"flutter" is bad, and why exactly?

[j-c-c]

Why Bad

Originally Posted by aerohead

* flutter is cyclic deformation
* cyclic deformation can lead to 'work-hardening'
* work-hardening can lead to embrittlement of the panel
* embrittlement can lead to fracture
* fracture leads to panel failure
* Panel failure alters pressure distribution in the vicinity of the failed panel
* the altered pressure distribution can affect aerodynamic stability.
* Flutter-induced aerodynamic instability has killed a number of people. Aircraft and record cars.

Granted, and you are stating the obvious IMO, my question implied, was from mainly an aero perspective rather than structural.

[Piotrsko]

Ok then simple: calculate the square footage of the surface movement or even guesstimate it, figure out how much your CoD is in square feet, and add this to the flutter drag. Shouldn't be a huge number unless the panel has a loose end.

[kach22i]

Originally Posted by j-c-c

Why Bad

Granted, and you are stating the obvious IMO, my question implied, was from mainly an aero perspective rather than structural.

It is curious that both the Wikipedia entry on "Aeroelasticity" and Aerohead's reply focus on the structural effects of flutter.

Is there a way to exclude the structural effects and just focus on the aerodynamic energy it takes to create and dissipate flutter?

Are these two elements so intertwined that one cannot talk about one without talking about the other?

I suppose it would help if we define an "A" and a "B" situation.

A: Flutter caused by structural deficiency, and why is it bad.

B: Flutter caused by shape/body/form imperfection, and why is it bad.

It seems to be we are talking about "A" when the original poster wants to talk about "B".

EDIT:

The PDF in this link may help explore the different aspects of this topic, I like the pyramid diagram it begins with.

https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAD

Finding the right question comes before finding the right answer.

Finding the right terms, the correct language is needed to communicate intended thought(s).

[freebeard]

Cut out the middle man: http://www.ltas-cm3.ulg.ac.be/AERO00...elasticite.pdf

The triangle is a good frame.

I suspect the effect is more acoustic than thermal.

[j-c-c]

Originally Posted by kach22i

It is curious that both the Wikipedia entry on "Aeroelasticity" and Aerohead's reply focus on the structural effects of flutter.

Is there a way to exclude the structural effects and just focus on the aerodynamic energy it takes to create and dissipate flutter?

Are these two elements so intertwined that one cannot talk about one without talking about the other?

I suppose it would help if we define an "A" and a "B" situation.

A: Flutter caused by structural deficiency, and why is it bad.

B: Flutter caused by shape/body/form imperfection, and why is it bad.

It seems to be we are talking about "A" when the original poster wants to talk about "B".

EDIT:

The PDF in this link may help explore the different aspects of this topic, I like the pyramid diagram it begins with.

https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAD

Finding the right question comes before finding the right answer.

Finding the right terms, the correct language is needed to communicate intended thought(s).

Most certainly.

Thanks for the link, might take few reads for all that to sink in, but this stood out:

"There are no empirical or statistical design
methods for aeroelastic design; flutter is a very
complex phenomenon"

[aerohead]

Originally Posted by j-c-c

Why Bad



Granted, and you are stating the obvious IMO, my question implied, was from mainly an aero perspective rather than structural.

Then we'd want to look at 'where' the flutter occurs.
Side body deformation could affect yaw moments and directional stability, depending on velocity, winds, gusts, etc..

If it's anywhere in the aft-body, it could trigger separation and induced-lift, laterally, or vertically.
Cyclic deformation could induce Karman vortex street-esque phenomena, tail wagging the dog.
Aeroelasticity implies unstable drag coefficient. I don't know how that could ever be beneficial.