Propeller Curve Modification on Test Rig

Fortunately, the speed in the propeller plane is not zero once the propeller runs. It will suck in and accelerate the air ahead of it as much as it pushes air out the back, accelerating it further. This was already formulated by Robert Edmund Froude and is called Froude hypothesis. Read this answer for more.

Using the equations from the linked answer you can already calculate your propeller's efficiency and the flow speed in the propeller plane once you run it on your test bench. Most likely your propeller is designed for more than the flow speed achievable with static conditions, so this will help you to calibrate your calculations only for low prop speeds. But since there is a flow speed already, all equations will work.

Your propeller has an advance ratio that tells you how fast it should be spun for a given flight speed. In order to extract more thrust, the propeller should be spun a bit faster, so a positive angle of attack at the blades results over the whole propeller span.

In static conditions, you will not achieve a good angle of attack over the whole span. The faster you spin the propeller, the more it will experience too high an angle of attack, a condition that will be worst at the root and only the tips will exhibit close to proper flow conditions. Since the inner part of the propeller is stalled, it will create lots of drag for little thrust. Therefore, the max. RPM and torque numbers are very hard to predict, and measurements at that point will be of no value for predicting the behavior of the prop once it runs at its design advance ratio. Air density should be less of a problem - it will drive up dynamic pressure and, consequently, the power which is needed to run the propeller at a given speed.


How does the extension of inboard flaps raise the effective critical angle of attack of the outer wing?

First it is beneficial to have an idea how the pressure field around an airfoil influences the flow around it. With powerful flaps, the suction peak on the upper side is already well developed at smaller angles of attack, so the surrounding air will be accelerated towards that low pressure area.

Now you need to extend that mental picture to 3D. The inner wing has those flaps deployed and, consequently, a suction peak near the leading edge and low pressure on the whole upper side. This will also suck in air from the side. As a consequence, the flow moving towards the outer wing will see a similar upward acceleration as does the flow streaming towards the inner wing, plus a sideways acceleration. This acceleration increases the local angle of attack at the leading edge of both wing sections. If the outer wing was already close to its stall angle of attack before the flaps were lowered, now the increased angle of attack will push the flow beyond the stall condition.

The geometrical angle of attack (measured as the angle between the flow direction at infinity and the reference length of the airfoil) did not change. The "real" angle of attack as experienced by the outer wing, however, will produce a flow similar to what would normally only be experienced at a higher geometrical angle of attack. This moves the outer wing into the stall region when the inner wing still works in the linear realm. This can lead to asymmetric stalls which produce a strong and sudden rolling moment, and at low altitude that is the last thing you need while lining up with the runway.

Adding slats will move the stall angle of attack up a few degrees, and now it will again be the inner wing which stalls first, as it should.


Does the mixture and throttle setting affect the quality of priming of fuel prior to start?

On a carbureted engine, the mixture and throttle setting does not affect prime, which uses a separate injection system that draws fuel into a syringe and injects it into the intake passages at the cylinders when you push in the primer's syringe plunger.

On a fuel injected engine, where the Bendix mechanical fuel injection system is pretty common, if the fuel system is pressurized and the mixture is rich, the system is injecting sufficient fuel at each cylinder for idle continuously.  So you prime them by doing just that, pressurizing and advancing mixture, for a set period of time, say, 3 seconds or whatever, then pulling the mixture back to idle cutoff to stop spraying gas.  This does the same thing as stroking the primer on a carb engine.  Like the carb engine, it doesn't matter where the throttle is at this point.

When you start an injected engine, you start with the throttle cracked like a carb engine, but unlike a carb engine where you put the mixture to rich for the start, you have to crank with mixture at idle cutoff and move the mixture forward after the engine fires before it consumes the fuel vapour in the intake passages created by priming, within a second or two.

Injected engines are more finicky to start because the amount of prime is a bit harder to regulate, being a timing function that you have to adjust for ambient temps and engine warmup state vs counting primer strokes so they are much easier to over/under prime, and as well the timing of the advancement of the mixture after start is important.  Do it too soon and you can get flooding or intake backfires and too late it dies before it really gets going.


What training is required for a class B endorsement?

I can not find any guidance other than what you have already noted for Class B airspace endorsements. The ground and flight training requirements seems to be left up to the discretion of the CFI. Though, it seems to be very similar to a solo endorsement as having criteria that is subjective to student and instructor.
Similar to a solo endorsement, a conservative CFI would only endorse the student for a specific airport, in a specific Class B airspace (and not the actual Class B airport), for a specific timeframe, and specific conditions. Even though the endorsement must be given within the preceding 90 days of the flight, the conservative CFI would specify a specific date and time instead of a blanket authority.
That being said, your entire logbook would then serve as a record of adequate training. Previous corresponding flights with the CFI would be logged in the logbook as evidence of training.


As with regular wings, the angle of attack and the dynamic pressure determine the lift of a frisbee.

This short paper by V. Morrison gives a short overview. If you want to dig deeper, Sarah Hummel and Eugene Motoyama (sorry, paywalled) have done more detailed work on flying discs. The following pictures were shamelessly copied from the work of Kevin Walsh. They show that the rounded edge improves airflow over the disc by delaying flow separation.

Flow around a frisbee (source)

The frisbee can be seen as a wing with an airfoil that looks the same from both directions. This incurs a small separation area at the rear end, but prevents much larger separation at the leading edge at medium angles of attack. Morrison found the farthest flying distances with an angle of attack of 12° and a starting speed of 14 m/s.

Since the center of pressure is close to the leading edge, a disc would quickly topple over due to the different locations of the center of pressure and the center of gravity. By spinning, it can be stabilized:

Difference between spinning and non-spinning frisbee (source). Inertia / gyro forces prevents the spinning frisbee from pitching up.


When did the military/Air Force start measuring fuel in pounds instead of gallons?

Good question! It makes sense for the conversion to have been done in 1951, as the film you saw states, because that is the year when JP-4 fuel was introduced. JP-4 has a lower freezing point (-60C) than earlier JP-x fuels, which were all derivatives of JP-1, first introduced in 1944. Lower freezing point means the aircraft can fly higher, and the changes in volume would have led to the change in measurement basis.

The reason is that the weight of fuel doesn't change with temperature or pressure, but the volume does. Rule of thumb is about one percent change in volume for every ten degrees centigrade up or down.

A little experiment to prove this would be to weigh a glass of water, cool it in the freezer for a few hours, and weigh it again.

If fuel quantity indicators on jet aircraft were based on volume they would indicate different levels depending on the aircraft's altitude and outside ambient temperature. That would not be very useful.

It does also make weight and balance calculations easier, otherwise the loadmaster would have to compensate for temperature when calculating center-of-gravity.


Why does Vx have a relationship with thrust but Vy has a relationship with power?

The angle a plane can climb at is entirely dependent on excess thrust.  With props, maximum thrust can be at a lower airspeed than Vbg, so even if the plane is not at its optimal wing AOA (more drag), the maximum line between drag and thrust is where you get your best climb angle, Vx.
That's the easy part.  How can a plane climb faster when it is climbing at a lower angle?  By going faster!
The formula for Power is Force (thrust) x Velocity
When you see this graph, note that the maximum distance between Power and Drag is Vy.  This plane will fly higher and farther for a given amount of fuel than at Vx.


What are the "Start & Acc" and "Pitch stab" circuit breakers for on the Piper Dakota?

It is for (two) accessories and the starter, they are on the same 15A circuit breaker. The page you want to look at in the POH is Section 7.17 (this is figure 7-11):

I know the image isn't all that clear, but the 15A breaker is on the right side of the alternator buss. It includes the cigar lighter, cabin light and starter solenoid.

  Why would the manufacturer combine the starter circuit breaker with cigarette lighter circuit breaker? If the cigarette lighter is not working in flight..is it really wise to mess with the starter circuit breaker?

I'm not sure why Piper put those two things on there, but they did. I don't see it as a problem though. If the cigar lighter isn't working that isn't a problem, you wouldn't mess with the breaker. If it is melting a hole in the dash then yes, you pop the breaker, hopefully you wouldn't need to use the starter in-flight. I would consider the need to pop that breaker (due to heating/smoke) an urgent situation (maybe not emergency, but I'd divert to the nearest airport).

As for the "PITCH STAB", that is probably for an autopilot or altitude-hold system. The Dakota was available with a number of different autopilot options that operate separately from the electric trim system.


Splayed wing tips are like .... Fowler flaps.  Totally useless for cruising flight unless .... you want to try the "coffin corner" at perhaps 60-70,000 feet.  The best wing for cruising remains the high aspect albatross style.  However, they may wish to fold them back in cruising flight.
The writer had imagined this for the Etrich Taube.  Unfolding them on approach would greatly reduce the probability of tip stall and make lots of drag.  Strictly a low speed gimmick.  (By the way, slats also do this very well, actually helping high AOA pitch control).

However, the design does hold some interesting concepts:  no vertical stabilizer AND a high wing mount.  Sort of a fuselage mounted on a flying wing with an Hstab for better control.
These concepts, along with engine mount location, bear further study.  The rest is for the birds.


What pieces of evidence do investigators have access to in the MH17 crash investigation?

Air Accident Investigation

Evidence available to the air accident investigators can include

Flight data recorder.
Cockpit voice recorder.
Aircraft wreckage.

residues, burn marks, punctures, tears and evidence of stresses.

ATC communication recordings and controller statements.
Airline records.

Aircraft maintenance records
Pilot schedules, dates of health checks, training, hours on type etc.

Radar and ADS-B data (position, speed, altitude etc).
Technical data transmitted in flight to airline, engine maker etc.
Photographs, measurements and other reports from investigators at crash site.
Eye-witness accounts from people on the ground.
Relevant NOTAMs.
Data from other aircraft in the vicinity at the time and in previous and following days (e.g. typical tracks and variations over eastern Ukraine).

In the case of MH17 the situation is obviously made more difficult by the armed conflict at the crash site and the wider political conflicts. Investigators have to take into account that some evidence may have been tampered with, destroyed or fabricated.

As others have noted, the purpose of an air-accident investigation is not to determine legal liability. Where needed, there is an entirely separate criminal investigation for that purpose.

Until they publish their report, we won't know whether the evidence available to them is sufficient for investigators to make any recommendations for changes by manufacturers, operators or regulators to reduce the number of future future occurrences of this type of incident (e.g. recommending airlines don't fly at any height over areas where there is armed conflict).

Other Investigations

Evidence relevant to other types of investigation might include

US records of alleged missile launches detected by strategic/tactical missile detection satellites.
Ukrainian alleged intercepts of separatist radio communications.
Online material allegedly published by Ukrainian separatists.
Online photos and videos alleged to be of Russian missile launchers in transit through the Ukraine-Russia border regions.

It is difficult to see how the conditions could ever be conducive to a satisfactory judicial investigation of this material acceptable to all parties with an interest in the incident.


The FAA does not define the terms turboprop and turbojet in the FARs.  These terms are defined in the Pilots Handbook of Aeronautical Knowledge.

Turbine engine. An aircraft engine which consists of an air compressor, a combustion section, and a turbine. Thrust is produced by increasing the velocity of the air flowing
through the engine.

Turbocharger. An air compressor driven by exhaust gases, which increases the pressure of the air going into the engine through the carburetor or fuel injection system.

Turbofan engine. A fanlike turbojet engine designed to create additional thrust by diverting a secondary airflow around the combustion chamber.

Turbojet engine. A turbine engine which produces its thrust entirely by accelerating the air through the engine.

Turboprop engine. A turbine engine which drives a propeller through a reduction gearing arrangement. Most of the energy in the exhaust gases is converted into torque, rather than using its acceleration to drive the aircraft.


Does the Cessna POH state the fuel consumption in Imperial or US Gallons?

The plane was certified with US Gallons. Use those for fuel consumption.

The conversion tables are there in case your FBO's fuel pump is calibrated in L or Imp Gal.


What are the best methods for calculating lift during different stages of flight?

As we have learned here at Avation Stack Exchange through many writings: thrust or power variation is critical in take off, climb, and cruise flight.
In straight line steady state flight (at the same speed) lift only equals weight in level flight, in climb or descent it is equal to the cosine climb or descent angle x weight.  In a climb the engine must provide the remainder of vertical lift, in a descent drag reduces vertical lift requirement.
Plugging in some numbers for cosine, we see lift is close to weight until climb or descent angles exceed around 20 degrees. (Cosine 10 degrees = 0.98 Cosine 20 degrees = 0.94)
Lift may exceed weight during maneuvering, known as "G's".
This involves curving flight.  Every plane has a G limit, even models.  But in straight line flight, under most conditions, lift produced is fairly close to the weight of the plane, and is governed by airfoil type, wing area, air density, speed, and angle of attack.


What are the structural differences between short- and long-haul airplanes?

Yes, short range airliners are designed for up to 90.000 cycles whereas long range airliners can be designed for 40.000 cycles or less. And it is not only the pressurized cabin that needs to be designed for more load cycles, also the landing gear has a lot more work to do. This should become clear when you calculate how many miles/kilometers an airplane will taxi in its life and compare that to the design life of a regular car.

Your average short range airliner will easily taxi 5 times more miles in its life than your average car will drive.


Why do jet generators produce a higher frequency power then household electricity?

This is a bit speculative, and if I am wrong, I will stand corrected.

Based on my little experience with power plant gas turbines, the frequency depends on the rpm of the turbine and the number of poles of the generator. A power plant turbine runs at 3000 rpm (for 50 Hz) or 3600 rpm (for 60 Hz), with two poles (this is the most reliable design, and works with turbines with rotors up to about 4 m diameter.

An aircraft APU is much smaller, and will run at higher for optimized power output. So, for the 400 Hz, you would have, for example, 12000 rpm and 4 poles (or 24000 rpm and 2 poles).

It already has been mentioned that transformers can be way smaller and lighter for higher frequencies, and it may also be that the higher freqencies of the harmonics cause less interference with other systems of the aircraft.

The speed of the generator is held constant, regardless of the engine's rpm, by the use of a Constant Speed Generator or Integrated Drive Generator.


Can autopilot track ILS without any internal heading reference?

I'll give an answer with the caveat that I haven't used the system in over 10 years. So maybe do some additional research.
The Collins Proline Flight Director used on the 200 (it's not the Autopilot per se, it's the Flight Director telling the AP what to do), and most similar ones I would expect, needs heading, bank angle and turn rate data to anticipate and judge correction heading offsets, intercept angles, etc, to track navigation solutions whether on "white needles" (FMS navigation) or "green needles" (direct radio signal navigation like VOR or LOC).
If you think about it, it has to; the Flight Director is substituting for your brain, and it needs the same data, about where the airplane is headed and how much it's turning, that you would need to hand fly an approach on raw data.
If you're hand flying and drifting to the left of the loc, you mentally estimate the heading change needed to re-intercept the loc, fly the new heading and wait.  Without compass information you would have a pretty tough time doing it with any efficiency.  If your heading indication did the same thing while you were hand flying, you would probably end up doing something similar if you kept trying to fly the LOC by ignoring the heading indication.
So if the AHRS gyrocompass unit the Flight Director is slaved to starts to slew on its own, it'll get confused and go into a kind of software loop with the resulting S turns.  I would assume that selecting XFER to select the opposite FD/AHRS system fixed the problem.


AC is easier to produce with the engines, that act as generators.
The engines have a rotating shaft that it is easily equipped with magnetic dipoles all around.

Then, depending on the instrument, the current is either used directly or, by the use of converters, in DC form as not only it is easier to produce, it is also easier to convert. So electronic devices that uses 12, 5 or 3V may contain their own voltage converter (though this is less and less true with modern efficient switch-mode converters). If DC conversion was as much efficient as AC conversion, we wouldn't see high-voltage lines. Last but not least, it's easier to switch, because the current is null twice per cycle. DC must be switched at full current, which is expensive and weight costly. (thanks mins)


Wing moment - providing stability or not

It's not about the moment but its change with AoA.
Any wing can be trimmed when the cg is at the center of pressure. What counts is how things change when AoA changes.
If you want stable behavior, use an inverted airfoil. A regular, cambered airfoil will cause unstable behavior.
For a trimmed airplane the moment around the center of gravity is zero. Now it is important how this moment changes when the airplane moves away from this trim point. If AoA increases and the moment becomes negative (nose down), the airplane is stable.
If the center of gravity is too much forward, the airplane cannot be trimmed in the first place because control authority is insufficient to produce enough downforce at the tail in order to compensate for the pitch-down moment of the lift force on the wing around the more forward center of gravity.


What is static discharging noise and what is its effect on radio communications?

The noise is created by sparks caused by static electricity. As the aircraft flies through the air, it picks up electrons from the air molecules. This extra charge will want to flow back into the air to equalize the charge. Small gaps in the conductive path on the aircraft will cause sparks to form. These sparks cause noise on radio frequencies, which can be picked up by the aircraft radios.
The static sparks will cause noise on the aircraft radios, sometimes a crackling sound.
Aircraft use static wicks on trailing edges to allow the charge to equalize. If components are electrically bonded well, static electricity should not be noticeable, other than under certain circumstances. The wicks are fixed and not telescopic but of course can be removed if replacement is needed.


Why are dirt and bugs on an aircraft so bad?

For (modern) gliders with highly optimized laminar flow airfoils, bugs (or dirt) are a non-negligible factor, especially in competition gliding. There are some older laminar airfoils that are notoriously allergic to bugs (and rain), but all are to a certain degree. This is also the reason why any glider pilot worth his or her salt will painstakingly clean their ship each afternoon and before each competition flight.

Sufficient bugs will degrade your performance by a noticeable amount - most gliding computers even have a special "bug" factor to include that into glide path calculation (even though the measuring and correllation of that is quite subjective). I´ve had a few flights in somewhat biblically bug-infested conditions (summer, hot, low thermals) that more or less painted the leading edge black (like in this picture from an article on the DG Flugzeugbau website).

Bug wipers are quite common on high-end and competition gliders and can be found e.g. at http://www.storka.at/. Or try to google for "Mückenputzer". Of course bug wipers are not without drawbacks (concerning cost, installation, ease of use, drag etc.). A friend of mine once stuck a banana peel on his wing and tried to remove that with the wiper, resulting in banana and wiper being stuck in the middle of the wing. It took some creative maneuvers to clear that mess, by which time probably a lifetime aerodynamic benefit of cleaning had been spent.

As for the comparison with cars, their aerodynamics differ in a lot of ways. In comparison to a wing there is no laminar flow to talk of at higher speeds (most of it is turbulent), which drastically reduces the influence of the surface smoothness on the drag produced.


Are there any training maneuvers that are only allowed when flying with a flight instructor?

Per the regs, no.  That’s the purpose of solo flying - to allow a student pilot to practice their skills on their own within a limited and safe environment.  However if you are renting the airplane, there may be prohibitions on certain maneuvers or operations eg spins, landing on unpaved runways, etc, so you will have to abide by those agreements.  Your CFI may place limitations on your solo endorsement at their discretion prohibiting certain flying for safety reasons which a student pilot must abide by.  As to any maneuvers required for a practical examination for a pilot certificate or rating, no there are no restrictions against flying them solo, provided they don’t conflict with other regulations eg operating an aircraft in controlled airspace on instruments without an instrument rating, etc.

Some schools also have limits as to what a student pilot can do solo.  I worked for a part 141 flight school once which forbade doing virtually every maneuver ie slow flight, stalls, steep turns, ground reference maneuvers, etc.  This just left the four fundamentals and changing heading, altitude and airspeed during flight.  They were training foreign students for the airlines and were pretty stringent.  I always though excessive.  But I’m sure they have plenty of bad memories where “you give ‘em an inch, they’ll take a mile”


Are gyroscopic effects of tail rotor noticeable with hover spot turns?

The tilt and the gyroscopic effect cause the helicopter to hover with a slight bank in a no-wind condition, a compromise that is acceptable. It should also be noted that a crosswind can exaggerate the bank, eliminate it, or even cause the helicopter to bank in the opposite direction.

In helicopters, the controls are rigged is such a way that when forward cyclic is applied, the helicopter moves forward, likewise for aft, etc.  To accomplish this, the pitch horn is offset 90º to the rotor blade.  The controls still tilt the swash plate in the same direction as the control input is made, but due to the pitch horn placement, the input to the blade occurs 90º earlier in the plane of rotation. The tail rotor as a gyroscope is rather insignificant

http://books.google.co.in/books?id=lTkiuG4RaFIC&pg=PA410&lpg=PA410&dq=gyroscopic+effect+%2B+tail+rotor&source=bl&ots=0t9R_FBArG&sig=pWRaKnWgjGAqkmeePDrmmclx7UA&hl=en&sa=X&ei=rSHhU7jSBMG0uAS9ioDIDQ&ved=0CD8Q6AEwCQ#v=onepage&q=gyroscopic%20effect%20%2B%20tail%20rotor&f=false

Also,  speed decreases all the way from the start of the approach to the hover point, and the power, controlled by the collective-mounted throttle, decreases during the first half of the approach, and then increases during the latter half - as the helicopter nears the hover spot and loses translational lift.

In a stable, no-wind hover everything is in equilibrium. The engine is providing just enough power to keep the main rotor turning at just the right rpm to hold the height over the ground and to keep the tail rotor spinning at just the right angle to counteract the torque of the main rotor. When you push one or the other of the tail rotor pedals forward, you upset this balance and must do something to compensate in order to hold the same hover height.

In a hover, the torque of the main rotor tries to turn the fuselage to the right and therefore pressure on the left pedal is required to keep the nose straight. Forward left pedal means the tail rotor blades are biting the air at a greater angle of attack and therefore producing more lift. If you add even more forward left pedal to initiate a left hovering turn, you increase the tail rotor blade pitch angle even more. This requires more power from the main gearbox and, if engine power remains constant, the only way the gearbox can satisfy this increased demand for power from the tail rotor is to allow main rotor rpm to decrease.

The tail rotor provides horizontal thrust but only to the right (nose left).  The tail rotor counters the torque on the fuselage caused by the engine driving the main rotor


Is there a manual which describes the algorithmic procedure on which the Vertical Navigation Guidance is based?

For this answer:

Hard altitude requirement - a fixed altitide which an airplane must
be at. (eg. 7000ft)
Soft altitude requirement - a window of altitudes for the aircraft to
be at (eg. abv. 3500ft, between 9000ft and 12000ft)
Using a 757 for all examples unless specified otherwise.

A simple FMS may simply assume and use the minimum of a soft requirement as the desired altitude, as you correctly stated.

However, in airliners, it is much more common to use what is called a "Cost Index" (CI) to calculate speeds, climb rates and the like.
Cost index can be calculated as so:

CI = (Time cost/hr)/(Fuel cost/lb)

A CI of 9999 means that the FMC will aim for Velocity Maximum Operating (VMO) in every stage of flight. Whereas a CI of 0 will result in the FMS aiming for the following:

+=================================+===============+===============+
|              Climb              |    Cruise     |    Descent     |
+=================================+===============+===============+
| Minimum fuel to cruise altitude | Maximum Range | Max L/D ratio |

So that will lead to the following speeds:

+============+=======+========+========+
| Cost Index | Climb | Cruise | Descent|
+============+=======+========+========+
|          0 | 290kn | .778m  | 250kn  |
+------------+-------+--------+--------+
|       9999 | 345kn | .847m  | 334kn  |
+------------+-------+--------+--------+

Now we have climb speeds, we can work backwards to calculate the best climb or descent rate for this speed (I can't find a reliable source for this, so that's where the practical examples end). From here; TOD, TOC and TTC. As long as an FMS can remain at its best CI speed to meet an altitude requirement, it will. Otherwise it will alter best CI speed by the smallest amount possible to meet the requirements.

Some good (debatable) reading is this report by MITRE, an information security organisation. They found that most FMS' tested had very little variation in the time they began descents and climbs, as well as altitudes for a fixed CI. They also found that the RTCA standards for RNP - called RTCA DO-236 where generally adhered to in every tested FMS.
That means the following was met:

  ... tolerances for a
  flight along a specified vertical path is 160’ for 0’-
  5000’, 210’ for 5000’-29000’, and 260’ for 29000’-
  41,000

MITRE also says:

  If a preceding waypoint is encountered before the altitude of the
  constraint specified for that waypoint has been reached, then the
  constraint altitude of the waypoint is adopted for the reference path
  altitude at the waypoint.

Now, armed with our new CI based climb rates and speeds, my other answer can be used to finish our calculations and work out where (in the Z dimension) the aircraft will reach a soft requirement.


Can a light glider without thermal protection land from the orbit, starting from the orbital speed?

No.

The stagnation point temperature goes up with the square of true air speed.

Temperature dissipation is proportional to true air speed and density.

Lift is proportional to the square of airspeed and density.

The lower wing loading of a glider (compared to the Shuttle, for example) means that all of the reentry will be slower, but that is not necessarily an advantage. Note that the Shuttle needed external cooling to prevent heat stored in the heat shield to dissipate into the Shuttle's structure. If the glider flies a longer reentry, it will be closer to thermal equilibrium. Also, the aerodynamic shape of a glider is a disadvantage here because the lowest heat load is possible with a blunt object - this is why reentry vehicles look like they do.

Just to give you an idea what temperatures are involved:

If we express speed as Mach number, a typical reentry speed would be Mach 25. This makes the reentry temperature at the stagnation point $$T_s = T_{\infty}\cdot \left(1 + \frac{\gamma-1}{2}\cdot Ma^2 \right) = 126\cdot T_{\infty}$$
at Mach 25. If we assume 195K at the edge of space, this comes out to 24,570K - theoretically, because ionization effects will cause the eventual temperature to be lower and the ratio of specific heats $\gamma = c_p/c_v$ is no longer constant. To calculate the real value needs a non-equilibrium gas model since the nose radius of typical glider wings and tail surfaces is in the order of one centimeter. The distance between the detached shock wave and the structure is too small for the gas molecules to reach equilibrium.

On the other hand, the epoxy resins used in glider construction cure at room temperature first and are then tempered at about 60°C. The glass transition temperature $\text{T}_g$ of such resins is at best a couple of degrees above the curing temperature. $\text{T}_g$ marks the onset of weakening of the composite matrix, and heating the glider above it will permanently damage it. Given that the glider will stay for dozens of minutes in air of a temperature of several thousand degrees and has no thermal protection will make sure that all which reaches the ground is a charred lump of material.


Would a two-seat light fixed-wing aircraft with a landing speed of 20 knots and a top speed of 180 knots be technically possible?

At least one airframe close to these specs already exists, its a highly modified Wilga by the name "Draco". It can get off the ground in 120 feet and has a stall speed of ~37mph and cruises at ~180mph. With its epic 4000 ft/min climb rate it can get out of tight spaces fast as well. The only thing it lacks compared to your specs is the retractable gear as it was designed as a big gear bush plane.

(source)

The same guy (Mike Patey) also built a pretty wild Turbolance experimental that has some epic short field and climb performance as well and its a retract.

His overall secret sauce is effectively putting a PT-6 on the front end of a small airframe to add a huge amount of power to a light airframe.


How prevalent are anti-explosion bladders in fuel tanks?

According to this wikipedia article :

Most jet fighters and all US military rotary wing aircraft have some type of self-sealing tanks. Military rotary wing fuel tanks have the
additional feature of being crashworthy. High altitudes require the
tanks to be pressurized, making self-sealing difficult. Newer
technologies have brought advances like inert foam-filled tanks to
prevent detonation. This foam is an open cell foam that effectively
divides the gas space above the remaining fuel into thousands of small
spaces, none of which contain sufficient vapour to support combustion.
This foam also serves to reduce fuel slosh. Major manufacturers of
this technology include Hutchinson, Amfuel (Zodiac) (formerly
Firestone), Meggitt (formerly Goodyear), Robertson Fuel Systems, GKN
USA and FPT Industries. FPT is now part of GKN. For military use,
tanks are qualified to MIL-DTL-27422 (includes crashworthiness
requirements) or MIL-DTL-5578 (non-crashworthy). An aircraft fuel tank
sometimes consists of several interconnected fuel cells. The
interconnecting hoses are typically also self-sealing.
In addition to fighter aircraft some military patrol vehicles and
armoured VIP limousines feature self-sealing fuel tanks.
Self-sealing fuel tanks using military technology are also required in some motorsport categories.

Given the fact anti explosion tanks were invented in 1917, and are in use since then, and have undergone many technological advances since then, they are being used quite commonly and in most of the planes where pressurization is required.


Can a CFII log Dual Given if flying as SIC?

It’s your logbook, so you can write in it anything you want. If a future prospective employer sees somebody doing what you described, the chances of being hired would fall drastically, since nobody in their right mind believes that the FO as PM is providing meaningful or valid “instruction” in a Part 135 or 121 environment to the Captain. If an FAA examiner sees that sort of time claimed as PIC to meet some requirement, I doubt the reception would be any better.

But, you go ahead & do what you want to do, since you will be the one who lives with the consequences. I think it’s a terrible plan, and I couldn’t see wanting to hire somebody who did that, not only because the PIC and Dual Given number are lower than shown, but also because of the brazen duplicity involved.

It’s playing with fire, and potentially risking a one-way ticket OUT of the airline industry. Which, for somebody who would actually do such a thing, would be the better answer.


Do any flight simulators go completely inverted?

Pulseworks makes some full motion sims that are capable of inverted flight and infinite barrel rolls.  These sims fall into the entertainment category more than the training category, but they are full motion, in cockpit sims.  I have also been in a similar type of sim at a Harris/Boeing sponsored party in Seattle made by a company whose name I cannot remember that did the same thing.  That one in fact was capable not only of rolls but also loops and could be pretty violent (I wanted to see if it would spin... it did).

Here's a video of one of the Pulseworks models.  They have some at the Udvar-Hazy center at IAD (free admission, and a shuttle from the terminal).  They cost a bit of money to get into.  They are also often setup in pairs so you can go into a dogfighting scenario with the box next to you.  Bring a friend.


Why don't combat aircraft have rear-facing *laser* weapons?

Such weapons are not used by countries that abide by the Geneva Convention:

  It is prohibited to employ laser weapons specifically designed, as their sole combat function or as one of their combat functions, to cause permanent blindness to unenhanced vision, that is to the naked eye or to the eye with corrective eyesight devices.

For the U.S.A., page 45 of Navy Shipboard Lasers for Surface, Air, and Missile Defense says:


Do airports use automated ground operation systems?

Advance Surface Movement Guidance & Control Systems (ASMGCS) in different levels are being used for this purpose.  Many airport in the world uses the concept of Follow Green, where the aircraft is supposed to follow the green taxiway centre line lights to reach the parking stand after vacating runway and vice versa.  Surface Movement Radars combined with MLATs aid for these purpose.

You can find more information on this from ICAO Doc 9830.


How, typically, do passengers and crew behave in a real-life airliner evacuation?

In the emergency landing of Emirates Boeing 777, EK521, 300 souls including 282 passengers successfully evacuated an aircraft that landed with only the left side of the main undercarriage extended, and was already on fire before it had stopped moving.

The aircraft was severely tilted over to one side, which must have made movement inside very difficult. Within a few minutes an explosion threw large pieces high into the air (possibly a slide or wing part) and the fuselage was gutted by the fire.

So at least in one case where one might expect very frightened passengers packed into a burning airliner to panic dangerously, it appears that they did not, and evacuated safely (one crew member was apparently hospitalised).

It's only one case, not enough to describe what typically happens, but please add to this answer with further examples to make it so.


What are the minimum requirements for passing medical for PPL?

The UK aviation medical standards are available online, so I assume you could go to any doctor with that information for a checkup.


What is the maximum number of cabin crew members on an A320 load sheet?

I believe that there are six crew seats in the A320 cabin. as long as the operating crew occupies these seats they will be included the crew figures for loadsheet purposes. In the event that these seats are occupied by non-crew they will need to be included manually. Not really common nowadays but it was routinely done in the 90s.

In the event that there is crew occupying a passenger seat (deadheading) they will be trimmed as a passenger.

The reason is most loadsheet programmes will adjust the Dry Operating Index  (and dry operating weight) depending on the number of crews entered in the crew field (eg 3/5). If a crew (deadheading or otherwise) is occupying a passenger seat, the system will only be able to account for this person if he is checked in.

Depending on the airline and the local country regulations it may not be possible for deadheading crews to travel on the General Declaration, instead they may be required to have tickets and be included in the passenger manifest.

To summarise, everything on the airplane must be accounted for, both in terms f weight as well as its effect on the trim, irrespective of whether it is a person on a jumpseat or passenger seat.

Hope this helps.


What's the minimum cruise speed of modern airliners?

It's called the stall speed. Below which the wings won't give enough lift to stay airborne.

Another minimal speed to adhere to is the minimal control speed. Below that the controls surfaces won't be able to counteract suddenly losing an engine.

However slowing down before landing has nothing to do with waiting on their turn/clearance. If they need to wait they go around in a circle instead.

The slowing down is so they touch down with as low speed as possible to limit the braking distance needed on the runway.


Screw the cap back on a plastic water bottle while in cruise, by the time you land the bottle will be crushed due to the change of cabin pressure.

If overhead bins were airtight, they would have been forced open or ripped during a climb. Best case scenario they will fail (e.g. crack) slowly after repeated cycles.

Answer is no, they are not.

Related: At which point does an airliner start to pressurize/depressurize the cabin? A typical cabin altitude is between 6,000 and 8,000 feet during cruise for a jetliner.

While this is best suited for Health.SE, the smaller the mammal the faster the breathing / heart rate. And if panicked, it is even more. In a confined space the CO2 from breathing won't be replaced quickly, which can eventually lead to asphyxiation.

See this from Biology.SE: Sitting in a closed room filled with regular air - for how long will the air last?

From BBC:

  Although, overhead lockers are not air-tight, lack of oxygen could have been the cause of the dog's death, US media report.


Can a lifting body work at supersonic speeds?

Lifting bodies were extensively used for reentry vehicles. In the Fifties and early Sixties there were two camps with different ideas how to go to space:

The Air Force wanted to increase vehicle speed and altitude incrementally such that finally a horizontally-launched, winged vehicle would reach space. Since the materials and propulsion were still lacking, they started at both ends of the flight envelope: One culminated in the X-15 research program, and the other researched how best to land a vehicle suitable for re-entry. This produced craft like the Northrop HL-10, which is shown below.

Northrop HL-10 with B-52 launcher overhead (picture source)

The US Army, on the other hand, tried to increase the size of rockets, traditionally used as an alternative to artillery, and got a helping hand from some other ex-Army guys who had lived through exactly the same split of technologies, where the Wehrmacht preferred rockets and the Luftwaffe preferred flying vehicles.

So not only can lifting bodies be made for Mach 3 and higher, they pretty much originated from the work done to fly at hypersonic speed, at least for a short while.


How much mathematics and what level should commercial pilots have?

So there are potentially two ways to interpret your question. First is a pilot who holds an FAA commercial pilot certification, second is a societal occupation label generally referring to a pilot performing as a crewmember of a 14CFR Part 121 scheduled air carrier airway, or colloquially, an airline pilot.

In both cases the idea that any pilot need to be exceptionally capable at math is a fallacy. I suspect it's a holdover from the 40's and 50's when all flight planning calculations needed to be done by hand. Now all of that is automated and even allowed during the FAA written tests. Additionally, needing strong math skills is often claimed when an individual is actually thinking of a test pilot or aeronautical engineer, which both require very strong algebra and calculus skills.

That said, there are some areas in the higher level written exams that rewrite you know how to calculate weight and balance, but these all relay on standardized some equations that aren't exceptionally difficult for even a novice. These written exams include the Airline Transport Pilot (which will be required for the second interpretation), Dispatcher Certificate, and Flight Engineer.


Do Airbus pilots have to practice flying in alternate law?

It appears in both situations that the PF had trouble stabilizing the aircraft roll attitude.

Note that roll control is secondary when recovering from a stall.

  Restoring normal pitch and roll, he stresses, are "of secondary importance"

The situation required that the pilots heed the stall warnings, be aware of the stall and put the nose down to trade altitude for airspeed.

  Have these recommendations changed in light of the accidents?

You can read the recommendations in the official accident reports. These usually explicitly state what such changes should be. I believe it is very rare (except when investigators disagree) for regulators, manufacturers and airlines to ignore any such recommendations.

AF447
QZ8501

From what I recall, the major problems in these two incidents were not that the pilots were simply unfamiliar with how control inputs affect flight in alternate law. major problems were that the pilots did not seem to be aware that they were in alternate law or even aware that the aircraft was stalled. In both cases the pilots were confused, failed to follow procedures and failed to coordinate their actions effectively (i.e. CRM failures)

Airbus Flight Crew Training Manuals do cover alternate law.

Recommendations included

  5.3 Aircraft Manufacturer
  1. The KNKT recommends that Airbus to consider in developing a means for
  flight crews to effectively manage multiple and repetitive Master Caution
  alarms to reduce distraction.
  2. The KNKT recommends that Airbus to consider and review the FCTM
  concerning the Standard Call-Outs in all phases of flight.

The Indonesian report lists  in some detail the actions taken by the airline and includes an Airbus article "What is a stall? How a pilot should react in front of a stall situation". It also includes some guidance issued by Airbus which includes recommendations concerning upset training in various control laws

  After that how much opportunity do they get to practice this skill?

This depends on airline (and relevant regulators) more than on manufacturer. Upset recovery is probably something that all pilots should be trained in, and maintain familiarity with, regardless of who manufactured the aircraft.


I can't speak directly to the ICON A5 as I neither own nor fly one, but for every aircraft I'm familiar with the manufacturer's "book numbers" are generous theoretical values - for example, they typically assume flying perfectly straight-and-level in a no-wind condition, and getting the best possible fuel economy performance from the powerplant.
The Icon folks are openly honest about this on their specs page: Performance specifications are estimates only., and range is certainly "Performance" in my book.

Personally I have no doubt that the A5 could manage 300NM under the conditions for which its designers did the math to arrive at that number - it's a slick little plane with a fuel-sipping engine - but they may have done a "to empty tanks" calculation (leaving you to account for the VFR fuel reserves you're legally required to have), and in the real world the 15-knot headwind you run into will substantially reduce your range (or, conversely, you can fly in the other direction and increase it).

As with all aircraft your mileage will, quite literally, vary depending on the day and direction of flight.


What are the properties of a good general aviation training aircraft?

Cost is certainly a primary factor in choosing smaller planes. It makes training much more accessible to people with less money to spend.

Small planes are also easier to fly for various reasons. They fly slower and respond more quickly than large aircraft, which gives the pilot much more margin for learning. Being more maneuverable can help them escape tricky situations.

These planes are also generally designed to be resistant to and recoverable from common aerodynamic disasters like stalls and spins. See this related question for more information. There are FAA requirements for single-engine planes in FAR 23.221.

Smaller planes generally also have fewer and less complex systems, which makes the necessary training easier to complete.

They can also operate from smaller airports, which gives a student more choices of where to do their training.

Of course, there are always exceptions to these qualities, and large planes can have similar ones, but they hold true in general.


What are the criteria for conceptual design of thrust reverser in the use of braking?

As @John's answer alluded to, the rules for actual landing distance (25.125) and the accelerate-stop distance on dry runway (25.109) effectively prevent a manufacturer from taking credit for thrust reverser (T/R) when demonstrating/calculating for these distances. However, 25.109 does allow a manufacturer to take credit for T/R when dealing with a wet runway. This means that having a (good) T/R gives an operator more flexibility when dealing with adverse weather conditions, and this translates to more money saved (vs sitting on the tarmac).

Therefore, just like any other performance numbers, the performance of T/R is subject to market objectives. There is no regulatory requirement on how powerful the T/R has to be at max reverse.

That being said, this NASA memo has some helpful information on why airlines want thrust reverser at all. The following two graphs are cited from this source, which outline the percentage of work done by the respective braking systems for a typical jetliner on dry and wet runways. You can perhaps back-calculate the thrust of T/R from your design point:

Other factors to consider for design:

Foreign object debris ingestion from T/R deployment, especially at lower speed
Compressor stall from hot reversed gas, especially at low speed
Inadvertent deployment of thrust reverser in-flight. For most airplanes, this would be catastrophic.
Controllability in single T/R deployment on ground
For rear mounted engines, aerodynamic interference with rudder effectiveness


Does windmill restart often work for airliner engines?

If the engine isn't damaged, and the restart altitude/speed are followed, the engine should start. Fuel starvation, bird ingestion, etc., do not count.

(YouTube) In-flight shutdown.
In-flight restart is tested as part of the aircraft certification, and it must work. In the link above is a video showing the procedure in a 777F simulator.

Engine Restart Capability - § 25.903 (e).
Tests should be conducted to determine that inflight restarting can be accomplished within the envelope provided. Restarts at the conditions of the critical corners of the envelope and at or near the high altitude extremes of the envelope should be conducted to verify the boundary conditions of the envelope (FAA).

Examples of successful restarts:

On British Airways Flight 9, all four jets on a 747 failed after entering a volcanic ash cloud, all 4 were restarted after exiting the ash cloud. One of the four failed shorty after, but volcanic ash is sticky, the particles are very small, they melt, and they clog moving parts. So three out of four isn't bad at all.

For KLM Flight 867 (a mirror of BA 9) it was four out of four successful restarts.


Flying a twin engine aircraft with 2-axis control

For an ultralight with rudder only roll control, which achieves lateral control with a lot of dihedral to create a really strong roll/yaw couple, the issue would be how much reserve rudder authority is there once enough has been applied to counteract asymmetric thrust.  That would determine how much roll rate you could still achieve trying to yaw toward the dead engine. If the engines are reasonably close together, it would probably be flyable but you would have a lot less turning authority into the dead engine than away from it.  In the end, you would have to go try it to see what happens, or get someone to do it with an RC model version.

I think your problem is more to do with simply single engine performance.  If one quits you are now at 50% power.  Using two engines doubles the chance of engine failure, and if you can't climb decently on a single engine, you're still in a glider after a failure, just one with a flatter glide.  IIRC, the Lazair twin was just able to maintain level flight on one engine at lower altitudes, and it was pretty clean as ultralights go.  The Bloop being a lot draggier, you would probably need more total HP that it uses as a single, to have decent reserve power when one fails.


What's the maximum seat configuration for a 747 that is actually used?

The maximum was likely 568 seats.
It is hard to find a definitive source for this, but it is likely that the 747-400D (Domestic) version had the largest number of seats since it was specifically built for this purpose. This type was used by Japan Airlines (JAL) and All Nippon Airways (ANA). JAL published the number of seats they used in a press release:

How many seats in JAL's passenger 747s: We have many configurations for international and domestic airplanes. The latest international route 747-400 has 348 seats - 12 in First Class, 99 in business class and 237 in economy class.
Our domestic Short Range 747s have as many as 568 seats in two classes: 24 seats in the domestic version of First Class, which we call Super Seat, and 544 seats in regular economy class.

(jal.com)
Here is the seat configuration used by JAL:

(image source: simpleflying.com)
I did not find a statement by ANA itself on their seating. The following article however lists 565 seats as their configuration, so 3 less than JAL:

The Boeing 747 – once dominant in the sky is slowly fading away. The latest airline to wave goodbye to the Boeing  747 is All Nippon Airways, who completed the final flights on its domestic routes.
It marks the end of Boeing 747-400s by a Japanese airline – and also the end of an era of the passenger heavy Boeing 747-400D aircraft.
These aircraft had a massive passenger load of 565 seats on a plane.

(economyclassandbeyond.boardingarea.com)
While not impossible, it is unlikely that another airline would have ever operated a 747 with a higher seating capacity.


What is the purpose of anti-skid surge accumulator in a 777-300?

When an aircraft touches the ground, brakes are applied to decelerate the aircraft. To execute this
on an efficient manner, an anti-skid system is installed. This makes it possible for the aircraft to perform
a stop with maximal deceleration and minimal wear of the tires. In this way the aircraft can
come to a safe stop without unnecessary maintenance.

Further info: https://anoukaviation.files.wordpress.com/2009/07/project-report-landing-gear.pdf (search for skid)

The anti-skid surge accumulator absorbs brake release surges from the left normal anti-skid valve module.
The right normal antiskid valve module does not need an antiskid surge accumulator because the right hydraulic system reservoir is very near to the right normal antiskid valve module.

From: http://www.plane.cc/html/ziliao/jiwu/2011/0426/23491_33.html


What drives the shape of an engine's intake on a fighter jet?

Are the design drivers solely based on supersonic pressure loss improvement?

Yes. And sometimes a few more considerations need to be taken into account.

We have covered the reason for intake shapes well on this site, but the details must be collected from several answers. In a nutshell: Higher flight Mach numbers need more elaborate and heavier intakes in order to convert the kinetic energy of the flow into pressure. A pitot intake is light and simple, but a poor choice for speeds in excess of Mach 1.6.

Rectangular intakes are normally chosen in order to make internal, moveable ramps possible which create a cascade of shocks in order to slow down the flow as efficiently as possible. Such designs are typical for Mach 2 aircraft (think Concorde, F-14, F-15, XB-70). Another way would be a central intake with a moveable spike, but those had to make way for big radar arrays in more modern designs. The JAS-39 intake is a little special: It sits next to the fully moveable canards, and those need a vertical wall in order to minimise the gap between canard root and fuselage/intake structure. Yes, a round intake would be slightly lighter, but is impossible due to the situation of the canards.

Detail of JAS-39 canard, taken from this picture.


What mental health standards must a candidate meet in order to qualify for a pilot's medical certificates?

Canada:

  1.3 The applicant shall have no established medical history or clinical diagnosis which, according to accredited medical conclusion,
  would render the applicant unable to exercise safely the privileges of
  the permit, licence or rating applied for or held, as follows: (a)
  psychosis or established neurosis; (b) alcohol or chemical dependence
  or abuse; (c) a personality or behaviour disorder that has resulted in
  the commission of an overt act; (d) other significant mental
  abnormality

US:

  Unless otherwise directed by the FAA, the Examiner must deny or defer
  if the applicant has a history of: [...] (8) Psychosis; (9) Bipolar
  disorder; (10) Personality disorder that is severe enough to have
  repeatedly manifested itself by overt acts; (11) Substance dependence;
  (12) Substance abuse; [...]

EASA (Europe) (abbreviated):

  AMC1 MED.B.055 Psychiatry   (a) Psychotic disorder   (b) Organic
  mental disorder   (c) Psychotropic substances   (d) Schizophrenia,
  schizotypal or delusional disorder   (e) Mood disorder   (f) Neurotic,
  stress-related or somatoform disorder   (g) Personality or behavioural
  disorder   (h) Disorders due to alcohol or other substance use   (i)
  Deliberate self-harm

  AMC1 MED.B.060 Psychology   (a) Where there is
  suspicion or established evidence that an applicant has a
  psychological disorder, the applicant should be referred for
  psychological opinion and advice.   (b) Established evidence should be
  verifiable information from an identifiable source which evokes doubts
  concerning the mental fitness or personality of a particular
  individual. Sources for this information can be accidents or
  incidents, problems in training or   (c) The psychological evaluation
  may include a collection of biographical data, the administration of
  aptitude as well as personality tests and psychological interview.
  (d) The psychologist should submit a written report to the AME, AeMC
  or licensing authority as appropriate, detailing his/her opinion and
  recommendation.


The blanket NOTAM includes this language:

  UNLESS THE AIRCRAFT OPERATOR MEETS AT LEAST ONE OF THE FOLLOWING REQUIREMENTS: A) THE AIRCRAFT OPERATION HAS BEEN AUTHORIZED BY ATC FOR OPERATIONAL OR SAFETY PURPOSES, INCLUDING AUTHORIZATION OF FLIGHTS SPECIFICALLY ARRIVING AT OR DEPARTING FROM AN AIRPORT DESIGNATED BY ATC USING STANDARD ATC PROCEDURES AND ROUTES


Can small airplanes be towed (or carried) as cargo to be dropped at some other location by air?

If you are talking about externally carrying/deploying other aircraft, this has already been done with the B-52 (albeit for testing purposes) carrying the X-15.

I'm not too sure about having an aircraft drop out of a cargo bay such as the C-130.

On a side note military gliders were used extensively during WW2 and some were capable of carrying light tanks. The gliders were usually towed behind larger bombers to give them the required altitude and speed. They were used because of their wooden construction allowing a stealthy approach due to the reduced radar signature.


Why does a DME ground station wait 50 microseconds?

The delay is not 50 milliseconds, but 50 microseconds.

It takes some time for the ground equipment to decode the incoming signal, decide it needs to reply, and fire up its transmitter. In order for the distance measurement to be reliable, this inevitable delay needs to be precisely defined and the same for all DME stations. It also gives the airborne interrogation some minimal time to shut down its transmitter and start listening even when it's right on top of the ground station.

50 µs must have felt like a suitable interval to standardize on, long enough for it to be reasonably possible to engineer the ground stations to meet it (given the technology of the time the design was made), yet short enough that one DME station can service an acceptable number of aircraft without needing to handle overlapping delays between different interrogations.

The standard delay also means that a DME station used for ILS can be located midway between the runway's thresholds and adjusted such that aircraft see the distance to the threshold rather than the distance to the physical antenna, by reducing the delay appropriately. (Such a DME does not give useful readings for aircraft not aligned with the runway).

Note, by the way, that the 50 µs is the time between receiving the second pulse of an interrogation pulse-pair and transmitting the second pulse of the resply. So the ground station actually has to start transmitting the reply less than 50 µs after it knows it has received a complete interrogation. For Y channels where there are 30 µs between the two reply pulses, the ground station actually has only 20 µs to react.


Why are private jets more expensive to travel in than commercial aircraft?

Aside from the economy of scale effect of a large aircraft vs a small one you can compare apples for apples by looking at the same type used on both roles.
The Canadair CRJ200 was sold as both a regional airliner and a corporate jet, called the Challenger 850, so it makes a good comparative example.
The Challenger 850, being, mechanically, a CRJ200 with a corporate interior, has pretty much the same numbers for fuel burn etc, as a 200.  But it's only carrying 1 to 12 passengers, vs up to 50.  So even "full", its fuel burn per occupied seat mile is always going to be several times higher than the airliner version operating with decent load factors (and they aren't much lighter; the corporate interior is very heavy and with 12 bodies aboard you are close to gross weight with a large fuel load - add in a long range fuel system option by STC for that airplane, and the payload with full fuel was 2 persons... yes, 2).
Then there's utilization.  The CRJ 200 airliner averages about 2500 hours a year.  A Challenger 850, like most corporate jets, averages 300-400 hours per year (corporate shuttle versions fly a lot more, maybe over 1000, but they have regular airline style interiors).  All the fixed costs of operation are amortized over a way smaller number of operating hours (most corporate airplanes would fall apart if you put airliner hours on them; they are not designed for that level of use - this made the Challenger 850, with an airframe meant for 2500 hours/year, absolutely bulletproof in its corporate role).
So you have a cost double whammy.  You're using several times more fuel to get around for each warm body on board (what I might call "warm-body-miles"), compared to an equivalent airliner, and you're doing it infrequently and so are paying through the nose for all the fixed costs like insurance and hangar space, etc.
The reason for the existence for most corporate airplanes is the time valuation of the "warm bodies" travelling on it.  A large company makes the calculation that the value of the CEO, and the CEO's lieutenants' time, justifies the astronomical operating cost of a corporate aircraft; in effect, the jet makes money for the company by making the senior management's job more efficient (in theory - no doubt a lot of it is just "because they can").
If you're the other type of corporate jet owner, the ultrawealthy who own the planes personally, economics doesn't even come into it (I knew a guy who looked after corporate jet purchasers pre-delivery, and he told entertaining stories of bizarre customer meetings, with oligarchs and their children arguing over 500,000 dollar interior options as if they were fighting over who got to lick the cake icing spoon).


What powers the air-conditioning on commercial planes?

What powers the airconditioning on most airliners is APU or main engine compressor bleed, which is being supplied at fairly high pressure, say, 80 psi, and temperature, around 3-400F, to the air conditioning packs.  You normally have a choice to select APU or main engine bleed.  You will obviously use APU bleed on the ground before engine start, but also may opt to take off with APU bleed running the air conditioning instead of the engines for slightly better takeoff performance.  On some airplanes, packs on APU bleed can be a requirement for departures in icing conditions because of the performance drain of bleed being used for anti-ice and air conditioning at the same time.
Large jet aircraft (and large turboprop) air conditioning doesn't use a gas vapour cycle like regular air conditioners (some smaller jets and turboprops, that can't produce the bleed flow, as well as piston a/c do however); they get the same result using just the high pressure, high temperature bleed air using a "bootstrap effect", where air is cooled off while still at high pressure, than letting it drop close to ambient pressure after a lot of the heat has been removed, resulting in air that can be very cold.
At the pack, part of the flow gets chilled and part gets bypassed while still hot.  Temperature regulation is by mixing the chilled flow and bypass flow. Electrical power is only required for the control system.
The air being chilled goes through an Air Cycle Machine. An ACM takes high pressure air, drops the temperature using heat exchanger pre-coolers (air-to-air radiators) while the pressure is still high, boosts the pressure and temperature again with a compressor, takes out some of the heat from that pressure boost with more heat exchangers, and you end up with air that is still at high pressure but the temperature is way less than the original bleed.  Then you suddenly let the pressure drop close to ambient by allowing it to expand into a much larger discharge duct.
Air that started off at 80 psi and 400F is now down to 150F while still at 80 psi.  When you let it drop to ambient, the temperature drop from the pressure drop will take the ACM discharge temperature down to just above freezing (theoretically, if you put all the bleed through an ACM, you can get the air down to deep sub-zero temps, but the control system will normally keep the discharge from going below freezing).
The compressor is powered by a turbine in the discharge flow where the expansion temperature drop happens. It's like a big turbocharger unit (the compressor driven by a turbine in the same flow is what constitutes the bootstrap effect).  The final temperature that goes to the cabin is a mix of chilled air and hot air that is bypassed from the ACM by the control system.
You may also be able run the system from a high pressure ground bleed air source (called a "Huffer Cart"), but airlines usually use Huffer Carts for engine starting and instead will run ground air conditioning units that connect directly into the aircraft low pressure ducting (when you see the yellow flex pipe hooked up to the fuselage at the gate, that's a ground low pressure air conditioning source).


How do I obtain permission to fly in surface class E airspace under FAR-103?

By default, all controlled airspace (class E and up) is owned by an ARTCC. In many areas, they delegate airspace (including class E!) to other ATC facilities, either a TRACON or a Tower.
Unfortunately, that info isn't on Sectional or Terminal Charts; you have to look in the Chart Supplement (formerly Airport/Facility Directory). For KGFL, we see:

ARTCC: BOSTON CENTER
...
ALBANY APPROACH: 132.825
ALBANY DEPARTURE: 132.825

So, this area is owned by Boston ARTCC and delegated to Albany TRACON, and it helpfully gives you the latter's frequency to call if airborne.
You probably can't reach them by radio from the ground, so you would contact their Clearance Delivery (CD) by phone, which for this airport is found in the remarks:

FOR CD CTC ALBANY APCH AT 518-862-2299.

Just tell them in plain English why you're calling and what you want, and be ready to copy any instructions they give you. They might, for instance, ask you to wait because they have other traffic going in or out in the next few minutes, or they might ask you to contact them in the air so they can keep track of you (I assume they won't see you on radar) and warn other aircraft you're there. Or they might not care at all and just tell you to have a good flight.


Where can I find airport diagrams from airports all over the world?

For Europe, the European AIS database (EAD) would be the best source.


What is the largest taildragger in history?

If you are going by MTOW, I believe that would be the Junkers Ju 390, which had a maximum takeoff weight of 75,500 kg.

Junkers Ju 390, By Bundesarchiv, Bild 141-0072 / CC-BY-SA 3.0, CC BY-SA 3.0 de, Link

Sadly, only a couple of these were built. If you are going by the wingspan, that would be the Tupolev ANT-20 'Maksim Gorki', which had a wingspan of 63m

ANT-20, By Unknown - http://www.dkvnukovo.ru/photos/museum/photos/35.jpg, Public Domain, Link


Why is the landing area of an aircraft carrier angled to port side, not starboard?

Farhan's answer covered why the deck is angled in the first place. As far as why the landing area of the deck points left instead of right, this is for several reasons:

Angling to port makes the most use of the deck area behind the catapults. Angling starboard would require the catapults to be shifted left off the centerline of the carrier (yes, the carrier does have two additional catapults on the port side, but these can't be used while the carrier is retrieving aircraft, which is more often than you'd think as the carrier maintains regular patrols).
Angling the landing strip toward the "island" (conning tower) of the carrier just doesn't sound like a good idea when you say it. That goes double when you realize the carrier is underway while you're trying to land on it, and therefore you have to lead the landing strip a little. If you don't, you'll end up "behind" the ship and the landing strip. With the landing strip angled to port, a plane on a "lagging" approach (lined up "behind" where the carrier's going to be at touchdown) will have a relatively clear path off to port for a wave-off. Angled to starboard, a plane that's "lagging" the carrier would be pointed right at the tower.
It would be possible to mirror the entire deck layout; island to port, landing area angled starboard. The reason the island is on the starboard side is primarily convention; all U.S. Navy aircraft carriers ever built have been either flush-decked or have had the island to the right. That's thus a familiar sight picture for naval pilots across all eras, and easy to train to. A new carrier design doesn't get the luxury of a whole new crew trained an entirely different way; the Navy's been training pilots since 1910, they've been landing planes on boats since 1927, and they'll do it they way they've been doing it for 88 years, thank you very much.

The Imperial Japanese Navy commissioned two carriers, Akagi and Hiryu, with island-left designs, fielded with the idea that the island-left carrier would sail in formation with an island-right carrier in the same flag group, with opposing traffic patterns that didn't conflict. This procedure never materialized in practice; most carrier groups in both Japanese and U.S. fleets ended up with a single carrier due to their high cost and lower total number, a pattern that continues today, and even when two (or more) carriers were close enough to be called part of the same naval group, they typically maintained a wide enough spacing to permit a left-hand pattern for both ships.


How does chord length affect wing design?

During design, chord length will be the result of wing span and wing area, because those two are what the designer wants to set. To be more precise, he tries to set a certain wing loading, trying to minimize wing area (and weight) such that the wing creates just enough lift for the estimated aircraft mass in all design cases. Take-off, maximum altitude and minimum turn radius are the classics which drive minimum wing area.

Now I will focus on aspect ratio, because Jan has already answered the rest with his excellent answer. The higher the aspect ratio, the less the wing tips will influence the airflow around the wing. This means that the wing creates more lift for a given angle of attack, but also that the stall angle of attack is lower. The ratio of wing span to aircraft mass (called span loading) is the driving force for induced drag. However, wing span and aspect ratio will also drive wing structural mass, so you need to find a sound compromise between low induced drag and low wing mass.

What is induced drag? It is the consequence of creating lift over a limited span. The wing creates lift by deflecting air downwards. This happens gradually over the wing's chord, and creates a reaction force orthogonally to the local speed of air. This means the reaction force is pointing up- and slightly backwards. This backwards component is induced drag! The wider the wing is, the more air can be used for lift creation, hence less deflection is needed. Consequently, the backwards tilt of the reaction force is smaller, resulting in less induced drag for the same lift.

If you fly fast, there is a lot of air mass streaming past the wing per unit of time, so you need to deflect the air only slightly. Your induced drag is small. That is why induced drag changes inversely with air speed.

Now you know that for high speed at high density, induced drag is not important. If you design an attack aircraft which has to fly at low altitude, a low aspect ratio will help: The lift increase due to gusts is smaller than with a high aspect ratio wing, and the induced drag is manageable.

How the lift curve slope changes with aspect ratio in subsonic flow is shown in the simple plot below. For a slender body (aspect ratio $\approx$ 0), the gradient of the lift coefficient $c_L$ over angle of attack $\alpha$ is $c_{L\alpha} = \frac{\pi \cdot AR}{2}$. Please note that the red line is only valid for AR = 0! Then the lift curve slope increases up to $c_{L\alpha} = 2\cdot\pi$  for $AR = \infty$ (and zero airfoil thickness and no friction effect), as shown by the blue line.

There are more influences, however. Dihedral means that the lift is tilted inwards, and the part which counteracts weight is only growing with the cosine of the dihedral angle $\nu$. Same goes for sweep: Sweeping means that the wing only sees a reduced angle of attack change. If you want to capture all effects, a plot will not suffice. Here is a table with formulas for most cases:

Nomenclature:
    $c_{L\alpha} \:\:$ lift coefficient gradient over angle of attack
    $c_{L\alpha\:ic} \:$ lift coefficient gradient over angle of attack in incompressible flow
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing
    $\nu \:\:\:\:\:$  the wing's dihedral angle
    $\varphi_m \:\:$  sweep angle of wing at mid chord
    $\varphi_{LE} \:$  sweep angle of wing at leading edge
    $\lambda \:\:\:\:\:$  taper ratio (ratio of tip chord to root chord)
    $(\frac{x}{l})_{d\:max} \:$  chordwise position of maximum airfoil thickness
    $Ma \:\:$  Mach number

Another consideration is wing volume: In most aircraft, the wing will hold most of the fuel, and a long-range aircraft needs big tanks. Sometimes, only choosing a lower aspect ratio will give enough wing volume for the required range. In order to keep induced drag constant, the span will be kept the same, so wing area increases with chord length. This has the added benefit of more lift, so less complex high-lift devices are needed. Since the structural mass of such a low aspect ratio wing with simple flaps is relatively low, the only disadvantage is the higher friction drag of this larger wing.

If maneuverability is important, wing span needs to be as small as possible. This reduces inertial moments and roll damping, so the aircraft can accelerate faster into a rolling motion and will reach a higher roll rate. This is extremely important in dogfights when the one who points his radar, gun and rockets at the adversary first will win. Here the chord is chosen for sufficient wing area at the minimum practical wing span.

Now we need to talk about viscous effects. Friction between air molecules and between air and wing. The ratio of inertial to viscous forces is expressed by the Reynolds number, and generally a higher Reynolds number means your friction effects go down, translating into less friction drag and a higher stall angle of attack. Especially for model airplanes, but also for gliders, it is sometimes better to reduce aspect ratio in order to gain absolute wing chord. The Reynolds number increases linearly with wing chord, and this can also be a consideration for choosing wing chord.

A normal wing has positive camber, and this means that the center of pressure moves forward with increasing angle of attack. Moment-wise, this means that the wing will create a stronger pitch-up moment when it pitches up. This makes the wing by itself unstable, and you need a tail surface to regain stability. Making wing chord longer will increase the unstable influence of the wing relative to the unchanged tail surface. This is why I said that increasing chord will decrease stability. During design, you watch for a size called tail volume. This is the area of the horizontal tail surface, multiplied with it's lever arm expressed as a multiple of the wing's reference chord. If you keep this constant while changing wing chord, your stability stays the same. But then you change your pitch damping, because this is affected by the square of the lever arm. Digging deeper will uncover more consequences, so I better stop here for today.


Where can I find an ATM simulation software to investigate traffic flow capacities?

I have already found answer for my problem. ACES and FACET from NASA Aviation System Division solve my problem. It should handle all statistical data, it has statistical output as well and it could also handle meteorological data. Currently this SW use FAA and some airline companies to modelate ATM concepts (aviationsystemsdivision.arc.nasa.gov).
Thanks for all your help!


What are the differences between porpoise; bounced; and nose-pointed-down landings?

If the nose landing gear (NLG) makes contact first, but the plane settles down on the runway, that's a nose-down landing.
If the landing is normal, i.e. the main landing gear (MLG) touches down first, but the plane bounces, only to settle down on the MLG, that's a bounced landing.
If the plane bounces, after scenarios 1 or 2, but proceeds to land on the NLG, leading to multiple bounces on the NLG, that's a porpoise landing. Risking structural failure.

Source: boldmethod.com


What are the mechanisms fitted in the SA321G Super Frelon rotor head?

All rotor heads need to deal with multiple forces but two in particular have a big influence on the design and complexity of the rotor head.

As a blade moves forward (the advancing blade), it experiences an airflow equal to the speed of the blade plus the air speed.  As the blade moves backwards (the retreating blade), it experiences an airflow equal to the air speed minus the speed of the blade.

Therefore, the advancing blade generates more lift and will rise which causes the airflow to hit the blade with a more vertical component, reducing the angle of attack and the lift generated.  The opposite happens to the retreating blade.

This causes the advancing blade to flap up and the retreating blade to flap down.  The rotor head must allow this to happen and deal with the resulting forces.

The second effect arises from the Coriolis effect.  This results in a force applied to the hub by each blade as it speeds up and down called lead/lag.

There are three main types of rotor head.

Fully articulated.

From danubewings.com, copyright of FlightLearning.com

The blades are attached to the hub with hinges that allow the blade to flap up and down and lead/lag (or drag) hinges around the hub, allowing these forces to be absorbed without applying them to the blade or the hub. The blades may also rotate in a cuff through which the blade is attached to the hub. Each blade can flap and lead/lag.  Note that dampers may also be fitted to reduce vibrations and to better absorb the forces.

These are the most complex heads, an example of which is in your first image.

Semi-rigid.

Copyright www.copters.com

The blades are attached to the head with lead/lag hinges only.  Flapping is enabled by allowing the entire head to "teeter" on hub so that if one blades rises, the other must fall.  They cannot flap independently. Since the entire disc tilts together, semi-rigid heads can only have 2 blades.

The coning hinges allow both blades to move up and down together, without regard to where the teetering hinge is, as power is changed collectively.  So, the flapping (or teetering) hinge enables cyclic flapping whilst the coning hinge enables collective flapping.

Rigid.

Copyright helistart.com

The blades are rigidly attached to the hub and the flapping and lead/lag forces are absorbed entirely through flexing of the blades.  This is the simplest of all heads.

The choice of rotor head type is a complex one with intended design and performance being primary drivers but, as the head gets more complex, rigid being the simplest and fully articulated being the most complex, the maintenance cost goes up and generally, so does the weight.  Conversely, fully articulate heads produce the lightest loads on the main rotor shaft, it's thrust bearings and the gearbox coupling allowing weight savings to be made there. Rigid heads also require the strongest blades, and therefore weight, although modern composites are enabling the manufacture of blades with high flexibility but lower weight.

The head you have shown is particularly complex as it is six bladed and has an automatic folding system so that it can be stored and hangared in small spaces and be ground manoeuvrable on aircraft carriers with limited deck space. The tail folds at the same time as the blades. Most of the stuff you can see apart from the blades, their cuffs and their hinges is hydraulic piping, pumps and motors, electrical bonding strips, sensors and transducers. There is also an oil lubrication system for the bearings - you can see the oil reservoir on the top of the hub.  The use of elastomers in bearings has removed a lot of the need for lubrication.

If you stripped all of that it away, it wouldn't look (quite) so complex.  I.e. Not so barking mad!

Copyright helistart.com


What component of an aircraft is most likely to fail?

Aside from the obligatory "The Pilot" answer, there are some components on an aircraft that will certainly fail at a higher rate than other components.
From the Piston GA side of the equation I can name a few (some of which are also applicable to turbine aircraft).

Incandescent Light Bulbs
A lightbulb is a supremely unreliable device: A delicate bit of wire is suspended in a thin glass envelope and heated until it glows - then subjected to vibration (from the engines, turbulence, etc.) in flight. We use them all over the airplane -- Position lights, landing lights, cockpit instrument lighting, etc. If you think about how often incandescent light bulbs burn out in your house it's probably not surprising that they fail quite often on aircraft. One such failure lead to a famous crash.

  We still use incandescent lightbulbs because they're cheap: A $0.25 light bulb can be replaced multiple times before its cost even approaches the capital investment in a better solution.
  Modern aircraft are incorporating an increasing number of LEDs to replace incandescent lightbulbs - these solid-state devices have a lower failure rate (and other benefits).

Batteries
Much like your car aircraft rely on batteries for some functions (like starting the engines or the APU). Batteries have a finite service life and will eventually fail to hold a charge and need to be replaced.
Sometimes battery failures can be rather dramatic.

  We still use batteries because hand-propping aircraft can be dangerous, and getting the APU turbine up to speed without a battery would be nearly impossible. Also if the engine-driven generators fail the battery is a useful source of electricity to help you get to a safe landing site.

Spark Plugs
Piston engines are spark-ignition, and spark plugs have a variety of failure modes (they can become fouled with lead or carbon deposits, the internal resistor can fail, or the electrodes can simply wear out).
These failures are not uncommon: Statistically if you fly piston aircraft long enough you'll probably encounter at least one of them.

  We use spark plugs for obvious reasons: Unless the fuel is ignited it doesn't generate any power. Without power the propeller doesn't turn (at least not very fast), so there's no thrust. No thrust means no flying.

Tires
Tires are another aircraft component with multiple failure modes. Interesting ones include leaks (air leaving the tire at a rate fast enough to be a problem), "catastrophic" failures where the tire explodes or disintegrates while rolling, and "self-protective" failures (where the tire reaches a temperature that melts the fusible plug and causes it to deflate to prevent it from exploding).

  Tires are also used for an obvious reason: Aircraft that constantly belly-land require expensive maintenance (to say nothing of the damage they do to the airport), and the alternatives - skis, pontoons, or flying boats - are limited in the areas from which they can operate.

Air Filters
On piston engines there is normally an intake air filter which is designed to keep dust and grit out of the engine. These filters can fail by becoming clogged (which I suppose isn't really a failure: The filter is doing its job), and certain paper filters can fail by disintegrating and being ingested into the engine (the FAA has issued airworthiness directives on this subject).

  We still use air filters - even the paper kinds that can disintegrate - because ingesting dirt into a piston engine greatly accelerates wear. The required maintenance on the air filter costs less than increased overhaul frequency.


Do you need an instrument rating to fly in IMC in Class G airspace?

In the US, an appropriate instrument rating is needed to fly when WX conditions are below VFR minimums, and at night for SVFR.  14 CFR 61.3(e)

Additionally, one needs an appropriate instrument rating to fly under an IFR clearance when in controlled airspace, regardless of the WX.

Notes: ATP and things like a category and class in an airship are exceptions. Also an airplane instrument rating works in gliders. Etc.

Addendum: Specific to the OP's citing a NTSB report, the following comment is added: To rely on the mentioned NTSB report, it is important to read the findings, and understand that, a.) the pilot intended to hit VFR conditions before 700AGL and upon entering controlled airspace, b.) the pilot told people he was taking off despite qualified observers noting 200 ft clouds, c.) the airport where approach was based said they were below IFR, which would leave the pilot few options if he needed to land nearby. Given that, it is easy to agree with the NTSB. Just because something is legal, doesn't mean it is best practice, and in this case it is likely the pilot did not do as stated.

One final point, IFR without a clearance in Class G is a decision which should not be taken lightly. Years ago, I routinely did it, and the airspace was uncontrolled at safe IFR enroute altitudes.  Departing a Class G airport, with less than VFR conditions, and expecting VFR before hitting controlled airspace at 700AGL is dubious. The vest majority of my IFR flights in uncontrolled airspace, that were without benefit of clearances, were where there are large areas of uncontrolled airspace, and safe IFR altitudes could be flown enroute. Furthermore, while ATC did not issue clearances for flight in uncontrolled airspace, coordination with ATC where possible, and also with local FSS were done. That is different from popping off an airport that is likely IMC, and stating that one intends to climb into VFR weather before hitting 700AGL and controlled airspace. The frosting on the cake is having the field in the area be below IFR limits for approaches.  Good judgment is hard to legislate.


Does slipping in turns allow higher climb rates?

Source: Wikipedia.

Origin of the theory

Klaus Holighaus, one of the famous glider pilots of the 70s, and himself a glider designer at Schempp-Hirth, is at the origin of a controversy when he recommended not to turn with the ball centered, and especially when climbing in thermals. Mr Holighaus did see two problems with the perfectly coordinated turn:

It doesn't reduce drag as in straight flight.
It reduces the aircraft margin for roll stability.

I'm not an expert in the field, so I'll just rely on the article by Richard H. Johnson published in Soaring Magazine and titled "Do you really want to keep the yaw string centered?"

Before going into Klaus Holighaus' theory, let have a look at lateral stability.

Roll stability: Dihedral angle

Unless you want a very agile aircraft, an aircraft must have positive stability on the three axis, i.e. if the aircraft straight and level attitude is unsettled by some event, the aircraft must have a built-in tendency to cancel the effect of the perturbation and to return to its initial attitude.

Roll stability is required to prevent the roll angle to increase automatically after a small unwanted roll input by the pilot or by a cross wind gust. The aircraft must return to a null roll angle automatically to prevent nasty consequences, including entering a spiraling descent.

Roll stability is mostly provided by the dihedral angle of the wing as explained in How does the dihedral angle work? In short: The dihedral angle uses the sideslip to create an opposite roll motion.

No sideslip: No dihedral effect

We know turning is not controlled by the rudder but by rolling the wing with the ailerons. But at some point the lowered wing aileron may also be deflected downward for turn rate control, and this deflection may happen to be excessive:

  When  the  lowered wing's  aileron  is  deflected downward,  not only
  is  its  lift increased,  but also  its drag is  increased, and a
  skidding turn  will  be induced.

At the same time the lowered wing, being closer to the turn center, is flying slower than the raised one. Slow speed, high angle of attack and more drag for the aileron can induce a stall: If the lowered wing or its aileron stall, drag on this side is increased and the aircraft is likely to enter a dangerous spiral.

However in most of the cases we can stop skidding:

  The skid can  easily be corrected for by adding some top rudder to
  keep  the  skid  ball  centered.

The solution implies to add drag to the rudder, which is not satisfactory from a performance perspective.

Get the best of both worlds

This is where the mild-slipping turn theory comes from: By turning with a slight slip instead of a perfectly coordinated turn:

We keep the dihedral benefit to stabilize the aircraft around the roll axis. This is safer.
The negative roll moment provided by the dihedral allows us to use less ailerons deflection, so less drag and more speed, and better climb in the thermal.
We use less rudder, so even less drag, and even better climb.

The article's author adds this explanation about improving lift with the sideslip:

  Why slipping improves the climb in some gliders is not well
  understood. In generating lift, wings also generate spanwise flow,
  outward along the bottom and inward along the top of the wings. It is
  possible that there is flow separation near the tip of some circling
  sailplanes, and that slipping changes the spanwise flow enough to
  eliminate or reduce this. Separation can increase the drag
  significantly long before the tip actually stalls.

The article also enter in the details of why this is different when winglets are used on the wing. Slipping may induce a stall instead.

How much sideslip?

  The optimum degree of sideslip depends to some degree on both the
  sailplane's wingspan and dihedral angle. After many hours of flying my
  16.6 meter ventus a and similar sailplanes, I find that my best overall
  circling performance and handling characteristics occur while
  the canopy mounted yaw string is deflected about 10 degrees on the
  high side of the turn (a gentle sideslip actually).

Yaw string vs ball

The yaw string is also more accurately named the slip/skid string, as it doesn't indicates a yaw angle but a quantity of skidding/slipping, like the ball.

As @ymb1 commented, the string being on the canopy, ahead of the CG, its indication is exaggerated.

In a coordinated turn, the ball of the slip/skid ball indicator will be centered while the yaw string will be already indicating a slight amount of slip. This error will be magnified with actual slip.

The author estimates the actual degree of slip in his case is more accurately about half the indication of the string. See also Peter Kämpf's comment: "exaggeration is also caused by the fuselage shape [...]".


How would one define or explain the term "unloading the controls?"

When maneuvering the aircraft by deflecting the control surfaces with the stick, the wing with the downward aileron and the tail will generate additional lift, which increases the load on that wing (using the ailerons) and on the tailplane (using the elevator).

Unload the controls is a request to neutralize the pressure on the controls. Usually this means bringing the stick back to the center position, reducing the controls surface deflection, the amount of lift generated, and therefore reducing the aerodynamic load on the wings and tailplane.


Why do airports in the UK have so few runways?

There are perhaps 101 non aviation-related reasons why the UK does not have larger airports, such as space consideration (we're only a small island!), politics (NIMBY!), civil engineering (Airports are commonly near urban centres and are often surrounded).

However, the most aviation-related related reason I can think is that we just simply rarely need cross runways. If you look at most large airports in the UK their runway(s) are east-west(ish). The reason for this is over 70% of the prevailing wind direction in the UK is West or SouthWest.

In addition, we rarely have extremes of wind - those exceeding the crosswind capabilities of common commercial airliners. Heavy snow is even rarer. I can probably count the number of times a runway at a large airport has been closed due to any of the reasons you mention in the last 20 years on two hands.

Bottom line; it's just not necessary. There is no socio/political/weather climate to warrant it.


What is the willingness of non-AME/pilot physicians to perform BasicMed exams?

I have Kaiser insurance and tried really hard to get them to conduct my physical, to no avail. I was thwarted by some degree by the fact that my regular physician is not seeing patients right now, but my suspicion is that she may not have done it either. However, I have also heard of Kaiser members who did convince their physicians, so apparently there is some wiggle room. I ended up going to a clinic that does the DOT exam after asking if they would also do basic med - the doc turned out to be a pilot himself. Saved just a few buck compared to an AME.

As to why some folks would do basic med rather than a third class, at a certain age the third class is only good for a couple of years, while the basic med exam is good for five. That's why I elected to go with Basic Med. (I read recently that BM won't allow flight outside of the US, including Mexico or Canada, so that's something to keep in mind if you fly in those areas...)


Replacing or supplementing turbofan with electric fan

Answer to the first question: yes you could, and the answer to the second would be theoretically yes, but it would make no sense. Here's why:
When designing aircraft, a simplified version of choosing the engines would be that the plane should be able to safely climb with half of the engines installed. So: cruising power is significantly less than T/O or climb power. Basically this imaginary hybrid 747 would be able to cruise with two engines only, be they electric or conventional.
If the question is about generating electricity with the 2 turbofans, the problem is that to provide electricity for the electric fan so that it could maintain cruise speed, the conventional engines would, of course, have to be running at rather high power setting, and therefore they themselves would provide enough thrust for cruise. Assuming (quite liberally) efficiency of 90% for both the generators and the electric motors, we would end up with a maximum efficiency of 81%. At least 19% of power would be lost along the "powertrain".
If the electricity for cruise was to come from batteries, the setup, simply put, will not work. The weight of the huge battery bank is way too heavy for economical operation.
A little more sensible setup would be one where conventional engines are assisted by electric fans or such for takeoff and climb, and the electricity would come from batteries. Here again, hauling a heavy battery set for great distances is not very efficient, even if the battery bank could be smaller in this case. in addition to this, the electric fans would cause drag during cruise if the electric propulsion system is not integrated into the conventional engine somehow.


How are attitude indicators kept accurate?

A gyroscopic AI has an erection mechanism, which continuously corrects the AI to be upright based on the local level, or downward acceleration vector. The correction rate is generally 3-5 degrees per minute.

The way that the AI corrects itself is a system of pendulous vanes. When the gyro is not upright relative to the local level, centrifugal force pushes open vanes on the gyro's case. Air escapes through the uncovered holes, applying a force to the case, and correcting for precession.

(FAA AC 65-15A)

The second half is somewhat counter-intuitive, but flying in a coordinated turn will not continuously increase the error in the AI. For the first half of the turn, the AI will add error; in the second half, it removes the error. After a 360 degree turn, the precession error will be removed completely. For more detail, see another answer: If I fly a balanced turn long enough, will the AI show I'm level?