Why do these tail-sitters not have bigger propellers in their main engine?

You're correct that it is more efficient to accelerate a large mass of air to a slower velocity. But then there are other things to consider here:

The attitude control i.e. transition is based on the downwash generated by the propellers (unlike helicopters). Either you should have high speed downwash or reach higher speeds for the flight controls to become operative. Reaching higher speeds in vertical flight would tax the engines further and the higher speed propellers, however less efficient would have been the better choice.
Huge rotors, like in helicopters would've been efficient, but also bring the related problems of blade flapping, lead and lag and droop, especially leading to problems during transition. There are also issues with tip speed, especially for the high speed interceptor role these aircraft were intended for.
One of the design considerations was shipboard (even submarines were talked about) use, conditions in which higher diameter rotors would've been a headache- you have to find ways to fold them, for one.

In the end, use of smaller rotors would've been influenced by a much more mundane reason- availability of powerful engine. Note that both of these aircraft were powered by variants of the same engine- modified Allison T40 turboprops, the only engine rated for vertical takeoffs and landings available- which consisted of two Allison T38s lashed together to run the same gearbox with contra-rotating propellers.

In fact, the heavier Lockheed XFV never made the transition flight, waiting for a higher powered T-40 and did only horizontal flights with long landing gears (which would've precluded using higher diameter rotors- though I'm not sure if that was a consideration).


What is the typical pilot to aircraft ratio in military squadrons?

As has been said, there is no one exact rule, but a broad estimate can be easily produced.

There are 12,500 active duty pilots in the USAF, and the service counts just over 5,000 manned aircraft. This will give an overall, rough, ballpark figure of 2.5 pilots per aircraft across the entire force.

Counting aircraft types by pilot seats, one can calculate the total number of pilot seats at around 8,350. About a thousand comes from training aircraft, however.

This gives an overall approximate figure of 1.5 pilots per seat, across the entire USAF.

This is not distributed equally. As mentioned in the comments above, combat units tend to run relatively low ratios. With the recent shortage of pilots, especially ones rated for combat aircraft, it has sometimes fallen below 1:1 in some units. For transport and utility aircraft, there are more crews.


What are the airflow patterns of a helicopter when operating in ground effect?

What happens at a height of 8 inches and below in the hover in ground effect is a function of rotor diameter: everything is relative. Ground effect becomes noticeable at about one rotor diameter from the ground surface, so if your rotor is 8 inches in diameter there is not yet a significant change of the downward air flow.

If we limit ourselves to discussions of flow as a function of rotor diameter, we can see the following happen as illustrated in the above figure, from J. Gordon Leishman, Principles of Helicopter Aerodynamics:

Out of Ground Effect, the ground has little or no effect on the rotor outflow. The spiralling lines in the figure are the blade tip vortices.
In Ground Effect, the rotor downwash appears compressed and spread out. One way of understanding how ground effect affects lift, is by considering that the static pressure underneath is increased and contributes to the lift.

The spiralling blade tip vortices are compressed and spread out as well, and this has a large effect on wake fluctuations, particularly noticeable for a ground observer. What exactly happens regarding spiralling gusts is not yet fully understood - from Prouty, Helicopter Performance, Stability and Control, page 68:

The wake in ground effect is not really a steady flow..., but a flow with large scale fluctuations that can be felt as gusts by an observer standing near the helicopter. Reference 1.21 speculates that these fluctuations are associated with the vortex that is made up of the individual vortices from the blade roots.This vortex apparently writhes like a pinned snake along the ground, causing the entire wake to shift and wobble.
Pilots occasionally report that when hovering in ground effect, they experience random yaw disturbances. This is probably due  to the effect of the root vortex as it writhes near the tail rotor.


How does lowering altitude conserve energy in Solar Impulse 2?

Generally, best range is at high altitude(thin air, less drag), and best endurance is at low attitude(thick air, more lift) and low power.

It makes sense that at night they would have to descend to a best endurance altitude to conserve battery power.

Source: solarimpulse.com


What modifications are necessary to the airframe and or instrument panel to add an autopilot to a light airplane (like a Cessna 172 or 182)?

I participated in a project to do this to a light aircraft some time ago. The requirements will vary on the basis of the type of autopilot you select and the requirements of the STC that comes with it, and which allows it to be installed on your aircraft. There might (and likely will be) one or more of the following requirements: panel mods, electrical mods, servos need to be installed (type, placement and installation procedure as per the STC), there will also have to be ground and flight testing, and if you intend to interface the unit to navigation equipment, then it gets really interesting. It all depends what other avionics you already have in your aircraft. You may or may not have to upgrade your existing equipment to achieve that.

To get a complete answer to your question for a specific aircraft you need to go to a reputable avionics shop that has done the work before (read: has references) and pose the question to them.

You should also expect to have to pay for a detailed quote and time estimate -- it takes quite a bit of work to prepare that, and avionics shop owners have to pay bills and put food on the table, just like you. :)


Can the fly-by-wire system of a modern airliner handle an unstable condition?

Yes it can - to an extent, depending on:

amount of CG shift;
airspeed;
aircraft weight (actually Moment of Inertia);
maximum deflection rate of elevators/ailerons.

If the airframe has aerodynamic static stability, a disturbance in Angle of Attack Creates aerodynamic forces that return the aircraft attitude back to neutral. If the Centre of Gravity shifts aft of the neutral point, the airframe becomes statically unstable - the aerodynamic forces now want to amplify the disturbance. The rate gyro's in the fly-by-wire system sense that the attitude deviates from the commanded attitude, and deflect the elevators/ailerons such that the aircraft is brought back.

Image source

Amount of CG shift
The ability of the Flight Control System to correct for unstable equilibrium depends on the degree of instability: the curvature of the right cup in the picture above.

Airspeed
Deflection of the elevators and ailerons generates aerodynamic moments proportional to $V^2$. At high airspeeds, a small deflection results in a large moment about the CoG - the critical situation is low airspeed, which mostly occur close to the ground. At low airspeeds large deflections are required.

Aircraft weight
If the aircraft is at a high gross weight, and if this weight is distributed away from the CoG, larger control deflections are required to correct disturbances in AoA. A heavier bowling ball in above picture makes for higher required forces.

Maximum deflection rate of elevators/ailerons
The frequency response of the flight control systems is a function of how fast the control surfaces can be brought to the required position, and this is a function of hydraulic fluid supply rate: the added capacity of all the operational hydraulic pumps.

The F-16 is designed to rapidly correct for any disturbance from the commanded attitude, in any flight situation. All systems are dimensioned such, that artificial stability can still be provided at the lowest airspeed and the highest MOI that the aircraft can encounter. The A320 is not designed with a flight critical FBW system - if all systems fail, the aircraft returns to a state with aerodynamic static stability. If the FBW system fails in an F-16, the pilot must eject.


If unexpectedly in IMC, does it help to climb into clouds to get on radar?

Absolutely not! If a pilot is not trained for instrument flight it would be near suicide to attempt flight in cloud due to spatial disorientation. In clouds you have to trust your instruments solely and be able to interpret them, which requires special training, retraining and practice. Without these pilots do not last long in cloud, see this related question for lots more details on inadvertent flight into IMC, which is applicable to your question.

What the pilot should have done is made a precautionary landing on one of his concrete compass lines or a field while he still had the option to do so. Instead, he had get-there-itis and got himself perished as a result.


How do I have to fold a emergency slide so it can be reused?

WARNING

These slides may contain explosive squibs and/or chemicals not safe for ingestion and it is NOT SAFE to mess with them if you do not know what you are doing! If an airbag in a car can kill or cause injury, imagine an enormous version of that. If one became available for sale, I would be very cautious as to whether it had been made safe/inert. Tread carefully.

Only authorised life support fitter type maintainers at the factory or the approved delegated authority will be able to fold slides up again to the correct standard. It is a specialist type job and a jigsaw puzzle. It is similar to trying to get a tent back in it's bag if you don't use the correct technique.

As with all aircraft maintenance tasks, it may sound like a cop out, but the answer to any how do you do that question is "in accordance with the approved procedure". Find the approved procedure and you will know. It will be in the airbus manual or from the manufacturer of the slide.


What causes 'wing rock' and how does it work?

It occurs on aircraft that have triangular or arrow-like wing shape.

Let's say at a high angle of attack, the left wing begins stalling first. The aircraft will turn slightly to the left. Immediately, there are two forces counteracting this:

when the left wing goes down, it stops stalling and the shadowed wing on the right begins stalling;
if the aircraft is laterally stable, the aircraft has a tendency to revert to the center position when turning left or right.

Therefore the aircraft will turn slightly to the right, and the same process repeats again.


Where can over age 65 airline pilots fly?

Pilot qualification- including age limit - is according to the law of the country where the aircraft is registered. What a pilot must abide by when flying overseas is the local operating/air traffic rules.


An end plate on a lifting surface (which the vertical tail is, during a yaw maneuver) reduces tip vortex formation, which means less lifting area is needed to produce the same lift force.  It also significantly reduces induced drag, though the parasitic drag of the plate is usually a net loss unless, as in the case of a horizontal tail, the "plate" serves some other function that would be required anyway.

Whitcomb and newer design winglets use careful design to give similar effects with less, or even negative drag -- but you'd need a horizontal tail anyway, so the reasons not to have a T configuration boil down to structural weight, elevator blanketing in a stall, and control routing issues.

For an example of an aircraft that makes good use of tip plates to allow a shorter wingspan, look up the Bumblebee -- at least at one time, it was the dimensionally smallest piloted aircraft ever flown, and it critically depended on tip plates on both upper and lower wings to produce enough lift to fly.


Why is there a time range for holdover times charts?

The document answers your question - Look under the table, in the section titled "Cautions:" --

   The time of protection will be shortened in heavy weather conditions. Heavy precipitation rates or high moisture content, high wind velocity, or jet blast may reduce holdover time below the lowest time stated in the range. Holdover time may be reduced when aircraft skin temperature is lower than outside air temperature.

Thus each category has a range of holdover times - longer for the most moderate conditions (barely enough snow to show up in the METAR), and shorter as conditions become more adverse.
For example if we split the difference in the "Rain on Cold Soaked Wing" category, Light Rain (-RA) would have a  holdover time around 5 minutes, Regular Rain (RA) would probably be around 3 minutes, and Heavy Rain (+RA) would wash the fluid off in 2 minutes or less.


That is the port-side ventral airbrake, as can be seen in this diagram:


How can I calculate the optimum loiter airspeed for an aircraft?

The optimum cruise speed is the speed at which fuel consumption is minimized per unit of velocity. So, you need to compute the derivative (C/v)' where C is rate of fuel consumption and v is rate of travel (airspeed). (I assume you want this by "loiter". If you want to minimize fuel consumption, that is called "maximum endurance" and that is explained below on the chart.)

Since fuel consumption is proportional to power, and power divided by velocity is thrust, we can graphically determine this point by the thrust required curve. The diagram below shows the relevant relationships:

So, to compute the optimum cruise speed, first draw the thrust-required curve, as shown in the lower part of the diagram above, then you draw a line from the origin tangential to the thrust required curve. The point of tangency lies above the optimum cruise speed on the x-axis.

Maximum Endurance

If by "loiter" your goal is to minimize the fuel flow while maintaining a particular altitude, then you use the power required chart (the upper chart in the figure above). The fuel flow is proportional to power, so the maximum endurance speed is found by locating the lowest point on the power required curve. In the example above, that point is located at 80 CAS. Mathematically, the maximum endurance is found by solving the equation P'=0, where P is the power required function.


What kind of tools are available to an ATC handling traffic in the terminal airspace to predict aircraft trajectories?

Yes, there are several ways for the controller to predict the trajectory of a flight. The closer the flight gets, the more precise the predictions also get.
It all begins with a flightplan. Prior to departure, a flightplan will have been sent to all ATC units expected to be involved with handling the flight. This includes an estimated time of departure (EOBT) and an estimated elapsed time (EET). Based on these, you can roughly predict when a flight will enter your airspace. The estimated time of departure in a flightplan, however, is not very accurate, since the flight is allowed to deviate from it with +/- 15 minutes.
In some cases, when the flight takes off, a departure message (DEP) will be sent to everyone who has received the flightplan. The DEP message contains an actual time of departure, which allows you (again based on flightplan data including EET) to calculate a more precise estimated time of entry into your airspace. This is still not very precise, since many different things can happen enroute that means the flight arrives some minutes earlier or later than expected.
Next step is coordination. For IFR flights, every transition from the area of responsibility of one ATC unit to the next requires prior coordination. Controllers often do this manually (via phone), but more and more systems support automatic coordination and exchange of estimates, for example via "On-Line Data Interchange" (OLDI) or other electronic message formats. You will typically receive a coordination for a flight somewhere around 5-10 minutes before it enters your airspace. The coordination will contain a precise estimate of when exactly the flight enters your airspace. The required precision for such an estimate is typically in the range of 3-5 minutes (if a delay occurs after the coordination has happened, exceeding the 3-5 minute tolerance, a new coordination has to be done). This is really the point at which the controller will start "paying attention to the flight" as you say.
Up until now, the flight has still not checked in to your frequency, but that is the next step.
When the flight calls you - assuming a radar based environment - you should be able to identify the flight on the radar. This gives you a precise location for the flight, along with current level, track and ground speed. Knowing these values lets you extrapolate the trajectory of a flight quite accurately. System complexity varies, but common for all radar systems I know is the option to show a "prediction vector". This is a vector (straight line) drawn from the radar track symbol of a flight in the direction of travel for a certain length, commonly based on the ground speed. For example, in a terminal environment, you might have 2-minutes prediction vectors enabled for all tracks, which means that, for all radar tracks, the system will draw a line indicating where the aircraft will travel in the next two minutes (assuming, and this is important, constant heading and ground speed). This is a very intuitive way to visualise for the controller both the current heading of a flight, and its speed, which is useful in many different situations. The controller usually has the option to change the look-ahead time of the prediction vector, either for all tracks or for a single flight, typically in 1-minute intervals.

The green lines shown here are prediction vectors
Note that a prediction vector only works based on current heading and ground speed. A change of either of these will change the prediction vector. There are systems that take into account the planned route of a flight when predicting the trajectory, such as Medium Term Conflict Detection (MTCD), but these are mainly used in the enroute (ACC) environment. In the terminal environment, aircraft are climbing and descending, which means they are constantly changing (ground) speed. Also, many aircraft in the terminal environment are under radar vectors, which means they are not following predefined routes, so the system has no way of knowing if and when an aircraft is going to make a turn (since this is decided by the air traffic controller on short notice). These factors make tools such as MTCD pretty much useless in the terminal environment.
There are also trajectory based safety nets, although that's not exactly what you are asking.
Short Term Conflict Alert (STCA) is used to warn the controller of possible impending losses of separation between two radar tracks. You can think of STCA as working similar to a prediction vector, the main difference being that the STCA uses a 3-dimensional vector, since vertical movement is considered as well as horisontal movement. However, just like a prediction vector, STCA only considers what the aircraft is doing right now and extrapolates that into the future. The system does not know if a flight is going to make a turn or level off in 10 seconds. Because of this, the threshold values for triggering an STCA are usually set lower that actual separation minima, to reduce the number of nuisance alerts (e.g. if the required separation is 1000 ft, an STCA might be set to trigger if the predicted separation is less than 800 ft).
There are also tools such as Minimum Safe Altitude Warning (MSAW) and Area Proximity Warning (APW/AIW) which present a warning to the controller if a flight is descending lower than a defined safe altitude or about to enter some sort of restricted airspace. For the most part though, these are based on current position and altitude of a flight, not predicted trajectory.
As for the last part of your question, no, there are no tools that tell the controller how to vector a flight. After all, that is what we are trained for and do very well. With commonly available computing power, there are simply too many variables to consider for a computer to vector and sequence aircraft as efficiently as a human controller. Although, in my opinion, it is probably just a matter of time before supercomputers can more or less take over such tasks.


In the rare event that the U.S. DOD shuts off the GPS, what's the alternative?

If the GPS is unavailable, it will be quite an impact to the aviation industry.

All airliners in-flight will experience degraded RNAV performance, but they would make it to the destination using VORs, DMEs and ILSs. For general aviation, things are not so lucky. The GPS display provides an excellent situation awareness in small aircrafts; without it, navigation reverts to old school VFR and reading charts. Most pilots will probably make it, but a few may get lost and end up in fuel exhaustion.

For airliners preparing for departure, initiating the INS is time consuming as the GPS coordinate is used as one of the startup parameters. The coordinates of the gates can be looked up in airport charts, some airports also have signs which specify the GPS location; both of these take longer time. Suddenly, pilots flying oceanic routes find out they need more planning for contingencies. Some routes may be changed to fly VOR-to-VOR. Departures around the world are going to be delayed, that is for sure.

Ground Proximity Warning Systems, which use GPS to determine the aircraft's location, are unable to use their terrain database to provide warnings to pilots, although warnings based on radar altimeters should still be available.

Basically, we are thrown back to the 80s or 90s, when GPS was not yet widely adapted. Many of those navigation aids are still in use today, so the industry can still fly, but traffic capacity will be reduced.


Do I need to get a new AFSP approval if I change my instructor or aircraft?

An AFSP application is valid for one provider, one aircraft category (TSA category, not FAA category), and one training event (single-engine, IR or multi-engine). If you change any of those things, you need to submit a new application.

If you're at a part 61 or 141 school that has multiple instructors, the approved provider is usually the school, not the individual instructor. So you can receive training from any instructor there without an issue.

If you're getting training directly from a freelance part 61 instructor, then it's possible that the instructor himself is the approved provider. In that case, you would need to submit a new application to get training from a different instructor or school.

In either case, your school or instructor should know exactly who's registered with the TSA as the provider.

As for the aircraft, you only need to submit a new request if you want to train in a different aircraft category. Initial training is usually done in category 3 aircraft (maximum MTOW of 12,500lbs) and you can train in one or many physical aircraft, as long as they're all in the same category. But remember that SEL and MEL are different training events so if your current approval is for SEL training you can't receive MEL training, even if the aircraft is under 12,500lbs.

Links to specific pages on the AFSP website don't work properly, but their FAQ is reasonably clear and you can email their helpdesk at AFSP.Help@dhs.gov if you need more information. AOPA has a useful guide, and the regulations (including category definitions) are in 49 CFR 1552.


How do pilots decide whether to circumnavigate bad weather?

Easy.  You don't go through, or close to, a thunderstorm cell (a red area, which is lots of water), period.  You decide on a heading change to navigate around it, request it from ATC, and if the heading you want is not forthcoming, you tell ATC you are altering heading for weather.  You are not required to endanger the aircraft to comply with an ATC clearance of any kind.  And getting close to a cell is endangering the aircraft.

Different airlines will have different policies on some of the details of getting around cells, like they have to maintain 20 miles minimum, upwind if possible.  In visual conditions where you can see the cell, same deal.  Alter heading to upwind side x miles (you don't want to fly under the anvil which is downwind, even if the air is clear in front of you, because you can run into hail falling from the anvil).

Besides thunderstorms, the other big bugaboo risk wise is icing the plane can't handle.  Same deal, you ask for higher or lower, and if icing is becoming dangerous and you need to move now, you tell them you are going higher or lower.


Why don't airlines install Faraday cages in their planes?

Cell phones and other electronic devices can interfere with the pilot's comms and other crucial avionics

As far as I can tell, nobody ever demonstrated an actual case of this. At least as long as the electronic device is FCC compliant, but all the consumer electronics has to be.

Keep in mind that all the avionic systems already have to be shielded against interference originating outside the aircraft and this shielding works for that in the cabin too.

  Due to these issues, the FCC forbids using cell phones on planes

No. It is due to the issues with the network. Moving mobile clients introduce frequency shifts due to Doppler effect and timing shifts. The system is only designed to handle them for the speeds of cars, but not much higher, so mobile client in an aircraft will not only have unreliable connection, but will also cause problems for the other clients on the ground.

In part, it is also so they don't have to explain everybody over and over why the batteries drain so quickly.

  FAA allows airlines to choose when they may be used, once the plane is out of range of the ground cell towers.

The aircraft is never out of range of ground cell towers, since the range is 35 km and the cruise altitude is only 10–12 km.

FAA allows airlines to choose when they may be used as long as appropriate relay is provided so they actually do work.

  without enforcing it, it doesn't do much.

As long as only effect ever actually observed is that that phone's battery quickly drains and the phone turns off anyway, nobody cares anyway.


In what manner does the Cockpit Voice Recorder timestamps?

As described, it is the flight data recorder time. The linked video in that Wikipedia article shows it as seconds. I could not find after how much time Flight 593 crashed, but 2400 seconds equal to 40 minutes.

An FDR typically records around 90 parameters, and certainly can and does monitor all of them all the time, even when several parameters change within a single second.

For the purpose of transcript for this accident, the article on Wikipedia (which is far less technical and detailed than an NTSB investigation report) omits all the entries from FDR recordings which are neither relevant to the story, nor interested to the reader. For example, the reader will care less the input from different sensors between 2303 and 2314.

Since the recording time of a CVR (30 minutes - 2 hours) is less than an FDR (25 hours), they are synchronized for an investigation. This is described here (PDF), for the investigation of Flight 1549:

  The CVR and FDR data were synchronized to one another by comparing the
  FDR “Key VHF” parameter with radio transmissions as heard on the CVR
  recording. By comparing the CVR elapsed time (time since the beginning
  of the CVR recording) for radio transmissions to the corresponding FDR
  Subframe Reference Number (SRN) for “Key VHF”, a relationship between
  the CVR elapsed time and the FDR SRN time can be developed.


What are Water Vapour Resistant (WVR) engine bags made from?

The specifics will depend on the product. Bags by Aerotest are made from supported PVC textile and coated with acrylic lacquer.


It's because leading edge devices allow a higher Angle of Attack.

The four types of leading edge devices work by pointing the nose of the wing downwards so that at higher AoA there is no flow separation at the upper surface near the nose. Deflecting the slats does not increase $C_L$, the aeroplane must increase AoA to do that. Lower stall speed comes with the higher $C_{Lmax}$

From this answer, which also contains a graph showing that flaps increase $C_L$ at constant AoA.


What are those 5-character alphanumeric waypoints?

That's part of the High Altitude Redesign (HAR) program.

As far as the available information, it's now available for flights above FL390, and only in certain ARTCC's in the U.S.

The waypoint naming convention is as follows:

There are plans to have this system implemented worldwide.

The pilot will no longer be limited by airways based on ground navaids. I.e. they'll make their own airways based on those waypoints. It's called Non-Restrictive Routing (NRR).

This way they can plan to fly around the weather, yet remain close to the great circle route. The waypoints are also easy to relay and eliminates confusion when re-routing, as the identifiers are based on their location.

Comparison to the ground-based navaids is shown below:

More information:

FAA AC 90-99, and NRS Description.


How do rotor tangs lock into wheel keyways?

The tangs just slot into mating recesses in the bore of the main wheel so they can float freely laterally as they are squeezed together while transmitting torque from the wheel to the rotors.  Excuse my crude sketch:

Here's a decent cutaway:


How do you find information about overnight parking at any airport that is not your home airport?

Generally, you call the FBO(s) at the airport. They are often listed in the A/FD or if you want a digital source, airnav has them. If you use Fore Flight, they will also list many of them. They will also provide you with fuel information as well as anything else you may need to know about the airport.

At smaller airports, you may be limited to a single FBO. At larger airports it's usually worth to talk to all of them (depending on your needs) since there can often be large differences in prices. It should be noted that some FBO's may waive ramp fees if you purchase some minimum quantity of fuel. Some airports may also charge landing fees (which you will pay through the FBO). When I flew out of KPNE there was a $5 a day landing fee (as many TO/LD as you wanted).

Pro Tip: the internet is riddled with forums and user groups these days. You may find that a simple "Hey thinking of flying into XXX next weekend" will return you a gaggle of information about the airport and what to do. If you are really lucky, someone may even offer you a spot in their hangar (if they have room).


Could modern military aircraft be retrofitted to work with alternative fuels instead of kerosene?

Petroleum isn't going to be finished for a very long time. We keep discovering and accepting trickier, dirtier, and/or costlier ways to get more oil - shale is just the last step in a long chain.

Yes, planes could be altered to use other fuels such as biodiesel. It has been done. This will require changes to the fuel system, to handle such considerably more contaminated fuel, increased fuel heating, possibly combustor alterations.

However, on a practical basis, it only makes sense to start replacing aviation fuels en masse once most road vehicles have switched to a different fuel. Aviation is weight-critical and an energy-dense fuel matters; it's also a smaller consumer than road vehicles. Also, aviation's safety and maintenance requirements call for cleaner and more consistent fuels than acceptable on the road.

For the military, fuel consumption and costs have traditionally been considered less important. It's going to get the fuel its jets need, since there will be plenty available for the foreseeable future.


It doesn't only use biplanes, searching "wingwalking monoplane" provides these examples, of some low wing monoplane and high wing monoplane.
Whatever the aircraft, it has to be able to fly slowly.

(source) (not 100% about this one but it looks like one Klemm aircraft)

(source)
(Here one quite rare danish SAI KZ III equipped with a hatch behind the wing, allowing acrobat Palle Johnson to get out.)

(source)
(Jaromir Wagner, Czech wingwalker holding speed record wingwalking at 270km/h here on a Britten-Norman Islander aircraft)


Is it normal for the flaps to move like this?

I believe the engine is mounted in front of that part.

This means that if the part moved along with the rest of the spoiler the jetblast would be deflected down which will create an upward force on the wing. You don't want that while you have full spoiler deployment.

Putting a gap in the spoiler will reduce stress on the full spoiler from the jet blast. This leads to less expensive maintenance as the stresses are reduced mostly to a single panel and its attachment points.

As @Ron points out the flap geometry is such that you can't have the full flaps adjacent to each other without them jamming up when they deflect. Putting an extra panel between them lets it move on top of the other 2 flaps when necessary.


Why does the second floor of the Boeing 747 occupy only part of the plane?

The basic design of the Boeing 747 was originally developed to for the US military's CX-HLS program for a large cargo aircraft. One of the main requirements of the program was for cargo to be loaded from the nose, and placing the cockpit above the main cabin made this possible. The Lockheed C-5 Galaxy was selected, but Boeing carried the same features over to the 747.

In the 1960s when the 747 was being developed, some believed that supersonic aircraft would be taking over the long-haul travel market. The relatively short "hump" was retained not for extra passenger capacity, but so that if the passenger market dried up, they could keep producing the aircraft for the cargo market.

Boeing did extend the "hump" further back to add capacity on passenger versions, first on the 747-300 (and later retrofitted to a few -100 and -200 planes), and again on the 747-8I. Extending the second deck all the way back would create too many major changes to the structure and aerodynamics of the airplane, essentially making it a completely new model. Boeing did study a full double-deck model to compete with the A380, but opted to focus on a smaller, more fuel-efficient market with the 787 instead.


Can someone explain this glideslope question?

If you are answering an FAA Knowledge Test question, the correct answer is to level off and intercept the glide slope.

While on the glide slope, pitch controls airspeed and power controls altitude, so you will need to add a bit of power. For small very small deviations caused by turbulence, just let the airspeed vary and use pitch for a short while. For larger deviations you won’t be able to capture the glide slope without adding power.

The amount of correction depends on how far away you are from the glide slope transmitter. Figure 139 from the Instrument Knowledge Test Supplement give you an idea of the amount of correction you need depending on how far away from the runway you are. So if you are near the outer marker, 2 dots would mean that you definitely need to add power, level off and intercept the glide slope. Near the runway 2 dots is less than 100' so a slight adjustment with pitch would be fine, presuming you were holding the glide slope until then.


Most de-icers are run by the airport FBO so the people who work on de-icing in the winter work on other FBO duties such as refueling and the like when there is no de-icing to do. Some de-icers are just hired permanently for winter times.


How did this F/A-18's execute a "low-boom maneuver"?

I did some reading and this is what I could find out so far:
https://www.nasa.gov/aero/nasa-prepares-to-go-public-with-quiet-supersonic-tech
This article is similar to the Engagdet one but goes into slightly more detail(though not enough for a proper explanation) about the dive maneuver.
However, Lockheed Martin is in the process of designing and building a low sonic boom demonstrator, slated to fly in 2021. The wikipedia page says that to prevent sonic booms from building up, the aircraft will have a long slender body and canards (thought the Concorde had these as well, so I'm not sure what the difference is). They will probably add canards to the F/A-18.
The dive maneuver happens in such a way that while the sonic booms directly underneath the aircraft are strengthened, there is a secondary pair of sonic booms created further ahead that are weaker, giving quiet thumps instead.
Hope this helps.


What are the details of opening a cockpit door from the outside?

I'm going to explain this for the Airbus (also known as the Cockpit Door Locking System or CDLS):

  How exactly does the person on the inside "cancel the unlock
      process" (Press a button, flip a switch, enter "counter code",
      etc...)

If the code is entered for an emergency external opening, the pilot has 30 seconds after the request period to toggle the door button to lock to deny the request or the door will unlock. It pops back the the 'Norm' position automatically.

  It seems there is a delay before the door opens. Is this
      correct? What's the duration of the delay?

30 seconds, unless the lock button is pushed, in which case the request is inhibited for 5 minutes.

  What are the "authority levels" of codes? Which levels exist, what do
  they mean? What is the confidentiality policy regarding those codes in
  theory and practice? (Who gets what authority level code officially?
  If
      stewards/stewardesses are not allowed to have the codes do pilots
      usually pass them on anyways?)

There are indeed two codes, but I believe the normal access one is optional. The (optional) normal code just chimes the cockpit for an opening request, while a secret code to the best of my knowledge is shared among the crew to request emergency access. "There are two different access request types : “Routine” and “Emergency” access request." These are however internal airline policies and differ from airline to airline, and I've read in some cases that they might even have the same emergency code across the fleet. In any case, the pilot(s) can still decline access.

Here is a video about cockpit door as well.

Source, Page 37 onwards. While the source suggests that the time can be changed, most sources I've read refer to 5 minutes and 30 seconds as the standard times.


What is the rate of acceleration based on downward pitch?

Assuming this is the standard inclined plane task from physics textbook, as here for instance, the acceleration is

$a = g \cdot \sin(\theta)$

where $a$ is acceleration, $g$ is the free fall acceleration (9.8 m/s^2) and $\theta$ is the pitch angle down (0 assuming horizontal).

This equation applies does not take the air resistance into consideration so would only apply to relatively slow speeds. The equation also assumes that the plane orientation matches the flight direction, this is obviously simplification.

Interestingly, under these conditions the acceleration does not depend on the mass of the plane. The equation should also apply for the positive pitch angles, but the acceleration would be negative in this case (slowing down).


ICAO and EASA classification of instrument approaches

First, you're reading the EASA table wrong. Type A approaches are not all the green rows, they're the vertical column that says "Type A, 2D or 3D" that covers all the specific column of all the green rows and the blue also. On the right side of that column, you see Type B approaches, divided to subcategories. All of those being 3D approaches.

Second, the approach you are asking about is a precision approach. Type B 3D approach if we want to use the new terms. It's an ILS-approach, it has a vertical flight path guidance. You should use precision approach planning minima. It does have a higher minima than ILS usually does. The higher minima is most likely because of nearby high terrain influencing the go-around requirement.

I would say it's Type B 3D because it's Cat 1 ILS, therefore it's a precision approach and it must be a precision runway. The lowest possible DH for Cat 1 ILS is 200ft. With these facts I would place it in the given category. Although this particular approach minima is higher, it is not because of the approach it self, but rather because of obstacles.


Why does IRS alignment take so much time?

GPS faster? Yes and no
GPS is faster depends on which case we want to consider: Cold start, restart or operational use.

Cold start, like for example the first time we use the instrument: Inertial reference systems (IRS) are faster than GPS to deliver the first fix (TTFF): Less than 10 minutes (alignment) against 12.5 minutes for the GPS, the time to receive the constellation almanac from any satellite, a message which is valid for 90 days.

Warm start, like from one day to the next: GPS is faster, on the previous use, it stored the almanac. It now has to get the ephemeris for each satellite in sight, a 12s data transmission repeated every 30s (interleaved with almanac data) and valid for 2 hours. If the restart occurs within 2 hours and ephemerides for satellites in sight where cached, then it takes only a few seconds for the receiver to lock on the satellites data steam and to assess the ionospheric effects on radio signal velocity. IRS initialization takes the same time than for a cold start.

Operational use: IRS is faster, it can deliver a position immediately and continuously when properly aligned, while the GPS may be able to deliver only 10 or 100 updates per second. This parameter is important for fast aircraft, in 0.1s an airliner at M.82 cruises by more than 200m (if you were to use the car navigation system you mentioned in the question, with an update rate of 1s, there would be 2 km between consecutive fixes).

So for day to day operations, IRS is definitely slower to initialize as you observed.
GPS and IRS are not used the same way
We may wonder why these slow IRS are still seen in the plane electronics bay. First, they have two considerable technical advantages:

They are faster to deliver information when aligned. This capability is of prime importance for performance-based operations.

They don't rely on the availability of an external infrastructure to be operational (satellites, monitoring/control stations, SBAS overlays like WAAS, EGNOS, SDCM...) nor on radio transmission. Prior to 2000, the GPS was subject to selective availability under the decision of US generals and it still could suffer from intentional jamming.

But regardless of these advantages, IRS have not the same objectives than GPS. GPS is used to get a position, a Doppler groundspeed and a time reference. Other information, like heading, attitude, linear and angular accelerations, wind vector (with the help of the air data unit), drift angle, all critical data for a large automated aircraft, must be obtained through other sources, the first one being the IRS.
For example the quick determination of attitude parameter is critical for flight envelope protection and yaw damper control. This can only be done with an IRS. When an Airbus aircraft loses its 3 IRS, it loses most of the fly-by-wire protection and the rudder control falls back to mechanical linkage, so the pilot can control yaw with pedals, feel the aerodynamic efforts on rudder and maintain them within acceptable limits, now that yaw rate detection has been lost.
IRS actually provides primary data to various devices like auto-braking (anti-skid), vertical speed indicator or thrust management computer.
This explains why IRS are not going to be removed from electronics bay (it can be INS, IRS, IMU or today combined with air data units like ADIRU). On the other hand as they are subject to continuous drift, their position can be periodically updated by the GPS position (or most likely by a weighted mix of different sources).
Let me detail the principle behind IRS and GPS, and how they are started.
Time to get a fix from an IRS
An IRS is composed of 3 accelerometer-gyrometers pairs mutually perpendicular. Gyrometers quantify angular motions, like yaw or roll, and set a frame of reference for the accelerometers. The accelerometers quantity linear motions to update the aircraft position.

Overall principle of a strapdown IRS, source
During alignment the accelerometers sense the sum of gravity acceleration and centripetal acceleration (due to tangential velocity from earth rotation, proportional to latitude) in order to determine the horizontal plane (from the gravity field), true north (from earth rotation axis) and latitude (from centripetal acceleration). But there is a challenge:

Determining pole axis requires knowing the local centripetal acceleration, which in turn depends on latitude, and

determining which part of the locally sensed acceleration is due to latitude (and not to gravity) requires knowing the direction of earth rotation axis (true north). This is numerically solved using successive approximations of both data.

This process is convergent, and both latitude and north direction accuracy increases as the process is extended in time.

The convergence is slow and reaching an operational accuracy indeed requires the long time we know.

The slowness comes from earth rotation produces only tiny effects on the acceleration sensors, and we haven't found more practical sensors yet. The effects depends on the distance from earth rotation axis, larger at the equator than at the poles, hence alignment is also faster at the equator.
Accuracy of true north bearing increases with alignment time:

Source: An Improved Alignment Method for the Strapdown Inertial Navigation System
Alignment requires the unit to be motionless, any erratic motion decreases IRS signal/noise ratio which slows this process (passengers boarding, wind acting on the tail surfaces, etc).
GNSS principle: Need to know the current position of the satellites
To compute a fix, the receiver must know:

The satellites positions.
The time it takes for the signal from each satellite to reach the receiver.

... both data with an astronomical precision.
To compute the position, the receiver needs the orbital elements computed on the ground, from control and tracking stations measurements, uploaded to the satellites which act only as relays to broadcast this information along with a time reference from a very accurate embedded clock.
The GNSS receiver then computes the satellite current position along its orbit, and determines the time which has been required for the GPS signal to travel in atmosphere, providing the receiver distance to a known point in space. With 4 satellites and 3D triangulation techniques, the receiver position can be determined.
Satellites parameters are broadcast at different rates:

Rough parameters for all satellites, aka almanacs, valid for 90 days, are transmitted by all satellites every 12.5 minutes (so it may take up to 12.5 minutes to a brand new receiver to deliver the first fix).

Complementary precise parameters for a given satellite, aka ephemeris (which include specific corrections), valid for only two hours are transmitted by this satellite only, every 30 seconds, so it may take up to 30s for a receiver with a valid almanac to provide an accurate fix after restart (if the cached ephemerides for the currently visible satellites are too old), even if a rough fix can be delivered nearly instantaneously.


Flight plan departure procedures vs real life departure procedures

1) Not to my knowledge, these are short-term deviations from plan that do not require an updated plan (similar to ATC offering direct routings - shortcuts).

2) Not sure. What qualifies as “often”?

3) Experience, local and airport procedure knowledge and a weather (wind!) forecast go great lengths in predicting departure runways and routings.


How exactly is the 51% rule applied for amateur-built aircraft?

The requirement which states that at least 51% of the tasks needed to make the aircraft airworthy must be accomplished by amateurs is 14 CFR 21.191(g). Presumably this would exclude finishing items like paint, some instruments, avionics, interiors, etc., as those are items which in most cases are not required for airworthiness.

The FAA has several checklists which inspectors use to evaluate the "major portion" requirement. Homebuilders thoroughly document the construction process (or at least, they should!) in a builder's log; a lot of these tend to turn into massive photoblogs. AC 20-27G contains guidance on what this documentation should look like and contain.

The "two weeks to taxi" builder-assist programs that exist out there generally get the basics working, but they certainly aren't "two weeks to flight". Most manufacturers carefully calculate the amount of work they can offer as a kit, based on the number of tasks remaining for the builder to finish.

I'm not a builder, so I can't say for sure, but I understand most of the advantage to these programs is not that somebody is helping you - it's that they can supply tools, jigs, and a lot of behind-the-scenes support like organizing your workflow and providing answers to questions with no turnaround time. They're not there building the plane with you; they're there to make it possible for you to build the plane more quickly... if that distinction makes sense.

EAA also offers a pretty good FAQ for the 51-percent rule, which I admit to paraphrasing here and there!


What is the largest and heaviest payload ever flown?

Source: Popular Mechanics

The Antonov-225 currently holds a number of records...

Heaviest maximum take-off weight at 710 tons (1.4 million pounds)
Total air lifted payload of 558,590 pounds
Single item payload of 418,830 pounds
Longest wingspan of 290 feet for any aircraft in service (Stratolaunch and H-4 Hercules had larger wingspans, but neither are currently in service)

The A380 by comparison has a maximum take-off weight of around 1.2 million pounds (600 tons) and is 260 feet wide.

For helicopters, the heaviest payload holder currently goes to the Mil Mi-26

Source: Wikimedia

It has the world record for a payload lifted to 2000 meters (about 6500 feet) of 125,153 pounds (about 62 tons).

As for the "largest" I'm not sure you can separate that. The Antonov 225 holds the largest single item payload referenced above, so that is held by weight. If you are asking about physical size, that could mean a number of things. Longest, widest, tallest, etc.

The Airbus Beluga held the world record for the most "voluminous" cargo ever lifted when it transported a chemical tank for a marine vessel.


Can a turbofan run without the fan to provide power without thrust?

No, the fan is directly connected to the outer compressor and turbine (N1). There is no direct connection to the inner compressor and turbine (N2), which could run independently, but there is no switch to somehow stop the N1 rotation in a 747 (and I am not sure, if it would run properly anyway).

Some turboprops (e.g. ATR-72) can run an engine without the propeller (Hotel Mode, see e.g. this question), which is connected to the engine via a gearbox. While there are also geared turbofans, you cannot completely disconnect the gearbox from the core engine.

As the other answers have said, it is however possible to build a jet engine without a fan in the first place. The Boeing 747 even has one in the tail: the Auxiliary Power Unit (APU), which will provide electricity and bleed air while the main engines are not running.


How long would the engine of a Tecnam P92 Eaglet run for with the fuel selectors turned off?

It comes down to the fuel volume in the gascolator, lines, pumps, and float chambers of the Bing carburetors the Rotax 912 uses.  Without knowing the precise numbers, we can make an educated guess.
So say it's burning 17 l/hr at cruise, which is 283 CC/min.  I don't know the exact number, but say the Bing carb's float chamber holds 50 CC for a total of 100, and the gascolator/filter on the firewall holds another 100 cc of gas, maybe another 50 CCs on the lines between the gascolator and carbs, and another 50 CCs in the lines running to the shutoff valves. Add another 50 CCs for the pumps etc.
So say somewhere around 350 CCs of fuel is available once you shut off the supply, although the pumps won't be able to draw all of it due to the lack of venting at the opposite end at the valves, and it'll depend on the effectiveness of the fuel pump in creating a vacuum between the fuel and valve as it's drawn.  Maybe it'll be able to draw 300, which will run the engine for about a minute, maybe a minute and a half at the most.  Maybe quite a bit less.
So I would go with somewhere between 30 and 90 seconds.


Can someone explain to me why these planes just don't turn about their center of gravity?

The thrust force from the engine should generate some clockwise moment, right?

If we take your photo as a reference (and thus we intend "clockwise in the picture plane"), yes, it is. It is called pitch moment, because it would change the pitch of the aircraft (in your case, a A-90_Orlyonok), and in the case shown in your picture is negative, because it would make the aircraft pitch down.

  Why wont it turn and just crash then? I guess the wings generate some sort of anti clock wise moment?

Because the wings and the horizontal stabilizer produce a total net pitch moment that counteracts the one generated by the engine.

They do so by having the center of lift in a different location w.r.t. the center of gravity.

The "normal" configuration for airliners would have an opposite pitch moment due to the engines, since in that case the engines are usually below the wings (and, being usually low wings, below the center of gravity). It is well illustrated in this image taken from the FAA:


Why has the A340 not been fitted with only three engines?

Because the third engine would need to be near on centerline. That means in the tail.

Putting the engine in the tail significantly changes its design requirements.

Supporting an engine requires a lot of structural support. Then you need to run fuel to it. The effective height of the rudder is decreased. You probably need to switch over to a T-tail. The center of mass is also shifted which influences where the wings need to go.

In short, adding a single engine requires a redesign of the entire tail. While adding an engine to the wings is much simpler.


The simplistic explanation is that you design the aircraft shape, run computational fluid dynamics (CFD) simulations to get loads, then run finite element analysis (FEA) on the underlying structure to size the components.

CFD might look like:

FEA might look like:

Then when you have finished this sequential process you do it over again because after resizing the components the weight of the structure changes, so you have to change wing area to match the weight change, which makes the loads change, which then requires another component resizing.

You might wonder if it wouldn't be better if all these objectives were solved at the same time, and you'd be right. A newer design process is called multidisciplinary design analysis and optimization (MDAO) and is just becoming possible with modern, high power computing systems.

MDAO might look like:

where all the red buttons are control points that the optimizer uses to refine shape. You have to give the optimizer rules on how to proceed, which might look like:

If you want to read about MDAO one good source is Univ Michigan at

http://mdolab.engin.umich.edu/

Read a couple of their published papers and you'll get a pretty good sense of the complexity. MDO is the same thing as MDAO.

If you are interested in the optimizer, OpenMDAO is open source software. It is not aviation specific, though it was developed in conjunction with NASA. It is at:

http://openmdao.org/


Why the gradient of $C_L$-$\alpha$ graph increases with the Mach number?

This increase in lift curve slope with Mach is commonly predicted via the Prandtl-Glauert correction for 2D airfoil:

$$C_{l_\alpha}=\frac{C_{l_{\alpha_0}}}{\sqrt{1-M_\infty^2}}$$

where $C_{l_\alpha}$ is the 2D lift-curve slope, $C_{l_{\alpha_0}}$ is the 2D lift-curve slope in incompressible flow, and $M_\infty$ is the free-stream Mach number (Ref. Anderson, Fundamentals of Aerodynamics), and is accurate before local shock appears.

The physical reason is the magnification of pressure change due to density change (compressibility), as understood from the isentropic relation:

$$\frac{\rho}{\rho_\infty}=\left(\frac{p}{p_\infty}\right)^{1/\gamma}$$

where $\rho$ is density and $p$ is pressure (Ref. Drela, Flight Vehicle Aerodynamics).


Why doesn't extending the flaps on a B-2 send it into an uncontrollable dive?

I don't think the flaps are used as high lift devices. Watch this video of a B-2 landing. Perfect view:


Does the EPU on the F-16 need to be manually extinguished after an emergency landing?

The Aviationist has an entire article on this: Hydrazine: A Significant Hazard Each Time An F-16 Crashes (Or Fires Up The Emergency Power Unit). It says:

  the impact site of a crashed F-16 can be extremely dangerous and one
  of the main hazards is Hydrazine [...] When activated, the unit
  provides emergency power for the aircraft’s systems in the case of an
  electrical failure: in case of flame-out, emergency power generated by
  the EPU is designed to give pilots the time they need to land the
  aircraft safely. And, the EPU is fired up by Hydrazine.

And (emphasis in the original):

  the toxicity of H-70 is such that special procedures must be used to
  manage crashes as well as in-flight emergencies that involved the EPU
  or hydrazine leaks.

The whole thing is too long to quote, but the emergency response team certainly takes some very specific actions to deal with the hydrazine. They isolate the aircraft, give the crew breathing masks to get them away from it, check for leaks and then clean up if needed:

  As soon as the first assessment has been completed, the first team is
  replaced by a “response team hydrazine” composed by 2 Italian and 1
  American operator, equipped with special overalls (Level A, since risk
  of contact with the liquid is higher), that clear the leak along the
  track followed by the aircraft from the runway to the parking area.


What is Special VFR? Why would a pilot request it?

Special VFR is used to leave or enter a control zone coming from or continuing the flight in airspace G (Golf), when the weather minima for VFR flight are not met within the control zone, but would be met in airspace G.

Example: Airspace G (Golf) requires a visibility of 1.5km and aircraft need to remain clear of clouds. Airspace D (Delta) requires a visibility of 5km and 1000ft vertical and 1.5km horizontal separation to clouds.

If the weather report would show a visibility of 4km/4000m and a cloud base of 1400ft, the flight would be allowed in airspace G but not in airspace D.

Requesting Special VFR within a control zone will drop the VFR weather requirements to the values required for airspace G, so flight may enter or leave the controlzone. The lower visibility requirements are compensated for in the control zone by stricter separation requirements between aircraft. SVFR is separated to SVFR and IFR traffic.


Would plain and slotted flaps increase lift substantially in a distributed propulsion application?

No, that thinking is incorrect.
The air involved in lift creation is roughly the amount that flows through a disk with a diameter equalling wing span, and your distributed propulsion concept will involve a far smaller amount of air.

The maximum Clmax of distributed propulsion is 12.

In theory maybe. Practical values are half that, at most. Now consider that this lift should ideally be independent of engine health and power settings, or you will plummet from the sky when power fails or you need to throttle back. Distributed propulsion will not save you from empty fuel tanks or batteries, so this scenario must be considered. Besides, the lift coefficients you cite in your question are valid for 2D flow; in reality the outer wing will contribute much less to provide some margin for control and stall behavior.


Why can't you just set the altimeter to field elevation?

Good question. The reason is things fail.
If you set the altimeter to show field elevation, but the altimeter is faulty, you could end up flying differently from the rest, leading to loss of separation or worse.
But if you set the QNH, and then the reading is within 75 feet of the field elevation, you're good to go.

3. Altimeter Setting Procedures
3.1.3 If the difference from the known field elevation and the altitude read from the altimeter is plus or minus 75 feet or greater, the accuracy of the altimeter is questionable and the problem should be referred to an appropriately rated repair station for evaluation and possible correction. (USA AIP ENR 1.7)


What is the difference between flutter and vortex induced vibration?

Flutter and vortex induced vibrations (VIV) are both dynamic instabilities arising from the interaction of unsteady aerodynamic, inertial and elastic forces. They both extract energy from the air stream to persist.

Instead of perceiving the interaction as aerodynamic forces causing structural motion or structural motion generating aerodynamic forces, it is more meaningful (and realistic) to describe it as a coupling, e.g.,  typically described as coupled differential equations, and observing the differences in how the aerodynamic forces are generated and its components.

For VIV, the wake instability that generates the alternating shed vortices (von Karman vortex street) in turn generates an oscillatory lift coupled with the structural oscillation. So, the wake instability and unsteady effects of flow separation dominate the oscillatory aerodynamic forces.

Flutter does not have to describe a dynamic instability associated with a fluctuating wake, e.g., panel flutter is the dynamic interaction and instability arising out of the out-of-plane motion of an aircraft panel in relation to surface fluctuating pressures. However, stall flutter does arise from flow separation and its resulting unsteady wake.

Wing flutter is the dynamical instability arising from the unsteady aerodynamic forces (including the shape of unsteady wake) coupled with the structural dynamics, however wing flutter does not require massive oscillatory flow separation as with VIV. For attached flows (unstalled), wing flutter could exhibit flutter (at a high enough freestream velocity, i.e., flutter speed) due to the resultant phase difference between the generated aerodynamic forces and structural oscillation creating a positive feedback. The time-varying shape of the wake still plays a role for wing flutter, e.g., the role of the Theodorsen function for unsteady aerodynamic lift generated by structural motion.


Why isn't the V flight formation being used for commercial purposes?

This possibility has actually been studied and discussed (e.g. here, here, here) as a way to save fuel costs, but there are several issues with implementing it today:

You need to schedule a number of aircraft all flying the same route at the same time for a significant amount of time
If different, competing airlines should participate in one formation then they have to cooperate and be satisfied that no one is at a commercial (dis)advantage
A lot of work would need to be done on procedures and training (how does the formation form up, who takes the lead, how/when does the formation leader change, how are emergencies handled, what flight levels are used, what separation is required between formation and non-formation flights etc.)
Autopilots, software and other equipment would need major updates, which in turn requires re-certification
All relevant regulations on separation, formation flying and so on would need to be reviewed and changed which in most countries means changing the aviation laws, and changing any law is usually a long, slow process

Having said all that, you'll notice that most of those issues are procedural, not technical. In theory it's a viable approach, but turning that theory into reality would require a lot of work.


If the aircraft is trimmed, the flight controls are in a state where no force needs to be exerted in order to continue straight and level flight. Aerodynamic and gravitational moments about all three axes are nulled out.

Changing the trim of the aircraft in pitch could happen in the following ways:

a shift in centre of gravity, for instance by shifting fuel from centre tanks to tail tanks, or payload shifting position;
a change in thrust of an engine that is located above or below the centre of gravity;
a change in horizontal tail angle or trim tab;
a deflection of the elevator.

If the aircraft was in straight and level flight and the trim changes because of a change in any of the above, it can be compensated for by the other factors. Elevator deflection is fastest but requires a pilot force which is uncomfortable for longer periods, that is why the forces can be trimmed out to make the new stick position the neutral force one.


What does the ‡ symbol in the Chart Supplement (A/FD) designate?

The ‡ symbol in the A/FD specifies that the location observes daylight savings time.

This is from the A/FD legend, which can be found online by going to the online digital A/FD and searching for an airport.  The A/FD Legend link will then be at the top of the search results (unfortunately the link changes every cycle so I can't include an exact link).

  6 TIME CONVERSION

  Hours of operation of all facilities are expressed
  in Coordinated Universal Time (UTC) and shown as ‘‘Z’’ time. The
  directory indicates the number of hours to be subtracted from UTC to
  obtain local standard time and local daylight saving time UTC–5(–4DT).
  The symbol ‡ indicates that during periods of Daylight Saving Time
  effective hours will be one hour earlier than shown. In those areas
  where daylight saving time is not observed the (–4DT) and ‡ will not
  be shown. Daylight saving time is in effect from 0200 local time the
  second Sunday in March to 0200 local time the first Sunday in
  November. Canada and all U.S. Conterminous States observe daylight
  saving time except Arizona and Puerto Rico, and the Virgin Islands. If
  the state observes daylight saving time and the operating times are
  other than daylight saving times, the operating hours will include the
  dates, times and no ‡ symbol will be shown, i.e., April 15–Aug 31
  0630–1700Z, Sep 1–Apr 14 0600–1700Z.


Is an elevon (elevator + aileron) considered as an all-moving control surface?

An All-Moving control surface is a surface where the complete structure acts as a stabilizer. For example, in case of a horizontal tailplane which can be completely moved to work as an Elevator - instead of just the trailing edge of the horizontal tailplane moving to work as a control surface. In such cases, it is called a Stabilator (Stabilizer + Elevator). Elevon is a control surface which is part of the main wing, but the trailing edge of the wing is moved to get Yaw and Roll control. This makes Elevon a normal control surface and Not an all moving surface.


Parasite drag is for the most part out of a pilot's hands, as it's a combination of:

Form drag: drag from an airplane's general shape
Interference drag: drag from airflow mixing around parts of the aircraft structure
Skin friction drag

You can reduce skin friction drag by keeping the airplane clean, dirt and smashed bugs cause friction, removing them reduces friction. You can also make sure all the little doors are flush. Other than that you can't do much without making changes to the airplane itself, for instance:

Flush fuel caps
Wheel spats: these aren't decorative, they reduce the wheels' drag by providing an aerodynamic cover
Seal kits: these reduce interference drag by smoothing airflow
Cowling replacements
Fairing replacement

Whether these are worth the cost depends on the airplane, Cessna 152/172s are very draggy to begin with because of their rivets and wing struts, you could dump thousands into additions for very little benefit. Other airplanes get measurable improvements in speed from a few seals here and there.


Why do pilots use airways instead of just "flying direct" every time?

Airways simply allow for better management of traffic.
Imagine for a moment that everyone had an off-road capable car, if all the drivers were going "GPS Direct" to their destination how would drivers ensure separation? How would you avoid hitting other cars if there were no roads?

Airways are the aviation solution to this problem: Defined routes between navaids (VORs, NDBs, and the like). Airways can also be defined using "fixes" defined by GPS coordinates which can provide something closer to "GPS Direct" routing while still providing a defined route.

Airways also provide a bunch of other benefits, including:

Traffic Flow Management

Flightplans in Europe are validated by the CFMU (Central Flow Management Unit) and checked for criteria such as direction of airways (which can change during the day, e.g. one airway being for eastbound traffic only between 1000 UTC and 1400 UTC), correct flight level ranges and airways correctly connecting waypoints, such as fixes, VORs or NDBs. The bottleneck in all flight operations is understanding airport capacity (how many operations/hour) and sector capacity (how many aircraft handled per sector/per controller). The goal is sometimes to distribute traffic between two sectors, although having the same destination. Below you will find two routings to Düsseldorf - EDDL, one departing from Leipzig - EDDP and one from Berlin-Tegel - EDDT (click on links to see visual representation):

EDDP - EDDL
ORTAG Q230 WRB T854 DOMUX

EDDT - EDDL
BRANE Y200 HLZ T851 XAMOD

The routing from EDDP to EDDL is going via WRB - TINSA - ADEMI - INBAX - DOMUX, which is within the boundaries of a sector called "Paderborn High" or PADH.

The routing from EDDT to EDDL is going via PIROL - DENOT - HMM - XAMOD, which is within the boundaries of a sector called "Hamm High/Medium" or HMMH/HMMM.

During peak hours, both sectors are separate and deal with traffic only within their sector, which uses the full capacity of each controller handling the sector. Outside peak hours, the sectors can be combined and worked by one controller. This allows a granular usage of controller resources and airspace.

Separation between Traffic

From the example above we have seen that there is 2 routing endpoints at Düsseldorf - EDDL for traffic arriving from the North-East and South-East, XAMOD and DOMUX. Both waypoints or fixes are respective STAR or transition entry-points for arrivals into Düsseldorf. By using a standardized routing to and from airports, we can now expect traffic to always arrive via these two points from the east, unless other coordination has been achieved by the ATC units involved. Looking at the reverse routing for both airports, we will see these routes:

EDDL - EDDP
NUDGO Z858 BERDI Z21 BIRKA T233 LUKOP

EDDL - EDDT
MEVEL L179 OSN L980 DLE T207 BATEL

MEVEL and NUDGO are two of the SID exit waypoints out of Düsseldorf, MEVEL being 10nm north of XAMOD and NUDGO being 26nm east of DOMUX, however the relevant fix here is ELBAL, which is one of the fixes on the SID23L from Düsseldorf to NUDGO, which is 16nm south of NUDGO. With something simple as using standardized entry and exit fixes to and from an airport, we have managed to maintain a traffic flow with ensured separation between departing and arriving traffic, something which would not be possible with GPS direct routing or would require constant ATC vectors.

Handoffs from ATC Unit to ATC Unit

The above examples show different routings and sometimes different sectors handling traffic on these routes. How is traffic handed off to other controllers and where? A handoff consists of moving the radar track of the aircraft from one controller to another and thereafter instructing the aircraft to change the frequency to the next sector controller. Handoffs are initiated at sector boundaries, at specific fixes, which have been agreed on between different ACC (Area Control Centers) or sometimes even within one ACC between single sectors. Since we are already familiar with Düsseldorf airspace, let's use the below routing from München to Düsseldorf.

EDDM - EDDL
GIVMI Y101 TEKTU Z850 ADEMI T854 DOMUX

From the graphical represenation you will see that traffic from EDDM to EDDL will pass the waypoint ARPEG, which is close to the destination airport. Before reaching the waypoint ARPEG, aircraft will be under control of either the Hersfeld (HEF) or Gedern (GED) sector (page 5) and need to descend towards the destination airport. The next sector for arriving traffic into Düsseldorf via ARPEG would be Paderborn High Sector (PADH). The agreements between HEF/GED and PADH are that arriving traffic to Düsseldorf via ARPEG is to be expected at FL240 level at ARPEG and released after handoff for further descent through PADH, even if the aircraft has not yet crossed the sector boundary and is not in PADH airspace. These coordination waypoints and handoff procedures are documented in Letters of Agreement between or within an ACC.

Weather

When weather (wrong-way lows, strong jetstreams, storms, etc) affects the Direct route, flight dispatchers will pro-actively suggest routes around it. It's not unusual for NYC-SFO traffic to be routed over Canada or over Kentucky when the Midwest is storming.

Exceptions - Free Route Airspace

Where airport and air traffic density allows, the use of airways is not mandatory or in some cases, not even expected or provisioned for. One example is the Free Route Airspace overhead Scandinavia, where a portion of airspace can be freely used between defined entry and exit points. Similar systems are also being discussed by NATS UK and the  FAA NextGen Air Transportation System.

For more information on airways and their use, see also the related question:
Is there a difference between how commercial jets and GA aircraft use airways?

  Some material courtesy of VATSIM or VATSIM Germany. While only for simulation use, the material used is as accurate and close to the real sectorisation or procedures as possible, so should be sufficient to explain the concepts presented here.


What are the differences between air brakes, spoilers and lift dumpers?

Air brakes increase drag with little change in lift. The following image shows the air brake being used in BAe 146

"Eurowings bae146-300 d-aewb arp" by Adrian Pingstone - Own work. Licensed under Public Domain via Commons.

Spoilers both increase drag and reduce lift- basically, they change the lift-to-drag ratio. Sometimes, they are also used as control surfaces in lieu of ailerons. This image shows a Boeing 777 spoilers being used in flight.

Screengrab from youtube.com

The lift dumpers are basically ground spoilers that are used to 'dump' lift, especially immediately after landing, where you want rapid reduction in lift. The following image shows lift dumpers being used in BAe 146.


Can a jet cruise with asymmetric thrust?

As a practical matter, the aircraft will probably land ASAP. Having lost an engine pretty clearly qualifies as an emergency for twin-engine aircraft!

That said, the aircraft would be capable of cruising with asymetric thrust. Rudder is applied to keep the aircraft flying straight.


Sometimes diagrams can be mystifying. This is a video of a variable displacement hydraulic pump of similar principle being torn apart (disassembled would be too gentle a term) by a foul-mouthed Canadian who gives an excellent detailed & clear description of its construction & operation. Language warning for those not used to frontier engineering.

Which will prepare you for this very polite Canadian who shows an actual aircraft fuel pump. (around 7:30)


Why are flight recorders generally located in the tail?

When an aircraft is crashed, the entire front of the aircraft is expected to act as a crush zone. By placing FDRs and CVRs near the tail, the shock wave that reaches FDRs and CVRs is reduced significantly.

The probability of survival based on seating is shown in this picture:

(Image Source)

Hence one can see that the shock wave reduces as it reaches the rear of the plane. That is the reason FDRs and CVRs are installed in aircraft's empennage section.

(Image Source)

Please note that the precise location of the recorders depends on the individual plane. Sometimes they are located in the ceiling of the galley, in the aft cargo hold or in the tail cone that covers the rear of the aircraft.


There are many websites and apps that do this for you already.  The website SkyVector will show colored dots that indicate what the airport status is.  There is also a ForeFlight app that will show colored dots on their maps.  I am not endorsing any products, simply pointing out tools that accomplish what you are asking.

All these companies use information found in AC 00-45H.  I added color for clarification.

Personally, I would stay away from getting into the details of what class airspace an airport is currently using.  Although, the information can be easily found, it may be a challenge to code successfully.  The airspace above an airport can also change depending on whether an control tower is in use, the day of time or other factors.

The other reason, is 91.155(c).  Hence, any ceiling below 1,000 FT makes the airport IFR.

  Except as provided in §91.157, no person may operate an aircraft beneath the ceiling under VFR within the lateral boundaries of controlled airspace designated to the surface for an airport when the ceiling is less than 1,000 feet.

To answer your other question.  The ceiling is defined as the lowest BKN or OVC layer.  In your example above, the ceiling is OVC 500.


Is there a difference between "aerobatic" and "acrobatic" flight?

Acrobatic is being incorrectly used, although it is slightly more complicated than that.

"Aerobatic" refers specifically to flight, and "acrobatic" refers specifically to feats of the human body, so referring to an aircraft as performing acrobatics is wrong.

That said, the word "aerobatic" is derived from "aero-acrobatics" and sounds nearly identical, so it's an understandable and relatively common error.


Why doesn't a radar-equipped Tower say "radar contact"?

From the ATC Orders 3-1-9(b)(4):

  Unless otherwise authorized, tower radar displays are intended to be
  an aid to local controllers in meeting their responsibilities to the
  aircraft operating on the runways or within the surface area. They are
  not intended to provide radar benefits to pilots except for those
  accrued through a more efficient and effective local control position.
  In addition, local controllers at nonapproach control towers must
  devote the majority of their time to visually scanning the runways and
  local area; an assurance of continued positive radar identification
  could place distracting and operationally inefficient requirements
  upon the local controller. Therefore, since the requirements of para
  5−3−1, Application, cannot be assured, the radar functions prescribed
  above are not considered to be radar services and pilots should not be
  advised of being in “radar contact.”


NSDAP was the elected ruling party in Germany from 1933 to 1945 (only the first part of it elected though); thus Lufthansa was given government money, not "Nazi"-money. During this time, they made the Swastika the flag of Germany. American Airlines sport the American flag all over their tail, and I'm sure they (at some point) have received government money as well. If you replace every occurrence of "Nazis" in your question (including title) with "government", you'll notice it becomes slightly less provocative, and the parallels to other airlines and other countries become readily apparent.

When the war started, I would assume the military requisitioned all the assets they needed including airplanes and services from Lufthansa. I'm not much of an historian though, so I can't give you any details, but I'm sure they're out there to find. I realize this doesn't really answer your question (Lufthansa's involvement with the German government), the point I'm trying to make is that it's very hard to answer, as with any airline and any government.


Is Jetman flying above other aircraft allowed? How it is possible?

Yes.  This is part of a series of promotional stunts, "adverts", Emirates are undertaking.  Aircraft can fly in formation, all other rules taken into account, if the captains agree.
By flying above the aircraft.  As the article states, it was meticulously planned for safety (after all, an accident would be disatrous PR), and the Jetman flyers would know exactly where not to go.
Yes.  The video shows that!  The aircraft will likely be flying at slow speed.  As you can see, the flaps are extended.  I'm guessing about 160 kts.  I would also imagine the flyers will have dived down from above to pick up speed.


How can someone get clarification from the FAA on the intent of a regulation?

Generally there are two ways to get an interpretation of regulations from the FAA.

The first (less-formal) way would be to call or email your local FSDO with your question -- they will usually get back to you pretty quickly with a verbal opinion or an email (on the two occasions I've contacted the local FSDO I've gotten an answer within 1-2 days).

Interpretations from your local FSDO are essentially valid within their coverage area (if you get an opinion from Farmingdale in New York the folks in Los Angeles, California may not honor it).

The second (very formal) way is to write an actual on-paper letter to the FAA's office of the chief counsel requesting a legal interpretation of some specific regulation(s) and mail it to their office:

Office of the Chief Counsel
800 Independence Avenue SW
Washington, DC 20591

This request should be as specific as you can make it, for example:

  May the FAA hold a person who performs maintenance on an aircraft responsible for the proper performance of that maintenance under 43.13(a) and (b) when that person was not the person who made the maintenance record entry required by 43.9?

If your request is inspired by some ongoing action (say a warning letter) you should reference it and include a copy to help speed things along.

The FAA's legal staff will chew on the request for a while, and eventually produce a legal interpretation (the linked interpretation, which answers the example question above, took about 5 months, and it is a relatively simple interpretation - The more complex the regulation that needs to be interpreted the longer it will probably take).

Counsel interpretations are organization-wide precedent, and on occasion they can overrule opinions/decisions from a FSDO. They are effective "The Final Word" on how regulations are to be applied (unless overturned in court).


Is there any automated go-around procedure?

For go-around, several things have to be done in the moment the decision is taken:

Apply full power (obviously),
disconnect autopilot glide-slope mode,
disarm spoilers and retract them if they are extended,
disarm autobrakes and
in some aircraft reduce flaps.

Modern airliners, and some smaller aircraft, have a method for doing all of these at once via the TO/GA button. On Airbus aircraft it is done by just advancing the thrust levers to the TO/GA (full power) position, but on Boeing aircraft and many other types it is a separate button on or near the thrust levers.

So if the crew "apparently decided to undertake this procedure manually" it means they moved the thrust levers forward and started changing the other things. And probably missed one of them.

Notes:

I am not sure whether lateral mode remains under automatic control or not and it probably depends on aircraft as some can connect autopilot to only roll or only pitch and others don't. Pitch control is manual immediately after go-around in either case.
The last flap setting usually adds a lot of drag and a little lift. In some types the drag is too large and the flaps have to be retracted to the last usable position. On other aircraft they can be used in any position and have to be left were they were to avoid loosing lift.


Does a plane have brakes to stop or slow down while flying?

An airplane can slow down and reduce its speed while in flight. The easiest way to do so is to reduce the amount of thrust that the engines are producing. This will produce an almost immediate reduction of the airspeed, especially if the plane is maintaining the same altitude.

There are also devices called air brakes and spoilers that can be further used to reduce speed. These, however, are never1 used in normal, level flight by passenger2 aircraft and are normally only used to reduce speed during the descent and landing phases of the aircraft3.

If an airplane reduces its speed too much, it will of course stall and start dropping precipitously, at which time the airspeed usually also increases again. The slowest speed an aircraft can maintain at a given altitude without stalling is listed in its flight envelope.

However in the scenario you mentioned (obstacles ahead), it's usually easiest to simply fly around the obstacle.

1: Never say never on the internet.

2: The situation is different in military aircrafts, you can see the approaching Su-27 using its airbrake in this video

3: The wheels of most aircraft also have brakes, similar to those found on automobiles. Obviously these can only be used when the plane is touching the ground. Lowering retracted landing gear will also increase drag. There are also thrust reversers on some aircraft that are used in the final stages of landing. Use of thrust reversers during flight can be disastrous although some older aircraft (including the C-17A) were designed to use thrust reversal to scrub speed in-flight.

Finally, some gliders and larger aircraft have drag or drogue parachutes to help slow them down, for example for use on short runways.


Does the Zenith have anything to do with the read-out of an IRU accelerometer?

Good question.

Another name for the "position of the Zenith" would be the gravity vector. Which for an aircraft is always down (shortest distance to reunite with terra firma).

  Note that it is necessary to subtract acceleration due to gravity from the vertical channel before performing the integration.—An introduction to inertial navigation

So the answer is yes, the acceleration due to the gravity vector is corrected.

Check the PDF for a detailed description and equations.


What is the typical weight distribution ratio between nose gear and main gear?

Look at the sketch of the recommended gear placement relative to the center of gravity (cg) from this answer:

We can calculate the load distribution for both extremes. For simplification we use the same angle of 60° for the nose wheel in both cases:

Main landing gear 6° aft of cg: $\frac{\tan 6°}{\tan 60°}$ = 6%
Main landing gear 20° aft of cg: $\frac{\tan 20°}{\tan 60°}$ = 21%

Add some dynamic loading from the application of wheel brakes. In this answer it is shown that the horizontal braking force is less than 30% of the maximum static weight of the aircraft, and applying this knowledge to the nose gear at 60° from the cg adds 0.3$\cdot\cos 60°$ = 15% of the maximum static load of a fully loaded aircraft to the nose gear load.

In extreme cases the nose gear would carry almost half of the aircraft mass, but then rotation would be impossible. In case of the Go-229 it was 45%.

Semi-finished Go-229 V3 (picture source)

On the other extreme you find nose gears with zero static load which were only intended for taking the braking forces.

Zeppelin Staaken R VI (picture source)


Rotor Tip Speed vs Forward Airspeed - IAS or TAS?

For this graph, only TAS can be correct.

More precisely, you should have the same kind of speed on both axes. Otherwise, you would need to qualify the altitude.

Your tip speed (the vertical axis) is (presumably) the simple geometric speed, which depends only on RPM. Or in other words, TAS (with no wind). It will have simple and universal linear relationship with forward TAS. But with IAS, it will be valid only at a certain altitude.

This could be both IAS, but I don't think helicopters just increase their rotor RPM with altitude the way airplanes increase TAS. This could be true for very slow rotors, but the real ones seem to be Mach-limited, so IAS is just not very useful. But correct me if I'm wrong.


How to do the base turn course reversal?

If your worried something will be on the checkride (which is practical) you need to seek out more practical instruction on the maneuver.

Procedurally this site offers a good explanation:

  Base turn consists of:

  a specified outbound track and timing or DME distance from a facility; followed by
  a turn to intercept the inbound track

  The outbound track and/or the timing may be different for the various
  categories of aircraft. Where this is done, separate procedures are
  published.


What callsigns do UK Medical Emergency Response Teams use?

Civil

For the UK as requested, this information is in § 2.32 of the Radiotelephony Manual (CAP 413). The call-sign for a Helicopter Emergency Medical Service (HEMS) is three parts:

HELIMED
Two-digit identifier unique to the aircraft (list on Wikipedia).
Suffix A or E

A for a helicopter en-route to an emergency or to a hospital with patient(s) on board
E for positioning back to base (a lesser priority than A but higher than the other traffic).

If the helicopter is responding to a scene, it can be pronounced Helimed 7-7 Alpha, for example. Note that Wikipedia lists three-digit identifiers for some helicopters, contrary to what the manual says.

Military

From § 2.44 of the same manual, the call-signs are 'rescue' and 'rescue helicopter', suffixed by the mission number. This is for search and rescue (SAR), no distinction is made for a purely medical mission in the manual.


Where can I get the FAA data that defines airspace, including MOAs etc.?

Take a look at the National Flight Data Center.  The data appears to be contained in NASR. I mentioned in my comment that there may be no official source for spatial data, but I think this may include what you are looking for.
These are derived products. The cannonical definitions are the legal descriptions found in FAA Orders with the prefix 7400. At the time of this writing, JO 7400.11 (current version E) covered airspace classes A,B,C,D and E as well as reporting points. The JO 7400.10 (current version C) covered special use airspaces. Both publications can be found at the FAA's Website.


What careers are available for someone with a PPL?

If you are talking about Europe (EASA) Doc 1178 states at PPL privileges:

a) The privileges of the holder of a PPL(A) are to act without remuneration as PIC or co-pilot on aeroplanes or TMGs engaged in non-commercial operations.
(b) Notwithstanding the paragraph above, the holder of a PPL(A) with instructor or examiner privileges may receive remuneration for:
(1) the provision of flight instruction for the LAPL(A) or PPL(A);
(2) the conduct of skill tests and proficiency checks for these licences;
(3) the training, testing and checking for the ratings or certificates attached to this licence.

Bottom line you could make money with PPL by being a flight instructor or a flight examiner. A side effect would be also accumulation of flight hours that would permit you to continue with a course for commercial pilot.


Why are commercial aircraft windows typically oval instead of circular?

It's done mainly for the passengers' viewing benefit in making structural trade offs over total opening area.  For a given area, a round window has less "meat" of fuselage structure between them.   Aesthetically, a round window looks too much like a ship's porthole unless you make it really large, and then it looks like a fish bowl.
So for a given area, a window that is elongated vertically allows for more variation in eye height than a circular one where the viewing area is equally distributed vertically and laterally, and provides more fuselage structure between the windows (important as an inflated tube in circular tension, or under "hoop stress").
The 787 went with very large passenger windows to take advantage of the carbon structure and bring as much light inside as possible.  But they still stayed with the round-corner vertical rectangular shape so that short and tall people both get a good view.
The CRJ200, as a corporate jet derivative, suffered from very small windows that were set low, and if you're ridden in one and are tall, you have to bend over to see out.  When the follow-on model, the 700, was in development, a lot of work went into moving the windows up and enlarging them so that most people got a decent view (actually it was solved by moving the floor down a bit).
And finally, actually the Gulfstream's windows aren't round, but ovalized horizontally.  This is likely to accommodate lateral seating variations as a priority over vertical variation because of the corporate seating arrangement and is disadvantageous structurally in terms of the fuselage tube's hoop strength.


Why does pulling the mixture to idle cutoff increase the RPM slightly?

Engine are usually run slightly richer than a stoichiometric mixture, to ensure reliable running and avoid overheating the pistons and valves. When you cut off the fuel, it goes from slightly too much fuel to none - and so it's briefly at a stoichiometric ratio.

The engine runs slightly faster at this ratio because it's not wasting energy heating up unburnt fuel.

If you see more than a 50rpm rise, it was previously running further from stoichiometric than necessary (as determined by the engine manufacturer, and many years of experience), reducing power and wasting fuel.


Why was the U-2 so different from the SR-71?

Because the requirements were different. When U-2 was developed, the requirement was for an aircraft which would fly high at 70,000' due to the (mistaken) belief that the Soviets would be able to detect and engage aircraft only below that altitudes.

Once the U-2 entered service however, it became obvious that they could detect U-2 (they complained about the overflights, though misidentifying the aircraft), and once an aircraft was shot down, it became obvious that U2 isn't going to be of much help.

SR-71, which came later, was the result of a requirement which expected it to not only fly higher, but more importantly, faster. Interestingly, the Soviets went the same way with the Mig-25R.

The main reason for the retirement of spy aircraft was the advent of reconnaissance satellites, which are immune to being shot down (not that it is impossible, but no one has done it except in tests). Spy aircraft are still operated only over areas where the threat from anti-aircraft systems are extremely limited or non-existent. At the time of its retirement, the USAF accepted that even the SR-71 is not invulnerable:

  In congressional testimony, Air Force Chief of Staff Gen. Larry D. Welch identified the increased survivability of reconnaissance satellites, SR-71 vulnerability to the Soviet SAM-5 surface-to-air missile and the cost of maintaining the SR-71 fleet.

As for why U2 has outlived the SR-71, the main reason is the operating costs- the operating costs of SR-71 is quoted to be anywhere from \$85,000 to \$200,000 per hour, while the U-2 costs much less than that (incidentally, U-2s operating cost is less than that of its proposed replacement, the RQ-4 Global Hawk).

From the same source as above:

  The Air Force decision to retire the Blackbirds in 1990 is based on several factors. ... The cost factor is the most significant to the Air Force because it limits expenditures in other areas. Reagan Administration Air Force Secretary Edward C. Aldridge Jr. estimated that the money used to operate the SR-71 fleet could operate and maintain two tactical fighter wings.


What type of helicopter is shown in Star Wars The Last Jedi featurette?

The helicopter is a Eurocopter EC135 T2+. The registration (just above the tail rotor) EI-ILS shows that this aircraft was registered in Ireland, this helicopter was sold to PDG HELICOPTERS in early 2016 and is now on the U.K. register as G-GLAB. Based on this information it suggests that this particular segment was filmed before or shortly after early 2016 when the aircraft would likely have been re-painted with the new registration.

Eurocopter are a popular "household name" in aviation with numerous models operated throughout Europe and beyond in various roles such as airborne policing, medical flights (air ambulance), and some military operations. Eurocopter now operate as "Airbus Helicopters" and subsequently the EC135 has been re-designated as the H135.


Is Cessna 150 with incorrectly marked ASI airworthy?

Take a look at the equipment list of the Cessna 150.  There are part numbers for every piece of equipment installed.  If the part numbers do not match, then the airplane does not comply with its type certificate data sheet and is not airworthy.  Take a look in the maintenance manuals and find the part numbers.  If the rental FBO refuses to let you see those manuals find a different FBO to rent from.
Unfortunately, that is not the whole story.  There are also other ways for this to be an airworthy airplane:

PMA part.  If the new airspeed indicator has been approved as a direct replacement parts manufactured approved part, it can go in along with the equipment necessary to make it work.  I doubt this is the case as the part would have to be FAA approved for that airplane.  The most common application of a PMA approved part is the installation of LED bulbs for incandescent bulbs.

STC.  The airplane has a supplemental type certificate that modifies the airplane in such a way the new airspeed indicator markings are required for the STC.