> As the rotor weight goes down for a given displacement
> the minimum load point goes up in the RPM scale. Rotor
> weight limits the red line RPM of the engine so the
> red line also goes up.
> --
> Paul Lamar ...No rotor no motor.

SO! how does the higher compression affect all this?
George (down under)

Higher compression also moves the point up.

--
Paul Lamar ...No rotor no motor.

Paul,
Given the RX8 has a lighter rotor AND higher compression, what would your
guess be at the point where the compression equals centrifugal force - 6,500
rpm?
George (down under)


There is not a heck of a lot of difference either way.
The old rotors were 9.7 and only just a very few ounces heavier.
Therefore the number is slightly higher for the RX8 engine.

BTW the corresponding number for piston engines is about
3600 RPM. That is where the inertial forces are balanced by
the compression forces on average. Large displacement low RPM
aircraft engines are limited by the compressive forces in the
connecting rods. High RPM engines the tensile forces dominate the
connecting rod design. Rod failure results in windowing
the block :)

Another interesting point. Walter inline inverted
Czech aircraft engines use aluminum rods. Double AA fuel
dragsters also use aluminum rods because the combustion forces
outweigh the inertial forces. Even at high RPMs. Aluminum rods
have a better compressive strength to weight ratio than steel rods.