A four pole turbo generator is used in conjunction with a 160 pole propulsion motor. If the generator is turning at 3,200 RPM, what is the current speed of the propeller?

Correct Answer: Option A — 80 RPM

Propeller speed in synchronous electric propulsion drives is determined by the pole ratio. With a 4-pole generator and 160-pole motor, speed ratio is 4/160 (1:40). Multiplying generator speed (3200 RPM) by 1/40 yields a propeller speed of 80 RPM.