[aerohead]

Originally Posted by sregord

Thank you aerohead.
I know I didn't describe the concept well ...as "fabric". of course you, freebeard, & I were discussing inflatable boattails back at 5-22-22 in this stream..where I mentioned billboard covers(vinyls/tarps)
https://ecomodder.com/forum/showthre...tml#post668627
They're like: https://www.ebay.com/itm/256297755605?
Something like this..as does coroplastic needs a "frame" to be strong at 70mph, plywood or aluminum sheet may not.

Yes, the frame allows tensioning of the fabric, which will then become a crude 'drumhead' with a percussive natural frequency of vibration ( flutter ), plus any resonant frequencies ( octaves ).
And as mentioned, 'stiffeners' might be a requirement.
When I attended the Solar-500 at Phoenix International Raceway, the pickup truck class was allowed to run full tonneau covers.
All of them were coated fabrics, like 'Naughahyde', and behind the cabs, it looked like Yoda was under the fabric, trying to stand up ( fabric sucked up towards low-pressure of the bed vortex ), while the rear half of the fabric was forced downwards into a 'pool', by the air passing over the vortex, and slamming into it from above.
No visible flutter was observed, but that doesn't say that it couldn't, at a different velocity.
NASA/ Lockheed has some great footage of the wings of a C-130 wind tunnel model coming apart due to flutter in the big tunnel at Marietta, Georgia.