What constitutes "the lights delineating the runway"?

Presumably it's your runway lighting (edge lights, such as HIRL, MIRL, etc, plus runway end identifier lights - REIL), centerline lights, and touchdown zone lights only, because being able to see the nearest approach light miles away isn't helpful if, by the time I'm at 200' half a mile from the runway (and past that outer-most approach light), I'm inside a dense fog bank with an RVR of 600 feet.

That said, it's a much more common case where the RVR at the runway (where it's measured) is about the same as the in-flight visibility farther out on final, so with an RVR of 4000' you can expect to see the threshold at typical Cat I ILS minimums of 200' AGL (okay, ATDZE for the pedantic & precise), but at 1800 RVR at the same point, you expect to see approach lights but little else.


Why would there be two RNAV waypoints co-located with a VOR?

Your Questions: Why do SOHOW and USIRE exist? And in particular why do they both exist?
Why do they exist: SOHOW and USIRE are published Waypoints on RNAV STARs into Gary, Ind., and Indianapolis, Ind., respectively. They exist and are published because they are part of the procedure being flown (as assigned by ATC).
Why do they both exist: Even though they are in extremely close proximity to each other in space, they are not physically located anywhere. The fact that both of these RNAV Waypoints are only "points in space" (geographic coordinates in a computer) reflects the value and flexibility of Area Navigation.  Perhaps both STARs (to Gary and Indianapolis) could have used either SOHOW or USIRE, but there is no physical reason to do this.  Also, since each of the Waypoints (SOHOW and USIRE) are part of different STARs going to different airports, there is less opportunity for confusion as to which procedure is being flown.
As a note, you mention in reason number 1 of your post (your Counterargument) that Spinner Vortac is a waypoint on the NATCA (RNAV) SID.  Spinner is actually a "transition" on the NATCA SID, which technically ends at NATCA.  See image below.
Good questions.


To answer question #1 (assuming you are flying an airplane):
§61.57 (c)(1) states that:

  Use of an airplane, powered-lift, helicopter, or airship for
  maintaining instrument experience. Within the 6 calendar months
  preceding the month of the flight, that person performed and logged at
  least the following tasks and iterations in an airplane, powered-lift,
  helicopter, or airship, as appropriate, for the instrument rating
  privileges to be maintained in actual weather conditions, or under
  simulated conditions using a view-limiting device that involves having
  performed the following—

  (i) Six instrument approaches.

  (ii) Holding procedures and tasks.

  (iii) Intercepting and tracking courses through the use of
  navigational electronic systems.

As of Sept 1, to maintain instrument proficiency, you will be required to accomplish items i-iii in either an airplane under actual or simulated IMC (you must have at least passed the FAF and begun the final segment of the approach under these conditions for it to count) or have accomplished this in an approved simulator or FTD appropriate to the category and class of aircraft you seek currency in.  See §61.57 (c)(2).  Therefore in Sept, you would be required to accomplish at least 1 IAP in order to remain instrument proficient for that month.  It is suggested at this point to accomplish the required 6 approaches, hold procedures and course tracking in Sept to avoid repeating this process often while still maintaining instrument currency, though this is not required to meed minimum instrument proficiency standards.

Question #2:  see first paragraph of §61.57 (c)(1) - you must have accomplished tasks i-iii within 6 months of any IFR flight where you are acting as PIC.  In scenario #2 you are never current as you have not accomplished tasks i-iii within 6 calendar months for any month shown.  Assuming that you were instrument current in December of the previous year (items i-iii accomplished within that month), you still have a "grace period" to fly the approaches with a safety pilot starting in July of this year.  If items i-iii of §61.57 (c)(1) are not accomplished by December of this year, an IPC will be required as of January 1 of next year to maintain instrument proficiency.

Item iii of §61.57 (c)(1) is a little bit of a contention, but if you are not flying contact or precision radar approaches only to maintain instrument proficiency, you will have used navigational electronic systems to fly these instrument approaches or fly the holding patterns with so item iii can be counted towards with the accomplishment of items i and ii.


Are there any models for planning aircraft placement in hangars?

I’ve not heard of software programs to do this, but the Navy has made use of a relatively low tech solution to address this problem for decades aboard their aircraft carriers.

Known simply as the Ouija Board, the aircraft handler and his crew utilize a scaled physical map of both the carrier flight deck and hangar deck along with appropriately scaled footprint models of aircraft in order to track and plan aircraft movements.

I’d guess a similar scheme could be employed to solve your problems.


Maximum Altitude/Minimum Range limits of ATC PSR

This paper seems to show beam elevation from 0 to 40 degrees, dropping off after that.
See slides 10 and 15.


Why is "NoPT" indicated on this KYKM approach?

FAA_H_8083-15B Instrument Flying Handbook 2012

Procedure turn. A maneuver prescribed when it is necessary to reverse direction to establish an aircraft on the intermediate approach segment or  final approach course.

This particular approach doesn’t have a course reversal—the DME arc takes care of the course change from the YABLU IAF and the DATVE IAF. (Cut off on your map.) BABRE is an intermediate fix, and again needs no reversal.

So as you mentioned, there is no reason to state NoPT.

The version of the chart you used in your post is out of date. The current chart doesn’t mention NoPT, probably because there is no reason to. I’m guessing that mentioning it on your version is a mistake that they have since corrected or they are conforming to newer standards for chart making.


What thrust is used for thrust to weight ratio?

Well, it depends on what you want to know. If you are interested in thrust-to-weight ratio in certain conditions, you should use thrust (and weight) in those conditions.
In terms of standard performance specifications, the maximum static thrust (zero speed, zero altitude, ISA conditions) is normally used. This is often the only thrust point specified anyway. The weight is often less certain; it would be fair to use MTOW for this figure, but some "practical" weight/configuration is often used instead, because it gives better (and possibly "more relevant") result. Technically, the conditions should be explicitly specified.
If you are interested which thrust formula is more correct, this is a separate question.


Airliner headlights flashing alternately

Some modern landing lights have a pulsating or alternating mode. It's just for being recognized more easily, has nothing to do with an emergency.

A constant white light heading right for you over a city full of lights doesn't get as much attention as a pulsating light which gets bigger each time as you get closer :)

Here is one example: https://www.preciseflight.com/pulselite-pulsing-aircraft-lights/

and their video:


Mathematical model used in free route airspace

En-route simulation by airtopsoft is a good simulation modeling software package that I have utilized in the past to model airspace routing. It also give you some pretty powerful tools to analyze the data afterward.

Another commonly used mathematical tool for modeling airspace and routing is the "Airspace Concept Evaluation System" (ACES). This platform uses four-degrees-of-freedom equations of motion to model aircraft performance and navigation data. Based on the trajectory data, it generates "pseudo-radar" tracks to help predict collision avoidance patterns. I believe this tool is more commonly used to predict routes in the NAS but I believe you could utilize it for free route airspace by playing with the input parameters.

Hope this gives you a good place to start!


How do you apply to offer WINGS credit for an event you are sponsoring?

A fly-in by itself doesn't usually qualify for WINGS credit, but if you're also running educational programs or seminars there's a good chance you've got something that will qualify.

Normally you'd work with a FAA Safety Team representative to help set up the program so it meets the WINGS credit requirements (they have access to premade presentations, slides/videos, and with a little notice they can usually help find presenters/speakers), and the representative will then coordinate with your regional FAA Safety Team manager to get the programs listed in SPANS so people can sign up and receive credit.

If you have an account on faasafety.gov you can search the FAASTeam directory for representatives near you:

(I did a cursory search and I didn't see anyone in Douglas, but there are a few folks in Tuscon.)

If you can't get in touch with any of the representatives your best bet is to contact your local FSDO (Scottsdale in your case) directly and ask for the "FAA Safety Team Program Manager" - they'll be able to work with you to get the program coordinated and set up in SPANS.

If you intend to do regular events with safety programs it would probably be worth getting yourself or someone else in your group set up as a FAASTeam representative. There's some (really simple/basic) training involved, and usually the regional program manager or one of the lead representatives in your area will want to meet with you just so they know what you look like, and once you're set up you'll be able to submit requests to have your programs listed directly.


Can I log PIC instrument time in a sim without a current medical or flight review?

You can log training time in a simulator but you can't log PIC time.

The rules on logging are in 14 CFR 61.51. There's no requirement anywhere that I can see to have a medical and/or flight review in order to log time.

Logging training time in a simulator is allowed by 61.51(h):

  (h) Logging training time. (1) A person may log training time when
  that person receives training from an authorized instructor in an
  aircraft, full flight simulator, flight training device, or aviation
  training device.

But, you cannot log PIC time in a simulator. 61.51(e) says (emphasis mine):

  (e) Logging pilot-in-command flight time. (1) A sport,
  recreational, private, commercial, or airline transport pilot may log
  pilot in command flight time for flights-

That means, the only way to log PIC time is in an aircraft.


What are the relative efficiencies of the various stages of a counter rotating propeller?

The key thing to think about is that the first stage doesn't just accelerate air downwards, it also causes it to rotate ("swirl") in the same direction as the first stage propeller.

This happens because the first stage propeller, being an airfoil, generates both lift and drag. The lift corresponds to air being accelerated down the axis of the duct; the drag corresponds to air being accelerated circularly around it. The amount of swirl force is therefore related to the thrust and the effective L/D ratio of the propeller.

The airfoil of the second stage propeller is then encountering air that is moving towards it at the tangential velocity of the propeller, plus the tangential velocity of the air that has now been circularly accelerated ("pre-swirled") in the opposite direction by the first stage.

That increased velocity means that the angle of attack for the second stage airfoil will be increased compared to that encountered by the first stage, and hence greater lift is produced at the same RPM.

To balance the load on the two stages you would need to adjust the pitch or RPM of the second stage propeller.

Note that after the second stage, the air will be "unswirled" back to being closer to a non-rotating flow, and this is one of the reasons that a contra-rotating pair can be more efficient than a single propeller: overall, the system wastes less power in swirling the air rather than accelerating it axially.


What effect would a afterburner have on the compressor if the nozzle outlet is not increased?

Yes, when the AB is lit, the nozzle needs to be opened, because the increase in exhaust temperature causes a decrease in density (pressure remains about the same), and so the same mass flow needs a bigger nozzle area to flow through. In AB, the engine mass flow is about the same as in max dry operation. The AB basically sits behind the core, and operates more or less independently, because the change in nozzle area compensates for the change in exhaust temperature.

And you are exactly correct, if the nozzle wasn't reduced when the AB is turned off, the spools would over speed.

If the nozzle area wasn't increased, the sudden lighting of the AB would most likely stall the engine - probably the fan as the back pressure wave can easily travel back up the bypass duct. AB stalls were common on first generation low bypass military engines. If you could light the AB slowly, it should just cause the spools to slow down, and mass flow to correspondingly decrease. Modern ABs light a bit progressively, to give a "soft" light. Older designs weren't quite so refined.

E.g. See page 208:

  The TF30 ... still had compressor problems going in and out of afterburner..

And here about the F100 saying:

  Some stagnation stalls were caused by "hard" afterburner lights, which were mini explosions that took place inside the afterburner when it was lit up. The pressure wave from the explosion then propagated forward through the duct to the fan, causing the fan to stall and sometimes even causing the forward compressor stage to stall as well. These types of stagnation stalls usually occurred at high altitudes and at high Mach numbers.

Also read Goodbye F100 Stagnation Stalls, see:

  To reduce the influence of pressure waves traveling back up the fan duct, the compressor inlet lip has been moved to bring it closer to the rear of the fan.


Can someone identify this scrapped high-wing plane?

It's an Aermacchi AL-60-B1 (original design by Al Mooney, Lockheed L-402 Bushmaster aka Lockheed 60)

(source)

(source)


What is the relation between aircraft altitude and ADS-B coverage?

The ADS-B signal used by FR24 is transmitted on 1090 MHz. Signals at that frequency do not follow the curvature of the earth very well. They work best in line of sight. Aircraft far away from the receiver must be at high altitude to be above the horizon.

At 1000ft, the horizon is about 33 nautical mile away. Aircraft further away will be shielded below the horizon. For 40000ft, the horizon is about 220 nautical mile away.

Due to a slight refraction of the signal the practical range is about 15% further.


What should I expect to happen when I get on a skydiving flight

is there anything I as a passenger can do to improve the safety of the flight

You should do exactly what your told, when your told and make sure you keep well clear of spinning propellers. You will have a marshall or the pilot themselves guiding you when airside - do exactly as you're told!

  what pre-flight checks should the pilot make before taking-off

If it's the first flight of the day the pilot will do a walk around of the aircraft. They will check the general airframe, as well as some specific things

The static ports being clear
Pitot covers/control locks all removed (those little red dangly things that say "remove before flight")
Control surfaces have free movement and their connecting rods are secure
Tyres & brakes satisfactory
Fuel is sufficient and uncontaminated
Propeller(s) undamaged
Oil sufficient in engines
... and a load of other things!

Before each take-off the pilot will also run the engine up and run it at idle. Just before take off they will perform some pre-takeoff vital actions. You will probably not notice any of this, but I assure you they'll be doing them - they may take mere seconds.


Why isn't the APU a standard diesel generator?

Weight.

Piston APUs for trucks are designed for frugal and quiet operation. This one produces 5.2 kW electrical power and weighs 375 lbs.

The APU for the A320 and B737 is a noisy screaming unit that produces 90 kW electrical power, 445 shaft kW. It weighs 375 lbs as well.

The main difference is in the weight of the engine itself. The turbine engine of the A320/B737 APU produces 445 shaft kW and weighs 145 kg. This diesel engine also produces 450 shaft kW and weighs 1542 kg.

Power-to-weight ratios:

The turbine produces 3.1 kW/kg engine weight.
The diesel engine produces 0.3 kW/kg engine weight, it is a standard industrial machine and not optimised for weight.
The Rolls Royce Merlin was very much optimised for weight, it used aviation fuel (gasoline) and produced 1.58 kW/kg


Did the Stuka Ju-87 really have a radio altimeter? If so, when?

It looks like the actual date is 1942. The 'Nachtschlachtgruppen' aircraft were given Ju 87 D aircraft with numerous upgrades including the FuG 101 radio altimeter.

This would make sense because to use the regular contact altimeter the pilot must have knowledge of the height of terrain above sea level and then add to that when preparing his aircraft for dive bombing. A radio altimeter should always give absolute altitude above the terrain. At night trying to estimate your height above terrain is basically impossible. It's either completely black or a sea of lights beneath you.

I found this information on page 58 of "Junkers Ju-87 Stuka", ISBN 978-83-89450-49-4. More information this book and excerpt is found here: http://mmpbooks.biz/ksiazki/46

Some brief information about the Fug 101: https://airandspace.si.edu/collection-objects/radio-altimeter-german-fug-101-1500-meter-type

https://forum.keypublishing.com/showthread.php?132745-FuG-101-Radio-Altimeter-S-101-Transmitter-Unit


Why do the engines of the PAK FA (Sukhoi T-50) seem not to be not aligned parallel to each other?

The Sukhoi T-50 operates Thrust vectoring nozzle control at low speeds. The nozzles are a part of the Fly By Wire system and will deflect as per the control input given by the pilot. The nozzles move in coordination with other flight controls and it is not necessary for them to be parallel in all conditions of flight. However on the ground they will appear to be parallel.


Does my PPL need to be checked again when I move to another country?

You have to take your logbook and your license to civil aviation of that country and then they will request a confirmation from the country that you have got your license from to be sure that if your license is still valid. After confirmation you have to join any ATO and undergo flight and ground training on the plane category that you have your licensee on (You might not need it but they must are the one who ask for an examiner for you and you can't apply by yourself) and then you must do the oral exam and also a flight test on your single engine type.Remember for converting any license, only your flight hours will be accepted and some of your exams and not your ppl flight test.In some countries you must also do 4 exams which mostly are Nav,Met,Hp,and Law but in some other countries can be only Law . It is depend to the rules of the country that you are willing to get you license new from .For us to EU you must only do the ppl law exam. All this Rules applied for a valid ppl license .Good Luck


Flaps have different actuation mechanisms from primary flight controls. Flaps deflection brings a shift of pitching moment with it, and it is done slowly to give the pilot time to adjust the aerodynamic trim. Usually with electrical screwjacks, with a fine pitch that stops the forces on the flaps from feeding back into the motors.

Yes flipping the switch switches the electric motors on. Most jetliners use Fowler flaps, which ride out on their little rails attached to the wing, and clad with an aerodynamic fairing at the trailing edge. This picture (source) shows the rails, flaps, and screwjacks when completely extended.


What does pneumatic operated and electrically controlled means?

Pneumatic operated: actuation by using air pressure. By opening a valve, high pressure air enters a cylinder, causing a piston to be pushed out. Typically, actuators of this type have two valves connected to two separate chambers, allowing for movement both ways.
The valves need opening and closing, though. This is what the "electrically controlled" part means: a small electric (typically electromagnetic) actuator will open or close based on an electric control signal.


How do I get attention on a busy radio channel?

As Ron commented, the basic answer is that you try to anticipate when a short gap is going to be, and jump on before someone else does. It sounds a bit daunting, but it actually works out pretty well in practice.

That being said, it's not exactly first come first serve. ATC tends to prioritize talking to the aircraft which need the most immediate instructions. So, an aircraft on final is going to get more priority than one which hasn't even entered the airspace yet. Even if you manage to get your request in, if the controller has a more immediate issue to address, you may get completely ignored. Sometimes they'll come back with "calling approach, say again" or sometimes you just have to try again later.

Either way, it's usually not too difficult to stay out of trouble long enough to get someone's attention. If you're IFR or have already made initial contact, you can probably just continue on your path and you'll eventually become a big enough priority for them that they'll call you if you still haven't a chance to get a word in. If you're VFR and haven't made initial contact, you can probably just avoid the airspace for a few minutes.


What is the meaning of this information provided by Air Traffic Control?

This is a METAR, a weather report. From the Wikipedia article:

  METAR is a format for reporting weather information. A METAR weather
  report is predominantly used by pilots in fulfillment of a part of a
  pre-flight weather briefing, and by meteorologists, who use aggregated
  METAR information to assist in weather forecasting.

The meaning of this METAR is:

Location: LTBA
Day of month: 16
Time: 21:20 UTC
Wind:  True direction = 030 degrees, Speed: 8 knots
Wind direction is variable between 360 and 080
Visibility: 10 km or more
Clouds: Broken sky , at 3500 feet above aerodrome level
Temperature: 06 degrees Celsius
Dewpoint: 02 degrees Celsius
QNH (Sea-level pressure): 1028 hPa
No significant changes expected in the near future

NOSIG means: No significant changes expected in the near future.

See this METAR-TAF decoder.


On the whole, smaller wings produce less drag, but they also produce less lift. Less drag means the same engine can reach a faster cruise speed, but less lift limits the weight capacity and means the aircraft needs to go faster to stay airborne: the stall speed, take-off speed, and landing speed will all be faster, which in turn means longer runways are needed (or systems like catapults and landing chutes).

For a fighter aircraft, that top speed matters a lot more than the lifting capacity or take-off speed, so they're optimised with these low-drag, high-lift wings. Compare to a utility aircraft of the same size: the utility aircraft will have a less powerful engine, and wings that produce more lift at lower speeds. A utility aircraft that needed the same kind of runway as a fighter would be pretty useless.

In the other direction, compare to an airliner. These wings are tuned like a fighter's: to be maximally efficient in the cruise. But the airliner has to lift a lot more weight, so the whole aircraft is much larger, and the wings are in proportion to that. They typically also require long runways, and fly faster than a small utility aircraft. But look at the Hercules military transport. It's designed to lift a lot, but it also needs to operate from poor-condition, short runways. It has less efficient, high-lift wings, so its take-off speed is very slow for its size, and it isn't that fast in the cruise.

In summary, wings (not just wingspan, but also the shape of the wing) allow you to trade off lift and drag. High lift and drag gives you slower take-off and landing speeds, but you pay for that with a less efficient cruise. Low lift and drag gives you a faster cruise, but you pay for that with ridiculous take-off and landing speeds and the extra runway that requires.


Why are three-bladed helicopters relatively rare?

Like with propellers, the blade count on a helicopter rotor is a matter of disk loading. Light helicopters get away with fewer blades. Complexity and losses increase with blade count, so helicopter designers try to fit as few blades as possible. However, this would result in huge rotor diameters for heavy helicopters. There are reasons to keep the diameter small:

Blade root loads due to centrifugal forces
Tip speed: The advancing blade will experience transsonic effects earlier if the helicopter flies in cruise the larger the rotor is. This will limit top flight speed.
Blade bending on the ground. The blade needs to be stiff enough to clear the tail when the rotor spins up.

Now let's compare a few helicopters. I used the technical data on the linked Wikipedia page and divided the maximum take-off mass by the area of the rotor disk:

Sud Aviation Aloutette II: 2-bladed rotor. Disk loading 19.6 kg/m². Disk loading per blade: 9.8 kg/m².
Bell 205 / UH-1D. 2-bladed rotor. Disk loading 25.6 kg/m². Disk loading per blade: 12.8 kg/m².
Aérospatiale AS-350 Écureuil: 3-bladed rotor. Disk loading 25.07 kg/m². Disk loading per blade: 8.36 kg/m².
Bell 412: 4-bladed rotor. Disk loading 34.6 kg/m². Disk loading per blade: 8.65 kg/m².
Sikorsky S-65 / CH-53: 6-bladed rotor. Disk loading 50.2 kg/m². Disk loading per blade: 8.37 kg/m².
Mil Mi-26: 8-bladed rotor. Disk loading 69.6 kg/m². Disk loading per blade: 8.7 kg/m².

I guess you see the trend by now. The UH-1D is the odd man out, but it also stands apart due to its unusually high blade chord. Normally, the ideal loading per blade seems to be between 8 and 9 kg/m², and a little more is deemed acceptable if it allows the designer to get away with only 2 blades.

There is no conspiracy to suppress three-bladed rotors. It's the overall compromise between performance and efficiency which determines the number of blades on a helicopter rotor, and the main driver is mass.


How do the Tiger Moth's anti-spin strakes work?

The vertical tail of the Tiger Moth is located a bit aft of the horizontal tail due to its sweep, such that the vertical will be in the wake of the root of the horizontal in a typical spin attitude (around 45° angle of attack). I would strongly recommend to fit the aluminium anti-spin strakes - those pilots who had no problem without them flew the Moth at a forward location of the center of gravity, which helps to end the spin. A lighter forward passenger/pilot will make the aircraft behave a lot differently; in spins small differences can translate in a markedly changed spin behavior.

Cut-away drawing of the Tiger Moth's tail. The anti-spin strakes are the parts marked 16.

A spin can be ended in two ways: Either the rotation rate is stopped by neutral rudder or a rudder deflection against the spin, or the separated flow on the wing is reduced by pitching down. The first way works better for aircraft with long fuselages and low wing span, and the second is preferred in aircraft with big wings like gliders. In the end, a combination of both works best and some aircraft need their own technique to end a spin safely.

Generally, it helps to have as much of the vertical tail exposed to undisturbed airflow as possible. Ventral fins are a tremendous help in upright spins but useless in inverted spins. Strakes or fillets ahead of the vertical tail are very effective, especially in fast spins when the angle of sideslip at the tail is high. In the 1930s, Arado in Germany built a range of airplanes where the vertical tail was positioned ahead of the horizontal tail, for the express purpose of making spins easier to end.

Arado 79 in flight (picture source)

The anti-spin strakes produce a vortex at high angle of attack, similar to that on a delta wing. This increases the dynamic pressure on the vertical tail and makes it more effective. Since every bit helps and the spinning characteristics can vary strongly with c.g. position, it would be careless to leave them off.


How should a Traffic Control Tower notify aircraft that their frequency just changed?

ATC frequencies don't change very often, but when they do they are planned well in advance.  NOTAM's are issued ahead of time to let people know, and if the airport has ATIS they will include the new frequency on the ATIS.

If it is an enroute frequency, the other controllers will simply hand you off to the new frequency, and you don't even need to know about it ahead of time.


What kind of ADS-B identification code is FFxxxx, where xxxx are numbers i.e. FF0024?

I am going to assume you use Flightaware's variety of dump1090 as a decoder.
When that receives a Mode A code, it publishes it as if it were a 24 bit address. The first two hexadecimal digits are filled with 'FF'. I have no idea why this may be a good plan.

In mode_ac.c, lines 368-370:

// Fudge an ICAO address based on Mode A (remove the Ident bit)
// Use an upper address byte of FF, since this is ICAO unallocated
mm->addr = 0x00FF0000 | (ModeA & 0x0000FF7F);

These may be drones but most likely they are just simple aircraft replying to Mode A/C interrogations.

If you are in the USA, FF7777 is a field test transponder (Range & Azimuth Beacon Monitor, RABM) , usually located not far from a radar to verify the correct working of the radar.


Is a Mooney M20 a difficult plane to fly as a beginner?

You need to be a bit more specific as "M20" refers to a lot of aircraft. An older M20C or M20D (with the fixed gear) should be quite manageable. An M20TN Acclaim is out of the question. Since you mention 60K I assume you are talking C/E variant but clocked out J's can be had for that. You can likely find an A/B but wooden wings are not for new owners or the faint of heart.

I have a Private Pilots License, an Instrument Rating, and a Complex Endorsement (which you need to fly just about any Mooney aside from the fixed gear D model) and have been pretty seriously looking at buying a Mooney as well as flying a few. Here are some thoughts:

The older Mooney's are on par with the other various trainers (PA-28/C172) size and load wise but tend to be about 10-15% faster on 10% less fuel. When it comes to flying, speed is generally what makes an aircraft "harder" to fly. The faster you go the faster things happen and the more likely you are to make a mistake or enter some airspace you shouldn't. In a Mooney, which is generally a faster plane you are of course more likely to have these issues.

You need to consider when training in a complex aircraft you are adding two additional things (gear and prop control) to an already confusing environment which can add to training time and increase your chances of messing something up.
Buying an aircraft for training can save a lot of money in the long run but what if you end up not liking it?
Although rentals are not always super well equipped in my experience they tend to be pretty well maintained as the flight schools are in the business of making money, so you dont lose training to the fact that you cant afford some AD or other maintenance issue.
Insurance premiums on a complex aircraft may be high for a new pilot. I can tell you that premiums for an M20C/E once you have your license are reasonable.
Mooney's have their own maintenance quirks but with the recent PA-28 spar issues that pretty much every GA plane has some kind of pricy issue.
You may want to define 2-3 passengers a bit better, a significant other and two kids is a lot different than 3 other "buddies". The back of most light aircraft is not exactly the most comfortable place.

I would take a serious look at this guy's thread he has a D model he has been working on for some time. The tale is a good example of what you are in for.


Can pop-out floats be installed post-manufacture on all helicopters?

Pop out floats can be installed easily on any helicopter with Tubular landing skid type landing gear. Its essentially an auto-inflatable tube attached to the landing gear. Have a look at this:


Is it possible to go-around at Lukla Airport?

No, it is almost impossible.

The only runway (06/24) Lukla Airport is just 1500 feet long. This article lists some interesting facts:

  The topography of the place makes any go-around impossible. At the
  south, the runway is the end of an angled drop of about 2000 feet.
  This cliff is fenced off as a precautionary measure. At the northern
  end of the runway there is a huge mountain terrain. It leaves no room
  for error.

A pilot mentions the same here:

  "Because there is no way to go around again, we have to calculate many
  things like air speed, tail wind, fog. If you don't do the proper
  calculation or proper exercise, then it (an accident) happens."

Planes land on runway 06 (Heading 060 or ENE) and takeoff from runway 24 (Heading 240 or WSW). This picture shows the cliff on North:

There have been several accidents at this airport.


What is the acceptable position of the brake wear indication for A320?

There are two wear pins. If the end of either pin touches the machined part of the piston housing the heat pack is worn out and the brake must be replaced. Measurement must be done when the brakes are cold. If one wear pin is missing, check to make sure the other pin is there and looks ok. If both pins are missing the brakes need to be replaced.


Can PPL, CPL, and ATPL be completed within a year?

Given the hours required for the ATP, the chance of doing that rating alone in under a year seems pretty remote.

Getting the private and commercial certificates done inside of a year is entirely possible, although not cheap. The writtens for the ATP are no big deal, but the hours simply will take a lot of time, as well as the right employment opportunity, to get.

The number of FO's at smaller (regional) airlines who have been flying for several years but who don't yet have their ATP attests to the time required. You can (and generally have to) pay for the flight time to get your Commercial, but paying for all the flight time required for an ATP is simply beyond those of whose last name isn't Gates, Bezos, Trump, or etc.


Can a commercial airliner be too heavy to take off?

It is possible to arrive at the runway with too much weight to takeoff, but this result is generally a mismanagement of fuel.  The most likely scenario this happens is when you are going to be at MGTOW for takeoff but need fuel to get to the runway (putting you over MGTOW at the gate) and are anticipating a long taxi or long lines at a de-ice pad.

If the long taxi doesn't materialize this can result in getting to the runway with too much fuel.  Recognizing this, fixing it is often as simple as taxiing with both engines instead of just one.  If you are really overweight you just ask to get put somewhere you can wait while running both engines and wait for the weight to come down.  There is really no benefit to taxiing around the airport versus just waiting in one spot to burn fuel.


Are certain NOPAC routes reserved for military use?

A local air force reserves chunks of its airspace as they see fit. But it never applies to publicly published inter-FIR routes. So the answer is no.

From Fundamentals of Air Traffic Control (on Google Books):

The routes stay out of Russian airspace, why that matters? Russia has a history of limiting civilian traffic through areas of their airspace. Like parts of the arctic circle, which only started to relax in the past decade or so.


What is the legal altitude to fly through Yosemite Valley (US)?

Short answer: you can fly in Yosemite Valley at 500ft AGL (most likely); there's no special regulation applicable there; the wording on the sectional is a non-regulatory 'encouragement' only.

By regulation, the minimum altitudes under VFR are in 14 CFR 19.119:

  (a) Anywhere. An altitude allowing, if a power unit fails, an
  emergency landing without undue hazard to persons or property on the
  surface.

  (b) Over congested areas. Over any congested area of a city, town,
  or settlement, or over any open air assembly of persons, an altitude
  of 1,000 feet above the highest obstacle within a horizontal radius of
  2,000 feet of the aircraft.

  (c) Over other than congested areas. An altitude of 500 feet above
  the surface, except over open water or sparsely populated areas. In
  those cases, the aircraft may not be operated closer than 500 feet to
  any person, vessel, vehicle, or structure.

I don't know what Yosemite Valley looks like and whether it's "congested" or not (see this question), but it's very likely that you could operate legally at 500ft AGL there, if not lower.

What the sectional says comes from AC 91-36, Visual Flight Rules (VFR) Flight Near Noise-Sensitive Areas. But as the AC itself says, it only encourages pilots to fly above 2000ft AGL (emphasis mine):

  This Advisory Circular (AC) encourages pilots making VFR flights near
  noise sensitive areas to fly at altitudes higher than the minimum
  permitted by regulation

If you read the whole thing, you can see the not-so-hidden message:

  The Federal Aviation Administration (FAA) receives complaints
  concerning low flying aircraft over noise sensitive areas such as
  National Parks, National Wildlife Refuges, Waterfowl Production Areas
  and Wilderness Areas. Congress addressed aircraft flights over Grand
  Canyon National Park in
  Public Law 100-91 and commercial air tour operations over other units
  of the National Park System (and tribal lands within or abutting such
  units) in the National Parks Air Tour Management Act of 2000.

  [...]

  Adherence to these practices is a practical indication of pilot
  concern for the environment, which will build support for aviation and
  alleviate the need for any additional statutory or regulatory actions.

In other words, 'please be responsible and considerate because if you aren't, Congress might force us to introduce more regulations like we had to do with the Grand Canyon'. Practically speaking, I guess that if you fly down Yosemite Valley at 500ft AGL every day, even if it's completely legal you can still expect a call from the FAA asking why you're doing it and 'encouraging' you ("cough 91.13 cough") to fly higher for 'safety' reasons.


What is the difference in performance between variable pitch prop and two fixed propellers for take-off and cruise speeds?

This doesn't specifically answer the question in the title, but from the body of your question I would say it's possible, if you had an electric push/pull configuration with a motor in the nose and one in the tail, or at the back of a fuselage pod with booms like a Cessna Skymaster.

The aft facing motor could use simple fixed pitch folding propeller that folds aft and trails in the slipstream when not being driven (popular with motor gliders) and it would be used only for take off and climb, with climb-optimized pitch.  In cruise that motor could be shut off and its batteries assigned to the front motor and its blades would fold into a near zero drag trail position.  The front motor could have a fixed pitch prop optimized for cruise.

The key issue would still be worst-case climb performance.  It would have to be able to make enough thrust on the single cruise pitched prop at the front to climb decently if the back motor failed.  Possibly if the front electric motor had some sort of emergency boost feature, where it's torque could be temporarily increased (enough to get its coarse pitched propeller up to red line) for a certain number of minutes without overheating, would be sufficient for single engine safety, with the rear propeller folding back on its own for you.

For single engine performance on the rear motor, you might get away with just a brake for the front propeller to stop it from windmilling if its motor failed.  Not as good as feathering, but far less drag than windmilling.


Why are some seemingly major waypoints nowhere to be found on sectionals (including enroutes)?

The CAVLR3 is an example of an RNAV procedure. A requirement to fly an RNAV procedure is for the aircraft to have navigation equipment capable of finding all of those points. There are many thousands of those waypoints, and it would create way too much clutter to show them all on a chart.

For a pilot planning on flying the CAVLR3, the Enroute H-10 chart can help them find the transition waypoints DORRN, THHMP, and TRSSK. Once they reach a transition, the approach chart covers the remaining route.

If the aircraft does not have the equipment to fly an RNAV approach, they would use a non-RNAV procedure like the COATT4. This follows fixes and VOR's, which are all included on the Enroute L-36 chart.


Why did the tower at a Class D airport not set me up with flight following on the ground?

Some towers have a data terminal that allows them to create and update flight plans*; these are typically the ones busy enough to have a separate Clearance Delivery frequency, but you'll find exceptions both ways.

Other towers do not and would have to call a facility that does, which takes that controller away from actually controlling traffic; these towers tend to be the ones with less traffic and lower staffing (maybe only one person on duty), so they're usually not going to do that for VFR requests.

However, all Approach and Center facilities have the ability to create and update flight plans* at every radar position, so it's usually no problem for them to set you up once you're airborne and talking to them directly.

(* VFR Flight Plans are not accessible by US ATC; when you get Flight Following, it is actually put in the computer as an IFR flight plan with a VFR altitude.)


Why are some US STAR fixes/waypoints included in FAA's legacy files but not in FAA's published STAR procedures?

Revisions are made to improve traffic flow, adjust for infrastructure(eg local airport change in number of flights or nav beacon decommissioned), simplify procedures for pilots and ATC, or address some other routing conflict or safety issue.
This is why IFR charts and terminal procedures are only valid for two months.

For example there is a victor airway near here that had its MEA raised from 3000 to 5000 because it was discovered that at the lower altitudes something was causing the VOR signal to bend significantly and planes were getting dangerously close to a mountain, I think they may have even had a couple of crashes.


What are the labels for this aircraft's JSON?

Community wiki answer:

06A0F8,         Mode S ICAO 24-bit address
51.3056,        lat
6.4601,         long
283,            heading
43000,          altitude in feet
459,            ground speed in knots
3245,           squawk (transponder code)
F-EDDK1,        radar receiver identifier
A359,           ICAO aircraft type Airbus A350-900
A7-ALD,         aircraft tail number / registration
1486231556,     time-stamp
DOH,            departure airport Doha (IATA code)
LHR,            arrival airport Heathrow (IATA code)
QR1,            flight number (IATA)
0,              ground flag (1=on ground, 0=airborne)
64,             vertical speed (feet/min)
QTR1,           ATC call-sign
0


Why are videos call and voice calls prohibited on airplanes?

Voice/video calls have not been approved by the FAA, and no one is particularly interested in having them approved, due to the frustration it would cause amongst passengers, having to listen to a multitude of conversations in a confined space, throughout the flight. Not to mention the fact that it would clog the limited bandwidth if even a sizable chunk of the passengers wanted to do it.

Virgin comes right out and says it with something along the lines of "For the safety and comfort of our guests, VoIP and Video Chat is also prohibited".


There is a good writeup here that explains the engine issues as well as the rest of the incident you mentioned.

Core lock happens when parts inside the engine cool off at different rates, causing interference between them. In the case of the CF34 engines on these Bombardier jets:

  GE isolated the problem to contact between components of the high-pressure-turbine interstage seal - a static, pressurized honeycomb component - and the rotating seal teeth on the outer torque coupling.

Working on getting a good illustration of what they are talking about.

This does not mean that the engine is "not functional." There is just much more resistance on the rotating components, but once the temperatures have time to equalize, the components will break free.

  According to the NTSB, FDR data indicate that the engine cores were beginning to break free just before the impact.

During core lock, the resistance makes starting the engine more difficult. A windmill start does not provide very much turning force on the engine components, so the resistance from core lock makes that method of starting difficult. GE has done engine testing, and when the windmill restart fails, they are able to use bleed air from the other engine to restart the engine, which provides more turning force.


An instrument applicant must have 40 hours of actual or simulated time. Can some of this be flown without an instructor?

The 25 hours that are not required to be "instrument instruction" may be flown under the hood with a safety pilot. This is the usual way to accumulate some of the simulated instrument time.

I believe this time may also be flown & logged in actual IMC with an instrument rated pilot acting as PIC (their name on the flight plan, etc.) and the instrument student acting as sole manipulator of the controls, but you may prefer to conduct your actual IMC practice with an instructor.


I have some time in a Seminole.  The issue with twins that causes most of the difficulty is the speed brake effect of two propellers when you pull the power off and they go to full fine pitch.  It's like you deployed a couple of drogue chutes, and makes your speed decay very rapidly and you will find yourself sinking quickly and needing large pitch inputs to try to arrest the sink, and with the Seminole's pitch behaviour this can be challenging to master.

The Seminole is not helped by having fairly high stabilator forces in pitch in the flare, and the T tail causes changes in stabilator effectiveness and sensitivity as the surface comes down into the wing's downwash during the pitch up.

You should be trimmed for hands off flight at your final approach speed (you trim to a speed - think of the trim wheel as your hands-off cruise control speed select dial) 90kts if near GW, 80kts when light.  Some pilots feed in a little bit of extra NU trim just before the flare to reduce the pitch effort, but this puts your trim speed even slower, and if you go around, you will be frantically spinning it ND and pushing on the column as you accelerate to blue line - more so than if you were trimmed at Vref.

Your aim point is 3-500 feet down the runway (in big aircraft it's 1000 ft).  The numbers will do fine as a reference. Your target condition is, as you are passing down below 300 ft or so, you should be trimmed with power set so you can let go of the controls and the plane will hold speed and track the glide slope without any input from you.  Then it's little nudges and small power changes to correct things.  The key is trim to hands off on-speed and on-slope so that the airplane works with you, not against you. For your questions:

Don't rely too much on crutches like standard clearances from objects in the cockpit.  Your target is to have the touchdown zone simply staying in the same spot in the windshield as you close in on it, wherever that spot is.  The "two fingers this, three fingers that" varies with loading so can't be used except as a very general reference for starting out.
In a twin like that you carry power through the round out and the start of the flare and you settle into ground effect. For starters, just leave approach power on until you are at about 5 feet then pull it to idle as you are feeling for the runway.  With experience you can work on feathering the power off from a bit higher up, getting to idle just before touchdown, but it's too much to think about early on.  When you want to make small or slow power reductions, it's easier to manage it by walking the levers in little alternating increments by rotating your hand.
The hard pull for the flare is characteristic of the Seminole and is just something you have to get used to.  As I said, you can trim to a slower speed during the round out to reduce how hard you have to pull, but if you do a go around you find yourself trimmed for, say, 65kt and as it wants to accelerate you will be pushing pretty hard on the wheel to keep the nose down to accelerate to blue line while frantically reaching for trim wheel.  Then if an engine quits and you are distracted doing the drill without retrimming, while holding a hard forward push, you will inevitably let it relax, and things go south.

The biggest factor that will help with your flying is mastering the use of trim for managing speed (it gets more complicated later because you pitch to speed when flying visually, but later when doing instrument approaches you pitch to slope because you have to maintain a precise path on a little needle - worry about that later).  You never want to be holding continuous pitch pressures for any more than short transient conditions.  You don't crank the trim wheel to make pitch changes (although you can) you make pitch changes and follow up with trim. This gets more and more important as the planes get heavier and the control forces go up.

Large turboprops are flown with power right up to the touchdown.  Jets come off the power a bit sooner, and jets that are clean in landing config (generally those without slats) come off the power quite early - in the CRJ200, you go to idle at 50ft.


What aircraft did this canopy come from?

This canopy probably came off a Boeing B-47.

I do know of at least two mishaps involving B-47s in Oklahoma but both occurred in places other than Wetumka.  I'll do a little more investigating on this.

Another possibility is that the previous landowners acquired this part as scrap at some point and left it there on their property for whatever reason.


Are there any accident reports that mention hacked/compromised avionics as a factor?

Searching the NTSB Accident Database which also covers some international commercial flights for the key words "hack", "hacked" do not provide any results related to hacked avionics. Likewise using the keyword "tampered" does not provide any results related to deliberate tampering with avionics (mostly "tampered" wreckage).

There is one individual, Chris Roberts, who claims to have hacked into the In-Flight Entertainment System (IFE) to cause the aircraft to deviate from its course, however I find it highly suspicious. From a security perspective, I can't of any good reason to have the IFE network on the same network as any avionics, however that isn't to say that there isn't some possible connection. The FBI certainly didn't think it was very funny.

So as of today there have not been any aviation accidents that are attributed to hacked or deliberately tampered-with avionics as a cause of said accident. The closest thing I think you will find is pilots loading incorrect flight plans, outdated (or even pre-dated) navigation data, and other cases of pilots not correctly using the equipment.

I did read your original question and would like to clarify. Conspiracy theories, guesses, and internet speculation are not a replacement for hard evidence. In the case of MH-17 the wreckage was recovered and no evidence has been presented in the favor of hacking, while there is a lot of evidence of the shoot-down. Airliners even at cruising altitude can be shot down by surface to air missiles rather easily.

As for MH-370, until the wreckage is found we may never know (and even if it is we may never know). Black boxes do not have an indefinite life span especially if they are under water. Until then theories of that flight being hacked are just as credible as those saying aliens abducted the entire flight and they are living on Neptune in specially constructed Igloos.


About ramjet efficiency in supersonic speed. Is there an optimal speed?

Well, that would depend on the design parameters, but for example this ideal ramjet would, with stoichiometric combustion process,  provide best thrust per unit mass flow at a speed of approx. 2.4 Mach

  ...the best operating range of a hydrocarbon-fueled ramjet is $ 2 \leq M_0 \leq 4$ . The parameters used are $ \tau_\textrm{max}
= 10$ , $ a_0 \approx 300\textrm{ m/s}$ in the stratosphere, $ f_\textrm{stoich} = 0.067$ for hydrocarbons, such that $ a_0/g
f_\textrm{stoich}
\approx 450\textrm{ s}$ .


Does a pilot follow the PAPI lights in the same way in all categories of aircraft?

The lights themselves are fixed, there is no way ATC or the airport operator can simply adjust them to suit the next inbound aircraft. If the pilot needs to they can fly the approach with 3 whites/1 red, but AFAIK that isnt really necessary in most situations (maybe for 747s and other longer aircraft).

It's worth remembering that the PAPI cannot provide precision to the foot. Having 2 white lights only means you are anywhere between about 2.8 to 3.2 degrees on a standard approach, which can be a considerable range when you're a few miles out.


What percent of the world's airline operations are in the USA?

It may be a bit hard to find this data for many different countries, especially if you want to separate takeoffs and landings.

According to this data for the US, there were 757.1 thousand flights in May 2014, including both domestic and international. Of those, 683.0 thousand were domestic, and 74.1 thousand were international.

Lots of information is available here. This indicates 8.3 million domestic and 1.4 million international flights in the US during 2013. This includes all carriers an all airports, including domestic all-cargo flights.

The best data for Europe I could find is only in passenger count (the more common statistic). It looks like you have to request access to get more detailed information.

However, this collection of data from Eurocontrol showed 9.548 million "IFR Flight Movements" in 2012. This would include all IFR flights, regardless of their type. A graph at the bottom shows figures for 2008. This shows a little over 8 million internal, and a little under 2 million arriving/departing. Since a domestic flight would be two movements (departure and arrival), this is 4 million and 2 million flights. As expected, Europe has a much higher percentage of international flights (about 1:2 international in Europe, versus about 1:9 in the US).

For domestic and international traffic in Australia, there are 702321 domestic flights and 162207 international flights in 2013, for a total of 864528 flights.

Data from the UK show that there are about 800000 domestic and 1000000 international flights per year.

You could also order a year of World Air Transport Statistics for only $799.


Could a Dyson fan scale up to be used as a bladeless aircraft engine?

No. Not a useful propulsion engine.

The first problem is power. The air stream from Dyson's fans is weaker than what you can get from a conventional fan the same size, and jet engines need a very powerful stream. You'll notice they're quite heavy as well; Dyson AM-06 has a thrust-to-weight ratio of just 0.06, 100 times less than a jet engine.

The second reason is they're very inefficient at high speeds. Dyson's fans use the Venturi effect, which is also used in aircraft evacuation slides, to turn a narrow stream of fast air into a wide stream of slow air. This happens through friction simply pulling slow air alongside the fast stream.

Current airliner engines do the same thing, but better. There, high-energy air spins a turbine, which then spins a fan. The conversion efficiency of this process is 3x-5x better and produces uniform velocity - important when you're close to the speed of sound. The fan approach also results in a smaller, lighter engine.

Jet engines imitating Dyson's fans would need cores and core intakes as least the same size as current ones. The reason Dyson chooses to protect their intake with a grate and Rolls-Royce or GE don't is Dyson fans produce on the order of 50 W of power, jet engines 50+ MW. No one cares about a few watts, they do about a few megawatts, which translate into a couple ocean tankers full of oil over a plane's lifetime.

If you want, you can protect a jet's intake with a grate too - see F-15SE, Su-57 (PAK-FA) with radar blockers, Mig-29's "dirt runway" top intakes. This has nothing to do with using an ejector or not. Dyson's design does remove the slow fan, but at the cost of a lot of weight and efficiency, and it's core damage that is the worst scenario in bird strikes.

The third reason is that Dyson's fans would not scale. To fly at Mach 0.8, the ejector stream would have to be highly supersonic, which is a problem in itself. To use them for hovering, where they are reasonably efficient, you'd face the problem of Venturi effect fading with distance - requiring an entire grate of ejectors, not one simple ring. Helicopter blades do the same thing better, while being far lighter and easier to fold.


How are fan and compressor discs balanced?

This article covers the issue (and is a pretty interesting read) but does not really explain how they do it. It just says

  After machine balancing, the part can then be manipulated (mass added
  or removed) and retested on the machine until satisfactory balance
  tolerance is achieved.

In answer to this question,

  And what method do they use to determine where the balance point is?

The device is pretty similar to that of a tire balance, here is a video of one in use and here is an interesting sales brochure for one.


Are there left seat qualifications specific to actual handling of the aircraft?

No, it is a non-factor, although in the Navy there are aircraft you only conduct carrier landings from in the left seat. To be qualified as an instructor in that aircraft, you have to demonstrate the ability to fly the same pattern from the right seat (but not actually land on the carrier).

I'll tell a story about switching hands. I was an LSO (landing signal officer) for E-2s, which had yokes and a central throttle quadrant. You always flew the carrier approaches from the left seat, though.

We had a pilot who had developed bad habits in the landing pattern. To break him of it, I had him fly the landing pattern from the right seat at the field, which just plain felt awkward since you never did it at the boat. This made him break out of the auto-flying and have to think his way around the pattern instead, and he was able to stop what he was doing wrong. He carried the fix back over to the left seat.


Why do many stealth aircraft have a similar shape and design?

First of all, the general idea is to avoid reflection of radar energy back to its source. Next, you want to direct the reflected energy into as few directions as possible in order to dazzle any observer with a momentary bright beam, surrounded by as little reflection as possible. That is the reason for the aligned edges and serrated patterns on stealth designs.

Next, there is quite some variety. How about this one (Northrop Battlefield Surveillance Aircraft eXperimental (BSAX), or Tacit Blue; source):

Or this (McDonnell-Douglas Bird of Prey stealth demonstrator; source):

Or this (BAE Taranis UCAV demonstrator; source):

If you think that all stealth airplanes look the same, maybe you are only looking at those which were designed for the same purpose?


Which light aircraft are known to have a quiet cockpit?

I assume that you're asking about piston engine light aircraft, so we can ignore gliders and electric engines for now.

The basic point is that they're all loud. One study compared a Cessna 172 (single engine) and a Piper Seminole (twin engine) and found that the average cabin noise was around 86 decibels, with no huge difference between the two aircraft. There's more analysis of a Seminole here. The FAA says that a light aircraft cabin is in the range of 70-90dB and this Cirrus owner measured 92-98dB in different Cirrus models. OSHA in the US requires ear protection and other measures for workers if the noise in their environment is 85dB or more.

Since decibels are on a logarithmic scale, the difference between 86dB and 98dB is large. But I searched a few aviation forums and there's very little discussion of cabin noise in light singles apart from a few subjective remarks. I couldn't find any good sources that said one aircraft type is well known as being noisier or quieter than average. The only consistent comment is that helicopters are louder than fixed-wing aircraft, which is also shown in the FAA document linked above.

Having said that, there are quite a few articles online about soundproofing aircraft in different ways. This one quotes the example of a jet:

  Aero Sound Shield is currently soundproofing a particularly large
  corporate jet - a converted McDonnell-Douglas MD-87 - for a Las Vegas
  hotel owner who is almost totally blind and who has compensated by
  developing extremely sensitive hearing. "He wants a 60-dB airplane,
  which is quieter than a Lexus," Nelson points out.

But the same article makes the point that modifying any aircraft to add soundproofing increases the weight to a point that makes the aircraft much less useful:

  Unfortunately, your airplane and mine can't accept the mass and weight
  of MD-87 measures. "I rode one time in a Piper Arrow that was very
  quiet," Nelson recalls, "but it was completely lead-lined. It could
  carry two people and half a load of fuel. That was fine for that guy,
  because that's all he ever wanted to carry, but it wasn't very
  practical."

Furthermore, it's worth remembering that modern noise-cancelling headsets are very good so the problem of noise (as opposed to vibration, which is also a factor for fatigue and health) has been more or less solved for most people. Even if you spend $1000 or more on a high-end ANR headset, that's a minor cost compared to altering the aircraft structure or materials and you still have full performance and useful load. I guess that for most GA pilots that's the decisive factor.


Is there a way to get descriptions of great circle routes?

Thread
In your Manchester to Vancouver question, I wrote that a great circle is like a taut thread on a ball.
If you have a tactile (Braille) globe, get two pins and a thread. Place the pins on the departure and arrival cities, and wrap the thread around the pins so that the thread is taut. You can then follow along with your finger.
Coordinates
Another method is to go to Route Finder website.
Enter the departure and arrival airports ICAO codes (you can get them from Wikipedia). And plot the flight plan.
The generated flight plan will be close enough to a great circle. The waypoints will be listed by their latitude and longitude. The distance and track (heading) for each leg will also be listed.


Why does disk loading mean anything when rotors/propellers are not disks?

The disc model is used wherever generalities of behaviour are studied without the need to know individual blade characteristics. It captures the mathematics of those generalities in a simple way that leaves out extraneous detail which would make the maths impossibly laborious.

Typically the aircraft designer will use the disc model in the design of their airframe, leaving the blade details for the propeller or rotor designer to figure out.


Determining the total drag of a propeller driven aircraft while turning with a load factor of n = 2?

Induced drag $D_i$ is proportional to the square of lift $L$:
$$D_i = \frac{2\cdot L^2}{\rho\cdot v^2\cdot\pi\cdot b^2\cdot\epsilon}$$
where $b$ is wingspan, $v$ is flight speed and $\rho$ is air density. $\epsilon$ is an efficiency factor which tends to be between 0.8 and 1. Compared to straight and level flight, induced drag will quadruple when turning at 2g and the same flight speed.
In order to know how much total drag goes up you need to know how much of your total drag is due to induced drag. Only then can the question be answered.
If your straight and level polar point is that for best range (when zero-lift and induced drag are equal), 2g flight at the same speed will increase total drag by a factor of 2.5.


Does aircraft/ATC get any information directly from a weather balloon?

No, neither ATC nor aircraft receive any information directly from a radiosonde balloon. However, in many cases the meteorological agency operating the radiosondes does use them to produce forecasts that are made available to ATC and pilots.


What are the states that the landing gear can be in?

Any instruments always show only three states:

Down and locked (green)
Up/stowed (extinguished)
Anywhere in between (red)

If you want to simulate it, remember that while the pilot can only command one of the two end states, the transition is a continuous process and you need to represent exact position of the gear in each frame of the simulation. So you need a value that will smoothly transition between 0 (stowed) and 1 (down and locked). Any value in between will indicate red on the instrument, but will correspond to different state of the gear animation.

The exact steps during gear extension (and in reverse for raising) differ by aircraft, but generally the animation will have three parts that you will map to suitable ranges of the gear state value:

opening the gear door,
lowering the gear and
closing the main gear door.

The last step actually complicates issues a bit, because the gear is already down and locked when the main gear door close and in case you do gravity extension the main gear door remain open.

So the suggested mapping is actually something like:

opening the gear door 0.0 to 0.3
lowering the gear 0.4 to 1.0
closing the main gear door 1.1 to 1.4

When you extend the gear normally, the value will transition up to 1.4 (and show green past 1.0), when you extend the gear via alternate mechanism (gravity drop), it will only transition to 1.0. If you want to simulate alternate extension, of course.

Tweak the values to make the animation look appropriate. The relative speed differs by aircraft. Some aircraft also don't have gear door (e.g. 737 only has one panel that is attached to the strut on main wheels; it still does have nose gear door, so the process will be slightly different for each leg).

Which leads me to note, that if you want to simulate failures, you definitely need separate value for each leg, because some failures, like jammed actuator, only affect one gear. Also in reality the legs take slightly different time to extend, so you can add some variability to the transition time if you wish.


What happen to schedule flight when airport close for undertermined duration?

If an airport is shut down, all flight operations are ceased, with maybe the exception to police, state or medical flights. Scheduled, non-scheduled and general aviation flights will be grounded until the airport is reopened.

Flights will be cancelled or the passengers will be bused to airports in the vicinity, from where flights are able to depart, e.g. passengers that were scheduled to depart from Dortmund Airport would be bused to Paderborn Airport. But since the reason for a shutdown usually involves public safety, passengers will be rather evacuated and the flights cancelled, rather then moving them to another airport.


Is "hacking small planes" a separate or larger problem from/than general small-aircraft security?

It sounds like just another theoretical scenario.
If that "hacker" wanted to do harm, he could also loosen a few bolts, disrupt the engine timing, plant a bomb, you name it.

Sure, in today's world of aircraft loaded with electronic systems the operators have little knowledge of and trust implicitly, it's quite possible that something that deliberately feeds wrong data to those systems goes unnoticed than disrupting the cylinder timing or mixture control cables would have in the past, but it's still a highly remote possibility.

What it sounds to like me is someone taking the scare of "hackers" breaking into your car and taking over the engine electronics to the next level.


What prevents Low Cost Carriers (LCCs) from cutting cost that compromise safety?

There are two main factors.

The law

One, as other answers have mentioned, is the law. There are strict regulations that cover everything in aviation, from the way people speak to the training they must have and the specifications and audit trails of almost every piece of equipment they use.

Now it's true that people, especially unscrupulous ones who are keen to save money and might be willing to take a few risks in order to do that, don't always obey they law or follow regulations to the letter. And after all, there are laws against murder with much more significant penalties than for (for example) flying with a bit less fuel than the regulations say you should, and yet people persist in murdering.

The culture

However, the other factor is the culture. A low-cost airline exists in the culture of aviation, not independently, and the culture puts safety first.

Each person working for the airline will have trained and may have worked outside the airline, and will already have acquired attitudes and ways of thinking that prioritise safety and adherence to regulation.

Each person working for the airline will be working with and encountering aviation industry individuals from outside the airline, on a daily basis - if they didn't share similar attitudes and ways of thinking, they'd stand out a mile, and so would a corporate culture that similarly failed to embrace the industry's culture of safety.


What are the STOL features on the Pilatus PC-6 Porter?

Quite simple.  Big wings with decent flaps, lots of power.

11.2 lb/hp at gross.  Wing loading of 19 lb/sf.

Comes down to how slow can you fly, and how fast you can get to that speed.  Without exotic high lift devices, it's mostly about wing loading and power loading.  The Pilatus only has to accelerate to a little over 60 mph and there is power to get it there in around 600 feet.  So there you go.

It's STOL, but not what I would call "super STOL".  For that you'd need full span flaps and slats and or bigger wings and a higher power to weight.  Like a Helio Stallion.

The Porter isn't a unique super-plane and it doesn't have any fancy high lift secrets.  It still needs about an 800 ft runway.  It just has a good all around configuration for its job, easy to load, and is simple and rugged.  It's the simple and rugged + good-enough-for-most-short-strips short field performance that's made it successful.


Which airfoil would be optimum for a glider?

For a particular task of optimizing an airplane design for a specific point, you will need to consider the following characteristics, together with the endurance parameter:

The pitching moment of the airfoil, (which will define the tail design, hence will affect weight and CG range and controllability)
Tolerance to contamination and geometric impurities (especially CFD based methods may converge to non-robust shapes)
Stall behavior (does it stall mildly or violently, as a wing)
Wing weight (spar location, spar web thickness)
Aeroelasticity (wing structural modes, static and dynamic aeroelastic properties)
Manufacturability (if somebody will really build it!)

Many of these would require working on a conceptual or preliminary sizing task, where you would design a planform, twist, dihedral, tail volume, CG, mass estimation, aeroelasticity computations etc.

Number 1-2-3 could be more vital and would help pick an airfoil with less efforts than the others.


Would one expect Canadair CL-215 or CL-415 planes to be equipped with a working ADS-B transpoder?

Military operators can request that their aircraft are not shown on flightradar24.

Operators of private or sensitive aircraft may request their tracking details be restricted or not displayed. Generally, aircraft requesting that they not be displayed on Flightradar24 are military aircraft.

From: https://www.flightradar24.com/blog/whats-this-plane-doing-answering-recent-frequently-asked-questions/
Whether or not an airplane is equipped with ADS-B is entirely up to the operator. Both the CL-215 and CL-415 were designed before ADS-B existed. However, if the mission demands it, ADS-B capabilities may be retrofitted to existing aircraft. Whether this is the case for these particular Canadairs, I do not know (I expect not), but regardless, it's impossible to make any definite conclusions based on the absence on FR24 and related tracking websites.


What military aeroplane seen at Prestwick is this?

Based on the fact that this looks like a 4-engined jet, with a T-tail, and winglets. I think it is a C-17.

(wikimedia.org)


What is this thing on the engine of a Cessna 500 Citation I?

Those are the fairings containing the mechanisms for the engine's reverse thrust system. See this photo (copyrighted) of the similar reverse thrust "buckets" deployed on a Citation 550.

See this example of a similar thrust reverser system deployed on a different aircraft type:

Image source, public domain

See also Wikipedia's article on Thrust Reversal systems.


What does the XFR button on the Challenger 300's autopilot panel do?

You can find manuals for many aircraft including the Challenger 300 at Smartcockpit. The Automatic Flight Control System section includes the function of the XFR button.

There are two flight guidance computer cards that drive the autopilot, including the flight director and yaw damper. The XFR button switches how the computers are used.

For most of the flight, only one computer is use and provides output to both left and right cockpit displays. Pilots will get warnings if this computer fails, and they can push the XFR button to switch to the other one. Without a failure, pushing the XFR button switches so that each side of the cockpit gets input from a different computer.

Precision approach and go-around modes are the exception where by default each side of the cockpit is driven by a different computer.


Application of Bernoulli Energy Conservation

Bernoulli's equation holds only if there is no energy source in the system. Since the fan adds energy, Bernoulli's does not apply across the fan; in the context of 1-D flow, pressure changes discontinuously across the fan.

Due to conservation of mass (no mass source for a simple fan), airspeed cannot change discontinuously across the fan interface. Therefore, right after the fan interface, both the static pressure and the total pressure have increased.

For more information, refer to this tutorial.


For how long can an Embraer E195 airplane glide at malfunction?

It's a rather 'clean' plane. Its maximum L/D is, probably, at least 14. (The table shows cruise L/Ds. The L/Dmax is probably much higher in all cases...) Properly handled, and from 35000ft, it might glide for more than 140 kms...

From https://en.wikipedia.org/wiki/Lift-to-drag_ratio :


What are accurate flight simulation models called? Is there a standard model?

14 CFR Part 60 regulates what constitutes a Flight Simulator Training Device (FSTD) for a particular aircraft model. FSTD is divided into two broad categories: Full Flight Simulators (FFS) and Flight Training Devices (FTD). A big difference between the two categories is FFS requires having motion cues, whereas motion cue is optional on FTD. Furthermore, the required accuracy of simulated flight dynamics (compared to flight test results) is much more stringent for FFS than is for FTD.

Each FFS and FTD is further divided into qualification levels (Level A to D for FFS, Level 4 to 6 for fixed-wing FTD). The higher the level, the more fidelity the simulator has to the actual aircraft. You may only get credit for Part 61 if you get training on the simulators with the appropriate levels for the systems/flight phases you are working with.

The simulator manufacturer must submit a Qualification Test Guide to the FAA to demonstrate that the simulator is good enough on aerodynamic model, flight deck, visual system, motion cue, sound system for the appropriate level.

Anyone can make a flight simulator, to any arbitrary level of fidelity; but making a flight simulator good enough for the FAA is hard and expensive. Read this for a more in-depth but lay-man explanation of the different qualification levels.


Why this huge discrepancy in flight times?

TL;DR Probably "Operational" reasons

I would hazard a guess that this is a combination of a few factors

A longer route flown inbound to London
Flying in to a busy airspace like London requiring particular routing, particularly oft requiring length hold patterns
The time of day the flight in to London arrives being particularly busy (late afternoon/early evening)

These three factors may cause the airline to list the flight duration as longer than it would usually, in order to account for the possibility of a lengthy flight time.

If you look at the track of the outbound flight and compare it to the inbound flight you see that, at least on that occasion, a much longer track was followed. The airline may know that the route back to London is longer (for whatever reason) and adjust expected flight times accordingly.

Also, when you compare it to the only other direct flight departing and returning to the same airport (LGW) on skyscanner for the same route, the time difference is much less (15 minutes difference) which is much more usual. It may well be that the route to/from LGW is more equal outbound/return than the route taken to STN. It may also be that this flight in to LGW is at a typically quieter time of day.


What is an airliner pilot's first go-to if he or she doesn’t have a positive climb rate immediately after take off?

The first thing I would do is advance thrust to maximum available thrust, make sure both engines are indeed operating.
Next I'd check is if the speedbrake is stowed.

I would not consider retracting flaps because when you are too slow to climb you are definitely too slow to retract flaps... could be deadly.

Normally this kind of situation can't happen unless you have at least one engine failure and the remaining engine not working at full thrust or the wings are contaminated with ice or snow. The aircraft is perfectly capable of climbing on one engine, so if you have two engines on max takeoff power and are still not climbing then something is seriously wrong.
In case of ice/snow on the wings, well there is not much you can do about that in the air, put on wing anti ice and hope that it is quick enough to clear the wings of any contamination, this comes at a penalty of losing precious thrust because of the bleed air extraction. This situation is usually avoided by removing snow and ice from the wings whilst still on the ground - before taking off.


Why can some runways only be used from one end?

Even if there are no physical obstacles visible - the airspace structure can be somewhat more difficult and one runway direction might run into other reserved airspace. Or just go over noise-sensitive neighborhoods...


How does engine noise change during descent / approach?

It is important to notion that an aircraft does not provide a uniform sound but features several sources of noise. The noise generated by the individual sources has separate characteristics and is transmitted into different directions.
For example, the sound of the engine front fan is sent into the direction of flight, creating a cone. The sound of exhaust jet and low-pressure turbine is transmitted backwards. Passive sound sources sent according to their positioning on the aircraft. Underside structures transmit downwards.
When you experience an aircraft transition overhead, the sound created by the aircraft may be steady but you experience the sound of changing sources.


What is the recommended procedure to land a taildragger in a crosswind?

My favoured technique in strong crosswinds, perfected in many hours of glider towing in Super Cubs, Citabrias and Pawnees, is to wheel it on tail high, wing down, and balance it like that until the speed drops enough to lower the tail, then put the tail down and plant it firmly with aft stick.

In those conditions it's desirable not to have the wing at high AOA when ground contact and especially tailwheel contact (traction) is marginal, as you get when you do a 3 point landing.  By wheeling it on (wing down obviously), you get firm mainwheel contact right away, AOA is low so gusts won't pop you back into the air, and you still have air rudder authority.  The technique keeps the transition from air rudder authority to tailwheel ground traction as short as possible.

Wheel landings seem difficult but are actually easier than 3 point once you learn the trick (For the trick to be revealed, send 10$ to my Paypal @...).  Actually, the trick is simply that you PUSH when the main wheels are a foot or two in the air. You'll go plop and won't bounce or skip.  In a crosswind, it's a little trickier because you have to push while holding a sideslip and you find yourself balanced on the one into-wind tire, with your feet and hands going a mile a minute.  As you slow down the other main wheel will come down, then as soon as you slow enough to be able to plant the tailwheel without becoming airborne again, you plant the tail and full aft stick.

Also, be ready to use brake during the rollout in case rudder and tailwheel authority are both insufficient to stop a swing (this can happen on wet grass for example).

Takes some practice, but once you perfect this technique you will have much more confidence in strong X winds.


What are the essential elements of a control tower?

The theoretical bare minimum would be a light gun to give light signals to aircraft. A more generally acceptable minimum is a two-way radio to do radio communications with aircraft.

From there up other systems can be added. The list below gives some examples but is not exhaustive.

A telephone. Always useful when you want to get in contact with other parties on the ground (e.g. air traffic control centre) or other parties with you.
Meteorological instruments can provide current wind and visibility at the runway to the tower controller. This is not directly to support the Air Traffic Control function, but to provide information services to pilots.
Airport lighting control: runway (and taxiway) lights are usually controllable from the tower. These systems can become quite complex on larger airports
A display with a feed from an approach radar. This present the air traffic situation around the airport to the controller. Whilst on larger airports the approach controllers are usually not located in the tower itself, smaller airports often combine tower & approach control. Even when approach controllers are physically located elsewhere, the approach radar assists tower controllers as well in building a clear mental picture of the situation.
An emergency button that makes the fire department jump to life.
Surface radar display. This presents the ground traffic situation to the controller. Often not found on small airports, but essential for efficient operations at busy airports, especially in low visibility.
More radio's. To split tower control who do the runways and ground control who do the taxiing aircraft. Further divisions can be made.
A system that shows which runways are active, which are closed for use by the airport authority (e.g. for maintenance)
Electronic flight strip system. The traditional paper strips are now often replaced by a digital equivalent. These E-strip system usually communicate with the whole flight data processing system, correlating strips to radar tracks.
Gate allocation system. It's always nice to now where those arriving aircraft should be directed once they are of the runway.
Gate video systems showing the situation at the gate. (to bust pilots that say they are ready for engine start / pushback whilst they are still loading cargo :-) )
Departure management system. When you have a complex airport with multiple runways and a maze of taxiways, a DMAN may help to get aircraft airborne at the right time in the right sequence in the right direction.
Arrival management system. With many aircraft arriving from all directions, headed for different terminal / gates it helps to have an AMAN to avoid overloading your Terminal Manoeuvring Area with incoming flights competing to be first.
Integration of the Surface radar, DMAN and Gate Allocation System with the lights control system. The level of integration varies. In the most extreme case pilots just have to follow the taxiways that light up green and stop at red stop bars. This avoids a lot of radio communications and confused pilots who didn't exactly remember a taxi clearing involving a dozen of taxiway letters.


Acceleration of a supersonic aircraft after breaking the sound barrier

Your Taylor expansion only uses the first two terms, so it is only a crude approximation. But still, your observation is correct, however, whether it applies depends on the aerodynamic quality of the particular aircraft.

Practical supersonic aircraft have been designed to minimize the Mach drag peak. The ways to do this should be familiar:

Stretch the aircraft lengthwise so it becomes long and thin.
Smooth out the cross sectional area distribution over length ("area ruling")
Use swept wings with thin airfoils

If this is properly done, the drag peak will be small enough to have overall drag increase with Mach number above Mach 1. In case of the F-16 the drag coefficient rises from 0.02 (subsonic) to 0.045 (Mach 1.1) and stays roughly constant with increasing Mach number, so the absolute drag still grows with speed squared. No significant decrease in the drag coefficient occurs because of the complex flow
around the entire aircraft. Only when you have a poor design will drag actually become lower at low supersonic Mach numbers.

Another factor is thrust: Since ram pressure at the intake increases, so does thrust of the same engine as speed increases. This is the main reason why Concorde could already super-cruise 20 years prior to Lockheed marketing inventing this term.


What is the smallest manned jet aircraft?

The BD-5J is what guinness world records claims to be the smallest but it is larger than the Cri-Cri in its jet implementation (the BD-5A is smaller than the Cri-Cri but prop powered)

If you want to count really experimental stuff the Martin Marietta X-24A lifting body has a wingspan of only 11 ft 6in. making it the smallest. Although I will admit it is predicated on a lose definition of "wing" and is rocket (not jet) powered.

Although if you broaden your definition of "aircraft" Yves Rossy's jet wing backpack is the smallest coming in at a wingspan of 7.9 ft. It is still piloted, jet powered although I do not think it can take off under its own power.


Why aren't grid fins used as wings for low speed aircraft?

No, not as/on aircraft, and there are good reasons.  They're useful elsewhere, and should make good kites.
Prototype multiplanes flew, quadruplanes reached production, triplanes served operationally in WWI, and biplanes were retired from almost all uses (military and civilian) by early WWII. The biplanes that still fly for purposes other than display are used for low-speed work.
As speeds increase - and we almost always want to get people and goods somewhere quickly - the power lost to drag increases dramatically, in proportion to the cube of the airspeed.  Any construction that increases drag is going to limit speed, payload, range or probably all of them for a given engine power. Biplanes (and to an even greater extent multiplanes) are inefficient at lifting because of the interference between the airflow over the lower wing and under the upper - now squeeze the wings closer together so you can fit more, and this gets worse.
The surfaces (or struts/wires) perpendicular to the lifting surfaces, making up the grid fin or the bracing of a multiplane don't contribute lift but do contribute drag.
Grid fins are sometimes useful: they're compact, more so if the aspect ratio means they can be stowed as by SpaceX and on missiles/glide bombs.  SpaceX use the grid fins in landing, where drag isn't a downside so long as it doesn't cause too much heating.


Is there a class E corridor in the class B north of San Diego International?

I'm a frequent VFR owner/flyer in that area for past 12 years. The box is clearly identifying the floor within in the box it is pointing into.  That 1800/3200' is to keep transitioning aircraft either below or above the MIRAMAR MCAS departure corridor.  Aircraft that are inbound to Montgomery Field will often transition with a Class B clearance when flight followed by SoCal on 119.6, at 2500-3000'  Inbound commercial jets for Lindbergh Field will come thru that zone at 6800' and above. And yes, as depicted on the chart, offshore of Torrey Pines and west of the OCN 152 radial, the floor is 1800'.  If you're looking for a "corridor"to the South Bay onto Brown Field, you could fly the shoreline at 3600'-4600', from Del Mar, over Mt Soledad, and then join the VFR corridor over Lindbergh Field, and onto Brown Field.


Why not use the engine of a model aircraft for other purpose?

A lawyer wrote that. It means if you use it for any other purpose, they are not liable and you are.


Why are cockpit alarms still so distracting and unable to be silenced?

A stall condition needs to be handled now, and once it's handled, the alarm will go away. What you don't want to happen is you are in an approaching stall condition, the pilot hits a "silence" button while the situation gets worse without the plane telling them.
An emergency is "AVIATE, NAVIGATE, COMMUNICATE" in that order. Fly the plane first, point it where you want to go second, and third, only if you have time/resources, is to talk to ATC about it. The pilot should be fixing the problem first, focus on flying the plane, ATC can wait.
They can't be turned off for that reason. Deal with the problem and the alarm goes away, you don't want to silence the alarm and forget about it. There is some merit to "overloading", where multiple alarms are happening at the same time, or when the pilot focuses on a low priority item and forgets to fly the airplane (Eastern Air 401).


Explaining development of sideslip due to bank

Sideslip is simply lateral movement due to the tilting of the wing lift vector away from vertical. Moving forward while moving laterally means the lateral movement becomes a horizontal arc and becomes a turn.  The vertical fin keeps the body of the plane aligned in the airstream, so the body follows the arc and you have a heading change and a coordinated turn.
You could say the lift force of the wing is a thrust force.  Any time the thrust force is tilted from vertical, the thrust force develops a lateral as well as vertical force component, and because the lateral thrust component decreases the vertical thrust component, the sideslip also introduces a descent.  To stop the descent, you have to increase the total lift to restore the original value of the vertical lift component, so you have to increase angle-of-attack to increase total lift.
Think of a helicopter hovering with the rotor disc level.  All of the rotor's thrust is vertical.  The pilot tilts the rotor with cyclic, tilting the rotor's thrust, introducing a lateral component to the thrust, and the machine moves sideways (and downward because the vertical lift component was reduced, requiring the pilot to increase total rotor thrust with collective), and if it's moving forward instead of hovering while this is going on, the sideways movement becomes an arc, or a turn.
The term sideslip, when applied to flying, tends to refer to the lateral movement without the yawing motion induced by the fin, so that the airplane is turning, but slewing sideways while doing so, and the fin's job is to stop the slewing by weathervaning the tail to keep the body aligned in the relative airflow.
Problem is, dihedral effect requires this sideways slewing to be present when the airplane banks, so that the differential lift created by the slewing motion (sideslip) provides a restorative righting moment.  A small amount of sideslip must be permitted to happen when the airplane is banked by a disturbance to allow dihedral effect to work, but not too much, and not too little.
Vertical fin sizing has to find the sweet spot where a bit of slip is allowed to develop when the plane is banked by a bump, without letting it get out of hand.  Make the surface too small, and the airplane develops too much slip when banking and generally yaws around too much, make it too big and the plane instantly yaws or weathervanes into the bank to remove the sideslip, dihedral becomes ineffective, and the plane tends to want to always spiral into the bank with any disturbance.


How many four-engine commercial passenger jetliner types are currently in use?

Well, the 3 points you make are easily demonstrable to be true, and also a fairly unique feature of all three if looked at side-by-side.

The 747 is the only one with an obvious hump towards the front of the aircraft. This upper row of windows is unlike either of the other two

Photo Aldo Bidini:: source: http://www.airliners.net/photo/Alitalia/Boeing-747-243B/1200648/L?sid=f499b3169d12a0d4f410846e6512443a

The A380 has an entire upper row of windows - it does indeed have 2 full decks.

   Richard Vandervord source: http://www.airliners.net/photo/Etihad-Airways/Airbus-A380-861/2574151/L

If it has 4 engines, but neither a half upper deck and hump or a full upper deck (and it's an airbus!) then yes it is an A340

Aero Icarus source: https://www.flickr.com/photos/46423105@N03/5445375360/

However, that is not all the 4 engine passenger aircraft.

The BAe 146 is a 4 engine regional airliner, and you could add to your distinguishing features "has a T-tail, must be a 146". It is also the only one of the bunch with a high wing.

   Adrian Pingstone source: https://commons.wikimedia.org/wiki/File:Lufthansa.rj85.arp.jpg

And then we're into the Ilyushins. The Il-96, is easily distinguishable from the similar(ish) A340 as it is considerably smaller - hard to tell from a close-in photo, but in real life if one were parked next to the other the IL-96 is smaller.

Anna Zvereva source:https://www.flickr.com/photos/130961247@N06/31268448486/

The Il-86 has 4 engines but does not fit your criteria, as it only remains in service with the Russian Military, but the Il-62 is still in commercial service. It's very easy to distinguish by having its 4 engines mounted on the tail

Tim Rees source: http://www.airliners.net/photo/LOT---Polish/Ilyushin-Il-62M/1033235/L


Check out this publication from the FAA

  Class E airspace extends
  upward from either the surface or a designated altitude to the overlying or adjacent controlled airspace. When designated
  as a surface area, the airspace is configured to contain all
  instrument procedures. Also in this class are federal airways,
  airspace beginning at either 700 or 1,200 feet above ground
  level (AGL) used to transition to and from the terminal or
  en route environment, and en route domestic and offshore
  airspace areas designated below 18,000 feet MSL. Unless
  designated at a lower altitude, Class E airspace begins at
  14,500 MSL over the United States, including that airspace
  overlying the waters within 12 NM of the coast of the 48
  contiguous states and Alaska, up to but not including 18,000
  feet MSL, and the airspace above FL 600.

This image may help to visualize it

(source)

In more general terms its the airspace that covers most of the US below 18,000ft. Its the area where a lot of the General Aviation traffic lives (although some of it is making its way into the flight levels these days)

Side note: Depending on how you look at it class E airspace is bound to an upper limit of either 400,000 feet (76mi) which is what NASA considers re-entry altitude or what The Fédération Aéronautique Internationale defines as space starting at 62 miles so either one of those can be used as an upper bound for Class E (although officially the FAA does not define an upper bound). Re-entry point is where air drag comes into play so you would be hard pressed to get a plane over that altitude. Practically speaking the jet altitude record is held by the SR-71 Blackbird at 85,069ft and the Concorde pulls in at 60,039 ft for commercial flight.