Perry Mick wrote:

Paul,
Here are some photos of the Cosman prop. Tractor, reverse rotation 2.17,
72" diameter, 88" pitch. The blades are carbon, the hub is
hardwood/composite 9" in diameter and 5" thick. The mounting holes still
have to be drilled. The pitch twist is maintained all the way to the
hub, as it is in ducted fans. I will be sending it to you for testing on
your test stand when it is ready.

--
Perry Mick
http://www.ductedfan.com

You do beautiful work Perry.

Paul Lamar

Perry, I bought a two blade composite prop for my 0320/Long about 20 years
ago with the thin inboard section like yours. On the first flight, both
blades broke about 12" from the centerline, chordwise, and the break was
total, but the blades were retained by the Kevlar covering. The blades were
floppy and smoking from the friction when I landed. This was a couple
minutes flying all in the pattern.

Mike Melville told me if either blade had departed, the engine would have
departed almost immediately and the elevators would not have been adequate
to hold the nose up with the cg that far forward.

I went back to the stronger inboard sections and feel like I used up too
many blessings on that flight to risk that much efficiency again.

Herb Sanders

On the other hand Perry has many hours on this type of design running at 5000 RPM
in a direct drive  rotary. It does need to be tested on the ground no doubt about it.

Also you had that prop on a 4 cylinder Lycoming which has a 
horrendous torque pulse. Well over 1000 ft/lbs. The torque pulse on a rotary 
is much much less. Lycomings are almost as hard on props as a diesel engine.

BTW all experimental aircraft should have safety cables to retain the
engine in case of prop blade failure.

Paul Lamar
 
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