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

Perry, the understructure was a laminated wood prop, covered in Kevlar

and a

topcoat of fiberglas for finishing (Kevlar gets fuzzy if you sand it).

The

builder had been flying a similar prop on the 0235 Long EZ successfully,

but

the 0320 broke it on first flight. I don't know the number of plys.
Herb

Herb,

Thanks for the response. Completely different structure than this prop. In
this prop the structure is all carbon fiber, no wood. If you sawed the blade
off near the root I think you would be shocked how much carbon is in there.
Our main problem will be providing enough HP to fully test it.

I tried kevlar on my prop, hoping it would resist leading edge rain erosion.
No luck. I've heard the best leading edge protection is the 3M tape
available from Aircraft Spruce.

Perry

 
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