Thread: Folding Aerocap
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Old 12-09-2019, 12:54 AM   #28 (permalink)
The Armadillo
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Originally Posted by aerohead View Post
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.
Thank you for your input on this, Areohead, I really appreciate it! I wasn't sure if the deformation was a good or bad thing, but a post like this helps me know what direction I should work towards for my next version.

The other day I was on the highway and I was driving next to a Porsche 911 convertible with its top up. I was looking closely at his convertible top at speed and I noticed that it did not deform at all. No wrinkles, no shaking, no bulging... it acted as rigid structure. Although I don't have the resources that an major auto manufacturer does, I think I should be able to create a aerocap that performs similar to that convertible top. I've learned a lot from this first version of my cap and I hope to use all these lessons to create a better version.
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