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

 Francois St-Germain wrote:

I agree with you but I think It is even worse for a
two rotor because the shaft is supported only by its
ends and it is much longer. So If it is true for a
single rotor it must be amplified by a double rotor
which does not have problems with it!
Of course It is only an opinion!

Frank

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