of doing this, as described in Part 2, but in all instances the resultant reaction or thrust exerted on the engine is proportional to the mass or weight of air expelled by the engine and to the velocity change imparted to it. In other words, the same thrust can be provided either by giving a large mass of air a little extra velocity or a small mass of air a large extra
图1-5 依靠喷水嘴的反作用力旋转的花园洒水器
velocity. In practice the former is preferred, since by lowering the jet velocity relative to the atmosphere a 喷气推进方式
higher propulsive efficiency is obtained.
METHODS OF JET PROPULSION
10.
The types of jet engine, whether ram jet, pulse jet, rocket, gas turbine, turbo/ram jet or turbo-rocket, differ only in the way in which the 'thrust provider', or engine, supplies and converts the energy into power for flight.
11.
The ram jet engine (fig. 1-6) is an athodyd, or 'aero-thermodynamic-duct to give it its full name. It has no major rotating parts and consists of a duct with a divergent entry and a convergent or
燃油喷嘴 燃烧室
图1-6 冲压式喷气发动机
Fig. 1-6 A ram Jet engine.
convergent-divergent exit. When forward motion is imparted to it from an external source, air is forced into the air intake where it loses velocity or kinetic energy and increases its pressure energy as it passes through the diverging duct. The total energy is then increased by the combustion of fuel, and the expanding gases accelerate to atmosphere through the outlet duct. A ram jet is often the power plant for missiles and .target vehicles; but is unsuitable as an aircraft power plant "because it requires forward motion imparting to it before any thrust is produced.
12. The pulse jet engine (fig. 1-7) uses the principle of intermittent combustion and unlike the ram jet it can be run at a static condition. The engine is formed by an aerodynamic duct similar to the ram jet but, due to the higher pressures involved, it is of more robust construction. The duct inlet has a series of inlet 'valves' that are spring-loaded into the open position. Air drawn through the open valves passes into the combustion chamber and is heated by the burning of fuel injected into the chamber. The resulting expansion causes a rise in pressure, forcing
13.虽然火箭发动机（图1-8）也是喷气发动机，但它们有最大区别。即，火箭发动机不用大气作为推进流体，而用它携带的液态燃料或化学分解而成的燃料与氧气剂的燃烧来产生它自己的推进流体，从而能在地球大气层外工作。因此，它只适用于工作时间很短的情况。
Basic mechanics
充气 (节气活门打开）
15. The mechanical arrangement of the gas turbine engine is simple, for it consists of only two main rotating parts, a compressor (Part 3) and a turbine (Part 5), and one or a number of combustion chambers (Part 4). The mechanical arrangement of various gas turbine engines is shown in fig. 1 -9. This simplicity, however, does not apply to all aspects of the engine, for as described in subsequent Parts the thermo and aerodynamic problems are somewhat complex. They result from the high operating tem-peratures of the combustion chamber and turbine, the effects of varying flows across the compressor 点火 (节气活门关闭)
节气活门
燃烧室
供油
进气道
喷管和推进喷口
the valves to close, and the expanding gases are
then ejected rearwards. A depression created by the
exhausting gases allows the valves to open and
repeat the cycle. Pulse jets have been designed for
helicopter rotor propulsion and some dispense with
inlet valves by careful design of the ducting to control
the changing pressures of the resonating cycle. The
pulse jet is unsuitable as an aircraft power plant
because it has a high fuel consumption and is unable
to equal the performance of the modern gas turbine
engine.
15．燃气涡轮发动机的机械布局很简单，因为它只包含两个主要旋转部分，即压气机(第3章)和涡轮(第5章)。及一个或者若干个燃烧室(第4章)。各种燃气涡轮发动机的机械布局示于图1-9。然而，并非这种发动机的所有方面都具有这种简单性，因
为正象以后几章叙述的那样，热力和气动力问题是比较复杂的。这些问题是由燃烧室和涡轮的高工作温度、通过压气机和涡轮叶片而不断变化着的气流的影响，以及排出燃气并形成推进喷气流的排气系
统的设计工作造成的。
13.
Although a rocket engine (fig. 1-8) is a jet
engine, it has one major difference in that it does not
use atmospheric air as the propulsive fluid stream.
Instead, it produces its own propelling fluid by the
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