Effect of cooling/cowl flaps on speed (1 Viewer)

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wuzak

Captain
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Jun 5, 2011
Hobart Tasmania
I was just looking at this report and found an interesting table on the effect of cowl flap operation on speed.

Cowl Flap PositionCowl Flap Opening (in)True Speed (mph)Speed Loss (mph)
Closed0284-
1/4 Open1-5/82786
1/2 Open3-1/426420
3/4 Open4-7/824935
Wide Open6-1/223648

This is a significant drag rise for cooling purposes.

I guess if the engine can stand extra temperatures for a few minutes that keeping the cowl flaps closed would help in trying to evade a pursuer, but not if it means the engine melting over enemy territory.

Is there any data with regard to radiator flaps such as on the P-51, Spitfire or Mosquito?

Later radial engine types used different systems, like the cowl ring, which provided the same function as the cowl flap but without sticking into the air stream.
 

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