Game Development Reference
In-Depth Information
Jet Engines
The second main type of airplane engine we will see in this chapter is the jet engine. This type
of engine uses a series of spinning blades known as a turbine to generate thrust. A turbine can
be thought of as a propeller with many blades. People have been playing around with turbines
and turbine engines for a long time. The ancient Egyptians made toys that rotated on top of
boiling pots of water. Leonardo Da Vinci invented a type of automated barbecue that was based
on hot gases from a fire passing through a turbine that turned a roasting spit.
Research on the development of a gas turbine for airplane propulsion was carried on inde-
pendently in England and Germany in the 1930s. The first successful jet engine, built in England
in 1937, generated 445
N
of thrust. The first jet-powered plane, the Heinkel HE-178, flew in 1939.
After World War II, military and commercial airplanes increasingly used jet engines because of
the superior power and performance that they offered.
The cross section of a typical jet engine is shown in Figure 10-17. Air enters the engine at
the inlet. A compressor compresses the air and forces it into the combustor. Fuel is mixed with
the compressed air and ignited, resulting in a high-temperature, high-pressure gas mixture.
The gas passes through a turbine, causing the turbine blades to rotate. The turbine rotation is
used to drive the compressor. The gas mixture then expands through a nozzle at the rear of the
engine, generating thrust that moves the engine (and the airplane attached to it) forward.
Compressor
Turbine
Inlet
Nozzle
Combustor
Figure 10-17.
A jet engine schematic
There are different types of jet engines. The one described in the previous paragraph is
called a
turbojet
engine. A
turboprop
engine is a jet engine that drives an external propeller.
Turboprop engines are somewhat of a bridge between propeller and turbojet engines. They
allow higher speeds than a propeller engine and offer greater efficiency than a turbojet engine
at speeds below 225
m/s
(500
mph
). A
turboshaft
engine is similar to a turboprop and is used to
turn the shaft of a helicopter rotor. A
turbofan
engine includes a fan at the front of the engine
that is used to increase engine thrust. Most airliners today use turbofan engines.
The thrust generated by a jet engine is equal to the change of momentum of the gas traveling
through the engine plus the pressure difference between the inlet and nozzle.
(
)
Fmvmv ppA
=
−
+
−
(10.19)
T
e
e
00
e
0
e
