工作原理
6.在渦輪噴氣發(fā)動機上實現(xiàn)反推力的方法有若干種。圖15-2顯示出其中的三種。這三種方法將在下面的幾段中陳述。
7.一種方法是用哈殼形折流門將排氣流反向，第二種方法是用一種帶外門的盾牌系統(tǒng)起類似功效。第三種方法用于渦扇發(fā)動機上，它是用阻流門將冷空氣流反向。
4.在螺旋槳作動力的飛機上，反向推力通過改變螺旋槳槳葉的角度來實現(xiàn)。這通常利用液壓機械系統(tǒng)響應(yīng)飛機功率桿即油門桿的操縱來改變槳葉角度進行剎車。
5.最理想的情況是將燃?xì)庖龑?dǎo)至完全向前。但這是不可能實現(xiàn)的，主要是氣動力方面的原因，排氣角度一般選為45度左右。因此，在油門桿角度相同的情況下，有效的反推力相應(yīng)地要比正推力小。
Thrust reversal
8.所描述的每一系統(tǒng)中采用的反推力選用方法和安全特性基本上是一樣的。駕駛艙中的反推力手柄用來選擇反推力；只有當(dāng)發(fā)動機以低功率狀態(tài)運轉(zhuǎn)時，才能將這一手柄推至反推力位置，如果反推力裝置未能推至全反推力位置，則發(fā)動機也達不到大功率狀態(tài)。如果工作壓力降低或出現(xiàn)問題，機械鎖將把反推力裝置鎖定在正推力位置；只有當(dāng)壓力恢復(fù)時，這一鎖定才會解除。反推力系統(tǒng)的工作情況通過機艙中一系列的指示燈來反映。
圖15-1 用與不用推力反向的著陸滑跑的比較
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.
哈殼形門系統(tǒng)
9.哈殼形門系統(tǒng)為氣壓操縱系統(tǒng)，詳見圖15-3。發(fā)動機的正常工作將不受該系統(tǒng)影響，因為在駕駛員選擇反推力之前，用以偏轉(zhuǎn)排氣流的管道是被這些門堵死的。
10.在選擇反推力時，哈殼形門旋轉(zhuǎn)打開排氣管并關(guān)閉燃?xì)饬鞯恼３隹凇Ｈ~柵的葉片將燃?xì)饬鲗?dǎo)引至向前的反向，所以噴氣推力和飛機的運動相反。
Thrust reversal
圖15-2 幾種推力反向的方法
Fig. 15-2 Methods of thrust reversal.
冷氣流反推力裝置在反推力位置
冷氣流反推力裝置在正推力位置
作動筒和戽斗式門在反推力位置
Thrust reversal
圖15-3 使用哈殼形門的一種典型反推力系統(tǒng)
Fig. 15-3 A typical thrust reverser system using clamshell doors.
Thrust reversal
圖15-4 一種典型的風(fēng)扇冷氣流反推力系統(tǒng)
Fig. 15-4 A typical fan cold stream thrust reversal system.
反推力位置
堵塞門(折疊式)
反饋齒輪盒
調(diào)壓器和斷流活門
空氣馬達裝置
燃油調(diào)節(jié)器
排氣
選擇活門
鎖定和順序活門
螺旋千斤頂
正推力位置
反推力選擇手柄
(反推力)
減速器
空氣馬達
柔性傳動
通氣孔
方向和速度
控制活門
11.哈殼形門是通過杠桿由氣動作作動筒操縱，這樣來為正推力位置時的門施加最大載荷。它保證在門邊緣處有效密封，從而防止燃?xì)庑孤ｉT的軸承和操縱傳動機構(gòu)在溫度高達600℃時仍可在無潤滑情況下工作。
鎖定指示器
照明電門
油門桿
堵塞門
齒輪盒
葉柵葉片
高壓工作空氣
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