Why are there no blended-wing passenger airplanes in operation?

All studies which so far showed an advantage for blended-wing bodies (BWB) were flawed.

The trick mostly used is to compare an existing airliner with a hypothetical BWB which uses equally hypothetical engines of improved efficiency, like what could be expected 20 years into the future. This masks the inefficiency of the BWB concept and makes the combination come out ahead.

The BWB will always have more surface area than a comparable conventional design. This translates into more friction drag and more skin mass, which more than offsets any advantage given by the bigger wing root (which helps to reduce wing spar mass). If you like real data, use the Avro Vulcan as an early BWB and compare it to its contemporaries. Note that design attempts for an airliner based on the Vulcan (type 722 Atlantic) went nowhere.

Why are these BWB studies published? The author gets more attention when he/she claims a "revolutionary breakthrough" than when he/she is more honest and admits that the concept is a dud. Even Boeing or Airbus like to publish BWB studies, so the public gets the impression they are ahead of the competition. It is sickening to read such academically dishonest studies - you need to spend time to dig to the bottom of the thing and to unravel the plot; however, once you have done this a few times, they all become alike. But compared to studies made 60 or 80 years ago, where the author factually lists what he did and why it didn't work out (which is the only way you can learn something), those modern studies are a waste of time.


Can I use any reference area for lift and drag coefficient?

The reference area is chosen according to the flow profile:

For long slender bodies, the wetted area is chosen because the main drag source is the shear forces between the boundary layer and the free flow.
For relatively short bodies, the cross-sectional area is most relevant because of the much larger contribution of pressure differential between front and aft of the stream.

Directly comparing $C_D$ of rockets and aeroplanes would not be very useful, because the reference area for aeroplanes is the wing area, which rockets do not have. Indeed $C_D$ * A is a much more useful comparison, if one knows what reference area A was chosen.


Do aircraft that operate at lower altitudes tend to have more cycles?

It's a lot more than just pressurization cycles (all sorts of things are being flexed), but yes. Turboprops are somewhere around 1 hour per cycle and regional jets about 1.2 or 1.3 hours per cycle (a typical regional jet will do around 3000 flying hours and about 2400 cycles in a year).  Mainline jets are closer to 2+ hours per cycle, with long haul jets around 3-4 hours per cycle.
So a turboprop with 50000 hours will tend to have 50000 cycles (averaged across the fleet), the RJ with 50000 hours will have around 40000 cycles, while a 777 with 50000 hours might only have 20000 cycles (keeping in mind wide variations from aircraft to aircraft).
So yes the short haul commuter and regional equipment does get flogged like mules compared to their luxuriating mainline big brothers.  Whether this becomes a "premature" problem depends on how robust the original design was.  The beefier the metal with a given load profile, the more times you can flex it before it starts to crack.  But when you make it beefier, you are adding "ballast" from the perspective of the short term mission. So it's a trade off between performance now, and viability when the airframe gets old (the extra beef reduces payload upfront, but adds greatly to the residual value of the airframe 20 years later - some operators will prefer one approach, some the other).
When the first high-time DeHavilland Dash 8 got to 80000 cycles, the original structural life expectancy, they only found a couple of minor cracks. This eventually led to an extension of the structural life limit to 120,000 cycles, giving a huge boost to the market value of old Dash 8s.  Airlines that own their Dash 8 cared greatly about this.  Airlines that leased their airplanes knowing they'll turn them in at a certain point long before, not so much.
CRJs on the other hand, are bit less robust and a CRJ200 needs quite a bit of patching of the structure after 40000 cycles to keep it viable to its 80000 cycle airframe life (a consequence of not doing a full fatigue test program at the very beginning - they only tested a fuselage barrel, with the full program being done about 8 years later). You can keep flying it past 40000 cycles without the reinforcements, but the frequency of the repetitive inspection requirements imposed make that uneconomical.
On the other hand, the cost of all the patches was brutal, and a lot of CRJ200s were simply retired at 40k, and their airframes stripped for spares, because the operators didn't want to spend the money to incorporate all the structural Service Bulletins (Embraers like the 145 are even lighter in their construction and considered even more "disposable" - a 145 once had its back broken, became an instant tail dragger, on a hard-ish landing in Brazil, a landing that wasn't hard enough to blow tires).
None of this really impacts safety if the maintenance program was developed properly, because inspection intervals and procedures prevent structural issues from progressing to a dangerous level, plus damage-tolerant structural design and very large (3:1) scatter factors applied to fatigue test results (if you bend a component repetitively in a fatigue rig, and it starts to crack at 60000 cycles, you have to impose an inspection or repair or life limit of some kind at 20000 cycles).
Notwithstanding "outlier" events like Aloha Airlines. Things always get through the cracks.


What are the typical facets of ownership costs, for a single engine aircraft?

I've heard it said that the break-even point for owning vs renting is 200 hours/year. I fly a lot less than that, but I don't like sharing my toys, so I own anyway.

I make it a point to not actually count my cost of ownership, because it wouldn't be fun any more, but I'll give you some rough numbers.

I bought a 1962 Mooney for \$30,000. That's about as cheap as it gets, and this was reflected in the condition of the plane and the high-time engine.

In the first year had it, I spent \$18,000 on an engine rebuild, new prop, new carb, new magnetos, new oil pump, and all the other firewall-forward upgrades that were required when I got the new engine. Five years later, I spent \$14,000 on new paint. It still needs a new interior, but that can wait. I spent about \$3000 at West Texas Aero installing speed upgrades.

Budget \$10/hour for your next engine rebuild.

Annual inspection typically runs \$3000 to \$6000 depending on what they find wrong. I'm getting a tank resealed this year, so it's going to be an expensive one.

Parking runs typically \$50-\$100/month, depending on where you are.

Insurance for my old crate runs \$750/year. Expect to pay more for a nicer plane or if you have less experience. Note: get a commercial license; it will pay for itself in reduced insurance in the long run.

I think gas will typically run \$5-6/gallon, depending on a lot of factors. My Mooney burns around 9.5gph, and flies 142 kts so it's really economical in that respect (and the main reason I don't upgrade).

Light twins are cheap to buy, but that's because their cost of ownership is through the roof. A low-time pilot can expect to pay \$12,000/year for insurance and the annual inspection will also be a back-breaker.

I used to have money. Now I have an airplane.


Why does the Beech Staggerwing have its low wing ahead of the high wing?

Notice the retractable landing gear? With a tail-wheel design, the main gear work best at or ahead of the center of gravity. The Staggerwing has a neat and efficient retractable main gear, that folds onto the lower wing. But the lower wing has to be farther forward than usual for this to work.

The two wings on a biplane interfere with each other, but the biplane structure is very strong and stiff for its weight. So the Staggerwing's design gives up some wing efficiency for strength and light weight. Then it gives-up a little more for the reverse stagger that puts the downwash of the lower wing right under what should be the high pressure under the upper wing.

However, the design gets good speed from the retractable gear reducing drag. And both wings, upper and lower, join the fuselage at 90 degrees, with no struts or other sources of drag. Aerodynamically, a very clean design. the Beech Bonanza looked more modern, but the Staggerwing had the same cruising speed, 176 knots, 202 mph. It also had a 450 hp P&W Wasp Junior, while the Bonanza got along with a 300 hp Continental.


Is a fixed wing more efficient in reaching a certain altitude than rotary wing?

A helicopter in forward flight is more efficient than a helicopter in vertical hover, due to less induced drag (and more form drag which becomes a problem at high fwd speed).

Fixed wing aircraft are more efficient than forward flying helicopters because:

The rotor flow in forward flight causes fearsomely complex aerodynamic interactions in flow with the fuselage and other components, which causes a particular type of drag that a fixed wing simply does not have.
When the helicopter is in forward flight, the rotor disk has the same characteristics as a fixed wing: less induced drag, higher form drag. But it will be a circular wing, which is always less efficient than a beautiful slender fixed wing. The slenderer (is that a word?) the better.


My best guess for the text below BÜLOW is "Deutsche Flugzeug Werke (newline) Leipzig".

Having three pairs of struts on each wing would make it a DFW B.I, C.I or C.II, as later models only had two pairs of them.

The small gap between the wings matches the photo too.

While some prototypes got a machine gun, the standard version of the DFW B.I was unarmed.

According to the book "German Aircraft of the First World War" (Peter Gray & Owen Thetford) the only difference between the C.I and C.II version is the position of the pilot (C.I: pilot in rear seat). Another source mentions the change of the machine gun from Parabellum to a synchronized one. A synchronization gear only makes sense attached to a fixed machine gun below the upper wing.

With a gun over the upper wing and assuming that Bülow is sitting in the pilot's seat, I'd say that the airplane is a DFW C.I.


How can an altimetry system error during cruise (500 ft at 35000 ft high) cause an insufficient fuel situation?

If the aircraft is cruising at FL350 it is operating in Reduced Vertical Separation Minima (RVSM) airspace (between FL290 and FL410).

With an altimetry discrepancy between the two altimeters of more than 245ft, the aircraft is no longer RVSM approved. It shall therefore descent or climb out of the RVSM altitude block.

For the Airbus A321 the operating ceiling is below FL410, so the only option is to descent to FL280 or below. Since the fuel consumption in those altitudes is significantly higher the aircraft is unlikely to complete its 6 hour flight with the amount of fuel on board. Therefore the decision to return is likely the right one.


How are evolution and variants of aircraft considered by certification authorities?

Variants are seen as a modification of an existing airplane design, and only the changed parts need to be certified. The real advantage is that the set of rules the certification has to comply with are frozen at the time of the initial application, so any additional rules that had been added later are not relevant. This is called "grandfather rules".

This definitely lightens the certification process and makes it less complex, but makes the safety enhancements, which were added after the type was certified first, optional for newly built airplanes.

The A318, A319 and A321 are all variants of the original A320, and the subtypes you name differ in their engine. Each engine option has to be certified separately, but all certification work not related to the engine can be shared between the variants. Additionally, the purchaser will select his options for instrumentation and furnishing, chosen from a limited set of previously certified options.

When a new version is introduced, the public will get a very different message from the airplane maker than the certification authorities. For the PR, the new variant is all new, but the FAA and the EASA will hear that almost nothing changed. In the end, it is similar to corporate profits: The shareholders get told the company made oodles of money, while the tax authorities will be presented with a bleak picture of mainly losses.


Exactly where can a stowaway hide in a wheel well?

For the 737, I think this rather sad photo provides one answer:

(Source)

  The body of a stowaway was found in a Kenya Airways flight from Kinshasa in the DRC on Sunday.
  The body was found after the plane landed at the JKIA, preliminary reports indicating the person froze to death.

And, as you can see in this photo, the ledge there (on the left forward side of the main wheel well) is indeed just wide enough for a slim person to contort themselves into:

(Source)

But, as you can see at the end of this video, there certainly isn't a lot of room for the stowaway's legs.


How do the airlines allot the passengers seats to make sure the balance is maintained?

It depends on the specific limitations of the aircraft and the flight booking load. If the flight is full, it not really an issue. Typically the check-in system will automatically distribute passengers throughout the cabin, starting from the front and moving backwards. Load planners may block rows during check-in if the flight is so empty the center of gravity will be exceeded, unless passengers sit in certain sections of the aircraft.


Why aren't contra-rotors used on the V-22 Osprey?

Instead of having a set of contra-rotating proprotors on each side, if you're after decreasing the disk loading, a span increase would also do the trick, allowing wider proprotors. However the Wikipedia paragraph starts by saying:

  Due to the requirement for folding rotors...

The main contributor to its less-than-ideal size is the folding requirement to save parking space aboard ships, since the primary operators are the US Navy and the USMC.

Adding another set of rotors or increasing the span won't help:

(Source)


Could a plane be constructed to be fly in fixed-stick roll-stable circles?

This will become another of my long posts; after all, lateral stability is more complex than longitudinal stability and involves many more factors. Short answer: It is possible, but not by aerodynamic means, and would incur a drag penalty.

Starting condition

Assume we have an aircraft with fixed controls, trimmed for straight flight, and make it a glider to remove propulsion effects. Next, let it fly through an asymmetric gust which lifts one wing. For what follows we assume calm air again.

Initial sideslip

For an outside, earth-fixed observer, a component of lift is pointing sideways and not compensated by weight, so the aircraft will accelerate to that side. From the point of view of the aircraft, lift is still acting in the plane of symmetry, but gravity does not and will cause it to sideslip. This will mainly evoke these reactions:

Directional stability $c_{n\beta}$: The aircraft will yaw into the wind because the vertical tail will create a side force ("weathervane effect").
Dihedral effect $c_{l\beta}$: The additional lift on the windward wing will lift this wing. Also, the additional side force on the vertical tail, which yaws the aircraft, will cause a supporting rolling moment. Roll damping ($c_{lp}$) will limit the amount by which the aircraft rights itself up, however.
Yaw moment due to dihedral and wing sweep: The lift difference due to dihedral and wing sweep will retard the upwind wing, causing a yawing motion into the wind. This effect can be added to the directional stability $c_{n\beta}$.

Eventual (almost) coordinated turn

The aircraft will start to fly a coordinated turn, because all forces try to drive sideslip to almost zero, and on their way to do so start a yawing motion. In contrast to that, the roll angle will not change further once sideslip stops, because the sideslip-induced rolling moments stop as well. However, if a roll angle remains, the aircraft will now begin to turn. This opens up a new bunch of effects, because  now we have asymmetric flow: Due to the yawing motion, airspeed varies over wingspan and sideslip angle varies over length:

Rolling moment due to yawing motion $c_{lr}$: The outer wing (which was the leeward wing during sideslip before) now travels faster, creating more lift. This causes a rolling moment which increases roll angle.
Since the angle of attack would be the same in a coordinated turn over the whole wingspan, drag will behave proportional to lift and increase with the local turn radius. This drag difference will create a small yawing moment which will let the inner wing advance, until the dihedral effect will kick in and create enough of a difference in angle of attack that the drag on the inner and on the outer wing are equal again. Since induced drag is proportional to the square of the lift coefficient, the wing will still create less lift on the inner wing than on the outer wing, but the difference will be reduced. If the airplane climbs or descends during the turn, angle of attack will vary over span and will create an uprighting moment on the descending airplane (and vice versa).
Yawing moment due to yawing motion $c_{nr}$: This is also called yaw damping and creates a yawing moment opposed to the yawing motion. Contributing factors are the vertical tail which sees a sideward flow component due to the yawing motion, and the drag distribution along the wingspan. Aircraft with a long tail have high yaw damping and, in combination with plenty of dihedral, tend to be more roll stable than short-tailed aircraft. Here the long tail forces the wing into a sideslip which uprights the aircraft. This configuration is found on free-flying models which do indeed upright themselves from shallow banks.
Centrifugal forces: The sideward component of lift is now balanced by the centrifugal force due to the turn. However, the centrifugal forces also will create an uprighting rolling moment which depends on the spanwise distribution of masses.

Note that the outer wing has a bigger turn radius $R$, but the same angular velocity $\omega$ as the rest of the airplane. This causes it to experience more centrifugal force $m\cdot \omega^2\cdot R$ than the inner wing (symbolized by the length of the parallel arrows). I used a rather steep attitude to get the point across, but the same holds true at shallower bank angles. This is the uprighting inertial moment.

Depending on the relative size of these effects, the aircraft will either right itself up, stay at this roll angle or dive ever deeper into the turn. Agile aircraft with low roll inertia will have too little uprighting moment and are likely to spiral dive. More stable configurations with big vertical tails and ample of dihedral will either continue to turn gently or right themselves up.

Effects at non-zero roll rates

Now this was all done under the assumption that the roll angle changes very slowly. A too small vertical tail and/or too much dihedral will excite the Dutch roll motion, and now the roll angle oscillates, adding more roll-induced effects. To keep this answer reasonably short, I will not list them here.

Sweptback configurations optimized for fast flight (= with small vertical tails close to the wing) are typical examples where the ratio $\dfrac{c_{l\beta}}{c_{n\beta}}$ is too high and the Dutch roll eigenmode has too little damping. Free flying model aircraft, on the other hand, cannot afford to fall into a spiral dive, and by giving them big vertical tails and long lever arms, which allows them to have substantial dihedral, and a high radius of roll inertia, they can be made to upright themselves.


Are there any IFR-certificated and equipped aerobatic aircraft?

Yes: Consider the Zlin Z 242. The type certificate shows that it is certified in the Acrobatic, Utility, and Normal categories. In the section for Optional Equipment, the aircraft can be sold with

  Communication and navigation equipment VFR DAY, VFR NIGHT OR IFR according to actual requirements of the customers

Generally, if the aircraft meets the minimum equipment requirements and inspections, and the POH, Type Certificate or other manufacturer's documents allow it, an aircraft may be flown IFR in IMC.

There would be no particular limitation on operations specifically because the aircraft is capable of aerobatics, but the pilot would still need to follow their clearance. This would significantly limit the benefit of the instrument certification. (Note that even if deviations in altitude and flight path were approved, aerobatics still wouldn't really be possible.)


In practical terms, no. If you wanted to save/recover the dumped fuel then you would have only two basic options: dump the fuel as usual and then recover it somehow from the air; or, pump the fuel in a controlled way into a container outside the aircraft.

The first option is probably impossible: how could you capture a huge cloud of fuel and fuel vapor mixed with the air? That would be like gathering water from clouds.

The second is theoretically possible, but for civil aviation at least it probably requires too much equipment and risk. You could pump the fuel into a drop tank then jettison it with a parachute for a soft landing. Or you could pump the fuel into another aircraft via a tube, in a kind of reverse air-to-air refuelling. Or if you're dumping fuel from a  helicopter (does that ever happen?) it could hover over a tank on the ground, pump out the fuel and then land.

But all of those suggestions are totally impractical (again, at least for civil aviation). Adding drop tanks or air-to-air hoses would add huge cost in materials and training and reduce the useful load of the aircraft significantly, all for a situation that rarely occurs. And for air-to-air pumping you would need an empty tanker aircraft to be available immediately, which is highly unlikely, plus there is the inherent danger of operating two aircraft very close together.

Since fuel dumping is an exceptional situation and many aircraft can't dump fuel anyway, it seems unlikely that investing in a recovery solution would be worthwhile.


What is the maximum (unloaded) range of the Beluga XL?

For an estimate, we can use the Brequet range equation:

$range = V\cdot t_f
= \frac{L}{D} \times I_{sp} \times \ln\left(\frac{W_i}{W_f}\right) $

with:

$V$: optimal velocity
$t_f$: flight time
$L$: lift
$D$: drag
$I_{sp}$:  propulsion efficiency
$W_i$: initial weight
$W_f$: final weight

Assuming the lift to drag ratio $\left(\frac{L}{D}\right)$ and the propulsion efficiency will stay constant, the range will depend on the ratio of initial and final weight.

$range = C \times \ln\left(\frac{W_i}{W_f}\right)$

In case the aircraft departs with the maximum payload, the weight is:

$W_i = W_{oe} + W_{payload} + W_{fuel} = W_{mto}$

$W_{oe}$: operating empty weight: 127 500 kgf
$W_{payload}$:  payload weight: 51 000 kgf
$W_{mto}$: maximum take-off weight: 227 000 kgf
$W_{fuel}$: fuel weight =  $W_{mto} - W_{payload}-W_{oe}$ = 48 500 kgf

The final weight at maximum range is then:
$W_f = W_{oe} + W_{payload}$

Filling in the numbers we find:

4000 km = $C \times \ln\left(\frac{\textrm{227 000}}{\textrm{127 500 + 51 000}}\right)$

That means $C \approx \textrm{16 640}$ for the Beluga XL.

If we now remove the payload and take-off with the same amount of fuel, we find:

$W_i$ = 176 000 kgf
$W_f$ = 127 500 kgf
$range \approx \textrm{16 640} \times \ln\left(\frac{\textrm{176 000}}{\textrm{127 500}}\right) \approx 5365$km

But that is just removing the payload without adding fuel. Of course we can now bring more fuel on board without exceeding the maximum take-off weight.

The fuel capacity of the Beluga XL is 73000 kg (source:Aircraft Characteristics
Airport And Maintenance Planning Beluga XL manual). This changes the numbers to:

$W_i$ = 200 500 kgf
$W_f$ = 127 500 kgf
$range \approx \textrm{16 640} \times \ln\left(\frac{\textrm{200 500}}{\textrm{127 500}}\right) \approx 7530$km

So the Beluga can fly approximately 7500 km when empty, enough to cross the Atlantic from Toulouse, even if there is normal headwind.


Why do helicopters have windows near the pedals?

These fall into a category known as vertical reference windows. They can be used for many purposes, but essentially, they allow us to gain a better spatial picture of the orientation of our aircraft, the skids, and anything that might be slung beneath the aircraft. As someone who has landed many helicopters on trailers, it is extremely helpful to be able to see through the floor when precisely placing the skids. Holding a pinnacle approach and hover is much easier to execute as well. Further, when you have something on a line, it makes it easier to keep it in view, especially when it is closer to the aircraft.


How much water is produced in jet exhaust?

According to Wikipedia Kerosene consists of molecules containing 10..16 C-atoms.
Assuming that the molecules are mainly Alkanes with formula $C_nH_{2n+2}$:

$C_{10}H_{22}$: 10 * 12g + 22g = 142g Alkane contains 22g H which burns to 22g + 11 * 16g = 198g $H_2O$
Ratio Water/Kerosene = 198/142 = ca. 1.39

$C_{16}H_{34}$: 16 * 12g + 34g = 226g Alkane contains 34g H which burns to 34g + 17 * 16g = 306g $H_2O$
Ratio Water/Kerosene = 306/226 = ca. 1.35

I.e. you get something between 1.35g and 1.39g Water per 1g Kerosene.

Comparison to Gasoline:
Main difference of Gasoline is that molecule chains are shorter (4-12 C-atoms).
I.e. H/C-ratio will be higher, i.e. Gasoline will yield more water per fuel than Kerosene.


Each manufacturer has its own conventions. For example, Airbus only use MSN (which is only unique per aircraft type). Boeing on the other hand uses both an MSN and "line number". Boeing's "line number" is unique per aircraft type (like Airbus's MSN) but the MSN is unique across all aircraft types.

Other manufacturers may or may not have the same conventions.


Do fly-by-wire fighter aircraft automatically reverse the direction of control surface deflections during a tailslide?

While the reversal of flight controls does happen, it is transient in nature, and in virtually all cases if you let the aircraft "fly" itself it will pitch down and recover.

Only aircraft with thrust to weight ratio of at least 1 to 1, and thrust vectoring of some sort if a jet, will be able to maintain the nose high attitude.

Prop aircraft are a different story as they essentially "hang" from the prop if the engine can develop enough power to do that.

Recovering from a tail slide is not like recovering from a stall or spin, you can't really use flight controls for anything until the aircraft develops enough airspeed for them to be effective, and in 100% of the times I have been in one, by that time the relative wind is normal and not reversed.

The exception is in prop aircraft where the prop wash against the rudder and elevator does provide some control effectiveness, but not reversed.


What is the rotor speed of an EC135/H135 helicopter?

The main rotor speed (100%) of the EC-135 is 395 RPM.


What factors determine magnitude and orientation of induced velocity at propeller blade?

Using Momentum theory (the french version known as Froude theory is much more detailed) and under several restricting assumption, we can find a relation between thrust ($T$), radius of the propeller ($S=\pi R^2$), flight speed ($V_0$) and induced velocity ($v_i$).
$T=\rho S(V_0+v_i)*2v_i$
A numerical example with $R=2.2m$, $\rho=1.225kg/m^3$ (air density in standard condition), $T=30'000N$ show the evolution of the induced velocity with respect to the flight speed.
$v_i$ as a function of flight speed $V_0$" />
As you can see the induced velocity is decreasing with flight speed. As we are designing propeller blades to be efficient at cruise speed, the induced velocity becomes in fact quite negligible when you are calculating the ideal twist of your blade.
On the other hand if you want to calculate the thrust available at takeoff you need to take the induced velocity into account as it will greatly decrease your propeller efficiency.
As for the orientation of the induced velocity, it has two component axial ($Uind$) and rotational ($U\phi ind$) velocity that are created by the propeller as clearly shown in your second picture. Therefore it is not exactly parallel to $V_0$. The rotational component is a direct energy loss and is therefore minimized during design phases. In the Froude theory there is an assumption saying it is equals to 0.


Basically, the faster you go, the more lift and drag a wing will produce. These two values are not proportional, though. When speeding up, the amount of drag produced is higher than the extra amount of lift - which is why you need additional power to maintain level at higher speeds.

When you go slower, the amount of drag will reduce more than the amount of lift produced - at least for a while. That's why going slow is better in terms of gliding distance. The amount of "drag per lift" is very low. However, slowing down beyond a certain point, the wing will rapidly start producing less lift, because airflow separates from the wing. This is what's known as a stall. The best glide speed is the speed as which the drag is as low as possible while the wing is still producing a relatively large amount of lift.

This is illustrated on a speed polar, like this one:

The black line indicates the rate of sink for a given airspeed. The optimum glide speed is the speed corresponding to the point where the red line touches the black line (Vbg).

The red line is a straight line going from (0,0) and touching the speed polar at exactly one point.

A change in aircraft mass will shift the curve along the vertical axis, which is why a heavier aircraft has a higher best glide speed than a lighter one. The intersecting point between the black and red line would shift to the right as the black line is shifted down, and vice versa.


How were bullets fired through the propeller in the Focke Wulf 190?

Note: See Peter Kämpf's answer for specifically how the Fw 190 Achieved this Electronically
This answer is specific to how this was achieved via mechanical means in earlier aircraft and not specific to the Fw 190.
It's called a "Synchronization Gear" and it allows the gun to fire only when the blade is not in front of the barrel.

Source: Kaiserliches Patentampt (Imperial German patent Office) / Franz Schneider - Patentschrift No. 276396, 1913 First published in Flugsport" (1914) and in many places since, Public Domain,

[From Wikipedia] Interestingly, the linkage between the propeller and the gun is achieved with a spinning drive shaft rather than a reciprocating rod. The impulses needed to operate the trigger, or in this case to prevent the trigger from operating, were produced by a cam wheel with two lobes at 180° apart situated at the gun itself, since the gun is interrupted by both blades of the propeller.

These have been around since before 1920, long before the aircraft you mention in your original post.
The one on the Fokker (not Focke-Wulff, but still German) differs a little bit from the patent image above:

Source: By Gsl - Version with English text of Image:Interrupter_gear_diagram.png, Public Domain
But not significantly, the basic idea is that the trigger mechanism follows a cam lobe which is tied to the propeller shaft. When the cam lobe spins, the trigger is allowed to fire the gun only when the propeller isn't "in the way".
See Wikipedia Article on the Synchronization Gear for more information.


Is there a button that pilots push to transmit on the radio?

There is a push to talk (PTT) button located at the yoke or sidestick, in small and large aircraft likewise. When the PTT button is not triggered, all communication is routed through the intercom and not broadcasted on the frequency. Once the button is triggered, communication is broadcasted on the active frequency.

In the below picture of a glider, it is located on top of the middle stick.
On the second picture is it behind the yoke, to be used with the index finger.

(Image Source: WikiPedia)

(Image Source: Private Blog)


Who was the first black person (in the world) to go airborne in an aircraft?

The earliest example I could find is Emory Malick, a African American Aviator who received his pilots license in 1912 but stopped flying after a series of crashes. For the first pilot with a major career, every source I could find points to Eugene Bullard, an American who studied in France and fought in WWI, receiving his license in 1917.

Specific searches to look for British, German, or Italian pilots of African descent came up with nothing from that time period, so I think it's fairly safe to say that these two were the first.

Outside of the US, Ahmet Ali Çelikten flew for the Ottoman Empire beginning in 1914, and is widely regarded as the second black pilot following Malick.

As for passengers, I doubt you'll find much unless logs from the time included race on tickets for aviation.


Why have helicopter top speeds not increased much over time?

The underlying limit is that the forward-moving blade tip must remain subsonic, and the receding blade must not stall.  Hybrids do better than conventional or compound helicopters because the rotor can be slowed when the fixed wing picks up some of the lift load -- but this only solves the forward blade tip speed issue; unless the rotor can be operated at zero lift, receding blade stall is still a problem.

Some futuristic designs have proposed completely halting the rotor in forward flight (see the aircraft in the movie The Sixth Day with Arnold Schwarzenegger -- cheesy movie, but the aircraft were based on a real concept), using an airfoil shape for the rotor blades that can develop lift with either edge forward.  Others have proposed completely folding the rotor once forward speed is high enough for the fixed wing to support the craft -- but as far as I know, no flying example of either of these concepts has been built.  Until they are, the same speed limitations apply to helicopters and autogyros that were discovered in the 1930s, only partially mitigated by hybrid configurations.

Bottom line is, a helicopter's niche is in going slow, not going fast.  Other VTOL solutions exist for high speed (thrust-hover jets like the Super Harrier and F35 are supersonic).  Attack and high-rate maneuverability in hover are the special domain of choppers; high forward speed is not.


What causes the phase to change in a VOR?

The latest decades VOR are Doppler VOR (DVOR) where the bearing signal is produced by a 14 m diameter circular array of fixed Alford loops antennas. An additional central antenna radiates the reference signal.

Thales Doppler VOR 432, source
DVOR is an improvement of the conventional VOR (CVOR) where the bearing signal is encoded by frequency modulation, more reliable than amplitude modulation used in the CVOR. FM is not produced in the station itself, it is a Doppler artifact created by the apparent displacement of the bearing signal source relatively to the receiver.
DVOR principle
The so-called dual sideband DVOR uses one pair of diametrically opposed antennas from the array at a time, switching to the next pair counter-clockwise at the angular speed of 30 revolutions per second (30 Hz, 1,800 rpm).

One antenna radiates an unmodulated signal at $\small f - 9.96$ kHz ($\small f$ being the frequency of the VOR)

The opposite one radiates at $\small f + 9.96$ kHz.

The receiver sees the two constant frequency sources moving along the circle, one approaching, one moving away. Because they move relatively to the receiver, their frequency is altered by a Doppler shift proportional to the relative velocity.

Doppler shift on the DVOR sidebands antennas
For the receiver, the observed signal frequency is increased for the approaching antenna and decreased for the retreating antenna. By chance for engineers, the Doppler shift applies in opposite quantity on the antennas, and the frequency remains mirrored relatively to the carrier frequency $\small f$ whatever the shift.
At the same time the central antenna radiates a carrier at frequency $\small f$, modulated in AM by the reference signal. This AM signal is not subject to the Doppler shift, as the signal source is fixed.
For the receiver the signal from the central antenna and the two signals from the rotating antennas appear as the three components of single HF signal of frequency $\small f$, modulated in amplitude at 30 Hz (by the reference) and a subcarrier at 9.96 kHz, itself modulated in frequency at 30 Hz (by the variable signal). This signal is therefore entirely compatible with one from a CVOR.
The Doppler shift depends only on the receiver relative bearing
While the timing of the reference is imposed by the VOR, the timing of the subcarrier modulation depends entirely on the aircraft position. E.g. the Doppler shift is null when the axis of the antenna pair is aligned with the aircraft direction, and both antennas move only from left to right from a receiver standpoint:

Doppler shift is null when the receiver is aligned with both antennas</sup
Similarly, and when the distance of the receiver is large compared to the array diameter, the maximum shift is observed when the antenna pair is perpendicular to the previous position (in practical the parallax error can be ignored).
Therefore the delay between the reference and the variable signal is representative of the bearing. Periodic signal phases are actually angles between 0 and 360°, so the bearing is determined at any time by subtracting the current phase of the FM variable signal from the current phase of the AM reference using a phase detector.

Phase of a sine signal
Note the receiver works only by comparison of the phases, their actual values is irrelevant, only the difference is meaningful. If that were not the case, the DVOR wouldn't be compatible with a CVOR receiver.
The CVOR also relies on the phase difference. It works by forming a rotating directional cardioid pattern by space modulation. The result of this modulation faces north when the variable signal which electronically steers the pattern has the value 135°. So the reference was aligned on this value and given the value of 135° for north (in the DVOR north is associated with the reference value 0°).
The diameter of the array gives the variable signal phase its correct value
The tangential velocity when moving along the perimeter of a circle is $\small v = \pi d \times rpm$. Applied to our array: $\small v = \pi \times 14 \times 30 \approx 1,320$. The relative tangential velocity of the sideband antennas is between -1,320 m/s and +1,320 m/s. The value of the Doppler shift for a given velocity is: $\small s = v \cdot f / c$. Applied to a frequency of 110 MHz, the Doppler shift is $\small 1.32e3 \times 1.1e8 / 3e11 = 484$, that is between about -484 Hz and +484 Hz. The exact diameter of the array is actually a bit less, in order to obtain the FM swing of the conventional VOR (480 Hz). This way the DVOR signal can be received by a CVOR receiver (there is no specific DVOR receiver).
As explained earlier, this shift is not encoded by the VOR into the variable signal but added by the Doppler effect in space. However the receiver sees the result and interprets it has if it had been generated by the VOR.
When the never modulated FM subcarrier is nevertheless processed by the receiver demodulator, it produces a 30 Hz sine which phase varies according to the Doppler shift which produced it, therefore depending on the correct diameter of the array.
VOR frequency spectrum
The receiver sees:

A signal at frequency $\small f$, AM modulated by the 30 Hz reference

A signal at $\small f - 9.96$ kHz, FM modulated by a 30 Hz sine (1,800 rpm).

A signal at $\small f + 9.96$ kHz, FM modulated by a 30 Hz sine but with the opposite shift.

It just decides those three signals are components of a single one from a single antenna: The first signal is the carrier, and the two other are sidebands.
It composites the whole thing this way:

This is a carrier of frequency $\small f$, modulated in AM by a 30 Hz signal (reference),

This carrier is also AM modulated by a subcarrier at 9.96 kHz.

The subcarrier is itself FM modulated by a 30 Hz signal (variable) with a modulation swing of 480 Hz.

VOR signal spectrum


What options are there to learning IFR flying on Garmin's G1000 (Cirrus Perspective)?

You can get books on the subject, but one of the best ways to learn the G1000 is practice.  Fortunately, Garmin sells a G1000 simulator which can be installed on your computer and replicates all of the G1000’s capabilities.  Along with a joystick and throttle you can plan and execute flight, fly approaches, and practice anything else on your PC.  They are available in a variety of G1000 setups, including the Cirrus Perspective.  Cost is $25.

https://buy.garmin.com/en-US/US/p/35045


Has this Google Maps imagery of 4 planes on a runway been tampered with?

Google Maps and Google Earth are made by stitching together many different images to create the illusion of a single massive picture of the globe.

The image you are seeing was almost certainly made by an aerial photography plane passing overhead of another plane landing.  In multiple snapshots, it captured the same plane on final, touching down, rolling out and stopping.

The images were assembled together to line up the ground and all static elements.  But items that are moving appear multiple times in different images.


How could I find the air velocity and lift force?

The indicated airspeed is the result of computation using basically the static pressure from the static pitot and the dynamic pressure from the dynamic pitot.
Further to apply your formula in addition to CL and the density, you need to know the active area S of the wings which at high speeds may depend on the speed itself, so you need the wings specific data.


Can a plane fly without the Vertical Stabilizer?

The plane will probably crash.

The vertical stabilizer provides stability in yaw to conventional aircraft. Aircraft such as the B-2 manage to provide stability through computer control, and aircraft such as the Northrop flying wings are designed to fly without one. But if an aircraft designed to be stable using a vertical stabilizer loses that surface, it will be very difficult for pilots to stabilize manually with the remaining systems. While roll and differential thrust will both affect yaw, they will both be slower to react than a rudder, especially in a large aircraft like an A380. This can also damage the hydraulic systems, making it more difficult to control the remaining surfaces.

If experienced test pilots are at the controls (as in the B-52 incident below), or if the failure is anticipated and trained for, it's possible that the aircraft would be controllable enough to land safely. However, as the incidents below show, this kind of failure does not happen often, and can easily exceed the crew's ability to control the plane.

Examples where this has happened:

Japan Airlines Flight 123 lost most of its vertical stabilizer when the rear pressure bulkhead failed. Despite also losing hydraulic systems, the pilots managed to keep the plane in the air for a while, but ended up crashing into a mountain.

American Airlines Flight 587 lost its vertical stabilizer when the pilot's rudder inputs over-stressed the structure. It crashed shortly after.

In 1964, a B-52 lost most of its vertical stabilizer due to extreme turbulence. The pilots were able to extend air brakes on the wing tips to provide some stability. The Air Force sent up a chase plane to help guide the pilots, and provided engineering guidance from the ground. The crew were able to bring the plane back for a safe landing (see a video). There were at least three other instances where the vertical stabilizer failed on B-52's, all ending with the loss of the plane. This particular flight was conducted with test pilots to intentionally fly through turbulence, recording data to help understand the failures on the other aircraft. However, the flight encountered unexpectedly severe turbulence, leading to the separation of the vertical stabilizer.


Why is an unpressurized takeoff performed?

Typically, the pressurization system is run by engine bleed air. Using that bleed air means you have less engine power available than is maximally available with the bleeds off. If you're on a runway that requires all your power, you do a no-bleeds takeoff, which means you have no pressurization. Shortly after takeoff you would turn the bleeds on.


Will occupants usually survive a decent autorotation?

If the pilot flubs the flare and landing, the result is frequently survivable.  The reason is that even a flubbed autorotation will reduce the vertical speed.

Student and instructor walked away from this one:

http://www.nydailynews.com/news/national/helicopter-crashes-westchester-county-airport-article-1.1560222


Why use different data bus for civil and military avionics?

There is actually quite a lot of difference between ARINC-429 and MIL-STD-1553.  They are different because they were developed by two different groups with different needs.

Both started in the 1970's. Before then there was almost no digital data of any kind on a an aircraft.  It was almost all analog or discrete. The biggest issue was noise and interference of the signals. The introduction of microprocessors in the early 70's opened up the option for reasonably priced digital bus technology.

The MIL-STD-1553 bus was a major component of the F-16. Like most military programs, this was a push for maximum performance. ARINC-429 came out of the Boeing 757/767 development effort. Civilian aircraft certification doesn't like a lot of risk and the simpler bus architecture made it easier to design, analyze, and certify.

Since then there have been a number of new buses introduced into aviation. Some have lasted longer than others. B777 introduced ARINC-629 and Fibrechannel. B787 uses ARINC 664 for the main buses with a large mix of ARINC-429 and ARINC-825 (CAN bus) as well.  There are a number of data concentrators/converters on the aircraft to get data where it needs to go.

The primary reason for moving away from ARINC-429 is that it is a single transmitter/multiple receiver architecture. This results in a large amount of physical wire. That adds weight and requires maintenance. A bus such as ARINC-664, which is based on Ethernet, can significantly reduce wire. The down side is that it costs a lot more and isn't very efficient when all you need is a small, low rate connection to an odd corner of the aircraft.  So you end up with a mix of buses.

And B787 opted for fiber optic cable for the ARINC-664 network to reduce interference from high-intensity radio frequency (HIRF) and lightning.

MIL-STD-1553 is a powerful bus, but it's not as good a fit as many of the newer buses available in the commercial market. The military keeps using it because they have a huge installed base of equipment, it's flexible enough to support their newer functional needs, and commonality reduces their logistics costs.

ARINC-429 sticks around because it's cheap and it has its own large installed base as well.


Why are most runways made of asphalt and not concrete?

Frankfurt Airport; a mosaic of concrete and asphalt

The runways at Frankfurt Airport are asphalt (old satellite imagery shows that they were concrete before), and the airport handles plenty of Superjumbos, the Airbus A380, so it's not a matter of handling heavy planes. All runways in big airports, even those covered in asphalt, have reinforced concrete foundations that vary in depth. They're deepest where the touchdown zones are located, shallower elsewhere. That's why runway extensions usually just add extra takeoff distance, but the landing zones remain the same, creating a displaced threshold.

Displaced threshold; can exist for other reasons

Zoom in

You'll see almost all the parking spots and holding areas for the runways are concrete, as well as the runway exits. This is where a plane is expected to be stationary. Concrete handles such stationary loads pretty well, while on a warm day the asphalt would deform.

Asphalt is called a flexible surface; concrete is called a rigid surface. Pavement classification number (PCN) is a standard used in combination with the aircraft classification number (ACN) to indicate the strength of a runway, taxiway, or apron (ramp).

Exposed concrete is notorious for cracking when exposed to extreme high and low temperatures. It's also more expensive to install and repair. But overall can be cheaper to install if you're already laying down concrete elsewhere, like most new airports, they just go for concrete everywhere, but it depends on where that new airport is located—

Hot Dubai; asphalt almost everywhere except parking areas and hold short areas

LAX; good climate and budget; concrete almost everywhere a plane touches

The variables come down to climate, use, load, budget, job creation, maintenance, etc.

A single runway (like at PBG) can also have both surfaces

Airport diagram showing the PCN for all runways; Flexible and Rigid

(NASA) Another point in favor of an asphalt runway, is that it's more gentle on the tires during touchdown (since it's flexible).

You can find runway data at airnav.com for US airports, elsewhere you'll need to check the airport's AIP, like this one for Amsterdam; check the section 2.12 RUNWAY PHYSICAL CHARACTERISTICS. Or try searching for a nonofficial runway data repository, there could be one.


What are the meanings of those SFO Taxiway Marking?

For 1, what is slightly harder to see is that the line which runs parallel with the taxiway is a double line. This denotes the taxiway edge and the thicker lines running perpendicular to the double lines shows which side of the taxiway edge isnt suitable taxiway. They are often coloured differently too, and in SFO case the unusable part of the ramp is green.

The pink circles with black text are geographic position markings, and are used by the airports Surface Movement Guidance Control System (SMGCS) in low visibility.

The white numbers in blue squares are not are not mentioned in the FAA Standards for Airport Markings but I suspect thy might have something to do with the skybridges.


How do blow holes compare to other means of tripping the boundary layer?

In modern gliders, active tripping of the laminar boundary layer helps to reduce or avoid a laminar separation bubble. There are three ways of doing this:

Noppenband (dimple tape):

Close-up picture of a spool of Noppenband (picture source)

Zig-Zag-tape:

Spool of zig-zag tape (picture source)

Blowhole tripping: a line of tiny holes (0.8 mm diameter, usually with a steel liner) along the span which are fed by dynamic pressure, usually created from a small scoop or a NACA inlet (sorry, no picture). Note that while you can add the first two turbulator types at any time, blowhole tripping must be designed into the wing from the start by placing a duct inside and adding the scoop.

The order in which they are listed is no accident: Robustness decreases and effort for production increases as you move down the list. The pimples are like bugs and trip the boundary layer directly. This is fine if you fly at one angle of attack and one speed only, because then the chordwise location of the separation is fixed. Just place the Noppenband 2-3% of chord ahead of the separation point and it will effectively avoid laminar flow separation by tripping the boundary layer.

If you vary both speed and angle of attack, the location of the laminar separation bubble on the upper surface will vary over a wide distance. If you try to optimise the transition for slow flight (= low Reynolds numbers and high angle of attack), you need to place the turbulator tens of percent ahead of where it would be best placed for fast flight, thus adding a lot of unnecessary turbulent boundary layer when friction drag counts most.

On the lower side of the airfoil, the effects of Reynolds number and angle of attack work against each other, and the separation bubble changes its position only slightly over the speed range of the glider. Now it makes sense to actively trip the boundary layer, but you still get some additional turbulent length when using Noppenband.

Zig-Zag tape will merely prepare the boundary layer for transition, so laminar flow continues for a few percent downstream until the local pressure gradient does the tripping. Now the variation in the separation point will not result in extra turbulent length. Normally, Zig-Zag tape is placed 2% ahead of where Noppenband would go for best effect.

Blowhole turbulators can even be placed inside the laminar separation bubble and will destroy it when positioned a few percent past the actual separation line. By blowing into the eddies of the separated flow, the tripping will alter the pressure distribution such that the laminar bubble is either much smaller or even disappears altogether. Now the turbulator can be placed further back and will add even less extra turbulent boundary layer.

With blowing also the upper separation bubble could be avoided if several rows of holes are placed along the span and the pilot can control to which one the airflow from the scoop is directed. To my knowledge, this has never been used in real life, though.


Aircraft Carrier Launches: ABE Checks and Signals

I'll take a stab at this.  It's been many years, but I was a shooter (yellow vest, green helmet).  Someone with a better memory can chime in.

You're correct that one of the hook-up operators is under instruction (U/I).  There are also 2 shooters in this video; one of them is under instruction as well.  Sometimes the instructor will give a thumbs up to indicate that the U/I operator's signals are correct and should be obeyed.

Before 0:27 they are looking toward the "island" for a green beacon that indicates the Air Boss is ready for the crew to launch planes.  At 0:27 they see the beacon turn green, then they look to the shooter for the hook-up signal.  The shooter is checking for several things: green beacon on, deck clear forward, jet blast deflector (JBD) raised, nobody on the wrong side of the foul-deck line, proper aircraft configuration (flaps down, tailhook up, etc), wind speed hasn't dropped since the catapult steam setting was entered, and thumbs up from the squadron QA folks (white shirts, behind aircraft on both sides) who are watching the jet for proper functioning, no leaks, etc.  When all those conditions are met, the shooter gives the hook-up signal, which triggers the hook-up operator to call for the jet to taxi forward.  The yellow-shirt (ABH) receives the "rolling" signal from the hook-up operator, then signals the pilot to pull forward, which causes the tow bar to drop down in front of the shuttle.
I think they are checking for a thumbs-up from the center-deck operator (sitting in the hole next to the shooter; thumbs up indicates good catapult steam pressure and good wind over the deck, which the shooter is no longer monitoring).  They also may be looking at some of the same things the shooter is looking at.
The holdback bar needs to be properly set in its slot in the deck, properly attached to the aircraft, not leaking hydraulic fluid, and IIRC there's a shiny metal ring between the orange and white sections that indicates proper functioning and tension.
The deck edge turns his whole body so everyone can see that he's looking fore and aft for clear deck forward and JBD up, and maybe also so he can see past his arms which are raised so that everyone can see he's not pushing the launch button yet.  At this point the shooter hasn't been looking forward because he has been mainly focused on the pilot and aircraft while the engine is running up and the pilot goes through flight-control checks, salute, etc.

Additional comments: most of the time the shooter and center-deck operator are below decks inside the glass "bubble" but they do practice deck launches to stay proficient.  I did my shooting on an older ship that didn't have the bubble at all.  Needless to say, communication is purely visual because you can't hear anything.  Even the operators with radio or phone headsets can't hear anything when jet engines are blasting nearby.

Finally, if you think this looks complicated and dangerous, remember this video was taken in daytime in good weather.


How is aircraft control positively transferred between pilot flying and pilot not-flying?

What you're quoting is the verbal portion of an important principle called Positive Exchange of Controls. This is a process of ensuring that someone (and only one) is always in control of the aircraft, and that there is no doubt about which pilot that is.

The best practice, taught to student pilots, is a three-stage handoff procedure:

  Pilot A: You have the flight controls.
  Pilot B: I have the flight controls.
  Pilot A: You have the flight controls.

Pilot A is the Pilot Flying before the handoff, and Pilot B is the Pilot Flying after the handoff. In an emergency situation like the above, the captain (Captain Sullenberger, HOT-1, in this transcript) is responsible for the safety of the aircraft, and can assign control as they determine is best. Skipping the first line of the handoff is a reasonable way of making this happen  quickly, while not giving up much in terms of clarity. The two-stage transfer also can happen whenever someone, generally more experienced or in a teaching role, wants to be in control of the aircraft. As DJClayworth points out, a CFI will commonly take the controls in this fashion if they wish to demonstrate a maneuver - no imminent danger required.

HOT-2 refers to the "hot microphone", or recorded feed from the pilots' headset mics, from the first officer. Any time there's a change in Pilot Flying (if the captain gets up to go to the bathroom, for example), the controls should be exchanged in a manner similar to what we see above. If the FO feels that they should have the controls, they can always ask. There is no standard procedure for refusing the exchange of controls, but generally, if the Pilot Flying does not reply to the request with something along the lines of "You have the controls", then the exchange is incomplete, and the role of Pilot Flying has not changed.


Where can I download the flight plan data around the world?

For historical FAA IFR flight plan data, you can get it from www.flightaware.com.  They show five minute delayed, and with a free registered account you can get access to the last 90 days worth of data.  You can pay for data older than that and I believe in different data formats.

I'm not aware of a similar source for other parts of the world.


Is there any way to relieve the Pilot in Command?

The regulatory bodies are reluctant in defining a regulation for that. Because there are first officers who do not hold an Airline Transport Pilot License. The airlines would need to add an extra flight member for that rare situation.

Instead, it's up to each airline's SOP when it comes to Crew Resource Management. There are various assertiveness training models, of which are PACE, and CUS.

Probe-Alert-Challenge-Emergency
Concerned-Uncomfortable-Safety

Facing battery depletion following an electrical failure, here's an example for what the last step of PACE could have been like on October 11, 1983:

  Captain, if you don't immediately reverse course and get back to night VFR conditions, I must take over control of the airplane. I cannot allow you to subject the passengers to such an unnecessary and high risk of certain death. Under these conditions, it is my duty and responsibility to relieve you of your command. (To Intervene or Not to Intervene? The Co-pilot's Catch 22)

Or, it can be much shorter when there's no time, such as asserting, "I have control," and pressing the TO/GA to initiate a go-around, for example.

Some airlines use only two steps, i.e., "I've mentioned my concern once, this will be the second and final time, else I'm taking command."


Can different airliners of the same type feel different to a pilot?

By "feel" I mean how the aircraft responds and behaves, as experienced subjectively by the pilot.

Yes, there are differences but they are generally small and might not be equally apparent to all pilots. That, of course, is a problem with "subjective differences."

However, I do remember a 747-200 that I flew that did have a distinctive difference from other -200s of the same configuration, and a difference that other pilots noticed.

"...when I pulled the power at 50 feet, the plane sunk like a rock....The captain later apologized for not warning me that this particular airplane (I hadn't been in it before) had a tendency to drop out of the sky when you pulled the power."

The quoted excerpts are from the third paragraph of https://terryliittschwager.com/Journal/1995-07-04.html.


Why has the folding wing option of the Boeing 777 never been ordered?

The folding wingtips are found mostly in naval aviation. The reason is the space constraint inside the hangar of the aircraft carrier.

"US Navy 070128-N-9712C-003 Aircraft fill the hanger bays on board USS Ronald Reagan (CVN 76) after recently embarking Carrier Air Wing One Four (CVW- 14)" by U.S. Navy Photo by Mass Communication Specialist 2nd Class John P. Curtis.

As can be seen from the photo, folding the wings offers the only practical way of fitting fighter aircraft inside the cramped hangar space. For example, the F/A-18C/D had a wing span of 11.43m; this was reduced to 8.38m with the wings folded, a 26% reduction.

However, the price to pay is an increase in complexity, weight, price and increased maintenance. The figure shows the wing folding mechanism of a F 18.

Source:polepositionimagery.com.au

The major drawbacks of folding wings are,

The increased weight and complexity due to the folding mechanism. The folding mechanism takes time to operate and there are safety concerns if they get stuck in a position.
The folding of wings limits the fuel capacity and as a result, the range of the aircraft, as fuel is usually not carried on the folding part of the wings.

Source: zarco-macross.wikidot.com

As can be seen, the F/A doesn't carry fuel in the folding part of the wing. In fact, after the airlines didn't take up its folding concept in 777, Boeing added fuel tanks to that area and increased range of the 777-200/300.

There has previously been no reason for airliners to fold their wings, as airports offered enough space for operations and ground movement. However, as the size of aircraft and their aspect ratios grow (to reduce drag), designers are finding it more and more difficult to keep the wingspan below the 80m 'box' which airlines believe is the maximum they can cope up economically.

The first major program to be affected by this limitation was the A380, which limited the wingspan of the aircraft to less than 80m and reduced its aspect ratio.

"Giant planes comparison" by Clem Tillier (clem AT tillier.net) - Original Work. Licensed under CC BY-SA 2.5 via Commons.

Basically, Boeing is facing the same problem. The proposed 777x is the largest-wingspan aircraft Boeing has ever produced. However, in the case of the A380, Airbus managed to reduce induced drag through the use of wingtip fences, among other design decisions. The 777x is expected to have a raked wingtip, which is not as space effective as the wingtip fence.

Source: Flightglobal.com

As a result, Boeing is considering folding wingtips. However, there are important differences between the original plan in 777 and the proposed plan in 777x.

In the original plan, Boeing proposed to fold 21' of the wingtip. However,the new plans call for folding only 10'.

Original Wing folding plan in Boeing 777. Source:www.seattletimes.com

Image:Boeing

As can be seen from the figure, the folding plan is much more modest. This is not expected to have the drawbacks associated with the the original plan, as,

The end of the wing will not house controls.
As the size of the wing to be folded is smaller, the folding mechanism will not be as heavy and complicated.
That part probably will not carry fuel.
Advances in actuation systems since the original 777 will reduce the weight penalty.

To put things into perspective, the 747-400's winglets were 6' feet tall.

Airlines have already placed orders for 777x and it is their operational record that will determine if other aviation manufacturers (Airbus, that is.) will follow suit.


What Transponder code to use flying between Oakland and Hawaii?

Whichever code is assigned to the individual flight by ATC. There isn't a fixed code to use for any one specific route. You might want to see: How does ATC know if you have been assigned a squawk or not?


The FC I used to belong to had it's own fuel trailer (custom-built with dual double-walled, insulated cryogenic 100-gallon tanks, a manually-operated fuel pump, a totalizer, a delivery hose and nozzle, and appropriate grounding cables.  Excluding the cost of the basic flat-bed trailer itself (one of the FC members loaned it to the club) we had less than $1500 invested in the outfit - including inspection and trailer licensing fees.

Considering we would be carrying 200 gallons of MOGAS on public highways we had to be VERY careful as to WHEN we were ON the highways (basically very late at night, and we drove on lightly-used roads/streets) - and we had to have insurance commensurate with the commodity we were carrying.  We used this trailer for several years - without any incident(s) - but, in the end, we all felt un-easy about doing so and eventually we abandoned the idea and reverted to using hand-carried gas cans.

The FC disbanded years ago and I don't know what ever happened to the fuel rig - I believe it went back to the FC member who built it in the first place (his materials costs and his labor bought him a club membership, whereas the rest of us had to ante up actual cash to help buy the airplane the FC bought.)

Ahhh, the good ol' days....


What should I know before getting the KAMRA laser eye surgery procedure as a pilot?

I'm not clear if you are asking about LASIK or KAMRA, the former is accepted by the FAA, while there is no explicit mention of the latter procedure.

The procedure site itself mentions halos as one of the side effects of the procedure:

  The KAMRA inlay procedure may cause blurred vision, difficulties with contrast sensitivity, problems with night vision, double vision, ghost images, glare, halos, and color disturbances.

In general, people with such adverse effects and complications are not allowed to serve as airmen:

  The FAA expects that airmen will not resume airman duties until ... there are no significant adverse effects or complications (such as halos, rings, haze, impaired night vision and glare), ...  and reviewed by an Examiner or AMCD.

The medical certificate for a person who had undergone such procedures is contingent upon the absense of any side effects affecting vision:

  An applicant treated with a refractive procedure may be issued a medical certificate by the Examiner if ... the applicant does not suffer sequela such as; glare intolerance, halos, rings, impaired night vision, or any other complications

It would be better if you consult a doctor to find out if the procedure is suitable for you and possibility of side effects.


Why don't the A380 and A350 have trim wheels?

(Source)

Both the A350 and A380 have alternate pitch trim control rocker aft of the flap lever in the cockpit to replace the pitch trim wheels near the throttle quadrant.

OPINION: I'd guess this was done simply in a continuous effort to improve the flight deck, reduce clutter and reduce weight. As a pilot myself, I’m not thrilled with it from a kinesthetic standpoint, as the wheel is much more natural to use.


Turbine blade manufacturing/assembly process

You'll have a hard time finding an exact answer, as that's unlikely to be public information, but here are some general trends:

In the case of the high pressure turbine, the blades are one of the key company jewels.  These are one of the highest technology pieces of the engine, and contributes a large part of the competitive advantage of one engine over another. Thus, this technology tends to be kept as a trade secret, and the parts are generally manufactured by the engine OEM themselves, and not outsourced.

For example, let's just say that tomorrow P&W discovered some new material that would increase EGT margin by 50 degrees.  That would give them a huge advantage over GE.  So they would want to keep it as closely guarded as possible.  If GE ever found out how to make that material, the competitive advantage is gone. So they want to keep all of the information as closely guarded as possible.  What's the best way to do that?  You make everything yourself.  If you outsource the manufacturing, then your material is out there in a place where you don't have control over it.  One or two blade might "walk away", and suddenly show up somewhere else.  You don't want that to happen.  So you keep it all in house.  In fact, you probably keep the information on a "need to know" basis.  I.e. the engineers who design the compressor or the fan aren't told the details of this new material.  They know it's there, and maybe some general information, but the details of how to make it aren't even widely known within the company.

Now that's for new engines. Ones that are actively being sold, where there is a competition, and customers are willing to pay a premium for performance.  Now consider on the other hand a very old engine.  Something like a CFM56-2, or a JT8D. That's ancient technology, so there's not really any competition on performance.  But there are still a lot them flying around, and they do need spare parts from time to time. The key driver for the spares market is going to be cost.  No one will pay a premium for performance here.  So you might see some of the manufacturing outsourced in this case.  You'll even see 3rd parties selling aftermarket parts for these engines (look up "PMA").


Why was the Electra uniquely vulnerable to whirl-mode flutter?

Flutter is a natural frequency resonance phenomenon.  Something is oscillating, and its oscillation, at some point, starts to match the natural frequency of the structure it's attached to, and a mutual input/feedback cycle starts that stores and returns the energy in such a way that it magnifies the initial input and away you go.

The outer wing was the saxophone... the engine nacelle was the reed.

The other airplanes?  Well, when you get down to it, fortunately they were just out of tune you might say, so they weren't affected.


What is the temperature of flap linkages during takeoff and landing in passenger and fighter aircraft?

Components like linkages on a wing flap system can be considered to be the local ambient temperature, subject to some lag if the plane is moving between large temperature changes, because of the time for the components to soak.
So a plane descending from 40000 ft after a cruise at that altitude may have components cold-soaked to ambient, say -40C, and if the airplane descends to 3000 ft to start an approach, where the temperature is +10C, by the time the airplane is at 3000 ft the components can be expected to be a bit cooler than ambient because of the lag time for the components to fully absorb the heat of the warmer lower temperatures.  How much lag would depend on a lot of factors, like the amount of exposure to the freestream, and things like heat being drawn toward cold fuel just ahead of the component.
This was a significant problem in fact on the CRJ200 program, because the screw jack flap actuators were sensitive to extreme cold and like to jam, and a good cold soak at high altitude followed by a quick descent and extension at low altitude, where it was still really cold down low (winter), could leave them still cold enough to have the system fail while still at zero.  There was a big AD related to it.


How are composite aircraft canopies constructed that sit flush with the fuselage?

That is a complicated process. You need:

A positive mold (mandrel) for the canopy.
A negative mold for the canopy frame. For a single prototype you can also use the unfinished fuselage itself.
A fuselage mold with a molded window sill.

First the fuselage positive mold core is built. From that the negative mold is taken, but also a negative mold only for the canopy area. From that negative mold the mandrel for canopy manufacture is built. If you have enough money, you can of course CNC mill the mandrel directly from a large block of aluminium.
The plexiglass canopy is deep-drawn over this mandrel by the canopy manufacturer, e.g. Mecaplex. There aren't many who get this process right!
Meanwhile, the window sill has been added to the fuselage mold and can be used for manufacturing the canopy frame mold. Once that is finished, the canopy frame is built by first lining the mold with diagonal weave fabric (glass or carbon, as you like) and filling the core of the frame with unidirectional rovings. Then another couple of diagonal weave layers is added on top. After removal from the mold the frame is trimmed and now the transparent part is added. The frame has a recess where the plexiglass fits in and the plexiglass is fixed to the frame with a special polyurethane adhesive. A couple of screws make sure it stays in the correct location.
To finish the canopy, the fittings are added and the frame is painted.


How is a type rating administered for aircraft that do not comply with 91.109?

The short of it is that most such ex-military aircraft, and replicas built new to spec on these designs, do not have a "type" as defined by the FAA at all. Because the absence of a type means the aircraft can't be certified as airworthy in the normal way, and pilots of these aircraft cannot receive a type rating to fly them, the certification of aircraft and pilot is a bit different.

The aircraft must first be issued an FAA "Special Airworthiness Certificate". This is essentially a slightly more rigorous form of airworthiness inspections for type-rated aircraft and virtually identical to that for experimental and/or home-built aircraft, resulting in the certification of the craft as airworthy in general even though it does not fall into a predefined aircraft type for which FAA instructors can issue type ratings.

The airman, because he can't be certified to fly a non-existent FAA aircraft type, must receive a special rating certification called a "Letter of Authorization", allowing the pilot to fly aircraft of a specific model, and/or a "set" of aircraft that have similar configuration, power, weight and other operational specifications and limits (but that aren't similar or common enough for a type rating). The training required for an LOA includes a combination of ground school and flight school containing information and in-flight training on the specific model to be authorized. But, when it is not possible or practical to do in-flight training in the exact model of aircraft to be authorized (usually because the aircraft in question is a single-seater with no two-seat configuration available), flight training in a "similar" aircraft can be a substitute. Pilots of vintage single-seat warplanes like P-51s typically get their flight training for the category in something similar to what military pilots of the day would have used, such as an AT-6. If the flight school just happens to have a Twin Mustang laying around, that would be even better, and also more directly applicable to multi-engine warbirds like the P-38.

Back to your example, say you get your hands on a "de-fanged" A-10 (which would require a ton of ballast weight to be added, literally; the GAU-8 weighs about as much as a Cadillac, but I digress). All flying examples are single-seaters; however, the avionics, especially of the original A-10A without the glass cockpit upgrade of the PEUP program, are comparable to any 70's-era jet trainer. So, you could receive flight training in a T-33, which is a trainer-compatible straight-wing turbojet with more similarities in its flight characteristics to the A-10 than differences. Coupled with ground instruction and/or simulator time on the specific systems of the A-10 (Which won't include any weapons integration, but honestly for the A-10A that was a single FLIR display and the arming/firing switches, and the C variant only upgraded that to a pair of MFDs; other than relative positioning, the flight instruments of the A-10 would be familiar to any PPL), you could be certified to fly your A-10 solo without any flight hours in an A-10 specifically.

The same might apply to aircraft that do have two-seater variants but where the flight school is unable to procure one. If you won the Powerball, and put a chunk of that money into your very own milsurp F-15C (\$38 million a pop back when they were being made and that's in late 1970s dollars), it's highly unlikely your local flight school would be willing to pony up for an F-15D two-seat configuration to train you on it (unless you bought the plane for them with another big chunk of your lottery winnings). They might, however, have a T-38 in their inventory or be able to loan one from the nearby naval air station, which would give you a primer into the capabilities of a multi-engine turbofan ex-military fighter. Honestly, though, if you wanted to fly an F-15, you'll probably want a two-seater, and your CPL, so you could give rides to paying customers and offset the cost of running this beast (typical fuel load without droptanks, 13,500 lbs which is about 1,985 gallons. With Jet A running about \$4.85/gallon, the cost of a fillup would be somewhere in the $10,000 neighborhood which would give you a cruising range of about 1,000 miles, so you could offer this as a special type of jet taxi).

Here's some more reading on the subject: FAA Flight Systems Information Management System - 8900.1 V5 Chapter 9 Sec 2 - Airman Qualification Requirements for Aircraft for Which the Operating Limitations Require an FAA‑issued Authorization to Act as Pilot in Command


Why are high-bypass turbofans faster than turboprops?

Tip speeds do not actually stay the same, turbofan (and turbojet) blade tip speeds can exceed the speed of sound, up to Mach 1.3 (actually stated M1.4 in the link, my experience is M1.3 but also my professor used to mention M1.4) as seen in link. As they are enclosed, the negative effects of the shock are much smaller than if it were an open propeller. Open propellers (and also propfans) are also affected by aeroelastic effects in transonic speeds which are very hard to isolate with their high span-to-chord ratios (I don't like calling it aspect ratio for propellers). Not to mention the NOISE that an open propeller generates at transonic speeds.
Additionally, due to the fan being followed by a stator (which uses the rotational component of velocity added to the airflow by the rotor) and the converging fan duct geometry, turbofans accelerate the flow further than propellers do. The exhaust from the turbine is also faster than the fan and constitutes a greater fraction of the air ingested by the engine, which increases the average exhaust velocity of the engine.
Imagine a turboprop flying at Mach 0.8 and the propeller tip speed being limited to Mach 0.9 . This requires the propeller tip to have a tangential velocity of M0.41 (Pythagorean sum). On the other hand, at the same flight speed, a fan blade tip limited to M1.3 can still have a supersonic tangential velocity of M1.024 . It is obvious that a fan blade turning more than twice as fast can exert greater forces on the airflow.
The thrust is generated by accelerating airflow. We can either accelerate a lot of air by a little bit (think of a helicopter rotor) or a little air by a lot (afterburning turbojet). A relatively slow-moving propeller blade (due to the reasons above) can do little to accelerate airflow going through it, relative to a fan that turns much faster in an enclosure.


Will I not be able to descend with an airfoil that stalls at -0.5°?

Don't believe everything that a computer tells you.

This airfoil is listed in the airfoiltools site, and I took the liberty to copy its XFOIL results here:

I selected the Reynolds numbers 500,000 and 1,000,000, which should be at the low end for a man-carrying aircraft. As you can see, the stall angle of attack is at 15° and the maximum lift coefficient is between 1.7 and 1.75. To achieve a lift coefficient of 1.89 with that airfoil will need a much higher Reynolds number, but max. L/D is already around 120.


What is the standard way for the ATC to ask a pilot to repeat him/herself?

Yes, and it is exactly the same: Say again.

  Station calling Georgetown Ground say again your callsign

  Lufthansa 123 say again speed

  Scandinavian 123 say again all after 'good morning'

Or simply

  United 345 say again


Why is there a need for a Top Altitude in FAA's SIDs?

It is needed for the new climb-via instruction (c. 2014).

Instead of issuing different maintain altitudes to the aircraft based on the SID, direction, etc., a top altitude is charted. From the FAA AIM:

  SIDs will have a "top altitude;" the "top altitude" is the charted "maintain" altitude contained in the procedure description or assigned by ATC.

Related:

Do Jeppesen SIDs have top altitude?
What altitude should you cross DBIGE at on the PALLEY FIVE Departure (SID)?
Are 'climb via a SID' instructions actually used in the US?


It appears to be a Rolls Royce Viper turbo jet engine made in 1966. The maker's mark (BSB) derives from Bristol Siddeley, formed from Armstrong Siddeley (the company that originally developed the engine) and Bristol Aero-engines. Bristol Siddeley were later taken over by Rolls Royce.

Source: Wikipedia


When wiil this person be able to replace his engines on a bunch of smaller ones to attach them on clothes?

From the outlet cowling and nozzle, it they look to me like 6 standard RC jet engines (JetCat or so; JETCAT P200RX, for instance, has about 50 lbs of thrust, so in the right order of magnitude).

I don't think there would be any benefit whatsoever to using many miniature engines.


Anyone able to help identify what aerofoil this is?

Try contacting the local FAA Flight Standards District Office (FSDO-'fizzdoe') for help. They may be able to tell you how to get a copy of the aircraft's certification documents which may indicate the airfoil used. Mention the aircraft's N-number: N301XZ. To locate the nearest Flight Standards District Office, see here:

https://www.faa.gov/about/office_org/field_offices/fsdo/


What does the term "white-scarf Air Force" mean?

A white scarf air force is one that values aircraft above all else (space-, cyber-, missile-warfare, etc.), i.e., an air force that is unwilling to evolve beyond flying planes.
Similarly for not embracing RPVs (remotely piloted vehicles).

Dealing with RPV pilots will probably be a little more difficult. The conventional wisdom is that pilots don’t like RPVs because they take the human out of the sky and stick them on the ground, what Thomas Ehrhard calls the “white scarf syndrome” (in homage to the scarves worn by World War I and interwar aviators).
The reason RPV projects fail, the syndrome claims, is that the Air Force starves them to avoid competition with its manned aircraft (source).

How that fits in the comment about the A-10 and close air support aircraft, I don't know.
The term refers to WWI pilots who wore white scarves—the tradition carried on beyond WWI. In WWI the silk scarves had a purpose: it's smooth so it does not chafe the skin when looking around, it keeps the pilot warm in the open-cockpit, and it's used in cleaning the oil and rain off the goggles—bright colors are good since you know which part is clean and thus can be used (source).
That's also why Snoopy is stylized with a scarf.
(Source) WWI pilot attire.

Although in the past the dominant operational perspective was centered on a specific system or aircraft type (bombers or fighters), the future will need to be centered on a capability not necessarily connected to a specific airplane type of mission (i.e., to be centered on synergistic-operations). This transition will be difficult in that the very nature of the Air Force has always been to focus on flying aircraft. However, as history has shown and as technology has advanced, the need for and appropriateness of manned flight as the primary USAF focus has diminished.
As a service, we have rightfully transitioned to thinking about cont rolling “domains” rather than the toys used to control them. Those in the USAF unable to separate themselves from their flying machines will eventually become relics and will he replaced by a new generation of “airmen” whose understanding regarding the depth and breadth of airpower goes well beyond aircraft and instead focuses on how best to advantage war-fighting domains (air, space, cyber). However, as Builder suggests,

as the Air Force is compelled in the near future to reduce its force structure under the pressure of budget reductions, there will be a strong tendency to preserve those forces which have dominated the mission spectrum in the past rather than those which might dominate in the future. To be explicit, there will be a natural tendency to preserve the fighter and bomber forces at the expense of the supporting forces . . . this tension between institutional proclivities and perceptions of the future illustrates the importance of the latter to the evolution of air power theory.

In this regard, the greatest challenge that the USAF must overcome is its inability to focus on the ends rather than on the means. When the USAF finally realizes that it greatest strength comes from its ability to take advantage of all elements within the airpower domain (air, space, and cyber, and not merely on a particular system, that is when the USAF will have obtained a level of maturity capable of sustaining its operations without fear of continual, periodic change. This long-view transition will require the USAF to force itself out of “white scarf syndrome,” where the means (flying aircraft) are more important than the ends of providing the nation with the greatest possible amount of airpower options. Unfortunately, if the USAF continues to rationalize its existence under the pretense of decisive operations, continually strives to prove its independence, and views its primary mission in terms of the aircraft it flies, then its future validity and relevance is questionable.
— Tomorrow's Air Force: Tracing the Past, Shaping the Future (2013) p. 221


Why are the intakes of some fighters not attached to the fuselage?

That's called a 'fuselage boundary layer diverter channel', or splitter plate.

The air near the fuselage or wings is slowed down (thereby losing energy). Those plates ensure the jet engines get free stream air, which improves the engine performance. This free stream air will be undisturbed, allowing a more uniform intake of air.

You can also find it on the Concorde.

Related: What is the function of the holes in splitter plates?


Are there any known incidents of ejections by capsule? What are the survival chances?

While the F-111 had a custom build escape capsule integrated with the cockpit, escape capsule designs have been used in the past.  One notable type was the Stanley Corp. Ejection Capsule.  It was a special type of ejection seat which used a pressurized clamshell-type enclosure which could be deployed rapidly once the ejection process had been initiated.  It was designed specifically to protect a pilot against a supersonic, high altitude ejection which would have almost certainly been fatal using a conventional ejection seat.  The system was used on both the B-58 and XB-70 aircraft.

The system was pressurized allowing a flight crew to use standard life support equipment as opposed to a full body pressure suit for high altitude flight.

One notable ejection involving the Stanley capsules was the loss of XB-70 prototype No 2 on 8 June, 1966 near Barstow, CA.  During a formation flight of several other aircraft with the XB-70 for a General Electric photo shoot, an NF-104 collided with the starboard wing and tailfin of the XB-70 and disintegrated in flames, killing NASA test pilot Joe Walker in the process.  The Valkyrie continued on straight and level, then waltzed out of control and began tumbling toward the desert, spilling plumes of fuel vapor as it went.  Commander Al White initiated the ejection process using his Stanley capsule and egressed the aircraft but was seriously injured by failing to clear his arm from the clamshell enclosure during deployment.  The copilot, Carl Cross, failed to initiate ejection and rode the crippled Valkyrie to the desert floor, killing him in the process.


Why is engine #1 still used when taxiing with one engine?

According to the "Supplementary Procedures / Green Operating Procedures - One Engine Taxi" in section PRO-SUP-93-20 of the A320 FCOM:

  Use Engine 1 for taxiing because it pressurizes the green hydraulic system (normal braking).

and

  Y ELEC PUMP.............................ON
  This pressurizes the yellow hydraulic system (nosewheel steering) without using the PTU.


What is the rationale behind "One engine - Two propellers" configuration?

It looks as if they rotate in opposite directions. This eliminates prop torque, which should improve handling, especially at low speeds.

On the other hand, you are right with your impression that it adds complexity, but at least it is not completely useless.

Asymmetric prop failure is indeed an issue and will markedly reduce handling qualities, and for that reason both props are close together, so if one is left, the yawing moment should be manageable if the craft flies fast enough.

Putting a single prop in the center would present it the messy flow coming from the unfaired cockpit and engine, so placing them left and right should improve inflow conditions. They are still close enough so the tail is in the prop wake and will have improved effectiveness at slow speed and on the ground. On the other hand, the outriggers will create additional drag, and it is hard to say if this arrangement will have performance benefits.


Are piezoelectric energy harvesters too expensive to be used commercially as a power source in drones or small aircraft?

What are the disadvantages of such a system being used as an auxiliary power source if not the main one? Is it not worth the money?

It's not worth the weight.

The power that can be extracted from piezoelectronics is on the order of microwatts (100 uW in the above article). In contrast, light aircraft have their power measured in kilowatts and commercial aircraft reach a megawatt of electrical power.

In other words, it would take 8-16 million of piezoelectronic harvesters to replace the alternator on a small aircraft, and 3-10 billion on a modern airliner. Drones use more power than small aircraft as they've got a lot of electronics.

Piezo harvesting is being developed to power completely unattended tiny sensors that won't have access to any other power source for years. All aircraft, including drones, already have their own power source - the engine - with fuel tanks that get refilled each flight. So power's cheap and available.


What drives and/or allows the move to higher-bypass turbofans on jetliners?

For a clue look at the development in the price of oil:

Historical oil price chart (source)

While the first development into the 5:1 region predates the first oil crisis (1973) and was driven by fuel economy, better range and lower airport noise, the next step was kicked off by the second crisis in the early 1980s. It took one decade to develop the engines and the airplanes which could fit them, so the Boeing 777 - GE90 combination came out in 1995 in a time of falling oil prices.

The next round was only kicked off after the US invasion of Iraq which made oil prices shoot up from 2003 on. Again it took a decade for the engines to become available, but now the increase in diameter is less dramatic and existing designs can be fitted with them (A320neo, 737MAX).

Before the early 1960s the bypass ratio could not grow more because

jet engines were developed for military aircraft, and more emphasis was placed on top speed than on efficiency. Airliners used what was available (note that the Convair 880 was powered by a simplified, non-afterburning version of the J-79, which powered the F-104 Starfighter, the F-4 Phantom II and the B-58 Hustler).
early airliners (De Havilland Comet, Tupolev 104) had their engines in the wing roots, so little space was available for an increased bypass ratio. When Rolls-Royce was developing the first turbofan engine, the Conway, they limited the bypass ratio to 0.25 so it could fit into the Comet and the HP Victor bomber, which also had its engines in the wing roots.

The first oil crisis of 1973 kicked off the development of the unducted propfan (UDF) engine, which has been held back by noise problems. Again, it took about a decade until it could take to the air.

GE36 UDF engine fitted to the MD-81 (picture source)

The development of a new engine takes longer than that of an aircraft, so every time a big push, triggered by a substantial jump in oil prices, was needed to start the development of a new generation with significantly higher bypass ratio. Once the engine technology was ready and certified, it would be quickly incorporated into many models, because the better fuel economy would force everyone to upgrade.


Cessna 172 steering system and torque link purpose

The Cessna 172 (152, 175, 177, and 182 as well as others) all use steerable nose wheel by pushing (not depressing) the rudder pedals in the direction you want to go. If you want the nose to turn to the right, you push the right pedal forward, same with the left. You can augment this with differential steering if tighter turns are needed.

So there are actually 3 ways to steer the 172:

The nosewheel steering using rudder pedals. This puts pressure on the bungee system that turns the nose wheel left/right. Pushing the pedal doesn't directly move the wheel, you need to move the aircraft forward a little bit for the wheel to turn.
Differential braking can help make tight turns, this causes the nose wheel to "caster" or turn based on which direction you are attempting to turn the aircraft.
Some turning force is provided by the tail rudder, it isn't usually a lot but it is noticeable when landing.

  Is there any connections between rudder or toe brake and nose landing gear related to steering? What is the purpose of torque link in front oleo ?

There is no connection between the rudder or toe brake and the wheel (in the purest sense, the rudder pedals are also connected to the bungees for steering), the rudder pedals  move the bungee system that puts pressure on one side or the other of the torque link on the oleo strut.

  Does nose wheel even turn ?

Yes! All tricycle gear aircraft with a nose wheel must allow the nose wheel to turn at least a little bit. The 172 allows the rudder pedals to give up to 10° of wheel movement while differential braking will make the wheel move up to 30°, this is outlined in Section 7 of the 172 POH (I won't link the entire POH here, but this is the excerpt):

Source: 172SP Pilots Operating Handbook

If you update your question with a picture of the fairing you are talking about I can comment on that, but really it should be a separate question.