Forget it chaps ! It just introduces uncertainties, complications, costs,
time and so on. The following is based on flying not theory.
1) Top-of-cowling vents have negligible effect on densifying air, even with
outlets at the bottom of the cowling as large as 1" all the way across. And
unless you fly at greater heights than is prudent on a VFR a/c, the craft
will turn in speeds and economy the envy of most competitors due to it's
slippery airframe.
2) The instrument module space and cabin get hot through conduction via the
firewall, and exhaust gases along the bottom of the fuselage, even in Uk.
NACA side vents just cool the outside legs of the crew. Running "cooling"
ducts from the frontal area to the footwells will become a heating system
unless you use insulating ducting. Certainly don't run hot air via the
dreaded heat-exchanger unless perhaps you are in Alaska.
Simplest and most refreshing for crew cooling are closable 2.5" x 1/2" slots
below the windscreen. AFAIK first seen on James McDairmid's machine and
unashamedly copied on to my own. Thanks James.
Head returning to below parapet.
Graham C. G-EMIN
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