Paul wrote:
One of my engineer friends at the airport tells me the problem
with the rotary is we don't know the thermal characteristics
of the engine as a function of the power out so I scanned
this chart for him.
This is why it is important to install a CHT probe on
your engine. The limit to how much power you can get out
of the engine on a continuous basis is right here.
Drill a small hole about 0.062 inch diameter 1.2 inches deep right
next to the leading spark plug and install a thermocouple at
the bottom.
Any improvements to the water jacket such as internal grooving
or water pump flow will show up here as a reduction in temperature at
the same power level. I would say 210 C or 410 F would be the upper
limit at which you would want to run your engine. Anything above this
and you risk shrinking the rotor housing. The engine won't
stop of course. However coolant will seep into the rotor housing when
the engine is shutdown and cooled off and the engine will be hard
to start again.
This is also why teflon coated silicone O-rings are advisable.
BTW it is very risky to run the engine plugs up as this is by far
the hottest part of the engine and you want to make sure there is
plenty of coolant here at all times. Bubbles rise of course and
you don't want them around here.
Paul Lamar
Here is a chart of the cylinder head temps of the liquid cooled Continental
Voyager engine. We are much better off than they are at 410 F at 7000 RPM wide
open throttle. That is probably close to 200 HP in a NA rotary. They are
looking at 512 degrees F between the exhaust valve and the intake valve at
2750 RPM at 110 HP in the O-200 version. Continental claims this is superior
to the air cooled version which run 600 degrees F in this area. Not only
that the aluminum piston dome is running 520 to 580 degrees F while we
have a non melting cast iron rotor! Course the silly exhaust valves are
running 1400 degrees F. No matter how you look at it
the rotary heat characteristics are better than the aircraft piston
engine water cooled or not.
This is from SAE 871042.
Paul Lamar
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