How the Jet Engine Was Developed

from an object acts to impart motion to that ob-

ject. The ejected matter, usually a liquid or a gas

discharged from the object through a jet or nozzle,

derives its energy from some kind of burning. The

discharge of matter to gain a force is an applica-

tion of the basic laws of motion, the explanation

and application of which will be covered later in

this text. In this section we are concerned more

with the development of reaction-propulsion mech-

anisms that contributed to the invention of the

present-day jet engine. The discovery of jet pro-

pulsion is not a recent one; but, as we will see in

this chapter, its development and application have

been slow.

1.

History of Jet Propulsion

The true discoverer of jet propulsion is un-

known, but the credit is generally given to an

Alexandrian scientist (perhaps Greek) named

Hero, who lived some time between the second

century B. C. and the third century A. D. His

contribution was in the form of a whirligig oper-

ated by steam (see fig. 1). This invention, a

crude boiler and ball device, was the first steam-

powered mechanism to operate on the principle of

jet propulsion. Steam from the boiler entered the

ball through its mounting crossbar and escaped

through a series of tubes located around the cir-

cumference of the ball. The ball, free to move on

its axis, was turned by the action of the escaping

steam. Hero may have gotten the idea of jet pro-

pulsion by noting that some aquatic forms obtain

motion by taking in water and ejecting it under

pressure.

The idea of jet propulsion was further advanced

by the discovery of gunpowder, the credit for

which was given to the Chinese. This discovery

opened a new field of experimentation which led

to the development of harmless devices like fire-

works, rockets, pinwheels, Roman candles, etc.

Of much more serious import to mankind was the

development of weapons.

Several centuries ago the English were defeated

in battle by enemy troops using rockets. The

English, quick to learn, soon developed their own

rockets and used them successfully. In our na-

tional anthem, Francis Scott Key’s phrase, “the

 

p2

Figure 1. Hero’s application of jet propulsion.