(2)
Using specially designed engines for lift only.
圖18-3 垂直起落／短距起落戰斗機
(3)
Driving a lift system, which is remote from the engine, either from the engine or by a separate power unit.
(4)
Swivelling the engines.
(5)
For STOL aircraft, using bleed air from the
engines to increase circulation around the
wing and hence increase lift.
In several of the projected V/STOL aircraft a combination of two or more of these methods has been used.
Lift/Propulsion engines
7.
The lift/propulsion engine is capable of providing thrust for both normal wing borne flight and for lift. This is achieved by changing the direction of the thrust either by a deflector system consisting of one, two or four swivelling nozzles or by a device known as a switch-in deflector which redirects the exhaust gases from a rearward facing propulsion nozzle to one or two downward facing lift nozzles (fig, 18-4).
8.
Thrust deflection on a single nozzle is accom-plished by connecting together sections of the jet
圖18-4 推力偏轉系統
Fig. 18-4 Thrust deflector systems.
開關式偏轉器
四噴管偏轉器
雙噴管偏轉器
對轉噴管截面
Vertical/short take-off and landing
垂直升力時噴管偏轉
推進位置上的噴管
可調噴管
升力／推進發動機
7.升力／推進發動機提供的推力可以為了產生一般的機翼升力來飛行，也可用于升力。這是通過政變推力方向來實現的，即通過含一個或兩個或四個可轉向噴管的偏轉系統；或通過稱之為開關式偏轉器的裝置，該裝置將向后噴的推進噴管排氣改向，引導至個或兩個向下噴氣的升力噴管(圖18-4)。
圖18-5 換向器噴管
Fig. 18-5 Deflector nozzle.
9.雙噴管和四噴管換向器系統使用側裝噴管(圖18-6)，它可在簡單軸承上旋轉90度以上。所以，可在需要時提供反推力。例蟣，在一簡單的驅動系統中可使用一個鏈輪和鏈子，并通過機械連接，使所有的噴管同時換向。對向前的飛行而言，為避免較大的性能損失和由此使燃油消耗的增加，必須精心設計排氣裝置和噴管的氣動力通道，以便把排氣流在兩個緊密相接的彎管(圖18-7)中折轉時所產生的壓力損失減至最小。
噴管
驅動鏈輪
鏈
滾珠軸承
8．單噴管的推力換向是通過將噴管各段連接在一起實現的。連接時噴管接合面呈一定角度。當它們相對旋轉時，噴管則從水平位置向垂直位置移動(圖18-5)。在噴管旋轉時，為避免推力側向分量或推力線偏離發動機軸線，第一個接合面必須與噴管軸線垂直。如果不希望噴管旋轉，例如在可調面積噴管的情況下，則需要與噴管軸線垂直的第二個接合面。
圖18-6 側裝的可轉向噴管
10．開關式偏轉器包括一個或一對牢固的加強門，當發動機存在正推力下運轉時，它形成噴管壁的一部分。選擇升力推力時，門被移動，以堵住常規的推進噴管，并將排氣流導入升力噴管(圖18-8)。升力噴管可設計成用機械旋轉來改變推力角度并允許選擇中間升力／推力位置。
11．第二種開關式偏轉器用于串列風扇或混合風扇可變推力矢量發動機(圖18-9)。在這種情況下，偏轉器被安置在混合流渦輪風扇發動機的風扇級之間。在正常飛行中，活門處于適當的位置，發動機以類似于混合流渦輪風扇方式運轉：在升力推力下飛行時，活門換向，使前部的風扇的排氣流通過面向下的升力噴管排出，同時，輔助進氣口打開，為后部的風扇和主發動機提供所需的空氣流。對于純亞音速垂直／短距起落飛機而言，燃油消耗是很重要的，可以不用此活門。發動機則以上面所述的后一種高涵道比方式持久地運轉。
12.推力偏轉噴管將產生上游壓力畸變，如果噴管系統離風扇或低壓渦輪葉片太近的話，則會使它們發生振動。可在風扇葉片上使用減震凸臺(第3章)以抗振。對低壓渦輪，可以使用葉冠(第5章)或金屬條帶來達到抗振的目的。
Vertical/short take-off and landing
pipe, the joint faces of which are so angled that, when the sections are counter-rotated, the nozzle moves from the horizontal to the vertical position (fig. 18-5). To avoid either a side component o! thrust or a thrust line offset from the engine axis during the movement of the nozzle it is necessary that the first joint face is perpendicular to the axis of the jet pipe. If it is desired that the nozzle does not rotate, as may be the case if it is a variable area nozzle, a third joint face which is perpendicular to the axis of the nozzle is required.
9. The two and four nozzle deflector systems use side mounted nozzles (fig. 18-6) which can rotate on simple bearings through an angle of well over 90 degrees so that reverse thrust can be provided if required. A simple drive system, for example, a sprocket and chain, can be used and by mechanical connections all the nozzles can be made to deflect simultaneously. For forward flight, to avoid a high performance loss and consequent increase in fuel consumption, careful design of the exhaust unit and nozzle aerodynamic passages are essential to minimize the pressure losses due to turning the exhaust flow through two close coupled bends (fig. 18-7).
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