<... The key appears to be the dynamic pressure available to produce the Mass flow through the radiator ....>
I was talking for a while at the Rough River fly-in last week with an engineer who argued pretty forcefully that it's the STATIC pressure that forces the air through the radiator core.  He said if you want to succeed, you need to have a big plenum.  The inlet needs to expand into the plenum so the kinetic energy of the air is converted to pressure which then forces the air through the core.  He was adamant that your ramp from the intake expanding into the plenum can't exceed 7 deg until the x-section of the plenum is twice, and preferably three times the inlet area.  This is so the flow will stay attached to the ramp and expand (kind of like an airfoil - too much curvature (as in chamber) and the flow separates (stalls) and you have a great big eddy of dead air behind the too-radical curve.  If your ramp "stalls", the flow pretty much stops.  If you ramp up "gently" the flow stays attached and expands uniformly and totally into high pressure air in the plenum.  I read stuff that sounded like this from PL's College or Convoluted Rocket Science a few years ago.  As I recall, the P-51 scoop on the P-51 ramped relatively slowly up into a largish plenum and a very thick radiator.  So the effectiveness of 7" thick radiators would seem to turn on the internal aerodynamics of the plenum.

But I've already told you more than I know .... Jim S..

Ed Anderson wrote:

... snip ... Now if your machine only flies at a speed of 80 MPH then logically you need to consider thinner radiators.  The key appears to be the dynamic pressure available to produce the Mass flow through the radiator.  So presumably if you fly a P-51 you can fly with 7" or thicker radiators.  Like in most cases, there is the theoretical perfect situation and then the real world situation.  The real world solutions almost always involved trade-offs and compromises - not perfect - but workable solutions.
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