12.戽斗式盾牌系统为液压传动系统，利用戽斗式门将热燃气流反向。推力反向装置门通过常规推杆系统来传动。一个液压作动筒与一个传动中介轮相连接，通过一对推杆来操纵门（每个门上有一根推杆）。
11. The clamshell doors are operated by pneumatic rams through levers that give the maximum load to the doors in the forward thrust position; this ensures effective sealing at the door edges, so preventing gas leakage. The door bearings and operating linkage operate without lubrication at temperatures of up to 600 deg. C.
Bucket target system
12.
The bucket target system is hydraulically actuated and uses bucket-type doors to reverse the hot gas stream. The thrust reverser doors are actuated by means of a conventional pushrod system. A single hydraulic powered actuator is connected to a drive idler, actuating the doors through a pair of pushrods (one for each door).
13.
The reverser doors are kept in synchronization through the drive idler. The hydraulic actuator incor-porates a mechanical lock in the stowed (actuator extended) position.
14.
In the forward thrust mode (stowed) the thrust reverser doors form the convergent-divergent final nozzle for the engine.
Thrust reversal
Cold stream reverser system
15.
The cold stream reverser system (fig. 15-4) can be actuated by an air motor, the output of which is converted to mechanical movement by a series of flexible drives, gearboxes and screwjacks, or by a system incorporating hydraulic rams.
16.
When the engine is operating in forward thrust, the cold stream final nozzle is 'open' because the cascade vanes are internally covered by the blocker doors (flaps) and externally by the movable (translating) cowl; the latter item also serves to reduce drag.
17.
On selection of reverse thrust, the actuation system moves the translating cowl rearwards and at the same time folds the blocker doors to blank off the cold stream final nozzle, thus diverting the airflow through the cascade vanes.
Turbo-propeller reverse pitch system
18. As mentioned in para. A, reverse thrust action is affected on turbo-propeller powered aircraft by changing the pitch of the propeller blades through a hydro-mechanical pitch control system (fig. 15-5). Movement of the throttle or power control lever 油门杆
图15-5 一种螺旋桨桨距控制系统
Fig. 15-5 A propeller pitch control system.
涡轮螺桨反桨系统
正如第4段所述，通过液压机械式桨叶角度控制系统(图15-5)来改变螺旋桨桨叶的角度产生反推力对以涡轮螺桨为动力的飞机产生影响。油门杆即功率控制杆把滑油从控制系统引导致螺旋桨机构，将桨叶角度减少到零，,再到负(反)桨距。油门杆移动时，通过与桨叶角度控制装置相连接的油门杆活门来调整向发动机的燃油供给，使发动机功率和桨叶角度相协调，以获得所学的反推力值。反推力也可用以操纵已停下的涡轮螺桨飞机使之后退。
Thrust reversal
19.在螺旋桨控制系统中已考虑到若干在螺旋桨出现故障时有用的安全因素，这些装置通常是液压机械式桨距锁定装置或止动装置。
图15-6 热气流推力反向装置
Fig. 15-6 Hot stream thrust reverser installations.
结构和材料
20.第9和第12段中介绍的哈壳形门和戽斗式盾牌门（图15-6）形成喷管的一部分。反推器的机匣与飞机机构连接或直接与发动机连接。此机匣支撑着两个反推器的门和操纵机构，在哈壳形门系统中，还支持装有叶栅叶片的排气管。燃气流的角度和面积是通过每一排气管中的叶片数量来控制的。
directs oil from the control system to the propeller mechanism to reduce the blade angle to zero, and then through to negative (reverse) pitch. During throttle lever movement, the fuel to the engine is trimmed by the throttle valve, which is interconnect-ed to the pitch control unit, so that engine power and blade angle are co-ordinated to obtain the desired amount of reverse thrust. Reverse thrust action may also be used to manoeuvre a turbo-propeller aircraft backwards after it has been brought to rest.
19. Several safety factors are incorporated in the propeller control system for use in the event of propeller malfunction, and these devices are usually hydro-mechanical pitch locking devices or stops.
CONSTRUCTION AND MATERIALS
20. The clamshell and bucket target doors (fig. 15-6) described in paras. 9 and 12 form part of the jet
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