Does stall angle of attack in inverted flight change due to the camber of an asymmetric airfoil? What is the stall angle in an inverted flight configuration? How does it relate to the stall angle in normal flight?

As visible in the image below, in upright flight the lower pressure is on the extrados of the wing. In inverted flight the lower pressure is on the intrados.

(source)

The air stream separation at the stall will occur on a side with different characteristics. One could expect the stall will happen differently.

Equivalent representation, where the gravity is inverted and the wing orientation remains in the same direction. Flying inverted implies flying at a negative angle of attack.

The values taken into account are the airflow direction and the chord line, reflected in the angle of attack value.

As commented, while the two previous images suggest a wing in horizontal flight, the situation can be extrapolated to any stable linear trajectory with a negative AoA.

The horizontal plan or the pitch angle are not necessary to determine the stall angle (though they influence the stall speed).

Short answer: Asymmetric airfoils have different positive and negative stall angles, the largest absolute value of the two depends on factors like nose shape and camber. With positive camber (normal and utility aircraft), the negative stall angle can be the largest (in absolute values) but the maximum negative lift available before stall will be smaller than for the positive stall. Larger Reynolds numbers push the stall further away in both directions

It depends on the airfoil. With symmetric airfoils, the stall angle is the same for positive and negative stalls. Positively cambered airfoils (the sort mostly used) have their negative stall at a smaller absolute value of the lift coefficient compared to their positive stall, but the stall angle can well be at a higher absolute value.

Below you see a polar plot for a supercritical airfoil which I used for this answer. The positive stall angle of attack is 8°, while the negative one is around -10°.

Polar plot of the R2A airfoil at Mach 0.6 (own work)

The stall angle depends on details of the nose contour and the camber: Positive camber means that the zero lift angle is shifted to negative values, so there is some bias to negative values in the polar. However, if the lower part of the nose has very high curvature, it will create a high suction peak which leads to flow separation just aft of the nose already at a small negative angle of attack.

One extreme case would be the Göttingen 417a airfoil. Airfoiltools unfortunately plots only a range of Reynolds numbers suitable for model airplane enthusiasts, but the plot below should get the point across. The positive stall angle is 12° at the highest Reynolds number, while the negative stall angle is only around -8°.

Gö 417 lift over angle of attack. The lowest Reynolds number (blue line) is 50,000 and the highest is 1,000,000 (olive green line). Note that all curves are XFOIL predictions - real-world data might look differently.

Notice inverted flight is very rare in birds, which have heavily cambered wings similar to the GO 417.

It is important to remember that inverting an asymmetric wing, in simple terms, is reversing all that is good about the lift generation "right side up".  The result is a loss of lift at that speed and angle of attack.  Further more, there is a very good chance the stall angle of attack of the inverted wing is lower.

In the case of a heavily undercambered wing, inversion would likely be a disaster.  Wind tunnel/smoke would show heavy turbulence over the top and very little lift from pressure underneath the wing.  Notice the two great virtues of thin undercambered wings have been reversed.

On the other extreme, fully symmetrical wings show little difference when inverted and are popular in aerobatic aircraft.

The flat bottom will behave better than the undercambered, but when inverted will generate less lift at a given AOA and exhibit flat plate stalling characteristics (stalling at a lower AOA).

Amazing how much interest the movie is generating.  We'll have to give Denzel a symmetric wing, and Sully a good set of floats.


How does engine primer work? Does anyone have good resources on how piston-engine primers work?
Looking for literature, schematics, or better yet, videos.
I was told that in carburetor engines, it bypasses the carburetor and goes straight into one of the cylinders, but the I was told it goes through a different path in the carburetor.
Thanks in advance!

It's just a syringe pump that draws gasoline from the fuel lines where they pass through the cabin.  The outlet of the primer pump runs though plumbing that becomes a network of very small (usually copper) lines snaking around the engine to one or more cylinders, where it terminates at each cylinder in a small nozzle threaded into the intake port just upstream of the intake valve. This plumbing network is completely separate from the fuel system under the cowling with the gascolator, hoses and carb.
I couldn't find any handy schematics online, so I made a silly sketch.  My own airplane runs primer to 3 cylinders like this.  You can prime all 4 or sometimes you see primer line only to one cylinder (airplanes that don't see much cold weather).

When you stroke the primer, it's like you're a doctor injecting something into your patient, except instead of an unfortunate person, you are pumping fuel into those lines running to the cylinders and spraying a mist of raw fuel into the intake port just up from the intake valve.  The fuel spreads around and settles on the walls of the intake port and duct, and starts to evaporate.
The evaporating fuel provides the additional fuel needed, beyond the carburetor's supply, to make the mixture rich enough for starting and to keep the engine running for a bit while it warms up, and works for a number of seconds after starting before the excess fuel has evaporated (by that time the engine is able to sustain itself on the carb's fuel - aircraft carbs normally run a richer than necessary mixture for the idle circuit, to help them run better when cold).  In non-aviation engines, a choke is used on the carb, but aviation practice traditionally avoids adding potential intake blocking gadgets like choke plates.
The more strokes you pump, the more fuel coats the intake passage.  When it's cold outside, you need more fuel to give a longer evaporation time so that the rich mixture lasts longer, so more strokes are required, although obviously, not too much or you flood it.
The caburetor has an accelerator pump that squirts extra fuel when you pump the throttle as well, but this is to help an already running engine cope with sudden power demands when the throttle is opened quickly.  You can pump the throttle to get extra fuel for starting, they way you used to do in ye olden tymes with carbureted cars, but too much fuel just dribbles down into the airbox when you do that and it creates a fire hazard, so it's not a good practice.
Fuel injected engines are primed in a similar way but they just use the injection system itself to spray fuel in when you turn the boost pump on with the mixture rich.  In those engines you don't stroke a pump, but just put the boost pump on, put the mixture to rich, count a couple of seconds, then pull it back to idle cutoff and hit the starter.

I wasn't able to find any documentation for this, but I can just tell you what I know.
A carburetor mixes fuel and air together into a combustible mixture that's then fed into the cylinders via a series of intake valves. It needs a (small) pool of gas, which is kept topped off by the line from the main gas tank(s). If an engine sits for a while, that tiny little pool of gas will gradually evaporate or leak out. This makes it impossible to start the engine until the reservoir can be refilled.
So, to start the engine, you need to pump enough fuel into that reservoir, so that enough gas will reach the engine for it to run. This is what "priming" the engine actually means. There are several different ways to do this:

On planes with a direct-drive fuel pump, you can continuously crank the engine to pump gas into the carburetor, until enough accumulates for ignition. This procedure usually isn't recommended, because the starter can overheat or drain the battery if you crank it for too long.

On planes with an electric fuel pump, you can run the pump for a few seconds to prime the engine.

Many plane's throttles are designed to pump a small squirt of gas into the carburetor when the throttle is pushed full forward. So, on these planes, you can prime the engine just by moving the throttle back and forth a few times.

Some (mostly older) planes have a separate primer knob. This is just a small, manually operated gas pump that bypasses the mixture control.

Another option is to "choke" the engine. This does exactly what it sounds like, restricts the flow of air into the carburetor so that gas is drawn into it via suction.

If all else fails and you really need to get in the air, you can theoretically open the carburetor and just pour gas into it. I've actually seen this done to an old carbureted car.


Why would METARs and ATIS both report exactly the same wind direction? I understand that METARs report wind direction as true and ATIS reports it as magnetic. But at Camarillo (KCMA) both are reporting the same wind direction and speed even though the magnetic variation is 12.5 degrees. Why does the written versus spoken rule not apply here?

For the US
From the FAA ATC manual:

2−9−3. CONTENT

NOTE− [...] The ASOS Operator Interface Device (OID) displays the magnetic wind as “MAG WND” in the auxiliary data location in the lower left−hand portion of the screen. Other OID displayed winds are true and are not to be used for operational purposes.

Which confirms the ATIS winds are magnetic.
I just listened to KCMA ATIS, the wind reported is 10 degrees more than the METAR.
Make sure you match the ATIS and METAR times. On liveatc.net they were not the same, I had to check the METAR from aviationweather.gov to get the correct reporting time.

For Europe
It's not the same.
Both METAR and ATIS report mean wind information, for the direction, both report in true heading. ATC report is magnetic.

ATIS wind velocity is latest two minute average. The wind direction broadcast is given in degrees true.
[...]
ATC plain language ad hoc wind directions given during final approach or just prior to or during the take off roll are likely to be given in degrees magnetic.
— skybrary.aero

Here’s the info for ASOS.

VOICE MESSAGES
ASOS computer-generated voice message are made
available through telephone dial-in access and are broadcast directly
to pilots via ground-to-air radio (where installed). The information
contained in the ground-to-air radio broadcast message and the
telephone dial-in message are identical. The voice message is composed
of the body of the ASOS observation and selected remarks. Selected
remarks can include variable visibility, tower visibility, or Density
Altitude when 1,000 or more feet above airport elevation. Control
tower personnel may add Notice to Airmen (NOTAM) or other information.
Note that wind direction in the voice message is given in degrees
magnetic.

http://www.nws.noaa.gov/om/brochures/asosbook.shtml


Are the holes inside the engine nacelle used for uniform intake of air? I read the post here: What is the function of the holes in splitter plates?

My question is, what are those hole looking things inside the engine nacelle?

It seems reasonable to me that as air enters the intake slower air would accumulate towards the outboard portion of the engine nacelle due to the shape of the leading edges. You want the air to enter the blades uniformly so you could add these pinholes which would remove the slower moving air. This would lead to more even distribution of faster moving air and subsequently better engine performance.

Am I tracking correctly?

Edit: here’s another picture

They are for reducing noise emissions. According to Wikipedia,

  Liners are applied on the internal walls of the engine nacelle, both in the intake and by-pass ducts, and use Helmholtz resonance principle for the dissipation of incident acoustic energy.

The Helmholtz principle (Wikipedia again) can be watched (or rather heard) when blowing over a bottle which produces a sound.

  Helmholtz resonators are also used to build acoustic liners for reducing the noise of aircraft engines, for example. These acoustic liners are made of two components:
  a simple sheet of metal (or other material) perforated with little holes spaced out in a regular or irregular pattern; this is called a resistive sheet;
  a series of so-called honeycomb cavities (holes with a honeycomb shape, but in fact only their volume matters).

  Such acoustic liners are used in most of today's aircraft engines. The
  perforated sheet is usually visible from inside or outside the
  airplane; the honeycomb is just under it. The thickness of the
  perforated sheet is of importance, as shown above. Sometimes there are
  two layers of liners; they are then called "2-DOF liners" (DOF meaning
  Degrees Of Freedom), as opposed to "single DOF liners".
  (Wikipedia)


When should an Obstacle Departure Procedure (ODP) be used? Buried away in the front matter of the FAA charts is a section titled "IFR TAKEOFF MINIMUMS AND (OBSTACLE) DEPARTURE PROCEDURES".  Note that this is not a graphical departure procedure that is in with the rest of the approach plates.

Knoxville, TN (KTYS) contains the following departure procedure in that section:

  DEPARTURE PROCEDURE: Rwy 5L, climb heading 048°  to 3400 before
  proceeding on course. Rwy 5R, climb  heading 048° to 3500 before
  proceeding on course. Rwy  23L, climb heading 228° to 3500 before
  proceeding on  course. Rwy 23R, climb heading 228° to 3500 before
  proceeding on course.

Question: If I receive an IFR clearance along the lines of "*N1234, cleared to XXX as filed, climb and maintain...." and I didn't file any kind of departure, am I expected to fly the above ODP, and will ATC know what I'm doing if I do?  Does it matter if it is VMC or IMC?

According to the definition of the FAA it is a recommended procedure, so there is generally no need to follow it.

  OBSTACLE DEPARTURE PROCEDURE (ODP)- A preplanned instrument flight rule (IFR) departure procedure printed for pilot use in textual or graphic form to provide obstruction clearance via the least onerous route from the terminal area to the appropriate en route structure. ODPs are recommended for obstruction clearance and may be flown without ATC clearance unless an alternate departure procedure (SID or radar vector) has been specifically assigned by ATC. (Source: FAA Pilot/Controller Glossary)

According to FAR 91.175 you are responsible to ensure sufficient obstacle clearance if the airport is IFR (of course also if the airport is VFR).

  (f) Civil airport takeoff minimums. This paragraph applies to persons operating an aircraft under part 121, 125, 129, or 135 of this chapter.
  (1) Unless otherwise authorized by the FAA, no pilot may takeoff from a civil airport under IFR unless the weather conditions at time of takeoff are at or above the weather minimums for IFR takeoff prescribed for that airport under part 97 of this chapter.
  (2) If takeoff weather minimums are not prescribed under part 97 of this chapter for a particular airport, the following weather minimums apply to takeoffs under IFR:
  (i) For aircraft, other than helicopters, having two engines or less--1 statute mile visibility.
  (ii) For aircraft having more than two engines--1/2 statute mile visibility.
  (iii) For helicopters--1/2 statute mile visibility.
  (3) Except as provided in paragraph (f)(4) of this section, no pilot may takeoff under IFR from a civil airport having published obstacle departure procedures (ODPs) under part 97 of this chapter for the takeoff runway to be used, unless the pilot uses such ODPs.
  (4) Notwithstanding the requirements of paragraph (f)(3) of this section, no pilot may takeoff from an airport under IFR unless:
  (i) For part 121 and part 135 operators, the pilot uses a takeoff obstacle clearance or avoidance procedure that ensures compliance with the applicable airplane performance operating limitations requirements under part 121, subpart I or part 135, subpart I for takeoff at that airport; or
  (ii) For part 129 operators, the pilot uses a takeoff obstacle clearance or avoidance procedure that ensures compliance with the airplane performance operating limitations prescribed by the State of the operator for takeoff at that airport.

In this case it seems to be the easiest way to follow the ODP, but it's not binding.

Lnafziger  correctly commented that this is not applicable for part 91 operation. That's why I like to add a part of this Article, which I've found on the AOPA website, to my answer.

  [...] We cannot assume that ATC will assign any special routing or altitude based on the ODP. They expect the pilot to fly the procedure if necessary without further clearance. FAA Order 7110.65R, Air Traffic Control--the controller's handbook--states, "If a published IFR departure is not included in an ATC clearance, compliance with such a procedure is the pilot's prerogative." In other words, you have to decide whether you need to follow a specific route or procedure and fly accordingly. Now, we might think this is wrong, dangerous, and dumb, but it is the way procedures are arranged.[...]

According to all this information ATC would expect you to follow this procedure, at least in IMC. If you like to fly it in VMC and it does not disagree with your ATC clearance you are also welcome to do so. If there is any confusion I tend to ask and clarify the situation.

In most cases an ODP says that you should climb on runway heading at least until passing xxx feet before turning in a direction. I would always comply with it and if there is severe CAVOK and ATC then asks me to turn earlier, I would do it, so everyone is happy and on the safe side.

I'd recommend reading this link:
Obstacle Departure Procedures.
Seems to have the answer you're looking for: in short if you are IFR you must fly the ODP unless you meet one of the alternative requirements or ATC advises you otherwise.


Is it possible to fly a B-24 under Bixby Bridge? If that sounds like a ludicrous question it's because I believe it is, but here is why I'm asking.

My grandfather flew B-24s in WWII and there was something of a local legend that he once flew a crew-laden Liberator under Bixby Bridge (near Big Sur along the CA coast). Here is a short video of the bridge:

I say no way. Aside from the the idea of a trained military aviator so recklessly risking crew lives (not to mention court martial, etc.) straining credibility, I think such a feat is physically impossible for an aircraft of that size. But then, I'm not a pilot - I just pretend to be one on X-Plane. I have relatives (also not pilots) who are convinced the story is true. Those of you who fly IRL, what do you think?

Unfortunately my grandfather passed before I was born so short of breaking out the Ouija board there isn't really a convenient way to ask him!

A Liberator has  wingspan of 34m, while the central span of the bridge is 110m wide, and 280ft high, so the aircraft will fit under the bridge.

Bixby creek approaches the bridge from the north-east, with a straight-ish approach of about 0.3miles. Approaching low from the north-east, and dropping down into the creek at the earliest opportunity might allow even a Liberator enough time to descend below the level of the bridge deck and recover over open sea, although the waves might be a little too close for comfort.

I wouldnt want to attempt it in a fully-laden B-24, but with a light fuel load and crew I'd say it's doable. Whether anyone ever did it is another story...

Possible? Yes.

Smart? No.

Legal? Probably not now, may have been then (paraphrased as "need to maintain 500 foot clearance from things unless landing").


How do I know my AGL altitude while in flight? I am about to start my PPL, still flying in my FSX.

I have a question, let's say I am flying from airport A to airport B. Both airports are in G airspace and I would like to stay in G airspace and don't go over 1200' AGL to class E. Let's say I would like to fly at 1100' AGL and keep this altitude from A to B. And let's assume we are in un-congested area, so we do not violate minimum safe altitude rule. But I do not understand if terrain in uneven, I mean its elevation is constantly changing, how do I keep my altitude 1100' AGL. I don't have radio altimeter like in Boeing. I understand that at the airport you can get your elevation, also you can have minimum safe altitude from sectional chart and also you can find any obstructions, but how do I know in a middle of my flight (if I need to).

If this question sound stupid and pilot don't fly in G airspace please let me know.

You can't know with 100% accuracy, even radio altimeters have limitations, and if you're flying on a PPL the aircraft probably wouldn't have one anyway. The VFR pilot flies with a map which shows the height of the highest terrain and noteworthy landmarks, but unless you are directly over one of these it is a matter of your experience in judging vertical distances.

I'm not sure if it's different wherever you come from, but where I fly in Australia, all airspace is measured in sea level altitudes or flight levels, never in reference to ground height, so we would never encounter your situation. Trying to stick to one height AGL might sound like a fun challenge to some but to me it sounds like less time to save my life when the engine quits.

You should be able to use the Quadrental altitudes on a VNC chart. That is all you need to determine your 3000 ft AGL for direction of flight. If u are in mountainous terrain it can be quite high


Do any aircraft carry spare parts for making repairs? I was curious to know, are there (or were there) any aircraft that regularly carry spare parts to be used for replacement or repairing the aircraft itself? If so, what are those spare parts?

I'm not talking about built-in redundant systems like a second radio, but rather actual physical spare parts. For example, a car carries a spare tyre.

South African Airways flights to 'less developed' locations in Africa often carry a mechanic and some spares on board. If there are no suitable repair facilities, supplies or maintenance personnel available at the destination, then their own guy can fix any minor mechanical issues. If there's a major problem then they would have to fly in additional repair supplies and staff (and fly out the stranded passengers).

I found this out on a flight from Johannesberg to Lilongwe (Malawi). A seat was broken in the passenger cabin and SAA's on-board mechanic was able to fix it after a short delay. The captain explained briefly why he was on board.

I assume that other airlines or operators who operate in undeveloped areas would do the same. It's a lot cheaper to carry a mechanic and a few spares than it is to have an aircraft, crew and passengers stranded. If anything on the MEL is broken then an airliner isn't airworthy so even a 'minor' issue can ground it.

I guess that the military might do the same for similar reasons, but I have no idea at all about that.

Google '747 5th engine'.

The early days of the 747 program did not have spare parts readily available at remote locations.  The 747 was originally designed to externally carry a 5th engine under the left wing in the event one 747 had to ferry an engine to a grounded 747 somewhere remote.


What are the dynamic stability properties of an aircraft with wings exactly at the vertical CoG? Please ignore for a moment the practical issues with building and operating an aircraft like this.

Suppose a fixed-wing aircraft which, when viewed directly along the roll axis, has the wings centered exactly at the vertical center of gravity. Suppose that this aircraft is in stable, level flight in otherwise still air. (Yes, this is a little like the spherical cow in a vacuum from physics.)

If there is a disturbance, such as a localized updraft or downdraft affecting one of the wings more than the other, then broadly speaking and as I understand it so far (feel free to address this if I've got it completely backwards), after exiting the disturbance and with no further control inputs, a high-winged aircraft will tend to return to neutral roll (dynamically stable) and a low-winged aircraft will tend to increase its roll angle further (dynamically unstable), as a result of the differences in localized airflow above and below the respective wings.

However, what would be the behavior in such a situation of our hypothetical mid-winged aircraft that I described above?

My hypothesis is that the aircraft would maintain its roll or bank angle, which (unless compensated for, say by rudder input) in turn will result in a rotation along the yaw axis and a subsequent turn.

Am I right or wrong? Why?

It is a common misconception that the vertical CG position (relative to the wing) plays a major role in roll stability. It doesn't; it's mostly about aerodynamics. (You mention it yourself in "as a result of the differences in localized airflow...")

There are other important factors at play as well: dihedral angle, wing sweep, design of the vertical stabiliser.

Presumably, you are interested in the behaviour of an aircraft with the perfectly neutral roll stability. If so, it needs at least these conditions:

General symmetry about the horizontal plane, which includes:

Zero wing dihedral;
Symmetric (e.g. round) fuselage;
Wing at the centre of fuselage (vertically);
Symmetric vertical stabiliser (e.g. with dorsal fin);
Absolute rigidity so that the symmetry remains under load.

Zero wing sweep (straight wing);
Lack of any artificial stability augmentation.

(Technically speaking, the geometric symmetry is not necessarily required: we can compensate one effect with another, say, wing sweep with anhedral. But in the spirit of the original question, let's assume the full symmetry).

We should also assume a reasonable stability in pure yaw.

So, if you induce a pure roll disturbance and then remove it,

the aircraft will start rolling.

Because it has some inertia about the roll axis, it will not simply stop when you remove the disturbance. The only force that will counteract the roll now is roll damping. It naturally occurs because the descending wing has higher angle of attack (and vice versa). The strength of the effect depends on the square of the wingspan, but in theory the spherical cow will keep turning forever, albeit with ever-diminishing speed.

So far, nothing would induce a yaw, and the airflow would still be symmetric.

However, as roll develops, and the aircraft keeps the same pitch balance, the lift will become insufficient to keep it level. The usual thing happens:

the aircraft enters a spiral dive.

Now, this is not a symmetric situation anymore. There is a side force from gravity; sideslip will develop; the aircraft will yaw due to its yaw stability that we assumed. Things start to get complicated (that is, 'normal'), with many variables involved. Even in the vertical plane, despite postulated symmetry, the shadowing and other cross-flow effects on the top and bottom of the wing will be different (the wing, by definition, cannot be aerodynamically symmetric when it generates lift), and thus some roll effect may be observed.

So it's hard to predict further behaviour in general. At one extreme, with stubby wings and slender body and very strong initial disturbance, the aircraft may barrel roll many times and may even enter a peculiar stable roll motion due to inertia coupling. At the other, the aircraft will just roll a little and will enter a gentle (nearly) coordinated turn with very slight descent.

In order for an aircraft to return to neutral roll the shape of the wings is an important factor as well and a number of other aerodynamic factors will play a role. A positive V-shape for example always helps to return to neutral. Furthermore wings are sometimes also designed to bend under load too which will have the same effect as the V-shape.

But if cows are spherical I would say your hypothesis is right. On high-winged aircraft the leverage of the lower wing when the aircraft is banked is longer than that of the upper wing resulting in a torque in the opposite direction of bank; resulting in a decrease of bank angle. If the wing is placed on the center of gravity the leverages of the forces on both wings would be equal regardless of bank angle and thus the total torque would be zero; the bank angle would stay as it is.


Do you have to lubricate the shock strut? I have a school report about the lubrication on the shock strut and I was wondering if there is a specific type of lubrication they apply it on.

This is for Cessna 150-152

Oleo struts and brakes used on light aircraft use MIL-H-5606H hydraulic fluid (the red stuff) as the internal damping agent/lubricant (be sure to check the manual anyway). It's a normal practice to clean the exposed chrome of the shock strut (it should be done with the tail held down to extend the strut all the way) with a clean cloth, then wiping it with a cloth with a little bit of 5606 to leave just a very light film to help lube the scraper and seals the next time the strut compresses (once that's done there is the film of internal fluid left behind by the seals).

The biggest enemy of oleo struts is silica particles (which are very hard) from outdoor dust which sticks to the chrome surface because of the fluid film left behind by the internal seals.  The silica collects in the seal cartridge and acts like lapping compound, accelerating wear (this is why desert operations are the toughest environment overall on any airplane).

As the strut ages and the seals wear and slowly start to leave behind more fluid each time the strut extends, dust collects faster and the whole process speeds up, so the strut should be kept clean as much as possible depending on how dusty the local environment is.

If it's your own plane, you should learn to do the published procedure yourself, because nobody else is going to do it between annuals.  If you're renting the plane, that's the owner's problem, and you just do your normal walkaround inspection.

By law, the FAA requires the POH to provide basic servicing instructions and approved lubricant. The exact information provided depends on the year of aircraft, older aircraft having less information (the FAA became stricter over time).
See: C150 POH Manual

For the C150-152 the Pilots Operating Manual (POH) provides all necessary basic maintenance information in two places - "Servicing Intervals" and "Servicing Requirements" (I'll leave it upto you to see if the nose strut is applicable).

There is a fundamental rule all teachers and instructors tell new or potential pilots, "... READ THE MANUAL!"

I am an A&P and Pilot. By FAA law the POH must provide the proper servicing lubricant type - READ THE MANUAL. The information is located on the next to last page of the manual I cited! It is against the law to use any lubricant not approved by the mfg or FAA. Motor oil is commonly wiped on the strut but unless there is a SB (service bulletin) from the mfg that is not legal.

The FAA prohibits the unauthorized mixing of dissimilar brands or types of lubricant except for motor oil (By law, motor oil must be able to be mixed). In this case the POH provides the authorized lubricant to be used on the strut.


What should a pilot do when facing a sudden tail, cross, or head wind? Consider a pilot is flying a conventional fixed wing airplane with a ground speed of 60km/h with no wind. Then suddenly the wind starts blowing at 20km/h in either of the following directions:

from back to front (tail wind).
from front to back (head wind).
from left to right (cross wind).

What should the pilot do to maintain speed and altitude in each of the possible situations above?

Many people stress energy and airspeed management, this is a good example.

Sometimes a strong gust can reduce airspeed faster than your engine can increase it.
The sudden tail wind gust is very dangerous near the ground. Increase throttle and pitch down. Use your potential energy plus the engine thrust to maintain airspeed.  Wind conditions found in microbursts can create this effect.  Constantly check airspeed.

A strong headwind gust has the opposite effect, causing a momentary increase in airspeed, and increase in altitude.  Rarely a problem, keep an eye on airspeed as the gust passes, continue to use pitch and power to control airspeed and altitude as needed.

Side gust effect will affect your heading much more than speed and altitude, as it's velocity change does not add or subtract from airspeed.  Effects here could include a sharp roll initially away from the gust, and the nose being pushed into the wind from side force on the empennage. A stable plane should mostly self-recover without significant loss of altitude.

The mantra "the plane just moves with the air mass" does not apply to gusts.  This is why pilots generally approach at slightly higher airspeed under those conditions.

On encountering a sudden tailwind or crosswind gust on par with the previous airspeed, the pilot should immediately deploy the ballistic parachute to avoid crashing.  With an equivalent headwind gust, pulling up into a loop to dissipate the excess energy is often the best strategy.


What considerations should be taken into account for landing on gravel airstrips? For the pilot of a Cessna or Piper 4 seater, what techniques and other considerations should be given before operating on a gravel/dirt airstrip?

Standard soft-field landing and take-off techniques work on dirt, gravel or grass. The differences are more in ground operations, and even then they aren't really big differences: it comes down to being aware of what's around you and what condition the surface is in. That includes taxi and parking areas, not just the runway.

With gravel, the main risk is damage to the aircraft (especially the prop) or nearby people, vehicles or objects caused by gravel being thrown up by the prop. With dirt, you're more likely to have to worry about drag or even getting stuck, especially if the surface is wet.

Some specific considerations for gravel are:

If you're parked on gravel, be careful where the aircraft is pointed when you start up. You don't want to spray some unfortunate person, vehicle or building behind you. Re-position the aircraft before starting up if you have to, and you could also brush gravel away from the prop.
For the same reason, pick your runup spot carefully
Keep back pressure on the controls all the time while taxiing, to keep the prop as far away from the surface as possible. Don't feel you have to taxi in a straight line: taxi wherever the gravel is lightest and the surface is smoothest.
Open the throttle smoothly for takeoff or runups to avoid suddenly throwing up gravel

Dry, well-packed dirt usually isn't much of an issue (apart from visibility), but wet dirt - i.e. mud - is potentially tricky:

If conditions are very dry then you can throw up a lot of dust. That may not be as dangerous as spraying gravel around, but it's still unpleasant for anyone nearby and there is a safety risk if people can't see you or other aircraft/vehicles because of it.
If conditions are wet then there's a risk of getting stuck in mud. Once you're moving, try not to stop unless absolutely necessary. Consider doing a 'rolling runup' if you're confident you can do it safely (practice on tarmac first!).
Calculate your required takeoff roll carefully and know exactly where you have to abort. Mud will create a lot of drag, and you don't want to push your luck on what is most likely a short runway.
If you take off from wet dirt you'll leave ruts behind you. When the dirt dries out those will still be there, and they could be a hazard to other aircraft using the runway (some dirt becomes very hard when it dries). Try to find someone who can smooth them out after you depart.
If you do get mud on your aircraft, clean it off if at all possible before taking off. As well as decreasing performance, it could clog up pitot-static ports or otherwise affect airworthiness.

Gravel and dirt are two totally different things. Gravel can damage or ruin a propeller. With gravel you normally try to take off as gradually as possible, rather than ramp it up to full throttle immediately. Also, you do not do the run up on the gravel if at all possible.

With dirt or grass you do what are called soft field take offs and landings. This should have been covered in your instruction. If you have a pilot's license and do not know how to properly take off on a grass strip then something went wrong.


Would it be feasible to develop a dirigible-based refueling station for fighter aircraft? The impossibly bad 2005 film Stealth featured a dirigible-based, mid-air refueling tanker station for the stealth fighters to use.

At first, this seemed like it might have been the singular good idea in the film as a dirigible would have a very long loiter time making it ideal for fighter refueling.

But I don't think it's possible, right? What is the maximum known air speed of a dirigible vs. the lowest possible air speed for a tactical fighter?

(Note: I do think it'd be possible for helicopters and osprey to use a dirigible tanker, right, as their stall speeds can be essentially zero?)

What is the maximum known air speed of a dirigible vs. the lowest possible air speed for a [stealth] fighter?

Airship fastest speeds

According to Guinness the world record speed for an airship was 70 mph by Steve Fosset in 2004.

Guinness also say

  The large rigid airships built by the USA and Germany in the 1920s and 30s could reach higher speeds (up to 140 km/h or 87 mph according to some sources), but these were never officially measured to FAI standards.

Stealth aircraft slowest speeds

The F-117 has a landing speed of 180 mph.

The F-35B is stealthy and can hover.

You mean a dirigible as in lighter-than-air aircraft?

So it has a long loiter time - it has to get the load up there
A lighter-than-air aircraft is not designed for a payload

Nitrogen is about 5.4 liters per pound
Hydrogen is about 0.4 liters per pound
A 10,000 lb payload is a balloon about 40 meters across

The problem is once you get it up there and dump 10,000 lbs of fuel you have to get is back to the ground.
Release a bunch of hydrogen to get it back to the ground is not exactly an ideal situation.  Hydrogen is combustible and not cheap.

10,000 lbs is about one fighter.
100,000 lbs is about 10 planes and now 80 meters in diameter.
100 planes (1,000,000 lbs) for like a mid Atlantic fuel station would be 170 meters in diameter. It just does not seem realistic to me. If it is big enough to get the load up there it is less than stealth.

The cost of the hydrogen to float jet fuel cost more than the jet fuel itself.  Hydrogen is fuel and is going to have at a minimum fuel cost.  So robokaren it is produced by (simple) electrolysis of water.  The water is cheap.  The energy to separate the hydrogen is the cost of energy and energy is not cheap.


Where can I find a canonical list of sources for worldwide digital GA VFR maps? Related question: Where can I find GA VFR maps for Australia?

For various areas of the world, where are authoritative General Aviation VFR maps, charts, and so on available on the web?

This answer is a Community Wiki. Please edit as appropriate.

Australia

OzRunways.com

United States

VFR Charts from the U.S. Federal Aviation Administration

The short answer is the most of the world is not covered very well, not even on paper charts.  Operational Navigation Charts (ONC) are available for most of the world, but they're not approved for navigation.  That said, if there's nothing else available, an ONC chart plus GPS can still be useful.


Is the elevator really an 'angle of attack control' as described in Stick and Rudder? I've been reading Wolfgang Langewiesche's book Stick and Rudder and am a little confused about the definition of the elevator as the "Angle of Attack Control" or rather, the idea that each position of the elevator corresponds to a unique angle of attack.
I was under the impression that Angle of Attack is the angle the wing meets the relative wind. Consider a certain elevator position for straight and level flight at cruise rpm. If I then add power and climb (while holding the same attitude) isn't it true the Angle of Attack will increase because the relative wind is now coming from in front and above the plane? If this is true, then how can I reconcile this with the idea the elevator is an "angle of attack" control. Isn't the plane's Angle of Attack based on not just the position of the elevator, but the motion of the plane through the air?
If anyone could give me some advice to clear this up it would be greatly appreciated!

Wolfgang Langewiesche is right to appropriate order of approximation. For every elevator position a statically stable airplane settles to a specific equilibrium angle of attack. That's how static stability works.
Airplane is statically stable if and only if increasing angle of attack causes higher increase in coefficient of lift on the aft airfoil (tail for normal layout). Then increasing angle of attack (by random fluctuation like turbulence) increases the lift aft more, the overall centre of pressure moves aft and the aircraft pitches nose down to return the angle of attack to the trimmed position.
By moving the elevator you adjust the coefficient of lift on the control surface, and the plane needs to assume a different angle of attack to shift the centre of pressure back to coincide with centre of gravity. Most aircraft are designed so this is quick enough that if you don't jerk the controls too much the angle of attack simply follows the elevator position.

isn't it true the Angle of Attack will increase because the relative wind is now coming from in front and above the plane?

The angle of attack is high when the relative wind is from below and low when it is from above.

If I then add power and climb (while holding the same attitude)

If you add power and leave the yoke as trimmed, the plane will start to accelerate, which increases the lift. That causes the plane to accelerate upward, which decreases the angle of attack. This decreases the lift more on the tail, so the tail sinks and the aircraft pitches up until it assumes the original angle of attack. At this point, the pitch angle is increased by the same amount as the flight path angle.
The aircraft is still moving faster than the original speed due to inertia, so the lift is still more than weight and the aircraft continues accelerating up and pitching up to maintain the angle of attack. When the speed returns to the trimmed, the aircraft is already pitched too much, so now it will slow down and pitch down again and repeat the cycle. This is called the Phugoid oscillation. In most planes it is damped, but still annoying if you don't counter it with a bit of elevator deflection. But if you don't touch the trim, just arrest the phugoid, the aircraft will settle in climb at the same speed.
It has some consequences:

Tendency of the plane to pitch down means it is losing airspeed.
If you are not pulling on the yoke, or trim aggressively nose up, you won't stall. Unfortunately pulling on the yoke to keep the nose up becomes too much of a muscle memory so it's easy to miss this clue.
It is how pitch for speed and power for descent rate works on descent.

See also How It Flies, specifically section 2.3 talks about trim and angle of attack, with more details further in chapter 6.

Your understanding of AoA is correct.  While the elevators do influence AoA they don’t control it, so you’re right that a particular elevator position doesn’t correspond to a particular AoA.  You example is flawed though - if you increase power to climb then your AoA might not change at all, or not significantly.


Between a helicopter and an airplane, which requires more power to fly, for a given TOW? For the given same mass (say it 400kgs), which one requires more power (in HP) between helicopter and airplane? Say that both are designed maximum (the required material are considered during design) to minimize the required power.

Edit: Question should be like this: Which one is requires more power to lift a helicopter (to make it hover) and to make a fixed wing airplane fly? Not to make them move at the same speed.

Airplanes fly by creating lift from their wings. This causes some drag, but good wings have lift/drag ratio's in the range 15-20. That means the lift-dependent drag is only 5% of the lift. Helicopters on the other hand generate lift directly from trust; there is no multiplier involved.

E.g. a 4000 kg plane will have a weight of 40.000 Newton, so the drag incurred will be 2000-3000 Newton. A 4000 kg helicopter will need to produce 40.000 Newton of lift just to hover.

Of course, planes and helicopters both have additional drag from forwards airspeed, and for planes this is obviously unavoidable to prevent stalls.

General rule of thumb with heavier than air craft is the bigger, slower lifting surface with less interference is more EFFICIENT at converting available power into lifting and/or propelling force.

The helicopter blade has greater efficiency in creating thrust compared with a propeller (see V-22 Osprey),  but the wing is far more efficient at creating lift,  therefore the Cessna 150 requires less POWER to create the same amount of total FORCE (lift and thrust).

You will notice this works for monoplane vs biplane (less interference),  propeller vs fan (much less interference), hi aspect glider vs low aspect speed plane (more efficient wing),  2 bladed helicopter vs 8 bladed helicopter (less interference), bird vs airplane (slower "propeller")

Thrust Force = Power x Efficiency

You will notice birds propel and lift more like helicopters.  Yet they are MORE efficient than the Cessna because their PROPELLERS are proportionally larger and slower.  But we do not see 400 kg birds or 800,000 lb Cessnas because NET thrust is what actually moves the aircraft.

A less EFFICIENT jet has much more power, so much more thrust is available, albeit with more fuel consumption per pound of thrust produced.

Finally, force required to "make the aircraft hover"  and "make the air plane fly"  really is comparable!  One must simply realize in both cases it is FORCE vs DRAG.  So, for direct comparison, they both need to be at flying speed.

POST EDIT - RESPONSE TO COMMENTS

For the benefit of @ MSalters and @ AirCraft Lover an examination of units is in order

F = ma kg m/seconds squared

Now the equation for Power = F x velocity = kg m/seconds squared x m/second

This is an unfortunate corruption of James Watts original weight lifting work with horses (origin of "horsepower") and should read:

Power = massxgravity + massxacceleration to reach speed and Power = massxgravity at constant speed F=ma=weight being lifted. Force vectors are ADDITIVE. Air drag and pulley friction are negligible. (Watt knew to take only the first meter)

Notice distance has NOTHING to do with POWER! (I'm sure football players struggling at the line of scrimmage (Thrust vs Drag Superbowl) appreciate this).

Let's fast forward to the THRUST curve of an Estes C6-0 model rocket and viola! That is what James Watt's horse is doing!

So we can think in terms of thrust, lift, drag, and gravity as ADDITIVE forces (much easier), and better yet, break them down into vertical and horizontal components!


What frequency should be used for air-to-ground communication other than airport ground operation? On a VFR flight, what frequency should be used to talk to somebody on the ground in USA?

In another word, if I am overflying my house and I would like to talk to the people on the ground, what frequency should I be using? Is it even legal to do something like this?

Radio frequencies in the USA are assigned by the FCC, not the FAA. There's no 'private' air-to-ground frequency mentioned in the AIM but section 4-1-11 does say that the FCC has assigned 122.900 as a MULTICOM frequency for:

  Activities of a temporary, seasonal, emergency nature or search and
  rescue, as well as, airports with no tower, FSS, or UNICOM

Arguably your fly-by is "temporary activity", however the definition of MULTICOM is:

  A mobile service not open to public correspondence used to provide
  communications essential to  conduct the activities being performed by
  or directed from private aircraft

So if your fly-by is "essential" (and safe!) then I guess you could use 122.9. There are procedures for requesting temporary air-to-ground frequencies for air shows, but that's obviously a special case.

As for legality, it seems that you need an FCC license to use an aviation handheld radio on the ground:

  You may only use your hand-held aircraft VHF radio in your aircraft
  under the terms of your aircraft license. You are required to have a
  separate Ground Station license to operate your radio on the ground.

But because this is more about FCC regulations than FAA ones, I suggest that you ask on ham.SE; they'll probably know a lot more about how it all works.

Some people use "fingers" 123.45 for non-standard radio communications. I don't think it conflicts with any existing radio stations and its legality is in in doubt. Sometimes you will hear on a busy frequency "BOB! FINGERS" which is never acknowledge either by the intended recipient or by ATC, but it means t come up on 123.45


What aircraft is this flying near Greenford? I live in the suburbs of London in Greenford (near RAF Northolt Base) and today I heard a droning sounds which, albeit from my limited experience, sounded like a propeller plane. I checked my generic flight radar application on my smart phone, no result. I then checked the ADS-B tracking website which identifies most military aircraft that aren't flying covertly but, again, no result.

I did manage to take a picture of the aircraft and it looks like a small passenger turboprop plane - so any ideas about what aircraft this is and why it wouldn't be showing up on any radars? It does not seem like a stealthy fighter jet by any means.

Spy planes!!! Looks like I found an answer after two years when I came across a blog called 'secret bases'.

"Keen MI5 spy plane spotters should continue to lurk around RAF Northolt. A company formed by former elite RAF pilots, 2 Excel Aviation, actually based at Sywell Aerodrome, Northamptonshire, is now performing those spooky Northolt tasks, as part of its Scimitar special projects team.

They are using Piper PA31 Navajo aircraft "G-SCIR" (ModeS 40729C), "G-SCTR" (ModeS 40029D) and "G-SCMR" (ModeS 40729E) — all registered to 2 Excel in February / March 2017. They joined regular "sneaky-beaky" craft "G-UMMI" (ModeS 400C86) which is regularly spotted with special communications equipment attachments.

All three RAF Northolt Piper Navajo PA31 craft had been purchased by 2 Excel from Mike Jones Aircraft Sales Inc in Murfreesboro, Tennessee, America, who specialise in Colemill Panther conversions for performance and safety boosts. G-SCTR previously carried registration mark N331DB. G-SCIR had been supplied with tail number N522AW and G-SCMR had previously carried N27773.

Military aviation enthusiast Alan Warnes blogged on the subject in August 2017 on his Warnesy's World website, but strangely he only noted two out of the three Piper Navajos and missed G-SCIR. Curious, as the three registrations all took place at the same time – February / March 2017.

The London Evening Standard's Business Pages reported on my findings in an article headlined "Lift Off: Home Office privatises MI5 spy plane operations"."

This a piper pa-31 navajo cdg 23b, g-scir.
It flies from doncaster everynight to patrol over the english channel. On the look out for migrants coming from calais. Ive been tracking it for the last 2 days. There is also a fixed wing drone patrol which takes off and lands back at llyd airport. Nothing top secrect im happy to say. The circle people are saying they see underneath is camera with infared and nightvision just like they have on the police helicopter.


What's preventing aircraft manufacturers to record every single possible value in FDRs? The preliminary report of the ET302 crash included some data from the Flight Data Recorder. However, the position of the trim cutoff switches is apparently not among the recorded values.

Given that storage is so incredibly cheap nowadays compared to the price range of an aircraft, why don't manufacturers decide to record every single possible sensor value (including all switches in the cockpit) into Flight Data Recorders? Is this a purely economic decision to not do too much more than required by regulations? Or is there some other reason for it?

I'm not an expert on FDRs, but I do have experience of hardware and software development in a regulated market (medical devices), so might be able to offer some insight.  Here are a few considerations that occur to me:

Development cost:  Adding storage to a FDR isn't like installing new DIMMs in your workstation.  As well as the design work, the changed device must undergo new verification and validation cycles, the supply of the new components needs to be assured, and the manufacturer must continue to support existing products as well as a new one.  The V&V may well include accelerated-life testing and other expensive activities; it's unlikely to be just a few days' work.
Customer demand: Aircraft operators require an FDR that satisfies regulatory requirements; it's a "tick-box item".  Consequently, that's the requirement that aircraft manufacturers demand of their FDR suppliers.  If there's no demand for extra storage (either for an extended loop time or for a greater number of sensor inputs), then there's no money to be made by offering that as a feature.
Interface limits: I don't know enough about FDRs specifically, but the input interfaces may well have a bandwidth limit which precludes providing more readings without providing further connectors (which then has a big impact on development costs; see above).

Because storage is the easiest thing to add. What you think should be easy actually requires monitoring for every single switch and device, which would add a lot of weight and complexity. In aircraft accident investigations, switches don't usually move from their positions during and after a crash. That is why there is no value in adding that to the FDR dataset.


A320/321 FMA indications with Both Flight Director Channel Failed I hope that someone can answer my question. My friend had “FD 1+2 Failure” in simulator during the low visibility approach. Flight Directors on PFD disappeared, but no FMA change and no approach capability downgrade. When a go-around was executed, lateral and vertical guidances of FMA went blank (SPD/ / ).
On the next approach, he captured G/S and LOC with both FDs failed, but no ROLLOUT indication after touch down.
Anybody can explain the logic behind this?
Thank you.

On the A320, the FAC takes commands from the FMGC to compute the FD bars. The FD bars and  certain FMA annunciations and speeds are provided to the DMC for display on the PFD.

Your FD loss scenario is a partial FAC failure which is why AP continued to work, since the FG function of the FMGC was operational, but the FMA annunciations are faulty. Yaw control is also a function of the FAC which affects ROLLOUT.

See Airbus Safety First Magazine 23 for a similar scenario: the aircraft was operating with an ADR channel disabled under MEL, encountered windshear causing discrepant AOA measurements, the FACs only had two measurements so they tripped off causing the crew to lose FD, characteristic speeds, and FMA.


Is falling a mode of flying? I frequently observe people arguing (on this very web site) about the question if falling is a mode of flying or not. It appears to me that the majority of people have a strong opinion that it is not.

Surely it is a matter of definition. I made the effort to look it up in a number of online dictionaries. Most sources provide many possible options to define flight, like Merriam-Webster:

  1a : an act or instance of passing through the air by the use of
  wings

but it continues with

  2a : a passing through the air or through space outside the earth's
  atmosphere

Wikipedia tried to put everything into one paragraph:

   Flight is the process by which an object moves through an atmosphere (or beyond it, as in the case of spaceflight) without contact with the surface. This can be achieved by generating aerodynamic lift associated with propulsive thrust, aerostatically using buoyancy, or by ballistic movement.

Flight may be aerodynamic, propulsive, aerostatic, or ballistic.

When one throws a ball, the ball is flying. It flies until it hits anything else than air. Why would it be different if the ball is thrown upwards, or pushed downwards, or just dropped?

In my understanding, falling is just a very special case of flying. Is this correct?

Since falling is just the final result of a ballistic arc if you let it go long enough, and ballistic arcs are considered "flight" per the Oxford Dictionary (as in the ballistic arcs of balls, spacecraft, arrows, etc being considered "flights"), then technically, a falling object is in flight.

You could give it just the tiniest lateral push when you drop it so it goes down with a slight ballistic curve;  in the end, no different from driving it laterally so it has horizontal energy/inertia with a high velocity that exactly counteracts gravitational pull, and give it a vacuum so it can do that indefinitely - a satellite - , the only difference being that and the ball being the location in or out of the atmosphere and energy put into it.

In other words, orbital vehicles, baseballs, bullets, are all "falling" and are technically in flight, and so is a ball you drop straight down... if the Oxford Dictionary definition is what you want to use.

In my own airplane, if I push over with just the right elevator input, and go zero G, my plane is now in a ballistic arc.  The wings are superfluous, for a few seconds anyway, and my plane is "falling", just not straight down.  So if you accept that in that condition it is still "flying", the falling is flight.

What is the definition of falling? Downward component to trajectory? Ballistic trajectory? Zero motion in horizontally forward direction? Zero aerodynamic force acting perpendicular to flight path, i.e. zero lift?  Vertical speed component negative and increasing rather than steady-state?  A non-zero acceleration component acting perpendicular to the flight path and also acting at least partially earthward, not skyward?  (I.e. semi-ballistic trajectory due to insufficient lift.)  Or something else?  We can't answer without knowing which we mean. Some have suggested that if an aircraft is sinking at a constant rate but the nose is pointed above the horizon, then that is in some sense a "fall". Many would not agree.

Is an orbiting spacecraft "falling", according to common sense?  And how about according to your chosen definition of "falling" from the list above?  It's not so simple to define "falling", is it.  Is the earth "falling"?  Is the earth "flying"?

Implicit in this answer, is a hint that the question may not be a very useful one, because it is insufficiently constrained.  But this may shed some light on possible answers nonetheless.


What does the term "trimming" most commonly mean in aviation? Why does an airplane need trim, and what does it do during the flight? Does an autopilot adjust the trim automatically?

In short: trimming neutralizes the force required to keep control surfaces in a specific position.

Most (if not all) aircraft have some sort of elevator trim control. For example, when the pilot has to keep pulling back on the yoke/stick during a climb, trimming "nose-up" will neutralize that force. The elevator will then remain in the same position without any force required on the part of the pilot. Trimming is usually done by means of a Trim tab on the control surface and is controlled by a trim wheel.

Elevator trimming is used:

During climbs: to maintain a constant air speed and rate of climb
During descents: to maintain a constant air speed and glide path
During level flight: to maintain altitude and speed

Although elevator trim is the most common, trimming can also be done on rudder (quite common) and ailerons (only on larger aircraft).

Rudder trim is used to maintain coordinated flight without rudder input by the pilot. Many single engine planes with powerful engines require rudder trim to offset the "left-turning tendency" caused by P-factor and propellor wash hitting the rudder. Aircraft without adjustable rudder trim will usually have a fixed trim tab on the rudder.

Most autopilots will control the elevator trim wheel because the servos controlling the elevator could easily be overpowered by the required force.

It's important to note that in most cases (especially on small airplanes) trimming doesn't actually move the control surfaces. It changes the force required to deflect the control surfaces. Although there are many types of trimming devices, the common trim tab makes the airflow do all the work. The trim tab causes the airflow to push the control surface in a specific position. On larger aircraft with hydraulically operated control surfaces, trim tabs are less common (see also this answer to another question)

Say you have trimmed an Aircraft than forces on aircraft i.e Lift == Weight & Thrust == Drag. So aircraft is flying (straight and level) or climbing or descending at constant speed or rate(of climb or descend).

Simple to remmember, Trimmed Aircraft means Lift = Weight and Thrust = Drag thats it.

There are lot of way to trim an aircraft: Trim Tabs on control surface, complete surface moves to trim corresponding control surface (ex: stabilizer moves in response to pitch trim command) etc.


Why do most commercial aircraft have their fuselage over the wing, instead of under? Almost all commercial jets today seem to have the fuselage/cabin mounted above the wing, why is this? why isn't it mounted under the wing like some freight airplanes?

Examples of above and under?

The related post, What are the pros and cons of high-wing compared to low-wing design?, does not address the passenger airliner related aspects.

Large commercial aircraft have low wings to stow away their long landing gears. Long gears make it possible to stretch the fuselage and still be able to rotate during take-off. Stretching makes it possible to tailor one basic design to a wide range of sizes, lowering the price of a single aircraft.

Large high-wing aircraft with their low fuselage position are easier to load and unload, at the price that the fuselage taper has to start shortly aft of the landing gear, so no stretching is possible. The military doesn't mind and prefers the high-wing variety. That Lockheed likes to stretch their transports (C-130, C-141) anyway is the exception that proves the rule.

Only turboprop-powered civilian aircraft may have a high wing, so there is more space for the propellers and the landing gear can be made short and light. Still, both versions exist. And the ones where the engineers did not know how to attach a jet close to the wing.

Aerodynamically a mid-wing position would be best. This is used when the payload is compact and needs little space, or is hung externally. In bombers, in other words.

In terms of stability and control both configurations are equivalent.

https://www.aircraftintel.com/article/view/high_wing_vs_low_wing_airplanes

Some Considerations:

High wing: easier loading
Low wing: structurally simpler
High Wing: Engines are farther from potential debris
Low Wing: Can have shorter landing gear (contra: B-24)

https://upload.wikimedia.org/wikipedia/commons/thumb/a/a3/Eurowings_bae146-300_d-aqua_arp.jpg/1920px-Eurowings_bae146-300_d-aqua_arp.jpg

https://commons.wikimedia.org/wiki/B-52_Stratofortress#/media/File:Boeing_NB-52A_with_X-15_No.1(SN_56-6670)_061219-F-1234S-001.jpg

I have to disagree with the stretching disadvantage to high wings:
https://upload.wikimedia.org/wikipedia/commons/thumb/e/e6/C-141A_C-141B_comparison.JPEG/1920px-C-141A_C-141B_comparison.JPEG


Do any countries besides the USA accept Basic Med? Are other countries accepting Basic Med for flights through their airspace, for example the European Union?

(I've made this a community wiki answer so that others can add new information if/when things change.)

These countries allow US pilots to fly with BasicMed:

The Bahamas
Mexico (from 10 Dec 2019)

It wouldn't matter, as BasicMed is only valid for flights within the United States.

Q23: Can I fly outside the United States under BasicMed?
A: No. You cannot fly outside the United States when operating under BasicMed.


What is the difference between a propeller and a rotor? I have been making the mistake of using words "propeller" and "rotor" interchangeably when they are not the same thing. What is the difference between a propeller and a rotor?

Short answer:

A propeller is used to propel something, the force at stake being called thrust. Thrust is usually horizontal (but not always, think about rockets). This device comes from the navy domain.
A rotor of a rotorcraft is used to control anything, including the altitude, the generated force being called lift. Lift is generally vertical (but not always, think about a rudder). Rotors have generally more than two blades.

Lift and thrust involved are components of the same physical force (the aerodynamic force) to which we refer to differently based on their purpose after an arbitrary breakdown based on the direction they act (compared to the direction of the aircraft or to the gravity field).

For our pleasure, let's also talk about a turbine rotor, which is a rotor/propeller which doesn't produce lift or thrust, but convert the fluid velocity (actually momentum) into torque. For example the wind turbine rotor. A turbine rotor is certainly a propeller, but we don't refer to it as a propeller, as it propels nothing.

Rotor is the most generic name for something spun by a shaft. It can be used for a propeller, the rotating wing of an helicopter, the rotating elements of a compressor or a turbine, etc. You can't be wrong using rotor for any spinning device. Rotor (rotating) is the antonym of stator (stationary). These terms are not specific to aerodynamics, in a electric motor there is usually a stator and a rotor as well.

The rotor of a rotorcraft comprises blades and is comparable to a propeller, if we except blades additional freedom in flapping and leading-lagging to limit vibrations created by repeated force swings encountered while performing a 360° turn.

Source: Wikipedia

But actually the main rotor is a (rotating) wing, and the anti-torque rotor is a (rotating) rudder. Their blades are meant to produce lift like the wing and the rudder they replace. Because lift is involved, we tend to name them rotors rather than propellers.

A propeller also comprises blades, fixed on the rotation axis.

Source.

The purpose of a propeller is to propel the aircraft, that is to push it in the direction of its flight.

Both a rotorcraft rotor, a propeller and a wing create the same aerodynamic force. However the conventions are:

A rotor and a wing are used to eventually counter weight and control altitude, and a propeller to eventually counter drag and control velocity along the flight path (I say eventually because to gain altitude you usually temporary increase thrust, that's a detail)
A rotor and a wing create lift, a propeller creates thrust.

Wing, propeller blade and rotorcraft blades work exactly the same from an aerodynamic standpoint. The resultant of their action is the total aerodynamic force, which is then broken down arbitrarily into lift, drag, thrust and torque to facilitate mechanical analysis.

Notes:

Moving an aircraft along its path (thrust) is easier than maintaining its altitude (lift), and therefore a main rotor is far larger than a propeller for aircraft of the same mass.
The horizontal displacement of the rotorcraft is also produced by the main rotor (cyclic control), so some part of the aerodynamic force can also be seen as thrust, and the rotor also acts as a propeller.
Propeller is used for simple propellers and not in turbine engines. While the fan of a turbofan is comparable to a propeller, participates to thrust production and aircraft propulsion, the fan is still only one part of a system (guide vanes, fan duct and exhaust nozzle greatly maximize final thrust). Bottom line the fan is a rotor, not a propeller.

Propeller is getting lift from the wing and thrust from the propeller but helicopter gets both from the rotor.
propeller aircraft can not hover over a spot but helicopter can.
Propeller aircraft can not perform vertical landing but helicopter can do.
Propeller blade is pre-twisted but helicopter blade are symmetrical.
Propeller aircraft has two hard/re-enforcing point such as: Wing root and Engine mount but helicopter has only one hard point that is "ROTOR MAST" and more differences are there.


Why do propeller blades not have winglets? On the first look this question might sound ridiculous and maybe it is.
But as propeller blades act by the same physical laws as wings, and winglets reduce the induced drag by quite a bit, then why are they not put on propeller blades?

I could imagine that it might be a material problem. But are there any more reasons? And why exactly might it be a material problem?

Winglets on wings help because they increase the volume of air on which the wing can act. Extending the wing span would be much more efficient, but when span is restricted or the maximum wing bending moment is limited, winglets bring a small improvement in efficiency at high lift coefficients.
On propellers, however, the winglets would run through air which is already affected by the tips of the propeller. No additional air will be involved, so no efficiency increase will be possible. Please note that propulsive efficiency is increased by accelerating more air by a smaller amount. The formula for the propulsive efficiency $\eta_p$ of an air breathing engine is
$$\eta_p = \frac{v_{\infty}}{v_{\infty} + \frac{\Delta v}{2}}$$
where $v_{\infty}$ is the speed of the inflowing air and $\Delta v$ the speed increase of the air affected by the propeller disc. A smaller $\Delta v$ acting on a higher mass flow makes the engine more efficient. This effect is most pronounced when $v_{\infty}$ is low.
The prop tip winglets would operate in a region of high dynamic pressure and generate more friction drag without contributing to the prop's efficiency.
Things become different when the propeller blades have a very low aspect ratio and there is a hard restriction on propeller diameter: This is true for ships, where draught puts a hard limit on propeller size. Here a sort of winglet does indeed help: The Kappel propeller has its tip bent forward and increases efficiency by 3 - 6 percent. Given that marine propellers even for large ships have efficiencies between 50% and 60%, this is a noteworthy increase in efficiency.
By the way: Whoever tells you that winglets reduce induced drag quite a bit has something to sell to you, but I digress.

The same reason why there are no winglets on gliders. The majority of propellers tips are small & pointy enough that there is a negligible spillover to cause wingtip vortices that makes the wing inefficient. Prop blades with wide tips like the ones in C130's  or Huey helicopter blades may be improved with winglets but such design also adds complexity(cost), weight and forces that may impede the reliability & safety the blades.


How exactly do ICAO's VOR-based minimum separation standards work? This question is aimed at Air Traffic Controllers who are familiar with ICAO Separation minima.  DOC 4444 states the following:

  Lateral separation between two aircraft exists when: VOR: both
  aircraft are established on radials diverging by at least 15
  degrees and at least one aircraft is at a distance of 28 km (15 NM) or
  more from the facility (see Figure 5-4)

Note that i have highlighted the word "diverging". The only example given here is when two aircraft are flying away from the VOR (diverging).

Q#1. In this scenario the VOR is located at the airport. Two aircraft are departing that airport, when the leading aircraft is 15nm or more from the VOR on radial 020, the following aircraft is laterally separated when he flies on radial 035. Is this correct?

Q#2 What if both aircraft are less than 15 nm? How many degrees of separation must there be in that case?

Q#3 What about when one aircraft is flying away from the VOR and the other one is flying towards the VOR? AC1 is flying away from the VOR on R015 and is 20nm from it at FL060 . AC2 is flying towards the VOR on R030 and is at 25NM descending through FL060. Are these two aircraft separated?

Q#4 Same scenario as mentioned above, but AC1 is 10NM from the VOR and AC2 is 20NM from the VOR (same radials and levels as mentioned above).  Are they separated?

Q#5 What if both aircraft are flying towards the VOR? AC1 is flying to the VOR on radial 010 maintaining FL200, 30NM from the VOR. AC2 is flying to the VOR and is at FL210 35NM from it on radial 025. Does this mean that since you have at least 15 degrees on the radials, that AC2 could continue its descent through FL200?

Also are there any sites,videos, other manuals or resources that have a better explanation on ICAO separation minima (other than DOC 4444)?

Exactly. As long as the aircraft are diverging (i.e. flying away from the VOR), one of the aircraft is at least 15nm away from the VOR and both are at least 15 degrees (radials) apart, the separation is achieved.
You cannot use VOR separation with less than 15nm distance. The other option that can be used is "geographical separation", ref ICAO Doc 4444 5.4.1.2.1.1.
As they are still more than 15 nm away from the VOR, I would say yes. There would need to be however a certain restriction in place for the inbound aircraft to cross 15 DME (or preferably much before to have some margin) at FL50/5000ft or below, to ensure separation.
Yes. As far as one aircraft is 15nm or more away from the VOR, the separation is ensured. The photo in your question nicely depicts this, as it shows that only one (the furthest) aircraft has to be 15nm or more away from the VOR.
Yes, but you would have to ensure that they are vertically separated before the last inbound aircraft reaches 15nm from the VOR.

For VOR separation ...both aircrafts to be outbound...one on 020 and other on 035..is ok but one aircraft must be at 15nm or more from the facility..the desired separarion (lateral) cant be achieved if both aircraft are less than 15nm from facility


Why are primary and supportive instruments in instrument flying different depending on the phase of flight? For example, in straight-and-level flight, the power's primary instrument is the Air Speed Indicator (ASI), and the supportive are the engine instruments.

In another example, straight constant-airspeed climb, the primary are engine instruments, and the supportive is the ASI.

Why does the primary instrument change?

Because during certain maneuvers, certain instruments provide more relevant information to a pilot than do others.

In straight and level flight, the heading indicator provides more relevant bank information as it tells you whether your current bank attitude is maintaining the desired heading.  The altimeter is providing the most relevant pitch information as it’s telling you whether your current pitch will maintain the correct altitude.  The airspeed indicator is the best indication for your required power as it’s telling you if the current power settings will maintain the desired airspeed.  Other instruments provide supporting information.  Here in straight and level flight the attitude indicator provides good supporting bank and pitch indications, the VSI provides supporting pitch information, etc.  Supporting instruments change to primary instruments in certain maneuvers and vice versa.

And, incidentally, in a established constant airspeed climb, your primary for bank is the heading indicator and your primary for pitch is the airspeed indicator.  Primary for power is either the tachometer, manifold pressure, torque, or fan speed gauges, depending on the aircraft you are flying.  Typically you would set to maximum continuous power in a light airplane for this situation.

"Why can't we use just one as a primary instrument?" -- sometimes we can.  I've seen video of a Cessna 120 being flown in cloud with all gyro instruments covered up.  The pilot's hands were not touching the control stick or throttle.  The airspeed, tachometer, altimeter, and vertical speed indicator (if present) were not covered up, but they might as well have been.  The aircraft was trimmed for a controlled descent in fairly smooth air and emerged from the bottom of cloud layer about 5 minutes after the video started.  The magnetic compass was obviously being used as the primary instrument.  Steering corrections were accomplished by using the rudder pedals to bank the plane slightly via the "dihedal effect" created primarily by the aircraft's high-wing configuration. Don't try this at home unless you understand what heading to use, and why.

This whole business of classifying instruments into "primary" and "supporting" is rather subjective and arbitrary.  Who gets to decide that the "in straight-and-level flight, the power's primary instrument is ASI", rather than, say, the tachometer?  Maybe a lower-than-expected airspeed in level flight is caused by ice on the wings, or by the pilot forgetting to raise the landing gear, rather than by poor engine performance.


May a student continue a discontinued checkride if the CFI who endorsed them voids that endorsement? The Situation
CFI Charlie endorses Student Sara's logbook for a checkride. Sara begins the checkride but discontinues, and receives a letter of discontinuance. So far so good.
Before Sara can reschedule the rest of the checkride, she and Charlie have a disagreement. Charlie has access to Sara's logbook and voids his endorsement by crosshatching the entire text of the endorsement before giving it back to her.
The questions

Is Charlie's endorsement actually considered void?

Sara has the letter of discontinuance in hand. Can she reschedule and complete the checkride without getting a new endorsement?

The test was discontinued. No reason the DPE would be looking in her logbook as a discontinuance is simply a pause in the testing process. She was eligible to test, she remains eligible to test. If she already told the DPE about this the smart DPE would make a note in her test records explaining what occurred. Once endorsed the applicant is endorsed. If the CFI wants to "revoke" her endorsement I believe it's too late.

The examiner won’t be looking at the endorsement but will look at whether Sara has received the required re-training.

§61.49   Retesting after failure.

  (1) The necessary training from an authorized instructor who has
  determined that the applicant is proficient to pass the test; and

  (2) An endorsement from an authorized instructor who gave the applicant
  the additional training.

Before the test a new IACRA form must be submitted and signed by an authorized instructor.

The crossed out endorsement is moot. The issue she faces is whether a new instructor would be willing to endorse her for the checkride after just giving training for the failed portion, or whether they would require more from her.


What are the barriers to feasibility of stratospheric cruising for commercial air travel? (i.e. Concorde?) In 2003, British Airways retired the Concorde for a few reasons.

Rising maintenance costs
Lack of demand due to safety concerns
Further decrease in demand due to 9/11 attacks

additionally, due to lack of competition, the Concorde was never properly maintained. Because no other airline had such a plane, British Airways kept the analog cockpit from 1970 up until the planes retirement.

Well, we live in a world where safety in aviation is continuing to increase, and the technology we have to utilize the world around us constantly gets better.

What engineering breakthroughs will allow commercial aviation to use the upper atmosphere and supersonic cruising speeds?

--EDIT--

I don't mind if you downvote my question, but it certainly annoys me if you downvote and you don't leave a comment telling my why. I've tried to make this question as objective as possible, if you're going to take the time to downvote, take the time to explain yourself, and I would be happy to try and mitigate your concerns.

I would argue that the Concorde was from the beginning economically unfeasible and instead served as a prestige technology for the British and French governments. Even the name Concorde, indicates that the two governments working together to produce the aircraft seemed the most important aspect of it.

Both British and France at the time had completely nationalized airlines and almost all their major aviation companies as well. Americans were going to the moon so Britain and France were looking around for a prestige technology of their own. Bigger and faster airplanes had been the rage for twenty years so the Concorde seemed like a cool thing to do. The Soviets came to the same conclusion.

In the US, civilian airline development was still wholly private so when when Boeing , Douglas et crunched the numbers they saw little value in supersonic transport with  it's non-linear cost. US supersonic transport never made it off the ground, but in Europe, the politically driven Concorde did because the people making the decisions weren't paying the bills.

As noted by others, the Concorde was essentially a military aircraft, produced by political compromise with the primary goal of expressing the technical powers of the governments involved. It was more an art project like building the Pyramids than it was a piece of mobile transportation infrastructure.

Edit: (May 14, 2014)

Some sources on the economics of the Concorde:

The Atlantic August 1977:

  Already Britain, and France spent £1.46 billion \$2.3 billion to reach this  (and a London political economist has recently argued that
  the true cost is roughly  three times this amount)...

  ...In May 1976, Professor David Henderson, newly appointed professor of political  economy at University College, London, argued
  that the government's figure of  £1.46 billion shared between Britain
  and France was a drastic underestimate.  It had been reached by adding
  the yearly expenditure on the project at the current prices.  If these
  were adjusted to 1975 prices, and interest charges of 10 percent
  added, then  the cost of Concorde was not £1.46 bilion but £4.26
  billion (\$6.82 billion at the  present exchange rate of \$1.60).

That would be $22 billion US (2014 dollars.) Just to get the thing into the air.

They built 26 of the aircraft, 20 of which that actually flew paid flights. So, around 1.1 billion per plane, roughly the cost of a B2 stealth bomber. I can't find any hard numbers on operating cost but with 1.1 billion per plane sunk capitial cost, it's clear it would never operate at a total profit.

I believe the plane only flew for 20+ years because the British government essentially gave it away, eating the billions of in development and deployment cost and leaving the plane to just have to cover operating cost. I'm not clear that it even really did that.

Considering how much money was thrown at the problem, not particularly elegant or interesting.

Edit 02:

In rereading the parent, I realized I didn't make my answer explicit to the original question. He wanted to know what it would take to bring a Concorde like plane back.

My answer was really just saying, "the Concorde itself had no economic foundation so firstly, you'd have to find an economic niche for SST."
There was never an economic demand for the Concorde's speed of travel and there doesn't seem to be one now, either.
Technologically, you'd probably need something hyper radical like a nuclear powered air spike so the plane wouldn't burn tons of fuel and could fly over land masses without sonic booms or destroying smaller aircraft. (Seriously, it would have to be that advanced.)
In our current luddite era, it would be saner to think about inventing anti-gravity drives than think that the political regulators would let that type of radical technology fly, even if it existed.

Could it happen? Yes. Anything could happen.
Is there a realistic chance of it happening at some point in the future? Yes, quite likely, if there's an incentive to develop the technology that would make it economical.

Is that moment likely to arrive during my lifetime? I seriously doubt it, especially given the lead times for such projects which are measured in decades, and I don't have centuries to live (which suggest of course that I don't envision the technology that makes such an aircraft economically feasible to become available within the next few decades).

There's no theoretical reason to assume that supersonic air transport can never be achieved. We know it's possible, it has been done. In fact it has been done several times.
Concorde, Konkordski, there was even (or so I've read) plans to create a transport version of the B-58 Hustler at some point, think a supersonic VIP and priority cargo transport for the US Air Force. There was an attempt to create a supersonic business jet by Sukhoi that was abandoned (I think) a few years ago. So we know it's possible, it's just not economical.
But who knows what may become economical in the future? If there's a large enough group of people who value their time more than the price of admission, there's a market. Right now that market isn't there, but it might emerge (the death of Concorde may have led to an increase in sales in long range business jet, if aviation laws get stricter, making it harder to use those, those owners might once again get interested in buying tickets on supersonic airliners and start asking airlines and governments, and aircraft manufacturers, to look into building them).

Or maybe there will be some revolution in aircraft design that makes it so cheap to build supersonic airliners that it just makes no sense to build anything else.

Of course that's all theoretical. There's no crystal ball anyone can look into and say definitely whether it will happen or not. But it might.


Where's the A318 on the runway that caused a 747 to go around? I screenshot 1:00 of a 480p YouTube video. The autopilot proclaims Minimums at 1:01, and the pilot flying decides to go around at 1:02 because an A318 was still on the runway, but I can't spot it, or any airplane, on the runway in the video! Can anyone? Or does anyone possess this video at a higher resolution?

Look for the blinking light in the center of the runway
That's the strobe lights of the A319. It's all you can see of it in the video.  I had to step frame by frame through the video to capture a frame where it was visible and another frame where it wasn't.

Sorry for the turbulence.  :)

As other's have noted, there are strobe lights just about visible on the centre-line, but the go-around wasn't specifically because this crew saw the other aircraft on the runway. They went around because they hadn't been cleared to land by the time they got to "minimum's" (the decision point whether to land or not). At about 0:28 they were told "you're traffic's just touching down, continue for runway niner" - so they've been told to continue the approach, but they don't have permission to land. As soon as the other aircraft cleared the runway, the controller would have specifically said "cleared to land". But they got to "minimum's" first, so without clearance to land, they have to go around.


At what exact point in time should we be giving the 10 minutes to diversion call to ATC? I wanted to get some clear information if it’s available as to which exact point should the 10 mins to diversion call be given to ATC with respect to our FOB. The way I have been doing it currently on the A320 is by looking at the FUEL PRED page and when that shows a time value equivalent to 10 mins I give the call to ATC. But this is not a very reliable way to do it while in a HOLD. As the FMGC only updates the extra fuel and time value after crossing the waypoint/PPOS/pseudo waypoint at which the hold has been inserted.
This 10 mins to diversion call is mainly given while flying in India to let ATC know that we only have 10 mins worth of extra fuel left for holding beyond which a diversion will have to be initiated to our filed destination alternate.
Is there any precise way to calculate when we will exactly be at 10 mins?

(I just came up with this, so it may not be the official solution - but it should be fairly simple this way)
You first need to know the fuel you need for the diversion with all safety requirements included. This is computed like normal using the MCDU, EFB, etc.. I'll call this your "bingo" fuel. You just need to add the fuel required a 10 minute period for your current flight situation. Once your FOB on the upper ECAM reaches that final result, call ATC.
The easiest way to compute the fuel required for the next 10 minutes is with the fuel flow indication.
On the engine display you have the fuel flow indication, which should be nearly constant during a hold at constant speed and constant altitude.

Add all fuel flow values together
Round up to the nearest 20 kg/hr or so to be safe
Then divide the total fuel flow by 6 (10 min = 1/6 of an hour) to give you fuel required for a 10 minute hold at the current conditions.

Example:
Let's say each of the two engines shows a fuel flow of 1000 kg/hr. Add together to get 2000. Then divide 2000 kg/hr by 6 to get roughly 340 kg fuel consumption for the next 10 minutes. Add this to your bingo fuel.
( 1000 + 1000 ) / 6 = 333 -> 340 ... (+ bingo fuel)
Quicker Alternative:
You could also take the higher of the two engine fuel flow values and divide by 3. Then round up:
1000 kg/hr divided by 3 = 333 kg -> 340 ... (+ bingo fuel)
Note: This works the same if you have fuel flow in pound per hour. The result will be in pounds of fuel required for 10 minutes.

I think it would be mostly your discretion on when you decide to divert. I don't really get your question, but I think what you mean is at what amount of fuel should you request a diversion and notify ATC. For this, it depends on the plane model, weather condition, and
much more.

For this example, let's say we're in a 737 approaching Toronto Pearson. We've just previously had two go arounds, and we'realmost on emergency fuel, with 40 minutes of fuel left. If the weather is clear, and you feel comfortable with the approach, you should probably notify ATC, but there is no reason to divert. On the other hand, if the weather is not clear and/or you don't feel comfortable with the approach, you can divert to another airport that you feel comfortable with or the weather is better there. , and if the weather's good, you can simply just declare an emergency and change runways.

If you divert, you should probably go to an airport that 1. is close to your current location (15 minutes away at tops) 2. has good weather and an easy approach, 3. meets your aircraft requirements. If you were at YYZ, the airports that you could divert to include Hamilton, Downsview, and if you've got enough fuel, you can try crossing the lake for Buffalo or Niagra. And if all 3 of these options are not able, you'll have to perform a ditching in the lake.

And as for the ten minute diversion call, it simply means when you have 10 minutes of fuel remaining + the emergency fuel. If you're at this stage, you MUST declare an emergency and divert if the weather or approach is not showing mercy.

I know this was a very complicated and long answer, but since we're all in quarantine, I figured we could all use up some more time. Hope I successfully answered your question, and I'm sorry no one else did.


Could flaps be raised upward to serve as spoilers / lift dumpers? I should preface that I'm by no means an aviation person. I'm just in a aircraft knowledge obsession phase and daydreaming about designing my own ultralight (will never happen).

The idea would be to simplify and lighten a small aircraft using the flaps as spoilers. As a practical example, the same handle could be used in one movement to get from flaps raised just before touchdown to spoiler raised just after it, making it fast and intuitive.

Basically you would have on a single axis :

high lift + high drag <-> normal lift + low drag <-> low lift + high drag

Is that possible? I guess not because I couldn't find anything like that, but why?

I name them flapoilers.

The Fairey-Youngman flaps seem to do that but all I could find as explanation is "so that the aircraft could be dived vertically without needing excessive trim changes" and I'm not sure how to understand that.

One reason is that any device you want to use as a lift dumper needs to be able to be instantly retracted and this is really difficult to do with a flap.  On an airliner when the lift dumpers come up, if you slam the thrust back up to TO, they immediately come back down.  A flap system with its slow moving drive line can't do this, and it's enough that it has to be retracted from landing to takeoff setting for a balked landing like that.

Plus, even in a normal landing, you would be landing with the flaps at the landing setting, and when you touch down they would need 10-20 seconds a typical drive system would need to move up past 0 to a fully up position.  You'd be stopped by then, and deciding to take off again on the rollout is out of the question.

So you can see that any system like this would require flaps that can move up and down rapidly like ailerons.  A really difficult engineering problem.

You might do this on a small airplane with manual flaps operated by a lever, but now you have to cater to twice the movement range as regular flaps, and you'd lose the mechanical leverage you'd need for manual flaps to work unless you made the lever move twice as far (by say having it move in a 180 degree arc - but now the lever handle is in the back seat).

Lots of gliders use flaps - without any spoilers - and they can in most cases be "reflexed" up a small amount, but this feature is done only to unload the trailing edge region for high speed running which has an effect similar to reducing wing area  and pitching moment to reduce both induced drag and trim drag.

For approach control and landing, they actually do the opposite of what you would think; you drop the flaps down to near 90 degrees when you want to come down steeply and for the landing roll.  Not everybody likes that kind of system because you have the same problem - you can't bring them up and down quickly like spoilers so you can't work the flap lever like a throttle on approach the way you normally do with regular spoilers/dive brakes, and they require different flying techniques, on which a pilot used to spoilers needs to be carefully briefed to avoid trouble.

Why upwards? They don’t dump much lift at the back of the wing. They do increase drag and reduce wing area a bit, like when deflected fully downwards, where they are much closer to after touchdown.

Re the design in Peter Kãmpf’s answer


When was the first THS (Trimmable horizontal stabilizer) used and on what aircraft? When was the first THS (Trimmable horizontal stabilizer) used and on what aircraft? Has any UL or GA trimmable stabilizer?

If the question is understood to encompass any form of horizontal stabilizer which may be adjusted in flight (with or without a separate movable elevator), then the answer would appear to be Sir George Cayley's 1849 full-sized glider which briefly took flight-- see http://www.flyingmachines.org/cayl.html.  The Wright brothers also used all-moving horizontal surfaces on their early gliders and airplanes, but located in front, as canards.

However, a comment has clarified that the question is meant to only encompass a horizontal stabilizer which may be adjusted for trimming the aircraft, with an attached elevator for pitch control inputs.

According to page 9 of the book "Aces Wild" by Al Blackburn (see this Googlebooks link), the first use of an in-flight-adjustable horizontal stabilizer was in 1929 by Clarence Gilbert Taylor in his B-2 "Chummy", which eventually evolved into the Taylor Cub and then the Piper Cub, all of which used the same stabilizer trim system.  Naturally, all these aircraft featured an elevator attached to the adjustable horizontal stabilizer.

The same source says that many old Waco biplanes used the same feature.  In this photo of a 1936 Waco biplane, the slot associated with the adjustable horizontal stabilizer is clearly visible.

The THS (Trimmable Horizontal Stabiliser) is just the Airbus name for the elevator trim. In Boeing planes it's called Stab trim. All planes have a trim on the elevator: the differences you can find is whether the trim rotates the whole elevator or only a small surface in it