I made a helicopter rotor and noticed the rpm of the blades would change if the playback speed changed. At 1/4 speed the rotor was spinning at 303rpm and at normal speed it spun at 263rpm. I did not change the pitch during this time. The rotor speed does not change if the simulation is played at x4 speed. If you was to try the helicopter I made to replicate this it is called "Heli Sorta Work"
