1. Two separate systems are required to ensure that a gas turbine engine will start satisfactorily. Firstly, provision must be made for the compressor and turbine to be rotated up to a speed at which adequate air passes into the combustion system to mix with fuel from the fuel spray nozzles (Part 10). Secondly, provision must be made for ignition of the air/fuel mixture in the combustion system. During engine starting the two systems must operate simul- taneously, yet it must also be possible to motor the engine over without ignition for maintenance checks and to operate only the ignition system for relighting during flight (para. 28).
2. The functioning of both systems is co-ordinated during a starting cycle and their operation is auto- matically controlled after the initiation of the cycle by an electrical circuit. A typical sequence of events during the start of a turbo-jet engine is shown in fig.11-1.
METHODS OF STARTING
Fig. 11-1 A typical starting sequence of aturbo-jet engine.
4. The starter motor must produce a high torque and transmit it to the engine rotating assembly in a manner that provides smooth acceleration from rest up to a speed at which the gas flow through the engine provides sufficient power for the engineturbine to take over.