Hi Jean,
How about using a 20B engine mounted tranversly. Drive one side off the
flywheel end and the other off the front of the e-shaft. This would be a
lot lighter than twin engines and the rotars seem to be bullet proof. It
would help offset the weight of the drive. Dog clutchs on each side to
disengage if one side fails. The props would be close enough to the
center that one side disengaged would not be as bad as conventional
twins.

Dale Davies

The front part of the shaft is not strong enough.

Paul Lamar



" The front part of the shaft is not strong enough."

Would you mind taking us through the math on that?
Decker, Michael



http://en.wikibooks.org/wiki/Strength_of_Materials/Torsion

J = pi/2 x (c)^4

J is the polar moment of inertia of a cylinder.
c is the radius of the cylinder.

What that means is the strength of the shaft is proportional to the
radius of the shaft  to the fourth power. Small changes in the diameter
of the shaft have drastic affects on the strength.

The max stress on the shaft is:
stress = T x c/J

Where T is the torque in inch pounds.

Simple.

Lets say the stock shaft is 1.5 inches in dia. c = .75 c to the fourth
power is .316.

OK Lets  we go down on the diameter to 1.3 inches c2 is then .65. c2 to
the fourth power is .178! Almost half as strong.

The same thing applies to the two rotor.
Forget taking full power out of the front of the engine.

If you make a new e-shaft with a larger diameter nose you will have to
totally redesign the oil pump drive and the thrust bearings not to
mention the front cover.

There is another problem with the 3 rotor. Now the tapered joint must
take twice the torque as it is now receiving torque from both rear
rotors instead of only the front rotor.

Paul Lamar


" Forget taking full power out of the front of the engine."

You'd only be taking 1/2 out the front in the proposed situation.  What
is the torque pulse, 1200 inch pounds?
Decker, Michael

I was guessing on the diameter for purposes of illustration.
It could be smaller.

2 to 3 times average. 400 to 600 foot pounds peek on a p-port.
600 foot pounds is 600 foot pounds is 7,200 inch pounds.

If you lose the load on one side the other side would shoot up to
max power. Scary design. Why would you want two props with
one engine?


Paul Lamar


Dale.I seems to me that the main design  goal of Jean's twin pusher design
is  an independent redundant propulsion system.
The two props would be to isolate the shut down engine from the running
engine. I am working towards a four or six rotor engine currently and one of
the early plans was to use two 20B engines in tandem using the same
belhousing equipped  side housings of the current design. I like Paul has
indicated am uncomfortable with three rotors putting power thru the smaller
diameter  front shaft, and the rarity and age of used core engines resulted
in the stacking of RX8 components.

I might point out however that the
third(front) eccentric of the 20B slides over a longer e-shaft and the
tapered joint still would only see the torque of it's own rotor since the
shaft runs completely through it to mount the oil pump, thrust bearing and
accessory drives. Also the lemans engine is a double ended version of a 20B
with slip on extensions on both ends and a full length tension bolt thru the
shaft holding the three piece e-shaft together.This shaft appears to drive
off the tapered joint since the drive hub is part of the slip on number four
eccentric.

That would be three  rotors driving thru the taper fit rather
than the two you have suggested.It might be that the lemans engine as
splines on the number four rotor but I have not found any reference to that
approach. I suppose we should drag out the books(the machinest manual for
instance) and see what the   1.178 inch diameter 4340  front  shaft will
transmit and see what the safety factor would be at 300HP. In addition to
the items Paul mentioned on building up the front shaft, remember the
counterweight is up against the thrust bearing and  it's required mass is
influenced by it's longitudinal position from the  rotor  journal. And
finally Dale , at least you are sharing what you are thinking and that is
how progress is made.

george grimes