(a post from the past - brought to you in person
since I couldn't figure out how to reference a single
message from the archives...)

refering to a skin vibration issue on an amphibian project.
(12/18/2001)

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The structure is built but has serious vibration problems?

If it's not something out of balance, then it's probably
(oh no!) resonant harmonics.

Something I learned here...

"brute force works fine, but you have to use enough of it".


All things have a natural vibration frequency.
When tapped, that's the note they "ring" at.
The natural resonant frequency of that thing.

Tapping on a tuning fork makes a single clear note.

Tapping on a bridge, say a column of soldiers marching
across in step, can destroy the bridge.

Two very different examples of harmonic resonance.

No way to offer specific corrections. But something to
think about?

You can't _see_ vibration. (unless it gets bad enough
that you can, but that's way too late)

But you can feel it. Fingertips and backs of the knuckles.

Generally, I'd immediately suspect long slender structures.
Especially highly stressed long slender things (like engine
pylons?)

Start her up and get her buzzing just a litle bit, and just
feel her up. Touch all her parts, and in different places.
See if you can find what's making her shake, and where she's
really excited.

(whew!)
Anyway...

That's where you'll want to stiffen it up...