I can't figure out if this is a "blog" or not so if this isn't the
proper
 way to start a new "thread" I apologize.

 Mr. Lamar: Could you possibly explain (in relatively small words, if
 possible) what characteristic (rotor size, combustion volume, type of
 fuel,
 etc.) of rotary engines causes one engine to develop its maximum
torque
 at,
 say, 9000 rpm and another to develop its maximum torque at 6500
rpm? Do
 you
 think a rotary engine could be developed that developed its
maximum torque
 at, say, 3000 rpm (thereby possibly eliminating the need for
reduction
 gearing for aviation applications)? Thank you.

 Bill Hobson.


 I can't figure what it was either so I called it a "newsletter".

 All engines generate their maximum torque when the total torque
generated
 by the engine
 minus the torque losses is a maximum. Internal engine friction is
a torque
 loss.
 So too is the pumping energy required to fill the engine with
combustion
 air.
 That is a torque loss. The internal friction loss torque goes up
with the
 RPM
 While the total torque of the engine is a constant or straight line.
 Total torque is merely the pressure in the combustion chamber
pushing down
 on the piston times the piston area (read displacement) times the
 stroke of the crankshaft or the e-shaft in this case.

 Now along comes pumping losses. If it were not for the organ pipe
tunning
 effect
 pumping losses would go up with the square of RPM. Pumping losses
manifest
 themselves in the form of a nagative pressure in the combustion
chamber.
 Minimize the pumping pressure and you will maximize the net torque
from
 the
 engine. This goes for the exhaust system as well.

 Intake manifold systems are just like a child on a swing. It takes
very
 little
 shoves to keep that child swinging back and fourth. It is almost an
 energy amplifier. Intake pipes can resonate with just a little help
 from the engine so pumping torque losses are a minimum at some RPM
which
 coincides the resonant frequency of the intake pipes. Hence
maximum net
 torque
 out of the engine.

 What you want is the largest diameter organ pipe you can fit in
there. The
 larger
 the pipe dia. the lower the skin friction drag with a given amount
air
 flowing
 through it. For the rotary that works out to about 18 inches long and
 about
 1/8 of an inch in inside diameter and about 6000 RPM.

 You could build a turned intake system at 3000 RPM and you might
see 200
 foot
 pounds with a p-port but the HP would be way down. HP is torque
TIMES RPM.

 It is horse power that makes airplanes fly and not torque.
 The engine would be near useless for an airplane as the power
 to weight ratio would be very bad.  Better to use a much bigger
 piston engine like an O-360 designed to be light weight
 at 3000 RPM. The rotary is only 158 cubic inches.

 This is not the same as saying the O-360 is a better aircraft
 engine than a geared rotary engine. The rotary wins overall
 in the power to weight ratio category. A p-port rotary
 will be about 200 foot pounds at 6000 RPM while an O-360
 will be about 360 foot pounds at 3000 RPM. Now gear the rotary 2:1
 (or more) and you have 400 foot pounds at 3000 RPM.

 Paul Lamar


So, in other words, the rotary engine will always have to endure
the weight
penalty of a PSRU or some other type of reduction device to gear
down its
high rpm. (Unless of course a propeller could be developed that
could be
spun at 6-9000rpm without disintegrating.)

Bill Hobson

Propeller blades are like wings in that they become very
inefficient if too short.
It is possible to use many short blades like the un-ducted fans the
airline people
tried a few years ago. They proved to be extremely noisy.

Paul Lamar Down Under

It's no different than the 'weight penalty' endured by turbines.

Chris Cosman