At the airport today I met a fellow devloping a water cooled

lycoming

0-360.

The discussion included the rotary and he liked it for its future

potential saying as others have

that it makes a better aircraft engine than auto engine.
His biggest criticism was poor cooling due to the constant focused

heat

with only "one" combustion

chamber, unlike recip's.
Has this consideration been solved ? overheating.

bd

Never was a real problem. Partly because the "combustion chamber"
is rotating around inside the rotor housing.

Paul Lamar

I do think this is the limiting factor in how much continuous power you

can

make with the rotary.  With the stock water pump,  around 200 HP is

probably

close to the limit for a two rotor.  Grooving the water jacket helps.
Nucleate boiling is taking place at this level and if you go much

higher,

the localized boiling turns to an isolating film on the CC walls and
temperatures start skyrocketing.

This problem can be overcome with brute force water pumps like Racing

Beat

is doing with the 900 HP 3 rotor, but this is way beyond what most
recreational aircraft builders are prepared to do.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

Nobody really knows because nobody has placed a thermocouple next
the combustion chamber and correlated the temperature data with
the continuos power generated. Not Racing Beat not Power Sport.
Not even Tracy Crook :) What the water does or does not do
temperature wise has absolutely nothing to do with it.

I suspect this particular urban myth got started when oil
used to coke on on  the rotor housings long before synthetic
oil was available. Old oil coked around 250 to 300 degrees F.
I have never, ever, in 30 years, seen a rotor housing damaged
by this kind of heat. I suspect that no car racer has seen it
either. I have seen collapsed cast iron rotors from a turbo
charged engine but that was probably caused by a plugged
oil squirter. The water pump on a Lemans four rotor is
no larger than the water pump on a 13B and that engine
developed up to 175 HP per rotor. 350 HP for a two rotor
...for the arithmetic  challenged.

I'll believe it when I see the temperature data. It is one
of the things I am going to do with our new temperature data
acquisition system.

I do have a bunch of data on the Continental water cooled aircraft
engines. Continental did do the homework and instrument this part
of the cylinder head. They found the temperature reached 500 degrees
within 1 mm of the combustion chamber and felt that was the upper
limit for aluminum. The Mazda rotor housing is lined with steel
and there is a lot more surface area not to mention the combustion
chamber moves dissipating the heat over one third of the rotor
housing inner surface.

Paul Lamar

True, nobody really knows the ultimate limit for continuous power but the
phenomenon I described has been demonstrated well beyond the point of
"myth".  Do you really mean that what water does or doesn't do temperature
wise is not a factor?   A bold statement in a water cooled engine.  

As you can see from the Continental chart the temp at the hottest spot
in the combustion chamber was not reduced by dropping the coolant temp
from 290F to 250F.

The "oil
coking" was not  a factor in what I was describing but it may be an
indicator.

I have determined experimentally at what point nucleate boiling begins in
the 13B on my plane (about  165 HP continuous).  What I don't know is how
much higher it will go before nucleate boiling can no longer handle the heat
flux.  Auto applications (even racing) don't duplicate the aircraft
environment because if the engine is throttled back even momentarily (like
for corners) the heat flux is reduced long enough for nucleate boiling to
re-establish and bring CC wall temp back under control.

Jusy my opinion, FWIW.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

How do you know you had nucleate boiling and where it began?
In other words how did you separate this phenomena from all
the other variables? Nucleate boiling is a local phenomena.
The tiny bubbles are carried off by the main flow and
dissipate.

I am still waiting to see some real temperature numbers. I 
would also like to see a melted rotor housing or one that showed 
any kind of failure between the steel liner and the aluminum.
We have plenty of rotor housings that have been severely 
over heated and NONE show failures in this area.

Cracks have been known around the spark plug holes but
that could be caused by a high temp gradient. In other words
TOO MUCH cooling on the back side of the combustion chamber
wall. Just about all one rotor NSU Spyder engines cracked
around the spark plug holes. Mazda themselves removed metal
from around the spark plugs on the late turbo rotor
housing by a simple single cut of the mill on both sides.

Until I see some failed rotor housings or some real world 
temperatures exceeding 500 F at the junction between steel
and aluminum I am still going to consider this a myth.
Even if the temp exceeds 500 F in this area does not
mean the rotor housing will necessarily fail to function
normally. Aluminum does not melt until about 1100 degrees.

The signs of combustion chamber wall failure in air cooled
aircraft engines is a pock marking or cratering of the surface. 
In WW II B29 engines that showed this effect in the exhaust port 
where automatically changed out. Jeff Auckland and I had a long 
talk about this when he was using a Chev big block engine in the Legend.
He saw the same phenomena in the Chev combustion chambers.

Paul Lamar
 
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