"Robinson, Chad" wrote:

Does the heat output scale linearly with the number of rotors?
That is, is the cooling challenge for a 20B exactly 150% of the
challenge for a 13B, or are there other issues related to the heat
density, maybe obstructions to the flow of coolant or oil,
or anything else like that here?

Thanks,
Chad

Directly proportional to HP. Lots of ducting issues. The obstruction
behind the radiator are more critical than the inlet duct because
everybody intuitively  understands an inlet duct for the most part.

I'm specifically referring to an undercarriage radiator arrangement 
a la "simple cooling solution". In that case, assuming you can get 
a radiator core with oblique fins, there are no obstructions past 
the radiator, no? It simply exhausts down into the airstream, right?

Thanks,
Chad

Right and that is the beauty of it. Perry's water rad is also of that type
air exit. I am not sure oblique fins would help all that much. Air turbulence
in the core is a big factor in the heat transfer between metal and air.
Turbulence is good so perhaps a smaller core without oblique fins would 
still be adequate.

It never ceases to amaze me about the wide variations in cooling systems that all
seem to work fairly well. Make one factor worse and another factor seems to
get better and make up the difference.  Probably because of the shear high number
of factors involved in a cooling system performance. Because of this it is 
very difficult to optimize a cooling system by measuring the coolant temperature change
alone. One must measure all the factors such as volume of coolant flow, temperature
drop in the coolant as it goes through the core, volume of air passing through
the core and the pressure difference between the front side of the core and
the back side to name just a few. 

A classic example is a two pass rad verses a one pass rad. Both appear to 
be about the same efficiency. A two pass rad will have twice the resistance 
to coolant flow but twice the internal coolant velocity as a one pass rad.
The over all flow of coolant through the 2 pass core will be less than a 
one pass core  when driven by the same water pump.

Paul Lamar
 
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