What is significant about the number 8069 ft?

Apparently you aren't the only person who wondered this; the FAA actually has it in an FAQ:

  What is the significance of a runway 8069 feet in length and why are two different aerodrome symbols used to depict hard surface runways on
  Sectional charts?

  For purposes of airport depiction, specialists
  represent a runway between 7970 and 8069 feet in length as 8000 feet,
  which equates to a line 0.192 inches in length on the Sectional chart
  scale. In this case, a circular aerodrome symbol is used.

  If a runway
  is between 8070 and 8169 feet in length, specialists round to 8100
  feet, which equates to a line 0.1944 inches in length on the sectional
  chart scale. This line is too long to fit into the largest circular
  aerodrome symbol FAA has available. Therefore, specialists place a
  line-work around the runway pattern forming a polygon (enclosed shape)
  for anything over 8069 feet in length.

  Specialists also place these
  polygons around the runway pattern of aerodromes with multiple runways
  that are less than 8069 feet, in cases where the multiple runway
  pattern does not fit into the largest, circular aerodrome symbol.


Why are the Boeing 747-8 engines on the wings spread apart?

That picture of the 747-200 you have with the engines in a pod together like a B-52 is a movie prop. http://www.airliners.net/photo/Boeing-747-236B/1070481/

All real 747s from the -100 through the -8 have their engines positioned like the first picture.

EDIT - Federico's response reminded me of another aspect of the engine position, and to answer your original question of why they're spread apart. Spacing between the 747s engines is important due to the need to maintain sufficiently clean airflow into the inlet. If the engines are too close together, they're essentially competing for the same amount of air, and at high power settings, the interaction between the two fans will disrupt their operation, potentially causing engine stall/surge. Additionally, the 747 uses thrust reversers, and the spacing between the engines helps ensure that the reverse flow from each engine doesn't impact an adjacent engine, for the same inlet distortion reason.

I assume, though I don't know the details of this, that the B-52 can have them that close together because they've shown that the inlet geometry, airflow required by each engine, whatever other magic of fluid dynamics that I know nothing about, prevents the engines from distorting each other's airflow enough to cause an issue. The 747 engines require a lot more air, and generate a lot more thrust, and are potentially more sensitive to inlet disruption than the engines on the B-52. This last paragraph is mostly a guess on my part as I'm not an aerodynamicist, but it's inferred from issues we've had to deal with on the 747 and other related airplanes.


Could the non-smoking sign still be turned off in modern airplanes?

It would appear that the aircraft you flew was D-AGWR, a A319 with MSN (Manufacturer Serial Number) 4285 delivered in April 2010 (hence fairly new).

There is a switch at the bottom of the overhead panel, next to the seat belt sign, slightly right of the middle. Flip it and they will extinguish. The functionality is a bit more complicated than it would appear, since it feeds into the central aircraft electronics.

Olivier Cleynen at Wikicommons

Out of interest, this button no longer exists on the Boeing B787, suggesting that it is on the way out. Only the seat belt option remains.

The slots for no smoking are being increasingly 'redeveloped' into a sign for electronic devices instead on some types. They just put a no smoking sticker on the seat in front of you to fulfil the same function. I do not know if they cockpit text has been modified on the aircraft that undergo this modification.

Source


How does the aneroid wafer expands? (ASI)

The aneroid wafer is just a metal balloon.  Add air into its interior, above ambient pressure, and it expands.

The outside of the wafer is exposed to ambient static pressure.  The inside of the wafer is plumbed to the pitot inlet.  Ram air into the pitot raises the pressure within the pitot plumbing to above ambient, which being connected to the interior of the wafer, inflates it.  The movement of the inflating wafer is geared to the airspeed indicator and voila, ya got yer speed indication.


Can the A380 ferry an extra engine, like the 747?

One of the main reasons the 747 was given the ability to ferry an engine was due to the lack of large cargo aircraft available at the time.

Don't forget the 747 was a major game changer when it came out, it was designed to replace the 707/DC-8, and was almost twice the size of these aircraft. As a result, there just wasn't anything available to transport a 747 engine by air if needed.

This was a major problem that had the potential to affect sales of the aircraft, and so they had to find a solution to this. It wasn't until the 747 began to be introduced as a cargo carrier that it was possible to transport these engines by air, in the hold of an aircraft.

With the introduction of the A380, there was no need to add engine ferry capabilities, as large cargo aircraft were common enough to transport them.


Is it practical to intentionally stall an aircraft to execute a fast, controlled descent?

It isn't practical for a number of reasons:

Intentional stalls are inherently dangerous. Stall-spin accidents are a major cause of accidents, stall recognition and recovery are taught specifically to avoid stalls.  Some airplanes have docile stall characteristics, but even those can still bite you. A Cessna 172 will drop a wing if mishandled, especially when heavy. Stall behavior at high altitude can be very severe
Some airplanes with a t-tail can enter what is known as a 'deep-stall', where turbulent airflow masks the tail and makes the elevator ineffective and the airplane unrecoverable
Situational awareness: dropping like a stone with the nose up does not give pilots a view of the outside, or see what mountain they may be heading towards
It takes time to do a controlled stall. You have to pull throttle and maintain altitude, degrading airspeed until you enter a fully developed stall. This isn't instant, in a light airplane it will take 30 seconds or so, I'm not sure how long it would be for an airliner at cruising altitude, but I imagine it may take a minute for a fully developed stall to develop and to get that high rate of descent, whereas you can be in a dive with a steep rate of descent in a much shorter time

Consider an emergency descent from FL400 (40 thousand feet) to FL100 (10 thousand feet) using the 2 methods: A dive at 8000fpm and a 'controlled' stall at 10000fpm, where it takes 30 seconds to get into a developed stall and high rate of descent:

60 seconds: the diving airplane is at FL320, the stalling airplane at FL350
2 minutes: the diving airplane is at FL240, the stalling airplane at FL250
3 minutes: the diving airplane is at FL160, the stalling airplane at FL150
3 minutes 30 seconds: the stalling airplane is at FL100
3 minutes 45 seconds: the diving airplane is at FL100

So, by these calculations the stall option saves 15 seconds to lose 30 thousand feet because of the time penalty to get into a stall in the first place. That's really not much, and considering the risks involved from the potential loss of control and spacial awareness it's simply not worth it.
Not only is it not practical, it's not necessary to descend faster. A high speed descent is required for a number of emergencies, a cabin depressurization being the most prominent one, but there you have emergency oxygen supplies which will last much longer than required, so a few seconds will make little difference to survival. With an in-flight fire or other emergency where landing quickly is imperative the limitation is not descent speed, but proximity to landing fields which determines survival.


What options are there in Canada for treatment of severe depression and anxiety for pilots?

I'm not going to address the legal aspects of your question, but I will tackle the psychological side as I have a degree in it - although I'm not a practicing psychologist. It sounds like you have been through a bad period and are likely coming out of it into a better period, what you need to do is see a professional and get some help very soon. Everything seems impossible when you're suffering depression, but it's very treatable and you may still be able to fly.
It's in everyone's best interest, especially yours, to have you well and functioning. As you have stated yourself going without treatment is unsustainable whether you are flying or not, so there's two possible outcomes with treatment:

You're better and you can still fly: pilots can fly on anti-depressants in most jurisdictions, including Canada, provided they get medical clearance
You're better and you do something else

Either outcome you're better, which is miles ahead of where you are now. You lose nothing by getting treatment, things can only get better with it.
Drug treatments exist for most types of depression and bi-polar type disorders, and studies show that they are most effective when they are paired with counseling. I would suggest cognitive-behavioral therapy (CBT) as you will learn better coping strategies and thought patterns. Things will get better if you get help, so see your doctor right away.


What should a pilot do to perform a successful emergency water landing?

What should a pilot do?

Follow the checklist?

  Is there any checklist?

There are many such checklists in the intertubes and whole books have been written on the subject

Here's the start of one for 737s

For comparison, here's one for a Cessna light aircraft

  Are commercial jets buoyant?

Yes, initially, if substantially in once piece. We know that because several intrepid pilots have tested this idea (obligatory hat-tip to Sullenberger).

It makes sense that the fuel tanks in the wings, especially once emptied of fuel, are buoyant. The wings are obviously capable of supporting the fuselage. The fuselage is a pressurised tube and should be buoyant too, until the passengers and crew start making large holes in it.


If skydivers cannot jump on a flight, what should I take care of when landing?

You should descend in a controlled way, taking into account that your descent rate should be ≤ 29 mph (less than 13 m/s), once below 2,500 feet.

If the descent rate is higher than that, then there is a risk of the AAD popping the skydiver's reserve parachute, mid-flight.


How to reverse course when there is no published course reversal?

If the approach doesn't contain a published course reversal (ie PT barb or Hold-In-Lieu), the approach must be flown straight in. In this case, you will either get vectors-to-final or you will get cleared via one of the feeder routes.


What does RPM mean in a propellor aircraft, compared to a jet aircraft?

RPM in a propeller aircraft is typically under 2400, as the prop spins at the engine RPM speed. Above 2700 the tips of the propeller begin going supersonic and make more noise than anything.

Jets engine spin much faster, as discussed here
Which are typical rpm values for aeronautical turbines?


How do preceding aircraft affect the ILS signals?

I've never noticed any perturbation of the ILS signal from aircraft ahead in flight. Aircraft on the ground crossing the runway, absolutely yes. Something big enough (747 or A-380) exiting at the far end, perhaps briefly, but not generally something you notice.

I'll let somebody else explain the theory, but that's my observed results.


So far as the FAA is concerned there is no 727-200C at least not that ever carried a type certificate. The 727 series has a common type cert which you can find here and it has no listing of a 727-200C type. There are however 727-100C and a 727C types listed and some other numberings that use the C nomenclature but none that use -200C. The image that @JuanJimenez links from wikipedia is incorrectly labeled. You can see it carries Canadian registration C-GXFA which is a 727-233 you can find more pictures of it here. Also note that the wikipedia section states only one was built and provides no citation at that.

Interestingly the Smithsonian has a model of one...


How does sideslip indicator react during crosswind?

1. Answer to original OP

In a stable airmass, the amount of sideslip/skid indication is irrespective of the wind strength and orientation; it is a function of the relative velocity of the airplane against the airflow only (stable winds are referenced to ground). That is, with all engines operating and rudder centered (assuming no inherent asymmetry), then the sideslip indication will be zero, whether you have winds or not.

In gusts, the winds are transitory against both the ground and the airplane frame of reference, which will induce change in airspeed, AOA and sideslip. This will result in change in aero forces and moments, until the inherent stability of the airplane stabilizes the airplane or the gusts die down.

In a pure lateral gust, this translates to a sideslip (and an increase in airspeed) measurable on the yaw string, and generates a side force measurable on the skid indicator.  Both would concur in measurement (opposite in visual direction).

2. Addendum to address the modified OP

  The air mass is no longer an inertial frame of reference.

No one ever uses airflow as a frame of reference unless you're doing fluid mechanics, which is not very relevant here. Airflow matters to airplane only because the latter responds to airflow changes (via aerodynamic forces).

The ball does not measure the crab angle; it's dumb and doesn't know what the airplane heading is or where it's going. The ball only measures the side force relative to the aircraft, much like a bubble level. With all engines operating (or no engine operating) and in flight, only aerodynamics can generate side force, most directly via sideslip (control surfaces can, too; but the magnitude pales in comparison).

In your scenario of a linearly increasing crosswind, sideslip increases with crosswind, measurable by the string. Increasing sideslip induces side force, measurable by the ball, whilst pushing the airplane off course, further increasing crab angle. At the same time, the airplane yaw stability responds by yawing the nose toward the crosswind. After some time, without pilot correction, the airplane has yawed sufficiently that the crosswind becomes a head wind.


What are the reasons for the particular range of VHF and UHF frequencies?

Short answer
The reason for a difference in ranges is historical. The figures from Wikipedia are the recommended ones (by ITU, the reference in radio spectrum matters), however the abbreviations VHF/UHF are also used in related contexts, often in an attempt to discriminate similar uses when being short of other means. In the current case, FAA likely wanted to give different names to different ranges:
118-137.0 MHz: VHF Air/Ground Communications
225-328.6 MHz: UHF Air/Ground Communications

This kind of approximation has actually no practical consequences, except adding confusion to a so much misunderstood field.
Classification of waves according to their frequency is just to determine ranges where waves behave similarly, e.g HF are known to be well reflected by ionosphere, while VHF are less sensitive to such reflection and propagate more along direct light of sight. However this is a progressive and slow change, crossing the border between HF and VHF is like crossing the equator: It has no particular effect (though for the latter, there are lots of good 'proofs' I'm wrong)
There are many examples of radio concepts used approximately, e.g. when we're talking about the 'FM band' to refer to the frequency range used to broadcast using 'wideband FM' (WBFM) modulation required to transmit the large bandwidth of a high quality stereo signal; this range has no particular properties and is not a 'band' and is indeed not technically more appropriate for using WBFM, except regulation forbid other uses.

Close frequencies behaves identically
While there are significant changes between 50 and 600MHz, there is none between 100MHz and 130, 220MHz and 300, or 320MHz and 340.
The only exceptions are not relevant to aviation. Sudden changes in behavior of waves with close frequencies are possible due to absorption of narrow isolated ranges by atmospheric components, e.g. water molecules are small antennas absorbing signals at their resonance frequencies, but resonance occurs at 22 GHz.
Significant differences in radio waves relate to frequencies which are remote
The most significant change in propagation is how much waves can be reflected by the atmosphere and the ground. When such reflections are possible, the communication range is spectacularly increased, as waves can be guided like in an optical fiber towards the receiver area. But again there is no big difference between frequencies belonging to adjacent classes, but near their common border. Broad modes of propagation:

Below 3MHz (a wavelength of 100m), transmission takes advantage of the ground wave (ground currents) to travel on long distances.

Between 3Mhz (100m) and 100MHz (3m), long distance links use the sky wave (reflection on ionosphere, during specific periods of time and according to solar activity, for more on that, see What is the night effect?). Current propagation predictions with close frequencies tending to propagate identically (thanks and credits: Paul L. Herrman et al $\tiny 73$):

Above 100MHz (3m), transmission strictly requires a line of sight and no obstacle in the 1st Fresnel ellipsoid which volume is dependent on the distance between stations, else significant losses occur.

These three first classes are perhaps the most fundamental, then additional divisions have been created above 100MHz (which at the time was already in the "very" high frequency class), because materials can behave significantly differently, e.g. at 150MHz, the only acceptable type of transmission line is coaxial, non-coaxial lines have too much losses, at 15GHz metallic lines are not usable anymore, due to skin effect, dielectric behavior, thermal noise, to name only the first reasons, hollow waveguides are used.
Why are there different classifications for radio waves?
Different segmentations of the whole electromagnetic spectrum have been proposed by different organizations, to focus on the differences that are important for them. These classifications have not to be particularly strict for the reasons explained above, and the limits in publications have varied.
The one Wikipedia is referring to uses segment frequency limits in "3" (3, 30, 300), these limits when expressed in wave lengths become 10m (30MHz), 1m (300MHz), 10 cm (3GHz), etc ($\small \lambda = c / f$).

Source
These limits are the ones recommended by the ITU in ITU-R  V.431, and they are the most commonly used. Not that there are bands without names (but all bands have a specific number).
Sometimes it is useful, or necessary to subdivide the spectrum into smaller chunks. For example TV broadcasting has operated different ranges of frequency spanning HF/VHF/UHF, transmitting at high power. However in the beginning it was not possible to build reliable powerful amplifiers at economical price, except at lower frequencies, so TV started in HF/VHF. As technology improved and higher frequency ranges became workable for amplifiers, new names were used to refer to frequency and associated electronics, exactly like cellular infrastructures and phones are known as 3G, 4G, 5G. We have all seen those names, when tuning the channels: Band I (broadly the "FM broadcast" band), II, III (174-230MHz), IV, V (582-960MHz).
Space communication engineers have their own classification of the SHF and upper bands as letters (L, S, C, Ku, Ka...). This split is well suited to describe the communication capabilities.

For example the US Orbiter communicated with a built-in S band antenna (2GHz), but could deploy a Ku band antenna (16GHz) from the payload bay when in orbit, to increase the transmission rate, e.g. for video streaming.

Radar people have also invented their own bands, for their specific use of the radio spectrum:

Source
And for many persons, waves are also known as short waves and long waves, categories which have been seen during years on radio receivers:

FM/SW/MW/LW on a legacy Grundig Satellit receiver
Likewise many engineers also use the term 'decametric' ('deca') to refer to MF/HF, or 'centimetric' and 'millimetric' for waves in the hyperfrequency domain. Those names have also been recognized by the ITU, though the mapping is somehow approximate.
Indeed aviation has had a need to create frequency segments.
VHF/UHF in aviation
"Aviation bands" include:
 - 108 - 112  MHz NAVAID (VOR, ILS Localizer)
 - 112 - 118  MHz NAVAID (VOR, LASS and SCAT-I))
 - 118 - 137   MHz VHF Air/Ground Communications
 - 62 -  174   MHz Fixed, mobile Communications

 - 225.0 - 328.6 MHz UHF Air/Ground Communications
 - 328.6 - 335.4 MHz NAVAID (ILS Glide Slope)
 - 335.4 - 399.9 MHz UHF Air/Ground Communications
 - 406.0 - 406.1 MHz Satellite Emergency Position Indicating Radio Bcn

Source: FAA order 6050.32 (page 29).
FAA has chosen to see the 225.0 - 328.6 MHz segment as being UHF, even if it starts before 300 MHz. This has no technical impact or implication, wave at 225MHz behave like these at 300, the actual difference from a technology standpoint is more between 150 and 350MHz.
Frequency allocation
In the US, the radio spectrum is allocated to users and final use according to this map (year 2016):

Source
In Europe, spectrum allocation is under ECC responsibility. Current status can be found in "ERC Report 25", aka the European Common Allocation (ECA) Table.


What would be a safe minimum vertical separation distance between passenger-carrying multicopter aircraft?

The downwash is directly related to total lift; more rotors just means each rotor is producing a smaller fraction of the total, and the end result should be no different for separation purposes than for one or two rotors.

There are a lot of obstacles to mass adoption of personal aircraft, but the exact lift mechanism is arguably the smallest.


What priviliges and limitations does an Aircraft(General) mechanic have versus an A&P?

None. It is required to pass your written general to move on to obtain your Aiframe/Powerplant certification via an Oral & Practical exam. There is no general certification.

If you're looking for a way to work without certification, you can work under a 145's certificate without any.


Why didn't Philippine Airlines Flight 113 dump fuel prior to forced landing?

If you had an engine fire, even though it may be "out", you want your airplane on the ground as soon as you possibly can.  You don't know what structural damage is lurking as a result of the fire.  Dumping fuel would take a fair amount time to get rid of any significant amount.

So it's "Screw the landing gear.  We're landing overweight".


What happens if an aircraft is only stable at higher angles of attack?

I find it hard to come up with an actual example that behaves like postulated. Normally, airplanes are most stable at low angles of attack and lose this stability at higher angles.
But there is indeed one case where angle of attack stabilizes the airplane: A swept flying wing without a vertical tail. Like the Horten designs. Those would enjoy increasing directional stability with increasing angle of attack. Your limits are a bit extreme, but a Horten IV was directionally indifferent at high speed when the typical angle of attack of the root airfoil would be between 2° and 0°. At lower speeds the induced drag would help to pull the airplane out of a sideslip as explained here.
Due to the high inertial moment around the vertical axis this behavior can be controlled by the pilot because sideslip angles will build up slowly. But it is not pleasant since it needs constant control inputs and puts an unnecessary workload on the pilot which might interfere with other tasks like navigation and collision avoidance.
Of course, this example is not quite what you wanted, since a higher sideslip will not stabilize the airplane. Only pulling up will.
If we hypothesize that an airplane behaves as you postulated, it will tend to leave the unstable region, but this might happen both in positive or negative AoA direction. An excursion into negative angles of attack is rather unpleasant (have you ever flown an outside loop?) and will probably make the pilot pull up hard. What happens next? The airplane flies through the unstable AoA region and picks up more pitch speed, only to arrive in the stable region with such a force that it overshoots the AoA limit and either stalls or, given enough flight speed, breaks up.
The Saab JAS-39 Grippen had such an unexpected overshoot at the most unfortunate of times, namely during a flight display on the occasion of the yearly Wattenfestival in Stockholm in 1993.
Any instability in the regular operating region is a bad idea and an invitation for mishaps that could be easily avoided.


An airplane has an engine that pushes its flight. What force pushes a glider to fly?

Airplanes do not fly because of their engines. Airplanes and gliders both fly because their wings turn thrust into lift and drag.

That simplistic answer, of course, just begs the question "how can you generate thrust without an engine?"

A glider is constantly trading altitude (potential energy) for airspeed (kinetic energy). Energy over time equals force, which in this case we call thrust. Airplanes do the same thing when descending. Both can also trade energy in the opposite direction, but only briefly until the wings stall.

The big difference is that an airplane can also turn fuel (chemical energy) into thrust, which allows sustained level or climbing flight. Gliders don't have that option.


The starting envelope determines the range of altitude (and possibly temperature) at which the APU can be started in flight. In your case, the manufacturer specifies that the APU can be started at altitudes between 1000 ft below MSL and 39,000 ft above MSL, which is also the operating envelope of the APU.
Here is an APU operation and restart envelope of an Airbus A320:

(source: Airbus A320 Limitations - APU)
The cyan range is the operation and restart envelope (as a function of altitude and temperature). This APU model can only be used for bleed air and electrical power up to 22,500 ft altitude. Above, it can only provide electrical power. It also says that the battery is capable of starting the APU below 25,000 ft.


(1) How can can other fluids contaminate the bleed air?

Engine Oil:
The engine fan and compressor stages are rotating pieces of metal on metal and thus need lubrication. Engine oil is used for this purpose and could come into contact with the bleed air in case of a leakage (see mooveaviation.com for details).
Hydraulic Fluid: Some components of the engine, e.g. the thrust reversers, are hydraulically actuated. Again, a leakage in a pipe could lead to hydraulic fluid entering the engine.
De-Icing Fluid: When an aircraft is deiced on the ground, the crew needs to disable the bleeds during the deicing in order to avoid any contamination, see e.g. Boeing 737 NG FCOMv1 XP.16.8 (Supplementary Procedures - Adverse Weather):

  CAUTION: Operate the APU during de-icing only if necessary. If
  the APU is running, ingestion of de-icing fluid causes
  objectionable fumes and odors to enter the airplane.
  Ingestion of snow, slush, ice, or de-icing/anti-icing
  fluid can also cause damage to the APU.

  [...]

  Engine BLEED air switches ......................................OFF
  F/O

  Reduces the possibility of fumes entering the air conditioning
  system.

  APU BLEED air switch .............................................OFF
  F/O

  Reduces the possibility of fumes entering the air conditioning
  system.

Some of the deicing fluid might flow into the engine afterwards and if the bleeds are turned on to early, the fumes might get into the cabin.

(2) Could the bleed air be tapped at an earlier stage?

Bleed air needs to have a high enough pressure to be usable for pressurizing the aircraft at cruise altitudes. Moving to an earlier compressor stage would reduce the available pressure. Some engines have bleeds in both the low and high pressure compressor and will automatically use the appropriate one depending on engine thrust and pressure.


Why don't we use hydrophobic (icephobic) coatings over traditional anti-ice methods?

I have no doubt that a lot of experimentation has been done using coatings on GA airplanes and to the extent that a coating would work, the main problem that I see is degradation of the coating from UV and erosion.  A coating would likely have to be restored regularly and would be likely too expensive for most tightwad GA pilots.

The other thing is that clear ice that forms quickly can tend to sit in place because it's "cupped" around the leading edge and a non-stick surface may not help since the ice shape can be more or less mechanically held in place even if it's unable to actually stick to the surface.  Rime ice that tends to build up out in front of the nose of the LE would probably shed from a non-stick coating a lot better.

On a side note, your chart doesn't include "evaporative" anti-ice, which is a sub-type of heated anti-ice.  On jets this is often used with hard (non-slatted) leading edges because of the need to avoid "runback ice".  A leading edge hot enough to melt ice, but below the boiling point, will allow the water to flow back and re-freeze farther back on the non-anti-iced part of the wing.  Anti-ice systems in that case will be evaporative, that is, so hot that water immediately vapourizes when it touches (like a steam iron).

Such anti-ice systems run at 105+ C temperatures.  A coating that could prevent adhesion of runback ice behind the LE might be quite useful and could allow those wings to run lower temperature systems (the heat plays havoc with the LE structure over the long run).

Runback ice is tolerable on slatted wings and those anti-ice systems will run a lot cooler, around 50 deg C.

On yet another tangent, I always used to wonder why some jets anti-iced horizontal tails and some didn't. Turns out you don't have to anti-ice the surface if you make it big enough.


For designing a runway, what are the largest cargo airplanes in use?

Size doesn't matter.*
If you are designing a runway, then you should get familiar with ACN and PCN.

The aircraft classification number (ACN) is a number expressing the relative effect of an aircraft on the runway pavement for a specified standard subgrade category.

* There can be the largest aircraft out there, but it may have a lot of tires, so the force it will exert [per tire] on the pavement might be lower than that of a smaller plane (e.g., A380 and MD-11).
From the linked Wikipedia article, the MD-11 stands out as the harshest on pavements (after discounting non-freighter aircraft).

Runway length, and wingspan
In most cases, aircraft are loaded according to the available length, not the other way around. Not all airports that handle 747s have 11,000-foot [corrected length] runways.
For the wingspan (or main gear span), the categories are defined by ICAO Aerodrome Reference Code.

Element 2 of the Code is derived from the most restrictive of either the aircraft wingspan or the aircraft outer main gear wheel span.


Why is the pilot in this video retracting the spoilers so shortly after landing?

The pilot doesn't retract the spoilers until the airplane has slowed down considerably, at the speed it's traveling at that point the spoilers would be adding no benefits so there's no point keeping them deployed.


As of currently, the answer to this question is in principle no for commercial aircraft, at least not remotely. There are two parts to this:

From a system perspective:

Aircraft systems could probably be 'hacked'- assuming you could for instance screw up the flight computer by changing the chips in the belly- but there is no way you could really pull this off without the pilots noticing the course being way off from the compass for instance, so they'd figure out and shut it off. Many systems are not connected in a way that allows them to be cause damage to others. Systems are also pretty dedicated- if it's supposed to fly the plane, that's what it does, if it's supposed to navigate, that's what it does.
Systems on aircraft generally a have limited, if any, connection to the outside world. There are a few systems that have the ability to connect to the ground, and this is generally limited to simple text messages. Most of the electronics on the 777 are from the type's introduction in 1994. A decent analogy I think is trying to hack an early cell phone remotely.

And from a practical standpoint:

Aircraft are generally very stiff when it comes to changes- they are often approved in a certain configuration, and that then sticks, so there's little need to change stuff, and hence it's not possible. This applies to the autopilot and flight controls- once it's there, it stays there.
As a few people have pointed out, these systems are proprietary and closed source, making it difficult to program them if you're an outsider, but in theory it might be possible.

The fact that no aircraft, even the computer-intensive Airbus, have really been hacked to any extent, the notion that the entire aircraft would be taken over and flown somewhere is impossible.

As for original question link:

  “The FAA has determined that the hacking technique described during a
  recent computer security conference does not pose a flight safety
  concern because it does not work on certified flight hardware,” he
  said.

  “The described technique cannot engage or control the aircraft’s
  autopilot system using the FMS or prevent a pilot from overriding the
  autopilot,” said Dorr.

  “Therefore, a hacker cannot obtain ‘full control of an aircraft,’ as
  the technology consultant has claimed,” said Dorr.

On a similar accord, I think I heard a story about a Bombardier Dash 8 that got a computer virus once, but I think it never got beyond the navigation system, the most processing intensive part. Unfortunately, I can't find a source for this.


Why is the thrust-specific fuel consumption much worse for high bypass turbofans at cruise?

Yes, that is typical for high bypass ratio (HBPR) turbofans.

  But why?

Because the entry impulse goes up while the exit impulse stays roughly constant. Thrust is the difference between both, derived over time.
The moving engine needs to slow down the airflow for combustion to take place, and then needs to accelerate the air by more than it has been slowed down to have positive thrust. Hence, SFC goes up in parallel with speed.

While the internal process inside the engine in flight is very similar to that at rest (only the pressure levels are increased by the ram effect of the moving engine and density drops with increasing altitude), thrust is reduced due to the smaller impulse difference in flight. Since a HBPR engine accelerates most of the air volume streaming through it by only a little, the average exit speed is relatively low compared to a jet engine with no bypass flow. This is similar (but less severe) to a propeller where thrust drops with the inverse of speed.

SFC gets even worse in supersonic flight. For a meaningful SFC comparison speed needs to be the same.

Thrust-specific fuel consumption in g/kN·s of a turbofan engine with bypass ratio 3. Y axis shows altitude in Meters. Isolines wer made with R contour function and should be more rounded in reality.


What is the pressure distribution around a supersonic wing?

Normally, supersonic fighter wings for which airfoil information is published use a very thin NACA 6-digit section with very little camber, such as
Aircraft                root airfoil      tip airfoil
McDonnell Douglas F-15  NACA 64A006.6     NACA 64A203
General Dynamics F-16   NACA 64A204       NACA 64A204
Lockheed-Martin F-22    NACA 64A?05.92    NACA 64A?04.29

This information is from The Incomplete Guide to Airfoil Usage by Dave Lednicer. As you can see, the F-16 uses camber throughout, indicated by the 0.2 design lift coefficient of the airfoil, while the F-15 uses an uncambered root airfoil.
Those airfoils are chosen because flow around them at supersonic flight speed is still heavily influenced by subsonic flow characteristics as long as wing sweep allows for a subsonic leading edge. This produces nose suction, and flow around the wingtips disturbes the pure supersonic flow characteristics even when the leading edge is supersonic.
How the idealised flow around a supersonic airfoil looks is explained in this answer.
The angle of attack in supersonic flight depends on air density and load factor, but generally is only a few degrees because drag increases with the square of angle of attack. In other words, if the plane flies at high angle of attack, it decelerates to subsonic speed quickly.
The angle of attack in straight flight depends on altitude, wing loading and aspect ratio and grows with decreasing air density. Normally, at low level the maximum dynamic pressure limit and engine thrust will only allow very low supersonic speeds around Mach 1.1 to 1.3. Only above 20.000 ft will the envelope expend enough to make flight at Mach 1.8 possible.
For a typical wing loading of $\frac{m}{S}$ = 300 kg/m² and Mach 1.3 at 10.000 ft (air density $\rho$ = 0.9 kg/m³, speed of sound $a$ = 330 m/s) the angle of attack is $$\alpha = \frac{2\cdot m\cdot g}{\rho\cdot (Mach\cdot a)^2\cdot S\cdot c_{L\alpha}} \approx 0.5°$$ with a typical lift curve slope of a supersonic wing of $c_{L\alpha}$ = 4.


What forces act on an airplane's door from the outside in cruise?

A door that is, say, 36" x 80" (0.9m x 2m), with a surface area of 2880 sq/in (1.8m2), at 8 psi (55kPa) max cabin pressure differential, which most airliners run at, will have roughly 12 tons (102kN) acting on the perimeter fittings trying to blow it out. Any other forces acting on it are microscopic in comparison.

For non plug type doors that depend on bayonet latch pins, the shear loads on the pins are such that it is impossible to move the latching mechanism.  If superman was able to move the operating lever, it may or may not just bend the linkage, but no human will be able to move it.

For a plug door of the dimensions above, it has to move inboard to start to open it, so you would have to be able to apply 12 tons of pull force to unplug it.

Just the acrylic cabin windows are holding back over half a ton each when you are cruising along at 38000 ft.

This is why you don't have to worry about a crazy person trying to open a window escape hatch in flight.


Why don't black boxes send a signal when above water?

The short answer is that when a plane crashes on land we (generally) have a pretty good idea where to look for the black boxes - there will usually be a relatively clearly defined debris field to search.

When a plane goes down in the water there's a lot more ocean to search, and currents can deposit parts of the airframe over a much wider area, so the underwater locator beacon ("pinger") helps guide people to the debris field.

The longer answer is that sending a signal when you are underwater is relatively easy.  The pinger has a water switch: when it gets wet the water closes an electric circuit and the pinger makes a noise that can be heard on standard passive SONAR gear.
Water is pretty good at conducting sound waves, so the pings can be heard over a large distance and can guide searchers to the black box (or at least the pinger: sometimes they get ripped off, but they're usually still near the debris field).
We get all of that functionality in a fairly small self-contained device that requires effectively no maintenance (you replace the unit when its battery expires).

Sending a signal when you're NOT under water is harder: you can activate the signaling device with a "G Switch" the same way the ELT is activated, but after that the problems get harder:

You can't use sound (effectively)
A "pinger" beeping in the air is much less effective than under water - the range would be extremely limited even at very high volumes. Add to that the fact that crash scenes are pretty noisy with firefighting and rescue crews working and the chances of anyone hearing an acoustic beacon on the surface are pretty slim.
You can't use light (effectively)
A strobe on the black box may work OK in the dark, but it's easily damaged and not terribly effective during the day, or if the recorder is upside-down, in dense foliage, under snow/mud, etc.
Radio locator beacons are problematic
Radio locator beacons require an antenna - if the antenna is damaged or torn off in the crash the effective range of a radio beacon would be drastically reduced, possibly to the point of being completely ineffective.
If the antenna remains attached the signal can still be reduced drastically if the box is buried under natural features (dirt) or aircraft debris (aluminum skin).
(Both of these issues are frequently raised in criticism of ELT technology.)

It's possible a locator system could be devised that works on the surface, but given the challenges and the fact that the location of the black box is generally known (to within the size of the debris field at least) when an aircraft crashes on the surface there hasn't been much effort invested in this.

Finally, remember that while the recorders are a very valuable part of the investigation process remember that from an investigation standpoint it doesn't matter if you find the black boxes on the first day or the last day of recovery operations:  Finding the recorders will not undo the crash or bring the dead back to life, so if it takes a little longer to find them while sorting through a debris field on the surface it's really not a major problem.


Why have none of the US /UK/Japanese airlines ordered the Irkut MC-21 yet?

Ordering an aircraft is a very complex business, and implicates a number of matters that don't actually (on the surface, anyway) have anything to do with the aircraft itself. Consider this from the point of view of a western European or north American airline.

Broadly political obstacles

These could include:

international trade agreements and disputes (Russia's relations with much of the world are not very friendly at present)
existing suppliers ("Lovely relationship we've enjoyed since the 1970s; it would be a shame if someone carelessly trampled it underfoot and soured it.")
governments and politicians ("Oh really? Well, it certainly has been nice supporting you fearlessly in Parliament/the Ministry/Congress/against my opponents who hate your guts. Bye!")
national expectation ("Traitors!")

History and reputation

Russian (like Chinese) design, technology, engineering and manufacturing have a reputation in the west that works against them. These things take decades, not years, to be overcome by stellar achievements in those fields (consider how long it took "Japanese" to become regarded as a positive rather than a negative adjective when applied to products).

However unfairly, this feeds in to other obstacles:

customers ("Get on a Russian airliner? No way!")
shareholders ("You're proposing to buy a what?!")

Risks

Then, it doesn't make sense to buy one plane to "try it out". Even with a single aircraft of the type, you'd need the same training, certification, engineering support, etc etc as if you had a fleet of them.

So, you'd be looking at a fleet of them, and now you're facing the purchase of a fleet of aircraft that very much represent an unknown quantity. It's a huge, huge risk; no wonder airlines cleave so strongly to the Airbus/Boeing duopoly - maybe it's not entirely to their economic advantage, but they don't expect too many surprises, which is arguably more important.

Some of these risks:

are simply technical ("How good will the product turn out to be in the long run?")
are economic ("Could the trade climate make spare parts and maintenance prohibitively expensive in the future?")
hinge on international relations ("Could our government ban us from working with this supplier in future? Could a meddling Kremlin disadvantage us?").

How could it work? Will it ever work?

Give it a couple of decades.

If airlines in places like India, Indonesia, Brazil, with fewer historical attachments and political obstacles than in the west, find that the aircraft and manufacturer prove to be good for them, bit by bit we may see that influence trickle into western airlines, especially as those non-western airlines and the economies they belong to expand and become more influential themselves.


Could a jet engine be made from cast aluminium?

Short answer: No.  Unfortunately the yield strength of typical aluminum alloys drops off after about 300° F and long term exposure to high temperatures dramatically affects their creep and fatigue lives.  Typical aviation gas turbine hot sections run between 3000°-3800° F and rotate at angular speeds as high as 40,000 RPM, making Aluminum totally unsuitable for this role.  Most hot section components eg cumbustors, stator buckets, rotor buckets, etc.  are manufactured from exotic nickel-cobalt superalloys and employ novel single crystal casting techniques as well as passages to bleed compressor air as a boundary layer over them to protect them from that kind of intense heat.


Is it economically viable for Emirates to use a 777 for some of these routes?

There are many reasons an airline may fly to a given destination and the economics of air travel are complex to say the least. I would like to fist address your question

  couldn't the people living around Bologna take a train to Milan to get
  to Dubai

Sure they could but airlines don't only service locations because of the people that live there they may service them for the very people that don't. I fly both commercially and as a GA pilot to explore new places. I generally fly out of the Philadelphia area which is one of the busiest in the US. From there I head to plenty of tiny airstrips all over the place, none of these airstrips are in towns that are as economically prosperous or busy as Philadelphia but they see my travel because I wish to explore the area. The same goes for foreign airports, simply because a country is less economically prosperous or "busy" than another does not mean it has less to offer culturally and in fact may be a hot bed for tourism.

I have personally been to both Prague and Bologna and they are great cities both with large tourist markets. I can see it being very economical to fly a wide body airliner there full of tourists and maybe only a few locals. While layovers may attract the lower budget fliers there are plenty of people who prefer a direct flight for both the convenience and time savings.

You may be able to find more stats here.


Is there a limit to how large an airplane wing can be?

No, there is no theoretical limit to the size of a wing. You could make a wing big enough to lift the entire Earth (assuming, of course, you somehow had an atmosphere to fly it in).
There are, of course, many practical limitations to wing size. The lift a wing develops is proportional to the square of the scale of the wing, all else being equal. However, the weight of the wing (and the rest of the airplane it's attached to, for that matter) is proportional to the cube of the scale. So, if you double a plane's size, the lift developed by the wings goes up four times, but the weight goes up eight times. So, in that case, the wings would need to be even larger compared to the plane in order to lift the added weight. This is referred to as The Square-Cube Law (Wikipedia, Aerospace Research Central, TVTropes). You eventually reach a point where there are no materials strong enough to withstand the stresses imposed on such a massive wing.


What is this unusual leading edge flap on a B737-200?

These are two leading edge Krueger flap surfaces at each side of the wing, you can see details about them according IPC and AMM documents I found over the internet:

Regarding the Addendum, and why it seems that there is no other flaps deployed, I found a similar topic at Airliner.net Forum. As it is mentioned there, when is no hydraulic pressure, they can be extended by their weight:

  ...it has to do with the shut off valves and the actuators relaxing with no hydraulic pressure on them.

and also:

  ...Pressurize the system and they all move to their present commanded position

and another sidenote:

  ...Someone pulled that Krueger Flap to the fully extended position. When they droop because of no pressure on the system there in the mid positions.

and as final note, this issue is also mentioned in the AMM:


Exceeding VLO and by how much is too much?

The gear itself and its attachments being pretty beefy, you can't really damage the gear legs extending them at any speed the airplane can fly at.

The limitations usually relate to the doors, which are more delicate, and having large surface area, are far more affected by air loads.  So the main effect of exceeding a gear speed limitation is the risk of bending or distorting, or in extreme cases blowing off, gear doors.

If you have a minor exceedance of 10kt, I'd just give a visual check of the doors later.  If it was a major exceedance of 20kt or more a tech should look at it. The doors may look ok at a glance, but if they are deformed they can prevent the gear from extending next time, if, say a distorted door's edge overlaps the opening and slips past on retraction but hangs up on extension.

Extension/retraction speeds, VLO, or speed you can operate the gear selector, and maximum operating speed with the gear down, VLE, or speed you can fly with the gear down and locked, are sometimes different (VLO is normally lower than VLE if they are) because there is a limit speed that affects the gear while in transit, whereas once down and locked you can speed up.  This can be from sequenced gear doors that are only open during the extension/retraction cycle, or a limitation on the ability of the hydraulic system to retract, say, a forward retracting nose gear against air loads (a speed limitation could also be related to a stability and control issue as well).

I dimly recall from my multi training days (but not totally sure) that the limitation on the Seminole was related to its rather weak hydraulic pump which had to work too hard above a certain speed, stalling the pump or popping the CB, something like that.  Some amount of safety margin would have been applied to the speed the problem was happening at, giving the published limitation of 109.


Is the longitudinal stability achieved the same for all aircrafts or does it differ?

Different types of aircraft do have differing requirements for longitudinal stability:
A dogfighter or aerobatic sportster needs to be minimally stable, even a little unstable, for maximum manoeuvrability. On the other hand a primary trainer must be stable, so the novice pilot finds it easy to fly.
Whether the plane is fly-by-wire also makes a difference; relaxing the stability reduces drag and therefore improves fuel efficiency, but it needs a computer to add artificial stability so the pilot does not get tired wrestling with the controls for hours on end.
Technically, longitudinal stability is determined by the position of the centre of gravity relative to the aerodynamic centre. If the CG is in front then the plane is stable, if behind then unstable. The designer has to be careful to attach the wings in the right place for the particular characteristics required.
Some planes can vary significantly in flight. The de Havilland DH.88 Comet racer had a big fuel tank in the nose. When full of fuel it was just stable, but as it emptied during a long flight the CG moved progressively aft and it became more and more unstable (and the pilot became more and more exhausted!).


Does RPM refer to the speed of the engine or the speed of the propeller?

Yes it is the propeller RPM.  If the engine is direct drive, the engine and propeller RPM are the same.  If the engine has a propeller reduction gearbox, then engine RPM and propeller RPM are different, the propeller RPM being the engine RPM minus the gear reduction.

Propeller RPM is controlled by a flyweight governor, like those spinning ball speed regulators you see on old steam engines.  The flyweights control the oil flow to the prop to vary the pitch. The prop control lever applies a spring preload to the governor flyweights and the amount of preload determines at what RPM there is a state of hydraulic equilibrium so there is no pitch change happening. The speed of the governor is a function of the speed of the propeller in either a direct drive or geared engine.


Could the center of rotation of a spinning aircraft move away from CG?

In some sense, rotation is rarely around the centre of mass. It is extremely convenient to consider any motion as rotation around CM plus translation of that CM, but it doesn't have to be so.

Take the most basic control input for example: from level flight, you pull up for a short climb. A typical explanation of what happens says that the tail produces a pitch-up moment, which rotates the airplane around its CM to a higher angle of attack, this increases lift and it starts to climb. However, a more detailed analysis will point to the fact that initially, the tail will produce an extra negative lift. This is not just a pure moment, this is an unbalanced force applied away from CM. As a result, the airplane will lose some of its lift and will start sinking. Only later will lift grow and pull the airplane up.

Now, if you consider it as a single motion (which it is, fundamentally), you can rightfully say that it is a pure rotation about a point ahead of CM. (It would be nice to draw a diagram here, but not now). The pilot will perceive it as such. On some designs, particularly with delta wings, this initial loss of lift from elevons is so strong that the virtual point of rotation can be ahead of the aircraft (and thus the cockpit). Space shuttle reportedly had such configuration. For pilots, this creates a weird sensation that the aircraft behaves contrary to the expectation, particularly on landing where perception of altitude is acute. This can lead to pilot-induced oscillations.

So, for any motion, not only spin, to say that rotation always happens around CM is a simplification. To be able to say that and remain valid, you have to consider all the translation effects as well. In most cases, this is still the easiest way, but if you want to speak of rotation alone, remember that the instantaneous centre of rotation rarely aligns with CM.


What is the probability that passengers can survive a ditching in a 747 at MTOW?

Aircraft are designed with ditching in mind, but the outcome depends on many circumstances, most importantly on how calm the water is and how well the aircraft can be controlled.

The Wikipedia article on Ditching lists emergency water landings and other accidents where aircraft ended in water.

There is no ditching by 747, so we don't have any specific reference. However:

B747 is not that different from other types of aircraft. Controlled ditchings on calm water were successful in different types; it is likely that one would be possible with B747 too.
How long the aircraft would remain afloat depends on the damage. But if it did not break up, it would likely manage to keep afloat for the 90 seconds needed for evacuation. And the slides can be used as life rafts.
There was one case where B747 ended up in water after overrunning runway (so at lower speed than landing), China Airlines flight 605, and the aircraft did remain afloat long enough to evacuate it.
Also any aircraft that will be used for flying across large bodies of water, which obviously includes all variants of B747, must be certified for ditching. This involves designing it so that, at least according to model, a controlled ditching will be smooth enough not to cause serious injuries to occupants and will leave it afloat long enough for successful evacuation.


SR-71 flew 2193 mph. How can this mathematically be Mach 3.3?

The SR-71 was only capable of Mach 3.3 flight at altitude. You can see the limitations in the pilot's operating handbook(POH) for the aircraft:

At higher altitudes the relative speed of sound is lower. If we use this handy NASA calculator in a standard atmosphere the relative speed of sound at 70,000 ft. is 660 MPH making your 2193 MPH equal to Mach 3.321

Its also important to note that the word "about" is often used as the SR-71 was flown to a maximum compressor inlet temperature(CIT) not a maximum Mach when doing a 3.3 run. According to the POH

  Mach 3.2 is the design Mach number. Mach 3.17 is the maximum scheduled
  cruise speed recommended for normal operations. However, when
  authorized by the Commander, Speeds up to Mach 3.3 may be flown if the
  limit CIT of 427°C is not exceeded.


Does Green Dot Speed Calculation include banking Angle?

The Green Dot speed is very stable on the PFD, unlike for example VLS which is a function of G (bank included), mach number and speed brake position.
According to Flight Crew Ops Manual(s) green dot speed varies only as a function of aircraft weight and altitude. For A320 a very crude formula is given: below 20000ft 2 x weight in tons + 85kts, above 20000ft add 1kt/1000ft.
Based on experience I would say FCOM is accurate on this matter. It wouldn't be the first time the whole truth is not revealed to the pilots, though :)


It Depends on the speed, and in some cases the context it is being announced or discussed, different pilots may also call things out differently depending on op specs or simply the way they are trained.

V1 is typically announced as "V One"

I typically announce V4 as "Trimming for XXX Knots"

Vfe for me is typically "in the white arc, deploying flaps"

Vr is typically announced as just "rotate"

Vx and Vy are usually discussed as such or some times as "pitch for best angle" or "pitch for best rate"

Some of the V speeds are never really announced but important to know. V speed numbers help define the operational envelope of an aircraft but are not always announced or even relevant to announce. For example unless you are in a really bad situation its unlikely you are ever going to announce Vne out loud but its a very important speed to know (and avoid).


The maneuvers listed are not really extreme, and it is certain that, catering for the general public, they will be accomplished at a relatively high altitude. The airplane is widely used in the aerobatic field and is generally regarded as reliable. Therefore I believe that there is no more danger than there would be if you were doing a regular flying lesson.
Edit: I have dug up some more numbers for the aircraft type. There has been one non-fatal accident listed involving an Extra 300 in the Aviation-Safety database for the year 2020. From 1992 until present there have been 82 accidents listed of which 42 were fatal, resulting in the deaths of 67 people, including spectators listed for this aircraft type at Aviation-Safety.
As far as aerobatic flying is concerned, you can refer to this article for an overview of aerobatic safety. Most accidents took place during airshows rather than during training.
Below is the NTSB's summary of aerobatic mishaps from 2008 - 2015.


Why is indicated airspeed rather than ground speed used during the takeoff roll?

Because wings work on air moving past them, not ground moving below them.

Heck, in a 35 knot headwind, the Antonov-2 could be rolling backwards at 2 knots and still take off!


Congrats on earning your wings!
Because ammeters measure the flow of current (positive or negative) they can immediately show when the alternator is no longer providing power and the battery is discharging instead. In a voltmeter, like most modern automobiles have, you would have to wait to see the charge level on the battery drop, and by that point, several minutes (or longer) may have passed. In an aircraft, where it may be important to quickly shutdown electrical devices and conserve battery power, every moment counts and the ability to see flow shift from positive to negative is very helpful.


How can I identify the FAF on this Jeppesen chart?

The terminology is different between ICAO and the US.
The following definitions are being used by Jeppesen (Introduction to Jeppesen Navigation Charts):

  FINAL APPROACH FIX (FAF) — The fix from
  which the final approach (IFR) to an airport is executed and which identifies the beginning of the final
  approach segment. It is designated in the profile
  view of Jeppesen Terminal charts by the Maltese
  Cross symbol for non-precision approaches and
  by the glide slope/path intercept point on precision
  approaches. The glide slope/path symbol starts at
  the FAF. When ATC directs a lower-than-published
  Glide Slope/Path Intercept Altitude, it is the resultant
  actual point of the glide slope/path intercept.

  FINAL APPROACH FIX (FAF) OR POINT (FAP)
  (ICAO) — That fix or point of an instrument approach
  procedure where the final approach segment commences.

  FINAL APPROACH POINT (FAP) (USA) — The
  point, applicable only to a non-precision approach
  with no depicted FAF (such as an on-airport VOR),
  where the aircraft is established inbound on the final
  approach course from the procedure turn and where
  the final approach descent may be commenced. The
  FAP serves as the FAF and identifies the beginning
  of the final approach segment.

So the FAF looks like this for non-precision approaches:

And for an ILS approach the FAP is number 8 in the following image:


Did Japan actually use any production aircraft with inverted gull wings during WW2?

At least one - the Aichi B7A - although it saw little action, coming very late to the war.

The Aichi B7A Ryusei (愛知 流星艦上攻撃機 Aichi ryuusei-kanjou-kougeki-ki)
("Shooting Star", Allied reporting name "Grace") was a large and
powerful carrier-borne torpedo-dive bomber produced by Aichi Kokuki KK
for the Imperial Japanese Navy Air Service during the Second World
War. Built in only small numbers and deprived of the aircraft carriers
it was intended to operate from, the type had little chance to
distinguish itself in combat before the war ended in August 1945. (source)

 (source)
 (source)
The director of The Wind Rises Hayao Miyazaki may also be familiar with another Japanese gull-wing design, the Kawanishi E11K "Laura" flying-boat, which too saw service in WW2. However, its wing is not inverted.
 (source)


Why do some aircraft have 4 nosewheel doors?

Having multiple door sections for the nose gear is a common design. Looking closely at the photo below may make the reason more clear:

When the nose gear retracts, it swings forward. You can see that the wheels will need a larger opening than the narrower strut. So instead of having one door with a strange shape or that is larger than it needs to be, it is split into two sections. This also allows the forward doors to be closed once the gear is extended, which reduces drag.

Splitting the doors down the middle allows for symmetry, and it reduces the amount of surface area each hinge or actuator must support. This results in 4 separate door sections.

Looking at the main landing gear, you can see it uses a similar design. For example, the outboard gears swing inwards on retraction. The doors that cover the main gear bays are larger, and are only open during extension or retraction, and are otherwise closed. The smaller doors at the locations of the struts remain open.


What are the pros and cons of wingtip tanks?

I happen to own a homebuilt with tip tanks for ALL of the fuel supply (Pazmany PL-2), and while they look really cool, I'd prefer the fuel was in the wing leading edges mid span.

There is no aerodynamic benefit.  The tuna fish shaped tank doesn't function like a winglet (it has to be a wing to work like a winglet) and is too small to have any kind of end plate effect of significance (an end plate has to extend for a full chord to do any good that exceeds its own drag).  The flattened and canted tanks you see on twin engine Cessnas was intended to produce a bit of vertical lift and an enhanced dihedral effect to offset some of the inertial issues in roll that the fuel mass creates; which leads to...
Inertial issues in roll.  The mass of the fuel way outboard in the wings is a total pain.  It deadens the aileron response.  The inertia magnifies roll and yaw disturbances. My airplane is much more snappy with minimum fuel vs full fuel, and wags its tail in turbulence much less. I prefer to fly it with about 1/2 fuel if I'm just going out for an hour or so.  The  mass also kills a lot of the roll-yaw couple and amplifies adverse yaw.  If I skid the airplane with rudder, the roll into the yaw is very mild, in spite of significant dihedral.
Significant form drag. On my plane there is about a 8kt speed penalty from having the tanks taking up space in the airstream (based on the performance of other PL-2s modified to tankless wet-wing).
Fuel imbalances have a huge impact because the arm is so long.  If I ran one tank all the way down with the other nearly full, I'm sure it would use up an unpleasant amount of my aileron authority at low speed (I don't really want to find out how bad - at minimum, it would take probably 10lbs plus of side pressure on the stick to keep wings level). Having no trim tab or bungee, I use the fuel balance as my lateral trim, and when solo, have to achieve about a 2-3 gal right side differential to get the plane to fly hands off.  Then I have to remember to switch back and forth every 10 minutes or so to keep the balance.  I know if I forget because the airplane starts to wander off toward the heavy side, like a horse that suddenly remembers where the barn is while you're riding it.
Structural issues are minor.  You are adding mass at the opposite end of the most highly stressed part of the wing, but you need to make the outer spar structure able to handle the local bending, so some minor reinforcement would be required at the attachment.
One plus is the fuel supply is far away from you, say if you flipped over.  I like that.
One minus is the fuel supply is far away from you, at the first point to touch the ground in any kind of landing excitement.

All that being said, the PL-2 is a delightful airplane even with the tip tanks, and dammit they look awesome.  If I was building one from scratch however, I would do leading edge tanks like the Van's RVs.  Just way more efficient in every way.  As a long range fuel supply add-on however, they can make sense, but I think most designers will just extend the wet wing volume instead, until they run out of that.

On airplanes like the Lear, they made sense because with the super thin wings they were the most practical way to put in a large fuel supply.  But you will notice that they did away with them in later models because other than a handy place to stick tanks that don't get in the way of something else, it's mostly negatives. I shudder to think about how to control a tip-tank Lear with one side nearly empty and one side nearly full, if that were to happen somehow.

A former colleague was an old F-101 Voodoo driver who also had a lot of time in T-33s and he recounted to me once that the T-33's really large tip tanks were a pain due to the flywheel effect of the fuel mass. A little bump would start it rolling, and with the big weights out there, it took more than the normal input to stop the roll and if the conditions were rough you were fighting that constantly.


What is this red canister on the tail of the YF-22?

The canister contains a small parachute and either a spring or an explosive charge to kick the chute out when it is needed. It is a precaution for spin flight tests, that's why it is called a spin chute. See here for a video of the spin chute of the F-35.

I guess now I should explain how a spin chute works.

When an aircraft spins, it will rotate around a vertical axis which is somewhere between slightly ahead of the aircraft (regular spin) or near the leading edge (flat spin). The pitch angle $\Theta$ is nose down and the angle of attack $\alpha$ is high (around 45° in a regular spin, up to 90° in a flat spin), so the airflow over most of the wing and horizontal tail is separated. But the rotation, which is a mix of rolling and yawing, will induce an angle of attack variation over span, so a part of one wing will operate in the normal angle of attack range, where lift is high and drag is low.

Now we have a receding wing with separated flow, at high angle of attack, with low lift and high drag so the resulting air force vector R (green, below) points mostly into the direction of local flow (which is up). The other wing has partially attached flow, a lower angle of attack, high lift and moderate drag, so the resulting air force vector is almost perpendicular to the local flow, pointing up and forward. This difference in lift and drag propels the rotation.

Speeds and resulting force on spinning wing sections. $\omega_z$ is the rotation speed around the vertical axis, y is the local wing station and the green v shows the local flow direction.

Without the rotation the aircraft would immediately pitch nose down, pick up speed and can be pulled out of the resulting dive. With the rotation, however, we get an inertial pitch moment due to the fuselage masses. All parts of the aircraft rotate with the same yaw rate, and the centrifugal force from this yawing motion grows linearly with distance from the spin axis. This difference in centrifugal force along the lengthwise coordinate of the aircraft adds a powerful nose-up moment which in some cases cannot be overcome by the tail surfaces - remember, they have less effectivity in separated flow. Flat spins are almost impossible to escape from.

This can be tested in spin tunnels, but Murphy's Law is very relevant to spin tests. So it is a good precaution to add a spin chute for the first tests: If the aircraft cannot end the spin with control surface deflections, it is in a trap from which it can only escape with something that will add a strong nose-down moment. In the chaotic airflow behind a rapidly spinning airplane. That is why the spin chute is not bolted to the skin of the airplane, but sits in an elevated position hanging out at the back. From there it will not be caught by the tail surfaces but will work as intended in all conceivable situations (save an inverted spin ...)


How is the bandwidth of an actuator selected for a primary flight control surface?

Actuator bandwidth requirements typically flow down from guidance documents like MIL-STD-1797 (Flying Qualities of Piloted Aircraft). Essentially, actuator bandwidth is selected to ensure the flight control system has a sufficient stability margin. For example, see p. 235 of the above referenced document where the bandwidth of the open-loop response from pilot command to control effectors has to fulfill a minimum gain and phase margin.

In particular, this paragraph is relevant:

  A measure of the handling qualities of an aircraft is its stability margin when operated in a closed-loop compensatory tracking task. We refer to the maximum frequency at which such closed-loop tracking can take place without threatening stability as bandwidth ($\omega_{\mathrm{BW}}$). It follows that aircraft capable of operating at a large enough value of bandwidth will have superior performance when regulating against disturbances. A bandwidth criterion is especially useful for highly augmented aircraft in which the response characteristics are non-classical in form (i.e., have large mismatch in equivalent system fits).

In any case, there are other reasons for actuator selection of which bandwidth is a major one. For example, here's the rationale for actuator selection for the A380 flight control system. The selected electrohydrostatic actuators have a higher actuator bandwidth versus the conventional hydraulic actuators fulfilling the stability margin requirements with the potential for improved disturbance rejection.

Higher actuator bandwidth enables the potential for even better handling quality, e.g., gust load alleviation, however that would need to be assessed in relation to actuator lifetime reliability and overall power requirements.


What limits the lifespan of helicopters?

Helicopters are also subject to metal fatigue and there have been accidents attributed to it but the primary determination is component life times.  All of the engine, transmission and rotor parts are lifed and most of the control mechanisms.  Depending on the helicopter, there will be many more lifed components.

Some helicopters also have fixed intervals between major overhauls by the manufacturer.  For example, the R22 is effectively rebuilt to an "as new" standard by Robinson at 2,200 hours.

Corrosion might also play a part.  There may be a time when it is just not economical to continue to repair and service the airframe.


By what scale is Latitude and longitude calculated on aircrafts?

If we travel by 1 metre on any side how much of longitude and latitude changes?

It depends where you start. One nautical mile is defined as a minute (1/60 of a degree) of longitude at the equator. This is about the same as a minute of latitude at the equator, but because of the shape of the earth, it's not the same as a minute of longitude anywhere else: lines of longitude get closer together as you head north or south, and they all meet at the poles. If the earth were spherical, the lines of latitude would all be the same distance apart, but it's not quite: it's squashed flat, like an orange, so latitude lines get closer together as well, but never meet.

Because it's simple geometry, you could make a formula to tell you the length of a minute of latitude at any latitude, and another to tell you the length of a minute of longitude at any latitude, but we don't do this, and here's why.

Latitude and longitude are a good way to describe where you are, but not how you're travelling. Instead, you plan to fly a certain distance in a certain direction. You can tell the distance by multiplying your speed by the elapsed time, same as any other navigation.

You can measure your position with reference to fixed points. In visual navigation (in sight of land), you can use geographic landmarks: a particular town is ten miles to the north, or you're directly over a lake. You can also use radio navigation aids: fixed radio beacons which tell you where you are in relation to them. These work even in bad weather or if you're too high to see the ground, and even airlines navigate this way. You can plan a route flying from one landmark or beacon to the next, until you reach your destination, without even thinking about latitude and longitude. When you need to report your position, even in an emergency, you do this by reference to these landmarks or beacons.

If you ever do need to know your latitude and longitude, you can do this by referring to your chart. You find the beacon or landmarks that you're at, mark your position on the chart with reference to those, and read off the latitude and longitude. No need for any formulae, and the only thing you have to calibrate is your compass.


Can an empty 747-400 with minimal fuel take off on two engines?

Hmm... I guess this will come down to how much of the drag is induced drag vs. how much is form drag. The induced drag will obviously be much less, but the form drag will not be much less than flying at the same airspeed at MTOW.

Given the requirement that it must be capable of continuing a takeoff and climbing out at MTOW on 3 engines, though, I'd be very surprised if it weren't capable of doing so at 42% MTOW on 2 engines.

For the most convincing argument in favor of 'yes' I can think of off hand, there's this. GE flew a 747 on one engine. Granted, that engine happened to be a GE90-115b, the world's most powerful commercial jet engine, which is used on the 777-300ER. However, the GE90-115b is rated at 'only' 115,300 lb. of thrust, while a pair of PW 4062s on a 747-400ERF would produce a total of 126,600 lb. GE's aircraft is a modified 747-100. Since Wikipedia lists its operating empty weight at 358,000 lb. and it was hopefully carrying some fuel in addition to that, its weight was likely not much different from the 386,000 lb. in your scenario. Additionally, in GE's case, some of the lift would have to be used to pull against the yawing moment created by flying with only the #2 engine producing thrust.

In light of this, I'd say that the answer is almost certainly, yes, it's possible. Advisable, of course, is a different matter entirely.

GE's Test Bed 747-100 with the GE90-115b mounted in place of its #2 engine. Source: Wikipedia


Why was the Graf Zeppelin's endurance when fully fuelled with both fuels less than the sum of its endurances with each fuel separately?

Graf Zeppelin LZ-127 carried 75,000 cubic meters of hydrogen and 30,000 cubic meters
of Blau gas, which has a similar density to air.  This helped them avoid buoyancy issues when fuel was consumed.

With gasoline, the extra weight had to be compensated with more hydrogen, hence less room for Blau gas.

But I wonder if they could burn some of the hydrogen as fuel instead of venting it when the gasoline was being used up.  This would increase the range considerably.


What is the cabin noise hertz in typical commercial aircrafts?

In a jet it's going to be pretty much all above 100hz. Most of the noise at cruise is broad spectrum "white noise" from the air flow and the engine core exhaust.  The fan however, running at, typically 4000 rpm, with 60 blades say, will be producing a 4000 Hz noise, and this along with the exhaust white noise will be the dominant sound prior to cruise.
In a propeller driven aircraft however, you will have noise below 100 hz from the prop.  A 2 blade propeller spinning at 2200 RPM is imparting a 73Hz pressure wave pulse on the windshield and this is one of the dominant forms of noise in that case.  Next is the exhaust pulse from a 4 cyl engine, 2 per revolution, also giving 73 Hz at 2200 RPM.  Then random frequency mechanical noise from the engine and white noise from the airflow.
So in a Cessna 172 at take off, running at 2700 rpm, you're going to have mostly a 90 Hz sound from the prop and the engine, then some random noise from other mechanical noise from the engine plus airstream white noise.
This is a problem for pilots who use foam earplugs only when flying.  Foam plugs only attenuate sound above maybe 5000 Hz and don't help all that much with the prop and engine noise. ANR headsets are a huge help here because ANR systems work best on low frequencies although not so good on high frequencies.
So when I'm flying I use both an ANR headset and ear plugs.
After I tried out a set of  Isolate Earplugs (and promptly lost them, although they do work), I've also developed my own low frequency earplugs by wrapping about 3" of half inch lead tape (used for ballasting golf clubs) around the shaft of a 3M Push-In earplug (the kind with the little yellow bulb on a blue plastic shaft) and covering the tape wrap with heat shrink tubing.  I put them in with a bit of lanolin on the foam bit to lubricate and improve the seal.  They do a fantastic job of attenuating low frequencies below 200 Hz, and make the ANR headset nearly redundant.


What are some disadvantages that come with a design like a B-2 spirit bomber?

The main problem with the B-2 Spirit (or any flying wing aircraft, for that matter) is that they are statically unstable.

Source

If the lift vector of the wing acts before the center of gravity (as is the usual case when only wings are considered), any perturbation which results in an increase in angle of attack results in a positive moment about the center of gravity, which further increases the angle of attack an so on.

The only way to control such an aircraft is through computers, which continuously detect any changes in the aircraft attitude and apply corrections as required, as it is near impossible (or incredibly taxing) for human pilots to fly the aircraft.

This is the method used in order to 'fly' the B-2 Spirit in the absence of a horizontal stabilizer. If there is any problem with the flight computer (which is remote) or with the sensors supplying data to it, the aircraft will become unflyable and crash.

Another control issue with the B-2 is that the aircraft has little directional stability with no vertical tail. The swept wing offers some stability, though not in the same level as a vertical tail.

Source

Actually, only 21 of these were built, for the following reasons:

The B-2 is costly; by costly I mean probably the most expensive aircraft ever built. With a total program cost of over 45b USD, each aircraft costs a whopping 2.1b USD (which was caused due to reduction in numbers from the initial 132). Also, the (hourly) operating costs of B-2 are twice that of other bombers in the USAF fleet.
With the dissolution of the Soviet Union, the B-2 had effectively become an aircraft without a mission, as it was primarily designed to penetrate Soviet air defence systems.


Possibility commuting using GA aircraft between rural towns?

As for the latter part of your question, is it doable everywhere, the answer would be a resounding no.

Unless you are a proficient IFR pilot, the climate would be one of the limiting factors in many places. For example where I live in, we have four seasons, of which the fall, with mostly IMC weather, lasts for about 6 months, leaving the other half of the year somewhat doable for a proficient VFR pilot. Now, I'm not kidding, it really is like that here: a couple of years ago it was cloudy (low level overcast) for three months in a row. Most of the cloudy days then were of the sort that would have made commuting under VFR very risky to say the least.

Another hurdle might be the cost. Again, as an example, where I live flying a private plane is ridiculously expensive. Even more so, if you want to hold an IFR -licence, which would be an absolute necessity if you wanted to commute by private plane here.

And one thing is scheduling. Unless you live and work very near an airport, you must consider transit times between your home, departure airport, destination airport and your workplace, and the other way around. Add half an our of flight preparation twice per day, and any time savings you might have thought of will quicky dissapear.

Generally I'd say it depends heavily on local conditions, but commuting by a private plane is (unfortunately) not a viable option everywhere. And I do not think it's a financially viable option anywhere...


Can I request VFR flight following in a practice area and without a flight plan?

(I've assumed you're asking about the US because you used the term "flight following". If you ask about regulations or procedures, please always tell us which country it is and use a country-specific tag if appropriate.)

Can you request VFR flight following for your local non towered practice area?

Yes. I did a tower tour at Huntsville, AL (KHSV) once, and the controllers asked us to request it in the local practice areas. First and most importantly, it helps improve safety and traffic management. But as a secondary point, it counted as an "ATC contact" or whatever they called it, and that helps to justify the existence of the ATC services in that area. That's a good thing for both controllers and pilots.

In general, ATC strongly prefers to be in contact with aircraft in or around their airspace, and I've heard that in multiple presentations from them. If they're really too busy to provide the service then you won't get it, but it never hurts to ask.

Can you have flight following without filing a flight plan?

Yes. They're complementary but not the same thing and they're managed by different groups: Flight Service manages VFR flight plans and ATC manages flight following. In fact, ATC doesn't even have access to VFR flight plans.

Can you also receive FF when flying low (800 AGL) locally for separation from pipeline patrols and ag spray planes?

Maybe. ATC needs to see you on radar to provide flight following and if you're too low you may literally be below the radar.


Why do aircraft use 400 Hz AC instead of the 50 or 60 Hz of wall outlets?

Induction motors turn at a speed proportional to frequency, so a high frequency power supply allows more power to be obtained for the same motor volume and mass. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft (and ships). Transformers can be made smaller because the magnetic core can be much smaller for the same power level.  Thus, a United States military standard MIL-STD-704 exists for aircraft use of 400 Hz power.

So why not use 400 Hz everywhere? Such high frequencies cannot be economically transmitted long distances, since the increased frequency greatly increases series impedance due to the inductance of transmission lines, making power transmission difficult. Consequently, 400 Hz power systems are usually confined to a building or vehicle.

Source

Further discussion of aircraft electrical systems

Further, further discussion of aircraft electrical systems

Added: cool discussion of the use of 400hz with Cray supercomputers on another S.E. forum


Why are the 737's rear doors unusable in a water landing?

The bottom of the door opening sits too close to, or below, the water line when the airplane is floating.


When flying into an area with colder air, how will the altimeter read compared to true altitude?

There are lots of questions on the FAA Knowledge Tests about altimeter readings at non-standard temperature and pressure settings. The non-standard pressure questions are fairly intuitive. We all know that pressure decreases as altitude increases. Therefore, if the pressure is lower than what the altimeter expects, the altimeter is fooled into thinking it is higher than it actually is. Likewise, if the pressure is higher than standard, the altimeter reads lower than it should.

Dramatic and dangerous effects most commonly occur when crossing a frontal boundary from an area of high pressure to an area of low pressure. If the altimeter is set to the local altimeter setting in the area of high pressure and the aircraft flies to an area of low pressure, without changing the altimeter setting, the altimeter reading will be too high, possibly by hundreds of feet. Less dramatic changes happen all the time when you fly. As an example, right now the altimeter setting at KSBP is 30.08. The setting at KSBA (62 nm away) is 30.01. If you fly to KSBA you would notice a change in altitude of -70 feet when you get the new altimeter setting from approach control. The aircraft is 70 feet lower than you thought. That is the origin of the memory aid, “HIGH TO LOW LOOK OUT BELOW”.

AIM 7−2−3. Altimeter Errors

  b. Once in flight, it is very important to obtain frequently current
  altimeter settings en route. If you do not reset your altimeter when
  flying from an area of high pressure into an area of low pressure,
  your aircraft will be closer to the surface than your altimeter
  indicates. An inch error in the altimeter setting equals 1,000 feet of
  altitude. To quote an old saying: “GOING FROM A HIGH TO A LOW, LOOK
  OUT BELOW.”

Instrument Procedures Handbook

  When cruising below 18,000 feet MSL, the altimeter must be adjusted to
  the current setting, as reported by a station within 100 NM of your
  position. In areas where weather-reporting stations are more than 100
  NM from the route, the altimeter setting of a station that is closest
  may be used.

You will notice that, when using flight following or flying IFR, after checking in with a new controller, the controller will usually respond to your check-in with the altimeter setting he is using for flights in your area.

Non-standard Temperature
The same thing happens with temperature changes but it is less intuitive because we don’t have day-to-day experience with changing the altimeter with variations in temperature. We also learned about combustion in the engine and associate high temperatures with high pressures and that can lead to us getting tangled up in our thought process. Lets start from scratch and build a mental model of how the altimeter works.

Think of the aircraft as siting in a column of air. The altimeter measures the weight of the air above the aircraft. It doesn’t really know how much air is below it or how high it is above the ground. It just knows that at a certain pressure from the air above it makes it read a specified height. It has been calibrated for standard temperature and pressure lapse rates. If the temperature or pressure don’t change as expected, the weight of the air above it will not be the same as it is calibrated for, and it will give erroneous readings.

Let’s start our thought experiment with temperature and pressure at standard (29.92″ and 15°C) and the aircraft at 5,000′ MSL and AGL. Now imagine that the entire air mass being heated to be warmer than standard temperature. We know from high school physics that air expands as the temperature goes up. The entire column of air now expands and as the column of air expands, the aircraft moves higher in the column. Note that the weight of the air above the aircraft hasn’t changed, it just takes up more room. Since the weight of the air hasn’t changed, the altimeter reading hasn’t changed. The aircraft is now at a higher AGL than it was before but the altimeter still says 5,000′ MSL.

The reverse occurs when air temperature is lower than standard. As shown on the graphic above, the altimeter will read lower than it should if the air temperature is colder than standard. The same memory aid we used with pressure applies, “HIGH TO LOW LOOK OUT BELOW”.

People often get the impact backwards when they try to relate it to knowledge of engine combustion. In an engine, higher temperatures indicate higher pressures. So they think that if the temperature is higher, then pressure is higher. Normally higher pressure means altimeter reading is lower. The reason higher temperatures equate to higher pressures in an engine cylinder is because of the ideal gas law PV= nRT. For a fixed volume, higher temperature means higher pressure. But the volume is not fixed in the atmosphere, so the reasoning doesn’t translate directly to this problem.

For those who care, the standard corrections for temperature are: For each 10° C the OAT is warmer than ISA increase the indicated altitude by 4% to give true altitude. For each 10° C the OAT is cooler than ISA decrease the indicated altitude by 4%.


Can you help me to identify this helicopter?

The helicopter is a S-65C-3 Yas'ur (Albatross). It is a CH-53D version similar to USAF HH-53C Pave Low. Here is a photo of the same.

The identification is based on the following:

Six bladed main rotor
The sponsons which hold the fuel
The only variant of CH-53D with in-flight refueling probe in service is the Israeli version. All others (HH-53 and MH-53) have been retired. CH-53E has refueling probe, but it has 7 blades.

Israel ordered 36 of these,of which around 23 are still in service.


Cross Country flight: what do I have to consider concerning radio communications?

There are three categories of radio communication to deal for each leg of a flight:

arrival and departure airport: tower/CTAF, ATIS/ASOS/AWOS, Ground/Clearance Delivery
En route ATC: arrival/departure, center
En route weather and information: Flight Service, Flightwatch, HIWAS, en-route ATIS

You have to decide which of these services you will interact with, and know where to find the frequencies (almost always a chart or the A/FD) and how to contact each of them.


Does the commercial helicopter training in 61.129(c)(3)(i) require a CFII?

A CFI can give the training because it's training "solely by reference to instruments". If it were "instrument training", you would need a CFII.

See the Jablecki (2016) interpretation, which addresses your specific question:

  In order to provide instrument training for a commercial pilot
  certificate or ATP certificate, a flight instructor must have an
  instrument rating on his or her flight instructor certificate.
  However, §61.129(c)(3)(i), unlike its counterparts in §61.129,
  does not have a requirement for "instrument training" as defined in 14
  CFR §61.1. Instead, §61.129(c)(3)(i) requires training on the
  "control and maneuvering of a helicopter solely by reference to
  instruments." Therefore, the training in §61.129(c)(3)(i) is not
  considered "instrument training" that requires a certified flight
  instructor to have an instrument rating on his or her flight
  instructor certificate.


What are the advantages of using a ramjet in an air-to-surface missile?

A rocket-powered missile carries both fuel and oxidiser and oxidiser is the heavier part. For example a gram of jet fuel needs almost 3.4 grams of oxygen to fully burn! Increasing the fuel load requires also increasing the power, which means even more fuel and this limits the practical range of a missile.

Ramjets are air-breathing, so they don't need to carry the oxidiser, which means the same amount of fuel gives them significantly longer range. Plus the other constituents of air, and extra air, that get pulled along and heated in the engine add to the available reaction mass, further increasing the propulsive efficiency.

Longer range means the aircraft can fire the missile further away and avoid coming into range of the defenses placed around the target, which might make difference between being able to attack a heavily defended target and not, so it is worth the expense to have some in stock.

Also note that ramjet is only more complicated, and expensive, than a solid-fuel rocket motor. Compared to liquid-fuel rocket it is simpler, because it only needs easy-to-handle kerosene while liquid-fuel rockets either need liquid oxygen, or nasty stuff like peroxide or hydrazine. It is also simpler compared to a full turbofan or turbojet (a small solid rocket booster is usually used to get it up to speed).


Is there a preferred turn direction for helicopters?

Most helis make CW turns because the pilots sit on the right and it is easier to judge position and drift when you can look out the window directly.  Turning CCW is no problem however but it takes a tad more concentration.

one drawback of CW turns from the right seat is that the ALT and ASI would be out of your field of vision, so you'll have some head turning to peek at them. In a CCW turn, its easy to glance at the instruments in the center console.


How is the area rule applied on airliners like the A380?

First of all, not the area should be equal, but the area gradient along the direction of flow should be shallow. The minimum drag with a given volume can be achieved when the area distribution is that of a Sears-Haack body. Ideally this rule applies only at Mach 1, and once you go faster, the cross sections which matter are those along a Mach cone, not those of the aircraft's cross section.

For subsonic flight, the penalty for neglecting the area rule is small; it only matters when local flow is supersonic ahead of a contraction of the contour of the aircraft. Subsonic flow would decelerate, whereas supersonic flow will accelerate further and result in a drag-intensive shock downstream. Adding something to fill up the contraction will reduce the pressure gradients and ideally avoid the shock. By this, area ruling will help to shift the onset of the Mach-related drag rise and enables airliners to cruise a little faster. Honestly, I cannot see the "obvious" area rule shaping on the A380 - to me this is classic subsonic aerodynamics which tries to avoid sharp pressure gradients in the area of the wing airfoil's rear loading. Especially the outer engine pylons could be done better, but I digress.

For airliners, it is much more important to have a constant fuselage cross section, which makes stretching the fuselage simpler and is much easier to build. Area-ruling the fuselage simply is not worth it (yet) when your maximum cruise speed is just Mach 0.85. It is enough to add some Küchemann bodies to smooth out pressure gradients.

Below is a comparison of a swept wing at Mach 0.9, on the left clean and on the right with Küchemann bodies. Note the massive flow separation on the left wing, whereas the flow pattern on the right wing shows attached flow.

Mach 0.9 wing comparison (picture source)


How much extra weight is added by strengthening a piston-prop fighter for carrier landings?

The British adopted the Spitfire and Hurricane for carrier use.
Using the Spitfire as an example, here's data from Wikipedia.

Spitfire Mk.VB is 5065lbs clean.

Seafire Mk.III is 6204lbs clean.

They're not exactly equivalent otherwise, but close enough.
So the Seafire is roughly 1140lbs heavier than the land based equivalent, or over 20%.

Of course this will vary wildly for different variants compared, but it's a ballpark figure


What was the first control room--used for flight test--established in aerospace history?

This article would seem to suggest that use of radio telemetry started being used sometime during the mid-fifties.

  Then you reduce these rolls of oscillograph readouts and learn to read the data, you will know more about what happened during a flight test than the pilot, the engineer and the designer. These rolls of paper are like novels. It is up to you to get the meaning, then sense the plot and determine whether flight objectives were satisfied.

The quote above is from chapter 5 of "Failure is not an option" by Gene Kranz, describing his first introduction to flight testing in 1954 when he started working for McDonnell Aircraft. As the quote would indicate, data processing happened after the flight was over and that there was no kind of control room monitoring the progress of the flight. An exception was for incidents such as one also described by Kranz, where a B-52 had lowered a missile from the bomb bay in order to fire it. The missile would neither fire or retract, but as the bomber had enough fuel the engineers had enough time to discuss various options.

I suspect that the first form for flight operations support would have been the chaseplane, although this is outside what you are asking.

The next closest thing I've heard about is Mercury Control, which was used to monitor and support flights during the Mercury Program.