Abstract: In a switching device for exploiting impedance differences between at least two loads, connectors are provided for coupling the loads to the switching device. The loads cooperatively define a non-zero virtual impedance. At least one connection point is included for accepting an output from at least one signal generator. The connection point is in electrical communication with the connector. The connector and the connection point cooperate with one another to selectively cause the loads to be interconnected at minimum of at least two of either series, parallel, first load alone, or second load alone, to exploit the impedance differences and/or associated virtual impedance.

Abstract: The invention is a method and system for fan flutter control. The output of circumferentially distributed sensors is used to calculate the asymmetry of a flow field. The asymmetry measurement is used to modulate a bleed valve, variable exhaust nozzle or other device to increase the fan's tolerance of flutter disturbances.

Abstract: The invention is a method and system for fan flutter control. The output of circumferentially distributed sensors is used to calculate the asymmetry of a flow field. The asymmetry measurement is used to modulate a bleed valve, variable exhaust nozzle or other device to increase the fan's tolerance of flutter disturbances.

Abstract: A pressure sensor (12) is located in the compressor stage of a gas turbine engine (10) to provide a pressure signal (PR1) that shows the compressor flow characteristics. The pressure signal (PR1) is applied to a bandpass filter (16) with roll-offs above and below N2. The difference between the filter output and a stored value for the pressure signal is integrated, and compressor bleed valves (18) are opened if the integral exceeds a stored threshold. The health of a compressor stage is determined by analyzing the magnitude of compressor pressure variations at N2 while accelerating the engine and by comparing the magnitude with values obtained from a compressor with a known stall margin.

Abstract: A control system includes a plant 56 having resonant modes and a controller 5 which receives plant input signals on lines 14,24 from the plant 56 and provides a controller output signal I, related to a filter output signal V, which controls the plant 6. The controller is provided with a non-linear notch filter 30 which receives a filter input signal x related to the plant input signals and provides the filter output signal V. The notch filter has at least one notch frequency near one of the resonant modes so as to attenuate one of the modes by a predetermined amount and has a phase lag a decade below the lowest notch frequency of said notch filter which is less than that of a corresponding linear notch filter, thereby allowing the control system 7 to exhibit faster time response and increased bandwidth than a system employing linear notch filters.

Abstract: A technique for controlling compressor stall and surge is disclosed. In a gas turbine engine, static pressure asymmetry is sensed at a plurality of locations along the circumference of the compressor inlet. Time rate of change of the mass flow in the compressor is also estimated using pressure measurements in the compressor. A signal processor uses these signals to modulate a compressor bleed valve responsive to the level of flow property asymmetry, the time rate of change of the annulus average flow to enhance operability of the compressor.