A rotorcraft has a drive system including a main rotor coupled to a main rotor gearbox to rotate the main rotor at a rotor speed, a main engine coupled to the drive system to provide a first power, a supplemental engine coupled, when a first clutch is engaged, to the drive system to provide a second power additive to the first power, and a control system operable to control the main engine and the supplemental engine to provide a total power demand, where the main engine is controlled based on variations in rotor speed and a power compensation command to produce the first power, and the supplemental engine is controlled to produce the second power in response to a supplemental power demand.