Military paintjobs matte for airshow also? Combat aircraft are painted in a matte paint to prevent them from reflecting moon/sunlight too much.

But what about liveries used for airshows? Those colorful paintjobs, are they also always matte, or are they sometimes painted in more shiny paint.

Matte paint creates drag and reduces the top speed. The sheen of the paint is often adjusted to suit operational conditions. For example during WWII an aircraft being prepared for a special high-speed mission, such as a dangerous reconnaissance flight, might have its matte camouflage waxed over to give it that edge of speed. Many combat jets have routinely been finished in a semi-gloss, as a compromise between the two. Special schemes for airshows do tend to be high gloss.


Why are there so few Lancasters still flying? According to Wikipedia there are 54 airworthy spitfires in the world (30 in the UK alone), yet there are only 2 airworthy Lancasters (Lancaster B X in Canada & Lancaster B I in the RAF's Battle of Britain Memorial Flight).

As far as I'm aware they are similar aircraft (in terms of technology, obviously different size and role) from the same era so why is there such a difference in the numbers?

Is there a fundamental issue with preserving the Lancaster or is it simply a financial/lack of interest issue?

I can give you lots of reasons, but as with most things they all really boil down to one: MONEY.

Perhaps the first challenge with preserving any classic warbirds in airworthy "flying exhibit" condition is finding one, but let's assume you can locate a mostly-intact Avro Lancaster (in a field somewhere, or as a static display at a museum that hasn't done anything to it that would render it unflyable).

The next major hurdle is restoring it to airworthy condition economically:
A side effect of their role in the military is that these aircraft are flown hard (they have to accomplish their mission and a little airframe stress or engine damage in the process is OK as long as you still get it back home in mostly-serviceable condition for repair), and of course they do tend to get shot at (9 out of 10 structural engineers surveyed agreed that bullet holes are a Bad Thing for airworthiness; The 10th wet himself and ran out screaming). They've also been sitting around for decades suffering the effects of time (corrosion).

Once you find the aircraft you have to determine what repairs it will require to render the airframe airworthy. You will probably be replacing skin panels, control cables, hydraulic and pneumatic lines, etc. at the very least. The longer it's sat, and the worse the environment, the higher the chance of more major repairs (structural corrosion requiring ribs or spars to be replaced/spliced), and as these aircraft are out of production there are some parts you can't just get off the shelf: Custom fabrication for skins, control surfaces, ribs, etc. adds to the price tag.

Once the airframe is addressed you can look to the engines, since an aircraft without a powerplant is still just a static display.
Much like with the airframe you may find engine parts are hard to come by (the two airworthy B-29s, Doc and FiFi, both required a lot of effort to get working engines).

Now that you have a working engine you need to outfit the cockpit -- Many of the instruments the aircraft originally shipped with were likely pulled by the military or intervening owners as service spares for other flying aircraft, so what's left in the cockpit may be non-functional or so obsolete as to be useless. If you want an aircraft you can safely/legally fly to shows you'll probably need to invest tens-of-thousands of dollars in outfitting it with instruments and radios that are some functional combination of "authentic" and "modern".

Finally once it's all assembled, airworthy, and navigable you still have to pay to operate and maintain it like any other aircraft. When you're talking about a Lancaster with 4 fat engines on it you're racking up quite a fuel bill (and burning a good amount of oil with it).
The engines will of course need routine maintenance (oil changes, etc.) and eventually things will wear out or break, requiring repairs and leaving you with the "out-of-production parts" issues again.

Most of the "big" flying warbirds like the two airworthy B-29s and the two airworthy Lancasters are maintained by organizations that do it as a labor of love & out of respect for the history of these aircraft, but they do not have unlimited funding and there aren't a large number of near-airworthy airframes to choose from for these projects (with the pool of available hulks ever-dwindling), so in that respect there's certainly a financial factor as to why there aren't more of these flying.

Psychologically there's also probably something about having "at least two" airworthy examples flying that may make folks look at restoring a different type as well: Having two flying examples of aircraft from this period provides a decent level of insurance in so much as if one is lost in an accident or develops a problem that can't be fixed at least there's still the other one flying. (When FiFi was the only flying B-29 there were some folks who felt it shouldn't be flown, as an accident would cost the only airworthy example. Doc joining the flight line has muted some of those objections.)


What plane is this instrument panel from? I came across this instrument panel being sold as a potential craft project. I instantly knew what I wanted to do with it. I am going to give it, filled with old pics to my father-in-law who used to be a pilot. It would, however, make for a better story if I can find out the type of aircraft this instrument panel came from. Can anyone identify it for me, please? Maybe even just a hint at where to look?

I was so close. I was looking at the de Havilland Otter but a mid 50s. A friend finally found it. It is a mid 70s DH-114 de Havilland Riley. Thank you verandaguy for leading to the de Havilland. That was most helpful. Now I can finish the Xmas present and be able to tell my Father-in-law the exact type of plane it came from. Cheers.


Which air traffic controller is responsible for a taxiway between parallel runways? When an airport use two runways that are parallel at the same time, my question is which tower controller owns the "ground space" between the runways?

Typically, neither. A separate controller, "___ Ground," controls taxiing traffic. On a big enough airport such as Denver (KDEN) or Atlanta (KATL), there may be more than one ground control, each on its own frequency. Their domains are split geographically: one controls east (DEN) or north (ATL) of the terminals, while the other controls west or south.
At some airports, though, a single Tower frequency owns both parallel runways, for example Austin TX (KAUS), and in San Francisco, one controller works all four runways (1L/R and 28L/R). No rookies working that position!


Wing pitching moment decomposition into two terms Summary: Assuming constant angle of attack $\alpha$, speed $V$, and lift $L$ applied at the center of pressure CP (whose position is $x_{CP}$), the distance $(x_{CP} - x_O)$ between the moment reference point $O$ (whose position is $x_O$) and $CP$ determines the sign (positive, negative or zero) of the pitching moment as long as $L\neq 0$:

$$M_O = (x_{CP} - x_O)L$$

However, the moment $M_O$ depends on $\alpha$, i.e. $M_O=M_O(\alpha)$, since changing $\alpha$ while keeping the reference point $O$ position constant, varies the magnitude $M_O$ since both lift $L$ and the position $x_{CP}$ vary.

Interestingly, when $O=AC$ and $x_O=x_{AC}$, the moment does not change with changing $\alpha$:

$$ M_{O}(\alpha) = M_{AC} = (x_{CP} - x_{AC})L = constant$$

We can move lift $L$ from its application point $x_{CP}$ to point $x_{AC}$ while adding a constant free pitching $M_{AC}$ whose magnitude is $(x_{CP}-x_{AC})L$. The moment $M_{AC}=0$ for symmetric wings and $M_{AC}\neq0$ for cambered wings.

In the case of a cambered wing, the equation
$$ M_{AC} = (x_{CP} - x_{AC})L$$ predicts that $$M_{AC}=0$$ when lift $L=0$. However, we know that a cambered wing has a a constant nonzero moment $M_{AC}$ for any $\alpha$ even when $L=0$ at the zero-lift $\alpha_0$. How do we transform the equation for $M_{AC}$  so it becomes equal to the sum of two terms, one solely due to camber and one solely due to lift:
$$ M_{O}(\alpha) = M_{AC} = (x_{CP} - x_{AC})L= M_{camber}+M_{lift}$$

where the term $M_{camber}\neq 0$ for any $\alpha$?

Interestingly, when $O=AC$ and $x_O=x_{AC}$, the moment does not change with changing $α$

Yes, but only if your lift is also applied at the AC! That's the whole point of the aerodynamic center. You replace the pressure distribution with a lift force (actually a resultant force, but let's neglect drag here) and a moment. If you place the lift force at the center of pressure, then the resultant moment about that point is zero. Then, the moment about any other point $O$ is only "created" by the resultant force. So in that case indeed:
$$M_O = (x_{CP} - x_O)L$$

If you now place the lift at your AC and also O=AC, then:

$$M_O = M_{AC}$$

This $M_{AC}$ is independent of $\alpha$. If you now move to any different O, you get:
$$M_O = M_{AC} + L (x_O - x_{AC})$$

The first term $M_{AC}$ is what you are calling "$M_{camber}$" and the second term is your "$M_{lift}$".


MH370 Curved Track / Arc to southwest...Isn't this also affected by the Earth's motion? How does the Earth's eastward motion figure into the tracks proposed by Inmarsat data etc?

Not significantly. The aircraft flies in the air. The air moves over the earth and takes the plane with it. Of course wind is affected by the rotation of the earth, but there is little direct effect of Earth's rotation on the motion of the plane. The coriolis forces have a negligible effect on the aircraft's track.

The Inmarsat satellite used is geostationary, so it rotates as fast around the earth as the earth around its axis. The nett effect is zero.


Can multiple aircraft share the same logbook? If a private pilot owns 3 planes can he use 1 logbook for all 3 or does he need to use 3 logbooks?  Would the answer change if he also owns a helicopter?

For pilot logbooks, the requirements of "what" needs to be logged to meet training time and aeronautical experience is specified in FAR 61.51. As long as you record all of the information required by FAR 61.51 (e.g., date, total time, day/night etc.) "where" you place the information is up to you. A single conventional logbook works fine, or you can use a spreadsheet, digital device, or any type of similar recording method you choose.  Separate logbooks for each airplane is not required.

Keep in mind that you must present your logbook (in what ever form that you use to record your flight time) for inspection (upon a reasonable request from persons specified in FAR 61.51 (i)) and, if you are a student pilot on a solo cross country flight, you must carry your logbook with you (proof that you have the required instructor endorsements, etc.).

So, it's a good idea to record your flight time in a method that is easy for you to access.  For this, a conventional logbook works well.


Can light GA aircraft implement fly-by-wire technology? Theoretically, I know it is possible. I know the benefits of fly-by-wire too.

My question(s) most revolve around:

why it hasn't been done?
What challenges1 would there be?
What benefits are there by not implementing it even for new light GA aircraft2 being produced?
I know that many smaller airplanes (e.g. Cessna 172) do have fly-by-wire flaps. Why the remaining flight controls don't use this technology?

1: Not considering money as an issue.
2: I couldn't find any reference of it for Cessna Skyhawk.

There are multiple factors here:

The first and main one is of course weight. Fly-By-Wire requires computers and hydraulics to actuate the surfaces in a small plane weight is critical and a FBW system may be the difference between 3 and 4 passengers in total capacity.

The next that comes to mind is certification, I'm not sure exactly how this works but I would think that FBW implementation in a current airframe would require a recertification of sorts. With that being said many GA planes flying out there like the 182, Piper Arrow and other similar things still made today are sporting designs first flown more than 30 years ago. It's a simple matter of, "if it ain't broke don't fix it".

I would think that basic service and maintenance would also become more complex and worst of all more costly. I don't know much about the cost of these systems so I wont comment father than speculation like this.

There is a safety concern in small planes (and I'm sure even bigger planes) if control feedback is not present. This Article outlines some serious concerns with the Cirrus side stick and its lack of feedback (not fly by wire but some of the ideas carry over to the FBW systems that don't have feedback).

A Note on the 172:

The way I understand FBW leads me to think the 172 does NOT have FBW flaps. While they are electronically actuated I consider FBW (and by definition):

  ...flight control computers determine how to move the actuators at each control surface to provide the ordered response

There is no computation done in a 172's flaps to my knowledge, if you move the switch they will move. While the flaps are not directly cable driven I would consider the lack of computer to keep the 172 out of the FBW category but thats just personal opinion.

Also of note, the 172 did not always have electronic flaps - that was a later addition to the aircraft in '65.

A Note On Cost:

Although you note that one must ignore cost in this case you really can't. A FBW system would make a GA plane even more expensive than they are. This is a very real and very limiting factor in aviation. With an unlimited budget you could develop, certify, and regularly fly a FBW small plane that was chock full of gadgets but the FAA approval process is what it is and cost is a very real limit for aircraft makers.


How close is the air resistance or drag force to being proportional to the airspeed squared? How is the total air resistance force exerted upon a body (aircraft or car) related to its speed relative to air at far away? A simple Newton's force momentum analysis suggests that the force $F \propto v^2$ where $v$ is the speed of the body. I am sure it is not exactly speed squared but how close is it for a car?

Subsonic aircraft drag is composed of two major components:

Pressure drag. Most of this is induced drag, but also some is from viscous effects which result in less pressure on the rear sections of aircraft.
Friction drag from boundary layer effects.

At high speed, friction can be the dominant drag contributor and here we have a less than quadratic dependency because with increasing speed the influence of friction is diminished. This is expressed by the Reynolds number and for first order approximations the friction drag coefficient changes in proportion to $Re^{-0.2}$. Since Re increases linearly with speed, the friction drag force is approximately proportional to $v^{1.8}$ at high speed.

At low speed induced drag is dominant and this decreases with speed squared. Of course, there is still a contribution from separation (which is a major problem at low speed), so the proportionality is smaller. Still, at low speed aircraft drag drops over speed.

With cars things are simpler. Here we have a rather blunt body with lots of separation at the backwards-facing surface. The suction on that separated flow is the dominant contributor to a car's aerodynamic drag and is much less influenced by Reynolds number effects. However, a small decrease in the friction drag coefficient over speed on the surfaces with attached flow remains, so the proportionality is a whisker below 2. For engineering, using $v^2$ is good enough, however.


Why would ATC issue a takeoff clearance and also tell the same aircraft to maintain visual separation at the same time? I heard this from the Phoenix Sky Harbor airport tower years ago on a sunny and hot day.

Is it because the controller is able to take off aircraft more quickly by putting the responsibility on pilots to maintain separation, rather than use the standard separation requirement if ATC does it?

Yes, the Tower's separation standards are different if the following aircraft accepts the responsibility to maintain separation visually.  If the following aircraft can't (or declines the clearance to) maintain separation visually, the controller has to wait significantly longer between subsequent departures.

Typically, the transmissions from Tower are something along the lines of:

Tower: "Airline 123, line up and wait 25R, confirm A320 on departure roll in sight."
Pilot: Airline 123, line up and wait 25R, Airbus in sight.

After the A320 has rotated:

Tower: Airline 123, 25R cleared for takeoff, maintain visual separation on preceding traffic, they will be turning north.
Pilot: Airline 123, cleared for takeoff 25R, maintain visual separation on the Airbus.

The advisory to the crew about they will be turning north gives them the awareness that they won't be following the other aircraft for miles and miles, just until it reaches the point a few miles from the airport where some traffic turns north and other traffic turns to the south (or proceeds straight-out).  The aircraft will generally be sequenced by Ground Control so that they line up at the runway in a sequence such that the departure directions are staggered.  When this doesn't work, at PHX anyway, that tends to be when there is a break in the flow of departures for a minute or so, and during that time aircraft that have landed on 25L (in this case) and are waiting down-field to cross the departure runway, can cross and then taxi to the terminal.  Tower will often let the "waiting to cross" queue build up to three or four aircraft -- each holding short of 25R at a different taxiway -- while they launch departures rapidly, and then one departing aircraft remains "lined up & waiting" while the arriving aircraft are cleared in rapid sequence across the runway.

And after they're all clear, the departures resume.

All in all, it's a pretty efficient way to "move the metal" & get lots of aircraft into the sky as quickly as possible on clear days -- which PHX has plenty of!


What is the procedure to follow for "traffic not in sight"? What would be the proper procedure to follow, when in the pattern or approaching an airport, if ATC gives you the position of an aircraft and you do not have them in sight? Do you just report "not in sight" and wait to turn base?

Please don't use "Not in sight". Parts of radio transmissions, such as single words, can easily be cut off or missed, making it sound like you said "In sight". I commonly hear pilots use the phrase "Looking out" or something similar, which conveys a clear message: "I understood what you said, but I don't see the traffic yet".

ATC provides traffic information when there is a risk of conflict, or in the traffic circuit if we want you to follow another aircraft. No matter the reason, we will continue to update you on the traffic either until it is no longer a factor, or until you report having the traffic in sight. So, when you receive traffic information, keep looking until you see the traffic. We will keep you updated as long as it is still relevant. And please do report when you spot the traffic, that is a super helpful piece of information to us.

In the traffic circuit specifically, if you can't see the traffic being called out, you can always ask the tower to confirm you are cleared for base and final turn. When I have someone on downwind who can't spot the aircraft to follow, I will typically just tell them to continue downwind and then I will call their base turn when appropriate. But, as always, if in doubt, ask.


How do pilots decide whether to circumnavigate bad weather? How does an airline pilot decide in the air whether to circumnavigate or fly through bad weather visibly looming ahead and/or displayed on the weather radar ?

Easy.  You don't go through, or close to, a thunderstorm cell (a red area, which is lots of water), period.  You decide on a heading change to navigate around it, request it from ATC, and if the heading you want is not forthcoming, you tell ATC you are altering heading for weather.  You are not required to endanger the aircraft to comply with an ATC clearance of any kind.  And getting close to a cell is endangering the aircraft.

Different airlines will have different policies on some of the details of getting around cells, like they have to maintain 20 miles minimum, upwind if possible.  In visual conditions where you can see the cell, same deal.  Alter heading to upwind side x miles (you don't want to fly under the anvil which is downwind, even if the air is clear in front of you, because you can run into hail falling from the anvil).

Besides thunderstorms, the other big bugaboo risk wise is icing the plane can't handle.  Same deal, you ask for higher or lower, and if icing is becoming dangerous and you need to move now, you tell them you are going higher or lower.


Do passengers notice if the aircraft is struck by lightning? I recently saw a video from Valk Aviation
(actual scene)
of a KLM B777-300 struck by lightning on departure. It happened a few days ago.

I know this looks more frightening than it really is and the aircraft usually isn't harmed. There are numerous posts here covering this.

But I wonder what a passenger would notice when the aircraft gets hit? Is there some kind of BANG or something? Do the lights flicker, for example?

Terrys answer implies you cannot tell for sure so I guess you won't notice at all. Is that true?

In my experience: Yes, the passengers notice, at least for some lightning strikes.

I was flying from San Francisco to Chicago, this was sometime in the 90s. There was a big snowstorm coming in to Chicago, and all you could see out the windows was snow illuminated by the landing lights. There was the usual murmur of conversations going on in the cabin, and all of a sudden there was an almighty BANG and the cabin went completely silent - everybody had stopped talking and was probably holding their breath. Several seconds later (seemed like a long time) the captain came on the PA and said

  Nothing to worry about folks, we were just hit by lightning. We will be on the ground in Chicago shortly.

I am 100% certain that every single passenger on that flight "noticed".


Can a pilot choose his co-pilot? How are pilots paired in the duty roster?

Pilots choose their co-pilots from a pool (whitelist)? (Pilot has the final say)
Randomly, but taking pilot wishes into consideration? (Airline has the final say)
Ramdomly, without taking anyone's wishes into consideration?

In the case of (2) or (3), can a pilot refuse to fly with certain other pilots (blacklist), thereby having the power to overrule the airline?

As with everything it varies from airline to airline, but for the most part it is option 2).

Larger carriers will usually give pilots the option of blacklisting another if they wish, but smaller airlines with only a few dozen pilot combinations might just tell the pilot to suck it up.

The airline will also avoid placing a brand new FO with a brand new captain, aka ‘green on green’ pairings. And on top of this are things like fatigue duty limits, workplace agreements, seniority (bidding), currency and other considerations. Rostering is a very complex exercise.


What is the legal interpretation of rest for FAA Part 135 operations? 14 CFR 135, Subpart F contains the rest requirements for Part 135 operations.

The rest requirement for 1 and 2 pilot unscheduled crews (typical) comes from:

  135.267(d)
  Each assignment under paragraph (b) of this section must provide for at least 10 consecutive hours of rest during the 24-hour
  period that precedes the planned completion time of the assignment.

What does the FAA consider rest and what actions by the company will interrupt the required rest?

The 10 hours of rest need to be uninterrupted, planned, and not spent on call. Essentially, the pilots need to have 10 hours in which they are not obligated to do any work for the company at all.  Note that it does not mean "10 hours of sleep", and it is up to the pilot what they do with their time off.  (They can even technically fly for another 135 operator during that time, but they run the risk of being "careless and reckless" if they aren't well rested.)

NATA has an article about some of the FAA's legal interpretations (pdf) that's pretty interesting and relatively recent (2011). Their paraphrase of the FAA's varying interpretations is this:

  the FAA has said that for a “rest period” to be legal it must be: 1) continuous, 2) determined prospectively (i.e. known in advance) and 3) free from all restraint from the certificate holder, including freedom from work or freedom from the present responsibility for work should the occasion arise.  Being on call is specifically mentioned as not rest.

This is an interpretation that is repeated throughout a lot of articles and forum discussions. It's also often pointed out that many (most?) 135 carriers blatantly ignore these rules, as most charter operations require pilots to be on call.

For example

You arrive at 19:00, and are done with paperwork / postflight / etc by 19:30 and leave the airport. The moment that you leave the airport is the beginning of your rest period; it will need to last 10 uninterrupted hours, which means until at least 0530 the next morning (1930 to 0530) to mean anything.

If you get a call from dispatch at 21:00 telling you about a flight that might take place in the morning and that you must be available for a call at 05:00 just in case - your rest ends at 05:00. Because your rest period ended 30 minutes early (when you were required to be available), you did not get the 10 hours of rest and can't take a flight without violating 135.267(d).

Another caveat:

There are no explicit limits on duty time (the exception being 135.267(c) involving a "regularly assigned duty period of no more than 14 hours" which doesn't apply to most 135 operators).  The limit is on planned flying conducted under 135.

As long as you plan on parking the airplane when you can show 10 hours of rest in the previous 24 hours (which is why some people incorrectly assume that you are limited to 14 hours of duty: 24 - 10 = 14!), you can be kept on duty afterwards.  You can even fly under Part 91 for the company.  You can clean the airplane, or do office work.  While none of that is rest and it is still duty, it is legal unless you get in the airplane to fly under Part 135 without getting the required rest.


What is the difference between "Land 2" and "Land 3" annunciations for Boeing autopilot systems? Another question's answers refer to certain Boeing jets having the capability to annunciate "Land 2" and "Land 3" when flying a coupled ILS approach. What does each of these modes require, and allow, beyond the basic coupled ILS? How are they different from one another?

From "Smart Cockpit"

B777 Automatic Flight (PDF!)

  AFDS Status Annunciation
  The following AFDS status annunciations are displayed just above the PFD attitude display:
   • FLT DIR (the flight director is ON and the autopilots are not engaged)
   •   A/P (the autopilots are engaged)
  •   LAND 3 (three autopilots are engaged and operating normally for an
  automatic landing)
  •   LAND 2 (AFDS redundancy is reduced; in some cases, only two autopilots are available)
  •   NO AUTOLAND (the AFDS is unable to make an automatic landing).
  With a LAND 3 indication, the autopilot system level of redundancy is such that a single fault cannot prevent the autopilot system from making an automatic landing (fail operational).
  With a LAND 2 indication, the level of redundancy is such that a single fault cannot cause a significant deviation from the flight path (fail passive).
  An EICAS message is displayed for any fault which limits the capability of the automatic landing system. Aural alerts for EICAS messages not affecting safety of flight are inhibited until after touchdown. Changes in autoland status below 200 feet, other than a transition to
  NO AUTOLAND status, are inhibited.
  From Chapter 9, pages 22-23


Can fuel be stored in the anti-shock bodies? lets say an airplane needs to get to a certain route but doesnt have the fuel to do and it needs to store in the anti-shock bodies. Is it possible?

Yes, and there have been cases of this. Tip tanks of the period when aircraft flew already supersonic and jet engines were still very thirsty are a good example. Below you see the area-ruled tip tank of the F-5.

F-5 tip tank (picture source).

Now that @voretaq7 got me thinking, I should also mention the "Doppelreiter" fuel tanks (slipper fuel tanks) which were used on some German fighter airplanes in WW II. They were mounted above and behind the wing, and to everyones surprise they had little impact on the top speed of the airplanes, and in case of the Me-309 helped to increase it slightly. They were the first practical application of Küchemann carrots and worked much like the flap track fairings of today's airliners.

FW-190 A with Doppelreiter tanks.


What are Runway Declared Distances? Perusing through the A/FD in the United States I see that some runways have declared distances while others do not.

What is the meaning of:

TODA
TORA
ASDA
LDA

From the AIM, 4-3-6 (c)(2):

All 14 CFR Part 139 airports report declared distances for each runway. Other airports may also report declared distances for a runway if necessary to meet runway design standards or to indicate the presence of a clearway or stopway. Where reported, declared distances for each runway end are published in the Airport/Facility Directory (A/FD). For runways without published declared distances, the declared distances may be assumed to be equal to the physical length of the runway unless there is a displaced landing threshold, in which case the Landing Distance Available (LDA) is shortened by the amount of the threshold displacement.

Now for definitions. These terms are defined by the FAA/ICAO in the PCG.
TODA - Takeoff Distance Available. The takeoff run available plus the length of any remaining runway or clearway beyond the far end of the takeoff run available.
TORA - Takeoff run available. The runway length declared available and suitable for the ground run of an airplane taking off.
ASDA - Accelerate-Stop Distance Available. The runway plus stopway length declared available and suitable for the acceleration and deceleration of an airplane aborting a takeoff.
LDA - Landing Distance Available. The runway length declared available and suitable for a landing airplane.
(also Declared Distances from wikipedia)
which lead to other definitions...
Stopway - An area beyond the takeoff runway no
less wide than the runway and centered upon the
extended
centerline of the runway, able to support the
airplane during an aborted takeoff, without causing
structural damage to the airplane, and designated by
the airport authorities for use in decelerating the
airplane during an aborted takeoff.
Clearway - An area beyond the takeoff runway
under the control of airport authorities within which
terrain or fixed obstacles may not extend above
specified limits. These areas may be required for
certain turbine-powered operations and the size and
upward
slope of the clearway will
differ depending on
when the aircraft was certificated.
then for those specified limits of the clearway, in 14 CFR Part 1 we find

Clearway means:
(1) For turbine engine powered airplanes certificated after August 29, 1959, an area beyond the runway, not less than 500 feet wide, centrally located about the extended centerline of the runway, and under the control of the airport authorities. The clearway is expressed in terms of a clearway plane, extending from the end of the runway with an upward slope not exceeding 1.25 percent, above which no object nor any terrain protrudes. However, threshold lights may protrude above the plane if their height above the end of the runway is 26 inches or less and if they are located to each side of the runway.
(2) For turbine engine powered airplanes certificated after September 30, 1958, but before August 30, 1959, an area beyond the takeoff runway extending no less than 300 feet on either side of the extended centerline of the runway, at an elevation no higher than the elevation of the end of the runway, clear of all fixed obstacles, and under the control of the airport authorities.


Why would a flight no longer considered airworthy be redirected like this? I ran across this tweet covering the saga of Smartwings 1201, a 737 MAX 8 that was apparently redirected from Prague to Ankara after the MAX was grounded by the EU.

(flightaware.com)

It seems like an odd decision to do this. The plane had to divert and apparently spent quite a long time in circling before it was allowed to land in Turkey. Why was it not allowed to land at Prague as scheduled and be grounded there?

There could be a lot of reasons for this...

EU closed airspace to 737's MAX 8's on March 12
They needed to go into a holding pattern until ATC figured out where to put them
They needed to be in the holding pattern until they could get a landing slot
They were redirected to an airport that had a maintenance facility that the airline uses
They redirected to an airport with code-share partners so they could rebook passengers without a major fee

Edit I'm not sure what is going on with FlightRadar24, but it shows that the plane continued to Prague the next day. It looks like they landed in Ankara then continued on to Prague. I'm not sure if the flight to Prague was just a repositioning flight, or if it had passengers.

Edit 2 Turkey subsequently (after this flight) also closed airspace to 737 MAX 8's. The EU closure allows for ferry flights, which are flights without passengers on board. The flight from Ankara to Prague was just a positioning flight so that the aircraft could be serviced when it came time to implement a fix from Boeing.


What is the power generating capacity for an airport GPU? What is the normal current for GPU power supply for commercial aircraft and how much power do they need while on ground (in kWh)?

I have read that aircraft need need 28V DC and 115V AC - what would be the percentage between both modes of supply?

Would it by possible to power GPUs entirely by solar power?

Power requirements are dependent on airframe and configuration (see this question for a general idea). GPU's come in varying sizes for varying aircraft types. For example this GPU (arbitrarily chosen) can deliver: 800 amps continuous, 2500 amps peak. While this GPU can only drive 70Amps continuous. Others may be able to drive more and some may drive less. Are you asking about a particular application? The GPU's at the tiny airport I fly out of that we use to bump start the occasional Piper are no where near the capacity of what you may find at JFK for starting up a 747.

  Would it by possible to power GPUs entirely by solar power?

Depends on the application but it would be unlikely to chose such a medium for powering a GPU the way things stand now (in terms of power requirements). You may be able to have a battery powered GPU that is charged by solar cells but that would only work well in the smaller scenario. Having a solar powered airport that can provide ground power is a whole different question.


Do any aircraft have liquid-cooled brakes? Aircraft wheelbrakes, especially those on heavy aircraft, get really, really hot during landings and rejected takeoffs, and cool down very, very slowly without active cooling.  This imposes limits on how short turnaround times can be between flights, in order to avoid overheating the brakes and wearing them out (which would be bad).  To counter this, many aircraft that make frequent, short flights have brakes with forced-air cooling.

However, air, being a gas, is far from the best coolant available; do any aircraft use liquid-cooled brakes for maximum brake cooling capability?  This seems like it would be most useful for very large aircraft that make frequent short, heavily-loaded flights from short fields.

A liquid heat exchanger system for brake discs, with coolant, lines, some way of transferring heat from the disc pack to the heat exchanger, that would somehow keep the entire apparatus liquid tight... yikes.  I can only imagine what a monstrosity such a design would be, even if it's technically feasible.

Brake temperature requirements don't affect gate turnaround times. 99.99% of the time you land and taxi in, and an hour later, off you go, long after they've cooled off.  On a reject, on the rare occasion the reject didn't require a return to gate for maintenance action of some kind, you have the Brake Temperature Monitoring System to tell you when the brakes are good to go even if you don't return to gate (most rejects are because of a Caution or Warning prior to V1 -  and if you reject in the "high energy" phase, usually above 80 or 90 kt, which is a callout during the roll, your airline will likely require you to return for a brake and tire inspection anyway, "liquid cooled" or not).  If the BTMS is MEL'ed, you will have to observe a minimum brake cool down time as per the associated MMEL Ops Procedure.

So yes there are times when regular brakes require you to sit and wait for a period of time, but it would happen on 1 departure in, well, thousands (departure delays from brake overheating, from pilots riding the brakes during taxi, is probably a bigger problem operationally).   In any case, in view of the actual operational impact, nobody would want to pay for such a cooling system even if it was feasible.


Is there a list of accidents due to poor communication in English? I would like a list of accidents satisfying the following criteria:

Poor communication between ATC and pilots was judged to be a major factor in the accident;
English was the language of communication between ATC and the pilots; and
The native language of the pilots and controller was the same, but not English.

I am not looking for discussion of whether using English is a good idea or not in these situations, whether its use played a role in these accidents, or whether better training in communications is needed. I just want a list of accidents where these conditions are met.

The poor communication need not necessarily have been attributed to insufficient knowledge of English.

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

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

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


Why are piggyback launches done by dropping the carried aircraft and not by "fly-off" launches? Every air-launched aircraft I'm aware of, with the exception of the D-21 in combination with the M-21 carrier, has been launched by dropping it. Is there a reason why drop launches are preferred to "fly-off" launches from the top of the carrier?

Its much safer, you don't kill the carrier aircraft if you drop away and have a major aircraft malfunction.  Gravity gives you the separation you need.

If you treat the two aircraft like a formation flight, which it essentially is, its dangerous for the critical aircraft to go belly up, ie blind, to the carrier.  In an emergency the first step in formation flying is to ensure separation which the critical aircraft can't do because it can't see if it's clear to descend and it may not have the ability to laterally sidestep.  Thus, a blind push on the nose could kill both aircrews.


How do the Kaman K-225 rotor "planes" work? I had the opportunity to go to one of the Smithsonian Air and Space museums today and they had a Kaman K-225 on display. For those who don't know, the K-225 is a dual side-by-side helicopter design with an open cockpit:

Source: Own Work

The blades look to be very basic wooden design without any kind of variable pitch on the rotor head. What I found very odd were the "planes" on the rotors:

Source: Own Work

Each rotor seems to have one of these "planes" on it located about 2/3rds of the way from the root. Here is a close look:

Source: Own Work

I wish I could have gotten a better picture but it looks like there is a rod going from the main blade to the smaller "wing" on the device. The rotors seem to be solid, so I'm wondering...

What are the purpose of these "planes" and how do they work (I'm assuming to change the AoA of the blade)?

These are a form of servo flap, commonly found on Kaman designs, but also on at least one early helicopter (namely, a coaxial rotor aircraft built by d'Ascanio (shown below):

As opposed to controlling blade pitch from the blade root using pitch links (which are, essentially, pushrods), as in a typical rotor head, the servo flaps allow for pitch to be controlled by a control surface on the blade (similar to how controls work on a fixed-wing aircraft).  The yellow "wing" is the flap, and the black item, I'd imagine, contains a hinge and actuator rod to pitch the flap up and down, generating a force at a small moment arm behind the blade, which then alter's the blade's pitch as desired.  Instead of using an actuator to twist the blade, you're using aerodynamics to do a lot of the work for you, similar to how a fixed-wing aircraft works (except, instead of changing the rotor's effective angle of attack, you're twisting it instead).

Hence, if you look closely at the first picture you posted, you'll noticed that there is no swashplate, no pitch links, and really nothing reaching up the rotor mast from the helicopter except for a structural brace.  This system does away with pitch links and their associated actuator systems and can decrease total system weight.  In addition, as the flaps are significantly more streamlined than a typical pitch link, there is a possibility for drag savings as well.  Compare the following two rotors heads -- the first is a semi-rigid 2-bladed rotor from a Bell 230, and the latter is a typical Kaman rotor head.  The Kaman head is a picture of simplicity when you realize the only bits sticking out in the wind, beside the blade grips, are bump stops.

Bell 230

Kaman H-43

However, there's no free lunch.  The price you pay for all this is that, instead of an actuator somewhere relatively "easy" (on the body of the helicopter), you have to put an actuator (albeit a much smaller one than would be required to drive traditional pitch links) out on the rotor blade and feed both control and power out to it.  Control and power isn't too bad -- it's already done for anti-icing gear to some extent -- but the actuator can be tricky, particularly, I would think, in terms of tuning blade dynamics.  Kaman (who built the K-225 and the highly successful KMAX, which also utilizes servo flaps) found a way to do this that works great, but it hasn't really made a splash in any other manufacturer's helicopters (to my knowledge).  Rumor has it that Sikorsky and Northrop put together an entry for DARPA's Unmanned Combat Armed Rotorcraft program that had servo flaps on it, but that program got cut in 2004...so who knows?  In the interim, swashplates have been the control method of choice for upwards of 80 years and work well for those who don't have experience with flaps.

Sources: https://www.helis.com/howflies/servo.php and rotor dynamics class.


Has a life raft ever been successfully deployed on a modern commercial flight? Has a life rift ever been successfully deployed in the event of an air accident involving a commercial aircraft?

For the purposes of this question a "life raft" is an inflatable device designed specifically and only to be used as a life raft and normally stored inside the aircraft, not some multi-purpose or makeshift device.

Criteria for inclusion:

A commercial jet flight after 1945
Carrying paying passengers
Minimum aircraft capacity 50 people, although fewer may have been on-board at the time
Raft stored inside the aircraft prior to deployment
Raft designed for this purpose, i.e. not just something a passenger was randomly carrying
The raft actually worked as intended, i.e. people were able to float on the water in it and not drown

In short I'm asking about the rafts often seen stored away on commercial flights. The raft may have been used on rivers or the ocean.

(Image source) A Boeing 737 ceiling compartment where such raft can be stored.

Passengers used rafts to get off the plane; news.com.au
Miami Air Flight 293 (3 May 2019)

More than 140 passengers have managed to escape from a plane crash as a Boeing 737 jet slipped off a runway and into a river. (news.com.au)

There is a list on Wikipedia for water landings, not counting non-jet and not counting overruns, and by checking photos, it seems none used cabin-storable-rafts. The accident shown and linked above is a runway overrun (although it was not excluded from the criteria listed).
This article also confirms the rafts came from inside:

Eric and the pilot wrestled one of the six life rafts out the forward cabin door, down the evacuation chute [i.e., slide] and into the water.


Why does elevator still raise and lower the nose when the aircraft is steeply banked? In a steep turn, the aircraft is basically sideways. However, when executing a steep turn, one still raises and lowers the nose of the aircraft by using the elevator.

Intuitively, it seems to be that in an extreme bank, the elevator and rudder have essentially changed roles, since they have been rotated with respect to their normal orientation. It seems to me that in a steep turn, pulling back on the yoke should tighten the turn. But this seems to not be the case in practice, since getting the nose up in a steep turn still involved just pulling back on the yoke and/or trim.

Why is this the case?

At 45 degrees Angle of Bank pulling back will both tighten the turn, and cause the nose to rise equally because you are halfway to 90 degrees.  You are correct though, at much steeper angles of bank the control inputs function the other way:  In a very steep high G turn the angle of bank is used to control altitude, and back pressure is used to control the rate of turn.  You definitely don't want to use rudder in this case though, bad things can happen in an accelerated stall with yaw.


How much thrust is gained from placing a propeller in a duct? Assuming that the power and diameter are the same, how much extra thrust can be gained by placing a propeller in a duct? How does it influence the RPM?

To clarify: take any prop, place it in a well-designed duct, what can we expect? I expect higher RPM for same power, but also duct enhanced thrust. An approximation based on sources would be great.

Relative to MAV, as opposed to large scale rotors:

Compared to the baseline open rotor, the shrouded rotors showed increases in thrust by up to 94%, at the same power consumption, or reductions in power by up to 62% at the same thrust.
At rotor collectives above 10°, all shrouded-rotor models showed improvements in performance over the isolated (‘open’) rotor — that is, higher thrusts and lower power requirements. At the same power consumption, increases in thrust over the open rotor by up to 94% were observed, or, conversely, up to 49% reductions in power at the same thrust, for the condition where the open and shrouded rotors are required to have the same tip speed. If, instead, the rotor disk areas are required to be the same, then up to 90% increases in thrust at the same power.
The effects of changing any one of the four parameters (tip, rlip, d, Ld) on the shrouded-rotors’ performance became more pronounced as the other three
parameters were changed to degrade the performance. It is therefore not possible to categorically state that any one particular parameter has a greater
effect on performance than any other, since the amount of influence of any
parameter depends on the values of the other parameters. The exception to
this seems to be the lip radius, changes in which had almost same effect no
258 matter what the values of the other parameters are.
Thus, in general, it would seem that changing the value of any shroud parameter so as to improve performance results in less sensitivity of the performance to changes in any of the other parameters; similarly, improving the efficiency of the rotor itself would seem to result in less of a performance benefit from the presence of a shroud.

Extracted from:
HOVER AND WIND-TUNNEL TESTING
OF SHROUDED ROTORS FOR IMPROVED
MICRO AIR VEHICLE DESIGN
Jason L. Pereira
Doctor of Philosophy, 2008
Dissertation directed by: Professor Inderjit Chopra
Department of Aerospace Engineering University of Maryland College Park
Rotor parameters including tip gaps, tilt and relative wind, collective, and motor characteristics will influence rotor RPM, and are indirectly addressed in Pereira's dissertation.  Again, there are very broad assumptions in the OP question, but Pereira substantiates generalized efficiency improvements for specific configurations.


Why are thrust reversers not used to slow down to taxi speeds? In reading this question (Would more throttle when using reverse thrust reduce stopping distance?), it prompted me to remember that on many of my flights (typically on 737s or CRJ type aircraft), it seems that thrust reversers are used for a few seconds after landing, but then are deactivated while the aircraft is still rolling at high speed.  The pilot then utilizes the regular brakes to slow down to taxi speeds.

I am wondering why the pilot does not continue to use thrust reversers down to approximately taxi speeds, to reduce the amount of brake usage (and heating of the brakes) needed.  My only guess would be to possibly avoid the reversers kicking up FOD back into the engine inlets at lower ground speeds, but not sure if that's the real reason or not.

A minimum max reverse power speed is often an airplane operating limitation.  It's mostly related to FOD (mostly sand grains and small gravel) and on some designs there may be compressor stall issues due to flow disruptions.

On the CRJ 700 max reverse is limited to 75kt although you can use up to 60% N1 down to zero speed.  On a 900 you have to be at idle below 60kt.

In practice, you start to come off max reverse during the landing roll transition from high energy to low energy (on the RJs, there is a speed call at 90 kts for this).  You come down to idle not too quickly and linger at idle for a second before stowing them; if you just slam the levers down to stow position, the reversers stow while the fan is still producing a lot of energy and you actually get a little kick of acceleration, which feels like you let off the brakes for a moment.

You can use idle reverse, which gives a little bit of braking, while taxiing if the alternative is riding the brakes and overheating them, say like a taxi along a downhill slope or along a slick icy surface where braking is marginal, and you don't want to taxi single engine, and in a pinch you may use reversers to try you save your butt if you start sliding off an icy taxiway with no braking control.


Why this huge discrepancy in flight times? I was looking at return flights from London - Azores islands and was astonished to see the huge difference in flight times, both flights are via Ryanair:

out: 3 hr 5 min
return: 4 hr 45 min

I am aware of differences due to wind conditions/jet streams and routes etc but for the return flight to take >50% longer really surprised me. What is likely to be the cause of this?

TL;DR Probably "Operational" reasons

I would hazard a guess that this is a combination of a few factors

A longer route flown inbound to London
Flying in to a busy airspace like London requiring particular routing, particularly oft requiring length hold patterns
The time of day the flight in to London arrives being particularly busy (late afternoon/early evening)

These three factors may cause the airline to list the flight duration as longer than it would usually, in order to account for the possibility of a lengthy flight time.

If you look at the track of the outbound flight and compare it to the inbound flight you see that, at least on that occasion, a much longer track was followed. The airline may know that the route back to London is longer (for whatever reason) and adjust expected flight times accordingly.

Also, when you compare it to the only other direct flight departing and returning to the same airport (LGW) on skyscanner for the same route, the time difference is much less (15 minutes difference) which is much more usual. It may well be that the route to/from LGW is more equal outbound/return than the route taken to STN. It may also be that this flight in to LGW is at a typically quieter time of day.


How are brakes cooled on heavy aircraft? As kinetic energy is not stored or recycled, large quantities of heat have to be evacuated in a short period of time when aircraft abort their takeoff or land:

B777 brake test, Youtube

Which approximate quantity of energy is transferred to the brakes in a rejected takeoff for heavy aircraft, e.g. Boeing 777 or Airbus A380? What are the typical systems used to cool brakes on these heavy aircraft? Is cooled air or liquid used, or just ram air?

Summary

The order of magnitude of brake energy after a rejected takeoff (RTO) for a very heavy aircraft is 1 GJ, or 100 MJ per wheel brake.

Aircraft brakes are cooled with ambient air, either through passive airflow or (optionally) through forced air ventilation.

Cutaway drawings of A380 wheel and brake (Source)

Energy Dissipation

Takeoff speed for heavy aircraft is about 150 knots or 280 km/h. The maximum speed to reject takeoff ($V_1$) depends on the plane, the load, the wind, and the condition of the runway. Let's assume 150 knots for the sake of a rough energy estimation.

The maximum energy that could be transferred to the brakes is more or less the kinetic energy of the plane at takeoff speed:
$$E_\rm{kinetic} = \frac{1}{2}mv^2 $$

The actual energy dissipation will be increased by

remaining power delivered by engines
tail wind
runway downward slope

and decreased by

airbrakes
reverse thrust
head wind
runway upward slope
drag
tire heat dissipation and tire wear

Neither A380 nor B777 have brakes in the nose gear. (Actually very few heavy aircraft have braked nose wheels. See: Are there any aircraft with a nose wheel braking system?)

Airbus A380

The maximum takeoff weight (MTOW) of the A380 is 575 t, and its main gear has 20 wheels. 16 main wheels have brakes and 4 main wheels do not. (See Why do some A380 main wheels have no brakes?)

$$E_\rm{TO,max} = 0.5\cdot 5.75\cdot 10^5\,\rm{kg}\cdot\left(\frac{280}{3.6}\frac{\rm{m}}{\rm{s}}\right)^2 = 1.7\,\rm{GJ}$$

The approximate maximum dissipated energy per wheel brake unit for an A380 after RTO is
$$E_{\rm{wheel}} = \frac{1}{16} E_\rm{TO,max} = 110\,\rm{MJ} $$

Boeing 777

The MTOW of the heaviest 777 is 352 t, and its main gear has 12 wheels.

$$E_\rm{TO,max} = 0.5\cdot 3.52\cdot 10^5\,\rm{kg}\cdot\left(\frac{280}{3.6}\frac{\rm{m}}{\rm{s}}\right)^2 = 1.1\,\rm{GJ}$$

The approximate maximum dissipated energy per wheel brake unit for a Boeing 777 after RTO is
$$E_{\rm{wheel}} = \frac{1}{12} E_\rm{TO,max} = 89\,\rm{MJ} $$

Active Cooling

Aircraft which are foreseen to take-off and land frequently may be equipped with electric brake cooling fans (BCF) which extract the interior hot air to the exterior. The BCF are used during ground time to shorten the turn-around time.

As an example, the main wheels of an A318 equipped with electric brake cooling fans:

Interestingly, there is a difference between steel and carbon brake disks. Steel disks wear out faster when hot, whereas carbon disks wear out faster when cold. Therefore it is preferable to reduce the cooling of carbon disk brakes to what is required for the following takeoff (see this answer).

Passive Cooling

Many (long range) aircraft have no active brake cooling. Passive cooling is caused by

airstream (induced by wind or aircraft motion),
convection,
thermal conduction,
thermal radiation.

Passive cooling of aircraft brakes follows Newton's law of cooling, which is - in terms of mathematics - an exponential decay (or exponential function with a negative exponent, if you prefer).

It may take many hours of passive cooling to reach the ambient temperature. Also see related question What is the temperature of the brakes after a typical landing?

The source of this graph does not indicate the unit of the x-axis, but minutes seem most plausible. The type of the aircraft under test is also unknown. The information is applicable to a range of Airbus aircraft equipped with carbon disk brakes, from A300 to A380.

External Cooling

External ventilation units exist and may be used whenever necessary. These can be electric, petrol powered,

or supplied by a remote compressor or extractor:


How can compartment bay loading informating be derived from the IATA load message (LDM)? In the IATA Airport Handling Manual procedures, messages are send to communicate with the transit station to describe the cargo load. The Load message LDM (AHM 583) is sent primarily to enable the transit station to know in advance the load which continues on the same aircraft.

  LDM ZZ999/13.ZZOEA.Y136.2/4
  -SHJ.15/22/3/1.T1500.3/1000.4/500.PAX/40.PAD/0
  -CMB.27/22/12/3.T3500.1/2800.5/700.PAX/61.PAD/0 SI

In here we got  hold id 3 total gross weight 1000kg,...
In our automated system, we need info in compartment bay level.

How can we get those information?

Any other message like Container / Pallet Distribution Message CPM (AHM 587)?
Or we have to manage manually (should distribute by load controller)

Paranee,
There is no such detail in the LDM, it is just a WEIGHT value. There maybe specifics for certain SL/DG (review AHM again for those) as some SL/DG are required to show location and some location and weight - explained in AHM.

BUT - LDM is just an overview, not very specific as it does not need to be. For a through flight A>B>C, where A is OFFLINE to your system, if you have received teletype LDM for processing and you are doing the sector B>C then any load B>C is just shown (know by the system) as TRA (transit) load - nothing more. No more detail.

However for unitized aircraft, the CPM complements the LDM to show the detail required by bay as opposed to HOLD and/or COMPARTMENT.


Why does CFR §91.215 part (b) list specific areas for transponder operations? Why does part (b) list individual sections where transponder operations are required when part (c) states that transponder operation is required in all controlled airspace? All sections listed in part (b) are part of controlled airspace anyhow? Similarly, the AIM says that transponder operation is required the moment the aircraft starts moving until the time it stops moving (a simplified interpretation).
Am I missing some subtleties?
Details:
CFR §91.215:
Part (b) contains sections that specify precisely where transponder operation is required. For example:

(1) All aircraft. In Class A, Class B, and Class C airspace areas;
(2) All aircraft. In all airspace within 30 nautical miles of an
airport listed in appendix D, section 1 of this part from the surface
upward to 10,000 feet MSL;
(4) All aircraft in all airspace above the ceiling and within the
lateral boundaries of a Class B or Class C airspace area designated
for an airport upward to 10,000 feet MSL; and
(5) (i) In all airspace of the 48 contiguous states and the District
of Columbia at and above 10,000 feet MSL, excluding the airspace at
and below 2,500 feet above the surface; and
(5) (ii) In the airspace from the surface to 10,000 feet MSL within a
10-nautical-mile radius of any airport listed in appendix D, section 2
of this part, excluding the airspace below 1,200 feet outside of the
lateral boundaries of the surface area of the airspace designated for
that airport.

Then part (c) says:

(c) Transponder-on operation. While in the airspace as specified in
paragraph (b) of this section or in all controlled airspace, each
person operating an aircraft equipped with an operable ATC transponder
maintained in accordance with §91.413 of this part shall operate the
transponder, including Mode C equipment if installed, and shall reply
on the appropriate code or as assigned by ATC, unless otherwise
directed by ATC when transmitting would jeopardize the safe execution
of air traffic control functions.

The AIM says:
AIM Section 1:

4−1−20. Transponder Operation a. General

Transponder and ADS-B operations on the ground. Civil and military aircraft should operate with the transponder in the altitude
reporting mode (consult the aircraft's flight manual to determine the
specific transponder position to enable altitude reporting) and ADS-B
Out transmissions enabled at all airports, any time the aircraft is
positioned on any portion of the airport movement area. This includes
all defined taxiways and runways.

Transponder and ADSB Operations While Airborne. Unless otherwise requested by ATC, aircraft equipped with an ATC transponder
maintained in accordance with 14 CFR Section 91.413 MUST operate with
this equipment on the appropriate Mode 3/A code, or other code as
assigned by ATC, and with altitude reporting enabled whenever in
controlled airspace.

I think what you're missing is that not all aircraft have transponders. The key words from 91.215(c) are (emphasis mine):

[...] each person operating an aircraft equipped with an operable ATC
transponder maintained [...]

To put it another way, (b) says "in order to fly in these areas you must have a transponder". Whereas (c) says "if you have a transponder, this is when it needs to be on".


Why is an elliptical wing planform so aerodynamically efficient in layman's terms? Below is part of an answer to the post 'For the elliptical wing, what is elliptical, and why is drag regularly distributed?':

  On the untwisted elliptical wing the local lift coefficient is constant over span, and changes in angle of attack over the linear range will change the lift coefficient equally everywhere. This, when combined with the elliptical chord distribution over span, means that the circulation distribution will stay elliptical over the linear angle of attack range. This is the special characteristic of an elliptical wing: While any wing can have an elliptical circulation distribution at one angle of attack (given the right twist distribution), the elliptical wing will keep that elliptical circulation distribution over the whole operating range.

My question is: how can the wing tips of an elliptical wing be considered to produce the same amount of lift as the root (see emphasis above)?

I believe that you misunderstood the answer that was posted.  The local lift coefficient is different from total lift.  In fact the question itself states the lift and drag decrease from root to tip.  If you include the previous two lines by Peter you will get a better context:

  It is both the planform and the circulation distribution. Note that circulation is not lift coefficient but bound vortex intensity. You can interpret it as local lift coefficient times local chord.

The amount of circulation created is related to the total lift.  See the Kutta-Joukowski theorem.  Peter says the circulation distribution is elliptical along the span (decreasing towards the tip) so the lift is not constant along the span of the wing.

A more Layman's way of understanding this: The lift decreases at the tip since the chord length decreases but the local lift coefficient remains the same.  Since the local lift coefficient is related to the local drag coefficient this also means that the local drag coefficient remains the same along the span.  But again because the chord length decreases along the span the total drag actually reduces at the tip of the wing.


How do airlines handle SIGMETS? In general, what is the action taken by airlines when presented with a SIGMET in the projected route. Will they go around it, cancel the flight prior to takeoff, or simply fly thought it anyway?

As an example, there is a large SIGMET over the Sierra Nevada mountains right now due to high winds causing wind shear and moderate to severe turbulence. Knowing that severe turbulence can be a serious issue, would airlines, in general, cancel the flight, go around the area or simply fly anyway?

WSUS06 KKCI 250040
WS6N
SFON WS 250040
SIGMET NOVEMBER 2 VALID UNTIL 250440
CA NV
FROM 80N FMG TO 30ESE OAL TO 60NE EHF TO 50ESE RBL TO 80N FMG
OCNL SEV TURB BTN FL280 AND FL410. DUE TO WNDSHR ASSOCD WITH JTST
AND MTN WV ACT. RPTD BY ACFT. REPLACES NOVEMBER 1. CONDS CONTG
BYD 0440Z.

Source: aviationweather.gov

Your options, as you pointed out, are either to climb over this area, To go around it, to go under it, or wait until the segment expires or is expected to subside.

Another option available would be taken by this information with PIREPS.  What are pilots reporting happened to them in this air space at this time?   The SIGMET noted that there was occasional severe turbulence expected in that area which is pretty vague.  If there are a very large number of PIREPS widespread throughout that block of airspace, it’s a good bet that it is very turbulent throughout and may not be a good idea to penetrate it.  If the PIREPS are few and don’t repeat much turbulence in that airspace, then it may be advisable to fly through.  Just keep the speed at that recommend by the manufacturer for penetrating turbulence and keep the fasten seat belt signs on.


What if all passengers move from one side to the other? Given the question What happens when all passengers jump at once?, I wonder what would happen if they all moved from side to side. If all the passengers moved from the front to the tail, or the other way around, there might be balance problems, but what if they moved from right to left (or vice versa)? I imagine the fuselage is not wide enough for this to seriously affect the aircraft's balance, but I would like confirmation for this assumption.

To have the greatest visible effect, the answer may focus on aircraft with relatively wide fuselages (for instance, A380, B747, B777). Maybe the effect is more visible for aircraft with smaller wingspans, thus, answers may also mention GA  aircraft with a large enough body-width-to-wingspan ratio (the opposite of a glider).

You can get a significant rolling tendency if you shifted cargo or pax all to one side, but not enough to affect controllability; it would just be annoying.  This would apply to most airplanes.

Transport airplanes will have a lateral Center of Gravity range that has to be respected, along with a maximum fuel imbalance limit, to ensure controllability in some critical case.   In the CRJs, which are quite narrow, if everybody piled into the seats in one side, you (or the autopilot) would definitely notice it and have to correct with aileron, although it would be no problem trimming it out.  A really large fuel imbalance would be a much bigger problem however and might use up quite a bit of the available roll authority, so there are fuel imbalance limits in addition to lateral CG limits.

FAR 25 requires that the roll trim system provide the ability to trim out the rolling moment from max lateral CG offset in the most critical case - on takeoff, one engine inoperative, climbing at V2 (engine failure safety speed), with maximum allowable fuel imbalance. On the CRJs this uses up only about a third of the airplane's total roll authority (the RJ's roll trim just offsets the neutral point of the control circuit).


Historical gap in high aspect ratio wing transport aircraft Reading about recent Boeing's high aspect ratio wing concepts for commercial aircraft, such as TTBW and SUGAR, I couldn't help but think of the Hurel-Dubois aircraft, where similar aerodynamic choices seem to have been made back in the 1950s.

Why has there been such a long gap in aircraft history, to see a rebirth of such a high aspect wing ratio transport/commercial aircraft family, since advanced materials to improve the concept were already available in the 1970s?

(TTBW)

(SUGAR)

(Hurel-Dubois 34)

(Hurel-Dubois 10)

High aspect wings provide the best efficiency, but the current airline business model needs more than just efficiency; it also needs to keep speeds up.

Modern airlines could save on fuel by flying slower, but they would lose some business to other forms of transport or airlines that did not slow down as much. As long as fuel prices remain under a certain limit, this trend will continue. In this answer, Peter Kämpf speculates that limit might be around 200USD per barrel (originally gallon, but likely a typo).


Why are downward pointing winglets more efficient? While most aircraft have upward-pointing winglets

Source

there are also some UAVs (I couldn't find any manned aircraft$^1$) with downward pointing winglets.

Source

I'm pretty sure that other considerations such as ground clearance, propeller/camera system protection and stability were the determining factors in the examples showed above.

However, according to a study (p.11) referenced in this question downward-pointing winglets are more efficient.

  This also means that winglets sticking up are not as efficient as
  folding them down.

I couldn't find the sources mentioned in the paper.

What makes downward pointing winglets more efficient? What are the efficiency-related differences between the two directions?

$^1$: No, neither the A-10's nor similar wingtips count.

For efficiency the orientation of winglets is not important. Best would be to stretch them out horizontally, but on a canard they do double duty as vertical tails.

Things look different when maneuvering is added: Now the downward-pointing winglet is superior especially if it carries a rudder. When roll is commanded by deflecting the ailerons, the lift change on the outer wing will carry over to the winglet. On upward-facing winglets this creates an opposite yawing moment while on downward-facing winglets this yawing moment supports the intended turning maneuver.

Also, they look cooler.


Who is India's equivalent of the FAA? I frequently fly within India as part of my work and every time I am sitting in an airliner preparing to take off, I observe a lot of differences in each crew handling the take off or the ground crew procedures.

I would like to understand if there is any board that certifies these crews and airlines for safety, like the FAA for the US, if these information are released to the public, like a certificates that are issued for public information.

This regulatory oversight is performed by the Civil Aviation Authority of a country. In India, this function is performed by the Directorate General of Civil Aviation (DGCA-India). Typically certification information is available to the public, but only high level information will be given.

Searching on the DGCA-India website I found this document that lays down the requirements on Cabin Crew Training.


Are fully electric helicopters suitable for military operations? I read this question about diesel-electric (DE) helicopters, which sparked the following question:

Are fully electric helicopters suitable for military operations?

They are more silent, and electric motors are lighter than combustion engines. Would the only drawback be battery weight?

Battery weight is a huge negative. Liquid hydrocarbon fuels have energy densities of about 45MJ/Kg, and the significant advantage that as you use them, their weight stops needing to be transported.

A lithium-air battery is theoretically capable of getting close to the energy density of hydrocarbon fuels, but the best that's been achieved so far in the lab is about 6MJ/Kg. The energy density of lithium-ion batteries, which are the best that's deployable at present. are more like 1MJ/kg, at the cell level, or rather worse at the pack level. If you want to drop used batteries, your operating costs go way up.

An electric helicopter could be built, but its flight duration would be very short. Just like quadcopter drones.


What's the inspection/repair procedure following damage from severe hail? Delta 1889 was forced to make an emergency landing last Friday (August 7th, 2015) after being battered by hail in a severe thunderstorm.

The picture in the news shows the two leading segments of the windshield have been ruined and will need to be replaced.  The nose cone of the jet has been caved in.  Zooming in suggests that the sheet metal ruptured where it made contact with whatever it behind it.  If that's the case I'm assuming it's too damaged to just have the dents pulled out and will also need to be replaced.

Beyond the obvious damage, what else will need to be looked at before the plane is able to resume normal operations?

They would have to work from the nose back to ensure there was no other damage but the first thing they would look at is the nose its self. As mentioned that cone is not metal as it houses the aircrafts weather radar behind it. Specifically a Honeywell unit like this one. By the looks of it the element was damaged and most likely needs replacing. From there you would come to the forward pressure bulkhead which, considering the damage would need to be closely inspected. Here is a pic of one from a Boeing for reference.

Degraded or improperly fixed bulkheads have lead to issues in the past. While this is happening they will also work on the windshield and check the struts around it for damage. They would also look over all forward facing surfaces, just a guess but they would check the wings leading edges for damage, engines, leading edges of the horizontal and vertical stabilizer as well as whole airframe for possible damage along its axis'. The question of will the plane ever fly again is more a question of cost than mechanical issues. For what its worth just about anything can be fixed, if and airline will fix it mainly depends on if its cheaper to fix or simply buy a new plane.


What does the callout "300... MINIMUMS" mean? MINIMUMS.... 400 APPROACHING MINIMUMS...   300 MINIMUMS.   Is this a reference to gravity? Needing more speed? Or the minimums you can see to the lights on your approach to land?

I looked this question up and someone said it had to do with being able to see the light on the runway when you are on your approach to land. But I have found that when you are in your minimums, 300 ft from ground, you need to increase your speed to avoid falling quickly or it results in a hard landing.

Do the minimums talk about gravity?

Your friend is right. The "minimums" call is done at the level over the ground at which you must have a visual reference to the runway environment in order to continue your approach. If you do not have a visual reference at minimums (due to bad weather), you have to perform a missed approach.


Why was the An-225 built when the VM-T Atlant already did the job? The Soviet Buran program decided to use a carrier aircraft to move their orbiter and Energia tanks similarly to the American Shuttle Carrier Aircraft. However, the Soviet Union built two types to do the job.

The famous An-225 project was started early, but they also decided to build a backup aircraft based on a Myasishchev 3M bomber. This aircraft, the VM-T Atlant, was finished much earlier. Since the An-225 wasn't ready yet the Atlant played delivery truck for the initial and only Buran launch.

Of course the An-225 is much more capable than the Atlant, but if the Atlant can do the job why go through the effort and expense of developing a second massive airplane?

Further reading on the VM-T Atlant.

As you can see in the second photo, the VM-T was unable to lift a fully-assembled Buran. The VM-T max payload is 50 tonnes, a Buran weighs on the order of 80 tonnes.

So for the VM-T flights they had to strip the Buran to get the weight down, including removing the tailplane.

The An-225 could lift a fully-assembled Buran, but was not ready in time, so they used the VM-T as an interim solution.


Is the FAA expected to issue more regulations soon on drone usage in rural areas? There are exponential increases in funding for small drone startups.  When is the next publication period for the FAA to issue regulations on use of small drones in suburban areas?

I'm not sure if this is really an aviation question because you're asking about how and when Federal agencies make regulations, and you might get a better answer to that on law.SE.
But having said that, agencies are required to publish their rulemaking plans twice a year. You can find them in the "unified agenda" for that agency. If you look at the Department of Transportation agenda there are currently six FAA rules that include "unmanned aircraft" in their title. Four are already final, the other two are:

Safe and Secure Operations of Small Unmanned Aircraft Systems
Prohibit or Restrict the Operation of an Unmanned Aircraft in Close Proximity to a Fixed Site Facility

I haven't read them and I have no idea about the timeline for them or if they include anything about rural operations specifically.


Do airlines weigh passengers and baggage before loading the aircraft? I'm aware of some aircraft that have systems to calculate weight and balance.  For those aircraft that don't have such systems, how does the pilot know they are within weight and balance limits?

While I'm not a pilot, I think it goes along these lines:

Airlines typically assume a value for passengers depending on gender and age. This distribution in the cabin will typically be quite random and a little variation does not do any damage.
Baggage however is weighed on the scales at check in. Each bag is
normally scanned as it is passed onto the plane, so that they know
where is bag is located. The values are then passed onto the pilots
who are able to work out that the numbers are ok. Sometimes there are preferences to load up bags in a certain way for fuel issues, so this is very important to make sure this is still resonable.

These values are then plugged into computers or worked out manually on a paper loadsheet to make sure they are good and within limits.

In fact the weight systems you are referring to are quite unusual I think, see this question.


What's the difference of Vs from Vs0 or Vs1? Vs: Stall speed or minimum steady flight speed for which the aircraft
  is still controllable

  Vs0: Stall speed or minimum flight speed in landing configuration.

  Vs1: Stall speed or minimum steady flight speed for which the aircraft
  is still controllable in a specific configuration]1

How is Vs different from Vso or Vs1? Is it safe to assume Vs is a generic term involving both Vso and Vs1?

Vs is the generic term.  However, since stall speed varies depending upon how the aircraft is configured (in particular the flaps), we break that down into Vs0 for landing config and Vs1 for cruise config.  In theory, we should list the stall speed for every possible configuration, but it's generally sufficient to list just those two because all others should be somewhere in between.


What is the definition of "occupant" in 14 CFR 91.307? Does a solo pilot performing aerobatics constitute an "occupant" for the purposes of requiring a parachute per 91.307(c)?

If you're solo you don't need a parachute (emphasis mine):

  Unless each occupant of the aircraft is wearing an approved parachute,
  no pilot of a civil aircraft carrying any person (other than a
  crewmember) may execute any intentional maneuver that exceeds [...]

Incidentally, 91.307 says nothing about aerobatics; that's in 91.303.

And this question is closely related.


What is the exact purpose of the string attached between front fuselage & the tail section of the transport aircraft's? ]2 228]3]3

Usually I got to notice a string attached between front fuselage to rear tail section of the transport aircraft's, what exactly might be the purpose or function of it? But comparatively, I don't find to see on commercial aircraft like Boeing 747, 737, A380 etc. why is that so!

That is an end-fed long wire antenna for HF radio use.


How would modern jet fighters engage and defeat prop driven fighters? How would modern jet fighters engage and defeat prop driven fighters?  Assuming all things being equal (avionics, weapons, etc), if the two aircraft were co-altitude in a level merge, what tactics would the jet use to quickly overwhelm his adversary?

Merge

Assuming neither aircraft tried for a head-on guns snapshot, the goal of the jet against the prop will be to go out of plane with the prop post merge and deny the prop a quick guns solution.  By far the easiest way for the jet to go out of plane is to extend and then take the fight vertically.  This means that the jet is in full AB coming into the merge and well above cornering speed, while the prop is coming into the merge at its best corning speed hoping to get a quick snapshot.  As the aircraft approach both pilots tighten down and pass as close as possible to prevent either aircraft from taking angles right after the merge (ie, so that neither aircraft has a turning advantage immediately post merge).

Post Merge

As the aircraft make their first pass, the prop (knowing full well the jet will take the fight vertically) begins a max performance turn hoping to quickly take angles and give itself a quick snapshot against the jet as the jet climbs.  However, the jet, knowing the prop is looking for a radius fight, extends the merge horizontally, at Mach 1+ and then begins a supersonic climb upwards.  Due to the lower thrust to weight ratio of the prop, most of the props potential energy comes in the form of its altitude; however, the jet has liquid potential energy in the form of fuel, and many can accelerate in the vertical, this gives the jet a decided advantage against the prop.  Because the prop cannot climb with the jet, and the jet is now outside of its guns range, the prop must remain at altitude and wait for the jet to attack.

Out of Plane

The jet, moving vertically, has now successfully moved out of plane with the prop rendering the turning radius of the prop moot.  An unchallenged out of plane maneuver is certain victory for the jet.  The jet can now cut the turning circle of the defender from above.  The best hope for the prop is to either pull hard into the jet trying to force an overshoot (and hope that the jet isn't already anticipating this and drawing a wall of lead between this anticipated spot and his current location) or, to wait until the last minute and pull into the vertical with the jet (causing a vertical merge) and hope for a head-on snapshot.  Either way, the jet can quickly disengage vertically again, causing the prop to bleed precious energy with these high G maneuvers, and then reengage when he has the advantage again.  Each time the jet disengages, the prop is left scrambling to regain its depleted energy, and the jet is maneuvering to prevent the prop from ever being able to fully recover.  This means that as the prop dives to gain speed, the jet dives after it, forcing another high G pull from the prop for another overshoot, or, if the prop tries to extend horizontally, the jet attacks again, forcing the prop to use more energy.

Conclusion

The jet will either force a mistake out of the prop and kill it, or the prop will eventually run out of altitude and airspeed and either auger into the ground, or be killed when he doesn't have the energy to force the overshoot, or climb vertically again.  This, of course, ignores things like thrust vectoring, and the flight computers, in aircraft like the super hornet, which give certain Gen 4/5 aircraft supermaneuverability--meaning, post merge, most Gen 4/5 aircraft could just out rate the prop and the fight would likely be over in seconds.


Is "wingman" strictly a military term? Does it have to be a potential combat situation for a pilot flying on another's wing to be called a wingman. If two aircraft are being flown in formation to a destination simply for the purpose of transportation, would the term wingman be used?  Is wingman used in civilian aviation?

While the combat military role of a wingman is established, the term is entirely appropriate and is used for non-combat formation flying as well.  And unless there is a better term, it would be logical to extend the use to civilian formations also.


Can a PP pilot fly large planes? Assuming I'm rich, take a PP course and buy a Boeing 737 or A320. Could I fly these planes for non-commercial purposes?

In the US, yes. There are no restrictions from the FAA on the size of aircraft you fly with a private pilot certificate. If the aircraft requires a type rating, you would have to get that added to your certificate along with the category and class. The insurance carrier covering that aircraft would probably have much more stringent requires over and above the FAA requirements.
John Travolta has/had a Boeing 707 (similar to a B737) that he flies out of his private home/airport.

§61.31 Type rating requirements, additional training, and authorization requirements.
(a) Type ratings required. A person who acts as a pilot in command of any of the following aircraft must hold a type rating for that aircraft:
(1) Large aircraft (except lighter-than-air).
(2) Turbojet-powered airplanes.
(3) Other aircraft specified by the Administrator through aircraft type certificate procedures.
(b) Authorization in lieu of a type rating. A person may be authorized to operate without a type rating for up to 60 days an aircraft requiring a type rating, provided—
(1) The Administrator has authorized the flight or series of flights;
(2) The Administrator has determined that an equivalent level of safety can be achieved through the operating limitations on the authorization;
(3) The person shows that compliance with paragraph (a) of this section is impracticable for the flight or series of flights; and
(4) The flight—
(i) Involves only a ferry flight, training flight, test flight, or practical test for a pilot certificate or rating;
(ii) Is within the United States;
(iii) Does not involve operations for compensation or hire unless the compensation or hire involves payment for the use of the aircraft for training or taking a practical test; and
(iv) Involves only the carriage of flight crewmembers considered essential for the flight.
(5) If the flight or series of flights cannot be accomplished within the time limit of the authorization, the Administrator may authorize an additional period of up to 60 days to accomplish the flight or series of flights.
(c) Aircraft category, class, and type ratings: Limitations on the carriage of persons, or operating for compensation or hire. Unless a person holds a category, class, and type rating (if a class and type rating is required) that applies to the aircraft, that person may not act as pilot in command of an aircraft that is carrying another person, or is operated for compensation or hire. That person also may not act as pilot in command of that aircraft for compensation or hire.
(d) Aircraft category, class, and type ratings: Limitations on operating an aircraft as the pilot in command. To serve as the pilot in command of an aircraft, a person must—
(1) Hold the appropriate category, class, and type rating (if a class or type rating is required) for the aircraft to be flown; or
(2) Have received training required by this part that is appropriate to the pilot certification level, aircraft category, class, and type rating (if a class or type rating is required) for the aircraft to be flown, and have received an endorsement for solo flight in that aircraft from an authorized instructor.


Who determines the fuel load? In the commercial side, who determines the fuel load required for any given flight?

The PIC/Captain? Company/Airline? FBO/Airport?

Disclaimer: this answer applies to airlines (operating under 14 CFR 121) but does not encompass all of commercial aviation.

The dispatcher that is working your flight plans the routing and determines the minimum fuel required from takeoff to destination to furthest alternate with additional fuel as required by regulation you operate under.  On top of this, contingency fuel is added which can account for enroute diversions, cruising at a different altitude, un-forecast winds, holding, etc.  The total of this fuel is the "release fuel" and you cannot takeoff below this number.  On top of this, extra fuel will be added for taxi time.

Ultimately, it is the captain's responsibility to decide how much fuel is needed.  For slight increases, airline policy may allow captain's discretion to add fuel.  For larger increases in the fuel order you generally need to call the dispatcher and amend the release -- after convincing the dispatcher you need the fuel.  If you decide you need less fuel (e.g. less contingency fuel) you always need to amend the release so you can legally take off.


Is it best to use a thick airfoil or an undercambered airfoil for slow speed flight? The more the thickness,the more the frontal resistance,hence the more the drag a thick airfoil will produce.
Under cambered can help increase lift without increasing the airfoil thickness , therefore not creating as much increase in resistance or drag . ..which is more plausible for a slow ultralight,a thick airfoil or an under cambered airfoil?

Source: https://www.flitetest.com/articles/beginner-series-basic-aerodynamics

First of all, the thickness-related drag increase is small, especially for airfoils below 15% of thickness. Thickness by itself mainly determines structural efficiency and wing volume and is chosen on those merits. A very common choice for GA planes is 15% - 16% at the wing root tapered to 10% - 12% at the wing tip.

Next, much depends on the wing's bracing. A pure cantilever wing will be heavy but produce very little drag, so it is the obvious choice for faster aircraft; however, bracing the wing will lower wing mass and, therefore, induced drag. For slow airplanes, bracing the wing helps to reduce drag at low speed. But how much bracing is the best?

Clearly, early designs used too thin airfoils and went overboard with the bracing. Look at the picture of a replica of the Etrich Taube, a very popular plane of the pre-WW I period.

Etrich Taube in flight. Note the truss below the wing and the many wires keeping it in shape (picture source).

Next, many low speed aircraft used two braces, one forward and one aft, and an airfoil of between 12% and 15% because this helps them to get most lift from a given area. Note that all use high-lift devices: Slats and slotted flaps are a must:

Westland Lysander (top, source) and Fieserer 156 "Storch" (bottom, source). Note the very similar wing bracing and flat-bottom airfoil.

Multi-element airfoils are complex, so maybe it will be best to look at gliders and motorgliders for inspiration - or even human-powered aircraft. Also, the Reynolds number, which is determined by the size and speed of the aircraft, needs to be considered. As a very rough rule of thumb: If you only want to fly slowly and operate at a Reynolds number below 1 million, use a highly-cambered airfoil like the Daedalus sequence (DAE11 at the root, DAE21 mid-span and DAE31 at the tip). For more flexibility and Reynolds numbers above 1 million consider a camber flap and a glider-type airfoil.


How did the US get the necessary knowledge to maintain their MiGs? I read a book entitled America's Secret MiG Squadron by Gaillard Peck some time ago. Just occurred to me though, how exactly did the US maintain these birds? Did we write any tech data? Did we acquire and translate it from elsewhere?

Its a combination of those. US did have manuals for quite a few of the Migs- Cold war alliances were shifting too frequently to prevent any leak of military technology. As warisboring.com notes:

Because Baghdad re-established its cooperation with London and the United States in late 1963, U.S. intelligence services not only received the opportunity to test-fly MiGs in Iraq, but also received all the related technical and training documentation.

The title page of the English translation of the tactical manual for MiG-21F-13 and MiG-21PF, as prepared by the USAF’s Foreign Technology Division. Notable is the date of issue — Nov. 5, 1965 — meaning that the original document must have been obtained much earlier. Tom Cooper Collection photo; Image from warisboring.com
As the Mig program was established in late 70's US would have had the required documentation for quite a few of the aircraft before that. The rest were done during the project using inputs from US intelligence and pilots themselves writing the flight manuals.
The Soviets sold their aircraft to many countries, the manuals for which could've been obtained from any of them. Also, there are multiple instances of pilot defection with manuals, which provided most of the required technical data for flying, though maintenance would have been difficult. As airforcemag notes:

This led to the second maintenance problem—the lack of instruction manuals  and  tech  data.  US  intelligence supplied  some  of  the  information they  needed  but  not  nearly  enough ...
Parts  were  their  third,  and  maybe biggest, problem. “For things like hydraulic pumps, we would use American components that looked about right,” said Stringer. “But it was only about five to 10 percent replacement. Most of the time we tried to recondition.”


What is the minimum number of people required to manually pushback a 747? Similar to :
Is there a minimum number of people needed for an aircraft pushback?

After watching this video I wonder what would be the number of people required to manually push back a 747.

I know small aircraft is usually pushback by the pilot and if possible a wing walker. Large jet at large airport has a few people involved in the process. But manual pushback a large jet is a special event where you need lots of people. How many do you need?

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.


Is night VMC still VMC if the underlying terrain is completely unlighted? The whole point of visual meteorological conditions (VMC) is that there is sufficient visibility for a pilot to be able to safely fly by visual reference alone, without reference to instruments.  This, by necessity, requires a visibility of at least one to several miles, plus staying a good distance away from any clouds (the exact visibility and cloud-clearance limits depend on the jurisdiction, but all have at least some minimum requirements for these factors); so far, so good.

In many countries, however (including a lot of the big ones, such as the US, Canada, the UK, Australia, France, Germany, and New Zealand), VMC is still VMC even at night, and night VFR flight is perfectly legal (albeit with somewhat greater restrictions on who can fly VFR at night and the qualifications necessary thereto) if the visibility and cloud-clearance requirements are satisfied.1

The underlying assumption is presumably that pilots will still be able to avoid flying into the ground (in either controlled or uncontrolled manner), or each other, by reference to ground lighting and each others' anticollision lights, but this line of reasoning breaks down if you fly over unlighted terrain (of which the countries permitting night VFR flight have quite a lot), especially if it's a moonless night.  If it's well and truly nighttime, the moon is either a thin crescent or completely absent from the sky, and the terrain is devoid (or nearly so) of light sources, the ground will be almost completely invisible, with the only hint of its presence being its occlusion of the background stars, and it is difficult to imagine how one would be able to maintain terrain clearance (especially if one's aircraft lacks a radar altimeter).  Even worse would be if the stars (and moon, if present) were obscured (by, for instance, high clouds, or smoke from forest fires), in which case one would have no external visual reference at all;2 a non-instrument-rated pilot would find it essentially impossible to maintain control of the aircraft in these circumstances, just as if they were trapped inside a cloudbank during a daytime flight, and even a pilot who is proficient in instrument flight would have difficulty maintaining terrain clearance, especially in mountainous areas (which, inconveniently for our pilot, tend not to be densely populated, and, thus, are rather more likely to be unlighted than flatter terrain).

To eliminate this problem, does the definition of night VMC (in the US or any other jurisdiction) require that the terrain in the area be lighted sufficiently for it to be visible?

1: In many other countries, VFR flight is not permitted at night, and the issue therefore does not arise.

2: Unless you're low enough for your aircraft's lights to illuminate the ground, in which case you're already way in deep shit anyways.

The short answer is no, the definition of night VMC does not specifically require any defined degree of ground illumination to be present.  (at least in the US)

You raise some excellent concerns in your question, demonstrating a solid understanding of the principles of Operational Risk Management:  Identify the hazards, assess the risk, make decisions, implement controls, and monitor.

Following these steps prior to, and during night flight is crucial to safety for the reasons you describe.  As long as visibility is relatively clear and there is enough ground lighting to form a discernable horizon, flying on even the darkest nights can be done safely, and can actually be fun.  It is easier to pick out other aircraft visually, and roads and cities really highlight themselves.  In areas where illumination is sparse, situational awareness of your position and the highest terrain in your sector is crucial.

It is rare for anybody to truly need to fly VFR at night, so if weather, visibility, ground lighting, or any other conditions are concerning to you, either don’t fly, or file IFR if you are so rated.