Page 153 - Aeronautical Engineer Data Book

126 Aeronautical Engineer’s Data Book
power turbine. Drive is taken off the power
turbine shaft, through a gearbox, to drive the
main and tail rotor blades. Figure 8.3 shows the
principle.

8.2.6 Ramjet
This is the crudest form of jet engine. Instead
of using a compressor it uses ‘ram effect’
obtained from its forward velocity to accelerate
and pressurize the air before combustion.
Hence, the ramjet must be accelerated to speed
by another form of engine before it will start to
work. Ramjet-propelled missiles, for example,
are released from moving aircraft or acceler­
ated to speed by booster rockets. A supersonic
version is the scramjet which operates on liquid
hydrogen fuel.

8.2.7 PULSEJET
A pulsejet is a ramjet with an air inlet which is
provided with a set of shutters fixed to remain
in the closed position. After the pulsejet engine
is launched, ram air pressure forces the shutters
to open, and fuel is injected into the combus­
tion chamber and burned. As soon as the
pressure in the combustion chamber equals the
ram air pressure, the shutters close. The gases
produced by combustion are forced out of the
jet nozzle by the pressure that has built up
within the combustion chamber. When the
pressure in the combustion chamber falls off,
the shutters open again, admitting more air,
and the cycle repeats.

8.3 Engine data lists
Table 8.2 shows indicative design data for
commercially available aero engines from
various manufacturers.

8.4 Aero engine terminology
See Table 8.3.