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# The types of aircraft engines

## 2.

Thrust is the pulling or pushing force developed by an
aircraft engine. Aircraft need thrust to propel them
through air. The required thrust may be developed
by rotating pulling or pushing propellers by means
of piston or reciprocating engines, or by throwing
back masses of air by means of gas turbine
engines.

## 3. The piston engine

A simple piston engine works on a four-stroke cycle,
consisting of induction, compression, combustion and
exhaust.

## 4. The ramjet

But air flows straight through a jet engine. Yet a jet engine has the same four stages. The
simplest of all jet engines is a ramjet. It is a tapered tube, open at both ends, into which
fuel can be injected. When the tube moves, air flows into the tube, and this corresponds
to the induction stage in the piston engine. Once inside the tube, the air slows down
because the tube widens. The kinetic energy released by this loss of velocity is converted
into pressure energy and heat, and this corresponds to the compression stage in the
piston engine. Then fuel is injected and ignited. As in a piston engine, this causes a big
rise in temperature, but there is very little rise in pressure because the exhaust gas is free
to escape through the rear of the lube. This corresponds to the combustion stage in the
piston engine. Finally the exhaust gases escape into the atmosphere, driving the engine
forwards, which corresponds to the exhaust stage of the piston engine.

## 5. The gas turbine engine

The gas turbine engine draws air from the atmosphere and, after compressing and heating, it
uses some of its energy to drive the turbine that powers the compressor. The application of
the gas turbine to jet propulsion has avoided the inherent weakness of the rocket and the
athodyd, for by introduction of a turbine-driven compressor an efficient means of producing
thrust at low speeds is provided. The mechanical arrangement of the gas turbine engine is
simple. It consists of two main rotating parts, a compressor and a turbine, and one or a
number of combustion chambers.

## 6. The turbojet engine

The turbojet engine is most suitable for high
forward speeds. At aircraft speeds below 450 miles
per hour the jet engine is less efficient than a
propeller-type engine.

## 7. The turboprop engine

The advantages of the turboprop engine have to some extent been
offset by the introduction of the bypass and ducted fan engines.
These engines deal with larger comparative airflows and lower jet
velocities than pure jet engines, thus giving a propulsive efficiency
which is comparable to that of the turboprop and exceeds that of the
pure jet engine.