Jerry Conners wrote:

Paul:

No cowl flaps but some version of air flow adjustment
is in the mill.

Jer

=====
Jerry L. Conners, PE
Civil Engineer
Comstock Aeronautics and Engineering
775-688-1253 (work)
775-847-0214 (home)
PO Box 509
Virginia City, Nevada 89440

If you cut it off at the front you will get some of the benefit when
it is fully closed. When it is partial closed or fully open there will 
be a loss of dynamic pressure in the cowl due to the obstruction of the 
mechanism itself... be it a butterfly valve or adjustable shutters.

Cowl flaps on the other hand can be optimized under all conditions 
to recover some of cooling drag by creating a slight thrust affect.
Sort of a minor ram jet affect. Air comes in, is slowed, heated
and ejected at a higher speed. The P51 is a well known example
but all properly designed cowl flaps work the same way.

When they are completely sealed all air is diverted around the intakes.
by a pressure build up in the cowl and the intake opening. This
is known as external diffusion. It is the reason a spinner never
showed a top speed advantage on blunt radial engine WW II fighter planes
like the Corsair.

Cowl flaps are worth several kts on my C182 and will be installed on
my Cruiser.

Paul Lamar
 
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