 Another
well-known propulsion
system is the jet engine
or gas turbine. There
are several types of gas
turbine engines, but the
simplest ones are the
so-called turbojets.
These engines are
shaped like a cylinder
containing several parts
inside, which rotates on
a central shaft. An
auxiliary electric motor
is needed to start the
turbine engines.
The
outside air enters the
engine through the inlet
into the compressor,
which consists of one
set of fixed blades
(stator) and another of
rotating blades (rotor).
The air is then
compressed at the
compressor section and
enters thereafter the
burner where the
fuel/air mixture is
ignited. This creates a
hot gas passing through
the turbine and out the
nozzle, which is shaped
to accelerate the hot
exhaust. The turbine
uses the energy from the
hot exhaust to rotate
and since the turbine is
linked to the compressor
by the central shaft, it
will also keep the
compressor rotating,
thus no longer needing
the electric motor.
 Normally
the model aircraft
turbines use
propane/butane gas along
with a glow plug to
start the ignition and
rise the burner's
temperature above 100oC
before liquid fuel is
injected through small
holes into the burner.
Once the combustion gets
started, the glow plug
is no longer needed.
The combustion
process may be
controlled or stopped by
regulating the amount of
the fuel available, the
amount of oxygen
available or the source
of heat.
Unlike the
conventional
combustion/piston
engines, the jet engines
don't have a natural
limitation of the rpm.
This means that the rpm
will keep rising as more
fuel is fed to the
engine until the
materials no longer
withstand the high
temperature and/or the
high rpm and will
breakdown. Therefore, an
Electronic Control Unit
(ECU) is required to
limit the max fuel flow.
The max value is set by
using an external device
called Ground Support
Unit (GSU).
 Since model aircraft
powered by gas turbines
flies very fast, with
speeds up to 500Km/h
(312mph), these type of
engines are definitely
not recommended for the
beginners. Besides,
operating gas turbines
also involves some
risks. So, it's highly
recommended to read the
BMFA operational
guide before using these
engines.
For further info
about the function of
other turbine engine
types such as Turbofan,
Turboprop and Ramjet,
check
here. |
