That which separates an airplane from a glider is the presence of some sort of
engine or motor. Before the invention of powered flight by the Wright brothers,
gliders and balloons were the only way to fly. The Wright brothers took the
idea of a glider and added an engine to it. They riggd the engine up to turn a
propeller and the prop. pulled the airplane into the air. From that time on,
until the advent of W.W.II, the propeller was the only way known of providing
thrust for an airplane. When W.W.II broke out, both sides rushed to design the
best aircraft possible. During the developement process of designing faster
fighter aircraft, German engineers developed a new type of engine capable of
propelling an airplane at immense speeds and has since become the only known
for getting an airplane up to, and beyond, the speed of sound. There are a
number of different types of jet engine, these are:
Ramjet: Ramjets work by having air pushed in to a chamber where it is compressed.
In this chamber the air, which was heated by compression, is mixed with fuel.
The fuel is ignited by the heated air and creates hot expanded gas is forced out of
the exhaust. The ramjet cannot start by itself its needs to gain speed to compress
the air, so it must be started out. The ramjet is generally not used in planes
because it runs at a high steady speed. Although the it is used in such things as
Turbojet: In a turbojet the air is sucked into the intake and
pushed into the compression chamber by a series of compression fans. It is then mixed
with fuel that is added through fuel injectors. Then the high temperature of the hot
air ignites the fuel which creates hot gas which rapidly expands and pushes towards
the exhaust. This gas is pushed past a turbine, the turbine is what turns the
compression fans. After that the remaining gas is forced out of the exhaust and
creates the thrust of the jet. A jet can create anywhere from 2,500 to 30,000 pounds
Pulse Jet:The pules jet was one of the earliest forms of jet propulsion. It was used by
the Germans during W.W.II in their V-1 rockets. The theory it works on is
very simple. It has inlet valves that let in air. These valves are spring
loaded in the open position. The valves let in air that is heated by burning
fuel. These burning gases expand and force the inlet valve closed and the
gases are then pushed out the outlet duct to produce thrust. In the absence
of burning gas the inlet valves open and let in more air and the cycle
repeats. This charge then fire procedure give it a pulse of thrust and then a
short stop thus its name the pulse jet.
Turbofan:Another commonly used kind of jet propulsion is the turbofan. This kind of
jet is used on most large jet liners such as the 747, 727, 767, and 737. This
engine is basically the same as the turbo jet except the central fan axle is
also connected to a large fan in front of the engine. This fan pushes air
into the jet but it also pushes air around the jet creating more thrust.
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