7.这一同样的反作用原理出现于所有运动形式之中，通常有许多应用方式。喷气反作用最早的著名例子是公元前120年作为一种玩具生产的赫罗的发动机（图1-4）这种玩具表明了从若干喷嘴中喷出的水蒸气的能量能够把大小相等方向相反的反作用力传给这些喷嘴本身，从而引起发动机旋转的道理。
8.类似的旋转式花园喷灌器（图1-5）是这一原理更为实用的
一个例子。这种喷灌器借助于作用于喷水嘴的反作用力旋转。现代灭火设备的高压喷头是“喷流反作用”的一个例子。由于水喷流的反作用力，一个救火员经常握不住或控制不了水管。也许，这一原理的最简单的表演是狂欢节的气球，当它放出空气或气体时，它便沿着与喷气相反的方向急速飞走。
4. 喷气发动机（图1-2）虽然与活塞发动机－螺旋桨组合貌似大相径庭，但是却采用了同样的基本原理来实现推进。正如图1-3所示，二者纯粹是通过将大量气体向后推而推进它们的飞机。
5.今天，虽然喷气推进与燃气涡轮发动机密切相关，但是，也有其它类型的喷气推进发动机，如冲压喷气、脉冲喷气、火箭、涡轮/冲压喷气和涡轮－火箭发动机等。
Basic mechanics
图1-2 惠特尔型的一种涡轮喷气发动机
喷管和推进喷口
Fig. 1-2 A Whittle-type turbo-jet engine.
4.
The jet engine (fig. 1-2), although appearing so different from the piston engine-propeller combination, applies the same basic principles to effect propulsion. As shown in fig. 1-3, both propel their aircraft solely by thrusting a large weight of air backwards.
5.
Although today jet propulsion is popularly linked with the gas turbine engine, there are other types of jet propelled engines, such as the ram jet, the pulse jet, the rocket, the turbo/ram jet, and the turbo-rocket.
PRINCIPLES OF JET PROPULSION
6. Jet propulsion is a practical application of Sir Isaac Newton's third law of motion which states that, 'for every force acting on a body there is an opposite and equal reaction'. For aircraft propulsion, the 'body' is atmospheric air that is caused to accelerate as it passes through the engine. The force required to give this acceleration has an equal effect in the opposite direction acting on the apparatus producing the acceleration. A jet engine produces thrust in a similar way to the engine/propeller combination. Both propel the aircraft by thrusting a large weight of air backwards (fig. 1-3), one in the form of a large air slipstream at comparatively low speed and the other in the form of a jet of gas at very high speed.
燃气室
涡轮
燃油
进气道
压气机
7.
This same principle of reaction occurs in all forms of movement and has been usefully applied in many ways. The earliest known example of jet reaction is that of Hero's engine (fig. 1-4) produced as a toy in 120 B.C. This toy showed how the momentum of steam issuing from a number of jets could impart an equal and opposite reaction to the jets themselves, thus causing the engine to revolve.
8.
The familiar whirling garden sprinkler (fig. 1-5) is a more practical example of this principle, for the mechanism rotates by virtue of the reaction to the water jets. The high pressure jets of modern fire-fighting equipment are an example of 'jet reaction', for often, due to the reaction of the water jet, the hose cannot be held or controlled by one fireman. Perhaps the simplest illustration of this principle is afforded by the carnival balloon which, when the air or gas is released, rushes rapidly away in the direction opposite to the jet.
9.
Jet reaction is definitely an internal phenomenon and does not, as is frequently assumed, result from the pressure of the jet on the atmosphere. In fact, the
9.喷气反作用绝对是一种内部现象。它不象人们经常想象的那样说成是由于喷气流作用在大气上的压力所造成的。实际上，喷气推进发动机，无论火箭、冲压喷气、或者涡轮喷气，都是设计成加速空气流或者然气流并将其高速排出的一种装置。当然，如第2章中描述的那样，这样做有不同的方式。
jet propulsion engine, whether rocket, athodyd, or turbo-jet, is a piece of apparatus designed to accelerate a stream of air or gas and to expel it at high velocity. There are, of course, a number of ways
Fig. 1-3 Propeller and jet propulsion.
换言之，给大量空气附加一个小速度或者给少量空气一个大速度能提供同样的推力。实用中，人们喜欢前者，因为降低相对于大气的喷气速度能得到更高的推进效率。
图1-3 螺旋桨和喷气推进
10.不同类型的喷气发动机，无论冲压喷气、脉冲喷气、燃气轮机、涡轮/冲压喷气或者涡轮-火箭，其差别仅在于“推力提供者”即发动机供应能量并将能量转换成发行动力的方式。
11.冲压喷气发动机（图1-6）按其全称是一种气动热力涵道。它没有任何主要形状零件，只包含一个扩张形进气涵道和一个收敛形或者收敛－扩散形出口。当由外部能源强迫其向前运动时，空气被迫进入进气道。当它流过这一扩散形涵道时，其速度或动能降低，而压力能增加。尔后，靠燃油的燃烧来增加其总能量，膨胀的燃气通过出口涵道加速并排入大气。冲压喷气发动机常作为导弹和靶机的动力装置，但不适于作为飞机动力装置，因为在它产生推力前，要求向它施加向前的运动。
Basic mechanics
12.脉冲喷气发动机（图1-7）采用间歇燃烧原理。与冲压喷气发动机不同，它能在静止状态工作。这种发动机是由类似冲压喷气发动机的一种空气动力涵道构成。但是，由于它的压力较高，其结构比较坚实。进气涵道有许多进气“活门”，在弹簧力作用处于打开位置。通过打开的活门吸入的空气进入燃烧室，并靠燃烧喷入燃烧室中去的燃油得到加热。由此引起的膨胀使压力升高，迫使活门关闭，然后膨胀的燃气向后喷出。排气造成降压，使活门开启。这种过程周而复始。脉冲喷气发动机已设计成直升机旋翼的推进装置，有的还通过精心设计涵道来控制共振循环的压力变化而省去了进气活门。脉冲喷气发动机不适于作为飞机动力装置，因为它的油耗高，又无法达到现代燃气涡轮发动机的性能。 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(3)
