What do the pointers on a Kollsman altimeter indicate?

I found some sources of definite information, so I will answer this to confirm the suggestion made in a comment that Federico referred to in his answer. Also to fill in the details of what the OP asks.

Triangles 4 and 5 indicate the altitude difference between ISA pressure at sea level and the pressure set in the Kollsman window.

TM 1-205 Air Navigation 1940, Chapter 1, Section VII, Paragraph 52, Altimeter, beginning on page 66, at https://archive.org/details/TM1-205 has an explanation about these triangles, or as they were called "reference markers".

This post at https://www.pilotsofamerica.com/community/threads/blue-and-yellow-does-anyone-remember.79471/ beginning at post #11 discusses altimeters with these markers. Post #25 has a link to an article in the January 1948 issue of Flying Magazine that has a very good explanation of altimeters and these reference markers.

Triangle 5 shows if an altitude difference is higher or lower by which side of the 0 it is on. A higher difference is to the right of the 0 and a lower difference is to the left of the 0. This is in thousands of feet.

Triangle 4 reads in hundreds of feet. Which way you read it depends on which side of the 0 triangle 5 is on.

In the image in this thread, the altimeter setting is 30.1. To see what the difference should be, I used TM 55-6610-247-40 Table 3-1. Altitude Pressure Table, Feet VS Inches of Mercury. I got this TM from http://www.liberatedmanuals.com it says that the altitude difference would be -165 feet.

Triangle 5 is to the left of the 0, between it and -200 feet on the thousands scale. Since triangle 5 is on the left side of the 0, triangle 4 is read from that side and shows -160 feet.

A couple more examples from the thread referenced in the OP What type of altimeter is this?

In the top image the Kollsman window is blanked out. According to TM 1-205 page 68, (3), this is because the limit of the pressure range has been reached. In this case, at the upper limit. The triangles indicate approximately -2380 feet, which would be in excess of 32 inHg.

The bottom altimeter is set to 29.16. According to the table mentioned above, the difference is 711 feet. The triangles are showing this value. Triangle 4 is read from the right side of the zero, because triangle 5 is to the right of the 0.


What is the drag optimized wing form for given lift and bending moment?

You have already found the most relevant articles. In 1933 Ludwig Prandtl published "Über Tragflügel kleinsten induzierten Widerstandes" in the Zeitschrift für Flugtechnik und Motorluftschiffahrt. 17 years later R.T. Jones came to the same conclusions in NACA-TN-2249. The 2013 article "Lift Distributions for Minimum Induced Drag with Generalized Bending Moment Constraints" by David J. Pate and Brian J. German goes one step further and optimises drag at a lower and structural mass at a higher lift coefficient.

But that is not all that relevant to your case. You want a wing which supports your weight plus the small surfboard which sticks out of the water. At those small loads, structural mass is almost negligible. Scaling laws mean that structure becomes more important as aircraft grow in size and mass. You know that elephants have much more massive legs relative to their body size than antelopes (or even ants, for an even more drastic comparison), since body mass scales with the cube of linear dimension while structural strength scales only with the square of linear dimension. This means that wing spar weight will be proportionally higher for larger aircraft.

As a consequence, insects have more elliptic wings than albatrosses, and model aircraft have optimum wings which are much more elliptic than the optimum wing of an airliner. The optimum shifts from an elliptic load distribution at very small scales to an almost triangular distribution at large scales.

What is more relevant is the angle of attack range in which this wing is meant to operate. The pumping motion seems to lead to quite large angle of attack variations, so you cannot optimise that wing for just one flow condition. Instead, it must be robust enough to produce tolerably low drag over the whole operating range.

Drag has two components: Pressure drag and friction drag. Pressure drag has one part which stems from lift creation, which in turn depends on the mass of fluid affected by the wing. That part drops with speed and wing span, so you want to be fast with super wide wings in order to minimise that kind of drag. However, friction drag increases with speed, so there is an optimum which varies with wing planform.

But there is another issue. Wide wings are very sensitive to angle of attack variations while more narrow, stubby wings will tolerate a wider angle of attack range. Also, the increased chord length of more stubby wings produces less friction drag per area than the narrow but wide wing.

Next to consider is the relative thickness of the wing's cross section (called an airfoil) and its camber. A thicker airfoil will create more static lift (buoyancy) but will create less dynamic lift. Make the airfoil too thin and its useable angle of attack range will become very small. I would select a thickness between 12% and 15% of chord length. Camber should reflect the operating lift coefficient: For highly loaded wings, use more camber. The tail surface, however, should be uncambered.

Another important factor is the incidence of wing and tail. The tail should have less for positive static stability, but you need to include the wing's camber into that calculation.

All those questions can only be answered when we know the flow speed, the mass on the board and the size of both surfaces. But you have to start somewhere. For that, it might be best to start with a proven design, collect the operating parameters and then go back to the drawing board with a sound basis for optimization.

For a first shot, start with a trapezoidal wing planform in which the tips have 70% of the chord of the root. Aspect ratio should be 5 or 6. You may add highly swept tips and 3D-shaping as you desire, but don't overdo it.


Is it possible to play music in the cockpit?

Depending on the equipment in the aircraft, the answer may very well be yes. A lot of modern headsets in civilian aircraft (particularly those with active noise reduction) have bluetooth capability that allows music streaming. Some more modern audio panels even have music inputs now. I even flew in an Archer that had a CD player on the panel and wired into the audio panel.

If you are lucky enough to have an automatic direction finder (ADF) eating up useful load in your aircraft you may be able to tune into AM radio stations. This may have contributed to the crash of Varig Flight 254.

While you are legally allowed to do this (at least in small planes) the sterile cockpit rules that most if not all air carriers have prevent professional pilots from doing so, as @Carlo Felicione points out in the comments


Why are some cardiac conditions disqualifying even if asymptomatic and corrected?

Basics :  Why did the event happen? Will it happen again?

Curative care is fine, but what about the possibility of the same, or similar, events happening tomorrow/next month/ad astra?

The FAA medical standards are for the protection of everyone other than the pilot.

I am the proud owner of 6 cardiac stents. But it has become impossible to maintain a Special Issuance Medical as I aged.


How close is X-Plane experience to real flying?

X-Plane is a much truer simulation of flying than that flight game Microsoft used to make. In fact, when coupled with certified hardware and a CFI, X-Plane can power a sim that you can actually log FTD time in.

Since you ask about airline flying for your comparison, there is a lot more to that than just the flying. An airline pilot is, with few exceptions, always operating under instrument flight rules (IFR). This means flying in the clouds with no reference to anything but instruments, weather as bad as a few hundred feet visibility and strong crosswinds for landing and takeoff are all part of normal ops. You are also operating under ATC, so radio ops are normal. The only comparable computer simulation of ATC to reality is VATSIM (as mentioned in comments), though it doesn't approach the level of busyness that you'll find in some airspace and airports (with the exception of some of their organized fly-ins).

A transport category jet is also a bit more complicated than "turn the engines on, release the brakes and go". The only computer sims that capture the level of detail properly are ones like the A-10 simulator by DCS. Before you can start the engines, you need to first power the aircraft and perform your receiving checklists, and if you are the first flight of the day, additional first-flight checks. These cover:

Thorough pre-flight walkaround inspection
Powering the airplane on batteries
Transition to ground power (GPU) or start the APU for power
Verifying the state of all systems
Fire test
Stall warning test
Anti-ice system test
Checking oxygen levels and masks
Autopilot test
Backup instrumentation checks

Before pushback:

Verifying fuel load
Get load information from flight attendant/gate agent/dispatch/ramp supervisor
Calculate weight and balance, move passengers and/or bags if needed
Get ATC clearance and program FMS
Flight crew and cabin crew briefings
Weather briefing
Start APU and disconnect ground power and ground air conditioning
Get clearance for pushback

During pushback:

"Before engine start" checklist
Set bleeds / packs for engine start
Communicate with ground crew for engine start

Now you can start an engine. Unlike a small airplane where you start the engine by turning a key in an ignition switch, in bigger airplanes its a series of knobs and buttons to press, sometimes dependent on certain events during the start. Engine parameters must also be monitored in case an abort becomes necessary.

At this point you can get a taxi clearance and start moving toward the runway. You'll go through a couple more checklists, "after start/taxi" and "before departure", to prepare the plane for taxi and takeoff. Once you are on the runway, with all checks completed, with more fuel than your minimum dispatch release, and an ATC clearance you may then release the brakes and go flying. One pilot will fly and the other will monitor instruments.

Much of the above is beyond the typical scope of X-Plane, though some can be addressed with specific aircraft add-ons, manuals and software like VATSIM.


What is an easy format for giving pilot reports?

Who you are:
Cherokee 1234A, a P28A
Where you are:
10 miles north of La Belle VOR, altitude 6000 feet
Build your own "METAR":
Five minutes ago (time) wind aloft 230 @ 24 (wind) imc (visibility) medium turbulence (weather phenomena) broken clouds at my altitude, clear below (cloud cover) temperature 10 degrees (temperature)

That's it!
There might be a way to exactly meet the form the controller needs to write it down, but this works fine and you have a fluent and well structured report.


Why do the intake of some helicopters have a bump body?

I don't know of the Apache, but the Russian helicopters have a dust separator there. This link shows how the dust protection system works on the Mi-17. The Mi-28 and Ka-52 have the same engines, so the system probably works similarly.

The system works by making the air follow a curved path from entry to the first stage of the compressor. Due to inertia, heavier-than-air particles are forced to the outside of the curve, which is the center of the intake protrusion. Air in the separator is forced through baffles to separate the dust from the air, then through a channel that leads overboard. A bleed air nozzle at the end of the channel creates vacuum at the baffle section to aid with removing dust.
The system reduces engine performance as it reduces the compression ratio with bleed air.


When do carriers overhaul their flight schedules with flight re-numbering?

At my carrier, there are no rules along the lines asked about; the rules that apply are generated by the Schedule Planning department, and will change as they see fit. They produce many schedules each year, and how much "this" one differs from the previous one depends on lots of factors regarding fleets and markets and priorities. Some things are seasonal, many aren't.
The change-over dates are similarly "whatever makes the most sense" as the schedules are being built. One carrier may be on a 6-week cycle, with another on a calendar month cycle; ours seems to change at not entirely regular intervals. Some schedules are longer than others - mid June thru mid-August may be one fairly constant schedule, but November & December may see 4 distinct schedules, as travel fluctuates around the two major holidays.
Increasing automation over the last 20 years has probably contributed to this variability.
There may be some "sacred cows" in the schedule, that flight 1 always is the first departure from (big east coast hub city) across the country to LAX or SFO, perhaps, or flight 711 always serves Las Vegas (dice roll of 7 or 11 is a winner), etc. But much of the schedule is, whatever makes sense to the planners this month or this quarter or this year.
The closest you'll come to having predictable guidelines would be to study one airline's schedules over time & observe enduring patterns... but even those may not be written in stone.


Do I need explicit clearance to taxi on an inactive runway?

Yes, you need an explicit instruction (not clearance) to taxi on any runway - and you got one!

The controller told you to "taxi on [runway] 10" which is about as explicit as it gets. If he did not want you to taxi onto the runway, he would have explicitly told you to hold short of runway 10. Note that it doesn't really matter if the runway is "active" or not. In the eyes of ATC, a runway is always a runway. Don't expect the controller to say something like "cleared to enter runway xx" - because it is not a clearance, but an instruction. The phraseology used will be along the lines of "enter runway xx", "taxi on runway xx", "cross runway xx" etc. - never "cleared". The only time you will hear "cleared" and "runway" in the same sentence is in a takeoff clearance or landing clearance.

That said, you did exactly the right thing. If in doubt, stop and ask. Especially when it comes to runways, if in doubt, never assume you have been instructed to enter a runway. Runway incursions are very dangerous, and the controller would much rather clarify an instruction instead of risking a collision.


Are walkalong gliders based on the principles of ground effect?

No the paddle acts as an inverted wing and pushes air up, this in turn will push the glider up.

Even with ground effect a non-powered glider cannot maintain height and speed.


Why did this departure from Buenos Aires seem to delay heading northeast?

It's following a departure procedure.

(chart source)

The path flown matches the route described for departing Runway 11 with the La Plata 6B departure.

See the map here to visually match up the described departure procedure with the flown path.


What are the correct names of the parking spaces for turn-around?

They are referred to as aircraft stands.

ICAO Definition:

  Aircraft stand.
  A designated area on an apron intended to be used for parking an aircraft.

Stands at the terminal building are commonly referred to as gates, while stands further away may be referred to as remote stands or remote gates. The aircraft stand term covers both types.


What types of air traffic controllers are there?

In Canada (and I believe similarly in the United States), there are four ratings which can be applied to an Air Traffic Controller license:

Airport Control
Terminal Control
Area Control
Oceanic Control

Within each of those ratings, the responsibilities are sub-divided a bit based on operational needs. For example, controllers at a tower (with an 'Airport Control' rating) would tend to be qualified in all aspects of tower operations including:

Clearance Delivery (issuing IFR clearances or assigning transponder codes)
Ground Control (issuing clearances for aircraft to move to/from the apron and runway areas via a taxiway system
Air Control (issueing clearances to aircraft in the runway environment and in the vicinity of the airport)

Terminal Controllers (if a terminal control area exists around the airport in question) would be responsible for flights in the immediate vicinity of the airport to approximately 20-50 nautical miles. Their responsibilities may include multiple small airports, just a single large airport, or even just one specific operation at an airport (such as arrival control or departure control). These controllers are usually allowed to apply a smaller amount of lateral separation between aircraft due to the dense nature of the terminal environment and the specific nature of their role.

Once the aircraft leave the terminal (if one exists), the Area Controller-sometimes called enroute control-takes over. They are responsible for anywhere between several hundred square miles of airspace to over several thousand square miles in the case of sectors in northern Canada.

In the case of an aircraft transiting the ocean, a specific type of area controller called an Oceanic Controller takes over. They possess slightly different training in order to safely separate aircraft over the ocean in non-radar airspace.


Why divide the blades of a 9 blade propeller into 3 groups?

If there was a technical reason beyond "it looks cool", I would guess it would be some benefit noise wise, where it may sound more like a 3 blade prop than a 9 blade, and the resulting lower beat frequency of one prop, interacting with its counter-rotating mate, was less objectionable.

I went on a mangrove airboat tour in Forida once in a 454 V8 powered boat and it was earplugs PLUS ear muffs together for me, so I can imagine that anything that helps with noise levels while absorbing all that power would be very sought after.


Is there a regularized width of yellow taxiway ground bands?

In the FAA's document about standards for airport markings, it says:

  e. Characteristics.

  (1)

  Width. The taxiway centerline marking width, which is either 6 inches (15
  cm) or 12 inches (30 cm), is based on the type of taxiing operation as described below. Uniform
  width must be maintained for the entire length of the taxiway except under the following
  conditions.

  (i)

  The taxiway or part of the taxiway is designated as a SMGCS taxi
  route. Under this designation, the width of the taxiway centerline must be 12 inches (30 cm)
  wide and, on light-colored pavement, further outlined in black. The taxiway centerline width of
  any remaining section of the taxiway that is not part of the designated SMGCS taxi route may
  change abruptly at that point or at the intersection with other taxiway centerline markings, for
  example, reduced from 12 inches (30 cm) to 6 inches (15 cm).

Source, chapter Taxiway Center Lines, page 43

For the taxiway edge lines, following rules apply:

  e. Characteristics.

  (1)
  The outermost edge of both marking schemes must be painted along the
  edge of the usable pavement.

  (2)
  The continuous taxiway edge marking consists of dual, continuous lines
  with each line being at least 6 inches (15 cm) in width and spaced 6 inches (15 cm) apart (edge to edge) [...]

Source, chapter Taxiway Edge Lines, page 48

This really is a great question, I have never thought about airport markings being such a complex thing.


What is the purpose of multiple autopilots?

Redundancy, particularly during autoland operations.

How it works depends on the specific airplane type. In the most advanced systems with triple (or more) flight guidance computers (FGCs), a "voting" concept is used during critical operations like autoland. All 3 computers calculate their commands independently, and vote on what to do. The middle value, or sometimes the average of the 2 "most similar" values, is then passed to the flight control actuators. In this way, if any one of the computers fails and starts producing garbage commands, those erroneous commands will not be selected (they are automatically rejected by the voting scheme). A monitoring system can also detect a failed computer in this way and take it offline, allowing "fail-active" functionality — an autoland can continue on the 2 remaining functional computers.

Less complex aircraft, and aircraft without autoland, still sometimes have 2 FGCs, but do not support fail-active operation. In these systems only one of the two computers is active or selected at any given time. A transfer switch in the cockpit allows the pilot to transfer control from one computer to the other if one fails.

And it's not just airliners. Business jets commonly also have dual FGCs, and in recent times even small general aviation airplanes like the Diamond DA-42 have dual systems (Garmin G1000 in dual-GFC700 configurations).

This photo (click for high res version) shows a Cessna Citation CJ business jet with dual Garmin autopilots. At the top of the PFD, notice there is a small green arrow pointing left; this indicates the left FGC is currently selected. The photo also shows the XFR (transfer) button on the mode select panel, top center, just underneath the master caution/warning annunciator panel. Pushing this button would switch to the right (#2) FGC and change the arrow on the PFD to point to the right. These indications are fairly representative of other dual-FGC systems.

Here's another photo of a Hawker 800 with Rockwell Collins Pro Line 21. You can see the same arrow on the PFDs. In this aircraft the transfer switch is labeled "AP XFR" and is again on the autopilot panel just underneath the glareshield at the top of the panel toward the left hand side.

And finally a photo of a 767 with 3 FGCs and full autoland capability. It's a bit hard to read in this photo, but just above the autopilot disengage bar (the "spacebar" looking thing on the right side of the mode select panel just under the glareshield) the 3 buttons are labeled "A/P ENGAGE", "L" "C" and "R" for the left, center and right FGCs. During an autoland all 3 would be selected and illuminated.


Can the airport name be omitted when contacting ATC if the frequency is not used by any other nearby airports?

When every transmission to the tower begins with "Executive Tower...." that is the keyword that makes the controller's ears perk up and start taking notes.

If you don't say the magic words, your controller may be a step or two behind as you rattle off your request.

Also, you think you're on the right frequency, and you think you know who you're talking to, but what if you mis-tuned the frequency knob by a digit or two, or forgot to hit the COM1/COM2 button?  You could be talking to the wrong receiver and not know it.  That is how airplanes sometimes land at the wrong airport.

Every initial transmission should start with the intended receiver; that is part of the rules and just common sense.  Don't try to shorten transmissions and end up causing more work for everyone.


Rattling that disappears after liftoff is normally associated with a vibrating tire transmitting vibrations up through the airframe, and causing some sort of interior panel that is a bit loose to rattle in sympathy.  On most airliners the brake system applies the main wheel brakes momentarily, once weight-off-wheels, to prevent the usual spin down vibrations during retraction (Nosewheels normally use a friction brake that contacts the tire when it's fully up for the same purpose).  So if the wheel is shaking and making other things shake it will stop as soon as you're airborne.

Airliner wheel assemblies are usually statically balanced vertically like motorcycle tires, not dynamically balanced on machines like car tires (I shudder to think of the cost of a dynamic balancer that can do wheels that big).  You can have a vibration mode that comes in at a certain tire RPM, so all of a sudden starts to shake, then you lift off and the brakes are tapped by the braking system to stop the  wheels, and the vibration stops.


What is the low resistance design path in an aircraft to withstand a lightning strike?

The conductive exterior body

Almost all aircraft have metal bodies, the electric current flows through the exterior metal.

Aircraft with composite hulls can have conducting material added to the composites to provide a path for lightning. This is typically a metal mesh.

Some smaller composite aircraft, lacking this sort of provision, simply cannot fly near clouds or anywhere where there is a risk of lightning.

photo by Boeing - see references

The outer conducting surface acts as a Faraday cage preventing the high voltages and currents from affecting the interior.

 a Faraday cage photo by Antoine Taveneaux

  It is estimated that on average, each airplane in the U.S. commercial
  fleet is struck lightly by lightning more than once each year.

  Initially, the lightning will attach to an extremity such as the nose
  or wing tip. The airplane then flies through the lightning flash,
  which reattaches itself to the fuselage at other locations while the
  airplane is in the electric "circuit" between the cloud regions of
  opposite polarity. The current will travel through the conductive
  exterior skin and structures of the aircraft and exit off some other
  extremity, such as the tail. Pilots occasionally report temporary
  flickering of lights or short-lived interference with instruments.

  Every circuit and piece of equipment that is critical or essential to
  the safe flight and landing of an aircraft must be verified by the
  manufacturers to be protected against lightning in accordance with
  regulations set by the Federal Aviation Administration (FAA) or a
  similar authority in the country of the aircraft's origin.

From Scientific American - What happens when lightning strikes an airplane?

  Planes are now built to absorb 250,000 amps, whereas the average
  strike generates 32,000 amps.

  "It only gets really serious when the radome [nose cone] is struck,
  the only part of the plane's shell not made of metal, as this is where
  the radar is located. But nose cones have special lightning conductors
  for just this reason."

From The Guardian - Should you be worried about lightning striking your plane?

  The 787 flight test team gathered the unexpected data last month after
  one of the Dreamliner test aircaft was struck by lightning. Unlike
  traditional aluminum aircraft where the entire aircraft is conductive,
  on a composite airplane the charge from a lightning strike would find
  its way to the conductive parts such as wiring or hinges. In order to
  avoid the risk of the charge damaging these kinds of parts, Boeing
  had to add conductive material to the composites in order to provide a
  pathway for lightning strikes.

From Boeing 787 Withstands Lightning Strike

Other references

Boeing - Lightning Strikes, Protection, Inspection and Repair
Protecting the 787
Lightning strike protection strategies for composite aircraft


What infrastructures are required for airlines to send PNL messages?

It's not just one. Private networks are used such as the IP-based ARINC AviNet, AFTN Teletype, etc.

For the specifics and standards, that information is not freely available (>\$3000). From IATA manuals, go to the Passenger tab, then the Security & Facilitation section. Or click here.

  IATA's Passenger Data Exchange Support Plus package provides governments with all necessary standards, helpfully grouped in a single purchase.

The following example is for France (may not be current):

There is also a presentation on the IATA website you may want to download and check.


How well can an airplane which is tied down be protected from a blizzard?

There are several additional measures which can be done to prevent a tied down airplane from harsh weather, storms and blizzards. However, nature is always more powerful than humans and  it can overcome any safety measures taken by them.

If your airplane is tied down properly and securely, hail is a bigger threat than storms or blizzards. A hangar protects an airplane more than the one outside, but it costs a lot more.

This article (and page 2) discusses several measures you can take to protect your airplane against harsh weather. To avoid redundancy, I am just pointing (and paraphrasing) a few here:

  Parking spot
  If you can, choose a spot which can break the wind intensity.

  Anchor points
  Depending on the aircraft, the anchor points' holding strength must be 3000-4000 lbs.

  Ropes
  You should use those ropes which do not shrink when wet (e.g., nylon or dracon ropes instead of Manila).

  Position
  If possible, park aircraft nearly into the wind as possible.

  Weight
  A lighter object is easier to get displaced. You can fill-up the tanks to add extra weight.

If you interested in reading some long articles, this and this provide some useful information too.

Regarding your second question about snow on the wings, I hardly doubt that something like this will happen:

The above happened because:

  ... when the tail hook was torn off and the plane was pushed forward, breaking the spar. (picture here)

Airplane wings are very sturdy. They can bear the weight of a foot or two of snow.


As an anecdotal answer to your first two questions, paved runways used by air carriers that have obviously noticeable vertical curves are a minority but not uncommon.

Unless they've redone the runway at Stansted, north of London, there's a significant hump in the middle. I used to operate through it at night in the early 1990s. As a bit of fun, we'd arrange legs so that a new first officer would have the leg into Stansted. On final at night the hump was not noticeable. However, when you touched down, the runway lights along the last half of the runway would disappear, at which point the captain would observe, "Hmm, not much runway left."

If you define a runway simply as a strip of land regularly used by aircraft, there's a whole lot of them that have vertical curves, and many with horizontal bends as well. It's gone now, but there used to be a strip at a lumber mill in North Fork, California, that had a 10-15 degree bend in the middle. McKenzie Bridge airfield just upriver from my home in Oregon has a steep incline on the east end.

Landings and takeoff on uneven runways are not significantly more complex than on straight runways. If the runway qualifies as an uphill/downhill runway, you generally takeoff downhill and land uphill. Touching down on the downside of a hump can make your landing feel a little softer than otherwise. Touching down on the upside of a hump makes it a little harder than otherwise.

Accommodating a horizontal curve is more challenging. It's worth remembering, though, that seaplanes often use a curved takeoff run.


Is flying as a post-retirement occupation possible?

It depends on your jurisdiction. A lot of places mandate a retirement age of 65 for scheduled commercial pilots (part 121 here in the USA). You are allowed to fly 91 and 135 (charter) operations over 65. While you state you don't want to fly for the airlines, it's worth noting that this retirement age causes a large influx of older out of work pilots many of whom still want to fly. As such there are plenty of high experience older pilots that are primed for flying 135 operations. These may be the people you are competing against for a job which as a low time, potentially inexperienced pilot would be an issue at the bigger outfits. In reality it will depend on a bit on if you are getting into it to make a living or just to fly and bring home some extra cash.

With that in mind there are plenty of commercial operations that seem to always be looking for people:

All of the flight schools near me seem to constantly be on the hunt for instructors. If you are willing to go that route I would think you should have no issue finding work.
There is a small charter op run out of the FBO I fly from. They run 3 King Airs and seem to always be short of qualified pilots. A lot of people use these as time building/jump off points so turn over is high. Presenting yourself as someone willing to stick around, has no interest of going on to the airlines, looks pretty good. There are lots of these smaller outfits, generally at local airports.
If your willing to move to somewhere potentially far far away mission flying is an option. This episode of Omega Tau covers it in great detail and is worth the listen.
If you are looking to spice up retirement, ferry flying can be high pay for the right situations.
Depending on where you are there is a fair bit of Ag Flying you can do.
If you are in or near a beach area and like to fly low and slow, towing banners is always an option.


In this MD-11 stall test video, are we seeing the tail stalling first?

The entire tail is shaking (not just the horizontal stabilizer) not because it's stalling but because it is in the turbulent wake of the main wing.  The tail is generating downforce as you can see from the up elevator.  The main wing's nose down pitching moment increases when the center of pressure shifts aft at stall, as well as the change in the overall center of lift outboard and aft due to wing sweep as the root stalls with the outer end still flying.
The increase in pitching moment exceeds the downforce that the tail is able to produce, and the wing wins the force balance tug-of-war with the tail, and the airplane pitches over.
If the tail itself stalled, the nose would pitch over radically from the near complete removal of downforce, as if the pilot suddenly shoved the stick forward. That's not what is happening in the video.  When this happens the tail's local AOA can increase further due to the pitch over and and a partially stalled tail can stall completely as if you sawed it off, and the airplane ends up pointed at the ground, as demonstrated in this testing in a Twin Otter.
I recall another incident in in a Twin Otter in the Canadian Arctic where tail stall was induced by the pilot pitching over hard after a zoom climb right after takeoff.  Extreme pitch rotation at low speed means very high local AOA at the tail's leading edge. The pitch over rotation cause the horizontal tail's stall AOA to be exceeded when the pilot re-applied up elevator, and once exceeded it just got worse, and the Twin Otter just pitched over straight into the ground.


What is Waterline and why is it called so?

Water lines (WL) designate location in the height of the aircraft, from ground up.

This is explained more in this question


What is the 'arm' at the rear of the X-29?

Two X-29's were built, and the only difference between the two is that #2 has an externally mounted spin recovery chute attached to the tail. That is what you are seeing in this picture. The chute is packed in the tube structure and the "arms" are structural to distribute load.

Source

  The only significant difference between the two aircraft was an emergency spin chute deployment system mounted at the base of the rudder on aircraft No. 2.

Here is a video of the chute deployed

And here are more details from NASA on the chute system

The reason that #2 needed this and #1 did not is that #2 was going to be conducting experiments at up to 67° angle of attack, where entering a spin was much more likely. #1's AOA was limited to about 21° and was considered the "phase-1" flight dynamics platform, while #2 was the "phase-2" platform.


Why is the font size of runway numbers in Canada small?

(Click either to view)

Short answer: Canada paints them by the book. They're not small.

Ottawa airport conforms to the standards set by ICAO Annex 14 for airport design. Those standards guarantee the legibility of the numbers.

  5.2.2.6 The numbers and letters shall be in the form and proportion shown in Figure 5-3. The dimensions shall be not less than those shown in Figure 5-3, but where the numbers are incorporated in the threshold marking, larger dimensions shall be used in order to fill adequately the gap between the stripes of the threshold marking.

Member states can deviate and then notify ICAO they have deviated, as long as the height of the characters does not go below 9 meters (30 feet).

There's no answer to why they are smaller than the rest, checking how +250 countries paint the numbers to compare with Canada is unattainable. Canada and many others (Crete, Athens, Cairo, Lisbon, ...) paint them like that, and that's the norm per ICAO.

Measurement from Google Earth for Ottawa.


Why do the A320’s primary flight controls have hydromechanical backups only for the rudder?

The mechanical backup is only meant to maintain basic controllability during a temporary failure of the whole fly-by-wire system. As the OP mentioned, the rudder is deemed sufficient for basic roll control, while the horizontal stabilizer is deemed sufficient for basic pitch control even without any stability augmentation. That being said, the mechanical backup is not meant to achieve continued safe flight and landing (I would be really surprised if the mechanical backup meets all of the ARAC minimum controllability guidance); it's expected that at least one flight control computer can be rebooted to take over control after the initial failure (Ref. Airbus A320 Crew Manual).

The reason for relegating the mechanical backup to rudder and trimmable stabilizer, instead of to elevator and ailerons, pretty much has to do with the choice of the passive sidestick as the pitch and roll inceptor. It lacks mechanical linkages to translate its motion to external assemblies, nor does it have a feel unit to provide feedback for the airloads. This leads to significant weight savings and simplicity in design, and is the primary advantage of the passive sidestick.

I suspect that the reason for even having a mechanical backup scheme is due to mistrust in FBW systems for civil aviation when they first came to use. As trust in redundancy and dissimilarity grew, newer generations of Airbus aircraft (e.g. A380, A350, A220) did away with it completely, and instead have an electrical backup servo control loop on each of the axis.


How should private airports or locations not regularly intended for landing be identified if you land at or take off from them?

In the USA, as far as your logbook is concerned, FAR 61.51(b)(1)(iii) only requires "Location where the aircraft departed and arrived," not the 4-letter ICAO identifier of your airports. When you abbreviate the airport with its identifier, that's all you're doing: abbreviating. You could, for instance, write "Nashville International Airport" instead of "KBNA."

Seaplane and helicopter pilots often land in places that aren't even airports. You might log the destination as "Murphy Lake" or "Walmart Parking Lot." Such is the standard convention.

For purposes of the flight plan, there are a few options if flying to a location that has no identifier. On an ICAO flight plan to a location with no identifier, you would enter ZZZZ as your airport, and in the remarks section include a DEST/ group including the lat/long of your destination. For instance, I think DEST/3607N08641W would work. On an FAA flight plan, you can list the nearest waypoint to your destination, and again, describe your actual destination as a common name or lat/long in the remarks.


Do pilots have separate volume knobs on the radio panel?

Some modern audio panels allow for independent volume control for pilot (left seat), co-pilot (right seat) and passengers.

For example, a popular panel, the Garmin 340 has controls on each side of the panel, left for Pilot, right for Co-pilot:

Another popular panel, the PS Engineering PMA-series only separates out the Crew from the Passengers. In that case, you'd want to use your headset volume control (see below)

There are a lot of audio panels out there, so you'd just have to see if the one in your airplane supports independent volume controls.

Additionally, there is a difference between the intercom (in-airplane communication) and radio (airplane-to-communication frequency) volume controls. Often the panel handles the master volume (the mix of both intercom and comm) volume.  Whatever radio you're using (see below for an example using a popular GPS Nav/Comm the Garmin GNS430) will likely have a volume control for the Comm and Nav functions (the Nav - to listen to the audio broadcast from a NavAid).  In this case, I set the volume I like on the audio panel and then adjust the Radio volume after.

However, I think all (or 99%) of headsets have their own volume control, either inline on the cord or the adjustment is on the ear cup, so you can always adjust your own volume that way if the audio panel doesn't support it.

Inline and ear cup.

Related to all this is the question "what does the squelch do?"  Essentially the squelch is the volume threshold needed to activate the mic (notice how you don't have to push a button to talk within the airplane?). If set too low, the noise from the engine will continuously activate the mic, set too high and it won't pick up your voice even if yelling or with the mic close to your mouth. It is usually adjusted by either an outer ring (look at the little diagram on the Garmin 340 where it says SQ), or in the case of the GNS430, you push the volume knob in to adjust it. Other equipment, you pull the knob, so it's really a matter of getting to know your avionics!  A friend of mine once said, what you really need to know to fly a plane, is how to work the radio!


What is the propeller efficiency, $μ_p$, of modern propellers for light sport aircraft?

Propeller efficiency is mentioned a lot here on Aviation SE, but lacks a good explanation. Here we go:

A propeller accelerates the air of density $\rho$ which is flowing through the propeller disc of diameter $d_P$. This can be idealized as a stream tube going through the propeller disc. This stream tube starts with air at ambient speed and a wide diameter d$_0$. As the suction ahead of the propeller accelerates the air in the streamtube, it starts to speed up and the stream tube contracts. In the propeller plane we witness a jump in pressure p: Here, energy is added to the flow, so Bernoulli does not apply momentarily. Past the propeller the air in the stream tube accelerates further and the tube contracts to the diameter d$_1$ when the pressure inside has dropped to the ambient pressure (dashed line in the pressure graph below):

The air speed ahead is $v_0 = v_{\infty}$ and the air speed aft of the propeller is $v_1 = v_0 + \Delta v$. The propeller effects a pressure change which sucks in the air ahead of it and pushes it out. Since the mass flow must be equal ahead and behind the propeller, the stream tube diameter is bigger ahead of the propeller and smaller downstream. In reality, there is no neat boundary between the air flowing through the propeller and that surrounding it, but for computing thrust this simplification works well if the airspeed is identical across the cross section of the propeller disc.

The efficiency $\eta$ of thrust creation is the work done on the mass flow through the propeller $W = m\cdot\Delta v\cdot v_0$ relative to the impulse change of the air $\Delta I = m\cdot\frac{v_1^2 - v_2^2}{2}$:
$$\eta^{opt} = \frac{2\cdot v_0}{v_1 + v_0} = \frac{v_{\infty}}{v_{\infty} + \frac{\Delta v}{2}} = \frac{1}{1 + \frac{\Delta v}{2\cdot v_{\infty}}}$$
This equation assumes that air is uniformly accelerated straight backwards. To be more precise, you need to add the swirl losses, since the air receives a rotational component $\omega$ from the propeller, spinning with the angular velocity $\Omega$, as well:
$$\eta^{opt}_{Prop} = \frac{1 - \frac{\Delta v\cdot \left({v_{\infty} + \frac{\Delta v}{2}}\right)}{d_P^2\cdot\Omega^2}}{1 + \frac{\Delta v}{2\cdot v_{\infty}}}$$
Still, we have not included friction losses yet and our prop spinner and engine nacelle are also not included. Now we must enter into a definition what propeller thrust is: Is it just the lift acting on the propeller blades in forward direction, or is it the remaining forward force after the additional drag of the airplane components in the slipstream of the propeller has been subtracted?

To avoid lengthy computations, charts can be used where the efficiency is plotted over a range of parameters.

To cut the discussion short: Generally it is safe to assume a top propeller efficiency of 0.85 (85%) with big, slowly spinning propellers (1000 to 1700 RPM). If the twist distribution along the blade does not match the local angle of attack distribution (say, if the propeller is optimized for high speed, but operated at slow airspeed, like during take-off), efficiency can easily drop to 0.7 (70%). Things become worse if the pitch of the blades is fixed. See below for a typical example of a variable pitch propeller. Each of the curves is for a different pitch setting, the x axis shows the advance ratio (the ratio between airspeed and circumferential speed; here off by a factor of 1/$\pi$), while the y axis shows the efficiency.

Efficiency chart of a variable pitch propeller. Source: McCormick B.W. Aerodynamics, Aeronautics & Flight Mechanics. John Wiley & Sons, Inc., 1979.

What can be seen from the equations above is that it is more efficient to accelerate lots of air a little than to accelerate a little air by a lot. This means that small propellers on ungeared engines, spinning at high RPM, are at a distinct disadvantage; this is why Roskam assumes only 70% for them and only 80% for GA propellers.

The 90% you name has to my knowledge only been scratched at by some very efficient (slow, large, contra-rotating) propellers operating under ideal conditions. To play it safe, I would choose a slightly smaller number for them.


Why do flight times differ between traveling East versus traveling West?

As Robbie's answer implies, the answer is wind - Trade Winds govern what happens on or near the surface and were historically important for sailing ships, and today in aviation we deal with the the Winds Aloft at whatever altitude your plane is flying.

As an example, consider two hypothetical flights at 30,000 feet with the winds shown below:

With these winds a flight from A to B (East-to-West) will be fighting headwinds the whole way. My handy flight planning program tells me that at 500 knots (airspeed) you'd be in the air for about 5 hours 30 minutes.

Traveling in the opposite direction from B to A you'd have a tailwind, and with the same 500 knot airspeed you would make the trip in roughly 4 hours.

The winds aloft vary seasonally, which can affect flight times for summer versus winter trips. According to one of our folks who is regularly up at those altitudes even the daily variations can be noticeable, and may make the difference between being able to make a nonstop trip or having to stop for fuel on the way.

Pilots and flight dispatchers will often review the wind data prior to flight and try to select an altitude that affords a "good ride" (free of turbulence) and favorable winds (either a tailwind or the lowest headwind they can find).


Knots vs MPH, is there some standard for when to use which unit?

According to the FAA Flight Navigators Handbook (the Flight Navigator Cert is rarely issued any more to my understanding but none the less).

  The standard unit of distance for navigation is the nautical mile
  (NM). The NM can be defined as either 6,076 feet or 1 minute of
  latitude

It goes on to talk about speed

  Closely related to the concept of distance is speed, which determines
  the rate of change of position. Speed is usually expressed in miles
  per hour (mph), this being either SM per hour or NM per hour. If the
  measure of distance is NM, it is customary to speak of speed in terms
  of knots. Thus, a speed of 200 knots and a speed of 200 NM per hour
  are the same thing. It is incorrect to say 200 knots per hour unless
  referring to acceleration.

It seems it comes down to what you measure distance in, then simply report the appropriate speed units.

Most pilots will calculate (and talk in units) based on the instrumentation in their plane. Some airspeed indicators contain both knots and MPH however its not uncommon for them to contain only a single unit (generally older GA planes is where I have seen MPH instruments). POH's will generally contain what ever unit the air speed indicators in the original build of the plane contained (some POHs will contain both units). Just to show some examples, Mooney reported speeds in MPH in their older POH's while say a Piper from that era shows Kts in its POH. For example this indicator contains both units.

(source)

In the end of the day its most important that the units are not mixed up and or used interchangeably.

As for the errors in airspeeds this is one of the reasons that air speed indicators have color queues to indicate things like stall range, flap extend range and smooth air operating range. This way if a pilot does accidentally confuse units there are other things to rely on. (Side note there are some important speeds that do NOT appear on airspeed indicators that should always be noted).

-Edit-
To answer the comments below.

I report distance in NM since thats what foreflight uses on its ruler function as well as its ring function (at least the way I have it set up). Most plotters I have seen are in NM so even if I had a paper map I would be reporting NM as well.

Im not sure the FAA has official declared that Knots are the only acceptable unit. MPH airspeed indicators are still considered air worthy so they must at least accept it on that level. There have been pushes to standardize instrumentation after the issues caused by the eastern vs. western attitude indicators but with the advent of glass cockpits most of these things can now be configurable in software and changed by a simple setting. The FAR's (such as 91.117) report speed in both KTS and MPH and that is the letter of the law from the FAA.


Has there been an aircraft with multiple type of engines?

The Convair B-36 Peacemaker had six Pratt and Whitney radial piston engine propellers and four GE turbojets. The turbojets were used during takeoff and shut down during flight.

 image source Wikimedia Commons


Are engines automatically stopped in an emergency landing?

There is no automatic shutdown. However, shutting down the engines is part of the evacuation checklist done by the flight crew.

It's happened before that the controls link was severed and an engine could not be shutdown, such as in Qantas Flight 32.

  Upon landing, the crew were unable to shut down the No. 1 engine, which had to be doused by emergency crews until flameout was achieved.

Normally the captain would then instruct the cabin crew to not use that side of the plane. Same thing happens when there is a fire on one side, in that case the captain would also steer the plane so that the good side is upwind.

Aircraft are tested to ensure all occupants can evacuate with 50% of the emergency exits not working (glass half-full: 50% of the doors working). See: How are evacuation tests made as realistic as possible?

About how long it takes for the engine to stop producing thrust, it's about 5 seconds. If there is no or little thrust, there is no suction to worry about. Also note that figure is for a spool down from full thrust (not from idle thrust, which is to be expected after landing).

(Source: Jet Transport Performance Methods)


When should pilots observe a "Sterile Cockpit"?

The "sterile cockpit rule" is an informal name for 14 CFR 121.542 and 14 CFR 135.100.  It says that no non-essential duties may be done during a critical phase of flight which is defined as "all ground operations involving taxi, takeoff and landing, and all other flight operations conducted below 10,000 feet, except cruise flight".  In your example, once they level off at cruise, even if it is below 10,000 feet, it no longer applies.

While this doesn't apply to Part 91 operations like you describe, it is a very good idea to follow the rule anyway to prevent distractions and increase the level of safety.

As far as the GPS, I would recommend fiddling with it on the ground before you takeoff and be familiar with its operation before you need to use it.  Being heads down for an extended period of time is never a good idea (unless you have a safety pilot along to keep an eye on things and look for traffic)!

The full text of the regulation is:

  §121.542   Flight crewmember duties.

  (a) No certificate holder shall require, nor may any flight crewmember
  perform, any duties during a critical phase of flight except those
  duties required for the safe operation of the aircraft. Duties such as
  company required calls made for such nonsafety related purposes as
  ordering galley supplies and confirming passenger connections,
  announcements made to passengers promoting the air carrier or pointing
  out sights of interest, and filling out company payroll and related
  records are not required for the safe operation of the aircraft.

  (b) No flight crewmember may engage in, nor may any pilot in command
  permit, any activity during a critical phase of flight which could
  distract any flight crewmember from the performance of his or her
  duties or which could interfere in any way with the proper conduct of
  those duties. Activities such as eating meals, engaging in
  nonessential conversations within the cockpit and nonessential
  communications between the cabin and cockpit crews, and reading
  publications not related to the proper conduct of the flight are not
  required for the safe operation of the aircraft.

  (c) For the purposes of this section, critical phases of flight
  includes all ground operations involving taxi, takeoff and landing,
  and all other flight operations conducted below 10,000 feet, except
  cruise flight.

  Note: Taxi is defined as “movement of an airplane under its own power
  on the surface of an airport.”

NASA has a great article called The Sterile Cockpit which goes into a lot more information, and includes some interesting statistics from the ASRS database about accidents/incidents that were in some way caused by not following this regulation:

  48% were altitude deviations

  14% were course deviations

  14% were runway transgressions

  14% were general distractions with no specific adverse consequences

  8% involved takeoffs or landings without clearance

  2% involved near mid-air collisions due to inattention and
  distractions.

Abiding by the sterile cockpit rule can help you to avoid situations like that! The article also gives some examples from the database and talks about a couple of crashes that were attributed to lack of compliance.


Why is full carb heat recommended when reducing power below normal setting?

When you close the throttle for descent, the airflow is constricted.  This constriction is going to cool the air more than it is during cruise configuration, and may increase icing.

From This AOPA document:

Throttle ice is formed at or near a partly closed throttle valve. The water vapor in the induction air condenses and freezes due to the venturi effect cooling as the air passes the. throttle valve.


This regulatory oversight is performed by the Civil Aviation Authority of a country. In India, this function is performed by the Directorate General of Civil Aviation (DGCA-India). Typically certification information is available to the public, but only high level information will be given.

Searching on the DGCA-India website I found this document that lays down the requirements on Cabin Crew Training.


Are there pictures of unassembled planes being transported around?

Here you have pictures of wing upper cover being handled and transported:

(Image Source: www.airbus.com)

Wing upper cover is biggest single composite component on A350XWB.

Additionaly try google: "wing upper cover A350", "wing lower cover A350". Those are the biggest. And you can see them in various stages in google.


Is V(L/D)max equivalent to best glide speed regardless of weight, engine, height, etc.?

According to the FAA's "Best Glide Speed and Distance" handout provided by the General Aviation Joint Steering Committee ("GAJSC"), on most airplanes, the best glide speed is halfway between Vx and Vy. See Exhibit 1


What is the purpose of logo lights on airliners?

There are multiple reasons.

First of all: Of course promotion for the airline.
Another reason is the visibility. Airliners have several lights and strobes (Nav lights, rotating beacon, ...) but this can be overseen. The logo light is used to see if there are any other aircraft crossing the taxiway or apron. It's just better to have a big, bright illuminated area, instead of a few small lights.
And ATC has also something to do with it. Many phrases regarding taxiing include airline names. For example:

  AFA739, give way to an Air Berlin A320 moving from left to right on taxiway Bravo

ATC and the pilot can visually identify the companies name thanks to the logo lights.


Where can I find the flight path data for the Russian spy plane that flew over the US on 9 Aug 2017?

It's on flightradar24.com blog:

  RF-85655’s Open Skies flights over the United States since the beginning of 2017

Here you can see more details over Washington.

Two of the recent routes are here. One of them flying as low as 3,800 feet.


What difference does the choice of paved runway surface make to aircraft?

Concrete is better for certain large airports. Asphalt never completely hardens, and will always behave like an extremely viscous liquid. So when you heat it up (on a hot summer's day), it becomes less viscous. When you put a heavy weight on it (like an airliner), it will tend to flow away from and surround that airliner. Planes pull up to a gate, sit for an hour or so, and suddenly their wheels have sank into the ramp six inches and they can't move. Same with runways, the constant shock of landing aircraft cause the asphalt to buckle and warp eventually.

Concrete has issues in the cold, however, especially if it is not laid well. It can buckle and crumble when it expands and contracts. However, it only gets stronger as it ages and it can easily be made to withstand the hardest of landing impacts.

The type of material does not make any noticeable difference to takeoff/landing performance.


How do I choose the correct airfoil for my UAV project?

There are two methods of aircraft aerodynamic design. One method is through using known airfoils (for wing and tail surfaces) and deciding other geometric parameters iteratively while meeting certain criteria for performance, stability, control, aeroelasticity, manufacturibility, etc.

The other method is deciding roughly on the size and then attempting to come up with an airfoil shape, that (again) meets certain criteria. This second sort of design process is named inverse design. Where you try to get a desired Pressure distribution through computational iterations.

There are open source and free software as well as commercial options for both methods. Search terms: Airfoil design.

Any general RC aircraft design guideline and relevant spreadsheets will speed up the learning process. Search terms: RC aircraft design guide.

For detail information about the theory and practice; please refer to aircraft aerodynamic design textbooks.

Hope this answer sheds some light onto this wonderful and exciting topic. Feel free to shoot specific questions.


How does washout affect the wing incidence required?

That depends on the taper ratio.

In the end, the wing with washout should produce the same lift as the one without. For a rectangular wing and 2° washout, your reasoning is right and the root should have 1° incidence so the whole wing produces the same lift as the one without washout and 0° at the root. If the wing has a triangular planform, however, the tip contribution to overall lift is much lower and the root incidence should only be 0.667°.

For a general rule, pick the position along the span at which half of the wing area is inboard of this position and pick the root incidence such that the local incidence at this position is 0°.


Would shooting the tyres prevent a takeoff?

(FAA takeoff safety)

If a tire failed/burst during takeoff at high speed, it is recommended to continue the takeoff.

The Face/Off method may work however, quickly grab a helicopter, shoot one of the engines, when that fails, land the helicopter on the tail. In Hollywood, haste is not required as they have endless runways.


What are the spiky things on the back of the Antonov-225 vertical stabilizers?

It appears to be the extension of the aerodynamic fairing between the vertical and horizontal tails (note that the horizontal tail extends outside the vertical one). It can be seen more clearly in the following image.

Image from diecastaircraftforum.com. Original image appears to be from airliners.net

This type of fairings (usually called bullet fairings) are found in 'T' tails and other types of tails (like cruciform tail) where two surface intersect each other at right angles and are used to reduce interference drag (and flow seperation). For example, the following image shows the fairing in C-141 Starlifter, an aircraft with 'T' tail.

airplanesofthepast.com


Have the results of the USAF's $AVE program research been implemented?

The C-17 has a special autopilot system including a component called the MILCAS-FR formation flying system by Honeywell and here is a link a sales brochure.

My military flight time was not in a C-17 but in my opinion once the precise formation locations were determined that achieve the fuel savings in the article it would be a simple decision to use them on any given formation flight based on the tactical situation.  The requirements of each mission would drive that decision.


What does the zig-zag pattern on Hawker Hunter's leading edge represent?

After doing a little more research I found the answer.

The zig-zag on the leading edge is a type of leading edge extension called a dogtooth extension.

Quote from wikipedia:

  A dogtooth is a small, sharp zig-zag break in the leading edge of a
  wing. It is usually used on a swept wing, but also on straight wings
  ("Drooped Leading Edge" arrangement), to generate a vortex flow field
  to prevent separated flow from progressing outboard at high angle of
  attack. The effect is the same as a wing fence.

  Where the dogtooth is added as an afterthought, as for example with
  the Hawker Hunter and some variants of the Quest Kodiak, the dogtooth
  is created by adding an extension to the outer section only of the
  leading edge.


It's just a syringe pump that draws gasoline from the fuel lines where they pass through the cabin.  The outlet of the primer pump runs though plumbing that becomes a network of very small (usually copper) lines snaking around the engine to one or more cylinders, where it terminates at each cylinder in a small nozzle threaded into the intake port just upstream of the intake valve. This plumbing network is completely separate from the fuel system under the cowling with the gascolator, hoses and carb.
I couldn't find any handy schematics online, so I made a silly sketch.  My own airplane runs primer to 3 cylinders like this.  You can prime all 4 or sometimes you see primer line only to one cylinder (airplanes that don't see much cold weather).

When you stroke the primer, it's like you're a doctor injecting something into your patient, except instead of an unfortunate person, you are pumping fuel into those lines running to the cylinders and spraying a mist of raw fuel into the intake port just up from the intake valve.  The fuel spreads around and settles on the walls of the intake port and duct, and starts to evaporate.
The evaporating fuel provides the additional fuel needed, beyond the carburetor's supply, to make the mixture rich enough for starting and to keep the engine running for a bit while it warms up, and works for a number of seconds after starting before the excess fuel has evaporated (by that time the engine is able to sustain itself on the carb's fuel - aircraft carbs normally run a richer than necessary mixture for the idle circuit, to help them run better when cold).  In non-aviation engines, a choke is used on the carb, but aviation practice traditionally avoids adding potential intake blocking gadgets like choke plates.
The more strokes you pump, the more fuel coats the intake passage.  When it's cold outside, you need more fuel to give a longer evaporation time so that the rich mixture lasts longer, so more strokes are required, although obviously, not too much or you flood it.
The caburetor has an accelerator pump that squirts extra fuel when you pump the throttle as well, but this is to help an already running engine cope with sudden power demands when the throttle is opened quickly.  You can pump the throttle to get extra fuel for starting, they way you used to do in ye olden tymes with carbureted cars, but too much fuel just dribbles down into the airbox when you do that and it creates a fire hazard, so it's not a good practice.
Fuel injected engines are primed in a similar way but they just use the injection system itself to spray fuel in when you turn the boost pump on with the mixture rich.  In those engines you don't stroke a pump, but just put the boost pump on, put the mixture to rich, count a couple of seconds, then pull it back to idle cutoff and hit the starter.


Are there examples of diverse departure assessment departures in the US or Canada?

A diverse departure is a default departure procedure, named "omnidirectional" by ICAO.

To answer your question: It is normally not published. The only thing that is required on aeronautical publications is a wording preventing or limiting the use of this procedure.

  BUCKLEY AFB (KBKF),  AURORA, CO  TAKEOFF MINIMUMS  AND (OBSTACLE)
  DEPARTURE PROCEDURES
  11013
  Diverse departure not authorized.
  Use published  departure procedures
  for obstacle avoidance.

Sometimes there is a reminder that it can be used:

  CANNON AFB (KCVS), CLOVIS, NM
  TAKEOFF MINIMUMS  AND (OBSTACLE)
  DEPARTURE PROCEDURES
  ORIG 15064
  Diverse departure authorized all runways.

This default procedure is valid only when:

Not explicitly prohibited,
There is at least one instrument approach for the airport
No obstacle departure procedure (ODP) and
No standard departure (SID) has been published for the airport.

A diverse departure is conducted this way:

Cross the runway end at 35 ft, maintain heading and a 200 ft/NM gradient until 400 ft above the runway end. The 200 ft/NM gradient is TERPS' minimum climb gradient, and corresponds to ICAO's 3.3% for the minimum procedure design gradient.
Continue or turn in any direction while maintaining a minimum rate of climb of 200 ft/NM.
Maintain this rate of climb until reaching a 1,000 ft obstacle clearance or a 2,000ft obstacle clearance in mountainous areas.

Source

The 40:1 ratio (152 ft/NM) delimits a surface from the runway end, named the obstacle clearance surface (OCS). The diverse departure ensures being above the OCS until enroute.

Whenever the conditions exist for a diverse departure, it is implicit ATC authorities have assessed the absence of obstacle above the OCS. This assessment is named the diverse departure assessment.

Given the 40:1 slope and obstacle clearances, the area assessed may have a radius from 25 to 46 NM.


What is the meaning of "Steer 1-2-0" in WWII texts?

To "steer" means to change the aircraft's track (the direction of movement of the aircraft) to a certain degree in relation to the lines of meridian (north–south lines). The units are degrees from north in a clockwise direction. North is 0°, east is 90°, south is 180°, and west is 270°. Note that, due to wind forces, track is not the same as the heading (where the nose is pointing).


Airbus Beluga, what is aft of the cockpit?

On the Beluga, the area behind the cockpit bulkhead 6 is unpressurized. It contains avionics (A19), the nose wheel and the crew entry hatch (17). It is connected to the forward underfloor cargo bay. That area is unchanged from the A300: it's where the passenger luggage is usually kept. Aft of the wing is another cargo bay.
The same goes for the Beluga XL: underneath the floor, it's identical to a normal A330.

This article indicates the underfloor cargo areas can be used:

... the Beluga XL can carry two A350 wings with additional space for other small components and cargo pallets underneath the main hold floor.
Underneath the freight area is room for 14 LD3 containers as well as a bulk cargo compartment in the far aft.


How much thrust can the thrust reversers create?

Estimations

We can at least estimate a reverse thrust case based on some numbers and some physics, a bit of a specific case of this question. The stopping distance equation:

$$d_f=\frac{v_i^2}{2a}$$

The information in Appendix B here for the 727-200 gives stopping distances for different cases. If we look at a sea level pressure altitude case with 120,000 lb gross weight, the stopping distance is 2452 feet. The correction for a reversers only case is 2.57, bringing the distance to 6302.

At a landing speed of 200 ft/s, the plane will take 11500 lb of force to stop in that distance. Each engine on the 727-200 provides 14500 lb of thrust force maximum. Considering that part of the stopping force will be provided by drag and surface friction, the reverse thrust is about 25% of the maximum forward thrust. The reversers will be more effective at higher air speeds, so the maximum will be higher than this.

Figure 39.5 here shows a graph of reverse thrust compared to forward thrust for different bypass ratios and reverse thrust types. This is a good check for a general case. The GEnx-1B64 has a bypass ratio of about 10, and reverses the fan but not the primary exhaust, which gives a ratio of 30% of maximum forward thrust.

Summary

The engine will not run at full power when in reverse mode, so accounting for this and the bypass ratio will leave you with about states that modern thrust reversers can convert up to 35% to 50% of their forward thrust into reverse thrust.


Is rudder deflection sufficient to maintain directional control on the runway at high speed, or is nose wheel steering needed?

There is some overlap in effectiveness, and therefore no real magic number, but most aircraft that don't have full time nosewheel steering will have some published airspeed at which one will be favored over the other.  For example, in the EA-6B it was 80 KIAS.  On take off roll you would hold the nosewheel steering button on the control stick down to maintain directional control with the nose wheel.  Accellerating through 80 KIAS it was a call-out to release the NWS button and rely on the rudder effectiveness to keep control up to rotation at around 145 KIAS.  The reason for this was not because the nosewheel was less effective due to less friction, (traction) but rather there was a risk of overcontrolling steering at higher speeds.


What would happen if the wing of a supersonic plane goes into the shock wave from the nose?

Not much.

The outer wing would fly in undisturbed flow and an inboard wedge would fly inside of the Mach cone of the nose. This is similar to a wing with a supersonic leading edge; something that has been quite common with Mach 2+ designs before swing-wing aircraft. The nose shock of a pointed nose is a weak, oblique shock which does not alter flow parameters dramatically,


What are the vertical pieces of metal on the Slingsby Swallow wing for?

You're correct -- they're speedbrakes, often referred to as spoilers, and are retracted when striving for efficient flight, but are generally extended in the landing pattern so that you have correction available if you start to get slightly low.  Also frequently extended when the glider is left on the ground to reduce the effect of gusty winds & the likelihood that they would lift a wing.


When to log time as PIC, Dual or Co-Pilot?

Canadian law is as follows:

At no time can anyone in a private C172 log SIC or co-pilot time, because the 172 is certified only for single pilot operations and the aircraft is not flown under the provisions of an Operating Certificate that mandates two pilot operation.

You can log dual (instruction) time when you are receiving instruction from a Flight Instructor certified to do so. (In Canada CFI refers exclusively to the Chief Flight Instructor of a Flight Training Unit.)

Otherwise, you can log PIC time, when you are PIC, otherwise you cannot log time at all.

If you are in simulated IMC, either you or your friend can log time, assuming you are both qualified to be PIC, and depending on who you agree between you is Pilot In Command, but never both of you, unless he is a qualified flight instructor. Even then, only one person can log PIC time, in Canada.

Note that in Canada it is not required for the "lookout" or "safety person" to be a qualified pilot of any kind, if the PIC wants to fly under the hood. It remains the PIC's responsibility to fly safely and look out for traffic, and he or she can discharge that responsibility by asking any responsible person to help them.

These rules are rather different from the ones that prevail in the US.

Hope that helps!


Is certification required to conduct runways repairs?

To the best of my knowledge, you do not require any certification to fix a runway/taxiway, and anyone with a proper equipment can do that. But to facilitate the process, the FAA has published a few checklists which have to be filled while doing this repair job. These checklists can be found Here. FAA also provides assistance in guiding the construction jobs and identifying risks, the link to which is in the same website as mentioned above.


What does the crew of a long range miltary aircraft eat during a mission?

It's not just the big bombers flying long missions; you'd be surprised how many of the sorties flying over Afghanistan, Iraq, Syria, Libya etc originate from airbases in Northern Europe with refueling stops over the Mediterranean (because closer airbases aren't available or are congested with aircraft from other forces or that have shorter ranges).

The short and simple answer is, aircraft crews eat whatever they can bring with them, that won't make a huge mess in the process. A bigger plane like a B-52 has some room to get up and move, so the pilot may take 15 minutes during ingress or egress, duck out to the entryway and eat a box lunch, then come back and relieve the co-pilot so he can do the same thing. Radar, nav and weapons systems officers typically have a little room behind or between seats to step away and eat, or they'll duck into the entryway as well.

In smaller aircraft, space is more limited, but the pilot's flight suit will still have plenty of pockets to carry food and drink pouches. There are some considerations as to the exact type of food, especially in one- and two-seat jets. A crewman has to prevent "foreign object damage" to the switches and displays in his cockpit, or else his crew chief (and his CO) will be all over him about it. Good choices include pre-wrapped bar-type snacks; granola, protein, energy, some types of candy bars, whatever. Depending on what's available in the mess hall, pilots may be able to assemble simple tortilla wraps with lunch meats and cheese, which are edible with one hand and fewer crumbs than a bread sandwich. Anything that can be put in a drink pouch, like broth or tomato soup, is also a possibility. Bad choices include things like trail mix, peanuts, M&Ms etc, as well as anything too loose to reliably keep together with one hand.

The bigger concern is, what to do when it comes back out? The B-52 has a rudimentary "head", with what amounts to a camping toilet (a bucket with a plastic bag liner and a toilet seat over the top) called the "honeypot". However, if it's used, the crewman who used it is often tasked by the crew chief with cleaning it, so it's considered a last resort. Crew of smaller aircraft have no such luxury, and unlike NASA astronauts, they wouldn't be caught dead wearing a diaper. Most fighter pilots eat a "low-residue" meal for the two or three meals before a very long mission or ferry flight, to reduce the chance they'll have to BM during the flight (some take an anti-diarrheal like Immodium as a preventive measure). Urination is a little easier to deal with, for men at least; pilots carry packets with an absorbent powder (not unlike what's in diapers) called "piddle packets". The difficulty is typically in... "maneuvering". You have to get the equipment out of your flight suit, when you're strapped down to the point of suffocation in a 6-point harness, then be able to aim into the piddle pack. Finally, you have to store this bag of piss somewhere until you get back to base, and as Rhino Driver is fond of explaining, if that base is a carrier, you have to make sure it's extra-secure, or on capture it'll go zooming forward toward the firewall and explode in a shower of damp absorbent crystals. Even if your squadron-mates don't see you getting out of the plane covered in this stuff, your crew chief will be sure to tell them all about it.


For a same propeller solidity, what are the tradeoffs between blade activity factor and blade number?

One way look at it is your engine is power and prop is load.  The amount of thrust you get will depend on the efficiency of the propeller x engine power output.
So, if one is going for the best fuel economy, the two blade is most efficient, but if you want the more thrust from a larger engine, you either increase the number of blades or increase the chord of the blades.
Both approaches reduce efficiency but increase thrust output, resulting in increased performance.
More high aspect blades, as in a helicopter, will be more efficient at lower airspeeds, but will suffer structural issues (bending) as forward airspeed increases.
Fewer low aspect blades offer a much higher forward speed range but will create a lot more blade interference turbulence at lower airspeeds.  These are commonly seen on turboprop freighters such as the C-130.
It is extremely important to evaluate the design speed envelope of the aircraft when choosing, as forward airspeed reduces interference turbulence.
I took the liberty of adding the A6 Intruder jet aircraft to your list, and found the expected improvement in higher airspeed performance, but a take off run almost 5 times that of the A2D-1 Skyshark.
Enough said there.  Contra rotating coaxial props, and keeping prop speeds below supersonic, also help improve efficiency.


Can an aircraft on loan in the US be based outside the US?

Any US-registered aircraft can be based in any country subject to that country's rules. Just check with your local aviation authorities in the country where you want the aircraft to be based before you reposition the aircraft. Some may require you to depart the country every so many days/weeks/months, sometimes in as simple a way as a short hop across a border, but to my knowledge most don't have any restrictions.


Is an A&P certificate ever required to work on military aircraft?

Not usually, A&P is an FAA regulation/certification, and the US Military is not required to abide by FAA regulations. Even military pilots don't (always) have pilots licenses (not FAA ones).

It is possible though that they may ask a civilian contractor to have an A&P, but this would be on a contract-by-contract basis. The US Military does operate a number of civilian-type aircraft that they may have serviced.


Good question. I was taught to anticipate turns and my Garmin 430 will anticipate turns so that you do not overfly the fix. But I don’t remember any specific guidance on the matter, so I looked it up. I found this in the AIM.

  5−3−5. Airway or Route Course Changes

  a. Pilots of aircraft are required to adhere to airways or routes
  being flown. Special attention must be given to this requirement
  during course changes. Each course change consists of variables that
  make the technique applicable in each case a matter only the pilot can
  resolve. Some variables which must be considered are turn radius, wind
  effect, airspeed, degree of turn, and cockpit instrumentation. An
  early turn, as illustrated below, is one method of adhering to airways
  or routes. The use of any available cockpit instrumentation, such as
  Distance Measuring Equipment, may be used by the pilot to lead the
  turn when making course changes. This is consistent with the intent of
  14 CFR Section 91.181, which requires pilots to operate along the
  centerline of an airway and along the direct course between
  navigational aids or fixes.

  b. Turns which begin at or after fix passage may exceed airway or
  route boundaries. FIG 5−3−1 contains an example flight track depicting
  this, together with an example of an early turn.

  c. Without such actions as leading a turn, aircraft operating in
  excess of 290 knots true air speed (TAS) can exceed the normal airway
  or route boundaries… Consequently, the FAA expects pilots to lead
  turns and take other actions they consider necessary during course
  changes to adhere as closely as possible to the airways or route being
  flown.


What is the name for the Mitsubishi A6M Zero's one-piece wing/fuselage?

The construction of the Zero was slightly different from that of its western counterparts. The aircraft had three major sub-assemblies:

wing/center fuselage
forward fuselage, and
aft fuselage.

The construction of the first sub-assembly was such that the both the wings were constructed as one piece integral with the cockpit. This is (presumably) what the author means in the article in question. Otherwise the wing was a semi-monocoque structure with two main spars, which is quite common.

The image below shows the sub-assembly in question (the wing+cockpit section) from a recovered zero. It can be seen that there is no great difference in design, only in the choice of the sub-assembly (a wing+cockpit section, instead of wing + fuselage).

A6M Zero midsection; image from lasamurai.blogspot.in

The images below show the different sections of the aircraft (middle and rear sections) from a rebuilt Zero.

Cockpit+wing sub-assembly; image from j-aircraft.com

Rear fuselage assembly; image from j-aircraft.com

I'm not aware of any special name for this. It appears to be a normal semi-monocoque structure.


Why don't large commercial airplanes have electric motors in the wheels?

In fact, this is currently on test.

This test is conducted by Airbus, Safran and Honeywell for the Airbus 320 familly on this aircraft.

An engine is installed on the wheels of the main landing gear

As you might know it take long time and lot of money to certified a system in aeronautics, this is why it's not in use yet.

I other hand, you need to run engine in idle for about 5 minutes in order to warm up the engine and stabilise systems (hydraulics, gyroscopes, etc)

You can find more here : http://www.greentaxiing.com/

Edit 1 : edit to add @Ben elements


How would flow angle change along the length of a propeller airfoil?

In order to explain the situation, I have drawn a couple of pictures.
Consider a propeller rotating with the rotational velocity $\omega$ (in $\frac{rad}{s}$), which is flying at a velocity of $u$ (in $\frac{m}{s}$).

(Please excuse my crude drawing skills...). If we cut the propeller at four places along the radius $r$, we get the following velocity triangles (at the respective positions 1, 2, 3 and 4). Note that in the following we look at the propeller from the tip in direction of the hub:

Note that the tangential velocity at each crosssection rises, however the forward velocity stays the same!
The tangential velocity can be simply calculated by the factor $\omega \cdot r$.
Now everything which is left to do is to calculate the angle $\alpha$, which can be simply done by taking the $atan()$ function (btw, I believe that Fern got this point wrong)
$$\alpha = atan(\frac{u}{\omega \cdot r})$$
Therefore in your specific case with $n=1 \frac{rev}{s}$ we get:
$$\alpha = atan(\frac{15}{2\cdot \pi \cdot r})$$
with $r$ going from 0 to 10 meters (in order to remain practical from 0.1 to 10 meters)


1) This does mean you should keep the nose up as long as possible, increasing the angle of attack when you are behind the drag curve increases the drag the wing produces and uses the elevator as a spoiler in effect. If you have done a full stall landing pulling up cannot get you back into the air, but if you land with extra speed pulling up could mean you start flying again, so you should only use this technique if you are sure you have a low enough airspeed. Good technique is not to yank the stick back, you pull it back while paying attention to the "feel" of the airplane, if it seems to want to fly again ease off on the back pressure.

2) Retracting flap after landing decreases lift and puts more weight on the wheels, making the wheel brakes more effective. It does decrease drag, however your wheel brakes are much more effective at slowing the airplane than drag from the flaps.


The class D airspace you are referring to is a control zone (CTR). According to article 24 of Regulation for Remotely Piloted Aerial Vehicles, the following applies to VLOS operations (emphasis mine):

Except as required by point 6 below, RPAS operations shall not be conducted:

a) within ATZ and beneath take-off and landing paths or at a distance less than 5 km from the airport (ARP or published geographical coordinates) where ATZ is not established;
b) within CTR, without prejudice to point 5 below;
c) within active restricted areas and prohibited areas.

Operations within CTR are permitted only to RPA with operating take-off mass less than 25 kg, up to maximum height of 70 m AGL and within maximum horizontal distance of 200 m. Beneath take  off  and  landing paths, beyond ATZ boundaries and up to 15 km from  the airport, maximum height shall be 30 m AGL.

When  operations  do  not  meet  the  requirements set  forth  in  points  4a), 4b) and  5 above, operations shall be  carried  out  according  to  procedures  published  by  ENAC. When it  is required to operate within airspace as referred in point  4c) above,  operations  shall  be subject to specific authorization according to procedures published by ENAC.

Although you are pretty much directly below the approach path to Linate's runway 18, since the park is just over 15 km from the airport, you should be OK to fly up to 70 metres above ground as long as the drone stays within 200 metres of you.
Of course, there are also other applicable rules to consider: for example, you must wear a high vis vest with "Pilota di RPA" printed on it, you are not allowed to overfly crowds (including wedding guests) and the drone must be registered and identifiable.


Why do all the rings of MH370's transmission locations have the same origin point?

Because the Inmarsat 3 series satellites that were used to transfer the ACARS system data are geostationary. They orbit at a speed and altitude that causes them to stay in the same location with reference to the earth. The signals were received specifically by the Inmarsat 3 F1 satellite which was, at the time, geostationary over the Indian Ocean.


What are the margins used to avoid a stall while slipping near the ground?

When I side slip my glider "correctly" the airspeed indicator drops to zero or at least shows large fluctuations between 30 to 90% of the actual airspeed. So the airspeed indicator essentially becomes worthless during a large side slip and can't give any estimate whether the aircraft is approaching a stall or not. And I wouldn't rely on it to judge if the aircraft is approaching a stall.
I can somewhat judge the speed from the sound of the wind and also how much rudder input creates what kind of side slip (slow usually creates more slip angle for full rudder deflection) and also the back pressure needed but the best indicator for the approaching stall is still the elevator buffeting or an angle of attack indicator or angle of attack warning. If you're planning on doing short field landings with low approach speeds then an angle of attack indicator is probably a good investment.

From a physical standpoint the indicated airspeed in a side slip condition should always be less than or equal to the airspeed that you're actually flying. So if you see an airspeed indication in a side slip configuration you're going to have at least that figure as actual airspeed. This is because the airspeed indicator just shows the difference between atmospheric pressure and total pressure (sum of dynamic and atmospheric pressure). And if you rotate your pitot tube from 0 degrees to 90 degrees off the direction of incoming air it will show less and less dynamic pressure and work more like the static port, thus the readout drops. But it can never show more than what the dynamic pressure actually is (disregarding small vibrations due to unstable inflow). So if you look at the airspeed indicator and judge by the speed it reads you should be on the safe side.

Whether or not the 10kt increment is enough depends on how steep your side slip is and what you are flying. Ground effect could also influence how much angle of attack is left before the stall. Only a numerical simulation would give you an exact number here.

But you can always experiment high up in the air, do a side slip down to what feels as low as you would want to go for a safe landing and then pull up even more and see how far you can go without it stalling or see how it departs (relax controls immediately to avoid any nasty spins) if it actually does anything. Maybe it will show some significant buffeting before it actually stalls (great indicator!), maybe it will just lower the nose (not ideal close to the ground but still safe) or maybe it drops a wing (not so good, add more safety margin).


How can the glide ratio in a balanced turn be estimated?

I get a variation of the glide ratio with $\frac{2}{\bigl(\cos\varphi + \frac{1}{\cos\varphi}\bigr)}$ for circles flown with a bank angle of $\varphi$ when compared to straight flight at the respective best speed for optimum L/D.

Your initial assumptions are right:

Lift: $L = c_L\,\rho\,\frac{v^2}{2}\, S\, n_z$

Load factor: $n_z = \frac{1}{\cos\varphi}$ with the bank angle $\varphi$

Drag: $D = D_0 + D_i = \Bigl(c_{D0} + \frac{c_L^2}{\pi\, AR\,\varepsilon}\Bigr)\,\rho\,\frac{v^2}{2}\, S$ (zero-lift drag + induced drag), and both are equal at optimum $L/D$:

$$\Bigl(\frac{L}{D}\Bigr)_{\rm opt} = \Bigl(\frac{c_L}{c_D}\Bigr)_{\rm opt} = \frac{\pi\, AR\,\epsilon}{2\, c_L}\text{ for straight flight at }1\, g \text{ ($n_z = 1$)}.$$

Now with load factor $n_z = n$ and unchanged speed:

$$\frac{L_{ng}}{D_{ng}} = \frac{\frac{c_{L_{1g}}}{\cos\varphi}}{\frac{c_{L_{1g}}^2\bigl(1 + \frac{1}{\cos^2\varphi}\bigr)}{\pi\, AR\,\epsilon}} = \frac{\pi\, AR\,\varepsilon}{c_{L_{1g}} \bigl(\cos\varphi + \frac{1}{\cos\varphi}\bigr)}.$$

The ratio between both glide ratios is $\frac{2}{\bigl(\cos\varphi + \frac{1}{\cos\varphi}\bigr)}$, which makes sense because it will become 1 for $\varphi = 0$ and become less than 1 for nonzero values of $\varphi$. Note that the glide ratio at n g doesn't carry an "opt" subscript anymore, because by increasing $c_L$ we move away from the optimum. If the best L/D would be maintained for circling flight, speed would need to increase, not lift coefficient.

The altitude loss in straight flight of a distance equal to the diameter of a circle with the radius $R = \frac{v^2}{g\tan\varphi}$ is $2\,\pi\, R \, \frac{D}{L}$. When flown at the correct bank angle, this altitude loss per circle $\Delta h$ will become
$$\Delta h =  \frac{\pi\, v^2}{g \tan\varphi} \Bigl(\frac{D}{L}\Bigr)_{1g}\Bigl(\cos\varphi + \frac{1}{\cos\varphi}\Bigr).$$

Plot of the glide ratio with bank angle divided by the glide ratio for straight flight (blue line). I also added the altitude loss for a full circle (red line, Basis: $L/D = 18$ at 100$\,$m/s in straight flight), both for flight at constant speed and constant lift coefficient:

Use the results from this plot with caution at higher bank angles: Lift would need to double at a bank angle of 60°, doubling $c_L$, so we fly much more slowly than any pilot would. The red line gives more realistic values, since here the aircraft speeds up for flying higher bank angles. Flying at constant speed gives less altitude loss simply because the circle becomes smaller than when flying at constant $c_L$. Note that for every meter flown the altitude lost is greater when flying at constant speed, indicated by the blue glide ratio degradation curve.

Two factors conspire to increase aerodynamic losses when flying at constant speed with higher bank angles:

You need to create more lift, which causes higher induced drag, and
Your optimum $L/D$ is at a higher speed when the bank angle increases, which again increases aerodynamic losses because you move away from the optimum.

If you try to express the altitude loss per circle $\Delta h$ as a function of $\varphi$, you will get a quadratic equation and two solutions, one high and one low bank angle:
$$\frac{\cos^2\varphi + 1}{\sin\varphi} = \frac{g\,\Delta h}{\pi\, v^2} \Bigl(\frac{L}{D}\Bigr)_{1g}.$$
Maybe MathSE can solve this algebraically; I would resort to iteration or tabulation here.


Why are so many small private jets sold just after a few years?

In the United States, aircraft that are owned and operated by businesses are often depreciable for income tax purposes under something called the Modified Accelerated Cost Recovery System (MACRS).

  This is beneficial since faster acceleration allows individuals and
  businesses to deduct greater amounts during the first few years of an
  asset's life, and relatively less later. (Emphasis mine)

But even more so, The 2017 Tax Cuts and Jobs Act provides for 100 percent bonus depreciation, allowing taxpayers immediate deduction of the cost of aircraft acquired and placed in service after Sept. 27, 2017 and before Jan. 1, 2027.

This means that perhaps if someone were to have a financial windfall (sale of a company, or a large sale of highly appreciated stock), they could purchase a rather expensive airplane, and if used for business purposes (generally at least 50%), they could offset their taxes for the entire purchase price of the aircraft in the first year!

To have an overly simplistic example: Say you had $10 million in ordinary taxable income this year. You could reduce that by purchasing a, oh let's say a (2020 List price approx) 2.6 million Cirrus Vision SF50 Jet. You'd be able to reduce your taxable income by 2.6 million and pay taxes on "just" 7.4 million.  Now say at least one year later, you could sell your jet and pay depreciation recapture long-term capital gains tax (which depends on the amount of your ordinary income and is capped at 25% ... which is less than the 2020 37% top tax bracket).  This would have saved you in this example 312,000 (12% of 2.6 million) in a year. Of course, I'm sure it's a little more complicated than this oversimplified example, but you can see how it might be advantageous from a tax perspective, if you have a large income where you can benefit from the 100% depreciation in the first year.

So yes, it could be a tax play. Or it could be like so many things, what you thought was fast/big before you got it, now you have it, and you start to notice faster, bigger things and want to upgrade :)


Is ATC communication subject to FCC profanity regulations?

I'm not sure if FCC broadcast regulations specifically apply to airband VHF: It's not really a "broadcast station" in the sense of FCC regulations, but rather a wireless service (RT) on spectrum delegated to another agency. The FAA handles regulation of the service, the FCC just gave them a particular chunk of the VHF spectrum to use for it.

Obscene or profane transmissions are generally frowned upon by both pilots and controllers though, and the FAA specifically prohibits "obscene, indecent,or profane language" on their communication services (JO 72103Z) - Controllers can face disciplinary action over it, and I imagine they could find something in the regulations to charge a pilot with if they wanted to.


From an ATC perspective, what is an "arrival gate"?

Different ATC facilities need a standardized way to manage handoff of traffic between them and make sure traffic headed in different directions doesn't conflict at the border, especially at the interface between Approach/Departure and Center where traffic is climbing or descending and therefore can't be separated by cruise altitude like en route traffic can.
The standard way this is done in the US is to establish "gates", which are fixes/waypoints on the airspace control boundary, and each is designated for arrivals (descending) or for departures (climbing).  Note that this boundary is not related to airspace class and is not charted, though you can often deduce where it is based on traffic patterns and SIDs/STARs.
Here is a conceptual diagram of the ATC gates for an airport in "south flow", meaning aircraft use the runways in the southerly direction:

Source: here
The black crosses in the corners are the arrival gates, and the white crosses on the sides are the departure gates.  When the airport is in north flow, the diagram is flipped vertically.  For airports that are oriented east-west, the diagram will be rotated 90 degrees for east or west flow.  Most traffic will use a runway on the same side as its arrival gate, but there are crossover paths for when Approach needs to rebalance traffic or some gates are closed due to severe weather.
When a gate is "open", there is an agreed maximum rate or minimum spacing that the sending facility can send aircraft through it, hence the term "metering fix" on the diagram legend.  If the sending facility exceeds this rate, the receiving facility may "close the gate" until they can sort out the resulting mess, which means the sending facility will have to slow down, reroute or hold traffic until the gate reopens.  Nobody wants that.