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Specs
First test flight:
1948
Engine weight: 1,100
kg (2,500 pounds)
Thrust: 22,000 newtons
(5,000 pounds of force)
Maximum altitude: 15
km (50,000 feet)
History
The J47 engine was first conceived in March 1946. Since
that time many variations of the J47, including many technical
innovations, have been designed and produced. In all,
GE built over 30,000 J47 engines. It has applications
in many types of aircraft, including bombers, reconnaissance,
interceptors, and fighter planes.
The
J-47 turbojet displayed at the Science Center has an afterburner
to increase engine power at takeoff and during altitude
acceleration. It also has an anti-icing feature, a more
efficient compressor for increased airflow, and a high-altitude
starting system.
Jet
Engine Function
The
main purpose of a jet engine is to shoot air quickly out
through the back of the engine, which pushes the plane
forward. Just like air rushing out of a balloon makes
the balloon fly around, hot gas shooting out the back
of an engine thrusts the plane ahead. Jet engines work
like piston engines in that they have four steps - intake,
compression, combustion and exhaust. The four steps take
place in one continuous flow rather than in back and forth
actions. Air is sucked in at the intake and is compressed
by a compressor turbine or fan. This dense air is then
mixed with fuel, which is burned, causing the gases to
expand very quickly. The hot burning mixture increases
speed rapidly and flows past a series of turbines, causing
them to rotate at high speed. The turbines are mounted
on the same shaft as the compressor, which provides its
rotation. Then the exhaust gases are emitted past a cone,
where Newton's
Third Law of Motion takes over. On the diagram below,
you can see the four steps air goes through as it passes
through the jet engine. Definitions for each of the steps
are included below the diagram.
| Intake |
sucks
air into the engine. |
| Compression |
squeezes
the air. Row after row of spinning blades force air
through and compress it, raising the air pressure.
The wing-shaped blades get closer and closer together
deeper into the engine. |
| Combustion |
heats
up the air. In the combustion chamber, pressurized
air mixes with jet fuel. A flame heats the mix, and
it expands very quickly. |
| Exhaust |
shoots
the heated air out the back of the engine. Fast-expanding
hot gases from the combustion chamber shoot out the
exhaust nozzle. Pushing the fast-expanding hot gases
from the combustion chamber out the back moves the
engine forward. |
Jet
engines provide great power with light weight, simplicity
and reliability. However, they are expensive to build
and use a lot more fuel than piston engines of similar
power. They are more efficient than piston engines at
high altitudes, where airplanes can fly faster in the
thinner air. They may provide thrust in one of several
ways: from their exhaust (pure jet), by driving a fan
(fan jet), or a propeller (prop jet). To learn more about
jet engines, check out the links below.
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