> It causes no vibration but it does generate a centrifugal force
     > on the rotor bearing. It is also balanced by the second rotor
     > 180 degrees out of phase on a two rotor engine. What is left
     > is known as a "couple". The couple is caused by the two rotors
     > not being in the same plane. That is the function of the front
     > and rear counter weights. They remove the couple completely.
     > A similar situation arises when balancing a tire. The balance
     > weights must be centered on the rim width (in and out) or a couple
     > will be generated. This is sometimes referred to as
     > dynamic balance.
     >
     > In the case of the one rotor the front and rear counter weights
     > balance the weight of the rotor. In all cases the Wankel rotary
     > engine is in complete balance unlike a piston engine that always
     > has parts rocking back and fourth such as connecting rods and valves.
     >
     > Here is a mathematical balance chart for rotary engines.
     >
     > The two rotor engine does not dip below zero but the one rotor
     > engine does indeed dip below zero as does a four cylinder four
     > cycle engine.
     >
     > Paul Lamar


    Good dissertation Paul.
    I cover Static, Force, Couple, and Dynamic in my seminars
    at OSH.
    Archie
    --
    Thanks, Paul.
    -*

    You mention the four-cylinder piston going into negative torque, but the
    six-cylinder piston will too, although at about half the amplitude
    (approx -50 percent of mean torque, compared to -100 percent on four).

    Only when you get to the eight-cylinder with its power pulse every 90
    degrees does instantaneous torque stop going into negative territory. So
    in that respect, the 2-rotor is better than a piston six and closer to
    an eight.

    Regards,

    Gordon.

    No I think you are wrong about that. Here are some more charts from
    Kenichi Yamamoto's 2nd book, also called Rotary Engine, published
    by Mazda in 1981.

    BTW I forgot to mention the fact that the rotary engine, in all
    of its configurations, one, two, three or four rotors has never
    required a torsional dampener. Almost all six cylinder and above
    piston engine are equipped with torsional dampeners. Even the
    vee eight cylinder engines. My original six cylinder O-470 engine
    in my C182 had only two. With the second 1500 hour overhaul the
    crankshaft was a mass of cracks. When I traded it in
    to Continental and picked up my newer version I specified the 2000 hour
    TBO engine version with four dampeners instead of just two.

    The last chart is of the Merlin which was a night mare for RR
    to develop.

    Paul Lamar


Paul,

I don't think I'm wrong about the six having a negative torque
amplitude. Torque fluctuations can vary on any given engine, but here is
one graph showing an even-fire six:

Six-Cylinder Instantaneous Torque Characteristic

Here is a graph for the odd-fire six:

Six-Cylinder Odd-Fire Instantaneous Torque Characteristic

These are from Jack Kane's website, epi.com

Regards,

Gordon.

I assume you mean http://www.epi-eng.com/
Very interesting web site. I don't know how Jack Kane came up with
that curve but I still think it is wrong. It could be calculated
making some incorrect assumptions while the curves in Rotary
Engine are probably measured. Perhaps he assumed no valve overlap.
Perhaps one engine had a heavy flywheel and the other did not.

Notice the six cylinder power stroke overlap from this chart from Bill Marvin.

In any event we are picking nits here as the portion of the time
the six does or does not go negative is a tiny percentage of the total.
Very little relevance to the world of Wankel Rotary engines.

Paul Lamar