Wing drop during stall

[shumway76]

What is the reason that there is a possiblity of a wing drop during a stall?

I can only think of 1 reason:
Left & right wings are not 100% same (though in theory they are supposed to be designed that way, but nothing is perfect), and also the airflow at left & right wing might not be the same due to sideslip or wind or some other force of nature, therefore the wings might stall at slightly different time.

Do I score at least 90%?

[bingofuel]

Yes you have got it correct.and you actually mentioned more than one reason.

A wing stalls because the angle of attack of the airflow to the wing exceeds the value where the airflow can stay smoothly attached to the aerofoil and becomes turbulent with a subsequent loss of lift. as you say, one wing may be rigged slightly differently, the aircraft may be yawing, or turning, there could be slipstream effects etc.

( I also note from one of your other posts you say you are a flight instructor, so you should be well aware of the reasons why!)

[BackPacker]

Even the left/right displacement of weight in the aircraft may make a difference. Reason why some side-by-side seaters show marked different flight characteristics when flying them solo. Fuel inbalance might also be a cause of this.

[Will Hung]

Let's not forget the prop. torque

[Genghis the Engineer]

There will be differences between the wings - nothing is manufactured perfect, flies do not die symmetrically on each wing (particularly given that the propwash is asymmetrically), the odds of managing exactly zero sideslip is roughly zero, lateral CG won't be exactly central, and there may also be a bit of asymmetry in the tail.

There are different types of stall, but if:

(1) The stall is marked by mainplane flow separation, and
(2) One wing, due to the asymmetries above stalls a significant time before the other, and
(3) The flow separation starts near the tip (rather than near the root).

Then you are likely to get wing drop at the stall.

G

[The500man]

Also some lift is still produced above the stall AoA, so any difference in AoA between the wings will generate some degree of uncommanded roll. Then the down going wing will have an increased AoA (less lift, more drag) due to the relative airflow and the up going wing will have a decreased AoA (more lift, less drag) which will perpetuate the initial asymmetry and set you up for a nice auto-rotation.

[Pilot DAR]

Airplanes must be flown, even through the stall. Therefore, you cannot "give up" maintaining roll and pitch control while you are stalling, and expect the plane to be perfect without your input. For all the reasons mentioned, both wings will not stall in the same way, at the same time. The prop and torque might be factors, if you have significant power applied during the stall, otherwise really are not.

The design requirements for handling and controllability prescribe tolerable amounts of wing drop and heading change, with normal use of the controls throughout the stall. I therefore suggest to you that the aircraft really does not have worrisome wing drop, if, during the stall, the pilot can control the aircraft with normal use of the controls and keep it within the attitude allowances. Do not lock the ailerons central, and expect the wings to stay level or rudder alone - normal use of the controls approaching the stall.

I have flight tested aircraft which, due to flaws with the aircraft itself, could not be controlled within the tolerances of attitude, no matter how much pilot effort went into the precision of the stall entry. One in particular, would spin half a turn every time. Those aircraft very certainly had wing drop, and were not compliant with stall handling requirements.

For certain aircraft, your first indication of a stall (though you already know you're close) will be a gentle and controllable wing drop. All Citabrias I have stalled come to mind.

You can spend a lot of time tweaking an aircraft to eliminate slight wing drop, and never get it. It's one of those things to learn to live with graciously as a pilot.

[rasti121]

Doesn't usually the same wing drops on one type of aircrafts? I always assumed this is cause by the air flow from propeller (maybe the torque too?), statistically speaking, manufacturing imperfections, wind directions, aircraft mass and CoG etc should be random and lead to 50:50 (or close to) wing drop distribution.

[flybymike]

OK I am in troll mode. Lets get cracking here.
You should always pick up a dropped wing with rudder.

[The500man]

Yes you should also go "Weeeeeeeeeeeeeeeeeeeeeeeeeeeee!" at the point of stall because that's the professional thing to do, and it gives your passengers much needed reassurance.

[Genghis the Engineer]

Yes, I've heard that too - I usually ignore such idiots beyond the point of making sure they don't have permission to fly any aeroplane that I own a share in.

Unstall the wings, then control everything else.

G

[bingofuel]

You should always pick up a dropped wing with rudder.

Or use rudder to prevent further yaw, as I am sure you know, using the rudder to yaw the aircraft in an 'attempt to pick up the wing' is just accelerating the down going wing, which may delay the onset of the stall slightly and result in a more equal stalling of both wings at the same time. Or if large rudder inputs are used may cause a spin entry in the other direction.

[Pilot DAR]

Or if large rudder inputs are used may cause a spin entry in the other direction.

Exactly. Been there, done that. The design requirements specify "normal use of the controls". It is not normal to control roll with the rudder, that's what the ailerons are there for.

In a few rare cases, I have seen flight manuals which state that the rudder is to be the primary control used during the recovery from a stall or spin - to the exclusion of the ailerons. This is because aircraft equipped the aircraft is equipped with spoilers, which go up with the aileron, and create undesired drag on that wing with large aileron.

So, if you're flying a certified aircraft, for which the flight manual does not recommend against the use of ailerons in stalls, you can, and should use them normally, to control the aircraft normally.

[Pull what]

I have seen flight manuals which state that the rudder is to be the primary control used during the recovery from a stall or spin - to the exclusion of the ailerons.

I always thought the elevator was the primary control that was used to recover from a stall or spin-looks like quite a few flight manuals need rewriting!

[The500man]

I don't think anyone would dispute elevator being the primary control used to unstall an aircraft, but when it comes to spinning, you as a pilot should read your POH as the recovery tends to be somewhat type specific. For example pro-spin aileron in a fighter jet can be sufficient to stop the rotation in a spin due to the adverse yaw generated.

[Pilot DAR]

elevator was the primary control

Well, yeah! I thought that we were past such basics by this point.....

That was the whole context, when I also wrote: "- to the exclusion of the ailerons." in the same sentence.

You don't work for EASA, do you PW?

[bookworm]

Also some lift is still produced above the stall AoA, so any difference in AoA between the wings will generate some degree of uncommanded roll. Then the down going wing will have an increased AoA (less lift, more drag) due to the relative airflow and the up going wing will have a decreased AoA (more lift, less drag) which will perpetuate the initial asymmetry and set you up for a nice auto-rotation.

Exactly. The difference between the unstalled and stalled regimes is that in the unstalled regime the aircraft is stable in roll rate (induce a roll with aileron, and the roll rate damps out). In the stalled regime, it's unstable, for the reasons 500man describes.

Blaming asymmetries between the wings is a little like saying "the ball bearing fell off the point of this pencil because this side of the point is slightly sharper than the other". Strictly speaking, it's true.

[DB6]

"Weeeeeeeeeeeeeeeeeeeeeeeeeeeee!" is almost obligatory .

[FANS]

Because each wing through its 30 year history is now very different!

[mikehallam]

An inauspicious, lop sided gust when crossing the hedge can spoil things too.

For light a/c a 'poorer' wing profile design could permit rapid transition from flying to stalled. The above case, may be a type leaning towards this area.
Not much fun if during the landing phase, which is a form of controlled stall.


mikehallam.