Byron Brandon Ward wrote:

A few questions:

What is a good change in diameter (or area) per length for a diffuser to
minimize friction?

Attached is a set of coordinates for an ideal diffuser from Kuchemann &
Weber.
Kuchemann-duct-Coord.gif

Also what are the (approximate) dimensions of a one-rotor engine?

Well it is 12.5 inches high and wide I would say the length as a guess
is around 12 inches. That does not include things like distributors or
oil
coolers.

For the people that are doing/have done under cowl rad installations,
could you go into a little more detail. Is the cooling air simply taken
from inside the engine compartment and then drawn through the rad to the
outside? Or is there a seperate diffuser that occupies the engine
compartment, but doesn't draw air from it. Isn't taking air from near the
propeller for cooling purposes bad because it is turbulent?

That is myth. Just about all air cooled air craft engines take cooling 
air from just behind the prop. There are plenty of drawings on this 
subject on the ACRE NL web site.
http://home.earthlink.net/~rotaryeng/    

Finally, has anyone experimented with taking air from right in front of
the canopy, where it is going slow anyway. This way it would seem you
could eliminate or at least shorten the diffuser.

Not to my knowledge and I think that might work well as it is
widely used in cars of course.

Thanks,

Byron

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