"Kent, Russell" wrote:

Paul Lamar wrote:

The big problem when it comes to aerobatics is finding a gear box
that will accommodate a hydraulic constant speed prop. We are just
not there yet and as I understand it an electric constant speed
prop does not change pitch fast enough for aerobatic use. I could
be wrong so check with Hoffman or MT. On the other hand it does
not hurt the rotary to overspeed to 10,000 RPM so this may not be
an issue. A piston engine will hand grenade if over speeded to
that extent.

The engine may not be the speed limiting component.  How's an MT or
Hoffman going to like spinning at 3500 RPM? (10,000 / 2.85)  Let's see,
centripetal force is F = mv**2/r.  Since m and r are constants for our
theoretical engine & prop, the force on the blade goes as the square of
the (rotational) velocity, and increases by a factor of 3500**2/2400**2
= 2.13 (i.e. 113% greater).  It is my understanding that props have
relatively tight safety margins...

Russell Kent

I think the FAA requires a test at twice top RPM or about 5,800 RPM
as I recall.

Paul Lamar
 
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