Thrust is the force which moves any
aircraft through the air. Thrust is generated by the
propulsion system
of the aircraft. Different propulsion systems develop thrust in
different ways, but all thrust is generated through some
application of Newton's third law of
motion. For every action there is an equal and opposite reaction.
In any propulsion system, a working fluid is
accelerated by the system and
the reaction to this acceleration produces a force on the system. A
general derivation of the thrust equation
shows that the amount of thrust generated depends on the
mass flow
through the engine and the
exit velocity
of the gas.
During World War II, a new type of airplane engine was developed
independently in Germany and in England. This engine was called a
gas turbine engine. We sometimes call this engine a jet
engine. Early gas turbine engines worked much like a
rocket engine
creating a hot exhaust gas which was passed through a
nozzle
to produce thrust. But unlike the rocket engine which must carry its
oxygen for combustion, the turbine engine
gets its oxygen from the surrounding air. A turbine engine does not work
in outer space because there is no surrounding air. For a gas
turbine engine, the accelerated gas, or working fluid,
is the jet exhaust. Most of
the mass of the jet exhaust comes from the surrounding atmosphere.
Most modern, high speed
passenger and
military aircraft
are powered by gas
turbine engines. Because gas turbine engines are so important for modern
life, we will be providing a lot of information about turbine engines and
their operation.
Turbine engines come in a wide variety of
shapes and sizes because of the many different aircraft missions. All
gas turbine engines have some parts in
common, however. On the slide we see pictures of four different
aircraft equipped with gas turbine engines. Each aircraft has a
unique mission and therefore a unique propulsion requirement. At the
upper left is a DC-8 airliner. Its mission is to carry large loads
of passengers or cargo for a long distance at high speed. It spends
most of its life in high speed
cruise.
At the lower left is an F-14
fighter plane. Its mission is to shoot down other aircraft in
air-to-air combat. It spends most of its life in cruise, but needs
high acceleration
when in combat. At the lower right is a C-130 cargo
aircraft. Like the DC-8, it carries cargo a long distance, but it
does not have the high speed requirement of the DC-8. At the upper
right is a T-38 trainer. It is used to teach pilots how to fly jet
aircraft and does not have the acceleration requirements of the F-14.
The DC-8 is powered by four high-bypass turbofan
engines, the F-14 by two afterburning
low-bypass turbofans, the C-130 by four turboprop
engines, and the T-38 by two turbojet
engines.
EngineSim
is an interactive Java applet which allows you to study different
types of jet engines. You can learn the fundamentals of turbine engine
propulsion with the EngineSim simulator.
RangeGames
is an interactive Java applet which allows you to study how different
types of aircraft use different types of engines to meet their mission.
Activities:
Guided Tours
-
Parts of an Airplane:
-
Propulsion Systems:
-
Jet Engines:
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