How about let's change the idea up, to air cool a rotary without cooling
   fans?

   Let's posit that we have an air-cooled rotary engine with no water
   jacket. Instead, on the outside of the engine, fins radiate from both
   the sides and the ends of the engine, to cool it like the barrel of an
   old radial piston engine is cooled. The fins are positioned and
   oriented so that air flow is optimized for appropriate cooling and for
   air flow in, through, and out of the engine compartment.

   No cooling fans, such as the Midwest/Diamond or Porsche engines are
   needed, so no power is drained, no unnecessary fuel is used.

   Such an air cooled rotary engine would certainly be physically bigger
   than its water cooled counterpart, but would not the air cooled rotary
   be smaller overall than the water cooled engine and its attendant
   radiators, hoses, etc.?

   Would not such an air cooled rotary engine be lighter, simpler, more
   efficient, more reliable than its water cooled counterpart? How would
   we know that it would be or would not be? How would we know that we
   knew?

   Let us also posit that each fin, where appropriate, has within it a
   properly-engineered heat sink. Heat sinks have no moving parts, so they
   would be reliable. Perhaps heat sink technology could siphon the heat
   out from the center housing into fins projecting into the air stream, so
   that even the center housing could be cooled.

   Would using a technology like a heat sink increase the cooling
   effectiveness of each fin? Would not heat sink technology make such air
   cooling more efficient? Could such technology help cool a rotary
   engine enough? Again, how would we know that it would or would not and
   how would we know that we knew?

   I would certainly like to hear your thoughts about this. I expect I
   will ask of you all, when you post, a lot of questions. Why? Not
   because I am trying to be argumentative, but because I do not know all
   the answers and I know I do not know. :-)

   Les Nordman :-)

   I understand. Good idea. I think you mean heat pipe rather than heat
   sink.
   I think it can be made to work. Got a couple of million lying around
   you are not using? :)

   Paul Lamar ...No rotor no motor.


I dealt with this same scenario on a electric car motor. The original
idea was to do cast fins. The casting looked like a vintage Ducati. As
it turned out, the area on the cast fins was very limited due to the
wall thickness of the casting. The fins need to be a certain thickness
in order to get the molten metal to flow.

They ended up using a corrugated fin. This gave something like two to
three times the cooling area but looked ugly. The fins were similar to
the link below, but it was able to flex and adhere around the OD of the
motor.

http://www.fs-thermalmanagement.com/html/products_radiacal1_fabfin.htm

Early 80's 2-stroke engines used to be air cooled. They were able to
build to higher tolerance once they went to water cooling. Much of this
has to do with the unevenness of air cooling. It is tough to get rid of
a hot spot if air does not flow in that air due to an engine mount.

A mars rover thermal engineer once explained to me that heat was like
electricity. To get it to flow you need a large potential difference. It
wants to travel down a good conductor. The larger the cross sectional
area the better. When you have two different materials or a air gap this
creates a resistance. He also said the prediction of how it travels is
pretty much black magic. There are just to many variables.

Bill S



The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://www.rotaryeng.net
Copyright 1998-2007 All world wide rights reserved.