Dynamic stall discussion

[Insuber]

Originally Posted by ACE-OF-ACES

Are we talking tens of seconds or tens of Millie seconds? If the later, than it is not worth adding the additional math to simulate the brief increase in lift because it will go un-noticed to the sim pilot. That is to say, in the real world an instrumented plane under test might notice (log the data) the Millie second spike of increased lift.. But the human won't.. So no need to simulate it IMHO.

This series of funny statements illustrates perfectly how ignorance tries stubbornly to rule the knowledge.
Dynamic stall is a violent phenomenon, leading to a huge loss of speed / energy. Just for sake of simplicity: pull strongly the stick at high speed in real life, even in straight flight, and you will stall. In this game you can pull strongly the stick at high speed, and your plane climbs. The flight envelope is false. So: big need to simulate the dynamic stall, in my educated opinion.

Cheers!

[Skoshi Tiger]

Aircraft can do loops and depending on how much energy and or power and or altitude you have on hand you can do multiple loops one after the other as long as your angle of attack does not exceed the stall angle. (ie you still have to fly the aircraft within it's flight envelope)

I expect this would effect the 'going vertical' manuvers where the pilot just yanks back on the stick and expects all their aircrafts energy to be converted to height or violent break turns.

I found (what i thought) reasonable description of a dynamic stall at
http://psasir.upm.edu.my/3610/1/An_E..._Inception.pdf

When an aerofoil is pitched through and beyond the incidence of static stall at a
sufficiently high pitch rate, the resulting series of events is often termed dynamic stall.
It is characterised by a significant lift overshoot, followed by a sudden loss of lift and a
major surge in pitching moment. Carr, (1977),

Interesting reading.

cheers!

[klem]

I'm no aerodynamicist but here's an explanation of Static, Dynamic and Accelerated stalls
http://www.futurecam.com/stalls.html
Yes, its written about parachuting but the principles should be the same: angle of attack; rate of change of angle of attack; the added effect of increased G loading.

Whether CoD models Dynamic and Accelerated stalls I'm not sure. I'd be surprised and disappointed if it doesn't. I guess we'd need some a/c data to test against to find out.

[winny]

I have a question...

Is a dynamic stall the same thing as what the British refered to as a 'high speed stall'?

[Skoshi Tiger]

Originally Posted by winny

I have a question...

Is a dynamic stall the same thing as what the British refered to as a 'high speed stall'?

I was just wondering the same thing.

After reading the Spitfire MKI manual, I was doing a few stalls. From 250mph I was pulling back on the stick into the climb before stalling at about 160mph, drops a wing violently and then enters a spin.

Unfortuately it's hard to work oput if this is due to a dynamic stall or an accelerated stall.

If we knew what G's we were pulling be able to calculate the stall speed. If that corresponded to the stall speed in the test, then that would indicate a accelerated stall and not a dynamic stall, Or we could ask a question to the developers (which Insubar already has) and wait for a response.

Cheers!

[bongodriver]

at 2 g's its about 1.4 times the static stall speed, I seem to recall the formula having something to do with the square root of the G's

[Insuber]

Originally Posted by Skoshi Tiger

... Or we could ask a question to the developers (which Insubar already has) and wait for a response.

Cheers!

Yes it is what I did, despite the desperate efforts of my friend Ace to entropyze the discussion ...

[IvanK]

Originally Posted by winny

I have a question...

Is a dynamic stall the same thing as what the British refered to as a 'high speed stall'?

No A High speed stall is the same as an accelerated stall. i.e. A stall occurring at greater than 1G therefore at a faster speed than the 1G stall ... but occurring at the same AOA. If your 1G Stall speed is say 100Kmh your 4G stall speed would be 200kmh (1G Stall speed X SQR of the Load Factor).

A Dynamic stall is another condition that involves Stall AOA and rate of change of AOA.

[ACE-OF-ACES]

Originally Posted by Skoshi Tiger

I found (what i thought) reasonable description of a dynamic stall at

That is the best definition thus far IMHO..

It highlights that the difference between a acc stall and a dynamic stall as being the rate of change in AoA.. And makes note of the 'brief' increase lift (lift overshoot) due to the high rate of change in AoA.. The point I think some are missing is the critical AoA must be reached in both cases to stall.. Just that the dynamic has a brief overshoot past that point with a brief increase in lift.. Thus if CoD is not stalling now due to large/fast stick movements.. Than it is not simulating acc stall either.. Or as I noted the stick force input is limited to such a low value that you can not move the elevator far or fast enough to cause it to happen.. To be honest, I dont fly like that (jerk the stick) so I have not noticed the acc stall missing if it is missing

Thanks for the link Tiger

[TomcatViP]

Dyn Stall =

A stall that has its root in a dynamic phenomena. A stall is essentially linear : the AOA increase (or the speed decrease at a given aoa). In the dyn stall the flow ard the wing is disturbed briefly inducing non linear effect

The source can be mechanical (aileron reversing), aerodynamic (temp vortex) or thermal (critical temp inducing critical external pressure change - eg turbulences)

An example will be the rotor blade turning around it's axis. The blade AoA hve to be raised when the blade travel backward in order to compensate for the loss of speed and equilibrate the lift generated by the rotor.

At certain speed the AoA variation can be critical to the airflow generating vortex on top of the blade that prevent the normal airflow circulation. The flow is separated at a higher than normal speed and the blade is stalled (generating a high amount of drag).

But this has more to do in the FM thread, no ?

An example here in a short vid http://www.aerobuzz.fr/spip.php?article866


PS: all the ppl that hve some sort of knowledge were among the "ignorants" before.