My hangar neighbor, Tracy Saylor, with the fastest RV6 in the world,
bought a German three blade so-called "composite" prop. 99% pure wood.
top speed went down from 243 mph to 223 mph. Klause thinks the MT is
untwisting. Tracy had his constant speed metal prop blades twisted
for optimum speed at around 250 MPH. He specified the same twist for
the MT.

Since the blades are 99% wood I find that highly plausible as the
modulas of elasticity of wood and fiberglass for that matter is rather
low. MT claims the low modulas of elasticity is necessary to help the
hub live under aerobatics conditions. This claim I buy. It does indeed
reduce the stress on the hub.

Three blade props are historically slower than two blade props
but not that much slower. Tracy re-installed his old metal
constant speed prop. He will race the airplane at Sun & Fun I think.

MT makes an excellent prop, and as you say, it is more wood than composite.
A Lancair owner at Camarillo also reported a reduction in top speed when
he replaced a fixed pitch prop with an MT. I tended to attribute this mostly
to my assumption that he was probably overspeeding for more HP with
the fixed pitch prop. However, the twist distribution of the MT is
no doubt optimized for the slower aerobatic and GA aircraft which is
their primary customer base. I would suspect that the constant speed
makers as a rule would tend to be inflexible on the twist schedule.
If someone could measure things like twist distribution, blade width
distribution and airfoil thickness in the outer radial zones, the reason
for the difference may show up. For top speed, I would expect a point
designed fixed pitch prop would be superior, particularly for
point to point top speed (take off and climb performance would be
compromised)

Incidently, the stated twist distribution for the LAEV blades is very
strange, and I have not heard any response on the reason and logic
of that decision - Vance J

As a guess Vance what speed would you say it is twisted for. 
I think Bill made some assumptions as to the actual direction of the in flow
around the hub. I think he assumed a certain amount of external diffusion
directly in front of the cowl as I recall. Is it the hub angles
of attack you are concerned with?

Paul Lamar
 
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