Dynamic stall discussion

[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 ACE-OF-ACES

Hard to say since I have not seen the topic.. Just curious as to what they think the difference is between the two if any

It was so off-topic that Uther created another topic for this.

Back on *this* topic: as anyone hopefully understands now, and as some clever guy pointed out already few posts above, the lack of Dynamic Stall in this sim allows one to convert all his kinetic energy (speed) into positional energy (height), at any AoA (Angle of Attack) and speed. This of course is based on my own essays, mostly on 109, Spit and Hurricane, and I will be glad to be proven wrong.
This is why I called out this subject as "very important" with respect to the FM.

Cheers,
Insuber

[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.

[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 ...

[Insuber]

Best answer to this thread, just published by BlackSix:

Originally Posted by BlackSix

Will the dynamic stall be implemented in the Flight Model?

4.
Yes, it’s one of the things the new FM programmer will work on.

[ACE-OF-ACES]

Originally Posted by Insuber

This series of funny statements illustrates perfectly how ignorance tries stubbornly to rule the knowledge.

No don't be so hard onyourself! I realise you were un-able to explain the difference which is why I ask you for the link in the russian forum

Originally Posted by Insuber

Dynamic stall is a violent phenomenon, leading to a huge loss of speed / energy.

Ah good so you agree with me and the link I posted a few pages back, i.e.

Advanced Topics in Aerodynamics

Where it defines a dynamics stall as..

Dynamic stall is a phenomenon that affects airfoils, wings and rotors in unsteady flows. It is due to changes, periodic or not, in the inflow conditions and/or angle of attack. In some cases, such helicopter rotors in advancing flight, dynamic stall is intrinsic to their state of operation.

Originally Posted by Insuber

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.

What your forgeting is there is a chance that CoD does simulates stick inputs the same way IL-2 did.. Where the stick input is not a position offset as much as a force input.. That is to say just because you move the still all the way 'back' does not mean your elevator moved all the way 'up'.. What is actully going on is when you move your stick all the way ack, your have appled the max force input.. Thus if your max force input is limited to 20lb and due to the airspeed it would require 60lb to fully deflect the elevator.. Well you can see your not going to fully deflect the elevator

Originally Posted by Insuber

So: big need to simulate the dynamic stall, in my educated opinion.

And your welcome to it! S!

[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.