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

Do you have any idea of the layup structure on the failed prop Herb? You said
it was composite.

This prop is built similar to my 5500 RPM fan that has 450 hours on it. The
blade has carbon skins and carbon spars. Just like the spars in your LongEZ
wings, they get thicker as you move inboard towards the hub. I think the
stresses may actually be lower for the slower turning prop than for the fan,
but the prop will have twice the HP applied. Yes it is experimental, and we
want to ground test it as much as possible.

Vance, I will send the design files for the prop to the list later tonight, as
I'm trying to get a 13B installed in my RX-7 today.

Perry

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