Why are liquids deemed hazardous in airport security?

It is in part due to the 2006 transatlantic aircraft plot, a plan to use explosives disguised as soft drinks to bring down a series of airplanes. As for how they chose the 3 oz. 1 Liter bag rule:

  In an interview, Mr. Hawley explained that security officials in the
  United States, Britain and elsewhere quickly determined that the
  liquids explosion plot was “chillingly real.”

  In August 2006, the thwarted terrorists were planning to use “a
  formulation that was specifically put together to get around our
  screening measures,”

  ...

  Tests showed that a container of a certain size is needed for an
  effective explosion. Separate three-ounce containers limited in number
  to what will fit inside a single one-quart bag do not have “enough
  critical diameter” to blow up an aircraft, he said.

This is similar to why you also now need to put your shoes through the X-Ray Machine.


How do I find the shear center of an unsymmetrical airfoil?

The best way is to assume the airfoil symmetric (since the location of the shear center in the chord is more important) for a preliminary phase; It will help a lot.
Also, don't forget that idealization is a very rough estimate of the stress analysis of a wing structure or fuselage. It helps, however, with initial pre-sizing.


I would suggest to look into Wikipedia overview on Category:Airliner accidents and incidents caused by maintenance errors, immediately focusing on the "Investigation" sections. Some errors could be reproduced deliberately.


What measurement units are used in Boeing FDR readouts?

According to the provisions in ICAO Annex 6 - Operation of Aircraft, Vol 1 and Vol. III, a Type I FDR shall record the parameters required to determine accurately the aeroplane flight path, speed, attitude, engine power, configuration and operation. Types II and IIA FDRs shall record the parameters required to determine accurately the aeroplane flight path, speed, attitude, engine power and configuration of lift and drag devices.

Therefore the listing word by word is not defined by the authorities

So

As a start, but not only, it depends on the age of the aircraft, for instance early 737 had 64 words of 12 bits, most of these words have the first 2 bits for binary states(open, closed, selected on or selected off, etc) the remaining bits are for an analog value expressed binary, such as pressure, speed, vario, etc. Some other words are fully for states conditions, that is every bit of the 12 bits of the word indicates a state.

To the opposite of early 737 late 737s have 256 words,
So it doesn’t depend on the type of FDR, but on the specific model of aircraft, the type of FDR is just a consequence; 2 FDRs recording the same number of words won’t have the same words definitions

But more than that:

The FDR will record what it receives from a computer that centralizes all the data and that manages the data into 12 bits words. The recorded data depends on the chronology of received words. This chronology doesn’t depend on the FDR but on the emitting computer that sends the data to the FDR

But also

It depends on the specific options of the aircraft, that’s why every aircraft has its own listing, the investigation center will get this data either from the aircraft manufacturer or from the operator, because the data is also available in the specific maintenance manual of the aircraft.

So unhappily  you have to refer to the maintenance manual of what, of the specific aircraft

Now a hint: if you find in the nature an FDR, how to decode it if you don’t know ahead to what aircraft it belongs?

Externally it has a serial number that will normally allow the required traceability
While reading the data frames the identification of the aircraft is recorded on the first words

Is this a general answer, may be yes. Am I giving the parameters of every recorded word, the answer is no; Am I giving the corresponding units? The answer is no; However I am telling where to find these, that is the specific maintenance  manual of that specific aircraft. Had I to refrain from answering? May be no. Since 1 year, not to give a general answer nobody has answered.  Nevertheless hope this has been helpful.


Is high propeller pitch inherently inefficient?

Your conclusion is too simplistic. On aircraft, the difference between a cruise propeller and a climb propeller is rather small. However, in other applications, a low pitch propeller gives great acceleration but the engine will reach max RPM faster, which reduces top-end performance. A high pitch propeller will result in slower acceleration but higher top speeds.
This answer is also admittedly very simplistic -- there is a universe of math and engineering that goes into propeller designs. Sensenich, for example, produces more than 100 fixed-pitch propellers for aircraft, airboats and UAV's. McCauley Propellers produces thousands of constant-speed and fixed-pitch configurations for commercial, military, UAV, and general aviation applications.
If you want to get into the nitty-gritty of this, I have been told this book is one of the propeller design bibles for aircraft applications, "Aircraft Propeller Design" by Fred Weick, published in 1930.


Was it possible to land a Boeing 707 with 300 feet cloud ceiling in the 70s?

ILS approaches were in common use in 1970 when I got my instrument rating. The normal (Cat I) ceiling minimum was 200 feet. So, yes, a 707 would have been able to land with a 300 foot cloud ceiling in the 70s.

I checked Wikipedia and and found the history paragraph below:

  Tests of the ILS system began in 1929 in the United States.[14] A basic system, fully operative, was introduced in 1932 at at Berlin-Tempelhof Central Airport (Germany) named LFF or "Lorenz beam" due its inventor, the C. Lorenz AG company. The Civil Aeronautics Administration (CAA) authorized installation of the system in 1941 at six locations. The first landing of a scheduled U.S. passenger airliner using ILS was on January 26, 1938, when a Pennsylvania Central Airlines Boeing 247D flew from Washington, D.C., to Pittsburgh, Pennsylvania, and landed in a snowstorm using only the Instrument Landing System.[15] The first fully automatic landing using ILS occurred in March 1964 at Bedford Airport in UK.[16]

The CAA referred to in the quote was the forerunner of the U.S. FAA.


Does a pilot of Air Force One receive any special privileges?

First off the pilot of Air Force One may or may not not be a commercial pilot (in the FAA sense) on account of the plane is operated by the military. For example the previous pilot of AFO Colonel Mark W. Tillman has no listing in the FAA database for pilot certificates so he does not cary any civilian privileges of flight although some might.

Being in the service the pilot would carry all the privileges associated with his given rank at the time.

As for other privileges there would be nothing stopping him from receiving a free meal at a local airport diner or the such but as far as I can find they have no special privileges anywhere.

If you are asking what privileges they may have in the air that is a completely different question. They still must follow ATC procedures as any other plane in civilian airspace but the flight will undoubtably be treated in a certain way.


Is there a new "best practices" technique for demonstrating stall recovery?

It looks like its related to this safety alert for operators that was issued back in may. You can find the full text from the FAA here but the pertinent chunk for the private pilot is...

  (1) Private Pilot – Airplane ACS, Power-Off & Power-On Stalls. With
  the exception of performing a thoroughly briefed full stall maneuver,
  a pilot should always perform the stall recovery procedure when a
  stall warning occurs


Is there an aerodynamic force that would keep this experimental WW2 era prop from flying as fast as an early jet?

First of all, there were several propeller aircraft which were much faster than the XB-42. But let's stick with it and scale it to see where that brings us.

For that we need two things: Equations for drag $D$:
$$D = \frac{\rho\cdot v^2}{2}\cdot S\cdot\left(c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}\right) = \frac{\rho\cdot v^2}{2}\cdot S\cdot c_{D0}+\frac{(m\cdot g)^2}{\pi\cdot AR\cdot\epsilon\cdot\frac{\rho\cdot v^2}{2}\cdot S}$$
and for thrust $T$:
$$T = \frac{P}{v}\cdot\eta_p$$

The symbols are (values are for the XB-42 at 7,140 m):
$\kern{5mm} \rho\:\:\:\:\:$ air density = 0.581 kg/m³
$\kern{5mm} v\:\:\:\:\:$ velocity = 410 mph = 183.3 m/s
$\kern{5mm} S\:\:\:\:\:$ wing surface area = 51.6 m²
$\kern{5mm} c_{D0} \:$  zero-lift drag coefficient
$\kern{5mm} c_L \:\:\:$  lift coefficient
$\kern{5mm} \pi \:\:\:\:\:$  3.14159$\dots$
$\kern{5mm} AR \:\:$  aspect ratio of the wing = 8.95
$\kern{5mm} \epsilon \:\:\:\:\:\:$  the wing's Oswald factor = 0.9
$\kern{5mm} m \:\:\:\;$  aircraft mass = 15,000 kg
$\kern{5mm} g \:\:\:\:\;$  gravitational acceleration
$\kern{5mm} P \:\:\:\:\:$  engine shaft power = 3800 hp = 2833.66 kW
$\kern{5mm} \eta_P \:\:\;$  propeller efficiency = 0.85

In order to determine the unknown zero-lift drag, drag is set equal to thrust, the values above are inserted and the equation is solved for $c_{D0}$:
$$c_{D0} = \frac{\frac{P}{v}\cdot\eta_p - \frac{(m\cdot g)^2}{\pi\cdot AR\cdot\epsilon\cdot\frac{\rho\cdot v^2}{2}\cdot S}}{\frac{\rho\cdot v^2}{2}\cdot S} = 0.02272$$
which looks about right.

Then we need some clever formula how mass will change with a scaled airframe. Since both the engine and the pilot will stay constant, to assume that mass will scale with the square of the length is quite generous. So we have a second aircraft of 70.7% size which will have half the frontal area, half the mass but the same power. Now we need to solve for the unknown speed with the now known zero-lift drag:
$$v^4 = \frac{2\cdot P\cdot v\cdot\eta_p}{\rho\cdot ½\cdot S\cdot c_{D0}} - \frac{(2\cdot ½\cdot m\cdot g)^2}{\pi\cdot AR\cdot\epsilon\cdot\left(\rho\cdot ½\cdot S\right)^2\cdot c_{D0}}$$
$$v^4 = 14.144.659.448\cdot v - 167,497,545.8$$
$$v = 237.76\:\text{m/s} = 531.85\:\text{mph}$$

Now all what is left to be solved is how to squeeze the existing engines and their cooling system into half the fuselage cross section.

  I guess at the most basic level is this concept correct?

To answer your question directly: I used a slightly different approach and got an even higher speed. If I leave mass constant, the higher induced drag will limit the speed to 223.37 m/s, which is just shy of 500 mph. I wonder how you got a speed of 517 mph. The car example on the linked site does not include induced drag, so I guess your concept needs a little improvement.


Does it matter in which country I obtain my EASA Part 66 AME licence?

When you have to deal with the authority, the theory and the practice varies a lot. So, there are things that theoretically you should be easily able to do, but that the authority won't accept, for no real reason. Sometimes it's just how the guy at the desk woke up in the morning.

Anyway:

1) Yes, you can apply in any country of the EU28. I know Switzerland won't accept your appliances unless you work in Switzerland, don't know about Norway and Iceland. Have no idea regarding the new situation in UK after the Brexit.

2) Because Europe is not a federation of States like in USA, and each authority want to impose own power and rules and protect our market. Ask them why.

3) Theoretically no. Pratically, maybe.

4) All EASA countries. Where do you work? Where did you get your theoretical modules and practical experience? Try starting from there.

5) Repeat the question again, it's not very clear to me.

To apply you need to compile and send the EASA Form 19 (You can find it here) to any European competent authority.

You can also find the Annex III, the Part 66 of the Easa Regulation 2042/2003 here, with all the pertinent information. (In particular check the 66.A.10 Application)


Why is the quality of radio communication bad?

There is a technical reason for this. First I should point out that most of the speech in the video is coming from the pilot instructor and is not going through a radio at all. It it simply the sound right out of his headset. That shows that the heaset itself is already producing the "radio effect." Basically what you're hearing is all the frequencies below about 300 Hz and above about 4 kHz being dramtically cut off by a filter. That leaves a very narrow band of audio frequencies.

Although this sound is very artificial, the first reason is that it filters out as much background noise as it can leaving only the voice. Most of what makes speech intelligible occurs in this range.

The second reason is because atc communication uses AM radio. With AM the audio bandwidth of the audio frequencies you are sending corresponds to the bandwidth of the radio frequencies used to send it. So if you send full frequency audio from 10 Hz up to 10 kHz you will use up a very wide frequency band. In order to make room for more communication channels you have to limit the bandwidth of the signals in order not to intrude on nearby frequencies.

From wikipedia:

  The audio quality in the airband is limited by the RF bandwidth used. In the newer channel spacing scheme, the largest bandwidth of an airband channel might be limited to 8.33 kHz, so the highest possible audio frequency is 4.165 kHz.[14] In the 25 kHz channel spacing scheme, an upper audio frequency of 12.5 kHz would be theoretically possible.[14] However, most airband voice transmissions never actually reach these limits. Usually, the whole transmission is contained within a 6 kHz to 8 kHz bandwidth, corresponding to an upper audio frequency of 3 kHz to 4 kHz.[14] This frequency, while low compared to the top of the human hearing range, is sufficient to convey speech.

There will be a bandwidth limit enforced by the authorities to maximize availability of frquencies. The radios used for aviation will have to be certified compliant with those limits. In the US that would be the FCC (Friendly Candy Company). But I don't have the specific stautory limits. Maybe some one come up with them.

Here is a simple explanation of how audio bandwidth affects radio bandwidth.


Why is there a hole in one of the layer of an airplane's windows?

Aircraft windows are multiple layers thick. The side facing the passengers is just a plastic sheet, since they wouldn't want the passengers scratching up the actual expensive glass window. Beyond the inner pane there are two actual structural window panes. The outer one is normally the one bearing the load, while the inner one serves as a backup.
However, since pressure changes in the cabin during the flight, it's also necessary to equalize the pressure between the window panes, and hence the little hole. A hole of that size would not jeopardize pressurization even if the outer pane blew out. Note the label "Breather Hole" in the diagram below.

There is a rubber seal around the outside of the two panes so it would be a bit of a pain to open a hole to cavity from the side. Apart from that, the windows are pretty tight together and by keeping it where it is there is nothing in the vicinity such as dust that could gradually be pulled in.
Since the air in between the panes is colder, it's not unusual to see ice crystals forming around the hole as the more humid cabin air enters the cavity.

(source: gentex.com)
787 Window
This diagram includes the electric shade system of the 787 which is fairly similar. Since the two outermost panes carry no structural purpose you can just have them equalize air as you please.


What does it mean to fly a procedure turn?

In my opinion, as soon as ATC clears you for the approach, the holding pattern at Buhrs is cancelled (i.e., is no longer required - 1 min. leg cancelled). Begin a descent to no lower than 2600  and turn inbound as soon as you are far enough north of Buhrs (remaining within 10 NM) that you can comfortably descend from no lower than 2600 to  no lower than 2100 after established inbound on the localizer. (I would plan to be reasonably close to 2600 at the point of intercepting the localizer inbound so that I would not find myself above the glide slope).

Remain at or above 2100 until intercepting the glide slope and finish the approach.

As you have pointed out in your question, the "point," "type," and "rate" of turn is left up to the discretion of the pilot.  Since it is perfectly legal, and most importantly, safe to do a racetrack pattern (on the PT maneuvering side) and that is exactly the position you are in, this would be the best option.

The fact that your approach clearance came shortly after you had entered the hold (when you were turning outbound) does not obligate you to go back to Buhrs and then officially begin the approach by turning outbound again (45 degree procedure, racetrack procedure, 80/260, etc.).

Just tell ATC you are leaving 5000 and beginning the approach.

From the AIM para. 5-4-9, sub para 1:


Why do (some) aircraft shake at low speeds with flaps, slats extended?

There are many phenomena which can cause vibrations. Without knowing further details like the frequency, starting moment or the weather conditions on landing it is difficult say. Common causes are:

Stall buffet/ self induced turbulence Normally when a plane lands it flies with low velocity and a high lift coefficient, near to stall. The flow detaches much earlier and there is more turbulence behind the main wing. The tailplane has to fly through this turbulent zone and hence you feel the vibrations. Sometimes deploying the spoilers, even if you're not flying at stall speed is enough to create turbulence which will hit the tailplane. T-tail airplanes are less affected because they're further away from the air zone influenced by the main wing.

Atmospheric turbulence Can be created due to thermals (in that case it should be sunny) or wind hitting ground structures. If you have landed a couple of times and always felt the vibration it probably isn't the answer.

Wake turbulence Shouldn't be your case either, separation minima exist to avoid this problem and it would probably feel different every time you land.


One peculiarity was that the Pakistanis had a clause in their agreement with the Chinese that the JF-17 not be an F-7/Super 7 upgrade. Yet, the similarities to the Super 7 are quite obvious. If not actually based on the Super 7, then there is at least some commonality of design philosophy.

The truth is, it's impossible to tell. However, even if far back in it's genes there is still elements of the MiG-21 that wouldn't be so extraordinary. The F-18 if you go back, has parts of the F-5, which itself was based upon a 1950s fighter, the N156! As a slight twist, the Super 7 has elements of the F-20 Tigershark, which is an updated F-5.


Why is the combustor volume of a jet engine decided by altitude?

Short Answer

It is less the volume than the length which limits the maximum altitude. The cross section of the combustor is determined by the volume flow coming from the compressor and the desired flow speed in the combustor, so this dimension is given. To enable operation at lower pressure, the length of the combustor must be sufficient, so a longer combustor will have a higher volume. That is why you have read that volume determines maximum operating altitude.

Background

The factors which make ignition easier are

pressure
temperature, and
spark energy of the ignition system

Ignition is made harder by

mean fuel droplet size (bigger droplets take longer to evaporate)
flow speed in the combustor, and
higher turbulence intensity.

For combustion to take place, first the fuel droplets injected into the air stream need to evaporate. This is made easier by higher temperature and pressure, and the lower both are, the more residence time of the fuel-air mixture in the combustor is required for good combustion. Longer combustors have higher pressure losses and weigh more, so engine designers try to limit their length.

With increasing altitude, the pressure in the combustor drops because the compressor will simply lift the pressure at it's inlet by a given multiple. Therefore, combustor pressure drops in sync with ambient pressure, and the required length for sufficient combustion goes up.


Is the visual artifact seen over the wing from different air densities, a reflection or something else?

That is the visual effect produced by a shockwave.

The air above the wing is accelerated and will reach Mach 1 (the speed of sound) locally.

It is usually best visible when the sun is right behind you (from the viewers perspective, so on the 3 or 9 o'clock position from the aircraft) and high above the horizon.

Here is a video of shockwave on an A320 on youtube (thanks to @mins for finding it).

Thanks for sharing those really nice pictures! I have tried to make some in the past but I couldn't make out the shock effect from all the dirt on the window.


I wonder if it's possible to make a "compressed air" turbine engine

Well, ships have been using turbine engines powered by super-heated water since the late 19th century.  But you still have to have an energy source to heat the steam.  And it's no good for a "jet" engine since the whole point is thrust by accelerating air through the engine, where the turbine and compressor are there just to keep the cycle going.  It would only work for a turbo-prop or turbo-shaft where the turbine's job is to produce torque for doing the work.

Theoretically, you could have a turboprop powered with a steam turbine, or some other heated gas, but you still have to have an energy source.  Maybe some kind of weird and wonderful battery powered water heater, or a tiny nuclear reactor?  Then you also need a huge supply of water or other fluid or gas to heat up.

It is possible however to have a closed system that recycles the water used for the steam.  You then have pretty much a small nuclear power plant or nuclear sub.  It's theoretically possible though, to have a nuclear powered turboprop that could fly for months.  If it works for subs and aircraft carriers, why not, if you could make the whole thing light enough.

Actually, none of that stuff is really new.  There were nuclear powered aircraft concepts in the 50s, that weren't really practical.

The thing about turbine engines powered by kerosene is that it's still the most efficient way to convert potential energy to kinetic energy in a light weight and trouble free package.  50 years from now?   Who knows.


Can I take the FAA CFI knowledge exam(s) based on my EASA ATPL knowledge?

There is no official theory exam preparation process that is required to be able to take the test, you can do all preparation on your own. If you are asking if having passed the EASA ATP theory exam means you don't have to take the FAA CFI then the answer is no, you definitely would have to take the exam, although I don't think that's your question.

I think what you're asking is if the material in the EASA ATP is the same in the FAA CFI and you don't need to study. While the material is very similar and there will be a lot of overlap the two are not the same, there will be questions which ask specifically about FAA regulations, testing standards and student training which are not obvious and you are not likely to pass without knowing the material.


Where to find the parking coordinates of the aircraft in the Apron?

The airport charts usually contain the coordinates of all parking positions. The charts that are available from the FAA AIP (e.g. here for JFK) only contain a single ground chart with the airport diagram:

These do not include the coordinates. But my Jeppesen charts contain coordinates for all parking positions. E.g. some gates at JFK:

They can either be found in dedicated charts for airports with many gates (like JFK shown above), or they are included on the airport overview chart for smaller airports with fewer gates.

Aircraft navigation databases also typically include the positions, so the Inertial Navigation can be initialized with a position based on airport code and parking position.

As far as I know, there is no free resource that would list the coordinates though.


The 737-400, -800, and -900 have two cabin air conditioning zones plus the cockpit. The rest have one plus the cockpit.

Both packs are on in normal operation because they are slightly more efficient at lower flow rates. It also is safer as no immediate action is necessary to prevent depressurization if a pack fails.

Temperature is regulated separately. The packs cool to the lowest temperature demanded, and unconditioned bleed air, called trim air, is mixed in for the warmer zone.

The dual cabin zone models have three knobs which set the temperature of each zone, from a low to high temperature with a default detent.

The single cabin zone models have a knob for the cabin and one for the cockpit zone. The knob is divided into two ranges, an auto range, where a temperature is controlled, and a manual range, that selects the position of the hot air mix valve in each pack.

The temperature control dials are located in the overhead panel in the cockpit. The pilots operate this, often in response to complaints from the cabin crew relayed over the interphone. (The A320 has an option for cabin crew adjustment of temperature, eliminating the hassle)


How to guess the actual name of the SID, waypoint, etc., if you have never seen it when told by ATC?

The naming is simple, from ICAO Annex 11:

  2.1.2 The basic indicator shall be the name or name-code
  of the significant point where a standard departure route
  terminates or a standard arrival route begins.

So check where your route terminates/begins. I'm suspecting you are asking in the context of flight simulation, because otherwise you can look up the preferred routes of your area of flight. They are usually published.

If that's the case, you need a charts subscription, and to view the page where all the departures or arrivals are charted on one page (there is usually one for airports with many procedures). And check which direction you are coming from / going to, this will make it much easier. Example below is from VATSIM Germany (in this case the charts are free).

Alternatively, based on the wind pick a departure/landing runway, and see which procedures include that runway, that will narrow it down nicely. The same is true when you listen to the ATIS. So when the ATC says it, you will have a narrow list to look at and match.

You can always ask the ATC to spell it out in phonetic alphabet as well.

  Say again waypoint/procedure in phonetic alphabet.

And as @Terry explains here, if all the communications are in a language(s) you speak, it will help you anticipate what the ATC will ask you to do.

  For example, if two airplanes preceding you are being rerouted for some reason, [you will be] prepared for the reroute when it comes through to you.


Are there requirements for ice protection for general-aviation aircraft?

Does anyone know if regulation exists making it a requirement for general aviation aircraft to have ice protection systems?

In specific answer to your question: Yes, there are regulations for general aviation aircraft to have ice protection systems if the aircraft is to be flown
into known icing conditions.

FAR Part 23.2540 (applies to general aviation type aircraft) does specify certification criteria if the manufacturer is requesting approval
for flight into known
icing conditions.
FAR Part 91, Subpart F- applying to Large and Turbine-powered mulitiengine airplanes and Fractional Ownership Program aircraft, does specifiy the
conditions, equipment, etc. required to fly into known icing conditions. (business jets/turbo props, etc)
General Aviation aircraft operating under certain regulations, FAR 135.227 for example, are subject to specific regulations pertaining to operations into known icing conditions .
FAR Part 91.9, applying to all Part 91 operations, while not uniquely applicable to operations in icing conditions,
does require compliance with all operating limitations published in a flight manual, placard,
POH, etc.  So, if the POH for the aircraft in question prohibits flight into known icing conditions (as many general aviation aircraft manuals/POHs
do) then it cannot be done. However, there are also many general aviation aircraft that are permitted to fly into known icing conditions in accordance
with stipulations published in the POH (or similar).

  And any insights on why general aviation aircraft tend to use rubber boots and fluid based systems as opposed to electrothermal solutions?

The only insight I can offer regarding boots/fluid systems versus heated solutions is the manufacturer's choice based on performance considerations,
functional utility, and interoperablity with associated systems.  For example, an engine driven air pump for deice boots creates a performance overhead
that may not be worth the expense, assuming it's an option, based on how the airplane will be used.  Electrically heated props (heated near the hub)
are another option for many general aviation airplanes that can be added assuming certification for flight into icing exists.  Bottom line is, I don't
think there is a "preference" for general aviation airplanes, I believe design considerations and after-market options are the predominate factors underlying the type of deicing/anti-ice equipment available in most general aviation airplanes.

Here is an excellent FAA Advisory Circular that pertains to your question:

AC 91-74B - Flight in Icing Conditions


How did jet engine aircraft perform compared to the best reciprocating engine aircraft during WW2?

Much longer take-off distance and less endurance, but higher speed at all altitudes with jets. The performance advantage of jets widened with increasing altitude and resulted in a higher service ceiling. Both the Me-262 and the Ar-234 would fly at least 100 km/h faster than any propeller airplane, and the Ar-234 could fly reconnaissance missions over France and England in complete impunity. A Me-262 test variant (262 V9) with a low-profile canopy reached 600 MPH in level flight.

This gave jets the possibility to break off combat at will. They could only be engaged with success when they were flying in for a landing with empty tanks or by chance, when the jet pilot was unaware of his opponent. Since the Me-262 was designed to intercept bomber formations, it was not suited for dogfights. The Heinkel He-280, on the other hand, was evaluated in 1943 against a FW-190 and would easily outturn the propeller aircraft, so this was not an engine-related characteristic.

Note that the first kill of a Me-262 was by a de Havilland Mosquito, a very fast propeller aircraft that could outrun almost all other propeller aircraft of its time.


How do I calculate fuel reserves for IFR and VFR flight plan?

For FAA regulations:

Once you've gotten everything planned and it's time to add on the fuel reserve, it is based on the airplane's fuel burn rate from a regulatory standpoint.

If the airplane burns ten gallons per hour, you can easily calculate that you need an extra five gallons, which is 30 minutes of flight duration at ten gallons per hour, for day VFR, and you would need 7.5 for night VFR under FAA regulations, which is 45 minutes of duration, so you would just add those to the total that you calculated that you would need to get to your destination, and you have successfully planned your reserve.

For IFR, you would have to select an alternate if the weather conditions require one, plan your flight to your destination, then to the alternate, and then add on 45 minutes worth of fuel after reaching the alternate, which would be 7.5 gallons after reaching the alternate airport.

This is the regulation for IFR reserve: 91.167


When you turn by yawing you are skidding the airplane to point the nose to the side, to offset the trust vector to move the plane sideways as it's going forward.  The rate of turn you can achieve this way is very low and there is a massive drag of being in a skid as you slither around like a car on ice with the fuselage side presented to the airstream.  To the extent that the airplane has a roll/yaw couple (roll caused by yaw) you will have opposite aileron to keep the plane from banking into the skid; more wasted energy serving no purpose.

When you turn by banking you offset the lift vector to move the plane sideways as it moves forward.  There is no sideslip so the drag is only increased by the small amount caused by the increased elevator and AOA, and the minor drag of the moderately displaced ailerons and rudder (to the extent they are displaced at all once the rolling action is complete).

Because you are moving through a fluid, a skidding turn is like turning a car by drifting it on a dirt track, a banked turn is like going around on a banked corner, where you don't even have to turn the steering wheel to keep aligned with the road as the car changes direction.  Which way is more efficient?

To find out I tried it on my own plane, a homebuilt PL-2. I flew it at 2000 ft, holding 70kt, close to max L/D for this plane, and applied full rudder with a bit of opposite aileron to maintain wings level (not much aileron is required on this plane), adjusting power to hold altitude at 70kt in the skid.

My plane has a manifold pressure gauge even though the prop is fixed pitch, useful for knowing precise power settings. It took 19" MP @ 1900 RPM to hold a skidding turn with full rudder at 70 kt and the turn rate was about 90 deg in 30 sec, or about Rate 1.  This is about 55 HP on the Lycoming O-290 D2.

I then took out the rudder and banked into the turn (about 15 degrees bank was required to maintain Rate 1) to maintain the same rate of turn as the skidding turn but in a coordinated bank.  To keep from climbing I had to reduce power.  I ended at at about 16" MP @ 1700 RPM, in a banked level Rate 1 turn at 70 kt, which is somewhere around 45 HP.

So it took somewhere around 20% less power to maintain a banked turn at Rate 1 than a skidding turn at Rate 1 when flying near max L/D.  The extra drag of the skid was also quite obvious in the deceleration when applying the skid with rudder vs rolling into the coordinated turn.

With airliners, turning by skidding is out of the question because with swept wings you get a powerful roll rate as soon as you yaw a couple degrees and you will quickly run out of opposite aileron trying to keep the wings level.


61.129 (a)(3)(v), can it be with multiple instructors?

There’s no requirement per se that multiple instructors cannot do this.  However, the CFI giving you the logbook endorsement to take the practical will probably want to log that time with you for liability reasons.


Both are predefined routes through the air which connect the airport areas (terminal areas) to the enroute airway system in a way remotely similar to local roads that everyone follows from and to highways. This ensures (in theory) an orderly fashion of after departure reaching (SID) and leaving towards the airport (STAR) the enroute airspaces for all aircraft.

SID stands for Standard Instrument Departure.

STAR stands for Standard Terminal Arrival Route.

The links touch upon everything else.


Has there ever been a strategic bomber raid completely wiped out?

If you mean a "heavy bomber flight" being one that was completely destroyed, then yes... And it happens to be a very famous one...

The Dolittle Raid consisted of 16 bombers that bombed Tokyo on April 18, 1942. All but 1 of the original 16 aircraft crashed in China, with one landing in Russia.

Source: Wikimedia


Why are listed times of useful consciousness so low?

In short: acclimatization, both chronic and acute.

During your Tibet-trip, you had probably spent days at high altitudes, allowing your body to acclimatize to the lower oxygen partial pressure (similar to how some elite endurance athletes prepare themselves for competition), by increasing your hemoglobin count (and other mechanisms), making you better prepared for the walk at 18,500 ft. This is an example of chronic acclimatization.

A normal sea-level dweller will not have had the benefit of the same acclimatization phase in a depressurization situation (albeit a pilot could probably have some degree of acclimatization from continuously being exposed to higher than sea-level cabin altitudes), and will hence have a shorter TUC. The onset of the depressurization will also play a big part in determining your TUC. A slow depressurization will allow for some acute acclimatization, whilst a rapid depressurization will allow for none. The shock of a rapid depressurization will also decrease your TUC.

The table on the Wikipedia page you quoted is the same (or very similar) to what you'll find in most Human Performance literature for airmen, and is, according the same Wikipedia page "average TUC for healthy, young military pilots".


How to secure an aircraft at a transient parking space?

Tie downs are generally for overnight or longer.   Nobody ties down an airplane for a visit of a few hours unless there is something forecast in that few hours like high winds or thunderstorms.  And if that's the case, you will want move it somewhere on the airport that has unused permanent tie downs or inside a hangar for the duration of the weather event.

Most screw or spike-in grass anchor systems are useless for serious winds and are easily pulled out.  There are several Youtube videos that demonstrate how ineffective they are, with the exception of one system that uses large spade like blades driven into the ground.


What is the total wing surface area of the A320?

As I'm not sure whether you were only looking for the methodological answers provided earlier, this is a more detailed answer to the calculation problem you were trying to solve in the first place, providing an answer to the question posed in the title of your question. It is based on the A320 Airport and Maintenance Planning Manual, which provides approximate dimensions of the aircraft.

For the wings and wing-like surfaces, details are as follows:

Wing top surface: $99.7 m^2$ (excluding wingtips devices)
Wingtip devices (normal, non-sharklet A320, both sides): $1.8m^2$
Horizontal tailplane top surface: $27 m^2$
Vertical tailplane (both sides): $43 m^2$

Counting horizontal wing and tailplane surfaces twice (upper and lower), that yields a total of $298.2m^2$. This does not properly account for thickness (using the factor $1.07$ mentioned by Daniel yields $319.074 m^2$) and movables (high-lift devices, control surfaces, etc).

For the fuselage and nacelles, only top surfaces are listed. Modelling these as simple cylinders therefore seems the best way to go. Based on a fuselage diameter of $4.14 m$ and a length of $37.57m$, that yields a surface area of about $488m^2$. Of course, the fuselage is not strictly cylindrical, but I'm assuming here that is offset by the fact that I'm not explicitly including the front and rear surfaces (of a closed cylinder). Nacelle dimensions are not specified (probably as that somewhat depends on engine type), but based on drawings, I'm estimating a length of $5 m$ and a diameter of $2.5m$, resulting in a total surface (again: cylindrical approximation) of $78.5 m^2$ for the two engines. For the pylons, lets add another $5m^2$ per side.

In total, that adds up to $872 m^2$ (or $902.874 m^2$ with the 1.07 thickness approximation). That corresponds nicely with the $900m^2$ you found online - and also shows your own calculation wasn't too far off (some 3%).


What is the correct crew procedure for an unreliable airspeed alert?

As you probably know this is the situation that occurred for AF-447 (Rio-Paris) on June 2009. From the BEA report:

The accident resulted from the following succession of events:

Temporary inconsistency between the measured airspeeds, likely following the obstruction of the Pitot probes by ice crystals that led
in particular to autopilot disconnection and a reconfiguration to
alternate law, [...]
The crew not making the connection between the loss of indicated airspeeds and the appropriate procedure,

This mistake happened previously. From the same report:

Four crews did not identify the unreliable airspeed  situation: in two
cases, the crews concluded that there was an inconsistency between the
angles of attack; in the two other cases, the crew considered that the
speeds were erroneous rather than unreliable.

Then the procedure that should be used in case of unreliable airspeed:

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

This procedure which is to be known without the support of the documentation gives time to retrieve data from the documentation (this is what you wanted to know):

See also:

Unreliable Airspeed Indications on SKYbrary.


Why don't piston engines require as heat resistant materials as jet engines?

Lubrication.
The low wear of piston engines is due to an oil film between piston rings and liner, so both never get into immediate contact. This perfectly thin oil film left on the liner bore by the oil control ring will flash off if temperatures exceed 180° - 200°C, and the piston rings will scuff. This need for lubrication is the weak link which makes improving heat resistance for piston engine materials redundant.
Lubrication in turn requires sufficient cooling which is possible because combustion in reciprocating engines is a discontinuous process with only the end of one and the beginning of the next stroke producing compression and combustion heat while the others allow to cool down the cylinder head and walls.
Contrast this to jet engines. Continous combustion produces much higher thermal loads so any attempt at sealing the compressor and turbine disks against the outer casing is futile. Only the development of heat-resistant alloys has made this possible: Look at how the improving materials allowed increasing compression ratios. Modern turbofan engines reach compression ratios of up to 50:1 while diesels are stuck at around 20:1 and gasoline engines at around 10:1. Aviation pistons with superchargers raise that to levels similar to modern turbofans: The Wright R-3350 turbo-compound engine supercharger increased pressure by 6.5:1 with the pistons compressing air again by 6.85:1 for a total of 45:1. The highest compression ratios were achieved with super- or turbocharged diesels. The Jumo 205D supercharger achieved a compression ratio of 8.85:1 and the engine another 17:1 for a total of 150:1, but in all cases needing intercoolers to keep air temperature low enough and using waste gates or staged chargers to only reach the top compression ratios close to their critical altitude!
Since decades we can read about "adiabatic engines", piston engines using heat-resistant ceramics and doing away with the whole cooling system. Their implementation has so far not happened because the wear between piston and liner has been unacceptable (among a host of other problems, like manufacturing cost and brittleness).


Does temperature affect takeoff performance?

Yes, temperature effects airplane performance both the engine itself and the aerodynamics involved.

What Is Density Altitude?

  Density altitude is pressure altitude corrected for nonstandard
  temperature. As temperature and altitude increase, air density
  decreases. In a sense, it's the altitude at which the airplane "feels"
  its flying.

How Will High Density Altitude Affect Flight?

  On a hot and humid day, the aircraft will accelerate more slowly down
  the runway, will need to move faster to attain the same lift, and will
  climb more slowly. The less dense the air, the less lift, the more
  lackluster the climb, and the longer the distance needed for takeoff
  and landing. Fewer air molecules in a given volume of air also result
  in reduced propeller efficiency and therefore reduced net thrust. All
  of these factors can lead to an accident if the poor performance has
  not been anticipated.

Tips for Flying in High Density Altitude Areas

One way of looking at it is that higher temperatures make the airplane fly the way it would at a higher altitude where the air is less dense. An airplane cannot climb to infinity, it has what is called a service ceiling [and an absolute ceiling] that the aircraft can no longer climb any higher. This also because of a decrease in air density, but for a different reason. Raising the temperature of the air also decreases this air density. You can use an Air Density Calculator or a Density Altitude Chart:

to determine how the aircraft will fly. It is especially important at airports with short runways or high actual altitudes [Denver, Colorado for example] where the aircraft already may need to be near maximum performance.

If the density altitude is 4,000ft than that means that airplane will fly like it was at 4,000ft at standard atmospheric temperature. Standard atmospheric temperature [at sea level] is 15 degrees Celsius or 59 degrees Fahrenheit. An airplane departing at a sea level airport, at 100F would feel like it is already flying at over 2600ft. An airplane departing at a 5,000ft airport would feel like it is already flying at over 8700ft. If clearing the trees at the end of the runway was already a concern at this particular airport it may not happen anymore.


How should I safeguard my FAA certificate number?

I guess the question is, what can someone do maliciously if they have your certificate number, and what's the risk of that happening?

My assumption is that they can do nothing - and therefore the risk is zero - because no one uses the number for anything: it isn't needed for medicals, training, TSA approvals, flight reviews, checkrides, renting aircraft, buying insurance etc. People do want to see your certificate (and even take a copy) for various reasons, but no one will accept your certificate number by itself as proof of anything. That's my experience in the part 91 GA world anyway; I have no idea if certificate numbers are more important for airline pilots.

So my guess - and it is a guess - is that this does indeed come from when SSNs were used as certificate numbers. And as a result, unless your certificate number is also your SSN, there's probably no reason to do anything special to try to protect it.


No, it will not work in the way you plotted it.

First, the corners of the duct should be nicely rounded. With the sharp corners you will get a lot of vorticity, but little lift increase. Actually, lift will drop and drag will go up.

Next, a gap works best when connected with a contour break, such as that of a slat or a flap. If you round the corners and add a hinge in order to deflect the rear part of the airfoil, then yes, the gap will help to delay flow separation.


Why did the CAA not use Monarch aircraft to repatriate stranded Monarch passengers?

Pondlife pretty much hit the nail on the head.

When a business goes bankrupt or bust, depending on jurisdiction, the assets of the company may not belong to the company anymore, they may belong to creditors. Monarch may not have even owned them in the first place, since some airlines use leases from other airlines or banks to get aircraft.

Even if Monarch did own the aircraft, and they went belly-up meaning the aircraft were basically nobody's, now you have to worry about insurance and liability. The aircraft need to be insured to fly, and there is an assumption of liability if something (like a crash) were to happen. There are logistics like maintenance, repairs, etc. Somebody will have to go through all the aircraft and make sure that they are legal to fly (review logs, maintenance records, etc).

Then you have the crews: they are not employed, and the CAA isn't going to employ a bunch of pilots for a couple of weeks just to run ferry flights. The pilots may demand benefits, etc. It would be difficult or impossible to contract them as private parties (since most insurance companies would not let you do that).

So the easiest option is to let somebody else take care of all that by using charter flights. They have the infrastructure (pilots, planes, fuel contracts, insurance, etc) to get these people out. The CAA just has to call them up and say "we need X number of people picked up from ABC on some-date", and the charter company takes care of it. Of course it is a little more expensive than doing it yourself, but you aren't trying to basically build a short-term airline and then shut it down again.


What is the ideal volume distribution for minimization of transonic drag?

Since Drag is proportional to S'', the key is to derive a shape that has a minimum S''.

The result is the Sears-Haack body.

  The Sears–Haack body is the shape with the lowest theoretical wave drag in supersonic flow, for a given body length and given volume.

The area is given by:

$$ S(x) = \frac {16V}{3L\pi}[4x(1-x)]^{3/2} = \pi R_\text{max}^2[4x(1-x)]^{3/2}$$

And the radius is given by:

$$ r(x) =  R_\text{max}[4x(1-x)]^{3/4} $$

Image source


Why are general aviation planes so expensive?

Simple: short production numbers. If light airplanes were as common as motor cars, manufactured by the millions, they would be much cheaper...


What body creates legally binding aviation regulations in Europe?

EASA regulations,  as emited by the European Council, automatically become law in all EU member states (it is part of EU adheration treaty).

PART-FCL, for instance begins with this text:

  COMMISSION REGULATION (EU) No 1178/2011

  of 3 November 2011

  laying down technical requirements and administrative procedures
  related to civil aviation aircrew pursuant to Regulation (EC) No
  216/2008 of the European Parliament and of the Council

Because of the way these regulations are framed, local regulations (emited as law by local parliaments) will take precedence over regulations emited by the European Parliament, so some local authorities (I’m looking at you UK) will amend/change/adapt these regulations as they see fit.

Make no mistake, EASA regulations are law within the European Union’s member states.


When sizing a powerplant for a GA aircraft, how do you estimate the power required for other electrical systems?

This depends heavily on how the plane is set up especially these days with the prevalence of glass in the cockpit even in GA planes. For a point of reference most small GA planes like the Piper Cherokee run 60-100 amp alternators which usually have a bit of headroom in them but power everything and charge the battery just fine. If you want to fly in most airspace you are going to need to power at least a transponder and a radio (more than likely two radios).

The Garmin GTX330 is a 250 Watt transponder and is fairly common in the Archers I fly.

Your run of the mill Garmin GTR 225 radio comes in 10 and 16 watt versions.

To get the total requirement just add up all of your components draw. Most manufacturers list power requirements (or voltage and current draw requirements) for any given piece of equipment and you will have your required power.

As for De-Ice requirements this depends on the type of system you implement. A weeping wing will only require power to drive the fluid pump and the windshield heater where as a boot style system will require enough power to drive the compressor that inflates the boots. Although its becoming increasingly more common to see FIKI on GA planes the majority of the small aircraft fleet still lacks FIKI capability.


Any unique characteristics to identify aircraft engine?

Some specific aircraft-engine combinations can be identified, but the engines themselves, no, because you don't see most of them—the nacelle is designed for each aircraft-engine combination. For example

  The CFM56 on a Boeing 737NG is easy. It has a flat bottom.

the CFM56 on a Boeing 737NG is easy mainly because it is the only engine type that aircraft uses. And the engines from the same series when used on A320-family don't have flat bottom!

For A320-family, the CFM56 engines use separate exhausts, with shorter nacelle and hot section jet extending behind it, while the IAE V2500 ones use mixed exhaust with long nacelle, so you can tell them apart on those aircraft. But on NEO both engine types used have separate streams, and the only visible difference is the slight one in shape of the blades.

It is actually quite common for aircraft to only use one engine type, and using more than two types is rare, so most of the time if you can tell the aircraft, including variant, you should already know.


Where is the 'zone of reversed commands...'?

This is commonly known as the Speed Stability, not to be confused with speed stability in the sense of static longitudinal stability. I think there's some common confusion with this phenomenon. The first part of this answer addresses the OP's question; the second part clarifies a common confusion.

1. Main Answer

In level flight (i.e. zero vertical rate), the longitudinal equation of motion can be succinctly written as:

$$m\dot{V}=T-D$$

$m$ is airplane mass, $V$ is airspeed, $T$ is thrust and $D$ is drag. Now if we express thrust and drag as first order approximation as a function of change in airspeed ($\Delta V$) from the trimmed condition, we have:

$$T=T_0+\frac{dT}{dV}\Delta V=T_0+T_V\Delta V$$ and $$D=D_0+\frac{dD}{dV}\Delta V=D_0+D_V\Delta V$$

At trim condition, we necessarily have $T_0=D_0$. So now we have a new equation of motion:

$$m\dot{\Delta V}=(T_V-D_V)\Delta V$$

This equation is a first order ordinary differential equation, and is stable if $T_V-D_V<0$ and unstable otherwise.

For a jet plane, thrust is fairly constant in flat rated conditions and $T_V$ is approximately zero. Thus, $D_V=0$ corresponds exactly to minimum drag or minimum thrust required (where $C_{D_0}=C_{D_i}$ for high aspect ratio, low Mach airplanes).
For a propeller plane, power is constant, but now the stability criterion is $-\frac{P}{V^2}-D_V<0$. This corresponds neither to minimum power required nor minimum thrust required.

2. Addendum

What does this result mean, exactly? If an airplane is trimmed in the speed unstable regime, will it decay toward stall if it experiences a speed perturbation with pilot hands-off, even if it's statically longitudinally stable?

Remember, the equation we began with only holds in level condition where the airplane is neither climbing nor descending. Thus, the pilot must be holding altitude with elevator while the speed is changing. The conclusion for speed instability is:

If the altitude deviates below the trim altitude, pulling up will decrease the airspeed, resulting in further energy deficiency. Speed will continuously decay in this manner.
If the altitude deviates above the trim altitude, pushing down will increase the airspeed, resulting in further energy excess. Speed will continuously accelerate until reaching a stable point on the other side of the polar.

Since the pilot is in the loop, it has nothing to do with the basic aircraft eigenmodes.

The same result can be obtained if we aim for constant flight path angle. In approach configuration, this is also called flight path stability, which I think is a better name than speed stability.


Can a slow small plane, flying at a few meters above the ground, drop to the ground if the headwind abruptly stops?

Yes.  The theoretical concept of "moving with the airmass" essentially says that for any given constant wind or no wind, airspeed is dependent on thrust and drag and reaches a steady state.
However, in nature, especially close to the ground, obstacles such as buildings, trees and hills can make airflow anything but constant.
This is why the modern aviator adds a little airspeed when landing on windy days.  A gust or a lull can momentarily change your airspeed faster than the plane can restore its thrust/drag balance.
Wind shears are an extreme example of this.  Were it not for the wind, flying that Cessna would not be more difficult than driving a car.


How to calculate ground speed using a map with a known scale and time?

If a plane traveled $8\ \mathsf{cm}$ on a map with a scale of $1:1\ \mathsf{million}$, then it traveled $8\ \mathsf{million\ cm}$ in the real-world.

$$8\ \mathsf{million\ cm} = 80,000\ \mathsf{meters} = 80\ \mathsf{km}$$

Convert 80 km in 18 minutes to a speed of kilometers per hour:

$$\frac{80\ \mathsf{km}}{18\ \mathsf{min}} \cdot \frac{60\ \mathsf{min}}{1\ \mathsf{hour}} = 266.6 \frac{\mathsf{km}}{\mathsf{hr}}$$

Groundspeed is traditionally expressed in knots:

$$266.6\ \mathsf{kph} \cdot \frac{0.54\ \mathsf{kts}}{1\ \mathsf{kph}} = 144\ \mathsf{kts}$$

To put this in perspective, 144 kts is a bit fast for a Cessna 172, unless it has a good tailwind, but not at all unreasonable for many small high-performance planes.

The answers to question #44 don't make sense.
The question is "The scale of the chart is...", but the possible answers are all KTS (knots).

The answers to #44 and #45 are clearly reversed.
However, the right answer of 144 kts, is not listed in the possible answers.

In general, I think that test is extremely poor quality.

Question #43 (movement of the earth around the sun) may not even be related to aviation.


Where does the flat plate theory in this paper come from?

Ludwig Prandtl's lifting line theory produces a Taylor series as the result of the lift equation, and in almost all books this has been simplified just to the first term of the series, which then was even robbed of its sinus function to simplify it even further by using a small-angle approximation.

What you will find in books today is something like: $$c_L = c_{L\alpha}\cdot\alpha$$

$c_l$ is the lift coefficient, $c_{L\alpha}$ is the lift curve slope and $\alpha$ is the angle of attack in radians.

What the author should at least mention (but I think most are ignorant of this detail) is that a more precise version would be: $$c_L = c_{L\alpha}\cdot\sin\alpha$$

And now the books should tell you that there are more members in the solution to the lift equation; the one above is only the first one which dominates the result for small values of $\alpha$. But they don't. That is OK when the aircraft moves only through the small angle of attack region of attached flow, but for the perching motion you need to look at bigger angles, so the small-angle solution will produce noticeable errors.

The lifting-line theory assumes inviscid flow and does not know about flow separation. Perched flight of birds would be impossible without the high angle of attacks which produce flow separation and makes use of instationary effects which delay separation. All this is not covered by lifting line theory, but nevertheless it produces quite useable results. I guess, however, that the equation in the paper was found empirically.

The lift equation cited in the paper is a consequence of observing forces in a 360° polar, one where the airfoil is rotated through full 360° instead of the narrow range between maybe -8° and +12° where flow is attached and lift forces vary linearly with the angle of attack.

The plot below is from Hoerner's book "Fluid Dynamic Lift" (Scribd) and shows the results of several measurements over 180°. Apart from the spikes around 15° and 175°, the forces correspond well with $c_L = x\cdot\sin\alpha\cdot\cos\alpha$, where $c_L$ is the lift coefficient, $\alpha$ denotes the angle of attack and $x$ is a proportionality factor (the paper postulates $x$ = 2).
$c_L$ over 180° angle of attack from Hörner's book">

A flat plate has no leading edge radius and, consequently, no leading edge suction, which would be responsible for the aforementioned spikes. Therefore, the simple trigonometric approximation will fit the data quite well.

Both the flat plate and Newtonian theories assume the aerodynamic force to be orthogonal to the plane of the wing or plate, and when you take the portion of that force which is orthogonal to the direction of movement, which is how lift is defined, you get above trigonometric equation. This is simple geometry and shows no deeper insight into fluid mechanics.


Would this "being paid while flying" scenario be considered "flying for compensation"?

The short answer is that you'd need a commercial certificate, and potentially a commercial operator's license, to do what you're describing. Standard disclaimer: IANAL, and if you wanted to do anything like this, you really should find an aviation lawyer and get answers from them in writing!

The rules that cover this are contained in FAR 61.113, quoted in relevant part:

  §61.113   Private pilot privileges and limitations: Pilot in command.

  (a) Except as provided in paragraphs (b) through (h) of this section, no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft.

  (b) A private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if:

    (1) The flight is only incidental to that business or employment; and

    (2) The aircraft does not carry passengers or property for compensation or hire.

  (c) A private pilot may not pay less than the pro rata share of the operating expenses of a flight with passengers, provided the expenses involve only fuel, oil, airport expenditures, or rental fees.

To point 1, the answer is no. You're being compensated for your time, which is spent flying. If you were alone, 61.113(b) would allow you to be compensated - but that only applies if the aircraft does not carry passengers. Since the 61.113(b) exclusion doesn't apply, you're stuck with 61.113(a)'s prohibition of flying for compensation or hire.

You make an interesting point at the beginning about salary covering strange hours. If you really were paid just for your productivity, and you had an arrangement where you could just go take a couple of hours off in the middle of the day to go flying (or any other personal activity) without burning leave or affecting your pay, you could claim that you weren't being compensated for your time. I might write to the local FSDO for clarity on that before actually doing it, though.

If you were an hourly worker (#3) and were not paid for the time you were flying, that would eliminate some of the compensation. Note, however, that the FAA constructs "compensation" very broadly, to include good-will from others. If you made this flight in order to make your boss happy, you're being compensated! The source of the incentive to fly would be important: if you and a co-worker had to get to a destination, and you suggested, "Let's fly there!", you're under much better grounds than if your boss told you to.

The second point would depend on your normal work situation. Let's look at two portions of the flight:

The portion from home to work, and from work back home: In this case, you could be compensated for the flight under 61.113(b) - both in salary and costs, as long as your employer has a policy of reimbursing staff for their commuting costs.
The "non-commuter" costs: You could ask for 50% of the costs of the flight under 61.113(c) (see Mangiamele interpretation) - but from your co-worker, not your employer. Where they get that money is up to them. One important point: 61.113(c) requires "bona fide common purpose" -- you and your co-worker must each have a reason, beyond the flight itself, for going to the destination airport. If you weren't required to meet the client (or do something else that requires you to physically be in Waco at that time), you could not even share the costs of flight. Note that you can't be paid or reimbursed for your 50% — you have to eat that cost yourself.

To #4, the owner of the plane doesn't matter that much here, for a private pilot. The question of who provides the plane becomes very important in common carriage, but that's a different question.

To your last point, I'm not a lawyer - but I imagine that being fired for refusing to take an illegal action would be wrongful termination.

Further Reading:

An FAA Article on cost sharing

Mangiamele Interpretation: a letter from the FAA Office of Legal Counsel discussing this topic


What is this old pusher propeller aircraft?

I found two mentions of it, one was a design article written by Molt Taylor and his Aerocar...

"To our amazement, we found that a fellow by the name of Edson Gallaudet had built a shaft drive airplane way back in the 1910-1912 era which was twice as fast as contemporary airplanes! Gallaudet flew his Al and A2 Bullet models in the 120-130 mph speed range at a time when his fellow designers were happy to be able to fly 60 mph. And while they were still sitting out there on their wings with their pant legs fluttering in the breeze, Gallaudet was snug in a cockpit that enclosed all but his head."

"His landing gear was largely enclosed a within bullet shaped fuselage and his three bladed propeller was mounted on the tail. It was this latter feature that we were interested in, of course. We were fortunate in finding that a dear personal friend had actually seen the Gallaudet airplane fly and knew a lot about it. He had even flown in one of the later Gallaudet seaplanes. We were also curious to learn why Gallaudet had been able to make the long shaft to the tail propeller work so nicely, only to have the course of aviation progress move completely away from the concept when it was so obvious that the tail was where the propeller really should be mounted. Certainly, the performance of the Al and A2 proved that."

"As it turned out, the answer was quite simple — he had used a rotary engine, which served as a spinning flywheel that smoothed out the power pulses that can be so destructive to shaft drives. This "torsional resonance" was the problem that plagued the Waco Aristocraft, the Douglas Cloudmaster, the BD-5 and a number of others with shaft driven propellers. Some of the more sophisticated designs like the XB-42, P-39 and P-63 incorporated successful shaft drives, but only at the expense of heavy, costly, high maintenance vibration damper systems and' special operational techniques."

The second mention is at http://affordaplane.com/alumribs.html

"The first airplane to use aluminum tubing for ribs was this one, the Gallaudet A2 Bullet. Built in 1912, the tube ribs were flattened at the ends so rivets could attach them to the caps and spars."


How come diverterless supersonic inlets haven't been discovered much earlier?

Designing a DSI inlet is not so simple. It required CFD, a field which had existed for a while but was still viewed with some suspicion in the 1990s. CFD is computationally intensive, so the field has benefited from the massive advances in computing power since the invention of the transistor.

  The DSI traces its roots to work done by Lockheed Martin engineers in the early 1990s as part of an independent research and development project called the Advanced Propulsion Integration project. The concept was developed and refined with Lockheed Martin-proprietary computer modeling tools made possible by advances in Computational Fluid Dynamics, or CFD. CFD is the science of determining a numerical solution to the governing equations of fluid flow and advancing this solution through space or time to describe a complete flow field of interest—in this case, the flow field of a fighter forebody, inlet, and inlet duct.


Why hang glider dont over pitch when inrease AoA?

The short answer is that the wing itself is designed to have sufficient excess pitch stability such that the glider-pilot system is still stable in pitch when the pilot's weight is shifted somewhat aft.  If the pilot's weight is shifted sufficiently far aft, however, a stall may occur. The glider might not recover into stable flight if the control bar is kept pushed that far forward, i.e. if the pilot's weight is kept shifted that far aft.
It is normal to trim a hang glider to fly in wings-level flight at an airspeed near the minimum sink rate, not too far above stall speed, when the pilot is exerting no pressure on the control bar.  It would be normal for the glider to stall if the pilot extends his arms as far forward as he can reach, in wings-level flight.  A hang glider pilot would not necessarily expect to see benign flight characteristics if he keeps the bar pushed forward as far as his arms can reach, in wings-level flight.


What are those structures at Taif Regional Airport in Saudi Arabia?

Those are hardened aircraft shelters, and each hangar is flanked by two blast walls (revetment). Those are for combat aircraft (the airport is mixed-use: public/military).

Since in that hemisphere the sun is to the south, the shadows tell us they are not sunken structures, i.e. the hangars and walls are higher than the taxiways.

The numerous taxiways are for redundancy against bombing. And the overall pattern makes it harder for a single bomb run to affect all hangars.

Here's an aerial close-up from another Saudi Arabian airport, Tabuk Regional Airport:

  Source: flickr.com


Could New York build a new mega airport?

I think I'd challenge your assumption of insufficient air traffic capacity.  You could equally well look at it as too many planes wanting to land, or (for NYC at least) insufficient passenger rail service.

Beyond that, have you looked at land prices in the vicinity of NYC or London?  Perhaps in some countries you can just seize land to build airports, over the objections of the people living there.  In the US (and presumably the UK, though I'm not certain), it's much more difficult to obtain, and should properly involve paying a fair market price - after long and expensive legal battles.

Then you have to consider trip duration.  It's not just time spent flying, but time getting to and from the airport.  In NYC, it's IIRC about a 15 minute bus ride from LaGuardia to Manhattan, and I think not much more from JFK.  Put the airport way out in the country, and people would spend an hour or two just getting there, negating the speed advantage of air travel for short & medium length flights.


If I need to do a course reversal before initiating an approach, do I need to notify ATC that I'm doing it?

It is implied.

When you are cleared for the approach you are cleared for the procedure turn, or base turn as indicated on the plate.  Since your current heading puts you outside the entry sector, you do a racetrack to get aligned with the entry to the base turn.

It is always good to know when you have to call and when you don't because there could be heavy traffic, high workload, or who knows what. But if we're talking a competency ride or something like that, you should know whether you need to make the call or not.  All that said, one can of course report the course reversal if there is doubt.

In this instance, there is no requirement to report the turn.


Why are fighter jets rated differently than passenger jets?

The philosophy of fighter cabin pressurization is different from that of the passenger aircraft. In case of airliners, the cabin pressure decreases while the aircraft climbs upto a certain altitude, after which the value is kept constant (usually at 6000 - 8000 ft cabin altitude).

In case of combat aircraft, the principle is different. The cockpit pressure is maintained at certain value to a particular altitude (usually 8k feet); then the pressure is maintained (at 8k ft) till the aircraft reaches another altitude (~23k feet); after that a pressure differential (~5 psi) is maintained between the cockpit pressure and the ambient pressure. This reduces stress on the airframe and is safer in case of rapid decompression during combat. So, a fighter cockpit at 40k feet is actually stressed less (due to pressurization) compared to an airliner at that altitude.

There is another thing to be noted- a combat aircraft is designed for much higher loads compared to a civilian airliner; so, the structure is capable of taking more stresses. So, pressurization is not the limiting factor in case of combat aircraft.

One way of calculating the life of fighter aircraft is to apply loads on the airframe depending on the expected mission profile (like TO- cruise- loiter- cruise- landing), then calculate the theoretical life based on how long the airframe survived. Of course, this means that the life will change if the mission changes- like what happened when some aircraft were shifted from high level bombing to low level penetration roles.


What is the difference between a 'live' NLG axle and a 'fixed' NLG axle?

A live axle is when the two wheels rotate together. Its function is to reduce shimmying.

The Lockheed JetStar and the Space Shuttle Orbiter have live NLG axles.

References:

Source: Aircraft Landing Gear Design: Principles and Practices

  The nose wheel is a split, forged aluminum alloy design but its bearings are located on a rotating or "live" axle rather than in the hub such as in the main wheel design. Both nose wheels are splined to the "live" nose axle providing a corotating feature which improves stability or reduces the tendency to shimmy.

Source: Orbiter wheel and tire certification, NASA

  Tire friction can also be used to increase the damping in the castor mode. If the gear has two wheels, connecting them by a live axle can have this effect. In the case of a single wheel, it is possible to obtain ‘anti-shimmy’ tires incorporating two contact areas.

Source: Landing Gear (Aircraft), sciencedirect.com


Why would a turboprop rev down just before going full throttle during takeoff?

Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then on takeoff, the propellers move into a maximum power setting, the engine snarls and slows a bit under the increased workload.


When temperature increases what happens to the air molecules and aircraft while landing and takeoff during hot weather?

If all else is equal, an increase in temperature will result in a decrease in density of air molecules. To fly, a wing leverages these molecules, so the aircraft will need to fly faster to generate the same lift. Therefore the takeoff and landing distances are increased.

Engine performance is also impacted. Most engines outside of NASA breathe air and so perform better when that air is dense. Jet engines also have a maximum exhaust gas temperature they can withstand, and in very hot temperatures the amount of thrust they produce needs to be lowered so as to not exceed that value. This is the basic premise of how Airbus ‘assumed temperature’ works, where the pilots tell the engine that the temperature is hotter than it actually is, so the FADEC automatically caps the thrust.


From The inside story of MCAS: How Boeing’s 737 MAX system gained power and lost safeguards by Dominic Gates and Mike Baker:

During flight tests to certify an airplane, pilots must safely fly an
extreme maneuver, a banked spiral called a wind-up turn that brings
the plane through a stall. While passengers would likely never
experience the maneuver on a normal commercial flight, it could occur
if pilots for some reason needed to execute a steep banking turn.
Engineers determined that on the MAX, the force the pilots feel in the
control column as they execute this maneuver would not smoothly and
continuously increase. Pilots who pull back forcefully on the column —
sometimes called the stick — might suddenly feel a slackening of
resistance. An FAA rule requires that the plane handle with smoothly
changing stick forces.
The lack of smooth feel was caused by the jet’s tendency to pitch up,
influenced by shock waves that form over the wing at high speeds and
the extra lift surface provided by the pods around the MAX's engines,
which are bigger and farther forward on the wing than on previous
737s.
(...)
Under the proposal, MCAS would trigger in narrow circumstances. It was
designed "to address potentially unacceptable nose-up pitching moment
at high angles of attack at high airspeeds," Boeing told the FAA in a
proprietary System Safety Assessment reviewed by The Times.

Another article from The Seattle Times published in March makes mention of a high speed stall:

Designed to activate automatically only in the extreme flight situation of a high-speed stall, this extra kick downward of the nose would make the plane feel the same to a pilot as the older-model 737s.

This indeed points to a stick-force-per-g test, as @Jimmy mentions in a comment. Since the B737 has a fully irreversible hydraulically actuated flight control system, with an artificial feel that is proportional to dynamic pressure but not to load factor, the obvious mechanism for "lack of smooth force feel" would be having to release the column to some extent due to extra nose-up moment that the aircraft generates.
It is very plausible that the added lifting surfaces from the engine pods create a larger pitch-up moment than the 737NG has in the same circumstances. I'm not really sure how the supercritical airflow over the MAX wing differs from that of the NG to create extra pitch-up.
All of that is the original limited cure for the stick-force-per-g tests. If this was the only thing that needed to be fixed, all would probably have remained well. But the first linked article also mentions:

The flight-test pilots had found another problem: The same lack of smooth stick forces was also occurring in certain low-speed flight conditions. To cover that issue too, engineers decided to expand the scope and power of MCAS.

As you can see, The Seattle Times is my source of information as well...there is no additional information on what were the "certain low-speed flight conditions".


Would it be a good idea to use dihedral on a biplane?

If your aircraft is meant to be a "free flight" model, meaning that it flies without any guidance from any pilot, then generous dihedral will help keep the wings level.

Even if your aircraft is meant to fly under radio control, so long as the mission is load-carrying rather than aerobatics, some dihedral will help ease the pilot workload.  You may want to mix some rudder to your aileron channel to help it turn better, otherwise the dihedral will tend to create some resistance to aileron roll/turn inputs.  If you don't have a rudder, don't use very much dihedral.  If you have only a rudder and no ailerons, use lots of dihedral.

Many full-scale (piloted) biplanes do in fact have dihedral on one or both sets of wings.  Most typically the lower wing has dihedral while the upper wing is straight, because that helps improve ground clearance of the lower wingtips, but in some cases both sets of wings have equal or nearly equal dihedral.  (See for example this 3-view diagram of the "Bristol Fighter".  The combination of a straight lower wing and a dihedral upper wing has never been used before, to the best of my knowledge-- here's your chance to be the first!


What is this feature on a Piaggio P.180?

The airfoils shown are delta fins.  They provide lateral stability during higher speed flight.  It helps to reduce dutch rolling tendencies and to prevent deep stall characteristics.

So much so that on the Learjets I fly, there is no need for an operable yaw damper.  There is also no stick pusher or stick puller system.  Older Learjets without delta fins are required to have those two systems installed.

https://en.m.wikipedia.org/wiki/Piaggio_P.180_Avanti


Is a turboprop or a turbofan more eco-friendly?

To compare them we need to compare the same mission (we can't compare an A380 against a regional turboprop).
For 82-86 passengers on a 1,100 km (600 NM) trip, the turboprop comes out on top (for this mission).
2.79 L/100 km/seat (Bombardier Dash 8 Q400)
3.44 L/100 km/seat (Embraer E-Jet E2-175)

Note: a Boeing 787-9 flies 304 passengers over 9,208 km at 2.31 L/100 km/seat.

From slowest to fastest, the economical choice would be turboprop, turbofan, and turbojet. Above ~700 km/h, the turboprop starts to lose.
The why:

Turboprop: The core runs at near full power, and with a reduction gear, the propeller runs at a slow speed suited for slow flight. If the blade tips reach Mach 1, efficiency starts to go down (at a fixed RPM, blades fly faster the faster the plane).
Turbofan: Same principle, but instead of a reduction gear, a low-pressure spool is used. And with the nacelle/shroud, the fan can run faster and move more air.
Turbojet: The core provides the propulsive power directly, this solves the slow exhaust of the turbofan in supersonic flight.

The common theme: gas turbine cores run best near their full power. That makes a turbojet bad at slow speed / low power.

Fuel mileage and image source: Wikipedia article 'Fuel economy in aircraft' (well sourced).
Also see: Why are propeller engines uncommon on airliners?


How does an elevator offload function works in fly by wire flight control systems?

Regarding the first point, from Lufthansa Technical Training Manual for 777, page 30:

  Elevator Offload Function
  Operates only in the AirCommands to Determine when the Elevator is not at the Neutral Position for more than two seconds minimum.Commands the Horizontal Stabilizer to move as a Function of Airspeed. The Movement of the Horizontal Stabilizer then causes the Elevator to move to the Neutral Position


Can I descend during downwind or I can only descend when I am at base?

See Chapters 7 and 8 of the FAA's Airplane Flying Handbook.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/airplane_handbook/media/10_afh_ch8.pdf

The descent point for the approach is going to be largely based upon the handling characteristics of the specific type or model of aircraft you are flying in.  In general it's commonly taught to pilots that you begin your descent from the traffic pattern to land when you are on the downwind leg and abeam the threshold of the runway you are going to land on.  You will select a descent power setting at this point, configure the aircraft for landing and begin the descent.  When you turn base or final is going to be up to your discretion but in general should be no more than 1-2 miles from the airport.  This turning point may also be given to you by ATC at a towered airport for aircraft spacing e.g. "Cessna 1 2 3 X-ray yankee, extend your downwind; I'll call your base."  You may also have to do the same thing at "beehives" or busy, non-towered airports for traffic spacing in the pattern as well.


What is meant by "Outbound leg timing begins over/abeam the fix, whichever occurs later" in FAR/AIM 5-3-8?

The text is written that way to take into account the various type of holding entries. In case of a parallel or teardrop entry, the outbound leg starts after passing over the fix. In all other cases the outbound leg start after passing abeam the fix, following a turn that starts over the fix.

Case 1: Established in a holding pattern

So when established in a holding pattern, the outbound leg starts abeam the fix.

The sequence is:

inbound leg
pass over the fix
turn outbound
pass abeam the fix
outbound leg
turn inbound
repeat from 1.

In this case it is clear that the time of the outbound leg should start when you pass abeam the fix, which occurs later in the sequence.

Case 2: Entry into holding pattern

Case 2.1: Parallel Entry into holding pattern

When entering the holding using a parallel entry ((a) in the diagram) the sequence  is:

fly to the fix
pass over the fix
turn outbound course
outbound leg (on non-holding side)
turn to inbound leg
intercept inbound leg
follow sequence for established in a holding pattern

In this case the timing of the outbound leg should start when you pass over the fix. From this, it follows that the outbound time will include the time spent in the outbound turn (3.).

Case 2.2: Teardrop Entry into holding pattern

When entering the holding using a teardrop entry ((b) in the diagram) the sequence  is:

fly to the fix
pass over the fix
turn outbound course
outbound leg (30 degree into holding side)
turn to inbound leg
intercept inbound leg
follow sequence for established in a holding pattern

In this case the timing of the outbound leg should start when you pass over the fix. From this, it follows that the outbound time will include the time spent in the outbound turn (3.).

Case 2.3: Direct Entry into holding pattern from holding side

When entering the holding using a direct entry from the holding side ((c) in the diagram, sector on the holding side) the sequence  is:

fly to the fix
pass over the fix
turn outbound
pass abeam the fix
outbound leg
turn inbound
follow sequence for established in a holding pattern

In this case it is clear that the time of the outbound leg should start when you pass abeam the fix, which is later in the sequence.

Case 2.4: Direct Entry into holding pattern from non-holding side

When entering the holding using a direct entry from the non-holding side ((c) in the diagram, sector on the non-holding side), you may not complete the turn before being abeam the fix. In that case the sequence is:

fly to the fix
pass over the fix
turn outbound course
outbound leg
turn inbound
follow sequence for established in a holding pattern

In this case it is clear that the time of the outbound leg should start when you pass over the fix. From this, it follows that the outbound time will include the time spent in the outbound turn (3.).


What operational differences were there in WWII for constant speed vs. fixed pitch propeller warbirds?

When war broke out, almost all high-performance military planes on all sides had variable-pitch propellers. Not necessarily constant-speed types, but adjustable nontheless. There was no difference between German and British planes.

If there was a difference it was the use of manually-adjustable propeller pitch, which was widely used in German airplanes, versus constant-speed propellers, which found more use in British airplanes. However, both sides had both types of propellers in their fleet, so it is hard to make a generalization.

Operationally, the manual adjustment gives the pilot more control, but increases workload because the pitch has to be adjusted when flight speed changes. This was less burdensome in bombers, but in fighter aircraft a manual adjustment would keep the pilot busy during dogfights.

Early types of the aircraft involved did indeed use fixed-pitch propellers, like early versions of the Me-109 A and B or the Hawker Hurricane Mk.I. By 1939, both types had long since converted to variable-pitch propellers.

Older airplanes with fixed-pitch propellers were still used for training or liaison, but not near the front lines. Exceptions are aircraft like the Polikarpov Po-2 which was used for night attacks until the Korean war. It had such a limited speed range that a variable-pitch propeller would not had made sense.


What are the pros and cons of single-engine vs. twin-engine?

In the light aircraft world there are a few trade-offs to consider.  The short version:

Single-Engine Pros:

Simplicity
One engine means fewer controls, a simpler fuel system, simpler vacuum system, simpler electrical system, etc.
Operational cost
Only one engine to feed, so you spend less on - fuel & oil per flight.
Maintenance cost
Only one engine to maintain - One set of spark plugs & cylinders, One engine to overhaul.

Single-Engine Cons:

No redundancy: You have one engine, if it fails you're a glider.
Singles generally tend to have less spacious cabins than twins.

Twin-Engine pros:

Redundancy
If you lose an engine the other will give you a chance to get to a landing site.
Cabin space
If you step up beyond "twin trainers" you can get a very nice cabin in a piston twin.
Equipment
Again, if you step up beyond the "twin trainers" twin-engine planes tend to be "traveling aircraft", so they often come with nice features like deice/anti-ice equipment.

Twin-Engine cons:

Operating costs
Two engines to feed (fuel & oil costs double).
Maintenance costs
Two engines mean twice the cylinders, twice the spark plugs, etc.
Complexity
The redundancy you can get in a twin comes at a price: Synchronizing the propellers, a more complex fuel system (crossfeed), paralleling alternators, vacuum system failover, etc.
Short and Soft field performance can be lacking.
Failure of an engine can be problematic.

In addition to the operational considerations there are some other practical items to consider: twin-engine aircraft require a multi-engine rating (which means more training time). Twins will also generally be more expensive to purchase/rent (and may be more difficult to rent when away from home), and will likely cost more to insure (particularly for low-time pilots).


How are individual rotor/stator blades identified during engine inspection for the CFM56?

I don't know specifically for a CFM56, but in general: fan blades are usually identified by a dimple on the spinner (blade #1 is next to the dimple and number from there). High pressure compressor blades can be identified by special "locking" blades, which will look different from the others. They will have screws in them to "lock" them into place.  These line up with a feature on the rotor, so they are always in the same place.  Locking blade will be #1 and number from there. I'm not sure how high pressure turbine blades are identified.  LPT blades are usually identified by finding the #1 fan blade and rotating it down to bottom dead center.  Then the LPT blade at bottom dead center is considered blade #1.


Effect of touchdown on angle of attack, tailwheel vs tricycle

Yes, it does make sense.
However, the angle of attack increase of the tailwheel airplane would only be possible if it touches down on the main wheels while there still is much clearance of the tail wheel or skid. Normally, the ground attitude of tailwheel airplanes should be very close to their landing attitude, so all three wheels touch down almost simultaneously.


For some general reasons, see Why is engine No.2 started first, instead of No.1?

Airbus A350

Specifically to the Airbus A350, I could not find any reason why one engine must be started first. As far as I know every modern airliner could start engines in arbitrary order.

The Airbus A350 has two hydraulic systems. From the Airbus A350-900 Flight Deck and Systems Briefing:

  The A350 hydraulic system has two independent
  hydraulic circuits:

  The YELLOW hydraulic circuit
  The GREEN hydraulic circuit

Each system can be pressurized with an engine driven pump from either engine, or electrically on the ground:

  Engine Driven Pumps (EDPs)

  Four EDPs pressurize the hydraulic system. On each
  engine there are two EDPs, one pressurizes the
  GREEN hydraulic circuit and the other pressurizes the
  YELLOW hydraulic circuit. Thus if an engine fails, the
  remaining engine can still pressurize both hydraulic
  circuits.

  Electric Motor Pump (EMP)

  One EMP per hydraulic system can provide hydraulic
  pressure on ground only, when all engines are shut
  down. For example, the EMP of the YELLOW circuit
  operates automatically for cargo door actuation.

The main wheel brakes are powered by both hydraulic systems:

And also the parking brake uses pressure from both accumulators:

Which engine is started first has therefore no impact on which hydraulic system is powered first or which type of braking is available.

Airbus A320

The situation is a bit different for the Airbus A320. As Jan pointed out in the comments, it is normal to start the right engine first, because it provides hydraulic pressure to the yellow system. From the A320 FCOM Hydraulic chapter:

  Green System Pump

  A pump driven by engine 1 pressurizes the green system.

  Blue System Pumps

  An electric pump pressurizes the blue system. A pump driven by a ram air turbine (RAT) pressurizes this system in an emergency.

  Yellow System Pumps

  A pump driven by engine 2 pressurizes the yellow system. An electric pump can also pressurize the yellow system, which allows yellow hydraulics to be used on the ground when the engines are stopped. Crew member can also use a hand pump to pressurize the yellow system in order to operate the cargo doors when no electrical power is available.

The yellow system powers the alternate/parking brake system:

However, starting the left engine first is still perfectly possible. Hydraulic pressure from the accumulator is still available after pressurizing the yellow system with the electric pump before pushback to provide braking.

Boeing 737

The Boeing 737 has two hydraulic systems: A and B. Both can be powered by electric pumps. From the FCOMv2 13.20.2 Hydraulics - System Description:

  Both A and B hydraulic systems have an engine–driven pump and an AC electric
  motor–driven pump. The system A engine–driven pump is powered by the No. 1
  engine and the system B engine–driven pump is powered by the No. 2 engine. An
  engine–driven hydraulic pump supplies approximately 4 times the fluid volume of
  the related electric motor–driven hydraulic pump.

The braking is provided by both systems. From the FCOMv2 14.20.3 Landing Gear - System Description:

  Normal Brake System

  The normal brake system is powered by hydraulic system B.

  Alternate Brake System

  The alternate brake system is powered by hydraulic system A. If hydraulic system
  B is low or fails, hydraulic system A automatically supplies pressure to the
  alternate brake system.

  Brake Accumulator

  The brake accumulator is pressurized by hydraulic system B. If both normal and
  alternate brake system pressure is lost, trapped hydraulic pressure in the brake
  accumulator can still provide several braking applications or parking brake
  application.

Again, there is no reason to start one engine before the other because of hydraulics/braking.

Conclusion

Engine start order is mostly tradition and will be specified by the airline op-specs. The shutdown oder also does not matter since both engines are usually shut down at (almost) the same time at the gate, except for a single engine taxi where the hydraulic system that powers the nose-wheel steering must be pressurized.


Can we trade some efficiency to curb high-altitude emissions?

There's a fundamental problem. A jet engine performs work by expansion of the combustion products. Compressing the combustion products would require at least as much work as was provided by the expansion of the combustion products. Only an external combustion engine (for example, a steam engine) would work in this case.

A second problem is that the mass flow of the CO2 is more than three times higher than the mass flow of the fuel. Your plane would get heavier as you fly, and since the max landing weight of a typical plane is lower than the max takeoff weight, this will severely limit the aircraft range.

All in all, you can probably manage to make a purpose-built plane that fits the bill but I highly doubt it will have much usable payload if any at all.


If maximum speed was a priority for modern military fighter jets and bombers, approximately how fast would they likely be?

Increasing the speed of an aircraft results in having to make trade-offs. Drag will increase as the square of the velocity, meaning a doubling of speed will take 4x the power to achieve. This problem is compounded by the fact that it is very difficult to design an engine (and an airframe) that performs really well at super sonic speeds, while still performing well at subsonic speeds.

All design decisions always end up in trade-offs. Increasing maneuverability generally requires doing things that will increase the drag, which means you will require more power to compensate (which then requires a larger engine, which will reduce your maneuverability due to the increased weight).

All of these decisions mean that, in the end, increasing the speed of a fighter inevitably requires the reduction of something else, either turning speed, or weapon payload, or range. While better technology has given us more powerful engines, and new materials and alloys allow us to create more maneuverable aircraft, we've actually seen the top speeds of aircraft go down compared to past fighter aircraft, even though we could create an aircraft as fast as anything from the past, with increased maneuverability and weapon payload in comparison.

These decisions are being made because by reducing the top speed of aircraft, they in return also get better maneuverability, so it's conscious decision to take the higher weapons payload, increased range, and higher maneuverability in place of a higher top speed because a very fast top speed is just not all that useful in warfare compared to everything else. Reconnaissance (which is what the SR-71 was designed for) is better handled by satellites, which can't be shot down in practice, and don't require flying over another country's airspace in a way that is likely to draw their ire. Bombers would rather carry a larger payload, and be fast enough to get to the target, but getting their significantly faster at the cost of a reduced payload won't buy you much. Same goes for fighters, they need to fly around somewhat quickly, but a pure speed advantage over an opponent isn't all that useful either (compared to just having a better fighter). So it's a combination of both physics and specifically what things the military values that just means that there's little value to purely increasing speed.


What are the "beta lines" of a gas turbine engine component?

Beta lines are either linear or parabolic shaped lines that are conveniently placed and spaced between the surge line and the choke line of the compressor (or fan) characteristic (also known as compressor/fan map). Such lines are also found in the turbine characteristics maps.
Basically, the Beta lines create a new axis system that prevent a solver from finding multiple (or the incorrect) operating point(s). The lines itself do not represent anything, they are simply added for convenience and calculation stability.
Compressor maps describe the relation between various parameters which are based on experiments or CFD calculations; corrected mass flow, pressure ratio, spool speed and efficiency. In gas turbine performance simulation, a new operating point needs to be found for a change in operating condition. Knowing that speed lines can contain a local maximum pressure, you cannot uniquely describe an operating point with a pressure and a speed, there can be 2 solutions for corrected mass flow. Hence, gas turbine performance engineers have created the concept of an alternative coordinate system that prevents that multiple solutions can be found; this is very useful when programmatically finding/iterating the new operating point.
Compressor maps typically are 2-in, 3-out parameter maps, to find the 3-out parameters (pressure ratio, efficiency and corrected mass flow) you require a unique pair of Beta and spool speed values.

Compressor map (Beta lines are hidden):

Compressor map (linear Beta lines are shown):

Example of parabolic Beta lines: