Bill Freeman wrote:

Rick,

Drag from alignment of flow is one of the reasons that we
are pushing for a diffuser in front of and a nozzle behind the

radiator.

A diffuser converts a high velocity ambient pressure airflow into

a high

pressure low velocity airflow, hopefully with good efficiency. The

idea is

to have low velocity air at a high pressure at the front face of

the radiator.

Since the velocity over the tubes is low and the dimension of the

tube in a

flow-wise direction is very short, the boundary layer would be

very thin, plus

you  intentionally destroy the boundary layer and create turbulent

flow

(turning a corner can help this) to  increase your heat exchange

to the air.

Since aero drag is proportional to the square of the velocity, a

diffuser

that lowers the air velocity from 200 mph to 100 mph will roughly

reduce

the expected drag in the radiator by a factor of 4.

After the radiator, there may be some modest gain to be had from

flow

alignment vanes, altho I don't follow the 'grain auger' concept.

In any

case, diffusers and an exit nozzle are the keys to keeping the

drag of

the radiator down.  And, as has been oft claimed for the P-51, you

just

might do good enough to get a net thrust due to the heat added to

the

air by the radiator, but I'm pretty skeptical of it working that

well.

Bill

Sent an article to Paul that said they Recovered 90% of the
drag from cooling with the setup used on the P-51. No net
gain however. Virg
 

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