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should it decide not to work. This
can be operated manually, or by an
air bottle.
Otherwise, landing gear is made up
of struts, that are attached to the
fuselage, and which have the wheels
attached to them (in tailwheel
aircraft, struts are fitted slightly
ahead of the C of G – otherwise,
they will be slightly behind). For
shock absorption, an oleo strut
contains a piston and a cylinder,
moving together inside hydraulic
fluid. There are holes in the piston to
allow the fluid through and damp
down the shocks. There may be
nitrogen or dry air instead of fluid.
Another function of a strut is to
force the tyre on to the ground.
With wheels, there will be brakes,
used for stopping, and sometimes
steering (not recommended in a
multi-engined aeroplane – use
differential engine power instead).
There will be a master cylinder for
each brake pedal, a reservoir, the
brakes themselves and connecting
pipes. The toe pedal activates the
master cylinder directly. A piston
inside forces fluid along the lines to
activate the brakes on the wheels.
Transmissions
This is how you get the power from
the engines to the propellers or rotor
blades. Because some engines work
at higher speeds than other
components, there will also be an
element of reduction involved.
Transmission systems will also have
their own, self-contained oil supply.
In a helicopter, a clutch may be fitted
between the engine and main rotor
gearbox. A centrifugal clutch (as found
on the Bell 47) is automatic and will
have more effect as speed is
increased so, if the engine stops, the
blades are free to rotate. A friction
or belt drive clutch (like in the
Engines & Systems 61
Enstrom) is manually operated by
the pilot, which allows the engine to
be warmed up without the blades
rotating (safer for passengers, too).
Some turbine helicopters have
clutches, too, like the Gazelle.
Others have a freewheel unit to let the
blades spin without engine power.
The engine RPM and rotor RPM
gauges are normally combined, with
the needles superimposed on each
other:
They are split in the above diagram.
Pneumatics
Compressed air is used for many
purposes, such as operating the
landing gear, doors, flaps, etc.
Nitrogen will sometimes be used for
backup pneumatics for landing gear.
Flight instruments are also operated
by air, and for deicing boots.
Heating Systems
The simplest system uses a muff
round the exhaust that makes air
flowing through it warmer, on its
way to the cabin. As a result, there is
a danger of carbon monoxide
poisoning if the exhaust is faulty.
Slightly more complicated is what
can best be described as a flame in a
tube, under some control, of course.
These need a rundown period which
should be observed, otherwise
carbon will form on the igniter and
stop it from reigniting.
A turbine powered machine can use
bleed air from the engine, which can
be mixed with outside air to regulate
the temperature.
Fire Detection
Fire has three elements—fuel,
oxygen and the heat. Take one away
and it stops. With dangerous goods,
you can get fire from the reaction of
flammable materials with an
oxidising agent – you don’t
necessarily need a source of ignition.
A Class A fire is an ordinary one,
that is, of normal combustible
material on which water is most
effective. A Class B fire is in a
flammable liquid, such as oil or
grease, where you would probably
use a blanket. A Class C fire is
electrical, for which you need a nonconducting
extinguisher. For the
latter two, you could use either CO2
or Dry Powder (which ruins the
avionics), but the fumes may be
toxic, so you will need plenty of
ventilation afterwards. You can use
Halon on anything, if you're allowed
to use it. A Class D covers other
materials, like metals, that may burn
if persuaded.
To help you identify the source,
smoke associated with electrical fires
is usually grey or tan and very
irritating to the nose or eyes (it
doesn't smell too good, either).
Anything else (say from the heater)
tends to be white, but you may get
some black from upholstery.
If you think you have an electrical
fire, it's no good just using the
extinguisher, because you may be
62 JAR Private Pilot Studies
treating the symptom and not the
cause, although there is a school of
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