Why photographing airports is banned if everything is perfectly pictured in Google Maps?

I believe the sign is to prevent plane watchers from gathering at the spot and taking pictures of every aircraft taking off or landing, which, judging by the existence of the sign, is not how the location is intended to be used.


How did aviation industry come to know about the drastic difference in air pressure in high altitude?

The entire reason why the Comet broke up in midair is because they pressurized the plane in the first place.

It was known for a long time that air at high altitude was thinner. This can be experimentally verified by taking a barometer up to a mountain. This was first done in 1648 (and subject to hot debate regarding the nature of air) more than 250 years before the Wright brothers first flew.


How to calculate the thrust of a piston or turboprop engine?

The simplest equation uses an assumed propeller efficiency $\eta_{Prop}$and converts power P into thrust T like $$T = \frac{P}{v}\cdot\eta_{Prop}$$
The tricky thing is to get $\eta_{Prop}$ right. Use 85% for lightly-loaded* propellers working at their design point. And make sure you subtract the power offtake from the engine for driving the accessories, so you only use the effective power at the propeller, not the rated engine power.

The equation only works if the propeller is in motion, so airspeed $v$ is not zero. For covering the static case, please see this answer.

*The load on a propeller can be expressed by the ratio of thrust to the propeller disc area, made dimensionless by dividing by the dynamic pressure $\frac{\rho}{2}\cdot v^2$. If $T$ is thrust and $d$ is the diameter, the dimensionless thrust loading coefficient $c_T$ is
$$c_T = \frac{T}{\pi\cdot\frac{d^2}{8}\cdot\rho\cdot v^2}$$
Sometimes this is simplified to
$$c_T = \frac{T}{\pi\cdot\frac{d^2}{4}\cdot v^2}$$
Note that this definition needs the propeller thrust at a specific speed. A different way of expressing the propeller loading, which lends itself to using the easy to measure static thrust, is by dividing thrust by the disc area and the dynamic pressure of the propeller tip at rest, with $n$ as the RPM of the prop:
$$c_T = \frac{T}{\frac{\rho}{2}\cdot\left(\frac{n\cdot\pi\cdot d}{60}\right)^2\cdot\pi\cdot\frac{d^2}{4}}$$
and again a simplified form of this can be found in literature:
$$c_T = \frac{T}{\rho\cdot\left(\frac{n}{60}\right)^2\cdot d^4}$$

Generally, a lightly loaded prop has a big diameter and flies at low to moderate speed. While WW II warbirds are still in the lightly loaded realm, all large turboprops (C-130, P-3) are firmly outside of it.


Does laser eye surgery prevent me from getting an EASA pilot licence?

LASIK is a type of refractive eye surgery and according to EASA's medical standards, you can be considered "fit" to fly after surgery if several conditions are met. The conditions depend on the class of medical; private pilots usually have a class 2 medical.

For class 1:

  (1)   After refractive surgery,  a fit assessment may be considered,
  provided that:
  (i)    pre-operative refraction was not greater than
  +5 dioptres;
  (ii)  post-operative stability of refraction has been achieved (less than 0.75  dioptres variation diurnally);
  (iii) examination of the eye shows no post-operative complications;
  (iv)  glare sensitivity is within normal standards;
  (v)   mesopic contrast
  sensitivity is not impaired;
  (vi)   review is undertaken by an eye
  specialist.

For class 2 (private pilot) and LAPL:

  After refractive surgery a  fit assessment may be considered provided
  that there is  stability of refraction, there are no postoperative
  complications and no increase in  glare sensitivity.

The LBA also has an FAQ on vision issues but it doesn't mention LASIK. It does say, however, that you need an optician to examine you if there are any questions about your vision that an aviation examiner can't determine himself (nicht durch den flugmedizinischen Sachverständigen durchgeführt werden können). I assume that means that if there's any doubt about your eyes, you'll need to have an additional eye exam.


Why and how do atmospheric properties sometimes vary from the ISA?

An ISA standard atmospheric day is really more like a global average.  Locally and regionally, there will always be deviations from the "norm" based on the natural cycles of the sun.  Overnight the temperature will cool, then the sun will rise and things will warm up again.  This phenomenon also produces variations in the pressure and density over larger areas.

Otherwise, what specifically do you not understand about how and why local and regional conditions are not always "standard"?


Are two twin-jet flights more efficient than one quad-jet flight?

The sales figures tell it all. The majority of airlines prefer twin-jets. From businessinsider.com:
Qantas CEO offers his insight on 2x 787 vs 1x A380:

According to [Qantas CEO], he can fly two 236-seat Dreamliners for less than the cost of a single 486-seat A380, which entered the Qantas fleet in 2008.
"If we were to fly two 787s tail-to-tail, the per-seat cost would be less than the A380," the Qantas CEO said.

Even though the 787 has a newer generation engines compared to the A380, the fact that the 747-8I (the passenger variant) didn't sell well confirms the above.

(wikipedia.org) Fuel per seat figures for a 7,200 NM sector.
A major issue in comparing is finding:

A twin whose ideal seating capacity is half that of a quad
And boosts the same range
And be of the same generation.

(DVB Bank SE)

See: Why are twin engine airliners more fuel efficient than three or four engine airliners?

RE edit and comments:

As one concrete example, say one A-380 @ 15000 km and 650 passengers vs. two A-350 @ 15000 km and 325 passengers each.

They fail one of the conditions above, the 350 and 380 have different engine generations. And it's like the Qantas 787/380 example above.

Would there be a twin & quad combination with roughly the same age?

The A330-300 (twin) and A340-300 (quad) are the same age, and even better they share the same fuselage, wing, and total thrust, but they too fail one of the conditions: the A330-300's range is shorter than the A340-300's.
The A340 has longer range because the outboard engines on the A340 increase the bending relief, allowing 30 tonnes more fuel (flightglobal.com):

Because of bending relief from the weight of its outboard engines, the bending moment of a four-engined aircraft is substantially lower than it is for a twin at the same maximum take-off weight. For the same fuselage weight, therefore, a twin needs a stronger, heavier wing than a quad.
It follows that, for the same wing, the payload carried in the fuselage must be less for a twin than a four, which is exactly what has happened with the A330/A340: the latter carries about 20% more payload. This translates to about 30t of extra fuel, giving the A340 its long-range capability and requiring the addition of a centre-fuselage undercarriage leg. Design strength required was "only 1% higher than the A330", says Jeff Jupp, BAe chief engineer, Airbus.

The A330-2/300 sold 5.87 times more than the A340-2/300 (now out of production) as of end of March 2018.

What about a 767 vs 747 limited to the 767's range?

Limiting the 747 to the 767's range is again not fair, because of the fuel the 767 will have to carry to reach its max range, while the 747 will breeze by because it won't carry its full fuel load. See this related post: How much fuel is burned to carry the trip fuel?


Why should a test flight be performed when the propellers are changed?

The purpose of the test flight is for the safety of passengers. For most maintenance, in a not-for-hire aircraft, a private pilot can perform the test flight and determine the aircraft is airworthy, but they must do it without passengers.

Title 14 chapter 91.407


What would happen to a flying aeroplane if there's suddenly a brick-size hailstorm?

There was a case where an easyJet Boeing flew through a hailstorm; the accident report is here, with a PDF download available, which lists some of the damage (which includes a cracked windscreen and damaged leading edges on wings and other surfaces).

There are photos showing the damage incurred, including the one below. Search for "easyJet hailstorm damage" to find more.


It appears that the flash sequences in Airbus and Boeings are different. For example, the following image gives the flashing sequence in Airbus A320:

Image from LED Anticollision Lighting system for A320 by UTC Aerospace Systems

Note the differing flashing sequences of different lights. Also, see this question.

As far as regulations are concerned, 14 CFR 23.1401 - Anticollision light system states that:

  (c) Flashing characteristics. The arrangement of the system, that is, the number of light sources, beam width, speed of rotation, and other characteristics, must give an effective flash frequency of not less than 40, nor more than 100, cycles per minute. The effective flash frequency is the frequency at which the airplane's complete anticollision light system is observed from a distance, and applies to each sector of light including any overlaps that exist when the system consists of more than one light source. In overlaps, flash frequencies may exceed 100, but not 180, cycles per minute.


Similar to a leading edge flap, fixed in the extended position with no gaps: The nose is lowered, so at high angles of attack the flow still has its stagnation point at the round nose where on an un-drooped nose it would had slipped below the nose section.

This reduces the suction peak near the nose of the upper surface pressure distribution and consequently makes recompression towards the trailing edge much easier. This helps to delay flow separation and to achieve higher angles of attack and lift. If an aircraft had a roll instability at high angle of attack, adding a drooped nose on the outer wing will cure it of misbehaving.

The downside is that now at low angles of attack a suction peak will form on the bottom side and might cause local flow separation. This increases the viscous drag just when this drag component dominates overall drag. Consequently, aircraft which had been modified with a drooped nose do not reach their old top speed anymore.


At which point does an airliner start to pressurize/depressurize the cabin?

The cabin pressure is maintained automatically by a controller. Before the flight, the pilots will input two numbers: the cruise altitude and destination airport altitude. From these two inputs, the controller will manage the cabin pressure schedule automatically.

From the Boeing 737 FCOM:

  The cabin begins to pressurize on the ground at higher power settings.
  (...)

  In the air, the auto controller maintains a proportional pressure
  differential between airplane and cabin altitude. (...)

  The descent mode is activated when the airplane descends 0.25 psi
  below the selected FLT ALT. The cabin begins a proportional descent to
  slightly below the selected LAND ALT. (...)

  While taxiing in, the controller drives the outflow valve slowly to
  the full open position depressurizing the cabin.

For passenger comfort, the controller is programmed so that the rate of cabin pressure change is kept to a minimum. The cabin is actually slightly pressurized on the ground both during takeoff and landing, i.e. the cabin altitude is lower can the outside altitude. It smoothly transitions to and from cruise cabin pressure as the plane climbs or descends.


For supplemental oxygen, what is preferred between masks and cannulas?

Cannulas are not effective above medium altitudes, and the FAA prohibits their use above 18,000 feet (FAA brochure on Oxygen Equipment, PDF). Because they only place oxygen at your nose, you don't receive oxygen when talking or breathing through your mouth, while a mask covers both nose & mouth. This is, obviously, not great.

Cannulas are also less comfortable than a nice-quality mic/mask, but that's my personal opinion. A lot of pilots do prefer cannulas for comfort at lower altitudes, as they're easier to don and allow you to continue using your normal headset mic boom. For most pilots, especially those flying normally aspirated aircraft types, it's a matter of preference.


Why did the backup landing gear deployment fail on LOT 16?

Gravity/freefall backup (or more precisely some backup) is mandatory, but in large aircraft running pulley from cockpit to the wheel wells to release the uplock (the thing that keeps the gear retracted) mechanically would be too complicated or the force required to operate it too large, so the uplock still needs to be released electrically.

Unfortunately the circuit breaker that protects the circuit responsible for releasing the uplock was "popped" (open), so the uplocks didn't release and the gear didn't fall down.

The crew was trying to troubleshoot the issue for 80 minutes and consulted maintenance over radio, but because the checklists for either central hydraulic system (which does the normal gear extension) failure or alternate gear extension did not mention the circuit breaker (C829) neither crew nor maintenance thought of checking it.

It is not possible to find why and when the breaker popped. They tested the alternate extension afterwards and it worked, but the breaker covers several other circuits and there could have been transient problem somewhere or it could have been maintenance error or some other reasons.

You can read excerpt from the report on The Aviation Herald.


Is GPS considered to be a navigational facility for the purposes of Ops Spec C055?

Yes, a GPS approach can satisfy the criteria of a navigational facility for the purposes of Table 1 in Ops Spec C055.

The FAA gives the following guidance in Notice 8900.218, Alternate Airport IFR Weather Minimums:

  G. 5) Planning for use of GPS-based IAP must be based on a single navigational
  facility when determining the approach facility configuration in Table 1, even if there are two or more RNAV (GPS) approaches to different suitable runways.

This guidance doesn't go to the length of explicitly including GPS in the definition of "navigational facility". However, it does mean that GPS-based IAP can be understood to substitute for a single navigational facility, thereby satisfying the criteria of the first row of Table 1.


What are the differences between these IFR Low Altitude Chart Navaid Symbols?

The shadow in the NAVAID box indicates that the NAVAID and FSS have the same name, as in your top image. If they are different, the FSS name is given in brackets below the NAVAID box, as in your bottom image. If the FSS is not available, a thin line box is used for NAVAID (without brackets at the bottom), as in the middle figure.

FAA Aeronautical Chart User's guide should help you understand it better.

Image from FAA Aeronautical Chart User's guide


How do I determine odd or even when working with altitudes?

Look at the thousands of feet only.
Is 7(thousand) even or odd?

I'm sure a mathematician views 7,500 as equally close to 8,000 as 7,000.

But in aviation terms, it is 7,000 plus another 500 feet, and therefore an odd altitude.


What are the major non-pilot causes of GA accidents?

For a statistical overview of General Aviation accidents I suggest checking out the Joseph T. Nall Report prepared by the AOPA Air Safety Institute. Everything I'm citing below comes from the most recent report (the 23rd report, covering 2011).

The leading causes of accidents in 2011 were:

Pilot Error - About 77%
This includes poor flight planning, weather encounters, and a host of other things that we could at least theoretically avoid if we actually did the things we were taught to do in training.
Mechanical or Maintenance related - About 13%
This includes engine failures, control system problems, landing gear failures, etc.

The largest chunk of mechanical failures are "powerplant failures", which account for 38% of the mechanical failures, or a bit under 5% of total accidents.

Everything Else - About 10%
This includes freak occurrences like a flight instructor "walking into a moving propeller" (I kid you not, it's in the report!). A large chunk of these are also engine failure for causes that could not be determined.

If we add all the engine/powerplant failures together (the explainable ones from "Mechanical" plus the unexplained ones from "Everything Else") they come out to be  11.5% of total accidents, and are statistically the number two cause of Non-Commercial General Aviation accidents after "Pilot Error".


Do designers use the same RAM (Radar Absorbing Material) coating across the length and breadth of a fighter aircraft?

According to this article and this book, they use a greater amount of wide-band structural RAM on the wing's edges, whereas they use a ceramic-matrix RAM on the exhaust nozzles. Not only is that the case, but the actual edges have proprietary material designed to be stronger, and have a different radar signature. Although, what you're seeing is probably a combination of the paint job as well as the material, considering the F-22's stealth is not only an aspect of radar, but also visibility.

Most of the stealth of the F-22 comes from the physical shape of the F-22, and reducing its radar cross-section. There are also specialized materials that assist in obscuring its infrared signature. The topcoat, a type of paint, assists in reducing the infrared signature, especially.


Do overland long-haul flights have something similar to SELCAL?

Yes SELCAL is provided over land in remote areas.

I checked the Russian AIP, and shown above is an example.

I'm not sure which FIRs the flight from Dublin to Hong Kong will pass through, mainly because the routing near China is not always consistent. Nevertheless, in remote Northern areas as shown SELCAL is provided.

According to ICAO Annex 10 it will be the operator's responsibility to arrange its use if they want to (or if it is mandated). For example:

  5.2.4.2.1 PANS.— It is the responsibility of the aircraft
  operating agency and the aircraft to ensure that all
  aeronautical stations, with which the aircraft would normally
  communicate during a particular flight, know the SELCAL
  code associated with its radiotelephony call sign.

Regarding the headset, the crew doesn't have to wear it unless mandated by the airline. During long cruise it's not uncommon to remove the headset and turn up the volume of the loud speaker in the cockpit.


Do airlines have an ATC schedule they have to adhere to?

The estimated off block time, EOBT, which is the time at which the flight is planned to leave the gate at the departure airport, has a validity of +/-15 minutes. If the plane is not able to depart within this window, the company must send a new ATC flightplan with an updated EOBT.

In some cases a calculated takeoff time, CTOT, is issued to a flight. This is the exact time the plane must begin its takeoff roll. It is given based on airspace or airport congestion along the planned route of the flight, to prevent overload in individual ATC sectors. The flight must begin its takeoff roll within -5/+10 minutes of the CTOT. If unable to comply, a new CTOT must be requested.


Why is the horizontal stabilizer forward of the vertical stabilizer on the P-51?

(Source) Corsair top, P-51 bottom.

The noticeable difference above is the taller rudder of the P-51.

A taller rudder is needed for a shorter lever arm (distance between empennage and wing) and/or the need for more yaw authority.

And as @Gerry pointed out, another benefit of having part of the rudder below the elevator line is for spin recovery when the horizontal stabilizer is stalled and sending its wake upwards. The alternative is like the Corsair, with the rudder ahead and clear of the horizontal stabilizer.

Is it unique? No, a Cessna is shown below:

Related: How many versions of the P-51 dorsal fin fillet are documented?


What is the difference between a high bypass turbofan and a low bypass turbofan?

The first turbofan, the RR Conway, had just a bypass ratio of 0.25. It was designed for installation into the wing root of airplanes like the HP Victor bomber or the Vickers V-1000 transport project, so RR strived to keep the diameter small. Of course, back then nobody distinguished low- and high-bypass engines. The P&W JT-3D, which powered most of the second generation of jet airliners (Boeing 707 and DC-8), had a bypass ratio of less than 1.5.

But when the new generation of engines (GE CF-6, JT-9D) with bypass ratios of around 5 were developed for the first generation of wide body jets, marketing needed a term to make clear that this was a new generation of engines, and the high-bypass ratio engine category was born. Generally, the threshold is around 5, but note that some CF-6 versions have bypass ratios as low as 4.24 and still fall into the high bypass ratio category. Therefore, Wikipedia sets the limit at a bypass ratio of 4.

There is no technical difference between a low- and a high-bypass engine, and the limit is arbitrary. The jump in bypass ratio from 1.5 to 5 brought significant improvements in specific fuel consumption and noise reduction, but part of the technical progress was also from better materials and aerodynamics, which allowed higher compression ratios and turbine entry temperatures.

Now, almost 50 years later, we see the first engines with bypass ratios above 10 entering service. Designs are being readied with bypass ratios of 12, so marketing will need a new word to describe those creations. With "ultra high bypass" already taken by the unducted fan crowd, the search is on.


Is it ever possible to auto-rotate with a missing rotor blade?

Highly improbable. If you've ever seen how much a washing machine can shake with a little imbalance in the laundry, at a relatively low energy spin, imagine the destructive forces that would be experienced by the imbalances in your theoretical rotors. Even if your missing blade manages to get away without causing impact damage to the other blades, there is going to be an immediate violent force translated through the aircraft. Your newly configured rotor formation is still going to try to spin around its center of mass, which is no longer concentric with the mast. The degree of imbalance will tell you how far off center the new center of rotation wants to be. The mast is still going to be trying to keep the rotor rotating on its own center, so now the rotor and mast are fighting to circle their common center, and basically this means the rotor, it it doesnt just go to pieces from all this force, will be yanking HARD and fast on the mast, which would probably rip it off the airframe.... but, if your magic rotor and mast stay intact, the violent motion would be translated to the airframe which will now be shaking super violently around you, which would likely cause it to rapidly disassemble. If it magically stayed together, the people inside (hello pilot) would be experiencing forces through the body like riding the paint shaker at the hardware store, but harder and farther, if not faster, on every shake. Watch that paint shaker and imagine your head being in that.

I do not believe your scenario would be survivable, even on the ground. It's odd to think, but a complete rotor disintegration is not the worst thing that could happen after blade loss.


Is it legal to use RC quadcopters for commercial purposes?

Is it legal to fly a drone with a go pro or something and take photos and video for commercial purposes?

Yes, many news businesses think so

  the numbers of drones licensed for commercial flights by the nation's Civil Aviation Authority (CAA), which regulates the use of unmanned flying aircraft, shoots up -- from 30 in January 2013 to more than 300 today

  Many news articles say that the FAA will not really care.

Most drone operators will not care too much what the FAA thinks. This is because the FAA don't have authority over most drone operations. This is mainly because they only really have authority in one country in one part of one continent. The FAA won't be arresting Mr 王 in 中国.

You can read what the FAA says about Unmanned aircraft.

  When the FAA discovers apparent unauthorized UAS operations, the agency has a number of enforcement tools available to address these operations, including a verbal warning, a warning letter, and an order to stop the operation.

Which suggests the FAA cares, at least about commercial UAS operations in the northern parts of the continent of America which aren't Canada or Mexico.

They also have a FAQ

  All UAS operations for commercial or business purposes are subject to FAA regulation. At a minimum, any such flights require a certified aircraft and a certificated pilot. UAS operations for commercial or business purposes cannot be operated under the special rule for model aircraft found in section 336 of Public Law 112-95.


What is the the origin of 12,500 pounds in the FAA's definition of large aircraft?

The answer by pithblot is more or less correct. The 12,500 lb. limit was chosen as an approximate halving of the DC-3 gross takeoff weight.
Consider the following quote:

As noted earlier, when first promulgated, the 12,500 lb. weight limit
could be understood in light of the general use of the DC-3, an
aircraft with a maximum gross takeoff weight of 25,000 lbs. and
carrying from 21 to 25 passengers in airline service... The imposition
of a 12,500 lb. gross weight maximum, by effectively limiting the
number of passengers that could be carried as well, did indeed protect
the local service carriers' interests.

(U.S. House of Representatives, 94th Congress, 2nd Session, 1976, pg. 48)
References:
U.S. House of Representatives, 94th Congress, 2nd Session. (1976). The future of aviation: Hearings before the subcommittee of aviation and transportation R. & D. of the committee on science and technology [no. 82]. Washington, D.C.: U.S. Government Printing Office. Retrieved from Google Books.


Can you push the throttle forward while using reverse thrusters?

In the B757 aircraft (RR engines), for example, the "reverse" thrust levers can only be raised/employed when the aircraft is on the ground and the "forward" thrust levers are in the idle stop position.  During reverse thrust operation, the forward thrust levers cannot be pushed forward.

This is different than many Turboprop airplanes


Why do early airliners have "backward slope" windows

If it's a good idea here, why not in the cockpit of an aeroplane, right?

Image source

The forward slope was designed to avoid reflection of lighted instruments in the window panes, but that turned out to create other reflections. From this site:

  The cockpit windshield of the first 247s was angled "forward" instead of the conventional aft sweep. This was the design solution (similar to that adopted by other contemporary aircraft that used a forward raked windscreen) to the problem of lighted control panel instruments reflecting off the windshield at night, but it turned out that the forward-sloping windshield would reflect ground lights instead, especially during landings, and it also increased drag slightly.[12][13] By the introduction of the 247D, the windshield was sloped aft in the usual way, and the night-glare problem was resolved by installing an extension (the glarescreen) over the control panel.[14]

Also mentioned in this answer.


What is the relation between roll angle and pitch angle?

Roll, pitch and yaw are rotations about the principle body axis of the aircraft. Roll angle, pitch angle and yaw angle together describe the attitude of an aircraft.

The principle body axes are:

X-axis is the longitudinal axis pointing out the nose of the aircraft. Rotation about the x-axis is called roll. Roll rate is denoted $p$, roll angle is denoted $\phi$
Y-axis is the lateral axis pointing out the right wing. Rotation about the Y-axis is called pitch. Pitch rate is denoted $q$, pitch angle is denoted $\theta$
Z-axis is the vertical axis pointing down. Rotation about the Z-axis is call yaw. Yaw rate is denoted $r$, yaw angle is denoted $\psi$

Initially when all angles are 0, the aircraft is wings level, nose pointing at the horizon and heading north.

The angles $\phi, \theta, \psi$ describe the attitude with respect to this initial positions. They are called Euler angles

The rotations are applied in backwards order, first yaw ($\psi$), then pitch ($\theta$) and finally roll ($\phi$).

This describes almost every possible attitude uniquely, unless the pitch angle is +/- 90 degrees. Then roll and yaw will become ambiguous.

Now back to your question. Initially on the runway the roll angle of the aircraft is 0 degrees. If the aircraft pitches up ($q$ becomes positive for a while), the roll angle will not change.

However, if initially the roll angle was non-zero, the roll angle will be affected by a pitch-up manoeuvre. You can easily visualise this with your hands.

Open your right hand with the palm facing up, you thumb at a right angle to the fingers. The middle finger is the X-axis, the thumb is the Y axis.

Now roll your hand 45 degrees counter clockwise, keeping the fingers pointed at the horizon. Your thumb will now point 45 degrees into the air. This was a pure roll manoeuvre, the pitch angle is still 0 degrees.

Now flap your hand 90 degrees up using your wrist, this is a pitch up manoeuvre since you rotate about your thumb axis which is the Y axis.

Now you see that your fingers are all in the same vertical plane, pointing 45 degrees up to your left. If you describe this position with respect to the initial position, the pitch angle is 45 degrees, and the roll angle is 90 degrees. So pitching 90 degrees resulted only in 45 degrees of pitch, but also in 45 degrees of extra roll.

Because the roll-angle was non-zero before we started to pitch, the pitch rotation affect the roll-angle.

If your sensor is not aligned with the body axes of the aircraft, you will see a lot of cross-effects between the angles during a take-off.

The mathematical relation is well described on this page, which is also the source of the images above.


You can navigate using VORs under either IFR or VFR. If visibility is zero, hopefully you are flying IFR.
These days, pilots are going to use GPS if at all possible, but if the GPS fails or if the plane doesn’t have GPS, we can fall back to using VORs. Most planes still have one or two VOR receivers for that purpose, even if they’re rarely used.


What airplanes can I fly with an EASA PPL license?

I was wondering about the same and here is what I found.
Yes, for LAPL license holders, when switching to another airplane within the same class rating (don't mix it up with type rating) the familiarization training shall be performed and signed off by instructor. It's stated in the "FCL.135.A LAPL(A) — Extension of privileges to another class or variant of aeroplane" section of the "Part FCL".

Before the holder of an LAPL can exercise the privileges of the licence on another variant of
aeroplane than the one used for the skill test, the pilot shall undertake differences or familiarisation
training. The differences training shall be entered in the pilot’s logbook or equivalent document and
signed by the instructor.

There is no such requirements for PPL(A) holders.
Further away there is the section "FCL.700 Circumstances in which class or type ratings are required" which has class rating SEP (land) with many aeroplanes: SEP (land), SEP (land) with variable pitch propellers, SEP (land) with retractable undercarriage etc.

All those are aeroplanes. The D to the right means that

Whenever (D) is indicated in one of the lists mentioned in paragraphs (a) to (c), it indicates that differences training in accordance with FCL.710 is required.

Ok, going down to the "FCL.710 Class and type ratings — variants" where we have

In order to extend his/her privileges to another variant of aircraft within one class or type rating, the pilot shall undertake differences or familiarisation training.

I don't know why aircraft is used in this section instead of aeroplane, but later again it's explained as

(a) Differences training requires the acquisition of additional knowledge and training on an appropriate training device or the aircraft.
(b) Familiarisation training requires the acquisition of additional knowledge.

Conclusion: the minimum required is "Familiarisation" which is just "acquisition of additional knowledge" which has no any requirements for legal sign off or so.


Are there any airlines that fly a route that has an arrival time earlier than its departure time?

I found such a route for you. KATL (Atlanta) to KHSV (Huntsville, AL) is a 57 minute hop from the Eastern time zone to the Central time zone. It appears how you would expect:


What is this fighter-like plane with huge wings?

The Martin/General Dynamics RB-57F Canberra is a reconnaissance aircraft.

The RB-57F was derived from the Martin B-57 Canberra, a tactical bomber and reconnaissance aircraft built on license from the British English Electric company. With its enlarged wings and more powerful engines, the RB-57F gained extreme altitude capabilities. It can climb up to 24,000 m (80,000 ft). It was developed and built for the US Air Force. The first flight was in June 1963.

900 British and 49 Australian Canberras were built. 403 American B-57s have been produced, of which 21 have been converted to RB-57F. Some aircraft were operated by the air forces of Pakistan and Taiwan. Two RB-57F crashed on USA territory, and one aircraft was lost over the Baltic Sea. Only a few aircraft have been salvaged. Most of the RB-57Fs ended up at the AMARC bone yard (source).

The particular aircraft on the question's picture with serial number 63-13291, was converted from a B-57 in 1964 and served the US Air Force till 1974, when it was put into storage at the AMARC bone yard.

picture source: NASA (https://acd-ext.gsfc.nasa.gov/People/Newman/wb57_pics.html)

picture source: NASA (https://airbornescience.nasa.gov/gallery/aircraft/WB-57_-_JSC)

Today there are still 3 planes (now called WB-57) in service for the NASA Airborne Science Program.

There is a Wikipedia article about this type.


Is there a list of accidents due to poor communication in English?

While in no way an exhaustive list, SKYbrary does provide a list of accidents and serious incidents which include air-ground communication as a causal factor. The list contains example of events, and is not meant to contain every single such event.

You can find it here: http://skybrary.aero/index.php/Accident_and_Serious_Incident_Reports:_AGC

You may also want to search for communication and related terms on The Aviation Herald: http://avherald.com/h?search_term=communication&dosearch=1&search.x=0&search.y=0


Is PVC tubing a good material for helicopter airframes?

No. The strength to weight ratio of PVC is poor compared to aluminum and you would end up with a very heavy, albeit cheap, machine, and will be even worse when compared to carbon fibre tubing, which would be the optimal choice performance-wise.  Extruded aluminum tubing would likely be the best choice cost wise.  Forget about building a plumb-O-copter.


What procedures are in place at London City Airport for emergencies after V1?

London City certainly has its challenges, with a steep approach and high rise buildings in close vicinity to the short runway, at the same time you have all sorts of places to divert to: Southend to the east, Stanstead and Luton to the North, Heathrow to the west, Farnborough, Gatwick, the list goes on. All of these places have longer runways with less constrained areas and fields all around. North Weald and Biggin Hill could also be used in an emergency. By the time you have returned to LYC you could have reached one of those.

It depends on the severity of the situation; if you have a mechanical problem but can land safely then going back to LCY is convenient for your passengers, if you're on fire or have control problems you're better off an another airport.

It is certainly possible to return to the airport in an emergency, and it has been done at least once. In 2014 an Avro RJ85 returned to the airport after a part of a nacelle came off. The headline is misleading, it says part of the wing fell off but it was really a nacelle. This is sort of "emergency-lite" as the flight could not continue, but the condition of the airplane was good enough that a normal approach could be made and the passengers moved to another flight.

The same year an Avro RJ100 diverted to Stanstead after an engine fire.

So the wisdom of returning to London City in an emergency is entirely dependent on context like the condition of the aircraft, weather, etc.


I assume by "middle pitch" you're talking about the pitch during cruse? In which case, the answer is, unfortunately, "it depends". Changing pitch changes the amount of lift, and the amount of lift needed depends on the weight of the plane. So, an airplane with more passengers and cargo will need a slightly higher pitch.

Changing speed also changes lift, which will need to be compensated for by changing pitch. However, we're talking about cruise flight here, so speed will remain relatively constant.


Why are flights from Fuzhou or Xiamen to Taiwan not allowed to overfly Taiwan strait?

The answer to this question is covered in good detail in this news article in The Straits Times. Essentially, it's a political dispute between the countries of China and Taiwan.


Flaps change the camber of the wing's airfoil. This in turn changes the zero-lift angle of attack, increases the maximum lift potential and, in case of fowler-type flaps, the wing's area.

Airliners use flaps on both take-off and landing, and most of the time they are only partly deflected. Full deflection is only set on final approach to reduce the landing speed as much as possible.

When simple camber flaps are used, the drag increase is negligible for small deflections (±10° for a 20% flap), and they can be used for both take-off and landing. Other types of flaps are designed to increase drag (split flap, Zap flap) and should be used only for landing. If flight speed stays constant, a flap deflection will only change induced drag if it redistributes lift over the wingspan. Modern gliders use camber flaps inboard and flaperons (a combination of aileron and flap) outboard, and changing flap settings will not affect induced drag.

Generally, the purpose of flaps is to shift the minimum airfoil drag to the desired lift coefficient $c_L$. Especially laminar airfoils have a pronounced range of lift coefficients with low drag. The pilot should attempt to stay within this region of minimum drag, and flaps give him/her the means to achieve this. See below for an example of an airfoil at a Reynolds number of 1 Mio.

Flaps for lift increase work the same way, but change camber much more. Normally, they need to be combined with leading edge devices (slats) which change camber at the airfoil's nose to unfold their full potential. Below are some examples for flaps, in combination with proper leading edge devices. Note that the solid outline of the fowler flap is the position for landing, while the dashed outline is the position for take-off. $\delta$ is the relative chord of the flap.

Junkers flaps were the best way to control big aircraft in the days before more elaborate force compensation mechanisms were developed, and split- and Zap flaps were very popular in the 1930s. They are still used on smaller aircraft today. The simple Fowler flap is used on the C-130, and airliners use slotted flaps like the ones in the lowest two rows of the table above.

Besides increasing drag, powerful flaps change the pitching moment of the wing by shifting the center of lift backwards, which requires sufficient tail size and control power. On airliners, the incidence of the full horizontal tail can be adjusted in order to create enough downforce to counteract the pitching moment. Note on the picture of the An-70 below that the stabilizer has a slat which operates in the opposite direction to that of the wing.


It depends on the operator's "opspecs" which are negotiated between them and the FAA. Generally in the US the vast majority of part 121 scheduled airline operations are required to be IFR, but plenty of part 135 charters are permitted to fly VFR. They may be subject to weather minimums higher than the general VFR limits.


Definition

A second officer (SO) is third in line of command on an airplane. The purpose of a second officer is:

  a Second Officer is used on international or long haul flights where
  more than two crew are required to allow for adequate crew rest
  periods.

I have never seen anyone besides a captain and first officer on a short-haul flight. Such flights normally don't even require either the captain or first officer to take a break to rest.

Duties

Second officers are qualified pilots and also type-rated for the airplane they are on, similar to the captain and first officer, but only with lesser experience. I do not know the exact career path for them, but most probably they are promoted to become first officers. This is same as first officers are promoted to become captains.

Jobs

There are certainly jobs available for second officers, but only on airlines which operate long-haul flights. Regional airlines with flights only for a 2-3 hours don't require a second officer1.

Cathy Pacific is hiring (also here). The experience of a second officer on Cathy can be read here. Aviation Job Search is listing many positions.

SO on Short-Haul

Each airline can have its own definition of second officer. What I wrote above is the general meaning. You mentioned JetA and Thomson (in comments to the deleted answer) but I couldn't find jobs for SO.

Flight Engineer

Their role is different than pilots and now they are a diminishing breed. Most of them were not pilots. Again, an airline may label a flight engineer as second officer, though Wikipedia did not mention that.

1: The aftermath of Germanwings crash can make some changes in regulations.


How do I tell if class E airspace extends to surface or starts at 700'?

Source: FAA VFR chart.

The magenta dashed is from surface, the magenta gradient is from 700 ft. AGL, and the blue gradient from 1200 ft. AGL.


Is flying at 14,000 MSL safe for children without supplemental oxygen?

Let me start out by saying that Aviation Stack Exchange is not a substitute for medical advice. Most of us aren't doctors (though I have medical training I am certainly not a doctor), and even if we were doctors we are not your doctor and we don't know your medical history (or your child's medical history).
If you're going to be flying with your kids in an unpressurized aircraft consult your pediatrician for their recommendation on supplemental oxygen. There are a number of factors at play, and your doctor will be able to consider all of them and give you comprehensive advice.

That said, let's talk about oxygen in general terms.

There's a lot of good information on supplemental oxygen use out there: AOPA talks about it here, and this website has a very detailed explanation, written by a doctor which get into what's going on as altitude increases (and the partial pressure of oxygen in your lungs decreases).

By regulation you are required to provide supplemental oxygen:

to the flight crew if you're above 12,500 feet for more than 30 minutes.
to the flight crew if you're above 14,000 feet for ANY length of time.
to everyone onboard if you're above 15,000 feet for ANY length of time.

Using the handy chart in the second website that equates to oxygen saturations (SpO2) of roughly 88%, 82%, and 76%, assuming you're breathing ambient air for an extended period of time.

To put this into perspective if you come to the hospital with an oxygen saturation below 90% you will almost universally be put on supplemental oxygen, and most guidelines call for maintaining SpO2 above 92%. (In aviation terms, the partial pressure of oxygen at 10,000 feet usually results in SpO2 around 90%).

So with that information the question now becomes "What is your standard of care for your passengers?" - the FAA sets minimum requirements in the regulations, and they are mainly focused on making sure the flight crew does not become impaired (they are less concerned about your passengers getting loopy, as long as the pilot is OK), but you as a pilot are free to set higher standards based on your own understanding of physiology and aeromedical factors.

I can't tell you what you should do, but I can tell you what I do: On any flight above 10,000 feet I carry supplemental oxygen, I use it, and I provide it to my passengers.
I also carry a pulse oximeter in the aircraft to check oxygen saturation (SpO2) on myself or my passengers as needed (and I set the oxygen flow rate based on having the worst person in the aircraft above 90%).


Why did Lockheed Martin give the F-22 stealth fighter such small fuel tanks?

The F-22 was developed in the 90's, primarily for use by the United States Air Force. This means it was designed to serve specific mission profiles. The F-35 however is going to replace the F-22 and serve all the air branches of the US Military. This means that it needed a broader mission profile. The last F-22 delivery was in 2016.

For the F-22 Raptor:

  Range: >1,600 nmi (1,841 mi, 2,963 km) with 2 external fuel tanks
  Ferry range: 1,740 nmi (2,000 mi, 3,220 km)
  Combat radius:
     460 nmi (529 mi, 851 km) clean with 100 nmi (115 mi, 185 km) in supercruise
     590 nmi (679 mi, 1,093 km) clean subsonic
  Service ceiling: 65,000 ft (20,000 m)

And for the F-35 Lightning II:

  Range: 1,500 nmi (1,700 mi, 2,800 km) +
  Combat range:
     669 nmi (770 mi, 1,239 km) - Combat radius
     760 nmi (870 mi; 1,410 km) - Combat radius (interdiction mission on internal fuel, for internal air to air configuration)
  Service ceiling: 50,000 ft (15,000 m) +

You can see that the F-22 range (not the combat radius) is very similar to the F-35. The problem with the F-35 is that because it is available in VTOL configuration, it burns a lot more fuel. The VTOL F-35 (F-35B) only has a mission radius of 505nmi. This is because during VTOL operations the F-35 burns an incredible amount of fuel. So much so that a VTOL take-off usually requires mid-air refueling shortly after take-off.

Either way this boils down to a trade-off between how much gas to carry and how much weapons and other systems to stuff into the aircraft. The VTOL versions need much more complicated internal systems that take up a lot of space, so the range and payload suffer. Tanks can be mounted on external hard-points, but then radar cross-section becomes much bigger and maneuverability is decreased.

With mid-air refueling all the aircraft must really do is be able to go from a friendly area where the tanker is, complete the mission, and get back to the tanker, so range isn't as important as versatility.


How can the wind speed and direction be calculated from on-board measurements?

With the set of parameters available to you, you cannot do this.

If you have the actual track instead of the desired track, you will be able to calculate the wind.

The simplest way to do this is using vector math.

There are three vectors to consider:

ground speed vector $\vec{V_{gs}}$
air speed vector $\vec{V_{as}}  $
wind speed vector $\vec{V_{ws}}  $

$\vec{V_{gs}} =\vec{V_{as}} +  \vec{V_{ws}}  $

$\vec{V_{ws}} = \vec{V_{gs}}  - \vec{V_{as}}  $

I assume the actual track angle ($\phi$) and heading ($\psi$) are with respect to the true North.

The north component of your air speed is then: $V_{as} \cdot \cos(\psi)$ and the east component of your air speed is: $V_{as} \cdot \sin(\psi)$

For ground speed the decomposition is: north: $V_{gs} \cdot \cos(\phi)$ and the east component of your ground speed is: $V_{gs} \cdot \sin(\phi)$

$$\begin{bmatrix}
       V_{ws,north}\\
       V_{ws,east}
        \end{bmatrix} = \begin{bmatrix}
      V_{gs} \cdot \cos(\phi) -
      V_{as} \cdot \cos(\psi) \\
      V_{gs} \cdot \sin(\phi) -
      V_{as} \cdot \sin(\psi)        \end{bmatrix}$$

You now have the north and east component of the wind vector. This you can change to a speed and direction, but I leave that last part up to you. Don't forget that wind direction is usually reported as the direction from which the wind is coming.

To find the wind speed from the North and East components use the root of the sum of the squares:

$V_{ws}=\sqrt{V_{ws,north}^2 +
       V_{ws,east}
^2}$

The wind direction can be found by

$\tan^{-1} (\frac {V_{ws,north}}{V_{ws,east} }) $

Note that this will give a division by 0 for winds exactly from north or south.

To implement it in a computer language the atan2 function can be used. This prevents division by zero and also returns the direction of the full range of the circle instead of semi-circular

wind_dir = atan2(-wind_north, -wind_east)

This should give the direction from which the wind is coming in radians.


On Air France 447, what would have been the lowest altitude to initiate recovery after the stall developed?

For the stalled flight to recover, the nose needs to be pointed in the airstream, and then the aircraft pulled up with load factor below the ultimate load. From the accident report:

  The recordings stopped at 2 h 14 min 28. The last recorded values were a vertical speed of -10,912 ft/min, a ground speed of 107 kt, pitch attitude of 16.2 degrees nose-up

Initial situation.

From earlier on in the report we can conclude that these values were typical for the complete stall from 36,000 ft to impact, except for the pitch attitude which was around zero for most of the stall. The flight state parameters were therefore:

Vertical speed was 10,000 feet/min = 51 m/s
Horizontal speed was 100 kts = 51 m/s, which constructs an airspeed of 72 m/s.
The engines were at TO thrust, creating a nose-up moment, compensated by the nose-down moment of the airstream hitting the horizontal stabiliser.
The automatic trim is retained in alternate law, so the stabiliser is trimmed full LE down = 14º.
Elevator is fully up = 30º on top of the trim - it is almost aligned with the stalled airstream.

Nose down manoeuvre.

At 72 m/s the aircraft is at about TO speed, and nose rotation speed should be comparable to TO rotation speed - a bit slower because one side of the elevator is stalled. It takes perhaps 5 - 10 seconds to rotate the nose down 45º (an estimated assumption from my part).
When at 45º nose down, gravity accelerates @ 0.7g and the engines at perhaps 0.25g. At this acceleration airspeed builds up with around 1 g = 9.8 m/s every second. If we take averages for nose down manoeuvre time and acceleration, airspeed builds up with 4.9 m/s for 7.5 seconds = 37 m/s. So when the nose is aligned the airspeed is about 110 m/s, but still accelerating fast.
During the 5 - 10 seconds nose down manoeuvre, the aircraft loses about 1,000 - 2,000 ft in altitude

Speed increase

Before the aircraft can be pulled from the dive, the true airspeed needs to be brought to the manoeuvre speed $V_a$. From the A330 FCOM:

  The load alleviation is only available when :

  The aircraft speed is above 250 knots.
  The FLAPS lever is in the 0 position.
  In normal or alternate law flight mode.

Above 250 knots the load alleviation system is active, in order to keep the maximum load factor at 2.5g. The manoeuvre speed (or cornering speed in military speak) seems to be set at 250 knots = 128 m/s. At 1g acceleration, it takes 2 seconds to increase speed from 110 to 128 m/s, during which the aircraft loses altitude of 500 ft:

$$\Delta h = sin(45) \cdot (V_0 \cdot t + \frac{1}{2} \cdot a \cdot t^2)$$

Pull-up manoeuvre.

Then during the pull-up manoeuvre, the load factor must stay under the limit load = 2.5g. 1g is taken up by gravity, and there is 1.5g available for the pull-up manoeuvre.

$$ m \cdot \Delta n \cdot g = m \cdot \frac {V^2}{R} \Rightarrow R = \frac {V^2}{\Delta n \cdot g}$$

With the values established above, we get R = 10,000 / (1.5 * 9.81) = 1,100 m = 3,300 ft. But that is at constant airspeed of 128 m/s, in reality the airspeed will still pick up at the beginning of the manoeuvre and the radius will be higher - let's say 4,000 ft. The velocity vector of the plane was 45º pointing downwards, so half the radius is used. This is from the moment the AoA is close to zero, which it needs to be in order to start the pull-up, which increases AoA again.

My estimate for the altitude required for a successful pull-up from the stalled situation, is therefore 2,000 + 500 + 2,000 = 4,500 ft if they end up skimming the tops of the waves. If they know exactly what to do, time things perfectly, and manage airspeed perfectly. The aircraft is protected against pulling too many g's, so once the nose is aligned the flight crew can pull the stick fully aft and let the aircraft manage the minimum pull-up radius. If for instance the pull-up is initiated 1 second later than the 2 secs estimated above, the airspeed increases to 138 m/s and the pull-up radius becomes 1,300 m = 4,000 ft, plus the aircraft loses an additional 300 ft during the 1 extra second diving down under full power - this 1 second delay in initiating the pull-up requires another 1,000 ft.

Recovering from a fully developed stall is now trained in Level D simulators. Picture below is from a company that makes the flight model and instructor station extension for any flight simulator to train the manoeuvre. Disclosure statement: I have done business with them in the past.


Why autogyros use pusher-, whereas, piston-engined planes use puller-configuration?

Pitcairn PCA-2 - By NASA/NACA, LARC [Public domain], via Wikimedia Commons

The original autogyros were tractor (google Cierva/Pitcairn).

The big thing with autogyros is thrust line relative to the vertical C.G.   The pusher craze was started by Igor Bensen with his homebuilt autogyro, which was done that way to keep everything compact and minimalist, and give the pilot a nice view.  The issue with Benson machines and variants is the thrust line is above the center of mass, and if you unload the rotor disc by doing a bunt, or hit major turbulence that makes you go zero G, they have a tendency to pitch over and tumble as the prop wants to spin the machine about its vertical CG in the absence of any resisting force.  It's called Power Push Over or PPO and is always fatal.  You must NEVER go zero G in a Benson or any machine with a high thrust line.  It's actually quite similar to the mast bumping problem with teetering rotor helicopters, although that happens on the roll axis.

A lot of gyros move the engine down as much as possible to lower the trust line to the vertical C.G. or close to it, and have that awkward spindly look as a result because it means making the gear a lot longer.  The other thing that helps is a large horizontal stabilizer to resist large pitching movements and most gyros have them now.

Tractor engine gyros have a better thrust line relationship (generally naturally lower, close to the CG) and also have a long tail with good moment arm and are generally immune to PPO (the fact that the engine is out front or behind is irrelevant in itself).  There are a couple of homebuilt gyros that use the engine out front.  You can tell however that the tractor machines just have way more structure to them so it's easy to see why the pusher setup is so much simpler and lighter.


How much can a plane benefit from another planes wake?

No, airplane wakes do not work like this. The streamlined body has very little wake, it is not like a cube shaped truck. The main wake on an airplane is found at the wingtips in the form of a strong vortex like horizontal tornado, aided somewhat by the down wash of the mid wingspan.

The tip vortex from a large plane will make a small plane spin like a windmill. A german bombardier challanger(mid size business jet) flew under an A380 at cruise altitude a few years ago and was turned over so hard the plane had to be sold for scrap, broke a one passanger's ribs, recorded near 4G force, lost 8000 ft of altitude before recovering control.


Are customs stops required for private flights within the Schengen Area?

The European Union has also something called EEA - European Economic Area. Within the EEA it is not required to fill out anything except a flight plan between Germany and France.
Switzerland, as stated, is not part of the European Economic Area and therefor customs are required.

Just in addition, Schengen is for passport free travel and not for taxes.


Why does the length of the 737 vary so much?

Airlines want to have different sizes of aircraft to match their passenger loads as well as possible. The different loads may be for different routes, times, or airlines. It is more efficient to fly a smaller plane if extra space isn't needed.

Aircraft manufacturers have some options for how to meet this demand. They can create a whole new airplane for each size, but this is expensive for everyone involved. Each plane would have to be certified separately, requiring much more time and testing. They may not be alike, requiring pilots to be trained on each individual one. And airlines would have to maintain all the different types of airplane.

Instead, aircraft manufacturers choose to stretch the fuselage to fit in more passengers. This can allow most other things on the plane to remain the same, with generally just minor modifications. This greatly decreases the amount of design and testing required to create the new size of aircraft. The same pilots and mechanics can work on any of the sizes, since most parts and features are common to all of them. There will be some inefficiency, in that parts on the small versions are designed to withstand higher loads of the bigger versions, but this is more than offset in the cost savings of having common parts.

Most aircraft come in different versions with different lengths, but it can be most noticeable on the smaller planes like the 737.

The manufacturers also market their products based on their coverage of different seat capacity. Each manufacturer is able to cover a wide range of seat capacity by offering different sizes of 3 basic models.

Source


What factors contribute to the poor off design performance of turbofans?

I am looking to understand why turbofans have a higher specific fuel consumption when ran at lower power settings and what can be done to improve it.

Actually, a turbofan has a higher efficiency at lower than max (read take off) performance. Why? Engines spend the majority of their life at cruise conditions, so compressors, turbines and fans are designed and optimized to deliver the cruise performance at the best efficiency that is possible according the technology at design time.

The manufacturers achieve this by designing the optimal blade shapes and angles for the condition the most amount of time is spent. Obviously, when you are further away from that optimal point the more likely you encounter non ideal conditions which lead to less efficient flow around the blades and as such this is translated to a higher specific fuel consumption. This is illustrated by the compressor/fan off-design characteristics, also known as compressor/fan map. A compressor/fan map shows the relation between the pressure ratio, efficiency and the corrected (non dimensional) mass flow for various spool speeds. This is shown from the Wiki image shown below:

Note that this is the performance of the isolated compressor, when connected to a turbine, an equilibrium (operating) line is established, ultimately, this operating line should follow the path of the "Peak efficiency line". This compressor map also shows than for a high spool speed (N4) to a low spool speel (N0) the efficiency first increases, to later decrease again. This is caused by the design and the way the flow enters the compressor stages and is exactly why the performance of the compressing turbomachinery has not the same efficiency throughout the whole operating area.

If you would sweep an engine (for real or through a simulation) from take-off power to idle power, the specific fuel consumption would decrease to cruise power to increase again to idle power. This graph, from a simulation of high power setting to a low power setting of an older turbofan engine with a bypass ratio of about 5, illustrates that:

  Perhaps a variable pitch fan is the best solution even as difficult as they are to make?

Variable pitch fans are needed when the fan pressure rise becomes low (below about 1.35); these low pressure ratios are seen in very large (geared) bypass designs as on the Rolls Royce Ultrafan design.

  Would it make sense to use an electric motor as a torque fill or to increase the rpm of the compressors when at lower power settings?

It would make sense to assist during take-off so that you essentially can use a smaller engine. Take-off power is several times more than cruise power. Also, the powers in gas turbines are so high and the electric motors are very big and heavy (and certainly the batteries) that this can be seen entering in the very far future. This is commonly known as hybrid propulsion.

  I have read about regenerative cycle engines which feed heat back into the combustor but these only seem to add a small amount of efficiency in practice.

Indeed, recuperating heat from the exhaust (which is on of the 3 major losses in gas turbine engines) would mean that you have to use less fuel to get to the same combustor exit temperature. This has been investigated in the European Clean Sky 2 project called NEWAC. The problem with recuperating heat is that on one side you have the highest (combustor/high pressure compressor exit) pressure, and low exhaust pressure on the other side, causing mechanical challenges. Also the core flow is at an enormous high speed, so there is little time to exchange heat; this means you need a very big surface area to exchange the heat. The bigger the area, the higher the weight, the higher the weight the heavier the aircraft the more drag and thus power are required.


Why would a glider have water ballast? If it is trying to stay aloft without an engine, wouldn't it be better to be as light as possible?

Mass doesn't affect the maximum distance, only the maximum endurance.

For example, image two identical planes A and B: A weights 50kg less than B. Assuming no wind (horizontal / vertical) and speed of best glide, both gliders will land at the exact same spot.

The lighter airplane A however will arrive later than B, as the speed of best glide is less than for B. In conclusion you can say, that additional mass only increases cruise speed, but not the travel distance.

Glider competitions are most of the time a route you have to fly in the shortest time possible. So that means, if you have a higher speed of best glide, you can fly faster in competitions.

The only downside to having a higher weight is, that your liftrate in thermals will be decreased and due to the higher speed it is harder to center the thermals.

It is to some extend also possible to shift the Centre of Gravity (CG) with the added load. The further it is to the aft limit, the higher your maximum distance is. This is because you will have less down-force from the stabilizer required. (If the CG is at the front limit, you will need to pull the control stick in order to fly level, therefore you have more drag). However I think this is rather a positive side effect and most of the time the water is used for flying faster.

Source: I am a glider pilot and currently doing my ATPL training.


You may find this manual of interest from the FAA. The short answer is that they don't have brakes like wheeled aircraft do. With sufficient runway you don't need brakes to stop a wheeled aircraft either. The airframe often provides enough drag to stop the airplane. You are generally correct that aerodynamics are not the primary method of braking, however they can in some cases be sufficient. On top of that ski operations are often flown from a frozen lake or similar area where there may be a great deal of unobstructed distance for takeoff and landing.

Some types of skis let the wheels poke through them for both snow and hard runways. In some cases the wheels may contact the ground beneath the snow and allow for traditional braking or they may be plowing through the snow providing drag.


Why do we need DME or RNAV when using VOR navigation above FL240?

The consensus of internet wisdom seems to be that no one knows for sure, but the most likely explanation is that before class A existed there was Positive Control Airspace (PCA) that started at FL240, and DME was a requirement in PCA. The main reasons for requiring DME were:

There's a limited number of high-altitude VORs so it isn't easy to use cross-radials from other VORs for fixes or position reporting; DME is a simple alternative
If there's no radar coverage then ATC can still manage lateral separation effectively using DME

That all seems plausible enough, but some sources out there say that PCA started at FL180, not FL240, e.g. this FAA history document:

  [VFR on top] was a principle [sic] factor in the [Grand Canyon] crash and led to
  "Positive Control Airspace" (PCA) FL180 and above. Because of the
  speeds of the aircraft involved, non-radar procedures were unwieldy
  (standards called for ten minutes between aircraft; some 80 miles for
  a typical jet), even with the development of aircraft installed
  Distance Measuring Equipment (DME) and the reduced separation
  available between DME equipped aircraft (20 miles).

FL240 is also where ATC starts using Mach numbers instead of knots (ATC orders section 5-7-1(f)) and the separation minima change (section 8-4-4). I don't know if that's for historical reasons or physical/operational reasons, but it looks to me like FL240 is considered the general starting point for high-altitude operations (14 CFR 61.31 requires a high-altitude endorsement for aircraft that can operate above 25,000' MSL).


Should I contact ATC if I don't have a transponder?

Every US controller I've ever heard from says they'd prefer to be talking to every aircraft in their airspace, period. This lets them know your intentions and allows them to move you around if needed, which saves them far more time than it costs giving you traffic advisories.

If you don't have a transponder, they can still tag your primary target with your tail number. Since you can't squawk or ident, they'll need a turn and/or an exact position for positive identification before they're allowed to do that. Once you're tagged, though, you look the same to them as someone with mode A only.

If you're practicing maneuvers, I suggest letting them know what to expect with something like "maneuvering at or below 3500 ft." That's a good idea even if you have mode C, but it's critical without it.


How do I determine the best altitude to fly for fuel economy?

The optimum altitude depends on your aircraft, the engines and the weather. But most important is to decide what you are trying to achieve. If you would like to optimize your fuel consumption per distance travelled, the altitude you will fly at will be higher than if you try to optimize your fuel consumption per time unit.

Fuel per distance travelled is usually better at altitude, while fuel flow per time unit is lower at lower altitudes. In other words, if you want to go far, fly high. If you want to keep flying long, fly low.

Winds play an important role as well. If you have a strong headwind high up, you might go further staying low.

There is quite some difference between reciprocating engines and jet / turbine engines here. The former perform better at lower altitudes, while the latter do just fine until much higher.


What's a typical first lesson of glider flying like?

I'm a glider instructor.  The first lesson would have been introductory and if there weren't any soaring conditions, I'm guessing the flight was pretty short, less than 15 minutes, so you probably did/saw a lot less than expected.  It's a challenging instructing environment because of the time limitations on no-lift days.

If you were disappointed with the instructor, note that in glider club operations you will generally fly with all of the club's instructors at different times and you will end up with a couple of favorites.

At least give it enough time to experience a good soaring flight with an instructor to find out what the potential is, and whether you think you can get hooked on the "game" you play with the atmosphere to stay aloft.  Some pilots get into it, some don't and would rather go with power.   Not much different from sail boats vs power boats. Me, I like both but if forced to choose, I'd go with soaring as a fun activity.

Assuming you are into it because you are interested in the sport of soaring, you should hang in until you are solo and get a good soaring flight by yourself.  The first thermaling flight on your own, climbing in many tons of rising air, is an incredible rush, more than first solo in my opinion.  Of course it all hinges on whether you get hooked on the game itself, of working the air to climb.

No two flights are ever the same.  Watch the private owners go out in their high performance machines and disappear for an entire afternoon.  4 hours in a glider is not like 4 hours in a power plane that beats your brains in with noise and vibration; it's like 4 hours of meditation - you return very relaxed and mellow.

Even if you don't think you'll take to the sport, and you plan to learn in power planes at some point, learning to fly gliders first will make you a far better pilot with respect to basic stick and rudder skills, speed control and energy management, so it's worth sticking it out just for that.


Why do Computer Navigation Fixes still exist now that GPS waypoints can be used to define tracks?

From the AIM 1−1−17. Global Positioning System (GPS)

  (2) A Computer Navigation Fix (CNF) is also a point defined by a
  latitude/longitude coordinate and is required to support
  Performance−Based Navigation (PBN) operations. The GPS receiver uses
  CNFs in conjunction with waypoints to navigate from point to point.
  However, CNFs are not recognized by ATC. … CNFs that do appear on
  aeronautical charts allow pilots increased situational awareness by
  identifying points in the aircraft database route of flight with
  points on the aeronautical chart. CNFs are random five-letter
  identifiers, not pronounceable like waypoints and placed in
  parenthesis. Eventually, all CNFs will begin with the letters “CF”
  followed by three consonants (for example, CFWBG).

As an example, the glide slope intercept for an ILS that I fly shows up in the Garmin 430 as a waypoint since the GPS requires a FAF to sequence to the MAP in order to conduct an approach. But it does not show up on the chart. (Remember that an ILS doesn’t have a FAF on the chart.) I have seen them on charts, but none come to mind right now.


What is the weight of the fuselage (only) of the Boeing 747?

The fuselage weight for 3/4 of a 747-300 Combi minus engines, fuel tanks, seats, catering, cargo handling, navigation gear, control surfaces, pumps, hose is 70,000 lbs, according to Big Imagination, the people that bought a 747, gutted it and took it to Burning Man. The 70,000 lb figure was used by the Nevada DOT to determine the oversized vehicle permit fee. If you add another 25%, you come up with roughly 93,000 lbs.

In comparison, a A 747-300 dry weight with engines, seats in airworthy condition is about 384,000 lbs.

I know this only partially answers your question, but every other source I have tried features the Operating Empty Weight (OEW), which is a basic working weight for each plane variant.

Additional Resources:

https://www.bizjournals.com/seattle/blog/techflash/2015/02/boeing-747-to-become-largest-ever-burning-man.html
http://www.bigimagination.org/747
https://en.wikipedia.org/wiki/Boeing_747

Good luck finding a better figure. I'd love to know myself.


How are leaks in door rubber seals detected?

Testing the doors (and windows) by pressurizing the cabin eats into the aircraft's pressurization cycles. Instead vacuum is used to simulate the in-flight conditions.

A special fabric and a sheet with attachments to hoses are attached to the outside where the door/windows are to be tested. Vacuum is created between the fabric and fuselage, thereby locally simulating an in-flight differential pressure. If the vacuum doesn't hold, it means there is a leak, which can be pinpointed from the inside with sensitive equipment.

Image and reference: Lufthansa Technik AG


Is lowering V1/VR (and runway length required) the only reason for flaps at take off?

For an aircraft designed for cruising efficiency it is important to have as little trim drag as possible.

See ATR 72 link:

The wing may appear unusually small, but it is made to produce the needed lift at cruising speed at its most efficient Angle of Attack, where lift to drag ratio is highest.  If the wing produced too much lift for level flight at its cruising speed, it would have to be "trimmed" to a lower AOA, at the expense of greater drag, there for a greater rate of fuel consumption.

The contribution of velocity to lift is described in the lift equation:

$$ L = \frac{1}{2} \cdot C_L \cdot \rho \cdot A \cdot V^2$$

with $L$ being the lift, $C_L$ the lift coefficient, $\rho$ the density of air, A the wing area, and $V$ the aircraft velocity.

The ATR 72 cruises at 280 knots.  In order to generate adequate lift at lower velocities it either has to dangerously increase its AOA, or increase its coefficient of lift by adding camber.

Lowering flaps add camber, which is why this plane does it, as part of its take-off procedure.
Higher flap settings are generally avoided because they produce too much drag.


Why are heading in PFD and map off by exactly 10 degrees?

KIAD has a magnetic variation of 10 degrees west, and KDCA has a magnetic variation of 11 degrees west, so true vs. magnetic north actually makes sense.


In a turbofan, why are there no stators behind the fan?

Right behind the fan you can see the stators.

Here they are from behind.

Here is the fan removed, with the (1) fan stators (outlet guide vanes), and (2) inlet guide vanes for the compressor (booster).

Just like I wrote here:

  On the funny side, here's a thumbnail from RR's own YouTube channel, absolutely bonkers exhaust. Don't trust illustrations.

(CFM56-5A manual)

You can watch the fan removal here: CFM56 7B Fan Blade Removal

Below is the stator assembly for the GE90:

Image sources:

https://commons.wikimedia.org/wiki/File:The_CFM-56_(3852495197).jpg
https://commons.wikimedia.org/wiki/File:Airbus_A319-114,S7-_Siberia_Airlines_AN1710042.jpg
https://c2.staticflickr.com/4/3194/2378036305_e14dab2949_b.jpg
http://memberfiles.freewebs.com/70/53/41845370/photos/GE90-BUILDUP/Image678.jpg


Could the Wright brothers fly across the US today?

It's possible, but it would be difficult under today's regulations.

Restrictions (regulations):

Avoid any controlled airspace that requires talking to ATC
For the sake of argument I'll pretend we have no radio on board, so no class B, C, or D airspace.
(You COULD call the controlling agency and coordinate with them, but let's just pretend we don't have a cell phone either.)
Avoid any airspace within a mode C veil
Because presumably we don't have a transponder on board we can't cross mode C veils.
Avoid any restricted/special use airspace
Duh.
Comply with any other restrictions noted on the chart
I did this in 10 minutes - I may have screwed up a little.
Fuel Reserves
This is the one that makes it tough.
With no wind 110 miles at 40MPH (the cruise speed) is ~2.75 hours endurance - I assume that's to empty tanks (which is how it's usually quoted for aircraft).
The FAA requires at least a 30 minute reserve per FAR 91.155, which means we can fly for 2.25 hours (90 statute miles, 78.2 nautical miles) before we need to land. All legs need to be under that. (It's possible a flight like this could get a waiver from the FAA, but let's assume nobody applied for one.)

Restrictions (Other):

Refueling
Where possible legs should end at airports that have fuel available.
(This isn't a hard "must" since presumably the Wright 1B can burn whatever kind of gasoline we can find once we're on the ground).
Airports
I'm excluding private / restricted airports from consideration as landing spots (again, we'll pretend our pilot has no cell phone and therefore can't coordinate landing access at these fields).

Simplifying Assumptions:

Simple fuel burn
Not having numbers for this aircraft I'm assuming fuel burn will average out such that the aircraft's endurance on all legs is about 2.75 hours (78.2 nautical miles with no wind). This simplifies the planning
There is no wind
(Or if there is, it's always a tailwind.)
There's an aviation GPS (or something like Foreflight) onboard
Frankly I wasn't going to spend an hour looking for landmarks.
You could probably manage the flight by dead reckoning if you had to though.
The Wright Model B can climb high enough to clear any obstacles/terrain
Again, not having numbers for the aircraft (service/absolute ceiling) I'm just making the assumption to simplify things.

So if we put all that together can we plan this flight?
What do you think I did with the first half of my lunch hour?

This is one possible route - there may of course be others

I believe I met all the restrictions, if I screwed up I'm sure someone will edit the flight plan (or come up with a different route).

A Note on Performance
As I mentioned in the assumptions I didn't have performance data available for the 1B when I laid out this route. Some folks helpfully pointed out in comments that there are flying replicas of the 1B.  These don't appear to be "exact reproduction" replicas, but I was able to find some performance data on them.
Given the maximum altitude in the performance figures (2,000 feet MSL) it would probably not be possible to fly the route plotted above with the reproduction equipment available (several legs are well above 2,000 feet MSL), and I would assume the original 1B had comparable performance.


How can a NACA2312 airfoil or similar have a camber location from 30 to 39% without a change in airfoil name?

The NACA airfoil numbers are coded as follows:

$$ \mathrm{NACA} \; M P XX $$

  $M$ is the maximum camber divided by 100. In the example M=2 so the camber is 0.02 or 2% of the chord
  $P$ is the position of the maximum camber divided by 10. In the example P=4 so the maximum camber is at 0.4 or 40% of the chord.
  $XX$ is the thickness divided by 100. In the example XX=12 so the thiickness is 0.12 or 12% of the chord.

source: airfoiltools.com

In your case you changed the position of the maximum camber ($P$) from 30% to 39%. Both result in $ P = 30 / 10 = 3 $ and $ P = 39 / 10 = 3 $ (when using integers, no rounding is applied). The airfoil name therefore only tells you the position of maximum camber with a 10% accuracy.


Are modern Airbus aircraft protected from excessive rudder input?

Yes, A320 and all newer models have rudder travel limiter that limits the maximum rudder deflection depending on speed.

It should be noted, that this has nothing to do with normal law. Normal law governs pitch and roll. Rudder is controlled by (hydro)mechanically connected¹ pedals and yaw damper, which is independent from the system controlling pitch and roll and simply reacts to side-slip (lateral acceleration actually, only A350 will have side-slip vanes) induced by the roll.

¹ Different Airbus models have different subset of controls with direct hydromechanical link as a backup in case of electric failure, so I am not sure rudder pedals have it on all models. They do on A320.


How can someone get FAA commercial flight training as part of an aviation degree?

In the US, there are 2 ways to become a certificated civilian pilot: Part 61 and Part 141.

Part 61 is done in informal classes and flights at a local flight school.

Part 141 is a professional pilot training program, with uniforms, classrooms, a full-time staff, and a uniform fleet of aircraft.

There are numerous US universities that offer bachelors' degrees using a part 141 program. You can find a list of such programs here.

Furthermore, many of these schools, such as Embry-Riddle, take the FAFSA, which is the  process for obtaining financial aid as for any other program.

After graduating from one of these programs, you will have obtained all the training necessary to work as a flight instructor, or as a commercial pilot under Part 119

Private Pilot Single Engine
Instrument Pilot Single and Multi-Engine
Commercial Pilot Single and Multi-Engine
Flight Instructor Single Engine
Flight Instructor Instrument
Multi-Engine Flight Instructor

You will have also earned either an Associates or Bachelors degree, usually in something like Aviation Engineering or Aviation Operations.

You will not, however, have flown enough hours to get a job flying air taxi or cargo under Part 135, which requires 500 hours to be the pilot-in-command.


What disadvantages does flying a drone close under a ceiling have?

For a quadcopter, flying close underneath a flat surface will increase the amount of lift produced, but this will make it harder to control (unless the quadcopter is equipped with appropriate control software).
According to comments by Alex and Peter Kämpf, if you fly a quadcopter close underneath a flat surface, the quadcopter will tend to get "sucked up" and collide with the surface. You will have to reduce power dramatically in order to go back down.
You could probably make a quadcopter under a ceiling easier to control by equipping it with a proximity sensor (or perhaps an accelerometer) and software which automatically reduces power when the aircraft gets close to a ceiling. It could take a lot of tuning, but with the right control algorithm, it would probably be easy to maintain a constant distance under the ceiling.
So, why does a quadcopter behave this way? I don't know if any research has been done on this, but I can make an educated guess.
For aircraft flying above a flat surface, the ground effect increases the amount of lift produced. When the wings are near the ground, a high-pressure region is created between the wings and the ground, thereby increasing the amount of lift.
So for aircraft flying below a flat surface, presumably something similar happens. The propellers create a low-pressure region between themselves and the upper surface. That once again increases the amount of lift produced.
(In the extreme case, with an object which is in contact with the upper surface, it's possible for the object to create a low-pressure region above itself, and thereby keep itself up, using no power at all. That's what a suction cup is.)
For posterity, here are the comments by Alex and Peter Kämpf that I referenced above:

I can say that when I fly my smaller sized quads indoors that its more of a suction cup response. The few that I have all have generally the same effect. If I fly to close to the ceiling I end up sucked up to it where then I have to dramatically drop throttle before they are released. It takes a surprisingly little amount of power to maintain the suction effect. Keep in mind they all have duct motors with a flat surface on top (no camera or antenna sticking in the way) so that may provide more suction action as well. – Alex 2019-01-16 15:50:56Z
There is an important difference: While 'regular' ground effect is dynamically stable, this inverted ground effect is the opposite. Coming close to the ceiling means that the quadcopter will be sucked up until it collides with the ceiling. – Peter Kämpf 2019-01-16 16:26:17Z


Do airlines continue operating in the vicinity of a hurricane?

The cross-wind limit is 35-40 knots for most aircraft with gusts allowed to perhaps 45 or so. The head-wind limit is slightly higher, but not much.

Knot is nautical mile per hour. Nautical mile is 1.852 km, that is 1.15 mile (and for those who prefer metric, knot is just a bit over ½ m/s). So wind more than 40 miles/hour may interrupt airport operations and wind more than 50 miles/hour surely will. I don't think there is a specific limit for rain; it is generally not a big problem if the runways are in good condition.

Problem is that good local forecasts are possible for at most around 24 hours. So it's not possible to tell whether it is likely there will be disruption of operations the day after tomorrow.

For one day ahead, the airport forecasts are publicly available on the internet. Search for TAF ("terminal aerodrome forecast") with the ICAO (the 4-letter one) code of the airport. They are published in strange abbreviations, but there are sites that will happily decode it for you.


Why does the Pilatus PC-24 have such a large "Airplane Support"?

To add to the other answer...

The Pilatus PC-24 is billed as a business jet that can operate out of rough airfields. Comparing the pictures of the PC-24 to the Phenom 300 or CJ4, you can see that there is quite a bit of extra ground clearance. You can also see that the rear landing gear on the PC-24 are much more robust (dual wheels, longer travel length) than the other two aircraft.

If you look at this picture:

Source: Wikipedia

You can see that the wheels also retract into that area. They probably wanted to keep the wing low to take advantage of ground-effect to improve short-field performance. So having a higher-up fuselage allowed them to put the engines up higher and avoid FOD damage, while the low wing allowed them an impressive short field take-off performance. The PC-24 can operate out of a field just 2,800 feet long. The Phenom 300 takes 3,200 feet and the CJ4 takes about 3,500.

So the "bump" is there to be able to handle additional loads, elevate the fuselage, and store the gear. I can't find any diagrams of the fuel system, but it's possible that it also houses fuel tanks or baggage.


Why do some helicopters, e.g CH-53, have some kind of hook thing protruding from the underside of the tail section, what is this for?

The device is often referred to as a tail rotor guard or tail skid, which hints at its purpose.

Helicopters that have tail rotors that sweep below the tail boom are usually equipped with this guard to prevent the tail/rotor from striking the ground during landing, both during a rolling landing or a vertical landing. It is especially useful for landing off-field where the terrain may not be flat near the tail rotor.

Many rotorcraft, both general aviation, transport, and military have this feature, and it may even be required by regulation (see 14 CFR 29.411 for transport category rotorcraft).

Here is the tail rotor guard on a Robinson R44:

Source: Airport-Data.com

While technically the same as in the original question, I do not believe the R44 rotor sweeps below the vertical fin. The Red/White guard protects the blade while the "stick" on the fin keeps the fin from contacting the ground. It may be possible to contact the rotor if landing on soft earth or tall grass...

You can search through Google Images to find many examples of rotor guards.


To add to the above points...
Circling Approaches are used when the Approach you want to use and the runway you want to use are not aligned with each other. Say for instance, you are arriving to the terminal area from the North. The runway you want to use is from the South (probably due to wind). You want to get down to the ground ASAP. You can get cleared to approach the airport using an IAP with a Southbound Final Approach Course. They will also clear you to circle the field in a certain direction. We will use East in this example. You will then get clearance to land on the Northbound (from the south) runway. A play by play would be to:

Follow the full procedure for the IAP with the 180° Final Approach Course.
Once you reach your Circling Minimums, maintain you’re altitude, and turn 30° to 60° to your left.
Turn back to your 180° heading in time to stay no more than 1.3 miles away from the runway surface for Category A aircraft (unless the airport has published alternate circling distances). It would be similar to a (right in this case) downwind leg
Parallel the runway to a point where you can make a normal downwind to base turn.
Start your descent to landing
Land on runway 36

If you never get the runway environment in sight, go missed at the original MAP.
If you lose sight of the runway environment at any time during your circling maneuver, immediately circle back over the runway to fly above it on your missed approach course. And go missed. Remember, the safest place in the airport environment is directly above the center of the runway.

One thing to be aware of on Circling Approaches is that the Circling Minimums are typically below Traffic Pattern Altitude. You will be flying slower and closer to the ground in the airport environment than you are used to. Caution must be exercised.

Also, the Circling Approach does not have to be a complete 180° turn around to land. It could be in any direction.

Finally, some approaches only have Circling as an option. This is due to the approach itself not being aligned with the runway. In the example below, the runway is aligned 179° and 359° magnetic.


Why are the windshield wipers in the A320 power-up checklist?

For the same reason you should turn your wipers off when you shut off your car (since very few people go through a power-up checklist in their car...):

Running the wipers on a dry windshield can damage both the wiper and the windshield as the dry blades drag small particles of dirt, grit, rocks, etc across the windshield. These particles can tear up the rubber of the wiper, and they can scratch the windshield. Dragging dirt and rock particles across a wet windshield isn't inherently good for either wiper or screen, but the water acts as a lubricant and significantly reduces the damage potential.

It's far cheaper to print an extra line in the check list and have the pilots take 5 seconds to check it than it is to replace wiper blades and windscreens.


Who should design the nozzle of jet engines on aircraft?

I suspect there will be some collaboration between the two (as the nozzle partly determines the performance of the engine), but this is primarily the domain of the aircraft designer. Only he/she knows the (aerodynamic) specifics of the integration of the power plant on the aircraft and is able to make a proper trade-off, for example regarding ground clearance.

A textbook example of that is the integration of the CFM56 on different aircraft. The Boeing 737 uses flattened nacelles, whereas the nacelles are circular  on the A320-family. The flattened ones are structurally less efficient, but at aircraft level, it was an easier/better option than increasing the landing gear height. (This problem, by the way, is still haunting the 737-series. A recent innovation featured on the 737 MAX-10 extends the landing gear using a new lever to prevent the tail from scraping the runway on rotation, another problem of a shorter landing gear.)


There were a series of RWY overruns during the days of the first group of jet airliners (early to mid 50's), possibly 3 within a 12 month period. Mainly early rotation resulting in the airplane stalling during the takeoff roll at full thrust. Such accidents caused review of the take off maneuver and birth of the RTOW (Regulatory Take Off Weight) calculations.
A description of 2 cases, 26th Oct 1952 and 3rd Mar 1953


What's the minimum roll rate a commercial airliner would have with maximum aileron deflection?

The achievable roll rate depends on altitude. At sea level, big aircraft have very low roll rates, because their roll damping is very high due to the large wingspan. Roll damping goes up with the square of the wingspan, whereas the aileron moment grows linearly with wingspan.

If the aircraft flies high enough, the roll rate will go up inversely to the change in density. This is because the flight speed increases inversely with the square root of density, so the same roll rate will cause less change in the local angle of attack on the outer wing (which is the mechanism which causes roll damping). Thus, in 12 km altitude the roll rate will be twice of what it is at sea level (at the same CAS). That is why large airliners have special high-speed ailerons at midspan: They suffice for control, and using the outboard ailerons would stress the wing a lot more. Also, outboard ailerons on high aspect ratio wings cause considerable torsion, such that the wing twist from aileron deflection will reduce aileron effectiveness. Inboard ailerons are much less affected by this effect.

I would wager to say that any airliner will be perfectly capable of 15°/s roll rates if you deflect the outboard ailerons (without overstressing the wings).

The high altitude research airplane Strato 2C had a roll rate during approach of only 2°/s! This was no real problem, because the large wing (56.5 m wingspan) would not be affected by gusts when the aircraft flew lower than approx. 30 m. The turbulence is so small scale close to the ground that the gusts would average out over the large wing, and the aircraft calmed down when sinking below 30 m, even in gusty weather. At 18 km altitude, however, it handled almost like a fighter aircraft.


In an Airbus, if the AOA sensor fails and the computer pitches the plane down, can the computer still only pitch down 10 degrees maximum?

The answer below is for the A320, as this is the only Airbus manual I have access to.

  would it go into a ballistic, unrestricted and dangerously steep dive

It'd likely stop somewhere before that. "Abnormal attitude law" engages when:

Bank angle above 125°
Pitch above 50° nose up or below 30° nose down
KIAS below 60 to 90, or above 440
Mach above 0.91
AoA above 30° to 40°, or below -10°

I believe the FAC will also give up at some point as the computed KIAS is so far away from what is measured. If it is a double ADR failure or double FAC failure it will go down to Alternate Law. If it is a triple failure it would go to Direct Law, as was the case of GXL888T.


What are the drawbacks of being a helicopter and fixed-wing pilot at the same time?

In case of an engine failure, the fixed wing pilots natural reaction is to push forward to lower the nose, then look for the correct glide airspeed. A helicopter pilot in most engine failures should pull back (although not agressively) to load the disc and restore, or increase rotor RPM.  Maintaining rotor RPM is the only way to get to the ground safely so flaring is an instinctive reaction trained in.  You don't look for airspeed or rotor RPM.  You dump the collective and flare, then have a look at airspeed and RPM.  Pushing forward will reduce rotor RPM which in some flight phases and some helicopters might not kill you but in many helicopters at altitude may well kill you.  In addition, a stall buzzer will prompt the fixed wing pilot to push the stick forward and increase power, which in a helicopter means pulling the collective.  In a helicopter the low rotor RPM buzzer sounds just like a stall warning but pushing the stick forward and pulling the collective will almost certainly kill you.

Another action that has to be instinctive is to stick in a boot full of right pedal (counter clockwise rotor) which is totally alien to a single engine fixed wing pilot in an engine failure and completely the opposite of what a twin engined fixed wing pilot might do, who will naturally "step on the failed engine".  In a helicopter, that can get you into a very bad attitude rapidly from which it might be impossible to recover.

Negative G in an aircraft is not a problem. In a 2 bladed helicopter, you must gently pull back to reload the disc.  Pushing forward has a real risk of a blade chopping off the tail or hitting the canopy. It might also cause "mast bumping" which can cause the rotor to separate from the aircraft.  Too many helicopter pilots have been killed this way. Most helicopter pilots avoid -ve G.  The main point here is that you do not push the stick forward to level out from a climb.  The instinctive reaction for a helicopter pilot is to to pullback as soon as they feel the slightest hint of rising out of their seat.

In a helicopter, to accelerate, you push the stick forward then increase power to maintain altitude or climb.  In an aircraft, you increase power, then push the stick forward to maintain altitude.

A running landing, and not a hover landing, requires you to push the stick forward to level the skids.  A fixed wing tricycle gear pilot wants to pull the stick back to flare which again, might chop off the tail.

Keeping trim (balance) is a function of power and not direction of turn.  It is perfectly possible to make a properly executed balanced turn in a helicopter with the opposite pedal pushed in.

Helicopters can slow down with a nose down attitude and you take off by pushing the stick forward to accelerate.

I'm sure there are others which I've forgotten but I think these are the main things and, most importantly, as I've shown, trying to fly a helicopter like a fixed wing can be deadly.

In summary, flying helicopters is very different to flying fixed wing and you need different responses which need to be intuitive, especially in emergencies.

My gut reaction response is that it is easier to transition from helicopter to fixed wing and that the lower time pilots will find it easier because the years of experience and muscle memory are not there.


How do most fighters slow down after landing?

The primary (and most effective) method to slow the jet down is aerobraking.

In the T-38 at ~130 knots full aft stick is applied at a rate that prevents the jet from becoming airborne again.  The stick will be back towards the seat pan.  Fly the nosewheel down to the runway at ~100 knots and apply wheel brakes.

In the F-16 the max aerobraking occurs at 13 AOA with speed brakes extended.  You do not want to exceed 15 degrees of pitch angle to prevent scraping the burner can and speed brakes.  The speed brakes will not fully extend while the nosewheel is not on the runway (however, it can be overridden but increases the possibility that the speed brakes will scrape).

In either case you do not want to let the nosewheel fall.  You also do NOT apply wheel braking until the nosewheel is down.