What is the rationale for single engine military aircraft?

Because single engine fighters are substantially cheaper to purchase and operate.  Exact figures are hard to obtain, but as an example, an F-15 squadron will spend about 25,000 USD per flight hour whereas an F-16 Squadron spends about 15,000 USD per flight hour.   Effectively, you can purchase and operate twice the fighter force with single engine fighters than with multi-engine fighters.   This becomes very attractive for land based air forces belonging to countries with small defense budgets to operate the maximum number of combat aircraft per unit of currency spent.

Another major advantage to single engine fighters is maximized performance in a minimal size and weight package.  Adding a second engine will produce more thrust but at the cost of greater weight and fuel consumption.  This in turn requires more fuel be carried with a heavier airframe, creating a vicious circle for the design of these airplanes.  Typically in fighter design you want a specific weight ratio $W_a = W_{af}/(W_{af} + W_f)$ as low as possible.  This translates into an airplane which is a nimble, high capacity gas can with as low an empty weight as possible for a given range profile.  This is extraordinary difficult to do with a multi engine airframe.

The major advantage to a multi engine fighter is the same advantage that any other multi engine airplane has: they can carry larger payloads with greater system redundancy.   The large airframes accommodate big powerful fire control radars for detecting and tracking targets at very great distances, etc.  Certain units, particularly the United States Navy, prefer multi engine airplanes for overwater operations for the redundancy of having an additional engine to get you back home.   So too is this a design feature of the A-10 attack jet which anticipates enduring battle damage and the additional engine offers a better chance of limping it home if it gets shot up.

While the redundancy of two engines may seem ideal for combat ops, keep in mind an engine failure combined with the compressor and boat tail drag from the dead engine results in an airplane which has lost 50% of its total available engine thrust and 80% of its combat effectiveness.  All you could do after an engine failure would be to limp the airplane home to a friendly base - provided the enemy is gracious enough to let you do so without jumping your six and blowing you out of the sky!


Do you need clearance from ATC to switch to a different approach at non-towered airport?

Quoted from the Instrument Procedures Handbook, page 4-6:

  APPROACH CLEARANCE

  The approach clearance provides guidance to a position
  from where you can execute the approach, and it also
  clears you to fly that approach. If only one approach pro-
  cedure exists, or if ATC authorizes you to execute the
  approach procedure of your choice, the clearance may
  be worded as simply as “… cleared for approach.” If
  ATC wants to restrict you to a specific approach, the
  controller names the approach in the clearance—for
  example, “…cleared ILS Runway 35 Right approach.”

  When the landing will be made on a runway that is not
  aligned with the approach being flown, the controller
  may issue a circling approach clearance, such as
  “…cleared for VOR Runway 17 approach, circle to land
  Runway 23.”

So if they name the approach, you are restricted to that approach.

I searched the rest of the book for items specifically related to non-towered operations, and found nothing that contradicted that.


How to get the correct speed/power on downwind?

I spend most of my flying time in C172s of various models as well as 152s, PA-28s and the like. In most C172s you can extend 10° of flap at 100kts, or even 110kts in some models. The white arc is usually for 20° of flap and above and that's 85kts not 80kts, but you should check the POH to be sure or it may be written on the flap handle placard. 10° of flap will certainly help, but it's more your technique that seems to be the issue here.

Your goal to not add power after you've taken it out is what is the biggest reason for your float, and isn't really constructive. It's normal to reduce throttle to meet a particular airspeed and then throttle up again, if you don't you are relying solely on drag to slow you down, which as you have discovered takes time. Cessnas are draggy beasts because of their low wing loading, wing struts and big rivets, so you can kinda get away with it, but if you tried that in a PA-28 you'd float much, much farther as it is less draggy, so it's not a good habit to get into as you'll be carrying too much extra speed throughout the approach.

You're never going to hit on the perfect throttle setting that will carry you around the pattern and touchdown at just the right point, there are too many variables to factor in like wind direction, wind speed, rising or falling air, etc. Fixing your throttle forces you to fly a specific pattern for the specific conditions, which won't be the same pattern as everyone else, and it will be different every time. There's no benefit to doing it.

The moral of the story is don't be afraid to use the throttle as necessary to control your energy, that's what it's for. When you need to reduce speed throttle back more, then increase again when you get to your target airspeed. In the approach make throttle adjustments required to maintain the descent rate you need, if you start to get a bit low add some, if you get to high pull it, and practice practice practice.

Don't worry about engine failure in the pattern either, if your engine quits you most likely have enough energy to make the field, just clean up and fly your best glide speed. Try it with your instructor: throttle back to idle at downwind and fly a curved approach onto the runway, you'd be surprised how much energy you have at the end.


Does bi-wings create essentially double the uplift as single wings?

In general, no it does not.

If by bi-wings you mean a biplane then the airflow above the lower wing and the airflow below the upper wing interfere with each other and lift is lost. The loss is kept acceptable if the gap is at least 1.25 times the wing chord, but it is still maybe 20% depending on the design. The advantage of the biplane is that it is light and compact, which at slow speeds can more than compensate for the loss of lift.

If by bi-wings you include tandem wings, then the wake of the fore wing creates a disturbed airflow over the aft wing, reducing its efficiency. This can be minimised by mounting the fore wing low and the aft wing high, but that introduces the risk of superstall at high angles of incidence. The advantage of the tandem layout is that it allows a large range of positions for the centre of gravity, giving high operational flexibility.


Is there such thing as "standard visual inspection" at all? Is it normal in such circumstances? What's its purpose and how necessary is it?
Visual inspections are very common. Military pilots train regularly to visual inspections of other aircraft, and typically close to within 25-50 feet of another (cooperative) aircraft to do so. At a 25-50 foot range, you can easily see if an aircraft panel is missing or even loose/flapping in the wind. Having said that, there is no "universal standard" for what comprises a safe and normal visual inspection and distances and closure rates that are considered safe may vary depending on your experience and aircraft type.
Isn't there any other method to this end, instead of "visual inspection"?
According to the researcher quoted in the article, the F-15 may have been attempting to see if the airliner had passengers onboard. You would need to close to well within 1/4 of a mile (1500 feet) to have any hope of determining that with a naked eyeball. If the F-15 had a camera system (common), that may have allowed them to remain farther from the airliner, however.
Is "1,000 metres" distance considered "safe" for such conditions?
1,000 meters is likely very safe, and it's really far away compared to how military pilots are trained. However, what matters is how the pilots of the airliner felt. They are likely not military trained, and were probably unaccustomed to seeing another aircraft that close to their airplane.
The article is a little misleading when it implies that aircraft typically maintain at least 600 meters separation to avoid hitting each other. That number (600 m), refers to two aircraft on different altitudes that not aware of the other's presence. For a military pilot who has a radar and is looking at an airliner, 600 m is not required at all.
In what conditions do passenger airliners stage a "safety manoeuver" like this?
Here's where we get into some speculation. I'm not sure what the article is referring to, but I suspect that the airline pilots were responding to a TCAS RA (Traffic Collision and Avoidance System- Resolution Advisory) generated by the F-15's proximity and closure rate to the airliner. In this case, the airline pilots may have been presented with a "Climb" or "Descent" command by the computer, which would explain their abrupt climb and descent.
Whether or not the climb they undertook should have been so violent that passengers were bounced out of their seat and onto the floor is a matter of the pilot's judgement and speculation without knowing exactly what happened between the two aircraft.


What do flight attendants do if a passenger asks what is going on in case of a potential emergency?

What's the general protocol for cabin crew, when asked by passengers
  who notice potential issues like this and get curious?

The flight crew and pilots are under no obligation to inform the passengers about non critical issues and broadly speaking it's often better to provide only needed information so as not cause some kind of panic. In the vast majority of situations on an aircraft there is nothing the passenger can do other than evacuate when told to do so.

Turning an aircraft around and heading back to the point of origin is not necessarily an emergency although it can be there is nothing to say it is or is not from a passenger point of view.

Even if a passenger insists the cabin crew will likely ask them to take their seats, buckle up and await any further instructions. It's possible that the cabin crew is not even informed of anything as the pilots try and work the problem.

The later part of your question is answered here and the general answer is, unless you are a trained pilot it's hard to actually know if something is going wrong. There is a very interesting example of this from the Air Florida Flight 90 incident which is the only incident I know of where a non flying pilot spotted an issue and took action, this would be a fairly rare case;

  Survivors of the crash indicated the trip over the runway was extremely rough, with
  survivor Joe Stiley – a businessman and private pilot – saying that he
  believed that they would not get airborne and would "fall off the end
  of the runway". When the plane became airborne, Stiley told his
  co-worker (and survivor) Nikki Felch to assume the crash position,
  with some nearby passengers following their example.


What is the purpose of those casing treatments and how were they designed?

The casing treatments shown work by providing an alternative path for the rotor tip leakage flows; which otherwise collect at the rotor tip when highly loaded and block the flow resulting in a surge.

The lack of change is because there was no significant improvement in computing power between the 50s and the 70s that would help with such designs, (in fact it is only very recently that the flows can be accurately modelled.) and the cost of the experiments required to substantially iterate the design would be prohibitive.

The difference in designs is partially driven by parallel development, partially by patent avoidance, and partially the desire to minimise the impact on the compressor's components and its efficiency.


Where can I find data on past forecasts of planned aircraft production?

Yes both Airbus and Boeing deliver 20-year forecast for the complete market. For Airbus there is a spreadsheet which may function as your database.

IATA also publishes 20 year travel forecasts, here is the latest. Airline travel is going to double over the next 20 years.

At he time of first production, forecasts for the aircraft are made based on market forecasts, plus the expected market share that the aircraft may achieve. Information that is of interest to the stakeholders of the company.


Why are updraft carburetors standard in aviation?

I can think of three reasons to use an updraft carburetor in a single-engine GA airplane:

Anti-flooding:

The float-bowl regulator in your carburetor is cheap and simple, but it is far from perfect under all conditions.  Short periods of zero-G or negative-G operation, caused by a quick dive, turbulence, or even bumping over uneven ground, can jiggle the float and spill liquid fuel into the venturi.

In a downdraft or sidedraft carburetor, this liquid falls into the intake manifold and wets the interior walls and may get into the cylinders, causing an over-rich mixture condition.  The engine is said to be "flooded" and will not run until the liquid is cleared out.

With an updraft carburetor, the spilled fuel tends to fall out before it can foul anything.

Gravity feed:

If your aircraft has fuel tanks higher than the carburetor when in cruise attitude, you may be able to remain under power if your fuel pump fails.  An updraft carburetor can be mounted lower in the engine compartment than sidedraft or downdraft types; in fact, it is usually under the engine.

Early automobiles did this to avoid the need for a fuel pump; fuel was fed by gravity from a fuel tank higher than the carburetor, e.g. just below the windshield.  The lower the position of the carburetor, the deeper the fuel tank could be.

Convenience:

If you look inside the cowling of most GA planes, you will see much more space under the engine block than above it.  That seems to be the best place for lots of auxiliary equipment and attachments, including the carburetor and air filter.


Why is a right pattern the standard for a hold?

This is a total shot in the dark. And, I have no citations for this. I always assumed that the a left-hand traffic pattern and a right-hand hold for a missed approach put the aircraft on the same side of the extended runway centerline. Presumably, this would be a more “protected” side of the airspace. Since standard traffic patterns for fixed wing aircraft are left, that would make the holds to the right.

Although, AOPA says the following...

  “Many holding patterns are executed in VFR conditions, which means that those in a holding pattern could encounter opposite direction VFR traffic that might be climbing or descending through the holding altitude. Veering to the right (as required by right-of-way regulations) to avoid opposite-direction traffic keeps the holding aircraft in its pattern. This would not be true when executing a left-hand hold, which is why left patterns are the exception, established only when necessary (because of terrain, for example).”
  https://www.aopa.org/news-and-media/all-news/2017/may/01/ifr-fix-what-were-they-thinking


Where can I find canonical examples of radio communications at non-towered airports?

What you're looking for is AIM 4-1-9(g)(6), recommended self-announce phraseologies. The self-announce phrases states position, altitude, climb/descent, among other things depending on the situation.

6. Recommended self-announce phraseologies:
It should be noted that aircraft operating to or from
another nearby airport may be making self-announce
broadcasts on the same UNICOM or MULTICOM
frequency. To help identify one airport from another,
the airport name should be spoken at the beginning
and end of each self-announce transmission.
(a) Inbound
EXAMPLE−
Strawn traffic, Apache Two Two Five Zulu, (position),
(altitude), (descending) or entering downwind/base/final
(as appropriate) runway one seven full stop, touch−and−
go, Strawn.
Strawn traffic Apache Two Two Five Zulu clear of runway
one seven Strawn.
(b) Outbound
EXAMPLE−
Strawn traffic, Queen Air Seven One Five Five Bravo
(location on airport) taxiing to runway two six Strawn.
Strawn traffic, Queen Air Seven One Five Five Bravo
departing runway two six. Departing the pattern to the
(direction), climbing to (altitude) Strawn.
(c) Practice Instrument Approach
EXAMPLE−
Strawn traffic, Cessna Two One Four Three Quebec
(position from airport) inbound descending through
(altitude) practice (name of approach) approach runway
three five Strawn.
Strawn traffic, Cessna Two One Four Three Quebec
practice (type) approach completed or terminated runway
three five Strawn.

Examples shown are from the Aeronautical Information Manual. I hope that helps!


This will vary from engine to engine and with modern engines controlled by computers for max fuel efficiency, the computer will constantly adjust the idle during the descent unless you manually select otherwise. However a minimum idle speed is necessary to prevent flame-out, and is as high as 70%** during severe icing conditions although 55% is the minimum. There are also different idle regimes, flight idle, approach idle and ground idle, controlled automatically.
The last aircraft that I flew, the B727, did not have any fancy FADEC and we manually closed the throttles at top of descent. The fuel control unit would adjust the fuel flow throughout the descent to keep a minimum 55% N1. This was evident from observing the fuel flow increase throughout the descent even though the throttles were at idle. If we needed more N1 due to icing, we would have to advance the throttles manually. Some planes had autothrottle but I don't think it compensated for icing.
Approach idle is also controlled automatically and is somewhat higher to allow a quick spool-up in the event of a go-around. It is deactivated after touchdown.
The 737Ng has similar regimes controlled by the EEC (Electronic Engine Control).
** Thrust requirements for for engine and wing anti-ice:

If Icing conditions exist with TAT -7° or above: 55% N1
If Icing conditions exist with TAT below -7° or moderate to severe icing observed at any temperature: 70% N1
Only one outboard engine supplying bleed air for wing 75% N1 on that engine.

To answer your question below, a jet engine works much the same as a piston engine wrt air/fuel ratio and the compression ratio is determined by its construction (see NASA). In a jet engine however you don't have a butterfly valve to vary air input, you can only vary fuel input-(there are exceptions with bleed-off valves, but let's keep it simple). The speed at which the engine turns determines air input and this speed is regulated by the amount of fuel injected into the combustion chamber. The jet engine will automatically settle at an equilibrium speed when the best air/fuel ratio is achieved.
So assuming an engine with only a variable fuel input (no automatic compensation for any variable parameters such as altitude)--- if for instance the altitude at start of descent is higher, less air is going to be taken in by the compressor, the fuel/air ratio will change resulting in a different engine speed than if the start of descent altitude was lower.
Ram air effect (Indicated airspeed) will also change the fuel/air ratio once again causing a different equilibrium engine speed.
Temperature will also affect the density of the air and cause a different rotation speed.
This is clearly unacceptable therefore some kind of governor must be provided to maintain stable parameters.
You can use the NASA engine simulator here to play around and test various scenarios.


What are the limits on myopia for a pre-eye refraction surgery for a class 1 medical certificate?

It looks like there are no limits for your pre-surgery eyesight:

  Flight crew having undergone refractive surgery will be considered for
  medical fitness for flying on a case-to-case basis. Such cases will be
  examined only after a minimum period of six months after the
  procedure. Medical fitness for initial issue of licence may also be
  considered for such cases, if the visual requirements for the license
  category are met with normal corneal topography, no post surgical
  complications like corneal opacity interfering with vision and
  unstable refraction.

That makes sense: LASIK physically changes your eyes, so whatever your values were before the surgery are completely irrelevant after it. The general class I eyesight requirements in India are taken from ICAO Annex 1, which isn't freely available online. However, ICAO's Manual of Civil Aviation Medicine says:

  Distant visual acuity with or without correction shall be 6/9 or
  better in each eye separately, and binocular visual acuity shall be
  6/6 or better. No limits apply to uncorrected visual acuity.


How do I obtain permission to fly an airplane that isn't airworthy?

You must request a Special Flight Permit from the nearest FSDO (Flight Standards District Office).

You'll need to fill out Form 8130-6, Application for U.S. Airworthiness, appropriately calling out the reasons you need a SFP (ferry flight, etc). Once the form is submitted, you may be subject to an inspection by an FAA official or representative, verifying that your aircraft is in fact in a condition for safe operation.

Avemco, the insurance company, has a good article on ferry permits that might be worth an extended read and which I don't intend to copy here.


When you pitch the nose down to gain speed, it feels as though you are pitching down a long way

This is because the change of the cockpit angle towards the horizon is the sum of both the angle of attack and the glide path angle change.
This means that at low speed your speed changes should move the target point up when you go faster (the point is only affected by the change in glide angle while your view is affected by the sum of angle of attack and glide angle change) while at high speed, when a speed change means only very small changes in angle of attack) the target point does not move much relative to the canopy any more (but it will still move a bit up when going even faster).

How does pitch relate to the polar curve?

All you need to do is to add the angle of attack at the respective speed to the polar curve and you get the pitch angle. Like this:

The blue line is the arcsin of the ratio of sink speed to flight speed. It should not be a coincidence that it looks like the sink speed polar. To that line I added the angle of attack (red line) which shows in which direction relative to the horizon the longitudinal axis of the plane points. Since the cockpit is a bit angled down, your viewing angle should be reduced by that amount. Now it is easy to see that the angle changes a lot at the low speed end but stays almost parallel to the sink speed line at high speed. Since I assumed a zero-lift angle of attack of -2°, the red line crosses the blue one at 52 m/s.


In which situations can a Dual-Aircraft Platform (atmospheric satellite) remain nearly geostationary?

Almost any situation

The only time you wouldn't be able to stay (near) Geostationary would be if the wind velocity is higher than your own maximum powered velocity, at all altitudes you are able to operate.

In any other situation, you simply fly in something resembling a circle over the area you with to loiter, or fly directly into the wind (zig-zagging if the wind is slower than your minimum airspeed). Which you choose will depend on your minimum/maximum airspeed, the windspeed, and how "stationary" you need to remain with reference to a point on the ground.

Then again, the above applies to almost any solar powered aircraft, so how about the specifics of this concept?

What are the potential advantages?

Winds at altitude are not always (or even usually) in the same direction, or at the same velocity. We can take advantage of this in some scenarios:

If you have, for example, a fast-moving stream of air near a slower moving body of air, or (even better) a body moving in roughly the opposite direction, you can fly slowly "upwind" in the slow moving stream (which doesn't use much energy, relatively speaking) then "surf" down the fast stream, harvesting energy as you go - you then use that gained energy to fly back into position, through the slow moving body.

If you get an even more ideal scenario, the slow moving body is in the opposite direction to the fast moving body, you can simply "float" around in the currents, harvesting energy most of the time.

The important part to note is that zig zagging (akin to tacking in sailing) - regular tacking requires you to change direction regularly to avoid going off course... with two aircraft tethered, however, they can "tack" away from each other without changing direction. Essentially, they can angle away from each other and vary the angle of incidence to remain relatively stationary within the wind: if the wind speed increases, you fly more "into" the wind, if it decreases, you fly more perpendicular to the wind (and therefore more "away" from your partner aircraft).

This combination of two aircraft tack-surfing (totally not a technical word, I definitely just made it up) mean you can "surf" the wind even when the windspeed  is lower than your own stall speed, without having to tack as a single aircraft would. Tacking has a couple of disadvantages - it's more involved, and it means you are constantly travelling laterally across the wind, while two aircraft surfing together can stay in almost exactly the same place, merely by angling more or less into the wind. They can also, by coordinating power between themselves, move laterally along the "face" of the wind

In short, you have much more fine-grained control over your position, in more conditions


What is the difference between the V-shape tail and the straight tail on the Beechcraft Bonanza?

V-tails have been fashionable in the Fourties and Fifties, and the claim was that they would cause less drag than an equally effective conventional tail. This has two reasons:

Average chord length is longer, so the Reynolds number of the airflow is higher, causing relatively less friction drag.
Instead of three surface-fuselage-joints, the V-tail has only two, so less interference drag is created.

Flight testing of V-tails showed only marginal advantages, and in damping they are less effective than a conventional tail which is dimensioned for the same control effectiveness. The control effectiveness of a control surface is proportional to the cosine of the V-angle, but the damping characteristics go down with the square of the cosine.

@nimbusgb mentions the tendency of the V-tailed Bonanza to fishtail: That is a consequence of too little lateral damping.

Also, when a combined elevator-rudder input is commanded, the V-tail will produce a very high deflection on one side, while the two commands will cancel out on the other side. This will reduce overall control power in cases where a combined elevator-rudder input is commanded over what is possible with a conventional tail.

Even the glider designers, who had enthusiastically tried out V-tails, have now returned to conventional tails (more precisely, T-tails) because the expected benefits did not materialize. And glider designers will try anything to improve the aerodynamic quality of their designs.


If we enter and exit through the emergency exit, then how come when the door is opened for the air bridge the slide does not inflate?

Take a look at the evacuation slide wiki page for full details.

As a part of the preparations for takeoff the flight attendants will arm the doors. This usually means moving a lever on the door.

If the door is armed when it is opened the slide deploys. If it's unarmed it doesn't.


Is a 100 hour inspection required for an aircraft to be used in a checkride?

The rule is that the pilot may not be "for hire".

He is for hire, but as a DFE, not the PIC (the one flying the plane), so he is not breaking the rule.

You are the one flying the plane (the PIC), but you aren't getting paid (in fact, you are paying someone else), so you aren't "for hire" either.


Is it cheaper to drop cargo than to land it?

That scenario only makes sense if your airplane stays at cruising altitude: although taxi and takeoff does use up fuel it's really the ascent to cruise that takes the most. You aren't really going to be able to drop cargo accurately from cruising altitude, so you'll have to descend pretty low, then you'll need to climb up again, and that would suck up lots of fuel and make it much less efficient a method of delivery.

Add to that the weight and cost of the parachute mechanisms as well as the massive protective packaging the cargo would need to survive the jolt (2-3 Gs when it hits the ground) and the whole thing becomes pretty uneconomical.

The military only air drops cargo when there's no other alternative - now you know why.


Do coaxial rotors provide twice the amount of lift?

What about the engine? Even if engine power was doubled, the coaxial rotor won't produce double the lift.
Airfoils don't like stacking neighbors.
(Source)
This double wing above (biplane) produced about 120% lift, not 200%.
Using the biplane above to illustrate a point, between the wings the pressure will neither be high enough for the upper wing, nor low enough for the lower wing.

In a biplane aircraft, two wings are placed one above the other. Each provides part of the lift, although they are not able to produce twice as much lift as a single wing of similar size and shape because the upper and the lower are working on nearly the same portion of the atmosphere and thus interfere with each other's behavior.

For the same engine output, we're looking at ~10% increase in lift.

Because the coaxial rotor does not require an anti-torque device such as a tail rotor, Fenestron, or Notar, a coaxial rotor helicopter requires about 10% less power than a single rotor/tail rotor helicopter.
For the same rotor diameter and power the coax will lift approximately 11% more weight. This equates to 30% greater useful load, which means more payload or fuel. The coax helicopter can hover at a 6000 ft higher altitude, or at a higher temperature (avxaircraft.com).


Do helicopters fly holding patterns under IFR?

In short, yes, helicopters fly procedure turns, hold, etc. just like airplanes.

Hovering at a fix is not practical, as they do not really have the nav capability to perform that, and it is contrary to normal ATC procedures.


What are the standard stability derivative formulas and typical GA values?

I don’t have it in front of me, but this book has the pertinent derivatives to consider, along with C172-ish values.

Aerodynamics, Aeronautics, and Flight Mechanics, 2nd Edition
Barnes W. McCormick
ISBN: 978-0-471-57506-1 September 1994 672 Pages


How much training does an A320 pilot need to fly an A321?

From Flight Training International:

  Airbus A320 Type Rating

  The Airbus A320 family of jet airliners consists of five aircraft:       the A318, A319, A320, A321 jet airliners and ACJ business jet.
  Only one type rating is required to fly these Airbus aircraft, as       they have similar flight decks.
  To earn a type rating for these Airbus aircraft requires the    completion of a technical course that lasts anywhere from 8 to 12 days depending on your pace.

So the answer from a regulatory point would be no additional training.  Some airlines might have policies that require a minimal check, probably in a sim.


What type of batteries are used in airline planes?

From this Concorde battery page, the Embraer E-145 can use a 44 Ah, 24 VDC Lead-Acid batter: Concorde RG-422

The Embraer E-145 can also use Ni-Cd batteries.

The Boeing 777 uses Ni-Cd batteries as well: Boeing 777 Saft Batteries


What are the effects of crosswind on glide angle?

Wind affects your flight path angle by affecting how far you travel while you're descending.
With no thrust from the engine an airplane is falling out of the sky at a roughly constant rate of descent. The wind direction affects the groundspeed, and thus the distance covered between when the engine failed & when the aircraft hits the ground.

This is more directly observable from outside the airplane.
Consider these 4 scenarios on a post-it note: The airplane has lost its engine, and the pilot is flying at best-glide airspeed while holding a constant magnetic heading (making no wind corrections):

No Wind
The aircraft descends along the no-wind glide path (about 45 degrees in my drawing), and travels in a straight line over the ground (the "ground track") while doing so.

Headwind
The aircraft descends along a steeper glide path (about 60 degrees in my drawing), because while it's still descending at the same rate the headwind is slowing its progress over the ground. Since it's a direct headwind (right on the nose) the ground track is still straight.

Tailwind
The aircraft descends along a shallower glide path (about 30 degrees in my drawing), because while it's still descending at the same rate it has a tailwind, which is making it move faster over the ground. Since it's a direct tailwind the ground track is still straight here too.

Crosswind
The aircraft descends along the no-wind glide path (because it has neither a headwind nor a tailwind), but the crosswind pushes the ground track (in this case into the inconveniently-placed tree).

Your endurance (time aloft) will be similarly unaffected: If you've set the aircraft up at its optimum glide angle-of-attack (best glide airspeed) the descent rate is pretty much the same regardless of whether you have a headwind, tailwind, or crosswind. You will fall the same distance in the same amount of time, it's just a matter of how far you travel while you're falling (which determines where you land).
You can test this for yourself in an airplane by doing engine-out drills: Line up with a headwind, pull the throttle out, and pitch for the aircraft's best glide speed. Note your vertical speed (rate of descent), and then repeat the test in the opposite direction (tailwind) or at 90 degrees to your original course (direct crosswind): The vertical speed will be effectively the same.


What is the reason for allowing pilots to take Pilot Aptitude Battery Test (PABT) only once?

A few thoughts:

They have no need in getting repeat candidates if the selection pool is  sufficient (which I imagine it is). Starting to accept repeat candidates would also make it harder for first timers, resulting in more work and tests for everybody. People also won't go for the fun of it, but will make their single attempt their best attempt.
I believe they would rather want you to nail it on the first attempt as part of the test. In other words: how do you respond to a new situation, how to you respond to the stress of knowing you have one attempt, etc... It would be effective for their purpose on multiple levels. This is more effective than you returning a second time and learning how to do the test.

While I can't comment on other air forces around the world, I know that German Lufthansa implements the same policy for acceptance.


Why are airliner underbellies generally painted differently?

Originally (way back before radar) the colors had a practical use for maintaining visual separation between planes, which was done by pilots looking for the other planes with their eyes:

Dark underbelly: Easier to see from below against bright clouds or sky.

Light top-body: Easier to see from above against (typically) dark ground.

The idea being that when you're looking visually for other civilian air traffic (or from the ground) one wants to maximize visibility without losing them in sky glare or ground clutter.

If you look at older military planes you'll often see the exact opposite (dark colors on top and blue on the bottom) because those military planes didn't want to be seen.


Why is the MD-88's front starboard door smaller than its port one?

The larger port side doors are for extra convienience during boarding. Passenger boarding is always done on the port side (left) while the starboard side doors are only used for servicing the galleys or as an emergency exit.


Can you accept a LAHSO on your private pilot checkride?

First, let's see whether it's legal. FAA Order 7110.118 notes that:

  7. EXPLANATION OF CHANGES.

  The following changes apply to all LAHSO.

  a. ...
  b. Solo student pilots will not conduct LAHSO.

However, you could interpret that as not applicable to your situation, as you are not the sole occupant of the aircraft:

  14 CFR §61.87

  (a) General. ... The term "solo flight" as used in this subpart means that flight time during which a student pilot is the sole occupant of the aircraft...

Though it might be allowed, note it does not say must:

  AIM 4-3-11(b)

  ...
  Student pilots or pilots not familiar with LAHSO should not participate in the program.

I'd recommend against doing so because LAHSO can add to your workload, especially if you're a bit nervous on your checkride. Also, the AIM note on discouraging LAHSO is rather valid and if done improperly, can affect safety. Having said that, the examiner is likely to ask questions on LAHSO during your practical examination, especially since LAHSO is a special emphasis area in the PTS. This may include:

Requirements to accept a LAHSO clearance
ATC pharseology for LAHSO
Pilot responsibilities while carrying out LAHSO

In any case, always remember that you do not need to accept a LAHSO clearance -- if you do not feel comfortable with doing so, ATC will provide arrangements to land full-length on the same runway or another one. You should not accept a LAHSO clearance if you believe doing so would compromise safety.

Note: this does not necessarily apply to all situations where a student pilot is prohibited from doing something that a private pilot would be able to do.


Does CG location affect the stability of the Dassault Falcon 7x while on the ground?

2% weight on nose wheel sounds plausible.

Almost all weight of an aircraft must be on the main wheels. Otherwise:

the elevator would have to be huge to generate enough force to lift the nose wheel off the ground on take-off and
on landing as the main gear contacts runway first it would create strong moment that would slam the nose into the ground.

See also Why do planes always land on rear wheels instead of the nose wheels?.

I've seen values like 4% weight on the nose wheel, so 2% for CG at aft limit makes sense. It is still enough to keep the aircraft level and leave some efficiency of the steering.

And yes, loading mistake can make an aircraft tip over on the tail:

(copied from this answer; original source)


Why is the critical AoA of most flaps 40° when most airfoils stall at 15°?

Flaps are located in the downwash of a wing. Their local angle of attack is not equal to their deflection angle, but equal to the deflection angle minus the angle the downwash leaves the trailing edge of the wing.


Will I be denied or fail a first class medical if I have a recent history of depression?

According to 67.107 which is the guideline for AME's for mental issues, depression is not listed as a reason for automatic denial for first-class medical certificates.

The issue with depression comes in when you are on medication to control it, as many antidepressants are considered "do not fly". It isn't impossible though even with medication and treatment, the FAA has published a guideline for AME's about antidepressants and treatement, and the granting of special issuance medicals.

What you do not want to do is to lie about it on your application, as falsifying your medical history is grounds for revocation. Getting your medical reinstated after lying about your prior conditions is very difficult (and expensive).


What should a Pilot do if they encounter foreign military jets?

According to ICAO conventions the offical international language of aviation is English therefore it is unlikely that Russian fighter pilots will speak in Russian to a foreign pilot. If the pilot overlfying American waters, it's unlikely that Russian fighters are free to intercept planes in American airspace.
If such scenario happens, the pilot can report the situation to the ATC, then the situation will quickly escalate. If the private pilot is in American airspace and Russian fighters are not authorised, the private pilot should be safe following ATC directions and/or continue the route as planned. USAF will take care of the rest.


What FAA sources of weather information can pilots use to mitigate the risk of flying in icing conditions?

Here's a list of official FAA weather information sources that pilots can analyze to avoid or mitigate icing risks:

AIRMET Zulu

An AIRMET Zulu will be issued for areas where icing conditions are forecast to be light or moderate.

SIGMET

A SIGMET will be issued for icing conditions forecast to be severe.

PIREPs

PIREPs are the best source of icing information. Unlike weather information sources which are forecasts, PIREPs are reports from pilots flying in the actual conditions and should be considered the most accurate source of icing information.

Here's an example of a PIREP where a pilot of a TBM-700 was descending into Atlanta. He reported a cloud layer topping at 7900 feet down to 500 feet AGL and picking up light rime ice between 7900 and 5000 feet.

UA /OV ATL /TM 1200 /FLUNKN /TP TBM7 /SK OVC015-TOP079 /IC LGT RIME 050-079 /RM DURD

Significant Weather Prognostic Charts

The top two panes of a prog chart help pilots visualize the freezing level. A zig zag line shows when freezing level is at the surface and height contours for the highest freezing level are drawn at 4000 foot intervals with dashed lines. This information gives pilots a forecast of temperatures which when combined with known precipitation can predict ice and help to avoid it.

Area Forecast (FA)

An FA is an additional source of information about where cloud tops and bottoms are. If you know that along with the freezing level you can get a better idea of where icing conditions are most likely.


Are there additional electrical grounding methods besides static wicks?

Many aircraft tyres conduct electricity which also dissipates charges.  The compound contains "carbon black" or graphites.

In the special case of helicopters using a hook to pick up a load from a hover, the wise ground handler will use a rod on the end of a grounded cable to earth the charge.  Helicopters can build up a lot of static and many a ground handler has been left with smoking underpants by not heeding this advice.


What is the difference between a tire deflation and a tire explosion?

An exploding tire while the plane is rolling will propel debris in various directions.

This happened with the crashed Concorde on takeoff. A chunk of the tire hit the tanks and caused a punctured in it. This then lead to the fire and loss of power.


As mentioned in this answer: there are seven commercial aircraft types with zero hull loss accidents:

B717
CRJ700, CRJ900, and CRJ1000
A380
B787
B747-8
A350
C-series
A320Neo

Only the first two types have logged more than 1 million departures. The remaining ones are relatively recent types and are still working on statistical significance; especially the long haul aircraft fleet takes a long time to accumulate 1 million departures at 1-2 flights per day per aircraft.


I can only answer from a US standpoint as that is the jurisdiction I know best, elsewhere in the world things may be different.

The first thing you can check is this data from the Bureau Of Labor And Statistics according to their data

  2015 Median Pay

  The wage at which half of the workers in the occupation earned more
  than that amount and half earned less. Median wage data are from the
  BLS Occupational Employment Statistics survey. In May 2015, the median
  annual wage for all workers was $36,200.

  For Pilots the 2015 median pay was 102,520 USD per year

You should read over this article as well as it covers a wide variety of how pilots are paid and the such.

Here is some more data on salary as well. You should how ever note that for many articles the data is submitted by choice and may not accurately reflect the true pay scale.

Here is some discussion on the per hour pay but I should caution you to be weary of per hour statistics for pilots. In many cases these numbers are computed using flight hours which does not accurately reflect how much a pilot may work as there is more time involved in a flight than just what the hobbs meter records. Here in the US it is my impression most commercial (121) pilots are salaried.

My two flight instructors recently went to the regionals after completing their ATP hours from talking to them it is evident that starting pay is very low (under 30K a year).

One interesting (and often debated issue) is that the FAA requires pilots to retire at 65 (was previously 60). This in theory puts a cap on their earning potential as an airline pilot (however they can fly non 121 operations like a 135 charter afterwords).

As for perks, that depends on the airline (and may to some extent depend on seniority). Its common to get some comped tickets for family members and the such but its not what it once was. I have heard that many pilots can fly standby on their own (or in company) airlines for free. They may also be able to ride in the jump seat if there is one. This can be attractive for a young single pilot but is not very efficient for family travel.

Free hotels and things will depend on the route you are flying. If overnight stay is required they may put the pilot up (i.e. long haul routes) but you should not expect 5 Star Penthouses and bottomless lobster dinners. However there are plenty of short routes for which a pilot may end up back at their base at the end of their shift.

If you are looking for a decent overview of the pilots life I would advise picking up a copy of Cockpit Confidential it has a lot of the answer you may be looking for and is very to the point.


Can a private pilot receive recurring training while waiting for a special-issuance medical approval?

My understanding is that your medical is currently invalid (because you had bypass surgery and need to get your medical reinstated), so you currently cannot exercise the privileges of your certificate - i.e. you can't act as pilot in command of a flight (or any other required crew member in a role for which a medical is required).

As Casey pointed out, you've got an out that allows you to still take training (and even to fly generally): Someone else with a valid medical and a certificate appropriate to the category & class of aircraft needs to act as the (legal, FAR 91.3) pilot in command while you're operating the controls.

If your CFII is willing to accept that role (and the attendant liability) while giving you your training you can go up with them and complete the recurrent training your insurance company requires, but this is something you need to discuss with your CFI prior to going up with them.


Do pilots need a clearance to go around?

No, and this applies to any pilot, not just an airliner pilot. After the pilot has been cleared to land (or even if you're landing at your own discretion at an untowered airport), he can decide to go around instead of landing if he's dissatisfied with the approach for any reason.

The pilot might need to abort the landing for reasons the tower can't possibly know about, such as a gear unsafe indication, failing to achieve a stabilised approach, not making visual contact with the runway, or some distraction within the cockpit. And even in the case of a reason the tower should be able to tell - such as another aircraft infringing the runway, lining up on the wrong runway by accident, or birds on short final - the pilot must still go around if he thinks it's not safe to land, without waiting to be told.

The same applies to taking off. Even after being cleared to take off, the pilot must not take off if he thinks it is not safe to do so, even if it's for a reason the tower should know about, such as a runway obstruction or a take-off clearance on a crossing runway.


You are right, the two rotors move in opposite direction. This is called a co-axial rotor and is used by the Russian helicopter design bureau Kamov. A co-axial rotor can also be found on many model helicopters for indoor flying. They are a subspecies of helicopters with contra-rotating rotors.

Helicopters with contra-rotating rotors do not need a tail rotor and are much easier to fly than Sikorsky-type helicopters, because they suffer much less from instability. This group also comprises intermeshing rotors like those used on Flettner or Kaman K-Max helicopters.

Kamov Ka-32 with co-axial rotors operated by HeliSwiss (picture source)

Kaman K-Max with intermeshing rotors modified as an unmanned vehicle (picture source)

For more info, just follow the links.


What is the best way to navigate a storm?

If you're flying through a thunderstorm, lightning is the least of your concerns. Airplanes are struck by lightning all the time, and while it may mess with your electronics (navigation, radio, etc.), it very rarely causes any more damage than that. But to answer the second part of your question, there's no one place in a thunderstorm that has any more or less chance of lightning than any other.

The big issue with flying through a thunderstorm is with the wind. There's a lot of vertical air movement in thunderstorms, and the wind shear can easily cause structural damage to your aircraft if you're not very careful (and sometimes the wind can damage or destroy aircraft even if you are careful. And that's leaving out other dangers, such as hail. Thunderstorms are not good places to fly).

The accepted method for flying in a thunderstorm is to fly straight through (as most thunderstorms are small enough that going straight gets you out of it faster than turning around) at less than your maneuvering speed (to minimize the chance of structural damage to your wings), accepting any changes of altitude (again, to minimize stress on your wings).


Why are passenger and cargo airplane noses manufactured separately from fuselages and then put together?

A radome, or nose cone, is essentially a structural cover serving a different purpose than the fuselage. These are made separate because they a special material invisible to the radar mounted beneath them. They are different shapes or sizes depending on the customer specific component they cover (radar antennas) and can be easily removed or replaced.

The radome serves two essential purposes. 1) It covers electronic equipment mounted to the forward bulkhead of the fuselage to protect it from weather, or from view. 2) It acts as an aerodynamic cover for the leading edge of the aircraft.

https://en.wikipedia.org/wiki/Nose_cone


APUs are like small jet engines, small enough to be started electrically. So you would use the power of the battery or an electric ground power cart to spin up the APU by its electric starter motor, and then introduce fuel into it once its spinning fast enough, just like a jet engine is started. Depending on the design, the electric motor will then either act as a generator to supply electrical power back to the aircraft or decouple when a separate generator is used.

The APU will spin up, and besides spinning the electric generator, some pressurized air will be 'stolen' from its compressor to supply "bleed air" for engine starting, the air conditioning packs, etc...

Big APUs like on the Boeing 777 have actually two methods of starting: They have both an air-driven and an electric driven starter motor. The method of operation is as follows: When the APU is started with the engines off, electrical power from battery or ground connection is used. After the flight, the APU will be restarted before the main engines are turned off. In that case, the APU will be started by the air-driven motor rather than the electric motor, with pressurized air supplied by the still-running main engines.

EDIT to answer question in comment:
Depending on size, the APU will take something between 30seconds and 2 minutes to start. The big APU of the 777 will deliver electrical power after 2 minutes or so, small units you are likely to find on regional jets can do that after perhaps 45 seconds. Then, it takes an additional 2-4 minutes until you can extract bleed air from it. That is because taking air from the compressor increases the exhaust gas temperature of the APU, and you want the APU to warm up evenly. The same is true for the shutdown process: You close the bleed-air valve and then let the APU continue to run for another two minutes or so to cool down, then shut it off completely. This lowers the thermal stress on the unit. On modern planes like the 777 this process is automated: You turn the APU selector switch to OFF and that will close the bleed air valve, initiate a 2 minute cooldown period, and eventually turn off the APU completely. The only way to shut it down immediately is in fact the APU FIRE handle.
So, you will turn the APU on typically while you are taxiing in after landing. Because of course you want it to be up and running and ready to take over the air conditioning by the time you are at the gate.
Some APUs like those found on the MD-80s have two settings for bleed air extraction: NORM and ECON. ECON takes less bleed air, thus not increasing the exhaust gas temperature of the APU too much. On particularly hot days, using the APU bleed in ECON might help not overheating the APU if it is to be used for an extended period of time.


Why does the mass penalty of cantilever vs externally braced wing decrease with aircraft size?

I think the Wikipedia article is wrong. Scaling the structure has other issues, but spar weight is not one of them.

The correct approach is to compare the scaling-up of a cantilevered monoplane wing with the same scaling-up of the equivalent wire-braced monoplane design.

In both cases, structural weight rises with the square of the linear scaling, for example doubling the length and span will give a fourfold increase in structural weight. The designer's challenge is to maintain the same weight of structure per unit of wing area, called wing loading, at scale.

The real difference comes not with scale but with speed. As the speed rises, the drag of the bracing rises more sharply, while the aerodynamic forces on the wing demand a stronger structure, especially thicker skinning. Eventually you reach a point, at around 200 mph (300 kph), where the drag of the bracing becomes excessive and the strength of the airframe will admit a cantilever construction without excessive additional weight penalty.

This was what triggered the historic change in design habits which the Wikipedia author was trying to explain and is, I suspect, what they would have said had they known better.

I have now substantially reworked that section of the Wikipedia article (current version here) and added a couple of citations.


I was wondering which one was better and why.

When done equally right they are equally good.

However, FBW makes it possibly to improve the quality of control beyond what's determined by the aerodynamics (e,g, making unstable airplanes stable, or making hard-to-fly airplanes easy to fly), and making the airplane robust against malfunctioning components (e.g. stuck actuators or control surfaces), or and adverse conditions (neutralizing turbulence, wind gust, etc).

Giving computers some authority also enables the computer to correct for human error (stalling, overloading, etc), hence improves safety as well.

Which one is safer?

FBW is extremely hard to design, tune, test, and validate. Although the benefit of FBW could make the flight safer in a lot of ways, the risk that a premature FBW system could introduce is quite significant as well.

In general, although it is hard to state that an airplane equipped with FBW is inherently safer than one with conventional controls, and often times the reverse seemed true in history due to early bad track record of some FBW equipped airplanes, yet if an airplane is designed with safety as priority, FBW could offer a lot of benefits, again, if done right.


How are performance variables accounted for when testing solar-powered aircraft?

Usually when test results are potentially affected by many factors, standard test conditions are defined. When tests are performed under these standard conditions, the results can be compared between products.

Since these standard conditions rarely exists in nature, testing under standard conditions is not possible. Instead, a test programme is developed that tests under a number of non standard conditions to identify the effect of individual factors and correct for that. In addition, components of the system under test can often be tested in an isolated controlled environment. In this way, standard conditions can be achieved for individual components and the effect of deviations for the standard conditions can be determined as well.

For the example of a solar aircraft, the efficiency of the solar panels could be determined independent of the aircraft. The same holds for the battery, the engine, the propeller and other components that the propulsion system may depend on. Not only the performance under standard conditions can be determined, but also under non-standard conditions.

The power requirements of the aircraft under a range of conditions can be determined by test flights. This could involve horizontal cruise flight segments at various speeds, altitudes and temperatures, and also gliding tests.

The maximum achievable flight time under standard and non-standard conditions can then be calculated from the results of all the acquired test results, without ever having flown under these standard conditions.

For validation of the methodology used, a test flight can be done do determine the actual flight time under non-standard conditions. When the results of the test flight agree with the calculated flight time under the same non-standard conditions, one can assume that the methodology is correct.

For you own RC plane such a test programme is probably out of scope. A simple way to gather some data is to perform two flights with the same aircraft. Both time start with a full charge (I assume there is a battery involved). Test how long the flight last with the solar panels. For the second flight, disconnect the panels and see how long the flight last then. You now know how much the solar panels contribute in terms of power production. Then fly with the non-solar plane and see how long that lasts. It will probably last longer than the solar plane with the panels disconnected because it doesn't have to carry the extra weight of the panels. This way you learn what the addition of solar panels costed in terms of flight efficiency.


Beside payload size, what precise factors are considered to choose the fuselages shape?

Assuming an engineering background, here’s a short list of factors affecting fuselage shape and size.

aerodynamic considerations
volume considerations
structural and elastic considerations
operational and interface considerations.

Aerodynamically, drag and stability are the major concerns.

Volume wise, payloads, subsystems, cargo, propulsion, etc must be considered. So it might take a few iterations for a preliminary design to converge at a feasible and optimum solution.

Structurally, elasticity of the fuselage is important, at least for weight efficiency, and general comfort. a bad shape can cause unwanted structural modes, which could risk failure in flight, or may cause difficulty in controls. If you were ever on a 747, you probably noticed how much it snakes towards the rear of the plane. The oval shape of the fuselage has parts to blame.

Finally, sometimes doors, openings, and structural interfaces dictate geometries of fuselages.

Additionally, geometric constraints such as tail strike prevention, or belly landing can be other reasons to shape the fuselage.


How do the VNAV and LNAV work on the 737NG?

I see some confusion about the Autopilot system here. First let's clear something up:

The B737 has 3 guidance: speed, horizontal and vertical. These are displayed on the top of the PFD from left to right.
Engaging Flight Director displays the guidance but not to follow it, engaging the Autopilot tells the plane to follow the guidance.
Each guidance has several modes. E.g. Possible horizontal guidance modes include "HDG SEL", "HDG HLD", "LNAV" etc. Possible vertical guidance modes include "V/S", "ALT HLD", "VNAV" etc.

LNAV is just one of the horizontal guidance modes. The FMC decides what is LNAV. If LNAV is not engaged, then the FMC does not take part in horizontal navigation.

Your confusion likely arises from armed modes. The B737 allows you to select one active mode, plus one armed mode. For example, consider the LNAV path in FMC is heading North (360 degrees). The plane is to the East of the intended path (right side). By doing the following:

Set the heading window to "340".
Set "HDL SEL" as active mode.
Set "LNAV" as armed mode.

The plane is on a heading to join the LNAV course. When the plane is close*1, the horizontal mode will automatically change from "HDG SEL" to "LNAV".

Similarly, "V/S" can be used to capture VNAV profile when the plane is above or below the intended altitude.

*1: The plane has to be within a certain nautical miles and the intercept angle cannot exceed a certain degree. I will update the exact number when I get reference to the B737 manuals.


What are the fatigue regulations in the US and Australia for military transport helicopters/rotorcraft?

The US Federal Aviation Administration does not regulate aircraft owned and operated by the military services. I suspect that is the same situation with Australia's CASA.

Parameters for aircraft service life for military aircraft are defined by the manufacturer. The aircraft is designed to meet the requirements specified by the agency requiring the aircraft. This is usually expressed in flight hours, cycles or a combination of that and possibly other parameters.


In the attached image of the Hoffman development of Arup design, the wing is shaped in a somehow anhedral way. Why?

This plane is very interesting as it highlights a few design options.  Firstly, in seems to have neither significant dihedral nor anhedral, but it does have landing gear underneath it, lowering its CG for stability.  Being low aspect ratio, the builder probably decided to forego dihedral as cross wind gusts could make for a rolly, uncomfortable ride.  A slight sweep in the leading edges of the wing would provide some "dihedral effect" when rudder was applied.

Now for the wing itself, not albatross or eagle, we'll go flying squirrel here.  But notice how low the landing speed is.  This is a virtue of lower AR wings, though not as efficient as high AR (albatross) wings, they do stall at significantly lower speeds.  This design was also applied to the Navy "flying flapjack" and it performed well.

And thanks for the article, the ads made good reading too!


What's the purpose of the cable connected on the top of the fin?

It is a Trailing Static or Trailing Cone used in test aircraft to measure free stream values. From Airdata Measurement and Calibration:

  By trailing a long tube behind the airplane, a nearly free-stream static pressure measurement can be taken. A perforated cone at the end of the tube acts as a drag device to keep the tube stable.

Image from NASA Airdata measurement and calibration

It is used in test aircraft. The image below shows the trailing cone attached to the 787 dreamliner (pictured at Paris airshow).

Image from flyingsquadron.com

This image shows the trailing cone assembly used in 787 dreamliner.

Image from airpigz.com

The device is specified by FAA and JAA as one of several methods that can be used to perform flight calibrations. According to FAA Advisory Circular 91-85:

  Where precision flight calibrations are used to quantify or verify altimetry system performance they may be accomplished by any of the ollowing methods. ...

  • Precision tracking radar in conjunction with pressure calibration of
  atmosphere at test altitude.

  • Trailing cone.

  • Pacer aircraft.

  • Any other method acceptable to the FAA or approving authority.


Why are ARINC labels are transmitted LSB first?

Revised answer

The ARINC 429 frame is composed of 4 bytes (32 bits numbered by convention 1 to 32 from right to left). Bits 11 to 29, which are the payload of the frame, can represent data using different formats, e.g. binary or BCD data. The label is used to indicate the content of the data field, and which format is used, and is necessary to convert data bits into useful information.

ARINC 429 frame used in BCD format (source)

The label is usually spelled as an octal quantity (rather than decimal or hexadecimal), e.g. 010101102 will be spelled as 1268 (01 010 110) rather than 5616 (0101 0110) or 8610.

The way bits are numbered somehow makes the label the "least significant byte" and bit 1 the "least significant bit". However:

The format above is for naming and ordering information, but doesn't tell how bits are really stored in components memory.
In digital engineering, bits are usually numbered from 0 to 31, as the number actually indicates the weight of the bit: 0 is 20 (1), 4 is 24 (16). In this convention bit 0 is indeed less significant than bit 31.

The ARINC 429 data bus is composed of 2 wires and the ground reference. When an ARINC frame is transmitted on the bus, it must be serialized, which means sending bits one at a time. The transmission order is:

The label byte transmitted first, "MSB" first: 8-7-6-5-4-3-2-1.
The other bits are then transmitted "LSB" first: 9-10-11 ... 30-31-32.

So, back to your question, why not using the left to right order for the whole frame? Or at least the left to right order for the label if it's sent first?

From Wikipedia:

  Like CAN Protocol Identifier Fields, ARINC 429 label fields are
  transmitted most significant bit first. [...] This notional reversal
  also reflects historical implementation details.

So let's assume there is no reason to reverse the label bits, other than historical implementations that wanted to mimic the behavior of CAN. In the French version of this Wikipedia article, it is stated that this reversal helped to read the label when looking at a frame using an oscilloscope. The MSB arriving first also appears on the left of the display (the signal on an oscilloscope generally enters on the right of the screen and scroll towards the left side as a function of the time):

ARINC 429 bit stream on a datascope (source)

I'm a bit baffled by this explanation, as engineers working with binary representations are used to read them is both directions quite easily after a short time.

Still according to Wikipedia, hardware used to serialize and de-serialize the ARINC word were actually insensitive to the order of the label bits:

  ARINC 429 transceivers have been implemented with 32-bit shift
  registers. Parallel access to that shift register is often
  octet-oriented. As such, the bit order of the octet access is the bit
  order of the accessing device, which is usually LSB 0; and serial
  transmission is arranged such that the least significant bit of each
  octet is transmitted first. So, in common practice, the accessing
  device wrote or  read a "reversed label" (for example, to transmit a
  Label 2138 [or 8B16] the bit-reversed value D116 is written to the
  Label octet). Newer or "enhanced" transceivers may be configured to
  reverse the Label field bit order "in hardware."

About odd parity

It is usual in digital serial communication to use data value changes (0 to 1 or 1 to 0) to derive a clocking clue in order to ensure the receiver samples the line voltage at the right time. This is less expensive than transmitting the clock signal on a separate wire. As each bit lasts the same time, the receiver uses a local clock that is roughly in sync with the transmitting clock. To actually maintain the synchronization in the long term, the receiver uses the raising and falling edges of the signal to detect bit borders and phase-align its clock.

Resynchronization of receiver clock on front and rear edges of the signal

That works well if the delay between edges is short. This means avoiding sending long series of 0 or 1. The parity bit can help. For data containing only 0 bits (or 1 bits) the odd parity bit will be 1 (or 0), preventing long edgeless streams to occur.

In some uses of ARINC 429, the parity bit is not transmitted, and is used for data, but nevertheless it seems superfluous for sync in this case since the link protocol is 3-level with return to zero, ensuring two edges for each bit of data.

Return to zero coding (source)


Do intermeshing rotor helicopters have a swasplate? If no, then how do cyclic and collective controls work?

What's missing from the picture is the hydraulic actuators that move the swash plate. The K-max and all other Kaman helicopters have cyclic and collective control via servo-tabs behind the trailing edge of the blades. These can be deflected manually. The servo tabs are visible on this picture:

Further info from this site, which also shows a cutaway drawing revealing the thin control rods inside the rotor hub fairing:

  The servo flap is a small airfoil located at about 75 percent span of the rotor blade, situated on the trailing edge of each rotor blade. These flaps are controlled by the pilot through push-pull control rods and their function is similar to that of an elevator on fixed wing airplanes. Moving the trailing edge of the flap upward moves the leading edge of the main rotor blade up. This increases the rotor pitch or the lift in very much the same manner as the elevator, on a fixed wing aircraft, changes the angle of attack on the wing. Thus the helicopter pilot can cause the angle of attack of the flap to increase or decrease in pitch, causing the helicopter to alternately dive or climb.


Could flywheel type gyros stablize a plane?

I actually have a lot of experience in the shipboard systems that you are talking about.

First, the gyro's do not keep the boat upright, they counter the rolling effect of waves but they cannot completely remove them. Gyro's of all designs work on the principle of conservation of angular momentum. That means that a spinning object will tend to impart a force 90° opposite of the force applied to it to conserve angular momentum.

In order for this to have a tangible effect on something of significant mass, the gyro itself (more specifically, the flywheel) must also have a significant mass. In shipboard systems this means that they usually use many (for an aircraft carrier, I would assume dozens even) of these devices that spin a flywheel weighing in the magnitude of tons. That is a lot of mass to be moving around!

So the first issue you have is to get the mass spinning fast enough to have an effect. Getting something that large spinning takes significant amounts of energy and time. Getting something that large to stop spinning can be equally problematic. Yes, you could use brakes (and many do), but you need to dissipate a lot of energy (heat).

So, taking into account that these gyros don't change speed very fast, and that they very heavily counter forces, you have a number of problems off the bat:

You have to carry a LOT of extra weight.
You need to have a lot of extra fuel/motors/generators to get the mass spinning.
Once spinning, the mass will counter changes in momentum, this will make the aircraft difficult, if not impossible, to bank (aka: turn).

So could they be used to correct a flat spin? Not really. In order to counter the flat spin you'd have to have a gyro mounted 90° to the angle of the spin, and then change the momentum of the gyro to counter the spin. Flat spins are not (apart from what Top Gun may have you believe) impossible to recover from given altitude and control authority. This happens in the world of aerobatics quite frequently (and on purpose).

Can they be used to control the plane? Again probably not. You are talking about changing the angular momentum of a huge mass very quickly. This would work for the braking side, but not the speed-up side. That means you'd have an aircraft that can perform a maneuver once in one direction, then have to fly off while the aircraft builds up gyro's again.

By the way, spacecraft use control moment gyros that work by using gimbals to rotate a gyroscopic flywheel to impart a rotational force on the spacecraft. These work because of a reduced gravity/drag in the operational environment of the spacecraft itself. The masses don't have to be as big as they would on earth.


Can a commercial airliner be used for military purposes?

Retrofitting is (as the comments to your post have already stated) rather difficult and unusual. In addition, the quality of service from such an aircraft you could expect to get would most probably not be great. Analogy: Try changing your minibus for 9 people into minivan for freight and industrial work.

It is also worth mentioning that the difference in operation is substantial between bombers and commercial jets. You would be better off using something that is not that complicated, like a Cessna Caravan for instance.

I think that energy, time and money would be better spent on building more dedicated aircraft. Changing the commercial ones is also not trivial and will require engineered changes.

It is however fully possible to design a military derivative of a commercial jet. The Boeing P-8 Poseidon is an example of this, being based off the Boeing 737 with the necessary modifications.

The armament is also fairly extensive:

  5 internal and 6 external stations for AGM-84H/K SLAM-ER, AGM-84 Harpoon, Mark 54 torpedo, missiles, mines, torpedoes, bombs, and a High Altitude Anti-Submarine Warfare Weapon system[


What kind of waypoints/routes are used to prepare a flight plan in practice?

In real life the flight planning process starts with where you are, where you are going, and then you make decisions on routing based on considerations such as weather, terrain, alternate airfields, airspace, VFR vs IFR, etc.  Looking at the chart you will then choose appropriate waypoints along that route of flight based on the aircraft navigation equipment.  You don't generally start planning by making a blanket decision on what category of waypoint you would like to use.


How many flight training hours can a student realistically do in a week?

There are a few external factors

Your CFI:
If we are talking about dual time (or supervised solos) here your CFI will need to be free.
The plane:
Keep in mind that school may have other students who may also book the plane, or it may be out for its 100 hour inspection or it is broken etc.
The weather:
Depending on where you are located, you may be limited by the weather grounding you for VFR flight.
The Wind:
A lot of flight schools (at least the one I go to) impose student maximum limits when it comes to crosswinds. At single runway airports this could cause an issue. You can mitigate this by training at a place with two runways.

Now if we look past all those and assume you have a working plane, a CFI, and clear weather, then I would think (assuming the school is open) you could log 3 hours in the morning and 3 in the afternoon if you really pushed it. If you started your day with 1 hour of ground from 8-9 then flew from 9-noon. Lunch. Then another hour of ground from 1-2 and flying from 2-5 that is putting you at close to 6 hours a day. Throw a few night flights in there, some more ground lessons at night and you may be able to squeeze the time in. Keep in mind you will also need to study for the written exam.

Note: The above projection is strictly based on everything working all the time which in aviation is often not the case. Your results may vary.


Aircraft fuselages being shipped on a boat

The aircraft you saw was N733UK (not Z733UK). It's a Boeing 737-300, most recently operated by European Aviation Group, and before that by easyJet  and bmibaby. It was stored at Bournemouth Airport in 2015 and subsequently dismantled.
This site suggests it's on its way to China to be used for training.
https://www.planespotters.net/airframe/boeing-737-300-n733uk-european-aviation-group/rovlz3


What happens with RNAV procedures on the way from AIP publication to FMS database?

The navigation database is technically a component of the GPS or FMS navigation system.  As such the manufacturer of the GPS or FMS is responsible for ensuring the database works with the equipment.

The database itself is usually prepared by a database provider such as Jeppesen. They have to work with the manufacturer to format and structure the database to work with the GPS or FMS.  After Jeppesen builds a database for a given cycle the GPS/FMS manufacturer will test the database before it's released.

Depending on their business agreement, the database subscription may be purchased from the manufacturer or direct from Jeppesen.

Jeppesen obtains the data from the ANSP and must process the data in accordance with RTCA DO-200B, Standards for Processing Aeronautical Data.  (Available for purchase from RTCA Inc.)

In the case of the FAA, the data is available in numerous formats, most commonly in ARINC 424 format.

There's a great deal of info available on the FAA Aeronautical Information Services website.


Should I land a Cessna 172 with or without a little power?

This is really a question for your instructor: if you've been taught both methods then he should be able to explain when to use a little power and when not to.

Having said that, it all depends: there are good reasons to land with and without power, depending on the situation.

A normal landing with full flaps in a 172 is typically done without power. The Cessna 172S POH I have doesn't even mention power in the normal landing procedures; it gives a target airspeed instead.

A short-field landing is also usually without power, to minimize the runway distance needed. The same POH says:

  Power -- REDUCE to idle after clearing obstacle

For a soft-field landing on the other hand, it's normal to carry a little power in order to touch down as gently as possible and avoid sinking into the runway surface. The FAA's Airplane Flying Handbook says in Chapter 8:

  Power is used throughout the [soft-field] level-off and touchdown to ensure
  touchdown at the slowest possible airspeed,

Finally, you might also use a little power if you bounce on landing, to stabilize the aircraft and re-flare (runway length permitting). But that's a bit more challenging and most low-time pilots should just apply full power and go around instead.


Is an aborted landing considered an incident for the FAA?

It depends.

There are two general situations.  One where the other aircraft was supposed to be on the runway and one where it was not.

In order to increase traffic density and keep the system working, aircraft do not wait for the aircraft landing in front of them to clear the runway or, in single runway fields, for the aircraft taking off in front of them to get airborne.  The separation distances and times are such that normally, the other aircraft will clear the runway but sometimes it doesn't work out.  A departing aircraft might have been given a clearance to take-off but doesn't respond quickly enough, or a landing aircraft might have a problem causing the pilot to stop on the runway to check it out or perhaps simply missing the turn-off they were supposed to take.

ATC might see this happening before the landing aircraft does and issue an instruction to "go around" or, the pilot might have seen that the runway was not clear and made the decision to do so.

This happens around the world dozens of times a day and is not reportable.  The system worked as designed and safety was not compromised.  It is most likely to be what happened in your case.

The other situation is where the other aircraft should not have been on the runway, called a "runway incursion". It might have been instructed to "hold short" of the runway but then entered it or might have mistaken the runway for a taxiway.

This is reportable. The captain has the authority and the duty to ensure that the runway is, or will be clear when they land and to abort the landing if not.  If the captain cannot be sure, they are required to go around rather than press on in the hope that it will be clear. Again, the system worked but safety margins were compromised and thus, the incident is reportable, both by ATC and the landing captain.  If it was a runway incursion, the crew causing it, assuming that they realise that they made a mistake, are also required to report it.

Although I've mentioned aircraft, there are many things that might not be authorised to be on the runway such as people, ground vehicles, animals, construction equipment etc.  Occasionally, pilots are attempting to land on the wrong runway, perhaps one closed for maintenance, and will go around when they see stuff on it.  These are all reportable.


Why are most turbofans tractors, but most propfans pushers?

"Most propfans" is a bit of a strong way to put it. The An-70 is the only production propfan aircraft, making the Progress D-27 the only mass-produced operational propfan. So its configuration is the norm.

As for the reasons for experimental propfans using the pusher configuration, it's generally more efficient in aircraft to begin with, as the airflow is accelerated after passing the obstruction (fuselage). In a propfan, it also avoids the need for a long LP shaft.

As for why turbofans near-universally use tractor, the main reason is that the compression provided by the fan takes part in compressing air for the core. I'm less than 100% sure that it's actually worth the extra components and drag for placing the fan forward, but the alternatives are either having a long suction duct or having a separate ring cowling for the fan, none of which are ideal.

The tractor configuration of turbofans also helps a bit with core cooling. That wouldn't apply to a propfan, which needs a cowling for the core either way.


Why does X-Plane 11 show the SR-71 at 200 knots but Mach 3 at 80,000 ft?

Indicated airspeed is derived from the measured total pressure and the static pressure, according to:

$$ V_i = \sqrt {\frac{2 \cdot (p_t - p_s)}{\rho_{SL}}} \tag{1}$$

At 80,000 feet, static pressure is 2761 Pa. Dynamic pressure as measured by a pitot tube, is measured after a supersonic shock wave according to the Rayleigh Pitot tube formula:

$$ \frac{p_t}{p_s} = \left[\frac{{(\gamma + 1)}^2 \cdot M^2}{4\cdot\gamma \cdot M^2 - 2(\gamma - 1)} \right]^{\gamma / (\gamma - 1)} \cdot \frac{1 - \gamma + 2\cdot \gamma \cdot M^2}{\gamma + 1} \tag{2}$$

with $\gamma = 1.4$ and M = 3, substituted in (2), gives $\frac{p_t}{p_s} $ = 12.06, so $$p_t = 12.06 * 2761 = 33\,290 ~\text{Pa}$$. Substitute this into (1) together with $\rho$ = 1.225 at sea level, and we get

$$ V_i = \sqrt{\frac{2 \cdot (33,290 - 2761)}{1.225}} = 158 ~\text{m/s} = 307 ~\text{kts}$$

In the order of magnitude of what the X-plane indicated airspeed indicates, a lot closer than the TAS: speed of sound @ 80,000 ft = 298 m/s, Mach 3 = 894 m/s = 1,738 kts


What is the dark spot visible below the cockpit on A-10s?

It's a false cockpit, a type of camouflage patented in 1980 by Keith Ferris, a US artist and camouflage designer. From some angles, it makes it difficult to determine the orientation of the aircraft. The Canadians were the first to apply it; pictured is a CF-18 Hornet with one:

Notice how at a glance, it takes a second to realize the Hornet is inverted and pulling towards the ground. During dogfights this can be enough to make opposing pilots think the aircraft is going a different direction. It might not seem like much in a photo, or if you're watching an aircraft fly past at an air show or airport. In the stress of combat while pulling extra Gs it's more than enough to confuse or delay a reaction.

For the air to ground mission, this is particularly important. If an A-10 encountered antiaircraft fire or an enemy aircraft it would have to rely on its own agility to escape or gain the upper hand. Other nations have adopted this technique — I've seen French and Russian types, and possibly Gripens of some air force. As far as I know, the A-10 is the only US aircraft regularly camouflaged in this way.


Does F-35 flight stick have a trackball?

That appears to be a button, not a trackball.
From pg. 17 in a presentation, Active Stick & Throttle for F-35 - Joseph Krumenacker - NAVAIR Flight Controls / JSF Vehicle Systems - 16 October 2008, found here:
It is used to engage/disengage stick sensitivity in hover. Inadvertent movement of the stick would disengage the altitude hold.
Engaging that S-5 button increases the force to needed to 'disengage'.

solution was a pilot-engageable “gripper” mode, in
which an altitude-hold augmentation could be
quickly engaged and disengaged
– with gripper engaged, longitudinal stick breakout
force is significantly increased to prevent
inadvertent disengagement
Pros

Hover stick force is “significantly higher” and provides pilot direct tactile feedback and
confirmation that the flight control system is in control of height axes
Push through or paddle off to begin vertical landing

Cons

Remembering to select height hold
More buttons required


Why are flight instructors in the US called CFIs?

Certified flight instructor = CFI. Add a multiengine rating to your CFI and now you are a multiengine flight instructor, or MEI. An instructor with single and multiengine instructor ratings is commonly referred to as a CFI/MEI.  What if you are a CFI but only in gliders?  CFI-G is the most common shorthand.
Pilot authorizations are specifically called "certifications" in the US, not "licenses."  My guess at the inclusion for the C in CFI is that any pilot can provide instruction but only appropriately certified and rated instructors can provide training that can be counted for a student's training for a new certification, flight review, or whatever.


What is the difference between single and dual annular combustor?

Here's an engine with old combustor cans:

Here's a single annular combustor:

And in cross section:

And now here's a dual annular combustor (DAC)  (pic from here) in cross section:

See how it's like one ring (or donut)  inside another ring.

Wikipedia states "like an annular combustor, the DAC is a continuous ring without separate combustion zones around the radius. The difference is that the combustor has two combustion zones around the ring; a pilot zone and a main zone. The pilot zone acts like that of a single annular combustor, and is the only zone operating at low power levels. At high power levels, the main zone is used as well, increasing air and mass flow through the combustor."


Is the Boeing 737 MAX 8 MCAS exceptional in operating when autopilot is off?

Are there other automated systems providing direct control surface actuator inputs when autopilot is off on the Boeing 737s?

One such system on the 737 Classic and NG is the Speed Trim System:

As you can see above, when certain conditions are met, of which 5 seconds has passed since a pilot trim input is made, the STS trims the plane if required.

The system's classification would be stability augmentation system. When light, rear loaded, and with plenty of power (during the climb phase of the takeoff or during a go-around), the 737 has a tendency to pitch (nose) up (since the engines are below the wing and below the center of mass); the STS would limit that.


What does an "X" at only one end of the runway mean?

I think the X does mean that it is closed in that one direction.  If you look at the 3D view you will see that there is a mountain off the approach end of the X runway making landing on that runway virtually impossible.  If you were to depart on the other non-X runway you would have to turn relatively quickly to avoid hitting the mountain.


How did the Thrust Reverser Deploy in Lauda Air Flight 004 crash?

The investigation into Lauda Air Flight 004 determined that the probable cause was the deployment of the left engine thrust reverser (TR) during climb. An unsuspecting crew would not be able to recover control of the aircraft after such an event. Damage to the components involved in the crash prevented identifying a definite cause of the TR deployment.
TL;DR: The hydraulic system that opens and closes the TR includes two separate valves. The investigation found certain electrical and hydraulic failures that could result in both of these valves malfunctioning, resulting in uncommanded deployment of the TR. 767 aircraft with different engine models used a mechanical system to control the TR valves, which were not susceptible to those faults.

Information here summarized and quoted from the accident investigation report, you may refer to it for more detail.
Two important components involved in the investigation were the Hydraulic Isolation Valve (HIV), which determines whether hydraulic fluid can flow into the TR system, and the Directional Control Valve (DCV), which directs hydraulic pressure from the HIV to either deploy or stow the TR. In normal cruise flight, the HIV should be closed, and the DCV should be commanding the TR to be stowed, which provides redundant control of the hydraulic side of the system. The report analyzes electrical and hydraulic failures that could have resulted in both of these valves being in the wrong position, allowing uncommanded deployment of the TR.
Both valves are controlled electronically based on the position of the reverse thrust lever in the cockpit. The HIV normally will not open without the landing gear sensing the airplane is on the ground, but it is also controlled by an "auto-restow" system.

The auto-restow circuit design was intended to provide for restowing the thrust reversers after sensing the thrust reverser cowls out of agreement with the commanded position. The auto-restow circuit powers the HIV to open regardless of indications from the air/ground circuit.

If the aircraft senses that the HIV opens while in the air, a REV ISLN (reverser isolation) message is given to the crew. About 6 minutes after takeoff the crew started to discuss an intermittent appearance of this message, and after referencing their manuals determined that no further action was necessary. The TR opened about 9 minutes later.

That an electrical wiring anomaly could explain the illumination of the "REV ISLN" indication is supported by the known occurrence of wiring anomalies on other B 767 airplanes.

With the HIV open, hydraulic power would be available to the TR system, but the DCV should still command the TR to be stowed. The DCV was also electronically controlled.

The investigation of the accident disclosed that certain hot short conditions involving the electrical system could potentially command the DCV to move to the deploy position in conjunction with an auto restow command, for a maximum of one second which would cause the thrust reversers to move.
...
Boeing could not provide test data or analysis to determine the extent of thrust reverser movement in response to a momentary hot-short with a voltage greater than 8.2 Vdc or the ability of the thrust reverser to return to the stowed position after tripping of the circuit breaker associated with the source of the hot-short.

So the investigation determined that it was possible for electrical issues to cause the TR to deploy in flight, but they could not determine whether the electrical system on the accident plane had any issues.

The degree of destruction of the Lauda airplane negated efforts to identify an electrical system malfunction. No wiring or electrical system component malfunction was positively observed or identified as the cause of uncommanded thrust reverser deployment on the accident airplane.

Electrical issues were not the only reason the DCV could malfunction. Contamination in the hydraulic system could also cause the DCV to command TR deployment. But the investigation was not able to rule out contamination of the DCV in question.

The condition of the left engine DCV which was recovered approximately 9 months after the accident, indicated that it was partially disassembled and reassembled by persons not associated with the accident investigation.

Without knowing the original condition of the DCV and aircraft wiring, the investigators could not identify a definite cause. Some of the issues found in the investigation were addressed by airworthiness directives (AD's) from the FAA, and by design changes by Boeing and the equipment manufacturers. This consisted of making the wiring less susceptible to faults and the valves less susceptible to malfunction from contamination.
The electrical failures were dependent on the configuration of the aircraft electrical system, and the hydraulic failures were dependent on the design of the valves. The report includes an FAA letter analyzing whether a similar failure could occur on other Boeing aircraft.
The accident airplane was a 767 with PW4000 engines. Once the investigation identified the above issues, the TR's on these planes were deactivated until a fix could be implemented. 767 aircraft with JT9D or CF6-80A engines were excluded at the time from any corrective action:

Since these thrust reverser systems employ mechanically actuated directional control valves, it is felt that they do not possess the same potential for inflight reversal as those systems listed above.

757 aircraft with PW2000 engines were very similar in design to the 767/PW4000 system, so system checks and valve replacement were mandated.
747-400 aircraft had similar systems to the 767, but were not immediately affected, because aerodynamic differences meant that a TR deployment in flight would not be as serious. The same fixes were to be implemented though.
767 aircraft with CF6-80C2 and RB211-524 engines had a different system, but inspections and tests were anticipated until design changes were made or determined unnecessary.
757 aircraft with RB211-535 engines had a different hydraulic design that wasn't susceptible to contamination failure, but the electrical system was analyzed for potential issues.
737 aircraft with CFM56-3 engines were not found to have the same issues.


Which prop location creates more lift? Leading edge or blown flap?

The X-57 should show the highest gain in lift from the props. They will wrap the full wing in accelerated flow. XFLR is not capable of capturing this effect, since the pressure distribution should be similar to the case without props, only the reference dynamic pressure is higher than that of the prop-less wing. Of course, swirl effects will add a spanwise pressure variation that is missing without the props.

Next best is the pusher arrangement of Kitty Hawk. Here the props can swivel, so maximum lift is less of a concern. The prop arrangement has been chosen to minimize noise from the prop blades cutting through the wing wake; that should explain the considerable distance between props and wing. At that distance the suction of the prop will affect the flow over the wing much less that what the X-57 should be capable of. In a pressure plot the main effect should be a delayed flow separation: The wing will tolerate a slightly higher angle of attack.

Worst of all is Lilium: Here the inefficient, small-diameter props sit in ducts which all have their own boundary layer and losses. Next, any accelerated flow only affects the upper side of the wing, so half of the effect will be lost. This arrangement, however, will make the plane sound much louder and powerful than Kitty Hawk's. Judge for yourself whether that is a worthwhile achievement.


Are aircraft being fitted with brighter anti-collision lights?

Its possible they are just fresh halogen bulbs and brighter than others you have seen but your key line is:

  against the low overcast clouds

Low clouds, fog, and the like give strobes something to reflect off of so they seem brighter in a localized way. I cant find a great image of it but this video showing the graphics updates in X-Plane 11 show the phenomenon
fairly well. On a cloudless night the strobes (an most aircraft lights) have little to reflect off of so they seem darker when looking at them. If you watch departures and arrivals in similar conditions you will also see the landing light throw a similarly "visible" beam. This is all somewhat similar to how laser light is visible in fog.