Abstract: A system for generating electrical signals which are intended to control a flow limiting device, in particular in a fuel control apparatus, has duplicate signal generating circuits which are responsive to operation of the fuel control apparatus and which generate nominally indentical output signals when an operating condition of the fuel control apparatus exceeds predetermined limits. Output signals from the duplicate circuits are supplied to the limiting device by way of respective control circuits each of which is enabled by the presence of a corresponding output signal from the other of the signal generating circuits. A device is provided for detecting a malfunction of one of the signal generating circuits and for permanently enabling the control circuit.

Abstract: A gas turbine engine fuel control has a main hydromechanical fuel flow control and an electrically operable valve in series with the flow control for speed limitation purposes. The valve is controlled by a signal N.sub.L or N.sub.H derived from an engine speed transducer. A phase advance compensation circuit advances the phase of the transducer signal and its output is applied to an error amplifier which compares it with a datum (which may vary with altitude). The error signal is applied to a non-linear amplifier the amplification factor of which increases when a certain error threshold is exceeded. The combination of phase advance and non-linear amplification ensures rapid limitation of speed without introducing stability problems.

Abstract: A gas turbine engine fuel control system includes an hydromechanical speed governor fuel flow control with an electromechanical trim. The trim is controlled by a proportional-plus-integral controller in accordance with the error signal from an error amplifier comparing an engine parameter with a desired value of that parameter. A trim datum signal is produced by a suitable generator circuit and, if the error signal (or its rate of charge) exceeds a set maximum, the integrator is set to a new value.

Abstract: An electronic fuel control for a multi-engine gas turbine engine provides either independent or master-slave operation according to the position of a selector switch. In one position independent speed demand signals are separately compared with independent actual speed signals and the error signals produced are fed to proportional-plus-integral fuel controls. In the other position engine fuel control receives a signal corresponding to the error between 1/2 of the sum of the average speed demand and the actual speed of that engine whereas the other engines fuel control receives only an error signal representing the difference between the two engine speeds.

Abstract: A digital computing apparatus, particularly for use in controlling a gas turbine engine, comprises two identical computing devices each of which is responsive to identical time control signals and to identical input signals, so as to supply nominally identical synchronized output signals, the sequential bits of which one output signal is comprised being compared, one at a time, with the corresponding bits of the other output signals, to provide monitoring of operation of both devices.