How to read the pressure diagram of an airfoil?

The drawing in your answer shows the contour of the tips of the local pressure vectors when they are plotted perpendicularly to the local airfoil contour. Yes, this will change with angle of attack. In potential flow theory, the local pressure can be calculated as the linear superposition of a contribution from camber and one from angle of attack. While the camber-related part is constant, the angle-of-attack related part varies linearly with this parameter.
Yes, since the diagram shows the pressure distribution at high angle of attack, the top surface shows mostly suction (= local pressure is smaller than ambient pressure) and all of the bottom surface pressure that is higher than ambient pressure. Static pressure is equivalent to potential energy and total energy is constant, so this means that flow speed is higher than the free flow speed over the red region and lower over the blue region.
Yes, measuring the perpendicular distance between the airfoil surface and the contour line will give you a pressure difference to the ambient pressure, but there is no scale, so all you can do is read relative pressures from that drawing. I recommend to use a different way of plotting pressure, see here for more.
Yes.
P2 has no specific name; here the flow accelerates through the free stream speed. The stagnation point is below the highest distance between airfoil and pressure contour near the nose (in the blue region). That the local pressure at the trailing edge is equal to free stream pressure is a coincidence - at lower angles of attack, the flow will decelerate below the free stream value near the trailing edge, so the blue region would wrap around the trailing edge. Here, flow separation at the trailing edge is imminent, and if the angle of attack is increased a bit, the pressure will turn to suction at the trailing edge.
I think this graph is not quite realistic but is meant to show the general tendency only. More can be seen when inviscid and viscous pressure are plotted together over chord in a cartesian coordinate system.


GA Headsets - is there a standard for the replaceable microphone?

It's not a coincidence, the connection is a modular microphone standard called U-172/U. The pins it connects to are the U-173/U standard.

You can't just get any microphone that has that connector though, it's not aviation specific. You need to get a microphone which has the right impedance and is designed to work with the voltage on an aircraft communication system. There's plenty of options, some which give better noise cancelling properties than others.

All you need to do is get the parameters of your hurl-covered one and get one with the same parameters.

There's information on aviation connectors and standards here, and here.


Why did moving the CG aft on the Wright Brother's plane improve handling?

It did not improve stability, but flyability.

The Wright Flyer had the CG located aft of the neutral point and was unstable in pitch. A longitudinally unstable aircraft will deviate from its trim point, and when flown by a human pilot, will have a wavy flight path. The Wrights called this undulation. It is caused by the delay in the pilot's response and his tendency to overcompensate, so the aircraft is oscillating around the trim point (= the angle of attack where all moments around the pitch axis are in balance). This delay is more problematic when the eigenfrequency of the motion is higher. All Zeppelins were unstable in pitch above a certain airspeed and in yaw over the full speed range, but nobody bothered. These things were so big that any motion needed a long time to develop and deviations from the trim condition were easy to correct.

With aircraft, things are different, because they are more maneuverable and much smaller. The characteristic parameter here is the short period mode which characterizes the pitch motion. Its frequency is around 1 Hz for small aircraft and can be approximated like this:
$$\omega_{\alpha} = \frac{v_{\mathrm{trim}}}{i_y} \cdot \sqrt{\left(\frac{c_{m\alpha}}{\mu} + \frac{c_{L\alpha}\cdot c_{mq}}{\mu^2}\right)}$$

Nomenclature:
    $\omega_{\alpha} \:\:\:$ Eigenfrequency of the short period mode
    $v_{\mathrm{trim}}\:$  trimmed airspeed
    $i_y \:\:\:\:\:$  Radius of inertia around the pitch axis
    $c_{m\alpha} \:\:$ pitch moment gradient over angle of attack
    $\mu \:\:\:\:\:\:$  reduced mass. $\mu = \frac{2\cdot m}{\rho \cdot S \cdot l_{\mu}}$
    $c_{L\alpha} \:\:$ lift coefficient gradient over angle of attack
    $c_{mq} \:\:$ pitch damping coefficient
    $m \:\:\:\:\:$  mass
    $\rho \:\:\:\:\:\:$  density of air
    $S \:\:\:\:\:\:$  reference area (normally wing area)
    $l_{\mu} \:\:\:\:\:$  mean aerodynamic chord

To answer the question, all it needs is the first factor of the equation. The frequency increases with airspeed and goes down with the pitch inertia of the plane. By adding a weight at the back of their airplane, the Wrights increased this pitch inertia, thus lowering the eigenfrequency and making it easier to control. Make no mistake: The Flyer became even more unstable, but the instability became easier to correct because the deviations from the trim point built up more slowly.

Modern replicas of the Flyer have their CG ahead of the neutral point and are naturally stable.


How can reducing power too quickly on a piston engine damage it?

The main concern cited in regards to reducing power too quickly is that you could shock cool the engine.  A sudden decrease in power, particularly at high altitudes where it is cold can cause a rapid decrease in temperature of the engine which can cause damage to the cylinder heads.

However the theory is very controversial because there is no evidence that the cooling causes a problem, and in fact the engine cools much more quickly when you shut it down at the end of a flight.  A very good article going into more specifics about cooling of aircraft engines is here:  the physics and metallurgy of "shock cooling".

One of the more interesting points that it discusses is that only about 12% of the heat generated from combustion ends up making its way through the block and is dissipated by air cooling (cooling fins).  This means that most of the heat is already going somewhere else anyway (the largest part goes out the exhaust), and the "air cooling" doesn't make that big of a difference anyway.

As always, be sure that you follow all recommendations and limitations from your POH or engine manufacturer in regards to engine cooling, CHT's, etc. since they could have procedures for other reasons as well.


Best Practices when removing/inspecting/mounting control surfaces?

Your airline should have proper holding fixtures, basically a wheeled frame that mounts the surface at key attachment points, for control surfaces, either purchased from the manufacturer or designed in house.  The table strapping business is probably because the airline is too cheap to get the proper equipment.


If pilots in a A320 or 737 had a dual engine failure, would they add flaps for the landing?

Flaps steepen the descent angle - in other words, you run the risk of falling short of the runway. So in a glide you keep the flaps up until you can be certain of making the landing point. Once the landing is guaranteed, you can then deploy gear as well as flap to slow down as much as possible - being aware that these actions will further reduce the gliding range, so constant reevaluation is required.


Why were early aviators' trousers flared at the thigh?

It's not too hard to figure out.  Wikipedia says Jodhpurs originated from India where they were part fashion and part practicality (the loose fit in the upper half for horse riding comfort) and evolved into the uniform of most western cavalry officers by the turn of the century.

And, in WWI, where did most, or at least a lot, of the pilots come from in the early days?  Cavalry.


Were there any instances of aerial combat between helicopters?

Yes, there has:
In the Iran-Iraq War, Wikipedia:

The war also saw the only confirmed air-to-air helicopter battles in the history of warfare, with Iraqi Mi-25s flying against Iranian AH-1J SeaCobras on numerous occasions. The first instance of these helicopter "dogfights" occurred on the first day of the war (22 September 1980): two Iranian SeaCobras crept up on two Mi-25s and hit them with TOW wire-guided anti-tank missiles. One Mi-25 went down immediately, the other was badly damaged and crashed before reaching base. The Iranians won a similar air battle on 24 April 1981, destroying two Mi-25s without incurring losses themselves. According to unclassified documents, Iranian pilots achieved a 10-to-1 kill ratio over the Iraqi helicopter pilots during these engagements and even engaged Iraqi fixed-wing aircraft.

These would be pretty loosely classified as a "dogfight" since the Iranian AH-1J's "crept up" on the Mi-25's. It is doubtful that the Mi's did any kind of evasive maneuvering or that the AH's did any kind of aggressive pursuits, but it is air-to-air combat between helicopters.
The page from the Mi-24 page gives a little more detailed report:

This war also saw the only confirmed air-to-air helicopter battles in history with the Iraqi Mi-25s flying against Iranian AH-1J SeaCobras (supplied by the United States before the Iranian Revolution) on several separate occasions. In November 1980, not long after Iraq's initial invasion of Iran, two Iranian SeaCobras engaged two Mi-25s with TOW wire-guided antitank missiles. One Mi-25 went down immediately, the other was badly damaged and crashed before reaching base. The Iranians repeated this accomplishment on 24 April 1981, destroying two Mi-25s without incurring losses to themselves. One Mi-25 was also downed by an IRIAF F-14A.
The Iraqis hit back, claiming the destruction of a SeaCobra on 14 September 1983 (with YaKB machine gun), then three SeaCobras on 5 February 1984 and three more on 25 February 1984 (two with Falanga missiles, one with S-5 rockets). After a lull in helicopter losses, each side lost a gunship on 13 February 1986. Later, a Mi-25 claimed a SeaCobra shot down with YaKB gun on 16 February, and a SeaCobra claimed a Mi-25 shot down with rockets on 18 February. The last engagement between the two types was on 22 May 1986, when Mi-25s shot down a SeaCobra. The final claim tally was 10 SeaCobras and 6 Mi-25s destroyed. The relatively small numbers and the inevitable disputes over actual kill numbers makes it unclear if one gunship had a real technical superiority over the other. Iraqi Mi-25s also claimed 43 kills against other Iranian helicopters, such as Agusta-Bell UH-1 Hueys.

I don't believe there has been any recorded instance since the Iran-Iraq war, but during that conflict there were multiple instances of helicopter-vs-helicopter battles.


Why are the character keys on the Flight Management Computer in alphabetical order?

"we are all used to the QWERTY or QWERTZ layout..." or AZERTY. But which one? Universally there is no one standard, so whichever of these 3 (and others) is chosen, it will be wrong for some users. So the only standard left is simple alphabetic.

Another thing to consider is that the QWERTY-types of layout were chosen to deliberately slow down typists on mechanical typewriters. This slow-down is not necessary on an electronic piece of kit, so the pure-alph format is quite fast once you're used to it.


It's an R&D and therefore ultimately a cost-benefits decision. Quieting techniques for helicopters aren't as simple as "hush kits" for fixed-wings, because the engines and rotors are a much more integral part of the entire airframe. So, to incorporate these features into a civilian helicopter is a much more involved process than swapping blades on a turboprop or putting hush rings on the exhausts of older airliner engines. Changing the physical properties of the rotors (lift, induced drag, moment of inertia) requires compensating changes in the engine; shorter blades reduces lift requiring higher RPM, more blades increases MOI requiring more torque, etc. Those engine changes will in turn require changes to tail rotor characteristics, and may also require frame and body tweaks, etc etc.

Most helicopters in civilian use today, like the Bell 200-series, Sikorsky S-70 family, Dauphin etc are Vietnam-era designs, almost unchanged save for a few minor tweaks along the way like incremental engine improvements or new avionics systems. They're still being built and flown because they work; take the rigorous proving tests required of any aviation system and the maintenance and inspection requirements of fixed wing aircraft, and add an additional level of caution for the inherent instability and lack of fail-safes in the design of a rotary-wing aircraft, and you'll have some idea of what it takes to get a new helicopter vetted for GA use. If the helicopter's engine cuts out or throws a prop blade, you can't just glide down to the ground the same way as a fixed wing. So, any changes you make to a basic, proven design would be subject to extreme skepticism and testing by both aviation regulators and owners, to say nothing of starting from scratch. This decreases initial sales of a new model in the civilian market, increasing the payback period of your R&D to develop this new design.

Second, in part due to this hesitance by GA to adopt new chopper designs, the funding availability to research and develop any new civilian helicopter design is dwarfed by military interests. As mentioned, practically every design you see in the skies today has a military pedigree and was designed primarily for that purpose, then civilianized for GA use (a notable exception being the Eurocopter Dauphin 2 which was established in the private and law enforcement sectors before militaries took a look). As a result, a lot of the newest stealth technologies available for helicopters, including noise reduction, are heavily classified. For instance, the modifications to the UH-60s used in the Bin Laden raid; civilians really only know that stealth Blackhawks exist, as what they look like and their performance/noise characteristics are all still top secret. That hasn't stopped the human imagination; artist impressions including the concept art for Zero Dark Thirty abound.

In addition, the civilian quiet-copter technologies that aren't classified, like Eurocopter's "Blue Edge" blade design, are mostly protected by international patent. Bell or Sikorsky can't just reverse-engineer the Blue Edge blade and stick it on their choppers. An independently-developed design must be different enough to be patentable, which probably means it will be more complex, and complexity is a bad word in aviation because it means increased probability of system failure or operator error. The other avenues would be to either license Blue Edge from Eurocopter (increasing the cost of a Bell or Sikorsky Blue Edge-equipped model) or wait 15-20 years until the patent expires (further delaying widespread adoption of the technology beyond one brand).


Why are there different types of winglets?

Winglet design is driven more by marketing than by engineering, so every aircraft brand tries to cultivate their own, supposedly better, shape.

A study by Nita and Scholz (PDF!), Chapter 6 gives a good overview over recent winglet studies. A raked tip performs better, and if winglets could point downwards, they also could do better. As they are, they give only 28% to 38% drag reduction of an equivalent span increase.

Raked wingtip of the Boeing 777-300


How does a Secondary Surveilliance Radar send data?

I'll describe the typical Mode-S radar system based on my mostly European experience. Details will vary but the general concept applies world wide.

The radio signal received from the aircraft is digitized, CRC checked,  compared to and combined with data from earlier transmissions from the aircraft. This data is usually encoded in ASTERIX format (typically category 048PDF) and transmitted over a datalink to a surveillance data processing system (SDPS) in the ATC centre. From the SDPS the data is further distributed to various client systems, among which the air traffic controller display system is one.

The radar processing itself is partly dedicated hardware and partly COTS (commercial-off-the-shelf) infrastructure. This is housed in a standard server cabinet. Network components are typically COTS high quality systems and duplicated for redundancy.

The datalink from the radar site to the ATC facilities can take many forms. Every country has its own regulator and local telecom market peculiarities, leading to a variety of implementations. Often a dedicated line will be used, usually with a backup line as well. Sometimes two telecom providers are used that have to provide fully independent data paths to the ATC centre. In a few cases radio links are used to connect surveillance systems, I know of surveillance systems (not radars) that use satellite links.

Within the ATC centre usually duplicated or triplicated networks are used for redundancy. These can be UTP or glassfibre networks. These are again based on COTS high availability/integrity components.


Why do military pilots report "gear down" during their traffic calls?

1In the U.S., for Military aircraft, ATC is required to:

  "Remind aircraft to check wheels down on each
  approach unless the pilot has previously reported
  wheels down for that approach". [ref: [FAA Order 7110.65W], para. 2-1-24]

Normally, the phraseology suggested in your question would reflect the pilot's response to this ATC reminder. (For example: "[call sign] Check Wheels Down, Cleared for [whatever]")


Under what conditions can the maximum angle of climb be achieved for jet and propeller aircraft?

What you say is true only for turbojets and aircraft with fixed-pitch propellers. Generally, all optimum points for variable-pitch propeller driven aircraft are at lower speeds than those of jet aircraft. The reason is the variation of thrust with speed: For propellers, thrust is inverse to speed, while it is roughly constant over speed for turbojet aircraft in the subsonic speed range.

Specifically, the optimum angle of climb condition can be expressed as $$\frac{\delta \gamma}{\delta c_L} = 0$$
If we assume a quadratic polar, constant propeller efficiency over speed (which means a variable-pitch propeller) and an expression for thrust which lets us model an exponential variation of thrust over speed ($T = T_0·v^{n_v}$), we can write this condition as $$\frac{\delta \gamma}{\delta c_L} = -\frac{n_v}{2}·c_L^{-\frac{n_v}{2}-1}·\frac{T_0·(m·g)^{\frac{n_v}{2}-1}}{\left(\frac{\rho}{2}·S_{ref}\right)^{\frac{n_v}{2}}}+\frac{c_{D0}}{c_L^2}-\frac{1}{\pi·AR·\epsilon}$$
The general solution is $$c_{L_{{\gamma_{max}}}} = -\frac{n_v}{4}·\frac{T·\pi·AR·\epsilon}{m·g}+\sqrt{\frac{n_v^2}{16}·\left(\frac{T·\pi·AR·\epsilon}{m·g}\right)^2+c_{D0}·\pi·AR·\epsilon}$$
For jets and fixed-pitch propeller aircraft ($n_v = 0$) the solution is quite simple, because the thrust terms are proportional to the thrust coefficient $n_v$ and disappear: $$c_{L_{{\gamma_{max}}}} = \sqrt{c_{D0}·\pi·AR·\epsilon}$$
For turbofan and variable-pitch propeller aircraft, we have less luck and get a much longer formula. This is the one for propellers ($n_v = -1$):
$$c_{L_{{\gamma_{max}}}} = \frac{T·\pi·AR·\epsilon}{4·m·g}+\sqrt{\left(\frac{T·\pi·AR·\epsilon}{4·m·g}\right)^2+c_{D0}·\pi·AR·\epsilon}$$
To arrive from here at a flight speed, I recommend to look up the speed in a polar. Solving this analytically will get messy. Below I have plotted a generic climb speed over air speed chart for different thrust loadings of a typical turbofan. The blue lines show thrust (right Y-axis) and the green lines the resulting climb speed. The two black lines show how the optimum flight speed for best climb speed and best climb angle (steepest climb) vary over thrust loadings. They are easy to find graphically: Pick the tops of the green curves for best climb and the steepest tangent from the origin of the coordinate system to the green lines for best climb angle. Note that they cross when moving from positive to negative climb speeds. With a propeller, the results will look similar, however, the best climb speed line would be vertical. This will collect all optima at the low speed range of the plot - using a turbofan makes the effects easier to see because the optima are spread out more.

Climb optima for different thrust loadings (own work)

The optimum climb speed (which is proportional to $\frac{1}{c_L^2}$) varies inversely with the square of the thrust loading ($\frac{T_{ref}}{m·g}$)² of the aircraft. With lots of excess thrust, the optimum is limited by the stall speed (the black line bends into a vertical trend), while with no excess thrust both optimum speeds $v_x$ and $v_y$ converge. This makes sense: If thrust is just sufficient to keep the airplane from descending at one speed, this speed will both give the best flight path angle and the best vertical speed (unfortunately, both will be 0 at this point). It also helps to reduce induced drag, so aircraft with a high aspect ratio wing will climb steepest at a higher lift coefficient (= lower speed).

The steepest climb optimum looks a little more compact if we use the induced drag coefficient directly: $$c_{L_{\gamma_{max}}} = \frac{2·m·g·(c_{D0}-c_{Di})}{T}$$
but since the lift coefficient is hidden again in the induced drag term, and so sits on both sides of the equation, it is much harder to draw conclusions from this version.

Nomenclature:
    $c_L \:\:\:$ lift coefficient
    $n_v \:\:\:$  thrust exponent, as in $T \sim v^{n_v} $
    $T \:\:\:\:$  thrust
    $m \:\:\:\:$  mass
    $g \:\:\:\:\:$  gravitational acceleration
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing
    $\epsilon \:\:\:\:\:$  the wing's Oswald factor
    $c_{D0} \:$  zero-lift drag coefficient
    $c_{Di} \:\:$  induced drag coefficient


Propellers are not obsolete by any measure.

The jet engine offers two important advantages over propeller aircraft- higher speed and better fuel economy over long range. However, for low speeds and shorter routes, propeller (tuboprop) aircraft are better.

Also, for light GA aircraft, jet aircraft is prohibitively expensive to purchase and maintain. Among other things, the higher speeds associated with jet aircraft make them unsuitable for use in GA. Also, every jet pilot is first trained in propeller aircraft; in fact, airline pilots should have a minimum prior experience before piloting jet aircraft.


Why are the airport pressure values for "altitude" (inHg) and "sea level" (mb) slightly different on the NOAA web sites?

The difference has nothing to do with unit conversion (which is correctly done in your question). The difference comes from temperature: the aircraft altimeter assumes a standard temperature lapse rate of 1.98°C per 1000 ft altitude when converting a pressure to an altitude reading. The reference pressure for the altimeter (QNH) is defined such that the aircraft altimeter will show the correct airport elevation when it sits on the ground.
The sea level pressure however takes the actual temperature into account. If this deviates from the expected value in the standard atmosphere, you will see a different pressure value here. The higher the elevation, the more pronounced will these differences typically be. That's probably why you noticed these differences at Denver. In your example, the temperature was 54°F, which is about 12°C, but the expected temperature at Denver is
$$ \vartheta = 15^\circ \text{C} - 1.98^\circ \text{C} \times \frac{5434 \, \text{ft}}{1000 \, \text{ft}} \approx 4.2^\circ \text{C} $$
Here is the full explanation from NOAA:

ALTIMETER SETTING: This is the pressure reading most commonly heard in
radio and television broadcasts. It is not the true barometric
pressure at a station. Instead it is the pressure "reduced" to mean
sea level using the temperature profile of the "standard" atmosphere,
which is representative of average conditions over the United States
at 40 degrees north latitude. The altimeter setting is the pressure
value to which an aircraft altimeter scale is set so that it will
indicate the altitude (above mean sea level) of the aircraft on the
ground at the location for which the pressure value was determined.
The altimeter setting is an attempt to remove elevation effects from
pressure readings using "standard" conditions.
MEAN SEA LEVEL PRESSURE: This is the pressure reading most commonly
used by meteorologists to track weather systems at the surface. Like
altimeter setting, it is a "reduced" pressure which uses observed
conditions rather than "standard" conditions to remove the effects of
elevation from pressure readings. This reduction estimates the
pressure that would exist at sea level at a point directly below the
station using a temperature profile based on temperatures that
actually exist at the station. In practice the temperature used in the
reduction is a mean temperature for the preceding twelve hours. Mean
sea level pressure should be used with caution at high elevations as
temperatures can have a very profound effect on the reduced pressures,
sometimes giving rise to fictitious pressure patterns and anomalous
mean sea level pressure values.

(NOAA - Pressure Definitions)


Which jet engines have the highest thermal efficiency?

Thermal efficiencies are very rarely quoted for aviation gas turbines. The metrics of interest are specific fuel consumption, and power to weight ratio. While a higher thermal efficiency will increase these, SFC and thrust/weight are performance terms that are easier to comprehend, and describe the performance in terms that can directly be used in performance calculations of the aircraft. However, this article from Pratt & Whitney indicates the best aviation gas turbines had just reached about 55% in 2010. But there is no indication of which engine has the highest figure.

Land based gas turbines are more efficient than avaition gas turbines, for a number of reasons. According to this article, the most efficient land based gas turbines, where just under 60%, in 2010. The most efficient installation was a Japanese company, with 59.1% verified on an M701G2 gas turbine at the 1500 MW Tokyo Electric Kawasaki power station in Japan.

Since then GE claimed on the 28th of April 2016, a world record for thermal efficiency, with 62.22%, for a combined cycle plant, in France. GE state that it normally takes about a decade to gain 1% in efficiency. The high thermal efficiency is significantly due to operating at a very high temperature. GE state this plant runs at 2,800 deg. F, but the real number is probably proprietary. They say it's like running the engine at takeoff conditions for its entire flight. As you could imagine, this makes cooling very important. It also takes about 30 minutes to get the turbine from idle to maximum speed. Clearly, that won't work in an aircraft.

This is the GE 9HA gas turbine. You can see the fuel nozzles (one circled) - and that weight does not matter. So, an aviation turbine will never match this level of performance.

In comparison, the first simple cycle model, developed in 1939 is said to have had a thermal efficiency of just 18%.

But maximum efficiency is not always the ultimate goal. A product director from Rolls Royce says:

  Everyone would love 60% but the cost is often prohibitive. Not everyone needs a heavy-duty combined-cycle plant. Machines that can achieve baseload within ten minutes such as the Trent 60 are important for the peaking market and a lot cheaper.

Land based combined cycle gas turbines are more efficient than aviation turbines, because;

their design can be optimised with out having to worry about weight. Fuel nozzles in particular are optimised in land based gas turbines.
they can use steam or water inlet fogging (see above!)
they operate at a single rotational speed, so can be optimised for that.


Why is the drogue parachute jettisoned on the runway?

For several reasons.

First to protect the drogue from damage by scraping on the pavement
second to prevent it from becoming snagged on nearby objects
third to prevent metal components on the drogue from hitting and damaging the tail of the aircraft,
and fourth to make it easier to taxi back to the ramp without the need for higher power setting to overcome the drag and prevent damage to the drogue from this jet blast.

One downside to jettisoning the drogue at a lower speed (< 40 kts) is that it now creates a FOD hazard on the runway and requires a waiting cleanup crew to retrieve it before another recovery is possible.


Can I log the flight as the authorized instructor on board? Commercial long cross country

Answer solved,

https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/data/interps/2014/kuhn%20-%20(2014)%20legal%20interpretation.pdf

Short terms, yes.


How can I calculate the moment coefficient around the center of gravity?


Are there regulations for water skiing in a ASEL aircraft?

(bush-air.com)

I couldn't find any regulations for it. But the closest thing to an official mention of it I found was in a 2009 piece on Anchorage Daily News, where an unlicensed pilot water skied, hit a sandbar, and it didn't end nicely for his Super Cub.

The FAA regional counsel said:

  The practice is called water-skiing, and it is not encouraged. It was developed for landing in tight quarters, like sand bars where space is short, but doing it wrong can be disastrous.


The aircraft (I presume you mean what’s visible behind the green F-4 Phantom in the right of the photograph) appears to be a rare surviving prototype of a Dornier Do31 VTOL transport aircraft.


What are the advantages of centerline armament?

Yes it's because of dispersion.  With wing mounted guns you normally "harmonize" them to converge at a point, say 300 yards or 600 yards to have a sweet spot where most of the projectiles are passing through a small area to maximize the fire concentration.

But at ranges closer and farther, the streams of projectiles are more dispersed and their effects are reduced.  Watch gun camera footage of strafing runs in something like a P-51, and you can see the bullet strikes widely dispersed and coming together into a tighter cluster as the range closes in.

Putting the armament in the nose eliminates the range issue and you have maximum concentration at any range.  The later versions of the 109 with the Mk108 30mm cannon were just about ideal for this because the cannon was very compact and had a really high rate of fire for its caliber (about 4-600 rpm), so a single cannon + two MGs was plenty of firepower and was probably the ideal configuration for the 109.

The ME262 jet had 4 Mk108s in the nose, providing close to the concentrated firepower of the A-10's 30mm 3000 rpm gattling gun.  A very short burst would bring down any fighter if it scored hits.


Why is a clock required to be mounted on the instrument panel for IFR flights?

The clock needs to be positioned such that you can see it easily as part of your instrument scan, and the sweep second hand needs to be there to make it easy to time intervals that are not whole minutes.

The regulation has been there for a long time, so the requirement should be considered in the light of how things used to be as well as what they are now.

A very practical example from 1969 follows. The regulation predates that by many years, I am sure, but the 1969 environment shows the need.

You're in a light single engine airplane (think Cessna 150 and later a Cessna 172). You're working on your instrument rating in actual conditions in the Pacific Northwest in a non-radar environment. You're in moderate turbulence and having to keep on eye on the icing. And, though it seems ridiculous now, we didn't use headsets but instead picked up a mic for each transmission, of which there were many because in the non-radar environment there were lots of reports.

You're inbound to the VOR on the airport, after which you'll proceed outbound to the NDB that is the final approach fix. Once at the NDB, you will fly 30 seconds farther outbound on the Rwy 16 ILS, which by the way since you have no HSI you're having to navigate by reverse sensing on the old VOR/ILS CDI with its swinging left/right needle. At the 30 second point, you're to turn right to the procedure turn outbound course and fly for 45 seconds (but maybe if that wind is from the east you should go for 60 seconds - better watch that CDI needle to see how fast you get full deflection).

Oh, damn, the instructor just covered up the directional gyro to simulate its failure. Now your only heading reference is the wet compass, which is bouncing around in the turbulence, and, besides, you can't remember whether it's going to precede or lag (and by how much) in the turn you have to make to reverse course for the inbound leg of the procedure turn. Ah, but wait, all you have have to do is fly a standard-rate turn for 60 seconds and you'll be in good shape.

So, thus far, we've had three separate needs to time things to seconds in a situation where we have our hands full - left hand on the yoke, right hand for throttle, carb heat, microphone.

Given all that, do you really want to have to keep pulling back the sleeve on your left arm to monitor a relatively small clock face? Much better to have a larger clock face right in front of you on the instrument panel.

Do we really need such a clock now? Perhaps not, but it doesn't hurt, and regulations are notoriously resistant to change.

And does anybody actually fly procedure turns anymore?


What are the advantages of Chemical Oxygen Generation over Gaseous Canisters on board of aircrafts?

Pressurized oxygen tanks have two big minus points: they are heavy, and they are essentially a small bomb. But they have two big plus points: they can be refilled easily and they don't generate any heat when you use them.

Chemical oxygen generator plus points are they are lightweight, self-contained and more-or-less maintenance-free (they don't leak). Minus points are they are single-use, time-limited and cannot be shut off.

As nearly everything in aviation is a balance of good and bad, we often see both systems being used at the same time. The flight crew will use oxygen on a regular basis - sometimes procedurally, sometimes just to clear up a headache. They need to be able to turn it on and off, and the airline doesn't want to replace the system each time.

Passengers rarely need oxygen, and when they do it's only until the plane descends to breathable altitudes (which will happen really quickly).


What is the difference between Turn Coordinator and Artificial Horizon?

Attitude Indicator
It shows your attitude (nose up / down, bank left / right) relative to a horizontal surface. Basically, it tells you the orientation of the plane if someone were to take a photo of the plane from the outside at this very moment.
It does not tell you which way you are going (e.g. you can be nose up but descending).
Turn coordinator
This is actually two instruments in one: the white plane and the little ball.
The white plane tells you which way you are yawing (rotation about the normal (vertical) axis)). If you are yawing to the right (e.g. N -> NE -> E), the right wing of the little plane is lower. If you are yawing to the left (e.g. N -> NW -> W), the left wing is lower.
If you are yawing at the standard rate (3 degrees per second), the wing of the little plane will align with the white mark.
Combining the two
Suppose that you manage to yaw the plane to the right while keeping it horizontal, like a spinning top:

You will get:


What would the altitude profile for a typical airline flight look like?

It is somewhat unclear what you want to achieve.

If you want to know how it looks like, you can search for some papers like this. To keep it short, altitude vs distance curve is pretty much similar to altitude vs time, but climb and descent segments are more curved with larger second derivatives for climb and descend. For details please read the paper.

If you are interested in some analysis, you need two components: flight data itself and data analysis software.

If you are looking for professional flight data analysis systems, for example, flightDataServices, generally they are not provided for free, but even if you have an access, you still need flight data for analysis. It can be more difficult to find it. If that is what you are looking for, just google "Flight Analysis Software" and "Flight Data".

You can do that analysis by yourself though, with a little less accuracy than a professional system. The closest option for getting an accurate flight data is FlightAware.com. They do not provide altitude vs distance out-of-the-box, but they provide plenty of data for further analysis. For example, this flight. You can open track log and see altitude/speed vs time (which is not you are looking for, but useful for a 'big picture'), and in the log itself you can find latitude, longitude, speed and rate of climb for some points. The points are provided with a less-than-a-minute frequency, which is pretty precise. It is not so hard to export them in any spreadsheet or CSV and generate whatever you are interested in: a pretty common data visualization task. It can be easily done with Matlab/Excel/LibreOffice. For example, altitude vs distance travelled, course vs time, rate of climb vs time, rate of climb vs distance etc.

If you are looking for data visualization software specified for flight analysis, I am not sure that something exists that fits all requests. Especially an online tool. The reasons are: flightaware provides both data and the most common plots (i. e. alt vs time and speed vs time); and if you already have data, it's pretty easy to plot whatever you want using Matlab/R/Python/Excel.


What do pilots operating under FAA 14 CFR 91 have to do to fly in any of the Special Flight Rules Areas (SFRAs)?

The "master list" of special flight rules areas (SFRAs) in the United States is FAR 93 (14CFR93)) - aptly named "Special Air Traffic Rules".

It contains a list of areas with "Special Air Traffic Rules", including the requirements for operating in those areas.

Charts with SFRAs on them include a notice directing you to FAR 93 (and often other helpful information about the SFRA):

In addition to "Special Air Traffic Rules" some airspace with "special" rules may be defined by "Special Federal Aviation Regulations" (SFARs), found at the beginning of Part 91.
The only one I see in there currently is the Grand Canyon National Park SFAR.


What are some symptoms of a clogged fuel filter?

The effect would almost certainly be similar to running lean - ie, if not enough fuel is making it to combustion your fuel to air ratio will be that of a lean mixture
Effects of lean mixture include

Overheating
Knocking sound when running, perhaps even popping/backfiring from exhaust
The RPM will "hunt", meaning it will increase/decrease attempting to find a stable RPM
Slow to pickup, ie when increasing throttle it will not change quickly RPM as it should


Where does the Olive Branch (KOLV) class D ceiling meet the Memphis (KMEM) class B floor?

The Class D airspace surrounding the Olive Branch airport extends upward to 2900 feet msl, excluding the Class B airspace.  So, your understanding is  correct.

Here is the official description of this Class D airspace from FAA Order 7400.11,  Airspace Designations and Reporting Points: (emphasis is mine)

  ASO MS D Olive Branch, MS
  Olive Branch Airport, MS
  (lat. 34º58'44"N., long. 89º47'13''W.)

  That airspace extending upward from the surface to and including 2,900 feet MSL within a
  4-mile radius of Olive Branch Airport; excluding that airspace within the Memphis Class B
  airspace area. This Class D airspace area is effective during the specific days and times established in advance by a Notice to Airmen. The effective days and times will thereafter be continuously published in the Airport/Facility Directory.

  AMENDMENTS 04/15/04 69 FR 5009 (Added)


What is the significance of a squawk code?

The squawk code is assigned by Air Traffic Control to the aircraft and is used for radar identification purposes. It is a 4 digit octal number (each digit has a value in the range [0-7]).

The flight crew enters the assigned squawk code into the transponder control panel and the radar extracts the code using a Mode-A interrogation (or UF5 / UF21 interrogation in case of a Mode S radar/ transponder).

The extracted squawk code can then be used to correlate the radar reply with an aircraft's flight plan. A number of squawk codes are reserved for generic purposes and emergencies. These codes are used in emergency, or when no flight plan correlation is needed. Some generic codes are:

1000 - Conspicuity code signalling the Flight Data Processing system to use Mode-S Aircraft ID for flight plan correlation. (Primarily in Europe)
1200 - Visual Flight Rules standard squawk code (USA & Canada)
2000 - Used when entering a Secondary Surveillance Area and no code has yet been assigned.
7000 - Visual Flight Rules standard squawk code (ICAO, USA & Canada use
1200 instead)
7500 - Unlawful interference / hijack (ICAO, worldwide)
7600 - Radio communication lost (ICAO, worldwide)
7700 - General emergency (ICAO, worldwide)


RATO used to get civilian aircraft out of airports with inadequate runway length?

The DH Comet was equipped with RATO.

The Fairchild SA226 had a RATO bottle in the tail to improve single engine performance.  As I recall, removing the spades on the main landing gear eliminated enough drag to render the RATO unnecessary.

Boeing built twelve "727-200/JATO" variants for use by Mexicana Airlines.

  The rocket installation was intended for emergency use only when
  flying out of a hot and high airport at maximum gross weight. Without
  the JATO, the aircraft would have to be payload restricted to account
  for the need to reach a safe altitude in the event of an engine loss
  after committing to takeoff. By having the JATO provision, Mexicana
  could operate its 727-200s at full payload. In the event of a loss of
  engine at past V1, the JATO unit would fire and allow the
  heavily-laden jet to reach a safe altitude and get aerodynamically
  cleaned up.

This old video shows a demonstration of that scenario with one of those special 727-200s:

  The JATO provision was eventually made obsolete by later developments
  in the JT8D engine that featured "APR" automatic power reserve. It
  sensed a power decrease from one of the engines failing on takeoff and
  automatically boosted the power to the remaining two engines by a
  significant margin.


How are compressor blades connected to the shaft in turbojet engines?

There are three primary ways that blades are connected to the shaft

Circumferential dovetails  Here is a nice site demonstrating it.  Includes STL files so you can 3D print your own demonstration part.
https://cults3d.com/en/3d-model/tool/jet-engine-component-1-1-axial-compressor-circumferential-dovetail-slot-type
Axial dovetails Here is a video demonstrating blades with an axial dovetail being assembled.  This particular video is a turbine, not a compressor, but in theory the same method can be used.

Blisk "Blisk" is a contraction of "bladed disk". The blades and the disk are physically welded together (or in some cases machined as one piece out of a solid block of metal).  Here's a wikipedia article on blisks
https://en.wikipedia.org/wiki/Blisk

Each of these methods has advantages and disadvantages in terms of weight, cost, vibration, etc.  Which one is picked depends on the circumstances.  It is also common to see multiple different methods within one compressor. For example the LEAP-1A HPC has a 10 stage compressor.  The forward stages are blisks, and the aft stages are circumferntial dovetails.


What is the expected reaction of a civil airliner pilot upon an invalid request from a fighter jet?

What do rules have to do with your hypothetical situation?  At that point the question is what a completely unarmed person, who is immediately responsible for the lives of other people (assuming there are passengers), should do when another person who clearly doesn't obey laws and has a deadly weapon demands something, and nobody else has the power to interfere.
It seems to me that the choices available to the civil pilot are to comply, to refuse, or to try some sort of trick.  A rational person at that moment would be completely concentrated on survival for the aviator and passengers, and wouldn't be concerned about rules.


How long does it take to refuel a Cessna Citation X+?

Basically fuelling time depends on how fast the hydrant or fuel truck can deliver fuel.
This comes from SmartCockpit:

The  Citation  X  fuel  system  is  comprised  of  the  storage,
distribution,  refueling/defueling,and  indicating  systems.    The
storage  system  is  made  up  of  a  set  of  integral  tanks  in
each wing,  and  a  center  wing  tank  which  includes  a  forward
fairing  fuel  tank.    Each  wing  tank  has  a hopper  tank  which
is  integral  to  it.    The  two  wing  tanks  incorporate  check
valves  and  baffles allowing  each  wing  tank  complex  to  function
as  a  single  tank.    Other  integral  components  of the  storage
system  are  the  gravity  fuel  fillers,  drain  valves,  flapper
check  valves,  vent  system                      components,
positive/negative   pressure   relief   valves   and   all   of   the
associated   system plumbing.    Transfer  capability  is
incorporated  enabling  all  usable  fuel  to  be  available  to
either engine.Each  wing  tank  holds  a  total  of  521  gallons
(3518  Lbs.)  of  fuel,  which  includes  the  hopper tank.    The
center  wing  tank  holds  888  gallons  (5594  Lbs.),  207  (1397
Lbs.)  of  which  are contained  in  the  forward  fairing  tank.
Total  fuel  capacity  of  the  airplane  fuel  system  is
1927 gallons; at 6.75 pounds per gallon the available fuel weight is
13,031 pounds.
SINGLE-POINT REFUELING DEFUELING SYSTEM
The  single-point  refueling  system  is  provided  to  enable  the
airplane  to  be  refueled  or    de-fueled  more  safely  and
conveniently  by  connecting  to  one  port,  which  is  not  open  to
the atmosphere.      Advantages   of   a   single-point   refueling
and   defueling   include   minimized refuel/defuel   time,   reduced
possibilities   of   fuel   contamination,   reduced   static
electricity hazard, less airplane skin damage, and there is no
personnel contact with the fuel.The  refueling/defueling  system  is
independent  of  the  airplane  system.    It  is  designed  for
refueling  with  a  truck  or  refueling  hydrant  (pit)  having
single  point  provisions.    The  major components  of  the  system
include  the  refueling/defueling  adapter  (receptacle),  the
precheck control  panel,  refuel  shutoff  valves,  the  pilot
(precheck)  valves,  defuel  valves,  a  sequencing valve,   manual
defuel   select   shutoff   valves,   internal   drain   valves   and
associated   system plumbing.Single-point  refueling  is  accomplished
by  connecting  the  refueling  truck  or  refueling  pit equipment
to  the  airplane  at  the  single-point  refuel/defuel  adapter  on
the  right  side  of  the fuselage just forward of the wing leading
edge.


Can I use the load factor to estimate the lift?

If you know where the CG is, and where the aerodynamic centers of the wing and the tail are (I am assuming a traditional configuration) so you know the distance from the aero center of the wing to the CG = d_wing, and similar for the tail, and you know the moment the wing generates (ignore the moment about the tail...it is small), and you know the load factor, then you can figure out the total lift generated by the wing. You have two equations:

Sum of moments about CG = 0 (constant pitch rate)

d_wing x liftWing + d_tail x liftTail + wingMoment = 0

Sum of lifts equals load factor times weight of aircraft

liftWing + liftTail = loadFactor x weight

Now solve for liftWing.


Can wind shear conditions be identified visually?

Can you see wind shear?  Nope, but you can sometimes see indications of it.  According to Airbus, windshear is usually associated with the following weather situations (photos found on Google images by me and are clickable to take you to the source):

Jet streams

Mountain waves

Frontal surfaces

Thunderstorms and convective clouds (and I added virga here too)

Microbursts.

Avoid these at all cost!  Actually, that's the easy part.  The windshear without the visible signs is more the issue, and csatlos's answer does a good job of telling you what to look for during flight (especially takeoff and landing when you are low and slow).


Are there countries where not all plane crashes are investigated (even if deadly)?

As of 2017 191 of the 193 countries are signed to the ICAO anex and there are 122 national aviation authorities so at least some countries lack serious formal aviation authority and often look to other nations for help. Smaller, war torn nations or nations that do not have the facilities of first world countries may simply not have any ability to provide SAR operations. Its not just about having a helicopter or two hanging around but having a trained crew, a flight doctor and a hospital to bring the potential survivors back to.

Countries are under no obligation to provide SAR operations and generally speaking international treaties can't really force any country to offer something like that. In some cases the crash sites can be difficult to access or outside the range of practical rescue at the time of the incident. In these cases there may be incidents where a country simply cant investigate as it may risk the lives of those investigating.

There are some notable exceptions, the FAA will provide aid to any investigation involving an American built aircraft or having Americans on board anywhere on the globe. This is of course assuming they are permitted to provide such aid (which may not always be the case). The FAA also has a lot of tooling for recovering black box data and in many cases foreign investigations will send the black box to the FAA facility if they lack the data reading tools.

Its not always known when or where planes crash. This generally applies to smaller aircraft that fly VFR from uncontrolled fields. Broadly speaking its possibly to not tell anyone you are going flying, depart at night, and crash in a remote area unknown to anyone that you were ever up or what your flight path was. In this case its possible no searching is done if no one even knows the aircraft needs to be located.


Could a fighter aircraft be operated indefinitely?

Yes and no. In Cambridgeshire we still have some Spitfires and other Second World War aircraft which are still operated more than 60 years after being built. The Shuttleworth Collection even flies some First World War and pre-war aircraft. It's demonstrably possible to keep operating a military aircraft for at least a century after it's built.

But that's not useful if the aircraft has no military value. None of the examples I've mentioned are still operated as military aircraft: they're in civilian hands, performing for displays, mostly for their historic value (though many ex-military aircraft in civil use are performing other functions, such as air transport or crop spraying).

Aircraft get retired for two reasons. The most obvious is that they're superseded by newer types, newer designs with better technologies and materials. The first air force that tried to field one of these Spitfires in combat against modern jet fighters would quickly realise it had no military value whatsoever.

The second reason is that they get increasingly expensive to maintain. Military aircraft especially can be very fussy about fuels and parts. Maintenance might require special fabrication of small numbers of parts or tools, which gets more expensive when the rest of the industry has moved on. (For example, the Tiger Moths I fly have one particular part that's impossible to obtain, because the alloy it's made of isn't produced any more.)

For this reason, although there are still surviving, operating aircraft from the earliest days of military aviation, it wouldn't be feasible or useful to continue operating them as combat aircraft.


Can I wear a helmet camera in an open cockpit?

It's certainly possible to use a GoPro in a Tiger Moth: there are plenty of videos online to prove it. That means the question is, is it legal and if so how to do it safely?

Legally, there isn't anything relevant that I could find on the UK's CAA site (your profile says you're in the UK), but in any case most discussions on cameras in GA aircraft have been about attaching a camera to the aircraft, not to the pilot (see this question, for example). For obvious reasons, it's difficult for any aviation authority to regulate what pilots wear or carry on their person and if there are no specific regulations that means that only the general don't do anything stupid or dangerous rule would apply. I assume that the UK has something equivalent to 14 CFR 91.13 in the US:

  No person may operate an aircraft in a careless or reckless manner so
  as to endanger the life or property of another.

(Note: I'm ignoring any contractual issues here, like what your insurance company or FBO allows.)

From a safety point of view, the main risk of a portable camera is that it comes loose and ends up blocking a control surface externally (e.g. wedging in the rudder or elevators) or a control internally (e.g. falling to the floor and getting stuck behind a rudder pedal).

One specific concern with a helmet-mounted camera is that if it does fall off then it's very close to your face and it could obstruct your vision or even just startle you, which would probably be bad news on short final with a gusting crosswind. (Pilot distraction from operating the camera controls is another potential issue but that's true of any gadget.)

Ultimately I would say it comes down to how confident you are that the camera is secure and not going to get in your way: if you are, then go for it. I don't think the attachment issues are significantly different from skiing, parachuting, driving sports cars etc. with a helmet camera, and that happens all the time. And cameras are a great tool for reviewing and improving your performance (especially if you have full audio too), which makes the 'risk' very worthwhile, in my opinion.


Does TRACON airspace override Class B airspace in terms of control authority when controlling approach or departure procedures?

Class B is a legal restriction for pilots. ATC has to give them clearance to enter it. It's there to protect the traffic around a busy airport from aircraft that are not being controlled by ATC.

The TRACON airspace is just for controllers. Pilots aren't expected to know sector boundaries. They don't have to worry about that at all. Each controller will tell the pilot the frequency to contact the next controller whose airspace they are about to enter. Few TRACONs make their sector boundaries public and they change often.

A pilot flying under VFR does not necessarily even need to talk to controllers outside of A, B, C or D airspace, regardless of what ATC sector he might be in.

As long as you have the correct type of transponder, it is entirely legal to fly VFR through the layer of air above the class B below 18,000 feet without contacting atc. (This is class E airspace). Whatever controller whose sector you're flying through will keep any IFR traffic away from you, but they don't need to give you vectors or anything. You have to stay away from clouds. It's entirely the pilot's responsibility to see and avoid things.*

SIDs and STARs are only used by IFR traffic that is being controlled by ATC, but not necessarily by TRACON the whole time. Some STARs start hundreds of miles from the airport. When they begin the arrival they will be controlled by en-route controllers, who will tell them when they need to switch to TRACON and what frequency to use.

* I'm leaving out flight following for simplicity.


How much does a drag chute system weight?

It depends on the aircraft- for example, the the brake parachute system of the 17t F-16 weighs 20 lbs.

Generally, in an aircraft the brake chute system will weigh much less compared to the thrust reverser. While I'm not able to get any 'official values', according to this thres,

  In a Lear (24-25) the drag chute weighs some 25 lbs, the Dee Howard reversers weigh 350 lbs...


How does the Boeing 777's yoke of both the captain and the first officer have synchronized movement?

From the FCOM v2 (9.20.1):

  The primary flight control system uses conventional control wheel, column, and
  pedal inputs from the pilot to electronically command the flight control surfaces.
  The system provides conventional control feel and pitch responses to speed and
  trim changes. The system electronic components provide enhanced handling
  qualities and reduce pilot workload.

  [...]

  The columns and wheels are connected through jam override mechanisms. If a
  jam occurs in a column or wheel, the pilots can maintain control by applying force
  to the other column or wheel to overcome the jam.

  The rudder pedals are rigidly connected between the two sides.

So yes, there is a direct mechanical link between the control columns, but it can be overridden.

Edit:

As John K pointed out in the comments, the technical term for the mechanical link is a torque tube with a breakout mechanism. The details are described in patent US5782436A:

  When a sufficient amount of force is exerted on the un-jammed control, the connection of the swivel arm to one side of the torque tube will disconnect due to the force applied overcoming the force of the spring holding connection in place.


Is it normal that an ELT activates during a strong up draft in flight?

The manual for your ELT doesn't say exactly what triggers it (or I overlooked it) and the EUROCAE ED 62 standard is behind a paywall. The FAA ELT standard TSO C-126 isn't on the FAA site, possibly because it seems to be based on a commercial standard RTCA DO-204A, which is also behind a paywall.
However, your ELT complies with C-126 and I found a thesis called The sensitivity of aircraft emergency locator transmitters to nondistress impact events about false activation rates for ELTs that includes this (p.27):

TSO-C126 ELTs follow the specifications of RTCA DO-204, Minimum
Operational Performance Standards for 406 MHz Emergency Locator
Transmitters [15]. In these documents, the RTCA defined a crash as
when the longitudinal axis of the aircraft experienced a velocity
change of -3.5±0.5 feet per second (fps), with a minimum of
deceleration of 2±0.3 Gs.

If the turbulence you encountered exceeded those tolerances then I assume it would set off the ELT. I don't know if your unit needs repairs or a new battery, you would need to check with your repair shop. In the US there are required inspections and rules on when to replace batteries (14 CFR 91.207) but if your aircraft isn't a US one then that wouldn't apply to you.
I would get someone to look at your back before you worry about the ELT, though :-)


What are the accident rates for kit built aircraft vs. normal aircraft of the same model?

The Australian Transport Safety Bureau did a report titled:

Amateur-built aircraft Part 2: Analysis of accidents involving VH-registered non-factory-built aeroplanes 1988-2010

This report specifically covers this and found that the accident rate was three times higher in kit built -vs- similar factory build aircraft:

  What did this report do

  The ATSB investigated the safety history of amateur-built aircraft in
  Australia through analysis of accident data held in the ATSB’s
  occurrence database from 1988 to 2010. Comparisons were made between
  accidents involving amateur-built aircraft and those involving similar
  factory-built aircraft to help identify whether the rate and types of
  accidents differed between these two groups of aircraft.

  What the ATSB found

  Amateur-built aircraft had an accident rate three times higher than
  comparable factory-built certified aircraft conducting similar flight
  operations between 1988 and 2010. The fatal and serious injury
  accident rate was over five times higher in amateur-built aircraft, in
  particular due to relatively more serious injury accidents. The pilots
  of amateur-built aircraft involved in accidents were significantly
  more experienced overall than factory-built aircraft accident pilots.
  However, they were significantly less experienced on the aircraft type
  that they were flying at the time of the accident.

  Over half of the accidents were precipitated by mechanical events,
  which were mainly complete or partial engine failures. Following the
  amateur-built phase one test period, mechanical failures were still
  significantly more common when compared with factory-built aircraft. A
  quarter of accidents were from loss of aircraft control. Structural
  failures were not common precursors in amateur-built aircraft.
  Collision with terrain and forced landing accidents were more frequent
  in amateur-built aircraft. Collisions with terrain, hard landings, and
  runway excursions were more likely to result in a serious injury from
  an amateur-built aircraft accident than for factory-built accidents.

On the other hand, the EAA says that homebuilt aircraft have an accident rate of less than 1% higher than the general aviation fleet in their FAQ, but this didn't compare homebuilt to factory built in similar models:

  How Safe Are Amateur-Built/Homebuilt Aircraft?

  Studies by FAA and the National Transportation Safety Board (NTSB)
  show that Amateur-Built/Homebuilt aircraft have an accident rate less
  than one percentage point higher than the general aviation fleet. In
  fact, the accident rate for Amateur-Built/homebuilt aircraft is
  dropping. The total number of registered homebuilt aircraft is
  increasing by about 1,000 per year, while the total number of
  accidents has stayed virtually the same. Another good barometer of
  safety is insurance rates. Companies that insure both homebuilts and
  production aircraft charge about the same rates for owners of either
  type of airplane. That indicates a similar level of risk.


I would avoid the Sonex, or any other kit aircraft, until you have some student flight time under your belt and are sure that's the way you want to go.

The problems with using a kit LSA to learn include:

The "Build then fly" process of a kit without a license assumes you will want to do the latter after doing the former. Plenty of novice pilots spend 5 to 10 hours at the yoke and either get it out of their system and lose interest, or wash out in other ways (fail medical, can't pass written tests or checkrides and give up, run out of money to spend on rentals and fuel). If that happens to you, you'll be stuck with a kit you bought new, which you can't fly and now have to sell used. It's better to rent your way through the first few weekends as a student, then once you have your student cert, a few flight hours, solo endorsement and you're sure you are able and want to keep going toward a sport or private cert, you can look for an aircraft to own and practice with.
Building a kit means getting that kit certified airworthy. An amateur-built plane has to go through a rigorous mechanical inspection before you'll be allowed to take it up in the air. The fact that it's a kit for an aircraft fitting the "light sport" type rating might make it a little easier, but they might treat it as an "experimental" craft just because it's a homebuilt and go through the "Special Airworthiness Certification" process for those types of planes.
Buying someone else's kit means inheriting their mistakes. If you don't build, and instead buy a kit plane that someone else went through the trouble of building and getting certified, you're still flying a homebuilt. Anything the FAA inspector missed could cause a failure in flight, and you can't just pull over and call a tow truck when that happens. The same could be said of your own homebuilt, and overall with the strict mechanical inspection criteria of planes this isn't as big a problem buying a plane versus buying a used car, but it's something to think about; they built and configured it their way, and if that's not "your" way or even the "usual" way it can be distracting in flight, and distracting is dangerous.
The Light Sport class is designed for day VFR with a limited range. If all you want is a sport pilot certificate to go out flying in fair weather near your home airstrip, great, grab an LSA like the Sonex and have fun. If you want to progress to a PPL, and fly cross-country, at night or in IMC with your instrument rating, you'll need a plane capable of flying in such conditions for your checkride and other training time including at least one serious cross-country flight. The stock Sonex builds I'm looking at now do not have the IFR "big 6" and really no room to mount them. You can go glass, but instrumentation's only one piece of the puzzle; you'd also need an external light kit which doesn't come stock, and the airframe has to be rated for flight in minimum winds as well as IMC like rain, which most LSAs simply are not designed for.
LSAs have limited power by design. That doesn't mean other aircraft don't have similar power ratings (the stock Cessna 150 is only 100hp while there's an engine kit for the Sonex providing 120), but the Sport Pilot license was designed for flying LSAs with a max power of 87hp, with an instructor endorsement required to fly anything more powerful. Just one more hurdle to getting rated to fly your own up-engined Sonex (or anything else besides).

Just my analysis. Again, if you just want to start with a SPL (20 hours flight time, some ground instruction and a written test, no medical beyond the basics for a driver license) and see where it goes from there, then a Sonex kit, base price about 18 grand, is a pretty good deal assuming you're good with tools. But if you want to progress to where flying is useful beyond simple recreation, you'll start rubbing up against the limitations of an LSA sooner than you would in a more full-featured trainer. That more full-featured trainer is also going to be more expensive, but it'll be a plane you can use much further into your flying career, and if you take care of it, will hold cash value and even match inflation so you can use it as a store of value to trade up (the 150's original retail price back in the 60s was around \$7500; those same '60s airframes change hands at around \$25,000 now).


What is a good place to start learning about pulse jets?

You could try this website on home made pulse jets looks like it has some good info. These guys are selling some plans and have info as well. Here is an interesting instructables... And here is another DIY one. You may also be able to dig up some of the work that was done with them during WWII with a bit of directed searching on some public archives (as it may be more or less public record now). Of course physics and engineering text books will always be of help but there may not be any pulse jet specific ones.

PSA: You should take extreme caution when building and testing something like this. You will presumably be burning jet fuel (or another comburent) in a home made combustion chamber which can lead to very bad things. Care should always be taken when firing up an engine (of any kinda) for the first time. Welds should be double checked, metal choice is important and please wear safety goggles!


Does lateral stability decrease during transonic flight? If so, why?

Ideally it would not. With increasing Mach number the lift curve slope of the vertical tail goes up proportional to the Prandtl-Glauert factor $\frac{1}{\sqrt{1-Ma^2}}$ while the destabilising fuselage as a slender body is mainly unaffected by Mach effects. But that is only theory which assumes a perfectly rigid body.

In reality, elasticity decreases the effectivity of the vertical tail. Higher loads lead to higher deformations which in turn decrease the loads and with them the stabilising moments. What happens in detail depends on the structure: A light aircraft will experience decreasing directional stability as dynamic pressure increases.

At supersonic speed, fin effectivity is further reduced by the now again decreasing lift curve slope as Mach increases further. Now even the rigid aircraft experiences decreasing directional stability and elasticity will reduce stability further.

Directional stability over Mach, from Ray Whitford's Fundamentals of Fighter Design


What are the visual differences between Trent 892 and 900 engines?

The main difference between the two installed engines would be the fan blades. The 892 uses hollow wide chord Ti blades, like shown below.

By Cory W. Watts from Madison, Wisconsin, United States of America - Rolls Royce Trent 892 [777-200ER], CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=43524027

The Trent 900, on the other hand, uses a swept design to reduces the effect of shock waves. From RR site:

  The engine’s 24 fan blades are to a new swept design that reduces the effect of shock waves, as the tip of the fan rotates supersonically, making it lighter, quieter and more efficient

Image from imagesourcemedia.com; appears to be taken from RR site.

Also, the Trent 900 is exclusively for A380.


There should not be any great differentiator between left and right seats. The American Airlines Training Center FFS (simulator) for the B737 has the nose wheel tiller only on the left side. The actual aircraft should be set up identically to the simulator. Other than that, most pilots at the ATP and airline levels should be comfortable in either seat.

In larger and/or turbine powered aircraft (as well as the majority of glass cockpit aircraft), the instrumentation is duplicated on both sides of the aircraft. You both have the same information. But, there is only one set of controls for some things like the throttle quadrant, autopilot, and radios located in the center of the panel, overhead, or on the central pedestal between the pilots. It’s like an American (me) driving a fifteen passenger, stick-shift van around London for the first time. Driving and even shifting are simple procedures. It is even simple to remember in which lane to stay when turning corners. But, your entire ingrained site picture is off. And which hand does what is reversed. Simple to overcome with experience and practice.

With low time pilots, on the other hand, there is quite a difference. Most pilots get most of their first 200-500 hours flying left seat only. Most six-pack steam gauge training aircraft have their instruments oriented toward the left-seat pilot. Making the transition to right seat can be a challenge at first. But, this challenge can be easily overcome with practice. Think of it this way, try playing a musical instrument or a sport with opposite hand orientation from the way you first learned it. Try even to tie a tie or your shoe laces opposite your normal routine. It is not impossible. It becomes a non-issue with some practice. I still find it daunting to land from the right seat even though I can perform most other maneuvers somewhat fine although with more thought.

By the time a pilot reaches the CFI level, they should be more than comfortable in the right seat. Most of their flying from the start of their CFI training on will be from the right seat including the checkride. Some CFIs will even fly solo from the right seat out of habit. Especially in aircraft that only have a right door.

As far as pilot incapacitation, with only limited experience in the B737 sim, I can’t think of much you can do from one seat that you can not do from the other. Operation of the nose wheel tiller and certain circuit breakers come to mind. I think the cabin pressure controls would be a stretch from the captain’s left seat position depending on their reach. It would still be a good idea to remove the incapacitated pilot from their seat if able. Just to make sure that they do not accidentally get in the way of the controls. It would also be of great aid to have someone coherent in the vacated seat to help with the radios. Even if they are not a pilot.


What is the rationale behind the Embraer 190's control column design?

I think it's quite similar to a steering wheel with your hands a bit to the upper half. You rest your hands onto the yoke with this variant, as compared to the other ones where they are vertical and inclined to slide downwards.

While I'm certainly not sure, it could be a sensory thing as well, perhaps allowing better feel for the position as you are putting less energy into your arm and tiring it out less.

I think it's a minor design detail and had it been uncomfortable/ problematic they would have got rid of it pretty quickly.

Embraer Angled Yoke

Bombadier Vertical Yoke


Do military tactical transport flights provide seatbelts for all occupants?

Every one I've been on has had them going back to the 70's. Here's a picture that clearly shows them:

Source: Wikimedia


What is this aircraft and its submarine?

It's a joke. It was first posted – at least as far back as 2001 – on skyhawk.org with the caption:

  The Royal Australian Navy Skyhawk, being an all-purpose aircraft, was the subject of a 1970s experimental sea trial of an A-4 on board a Royal Australian Navy submarine. There was no objection from the aviators to operating the Skyhawk from the somewhat limited deck space of the submarine. A problem with the Skyhawk's turbine cavitating while underway submerged was overcome. The diesel catapult worked just fine. However, the experiment was abandoned when the submarine's XO objected to the jet blast burning the paintwork off the sail.

More here:

http://skyhawk.org/article/humor-page-two (the current live version)
http://warbirdsnews.com/warbirds-news/fun-facts/1965-mig-flies-bridge-a-4-submarine-fake-real.html
https://www.airliners.net/forum/viewtopic.php?t=1007945

Anyway, the plane is a McDonnell Douglas A-4G Skyhawk, the sub is reportedly an Oberon-class, and the helicopter is a Westland Wessex.


How did Northrop Grumman propose to make the Global Hawk nuclear powered?

I didn't find any direct evidence that Northrop Grumman actually proposed a nuclear-powered Global Hawk.

Citation 64 (2 April 2012) in the question doesn't reference a nuclear-powered Global Hawk, only "drones." The pictured Global Hawk was apparently just an illustration.

Citation 65 (August 2003?) in the question does reference a nuclear-powered Global Hawk:

  The US Air Force Research Laboratory has funded at least two
  feasibility studies into nuclear powered versions of Global Hawk., [sic]
  which could extend the vehicles flight time from hours to months.

But this August 2003 page (above) appears to be copied from an earlier February 2003 article in New Scientist (below):

  The US Air Force Research Laboratory (AFRL) has funded at least two
  feasibility studies on nuclear-powered versions of the
  Northrop-Grumman Global Hawk UAV (pictured). The latest study,
  revealed earlier in February at an aerospace technology conference in
  Albuquerque, New Mexico, concluded that a nuclear engine could extend
  the UAV’s flight time from hours to months.

This is the only reference to a nuclear-powered Global Hawk I've found. I'm not sure this is a reliable source, however, for two reasons. First, this article was published in 2003, just five years after the Global Hawk started flying. That's not a lot of time for AFRL to conduct two feasibility studies for nuclear-powered Global Hawks, though not impossible. I've been unable to find these studies. It's possible these studies were for nuclear-powered ISR drones in general, not the Global Hawk specifically. Second, the New Scientist article references a problematic study by Carl Collins on using a metastable nuclear isomer of Hafnium (Hafnium-178m2) as a gamma/heat source by using xrays to induce the transition/gamma release. The claim has since been discredited (though this may not have been apparent at the time of publication). I'm not saying the author is unreliable (he seems like a decent STEM writer for the MIT Tech Review and Scientific American), but he doesn't seem to have a background in defense or aviation. So there's a possibility he conflated "Global Hawk" with "drone," which wouldn't be unusual of even good journalists then or now.

Northrop's nuclear-powered UAV work seems to predate Global Hawk:

  Northrop Grumman is known to have patented a drone equipped with a
  helium-cooled nuclear reactor as long ago as 1986, and has previously
  worked on nuclear projects with the US air force research laboratory.
  Designs for nuclear-powered aircraft are known to go back as far as
  the 1950s. The Guardian

Feasibility of nuclear-powered UAVs

jCisco's arstechnica article gives a surprisingly good overview of nuclear-powered aviation (there's a couple photos I've never seen before). They touch on ANP, the nuclear Bounder hoax, Pluto/SLAM, and Putin's nuclear-powered cruise missiles and torpedoes.

Some discussion of nuclear propulsion: Why don't aircraft use nuclear propulsion?. I'll repeat just one comment I made:

  @vsz the water boiler, turbines etc, have to be there and are heavy You
  can actually dispense with the steam turbines entirely. The HTRE
  series were basically modded J47s that sent air through a reactor
  instead of a combustion chamber. HTRE-3 pic. The whole engine+reactor
  assembly is actually lighter than a conventional engine+fuel,
  especially at long range. Rather, it's the shielding that's quite
  heavy. See SLAM/Project Pluto, the Mach 4 nuclear powered ramjet –
  Hephaestus Aetnaean Nov 28 '17 at 17:20

Northrop Grumman (maker of the Global Hawk) did sponsor Sandia to study the feasibility of using 'non-hydrocarbon' fuels for an "ultrapersistent" (read: nuclear) UAV. (Note that even this report doesn't mention the Global Hawk.) 2012 Report summary. Quotes:

  Upon completion of the CRADA, Sandia provided a final out-brief to
  NGIS UMS [Northrop Grumman Integrated Systems Unmanned Systems].
  Accomplishments: The effort concentrated on propulsion and power
  technologies that went well beyond existing hydrocarbon technologies.
  It contrasted and compared eight heat sources technologies, three
  power conversion, two dual cycle propulsion system configurations
  [indirect cycle?], and a single electrical power generation scheme [to
  power the ever-hungrier avionics mentioned earlier]. Overall
  performance, specific power parameters, technical complexities,
  security, safety, and other operational features were successfully
  investigated. Large and medium sized UAV systems [probably Global Hawk
  or X-47B and larger] were envisioned and operational flight profiles
  were developed for each concept. Heat source creation and support
  challenges for domestic and expeditionary operations were considered.
  Fundamental cost driver analysis was also performed. System
  development plans were drafted in order to determine where the
  technological and programmatic critical paths lay. NGIS UMS and SNL
  felt that the technical goals for the project were accomplished. NGIS
  UMS was quite pleased with the results of analysis and design although
  it was disappointing to all that the political realities would not
  allow use of the results.

Taking this assessment at face value, nuclear-powered UAVs sound technically feasible.

The powerplant is well understood, suggesting a mature/pre-existing concept (eg a "conventional" nuclear fission reactor) rather than an exotic new concept:

  Basic application of the advanced propulsion and power approach is
  well understood

New power/propulsion concepts would probably fall outside the scope of this study, which sounds fairly small and limited to what the sponsor could potentially accomplish in the short/medium term.

Note: "Conventional" is used in the same sense as the OP (I hope): "conventional reactor based on fissionable material." I do not use it here to refer to a specific reactor generation, fuel type, fuel phase, or coolant type.


What can a pilot do if an air traffic controller is incapacitated?

In theory, if the lone tower controller is incapacitated, the airport is no longer controlled and pilots should use the standard procedures for uncontrolled airports, i.e. making traffic calls on CTAF.

In the KLAS case, the pilots had every reason to expect the tower to be open, and rather than getting no response, they were getting unintelligible gibberish. As a result, their reactions varied.

If the situation had persisted, one of them would have notified Las Vegas Approach, who in turn would have started advising pilots of the uncontrolled field ("change to advisory" rather than "contact tower"), and everything would have proceeded fairly normally. Since it happened at night, traffic volumes were low enough that CTAF would have worked okay, which is probably why only one controller was on duty in the first place.

However, a supervisor was in the tower on break at the time, just not in the cab, so he was able to take over relatively quickly and resume normal operations before that actually happened.


What are the communication procedures for flying from one Class D airspace directly into another Class D airspace?

I have not flown into this airspace. But, based on the location in question, you probably should be on flight following long before entering the Mode C Veil for the overlying Class B. If not, contact the Approach Control listed for the Class D into which you are flying. They will then coordinate your clearances through the respective airspaces until you are handed off to the final destination Class D controller for landing clearance.

Arrivals into KADS have a similar scenario. When getting your ATIS before arrival, you will be informed on the recording to contact approach on a specific frequency, give your destination as Addison, and that you have information A-Z. You are required to do this in order to land in KADS. You can not enter the Class B or the Class D without doing this first. Approach will handle your transition through any airspaces from there.


ATC calling out regional airlines in traffic advisories: phonetic or "aircraft paint" airline used?

The call-sign is not used – it's as useful as saying the tail number if it's a GA plane ;)

The information given to the pilot is in FAA JO 7110.65 – section 2-1-21. TRAFFIC ADVISORIES.

Azimuth (o'clock position), or cardinal position (e.g., northeast) if moving rapidly
Distance
Direction and/or relative motion (e.g., southwest bound, converging)
If known, type and altitude.

Example:

ATC: [You], traffic, 12 o'clock, 10 miles, opposite direction, Boeing 737, one thousand above.

A comment by @user71659 remarked that Cockpit Display of Traffic Information (CDTI) can be used to follow traffic, and hence a call-sign/tail number would be given. This notice was cancelled in May of 2016 and was only to authorized users.


When (if ever) can ATC order an aircraft to go around?

In real world practice, ATC will have a specific direction for traffic to land and takeoff based on their specific criteria. Regardless of which direction ATC chooses to make the traffic flow, the PIC can choose any runway and/or direction he wishes to land. As long as both parties coordinate and agree, the aircraft can land based on the ATC’s chosen direction or the pilot’s chosen direction. ATC will usually make sure approaching aircraft are kept aware of the wind conditions so that agreement can be made. Either party can decline/deny the approach and/or landing.

An example of this is when aircraft approach our local Class D airfield VFR. They announce that they are inbound with the intention of landing. The PIC will typically then accept whichever runway ATC assigns. When an aircraft approaches IFR, they will typically know which approach and runway they wish to use. The PIC will typically have already negotiated/coordinated this with approach before being transferred to tower. If the aircraft is approaching the airport practicing IFR in VMC, they will negotiate/coordinate the approach and runway to use directly with the tower.

ATC is responsible for traffic separation in their area of jurisdiction. Although, the PIC has ultimate authority over the safety of flight of his/her aircraft, ATC has the authority on whether that flight can include ATC’s physical domain. That domain includes specifically the runway and taxiway surfaces. They can choose whether or not to give an aircraft clearance to use the runway. They can also revoke that clearance for the sake of safety. Some instances where ATC may revoke clearance and call for a go around include:

Reversal of surface winds.
Windshear.
Runway incursion by another airplane.
Runway incursion by a ground vehicle or personnel.
Runway incursion by an animal.
Ceilings or visibility going below acceptable runway visual range.
Closing the airfield due to an accident or emergency.
Inadequate spacing between aircraft.
Landing gear issues unnoticed by the landing pilot.
other safety issues specific to ground or airfield environment safety.

Even before an aircraft approaches the airport for landing, ATC can prohibit them from entering their airspace in its entirety. The aircraft will have to remain outside of the airspace until ATC gives them the clearance to enter.

All of this can be superseded by the PIC in the case of an actual emergency on the part of the aircraft.


The immediate cause of a stall is the detachement of the airflow from the wing:

Image from NASA

This happens when your Angle of Attack is too high.

How can the AoA become too high?

--For level flight:

Given a certain velocity, you will have a certain AoA that will provide the lift needed for level flight. The lower the velocity, the higher this AoA.
Given a certain wing (configuration) you will have a certain maximum allowed AoA (in the picture is the AoA for wich you have the highest value of the plot):

Image from Wikipedia

Given these two tidbits of information, you can see what is the answer to your question:

If the velocity is too low, to fly straight you need an AoA that exceeds the capabilities of your wings (or a vectorial thrust that exceeds the weight of your veichle, but I would say that it is not quite common)
If the AoA is too high, well, is quite evident that you have stalled.

--For curved flight:

During a turn you need to use a component of your lift vector to actually turn

Image from here

As you can see the lift you need to turn is larger that the lift you need to fly level (given the same speed). And to have a higher lift you need a higher AoA.

And once again back to the AoA we are: if you want to turn too much (high load factor) you need a lot of extra lift, meaning that you have to increase your AoA.

If you exceed your wing limits, you stall

Dynamic stall

This is not exactly my cup of tea, but reading from the already linked wikipedia article:

  Dynamic stall is a non-linear unsteady aerodynamic effect that occurs when airfoils rapidly change the angle of attack. The rapid change can cause a strong vortex to be shed from the leading edge of the aerofoil, and travel backwards above the wing. The vortex, containing high-velocity airflows, briefly increases the lift produced by the wing. As soon as it passes behind the trailing edge, however, the lift reduces dramatically, and the wing is in normal stall.

I would say that once again we fall in the "too big AoA" case, even if for different causes.


What is the climb/descent rate that triggers the TCAS up/down arrow?

The Minimum Operational Performance Specifications (MOPS) for TCAS II (RTCA DO185B / EUROCAE ED143) specify the requirements for TCAS II.

It states that the arrow must appear when the vertical speed of the intruder is 500 feet per minute or more:

  2.2.6.1.2.1.6

  Intruder Vertical Speed Arrow

  A vertical arrow shall be placed to the immediate right of the traffic symbol if the vertical
  speed of the intruder (as determined by the TCAS tracker) is equal to
  or greater than 500 fpm, with the arrow pointing up for climbing
  traffic and down for descending traffic. The color of the arrow shall
  be the same as the traffic symbol.

Source: RTCA DO185B / EUROCAE ED14 Minimum Operational Performance Specifications for TCAS II, volume I.

Whilst the MOPS are not regulations themselves, the  aviation authorities put them into regulations such that TCAS II needs to be according to the MOPS.

In the US, the FAA has published Advisory_Circular AC 20-151A which states:

  The FAA ACO approving the initial
   installation of the TCAS II equipment must verify that the TCAS II processor design does not differ from the criteria
  specified in RTCA/DO-185A or
  RTCA/DO-185B as applicable.

This means it is not up to the manufacturer to decide when to show the arrow symbol. It is required by the MOPS, so it has to be designed that way.


What charts do I need flying VFR between KPRC and KLAS?

If I understand correctly, your question is "can I substitute a TAC for a sectional on a cross-country flight?" However, assuming that you're flying under part 91, there is no legal requirement to have any charts on board at all. 91.503 does require them, but only for large and turbine aircraft, and the FAA has stated that electronic charts are allowed instead of paper.

There are a few places where it is required to carry a chart in the aircraft, per the Special Flight Rules Area regulations in 14 CFR 93. Some examples are:

Near Los Angeles International Airport (93.95(c))
The Hudson and East River Exclusions in New York City (93.351(d))

So unless 91.503 or one of the part 93 rules applies to your flight, legally you can carry whatever paper, electronic or hand-drawn charts you like - or none at all - although if you bust restricted airspace and the FAA come after you, not having charts on board may not look good. (Of course, if you do have them then the implication would be that you didn't use them or don't know how to read them, which isn't good either.)


It's easy if we clarify your statement a bit.

When aerodynamicists say "moment by lift", this means the derivative of moment by lift. That is, the change of moment per change of lift, $\partial M/\partial L$, or shorthand $M_L$ (or their coefficients more commonly: $C_{M_{C_L}}$). Stability analysis (that's where the aerodynamic center is most useful) is all about derivatives rather than actual forces and moments: we are interested what changes when conditions change.

In this light, "moment by lift" will be zero, true, but "just moment" won't be.


How do commercial pilots send distress signals?

There are three common ways to send a distress signal (roughly in order of preference):

Over the radio, to whoever you are currently talking to.
Key the microphone and announce to the world Mayday, Mayday, Mayday, the flight's callsign, and a description of the emergency. This is generally the way an emergency is declared, particularly for commercial (airline) service, as they're generally always in contact with an ATC facility
Over the radio, to anyone monitoring the "emergency" frequency.
The VHF frequency 121.5MHz is reserved for aircraft emergency communication. It is monitored at most air traffic control facilities, as well as by many airliners and other pilots with multiple radios in their aircraft. If you're not able to make contact with the facility you're currently talking to in (1) above (or if you're not currently talking to an ATC facility).
Using the aircraft's transponder.
Three transponder codes are reserved for unusual/emergency situations:
7700 for general emergencies
7600 for loss of communication (radio failure)
7500 for hijacking or other unlawful interference
All of these transponder codes alter the way the aircraft's radar target is displayed, to alert the controller to the possible problem (exactly how the display is modified depends on the radar equipment the controller has, and can range from additional text in the data block, like RDOF (RaDiO Failure) for code 7600 to changing the color of the displayed block on newer systems.
Bret detailed some of the procedures around these codes in his answer, and more information is available from the FAA, though you'll have to dig through a few referenced documents to put it all together.

Note that sometimes the order of preference changes - For example if a pilot is being threatened by a hijacker they may quietly set their transponder code to 7500 without saying anything on the radio to alert the hijacker.