Letters of Authorization (LOAs) are authorization to conduct various types of commercial flights in certain airspace.  They are defined and governed by FAA Order 8900.1 and can be obtained from the regional Flight Standards District Office (FSDO) for that area.  It is not necessary for non-commercial general aviation operations.  I suspect (and I don't know the full details as to how you contacted Ft Worth Approach) that the controller thought you were a commercial operation requesting to start doing some sightseeing over the Dallas Ft. Worth Area without having done this paperwork.

Usually as a GA pilot, you can simply contact approach control for a Class B airspace and request a transition through Class Bravo.  This request may or may not be granted depending on commercial traffic congestion that day, etc.  They may also want you to stick to existing VFR traffic transition routes and not deviate from that.  Class B, as a general rule, is not very accommodating for sightseeing and other leisure flying.


What control inputs are required to perform a "turning-while-in-flight" maneuver in a helicopter?

Yes it's cyclic inputs only for banked turns because there is no adverse yaw due to ailerons to compensate for.  You will be working the pedals to keep the ball centered, but this is only in reaction to torque changes from increases in rotor pitch and power demands.
Note that the airplane isn't using rudder to turn either; only to correct for adverse yaw.  What brings the nose around in the turn is the vertical fin.  The banked wings creates a lateral force vector, moving the airplane sideways as it goes forward.  The sideway motion cause the airstream to strike the vertical fin from the side, and the airplane's inherent weathervaning tendency brings the nose around to keep it aligned with the arc of a turn.  If an airplane had no adverse yaw at all, you would not need to use any rudder to help with turns.
A helicopter is the same.  There is a small fin back there that gives it modest weathervaning tendency (the disk area of the tail rotor also contributes).  The pedals are just there to change tail rotor pitch to adjust for off-axis yawing motions induced by torque changes (which can be in either direction, depending on whether torque is going up or down); just as on the airplane the pedals are just there to compensate for adverse yaw due to aileron displacement. If the helicopter had some automated system to always compensate for torque changes, you would not need to touch the pedals to turn.
In practical terms, in both cases, when flying you simply do whatever you have to do with your feet to keep the skid ball centered; in the airplane you are generally reacting to aileron movements, and in the helicopter to torque/pitch changes.  The power plane pilot learning helicopters has to adjust to get out of the habit of squeezing a little into-turn rudder to anticipate adverse yaw, and has to instead anticipate the subtle yaw changes - in either direction - from the power and pitch changes the pilot may input during the turn.


Where can I find United 757 Checklists? (CRM, Pre Start, Pre Takeoff)

I doubt that you can get an airline specific checklist for an airplane, but for Boeing 757-200, a generic one is available. Please note that they might be for simulators (as Ben mentioned) but are close enough.

PDF
Trello
X-Plane (screenshot below)


How to interpret 14 CFR Part 61 Requirements 61.129 on instrument training time?

The experience requirement for a commercial rating need not be acquired during training for a commercial rating.


A headwind gust for a given elevator trim condition will result in an increase in airspeed,
which will pitch the nose up.  The aircraft will also "balloon" upwards from increased lift.
Vertical rise will contribute to lower relative wind, but will also put additional downward pressure on tail, again raising the nose.  The effect will be temporary as AIRSPEED will rebalance to the air mass.

As always, the trim will only allow the AOA to increase a to a point before the tail goes from lift negative (downforce) to lift positive (upforce), preventing further increase in AOA.
An excessively forward CG with greater trim will make these effects more noticable.

The real danger under these conditions would be turbulence from the wind shear and
mountainous terrain.  In light recreational aircraft, one may wish to be very cautious about
air travel until weather improves.  In the mountains, wind speed and direction can be extremely localized and variable, and should be carefully monitored.


There are experimental electric planes. Some are promising enough that they might end up useful as trainers and private GA flown for the love of flying.

Long-range electric will not work. The electric equivalent of the Breguet equation is R=L/D*E/W*n/g, where E is stored energy and n is propulsive efficiency. For a 100% efficient L/D=20 aircraft that is 100% battery with 250 Wh/kg cycle depth, that's 20*250*3600*1/9.8=1.8*10^6 meters, or 990 nmi. This is the hard limit. With 80% efficient props and real world factors, you can expect 5-8 nmi for each % takeoff weight dedicated to batteries.

Hybrid aircraft are, even on paper, only moderately interesting. Aircraft throttle in cruise at 45-75% for GA, 70-90% for small jets, and 80%-95% for long-haul widebodies. This is due to the engines "self-throttling" in a way - power and fuel consumption reduce due to lower air density as you climb.

So major airliners have nothing to gain from going hybrid, they can only shrink their engines by 5-10% with a hybrid system. This is very different from cars, which run duty cycles as low as 10%.

And there are no start-stops or regenerative braking to recover energy in flight. More precisely, aircraft already use regenerative braking - by pitching up or deploying flaps, speed gets traded for lift. So that braking energy is already being harvested, and stored as altitude (potential energy).

Smaller propeller aircraft could replace up to 30% of their power, so it's less cut and dry. However, when you want full throttle, you often want it for a while, like in climb. The only way for a non-plug-in hybrid to save energy is to use a lighter/smaller engine, and it's difficult to shrink enough to offset the hybrid system's weight.

A plug-in hybrid could benefit from the lower cost of electricity vs avgas, but fuel averages to less than a third of private flying expenses. Pure electrics have a shot at making flying more accessible through simplicity. With no fuel, very simple and reliable engines, it makes sense to relax the rules, like is done for ultralights. Hybrids have all the complexity of a piston-engined plane and then some.

The hybrid route makes sense for cars. The only safety-critical parts of a car are steering and brakes. Engine power is almost arbitrary, most hardware is just nice to have, and there's the universal failsafe of pulling over. In a plane, things need to work. Two systems that both have to work to fly safely is a complication and will likely increase costs.

Alternately, either system needs to supply takeoff thrust on its own. That could work in the 19-seater class, if the authorities accept a hybrid "twin"-engine single prop as sufficient redundancy. But there's a lot of "ifs" in this.

In a zero-weight scenario, some military aircraft (fighters, naval) could benefit from a hybrid system, as they have excess power like cars do. That's where reality hits: for given output, electric motors are lighter than car engines, but much heavier than aircraft jet engines. Since they're not lighter, there's nothing to be gained.


How quickly should heading changes be accomplished?

According to Wikipedia, a "Standard Rate Turn" is three degrees of heading change per second.

The bank angle required to achieve this depends on your true airspeed; at a low TAS a standard rate turn is easily achievable with normal, comfortable bank angles (say, 20°, plus or minus).  At high true airspeeds, the bank required becomes excessive, and "half standard rate" is used if anything is used, but at least in airline flying it's not particularly common to use either.  We just reference an angle of bank — but what that gives you in degrees per second is variable (as a function of TAS again).

The upper limit of what an airliner (or pretty much any IFR aircraft) is going to give the controller in terms of turn rate is whatever you get with a 30° bank.  And if that produces less than standard rate or whatever, then so be it.  At high altitude (say 35,000' and above), even 30° can be on the edge of problematic (mainly, with regard to wing loading and Mach buffet), and controllers are used to rates of turn that are less than what you'd see down low.

But if you're looking for a ballpark, 3 degrees per second at low airspeeds (say, under 200 knots), then 2 degrees per second up to maybe 300 knots, and 1 degree per second above that.  Ballpark, but reasonable numbers.


In the event of a crash over thick snow or a forest, would it be safer inside the aircraft or free-falling?

Statistically, there has got to be graphs you can combine to show the number of airplane crashes to fatalities and a graph with skydives (without a chute/malfunctions) to fatalities. I'd venture to say that the odds are far greater to surviving an airplane crash than a freefall.

Let's look at the factors...

A freefall:

your velocity in not slowed by anything
your body is not protected by anything
you have no control on where to 'crash'

A crash landing:

passengers are slowed greatly by the aircraft
passengers are greatly protected physically (airframes are designed to minimize risks from explosions, shrapnel, and crash G's)
there is a greater chance the aircraft can be controlled somewhat to crash in the best place.

The only time it would be better to jump without a parachute is if you are this guy or the aircraft is about to be torn apart.


Does the Cessna 152 or 172 have emergency door cable releases?

The Cessna 150 Aerobat and 152 Aerobat both have jettisonable doors.

I don’t believe any version of the Cessna 172 does as there in no aerobatic C172 versions.

This Photo shows two “D” rings which are pulled to jettison the doors.


Can I get pop-up IFR clearance to waypoint (intersection)?

Yes, you can file to a waypoint or navaid and can cancel IFR anytime you want. Whether or not ATC will grant a popup clearance depends on the facility and their workload. In places with a lot of flight training (Florida, Southern California), ATC, in particular the TRACONs, usually grants popups.


Why did the F-104 Starfighter have a T-tail?

The initial preliminary designs had the horizontal tail in multiple locations (including in-line with the wing and cruciform), before settling on the T-tail by December 1952. The reason for selecting the T-Tail is given by Glenn L. "Snake" Reaves, Lockheed Production Flight Test Pilot in the F-104 Test Pilot notebook as

The high tail position was selected ... after extensive wind tunnel tests (which) proved that the location was necessary to obtain optimum stability and control about the pitch axis throughout the wide Mach range. The position also results in minimum transonic trim changes while accelerating to supersonic.

Another advantage was that the high tail on the swept vertical fin reduced interference drag. While the problem was inertial coupling was quite well known during 1950's, the design of the F-104 was frozen during the same period, so it is difficult to tell conclusively if that is the reason for F-104 having a T-tail.
The test pilot notebook also has some explanation about how the T-tail reduces the problem of inertial coupling:

If we now consider two facts about these rolling maneuvers, it will become clear how inertial coupling builds up:

The sideslip build-up is controlled by the induced rolling moment.

As sideslip builds up, the centrifugal or rolling forces increase and this tends to displace the aircraft fuselage perpendicular to the flight path.

The T-tail controls the the sideslip build-up by inducing a rolling moment. From the same document:

... the high tail position of the horizontal stabilizer raised the center of pressure.

Image from F-104 Test Pilot notebook

... whenever we sideslip an aircraft, a rolling moment is induced that resists the sideslip. This induced rolling moment is generally termed dihedral effect.
... with any sideslip, the restoring force acting through the center of pressure does not act through the c.g of the aircraft. Therefore, a sideslip condition actuates the restoring force on the tail but at the same time, induces a roll. ... now that we have raised the tail and consequently the center of pressure and the positive dihedral effect has been increased considerably.

The T-tail reduced inertial coupling by preventing sideslip buildup.


Does huge rotating AWACS radar affect flight characteristics?

On the E2 Hawkeye the dish does not rotate very fast (ie, very slowly), and so the torque is probably negligible.  Usually the radomes are designed to help generate lift, and while certainly not as effective as a wing, do offset their own weight quite a bit.


What was wrong with my answers to how to deal with low volt annunciator, and icing, both in IMC/IFR?

Based on a 172S G1000

I wouldn't say your answer for the first question is wrong, but your steps are out of order. Before contacting ATC you need to verify the issue via whatever the POH says. On a 172S that means you will cycle the alternator switch and verify low voltage on the G1000 and whether or not the battery is charging. Do realize that the G1000s have a backup battery that provides x amount of backup time and it should have already been tested in the pre-flight and set to arm, if you verify the issue then limiting battery load and  contacting ATC would be the next step, never the first, and the value of backup time should be known and planned around(can't recall at this time, sorry).
I think this question is more semantics and specifics, he/she may not have liked climbing or descending as your only answer really, getting out of icing is the most important thing whatever the direction is, but I agree in general with climb/descent based on information. Asking for an altitude change I assume is implied when you say climb or descend. What you describe here is pretty text-book as far as dealing with icing to my knowledge.


Can a Eurofighter 2000 trainer be converted to a combat capable Eurofighter 2000?

From the Wikipedia page on the Eurofighter Typhoon, under Variants:

  The Eurofighter is produced in single-seat and twin-seat variants. The twin-seat variant is not used operationally, but only for training, though it is combat capable.

No source is cited for that claim, but it seems logical enough.


Is there any particular reason for the cockpit of the 747 being on the upper deck?

Boeing actually never expected the 747 to be so successful. They thought supersonic aircraft were the future. But Boeing knew that an aircraft the size of a 747 would be great for the cargo market. So they designed one aircraft that could be easiy converted into a cargo version.

The cargo 747s can literally open their nose. It is quite impressive. To accomodate this, the cockpit needed to be on the upper deck. Hence the passenger version had the same requirement.


On the F15-E, can the WSO take over if the pilot is incapacitated?

Short answer, yes.  However, it is important to note that the WSO is not a pilot.  The WSO is trained to operate the weapons systems, not fly the aircraft, but does have basic flight controls including throttle, stick, rudder pedals, compass, HSI, etc.  He does not have good forward visibility and would likely have to be talked in on final approach by the tower, as his view is obstructed by the pilot's seat.

Although the F-15E was developed from the D-model used for pilot training, the airframe was significantly redesigned for it's new purpose, and the back seat of an E-model bears only a passing resemblance to the back seat of a D-model.  The WSO has a very specific and complex set of tasks which does not include flying the airplane, and his controls are designed around that purpose.  He has more screens than the pilot to look at, and two side-stick controllers (not part of the flight control system) that are used for controlling / selecting / guiding / programming / etc. a large variety of weapons. He also has primary control over the FLIR and laser pods used for target designation and tracking.

On a final note, it is not uncommon (although less common in these days of sequestration) for non-aircrew personnel to be given 'incentive rides' in the back seat of aircraft like the F-15D/E or F-16D, and during these rides control of the aircraft is invariably passed to the passenger.  I was privileged enough during my Air Force career to get a ride in the back seat of an F-15E (tail number 88-1671 at Seymour Johnson AFB, NC) and can say from personal experience that it is possible to fly an F-15E from the back seat.  It was the most exhilarating 5 minutes of my life.  Fortunately for both of us, the pilot didn't experience any problems during the flight...


How to fill out IFR flight plan for manned helium balloon flight into class A airspace with no predetermined route or destination and less crew?

I just helped a University launch of an unmanned balloon and I used an E-6B for completing the NOTAM for the launch.  GPS and tracking showed that the estimated path deviated from actual path by small numbers.

We were advised that no IFR FP was required for a small (~3kg payload) unmanned balloon, so none was filed.  We did advise center at launch, and with updates on the way up and down.

Addendum #1
After thinking about this, there are really two parts to this question. The part about route prediction I have addressed in part.  Keep in mind that gliders file IFR and they have little ability to climb higher on demand. The FP can provide an area, just like an IFR FP or and IFR clearance for aircraft can have block airspace, or even routing at pilot's discretion.

The other issue is whether a FP is needed. For manned balloons in controlled airspace, operating under IFR, the answer is clearly yes. But again, there is allot of latitude in what a FP can specify, and what clearance might be issued.

For unmanned balloons, which is where I have more experience, the rules are quite different.  And size is limited.

But again, the FAA can issue waivers, and they are done regularly for all kinds of flights. So just because the rules prohibit or do not allow, doesn't mean that a waiver could be issued to allow.


It's because the spider duct that connects the carb to the intake runners going to the cylinders is cast into the oil sump and the carb mounts directly to that. So the carb gets a lot of engine heat that warms the carb body by conduction. Also, it's getting radiant heat from the sump directly above.

On Continentals the carb is insulated from the engine by its mounting and location relative to the sump.  Continentals without pressure cowls like J-3 Cubs are the worst for carb ice formation.

Carb icing is relatively rare on Lycomings but is still possible if the conditions are sufficiently favourable, so you still have to use normal carb heat protocols.


How do check valves regulate the air in a multi-engine airplane's vacuum system?

On each side of the check valve manifold there is a check valve that only allows air to flow toward the vacuum pump on that side.  For the left pump, the check valve is the rectangular bit between the far left line going to the vacuum gauge and the adjacent line going to the deflate valve, and for the right pump it is between the far right line and the gyro suction line.

The result is if one vacuum pump no longer is producing suction, the vacuum gauge indication on that side, being "upstream" of the check valve now that only the opposite pump is pulling air, will show no vacuum; meanwhile the operating pump can still pull air through the other three lines and can still operate the deflate valve and vacuum gyros.  Its vacuum regulator will control the vacuum level.  Everything will continue to work normally with only the loss of vacuum indication for the failed pump providing an indication that something is wrong.


Why do most radial engines use an odd number of cylinders?

An odd number of cylinders is required by the combination of the single-crank radial design, the four-stroke (Otto) work cycle, and the desire to keep the power strokes evenly spaced in time.
To keep the design simple and lightweight, a single-bank radial airplane engine has one crank, which means that the pistons must reach the top of their travel in rotation order. But the four-stroke cycle requires that a piston must reach the top of its travel twice for each power stroke. The only way to promote evenly timed power strokes is to fire every other cylinder in rotation order.
With an even number of cylinders this would require a hesitation or skip in the firing sequence on every rotation as the engine switched between the odd and even cylinders. With an odd number of cylinders the timing is quite naturally smooth. For example, the firing order of an eight-cylinder radial would be
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
*   *   *   *     *   *   *   * *   *   *   *     *   *   *   *

while the firing order of a nine-cylinder radial is
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9
*   *   *   *   *   *   *   *   *   *   *   *   *   *

If you could watch a radial airplane engine in slow motion you would see that when a cylinder is in its compression stroke, the cylinders on either side of it are in their exhaust strokes, and when a cylinder is beginning its power stroke, the cylinders on either side of it are near to beginning their intake strokes.
Two-stroke radial engines do not need to have an odd number of cylinders.


What is the purpose of extending one degree of flaps (perhaps with spoilers)?

Normally, one degree of flaps in fact only translates to an extension of the leading edge devices (e.g. slats), trailing edge flaps remain fully retracted.

On some aircraft this configuration can be used for take-off.

Combination of flaps and spoiler is for example used in slow flight on steep descends. The flaps ensure that the wing doesn't stall, the spoilers dump part of the lift and act as airbrakes to keep the speed under control.


Why does having a geometry-limited aircraft lead to lower VLOFs?

Unless someone can find an old 14CFR Part 25 ruling that has the explicit reasoning, I believe you are right to consider that the rationale for giving extra performance credit to airplanes that have demonstrated minimum unstick speed ($V_{MU}$) limited by tail contact is that they are not limited by aerodynamics. However, I should point out that the intent is to reduce the rotation speed ($V_R$) and not $V_{LOF}$, which is not a performance V-speed.

For Part 23 aircraft, which does not require $V_{MU}$ testing, 14CFR 23.51(c)(2) (pre Admt 23-64) requires $V_R$ to be no less than 1.10$V_{S1}$, or 110% of the stall speed for takeoff configuration obtained out of ground effect.

This mirrors the Part 25 requirement of 14CFR 25.107(e)(1)(iv)(A), which you have cited in the OP. The difference between the two is that Part 25 allows the applicant to lower the $V_R$ by taking credit for the ground effect and the rate of rotation, but also poses additional onus on the applicant to flight test the $V_{MU}$ (which is involved and high-risk).

Vmu can be limited by either:

Stall in ground effect, or
Stick pusher in the takeoff phase, or
AOA limiter (FBW only) in the takeoff phase, or
Tail contact with the ground (i.e. geometry limited).

In the last case, the aerodynamic capability of the airplane has not been reached. Therefore, 25.107(e)(1)(iv)(B) extends some credit to reduce the rotation speed. However, as specified in AC 25-7C, this credit can only be taken if the airplane is actually shown to be geometry limited from 96% to 100% of the lift-off speed ($V_{LOF}$) with the lowest thrust-to-weight ratio allowed for takeoff.


Weather sensors required for ILS approach operations?

Whether or not an ILS may be conducted without proper weather reporting will depend on the regulations under which the flight is operated.

In simple terms, a flight operated under 14 CFR 91 may perform an ILS without this weather reporting.

This may also be allowed under the eligible-on-demand rules of 14 CFR 135, if all pertinent requirements are met.

Otherwise, a flight operated under 14 CFR 135 or 14 CFR 121 will generally not be approved to conduct an ILS without approved weather reporting.

This answer applies under FAA jurisdiction.


Can an American citizen schooling abroad join the airforce?

In which countries have you been studying? It probably won’t make any difference. Also, you do realize that there is no way to apply to be a test pilot ar entry into the military. You would have to serve as a pilot first before getting the opportunity to be a test pilot.
It is very possible for you to become a military test pilot. Follow these steps. Move back to the US. Get into a university. Join AFROTC. Graduate from both. Pass the FBI background check. Join the military. Become an officer or warrant officer (for helicopters). Become a military pilot. Serve and gain experience as a military pilot. Apply for test pilot school. By the time you apply to test pilot school, it won’t make any difference that you spent 10 years living abroad.
You may still be able to become a military test pilot without moving back to the states or graduating ROTC before your background check. It just makes the process more difficult. Unless, of course, you were overseas because your parents were serving a diplomatic or military mission. Living in an allied country or a community of American expats would help the process of the FBI background check as well. Read about Andy Thomas, an astronaut from Australia that did not even become a US citizen until he was 30.


When flying on a glide slope, does the G meter show 1G or less?

I presume, an implicit assumption in your question is that we are flying a perfect glideslope, that is, a straight line with a constant speed, and without disturbances.
If this is the case, the acceleration will be zero by definition, and the only effect we (and an accelerometer) will feel is gravity.
The 'G-meter' shows the acceleration (incl. gravity) with respect to a calibrated standard 1G. Now, the question is, will gravity be the same from the point of view of the device/pilot?
The answer is: almost, but not quite.
First of all, the 'G-meter' typically shows the normal acceleration: that is, along the body Z axis. It is 'vertical' for the pilot, but not necessarily vertical for the Earth. This is the critical acceleration component, the greatest one (because the wing can produce by far the greatest force on an airplane), the one that is always specified in the flight manual and the one that you might exceed in normal manoeuvring. This is why the device shows it and not the 'total' combined acceleration.
Thus, the gravity component as measured by the 'normal' accelerometer will depend on the airplane attitude. In terms of G, the factor will be $cos(pitch) \cdot cos(roll)$. For the given example, if we assume the glideslope angle -3°, pitch will be $14-3 = 11°$, and with zero roll, the measured G will be $cos(11°) \approx 0.98$. Very small difference indeed.
However, in a more extreme example of a vertical dive, the accelerometer will show zero (0G).
But that's not all. If we want to be really pedantic and measure beyond 1%, we'll need to take into account that the apparent gravity changes depending on the location. Given that the accelerometer shows, essentially, weight of a calibrated mass, it will indicate different G even if the aircraft is standing on the ground.
I'm not talking about gravity anomalies, which are truly miniscule. The biggest contributor is Earth rotation, which adds some centripetal acceleration, the more of it the closer to the equator you get. At the equator, it reduces your weight by almost $0.4$% with respect to the pole.
A further $0.1$% can be accounted by the fact that Earth radius is greater at the equator than at the poles - by about 21 km. This is typically a bigger contributor than the aircraft's own altitude (esp. given that glideslopes are usually near the ground).
Altogether, if we calibrated at a pole and then make an approach near the equator in the stated conditions, we can expect almost $2.5$% reduction of the indicated G-force.
In truth, the calibration is usually done for middle latitudes (and digital AHRS may calibrate before takeoff on the actual location), so the difference will be even smaller. But anyway, the biggest contributor - attitude - is unaffected by these small changes. Yet, it is still small by itself, often below the accuracy of the G-meter.


Why haven't airlines added safety pads to their carts?

Because an inch or two of rubber isn’t going to stop a 300lb cart from breaking your foot if it goes out of control down an aisle. If your elbow is in the wrong position, you could hit it with a 300lb roll of memory foam and cause a compound fracture.
The maker of this video is just looking for things to complain about. Keep your body parts out of the aisle and you’ll be fine.


How long before a Medivac should the pilots be ready?

Medivac pilots (at least the ones in my city) are at the hanger/pad 24/7.

My home field (KPNE) happens to be where some of the medical choppers are stored and dispatched from. In Philadelphia they tend to not be stored at the hospitals. I have met some of the pilots and one of the crew nurses. Where I am the facility is staffed 24/7 much like a road ambulance facility so that as soon as a call comes in they are ready to fly. The helicopters them selves are kept in a hanger, always fueled and alway ready to fly, on these neat rolling carts so that a tug can pull them out as the pilots are getting things squared away in the cockpit.

One of the hospitals in the suburbs keeps their chopper at the hospital (which is fairly close to KDYL) and is avalible 24/7 as well.

I also happen to over look one of the 4 hospital helipads in the city from my home. The pad is generally kept open for arrivals and on a decent weather day that can mean upwards of 10 landings (I have no idea what they are transporting).

I had the pleasure of meeting one of the guys that helped design the Philadelphia Class B. The airspace is specifically designed so that all of the hospitals sit under shelves such that the helicopters can come and go without needing a bravo clearance to expedite their travel times.

Its worth mentioning that ready to fly and will fly are not the same thing and the latter is at the operators discretion. Ultimately the pilots make the go no-go decision and if the weather is dicy rescue teams generally will not fly.


What is a "round-robin flight", in layman's terms?

It's simply a flight that returns to the original airport after stopping at one or more other airports.  ATC doesn't have a good way to code those types of flight plans in the computer, so the pilot will usually just tell the controller that he/she is planning to land at the intermediate stop for x amount of time.

The controller will then either close their flight following (or IFR clearance as appropriate) and have them reopen when they take off again, or just keep it open.  It depends on how busy their airspace is.  Often they'll just leave it open if it's in the middle of the night.


Robinson R22/44/66 Headset Plug For Bose A20 Headset

Helicopters use a U-174/U or U-93A/U single-plug headset connector. Most aviation headsets come with PJ-068 & PJ-055B or equivalent. You will need an adapter. The second part of your question calls for an opinion, which is out of scope for this service.


What are "approved weather reporting services" and do they apply to part 91?

First, within the context of the question, the term "operator" in the Alternate Mins section refers to a person or company that has an operating certificate.  Not just Joe the Pilot who is "operating" an aircraft. So, a "Part 91 pilot" (taken from the context to mean: "pilot flying for pleasure or personal business") cannot file this airport as an alternate when the tower is closed.

Second, the term "approved weather source":  In the FARs, various Parts apply to various operators (121, 125, 135). They each have similar verbiage about approved weather reporting services.  For example, Part 121.101 (for domestic and flag operations) says the following (paraphrased):

  No certificate holder may use any weather report to control flight
  unless it was prepared by the U.S. National Weather Service or a
  source approved by the U.S. National Weather Service. Each certificate
  holder shall use an approved system for obtaining forecasts and
  reports on each route to be flown and at each airport to be used.

You can see this related question: What sources of weather are approved by the U.S. National Weather Service? for more information.

BUT... the important point from that FAR Part 121 quote is the second sentence. ALL operators must have Operational Specification (OpSpecs) approved by the FAA before they can operate. One of the items within the OpSpecs will specifically address how and from where these weather reports and forecasts will be obtained.

So, this is the bottom line answer to the question: only "operators" can use this airport as a filed alternate when the tower is closed, since that operator will have their own "weather source" that is approved by the FAA and listed in that operator's OpSpecs.


Why would one plane in this picture not have gear down yet?

Why does the 747 not have its gear down yet?

Based on the image it is hard to say how far these aircraft are from the runway. The 747 could still be be quite far from the runway and thus does not need to have its gear down yet.

The 747-400 FCOM (NP.21.47 Normal Procedures) says:

  At glideslope alive, call:

  "GEAR DOWN"
  "FLAPS 20"

It looks like the 747 in the picture has already intercepted the glideslope, but this is hard to say from this perspective. Also, operators may have different rules for when to lower the gear.

Then why does the third aircraft already have its gear down?

The most probable reason for this is drag. A flight crew may choose to lower the gear earlier than necessary to reduce its speed. ATC could have instructed this aircraft to fly at a lower speed for spacing and the crew then dropped the gear, which adds significant drag. This is pure speculation, of course.


What will happen if we start the A320 engines but we don't wait for the amber crosses on the E/WD to disappear?

Amber X's mean the FADEC is not yet energized. Once the X's disappear it means the FADEC is ready and can provide monitoring (even passive monitoring in a manual start).

Without FADEC there is no means to start the engine, as the valves are also FADEC controlled.

(A320 FADEC schematic.)

FADEC is needed even for manual start.


How do I know when to read a number as (for example) 241 or 24.1 off the navigation computer?

If you are talking about an E6B, you follow the same rules for your result as you followed for your inputs. If you used a factor of 10 for your inputs, you use a factor of 10 for your results. If all else fails, you use the common sense rule. For your particular calculations, does 241 make sense? Or, does 24.1 make sense?


The vortex itself isn't the issue, it's the "leakage" that is resulting in the vortex.  The leakage is from the air near the tip being free to flow around it and results in wasted energy.

The wing is moving along driving air down, but near the tip some of the air, instead of being made to accelerate down, is taking the path of least resistance around the tip (being sucked toward the low pressure side you might say) instead and doesn't contribute to the lift force.  It was displaced, and energy was consumed, but the displacement was out and around the tip instead of down.

The tip plate is just supposed to inhibit some part of the lateral flow around the tip by blocking it, reducing the leakage and resulting in more of the air package being forced downward than without the tip plate.  What is referred to as a reduction in induced drag is just an improvement of the ratio of lift to drag due to less leakage losses, so for a given amount of total lift force, the induced drag is less than for the same lift force without the tip plates.

To do any good, tip plates have to be quite large (because the circulation field extends quite a distance from the wing), which being draggy themselves, cancels out most of the benefit, which is why you don't really see them used very much, except where the end plate effect can be created by default, such as with a T tail where the horizontal stab makes a nice end plate for the top end of the rudder.


What is the difference between “affirm” and “acknowledged”?

"Acknowledged" means I heard you & understood what you said & I take responsibility for the information you just gave me.
"Affirm" and its opposite, "negative," are answers to a yes/no question.
They aren't really interchangeable, although Hollywood script writers are notorious for getting details like that wrong.
An example of correct usage would be, "Callsign 123, is your ride smooth at FL350?" "Callsign 123, affirm." (Answers the question, yes the ride here is smooth.") Then, "Callsign 123, we've had reports of light turbulence at your 12 o'clock and 100 miles." "Callsign 123, acknowledged." (Or, "roger" is more common, but same meaning... either way, I've received & understood the turbulence report.)
To reply "roger" or "acknowledged" to the question "is your ride smooth" is incorrect, because all you'd be saying is, I heard your question. There isn't any "yes" or "no" component to either of those replies. Likewise, to reply "affirm" to the "turbulence ahead" call is wrong because there was no question being asked there. The controller just needs to know that you heard the information so that it doesn't have to be repeated.
Interestingly, the FAA Pilot-Controller Glossary doesn't list "acknowledged" at all, but lists "acknowledge" as a directive: tell me that you heard me.
It also lists "affirmative" and not "affirm" -- that may be more used elsewhere. Also, with the quality of modern radios, the risk of the initial syllable(s) getting lost & the receiver left puzzling over "...ative" has probably diminished over time.


How was the high-bypass concept invented?

The need for a turbofan was realized as early as the mid-30s.

The first jet aircraft were subsonic and the poor suitability of the propelling nozzle for these speeds due to high fuel consumption was understood, and bypass proposed, as early as 1936 (U.K. Patent 471,368). The underlying principle behind bypass is trading exhaust velocity for extra mass flow which still gives the required thrust but uses less fuel. Whittle called it "gearing down the flow".

In the mid-60s, the USAF A-X and CX-XX programs accelerated the development of the high-bypass jet engines. The winners of the programs were the Fairchild Republic A-10 Thunderbolt II and the Lockheed C-5 Galaxy, respectively.

To meet the [CX-XX] power and range specifications with only four engines required a new engine with dramatically improved fuel efficiency.

The TF39 on the C-5 Galaxy was the first production high-power, high-bypass jet engine. It first ran in 1964. The XV-5's lift-fan-inspired-demonstrator helped confirm to GE the feasibility of high-bypass jet engines.
The demonstrator was the GE1/6 (cruise fan variant), it featured a GE1 core engine energizing remote tip-turbine-driven cruise fan of high-bypass. (Sadly, I can't find photos/illustrations.)
Around the same time the Convair 990 Coronado was powered by the CJ805-23, which featured one of the first aft-mounted fans.
(Source) CJ805-23 with the aft-fan.

Transatlantic service needed a higher thrust version of the existing turbojet and a demonstrator engine with a single-stage front fan attached to the compressor was run. It was difficult to start and operate. This experience led to the aft-fan which didn't compromise the operation of the gas generator.

For its time, the TF39 had unique features—namely the 1½ fan-stage—which resulted in an impressive 8:1 bypass ratio, higher figures were seen only decades later on the Boeing 777's GE90.
(Wikimedia) TF39.
The front of the engine features a mini-fan that rotates inside stationary vanes. Behind this first ½ stage is a full-sized fan. A fair proportion of the air entering the ½ stage is also ducted to the bypass stream.
(FLIGHT International, 13 March 1969)

The two-spool high bypass General Electric CF6 (top half section) is based on the same gas generator and turbine as the TF39 (bottom section) which powers the Lockheed C-5A Galaxy.

The mostly civilian and much simpler CF6 was based on the T39, it is found on the Airbus A300/310/330, Boeing 747/767, DC-10/MD-11, and others.
Honorable mentions
Two years before the A-X program, Avco Lycoming was working on the earliest experimental turbofans, but not necessarily high-bypass. With development and various derivatives contributing to the Lycoming ALF 502 which powered the Northrop YA-9 entry for the A-X program.

(FLIGHT International, 10 February 1972)

The only production fan engine to use an aft-mounted fan is the CF-700, power unit of the Fanjet/Mystere 20.

(Source)

Sources: Various issues of FLIGHT, Wikipedia, and The Power to Fly: An Engineer's Life.


How do you properly enter the NDB34 published approach at Friday Harbor (KFHR)?

First of all, do not let the depicted holding pattern confuse you.  It is only there because the missed approach procedure happens to have the hold at the same place, and for the purposes of the course reversal may be ignored.
In this case, you have options because the course reversal is simply a "barbed arrow".
AIM 5-4-9. Procedure Turn and Hold-in-lieu of Procedure Turn(a)(1) says:

On U.S. Government charts, a barbed arrow indicates the maneuvering
side of the outbound course on which the procedure turn is made.
Headings are provided for course reversal using the 45 degree type
procedure turn. However, the point at which the turn may be commenced
and the type and rate of turn is left to the discretion of the pilot
(limited by the charted remain within xx NM distance). Some of the
options are the 45 degree procedure turn, the racetrack pattern, the
teardrop procedure turn, or the 80 degree 260 degree course
reversal. Racetrack entries should be conducted on the maneuvering
side where the majority of protected airspace resides. If an entry
places the pilot on the non-maneuvering side of the PT, correction to
intercept the outbound course ensures remaining within protected
airspace. Some procedure turns are specified by procedural track.
These turns must be flown exactly as depicted.

In other words, do what you want as long as you either stay on the protected side or correct to intercept the outbound course if you find yourself on the non-maneuvering side and you stay within 10 miles of the NDB.
Personally, I would:

Cross the NDB and then simultaneously:

Turn left to a heading of about 129 degrees (depending on the wind)
Descend to 2,300 feet

Start the outbound timing as I cross the 69 degree bearing TO the NDB (90 degrees)
Intercept the outbound course of the procedure turn and then fly the rest of the course reversal as depicted (the 45 degree procedure turn).

However, as I said in the beginning, you can do it however you like within the constraints that the AIM gives.
I did find a rather interesting article which states that ICAO rules are a little different, but I won't go into the specifics since this is an FAA chart.  For those who are curious though, take a look at it here:  Course Reversals.


Is there a difference in landing fees for charter and scheduled flights?

This is almost completely dependent on the airport but we can talk somewhat generally.

For what its worth airlines (scheduled carriers) can often negotiate lower landing fees by being able to guarantee a specific amount of flights into an airport. Charter companies don't have this luxury since it can be hard for them to predict where and when they are going. On the other hand some fees are set by the local government, for example here in Philadelphia any airport in the city (KPHL and KPNE) has landing fees set by the city. You can find the official legislation here and I assume thats non negotiable but I cant be sure.

There is also a bit of a discrepancy due to the type of planes. Landing fees are often charged by weight and in most cases charter planes are flying smaller stuff than the scheduled carriers and their fees may be lower as a result (even though the scheduled carrier has a lower rate). If we look again at Philadelphia we can see that they have fees for both weight and passengers which generally go hand in hand however a charter company may be flying a big RJ for just one guy while a scheduled carrier may be operating the same plane at its maximum seating arrangement.

Charter carriers may also have the luxury of flying into smaller satellite airports where the fees may be lower or structured differently. Since some of these airports could potentially be private or private/public they have the ability to charge what they chose. Some will even have no fee if you buy a pre prescribed amount of fuel.

For other points of reference you can check out the

New York Landing Fees
Miami Landing Fees


Can pilots wear glasses/corrective lenses inside the cockpit?

Yes.  All current classes of FAA-issued medical certificates allow for the use of corrective lenses in the cockpit.  See Title 14 §67 Medical Standards and Certification.


What criteria does ATC apply to determine if an aircraft is established on the localizer if the pilot does not report it?

Each instrument approach consists of a lateral part and a vertical part, in the case of the ILS approach these are: localizer and glideslope.

Aircraft are usually vectored to intercept the localizer approximately 1-2nm before the Final Approach Fix (FAF), where the glideslope is captured. Aircraft can be vectored onto the localizer as far as 20-25nm out, depending on terrain, localizer equipment and many other factors. If an aircraft is not established on the localizer, there is no point in continuing the approach, so it will be cancelled and the aircraft revectored.

If the aircraft is established on the localizer, it will try to intercept the glideslope, which is the vertical guidance system in the ILS approach. For VOR/DME, LOC/DME, NDB/DME or RNAV approaches, the vertical guidance is either achieved through correlation of location to a specific altitude in the chart or technical means which do not require a glideslope.

If an aircraft passes the Final Approach Fix and does not seem to descend, it will be considered as not established and the approach clearance will be cancelled, instructing the aircraft to either follow the missed approach procedure or manually vectoring the aircraft for another approach.


Are there any aircraft with powered landing gear?

WheelTug makes an addon motor for a nose wheel. This is a demo of the unit being developed for a B737. They intend to lease it to airlines. It works well under most circumstances, but has difficulty on icy aprons and the aircraft would need a pushback so it could taxi using its engines. The terms of the lease would financially compensate. They have "reservations" for 1100 units from two dozen airlines.

youtube

There are a number of financial considerations, such as cost to carry the weight of the unit. Here is a presentation of their business case. They claim direct cost savings similar in value to installation of winglets, and time savings value twice as great as replacing a current generation 737/320 with a Max/Neo.

youtube

Safran also had a joint venture to develop a similar unit for aircraft maingear, but that is no longer being pursued. I don't know of any OEM that offers this kind of capability on commercial aircraft.


How are the dimensions of the empennage determined for jetliners?

The tail volume coefficients for the horizontal stabilizer ($C_H$) and vertical tail ($C_V$) for jet transports are 1.00 and 0.08 respectively.

For the horizontal stabilizer, for example, with the $C_H$ given, and the lever arm, [main] wing reference area ($S_W$), and MAC known, the area can be calculated.

The shape, sweep angles, aspect ratio, etc., of each surface have their own rules.* Knowing the shape and area, the span or height is calculated.

Example 1: When the lever arm was reduced when the A319 was shortened to become the A318, they had to compensate by increasing the vertical stabilizer area, which meant a higher tail.

Example 2: Boeing designed the 757 and 767 simultaneously, so in order to reduce the fabrication and tooling costs, both shared the same tail, with the 757 tail shortened at the root (Flight, 1979).

(Own work)

* Reference and further reading on the aforementioned rules: Empennage General Design (.pdf), Hamburg University of Applied Sciences.


What is the ratio between time in the air and time on ground for an aircraft?

It will vary widely from aircraft to aircraft, but I will try to give some general estimates.

Time on the Ground

Part of what you are referring to what is sometimes called aircraft turn time. It's not really directly related to my calculations for your overall question (though it is certainly a factor for short-haul jets), but in this article, minimum turn times for the Boeing 757 was studied, and it was found that the estimated turn time for a 757-200 was 52.5 minutes, based on actual operations. The 757-300, a stretched model with more seating, would take about 59 minutes.

From this presentation, presented by United Airlines, they show a general guideline MSGT (Minimum Scheduled Ground Time), that is a generalization depending on flight locations, field facilities, and airlines. Some times are:

Boeing 747: 80 minutes
Boeing 777: 70 minutes
Boeing 767: 60 minutes (-300 model)
Boeing 737: 35 minutes (-300 model)
Airbus A320: 40 minutes

This link has a discussion of a number of airliner turn times, however none are from official sources. Most vary between 20-45 minutes, depending on if cleaning is required.

So for a typical airliner we can say it takes about 45 minutes-1 hour for a typical servicing.

Aircraft Lifetime

Now as to how many times they fly, you can find their aircraft design cycle limit (essentially, how many takeoffs and landings it can make in its lifetime) in this Federal Register document (summarized here). Some listed numbers:

Boeing 747: 20,000 cycles
Boeing 777: 40,000 cycles
Boeing 767: 50,000 cycles
Airbus A320: 48,000 cycles (60,000 hours)
Airbus A300: 40,000 cycles

So for a 'typical' airliner we can say it can survive about 40,000 cycles in a lifetime

You can find the average age of airliners in different places online. This site splits up by airline and aircraft, and most airliners have an average age of 12-15 years. But note that this is the active fleet. The average age at retirement for an airliner is now around 24-25 years.

You can find a related Aviation.SE question here

Aircraft Usage

This thread discusses the average cycles and flight hours per day. Long haul aircraft (like the 747, 777, A380) tend to spend more hours in the air per flight, but also have less cycles per day. I can't find official sources, but the thread presents a couple example averages for peak usage rate:

Delta Boeing 757: 9.5 hours/4.8 cycles
United Boeing 747: 13.2 hours/1.6 cycles

(I find these probably accurate, as there have been some publicized accidents that have much higher usage, like this one, which flew 48,740 hours and 39,781 cycles in 15 years - about 7 flights/day; short-haul jets like the one in the article end up with more cycles than long-haul, as I noted above).

It is difficult to find hard numbers, but overall, the average flight length for a short-haul jet is about 2 hours, whereas a long-haul jetliner is around 6-7 hours.

Again, there are a lot of variables in this question, but using the above data, we can estimate the answer to your question, using these estimated figures from above:

40,000 cycles (~20,000 flights)
25 years
2 hours/flight

This means approximately 40,000 flight hours for a typical short-haul jet; over 25 years (219,000 hours), this works out to about 1 hour in flight for every 5 on the ground. Obviously this varies widely, but for a ballpark number, that's the best I can do. The highest usage would be a heavily used long-haul jet used on the longest routes from a busy airline (i.e. trans-Pacific; Middle East to U.S.), whereas the lowest would be a moderate-length flight on a low-volume route. In general, you are probably looking at about 1:3 to 1:5 air:ground time.


What is the link OR difference between change in momentum & pressure difference?

It's mr Bernouilli's signature discovery: total pressure is dynamic pressure (momentum change) plus static pressure. Both static and dynamic pressure are the result of the impact of air molecules upon the wing or turbine blade, which acts as the lifting surface. The main distinction between the two is that static pressure is the result of random velocity vectors averaging zero, while dynamic pressure has an average molecule velocity unequal to zero.

Bernouilli's law can also be written as

$$p_t = p_s + \dot{m} \cdot V$$

With $\dot{m}$ the mass of air that impacts the lifting surface per second, and $V$ its velocity. Since that is not a convenient way to make computations regarding aircraft structures, we usually see it in a format that uses air density and wing area.

There is an analogy with potential and kinetic energy. Both are forms of energy, and one form can be freely exchanged for another one. A falling object transforms $m\cdot \Delta h$ into $\frac {1}{2} \cdot \rho \cdot \Delta V^2$, but the total energy remains constant at any point in time.

The same goes for pressure, which is actually a measure of the energy of air molecules. A jet engine adds energy to the air molecules going through it. A turbine blade can be driven by either the dynamic pressure, or by the difference in static pressure before and behind the blade - there are different design blades according to the proportion of static & impulse. The exhaust shape of the engine can leave the outflowing air with a higher static pressure than surrounding air, or expand the higher static pressure completely into dynamic pressure.

Static pressure and impulse change are summed together because they are two forms of exactly the same entity: the energy added to the air stream.


When you consider the aircraft as a whole, lift equals weight in level flight. This must be true following the laws of physics.

However, if you break down the forces, the lift produced by the wings does not necessary equal to the weight of the aircraft. Lift is also generated by the body (albeit very inefficient) and by the tail. Most horizontal stabilizers generate negative lift, but some (e.g. the A380) generate positive lift.

If we ignore the fact that fuselage produces lift, and assume a configuration where the tail produces downward force, then you are correct. But the fuselage does produces lift. Modern aircraft designs use software to take that into account.


How is hypothetical max altitude of a helicopter calculated?

From the Source:

 It shows how to calculate theoretical maximum altitude a Helicopter can achieve


The squat switch is essentially a sensor that senses if the weight of the aircraft is resting on the gear. This can be done by load cell or displacement sensor on the suspension arm.

Like any other component these sensors can fail though engineers prefer them to fail in an always on (weight on the gear) state; that way the pilot just needs to deal with gear failing to retract after takeoff and needing to land again to check it out rather than dropping the plane on the ground and causing more damage.


Why does an Exhaust Gas Temperature (EGT) gauge require a power source?

The thermocouple voltage is a DC millivoltage. Presuming you’re talking about an analog gauge, there simply isn’t enough potential to “drive the pointer.” As such, that small voltage is usually amplified. The amplification requires that a larger power supply be used.

For a digital gauge, that millivoltage is capable of being read by a microprocessor, but the rhetorical question of “What powers the microprocessor?” Should be enough to resolve the rest of the question.


What is the sense of the Aerodynamic Centre for Design Process?

Aerodynamic Centre (AC) is particularly handy when we analyse the dynamics, that is, changes. For instance, changes due to disturbances: stability.

First thing, for analysis, we split all forces into forces acting where we want plus moments caused by the fact that these forces actually act somewhere else. And then when we write our balance equation, we need to balance both the forces and the moments.

We want forces to be at CG? Fine, let's declare that lift happens at CG. But then we acknowledge that apart from just lift, there will be an additional moment with respect to CG.

Now, due to linearity of aerodynamics at small angles of attack (AoA), this moment will change linearly with AoA. This effectively means that there will be a certain fixed point at which the moment will not change; or in other words, a point at which all the additional lift (due to pure AoA) can be thought to be happening. This point is the AC.

This is great, because:

We can express this extra AoA-related lift as $L_{w\alpha} \cdot \alpha$, where $\alpha$ is AoA and $L_{w\alpha}$ is the wing lift derivative by AoA, which is an intrinsic measurable property of a wing (or airfoil/aircraft).
The moment produced by this lift (with respect to CG) is that lift times its arm $x_{wac} - x_{cg}$ ($x$ is a relative distance (coordinate) of a point with respect to some datum, typically the front of the mean aerodynamic chord (MAC), which is another fixed property). So, our moment from lift will be $L_{w\alpha} \cdot \alpha \cdot (x_{wac} - x_{cg})$.

Remember though that for all but symmetric airfoils there will also be a static moment $M_0$ due to the camber-related lift also not acting at our CG.

In the above moment equation everything except for $\alpha$ is constant for a given wing/airplane. When we analyse longitudinal dynamics, which is all about AoA changes, we need the derivative by AoA. This leaves us with a constant, which unequivocally characterises our static stability.

Let's add the tail. It's lift will be trivial, $L_{t\alpha} \cdot \alpha_t$ plus some static lift at the chosen zero AoA. The arm of the AoA-related lift with respect to CG will also be constant: the distance between CG and AC of the tail. (Given that the tail airfoil is often symmetric, the whole lift arm is simply the distance to 1/4 tail MAC).

So, when we equate the moments for a straight-and-level flight (and ignore the downwash effect for a moment, which changes the tail AoA $\alpha_t$ from the base AoA), we get
$$(L_{w\alpha} (x_{wac} - x_{cg}) + L_{t\alpha} (x_{tac} - x_{cg})) \cdot \alpha = const \Leftrightarrow M_\alpha \cdot \alpha = const$$

The $const$ represents the static moments to be trimmed out; but what's important for the dynamics analysis is that we get a constant moment derivative $M_\alpha$: everything in the brackets is constant thanks to the 'constancy' of AC. We can break it up as $M_\alpha = L_\alpha \cdot (x_{ac} - x_{cg})$, which defines the overall AC of the wing + tail system, often called neutral point (NP).

Now if we want a statically stable aircraft, i.e. the one which negates the changes to AoA, we need, by definition, a negative $M_\alpha$ (and that's regardless of the trim $const$). From there, you can easily derive the requirements for the CG position with respect to AC. This very convenient, and this is why we need AC more than anything else. (In aircraft design, unlike pure airfoil/wing aerodynamics, CP practically never appears anywhere). Finding the AC is not always trivial though.

(Of course, in practice engineers use dimensionless coefficients rather than actual forces/moments, but I didn't want to introduce more entities than necessary here).


Does terminal control have final say on which runways the towers should use?

No, that's handled by the towered airport itself.  Now approach control is going to know what runways are currently in use at that airport and will direct incoming aircraft to approaches for the runways in use.

Ultimately its up to the pilot in command to use the runway ATC directs or request another runway.


How can a flying wing style airplane recover from a spin without a vertical stabilizer?

The answer depends on the type of flying wing aircraft.

Drag rudders

The B2 for example is an example of a flying wing aircraft with rudders. It's just that it doesn't use conventional boat style rudders attached to vertical stabilisers since it doesn't have any vertical stabilisers. Instead it uses drag rudders.

There are several different types of drag rudders. The B2 uses one of the most effective designs as proven by countless experiments: the split elevon (sometimes called duckerons since they look sort of like duck bills). If you look at pictures of B2 landing you can clearly see them open at the wingtips.

Regardless of the type of drag rudders, they work via 2 principles:

The simple to understand one whereby if you increase the drag on one wing you make it advance slower than the other wing thus inducing a yaw.
The less obvious principle of shifting the center of drag backwards. This is the same principle of how badminton shuttlecocks work. Indeed, this is the same principle of how vertical stabilizers work. If the center of gravity is in front of the center of drag you get a weathervaning effect where the draggy part would swivel to the rear. The B2 achieves this by opening both drag rudders. In effect the B2 is creating a less efficient, more draggy, virtual vertical stabilizer. In practice you'd only need this extra stability when flying slow. At cruise speeds the drag rudders would be mostly closed (especially if you have them gyro stabilized, if you don't have computer controls and gyros you'd keep them partially open for stability).

Wing twist/washout

Some flying wings don't have drag rudders. Instead the wing is twisted to achieve a lift distribution that would cause the wing to have proverse yaw. The Dunne series of flying wings were promoted as inherently stable aircraft because they didn't experience adverse yaw. If you have proverse yaw you can simply use your ailerons to turn the plane without rudders.

The big disadvantage designs that don't use drag rudders or any vertical stabilizers is that you depend on banking in order to yaw. This makes landing on straight runways impractical so most such planes land on grass fields which allows the pilot to choose landing direction so that crosswind is not an issue. A lot of Dunne flying wings were seaplanes.


Do turbofan engine cowlings dilate during spool-up?

Now that's an interesting phenomenon! I do not believe that this is a case of an illusion of any sort, or the engine dilating. What the video probably shows, is the engine slightly turning towards the window as takeoff thrust is being applied.

Engine mounts are not 100% rigid, this can easily be observed on pretty much any passenger flight if you can see the engine. Any movement of the fuselage and/or wings, and the engines are clearly "bouncing around". The reason for this is to act as a damper between the engine and the rest of the airframe.

In the case of the plane in question, applying T/O thrust imposes a significant force on the engine mounts and the part of the fuselage that the mounts are attached to, resulting in a small inwards turning of the engine nacelles, thus making it appear as if the cowling is expanding.

This video shows the exact same phenomenon from a slightly different perspective. At approximately 2:15 mark, as T/O thrust is applied, a red mark on the outer flap mechanism fairing dissapears from view as the engine is shifted a bit.

And to further prove my point (having some extra time by chance), here are two images I've created to make this phenomenon more visible:

This is a combination of two crops from the video. Exact same location, but different time. The other is just before T/O thurst is applied, the other just before brakes are released. Image is divided into four segments, two of former, two of latter point in time. A vertical and horizontal lines are added for clarity to separate segments "Dilation" is clearly visible:

The second image is a combination of the same original images as before, but full frame. They are layered on top of each other, and the one on the top is defined as "difference" layer in Pixlr. This creates an effect that shows areas of the images that differ from each other as bright, while similar areas are dark:

As you can see, bright area is visible around engine nacelle. Also horizon line and the runway edge are bright, these brighter lines widen towards the right edge of this composite image. This is because the aircraft tilts from the thrust being applied against the brakes.


Why is Denver International Airport runway 16R/34L rarely used?

KDEN has a lot of runways, so they have the option of not always using some of them. As FreeMan pointed out, 12,000 feet is plenty for just about any aircraft flying in or out, even at 5,300 feet elevation. Being such a long runway, it may also be good to leave it open so that no aircraft need to be moved in case an aircraft declaring emergency would need the extra length. Runway use will depend on the wind and traffic, so depending on when you are observing, you may not often see conditions where it is used.

North flow: arrivals on 34L could interfere with runway 7/25, and for departures it is further from the terminal than 34R. TomMcW also points out potential noise abatement concerns.

South flow: departures on 16R could interfere with runway 7/25, and for arrivals it is further from the terminal than 16L.

Even with 17L/35R currently closed it is not always necessary to use 16R/34L. 8/26 and 7/25 can be used for east/west departures and arrivals, and 17R/35L can be used as well.

Runway 16R/34L can still be used as a secondary runway though. It can certainly be used as 16R for parallel approaches with 16L, or departures as 34L with approaches on 34R.

To put things in perspective, Denver has more runways than both KLAX and KATL, which see more aircraft movements.

Also, while far from authoritative, the virtual Denver ARTCC lists 16R/34L as a secondary runway in all situations.


OK, I found one, from a friend's suggestion about hang gliders.  The late 1970's UFM Easy Riser, initially a go-kart engine strapped to a foot-launched hang glider, the "first ultralight."
But this is even more Octave Chanutesque than the 1912 Dunne!  Are there any, shall we say, nonprimitive models?  If not, why?


What are service letters and service bulletins?

In the United States and presumably in other countries, there is no Government oversight on how a manufacture communicates to aircraft owner/operators except that they must issue some form of mandatory compliance "Service Bulletin" for Part 135/121 commercial operators. There is no industry guideline for what a document is called, or the information it conveys.

Manufactures often use an assortment of documents and the type of information in each document is left up to the company. For example, Continental Motors uses almost every kind of document I have ever seen...

"Service Bulletin" i.e. SB "used by most manufactures..."
"Critical Service Bulletin" i.e CSB 01-1 "Fuel Pump Inspection..."
"Service Bulletin Mandatory" i.e M64-18 "Field Conversion to
    Turbocharging..."
"Service Information" i.e. SIL99-2A "Current Listing of Sealents..."
"Service Information Directive" i.e. SID97-4C "Cylinder Bore And Piston Fit..."
"Service Letter" i.e 556c "Shouldered magneto drive shaft bushing..."

There are others I don't have copies of such as information sent to marketing, promotions, or financial departments. Additionally, the FAA will require specific forms to be used as part of the approval for Part 135, 119, and 121 operating rules. For example some type of "trace-ability" paperwork is required to be attached to all materials and parts. A "trace-ability" document provides manufacture, model, mil-spec, fire resistance, etc.

It is interesting to note that despite the universal use of the Red, Yellow, and Green parts tagging system, their is no FAR regulation requiring it's use.


The answer is pretty simple...

It is because those cups have matching lids that won't fit the passenger cups. Lids are used on the flight deck to keep the liquid inside from spilling on the (ever increasing) electronics, especially those located in the center console between the pilots (which house the radios in a lot of airplanes).

So some airlines have made a policy of any cup going into the cockpit must have a lid, and these cups specifically have lids.


What activities take place in the warning areas offshore of Washington, D.C.?

Answering my own question, these areas are designated for a variety of naval training and testing exercises including missile launches and heavy guns firing, which is the primary reason it's hazardous. The airspace can be traversed under guidance from either Washington Center or FACSFAC VACAPES, but entry by VFR aircraft without established comms is not recommended.


What are the dimensions of the parking apron?

The Apron Planning and Design Guidebook is used in the US. The goal was to provide a one stop shop for all the relevant information. The FAA maintains a list of standards.

Further, there is special CAD software for the design of airports. This includes the turn radius planning for a large number of aircraft.

Finally, because of the complexity and the large number of regulations there are companies, that specialize in airport planning and design.

Or you could always just wing it like the Germans and be ten years late and six times over budget and still incomplete ...


What type of airspeed are wind speeds given in?

Wind is measured in true airspeed. That's why whether it's surface wind or a jet stream, subtracting the head/tail wind component from the airplane's TAS yields the ground speed (tailwind being a negative value). And a 25 knots crosswind—the example you give—will create the same crab angle for the same TAS being flown. But since pilots fly using IAS, the crab angle will be smaller the higher the airport.
Cup
Think of a cup anemometer, if the air is lighter (high altitude, high temp), there will be lower resistance and the same wind speed will result in the same rotation:

The remarkable thing is that the calibration does not depend on the air density. Who would have guessed? The cup anemometer responds to wind forces, and those wind forces have a magnitude directly proportional to density. Yet because in a steady state those forces are balanced, density vanishes as a factor.

The same thing applies to the propeller-vane anemometer.
Tube
In tube anemometers (pitot-static on a stick), corrections are applied:

[Due] to differing temperature, elevation or barometric pressure, a correction is required to obtain the actual wind speed. Approximately 1.5% (1.6% above 6,000 feet) should be added to the velocity recorded by a tube anemometer for each 1000 ft (5% for each kilometer) above sea-level.

Ultrasonic
Ultrasonic anemometers are like cup anemometers, density is cancelled out since measurements are taken in multiple directions:

[Scalar] values (temperature, humidity, density) are eliminated and the result comprises wind speed.


What regulations discuss the red/white marked areas on a tarmac at a terminal?

I believe it's a non-standard marking to indicate a Security Identification Display Area (SIDA), where you need a specific badge to have access. The TSA sets the requirements for access. If you zoom in you can see the words "AIRLINE EMPLOYEES ONLY" beside the markings.

I don't think there's any standard marking for SIDAs. There was a proposal in the draft version of AC 150/5340-1K - Standards for Airport Markings (see section 5.15 for all the details):

  The SIDA marking is a rectangular stripe with white legends that are
  centered within a red background. Paint colors are per AC 150/5370-2,
  Item P-620, Runway and Taxiway Painting.

But, it didn't make it into the final version:

  Drops a proposed new surface marking for areas designated by the
  Transportation Security Administration (TSA) and the airport operator
  as a security identification display area (SIDA) (reassigned paragraph
  5.15 to cover markings for aircraft deicing facilities and removed proposed figure C-14). TSA accepted the task to address future
  markings for the airside.

And as ymb1 pointed out in a comment, it's not in the current version of that AC either. Presumably the TSA is still working on it.

If you look at a SIDA at another airport, you can see differences. The SIDA at KLEX (Lexington, KY) is marked by a single red line, for example:


What happens if Marine One's rotor blades fail?

No helicopter can fly if the blades fail.  The overwhelming majority of the lift produced, required to counter gravity, is from the blades. There is some lift from lots of other parts of the helicopter but all combined, nowhere near enough to keep it flying.  The blades are also required to manoeuvre the helicopter.

It is also most probable, and this what usually happens, that if one blade fails, or is lost, the resulting imbalance in the heavy, fast rotating rotor assembly leads to instant breakup of the aircraft.

The wing at the rear is called an horizontal stabiliser and its job is to push the tail up or down, depending on the load and speed of the helicopter, to keep the fuselage more or less level throughout the operating range of the craft.

Marine One would simply plummet if the blades failed.


Is it legal to take off with an iced windscreen?

When operating under Part 91, taking off with an iced windshield is not permitted. It does not differentiate between IFR and VFR operations.

  § 91.527 Operating in icing conditions.

  (a) No pilot may take off an airplane that has frost, ice, or snow
  adhering to any propeller, windshield, stabilizing or control surface;
  to a powerplant installation; or to an airspeed, altimeter, rate of
  climb, or flight attitude instrument system or wing, except that
  takeoffs may be made with frost under the wing in the area of the fuel
  tanks if authorized by the FAA.

Now in the case that the winshield is simply covered in condensation (not ice), I'm not so sure about that, though it'd be pretty stupid to takeoff without heating the windshield and pretty much zero visibility for no particular reason. In that particular video though, that's definitely ice.


You've asked a question the answer to which is in large part a matter of opinion. Also, which three-person cockpit aircraft you're talking about also enters in, as does the stage of flight, as do the conditions at the airport of intended landing. All this, in my opinion, means the answer is "maybe" insofar as an FE who had had flight training be able to get the airplane down safely, and the currency of the FEs piloting would be important as well.

As far as the minimum number of pilots required to safely land a jet with a three-person cockpit (a separate question really), one pilot and the FE can safely land the airplane. In a normal landing, the flying pilot is doing most of the pilot work. The non-flying pilot typically is doing the radio work and manipulating the gear and flap levers at the command of the flying pilot. Since pilots usually trade legs, both are used to doing all that needs to be done. If a non-flying pilot is not there, the flying pilot can easily reach the flap and gear controls, and he's used to manipulating them when acting as the non-flying pilot.

In the scenario of an FE leaving his seat and sitting in a pilot seat and performing the piloting, there is the problem that the FE panel generally cannot be reached from a pilot seat. To a degree, depending on the stage of flight, the FE could pre-set his panel for the landing.

Some years ago I wrote a novel (unpublished) in which I had a single pilot fly a 747. In the novel the pilot had fashioned a wooden pole long enough to reach the FE panel from the captain's seat. The pole had at one end an arrangement that allowed the pilot of manipulate the necessary switches and dials on the FE panel.


How can you do preflight fan inspection when it's windy?

(YouTube) Reversers would slow down or stop the windmilling by blocking the majority of the bypass.

If repositioning the aircraft abeam the wind is not possible, then deploying the reversers does the trick. It's the same method used when starting a jet engine in strong tailwind.

Windmilling can be very fast. The clacking sound you hear is normal.

Jetliners don't have shaft brakes, but some turboprops do.


What was the lift-to-drag ratio for WWI biplanes?

AE Berriman published his respected survey of Aviation in 1913. At that time drag was known as resistance, with other terms such as head resistance or drift also used. He discusses the lift:resistance ratio only with respect to aerofoil design.
It is unlikely that the l/d of the whole aircraft was ever considered quantitavely as a useful number. One might gain some idea by looking at Farnborough wind tunnel results for propeller thrust at given airspeed and RPM, and then comparing those with aircraft fitted with that propeller, but that would have been of little value in a hectic war and would not have been done. Of more use was the relative speeds of different types when given the same engine and propeller, or of a given machine when fitted with a new propeller.
Pilots would have had some idea of how far their machines would glide when the engine failed, as happened often enough, but only hazy notions of actual speeds and sink rates. They would also have struggled with the fact that the gliding speeds and angles for minimum sink rate and maximum distance were different.
With hindsight we can make guesses. Glide slopes remained well below 1:10 until the German soaring gliders of the 1920s. Airspeeds were slow, around 100 mph, so thrust and drag were not as high as might be expected today. While engines had relatively poor power-to-weight, airframes were so light they would sometimes break up under the extreme manoeuvres of combat. A steep gliding angle of say 1:4 would have required an unrealistically powerful engine to generate thrust (nominally) equal to a quarter of the gross weight, so wings were relatively large and lightly-loaded to give better lift at lower speeds.
So I'd hazard that around 1:5 to 1:8 would have been the norm. If anybody knows of a better-researched analysis, I would be delighted to be proved wrong.


How do I fly a direct entry holding pattern when approaching from an awkward angle?

To add to Michael Hall's answer, the direct entry is the one where you get straight on to the "racetrack" with minimum maneuvering and that is possible from anywhere within the direct entry sector.  The other two entries involve initial maneuvering "off the racetrack" so to speak.

That entry diagram is a procedural convention, not a hard regulation you must follow exactly.  The whole area is protected airspace, so it's not all that critical that you fly exactly this or exactly that as long as you stay in the protected airspace. You'll get dinged on a check ride for using a bad entry (using a sector's procedure while significantly outside of the boundary of that sector), but ATC would never bust you because you didn't follow the entry protocol perfectly, as long as you didn't leave the protected airspace and you got established properly without too much meandering around.


Rules and restriction for toy UAV in India on very low heights ? (max 50 meter from ground )

A public notice issued by the DGCA in October reads: “DGCA is in the process of formulating the regulations [and globally harmonise those] for certification & operation for use of Unmanned aircraft systems [UAS] in the Indian Civil Airspace. Till such regulations are issued, no non-government agency, organisation, or an individual will launch a UAS in Indian Civil Airspace for any purpose whatsoever.”

...

  “There are no regulatory guidelines concerning the sales and operation of such aircraft. So when a request is made for the use of drones we allow it on a ‘case-by-case’ basis. If we feel that they would not pose any security threat or cause any traffic snarls, we allow the request,” explained another senior police officer.

The Hindu, December 24 2014


Can you become FAA/TC commercial pilot with metal implants in hand?

The simplest way to answer this is to have your friend call an AME in the city they intend on training and ask them if they feel they will pass the required medical for a CPL. AME's are pretty forthcoming about this kind of stuff and they will often give you an idea over the phone if they feel there is a real issue. AME's are also the ONLY people that can definitively answer this question for your friend as they are the only people that can issue medical certificates.
Generally if the desired applicant has no practically limiting factors (in this case full use of their hand) the worst I would foresee needing is a Statement of Demonstrated Ability (SODA) which basically means they can show that they can execute the required actions of a pilot.
Under the Musculoskeletal section of the AME guidelines it states:

(b) No other organic, functional, or structural disease, defect, or
limitation that the Federal Air Surgeon, based on the case history and
appropriate, qualified medical judgment relating to the condition
involved finds

(1) Makes the person unable to safely perform the
duties or exercise the  privileges of the airman certificate applied
for or held; or

(2) May reasonably be expected, for the maximum
duration of the airman medical certificate applied for or held, to
make the person unable to perform those duties or exercise those
privileges.

If your friend can perform the duties of a pilot he should be ok.


How much does it cost to fly a plane? INCLUDING lessons, and everything else

As Ben says, it depends a lot on which country you're in: Both due to natural differences in the cost of things (Germany is more expensive than, say, Vietnam for instance) but also because different countries have different requirements for how much experience you need before they hand you a license.

But as an example let's go with the USA, based on the prices from my old club in MA:

Going from zero experience to a private pilot license will typically cost you around \$8-9k. A bit less if you learn quickly or a bit more if you need extra practice. If you already bought your own plane then this will be reduced quite a lot. The exat figures will depend on how much time you need with an instructor vs how much time solo but you can, ballpark estimate, halve the cost by using your own aircraft. This only works in some countries, though. Others (including EASA in Europe, I think) require a 'company' aircraft.
A  basic plane will cost anywhere between \$15-25,000. The cheapest I've seen recently was just over \$13k but it looked like junk.
Fuel costs around \$6.50 per gallon and you use anywhere from 5-8 gallons per hour, typically. Maintenance depends a lot on the plane, my old flying club used to spend about \$3500/year on each of their Cessna 172s.  You also have insurance on top of that, which is likely to be around \$2.5k


What does induced flow exactly means on helicopters flight? How is it different from downward deflection of air?

These are referring to the same thing.  The induced velocity is the change in air velocity due to aerodynamic interaction with an object.  The downwash from a helicopter is the vertical component of the main rotor's induced velocity.  This is the induced velocity of a bunch of rotating wings.

A wing on a fixed wing aircraft produces induced velocity too, but it's located in a region of lower induced velocity during flight.  The induced velocity varies in space and time.  As a fixed wing induces velocity in the flow field, it "flies away" from that region.  So it's flying in "cleaner" air.  An exception would be if a fixed wing could fly in a tight circle.  In this case it would fly through more of its induced velocity, experience more induced drag like a helicopter, and have a large downwash below the circle.

Another way to say this is that the fixed wing's induced velocity is more spread out in space, and hence not as concentrated at any one point.  The hovering helicopter's induced velocity is highly concentrated in the region around the helicopter.

You can probably find visualizations or animations of vortex lines on the web.  In those, you will see that a fixed wing primarily trails vortex lines behind it, while a hovering helicopter produces a helix of vortex lines below it, but close by, which keep the induced velocity at the rotor disk high.


Can an ultrasonic sensor mounted on a drone pick up another drone strongly enough to sense and avoid?

The range of the ultrasonic sensors ends up at somewhere 5 meters (here is the pre-configured search). However a simple sensor would only measure the distance, by the signal travel time. It does not provide the angular co-ordinates or exact location. Same problem as with the simple radar.

May make more sense to fit the drones with transponders so that they could actively broadcast they own location, speed, orientation and intentions to other members of the flock.


Why does the F-35 Lightning II have only 1 crew when the F/A-18 Hornet had 2?

According to program officials involved in the development of the F-35, the F-35 is a single seat aircraft because:

  New advances in avionics and sensor fusion technology, which can
  allow  a single pilot to perform missions that previously required two
  crew members.

Given the fact that the F-35 is build around the concept of
Network Centric Warfare there is less cockpit workload for most strike missions. Consequently, the need for a co-pilot is a lot less.
The single-seat configuration also maximizes commonality between the
three variants of the F-35 thereby keeping development costs low.
The survivability of the F-35 includes limiting the probability of   detection. Ergo, a two-seater version can very easily increase the RCS of the F-35 thereby compromising its stealth capabilities

West 2014: Joint Strike Fighter: What Do the Pilots Who Are Flying It Today Have to Say?

That said, one major drawback that remains on the one seat design is the demand on one pilot to assimilate and decide on all the information available.


What backup systems are in place for flaps actuated by sliding block guides?

Given the footage in that video (rotating shafts rotating a jackscrew) There are 2 main failure modes I can think of: the linkage to the jackscrew fails or the jackscrew itself fails.

If the linkage fails the flaps will just not work. Jackscrews will hold the position of the flaps making the flaps fail up (not extended). There should be a feedback mechanism to stop the operational set of flaps before the asymmetric flaps affect the flight.

The jackscrew itself is engineered to not fail if properly maintained. There are also multiple jackscrews per wing

When flaps fail up the plane can still land. It just needs a much longer runway to account for the higher landing speed and a brake inspection. For example in this incident a Boeing 737-800 landed (almost) normally.

When flaps won't retract after takeoff the crew will circle back to the airport and land again with the flaps in takeoff position. This is somewhere between flaps full up and flaps in normal landing configuration.


What is the definition of load factor and how do you apply it?

The load factor is the total acceleration you feel, pointing downwards. In straight and level flight, the load factor is 1: you only feel the acceleration of gravity. So a load factor 1 equates to 9.81 m/s$^2$ (If gravity was higher, let's say 15 m/s$^2$. load factor 1 would equate to 15 m/s$^2$. But that's another story.)

Image source

Bank the aircraft 60° and fly a co-ordinated turn, and you'll experience a downward acceleration of 2g. This is a case that is easy to understand since it is a static situation with constant velocities. If we have a dynamic sine wave for instance, the load factor would be a function of where we are in the cycle, if the aircraft is accelerating up or down. The actual acceleration is added to the gravity vector.

Load factor does not ignore the weight of the aircraft:

In steady horizontal flight, load factor is 1 because it is the same weight that would show up on a scale on the surface of the earth.
All dynamic accelerations are added to 1. If the aircraft accelerates downward with -1g, the load factor is zero and everyone on board is weightless.
Forces are vector entities. For the load vector, we're only counting the resulting accelerations in the z-axis of the aircraft. After summing the forces in 3 degrees of freedom, the z-axis force F drives the airplane up/downwards with an acceleration of a = F/m.


At what Mach Number do variable cycle engines (VCEs) start showing benefits over turbofans?

It's not a high Mach number that gives a variable cycle engine an advantage over a turbofan. Most air-to-air combat happens at subsonic speeds, because drag gets very high when you start trying to turn sharply at supersonic speeds. For combat, you need high specific excess power (SEP), which comes from a low bypass ratio turbojet. But, cruise speeds are also typically 0.8 to 0.9 Mach, even for fighter jets. But lower fuel consumption in cruise occurs with a high bypass ratio turbofan. That's because the exit velocity is not much higher than the aircraft velocity, which means the propulsive efficiency is high. But, it means the aircraft doesn't have excess power, to suddenly accelerate, or stop energy bleeding off in multiple, rapid turns.

So, in both cases, cruise or combat, speeds are subsonic, but the desirable type of engine is quite different. To illustrate, the specific fuel consumption (SFC) of a CFM56-7 is about 0.37 lb/hr/lb, with a BPR of about 5.4. In comparison, the F100-PW-229 has an SFC of about 0.73 lb/hr/lb (non AB), and a BPR of about 0.36. That's pretty close to a factor of two. Obviously, a VCE engine can't change the bypass ratio as much as in this example. I don't expect the variation of bypass ratio (BPR) in a variable cycle engine is published anywhere.

So, the advantage of a VCE occurs even if you don't need or want to fly supersonic. The advantage occurs when you suddenly need excess power, even at subsonic speeds. Military aircraft benefit from a variable cycle (variable BPR) not because of the large speed range over which they fly, but because of the wide variety of mission types they fly. Civil aircraft just need to be optimised for cruise. Variable cycle allows military aircraft to be better optimised for combat and cruise, not just the first.


How to calculate the radius of a turn as a function of speed, bank, wing-loading, and Cl?

The formula for turn radius is Velocity squared divided by radial G. And since Radial G, (assuming a level turn) is absolutely dependent on bank angle, the turn radius IS absolutely dependent on Velocity and bank angle. No other factors are necessary.
You are incorrect that two aircraft with different wing loading will have different turn radii at the same airspeed and bank angle. Anyone who has flown formation, even if they are not familiar with the physics/mathematics involved, knows this from experience.


How bad is the efficiency of jet engines under low loads?

Current jet engines are actually not built for efficiency rather than performance.

If you consider efficiency, you don't build a VTOL aircraft. This is why the F35 has multiple versions with and without VTOL capabilities.

Also, jet engines even during flight have to be able to sustain fast speed change, fast altitude increase and high load factors, all combined with lightweight designs. Therefore, I wouldn't consider takeoff as the most demanding phase of flight for such engines, but I may be mistaken on that point.

All these conditions make it difficult to reach the efficiency of say turbofan or turboprop engines.


Why did the early versions of the Me-109 use a braced stabilizer?

To understand that particular design decision, some background may be necessary.

In the 1920s, Willy Messerschmitt had started a small aircraft factory in Bamberg with limited economical success. When he requested financial help from the Bavarian state, he was forced to merge with another aircraft factory in Augsburg, into Bayerische Flugzeugwerke. Since few of his designs enjoyed commercial success, he was forced to accept the production of other designs under license to keep the workforce of the combined companies occupied.

The only Messerschmitt design which had been accepted by Lufthansa was the M.20, and a close friend of a Lufthansa director was killed in a test flight of the M.20. When that director was promoted to the German air ministry and became responsible for selecting aircraft for building up the new Luftwaffe, he made it clear to Messerschmitt that he would avoid purchasing his designs because he disapproved of his reaction to that fatal accident of the M.20.

Messerschmitt M.20 (picture source)

The most successful type of Messerschmitt's designs was the M.23, a two seater sports plane. It had suffered two accidents in which the tailplane broke off in flight, so struts for the tailplane were added while initially produced aircraft had an unbraced tail.

Early Messerschmitt M.23a with ABC Scorpion engine (picture source)

Messerschmitt had gained a reputation for aerodynamically clean and very lightweight designs, and accidents of the M.20 and M.23 in which the tail section failed made pilots wary of the structural soundness of his designs. Nevertheless, his aircraft achieved surprising performance with very limited engine power, so he was unofficially asked to contribute a design when a competition for a new standard fighter was announced in 1934. As an outsider, he had to make sure that his design would be accepted by his critics, so he played it safe and braced the tail, as he had done on the M.37 (which was to become the Bf-108 and was in many ways the dress rehearsal to the Bf-109).

That is the real reason for the struts: Messerschmitt had to play it safe to not threaten his chances as an outsider for a very lucrative contract.


What happens if an aircraft declares an emergency while there is another aircraft ahead cleared to land?

No, the airport wouldn't be closed, and the #1 aircraft doesn't need to go around nor be sent around.

The risk of him shutting down the runway is very slight, and is probably of the same magnitude of risk that sending him around to hold until #2 has landed & the runway has been checked and reopened, would put him into a low-fuel emergency state.

If they are both about the same distance (actually, time) away, then the emergency aircraft has priority (assuming that he doesn't decide to hold in order to troubleshoot, burn down fuel, prepare for the landing, etc), but essentially closing the airport from the time that the emergency has been declared until the emergency aircraft lands, isn't something I've ever seen or heard of.

The runway is often closed following an emergency landing until it can be checked by an airport vehicle, to ensure that it is clear of debris, spilled fuel/oil/hydraulic fluid/etc. And if the emergency aircraft can't clear the runway under its own power, it takes time to get it towed off, possibly pinning the landing gear (to prevent unintended retraction) first. Plus there may be an evacuation after the landing. So closing the runway for some time after the emergency aircraft lands, is entirely possible.

But if the airport has planes in the pattern & the emergency aircraft is 50 miles out, it'd be better to let those who want/need to land, do so, rather than risk them running low on fuel airborne while awaiting the runway's reopening.  Same basic logic applies in the #1 / #2 scenario posed above.

If aircraft regularly had their gear collapse & shut down runways unexpectedly, that would be a different story. But that's exceedingly rare, so that isn't the contingency that all planning is based on.


Has a C-130 ever been designated as "Air Force One"?

As I am sure you are aware, the convention is that any aircraft that has the current US president on board is given the "One" call sign.

For military aircraft, this is the branch of the military followed by "One", which is why you have Air Force One, Marine One, Navy One. If he is on a civilian jet, it is called Executive One.

The actual plane that everyone calls Air Force One is called VC-25, which is the military version of the 747.

There have been many planes that have been called Air Force One, from a King Air B90 to Gulfstream jets and even a combat aircraft like the S3 Viking (which was called Navy One).

However, as far as I know - no president has flown in a C-130 while in office.

Just to close this off, if a president is no longer sitting and is transported; then the callsign changes to SAM (Special Air Mission); so for the "Air Force One" 747, this would be SAM 28000 or SAM 29000 - depending on which of the two is being used.

The classified callsign for Air Force One is Angel.