With a single rotor engine in particular, it is beneficial to keep the
counterweights as close to the rotor as possible. This reduces the shaft
deflections and slopes through the bearings. Imagine the shaft as a simple
beam, with the rotor pulling downward in the center, and the two
counterweights pulling upwards at the ends. You can envision the crankshaft
then always being shaped in a gentle arc. The arc will get larger as engine
speed increases because the centrifugal force from the rotor, eccentric and
counterweights increases as the square of the speed. Also, firing pressure
tends to straighten the shaft once per revolution. This cyclical loading
makes fatigue a concern. The shaft deflections in single rotor engines need
to be carefully considered during the design and also in the application of
mating hardware (such as PSRU's) which may not be capable of handling "whirl"
at their inputs....

Jon Lauter
Rotary Power Marine Corporation

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

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