Re Liquid cooling:It's interesting to note that various models of
motorcycles continue to transition from air/oil cooled to coolant/oil
cooled.And, those same models continue to get lighter.That says to
me that liquid cooling, while somewhat more complex in some ways
(though less so in others), isn't heavier.Maybe someone knows of a
counter example..

Regards,

Matt-

Matt,
much of going to liquid cooling isn't about the weight. It's about
combustion control. Liquid cooling controls the temperature of the cylinder
head much better than an air cooled head. This allows making more hp for the
same displacement. When an air cooled cylinder head gets hot, the combustion
chamber becomes very prone to detonation, with this being the hp limiting
factor on many air cooled applications.
Larry

Right.. For a given displacement, more horsepower can be had from a
liquid cooled engine.. Countering the added weight of the liquid
cooling system.

Also, people might point out that liquid cooling is for emissions.
While I agree with that, I would say that an engine that produces
fewer emissions often will run cleaner and fewer service difficulties.

Matt-

Matt,
With modern heat exchangers it is veryhard for an air cooled engine to get anywhere close to a water-cooled engine in hp/cu.in.When you consider all factors I believe the flexibility of configuration isimpossible for an air-cooled engine to match.The switch to water cooling in modern motorcycles WAS NOT caused by emissions requirements. The change was well underway before those requirements became very stringent. Packaging was the reason.With water cooling you can make an inline four cylinder short enough to be anacceptable power plant for transverse mounting in a motorcycle.VariousV configurations are also possible that wouldn't be able to be cooledif air cooling was chosen. Getting back on the proper rotary track, air cooling of the rotary while possible, just isn't the way to go. The liquid cooled version will always be a more flexible package.
Bill Jepson


While I would agree that when simply comparing liquid and air cooled
engines, liquid cooling is more efficient in every way. However, to
compare a motorcycle, or automotive engine for that matter, with an
aviation power plant is not a good way to go about the discussion.
While power-to-weight and packaging are the main concerns in in
automotive and powersport application, aviation engines seem to
value reliability above all else. In short, while a liquid cooled
engine may prove better thermal protection and a greater power output
enough to justify the additional weight, reliability does suffer no
matter how simple the liquid cooling system. While the air cooled
engine may suffer from lack of power, it will NEVER (emphasis added)
suffer a malfunctioning water pump, thermostat, leaking coolant hose
or radiator. While I personally prefer air cooling for aviation use,
more opinions on the matter may be needed before I  dedicate myself
to either system.
Vladimir

You don't have much of a choice with the Wankel as it is too hard
to cool the center housing with air. If you add a blower that
will suck more fuel. An air cooled one rotor might work as long
as it is not charged cooled.

Paul Lamar


Is it not a possibility to oil cool the center while air cooling the rotor
housing?

Vladimir

That might work.
Paul Lamar