Method and apparatus for controlling thrust in a gas turbine engine

Apparatus for controlling thrust of a gas turbine engine of the type having a compressor, a combustor and a turbine with means for producing signals proportional to engine inlet temperature, engine inlet pressure and compressor physical rotational speed, a fuel controller, and a power lever adapted to be set to different angles to select a different desired engine thrust at each power lever angle, wherein the improvement comprises means for providing a demand compressor physical speed signal adjusted by engine inlet pressure and temperature, means for comparing said compressor physical speed signal and said demand compressor physical speed signal to develop an error signal, said error signal being coupled to said fuel controller in order to maintain said desired thrust at each selected power lever angle wherein said means for providing a demand compressor physical speed signal comprises means for producing a temperature correction factor signal as a function of engine inlet temperature which relates compressor physical speed and compressor corrected speed at engine inlet temperatures other than sea level standard day temperature, means for producing a demand compressor corrected speed signal as a function of power lever position and biased by a predetermined lapse rate as a function of engine inlet pressure, means for producing a separate demand compressor corrected speed signal as a function of engine inlet temperature, means for selecting the lesser of the two demand compressor corrected speed signals and means for applying said selected lesser corrected speed signal and said temperature correction factor to produce a demand compressor physical speed signal as a function thereof.

In a gas turbine engine of the type having a compressor, a combustor, a turbine, a fuel controller, and a power lever adapted to be variably positioned to select engine thrust, a method of controlling thrust for varying values of engine inlet pressure and temperature comprising the steps of:

• producing signals respectively proportional to engine inlet temperature, engine inlet pressure and power lever position;
• producing a temperature correction factor proportional to engine inlet temperature which related compressor physical speed and compressor corrected speed at engine inlet temperatures other than standard day temperature;
• producing a demand compressor corrected speed proportional to a selected power level position and biased by a predetermined lapse rate proportional to engine inlet pressure;
• producing a separate demand compressor corrected speed proportional to engine inlet temperature;
• selecting the lesser of the two demand compressor corrected speeds;
• applying the selected lesser speed and the temperature correction factor to produce a demand compressor physical speed as a function thereof;
• and
• applying said signals to said fuel controller to automatically adjust compressor physical rotational speed at a fixed power lever position, whereby a selected thrust level is maintained at varying engine inlet temperatures within limits imposed for turbine overtemperature protection and compressor physical speed is modulated with variations in engine inlet pressure to provide a thrust rating schedule which varies with altitude.