If all fighter jets become stealthy, how will they fight each other in the future? In dogfights?

Table of contents

  Future focii
  Short answer - Important: stealth, sensors (radar & IR), data fusion, networking, long-range weapons. Unimportant: dogfighting with guns.
  Future counter-detection and counter-measures - Important: RF and IR stealth, lasers, hard-kill defenses
  How will stealth fighters fight each other? - including THE MOST IMPORTANT LESSON
  Busting myths

  Myth: Stealth aircraft can't use radars / radars reveal your location - LPI radar
  Myth: IR sensors render stealth obsolete - IR range is short; shorter than radar range against nonstealthy a/c, but greater than radar range against stealthy a/c
  Myth: US lags behind Russia/Europe in IR tech - US had less need (better radars); US has very good IR tech
  Myth: Stealth makes you invisible to radar  - very hard to see, not invisible
  Myth: Stealth is obsolete / a hoax / just marketing - vastly reduced detection range; more efficient jamming; dictate engagements
  Myth: WWII/low-freq radars make stealth obsolete / an F-117 was shot down with this one simple trick - Low-freq radars have limited use; F-117 story is untrue.
  Myth: most combat is WVR dogfighting - not since the 1960s
  Myth: Guns are primary weapons. F-4's were massacred by obsolete MiG-21s in Vietnam because they didn't have guns.

  F-4 guns myth - the F-4s did just fine
  Welcome to the BVR missile era - where missiles take all the credit, and you usually don't see your enemy

  Resources - for modern air combat
  Glossary

As aircraft become stealthier, we'll rely more on the following:

Non-radio sensing

IR search and track (IRST)
Optical sensing
(EO/IR are/can be combined into essentially an EO/IR telescope. Future designs will use multiple bands (MWIR, SWIR, color HDTV), have wider fields of view
Mid-future: laser tracking and targeting.
High-powered lasers (100s of kW) for fighters won't debut for decades, but in the meantime they could obtain very high quality bearing, range, speed, and altitude information.

Networking and data fusion

Highly integrated aircraft sensors
Off-board targeting
Eg, a very stealthy sensor platform feeding targeting info to less stealthy (even non-stealthy) launch platforms.

Advanced radars

Multi-band or broadband radars (integrated mid/high-frequency capabilities)
More powerful AESA radars
Better processing
Multi-static arrays to detect side-aspect radar returns.
Side-looking radars.
Again, VLO a/c are not equally stealthy in all directions. They are least detectable from the front aspect.
For instance, the F-22 was to be upgraded with cheek-mounted, side-looking radars, but these were cancelled to reduce cost.

Even better stealth

Short answer

Detection ranges will shrink (against other LO fighters). IR sensors may become the primary means of detection. Fighters may cruise at low subsonic speeds to delay detection.

Radar will still remain the primary sensor for years to come (at least 2 decades, the minimum time for adversaries to field large numbers of LO a/c).

Stealth remains essential.

DATA FUSION and NETWORKING become hugely important; large forces must fight as seamless units. Remote targeting will become more common. Very, very stealthy sensors (eg, F-22 successor) may pass targeting info to less stealthy shooters (eg, F-22, F-35, F-15, missile truck with VLRAAMs)

Future AAMs will feature datalinks and multimode seekers (eg, IR, RF, and laser), improving counter-measure resistance. Many AAMs already have datalinks---shooter guides the missile until the missile's own seeker acquires the target. Advanced propulsion systems debut (multi-pulse motors, ducted-rocket/ramrockets, scramjets), yielding longer range, higher speed, imrpoved kinematics.

Defenses will improve, requiring deeper magazines (smaller weapons and/or larger internal payload bays).

Space, weight, power, and cooling requirements go up. Aircraft grow larger.

Dogfighting will remain rare. Short-range, maneuvering combat will remain unsurvivable with the advent of reliable, high-performance, high Pk, HOBS missiles and helmet-mounted cueing systems. Also, lasers don't miss. (See Myth: guns below.)

5th gen fighters (F-22, F-35) will thoroughly dominate over 4th gen fighters (F-15, Su-35, Typhoon).

Regarding counter-detection and counter-measures

Fighters will better hide their RF and IR signature. See: engine exhaust troughs on F-117, B-2, YF-23, and 6th gen fighter concepts. See: AETD, ADVENT, and F135 upgrades. Tails may disappear.

EW (eg, jamming) will remain important (See: Myth: Stealth a/c can't use radar).

DIRCM (directed IR countermeasures, an IR laser to jam/kill missile IR seekers) will protect fighters and bombers. Already slated for the F-35.

Hard-kill missile defenses will debut (likely small anti-missile missiles in near-term; anti-missile lasers 20+ years hence). Today, we rely primarily on soft-kill defenses, like jamming and decoys.

Answering the question: how will stealth fighters fight each other?

With better sensors and better stealth.

With mid- to long-range missile shots, but mid-range detection (eg, networked, off-board targeting).

With more lethal weapons (faster/short fight time, improved terminal kinematics, less spoofable sensors).

And with better defenses.

In other words, not unimaginably different from how the F-22 sometimes fights today -- a variation on 5th gen combat. Why? [See note.]

Because stealth hasn't changed the most critical component of aerial combat since WWI: SA -- situational awareness -- obtain SA and deny it to your enemy.

THIS IS BY FAR THE MOST IMPORTANT LESSON IN THIS ENTIRE POST. If you learn nothing else, learn this: SA and OODA.

Then do exactly this:

Watch F-18/22/35 pilot and TOPGUN instructor LtCol Chip Berke discuss 5th gen combat.
Go to the resources at the bottom of this post.

Read CSBA's Trends in Air to Air Combat: Implications for Future Air Superiority (or listen to the 1hr presentation) to see how modern air combat is actually fought.
Read The Radar Game to find out why SA (and stealth) is so important.
Read the Gulf War Air Power Survey. Short, concentrated glimpse into modern air wars.

Learn to fly a fighter.

Seriously. Go pick up FSX or DCS and learn. There's a vibrant community to help you out if you get stuck. (You only fly the F-16 in FSX, but it has a dynamic campaign. DCS has far more pilotable a/c. Both are VERY realistic.)
You'll quickly learn that flying the plane takes a lot more effort and is a lot harder than you imagine. You'll spend much of your time flying the plane (or crashing), not actually fighting... which makes sense because it's the same in real life. (The F-14 has two crew for a reason.) You'll quickly appreciate the luxuries of modern conveniences (like auto-trim). "Data-fusion" and "networking" will start to mean something. SA will become the difference between life and respawn.
You'll also learn that dogfighting is very dangerous. You'll rely more on your AMRAAMs than you guns (once you learn to use the radar ;)). You'll resent the Russian IR AAMs, which don't show up on your radar warning receiver. You'll learn the F-16 is not nearly as agile at medium altitude as headlines led you to believe... especially not when loaded with weapons, fuel, and sensors.

To give you a snippet of The Radar Game:

In most victories, the target isn't aware they're being shot at. SA was determinant.
The most successful aces don't engage in gladiatorial 1v1 dogfights -- more like hit-n-run.
Points 1 and 2 apply from WWI to the present day.
Reaction times are measured in seconds, a function of detection range and closing speed. Radar increases your reaction time; stealth decreases your enemy's reaction time.

[Note well: 5th gen platforms already operate differently from their predecessors ("speed is life")].

[Note: it goes w/o saying my prognostications are opinions. Although I'm confident in my predictions -- which are vague but reflect longstanding trends and realistic S&T developments -- I don't pretend certainty.]

[Note: timeframe is near- to mid-future.]

Addressing myths

Myth: Stealth aircraft can't use radars / turning on radars instantly reveals your location

Low-probability of intercept functionality allow you to use your radar without being detected you. Principals of operation include using wider-frequency bandwidth (wideband), frequency hopping, using a frequency-modulated continuous-wave signal, using only the minimum power required for the task, and pulse compression. Wiki has a good summary. AESA radars are particularly suitable because of their thin, pencil-like beams and minimal side-lobes.

Here's a Naval Postgraduate School thesis on the detection and jamming of LPI radars.

This is similar to how LO a/c communicate without being detected. The F-35 is equipped with MADL - multifunction advanced datalink - a stealthy, secure, minimum power, high data rate, line of sight comms system.

Myth: IR sensors render stealth obsolete

Bodies heat up when moving through air.

Vid: F-16 seen through an F-35's EODAS

Vid: F-15E in IR.

IR sensors do not see as far as radar (contrary to other answers here).

Against 4th gen fighters (non-stealthy platforms):

IRST detection range is typically measured in low-dozens of miles.
The F-15's radar ranges out to 100 nmi
The F-22's radar ranges out to 150 nmi
The E-3 Sentry's radar ranges out to 400 nmi

For reference, the F-14's optical (not IR) system could ID and track bombers out to 50 nmi. Perhaps 15-25 nmi for fighters. (Some IR bands are less readily  absorbed by the air than visible light.)

The PIRATE IRST may detect a VLO fighter (with RF and some IR reduction) from these ranges (CSBA):

Altitude  | Mach | Stag temp | Ambient | Contrast | Detection range
==========|======|===========|=========|==========|================
45,000 ft | 1.8  |  85 C     | -56 C   | 141 K    | 150 nmi
45,000 ft | 0.8  | -28 C     | -56 C   |  28 K    |  48 nmi
45,000 ft | 0.5  | -45 C     | -56 C   |  17 K    |

(150 nmi figure assumes no afterburner, ie supercruise.)

While IR is harder than radar to jam at long range, it can't estimate target range as easily.

Myth: US lags behind Russia/Europe in IR tech

Again, IR sensors don't see as far as radar, but they are harder to jam from long range. Historically, NATO fielded better radars and jammers than the Soviets, who therefore couldn't rely as heavily on their radars. So the Russians added IRST capabilities to augment their radars.

Remember also that the US flies dozens of AWACS that usually detect enemy a/c long before even an F-15's radar. So IRST wasn't as critical for US fighters.

The F-22 has a space reservation for IR sensors, but that upgrade was cut to reduce costs.

The F-14 received an EOST relatively early because its main targets were large, Soviet bombers, which are easier to detect.

The US eventually added IRST to late-block F-16's, Super Hornets, and of course the F-35, which fields the most complete IR sensor suite of any fighter. The F-35 has a stealthy, built-in IRST that doubles as a targeting pod. (Demo.) Its DAS also allows pilots to see in a complete sphere (4 pi steradian) around the a/c, even through the floor and headrest (no blindspots); its primary function is missile approach and warning.

The F-35 is an important example here because it'll soon comprise the backbone of NATO aviation for decades. Some 3,400 F-35s are slated for production, more than all F-15s, Super Hornets, Rafales, Gripens, Eurofighters, and Su-27s produced to date combined.

(Btw, if you're skeptical about the F-35 -- kinematics (speed, dogfighting v. F-16), range, stealth, weapons (gun), software, cost -- I'll direct you to these two..comments on kinematics, this compendium, and this community. (To start, a fully loaded F-35 with 5k lbs weapons accelerates like a clean F-16 and points its nose like a Hornet.) If you're still skeptical, I can start another 30,000 character post.)

Myth: Stealth makes you invisible to radar

Not quite.

Stealth vastly reduces your RCS, but does not completely erase it.

VLO a/c are much, much harder to detect and track. Active radar detection range goes with RCS1/4. So a 10x reduction in RCS roughly halves detection range. [See radar equation.]

For example, an F-22 or F-35 has an RCS of 0.0001 m2. A clean [unarmed] F-16 has an X-band RCS of about 2 m2. The F-22/35 will be detected at 12-22x shorter ranges than the F-15/16---effectively under 5-10 miles when using a fighter-class radar. That's almost close enough to see [see note] and certainly within IRST range.

Platform | RCS m^2 | 1/range | Detection range
=========|=========|=========|==================
 F-15    | 25      |  1.0    | 100.
Su-27    | 15      |  1.1    |  88.
 F-16C   |  1.2    |  2.1    |  47.
 F-18    |  1      |  2.2    |  45.
Rafale   |  1      |  2.2    |  45.
Typhoon  |   .5    |  2.6    |  38.
Bird     |   .01   |  7.1    |  14.
Insect   |   .001  | 13      |   8.0
 F-22    |   .0001 | 22      |   4.5
 F-35    |   .0001 | 22      |   4.5

(RCS values are ballpark figures for clean aircraft. External stores greatly increase RCS. A typical F-16 loadout for permissive environments (eg, ISIS, COIN) includes 2x 370 gal fuel tanks, 2x 2000 lb JDAMs (or equivalent), 2x AMRAAMs, 1x Sniper targeting pod. 2x AMRAAMs, 2x AIM-9s, a nav pod (eg LANTIRN), and an ECM pod may be added in more challenging environments. Like this. Not like this. Exception: F-22 and F-35, which carry their stores internally in high threat environments.)

[Note that visual range is theoretically up to 20 miles. But in 99.9% of real life cases it's <5 miles. Often just 2-4 miles.]

Note that once loaded with fuel and weapons, the F-16 and F-15 have much larger RCS values, so will be detected from even further out.

Also, while we no longer use large faceted designs (see: F-117) thanks to modern computing, we still shape our a/c to direct radar energy in certain directions away from the transmitter -- mostly to the sides and above -- in narrow lobes or "spikes."

Illustration (video). Skunkworks engineer discusses designing stealth. Listen closely.
Screencap:

Placeholder: once detect radar transmitter, stay out of detection range. Because detection range is so short, you have a lot more elbow room than non-stealthy fighters.

No, you're not invisible to radar, but operationally, it's much easier to remain undetected.

Placeholder: B-2 spike management. mission planning.

Myth: Stealth is obsolete / stealth is a hoax / stealth is marketing

LO remains relevant (and very useful) for the same reason armor didn't become obsolete when antitank guided missiles were fielded.

LO also makes jamming far more efficient. Jamming basically hides your aircraft's 25 m2 RCS. If your RCS is only 0.0001 m2, it takes far less power to hide yourself, and your jamming will work at far greater range. Primer: how jamming works.

LO technologies drastically reduce detection ranges and warning times. Sensors that work well against stealthy aircraft would work far better against non-stealthy aircraft.

What's the alternative to stealth? No stealth? Make our aircraft easier to detect and track?

All future combat a/c designs must consider signature reduction going forward---at the very least some signature reduction, if not outright VLO designs---camouflaged tanks are always more desirable than this (or this):

Myth: WWII radars / low-frequency radars make stealth obsolete / an F-117 was shot down by an 1960s radar with simple modifications

First, the F-117 story is untrue. The Serbs claimed they made simple modifications to their old Soviet radars, allowing them to easily spot the F-117s. But Zoltán Dani, the Serbian commander who shot down the F-117 in Kosovo, later admitted on national TV that he never modified the radars, merely used the lowest frequency setting. He explained that he fabricated his story for propaganda. Others alleged he did it to take [more] credit for shooting down the F-117.

Also, NATO jamming support was unavailable the night the F-117 was shot down. Dani was aware, so he turned his radars on a third time without relocating, which allowed him to obtain the fateful radar lock.

But more importantly (and accurately) the F-117 was shot down because of lazy mission planning by the US. The F-117 flew the same route night after night at roughly the same hours. So the Serbs moved their radars directly beneath the anticipated flight path. After a number of attempts were made over several nights, they finally got a lock at just 8 mi (13 km) when the bomb bay doors opened. The F-117 doesn't have a radar warning receiver---the pilot never knew he was directly overflying a SAM radar site (doable, but still ill-advised for any stealth fighter). He only ejected because he visually spotted the missile heading for him.

People forget the F-117 is an old design. It entered service in 1983, just five years after the F-16 and nine years after the F-14. Back then, we didn't know how to integrate radars and other apertures into the skin without compromising its low signature.

To be clear, a kill is a kill, and Dani deserves credit. People also forget that the Serbian forces were motivated, competent, and well-trained---measurably more so than Saddam's air defenses. The Serbs performed much better than the Iraqis and learned much from the lessons of Desert Storm.

The F-117 was only shot down once in its entire career, despite regularly flying into some of the most heavily defended airspace in the world, a feat no other platform could perform without massive support (expensive!)...

...or massive losses (save the B-2, F-22, F-35). Stealth alone allowed the F-117 to survive. Even F-15s and Su-35s would have been shot down in droves if we sent them on the same missions alone. (Image source)

Second, low-frequency radars have several drawbacks:

extremely large and power hungry, suitable only for ground-based platforms, not fighters. Some are vehicle-based, but as so large, they're only semi-mobile
require large apertures to function, owing to their long wavelengths
easiest to spoof
easy to detect from long range
detection range is grossly over-advertised
resolution is terrible (on the order of kilometers), making them unsuitable for targeting.
the most straightforward countermeasure to low-freq radars is to make aircraft larger. So VLO bombers (large a/c) are far less detectable by low-freq radars

(Principal: long wavelengths approach the feature size on aircraft, like tails, so shaping is less effective in redirecting radar returns)

all the above make them easy targets for long-range weapons like cruise missiles.
for all the above reasons, they're usually used as early warning radars or to cue higher-frequency radars.

High frequency radars are suitable for targeting, are more jam resistant, and are smaller/lighter. That's why fighters are optimised for stealth at higher frequencies.

Analogy: you can hear a fly buzzing around your room somewhere (detection), but you must see it to swat it (higher resolution sensor for weapons quality track). You can use your ears to cue your eyes, but you'll never hit it with your eyes closed.

(Lo-freq on left, hi-freq on right. SMSgt Mac, elementsofpower.blogspot.com)

Myth: WVR combat / dogfighting is the primary arena of aerial combat

First, WVR combat =/= dogfighting =/= guns.

Second...

Myth: Guns are the primary weapons of aerial combat. F-4's were massacred by obsolete MiG-21s in Vietnam because they didn't have guns.

Common F-4 myth

When Vietnam started, USAF and Navy F-4's claimed just a 2:1 kill/loss ratio. Here commentators often blamed malfunctioning missiles and lack of a gun.

So the USAF added a gun to the F-4, but their K/L remained at 2:1.

In contrast, the Navy began a new program to better train pilots how to use their missiles. They also trained the maintenance crews how to properly handle and maintain their missiles. They did not add a gun.

By war's end, the "sluggish" Navy F-4's claimed a 12:1 K/L ratio against its more maneuverable adversaries like the "agile" MiG-21.

That training program? It became TOPGUN. (Source.)

Welcome to the BVR missile era

The last fighter v. fighter guns kill was in 1989, an Iranian F-4E shooting down an Iraqi Su-22 (CSBA). The F-35's gun is largely for air to ground.

The vast majority of kills over the last 40 years were achieved with missiles:

(Global, fixed-wing v fixed wing. "Other" includes things like CFIT and flying into your own drop tanks. CSBA. See pg 24, pg 36 of 76). Annotation.

In the 1960s, guns still dominated. Most gun kills were achieved by Israelis; they used guns exclusively because no one would sell them missiles.

However, by the 1970s, missiles accounted for more kills than guns.

Even in Vietnam, the AIM-7 Sparrow missile accounted for more kills than any other weapon.

North Vietnam also favored missiles for the balance of its air to air kills, especially as the war progressed.

By Desert Storm, most shots were fired from BVR. Few air to air engagements required any significant maneuvering at all. Only two air to air guns kills were claimed: A-10s vs helos. In another engagement, a helo was destroyed by a laser-guided bomb. In other words, "A2A" bombs killed nearly as many a/c as guns in the Gulf War. Iraq also lost 3 a/c to CFIT.

And yes, we make supremely better missiles today.

Early AAMs were more akin to guided cannon shells: narrow field of view, short range, and low maneuverability; often only chased a target in front of them (tail chase).

Modern AAMs (HOBS, LOAL) have comparatively stupendous ranges: a modern SRAAM (188 lb AIM-9X Sidewinder) has roughly the range of the original AIM-7 Sparrow (a much larger 500 lb MRAAM); and the new AIM-120D AMRAAM (335 lb MRAAM) has nearly the range of the legendary AIM-54 Phoenix (1000 lb LRAAM).

You will not easily outrun a Mach 3 missile pulling 50 g's with a 200° field of view. Why turn 720° when you can shoot almost directly behind you? (video of AIM-9X testing, 2000). (Realistically, some level of maneuverability is required for good shots, but far less than for a guns solution.) More videos, gifs, gfys, and MICA.

Reliability. In ODS: shot 28 AIM-7s at BVR, 22 hit the target or fireball; 10x more reliable than AIM-7s in Vietnam.

Essentially, missiles are now far better dogfighters than fighters.

But the best dogfighting weapon by far is neither gun nor missile: it's a wingman. Fighters don't fly alone. When you dogfight, A) you rapidly bleed speed and altitude, and B) your SA evaporates because you can't afford to focus on anything else except the guy you're turning with. You're effectively a sitting duck and blind, an easy target for anyone outside the fight.

Dogfighting is extremely dangerous. Two modern fighters are liable to both die in a dogfight, ie a kill/loss ratio of 1:1.

I know of no pilot who prefers dogfighting over taking BVR shots.

Dogfighting may not be dead. But it sure is on life support.

Resources

CSBA: Trends in Air-to-Air Combat: Implications for Future Air Superiority --- essential reading
The Radar Game --- Radar and stealth primer. Requisite reading.
RadarTutorial.eu --- radar tutorial. How radars work. Very useful explanations. Explains some of the limitations/necessities of targeting/guidance.
Gulf War Air Power Survey (GWAPS) --- how the Gulf War air campaign was fought (these are some of my notes; the entire report is ~3500 pg).
War with Iraq: Critical Lessons --- General Glosson's book on the war (he orchestrated and designed the campaign) and "explains the deeper strategy and thinking behind the air campaign"
A great selection of books on ODS.
Air Warfare in the Missile Age by Lon Nordeen. Covers every major conflict from 1965 to 2003.
Modern aerial warfare and doctrine.
RCS values on Global Security. Note that the F-35 values were estimates from early in the JSF program, before any production airframes were built. After the F-35 had been built, flown, and tested, officials from the test program (including a pilot) went on record saying the F-35 was actually stealthier than the F-22.
Resources I most frequently recommend

Glossary:

1

AAM - air to air missile
a/c - aircraft
Allied Force - NATO bombing of Yugoslavia, Kosovo War
HOBS - high off-boresight - describing very agile missiles with a wide field of view
LOAL - lock-on after launch
ODS - Operation Desert Storm, part of the Gulf War
RCS - radar cross section
RF - radio freq

2

EO - electro-optical ("telescope")
EOST - " "
IRST - IR search and track ("IR telescope")

3

SR - short range
MR - medium range
LR - long range
VLR - very long range

4

BVR - beyond visual range
WVR - within visual range

5

LO - low observable - ("stealth") a broader term, sometimes interchangeable with VLO
VLO - very low observable - ascribed to only "true" stealth platforms - eg, F-117, B-2, F-22, F-35

(30,000 character limit exceeded)

Placeholder: kinematics still matter

Placeholder: Alleged flaw: Dogfights are more common if US fought USSR instead of easy foes. Why would an adversary with better, longer-ranged sensors and weapons want to get closer where he is also more vulnerable? Related: Combat between peers results in dogfights. Most kills during the 80s resulted from the 8-year Iran-Iraq war between pretty evenly matched opponents. Missiles still dominated. Related: Comparison isn't fair; US had better tech. That's the point. Don't want to fight fair. If high-tech produces fantastic victories, then high-tech sounds like a good idea.


Vertical and horizontal separation between cruising and climbing aircraft

I think you may have answered your own question note the use of the word OR

  To my understanding, aircraft at these altitudes should always have a
  separation of least 1000 ft or 5 nm.

If you take a look at your data the aircraft are always separated by 1000 feet OR 5nm. The singular exception to this is when you have the separation quoted at 4.81 miles and 982ft. This can to an extent be explained away by the inaccuracies in systems like FlightRadar24


How do ground effect vehicles perform turns?

It turns like an airplane by tilting the lift vector. Watch carefully in this video, especially about 50 seconds in, and you can see the craft is turning by banking.

It just can't bank very hard unless it climbs a little higher. This is one of the problems of GE aircraft; they aren't very maneuverable because they can only make gentle turns at the normal cruising level close to the surface.

The alternative to banking, if you don't have enough room to roll, is skidding, where you are redirecting the thrust vector and also generating some lateral force from the sideways presentation of the craft's body. Basically like a hovercraft. A lot less efficient though because of the drag rise from the skid. Some of those really big GE machines like the Ekranoplan would have used skidding (kind of obvious from the huge rudder that it's designed to skid) and maybe a little bit of bank.

It's probably a good thing that this concept has not been all that successful. If the world was full of these types of machines crisscrossing every which way over oceans and lakes, all at the same level and going pretty fast, you probably have a lot more mid-airs than you get with airplanes, or boat collisions for that matter.


How does gross weight affect helicopter autorotation?

If you look at the situation in terms of power, an increase in weight (or any increase in loading) requires more power. As you don't have this power, the helicopter will descend faster, more air will go through the rotor leading to an increase in RPM. Hopefully this increase in RPM will provide enough lift to stabilize the vertical speed. Increasing the pitch to maintain the RPM within limits provides lift in a slightly more efficient manner so the vertical speed will be slightly reduced (compared to the situation of descending with the collective flat down and RPM screaming over the limit)
That said, I find the affirmation in your book very confusing. Maybe I'm missing something, but a heavier helicopter will descend faster than a lighter one under the same conditions. It needs more power to fly and the only way to get it is to descend faster. That makes landing more dangerous, because you have more vertical speed to offset during the flare and more weight to cushion before touchdown. If increased weight and increased rotor loading would provide lower descent speed I guess everybody would autorotate in fully loaded helicopter and doing tight turns all the way to the ground :)


How does the aviation industry train and certify English proficiency?

Proficiency in English is something very much required in aviation. One other major accident I remember is the Charkhi Dadri mid-air collision, which resulted in 349 fatalities, and one of the major reasons was believed to be the poor English of Kazakh Airlines crew.

Keeping such importance of English in mind, and the need to standardize English testing and training, the ICAO  has issued Guidelines for Aviation English Training Programmes.

Training

Candidates are trained for Aviation English in a very similar way to it would be for any other purpose, other than ensuring the following points:

Use of operationally relevant, work-related language.
Exposure to an aviation environment.
Practical training activities such as Listening practice in ATC lab.

Testing

The Test of English For Aviation is a test Developed by Mayflower College in accordance with ICAO's ratings.

Here is how the candidates are tested in TEA:

TEA candidates can score from Level 1 to Level 6 but most candidates score Level 3, 4 or 5. Candidates are awarded a mark from 1 to 6 for each of the 6 skills: pronunciation, structure, vocabulary, fluency, interactions, comprehension.

Read this document


Provided the drone is flying where the red dot is, you are correct and Class G extends from the surface to 700 ft AGL.  If you really wanted to play it safe, call the tower at KBKL to establish two way radio comms before flying there.


How can L/D Max be both Best Glide speed and Max Range speed?

I'm going to answer with the caveat that I don't have as deep of an understanding of this as I would like, and someone smarter than me may be able to correct or expound on my response.
Best Glide is a purely aerodynamic concept. There is no powerplant involved, so you're simply converting potential energy (altitude) into forward motion, at a rate and L/D ratio that is driven by the angle of attack. It's a simpler concept.
When you add a powerplant into the equation, it gets a lot more complicated. The powerplant itself has modes where it's more efficiently converting fuel energy into thrust, and modes where it's less efficiently doing so. Max Range, therefore, depends not only on aerodynamics, but also how efficient the powerplant is. When you add powerplant dynamics into the equation, you might settle on a best range speed that is different than the purely aerodynamic best glide range speed.
Simply put...

Best Glide is where L/Dmax occurs.
Max Range occurs when (FuelBurn / GroundSpeed) is the lowest.

On a related, but slightly different, note: Piston airplanes and Turbo(fans/jets) behave differently when it comes to producing power at different airspeeds. It's why we generally measure turbofan engines in thrust, and piston engines in horsepower. This difference is why Max Range and Maximum Endurance speeds correlate with Best Climb Angle and Best Glide speeds differently, when you compare pistons to jets.
I hope this helps.


Do aircraft need special modifications for polar routes?

There are several considerations for flying polar routes, but no special modifications are necessarily needed.  Navigation is different, as Lat/Lon (specifically longitude) converge to become meaningless close to poles, so aircraft traditionally use a grid navigation system.  Aircrew should also be aware of the difference between magnetic and true north, as the magnetic "North Pole" is different than the geographical North Pole.

You should also understand your aircraft's temperature boundaries.  If you fly through the arctic in the depth of winter, you should ensure that all of your aircraft components are suitable for the temperature.  Usually, this isn't an issue - and if it was, you can always descend a bit to find "warmer" air.

Otherwise, air provides lift in the polar regions just like in the equatorial regions, and Bernoulli keeps your aircraft afloat!


Can ailerons be used for pitch change in the event of elevator failure?

If the ailerons could be moved in the same way on both wings, the linkage between both is broken and they would float up near their maximum negative (trailing edge up) deflection angle. Even a hydraulic aileron booster would not help, since here still an interlink between both ailerons exists to keep actuation forces down. Only in a fly-by-wire aircraft with fully powered aileron actuators could the control system be programmed to allow symmetric deflection.

The effectivity of such a means of pitch control is very low, and only wing sweep can help to make it useable. Any pitch control input will change lift on the outer wing, and pitching up would mean a loss of lift and result in a plunging motion of the aircraft. If that happens on landing, when the pilot uses to pull the stick to raise the nose gradually, the resulting ground contact will be rather early and bumpy. Pilots of flying wings know this; they are very careful with their pitch control during a flare.

When an ASW-20 glider had crashed a couple of years ago because the pilot had forgotten to connect the elevator linkage, Gerhard Waibel flew to the glider club and demonstrated how to fly the ASW-20 with flaps for pitch control alone. The downside is a much reduced speed range and a high landing speed, because you need to reduce camber in order to pitch up, but it works. Since the flap span is higher than the aileron span, I would strongly recommend to rely on the flaps for pitch control when your elevator stops working if flaps are installed. They also do not need any modification to work as pitch controls since they are rigged to move symmetrically.

If the engines are mounted low or high, their thrust can also be used for pitch control. This was used on several occasions to bring an airliner down after all hydraulic circuits had failed.

EDIT:
Mike Dunlavey insists I should mention flaperons. He is right, they are possible with mechanical linkage only, but you will find them only on wings which have flaps anyway. All modern gliders with flaps will also move the ailerons in sync with the flaps.

But they are the worst choice for pitch control. For one, they are on the part of the wing with the smallest chord. Their lift change will go with the smallest pitch moment change of all controls except the rudder, so it would be much better to use the flaps for pitch control. That the ailerons do move with the flaps will have little effect. Besides, well designed flaperons will have less deflection change for a given flap change so the spanwise lift distribution will stay close to the optimum. This will make them even less effective than the flaps.

I choose not to mention them to make the answer concise. But I'm afraid short answers are not appreciated anymore.


What might happen if I receive flight instruction in a plane with an airworthiness deficiency?

It can’t void the time, but if an Inspector ever caught a CFI doing something like that, he’s in big trouble.  And more importantly, that CFI should know better than to do something like that in front of a student.


How did aircraft flying in formation use flares to communicate with each other?

This break down of a B24 Missions seems to outline the usage of flare on a mission well:

Assembly
After takeoff, a pilot usually kept on a straight course for about two
minutes, in part because the B-24 was not very maneuverable until it
had gained speed and altitude. The pilot then climbed at a
predetermined rate (about 300 feet per minute at 150 mph Indicated Air
Speed) to the assembly area assigned to the 392nd. A ship, usually
41-23689, Minerva, orbited a radio beacon at the prescribed altitude and fired designated colored flares to signal 392nd BG a/c. The
specified assembly altitude was based on cloud conditions. Clear skies
meant assembly could be at 5,000 to 10,000 feet. Often, though, pilots
had to climb to 20,000 feet or higher to get above the clouds, relying
on instruments to maintain headings, speeds and timed legs.

When on the actual mission...

Mission Routes
Routes were scheduled to avoid major flak areas as much as possible
and to mislead enemy fighters about the intended target. Each route,
then, included several course changes until the Initial Point (IP) was
reached. The IP was usually an unmistakable landmark, both visually
and on radar. At the IP, the lead plane alerted the formation to turn
toward the target by signal flares or by opening its bomb bay doors.
All other planes promptly opened their own bomb bays and made the turn
while simultaneously aligning in trail. On the bomb run, Groups were
usually two to five miles apart.

Then on the way home:

Wendling
By this time, the formation was down to a few hundred feet. While in the landing pattern circuit, the engineer confirmed the
wheels were down and locked. Planes with wounded aboard or severe
battle damage fired two red flares and landed first.

A few sources cite the M8 Flare gun being the one that was likely used during WWII. There is a discussion that covers some of the colors and cartridges here.

This book which talks about flare usage quite a bit, discusses a lot of the ground <-> air communication done with flares:

The increasing amount of airfield bombardment led to the establishment
of false aerodromes. These false fields gave the appearance of active
aerodromes by day and night in the hope that enemy bombers would be
fooled into releasing their bomb loads a mile or two from the real
airfields. At night, active fields remained concealed in darkness
until an airplane was properly identified through flare signals.

It goes on to say:

Signaling devices were necessary for communications with the ground.
The flare gun provided the most basic means of signaling. The Allies
used the Chobert, more commonly known as the Very pistol. British and
American night squadrons used three different colored Very cartridges,
red, white, and green. Each cartridge had a different milling along
its metal base flange so that aviators could quickly feel for the
correct shell in the dark.

Some flares were also used for ground illumination

Illuminating flares were developed for target acquisition and landing
assistance. One of the most important was the Holt wingtip landing
flare. Useful in an emergency or under inadequate field lighting
conditions, the Holt flare was ignited electrically (by dry cell
battery) from a push button in the cockpit. Typically the flare would
burn for a maximum of two minutes at up to 20,000 candlepower.


The standard solution for keeping aircraft parts "above icing temperature" when on the ground is, as was pointed out in the comments, a nice heated hangar.
This has the secondary benefit of keeping all the other components at a warmer temperature where they're more amenable to operating (gyros spin up better, wheel bearings rotate more easily, etc.)

Once outside of a hangar deicing fluid is used, and provides "anti-icing" protection for a specific period (the fluid's "holdover time") - we discussed that in more detail on this question.
Obviously once the aircraft has been exposed to icing conditions or snowfall for a period exceeding that holdover time it must be de-iced again as there is a chance for ice to begin accumulating.

There is also the potential to use the aircraft's ice protection systems (in particular electro-thermal systems such as used in the Boeing 787 which heat the wing in the manner you allude to in your question), though I'm not aware if any systems are currently approved to be used in this way.
One of the key challenges there would be verifying that the wing surface is indeed free of ice, snow, and frost - that's easy to do from the deicing truck (particularly since deicing fluid is tinted so you can see where it has been applied), but on a typical passenger jet the pilots can't see the wing from the cockpit, and poor visibility from blowing snow, fog, etc. may make the visual determination difficult from the cabin as well.


What permits are needed to operate a human-flying drone in the United States?

According to https://www.faa.gov/uas/beyond_the_basics/#55:

  To fly a UAS that weighs 55 lbs. or more, operators will need to use the existing Section 333 exemption process.

The Section 333 page has further links.  Spot checking some of the approved exemptions shows that the exempted status tends to look quite a lot like the 14 CFR 107 (sUAS) rules and include phrases like "carrying no passengers or crew", "weighing less than 55 pounds including payload".

As far as pilot certification would be concerned, exemption 11422 (which is one I spot-checked with) says:

  Under this grant of exemption, a PIC must hold either an airline transport,
  commercial, private, recreational, or sport pilot certificate.  The PIC must also hold a current FAA airman medical certificate or a valid U.S. driver’s license issued by a state, the District of Columbia, Puerto Rico, a territory, a possession, or the Federal government.  The PIC must also meet the flight review requirements specified in 14 CFR §61.56 in an aircraft in which the PIC is rated on his or her pilot certificate.

So, the FAA could decide to issue an exemption under section 333 for such a flight, and declare whatever limitations they wanted (or, of course, reject it outright).  If approved, I'd expect it to come with limitations like:

Must adhere to 14 CFR 107, treating the flight as an sUAS flight even though it exceeds the sUAS maximum weight.
The PIC must be certificated for Remote Pilot (sUAS) or hold an airline transport or commercial certificate with a corresponding class 2 medical and valid government-issued photo ID.

(Every other restriction I could think of is already part of 14 CFR 107, and the carried human would probably be treated equal to a wing walker... and I can't dig up any extra restrictions regarding them)


Do pilots pilots keep track of their groundspeed, by head?

That depends on what you have in the cockpit, most planes these days fly with some kind of GPS be it a full blown panel mounted IFR certified unit or just an iPhone app. All of the ones I have encountered either by default or with minimal effort will display your ground speed for you and there is really no need to manually compute it.

The main purpose of ground speed is to ensure that you actually arrive at your destination with more than vapors in your tank. Let's say you need to travel 100 nautical miles in a Cherokee. You have 1.5 hours of fuel on board which is legal for a VFR flight. You unexpectedly hit a 55 Kt headwind at altitude. You trip is now going to take you a little over 2 hours assuming you cruise out at 100 Kts/Hour. Knowing your ground speed ensures you have the information you need to know that you will need to land ~50 miles into the flight and gas up.

When flying IFR its also important so that you can provide ATC an appropriate time deviation if you are not going to make a way point when expected.

On a similar note, most decent flying apps will do fuel computations en route for you as long as you provide a performance profile.


Is there a minimum level of lighting required for a runway to have an instrument approach?

I have no idea about ICAO but as far as I can tell from the FAA's TERPS, there's no general requirement to have any runway or approach lighting at all (see below for an example), although some specific approach types (like CAT II/III ILS) do require it. Where there is lighting, it's used to reduce the visibility minimums, but the calculations assume no approach lighting by default.

This is from 3-1-2(c) (emphasis mine):

  Approach lighting systems extend visual cues to the approaching pilot
  and make the runway environment apparent with less visibility than
  when such lighting is not available. For this reason, lower
  straight-in (not applicable to circling) visibility minimums may be
  established when standard or equivalent approach lighting systems are
  present.

The TERPS concept seems to be that the approach minimums can be reduced depending on the lighting type available. Section 3-3-2 has an example of calculating visibility minimums when there are no approach lights available.

As for a specific example, MDO/PAMD (Middleton Island, AK) has three approaches (2 RNAV (GPS), 1 VOR) but - as far as I can tell - no lighting of any kind. The chart supplement says:

  Rwy 02–20 marked with rwy cones. Rwy 13–31 marked with cones and OTS
  lgts. Many missing.

As you might expect, the approaches are not authorized at night :-)

Finally, part 121/135 passenger flights can't land at night unless the runway is lit (121.590, 135.229), so any airport that handles those flights will have runway lighting at least, and almost certainly approach lighting too.


Can X-Plane be used as a professional simulator?

Maybe.

From the page linked by falstro above:

  These include the ability to use cylindrical and spherical projection (as found in large simulators), and the ability to drive real Garmin 1000, Garmin 430, Garmin 430 WAAS, Garmin 530, and Garmin 530 WAAS units.

Pictures are included of a particular setup. The large projection format allows all-around visuals. The simulator can drive real Garmin devices, not just replicas. They recommend this vendor for FAA approved hardware (and for $2,100 I would hope a yoke could be FAA certified).

You can use an IOS even with the personal license for the simulator, on the same computer or a separate one.

X-Plane also explains that only the complete hardware+software combination can be certified for use as an FAA approved flight simulator. So it may be easier to just buy a package from a company like PFC, which has the combination already certified. They offer BATD and AATD simulator setups that use X-Plane.

If you need more information, you can contact X-Plane via the link on the same site linked above. They do not keep track of what people use their professional licenses for, but they may be able to comment on what level of certification is achievable.


Can the Master Caution illuminate without the System Annunciator Panel on the 737NG?

If everything is working as designed then the Master Caution is always accompanied by one of the 12 annunciator lights (or more than 1, depending on the situation).
If things aren't working as designed, then what you'll see depends on the nature of the malfunction. If it's as simple as a burned-out bulb in the annunciator panel, then you could get the Master Caution without an accompanying light. That's usually followed by a disgruntled "oh, great" followed by heads swiveling around to find what individual amber light is illuminated. And/or pressing the Recall function (see what fails to light up, or comes on now), and/or using the Lights Test switch.


No. Diversions can happen for all sorts of reasons, and often on very short notice. Info about diversions is not communicated and compiled systematically. Generally speaking, only the crew, ATC, airline, original destination and actual destination airport will know, none of which have any interest in publishing the data.


What was the first production jet engine to use a semiconductor based control system?

The RB211 as found on the L-1011 (first flight Nov 16, 1970) had a fuel control amplifier that, while it was not the primary control of the engine, was capable of controlling fuel flow.


Is AMS (Schiphol) Polderbaan the runway furthest away?

One possible contender is Pyongyang airport. The far end of the new runway (01/19) is around 7 km away from the terminal (as the crow flies). With taxi distance, it is almost 8 km:

Source

While the taxi times at Amsterdam can be very long, it is a bit misleading to blame it on the runway being 7 km away. Runway 18R is not used for takeoff. Unlike Pyongyang, there is no parallel taxiway on that 'end' of the runway, and Schiphol ATC would never want to wait for an aircraft to backtrack. Hence, it would be more sensible to use the distance from the first taxiway for landing aircraft on 18R, located 5.5 km from the tower.


Why are there so few high-wing jetliners?

Large commercial aircraft have low wings

to easily stow away their long landing gears in the wing root,
to hide the wing spar carry-through below the passenger deck,
and to improve the accessibility of wing-mounted engines.

Long gears make it possible to stretch the fuselage and still be able to rotate during take-off. Stretching makes it possible to tailor one basic design to a wide range of sizes, lowering the development cost of a single aircraft.
Pressurized fuselages need to have their passenger floor a bit below the center of the fuselage tube, leaving ample space below for cargo, systems and structure. Placing the wing high would produce a hump on the fuselage, which adds wave drag at the transsonic cruise speed of typical airliners.
The low position of the wing-mounted engines makes them much better accessible for maintenance; a major reason this configuration was selected in the early jet transports. Civilian freighters use mostly converted passenger planes, and their small number precludes custom designs. Initial concerns about foreign object damage (which resulted in a number of early jetliners with tail-mounted engines) proved to be unfounded.
Large high-wing airplanes with their low fuselage position are easier to load and unload, at the price that the fuselage taper has to start shortly aft of the landing gear, so no stretching is possible. The military doesn't mind and prefers the high-wing variety. Also, the high wing reduces the risk of engine damage by foreign objects on improvised runways. That Lockheed likes to stretch their transports (C-130, C-141) anyway is the exception that proves the rule.
Turboprop-powered civilian airplanes may have a high wing in order to provide more space for the propellers. Here, the fuselage-mounted landing gear can be made short and light (which is how the Do-328 JET evolved). Still, both versions exist. And the ones where the engineers did not know how to attach a jet close to the wing*.
Aerodynamically a mid-wing position would be best. This is used when the payload is compact and needs little space, or is hung externally. In bombers, in other words. Civilian transports will always either have a low or a high wing since nobody wants their passengers to climb across a wingspar carry-through on their way to their seat. At least since 1933.

*  To be fair to the Avro engineers: The high wing position gives that airplane a very high maximum lift coefficient without requiring slats.


How does maintenance differ for military fighters/bombers vs. commercial airliners?

I think a few things need to be examined here:

1) The type of flying.  A commercial aircraft is closer to a military C-17 than a B-52 or F-16 in how it is used.  It has several stops throughout the day for loading and unloading.  The maintenance in between stops does not need to be very extensive - because it has just landed, presumably working fine, the things that need to be checked primarily involve what has the most chance of decaying during a flight (tires, oil, general wear and tear, etc).  Fighters/bombers don't generally fly several legs in a day.  Fighters might double/triple turn, and in between each of these flights the maintenance inspection is a much lower requirement than between each day of flying.

2) Component Requirements.  Supersonic jet engines need maintenance more often than high bypass commercial engines.  They are stressed much more, and work on a much tighter margin of error, thus fighter/bomber aircraft need maintenance more often.

3) Age.  Military fighter/bomber aircraft are on average much older than the average commercial aircraft.  B-52's are from the 50's, and B-1's are from the 80's (along with most of the fighter fleet).  Older aircraft require more maintenance, and there is no avoiding it.

Between fighters and bombers, they each have different flying styles.  Fighter engines work a lot harder than bomber engines (except the B-1, which essentially has the same engine as an F-16), and thus require maintenance more often.  Bombers are much larger, and have more systems that can break.

Hope this helps.

Update: Incorporating a suggestion from the comments below, it is probably useful to specifically mention a few more specific maintenance items unique to combat aircraft

1) Ejection Seats:  Most military combat aircraft carry ejection seats, which have a very specific maintenance routine.  This may include repacking the associated parachute, and checking to ensure that all components are functional/in good repair.

2) Weapons:  The obvious difference between fighters/bombers and commercial airliners is that they carry weapons.  This means that there is a software package that needs to be maintained (that controls the weapons), the aircraft hardware needs to be maintained (ie bomb bays, missile racks, hard points, etc), and the weapon itself requires building/deconstruction.

3) Flight Computer:  Combat aircraft often have tactically specific functions in their flight computer that a commercial airliner would not.  There are routines to help calculate bomb trajectory, to link with other combat aircraft and many other military specific tasks that a commercial airliner would not need.

I would agree with an earlier statement stating that performance has a slightly higher emphasis than reliability in military aircraft than in commercial aircraft.  It's easy to see how the requirement to carry bombs/missiles increases aircraft gross weight, which lowers fuel efficiency.  Every internal bomb bay could potentially be a fuel tank extending range.  Hard points, even when bombs aren't installed, cause drag lowering performance.  In the end, designers have to determine which capability is more important - endurance, payload, power, etc.  You may want to install a triply redundant INS in a fighter aircraft, but you're adding weight that decreases performance, and taking space which could be devoted to other avionics (like radar).


What are the correct names for the two faces of an airfoil?

You can call the two opposite sides suction side (for face on the convex side of the camber curve) and pressure side (for face on the concave side of the camber curve).

This has been used in a number of cases- for example in NASA Report CR-1767 Section Data for Thin, Highly Cambered Airfoils in Incompressible Flow:

  .. flow separation on the pressure side at negative incidence angles and on the suction side at positive incidence angles.

for airfoils and in National Energy Technology Laboratory Handbook:

  The airfoils are curved, convex on one side and concave on the other, with the rotor rotating toward the concave side. The concave side is called the pressure side of the blade, and the convex side is called the suction side of the blade.

for compressor blades.


Why do some airlines not use containers for luggage?

In addition to the reasons given by @aeroalias, cargo containers also waste space.

From the A320/321 Operator's Manual:

The A320 can hold up to 7 containers. The A319/320/321 do not use the standard LD3 containers. They use the slightly smaller AKH container.

Each of these has a volume of 3.7 m3, so seven of them totals 25.9 m3. When bulk loaded the A320 has 37.28 m3 of cargo space. That's almost 44% more room.


Why must some aircraft get permission to start their engines?

Airliners usually push back from the gate and then start their engines when well clear.

If the aircraft has an unserviceable APU, a ground based power supply must be used at the gate for the start. Permission(coordination) is required so that their are no hazards for ground crew and vehicles in the gate area.

After one engine is started at the gate, the aircraft is pushed back. The next start, still needs permission(coordination) because the operating engine usually has to increase it's thrust above idle in order to have enough bleed air pressure for the "Cross Bleed Start".

EDIT:  "Permission" may be not be mandatory at many airports, so "Coordination" with Apron Control, Ramp Control, or Ground Control may be a better description.


Why did Air France flight 447 fail to recover from the stall?

I‘ll attempt a very brief answer based on the report against your questions:

1) Why did the aircraft stall?
The aircraft stalled because crew pitched the aircraft up beyond the performance limit at that altitude (they pitched into a climb which the available engine thrust could not sustain, bleeding off speed until the aircraft stalled).

2) Why was power not reduced?
I don’t know, but in my view that didn’t play a crucial role, either.

3) Why did the aircraft not pitch down by itself?
Because crew didn’t realise they were stalled and continued to apply „nose-up“ control input. Seemingly inconsistent behaviour of the stall warning system and unexpected parameters on their instruments (i.e. a combination of speed and vertical speed not ever seen in normal flight) contributed to the situation.


Taxi to spot?? Hot spot? What is meant by this?

The word “spot” just means a designated place, or part of the airport where the aircraft is to be parked and shut down.  Sometimes they are numbered.  Presuming the pilot knows where that is, the controller is simply clearing them to go there.


That's a US Airways Embraer E190

Here is another view of the E190 wing for comparison.


Do controllers take wind into account when giving headings?

When the controller says heading, he means heading.
So if he wants you to go into a specific direction, he will take wind into account. The reason for issuing heading are:

Every aircraft can fly it, because a compass is fitted on every aircraft. Track keeping requires more sophisticated avionics.
If two aircraft fly adjacent to each other, the wind will offset them by the same amount and therefore separation is assured.

Quite often a controller will ask you to report your present heading prior to instructing a one so he can make more accurate adjustments to your course, especially if you were under own navigation before being vectored.

With Mode S radars and the right equipment in the aircraft, the current heading can be downloaded from the avionics without the pilot being aware of it.


Does a tandem ultralight need flaps on the rear wing if the front wing has flaps?

As the love of tandems continues I will answer.  Because you are balancing lifting duties between two wings and (hopefully) still have the one in front stalling before the one in the rear, any configuration change in the front should be proportionately matched in the back so that the stall characteristics remain safe when flaps are deployed.

Deploying flaps increases the Angle of Attack of the wing and may cause a shift in the center of pressure.  So the design needs to be approached with care.

You could also put slats and flaps on both wings of a biplane too, but the whole point is to have one (smaller/less drag) wing for faster cruising flight and a larger, higher lifting wing for low speed flight (take off/landing).

For a GA personal use recreational aircraft, you may not need flaps at all.


Is airspace above KKIC class G at 3,500’ MSL?

As long as the flight climbs above 1,200’ AGL before exiting the area where class E begins at the surface, the whole flight is conducted in class E airspace until descending below 1,200’ AGL on the approach to the KKIC airport.

The point of confusion I think is where you've read that class G airspace goes up to 14,500 MSL.

  Class G Airspace within the United States extends up to 14,500’ MSL.

But first you must consider the following.

  Class E Airspace exists at 1,200’ AGL unless designated otherwise.

We can see to the west that there are areas where there are exceptions to the 1,200’ AGL specification, but this flight plan does not go through them. This means that the en route phase of the flight, if conducted above 1,200’ AGL is conducted in class E airspace.

We can reference all this using the Aeronautical Chart User's Guide.


What are U-2 loiter and stall speeds at low altitude?

A copy of the flight manual was released under a FOIA request and can be found here. It actually does not say a whole lot about stalls but it does reference some minimum speeds in the emergency engine out procedure section under "COMPLETE POWER FAILURE IMMEDIATELY AFTER TAKEOFF"

Maintain a safe flying speed and control until contact is made

NOTE: The following minimum safe speeds (10kts above stall) are recommended for the accompanying take off fuel loads
...
Fuel  |      Min Speed
...
685 | 90

So at ~runway altitude lightly loaded the plane could fly as low as 90Kts which is 10 Kts above the stall speed which is in line with other answers here. (Operations Manual Page: 3-3). At full fuel the stall speed rose to ~105Kts.
The manual devotes a whopping 2 paragraphs to stalls and lists no performance figures for them in section 6.
Strangely (or perhaps not so strangely) the the document lists an "Appendix I" which should contain the Operating Data (performance figures) but is absent from the document and regrettably where you would find the true answer.
Keep in mind this is the Handbook from March 1st 1959 and there have been several variants since so the numbers may vary.
Note the takeoff speed for a lightly loaded U2 was indeed 95-100Kts (Operations Manual Page: 2-12)


Has there ever been a centrifugal turbine in an aircraft engine?

The Heinkel Hes 3b, which powered the Heinkel He 178, had a radial turbine. This was the first operational jet engine to power an airplane.


What does a higher pitching moment mean? (ie -0.095 vs -0.0022)

A negative pitching moment is stabilising: it is a nose down pitching moment, which is what is required for static stability.

If the stabilising moment of the wing profile increases with AoA, the horizontal tail volume can be smaller - less resistance.


Why runway 13L/31R of JFK Airport does not mention any Threshold Crossing Glide Path Height for its reciprocal end?

That information is shown on the approach plates

It appears that 31R is not equipped with a VGSI. At least not that I can find. That would be why the data is missing.

On 13L the GS and VGSI are both 3°, but since the VGSI is located about 300ft further down the runway than the GS antenna the TCH is higher.


Does ATC have to maintain separation on diverging aircraft?

Yes, this is allowed, subject to certain conditions. See FAA Order 7110.65 (the ATC "bible"), section 5-5-7, for the full details.

  ...all other approved separation may be
  discontinued and passing or diverging separation applied when ... Aircraft are on opposite/reciprocal courses and you have observed that they have passed each other; or aircraft are on same or crossing courses/assigned radar vectors and one aircraft has crossed the projected course of the other, and the angular difference between their courses/assigned radar vectors is at least 15 degrees.

That's in the terminal environment; it's still possible in the enroute environment but a bit more restrictive due to the greater aircraft speeds and poorer radar accuracy.


How significant is the static buildup on the blades of the main rotor? And some questions related to this

1) Technically, yes, it's possible to be electrocuted by a static discharge. The chance of it happening is so vanishingly small, though, that it's not generally a concern. A helicopter simply doesn't have the capacity to store enough electrical energy to be a direct danger. The real threat from static electricity is that it can potentially ignite a fuel spill, or something of that nature.

2) Depends on how you define "grounded". The linkages are coated with grease, which typically has a pretty high resistance. This means that low voltage (where "low" in this case can be up to 500 volts) across the junction probably isn't going to generate a meaningful current. However, static charges routinely exceed 10,000 volts, which isn't going to be affected by a thin layer of grease. So, you can generally consider the whole plane to be at the same potential.

3) Same thing that happens if you're on the ground and touch it. When you touch metal, you'll get a spark, yank your hand back, probably shake it a few times if the spark was particularly bad, and resolve not to do that again.


Is it legal to bring (or allow someone else to bring) a firearm on a private flight?

This is a tricky question, because it depends greatly on the laws of the locations you're flying to / from.  Here's a few of the things you have to take into consideration.
Transporting is generally ok

According to 18 U.S.C. 926A:

Notwithstanding any other provision of any law or any rule or
regulation of a State or any political subdivision thereof, any person
who is not otherwise prohibited by this chapter from transporting,
shipping, or receiving a firearm shall be entitled to transport a
firearm for any lawful purpose from any place where he may lawfully
possess and carry such firearm to any other place where he may
lawfully possess and carry such firearm if, during such transportation
the firearm is unloaded, and neither the firearm nor any ammunition
being transported is readily accessible or is directly accessible from
the passenger compartment of such transporting vehicle: Provided, That
in the case of a vehicle without a compartment separate from the
driver's compartment the firearm or ammunition shall be contained in a
locked container other than the glove compartment or console.

926A says nothing about the method of transport.  Most often it applies to motor vehicles, but it can just as easily apply to aircraft.  Therefore as long as you're ok to carry at the departure airport and the destination airport, federal law protects you in between.
Also, remember that 926A only protects you if the firearm is unloaded and locked / inaccessible.
Ok, but can I bring my gun unloaded onto airport property, right?

Not in a sterile area
You can't take a firearm into the sterile area of an airport.  49 CFR 1540.5 defines a sterile area as:

Sterile area means a portion of an airport defined in the airport
security program that provides passengers access to boarding aircraft
and to which the access generally is controlled by TSA, or by an
aircraft operator under part 1544 of this chapter or a foreign air
carrier under part 1546 of this chapter, through the screening of
persons and property.

So, if the terminal and the GA ramp are two separate entities, you're probably ok.  However, I've flown to some smaller airports where the GA ramp and the TSA terminal are right next to each other.  In these cases, you need to be careful that you don't get into the sterile area with your firearm.
Maybe not anywhere on the airport
Local law might prohibit the possession of a firearm anywhere on airport property, or the airport itself might ban firearms on their premises.  The only way to know is to check the specific airport you intend to fly out of.
What if I want to carry loaded?

The first thing to remember if you carry loaded is that 18 USC 926A does not protect you.  In that case, you're exercising the privileges of either open or concealed carry according to the laws of the departure and destination states.
Open carry
Some states prohibit open carry.  Others allow open carry when unloaded.  Others allow open carry when loaded.  Some require a permit.  Some don't.  Some only require a permit for handguns but not long guns.  If you're going to open carry (perhaps a hunting rifle on a sling), make sure that the local area allows this.
Concealed carry
Some locations prohibit concealed carry outright (to the best of my knowledge, you still can't carry concealed in Chicago, for example).  Other states allow concealed carry with a permit from either that state or a state which they have reciprocity with.  So, for example, a Mississippi permit would be honored in Texas, but not in Nebraska.  Others allow concealed carry without a permit at all (that is, the 2nd Amendment is your permit).  First, be sure that your concealed permit has reciprocity with the destination state.
Even if you think you're open carrying, watch out.  In some states, the act of being in a vehicle, no matter how visibly your firearm is displayed, makes it concealed carry.  If you don't have a concealed carry permit, you may be in violation.
Is there anything else waiting out there to bite me?

Oh yes.
For example, Rhode Island.

A Rhode Island carry permit is generally required to
transport a handgun in a vehicle. This requirement does not apply,
however, to the holder of an out-of-state carry permit who intends to
travel uninterrupted through the state.

Is a fuel stop an "interruption"?
Or New Jersey.

[New Jersey] State law generally prohibits any person from knowingly possessing or
transporting any rifle or shotgun without first having obtained a New
Jersey firearms purchaser identification card (FPIC),or from
possessing or transporting any handgun without first having obtained a
New Jersey handgun carry permit.

Or Chicago.

Chicago, for example, bans handguns declared “unsafe” by the
Superintendent of the Department of Police, so-called “assault
weapons,” machine guns and other firearms regulated under the National
Firearms Act, “laser sight accessories,” firearm silencers or
“mufflers,” “high-capacity” (i.e., more than 12-round) magazines, and
“metal piercing bullets” (which include ammunition with non-lead
projectiles).  All these items are subject to seizure and forfeiture.
In some cases, the local ordinances have no explicit exceptions to
these bans for travelers merely passing through the jurisdiction

Or New York City.

Possession of a handgun within New York City requires a New York City
handgun license or a special permit from the city police commissioner
validating a state license within the city. Even New York state
licenses are generally not valid within New York City unless a
specific exemption applies, such as when the New York City police
commissioner has issued a special permit to the licensee or “the
firearms covered by such license are being transported by the licensee
in a locked container and the trip through the city of New York is
continuous and uninterrupted.”

Look, just tell me what to do.
Fine.

Carry your firearms unloaded, locked, and inaccessible.
Make as few intermediate stops as possible
Know and comply with all local laws both at your departure and your destination
Stay out of sterile areas while armed on airport property


What is the difference between the Bell 412 and the Bell CH-146 Griffon?

Fundamentally, the CH-146 is a Bell 412EP, which you can still buy from Bell today.

Some features on the CH-146 you won't find on civilian counterparts:

Weapons.  The CH-146 has attachment points for weapon mounts that aren't typically found on the Bell 412.
Wescam T-16D-A Thermal Imaging System. This wasn't a production addition to the CH-146, but it appears be common on these helicopters.  Similar aftermarket systems might be in use on Bell 412s in police use.
Wire Strike Protection System - some civilian helicopters do have this, but they're particularly common on the CH-146 and other military helicopters.
A Canadian Forces paint job.


Is it possible for a modified hang glider to land safely coming from orbit?

That's pretty much how space shuttles and other orbiting craft work.

They are dropped from orbit, they do calculations to enter the atmosphere at a velocity and attitude that doesn't burn up the aircraft, then they glide to their landing airport.

The entire journey is controlled, but unpowered flight. The flight surfaces are there to allow the pilots the ability to reduce the velocity and attitude of descent in order to get controlled descent into the atmosphere.

So a glider can also land; assuming of course it had some way of slowing down and is sufficiently hardened and shielded against the atmospheric effects. I am not too familiar with gliders but from what I know they don't have any spoilers or other such controls.


Can one "create" a private interpilot air-to-air frequency to chat?

Every frequency is allocated somewhere, in fact the same frequency will be used over and over throughout the world. This works because air band radios are relatively short range, about 200nm at best, so all you really need to do is find a frequency that isn't used anywhere near you and tune to that. This is what formation or group flights do.

That will not be private in the sense that it cannot be overheard, anyone with an air band radio can listen in. It will also not be private in that only you could use it, again anyone could tune into the same frequency for the same purpose. Formations often have secondary frequencies to tune to in these cases, but it's rare they need them.


What is the cockpit shown in this picture?

The cockpit shown in the photo is of a Boeing 747-400.
You can tell that it must be a 747 by the fact that it has 4 thrust levers (so 4 engines) in the typical Boeing design. The 6 screens with the EFIS controllers rule out anything older than the 747-400 (like a B707 or older B747 variants). The large gear lever with the 3 positions rules out the new 747-8 variant.
Here is a cockpit picture for comparison:

(image source: Wikimedia)


Conditional clearances can be issued for any stage of flight, but are usually not as they increase risk outside of the areas that you have listed.
In the en route environment a controller can issue conditional climb instructions for example:
SIA1223 at DOGET climb to FL340
BAW2283 passing FL250 track direct DROGO
I have never issued a clearance like that and some contries have made them not available in their regulations. But they do exist in other phases of flight.


For a given airfoil, with known Cl and Cd curves, how can I calculate the autorotation AoA range?

This NACA report may help you further.

Basically, determine $v_i$ = the induced velocity in the hover, then vertical autorotation speed is around:

2 * $v_i$ for a rotor with 12 degree blade twist.
1.8 * $v_i$ for an untwisted rotor.

More detailed information in Prouty chapter 2, although the annoying non-metric constants pop up all the time.


Can I fly the LNAV MDA when the GPS is set up for LPV?

GPS approaches are designed for you to fall back to LNAV if a 'higher' precision option like LPV fails during the approach. Just like going from ILS to localizer only if the glideslope fails.
The Instrument Procedure Handbook p. 4-26 says:

Flying a WAAS LPV approach requires an aircraft with WAAS-LPV
avionics. If for some reason the WAAS service becomes unavailable, all
GPS or WAAS equipped aircraft can revert to the LNAV MDA and land
safely using GPS only, which is available nearly 100 percent of the
time.

So you can just ignore the vertical guidance and fly the LNAV step downs using lateral guidance only from the GPS, and your regular altimeter (not your GPS) to identify altitude.
If you haven't done it already (or recently), I'd suggest practicing it before your checkride to see how your avionics behave. You might get alerts that you have to ignore and they could be distracting. It would be best to get a feel for that ahead of time rather than experience it for the first time with an examiner sitting beside you.
You can also just check with your examiner in advance that they're comfortable with what you want to do.


Is it technically viable to reintroduce sleeping berths?

Some airlines already offer sleeping facilities, by taking advantage of the A380's tremendous size:

A double-bed suite on Singapore Airlines

A first-class seat on Emirates

A first-class seat on Qantas

That top bed looks very tempting, but I dread to think how much it costs!


First, the precise terms is not fins, but control surfaces. Fins would be fixed but the four rear surfaces can rotate around a spanwise axis. By rotating, they can be positioned at an angle to the airflow, thus deflecting it and creating an opposing force.

Compare that to a V-tail on an aircraft. They work in the same way by creating a force normal to their plane. While this force has a vertical and horizontal component, the horizontal components of the single surfaces cancel each other when all surfaces are rotated by the same angle. Their vertical components will add up, creating a pitching moment.

When the left and right surfaces are rotated by the opposite angle, their vertical force component will cancel while the horizontal component will add up, thus creating a yawing moment which swings the tail around.

  If it were to pitch downwards, which fins would need to move and in
  which direction?

All four surfaces will move trailing edge down, so the resulting force will point up and pitch the whole craft nose down.


Will 3D wing has smaller drag than 2D at same AoA and airflow speed?

Summary

At relatively high Reynolds number (>1 million) and in attached flow, where the boundary layer is thin, 3D wing should always have larger overall drag than a 2D airfoil (infinite span), at the same free-stream incidence angle.

Why?

The downwash generated from trailing vortices is actually very small compared to the free-stream airspeed; therefore, the reduction in effective AOA is also very small.

This results in three effects:

Reduction in lift due to tilting. This effect is exceedingly small, since cosine of a small angle is essentially unity.
Reduction in lift and pressure drag due to lower effective AOA. The reduction in lift is small but definitely non-negligible. For unseparated flow around an airfoil, the overall pressure drag is very small to begin with, so the reduction is even smaller.
Creation of induced drag due to tilting of the lift vector. This is the main one, since sine of a small angle produces non-negligible linear factor. For example, if the local lift coefficient, $C_l$, is 0.4, and we have an effective decrease in AOA of 1.0deg, then $C_l\cos{\frac{1.0\pi}{180}}\approx 0.9998C_l\approx0.4$, while the local induced drag coefficient, $C_{d_i}$, is $C_l\sin{\frac{1.0\pi}{180}}\approx0.0175C_l=0.007$.

By the way, the drag polar you cited doesn't help your argument since it's for the whole wing (at aspect ratio of 6). What you really want to cite is the airfoil drag (from Airfoil Tools):

As you can see, the form drag (includes pressure drag) is a small portion of the overall 3D drag at aspect ratio of 6, in the linear lift range. The pressure drag increase is even smaller.

Addendum:

From your comments, it seems you have totally missed the point about induced drag. Induced drag is completely absent in 2D. In fact, if you assume that the flow is inviscid and without local supersonic flow, you have zero drag on any 2D airfoil. This is called d'Alembert's paradox.

As mentioned above, induced drag appears in 3D inviscid flow due to finite span and induced downwash.


When may I change my transponder code to 1200 when being handled by ATC?

ATC will tell you something like, "N1234R radar service terminated. Squawk VFR. Frequency change approved; good day" which you will repeat back as an instruction.
You do not change from the assigned transponder code until instructed.
If you're in a hurry to get away from ATC, you may request to terminate radar service as soon as you are out of their regulatory airspace.


What is the minimum possible number of hours required to carry passengers?

I believe the answer, at least in the US is 20 hours of flight time, plus however long a checkride takes. A sport pilot can carry a single passenger and the minimum requirements are outlined in 14 CFR §61.313:

If you are applying for a sport pilot certificate with [...]
Airplane category and single-engine land or sea class privileges,
Then you must log at least [...]
20 hours of flight time, including at least 15 hours of flight training from an authorized instructor in a single-engine airplane and at least 5 hours of solo flight training in the areas of operation listed in §61.311,

If a sport pilot applicant logged exactly 20 hours, got signed off, and then passed their checkride on the first attempt... they would be able to fly passengers as soon as they completed the checkride. That means, realistically, probably 21 to 21.5 hours.


Is there a serious effort underway to move from a highways-in-the-sky approach to a mesh-network approach?

Currently SESAR (Single European Sky ATM Research) works on implementing a similar system in the European Union.

As stated on the website :

  SESAR’s vision builds on the notion of trajectory-based operations’ [...] meaning that aircraft can fly their preferred trajectories without being constrained by airspace configurations.

The aim is to improve capacity in the European sky and be more flexible among the actors too (like temporary closed airspace for military training, handle volcanic eruptions and disruptions of the airspace).

SESAR has different projects to address the needs of imporving Air Traffic Management in Europe that you can find on their website.

Edit

There are current concrete solutions from SESAR and EUROCONTROL (the European organisation for ATM in Europe) to make this happen at the moment in the European airspace, such as the Free Route Airspace with set target of implementation (that we could consider "serious effort") :

  By the end of 2017, 51 ACCs have either fully or partially implemented Free Route Airspace operations [...] By the end of 2019, most European airspace is expected to have implemented FRA, with all airspace having this type of operations by 2021/2022.


What is the standard for tachometer calibration / Hobb's equivalency?

Hobbs time is most useful for tracking log time (and billable time in rentals.)

Tach time is simply a counter of revolutions of the engine, displayed as "hours."  Calibration is basically at normal cruise RPM, which can vary for different engine/prop/desired speed.  The tach counter is approximate at best, but it is what we have.


Why is it not allowed to dispatch an Airbus A320 with an inoperative ELAC 2?

As pointed out by this discussion on PPRune, ELAC 1 only controls elevator actuators hooked in to the Blue hydraulic system. ELAC 2 is split across Green and Yellow.

If ELAC 1 is the only operational computer and the aircraft enters emergency electrical configuration, blue hydraulics will be lost until the RAT deploys. Further, the fallback for ELAC 2 (G/Y hyd) is SEC 2, which is not powered in EEC. Thus, the aircraft will have no primary pitch control.

The solution is that if the fault is in the ELAC computers themselves, to swap the units before dispatch.

In general, if there's something weirdly asymmetric about the A320, the first guess should be something to do with EEC. This is because EEC, by design, tries to only power one unit, typically number 1, of each system.


How does fuel get to the engine during acrobatics?

The basic problem is that no matter how the aircraft's fuel tanks are designed, if there is an air gap in the tank, then there is an attitude and/or a g-loading that puts that air gap over the inlet to the fuel line running to the engine.

There are a lot of solutions to this problem. The first is exactly as you say; don't sustain any maneuver that starves the fuel pump (and by extension the engine) for a longer period than you have fuel in the lines to feed the engine. You can actually do a lot without the fuel system seeing a single hiccup in supply; the fuel tanks are designed to feed while under positive G-load (otherwise you couldn't get any fuel to the engine just sitting on the tarmac), so hard turns, rolls, loops etc that keep a force on the aircraft and its contents acting downward towards the floor of the cockpit will keep the fuel flowing into the engine. Spins and high negative-G maneuvers tend to be the things that starve the engine; if the tanks are in the wings, a hard spin, snap roll or zero-g parabola will push the fuel out away from the inlets at the wing roots.

Most fuel systems except on the lightest aircraft have at least two fuel pumps per engine; one electric pump on the tank side to shove fuel into the line, and one crankshaft-powered pump that draws fuel out of the lines into the carb chamber or other fuel delivery system. The checklist often involves turning on the electric fuel pumps just before startup to prime the fuel lines, then turning them off once the engine is running smoothly, but you can keep the electric pump on if you plan on really twerking the aircraft in flight. The line between these two pumps actually holds a fair amount of fuel, plenty for a minute or more of sustained operation with the inlet at the tank totally starved, and coupled with a bleed valve on the engine side to release any air that's entered the line, the two pumps running together can usually keep an uninterrupted flow of fuel into the engine by having the electric pump shove fuel down the line as fast as it can whenever the inlet is under the liquid level.

For mild aerobatic maneuvers, a "flop tube" is put into the fuel tank. This is simply a flexible hose with a weight, that keeps the hose under the liquid level, no matter what forces are acting to move the mass of liquid around in the tank. This is a simple and very effective way to keep fuel flowing to the engine while the aircraft is under load in any direction, but because the flop tube requires a significant volume of fuel to sink underneath and draw from, flop tubes can increase the "unusable fuel" capacity of the aircraft (fuel that exists in the tank, but the fuel system can't draw out in some normal circumstance). However, there's a tradeoff; the heavier the weight on the end of the flop tube, the more reliably it will stay under the fuel level regardless of attitude, but the more force with which it will impact the sides of the tank in violent maneuvers (and padding the weight further increases unusable fuel).

For the real aerobatic nuts, though, the maneuvers are so violent and so long that even a flop tube, redundant fuel pumps and bleed valves might get starved as the fuel sloshes and churns and there isn't a real "liquid level" to draw from. Many of these aircraft go one step further; a bladder-style fuel container. Within the fuel tank is a flexible polymer vessel that actually holds the fuel (typically in either wingtip tanks or a fuselage tank; it's usually impractical to try this with in-wing tanks). This bladder keeps the liquid and gas in the tank shell separate as the tank empties, and may also keep the fuel under some static pressure. If there's no air to draw into the fuel lines, then no matter how the aircraft is oriented or how many Gs it's pulling in any direction, the fuel lines can't be starved.

Of course, the fuel lines are only one consideration. Most "normal"-rated aircraft have float-type carburetors, which hold a reservoir of fuel with another air gap, and the fuel level in the reservoir is controlled by a float that opens the inlet from the fuel pump (this system also deals with small hiccups in the fuel flow from the tanks; the air just forms part of the air gap and the float keeps the inlet open until fuel flows in to raise the level). This type of carb will starve the engine during any maneuvers involving less than 1g of force acting towards the "floor" of the float chamber, as the float will keep the inlet closed and the reservoir will starve the fuel feed tube that allows fuel to dribble into the throttle body at the throat. For aerobatics, either a diaphragm-chamber carb (which has a flexible wall on one side of the reservoir chamber that is connected to the fuel inlet) or a fuel injection system must be used to avoid dependence on gravity to get fuel into the engine. The downside of these systems are increased complexity, and in the case of the diaphragm-chamber carb, intolerance of air this far along the fuel system (requiring an air bleed to purge any bubbles in the line before the fuel enters the reservoir).


Definitions from this page.

Metering:

  A method of time-regulating arrival traffic flow into a terminal area so as not to exceed a predetermined terminal acceptance rate.

Metering airport:

  Airport adapted for metering and for which optimum flight paths are defined.

Metering fix:

  A fix along an established route from over which aircraft will be metered prior to entering terminal airspace. Normally, this fix should
  be established at a distance from the airport which will facilitate a
  profile descent 10,000 feet above airport elevation [AAE] or above.

But behind these definitions, that's a whole domain under research and experimentation to shape the future of air traffic management.

Metering methods are currently designed to respond to traffic increase, resulting airports congestion, and requirement for fuel saving and less nuisances from aviation. Solutions are known collectively under AMAN acronym for Arrival Management.

As said, this fix is established on a route prior to the terminal airspace, 10,000 feet or more above the airport elevation. It can be the feeder fix.

The concept is to manage cruise speed to arrive at the metering fix in time, instead of holding/vectoring before (or in) the terminal area. ATC can determine in advance times aircraft will be allowed into the TMA, based on aircraft capabilities, traffic and weather). ATC is able to issue a "EXPECT descent in n minutes" to facilitate planning by crew using their FMS.

This allows for limited vectoring and holding prior to the TMA. When holding/vectoring is still needed, it happens at higher altitude, which is better for noise/emissions management.

Thales AMAN/DMAN concept in Europe,source

For example, there is such metering for arrival at Sydney. Sydney has a curfew at night, aircraft are descended in the order they arrive, which encourage crews of early flights to arrive before the end of the curfew and hold. But because many crews use this trick, waiting time increases. By using metered arrivals (ALOFT in-house system and MAESTRO AMAN from Thales), crews are provided with a narrow time window for crossing metering fixes, one at 160 NM from the airport, the other at 40 NM. Once you have the window, there is not need to hurry and then wait. The time crossing the first metering fix can be provided up to 1,000 NM before arriving at this fix.

  What's exactly a profile descent and how is it related to the metering
  fix?

The descent profile is the curve of altitudes followed for descent. The most efficient way to descent is the continuous descent without level segments. The aircraft just glides with idling engines and clean configuration (less noise, less fuel, reduced wake).

This profile is only possible if nothing prevents to descent at any point, e.g. a congestion in the terminal area. By ensuring a free descent after the metering fix, this portion of the descent can be optimized for fuel saving and noise reduction.

  So how does a metering fix work to absorbs arrival delays?
  What merits does it have as compared to delay vectors and holds?

The idea behind AMAN is to regulate traffic the most upstream possible, start sequencing early, and prevent wait time in flight. There is a complementary solution which is currently investigated too: DMAN for Departure Management, with transition fixes (also visible on the picture).

AMAN and DMAN systems can be coupled. As pointed out by @Lnafziger, metering fixes can be used more upstream than terminal area, up to departure. Such upstream fixes are visible on the picture. If we add Surface Management (SMAN), block-out times can be optimized effectively, minimizing taxi and airborne time, and at the same time minimizing delays and nuisances.

These systems tend to switch from distance sequencing to time sequencing. This field is currently actively experimented, both in the US, Europe (LFPG experimenting coupled AMAN/DMAN) and Australia and a few other locations.

Source

For more, see also: Accelerating Air Traffic Management Efficiency: A Call to Industry

I hope @DeltaLima will show and provide additional elements for Eurocontrol.


For aircraft with variable-sweep wings, how unstable is it to have each wing in a different position?

This was an intentional test run by Grumman in response to US Navy concerns about asymmetric wing sweep.

From The story of F-14A, Aircraft No. 3, BuNo. 157982

  One of these [flight tests] was in response to concerns raised by the US Navy regarding asymmetrical wing sweep. No. 3 is best remembered for photo shown at right. A series of flight tests were conducted from December 19, 1985 to February 28, 1986. Grumman's Chief Test Pilot, Chuck Sewell, conducted several trials with the right wing locked in the forward position of 20 degrees, and positioned the left wing at 35, 50, 60 and 68 degrees of sweep in flight. 60 degrees was determined as the maximum for landing. In the event of an operational in-flight malfunction, Sewell found the aircraft to be acceptable for carrier landings in this configuration.

Evidently it was manageable, and safe enough that carrier landings were permitted with asymmetric sweep.  There's no control available for the pilot of the Tomcat to intentionally asymmetrically-sweep the wings in flight, though.

How the handling qualities change I haven't seen reported anywhere.  I agree with Robert DiGiovanni that you'd expect additional drag on the side with the extended wing, but the Tomcat has additional options on how to move spoilers and other control surfaces and it isn't clear to me if it can detect and respond to asymmetric sweep or if it's just up to the pilot to do so.


What are the rules of airfoil thickness from root to tip on tapered wings?

Airfoil thickness at the root was chosen to obtain a good cantilever ratio: the bending moment is highest there, and you need to give it structural height. Also, you want to create most lift at the wing root, that is why chord, thickness and incidence angle are all highest there. All three tapering down towards the tip for structural reasons.

There is a bit more info in this answer.


What were the disadvantages of early prop driven blended-wing aircraft?

Generally, to create lift means to deflect the oncoming airstream downwards. How and where this is done in detail on an airplane is less important than doing it with a smooth spanwise lift distribution such that the wake behind the aircraft is trough-shaped.
A fuselage is disturbing this lift distribution, but not severely. The length of the fuselage means that it creates considerable lift at small incidences, even with the low lift slope of slender bodies. In case of the N-250 it was found that an incidence of 2° produces the lowest drag. However, this also means that the lift is only just right at one angle of attack, and when the aircraft is flown in different conditions, the fuselage can mess up the lift distribution quite easily, especially if it is wider than necessary.
During the 1930s and 40s, when this was understood in detail not only in academia, but also in the design offices, progress in engine technology pushed operating altitudes up until planes needed pressurized cabins to transport passengers comfortably. Pressurisation demands a round or nearly-round fuselage cross section to keep structural mass down, so any attempt at widening and shaping the fuselage would result in an unacceptable mass penalty. This ended the experimentation with lift-creating fuselages.
As for the N-250, the idea of fuselage inclination in cruise is correct in theory, but resulted in massive protests from the cabin crew which now had to push their carts uphill, ending this kind of optimization quickly. This is why it never caught on.


How does the static pressure system keep the ambient pressure?

Test. Calibrate. Repeat.
There is a new method developed by NASA based on GPS tracking. And here's the same thing but as a video (also NASA).

New Method for Pitot-Static Calibration
A precise, time- and cost-effective method based on global positioning system technology using output error optimization (...) enables near real-time monitoring of error in airspeed measurements, which can be used to alert pilots when airspeed instruments are inaccurate or failing.

Webpage also mentions the current methods that include the trailing cone (the one you see on modern airliners while they are being tested), tower fly-by's, and pacer airplanes.

Trailing cones were first developed and tested in the 1950s and 1960s as a simple means of calibrating the static pressure error of an aircraft's pitot-static system.

So apart from it being time consuming, it should be relatively easy. If it says I'm doing 100 KIAS but I know I'm only doing 96, just calibrate the 100 to be 96. Probably needs a screwdriver and a certified mechanic. But doable. Same for the altimeter and so on. Altimeter would be easy to calibrate on ground. Put in the current QNH, check the reading against the actual (from an airport diagram) and take out your screwdriver (not literally).
The pitot-static system doesn't know the right pressure, it just needs calibration. Which also answers why the cabin atmosphere won't be as precise, it wasn't calibrated for that.


Very difficult to say as we don't have enough real-world examples.

Vertical impact forces would be lower on the upper deck as the lower deck acts something like a crumple zone and absorbs some of the acceleration.
That said, an evacuation from the upper deck can result in more injuries due to the longer, steeper, slide that's needed.


Can I use a personally owned aircraft in the EU for PPL flight training?

Can I use my own C152 to gain my PPL (EASA) with a qualified instructor?

It doesn't matter who the owner is, so yes. As long as you pay to keep it in an airworthy condition and fuel her up, she's all yours.

  Is this a considered a commercial flight?

The fees the instructor is getting is for teaching you to fly, so no. Also you'll be the one who's paying.

  Can you define a 'training flight'?

Definition (my own, Google not helping): Any flight with a CFI on board, or approved by your CFI, with the goal of getting a higher certification.

Which in the broadest sense, every single flight is a training flight. Don't let the over confident pilots fool you, every flight is indeed a lesson.

  Is hour building a commercial flight?

Any flight builds hours. The answer is no if you're training, in your own plane or otherwise.

  If I use my private 152 how about insurance?

The EU is big. Check with insurance companies. But most likely it's no different than normal insurance. What if a flight school owner (who is not a pilot) decided to learn in one of his planes and the instructor is one of his employees, would that change the insurance terms? Nope.

Last paragraph actually answers all questions.

Fly safe!