My 2 cents worth on the subject - I have not seen the so called high

twist version of the

Ivo prop
but the flat 2 bolt mounting does not preclude having  a steeper angle

near the hub. This is

no
different than the flat area on either awodd or metal fixed pitch prop,

so he could set this

area
at a good compromise angle if he invested in the tooling to do so. My

main concern withe the

Ivo is in making making it torsionally flexible enough to be twisted

with that small rod, it

now concerns me about flutter. The 2 bolt mounting also worries me, and

even he advises

against the use on engines with high pulsing loads such as the big

fours.. A contollable

prop
is relatively easy to design, and not that hard to fabricate - but

sphincter tightening bear

to prove.
I am building a 3 blade variable system, but intend it for use as a sort

of ground based

air dynomometer for a long time before even considering fitting it with

flight worthy

blades.
Vance

 Robin Ream wrote:

Hi Vance,
    Are you sure this drawing is right?  That doesn't really look like it
would twist all that much.
Robin

That drawing (I made came) from a broken IVO prop somebody gave to me.
I think it was Chuck Harbert as I recall. After his second forced
landing with the main gear still up.

Ironically the variable twist steel tube version does not twist 
on its own because the modulas of elasticity of the steel tube
is 30,000,000 while the fiberglass skin is a rubber band by comparison.
Hand laid up fiberglass is probably less than 1,000,000. Not to 
mention there is only one layer of bid or so.

This drawing is of the variable twist version. The steel tube is
rotated in the hub to change the angle of attack of the outer 20%
of the prop blade there by changing the twist. The non variable
twist version does not have this steel tube so consequently it is
easily twisted by aerodynamic forces and I think that was what
Vance was referring to.

The carbon cloth adds nothing to the torsional stiffness of the blade
as it is out powered by the rotating steel tube and is not formed into
a complete torque box. IMHO it is merely a marketing ploy to claim it is a 
carbon composite.

Paul Lamar

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