Starting and ignition - Air

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Air

Fig. 11-6 An air starter motor.

9. Air starting is used on most commercial and some military jet engines. It has many advantages over other starting systems, and is comparatively light, simple and economical to operate. 10. An air starter motor transmits power through a reduction gear and clutch to the starter output shaft which is connected to the engine. A typical air starter motor is shown in fig. 11-6.



11. The starter turbine is rotated by air taken from an external ground supply, an auxiliary power unit (A.P.U.) or as a cross-feed from a running engine. The air supply to the starter is controlled by an elec- trically operated control and pressure reducing valve that is opened when an engine start is selected and is automatically closed at a predetermined starter speed. The clutch also automatically disengages as the engine accelerates up to idling r.p.m. and the rotation of the starter ceases. A typical air starting system is shown in fig. 11-7.