Now I suppose we will have to discuss the squared/cubed law.

Don.

Bill Freeman wrote:

Do you mean similitude? (scaling?)

Bill

Don Forsman wrote:

Well, not exactly.  This little engine, and most other air cooled
engines that I can think of, use their external surface area to provide
the heat exchange area for cooling.  That surface area is maximized
through the use of finning.  The heat generating source can be looked at
as the interior of the engine, or its volume.

Surface area increases to the second power.  Volume increases to the third
power.  As anything with a heat generating volume increases in size, the
ratio of surface area (heat emitting) to volume (heat generating) becomes
a smaller and smaller number.  Or, take the inverse and the number becomes
bigger and bigger.

As an analogy, compare a hummingbird with an emu.  The little hummingbird
must make heat like crazy just to stay alive because its radiating area is
so great compared to its volume.  The emu pokes around to keep from
overheating.  Works with people too.  Small skinny people fare much better
in warm climates than in cold ones.  Ever see a small, skinny eskimo?

Don.

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