Old 11-14-2020, 07:04 AM
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speedracerntrixie's Avatar
Join Date: Jun 2010
Location: Happy Valley, Oregon
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As has said already, there are many variables. One that hasn't been brought up yet is the shape of the exit. If at all possible try to create a low pressure area at the exit. For example, on some of the big twin engines some guys used to add a lip at the front of the exit hole. A current project of mine has the bottom edge of the cowl dropping down 1.5" lower then the fuselage. It's much more efficient to pull the air through the cowl then it is trying to push it. As mentioned, you need to get flow through the fins and not just around them. A good example of this is some of the F-1 racing airplanes.

F-1 race plane. Fairly small intake due to efficient baffling.

A current project of mine, the original owner went a bit overboard with the intakes. I've also closed up the bottom.

Gas engines produce more heat then equal size glow engines. My YS 140 doesn't require anything more then having the cylinder head peeking out the bottom of the cowl.