Abstract: A control system for operating a compressor bleed valve in a gas turbine engine to prevent compressor operation in surge region determines engine stability in response to a plurality of sensed engine parameters, and calculates and stores engine parameters to estimate compressor performance relative to a stability limit which is indicative of a surge operation. The control system further maintains a rolling average of the estimate of compressor performance for up to a predetermined number of engine flights. This rolling average of the estimate of compressor performance is indicative of engine usage and associated engine degradation. The control system determines a bias for the bleed valve in response to calculated engine parameters and adjusts the operation of the bleed valve in response to the compressor performance so as not to exceed the stability limit.

Abstract: When a stall is dectected during high power operation, the engine is given one chance to recover without a change in bleed schedule. Should a record stall occur within 10 seconds the control system switches to an override bleed schedule for 51/2 minutes, or until throttle is reduced. This supplies a minimum adaquate thrust for a limited time.

Abstract: When a stall is detected during high power operation, the engine is given one chance to recover without a change in bleed schedule. Should a second stall occur within 10 seconds the control system switches to an override bleed schedule for 51/2 minutes, or until throttle is reduced. This supplies a minimum adaquate thrust for a limited time.

Abstract: A gas turbine engine control system operates based upon a synthesized value of a parameter upon loss of the actual measured value of the parameter. To provide smooth engine operation upon switchover to the synthesized parameter a fixed trim is applied to the synthesized parameter which, upon switchover, makes the synthesized parameter equal to the last known measured value of the parameter. Thus, the engine will see no sudden change in operation at the instant of switchover. Thereafter the trimmed synthesized parameter changes in value by the same amount as does the untrimmed synthesized parameter.

Abstract: A gas turbine engine control system which regulates fuel flow based upon a schedule which is a function of a primary parameter, such as engine pressure ratio, switches to a schedule based upon a secondary parameter, such as compressor speed, upon the inability to function in the primary parameter mode. Upon switchover to the secondary parameter mode the scheduled value of the secondary parameter is down-trimmed to make it equivalent to the last known good value of the primary parameter so that the engine will not experience a sudden change in power level upon switchover. The down-trim is limited. When the primary mode failure occurs during a transient the down-trim is limited to the difference between a scheduled reference value of the secondary parameter and a value of the secondary parameter calculated immediately preceeding loss of the primary parameter mode and based upon a known relationship between the primary and secondary parameter.

Abstract: In a twin spool gas turbine engine the electronic engine control modulates the open area of the compressor bleed valves during engine transients as a function of a ratio of the actual rate of change of the compressor speed to a maximum scheduled rate of change such that the bleeds are opened more as the actual rate of change approaches the scheduled maximum rate. This continuous modulation provides smooth thrust transition from one steady state condition to another while maintaining a proper safety margin relative to the engine surge line.

Abstract: In a gas turbine engine electronic control system the engine total inlet temperature is synthesized from aircraft Mach number and the nozzle expansion ratio. When the engine is in a transient mode of operation the synthesized value of the total inlet temperature is maintained constant at the value calculated just before entering the transient mode. The synthesized temperature is used when the actual measured temperature is unavailable or unreliable.