Flight physics for a roll I am working on a pet project to write a game with flight physics. It will not be a simulator but instead much simpler.

What I have done so far

I have created winged components that generate lift and drag using the basic formulas I found online. I apologize if some of the debug info is not standard terminology.

The green arrows in the image show the force and magnitude begin applied. The yellow lines are the relative airflow.

What I cannot get working and understand

At first all the components used the same forward speed calculated by looking at the CG. Just an easy way to see what speed the plane was moving. The plane flew straight when "thrown" level and if will self correct if thrown with a slight roll angle.

The problem starts when each component starts calculating its individual forward speed. Even with dihedral applied to wings the plane will start rolling to the left more and more.

You can see that the left wing has a slightly higher AOA as the result of the dihedral. BUT it has a lower velocity than the right wing because the plane is yawing (I think). This lower velocity causes the right wing to produce more lift and the plane rolls more to the left. The more it rolls left the more the right wing speeds up causing it to produce even more lift.

I have tired to increase the rudder, but that didnt help at all. Removing the rudder causes the plane to over correct, and then to roll to the left too.

Can any body explain what is suppose to happen when a plane rolls.
From what I see the plane rolls left, it pitches slightly down. The right wing "swings" forward faster than the left causing more lift.....

Typical airplane is not stable in roll. The outside wing flies a bit faster, which does indeed make it produce a bit more lift and that in turn will make it bank into the turn, tightening it and if left uncorrected, ending in a spiral dive.

In a coordinated turn, an aircraft even can't be made stable in roll. There is no way to create a restoring force without involving side-slip.
The only thing that can be provides is the yaw-roll coupling where a slip produced a rolling moment into the slipping turn. This rolling moment is affected by dihedral and sweep.

Fortunately as the turn tightens, if the rudder is held fixed, some slip does develop that can provide the restoring force reducing the bank. However, it causes another dynamic mode, the Dutch roll.

As the bank increases, the tendency changes from Dutch roll to spiral mode. If you wanted to avoid the spiral mode, the Dutch roll would be very strong, so practical aircraft are designed with moderate yaw-roll coupling and do require a bit of opposite aileron in turns.


Why do we use composite aluminium or titanium stacks in airplanes? Why do we use composite aluminium or titanium stacks in airplanes? What are their machining conditions?

I've boldfaced the parts of this abstract that answer the question.

  Abstract: Ever since the advent of fiber reinforced polymer materials in the field of Aerospace, Metal-FRP stacks started to gain importance due to their superior fatigue performance, phenomenal low weight and good specific strength. However the machining, specially drilling these multi stack materials has always proved to be a challenge ... The very properties that make the FRP composite superior make it a challenge for machining. The mechanism of machining viewed here is more or less fracturing and breakage of the fibers present in the system. This breakage of fiber also induces fractures in the tool resulting in accelerated tool wear. These characteristics render the process unreliable. Also the temperature during the machining of composites is higher than while machining a metal due to the lower thermal conductive properties of the composite. When two such extremely different elements are brought together in the form of a FRP-Metal stack, various challenges are faced to achieve required hole size, quality, tool life, ...

-- Peter Mueller-Hummel, Prithvi Sripathy, and Abdelatif Atarsia, "Fail Safe Drilling of CFRP/Titanium and /Aluminium Stack with H8 Quality for Aerospace Applications," SAE International, 2013.

Cutting speed, cut depth, and feed rate depend strongly on the particular stack's composition: which metals, which composites (carbon, aramid, fiberglass), their ratio, each layer's thickness.

Metal/composite stacks are used all over an airframe.  The 2011 article "A review: Fibre metal laminates, background, bonding types and applied test methods" by Sinmazçelik et al calls them FML's, fiber metal laminates, and figure 3 from there shows where they're found on the Airbus A380:


How does a turbofan with afterburner continue to function in extreme humidity and rain? From what I understand, the fan(s) collect(s) and compress(es) air into the compression chambers, where fuel is added to the air & combusted to create an even bigger pressure/thrust, right before the fuel-air mix hits the final chamber where even more fuel can be added & combusted (if you go +afterburner).

My question is this: If it's very wet out, and the engine is sucking up multiple gallons of water per second, then exactly how is combustion achieved with all that water contaminating the air?

The air is compressed in the compressor section of the engine and heats up. Hot air is able to hold disproportionally more water in gaseous form than cold air, so all that water will vaporize and enter the combustion process together with the air. Since it is already vaporized, it will not absorb that evaporation enthalpy again that makes water such a good extinguishing agent. On the other hand, since the evaporation enthalpy was sucked from the air in the compression process, the air will be cooler when it enters the combustion chamber, so more fuel can be burnt (up to the stoichiometric ratio of course) and power can be increased.

This trick was used on high performance piston engines and early jets. The Boeing 727 would inject water into the compressor on purpose on hot and high take-offs to increase engine thrust.

If the amount of water entering the engine overwhelms the absorbing capacity of the hot air, the engine runs the risk of flaming out. Regular precipitation does not pose this threat, however.


Why do chunks of aircraft debris float? In reading about various theories of what happened to flight MH370, there's a lot of discussion about it possibly crashing into the ocean, breaking up, and pieces of the aircraft floating hundreds of miles away.

Is it generally expected that large pieces of an aircraft will float fairly well? E.g. in the linked article, there's a picture of 4 guys carrying what looks like a big chunk of wing. How did that float?

My assumption would have been that that chunk was hollow aluminum fuselage, maybe with some electronics and hydraulics inside, and maybe a portion of a gas tank. I don't get how it would float unless it got lucky and a subsection of gas tank that was empty and did not get pierced during the breakup landed with its inlet/outlet pointing up.

Thanks.

Lighter materials such as plastic will naturally float.

Composites can have large sections of honeycomb core with trapped air. Even if these parts are broken, the honeycomb is sealed against both sides of the panel, still trapping air.

Large sections, whether made from composite or metal, will generally be hollow to save weight, and sealed to prevent collecting moisture which could cause corrosion. There may be small drain holes, but they wouldn't be enough to cause significant leaks.

Fuel tanks are sealed but they are also fairly large and contain baffles to allow fuel to flow within the tank. As you would guess, a catastrophic crash would be unlikely to leave a significant portion that doesn't contain holes.

The parts found suspected to be from MH370 all have these qualities.


What are the criteria for "variable" in METAR reports? Regarding variable wind direction in METAR reports, what are the criteria for VARIABLE when the authority uses "VRB"?

An Advisory Circular mentions the authority uses "V" when the wind direction varies by 60 degrees. But how about "VRB"?

There are two official sources to take into account:

ICAO Annex 3 to the Chicago Convention is the reference for meteorological information. Annex 3 applies to all ICAO members (countries), unless stated otherwise.
Members departing from ICAO recommendations state differences in their country AIP, section GEN 1.7.

ICAO Annex 3

§ 4.1.5.2:

  1) when the total variation is 60° or more and less than 180° and the
  wind speed is 6 km/h (3 kt) or more, such directional variations shall
  be reported as the two extreme directions between which the surface
  wind has varied

  2) when the total variation is 60° or more and less than 180°
  and the wind speed is less than 6 km/h (3 kt), the wind direction
  shall be reported as variable with no mean wind direction; or

  3) when the total variation is 180° or more, the wind direction shall be
  reported as variable with no mean wind direction"

So for ICAO there are three cases:

The wind is significant (more than 6 km/h) and there is a predominant direction (varying by less than 60°), possibly with some gusts: the three data are reported in the form 31015G27KT.
There is a significant wind (more than 6 km/h) but the direction varies a lot (between 60° and 180°): Mean direction, speed and gust are reported in the same form, and direction range is reported using V, e.g. 31015G27KT 280V350.
There is no clear wind direction, either because the speed is low (less than 6 km/h) or the direction varies by more than 180°: No direction is reported, only a speed with the indication VRB is used, e.g. VRB02KT.

Country AIP

US AIP:

  The wind direction may be considered variable if, during the 2-min
  evaluation period, the wind speed is 6 KT or less. Also, the wind
  direction shall be considered variable if, during the 2-min evaluation
  period, it varies by 60 deg or more when the wind speed is greater
  than 6 KT.

  Practices define wind gusts as rapid fluctuations in wind
  speed with a variation of 10 knots or more between peaks and lulls.
  Wind speed data for the most recent 10 minutes is examined and a gust,
  the maximum instantaneous wind speed during that 10-minute period, is
  reported if the definition above is met during that period.

ATC instructions given in PANS ATM Doc 4444, § 12.3.1.7a are also refined:

  In the U.S., the criterion for a variable wind is: wind speed greater
  than 6 kt and direction varies by 60 degrees or more. If the wind is >1
  kt but <6 kt, the wind direction may be replaced by ”VRB” followed by
  the speed or reported as observed. “VRB” would be spoken as “wind
  variable at .”

In the US, VRB indication is slightly different than in ICAO recommendations: VRB can be used regardless of the direction variation, when the wind is less than 6 kt (not 6 km/h) or if the variation is more than 60°. This covers the last two cases of ICAO.

METAR panel at Weeze tower (EDLV). source: Airplane Pictures, photo by Zonan Adolfse


Why can't sonic booms be heard at air shows? At air shows with fighter jets I would expect there would be a demonstration of supersonic flight. But in this flight of a Eurofighter Typhoon, no sonic boom was heard.

What is the reason?

Is it that there is no supersonic flight involved due to loudness or needing a bigger distance to accelerate?

Or is the sonic boom inaudible for a reason related to the short time delay of the sound between the noise source and the microphone, or some other physical reason?

Just for a bit of flavour, I recall an article from Air Progress from the late 70s about Darryl Greenamyer setting the low altitude absolute speed record, in his "homebuilt" F-104, of Mach 1.3 (mentioned in this article) in 1977.

For the run he had to cross very low over timing trigger devices at the start and end of the speed course at the dry lake bed at Edwards, which were set up with cars parked beside them.

I remember the description of the event by the writer who witnessed it from somewhere along the middle of the course, a safe distance away with other observers.  The F-104 passed over the car at the 1st speed trap at 60 ft AGL and passed the writer in absolute silence, and it wasn't until a second or so had passed that a sound like a dynamite explosion a couple hundred feet away went off.  All the glass of the cars at the speed traps blew out and their trunks popped open.  The writer was warned in no uncertain terms that if he didn't protect his ears he'd get hearing damage, and not to be fooled by the initially silent passage of the jet itself into taking his fingers out of his ears.

Imagine that happening at an airshow.


How do viscous drag and form drag individually change as a function of angle of attack? Typically, when dealing with airfoils, the drag coefficient $C_d$ is given as a function of angle of attack. If we limit the discussion to 2D subsonic incompressible flows, then the drag is the sum of the viscous drag and the form drag (pressure drag), equivalently:
$$C_d = C_{d,\text{visc}} + C_{d_,\text{form}}$$
Where: $C_{d,\text{visc}}$ is the viscous drag coefficient, and $C_{d_,\text{form}}$ is the form drag coefficient.
I've never seen, these coefficient plotted as function of angle of attack individually. That is, $C_{d,\text{visc}}=f(\alpha)$, or $C_{d_,\text{form}} = f(\alpha)$.
The reason I want to see them plotted individually, is to emphasize the contribution of each type of drag (qualitatively, I know that for angles of attack below stall, the viscous drag is higher than form drag, but for angles beyond the stall, (boundary layer separation), the form drag dominates).
Are there any graphs showing these coefficients individually, say for NACA airfoils?

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


What do solo pilots do between reporting points on longer flights? On some IFR flights, it can be a long time between waypoints. Obviously you must continue monitoring ATC for instructions, but during the rest of the "idle" time, what tasks do pilots have that keep them occupied?

I'm specifically interested in what solo pilots do.

The short answer is that you keep checking everything in the aircraft is doing what it should. For light piston GA operations, one common acronym for en route checks is FREDA. Here are some things that could be included (pilots often use their own checklists for things like this):

Fuel. How much have I burned? Is my navigation log up to date? Have I burned the amount I expected? How much longer can I fly for before I have to land? Which airports are within my current range ring? Is it time to switch tanks? Is the aircraft still within weight and balance limits? Is the airport where I planned to refuel still the right place to go?
Radios. Do I have all my radios set to correct and useful frequencies? How am I going to identify my next waypoint? Do I need to tune and identify a new VOR? Have things been suspiciously silent for a while? Should I file a PIREP? Do I need to tell ATC I need a deviation for weather? What's the latest weather information from ADS-B or another source? Can I guess which frequency ATC is going to hand me off to next? Did ATC ask me to report at a certain time or place?
Engine. Are all temperatures, pressures, gauges etc. showing the values I expect? Have I leaned the mixture properly? Are the exhaust gas temperatures correct? Is manifold pressure correct for this altitude? Has anything changed unexpectedly since the last time I checked them? If the engine dies right now, where am I going to land?
DI to compass. Reset the directional indicator to match the wet compass, to avoid gyroscopic precession errors.
Altitude. Is this altitude correct for my current heading? Is this the altitude I was assigned? If I lose comms now, what altitude should I fly at? Do I know what terrain is below me? What's ADS-B showing me right now? Any potential traffic conflicts? If I encounter icing here, will I descend, climb, or turn around? Is the autopilot correctly configured? Have I entered the current altimeter setting in all the instruments?

After you've worked through all that, it's usually time to go back to the beginning and start again :-)

Of course, there are plenty of other things that pilots are likely to be doing, like having drinks or snacks, taking pictures, admiring the view, listening to music, trying to find their spare headset batteries at the bottom of their flight bag, and so on.

But an IFR flight - or any flight - is never just sitting back between waypoints and waiting for ATC to call. The point of the constant checks is to detect any problems as soon as possible. For example, if you notice the oil pressure dropping gradually, you can take action while you still have engine power; if the first you know about it is that the engine suddenly stops then you have a big problem. Not only have you lost engine power, you're also not mentally 'primed' to deal with the situation and that could turn a tricky situation into a dangerous one.


Why separate autopilot controls for course and heading? Is there an explanation better yet equally pithy than the beneath, in fewer than 50 words?

Course is the direction in which the aircraft is flying over the ground. Heading is the direction in which the aircraft is pointing.

This quote motivated me to question the quote beneath:

[2.] See it like this... When Tomtom directs you from Amsterdam to Barcelona via Paris, Barcelona is your final 'course', but for now... you're 'heading' towards Paris... (taking in mind that you just left from Amsterdam...)
[3.] Other example: If you're doing an approach for landing at, let's say, LEBB (Bilbao) Airport on RWY 30, your Course is 300 but you can have various 'headings' TOWARDS your final course, Course 300 for RWY 30.

Why would heading and course need be controlled separately? If I'm flying to Paris first, then wouldn't I just input the heading to fly to Paris? Only after reaching Paris would I change the heading for Barcelona. Isn't 'course' redundant?

In the 'other example' above, isn't 'heading' redundant? Wouldn't I just input the course for Rwy 30 which is by definition 300?

Does anything above explain this picture, where the crosswind requires the plane to angle its nose to land?

First, I'll try for the 50 words or less: Course is the line across the ground that you want to go. Heading is where you have to point the aircraft to fly that line.

That's less than 50 words, but I'm not sure it's any better.

Let's look at the obvious first. Let's say, over a short distance, you want to fly a course of 270 degrees true. If you fly the airplane on a heading of 270 degrees, you will fly that course ONLY if there is no wind, which for all practical purposes is never the case. If there was a wind from the north, you would have to maintain a heading greater than 270 degrees to make good a course of 270 degrees.

Actually, you can never say that the course between point A and point B is a single value in degrees unless those two points are very close together. If you draw a line between point A and point B and those two points are not close together, and then measure the course leaving point A (the angle between north and the line as it leaves point A) you will find that it is different from the course as you arrive at point B.

You can, however, tell the autopilot to fly a direct course from point A to point B and it will do it, changing the heading as necessary to account for the wind and fly that course.

So, why does an autopilot need to have a "course" function and a "heading" function. In my experience, the greatest single use of the heading function is when a controller is vectoring you and tells you to fly heading so and so. The second is when a reroute from your existing course is necessary, and you use the heading function to keep the airplane going straight ahead for a bit while you redo the revised course setting you want to use.

If you forget to again use the course function after putting in the revised course, the airplane will continue on the heading it was on while you were updating the course, and you will shortly be off course. That mistake has been responsible for aircraft being hundreds of miles off course.

During the first Gulf War, I heard a Canadian controller inform a USAF aircraft that they were over 300 miles off course when Canadian radar picked them up prior to landfall coming in from Europe.

A captain at the first 747 carrier I flew for got over 50 miles off course and was demoted to First Officer. He had forgotten to switch from the heading function to the course function.

Finally, as an added problem, if you choose to define your course in degrees magnetic, you must also account for the change in magnetic variation as you proceed along that course.

Insofar as item 4 is concerned, you (or the autopilot) is going to change heading as necessary to keep the airplane proceeding along the course as defined by the runway centerline. There's a bit of confusion of terms here in that runway directions are typically referred to as the runway heading rather than the runway course.


IFR requirement for altimeter question (i.e. +/- 75 feet) What if the ATIS/AWOS/ASOS results in a very low or very high altimeter setting (i.e. barometric pressure)? Surely this setting will result in an altimeter setting way outside the envelope of the +/- 75 feet related to field elevation? Since each inch of Hg results in 1,000' change...what am I missing w.r.t. the altimeter check?

Barometric pressure isn't a constant. Just because you're at sea level, doesn't mean the air pressure is going to be exactly 29.9212 inHg. That's just the average sea-level pressure. So, for instance, if the sea level pressure is currently 30.9 inHg, then all altimeters in the region are going to read 1000 feet below the actual altitude of the airplane.
Those fluctuations are the point of the altimeter corrections provided by AWOS/ASOS/ATIS. By entering the actual sea-level atmospheric pressure into the altimeter, you can correct for those fluctuations and get a more accurate reading of your current altitude.


How could a 45 years old DC10 be still in service with one of the largest cargo airline? It is amazing to see this 45-year-old DC10 freighter still operating for FedEx regularly:

I know the lifespan of an aircraft is not rated by ages but flight cycles, but an actively used DC10 over 45 years must have exceeded the designed flight cycle right?  However, I regularly come across 30+ or even 40+ years old aircrafts on FR24 that are still in service, mostly freighter though. Wouldn't they raise any safety concerns? Besides, how could airlines operate them efficiently?

The DC-10’s have all been converted from DC-10’s to MD-10’s. The last conversion was in 2007, I believe. The entire aircraft wiring was replaced, the avionics package converted to glass cockpit and other structural work was also performed. As a result, the airframe was “zero houred” upon completion of the conversion.

Although they’re getting older, they’re still warhorses and their reliability is still good.

Also, cargo operators don’t put nearly as many cycles on their aircraft as passenger carriers. As a result, there is a lot less wear and tear on the aircraft.


Which airplane is this lego model? I'm wondering about the type of jet in this lego kit:
https://shop.lego.com/en-US/Airport-Air-Show-60103

One of the jets appears to be an F-18 (the one with twin tails, of course) but I can't place the other one. It looks vaguely like a Eurofighter, except this model only has a single engine.
I realize that these are stylized models, but I was hoping someone could at least identify what they are "based" on.
Thanks!

To be perfectly honest, LEGO does have a habit of mashing similar airplane designs into their own models. The twin-tail airplane has most of the features of the F/A-18 with its trapezoidal wings and slanted, trapezoidal vertical stabilisers. The F-14's contribution to that design is mainly in the engine intakes.

The single-tail airplane has most of its design from the Saab JAS 39 Gripen but the vertical stabiliser looks like it comes from the Dassaut Rafale (Knowing LEGO pieces, it could also be that they couldn't find a proper piece to fit).

Of course LEGO also has this unholy mash-up of the F-22 and F-35. So it does not surprise me that they have multiple plane designs in these airplanes.


Why is Python used on aircraft although it may not be certifiable? I recently had a discussion with people who were active in the aviation industry and told me that one of the main languages/tools they use is Python.

On the other hand I have always known that people avoid C++ or eg Linux due to certification reasons for avionics. Certification is also one of the reasons you don't see AI and computer vision in C++ on aircraft. Yet, those people use Python all the time.

I didn't have (and never will have) the opportunity to ask why and for what they used it. Could someone explain why and for what people would still use Python although it may be very difficult to get it certified?

Just because aviation developers use Python, does not mean that Python actually goes flying.

Lots of aviation development is about testing, stressing, validating, analyzing, and documenting the code that does go flying.

Python is an excellent language for all that validation work, even though it stays on the ground.


What forces act on cascade-type thrust reverser blocker doors? What is the stress or force that loads the cascade-type thrust reverser blocker doors? As we know, blocker doors are closed and block the airflow going through the C duct. The engine is a V2500 with 25000 lbs thrust.

ATTENTION, very coarse analysis !

This is a bit vague, but maybe this will give you a starting point.

Generally on turbofans, about 70% of the total thrust is provided by the fan.
If you consider a high power brake using 80% of the max thrust, this gives you
TADAAAAA 25000*0.8*0.7 = 14000 lbs (yup that's rocket science).

Now, this gives an approximation of the power provided by the fan. However, the outlet angle is not parallel to the main flow. Assuming that the mass flow rate as well as the magnitudes of the velocities are conserved in the transfer and that the outlet angle is about 45° from the engine axis, it gives

qm x (v2-v1) = F where qm is the mass flow rate, v2 the outlet velocity vector and v1 the inlet velocity vector, while F is the force of the fluid on the structure.

Because of the angles this gives qm x (0.5+1) x v1 = FX and qm x 0.5 x v = FY on the doors.

Then, assuming (yes, I said to pay attention at the beginning of my answer) that Ffan = qm*V1 = 14000 lbs, which is quite doubtful unfortunately, we obtain FX = 21000 lbs and FY = 7000 lbs.

Regarding stresses, it is IMHO far to dependent on the actual parts of the engine to assess.

If anyone can check this to be sure, be my guest ;).


3-D Printed Carbon Fiber UAV Skin aviation pros!

New to the aviation/RC world and would like to ask a serious question about using composites for the skin of a UAV I am developing my first time out.

Want to use carbon fiber for a planned UAV approx 6-8 feet in length and weighing in at about 200 lbs powered by electric motors.  But, instead of making a carbon fiber skin from a stryofoam (or similar) mold, I am thinking of printing out the skin (using a carbon fiber filament) from a large format 3-D printer as separate panels up to 20" x 20".  They would then be attached to the UAV's metal airframe (of a semimonocoque style).

It just seems like a much simpler way than molding the skin from a plug.  Yes, I am concerned about the necessary strength and elasticity needed from the skin but I am hoping that a well thoughtout design for the panels (and especially for the nose and empennage) along with a CF/nylon filament will provide that.  I have also considered the production time and filament costs associated with this method, but it just seems so darn simple and easy.

But what do the pros think.

Thanks.

"Carbon fiber filament" for Fused Deposition Modelling (FDM) printers doesn't have the properties you believe it does.  While perhaps a little stronger than a plain filament, in comparison to traditional items made of carbon fiber it is actually quite brittle and easily snapped, because the fibers are all chopped up into short pieces and mixed with the plastic resin.

To build something useful for an aircraft, you need fibers of meaningful unbroken length - either large pieces of cloth, or to run a continuous filament back and forth many times.

There have been thoughts of making FDM printers which would place a continuous carbon filament along with a thermoplastic "printer filament" as a binder, but that's not what a roll of "carbon fiber printer filament" gets you.  Also note that even a filament-stringing machine would only make structures which were strong in the plane the layers, but not against delamination between layers; to get a strong 3d shape like an aircraft panel, you would need a six axis machine which built in a way sensible for the shape of the component being built.

You could potentially use some ordinary or soluble filament to print a mold for conventional carbon fiber layup.


Are loops or rolls allowed in the "utility" category in any US-certified airplane or glider? In actual practice, is there any US-certified airplane or glider where the approved flight manual, or cockpit placards, indicate that loops, rolls, or any other similarly aerobatic maneuvers other than "spins (if approved for plane), lazy eights, chandelles, and steep turns, or similar maneuvers, in which the angle of bank is more than 60 degrees but not more than 90 degrees" are allowed when the aircraft is operated in the "utility" category?

Also, in theory, would it ever be permissible for this situation to occur for a US-certified airplane or glider, if the manufacturer proved that the aircraft was safe for the maneuver in question?  Perhaps in conjunction with additional restrictions on weight or CG location?

See this closely-related question that notes that this IS the case for some airplanes and gliders certified in other countries: In the US, would it ever be legal to fly a loop in any airplane or glider that was operating in the "utility" rather than "acrobatic" category?

The current question is only asking about US-certified airplanes or gliders.

The main difference between Utility and Normal category in FAR 23 is spins and the limitation of bank angles in maneuvers.  Normal category is banks up to 60 deg and no spins.  Utility allows spins if certified for them, and banks up to 90 degrees.

  Limited   acrobatic   operation includes: (1)  Spins  (if  approved  for  the  par-ticular type of airplane); and (2) Lazy eights, chandelles, and steep turns,  or  similar  maneuvers,  in  which  the  angle  of  bank  is  more  than  60  de-grees but not more than 90 degrees.

I would imagine that a Hammerhead, being a chandelle taken to an extreme, would be allowable since done properly the wings don't go beyond 90 deg,  but loops and rolls are definitely out in Utility Category.


How can I take off in a straight line if the runway isn't visible ahead? In a C152, flying VFR, if you point your nose up you wouldn't be able to see the runway, thus it would be difficult to keep yourself aligned to it.

So once you take off with a C152, do you climb in a fixed climb rate or do you level off at a certain altitude whilst over the runway, and start your climb again once you've reached the threshold of the runway?

Thats what the compass is for.   Continue to fly runway heading according to the compass & heading indicator.

While you may not be able to see the runway, you may have other markers.   Even a good cloud in front of the airplane can serve as a VFR reference point.

Or look out the side to the left-and-right of the plane.  You should be able to tell if you're going straight or turning by what you see going past the sides of your plane.


Can I descend during downwind or I can only descend when I am at base? If I am close to the end of downwind, can I commence a descend first or I must make a turn first, e.g. leaves downwind and enter base, before I can descend?

Is there a official reference to support this?

See Chapters 7 and 8 of the FAA's Airplane Flying Handbook.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/airplane_handbook/media/10_afh_ch8.pdf

The descent point for the approach is going to be largely based upon the handling characteristics of the specific type or model of aircraft you are flying in.  In general it's commonly taught to pilots that you begin your descent from the traffic pattern to land when you are on the downwind leg and abeam the threshold of the runway you are going to land on.  You will select a descent power setting at this point, configure the aircraft for landing and begin the descent.  When you turn base or final is going to be up to your discretion but in general should be no more than 1-2 miles from the airport.  This turning point may also be given to you by ATC at a towered airport for aircraft spacing e.g. "Cessna 1 2 3 X-ray yankee, extend your downwind; I'll call your base."  You may also have to do the same thing at "beehives" or busy, non-towered airports for traffic spacing in the pattern as well.


What is "temporary flight plan" in A320 MCDU? I have been reading FCOM to undestand how MCDU works, there are severel mentions about "temporary flight plan". Does anyone knows what it is?

The temporary flight plan is visible on the mcdu in yellow when you modify the actual flight plan. It will be shown in yellow as well on the ND (for modes ARC, NAV and MAP) until you press the 6R button of the MCDU, which mean * insert.
The goal is to let you see your modification before inserting it in your flight plan. Knowing that most of the time you will create a discontinuity in it and you will have to review and delete the discontinuity.
If you use secondary fplan you will have the information in white.


What is the relation between N1 and Wing anti-ice When wing anti-ice is selected, the N1 or EPR limit is automatically reduced, and the idle N1 or EPR is automatically increased. What does this statement mean ???

When engine or wing anti-ice are needed, the required amount of bleed air increases. In order to provide enough bleed air at the required pressure, the engine idle speed must be increased. That way, the compressor runs faster, which provides more high pressure air to the bleed valves. Note that this will result in more idle thrust as well, which can have an impact on descent performance as discussed for the Boeing 737 here: What is the impact of thermal Anti-Ice on descent performance?
For the A320, this is already taken into account for the descent calculation:

The idle segment assumes a given managed speed flown with idle thrust plus a small
amount of thrust. This gives some flexibility to keep the aircraft on the descent path if
engine anti-ice is used or if winds vary.

(Airbus A320 FCTM - Normal Operations - Descent)
When more bleed air is taken out of the compressor stage of the engine, the EGT (exhaust gas temperature) will increase because more fuel flow is required to maintain the same N1 speed. This implies that the N1 or EPR limits must be decreased in order to protect the engine, meaning the lower limit will result in the same EGT as before.


Is the actual VMC to IMC transition a challenge (for IFR rated pilot/craft etc) if, say, sudden or unexpected? I assume that even on an IFR flight, being in even marginal VMC can be helpful, and that pilots consciously or subconsciously use cues such as the horizon to assist them in their flight even though they are principally flying by instruments.

I was wondering if that makes a sudden transition to IMC a psychological challenge, particularly if unexpected. That must be quite a "task switch", scabbling for information, switching focus, and so on?

It seems like that might be much more of a personal challenge than when flying deep in IMC for some time (to a trained and qualified pilot/aircraft) when a routine of going from instrument to instrument is established along route.

Is this a major challenge or a minor or even unnoticeable one in the grand scheme of things?

If you are an IFR pilot hand flying in VMC and suddenly your horizon reference disappears, or becomes untrustworthy (flying over sloping terrain in low visibility, or flying between cloud layers that are sloping), you do have to make a conscious mental transition from external scanning to internal scanning and it will increase the stress level slightly when you're new, but this declines as you get experienced doing it and it eventually becomes a non-event.

This is mainly because if you are flying IFR a lot, especially commercially, you will be doing this all the time on departures in instrument conditions, where you take-off visually, looking outside, and immediately enter cloud, often even before it's time to engage the autopilot (you wouldn't really want to to do a lot of IFR flying without one).  So effectively you have to make that VMC to IMC transition on every departure in IMC weather that you hand fly while entering cloud and you get used to the look-out-to-look-in transition pretty fast.

So I would say the answer is yes to a new pilot, but quickly becomes no, once experienced a bit.  That being said, "grey area" conditions, like I mentioned at the start, where you need to go on the gauges even though there is still a view outside, would be more of a challenge compared to just charging into cloud where the view goes from green to grey instantly and the distraction of a misleading outside view isn't there. That requires a bit more concentration and self discipline to ignore the view outside, and therefore a bit more experience to drop the stress level of the transition.  But still, after doing it a number of times, it should be no big deal.


What are the major causes of flameout, excluding ingestion of foreign objects? What are the most frequent causes of flameout, excluding ingestion of foreign objects and other sudden forms of damage to the engine?

I'm limiting this to modern turbojet and turbofan engines with a computerized (digital), closed loop engine management system.

E.g. what could cause a F119-PW-100 engine to flameout or otherwise fail?

I'm not looking for a thorough study or carefully detailed statistics, I doubt something like that even exists. I'm basically asking if this ever happens, or if this is basically a thing of the past with early fighters, such as the Me 262. Are modern jet engines "bulletproof"?

If it does happen, then how?

You might be counting this as FOD, but I'm going to go with water.  That is, more rain volume than the engine can handle.  It's the reason you select continuous ignition while in moderate to heavy rain because the chance of flameout is quite high.

Next in line would be flow disturbances at very high altitude, that are normally tolerable at low altitude.  Airliners that have gotten into high altitude stall incidents can flame out one or more, especially airplanes with tail mounted engines that are in the wing's down wash.

On some airplanes the stall protection system will activate continuous ignition automatically when you are close to or at stick shaker.  Modern FADEC engines usually have an auto-relight function built in and have to demonstrate auto-relight capability for certification.

Fighters like the 262 and other first generation engines had a fuel control system that was basically a needle valve connected to the thrust lever. The pilot's eyes and brain was the real fuel control and the gauges had to be monitored carefully when making power changes.

In the early 50s hydro pneumatic fuel controllers allowed "slam acceleration" without flaming out, but engines were still sensitive to flow disruptions.  Then  variable guide vanes came along to manage the flow through the axial compressor to control blade angle of attack, and flame outs due to flow disruptions only occurred with more extreme conditions.


At which point does an airliner start to pressurize/depressurize the cabin? Do airliners start changing cabin pressure at takeoff or after reaching a certain altitude? Also when do they start depressurizing the cabin ?

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

From the Boeing 737 FCOM:

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

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

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

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

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


Why are 737-200 engines more susceptible to separation? It seems the 737-200 had an issue with separation of engines from the wings. Considering that the engines are mounted completely under the wings, there should be more attaching points than a modern jet engine the question is why is this aircraft so prone to this sort of incident? Is it something to do with the airflow and the forces associated to it? Or is it purely a manufacturing defect?

Source:
https://www.flightglobal.com/news/articles/nationwide-737-engine-loss-inquiry-finds-fatigue-crack-in-mount-220017/

Snippet from the article:

  Fatigue failure of aft cone bolts has been attributed to a number of
  engine-separation incidents involving 737-200s – among them a US Air
  aircraft at Deptford in December 1987, a United Airlines jet at
  Chicago in January 1989, and a Delta Air Lines aircraft at Dallas in
  January 1992. All three lost their right-hand engines on take-off.

In general, jet engines are mounted under wings using only a few attachment points- Boeing uses cone pins in 737-100s and 200s (these were changed into fuse pins from 737-300s).

Older 737s with cone pins (the SA 737 is a 200) has a history of failure and almost all the the cases being blamed on the fatigue and manufacturing defect of the aft bolt (which usually resulted in over-stressing and failure of the two front bolts). I've just listed some of the incidents and the probable causes (from NTSB):

Incident: January 03, 1986 involving BOEING 737-2H4, registration: N86SW

  Probable Cause: ...EXAMINATION OF THE CONE BOLT REVEALED THAT IT FAILED AS A RESULT OF FATIGUE, MOST PROBABLY DUE TO IMPROPER INSTALLATION OF THE BOLT, SPECIFICALLY, THAT IT WAS UNDER TORQUED WHEN THE OPERATOR RE-INSTALLED THE ENG.

Incident: December 05, 1987 involving BOEING 737-2B7, registration: N319AU

  Probable Cause:  ... THE AFT MOUNT CONE BOLT FOR THE #2 ENG HAD FAILED FM FATIGUE THRU THE THREAD RELIEF UNDERCUT RADIUS. FATIGUE CRACKS HAD INITIATED ON DIAMETRICALLY OPPOSITE SIDES OF THE RADIUS.

Incident: January 20, 1989 involving BOEING 737-201, registration: N242US

  Probable Cause: PREVIOUS DAMAGE TO THE AFT CONE (ENGINE MOUNTING) BOLT, WHICH RESULTED IN MISMATCHED SURFACES BETWEEN THE BOLT AND ISOLATION MOUNT, LOSS OF TORQUE DURING CYCLIC LOADING OF THE MOUNTING BOLT, AND SUBSEQUENT FATIGUE FAILURE OF THE BOLT

Incident: January 07, 1992 involving BOEING 737-232, registration: N322DL

  Probable Cause: THE FAILURE OF THE AFT CONE BOLT AS RESULT OF PREEXISTING FATIGUE CRACKING DUE TO IMPROPER MAINTENANCE, AND THE FAILURE OF THE SECONDARY SUPPORT STRUCTURE AS A RESULT OF LOADS THAT EXCEEDED THE CAPACITY OF THE ATTACHING HARDWARE AND THE CRUSHABLE HONEYCOMB CORE.

The incident involving the Nationwide 737-230 was also traced back to fatigue of the engine bolt:

  The right-hand engine separated from the aircraft due to the failure of the aft cone bolt as a result of a pre-existing fatigue crack which was most likely caused by incorrect installation of the cone bolt.

No investigation has pointed to any problem with the airflow or associated forces.

In a related note, 747s, which use fuse pins also had a number of incidents/accidents caused due to failure of the pins and Boeing changed the design quite a few times.


What is the sink rate of a glider during a roll? For a glider in a steady bank at angle $\mu$, to a good approximation, the sink rate has a factor $1/\sqrt{\cos \mu}$ relative to the sink rate at zero bank angle.

What are the dynamics of the sink rate during a roll, for instance, when rolling from a bank angle of zero to a bank angle of $\mu \sim 20^{\circ}$ in one second?

I'm not looking for a very precise, quantitative answer but rather some qualitative idea of the physical effects that underlie the dynamics of the sink at such roll rates for a model plane.

Any references or guidance will be helpful, thanks!

As always, it depends. Besides the steady-state drag sources of lift creation and friction, you need to look at the drag created by roll acceleration and manoeuvring, including adverse yaw.

If the glider starts the roll at a bank angle which is sufficient to reach a steady roll rate by the time it rolls through 0°, the roll acceleration term becomes zero. However, now you have deflected ailerons and a deflected rudder to counter adverse yaw, which all add their own drag. How much depends on the roll rate and the needed deflection.

On top, now the local incidence of the wing shows a discontinuity at the spanwise station where the ailerons begin. This will create a less than optimum lift distribution over span, so the induced drag of the rolling glider is higher than that of the same glider in a steady glide. Again, the magnitude depends on the roll rate, and the aileron placement and deflection angle.

I would not be surprised if the sink rate in a brisk roll increases by 50% over that in a steady glide at the same speed, even with zero sideslip. If adverse yaw is not properly countered by the rudder, the additional drag from the resulting sideslip angle can easily double the sink rate.


How Earth's rotation affect flight times? How much does Earth's rotation affect flight times in going East or West, and how could you calculate if zero winds?

It does not affect as much as one would think.

The atmosphere moves along with Earth's rotation. An airplane taking off from one place on Earth has to move through the atmosphere which is moving with Earth.

Now you may ask when does it take longer when we travel from Western Europe to Eastern USA, compared to USA to Europe? That depends on Jet Stream:

  Jet streams are fast flowing, narrow air currents found in the atmosphere of ... Earth.

Many air routes take advantage of jet streams, as you can see as follows:

Pilots know about the jet streams and will try to gain benefit of them. Recently, there were some news that a flight from New York to London traveled faster than expected because it was in jet stream (details here and here).

If you want to know why Earth's atmosphere moves with it, please see this.

There is a similar question on Physics.SE.


What would be the effect of skinning over the gap in fixed leading-edge slats? The Zenith STOL CH-750 experimental aircraft uses a modified NACA 650-18 airfoil (having a 17% fatter-than-normal thickness) with a fixed leading-edge slat.   In an effort to reduce drag and improve cruise performance, some of the builders remove the leading-edge slats.  Instead of removing the slats, I am curious what the effect would be if one left the slats in place, skinned over the slots with a removable leading edge (shown in red dotted line), and added vortex generators.

How would this modification affect the center of gravity for the aircraft?

Would this modification affect the chord length?

What are the pros and cons of such an experimental modification?

To answer your question, I suggest to look at the effect of slats. NACA technical report 407 studied a fixed slat similar to what is used on the Zenith CH-750, and the result of the optimum geometry is plotted below. Dashed lines are for the airfoil with a fixed slat and solid lines for the airfoil with the slot between slat and wing filled:

Lift and drag coefficients for a wing with and without a fixed slat over angle of attack, from NACA TR 407.

Three conclusions are obvious:

Drag is higher with a slat for no benefit in lift (even a small reduction, actually) up to an angle of attack of 15°. Don't let the scale of the plot mislead you: Zero-lift drag for the slotted wing was 0.0229 compared to 0.015 for the plain wing, an increase of 52.5%.
The maximum angle of attack has been increased by 9° by the slotted wing, from 15° to 24°. This translates into an increase in the maximum lift coefficient of 34.6% (from 1.297 to 1.751)
The stall behavior has changed from benign to outright nasty by the addition of the slot.

While the airfoil studied in NACA TR 407 is quite close, it is not exactly what happens once the slat is removed: While the outer contour of the airfoil did not change in NACA TR 407, those builders removed part of the wing when removing the slat. Therefore, wing area would be reduced and the loss in lift will actually be even greater. NACA TR 400 hints at a lift loss of more than 40%, which would increase the minimum speed of the Zenith CH-750 by about 30%. Note that the take-off and landing distances will grow accordingly - the STOL in the aircraft's name will not apply any longer!

When putting a glove over the slot, the wing area will be maintained and the minimum speed will not go up quite so severely. Using the 34.6% from NACA TR 407, the minimum speed increase would only be 23.6%. The change in airfoil shape (with the glove the point of maximum thickness is further back and the relative thickness smaller than with the slat removed) will not alter the flight characteristics in a significant way - in both cases the airfoil is of the peaky upper surface type with a large nose radius, so separation around stall will start from the trailing edge and move forward with increasing angle of attack. Long laminar runs on the top surface cannot be expected in both cases.

Now I only wonder why you would add vortex generators. I thought the idea was to reduce drag and improve cruise performance?


How far are shortened replies to ATC allowed to go? Pilots often use non-standard-phraseology for readbacks. Some examples:

  ATC: DLM, switch to tower, 121.2

  P: tower, for DLM

or

  ATC: DLM, identified, climb via the RIDA9 departure

  P: roger, climb via, DLM

or

  DLM, cleared for takeoff runway 17

  P: cleared for takeoff, DLM

The last two example are from two videos by Boldmethod, How To Fly An IFR Departure Procedure With A "Climb Via" and How To Fly An Instrument Arrival Procedure (STAR), used by an ExpressJet-pilot.

Especially the two last ones were a bit shocking to me when I heard a professional pilot using them. So I now want to ask, how far is this "ATC-Slang" allowed to go?

ATC is required to always use standard phraseology, and tapes are randomly reviewed to verify this--and too many violations gets them pulled off for retraining. This makes sense since talking is literally their entire job and it could be with anyone from students to veterans, including people who don't natively speak the language.

Pilots can use whatever wording they want as long as ATC can understand what they're saying, which naturally leads to shortcuts.  It saves time/effort and helps keep the frequency clear for others. In fact, if/how you abbreviate things is a sign to ATC of how experienced you are. If you read back "climb and maintain three thousand five hundred feet", they'll treat you a bit differently than if you say "up to three point five". Listen to a busy airport or approach on LiveATC and you'll pick up the patterns in just a few minutes.

"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." --Antoine de Saint-Exupery


How much does each engine on a Boeing 747 weigh? The Boeing 747 weighs 404,600 lbs in total, but how much of that does each engine take up?

Boeing 747 can be operated with different types of engines (and in general a specific model has multiple models of engines compatible with it due to competition between different engine manufacturers). Here are some of the engines that are compatible with B747 and their weights:

GE CF6-50: 8,825–9,047 lb
Rolls Royce RB211-524G/H : 12,540–12,764 lb
Pratt & Whitney PW4000-94: 9420 lb

So as you see, from model to model the engine weight might differ and all these engines have been used on B747 at some point.


How does scaling of UAV size impact range? Lets say you have two autonomous small aircraft, one with a wingspan of 200 cm and one with 400 cm. Both have the same general design. They are both optimized for travel distance on one full tank (gas tank size, engine size, optimum speed, etc). Which one has greater range?

In other words, does it help to be large or small if you want to make a travel distance record?

If you compare geometrically similar aircraft, the larger one will have more range.

First, its volume grows by the third power while areas grow only with the square of its scale, so wing loading will be higher for the larger aircraft. This will translate into a higher cruise speed, because the range optimum dictates an optimum speed for each aircraft. In a first order approximation, an aircraft of twice the size will fly at 1.41 times the speed of a smaller aircraft. The much higher internal volume will allow it to carry much more fuel, but even when the fuel fraction for both designs is kept constant will the larger aircraft fly farther.

If we restrict fuel to the same fraction of total mass, the exponent for mass increase is slightly above 2. All surfaces grow by an exponent of 2, but the stresses would be higher in a linearly scaled structure, so the structure of the larger aircraft needs no be beefier. An exponent between 2.2 and 2.3 has been found to best represent reality. This means that doubling dimensions will result in a mass increase by a factor of 4.76. In order to fly at the same polar point, the large aircraft needs to fly at 109% of the speed of the small aircraft.

In a more detailed analysis, we need to first look at the installed power: If we focus on piston engines and scale the engine in the way we scale the aircraft, for a size increase by a factor of two will the displacement grow by a factor of eight while the engine speed will decline by a bit less than a factor of two. The smaller engine will have higher friction, thermal, sealing and combustion losses, so it will have a noticeably lower efficiency. If we just look at statistical data, power output grows slightly less than linearly with displacement:

Statistical data for power over displacement. Source: Menon, S., and Christopher P. Cadou. "Scaling of Miniature Piston-Engine Performance, Part 1: Overall Engine Performance." Journal of Propulsion and Power 29.4 (2013): 774-787

Next, we need to look at Reynolds number effects. The larger aircraft will fly at a higher Reynolds number for two reasons: Increased length and increased speed. Together, a doubling in length will translate into a first-order Reynolds number increase by a factor of 2.18. The coefficient of friction will scale with Re$^{-0.3}$, so doubling the length of an airplane will reduce the friction coefficient of the large airplane to 79% of that of the small airplane. This will not only affect total drag, but also the polar point for best range. Since the optimum lift coefficient is proportional to the square root of zero-lift drag, the optimum lift coefficient for the large airplane will only be 89% of that of the half-size airplane and cruise speed will be higher by a factor of 1.225. This means that dynamic pressure is higher by a factor of 1.5.

Ideally, this calculation needs to be iterated, but for now I keep it at one iteration step.

This higher dynamic pressure now needs to be multiplied by the increase in reference area to arrive at the zero-lift drag: 1.5 times 4 times 0.79 means that doubling the size will let zero-lift drag grow only by a factor of 4.74. Since zero-lift and induced drag are of the same size at the optimum cruise point, the same factor applies to the total drag. The required power, however, is proportional to speed, so doubling the size will increase the power demand by a factor of 5.78. This is well below the power increase from a scaled-up engine, so the larger aircraft actually needs a proportionally smaller and lighter engine, leaving more reserves for fuel. Or it can scale up the engine linearly and load proportionally more fuel.

Fuel consumption is proportional to engine power, but we get another advantage from the larger engine: Its specific fuel consumption will be slightly better:

Specific fuel consumption over displacement (same source as figure above).

In sum, the larger aircraft will

cruise at 122.5% of the speed of the small aircraft
will consume 5.5 times as much fuel per time for a mass increase by a factor of 4.76. Combined with the speed increase this leaves only a 5.5% advantage.
If we assume a scaled-up engine with an increased power by a factor of 7.27, the mass increase can be by a factor of 6 with maybe twice the fuel fraction of the smaller aircraft and 7 times higher fuel flow per time. This takes into account that the cruise speed will grow with aircraft mass.

This 70% longer flying time coupled with the then 24% higher cruise speed will leave the smaller aircraft in the dust.


How does a commercial airliner measure its weight/mass? Other questions currently being answered cover situations regarding planes near, at or even above their MTOW. It raises a more basic question: how is the exact "ramp weight" of an airliner measured or estimated?

On most airlines, luggage is weighed and counted, so the pilot would know within 100lbs or so how much mass is in his cargo hold. He'd also know the "operating empty weight" of the plane itself (the weight of the airframe, all fluids besides usable fuel and the weight of the crew), and the mass of the fuel he's taking on.

The biggest variable, then, is the weight of the passengers and their carryons/personal effects. Last time I flew, I wasn't knowingly weighed and neither was anyone else getting on with me. So, while you know the number of passengers, the total "cabin weight" is a big unknown.

So, do planes have load sensors in their gear which could be used to exactly measure the plane's ramp weight? Or is a median passenger and carryon weight used, with a more conservative total passenger rating used in case a few planeloads err on the heavy side of the bell curve?

Short answer

Determination of mass and balance (or weight and balance) is a critical task for the crew, an error in this operation may have tragic consequences.

Weighing passengers and carry-on items is mandatory per regulation.
Either standard predetermined weights, or actual weights can be used in this operation. Airlines usually use predetermined tables. Tables values take into account different types of travel (e.g. regular and charter).
While the weight must be checked, the center of gravity location is of equal importance. The distribution of the passengers in the aircraft is also taken into consideration.
Aircraft are not weighed prior to each flight, but the basic empty weight must be known and checked periodically per regulation.
Aircraft are weighed simply using scales under the carriages :-)

(source)
The other method is to use jacks. See further below for an image.

So this was the short answer. To understand why and how to balance the aircraft, there are quite a lot elements to introduce. For those interested, just continue!

Weight...

The different elements composing the takeoff weight:

All of these elements must be determined prior to taxi and takeoff.

The mass of these elements are necessary to check that the different maximum weights are not exceeded. However there is another aspect of the masses which needs to be secured: Where are the masses located?

Taking KeithS' example, if there are many heavy people grouped in the forward section, we may have a problem at Vr, even if the MTOW is not exceeded.

... and balance. Location of the center of gravity vs. the MAC

The masses must be distributed so that the center of gravity of the aircraft is located within limits determined relatively to the aerodynamic chord, and the center of lift.

This is required to ensure the stability and the maneuverability, to minimize the efforts on the horizontal and vertical stabilizers and to increase the maximum lift and reduce the drag. On airliners, the center of lift must be located between the CG and the center of lift of the horizontal stabilizer, so that the latter pushes downward to balance the weight.

On airliners the width of the wing is greatest where it meets the fuselage at the wing root and progressively decreases toward the tip. As a consequence, the chord also changes along the span of the wing. The average length of the chord is known as the mean aerodynamic chord (MAC).

The MAC is a portion of the wing, delimited by LeMAC (leading, 0%) and TeMAC (trailing, 100%). The CG must be located in the MAC.

In large aircraft, center of gravity limitations and the actual center of gravity are often expressed in terms of %MAC (on the roll axis, similar limits exist on the two other axis).

(image and text around: Aircraft Design, Mohammad H. Sadraey)

In general, in large transport aircraft, the most forward CG is located as forward as 5% MAC, while the most aft location as aft as 40% MAC. The average CG limits in large transport aircraft are between 20 and 30% MAC.

As commented by Calchas, using wrong weights for the passengers (adults instead of children) may move the CG to a wrong location, not balanced by the trim, and create strong difficulties during the takeoff and the initial climb.

PAX weight applicable procedures

For an airliner, the PAX portion is relatively small compared to the total mass, so the passengers mass is usually estimated based on standard passenger mass tables and the number of PAX per cabin section. Each airline may provide its own standard mass tables, but standard tables are proposed with the applicable regulation:

JAR-OPS1 or EU-OPS1 for Europe (section JAR - OPS 1.620 Mass values for passengers and baggage). Values valid in 2008:

(source)
Those tables have been establish using airlines data obtained by surveys. They are updated from time to time.
In case the operator wants to establish their own equivalent tables, JAR - OPS 1.620 provides a detailed operating mode to sample passengers and weigh them.

For the EU, a new survey was conducted by the European Aviation Safety Agency in 2009 and a proposal for table updates issued:

Passenger and Baggage weight survey

At this point you may want to download the documentation I'm mostly using for this post: Mass and Balance in Aircraft. We are at page 54.

Special cases

There are cases where it is obvious the actual mass and balance will be erroneous if the standard tables are used (this is especially true for a small cabin).

In these cases the operator must improve the evaluation by actual weighing of either all or a sample of passengers and their baggage. The procedure already mentioned for establishing standard tables is used (JAR - OPS 1.620).

Putting all elements together

All masses, arms (distance to the reference center) and moments are finally reported on the aircraft manifest to calculate the correction that must be used for the takeoff (trim amount).

Basic empty weight determination

The aircraft is not weighed for each takeoff, still it has been weighed to determine its basic empty weight and its center of gravity. This operation must be done every 3 or 4 years (9 or 18 years in a large fleet, this is a specific process) according to JAR Ops 1.605, Appendix 1.

Platform scales under the carriages may be used:

(source)

Another method is to use jacks equipped with a transducer at their top:

(source)

Related FAA regulations and JAR-OPS

FAA AC 120-27E and JAR-OPS 1.620 to determine the mass of the baggage, passengers and carry-on items.
FAA AC 120-27E, JAR-OPS 1.607, JAR-OPS 1.615 for the determination of operational items, which include the crew and the crew baggage (there is also a table, that I won't include to prevent comments on the differences with the passenger table -- All tables are based on survey from airlines). The operational items also include catering, emergency equipment, spare parts..

May be interesting too:

There is a confirmed trend of weight increase among the population (including myself). This has an impact on the operational costs. The way airlines manage this impact can be read in a two-part article: The true costs of heavier passengers, part 1, part 2.

Related:

Do some airplanes have weighing scales on the landing gear?
Do airlines weigh passengers and baggage before loading the aircraft?
How much time does it take to calculate the leveling and weighing of big and small aircraft?


Why vacuum instead of pressure to power gyros? Why are most air powered gyro instruments powered by vacuum rather than positive pressure?

There are piston aircraft that use positive pressure to power gyros.  The Beech Baron and Bonanza lines as well as the Piper Navajo line use pressure instead of vacuum. We're not talking about one-off airplanes here!  The Baron/Bonanza and Navajo are some of the most popular airplanes in their respective categories which, when summed, total many thousands of airplanes (and pressure pumps).

The turbines I've flown used ejector pumps, not mechanical pumps, to draw vacuum so I will assume that this class of plane is out of scope for the purposes of this question.

A technical answer to your question will require an aircraft system engineer (perhaps Peter?) to weigh in.  My guess is that vacuum pumps were installed to replace venturis.  Since systems (and instruments) were already designed to run vacuum, the pumps were installed to draw vacuum instead of apply pressure.  Why change what works?


What is this fighter jet that flew over KJST? This aircraft was doing low level flights over my office a few minutes ago.  From the route it was flying some of my coworkers thought it might have been doing approaches or touch and go landings at the local airport (Johnstown, PA (KJST)).

After it left the area I tried comparing it against pictures of active US fighters; but the wings didn't appear to match with anything I saw.

It's an F/A-18 Super Hornet.

Defining characteristics:

Slightly angled twin vertical tail
Twin engine with little space between them (eliminating the F-14 and similar)
Almost straight trailing edge of the wings
Horizontal tail with significant sweep angle that also protrudes behind the engine exhaust
Massive wing strakes (thanks Dan Pichelman!) along the fuselage under the cockpit
The wing "notch", as noted by Ron Beyer in the comments

Also the shape of the horizontal tail excludes the YF-17:

Source

As mentioned by Penguin, the wing notch, together with the single curve leading edge extensions are the indicators that mark this aircraft as a "Super" variant (E-F, single seat and two-seat, respectively) rather than an earlier vanilla "Hornet" variant (A-C), as seen in this figure:

Source

Note also the less round profile of the horizontal tail, like the one seen in OP's photo.


Where are the bags generally stored on an airliner? I don't mean carry on bags. What I mean is where are the locations of the non carry on bags on an airliner. Also does it depend on the airliner of where the bags are stored.Source:(gokaysarioz.com)

In smaller aircraft, the baggage is put directly inside the cargo hold.

Source: jacksonville.com

In case of larger aircraft, the baggage is put inside the conformal cargo container or the unit load device, which is then placed inside the cargo hold.

Source: roger-wilco.net

Source: supath.net


What is auto-rotation? Inspired by this question.

My knowledge concerning helicopters is quite limited:

what is auto-rotation?
are there other "rotations" possible?
in what do they differ?

When a helicopter engine fails, the pilot lets the rotor blade rotate freely pushed by the wind as the helicopter is falling out of the sky. This is called auto-rotation.

Normal rotation is with the engine powering the rotor.

The most important goal of auto-rotation is to get enough lift right before touch down by flaring so the landing is not a crash.

You would also enter into autorotation when the tail rotor becomes ineffective and you can't recover it otherwise.  Once the tail rotor is back into action you can drive the rotor again.


How to find out if Restricted Area is "hot" before taking off? For example, I often fly from KCHO to KOXB and almost always get cleared through R-4005 and R-4006. Occasionally they will be hot and I will have to go around, wasting time and fuel compared to if I had planned that route originally.

Is there anyway to call Patuxent Approach (or Washington Center) on the phone ahead of time to ask if the Restricted Area is hot?

Restricted areas that have scheduled times will be noted in the (sectional) chart margins. In this example you'll find this at the bottom of the Washington sectional chart:

Ones without regularly scheduled hot times will say something like 48 hrs in advance or other times by NOTAM.

As you've noted though restricted areas with posted hours may not always be "hot" during those hours - sometimes you get lucky. The best way to check if you're going to be lucky prior to departure is to ask Flight Service (1-800-WX-BRIEF): The briefers have access to the same data as ATC, and will know definitively if a restricted area is hot (at least as of the time you call them).

Obviously you should still call the controlling agency when airborne to verify the status of any special use airspace prior to entering it (briefers can make mistakes, and some restricted areas may be activated on short notice which means they may go hot while you're enroute).


Where is the regular wheel brake input on modern airliners? I learned that on modern airliners, the Rudder input is given by the pedals located under the pilot's feet, and that got me thinking:

how do the pilots give the command to brake the plane in order to slow it down on ground (landing/taxing)?
Is the parking brake and "regular" wheel brake part of the same system?

The same way it is done in small airplanes and older airlines -- toe brakes.

The rudder pedals translate forward and back to actuate the rudder and they pivot around the lateral axis to actuate the brake system.  Each pedal independently controls only the brakes on its side of the airplane (e.g both pilots left toe brake actuates the brakes on the left main gear).

Planes will often have an emergency or parking brake, which will be a lever somewhere that actuates the brake system.  This system, outside of emergencies is only used when the plane is not moving and you want it to remain that way.

Larger airplanes with also sometimes have autobrakes which provide a triggered automatic application of a certain level of braking.  This kind of system is used both to provide automatic maximum braking for a rejected takeoff (RTO) and some lesser automatic braking upon landing rollout.

To summarize, for taxi and ground movement the brake input is coming from the toe brakes.  When the aircraft is stopped, brake input will be transferred from the toe brakes to the parking brake.  When the plane lands, if it is so equipped and enabled, the autobrakes will begin brake application and the pilot will take over with the toe brakes and continue to use toe brakes for the taxi in.


Could someone really die in the way that Goose did in the movie "Top Gun"? Looking at this question I remembered a question I always wanted to ask:

In the movie "Top Gun" one of the main characters dies when trying to eject from the F-14. Here is the scene where this happens. Did an incident like this ever occur in real life, or is there at least a theoretical possibility that a pilot could be killed this way?

Top Gun was filmed in the mid 80s, which is quite a while ago. If there were incidents, did they do something to fix that issue? And this question goes not only for F-14s but also other aircraft with ejection seats.

Some sources I found claiming the event was real:

  A flat spin creates a low-pressure area and stalls the canopy when
  ejected. Producers wanted a midair crash but based this accident on a
  real-life incident instead.

(source)

  The way Goose died was actually based on a real life incident that
  happened to a 14 crew in the Navy. Don't remember the specifics, just
  found this out recently while reading an article in one of last months
  flying mags (not Flying)

(source)

  I have a photo of the 'real' Goose and it's true that he died of seat
  ejections but not exactly like the movie.

(source, with pictures)

There's also an interview of Steven C. Schallhorn, who apparently was one of top gun instructors interviewed for the movie:

  Dr. Schallhorn said during his interview for the movie, he explained
  how a flat spin could actually happen with an F-14 and that it
  complicates ejection. "The aerodynamics of the F-14 flat spin affect
  the timing of the ejection sequence," Dr. Schallhorn said. "The canopy
  is jettisoned, followed by the ejection of the back seat, followed by
  the front seat. In a flat spin, the canopy, when it ejects, bobbles
  for an extra few hundredths of a second above the aircraft. That
  upsets the carefully engineered sequence because the guy in the back
  could then hit the canopy. That sequence made it into the movie."

(source)


Is a monobloc variable incidence wing viable (updated)? Could this be a viable way to control roll on an aerobatic airplane, using some sort of tab to control a monobloc variable incidence wing? Both wings are mechanically linked together in order to only allow roll ( like conventional ailerons are )

Advantages could be a very high roll rate (deg/sec) and low effort on stick (get rid of ailerons aerodynamic compensators)

Yes it is a viable way for roll control - aerodynamically that is. The mechanism you describe is a proper servo tab, where the aeroforces on the tab are fed back, and the tab acts like a lever on the main control surface. This was the way the post WW2 airliners were controlled, before they got too big and fast and only hydraulics could do it.

However, as usual, an aerodynamically beneficial solution has some serious structural drawbacks. An aerobatics plane can do 6g and the wings must be seriously strong and resistant to bending and warping. Normally, a wing has two spars which form a torsion box with the upper and lower skin.

If this torsion box can extend from wing tip to root, it is a strong and light construction. But if it has to be cut somewhere and the two wing halves are to be connected by a hinging rod, that spot will be a weak spot in the wing. It can be made strong enough, but the real problem is wing stiffness.


Checkride and Basicmed I am about to take my check ride, but my FAA 3rd class medical is still pending. I have not been denied, just jumping through some FAA hoops.
I have taken and completed the online course for basic med. Am I OK to take my check ride?
The only thing basic med asked is if I had applied for a FAA physical before... which I have.
I haven’t found much on this particular problem, so I’m looking for help. Any input is appreciated!

Unfortunately if you have never held a valid medical certificate since July 14, 2006, the answer is no.  One of the eligibility requirements for BasicMed is that you must have held a medical certificate after  that date.
§61.89(d) states

The holder of a student pilot certificate may act as pilot in command
of an aircraft without holding a medical certificate issued under part
67 of this chapter provided the student pilot holds a valid U.S.
driver’s license, meets the requirements of §61.23(c)(3), and the
operation is conducted consistent with the requirements of paragraphs
(a) and (b) of this section and the conditions of §61.113(i). Where
the requirements of paragraphs (a) and (b) of this section conflict
with §61.113(i), a student pilot must comply with paragraphs (a) and
(b) of this section.

§61.113(i) required that pilot hold a valid U.S. driver’s license, meet the requirements of §61.23(c)(3), and complies with this section and the conditions listed in §61.23(c)(3).
But §61.23(c)(3)(B) states that a person operating an a/c without a medical certificate under §61.113(i) must have:

At any point after July 14, 2006, have held a medical certificate
issued under part 67 of this chapter.

As such you will have to acquire a medical in this case before you can take the checkride.


PPL 40 hours requirement, are you really ready? Are 40 hours of flight really enough to gain experience to fly a small private plane alone anywhere? The rules state so but from experience off you pilots, is it really enough or should be more hours be clocked with another experienced pilot next to you before venturing out?

Today I had my first flight on a 152 from Dar es Salaam International Airport, and the area is quite busy. There were bigger aircraft taking off and approaching and  many other taxiing.

Putting an inexperienced pilot that has barely 40 hours in an environment like this could cause serious problems even though he has gone through courses and exams. As you know one thing is theory and another is practice.

I would appreciate some clarification.

With the caveat that this is based on experience mostly in the US:

Most people take 60-80 hours to get their private pilot license:
http://www.aviationcareerguide.com/private_pilot_license.asp

The harder you work, and the more often you fly, the fewer hours you'll need.  The average hours are inflated somewhat by the many pilots who run out of time or money partway through, have to stop, and must then relearn what they forgot when they start back up again.  If you have the time, money, and dedication to fly two or three times a week, you'll get your license in fewer hours (not to mention fewer days!).

Don't worry too much about the safety of it though.  Your instructor won't let you take the exam, and your examiner won't pass you, if you're not ready.

As far as flying out of a major airport, my opinion is that it doesn't much affect the time or amount of experience required.  In the US, it's usually more expensive because costs are higher at large airports, but you may not have the option.  For most pilots, the hardest part of flying into a large airport is getting lost on the taxiways - but it will not take long to learn your way around your home airport.  If anything, it will make you a better pilot.  Today much of flying is dealing with controllers and airspace rules, and if you learn at a major airport, you'll have plenty of practice with that.


What is a "runaway supercharger"? During World War 2, my uncle was a navigator for a B-17G bomber based in the UK. On return from a bombing run over Frankfurt, the crew was forced to bail out over Belgium at 3000 feet altitude. My uncle and 3 of his crewmembers were rescued by Belgian resistance members and hidden for 8 months when Allied forces liberated western Belgium.
In the Escape and Evasion report the pilot gave on his return to 8th Army HQ, he wrote that the crew bailed out because "No 2 and 4 engines had runaway superchargers, lost oil. Would not feather with full oil pressure."
Could someone help me out here in understanding what's the likely causal sequence of events here? Why would the plane experience a "runaway supercharger?" Was that the cause of lost oil, or was it the other way around - some sort of oil loss causing loss of control of the supercharger?
Or was it that the propellers for 2 and 4 engines wouldn't feather properly (due to mechanical trouble or maybe flak damage?) causing the engine to overheat and burn oil?

The B-17 had General Electric exhaust-gas-driven turbochargers (or more correctly, turbo-superchargers) that had pilot selectable boost levels. A selector dial in the cockpit controlled the operation of the wastegate that controls whether exhaust goes through the turbine and provide engine boost, or is bypassed directly outside.  The pilot's indication of the state of boost being provided to the engines would come from the engine manifold pressure gauges.
"Runaway superchargers" would suggest that the wastegate control systems on those engines were malfunctioning, such as the waste gate failing closed and directing all the exhaust flow through the turbo, causing the turbos to over boost the engines (the "running away" part), which would cause sky-high manifold pressures, detonation, and send the cylinder head temperatures through the roof.  This would necessitate a precautionary shutdown to keep them from blowing cylinders.
During the shutdown, even though they had oil pressure indication for the engines, the propellers, which operate hydraulically using engine oil, wouldn't feather. There is a feathering pump for each engine, normally electrically operated, that draws oil from somewhere in the system and can drive the prop into feather even without any engine oil pressure, as long as the pump itself has a source of oil to its suction inlet.
The turbosupercharger waste gate uses engine oil pressure for servo power for regulating the waste gate, that is also used to lubricate the turbo's bearings.
So... thinking it through, the turbo waste gate needs engine oil, and the feathering pump needs engine oil.  My guess is that there were oil system problems that impacted the waste gate control systems on those two engines, causing the boost runaway, and the same problem was also starving the engine's feathering pumps so that they were unable to complete the feathering of the propellers.  Maybe flak damage, or just a technical issue with the system (it would be odd for flak shrapnel to cause identical problems in two engines on opposite sides of the aircraft).
A B-17 at low altitude, well lightened, having burned off most of its fuel, dumped its bombs, and expended ammunition, would probably have been able to make it back to the UK on two engines, IF the two dead ones had feathered properly.  Having two unfeathered propellers windmilling away however, is massively draggy, and would have turned it into a two-engine glider, leaving the option of a forced landing or bailing out; and it looks like they chose the latter.


Did the Westland Lysander have a helmet/face mask for radio communication during WW2? I have a character in some war-time fiction I'm writing 'acquiring' an aircraft (a Westland Lysander).

Just need to know: was there a helmet/face mask for radio communication for these aircraft? And, by default, was it present in a 'parked' plane?

fwiw...my character's genned up with the entry, startup and takeoff procedure.

Since they were not suited for combat, they transitioned to supporting clandestine operations where, to quote the  Royal Aviation Museum of Western Canada,
To give it the long range it needed, the aircraft had to be lightened by removing all unnecessary equipment such as guns, armour protection and excess radio equipment, retaining only the radio/telephone for communication with the ground.
It appears that they did have radios, not sure about how they were used. But if you look at the video in the linked page at about 2:33 the pilot appears to be wearing a helmet with built-in headset and a face-mask type microphone. At 6:19 the rear crewmember looks like he is wearing a mask as well.
This is the same aircraft that features prominently in Code Name Verity by Elizabeth E. Wein.


Why is there no lift component when calculating rate of climb? I read this post about how to calculate the rate of climb
How does climb-rate vary with density/pressure altitude?
So in the image, all the forces are drawn. I am wondering, why the rate of climb does not depend on the lift force (or not directly (?) ).
So the forces acting in the vertical direction are: a small drag component, a big lift component, a weight component and a thrust component.
A steady climb would mean, that all forces are in balance - so no acceleration in any direction. But on the other hand in on post it is said "Calculate how much power is needed to overcome drag, and any excess can be used for climbing" - so when there is more force available in one direction - there should be an acceleration in this direction?
I am a bit confused ... is the rate of climb = velocity in the body fixed airframe (so where the airplane is flying to) ? Or is this the vertical velocity in z-direction?
Thank you for your support says
Helmut

Power and force are different things. Power is force times velocity.

The calculation is done in the reference frame of the air mass. In the reference frame of the aircraft none of the forces are doing work, and the engine power all goes to accelerating the air, but we don't have formulas for that.

The lift is, by definition, orthogonal to the flight path, so it does not do any work. That's why it does not enter the equations directly (it does indirectly due to reduction of induced drag at high flight path angles).

The “power needed to overcome drag” is needed for overcoming the aerodynamic drag. In climb the “aft” direction is tilted own, so part of gravity is added to drag and the “excess can be used for climbing” means the engine is able to produce the higher thrust needed to balance the sum of them.

Rate of climb is vertical velocity, i.e. velocity in the $z$ direction. But for that derivation to work, you need the velocity in the $x$ (horizontal) direction too.


What is this transport aircraft, and why does it sometimes cary an air data boom when the Soviet Buran Space Shuttle is on top of it? This comment in chat points to a "google search of the day" which was for Buran the Soviet version of the Space Shuttle. Looking there I saw images of a large transport aircraft with the Buran shuttle on top. What caught my eye were some photos of  the transport aircraft with what looks like a large, orange air data boom at the end.

My understanding from Quora answers is that these are used for supersonic flight, and I wouldn't expect this shuttle to be transported supersonically.

Question: What is this transport aircraft, and why does it sometimes cary an air data boom when the Buran shuttle is on top of it?

According to this blog it is an Antonov AN-225 but I don't think that is a supersonic aircraft.

above: From thelivingmoon.com. Click for full size views.

below: I believe this is Buran itself, According to @Hobbes' correction/comment, this is the "OK-GLI: a Buran analog (shape is correct, systems are not identical to the orbital vehicle) with 4 jet engines that was used for flight testing in the atmosphere", also with an air data boom. I've kept this here because it's actually pretty cool. From pinterest.

The only aircraft that ever had a shuttle on top of them is NASA's modified Boeing 747 and Russia's Myasishchev and the Antonov 225. All of them were subsonic.

The one in the picture is the high wing 6 engine Antonov 225.

The air data boom is likely to gather data for test flights for the shuttle. Subsonic craft will affect the air in front of them (that's why you can hear them coming) so putting the sensor on a boom will help put the sensors in clean air.


Is it possible to fly horizontally with zero angle of attack? If an aircraft has a zero angle of attack and the wing doesn't, is it possible to fly horizontally? Because as the book says, there is no lift in this condition,

Is this zero angle of attack of the airframe or the aerofoil?

Can you give a simple explanation?

Unless you tell us which book you read this in (and what exactly it said), it is not possible to answer your question (the answer depends on whether the zero angle of attack is that of the airframe or the airfoil (wing)). We can try for a general answer though.

As far as angle of attack is concerned, there are two kinds- geometric and absolute. First, angle of attack is the angle between some reference line and the freestream (i.e. the velocity vector). The selection of reference line determines the 'kind' of angle of attack.

Geometric angle of attack, $\alpha$ is the angle between the chord and freestream; this is the one usually used. Absolute angle of attack, $\alpha_a$ is the angle between the freestream and the zero lift line (the line, which when parallel to the freestream, produces no lift in the wing).

The geometric and absolute angles of attack can be related through $\alpha_a = \alpha - \alpha_{L=0}$, where $\alpha_{L=0}$ is the angle between the chord and zero lift line.

Relation between geometric and absolute angles of attack, image from gtae6343.wikia.com

For a cambered airfoil, the zero lift line is negative i.e. the airfoil will produce lift even when the geometric angle of attack is zero (in this condition, the absolute angle of attack is positive). For a symmetric airfoil, of course, the zero lift line coincides with the chord and as such, the airfoil produces no lift when the geometric (or absolute) angle of attack is zero.

As far as the lift is concerned, what matters is the absolute angle of attack, while we usually use the geometric one. Simply put, what matters is the absolute angle of attack of the wing. If this value is positive, lift will be produced and level flight is possible, whatever the aircraft attitude.


Which countries allow pilots to fly over the age of 65 for International Part 135 Operations? The FAA does not have an age limit for pilots flying under Part 135 regulations, however ICAO specifies an age limit of 65 (with other restrictions after the age of 60).

The NBAA has a nice Age 60 Briefing which discusses this, but at the end they say:

  Most of the States that have authorized their pilots to fly as
  pilot-in-command in commercial air transport operations after they
  reach the age specified in 2.1.10.1 also authorize pilots holding a
  license issued or validated by another States to fly in their own
  airspace under the same condition.

  However, ICAO does not collect information on States authorizing
  pilots to fly in their airspace after reaching the age of 60 and
  cannot provide information on the subject. Pilots seeking such
  information must contact individual Civil Aviation Authorities.

Is there any resource available which covers which countries allow pilots to fly over the age of 65?  For instance, I know that Europe does not allow it, but that some others do.  I am particularly curious the countries close to the US, such as Canada, Mexico, the Bahamas, and those in the Caribbean, Central and South America.

Australia, Austria, Brazil, Canada, Costa Rica, New Zealand, Russian Federation, Senegal, and Ukraine

According to a 2006 ICAO report (mentioned also in this presentation) (emphasis mine),

  Nine States (Australia, Austria, Brazil, Canada, Costa Rica, New Zealand, Russian Federation, Senegal, and Ukraine) have no upper age limit, whereas fifty-five have an upper age limit higher than 60 years, ranging from 62 to 72 years.

This, of course, applies only to domestic flights, not international flights, as I imagine you have already read about:

  The ICAO Council adopted on 10 March 2006 an amendment to Annex 1 — Personnel Licensing that increases by five years the upper age limit for commercial pilots operating two-pilot aircraft, subject to conditions. The new provisions become applicable on 23 November 2006 and read as follows:

  2.1.10.1 A Contracting State, having issued pilot licences, shall not permit the holders thereof to act as pilot-in-command of an aircraft engaged in international commercial air transport operations if the licence holders have attained their 60th birthday or, in the case of operations with more than one pilot where the other pilot is younger than 60 years of age, their 65th birthday.

  2.1.10.2 Recommendation.— A Contracting State, having issued pilot licences, should not permit the holders thereof to act as co-pilot of an aircraft engaged in international commercial air transport operations if the licence holders have attained their 65th birthday.

Note that the ICAO typically gives constituents recommendations, not necessarily enforceable laws. Those are generally up to the countries themselves, which is why these nine are able to not have upper age limits.

I wanted some confirmation on the original list from something more recent, so I checked out a few sources. I was only able to find information for two.

Australia

From the Civil Aviation Safety Authority, it is noted that the ICAO age limits for pilot in command (PIC) and co-pilot are not relevant in Australian domestic flights, and seems to imply that age does not affect the ability to hold a pilot's license.

Canada

The best I could find was this article from The Globe and Mail, originally from 2009 but possibly updated in 2012.

  There is no upper age limit to acquire or renew a pilot licence in Canada - all you have to do is log the hours, complete the training and pass the medical exams, when necessary.


Why do F16's have anhedral tail wings? I just wonder why F16's have anhedral tail wings?

Is it kind of a design choice to increase maneuverability by compromising stability?

The purpose of the anhedral is to get the tail surfaces away from the wing wake. The distance between the wing's trailing edge and the horizontal tail is low enough so that the tail needs a vertical offset in order to have full dynamic pressure available locally.

Earlier designs moved the tail up for the same reason (Lockheed F-104, Grumman F-9F) until it became obvious that at some angle of attack some airplanes could get into a deep stall. Especially with the wider angle of attack range possible with swept, low aspect ratio wings no position above the wing's plane is safe anymore.

For that reason all modern fighter aircraft position the horizontal tail as low as practical. This in turn has led to situations where ground effect is so strong that other tricks had to be employed to get the airplane to perform as intended.

Stability is not affected, aside from a small positive contribution to the sideslip-induced rolling moment. This is easily compensated by adjusting wing dihedral properly. Or, in other words, the F-16 wing can have zero dihedral because the horizontal tail in combination with the ventral fins reduces the rolling moment of the vertical tail in a sideslip to the desired value.


How do airports generate "indirect" income? How do airports generate "indirect" income i.e. income from things other than aviation operations (landing, FBO services, repairs)?

One way to approach this question is to look at the annual budget for an airport. I'm going to assume that you mean a large passenger airport as opposed to one focused on serving general aviation, cargo, etc...

Let's use SFO (San Francisco International) as our example. It's a city-owned airport, so the budget is a public document. Here's the budget for FY2014/15 and FY2015/16.

Page 5 (page 7 in the PDF) breaks down major sources of revenue. We have some that fall into the category of "direct" revenue in your question: landing fees, terminal rentals, etc... under the "aviation" category. Some of the terminal rental fees include space for purposes you might not consider aviation uses, like back offices for airline staff We also have $60-80M in "PFC Revenue." PFC stands for "Passenger Facility Charge"; it's a charge that is added to the ticket price of everyone flying out of that airport.

Finally, there are the non-aviation revenues. The bulk of those come in two categories: parking and concessions. Parking is self-explanatory. Concessions describes all the independent businesses that operate at the airport. Many businesses lease terminal space for retail shops (including duty-free), restaurants and take-out food, lounges, currency exchange, etc... They all pay rent and/or a share of revenue to the airport based on the terms of their lease. SFO also books about $23M/year in revenue off the sale of electricity, as the airport sells electricity to its tenants (airlines, concessions, etc...). I suspect, but am not positive, that these electricity sales are a nice moneymaker for the airport, as it can purchase hydropower from the City at extremely low cost and resell it at market (utility company) rates to its tenants. This is a quirk particular to San Francisco however.

If you scroll through the detailed budget in the PDF, you'll find entries for other revenue categories. Examples include advertising fees (Clear Channel pays the airport to put up ads in the terminals and other areas), revenue for things like ATMs and baggage carts, leases to rental car companies, fees paid by taxicabs and airport buses for the right to access airport property, and even permit fees paid by filmmakers and photographers using the airport. Heck, the airport even charges the regional transit agency $3.2M/year in rent and custodial fees for the airport train station. Browsing through the budget should give you a pretty good idea where a large US airport can make money from non-aviation services.