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Over-achiever fin fillets?


Old 06-27-2015, 05:05 PM
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Default Over-achiever fin fillets?

I see a lot of high-power rocket build threads where the builder shows off the construction of ample-to-monstrous fin fillets. So far, I have refused to do this if Iím able to get ample epoxy inside between the motor mount and airframe.

So I donít want to shed fins, either, but my meager understanding of aerodynamics says that fillets can actually have more drag than a 90-degree butt-joined airfoil on a round fuselage. Case-in-point, the F4U Corsairís bent wings eliminated the need for fillets by joining at 90 degrees (while giving good prop clearance with short landing gear). I looked at pictures of the X-1 and X-15 and they appear to me to have tiny, if any fillets, too.

So what gives? Is this tribal knowledge gone out of control or do the standard rules not apply at smaller scales?

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Old 06-29-2015, 04:04 AM
Bob Jablonski
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Small fillets IMOHO help fill the small voids in the tube slots which also stiffiins up the fin to prevent flutter (a bad thing). The large fillets on some rockets would be more for the looks then the structure.
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