So, making heat on a volumetric basis and rejecting it on an areal basis

is

a problem
at some point, no question.  The issue is "Can a 200hp @ 2800 RPM Wankel

be

made
to cool properly with air cooling".   I'd bet yes, but can't prove it.

Jeff has run the calcs and built the engines.   I'd love to hear his

take on

this.

Bill
Long EZ builder & pilot
BSME, MSME

Jeff Spitzer wrote:

I really haven't followed the whole debate here, sorry, but I saw my name
and thought I'd respond.

The statement above is only looking at one side of the problem...getting rid
of the heat.  OTOH, the low surface to volume also means that less heat gets
out to be rejected in the first place thus making larger displacement
engines more efficient.  This is highly supported in practice.

On the issue of air cooled rotaries, I think that it can easily be made to
work for a single rotor for any size of interest to us.  When you start
talking about multi-rotors things get a little more interesting.  The first
issue is that the high heat areas are all tightly packed together.  So in
order to get adequate fin area the engine must get larger, wider, etc
compared to the liquid cooled. The first problem is:  how do you cool the
center housing in the combustion zone?    Obviously air must move through in
a chordal/circumferential manner.  This might be considered a problem if you
think you can use axial fins on the rotor housing until you realize that you
can't because the front rotors cool and the back rotors don't.  So, you
pretty much have to run the fins circumferential on the rotor housing too.
This results in long skinny air passages that make lots of resistance.  The
fins in the center housing also make it much wider than the liquid cooled
version which adds weight and crankshaft bending.  Can it be made to work?
I'd say yes.  Is it advantageous (i.e. lighter and/or smaller)?  I'm
thinking no.

Jeff Spitzer

Jeff,

Thanks for the response.  I was just dreaming that a 4 liter direct drive
two rotor, aircooled Wankel might be the dream motor for personal aircraft.
Fly with three moving parts (excepting oil pump).  What about heat pipes
to help in the most extreme hot zones, plus of course the large heat
dump to the oil?  Just dreaming, it would take a real visionary with a large
wallet to make this happen.  I believe it would absolutely revolutionize
light aviation, tho.

Bill

 
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