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Angle of attack and stick position


Icaro_07

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Pre transonic Aircraft stall at pretty much a constant AOA as long as no lift devices deploy. Stall speed is a function of g load.

 

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In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases.This occurs when the critical angle of attack of the foil is exceeded. The critical angle of attack is typically about 15 degrees, but it may vary significantly depending on the fluid, foil, and Reynolds number.

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Sorry there are a few possibilities. Is the aircraft slowing down ? At the end of the day it comes down to AOA. Take a look at the guage in the Aircraft.

 

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Try yourself put the fw190 at certain stick position when you fell the buffet, then with ailerons put it nose down and the buffet will disappear but with nose up the buffet will appear again, it's like the f-15 flcs that you control g instead of AOA I don't know if I explain correclty

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Ok maybe this helps. The Aircraft is designed so when it stalls the Elevator will also stall. The elevator is producing a downward force in normal flight when it stalls the downward force is lost and the nose will drop unstalling the wing. If you leave the stick in a constant position the elevator and wing will unstall the nose will raise again and you will restart the cycle entering a stall again. No FCS just Aerodynamics.

 

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Yes agree totally with you, but the elevator can not stall if you hold a constant position = constant AOA, if the airplane slows down lift will reduce and will seek for balance and will drop the nose down but will not stall will not feel the buffet agree with that? Is just when you pull the elevator to the critical AOA is when the wing will stall regardless of your speed and altitude agree with me ?

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  • ED Team
Do you know Whee i can get more info about this? And hay is more complex?

 

At different Mach numbers the critical AoA is different. And it starts to be noticable from relatively low M - 0.3...0.4. As the trimmed AoA is quite constant up to M > ~0.7 you see the effect you mentioned.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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...but the elevator can not stall if you hold a constant position = constant AOA,..

In reading your comments, I get the impression that you are confusing pitch with AoA. The two are not identical. At any particular pitch angle, your AoA will vary with speed even though your nose (and consequently your wing) is pitched up or down by the same amount throughout.

 

EDIT:

Does any one knows if for every trim setting a stick position corresponds to an specific AOA because if it's that way it stalls at different AOA

So to answer your original question, no. Not until you take your airspeed into consideration. At a given airspeed, a given stick position will yield a particular AoA. Or inversely, a particular AoA (not pitch) with a particular stick position will give you a specific airspeed. But you can only calculate the inverse, if you know your wing's AoA. Otherwise you're missing part of the equation.


Edited by Ironhand

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Well is just that simplistic, fly the f-5 and for every position the stick moves corresponds to specific AOA

 

Different planes have different Mach-dependant trim curves. F-5 wing is a very different thing comparing to the conventional airfoil high-aspect non-swept wing of WWII planes. Moreover, even WWII planes had very noticable differencies either in CLmax(M) or trim curves vs M.

For example, P-51 CLmax(M) had very distinctive "shelf" at moderate M, though other planes had constantly decreasing dependance. Spitfire was more preferrable regarding high-M trim changes than P-51 and P-47, tc.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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Well is just that simplistic, fly the f-5 and for every position the stick moves corresponds to specific AOA

Are you saying that, if you hold the stick in one position, the AoA will not change even when your airspeed changes? If so, I'm not buying it. Whether in the F-15, F-5, P-51, Dora, or any other aircraft, the AoA will get smaller as your speed increases and larger as your speed decreases, if you do not change the stick position.

 

EDIT: But, of course, I reserve the right to be wrong...


Edited by Ironhand

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AoA is the same principle for all aircraft. AoA is the angle between the wing chord line and relative wind. This has nothing to do with speed, pitch, roll or whatever. Each wing has a Critical angle of attack. This critical aoa will remain the same, but the factors causing the wing to reach that critical aoa may differ. Speed, bank, pitch just to name a few. This is why a wing will stall at any speed.

 

So to answer the OPs question, no, "stick position" has nothing to do with critical AOA. The relationship between the wing and relative wind are the only thing that will impact the aircraft and its stall. Now what you do with the stick to place the wing at its critical aoa is a different story.

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Are you saying that, if you hold the stick in one position, the AoA will not change even when your airspeed changes? If so, I'm not buying it. Whether in the F-15, F-5, P-51, Dora, or any other aircraft, the AoA will get smaller as your speed increases and larger as your speed decreases, if you do not change the stick position.

 

EDIT: But, of course, I reserve the right to be wrong...

 

Your statement is right only if you add "for the same lift" or "for 1 g level flight" as a part of this conditions.

 

Generally, for the STABLE airplane you need to push the stick forward as the speed increases to maintain this constant lift. By the way, for the neutral stability for fixed stick its position remains the same, but, anyway, you need to decrease AoA with double movement (push, then return to the same position to hold new AoA).

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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Your statement is right only if you add "for the same lift" or "for 1 g level flight" as a part of this conditions.

 

Generally, for the STABLE airplane you need to push the stick forward as the speed increases to maintain this constant lift. By the way, for the neutral stability for fixed stick its position remains the same, but, anyway, you need to decrease AoA with double movement (push, then return to the same position to hold new AoA).

Yes, I had 1G flight in mind. Should have stated that. I assumed that was the case, since the OP was asking about trim settings.

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Well don't believe to me, check the F-5 trim the stick and check the AoA regardless of speed portion etc holds constant AOA

What probably confuses you is the following:

F5 has AUTO trailing and leading flaps switched ON ... these enable pilot, by constantly readjusting, to hold fixed position of the stick for selected AoA. In other words, if you turn them OFF (EMER UP), you will not be anymore able to hold constant AoA with the same stick deflection ...


Edited by Vatikus
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I don't own the F-5 module, so it's not something I can check.

 

This video is interesting because it demonstrates exactly what I'm saying. The time period 6:15 to 6:27, for instance, is an excellent example (as is the next sequence at full power). He pitches up, holds the same stick position and, as his airspeed deteriorates, the angle of attack slowly increases by roughly 20 degrees until he eventually stalls the wing.

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I don't own the F-5 module, so it's not something I can check.

 

This video is interesting because it demonstrates exactly what I'm saying. The time period 6:15 to 6:27, for instance, is an excellent example (as is the next sequence at full power). He pitches up, holds the same stick position and, as his airspeed deteriorates, the angle of attack slowly increases by roughly 20 degrees until he eventually stalls the wing.

 

That's not true what he says its that with the stick position you control AOA regardless of speed that's why a landing can be made with just the AOA

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That's not true what he says its that with the stick position you control AOA regardless of speed that's why a landing can be made with just the AOA

He does not say what you think he says. I guess you are not a native english speaker?

When he says that with stick position you control AoA, he does not mean that X stick deflection = Y AoA regardless of speed. What he means is that if you have AoA indicator, you use your stick to correct for the desired AoA, while with throttle you control the angle of approach.


Edited by Vatikus
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