Why does "V1 increase with decreasing density"?

I guess the statement is about V1 from the balanced field length, which is where the accelerate-go distance is equal to the accelerate-stop distance:

(image source: boldmethod > Engine Failure On Takeoff: Do You Stop Or Go?)
How do these curves change when the density decreases? Lower density means less thrust, therefore accelerating will be slower and uses more distance. This affects both curves equally for the acceleration to V1, but afterwards only the accelerate-go distance:

Let us call the force accelerating the aircraft initially $ F = 2 \times T $ (thrust from two engines).
In the accelerate-go case, you would only accelerate with a force of $ F = T $ after the engine failure.
In the accelerate-stop case, you brake with a certain force $ F = F_\text{brake} $.
Now, at lower density, the thrust $ T $ will decrease, but the brake force $ F_\text{brake} $ will be unaffected.
The accelerate-go case is therefore affected during the entire time by the lower value of $ T $.
The accelerate-stop case is only affected during the accelerate part, but afterwards the brake force is still the same.

Therefore, both curves will move up in the diagram, but the accelerate-go distance will move up more. This implies that their intersection (the balanced field length) will occur further to the right, resulting in a higher value for V1.


Optimizing the airplane for best cruising altitude and velocity

Are you designing a new airplane? If I understand the question correctly, For a normally aspirated engine, the engine is most efficient when the throttle is fully open at a particular altitude, where it produces approximately 65% -75% power. Therefore the airframe with respect to wing design, angle of incidence etc should be matched to give the best lift/drag ratio at that altitude. You will have to consult with the engine manufacturer to establish what that altitude is. Your choice of propeller is also going to have to be factored.
Then you calculate the fuel reserves accordingly.
Fuel reserves are calculated according to legal requirements of the country in which the airplane is registered and also in which it is operating. This varies according to the type of aircraft and the operation. For instance the minimum legal reserves are different for a passenger jet on a commercial flight, to a single engine airplane being operated on a VFR flight in the private category. Most countries laws are similar but there might be small variations, and they all have to satisfy ICAO standards if the country is an ICAO member state.


What is this vintage small airplane with low wings and twin propeller engines?

It's a LET L-200 Morava, a Czech plane...
http://www.aviastar.org/air/czech/let_l-200.php


How are skis stowed on retractable gear aircraft?

The skis partially retract.

Here is an image of one with the gear retracted:

Source: UW Oshkosh

  Do the skis become part of the gear door?

From looking at the images with the gear deployed and then the ones with the gear stowed, it appears that the skis do form the gear doors.

  Is there enough room in the gear bay for the skis?

No, the skis are not retracted into the aircraft.

  Are modifications to the gear bays necessary to accommodate the skis?

It doesn't appear to be, but there may be modifications to the retraction mechanism to allow the wheels to be stowed while the ski is still outside of the aircraft.

  Is there any modification necessary to the movement of the gear to accommodate the skis? (i.e. some gear rotate as they stow. I'm not sure if the C-130s do or not.)

It does appear that there is, yes. The ski's can be deployed without the wheels touching the ground, or the skis can remain retracted and the wheels extended for paved runway operations. Take a look at these two photos:

Source: PIntrest

Notice how the wheels are on top of the skis? Now take a look at this one:

Source: FlyIan.net

You notice that the skis are still retracted and the wheels are extended through the skis.

If you want to know what was modified for the gear doors, take a look at this image of a "normal" C-130:

Source: YouTube

Notice how the rear gear door goes a quarter way up the "pontoon"? The version with skis has a fixed panel that replaces the gear door and matches up with the profile of the skis to reduce drag.


Can an air traffic controller refuse to give service to an aircraft based on moral grounds?

No.

The purpose of air traffic control is to prevent collisions and expidite and maintain an orderly flow of air traffic. An air traffic controller has no say in who gets to fly and who doesn't. Refusing a certain flight would be something that needs to be done at a political level, and certainly far away from an operational level.

Also remember that, except in special cases, air traffic controllers have no way of knowing who is onboard a certain aircraft. Essentially, all we see is a flight ID and a route. Air traffic controllers are not in contact with passenger lists at any time.

Furthermore, air traffic controllers do not have any physical way of preventing flights from taking place. See this slightly related answer: Can a pilot take off at his own discretion?


Is it viable to put an engine at the rear of the plane like in this photo?

As you look closely to the picture, there are also engines located under the main wings. Thus this is a trijet, a concept that has been used in the past by for example the MD-11, Lockheed tristart and Boeing 727. The main reason for choosing a trijet configuration was the ETOPS requiring twin engine aircraft to always be within a certain range of an airport. This was in a time when engines where less reliable. With three engines the aircraft did not have to bother with ETOPS regulations allowing it to fly routes impossible to fly for twin engine aircraft. But as engines became more reliable and the ETOPS got lengthened the trijets became redundant.

A big downside of the trijet is the structural complexity of an engine in the back, the fuselage needs to be reinforced to withstand the extra forces. From a maintenance perspective it is difficult to access the middle engine because it is high of the ground requiring a stair for visual inspection. Then there is the economical aspect, if you can do it with less engines it will always be more fuel economical. The next iteration of 777 can carry as many passengers as the 747 with half the engines.


How much time is a commercial aircraft (e.g. A320 / B737NG families) flown manually?

Today's aircraft automation is just not set up for unattended operation.
There are too many individual tasks, that pilots must complete, to list here. The lowest workload for pilots is during cruise but even then ATC can instruct you to change speed, routing, or altitudes. Maybe one day this could be controlled from the ground but today only the pilots can make those changes.
I think you want to know how many minutes of an average flight are the pilots actually manipulating the controls either manually or through the A/P.

The A/P comes on somewhere between 30 seconds and 7 mins after takeoff and it stays on continually for the whole flight until maybe 2 mins before touchdown.
Every flight is different and sometimes there is lots of vectoring by ATC on departure/arrival and lots of step climb/descents, which requires the crew to "fly" the A/P. Sometimes the arrival/departure are linked up directly with the en route portion and you get a direct climb/descent.
So as a rough guess on an average flight the pilots might manually fly the aircraft for about 3–10 minutes and "fly" the A/P for about 5–10 mins. The rest of the time is spent talking to ATC, doing checklists, checking weather, fuel checks, and trying to keep yourself busy any other way you can think of. :)
I personally fly mostly ultra long haul flights of 13–15 hours as part of a 4-man crew so I also spend about 6–7 hours sleeping in the bunk.

In every phase of flight the crew is needed to do much more than just monitor the automation. The automation can not be used unless the pilots first enter all the required parameters, and then activate the automation at the right time, and in the correct order.
There is no aircraft that can take off on autopilot. The autopilot can only be engaged after takeoff. Once airborne at cruising altitude the aircraft could follow a programmed flight routing but any change in heading, routing or altitude must be manually entered by the pilot.
At the destination the approach must be manually programmed for the approach and runway in use. Once the aircraft in on the ILS approach an aircraft with autoland capability can land itself but it still needs the pilots to clear the runway.
Autopilot/autothrottle policies can vary with each airline. Typically airline pilots hand fly from takeoff to at least 200' but many hand fly to 10,000' or more for practice. When landing most pilots hand fly from about 1,000'.
Depending on the specific aircraft, autothrottle is usually engaged during the the takeoff roll and stays on until the flare just as it lands. There is no automation for landing gear and flap operation. It is 100% manual.


Why does Thrust Reverser need to be operative during the cargo door operation?

“It is stated that when the Electric Pump push button is depressed, the electric pump is automatically running as long as the cargo door selector valve is set to either OPEN or CLOSE position”

This is not correct. Cargo door operation will automatically energize the Elec Pump while it is in the OFF position. (not depressed)

“My question here is why thrust reverser ENG#2 needs to be operative during cargo door operation”

It doesn’t need to be operative. It needs to be Not Inhibited,  in case there is a malfunction.

The cargo door uses the Yellow system. It is designed to be used on the ground even with the Electric Pump in the OFF position. The pump will come on automatically in this case to supply hydraulic power to the cargo door. It will inhibit all the  other items on the yellow system to insure adequate hydraulic power to the cargo door.

BUT......If there was a malfunction in the Cargo Door system while in flight, it could possibly cause the Yellow Elec Pump to engergize while it is in the OFF position. If that were to happen, it is designed to inhibit all items on the Yellow system. That would be bad, so they designed the switch to inhibit everything except Alt Brakes and #2 Reverse.

This situation could only happen if the Yellow Elec Pump was automatically commanded ON while in the OFF position.


Are there turbofan/turbojet analogues to a centrifugal-compressing jet engine?

Yes, but the classification is not a matrix.

A turbofan by definition needs a fan, but at its core it can have a centrifugal compressor. A good example is the Pratt & Whitney Canada PW600 series. This allows a compact design, at the expense of compression ratio. It works well for low-thrust applications such as the Cessna Mustang. The advantages are the engine being small, lightweight, and having fewer parts.

(Google Patents) The arrows point at the two-stage compressor. The first stage is a mixed flow compressor rotor, and the second stage is a centrifugal compressor. Label 9 is the fan up ahead.

The PW617F provides a whopping 7.18 kN (1,615 lbf) of thrust and weighs under 180 kg. (The fan is slightly bigger than a human hand.)

You can watch a moving cutaway model for the JT15D turbofan with a centrifugal HPC here.


How do pilots "turn an airport around" at nontowered fields?

Your example is too specific to be useful to others, so let's consider the general case instead.

At an untowered field there is no "active" runway - they're all active.
There is usually a "preferred" runway - the one best aligned into the wind - but any runway can be used by any aircraft at any time, subject to whatever safety considerations the pilots mutually agree on. (At untowered fields with intersecting runways that have a lot of training on the field it's not uncommon to have traffic on the crosswind runway intersecting the preferred runway when students need to practice crosswind landings. It can be coordinated safely with a little cooperation between the pilots involved.)

The runway is "changed" by pilots announcing they're using a different runway.  There may also be a unicom operator at the field who announces a change in the preferred runway and lets incoming aircraft know about it.
Usually pilots who are already in the pattern for the "old" runway will complete their circuit and land, clearing the runway as expeditiously as possible.
Similarly pilots waiting at the threshold when the wind shifts may elect to either make their takeoff from where they are, or taxi around to the new preferred runway.  (In a case where the aircraft must enter the runway to turn around, or where they must back-taxi on the runway this obviously needs to be coordinated with the other pilots. The standard phraseology to use for this is "N12345 back-taxiing on runway XX" )

To your specific example, the directions of traffic patterns don't really matter much: As I mentioned aircraft already in the pattern will probably complete their circuit and land on the runway they were lined up for. Even in the case of Left Traffic for 13 and Right Traffic for 31 and two aircraft maneuvering to enter the pattern for opposite runways the standard pattern entry (45-to-downwind) will tend to keep airplanes apart (they won't ever be heading at each other in the downwind leg if they enter it on the 45, and it should at least ensure they see each other in the opposite-direction 45 and can coordinate to ensure they're never flying at each other). One airplane will probably have to extend their pattern to allow the other to clear the runway safely before they can land, however.

  Traffic really should not really be arriving to both downwinds simultaneously anyway, particularly in your example with a single runway: Inbound aircraft should coordinate to arrive in the pattern for the preferred runway.

Aircraft already in the pattern have two choices: Land downwind if safe, or depart the pattern and re-enter it to land on the new preferred runway.  A downwind landing must obviously be coordinated with aircraft which may be preparing to depart in the opposite direction.
If landing downwind is unsafe (due to wind speed) or otherwise undesirable (e.g. due to other traffic) climbing above pattern altitude, leaving the area, and returning via a standard pattern entry for the opposite runway is usually the safest course of action.

Aircraft waiting to depart also have two choices: Depart downwind (which must be coordinated with aircraft arriving to the preferred runway), or taxi to the preferred runway end for takeoff. In cases such as you've described where back-taxiing is necessary this must be coordinated with pilots landing (in either direction) as the back-taxiing aircraft will be occupying the runway they need for landing.

The major complicating factor you didn't specifically mention, but which is implied by multiple aircraft "in the pattern" is closed traffic (aircraft making touch-and-go or full-stop/taxi-back landings and immediately taking off again).

Full-Stop/Taxi-Back landings are not a problem: Much like "regular" landing traffic they can land downwind, and upon exiting the runway taxi back to the preferred runway end for their next takeoff.
Touch-and-Go aircraft have two main choices: Land downwind as a full-stop and taxi around to the preferred runway end (which is probably the safest and most considerate thing to do), or complete a touch-and-go with the intention of departing the pattern and returning to set up for circuits to the new preferred runway.

Another important consideration are aircraft without radios (NORDO)- yes, these do exist). A visual scan of the traffic pattern is required at any uncontrolled field at any time to ensure you are not conflicting with NORDO aircraft.
These are often slower planes, so having one in the pattern landing "the wrong way" may require you to wait a while for them to complete their circuit before you can begin operations on the new preferred runway.


What is the difference between flow separation and turbulent flow?

At what point does one say "oh, this flow has changed from turbulence to separation"

At the point where the flow reverses direction.

Flow separation. The bold curve is the surface/wing.
Yes, that can happen.
Both turbulent and laminar flow can separate. Turbulent flow is in fact less likely to separate than laminar flow. This is why aircraft wings often have devices that deliberately create turbulence on the wing.
(Yes, separated flow produces negative skin friction, but at the price of huge pressure drag)
Here's a (badly hand-drawn) diagram showing the difference between laminar, turbulent and separated flows.

Just a clarification about stall. The stall is when the lift reduction caused by flow separation overwhelms the lift increase caused by flying at an increased angle of attack. Flow separation can happen without stall, and it will reduce the benefit gained from a higher angle of attack in proportion to the extent to which the flow is separated, but stall cannot happen without flow separation.
Indeed, many wings have separated flow at the trailing edge sometime before "stall" is reached. As one draws closer to "stall", the region of separated flow expands forward. The turbulence created by the wake of this separated flow hits the tail, causing "buffeting", which gives the pilot a warning that he is approaching stall. Airfoils that lack this feature, such as supercritical airfoils or sharp supersonic ones, tend to be dangerous to fly at slow speed with it's inherent high angles of attack.
And as you can see from the diagram, the flow separation at a given angle of attack is much worse for laminar flow than for turbulent flow. So the laminar separated case is more likely to be a stall than the turbulent separated case.

Lift vs angle of attack for thin, sharp wings vs thick ones. Airfoils designed for laminar flow fall in the thin category. And as above, just having or not having laminar flow on a wing can make a similar difference.
And yes, vortex generators prevent separation by creating turbulence, which causes high speed freestream air to get mixed with low-speed boundary layer, speeding up the boundary layer. It's a tradeoff between the drag of a turbulent boundary layer and the even greater drag and lift loss from flow separation.


Why is the wrong explanation of "air travels a longer distance and creates a lift" so popular?

Long story short is that both Newton's third law and the Bernoulli's effect are two different ways of explaining the same phenomena. Accurate equations have been written to explain both. Newton's third law, the air being forced down and forcing the airplane up, is actually the effect of lift though not the cause. The cause of lift is the change in pressure.

The falsehood that is taught is usually that the two little air particles actually meet up at the same point downstream at the trailing edge of the wing at the same time. This is completely false. In fact, if you were to actually track two air particles, one over the top, and one across the bottom, the one going over the top of the wing will probably arrive much sooner than the one on the bottom! [Even though the distance IS longer] It picks up that much speed. Also they don't actually really meetup again afterwards at all.

The real pivotal relation (which I learned in my Advanced Aerodynamics class at ERAU using John. D. Anderson's book Intro to Flight) is the Kutta-Joukowsky theorem. Taking the time to explain this to a Private Pilot student would probably be a waste of your time and theirs but I will sum it up here anyway to be fair to the question. I will assume incompressible flow because after about Mach .3< it starts to get more complicated.

The Kutta-Joukowsky theorem takes the integral of velocity times the cosine of the incremental angle of the distance along the closed curve. This is a quantity called circulation. The lift equation is then formed as lift equals density (altitude basically) times velocity times circulation. So if you really want get in-depth here is an article from MIT that explains potential flow theory.

What you will find is that the cause of lift is indeed directly related to Bernoulli's principle in that the change in pressure is what creates the lift. However it has nothing to do with particles meeting up at the trailing edge because they never really do meet up. This doesn't discount Newton's third law either: lift can be explained that way but it is the effect of lift, not the actual cause. And yes, like you mentioned, even a flat-plate for example can create lift when angled right in a wind tunnel.


Most jet nacelles contribute little or no lift, but there is at least one highly notable exception.
The airflow inside the nacelle is dominated by the engine and any chance to create differential pressure between upper and lower leading sections is kept negligible in order not to disrupt the intake flow.
The outside is more of a stubby fuselage than an annular wing and low drag dominates the design. The avoidance of interference with the leading edge of the wing, part way along and just above, is also a major consideration for the upper profile. Lift is not really considered, and is not present to any significant extent.
Having said that, for a large high-bypass turbofan, when placed well forward the lifting area can become significant at high angles of attack (whether positive or negative). It can be powerful enough to move the centre of lift forwards, reducing pitch stability and at steep angles leading to a tendency for the angle to diverge further. When Boeing were developing the Max variant of the 737, its new engines suffered just this problem on takeoff and landing. Boeing's solution was to introduce a Manoeuvring Characteristics Augmentation System (MCAS) which automatically operated the elevator to reduce the angle sharply if it got too steep. Tragically, in their hurry they botched the job, two commercial flights crashed fatally and the 737 Max has been grounded indefinitely until they can get a fix certified.


Do the A-320 landing gear extend if the mechanism is activated above a limiting speed?

The hydraulic pressure of the landing gear is shut off above 260 KIAS. The maximum gear retraction speed as for the placard in the cockpit is 210 and the max extension speed is 250 KIAS if I'm not mistaken.
From the FCOM 1.32.10
(download from here for example: http://www.smartcockpit.com/plane/AIRBUS/A320.html)
A320 Landing Gear, page 3
OPERATION OF GEAR AND DOORS

NORMAL OPERATION
The green hydraulic system actuates all gear and doors. When the aircraft is flying faster than 260 kt, a safety valve automatically cuts off hydraulic support to the landing gear system. Below 260 kt, the hydraulic supply remains cut off as long as the landing gear lever is up.

The logic is then described in a diagram in the FCOM (see link above).

If ( ADR1 < 260KT || ADR3 < 260KT || MLG on gnd ) && ( LG lever down || safety valve already open )
-> open safety valve

If I interpret this diagram correctly you can leave the gear lever down and the gear should start to extend once below 260 kt because the second side of the and gate just requires the gear lever to be down.
On the contrary if you want to retract the gear and you fly faster than 260 kt then the safety valve closes. Even if you fly slower than 260 kt it will stay closed because the second half of the and gate is not fulfilled. You need to move the gear lever down, then the safety valve opens and then you can move it back up and the self maintained state of "valve already open" will allow you to retract the gear after this cycle of the landing gear lever.
Part 2 of the questions regarding the indications
Indications are as follows:

3 red lights above the gear lever as long as landing gear is not locked in the selected (down) position according to A320 FCOM LANDING GEAR page 18, GEARS AND DOORS, LANDING GEAR INDICATOR PANEL
A red down arrow next to the landing gear lever when the gear is not locked down when the aircraft is in the landing configuration (page 19)
6 red triangles on the ECAM wheel page (3 gears, two redundant landing gear control units) (page 21)
An amber pulsating L/G CTL legend on the ECAM wheels page when the landing gear position and gear position do not agree (page 22)
GPWS audio call out and associated red light outboard of each PFD (see below)
ECAM warnings as follows

ECAM warnings according to the WARNINGS AND CAUTIONS section of the FCOM LANDING GEAR chapter, page 23:

red flashing master warning and cricket aural warning: GEAR NOT DOWNLOCKED on the upper ECAM display, ECAM WHEELs page is called automatically on the lower ECAM display with the indications stated above
red flashing master warning and cricket aural warning: GEAR NOT DOWN, when below 750 ft radar altitude with both engines below 75% N1. Other conditions require flaps to be extended to 3 or FULL but above 260 kt you probably would cause structural damage if you were to attempt that.

From the A320 FCOM Chapter 34 NAVIGATION, GPWS, page 6.

Two aural warnings may be triggered, depending on the area: "TOO LOW-GEAR" [below 190kt and 500ft RA] or "TOO LOW-TERRAIN" [above 190 kt, up to 1000ft RA]

If you are flying faster than 260 kt the GPWS should create a "TOO LOW-TERRAIN" warning.


Is there a wordpress plugin for live NOTAMs?

As mentioned, this is off-topic and more related to understanding APIs and Wordpress plug-ins.

If you want a place to start:
https://developer.laminardata.aero/documentation/notamdata might give you API access, but you'll have to build it yourself which is beyond the scope of this site.

As @Zach Lipton mentioned in the comments, even the official sites have a disclaimer, but here are a couple official sites you could check out:

https://notams.aim.faa.gov/notamSearch/nsapp.html#/
https://www.notams.faa.gov/dinsQueryWeb/

Somewhat related: Is there a Flights API to get flight information months in advance?


What type of engine is mounted on the Cessna Citation Hemisphere?

The Cessna website mentions the engine type used (emphasis mine):

  The Citation Hemisphere will be powered by two next-generation Safran™ Silvercrest™ engines delivering over 12,000 pounds of thrust. The Silvercrest engines incorporate the latest advanced, field-proven technologies to offer unrivaled performance in its class in terms of direct operating cost, propulsion efficiency, reliability and environmental friendliness. These engines lower fuel consumption by up to 15 percent, reduce NOx emissions by up to 40 percent under CAEP/6 standards and half the noise footprint compared to other engines in its class.

According to Wikipedia, this engine will have a bypass ratio of

$$5.9 \, : \, 1 $$

which would certainly count as a high-bypass turbofan engine. Also see: What is the difference between a high bypass turbofan and a low bypass turbofan?


According to the Airbus website, Brake to Vacate is a feature installed on newer A-380s and also on the new A-350XWB that allows the pilot to select which runway exit s/he needs to use, and the system will brake hard enough, but just hard enough, to slow the plane to taxi speed by that turnoff.  This minimizes time on the runway.  The following quote is from the Airbus website.

  Brake to Vacate allows pilots to select the appropriate runway exit during the approach to landing, and regulates the aircraft’s deceleration after touchdown – enabling it to reach any chosen exit at the correct speed under optimum conditions, no matter the weather and visibility.

To my knowledge, Airbus is the only aircraft manufacturer to incorporate this feature - to date.

This feature does not reduce the amount of runway the aircraft uses.  Maximum Braking is still maximum braking.  It does however, optimize the braking so that the aircraft gets to the taxiway intersection sooner (doesn't brake too hard too soon, keeping speed up) and also prevents overshooting the intersection requiring a relatively slow taxi to the next turn off.


How are takeoff and stall different from each other?

On take-off the pitch is increased to increase lift, but only to a point well before stall occurs. An aircraft's minimum speed is defined by the maximum lift it can create before the flow over the wings stalls, and the high-pitch attitude is only attained when the aircraft flies faster than that. As soon as lift is sufficient for lift-off, further pitch increases are increasing the flight path angle. If the aircraft keeps accelerating during the initial climb, stalling is impossible.

Technically, both are very different. Their only commonality is that they involve high angles of attack.


Are there downloadable versions of the Canadian VNC and VTA charts?

There is a plan to produce electronic versions but they don't seem to be available yet and you can still only order paper ones.  Go here:

http://www.navcanada.ca/EN/products-and-services/pages/aeronautical-information-products-charts.aspx


Is this plasma-thruster experiment actually measuring thrust?

No, it's not measuring thrust.  It might be measuring a proxy for thrust density (force per unit area).  Anybody could use their setup to measure a ducted fan or a turbojet or even a rocket, but nobody does.  They themselves could have calibrated their rattling-ball instrument with a conventional thruster of known, conventionally measured, thrust (a $20 electric ducted fan from a hobby store).  (What's the threshold for rattling, anyways?)

As Jpe61 commented, it would have been much cheaper and simpler to place their thruster on a load cell (a fancy bathroom scale) and observe how downforce increases when the thruster is running.  $100 instead of fancy metalwork.  See, for example, fig. 6 and reference 23 of Prasad et al, "A laser-microfabricated electrohydrodynamic thruster for centimeter-scale aerial robots," https://arxiv.org/pdf/1906.10210.pdf.  See also the fancier inverted-pendulum thrust stand used at Princeton to measure plasma thrusters.


Can a "Destroyed" Helicopter be repaired and flown?

The NTSB defines Destroyed as

  Damaged due to impact, fire, or in-flight failures to an extent not economically repairable.

Another common definition is:

  The estimated or likely cost of repairs would have exceeded 50
  percent of the new value of the airplane had it still been in
  production at the time of the accident.

This fact that the costs of repairing are estimated to be exceed the economical value of the aircraft does technically not prevent the aircraft to be repaired and made flyable again. It can be recertified on the original airworthiness certificate. See FAA order 8130.2H.
Special attention needs to be given to the identification plate (serial numbers etc.) of the aircraft; the original plates of the aircraft have to be installed.

Do not expect any support from Bell as on their website they state:

  There are some aircraft that have been destroyed in an accident or
  retired from service that are no longer considered to be genuine Bell
  Helicopter Aircraft. These aircraft will not be supported by Bell
  Helicopter.

This makes resurrected Bell helicopters very difficult to sell in the future.


Is there a maximum airspeed to deploy a ram air turbine?

The ram air turbine (RAT) can be extended and used at any speed above a minimum speed, because under this minimum speed, power is difficult to generate.

Generated power may be decreased below 130 knots, and extension is prevented below 100 knots because of additional drag produced for nearly no power obtained.

The RAT can be extended automatically (loss of engines or pressure) and manually, e.g. logic for RAT extension on A330 (note the inhibition by airspeed below 100 kt and by on-the-ground sensor:

Source: Airbus A330 FCOM - Hydraulics

  Can airspeed be determined from the rate of its propeller rotation?

No, the RAT turns at constant speed to produce a constant AC frequency or hydraulic pressure or both. The rotational speed is stabilized by a governor which adjusts the angle of attack of the blades according to airspeed.

If the governor fails to maintain the speed, there is a security to prevent overspeed and blade damage/release.

Emergency Airplane RATs, Michael J. Zolidis, Hamilton Sundstrand, 2006.

A ram air turbine from Hamilton Sundstrand has a mechanical speed governor to vary the RAT blades angle according to the airspeed, and maintain a constant rotational speed.
At low speed, the blade angle is maintained near-perpendicular to the airflow to extract the most energy possible. When the ram speed increases, the angle is progressively reduced.
HS seems to measure the RAT power at 130 KEAS (Knots Equivalent Air Speed), e.g. the A380 RAT is 62” (1.57 m) diameter and delivers 85 HP (63 kW) at 130 KEAS. This mean at 130 KEAS or above, the full power is delivered.

Uncommanded Ram Air Turbine (RAT) extensions - Airbus

The RAT auto-deploys when both engines fail, or manually from a panel overhead. It's prevented to deploy on the ground, and below 100 KCAS
The speed value is provided by the ADIRU.
The RAT is able to be extended in all flight envelope conditions.

Embraer 190 - Airplane Operations Manual

There is no maximum altitude or speed for RAT deployment
Deployment occurs whenever AC buses are not powered or manually.
RAT deployment takes 8 seconds.
RAT has its full capacity at 130 KEAS or above.
Below 130 KEAS, only the AC bus is powered. DC buses are powered by the batteries, as well as the standby AC bus through a DC/AC converter.

ETOPS CAA

For ETOPS, three electrical power sources are required. If the RAT is one of them, it must be demonstrated as reliable (extension and generation).
The extension mustn't rely on engine power :-)

The most popularized RAT use may be for AC143 Gimli Glider, with a dual engine loss.

More:

RAT article on Wikipedia.
A320 RAT extension and retraction on Youtube.

Bombardier BD700-1A11 Global 5000 (source)
Airbus A320 Flight test (source)
Bombardier CRJ700 (source)
US Navy T-45A (source)
Airbus A330 (source)
Boeing B747-8 (picture by Gregor Schläger, source)
Boeing B777, RAT extension switch (source)


Is aerodynamic braking really effective?

The aero brake in this picture is the chute! and yes, it works!

Your wiki source is mistaken in stating that this use of elevator increases load on the main gear. The wing angle of attack will increase wing lift in multiples of the tail download, as you observe in the extended gear struts.

Landing like this allows the aircraft to slow with less use of brakes. It is counter-intuitive to claim to both save brakes and increase main gear load, which is intended to allow greater use of brakes.

Military jets land at comparatively high speeds, making this more useful since aero drag is proportional to speed squared. It may even be more effective at high speed than brakes, saving brake capacity for later in the landing when aero braking becomes less effective. Brake capacity may be limited to keep brakes small and light.

Nose gear does not have brakes and adds negligible friction.


Do airline pilots use this high-speed, high-drag technique for losing altitude?

Airline pilots certainly do use gear/flaps/spoilers to descend more quickly if needed. However, SOP typically requires an approach to be stable upon reaching a certain altitude on the approach. This means having speed and airplane configuration set for landing, and being lined up with the runway and on the glideslope. Unstable approaches are more likely to result in landing mishaps.

Some situations such as a runway change may require late changes to the approach. It is up to the crew whether they can safely make this change or if a go-around is the better option. S-turns are another way to lose further altitude.

When Air Canada Flight 143 ran out of fuel, the pilot used his glider experience to perform a forward slip to lose altitude. These sorts of maneuvers would be reserved for an emergency on an airliner.


What is the effect of altitude on true airspeed?

If you know GS and local wind speed, the TAS always the same, regardless of altitude. The true airspeed is called "true" because it is exactly how fast you are moving relative to the air. Picture it as a person in a weather balloon (which does not move relative to the surrounding air, i.e., TAS=0), pointing a radar gun at your aircraft to measure its speed. The results would be the same regardless of altitude, temperature, pressure, etc. This is what sets TAS apart from pretty much any other speed like IAS, CAS, EAS and Mach.

Only at truly ridiculous altitudes you would have some problems with calculating TAS, due to the increased orbital radius from the center of the Earth. However, at this point, you're well into the near vacuum of space which means that the whole concept of 'air' speed is quite silly.


They are DME (TACAN) channels. If you look close the the VORs, you'll see that they are either a VOR/DME or a VORTAC station. DME is the distance portion of a TACAN. When added to a VOR, you have a VOR/DME. If a complete TACAN is co-located with the VOR it is identified as a VORTAC.

The military uses TACAN. If you were to have a TACAN receiver, you wuold tune it using the channel number.

DME is available to civilian users with a DME receiver. The DME channels are paired to VOR/ILS/VHF frequencies (It's a multi-page table in the DME standards.) For convenience, DME receivers are tuned using the paired frequency.

When you tune a VOR or ILS, that frequency is also sent to the DME automatically tuning it to the proper channel. They are channels because DME actually uses two frequencies, one for transmit and one for reply.

So, to answer the question: unless you have a TACAN receiver, you don't do anything with the channel number. They are on the chart for reference.


Does the "west evens / east odds" rule apply when flying without a specific destination (sightseeing, etc)?

14 CFR 91.159 says:

  Except while holding in a holding pattern of 2 minutes or less, or
  while turning, each person operating an aircraft under VFR in level
  cruising flight more than 3,000 feet above the surface shall maintain
  the appropriate altitude or flight level prescribed below, unless
  otherwise authorized by ATC: [etc.]

So if you're above 3000' AGL and not turning or in a hold, then you're required to follow the odd/even rule. Personally, I've never found it to be an issue because if I'm on a sightseeing flight or just following a river or whatever for fun then I'm usually below 3000' AGL anyway (and 91.159 is one of the reasons why).


Who is responsible - CFII or the Private Pilot?

There is a contradiction in your question.

You say both the student and instructor are logging PIC.  This is fine, but the authority for this to happen depends on certain things.

The instrument student logs PIC under 61.51(e)(1)(i)

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

  (i) When the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, or has sport pilot privileges for that category and class of aircraft, if the aircraft class rating is appropriate;

They are acting as PIC as the sole manipulator of the controls and must be rated for the aircraft.
The instructor logs PIC under 61.51(e)(3)

  (3) A certificated flight instructor may log pilot in command flight time for all flight time while serving as the authorized instructor in an operation if the instructor is rated to act as pilot in command of that aircraft.

This only applies on instructional flights, where the instructor is providing instruction and is rated to act as PIC (e.g. if the instructor lacks a medical and could not act as PIC, they could still provide instruction if the student is the PIC, but the instructor would not be able to log PIC).

The reason I say this is a contradiction is that you claim

  Let's say it is just a normal VFR flight, and they're getting back to their home airport after a training flight.

This makes it sound like it is not a training flight and in that case only one of the pilots could log PIC using the sole manipulator rule in the absence of instruction taking place.

It turns out the above isn't directly important, as logging != acting PIC, and the acting legal PIC is what matters from an authority and enforcement perspective.  What the above logging issue gets at is hinting at who might be the legal PIC absent the two pilots agreeing who would act as the legal PIC.

In the case instruction is taking place even though the student is logging PIC  the instructor is also logging PIC and is the "ranking" pilot in the flight and may be viewed as the legal PIC.  In the case of a non-training flight (which would be hard to justify if you both logged PIC), then it comes down to the question -- who agreed to act as the legal PIC?  Either of the student or instructor could act as the legal PIC, but on a non-training flight only the one of you actually manipulating the controls could log PIC.  If there was no agreement prior to the flight over who is the legal PIC, the FAA will still probably decide the CFII was the legal PIC or the FAA may decide to go after both of you.  I believe there is precedent for this in enforcement action, but I don't have any cases handy to reference.

What should you do about this?  Both the student and the instructor should fill out a NASA ASRS form and preserve evidence that you submitted it within 10 days of the event.  If the deviation was not willful and the controller decides to pursue action, this will protect you from enforcement.


Does Wing Area vary with angle ot attack?

Wing area does not change with angle of attack. The only way wing area can change in flight is if there are devices on the wing that can extend and retract, making the wing longer, shorter or wider.


What are the FAA regs regarding landing a helicopter off airport?

There are no Federal Laws prohibiting landing rotor craft off field.
14 CFR 91.119

(1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA;

Part B and C, for reference

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

However, state laws, local laws, zoning laws, etc. change from location to location. You need to make sure you plan where you are landing beforehand and check these laws.
For example, in the State of New Jersey, helicopters can only be landed at the following locations:

Permanent public use heliport or vertiport
Permanent special use or restricted use helistop or vertiport
Temporary helistop or vertiport

(Reference)


What aircraft has this pattern of white strobe lights?

Twenty cycles per minute means it wasn't an FAA-approved aircraft, so it probably wasn't manned, or even a weather balloon.

Satellites need no anticollision lights.

The bright strobe combined with the longer fading lights suggests something homebuilt.  The light may have been adapted from consumer bicycle lights, which have quite a variety of patterns.  Professional lights such as Whelen's models prefer flickering to fading, for both efficiency and visibility.


You didn't specify the jurisdiction that you were asking about, but in the US there is a regulation that covers the minimum that you must do before flying.

Much of it is common sense:

You want to check the weather, because it can impact you much more than it usually does in your car and you don't want to get stuck in a really bad situation.
You want to check the Notices to Airmen (NOTAMs) to make sure that you can use the airport (i.e. it isn't closed, or the runway isn't closed, etc.)
You want to make sure that you have enough fuel, because you can't just pull over at the nearest gas station when you get low.
You want to make sure that the runways are long enough and that the airplane can climb well enough so that you don't crash into something.

That being said, if you are familiar with the area and the airports in the area, you have used them before and are already familiar with the performance numbers for your airplane, then you don't really need to do much more than check the weather/NOTAMs and make sure that your airplane is legal and safe to fly.

Things are a little different than back in the barnstorming days, but then there are fewer accidents too.  :-)

  §91.103   Preflight action.
  Each pilot in command shall, before
  beginning a flight, become familiar with all available information
  concerning that flight. This information must include—

  (a) For a flight under IFR or a flight not in the vicinity of an
  airport, weather reports and forecasts, fuel requirements,
  alternatives available if the planned flight cannot be completed, and
  any known traffic delays of which the pilot in command has been
  advised by ATC;

  (b) For any flight, runway lengths at airports of intended use, and
  the following takeoff and landing distance information:

  (1) For civil aircraft for which an approved Airplane or Rotorcraft
  Flight Manual containing takeoff and landing distance data is
  required, the takeoff and landing distance data contained therein; and

  (2) For civil aircraft other than those specified in paragraph (b)(1)
  of this section, other reliable information appropriate to the
  aircraft, relating to aircraft performance under expected values of
  airport elevation and runway slope, aircraft gross weight, and wind
  and temperature.


Can Airbus A400M take-off from the beach fully loaded?

The surface of the beach will need a certain California Bearing Ratio to be allowed to have the aircraft land there. This will be measured by the ground support prior to the arrival of the aircraft.
This will allows the aircraft to operate largely normally when on the ground roll and taxiing, however the crew would need to be mindful about brownout when using reverse thrust and to be gentle when turning so as not to bury the nose wheel.
The aircraft will have a maximum mass for operations at the given CBR. There will also be a max mass based on the aircraft performance versus the field conditions and parameters with margins for safety (though not the same as standard Engine-Out performance or Balanced Field) which is unlikely to be its normal maximum takeoff mass.
EDITED for scope.


Relationship Between Aircraft Thrust and Jet Exhaust Velocity?

The thrust produced is propotional to the exhaust velocity and mass flow, in simple terms. The thrust equation can be written as,

$T$ = $\dot{m}_{e} v_{e} - \dot{m}_{o} v_{o} - (P_{e} - P_{o}) A_{e}$

where, $\dot{m}$ is the mass flow rate $v$ is the velocity, $P$ is the pressure and $A$ is the (exhaust) area. The subscripts 'o' and 'e' denote the freestream and exhaust values respectively.

There are multiple ways to go about noise reduction in aicraft engines, all with some kind of penalty- the Boeing method is to use chevron shaped exhausts (Interestingly, the type chosen is the one with lesser thrust penalty, not the most effective in noise reduction). However, Airbus has cited higher fuel consumption as the main reason for them not using it. Airbus uses acoustic liners in the engine to reduce noise:

  The thrust reverser structure was acoustically treated along approximately
  half of its internal surface. It was clear that increasing this acoustic area would increase the acoustic sound absorption and hence decrease the overall measurable exhaust noise.


Are there 5000+ companies with IATA (two-character) codes?

It's obviously an error in that Wikipedia page. The "5000 airlines with IATA codes" text actually links to:

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

which lists lots of airlines (over 6000), but most of those have ICAO (3 letter) codes, but not IATA (2 letter) codes.


Looking for the correct propeller shape to create a small copter

Use Mark Dela's XROTOR - it will give you the chord and twist distribution over span for a given speed, torque and thrust (well, two out of three).

It is based on Larabee's theory (PFD!) for a minimum induced loss rotor.

For a practical solution try to design an optimum propeller for the speed and torque of your motors and then try to find something similar in a  hobby shop. Building the propeller yourself will be a major effort - just balancing them well will not be easy.

If you are into doing everything yourself, try to carve a master and make a mold, maybe from silicone rubber. Then you can pour as many propellers as you need. Put glass- or carbon fibers into the mold and fill up with thickened epoxy. For thickening use a mixture of cotton short fibers and Aerosil 200.

The links to the materials are only for background information - I cannot endorse the sources because I have never ordered from those specific suppliers. The method in general will work, though.


What do pilots do, when there is a long wait before take-off, after gates are closed?

Apart from what Daniel listed already, they're also nervously watching the clock.
If they're late by too much they may miss their mandatory crew rest period and have to cancel the flight or hand over to another crew.

This can of course get very expensive for the airline, especially if all or most passengers have to be accommodated in hotels overnight for a departure the next day in case no replacement crew can be arranged or the forced delay causes the flight to be unable to take off due to closing of the departure airport before departure or closing of the destination airport before arrival there.


Becoming a CFI in the USA as a non-US citizen

You do not need to be a citizen to be a U.S. CFI.

You need to have US ratings, so you would have to have all your German licenses/ratings converted, which takes some time.

You have to be absolutely FLUENT in both spoken and written English.

If you want to charge students money for your services, you have to have US residency or other work visa authorization. You do not need a work visa if you train students for free.


The added weight, space, and complexity of a second recorder have to be taken into account, and all are very important for an airplane.

If you are just interested in location, then there could just be a simple beacon designed to float. Although less, this will still have the above costs. And you have to design something light enough to float, sturdy enough to survive an extremely violent crash, yet still be a functional electronic device.

Considering that the situation of a lost aircraft at sea is fairly rare, it is questionable whether the benefits justify the costs.


Why would a helicopter climb in a spiral?

A helicopter will achieve its best climb rate at a moderate forward speed. Climbing in a spiral helps to have forward speed in what is essentially a vertical climb.

In a hover all the airflow which is available for lift creation must be generated by the rotation of the main rotor. This means that a small amount of air must be accelerated by a lot. If the helicopter adds forward speed, it can achieve a higher mass flow through the rotor, and now less acceleration is needed to achieve the same lift. This improves the efficiency of lift creation. If the helicopter goes faster than its speed for maximum rate of climb, aerodynamic drag grows too high and reduces efficiency again.

The difference can be dramatic: Below is a plot of the speed versus altitude of a generic helicopter and turboprop plane in comparison to the V-22 tilt rotor. Remember that the available power is roughly proportional to air density, and you can start to see how much more power is available for climbing when the helicopter flies with a moderate forward speed.

Flight envelopes of a generic helicopter, a turboprop plane and the V-22 tiltrotor (picture source). Thanks to @mins for inspiring me to expand the answer a little.


Where can I find information about post-WW2 airports in Saudi Arabia?

There have always been three primary airports, representing the commercial hubs of Saudi Arabia:

Dhahran International Airport / Dammam - King Fahad International Airport

This was a dual use, single runway airfield which was the primary international commercial airport for the Eastern province, until the new Dammam International was commissioned and opened for the first flight in November 1999; Dhahran has since been reverted back to military use and is still actively being used today.

Riyadh Airport / King Khalid International

As with Dhahran - Riyadh Airport is a military dual-use airport until the dedicated King Khalid was opened in 1982, and the old Riyadh airport (OERY) was reverted back to military use.

Jeddah Airport / King Abdulaziz International

This is busiest airport in the kingdom, also one of the largest terminal buildings in the world. It is also the hub of the state carrier Saudia. It opened for service in 1981.

There then the secondary airports which also service international flights:

Medina / Prince Mohammad Bin Abdulaziz International (OEMA) - Opened in 1950; new terminal opened in 2015.
Taif International - Opened in 1976, it gained importance as it is the closest airport to Makkah (the Holy City) - and it is one of the most popular summer destinations in Saudi Arabia.

There are a lot more regional and domestic airports is Saudi Arabia. You can find information on those from the General Authority for Civil Aviation (GACA) website.

Saudia (the flag carrier) has great information dating back to 1945 available on their website.

King Abdulaziz: His Plane and His Pilot is a great book that covers the history of Saudi aviation.


What is the correct name for clearance delivery at KSAN if the tower is called "Lindbergh Tower"?

Lindbergh is used as an identifier shortcut because "Lindbergh Field" is the official name of the airport. So I would call in with "Lindbergh Clearance Delivery".


Why do I missing 1090 Rebroadcast Traffic (ADS-R) Targets from Ground Station as part of 978 Uplink?

Ground stations only send ADS-R/TIS-B messages for targets within a certain distance horizontally and vertically of ADS-B targets with the CDTI (Cockpit Display of Traffic Information, aka "ADS-B In") flag set. Assuming your CDTI flag is set correctly, the targets you're missing probably aren't close enough to qualify.


Air traffic control system is the computer system that air traffic controllers use to keep track of the aircraft they are controlling.

The system processes data from the primary and especially a secondary radar and displays them in suitable fashion for easy understanding by the controllers. The radar processing itself is not interesting for database class. But there is a bunch of information about each aircraft that needs to be remembered and associated with it's radar image:

The assigned transponder 4 octal digit code (usually called "squawk"). This is a code the secondary radar receives from the aircraft used to associate the data to the correct radar return.
Identification, also used as callsign. It is registration number or flight number (sometimes internal company flight number that is different from what they show in time tables)
Aircraft type

The aircraft type is needed so the controller knows the performance of the aircraft, so it needs associated performance data like maximum speed, approach speed, maximum altitude etc.

Flight plan. This needs to contain:

Start and destination airports
Preferred cruise altitude and speed
List of waypoints

You may consider current clearance limit (altitude and waypoint); I am not sure whether the current systems include it or not.


Are air traffic controllers required to obtain a pilot license?

No, there is no such requirement here in Germany.


Can wing-tip vortices be reduced/eliminated with a rear-facing propeller near the wing-tip?

Yes. From an aerodynamic standpoint it makes some sense to use the wingtip vortex in combination with a propeller.

In this article by Sinnige et al., the researchers modeled and tested a propeller in various positions along a semispan, concluding that there were real gains to be had due to the increased span efficiency. Up to 15% less drag was measured when the propeller was positioned at the wingtip compared to a conventional mounting:

  By positioning the propeller at the tip of the wing, the slipstream interacts with the flow around the wingtip, thus affecting the roll-up and downstream behavior of the wingtip vortex. PIV measurements downstream of a propeller–wing model showed that this leads to a reduction in overall swirl with inboard-up rotation, for which the swirl in the slipstream is opposite to that associated with the wingtip vortex. At the same time, the system performance was found to improve due to a reduction of the wing induced drag, leading to the conclusion that the decrease in swirl causes a reduction in downwash experienced by the wing.

  Apart from the change in drag, the interaction of the wing with the propeller slipstream also modifies the wing lift. The locally enhanced dynamic pressure increases the lift over the spanwise part of the wing washed by the slipstream, which is amplified by the induced swirl for the case with inboard-up rotation. As a result, a strong spanwise variation in lift occurs with the propeller on. The induced velocities caused by this lift gradient lead to a spanwise shearing of the slipstream. With outboard-up rotation, the swirl in the slipstream acts to locally oppose the increase in wing lift due to the propeller-induced dynamic-pressure rise. Compared to the inboard-up rotation case, this leads to a reduction in wing lift at a given angle of attack, thus also a reduction in maximum lift coefficient. Furthermore, the direction of the spanwise shearing of the propeller slipstream is inverted on both sides of the wing.

  To quantify the potential aerodynamic benefits of the wingtip-mounted configuration, a direct comparison was made with a conventional configuration, with the propeller mounted on the inboard part of the wing. The increase in wing lift due to the interaction with the propeller was 1 - 4% smaller for the wingtip-mounted configuration than for the conventional configuration. For the latter, the enhanced dynamic pressure and swirl in the slipstream acts over double the spanwise extent, and on a part of the wing where the section lift is higher than for the wingtip-mounted configuration. At higher angles of attack, the lift advantage for the conventional configuration could be further enhanced
  by the local angle-of-attack increase in proximity of both sides of the nacelle.

  In terms of drag performance, on the other hand, the wingtip-mounted configuration showed superior performance. At a wing lift coefficient of $C_L = 0.5$ and a thrust coefficient of $0.09 < C_T < 0.13$, the drag reduction amounted to about 15 - 40 counts (5 - 15%) compared to the conventional configuration. The aerodynamic benefit of the
  wingtip-mounted configuration further increases with increasing wing lift coefficient and propeller thrust coefficient, leading to a drag reduction of 100 - 170 counts (25 - 50%) at $C_L = 0.7$ and $0.14 < C_T < 0.17$. An analysis of the wing performance confirmed that this drag benefit is mostly due to a reduction of the wing-induced drag. Compared to the conventional configuration, a relative increase in span efficiency of up to 40% was measured for the wingtip-mounted configuration. Although the exact drag benefit will be specific to vehicle design and operating conditions, it is concluded that the interaction between the propeller slipstream and the wingtip vortex leads to a clear drag reduction for the wingtip-mounted configuration.

Keep in mind this is purely aerodynamical, of course, and from a structural standpoint things might not be so clear-cut. While weight in the wings helps alleviate the bending stresses generated by lift, a large mass at the tip can lower the first bending eigenfrequency to unacceptable levels, risking a coupling of the wing oscillations with some other mode in flight or on the ground.

As far as I am aware wingtip fuel tanks have mostly been used on relatively low aspect ratio wings, which lends some credence to the magnitude of this problem.


Why there so many pitch control surfaces on the Piaggio P180 Avanti?

Surface 1 is a  horizontal stabilizer with elevator, just the same as on any other aircraft with a T tail arrangement.

Surface 2 is called a rear strake or a tail fin. There is one on each side of the fuselage. They provide extra stability during operation at high angles of attack when the fuselage is disturbing the airflow to the vertical tail. They are not movable.

Surface 3 is a canard, providing extra lift. The canards on P.180 have a trailing edge flap. The flap is necessary to counteract the nose down trim of the flaps in the main wing. Without the canard flaps the elevator would not have sufficient authority to maintain adequate pitch control when full flaps are deployed on main wings.

Surfaces 1 and 3 have movable parts, but surface 1 is the only surface connected to pitch axis control of P.180.

Piaggio P.180 article on Flying magazine explaining design features (and a lot more).

Rear strakes- tail fins on Wikipedia


What fundamental differences separate low-budget airlines from traditional airlines?

Generally speaking:

They operate a limited number of airframes if not a single one (for example Ryanair operates 420 737-800's and only a single 737-700 for chartering). This allows them to buy planes in bulk as well as cut down on spare parts reserves, pilot proficiency training in multiple airframes and overall maintenance costs by only needing to hire mechanics proficient in a single airframe. They can also easily substitute an aircraft on a given route as they are all configured the same.
By having seats that don't recline and sometimes no first class they can really pack people in. Those extra customers make a big difference. There has even been some buzz about packing more people in with "standing" seats but I have not seen anything certified on that front as of yet.
In my experience they tend to have less lenient refund and change policies. For example Spirit charges a $90 cancelation fee and most tickets are around that price.
The meals tend to be pre-packed and may have a longer shelf life than the hot food served on other airplanes. This means they can buy it in bulk (read cheap), in advance and store it, and there is no need to coordinate the delivery like there is with hot food. Cold food can hang out at the gate waiting for the plane.
There has been a big move to use mobile devices for a lot of classic functions like check in and boarding passes. This allows them to not need checking counter employees or curb side employees etc. This labor cost is a huge savings. In many cases the flight attendants may also be the  boarding/gate personnel.
Some of them also avoid major airports and may elect to fly out of smaller regional airports. This helps keep fees down and some satellite airports may be substantially less busy allowing them to get in and out faster.

As per @Jamiec's comments

Shorter turn around times

No seat back pockets so nothing to clear out.
No pillows and blankets to pick up
Cabin crew may do the majority of cleaning

As @757toga notes some of them also may keep pay low or act as a jumping off point for young pilots to get their type certs and build hours.

Related questions:

How can Ryanair offer flights for a penny?
What's the typical cost (and its breakdown) for a long-haul commercial flight?


How to fly an RNAV (RNP) approach with VNAV in a Boeing 737?

This usually depends on the airline SOPs. The safest thing to do when cleared for the approach is to set the MCP altitude window to the lowest altitude restriction because that way you won't forget to lower it again. As long as the aircraft is descending in VNAV PTH mode, it will follow all altitude crossing restrictions.
When cleared for final approach, one can also set the DA (Decision Altitude) for the approach instead of a crossing restriction into the window. This will allow VNAV to descend further and is required unless IAN  with G/P is used:

The Integrated Approach Navigation (IAN) modes are armed/engaged by
selecting the APP button on the AFDS Mode Control Panel (MCP). Once armed,
the autopilot/flight director will capture and track the localizer/final approach
course and glide slope/glide path.

(Boeing 737 NG FCOMv2 - 4.20.20 - Automatic Flight - System Description)
Once the aircraft is descending on final approach, one can set go-around altitude into the window:

When the FMC is “on approach”, the following features are available:

when preparing for a missed approach and the MCP altitude is set at least
300 feet above the current airplane altitude, VNAV will continue to
command a descent

(Boeing 737 NG FCOMv2 - 11.31.37 - Flight Management, Navigation - Flight Management System Operation)

Using SPD INTV will usually cause the vertical mode to switch from VNAV PTH mode to VNAV SPD mode, which does not care guarantee to comply with crossing restrictions:

If speed intervention is engaged:

during a path descent with flaps up on an idle leg, VNAV switches to VNAV SPD
with flaps down, VNAV remains in VNAV PTH

(Boeing 737 NG FCOMv2 - 11.31.38 - Flight Management, Navigation - Flight Management System Operation)
So if you already have flaps selected, VNAV PTH will remain active. During VNAV SPD operation, it is the pilots duty to ensure all crossing restrictions are met. Once the aircraft goes back on the path, VNAV PTH mode will engage automatically again (assuming you are on a STAR or approach):

A speed descent cannot automatically revert to a path descent, except during
STAR, approach transition, or approach leg with a vertical angle.

(Boeing 737 NG FCOMv2 - 11.31.33 - Flight Management, Navigation - Flight Management System Operation)
Changing the target speed in the FMS will compute a new descent profile. This usually results in the aircraft no longer being on profile and therefore the vertical mode will switch to VNAV SPD as well.
Note that VNAV SPD will not violate altitude restrictions, if possible:

The descent attempts to comply with waypoint altitude restrictions, and will not
violate these restrictions. The VNAV speed descent will not, however, guarantee
the airplane reaches an altitude restriction at the required point.

(Boeing 737 NG FCOMv2 - 11.31.33 - Flight Management, Navigation - Flight Management System Operation)


if your Seneca weight is 4000 pounds , and you have 800m visibility, would you take off?

What he wants to know most likely is do you have accelerate-stop and accelerate-go distances computed for that airport and ambient atmospheric conditions at that takeoff weight. Do you also have adequate runway available for that as well as a climb rate adequate for obstacle clearance in the event of a critical engine failure after Vr?  And if that’s the case, do you have a plan in place for that emergency situation?  Multi engine flying is a lot about anticipation for these kinds of contingencies.  Having a plan for takeoff and departure and anticipating engine failure on takeoff is all part of safely flying light and medium twins.  If you can’t do that, you’re in dangerous waters and the examiner wants you to think about that.

I don’t have a Seneca AFM available to me, but you should probably go back and review your takeoff and climb performance data for OEI as well as information related to your airport and departure procedures.  This should give you a much better answer to this question.

From a legal perspective, it also all depends upon under what flight regulations the flight is being conducted under.  With approx 1/2 sm visibility and flying a two engined aircraft, the departure would be illegal when conducted under Part 121, 125, 129, and 135 commercial operations, but is legal under a Part 91 flight operations.  Make sure that is included in your decision as well.

Finally, just because you CAN do something does not necessarily mean you SHOULD do something.  These conditions are pretty tight and you are painting yourself into a really uncomfortable corner with little margin for error should anything go wrong.  Are you really that competent to operate a twin, including handling an engine failure, with such low weather minimums or in complete zero-zero conditions?  Are you willing to bet your life on that knowing that once you’re airborne in that environment and on course, there’s no turning back?  Can you maintain the correct airspeed, altitude, heading, and climb rate which the AFM lists all while juggling an engine failure or some other emergency while in IMC?  Are you sure these conditions don’t exceed your personal minimums given your experience with multi-engine flying and, in particular, operation of a Piper Seneca?  If the answer is no, then you should not fly under these conditions.


Why do some airplanes have their winglets at different angles?

Winglets are symmetric, meaning they are the same shape, size and angle on both sides of the airplane. Different shapes and/or angles would mean the wings would have different aerodynamic properties, i.e. they'd fly differently from one another, which is generally a bad thing. It's probably been done for testing purposes, but not in production aircraft.

It's possible that your friend noticed that different makes and models of airplane have different winglets. Some look like this:

Some look like this:

There's other shapes too. Viewed from different angles it's possible they may look like different shapes, but they're going to be the same even if it doesn't seem that way.


what's the difference between priority and sequence valve in aircraft?

A priority valve will manage the flow in a hydraulic supply that feeds two different circuits such that if the input flow, that is normally enough to satisfy both circuits' demands, drops below a threshold, the valve will starve or cut off the low priority circuit in favour of the high priority circuit to keep it supplied.  So if I have two subcircuits in a system running on the same source, and I determine that one is critical to safety, I'll put in a priority valve to make sure the critical circuit continues to get pressure if the inlet flow is not able to supply both.

Not to be confused with shuttle valves in brake systems that block off one inlet when pressure is applied at the other inlet.

Sequence valves require a mechanical condition (or electrical condition in the case of a solenoid sequence valve) to be satisfied before supplying or cutting pressure to a circuit.  Like to control gear doors that need to be timed to open or close when the gear legs are at position X or Y.


Does a multi-engine rating propagate down from commercial to private?

Note Part 61.31(c):

  (c) Aircraft category, class, and type ratings: Limitations on the
  carriage of persons, or operating for compensation or hire. Unless a
  person holds a category, class, and type rating (if a class and type
  rating is required) that applies to the aircraft, that person may not
  act as pilot in command of an aircraft that is carrying another
  person, or is operated for compensation or hire. That person also may
  not act as pilot in command of that aircraft for compensation or hire.

Since you will have the Category and Class rating, then you may carry another person.

Your old license says:

Private Pilot
Airplane Single-engine Land
Instrument Airplane

Your new license will say:

Commercial Pilot
Airplane Multi-engine Land
Instrument Airplane

Private Privileges
Airplane Single-engine Land

You may fly under part 91 ASEL, AMEL, and IFR

You may fly part 119 or 135 (or other commercial operations) AMEL and IFR1. You may NOT fly part 119 or 135 or any commercial operations ASEL. If you want to fly ASEL in a commercial operation, you will need to upgrade your ASEL by passing another commercial checkride in an ASEL.

This is the back of my certificate. I took the ASES checkride when I had a Private certificate.

1. Assuming you have the correct medical and any other checkouts you may need


How does the pitching moment change as the speed of A/C approaches critical Mach number?

Yes most aircraft which operate in the transonic zone experience a nose down pitch with increase in speed. The two main causes are :

Rearward movement of centre of pressure
Because of supersonic acceleration at higher speed, pressure continues to decrease past the 50% chord point, thus increasing the amount of lift produced by mid chord part of wing.
Modification to airflow over the tailplane
Most tailplane work in a region of downwash from the mainplane, in case of swept aircraft the downwash can be considerable. The formation of shockwave on main plane modifies the flow such that the downwash is reduced and this will pitch aircraft nose down


Where can I get aviation weather information?

NOAA collects METARs (current weather) from all over the world and publishes them at http://weather.noaa.gov/pub/data/observations/metar/stations/.

They also collect TAFs (forecasts) and publish them at http://weather.noaa.gov/pub/data/forecasts/taf/stations/.

These reports are what the information told to pilots by controllers or broadcast in ATIS is based on, written in shorthand format designed for efficient transmission over teletype. If you look around the directory structure, there are also decoded versions.

The above links are complete, but intended more for machine consumption, being plain text files. You'll find many other sources that look more like normal web pages if you google for some airport code and “METAR” or “TAF”, but different parts of the world will be available at different places. The above links are most comprehensive source.


Can anyone identify this 1970s Mitsubishi pushback tug?

I Have found out this Mitsubishi pushback tug in real life at Haneda airport, Tokyo. but I wasn't able to get the original model number but I belive Mitsubishi hasn't set one for it otherwise the TOMICA toy co. would have named it as the other toys.

This pushback tug was only associated to pushback the B747 only, since all the photos the tug was with B747 only! cheers

References:-
-https://aflyinghistory.com/search-aeroplane-photographs?query=tokyo+haneda+airport&page=1
-https://www.airliners.net/photo/China-Airlines/Boeing-747-132/2246060
-http://motorcade.weebly.com/mitsubishi.html


Yes it can. The steady-heading sideslip (SHSS) maneuver is used in flight testing to demonstrate static lateral/directional stability (similar maneuvers exist as sideslip approach in crosswind, or stabilized control with one-engine-inoperative at low speed). In this maneuver, rudder is applied to hold a sideslip, which generates an opposing side force and rolling moment. The rolling moment is neutralized via ailerons, and the side force is canceled out by banking to the opposite side. Once at steady-state, the aircraft is maintaining a rectilinear course, while banked.

Adapted from NASA IS-97/08-DFRC-01


Do military pilots have a phrase like "aviate, navigate, communicate"?

I am a Naval Aviator and have commanded a flight training squadron.  We actually teach that very phrase.  Aviate, navigate, communicate was one of the first things I learned, and it has served me well over the years.

It applies no matter the situation.  The target fixation example you gave is a good one.  Getting an aircraft where it needs to be to put a bomb on target is clearly in the navigate realm.  It is superseded by not flying into the ground...which is in the aviate realm.


Why are many military fighter aircraft designed to fly supersonic?

One reason is interception (with interceptor, not missiles).

Defence is probably more important. Defence with fighters is still important for three reasons:

There are relatively effective counter-measures against surface-to-air missiles. A fighter pilot can adjust the strategy to the counter-measures encountered, missile can't.
In peace or limited conflict situations it is often not known whether a suspicious target is hostile at all and the only way to identify it is to have a fighter fly to it and have the pilot identify it with their eyes.
Fighter can also do other things than use lethal force. In peace time you generally don't want to shot down an intruding military aircraft of another country straight away. Fighter can chase it away from your territory or can try to arrest it (force it to land on your own airbase). And fighters are also used to identify and possibly navigate to safety civil aircraft that lost radio contact.

So when a potentially hostile aircraft is detected entering your territory, fighters are sent to intercept it and help it, arrest it or shot it down depending on what it turns out to be.

If the fighters are slower than the intruder, they may not be able to intercept it at all (they don't usually know where it is flying so they can't wait for it). The faster they are, the larger area they can defend. In this case the interceptors take off without external fuel tanks (as they won't be flying very far) and with only relatively small air-to-air missiles, so they can fly fast.

Conversely if you try to penetrate the enemy territory, flying faster limits the number of fighters that can intercept you. However in this case it is more useful to rely on stealth or flying low to evade detection, so attack aircraft often are either not supersonic or have lower maximum speed.


Does the flap settings for the best lift/drag ratio change with speed on the Diamond DA20-A?

You did the right thing when asking a new question. Comments are poorly suited for the explanation of non-trivial issues.

Now follow several links to older answers. They should help to explain a couple of things, such as:

what flaps do to L/D.
how thrust changes over speed for propeller aircraft.
and how efficient propeller airplanes are in cruise.

  does the flap settings for the best lift/drag ratio change with speed?

Below you see the polar plot from the first linked answer. It shows the airfoil drag in 2D flow. Clearly, the best L/D is achieved with the +10° flap setting, but at this setting the airfoil becomes rather poor below a lift coefficient of 0.3. In order to reduce drag, the flap should be raised when flying fast enough so that the lift coefficient drops below that value.

So the answer is yes, the optimum flap setting does change with speed. Only the flap setting for the overall best L/D will be found at the same flap setting, but then this best L/D can only be reached at one specific lift coefficient (which is equivalent with one specific speed if mass does not change).

  I can understand it's either up or down for the best L/D ratio but I don't get why does it change at a specific speed?

It does not change at a specific speed. It changes continuously with lift coefficient (and, implicitly, speed). If you compare specific flap angles, you will find crossover points when the L/D of one flap setting drops below that of another flap setting as the lift coefficient changes. Normally, airplanes only allow a few specified flap angles, so it might seem that L/D changes abruptly when changing flap angles. However, flaps could also move continuously, adapting the wing to its optimal setting for each operating point.

  why would someone design a wing that's less efficient to fly in Cruise then in Climb?

Cost. GA aircraft don't have the complex flap systems of airliners and, consequently, have a much larger wing than what is required for cruise. Wing area is sized for the mandated minimum airspeed of 61 kts or less and installed power means that the airplane at low level cruises at a speed where friction drag dominates and induced drag is almost negligible. While technically possible, the complex high-lift systems of airliner wings would make any GA airplane a lot more expensive, a death trap for untrained pilots and a maintenance nightmare.


What implications does automobile electrification have for the supply and cost of Avgas?

I have not seen any studies on this, nor would I expect to as Avgas is such a niche product and the price of it is not heavily dependent on the price of the underlying fuel itself. If you look at this answer the reason avgas is so expensive is that it has special requirements for making it, storing and transporting it and so little is produced that there's no economy of scale.

In any case your question is based on the premise that gasoline production is going to decrease. Even with the rise of electric cars most oil companies aren't forecasting a drop in gasoline demand until the 2030s, maybe even the 2040s as the increase in demand for new cars will oustrip the number of electic cars for some time. As a decline in consumption does not guarantee a price rise, any forecasts of this kind would be premature, and not likely to be reliable.


Who made the first high-wing jet airliner?

Perhaps the Baade 152, built in Germany (GDR) in the late 1950s...
https://en.wikipedia.org/wiki/Baade_152


Does asking for deviation due to weather give ATC any leeway for reducing separation between aircraft?

No, it does not. ATC can specify a restriction to the deviation, especially in a non-radar environment where they can't keep an eye on you.

The only thing that frees ATC of separation responsibilities between two IFR (or IFR/VFR depending on airspace) aircraft is if one them reports the other in sight, and is issued an "maintain visual separation". After that the responsibility of not hitting the other aircraft, or its wake, rests solely with the pilot in command.


What is the direction of the sideslip induced by roll on a conventional aircraft?

To answer what you wrote: $c_{n_q}$ is the yawing moment induced by a pitching motion. In a conventional, symmetric configuration this is zero for the airframe and has a small value for propeller aircraft, depending on the rotation direction of the propeller. If the tractor propeller is spinning clockwise (when seen by the pilot), a positive pitch motion $q$ (nose up) will cause a small negative sideslip angle $\beta$. A positive pitch acceleration will add a precession moment which similarly pulls the aircraft's nose to the right. But I think you want to know something else.

To answer what you meant: $c_{n_p}$ is the yawing moment induced by a rolling motion. The axis system you propose (with z pointing up) is used to measure relative positions within the airframe, but for flight mechanics we prefer to put the x-axis in flight direction, y to the right and z down. A positive rolling motion $p = \omega_x\cdot\frac{b}{2\cdot v_{\infty}}$ (or $p = \omega_x\cdot\frac{b}{v_{\infty}}$, both definitions are used) is right-wing-down, and a positive yawing moment means the aircraft's nose moves to the right, causing negative side slip angles.

When a positive rolling motion happens in still air, the resulting yawing moment is negative, pulling the aircraft's nose left, as Federico said. Thus, $c_{n_p}$ is negative.

But the reason is different: When the pilot deflects the ailerons and causes a difference in lift on the left and right wings, and consequently a difference in induced drag, the yawing moment caused by that difference in induced drag is called $c_{n_\xi}$, the yawing moment due to aileron deflection. $c_{n_\xi}$ is positive.

Once the aircraft is in a steady roll, the roll damping $c_{l_p}$ will fully compensate the differential lift caused by aileron deflection. Now the rolling motion will increase the local angle of attack on the downward moving wing the farther you are away from the center, and decrease it on the upward moving wing. Since lift is perpendicular to local airflow, the air force vector on the downward moving wing is pointing slightly forward, and that on the upward moving wing slightly backwards. Please note that the total lift produced by each wing is roughly the same! The rolling moment of both is exactly zero once the roll rate is steady. However, the aileron deflection will decrease lift on the downward moving wing such that it just compensates for the increased angle of attack due to the rolling motion, and the same holds for the upward moving wing with its trailing-edge-down aileron deflection.

What is different is not the magnitude, but the direction of lift on both wings. This pulls the downward-moving wing forward and the upward moving wing back, causing a negative yawing moment in a positive rolling motion. That is why your conventional $c_{n_p}$ is negative.


What was the first flight instrument ever used in an airplane?

It's the yaw string:

  The yaw string dates from the earliest days of aviation, and actually
  was the first flight instrument.

Picture:

Source


Has a commercial or military jet bi-plane ever been manufactured?

Yes

I present to you, the Belphegor, a jet powered, crop-dusting, biplane. I think I need not say that this is a Soviet Bloc design, from Poland in particular.

Note the braces between the wings acted as tanks for whatever chemical agent it would be dispensing over the kolkhozy. It was not very successful due to a host of disadvantages, including:

Jet engines are not efficient at slow speeds, which are in turn required for crop dusting operations. The designers may have hoped to do away with this requirement by using it over the large collectivized farms of the USSR, but the straight wing attests to the top speed being low by design. The jet engine was apparently mandated by soviet planners wanting to simplify the logistics of fuel and maintenance by reusing the AI-25 engine.
Biplane configurations are less efficient than monowings of the same total area due to interference between both lifting surfaces.
For crop-dusting applications in particular, @Harper points out the fact that the shorter span of biplanes is detrimental to effective spraying, by limiting the width of the spray system, which needs to end short of the wingtips. Otherwise the agent will get picked up by the wingtip vortexes and spread in unintended directions.

On the other hand:

One advantage of biplanes is low roll inertia due to the shorter wings, which is mostly useful in dogfights and thus not highly-sought nowadays.
Another advantage of biplanes is the lower bending moment at the root of the individual wings, due to them being shorter. This allowed earlier designs to get into the air in spite of poor building materials and QA procedures; this solution was gradually abandoned as aircraft moved away from wood and fabric and towards aluminium alloys.
The lower span of biplanes might be useful in application that are span-limited, like modern airliners, which are limited by airport parking and runway restrictions. If you absolutely need to obtain more lift out of an airframe that is already at its maximum span, adding a second wing is not unreasonable.


Why wasn't Solar Impulse 2 cleared for takeoff?

Interesting question. The ATC orders mention only two reasons that controllers have to say "at your own risk":

The pilot "insists" on using a closed or unsafe runway (3-3-2)
A helicopter takeoff or landing uses a non-movement area (3-11-2, 3-11-6)

Obviously Solar Impulse 2 isn't a helicopter, so that leaves the closed or unsafe runway reason. I don't know for sure why the tower used the "own risk" phraseology - it would be great to hear from an actual controller - but some possibilities are:

The runway was marked as closed (for Solar Impulse 2) on the tower controller's displays, and he said "at own risk" more or less out of habit
There were vehicles on the runway, therefore it was "unsafe"
Solar Impulse 2 is such an unusual aircraft that the controller felt he couldn't contribute anything to the safety of the takeoff, so he was simply saying "go for it, I can't do much to help you"

Of course, the problem with all those suggestions is that they should apply at all the airports, not just half of them. But I did find this quote from a controller on the AOPA forums (members only):

  Although it's normal for helicopters, I issued this "departure will be
  at your own risk" to an aircraft once. The runway was open, he wasn't
  departing from a taxiway or anything like that. The problem was fog,
  where I couldn't see the runway from the tower, and therefore I
  couldn't determine whether the runway was actually "clear" for his
  takeoff.

  I don't know if this is the right response in this situation or not,
  but I was a pretty new controller at the time, hadn't faced this
  situation before, and figured the "at your own risk" was appropriate.

That could have applied to the Solar Impulse situation: with other vehicles and personnel on the runway, the controller can't say it's "clear". And just like the controller on the forum, perhaps some of the controllers handling Solar Impulse 2 felt that the non-standard wording was appropriate for a very unusual situation. The other controllers who did issue a takeoff clearance presumably felt differently.


Is yelling "clear prop" required by FAA regulations?

Like @mongo, I am not aware of a regulation and don’t recall seeing anything about it in the AIM. However, the Airplane Flying Handbook (FAA-H-8083-3B) says this about engine start:

  Prior to engine start, the pilot must ensure that the ramp area
  surrounding the airplane is clear of persons, equipment, and other
  hazards from coming into contact with the airplane or the propeller.
  Also, an awareness of what is behind the airplane prior to engine
  start is standard practice. A propeller or other engine thrust can
  produce substantial velocities, result in damage to property, and
  injure those on the ground. The hazard of debris being blown into
  persons or property must be mitigated by the pilot. At all times
  before engine start, the anti-collision lights should be turned on.
  For night operations, the position (navigation) lights should also be
  on. Finally, just prior to starter engagement, the pilot should always
  call “CLEAR” out of the side window and wait for a response from
  anyone who may be nearby before engaging the starter.


Do we fly full size aircraft with video game style joysticks?

They are used, they are just bigger joy sticks than used for RC flying.

A current example is the Airbus A320 (and related family) of passenger aircraft.  A short video of the joystick in action(called "side stick", start at about 1 minute in).  There is no direct mechanical linkage between the stick and the flight controls.

(For the A330, but basically the same).

For more detail, you can download this (slightly out of date, but with enough information to be useful) Flight Controls lesson for the A320 here.

  I am more curious about thumb controlled flying as you could control
  everything from what essentially looks like a video game controller.

@Rory Alsop noted that ...

  ... even video game controllers are terrible for this. The bigger the stick the better fine control you have over it. This is why for flight
  sims for PC's and consoles, keen players buy proper joysticks -
  otherwise they are twitchy and hard to handle

Video game controllers require two hands, have poor sensory feedback (as compared to a stick type controller) and are not as ergonomically effective as a multi-axis stick.  Also, there are some "push buttons" on a control stick that allow moving a finger or a thumb to activate other functions, like the "take control" button in the side stick(For swapping control between left seat and right seat pilots).  On some sticks you'll also have the "push to talk button" for the radio, as has been done for decades.  It's an efficient use of the hand, without having to move the hand for multiple tasks.


SR-72 --- is the speed reported in this story wrong?

is the speed reported in this story wrong?

No
No it is not a misprint that the SR-72 is intended to be capable of Mach 6
From the horses' mouth:

Envisioned as an unmanned aircraft, the SR-72 would fly at speeds up to Mach 6, or six times the speed of sound. At this speed, the aircraft would be so fast, an adversary would have no time to react or hide.
The SR-72’s design incorporates lessons learned from the HTV-2, which flew to a top speed of Mach 20, or 13,000 mph, with a surface temperature of 3500°F.

Yes
Yes it is not true that Mach 6 is necessarily 4567.2423 MPH
From elsewhere:

Cmglee. License:CC by SA 3


Is it possible to get permission for a GA flight to land at Reagan National Airport?

The TSA operates the DCA Access Standard Security Program (DASSP), which allows general aviation flights originating at designated gateway airports to fly into DCA, however there are many restrictions in place, some of the most significant being:

You will need an FAA "reservation slot" to fly in to DCA
(This is required for all unscheduled flights into DCA)
You will need to submit a flight manifest & undergo TSA passenger/baggage screening
The flight crew will need to be cleared by the TSA (fingerprint/background check)
You will need to carry an Armed Security Officer onboard

So the answer is "Yes, you can do it, but you probably don't want to."
It also makes no sense to do it in something like a Cessna 172 as you're giving up at least one seat for the security officer. The program is really geared toward larger aircraft (business jets, etc.) transporting executives with a business reason to be in DC, like testifying before Congress.


Why did this A320 stall protection demo not hold Valpha max?

You need to look earlier in the video. At 3:59 the sidestick goes full back and full left. The aircraft exceeds the 33deg bank limit on automatic maintenance of pitch and bank, requiring the pilot to hold pitch and bank.

The pilot is in command from 4:54-5:13, not choosing Valpha max. He hits the bank angle and stall limits to demonstrate flight envelope protection, the point of the video.


How much effect does the nose design of the plane have?

Good question! The raised cockpit and the hump behind it make the 747 look like the goose. Raising the cockpit allows the hinged nose to come up to load freight. The raised area behind the cockpit was initially a lounge, and was then used for seating or cargo.

How the 747 Got Its Hump, Smithsonian Air and Space

Boeing 747-8F:
Photo by Olivier Cleynen


How are redundant twin engines coupled on a helicopter?

Multiple-engine configurations use multiple freewheeling units that couple the rotor with the engine and allow the first to revolve faster than the latter but not the other way around. If just one of the engines fails, the freewheeling unit for that particular engine will effectively disengage the engine from the rotor (as the rotor is now revolving faster than the failing engine), allowing the other engine(s) to drive it.

How a freewheeling unit functions on a mechanical level is described on page 6 of this document.


What's the reasoning for safety wire on aircraft, and the reasoning behind the way it's routed?

Safety wire (positive wire locking) is done in areas where there is a possibility of the bolt getting loose due to vibration (also in other critical areas); this is done in a way such that the loosening of the bolt is counteracted by the tension in the wire i.e. in case the bolts loosen, the locking wire becomes taut and prevents further movement of the bolt.

safety wire examples; image from www.stangtv.com

There are different ways of doing wire locking for locking depending on the number of fasteners involved, but the basics are the same.

Safety wires; image from FAA AC 43.13-1B - Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair


If operating an ultralight with private pilot certificate, which rules apply?

If the aircraft is not registered, it can only be operated under part 103.
FAR 103.1 states that an ultralight may not "have any U.S. or foreign airworthiness certificate".  So a registered aircraft could not be operated under Part 103.
Your question mentioned transponders.  Bear in mind that FAR 91.1(e) exempts ultralight vehicles from all of Part 91.  Therefore, if operating under Part 103, there is no particular airspace that would become available if a transponder were added to the ultralight, that would not be available otherwise, unless a particular ATC facility chose to grant the "prior authorization" required for Part 103 operations in certain controlled airspace, specifically on that basis.  This seems unlikely.  In fact, it is probably safe to assume that the FAA would attempt to prohibit a transponder from being added to an aircraft operating under Part 103, although it's not clear what regulation this would be based on.
Related:
In the United States, are ultralights legally considered aircraft?
Would FAR 91.227, or any other regulation, forbid use of ADS-B-out in an unregistered ultralight?