No flutter or stress on airframe at max speed or above

1st Official Post

    In the ASG29 there is no penalty for flying above max speed. You can even manouver without any trouble. Also I do not see any difference between the manouverability at low speeds or high speeds. I can perform all kinds of tricks with the glider above the limits for max manouverability without stressing the airframe. Last but not least, I did not find any difference in imput of the controls at low or high speeds. I haven't tried this extensively but It looks like I have to give just as much stick and rudder at low speeds as at high speeds. This should of course be different, e.g. Much less rudder and stick is needed at high speeds.

    • Official Post

    Question: did you use correct flap settings for all speeds? If you use a more forward flap setting (negative camber) you will not only get less lift coefficient and lower drag but you will also have a reduced differential flap deflection with aileron. This could explain a similar roll rate at high speeds. Given that the induced drag and inheritly the adverse yaw are a function of the angle of attack which itself is a function of the flap setting + the speed you try to fly. So as you decrease the flap deflection towards the negative camber your angle of attack increases again and the adverse yaw increases with it. Ergo there should be a need for a little bit of rudder at all speeds, theoretically. (Is that correct what I am saying?)

    The only glider with flaps that I flew in real life is the Ventus 2cxT. It needs some rudder at higher speeds (feels like more than usual) and needs very very much at low speeds (also more than usual, compared to a Discus or even a Duo Discus with greater span).
    Other gliders I have flown also needed only a little bit of rudder at lower angle of attack and more rudder at higher angle of attack. But the ASG 29 isn't that far off I think.

    Now regarding the stress or flutter:
    Yes I would love to the that, but I don't quite like how its done in Condor for example. I get flutter very fast even at low altitude just slightly above the maximum allowed airspeed. I don't want to try it in real life but I think there is quite a bit of margin before you enter flutter. And it should also be a function of the angle of attack (at least from my understanding), which it isn't in Condor. If flutter is more or less an oscillation between positive and negative angle of attack of a locally twisted part of the wing then offsetting that angle of attack should reduce the amplitude, shouldn't it?

    Cheers,
    Jan

    • Official Post

    Flutter can theoretically occour at any speed if you have too much play in the control rods to the control surfaces on the wings. Additionally masses are added in front of the hinging point to make the control surface itself aerodynamically stable.

    But at higher speeds, above the velocity never to exceed (Vne) even those mass balances could not be enought and even with little play the control surface can start to vibrate which creates oscillating pitch up and pitch down moments on the wing it is attached to. If the frequency (which is a function of the mach number I think) is just right and is about the same frequency or a multiple of the natural frequency of the wing the oscillation can become so strong that the entire wing is ripped apart.

    To answer your question: No flutter is not necessarily biased towards higher speeds its more descritive at higher speeds though.

    Cheers,
    Jan