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These may be made so sensitive that they respond
only to the ultra-violet and infra-red rays emitted from
a kerosine fire.
FIRE CONTAINMENT
19. An engine fire must be contained within the
power plant and not be allowed to spread to other
parts of the aircraft. The cowlings that surround the
engine are usually made of aluminium alloys, which
would be unable to contain a fire when the aircraft is
static. During flight, however, the airflow around the
cowlings provides sufficient cooling to render them
fireproof. Fireproof bulkheads and any cowlings that
are not affected by a cooling airflow, and sections of
cowlings around certain outlets that may act as
’flame-holders’, are usually manufactured from steel
or titanium.
Fire protection
156
Fig. 14-3 A continuous element fire detecting system.
FIRE EXTINGUISHING
20. Before a fire extinguishing system is operated,
the engine must be stopped to reduce the discharge
of flammable fluids and air into the fire area. Any
valves, such as the low pressure fuel cock, that
control the flow of flammable fluid must be situated
outside the ’hot’ zone to prevent fire damage
rendering them inoperative.
21. After a fire has been extinguished, no attempt
must be made to start the engine again as this would
probably re-establish the fluid leak and the ignition
source that were the original causes of the fire.
Furthermore, the extinguishing system may be
exhausted.
22. The extinguishant that is used for engine fires is
usually one of the Freon compounds. Pressurized
containers are provided for the extinguishant and
these are located outside the fire risk zone. When the
relevant electrical circuit is manually operated, the
extinguishant is discharged from the containers
through a series of perforated spray pipes or nozzles
into the fire (fig. 14-4). The discharge must be
sufficient to give a predetermined concentration of
extinguishant for a period that may vary between 0.5
seconds and 2 seconds. The system is generally one
that enables two separate discharges to be made.
ENGINE OVERHEAT DETECTION
23. Turbine overheat does not constitute a serious
fire risk. Detection of an overheat condition, however,
is essential to enable the pilot to stop the engine
before mechanical or material damage results.
24. A warning system of a similar type to the fire
detection system, or thermocouples suitably
positioned in the cooling airflow, may be used to
detect excessive temperatures. Thermal switches
positioned in the engine overboard air vents, such as
the cooling air outlets, may also be included to give
an additional warning.
Fire protection
157
Fig. 14-4 A typical fire extinguishing system.
Rolls - Royce Gem 2
Armstrong Siddeley Python
The Python was developed from the ASX
axial-flow turbo-jet which first ran in April 1943
and was producing 2800 lb thrust by 1944.
With the addition of a propeller gearbox the
engine produced 3600 shp plus 1100 lb thrust
and was known as the ASP. Renamed the
Python it entered service as the power plant
for the Westland Wyvern S4 turbo-prop
fighter.
15: Thrust reversal
Contents Page
Introduction 159
Principles of operation 160
Clamshell door system
Bucket target system
Cold stream reverser system
Turbo-propeller reverse pitch system
Construction and materials 166
INTRODUCTION
1. Modern aircraft brakes are very efficient but on
wet, icy or snow covered runways this efficiency may
be reduced by the loss of adhesion between the
aircraft tyre and the runway thus creating a need for
an additional method of bringing the aircraft to rest
within the required distance.
2. A simple and effective way to reduce the aircraft
landing run on both dry and slippery runways is to
reverse the direction of the exhaust gas stream, thus
using engine power as a deceleration force. Thrust
reversal has been used to reduce airspeed in flight
but it is not commonly used on modern aircraft. The
difference in landing distances between an aircraft
without reverse thrust and one using reverse thrust is
illustrated in fig. 15-1.
3. On high by-pass ratio (fan) engines, reverse
thrust action is achieved by reversing the fan (cold
stream) airflow. It is not necessary to reverse the
exhaust gas flow (hot stream) as the majority of the
engine thrust is derived from the fan.
159
4. On propeller-powered aircraft, reverse thrust
action is obtained by changing the pitch of the
propeller blades. This is usually achieved by a hydromechanical
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