MODULATED COMBUSTOR BYPASS FOR HYBRID IDLE

A hybrid propulsion system (100) includes a gas turbine engine (20) having a low speed spool, a high speed spool (32), and a combustor (56). The low speed spool (30) includes a low pressure compressor (44) and a low pressure turbine (46), and the high speed spool includes a high pressure compressor (52) and a high pressure turbine (54). The hybrid propulsion system also includes a motor (212B) configured to augment rotational power of the high speed spool, a flow modulation device (226) configured to control a combustor bypass air flow (230) around the combustor (56) to the turbine section (28), and a controller (256). The controller (256) is operable to determine a mode of operation, apply supplemental power to the high speed spool using the motor, modulate the combustor bypass air flow using the flow modulation device, and adjust a fuel-air ratio (410) at the combustor based on modulation of the combustor bypass air flow and the supplemental power applied to the high speed spool.