Direct-drive at 7000 shouldn't be a big problem, I was turning mine at 5400.

Centrifugal acceleration at the tip is V^2/R, V is tangential velocity,
generally around 750 to 900 fps to keep it below the speed of sound.
The V^2 term then is constant as you increase RPM and decrease R.
Centrifugal acceleration is increasing only inversely proportional to R.

For 7000 RPM and a tip speed of  750 fps you would want a diameter of
about 20.2 inches. Use very strong but lightweight materials to keep the
mass to a mimimum, force = mass * acceleration.

Perry

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I have an idea Perry. Got any of those old direct drive fans
and old direct drive fan extensions lying around you can sell/send to
Doug? Doug could cut some off the tips to get them up to 7000 RPM.


Paul Lamar ...No rotor no motor.

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No, I've sold them all except fan3, the one that I flew for 500 hours.
I want to keep that one.

Perry

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Is the person you sold them too going to use them on a rotary
powered airplane? Just curious.


Paul Lamar ...No rotor no motor.

I sold the six-blade to someone who was going to use 300HP on a seaplane,
don't know what engine.
I sold the 3-blade to a guy who wants to use it on a gyrocopter, I think with a subaru. I didn't offer these for sale, experimenters out there contacted me for old unused items.

Perry

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