Do parking brakes lock the wheels and airframe together?

Yes, the parking brakes lock the wheel and the airframe together. If the brakes are not applied, the wheel can rotate round the axle.

If the wheel's position is fixed to the ground (e.g. by adding chocks, but the brakes are not applied, then the aircraft will rotate round the wheel axle when the tail is lifted by the blue man.

If the brakes are applied, but the wheel's position is not fixed to the ground, the aircraft will rotate round the wheel's point of contact with the ground. Since the contact point moves as the wheel rolls, this results in translation in addition to the rotation.

If both the brakes are applied and the wheels are on chocks, the wheels either have to roll over the chocks or something (the wheel, the chock or the brake) will have to slip.


Is this equation for propeller thrust correct?

From the comments:what I want is a derivation of thrust as a function of power absorbed, prop diameter and prop axial velocity..

Power absorbed $P$ is engine torque  times prop angular velocity $\omega$: $P =  \cdot \omega \tag{1}$.
Prop axial velocity at the tip $V_t =\omega \cdot D \tag{2}$

$P$ is the power applied in the axial direction, while thrust is generated in the direction perpendicular to the propeller plane - there must be some function describing the relationship between the forces in both directions. This function would be one describing efficiency and losses, since the primary force application is the engine torque and the thrust is the net resulting force.

If the goal is like is stated in OP ...propeller of diameter  moving at an axial speed  is 100% converted to the acceleration of a mass of air... this means that there are no losses, and we can use the simple impulse theory of the magic disk. This is comprehensively explained in this post, which results in the following equation between thrust and power:

$$P = \sqrt{\frac{F^3}{2\rho A}} \tag{3}$$

If we want $V_t$ in there we need to substitute (1) and (2):

$$\frac { \cdot V_t}{D} = \sqrt{\frac{F^3}{2\rho A}} \tag{4}$$

Since A = propeller disk area = $\frac {\pi}{4} \cdot D^2$, (4) further boils down to:

$$F^{3/2} = k \cdot  \cdot V_t \cdot \rho^{1/2} \tag{5}$$

Note that (3) contains $P$ but no $V_t$, while (5) contains $V_t$ but no P. We could lump the motor torque into the force $F$ dimension, but all my engineering genes scream to not do that because of the origin and effect relationship: no engine torque, no net thrust.

Both (3) and (5) contain $\rho$, which is a must considering that the thrust is obtained by acceleration of a mass of air. The mass flow dimension can disappear into a force dimension as well when multiplied by a velocity, for instance a propeller tip velocity...

This answer shows the relationship between thrust and power of a helicopter rotor in the hover (and therefore of a propeller) using modified momentum theory with losses:

$$C_P = \frac{\kappa \cdot {C_T}^{3/2}}{\sqrt{2}} + \frac{\sigma \cdot {C_D}_0}{8}$$

with $\kappa$ = loss factor and $\sigma$ = blade solidity. So the exponent of the function (induced power) vs. (thrust) is 3/2. Also, there is an additional term that the dimensional analysis cannot catch, which is power required in the propeller plane.


How much noise does flow separation cause?

Flow separation makes a lot of noise. Usually, it is masked by engine noise and/or damped by insulation. Any pilot of a light plane may climb to a safe altitude and then idle the engine, start a glide, and then slowly pull the stick until the wings start to stall. He will hear a lot of noise, and feel a strong vibration, too... The cause is the turbulence associated with the flow separation.


Does density altitude affect actual altitude?

(Source)

The basics

Height: absolute height above ground, measured using a radar altimeter (like the helicopter on the right)
QFE: the barometric setting an airport broadcasts that makes an altimeter on ground read zero. This gives height only around the airport if the area is relatively flat. Also known as Above Field Elevation
QNH: the barometric setting an airport broadcasts that makes an altimeter on ground read the airport's elevation (height above mean sea level)
Aircraft using the same QNH below the transition level* in the same area are all flying the same indicated altitudes
Aircraft using QNH 1013 mb (29.92 inHg) are all flying the same pressure altitudes. Above the transition altitude* they're called flight levels

* The transition altitudes and levels vary from place to place. For flying below 18,000 feet in the US, you can ignore flight levels for now.

QNH is good for separation since everyone is using the same measurement system. Even if the temperature's rate of change with altitude (lapse rate) is different from the standard.

Lapse rate

(Source)

On the left is a hotter than usual lapse rate, i.e., it gets colder less slowly. Still, all aircraft using the same pressure setting will still be flying the same indicated altitudes / flight levels.

Pressure altitude (what the altimeter reads when set to 1013/29.92) adjusted for lapse rate deviation is density altitude. It's used for performance calculations.

The answer

You said, "[The] atmosphere actually expands and becomes taller under hot conditions".

Yes, but not for that reason. A hotter than standard day means the air molecules are more jumpy, i.e., they are producing more pressure. That's why 1,000 feet on the left is higher. Think of it this way, air is hot, it's still keeping pressure a bit higher (height).

Remember, a basic altimeter senses only pressure from the static port, it doesn't know the temperature.

Since the pressure is the same for the same altitudes, and the variable is the temperature, it will be lower air density on the left due to the higher temperature (angry molecules don't like to cozy up). That's why engine output and lift are impacted.

For cold weather, usually at or below 0°C (32°F), this deviation can become dangerous in mountainous areas. There are special rules and equipment for that, which are listed on the appropriate charts for airports that usually face such conditions.

Further reading:

Wikipedia: Flight level
SKYbrary: Altimeter Temperature Error Correction
SKYbrary: Transition Altitude/Level
How is non-standard OAT accounted for?
How does altimeter reading vary when departing from ISA conditions?
When calculating takeoff performance why include airport elevation in pressure altitude?
Why is Cessna 172 POH performance chart based on Pressure Altitude and Temperature instead of Density Altitude?


Can I fly internationally as a commercial pilot, without an ATP certificate?

A US rated pilot (private, commercial or ATP) can operate an N- registered airplane anywhere on earth (subject to the persons ability or inability to enter certain countries airspace).

At the regional airlines it was common that the first officer only possessed a commercial certificate (the full ATP is earned during the pilots first upgrade training to become a captain).  These first officers will have no restriction on international travel based on their certificate and can operate international flights. These days FOs will have restricted ATPs rather than commercial certificates, but this is unrelated to the ability to operate internationally.

Outside of airlines you'll find positions where the only a commercial certificate is necessary and these pilots can operate internationally.

If the airplane in question requires a type rating then if the copilot does not have a full type rating, they will need an "SIC type" to operate internationally. This stems from an ICAO requirement that both pilots be type rated. The SIC type can be added to a private or commercial certificate, not just an ATP so this won't be a restriction based on certificate level.


Can ekranoplans (GEV) be more efficient than traditional airliners?

As some of the comments above (which are really on the money) suggest it's a complicated question to answer because it is a case of "horses for courses" and that is even if we focus purely on straight-forward fuel efficiency. But given the programs that have been attempted (or are still ongoing) and also various studies it seems that ekranoplans seem to work best in two very distinct roles. Either as small, short range puddle-jumpers or as very large trans-oceanic monsters. For the later see also this which may well come to pass.

I guess at some level such utterly different roles is a problem for ekranoplan development. But, yes, in principle, there would certainly appear to be certain, very different niches, for which the ekranoplan is extremely competitive in terms of fuel consumption. Having said that the second niche is arguably also competing against conventional surface sea-freight which of course complicates matters but offers interesting possiblities. Aircraft like the Boeing Pelican (which didn't get past concept stage) was designed not for standard air-cargo pallets but for ISO containers. Now that capability is a real game changer as long as the cost per kg/km fuel economy is as good or better than a conventional air-freighter which I suspect is very doable. At least in principle.


How are flight schedules displayed without ambiguity on DST change days?

It's only really ambiguous once a year, when moving from summer time to winter time and the hour is 'repeated' - in this case, departures and arrivals are scheduled in the 'first' instance of the hour: eg if the flight is scheduled 01:30, it will depart 1.5 hours after midnight. The clock will then go back eg at 2am, and the airport will be relatively for one hour with no departures (although, of course, arrivals may still come in)

On the other shift, the hour is 'lost' so the departure takes place later. In practice, no planes are scheduled to arrive or depart in this missing hour, and since almost all nations make the change in the middle if the night when airspace is very quiet and most airports have no departures at all there is virtually no knock-on effect. Arrivals arrive when they arrive, departures are simply scheduled for a 'real' hour, if there are even departures at all at that time of day anyway.

Note that this is only for passenger scheduling - in air traffic control etc all times are Zulu (UTC) which has no ambiguity.

TL;DR: Fall/Autumn, aircraft depart in the "first" instance of the hour. Spring: scheduling works as usual, but with no flights scheduled in the "missing" hour (eg 2-3am)


Is the turning error of a magnetic compass greatest when tuning through South in the Southern Hemisphere?

“The turning error of a magnetic compass in the Southern Hemisphere is greatest when turning through South. Is the statement true or false?”

True

I am going to answer this question for a second time and delete the first try. It was a mess. Hopefully, this one will make more sense even though it has the same information. Just a better structure.

There are three factors that would explain why turning errors are greatest when turning through North and South. They are specific to the aviation wet, liquid-filled, or whiskey compass. Officially, two of them are magnetic dip and acceleration errors caused by magnetic dip. Unofficially, the final one is the counterintuitive way that you have to read the compass.

The magnetic compass turning errors that we usually identify as UNOS and ANDS while in the Northern hemisphere are caused by a combination of magnetic dip and the off center balancing of magnetic dip. As you have stated in your comment, a compass has the tendency to dip it’s North-seeking element down towards the Earth in the Northern hemisphere. The same is true for the South-seeking element in the Southern Hemisphere. The Northerly turning errors (UNOS) are greatest (up to the same amount of error as your degree of latitude) when turning through North or South.

In the picture below, the black text is the actual direction to which you are turning. The red text is the amount of compass error at 30° latitude.

An aviation, liquid filled, “whiskey” compass works the same way as a handheld lensatic compass. It has a magnetized bar held in place on a low friction bearing, needle or pin point. In the case of the whiskey compass, there is also a card noting the bars direction attached to it that is read counterintuitively.

To better understand this, remember, with a whiskey compass (as opposed to a dry, vertical card, compass) you are reading the directional card from the opposite side of the actual direction that you are facing. You read the North direction from the end of the side facing South, and the East direction from the end of the side facing West. Picture it like the lid of a bottle or can. If you are looking at it from above, you can mark “N” at the edge of the top closest to North. If you are looking at it from the side, you can not see the top. So, you put an “N” on the side furthest away from North because that is the only side you are able to see when facing North. The same goes for the other directions. Therefore, East is physically to the left of North (clockwise when viewed from the top) on the direction card. The numbers of degrees is read in increasing increments from right to left. A good mnemonic memory aid for this is, “If you always run/turn away from the one you want, they will chase you.”

The magnetized bar will always try to align itself or stay aligned with the magnetic flux lines of the Earth. The Earth is a giant magnet. The flux lines Of the Earth exit the Earth at its magnetic South Pole and re-enter it at its magnetic North Pole all the way around the Earth. This places the flux lines comparatively horizontal (parallel to the ground) at roughly the equator, and vertical (perpendicular to the ground) at either Pole. The closer you get to either Pole (the higher the latitude), the more the compass bar will try to align itself vertically.

To counteract this phenomena, compasses are sometimes weighted to move the center of gravity of the bar & card arrangement closer to the side of the bar that would point upward, away from the Earth. In the Northern Hemisphere, the CG would favor the magnetic bar’s Southern pole. In the Southern Hemisphere, the CG would favor the magnetic bar’s Northern pole. This is done so that the bar or anything attached to it will not touch the inside of the compass housing. Any type of contact, friction, or drag could stop the compass from moving and realigning itself freely. When the compass is not weighted to move its CG, a compass that is suspended from its top will move its CG towards the opposite direction of the compass’s magnetic dip on its own.

The CG of the compass’s moving parts is very important in its movement. It creates inertia. The inertia of the offset CG will be apparent whenever there is a change in speed or a change in direction of movement. The CG will always want to remain at the same speed and travel in the same direction as it was. The CG will want to lag behind during acceleration, keep moving forward during deceleration, and keep going straight, swinging to the outside of a turn/curve. Picture it as the same phenomenon that will cause a glass marble in a Petri dish to roll around due to velocity change. Changing speed and/or direction will cause the compass to become misaligned until speed and direction are stabilized. When facing North in the Northern hemisphere, a right hand turn to the East will cause the compass to initially spin clockwise (relative motion to the aircraft) to the West backside indication. Here is a good article on turning errors that explains it much better than I can. Or, this one from AOPA.

In the case of a compass where an off-center CG is not affecting the compass, aircraft banking will cause magnetic dip to swing the directional card out of alignment. When facing North, banking to the right (East) will cause the compass to initially spin clockwise (relative motion to the aircraft) to the West backside indication. Due to this directional indication from the perspective of the backside of the directional card, magnetic dip while in a coordinated bank (where g-forces keep the weight of all objects inside the cockpit acting perpendicular to the floor) would cause the compass to initially indicate a turn in the opposite direction of the actual physical turn of the aircraft if your direction is North in the Northern Hemisphere and South in the Southern Hemisphere. This means that the compass would initially spin clockwise in the above North to East turn. The compass would then lag the actual turn until the bank is brought back to level, or your aircraft reaches an East or West heading. This article, as well as this one here both explain the above phenomenon better.


Forces "felt" by pilot, G-meter, inclinometer--are they the aerodynamic forces generated by the aircraft, or the sum of weight+centrifugal force?

Can more than one of these things be true at the same time?

Yes. It is only a matter of the point of view, or, more precisely, the reference system.

Consider a trivial case first: The aircraft sits on the ground, engine off. The pilot will feel his weight pressing into the seat even in the absence of aerodynamic forces. What he feels is gravity, and the force is the product of his mass and gravitational acceleration.

Now do the same with the aircraft flying in level flight. The forces acting on the pilot are still the same, so it is again gravity what he feels. Only that now the aircraft is not supported by its landing gear and the ground, but by wing lift (and the ground again).

Next step: The pilot flies a dive, followed by a 2g pull-up, meaning that the g-meter reads 2 gs. Again we look at the moment when the aircraft is level, but now it flies on a curved flight path. This adds a centrifugal load of 1g to the 1g of gravity and the pilot feels twice the weight force that he felt before. The nitpickers will now say this is not weight, because weight is the product of mass and gravitational acceleration, but our pilot couldn't care less at the moment. It hurts in his buttocks, that's what counts.

And neither the g-meter nor the pilot could tell gravity apart from centrifugal force – they all feel the same and only the sum of all is felt as a single sensation.

Now switch reference systems and look at the flow around the wing. Speed and angle of attack combine to produce a lift force of twice the weight the aircraft had in level flight. This is pure aerodynamics, no gravity or centrifugal load involved. Strictly speaking, the aerodynamic force on the wing is even a bit higher in order to compensate for the higher tail downforce resulting from trim to overcome pitch damping. Looking at the full aircraft as one object, its total lift force is now twice as high as in level flight.

This force gets transmitted to the pilot seat and the instrument panel and is felt there as a resistance against the acceleration. Depending on your point of view, either the pilot is accelerated into his seat or the seat pushes against the pilot. Actio equals reactio.

Next switch: The same curved flight path, but now at the moment when the aircraft is inverted. Now centrifugal and gravitational acceleration cancel each other, the g-meter reads zero and the pilot feels weightless. In order to do so, the pilots needs to push the stick forward and reduce wing lift to about zero, or wing lift would pull the aircraft down. At this moment we have no aerodynamic contribution to the vertical forces felt by both the pilot and the g-meter.

Now the pilot pushes the stick even more forward so his flight path becomes straight and level again, only with the aircraft in an inverted position. The g-meter now reads -1 g, the force of the harness pressing on the pilot's shoulders is again his weight times gravitational acceleration, but what allows the harness to support the pilot is the lift of the wing the harness is attached to. Change your reference system, and it is again aerodynamics that the pilot feels. Let him wiggle the stick and the change in aerodynamics is immediately felt on his shoulders.


Do I need a driver's license to get a PPL in Canada?

It does not appear that a driver's license is required. From General information on pilot licences and permits, which details the requirements for getting various kinds of pilot licenses, there is no mention of a driver's license.

Prior to the issue of a permit or licence, an application must be submitted and the following requirements met:

proof of age and citizenship (not required if previously submitted)
proof of medical fitness;
proof of having met the knowledge requirements;
proof of having met the skill requirement;
proof of having met the experience requirement;
payment of the appropriate fees.


What's the purpose of this red marking on the fuselage of a Boeing 737?

@SMSvonderTann is correct. The marking is there for warning ground personnel about engine hazrd. In this photo (of a 737) you can see 'INGESTION HAZARD' written above the line.

Image from airliners.net

In this image it is possible to zoom in to see it much more clearly. Note that this marking is not found in all 737s. The danger area is marked with two lines- one in forward fuselage and another in the engine, as can be seen in @mins photo, which I've put below.

Image from airlinereporter.com

Also, as @mins notes, the lines in 747 are for equipment positioning (to prevent damage to fairing, looks like)


Why don't big airliners have bigger doors?

Multi-aisle commercial aircraft adopt a multi-door boarding strategy rather than a single-huge door (see the A380 or the B747, both use two doors). This helps under the structural viewpoint: the presence of a door (cargo or passenger that might be) induces design problems that are amplified if the compartment has to be pressurised.

A door interrupts both frames and stringers and weakens the overall aircraft structure. A huge door interrupts many more frames than a small one and two small ones can be set apart from each other to have some continuous frames between the two, restoring some rigidity.

The complex closure systems ensure that part of the stresses are carried by the door material, but it will never be perfectly transmitted as it would be without a door. As mentioned before, the stresses are heightened if the compartment is pressurised (as when passengers have to be transported).


Could you help to identify this WW1 fighter?

Pretty sure it's an Albatros C.I. Look at the access hatch with the double gills directly behind it, the three metal covers on the engine, the horizontal and vertical black marks on them, the upper wing support ending right between the two metal covers, the front support for the undercarriage ending right before the second gill.

Albatros C.I (Picture copied from the link above)

The Albatros C.III has a different tail, but that's invisible in the picture above.

Here is another picture, showing the plane from the other side. Note the flush radiator on the side of the fuselage. (image source)


Is FAA approval required in order to fly an RNAV SID/STAR for a private aircraft operated under FAR Part 91?

The best answer I can give is generally, no.

In relatively few cases – for aircraft operated under Part 91 Subpart K, which applies to fractional ownership like Netjets – the operator must possess an Mspec, which would be applied for at the local FSDO. I'm not sure what that process looks like, but the FAA's Commercial Operations Branch has some good information on that front.

For all other Part 91 operations the aircraft simply needs to be appropriately equipped.


What is this NASA UAV, and what is its function?

This is a Northrop Grumman RQ-4 Global Hawk. NASA has done some research on civilian applications for drones and this one appears to be for storm research. You can find more info on the project here.


What can trigger the ELT on GA aircraft?

There are four different types of ELTs:

Automatic fixed ELT (ELT(AF)). An automatically activated ELT which is permanently attached to an aircraft.
Automatic portable ELT (ELT(AP)). An automatically activated ELT which is rigidly attached to an aircraft but readily removable from
the aircraft.
Automatic deployable ELT (ELT(AD)). An ELT which is rigidly attached to an aircraft and which is automatically deployed and
activated by impact, and, in some cases, also by hydrostatic sensors.
Manual deployment capability is also provided.
Survival ELT (ELT(S)). An ELT which is removable from an aircraft, stowed so as to facilitate its ready use in an emergency,
and manually activated by survivors.

All the aircraft I fly in (all two of 'em) have the third type. If the aircraft is submerged or experiences a high G-force, the ELT will be triggered. There's also a button on the panel to activate it manually.

I'm not sure what G-forces are required to set off the ELT, but they must be fairly significant—I've slammed my plane down pretty hard while misjudging my landings, and never had it go off.

According to https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-44A.pdf:

  To meet the "g" force requirements of TSO-C91, automatic fixed-type inertially activated ELT's (except overwater type) must activate at any inertial force, parallel to the longitudinal axis of the aircraft when installed in accordance with the manufacturer's instructions, of 5(+2, -0)g and greater for a time duration of 11 (+5, -0) milliseconds or longer.

So, there you have it. You need 5–7 Gs for 11–16 milliseconds—but only in the direction the plane is pointing. Misjudging your landing flare and stalling the plane 20 feet off the runway won't set it off, as that's not on the axis they're measuring.


How many LRUs are there in modern aircraft like a Boeing 747 or an Airbus A380?

It's difficult to precisely answer your question, because they are not public information and depend on the aircraft sub-model, customer configuration, etc.
I built this approximate plot using the data from [1] that shows the trend in Airbus models:

It should be quite surprisingly to you that the A380 has the same number of computing units of the A340. This is because of the transition from the LRUs design to the IMA design (see this question for the difference), that allows to considerably reduce the number of computing units required, called Line Replacement Modules (LRMs). Airbus claims they were able to cut the 50% of the required computers in A350 thanks to IMA approach [2]. A similar claim has been made by Boeing for the 787.
The data does not show the recent aircraft models, but I expect they are still around 100 or slightly above on newer aircraft like A350XWB (which shares most of the A380 avionics). This is because increasing the number of avionics computers is very problematic as it has terrible cascade effects:

This conceptual diagram may look exaggerated, but consider that Boeing claims the reduction of 2000 lbs (~900kg) switching from the LRU approach to the IMA approach [3]. Saving 900 kgs means adding 10 people to the cabin, and it's easy to imagine the money saved by the airlines in the lifetime of the aircraft.
Anyways, check this video which shows the avionics bay of A350XWB: pretty impressive.


What are the consequences of falsely and/or unnecessarily declaring an emergency?

My experience is it is whether ATC files a complaint against you. It has to be pretty serious for them to do that. It works both ways, pilots rarely report ATC mistakes and so there is a gentleman's agreement to not sweat the small stuff. I have had ATC try to kill me at least 4 or 5 times and I never saw the need to report it. I figured the controller already knew the seriousness of it and if a supervisor noticed it, more than enough bad things would happen to them.

Just to be fair, I have screwed up seriously twice. I misunderstood instructions in flying over Vancouver International in  Canada and flew right in front of landing traffic. The second occurrence was when I was flying a twin. I got really busy after the controller unexpectedly routed me to a different runway during approach to Anchorage International, I switched tower frequencies for the new runway and forgot to get "cleared for landing" with the new tower frequency. In both cases the controllers very sternly told me what I had done wrong but never reported it.

In 1975 I had ATC file a complaint with my flight school when I was a student. I turned off the engine when it was obvious I had a 10-15min wait for takeoff. I later found out the FARs require at least one engine running on all ground control areas - no one had told me, Oops.

I have had two very serious problems in my 2500hrs of PIC. I lost an engine in a Cessna-337 (actually I was practicing engine out and one prop accumulator had leaked so the prop would not un-feather). ATC asked if I was declaring an emergency, I said no, and they declared one for me anyway.

The second emergency was when a carb intake became obstructed by an air straightener on a Navion Bendix PS5 pressure carb. Right after taking off I lost about 50% power. I slowly circled back because of "..low fuel pressure.."  , and I said I needed a "precautionary landing". Once again they declared an emergency anyway and I landed safely.

Most pilots don't know the definition of an emergency - In my early years I didn't

One of the possible problems with getting in trouble with the FAA is not knowing what an emergency really is. (They are quite lenient and understand this gap in knowledge. For example I have never seen a FAA definition.)

In about 1985 I discussed my experiences over coffee with a 10,000hr Atlas B747 captain that had been an instructor. He listened attentively, then calmly ask me if I knew when to declare an emergency? I said "if I thought I might die!" He calmly instructed me...

  An emergency is when "safety of flight is in doubt",

  OR when the aircraft is not able to perform as intended,

  OR when the aircraft might not be able to perform as intended.

  It's that simple!!

  Also, a pilot is required to inform ATC (but not report a
  emergency) any time an aircraft is not able to climb at least 500fpm.

Note the emphasis on "might not be able to perform as intended". That may not sound like an emergency but that is how the FAA and ATC see it. And that is pretty low criteria - it gives the PIC lots of legitimate wiggle room.

Once I was told this, it made so much sense and I knew I could defend my actions as PIC in the future. It seems ATC likely has received better training than pilots on what an emergency is, even if the pilot is overly cautious to declare an emergency (as I use to be).

When the prop would not un-feather and I lost partial power, both aircraft would no longer perform "as intended" and I should have declared an emergency.


What will be in 'radiotelephony privileges' part of EASA PPL without practical RT examination?

what do you mean "radiotelephony privileges"? The PPL itself doesn't allow you to use radio at all (legally - you shouldn't be even listening to the traffic).

You have to get a separate "Flight Radiotelephony Operator's Licence" issued by any member state (usually issued by the telecommunication regulator).

For each state - you should contact any aviation school / club and they should help you at least pointing out the direction (or giving out some training). This way I got my radio license (aviation RT operator) even in non-domestic country.


Can I generate & transmit ACARS message via software?

You are unlikely to have a permission for sending technical messages over radio channels used by real aircraft.
But if you just want to make your drone to send you ACARS messages over WiFi, there are 144 open source projects currently on GitHub to deal with these messages. Most of them are parsers, not senders, but anyway selecting the best projects and then understanding the code should give enough insights about the message format. Also, parsers can be used for checking that your sender works properly.


How much safer does painting prop tips make a plane?

An FAA study looked into that, it's titled: A Review of Civil Aviation Propeller-to-Person Accidents: 1980-1989.

This part stands out:

  While propeller and rotor paint schemes may reduce the number of propeller-to-person accidents, there is little information available regarding the various circumstances surrounding the accidents that do occur.

So there is little information. Their summary is:

  Persons most at risk for a propeller-to-person accident are deplaning passengers and passengers attempting to assist the pilot. That finding clearly assigns considerable responsibility to pilots to ensure safety of their passengers in this regard.

As you see, they did not stress on the paint, they also highlight that since the past, propeller driven aircraft are no longer the most popular type [for civil air transport].

An older study but relevant was conducted by the US Army. The document does not list accidents or statistics, so it's safe to assume it's a precaution. Better safe than sorry.

And in an environment such as an aircraft carrier's deck at night, it most certainly helps (but that's my opinion), there isn't a control set for a scientific assessment (as far as I can tell).


How do viscous drag and form drag individually change as a function of angle of attack?

Wind tunnels are stingy with the data they reveal. They only give the total value but not neatly split into its contributions. Therefore, any such table needs to be calculated.
Since XFOIL, which is now around for more that 30 years, we have such a tool and it does output the single contributions. However, I know of no publicly available collection which lists those drag components for a range of airfoils. And since XFOIL becomes unreliable with larger flow separation, the data is only valid for attached flow and maybe a bit beyond. But certainly not up to 30°.
In Xfoil, load an airfoil and enter OPER. Compute the desired point and switch into VPLO. There you can plot the skin friction coefficient with the CF command. In order to extract its numerical value, toggle the PACC switch in OPER and save a range of points to file. In the file you will find to the right of the CD column one labeled CDp. This is the pressure part of the drag. Use a tabulation software of your choice to calculate the difference between CD and CDp: This should be the friction part of the drag coefficient.


Is designing a small GA airplane with a wing loading of 20-25 lbs/sq ft a bad idea, or is that wing loading too high?

Racing airplanes do that and live with high landing speeds.  25 psf is about the wing loading of a Beech Baron.  The Baron stalls in the landing configuration, gear and flaps down, at 84 mph/73kt.
This mean you fly approaches at 110 mph with flaps.  Not too many GA pilots are safe with an airplane that hot without a lot of extra training and lord help you if you have to put the thing in a field that fast (a single I mean, the Baron being a twin and the expectation of off field landings being low).
You can make the flaps fancier, and maybe get that down under 100 mph, and then add wing slats and maybe get it down to 90, but you just added a lot of weight and cost.  Not worth it for a few knots at the top.


Has an aircraft carrier ever assisted a civilian passenger flight?

It has happened before.

There are definite cases of light civilian aircraft landing on a carrier, the most well known was in April 1975 when South Vietnamese Air Force Major Buang Lee landed an O-1 Bird Dog on the deck of the USS Midway trying to escape with his wife and 5 children from the fall of Saigon to North Vietnamese forces.

Landing aboard an aircraft carrier presents several difficulties, namely limited landing roll and available deck space.  A Nimitz Class carrier is just shy of 1100 feet in total length and 250 ft at its widest point.  The designated landing area or LA is approx 75 x 650 ft.  The ship is capable of steaming at 30+ kts so it can develop quite a bit of wind over the flight deck reducing the effective unarrested landing roll.

Then you need to stop the aircraft once it's on the deck.  Carrier based fixed wing jets use tailhooks designed to work with the arresting gear and reduce the landing roll to about 330 feet.

The largest carrier aircraft in service were the Douglas A-3 and the Grumman C-2 and E-2, each one about the size of a regional jet.  The largest aircraft which I am aware of which made a successful unarrested landing was a Lockheed C-130.

Large commercial aircraft like a Boeing 747 or an Airbus A-380 simply cannot fit on the deck without the wings clipping the island or other deck antennas, etc, not to mention requiring landing rolls of over 3000 ft even in the most extreme short field attempts.

So HAS a carrier aided a civilian passenger flight via recovery operations?  Yes but only with small aircraft.  COULD a carrier aid in recovering larger commercial aircraft?  Possible depending on the size of the aircraft, its loadout and fuel state and performance capabilities.


Does altitude influence the flight range of an engine driven aircraft?

Your book may not be wrong, but it is misleading, because the answers depend on the the aircraft type, and the type of engine. (piston, turboprop, turbojet, turbofan)

In general:

All aircraft have the best range at higher altitudes.

Piston powered aircraft have the best endurance at low atitude.

Jet powered aircraft have the best endurance at their optimum altitude. (not too low and not too high)


Why is there no "reverse sensing" on a horizontal situation indicator (HSI)?

Essentially because you turn the instrument upside down and read it normally.

On the back-course, the signals are reversed. That is a property of the ILS signal. When using traditional ILS/LOC instrument, the needle moves right when it senses more of the right signal, but since the signal is now on the left, you get reverse sensing.

On the HSI, the needle still moves right when it senses more of the right relative to the arrow when it senses more of the right signal. However, the needle points in the selected heading and is rotated with compass. So when you fly a back-course, you dial the normal course of the ILS and since you actually fly opposite direction, the arrow points down and right relative to it is left. And you get normal sensing.

For VOR, the situation is similar. In VOR, the needle moves normally if you are flying the heading selected and it moves in reverse if you are flying the opposite heading. And when you are flying the opposite heading, the HSI arrow points down, reverting the sensing back to normal.


On an engine failure, can I contact the tower instead of 121.5?

I'm basically going to echo what's already been said, but with a twist.

Yes, of course you can keep talking to the people you're already talking to, on the frequency you're already on. If you're actually talking to someone already, that's probably your best bet, not least because they know you're there.

In fact, especially if you're in controlled airspace, one might argue that speaking up on the radio immediately upon engine failure isn't a horrible idea, if and only if you are able to do so safely. Even a simple "Springfield tower, Cessna '345, pan-pan-pan, engine failure, attempting restart", maybe even while you're pulling out the in-flight engine failure checklist, will give ATC a heads-up that, at the very least, you won't be able to maintain altitude. That would allow them to take your situation into account when vectoring other traffic. If all they see is a VFR GA plane starting to descend, for all they know that's perfectly intentional maneuvering on your part.

Only if you can't reach anyone (who is able to help) on the frequency you're currently on does it make sense to consider fiddling with the radio to switch to 121.5. Fiddling with the radio to change frequency should be well down your mental list of actions to take.

The same reasoning applies to the transponder; you certainly can change to 7700 if you want to and you feel that it is appropriate, but you don't have to. Squawking 7700 will cause your radar return to light up like the proverbial christmas tree at ATC, but saying mayday or possibly declaring emergency is also a pretty good way to get peoples' attention in a hurry.

Once you realize that the engine isn't going to cooperate in restarting, and especially if you realize that you'll be able to make a controlled (but forced) landing on the nearby airport, I'd pretty much just treat it as an ordinary landing, with the caveat of declaring at least pan-pan-pan, possibly mayday, and telling ATC that you have no engine power. Let them deal with the other traffic and just focus on executing a safe landing and vacating the runway as quickly as you are able, but no quicker.

If you realize that the engine isn't going to cooperate, and that you can't make it to the nearest airport, well, that's when a forced outfield landing likely becomes a tempting option. Telling ATC (possibly on 121.5, with the above caveat on whether you're already talking to someone) what your position and intentions are will still allow them to get help out your way in case you do botch the landing. If you do make it down safely, be sure to tell them, relaying via another aircraft if necessary.

Aviate, Navigate, Communicate is a good rule of thumb, but it's a rule of thumb, not dogma. If you're able to communicate while still aviating and navigating, then doing so might help ease at least the burden of navigation.


How does the A320 FMGC (autothrust, autopilot) decide which radio altimeter readings to use?

First of all, RA1 is showed on the captain PFD and RA2 is showed on the F/O PFD. If one is detected as failed, the functional one is showed in both PFDs. This behavior is fixed, there is no way for the pilots to change it (instead, you can change the IR and ADR data with the relative knobs on the pedestal).
Now, two questions bring up:

How the system detects a failure in one RA if you have only 2 RAs and it cannot perform voting?

In this case, the only way to detect the failure is the self-detection, i.e. the control hardware and software specific to each RA performs the sanity checks. Since you cannot vote, there is no way to externally detect which one failed if they disagree (unless you cross-check with other data like database terrain or similar, but I doubt it does that). The disagreement triggers the ECAM message "NAV RA DEGRADED".

What the systems (GPWS, GLS, windshear, FWC, etc.) use if the two RAs disagree?

According to this Airbus document:

GPWS uses RA1
AP1/FD1 uses RA1
AP2/FD2 uses RA2

It doesn't state about other systems using RAs, probably they use only one side like GPWS and AP. At least these systems use RA information: reactive windshear, GLS autoland, TCAS, ROW, because in case of RA1+2 failure they are on the INOP SYS list. The FWC (Flight Warning Computer) is also using the RA signals to compute the flight phase (for example, to inhibit certain ECAM messages on takeoff and final). I can't find any information on FWC, it probably just disables message inhibition.
Differently it is in the A380, where you have 3 RAs, so they can vote, and all the systems use to the same value.


In canada and I assume in a similar way in the United States, fireworks are treated like any other obstacle such as a communication tower, building, or crane. The location and elevation of the firework activity is assessed for impacts to any instrument procedures, airways, minimum altitude areas, etc. and NOTAM to temporarily amend affected procedures will be issued prior to the activity to advertise the changes and their effective periods.

Having said that, this doesn't address the VFR side of things. Operating near fireworks is essentially the same see and be seen idea. NOTAM get issued here all the time for the fireworks activity themselves and they would include a radius from the centre point. Simply avoiding the area is usually sufficient.


Can a seaplane make a long distance sea voyage on the sea?

Not very well. If we look back to the 1930's, the age of the large flying boat airliners, they were designed to take off and land in minimal sea states - no more than 3 foot swells. Typical usage would be in large rivers or protected bays, and the flying boat was used because long runways weren't available. Nor did those airliners tend to stay on the water for long, usually they were brought onto land with beaching gear if they weren't in service.

The problem is - an aircraft on water is highly susceptible to changes in wind - it is, after all designed specifically to use flowing wind to remain airborne, so gusts of wind while on the water will have a stronger effect on an aircraft than they would on a ship. As well, the aircraft's hull in the water tends to anchor it, subjecting the airframe to stresses from wind in varying directions, that it wouldn't encounter while flying.

Amphibious aircraft and the pure flying boats, left on the open ocean, tend to become damaged to the point of becoming non-airworthy.

Couple of examples:

While on lifeguard duty off of Truk during WW2 and landing to pick up a shot down pilot, Lt John Dowdle's OSU-2 Kingfisher had overturned due to a gust of wind. Lt John Burns also lost his Kingfisher due to the hull springing leaks from being pounded by waves, while he rescued Dowdle and the downed pilots. Both Kingfishers were lost, but their crews plus the airmen they had rescued were saved by submarine USS Tang, in an epic lifeguard mission that saw Tang pick up 22 aircrew.

The Bermuda Sky Queen, a Boeing 314 formerly known as the Pan American Capetown Clipper, ran short of fuel while flying from Foynes, Ireland to the US. It did survive for over 24 hours on the ocean before the 62 passengers and crew could be rescued, but after that much time on the open ocean, the plane was coming apart from the pounding of the waves (the tail section was starting to come loose) plus damage from colliding with the Coast Guard cutter picking up the people. As a result, the Bermuda Sky Queen, the last airworthy 314, had to be scuttled.


How do handling characteristics depend on flying with a full vs. an empty tank?

All aircraft are subject to performance changes due to fuel burn, and since weight, lift, thrust and drag are all tied together for every aircraft in the same way the changes scale nicely. Let's look at some extremes:

One of the most interesting examples of this was the Concorde. Since the Concorde flew ~20K above every one else in the sky in those days it didn't have the same altitude holding restrictions that regular airliners (or any IFR airplane) has. The Concorde was give a block altitude basically to do what it wanted up around 50,000 feet (ca. 15 km). Since it burned quite a bit of fuel at Mach 2.1 and gradually became lighter during the flight the pilots let the plane slowly drift up to gain efficiency as well as gliding distance if needed.

The Concorde also used its many fuel tanks to trim the aircraft as well as cool the nose cone. Fuel burn was closely monitored and constantly pumped around to ensure the aircraft remained in trim.

Even the dinky Piper Archer I fly is affected by partial tanks. If I fly the tanks from full to VFR legal reserves, the CG moves forward a full inch. Granted this does not seem like a lot you will need to trim to compensate for this throughout the flight. You will also be landing a full 240 LBS lighter which is about 10% of the total weight from takeoff. If you come in hot and high you can get yourself into trouble.

Yes you can feel it, generally pilots are not going to do “faster” maneuvers but the maximum G load may change (see your aircraft's POH for more info).

Any smart pilot should practice flying their aircraft at various fuel loads to understand the differences it makes in performance and handling. Some aircraft with things like tip tanks or auxiliary tanks even have fuel burn limitations that define where the fuel is to be burned from and in what order, again going from something as small as a Bonanza all the way up to the Concorde as discussed above.

Just how much can the handling change? Assuming you did your due diligence in pre-flight and calculated your W&B on both ends of the flight accounting for fuel burn to ensure you are within your CG limits the flight should occur with in the limits of the aircraft's POH and generally speaking within operable limits of the airframe. FAA certified aircraft have control force limits so even at the extents of the CG range you should be able to trim the aircraft to handle “normally”. You will likely notice pitch differences (at either extreme) as well as various performance number differences.


How do airlines choose what food to serve?

1. Money

Meals are available at different prices. Most US airlines know you aren't choosing them on the basis of cuisine and pick the lowest priced meal they can get away with. Other airlines eg Emirates, Singapore compete by offering high customer services and so invest more money in better food and service.

2. Culture

Airlines which are mostly flying a home market will adapt the food to the traditions of the country. EL-AL aren't going to be serving bacon cheese-burgers and Air India used to do very good veggie curries.


Russian-built and NATO (USN, European) probe-and-drogue -- are they interoperable?

The drogue system was standardized in the 50s and reverse engineered by the USSR in that time so nearly all aircraft that use it are compatible with each other.


Why does the A340 have 4 engines instead of 2?

The A340 was designed at a time when ETOPS (Extended-range Twin-engine Operational Performance Standards) had not been developed. Some airlines preferred two engines which reduced operational costs, while others preferred four engines with increased reliability at an additional cost.

Airbus decided to split the development into distinct aircraft having the same wing and airframe - A330 with two engines and A340 with four engines.

However, as time has passed, ETOPS has become the norm with improved engine reliability, and A340 production has been stopped. Almost all the civil airliners under development now have two engines.

The Boeing 777, on the other hand, was developed with twin engine operation in mind.


How can planes with the same stall speed and power-to-weight ratio have such different takeoff field length, climb rate, glide ratio, etc?

Are we comparing apples to oranges again? The differences in take-off length are far too big with such similar performance numbers, and I agree that they should be closer together - if we are really comparing the same thing.

Take-off means that the aircraft has to gain an energy difference with a potential and a kinetic component. FAR 23.53 demands a height of 50ft, and FAR 23.51 a speed of 1.2$\cdot\text v_{S}$, but adds more conditions that could be significant here. If the speed for continued safe flight is found to be higher, that speed must be used as the basis of the take-off performance.

The 61 kts stall speed limit only applies to aircraft below 6000 lbs MTOW, so two of the three are not constrained by this limit. Interestingly, the heavier aircraft have longer take-off lengths.

If the airplane weighs more than 6000 lbs and is certified in the commuter category, FAR 23.59 comes into force. It relaxes the height requirement (35 ft instead of 50) but adds a factor of 1.15 to the demonstrated length.

If all take-off distances would had been determined with the same rules and if the stall speed in take-off configuration would be equal between all three types, the take-off distance would be very similar. But I am sure both conditions are not met.


What does the number of white bars in runway's threshold mean?

For runways built, refurbished or repainted after January 2008, the number of bars in the Threshold Markings indicates the width of the runway, as is described in Section 3 of the AIM. Older runways may still use an outdated scheme.

Runway threshold markings come in two configurations. They either consist of eight longitudinal stripes of uniform dimensions disposed symmetrically about the runway centerline, as shown in FIG 2-3-1, or the number of stripes is related to the runway width as indicated in TBL 2-3-2. A threshold marking helps identify the beginning of the runway that is available for landing. In some instances the landing threshold may be relocated or displaced.

(source: faa.gov)

Runway Width   | Number of Stripes
==================================
60 feet (18 m) | 4
75 feet (23 m) | 6
100 feet (30 m)| 8
150 feet (45 m)| 12
200 feet (60 m)| 16

With regard to how to tell the difference between Configuration A and B, Advisory AC 150/5340-1J goes into significantly more detail. It states that

The threshold markings may have either of the characteristics in (1) or (2) below, but after January 1, 2008, only those characteristics in (2) will be acceptable.

The details:

Configuration A. The runway threshold marking consists of eight longitudinal stripes of uniform dimensions spaced symmetrically about the runway centerline as shown in Figure 1. The stripes are 150 feet (45 m) long and 12 feet (3.6 m) wide and spaced 3 feet (1 m) apart, except for the center space, which is 16 feet (4.8 m). For runways less than 150 feet (45 m) in width, the length of the markings is not changed, but the width of the markings, spaces between markings and distance of markings from the runway edge are changed proportionally. For runways greater than 150 feet (45m) in width, the width of the markings and spaces between the markings may be increased proportionally or additional stripes may be added to both sides.
The rule for Configuration A markings requires scaling the width of the stripes and their spacings (and the outboard spacings from the runway edges) proportionally, keeping the length fixed. For a runway 150 feet wide the Configuration A stripes are 12 ft wide with 3 ft spacings (and an 8 ft spacing from the inboard stripe to the centreline, leaving 10 ft between the outboard and runway edge). The Configuration B stripes are given a fixed width of 5.75 ft with spacings of 5.75 ft also. If a Configuration A scheme were used on a narrow runway such that the stripes were equal to the width of the Configuration B stripes, the runway width would need to be about 72 feet (12 ft stripe width for a 150 ft runway width scaled to 5.75 ft for 71.875 ft). For a 72 ft wide runway bearing the Configuration A scheme the spacing between stripes would be reduced to slightly less than 1.5 ft. The difference between the schemes therefore ought to be apparent.

and

Configuration B. For this configuration, the number of stripes required is related to the runway width as indicated in Table 2. The stripes are 150 feet (45 m) long and 5.75 feet (1.75 m) wide and spaced 5.75 feet (1.75 m) apart except the center space is 11.5 feet (3.5 m) as shown in Figure 1. The outboard edges of the outboard stripes extend laterally to within 10 feet (3 m) of the edge of a runway or to a distance of 92 feet (27 m) on either side of a runway centerline, whichever results in the smaller lateral distance.

This is further borne out by a May 2004 advisory (CERTALERT 04-04) which states:

The purpose of this CERTALERT is to remind Airport Operators, Airport Certification Safety Inspectors, and Program Managers that paragraph 9(d) states the threshold markings may have either the characteristics in (1) Configuration A or (2) Configuration B, but after January 1, 2008, only those characteristics in (2) Configuration B will be acceptable.


To what extent is remuneration under a PPL enforced in the UK?

The rules are as follows:

  Privileges and limitations

  A holder of a PPL may, for compensation or hire, act as a crewmember of an aircraft in connection with any business or
  employment if—

  a. the flight is only incidental to that business or employment; and
  b. the aircraft does not carry passengers or property for compensation
  or hire.

"Compensation or hire" means income, not expenses. You can always be reimbursed for expenses such as fuels. Only income is forbidden under certain circumstances (see below).

Concerning getting income, you can be paid income if both of conditions (a) and (b) above true. That means your business cannot be anything to do with flight. If your company is Boeing or any air-travel related business, you cannot receive ANY income (even your salary) for piloting such a flight.

The aircraft cannot be used to carry paying passengers or cargo.

So, basically what this means is that if you fly anybody from your company, they can pay only the expenses of the aircraft and nothing else. You can be paid your salary, only if flying is not your job in any way. As long as you have a regular job and it is fully incidental to flying, then you can fly clients and fellow employees and receive expense reimbursement only. If you are flying clients, they cannot in any way be paying money for the flight other than direct expenses like fuel.

The usual consequence of violating these regulations is that your license to fly can be suspended or revoked. Technically speaking, flying for hire without a license is a minor criminal offense (see below), however prosecutions in the past have only been given out for egregious violations (like working for a charter company without a commercial license).

The way these regulations are enforced is the following:

(1) If you are flying passengers or cargo for hire, and somebody rats you out, complains to the CAA, or it otherwise comes to their attention, then they will investigate and revoke your license if they determine you are flying for hire.

(2) The CAA has inspectors and they may do surprise inspections of aircraft. If you start flying passengers regularly, you may get inspected. If the inspector finds you are flying a bunch of passengers with a PPL, they will closely question your passengers about what money those people are paying. If the inspector determines they are paying money other than incidental expenses to be flown, you will likely have your PPL license revoked.

EXAMPLE:

You are flying 3 colleagues to a business meeting. A CAA inspector directs you to park on the ramp and inspects you and finds out you have a PPL. He will then question your passengers. How much are you paying for this flight? Colleagues answer:

(1) "nothing". You are ok.

(2) "18 pounds". You are probably ok.

(3) "200 pounds". You will lose your license.

If he see cargo on the aircraft, then there are two possibilities:

(1) He determines that the cargo is incidental to the flight and it belongs to you. (Like scientific equipment and you are a professor flying to an archeological site). You are ok.

(4) He sees cargo on the aircraft that does NOT belong to you (like 8 cases of computer chips being delivered to an electronics company). You will lose your license because you are flying cargo for hire.

Criminal Issues

Note that technically, flying for hire is a minor criminal offense in the UK and can be punished with a fine up to 2500 pounds in a magistrate court. However, it is very rare for this kind of offense to be criminally prosecuted. In the linked news story it was found there was only a single prosecution over the course of a year, and in that case it was a pilot working for a charter company and doing many commercial passenger flights, which was a blatant violation of the rules.


Should the weight of the lifting surfaces be deducted from the weight used to calculate the C of G of the aircraft?

The center of gravity is relevant for all inertial forces. For example, if you turn, the centrifugal force would be calculated with the mass of all aircraft parts, including wings and rotor blades.

If you want to calculate the loads on the aircraft structure, things depend on the location. If, for example, you want to know the load on the wing root or the helicopter rotor shaft, you use the total mass minus wing / rotor mass times the acceleration to calculate the force.

While there are cases where the wing mass needs to be subtracted, center of gravity calculations must include it.


Did the Space Shuttle boat tail used in the transport configuration save fuel?

I have always been under the impression that it was mainly installed to protect the engines. However this blurb (and cool photo) claim it did reduce drag.

  ...reduces both drag and turbulence created by the piggy-backing spacecraft while also protecting the engines


What should I look for in weather reports in order to pick a day for glider flying?

For thermal soaring, which is the majority of the time in the sport in North America, the best soaring days are usually the day or two or three after the passage of a cold front with high pressure behind it, where light to moderate winds are forecast.  You want relatively unstable air without any inversions, no mid to high level clouds, and low humidity but preferably enough to form cumulus clouds to mark the thermal tops (if the air is really dry you have no clouds at all and have to troll randomly looking for lift, or look for thermaling birds, or look for other gliders that have found lift). In other words, it's those clear sunny days after a high moves through, the temperature cools off, and you get those nice puffy widely separated cumulus clouds and light to moderate winds.

If a front ahead of high pressure has a strong pressure gradient behind it, it's likely that the winds the next day will be strong and this is bad because it tends to break up the thermals.  In that case I would plan to go the day or two after as the high moves in and the winds die off.

There are a lot of other factors, like the ground moisture content (wet ground sinks heat and inhibits thermal formation), but as a way to try to judge the best likelihood of good soaring conditions, the 2-3 days following passage of a cold front rule is the most reliable.

If you're not much at interpreting weather maps and can only go by the public forecast, and have to pick a day in advance, try to pick one of the first days following the day with storms and a temperature drop in the forecast due to a cold front, where it shows sunny or "partly cloudy" (which will usually be be desirable convective cumulus) for a few days after, and avoid really windy days which if it happens is typically the first day after frontal passage.

Exceptions to this are desert areas which have sunshine and good convective conditions for thermals pretty much all the time, and places like Florida where during any kind of sunny weather there is always convection (there is a localized thunderstorm somewhere in the state just about every day in summer).


What is the difference between flap load relief protection and overspeed protection?

According to this document/study guide

  Flap Load Relief – on the 757 and a few 767s, if the flaps are at 30
  and Flaps 30 speed is exceeded, the flaps automatically retract to 25.
  On most 767s, if the flaps are at 25 or 30 and the placard airspeed is
  exceeded, the flaps automatically retract to 20. The flaps will
  automatically re-extend when airspeed is reduced. If the Flap Load
  Relief fails to operate when it should, the Trailing Edge light will
  illuminate and the FLAP LD RELIEF EICAS message will display

So flap load relief is a system that specifically protects the flaps. This is the result of accelerating to higher speeds.

Overspeed is a more general term and the actual speed that defines overspeed may vary with configuration, the 767/757 has a warning for that

  Overspeed Warning – Master Warning, EICAS message, discrete light and
  siren when airspeed exceeds Vmo/Mmo.

It appears that overspeed protection is a function of the auto throttles.


What are these beams sticking out of the Su-17's nose?

conical nose reminded of its predecessor as much as the MiG-21, and ended with two long poles, one of which contained the very classic Pitot tube and the second a fire control calculator.

Source :https://www.avionslegendaires.net/avion-militaire/sukhoi-su-17-20-22-fitter/

  Two protuberances extended the nose: a Pitot tube and above all a pole supplying measurements to an ASP-5ND fire control system

Source:https://aviationsmilitaires.net/v3/kb/aircraft/show/2208/sukhoi-su-17-otan-fitter


Are glider winch launches rarer in the USA than in the rest of the world? Why?

To expand on Quiet Flyer's answer, it's technical and economic at the same time.

Technical: Winch is limiting because you are deposited in the same spot over the field, whereas a tow, if the pilot knows what he's doing, can take you to a thermal up to a few miles from the field.  Plus you can get towed higher.  If you had to choose the launch method that gives the highest probability for a successful flight, aerotow's a no-brainer.

Economic: Because of the higher average individual purchasing power in the US (and Canada to more or less the same degree) of disposable income (for example, power flying is a middle class, even lower middle class, activity in the US and Canada, and an upper middle class activity in EU), glider pilots can afford the higher cost of a tow, but which is still cheaper than a tow in Europe because overall operating costs for power planes are less.

So given the choice between paying 15-20 bucks for a winch launch to hopefully 2000 ft (if you have a runway long enough to fit the cable) and 30-40 bucks to be hauled to 3000 feet in a Pawnee, whose pilot, if reasonably skilled, will find and drop you off right at a thermal, most North American glider pilots will pay the 30-40 for the tow.

So the result is there is very little market demand for winch operations in North America, except with some small clubs in out of the way places without the money and resources to run a tow plane.


What is the minimum number of people required to manually pushback a 747?

The rope must be attached one end to the aircraft and another to some stationary point. Humans should push it onto the side from the middle point. This should amplify the force significantly, reducing the number of people required by at least the factor of ten or about, so I think somewhat all passengers could do, even if half of them is not fit (there are about 400 in three class layout and we need about 200 strong enough humans). Here is the description of the idea with all mathematics involved.


Why is the range of transponder digits 0 to 7 rather than 0 to 9?

The four-digit transponder code that is entered by a pilot is an octal number rather than a decimal number, and in the octal numbering system, only the digits 0-7 are valid.

As far as why, internally it's actually a 12-bit binary number and octal works really well since can be used as a "shortcut" for entering groups of three binary digits at a time (000 - 111, which is 0-7 in octal).

If it were designed today, with the additional computing power and software complexity available, it would be possible to use a decimal number even if it is stored as binary internally, just so that it is more familiar.  At the time that the system was created though, changing the dials directly set the code in hardware and doing the conversion would have been much more complex / difficult / expensive.

In short, it was convenient for the engineers and manufacturers, and just an oddity for the end users, so they left it that way.


How long would a cruising aircraft take to crash if everyone spontaneously vanished?

There is a far more important question (and the real deciding factor)

How much fuel is on board?

If left unattended a plane will fly until it runs out of gas quite literally, the more gas in the tanks the longer you have. This has happened on occasion before. The Helios Airways Flight 522 is about as close as you can get to this hypothetical situation in real life. The plane may travel farther (since its lighter) but it will go until its out of gas. The same thing applies to smaller GA planes as well.

This is all of course assuming that the plane is not intercepted before running out of gas. Helios 522 was intercepted by F-16's before it crashed and they visually established that the crew was incapacitated (although a flight attendant tried to save the plane). I don't know what the procedure is for interceptions like this but if the plane were headed for a highly populated area they may not let it run out of fuel.


Has a general aviation twin-engine turboprop with counter rotating propellors ever been built?

The only aircraft with turboprop counter rotating propellers that I can think of is the Piaggio P 180 Avanti, whose design is unusual in so many ways.

Check out http://www.mpa.piaggioaerospace.it/, which gives the specifications of a Maritime Patrol Aircraft(MPA) based on the P 180.


How does the heading selector on the ADF work?

It's just a manual compass card (or some call it a heading ring), not an "omnidirectional bearing".  The ADF needle just points to the station (NDB or AM radio station) relative to the airplane; that's it that's all.  If the needle's at 9 o'clock, the station is off your left wing.  The compass card is just a reference device to provide a mental shortcut for determining the magnetic compass bearing of the station relative to the airplane when you are flying a particular heading.
To use, you set the compass card to the heading you are currently flying, and this gives you a quick way to see the compass direction of the ADF station relative to the airplane.  Ideally, you would want the compass card slaved to a gyrocompass system so it shows your heading directly and fancier systems (RMIs) do that, but a standalone ADF doesn't have that feature so you have to set it yourself.
The NDB in the picture is 60 degrees off the nose of the plane. You're flying a heading of 030 and want to know the actual compass direction from the plane's current position to the NDB; in other words, the compass heading to fly to proceed direct to the NDB.
You could just subtract 60 from 30 to get 330 as the bearing to the station, but instead of having to do that little bit of mental math, you dial the compass card to 030 and there's the needle pointing at 330.  Of course, the card is just fixed where you set it, so you have to make sure your actual heading matches the card setting at the time you check the reading.


Is there a maximum possible size for an airplane?

It is no accident that the biggest birds are flightless. The ability to fly goes down with increasing size, so there is also an upper limit for aircraft. The main reason is that as size increases, masses go up with the cube of the size increase while the load-carrying structures like wing spar cross sections only grow with the square of the size increase. This power law is the simplest of the scaling laws.

Since the loads on an aircraft's wing depend not only on its size, but also on many more parameters (angle of attack, speed, aspect ratio …), there is no clear boundary, and advances in materials help to shift the size limit up. If one would try to build the biggest airplane in the world, the wingspan could easily be double of what todays biggest airplanes measure, but the utility of this airplane would be very limited.

Using this airplane for passenger travel would add more restrictions like the number of emergency exits and the maximum distance to the nearest exit, but this could be overcome by using several smaller fuselages. A double-hull airplane would also spread out the payload weight, so the wing would experience a reduced root bending moment. Going from this (source):

to this (source):

would immediately raise the size limit substantially. However, it would require new, wider runways to take off from. And adding more fuselages to the same wing will run into flutter problems soon.

The next indication could be designs which have been studied and deemed feasible but were eventually not built for economical reasons. Here the biggest are ground effect vehicles: Flying slowly in dense air pushes the size limit up. The Boeing Pelican was planned with 152 m wingspan, and Beriev proposed one with 2500 t take-off mass and 125.5 m wing span.

I would guess that a wingspan of 200 m is still feasible, and when spreading the weight even 500 m should be realistic, but totally unpractical. Taking a lesson from history, this would be a multi-hulled flying boat which flies in ground effect, similar to the (mono-hulled) biggest aircraft record holders in the 1920s.


How do you win a simulated dogfight/Air-to-Air engagement?

Bear in mind that most of my maneuvering was done from a defensive position due to the aircraft I flew, and that my experience spanned a period 15-30 years ago.  But, I have some perspective that may help answer the question.
First, as a comment mentioned, some are decided at the bar later.  (with hands shooting down watches…)  We also had a saying:  “First person to the chalkboard wins”.  This is in reference to the post-flight debrief practice of diagraming each engagement out on the board, and how whoever was doing the debrief may slant their interpretation of the fight to favor them.
The reality though is that despite egos and the competitive nature of practice fighting we never really tallied or recorded "wins" and losses.  The objective was always to learn, practice, and improve.  There is an honor system in place, and truthfulness is expected to prevail in the debrief.  Just like when wrestling or playing other games as a child, you pretty much know when you have been bested.  And if you try to BS or make excuses you will be called out and very quickly discredited.  So the short answer is that your guess that it is determined by who can sit at their opponent's 6 O’Clock isn’t all that far off.
To get more specific regarding the details of your question, it also depends on the equipment on the aircraft, as well as the level of training being conducted.  ACM (air combat maneuvering) can be as informal as a couple of squadron peers with no special gear scheduled for a local 1v1 proficiency flight, (and good naturedly arguing over who won later) or it could be a large scale coordinated exercise like Red Flag, or a Battlegroup at sea.
In the case of the former, BVR or even close in missile shots or guns would be called on the radio.  The target aircraft will usually respond “chaff/flares” and continue to maneuver.  If the shooter assesses a high probability of countermeasure success, they would respond “continue”.  A successful bug-out or assessed simulated kill by the flight lead would result in a “terminate” or “knock-it-off” call, followed by resetting to predetermined positions and altitude blocks for the next engagement.  Brief notes and fight diagrams will be drawn up on the pilot’s kneeboard during each reset to facilitate debriefing later.  Any disputes can likely be settled by reviewing the HUD video.
If the aircraft is equipped with a CATM (captive air training missile) and/or chaff and flares it will make the training that much more realistic.  The CATM will have all the electronics of a live missile, but no propellant or warhead.  This will allow the offensive fighter to obtain a missile lock, triggering the defender’s RWR, (radar warning receiver) and give the defender a chance to break the missile lock by dispensing actual countermeasures.  (and reinforce use of the correct button – because in a real fight you would want to pump out actual chaff/flares, not key the radio mic!)
In training there are often altitude restrictions on the use of flares, or they may be prohibited entirely depending on the fire danger in the training range area.
For large scale multi-aircraft exercises, the aircraft are usually fitted with an ACMI pod as described here:  https://en.wikipedia.org/wiki/Air_combat_maneuvering_instrumentation
Results are live streamed back to the exercise commanders and staff.  (Picture Flightaware combined with LiveATC, displayed on a wall sized screen, with a room full of professional pilots and controllers critiquing every move.)  These exercise monitors will act as referees in real time, and call out kills as they occur.  The “dead” aircraft will acknowledge, change their squawk to a prebriefed code so they can be identified by remaining participants, change altitude to a safe block, and transit to a designated area to hang out (in shame) until the end of the engagement.
The entire exercise is played back later on the big screen in a theater sized debrief room.  It can be sped up or slowed down as needed.  (As cheesy as the first TopGun movie is, you can see an example of the kind of displays that were in use at the time, and that as I remember were very similar to what was still being used in the early 2000s when I did my last Red Flag)
The debrief lead will provide commentary as it goes, and may pause to ask the pilots for their perspective.  For example:
Debriefer – “Hammer15, you were in missile range here when you called the ‘Fox2’, but based on the opening speed of Nail30 we assessed this as a successful bug-out, do you concur?”
Hammer15 – “Yes, I was showing ___ knots, and the CATM broke lock shortly after that…”


Are municipal airports in the U.S. treated differently than most public places in regards to legal, holstered, loaded firearm carry?

As you hinted, it depends on the state. And the airport.

Some states allow travelers to carry their hunting rifles or pistols aboard general aviation planes. It is recommended that they buy the ammunition at their destination, if they can, for safety reasons.

Best answer I have is this:

  Any private pilot desiring to transport a firearm, weapon, or similar device must review the appropriate regulations and should contact the local airport management or law enforcement authorities for approval to land at any airport if any firearm is on board.

Source: AOPA

Another way to look at it, if you have your own private airstrip, who's to stop you? Just contact the local authorities of your destination before heading out.

For unconcealed firearms in a public airport:

  44 States allow lawful carry of firearms in the common terminal and baggage claim areas of airports.

Source: Florida Carry and CBS News (2008)

Disclaimer: contact local authorities before trying it, aka don't try this at home.


How is it possible to perform a rapid climb / tight loop without stalling?

Short answer:
The maximum angle of attack is never reached in this video, thus the aircraft is not stalled.
Longer answer:
Stall is a problem mainly occurring during low speed flight. Our angle of attack is always depending on our flight path.
Let's first assume, that are at cruising altitude in a level flight condition. In this case the pitch angle of the airplane equals our angle of attack. As generated lift is dependent on your airspeed and the lift coefficient (which is again dependent on your angle of attack), reducing airspeed in level flight while maintaining your altitude will force you to in increase the angle of attack. At some point a further increase will result in a too high angle of attack and thus stall the aircraft.
Now, let's look at your problem:

(source: aeroskytech.com)
The main difference is your speed, or so to say the excess power used for climbing. During climb, the trajectory of the plane is not equal the horizontal axis. Therefore, also your angle of attack is not equal to your pitch angle (the angle between the longitudinal axis of the plane an the horizontal axis), but to the angle between the trajectory and the longitudinal axis. During the loops showed in the video the airplane is not only changing its pitch angle but also its flight path, therefore it is not stalled.
An interesting example for maintaining your flight path while increasing are military aircraft in combat maneuvers, their pilots rapidly change their pitch angles while still flying in the same direction. This works as a decent speedbrake, allowing them to intercept other aircraft.


One simple way is to compare thrust requirement for level flight at Vbg, where lift to drag ratio is optimal, to the weight of the plane.  This ratio of pounds of thrust, which is equal to pounds of drag in steady state level flight, to the weight of the plane should give a good approximation of the glide ratio.  Glide ratio is how much altitude do I give up to move how far forward.  The altitude is the power source.  How far forward you move is dependent on drag.

So an 1800 lb Cessna would require 200 lbs of "thrust" to glide 9:1.

Now to design for it, speed is a critical factor in selection of wing type and loading.  This is the albatross vs eagle consideration.  Higher speed cruisers favor the albatross.


This is a very broad topic and is heavily opinion based.

Vast majority of commercial pilots do love flying and that's the reason they go through the abuse by airlines. All GA pilots also love flying but either cannot afford the abuse or don't have time for it, so they just pay to satisfy this hobby.

So to answer your question, some of the burdens are:

High costs of training
Waiting a long time (2 years or more on occasions) before getting hired by an airline
Very low salaries in the beginning (several years)
Losing seniority (very often) when you go to another carrier
Staying away from home a lot
Very unstable industry
Many pilots eventually get bored and frustrated (regardless of initial enthusiasm)

Having said that, there are many many great benefits, too. The bottom line is that people only get into this career if they love it deeply.

The question you have to ask yourself is: Am I willing to undergo this trouble for my passion?

P.S.: The above holds true for the airlines and pilots in the US.


Is precipitation static a concern for small drones?

Static electricity buildup could affect communications. Static wicks on trailing edges of flaps, ailerons, rudder, elevator dissipate the static electricity.  I would imagine drones could be mostly fiberglass construction, so some additional details need to go into construction to provide a path for the electricity to flow, vs an all metal craft where the outer skin can be that conductor.


Can a runway have a displaced threshold and a closed section in the same area?

In any case, threshold and runway numbers are highly desirable in a new position. Possibly it is the reason why pilots were confused with your initial variant.

At least by FAA regulations, if you don't want to allow takeoff from this area, it should not be a displaced threshold. I believe that you have a relocated threshold (part of runway closed for takeoff and landing). It can still be available for taxi though, but you don't have a taxiway from that end of a runway. It should look like this:

FAA reference is here, in "Partially closed runway" paragraph.

I saw partially closed runway in Europe as well, and it looked like that (actually they marked that part as a blast pad, and I saw that several times):

Unfortunately did not find anything similar for Canada (used Canadian AIM), but "relocated threshold" is mentioned in some accident investigation in Canada: report. And I still don't understand why the runway should not be marked just as "closed", without threshold displacement markings. Like here:

Arrows may confuse pilots, because it usually means that that part of a runway can be used for takeoff, or landing in opposite direction.


Is it legal to use handheld radios to listen to aviation frequencies in the USA?

Your receiver must comply with USC 47 302a, the law that says, "you can't interfere with other equipment".

USC 47 301 in general is all about "transmission of energy", or broadcasting.
And it really is beyond the scope of government to say you can't stick a piece of metal in the air and process the signals it receives, provided you don't cause interference to anyone else.

Assuming your radio is receive-only, you really won't have a problem with that. (short of a total malfunction!).


How are elliptical winglets better than blended winglets?

The best way to understand why elliptical winglets may be better than blended winglets is to read the text of the patent obtained by the inventor of the elliptical type, Dr. Fort Felker, a former NASA wind-tunnel researcher and expert in the field of computational fluid dynamics, and co-founder of Winglet Technology LLC.

The short answer is that the curvature of the winglets as they extend outward from the intersection with the wings approximates part of an ellipse (hence their name), and this apparently ensures an elliptical distribution of lift both horizontally and vertically, resulting in lower induced drag than a blended winglet.


Is it common for automated control systems to use non-redundant sensors?

In general, yes. Except in certain configurations, namely autoland, autoflight functions are usually fed with one set of sensors.

This matches the fact that pilots flight instruments are fed from a single source as well. Therefore, the autopilot behavior and instruments should have a coherent and predictable response.

The main reason is fault isolation. If the flight crew identifies a fault with the captain's instruments, then disabling instrumentation and autoflight functions on the captain's side will guarantee the faulty data will not influence the copilot's instrumentation and controls.

If you have the system try to "intelligently" vote, you run the risk of not being able to isolate a faulty sensor, especially in 2 faulty of 3 sensor situations. Another classic problem is how to prevent the voting system from becoming a single point of failure.

Instruments are accompanied by a comparator, which detects significant differences between redundant readings and causes an appropriate warning. Most systems treat the warning as binary: the flight crew manually compares all readings and using human logic, decides which are discrepant.


Why are the strings on paramotors so long?

The answer to this is mechanical leverage.

For this, you must understand that the center of mass for a paramotor is usually just above the pilot's head, and that the center of lift is more upwards.

The shorter the strings on a paramotor, the harder that it is to climb, because the length of the effort arm is reduced, requiring a greater power to tilt the paramotor into a climb.

As the motor power increases, you don't actually go much faster. You tip backward, and maintain speed. This is what helps you climb, essentially comboing the wing with the elevator.

The long strings allow for slower, more efficient flight by increasing leverage. This is the same mechanics that are used in most trainer crafts (outside the military) to allow the learner a long, slow flight.


For military aircraft on "alert", there is a position called cocked on (or as some news sites call it, "hot-cocked").  This procedure is run before the aircraft is placed on alert, and does a pre-flight check of all the instruments and then places them in a state that allows power application in a rapid manner.  This way, only minimal steps are required for the aircraft to be ready.  In addition to cocking on the aircraft, they can be parked in special areas (some are called Christmas Trees because of their appearance). This allows the aircraft to reach the runway quickly. Also, in the old SIOP days, there was an Alert Facility near where the aircraft were parked, where the crew would stay in a state of readiness.

Currently the full SIOP mission isn't active (it was ended in 1992 by President Bush, but there are still forces dedicated to it in a new capacity). However, the facilities still exist on many bases.  They can use these facilities still for whatever alerts are required.

With an aircraft in cocked on position, with a pilot on alert (cockpit or facility), an aircraft can take off in a very, very short time (from seconds to minutes).  In general, the mission requirements will dictate the amount of time that the pilot is given to take off (as you note in your question).  So sadly, I can't give a specific answer to your question, because it depends on parameters you haven't specified.


Why would you think the weight was not correctly distributed? If the center of pressure and the center of gravity coincide, there is no problem. Every pilot needs to bring the center of pressure right above or below the center of gravity when flying; this is commonly known as trimming the aircraft. Almost all aircraft have small asymmetries which need to be counteracted by small control surface deflections or trim tab settings.

Note that the fuselage of the BV-141 is offset to the left and the cockpit is offset to the right. This keeps the spanwise center of gravity location near the center of the wing, so any resulting rolling moment is small. What remains (maybe due to an unusual high or low loading of the cockpit) can be trimmed away with the ailerons. A yawing moment due to asymmetric thrust can also be corrected by rudder trim, and the engine was placed on the left so the p-factor of the propeller (which creates more yawing moment at low speed) would counteract the yawing moment due to its out-of-center position.

The BV-141 was designed as an observer platform with an unrivaled field of vision. By using an offset fuselage, only the left side was obstructed by an engine or tailboom. If you compare the BV-141 with its competitor for the same tender, the Focke-Wulf 189, the advantage should become obvious.

Focke-Wulf Fw-189 (picture source)

Note that the BV-141 was a private entry in this contest and was not selected.

A similar aircraft with an asymmetrical mass distribution was the Flyer I of the Wright Brothers. Here, the right wing was 4 inches wider than the left to create additional lift for the heavy engine which was positioned to the right of the pilot.

Front view of the 1903 Flyer I (picture source). Note the offset engine position.


In modern commercial aircraft, is it possible for pilot inputs to exceed the tolerable structural loads?

Airbus fly-by-wire aircraft have what is called envelope protection which is to prevent pilot inputs from exceeding structural limits as well as keep them from getting the aircraft into an upset flight regime (stall, overbank, etc.). The philosophy behind it is that, if the pilots need to perform an extreme maneuver they can be as aggressive with the controls as they want, confident that they won't break the plane.

Boeing generally disagrees with this approach saying that, in an emergency, the pilot needs to have all possible force at his disposal, even if it breaks the plane. See the question Federico linked to in comments for more on this.

Of course, the Airbus system can only provide these protections when systems are all functioning properly. If part of the system is not working the protections are removed. Examples: AF447, XL Airways 888T, Indonesia AirAsia 8501,

As far as AA587, the A-300 is not a fly-by-wire aircraft and doesn't have envelope protections. It's debatable, though, if envelope protection would have helped in that situation. None of the rudder inputs by itself was outside of the structural limitations of the aircraft so the computer would probably not have prevented them. The failure was due to the pilot making alternating inputs in quick succession which caused the sideslip angle to build up to twice the certified design strength of the vertical stabilizer. The A300 system was designed to limit the rudder travel available as speed increased, which is probably fairly similar to what the fly-by-wire computer is programed to do in other Airbus planes. But it would be difficult to determine what complex combinations of inputs might exceed the limits and prevent them.


How do pilots make rudder inputs during negative G flight?

The short answer is that at negative 2 G, the airframe limit for the A7-E, it took little effort to keep your feet on the rudder pedals.

In controlled flight there are aircraft limitations on both positive and negative G. I flew the A7-E for the US Navy and have some operational experience that might offer some context to the question.

I believe the positive G was limited to somewhere between 7-9 G. Can't quite remember the exact number, and it did depend on the external store configuration as well. Newer aircraft have higher G loading capabilities, although the human body has its own limit. Fitness and training can extend the pilots envelope to high G.

As mentioned negative G in the A7-E was limited to -2. There was no issue at these sorts of values keeping your feet on the rudder pedals. It is worth mentioning that the rudder is controlled by the AFCS (Automatic Flight Control System) system and so there is no real need to keep your feet on the pedals, although I did use them at times. Negative 2 G's was hard on the body, and a pilot would come back to the ship with bloodshot eyes after undergoing maneuvers that required this sort of thing.

I can think of 3 times that a pilot would find themselves in a negative G environment. I am not including standard acrobatic maneuvers, but more tactical situations. One, and this wasn't typical, was during training. At a high altitude you unloaded the aircraft to -2 G's and set a 45 degree dive. As the airspeed increased it entered an area on the IAS instrument that was no longer valid, and this was close to Mach. The goal was to observe the characteristics of the aircraft when it went supersonic. There was a gentle pitch down as you broke the sound barrier. I did this maneuver once, although I commonly practiced 45 degree dive bombing deliveries.

The second, and quite common, situation was a maneuver called a bug out. A bug out was used by a flight to engage other aircraft in air-to-air combat. It was at once a defensive and offensive maneuver. The lead called "Bug out. Bug out," and the flight went to -2 G's, unloading the aircraft, and giving up altitude for airspeed. As your adversary turned towards your 6-o'clock the flight would "Pitch back," and pulling positive G's, gaining altitude. Trading airspeed for altitude got the aircraft into slower flight where its turn rate could be maximized.

The bug out placed the aircraft immediately in free fall with military thrust applied. Rolling inverted and applying positive G's is like being in a turn in the sense that the positive G bleeds energy.

The third situation was a defensive maneuver. At low airspeed and with someone directly on your 6 o'clock the pilot might try to "jink." Jinking was a last ditch maneuver where the pilot randomly pulled maximum G, and then went full negative G. I used this against an F-14 in a fight, and afterwards the pilot came and told me he couldn't get a firing solution.

As for uncontrolled flight there is the flat spin which can exert substantial negative G on the pilot. If I remember correctly a flat spin had never been positively observed in an A7-E. It was postulated, however, that given asymmetric wing loading it might be possible. On the other hand the F-14 could enter a flat spin. Talking with pilots who had knowledge about this sort of flight I was told that the negative G could be large enough where it would not be possible to get your hands on the ejection handle, either low or high. Not sure about the feet :)

An interesting side note. At times a pilot will find themselves in a high g turn, grunting against the inflated g-suit, and fighting the encroaching tunnel vision. When I found myself here I would pull on the stick a bit more and watch my peripheral vision go dark (tunnel vision). A bit more g and the tunnel got even narrower, until it was like I was looking through a hole. Then I would ease the stick and watch the hole get bigger. Pull back and smaller. Kind of interesting.


Why do some commercial flights start off unpressurized?

The 737 like most modern airliners (notable exception, the 787) is pressurized by bleed air, from either the engines or the APU. Drawing bleed air from the engines reduces the thrust available for takeoff.

From most common to least common, takeoff configurations are:

Engine bleeds on (supplying bleed air to the pneumatic system), APU off. This is a pressurized takeoff & generally the most common scenario.
Engine bleeds off, APU bleed supplying air to the pneumatic system. This also results in a pressurized takeoff, with more engine thrust available. Used when max thrust is desired, typically due to heavy weights, short and/or contaminated runways, close-in obstacles requiring steep climb gradients, and similar circumstances.

In the case that the APU is inoperative but taking off with the engine bleeds off is still required, you get:

Engine bleeds off, APU bleed off. This results in the unpressurized takeoff referenced in the question.  At a suitable altitude (typically 2000 to 3000 feet into the climb, a minute or two after takeoff), the engine bleeds are turned back on & the aircraft pressurizes normally.

This is uncommon, but still considered a normal procedure (not an abnormal one out of the QRH).

Edit:

Link to Pneumatic System description for the 737

Link to PDF discussing pneumatics & pressurization on the 737


In case of emergencies, yes. The pilot in command has the final authority and responsibility for safety of the flight and can disobey ATC commands in case of emergencies. The reasons for that and the results will decide the consequences.
From 14 CFR §91.123 Compliance with ATC clearances and instructions:

(a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory.
(b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.

From 14 CFR §121.557   Emergencies: Domestic and flag operations:

(a) In an emergency situation that requires immediate decision and action the pilot in command may take any action that he considers necessary under the circumstances. In such a case he may deviate from prescribed operations procedures and methods, weather minimums, and this chapter, to the extent required in the interests of safety.

Emphasis mine. Obviously, it would be prudent for the the pilot (and required under FAR 91.123(c), as @Pondlife points out) to report the deviation to the ATC as soon as possible.


What is this metal piece sticking up on the roof of a 182?

This appears to be an Outside Air Temperature probe.


How can larger wingspan decrease the strength of wingtip vortices?

The strength of the wing tip vortices depends upon the pressure differential between the top surface and the bottom surface. In general larger heavier planes produce stronger vortices.

Now consider two planes with the same weight but one with shorter wing span and one with longer wing span. The pressure differential between the top and bottom surfaces of the wing for the plane with the longer wingspan will be less ( pressure=force/area). Thus the strength of the wing tip vortices for the plane with the longer wingspan will also be less.