"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.

Paul Lamar

Do you just convert the HP into watts to figure out how much heat to
disapate?

Does 100 hp = 65 kw watts...ballpark?

Phil

Basically yes. 746 watts = one HP.

Engines have what is called a heat balance. You can take a gallon fuel and
divide it
up. 25 to 30% as mechanical energy out, 35 to 30% into the cooling system and
50% out the exhaust in the form of waste heat. Here are a few heat balances
for different engines. Also go on the web site below and read the cooling
article.

Paul Lamar

Paul,
Can you give some guidelines on how to determine the size radiator needed
for a given amount of btu's.  I know it will vary depending on core
thickness, airflow, gpm, etc.  So, how does one figure out how much
radiator is requried?
Mark S.

Easy. Most people use about 600 cubic inches of rad volume on average for a 13B :) 
That number will drop in the future as we learn how to get the air in and out of
the rad more efficiently. It will also drop when more people start using thinner 
cores IMHO. That is the direction of the auto and truck industry.

On the other hand larger core volumes can compensate somewhat for
bad duct design and too thick rads. That is the usual sledge hammer
approach to inadequate cooling.

So far nobody has complained about over cooling :)

IMHO Perry Mick is at the leading edge of air duct design and now
appears to be the most successful. He has a relatively tiny water rad in terms
of core volume. It could also be attributed to his ducted fan so 
until we get more data from conventional airplanes he is the leader.

Also IMHO at the current time there are too many unknowns to use a 
mathematical solution. It would help if more people would measure
the air and water pressure drop across their rad and the temperature 
of the water going in and coming out of the rad. Another factor is the
temperature of the metal within 2 mm of the combustion chamber
in the area of the lower spark plug. The temperature of the water 
is not the whole story.

Paul Lamar
 
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