Paul wrote:

I am glad you appreciate that 30% Tracy.
And you are not using cowl flaps? The dynamic pressure
is four times higher at 200 mph than it is a 100. You need a lot of air at
100 MPH to cool during climb but you don't need it at 200 MPH. Cowl flaps
are a cheap way of cutting the drag. I have no sympathy for you guys :-)

Jerry Hey wrote:

I am putting internal scoops in the tail section that will have
flush openings.  I think this will cut drag as far as it can be cut.
Jerry

The cowl flaps cut the drag of the intake belly scoop when they are 
near closed at high speed. They do this by increasing the pressure in
the whole system and  diverting the unneeded air around the high drag 
opening and internal cooling system. Same as a P51. Cowl flaps 
also speed up the exit air which adds a bit of thrust that counteracts 
the cooling drag by a little bit.

Its got little to do with the drag of the air out let openings per se.

My guess is well designed cowl flaps would be good for around 7 MPH at 
200 MPH with a well designed cooling system.

Paul Lamar
 
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