How quickly could a commercial airline integrate advances in technology into its fleet?

It depends on the advance. Generally, there are three ways how airliners can be improved:

Operations and procedures: This can be as simple as faster turn-around times so aircraft will be more profitable, or as complicated as doing away with airways which would help to shorten trips, but depends on changes in regulations which have been in place for decades.
Better equipment: All parts of an aircraft are designed to be individually replaceable, and swapping old engines for newer, more fuel efficient ones will bring already two thirds of the efficiency benefits of replacing the whole aircraft. Other examples could be less heavy furnishings or more precise instruments. But there are limits, and every change needs to be approved by regulatory authorities.
Newer aircraft models: This brings aerodynamics, engines and equipment up to the status quo, and is done by airlines on a regular basis to improve both their attractiveness and their profitability. Examples are Singapore Airlines, which pride themselves on an average age of their fleet of just seven years, or Vueling, which thanks to a recent expansion has lower seat-mile cost than all their competitors.

Generally, the days of dramatic technology advances are long gone. Today, years of research are justified by single-digit percentage advances, and a new development like the A380 is started with a promise of just 15% less seat-mile cost when compared to airliners which are two decades old by the time the new plane is put into service.

To answer your question directly: Changes which produce meaningful improvements need years of preparation and testing for approval by the authorities. Quick gains are not possible anymore.


Why is Russian super-maneuverable thrust vectoring more prevalent than American?

This is a case of divergent design, and you can't know the answer without asking why current aircraft are designed they way they are.

Following the work of Col. John Boyd in the 1960's in developing the 'Energy-Maneuverability Theory', the U.S. and allies primarily designed combat aircraft and tactics around the idea that an aircraft's specific energy state defines its performance during basic fighter maneuvering (dogfighting).

Under the E-M theory, in order for a fighter to be survivable (and consequently victorious) during aerial combat, it must maintain a high specific energy advantage throughout its maneuvering - this means it either has higher potential energy (altitude), or higher kinetic energy (speed), and should aim to maintain the capacity to trade one for the other efficiently. In a fight occurring only in the vertical plane, this is easy to quantify, but in a turning fight, induced drag from turning bleeds energy from the aircraft, and E-M theory allows this performance efficiency to be quantified for a particular design or tactic.

Consequently, U.S. 4th Gen fighters like the F-15, F-16, and F-18 are designed specifically around energy maintenance in all flight regimes - high thrust for climb performance (gaining potential energy via altitude) and to maintain speed (overcome induced drag by turning), low wing loading (lower energy bleed in turning due to induced drag), and improved aerodynamics in the expected combat envelope (reducing overall drag in the subsonic regime), and their tactics emphasize maneuvering energy-efficiently, over expending all your energy in tight turns to simply 'get a bead' on your bogey first.

The practical effect of this is that if your first attack pass fails, you still have sufficient energy to either outmaneuver your opponent and get into position for another attack, or run. The disadvantage is, when your kinetic energy is higher than your opponents (speed) you can't turn as tightly as he can - but the hope is your greater ability to maneuver in 3 dimensions with that energy will give you the upper hand for a second attack - classically, this would be considered 'boom and zoom' tactics.

By contrast, the Russian designers have been focusing on 'Supermaneuverability', the ability of the aircraft to remain within the controllable envelope, outside the envelope of aerodynamic control. This is facilitated by 'funny' aerodynamics on aircraft like the MiG-29, Su-27 and Su-33, and by thrust vectoring on the aircraft you mention in the OP. This allows for high angle-of-attack maneuvering at low speeds (low energy state) - with the goal being to allow the pilot to point their aircraft at their opponent to facilitate a weapon release - it's the 'shoot first' strategy. Even if your shot misses, you force your opponent to go defensive, giving you the upper hand for a second shot, often facilitated by high off-boresight missiles like the R-73.

As speed decreases, so does turning radius - however aerodynamic control authority decreases at a greater rate. Thrust vectoring allows you to overcome the decreased aerodynamic control authority - your ability to change the attitude of the aircraft is now mostly independent of its aerodynamic control surfaces. Thus using supermaneuverability, you no longer need to outturn your opponent, you just point the aircraft in a totally different direction to where you were flying, possibly allowing a 'snap shot' with missiles or guns. The classical equivalent is 'turn and burn' tactics.

The practical effect of this strategy is that you might outturn your target and get a shot off first, but if that shot fails, you now have no energy (because you bled it off due to the massive induced drag of a high-alpha turn), and are effectively a sitting duck to your opponents wingman - you have no speed to run, you're losing altitude, all you have is thrust, and thrust is comparatively slow to regain energy. You can spin in place and keep shooting, but if your opponent uses their energy to run, you don't have the energy to chase.

So, why has the U.S. primarily ignored thrust vectoring? Because it's not tactically relevant to them. The West experimented with supermaneuverability towards the end of the Cold War with aircraft like the X-31 and F-15 ACTIVE, and after getting their hands on MiG-29's and Su-27's at the end of the Cold War, and wargaming them, decided that the 'supermaneuverability' advantage just wasn't worth it, when E-M based tactics could simply be adapted to defeat it. The one exception being the F-22 - an aircraft designed before the Wall fell, specifically designed to counter what Western tacticians had imagined the MiG-29 and Su-27 were capable of - illusions that were shattered just several years later.


Update. Added: much more informative P-8 diagram, sonobuoy diagram, ASW training film (see bottom), ESM, minor formatting fixes. Removed: consolidated two sonobuoy loading pics (linked but not shown inline).

This principle method of airborne sub-hunting is using sonar to search a wide area around your ships in the direction of advance. The intent is less tracking subs as it is to deter them from getting into a good position to shoot and/or obtaining a firing solution on your ships.

ASW is a long, complex topic (see bottom for USN training film). This answer will be brief unless someone has more questions.

Airborne sensors include:

Sonobuoys

Passive - (omnidirectional or directional) - subs are very quiet today. Detection ranges is extremely short. <100 m by some accounts.
Active - all subs are coated with anechoic tiles to absorb acoustic energy
A P-3 would go through about 10-30 buoys over a 6-10 hour mission
A P-8 can apparently cary 120 sonobuoys.
Some vendor specs are available.
GREAT video of sonobuoy deployment. (This is one type. Not all are this complex.)

Source. Illustrator.

Alternate view #1. Alternate view #2. Credit.

Dipping sonar

Unique to ASW helos

Credit: USN

MAD - magnetic anomaly detector

The large boom extending behind the tail:

Credit: DoD

looks for large metallic masses
limitations: short range (100s of meters), which requires aircraft to fly very low over the surface (increasing airframe fatigue and fuel consumption). Descending from cruising altitude also takes time.
upside: good localization (spatial accuracy), relatively few false positives.
downsides: Equipment is large and heavy. For these reasons, a MAD boom is not included on the current USN P-8, the navy's newest long range maritime patrol aircraft.
Counter-measures:

Sub can dive deeper to reduce their chances of being detected. Typical SSN operating depths are 400 m. The Type 214 claims a 700 m test depth.
Some modern subs are made from non-magnetic steels (eg, German Type 212, Type 214) or titanium (Soviet Sierra, Alfa, and Papa class SSNs, portions of the Typhoon's 5 pressure hulls).
Subs also undergo degaussing

LA-class USS Toledo (SSN-769) prepares to get underway after four days at the Magnetic Silencing Facility. 5 Feb 2010. Credit: USN

Radar

Historically, more useful for detecting subs on the surface, forcing them to spend more time underwater, where they were less effective (slower, limited endurance, limited sensor range). For much of WWII, German U-boats were essentially submersible torpedo boats. Most of their attacks were actually made on the surface.
Today, our improved radars can detect submarine periscopes (and their wakes) at significant distances, forcing subs to take only very short glimpses. The periscope is actually quite useful for ID-ing targets and obtaining ranges and headings much more quickly than stalking with sonar alone.

Signal intercept, ESM

You may detect a sub communicating over radio. You may also detect a sub if it uses its radar (very seldomly).

Visual

If you're directly above a sub at shallow depth, you can see it. Needless to say, this is extremely rare, but is one reason operating in shallow, littoral waters is dangerous. If you're lucky, you might spot a periscope wake. It's also unlikely you'll see a surface wake. At periscope depth, subs move very slowly. And at operating depths, surface wakes are extremely minute, likely undetectable even by radar and advanced processing, although attempts have been made.

Credit

EO/IR

General SA but may occasionally detect exhaust fumes (eg SSK snorkeling) or periscopes/wakes.

Other non-acoustic methods

Chemical (eg hydrocarbon sensor) - to detect snorkeling subs recharging their batteries
LIDAR - potentially faster than MAD. Limited depth and search band. Less effective in turbid coastal waters. Not used operationally.
Radar to detect the minute thermals from warm water heated by reactors. (Claimed by Russians, not demonstrated by US.)

Examples

Land-based maritime patrol aircraft examples: P-3 Orion (modded L-188 Electra), P-8 Poseidon, ,

P-8 Poseidon (modded 737-800ERX).

The Boeing 737 Technical Site. Source page with lots more info.

BAE Nimrod (based on the de Havilland Comet)

Source

Carrier based platforms include: S-3 Viking, SH-60 Seahawk

SH-60 Seahawk - sensors includes a variable-depth active/passive sonar, sonobuoys, and MAD.

MAD bird (orange/red). Credit: DoD

Anti-submarine warfare intro

COORDINATED ASW PART 1 - Coordinated Anti-Submarine Warfare 2089 (HD version below)


Do pilots breathe the same air as passengers?

In General, Yes.

As your image already shows, the same air is distributed throughout the cabin and the flight deck. For example, in the 737 NG FCOMv2 2.30.4 (Air Systems - Air Conditioning Description) it says:

  Since the flight deck requires only a fraction of the air supply provided by the left
  pack, most of the left pack air output is mixed with the right pack supply and
  routed to the passenger cabin.

So on the 737, the left pack supplies air to the flight deck and the cabin, the right pack only to the cabin (in normal operations).

Air from the cabin is also reused in the recirculation system:

  The recirculation fan system reduces the air conditioning system pack load and the
  engine bleed air demand. Air from the passenger cabin and electrical equipment
  bay is drawn to the forward cargo bay where it is filtered and recirculated to the
  mix manifold. The fan is driven by an AC motor. The fan operates with the recirc
  fan switch in AUTO except with both packs on and one or both in HIGH.

This implies, air previously exhaled by a passenger could make its way into the flight deck, but it is filtered first. In case of smoke in the cabin, the recirculation system would be switched off. However, during normal operations, the left pack supplies the flight deck directly:

(source: 737 NG FCOMv2 2.30.4)

All air quality parameters you mentioned should be identical or very similar for the flight deck and the cabin, except for temperature. Most aircraft allow separate temperatures for different zones. E.g. the 737 again:

  There are three zones: flight deck, forward cabin and aft cabin. Desired zone
  temperature is set by adjusting the individual Temperature Selectors. The selector
  range is approximately 65°F (18°C) to 85°F (30°C).
  The packs produce an air temperature that satisfies the zone which requires the

Temperature Selectors in the 737 overhead panel:

(source: 737 NG FCOMv2 2.30.4)

The details will of course depend on the exact aircraft model!


Does it ever happen that increasing the prop RPM without moving the throttle actually decreases the thrust and power delivered to the airframe?

You may get a speed increase but it's likely to be almost too small to detect (although this depends a lot on the plane and propeller combination).

When you increase prop RPM leaving MP constant, you are increasing the engine brake horsepower although there is a small drop in MP when you do that (and the opposite happens when you reduce RPM) that limits the total horsepower increase.

Say you have a Lyc O-360. Running it at "23 square", 2300 RPM and 23" MP, the engine is making roughly 108 HP at the prop.  If you raise the prop to 2700 rpm from 2300, and the MP stayed at 23", you are now making about 128 HP.  But actually it's not quite, because increased velocity demand of the intake flow drops the MP a bit with the throttle butterfly unchanged.  If you went from 2300 to 2700 the MP would drop somewhere around 1" of MP and this would reduce the engine's brake HP to 120.  Still more than 108.

At the high RPM, you will also likely have the prop operating at a less efficient blade angle from low blade AOA - the governor doesn't know or care what the blade angle is, it just rotates them to load to blades to keep the RPM where it's set by the prop control (a spring pushing on a set of flyweights) so there will be another minor loss from the blades being at a sub-optimal AOA.  Say, optimistically, 3%. So you end up with the equivalent of maybe 112-115 HP in net thrust compared to what you had before (this can vary a lot with different propellers).

So the result is, in a best case condition, you actually only increased the net thrust by a few percent and taking into account of the power-required-increases-at-the-square-of-the-speed aspect, there is a net airspeed increase of maybe a couple mph at best. If the prop efficiency really dropped off badly, you might find yourself going slower by a knot or two.

It also matters how you do it. If you were cruising along and raised the RPM suddenly by shoving the control forward, you will get a temporary deceleration as the governor unloads the blades to raise the RPM (it will also overshoot the redline giving that WEEEEEEEEOOWWWWWWWW sound you sometimes hear when pilots do that) and then the plane will slowly catch up.

If you just raise the RPM gradually, the proper way to do it, there should be little obvious acceleration or deceleration, but the speed may creep up or down a little bit and after things settle down you'll be a few knots faster, the same, or maybe a couple knots slower because the prop was operating at a very inefficient blade angle and the losses exceeded the minor Brake HP increase of the rise in RPM.

If you're at a very low manifold pressure setting, just off idle say, and the prop control is at Max RPM, the prop governor has a "command" (fly weight spring pressure) to let the engine run to redline and regulate RPM there, but the engine isn't making enough torque to spin the blades at redline.  The governor will unload the blades trying to do that, until the blades reach the fine pitch limit.

Or, if you're at full throttle/Max RPM and pull the throttle way back, at some point the blades hit the fine pitch limits and the RPM starts to drop from redline.  The prop has "come off the governor".  Now the prop is effectively an overly fine fixed pitch prop.  If you are at a certain fairly low MP, say 16", with the RPM at, say, 2200, and you move the prop lever up to Max RPM, the RPM may rise just a little as the blades were already near the fine pitch stops to keep 2200 RPM at 16". Add throttle, and the RPM rises like a fixed pitch until the RPM matches whatever RPM the prop lever is set to, and it "comes back on the governor" as the blades are moved off the fine pitch stops to keep the RPM at the selected setting.

As a general operating technique, you always lead with RPM on power increases, and lead with throttle on power decreases.  And you get to know that each RPM change affects MP and learn to allow for it with each RPM change. For example, if you are climbing at 24 square and want to cruise at 22 square, you'll reduce the MP to about 21.5-ish, then reduce RPM to 2200, knowing that this will pick the MP up to 22"-ish, requiring a minimal subsequent throttle tweak to get it right on.


Why are wings not tapered all the way to reduce vortex drag?

One of the approaches to reducing this drag is taper the wing

No, not at all. The vortex strength depends on the lift at the center wing. This strength invariably tapers to zero towards the wingtip, regardless of the wing's geometric taper ratio. The taper ratio will only change the local gradient, not the absolute decline in vortex strength. In the end, what happens at the tip is insignificant for the shape and strength of the wake.


What does the balance ball actually indicate?

1. Preamble

The ball reacts to the body force (or acceleration), with the exact same working principle as a bubble level. In airplane frame, the force is expressed as:

$$Y+mg\cos{\theta}\sin{\phi}=m(\dot{v}+ru-pw)$$

where $Y$ is all external side forces minus gravitational component, $m$ is airplane mass, $g$ is gravitational acceleration, $\theta$ is pitch angle, $\phi$ is roll angle, $\begin{bmatrix}u & v & w\end{bmatrix}^T$ is the inertial velocity in vehicle frame, $\begin{bmatrix}p & q & r\end{bmatrix}^T$ is the angular velocity in vehicle frame.

First, as any accelerometer, the ball does not react to gravity. Second, and this is a preference in bookkeeping, you can consider the accelerometer (or the ball) to only react to the external forces (i.e. $Y$), or only react to the inertial forces minus gravity (i.e. the right side of the equation minus the gravitational component).

2. In Flight

Taking thrust out of the question, then in flight, the only thing that can contribute to $Y$ is aerodynamic forces. What's the largest source of lateral force in air? Sideslip. There you have the relation between ball measurement and sideslip angle measurement. If you're unconvinced, read the sub-sections below.

2.1 Symmetric Thrust and Airframe

For symmetric thrust and airframe, the only yaw moment sources come from aerodynamics, and the largest contributors are sideslip and rudder (ailerons and spoilers also contribute due to differential drag, but the effects are even smaller).

Using the B737 model in AVL at Mach 0, flap 0 and AOA 0 for a rough idea, -5 deg rudder generates about 4.4deg of sideslip (nose left), at which point their yaw moments cancel each other out. However, the total $C_y$ is 0.055 to the right.

Comparing the stability/control derivatives (per rad), $C_{y_\beta}$ is -1.2, whereas $C_{y_{\delta_r}}$ is 0.44, which means that at the aforementioned conditions, the sideslip is overpowering the rudder by 140%, in terms of side force.

2.2 Asymmetric Thrust

In the case of one engine inoperative (OEI), we need to overcome the yaw moment from thrust asymmetry via rudder.

For wings level, there is side force from rudder that must be compensated. This can be accomplished by generating more sideslip into the live engine (which means more rudder deflection is needed than to overcome the thrust yaw moment). At steady-state, the net side force is zero, the ball is centered, but there is steady non-zero sideslip.

If we allow the wings to bank toward the live engine, a portion of gravity can be used to compensate for the side force from rudder, which means that less sideslip induced side force is required to maintain steady-state (therefore less rudder required). However, since the total side force minus gravity ($Y$) is non-zero, the ball is skewed to the live engine.

In either case, with thrust asymmetry, the relationship between sideslip and side force are "broken".

3. On Ground

On ground, any point of contact with the ground provides additional sources to $Y$. This is why tilting the bubble level with your hand makes it not measure level: it's not that the level is responding to gravity, but rather that it's responding to the normal forces exacted by your hand.

For an airplane, the source is obviously coming from the landing gear contact. At high speed taxi on a straight runway, with crosswind, the sideslip creates aerodynamic side force. The landing gear resists lateral motion via an opposite side force (however, you'd need to deflect nose wheel or rudder to resist yaw moment). At steady-state, the yaw string would measure sideslip, but the net side force is zero, so the ball would measure nothing.

Things are different when it's a circular runway. Because the airplane needs to track a curvature, the combined lateral forces must provide the centripetal forces necessary to maintain the track curvature. Therefore, the ball would react to the equivalent centrifugal force.

4. Sensor Positioning

Thus far, we've been assuming that the ball is placed exactly at the airplane CG. If the sensor is offset, then it will also react to the angular rates. That's why large airplanes need to calibrate the sensor measurements to the assumed CG position.

To answer your last question, unless the airplane is tracking linear motion, placing the sensor at different locations will give you different readings.


Why are the outboard Krueger Flaps retracted before the others on the B747?

This is from memory and applies to 747-100/200 aircraft, which I last flew in 1999. The video shows, I think, a -400. However, to the best of my knowledge, it has the same flap settings.

The flap selection handle detents and resulting device positions are:

0° — leading and trailing edge retracted
1° — leading edge inboard of the engines extended, trailing edge up
5° — all leading edge extended, trailing edge 5°
10° — all leading edge extended, trailing edge 10°
20° — all leading edge extended, trailing edge 20°
30° — all leading edge extended, trailing edge 30°

At least one carrier, TWA, but maybe others, ordered aircraft with additional setting. I seem to remember 15° and 40°, but the above was the 'standard'.

  Why the staggered retraction?

On takeoff, it's all about changing the wing from a low-speed wind to a high-speed wing. Normal takeoff flap setting for the -100/200 was 10°. I think it's 20° for the -400 but I never flew them. As you retract the flaps (both leading and trailing edge), the minimum safe airspeed increases approximately 20 knots for each decrease in flap extension. That gave you a safe bank angle of 15°. Add 10 more knots and you could, as I remember, bank 30°.

So, in the video the airplane is accelerating, and flaps are being retracted in stages as it reaches the minimum safe airspeed for that stage.

I'm not knowledgeable enough to authoritatively explain why, if you want to change part of a swept wing to a lower-lift wing while leaving part of it as a higher-lift wing, you need to make the change to lower-lift from outboard to inboard, but I do know, at least I think, that you must avoid the possibility of the outboard wing stalling while the inboard is still flying. You need to retain outboard aileron control as long as possible. Thus, retract the outboard leading edge devices before the inboard devices.

  Does each leading-edge flap configuration have its own unique setting on the pilot's flap-control lever?

No, the leading edge flaps do not have a separate selection. They're tied to the trailing edge flap setting. Note that flaps 1° doesn't actually put any trailing edge flaps down (although I seem to remember it took them out of the retract position and moved them backwards, but I may be wrong), but extends only two of the four leading edge flap sections.

  On approach, are the leading-edge flaps extended in a reverse staggered order?

Yes. On approach you're slowing, and you must not slow below the minimum safe speed for your flap setting. Those speeds will be lower than the respective takeoff speeds because you're lighter. I just looked up the fuel for a -400 that I have on my weight and balance web page, and it shows 359415 max fuel. Thus it's not unreasonable that you might be as much as 340000 lbs lighter than at takeoff and the minimum safe airspeed for a given flap setting could conceivably be in the range of 40 to 50 knots slower than at takeoff.

For those interested in more detail about the -400 leading edge devices, go to this incident report detailing an un-commanded retraction of the leading edge devices inboard of the engines. The single paragraph that most caught my attention is:

  The serious incident involved the un-commanded retraction of the automatic
  Group ‘A’ leading edge flaps on rotation for a period of about 23 seconds.
  Subsequent to the initiation of the retraction of the Group ‘A’ leading edge flaps, the aircrew was faced with unexpected stall warnings. The pilot flying was able to prevent the aircraft from stalling, with support from the other crew members and to keep the aircraft flying until the leading edge flaps re-extended and normal performance capability returned.


What is the purpose of these labels on an aircraft's wings?

Closer than you may think: notice that these panels all have fasteners visible-- these panels are removed frequently for engine work.  The labels are there so that the maintenance crews can both more easily reattach the panels, and so when they're inspected (again as part of maintenance) you're can quickly confirm that everything is in the right place.

When you have a plane in parts, all the panels start to look very similar lying on a workbench... Having the labels makes things more efficient and safer.


What other circumstances may cause the autopilot to trip out?

There are numerous circumstances, a few at random

pilot presses the autopilot disconnect pushbutton.
applying force to control-stick that contradicts autopilot.
entering a stall.
activation of high AoA protection.
descending below MDA on a non-ILS approach.
inconsistent data.

  will it not inform you of why it has tripped out?

Pilots check the ECAM for messages and suggested actions.

The AF447 accident report contains ECAM messages, note the ones at 02:12:44:

The Pilot in charge should assign which pilot handles ECAM messages, they should then have applied the ADR Check Procedure

  1.16.8.2 Case of speed display anomalies

  The philosophy for processing the anomaly is described in the “UNRELIABLE AIRSPEED INDICATION / ADR CHECK PROCEDURE” that is in Flight Manual (AFM) and transcribed in the Airbus FCOM and the Air France Operations Manual.

  Airbus

  The FCOM procedure indicates that:

  The crew identifies the loss of consistency in indicated airspeeds;
  And if the safety of the flight is affected by the indicated speed anomaly, and until the aeroplane reaches the safety altitude or the aerodrome circuit altitude, the crew first performs the  Memory items indicated in the “UNRELIABLE AIRSPEED INDICATION / ADR CHECK PROCEDURE” inset. The objective of these memory items is to maintain the aeroplane within a safe flight envelope and to stabilize the flight path to allow time to find, in the QRH, the tables giving the more precise pitch attitude and thrust values to be used for the flight:

Notice that the first two items are for the pilots to make sure the autopilot (AP) and autothrottle (A/THR) are OFF.

The pilots did not systematically work through ECAM messages and did not apply the ADR check procedure (one they would have memorised in training). They were confused and acted erratically. They stalled the aircraft, ignored the stall warnings and held the aircraft in the stall from above it's operational ceiling right down to sea level.

The sad truth is that the only action really necessary was to keep the wings roughly level for a few minutes. It is possible that if both pilots had folded their arms, tucked their legs back and taken a 5-minute nap, everyone on that plane would still be alive.

Glossary

- ADR = Air Data Reference
- AFM = Flight Manual
- ALT = Altitude
- AOA = Angle of Attack
- AP/FD = Autopilot / Flight Director
- A/THR = Autothrottle
- CLB = Climb (throttle setting)
- ECAM = Electronic Centralised Aircraft Monitor
- FCOM = Flight Crew Operating Manual
- ILS = Instrument Landing System
- L/G = Landing Gear
- MDA = Minimum Descent Altitude
- MSA = Minimum Safe Altitude
- NAV = Navigation
- PF = Pilot flying
- PIC = Pilot in command
- PROC = Procedure
- RED = Reduction (thrust reduction altitude - during climb after take off)
- SPD = Airspeed indicators
- TOGA = Take-Off / Go-Around (throttle setting)
- QRH = Quick Reference Handbook


How are helicopter cyclic and collective jacks connected?

The helicopter Collective and Cyclic controls are connected to the rotor bladesby swash-plates. The following is a swash-plate :

The following animation shows the connection assembly working :

Swash plate in the resting position.

A raised swash plate causing negative collective blade pitch and thus down force. Note that the control arms are on the trailing sides of the blades, causing raised swash plate to decrease the blade pitch.

A tilted swashplate giving cyclic blade control. Note the change in pitch of the blades during rotation.

Source : Wikipedia


Does the size of code F aircraft parking apron enough for 2 code C plane?

This type of parking system is called MARS (Multi Aircraft (or Apron) Ramp System) and is being used or explored by many airports.

You can see markings for them on the ground at CLE.  Here is a google maps link to one of the stand areas.  CLE terminal

Here is an article on the stands.


How do manufacturers engineer their aircraft to deal with tail strikes?

During testing, the rear fuselage is protected by a beam made of oak or even steel to distribute the tail strike loads and to protect the aircraft skin.

A340 during tail strike tests. This one is literally blazing along the runway …

For normal operations, the protection is removed. However, tail strikes must not cause flight-critical damage, so a few precautions are taken during design:

No hydraulic or electrical lines must run along the bottom of the rear fuselage.
If there are still mechanical control elements like pushrods, they and their collapsing supports must not be close to the bottom of the fuselage.
The tail strike location must be outside of the pressurized part of the fuselage.

The main protection against tail strikes, however, is procedural: The rotation speed must be high enough to allow lift-off before a critical pitch attitude is reached.

Delta wing aircraft are much easier to over-rotate, so the Concorde used a retractable tailwheel for tail strike protection:


How do helicopter pilots practice auto rotation?

It seems that you already understand what an autorotation is but for the benefit of other readers, I'll recap what the flare  is all about.

There are two really critical parts of an autorotation.  The entry and the flare.  If you get the entry wrong, then there is no autorotation.  You become a passenger all the way to  the scene of the crash.

If you get the flare very wrong (not enough speed when you flare or flaring far too high), you become a passenger all the  way to the scene of the crash.

If you make a mess of the flare, perhaps plenty of speed but too early, or too late, or not enough speed but flaring at a good height, then you will survive.  You might not get to use the helicopter again and you might spend some time in hospital but you're not going to  hit the  ground with enough energy to ruin all your mushy internal parts.

The reality is that most GA and low hour pilots faced with a real autorotation have a high chance of messing up the flare, and the subsequent touch down, damaging themselves and the machine but surviving.  The accident statistics and reports confirm this.  Chopping off the tail and rolling over are common outcomes of real autos.

In training and practice, the idea is that you walk away and get to use the helicopter again.

So, what height is the "right" height for the flare?

The POH emergency procedures section will also detail the height but, it will use slightly vague words such as "about 50 feet".  This is because most practice autorotations end with you at 50 feet with around 60kts airspeed and the nose straight - "the ideal autorotation".  The are many factors which affect this, mainly weight and wind (ideal ones always finish into wind).

Take a look at the "height velocity" diagram for a typical GA/sport helicopter.

(Source Rotorwandwing.com)

The shaded areas show the combinations of height and velocity from which a successful safe landing cannot be accomplished in autorotation.  When you flare, you are going to be close to the ground.  You have no choice in that!  When you start the flare, you want to be well away from the shaded areas of the diagram.  A normal autorotation aims for an entry into the flare with 55-65 kts airspeed.  Look at the diagram again and note that being at around 40-50 feet at that speed is well away from the shaded areas - bang in the middle of the "safe corridor".  This is the area you are aiming for.  At this point, you have enough energy, both kinetic and potential, to land safely.

You can see why flaring too high, too low or with not enough speed can lead to a bad weekend if you make a mess of it or, a permanent removal of flying privileges if you get it really wrong.

Hopefully this gives you a good idea of what the "right height" means.

When doing ab-initio training, you are gently led into autorotations. Your instructor will demonstrate one to you very early.  If you are clearly confident and not nervous, maybe on the first lesson which my instructor did.  Indeed, at my school, every single dual flight included at least one demonstrated or practice autorotation so you get a feel for the height early on.

You will also, perhaps every time (I think this is true in the US) finish an autorotation with a power recovery.

I chose that video because there's a good illustration in it of how to judge the height - and given that "about" is as good as the POH gives you, it's all about judgement.  In this video, you can see everything.  Watch it and look straight ahead.  Do not look at the ground, let your peripheral vision do the work. Notice how as you get closer to the ground, it seems to be coming towards you at a constant rate then suddenly, it seems to rush towards you - the "ground rush"?  That's when you start the flare.  You already know from the power recoveries you've practiced and the demonstrations what the correct height looks like so you know roughly when to flare but that sudden ground rush is the sure sign that now is the time to start slowing down.

What you are aiming for is to arrive at 0 rate of descent at or just above the ground so that a little bit of collective can be used to cushion the touch down.  With some wind on the nose and good airspeed, it is possible to bleed off most of the descent rate and ground speed with the flare.  A skilled pilot might not even use collective until the last couple of feet for a really gentle 0-0 touchdown.

There are a lot of different kinds of autorotations and some advanced ones don't use flare at all - or very little flare from low speed.  Really skilled pilots in light helicopters can go more or less vertically down with just enough airspeed to keep translational lift.

In summary, good judgement which is arrived at from the POH reinforced with demonstrations and practice.

Note to other rotary pilots:  I know that using the HV diagram is not how it's trained but it's useful in my opinion to understand what the correct height is.


Were WW2 American fighters designed to operate from dirt airstrips?

(Source)

Opening theaters in the Pacific, for example, using fighters/bombers fitted with bush tires would not have been a good choice indeed. Maybe one pilot can pull it off. But not all, and certainly not the damaged planes.

As planes got heavier before WWII, and especially during WWII due to the massive engines and the all-metal construction, came the need for inflated tires, paved runways, hydraulic brakes...

... and the need for the Marston Mat. By using perforated steel planks, a runway can be built almost anywhere in a relatively short time (source).

(Source)

Above shows a North American P-51 taking off from Iwo Jima. Note the pattern on the ground. From far away in other B&W images the pattern does not become clear and the planes look as if they're using pure dirt runways.

  Marston Mats were among the most important inventions of World War II (airspacemag.com).

As seen in your other question, How are modern jets modified to takeoff/land on a dirt runway?, Russian fighters are built with unpaved runways in mind. As are modern military transports. Transports have the luxury of space for many tires. But for jet fighters, it was the advances in tire manufacturing, which itself was due to the jet age that brought the swept wings and consequently the faster takeoff and landing speeds.

(Source)

Of course a humid tropical rainy island is different from a bone dry desert. The different soils and the water content affect their bearing and shear strengths. In North Africa, you may not need special reinforcements for the soil where its strength can be 4 times as high (think dry lakebeds).


Can a helicopter be stable without moving the control inputs?

In answer to your main question, Yes that is how they behave.
In theory in a perfectly world, there would probably be some sort of balance point, but in real life there is always something slightly affecting the helicopter causing it to start to drift.
As for how to actually fly, beyond telling you to get real lessons [don't do it], the strategy of constantly moving the controls is something sometimes called "stirring the pot" and in real life is generally a sign of an inexperienced pilot. With training and experience your control inputs will eventually become so small and so far "ahead" of the aircrafts movements that it will look like your not moving your controls. if you are not using full size controls for your sim, this may be impossible to achieve.


Can you help me to identify a Boeing 727 maintenance task involving a safety risk for a research project?

It's been a while since I worked the 727. It was a very forgiving airplane, so you had to do a lot to make a critical safety error from a maintenance perspective.

However, I do remember elevator position transmitters being a major pain to adjust. Although the manual wasn't necessarily bad, I never felt comfortable with the adjustments because of how sensitive they were. The manual made it sound so easy, when in all reality, I would have felt better if there was some note that said something to the effect of "this may take a while." Plus, you always had Skydrol dripping in your face when doing it off a lift in the howling wind.

Even tightening the bolt of the transmitter down was enough to bring it out of tolerance. So, ordinarily, you had to rig it out of tolerance, then hope that the tightening of the bolt brought it in tolerance. Sometimes it'd take 5 minutes. Other times it could take all night.

There is also a "dog bone" that attaches between the transmitter and the flight control surface. Sometimes the bearings in that dog bone would develop slop, and cause autopilot issues as well.


What happens to the fuel lines when a jet engine falls off?

Engine separation won't cause automatic closure of valves, but the resulting low pressure will illuminate lights (including the Master Caution light) on the panels and display messages on the displays.

The pilots will have to react to the engine separation, the same way than for an engine fire or severe malfunction. This non normal procedure includes shutting down the fuel line by setting the engine start lever to CUTOFF or triggering the fire bottles on the affected engine.

There is a spar fuel valve (or fuel shutoff valve) fixed to the wing and to the fuel tank, which stays on the wing in case of separation. This valve is to prevent leaks due to a broken line. As the hydraulic power may be missing after the engine damage or separation, the valve is controlled by an electric motor with a backup battery and a double wiring redundancy.

Example on the the B737 NG:

(Shut-off valves framed in purple, source)

Non-Normal checklist used: ENGINE FIRE or Engine Severe Damage or Separation (NNC 8.2 of the Quick Reference Handbook).

(Click to enlarge, source)


Will afterburner work at settings less than full dry thrust?

Afterbuner simply injects fuel directly into the jet pipe (i.e. beyond the turbine) in order to greatly increase thrust. The way throttle levers are normally set up, afterburner is engaged once the lever is advanced past maximum dry thrust, but I can't imagine why, theoretically, you couldn't set one up to be engaged at less than maximum dry thrust.

Mind you, it would be awfully inefficient to do so, as thrust output is exponential, with most of it being delivered in the top 5% of the RPM band; engaging afterburner while you still have a lot of dry thrust available would just be a massive waste.

What's more, jet engines are much quicker to respond today, and, in addition, landing approaches are not performed at idle thrust; the main benefit of flap settings greater than 20 degrees is that they slow the aircraft down, allowing for steeper approaches. In jet aircraft, this also allows the engines to be kept spooled up above flight idle, specifically in order to reduce response times in the event of a go around.
In other words, throttle might be reduced to flight idle for the initial descent, but the final approach will use a higher thrust setting.

The benefits of adding afterburner to civilian transport aircraft are usually massively outweighed by their costs (see the Concorde and Tu-144).


How can I fix the stalling of an RC plane after the addition of floats?

Your model is based on the FX-803 Piper Cub model shown in this video. It's made from expanded polystyrene wings and fuselage, with a two channel radio that controls thrust from two motors mounted below the wing, with overall thrust controlling pitch and differential thrust controlling yaw. There are no moving control surfaces, and the propeller on the nose is a cosmetic windmilling attachment.

Your extra wing, lashed on with elastic bands, may or may not produce lift, but adds additional weight and drag below the thrust line, inducing a significant nose down moment. Your carved foam floats add additional drag even further from the thrust line exacerbating the nose-down problem, and further increasing the weight.

The original model was built and trimmed to give flying characteristics that could be controlled by simple thrust adjustments. There is no moving surface with which to counter the added drag, and even if there were, it is unlikely it would have sufficient authority to overcome the problem.

The modifications may also have moved the centre of gravity significantly, possibly beyond the point where it is fixable.

The model shown in the video has sprightly performance on limited power. The additional weight and drag you have added could easily overwhelm the available power.

You could try adding a fixed elevator to provide significant down force at the tail, but this will further compound the drag issue, and could also affect centre of gravity.

Realistically, I doubt you will be able to get this to fly. If you do, please come back and post a video!


Are there any serious plans for a new supersonic civilian aircraft?

Aerion is planning a supersonic business jet which has a projected completion year of 2021:

Here's an article Forbes have written about it.


TCAS II is required for most airline flights. This is not a requirement for certification, and the TCAS may or may not be on the MEL. However, most flights under part 121 (scheduled airline service, as well as some freight) require TCAS II.

As noted in FAR 121.356, "Turbine-powered airplane of more than 33,000 pounds maximum certificated takeoff weight" must be operated with equipment that meets a list of standards, but is essentially equivalent to just requiring TCAS II. Smaller aircraft with 10-30 seats can use TCAS-I.


Has there ever been a plane not controlled from the nose?

The de Havilland DH.83 Fox Moth put the passenger cabin and engine in front of the pilot

Author: RuthAS, source: Wikimedia Commons, licensed under Creative Commons Attribution 3.0 Unported licence.


For airplane spotting, what minimum specs should a telescope have?

I would not recommend a telescope for viewing aircraft.
As others have pointed out, a telescope that is suitable for astronomy would be incredibly overpowered for viewing aircraft - the aircraft would move out of the viewing frame very quickly, and you would have a difficult time tracking them.

I would suggest picking up a spotting scope (the kind of thing bird watchers and hunters use - good ones can be had in the 50 to 100 dollar price range, and excellent ones abound from about $100 up), or a pair of good binoculars for your plane watching. The zoom factor is far better suited to plane spotting, and either option would be substantially more portable than a full telescope rig.

As for advice on a telescope, there is an Astronomy stack exchange site, and while the entire network generally doesn't do "product recommendations" the Astronomy site's chat might be a good place to ask for advice on picking a telescope. (I'm not sure how active their chat room is, but it's worth a shot!)


Can a pilot who is not a CFI give instruction?

I'm assuming that you're asking about FAA regulations. Anyone can train anyone else - how effective and safe that training is is a different question! - but only an instructor can issue endorsements, including signing off on training time, endorsing solo flight, and accepting a student pilot application (see 14 CFR 61.193 and 61.215).

This is from 14 CFR 61.51:

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

  (2) The training time must be logged in a logbook and must:

  (i) Be endorsed in a legible manner by the authorized instructor; and

  (ii) Include a description of the training given, the length of the
  training lesson, and the authorized instructor's signature,
  certificate number, and certificate expiration date.

In theory, a non-CFI could train a student to perform as required by the ACS. But, a non-CFI couldn't authorize the student to fly solo, and he couldn't endorse the student's training time in his logbook. The student would end up able to fly but unable to get a certificate because he'd have no official training time and no solo time. So it wouldn't really be helping the student much: he'd have to go and do the required hours over again with a CFI anyway.


Are there any known instances of airline pilots passing off aerobatics as “turbulence”?

Recent discussion with friends who work or worked for one  major US airline, say they never witnessed such a thing.

One of them points out that on Navy P3 flights, they would do it to newbies. Not often, but sometimes to recalibrate newbies.

With respect to commercial flights, all pointed out that flight attendants are at high risk for injury, and would not tolerate such actions. All it takes is one person getting hurt. A neck injury from an unsecured passenger, or a burn from hot coffee happen often enough on flights with "natural" turbulence.  Creating turbulence could be career ending, and could have civil liability.

The population of pilots I was dining with are all over 45, and tend to be rather risk adverse. One, who has been retired for quite some time (he's in his 80's) says that people joke about it, but in all his experience, he too has never witnessed "pilot induced turbulence."

I have a blow-up of that far-side at my desk, though...


Is it best to use a thick airfoil or an undercambered airfoil for slow speed flight?

First of all, the thickness-related drag increase is small, especially for airfoils below 15% of thickness. Thickness by itself mainly determines structural efficiency and wing volume and is chosen on those merits. A very common choice for GA planes is 15% - 16% at the wing root tapered to 10% - 12% at the wing tip.

Next, much depends on the wing's bracing. A pure cantilever wing will be heavy but produce very little drag, so it is the obvious choice for faster aircraft; however, bracing the wing will lower wing mass and, therefore, induced drag. For slow airplanes, bracing the wing helps to reduce drag at low speed. But how much bracing is the best?

Clearly, early designs used too thin airfoils and went overboard with the bracing. Look at the picture of a replica of the Etrich Taube, a very popular plane of the pre-WW I period.

Etrich Taube in flight. Note the truss below the wing and the many wires keeping it in shape (picture source).

Next, many low speed aircraft used two braces, one forward and one aft, and an airfoil of between 12% and 15% because this helps them to get most lift from a given area. Note that all use high-lift devices: Slats and slotted flaps are a must:

Westland Lysander (top, source) and Fieserer 156 "Storch" (bottom, source). Note the very similar wing bracing and flat-bottom airfoil.

Multi-element airfoils are complex, so maybe it will be best to look at gliders and motorgliders for inspiration - or even human-powered aircraft. Also, the Reynolds number, which is determined by the size and speed of the aircraft, needs to be considered. As a very rough rule of thumb: If you only want to fly slowly and operate at a Reynolds number below 1 million, use a highly-cambered airfoil like the Daedalus sequence (DAE11 at the root, DAE21 mid-span and DAE31 at the tip). For more flexibility and Reynolds numbers above 1 million consider a camber flap and a glider-type airfoil.


What may be the cause of hot start problems in a Lycoming fuel injected engine?

The issue is undoubtedly vapor lock. In the fuel injected Lyc 540, the fuel injection plumbing is on the top of the engine which is the cold side of the engine when you are flying but when parked, heat rises! The following procedure runs cooler fuel through the plumbing while flooding the engine, then the flooded start procedure is necessary.

First, check your POH for the hot start procedure for your plane.  If not there, try this as it is for a very similar airplane:

Hot Starts on the Saratoga PA-32-300:

Intentionally flood the engine.  This runs cool fuel through the plumbing and "breaks" the vapor lock.

a) Full rich
b) Wide open throttle
c) Fuel pump on, watch fuel flow gauge
d) When gauge registers flow, wait 3-5 seconds then red knob to ICO and pump off.

Crank engine with red knob still at ICO and with throttle wide open at first. Gradually close throttle (at a rate that will take you about 10 seconds to close the throttle) and it should start up at some point.
When engine catches, do several things more or less simultaneously:

a) release ignition key
b) throttle to idle to avoid over-revving
c) mixture full rich.


What causes the average speed difference between the JFK to DEN flights and the JFK to LAX flights?

There is certainly a difference, but most of it definitely has a good explanation. Most of it is overhead such as taxi time that applies to both flights (almost) equally. This has a relative big impact on short flights.

The taxi out time for both flights will be about 27 minutes; JFK is not exactly known for its quiet taxiways. Both flights will add about 30 nautical mile for their departure route.

Both flights will fly approximately great circle routes, probably less than 2% extra distance during cruise.

The LAX flight will typically do a straight in arrival, almost no extra distance there.

The DEN flight will typically do a full arrival, 30 NM extra distance there.

The taxi in at LAX is 13 minutes on average, and 9 minutes at DEN.

Let's assume that both aircraft fly 460 knot true airspeed with 20 knots headwind during cruise, so 440 knots ground speed.

My estimates for the total flight times are then:

JFK-LAX

GC distance 2150 n.m
Departure detour 30 n.m
Arrival detour 0 n.m (straight in)
Cruise detour 25 n.m
Total distance 2205 n.m
Taxi out: 27 minutes
Climb out: 60 n.m. @ 300 kts = 12 minutes
Cruise: 2085 n.m. @440 kts = 4 hour 44 minutes
Descent/Landing: 60 n.m @ 240 kts = 15 minutes
Taxi in: 12 minutes
Total time: 5h50 minutes
Margin: 10 minutes

JFK-DEN

GC distance 1400 n.m.
Departure detour 30 n.m.
Arrival detour 30 n.m.
Cruise detour 15 n.m.
Total distance 1475 n.m.
Taxi out: 27 minutes
Climb out: 60 n.m. @ 300 kts = 12 minutes
Cruise: 1355 n.m. @440 kts = 3 hour 05 minutes
Descent/Landing: 60 n.m @ 240 kts = 15 minutes
Taxi in: 9 minutes
Total time: 4h07 minutes
Margin: 33 minutes


What was the first Russian jet designed with the use of area rule?

Hard to say with any certainty, but Tu-16 and Tu-95 carry obvious signs of application of the area rule. Both had first flight in 1952, which makes it earlier than the Whitcomb's publication.

Whitcomb may have discovered the rule independently, but Germans knew it since 1940s, so my guess is that the Russians either found it from them (lots of very valuable aerodynamic research data was captured after the war), or developed independently (Russians had/have their own NACA, after all).


What are some advantages and disadvantages of have the wing on top of the airplane?

The SUGAR Volt and SUGAR Freeze concepts use a high wing purely to make effective bracing possible. It is a design for a world where oil costs $200 per barrel and above. Mainly, two things make its aerodynamics much more efficient than current designs:

A very high aspect ratio of its wing, enabled by the bracing, and
A lower flight Mach number, which in turn makes the wing more efficient by requiring less sweep. Boeing doesn't give a Mach number in their web page, but I would bet it is somewhere around 0.75. See here for a discussion of a very similar design.

Todays airliners use a low wing to enable them to stow away their long landing gears and to put the wing spar below the passenger deck. Long gears make it possible to stretch the fuselage and still be able to rotate during take-off. Large high-wing aircraft, 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.

Both concepts use rather speculative engine designs, in case of the SUGAR Volt even one with hybrid natural gas / electric propulsion with onboard batteries. The SUGAR Freeze uses a less speculative engine burning liquefied natural gas. In the SUGAR study, Boeing set the goal to reduce fuel consumption by 70%.


Quadcopter: would putting 3 blades on the same level and the other blade below the first three work?

There are designs with overlapping blades. It's all a tradeoff on space, structure, clean aerodynamics, efficient aerodynamics, etc. This is the Malloy Hoverbike, for example.

So you can definitely have them at different levels, and you can even definitely have them overlap. If the 3 rotors' flow is not involved substantially with the 4th rotor's (not too big a difference in height), it should be no big deal.


Are there any truly 'unrecoverable' situations?

One of the more common causes of crash and fatality is a low altitude stall-spin.  A spin, in a modern aircraft, isn't of itself deadly -- with many designs, all you have to do it let go of the controls, and the aircraft will unstall and let you simply fly out of the resulting spiral dive (if you don't wait too long and go past Vne, anyway).

If you get into a stall when low and slow, however, and due to control positions or pilot error initiate a spin, you're likely to hit the ground before you can recover.  Since ground impact in these cases is usually near vertical, nose down, and partially inverted, pilot survival is hardly assured.

Avoiding this kind of fatal mistake is why you practice stalls (with plenty of altitude under you) during flight training -- so you can recognize the conditions that bring on a stall, the aircraft behavior that announces it, and learn how to manage the airplane after the stall occurs to avoid, or intentionally initiate and recover from a spin.

This is (or ought to be) a part of the check ride before flying an unfamiliar type, as well.  Many older designs are less stall friendly than modern (say, post-1960) aircraft -- and if you learned to fly in a Cessna 152, you won't ever have experienced an unintended spin (because the type is difficult to spin even intentionally, and won't do it without large control inputs).  Stall a 1930s light plane at 100 feet, however, and you're likely to fail the "walk away" test.

Another situation that, once in, you can't get out of occurs in mountain flying.  If flying in a canyon under a ceiling (or near your aircraft's ceiling) you may find yourself without room to turn around, but with ground ahead rising into the overcast or faster than your aircraft can climb.  This leads to either "weather" or "Controlled Flight Into Terrain" being the listed cause of the accident, when in both cases it was genuinely pilot error -- this is a situation an aware pilot will avoid.


There are several reasons:

For departure clearances. An IFR clearance may have a void or release time so that clearance is only valid between certain times.
For holding pattern legs. A standard holding pattern is based on a time of one minute at or below 14,000' MSL and 1.5 minutes above 14,000' MSL on the inbound leg.
For holding pattern clearances. Holding instructions include an EFC (expect further clearance) time, so that if you have a communication failure while holding then you know when you can safely leave the hold and start an approach.
For timed approaches, where an aircraft is cleared to start an approach at a specific time
For timed turns. A standard rate turn is 360 degrees in 2 minutes, so with only a timer and a turn coordinator you can turn a specific number of degrees.
For en route reporting and general time/distance calculations. Especially in a non-radar environment (i.e. when ATC can't see you on radar) you may be required to give ATC actual or estimated times for passing certain fixes. (This is not strictly IFR only, but it's still relevant.)

All of these scenarios are discussed in detail in the FAA's Instrument Flying Handbook and in the AIM.


What prevents a government from selling/leasing publicly owned airports?

One possible impediment might be the grant assurances that come with accepting Federal aid to improve the airport.

In short, if the local airport accepts money from the Federal government to improve the airport, that money is often granted "with strings attached" - requirements that the airport remain open, etc.


How do you write 'to', 'then', or 'via' in IFR clearances shorthand symbols?

Do what works for you, and omit what you can. For example, "N123 is cleared to KABC" can be condensed to "ABC"... assuming the clearance is for you, why copy your own tail #? You're copying a clearance, so "is cleared to" is, to me, entirely implied by the fact that there is something written.

"Climb & maintain 7,000" is for me an "M" with a horizontal line through it, and "7". If it was 5,500 I'd either write it as 55 or 5.5, since neither 550' nor 55,000' would make any sense. "Expect FL210 in 10 minutes" is "x 210 / 10" -- or "x21/10" -- because I know that I won't be cruising at 2,100', "21" isn't ambiguous.

"As filed" is AF, "climb via the (filed) SID is "via". Direct is a "D" with a horizontal line through it. (Or an arrow, but omitting the arrowhead saves writing & is equally clear that this is a symbol with specific meaning, rather than a letter.) Some people use "DCT" for direct, which is fine, although the D symbol will never be confused for being a navid I need to locate. "Right" and "Left" are circled R and L, if needed.

"Squawk 1234" is "sq 1234" and "departure on 126.55" is copied as just the frequency, unless there are several - then "dep 126.55 mtr 121.65 5 pr" would record the need to also call Metering 5 prior to start. If it's Ground or Clearance I need to call 5 prior, I'd probably just abbreviate those as G or CD, without the frequency unless there are more than one -- I have all of those on my EFB so "Gnd 121.9" is no more info for me than just "G".

For me, the recorded clearance isn't a document I need to refer back to months from now so I can recite verbatim what the controller read to me; it's a memory aid so that for the next hour or two I can know the pertinent elements without having to remember them. So numbers like squawks, frequencies, headings, and altitudes are vital. Fixes and procedure names likewise, which is easier with a printed copy of the filed route handy, where I can underline those elements I was given.

For example, if the filed route for KABC to KXYZ is to the ABC VOR, then to AFFIX then to BBFIX then V123 to DEF then the WHOZT1 arrival, the clearance might be "on departure fly heading 150, radar vectors to BBFIX then as filed," so I'd write "H 150 RV" then underline BBFIX, and below that I'd write "AF". After I'm done reading that back, I'd line out the ABC VOR and AFFIX (that weren't part of the issued clearance).

Your instructor may have a different way that's preferred, and in that case go with what you're being taught. But over time, this is what I've found works well for me. Less writing, no need to scramble, what I need & no excess when I come back to look at it later.


Has anyone considered filling aircraft voids with helium to reduce the risk of fire?

Yes, it has been considered, but with some differences.

First, the inerting gas used is not helium - it's nitrogen. Nitrogen also doesn't support combustion, and is for practical purposes inert. It also has major advantages over helium in this role. For one, nitrogen is very close to air in density, and doesn't leak as easily as helium, so it's easier to retain.

Nitrogen is also much easier to obtain by separating air. It can be done on the ground with nitrogen carried in cylinders, or generated onboard with OBIGGS. If you were to use a more exotic gas, it would be halon, which also breaks the chemical reaction sustaining most fires.

In practice, inerting is only applied to fuel tanks, not to avionics compartments (which house the batteries). One reason is that inerting won't prevent lithium fires: the batteries already contain all the reagents they need.

Nitrogen would prevent a secondary fire, but another reason comes in play: avionics compartments aren't sealed. Fires in these bays, like in the cabin, can be addressed by the crew. This requires insulation for the lithium cells (as has been installed) and fire detection in the compartment to allow response before the secondary fire is out of control.

But, as the first linked paper states, it's certainly possible to improve on that with quick automated fire suppression. Aircraft safety design is a set of tradeoffs and it's an evolving field. It's possible that in some years, as the amount and importance of avionics inevitably increase, more weight will be spent on their fire protection.


What additional aircraft equipment is required to fly a US registered airplane in Europe?

An overview of ATC related avionics can be found on the Eurocontrol website. There are a couple of things changing in 2015.

The list below includes change to ATC related avionics requirements in 2015.

In addition other avionic requirements not related to ATC are imposed, but that is outside my field of expertise.

Surveillance

Commission Implementing Rule (IR) (EU) No 1207/2011

Commission Implementing Rule (IR) (EU) No 1028/2014 (Amendment of 1207/2011)

ADS-B

ADS-B (1090ES) will be mandated  from 7 January 2017 for aircraft with MTOM > 5700 kg and Max cruise TAS > 250 Kts with an individual  certificate  of  airworthiness  first  issued on or after 8 June 2016. For aircraft certified before 8 June 2016 with the same MTOM and max cruise speed class ADS-B will be mandated after 7 June 2020 .

Applies to all IFR flights in the European Civil Aviation Conference (ECAC) airspace, excluding oversea territories.

Mode-S Elementary Surveillance (ELS)

Mode S ELS will be mandated for all aircraft operating according to Instrument Flight Rules from 8 January 2015

Applies to all IFR flights in the ECAC airspace, excluding oversea territories.

Mode-S Enhanced Surveillance (EHS)

Mode S EHS will be mandated for new aircraft with MTOM > 5700 kg and Max cruise TAS > 250 Kts from 8 January 2015. For existing aircraft in the same MTOM and max cruise speed class Mode S EHS will be mandated after 7 December 2017.

Applies to all IFR flights in the ECAC airspace, excluding oversea territories.

Communication

Commission Implementing Rule (IR)(EU) No 29/2009

Controller-Pilot Data Link Communications (CPDLC)

CPDLC (VDL Mode 2) is mandated above FL285 from 5 February 2015

Applies to all IFR flights in the ECAC airspace, excluding oversea territories.

Safety Enhancements

Commission Implementing Rule (IR) (EU) No 1332/2011

TCAS

From 1 December 2015 TCAS II version 7.1  will be mandated for all aircraft build before March 2012 with MTOM > 5700 kg and Max cruise TAS > 250 Kts operating in EU airspace. Aircraft first certified after 1 March 2012 already need to operate with TCAS II version 7.1.

Outside EU airspace, but within ECAC airspace, TCAS version 7.0 is still allowed.


What is the relationship between aspect ratio and divergence speed?

Because the wing has less torsional stiffness for a given area. This lets lower torsion moments overpower the ability of the wing to resist that torsion.

The torsional stiffness is proportional to the skin thickness and the cross sectional area of the airfoil. For a given wing area and lifting potential, a higher aspect ratio will reduce that cross section, so less stiffness remains.

Divergence occurs when the increase in the aerodynamic torsion moment from the twisting of the wing is bigger than the increase in restoring moment from the wing's torsional stiffness. It does not help that a wider wing has more span to accumulate that twist, so the aerodynamic torsion moment on a high aspect ratio wing is high despite the smaller chord which helps to reduce that torsion moment. However, while chord length is inversely proportional to aspect ratio, the airfoil's cross section is inversely proportional to the square of aspect ratio, so the higher aspect ratio wing has a lower ratio of torsional stiffness to aerodynamic torsion moment.

Theoretically, an aero-isoclinic wing shows no torsion under bending and is supposed to have an infinite divergence speed. However, such a wing must do without ailerons or any other imperfections which might upset the fine balance that is required for its isoclinic nature. The linked report shows that the aero-isoclinic condition is not sufficient to prevent flutter or divergence.


At what altitude, if any, may an ultralight overfly the Gallup airport (KGUP) with no prior authorization without violating FAR 103.17?

You can not fly an ultralight there without prior authorization if I am reading 103.17 correctly. The way that I am reading this, it seems that you may not be in controlled airspace around an airport without prior authorization, period. And, above  18000 is a no-go as well.

The highest concentration of aircraft traffic is at airports, Navaids like VORs, and on airways. You want to steer clear of those unless you are in clear and direct communication with those in charge of the airspace. Gallup has all three.

As far as Class E airspace, the way that 103.17 reads, It makes it sound like you are not allowed to fly in any Class E airspace over an airport without prior authorization. Admittedly, it’s splitting hairs. Everywhere else in 14 CFR, the description of Surface Class E has slightly different verbiage.

  103.17 Operations in certain airspace.
  No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

  137.43 Operations in controlled airspace designated for an airport.
  (b) No person may operate an aircraft in weather conditions below VFR minimums within the lateral boundaries of a Class E airspace area that extends upward from the surface unless authorization for that operation has been obtained from the ATC facility having jurisdiction over that area.

  3–2–6 Class E Airspace
  1. Surface area designated for an airport where a control tower is not in operation. Class E surface areas extend upward from the surface to a designated altitude, or to the adjacent or overlying controlled airspace. The airspace will be configured to contain all instrument procedures.


Does the Antonov An-225 have an Auxiliary Power Unit (APU)?

No. It doesn't have an APU — it has two of them.

They are located close to the main landing gears. From An-225 Mriya is the world’s largest aircraft (English version):

  Auxiliary power plant consisting of two TA-12 turbofans installed in the left and right chassis fairings provides independent power to all systems and starts the engines.

I think "turbofans" is not the proper term here. Actually the TA-12 is (just) a gas turbine (Wiki (Russian), Google translation).

The location of the APUs being much closer to the tarmac might be a reason why Copenhagen airport has (or had) special regulations for its operation on an An-225 (source):

  Special regulations for AN124 and AN225.
  Aeroplane type AN124 and AN225 must not operate their APU unless the pavement
  underneath is protected against heat and blast effects from the exhaust.

I couldn't find a better picture but the exhaust pipe is quite visible here (red circle):

(Source)

I'm not perfectly sure whether the green circle marks the intake, but I guess so.


Why are aircraft registration details made public?

Aircraft registration are no more or less public than car registrations (although they are a bit easier to get access to). Generally speaking you can go down to the DMV and request data on a plate number, for example here is the form for doing it in PA (there is a fee involved). Since cars are registered by state its up to the states how this works, planes however are registered federally and thus governed a bit differently, the FAA provides a nice portal here for looking things up.

From the FAA...

  In accordance with the underlying statutory framework (49 USC Chapter
  441) and as described in the applicable SORN, the information
  maintained in the aircraft record is available to the public upon
  request. This is to facilitate aviation safety, security, and
  commerce, the main purpose for which the record system exists. The
  public nature of the aircraft record allows for title searches by
  prospective buyers and/or financiers of aircraft purchases as well as
  for other interested parties to gather information concerning the
  aircraft including its airworthiness. The existence of recorded liens
  against the aircraft as well as the priority of those liens can be
  determined by a careful review of the documents maintained in the
  aircraft record.

This is done for a few reasons, first off many things in aviation may be billed by tail number. For example if you fly into an airport, say KPNE which has a city imposed 5$ landing fee, and the FBO for some reason does not collect this. The airport needs a way to look you up to send a bill. The FAA may also do this to make it easier for non-federal employees (local police etc) to access information related to an aircraft.

For what its worth the FAA also lists pilot data pretty freely, however you can now elect to hide your personal data (but not your name)in the FAA portal.


What is the difference between a forward slip and a side slip?

There is no difference aerodynamically. The only difference is in intention and presence of the wind. The airplane does not care about the ground track, all it feels is the movement through the air. Both side- and forward-slip make the airplane fly slightly sideways through the air, somewhere in the direction between nose and downwards pointing wing.

If there is no wind, your ground track will be exactly the same, between wing and nose, and you will feel that the nose points away from your track and call it forward-slip. If the wind is blowing and you manage the right amount of slip, you are moving sideways through the air, but the ground track (combination of wind- and slip- movement) can be aligned exactly with the nose and you call it side-slip.

There is really no difference aerodynamically and thus no difference in applied controls either.


How is Maximum Take Off Weight determined?

Pilots do not determine the official MTOW of an aircraft. MTOW will be estimated by the manufacturer during the design of the aircraft based on the required payload of the aircraft and the design configuration. It will be adjusted based on the detail design of the aircraft to comply with regulation requirements.

  §25.1533   Additional operating limitations.

  (a) Additional operating limitations must be established as follows:

  (1) The maximum takeoff weights must be established as the weights at
  which compliance is shown with the applicable provisions of this part
  (including the takeoff climb provisions of §25.121(a) through (c), for
  altitudes and ambient temperatures).

MTOW affects many other aspects of an aircraft's performance. It will affect stopping distance after a rejected takeoff, takeoff performance (including engine failure), climb performance, taxi weights, and many structural aspects. MTOW will be chosen so that the requirements for all of these conditions are met. This is why new engines or winglets which improve performance will allow a higher MTOW.

Of course, as always, the pilot has the authority to set their own personal MTOW more conservatively, if they feel it is necessary for safer operation of the aircraft.


How does retracting flaps help extend the glide of an aircraft?

Some answers presume that raising flaps reduces lift.

That is wrong.*

All it does is to increase angle of attack, until the change in flap setting is so severe that the airplane stalls. Only then will the airplane lose lift. With a smaller flap setting, the pitch trim changes and the airplane pitches up a little to keep lift constant. If the (auto)pilot does not correct the pitch trim for the new flap setting, the airplane will settle at a new, higher speed. Here, however, we can be sure that the autopilot kept speed constant (it only disengaged at 150 ft, and then the copilot took over. He certainly did not dive to pick up speed at this altitude!).

Raising the flaps does, however, reduce drag. See below for the A320; with a B777 the result will not be all too different.

A320 polar with 3 different flap settings (picture source)

Assume the airplane flies at a lift coefficient of 1.2 with flaps at 35°. Raising them to the next setting of 22.5° will move the operating point horizontally forward to the 22.5°-polar curve. Here the airplane flies at the same lift, but a smaller drag coefficient.

Retracting the flaps completely will not allow it to stay at this lift coefficient because the baseline polar stops below a lift coefficient of 0.9. The airplane will stall and needs to accelerate to keep flying. Only then will the airplane have to pick up speed.

I remember two occasions where that happened to me and raising the flaps saved my butt:

Landing in a field that turned out to be an asparagus field on short final. Ugh! Poor preparation - from higher up the field looked fine, even and smooth without vegetation. Coming closer I saw the rows of earth under which the asparagus grows (see here for a picture how this looks). Flying an ASW-20C and with flaps on "L", I changed them back to "4" and made a 90° turn to a different, adjacent field. I had played with the flaps at altitude before, so I knew that switching between "L" and "4" does not affect altitude.
Landing the SB-8 on an unfamiliar airfield that sits on a hill. Landing against the wind means I fly trough the leeward side of the hill during approach, but I did not keep some margin for the downdraft but started final at an altitude appropriate for a normal airfield without downdraft. I quickly noticed what was going on and switched the flaps from +8° back to 0° without changing speed and also retracted the wheel again. I just made it. When I climbed out of the airplane, someone came closer with a big grin and revealed to me that just a week before another pilot (who was as unfamiliar with the airfield as I was) had landed his glider into the bushes which mark the airfield perimeter. Of course, I also had tried out the effect of different flap settings at altitude when getting familiar with the SB-8.

* Since this statement raises blood pressure in others, let me explain. I only posted here after one answer after the next repeated this meme. Now some authors have edited and improved their answer. Would that had happened without clear words? Judge for yourself.

Now to the issue of lift loss: When the flaps move up (slowly), the lift force decreases just a tiny bit. The aircraft starts to sink, which immediately raises the angle of attack and puts an end to any further lift loss. Liftforce is immediately restored to its old value. That is why I simplified this process and said there is no lift loss, because there effectively isn't.

Next, the change in pitching moments from flap movement lets the aircraft pitch down unless pilot or autopilot retrim for the new flap setting. This is a much slower process because it involves a rotation of the airplane and its lengthwise acceleration.


Why don't airports use arresting gears to recover energy from landing passenger planes?

The energy unit costs for companies in Germany are much lower than for households. Where as a citizen you pay approximately 30 ct / kWh, the airport will pay much less, probably around 15 ct / kWh.

Adjusting your calculation for this price, we have 37.5 k€ per year in terms of energy cost saving to offset the depreciation and maintenance of the installation.

Let's assume our bean-counters want to see their investment money back in 10 years (10% depreciation per year), and the yearly maintenance costs are 10% of the initial system price. That means the cost of such an installation at Hamburg airport can be at most 187500.

But mind you, Hamburg has two runways, and each can be used in two directions. To catch 2/3 of the total traffic, we would need to install at least two systems. Runway 23 and runway 15 combined get approximately 75% of the landing traffic, they would be the preferred choice. (traffic percentages per runway are here)

This brings the maximal cost of a single installation to 95 k€; including project management costs, costs of the equipment, cost of the installation works, cost of closing the runway etc etc.

That is absolutely nothing! You can't develop and install a system that needs to recouperate 21 kWh in thirty seconds (the duration of the deceleration phase) for such a price.

And then there is the airborne side of the story. Who is going to pay for the modifications needed on the aircraft, such as an arrestor hook? And for the fuel that it costs to carry this hook around during flight (a hint, it will cost more energy to carry this extra weight around all the time, than that it would harvest at the airport)? And who is paying for the certification of the system?

There is no business case for such a system, not even close.


What is the purpose of a Traffic Pattern?

I think there are two parts to your question: why do traffic patterns exist, and why do people fly around them in circles?

First, a huge amount of aviation effort goes into avoiding collisions, for obvious reasons. One part of that is making everyone behave as predictably as possible, so that you know what to expect from other pilots and where to look for aircraft near you. That's why there are regulations on airspace, altitudes, speeds and all sorts of other things that affect how and where aircraft fly: if everyone is following the same rules then life is much easier. For example, if you're driving down a one-way street in your car, you can be (reasonably) confident that you won't meet someone coming the other way, and drive accordingly.

Because aircraft operate very closely together around airports, there's a higher risk of collisions and it's especially important to have very clear rules for how and where pilots take off, approach the runway and land. The traffic pattern is the aviation equivalent of road markings: it 'shows' where you should fly in order to fit in with everyone else, fly in the same direction, be visible to others, and generally be as obvious and predictable as possible.

Second, why do pilots take off, fly around the pattern and land again? Usually, because it's a great training exercise. In the process of going around the pattern you have to perform multiple important maneuvers and tasks, including:

Taking off
Climbing out in a controlled, precise way
Making coordinated turns
Managing airspeed
Operating key aircraft systems like the landing gear, flaps, lights etc.
Using checklists
Working with ATC (if it's a controlled airport)
Descending in a controlled, stable approach to land
Landing

Since taking off and landing are often considered the riskiest parts of a flight, doing pattern work is a great way to get as much practice as quickly and easily as possible. For example, I just got back from doing some night pattern work: I did 10 takeoffs and landings in about 35 minutes. That packs a lot of practice into a short amount of time, which is useful for everyone but especially for student pilots.


Smoke in jet engines is usually from unburnt or partially burnt fuel (or by water injection). Early jet engines used to create a lot of smoke due to these reasons (and due to lack of environmental regulations).

KC 135 engines creating smoke due to water injection By USAF Photographer - USAF photo, Public Domain, Link

Water injection, while cooling the engine, quenches the flames to an extent, resulting in unburnt fuel, which comes out as smoke. However, aircraft have moved away from water injection, reducing emissions.

Another reason for the smoke is inefficient combustion- older jet engines (turbojets in first aircraft and low bypass turbofans) were not as efficient as engines today, which premix the fuel with air and pre-vaporise it before combustion, rather than using droplet combustion- basically mixing fuel more evenly with air. Requirements of fuel efficiency along with stricter regulations mean that engines today have less emissions compared to their predecessors.

Smoke during Boeing 707 takeoff; image from nycaviation.com

In this case re-engining the aircraft with more efficient ones usually results in a reduction of smoke. For example, the USAF re-engined the KC-135s (from Pratt & Whitney J-57-P-59W turbojet to the CFM International CFM56 turbofan), which along with the elimination of water injection, reduced smoke.

On the top is KC-135s from an exercise in 1979; image from network54.com. Below that is KC-135Rs from Singapore Airforce; image from reddit.com


It's one of NASA's three WB-57F aircraft attached to Johnson Space Center in Houston, Texas, and operating out of nearby Ellington Field Joint Reserve Base. The B-57 was a tactical bomber that first flew in 1953, and the WB-57F was a modified version that the US Air Force used for strategic reconnaissance. The three aircraft with NASA are the last flying examples of the type and are used for Earth science, and are very versatile as they can fly up to 60,000 feet or higher.

The image below from Wikipedia shows one of the aircraft with pods on each wing.

Source


How are wingtips attached to the aerofoil while maintaining structural rigidity?

There are a number of winglets available in market for retrofitting and their method of attachment will also vary. Boeing details the procedure for attaching a winglet to their BBJ and it is quite instructive. According to the article the main issue is modifying the wing to accommodate the winglet, rather than the attachment itself.

  The more time-consuming part of the retrofit is installation of the
  wing modification to accommodate the winglet.

For this particular aircraft, the following steps are given:

  Removal and replacement of the outboard upper and lower skin panels
  Removal and replacement of rib 25, which is third from the outermost rib
  Installation of stiffeners across rib 25.
  Cutting of the closure rib (rib 27) and trimming of the two spars
  Installation of the new center section of rib 27 and the
  new winglet attach fitting
  Installation of the spar attach fittings
  Installation of the aft-position light.

which is followed by installation of the winglet.

Installation of winglet, from Boeing Aero.


What might have been the reasons for this low flight altitude?

Looking at the route your plane took, this low altitude flight was likely to avoid the polar jetstream. This is a band of wind that blows west to east in roughly the area the first half of your flight was flying through. It exists mostly between 30,000 and 39,000 feet altitude, and can range from about 60mph to over 200mph. I suspect that the low altitude was to keep the plane below this jetstream, avoiding the headwind and fuel and time costs that flying through it would create. To answer the other part of your question, as I mentioned in the comments, weight shouldn't have been an issue because the plane you were in (a 777-300ER), has more than enough engine power to maintain a higher altitude, even fully weighted.


Why are biofuels usually blended with standard jet fuel when used?

The issue with the biofuels is the low aromatic content, which changes the behavior of the fuel tank sealants. That's why blends are needed for the time being.

  (...) very low aromatic contents may cause seals and sealants to shrink and
  harden leading to acute or chronic failure. Unfortunately, most of the material qualification tests are more concerned
  with excessive swelling than shrinkage and there is little guidance offered as to an acceptable level of shrinkage or
  other changes in physical properties related to low aromatic content (NASA).

  At this stage,
  approval has been given for airlines to operate flights
  using the BtL and HEFA processes up to a limit of 50%
  biofuel and 50% conventional fuel. This is a precautionary
  measure enabling the industry to start using biofuels
  while additional assessments are undertaken on the
  need to maintain required levels of aromatic content
  in fuels. Aromatics are hydrocarbons found naturally in
  fossil-based fuels and are a necessary component for
  conventional jet fuels, forming up to 25% of the volume.
  They are not found in biomass-sourced fuels and this
  restricts the use of jet biofuels to 50% blends in order
  to guarantee aromatic content. The restriction allows
  time for an assessment of whether a synthetic aromatic
  source needs to be developed (Air Transport Action Group).

  Biofuels and FT fuels are very poor in aromatic content. This causes problems with
  seal shrinking and thus aromatics must be added to drop-in fuels in flight tests such
  that a concentration of 8% is achieved (European Commission).

  (...) aromatic hydrocarbons are
  more aggressive and cause more swell in seal materials than do paraffinic hydrocarbons

  (...)

  After the second cycle [of a jet fuel analog], the volume swell dropped
  from +22% to +13% as would be expected from the
  lower aromatic content in the fuel. However, this second cycle also caused the compression set to increase dramatically from 3% to 43%. Upon drying, the
  material again returned to its original volume, and
  compression set improved slightly. The reason for this
  significant increase in compression set is not obvious,
  but it is concerning (SAE International).

Trivia: there's been at least one demonstration flight on a jet that used 100% biofuel.


What aerodynamic characteristics arise from trailing edge sweep angle?

One aerodynamic behavior appears at high angle of attack : dihedral or anhedral wake, which affects (in some weird mixture) both roll and yaw stability. Forward swept trailing edge is much more stable than backward swept trailing edge.

Some jet fighters (let's say F-22) and most aerobatic airplanes (let's say SU-31) adopted forward swept trailing edges in order to increase stability at high AoA.


Do some aircraft lower the landing gear mid-flight?

That's nowhere near midflight. You are seeing aircrafts approaching Begumpet Airport (VOHY)'s runway 27. This airport has no airline service, but it is used for some general aviation including VIP flights and as military airbase.

The point directly north (about 3 km) from the coordinates you gave (N17° 25' 30", E78° 32' 27") is about 6 km, or 3.2 nm, from threshold of VOHY runway 27. Given usual 3° glide slope the aircraft would be just about 1000 ft above runway elevation, which happens to be the latest point where landing checklist should be complete. Yes, that means gear down. It also means it will be touching down in about a minute and a half.


In calm winds, which runway should I select at an untowered airport?

Often uncontrolled fields will publish a preferred calm wind runway in the Airport/Facility Directory. When one isn't published the calm wind runway is usually the longest runway, which gives you a 50/50 chance at guessing right.

To further reduce your likelihood of winding up face to face with another arriving aircraft you should self-announce on the CTAF and overfly the field to observe the traffic pattern. Also, turn on all the external lights 5 miles out. If there is traffic in the pattern you should work yourself into the same pattern everyone else is using.

If the pattern is empty my personal practice is to pick the approach to the longest runway with the fewest obstructions, and ideally one that doesn't overfly residential areas (where it's practical to avoid doing so).


Why is this type of rotor hub so rare...?

It's basically the teetering Bell/Robinson 2 blade rotor concept applied to a 4 blade rotor.  Like a teetering system, the gimballed rotor head accounts for most of the lead/lag/flapping, with whatever isn't accounted for absorbed by flexing of the long skinny root shafts.

With a 2 blade teetering system you have the weight of the machine hanging from a big cross bolt - pretty simple.  This system appears to be a bit complicated in the manner that the load of the machine is suspended from the rotor head, and that may have worked against it when other designers considered it.

The designer may have seen it as the advantages of a teetering system and an articulating multi blade system combined, whereas other designers saw mostly the disadvantages of the two.  An example: a teetering rotor, unlike an articulated one, can't tolerate hitting the teetering limits in flight because it puts huge bending loads on the mast (mast bumping) and makes the mast come apart.  This is why you never let a 2 blade machine go zero G.  I would expect this system could have a similar limitation, which a conventional articulated hub doesn't have.


Would a 19,000 ft descent in 6 minutes feel noticably different to passengers?

From the physical side, you can not measure / feel if you are at a constant altitude or if you are ascending / descending with constant speed. What you can feel is the change of speed in any direction, and acceleration acting in an unexpected direction. This causes the usual sensations:

Accelerating / braking on the runway: You are pressed into the seat / belt.
Weird feeling right when the aircraft becomes airborne: The aircraft accelerates upwards, which presses you into the seat with more than 1g. This higher g-force feels strange.
While climbing, the aircraft still accelerates, but the more strange feeling comes from the fact that the force doesn't point down to the floor of the aircraft, but more backwards. Your eyes see that you are sitting upright in the aircraft, but it feels more like lying.
At some point, usually when the flaps are retracted, the climb rate decreases suddenly and it feels as if the aircraft falls. This is because the aircraft accelerated downwards - tough it still climbs, but at lower rate.
Usually, you don't feel much during a coordinated turn. Maybe you feel a little heavier, but when you look out of the window and don't see horizon, this again gives a strange feeling.

Of course, the passengers of that flight did have several sensations. right after the incident, the aircraft for sure has done some unusual movements, plus what the pilots did.

The reference #7 of the Wikipedia article contains this diagram on page 36:

Directly after the incident, the aircraft climbed a little and the speed brakes were deployed (50%) to reduce speed. This was for sure noticeable by the passengers. And I guess the aircraft started to descend faster than usual, so the sensation of "becoming lighter" will have been much stronger/longer than usual.
After this, the aircraft descended with a quite constant rate for several minutes. This doesn't cause the feeling of being lighter. Maybe the attitude was unusual which means gravity doesn't push you vertically into the seat.

Later, when the aircraft reached 10,000ft, it accelerated upwards to stop the descent. At this moment, the passengers felt heavier.

(If you have a closer look, the descending part isn't a perfect straight line. This wasn't a smooth ride, but as said, a constant descent rate doesn't cause a sensation)

Of course, this is just about the sensation of acceleration so far. The passengers for sure have noticed the drop in cabin pressure, drop in temperature, more noise and so on.


Was the 737-300's wing an early supercritical wing?

Supercritical yes, but early? Not really.

BACXXX airfoil plot, shamelessly copied from airfoiltools.com.

The plot of the BACXXX above shows typical contour characteristics of supercritical airfoils:

blunt leading edge
very little curvature on the top surface at mid-chord
higher curvature at the bottom, resulting in negative camber around mid-chord
rear loading: Higher camber at the rear, thinner part of the airfoil,

however, this airfoil does not take those techniques to their extreme. It was a redesign on the original 737 wing, extended by 4.4% of chord at the leading edge and overall a compromise between high commonality with the earlier design and improved aerodynamics.

At the time when the "classic" series of the 737 was designed in the late Seventies/early Eighties, supercritical airfoils were already firmly established. They were first researched by K. A. Kawalki in Germany in 1940, who arrived at identical shapes as R. T. Whitcomb at NASA a quarter of a century later. The first operational supercritical airfoils, at the time called rooftop due to the roof-like shape of the upper surface pressure distribution, were employed by Vickers in the VC-10. This remarkable aircraft is to this day the fastest airliner with a maximum cruise Mach number of 0.89 and flew first in 1962.

Boeing became aware of supercritical airfoils only after the original 737 was designed, so the redesigned wing of the classic series carries some of the baggage carried over from the earlier design.


In Airbus flight control laws what does it mean that "control sensitivity depends on airspeed"?

In aircraft with mechanical controls, the position of the control column corresponds to position of the control surfaces and the force on the control column corresponds to the force on the control surfaces. At higher speeds, the same deflection generates larger force and correspondingly stronger response from the aircraft.

However in Airbus the forces are not carried and the side-stick is spring-loaded. In normal law the side-stick deflection commands specific wing loading (which mostly corresponds to pitch rate) in pitch and roll rate in roll. So you get the same rate or pitch/roll with the same deflection independent of speed.

But in direct law, the position of the side-stick corresponds to the position of the control surfaces. Because the same deflection causes larger aerodynamic forces, it leads to higher pitch/roll rate at higher speed. Significantly higher, because the control forces grow with square of speed.


What will happen if an X shape wings mounted on biplane?

Drawing from the hypothetical of "could a starwars X-Wing fly" which is brilliantly answered by James Gull here it is possible to achieve flight in this configuration

  ...It's not a very aerodynamic design. All those intersections at the
  fuselage will create a ton of drag due to interfering aerodynamics.
  The engines and wingtip pylons are not helping in that regard either,
  as they are not well blended in. The wings are essentially a biplane
  configuration, which definitely works. The designer would need to take
  extra care near the fuselage due to the surfaces being so close
  together; their wakes would interfere with each other. Careful tuning
  could help turn this into somewhat of an advantage in slow flight.

The Strop SP-7 was an early proposed design for such an aircraft. But it only
remained in this configuration for takeoff and slower flight segments, the wings folded into a mono plane configuration for high speed cruise. I cant find any evidence that it ever actually took flight.

Some aerodynamic "trials" have been done on the "design".

If you are asking about an "X" looking from the top down, it appears that Sikorsky dreamed up something like that and went as far as running tests on the design as well as building some of the major components but the project was ultimately canceled and it never flew.