工作原理
6.在涡轮喷气发动机上实现反推力的方法有若干种。图15-2显示出其中的三种。这三种方法将在下面的几段中陈述。
7.一种方法是用哈壳形折流门将排气流反向，第二种方法是用一种带外门的盾牌系统起类似功效。第三种方法用于涡扇发动机上，它是用阻流门将冷空气流反向。
4.在螺旋桨作动力的飞机上，反向推力通过改变螺旋桨桨叶的角度来实现。这通常利用液压机械系统响应飞机功率杆即油门杆的操纵来改变桨叶角度进行刹车。
5.最理想的情况是将燃气引导至完全向前。但这是不可能实现的，主要是气动力方面的原因，排气角度一般选为45度左右。因此，在油门杆角度相同的情况下，有效的反推力相应地要比正推力小。
Thrust reversal
8.所描述的每一系统中采用的反推力选用方法和安全特性基本上是一样的。驾驶舱中的反推力手柄用来选择反推力；只有当发动机以低功率状态运转时，才能将这一手柄推至反推力位置，如果反推力装置未能推至全反推力位置，则发动机也达不到大功率状态。如果工作压力降低或出现问题，机械锁将把反推力装置锁定在正推力位置；只有当压力恢复时，这一锁定才会解除。反推力系统的工作情况通过机舱中一系列的指示灯来反映。
图15-1 用与不用推力反向的着陆滑跑的比较
4.
On propeller-powered aircraft, reverse thrust action is obtained by changing the pitch of the propeller blades. This is usually achieved by a hydro-mechanical system, which changes the blade angle to give the braking action under the response of the power or throttle lever in the aircraft.
5.
Ideally, the gas should be directed in a completely forward direction. It is not possible, however, to achieve this, mainly for aerodynamic reasons, and a discharge angle of approximately 45 degrees is chosen. Therefore, the effective power in reverse thrust is proportionately less than the power in forward thrust for the same throttle angle.
PRINCIPLES OF OPERATION
6.
There are several methods of obtaining reverse thrust on turbo-jet engines; three of these are shown in fig. 15-2 and explained in the following paragraphs.
7.
One method uses clamshell-type deflector doors to reverse the exhaust gas stream and a second uses a target system with external type doors to do the same thing. The third method used on fan engines utilizes blocker doors to reverse the cold stream airflow.
8. Methods of reverse thrust selection and the safety features incorporated in each system described are basically the same. A reverse thrust lever in the crew compartment is used to select reverse thrust; the lever cannot be moved to the reverse thrust position unless the engine is running at a low power setting, and the engine cannot be opened up to a high power setting if the reverser fails to move into the full reverse thrust position. Should the operating pressure fall or fail, a mechanical lock holds the reverser in the forward thrust position; this lock cannot be removed until the pressure is restored. Operation of the thrust reverser system is indicated in the crew compartment by a series of lights.
Clamshell door system
9.
The clamshell door system is a pneumatically operated system, as shown in detail in fig. 15-3. Normal engine operation is not affected by the system, because the ducts through which the exhaust gases are deflected remain closed by the doors until reverse thrust is selected by the pilot.
10.
On the selection of reverse thrust, the doors rotate to uncover the ducts and close the normal gas stream exit. Cascade vanes then direct the gas stream in a forward direction so that the jet thrust opposes the aircraft motion.
哈壳形门系统
9.哈壳形门系统为气压操纵系统，详见图15-3。发动机的正常工作将不受该系统影响，因为在驾驶员选择反推力之前，用以偏转排气流的管道是被这些门堵死的。
10.在选择反推力时，哈壳形门旋转打开排气管并关闭燃气流的正常出口。叶栅的叶片将燃气流导引至向前的反向，所以喷气推力和飞机的运动相反。
Thrust reversal
图15-2 几种推力反向的方法
Fig. 15-2 Methods of thrust reversal.
冷气流反推力装置在反推力位置
冷气流反推力装置在正推力位置
作动筒和戽斗式门在反推力位置
Thrust reversal
图15-3 使用哈壳形门的一种典型反推力系统
Fig. 15-3 A typical thrust reverser system using clamshell doors.
Thrust reversal
图15-4 一种典型的风扇冷气流反推力系统
Fig. 15-4 A typical fan cold stream thrust reversal system.
反推力位置
堵塞门(折叠式)
反馈齿轮盒
调压器和断流活门
空气马达装置
燃油调节器
排气
选择活门
锁定和顺序活门
螺旋千斤顶
正推力位置
反推力选择手柄
(反推力)
减速器
空气马达
柔性传动
通气孔
方向和速度
控制活门
11.哈壳形门是通过杠杆由气动作作动筒操纵，这样来为正推力位置时的门施加最大载荷。它保证在门边缘处有效密封，从而防止燃气泄漏。门的轴承和操纵传动机构在温度高达600℃时仍可在无润滑情况下工作。
锁定指示器
照明电门
油门杆
堵塞门
齿轮盒
叶栅叶片
高压工作空气
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