Why can't helicopters or Zeppelins drop fire-fighting material on burning buildings?

First, they have been used, like in case of the Federation tower fire in Moscow on 2012. The image below shows a Kamov Ka-32A11BC being used to fight fire in that case.

Helicopter fighting Federation Tower fire in Moscow; image from dailymail.co.uk

According to a news article

  The Ka-32A11BC proved its fire-fighting credentials in April 2012, when a blaze engulfed ... the 67th floor at the Federation Tower in Moscow, Russia, more than 270 meters above ground level. ... the fire was only contained after two Ka-32As belonging to the Russian Emergencies Ministry were called into action and ferried in water from the nearby Moscow River.

However, there are multiple issues in using helicopters for urban firefighting.

Helicopters are all but powerless is case of fires breaking out over the lower floors. Even in the above case, the helicopters were useful only as the fire broke out in the top floor of the (then under construction) skyscraper. For lower floors, the helicopter would have to carry the spraying equipment in the fuselage, which would make the useful payload impractical. Airships are all but useless in this case, while even helicopters would have difficulty getting through the buildings.
Firefighting using helicopters is not a precision business as it would be difficult to position the helicopters directly overhead due to the intense heat and the turbulence produced. For safety, the helicopters have to fly higher, which reduces efficiency due to winds.
Aerial firefighting is a costly business. As LA times puts it:

  It costs up to \$14,000 a day to keep an air tanker on call and as much as \$4,200 per hour to put it in the air. Heavy-duty helicopters, the workhorses of aerial firefighting, can cost \$32,000 a day on standby, plus \$6,300 per hour of flight time.

and this in the US where the need to put out forest fires is all but certain.  Major fires in skyscrapers are infrequent and too scattered around the world to justify the expense of keeping a helicopter on standby in any given city.
The crew have to trained for this- firefighting is a dangerous business:

  But unpredictable atmospheric conditions make flying over wildfires difficult and dangerous. Thirty-seven firefighters have died in aerial firefighting accidents in the last decade.

Urban environment with high rise buildings and power lines pose a separate set of challenges.
Water and firefighting slurry supplies have to made available- this is important in cases where for example, the rivers are seasonal. Not only is the normally used firefighting slurry costly, it is also not environment friendly.

  ... the slurry, which is rich in nitrogen, can harm fish, wildlife and watersheds, despite agency guidelines to prevent drops onto vulnerable areas.

  Aerial firefighting is expensive. Tankers cost upwards of \$6,000 per hour to operate. The slurry itself averages about \$2 per gallon, and the Forest Service used almost 9 million gallons of it last year.

Airships have the same issues, and some more (payload and speed/maneuverability come into mind).


Do some airplanes have weighing scales on the landing gear?

Yes, such system exists, for example the Honeywell WBS.* It was developed during the sixties and installed as an option on the Boeing 707-300 freight aircraft. Other aircraft that had a similar (optional) system include the L1011 and Boeing 747.

It is mostly found on freight aircraft because they have a less predictable load distribution (centre of gravity) than passenger aircraft.

The reason they are not common is that they add cost in the form of installation, weight and maintenance. While quite accurate when in good condition, the reliability of the weighing systems used to be poor, which probably contributed to the fact they never became wide spread.

Because crew are commonly operating on several aircraft types these days that have take-off weights of more than 100 metric tonne difference (e.g. A330 and A340, B747-400 and B747-8) there is an increase in take-off weight confusion related incidents. This, combined with the fact that systems are becoming more reliable, makes it likely that these weighing systems will be used more in the future.

* An advert for it in a 1987 Flight issue.


According to Boeing (on the "interesting facts" page on the (former) tour website for their Everett facility) their 767 aircraft contain...

...3.1 million parts in a 767 provided by more than 800 international suppliers.
Boeing 767 Facts - Boeing.com


How much operating documentation is produced for an airliner by the manufacturer?

But, just how much documentation would actually be delivered to the customer? Could it indeed be 170+ tonnes' worth?

The days of delivery of air carrier aircraft technical manuals being delivered by paper manuals are over, so it's certain that 170 tonnes of paper aren't now delivered. Whether or not, if you printed one copy of every manual available and then weighed them, that would reach 170 tonnes per airplane, I have no idea. That sounds a little high though to me, but if you included the weight of all of the engineering paper generated back when they actually produced blueprints, that would certainly be very substantial.

Boeing, as an example, delivers manuals as PDFs, perhaps by other means as well.

A few points:

The carrier gets what they need, and that will vary greatly. For example, if the carrier is receiving a passenger airplane, there's no need for them to have documentation concerning pallet tie down information for the aircraft's main deck.
Manuals need to be updated, and now you just get an current PDF rather than a few pages to be inserted in paper copies you already have.
Individual airplanes get manuals that are customized for that airplane, so you're talking about a lot of different manuals for a model of aircraft.
If the airplane goes through a modification program, the company doing the modification will typically supply manuals (also digitally) that deal with the modification. This is especially true for older passenger aircraft being converted to freighters.

Boeing supplies sample manuals for information expected to be common across variants of a model. Here's a 767-300F sample manual link. Of course, the information in an airplane's individual manuals takes precedence over that in sample manuals.

Perhaps if you printed every copy of every manual of every update, maybe you would get to the weight of a single aircraft of that model.


What is the impact of one trailing edge rotary actuator failing?

The 747 has two motors per flap group.  The primary means of moving them is through a hydraulic motor, while the second motor is a backup electric motor which is only used if the primary doesn't work correctly.

There are also two groups of flaps on each wing, and they are mechanically linked to the same flap group on the other wing so that they always extend at the same time.

You are correct about a failure on the ground.  The pilots would take the airplane back for maintenance before they departed.

In the unlikely event that both the primary and secondary motors failed, or if the flaps were to somehow become jammed and not extend once airborne, the flaps would not be able to do their job.  Since they wouldn't make the wing bigger or change it's shape to create more lift, the aircraft would be forced to land at a higher airspeed, which would cause it to use more runway.  This isn't a big deal if there is sufficient runway at their destination, but if not they would have to divert to a suitable airport.


What is this F-18 Hornet "air intake" for?

It's for keeping the boundary layer flow from entering the intake, it's called a splitter plate. I think it's done to prevent turbulence inside the turbine (prevent compressor stall) and to make sure the intake doesn't ingest slow air, to maximize efficiency.


Relation between lift force and torque produced in propeller used for vertical take-off and landing aircrafts

The relationship of torque produced by the engine and lift force will be the drag of the rotor.  Increase in lift force by increasing rpm or AOA will require a proportional increase in power output from the engine.  Air density also plays a role.
With a common helicopter, torque is counter balanced by increasing or decreasing torque of the tail rotor.


I just watched at least 20 airplanes flying northeast over Washington, DC every 15-20 seconds, what were they?

This is very likely the "train" of satellites from Launch 5 of SpaceX's Starlink constellation. They have about that spacing at the moment, there are 60 of them, and the timing is about right. I saw them myself last night over Nevada.


Water salutes are purely ceremonial and have no practical value. There are no confirmed reports on when it started in aviation, but it became common in the 1990's.

Before aviation, this practice started for ships on their inaugural voyages or returning from a long voyage. At New York harbor, jets of water were sprayed from fire boats.

Commonly, water salutes are done for:

first flight of an airplane
first or last revenue flight of an airplane
last flight of a retiring pilot
carrying a fallen soldier

Mostly, it attracts attention and looks cool without costing a huge amount or having anything to clean up.


Is special equipment required to perform high-voltage line inspections?

I work in this area and, to my knowledge, I never heard about any special aid to help the pilot. They know precisely which are the wind speed limitations to do the work safely, the rest is basically skill.

What they do install in helicopters, is the so called Wire Strike Protection System (WSPS), which should cut the cable if the helicopter strikes it, avoiding damages on the main rotor (see the picture https://upload.wikimedia.org/wikipedia/commons/b/bf/Ntsp-oh58-N170FR-070205-01cr.jpg that Bell has two WSPS, one over the cabin another underneath the avionics bay). But this is more important on power line inspection, which is made at around 60-80 km/h with cameras and LiDARs. When the helicopter is hovering by the cables this doesn't bring much aid.

But this is a risky job anyway and if you search, you will find plenty of accidents which happened with helicopters and power lines.


How is altitude correlated with true airspeed?

(Airbus via SKYbrary)

Is it true that for a given specific aircraft there is a single specific TAS that aircraft can travel on given FL (due to wings lift forces produced, etc)?

Above shows a common climb profile, and is the best illustration to the main title question. As you can see, what the plane would typically be programmed to target is IAS or Mach.

Related to that point and graph:

How is the airspeed-Mach number transition handled in modern airliners?
What is the reason for changing the speed reference (IAS or Mach number) with altitude?
How did ICAO SARPS come to include the 250 knots speed limit for aircraft below 10,000 feet?

I thought aircraft are capable of traveling with a range of speeds at given altitude depending on Angle of Attack (AOA).

There are ranges of speeds, but the economic range (see: What is Cost Index?) is not that big (approx. ±20 knots), and the dataset you have simply shows the typical value ATM can expect, for simulation purposes for example as the website says:

  The BADA APM is designed for simulation and prediction of aircraft trajectories for purposes of ATM research and operations. Aircraft performance parameters and trajectories can be calculated using information and data contained in BADA.

The filed flight plan would also include the planned TAS for the different flight levels, and as long as the pilots don't deviate by more than ±5%, they don't need to notify ATC.

Or maybe what I am looking at (...) the only one FL+TAS pairs that makes sense in practice (as flying otherwise would be highly inefficient).

In essence, yes. Also worth pointing out is that a lightly loaded jet-liner would typically aim to fly higher if permitted and if possible. The same is true even for short-haul flights (What should be the minimum time spent in cruise (for e.g. a B737)?). So basically optimization is solved by aiming for the optimum FL.


What is the typical value of maximum lift coefficient for aerobatic aircraft?

First, don't take the two-dimensional value from an airfoil chart and use it for the full aircraft. Subtract 15-20% for wingtip margin and fuselage influence. Wingtip margin means that the wing is less loaded towards the tips to keep a lift margin for aileron control and to avoid a tip stall.

Next, aerobatic aircraft have lower maximum lift coefficients than GA aircraft. Their wing loading is lower, so they can afford this. A symmetric airfoil mounted at zero incidence has proven to be the best choice, and while some older aerobatic aircraft use cambered airfoils, the camber creates a distinct disadvantage in transitions from normal to inverted flight and vice versa.

And last, the maximum lift coefficient depends on quite a list of parameters. If you need a value for the calculation of structural loads, make sure you add enough strength to cover the increased lift possible with high pitch rates.

If you need a figure for a single-seater piston-powered aerobatic aircraft without flaps for the estimation of minimum speed, use a lift coefficient of 1.3.


How criminal is it to take off without authorization?

The FAA has limited ability to enforce criminal actions for non-compliance with FAR's. Essentially the pilot (certificated or not) would be subject to either Informal Procedures/Settlements, Certificate Actions, or Civil Penalty.

The FAA's policies, procedures, and guidelines are located in the FAA Compliance and Enforcement Program, Order 2150.3B.

In the case of stealing an aircraft by a non-certificated individual, the only recourse the FAA would have is civil penalties. The authority for the FAA is located in 14 CFR 13.14 or 13.18. The FAA has the authority to issue civil penalties up to \$400,000 against "persons other than individuals and small business concerns" (aka large businesses) or for individuals and small businesses up to $50,000.

In the case of the stolen aircraft, the charges would probably be theft and whatever other federal/local charges could be levied, but the FAA would probably not intervene here.

Teen aircraft thief sentenced to 13 months in prison (60 days served)
Felony theft charges for stealing airplane
Barefoot Bandit

It isn't strictly "illegal" to disobey an ATC "order". A PIC (supposing they are a licensed pilot) can disregard ATC if they feel that the safety of the flight would be in jeopardy if the order was followed. Specifically this is allowed by JO 7110.65W, page 3-3-1 and 14 CFR 91.123.


Do helicopters need a class B entry clearance when air / hover taxiing?

No. Hover taxiing with a helicopter follows the same regulations as taxiing with an aircraft (or helicopter) on wheels.


What does the term "tanker" mean when used in regards to a passenger airliner?

Since the 1960's and 1970's when political hijackings were a problem, airplanes started to only carry the fuel required for the flight.  This means a typical fuel load will be something on the order of:

taxi fuel at the departure airport
fuel to fly and land at the destination at a given altitude and forecast winds
if an alternate is needed:

fuel to fly to the alternate airport

45 minutes of reserve fuel
perhaps a bit extra for contingency and to keep captains happy (e.g. 5-15 minutes worth of fuel).

For a normal flight this means you'll land with around 45-60 minutes of fuel on board, sometimes less.  You'll fill up for the next leg at this airport while you deplane and enplane passengers.

Fuel at the hub airports is sometimes a bit cheaper due to the fuel contracts the airline can secure when they order massive amounts of fuel every day.  Fuel at outstations that don't see a huge volume of fuel may be quite a bit more expensive.  In this case, and if your weights allow, the airline may elect to load extra fuel that isn't needed.  The purpose of this is so you do not need to buy as much fuel at higher prices at the outstation.

I only saw this happen operationally when we were going to be very light and the outstation fuel was very expensive.  Usually our loads were high enough that we were struggling to get all 50 passengers, bags, and especially jumpseaters on board with the required fuel load.  In that case it would not be economical to take more fuel because we'd have to take fewer passengers.


Who operates delivery flights for commercial airlines?

When I worked for Boeing as an intern in 2000, I got to see Boeing’s wide body delivery center in Everett, WA.  Back in those days at least, the airlines brought out a crew of lawyers, aircraft brokers and test pilots.   Typically what happened was the airline’s test pilots would take the new aircraft up for a check flight with Boeing’s factory test pilots.  This consisted of flying the aircraft from KPAE east to Moses Lake (KMWH) where they would shoot a couple of approaches and test the avionics and systems on the new airplane, then fly west out past KPAE over international waters where they, at least technically, “bought” the airplane.  Doing this outside the boundaries of the US allows the airlines to avoid paying 8% Washington State sales tax on a $200 million airplane.  The test flight concluded, they returned and landed at KPAE.  After that the airline’s lawyers and broker met with Boeing’s lawyers and a purchase price was agreed upon.  A phone call was made and the funds were electronically transferred from The airline’s bank accounts to an account belonging to Boeing.  After that, the airline’s test pilots flew the airplane out and put it into immediate service.  Typically if the airline had scheduled service from KSEA the airplane was flown on a short VFR hop down to SeaTac and parked at a gate, where it was immediately prepped and began passenger service.  When I was there, Aeroflot took delivery of a 777 which was flying from Seattle to Moscow the very night the airline took delivery.  Other strange things are negotiated in the purchases.  Cathay Pacific once made a deal with a WA state cherry co op along with the purchase of an 747-400F; the airplane flew back to China brand new with 20,000 lbs of bing cherries aboard!


Is a new type of TSA pre-approval required before commencing flight training?

(Answer completely rewritten based on new information)

Does the TSA plan to implement rules that require every prospective student to seek pre-approval from a government agent (not just a flight school) prior to beginning flight training?

Not exactly. US citizens can still start flight training whenever they want. But from April 1, 2016 pre-approval from "a government agent" (the TSA) is required prior to soloing. Foreigners will still need TSA approval before starting flight training.

The final rule on this has now been published in the Federal Register and the TSA will indeed vet all student pilots, as of 1 April 2016 (my emphasis):

  This action requires  applicants to apply for a student pilot
  certificate through a Flight Standards  District Office, designated
  pilot  examiner, airman certification  representative associated with
  a pilot  school, or certified flight instructor.  Aviation Medical
  Examiners will no  longer issue a combination medical  certificate and
  student pilot certificate.  Student pilot certificates will be issued
  on the same medium as other pilot  certificates and will have no
  expiration  date. All student pilot certificates issued  before the
  effective date of this final rule  will expire according to their
  terms  unless they are replaced by another  pilot certificate. This
  final rule responds  to section 4012 of the Intelligence  Reform and
  Terrorism Prevention Act  and facilitates security vetting by the
  Transportation Security Administration  of student pilot applicants
  prior to  certificate issuance. This action  withdraws the proposal
  for pilot  certificates to include a photograph of  the individual
  pilot.

But note that a student pilot's license is still not required in order to start training, it's only required in order to solo. So under this new rule, a US citizen can start flight training as usual, but can't solo until he gets TSA approval for his student pilot application:

  IRTPA [the Intelligence Reform and
  Terrorism Prevention Act] required that security vetting  of all individuals, including
  pilots, must  be successfully completed by TSA  before the FAA issues
  a certificate.  Therefore, applicants for student pilot  certificates
  must be vetted to receive  their certificates and operate an aircraft
  as pilot in command.

This also means that AMEs will no longer issue student certs, only medical certificates. The FAA expects that processing will take several weeks, which may be an issue for accelerated training programs that aim to get you a full pilot's license in a month or less:

  The FAA estimates that the  turnaround time for student pilot
  certificates can be reduced to an average  of 3 weeks or less,
  provided that initial  security vetting by TSA indicates that  the
  applicant is eligible for the  certificate.

There was also some concern that it wouldn't be possible for pilots to solo on their 16th birthday any more because of the processing time, but the FAA specifically addressed that point, essentially by asking students to submit their application well in advance.

On the 'plus' side, the new regulation specifically says that pilots licenses will still not have a photograph (at least for now), which would have added more time and costs to the whole process. And the new student certificates will be plastic, not paper.


Would formation of the three planes benefit from increased distance of the ground effect?

I would think not; the ground effect comes from the wing pushing air down, which would not help the plane in the middle. If anything, I think the plane in the middle would be impacted by the wingtip vortices created by the larger planes, once out of ground effect (one wingspan above the ground) if the smaller plane did not stay ahead of the larger planes.
http://www.pilotfriend.com/training/flight_training/aero/wng_vort.htm

A position slightly behind, drafting like birds in flight do when they fly in V formation, might help.
https://www/ciencemag.org/news/2014/01/why-birds-fly-v-formation


Can you breathe with a drop down mask under water?

No, you cannot - at least not with the default masks.

In principle, the oxygen systems on board can all provide at least 15 mins. of oxygen, in some of the worst conditions (indeed, that's what they're designed to do). However, their sole purpose is to make high altitude air breathable. The key principle here is partial pressure. Basically, the partial pressure of a gas is the fraction of a certain gas in a gas mixture times the ambient pressure. Since normal air consists of about 21% oxygen, the partial pressure of oxygen at sea level is 0.21 atm (atmosphere). If the partial pressure of oxygen is too low, your lungs actually lose oxygen to the atmosphere when you breathe - much like a deflating balloon.

When the cabin pressure drops, the partial pressure of oxygen drops proportionally. In that case, oxygen masks are provided. They do not raise the pressure of the air you breathe in, but raise the partial pressure of oxygen by filling your mask with oxygen. If the cabin pressure would drop to 0.2 atm, and you would be given 100% oxygen, the partial pressure of oxygen would be 0.2atm, which is about the same as at sea level - perfectly survivable. The mask as such does not need to be airtight - it just needs to make sure that there's enough oxygen flowing into your mask to displace all the useless nitrogen in the air. Indeed, the mask you will see on airplanes are generally flimsy, plastic masks.

Under water, these masks are not sufficient at all. They will probably turn into a frothy, bubbly mess of a water/oxygen mixture, especially when the aircraft is filling up with water, due to strong currents. So, you would have to wait for the currents to diminish, and then hold your oxygen mask in such a way that no water will enter it - this probably means you will have to face upwards all the time.

Of course, you can get creative (pull the mask of and breathe from the tube), or luck out with a high quality mask that happens to work underwater. But I'm afraid that as soon as your plane is sinking, it's too late to play the hero, and your best bet would be to get out and at least save your own life.


Do the speed brakes on an F-16 change its pitch?

Because the speed brakes are tail mounted, and because they deploy upwards and downwards equally, pitch should not change.  The airplane's fly-by-wire system likely dampens any slight pitch changes caused by the buffeting.

The only photos I've seen of the speed brakes open are of them fully open, not partially open.  So they may open gradually with different deflections up and down, or with different resulting air loads up and down, or both, or neither.  But in any of those four cases, the FBW should correct for pitch excursions by deflecting the other control surfaces.


What is the commercial passenger aircraft top speed record?

"Speed" is not a singular term in aviation. There are many different ways to measure speed. See for example Why is there a difference between GPS Speed and Indicator speed? Most commercial jets cruise with a true airspeed in the range 400-500 knots and an indicated airspeed in the range 200-300 knots.

For the purpose of passenger transportation, ground speed is interesting since it is a determining factor in how long it takes to get from A to B. But do note that ground speed has relatively little to do with aircraft performance, since two identical aircraft could have vastly different ground speeds if one was flying in a headwind and the other in a tailwind.

According to groundspeedrecords.com, the fastest ground speed ever recorded for a commercial aircraft is the Concorde with a record of 1205 knots. This website relies on pilots snapping a picture and uploading it to the site as proof, so it is possible that that record has been broken without it being recorded.

Excluding the Concorde, which is no longer in service, the fastest record is a Boeing 747-400 recorded at 752 knots in 2010. At the time of reaching that speed, the aircraft had a 213 knot tailwind (probably flying in a jetstream).


What is the difference between SUA and SAA?

SAA is a project being undertaken to unify how SUA's (and ATCAA's) are defined, managed, and shared.

  [SAA will] define SUAs and ATCAAs in a consistent manner using an editing tool
  Use a Service Oriented Architecture (SOA) to distribute that data to interested users
  Manage the schedule and status of those airspaces through a SOA.

SAA is part of the System Wide Information Management (SWIM).

In short, SAA encompasses SUA, ATCAA, etc.

Source: SAA Modernization (.ppt file)


Where can find Service Ceiling of an aircraft?

It is in the pilot handbook, before the title page [PDF], under "performance-specifications"


What are the differences between the MiG-15 and MiG-17?

I'm surprised no-one's mentioned the length - the MiG-15 has a much stubbier appearance than the MiG-17, because it was rather shorter (10.10m vs 11.26m)

The wings of the MiG-17 are angled at 45°, rather more than the MiG-15 (helpful to identify from above), and the tailplane is has a small amount of extra rake too.

Overall, the MiG-17 has a longer, sleeker profile than its older cousin. Here's a comparison, 15 in blue, 17 in red.


Why do some helicopters have wheels instead of skids?

AOPA has a nice little blog post on the matter

  Skid landing gear is simple and lighter weight, so it is the best
  choice for small helicopters as weight is always a consideration.
  Also, skid landing gear needs very little maintenance, but the
  drawback is that ground handling is more difficult.

And for wheels

  On larger more powerful twin-engine helicopters weight is not as big
  of a concern and retractable wheels make sense. Wheels are nice
  because a helicopter can ground taxi (as opposed to hover taxi) around
  other aircraft and people without worrying about producing a high
  downwash. Retracting the gear also reduces drag, allowing for a higher
  cruise speed.

So skids are light and simple and wheels are convenient when you have the useful load and space.

This article also notes thats skids are preferred when parking on an non-level surface
to prevent accidental rolling around and or sliding off the deck of a carrier.

This article offers more info from the pilots perspective but comes to basically the same conclusions.

The answer seems to be that they are chosen based on the mission profile of the helicopter as well as the size to some extent.


It's an expression of power required to maintain level flight throughout the speed range of the airplane and forms a U shape.  The lowest point of the curve, bottom of the U, is the point of minimum power required for level flight and is normally just below maximum L/D speed (flattest glide speed).  To go faster moves up the U to the right and requires more power.  To go slower moves up the U to the left and also requires more power.

The main bogey man that pilots have to be aware of is the issue of being on the "back side". If you slow to below min power airspeed, slowing any more will require more power to keep from descending; that's the back side.

This becomes a crisis situation in marginal conditions, especially when flying at very high altitudes, and is one of the things that makes flight at the upper flight levels riskier than at lower altitudes; if you are flying at Min Drag  speed or close to it at service ceiling, say FL410, and fly though some down flowing mountain wave air that is sinking at 100 fpm (nice smooth air that you likely won't notice), the autopilot in ALT hold mode will just pitch you up to keep from descending and the jet will slow down.

If you aren't paying attention and let the speed bleed off too much, you will find yourself in a pickle entering the back side of the power curve, with little reserve thrust to speak of, and will have no option but to tell ATC you have to descend NOW and start down until you can recover your speed.


How do I include a STAR in an ICAO flight plan?

ICAO Doc 4444 Appendix 3 has the clearest text (and an example):

Standard arrival route
The designator for the standard arrival route from the point of leaving the defined route to the point at which the approach procedure is initiated.
Note.— Standard arrival route need only be included where appropriate.

Let's break down the language:
"The designator for the standard arrival route from the point of leaving the defined route to the point at which the approach procedure is initiated."
Which means:
(defined route – airway)
(last applicable point on airway)
(first point on STAR)
(STAR designator)
In the example given (below), both points are shared (FTM), similarly for the SID – emphasis mine:

N0460F290 LEK2B LEK UA6 FNE UA6 XMM/M078F330 UA6N PON UR10N CHW UA5 NTS DCT 4611N00412W DCT STG UA5 FTM FATIM1A

(Highlight mine.)


Can I file a VFR flight plan for a training flight?

Absolutely. In fact it's not a bad idea to do so, if only to get some practice filing flight plans and using the system.

In the US VFR flight plans are a search-and-rescue tool: They're only used if your aircraft is overdue to give the rescue folks information to help plan the search.

In your particular case I would file a flight plan that lists your home airport as your departure and destination, with the airport you intend to use for your touch-and-go landings as an intermediate waypoint.  If you want to enter information on the nature of the flight (training, touch-and-gos at XXXX, etc.) in the remarks field you can do that too.

Activate the flight plan when you depart, and close it when you return to your home airport. You can optionally also call Flight Service over the radio when you get to the touch-and-go airport to give them a position report and let them know you've reached that waypoint (I would do this on your way out of the area to return home, along with an ETA update if appropriate).

As an alternative (or in addition to the VFR flight plan) you could get flight following from the ATC facility responsible for your airspace. Be aware that they may drop you and ask you to squawk VFR while you shoot your touch-and-gos since you'll probably be going off their radar, but you can always request service again when you start your return leg.


When leaving ground effect, why is there a nose-up change in moment?

The aerodynamic centre of a wing shifts when it is in ground effect. Out of ground effect, the wing produces lift by accelerating air downwards. In ground effect the ground prevents the air from being deflected downwards, and more lift is produced due to increased pressure underneath the wing. This pressure has a different distribution than out-of-ground effect pressure, hence the change in pitching moment.

Consider a cross section of a wing: free stream lifting force centre is at the quarter chord point. If the wing was supported by just static pressure only, like a hovercraft, the force centre point would be at 50% chord.

  Actually not sure now if the horizontal tail has much influence but
  I'll leave the original answer underneath:

Ground effect works by increasing static pressure underneath the wing and the horizontal tail. The aircraft flies out of ground effect in a nose-up attitude, and depending on tail configuration it can be possible for the main wing to be out of ground effect while the horizontal tail still experiences increased pressure underneath, therefore creating a nose-down pitching moment. Once the horizontal tail flies out of ground effect as well, the nose-down pitching moment disappears. I would not expect that T-tails have this change in pitching moment but I have never flown one.


Why is fuel usage discussed per time, not per distance?

Unlike with driving, in aviation the major variable when planning fuel consumption isn't how far you're traveling but how long you're traveling: Distance traveled in aircraft is a derived value (calculated from groundspeed and time - groundspeed also being a derived value affected by many factors including wind).

A pilot may not readily know their groundspeed (it can be quite different from airspeed), but at a given power setting they know an engine will burn a specific quantity of fuel per unit time, therefore fuel consumption is generally expressed that way (in gallons per hour or pounds per hour), and if they know how long they've been flying they can reliably estimate how much fuel they've burned, how much is left in the tanks, and how much longer they can keep flying before running out of fuel.

To illustrate why this is superior for flight planning consider the following (extremely simplified) flights fitting the following profile:

A 200 nautical mile trip
An airspeed of 100 knots
A fuel burn of 10 gallons per hour
A 25-gallon fuel tank.

Scenario 1: No Wind
With no wind the flight will take two hours to complete.
The groundspeed is 100 knots.
The aircraft will burn 20 gallons of fuel.
The fuel efficiency is 10 miles per gallon.

  In this scenario we land with 5 gallons of fuel left in the tank - that corresponds to 30 minutes, which is the minimum legal reserve for day VFR flight per FAA regulations.

Scenario 2: 25 Knot Headwind
With a 25 knot headwind the flight will take about 2:40 minutes to complete.
The groundspeed is 75 knots.
The aircraft will burn 27 gallons of fuel.
The fuel efficiency is 7.5 miles per gallon.

  In this scenario we run out of fuel 2:30 into the flight. Running out of fuel is generally considered to be a Bad Thing: The passengers complain, and the FAA asks a lot of uncomfortable questions.

Scenario 3: 25 Knot Tailwind
With a 25 knot tailwind the flight will take about 1:40 minutes to complete.
The groundspeed is 125 knots.
The aircraft will burn 16 gallons of fuel.
The fuel efficiency is 12.5 miles per gallon.

  In this scenario we land with almost an hour of fuel still in the tank - a very comfortable reserve.

On longer flights, and in slower aircraft, the effects of wind can be extremely pronounced, and a 5 or 10 knot difference from the forecast winds can mean the difference between arriving at your destination or having to add a fuel stop.


Are most/all flights affected by a noticeable amount of turbulence?

It's very difficult to answer this question as it depends upon so many different things:
 - Location
 - Time of day
 - Season
 - Flight level
 - Terrain below
 - Current weather (of course)
 - Type of aircraft
 - The crew and their knowledge / weather radar use.

What also makes it hard is that what 'feels uncomfortable' for one person might not for another.

In the tropics it's quite common for flights to be affected by turbulence. Most will see at least some light chop. In my experience of a few hundred long-haul flights through the tropics I've only had a couple with no moderate turbulence (what you might call uncomfortable). In a similar number of short-haul flights in Europe I'd say that around 50% had no significant turbulence at all and only around 5% had moderate turbulence.

You're more likely to experience turbulence in the tropics as there's a lot more convective activity there (air rising and falling). Away from the tropics the USA tends to generate turbulence whilst Europe does not (relatively speaking). SE Asia is particularly well known for turbulence encounters.


How common is an airliner activating reverse while still in flight?

The system will allow deployment based on various criteria, and radio altitude height may be one of them, so even for a system not designed to operate "in flight", you still can deploy the TR's a few feet off the ground. Pretty ugly, rough touchdown when you do, though, and certainly not advised. How often that happens would be speculation, but probably very rare.


Factors to be considered when re-engining aircraft

This depends greatly on the engine. However, given the 737 MAX situation, I'll assume you mean re-engining with larger, more efficient engines. This still leaves a lot of room for interpretation- what aircraft are we working with? Something like the 757, with tons of ground clearance? Or something like the 737, with very little clearance? I'll answer both.
In the first scenario, re-engining a 757, there's not a WHOLE lot that needs to be changed. The engine mount/pylon, wing structure (to account for a heavier engine), and maybe the FADEC. That's really all I can think of. Maybe the fuel system.
The second scenario is where things get interesting. If you want to avoid a 737 MAX style situation, you'll need to extend the landing gear legs and find some way to stow them. If you can't find anywhere on the airframe that's beefy enough to accept that, then you'll have to find an ideal spot and reinforce it. Then change everything that I mentioned in the first scenario.
I'm no aerospace engineer, and I'm sure I'm missing countless things here, but these are all the major things that I can think of.


Why do Vx and Vy coalesce at an airplane's absolute ceiling?

I think the answer to your question lies in the fact that approaching the absolute ceiling, the terms "climb rate" and "angle of climb", in regards to an airspeed, begin to lose their meanings.

As a plane approaches the absolute ceiling, the climb rate will be zero or close to zero, so the best angle of climb approaches 0 degrees above the horizontal plane as well making your "best-rate" speed also be your "best angle" speed; both the rate of climb and thus the angle of climb being, effectively, zero.

Any speed which yields less than the best rate of climb (if you want to call it that) of zero at the absolute ceiling would be causing a descent, and thus a negative angle of climb as well making any speed other than the best rate of climb speed also not be the best angle of climb speed, which is why that is the altitude at which best-rate and best-angle speeds coalesce.


Are there any helicopters equipped with pressurized cabins?

Helicopter cabins are not usually pressurized as they are not expected to be operated at high altitudes.

The largest operational helicopter, the Mil Mi 26 Halo has a pressurized crew cabin.

The Russian Mil Mi-24 Hind and Mil Mi 28 Havoc feature pressurized cockpits. However, these are for operating in an NBC environment, not for high altitude operation.


Which regulations require the ARROW documents?

It is in several places:

Airworthiness Certificate  FAR 91.203
Registration Certificate FAR 91.203
Radio Station License (international flights only)
Operating Handbook FAR 91.9
Weight and Balance FAR 23.1589

CFR 91.9:

  (a) Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry.

  (b) No person may operate a U.S.-registered civil aircraft -

    (1) For which an Airplane or Rotorcraft Flight Manual is required by § 21.5 of this chapter unless there is available in the aircraft a current, approved Airplane or Rotorcraft Flight Manual or the manual provided for in § 121.141(b); and

    (2) For which an Airplane or Rotorcraft Flight Manual is not required by § 21.5 of this chapter, unless there is available in the aircraft a current approved Airplane or Rotorcraft Flight Manual, approved manual material, markings, and placards, or any combination thereof.

CFR 23.1589:

  The following loading information must be furnished:

  (a) The weight and location of each item of equipment that can be easily removed, relocated, or replaced and that is installed when the airplane was weighed under the requirement of § 23.25.

  (b) Appropriate loading instructions for each possible loading condition between the maximum and minimum weights established under § 23.25, to facilitate the center of gravity remaining within the limits established under § 23.23.

FAR 91.203

  (a) Except as provided in § 91.715, no person may operate a civil aircraft unless it has within it the following:

  (1) An appropriate and current airworthiness certificate. Each U.S. airworthiness certificate used to comply with this subparagraph (except a special flight permit, a copy of the applicable operations specifications issued under § 21.197(c) of this chapter, appropriate sections of the air carrier manual required by parts 121 and 135 of this chapter containing that portion of the operations specifications issued under § 21.197(c), or an authorization under § 91.611) must have on it the registration number assigned to the aircraft under part 47 of this chapter. However, the airworthiness certificate need not have on it an assigned special identification number before 10 days after that number is first affixed to the aircraft. A revised airworthiness certificate having on it an assigned special identification number, that has been affixed to an aircraft, may only be obtained upon application to an FAA Flight Standards district office.

  (2) An effective U.S. registration certificate issued to its owner or, for operation within the United States, the second copy of the Aircraft registration Application as provided for in § 47.31(c), a Certificate of Aircraft registration as provided in part 48, or a registration certification issued under the laws of a foreign country.

The other "R" for the radio station license was in the FCC documents, but since it is no longer required, it does not appear. If you are operating within the United States, the acronym is AROW. Outside of the United States you would have to see the Canadian, Mexican, or other countries requirements. Here is the Canadian information as an example.


Why does this chart seem to show airports with magnetic variation up to 90 degrees?

How do you think "the figure seems to show an extreme variation of up to 90 degrees"?

I don't think you're understanding that diagram correctly.

There is nothing close to a variation of 90° anywhere that is populated.

The angle of the curve has nothing to do with how strong the variation is.
All points on a single curve share the same variation.  If you find a 10° variation on a curve, and trace that curve a thousand miles away, that point will also have a 10° variation.

Look at about Washington DC, with -10° variation.  Follow that curve all the way down to the middle of South America.  That point also has -10° variation.

Look near Denver, CO, where it is +10°.  Follow that curve out to near eastern Hawaii.  The curve there is almost due East-and-West, but that doesn't matter.  That area also has +10° variation, because it is on the same curve.

The bold curves are at 10°, 20°, 30° etc variation.
The red curves have a positive (east) variation.
The blue curves have a negative (west) variation.

All of this information is in the legend at the bottom of the map.


Could flaps be raised upward to serve as spoilers / lift dumpers?

One reason is that any device you want to use as a lift dumper needs to be able to be instantly retracted and this is really difficult to do with a flap.  On an airliner when the lift dumpers come up, if you slam the thrust back up to TO, they immediately come back down.  A flap system with its slow moving drive line can't do this, and it's enough that it has to be retracted from landing to takeoff setting for a balked landing like that.

Plus, even in a normal landing, you would be landing with the flaps at the landing setting, and when you touch down they would need 10-20 seconds a typical drive system would need to move up past 0 to a fully up position.  You'd be stopped by then, and deciding to take off again on the rollout is out of the question.

So you can see that any system like this would require flaps that can move up and down rapidly like ailerons.  A really difficult engineering problem.

You might do this on a small airplane with manual flaps operated by a lever, but now you have to cater to twice the movement range as regular flaps, and you'd lose the mechanical leverage you'd need for manual flaps to work unless you made the lever move twice as far (by say having it move in a 180 degree arc - but now the lever handle is in the back seat).

Lots of gliders use flaps - without any spoilers - and they can in most cases be "reflexed" up a small amount, but this feature is done only to unload the trailing edge region for high speed running which has an effect similar to reducing wing area  and pitching moment to reduce both induced drag and trim drag.

For approach control and landing, they actually do the opposite of what you would think; you drop the flaps down to near 90 degrees when you want to come down steeply and for the landing roll.  Not everybody likes that kind of system because you have the same problem - you can't bring them up and down quickly like spoilers so you can't work the flap lever like a throttle on approach the way you normally do with regular spoilers/dive brakes, and they require different flying techniques, on which a pilot used to spoilers needs to be carefully briefed to avoid trouble.


Why did upward turning propellers in the F-82 Twin Mustang cause a loss of lift in the center wing section?

I'm not sure the history provided in the Wikipedia article is entirely accurate, for the fact that both engines in an outward spinning, two-prop counter-rotating configuration are critical.  This is confirmed in the introduction of this book, though it seems to be written well after the fact and without reference to the oft-quoted story of not getting enough lift on its maiden run:

  Turning the propellers toward the fuselage meant much better control during single-engine operation.

Likewise, the republished F-82 Operator's Manual boasts, "Single-engine control characteristics of this airplane are exceptionally good."  Again (but also as expected), no mention of any trial and error in the design phase.

And the more I researched the F-82's design, I found various and unsourced information.  Many sites repeated the initial flight test story, while another said the first attempt's failure was attributed to weight.

My guess is that initial designs of the F-82 simply borrowed from the slightly earlier P-38's final configuration, where the outward-spinning counter-rotating propellers reduced downwash on the horizontal stabilizer and made for a more stable gunnery platform.

As for figuring out the lift cancellation in the F-82's center wing section, it is probably helpful to explain first what effect a single propeller has on the wing behind it.

Generally speaking, a spinning propeller creates a downstream vortex in the same direction as the propeller is rotating.  The area of wing behind the upswing of a propeller blade experiences a higher angle of attack to the resultant airflow, resulting in increased lift and drag across that section of the wing.

Image source: Civil Aviation Authority of New Zealand

Likewise, the opposite occurs on the downswing side, resulting in a net increase in lift and net decrease in drag behind the engine as a whole.  This single-engine airflow model is generally true for multiple-engine models with all propellers spinning in the same direction:

  The interaction of the slipstream with the wing produces an increase in overall lift coefficient. This net increase is the result of a local increase in local lift coefficient $C_L$ for the part of the wing located in the slipstream with up-rotation while the downrotation induces a local decrease in $C_L$. The local drag coefficient $C_d$ is locally increased in the uprotation part and decreased over the down-rotation section.  The net result is generally a reduction of drag on the wing.

So the F-82 seems to be an enigma in this regard.  Theoretically, an outward rotation should have increased lift on the center section, not reduced it.  So why didn't it?  Perhaps there was too much interaction between the two propeller wakes.  Again, consider the P-38 Lightning.  Though they both have twin counter-rotating engines and two tail booms connected by a shared horizontal stabilizer, the P-38 has a big center fuselage for the pilot sitting right between the two engines, effectively isolating the individual propeller slipstreams.

A study on the "Down Between Engines" (DBE) configuration of the Airbus A400M noted "[strong] interact[ion]" of its counter-rotating engines' slipstreams

  especially [in] the part of the wing located between both engines and results in a local decrease in lift coefficient that is not entirely offset by the local increase on those parts of the wings that experience upward motion (emphasis mine)

resulting in both decreased lift and increased drag in the wing section between the engines.

Note that DBE (i.e. inward-spinning propellers) was the fix for the F-82's lift woes; that the inter-engine wing region still experiences decreased lift and increased drag in the more preferable counter-rotating configuration underscores the notion that interaction of propeller slipstreams is not desirable.  My guess is that this switch removed just enough of the adverse lift conditions so as to enable the aircraft to get airborne.  It would be interesting to find out if anyone modified an F-82 to remove the counter-rotating aspect.

UPDATE:
At long last, I have found what appears to be the most credible source for the Wikipedia article, a 2013 issue of Warbirds magazine.

The first flight was (at least somewhat) attributed to being overweight.  A second attempt on 16 June 1945 went unexpectedly airborne for over an hour after taking off with a limited fuel load.
The interaction between the propellers created an early stall condition forward of the wing when combined with the normal upward flow, causing the lift over the center wing to predictably suffer.  According to NAA aerodynamicist Ed Horkey:

  "What was happening was that we had propellers rotating in different directions on the left and right engines.  For some reason, which I can't remember, we started with the blades moving upward in front of the center section.  What this does, particularly at high angles of attack, is to create upward flow approaching the leading edge of the center section of the wing.  You also have normal upflow ahead of the wing.  The two upflows would add together to create an early stall.  The center section represented a large portion of the wing's area.  What was happening was that we were stalling out early and just not getting enough lift. ... We changed the rotations to go down the middle and we had the problem solved."


The main issue is what is referred to as the Weight and Balance of the aircraft. When an aircraft is in flight, its weight and balance needs to be within a controllable range in order to ensure the plane can both recover from a stall condition and rotate on takeoff. This is visualized by the weight and balance "envelope:

As you can see, there are limits where the aircraft is not fit for flight. We must stay inside the drawn lines in the center.

To answer your detailed questions:

On airlines, a "Magic" number was used to approximate all weight for passengers and baggage. This caused at least one  notable accident: Air Midwest Flight 5481. As a result of this accident, policies were changed to get more accurate baggage and passenger weight.

In GA flight, it is not uncommon for pilots to ask for passenger weights. Usually, as a rule, we add a bit to that in case people are embarrassed (10%). It is very common for pilots to assign seating on smaller aircraft with heavier people sitting in a location where the distance to the datum is smallest (near the front).
Weight and balance can be moved out of limits by fuel burn. In fact, a few questions on the private pilot written exam deal with this exact scenario. Most planes have tanks near the CG, so they don't experience problems with fuel burn. In planes with an aft belly tank, the CG can move forward significantly and out of limits. This would cause the aircraft to be unable to pitch up as desired. Swept wing jets that use horizontal stabilizer tanks in the tail of the aircraft have computers and pumps to move the fuel as desired to keep their CG in the desired place.

Pilots of smaller/less traditional airplanes need to be conscious of this, and plan accordingly. Especially those with a-typical fuel tank positions. Pilots of larger commercial style aircraft are less concerned with the exact position of 1 or 2 large people or heavier bags because their aircraft has a much bigger capacity and less "sensitive" envelope. They still are affected by the physics, though, just like everyone else.


What exactly does the MB-326's 'relight' button do?

The Aermacchi MB-339 was developed from the -326 and it is also powered by one Rolls-Royce Viper Mk. 632 turbojet. From its aircraft manual, the relight button is for the in-flight re-ignition:

  Premuto - Attiva il sistema di riaccensione in volo.
  Pressed - Activates the re-ignition system in flight.

The start button in your picture is for activating the starter, and the guarded ignition next to it is likely a ground/start-only ignition mode.

Typically, an in-flight ignition mode is of a lower energy rating compared to the start mode, this helps prolong the life of the igniters. It's used when flying in rain or icing conditions, and for maneuvers that could momentarily choke the engine (e.g., an extreme spin or side-slip with side-mounted intakes).


What would happen if blades are not pitched correctly on a propeller blades?

For a start, whoever built the propeller would get investigated for possible drug/alcohol impairment on the job.

In terms of trying to run the propeller, it would generate a lot of noise (from turbulence of the blades running in "reverse pitch", possibly stalled relative to the airflow induced by the previous blade) and very little or no thrust.  If it's on a piston engine (or electric motor, assuming a model aircraft or drone case), the engine/motor is likely to overheat after a short time due to lack of cooling airflow.

Finally, it's possible vibration induced by the noise-causing turbulence could lead to a structural failure of either the propeller itself, the engine/motor, or the engine/motor mounts.


How critical is it if a pebble blows into a propeller?

This sort of FOD is often not an immediate problem, however introducing any slight knick or gouge to a propeller could be the beginning of a stress fracture. The last thing you want is a catastrophic prop failure whilst flying!

The correct course of action, much like any minor damage to the airframe, is to note it in the logs, have a mechanic look at it, and make the call if a repair is necessary.


What happens if you exceed the maximum speed on a C172?

You can, but you have to live with the consequences. There are several things that can happen:

Depending on the vertical gusts ahead, you might not even get close to v$_{NE}$. There is another speed limit for gusty weather called v$_B$, and exceeding this will run the risk of overstressing the wing structure. Going above v$_B$ will overstress the wings in a gust of more than 50 ft/s, and more than 25 ft/s when flying above v$_D$. The exact values can be found in the flight envelope diagram of the flight manual.
On a calm day, you can fly v$_{NE}$ and even a little faster, but once you fly fast enough, flutter will become very likely. Note that flutter needs some initial excitation, so you might fly well into the flutter speed range before flutter occurs. When it does, control surfaces will be ripped from their fittings which will make the aircraft pitch up. At that point the wings will break off.
The engine on a C 172 is not powerful enough to sustain level flight at v$_{NE}$. You need to dive the aircraft, which requires some altitude. Maintaining the speed will mean that you dive into the ground, so you need to pull out of the dive in time.
On really fast aircraft the pitch trim will get more nose-heavy when the aircraft approaches the speed of sound. You don't run that risk in a C 172, but faster aircraft found themselves locked into a dive which they could not end.


Advance ratio formula for drone propeller in vertical climb

I could not find equation (2) in my copy of J. Gordon Leishman' Principles of Helicopter Aerodynamics. Some relevant info on momentum analysis in forward flight can be found here on page 63.

Advance ratio as a useful measure of blade twist is less meaningful in helicopters, due to the much greater variety in the direction of the velocity vector. It makes more sense to optimise blade twist for forward flight than it is to optimise for vertical flight, a state with much higher fuel consumption which helicopters do not particularly like.

If you would like to use the advance ratio for helicopters as stated in the wiki article, it makes more sense to use the helicopter one. There may be a direct parallel between the states you describe in your question, but for the helicopter case it is not the design state while for the fixed wing it is.

Whether either is relevant to a propellor drone depends on the design of the drone, whether the propellor is shrouded etc. But for a drone, free velocity would usually not be close to perpendicular to the propellor plane, just like in a helicopter.


An RVSM LOA is given to an operator not a pilot.

RVSM airspace can be used under part 91, so it is not limited to commercial operations. It can be a private owner or a non-aviation business. FAA Advisory Circular 91-85A says this:

  3.4.1 Who is the Correct Person to Apply for and Have Issued the RVSM Authorization?
  The person exercising operational control of the aircraft during the operation requiring an RVSM authorization is the proper person to be the applicant for that authorization. It is important to note it is the RVSM applicant’s responsibility to submit a request for RVSM authorization in the name of the person having operational control of the aircraft, not the responsibility of the FSDO or a specific ASI to make such a determination. The following general information may be useful in assisting the RVSM applicant in determining if the appropriate party has been properly designated as the legal Operator with respect to the RVSM authorization request:

  For non-commercial operations conducted under part 91 and part 125
  (A125 LODA holders), the authorization applicant and legal Operator should normally be one of the following persons, in which event the authorization will be issued in the form of an appropriate letter of authorization (LOA):

  A registered owner of the aircraft operating the aircraft incidental to its own non-air transportation business or personal activity.
  A person assuming operational control of the aircraft through a lease or use agreement for that person’s operation of the aircraft incidental to that person’s own non-air transportation business or personal activity.

  *emphasis mine

So if it is a company plane then the company will be the holder of the RVSM authorization, and there must be a responsible party within the company that is knowledgeable about the operation of the aircraft (i.e. responsible to ensure maintenance requirements are met, the pilots are “RVSM-knowledgeable,” that proper procedures are followed, etc. - not necessarily a pilot).

The authorization will be specific to the aircraft (or a group of similar aircraft) and it must meet the equipment requirements laid out in Part 91 apppendix G.

So, what makes the pilot “RVSM-knowledgeable?”

The same advisory circular says:

  3.3.1.1 For an applicant operating only under part 91 or part 125 (including
  A125 Letter of Deviation Authority (LODA) holders), demonstrating it has RVSM-Knowledgeable Pilots will consist of providing sufficient evidence each pilot has an adequate knowledge of RVSM requirements, policies, and procedures as required in part 91 appendix G, section 3(c)(2).

  The following are acceptable means for the Operator to show the FAA its pilots have adequate knowledge of the RVSM operating practices and procedures: 14 CFR part 142 training center certificates without further evaluation; certificates documenting completion of a course of instruction on RVSM policy and procedures; and/or an Operator’s in-house training program.

  Note: The FAA, at its discretion, may evaluate a training course prior to accepting a training certificate.

  *emphasis mine

Most likely, in a non-aviation company there won’t be an acceptable in-house training program, so any pilots will need certificates documenting completion of a course of instruction on RVSM policy and procedures. There are several flight schools with approved courses that can provide such certificates.

What it boils down to is the company that owns or leases the plane must get an LOA for their aircraft. The aircraft must meet RVSM requirements and to use RVSM airspace the pilot also must be certified.

If you own your own aircraft then you are, by default, the operator. So you can apply for an LOA as the operator. You would be your own responsible party and anyone who flies the aircraft in RVSM airspace, be that yourself or someone else, must be an “RVSM-knowledgeable” pilot.

If you rented your personal plane out to someone, say to a flight school, then they would become the operator while it is in their possession, so they would need to have their own LOA to operate in RVSM airspace.


Why is dual crossfeeding prohibited on DA42?

As I also could find no satisfactory explanation within the diagrams, AFM, POH or Maintenance Manual, I sent an email to the technicians at Diamond Aircraft.

This was their response, so far:

  Hi Chris, I can only assume that if this procedure became too routine, eventually a pilot would select the second electric boost pump on with both systems in cross feed, in flight.  The high pressure created would damage fuel lines and possibly damage the HPPs for both engines.  That would not be a good day.  You can see the step prior to going to cross feed, Fuel Pumps check Off.  I have asked Austria for an explanation but I think I am close to the mark.

  Customer Support,
  Technical Services Specialist

Please note, that the customer service technician actually did include his contact information, but that I have removed it for privacy.


Would airline got charge for late on depart from the gate due to passenger boarding issue? If so, what is the charge like?

Chain of delays

Being late on departure is likely to cause you to be late on arrival, this has the following immediate consequences:

you may be delayed even more on arrival in congested airports (e.g. London) if you miss your scheduled landing timeslot, being forced to circle around for, say, 20-30 minutes wasting fuel and time until you're allowed to land; I have been on a flight like that.
the main immediate effect is that some transferring passengers may be delayed because of this, which may possibly result in costs to you to reroute or compensate them.
you likely have scheduled the same airplane for the next flight with a minimal turnaround time; and delayed arrival may easily cause your next flight of that same airplane to be delayed (again, I have personally seen delays caused by this)
you likely have scheduled the same crew for the next flight, and in certain situations that delay may push them over the allowed work/rest schedule, so they are prohibited to fly their next (last in their shift) flight - so you need to rapidly find a new crew for the scheduled flight or cancel it.

For these reasons, a single delay sometimes might cause a chain of other delays or even cancellations, and become quite expensive.


Why do few small planes have reflexed flaps?

I'd guess that it's because gliders are optimised for low speed in rising air and their aerofoils have lots of camber. Reflexed flaps allow them to reduce the camber for high speed flight, but the resultant aerofoil isn't as good as a proper low-camber, high speed aerofoil.
RC power models generally have plenty of power to spare and either don't care about drag or it only matters at high speeds. Their aerofoils are generally low (or zero) camber already so they don't need reflex flaps to achieve it.


How much does the FAA private pilot's license checkride cost?

There's no standard fee for the checkride because each Designated Pilot Examiner (DPE) is free to set his or her own price. I've seen numbers for a private checkride in the \$400-600 range depending on the location, but your instructor should know the local examiners and what they charge. Or just ask the DPE directly, of course. Bear in mind that you might have to pay extra if you have specific requirements like needing a checkride at short notice, on an awkward date, or at a particular location.

This question might be useful too, and see this one for the (unusual) option of using an FAA examiner instead of a DPE.


Why are many early gliders high-wing designs as opposed to newer designs?

It has to do with improvements in the understanding of aerodynamics and the various tradeoffs discovered over time. High wing has less visibility in turns, especially during thermaling. Low wing has better ground effect, but gives you less options when landing in a crosswind. High wing has better ground clearance, which helps in off-field landings.


Does a plane have more lift while flying in a cloud? (All other things equal...)

No, higher humidity air is less dense than lower humidity air.  This is because water molecules are lighter than the nitrogen and oxygen they would replace in an airmass.

https://science.howstuffworks.com/nature/climate-weather/atmospheric/is-humid-air-heavier-than-dry-air.htm

  any water vapor that gets added replaces either nitrogen or oxygen in our free-moving air. Nitrogen and oxygen make up the majority of our atmosphere, and they're displaced -- or evaporated -- when water takes their place in the air. And water vapor molecules are lighter than both nitrogen and oxygen. In other words, humid air is going to have less heavy nitrogen and oxygen -- and lighter hydrogen and oxygen -- in its place. Remember that they have the same number of molecules, but the air with water vapor is simply less dense

Humidity, therefore, is also an important factor in density altitude calculations.


What is the performance of a flat plate wing?

I cannot answer all your questions, but maybe point you to some facts to come closer to an answer.

Most important is the thickness of your parallelepiped - more than a few percent will just increase drag, without benefiting performance. It should be as thin as structurally possible. There are lots of model airplanes using flat plates for lift. The most popular are flying discs like that below:

(picture source)

Lift

The lift curve slope of a flat plate is the same as that of regular airfoils, complete with stall. They have a zero-lift angle of attack of 0° (obviously) and separated flow on the suction side. The maximum lift coefficient of 0.7 to 0.8 is reached at moderate angles of attack - details depend on the aspect ratio.

Your typical four-digit NACA airfoil will have a maximum lift coefficient of 1.2 to 1.6, depending on camber and Reynolds number (picture source).

Drag

Due to the missing nose thrust, the aerodynamic force vector will stand almost perpendicular to the plate's plane. It will be slanted slightly backwards due to friction, but the separated flow on the suction side means that friction will mostly happen on the pressure side. As a rough approximation, the drag coefficient of the flat plate is $$ c_D = c_L \cdot \sin\alpha + \frac{0.43}{log\left(\frac{100}{R}\right)^{2.56}} + 0.3 \cdot\delta\cdot\cos\alpha$$
with $R$ the relative surface roughness, $\delta$ the relative thickness and $\alpha$ the angle of attack. The first part is caused by the direction of the lift vector, the second part is the friction contribution and will be dwarfed by the pressure part, and the third part is an approximation for the suction along the thick trailing edge. At $\alpha$ = 5° and a lift coefficient of 0.5, the drag coefficient will already be around 0.05.

Regular NACA airfoils will have a $c_{D0}$ of 0.004 to 0.01, depending on Reynolds number, and their $c_D$ at stall is normally between 0.02 and 0.025.

Performance

From the above it is fair to assume that drag in cruise condition will easily be 4 times higher (induced drag is not affected), and the optimum cruise condition will be at a lower speed due to the higher zero-lift drag. On top, the airplane will need a bigger engine to stay airborne, which will reduce its useful load. Expect fuel consumption to increase in line with the drag increase.

The stall speed of an aircraft with a flat plate wing will be approx. 50% higher than with a proper airfoil on the wing, and drag will increase much more at high lift coefficients than usual, which translates into very low sustained turn rates and load factors.

Only the angle of attack range will stay similar. All other parameters will be markedly affected.


What is the Function of Pressurization Light on Exit Doors for Commercial Airliners?

It is there to prevent "violent door openings":

(figure 1b source)

  In some abnormal cases, outflow valves can remain closed, when the
  aircraft is on the ground, causing the air pressure in the cabin to be
  higher than the ambient air pressure outside the aircraft (fig.1b). In
  this case, there is a risk that an aircraft door could violently open
  and injure the operator or damage the aircraft.

(fig 2 source)

  The Residual Pressure Warning Light (fig.2), part of the residual pressure
  warning function, warns anyone who wants to open a door if the
  aircraft is pressurized. This device is installed on all Airbus
  aircraft except for some A300, A310 and A300-600 where it was offered
  as an option. On these aircraft not fitted with the warning light, a
  caution placard located on the door reminds the operator of the risk
  that residual pressure may cause violent door opening.

This brief from Airbus has a lot of good info on residual cabin pressure as well.

Not to be confused with the "Slide Armed" light.


Why are there no supersonic propellor driven aircraft?

The NASA has done research on the supersonic propeller at the end of WWII, which can be found here and here.

The main reasons that we don't see any supersonic propellers are the following:

The supersonic regions at the blades create tremendous forces which will tear the propeller apart. Thus the design needs to be such that these forces can be mitigated. This is also the case for jet engines, which is why the ducts are designed such that the airflow into the engine is slowed down to subsonic speeds.
The developments in jet engines were going at such a fast rate that the propeller was soon surpassed and was written off. However, since turboprops are much more efficient than jet engines they might pop up on the research radar in the near future.


Do vapor clouds increase the radar scross section of an aircraft?

As with most things involving the military, the latest generation of radar detection is classified, and no one really knows all the tricks it uses to work.

However, ignoring the newest bells and whistles let's answer your question with simple radar implementations.

At it's core, radar is a broadcast of an electromagnetic pulse that bounces off anything which reflects it. This reflection is then picked up by a receiver, and after some computer math you get radar predictions.

So the important question to ask, is what band of electromagnetic radiation is being used, and will that particular band of radiation be deflected by cloud vapor?

Most aircraft detection radar uses radiation in the low frequency areas. As you can see on the chart below, long waves are also called "radio waves" is the normal frequency.

This is also what weather radar uses, so it's quite obvious that yes the vapor cloud of the plane will deflect the radio waves. In fact most ham radios operating off similar frequencies rely on the deflection of clouds/upper atmosphere imbalances to communicate with other radios without having a line of sight.

However this is the interesting part. The vapor cloud a jet fighter produces doesn't normally last that long, and when the receiver starts getting the strange data of a small cloud appearing and disappearing it's up to the radar operators/manufactures what to do with this data.

Do you write it off as noise? Or do you say "hey this cloud is moving at mach 1, and is appearing and disappearing in a predictable flight path, we should probably shoot a missile at it."

I'd imagine the military would chose the latter, and I would think the military of any powerful nation would learn to exploit these vapor clouds.

However again that's kind of classified information, so I'm really guessing at this point.

I could end the answer here, but I want to explore another aspect of next gen radar which is the use of infrared radiation. Also called "heat" radiation.

Infrared radar uses a receiver to detect objects in the sky that are emitting heat. Jet engines obviously leave quiet a bit of heat in their wake so this works pretty well.

Now can the vapor cloud diffuse this type of radiation? Maybe, but probably not.

I say maybe because I've never been able to measure the temperature of a jet's vapor cloud, but I'd imagine it's pretty hot. However if you want to make the argument that it's only slightly above ambient temperature then maybe this will temporarily help mask the aircraft's heat signature.

If though you think like me that the vapor is very hot considering the extreme pressure the air just went through to make the vapor cloud in the first place, then this will work against the aircraft to expose more heat to ir detection.

So to answer your question, yes this could cause a problem with radar detection, however I hope that anyone who puts billions of dollars into building these aircraft know about this limitation and inform pilots not to do a vapor causing maneuver within enemy radar when stealth is needed.


What is the fastest recorded backward flying plane?

EDIT: This first paragraph previously only referenced the Harrier, but I've since found evidence of the Osprey doing the same, and the F-35B has since been reported to perform the feat.

The only true answers I'm aware of are the Hawker Harrier (or Harrier derivatives thereof), the Osprey, and the F-35B. These are all VTOL aircraft which can fly backwards, and can also fly very fast forward... thus they are the "fastest" aircraft which can also fly backwards.

Previously this crown belonged to the Harrier, but since the F-35B is faster it now takes the accolade of being the "fastest recorded backward flying plane": it can fly backwards, but also fly at mach 1.6.

As to your original question, the answer is that any aircraft is capable of this feat of "moving in reverse relative to the ground", if the wind speed is higher than that aircraft's stall speed.

I'm not quite sure what your question is, as you ask what is the fastest plane which can do this: Do you mean "What is the maximum speed of any aircraft which can achieve this?" or did you mean "How high can this relative speed be"

For the former: With the maximum wind speed recorded on Earth being over 230mph, any aircraft with a stall speed of 230mph or lower (ie, almost any plane), can do it. Therefore the fastest aircraft which can achieve this is the fastest aircraft on the planet. I'm not 100% sure on the fastest aircraft, but the SR-71, for example, can fly at well over Mach 3, but is also capable of flying "backwards" if the wind speed is above around 180 knots.

In theory the SR-71 could therefore fly at Mach 3 "forwards" or around 50mph "backwards" (in the context of this question) by travelling at 180 knots into a 230mph headwind. I wouldn't recommend attempting this, however....

Or to answer the real question I think you're asking which is "How fast can an aircraft performing this feat travel relative to the ground", the answer would be "the aircraft with the slowest possible stall speed" and the relative speed would be approximately 200mph.

An aircraft which can fly at under 30 knots, flying into that 230mph headwind, would be travelling "backwards" at 200mph relative to the ground, and at 30 knots relative to the wind.

So actually with it's very low stall speed the An-2 is probably a contender, although I believe there are aircraft with lower stall speeds.

(Apologies for mixing Knots and MPH almost at random in this reply: all numbers are approximate, however, so it probably doesn't matter too much. For the purposes of this answer, I'm treating 1 kt and 1 mph as approximately equal)


there is a lot going on here.  Short answer is that a ducted fan (what you have pictured) can produce a lot more thrust (experiments from one paper say twice as much) than an open rotor of the same size.  The big thing that these ducted fans have going for them is the fact that tip losses become negligible because there simply isn't room for the tip vortex to develop because there is a duct in the way!  Simple, easy solution that works well.

However, nothing comes for free.  One, you have to have the duct there, which is weight & money (you have to build the duct and the support structure, which adds some drag too).  Think of scale too--as propellers get larger, the duct has to grow with them.  Imagine the difficulties in putting a 20' duct on a B-36 propeller!

Second, the manufacturing tolerances on the duct are critical--the tighter it is, the more efficient you are (to a limit, naturally)...but the tighter it is, the more susceptible you are to having your blades strike the duct due to flexing of the duct or the blades.  And, speaking of flexing blades and the necessary support structure you'd need, this could make pitch control (on a propeller, variable pitch, and on a rotor, cyclic and collective) difficult to implement, depending on which of those schemes you're looking to do.  Then again, for a small implementation using RPM control...maybe you don't need those anyhow.

Similarly, while a crosswind on an open rotor leads to a sudden decrease in power, a crosswind on a ducted fan leads to a sudden pitching moment due to the lip of the duct and the asymmetric inflow to the fan (which, since you're now producing more thrust to begin with, asymmetric inflow effects become even more pronounced).  Now, if you stick this on the front of a typical Cessna 172, say, and throw a crosswind at it (which, if you think of takeoffs and landings, which since they must be in a certain direction, having a crosswind is actually quite likely) imagine the yawing moments that would be induced by the propeller (proportional to the static thrust) -- even before the aircraft got off the ground and before you have a lot of control authority to counteract it!  A similar scenario in the air could be as dramatic.  And, yeah, you could throw some guide vanes at it to help, but nothing comes for free.  Guide vanes, which is a workable solution, now mean that you need to have actuator(s) for those vanes, power & maybe hydraulics for the actuator(s), mounts for the actuators, hinges for the vanes, linkages from the actuator(s) to the vanes, redundancy for the actuation or some means of facilitating control in an emergency...it's a lot of work.  Or, by contrast, you could just bolt a fixed pitch prop on a shaft at the front of said Cessna 172 and call it a day.

In the long run, and this is some speculation, I think it just leads to a more complex system, particularly in full-size implementations, which is a maintenance, cost, and manufacturing headache that isn't worth having if you can get plenty of performance from a regular open propeller.  If you venture into the world of diffuser augmented wind turbines, there have been similar debates going on for decades...and a ducted wind turbine has yet to be successful on the large scale.  Similarly, while ducted fan aircraft have flown...

(Ryan XV-5A Vertifan, circa 1950.  The ducted fans are underneath the circular domes on the wings and another under the shuttered area on the nose for pitch control. Source: http://www.aero-web.org/specs/ryan/xv-5a.htm)

...there aren't any non-MAV examples around today that I know of.

Source:
https://theses.lib.vt.edu/theses/available/etd-05262005-170916/unrestricted/WGraf_Thesis_2005.pdf


How can I find information about the aircraft with registration / tail-number N58644?

I have checked the 01 July 1965 FAA register, and it does not show there. My father had a BT-13A N61907, and it doesn't show either. The usual fate of postwar BT's was sale to crop duster companies; they were of value only for their R-985 engines and 2D30 props to be fitted on Stearman dusters or airshow planes. The airframes were scrapped.

If you can convince someone at FAA OKC, they could call up their archives (in Ft. Worth IIRC) and get the answer you seek.


For an FAA commercial license, can I use EASA/ICAO 2nd class medical?

You can "obtain" an FAA Commercial Pilot Certificate with a Third Class Medical Certificate; the Second Class Medical Certificate is only required to be able to "exercise the privileges" of a Commercial Pilot.


Why did air traffic levels decrease dramatically in the US through the 2000s?

It isn't just one thing, but a vicious cycle:

Airline travel is expensive. One person flying and one person driving end up about the same price once you figure in gas and hotels, but the airline will want that same price for each passenger, while you can fit up to three more people in the same car at practically no additional charge (the extra weight will slightly increase gas costs and at some point everyone you can put in a minivan won't fit in one hotel room, but the incremental costs still don't compare at all). This makes time practically the only advantage to flight, especially for a family group; if you have the time to drive, many people who need to get somewhere don't even consider flying as a viable financial option.

You choose your car, among other things, for a certain level of comfort; the airline sets up their planes for volume over all else. Even the smallest sub-compacts have more legroom (for the front seat passengers at least) than the average economy airline seat. Upgrade to first class and the ride's better, but then the cost doesn't compare at all.

Customer service ratings are at an all-time low. Flight attendants are moving further and further from the "stewardess" role they had in a bygone age when airlines lived and died by their service quality (because regulation gave them little control over anything else in their business model). Now they exist for little else than to make sure nobody dies, or worse, breaks Federal aviation laws. Get them on the plane, give the speech, make sure everyone's belted in for take-off and landing, then get them back off the plane, all without killing themselves or each other. Anything else the the flight crew does during the flight is gravy at this point.

The major U.S. carriers have practically all adopted Spirit's business model. The average person considering air travel today might think Spirit's the only airline that charges you extra for every single additional amenity or service, but in fact Southwest, a "discount" carrier, is the only one that still rolls 2 checked bags, snacks and drinks into the ticket; American, United, Delta, USAir, they all charge \$25 for the first checked bag and \$50 for the second, and most of them are also charging for any food or drink served on board.
This is due to the hypercompetition on price, which is partially our fault as consumers. In a related but different industry, StubHub recently abandoned its "all-inclusive" pricing model, because it saw its sales drop by half due to StubHub being the highest price in most side-by-side comparisons. It's the same with the airlines; if you need a flight, you go to Google or TripAdvisor or Expedia, enter your route and the date window of your trip, sort by price, and pick one of the top three, maybe the top five. That means that anything the airlines can do to lower the price they show you online at first glance gets them the customers, and airlines wanting to keep the all-inclusive model, like Southwest, have to aggressively remind customers that what they see online is what they will end up paying when it's all said and done (hence the "Bags Fly Free" ad campaign that is now painted on their planes' cargo hatches).

Security is a nightmare. I remember a time, not that long ago really, when you put your carryon or purse on the conveyor belt, your coins in a dish, and walked through a metal detector. Simple. You didn't even need a ticket to get into the secured area, so you could meet whomever was flying in at their gate instead of at the curb. Those days are gone, and it will take a couple big technological leaps to get anywhere near that again (like being able to walk through a full-body scanner with your shoes and all your bags, instead of adopting the "felony stop" position in stocking feet with the contents of your briefcase laid out in grey tubs).

The expense of any kind of travel is redefining the idea of a "vacation". Leisure time overall has been decreasing since the advent of the Information Age with everyone interconnected and instant gratification being practical in more and more aspects of our lives. Those who still use their two weeks a year (if they even get that) for real leisure are opting more and more often for a "staycation", either staying home relaxing and visiting local attractions, or driving a relatively short distance to a hotel or resort (DFW has two big destinations, the Gaylord Texan and the Great Wolf Lodge, which cater primarily to people who already live in the Metroplex).

Video calling has created a difference between "face to face" and "in person". They used to be synonymous, but now the kids can not only talk to Grandpa, but see him, and he them, over a mobile phone or a computer with a webcam, at virtually no cost beyond the telecom plan. This development has more thoroughly revolutionized business travel; you no longer need to fly to the corporate office to get face time with an executive or have a big corporate meeting; you just sit down somewhere with a computer, camera and microphone.

All of these things have deterred all but the most necessary travel by air; getting on a plane is so expensive, so dehumanizing and so uncomfortable that it's only done if you have to get somewhere and can't take the time to drive there (or you have to cross a major body of water to reach it). That has reduced total passenger count, and since a flight only makes a profit if it's very near full, that reduces the number of flights airlines make. However, that decreases total revenue to offset the overhead of the airline (marketing, scheduling, maintenance, etc), so airlines cut costs by slashing services, making a flight on their planes even more miserable, reducing the general desire to fly, reducing passenger count. The vicious cycle continues.
This reduction has been offset somewhat by U.S. airlines "rightsizing" their fleets, opting for more flights with smaller planes. This gives passengers their choice of flight times while keeping planes full and pilots/flight attendants employed. Boeing is focusing primarily on this market in new plane orders with the smaller, more efficient 737, 777 and 787, while the original "jumbo jet", the 747, is on its way out of most passenger fleets and the A380 is struggling outside a couple relative niche buyers like Emirates and Qantas that specialize in ultra-long-haul flights.
Increased air cargo flights have also made up some of the difference; boxes don't care nearly as much about being stacked like sardines in an old aircraft (when was the last DC-10/MD-11 you flew in as a passenger? UPS still has dozens of them in the cargo fleet) with minimal amenities, so thanks to the success of e-commerce, FedEx and UPS are raking it in and growing their air fleets (though they passed on the A380 in part due to Airbus not prioritizing the cargo variant), while American is scheduled to reduce its fleet by 30 planes this year and is still struggling to report a profit even with prices and services cut to the bone.


If your plane is out-of-control, why does military training instruct releasing the joystick to neutralize controls?

Many abnormal situations can be at least partly pilot-induced.

Most civil airplanes (modern military ones are another topic - but computers add to that... ) are aerodynamically stable. Releasing the controls gets rid of probable faulty input and gives the plane a chance to stabilize. This might work (did in this case), but if there is a situation where the normal stability is no longer present - it might increase the problem.


How would a Flying Fortress behave if it lost its empennage mid-flight?

Depends on the extent of the damage as well as what systems are affected.  Lose the vertical fin, it's possible the aircraft could make it home but with limited yaw stability.  Lose the vertical fin and the tailplane, the airplane would nose over and depart from controlled flight due to longitudinal instability.


Why does maneuvering speed vary with weight?

At the normal stall speeds given by $V_s$, the load on the aircraft is 1g, and the lift is equal to weight. i.e $L = W$.

In case of maneuvering, the load factor is greater than one, and we have $L = nW$, with $n$ being the load factor.

We have,  $L = nW = \frac{1}{2}  C_L  \rho  V^2 S$.

This gives maneuvering speed , $V_a$ = $V_s \sqrt{n}$

It can also be written as $V_s$ = $\sqrt{\frac{2 n W}{\rho C_{Lmax} S}}$

At maximum weight, this gives,
$V_A$ = $\sqrt{\frac{2 n W_{max}}{\rho C_Lmax S}}$

For other weights, we have,
$V_a$ = $\sqrt{\frac{2 n W_{a}}{\rho C_Lmax S}}$

For the same load factor, we then have,
$V_{a} = V_{A} \sqrt{\frac{W_{a}}{W_{max}}}$,
where
$V_{a}$ is the maneuvering speed at weight $W_{a}$ and $V_{A}$ is the maneuvering speed at maximum weight $W_{max}$

As the maneuvering speed depends on the load factor and the stall speed, it depends on the weight of the aircraft (which decides the stall speed). It is basically a structural limit.

Another thing to note is that the aircraft can sustain structural failure even below maneuvering speed when multiple large control inputs are given.


How do UAV designers improve visual quality without compromising computational efficiency in mini UAVs?

First look at the frequencies involved. If your camera frame shakes so badly that the picture quality suffers visibly, I would suspect that your camera mount has an eigenfrequency close to whatever causes the vibrations (the engine, most likely). Maybe it is enough to shift the eigenfrequency of the camera mount away, either by changing the mass of the camera or by changing the stiffness of the mount.

It could also be that some structure other than the camera mount is in frequency neighbourhood with the engine and the camera is mounted near an antinode - maybe it is enough to shift the camera location a little.

Vibration problems are hard to diagnose from the little information you give, so all I can do is to guess the most likely cause of your troubles.


What would be the best alternative during a dead-stick approach?

Attempting a tight turn, while low and slow, is an almost certain recipe for disaster.

Your first option of landing with a tailwind is possibly preferable - there is no inherent danger landing with a tailwind - it'll extend your landing, and is not ideal. However, it is much safer than trying to maneuver into a position with a headwind with only part of the runway remaining. And with a short runway to start with (if that was the case) you might not have enough distance to land safely anyway.

There is a third option, with the setup you describe, which is to completly disregard the (seemingly) obvious runway close by and look for a suitable area to land in front - a field, a highway, a beach - any of the usualy places you might make an emergency landing in the case of an engine failure.

(Disclaimer: My experience is with single engine propeller aircraft, but I am fairly sure the mantra of Aviate, Navigate, Communicate applies to all aircraft types. Really, in this situation its only the aviate that is relevant)


Is it sensible to harness wind energy on an airplane?

Normally not: Extracting energy from the airflow produces drag, which must be overcome by added thrust. Since every form of energy conversion produces losses, more thrust energy must be added than can be gained from the airflow.

Only when the engines fail and the generators stop running does it make sense to extract energy from the airflow. In airplanes there are two applications which are driven by "wind energy":

Older airplanes use gyros for the artificial horizon which are powered by ram air. This way the gyros work even after an engine failure.
Jets use Ram Air Turbines (RAT), propeller-driven generators which are moved into the airflow when all other means of generating electricity and hydraulic power have failed. Note that this is done in unpowered flight and increases the sink rate.

Deployed RAT (picture source)

Rocket-powered airplanes have no easy way to generate electricity, so the Me-163 B used a small windmill at the tip of the fuselage to drive a generator.

Me-163 B (picture source)

EDIT:
With your question's new focus on electric propulsion the answer will become different. Now you most likely will have propellers which are powered by electric motors. During landing, those could run inverted and charge a battery, which will most likely be empty by the time the aircraft lands. This can be done during final approach until the end of the runout after touchdown. It can be expected that any electric airplane will have a high L/D, so deploying speed brakes to allow for a steeper approach makes sense.

I would be surprised if an additional device would be economical, however. This recharging must be done by the regular propulsion system, or it would add dead weight during most of the flight.

You asked for formulas, but all I can provide here are some back-of-the-envelope calculations. First, it must be said that variable-pitch propellers will be lousy as windmills, because their camber and twist are wrong for windmilling mode. I would expect that their efficiency is around 30%, which means that only 30% of the energy extracted by drag will be converted into mechanical energy which drives the electric motor.

Next, running an electric motor as a generator will again require compromises. Good motors make poor generators, and re-wiring the motor for better generator performance will degrade its efficiency in normal use. You will quickly lose more than you gain from the short flight phase when running the motor inverted makes sense.

Now let's assume that you keep your propulsion system at top efficiency (say, 90%) and accept that it will only convert 10% of the drag energy into electric energy. Let's also assume that your prospective solar airplane has an L/D of 30 which needs to be reduced to 10 for a practical approach. You do this from 1000 ft downwards and use the windmilling propeller also during the runout. Approach speed is $v$, mass is $m$ and the initial energy of the airplane is $305\cdot m\cdot 9.81 + \frac{m}{2} \cdot v^2$. Two thirds of the potential energy go into propeller drag, and to be generous we assume that 100% of the kinetic energy will also go into propeller drag, even though the braking force of the propellers at low speed is really lousy and needs support from wheel brakes.

Now it is important how fast your airplane flies, because this will shift the ratio between potential and kinetic energy. To keep things simple, I will relate both to the energy required for the next flight. 10% of the full kinetic energy will accelerate the aircraft to less than one third of its flight speed - after this, the remaining 91% of the energy to reach $v$ must be added by charging the batteries between flights.

The electric energy taken from the potential energy will help you climb to 60ft or sustain level flight at $v$ for a distance of 1800ft. At an L/D of 30 the airplane will fly a distance of 30,000ft without thrust, and by braking you will extract the energy to cover 20,000ft, which at 10% conversion efficiency (and 90% propulsion efficiency!) will carry you over just 1800 ft.