What is the most carbon-efficient way to take off in a passenger plane?

You are right, climbing adds to the fuel consumed, and increases the energy which is added to the plane, but this energy is conserved and can be reclaimed later, on descent. There are two kinds of energy to consider, potential and kinetic energy. Potential energy is weight times height, and kinetic energy is mass times speed squared, and both can be interchanged.
$$E = \frac{m}{2}\cdot v^2 + m \cdot g \cdot h$$
Nomenclature:
    $E \:\:\:$ energy
    $m \:\:\:$ mass
    $v \:\:\:\:$ speed
    $g \:\:\:\:$ gravitational constant
    $h \:\:\:\:$ height

The thrust of the engines over what is needed to overcome drag, accumulated over time, builds up energy. Lift and Drag, in turn, are proportional to airspeed squared times density of air, so if the airplane climbs, it needs to fly faster to compensate for the thinner air, and drag will stay roughly constant. Thrust is also proportional to the density of the air around the aircraft, and the same goes for fuel consumption. This means that the aircraft will approximately consume the same amount of fuel over time when it flies low and slow, and when it flies high and fast. Since the task is to transport people or goods to a specific destination, flying high and fast will result in less running time at the same fuel flow. This is the reason why flying high results in less CO2 produced!

When the aircraft comes close to its destination, it can now put the potential energy which has been stored as altitude to good use: In a descent, the thrust generation can be reduced by the amount of energy which is now reclaimed, just as you can ease off the gas pedal in your car when coasting downhill. So for the last half hour of the flight, the aircraft will now consume less fuel than before, and by the time it has reached its destination, the difference is just as big as the excess in consumption which was needed during climb.

For the nitpickers: The aircraft will weigh less at the end of the trip (fuel has been consumed), so the descent will not completely compensate for the climb. On the other hand, the lower temperature at altitude will reduce fuel consumption by letting the engines run more efficiently, so in the big picture a definite gain remains.


Which is more accurate for height measurement: GPS or barometer?

For surveying glacier movement, or a mountain range's growth/decay, GPS is more accurate.

For airplanes: refresh rate, reliability, and simplicity matter more. When it comes down to accuracy, ground augmented GPS provides ILS CAT I accuracy using LPV. So alongside refresh rate, and accuracy, comes the question of application. For airplanes in cruise, where separation matters, reliable devices are best.

GPS signals can be jammed. As can be seen in the news lately in California and Egypt. And GPS signal can be lost due to ionospheric interference. So, any equipment that doesn't rely on external sources is safer.


Why is the empennage of some aircraft not placed on the centerline?

The vertical stabilizer is on the centerline.

The line you see is not the centerline, it's the overlap of the aluminum sheets that form the circular fuselage.

(Source)

(Source) Non-aviation example of what I mean by overlap and centerline.

On the other hand, propeller aircraft may employ different methods to counter the left turning tendencies.

  Tail

  The tail group consists of a vertical stabilizer, a horizontal stabilizer, two
  elevators, and a rudder. The vertical stabilizer is mounted on the aft
  fuselage, and the horizontal stabilizer is mounted on the top of the vertical
  stabilizer. The rudder and elevators are mounted on the vertical and
  horizontal stabilizers, respectively.

  The vertical stabilizer is fully cantilevered and sweptback. A scoop for
  cooling the air-conditioning systems is located on the lower leading edge
  section and is heated when the Airfoil Anti-ice is operating.

  – MD-80 Flight Manual

Back to the MD-80 in the photo, from its manual there is no mention of an offset. I searched for multiple terms such as offset, angled, and off center.

Finally, from an official CAD drawing from Boeing's website:


Magnetic Bearing:
This is the direction of the plane's nose relative to magnetic north at the plane's current position. Simply stated, it's the bearing that your plane's heading indicator gives you. It's from 000 to 359 degrees(where 000 is north, 090 is east, 180 is south and so on). ATC directions are also given usually in magnetic bearings. Most aircraft heading indicators give reading in magnetic bearing only. Note that bearing is always stated in 3 digits.

Magnetic heading/heading. Same as magnetic bearing.

Track:
This is where things get a bit complicated. Suppose your plane is flying with its nose pointed at 090 degrees(east). You also have a wind blowing in from 000(north). This 'blows' the plane to the south a bit. Now even though your plane is pointed towards east the direction of its flight path is different! This is where track comes in: it's the direction of the flight path of the plane. In some cases it may be the same as magnetic heading (no winds etc), in others it might be different (crosswinds).


How close is an obstruction allowed to be in an instrument approach?

FAR Part 77 provides standards for what objects constitute an obstruction to navigation:

200 ft. above ground level or 200 ft. above the airport elevation (whichever is greater) up to 3 miles (for runway lengths > 3200 ft.) from the airport.

Increase 100 ft. every mile up to 500 ft. at 6 miles from the ARP (airport reference point)

500 ft. or more above ground level at the object site
Penetrates an imaginary surface (a function of the precision of the runway)
Penetrates the terminal obstacle clearance area (includes initial approach segment)
Penetrates the enroute obstacle clearance area (includes turn and termination areas of federal airways)

There are 5 imaginary surfaces:

Primary - aligned (longitudinally) with each runway
and extends 200 ft. from each runway end
Approach - longitudinally centered with the runway and extends beyond the primary surface
Horizontal - horizontal plane 150 ft. above the established airport elevation. Constructed by swinging arcs around the end of the primary surface
Conical - 20:1 slope surface extending beyond the horizontal surface
Transitional - constructed to join approach and horizontal or approach and transitional surfaces

Additional dimensions are also dependent on the types of approaches used at the runway. A precision instrument runway has a primary surface 1,000 feet wide, and a horizontal surface radius of 10,000 feet. Approach surface width at end is 16,000 feet, total approach surface length is 50,000 feet, and slope is 50:1 for inner 10,000 feet and 40:1 for the additional 40,000 feet.

The idea is that the FAA is notified of any new obstacle that meets the criteria above, and it is up to the FAA to provide a determination of how it will affect procedures. If an obstacle cannot avoided, special procedures may be required.

For the specific example of Boston's runway 14, using the most conservative visual approach clearance requirements, the obstacle is well within the imaginary surfaces:

The primary surface is 250 feet wide for a visual runway and gets wider through the approach section, so at 70 feet from center line, this building will be within that zone.
The approach surface for a visual runway is 5,000 feet long, so at 1364 feet the building will be within that zone.
The approach slope for a visual runway is 20:1, which is a height of 58 feet at a distance of 1364 feet from the runway, so the building at a height of 174 feet is well into that zone.

The runway would need a displaced threshold of at least 2320 feet to clear the building for a visual approach. This would mean you could only use runway 14 for visual approaches, and there would only be 2680 feet remaining. You could use it for non-precision instrument approaches but only with propeller driven aircraft of 12,500 pounds maximum gross weight and less. Anything more than that, and the approach slope gets even more shallow.

Note that other runways at BOS list obstructions as well, but all others list the slope to clear the obstacle. Runway 14 would have about a 6:1 slope to clear that building. Runway 4R/22L has slopes of 8:1 and 7:1 respectively to obstacles, but is also twice as long, allowing for a displaced threshold.


That is an Aero L-29 Delfin

Source: onespotter, photographer/copyright: Evgeniy Lebedev


How and why does the ATR-72 sometimes use reverse thrust to push back from its parking position?

As other answers note, for most aircraft, the risk of the engines ingesting FOD while powering back is too high. This is particularly true for turbofan engines mounted under the wings.

Turboprop engines tend to be mounted on high wings (such as on the ATR-72), and they tend to serve smaller airports where an airline may not have tugs available for pushback. Regional and private jets, which often have fuselage-mounted engines, also tend to serve such smaller airports. These planes were designed with the engines mounted higher specifically to reduce the risk of ingesting FOD, thus allowing them to safely power back when needed.

Note that powering back still burns a lot of fuel, and even with high engines the FOD risk isn't zero, so when operating at larger airports that do have tugs available, airlines will generally use them.


What are the Area Control Center (ACC) frequencies for Germany?

The radio frequencies used by German ACC sectors are listed in AIP Germany ENR 2.1 (page 36 onward). This is the standard place to find ACC frequencies for any country in the world.

There are too many frequencies to list here, but you can find the full document here. Below is a screenshot of page 36. Column 1 contains the sector name and dimension, column 4 contains the frequency(ies) used by that sector.


What is the procedure for a rejected Jet/Rocket Assisted Takeoff (J/RATO)?

JATO (more correctly: RATO) typically uses simple solid-fuel rockets for their ease of maintenance, simple construction, long-term storability, robustness, and reliability. However, a simple solid-fuel rocket has to burn out once ignited, there is no way to shut it down. Techniques for extinguishing and even throttling solid-fuel rockets do exist, but they were developed rather recently, have not yet been commercialized, and clash with the goal of simplicity.
Currently, the "usual" way to shut down a solid-fuel rocket is to rapidly decrease the pressure in the combustion chamber, aka an explosive Flight Termination System, aka blowing up the rocket – not something you want to happen with a rocket strapped to your wings (IOW directly below the fuel tanks). Alternatively, you could get rid of that extra thrust by jettisoning the rockets. Having a dozen or so flaming projectiles uncontrollably flying around the airplane is also not a good idea.
So, you either reject before igniting the rockets or you don't reject at all. V₁ is when you hit the button, which may be as low as 0 kt, depending on the specific application.


Why are accident rates higher on smaller aircraft?

The amount of resources that go into commercial aviation are really amazing -- the amount of time, talent, money, and effort that have gone into making the airlines the safest mode of travel known to recorded history is really extraordinary, and the results reflect that.

Design

Aircraft are expensive, but a part of that expense is the extreme care that has been taken to make them highly reliable, with redundant systems and lots of advance warning systems when something is nearing the point of failure.

Fifty years ago, aircraft were less reliable; the engineers have incorporated the lessons learned.  And, considering how much money an airliner make, airlines are generally willing to pay absolutely top dollar for the very safest design possible.

Small aircraft have also benefited from this learning process, but as a matter of economics, they don't get quite as much redundancy or refinement.  While 99.999% might be "good enough" for the general aviation, the airlines can afford the (high) costs of adding more 9's onto the end of that number.

Maintenance

Again, the airlines can afford a maintenance process and inspection regime that would raise the cost of flying a light aircraft significantly.

Mechanics are trained to uniform standards and work in a carefully monitored environment where parts are exactly tracked and the aircraft have an incredibly detailed history of all that's been reported and fixed over their lifespan.

Manufacturers like Boeing and Airbus can see millions of hours of data and spot trends that are developing to head off incipient problems before they become widespread. This, combined with the way that the aircraft are engineered, makes things really, really reliable.

General aviation maintenance is good -- I'm not bashing that -- but airline maintenance, especially at the major airlines, is amazing.  That's not free, but the results are there.

Pilot experience and training

Light aircraft are often flown single-pilot, by a pilot who probably has under 2000 hours, and who may have flown 200 hours in the past year.

On the other hand, airline pilots are typically hired with at least 1000 to 2000 flight hours, often more, and a captain at a major airline may well have 10,000 to 20,000 hours.  Added to that, the crew has probably flown between 400 to 800 hours in the last year, as well as getting multiple days of training -- both ground school and simulator -- as well as at least one if not two checkrides.

Flying is their profession, not a hobby, and they spend time continuously studying the aircraft, its systems and checklists, the environment, and the regulations.  And, they're trained to work as a crew -- if one pilot is about to make a mistake, the other pilot is there to catch it and keep things on track. Not everybody flying light aircraft has these resources.

All of this is possible because, while it is all expensive, airlines can afford it.

And the records speak for themselves -- one fatality in a commercial U.S. aircraft over the last several years -- which includes many millions of flights.  I don't think any other human activity -- including sleeping in your own bed at night -- can claim a similar safety record.

The relevant point isn't that light aircraft flying is "dangerous" compared to commercial aviation; it's plenty safe by normal comparisons.  It's just that airline flying is so incredibly safe, any other activity will look more risky in comparison.


Can an aircraft be controlled after an ejection?

I'm going to interpret safely as meaning successfully. Ejections mean safety has gone out the window - literally.

There was a case in the Vietnam War where a pilot continued to fly his heavily damaged F-4 after his RIO (back seat radar operator) ejected. He managed to keep it together long enough to get back over friendly territory before ejecting himself. Note, this was an interview I saw some years ago, I haven't been able to find a link to post.

In this case the airplane had been hit badly enough that landing was not going to happen, however if the RIO had ejected accidentally or the airplane less damaged then a safe landing would have been possible. So yes, flying has been done and landing is entirely possible after someone has ejected.


Have contrails ever occurred at low altitudes, such as at takeoff?

This is entirely possible if it's cold enough and has also happened. Here's a video of a Tu-204 taking off from Yakutsk at -45°C.

Source


How is the lift generated by a number of out-of-plane staggered wings calculated?

It depends on the vertical distance between the wings. Munk's theorem only covers the effect of their horizontal distance (in flow direction) and says it doesn't matter (in inviscid flow).

Your statement is correct if this distance is infinitely high (and the atmosphere has constant density over altitude). Only then there is no interference between the separate wings and their combined lift is the sum of the lift of every isolated wing.

On the other end of the scale, all wings together will just have the lift of a single wing if they are not separated at all. This is trivially easy to prove, but not practical.

For distances between the two extremes, lifting line theory gives you a good answer when the distance is not small. Below that, viscous effects will start to dominate the picture, and if the wings are separated only by something similar to the wing's thickness, they will impede the flow between the wings, making the combination appear as one blunt object to the outer flow, with consequences like flow separation and the collapse of lift.

Once you move the wings apart by more than their chord length, you will get practical solutions where the wings will produce more lift than a single one and even have lower induced drag than a single wing creating the same lift force. However, a distance sufficient to make interference negligible will mean that the struts between the wings will become long and heavy, so their mass cannot be neglected. I would expect that there is an optimum of lift minus mass which is somewhere around a vertical distance of one to three chord lengths.

Unfortunately, literature on the topic is more concerned with reducing drag, so the closest I could find is a work by Ilan Kroo on non-planar lifting systems. Using the solutions for biplanes will not give an answer to your question, because every wing interfers with every other, so adding a fourth and fifth wing to a triplane will reduce the lift of the triplane, but will in sum increase lift.


Could the principle of owls' silent flight be used for stealth aircraft?

Their primary wing feathers have an unusual structure incorporating a fringed, comblike leading-edge, which reduces wind noise.  The wing feathers also have an overall softness or flexibility.  The trailing-edge of the wing is also dominated by soft, fringed edges.  Even the underwing lining (covert) feathers have an unusual softness that plays a role in sound suppression.

See for example --
https://www.owlpages.com/owls/articles.php?a=7n ,
https://animals.howstuffworks.com/birds/owl-fly-silently1.htm .
Google "owl feather structure" for more.

I'll leave it mostly unsaid, as to whether any of these features are worth incorporating into a jet-powered aircraft.  Maybe some of these features might be applied to the intake or exhaust areas, in a more rigid metallic form?


When is the autopilot engaged and disengaged?

I am a B777 pilot. On departure, we generally hand fly until about 10,000' to keep up our skills. If the departure procedure is complicated, we will ask for the AP on at 200' so there is no chance of messing up the departure procedure.

On approach I typically disconnect the Autopilot at about 1500' AGL once visual contact is assured and I am inside the Final Approach fix.

If there is any chance of a possible missed approach due to weather, or other conflicting aircraft, on the runway or elsewhere, I will leave the AP on until there is virtually no chance of a missed approach.

Most of the pilots I fly with tend to do the same.


Are zero visibility landings a possibility for the future of commercial aviation?

Practically there are no zero visibility landings.  There is reduced visibility of varying levels.  Reduced visibility landings are only allowed when the appropriate ILS equipment is operational.
The practical issues are actually not the landing itself but separation from aircraft landing afterwards.  On the ground the runway lights are bright enough and close enough for slow navigation.  However the aircraft takes longer to clear the runway and this means increased separation between landing aircraft is required.   It is this that causes delays as aircraft waiting to land are pushed further and further back.

A ground tug to facilitate speedy removal of the aircraft from the runway makes sense in theory, but would be hazardous and the acquisition time wold be non trivial.  While an estimated stopping location could be calculated for an aircraft finishing its roll out after landing it would be subject to a very large variation and the tug would have a large distance to cover to get to the aircraft.  It would then have to connect and start the tow.  The question is whether this wold be quicker than the current arrangement and what the mass penalty would be in terms of changes to the aircraft structure to enable it to use the tug.

In response to comments I would like to clarify that my point about the acquisition time of the aircraft by the tug is concerned with the non trivial and varying distance the tug would need to cover to reach the aircraft.  Any tug configured to pull an aircraft weighing in excess of 100tons would need to be large, heavy, and have high torque to help it safely move the aircraft.  These are all things which will reduce its top speed and so increase the time it takes to get to the aircraft from some optimal starting location.

Multiple tugs:
Multiple tugs would increase the probability that the aircraft would stop within optimal distance of one of them but would also increase the collision risk and add complexity to the local airflow over the runway.
Starting locations:
To facilitate quick response and removal of the aircraft from the runway the tugs would need to be located close to hand.  However they cannot be on the runway and would be required to be back from the edge by a significant distance.  When you consider the finite number of taxiways and the sheer variation in aircraft roll outs this presents a very wide range in possible locations the tug would need to get to with a consequential increase in response times.
Aircraft Rollouts:
When an aircraft lands it typically uses a small amount of remaining velocity to keep it rolling and move off the runway.  This would almost always be quicker than waiting for a tug.
Hybrid tug system:
A hybrid system in which the aircraft uses residual speed to clear the runway and meet a tug has some advantages in terms of optimal tug positioning however it reduces the advantages in fuel consumption and increases the amount of vehicles independently moving around the airfield.


Where can I find accident statistics on zero gravity flights?

A reduced gravity flight is just as a normal flight but doing some stuff at a high altitude, typically between 24,000 and 32,000 feet. The stuff they do is this:

Image Source

Regarding the safety, FAA spokesman said:

  Asked whether these parabolic flights will be as safe as normal
  commercial flights, [FAA spokesman], “If they operate within the
  parameters that we set out, yes, they will be safe.”

There have not been any accidents occurred for a commercial reduced gravity flight.


Is it legal for a crop duster to fly right over my house while spraying?

No. 14 CFR 137.37 - Manner of dispensing is pretty clear:

  No persons may dispense, or cause to be dispensed, from an aircraft, any material or substance in a manner that creates a hazard to persons or property on the surface.

Flying directly over you or your house while spraying is illegal. There are factors like altitude etc, but spraying pesticides over people is rarely legal.


Is ground school required to get a Private Pilots License?

In Canada, you are required to have 40 hours of ground school instruction. See Canadian Aviation Regulations 421.26 (3)(a):

  completed a minimum of 40 hours private pilot aeroplane ground school instruction on the following subjects ...

Ground school instruction is defined as (CARS 400.01):

  classroom-type instruction generally given to one or more persons and covering an organized program of lectures, homework or self-paced study that adheres to an approved training program.

So, you can learn by self-study, but it needs to be an approved training program. This would mean that a flight instructor would need to sign off on the self-study program.

The FAA says:

  If you are unable to attend a ground school, the self-study method can be satisfactory, provided you obtain the proper study materials and devote a reasonable amount of time to study.

The regulation is at Title 14 Code of Federal Regulations, §61.35(a)(1):

  Received an endorsement, if required by this part, from an authorized instructor certifying that the applicant accomplished the appropriate ground-training or a home-study course required by this part for the certificate or rating sought and is prepared for the knowledge test ...

Because in both cases an instructor must sign off on your preparedness for the examination, and passing the examination demonstrates that you meet the standard, in my opinion, the only thing that would make self-study a bad idea is if self-study is not an effective learning method for you, which could delay your training.


Why does the F-16 canopy have a K-shaped 'latch'?

The function of the form is to act as a throttle stop when the part is in the position shown in the picture. It prevents full movement of the throttle when canopy is not securely closed and sealed.

When the canopy is closed, the latch is moved by pushing the bottom part of the latch towards the outside of the plane. This moves the throttle stop out of way and actuates the canopy seal.

See this Youtube video for an example, latch operated at 0:25.


After takeoff, why do some airlines' flight attendants rise from their jump seats earlier than other airlines'?

The industry standard is to switch the seat belts signs off while crossing 10,000 ft. And this is usually the moment when flight attendants get up. But really depends on company policies as you saw. Even within the same airline there may be different standards for different fleet, which actually depends more on timing for service that on safety.

In any case, the decision to let the flight attendants to get up depends solely on the captain, who is the one looking after their safety. If he suspects turbulence ahead he will delay the signs as much as required.

You have also to consider that flight attendants receive special training on how to move safely around the aircraft, even with severe unexpected turbulence. If you encounter some light turbulence in your next flight pay attention on how they move: looking for a stable position opening the legs more than usual walking and pointing their hands to places they could grab immediately.


Does pilot-controlled lighting work if you are interrupted by another voice transmission?

From a technical standpoint, it's extremely difficult to tell two different signals on the same frequency apart. So, if someone steps on you while you're trying to turn the lights on, then the ground equipment can't tell the difference between their radio and yours. So, unless the other radio is far enough away that it doesn't register on the PCL receiver at all*, it won't activate. You'll just have to try again when the other pilot's done talking.

In general, it's usually nothing to worry about, because the other pilot(s) nearby will hear you clicking, and know to avoid using their radio until you're done.

* Many airports turn the sensitivity on their PCL down so that distant planes on the same frequency won't interfere with a local pilot trying to land.


Why don't pushback tugs take the aircraft to the runway?

Way slower, more congested, more damage risk, many more expensive tugs required.  Taxiing under power is much faster and safer than towing in general (towing is a high risk operation and all sorts of bad things happen when tugs move large aircraft). It would be a mess on a taxiway with a line up waiting to take off with trucks and personnel mingling with ready to fly jets.  Generally, when you are flying you want the towing unit disconnected and gone ASAP.

The only reason you have tugs at gates in the first place is because of the need to back up; they're just there for the pushback.  If someone designed a gate with a pass through design that didn't require backing up and allowed for at at least one engine running, you wouldn't have tugs there at all.


How would you brief passengers who will try flying your plane?

I find that virtually all the passengers I've let fly for the first time were already so scared of the controls that no "safety briefing" of that sort was necessary.

  Don't fight me on the controls.

  If I say let go, let go immediately.

If you suspect there's even a remote chance of either of these problems, maybe you shouldn't be letting this person fly your plane.

  Don't move any of the controls very rapidly.

  Don't move any of the controls to their limits.

In most small airplanes without hydraulics, it takes quite a bit of force to deflect any of the controls rapidly to their limits. And as soon as your first-time passenger starts to push on the controls, they're going to feel increasingly strong g-forces as the plane responds. For first-timers, this is usually a pretty intimidating feel. If someone is pushing too hard, they're going to feel it, and almost certainly back off or let go entirely.

"Positive transfer of control" using 3-step acknowledgment such as "You have the controls" / "I have the controls" / "You have the controls" is a good idea for flight training, or for flights with 2 pilots taking turns at the controls; but in my opinion it's not necessary for a joyride with a friend. As the PIC, and the only licensed pilot in the cockpit, you need to be monitoring the situation at all times anyway. If you decide the situation requires you to reassert control, you can simply ask them to release the controls. If you can't trust the person to do this promptly, you probably shouldn't be letting them fly your plane anyway; a preflight safety briefing isn't going to solve that.

To be as safe as possible, you can take the following steps before allowing your passenger to fly (some of these you already stated):

Select a location away from controlled airspace, busy airway/routes, or other special-use areas like drop zones.
(Optionally, if you don't mind the extra radio chatter) Tune a nearby ATC radar facility (approach/center) and request radar advisories. Tell them you'll be maneuvering in a certain area.
Climb to a sufficient altitude to allow good clearance from all terrain and obstacles (antennas, etc.), and to allow enough altitude for recovery if your passenger should somehow manage to stall or enter a steep dive or something.
Trim for straight & level flight at $V_A$ for your current weight (lower than the gross-weight $V_A$ you get out of the book).
Make a set of clearing turns and scan for any traffic in the area.
Give your systems a once-over and verify you have sufficient fuel.
Hand over the controls!

You didn't specifically ask about this, but I've flown with a lot of first-time passengers, people who have never been in an airplane. Both children and adults. Many of them are understandably quite nervous. Here are some things I try to do to make it as easy, fun, relaxed and stress-free as possible for them:

Give them a simplified, plain English description of the flight. Tell them exactly what you plan to do and what order things will happen in. E.g.

  First we're going to start the engine. I'll get on the radio and get clearance from the control tower. Then we'll taxi out to the runway and stop for a few minutes while I go through some checks to make sure the plane's in good shape. Then we'll take off and head out to the east to do some sightseeing. While we're up there, if you're comfortable and would like to try your hand at the controls, we can do that. When we're done with that we'll turn around and head back to the airport, land, and taxi back in.

Don't use fancy words or terms that a non-pilot wouldn't understand.
Help them enter the airplane. Show them how to open and shut the door. Show them how to buckle and unbuckle their seat belt.
Ask them if they have any questions.
Do your normal preflight safety briefing, again using simplified English and avoiding pilot terms. Limit it to points that are relevant to a passenger (avoiding the controls, staying quiet if asked, opening the door). They do NOT need to hear about what you're going to do if you have an engine failure on climbout. If this is a normal part of your preflight / before takeoff briefing (as it should be), say it to yourself mentally, not out loud.

During the flight:

Talk your way through everything you're doing. When you're ready to do your run-up, tell them:

  I'm about to run the engine up to power to make sure everything's running smoothly. I'm holding the brakes so we're not going to go anywhere, but the engine will get pretty loud for a minute.

When you're doing your magneto / prop governor checks:

  Now I'm going to do some things to the engine to make sure it's running right. It's going to make some pretty funny noises, but it's perfectly normal.

Talking through everything accomplishes a few goals:

Avoids startling the passenger with something unexpected. A prop governor check sounds really bad to somebody who knows about engines but nothing about planes. A stall horn in the flare may be perfectly normal to you but a loud buzzing alarm is the last thing the first-timer will be expecting to hear. Tell them about it ahead of time.
Makes the passenger feel like they're a part of the flight and not just dead weight in the plane.
Keeps you focused on your tasks as PIC and discourages you from getting distracted in conversation with your passenger.

Make the flight as smooth as possible. Don't overcontrol the airplane. If you drift 100' from your intended altitude, don't pull 2 g's to get back up to it. Make it slow and gentle. They're not a pilot, chances are they're not going to know you drifted 100 feet. They will know if you jerk the thing around. DO NOT hot dog the airplane. You may be bored with slow, gentle flight, but your passenger isn't.
Speak slowly, clearly and confidently.
Smile and try to look like you're having fun. Your first-time passenger is probably feeling pretty vulnerable. When people are vulnerable they feed on the emotions of the people around them. If you look like you're having the time of your life, they're probably going to have fun too. If you look angry, ticked off or scared, you're going to scare them too even if the flight is perfectly smooth. This is especially true and critically important with children!

If/when they're ready to take the controls:

Show them how the yoke controls pitch and roll. Do some (very) gentle climbs and rolls to illustrate what various control inputs do.
Tell them to look outside and not to worry about all the fancy intimidating lights and dials in the cockpit. Tell them that the only tool a pilot needs to fly the plane in good weather is their eyes.
Tell them to relax and have fun! Assure them that they aren't going to crash the plane or break anything and that you're there watching and won't let them do anything unsafe.
After a few minutes, once they get the hang of basic control inputs, you can start to tell them about sight references: show them how to look at the horizon and tell if they're banked, climbing or descending. After 15-30 minutes you should be able to get virtually any passenger to be able to hold straight & level attitude and make gentle turns. Being able to accomplish this is very rewarding for your passenger and makes them feel like they achieved something. It encourages their excitement about aviation and makes them want to fly again.
Don't forget to do your job: scan for traffic. Monitor your engine gauges. Listen for ATC calls. Don't stray into controlled airspace. "Maintain situational awareness."

I've had a great deal of success using these tips when flying with first-timers and children. In 16 years of flying I have had only one bad experience, with an adult passenger who had an unknown (to me) and pretty severe anxiety problem and had a panic attack shortly after takeoff. A couple of kids have fallen asleep on me (which I took as a compliment). Everyone else had the time of their life. And let me tell you... if you're someone who loves flying, there is no better feeling than sharing that with someone else and watching their excitement. It's the closest you'll ever come to reliving your own first flight, which hopefully you remember fondly because somebody cared as much as you do about being the best possible ambassador for aviation!


It appears to be a Celera 500L, owned by Otto Aviation Group.

This article has more information: "Unmasking The Bullet-Shaped Mystery Aircraft After It Reemerges At Victorville"

  The registration also provides us with a designation for this mystery
  plane—the Celera 500L. It is the only aircraft registered by the
  company with the FAA. The War Zone contacted the Otto Aviation Group
  by phone and they said they could not comment on the aircraft in any
  way.

  This new high resolution image shows the rear of the airframe, which
  is the perfect companion photo to the lower resolution, front aspect
  image that we posted last April. We can now clearly see the five
  bladed, variable pitch, "pusher" propeller that will provide thrust.
  The airframe also features what appears to be all-moving vertical and
  horizontal stabilizers, and long, slender wings that are likely
  optimized for laminar flow.

  The Bell X-1 like teardrop fuselage design, which includes a cockpit
  windscreen seamlessly blended into the fuselage, gives the aircraft a
  large internal volume and high aerodynamic efficiency. It's safe to
  say that efficiency is what this aircraft is primarily about. Even the
  prop size looks small in relation to the overall aircraft, which would
  point to the possibility that it makes very good use out of the thrust
  it has on hand.


Why does this B-52 carry a payload only on its right wing?

@Peter is right.

The aircraft in question is the "The High and Mighty One" a NB-52A serial number 52-0003, which was used as a launch aircraft for the North American X-15, a hypersonic rocket powered aircraft. The 'missile carrier' (pylon) is used for carrying the X-15.

Here is a view of the carrier itself, just after launching.

"X-15 launched bw". Licensed under Public Domain via Commons.

This was used as the X-15 was not designed to takeoff under its own power; it was rather designed to be carried aloft and drop launched from under the wing of a NASA B-52 'mother ship'. As of March 2016, the X-15 holds the official world record for the highest speed ever reached by a manned, powered aircraft.

Image from air-and-space.com; Photo courtesy North American Rockwell.

The aircraft underwent significant modifications for installation of the pylon, including removal of the wing (no. 3) fuel tank, disabling the inboard flaps in the starboard wing and cutting a notch to accommodate the X-15's vertical stabilizer.

The heaviest weight the aircraft carried on the pylon was ~53,100 lb, for X-15 with external fuel tanks. A number of tests were carried out and it was found that the carrier aircraft were capable of trimming out the unbalance of the B-52/X-15 combination. So this caused few problems in flight in the operational range.


To a pilot, does turbocharging differ from supercharging?

I have some of the answers:

•Is it easier or harder to overboost a supercharger? If you do, are there waste gates?

This is an important point.  Waste gates, when opened, allow exhaust to bypass the turbocharger, reducing manifold pressure by slowing down the turbo.  Older turbos had manually adjusted waste gates, and even fixed waste gates.  The pilot would have to monitor boost pressure and adjust the waste gate to avoid overboosting the engine.  Newer turbos have automatic waste gates.  Superchargers, being belt or gear driven, do not have waste gates as the supercharger is not dependent on exhaust gas flow.  I do not know if they have manifold pressure releif valves in case of overpressure but I doubt they would.

So a key difference in a pilot's operation of the engine is that in a manual waste gate engine, the manifold pressure gauge needs to be scanned frequently and the waste gate adjusted accordingly.   Less important in an automatic waste gate or supercharged engine.

•Do engines with superchargers need a cool-down period before being shut off?

No.  The cooldown period in turbochargers is necessary to cool down the bearings in the turbocharger after high cruise power settings.  Idling on the ground allows cooler oil to flow through the bearings, removing excess heat.  Look at your exhaust gas temperature gauge - this is the temperature of the gasses flowing through your turbocharger.  The oil present in the turbocharger bearings will "coke", or turn into a solid at that temperature.  Upon landing, a slow taxi to the ramp will usually provide sufficient cool down time.  Usually!  Time this and don't forget to cool down as recommended.

Superchargers are geared to the engine (or belted) and do not use the hot exhaust as their source of power.  So even though they can get quite hot, they don't approach the heat of the exhaust gasses.

•Any other operational differences that would be meaningful for pilots to know.

This is not really an operational difference, but in addition to turbocharged and supercharged engines, there are also turbonormalized engines.  TN engines are turbocharged engines with their boost limited to atmospheric pressure at sea level.  Say 30 inches, not the 40 inches you might expect from a turbocharged engine.  The TN engine permits sea level performance up to a critical altitude, above which the TN engine cannot maintain sea level manifold pressure.  In other words, performance at a sea level takeoff will not be materially different from that of a naturally aspirated engine, but as you climb, the power will not decline as you climb.  So your Leadville CO takeoff will be the envy of the stock C-172 crowd.


What is the missed approach procedure when initiated below MDA/DA/DH?

When would you go missed if below MDA/DA(H)?

You're only allowed to operate below the MDA/DA(H) if all of the following are true (14 CFR 91.175(c)):

You can land using normal descent rate and maneuvers
You have at least the flight visibility required for the approach
You have at least one visual reference from the list (not just the approach lighting system)

91.175(e) says that you must go missed if those conditions are not met and you're below the MDA, at the MAP, at the DA/DH, or "at any time after that until touchdown", i.e. below MAP/DA(H). Essentially, if any of the conditions in 91.175(c) are no longer true, then you have to go missed immediately. Practically, the most likely issue is seeing the runway environment, but you should also go missed if your approach is unstable, for example.

On an ILS approach specifically, that would most likely mean that you saw the approach lights at DA/DH (or above), followed the glideslope down to 100' above TDZE, but then didn't see any more visual references. That should be very unlikely if you really do have the flight visibility required for the approach but I'm sure it could happen somehow, e.g. there's ground fog in the wrong place at the wrong time. Or something else could go wrong: the runway lighting completely fails because of a power cut, or there's an obstruction on the runway.

Is obstacle clearance assured if going missed below MDA/DA(H)?

No. The Instrument Procedures Handbook (chapter 4) says several times that if you go missed below MDA/DA(H) then you have no guarantees and it gives some general advice on what to do:

  If the aircraft initiates a missed approach at a point other than the
  missed approach point, from below MDA or DA (H), or on a circling
  approach, obstacle clearance is not provided by following the
  published missed approach procedure, nor is separation assured from
  other air traffic in the vicinity.

  [...]

  In the event a balked (rejected) landing occurs at a position other
  than the published missed approach point, the pilot should contact ATC
  as soon as possible to obtain an amended clearance. If unable to
  contact ATC for any reason, the pilot should attempt to re−intercept a
  published segment of the missed approach and comply with route and
  altitude instructions. If unable to contact ATC, and in the pilot’s
  judgment it is no longer appropriate to fly the published missed
  approach procedure, then consider either maintaining visual conditions
  (if possible) and reattempt a landing, or a circle−climb over the
  airport.

This part is directed at pilots using night vision systems, but it looks like good advice for any pilot considering going below MDA/DA(H):

  If a pilot initiates a go-around at a point below DA/DH or after the
  MAP, obstacle clearance is not necessarily provided by following the
  published missed approach procedure. Prior planning is recommended and
  should include contingencies between the published MAP and touchdown
  with reference to obstacle clearance, aircraft performance, and
  alternate escape plans.


Not all fuel is stored in the wings. Some is also stored in the fuselage. The ER variants have a larger, or additional, centre (fuselage) tanks at the expense of cargo bays volume.

The centre tank is located between the wings to minimize the change in centre of gravity as the fuel is consumed. The wing spar, which must go through to provide sufficient structural strength, does not allow the cargo bay to be continuous in most designs anyway.

The ER models may be also fitted with more powerful engines to increase the maximum take-off weight (engine out performance is usually the limiting factor), so the plane can still take reasonable amount of payload when the tanks are full.


Can I land at an uncontrolled airport under class C without talking to ATC?

It looks to me like New Kent is entirely below the shelf of the class C space.   You don't need to go through the Class C Core at all, so I don't see that you need to speak to them.  The detour to avoid the core looks minimal

You can see the shelf height shown as 42/14, meaning that the class C space starts at 1400 feet, and goes up to 4200 feet.   Just stay below the shelf, at about 1100 feet. At that altitude, pay extra attention to any obstacles like radio antennas!  I do see several obstacles going up to 500 / 600 feet!

If you want to let them know of your intentions, I'd just say:

"Potomac Approach: N12345, Departing Richmond Exec, to New Kent, VFR below Class C.  On Frequency."

They will likely respond with:

"N12345: Proceed as requested. Maintain VFR"

Link to Flight Diagram


What's the typical cost (and its breakdown) for a long-haul commercial flight?

Fuel

The fuel consumption of the A380 is about 11 metric tonnes per hour. With a fuel price of \$1000 per metric tonne, this results in \$11000 per flight hour.

Amortization

An A380 will cost about \$350M. The aircraft will be used for about 25 to 30 years, but let's assume the amortization period is about 20 years with a residual value of \$50M. With an interest rate of 5%, you would pay about \$24M per year.

That is about \$2740 per hour, or \$0.76 per second, flying or not.
Assuming a usage of  60%, taking into account turn around times at the gate and maintenance downtime,  it boils down to \$3915 per flight hour.

Crew

Captain costs \$160K per year, the F/O \$90000. Let's assume they fly about 60 hours per month, the combined flight deck crew cost is about \$350 per flight hour for the base salary. Another \$80 needs to be added for allowances bringing the total to \$430 per flight hour.

Cabin crew rate would be around $40 per hour, so for 20 crew the cost will be \$800 per flight hour.

Also allowances for overnight stays and hotel costs need to be taken into account

Airport charges

These vary extremely between airports. You can basically break the costs down into costs related to the aircraft, the passengers and various taxes by the government.

Aircraft cost usually are related to the Maximum Take-off Mass (MTOM) of the aircraft and the noise category. A Boeing 747-400, while less heavy than an A380, will in some cases be more expensive due to the higher noise level. Many airports differentiate between peak and off-peak hour landings.

I can't find accurate data for the A380 but an old table that I have for the Boeing 747-400 suggest that total the cost vary between about \$6000 to \$25000.

Overflight charges

Fees are levied by countries whose territory is flown over, mainly to cover ATC cost. The cost is typically based on the distance flown and the MTOW. For a 747-400ER over Europe, the fee is on average 145EUR per 100km. Assuming an average speed of about 900km/h, the hourly cost is about 1300EUR/h. These costs are lower over the high seas and over the US.

Rough total

Based on the above, the total will be between \$22,000 and \$41,000 per hour.


How much weight does a thrust reverser add?

For the LEAP-1B example, the weight you found is a dry weight that does not include the reverse system per the type certificate. Such weights are very hard to come by, even from the respective system manufacturer. However, statistical data can help.

According to NASA, the reverse system of a GE90 class engine can weigh upwards of 30% of the nacelle weight.

  [Studies] conducted by General Electric Aircraft Engines
  indicate that the thrust reverser system accounts for more than 30 percent of
  the nacelle weight (not including engine) for an engine having a fan diameter in
  excess of 100 inches. This could be as much as 1500 lb [680 kg] for a GE 90 class
  engine.

As for the nacelle, an older NASA paper says the weight is in direct relation to its surface area constructed from simple cylinders.

  [For the nacelle, the surface] area is used to correlate weight, and, rather than introduce
  the complexity of the actual nonaxisymmetric shape of the nacelle, simple
  cylinders are assumed, using the fan diameter, the turbine diameter, and the
  lengths from the previous section.

  [And] a unit weight of 17.1 t o 19.6 kg/m2 appears reasonable.

From the same paper, here are some examples for the weight of the reverse systems of different engines:

Since the CF6 days manufacturers were able to reduce the weight of the nacelle and its components due to the "extensive use of composite materials."


Tail numbers not starting with N, with domestic US carriers?

Yes, these can be legit.  For example, EI- means the aircraft is registered in Ireland.  Others look corrupt, though.  HZ-AAA is Saudi Arabia, but your HZ example looks too short.  The examples starting with four numbers don't match any country's pattern.
https://en.wikipedia.org/wiki/List_of_aircraft_registration_prefixes
The examples here that start with a string of digits all resolve to actual aircraft, if you prepend an N to them.  (Commenter Ralph J suggested this.)
Corrupt data wouldn't be too surprising.  For 2005, for example, 15000 of the 594000 entries had no tail number at all.


What is the aerodynamic centre and how does it relate to the pitching moment?

A pitching moment is every moment acting around the lateral axis. Since a moment is the combination of a force and a lever arm, the magnitude of the moment depends on the choice of reference point, the point around which the pitching moment is defined. For flight mechanics, it helps to choose the center of gravity for all pitching moments, because then the weight force will not add a pitching moment of its own. Also, the center of gravity is special because this is the point around which the airplane rotates while in flight.

I guess you mix up aerodynamic center and center of pressure. For me, it helps to use the term "neutral point" instead of aerodynamic center. Why?

Center of pressure describes clearly what it is: If you integrate all the pressures acting perpendicularly to the airflow, the resulting force acts in the center of pressure, just like all masses are summed up in the center of gravity (which, therefore, should be better called the center of mass).

In contrast to the center of mass, this center of pressure is not fixed, but moves when the angle of attack changes. If the airfoil has positive camber, the center of pressure moves forward with increasing angle of attack. If you now move your point of reference away from the center of pressure, you need to replace the lift force by the combination of the lift force and a moment (cogging torque). The motion of the center of pressure is such that at one point the cogging torque is constant regardless of angle of attack and lift. This is the aerodynamic center or neutral point, and I think "neutral point" describes much better what it is: The one point where the cogging torque behaves neutrally regarding angle of attack changes.

The real reason for this name is that static longitudinal stability is neutral (neither positive nor negative) if the center of gravity falls on the neutral point.

In stable flight the pitching moment around the center of gravity has to be zero; otherwise the airplane will display an accelerating pitch motion. To zero the pitch moment, the center of pressure is shifted onto a vertical line through the center of gravity. This shifting can be done by adding or subtracting lift at the tail, which in turn is done by adjusting the elevator deflection or the stabilizer incidence (if the plane has a moveable stabilizer)

Background

In potential flow theory, lift can be calculated as the linear superposition of a contribution from camber and one from angle of attack. While the camber-related part of lift is constant, the angle-of-attack related part varies linearly with this parameter. The center of pressure of the camber part is somewhere at mid-chord (details depend on the camber line; with a Joukowski airfoil the center of pressure is precisely at mid chord). The center of pressure of the angle-of-attack dependent part is at the quarter chord (the center of the area below the chordwise Birnbaum distribution of lift). The important part is the self-similarity of Birnbaum distributions for different angles of attack: The center of pressure of the angle-of-attack dependent part is constant.

Since lift at zero angle of attack is solely from camber, the center of pressure is at around mid chord and moves forward towards the quarter chord point as angle of attack increases. The cogging torque of the camber-related lift contribution around the quarter chord point is also constant, and since the angle-of-attack dependent part of lift has its center of pressure in exactly this quarter point, it will not add a pitching moment of its own at this point. Ergo, the cogging torque of lift in potential flow is constant if the reference point is the quarter chord point.

Fun fact: The center of pressure will move into infinity as the angle of attack is reduced to the zero-lift angle of attack.


Notwithstanding the case that Quiet Flyer mentioned, generally no, because aerodynamic forms are inherently beautiful, so the need for dedicated stylists isn't there because an un-artistic designer striving for the best configuration will tend to produce an attractive shape by default (with exceptions of course, but overall).  This tends to fit in with the old observation that beautiful aircraft tend to fly better than ugly ones.
Sometimes however, a particular contour, especially vertical fin shapes, become associated with a "brand" (since almost all airplanes are identified by their side profile) so the designer will conform to the brand shape to some degree. That doesn't take a dedicated stylist however.
The biggest example of automotive style styling practices infecting aviation I can think of is Cessna's entirely marketing driven change to their single engine line in the mid 60s, going from straight to swept vertical tails.  Swept tails on 120 mph airplanes made a negligible difference to performance or handling (yes there is probably a theoretical benefit, but I've never seen any evidence that they made any practical difference that could be measured or observed and there is a significant manufacturing cost) but were done to look modern, since faster airplanes all had swept tails and they certainly do look sleeker. You will notice that they didn't also sweep the horizontal tail, just the vertical one, because no one cares about the view from below (lots of airplanes have swept horizontal tails; I'm just pointing out that Cessna saw no benefit to changing their single engine line this way).
Another one was "Omni-Vision" where turtle decks were cut down to add a rear window, partly for a more airy cockpit and visibility, and partly to look a bit more like a car. There was a significant drag penalty to Omni-Vision, costing a couple mph in speed when adopted vs the old straight turtledeck, but it was obviously considered worthwhile for both practical and aesthetic reasons as it became ingrained in Cessna's "brand".
In the 50s and 60s Cessna also adopted other (goofy) automotive marketing terms to describe useful engineering changes like adoption of steel gear legs, "Land-O-Matic Gear" (after acquiring Steve Wittman's leaf spring gear leg patent) so I think they probably brought in marketing types from the automotive industry, but I don't think dedicated stylists were necessary.


How is the compliance time in this AD interpreted?

Break down the timeline logic.  The key word is "later".

AD released today.

Last inspection may or may not have been done 50 hours ago, which pre-AD was voluntary or part of a non-mandatory maintenance program, or part of some recommended Service Bulletin, that is now being mandated, or maybe it was never done at all.  Assume it was done 50 hours ago.

Which requirement is later?  25 hours from today, or 100 hours since the inspection done 50 hours ago?  100 hours from the last inspection is still 50 hours out from today, so it is later than 25 hours from today, so do it in 50 hours.

Say last inspection was 90 hours ago.  Hundred hours later comes up in 10 hours.  But the AD says whichever is LATER.  25 hours from today is the later than 10 hours from today, so that applies.

Or inspection has never been done before.  25 hours from today.

In no case do you have to do it in less than 25 hours.  It's more or less the same as that other one you posted about landings, but with a bit different wording.


What wing spacing is best for a tandem wing configuration?

A tandem wing is never the most efficient planform, but makes for a compact airplane. A case in point is the French design Pou du ciel ("sky louse") which was a very popular homebuilt in the 1930s. The closely coupled wings and the short wing span made it one of the smallest man-carrying designs, but since the rear wing could act like a slotted flap, producing nonlinear lift increases, the aircraft needed careful handling.

Pitch control was achieved by changing the incidence of the forward wing, and a trailing edge down movement normally created a pitch-up moment. Once the gap between the forward wing's trailing edge and the rear wing became too small, the rear wing would show a nonlinear lift increase and add a nose-down movement which became stronger when the pilot pulled the stick further aft. In this condition the aircraft would dive into the ground unless the pilot counter-intuitively moved the stick forward again.

Mignet HM 14 Pou du Ciel (picture source). The initial type flew with a motorcycle engine of 17 HP.

Your idea of moving the wings apart is sound. However, in order to make the plane statically stable, the rear wing needs to produce less lift per area relative to the forward wing, making it less efficient. If you now run an optimizer which varies wing area and minimizes overall drag, you will invariably end up with a conventional design in which the rear wing has 15% - 20% of the area of the main wing.

What is the optimum distance between the wings? This depends entirely on your preferences. You need to know that stability increases linearly with wing-tail distance while pitch damping increases with the square of it. If you want an agile aircraft, keep both close together. If you want to reduce the tail surface and don't intend to fly aerobatics, move both apart. The key figure for stability is the tail volume, which is the product of tail surface area and the distance between wing and tail. Look at airplanes you think are worth emulating and try to match the tail volume of your design to theirs. But don't use a magic number.

In order to minimize engine power, reduce speed. The power need of an aircraft scales with the third power of speed, and many designs of the 1920s successfully used motorcycle engines. A high aspect ratio and a low wing loading, like in a glider, will help to get airborne with just 25 HP. Successful designs with such small engines were the Daimler L 20 or the Messerschmitt M 17.

Messerschmitt M 17 (picture source)


Which are the largest planes to have operated on an aircraft carrier?

U-2s also landed and took off from aircraft carriers.


How turbercle wings could generate aerodynamic advantage?

No, please, not another revolution of how we build airplanes again!

The linked article mentions two guys who pose as the discoverers of humps on whale flipper leading edges. What precisely have generations of marine biologists overlooked before?

Now to the humps: They produce a 3D flow pattern close to the leading edge which will help the flow to transition to a turbulent boundary layer more quickly. This is helpful at high angle of attack at intermediate Reynolds numbers (around 1 Mio) and will make the whales more maneuverable.

This is not to say that it will help any existing aircraft. Had nature given the whales the opportunity to integrate slats and double-slotted flaps into their flippers, they sure would have done so. This will help much more to increase maximum lift. Also, typical aircraft Reynolds numbers are much higher than those on whale flippers, and there turbulent transition is very quick. Right now, most efforts center on delaying this transition to reduce friction drag.

Swept wings will see a massive drag increase if this sort of leading edge is used.

The "tubercles" are a very specific form of turbulators and optimized for a narrow application. In other words, don't invest in this WhalePower company!


What is the correct way for pilots to say the time?

"Zero seven five seven" is the correct way to state the time, pronouncing each digit separately per the table below.

Aircraft call signs are sometimes grouped instead of annunciating each digit, for example United 6330 would be "sixty three thirty" instead of "six three three zero".
 Otherwise, headings, time, coordinates, and all other numbers used in aviation radio communication are generally spoken individually, digit by digit.

It is important to note that in aviation the need for clarity overrides common English usage.  For example, while it is common to pronounce the number zero as "oh" in the everyday world, aviators are taught that zero and O are distinctly different:  One is a number, and the other is a letter of the alphabet.  They should never be substituted for one another, or used in the wrong context.

Finally, the example you offered is incorrect because it isn't "seven hundred and fifty seven hours", past time zero, rather it is "seven hours and fifty seven minutes".  (Except it isn't said like that...)


Why does a de Havilland Comet have radiation symbols on the instrument panel?

Instrument markings back then were painted with luminescent paint containing radium, so they would glow in the dark continuously without having to be energized by a light source.
You can buy luminous watches today with the same feature that use tiny vials containing tritium gas for each marking (much less radioactive than radium and produces negligible amounts of radioactivity, so the watch can't hurt you). These also glow 24/7, but tritium has a shorter half-life and they lose about half their brightness every 7 years or so.
The radium paint was mostly a danger to the women who painted the instrument faces, who would lick the brush tips to get a fine point and could potentially ingest enough radium to develop radiation poisoning.
The radioactivity warning signs may be perhaps a little bit of overkill since the actual radioactivity emissions aren't that high and most of the risk is from ingesting radium directly; it's advised to avoid opening an instrument and poking around without appropriate precautions (If people knew the amount of radiation they're exposed to just being out in the natural environment, they'd probably want to move into a lead house.  I recall a story about a 3 Mile Island Nuclear employee who was setting off the radiation detectors at work while coming IN to work, not while leaving.  From some kind of radiation exposure while off work.) .


Are evacuation slides meant to be used as safety boats?

The inflatable slides are indeed also life rafts and they are meant to be detached. Consider United 1549 (landed on the Hudson). Here you can see the slides inflated and floating

Here you can see people in the slide, which has been detached from the airplane

The Wikipedia article mentions it specifically

  Sullenberger advised the ferry crews to rescue those on the wings first, as they were in more jeopardy than those on the slides, which detached to become life rafts.

It's impractical to keep an airplane afloat in the water. Assuming you successfully land intact, the plane is still a metal tube on the water. It may be airtight, but water will eventually begin to invade. Airbus has a water ditch button to help slow (but not prevent) flooding

  Some aircraft are designed with the possibility of a water landing in mind. Airbus aircraft, for example, feature a "ditching button" which, if pressed, closes valves and openings underneath the aircraft, including the outflow valve, the air inlet for the emergency RAT, the avionics inlet, the extract valve, and the flow control valve. It is meant to slow flooding in a water landing.

You want to evacuate as soon as possible. Remember, the slides help keep some water away from the door, but the plane will eventually flood and sink.


What is the correct answer to this Mass and Balance calculation?

The answer is 19,428, but I could only get there by Googling 'MRJT' to get the missing information:

DOM + all of the fuel is 43,372.

And since MSTOM is 62,800, that leaves you with 19,428 for payload (allowable traffic load).

$$62,800 - (27,372 + 12,000 + 4,000) = 19,428$$

Below you can see the calculations for MTOM, MLM, and MZFM. Since the traffic load for the 'MTOM limited case' is the lowest, the maximum traffic load for the flight is 19,428 kg.

(Table courtesy of DeltaLima.)


What is that pitot-like device under the left wing of the Cessna 152?

It's the fuel tank vent. It prevents forming a vacuum in the gas tank as it's drained, which would prevent further fuel flow to the engine.


Is the lift vector reversed during inverted flight?

This is easiest to understand with a fully symmetrical wing, which indeed are popular with aerobatic aircraft.  The direction of "lift" has nothing to do with sky or ground and everything to do with your angle of attack to the relative wind.

When inverted, you simply (as the professor said) push forward on the stick, which makes the wind strike the "top" of your wing.  Inverted, this does the trick as lift is now towards your floor, but gravity is toward your head.

Right side up, you make the wind strike the bottom of your wing by pulling back on the stick.


Is excess fuel leaking normal during take off of a B737?

No it is not normal. It can happen if the wing tanks are fully filled, typically for long trips or when the airline is tankering fuel to airports where fuel is more expensive. When cold fuel warms up it expands. With full tanks, the fuel has to go somewhere and it flows through the vent channels and will end up in the surge / vent tanks in the wing tips. From here the fuel can flow back into wing tanks (when there is space again) through a check valve.

 Boeing 737 fuel vent system. Source: Aeronautics guide

There is a little NACA duct at the underside of each wingtip (about a meter from the tip) in the surge tank. That ensures a positive pressure in the surge tank and through the vent channels in the fuel tanks. This help the fuel pumps, reduces evaporation of the fuel and prevents a vacuum when the fuel is being used.

source: www.b737.org.uk

If the wing tanks are overfilled, this is where the fuel will come out.

source: the aviation forum: user Keithnewsome

During the take-off the fuel tanks are changing their shape a little bit because the wing is flexing up. This may slightly reduce the volume of the tanks so if they are fully filled you will see a fuel trail spilling from the fuel vents at take-off.

Another situation where this may occur is at zero-gravity. I have seen this many times during parabolic flights with a Cessna Citation. At zero gravity the fuel will start to fly around in the tank and it will find its way to the exit (the vents at the wing tip) resulting in an impressive cloud of fuel from the wingtips. Whilst it looks like a big cloud, it is actually very little fuel that is lost.

In the video, you see the fuel trail starting below the wing (at 1:28), a couple of seconds into the 0-G part of the flight.


How do propeller-driven, fixed-wing UAVs counter negative torque from engine rotation?

In exactly the same way as any conventional, single-prop aircraft does

Which is to say, by using stabilizer and aileron/rudder trim, and the natural resistance that wings/stabilizers give.

The wings/stabilizers will naturally resist rolling forces to some extent, particularly at flight speed. At lower speeds (eg when taking off or landing) the control surfaces can counter the force quite easily - a little opposite rudder and aileron is all that's required.


What is this ring-shaped device behind this DC-8's jet engine?

(airliners.net) Ejector on the Rolls-Royce Conway of a DC-8.
It's called an ejector.
Introduced in c. 1958 by Douglas for their DC-8, it is extended during takeoff and landing, and stowed during the flight because it increases the drag at high-speed flight.
In the extended position it acts as a noise suppressor, and it also reclaims thrust that has been lost due to the corrugated exhaust nozzle. Doors within the ejector also close to provide thrust reversal.
(Flight—PDF)

Two views of the device developed by Douglas to suppress the sound and reverse the thrust of the DC-8. The corrugated exhaust nozzle is combined with a cylinder which extends beyond the nozzle during take-off. This "ejector" is claimed to reduce the sound level by 3-4 decibels and increase the thrust sufficient to offset the loss caused by the nozzle. The indentation near the forward lip of the ejector is one of the two doors which close to form a thrust brake. Noise level with the ejector ring and nozzle combined is said to be reduced by 9-12 decibels.

(Images from aamalebourget.fr and flightglobal.com)
The image on the right shows a similar installation on the BAC One-Eleven with the positioning screw-jack mechanism.
(YouTube) Factory testing of the ejector on the DC-8.


Why does an aircraft leave a white smoke trail?

Actually, there are three types of trails an aircraft can leave in the sky:

1. Condensation of water vapor in the exhaust gas and/or the wake

This needs the very cold, very dry air at higher altitudes between 6000m and 12000m. Water vapor in the exhaust stream condenses and, pushing the local air above its saturation water content, forms a white, frozen mist. Also, particles from partially burnt fuel form condensation cores wich stabilise the contrail and let it grow over time from humidity already present in the air. Depending on the atmospheric humidity, these contrails disappear rather quickly by sublimation or can stay in place for hours and even grow into cirrus clouds. They are called condensation trails or short "contrails".

Cirrus clouds triggered by aircraft contrails (picture source)

While the added water vapor in the exhaust gas helps in contrail production, the condensation happening in the pressure field around an aircraft can already produce a contrail all by itself. If the relative humidity is close to saturation and the condensed droplets freeze quickly, the aerodynamic contrail will disappear rather slowly. The same condensation happens also at lower altitude but will not leave a contrail  in temperatures above 0°C. Fog (liquid droplets) will vaporize quickly, but when frozen the condensation will last longer, until the water is re-absorbed by the air by sublimation, a much slower process than evaporation.

Engine and aerodynamic contrail forming behind an A340 (picture source)

2. Smoke from unburnt or partially burnt fuel

This was prevalent in early jets and allowed to spot them from a distance - just follow the black line, at its tip is an aircraft. Smokeless combustor cans which allow more fuel-air mixing put an end to this. For more information I recommend the excellent web page contrailscience

This B-47 uses rockets to accelerate quickly which leave the biggest smoke trail, but also the old J-47 left a lot of smoke behind (picture source).

3. Oil mist or smoke flares

The third source is shown in your picture: Oil is injected into the hot exhaust stream which forms a dense mist. This can be done with jets and piston engines, and gliders or parachutists use smoke flares. Once they are ignited (in most cases electrically) they burn down and cannot be switched off.

Smoke flares on the wingtips and fuselage of a glider (picture source)

There are many more things that can be sprayed from an aircraft (fuel, obviously, when it has to be dumped in an emergency, fertilizer or insecticides, silver iodide to seed clouds), but these are special cases. I encourage you to visit contrailscience.com for an exhaustive list of those other cases.

LS-10 glider dumping ballast water (picture source)


Can a commercial pilot rent an airplane and use it for hire?

It doesn’t matter whether the pilot rents, leases or owns the plane; if they are offering “aviation services” to the “general public”, then they are “holding out” and would need an Air Operator Certificate.


Why was the Iraqi airspace closed on 12 Mar 2020?

The diversion was roughly 3 hours into the flight (based on FlightAware), at about 0000 UTC (the 13th).

At "12 MAR 22:50", i.e. about an hour before, the US issued the following NOTAM (notice to airmen):

  Those persons described in paragraph a (applicability) below are prohibited from operating in the Baghdad flight information region (FIR) (ORBB) at all altitudes due to heightened militia activities and increased tensions in Iraq, which present an inadvertent risk to U.S. civil aviation operations due to the potential for miscalculation or mis-identification. [converted case from all caps; emphasis added]

KICZ A0036/20 (PDF)

Note: "Those persons" refers to "U.S. air carriers and commercial operators". It's likely the UK issued a similar NOTAM.

Such communication – and the solution (reroute, return, land*) – will typically be sent from BA's ops to the plane via datalink (ACARS).

* Interestingly, the same flight turned around and landed at Istanbul on the 11th, followed by IST–DXB two hours later. This suggests on the 12th (your flight) they planned for this contingency and loaded enough fuel. The longer (Big Dipper) route adds an additional 580 NM (1,100 km) – not accounting for the increase in the air distance due to turning across/into the jet stream.

For how to find out generally, here I used EASA's Conflict Zone Information Bulletin.


Why can't jet engines operate with supersonic air and how do they slow it down?

In a nutshell

A compressor blade works best in subsonic flow. Supersonic flow introduces additional drag sources which should be avoided if efficiency is important. Thus, the intake has to slow down the air to a Mach number between 0.4 and 0.5. Note that the high circumferential speed of a large fan blade will still mean that its tips work at around Mach 1.5, but the subsequent compressor stages will operate in subsonic conditions.

A scramjet is possible with fuels with supersonic flame front speeds and rapid mixing of fuel and air. If the engine would burn regular kerosene, the flame would be blown out like a candle if the internal airspeed would be supersonic, and even if flame holders keep the flame in place, most combustion would take place only after the fuel-air mixture has left the engine due to the slow mixing of kerosene and air. By using hydrogen, a stable combustion can be achieved even in supersonic flow. Due to the high flight speeds, compression is possible by a cascade of shocks, so no moving turbomachinery is needed in ramjets and scramjets.

Background: Maximum heating of air

All jets decelerate air in their intake in order to increase air pressure. This compression heats the air, and in order to achieve a combustion which produces thrust, this heating must be restricted. If air is heated above approx. 6,000° K, adding more energy will result in dissociation of the gas with little further heat increase. Since thrust is produced by expanding air through heating, burning air that enters the combustion process already at 6,000° K will not achieve much thrust. If the air enters the intake at Mach 6, it must not be decelerated below approx. Mach 2 to still achieve combustion with a meaningful temperature increase - that is why scramjets are used in hypersonic vehicles.

Full disclosure: Oxygen starts to dissociate already between 2,000° and 4,000° K, depending on pressure, while Nitrogen will dissociate mainly above 8,000° K. The 6,000° K figure above is a rough compromise for the boundary where adding more energy starts to make less and less sense. Of course, even a 6,000° K flame temperature is a challenge for the materials of the combustion chamber, and ceramics with film cooling are mandatory.

The equation for the stagnation temperature $T_0$ of air shows how important the flight speed $v$ is: $$T_0 = T_{\infty} \cdot \frac{v^2}{c_p} = T_{\infty} \cdot \left(1 + \frac{\kappa - 1}{2}\cdot Ma^2 \right)$$

$T_{\infty}$ is the ambient temperature, $c_p$ the specific heat at constant pressure and $\kappa$ the ratio of specific heats. For two-atomic gases (like oxygen and nitrogen), $\kappa$ is 1.405. Temperature increases with the square of flight speed, so at Mach 2 the factor of heat increase over ambient is only 3.8, while at Mach 6 this becomes 26.3. Even at 220° K air temperature, the air will be heated to 5,800° K when it is ideally compressed in case of a hypersonic vehicle traveling at Mach 6. Note that real compression processes will heat air even more due to friction.

Compression with shocks

Supersonic flow is slowed down by a pressure rise along the flow path. Since no "advance warning" of what is coming is possible, this pressure rise is sudden: Pressure jumps from a fixed value ahead to a higher, fixed value past the jump. This is called a shock. The energy for the pressure rise is taken from the kinetic energy of the air, so past the shock all other parameters (speed, density and temperature) take on new values.

F-16 air intake (picture source)

The simplest shock is a straight shock. This can be found at the face of pitot intakes like the one of the F-16 (see the picture above) in supersonic flight. More common are oblique shocks which are tilted according to the Mach number of the free flow. They happen on leading and trailing edges, fuselage noses and contour changes in general: Whenever something bends the airflow due to its displacement effect, the mechanism for this bending of the flowpath is an oblique shock.

straight and oblique shock (own work)

The index 1 denotes conditions ahead of the shock, and 2 those downstream of the shock. For weak straight shocks the product of the speed ahead of the shock $v_1$ and the speed past the shock $v_2$ equals the square of the speed of sound: $$v_1\cdot v_2 = a^2$$
If $Ma_1 > 1$, then $Ma_2$ must be smaller than 1, so the flow is always decelerated to subsonic speed by a straight shock.

The same equation works for the normal speed component $v_n$ ahead and past a weak oblique shock: $$v_{1n}\cdot v_{2n} = a^2$$
Note that the tangential component $v_t$ is unaffected by the shock! Only the normal component is reduced. Now the speed $v_2$ is still supersonic, but lower than $v_1$, so a weak oblique shock produces a modest increase of pressure, density and temperature.

The angle of the oblique shock wave is determined by the Mach number ahead of the shock.

Supersonic intakes

Weak shocks are desired, because they produce only small losses due to friction. Pitot intakes with their single, straight shocks work well at low supersonic speeds, but incur higher losses at higher Mach numbers. As a rule of thumb, a pitot intake is the best compromise at speeds below Mach 1.6. If the design airspeed is higher, more complex and heavier intakes are needed to decelerate the air efficiently. This is done by a sequence of weak, oblique shocks and by means of a wedge intake. The picture below shows the intake of the supersonic Concorde airliner:

Concorde intake (picture source)

Gradually increasing the angle of the wedge is causing a cascade of ever steeper, oblique shocks which gradually decelerate the air. The design goal is to position this cascade of shocks caused by the wedge on top such that they hit the lower intake lip. This is done by a moveable contour of the upper intake geometry and/or the lip. The goal is to achieve a uniform speed over the intake cross section and not to waste any of the compressed air to the flow around the intake. See the picture of the Eurofighter intake below for an example of a moveable intake lip (which admittedly is mainly for increasing the capture area at low speed and for avoiding flow separation even with a small intake lip radius).

Eurofighter intake (picture source)

Once the air has entered the intake, it is only mildly supersonic and can be further decelerated by a final, straight shock at the narrowest point of the intake. After that point, the intake contour is gradually widened, such that the air decelerates further without separation. To achieve this, a very even flow across the intake area is mandatory, and even the slight disturbance caused by the boundary layer of anything which is ahead of the intake must be avoided. This is achieved by a splitter plate which is clearly visible in the pictures of the F-16 and Eurofighter intakes. The splitter plate of the Eurofighter intake is even perforated to suck away the early boundary layer there.

The deceleration of the intake flow results in a significant pressure rise: In case of the Concorde at Mach 2.02 cruise, the intake caused a pressure rise by a factor of more than 6, so the engine compressor had to add "only" a factor of 12, such that the pressure in the combustion chamber of the four Olympus 593 engines was 80 times that of the ambient pressure (admittedly, this ambient pressure was only 76 mbar in the cruise altitude of 18 km).

This pressure increase means that a supersonic intake must be built like a pressure vessel, and the rectangular face of the intake must quickly be changed to a round cross section downstream to keep the mass of the intake structure low.

Intakes at higher speed

Going faster means the intake pressure recovery increases with the square of flight speed: In case of the SR-71 intake at Mach 3.2, the pressure at the engine face was already almost 40 times higher than the ambient pressure. Now it becomes clear that going faster than Mach 3.5 does away with the need for a turbocompressor: At these speeds a properly designed intake can achieve enough compression by itself for the combustion to produce enough thrust, and going above Mach 5 will need restraint in slowing down the intake flow in order to have enough temperature margin for combustion, requiring supersonic flow in the combustion chamber.


How does Reynolds Number affect skin friction drag?

First of all, friction is bad for efficiency. It slows moving things down and needs a constant energy supply to be overcome. The more friction, the more energy has to be supplied, and this energy is lost as heat.

Aerodynamic friction is caused by viscosity. The Reynolds number tells you how big viscosity is in relation to inertial forces. A bigger Reynolds number signifies lower viscosity. This means a higher Reynolds number almost always results in lower friction. If you look at the plot below, the downward trend can be easily spotted.

Friction drag coefficient of a flat plate over Reynolds number (picture source). Note the double logarithmic axes.

  Is there something like " higher Reynolds number, higher drag force " stuff ?

Yes, sometimes. Please look at the transition curve: Here a flow which is initially fully laminar slowly changes with increasing Reynolds number into one with a laminar start and a transition to turbulent flow somewhere downstream. This adds a section of turbulent boundary layer where at a lower Reynolds number the flow would had been laminar. You will notice that for the same Reynolds number, a fully laminar flow (lower line) is much less draggy than a fully turbulent one (upper line). Therefore, replacing some of the laminar flow with a turbulent one will result in more drag.

Now I need to explain why increasing the Reynolds number leads to more turbulent flow. For this, I turn to this answer:

Inside the laminar boundary layer, small disturbances become less and less damped the higher the local Reynolds number becomes, and at a Reynolds number of around 400,000 in unaccelerated flow some frequencies become unstable (see Tollmien-Schlichting waves) and will eventually create so much cross movement that the boundary layer becomes turbulent. Now parcels of air which flow at high speed in the outer part of the boundary layer will move close to the wall and kick the slow parcels there ahead, greatly reducing the deceleration of the flow close to the wall, at the price of slowing down and expanding the whole boundary layer.

Simply put: A laminar boundary layer cannot be sustained indefinitely but will change to a turbulent one if the Reynolds number is high enough. This will swap some of the previously laminar portion of the boundary layer to a turbulent one, increasing drag.

While all of the above is only strictly true for flow over a flat plate without a pressure gradient, real flow will complicate things again: Now turbulent flow is not all bad; the example of the dimpled golf ball shows that a turbulent boundary layer in flow with a pressure gradient can also lead to lower drag, given the right circumstances.


Some things to consider:

Don't make it a potential weak point on the aircraft. This was/is a big problem with some of the Mooneys out there where the nose gear can be damaged if a very tight turn is made while towing:

  One other caution: Many Mooneys suffer damage to the nose gear trunion
  when towing turn limits are exceeded via power towing. Owners learn to
  watch the ramp rats carefully.

Make sure you can maneuver the aircraft around the desired airfields. If you are building an aircraft that is intended to operate out of small GA fields with tight taxiways and short runways, keeping turning ability tight is key. If you are designing an airliner, make sure you can get around major airports (taxi diagrams are readily available). You don't want turning radius to be a limiting factor when buying/selling an aircraft.
To caster or not to caster, there are plenty of aircraft out there with castering nose wheels steered with differential breaking only this might have an impact on radius but a benefit in simplicity of design that is for you to decide.


Clearance limit of VFR practice IFR approach?

I'm assuming you're asking about the US, in which case the answer is no. The AIM 4-3-1(e) says:

  VFR aircraft practicing instrument approaches are not automatically
  authorized to execute the missed approach procedure. This
  authorization must be specifically requested by the pilot and approved
  by the controller. Separation will not be provided unless the missed
  approach has been approved by ATC.


Is there a better solution than the U-shaped tailplane for this Airbus concept?

In airplane empennage design, there is a thing called Tail Volume Coefficient. Mind you, there are no volumes here, but you are working with $m^3/m^3$. It is calculated as follows:
Horizontal tail volume:
$V_{HT} = \cfrac{ l_{HT} \cdot S_{HT} }{ c_{REF} \cdot S_{REF} }$
Vertical tail volume:
$V_{VT} = \cfrac{ l_{VT} \cdot S_{VT} }{ b_{REF} \cdot S_{REF} }$
here

$c_{REF}$ - mean geometric chord (~MAC)
$b_{REF}$ - wingspan
$S_{REF}$ - reference wing area
$l_{HT}$ - horizontal tail arm
$l_{VT}$ - vertical tail arm
$S_{HT}$ - horizontal tail area
$S_{VT}$ - vertical tail area

Now, with that in mind, you can have a perfectly reasonable cruciform solution, U-tail, H-tail, or triple-tail solution, or whichever.
However, freely choosing empennage configuration is not the only condition in design. Engineers likely have other requirements. These two vertical stabilizers (VS) look relatively slender. Perhaps a single VS would be too slender and cause structural issues, perhaps flight dynamics department required better yaw or sideslip control, in which two VSs would maybe be proved better. I think Russians designed An-225 with an H-tail to carry extreme payloads (like Buran), whereas Americans didn't modify 747's empennage for Space Shuttle carrying. There are a number of considerations here. One of which, mind you, is also aesthetics, especially for a passenger airliner.
So, is there a better solution than the U-shaped tailplane for this Airbus concept? It depends. There is no single universally best solution in these things.

Equations from S. Gudmundsson: General Aviation Aircraft Design


What do airlines do with planes at the end of a multi-stop route?

Deadheading is rarely done because it is a non-revenue movement.

The most common use of deadheading (that is, flying the aircraft empty) is done for maintenance runs.

At the end of a scheduled route, the plane is parked at the last destination.  Sometimes, the next flight around uses the plane (if the route can be serviced by the aircraft).

Typically, airlines try to "park" their planes at their hub locations (where they have favorable landing and parking fees) rather than leave the aircraft at another airport.

Flight operations and planning make sure the aircrafts are maximized on revenue movements.

To give you an example - the shortest scheduled commercial flight for the A380 is Dubai - Kuwait (EK857); and the return flight Kuwait - Dubai (EK858).

The inbound aircraft on the flight yesterday (A6-EOH) was inbound from Perth to Dubai; and then flew to Kuwait and then back to Dubai. The next day (July 1st), the same aircraft is scheduled for SFO. (See the flight log at flightradar24).


How do RC airplanes create thrust without using propellers or rockets?

They create thrust the same way that the full size ones do.

In the case of a piston engine type aircraft they have either have a miniature version of a piston engine, or an electric motor which turns the propeller.
In the case of jet engine, like your picture, they have miniature versions of a jet engine.
Sometimes, the jet engine in an RC aircraft is actually a propeller made to look like a jet engine.

  Also, how do they control aileron

Usually by using servos to pull cables and pullies - essentially like aircraft used to before fly-by-wire systems were introduced.

  Does an RC plane have rudder?

Some do, some don't. Its the difference between 2 and 3 axis controls. Anything like the one in your picture almost certainly do.

  Do RCs have to be registered with local aviation authorities

Sometimes, It depends on jurisdiction and and often weight.


Regarding 49 CFR 830, what is considered an in-flight fire?

No, there does not need to be visible plasma, and smoke alone is enough to constitute a fire onboard an aircraft.

FAA Advisory Circular 120-80A contains the following definitions that indicate that a visible flame is not the only definition meaning "fire" pertaining to aircraft.  In my experience, it's reasonable to expect that the FAA's definitions in this case would fall in line with the NTSB's definitions.

Hidden Fires:

  Fires that are “hidden” are not readily accessible, may be difficult
  to locate, and are more challenging to extinguish. Some examples of
  hidden fires would be fires behind sidewall paneling or in overhead
  areas.

Smoldering Fire:

  Combustion without a visible flame and a slow combustion rate are
  characteristics of a smoldering fire. A smoldering fire left
  unattended or an incompletely extinguished fire can ignite and grow
  into a larger, uncontrollable fire in a short time.

Suppressed Fire:

  A fire that has been partially extinguished which may or may not have
  visible flames. A suppressed fire, if not extinguished, may
  reestablish itself and grow into a larger, uncontrollable fire in a
  short period of time.


Emergency order issued by the FAA allows for special flights including production flights testing, ferry etc.
The order is available on the FAA website.


Is a holding pattern required on the Twentynine Palms VOR for RWY 26?

This chart provides two ways to begin the approach. The first is at the TNP VOR, which is labeled as an IAF (Initial Approach Fix). Since a holding pattern is charted, you are required to fly that holding pattern as part of the procedure if you begin at TNP.

The other way to begin the approach is at JEHLI, which is labeled as an IF (Intermediate Fix). The "NoPT" instruction only applies if you start the procedure at JEHLI, as this establishes you on the 255 inbound radial to TNP and no hold is needed.

If a hold or procedure turn is charted, you need to fly that maneuver unless you are coming from an IAF or IF with the "NoPT" instruction (or if ATC clears you "straight in").


Is interfering with the "go/no-go" decisionmaking of a flight crew a violation of 14 CFR 91.11?

If the airport received (US) federal funding, then it must be available for emergency or distress landings. The guard could require the people not camp, but forcing a flight to an aircraft without sufficient fuel, reserves, WX briefing, etc. is unprecedented.

As a matter of practice, disoriented pilots who land at private and uncharted corporate airports in northern Canada are normally given fuel, food, and calls to get WX and file flight plans.

Perhaps someone better versed in Admiralty Law might comment.


What did Paris' de Gaulle airport look like before the t2 expansion?

You will hardly find anything complete on the web as :

at the time of the expansion a bunch of years ago, you didn't have that much computer assisted medias to produce representative documents.
most accurate documents are inside old books you can only access at specialized libraries, rare copies owned privately or museums.
Because Charles de Gaulle is a french airport, you'll likely to find what you're looking for in french !

I do have an Air France magazine with Charles de Gaulle history til 2002, and another dedicated to the Terminal 2F extension, but because those are copyrighted materials, I can't post them here. Sorry.

Though, you can head to the following sites :

http://www.entrevoisins.org/paris-charles-de-gaulle-de-1945-1975.aspx
(video - if you don't mind quality of the era)

http://www.aeroportsdeparis.fr/groupe/presse/40-ans-paris-cdg/photographies
(a couple pictures)
http://airinfo.org/2014/03/07/paris-charles-de-gaulle-fete-ses-40-ans-video-photos/ (dedicated copy of the above)

http://www.goussainlivres.com/librairie/librairie/aeroport-roissy-charles-de-gaulle=198.html
(one small cropped overview from a book - bear in mind that most relevant structures of the airport is inside that picture and everything around are empty areas)

Basically, you only had the Terminal 1, and one runway. Airport name was "Paris Nord" before becoming "Roissy-en-France", then finally called "Charles de Gaulle" just before inauguration (8 of March, 1974). And initial planned extensions were identical copies of the Terminal 1 all other the place including where T2 and T3 are today. Sorry, I can't post a plan from the Air France book, but it's rather similar to the one you can spot in the video above.

There are also rare documents you could retrieve from old magazines issued at the time (Air & Cosmos to name the one I know of) or magazines like EntreVoisins (used to collect them at Maison de l'Environnement, Athis-Mons, near Delta Museum) which sometimes raises issues about noise pollution from Paris Airport platforms (comparative maps of the airport through the years)


Why do some aircraft have symmetrical tip airfoils while others do not?

Camber shifts the airfoil's section of lowest drag of the drag polar to higher lift coefficients. In order to create the least amount of drag in level flight, an airplane wing benefits from moderate camber. Most of the lift is created in the mid section, but enough lift is left towards the tips to justify camber there, too. In case of elliptical or tapered wings, the design lift coefficient for lowest drag at a given lift will be equal over the whole span (elliptic wing) or even peak near the tip (highly tapered and untwisted wing with no regard given to stall behavior or spar mass).
Normally the tips carry less load than the inner wing, details depending on wing taper and twist. This helps to prevent the tip section stalling first at high angle of attack. Good aileron effectiveness also requires an airfoil which equally produces positive and negative lift at low drag.
One example would be the Me-262. When Ludwig Bölkow designed the wingtip, very little was known about transsonic effects and a thin, symmetric airfoil with an elliptic nose was chosen because it showed a late onset of transsonic effects in wind tunnel tests.
When North American later designed the F-86, the outer wing design of the 262 was copied over because it had worked well in the German design.
Many Horten flying wings used symmetric tip airfoils because the bell-shaped lift distribution needed for stability resulted in a slightly negative lift at the tips at low angle of attack and very little positive lift at high angle of attack.
With some designs I am sceptical that a symmetric airfoil has been used even if it is claimed so in David Lednicer's outstanding collection. The Lockheed P-3 is there listed with NACA 0014 at the root and NACA 0012 at the tip - no, the Lockheed engineers 60 years ago knew better than that!