Fresh stuff from sukhoi.ru (Discussion)

[Skoshi Tiger]

Originally Posted by Insuber

Dynamic Stall: go to Wikipedia if you want. Today only the normal stall is modeled - not good for a flight simulator.

Cheers,
Ins

When you go to wikipedia and look up dynamic stall it redirects you to stall where it says

"Dynamic stall is an effect most associated with helicopters and flapping wings. During forward flight, some regions of a helicopter blade may incur flow that reverses (compared to the direction of blade movement), and thus includes rapidly changing angles of attack. Oscillating (flapping) wings, such as those of insects— including the most famous one, the bumblebee — may rely almost entirely on dynamic stall for lift production, provided the oscillations are fast compared to the speed of flight, and the angle of the wing changes rapidly compared to airflow direction.[22]"

Is this relavant for the fixed wing aircraft in this sim? If so how?


Cheers!

[Swoop]

Just had a session on ROF with some mates, second time online and not much sucess. Had 10 minutes to kill so jumped on the ATAG server in a Spit2 and what a blast, the speed and the feel. Took out a 109s elevator and shot up a couple of bombers. I guess what I'm getting at is this sim is just great fun and thankyou all for the hard work your doing

[ZaltysZ]

Static stall: 1G flight, your speed decreases, you increase AoA to compensate. Stall happens when critical AoA is reached.

Accelerated stall: same us above, but there must be >1G. In such condition, you need higher AoA than in 1G flight, because lift is countered not only by weight, but by sum of weight and centrifugal force.

Dynamic stall: you increase AoA past a critical value very quickly, vortex is created at leading edge, lift increases, then vortex detaches and you experience rapid loss of lift and sometimes even a high nose-down pitching.

I think, important things about dynamic stall is: amplitude and rate of AoA change, and increase of lift before the stall.

[Ataros]

Impressive mission from a sukhoi.ru member posted. Video of air attack and track of a tank attack are included. Works like a strategy game too: you can call reinforcements and schedule your tank attack carefully.
http://forum.1cpublishing.eu/showthread.php?t=28595

Worth flying and/or watching with external views.

[ACE-OF-ACES]

Originally Posted by ZaltysZ

Static stall: 1G flight, your speed decreases, you increase AoA to compensate. Stall happens when critical AoA is reached.

Accelerated stall: same us above, but there must be >1G. In such condition, you need higher AoA than in 1G flight, because lift is countered not only by weight, but by sum of weight and centrifugal force.

Dynamic stall: you increase AoA past a critical value very quickly, vortex is created at leading edge, lift increases, then vortex detaches and you experience rapid loss of lift and sometimes even a high nose-down pitching.

I think, important things about dynamic stall is: amplitude and rate of AoA change, and increase of lift before the stall.

Thanks for the feedback Zaltys..

Looking at your definitions of Accelerated and Dynamic..

Your dynamic def reads just like the link I posted.. Except there is no mention of how the variations in stall are due to the variations atmosphere.. From the link I posted they point out how the stall can vary due to the variation in wind (atmosphere). Other than that the two defs are very interchangeable.

One other thing, you stated you 'need higher AoA than in 1G flight'.. IMHO you should re-word that to read 'during a constant altitude banked turn the AoA will have to be higher than it would be during level flight (1g) at the same speed'.. That example is a little easier for most to visualize. It is also important to note the critical AoA at which the stall occurs is the same for all three cases.

[ACE-OF-ACES]

Originally Posted by Insuber

Dynamic Stall: go to Wikipedia if you want. Today only the normal stall is modeled - not good for a flight simulator.

Ok looking at the wiki, i.e.

wiki dynamic stall:
Dynamic stall is a non-linear unsteady aerodynamic effect that occurs when airfoils rapidly change the angle of attack. The rapid change can cause a strong vortex to be shed from the leading edge of the aerofoil, and travel backwards above the wing. The vortex, containing high-velocity airflows, briefly increases the lift produced by the wing. As soon as it passes behind the trailing edge, however, the lift reduces dramatically, and the wing is in normal stall

Based on that looks like ElAurens is close to the mark.. basically an accelerated stall situation.. Thing that is interesting is it also states you get a brief increase in lift.. So other than the brief increase, it follows the standard stall def

Also note the wiki reference #22 is from here

Unsteady aerodynamics
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.

A comprehensive review of CFD methods for dynamic stall has been published by Ekaterinaris and Platzer (1997); for physical insight, see McCroskey (1981).

In wind turbines it is the result of atmospheric turbulence, wind shears, earth boundary layer, etc. The aerodynamic characteristics are affected to an extend that depends on the frequency of the changes, their amplitude and the point of operation.

Other factors affecting dynamic stall are the Reynolds and Mach numbers and the geometrical shape. There other, maybe minor factors, like the vortex effects, blade flapping and bending, etc...

In the following discussion we will consider the airfoil dynamic stall, which is a particular case of rotor and wing stall. The airfoil is subject to two fundamental periodic oscillations: plunging and pitching.

A plunging oscillation is a periodic translation of the airfoil in a direction normal to the free stream. A pitching motion is a periodic variation of the angle of attack.

Looks like Skoshi hit close to home on that with the helo rotors.. Also reading that I get the impression this is geared more for a computational fluid dynamic (CFD) flight model than the standard 6DOF flight model.. Where the change in the atmosphere has more affect.. The question is will the user even notice the effect? That is to say at the design level it may be noted, or during flight testing it might show a spike in the data.. but would the user of the flight sim notice it?

All in all it appears the standard def of stall still applies in both, just the changes/turbulence due to the atmosphere causes it to stall a little sooner or little later depending on the situation

Originally Posted by Insuber

GUI: RoF is a good example.

example of what?

Originally Posted by Insuber

Bullet damage to radiator: you can fly for a lot of time despite the message "radiator leak", at least in the 109, imo it is a bug.

It would be a bug if it could fly forever.. In that I don't know if there was any sort of self sealing radiators in WWII?

[BlackSix]

So, what can I do with Dynamic stall? Remove the question?

question 12, new form:
Will the GUI be remade?
ok?

[furbs]

Yes...B6 and ask if we will see FSAA in CLOD, or where are the 2D clouds?

[ACE-OF-ACES]

Originally Posted by BlackSix

So, what can I do with Dynamic stall? Remove the question?

Please don't based on what I said! I was just curious as to it's meaning!

[Insuber]

Originally Posted by BlackSix

So, what can I do with Dynamic stall? Remove the question?

No better, remove Ace of Aces

Originally Posted by BlackSix

question 12, new form: Will the GUI be remade?
ok?

I would reformulate it like this:
question 12: will the GUI be optimised, to be less clumsy and more ergonomical (today you need several clicks to do simple things), in the same way that RoF optimized their GUI? Today RoF is a great exemple of an appealing, sexy and functional user interface.

Cheers!