Byron Brandon Ward wrote:

In the P51 ostensibly  there was thrust from the cooling system
exceeding the drag of the cooling system for a net increase
in the speed and efficiency of the airplane.

Which brings up another question I've always wondered which is if there is
as much energy in heat going out the radiator as the e-shaft why doesn't a
decent (homebuilt) system capture even a little bit of it. Even 5% on a
200hp engine is a significant amount. In my mind one of the main
advantages of a rotary (or any liquid cooled engine for that matter) is
that cooling can be made much more efficient and things are neater up
front.

We'll just have to try it to find out I guess.

When I get to that stage (probably quite a while) I'm going to try and
twist some of my professors arms to see if I can get some help on this. It
certainly seems like a well thought out duct could a least have very
minimal drag. I suppose it all goes back to the cost/time issue. If we
were developing commercial airplanes or had a nice military contract a lot
more testing and development could be done.

BTW things get a lot more interesting when you throw temperature
into the equation (P1 X V1) / T1 = (P2 X V2) / T2

What do you mean by this?? I always assumed the shape of the ducts took
into account the change in P,V, & T due to the rads. Is this not the case?

Byron

I am sure the good installations Like the P51 have taken temperature
into consideration. It would be interesting if they did this in a wind
tunnel.
I don't think Hoerner mentioned it in liquid cooling chapter of Fluid
Dynamic
Drag.
 
The loss in the exhaust is twice as high as the loss in the cooling and
the best anyone has been able to do so far is recover 20% more HP out
of the exhaust. Namely the Curtiss Wright R3350 turbo compound. The P51 
was rumored (and there is evidense to support this) recovered something 
from the cooling system. That is one of the reasons it was faster than
the 
Spitfire with the same engine and prop.
 
Paul Lamar
 
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