What are the regulations and testing that determine whether a "Spins Prohibited" placard is required in an aircraft?

Spins require a demonstration for certification, but can be bypassed with an FAA waiver as Cirrus did for the SR-20/22. The waiver was granted under the understanding that the only way to recover a Cirrus is to pull the chute.
FAA CFR Part 23 governs the process and requirements for certifying general aviation aircraft. Specifically for spins you are wanting to read CFR 23.221 which outlines the process of spin testing:

(a) Normal category airplanes. A single-engine, normal category airplane must be able to recover from a one-turn spin or a three-second spin, whichever takes longer, in not more than one additional turn after initiation of the first control action for recovery, or demonstrate compliance with the optional spin resistant requirements of this section.
(1) The following apply to one turn or three second spins:
(i) For both the flaps-retracted and flaps-extended conditions, the applicable airspeed limit and positive limit maneuvering load factor must not be exceeded;
(ii) No control forces or characteristic encountered during the spin or recovery may adversely affect prompt recovery;
(iii) It must be impossible to obtain unrecoverable spins with any use of the flight or engine power controls either at the entry into or during the spin; and
(iv) For the flaps-extended condition, the flaps may be retracted during the recovery but not before rotation has ceased.
(2) At the applicant's option, the airplane may be demonstrated to be spin resistant by the following:
(i) During the stall maneuver contained in §23.201, the pitch control must be pulled back and held against the stop. Then, using ailerons and rudders in the proper direction, it must be possible to maintain wings-level flight within 15 degrees of bank and to roll the airplane from a 30 degree bank in one direction to a 30 degree bank in the other direction;
(ii) Reduce the airplane speed using pitch control at a rate of approximately one knot per second until the pitch control reaches the stop; then, with the pitch control pulled back and held against the stop, apply full rudder control in a manner to promote spin entry for a period of seven seconds or through a 360 degree heading change, whichever occurs first. If the 360 degree heading change is reached first, it must have taken no fewer than four seconds. This maneuver must be performed first with the ailerons in the neutral position, and then with the ailerons deflected opposite the direction of turn in the most adverse manner. Power and airplane configuration must be set in accordance with §23.201(e) without change during the maneuver. At the end of seven seconds or a 360 degree heading change, the airplane must respond immediately and normally to primary flight controls applied to regain coordinated, unstalled flight without reversal of control effect and without exceeding the temporary control forces specified by §23.143(c); and
(iii) Compliance with §§23.201 and 23.203 must be demonstrated with the airplane in uncoordinated flight, corresponding to one ball width displacement on a slip-skid indicator, unless one ball width displacement cannot be obtained with full rudder, in which case the demonstration must be with full rudder applied.
(b) Utility category airplanes. A utility category airplane must meet the requirements of paragraph (a) of this section. In addition, the requirements of paragraph (c) of this section and §23.807(b)(7) must be met if approval for spinning is requested.
(c) Acrobatic category airplanes. An acrobatic category airplane must meet the spin requirements of paragraph (a) of this section and §23.807(b)(6). In addition, the following requirements must be met in each configuration for which approval for spinning is requested:
(1) The airplane must recover from any point in a spin up to and including six turns, or any greater number of turns for which certification is requested, in not more than one and one-half additional turns after initiation of the first control action for recovery. However, beyond three turns, the spin may be discontinued if spiral characteristics appear.
(2) The applicable airspeed limits and limit maneuvering load factors must not be exceeded. For flaps-extended configurations for which approval is requested, the flaps must not be retracted during the recovery.
(3) It must be impossible to obtain unrecoverable spins with any use of the flight or engine power controls either at the entry into or during the spin.
(4) There must be no characteristics during the spin (such as excessive rates of rotation or extreme oscillatory motion) that might prevent a successful recovery due to disorientation or incapacitation of the pilot.

Another good read is the Aircraft Certification Service - FAA Flight Test Responsibilities, Procedures, and Training which states:

506. Spin Tests. Spin tests conducted by FAA FTPs should be flown initially with a spin chute (or equivalent equipment) installed on the aircraft and approved by an FAA structural and/or systems engineer. (See Appendix 3 for additional guidance on requirements for spin recovery devices). After all spin modes have been evaluated and found satisfactory, the spin characteristics should be checked with the external spin chute removed, unless it is determined
that the spin chute installation has no significant effect on spin characteristics.

(Emphasis Mine)


Both DUAT (DTC) and DUATS (CSC) provide the same information. They are functionally equivalent.
You also left one out: Lockheed-Martin operates a web-based briefing service at
https://www.1800wxbrief.com/ .

Which you prefer to use for interactive access is largely an aesthetic consideration - as a pilot you can sign up for an account on each of these services, so the usual advice is to sign up for all of them and use the one you like better (personally I used to prefer DTC's DUAT interface, but the direct (1800wxbrief.com) system is a now my preference for web-based briefings when I'm not using ForeFlight).

From a non-interactive standpoint, CSC DUATS has an API that can be used by other programs (like ForeFlight) to receive weather/NOTAMs/etc. and to file flight plans. This can be advantageous, however Lockheed-Martin has recently (2013) implemented an XML-based API that lets application developers directly communicate with the automated flight service system, and it is likely that this will be the preferred way to handle this sort of thing as time goes on.


Are TI graphing calculators permitted on the FAA knowledge exams?

The document you cite actually goes on to explain what the procedure is for calculators, and when testing centers can prevent you from using your own (you'll be provided a loaner):

  Testing centers may provide a calculator to you and/or deny use of your personal calculator based on the following limitations:

    a. Prior to, and upon completion of the test, while in the presence of the Unit Member (formerly referred to as proctor), you must actuate the ON/OFF switch and perform any other function that ensures erasure of any data stored in memory circuits.

    b. The use of electronic calculators incorporating permanent or continuous type memory circuits without erasure capability is prohibited. The Unit Member may refuse the use of your calculator when unable to determine the calculator’s erasure capability.

    [...]

Basically, you can bring a graphing calculator and wipe it, but unless the center is able to confirm that you've removed all stored memory, they're probably just gonna say "nah" and hand you a basic calculator. There's a pretty good chance that your graphing calculator falls under the "permanent or continuous type memory circuits" category anyway.


Why are the spoilers used as the backup controls instead of ailerons on the Boeing 777?

The B777 is a high subsonic aeroplane, and at high airspeeds the ailerons remain stationary because wing twist may cause aileron reversal.

By using inboard spoilers as mechanical backup roll control surfaces, there is roll control available at high airspeeds as well. Roll authority would be limited at approach speeds due to the smaller moment arm than the aileron provide and due to negative lift on one side only.


Are aircraft sounds publicly available in a repository?

One place to look is models of the planes for flight simulators. There is generally a "sounds" folder of some sort inside the airplane folder that includes some cockpit sounds.

I'm guessing the original files are proprietary and there is really no reason for the companies to freely share them. Shows like Air Crash Investigation might get access to a simulator that can make all the real sounds.


Does Russia still use a Snowtam to report normative brake friction?

Long story short, as best I can tell everywhere except Kazakhstan uses the ICAO SNOWTAM format. Kazakhstan uses two different Russian formats depending on what airport you're at, which is an interesting approach to say the least.

First, the Russian format is described here, it's a decimal value where less than 0.31 is "unreliable" and more than 0.41 is "good". In fact, there are two Russian values: the "raw" value as measured directly by a friction device, and the "normative" value that is derived from the raw one (although I couldn't find any explanation of how). I guess that the raw value is supposed to be the actual coefficient of friction.

The ICAO format, on the other hand, is an integer value from 1 to 5.

(Incidentally, I'm aware that I'm blurring the distinction between format and values here, but since there is so little definite information on this topic available - at least in English - I don't think it matters much.)

The Russia and CIS AIP includes a Snow Plan 2013-2014 that states:

  [...] friction coefficient will be distributed by means of SNOWTAM in
  ICAO format (Annex 15)

That immediately suggests that Russia and the CIS now use the ICAO format, and considering the lack of any information about Russian format SNOWTAMs in the AIP or on the web in general, it seems very likely that the ICAO format is now the main or only one in use.

However, Kazakhstan appears to be an exception. There is a permanent NOTAM for Almaty airport (ICAO: UAAA) in Kazakhstan that includes this remark:

  K0706/13 NOTAMN Q) UAAA/QFBCS/IV/M/A/   /   /4321N07702E A) UAAA B)
  1312010001 C) PERM E) AT ALMATY AERODROME THE INFORMATION ON RUNWAY
  BRAKING ACTION IS TRANSMITTED BY ATIS AS FOLLOWS: IN ENGLISH-IN VALUES
  OF ESTIMATED SURFACE FRICTION RELATIVE TO MEASURED ''SFT'' FRICTION
  COEFFICIENTS. IN RUSSIAN-IN NUMERICAL VALUES OF NORMATIVE ''RUSSIAN''
  FRICTION COEFFICIENTS.

There is a very similar NOTAM for Shymkent (ICAO: UAXX) that includes this almost-but-not-quite-the-same remark:

  K0707/13 NOTAMN Q) UAXX/QFBCS/IV/M/A/   / A) UACC UATT UAII B)
  1312010001 C) PERM E) AT ALL AERODROMES EXCEPT ALMATY THE INFORMATION
  ON RUNWAY BRAKING ACTION IS TRANSMITTED BY ATIS OR ATC AS FOLLOWS: IN
  ENGLISH-IN VALUES OF ESTIMATED SURFACE FRICTION RELATIVE TO NORMATIVE
  ''RUSSIAN'' FRICTION COEFFICIENTS. IN RUSSIAN-IN NUMERICAL VALUES OF
  NORMATIVE ''RUSSIAN'' FRICTION COEFFICIENTS.

There is no similar NOTAM for any major Russian airport.

If I put all this information together, it appears that:

Russia and the CIS now use the ICAO format for SNOWTAMs
Almaty in Kazakhstan reports braking action in the 'raw' Russian format
All other Kazakhstan airports report braking action in the 'normative' Russian format


How do plane landing-gear tyres roll before take off?

Normally, aircraft wheels are rotating freely around their axle, unless the brakes are activated. The ground roll was a convenient time for engine warm-up in the days of piston aircraft.

However, rolling on the ground using jet engines is very inefficient; fuel consumption could be reduced if the aircraft uses other means of propulsion on the ground and only starts the engines right before take-off. Therefore, electric propulsion using hub motors is actively studied. The batteries could be charged (partially) during landing, when the hub motors are switched to generator mode, and the rest of the power could be provided by the APU.

Pushing back from the gate using jet engines is unwise, so a tug is used to move the aircraft to a position from which it can continue the ground roll to its take-off position. These tugs push a bar which is linked to the nose wheel of the aircraft. Towbarless (TBL) tugs scoop up the nosewheel and lift it off the ground, allowing more-secure control and faster maneuvering.

Conventional tug Goldhofer F110E (picture source)

Boeing 777 being pulled by Goldhofer TBL aircraft tug (picture source). They are really hard to see when you are sitting in the cabin.

Towbarless tug detail (picture source)


How likely are flares to be fire hazards once touching the ground?

I have no idea how likely it is general, but it seems that flares are indeed sometimes blamed for causing wildfires on the ground.

In New Jersey (2007):

  A massive wildfire that has already burned thousands of acres in the
  Pinelands and forced the evacuation of residents in two towns likely
  started this afternoon when an F-16 fighter jet dropped flares as part
  of a maneuver over a gunnery range, New Jersey National Guard
  officials said tonight.

  [...]

  "We believe it was one of our F-16s on a routine training mission that
  dropped the flare that started the fire," said Lt. Col. James Garcia,
  a spokesman for the state Department of Military and Veterans Affairs.
  "There's going to be an investigation."

In Oregon (2017):

  A remnant of a military flare was found at one of the areas burned,
  triggering a call to the Air National Guard, which uses flares in
  self-defense training exercises over those same areas that burned.
  Flares are deployed in air combat to draw heat-seeking missiles away
  from their targets.

  After being contacted by investigators about the fires, the Oregon
  National Guard agreed to suspend the use of flares. Agencies also
  engaged them about mitigation techniques to employ if it is determined
  that the guard was the cause.


On an A320, will the aircraft compensate for constant pilot rudder input?

Will the aircraft compensate for constant pilot rudder input? No.
It seems you're asking if a pilot can deliberately sideslip an A320 while in normal law (Gimli Glider style).
The answer is yes. The normal law won't fight back.
The question has been asked years ago on pprune.org, where one person replied:

Great question....one that is misunderstood by many....too many.
Please refer to FCOM 3.04.27 P4, FCTM NO-160 P 3/12 (24 JUN 09), and Airbus Flight Operations Briefing Note "Landing Techniques....Crosswind Landings" (April of 2006).

The user is referring to the pilot being able to indeed induce it during a crosswind landing before touchdown (unlike pitch, there is no flare mode for roll/yaw).
But if you're like me, you'd want more proof. Sadly the proof comes from a 2012 incident where the captain was incapacitated and involuntarily pushed on the rudder pedal:

(Final report)
The relevant text from the final report reads:

Approximately seven seconds after the captain’s last attempt to communicate, autopilot 1 was disengaged by the co-pilot, at this time the travel of the captain’s right rudder pedal reached approximately 13 degrees, and the Aircraft started to sideslip. The co-pilot disengaged autopilot 1 when he decided to take over control after realizing that the Aircraft was side-slipping. However, after the autopilot disengagement, the captain’s right pedal was still being subject to pressure continuously while it maintained a position of 14±1 degrees for another 18 seconds.
Autopilot 2 was engaged by the co-pilot in order to reduce the workload, but after seven seconds, the co-pilot disengaged it due to, most probably, noticing the continuous input of the captain’s right rudder pedal, which put the Aircraft into a 10 degree sideslip, and to lateral acceleration that reached approximately 0.26 g.
After the 18 second period of constant pressure on the right rudder pedal, the rudder input started to decrease and the pedal returned to the neutral position within 11 seconds. During the 29 seconds from the captain's full coma until the pedals returned to the neutral position, the co-pilot was making continuous attempts to recover the Aircraft to straight and level flight manually.

Addendum: Note that the A320 normal law doesn't aim for zero sideslip, rather coordinated turns, i.e., when a roll is commanded with no pedal input. Also a pre-programmed partial rudder input is made when an engine fails, but the remaining required input is left to the pilot (to maintain the pilot's instinctive reaction). And finally yaw damping acts on the yaw-rate (oscillation) due to Dutch roll. None of which would (nor should) act against a pedal action (as the incident and crosswind landing technique demonstrate).
In yaw damping and turn coordination, the one-way artificial feel cancels any feedback on the pedals (and adds feedback when yaw trim is input), but a pedal action will always work the opposite way on the rudder.


Someone's shooting at my plane out of the blue! What do I do?

For my answer I'm going to assume that someone is genuinely trying to shoot you down for some reason, it's not some sort of legal intercept. If you ignore a legal intercept then I can see a warning shot being fired to get your attention, in which case I would tell ATC I've been intercepted and get on guard (121.5) and communicate with them and follow their instructions, evasive maneuvering in this case is a bad idea. I'm also assuming that no missiles are involved because if you are against a missile equipped enemy in a PA-28 the missile's going to win. It may be called a Warrior but let's face it, it ain't.

In the incredibly unlikely event that someone is trying to kill you without warning then communication with the ground would be my last priority in the situation you describe because ATC cannot help you and you don't have time to explain it to them anyway. If you have a one-button squawk emergency button by all means hit it, but first and foremost you need to keep positive control on the airplane. If you exceed your critical AOA and end up in a spin you are in a worse emergency and if you rip the wings off you are dead.

If it is at night then turning off your lights would be a smart idea, this won't help if the fire is radar guided but it will if the fire is visual. If there's a cloud very close by going into it is probably a great idea.

Next you need to determine whether the fire is air or ground based. If it's ground based you will know because the tracers will be going from below you to above you (hopefully not through you) then your best bet is to throttle up and clear the area as quickly as you can by staying on the same track so you get away from the guns. Diving will increase your airspeed allowing you to clear the area faster but keep it below the vne! Some small left/right turns may help to throw of the aim of the guns, but large turns will only serve to keep you close to the guns for longer. If there's terrain nearby which you can put between you and the guns then use it.

If the fire is air based then the tracers will be closer to the horizontal. If you are being shot at from another aircraft then flying in a straight line is likely the worst possible idea, you need to maneuver. If your airplane is faster than theirs then dive and outrun them, but chances are you aren't going to be able to do that, so personally I would corkscrew down and cling to the nap of the earth. Use your short turning radius to its best effect and don't fly a predictable path. Ideally I would use terrain and/or clouds to try and break visual contact so I can escape.

If you can spare a few cycles in all this you should make a mayday call to ATC and tell them you're being shot at, and whether it is another aircraft or someone on the ground. Say your intentions, your aircraft condition, and the number of people on board. This isn't likely to immediately help you, but it may help to keep someone else from flying into the same situation if there's a nutcase on the loose with an anti-aircraft gun or someone's strapped a 50 cal to their SR-22 and is playing red baron with passing aircraft. If you're lucky local law enforcement or the military may be able to scramble something fast and take the heat off you, but most likely it's all over by the time they get there.


Is a failed ditching of an aircraft also Controlled Flight Into Terrain (CFIT)?

Boeing defines it in the following way:

  Controlled flight into terrain (CFIT) describes an accident in which a
  flight crew unintentionally flies an airplane into the ground, a
  mountain, water or an obstacle.

Since it's not unintentional, it's better described as forced landing or in your case, ditching.


Thankfully, aerodynamics in the usual flight range is linear.

Therefore, there is a gradient of lift over angle of attack and another one over the flap deflection angle. Both are constant over a range of maybe ±15° and can be combined. The angle of attack is referenced to the fixed part of the flight surface and the deflection angle to the moving part relative to the fixed part.

Another parameter which influences lift is the camber of the flight surface. Positive camber produces more lift at the same angle of attack. Deflecting a flap changes this camber, and its effect can be linearly added to that of the angle of attack.

  Is it air being deflected thus a change in momentum occurring to pivot the aircraft's tail down?

Yes, when a flap moves, the angle of attack stays constant but the camber of the flight surface changes, thus producing a change in lift. In your example, a trailing-edge up deflection decreases camber, the surface produces less or negative lift which produces a moment around the center of gravity.

And yes, lift is produced by deflecting a stream of air.

Things get more complicated and interesting when the aircraft leaves the angle of attack range in which aerodynamics is linear.


What can ground personnel do in the event of in-flight depressurization?

No.  If the crew and passengers have all passed out due to lack of oxygen and the plane has not been commanded for a descent, they will never wake up.  This has happened before, e.g. the Payne Stewart fatal accident.  In cruise flight an autopilot is only commanded to perform lateral navigation and absent instructions from the crew to initiate a descent it will fly to its last fix and then maintain its current heading, all the while maintaining altitude.  When fuel is exhausted it will maintain altitude at the expense of airspeed until the stick shaker activates, disconnecting the autopilot.  Absent the pilots input, the stick pusher should next activate to forcefully prevent a stall.  You'll probably get some oscillations in pitch but ultimately a steep descent that even if the (literally) brain dead crew could somehow wake would not give them time to act.

While ground crews can get data from the airplane and can attempt to contact the crew, they cannot remotely control the airplane so the best they could do, if aware, is watch.  They could perhaps get a fighter scrambles to intercept and visually inspect the cockpit, but that still would not allow them to alter the outcome (just verify the scenario).

Note that this scenario is much more likely to happen in an extreme depressurization event in which the crew is unable to don O2 masks in time.  A slow gradual depressurization will give plenty of warning as the cabin begins to climb and automated sensors start complaining.  In the EMB-145 you'll start getting aural warnings when the cabin exceeds 10,000 ft pressure altitude and somewhere shortly above that you'll get master caution alarms and automatic pax 02 deployment.  These altitudes should give the crew ample warning before becoming hypoxic (you can reach these altitudes for limited time with no supplemental O2 in a Cessna 172 for example).  Even at cruise, it only takes a few minutes to get the plane back down to 10,000 ft and as such a slow gradual depressurization should not pose a threat unless multiple warning systems are malfunctioning.


The Wikipedia article is clear: engines are numbered sequentially, left to right, as seen by the pilot facing forward. That corresponds to the second of your diagrams.

Twin engined aircraft have just engines 1 and 2 on the port and starboard wings respectively.

Three engined aircraft follow the same convention with the number 2 engine in the fuselage centre line.

Since this appears to be an arbitrary convention I'm not sure what more explanation you're expecting.


Do you need a commercial rating for aerial application work?

Short answer: you can do aerial application on your own crops with a private certificate, but if you're going to do it commercially then you need a commercial certificate. In both cases you also need an agricultural aircraft operator certificate.

An agricultural aircraft operator certificate is required for aerial application, per 14 CFR 137.11. The airman certification requirements are in 137.19:

  (b) Private operator—pilot. The applicant must hold a current U.S.
  private, commercial, or airline transport pilot certificate and be
  properly rated for the aircraft to be used.

  (c) Commercial operator—pilots. The applicant must have available the
  services of at least one person who holds a current U.S. commercial or
  airline transport pilot certificate and who is properly rated for the
  aircraft to be used.

The FAA's AC 137, Certification Process for Agricultural Aircraft Operators has all the details about how to get an operator's certificate and the airman requirements are in section 2-3. It says:

  Pilots designated to conduct operations for the commercial operator
  applicant must hold a current commercial or airline transport pilot
  certificate with the appropriate ratings

A private operator is limited to working his own crops:

  Private agricultural aircraft operators may not conduct operations for
  compensation or hire, or conduct operations over a congested area. The
  operator must provide proof of property ownership or other property
  interest in the crop located on that property where the operation will
  be conducted.

By the way, there's no such thing as a "commercial rating" in the US; private and commercial are both certificates.


For a rotor in vertical autorotation, what is the relation between pitch, vertical speed and rpms?

Unless I am misinterpreting your question, if you add pitch [pulling collective in a helicopter] your RRPM [rotor RPM] will decrease, as it is being used to accelerate air down decent, if in a vertical decent the aerodynamics are screwy. Now if you have some forward speed increase Pitch trades RRPM for lowering vertical speed. Decreasing Pitch, allows you to trade altitude for RRPM giving you higher VS and higher RRPM.


What is the altitude of the nose vs tail in airplane flight?

Yes that data exists , it is recorded during flight test data gathering for full flight simulators. The transducers used are not two bars altimeters, but direct gravitational angle finders and gyro's for increased frequency response. Sample rate was 30 Hz in the olden days, now 100 Hz or higher.

A full set of measurements consists of correlated sets of

pitch, roll, yaw angle measurements from dedicated mounted transducers;
angle of attack and sideslip, dynamic and static pressure, magnetic course, and all other parameters recorded by the aircraft instruments;
stick and control surface positions from dedicated mounted transducers.

The aircraft data sets are sold for a lot of money, your best bet would be to try to get your hands on flight data measurements for an older type aircraft or a type that is not produced anymore.

Next time you fly, you could even measure this yourself by using the transducers in your mobile phone, which has acceleration, rotational velocity and angle transducers, plus a set of linear GPS co-ordinates.


Why do all fifth generation fighters (J20, F22, SU57) put their wing above the fuselage?

One big reason is to make room for external stores such as fuel, weapons and electronics packs. A low-wing design must have longer and therefore heavier and bulkier undercarriage if ground access to the underwing hard points is to be adequate.

Also, the upper surface of a high wing is larger and cleaner, providing better lift over the fuselage and reducing the overall size of the wing.

Another trick which it allows is to create a waverider effect between the engines, providing supersonic lift with less drag.

The extra stability of the high wing position is unwelcome in a fighter and is typically countered by giving the wings a little anhedral, a slight downwards slope from root to tip.


When to disconnect the A/P on approach in an airliner?

You are experiencing what real world pilots also experiences as they level up: unable to keep up with the plane.

You are unable to keep up with the plane because your mind is behind the plane. You are doing what you'd do if you're flying a Cessna: you react after you see. In a jet, things happen very fast. A large aircraft, like a B737, is also heavy and the controls are not as responsive. That is why it became impossible to you.

To fly high-performance aircraft, your mind has to stay ahead of the plane. Anticipate what will happen. Do not react to what is happening. If you only react to something that has happened while flying a jet, you're already too late.

Technique-wise, you should focus more on the attitude indicator (AI). The AI is the only instrument which tells you the future. Altitude tells you the present, and the vertical speed indicator tells you the past. These instruments let you verify if 2 seconds ago you did correctly. To predict what the plane is going to do in the next second, you need the attitude indicator. Say the plane is now pitched zero degrees, and it is descending too fast. First, make up your mind about the new pitch angle, say 2 degrees up. Then, look at the attitude indicator and adjust pitch to 2 degrees up. Only after that, you give the VSI a quick scan to verify your descend rate is indeed reduced. Do not adjust pitch by looking at the VSI. It will never work.

You may also be too ambitious by attempting to fly airliners in the sim before you have a solid piloting skill. Move up progressively. Fly on small planes first. Practice maneuvers, like steep turns. As your skill improves, slowly move up to faster and larger aircraft.


How common are regulations limiting when the FO can be PF?

All the airports listed in the AIC are quite tricky to takeoff/land in. For example, the Lengpui airport runway is a classic example of tabletop runway.

Source: www.misual.com

The Leh runway is surrounded by steep hills.

Source: geolocation.ws

The kullu airport runway has a river in both its ends.

Source: www.airportsindia.org.in

This is the reason for these restrictions. I'm not aware of any such regulatory restrictions in case of other countries. However, the operating airlines can have their own rules about (Category C) airports.


A-10 entered service in 1976 and is the only production-built aircraft that has served in the USAF that was designed solely for close air support(CAS). With huge losses of A1 (226) in Vietnam war called for development for a aircraft capable for providing air support to ground troops and conduct counterinsurgency. If we look at the history of development of CAS it had direct competition from Army helicopter ( e.g AH-56 Cheyenne) for the above mentioned roles.

The CAS study provided two important recommendations for the Air Force: “(1) the Air Force should take steps to highlight in official USAF doctrine, tactics and procedures publications the methods for accomplishing those missions for which the armed helicopters were provided and which the Air Force considered part of the close air support function; and (2) to fulfill the requirements for the 1970 plus time period, the Air Force should take immediate and positive steps to obtain a specialized close air support aircraft, simpler and cheaper than the A-7, and with equal or better characteristics than the A-1.Based on Air Force and contractor studies, the estimated unit flyaway cost for the A-X was \$1 - \$1.2M (FY70)depending on purchase quantities. Research and Development costs were estimated at 240Million \$. Also for the projected unit cost (FY70)for the turboprop version was \$0.837M (600 aircraft buy) - \$0.937M (400 aircraft buy). The projected unit cost for the turbofan version was \$0.989M (600 aircraft buy) - \$1.092M (400 aircraft buy). Hence with the budget that airforce had they put up a order of 715 aircraft.

Production of the 715 A-10 aircraft finished in 1984. With A10 seeing most of action and noteworthy performance in Afghanistan and gulf wars by the turn of 1990s the aircraft was outdated in terms of avionics and more modern helicopters capable of performing same role (e.g Boeing AH-64 Apache). In 1992 air force purposed F-35 multi role fighter to replace A-10. To put numbers into perspective the U.S. Air Force stated that retirement of A-10 would save \$3.7 billion from 2015 to 2019.

With delay in F-35, air force retrofitted all A-10 and OA-10 aircraft in the fleet to the A-10C standard with a new flight computer, new glass cockpit displays and controls, two new 5.5-inch (140 mm) color displays with moving map function, and an integrated digital stores management system.

References:

https://web.archive.org/web/20150910033808/http://www.dtic.mil/dtic/tr/fulltext/u2/a530838.pdf

http://www.gao.gov/htext/d07415.html

http://www.airforcemag.com/MagazineArchive/Pages/2008/June%202008/0608fade.aspx

http://www.defenseindustrydaily.com/a-highertech-hog-the-a10c-pe-program-03187/

http://www.af.mil/AboutUs/FactSheets/Display/tabid/224/Article/104490/a-10-thunderbolt-ii.aspx


What are the tube shaped structures on the back of the fuselage of this 737?

The aircraft is the Indonesian Airforce Boeing 737-2X9 “Surveiller” aircraft, used for Maritime Patrol. The fairings house Side looking Airborne Radar for matitime surveillance. From b737.org:

  Fitted with Motorola AN/APS-135(V) Side Looking Airborne Modular Multi-Mission Radar (SLAMMR) The antenna of which was mounted in two 16ft housings on the upper rear fuselage. This system could spot small ships at ranges of 100nm.

Indonesia Operates three of them- AI-7301, AI-7302 and AI-7303.


What is the official term of a plane flying under another plane to avoid radar?

My copy of "EW 101: A First Course in Electronic Warfare" calls it "formation jamming".

Mind you, an operator of a radar with non-cooperative threat recognition capability will at least suspect something is wrong (although not from all aspects and ranges).


How is engine thrust measured in flight?

VectorVictor gives the right answer for jets.

However, for propeller aircraft this is really hard, and in the end only the difference between drag and thrust can be measured. By measuring the brake power of the static engine and the drag of the aircraft in a windtunnel, some data points can be acquired which help in calculating what the real thrust in flight could have been.

You are right, in the end it is impossible to produce a precise measurement of thrust. The most important part of the measurement is actually a precise definition of what thrust is: How do you account for the increased friction drag in the propeller slipstream? Is cooling drag part of the airframe drag, or should it reduce thrust? Measuring thrust is foremost an exercise in precise, meticulous bookkeeping.


Wouldn't a triplane be much more efficient than a monoplane of same
  wing area?

In strictly forward flight probably, but what are you looking to gain?

You could make the mono wing have a higher aspect ratio and gain the same efficiency, all while being able to use a normal tail stabilizer and predictable flight dynamics.

There's only 2 disadvantages going this route. First the aircraft won't have as fast of a roll response because of the long wing span. Second the long wingspan may be harder to store depending on your ground operations.

But maybe you want to build an efficient aircraft that could land on public roads. So you need the wing span as short as possible while still being efficient, would your idea work?

Probably, but not without it's drawbacks. First how will you pitch stabilize it? If you use a conventional tail, you need to take your "2 cord" rule into effect for this "4th" wing. (I'm assuming for now that the 2 cord distance is correct, but I'll put my own thoughts in on this later).

Mono planes generate lift from 1 spot, pretty easy to predict where (where the wing is) and placing that wing just behind the center of gravity means the stabilizer tail doesn't have to produce much down force to keep the plane in stable flight.

However your center of lift will be moving depending if your the wind hits one of your wings in a different way than the others. You will also have to consider how you're going to make the lift of all 3 wings equal roughly the center of gravity.

Anything off of this mark and would have to provide enough down force to compensate, reducing efficiency.

Now my thoughts on if 2 cords apart is enough for a wing. It probably is in forward flight, but fluid dynamics are hard to predict and when that aircraft starts pitching up and down and the vortexes each wing generate get aimed in different directions your wings will interfere with each-other.

Take a look at the quickie aircraft. It was a "bi-plane" design similar to what you propose. Notice how the wings are not only far apart, but also on separate vertical levels. This is to help dampen pitch response, and give the wings more breathing room in non level flight.

Using this idea for a 3 wing aircraft seems even more difficult, as the more vertical distance your wings take up the less pitch authority you have. A little bit of dampening is okay, but too much and you can't pitch the aircraft.

You'll also notice the quickie doesn't use a normal tail stabilizer (because of the problems discussed above). So differing lift coefficients between the wings are used, but that does make the aircraft harder to fly in general.

Anyway if you're really interested in this idea I'd recommend checking out the quickie project and learning what challenges/breakthroughs they faced/made.


What is the loading diagram for a C-130J?

As listed on a CNI-MU emulator designed for use by C-130J loadmasters, the following is a list loads and moment arms for the aircraft:

Basic weight: 80,000 lbf/STA 530
Crew weight: 600 lbf/STA 153
Fuel weight: 38,000 lbf/STA 551 -- this weight is, naturally, variable,
although the moment arm appears to stay relatively constant.
CG limits: 21-30% MAC

Finally, payload moment arms can be determined via use of of DD form 2130-2 on page III-V-17 of the 2015 Defense Transport Regulations (http://www.ustranscom.mil/dtr/part-iii/dtr_part_iii_app_v.pdf).


Why can't commercial aircraft have a wing boundary layer suction system?

Boundary layer suction systems have been considered for a very long time, since they provide significant advantages.

However, their main disadvantage, which has never been satisfactorily overcome, is their propensity to clog with dirt and biological matter. The maintenance costs to ensure the system is operational would outweigh the gains in aerodynamic efficiency.

Additionally, this is not the kind of system that could be left to its own devices (good if it works, fine if it doesn't); it would need to operate consistently because the critical angle of attack would depend on it.

Furthermore, this system would require power to operate the pumps, and it is not obvious that the efficiency gains would make up for the power requirements in all scenarios.


Can someone tell me what kind of airplane this is?

The aircraft with the inscription on the rudder "Capt Nungesser" is the French aircraft "Potez VIII" 1922 model type, the second version, equipped with a 70 hp. Anzani engine.
http://www.airwar.ru/enc/law1/potez8.html
Here is one picture from that site:


Can I get a 20/40 requirement waiver after cataract lens replacement?

If you are a member of or join AOPA I recommend consulting AOPA member services for help with questions like this. I have consulted them multiple times and they always get a good answer for me or set me in the right direction.

Of course you can consult an Aviation Medical Examiner (AME) first but I recommend you figure out what you need to do and go into your AME knowing you’ll pass the medical exam... once you’ve failed it can be a nightmare to get your medical back and take a long time (and cost lots of money).

Source: I’m a pilot who has used this service of AOPA before


How does the mixture of an engine affect the engine's operation?

Simple Answer: Running the engine lean or rich at different altitudes.

Longer Answer: There are a couple of reasons you want to adjust the mixture of a aircraft engine.

Since air density changes with altitude, it's a good idea to be able to change the fuel/air mixture at different altitudes.  If you did not adjust the mixture at high altitudes you may not get full power because the air is thinner and now there is same amount of fuel being mixed with less air.  All the unburnt fuel can cause issues like loss of power and/or fouling of plugs.
Being able to lean the mixture at higher altitude lets you save fuel, so you can go further on a full tank.  (hence saving money)
Running a engine rich can help cool engine.  Fuel acts like a coolant in this manner.  Typically on climbing you want to run the engine a bit rich because your going slower and less air is able to help cool the engine.
Traditional piston powered aircraft engines are shut off by pulling the mixture to the off position.  This starves the engine and burns off remaining fuel in the cylinders.

This topic can also bring up other discussions.  Like EGT, CHT, running an engine rich of peak or lean of peak, monitoring fuel flow rate with a flow meter, and fuel injectors on fuel injected systems.

Hope this helps.


What is the purpose of aluminium foil on the wheels?

They are reflective covers to protect the tires from the elements, especially UV. Similar to the shades visible in the windscreen. Goodyear says:

  Aircraft tires, like other rubber products, are affected to some degree by sunlight and extremes of weather.
  While weather-checking does not impair performance, it can be reduced by protective covers. These covers
  (ideally with light color or aluminized surface to reflect sunlight) should be placed over tires when an
  aircraft is tied down outside.

It also protects the tires from other substances like oil and hydraulic fluid.

The plane is not necessarily mothballed. I would expect it to be parked much more out of the way in that case. But the wheel and window covers do suggest that they expect it to be parked there for some time.

Information is a bit sparse, but it appears that Happy Air only has that one Saab 340 now, but since September all flights are operated by Nok Air, who operates Dash 8 Q400, ATR 72-500, and 737-800 aircraft.


Why are commercial propeller aircraft smaller than commercial jet aircraft?

There are a number of problems:

Speed

Traditional Propeller aircraft are much slower than jets. Propellers decline in efficiency as they increase in speed.

Noise

For the same thrust, propellers are noisier then jets.

Development Cost

There have been efforts for propellers but so far they have not been justified by economics.

GE36 Engine


How does compressibility affect the critical angle of attack?

First, I have to define what the critical angle of attack is:

When an aerodynamicist speaks of critical conditions, he or she means the condition when the speed of sound is reached locally. The critical Mach number is the speed, measured in multiples of the speed of sound, when the top local speed in a flow field equals the speed of sound.

The critical angle of attack is the one when the local flow speed first reaches the speed of sound. Since it depends on the initial flow speed, it is only valid for a given flight speed.

Two parameters are responsible for the local increase in speed: Thickness and angle of attack. A body needs to displace air, so the air will squeeze around it, speeding up in the process (or slowing down in fully supersonic flow).

When the angle of attack is increased, the stagnation point moves below the airfoil nose so the air flowing over the top of the wing needs to negotiate its leading edge first. This speeds it up and leads to a suction peak. Another view of the same phenomenon is that increasing suction on the upper side of the airfoil will accelerate the air flowing towards it.

With a higher flight speed, less local flow acceleration can be tolerated before the critical conditions are reached. There is even a maximum speed in that suction region of high local curvature that will not be exceeded in subsonic flight and which limits the maximum possible lift coefficient. Higher flight speed leaves less margin, so the angle of attack for maximum lift is reduced with increasing flight speed.

If by critical angle of attack you mean the one where maximum lift is reached (conventionally called stall angle of attack), please read here how it can be influenced. Depending on the flight Mach number, flight speed should be increased or decreased to maximize it.


Is the in flight emergency manual of a Boeing 737 Max 8 available to read online?

The in flight emergency manual is called the Quick Reference Handbook (QRH) and is in general not made publicly available by the manufacturer or airlines.

It is however possible to find quite a few online. Pages like smartcockpit.com have a lot of resources available. The Boeing 737 MAX is not mentioned on their page. A Google search for "737 max qrh" may help you find something.


Where did the US 'N' registration letter come from?

The origins of this can be traced back to CINA (the Commission Internationale de Navigation Aerienne / the Convention for the Regulation of Air Navigation) established as part of the Paris Peace Conference immediately after WWI.

A part of this conference was the adoption of a system of international aircraft identification still in use today. The U.S. delegation was allocated "N".

A number of theories exist as to why "N" was chosen specifically, and there's a great article about it over at the American Aviation Historical Society.

Theories range from, the largest number of states begin with the letter N; to the recognition of the development of wireless communications by the U.S. Navy that had been using "N" as the prefix to its station call-sign identifiers since 1909.


How do the vortices of a fixed wing and horizontal stabilizer interact?

The vortices coming off the ends of the wing are outside the width of the stabilator or stabilizer/elevator, thus there would be little interaction.

In my plane for example, the wings are 35 feet 6 inches wide, the stabilator only 11 feet 10 inches.
Thus the end of the wing is 17.25 feet from centerline, the end of the stabilator at 5.9 feet, thus 11+ feet of clearance.


Are helicopter with coaxial rotors equiped with blade flapping mechanism?

Yes and no, but mostly yes, especially the Kamov family.

Here's a picture(Wikipedia, CC-SA) that shows the (pair of very complex) flapping mechanism on Ka-27. Even though two rotors together should be able to balance out the asymmetric lift, the rotor hub and rotor for each individual rotor isn't rigid or strong enough for handle its own asymmetry (when it happens accidentally, e.g. the receding blade stalled, the receding blade of the top rotor will bend down and hit the advancing edge of the bottom rotor bending up and cause a catastrophic failure, e.g. Ka-50 had a series of rotor collision accidents).

However, there are rigid rotor helicopters and these don't bend nearly as much and don't need to flap, but none of them are among the Kamov lineage.

This is especially useful for high speed helicopters (e.g. Sikorsky S-97 Raider) because no amount of flapping will generate enough lift before stalling to cancel out the lift asymmetry, for the receding edge is too slow, so it has to let each rotor remain asymmetric and let the two rotors cancel each other.


Are there any aircraft that were grounded and later approved for flight?

The de Havilland Comet quickly comes to mind, with the airplane grounded after two catastrophic break ups in flight.  The Comet was returned to service once the problem had been identified and corrected in 1958.  Too late, however for the airplane to be a commercial success as the Boeing 707 had captured most of the commercial jet market in the intervening time.

So to was the McDonnell Douglas DC-10, which was grounded due to a faulty cargo door design, leading to two fatal accidents, but after operators implemented the required Airworthiness Directives from the FAA, the airplane was returned to service.

In fact many well known airframes have been temporarily grounded during their service lives then returned to service, including, but not limited to:

McDonnell Douglas DC-8
Aerospatsiale-British Aerospace Concorde
Boeing 767
Boeing 787
BAC One Eleven

Several aircraft were nearly grounded and faced public disfavor for a period of time thereafter.  The Boeing 727 was nearly grounded after 3 727-100s crashed in 1965, killing 131 people.  So, too, was the BAC 146 'WhisperJet', which was nearly grounded by the British government in 2000.

Military aircraft, too, have been temporarily grounded due to defects or service problems.  Lockheed's F-22 was grounded in 2011 after multiple pilots suffered hypoxic symptoms from the plane's malfunctioning OBOGS system.  The F-35 was temporarily grounded last November after a crash of an F-35B near Beaufort, SC.

Despite the best efforts of OEMs to conduct a rigorous and thorough development and flight test program to ensure a safe product, many potential problems simply can’t be identified until an incident or accident occurs in the fleet.  It’s virtually impossible to foresee every potential safety concern with a product that contains 4 million parts, 6 million lines of software code, terabytes of engineering data and tens of thousands of pages of operating protocols.  All of which must be able to function in perfect harmony and unison, without any conflicts.  Unfortunately much of what we know about aviation safety was paid for in the lives of the less fortunate.  Engineering OEMs strive to build better machines with each generation building upon the lessons learned from the past, but it’s not totally foolproof.


What is the distance unit on a navigation display?

They are nautical miles, which is the standard for essentially all discussions of distance in aviation. (Visibility being an exception; it can be reported in essentially every unit except nautical miles.) The software certainly could switch the display to another scale such as kilometers, although I’m not familiar with any systems that provide that option.


What are common airline crew titles and positions?

As the EET is variable from flight to flight you should better say that it is dependent on specific kinds of operation or routes, which is quite the same but includes also the time before and after the flight. Flight duty time starts at check in and ends at check out.

There are general requirements based on the maximum allowed duty time of a crew member, which are again based on the regulations of the aviation authority of the operators country. Finally it differs from airline to airline and is regulated by the operations manual, which can of course be not less restrictive than the authority, but there are some general titles you often hear:

Captain The Captain is the PIC (pilot in command) of this flight and responsible for a safe operation. He must be on station for departure and arrival.
First Officer The F/O is also found on every airliner operation. On short or medium ranges he is the 'Copilot', some airlines fly with two F/Os on long haul flights and in some portions of this flight most probably the two F/Os are in the cockpit and the captain takes a nap.
Second Officer When starting at an airline, you sometimes begin as a S/O and are only alloweed to do specific tasks. So for example handling the radios during departure and arrival, or having the controls during the cruise phase.
Cruise Captain Well, read the name ;) He might be a Captain and only in the function of a Cruise Captain for a specific flight, but once again, it depends on the operator.


Do non-towered airports commonly have ILS?

Nontowered airports absolutely can have ILS approaches, and it's fairly common, though of course not as common as at towered fields.

Two examples in my neck of the woods are KIKK (Kankakee, IL) and KMTO (Mattoon, IL).

Also, at many towered airports, the tower is not 24/7 and closes at night. If such an airport has an ILS, it's still available after the tower closes; ATC services for IFR approaches are provided by a nearby/higher facility like a TRACON or ARTCC, just like a nontowered field. Two examples of this in my neck of the woods are KCMI (Champaign, IL) and KBMI (Bloomington, IL).

I am not, however, aware of any Cat II or III ILS approaches at nontowered fields.

Protecting ILS Critical Areas is usually the responsibility of the tower, but even VFR aircraft are prohibited from entering the ILS Critical Area when the tower is closed:

  (1) Localizer Critical Area. Except for aircraft that land, exit a
  runway, depart, or execute a missed approach, vehicles and aircraft
  are not authorized in or over the critical area when an arriving
  aircraft is inside the outer marker (OM) or the fix used in lieu of
  the OM. AIM 1-1-9(k)


Is there independent evidence that the Wright brothers celebrated Roosvelt's election in 1904 by a flight of over 5 minutes?

The short answer is No. The independent witnesses are missing. Only Wilbur, Orville, and possible their father, saw the Nov. 9, 1904, flight.
There exists a commented collection of old documents of the period 1903-1905 (most of them from 1904), over 200 letters and articles, all quoted in full, that studies, based on primary sources, whether the Wrights really flew a plane in 1904 (they claimed 105 landings for that year).
This book is titled: "The Wrights and their impossible 1904 flights"

The 1904 plane as imagined by C. Dienstbach in his March 1905 article in German (Source: "The Wrights and their impossible 1904 flights", page 62)
Regarding the existence of the Nov. 9, 1904, flight, besides the letter sent to Octave Chanute, this is the evidence I could find, in the above mentioned work:

November 9, 1904 - An entry in Bishop Milton Wright's diary reads: “… I go on 11:00 car to Sims. At 2:00, Wilbur flew three (lacking one-fourth) miles in 5 minutes and four seconds. The distance was only limited by failure of engine.” (col. 1, p.28)
November 9, 1904 - Wilbur recorded, in one of his notebooks, a flight of 5 minutes and 4 seconds as the 82nd trial of that year. Orville also mentioned the flight in his logbook. (p. 95)
December 17, 1904 - The Dayton Press published an anniversary article, stating: "Their work and trials have been carried on quietly. They have not made any public trial, and have no intention of making any in the near future. … The longest fights yet accomplished by the machine occurred on November 9 and December 1, when the flyer made almost three miles in five minutes.” (p. 36)
December 20, 1904 - Wilbur mentions, in a letter to G. A. Spratt (a fellow aviation enthusiast), that the longest flights of 1904 occurred on November 9th, 16th, and December 1st. (col. 1, p. 18)
December 21, 1904 - Orville Wright wrote to the German journalist Carl Dienstbach saying, amongst other things,: "The two longest flights of the season were made on the 9th of November and the 1st of December. In each of these flights we made almost four complete circles and covered a distance of a little over four and one half kilometers, at a speed of about 35 miles an hour. In the flight of November 9th a weight of 50 lbs. (iron bars) were carried in addition to the weight of the operator; in the flight of December 1st, 70 lbs." The letter of Orville was published in German under the heading: “Das erste Lebensjahr der praktischen Flugmaschine”, Illustrierte Aëronautische Mitteilungen, March 1905, pp. 91-93. (p. 19)
February 3, 1904 - The Holt County Sentinel (Oregon, Missouri) published a short text that quoted the father of the two inventors: " After years of unsuccessful efforts by some of the world’s greatest scientists, it appears that the Wright Brothers, of Dayton, O., have solved the problem of the flying machine. Accounts of a successful test made by them appeared in the papers last summer, and it seems that they are making rapid strides toward perfecting their invention. We quote the following from a letter from their father, Bishop Milton Wright, of Dayton, to his niece, Mrs Frank Petree. “Wilbur, on November 9th, celebrated Roosevelt’s election by a flight of nearly three miles, in five minutes, and Orville did the same December 1st. I was there. They are improving their engine and will put the experience of 1904 into a new machine by April.” " (col. 2, p. 89)

In conclusion, the Press states that nobody saw a powered flight performed by the Wrights before December 17, 1904. The only possible witness (not really independent) of the Nov. 9th long flight could have been Bishop Milton Wright. However his diary just implies he witnessed the performance of that day. The father of the two inventors does not explicitly use the words "I saw".
If somebody else finds new evidence, in the book or from other primary sources not quoted there, I would be happy to see it.


Do interceptor squawk codes suppress TCAS RAs?

To avoid an RA, the interceptor would almost certainly turn off at least his Mode C, and to avoid a TA and the concern in the intercepted aircraft of "what is this no-altitude traffic doing closing rapidly on me???" he will probably turn off his squawk altogether before he gets to the last few miles of the intercept.  (There were cases years ago when TCAS was pretty new of intercepted aircraft getting a series of RA's as interceptors -- squawking everything -- closed on them, maneuvering to continue the intercept even as the target climbed and dived all over the sky in response to the RA's. That scenario is undesirable for all sorts of reasons!)

A wingman may well hold a squawk and park himself some miles in trail of the target, monitoring both the interceptor and the target with his own air-to-air radar.  ATC can see the wingman and the target, and knows that there is an interceptor somewhere between them -- which is probably enough for their purposes.

Each specific case probably has letters of agreement between the ATC facility and the specific interceptors, so they'll all know in advance who's where, doing what, squawking or not squawking what, and who's talking on which frequencies.  Those sorts of specifics probably aren't available in the public domain.


What are the advantages and disadvantages of a delta wing compared to a swept wing?

Benefits of a delta wing:

Due to the large root chord, a delta wing combines low relative wing thickness with a sufficiently thick wing spar for a lightweight structure. Since a low relative thickness keeps wave drag down (a drag component which occurs only in supersonic flow), this makes delta wings especially attractive for supersonic aircraft.
The large root chord gives the delta wing a high internal fuel volume even at a low relative thickness.
The large root chord also provides it with a large surface area which helps to bring the minimum speed of the aircraft down.
With sufficient leading edge sweep, a delta wing produces vortex lift, so flow separation can be turned into a means of increasing lift.
A delta wing is naturally stable in pitch, therefore it does not require a separate tail surface.

Drawbacks of a delta wing:

The large wing area causes more viscous drag for the same amount of lift compared to a high aspect ratio wing. Swept wings have a better lift-to-drag ratio (L/D) than delta wings.
High-lift devices like fowler flaps are hard to integrate into delta wings. The higher relative thickness of regular airliner wings allows to integrate large flaps more easily, and the rearward location of the trailing edge of a delta wing will produce intolerable pitching moments if such flaps would be deflected.

Generally, the moderately swept high aspect ratio wings of subsonic airliners are ideal for flight at high subsonic Mach numbers. Delta wings are superior only in supersonic flight, and due to their good low speed characteristics they offer the best overall compromise for supersonic aircraft.

North American XB-70 in flight, a classical delta wing design (picture source). Note the canard wing, which has little sweep and a low aspect ratio: This kind of wing is ideal for supersonic flight, provided it has a low relative thickness. The main wing of the XB-70 is a delta wing to keep the take-off and landing speeds relatively low and offers the best compromise of low and high speed characteristics. Also, the wing tips could be deflected downwards to improve directional stability at supersonic speed and to improve L/D by using the waverider effect.

The wings of both the Boeing 787 (top, picture source) and the Airbus A350 (bottom, picture source) show their powerful high-lift devices in these pictures, which allow them to fly with less than half the wing area of a comparable delta wing aircraft. Also, the lower surface area translates into lower drag at high flight speed, and the higher possible wing span helps to reduce induced drag, making those wings far superior for efficient flight at high subsonic speed.


Why use an airplane with non-retractable landing gear for aerobatics?

As you mentioned, drag is one of the reasons why retractable landing gears are used in the first place. But in order to use it, there are way more considerations than just drag.

Scale: Size of the aircraft plays a big role here. Big aircraft have more room to keep the retracted landing gear. This is an issue as planes get smaller.
Weight: Retractable landing gears not only require more space, but they impose more weight
Cost: They add extra costs in installation and maintenance.
Application: High speed applications justify a retractable landing gear for a more aerodynamic shape. Does the present situation really need the application of a retractable landing gear?

These are some considerations that go into it, but not all of it. In the case of a high performance sports plane (like in the video above):

Scale: the planes are small. The retractable landing gear systems (system) need a lot of space. This is not what we want in a sports plane
Weight: A high percentage of the overall weight is taken by the system. This in turn increases the inertial forces* and decreases the overall maneuverability.
Cost: It is expensive to install. And it may cost even more due to the low volume requirements.
Application: More than high speed, high maneuverability is needed.

* Inertia is the tendency of a body to stay in the existing state of rest or motion. So inertial force is the force that keeps the body in its existing state of rest or motion.

[EDIT]
Based on a very good response below (from @Devil07), I am adding this important point here (just for a better overview of all important aspects):

Complexity: Retractable landing gears are complex piston mechanisms. Eventually it adds to the cost of installation and maintenance of the system.


Could a moving film of gas reduce aerodynamic drag?

No, it doesn't reduce drag through reducing boundary layer speed, but it does create thrust by creating a region of low pressure in front of the vehicle (I mean technically, if the entire vehicle produces thrust, it does reduce vehicle drag, but in either case the reason why that happens isn't because the boundary layer speed is reduced). If you mount the device like in the image, then the low pressure zone will be created. The pressure at the bottom of the vehicle is higher than on the top, so it will generate forward thrust (well, in the orientation of the image, upwards thrust). This is because a jet of fluid will entrain it's surrounding fluid (aka "pull the fluid along with the jet"), which will create a region of low pressure around the jet. There actually are real-life implementations of this concept -

            ,

            .
However, the reason why this isn't used in real life is because if it's low efficiency - there's other ways to generate that thrust, such as using a propeller, a turbofan engine, etc, that don't require nearly as much fuel to produce the same thrust.


Why use different airfoils on the same wing of an aircraft?

Because the wind tunnel has determined what the best airfoil is, at this particular span, over the whole operational range of flight:

Stall speed: docile pre-stall behaviour with outboard wing stalling last to retain roll control.
Landing speed with flaps & slats out: high stall angle, high $C_L$
Climb speed: low drag in high lift conditions.
Cruise speed in clean configuration: low drag, low pitching moment, high drag/lift divergence speeds.

The design goal is the performance of the total wing, wing profile is one of the parameters that can be used to optimise performance, minimise drag, provide good structural characteristics, and provide a large volume for the on-board fuel.

For the wing root, the aerofoil must have a good cantilever ratio (thickness) for torsional and bending stiffness.
For the wing inboard section with flaps extended, aerofoil drag must be low in high lift conditions.
For the wing tip, the aerofoil must have a high maximum $C_L$ and gradual stall characteristics)
For all wing sections, the aerofoil must have a sufficiently high critical Mach number.
For all wing sections, pitching moment coefficient should be low to moderate, to avoid high trim drag, and high torsion at high dynamic pressure.
For all wing sections, aerofoils must not be extremely sensitive to manufacturing tolerances, dirt/bug build-up etc.

So different bits of wing have different design characteristics. The whole wing is a gradually blending unit of different aerofoils.


What improvement was made in Su-35 over Su-30?

The Su-30 is an modifications of the SU-27UB
The Su-35 is an Su-27 shaped aircraft with many new parts from the Su-34 (T-10BM)
in detail
Radar N035 Irbis-E PESA
Rear-looking self-defense radar
new fly-by-wire flight-control system
new fully-glass cockpit
Electronic-warfare self-defense system L175M Khibiny-M
Engine AL-37FU/ 117S
larger Air Intakes, no canards, reduced-area empennage

Su-35 has been also called early export versions of the Su-27
and to make more confusion, the production factories (Irkut / Amur) does not name their product Su-35

Please take a look at   http://www.sukhoi.org/eng/planes/military/Su-35/
and   https://defence.pk/pdf/threads/su-30mki-vs-su-35s.222304/


What is the resistance range for the Bendix King KN-64 DME Photoresistor?

According to http://www.flymafc.com/docs/manuals/king-KN62_KN62A_KN64.pdf, The Maximum Sensor Range for the Bendix King KN-64 DME is determined by altitude and ground station output power and sensitivity. Under normal circumstances, the KN-64 DME has a maximum display range of 389 Nautical Miles, as shown below:

The Change in Accuracy of the KN-64 DME change from .1 Nautical Miles or .14 Nautical Miles from 0 to 99.9 Nautical Miles, as shown below, along with Sensitivity:


you're in luck, somebody did the calculation/ simulation.

Mars: To see what happens to aircraft on Mars, we turn to X-Plane.

X-Plane is the most advanced flight simulator in the world. The product of 20 years of obsessive labor by a hardcore aeronautics enthusiast who uses capslock a lot when talking about planes, it actually simulates the flow of air over every piece of an aircraft’s body as it flies. This makes it a valuable research tool, since it can accurately simulate entirely new aircraft designs—and new environments.

In particular, if you change the X-Plane config file to reduce gravity, thin the atmosphere, and shrink the radius of the planet it can simulate flight on Mars. (Note: Thank you to Tom J and the folks in the X-Plane community for their help with aerodynamic calculations in different atmospheres.)

X-Plane tells us that flight on Mars is difficult, but not impossible. NASA knows this, and has considered surveying Mars by airplane. The tricky thing is that with so little atmosphere, to get any lift, you have to go fast. You need to approach Mach 1 just to get off the ground, and once you get moving, you have so much inertia that it’s hard to change course—if you turn, your plane rotates, but keeps moving in the original direction. The X-Plane author compared piloting Martian aircraft to flying a supersonic ocean liner.

Our Cessna 172 isn’t up to the challenge. Launched from 1 km, it doesn’t build up enough speed to pull out of a dive, and plows into the Martian terrain at over 60 m/s (135 mph). If dropped from four or five kilometers, it could gain enough speed to pull up into a glide—at over half the speed of sound. The landing would not be survivable.

so, you would need runways that look at each other, as turning is almost unfeasible, and these runways will have to be really long, as you have to get to Mach 1 to take off and you have to decelerate from that same speed once you touch down.
GPS would not be really needed.


How should I interpret the Douglas DC-4 approach climb performance chart?

I interpret the dotted line to indicate the conditions needed to meet the minimum required performance, as specified in CAR1 (the certification standards used when the DC-4 was originally built.). Conditions to the right of the line are "Good", to the left of it are "No Good".  I.E. if you had a gross weight of 60,000 lbs, and were configured as specified, the aircraft would not be able to meet the required performance at any altitude above ~6400 Ft.

I believe the "C=blah etc" statement is referencing the airspeed used to determine these performance results. C= Calibrated Airspeed, VsO² is stall speed in this specific configuration, and I'm guessing that the ".04" means 4% above said stall speed.

I hope this has only confused the question tremendously, and as solely my opinion, is worth precisely what you have paid for it. YMMV. Do not attempt at home. This offer not valid.


What type of flow is preferable for jet engines?

The noise within the engine will make all flow turbulent. There is not much liberty for the engine designer to choose the type of boundary layer.

Generally, a laminar boundary layer is preferable as long as the flow is accelerated, because viscous drag will be lower, and a turbulent one is better when it is decelerated, so separation can be delayed.

Outside of boundary layer phenomena, turbulence is helpful for keeping the combustion process going in the combustor and especially in the afterburner. Ahead of the combustor all engines have a diffusor to slow down the compressed air, so it has time to mix with the fuel and burn as much of it as possible. Note that the diffusor only slows down the axial movement of the air, so radial velocities will not be affected and be relatively larger relative to the axial flow at the entry of the combustion chamber. This makes the flow more turbulent, which is helpful for better fuel-air mixing.

In the afterburner, flame holders are needed to produce pockets of slow-moving, hot gas which can ignite the fuel-air mixture. Again, they cause more turbulence.

Flame holder (10) with annular selectors (9) of an afterburner (picture source)

At the nozzle, turbulent mixing of the hot core flow and the bypass flow reduces noise. Engine nozzles use a variety of means to speed up the mixing process.


Why the need to use right rudder during stall recovery?

You wrote:

When recovering from a stall, you need to add power. The increased power induces a torque in the opposite direction.
My problem with this answer is that torque will result in roll and usually ailerons are used to control the roll. Why rudder in this case?

I think you already know that a stall happens when you no longer have smooth airflow over the wings. Because you don't have effective airflow over the wings, your ailerons are not working. (they may be partially effective, or have no effect at all)
You are right that ailerons are used to control roll during nominal flight; but a stall is not nominal, and the ailerons are no longer effective.
The rudder, as a vertical surface, is not stalled the same way that the wings are.  So while it may not be the ideal way to counter a roll moment, its more reliable than the ailerons.


Why is the ratio of TSFC at altitude vs. sea level different for hi-bypass vs. lo-bypass turbofan engines?

The factor affecting TSFC is speed, not altitude. Altitude is indirectly responsible because the lower density requires a higher flight speed.

Low-bypass engines have a higher exit speed, so the change in speed affects their efficiency less. High-bypass engines double their TSFC between static and Mach 0.8 and only the lower temperature at altitude reduces the difference a bit. If you look at the formula for thermal efficiency in this answer, you see that efficiency drops more over speed for high-bypass engines. Only the much better propulsive efficiency of high-bypass engines makes them overall better for airliners.


What navigation systems were used by the Space Shuttle during reentry?

With the exception of GPS upgrades, I don't believe there were any substantial differences in navigational equipment between the various Space Shuttle Orbiters for most of their operational history.

Each space shuttle had:

3 Inertial Measurement Units
3 TACAN receivers* see GPS Upgrades
4 Barometric Altimeters
3 MSBLS Receivers
2 Radar Altimeters
2 Air Data Probes
Star Tracker (on-orbit)
Rendezvous Radar (on-orbit)

There is lots of information about the Shuttle's navigational equipment in the Shuttle Crew Operations Manual.

GPS Upgrades

In the early 1990s, it appeared that TACANs were going to be phased out, so NASA began evaluating GPS as a possible replacement. Space Shuttle Endeavor was the first to have a single GPS receiver installed in 1993, followed by the other shuttles beginning sometime around 1996.

By 2002, each shuttle had 1 GPS and 3 TACAN receivers. The plan was to remove the TACAN receivers and install two additional GPS receivers - resulting in a 3-string GPS system. However, after the loss of Columbia in 2003, it was decided that the Space Shuttle Program would be discontinued in 2010 (later extended to 2011), and therefore it wasn't worth upgrading all three remaining shuttles. Only Endeavor was upgraded. Discovery and Atlantis continued to fly with 3 TACANs and 1 GPS for the remainder of the program.

You can read a lot more about the history of the GPS system here: Operational Use of GPS Navigation for
Space Shuttle Entry.


Why does the DHC-6 pitch down when the flaps are retracted, rather than up?

The Twin Otter isn't unique.  Flaps have varying effects on different airplanes.  Some pitch up with flaps extended, some pitch down.   The pitching moment from flaps isn't just from the nose down moment from the increase in airfoil camber; it includes effects of increased downwash on the tail, which creates a pitch up moment, and to some degree, changes in the vertical aerodynamic center resulting from adding drag up high or down low (like the mild pitch down moment caused by gear extension).

In the Twin Otter the double-slotted flaps are extremely powerful and create a very strong downwash increase at high angles as opposed to just mostly turbulence you get with simpler flap setups. The result is the net effect of flap extension, with the high wing and the location of the horizontal stabilizer, is pitch up because those forces are stronger than the nose down moment created at the wing itself by the camber change.


No.

This would require a docile pitch behavior of the airframe up to approx. 110° angle of attack. The design of both the Su-27 and the MiG-29 is based on a geometry that has been carefully optimized by TsAGI to behave nicely over its full AoA range, a care that has not been spent by General Dynamics while designing the F-16. The specifications did not call for it, because the idea was to create a low-cost lightweight fighter to complement the heavy F-15.

However, even the F-15 is AoA limited because less care was spent on its aerodynamic refinement. At higher angles of attack, both the F-16 and the F-15 show a nasty pitch-up which cannot be controlled with the aerodynamic control surfaces - only thrust vectoring can manage this. Contrast this which the Su-27, which shows balanced and slightly negative (nose down) pitch moments over the full AoA range, so the limited control authority coupled with the aircraft's dynamics can make the Cobra maneuver possible.


What kind of flight-control redundancy does the Tu-204 have?

The Tu-204 does not have mechanical back-up, but it does have analog back-up. Its FBW is three-channel (same hardware, but different software).

(...) being the only Soviet airliner to have flown with a fly-by-wire control system, lacking any mechanical backup (...)
The Tu-204's digital fly-by-wire control system is probably the most advanced feature of any Soviet airliner. It works on all three axes—pitch, roll, and yaw—and is broadly similar in function to that found in the A320.
(...)
The same hardware, but dissimilar software, is used in the three channels of the digital fly-by-wire system, says Lanovski. A "quorum filter" monitors their outputs, and if two channels fail a three-channel analogue system automatically takes over, giving a catastrophic failure probability for the complete system of less than 10-9 per flight-hour, says the Soviet official. Pilots have felt no difference when the analogue system has been switched in during flight tests, says Lanovski.

Source: Tupolev's new twin, Flight International, 20 May 1989


Possible military aircraft ID, N. Carolina

This looks like a V-22 Osprey.  Here is a photo.  (it happens to be refueling, so ignore the nose hose.)


Historically, a runaway airship cannot be caught or entered. Eventually it will come down - they all did so far. Only in one case did a Zeppelin fragment of a ship which broke up in a storm make a soft landing so the crew aboard could survive. In all other cases both ship and crew perished or were never seen again.

While the Zeppelins had vertical shafts which allowed the crew to climb to the top of the hull, a blimp can only be entered below the hull. Trying to lower someone James-Bond-style from above will fail, because the big hull will shield the entry points of the gondola very effectively.

Defensive gunner position on a Zeppelin. Note the square hatch at the bottom which leads down to the bottom of the ship.

Also, shooting it down will be an exercise in futility. All it will do is to increase the rate of helium loss, so the flight will be some hours shorter. Helium is inert and will not burn, and those small holes will be tiny relative to the big surface of the hull.

At 15,000 ft it will be hard to try to catch one of the lines most likely hanging from the blimp with a helicopter. Remember that the blimp floats, so the helicopter has to hover at this altitude. Very few are able to do so. Towing will only be possible with another blimp or a helicopter; an airplane will not be able to fly fast enough with a blimp in tow.

The next trick depends on the color of the hull: If it is dark, covering it with something highly reflective will cool it and reduce the blimp's buoyancy. I have, however, no idea how to get a big blanket on that thing. The same will happen when night falls, but first the air will cool and the blimp, which will cool down more slowly, will go up. Later in the night and early in the morning it will sink again.

The wet parts of rain clouds will mostly be below 15,000 ft (water content is proportional to air density, after all), so a shower which drenches the hull and makes it heavier is highly unlikely. There is no obvious way how this thing will come down fast. Except, that is, it climbs further and the hull bursts. This will change the dynamics of this escape in a dramatic way.

The chase planes will help ATC to route traffic around the blimp, and all that can be done is to watch it. With luck the landing will be soft enough that it is not a complete write-off.


What are the effects of shockwaves on normal and supersonic aircraft?

Not much, really, the shock wave just streams off of the nose of the plane, and an anti-shock from the tail. They stream away from the plane and don't hit it.

Image source

The shock itself is the compression that the flying aeroplane imparts upon the unsuspecting air in front of it: disturbances travel with the speed of sound, if the aeroplane travels faster there is no warning and air gets compressed suddenly when the aeroplane arrives. This is the nature of the shock.

The amount of compression is spread out It's not a shock like a bomb explodes, only a loud noise. Flying over Mach 1 is not inherently more risky than flying subsonic. When first attempted 70 years ago there was some unexpected behaviour to iron out, but that's aviation in a nutshell for you. Once understood, a problem is only an invitation to find a solution, and that is what the aero guys did.


Why are Stratolaunch's engines so far forward?

The forward location has two benefits:

Wing upwash is smaller, so the flow direction at the intake varies less with speed and altitude. This makes the intake more efficient and requires less robustness in its layout.
The forward location shifts the wing's center of gravity forward and gives it better flutter damping. How that works is explained here.

Wing torsion in combination with the two fuselages will produce a flutter mode where both fuselages pitch in opposite direction, torquing the center wing in the process. The slender wing in combination with the high pitch inertia of the fuselages will result in a very low flutter frequency. I suspect that damping this mode is of paramount importance for the Stratolaunch.
I also suspect that the high wing on a high fuselage allows more vertical distance between engine and wing, so the exhaust stream will pass below the lowered flaps. The high turbulence in the exhaust stream would put additional loads on the flaps; to avoid this, Boeing uses exhaust gates or a gap in its trailing edge flaps. Such a gap would not be needed with the lower engine position of the Stratolaunch. However, to place them lower does not require to shift them forward, too.


Do frequency response / Bode plots for an aircraft or helicopter come from modeling or empirical testing?

The answer is both modelling and/or empirical methods are used.

For aircraft with a closed loop Flight Control System then the clearance requirements before flight requires that sufficient gain and phase margins exist for the system. For example with Military Aircraft this was defined in MIL-F-9490D. This would involve building mathematical models of the aircraft and control laws and calculating margins from the frequency response of the model. This allows the engineers to analyse the robustness of the system under various tolerance and failure states before flight.

It is possible to analyse stability margins from flight data, but note even the RTSM software referenced in the comments talks about comparing the flight data calculated margin against an a priori model.

Also note that Handling Qualities requirements, i.e. saying it is PIO prone, are additional requirements over and above the basic stability requirements. This introduces another feedback path with a pilot in the loop. For this there are additional frequency response parameters to meet, for example average phase rate. Again examples in MIL-Spec requirements MIL-F-8785C, these will all be assessed using mathematical models.


Why was Pan Am Flight 103 flying over Lockerbie?

The direct route you show is actually only a straight line on your map projection. The surface of the Earth is curved and the straight line between London Heathrow and New York JFK looks like this (courtesy of greatcirclemapper.net):

That still does not quite get you over Scotland, but the actual flight path over the Atlantic typically uses a North Atlantic Track. These are routes, which are redefined twice a day to make optimal use of the prevailing enroute winds. Here is one example for such tracks:

(image source)

The entry points to these routes can be quite high north, therefore resulting in an optimum route over Scotland.


May an ultralight vehicle pass directly above KEGE at 9200 MSL at 1600Z with no prior authorization without violating FAR 103.17?

Yes, an ultralight aircraft may fly over KEGE ( http://vfrmap.com/?type=vfrc&lat=39.643&lon=-106.916&zoom=10 ) at 9200' MSL at 1600Z -- i.e. above the ceiling of the Class D airspace when the control tower is open and the Class D airspace is in effect-- with no prior authorization without violating FAR 103.17.  Just as is the case above any Class D airspace with projecting areas of Class-E-to-surface airspace where the airspace designations have been handled in a more conventional manner, such as at KMFR ( http://vfrmap.com/?type=vfrc&lat=42.374&lon=-122.874&zoom=10 ).

The design of the airspace at KEGE as described in the FAA's "Airspace Designations and Reporting Points" document, JO 7400.11C, is unconventional and possibly flawed, as described in more detail in this related question Can the Class-E-to-surface airspace near Eagle County Regional airport KEGE be ignored when the tower is open?.  Here are all of the most plausible interpretations of how the Class-E-to-surface airspace around KEGE is intended to function.  None of these interpretations require an ultralight aircraft to seek prior authorization before overflying KEGE at 9200' MSL when the Class D airspace is in effect.

All of these interpretations address this question -- "During the hours that the Class D airspace is active at KEGE, is there any E2 airspace at KEGE, and if so, where?"   To understand why, generally speaking, E2 airspace, and only E2 airspace, appears to be the best fit for the meaning of "the surface area of Class E airspace designated for an airport" in the context of FAR 103.17, see this related answer Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?

1) The best description of the situation at KEGE appears to be that the airspace has been designated in the same way as the 21 airports described in this answer to a related question What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night? , except that no E4 airspace description has been provided to create Class-E-to-surface airspace in the projection to the east when the tower is open and the E2 airspace is inactive.  according to this interpretation, this omission is accidental.  A careful study of the "Airspace Designations and Reporting Points" document makes it clear that any given block of designated airspace (e.g. E2, E4, or Class D) is intended to become effective or ineffective as a single unit, so when the Class D airspace is in effect at KEGE, none of the E2 airspace is in effect. So technically, as the description has been written, it appears that there is no Class-E-to-surface airspace in the projection to the east when the tower is open. Local ATC treats the airspace as if there is Class-E-to-surface airspace in the projection to the east 24/7, i.e. as if an E4 airspace description had been provided to cover the airspace in the projecting area to the east when the tower is open and the E2 airspace is not in effect.  Naturally, it would be wise for a pilot to treat the airspace in the projection to the east as if it were some form of Class-E-to-surface 24/7, because this is the practice of the local ATC.  Nonetheless, an ultralight overflying KEGE above the Class D ceiling when the tower is open is not within the lateral boundaries of any active E2 airspace, so no prior authorization is required by FAR 103.17.

2) The airspace around KEGE has been designated in the same way as the 21 airports described in this answer to a related question What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night? , except that no E4 airspace description has been provided to create Class-E-to-surface airspace in the projection to the east when the tower is open and the E2 airspace is inactive.  According to this interpretation, this is intentional and is based on the theory that when the Class D airspace is active, only that portion of the E2 airspace which coincides with the Class D is superseded by the Class D, while the rest of the E2 airspace remains in effect.  (KEGE appears to be the only airport in the US where this unusual theory has been applied; normally any given block of designated airspace (e.g. E2, E4, or Class D) is intended to become effective or ineffective as a single unit.)  However, a fundamental characteristic of any given column of E2 airspace is that it contacts the surface.  Therefore when some portion of the E2 airspace is superseded by Class D airspace up to 9100' MSL, all the immediately overlying E2 airspace also detaches from the rest of the E2 airspace and becomes E5 airspace.  When the Class D airspace is in effect, none of the airspace above the ceiling of the Class D can be considered to be E2 airspace.  Therefore an ultralight overflying KEGE above the Class D ceiling when the tower is open is not within the lateral boundaries of any active E2 airspace, so no prior authorization is required by FAR 103.17.

3) The airspace around KEGE has been designated in the same way as the 21 airports described in this answer to a related question What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night? , except that no E4 airspace description has been provided to create Class-E-to-surface airspace in the projection to the east when the tower is open and the E2 airspace is inactive.  According to this interpretation, this is intentional and is based on the theory that when the Class D airspace is active, only that portion of the E2 airspace which coincides with the Class D is superseded by the Class D, while the rest of the E2 airspace remains in effect.  (KEGE appears to be the only airport in the US where this unusual theory has been applied; normally any given block of designated airspace (e.g. E2, E4, or Class D) is intended to become effective or ineffective as a single unit.)  Therefore the airspace above the ceiling of the Class D can be technically be construed to be E2 airspace 24/7.  However, FAR 103.17 does not specifically and explicitly reference E2 airspace.  While in most cases, as noted in the related answer Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?, E2 airspace, and only E2 airspace, is the best fit for the meaning of "the surface area of Class E airspace designated for an airport" in the context of FAR 103.17, any piece of E2 airspace that is not actually part of a column of Class E airspace extending all the way to the ground is clearly an exception to this general principle.  An ultralight may overfly KEGE above the Class D ceiling when the tower is open with no prior authorization without violating FAR 103.17.


How is minimum runway length related to V1?

Takeoff Field Length
The “FAR” Takeoff Field Length determined from the FAA Approved Airplane Flight Manual (AFM) considers the most limiting of each of the following three criteria:
1) All-Engine Go Distance:
115% of the actual distance required to accelerate, liftoff and reach a point 35 feet above the runway with all engines operating:

2) Engine-Out Accelerate-Go Distance:
The distance required to accelerate with all engines operating, have one engine fail at $V_{EF}$ at least one second before $V_1$, continue the takeoff, liftoff and reach a point 35 feet above the runway surface at $V_2$ speed:

3) Accelerate-Stop Distance:
The distance required to accelerate with all engines operating, have an engine failure or some other event at $V_{EVENT}$ at least one second before $V_1$, recognize the event, reconfigure for stopping and bring the airplane to a stop using maximum wheel braking with the speed brakes extended.

$V_1$ Speed
$V_1$ is the speed chosen by the manufacturer as "the pilot’s initiation of the first action to stop the airplane during the accelerate-stop tests."  Note that this is particularly important in that it is not a takeoff decision speed as some pilots like to think of it.  The decision must have been made prior to $V_1$ so that there is time to react by $V_1$.
This speed is chosen by the manufacturer and must be between the engine failure speed1 and rotation speed.  Within this range, they could choose any speed, but typically they choose the speed which gives a balanced field length (see next section).
There are also other factors to consider such as the maximum brake energy limit ($V_{MBE}$) which will prevent $V_1$ from being too high.

Balanced Field Length
If we takeoff from a fixed length runway (like, say one that matches the Takeoff Field Length from above), changing the $V_1$ speed will affect the weight that we can successfully continue the takeoff or abort within the available runway.
At a particular weight, a lower $V_1$ will enable us to stop sooner if we abort but will take more distance to continue the takeoff.  A higher $V_1$ will require more distance to stop but will take less distance to continue.  If we graph these values, there will be a point where the $V_1$ speeds for the abort/continue lines meet, and this is known as the balanced field length.  It is the value typically given in the AFM:

This is nice because it gives the pilot one important number to remember instead of different stop/continue $V_1$'s.
If they were to choose an extremely low $V_1$ as in your question, then it would require considerably more runway in order to continue the takeoff than if it were higher, and it would not be balanced.  Some AFM's do include separate charts for accelerate-go and accelerate-stop though so you could figure out exactly how much runway that you would need if the engine failed at a lower airspeed.

Rotation Speed
$V_R$ is determined independently from $V_1$, and if it is ever less than $V_1$ then it must be raised to be equal to $V_1$.

References
The regulatory information for takeoff performance on transport category aircraft is listed in 14 CFR Part 25, Subpart B, Performance, 25.101 - 25.113.
Of particular interest for this question would be 14 CFR 25.107 - Takeoff speeds and  14 CFR 25.113 - Takeoff distance and takeoff run
An easier to read document is the FAA's Pilot Guide to Takeoff Safety which covers this and a lot more.  Much of my answer was taken directly from this document, and I would highly recommend anyone that is flying a multi-engine aircraft to read the entire thing.

1 $V_{EF}$ itself must be above the minimum controllable airspeed on the ground plus acceleration while the pilot reacts to the engine failure.


A washout filter is used in a yaw damper autopilot to remove the steady state component from the yaw rate sensor. Feedback from the rate sensor is used to damp dutch roll mode, but during turns coupling between yaw and roll results in the aforementioned undesirable steady state yaw rate component. Detail is on pg103 of: this document


Where inside a black box is the data storage located?

The image of the recovered "black box" is showing the Cockpit Voice Recorder (CVR). The data is stored in the cylindrical housing that was relatively undamaged in the crash.

The housing consists of a stainless steel outer shell to withstand impact forces. Beneath it is a layers of high temperature insulation to protect the data storage from post crash fire.


What are these large yellow circles painted across the runway?

That would be the "line" telling military pilots where the arresting cables are. If you look to the side of those circles, you can see the arresting mechanism these. It would be yellow so that it would still stand out to the pilot and not be confused with the white runway markings.

You can find more about them here.


What qualifies as a "takeoff" and "landing" in currency requirements?

There's more than enough room to land to a full stop, take off, climb to (e.g. 50 feet AGL), then immediately land again to a full stop without needing to go around the pattern.

50 feet is completely arbitrary. Why not 5 feet? If the wheels leave the ground and touch back down, you took off and landed didn't you?

The regs exist to make sure you're maintaining some basic proficiency. Cutting corners to fulfill the letter of the law without actually refreshing your skills does no one any good — least of all you. Besides, as jwzumwalt pointed out, it most likely wouldn't meet the FAA's definition of takeoff and landing.