need GNSS capability to fly it?

If you don't have DME/DME/IRU and are RNAV (non-GNSS) capable, can you legally fly the approach?

The chart the OP refers to is shown below.

As you can see from the STAR (standard terminal arrival), which is not an "approach" you have to have either "GPS" or a "DME/DME/IRU" capable RNAV system. Older RNAV systems that do not have an IRU (inertial reference system) would not qualify for this STAR.


Could a larger consumer drone "take down" a passenger plane?

If your definition of drone is any remote control aircraft freely available to consumers, then the answer is yes, but highly unlikely.

Its very unlikely, but it is possible. First, I'd like to point out that Radio Controlled Aircraft (RC Aircraft) have been available to consumers since at least the late 1950s. Hobbists build RC aircraft all the time, and when I was a kid I built my own RC aircraft that was much bigger than most commercially available "drones". To focus on drones alone misses a big slice of the pie. RC aircraft are sometimes built as 1/4 scale models of the original aircraft and can weigh 100lbs or more, so imagine a remote control aircraft that is 25% the size of the real aircraft.

So, the potential has always been there for at least the last half a century for a remote control aircraft to have enough mass to potentially cause a serious collision with a real aircraft. Imagine if a couple of 18lbs geese took down  Flight 1549, what would a 100+lbs quarter scale RC Aircraft do.

Personally, I've never been too concerned with this because I've flown both RC aircraft and real aircraft. It would be extremely hard for a drone or RC aircraft pilot to target an aircraft and hit it in its most vulnerable locations such as cockpit or engines.

So, yes, its possible, but I would not lose any sleep over it.


What does a sport pilot have to do to get a private pilot certificate in the US?

If you hold a Sport Pilot certificate and are looking to upgrade it to a Private Pilot certificate, your best bet is to use the requirements of Part 61 Subpart E. All of the flight time you logged earning a Sport Pilot certificate applies towards Private, but additional hours and types of flight time need to be logged.

The requirements for each are paraphrased below. You'd have to log the difference, which is a minimum of 20 hours, including another 5 hours of dual and 5 hours of solo. There's a lot more to it than what I reference below, but this is the basics.

How much of the training will have to be re-done? This should vary wildly from pilot to pilot. You'll need to redo training as required to meet standards. If you're transitioning right away, theoretically none, but it's likely that some retraining will be required.

Does it depend on the type of your flight instructor's certificate? Yes.  If the instructor has only a sport pilot instructor certificate, none of the dual instruction hours are able to be counted for the private pilot dual hours criteria.  They are not an "authorized instructor" for private pilot privileges.  If the CFI had a CFI-airplane certificate then those dual hours working towards the sport pilot certificate will count toward the dual hour requirements of the private pilot.

See the Kern INK Interpretation

Required for Sport (citation)

20 hours of flight time, including at least:
15 hours of flight training from an authorized instructor and at least:
5 hours of solo flight training in the areas of operation listed in §61.311

Required for Private (citation)

40 hours of flight time that includes at least:
20 hours of flight training from an authorized instructor and:
10 hours of solo flight training in the areas of operation listed in §61.107(b)(1)

If you've chosen a flight school that operates a Part 141 program, you get to do it all over. Hooray!


Why/How does a "Powerflow" exhaust increase horsepower?

It has to do with resonance.  Think of a pipe organ - each pipe resonates at a certain frequency, which we hear as a note or tone.  The length of the pipe determines its note/tone/resonance frequency.  Your plane's exhaust system has a certain resonance frequency.

Your plane's engine has a certain note or tone, too.  That is largely determined by engine RPM.  A powerflow exhaust matches the exhaust resonance frequency with the engine's rpm at a typical high cruise setting.

On a micro level, here is what happens.  After a cylinder's power stroke, when the exhaust valve first opens, exhaust floods out into the exhaust system.  Soon the exhaust valve shuts and the inertia of the gasses moving down the exhaust system cause the exhaust gas to continue towards the exit, creating a lower pressure behind it (near the exhaust valve).  If the resonance frequency of the exhaust system matches the rpm, at that point the exhaust valve opens on the next cycle, and the lower pressure area in the exhaust assists in scavenging the exhaust out of the cylinder.  On the subsequent intake stroke, there is less residual pressure in the cylinder and it can "suck in" more fuel/air mixture.  More fuel/air, more power.

Another way to say this is that it takes power for the engine to force the exhaust out of the cylinder and through the exhaust system.  The Powerflow system reduces the power required to do this.


In the US, you can get flight following anywhere there is radar services from ATC. It is not dependent on a control tower. However, it is dependent on ATC workload. Most controllers in our area would prefer to talk to every blip on their screen. Especially near or under their Bravo shelves.
You can pick up flight following by contacting the appropriate controlling authority/agency in controlled airspace. If you are at an airfield with a control tower, find out from them if they have radar services. Some Class D airports do have it. They will give you an abbreviated CRAFT clearance (more than likely when you contact Ground) so that Approach Control can identify you after takeoff and climb out.
If the airfield does not have a tower with radar services, you will have to climb to an altitude to be able to be seen on either Approach or Center’s radar. Cold call them on your initial call with just your tail number and the words “with request”. When/if they respond, request flight following to your destination at your desired altitude. They will let you know if their workload permits it. If they do not respond, climb higher and/or fly further into their controlling airspace (unless you have not received clearance when applicable). Or, you can try another nearby controlling agency.
Your sectional chart will tell you the information for Approach and Center. If you have difficulty locating it, look at the approach, arrival, or departure charts of any airport with instrument procedures, regardless of if they have a tower. Another alternative for getting the information is the US Cart Supplement. The controlling authority/agency information will be listed if they provide radar services to the airfield.
You can also request flight following while airborne enroute or within the terminal arrival area. Some busy airports actually require it. The information for Approach may be listed on the ATIS in this case.


Does waverider have much lower drag than Sears Haack body?

A waverider will prevent the compressed air under the airframe from escaping sideways. An equivalent view is that the sideways component of the air displaced by the body is used for lift creation by straightening it and pushing it down at the wingtips. This allows it to fly at a lower angle of attack for the same lift, which reduces supersonic lift-related drag linearly with the reduction in angle of attack.

The drag of a Sears-Haack body is the lowest for a given volume and a given fineness ratio. Increasing the fineness (essentially, the local inclination times the circumference of each body section) will reduce drag. This increased fineness, however, will now cause less sideways displacement of airflow which could be used for the waverider effect.

In the end, the question as asked is not answerable. What can be said is:

A blunt Sears-Haack body will profit the most from the waverider effect.
A waverider is still a Sears-Haack body if it has the right cross section distribution over length.
A waverider will maybe lower drag by 20% or 30% in a realistic configuration and at Mach numbers between Mach 3 to 5.

The empirical equation for the L/D of a waverider looks suspicious. Without knowing the constraints of its validity, I would not trust its results. Also, the drag coefficient of your Sears-Haack body looks like the zero-lift drag. You might need to add the lift-related drag to arrive at the complete drag.

And the biggest mistake is to operate it at ground level - 2000 m/s would be appropriate in 30 km altitude. Get the drag figure there and you will arrive at a much lower drag just by operating it in the appropriate density.


How are CPDLC VHF messages transmitted between ATC and aircraft?

For non-oceanic operations, aside from the tower radios, most ATC communications go through remote communications outlets (RCO) scattered around to get the necessary coverage.  most are co-located with VORs or other navigational aids.  The controllers are located in either a TRACON or Center facility that's often a long distance to the RCOs.

The problem is this equipment is these systems were designed for voice comm (double-side band AM radios).  For data link, the radios operate as a radio modem using VHF data link (VDL) Mode 2.  So three things have to happen: 1. the controller needs a data link enabled workstation, 2. there has to be a network connection to the RCOs, and 3. the radios need to support VDL mode 2.

So the real issue boils down to the two primary factors; time and money.  The implementation in the US is part of Nexgen.  To speed up the implementation, there is the alternative of leasing services of network providers such as ARINC and SITA.

BTW, the most comprehensive reference on data link is the Global Operational  Data Link Document.


If I've done multiple checkrides, when is my next flight review due?

The due date of your next Flight Review is based on your last check ride (your Commercial Check Ride). You will be required to complete a Flight Review (or equivalent) by the last day of February 2020.

§61.56   Flight review: (emphasis is mine)

  (a) Except as provided in paragraphs (b) and (f) of this section, a flight review consists of a minimum of 1 hour of flight training and 1 hour of ground training. The review must include:

  (1) A review of the current general operating and flight rules of part 91 of this chapter; and

  (2) A review of those maneuvers and procedures that, at the discretion of the person giving the review, are necessary for the pilot to demonstrate the safe exercise of the privileges of the pilot certificate.

  (b) Glider pilots may substitute a minimum of three instructional flights in a glider, each of which includes a flight to traffic pattern altitude, in lieu of the 1 hour of flight training required in paragraph (a) of this section.

  (c) Except as provided in paragraphs (d), (e), and (g) of this section, no person may act as pilot in command of an aircraft unless, since the beginning of the 24th calendar month before the month in which that pilot acts as pilot in command, that person has—

  (1) Accomplished a flight review given in an aircraft for which that pilot is rated by an authorized instructor and

  (2) A logbook endorsed from an authorized instructor who gave the review certifying that the person has satisfactorily completed the review.

  (d) A person who has, within the period specified in paragraph (c) of this section, passed any of the following need not accomplish the flight review required by this section:

  (1) A pilot proficiency check or practical test conducted by an examiner, an approved pilot check airman, or a U.S. Armed Force, for a pilot certificate, rating, or operating privilege.

  (2) A practical test conducted by an examiner for the issuance of a flight instructor certificate, an additional rating on a flight instructor certificate, renewal of a flight instructor certificate, or reinstatement of a flight instructor certificate.


How does ATC maintain separation between aircraft flying at different speeds?

FL250 for a Boeing 737 in cruise at 850 kph/460 knots GS is an unlikely value. Aircraft in the same category of speed, such as the Boeing 737/747/767/777 usually fly at higher altitudes, e.g. FL300-FL400. Slower turboprop aircraft such as the ATR72 usually fly in the ranges of FL200-FL250. During cruise, airspeed will be matched by ATC for all aircraft where the trailing aircraft might catch up to the preceding aircraft.

ATC sees the ground speed on their radar screens and can thus compare and evaluate if they need to assign speeds to maintain separation.

(Image Source: What data does ATC see on their screens? - Speed: 395 knots GS)

R: DLH123, report mach number.
A: Mach .78, DLH123
R: BER456, report mach number.
A: Mach .79, BER456
R: BER456, reduce speed to mach .78
A: Reducing mach .78, BER456

The same principle applies to aircraft in the terminal area, the lower you get, the more will aircraft have the same groundspeed when assigning the same indicated airspeed, as air density and wind approach the same values. ATC will sometimes assign a slower speed to trailing aircraft if they need to achieve the same groundspeed at different altitudes.

R: DLH123, descend to 3000ft, reduce speed to 210 knots
A: Descending to 3000ft, speed 210 knots, DLH123
R: BER456, descend to 4000ft, reduce speed to 200 knots
A: Descending to 4000ft, reducing speed to 200 knots, BER456

For aircraft that still have significantly different groundspeeds on the same airway, ATC can also vector aircraft around the preceding aircraft and put it back in front or they can issue a direct that will achieve the same effect, changing the sequence of the aircraft. A climb or descend can be coordinated with the pilots, e.g. the trailing aircraft can be asked if they are able to accept a climb to another flight level, maybe even temporarily.


Why hasn't there ever been a large 4-engine commercial airplane with 2 engines on the wings and 2 engines at the tail?

Such a configuration would save weight on the wings, because the wings wouldn't need to be so strong to support 2 outboard engines far away from the fuselage.

You seem to be under the impression that the fuselage supports the wings. The reality is the other way around (in flight, at least.) The wings are the most efficient place to hang weight, as they are what is providing most of the lift. This is why the main fuel tanks are usually located in the wings, for example. The strength required to support an outboard engine while the plane is sitting on the ground should be relatively small compared to the strength required for the wings to support the weight of the entire fuselage (including your proposed tail-mounted engines.) Aircraft with tail mounted engines actually need a heavier wing spar, not a lighter one.

It's also important to note that aircraft with 4 engines nowadays are usually very large aircraft with very large engines, such as the 747-8 and A380. Engines of this size would be very difficult to mount from the tail, especially with the modern high-bypass turbofans and their enormous diameters. Think of a GEnx with 2.8 m / 111 inch diameter fan, for example. This would require strengthening the fuselage as well as the wing spars and would also wreak havoc on the center of gravity. Having twin tail-mounted engines would also probably require converting the plane into a T-tail, which causes yet more engineering problems for an aircraft that large. The bending moments on the engine mounts would be enormous, too.

Can you imagine this hanging from the side of the fuselage? Note the size of the engine compared to the size of the van parked beside it.

GEnx hanging from a 787 wing Source: Wikipedia

It is usually only much smaller aircraft that have had tail-mounted engines. This is done largely to allow them to keep the wings low to the ground. For larger aircraft, there's usually already enough clearance under the wing to mount the engines anyway or, at least, the increase in wing clearance needed to wing-mount the engines is not as much as would be needed in a smaller aircraft. Of course, for high-wing airplanes, clearance is also not an issue and most of these do indeed wing-mount the engines, even on small regional jets. For example, the Avro RJ-100:

SWISS Avro RJ-100 with wing-mounted engines Source: Wikipedia

The question Why do large aircraft have their engines mostly on the wings, while smaller ones tend to have them in the tail or the tip? provides more detail on this. As usual, Peter's answer is informative and there are other good answers, too.


How to calculate lift and drag coeffecients for VTOL aircraft in the takeoff stage?

At $\alpha$=$\pi$/2 the flat plate is perpendicular to the air stream.

CL is defined as the force perpendicular to airstream, CD as the force in direction of the air stream. When the craft takes off vertically, its CD is high and its CL is zero.

A graph and a most excellent explanation here


What is the difference between fixes and waypoints on an arrival plate?

As described in the answer to the previous question, all of the points on the chart are both waypoints and fixes. The difference between the printed icons is how they are identified from the air.

The waypoints marked by hexagons, some with darkened edges and some printed inside a square, note where the waypoint is on top of a VOR. This includes Razorback, Walnut Ridge, Gilmore, and Memphis. The icons with bolded sides are a VOR collocated with TACAN; inscribed inside a square notes a VOR collocated with a DME station.

Triangles are waypoints determined by a radial and distance from a VOR station. The star icons are determined by an RNAV (area navigation) system, which does not require the aircraft to fly a particular VOR radial to determine its course. Note that the procedure you provided is not available for RNAV-capable aircraft, likely because there is an RNAV arrival procedure that is preferred by ATC.

To fly the procedure, starting from the left, a pilot would identify the Razorback (RZC) point by their CDI showing that they had flown over the beacon itself. The next waypoint is MARBI; that is determined by flying along the 098 degree radial to a distance of 34 NM from RZC. Similarly, IGLOO can be identified by flying the 098 degree radial another 85 NM for a total distance of 119 NM. The distinct icons tell pilots how to identify the waypoints using their onboard equipment, but they otherwise have the same meaning.


Was there any Hawker Trident installed cockpit voice recorder before BEA Flight 548 incident?

It doesn't appear that CVRs were installed in any Tridents before the BAE 548 accident.

The accident report noted that CVRs are installed in some British Aircraft, but stays silent on the Tridents:

  This, at least as far as CVRs is concerned, we do not regard as
  satisfactory. ... They are fitted as standard equipment to all BOAC's 747s and most large United States transport aircraft.

If any of the Tridents had CVRs, the report would've surely mentioned it. The Chinese Tridents didn't appear to have CVRs long after the accident. In fact, the accident report of a Trident 2E in 1988 notes,

  The  aircraft  was not equipped, neither was it required to be equipped, with a cockpit voice recorder (CVR).

Based on these, it does not appear that any Tridents were fitted with CVRs before the accident.


Why doesn't the pressure inside an airliner push the doors open?

Most of the airline doors are plug type- i.e. they are wedge shaped, so that the pressure differential pushes it against the fuselage and prevents opening. For example, the following image shows the Boeing 737 door.

Image from airteamimages.com

Note that the door is bigger on the inside, so that when it is locked in position, the pressure will push it against the fusealge, preventing it from opening. For opening the door, it has to be swung inwards before moving out.


What does the phrase “turnouts approved” mean?

When departing from a towered field pilots may request something other than a "standard" departure. As an example, consider the noise abatement procedures for my home field shown below:

When departing from Runway 14 the standard noise-abatement departure for light aircraft requires you to turn south (heading 190) when you pass the departure end of the runway.  This is obviously inconvenient if your destination is to the north, so you can request a northbound departure.
If the tower can accommodate your request they will clear you for the non-standard departure, usually with the phrase "left turn-out approved" or "northbound departure approved", and a heading if necessary.


Combating flutter with mass distribution?

Do I understand correctly that with this approach, the wing will act similarly to the following model, where the motion is rather chaotic?

No, your combination of masses and springs will have several eigenfrequencies. For aeroelastic analysis only the lowest eigenfrequency counts because this will couple with aerodynamic frequencies at the lowest flight speed. Once you fly faster, the next eigenfrequnecy in line will resonate, but that is only hypothetical because flutter caused by the lowest frequency has already destroyed the airframe.
In very rare cases the lowest eigenfrequency will already couple with aerodynamic oscillations at speeds below stall speed. Then the aircraft can be operated in the gap between the lowest and the second-lowest eigenfrequency.

This should have no certain frequency. Does this mean flutter is avoided?

No, since it has several eigenfrequencies, flutter is as certain as before.

Does this mean flutter can be avoided by redistributing mass around the wing, without increasing stiffness or reducing mass?

Flutter cannot be avoided, only its speed shifted up by damping. The rule always is to place the center of gravity ahead of the axis of rotation (that would be the elastic axis in case of wing torsion), so any movement causes an inertial damping force. This is the reason for the forward location of wing mounted engines.


On crosswind landings, is it preferable to side slip or crab on final approach?

Neither technique is "preferable" - the assumption that one is superior to the other is one of the most common false dichotomies (and over-simplifications) in aviation.
With some notable exceptions (like the Ercoupe which is incapable of a slip and lands crabbed) a proper crosswind landing should involve elements of both techniques.

Crabbing
Crabbing involves turning the nose into the wind so that some component of the aircraft's thrust is counteracting the crosswind, allowing the aircraft's ground track to align with the runway.
Advantages
Flying on final it is advantageous to crab into the wind: It is aerodynamically more favorable than a slip, and as the aircraft is kept coordinated it is more comfortable for passengers than a slip.
Pilots often find a crab subjectively "easier" to maintain for extended periods of time compared to a slip: It does not require the pilot to maintain "crossed controls", and it's similar to how we maintain our course in other phases of flight (you were probably crabbing into the wind on downwind just a few seconds ago, and on instrument approaches flying the localizer in a crab is analogous to tracking a VOR on the enroute portion of your flight).
Disadvantages
On touchdown however landing in a crab will put a side-load on the landing gear (the aircraft is traveling along the runway centerline, but the gear is not aligned with that direction of travel). In extreme cases this can damage the tires, cause difficulty controlling the aircraft, and possibly even damage the landing gear assembly itself.
"Kicking out the crab" to align the landing gear with the runway requires an abrupt control movement at low altitude (generally not a good thing), and if done too early the crosswind will begin to blow the aircraft across the runway (leading to a landing that's not on the centerline, a side-load on the gear, and in the worst case an unintended departure from the runway surface.

Slipping
Slipping involves banking the aircraft so that some portion of the wing's lift is counteracting the crosswind. Ordinarily the aircraft would tend to turn in the direction of the bank, so opposite rudder is applied to prevent the aircraft from turning and maintain the ground track parallel to the runway.
Advantages
Touching down on the runway a slip has the advantage of allowing you to align your landing gear with your direction of travel (down the runway) and avoid side-loading the gear. It also allows you to touch down on the upwind landing gear first which helps to stabilize the early roll-out, and positions your ailerons appropriately for taxiing with the crosswind.
Disadvantages
Slipping down final however is likely to make your passengers uncomfortable - the plane is slanted in one direction, the rudder is pushing the nose around in the other direction, and folks start to feel like their butt is sliding out of the seat.
Aside from passenger comfort a slip is a terribly inefficient aerodynamic arrangement (you're essentially trying to fly sideways), and not a "normal" way to fly in other phases of flight. You may have difficulty estimating the aircraft's performance and require power to maintain your glide path in this configuration.

Combining the techniques
So a crab is advantageous on final (and flying an instrument approach), and a slip is advantageous on touchdown. It logically follows that the two techniques can be combined to provide the advantages of both:

Crab down final (or on the localizer).
At some point transition into a slip.
Exactly where you make this transition is pilot preference, but the transition should be smooth, simultaneously bringing the nose around to align with the runway while banking into the wind to counteract the crosswind component.
Touch down in the slip.
Complete your rollout with the appropriate crosswind aileron deflection, controlling your ground track with the rudder as needed to prevent weathervaning.


How come some aircraft have really cool registration numbers?

Aircraft registration numbers are assigned by the country where the aircraft is registered. Each country has a prefix (see the full list on Wikipedia), like e.g. D- for Germany. The prefix is usually separated from the rest by a dash, but some countries deviate from this, most notably the United States, where registration numbers begin with N.

Whether or not custom registration numbers are available depends on the country. In Germany, the authority in charge of assigning registrations is the Luftfahrtbundesamt. It is possible to ask for a custom registration number via the form Antrag auf Vormerkung eines Kennzeichens (§ 19 Abs. 2 LuftVZO). The fee is currently 30 Euros. In order to get the custom registration, it must be available of course, but also follow these rules:

  D-AAAA to D-AZZZ for aircraft with more than 20 t MTOW
  D-AUAA to D-AZZZ (test registrations) for aircraft manufactured by Airbus at Finkenwerder
  D-BAAA to D-BZZZ for aircraft with 14–20 t MTOW
  D-CAAA to D-CZZZ for aircraft with 5.7–14 t MTOW
  D-EAAA to D-EZZZ for single-engine aircraft up to 2 t MTOW
  D-FAAA to D-FZZZ for single-engine aircraft from to 2–5.7 t MTOW
  D-GAAA to D-GZZZ for multi-engine aircraft up to 2 t MTOW
  D-HAAA to D-HZZZ for rotorcraft
  D-IAAA to D-IZZZ for multi-engine aircraft from 2–5.7 t MTOW
  D-KAAA to D-KZZZ for powered gliders
  D-LAAA to D-LZZZ for airships
  D-MAAA to D-MZZZ for powered ultralight aircraft
  D-NAAA to D-NZZZ for non-powered ultralight aircraft
  D-OAAA to D-OZZZ for manned free balloons
  D-0001 to D-9999 for gliders.

So it was at least in part luck that D-ICEY was available and fit the rules for a Cessna Citation.

In the UK, the authority in charge is the Civil Aviation Authority (CAA), which also allows custom registrations (called out of sequence here). The fee is currently £158.

This answer explains the procedure for the US and Canada.


Do seaplane have designated landing areas?

Taken from seaplanes.org:

While most pilots assume the FAA has jurisdiction over landing areas, including water-based landing areas, the truth is much more complex. Jurisdiction rests with the person or organization that "owns" the waterway. This may be a Federal or state agency, a local government, a private corporation, or an individual. Determining who controls a waterway is the first step in determining whether it is legal to land on that body of water.
A second complication enters in the picture with overriding jurisdictions, most commonly state-imposed seaplane base licensing requirements. In several states, notably Ohio, New Jersey and Indiana, seaplanes may not land unless the proposed landing area is certified as a seaplane base, regardless of whether the waterway owner provides permission or not. To determine whether this is an issue in your area, call your state aeronautics office (often a division of the state department of transportation), check the Water Landing Directory, or call SPA Headquarters (863/701-7979).


What are the ACARS frequencies and what is their usage?

According to the specs ACARS supports direct to satellite linking so planes flying over you may not be broadcasting on one of those frequencies. Similarly, if broadcasting over VHF you are line of sight limited. At high altitudes you may see ranges up to 200 Nautical Miles however if the planes are low overhead they may not be broadcasting as they are out of sight of the possible ground station. Your dongle may also filter/ignore low power signals or it simply cant pick up certain signals due to their strength.

Here is a list of common ACARS Frequencies.


Do autopilot headings consider the earth's shape?

Yes, almost all modern computer navigation systems take this into account.

The track between two points along the "spherical" earth is called the great-circle track. Except for a N/S heading (or a E/W heading at the equator), the heading will vary along the track. Ed Williams has compiled a formulary for great circle navigation here, mostly derived from the Haversine formula. The formula you are interested in is "Course between points" for calculating the initial heading to fly from point A to point B.


Why Helicopter compulsory need helipad to land?

Helicopters don't need a helipad to land. It is simply safer landing in a helipad. I think the decision was taken in view of safety not to land because of the presence of the minister on board.

See this picture.

That said, why did they come in helicopter if there was no helipad?


Couldn't airplanes have more emergency exits?

Money.

Doors cost (and weight) a lot more than plain aluminum panels. And the exit row on larger planes usually consumes one row of seats. So lets say we are on a 767 and take out every 6th outer row, that's 5 extra exit rows and 20 fewer paying seats, or $6,000 less per flight which quickly adds up to nearly the cost of the aircraft itself over its service life. And that's quite a lot of money for something that will very likely never be used. Remember that exit doors only help if the plane crash-lands in a mostly upright position. Severe crashes often add large exits by splitting the fuselage open, and lawn-dart mode accidents don't leave too many survivors.

The flying public has indicated that they are very interested in ticket price, but somewhat less interested in the safety factor. The current accident rates appear to be acceptable to those paying for the service.


Why did the 747-8's freighter version make its first flight before the passenger version?

The launch customers for the 747-8 were Cargolux and Nippon Cargo Airlines, both air freight operators who wanted the 747-8F. The first orders for the 747-8I didn't materialize until several months later.

Source: Wikipedia


What is the correct procedure in case of vertical stabilizer failure?

There is no procedure, generally a vertical stabilizer failure makes an airplane uncontrollable, meaning everyone dies. There have been examples where vertical stabilizers failed and people survived, see this question for details. A pilot local to me cut 2/3 of his vertical stabilizer on high tension power wires while scud running and still landed safely.

When there's any control surface failure pilots will have to learn how to fly the airplane and control it using whatever means possible. Differential thrust and speed brakes have been used to control lateral movement (yaw), trim can be used if controls are seized, etc.

Reducing speed may not be a good idea, or at least not all at once, if the vertical stabilizer fails airflow over whatever stump remains may be the only think keeping it straight. If the control is stuck then reducing speed would make sense, it all depends on the nature of the failure. Descending is absolutely a requirement, you have to land somewhere after all, but unless you've depressurized there's no need to rush it, you'd want to work the problem and find out what the new parameters are, then gingerly work your way down.


What are the differences between FANS A, B, and C? Is FANS C commissioned?

A, B, and C are the names used by Airbus. As a short summary:

If you want text communication with ATC (CPDLC), you need FANS A in USA/oceanic, and FANS B or C in Europe.
If you want position/trajectory reporting at set intervals (ADS-C) in continental Europe, then you need FANS C (still being tested).

  (Own work)

See the Airbus slide below for more:

  Source: Airbus via icao.int (PDF)

Operational demonstration of FANS C started a year ago in Europe.

Related:

How does ADS-C and FMS relate to FANS?
What's the relationship between FANS and CPDLC?

Acronyms list:

  ► A623: ARINC protocol defining a set of data
  link applications (DCL, OCL, D-ATIS)
  ► ACARS: Aircraft Communication and
  Addressing Reporting System
  ► ACR: Avionics Communication Router
  ► ADS-C: Automatic Dependent Surveillance -
  Contract
  ► ADS-B: Automatic Dependent Surveillance -
  Broadcast
  ► AFN: ATS Facility Notification
  ► AOC: Airline Operations Control
  ► ATN: Aeronautical Telecommunication
  Network
  ► ATSU: Air Traffic Service Unit
  ► CM: Context Management
  ► CPDLC: Controller Pilot Data Link
  Communication
  ► CVR: Cockpit Voice Recorder
  ► D-ATIS: Digital ATIS
  ► DCL: Departure Clearance
  ► DR: Data link Recording
  ► FANS: Future Air Navigation System
  ► FMS: Flight Management System
  ► HFDL: HF Data Link
  ► HFDR: HF Data Radio
  ► IMA: Integrated Modular Avionics
  ► LRU: Line Replaceable Unit
  ► OCL: Oceanic Clearance
  ► RMP: Radio Management Panel
  ► SDU: Satellite Data Unit
  ► VDL: VHF Data Link
  ► VDR: VHF Data Radio


What does a pilot have to do in order to fly as a second in command in a private jet?

Don't know if the same rules still apply, but back in the 70s and 80s I used to fly legally as the second pilot on corporate jets with just a commercial license with IFR and multi-engine ratings. At the time I had no type ratings.


What measures were taken to keep Soviet airline pilots in the Soviet Union?

Civilian pilots had a quite comfortable life. Flying high-tech gear has an attraction in itself, and the propaganda did what it could to strengthen patriotic spirits. There were not many reasons to defect if you did not mind the nonsense in the papers but appreciated to be part of a privileged class. And everybody knew that defection would have dire consequences for all relatives left behind.

The same is true for military pilots, and on top the Russian air defense was organized quite differently from NATO's, thus military pilots flew almost by remote control. This went as far as using radios which had only a dozen of pre-set frequencies. The pilots did not know the frequency, they just pushed the button with the number they were told by ground control.


How can I progress from tactical aircraft mechanic in the air force to an airline?

This answer assumes you intend to join the US Air Force and seek certification as a mechanic with the US FAA.

I would suggest you keep a personal log of all your training and all the work that you do while in the Air Force. This, along with your service record, can then be used as evidence to support an application to the FAA to be allowed to take the exams for the Airframe and Powerplant Mechanic (A&P) that will allow you to seek work with airlines. You take three exams -- General, Airframe and Powerplant, then an oral and practical exam with a Designated Examiner. If you pass all of that, you are issued your license as a mechanic and off you go!


What do aircraft designers like Burt Rutan do to cheaply practice geting good at designing aircraft?

Let's look at every of your concepts:

Joining a large company: As you noticed yourself, you won't get a broad range of skills, but a deep understanding of a narrow field, unless you rotate between departments every few years. This will be hard to pull off, and will take time. If you are good at what you do, your boss will try to keep you (they always try to promote the duds away in big companies, and the good people get stuck. Really!)
Building RC models is great if you want to become a configuration expert at low speed aerodynamics. You will gain no experience in transsonic aerodynamics, structure, systems - 90% of the needed knowledge cannot be gained from model aircraft. But after 20 models you will be great at understanding flight mechanics and the pros and cons of different configurations.
Forget flight simulators. Things only get interesting once you leave the realm of attached flow. Stalls, spins, flutter, oscillating shocks - that is what you need to understand when you want to do good work, and flight simulators will not teach you this. At all. Also important is to understand the effect of single failures on the whole aircraft, and designing for robust response. Again, no simulator will give you anything even resembling a realistic response.
Hybrid: Now we are talking: Keep your eyes and ears open! Visit conferences, museums, exhibitions and talk to the people. Get a pilot's license and fly yourself! Read books and technical reports. Be open to all things, be it metallurgy, fuel chemistry or whatever. Try to do stints in workshops and flying clubs. Volunteer for workshop duty and do maintenance and repairs. Don't be shy to ask, and if you see something strange, don't stop until you have arrived at a convincing explanation. Do this 10 hours a day for 10 years, and you will collect the necessary all-around knowledge.

The best way will be to participate in as many aircraft design projects as possible, from start to finish. This has become extremely hard, and some engineers will spend their whole professional life working on just one design. Let's face it, the golden days where you would work on a new design every year were maybe 80 years ago. On the other hand, the Internet can bring you an incredible wealth of information and past experiences from which to learn. Like this site. Use it!


What do pilots do on a windshear alert after V1?

V1 is the calculated decision point at which takeoff must continue. Unless the aircraft is suffering a catastrophic failure, the pilot should not abort takeoff after V1.

The danger when taking off during windshear is the sudden lost of airspeed may result in the airplane settling back on the ground after it has become airborne. The technique, therefore, is aimed at gaining ground clearance in the shortest amount of time possible. In general, this involves:

Apply max thrust
Delay rotation
Once rotation is initiated, quickly pitch up to gain altitude

Below is an extract from the Boeing 777 FCOM about taking off when windshear is suspected (my emphasis):

  Takeoff with less than full rated thrust is not recommended (...)
  Use the longest suitable runway (...)
  Consider increasing Vr speed to the performance limited gross weight rotation speed. (...) If windshear is encountered at or beyond
  the actual gross weight Vr, do not attempt to accelerate to the
  increased Vr, but rotate without hesitation.
  (...) Minimize reductions from the initial climb pitch attitude until terrain and obstruction clearance is assured, unless stick
  shaker activates.
  (...) Stick shaker must be respected at all times.


Who has final say over an aircraft flight path?

The pilot has 100% responsibility for how, where and when to fly/land. The movies make it seem like pilots are just mindless drones, under the control of ATC.

In actual fact ATC are there as an aid to the pilot, helping stop big metal tubes from colliding with one another.

This was borne out (to some extent) on US Airways 1549 where ATC were advising the pilot he could aim for his nearest airfield. His skill and experience (and of course having a front-row seat!) told him he would not make it, and he took the action to ditch on the Hudson river - saving all on board. We will never know what the outcome would have been if he had followed ATC advice, but multiple trips in a simulator have told us it might not have ended so well.

Final say is ALWAYS, 100% of the time, with the PIC.


I have usually seen people in the industry pronounce it as eye-kay-oh. Technically, the correct way would be to pronounce the letters individually as per the English language which is why the dictionary has that but I have never seen anyone pronounce it that way.


Are private jets allowed to land at London Heathrow?

The answer appears to be "yes", but unless you're transferring directly from the private jet to/from an international flight in/out of Heathrow, it's a poor choice. Fees are high and delays are common.

With no fewer than 13 other airports to choose from, chances are that one of the others will be a better choice. Luton and Farnborough are the most popular choices for private jets.

Reference:

PrivateFly: Inside London Airports - Private Jet & Helicopter charter


Why aren't thin, delta-shaped wings used for fighter aircraft?

Yes, it is. It was used on may 2nd generation designs already mentioned by habu, and it is returning now in the 4.5th generation, now with canards:

Eurofighter Typhoon:

JAS-39 Gripen:

Dassault Rafale:

And occasionally without too:

HAL Tejas:

And most of the other designs, while having horizontal tail surfaces, are not really far from that layout either:

Mig-29 (Su-27 looks very similar and all the newer Russian fighters are derived from either of those two):

F-18 Hornet:

The F-22 and F-35 with their negative sweep trailing edge are more of an exception, their layout being governed more by requirement for lower radar cross-section than aerodynamics.


If I'm instrument current in an ASEL, am I also considered current in an AMEL?

Yes, you maintain instrument currency by category, not class. 61.57(c) only mentions class in the glider-specific requirements in (c)(3). The FAA doesn't mention it at all in related legal interpretations.
Note this wording from 61.57(c)(2) (emphasis mine):

A pilot may accomplish the requirements in paragraph (c)(1) of this
section in a full flight simulator, flight training device, or
aviation training device provided the device represents the category
of aircraft for the instrument rating privileges to be maintained and
the pilot performs the tasks and iterations in simulated instrument
conditions. A person may complete the instrument experience in any
combination of an aircraft, full flight simulator, flight training
device, or aviation training device.

See also this legal interpretation, Griffith (2008) (emphasis mine):

Generally, all appropriate endorsements for passing the instrument
proficiency check, which would be otherwise given if the check were
passed in an aircraft, can also be given when one passes the check by
using an FTD, as long as the FTD represents the appropriate aircraft
category for the instrument privileges sought.

It's true that you have to pass an instrument checkride (or at least some specific tasks) in a class before you can exercise those privileges in that class, but that's a one-time thing that doesn't affect how you maintain currency. See this question for more details.


Why is the A380's fuselage designed with a flat bottom?

There are 2 main reasons:

The wing spars run through that area. If you wanted to keep the wing spar within the oval cross-section, you'd have to install the wing much higher on the fuselage which means the wing spar goes through the passenger cabin.

Behind the wing spars, the landing gear is stored. The flat bottom provides more internal space.

Another image showing more detail of the structure:


Can a US pilot fly a German D-xxxx aircraft in Germany?

No. A US licenced pilot can not fly a German registered aircraft in Germany.

Generally you must always have a pilot licence issued by the state that the aircraft is registered in.

Obtaining a licence for that country can be relatively easy based on the fact you already have a licence from another country, but you will need a new licence or some kind of documentation issued by the governing country.

There is an FAA rule that allows a US licenced pilot to fly a foreign registered aircraft the USA, but I think this is rather unique as I believe no other country allows this.


What is the range of frequencies of vibration in a helicopter due to the main rotor alone?

The vibration from the main rotor (and of the tail rotor) are harmonics of the Blade Passing Frequency: number of blades times rotational velocity. This site contains some data on the Blade Passing Frequencies of some helicopter types, for analysis purposes for military helicopters which must comply with MIL-STD-810F.
Image source

MIL-STD-810F, Method 514.5, paragraphs 2.2.6 and 2.3.3 are concerned with the vibration levels that helicopter components and cargo must withstand.
The helicopter vibration environment is a combination of many sinusoidal components due to the main rotor, tail rotor, gearbox, and engine.

Image source
Since the vibrations are also imparted on the surrounding air and then onto the fuselage, acoustic measurements are a good indication of the mechanical vibrations as well. Above graph shows acoustic measurements of seven Hueys flying by, and shows harmonics at intervals of 12 Hz. From the referenced article:

The first notable peak occurs at 24.0 Hz. A series of harmonics occur at 12 Hz intervals thereafter. These are the blade passing frequencies of the main rotor.
The main rotor blade passing frequency is: 5.40 Hz x 2 blades = 10.8 Hz
The Doppler shift increases the apparent blade passing frequency to 12 Hz. The theoretical speed of the helicopters was 76 mph based on this shift.

An interesting factoid is that the highest peak is not caused by the main rotor but by the tail rotor: the one at 123 Hz.
The highest main rotor vibration peak occurs at 60 Hz, five times the main rotor Blade Passing Frequency. There are still noticeable 12 Hz peaks at up to 300 Hz sound frequency = 270 Hz frame vibration frequency.

EDIT

This presentation shows vibration measurements taken off of an unnamed helicopter. The rotor frequency is detectable as a small peak, the blade frequencies are much more dominant.


Why does a helicopter need cyclic control rather than just tilting the whole main rotor?

Tilting the rotor doesn't do much, in fact the body will be tilting more than the rotor. The gyroscopic effect will work against you.

The cyclic increases lift on one side of the rotor which will tilt the rotor. Which will then move the craft in the correct direction.

In other words the cyclic system gives a more direct response to input.


How fast can a large passenger jet descend and slow from cruise to emergency land?

A 5-minute descent from FL320 to 10,000 feet is pretty quick. As noted in the comments, the descent rate is 4,400 ft/min. For reference, during final approach descend rate is 300~500 ft/min in a small airplane, 500~700 ft/min on an airliner. A typical descent from cruise altitude is performed at 1200~2400 ft/min.
Getting down fast
A "dive bomb" flight-simulator-style descend is not practical if you intend to land. After all, you have to arrest the descend and bring the aircraft to a stable state. You may very well break the plane when trying to pull out of the dive.
Now, what is the fastest way to lose altitude? According to the Boeing 737 QRH, the Emergency Descent checklist (which is conveniently listed on the first few sections) says...

(...) Spreadbrake...FLIGHT DETENT
(!) If structural integrity is in doubt,
limit speed as much as possible and avoid high maneuvering loads.
Set target speed to Mmo/Vmo. (...)

In other words, deploy the speedbrakes, then pitch down to max airspeed.
Note that, however, this procedure is only used when it is absolutely necessary to get down as quickly as possible. The Boeing 737 FCOM also contains the following, in bold letters:

WARNING: Use of speedbrakes at speeds in excess of 320 KIAS could
result in severe vibration, which, in turn, could cause extreme damage
to the horizontal stabilizer.

Landing gear & Flaps
Deploying the landing gear is not good because:

The maximum flying speed with gear extended is 320 knots, while Vmo is 330 knots. Therefore, if you descend with the gear extended, you will lose altitude slower.
The maximum flying speed for extending the landing gear is 270 knots. Therefore, if you wish to extend the gear, you will have to slow down to 270 knots first, then lower the gear handle, wait for the gears to be locked, then pick up speed again.
Flying with the gear extended introduces vibration to the airframe. Deploying speedbrakes already introduces vibration. A damaged engine further adds vibration.
You need the gears to touchdown, so better protect them in the landing gear bay.

Extending the flaps is even worse because the maximum speed for flying with flaps is even lower. The maximum flap extension altitude is also 20,000 ft.
Cross control
Cross-control can probably lose altitude even quicker, but it is not a maneuver you would do on a passenger airliner. When crossing control, the gravity vector is not down, but sideways - meaning passengers will be forced to the side of the seat, a sensation they are not used to. Furthermore, the passengers sitting on the window side will likely perceive the attitude as extreme bank angle and think that the plane is going to crash! The last thing we want in this scenario is a cabin with panic passengers.


Is it normal for gliders not to have attitude indicators?

Yes, it is normal. With very rare exceptions, gliders are not allowed to operate in IMC (instrument Meteorological Conditions) and must remain clear of clouds. There are also powered aircraft that do not have attitude indicators, mostly for the same reason (VFR, Visual Flight Rules only).


Is Vertical Speed based on True Airspeed or Groundspeed?

Vertical speed, as measured by the Vertical Speed Indicator (VSI) should be measured entirely by the changing air-pressure at the static port, and should be completely unrelated to airspeed and ground speed.

The static port is a small hole, (about the size of a large needle or tiny nail) in the side of the airplane, with a pressure-sensor inside.  As that sensor measures a decreasing pressure, it indicates that the airplane is climbing.

An increasing pressure indicates the airplane is descending.

Neither measurement should depend on the plane's air or ground speed.  The sensor should still work even if mounted on a hot air balloon (or other stationary craft).

Source: http://www.boldmethod.com/learn-to-fly/aircraft-systems/how-does-a-vsi-work/


When do controllers assign a squawk code to VFR aircraft in Canada?

The controller will assign you a squawk code if they want to differentiate your radar return from other aircraft. It has nothing to do with whether you're getting flight following or not. If they're happy they know which blip is you for the length of time that they'll be watching you, then they may not give you a squawk. In some airspace, the moment you begin talking to them then they'll give you a squawk. All depends.


Is communication with cabin crew or ATC included in emergency checklists?

In the case of A320, yes it does. Here’s an example of the emergency procedure for ditching. Note there are four instances where it tells the pilot to communicate with the cabin.


ARINC429 - Encoding and Decoding of BINARY DATA

Going off of the resolution, it looks to me like the actual label range would be 0-32.0, which with 11 significant bits gives an LSB of $\frac{32}{2048} = \frac{1}{64} = 0.015625$.
$1.5 * 64 = 96$


who owns the abbreviated name of an airport

4-letter names are too trivial to be protected by copyright. Trademark protections require 1) specific applications, 2) commercial usage, 3) that the offending use is relatable enough to the original business to dilute the trademark or harm the business.

(Thus, for instance, an "Airbus" car would be a clear a trademark violation, for a model plane called "Airbus A320" some agreement is preferred just to be safe, and for a book titled "Airbus A320" no communication with Airbus is needed, as it does not compete with any Airbus product, nor does such a title on a book imply being one.)

IATA and ICAO codes amount to nothing more than telephone numbers. They cannot be copyrighted, since they represent abstract concepts rather than a creative expression of one, and they aren't trademarked.

More than that is a question for Law.SE.


How does EEC/FADEC recognize/anticipate engine acceleration/deceleration?

You probably need to go ask your professor for clarification.  But let's look at it this way: what would it mean if $Pt3 > Pt3_{min}$ and $N2/\sqrt{\theta}>N2/\sqrt{\theta}_{idle}$. It means that the engine is probably NOT at idle. So in that situation, if you move the throttle, you probably do want to increase thrust, but not from idle.  The EEC may have different control schedules for idle vs above idle operation.


Is it possible to take a liquid/gas inside aircraft cabin to contaminate the air?

To answer your first question: it depends what you mean by "contaminate". The air in an aircraft cabin is constantly being renewed every two or three minutes (source (Airbus) - Boeing aircraft are similar), and the airflow pattern is such that the air only flows "across" the cabin, not along it. In other words, any contaminant you introduce will only reach the passengers seated in the same row as you (and perhaps the rows directly behind and in front of you), and will only stay there for a few minutes before the air exchange carries it overboard.

About 50% of the air which leaves the cabin is recycled back into the cabin, but it passes through filters first, which will stop any particles but will let gases through. Statistically, the concentration of whatever was introduced will drop to nearly zero after two passes through the ventilation system (due to dilution with fresh outside air).

My understanding is that the "100ml" rule is more designed to stop passengers from building liquid explosives aboard an aircraft (source (TSA)) than to stop them introducing harmful contaminants into the air.

I don't know of any incidents where an airborne substance was used maliciously in an airplane cabin, but you would get a similar effect through an on-board fire. The aircraft's ventilation system is designed to clear the cabin and flight deck of smoke within a short period of time (often by disabling the air recirculation system and increasing the fresh air flow into the aircraft).


Why are some vertical stabilizers painted 'after' installation?

The most important safety consideration when painting the tail of an aircraft is balance of the flight control surfaces to prevent flutter. This means painting of the stabilizers can happen whenever the manufacturer finds it most convenient, since they are not flight controls.

Flutter begins when the support structure of a flight control is displaced and the control is unbalanced, ie. heavier behind its hinge line. In an aileron, which is the flight control most sensitive to flutter, a gust might displace the wingtip upwards. The unbalanced aileron, heavy behind the hinge, deflects downwards due to inertia. This increases lift amplifying the effect of the gust. When the structure flexes enough to reverse the excursion of the wing, the aileron continues to rise due to inertia and deflects upwards. This reduces lift on a wing that is already descending, amplifying that motion. Uncorrected, this develops into an oscillation of increasing amplitude until structural limits are exceeded and the structure fails.

One less efficient way to deal with the weight of paint is to overbalance the flight control, meaning make it heavier ahead of the hinge line. This prevents flutter from developing because all the inertial effects on the control run counter to the deflection of the supporting structure. It is less efficient because there is unnecessary weight in the control, but it does mean that you could theoretically calculate paint weight and add some margin to ensure that overbalance is maintained after painting. Airliners don't take that theoretical route due to regulation and desire for efficiency.

Painting/repainting of the rudder, elevator and ailerons in commercial airliners always requires balancing of the control surface. This means that the mass of the control ahead of the hinge line equals the mass behind the hinge line. On a b737, the rudder can be balanced while installed on the aircraft. The horizontal stabilizer can also, but in a more restricted manner. Ailerons have to be removed, as they are most sensitive since their support structure (the wing) flexes far more than the aft fuselage where the other controls are located.

For both your aircraft all the controls will be balanced prior to flight. The A350 apparently allows balancing of the rudder while installed on the aircraft, just as the B737 does. This means it does not need to be painted prior to installation, and the manufacturer is indifferent to any cost differential.


In wing design, how is factor of safety related to G-limits?

Structural Factor of Safety is the margin between the normal limit load and the ultimate load the structure has to take.  It is normally 1.5 times the yield load or limit load of the structure.
The structure is designed to withstand the Limit Load that is applicable to the category, in the case of Transport airplanes 2.5G, without permanent deformation.  The Factor of Safety is applied on top of this value as a minimum, below which the structure may permanently bend, but not break completely.
So an airliner has to be good for 2.5G without permanently bending the wings, with a Safety Factor value of 3.75G before the wings break off, and you have to design your structure taking into account of the elasticity and ductility of the material, to achieve both those requirements.
The Limit Load is the maximum load the airplane is expected to encounter out in the world doing its thing.  The 1.5 Safety Factor been been in use since the 1930s and is a fudge factor to account for all sorts of variables, like assembly defects, calculation errors, aging damage etc.
So to answer your question, although you said 3G, we'll say the value you're interested in is the value for light planes in the Normal Category, which is 3.8G, which would be the design limit load that it's expected to be able to take with no permanent damage.  The Safety Factor, which by industry convention is 1.5, is added on top of that value to get 5.7G and is expressed as design ultimate load for Normal Category. So you have to make sure your wing can take 3.8G and still return to its original shape, and 5.7 Gs before breaking off.
You try to get as close to these limits as you can in your design, because every pound of weight above the minimum requirement is wasted ballast as far as the airplane operator is concerned. However, designers may add additional structure on top of that calculated to meet the regulatory minimum just to be safe (especially if the materials are new), or to improve fatigue life. This is why wing structures typically get tested to failure after their fatigue test program is completed, to see what will happen and to prove they can meet ultimate load requirements, and usually fail well above the design ultimate limit.
You might find this report from the 1950s helpful.


Do helicopter rotors have anti-ice systems like propellers and wings?

Yes, helicopter blades are no different from wings and propellers when it comes to ice, and there exist rotor de-ice and anti-ice systems for helicopters that require the ability to fly in known icing conditions, typically military types. Some examples include the Sikorsky S-92 and MH-60, and the Kamov Ka-50.

Rotor anti-icing systems are usually electric devices like heated mats, which are mechanically simpler that typical fixed-wing solutions like pneumatic boots and bleed-air-heated leading edges.

Not only the blades require anti-ice systems, however: elements like the engine intakes and air data sensors also need to be kept free of ice just like in fixed-wing aircraft.


Which pilot license is required in the US to engage in glider towing?

A private pilot certificate is the minimum required.  In addition you need the following experience and endorsements to be current:

CFR, part 61, section 61.69, outlines the requirements for towing privileges.
You must:

  1) Hold at least a private pilot certificate with the appropriate
  category rating;

  2) Have logged a minimum of 100 hours as pilot in command in the same
  category aircraft used for towing;

  3) Have a logbook endorsement from an authorized instructor certifying
  you have received ground and flight training in gliders or unpowered
  ultralight vehicles, and is proficient in the areas listed in part
  61.69(a)(3)(i)(ii)(iii) and (iv);

  4) Have a logbook endorsement from a pilot that already meets the
  requirements of part 61.69 (c) and (d), who has accompanied the pilot
  on three flights which has certified them to have accomplished at
  least three flights in an aircraft while towing a glider or unpowered
  ultralight vehicle, or while simulating towing flight procedures; and
  In the preceding 12 months has performed three actual or simulated
  tows accompanied by a qualified pilot or has been towed for three
  flights in a glider or unpowered ultralight vehicle. In accordance
  with part 61.52, pilots towing under an ultralight exemption may
  credit experience obtained in ultralight vehicles for their towing
  experience and endorsements.

Added per comment on question above:

Yes, a private pilot can be compensated for glider towing.

https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/data/interps/2010/umphres%20-%20(2010)%20legal%20interpretation.pdf

Source: https://www.faa.gov/licenses_certificates/airmen_certification/sport_pilot/media/towing_req.pdf


Is there a difference between a chart and map?

Colloquially, I would say not really, by definition yes.
I think the simplest way to put is is:

All charts are maps but not all maps are charts.

Websters defines a chart as

: map: such as
a : an outline map exhibiting something (such as
climatic or magnetic variations) in its geographical aspects
b : a map for the use of navigators

while they define a map as

a : a representation usually on a flat surface of the whole or a part
of an area
b : a representation of the celestial sphere or a part of it
c : a diagram or other visual representation that shows the
relative position of the parts of something

In other words, maps are outlines of part or all of something while charts contain potentially more information like that needed to navigate or identify airspace. Interestingly according to the definition, if used for navigation its a chart.


What's the precision of a modern Inertial Measurement Unit, and how is it obtained?

Let's have a look at documentation of actual modern IRS. It says (on page 6) that if GPS data is lost, it will maintain RNP0.1 for 8 minutes, RNP0.3 for 20 minutes and RNP1 for 2 hours. That means that in 8 minutes the error is no more than 0.1 nautical mile with 95% confidence, in 20 minutes it is no more than 0.3 nm with 95% confidence and in 2 hours the error is no more than 1 nm again with 95% confidence.

For general description how it works see What is an Inertial Navigation System? How does it work? and of course the appropriate Wikipedia article. Basically it measures acceleration and rotation (with gyroscopes) and integrates it over time. Modern systems do the calculations digitally with sophisticated filters to smooth over some errors.


Many of the features marked on your sectional chart are there precisely because they're things a VFR pilot should be able to see from the air and use as landmarks for navigation using "pilotage".

If you're preparing for a cross-country trip, you start with a straight line from origin to destination than then adjust it slightly so that it passes over these features as checkpoints every 10-15nm, and you'd put each of those points in your nav log as your flight path.  Then you do the additional calculations (wind, time, etc.) to turn that into something you could, if necessary, follow via "dead reckoning".

Even if you don't have GPS, you may have a VOR receiver (or ADF, if in a really old plane) that could be used as well.  DPEs here require that you be able to use VORs to fix your location on a PPL checkride; I don't know if that's everywhere, but IMHO it's a good idea regardless.

If all else fails, or any time you are in immediate danger, you can always call ATC and ask for help.  But until you've had the training on all the above options and demonstrated reasonable competency with them, your instructor shouldn't be allowing you to get yourself into such situations.


What is the difference between an aviation training device (ATD) and a flight training device (FTD)?

14 CFR Part 141, Chapter 41 Flight simulators, flight training devices, and training aids. Requirements for a FTD:

  (1) Be a full-size replica of instruments, equipment panels, and
  controls of an aircraft, or set of aircraft, in an open flight deck
  area or in an enclosed cockpit, including the hardware and software
  for the systems installed that is necessary to simulate the aircraft
  in ground and flight operations;

The important mention is it must be a full-size replica of controls and panels. This doesn't apply for an ATD (see definition in AC 61-136A, appendix 2).

See also:

Sorting the simulators.
FAA withdraws ATD rule.


Why is a weight and balance graph lozenge-shaped?

In a strict mathematical sense the graph should be extended into a complete right triangle, not a rectangle. However there are practical limits on how far forward you can fill the compartments so the graph can be cut off at 83 inches in this case. The top is clipped because increasing weight above that point reduces performance and safety margins below design intent and angers bureaucrats.
The reason for a right triangle is because the acceptable location of the center of mass is more critical at increased gross weight. When the plane is very low weight the center of mass can be very far forward and not overwhelm the tail down force and leverage. At high gross weights the tail needs more leverage to counter the nose down moment, so the forward limit of the center of mass must be brought back closer to the center of lift. There is no angle on the aft limit side of the chart because moving the center of mass behind the center of lift, at any loading, will make stall and spin recovery impractical or impossible on a traditional wing and tail layout.
The slight radial flair in the particular chart pictured is simply styling.


Why do shipping companies opt for the Boeing 747 instead of Antonov An-124?

This won’t be a real great answer, just major hurdles off the top of my head for wider AN-124 service.

Much shorter range. At 80,000 kg the AN-124 gets 4500 nm. 747-400 has a range of 7670 nm. 1
747 is slightly faster, cruising at .855 Mach
AN-124 is designed for a crew of 6; 747 has a crew of 3, or even 2 in the 747-8F
It would probably take Antonov a long time to catch up with Boeing’s production rates. 747-8’s are being produced about one a month. Back in the 70’s they were pumping out 80 or 90 of them per year.

I can’t find any numbers on fuel efficiency, but being that the Antonov was designed for military transport I would be very surprised if it could compete with the 747 in fuel usage.

1 I was not able to find good range numbers for the Antonov. It’s hard to really pin down the numbers on the 747 also due to the number of variants. The numbers here are taken from the Wikipedia page for each.


What are the disadvantages of fitting underwing flaps to a Mirage III/5 fighter jets to lower landing speeds?

Every airplane is a compromise of conflicting demands. While I am not intimately familiar with the Mirage family, I can easily see why flaps were never included.
In the early Fifties when work on deltas started at Dassault, the most important design parameter was top speed. High landing speeds were accepted, and given the design alternatives to a delta (think F-104), the landing speed could be considered low and another plus on the side of deltas.
When the first Mirage III were ordered, they had to serve in four different missions: As an advanced trainer (Mirage III B), an interceptor (Mirage III C), attack aircraft (Mirage III D and E) and for reconnaissance (Mirage III R). In order to allow for the widest variation in external loads, the lower wing should be free of flaps or other equipment which would restrict the attachment of tanks, armament or reconnaissance pods. Mounting any flaps at the straight trailing edge would require an opposite deflection of the elevons, negating any lift gain.
Flaps on naturally stable tailless aircraft are only helping if they are attached at a point ahead of the pitch trim flaps. This is possible with swept wings (see the Horten IX glider with its small flaps below) or with split flaps at mid-chord, like on the Gloster Javelin. With a straight trailing edge, no lift increase with a naturally stable configuration will be possible since the additional pitch moment of those flaps must be compensated at the same lengthwise location by the pitch control surfaces. What is gained with the flaps must be destroyed for pitch trim.

Horten IX V1 in tow, flaps lowered (picture source)
Since the Mirage line was never considered for use with aircraft carriers, its landing speed was accepted as part of the overall package. The Gloster Javelin was designed as a pure interceptor which put fewer demands on its lower wing. Also, the Javelin's tail helps to trim the aircraft in the landing configuration.
From the US translation of "Aerodynamique de la Nouvelle Generation d'
Avions de Combat a Aile Delta", published in the AGARD Conference Proceedings No. 241:

Its [the Mirage III] aerodynamic formula, a delta wing swept back 60° at the leading edge, allowed Mach-2 flight with a single engine of 6 tonnes thrust, while its competitors were equipped with a 7-tonne J79.
The trade-off to this supersonic performance was a large increase
in the approach speed, 180 knots instead of 140 kt for the Mystere family. This constraint was accepted for the Mirage III, but later program specifications from the General Staff of the French Air Force required an approach speed below 150 kt.

So the Mirage III users had second thoughts, after all. The result of this lower approach speed requirement became the Mirage F-1.
Note that artificial stability allows to lower trailing edge flaps on a delta wing; the Mirage 2000 could be flown down to 100 kts airspeed.


Which one has a higher success rate between Infrared homing and Radar homing missiles, for air to air combat?

This topic is very broad, and there is copious material available on it. Therefore, this answer will be generalized.

IR targeting is very useful against jet engine aircraft, because there is a clearly defined thermal contrast in the thermal output of the engines. At close range it is low cost and low complexity compared to a passive radar targeting system. It is essentially, a point and shoot.

Passive radar targeting utilizes a more powerful, larger antenna on the deploying aircraft, and relies on the more powerful illumination which the targeting aircraft is capable of. If the illuminating transmitter is in the front of the deploying aircraft, then the aircraft's attitude must be maintained to continue to illuminate the target until strike.  This exposes the deploying aircraft to increased risk, and is avoided in close quarters.

Active radar targeting requires more on the missile electronics, but can work better in a point and shoot environment, and does not require the deploying aircraft to continue illumination of the target, allowing evasive maneuvers and pursuit of other threats.

The trade space between targeting methodologies is great and is dependent upon situational conditions. For example, at a long range, a passive radar targeting method can provide increased target strike assurance, and lowers the SWAP (size, weight and power) of the targeting package in the missile.

At close range, IR homing is often selected because it works well on close targets, has the best SWAP, allowing more weight for ordinance and motor.

All targeting systems have their disadvantages.  For example, while IR is very effective against jet engines, having the sun, or even glint can foil them, as can IR flares. Shooting against a ground target may not be as effective with an IR seeker, but it is done.  A passive radar seeker can be more effective against countermeasures, particularly when multi-static radar is employed.  In that case, several transmitters illuminate the target, from different aspects, and the passive receiver in the targeting unit can eliminate most countermeasures.

In the world of countermeasures, there are similarities. For example, IR Chaff is about as effective as RF Chaff, and does a good job at breaking target lock and inhibiting target acquisition.

Getting back to active radar, the SWAP is greatest for this targeting system, but it has the ability to act autonomously, similar to IR targeting. Antenna diameter is a limiting factor for good SN ratios. But this strategy is good for point and shoot, and works well at closer ranges.

With respect to kill rates, that is highly dependent upon the type of target and we haven't narrowed the discussion to aircraft vs ship vs vehicle, which influence the choice due to background radiation, reflections, etc.

The question is extremely broad, and coverage of the broad topic with multiple questions in this venue is limited.


Can a Greek EASA Part 66 License be converted to a German EASA Part 66 License?

You have to send the request to the Greek Authority.
They will contact the German one, and the German Auth. will probably contact you to fill a Form 19.
(details depend of the Auth. procedures)


How does aircraft maintain precise speed, e.g. in formation flying or refueling?

The key in holding the same speed as your wingman or the other aircraft is not to find the "perfect" throttle position, the key is to slightly adjust the throttle.

When you look at cockpit-videos of those formation pilots (like this - move the camera to the throttle, it's a 360-degree video), you can see that they are constantly moving the throttle. They almost never stick the throttle at one position. In that way, they can slightly adjust the speed and stay in formation with the wingman for a long time.

While flying in close formation at high speed, it's the same. Little adjustments of the throttle helps the pilot to keep the same speed as the wingman-aircraft. Flaps are not used in high-speed-flying because they can only operate below a maximum speed, otherwise they could get damaged. By using the air-brake, the handling of the aircraft changes, therefore the air-brake is not used very often while flying in formation.

tl;dr:

Skill


How much do you have to respect checklist order?

Yes, the published sequence must be respected. Here is a quote from published instructions on checklist usage by one of the major manufacturers based in the USA:

". . . . The crew may need to stop a checklist for a short time to do other tasks. If the interruption is short, continue the checklist with
the next step. If a pilot is not sure where the checklist was stopped,
do the checklist from the start. If the checklist is stopped for a
long time, also do the checklist from the start."

If this philosophy is not already spelt out for some current aircraft types, the Regulatory bodies and Industry are (correctly) pushing it that way. Tedium is not considered as a sufficient reason to dump the C/L sequence, it is actually one reason for having a checklist!
The purpose of cockpit checklists for both Normal and Abnormal/non-Normal situations would largely be defeated if the published sequence were not followed as they are designed to ensure that the aircraft is correctly configured and safe for the next step.
In an unusual situation though (read esp: impending catastrophe), the above is to be understood in the light of the necessary disclaimer, quoted from the same manual that's quoted above:

"The flight crew must be aware that checklists cannot be created for all conceivable situations and are not intended to replace good
judgment. In some situations, at the captain’s discretion, deviation
from a checklist may be needed."

The statement - “ . . even if it makes no difference . . “ is a tricky one and it evokes a response of, “where do you draw the line?" - checklists are a manifestation of the need for Standardisation.
Here's a sum up, intended to complement the advice given by  many on this page.

Checklists are made very scientifically, but even so, the endeavor is based on a best effort basis and checklist philosophy is constantly evolving.
instances of abnormal/non-normal  situations can exist or can be conceived to support either side of the discussion.
Checklists are aimed at providing the highest probability of a successful outcome based on the best knowledge of the day and age.
Institutional Policy must be sufficiently evolved to look at variations from SOP in a practical manner.
A C/L sequence that regularly invites 'modification’, as reported by crew or as found by a surveillance system, requires a rethink.
In current day practice, ‘one off’ occurrences of a breach of checklist sequence are looked at in a benign manner by all but a few agencies.
As a policy, “not following the checklist sequence” cannot be  regularly condoned.


What is the Difference between mogas and avgas?

Chemically speaking, The difference in the fuels is the inclusion of lead-based additives that increase the Octane rating of the fuel, which are otherwise banned for use in other settings due to the negative effect on air quality. The other common use of leaded fuels I can think of is in auto racing, which also doesn't particularly prioritise air quality. Unleaded high-octane fuels do exist for aircraft engines, but those engines have to be certified to use those fuels, a long and expensive process. This is why they are less common.

Octane rating itself measures how resistant the fuel is to detonation.

Engines run at a specific level of compression. Simplistically, More compression produces more power, which is important in smaller piston engines. But having too high a compression ratio causes the mixture in the cylinder to detonate on it's own before the proper point in the timing cycle where it should be ignited by the spark plug. This is called 'knocking'.

In the best case, the result is increased fuel consumption as the ECU (ironically) throws more fuel into the mixture to reduce the possibility of detonation (at least in fuel-injected car engines this the case). In the worst case, the result is damage to the engine as uncontrolled detonation can put large unwanted loads on the crankshaft and the con-rods. Power output will be reduced in any case, which can be a massive issue for heavily laden aircraft attempting to climb in high or hot conditions.


Does the F-22 (or any other stealth aircraft) carry chaff?

It certainly seems so.

Stealth aircraft are not invisible to radar, only less visible.  Under certain conditions the adversary will be able to get a radar lock:

At close distance
With very high (focused) radar energy
At certain angles of incidence

Given these risks and the low weight of chaff, it wouldn't be be wise to not carry it.

One source that claims the F-22 carries chaff: http://science.howstuffworks.com/f-22-raptor8.htm

  It releases flares to confuse heat seekers and sends out chaff, small pieces of reflective material, to disperse radar waves and confuse a radar-guided missile's tracking system.

It's even been used in the field, according to The Washington Post:

  the [F-22s] shot flares and even chaff — clouds of metal meant to confuse radar systems but possibly used in this case as an additional visual warning.


Do aircraft weigh less on an eastward flight than a westward flight, due to the Eötvös effect?

Technically yes. But as Jeffrey said, it's quite negligible. We can do the math knowing that the earth rotational speed is $360°$ per $24h$, you get $0.004°$ per second or $\omega =  7.27 \cdot 10^{-5} rad/s$. We can then calculate the centrifugal acceleration related to this speed assuming the earth radius is $r=6371km$ and neglecting flight altitude.
$$a_c = \omega^2 r= 0.0337m/s^2$$
So if you're flying at a relative ground speed equal to the earth rotation, your centrifugal acceleration is either $0$ or $0.134m/s^2$ depending on which direction you are flying. Compare that to the gravitational acceleration $g=9.81m/s^2$ and you get $1.37\%$ of weight difference flying at Mach 1.5 with the earth rotation or against it.
Now remember that to have your weight reduced you need to fly with the earth rotation which means eastwards. And there you get a somewhat bigger problem reducing your performances in flight. Jet stream. Jet stream magnitude can be up to several hundreds of kilometer per hour meaning reduced ground speed around 10% are quite usual, resulting in 10% increase of flight time and fuel consumption thus destroying any opportunity to notice the 1.37% reduction of lift you're getting by flying east.
And even less useful when you know that the concorde used 2 tons of fuel to taxi from gate to Runway and 50 more tons to reach cruise speed and altitude in less than 45min....