Thread: Folding Aerocap
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Old 12-07-2019, 04:09 PM   #22 (permalink)
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Originally Posted by Hersbird View Post
Would the deforming be necessarily bad? If there was a high pressure area and it could push in vs a low pressure area that it could expand into. I guess the problem being the rigid parts that have to stay in one place.

How much does material make in the surface skin drag at say 70 mph? Would it be worth using a smooth fabric like Sunbrella vs rough duck canvas?

Actually Sunbrella is also woven, maybe PVC vinyl?
If you'd nailed a really clean shape,and then the airflow itself altered that form,you'd have a can of worms,as the deforming force would be varying as the square of the velocity and shape,all over the place,depending on elasticity.The stiffer the fabric the better.
It's why fabric-covered aircraft are shrunk-tensioned and doped to 'fix' the shape.You don't want the center of pressure moving around on you.
Race car driver,Bernd Rosemeyer was killed when under-spec,weak sheetmetal deformed at high speed,producing uncontrollable,destabilizing aerodynamic forces. Early V-2 development rockets crashed for the same reason.Wernher von Braun had to risk his life,close to the crashing in order to figure out what was happening.
Skin friction is only a minor portion of air drag.You could probably use carpet back there if you wanted.That entire area is already within a turbulent boundary layer,with the free,inviscid flow a couple inches above it,flowing laminar over all,as if it were on Teflon'd glass.Aeroelasticity is not your friend.
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