Abstract: A gas turbine engine power unit (10) comprising a gas turbine engine hot gas generator (10a), the exhaust efflux of which drives a turbine (20) having a power output shaft (22). The exhaust efflux from the turbine (20) is directed into a chamber (23) having two outlets (24,25) to atmosphere. The outlets (24,25) are provided with valves (26,28) which are operable to ensure that only one outlet (24,25) is open at a given time. The first outlet (24) contains a heat exchanger (15) whereas the second outlet (25) contains a further turbine (30). The further turbine (30) drives an air compressor (32) the output of which is directed to an air inlet (36) of the gas turbine engine (10a) in order to facilitate a boost in its output power.

Abstract: A speed control for a DC motor drive having regenerative braking and a field reversing control, has a field current feedback circuit which includes a modifier to change the feedback signal in accordance with the saturation curve of the field to provide a feedback signal representing field strength or field flux. Because motor field strength is regulated as a function of the required field strength, the control tends to make the speed of response independent of actual field strength. Also, a feedback signal is provided which is a function of the product of actual field strength and desired armature current, i.e., related to torque, and this controls the speed signal so that the gain of the speed regulating amplifier is inversely proportional to field strength. This allows drive operation at reduced field strength while maintaining the response.