Fuel control system in Aircraft Engine:
The computer controls the fuel flow to the engine to maintain a constant rotor RPM. During normal operation the optimum engine/rotor speed is selected by a speed selector lever, and the varying power demands are met thereafter by the automatic fuel computer. The computer varies the rates of fuel flow to the engines to suit the changing power demands occasioned by alterations of rotor blade pitch. The position of the throttle valve is set by an electric actuator controlled by the computer. The speed select lever in the cockpit is directly connected to the computer, and by operating this lever the pilot can select a power turbine speed that is maintained by the computer within built in control laws. In addition to speed selector lever positions , the computer receives signals of power turbine speed N1, gas generator speed N2, power turbine inlet temperature (PTIT), collective pitch angular movement via an anticipator, and throttle position. In the computer the signal representing actual power turbine speed is compared with the sped selector lever position , and any difference causes a signal to be transmitted from the computer to the throttle actuator, which adjusts the throttle opening accordingly. I however this were to cause the PTIT to exceed a pre-determined value or to increase at too rapid a rate, the computer signal is modified so that the throttle is held or closed until the PTIT is reduced to a safe level.
The function of the anticipator is to provide signals proportional to change of collective pitch angle.