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As I understand, both are dynamic effects of aeroelasticity - however, what is the exact difference between buffeting and flutter?

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    $\begingroup$ Perhaps it would help if you stated precisely what you think those two terms mean, which should be easy to look up. Then, the difference will probably be fairly clear. $\endgroup$ – David Richerby Apr 3 '18 at 9:23
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    $\begingroup$ @ymb1 And, yet, the mouseover text for the downvote button says, "This question does not show any research effort [...]", indicating a clear network-wide policy that askers should do at least some research before asking questions. The current one-sentence question shows zero evidence of that, and also gives potential answerers little hint about what level to pitch an answer at. $\endgroup$ – David Richerby Apr 3 '18 at 13:24
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The vernacular meaning is...

1) Flutter is un-commanded self perpetuating (positive feedback) destructive & adverse cyclic movement of any part of an aircraft. It most commonly occurs on a control surface but may be an entire wing, tail surface, or more rarely fuselage or other part or device. Flutter may be induced either mechanically or aerodynamically and may be sustained mechanically (i.e. engine or prop, landing gear or ground resonance of a helicopter skid) or aerodynamically by self perpetuating (positive feedback) force. Mechanical inception can be (but not limited to) brisk or pilot induced oscillation, weak, unsupported, or flimsy structures. Aerodynamic inception can be (but not limited to) undesirable cg, or aerodynamic forces on parts. Flutter is always undesirable, dangerous and a destructive force.

2) Buffeting is a turbulent stream of air striking any part of the airframe. The turbulent air may be completely external (weather) or created by the aircraft it self (prop, wing,etc). The most common form of buffeting is turbulent airflow over a wing (i.e. during a stall or wind gusts) striking the wing or horizontal tail. Buffeting is not usually considered self perpetuating with positive feedback, nor is it considered to be precisely cyclic or harmonic - though it may be repetitive. Buffeting is usually considered undesirable but benign and not a destructive force.

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Flutter is characterized by a frequency neighbourhood of a structural eigenmode and a cyclic aerodynamic load. This causes their motions to be mutually reinforced.

Buffeting, on the other hand, is just the consequence of a cyclic aerodynamic load, such as an oscillating shock, or separated flow hitting another surface downstream.

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Both buffet and flutter is a vibration of a surface of the aircraft, such as a wing or tail, due to the air flowing over it (especially if the air is turbulent). The difference, I would say, is;

  • If the surface does not exhibit an increasing amplitude, as it is naturally damped at the frequency of the excitation force, it is called buffet.
  • Conversely, if the surface is not naturally damped at the frequency of the excitation force, its amplitude of oscillation will continue to grow, and likely structurally fail, catastrophically, it is called flutter.

In flutter, there is a coupling between the aerodynamic forces and structural response, that needs to be taken account of, in analysis of flutter, which is not required in buffet. See the first paragraph of this technical paper.

The flutter analysis is generally conducted by complex eigenvalue analysis, whereas the buffeting response is typically estimated using a mode-by-mode approach that ignores the aerodynamic coupling among modes.

As examples of each, here is a video of flutter. As can be seen, the amplitude of vibration starts to grow, and it wouldn't appear surprising if the tail plane failed very quickly.

In comparision, the F-18 has experienced tail buffet from vortices from the wing leading edge extensions. As can be seen, the tails vibrate, but its a much smaller oscillation than the flutter example. While it could cause cracking in the long term, it would not be expected to fail instantly.

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  • $\begingroup$ " ...due to the air flowing over it " - not necessarily... it can be induced mechanically such as landing gear, engine or prop vibration. $\endgroup$ – jwzumwalt Apr 4 '18 at 12:51
  • $\begingroup$ @jwzumwalt. Hi. I agree a "mechanical" event such as PIO or turbulence off the landing gear could trigger the occurrence of flutter. But, in either case an aerodynamic force still results on the surface. So, as I see it, the air flowing over the surface, still plays a fundamental role. Or have I missed something? I think all answers are very similar, just a different way of saying it. Regards. $\endgroup$ – Penguin Apr 5 '18 at 11:37
  • $\begingroup$ This list tends to have folks that split hairs - I believe more in a sensible approach. Its more of a FYI that there is both mechanical AND aerodynamic flutter, and combinations. Pilots usually only think of control surface flutter - but there are a number of other types. Purely mechanical with no aerodynamic input is a helicopter skid that produces ground resonance that can completely destroy a helicopter in less than 10secs. Flutter in the landing gear such as a tail wheel can tare the whole tail off an airplane - no aerodynamics there either. There are others... $\endgroup$ – jwzumwalt Apr 5 '18 at 12:15
  • $\begingroup$ @jwzumwalt. OK, with the tail wheel example I think what your are suggesting there is a type of "shimmy". If that's the case, I now see an example that is totally mechanical. So, thanks for the comment. I had interpreted "flutter" to be only the aerodynamic type (especially as it was being compared with buffet). $\endgroup$ – Penguin Apr 6 '18 at 10:11

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