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Stall at Hi g maneuver


Neon67

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Hi all

 

I was wondering, how could an airplane flying at hi speed, making a hi g maneuver and stalls like the f86f and F15-C in DCS.

 

I thought stall occurred only when the airplane doesn't have enough speed to maintain airlift under the wings ?

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The newly added "shake" effect sometimes confused me into thinking i would stall out. Could it be that?

 

That's called AOA buffet and starts at about 18~20 units AOA, when you'll experience a slight shake if you pay (a lot) attention to this.

 

The AOA buffet increases in intensity to 23 units, then remains fairly constant. And 23 units AOA is far from critical AOA, which is 45 units in a F-15C.

EFM / FCS developer, Deka Ironwork Simulations.

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If you mean when you're flying in a straight line and yank the stick back and the plane starts to spin and you lose control.... that is a stall because of too much change in AOA.

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Almost everything can lose control at high speed & high g, due to various reasons, from warbirds all the way to 4th gen aircraft.

 

If you overshoot critical angle of attack (more likely at higher g loads) your wings may stop producing lift, and high speed control losses tends to be more dangerous than low speed stalls. Computerized FLCS in aircraft like F-16 specifically limits the pilot inputs to prevent this from happening.

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Stall is exceeding the critical angle of attack. Stall has nothing to do with speed.

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That's called AOA buffet and starts at about 18~20 units AOA, when you'll experience a slight shake if you pay (a lot) attention to this.

 

The AOA buffet increases in intensity to 23 units, then remains fairly constant. And 23 units AOA is far from critical AOA, which is 45 units in a F-15C.

 

 

AOA Buffet of course. Thank you.

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You're not going to stall a real F-15 at 'high speed and high g'.

 

The dive recovery procedure is 12g, and there's record of an F-15A performing it at anywhere between 12g and 15g (It became a museum piece because the maneuver bent the airframe, making it impossible to maintain).

 

There was no 'stall'.

 

Almost everything can lose control at high speed & high g, due to various reasons, from warbirds all the way to 4th gen aircraft.

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Well, the "high speed control losses" may be referred to as a "departure".

 

A departure is a loss of aircraft control that is characterized primarily by uncommanded aircraft motions or failure of the aircraft to respond to control commands, and is very different from what we called a "stall".

 

For instance. The critical AOA of an F-16 is 35°, and the aircraft stalls above critical AOA.

 

At the same time the F-16 experiences a loss of efficiency of the elevator (and therefore a loss in nose down control effectiveness) when exceeding 25° AOA, which is called a pitch departure. The pitch FLCS prevents pitch departures and has nothing to do with stalls.

EFM / FCS developer, Deka Ironwork Simulations.

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I don't think anyone is arguing what a departure (= loss of control) is :)

 

If you stall, you've departed controlled flight.

 

You're not going to depart a high-speed F-15 unless you try really, really hard. You're not going to roll couple it, you're not going to spin it, you're not going to break it.

 

In case it wasn't clear enough, F-15's have 'relatively often' been over-g'd to 10g and 12g. No departure. Only one F-15 is known to have exceeded that number, and it's a museum piece as posted above. I'm not even sure you can reach anything resembling critical AoA at high speed.

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Reminder: SAM = Speed Bump :D

I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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You're not going to depart a high-speed F-15 unless you try really, really hard. You're not going to roll couple it, you're not going to spin it, you're not going to break it.

 

In case it wasn't clear enough, F-15's have 'relatively often' been over-g'd to 10g and 12g. No departure. Only one F-15 is known to have exceeded that number, and it's a museum piece as posted above. I'm not even sure you can reach anything resembling critical AoA at high speed.

 

Nah..Just a reminder, or blathering cuz someone mentioned F-16, never mind.;)

 

Good to hear what a real F-15 is like.

EFM / FCS developer, Deka Ironwork Simulations.

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Stalls happen at ANY speed, just pull hard enough and it will come...maybe, as in the case of the F-15, the G-limit of the human body is way before that point, but if you could pull harder it would also stall, there is no escape from this law.

With WWII planes this does happen well inside our G-Limits and is somewhat common when you overdo the stick. Well, meanwhile the P-51 tends to loose a wing before this happens but basically,

you can force any plane into a high speed stall.

 

 

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It would also benefit from all participants realizing that you cannot pull enough stick to stall an F-15 at high speed.

 

 

Well, that might be limited with the F-15 or any other modern FBW system, but in principal no design is free of high speed stalls afair.

 

Sure, if your FBW is smart enough it won't let you pull that far, but that doesn't mean it wouldnt occur if you pulled more AoA if just allowed to do so.

 

 

I am talking principals, not if one or the other implementation is smart enough to avoid it.

 

 

The more Delta-like your airframe is the more G's you can pull before it happens, but it will happen.

 

 

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Well, that might be limited with the F-15 or any other modern FBW system, but in principal no design is free of high speed stalls afair.

 

You cannot physically get enough AoA to stall that plane at high speed.

 

I am talking principals, not if one or the other implementation is smart enough to avoid it.
Do those principles include available elevator deflection?

 

An aircraft isn't just a wing, and we are talking about specific aircraft - the OP mentioned two. I don't know about the F-86, but I know you won't stall an F-15 at high speed just by providing maximum pitch input.


Edited by GGTharos

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I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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The correct term "high speed stall" does, according to Wikipedia, only apply to subsonic airfoils that operate near sonic velocity, thus inducing the shock wave in front of the wing, leading to "High Speed Buffet".

 

I think what we mean is the ordinary stall induced by too high AoA.

 

Wikipedia does not mention that is does not occur at high speeds, it only says it depends on the correlation of IAS, AoA and banking angle if not level.

 

At least for subsonic flight I do now it does happen even at the highest speeds you can go, just pull hard enough and you will "dice out" like a rolling dice. I often do this with the P-51 to barrel roll quickly, pull hard and it will snap on you, if done right it will stop 360° later, about 50 kmh slower, not a bad maneuver to get from 12 to 6.

 

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Like I have posted previously ... if you do it in an F-15, you're going to gate insane amount of g and you're going going to bend the airframe. What you won't do is stall, roll, or yaw uncontrollably.

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Reminder: SAM = Speed Bump :D

I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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