(2)
Using specially designed engines for lift only.
图18-3 垂直起落／短距起落战斗机
(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
图18-4 推力偏转系统
Fig. 18-4 Thrust deflector systems.
开关式偏转器
四喷管偏转器
双喷管偏转器
对转喷管截面
Vertical/short take-off and landing
垂直升力时喷管偏转
推进位置上的喷管
可调喷管
升力／推进发动机
7.升力／推进发动机提供的推力可以为了产生一般的机翼升力来飞行，也可用于升力。这是通过政变推力方向来实现的，即通过含一个或两个或四个可转向喷管的偏转系统；或通过称之为开关式偏转器的装置，该装置将向后喷的推进喷管排气改向，引导至个或两个向下喷气的升力喷管(图18-4)。
图18-5 换向器喷管
Fig. 18-5 Deflector nozzle.
9.双喷管和四喷管换向器系统使用侧装喷管(图18-6)，它可在简单轴承上旋转90度以上。所以，可在需要时提供反推力。例虮，在一简单的驱动系统中可使用一个链轮和链子，并通过机械连接，使所有的喷管同时换向。对向前的飞行而言，为避免较大的性能损失和由此使燃油消耗的增加，必须精心设计排气装置和喷管的气动力通道，以便把排气流在两个紧密相接的弯管(图18-7)中折转时所产生的压力损失减至最小。
喷管
驱动链轮
链
滚珠轴承
8．单喷管的推力换向是通过将喷管各段连接在一起实现的。连接时喷管接合面呈一定角度。当它们相对旋转时，喷管则从水平位置向垂直位置移动(图18-5)。在喷管旋转时，为避免推力侧向分量或推力线偏离发动机轴线，第一个接合面必须与喷管轴线垂直。如果不希望喷管旋转，例如在可调面积喷管的情况下，则需要与喷管轴线垂直的第二个接合面。
图18-6 侧装的可转向喷管
10．开关式偏转器包括一个或一对牢固的加强门，当发动机存在正推力下运转时，它形成喷管壁的一部分。选择升力推力时，门被移动，以堵住常规的推进喷管，并将排气流导入升力喷管(图18-8)。升力喷管可设计成用机械旋转来改变推力角度并允许选择中间升力／推力位置。
11．第二种开关式偏转器用于串列风扇或混合风扇可变推力矢量发动机(图18-9)。在这种情况下，偏转器被安置在混合流涡轮风扇发动机的风扇级之间。在正常飞行中，活门处于适当的位置，发动机以类似于混合流涡轮风扇方式运转：在升力推力下飞行时，活门换向，使前部的风扇的排气流通过面向下的升力喷管排出，同时，辅助进气口打开，为后部的风扇和主发动机提供所需的空气流。对于纯亚音速垂直／短距起落飞机而言，燃油消耗是很重要的，可以不用此活门。发动机则以上面所述的后一种高涵道比方式持久地运转。
12.推力偏转喷管将产生上游压力畸变，如果喷管系统离风扇或低压涡轮叶片太近的话，则会使它们发生振动。可在风扇叶片上使用减震凸台(第3章)以抗振。对低压涡轮，可以使用叶冠(第5章)或金属条带来达到抗振的目的。
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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