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．升力發動機是為垂直／短距起落飛機在起飛和降落時產生垂直推力而設計的。由于該發動機在正常飛行中不使用，所以它必須重量輕，體積小，以避免飛機產生過大的損失。升力發動機可以是一種提供一定推力且重量和體積最小的渦輪噴氣發動機。如果需要低噴氣速度，則可使用升力風扇。
升力發動機
14．推重比約為20：1的純引力噴氣發動機已研制出來。今后可能達到還要高的推重比值。由于盡量保持發動機設計簡單和廣泛使用復合材料(圖18-10)，因而降低了重量。由于該發動機只是在特定飛行條件即起飛和降落時使用，所以燃油系統可以簡化。還可以采用總損失滑油系統(第8章)，將使用過的滑油排出機外。
15.升力發動機可設計成或者在垂直位置或者在水平位置工作，所安裝的推力偏轉噴管具有可變推力矢量的一些優點。另外，發動機也可以是這樣安裝，即使其能沿一大角度旋轉，以將推力轉向。升力噴氣發動機具有極熱的高速噴氣流。未來降低由噴氣而引起的地面腐蝕，也可用多瓣噴管來取代常規的噴氣噴管，以提高排氣與四周空氣的混合率。

16.升力風扇發動機的設計旨在降低噴氣速度和對地面的腐蝕，從而使其能在無準備的地面起降。它還可大大降低噴氣流噪聲。已經為這種發動機考慮了廣泛的設計備選方案。圖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.

圖18-9 可變推力矢量的發動機
Fig. 18-9 Vectored thrust engine.
192
遠距升力系統

17.直接升力遠距系統將外涵空氣或發動機排氣導入遠離發動機的面向下的升力噴管。這些噴管可設置在飛機的前機身或機翼中。發動機涵道通過類似于第10段中所述的偏轉器來堵塞。
Vertical/short take-off and landing

18．遠距升力風扇(圖18-12)安裝在飛機的機翼或機身上，由機械傳動，或由導入葉尖渦輪的空氣或燃氣來傳動。傳動系統由主推進的動力裝置或單獨的發動機來提供。
　
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