<< 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
  >>

Vance, I am going out of town for a few days, when I return I will look into
the "math" with more rigor. One thing to think about intuitively, however, is
that each rotor and eccentric serves as a "counterweight" for the other in a
twin. Also, in a single, the rotor / eccentric mass is 180 deg opposite both
counterweights, so the single rotor crank is in the worst possible bending
situation -- simply supported beam with a concentrated load approximately at
its center. In a twin, the counterweights are 180 deg away from each other.
The twin crank tries to bend in an "S", but the stiffness of the gooseneck
restrains the deflections considerably.

This is not to say that a single rotor engine is "bad," it just needs to be
understood and designed properly, and mating equipment designed to suit. (You
may recall some discussions a while ago where I was defending single rotor
engines against an individual who had a bad experience, either because the
engine was not made correctly or it was misapplied.)

Jon Lauter
Rotary Power Marine Corporation

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

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