There is still the PSRU requirement due to the  engine still
  running at 6000 RPM where Tracy's box looks like overkill and timing belts
  at
  125 HP start getting bulky  and at 3 to 1 the large sheeve is also pretty
  large. Might be that a rotrax 914 gearbox  could be adapted to Jeff's psru
  plate and spacers.

  george grimes

  The torque pulse amplitude is the same for one rotor or two rotor.

  To scale the gear box down is a technical risk.

  Paul Lamar

 Paul, very good observation. Makes me wonder if a four rotor firing at 90
 degree intervals might be able to use Tracy's gearbox after running FEA on
 the thrust bearings.

 george grimes

 Probably. The gear set is normally used with a 650 ft pound Ford Power
 Stroke
 Diesel pick up truck engine and diesels are known for their sharp torque
 pulses.


 BTW In fact the Renault aircraft diesel would destroy constant speed props
 in a
 heart beat.

 That is probably why the Continental two stroke aircraft diesel engine
 never
 made it out of the prototype stage. I don't know how the Junkers Jumo ever
 lasted in 1935 or the Packard diesel before that. The props had to be
 cannon proof.

 Hope springs eternal :)

 Paul Lamar


 By the way there are folks who
 Are trying to develop a Jumo type twin crankshaft diesel today for the LSA
 market.

 Clifton

Paul, I think the engines of the early thirties used wood props with pretty
much an infinite fatigue life. The benefit then and now of two oposing
crankshafts in a deisel is having only half the stroke and therefore a
crankshaft with less inertia loading. This allows much higher RPM and since
HP = torque X RPM / 5252 more power for the same displacement or a smaller
lighter engine for the same displacement. The smaller bore size also gets
away from the flame front propagation time on cylinders with more than  5"
bore which limits the maximum RPM particularly on spark ignition engines.
These factors more than offset the weight of  the gears or chain drive
connecting the crankshafts. With a positive displacement supercharger and
intake at one crank's Bottom dead center and exhaust at the other end of the
cylinder a 2 stroke version of the twin crank is possible. While this
arrangement  is undeniably more complex than an in line single crank engine
it can be lighter at a given HP. Lest we forget somebody thought the 4
crankshaft rotary valve Napier bomber engine had some merit although it
makes a modern formula 1 engine look like it was built by brigs and stratton
by comparison.

george grimes

My bud, Jeff Spitzer, now chief engineer, at GA Aircraft designed and built one and showed it at OSH a few years ago. They opted out of putting it in the Predator for some strange reason.

Paul Lamar