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 it 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
  1-7/8 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
 --
 Hi Bill, Try this explanation:  1. Torque is a direct result of the
 combustion
 chamber's volumetric efficiency (rotary or piston engine). When this
 efficiency peaks; torque peaks.

 2. The V.E. is mainly governed by the intake system. In the intake pipe
 the rush of air resonates, that is each time the combustion chamber
 intake closes (whether rotary, 2cycle piston or 4cycle piston) the
 air rush stops (sometimes even reverses).

 3. This very brief stop sends an energy pulse back up the pipe toward the
 open inlet.

 4. # 2,and 3 change with RPM.

 5. A perfect length intake pipe for a GIVEN RPM will contain that energy
 and
 revert it to push the next charge TOWARD the combustion chamber.
 This is "resonating."

 6. This is important: Look at #5 again. The pipe length that works
 perfectly at XXX RPM is not the correct length for YYY rpm. So, what to
 do?

 Adjustable length intake pipes have been used on racing engines but
 are too cumbersome for aircraft use. So the next best choice is to
 pick an RPM that the engine likes and tune the intake to operate
 there and accept less V.E. at RPM's above and below that engine
 speed.

 The aircraft piston engine (big bore/big stroke = lots of
 mass moving back and forth large distances) is happiest at about
 2500 RPM and the intake is designed around that.

 NASCAR engines
 (big bore/ short stroke = lightweight mass moving back and forth
  short distances) are happiest around 8000 RPM and their intake is
 designed around that (put a NASCAR intake manifold on your family
  ride and you will be terribly disappointed)

 The rotary engine
 (lots of mass but NO DIRECTIONAL CHANGE) is happiest around
 6000 RPM (rotor speed is around 2000 RPM, bearing loads are
 lightest, V.E. is pretty good, vibration is quite low, power
 output vs. engine wear is very good).

 So with an engine that
 wants to run forever at 6000 RPM that's where aircraft conversions
 are run and the intakes are designed for that speed. To get back
 to a proper propeller speed requires a +/- 40% reduction box.
 Seems like a hell of a penalty until you look at the whole picture.
 Even with the added weight, the power to weight ratio for a P-Ported
 rotary easily surpasses today's standard aircraft engine.

 If you've
  ever shock cooled your Lycoming, your repair bill exceeded the cost
 of TWO COMPLETE rotaries. Can't happen with liquid cooling. Have you
 priced a Continental exhaust valve lately? Rotaries have no exhaust
 valves. This is only some of why we're here. Stay with the newsletter,
 there are nuggets of valueable info here. Hope this affords some more
  understanding.
 Dave M

Dave: Thanks - For some reason I understood what you said. It's kind of
amazing that just the length of the intake pipe could have so much impact.
I
presume it also explains why turbo charging is a good way to boost power.
Thanks for taking the time to re-explain it to me. I wasn't really
complaining about the penalty of the PSRU - just pondering if there wasn't
a
way to avoid it. (As I understand it, the recent and unfortunate crash of
the Sadler Vampire was caused, at least in part, by a failure in the PSRU.
It got me wondering why or if it was absolutely necessary.) I guess it was
just the weakest link in the chain.

Bill Hobinson

I see nothing in the NTSB preliminary report to implicate the PSRU.

Paul Lamar

_________________________________________________________________________
NTSB Identification: CHI08LA274
Accident occurred Wednesday, September 03, 2008 in Findlay, OH
Aircraft: Sadler Vampire, registration: N333SV
Injuries: 1 Minor.

This is preliminary information, subject to change, and may contain
errors. Any errors in this report will be corrected when the final report
has been completed.

On September 3, 2008, at 1257 eastern daylight time, a Sadler Vampire,
N333SV, received substantial damage on impact with terrain during a forced
landing. The airplane experienced a total loss of engine power after
takeoff from Findlay Airport, Findlay, Ohio. Visual meteorological
conditions prevailed at the time of the accident. The 14 CFR Part 91 test
flight was not operating on a flight plan. The pilot sustained minor
injuries. The local flight was originating at the time of the accident.
________________________________________________________________

I spoke to the people at Sadler.

Bill Hobson


I think Skip Gorman was there when it happened.

Paul Lamar