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The cost of fuel control systems for small gas turbine engines is quite high and could be significantly reduced by simplifying the fuel metering system and bringing it under electronic control. Such an attempt has been made regarding the popular Bendix DP-F2 fuel control unit (FCU). Presently, the DP-F2 FCU is using a metering valve with a complex profile head, being moved in a calibrated orifice using double bellows operated by the compressor pressure. The differential pressure across the metering valve is controlled by a bypass valve fitted with a diaphragm which moves a shaped plunger inside a multi-orifice barrel. It is proposed to use a pressure balanced metering valve with a plunger moved in a slitted barrel by a stepper motor, which is changing the valve flow area according to the engine compressor pressure signal.

Typical fuel metering systems for small gas turbine engines consist of a metering valve and a bypass valve which is maintaining a constant differential pressure across the metering valve orifice. The metering valve is operated by the compressor pressure signal and the bypass valve acts automatically. It is proposed to bring both the metering and the bypass valves under the control of two digital linear actuators. The first one would move the metering plunger according to the compressor pressure and the second would move the bypass plunger in such a way, that the differential pressure across the metering orifice would be maintained constant only during steady state engine operation. During the engine transient processes, however, it would be increased or decreased as required, to speed up the change in the nozzle flow rate and consequently the engine dynamic response.