10.
The switch-in deflector consists of one or a pair of heavily reinforced doors which form part of the jet pipe wall when the engine is operating in the forward thrust condition. To select lift thrust, the doors are moved to blank off the conventional propelling nozzle and direct the exhaust flow into a lift nozzle (fig. 18-8). The lift nozzles may be designed so that they can be mechanically rotated to vary the angle of the thrust and permit intermediate lift/thrust positions to be selected.
11.
A second type of switch-in deflector system is used on the tandem fan or hybrid fan vectored thrust engine (fig. 18-9). In this case the deflector system is situated between the stages of the fan of a mixed flow turbo-fan engine. In normal flight the valve is positioned so that the engine operates in the same manner as a mixed flow turbo-fan and for lift thrust the valve is switched so that the exhaust flow from the front part of the fan exhausts through downward facing lift nozzles and a secondary inlet is opened to provide the required airflow to the rear part of the fan and the main engine. On a purely subsonic V/STOL aircraft where fuel consumption is important the valve may be dispensed with and the engine operated permanently in the latter high by-pass mode described above.
12.
Thrust deflecting nozzles will create an upstream pressure distortion which may excite vibration of the fan or low pressure turbine blades if the nozzle system is close to these components. Snubbers (Part 3) may be used on the fan blades to resist vibration. On the low pressure turbine, shrouds at the blade tips (Part 5) or wire lacing may be used to achieve the same result.
Lift engines
13.
The lift engine is designed to produce vertical thrust during the take-off and landing phases of V/STOL aircraft. Because the engine is not used in normal flight it must be light and have a small volume to avoid causing a large penalty on the aircraft. The lift engine may be a turbo-jet which for a given thrust gives the lowest weight and volume. Should a low jet velocity be necessary a lift fan may be employed.
14.
Pure lift-jet engines have been developed with thrust/weight ratios of about 20:1 and still higher values are projected for the future. Weight is reduced by keeping the engine design simple and also by extensive use of composite materials (fig. 18-10). Because the engine is operated for only limited periods during specific flight conditions i.e. during take-off and landing, the fuel system can be simplified and a total loss oil system (Part 8), in which
13．升力发动机是为垂直／短距起落飞机在起飞和降落时产生垂直推力而设计的。由于该发动机在正常飞行中不使用，所以它必须重量轻，体积小，以避免飞机产生过大的损失。升力发动机可以是一种提供一定推力且重量和体积最小的涡轮喷气发动机。如果需要低喷气速度，则可使用升力风扇。
升力发动机
14．推重比约为20：1的纯引力喷气发动机已研制出来。今后可能达到还要高的推重比值。由于尽量保持发动机设计简单和广泛使用复合材料(图18-10)，因而降低了重量。由于该发动机只是在特定飞行条件即起飞和降落时使用，所以燃油系统可以简化。还可以采用总损失滑油系统(第8章)，将使用过的滑油排出机外。
15.升力发动机可设计成或者在垂直位置或者在水平位置工作，所安装的推力偏转喷管具有可变推力矢量的一些优点。另外，发动机也可以是这样安装，即使其能沿一大角度旋转，以将推力转向。升力喷气发动机具有极热的高速喷气流。未来降低由喷气而引起的地面腐蚀，也可用多瓣喷管来取代常规的喷气喷管，以提高排气与四周空气的混合率。
16.升力风扇发动机的设计旨在降低喷气速度和对地面的腐蚀，从而使其能在无准备的地面起降。它还可大大降低喷气流噪声。已经为这种发动机考虑了广泛的设计备选方案。图18-11表示了其中的一部分。
Vertical/short take-off and landing
the used lubricating oil is ejected overboard, can be used.
15. Lift engines can be designed to operate in the vertical or horizontal position and a thrust deflecting nozzle fitted to provide some of the advantages of thrust vectoring. Alternatively, the engine may be mounted so that it can swivel through a large angle to provide thrust vectoring. The lift-jet engine will have an extremely hot, high velocity jet exhaust and to reduce ground erosion by the jet the normal
exhaust nozzle may be replaced by a multi-lobe nozzle to increase the rate of mixing with the surrounding air.
16. The lift-fan engine is designed to reduce the jet exhaust velocity, to reduce ground erosion and allow operation from unprepared ground surfaces. It also reduces the jet noise significantly. A range of design options have been considered for this type of engine and some are shown on fig. 18-11.
图18-9 可变推力矢量的发动机
Fig. 18-9 Vectored thrust engine.
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远距升力系统
17.直接升力远距系统将外涵空气或发动机排气导入远离发动机的面向下的升力喷管。这些喷管可设置在飞机的前机身或机翼中。发动机涵道通过类似于第10段中所述的偏转器来堵塞。
Vertical/short take-off and landing
18．远距升力风扇(图18-12)安装在飞机的机翼或机身上，由机械传动，或由导入叶尖涡轮的空气或燃气来传动。传动系统由主推进的动力装置或单独的发动机来提供。 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：劳斯莱斯喷气引擎－中英(93)
