enginehistory.org

[rwahlgren]

http://www.youtube.com/watch?v=51BEbZlps80

At about 4:45, "a propeller system turning 12,000 rpms."

[kmccutcheon]

I would guess that is a "typo"; 1,200 rpm is much more likely.

Propeller rpm is typically limited such that the tips stay subsonic. This is a function of propeller rpm, aircraft speed, altitude and temperature. The tips can be swept back (like the ones in the video) to postpone the onset of shock wave formation.

Model airplane propellers, 3" diameter x 1.25" pitch, on Cox 0.010 in³ Tee Dee engines, turned 30,000 rpm. Large props, intended for the big post WWII bombers, aimed at 800 - 1,000 rpm.

There have been a few unsuccessful attempts to build supersonic propellers. Most notable was probably the Republic XF-84H, which was so noisy that it made people sick.
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Kimble D. McCutcheon