Patent ID: 8220245

Claim:
A gas turbine engine, comprising: a) an air inlet; b) a low pressure compressor downstream from and in fluid communication with the air inlet for compressing air traversing the air inlet; c) a combustor downstream from and in fluid communication with the low pressure compressor for combusting a fuel mixture; d) a low pressure turbine downstream from and in fluid communication with the combustor, the low pressure turbine operably connected to the low pressure compressor by a first drive shaft, the low pressure turbine being adapted to generate power from a combusted fuel mixture passing therethrough to power the low pressure compressor; e) a power turbine downstream from and in fluid communication with the combustor and the low pressure turbine, the power turbine being adapted to generate power to power a load external to the engine, the power turbine mounted on a second drive shaft; f) an engagement mechanism adapted to selectively engage the first drive shaft to the second drive shaft, wherein the first drive shaft and second drive shaft rotate at substantially the same speed when the engagement mechanism is engaged, wherein the low pressure turbine and power turbine have an aerodynamic design speed such that the power turbine produces power at substantially a same speed as the low pressure turbine, thereby allowing the low pressure turbine to provide power to the output shaft when the low pressure and power turbines are selectively coupled by the engagement mechanism; g) a high pressure compressor downstream from and in fluid communication with the low pressure compressor; and h) a high pressure turbine downstream from and in fluid communication with the combustor, the high pressure turbine operably connected to the high pressure compressor by a third drive shaft, the high pressure turbine being adapted to generate power from a combusted fuel mixture passing therethrough to power the high pressure compressor.