Ailerons Initiating The Spin

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pelmet
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Ailerons Initiating The Spin

Post by pelmet »

They say that the aircraft will roll in the direction opposite of the aileron input when stalled. This video seems to prove it.....twice.

https://www.youtube.com/watch?v=IUDS3QuUWls
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Re: Ailerons Initiating The Spin

Post by digits_ »

pelmet wrote: Wed Dec 02, 2020 5:56 pm They say that the aircraft will roll in the direction opposite of the aileron input when stalled. This video seems to prove it.....twice.

https://www.youtube.com/watch?v=IUDS3QuUWls
That's a dangerous generalization. By that logic, you could use aileron in the direction of the spin to recover from it.

The crux of the matter is that during a spin entry or stall, especially an inadvertent one, you do not know what the effect of the aileron will be. It depends on which wing is stalled, if any, and how much the wings are stalled.

It is definitely possible that an aircraft can roll in the direction opposite of the aileron input. Saying that it will do this, is incorrect.
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Re: Ailerons Initiating The Spin

Post by photofly »

I imagine it rather depends on the airframe. The POH for the Grumman Tiger appears not to agree with "them", because it has this to say about stalls:
Screen Shot 2020-12-02 at 8.46.32 PM.png
Screen Shot 2020-12-02 at 8.46.32 PM.png (47.79 KiB) Viewed 1454 times
I can confirm it has excellent roll control with ailerons through a whole range of stall scenarios.
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Re: Ailerons Initiating The Spin

Post by digits_ »

photofly wrote: Wed Dec 02, 2020 6:51 pm I imagine it rather depends on the airframe. The POH for the Grumman Tiger appears not to agree with "them", because it has this to say about stalls:
Screen Shot 2020-12-02 at 8.46.32 PM.png
I can confirm it has excellent roll control with ailerons through a whole range of stall scenarios.
Interesting...
What is the spin recovery procedure for this airplane?
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Re: Ailerons Initiating The Spin

Post by photofly »

Conventional.
Screen Shot 2020-12-02 at 8.58.28 PM.png
Screen Shot 2020-12-02 at 8.58.28 PM.png (71.93 KiB) Viewed 1448 times
I've always imagined that not using the ailerons in a stall scenario has more to do with avoiding adverse yaw towards the downgoing wing; if you're prepared to counter with enough rudder, ailerons often seem to work well enough. If you lower an aileron you are increasing the angle of attack of that section of the wing but also increasing its camber, which increases the critical AoA. The data in the NACA book of airfoils for lift curves of wings with and without flaps extended seems to suggest it's not feasible to stall a wing merely by lowering a flap, and a simple flap is very much the same as an aileron.
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Re: Ailerons Initiating The Spin

Post by pelmet »

digits_ wrote: Wed Dec 02, 2020 6:45 pm
pelmet wrote: Wed Dec 02, 2020 5:56 pm They say that the aircraft will roll in the direction opposite of the aileron input when stalled. This video seems to prove it.....twice.

https://www.youtube.com/watch?v=IUDS3QuUWls
That's a dangerous generalization. By that logic, you could use aileron in the direction of the spin to recover from it.

The crux of the matter is that during a spin entry or stall, especially an inadvertent one, you do not know what the effect of the aileron will be. It depends on which wing is stalled, if any, and how much the wings are stalled.

It is definitely possible that an aircraft can roll in the direction opposite of the aileron input. Saying that it will do this, is incorrect.
Dangerous generalization? More like reality for many light aircraft....as seen in the video.......Of course, one can no doubt find some airxraft where this is not the case, But what I said is accurate as a generalization.

https://www.flightsafetyaustralia.com/2 ... and-spins/

"Let’s go back to the original definition of angle of attack: the angular difference between the chord line of the wing and the relative wind. ‘Chord line’ is a line drawn from the leading edge to the trailing edge. The curvature of the wing along this line is called the wing’s camber, and that’s important to this part of the discussion.

When you deflect an aileron, you’re moving the trailing edge of that portion of the wing up and down. This changes the camber of that part of the wing, hence the angle of its chord line. Since the relative wind hasn’t changed (at least yet), the angle of attack of that portion of the wing changes. When an aileron is deflected upward it has less camber and a lower AOA. Deflected downward, it has more camber and a higher AOA. Since ailerons act in opposition—that is, when one goes up the other goes down—moving ailerons creates an asymmetry in AOA between the span of each wing that includes the ailerons.

Say you’re slowing the aircraft and/or increasing aft elevator pressure. The wings’ AOA increases. Now you add some aileron deflection—introducing asymmetry between the two wings’ angles of attack. The wing with the downward-deflected aileron may reach critical AOA and stall while the wing with the upward-deflected aileron is still generating maximum lift. When the stall breaks, the aircraft can spin toward the ‘down’ aileron. This can happen even if the rudder ball is centered—the asymmetry of AOA, and the spin, is caused by ailerons, not by rudder.

Here’s the real danger: you’re wings level and stall the wing, intentionally or not. If a wing drops, from lack of rudder coordination or propeller turning forces, the correct response is to push the elevator control to unload the wing while leveling the wings with opposite rudder. However, you naturally interpret a wing drop as a turn and the instinctive response is to turn back toward level flight—using ailerons. For example, the left wing is the one that drops. If you respond by turning the yoke or moving the stick to the right, the right aileron goes up and the left aileron goes down. The left wing’s AOA increases, sustaining the stall, while the right wing’s AOA decreases, potentially lowering it enough to return to maximum lift generation. The aircraft snap rolls toward the downward wing."


https://www.puc.edu/__data/assets/pdf_f ... -Ch4-6.pdf

"When the airplane is in a stalled condition, the
wingtips continue to provide some degree of lift, and
the ailerons still have some control effect. During
recovery from a stall, the return of lift begins at the tips
and progresses toward the roots. Thus, the ailerons can
be used to level the wings.
Using the ailerons requires finesse to avoid an
aggravated stall condition. For example, if the right
wing dropped during the stall and excessive aileron
control were applied to the left to raise the wing, the
aileron deflected downward (right wing) would
produce a greater angle of attack (and drag), and
possibly a more complete stall at the tip as the critical
angle of attack is exceeded. The increase in drag
created by the high angle of attack on that wing might
cause the airplane to yaw in that direction. This adverse
yaw could result in a spin unless directional control
was maintained by rudder, and/or the aileron control
sufficiently reduced.
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Re: Ailerons Initiating The Spin

Post by digits_ »

Consider an airplane of your choice. If turning (aileron control) against the wing drop always makes things worse, then that would mean that turning into the dropped wing would make things better. So why not turn into the dropped wing to recover from an stall with wing drop?
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Re: Ailerons Initiating The Spin

Post by pelmet »

photofly wrote: Wed Dec 02, 2020 6:59 pm If you lower an aileron you are increasing the angle of attack of that section of the wing but also increasing its camber, which increases the critical AoA. The data in the NACA book of airfoils for lift curves of wings with and without flaps extended seems to suggest it's not feasible to stall a wing merely by lowering a flap, and a simple flap is very much the same as an aileron.
Making an aileron deflection when near the close to the stall AoA can definitely be what leads to the critical AoA being exceeded(you created a stall(or partial stall at least) by deflecting the ailerons.
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Re: Ailerons Initiating The Spin

Post by pelmet »

digits_ wrote: Wed Dec 02, 2020 9:51 pm Consider an airplane of your choice. If turning (aileron control) against the wing drop always makes things worse, then that would mean that turning into the dropped wing would make things better. So why not turn into the dropped wing to recover from an stall with wing drop?
If you are in a spin to the left and have the control wheel/yoke/stick to the right, return the ailerons to neutral, that is your 'turn into the dropped wing' which will be a positive in terms of the overall recovery process. Obviously, there is more to the recovery process as well.
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Re: Ailerons Initiating The Spin

Post by photofly »

pelmet wrote: Wed Dec 02, 2020 9:53 pm
photofly wrote: Wed Dec 02, 2020 6:59 pm If you lower an aileron you are increasing the angle of attack of that section of the wing but also increasing its camber, which increases the critical AoA. The data in the NACA book of airfoils for lift curves of wings with and without flaps extended seems to suggest it's not feasible to stall a wing merely by lowering a flap, and a simple flap is very much the same as an aileron.
Making an aileron deflection when near the close to the stall AoA can definitely be what leads to the critical AoA being exceeded(you created a stall(or partial stall at least) by deflecting the ailerons.
I don’t know that you’re correct, in general; and the NACA data is against you. On the other hand the opposite of “can sometimes” is “cannot ever”, and I suppose that’s a bit strong. Do you imagine it’s a significant issue in a flight training aircraft?

In a majority of small aircraft, flaps are simple hinged trailing edge elements with identical geometry to the ailerons. Why is the same not true for extending the flaps, which extend very much further than the usual 10 degrees of aileron depression? You might imagine that extending flaps when near the critical AoA would lead to the critical AoA being exceeded and an aerodynamic stall occurring: yet it doesn’t. In fact that is done often, in slow flight, to full flaps (45 degrees on a Cherokee, for example) with the stall warning horn sounding, without a stall occurring.
pelmet wrote: Wed Dec 02, 2020 9:42 pmThe wing with the downward-deflected aileron may reach critical AOA and stall
Lowering the aileron increases the camber, which significantly increases the critical angle of attack. That is the purpose of a cambered wing, after all. Hundreds of pages of NACA engineering data suggests that lowering an aileron cannot induce a wing to stall, and in fact does the opposite, increasing the stall margin.
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Re: Ailerons Initiating The Spin

Post by photofly »

More information about ailerons not initiating a spin:
FAR 23.201 - WINGS LEVEL STALL:
(a) It must be possible to produce and to correct roll by unreversed use of the rolling control and to produce and to correct yaw by unreversed use of the directional control, up to the time the airplane stalls.
I note the contrast between the suggestion in the first post about "when stalled" and FAR23.201 "up to the time the airplane stalls", but this regulation does suggest that no FAR23 aircraft will generate a wing stall by lowering an aileron.

This is a requirement under all of the following conditions:
(1) Wing flaps. Retracted, fully extended, and each intermediate normal operating position.
(2) Landing gear. Retracted and extended.
(3) Cowl flaps. Appropriate to configuration.
(4) Power:
(i) Power off; and
(ii) 75 percent of maximum continuous power....
So for both aerodynamic and regulatory reasons, worrying about spin developing from sloppy aileron control isn't top of my list.
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Re: Ailerons Initiating The Spin

Post by pelmet »

photofly wrote: Thu Dec 03, 2020 6:57 am So for both aerodynamic and regulatory reasons, worrying about spin developing from sloppy aileron control isn't top of my list.
I think the video was quite clear. I thought this was a basic of practice stalls. Ailerons neutral as they will make things worse.

Perhaps just disagreeing with me just to disagree :wink: You did eventually agree with me on the selection of coarse prop to improve gliding range after a flight test. How about another flight test for this subject.
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Re: Ailerons Initiating The Spin

Post by photofly »

The basic of practice stalls is don't use the ailerons. Whether the widely-supposed rationale for not using ailerons is right, or wrong, whether there's a different rationale for not using ailerons, or in fact no rationale at all for not using ailerons, isn't clear. I put elephant powder around my house every spring to keep the elephants out, and it works every time - definitely no elephants.

To be honest, I don't pay much attention to who's writing something. This is easy enough to go and try.
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Re: Ailerons Initiating The Spin

Post by pelmet »

photofly wrote: Thu Dec 03, 2020 8:09 am The basic of practice stalls is don't use the ailerons. Whether the widely-supposed rationale for not using ailerons is right, or wrong, whether there's a different rationale for not using ailerons, or in fact no rationale at all for not using ailerons, isn't clear. I put elephant powder around my house every spring to keep the elephants out, and it works every time - definitely no elephants.

To be honest, I don't pay much attention to who's writing something. This is easy enough to go and try.
It would be interesting to hear the results from somebody on this forum doing an check(in a safe manner) about this.

But to quote an aeronautical engineer with a patent for "Improved aileron for fixed wing aircraft".......

"Adverse yaw produced by the conventional aileron contributes to spin entry. Instinctive application of conventional ailerons during attempted spin recovery merely aggravates the spin condition."

https://patents.google.com/patent/EP1042165B1
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Re: Ailerons Initiating The Spin

Post by photofly »

That's exactly what I wrote, earlier in the thread:
I've always imagined that not using the ailerons in a stall scenario has more to do with avoiding adverse yaw towards the downgoing wing;
I don't think it has anything to do with the aileron generating a stall. But, like I said, worth trying.
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Re: Ailerons Initiating The Spin

Post by RedAndWhiteBaron »

digits_ wrote: Wed Dec 02, 2020 6:45 pm
pelmet wrote: Wed Dec 02, 2020 5:56 pm They say that the aircraft will roll in the direction opposite of the aileron input when stalled. This video seems to prove it.....twice.

https://www.youtube.com/watch?v=IUDS3QuUWls
That's a dangerous generalization. By that logic, you could use aileron in the direction of the spin to recover from it.

The crux of the matter is that during a spin entry or stall, especially an inadvertent one, you do not know what the effect of the aileron will be. It depends on which wing is stalled, if any, and how much the wings are stalled.

It is definitely possible that an aircraft can roll in the direction opposite of the aileron input. Saying that it will do this, is incorrect.
Emphasis mine.

Not that I really have much experience with spins, but I would tend to agree with PF here - best practice is to just not use ailerons at all.

But, it also depends on the airframe. The Grob 115 I'm training in specifically recommends into-spin aileron to recover from "difficult" or "extreme" spins:
Image
I put elephant powder around my house every spring to keep the elephants out, and it works every time - definitely no elephants.
I strategically place a few tiger rocks myself. Definitely no tigers.
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Re: Ailerons Initiating The Spin

Post by digits_ »

RedAndWhiteBaron wrote: Thu Dec 03, 2020 8:51 am
Not that I really have much experience with spins, but I would tend to agree with PF here - best practice is to just not use ailerons at all.
I agree as well, I was merely stating that the initial assumption could lead to that conclusion. I don't agree with the conclusion, and was using that as anrgument that the initial assumption was wrong.
RedAndWhiteBaron wrote: Thu Dec 03, 2020 8:51 am But, it also depends on the airframe. The Grob 115 I'm training in specifically recommends into-spin aileron to recover from "difficult" or "extreme" spins:
Image
Do they actually want you to pull fully up while in a spin? If anything, you would think that this would keep you stalled. Any idea what the logic behind that would be?

If you want to avoid the flat-ish spins, then aileron into the spin will help, but not sure how the pull up motion will help. I was under the impression that to get out of a flat spin, you'd want to increase your bank angle and get the nose down.
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Re: Ailerons Initiating The Spin

Post by RedAndWhiteBaron »

Huh... I had always interpreted that sequence to mean pulling up only after recovery is possible - but you're right; it says full up elevator while recovering.

The only reason I can think of, aerodynamically, is to in fact keep the aircraft stalled to avoid turning your flat spin into a sprial dive from which you cannot recover. If takes enough time to turn the spin into a recoverable state, perhaps Vne could be exceeded, and this can be avoided by keeping the aircraft stalled?

I don't know really, but that would make sense. Hopefully someone with more knowledge then I can comment on that.
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Re: Ailerons Initiating The Spin

Post by Big Pistons Forever »

My 02 cents

1) Re the video on the first post. It is impossible to see the rudder inputs just before the stall. My personal opinion is that the inadvertent spin was primarily caused by the airplane bring in a significant skid at the time it stalled and the aileron inputs aggravated what was already going to be a spin entry.

2) Cessna published a model specific guide to spinning their airplanes. You can google "Spin Characteristics of Cessna Models" or the publication number D5014-13. It specifies aileron neutral as the first step in the spin recovery for all models.

3) In aerobatic airplanes ailerons can be used to vary the speed of rotation and out of spin aileron will cause a rapid increase in rotation rate when the airplane is in a fully developed spin. In the ultimate category airplanes all the rules go out the window, For instance in an Extra 300 you can recover from a spin with a sudden application of full out of spin aileron. The ailerons are so powerful that the airplane will do a half roll right out of the spin.

4) Personally I think the part that is missing in flight training is the absolute importance of stopping the rotation before applying the down elevator input. In some non aerobatic airplanes applying forward stick pressure before the rudder input could prevent the recovery.

5) Spins are an aerobatic maneuver and should be explored as part of dedicated aerobatic training in an aerobatic capable aircraft. In PPL/CPL/Instructor rating training the emphasis should be on spin recognition and immediate recovery. Any spin that goes past 1/2 turn is negative training as it means the spin recovery was delayed. The most common trainer now is the C 172 and it is IMO the worst possible airplane to teach spin recovery because almost any control input will recover the airplane. This extremely docile behavior is not typical and IMO gives a un-warranted impression to students that spins are hard to get into and easy to recover.

6) The Only way to recover from a spin is to strictly apply the POH actions in the exact order specified in the POH
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Re: Ailerons Initiating The Spin

Post by RedAndWhiteBaron »

Big Pistons Forever wrote: Thu Dec 03, 2020 10:12 am 6) The Only way to recover from a spin is to strictly apply the POH actions in the exact order specified in the POH
The manual I reproduced here provides multiple methods of spin recovery. It isn't possible to "strictly" apply the actions specified. One method is given for "normal" spins, and another method given for "difficult or extreme" spins. They are mutually exclusive, and which method you employ depends entirely on the definition of "difficult or extreme" spin. While I take that to mean a flat spin, the PoH provides no definition, and at which point a spin becomes "flat" is also a matter of some debate (well, unless there is an official definition of which I am unaware, in which case my whole argument is moot here).

The point is, it is still useful to debate the aerodynamics of spin recovery beyond those specified in a PoH, because a PoH cannot cover all scenarios.
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