If the two rotor is similar to a 4 cylinder 4 stroke piston engine, wouldn't a one rotor be similar to a 2 cylinder 4 stroke engine? Lamar has published the plots many times showing no torque reversals for a two rotor but very strong torque reversals for a one rotor.

I don’t believe that a torque reversal at the output shaft is a necessary condition for a resonant torsional vibration to get started.

Al