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

There have been air cooled powered aircraft lost because of massive
cylinder
failure (separation of head from barrel), often followed by a windowed
case,
followed rapidly by complete oil starvation and engine failure.  This is
arguably caused by the extremely challenging conditions that the air cooled
aluminum cylinder head must endure.  These engines are necessarily operated
near the temperature which causes aluminum to lose much of its strength.
Thermal cycling aluminum to this temperature increases its brittleness and
makes crack propagation and other failures much more likely.

How many air cooled aircraft engine cylinder recalls and mandatory
replacement AD's have there been on supposedly well test designs?  Recently
there have been quite a high number.  This is not because the engine
manufactures are really bad at what they're trying to do, it's that they
are
trying to do something that's quite difficult - high longevity, high output
aluminum cylinder heads.


Matt-


Matt,
Regarding your comment about certified a/c engine cylinders failure rate:
As a student pilot, I experienced a cylinder failure on the newly overhauled
O-200 in a C-152.  Luckily, my CFI was with me and took over.  We managed to
make it back to the airport (declared an emergency) and the engine quit just
as we flared.  We rolled off the runway onto the taxiway with oil pouring
out onto the ground.  We were only seconds away from total engine siezure,
and being on the 6 o'clock news.  I bring this up because this experience
was the catalyst in my choosing a rotary engine for my Lancair project.  So
far, I'm  convinced that I made the right decision.

Mark S. (Texas)