Did some more pressure measurements on the first gen RX7
today. Since the pressure in the cowl was high
I thought I would try opening the cowl flaps.

No luck. Only a minor improvement in under hood pressure.
3.7" H2o in front of the rad 2.7' H2o behind the rad and
1.8" H2o on the firewall. Essentially the same as it was with the
hood closed. I surmise the reason for this is the pressure
at the base of the windshield is real high. Air is going in
the engine compartment from the base of the windshield and not
out as one would think.  We shall see with the next test.

Paul Lamar

OK here is what I did. I placed one of the pressure taps about
two feet ahead of the windscreen and one at the base of the windscreen.
The idea here is to find the best place for a rad air outlet.
The forward one is just above and behind the rad.

As I thought the pressure at the base of the windscreen was 3.6" H2o
roughly the same as it was on the front of the rad. The pressure
on the hood however was minus one inch of H2o. One inch of water
BELOW atmospheric pressure! Ideal place for
a rad air outlet if it were not for the fact that the hot
air from the rad would go into the cowl air intake for the
passenger compartment. That would give a pressure drop across the rad of 
roughly 4.7" of H2o at only 85 MPH. That is why you see so many race cars
with rad air outlets in this position.

BTW here is a picture of the pressure tap behind the rad.

Enough of this car stuff. Hopefully I will get to test Tracy's
airplane next week.

Paul Lamar
 
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