VARIABLE DRIVE GAS TURBINE ENGINE

A system and method for variable drive of a propeller or fan of a gas turbine engine. The gas turbine engine has a combustor and a turbine arranged to be driven by a combustion product from the combustor. The variable drive system comprises a primary shaft arranged for transmission of torque from said turbine to the propeller; an electric generator arranged to be driven by said turbine; and an electric motor arranged to be driven by the output of said generator. A clutch is mounted between the propeller and the primary rotor and is operable to mechanically disconnect the shaft from the propeller so that the propeller can be driven by any or any combination of the turbine and/or electric motor. The invention may be applied to a turboprop or turbofan engine having a gearing between the shaft and propeller or fan and may be particularly suited to unmanned aerial vehicle propulsion.