I think a turbo compound small four rotor engine running at 25,000 RPM
with aluminum beryllium rotors would make a great Formula 1 engine.
Two Ferrari piston engine have blown up in the last two
Formula 1 races. Probably crankshaft fatigue. Formula 1 engines only last two races anyway.

These numbers are for a large aircraft piston engine running at only 2500 RPM but you should get the idea.

Let's assume for the moment the connecting rod, the piston pin and the
piston with the rings weighs seven pounds. They all move the same way the
piston does. Mr. Newton said, and he seems to be right, force equals weight
times G's. The three pound piston alone looks like 870 pounds to the rod in
the form of inertial load.  Mr. Connecting rod has to push and pull that 870
pound piston back and fourth once every .006 seconds. As far as Mr.
Crank-pin is concerned that seven pound collection of parts looks like it
weighs about 2000 pounds! 290 G's times seven pounds is about 2000 pounds of
inertial load. Mr. Crankshaft says "OUCH!".

This is a simplification of course. The compression and combustion pressure
loads sometimes adds to and sometimes subtracts from these inertial loads.

Metal fatigue happens when the force and therefore so too the stress
repeatedly reverses on a part. The cylinder spacing, rod length, rod journal
diameter, main journal diameter and cylinder bore all have a large effect on
the fatigue life of a piston engine crankshaft.

The beauty of the Wankel on the other hand is the eccentric shaft is
straight through yielding no concentrated stress problems up through four
rotors and maybe more. The loads on the eccentric shaft are always in
one direction. They do not reverse.

Consequently the life of an eccentric shaft is not
limited. The same thing can be said of the rotor. If the wear of the
seals and the sliding surfaces can be reduced to very low levels then
the life of the rotary could be 10,0000 hours or more. There is some
evidence that silicon nitride ceramic apex seals moving on the chrome
plated rotor housings may have a life of 30,000 hours.


Paul Lamar