This chart, from the Mazda book "Rotary Engine" by Kenichi Yamamoto, of

bearing

load shows why rotor weight is the main limitations to RPM.
The rotor CG is making an orbit around the e-shaft center lines so
the load on the rotor bearing is m*V^2/r.  m is the mass of the rotor,
V is the tangential velocity of the CG of the rotor and r is the radius
from the e-shaft center line to the CG of the rotor.

Paul Lamar

 Interesting charts, Paul
Fig 3.26 would seem to imply that by keeping rpm at 5900 rpm that bearing
load/wear would be less than at any other rpm higher or lower.

Ed Anderson

Yes. I think it is like a piston engine where the combustion pressure over 
comes the inertia pressure on the piston. With the first half of the curve
the combustion pressure effect is dropping as a percentage of the
total max load on the rotor bearing. BTW for those that have the book 
the Rotor bearing load figure was mislabeled "Main bearing load". This 
becomes obvious when you read the text. I suspect Bruce is being a 
bit conservative on his RPM limits for the heavy rotors and the picture
I uploaded of the damaged bearings had more to do with overheated oil 
than excessive RPM. I could be wrong about that as I have no idea what 
maximum RPM really occurred in that particular engine.

Paul Lamar
 
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