fin safe speeds?

[Mitch Smith]

Ok, anyone have a estimate for the safe speed of 1/4″ wood fins? A few of the engines I am looking at for OF will push it just about mach. The only reinforcement on them is f/g on the motor mount and on the external fillet. I am looking to find what the largest motor I can safely fly for altitude. This will be for my extended Magnum. http://www.tripolicolorado.org/photos/2009_Fall_Frenzy/tcfallfrenzy09-040.jpg

[Warren B. MusselmanModerator]

There are a LOT of variables to that question – first two would be the size and shape of the fins. The larger the semi-span, the more prone to fracture due to flexing. Conversely, the shorter the semi-span, the more likely they will survive. Generally full tip to tip fiberglass or carbon is considered normal for birds that approach mach.

Warren

[Mitch Smith]

Thanks Warren. That is the type of info I was looking for. I am thinking keeping the speed to .85 mach maximum and then building another rocket fully glassed for speed.

[Jeffrey Joe HintonModerator]

Actually, finding the speed of cardboard or plywood or fiberglass or carbon fiber is a very worthy endeavor and I’d do that if I were you. But from a safe distance, of course. Let ’em fly!

[Mitch Smith]

Safe distance?…you mean I can’t use a lighter and light the fuse?

[Warren B. MusselmanModerator]

Fin flutter is a real interesting problem. If you’d like, come by my EZ-Up (probably next to the admin EZ-Up on the flight line) and I’ll show you some fins meant to handle Mach 2 or better.

Warren

[SCOTT EVANS]

Ok, anyone have a estimate for the safe speed of 1/4″ wood fins? A few of the engines I am looking at for OF will push it just about mach. The only reinforcement on them is f/g on the motor mount and on the external fillet. I am looking to find what the largest motor I can safely fly for altitude. This will be for my extended Magnum. http://www.tripolicolorado.org/photos/2009_Fall_Frenzy/tcfallfrenzy09-040.jpg

Just try it, (what ever motor) and let us know how it worked!
Maybe we will know what not to do next time. 😉

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