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


Yes Bill a rotary engine will work just fine direct drive. That's the
route I've taken after
hundreds of hours of testing.

It's basically what has held the rotary from becoming a aviation favorite.
Running around the skies
screaming the engine at high RPM's is totally    unnecessary.

Anyhow I've done it and it works(direct drive). I'm building two
engines
to do just that application.

Skip Gormqn

Have you had it on a dyno Skip?
According to this RX8 power curve the engine has only 67 HP at
3000 RPM and will weigh at least 260 pounds firewall forward.

Paul Lamar in Aus


Thanks Skip. I'm still curious though as to why one single rotor rotary
engine develops its peak torque at a particular rpm and another similar
engine develops its peak torque at a significantly different rpm. (For
example compare the RotaMax 65 to the Aixro 50). There must be some
fundamental reason for the difference. When setting out to design a rotary
engine what would one do to to try to produce more power at lesser rpm?

Bill Hobson

Perhaps I did not explain intake tunning clearly.
Perhaps someone else will please  take a stab at explaining it?

Paul Lamar


Paul, forgive my ignorance, but reading the description of the tuned intake, was the 1/8 of an inch dimension a typo? It just seems a tiny little hole to aspirate an engine, particularly when the images of the P-port look like the opening is more like an inch an a half. How would such an intake look like. how wold the transition from 1/8 of an inch to the P-port take place?
C. Smith

Ops that should have been 1-7/8th of an inch.

Paul Lamar