Abstract: A fuel control for a gas turbine engine has an actuator (24) for a fuel metering valve (22) which includes two stepper motors (46 and 48) which selectively drive a differential mechanism operatively connected to the valve. The differential mechanism includes two identical gear assemblies (60, 64) which are mounted for rotation upon a shaft (26) connected to the valve. The gear assemblies include worm gears (58, 62) in engagement with worms (54, 56) driven by the stepper motors and bevel gears (68, 70). A spider bevel gear (66), carried by the shaft, is in meshing engagement with the bevel gears of the gear assemblies such that rotation of one of the gear assemblies with the other at rest causes a circumferential movement of the spider bevel gear which rotates the shaft and positions the valve. Two identical electronic control units (A, B), which each sense selected engine parameters are respectively connected to the stepper motors for controlling their operation.

Abstract: A fuel metering system for a gas turbine engine with a low pressure drop fuel vaporizing system includes an engine driven centrifugal pump (10) supplied with fuel at a given absolute pressure (Pi) from a tank. The pump discharges fuel to a rapidly pulsed, solenoid operated ball valve (20) which functions as a metering valve in controlling flow to the engine. The solenoid (38) of the metering valve receives periodic voltage pulses of appropriate width from an electronic control which senses selected engine parameters and computes the required fuel flow and the pressure differential (Pr-P.sub.D) across the metering valve. Since the pressure differential across the metering valve increases with engine speed, favorable flow turndown ratios may be achieved without operating the metering valve at high or low values of duty cycle.