ROTOR DYNAMICS ACCOMMODATION USING ELECTRICAL POWER ASSIST

Hybrid electric propulsion systems 100 are described. The systems include a gas turbine engine 20; 120 having low and high speed spools 30, 32, each spool having a respective compressor 44, 52 and turbine 46, 54. A mechanical power transmission 150A, 150B is configured to at least one of extract power from and supply power to at least one of the low speed spool 30 and the high speed spool 32, an electric machine is configured to augment rotational power of at least one of the low speed spool and the high speed spool, and a controller 256 is operable to determine a rotational speed of the low speed spool, determine a rotational speed of the high speed spool, determine if a predetermined operational zone 406 of operation based on the determined rotational speeds is present, and when a predetermined operational zone is determined, control a power augmentation of at least one spool to limit dwell operation of the gas turbine engine within the predetermined operational zone 406.