Reflected Posted January 23, 2014 Posted January 23, 2014 Can anyone explain me the physics of wing flutter? I’m a bit confused as to how it all begins. Some sources mention vortices coming off the trailing edge, making the wing vibrate, other sources say it begins when the wing’s elasticity overcomes the forward twisting force of the high speed of the airflow, then the wing kinda “bounces back”, making the AoA much bigger, generating lift and drag, and bending the wing up and back, then the same thing happens on the top. So what’s the truth? I’m familiar with what happens during flutter, I just don’t understand how it all begins? Thank you in advance!
Rama Posted January 23, 2014 Posted January 23, 2014 The way I understand it is that the wing is normally subject to two kind of oscillation, a twisting oscillation and a bending oscillation. The frequencies of these oscillation are different and both depends on wing rigidity, aerodynamic pressure, etc... so mostly on speed and AoA. As long as both frequencies remain significantly different, you get no flutter. When both frequencies converge, they begin resonating (this leading to oscillation amplification => flutter). So it's IMO a classic resonating phenomenom.
DD_bongodriver Posted January 23, 2014 Posted January 23, 2014 classic video that is used to explain it and show the actual effects. http://www.youtube.com/watch?v=qpJBvQXQC2M
Sternjaeger Posted January 23, 2014 Posted January 23, 2014 there's a good video explanation here but yes, it's a harmonic oscillation that is strictly dependent on the fluid you're moving in, this is why wing flutter may not occur at the same speeds but different altitudes. and this is what it looks like from the outside (mind you, those are very flimsy, long glider wings, so the oscillation is quite dramatic!)
DD_bongodriver Posted January 23, 2014 Posted January 23, 2014 This ones interesting. http://www.youtube.com/watch?v=6mbIRXnCSts
Reflected Posted January 23, 2014 Author Posted January 23, 2014 Thanks a lot for the videos, very interesting! Although, I still don't understand how a high speed current can cause a wing or a bridge to vibrate. How does it begin? I understand why it gets amplified, but how does the first little move happen?
Rama Posted January 23, 2014 Posted January 23, 2014 A wing or a bridge allways oscillate when submitted to aerodynamic pressure. no wing and no bridge is perfectly rigid. Actually, it's their relative rigidity and their resistance to aerodynamic pressure that initiate the oscillations, since the aire pressure is never constant (never perfectly linear), the oscillation is maintained (like for a maintained pendulum). The thing is that usually the oscillation amplitude is small enough and the frequency low enough (because of rigidity) you don't notice it. It's only when the oscillation is amplified by resonance that you may notice it.
Sternjaeger Posted January 23, 2014 Posted January 23, 2014 it's kind of like when you put your hand out of your car window, and as speed increases you'll struggle to keep your hand steady, and it will oscillate in the wind stream.
Gort Posted January 24, 2014 Posted January 24, 2014 (edited) Thanks a lot for the videos, very interesting! Although, I still don't understand how a high speed current can cause a wing or a bridge to vibrate. How does it begin? I understand why it gets amplified, but how does the first little move happen? Turbulence, control input, anything that perturbs the airflow and inertia of the surface. In conventional control airplanes in the "old days", test pilots would set up a parameter, then rap the stick or pedals to try to try to induce flutter. Thanks for giving the pilots here nightmares for the next couple of weeks by the way. Edited January 24, 2014 by Victory205
II./JG27_Rich Posted January 24, 2014 Posted January 24, 2014 Go to 50 seconds and apeoftheyear will explain
DD_bongodriver Posted January 24, 2014 Posted January 24, 2014 But he doesn't explain it at all, plus there is actually no wing flexing in BoS at all.
II./JG27_Rich Posted January 24, 2014 Posted January 24, 2014 (edited) But he doesn't explain it at all, plus there is actually no wing flexing in BoS at all. Sorry didn't get what the subject was at first. I thought we were talking about what happens uin the game Edited January 24, 2014 by II./JG27_Rich
Sternjaeger Posted January 24, 2014 Posted January 24, 2014 I have seen a screenshot of someone with bent wings, but wing flexing should definitely be implemented.
Reflected Posted January 24, 2014 Author Posted January 24, 2014 I have seen a screenshot of someone with bent wings, but wing flexing should definitely be implemented. I don't think so. It's not too relevant from the game's point of view, andi t would be a huge hit on our PC-s. So I'd be happy if we didn't see the wings flex, or shake (FFB is a good replacement for this one), but they would just break off, or get damaged when we go past Vmax.
Sternjaeger Posted January 24, 2014 Posted January 24, 2014 Wing flexing is a VERY important part, it was even present in now ancient simulation games like Fighter Squadron, and it's the step before structural damage caused by overstress. Wings need to flutter as well, since it's all part of the process. I'm honestly gobsmacked when I read such comments.. I mean, do you want a simulation or an arcade?
Reflected Posted January 24, 2014 Author Posted January 24, 2014 I want a simulation, and I want all of its consequences implemented in the DM. What I'm saying is that I don't want to sacrifice CPU power, and trade 30 aircrafts and 50 ground units, and an ultra-high setting for the sake of being able to see my wings flex when I look sideways. I couldn't imagine a bigger waste of resources actually, as long as the non-visual parts are implemented (structure damage, shaking FFB, structure "squeak", etc..)
Sternjaeger Posted January 24, 2014 Posted January 24, 2014 it would not affect CPU power, it's already part of the DM, it's like opening or closing a landing gear, or a propeller tip bending, it's a triggered effect.
Reflected Posted January 24, 2014 Author Posted January 24, 2014 it would not affect CPU power, it's already part of the DM, it's like opening or closing a landing gear, or a propeller tip bending, it's a triggered effect. If it doesn't, then sure, let's have it. But I highly doubt that.
Sternjaeger Posted January 24, 2014 Posted January 24, 2014 (edited) think about it: the calculation for the DM is already there, an animation of the overstress is not going to affect your FPS in any way, it's just about making it look realistic. http://youtu.be/3KJJmjM0B2M?t=3m44s Edited January 24, 2014 by Sternjaeger
II./JG27_Rich Posted January 25, 2014 Posted January 25, 2014 It almost reminds me of one of those awful speed wobbles on a bicycle or motorcycle. Nothing more scarey
JtD Posted January 25, 2014 Posted January 25, 2014 Oscillation starts because at near zero deformation, the resistance to deformation is near zero. So even the smallest force will cause a very small deformation. And then, as already stated, natural frequencies begin to matter. 2
Rama Posted January 25, 2014 Posted January 25, 2014 Oscillation starts because at near zero deformation, the resistance to deformation is near zero. So even the smallest force will cause a very small deformation. And then, as already stated, natural frequencies begin to matter. Yes, because no material is perfectly rigid.
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