Quote:
Originally Posted by NoDOHC
The rotor balance is not important.
What you are really balancing is the eccentric shaft.
Without the counter weights, when the front rotor is accelerating upward, the rear rotor is accelerating downward. The reactive force will make the engine want to pitch forward in the car. The counter weights offset this tendency by working opposite the rotor, because the weight is offset more than the rotor from the rotating center of the E-shaft and they are also offset more from the pitch axis (which lies approximately in the center of the offset in the E-shaft and parallel with the front axle), the counterweights can be significantly lighter than the rotors.
Balancing a rotary is much easier than a piston engine, as there are no strange factors to multiply the piston-rod assembly weight by (which are actually slightly dependent on rod to stroke ratio) but only the weight of the rotor, seals and some oil (I use 200g for the oil).
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ive seen an engine run out of balance and its WEIRD, it does almost exactly what you say, except there is a side to side bit too.
i'd do the out of balance rotor dance if we were in the same room
-mike