set of compressor blades are counter rotating in operation the differential gear assembly enables rotational speeds of the multi stage fan and the low pressure compressor to accommodate various operational requirements by way of example for high speed flight operations the forward fan stage and first set of compressor blades can be set to a relatively high rotational speeds while the rotational speeds of the rear fan stage and second set of compressor blades can be lower achieving a desired rotational speed can be accomplished by altering the flow of air to the tip fan for instance by increasing the flow of air to the tip fan fan pressure ratio of the first stage fan is increased which causes a corresponding decrease in rotational speeds of the first stage fan and the first set of compressor blades responsive to this speed decrease the differential gear assembly causes the rotational speeds of the rear stage fan and the second set of compressor blades to increase with respect to low speed operations the forward fan stage can be controlled to exhibit a higher fan pressure ratio which results in corresponding reduced rotational speeds of the forward fan stage and the first set of compressor blades responsive to these reduced speeds the rear fan stage can exhibit a higher rotational speed which also is exhibited by the second set of compressor blades and a corresponding lower fan pressure ratio notably the counter rotating configuration embodied provides high relative velocities between adjacent low pressure compressor blades resulting in relatively high levels of pressure ratio this counter rotating arrangement allows for a preservation of core supercharging and thermodynamic efficiency as fan speeds are modulated through the epicyclic differential gearbox in transitioning to high speed operations the flow of air to the tip fan.