OK. I've been toiling with developing a way to test our fin designs in a high speed wind tunnel:

1) We could build a compressed air wind tunnel and get fast (perhaps supersonic) flows, but only for a brief period and not at one steady flow rate.


2) We could build a small high speed wind tunnel using a 2 stage centrifugal fan driven by a small block chevy (the red-neck in me loves this idea), or perhaps a more manageable surplus 4 cylinder engine from work (50 HP, $30).

What about moving the fin in the air?

1) Moving the fin on a test rocket doesn't allow steady state testing, and instrumentation is a problem.

2) The fin travels a long way at 300 meters/second, so a linear track is out of the question.

Finally an idea hit me: Move the fin in a circle! (Naturally, this idea came to me while I was working on my helicopter).

We can remove the rotor blades from a gas powered helicopter and replace them with carbon fiber tubes (available at local hobby shops). At the end of the tubes, we attach our fin design. With the existing helicopter mechanics, we have precise control of the blade's angle of attack. I happen to have an old helicopter that I can donate to this cause. Naturally, this test would take place behind a shield and/or at a remote location.

At typical rotor head speeds of 2000-3000 RPM, a fin mounted at a radius of 600 mm from the center of rotation will see airspeeds of around 125-190 meters/second! That's 280-425 miles/hour!

Further, we can evaluate the lift / AOA curve using a scale under the helicopter.

This could easily be expanded to a 1 meter swing radius, getting us into the trans-sonic speed regime. Filming the blade with a high FPS camera would show us shock lines if we get there.

Fire away with thoughts, check math, etc.





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