Tracy Crook wrote:

Paul wrote:


BTW I suspect these thinner rads are more aerodynamicaly efficient.
Less drag for a given heat transfer.

Paul Lamar

Here is my 2 cents on  radiators for aircraft.

 Those radiator cubic inch specs you put out are very significant.  That is
perhaps the most important spec on the radiator itself.   OTOH,  I would
argue that THICKER radiators are the way to go on aircraft.  Thinner is more
efficient if you don't care how many CFM you use to do the cooling job.
This results in the lowest rise in inlet air temp through the radiator but
you need more CFM.  More CFM used for cooling = higher drag.

With a thicker radiator, the temp rise is higher but fewer CFM are needed.
This requires more internal area in the rads to get the job done (because
the fins toward the back are working in pre-heated air) but this is not the
parameter we are trying to optimize.  Everything is a compromise but If size
& weight were not a factor, the most aerodynamically efficient radiator
would heat the air to within a fraction of a degree of the coolant temp.
As I recall, the P-51 radiator was quite thick.

One result of a thicker rad is more air resistance which is why all this
past discussion on pressure recovery in the duct is so important.  All this
argument is out the window when talking about car cooling systems, but who
cares about cars?

Tracy Crook
 rws@altavista.net

I am not sure I buy this Tracy. I think it is better to have a thin
large
frontal area radiator rather a thicker one of the same volume  
with less frontal area. You just mentioned one of the problems
with a thick radiator. The rate of heat transfer is better when the
difference
in temp. is greater. I forgot the function but I am sure Jeff knows it.  
As the air flows from front to back it gains temperature so the back of
the
radiator  does not work as well as the front part.

Mounted in the tail cone or at a steep angle in the cowl the frontal
area is not a problem with a proper internal diffuser.

It is the same as a parrallel cooling system verses a series cooling
system.
The average temp difference is higher for every square inch of fin area. 

Jeff has come up with a test rig that can be mounted on a pick up truck.
I am drawing it up as we speak. The engine will have to be re-plumbed
to the test radiator and a drag racing parachute could be used to 
increase the load (heat output) on the truck engine. I am thinking 
that thick wall plastic plumbing pipe might be used to plumb the engine 
to the test radiator. It is real fast to just glue it together.

Paul Lamar

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