SUPERPOSITION GEARBOX FOR ENGINE PERFORMANCE

A gas turbine engine (20) including a low speed spool (30) including a low pressure compressor (44), a low speed output gear (82) disposed on the low speed spool (30), a high speed spool (32) including a high pressure compressor (52), a high speed output gear (84) disposed on the high speed spool (32), a first tower shaft (76) engaged to the low speed spool (30) at the low speed output gear (82), a second tower shaft (78) engaged to the high speed spool (32) at the high speed output gear (84), and a superposition gearbox (66). The gas turbine engine (20) further including a ring gear shaft (92) coupled to drive the ring gear (108), a ring gear shaft drive gear (90). A low speed spool drive train gear ratio is between 0.5 to 2.0, the low speed spool drive train gear ratio being measured from the low speed output gear (82) to the ring gear shaft drive gear (90).