I see. You are thinking of a pusher. Well perhaps you will need a shield
to deflect any oil vapor that tends to accumulate on the front side of the
spinner bulkhead. Good point. The Hoffman, IVO and the MT would have the
same problems.

You are right, so far people worry about props other than composite or wood on pushers due to the loading/unloading as the blades pass behind the trailing edges of the cowling. All metal props are a no-no. Just the turbo 13b alone is such a significant boost over the IO-360 that we will be happy with some flavor of fixed prop for awhile.
...Chrissi

Most high speed tractor hombuilts have such a high power to weight ratio that the fixed pitch prop
can be optimized for cruise and still allow the airplane to take off in less than 1000 feet.

I am not sure I can say that about canards however. I am not sure why. Just
an impression I get from talking to people. Perhaps the canard does not have
enough elevator authority to rotate the wing to an optimum angle of attack
for a short takeoff. If true you will need a variable pitch prop to
optimize both takeoff and cruise MPG.

This is what one prop company claims a variable pitch prop can do for
takeoff and climb.

Of course with a turbo rotary you can always run up the boost and not
worry about blowing the cylinder heads out through the sides of the cowl :-)
Dave Garber and Greg Richter proved that.

Paul Lamar

Paul
How does the controllable pitch prop compare to a "constant speed prop"?
Royce

A constant speed prop keeps the RPM constant through a fly ball governor
mounted in the governor (what else? duh :-)). When a fixed pitch prop airplane
climbs the RPM slows, the engine is loaded more but the potential HP is 
reduced. When it dives the RPM increases but the prop load on the engine 
is much reduced. With a controllable pitch prop you set the pitch
for max RPM and max HP for climb. When you get to cruise alt you
set the pitch and RPM for max MPG at what ever cruise speed you choose.
Lower calm air cruise speed more MPG.

BTW the intake runner length should be tuned for max torque at your cruise RPM
which will give the best BSFC. That does not necessarily mean the 
intake and exhaust port timing is any different than the intake and
exhaust port timing for max HP but it could be. The wankel port
timing leaves little room for adjustment. The Leman peripheral port 
engine has about the same intake and exhaust timing as the 13B six port.
The area of the intake ports is greater but that always helps torque.
What differs greatly is the intake runner length. Now having said all that
there is potential for varying the intake length for max BSFC at cruise
and at max HP RPM just like the Leman engine does but at a lower speed
range. How did I digress so far from the topic? :-)

Paul Lamar
 
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