A two rotor engine has less shaft slope and whirl than a single for a two
reasons: first, the thick section "gooseneck" between the eccentrics provides
stiffness; second, the counterweights on a twin are lighter, so there is less
bending moment and consequently less shaft slope towards the free ends of the
crank.

Jon Lauter
Rotary Power Marine Corporation

Jon - looking at the equations, and estimating the engine proportions, it would
appear that the
counter weight mass radius product  at each end of a twin rotor would be roughly
the same
as each end of a single, and the local bending moment also about the same. I know
that
does not seem logical, but the math suggests that, and it appears consistant with
the job they
are doing in each case. The twin is better for a power to weight ratio since the
total probable
weight of the counterbalance system  is the same for one rotor as two- Vance

 
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