9.空气起动应用于大多数民用和若干军用喷气发动机中。与其它起动系统相比，它有重量较轻，简单而且使用经济等许多优点。
10.空气起动机马达将功率通过减速齿轮和离合器传递给起动机输出轴，该轴与发动机相连。典型的空气起动马达示于图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
11.起动机涡轮由来自外部地面气源的空气带转，也可以用辅助动力装置（APU）带转，或者用正在运转的发动机进行交叉供气驱动。向起动机供气的外部气源由电控制器和减压活门加以控制。该活门在起动机起动时打开，当达到预定的起动机转速时自动关闭。当发动机加速到慢车转速时，离合器自动打开，同时起动停止转动。一种典型的空气起动系统示于图11-7。
高压开关
排气管
转速控制开关
电嘴
点火开关
起动机马达
点火器
燃油旁路
燃油和空气回油泵
控制盒
旁路空气
燃油箱
起动机按钮
飞机电源
Starting and ignition
图11-5 一种异丙基硝酸酯起动系统
Fig. 11-5 An iso-propyl-nitrate starting system.
12.有时在已装有空气起动机的发动机上还有燃烧室起动机，当没有外部空气源的情况下用于向起动机供气。这种起动机有一个小型的燃烧室，它使用飞机丄佩带的气瓶的高压空气，及发动机燃油系统的燃油控制活门调节气源的供气，气源对燃油蓄压器加压，以提供足够的燃油压力进行雾化，而且还激发连续点火系统。燃油、空气混合气在燃烧室中点燃，产生的燃气被引入空气起动机的涡轮。当起动循环完成之后，有一个电路将气源断开，并进而终止燃油和点火系统的工作。
涡轮转子
减速齿轮
空气进口
离合器
13.有些涡轮喷气发动机上不装起动机马达，但利用空气冲击涡轮叶片作为带转发动机的一种方法。空气可以取自外部气源、或正在运转的发动机，并经单向活门和导向器导入涡轮叶片。一种空气冲击起动的典型方法示于图11-8。
发动机驱动轴
空气出口
Starting and ignition
燃气涡轮起动
14.燃气涡轮起动机用于某些喷气发动机中，这种起动方式是完全自立的。它具有自己的燃油和点火系统、起动系统（通常是电的或液压的），以及自备滑油系统。这种起动机使用经济，而且以比较轻的重量提供高的功率输出。
15.这种起动机含有一台小而紧凑的燃气涡轮发动机，其一般特点是采用涡轮驱动的离心压气机，回油式燃烧系统和一个机械上独立的自由动力涡轮。它由动力涡轮经由两级游星式减速齿轮、自动离合器和输出轴与主发动机相连。一种典型的燃气涡轮起动机示于图11-9。
图11-6 一种空气起动机马达
Fig. 11-6 An air starter motor.
rotation of the starter ceases. A typical air starting system is shown in fig. 11-7.
12.
A combustor starter is sometimes fitted to an engine incorporating an air starter and is used to supply power to the starter when an external supply of air is not available. The starter unit has a small combustion chamber into which high pressure air, from an aircraft-mounted storage bottle, and fuel, from the engine fuel system, are introduced. Control valves regulate the air supply which pressurizes a fuel accumulator to give sufficient fuel pressure for atomization and also activates the continuous ignition system. The fuel/air mixture is ignited in the combustion chamber and the resultant gas is directed onto the turbine of the air starter. An electrical circuit is provided to shut off the air supply which in turn terminates the fuel and ignition systems on completion of the starting cycle.
13.
Some turbo-jet engines are not fitted with starter motors, but use air impingement onto the turbine blades as a means of rotating the engine. The air is obtained from an external source, or from an engine that is running, and is directed through non-return valves and nozzles onto the turbine blades. A typical method of air impingement starting is shown in fig. 11-8.
Gas turbine
14.
A gas turbine starter is used for some jet engines and is completely self-contained. It has its own fuel and ignition system, starting system (usually electric or hydraulic) and self-contained oil system. This type of starter is economical to operate and provides a high power output for a comparatively low weight.
15.
The starter consists of a small, compact gas turbine engine, usually featuring a turbine-driven centrifugal compressor, a reverse flow combustion system and a mechanically independent |free-power turbine. The free-power turbine is connected to the main engine via a two-stage epicyclic reduction gear, automatic clutch and output shaft. A typical gas turbine starter is shown in fig. 11-9.
16.
On initiation of the starting cycle, the gas turbine starter is rotated by its own starter motor until it reaches self-sustaining speed, when the starting and ignition systems are automatically switched off. Acceleration then continues up to a controlled speed of approximately 60,000 r.p.m. At the same time as the gas turbine starter engine is accelerating, the exhaust gas is being directed, via nozzle guide vanes, onto the free-power turbine to provide the drive to the main engine. Once the main engine reaches self-sustaining speed, a cut-out switch
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