Anyway I'll get to the point. Dick has a few rules of thumb for cooling

liquid cooled aircraft engines. He says 2 cubic inches of rad volume
are necessary for every HP. That means we should be cooling with 400
cubic inch rads and right now it is taking 500 to 600. We are not
doing a good enough job on the scoops and ducts.

Another rule is the outlet area should be 150% of the inlet area.
Many of our installations are violating that rule as well.<

Hum-m-m.  My analysis led me to have about 3 cu. In. of rad per HP.  Am
I going to be over-cooled?  We'll see.

I'd guess the 1.5 ratio of outlet to inlet area is based on empirical
evidence.  By Charles law (volume proportional to the absolute temp),
with the air going in at about 80F and coming out at about 135F we have
an expansion of 1.1.  That means with a ratio of 1.5 the outlet air
velocity is considerably below free-stream velocity, leading to some
amount of drag.  I think it may be quite dependant on efficiency of the
inlet ducting and the design of the exit.

Al

 
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