Coincidently 6000 RPM  is where the rotor bearing loads are a
minimum so that is a good cruise RPM. Bearing loads are higher
both above 6000 RPM and below 6000 RPM.


Could you explain this to a non-engineer?

R Berglund

Rotor bearing loads come from two sources.

A. Combustion pressures acting on the face of the rotor causing an inward
force on the bearing.

B. Since the 9 pound rotor is rotating around the center of the
e-shaft there is a centrifugal outward force acting on the rotor
bearing.

At 6000 RPM the two forces cancel each other.
Below 6000 RPM the combustion forces dominate.
Above 6000 RPM the centrifugal force dominates.
At about 10,000 RPM the centrifugal force is so high
it is the limiting factor on the functioning of the
rotor bearing.

All this assumes a normally aspirated engine with a 9 pound
cast iron rotor. If you use a lighter titanium rotor this
RPM point rises as the centrifugal loads are reduced.

If you turbo charge the engine, increasing the combustion pressure
on the rotor, this  RPM point also rises but don't suddenly reduce
the boost or you will still fail the bearing at RPM's over 10,000.

This is the key to the extraordinary amount of power one
can obtain with boost levels over 100 inches of Hg in a Mazda
Wankel.


Paul Lamar


Paul,


Although above is true, one must not forget that the rotor bearing is fully
loaded by the centrifugal forces when a flank is at the exhaust / intake
side. That happens 180 degrees later to above described condition at a
power stroke.

In other words the 'unloading' of the bearing at firing TDC is a blessing
only for that condition, reducing bearing load and friction for about half
of a rotation, however the real limit is centrifugal load based on rpm and
piston weight that occurs when a flank is at the exhaust / inlet ports as
there is no gas pressure to act against centrifugal loads. That is half the
time.

This is equivalent to the 4 stroke RPE where the highest bearing load on
crankshaft and connecting rods happens at TDC when the valves are open for
the gas exchange. On the next rotation when firing occurs the centrifugal
loads are counteracted by the gas pressure of compression and power stroke.
Here too, only the rpm counts for maximum bearing loads the crankshaft and
connecting rods have to support, not the gas pressure or degree of
charging, although half of the time or every other stroke, the gas pressure
provides a reprieve.

Rolf Pfeiffer

When one flank is on the expansion stroke the following flank is on the compression
stroke.  It is the vector sum of all the flank pressures. The vector of interest
is the radial vector pointing at the center of the e-shaft. It is aligned
but opposite with the rotating centrifugal vector. The rotary is a close
cousin to a continuous combustion engine similar to a turbo jet.

Paul Lamar