What are the requirements for a PPL to upgrade from SEL to MEL?

The appropriate paragraph of Part 61 of CFR 14 is 61.63 (emphasis mine, the 'unless' part does not apply in your case):

  (c) Additional aircraft class rating. A person who applies for an
  additional class rating on a pilot certificate:

  (1) Must have a logbook or training record endorsement from an
  authorized instructor attesting that the person was found competent in
  the appropriate aeronautical knowledge areas and proficient in the
  appropriate areas of  operation.

  (2) Must pass the practical test.

  (3) Need not meet the specified training time requirements
  prescribed by  this part that apply to the pilot certificate for the
  aircraft class rating sought; unless, the person only holds a
  lighter-than-air category rating with a balloon class rating and is
  seeking an airship class rating, then that person must receive the
  specified training time requirements and  possess the appropriate
  aeronautical experience.

  (4) Need not take an additional knowledge test, provided the applicant
  holds an airplane, rotorcraft, powered-lift, weight-shift-control
  aircraft, powered parachute, or airship rating at that pilot
  certificate level.

So, to answer your question, no, you do not need a cross-country, you do not need any solo time in a multiengine airplane, either. All you need is a sign off from your instructor.


What visibility and cloud clearances are required for airplanes conducting visual approaches?

This depends:

Under part 91, you just have to remain clear of clouds and have a minimum of a 1,000 ft. ceiling and 3 SM visibility.

Commercial operations (121 and 135) are further restricted by their Operations Specifications and have to maintain VFR weather minimums appropriate for the airspace that they are in (among other things, see below).

Here is an excerpt from the AIM (there is more details there for different operations, with the differences between controlled and uncontrolled fields, etc.)

  5−4−23(a). Visual Approach

  a. A visual approach is conducted on an IFR flight plan and authorizes a pilot to proceed visually and clear of clouds to the
  airport. The pilot must have either the airport or the preceding
  identified aircraft in sight. This approach must be authorized and
  controlled by the appropriate air traffic control facility. Reported
  weather at the airport must have a ceiling at or above 1,000 feet and
  visibility 3 miles or greater. ATC may authorize this type approach
  when it will be operationally beneficial. Visual approaches are an IFR
  procedure conducted under IFR in visual meteorological conditions.
  Cloud clearance requirements of 14 CFR Section 91.155 are not
  applicable, unless required by operation specification.

The Part 135 Ops Spec for this contains the following requirements for a visual approach:

  b. Terminal arrival IFR - Visual approach or a Charted Visual Flight
  Procedure (CVFP).
  The flightcrew may accept a visual approach or a
  CVFP provided all the following conditions exist. The flightcrew may
  not accept a visual approach or a CVFP unless the limitations and
  provisions of subparagraph f. of this operations specification are
  met.

  (1) The flight is operated and remains in Class B, C, or D
  airspace, within 35 miles of the destination airport in Class E
  airspace, or the airspace beneath the designated transition area.

  (2)
  The flight is under the control of an Air Traffic Control (ATC)
  facility.

  (3) The flightcrew must maintain the basic cloud clearance
  as specified in Section 91.155.

  (4) For a visual approach without a
  CVFP - The flightcrew must be able to establish and maintain visual
  contact with the airport or maintain visual contact with the traffic
  to be followed as directed by ATC. In addition, the following
  provisions and weather conditions at the airport during the approach
  must be met:

  (a) Reported visibility must be as specified in Section
  91.155, but not lower than a visibility of three miles and reported ceiling must be 1,000 feet or greater, or

  (b) When in the terminal
  area with the reported visibility not lower than three miles and
  ceiling not reported, the flightcrew may continue to a landing if the
  runway of intended landing is in sight and the flightcrew can maintain
  visual contact with the runway throughout the approach and landing,
  and

  (c) Ceiling and cloud clearance must be as such to allow the
  flightcrew to maintain the minimum altitudes prescribed in Section
  91.129, 91.130, or 91.131, as applicable for the airspace class in which the flight is operated.

  (5) For a CVFP - The flightcrew must be
  able to establish and maintain visual contact with the airport or the
  charted visual landmark(s) for the CVFP throughout the approach and
  landing. In addition, the weather conditions at the airport at the
  time of the approach must be reported to be at or above the weather
  minima established for the CVFP, but never lower than the VFR landing
  weather minima stated in Section 135.205 in uncontrolled airspace.

  ...

  f. Special Limitations and Provisions for Visual Flight Rules. All VFR operations authorized by this operations specification shall be
  conducted in accordance with the following limitations and provisions.

  (1) The certificate holder must identify obstacles and use airport
  obstacle data which ensures that the performance requirements of Part
  135 are met.

  (2) The weather conditions must allow the flightcrew sufficient
  visibility to identify and avoid obstacles and safely maneuver using
  external visual references and to maintain minimum altitudes.


I think the answers so far neglect the curvature of the paraglider sail. Changing the lift at the tips creates an imbalance of the side force caused by the downward pointing tips. This side force will pull the sail sideways and cause the sail-pilot combination to roll.

To illustrate my point, I shamelessly copied this picture and added vectors perpendicular to the sail surface, like this:

Now you will see why I used a photo: The tips of the sail are almost vertical so the side force caused by pulling the local trailing edge down has a sizeable lever arm with the center of gravity (which I assume to be near the pilot's head). @Ken's graphical representation hides this detail and fails to show the lever arm.

This side force will do two things:

It pulls the sail sideways so it will shift away from a position vertical over the center of gravity.
It causes the whole sail-pilot-arrangement to roll, in this case clockwise (from the perspective of the observer).

Next, the increased drag on the pulled-down side will retard this part of the sail, adding a yawing moment and yawing rotation which will now stabilize the bank angle. The whole paraglider turns. With the banked paraglider the side force component of the lift force compensates the centrifugal acceleration (rotating system of reference) rsp. creates the centripetal acceleration (fixed system of reference) which keeps the yaw rotation alive.

Also here the rolling motion is started by a lateral shift of the lift vector, but the vertical component of lift counteracts the desired rolling motion. Only the lateral force, which dominates due to the inclination of the sail, is responsible for the rolling moment.

Exiting the turn is achieved by doing the same, only in reverse.

Now for pitch control: Pulling the trailing edge down on both sides increases camber and lift, so the paraglider rises and the added drag retards the sail. This causes a pitch-up motion around the center of gravity and slows the paraglider down further. Relieving tension on the risers reduces camber, lift and drag so the sail accelerates and the whole paraglider pitches down around its center of gravity.

Therefore, any rotation is around the center of gravity. This does not need any hypothetical pendulum movement or "pendulum effect", which does not exist and is a fallacy anyways.

Oh, and one last word for the believers in the cult of the pendulum effect: I don't care that you downvote what you don't understand. Please try and argue logically and while observing the laws of physics. This, however, will involve the clear danger that you will lose your faith. Apologies for any loss of direction in your lives. That direction was wrong, anyway.


Why are the first sounds of an approaching enroute airliner low frequency, booming ones?

The air attenuates high frequencies more than it does low. Thus, lower frequency sounds travel farther, so you hear them first. Also, longer wavelengths will appear to "bend" around obstacles more than ones with shorter wavelengths, so buildings around you will in many cases develop acoustic "shadow" zones for higher frequencies as those buildings' dimensions are significantly larger than their wavelengths.


How has afterburner design changed since its inception?

This article suggests that they have. To name a few:

alluding to improvements in fuel diffusion
adding additional igniters downstream of the first to even out the burn
vectoring improvements to better keep the superheated gasses in the center and avoid overheating the structure at the sides
introducing cool air in a ring around the superheated exhaust stream to aid in a smaller thermal footprint
incorporation of stealth materials


Do Grumman F-14s, Panavia Tornados, and other swing-wing airplanes count as "fixed-wing aircraft?"

Yes - they are still considered fixed wing aircraft. Just because they have variable-sweep sections doesn't change what type of aircraft they are; their aerodynamics, behavior, and performance characteristics are still squarely in the 'fixed wing' category.


Is a pilot's instinctive reaction to a stall counter-intutive?

The correct way to recover from a stall is counter intuitive, not because pilots are trying to climb, but because the nose of the airplane drops due to the loss of lift and aircraft design.  99.999% of the time (when the aircraft is not in a stall), if the nose drops, you simply pull back in order to raise it and this muscle memory is built over time.

Unfortunately, if the aircraft has stalled, pulling back will only worsen the situation and you need to push forward in order to gain sufficient airspeed for a recovery.

Yes, stall recovery is taught in both primary training, and during simulator training for pilots, although not typically to a full stall in the simulator.  Instead, the aircraft is slowed to the first indication of a stall which may be a stall warning system instead.  At this point they are expected to apply the correct stall recovery techniques recommended by the manufacturer / their SOP's.

There is a fairly large difference between recovering from a stall in a training environment because you know that it is coming and already know what you are going to do when it happens.  A large part of stall training is for stall recognition so that hopefully if it were to happen outside the training environment, the pilot will recognize the warning signs before it happens and can apply the proper stall recover technique before the aircraft enters a full stall.

Unfortunately, out "in the real world" most unplanned stalls that occur happen because the pilot is distracted by something else and they aren't expecting it. That lack of anticipation sometimes causes them to fall back on muscle memory and pull up just because the nose fell without realizing what happened.  This can be more likely when the stall doesn't happen quite like it does in training.  In some situations there may be fewer warning signs, or a component of the stall warning system isn't working as expected and can delay the realization that they are in a stall.

For more information on what a stall is and why pilots practice them, see another question that was asked before here: What happens when an airplane stalls and why do pilots practice it?


Apache is pure attack helicopter with just two crew. Hind is a mixed role attack and light transport helicopter with additional room for 8 troops. Different role, different size.


Why does a hovercraft lift blade look one way, but a propeller another?

Because lift propellors need to provide static pressure to inflate the airbag and hover. This means more fan blades to stop backflow.

The thrust propellors need to provide force which is a combination of static pressure and airflow but relies mostly on airflow. This means less fan blades to facilitate large airflow.


What is the difference between placing wheel chocks on the outer wheels as opposed to the inner wheels of the main landing gear?

If the inner wheels are chocked, the ground crew person would likely have to place their arm/hand in the path of the wheels to grab the rope and pick up the chock.


Is there a significant difference between the jet blast from Airbus and Boeing?

Probably not.

Airbus and Boeing aircraft may even have the same model of the engine. For instance,  2.4 m diameter Pratt & Whitney PW4000 is used on Airbus A310-300, A300-600 and also Boeing 747-400, 767-200/300. General Electric CF6-50 is used on both Airbus A300 and Boeing 747.

I would expect much more differences between jet blast from of Airbus A380 versus Airbus A220. A220 is near ten times lighter (575 vs 60 t).


What names are used for certified "mechanics"?

From Wikipedia:

  An Aircraft Maintenance Engineer (AME), also Licensed Aircraft Maintenance Engineer (LAME or L-AME), is a licensed person who carries out and certifies aircraft maintenance. The license is widespread internationally and is recognised by the International Civil Aviation Organization (ICAO).


How is a horizontal stabilizer attached to the fuselage and works as a trimmable Horizontal Tail as well?

Fighter aircraft usually have their tailplane connected to the fuselage with a single pivot joint, as visible in this F-15 drawing:

Passenger aircraft often have a horizontal tailplane which is a single part, and as such, the entire stabilizer is being trimmed by an actuator around a pivot, as can be seen in this 727 drawing. The actuating system is different on newer aircraft, but the idea is the same.


What constitutes an "emergency" in flight procedures?

There is a really good explanation of emergency situation over at the SkyBrary:

An emergency situation is one in which the safety of the aircraft or of persons on board or on the ground is endangered for any reason.
An abnormal situation is one in which it is no longer possiible to continue the flight using normal procedures but the safety of the aircraft or persons on board or on the ground is not in danger.
Emergency or abnormal situations may develop as a result of one or more factors within or outside an aircraft, for example:

Fire on board the aircraft;
Aircraft component failure or malfunction (e.g. engine failure, landing gear malfunction or loss of pressurisation);
Shortage of fuel (or other essential consumable substance);
Flight crew uncertain of position;
Worsening weather;
Pilot incapacitation (e.g. as a result of illness);
Aircraft damage (e.g. as a result of collision, bird strike or extreme weather;
Illegal activity (e.g. bomb-threat, wilful damage or hi-jacking).

So in short, anything that puts the flight in danger can be considered an emergency.

Is ATC allowed to judge what is or is not an actual emergency, or must they prioritize any aircraft declaring one?

If the pilot declares emergency, ATC will provide assistance and support to the flight without judging whether it is an actual emergency or not. ATC cannot know in most cases, nor are they really required to analyse the situation to come to that conclusion. Their whole responsibility is to ensure the flight receives all required information and support to either end the abnormal/emergency situation or land at a suitable airport.

Does fault or blame matter at the time the emergency is declared? Will ATC de-prioritize a situation that is obviously the pilot's fault, like flying into the only cloud for 50 miles in any direction?

No, they will not de-prioritize based on the type of emergency. Even if a pilot flew VFR into IMC conditions, he is still in a life-threatening situation from which he needs to recover, so assigning blame or guilt is not helpful here, nor would that be the ATC's job. This is the Civil Aviation Authorities' responsibility, once the flight is back in safe conditions. ATC may file a report, though, but not during the emergency, but as an aftermath.

Is there anything you still can't do as PIC in an emergency situation? Apparently in an emergency you can do a lot of things that would get your license pulled in any other scenario, like violating separation minimums, entering airspace that's normally off-limits like R-zones and Class A space, running on instruments without a rating, etc. While these things are still dangerous, it is apparently the pilot's prerogative to resolve the emergency however he can. Is there anything a plane declaring an emergency still must do other than fly the plane, or conversely something he still cannot do like get too close to Air Force One?

Technically, once you have declared an emergency, you can do whatever is required to keep the flight safe and prepare for an emergency landing. If you need to enter otherwise controlled or restricted airspace, this will be made possible by ATC via coordination with adjacent units. Without knowing FAA regulations on this specifically, I would daresay that distress traffic could have priority over the Air Force One.

After declaring an emergency in flight, what should be done after the plane's back on the ground (hopefully safely)?

Unless your CAA or their respective investigative service is not already waiting for you, you should remain with your aircraft (unless being treated for medical issues and taken to a hospital) and wait for them to arrive. If in doubt, you can call the police and they will notify the relevant authorities.


Why do some airports have to put 2 jetbridges on one aircraft?

It is not strictly necessary. But it is done in order to save time.

More points of passenger loading leads to faster loading, potentially reducing delays, airport charges etc.
In some cases, there is a seperate jet bridge for first/business class.
For large aircraft like A380 etc, is quite common to use multiple jet bridges as use of a single one may lead to quite large loading time.


Would TCAS ever issue a "climb, climb!" RA that would stall a jet with a low airspeed?

The FAA publishes Advisory Circular 20-151A, which says in section 2-17(a):

  Because TCAS II can only accept a limited number of inputs related to
  airplane performance, it’s not possible to automatically inhibit CLIMB
  and INCREASE CLIMB RAs in all cases where it may be appropriate to
  inhibit such RAs. In these cases, TCAS II may command maneuvers that
  may significantly reduce stall margins or result in stall warning


Does an overhaul reset the 'life limit' of a turbine engine?

All nations operate with very similar rules. For the US, the short answer is nearly all turbine powered aircraft operate under part 119/121 (air carriers) rules. Each company has maintenance and operations specifically tailored and tied to their operating certificate and so it depends on the approved procedures of that companies operating certificate.

In your example, no mention is made of the part being "rebuilt", therefor the use of the part will continue where the previous use left off. The card says it is a "life limited" part so it's use will run out according to operating hours, calendar time from first installation, or number of operating cycles, etc. The parts life span is set by the mfg or operating certificate rules.

For example if a part  has a 7yr calendar "life limit" (like some seat belts) and the part was installed January 1, 2015 then removed 10 days later, the part would become worthless Jan 1, 2022 even though it was used less than 1 month - the clock starts ticking from it's first use.

This card says the part has a 15yr calendar limit which will usually be in addition to other limits. It will either be limited from it's first date of use, or it's date of manufacture (whether the part is used or not). Once again, exactly how it should be interpreted will be based on the mfg or operating certificate rules.

Most life limited part life spans are TIS (time in service) and therefore expire after a certain number of hours of operation. If TIS for the turbine blade is 5000hrs and airplane "A" used it for 4000hrs, it could remain on the shelf indefinitely - be re-installed on airplane "B" and used for an additional 1000hrs. The card is designed to keep track of the dates and how long the part has been used - TIS, calendar, cycles, or whatever.

[I'm guessing for this particular part, but for many critical parts on helicopters and turbines a combination of TIS and calendar are used. So it would be something like 5000hrs TIS or 15yrs calendar from date of mfg - whichever comes first. Even if it sat on a shelf and was never used, it would have to be destroyed when the 15yr limit was up.]

NOTE: Due to a problem of expensive time limited parts being counterfeited, re-sold, or re-used, the FAA requires companies using life limited parts (once the service life is up) to make the part unusable by returning to a mfg, defacing, or destroying it.

Parts

On any US registered aircraft, "overhaul" and "rebuild" have very specific legal and maintenance meaning. "overhaul" per FAR 43.2(a) means "Disassemble, cleaned, inspected, repaired, reassembled, and tested to service limits", whereas Rebuild FAR 43(2)(b), 43(3)(j) means "disassemble, clean, inspect, repair, reassemble, and test to new part tolerances".

"Overhaul" means repair or fix the old part and does not change the wear or life of a part.

"Rebuild" means to make a "new" part out of the old one and the part's life is started over - "zero time". The part is treated as if it is a brand new part and many mfg even stamp a new serial number on the part.

Entire Engines

The above FAR's relates to "parts". For an entire engine, the FAA's AC-43-11 (Reciprocating Engine Overhaul Terminology and Standards) goes into great detail on what the terms mean and who may perform the work.

Why would AC-43-11 (entire engine) be limited to reciprocating engines? Because nearly all turbine engines are operated under Part 119/121 (not 91 or 135) operators. Part 119/121 receive FAA approval on a company by company basis and each company has maintenance and operations specifically tailored and tied to their operating certificate.

When a part 119/121 company has their operations approved, the FAA's standard practice is to hold them to all existing FAR's unless they show a "as good" or "better" way of maintaining the same level of safety. So, the spirit of AC-43-11 would be applicable unless some exception was given.


What kind of supervision do new captains get on their first flight?

After a new captain is done with schoolhouse training (classroom and simulator) they will fly on-line as a captain and will have a training captain in the right seat.  After some number of flights (for me it was a 4-day pairing) you will be joined by a check airman in the jumpseat and have a line check.

Once you pass the line check if you are a first time captain you are a high minimums captain for your first 100 hours and then a normal captain. During high mins time you are subject to a few restrictions in approaches you can fly. All the flying after the line check is with normal (low time) first officers.


Is it really required for a pilot to have good eye sight?

Here are the guidelines regarding medical qualifications (including eyes) for obtaining a U.S. medical certificate:

From the FAA's "Guide for Aviation Medical Examiners" (Link is here)
From FAR Part 67- MEDICAL STANDARDS AND CERTIFICATION (Link is here)

Hope this helps.


How does a ring paper airplane fly for a long distance?

No takers? Then I'll bite.

This question addresses how paper airplanes generate lift. This lift is caused by higher pressure on the lower side and lower pressure (suction) on the upper side, and if both are added up, the chordwise pressure distribution is shown below:

Flat plate pressure distribution (picture source)

If you collect all the local forces in one point, the lift acts at a quarter of the wing's chord. That is why the forward half of the paper which in the end will be bent into the ring needs to be folded onto itself: The center of gravity of the wing is also at one quarter of chord. Thus, the lift and the weight will act a the same station and no pitching moment results.

To achieve a flight distance of 25 m, your friend threw the ring with some force to give it a high initial speed. This speed would allow it to create enough lift with very little angle of attack, so it did not suffer from flow separation initially. This resulted in low drag and the high launch speed gave the ring some kinetic energy.

Friction slowed the ring down gradually, but the decrease in lift at lower speed was compensated by a gradual increase of the ring's angle of attack. Why would the angle be just right to prevent the ring both from rising and dropping, you might ask? Any imbalance between lift and weight would add a vertical acceleration which would immediately change the angle at which the ring hits the flow. Its chord length and inertia would prevent it from rotating nose up or down, so it would pretty much stay on its initial path until most of the speed was eaten up and the angle of attack was so high that separation sets in. At this point, the drag would go up and speed up the deceleration process, and the ring would sink to the ground.


What's the definition and the meaning of “soft dirt runway”?

The are many types of runway. But the basic are paved, unpaved. Paved runway may be in form of rigid and flexible. Rigid is one which is made of concrete.Flexible runway are made of like bituminous. And the soft runway is one which is not paved. The runway may be on ice sand or water. But generally for a soft runway we can assume it as a grassy runway.    I did not find anything specific about the dirty runway. But in general we can think dirty means the runway conditions which are not so good for the engine when using of reverse thrust , applying brakes or maintaining direction while on take off roll.


Your question is too general. It would be more helpful if you specify the flight conditions and the types of aircraft that you are interested in. For instance, give us a range for the Reynolds number.

However, I have a fast answer for both high and low Reynolds. For high Reynolds ($Re \geq 10^6$), NLR-7301 (main and flap) and MDA (slat, main and flap) are airfoils for which you can find published experimental and numerical results (NASA, AGARD, etc.). For low Reynolds numbers ($Re < 10^6$), there are really not many experimental results that I know of. In fact, I was once lucky enough to find an airfoil catalog of F.X. Wortmann (printed format and in German) that had aerodynamic results for some fowler flap airfoils. Also, during my diploma thesis, I worked on an aerodynamic method for the fast analysis of multielement low Reynolds airfoils (based on XFOIL) and thus I used my method to analyze certain multielement low Reynolds number airfoils that I designed (starting from the S1223 airfoil of Selig). The document can be found here but it is written in Greek. Nevertheless, you can check the figures (NLR-7301 is also included in my study and you may trace the relevant references for further info).


Can quadrotors be used for commercial passenger flights?

The three most important factors in passenger air travel are safety, safety & safety. So that is where most of the questions will focus on, and where most of the engineering effort will be put into. Couple of questions:

Artificial stability: what happens if the stability circuit breaks down?
What happens if one of the motors fails, for instance one of the big aft ones? Can the craft still stay upright or does it topple over? If it stays upright, can the remaining motors still provide enough lift to keep the craft flying?
What happens if the battery runs down or fails during flight?

These are redundancy problems that need to be solved. Any system that causes an unsafe situation when it fails must have a redundant layout. So at least a penticopter instead of a quadcopter: upon engine failure, 4 props can safely land the craft.

The redeeming feature for quadcopter is ease of manoeuvring with variable rotational speed per propeller, instead of having to make a swash plate arrangement. But light single rotor helicopters have been around for a long time and the technology is mature - I don't see what particular problem the quadcopter can solve that for instance an R44 might have.

On your questions:

Q1 Noise: yes electric motors are nice and quiet, and the shrouds shield noisy tips in most directions.
Q2 Regenerate energy: it can only do that during authoritative descent, which would be frighteningly fast due to the relatively small total rotor disk area.
Q3 Not a UAV: sure, tilt rotors exist already

Edit: the propulsion system you draw is not so revolutionary. If you travel to Niagara Aerospace Museum, you can see the X-22, built in 1967.

From a comment:

  •I have had one rotor fail (larger) and be able to land the aircraft safely, even maintain a hover but not climb. Aircraft does not topple in simulations, software used Xplane 10 and 11 ultra releastic. – Robert Gomez

That is a claim that sounds hollow. It depends on the location of the centre of gravity: if it is within the triangle formed by the remaining three rotors, it will stay upright. Picture an X cross connecting fwd left - right aft, fwd right - left aft.

If CoG is behind the middle point of the cross, either one of the front rotors can fail and the craft will fly stable on the remaining rotors, because CoG is within the triangle formed by the operational rotors. But not when one of the aft rotors fail.
If CoG is forward of cross centre, either one of the aft rotors can fail. But not a front rotor.
If CoG is exactly at cross centre, the rotor diagonally opposite the failed rotor cannot exert thrust otherwise the craft will roll. So one rotor fails means only two can be operational.


What is the rationale behind very short distance flights?

Because air travel is the best option in those places.

The shortest commercial route in the world is between Westray and Papa Westray in the Orkney Islands, a distance of 1.7 miles.

If you see the list of short routes, almost all of them are between islands. That instantly rules out buses and the like unless a bridge is built, which in most cases is not commercially viable. One can use a boat or ferry, but in most cases, the sea may not be deep enough or calm enough.


where can i get a aviation map of korea with the moes, and highways and vectors

Those are available in section ENR 6 of the South Korean AIP. Direct link.


Can the back tail of an airplane move the neutral point backwards?

Yes you can, the tail volume needs to be such that the neutral point shifts aft of the CoG. This answer has some details - positive lift from the tailplane, but it must never stall!

More details about tailplane design in the answers to this question. The absolute safest config at a wide range of CoG is the CoG in front of the Centre of Pressure of the main wing, and a downforce from the horizontal tail.


What is this jetliner seen in the Falcon Crest TV series?

It is a Grumman Gulfstream II business jet, not an airliner.
The oval windows are very unique to both the Grumman Gulfstream I business turboprop, and Grumman Gulfstream II business jet. The small engines are Rolls Royce "Spey" engines meaning it is either a Grumman Gulfstream II or Gulfstream III. (later Gulfstream versions had the larger "Tay" engines) The lack of wing tip "winglets" means it is has to be a Grumman Gulfstream II.
Grumman Gulfstream II


Does an accelerating airplane also start climbing?

You assume that three of the four forces are constant. This is not quite right: Only the mass is given, all the other forces are variable.

Thrust $T$: Changes with throttle setting. Also, thrust can vary with flight speed $v$ in a way that can be expressed as $T \propto v^{n_v}$.
Lift $L$: Depends on speed and on angle of attack $\alpha$, as in $L \propto v^2 \cdot (\alpha - \alpha_0)$. The accelerating airplane is held level by gradually reducing the angle of attack, such that lift exactly equals weight. The elevator is the instrument for controlling angle of attack.
Drag $D$: Like lift, drag depends also on speed and angle of attack: $D \propto v^2\cdot (\alpha - \alpha_0)^2$

Your option a is the correct one: The pilot compensates by adjusting the angle of attack by gradually pushing the stick forward. If he would keep the stick (and consequently the elevator) unchanged, the airplane would climb.

Now it might be opportune to introduce the concept of specific excess power ($SEP$). This is the extra power available to the pilot, related to the aircraft weight to make it comparable between airplanes. $$SEP = \frac{P_{eff}-D\cdot v}{m\cdot g}$$
where $P_{eff}$ is the effective power: $P_{eff} = T\cdot v$. When the pilot commands more thrust than needed for level flight, the excess thrust can be either converted into kinetic energy (speed) or potential energy (altitude). If you look at the units, $SEP$ is a speed. It tuns out that it is the possible climb speed available if flight speed stays constant: $$SEP = v_z$$
In reality, the practical climb speed is smaller because the airplane needs to speed up when climbing to compensate for the decreasing air density.

The possible acceleration is almost as easy to calculate from the specific excess power: $$\ddot x = SEP\cdot\frac{g}{v}$$

Of course, a mixture of both is also possible, as is trading in one for the other. By adjusting the elevator and with it the flight path, the pilot decides what happens.


Are there any situations in which drones may legaly fly higher than 400ft?

As they say with any regulation, there’s a waiver for everything.  If you do wish to operate your sUAS at or above 400’ AGL, you are advised to contact the local FSDO in your area.  Protocol varies from area to area, but you will be required to file an request with local ATC with the dates, times and areas you intend to operate in so NOTAMS can be issued.


What are the different kinds of de-ice fluid?

Fluid Types

Wikipedia contains a good summary of the different types of fluid:

  Types

  Type I fluids have a low viscosity, and are considered "unthickened". They provide only short term protection because they
  quickly flow off surfaces after use. They are typically sprayed on hot
  (130–180°F, 55-80°C) at high pressure to remove snow, ice, and frost.
  Usually they are dyed orange to aid in identification and application.
  Type II fluids are pseudoplastic, which means they contain a polymeric thickening agent to prevent their immediate flow off
  aircraft surfaces. Typically the fluid film will remain in place until
  the aircraft attains 100 knots or so (almost 200 km/h), at which point
  the viscosity breaks down due to shear stress. The high speeds
  required for viscosity breakdown means that this type of fluid is
  useful only for larger aircraft. The use of type II fluids is
  diminishing in favour of type IV. Type II fluids are generally light
  yellow in color.
  Type III fluids can be thought of as a compromise between type I and type II fluids. They are intended for use on slower aircraft, with
  a rotation speed of less than 100 knots. Type III fluids are generally
  light yellow in color.
  Type IV fluids meet the same AMS standards as type II fluids, but they provide a longer holdover time. They are typically dyed green to
  aid in the application of a consistent layer of fluid.

  Chemical Composition

  The main component of deicing fluid is usually propylene glycol or
  ethylene glycol. Other ingredients vary depending on the manufacturer,
  but the exact composition of a particular brand of fluid is generally
  held as confidential proprietary information.

Call ahead to the airport to see what kind of deice/anti-ice fluid that they have because each one is different.

Time Limits

Every year, the FAA publishes tables which include information about how long the various deice fluids will provide protection under various weather conditions.  Here is an example table:

For this particular fluid (ABAX ECOWING AD-49 Type IV) we can lookup a specific example such as:

-10 Degrees Celcius
75% fluid and 25% water
Light Snow

This shows that the fluid will provide protection for 1:40 to 2:05. If you are delayed longer than that, you will need to deice again.  Since every part of the aircraft needs to be protected, the timing starts when they first start spraying the aircraft.  Note that other types of fluid (particularly Type I fluids) have much shorter holdover times than this, so be careful and make sure that you check!

Resources

OFFICIAL FAA HOLDOVER TIME TABLES WINTER 2013-2014
AC 120-60B - Ground Deicing and Anti-icing Program


Does FAA recommends specific maneuvers for complex endorsements?

To answer question #1:
A complex endorsement is just that. It’s an endorsement. There are not any prescribed maneuvers to receive the endorsement. But, the instructor is holding himself liable for your performance after receiving the endorsement. Primarily, the areas where that liability may prove hazardous to the instructor, their certificate and career is on every single one of your takeoffs, landings, and go-arounds after the instructor is no longer in the aircraft. The flows and checklists for that aircraft have to be consistent and second-nature to you even without the instructor’s prompting.

A 2 hobbs-hour flight from start-up to shut-down is typically the limit of learning for most people. Two 2-hour flights along with a couple of hours of ground instruction seems reasonable for satisfying your instructors confidence in your ability. That is all conditional to your actual performance. It is also a very subjective assessment.

To answer question #2:
As far as correcting someone with more knowledge and experience than yourself, that can and should be done if (big if) they are wrong. Many things in life and aviation are subjective. There can be multiple right answers. In the case that an instructor gives you a wrong answer, be courteous and cordial in your correction. But, your answer must be backed up with fact. You should question your own answer until it can be: backed up with a regulation or recommendations out of the FAR/AIM; documented from an FAA handbook, publication, advisory circular, or other official document; referenced from the POH, AFM, owner manual, or other manufacturer source; cited from a reputable source.

If the question can not be answered objectively, the answer may only be a matter of opinion, style, or personal technique. Or, it could be a quirk of that particular aircraft or environment. Either way, it would probably be best to tailor your training to the criteria of your evaluator.

Remember, your instructor is human. They are fallible. But, so are you. And, they have been doing this aviation thing safely way longer than you. But, regulations do change. Take a slice of humble pie before you have to eat crow. You both may learn something new or improve upon something old. And remember, a good pilot is always learning.


Requirements for Steady Level flight at various speeds

From a purely practical standpoint, let's say you're in a Cessna 172 (a common light aircraft often used for training) and you're in economy cruise at 2400 rpm at 6,000 feet on a standard day. According to the cruise performance chart I have here, you would be using 60% power, burning 6.8 gph, and have a true airspeed of 109 kts. You're hand flying the airplane as it has no autopilot.

Now the cute gal that you've talked into taking this trip with you mentions that she's beginning to need a bathroom. You neglected to bring along a urinal (and maybe more than a urinal is needed), so you decide to speed up to the maximum cruise speed for 6,000 feet. You consult the cruise performance chart and see that you can get 75% power at 2600 rpm. That will increase your cruise speed to 120 kts at the cost of burning 8.4 gph.

You would smoothly increase the rpm to 2600. As the power came up, you would have to hold a little forward pressure on the elevator to keep from climbing. If you're used to the airplane, you might unconsciously reach down to the trim wheel and roll in a little down elevator. In any event, you will eventually want to trim out the down elevator force you're holding on the control wheel.

If you set 2600 rpm to start the speed up, you'll notice that the rpm goes a little above 2600 as your speed increases (this is a fixed pitch propeller), so you monitor and adjust the rpm as necessary to settle on 2600 rpm with elevator forces trimmed.

If you have an autopilot with an altitude hold function but that doesn't control the power, all you'll have to do is control the power.

If you have an autopilot with FADEC, just set what you want and it will do all the work from there.


How to determine angle of bank caused by shift in centre of gravity in an aircraft?

You can't. Aircraft are not stable in roll!

Once there is an offset between the centre of gravity and the lift action line, there will be a rolling moment until the aircraft is banked at 90°, at which points the forces become perpendicular, so they can't generate any moment.

The moment will cause roll acceleration, but as the wing going down will have higher angle of attack, its lift will increase, causing opposing moment that will stabilize the aircraft at some roll rate. Which will slowly decrease as the moment between lift and gravity decreases with the increasing bank. But it will not vanish until 90° bank, so the aircraft keep rolling and end in a graveyard spiral.

If there is some roll-yaw and yaw-roll coupling, and the imbalance is small enough, the side-slip created by the incipient turn will generate enough opposing roll moment to return the plane to a dutch roll instead. But that is an oscillating motion, so you still won't have stable bank angle.


Can you flag down / contact an airplane with a handheld radio in case of emergency?

Yes, this is legal. As far as I understand, it used to be common practice, and some hiker's beacons still squawk 121.5. Nowadays, more advanced beacons are suggested, but it sounds like yours isn't working. Some police and EMT stations still monitor 121.5, too.


Hurricanes move en masse pretty slow compared to a jet airliner.
Heck even compared to a small plane. It is not a problem to fly a path around them to avoid them.  Eventually the winds and rain will impact local travel, but the hurricane must be 'pretty close' for that - how close will depend on the aircraft size.  Wind/Rain/ceilings will impact small aircraft sooner than large jet airlines that fly hundreds of miles faster.


Why are the engines of the Airbus A400M slightly tilted down?

As Jeffrey points out in his comment to the question:

  In flight, they are probably horizontal.

When that plane is at cruise conditions, it will be in a very slightly nose-up pitch attitude. the thrust line from the props will then be in the direction of travel.


For how long is an engine start clearance valid?

From ICAO Doc 4444:

7.3.1.1 Start-up time procedures
7.3.1.1.2 Start-up time procedures should be implemented where necessary to avoid congestion and excessive delays on the manoeuvring area or when warranted by ATFM regulations. Start-up time procedures should be contained in local instructions, and should specify the criteria and conditions for determining when and how start-up times shall be calculated and issued to departing flights.

Procedures should be locally implemented. If no delay is anticipated by the ATC, the controller can issue "start-up at your own discretion" (7.3.1.1.4). Of course any delay on the pilot's part that will make them miss the takeoff time, they are supposed to report that delay. After all the ground crew, for example, won't wait forever.
For Thailand:
For the start-up time procedures mentioned in Doc 4444, you need to check the AIP if such procedure is applied. For Bangkok (VTBD), for example, the AIP notes:

Starting up Procedures
Pilots are to call Don Mueang Ground on 121.9 MHz for push back and start up and should give parking stand number or location and ATIS information.
Unless other ATC restriction is imposed, the aircraft must be push back within 5 minutes from the time ATC clearance is received otherwise the ATC clearance will be cancelled.
Additionally, in order to provide a more flexible ground traffic movement, all domestic departures shall no longer be required to push back within 5 minutes after clearance received.

Which means the 5 minutes push back limit does not apply to domestic flights. The same document also lists the different procedures for each stand, for example for parking stand 21:

The aircraft may start one engine to idle power. They will be pushed back onto "taxilane B" to face either north or south behind the holding line, where remaining engines may be started. Breakaway thrust will be applied when cleared to taxi.

If unsure, always ask the ATC. If the push and start clearance is split, the ATC should specify that.


Measuring speed and altitude from personal phone midflight

Depending on the reliability of the sensors in your phone, yes that sounds completely possible. Most modern aircraft use GNSS for navigation, and your phone relies on the exact same technology.

Be aware that you will get the ground speed - see this question for further details: Why is there a difference between GPS Speed and Indicator speed?


In the physics realm $Power$ = Mass x Acceleration x distance/time

To many it means "how much throttle" , which is how much fuel/time.

"Throttle" x prop efficiency = $Thrust$

This gives you a unit of Force that can be directly compared to glide data as follows:

Potential energy Mass x Gravity x altitude loss = $Thrust$ x horizontal distance flown

This rearranged to $Thrust$ = Mass x Gravity x altitude loss/horizontal distance flown

$Thrust$ = force required for straight and level flight, expressed in "pounds or Newtons"

So if your plane weighs 10 lb and glides 5:1, you need 2 lb of thrust for straight and level flight.

One would at least double, or even triple this for "takeoff power", depending on your performance preferences.  Sufficient "takeoff power" will give a safe climb rate to avoid difficulties with downdrafts.

For example:  my plane glides 5:1 at 60 mph or around 5000 feet/minute and loses 1000 feet/minute.  At 10 lbs it was calculated to need 2 lbs of thrust for straight and level flight.

How much more thrust do we need to climb 500 feet per/minute.  Again, the glide data provides a very good estimate, 2 lbs x 500 fpm/1000 fpm = 1 lb additional or 3 lbs total at 60 mph.  Higher speeds with more drag,  or lower speeds "behind the power curve" will require more than 3 lbs of thrust.


Are airline pilots worn out at an age of 55?

My experience, speaking as a pilot who had to retire in 1999 from a small 747 carrier when the US age 60 rule was in effect, was that NONE of us close to retirement wanted to retire. More often than not, the attitude was, "It's hard to believe they actually pay us for this." We didn't want to quit; we were at the top of our game; the world was our playground. The money was also very good!

Insofar as worries of a "steep decline in capabilities of older pilots," there is no statistical evidence that I am aware of to support this, although whether there is at least some decline has been a matter of controversy. You can Google "age 60 rule" and find reams (screen loads?) of info on this. A particularly good link IMO is http://www.avweb.com/news/aeromed/181875-1.html

What makes a good air carrier captain is not so much being a good stick or quick reactions, but being situationally aware, learning what to avoid, being able to read the politics of a situation (especially in third world countries), and other things that come to one primarily through experience.

For example, when I hired on to my second 747 carrier as an f.o., I was paired with a relatively young, fresh captain. I was older, had been a 747 captain at a previous carrier, and had more hours in the airplane. We landed in Harare, Zimbabwe to pick up a charter. Our APU was inop, so as per standard procedure, we left #4 engine running to supply the pneumatic air we would need to start the other engines. However, when the ground handlers told us there would be a delay of a couple of hours, the captain ordered the engines shut down, saying that we would use a huffer to start. Both the f.e. and I simultaneously objected, both saying in so many words that we couldn't depend on there being a usable huffer in Harare. The captain ignored us and shut down the engines, believing that the capital of a country would surely have such. The fun started when he asked for a huffer to be hooked up for our start. Long story short, what would have been but a two hour delay turned into something like a 10 hour delay. It included hooking up 4 different beat up old huffers to the airplane, but even using the two best at once (the 747 can accommodate 2 hookups) failed. Finally, a mechanic worked on those two best units and managed to get enough pressure to start us.

The captain was a good stick; he just hadn't had enough experience.


Can autothrottle be used without autopilot (and vice versa)?

They can be used individually, yes. When flight directors (or autopilot) are on then they dictate what auto throttle should do. But it's not a good idea to fly manually, use auto throttle and have flight directors still on and here is why:

When autopilot is off but the flight directors are on and auto throttle is on you can select a vertical mode like flight level change or vnav and then auto throttle will take commands from that selected vertical mode. In flight level change, for example, thrust is either full climb thrust or idle thrust, which means: If you as a pilot flying don't pitch for speed then you just have throttle stuck in either full or idle and you either overspeed or stall. Not a good idea to leave flight directors on and use autothrottle on its own!
When autopilot is on but auto throttle is off then autopilot and you select a vertical mode like vnav or flight level change then you are in command of delivering thrust, so you need to advance throttle to start climbing or you need to retard throttle to descent. And if you use vertical speed mode you are in control of airspeed. So you have to monitor your climbs and descends and airspeed but it's not too bad. In the end there are other aircraft types that have an autopilot but no auto throttle.
When autopilot is not engaged and flight directors are off then auto throttle controls just speed, this is safe. Airbus' landing checklist has an item for this: "auto thrust? - SPEED".

This applies to 777, 747, 737, A320, A380 and probably (have not checked the fcoms) A350, A330, A340, 757, 767


How do you start a jet engine if the start valve is stuck closed?

Perusing the A380 Training Guide, Edition 01, 01 Sep 2008, Section 5 - Engine Starts, Subsections 5.8.6 (Engine Start Valve Stuck Closed),

  5.8.6 Engine Start Valve Stuck Closed

  ECAM actions – ENGINE MASTER OFF.
  Check MEL, and in conjunction with, advise LAE of situation in preparation for Start Valve Manual Operation.
  For Start Valve Manual Operation on Engines #2 and #4, the adjacent engine (if already running) will require shutdown, to enable LAE’s
  access to the manual start override procedure on the port side of the
  affected engine.
  As the CAB Pb on the RMP is common to the Cockpit, Ground and Cabin Crew, advise the Cabin Crew to refrain from using the Cabin Interphone
  during the procedure.
  When ready, accomplish normal engine start sequence:
  a)    Engine Start Selector to IGN/START.
  b)    Engine Master Lever to ON.
  c)    Command LAE to OPEN START VALVE AND KEEP OPEN.
  d)    At 50%N3, command LAE, START VALVE CLOSE.
  e)    Monitor engine parameters closely until stabilized.
  Advise Cabin Crew upon completion of procedure.
  In flight, only windmilling start will be available.

Glossary (correct if needed, please):
ECAM = Electronic Centralised Aircraft Monitor
LAE = Licensed Aircraft Engineer
CAB = Cabin
Pb = Pushbutton
RMP = Radio Management Panel
IGN = Ignition
N1/N2/N3 = N1 is LP (Low Pressure stage), N2 is IP (Intermediate Pressure stage), N3 is HP (High Pressure stage)
MEL = Minimum Equipment List

ECAM will display "ENG MASTER X ........ OFF" (X will be the engine with stuck valve)
(A320 display, only shows two engines, instead of four) (The message will appear in the lower left quadrant.)
Check the Minimum Equipment List (MEL) to determine if loss of engine is GO, GO IF, or NO GO, if failure is not in the MEL, it is classified by default as NO GO. Advise the on-site Licensed Aircraft Engineer (LAE) of the warning message in preparation for completing the Start Valve Manual Operation procedure.
If the engine with the stuck valve is #2 (left side inboard) or #4 (right side outboard), the adjacent engine will be required to be shutdown before commencing the manual start procedure. (This is because the engineer has to access the left side of the engine and for safety's sake the other engine, which would be gehind him must be shut down. If the fault is on the left outboard (#1) then the engineer would be on the far side of the engine from the #2 so #2 does not need to be shutdown.)
Since the Cabin Pushbutton (CAB Pb) on the Radio Management Panel (RMP) is common to the Cockpit, the Cabin Crew area AND the Ground circuit, the pilot should advise the Cabin Crew to not use the Cabin Interphone during the procedure. (If the pilot and the engineer are discussing starting the engine (or not) they don't want a flight attendant to be talking about starting pre-flight stuff at the same time, if the engineer heard the word start, he might wrongly assume it was the pilot.)
When pilot and engineer are ready, begin the normal engine start sequence with changes:

a) Turn the Engine Start Selector to IGN/START. (This is a panel from an A320, so only two engines are shown.)

b) Flip the Engine Master Lever (For the faulted engine) to ON. (This is a panel from an A320, so only two engines are shown.)

c) Over the interphone, command the engineer to manually open the start valve and keep it open. (I haven't yet looked for and found a schematic for an example engine, sorry. As shown in other diagrams/answers, it might be a socket wrench, etc.)

d) Watch the Engine Warning Display. (Again, A320, only two engines.) (This is an A380, showing N3) Once N3 is spun up to 50%, over the interphone, command the engineer to manually close the start valve.

e) Monitor the engine parameters closely until all are properly stable.

f) After the engineer has closed up the engine and vacated the area, start the other engines, if one was shut down per step 3.
Over the cabin interphone, notify the cabin crew that the procedure is complete. ( so they can resume using the interphone if needed. )
If the engine failed in-flight and upon restart a stuck valve warning was shown, all of the above would not be possible. At that time, the only way to restart the engine would be to attempt a windmill start (using the flow of air through the engine to turn the engine), there are other procedures for that.

Also, I do not yet have the engine schematics to show what the LAE actually does.


Why does the chevron-shaped engine suffer losses in thrust performance?

The chevrons need a small pressure difference between the fan flow and the surrounding air. Then they will work like small delta wings and create two strong vortices per triangle, which will help to mix fan flow and outer flow. This mixing is responsible for the reduced noise, because it will distribute the kinetic energy of the fan flow over a bigger mass of air.

This mixing by itself uses up some of the energy of the fan flow, and thrust is produced by the conversion of the pressure increase due to the fan into kinetic energy. With the chevrons, a little of this kinetic energy is now spent for mixing and cannot contribute to thrust anymore. Hence the reduced efficiency.

You're right to assume that less sound should mean more thrust. In fact, the sound energy is not evenly distributed over all frequencies, and by adding some noise at frequencies with low noise contribution, the peaks at the lower frequencies which contain most of the noise can be lowered.


This answer is for the US. A parachute is required of everyone when the aircraft is carrying someone who is not a crew member.  The maneuver must not be prohibited by the aircraft flight manual. (Or must it be specifically permitted?)   (Future edit needed.)  And of course you must not exceed the permitted airspeed and G-load parameters.

There is no relation to the license (certificate) the pilot holds.

Actually, this related answer indicates that the airplane or glider must be in the "acrobatic" category: What are the US definition and restrictions on aerobatic flight?. But it's not clear what specific FAR is involved, if any.


What dictates the prop RPM used during cruise?

"Dictate" is the wrong word.  Within the ranges listed in the POH, the pilot may select rpm/MP settings as he pleases to meet other criteria.

Charles Lindbergh instructed many WWII pilots in a technique to extend range, by flying with low rpm and high manifold pressure.  This extended range by reducing the "pumping losses" required to maintain low manifold pressure.  Over long distances this technique did extend range considerably.

Secondly, lower rpm reduces noise - remember that the propeller is the largest contributor to a propeller-driven plane's noise signature.  This is important in the terminal environment where the noise can affect the ground, but it also affects in-cockpit noise regardless of altitude.

This answer does not contradict the former answer, but it extends it to point out that there are other important factors that the pilot should consider in selection of engine operation parameters.


Do aircraft technicians need additional certifications to work in other countries?

I don't have personal experience, but this is absolutely something you can do.

Unfortunately many countries do not have the exact same standards or licensing scheme, so often your licence is not automatically converted, but you rarely need to start from scratch.

For example, if you wanted to come to Australia, you would need to attend a CASA approved Part 147 training organisation, which are located around the world. They will assess you, possibly provide you with some extra training, following which you can apply for an Australian Part 66 engineer licence. Once you get that licence you shouldn't have too much difficulty migrating, but that's a discussion outside of my league. More details on this conversion process are on the CASA website.


Is this an accurate depiction of the internal shape of a turbofan engine?

Strictly speaking, no. It is an artist's concept to help us understand the engine schematics better. A better figure would look some thing like this :

GE-90 Cutaway; image from web.stanford.edu

The blue colored region more or less shows the 'cold flow' region (where the bypass air flows). This graphic is better for two reasons- not only does it show that much of the flow takes place in the cold flow half-ducts, but it also shows that how the pipes and tubes that are all over the place are covered.

The figure you linked in the question doesn't show the cold air flow ducts, for simplification. Also, the shape and size of the bypass duct varies from design to design (though they are similar overall).

Differences between two and three shaft engines; image from 1.bp.blogspot.com

In the above figure, you can see that the though both the similarly shaped bypass ducts converge, their location and length is different. Of course, in the real aircraft, these ducts host the thrust reversers, as explained by @mins elsewhere.


Do all GA autopilots use cable "clutches"?

From the Approval of Flight Guidance Systems AC-25-1239-1C document:

  30. Override of the FGS.

  a. General. An override of an engaged FGS function is defined as an action taken by the flightcrew intended to prevent, oppose, or alter an operation being conducted by the FGS function without first disengaging that function.

  b. Autopilot override.

     (1) With automatic disengagement.

         (a) Override force. The autopilot should disengage when the flightcrew applies a significant override force to the controls. The applicant should interpret “significant” as a force that is consistent with an intention to overpower the autopilot by either or both pilots. The autopilot should not disengage by minor application of force to the controls, such as a pilot gently bumping the control column while entering or exiting a pilot seat during cruise.

(Page 37)

It goes on to say that 25lbs of force has been determined to be a significant override force level for "other than approach" operations. This may be difficult to measure using a system that just looks at the force on the control surface since normal operations may cause force feedback through the surface. There would have to be a way to measure the pilots force in conjunction with the control surface force and determine if the pilot is trying to override the servo.

GA aircraft are not normally equipped with all the "bells and whistles", autopilots are typically optional equipment. This means that the autopilot system needs to "fit in" to the existing control system architecture. Adding bosses, actuators, connection points, holes, etc to an airframe to accommodate an autopilot is a "significant modification" that may require a new type certificate or an STC.

The easiest way around this is to use servo controls with clutches that move existing control cables. This way the pilots force is directly measurable on the control system. Using magnetic clutches the autopilot can easily disconnect itself, worst case, by popping the autopilot breaker (although this is not an acceptable disconnection procedure).

I can't say that there are no GA aircraft that don't use a different mechanism, but I've never heard of one.


Two words: chase planes.

A few more words: The easiest way to film an airplane in flight is with another airplane in flight. Here's one article on how that's done, including images captured from both sides; the chase plane (a Learjet 25B) getting the shots of the 787 Dreamliner, and crew aboard the Dreamliner getting a few snapshots of the chase plane.

Early shots taken from chase planes often used simple handheld cameras; a two-seater would normally be used with the pilot in front and the photographer in back. This is still a totally viable way to do it, but more modern professional shoots utilize aircraft specifically modified for the task by adding internal or external camera mounts, optical-quality viewports, etc. Here's a modified T-33 used by Boeing specifically for air-to-air photography, including some of the initial publicity shots of the 787 in flight; notice the camera mount between the seats that can be used by the GIB (he's using a handheld in this photo:

For lower-speed shots, you can also use a helicopter. Many of these such as news choppers have remote-control cameras on gyro-stabilized mounts, so the vibration of the airframe is minimized in the shot even at high zoom:

These same camera systems can be used for air-to-air shots as well, however the maximum airspeed of the helicopter becomes a limiting factor. Still great for publicity shots of small prop planes, or takeoffs/landings.


Why didn't Cirrus make the SR-22's parachute steerable?

Remember what the purpose of the CAPS/BRS airframe parachute is: It's a last-resort emergency measure to put the aircraft on the ground in a condition that is likely to be survivable for those onboard.

Steerable parachutes add considerable complexity: Control lines would need to be routed into the cabin, and connected in such a way as to not interfere with the chute deployment under any circumstances.
Assuming a suitable design could be devised to accomplish that a steerable parachute (even for a single person) requires quite a bit of training and skill to use. This is not something that can be adequately trained for in the case of the Cirrus airframe chute (because pulling the chute on perfectly good aircraft to teach steering would be cost-prohibitive).

Faced with the risks and complexity of a steerable chute or the relative simplicity and safety of a simple drag chute to decelerate the airframe prior to impact (hoping you land in a suitable 40-by-40 foot square) Cirrus and BRS opted for the latter. The result is a dead-simple "Pull the handle!" system that's proven very successful thus far.


Can we fly in Japan and/or Australia with EASA approved training and licences?

Generally speaking, you need to hold a licence issued by the same country that the aircraft is registered in. There may be exceptions but you cannot fly an Australian aircraft on your EASA licence.

Luckily, converting a PPL between countries is generally straightforward when it has been issued by an ICAO-contracted state (which is most advanced countries and EASA).

For Australia, no additional tests are required (for PPL only, exams and flight tests are required for higher levels). You just need a medical, to pass a security check, and pay a fee. I believe EASA licences come with English Language Proficiency (ELP) level 4 to 6 so an English test is not required. Side note, the US does not have the ICAO ELP scheme so even native English speakers from there need to pass an English test when they convert to Australia.

I'm less familiar with Japan but according to AOPA Japan you need to sit a law exam and obtain a radio operator certificate.


What exactly is a variable incidence tailplane?

Incidence is the angle at which an aerodynamic surface is mounted to the remaining structure of an aircraft. Variable means that this angle can be changed in flight. Normally, a control surface is split between a forward part, called the stabilizer, and the rear part, called the elevator. On aircraft with less powerful wing flaps, the stabilizer incidence is fixed and only the elevator can move, while more complex aircraft can also move the stabilizer.

A third way is to do away with a separate elevator and to move the whole tail surface. This is a variable incidence tailplane.

Benefits of a full-flying tail surface

By avoiding a contour break due to a flap deflection, all-moving control surfaces can avoid the shocks which would otherwise occur at high subsonic speed. This is especially beneficial for supersonic aircraft.
At supersonic speed, the uncambered surface will produce less drag, so for supersonic speed the all-moving control surface is more efficient.
By moving all of the tail surface at high speed, an all-moving control surface will produce the highest rate of moment change over time possible. To produce also the highest sustained moment change, however, it needs to be larger than a comparable stabilizer-elevator combination because it forfeits the benefits of variable camber.
The all-moving control surface has no gaps which could add radar reflections, allowing for a more stealthy design and slightly reducing drag.
Lower mechanical complexity. This is somewhat offset by the need for much beefier hydraulics.

Some gliders have full-flying horizontal tail surfaces for reduced complexity. They have a slight back sweep to shift their aerodynamic center and their center of gravity to the same location. This makes the tail light and simple and avoids the added drag of the elevator hinge gap. However, such tail configurations have caused a number of crashes in the early phase of a winch launch when the pilot did not keep the stick neutral. At low speed a fully deflected tail surface has separated flow on the suction side, rendering the tail less effective. Only when the flow suddenly attaches as speed picks up the tail effectiveness is regained. In combination with the pitch-up moment of the tow line this lead to very steep angles of attack right after take-off which the pilot could not correct with the still ineffective tail, and some gliders stalled, rolled and crashed as a consequence. Therefore, modern gliders avoid this feature.

Schempp-Hirth Cirrus with full-flying tail (picture source)


How can I overlay a VFR sectional on another map to identify features and landmarks?

Seems to me you're going to be directed by SoCal approach that whole route per the routing shown in Skyvector.com, especially with the LAX Class B right there, and the TFR will be the last of your worries. Put your enroute and the final destination into your GPS (Foreflight or whatever), and be ready for deviations.


It's essentially a combination of the capabilities of FLIR and NVG's, although built into the aircraft and displayed in the HUD rather than worn as goggles.

FLIR, short for Forward Looking Infra Red, uses far-IR to see the heat of terrain, and essentially turns the night into day, at least for the field of view that it "sees."  NVG's (Night Vision Goggles) use near-IR and magnified visible light.  The near-IR doesn't see terrain except to the extent that it's illuminated by something (moonlight, starlight), and far-IR can't do much to tell the difference between a light that's on or off (so you can see the runway edge, but you can't see the runway edge lights using FLIR, for instance).

The two systems have slightly differing capabilities and limitations; when both are fused together onto a display (i.e. a Heads-Up Display, or HUD), the pilot gets a pretty amazing picture of what is directly in front of him: the far IR shows him the runway edges, taxiways, pavement, buildings, obstructions,etc, and the near-IR makes lights (i.e. runway and taxiway lights) stand out.  In low visibility, the far-IR tends to be somewhat more degraded than the near-IR, whereas at night & with no moon, the near-IR shows the lights but not much else.  Together, the pilot can get the runway lights in sight sooner than he could unaided, and by the time he's landing he can see "everything" in the field of view of the HUD, not just the lights themselves.

Example videos:

YouTube
Vendor's Website
AvWeek

When the videos get down close to the runway, you can pick out the glowing approach and runway lights, which is where EVS differs from pure FLIR.  With FLIR, you'd see (sort-of) the lights and any framework that they're mounted on, but they wouldn't particularly glow -- they might as well be off.  With EVS, the crew can fly a CAT I ILS and actually have the approach lights, runway, runway lights, etc all in sight at the 200' DH, even when the visibility is such that with the naked eye, none of that would be visible.  At major US airports, CAT III approaches are often available, but elsewhere they may be rare or nonexistent.  The EVS capability has the promise of allowing crews to successfully land out of a Cat I approach (i.e. at an airfield that only has Cat I ground equipment) even in Cat III weather; from the OP's quote, it looks like they already have approval to use it for Cat II conditions. And for a global carrier like FedEx, that's a capability worth having.


How would the FAA catch people without licenses?

If they are conducting a ramp check and you don’t have a license, the chances of getting caught are 100%.  The size of the airport, the presence of a control tower, or the surface of the runway is immaterial - if it is a public airport the FAA could be there.
If they are not conducting ramp checks, you would only be caught if there were a reportable incident that brings your activity to their attention.  (airspace violation, noise complaint or tip, mishap, etc.) Otherwise, how would they know?
I’m not sure how it might work at a private airport, but I would imagine the FAA would be held to the same standards as law enforcement; i.e. they would require either consent, probable cause, or a warrant to enter your property.


Why does the European MALE RPAS UAV use twin engines?

According to the Airbus press release:

  The MALE RPAS is the first unmanned aerial system designed for flight
  in non-segregated airspace and will be capable of performing a range
  of missions in intelligence, surveillance and reconnaissance, both
  wide area and in theatre. A twin-turboprop propulsion system will
  deliver energy for the mission system and provide proper redundancy to
  limit restrictions when operating over European densely populated
  ground and unrestricted airspaces.

Essentially, the aircraft is intended to be operated in the same airspace as existing air traffic, over large urban areas. The twin engine configuration is to provide redundancy and thus stop a robot plane from crashing on people.


What is the optimal altitude for performance and mileage in normally aspirated GA planes?

First off this highly varies by aircraft. Piston aircraft that fall under the GA header these days have a pretty wide range of altitude capabilities. The Piper Archer I fly wont really get over 10,000 but you can get your instrument rating and grab a Mooney Acclaim which will take you well into the flight levels and get you up to 25,000 Ft.

  best altitudes for ground-speed....

The simplest answer here is the altitude at which your tail wind component is the best. Wind speed and direction does shift with altitude and in many cases your [(increased performance/cruise time) + tail wind - (reduced climb speed/climb time)] is best where ever the tail wind component is greatest and your climb does not take impractically long.

Very Generally speaking performance increases with altitude to an extent. However climb rate usually decreases so there is a break even but it for sure varies by airframe and configuration.

  fuel efficiency...

Again this varies by aircraft as well as how you chose to operate the plane. Things like running lean of peak can effect efficiency at the cost of speed typically. Some planes have little to no change in endurance at varying altitudes (although your change in airspeed may allow you to cover more distance). At 75% power my archer has almost no change in endurance as I climb.

Variable pitch propellors also offer a great deal of power setting options that can allow you to tune your efficiency even further.


Can aircraft depart/arrive after another aircraft has sprayed snow on the runway?

Aircraft can land in snowy weather without a problem, the fact that there is a little bit of snow on the runway does not change that. The amount of snow can cause problems if it too deep and will interfere with the engines/landing gear struts etc.

The snow sprayed on the runway by the A380 is just a small film and no problem for aircraft to take-off and land on. The runway can become a bit more slippery decreasing the braking performance of the aircraft.


What is the relationship between your tail number and air traffic control?

Sometimes your callsign is your tail number, particularly on General Aviation flights. For example, if you are flying the Cessna 152 with tail number "N123AB", you would call ATC with "November-One-Two-Three-Alpha-Bravo".
Commercial flights, on the other hand, tend to use their flight number as the callsign. E.g. if an aircraft is operating for Delta Air Lines flight 123, the callsign would be "Delta-One-Two-Three". This is not applicable to GA as GA do not usually fly a particular route or for a particular company. Assigning a flight number to every GA flight would be troublesome, it is simpler to just use your tail number as it is guaranteed to be unique.
Controllers may identify a plane by tail number when you are on the ground, but once in the air it is almost impossible to sight a plane this way. If this is your initial call to the controller, you would describe your location, which allows the controller to identify you on the radar screen. If the controller is unsure, you may be assigned a squawk code and even asked to push the IDENT button. You may also describe your type to the controller, like:

"Tower, N123AB is Cessna 152, 5 miles South of XYZ, (...)"

You are correct that if you do lie about your callsign, ATC as no way of knowing it unless somebody sees you, as described in the "Inside Air Force One" documentary by National Geographic when they tried to pretend to be a GulfStream aircraft to secretly transport the president. If you have ADS-B installed ATC will be able to see your callsign as it was programmed into the ADS-B unit, but even that can be re-programmed.


Are artificial magnetic fields used or proposed to be used to shield high altitude pilots and astronauts from charged, high energy radiation?

This won't work.

What to shield

Most of the cosmic radiation has quite low energies and can easily be shielded by the hull of an aircraft, spaceship or spacesuit. This would also be shielded by the atmosphere, but it would also burn/blow it away over time due to the intensity of the radiation. For luck, the magnetic field of the earth shields us from this radiation before it reaches the atmosphere.

And then there is the nasty stuff. Particles with energies which can easily punch through several centimeters of iron, lead or whatever. This stuff can not really be shielded by the magnetic field of the earth, nor could it be by artificial fields. Even worse, when this stuff hits a nucleus in the hull of a spaceship, it would smash it into many pieces, which will then fly along the direction of the original particle. Yes, this means radiation can be even higher behind a too thin shield! And since this happens in the hull or in the spaceship, one can't shield that by fields outside the ship.

In fact, most of the radiation in aviation is not made of the primary particles from space, but of secondary particles created in collisions between the primary particles and atoms of the atmosphere.

Field strength

The most important factor of field strength of a magnetic dipole is

$$B(r) \sim m/r^3$$

(Yes, to the power of three)

$m$ is the magnetic dipole strength, which for a simple conductor loop is given by current times area enclosed by the conductor.

So, if we build a coil of several thousand windings, resulting in a total current of several thousands of amperes, and an area of some ten squaremeters, we end up with an $m$ of several 10000Am². In contrast, earths magnetic field has about $8\cdot10^{22}$Am², which is a totally different order of magnitude.

Earths field strength might not be high - only about 40µT at the surface, but it reaches far, far into space. So, the time / distance the field acts on a particle is quite long, an can deflect it easily. In contrast, a human-made field will decrease to near zero within just a very few meters, and that's not enough.


How do I select an appropriate controller gain for this roll control autopilot?

You want fast response, but not any overshoot. The perfect response to a step input in this case would be a critically damped one. Matlab/Simulink are your friends here.

Things to consider in your feedback loop:

Aircraft dynamics - is the initial inertia response modelled? Meaning, does the aircraft roll spool up to its final roll rate upon aileron deflection?
Is aerodynamic resistance to roll modelled?
Is it a digital loop, and if so what integrators are you using? If Euler your loop rates need to be high.

I've seen a similar design for a helicopter with a controller gain of 20 and an additional roll compensator $\frac {s + 1}{s}$ in the forward loop, and a negative unity feedback.

You could eyeball the response, use different settings for the feedback gain, and find the fastest response without overshoot. You'd have to testcase it for several extremes. You do need some form of damping feedback as well, I reckon your first task would be to find a response that is not oscillating.


What is the highest service ceiling for turboprop airplane like a Cessna 425?

The PA-46-500TP Malibu Meridian can climb to FL300 and you may be able to find a high time one for under a million.

Socata TBM has a quoted ceiling of 31,000 ft and you may be able to find an older TBM 700 high time airframe for in and around a million.

In the multi-engine category:

A PA-42 Cheyenne will put you up to just under 36,000 ft and can be had used for under a million.

A Beech King Air C-90 will get you up to 30,000 feet and can be found used on the lower end of the price spectrum.


I'm thinking of building a balloon-launched glider, is this idea plausible?

This idea is entirely plausible and has been tried before, and even successfully. But I guess you have already read through all the pages which you can find via Google.

Several things are to be considered:

It is really cold up there (see below), and the ascent will take long enough that you need to heat the batteries and to remove grease which will likely freeze solid up there. It would be a shame if the onboard camera cannot document the flight because its battery was too cold.
Due to the low air density, flight speed will be high, so your sailplane will likely experience flutter if you try to use a regular RC glider. A more sturdy configuration which is less optimized for high glide ratios might serve you better.
Winds can be very high at altitude, especially between 10 and 16 km height. You need to factor wind drift into your planning. Try to launch on a calm day (calm all the way up, that is), or the plane might not reach the waypoints.

Since lower temperature means a lower Reynolds number, viscous effects will be higher at altitude than on the ground. This means that your glider's drag for a given lift will be higher at altitude. How much depends a lot on the choice of wing airfoil. If you go with an existing model, pick one which flies well over a wide speed range. A reasonable glide ratio for a model at altitude would be between 10 to 15, so it will glide 10 to 15 km for each km of altitude.

The maximum altitude in which subsonic flight is possible depends on the wing loading (among other things), so try to keep masses down.


Which is the smallest available widebody on the market?

This question is broad enough to try out the new table feature:

Smallest by
All time
In production

MTOW
Airbus A310-200 (144t)
Boeing 767-300F (186.9t)

Length
Airbus A310-200 (46.66m)
Boeing 767-300F (54.94m)

Outside Width
Boeing 767 (5.03m)
Boeing 767 (5.03m)

max. Payload
Airbus A310-200 (32.8t)
Boeing 787-8 (43.3t)

Exit Limit
Airbus A310-200 (275)
Boeing 787-8 (381)

Passengers*
Boeing 767-200 (214)
Boeing 787-8 (242)

Seats Across*
Boeing 767 (7)
Airbus A330neo (8)

* number of seats for typical 2-class layout, seats across for typical economy
(source: Wikipedia)
In summary, the Airbus A310 was the smallest wide-body ever produced by most measures. The smallest wide-body still in production today is the Boeing 767, but only the freighter variant is still produced. The smallest passenger wide-body in production is the Boeing 787 Dreamliner.


Why does it take months, sometimes years, for the BEA and NTSB to complete aviation accident investigations?

When it comes down to it, accident investigations involve lots of coordination between many different groups, companies, and agencies, often around the world. These groups may range from helpful and responsive to completely uncooperative.

Visiting the Site - First there will be a team that heads to the incident site to collect information. If the site is easily accessible, this may be a fairly quick process. If the site is tough to access, or takes a while to find, this will of course take much longer. This is generally the part most visible to the public, but is only the tip of the iceberg in generating a useful report.

Research - There is also a lot of research that must go on behind the scenes. Especially if a possible cause is not clear, investigators must look into many factors to rule out the options. This can be a lot of information and may involved many different groups around the world:

Previous maintenance done on the plane
ATC and weather information about the flight
Information about the crew, the passengers, and the cargo on the flight
Many individuals may also be interviewed

If any of this initial information provides clues as to possible causes of an accident, they will also be gathering information about related aircraft design and functions. This can be a lot of information and may involve working with many different groups. The process of narrowing the focus of the investigation may involve tracking down different leads which end up being irrelevant. It may take a lot of effort just for the report to end up saying "X was not a factor."

Flight Recorders - Gathering the flight recorder data is not always as simple as plugging it in and reading the data. If there is damage, extracting and repairing the memory may take time. The FDR data must be analyzed and it may take additional work to investigate and verify the parameters. The CVR must be read out and then transcribed. Transcription is also a long process, involving different parties to the investigation, and must be synchronized to ATC and FDR information.

Analysis - Once the information has been collected, it must all be analyzed. Investigators may need to contact and work with many different groups and experts to develop an understanding of parts and processes that took groups of engineers years to analyze and design. Components may need to be analyzed down to a microscopic level. This is generally the longest part of the process. Investigators may realize that they must go gather more information. This may involve running tests on equipment to recreate issues. It may take a lot of work to not only explain what failed, but also the reasons behind the failure and how it could be avoided in the future. Most reports will find issues in many different areas, including human factors, regulations, procedures, and aircraft design.

The Report - The investigators will eventually need to come to some conclusions among themselves. This must all be written up in a report. Some reports can be quite lengthy. If you've ever had to write something like this, you might know that writing the report can easily take much longer than the work that went into it. There will also be an opportunity for parties to the investigation to make comments and provide feedback before the report is released. This is where the investigators get to share the results of all their hard work, and it will be published to get picked apart by the whole world, so it's worth taking the time to get it right.

Law - While most agencies like the NTSB focus on producing a factual report and not assigning blame, lawyers may also need to get involved. Investigations may involve dealing with proprietary or sensitive information, or groups that are reluctant to divulge information (see "completely uncooperative" above). Some accidents may involve criminal investigations as well, in which case organizations like the FBI may also be involved.

Followup - It's not even over after the report has been released. The agency will still need to follow up with regulatory agencies (like the FAA) about recommendations made in the reports and determine whether the responses are adequate.

Additional Duties - On top of all this, many investigators will not be working on one incident full time. Agencies like the BEA and NTSB investigate many smaller incidents as well. So imagine that at any given time, an agency may have many active investigations at different points in the above process. In the case of the NTSB, all of this is accomplished by about 400 people with a budget of around $100 million per year. While aviation safety is the largest part of this with about 130 employees, the NTSB also investigates highway, marine, and railroad/pipeline/hazardous material incidents. Employees also spend time on other things such as educating the public about safety issues, looking for ways to improve safety, and producing additional types of reports.


Can passenger plane do an aileron roll and fly upside down?

In fact this has been done before.  A well documented case is of "Tex" Johnston rolling a 707.  In general airliners cannot do sustained inverted flight as they lack a fuel system (and lubrication system) for sustained inverted flight.

A barrel roll is readily executable. Youtube has a video of Tex Johnston doing a barrel roll.

Edit: I gave a quick answer and felt guilty about it. There is more to the story. The OP talks about aileron rolls. An aileron roll is a maneuver where the plane does not substantially change altitude. The G forces will be negative at some point, and it is more "violent" than a barrel roll.  A barrel roll is a maneuver where the plane is rolled about the longitudinal and lateral axis, if you will, a loop and a roll in one.  Properly executed the barrel roll is a positive G maneuver.

Years ago, when I was young and some old geezer was teaching me aerobatics, he would climb into the plane with a full cup of coffee.  My job was to get to the practice area, and execute some maneuvers, including barrel rolls in each direction, without spilling his coffee.


What is the weight budget of a fully loaded A380?

These weights are all based on the maximum an aircraft will ever see. The maximum allowed weight of passengers (+luggage) and cargo (called payload weight) is the difference between the Operational empty weight (about 270,000 kg) and the Zero fuel weight (361,000 kg). This means the payload weight is about 91,000 kg. The passenger and crew weight can be estimated by the following numbers:

175 lbs per pax + 30 lbs of baggage for short medium range distance (or 40 lbs for long range)
175 lbs per crew member + 30 lbs of baggage$^1$

So let's say that (for easier calculations) the average passenger + luggage weight is 100 kg.
When we assume 530 passengers and 25 crew, then the weight would be $555\times100=55,000kg$. That leaves 36,000 kg for cargo.
All the weights listed are, of course, maximum weights. That means that an aircraft in general does not meet these values.

The maximum fuel weight is the difference between maximum ramp weight and zero fuel weight (which is $562,000-361,000=201,000kg$). About 2,000 kg is taken for the time the engines are running while the aircraft did not yet take of (for taxiing etc). This is the difference between maximum ramp weight and MTOW.

The amount of fuel varies so much per flight that I really can't say anything about it. It depends on the air pressure in the flight path (aircraft choose their routes depending on that, for a faster flight), weather along the route, and much more. For quite a good overview I suggest for you to read this Wikipedia page.

I hope I answered your question sufficiently.

$^1$ Source: Jan Roskam, Airplane design, Part I: Preliminary Sizing of Airplanes (1985)


What counts as "runway in sight" when flying an IFR approach to minimums?

From FAR 91.175:

  (3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

  (i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.

  (ii) The threshold.

  (iii) The threshold markings.

  (iv) The threshold lights.

  (v) The runway end identifier lights.

  (vi) The visual approach slope indicator.

  (vii) The touchdown zone or touchdown zone markings.

  (viii) The touchdown zone lights.

  (ix) The runway or runway markings.

  (x) The runway lights


Why are turbofan inlets leaned/angled forward?

The inlet angle is a compromise between cruise, when the aircraft has a low angle of attack, and the take-off and climb phase, when the engine runs at maximum thrust, and the angle of attack is several degrees higher than during cruise. Especially right after rotation, when the aircraft is heavy and slow, the angle of attack might reach into the lower two-digit territory, and flow disturbances must be avoided especially in this phase.

Note that the fuselage should be horizontal during cruise to avoid making the work of the cabin personnel harder than it already is. A few degrees of intake misalignment can be tolerated, and the misalignment is usually split between cruise and post-rotation climb.

With supersonic intakes, things are different: They are much more sensitive to misalignments, and the intakes of planes like the SR-71 have been carefully optimized for their cruise condition.


What is the drag induced by a high bypass jet engine on an airliner?

What you are asking about is inlet performance.

Instead of sucking air, think of it as eating air, that's a better more correct analogy (like Pac-Man eating dots). As the plane flies through the air, it may literally bite off more than it can chew. Causing spillage. The extra air stuck in the inlet tries (but fails) to go out. Creating drag.

But this drag for the subsonic airliners you ask about is offset by the suction at the inlet due to the inlet's design.

See here for how they cancel each other: How does inlet spillage drag produce a lip suction effect?

Related: Does the air resistance of a jet engine air intake count towards the jet's total air resistance?


What is the significance of the exclamation mark (!) on ACARS page of a Boeing 737?

Okay guys, the verdict is in.

It is a symbol to indicate the crew alerting chimes are inhibited.
From OUT (off block) until OFF+15 and estimated ON-10 until IN (on block) the chimes to alert for new data and messages are suppressed to avoid nuisance warnings during critical flight phases.

Happy landings!


Where do standard torque values in maintenance manuals come from?

The standardized values are related to the yield strength and elasticity of the fastner.  Bolts in normal tolerance holes are effectively spring clamps (bolts in close tolerance holes can be better thought of as spring clamps + shear pins) and when you are tightening a bolt you are using a spiral wedge, the threads, to force the bolt to stretch to clamp the parts together.

You want to be able to stretch the bolt to apply as much clamping force as possible without exceeding its yield, or permanent deformation threshold.  It's like stretching a spring too far, so that when unloaded, it is longer than before.  You would say that the spring is ruined if that happens.  Same with a bolt. If you overtorque it and exceed its yield strength, it will be a bit longer than before when loosened and will have lost some of its ultimate strength after being permanently elongated.

So the standard torque tables are limits on how much the bolt can be stretched, converted to the equivalent rotational force applied to the spiral wedge of the threads.  The values are those that keep the axial tension force below the yield threshold, with some safety margin.  The standard limits are a function of the material strength and elasticity of the material that a particular bolt is made from.

A lot of the time torque values are given that differ from the standard values because the designer wanted to customize the clamping force for some other purpose, such as to limit clamping force on the base material or gasket or washer, or limit shear loads on parent material threads (like a steel bolt in an aluminum casting).  The normal engineering practice is to quote a torque value on the engineering drawing (and hence in the Maintenance Manual procedure) when it differs from the standard tables.

So as a general rule, when a torque value is from the standard torque tables, it's a limit for the bolt itself and is related to its tensile yield limit.   When a special torque value is given, it's a limit to control force applied to something other than the bolt itself for various other reasons.


Would the Wright Flyer have flown better with thicker airfoils?

There were several other limitations on the first Flyer besides the airfoil -- the engine weighed four times what the brothers had been promised it would (because the block was cast, rather than fabricated from sheet), and would have been underpowered by today's standards even if it had delivered to spec.  The whole machine came in just under 300 kg; a modern ultralight that size would weigh less than half as much and have nearly twice the power.

Given those limitations, the airfoil is a relatively minor consideration.  Yes, there are modern airfoils that would perform better in terms of coefficient and lift-to-drag -- but the thing that would have helped the most would have been saving 40 or so kg. on the engine weight.

It's worth noting that through the First World War, with aircraft flying at four or five times the speed of the first Flyer, at altitudes up to 4000+ m, inverted and other aerobatic maneuvers, what we'd call relative thin, cambered airfoils persisted.  Look at the wing section of a Sopwith Camel -- though slightly thicker and more deeply cambered than the original Flyer's airfoil, it was still thinner than anything you'll find today except on single-surface hang gliders and ultralights.

How thickness and camber affect flight characteristics is subject matter for a full length college level textbook, but short version: more camber tends to increase lift coefficient over some range of angle of attack, but increases drag in proportion; adding thickness increased coefficient over a broader AoA range, with less drag increase, but has less effect at low AoA than increasing camber.  There's a compromise, with both increased by similar amounts, that includes the well-known Clark Y, NACA 6409 and 6412, and many other common airfoils used in general aviation, especially when wood and fabric were the building materials.