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Fire
Protection
With
the engines installed, the nacelle is divided into two
compartments on each side, and a third compartment rousing
the accessory gearbox. This split-up is achieved by means
of special, firewalls and bulkheads as
shown in figure 8. Each nacelle has a vertical firewall
forming a centre keel and isolating the two engines from
each other.
The
engine has an integral intermediate firewall permanently
attached and sited around the combustion chambers. This
mates up with a permanent portion of firewall on the
nacelle foming a complete firewall between the hot and
cool portions of the engine.
The
front portion, or zone 1, which also forms the plenum
chamber contains the engine accessories and oil tank
etc., while the rear portion or zone 2, contains all
the hot portions of the engine, combustion chambers,
turbine casing, and jet pipe. The intermediate firewall
is to prevent the high pressure fuel from a burst pipe
or joint being sprayed on to the hot side.
The
rear portion of zone 2, extends in the shape of a tunnel
back to the jet nozzle and is completely lined with stainless
steel firewalling and sealed against ingress of fuel
or oil.
Fire
from a burst combustion chamber or perforated jet pipe
would be confined within this zone out of reach of electrical
and fuel lines or the aircraft structure.
The
above system of firewalling also isolates all engine
parts from the accessories and gearbox, which are in
the space above the conical firewalls, shown on figure
8, as zone 3.
Edison
resetting type fire-detectors are used and a methylbromide
system of extinguishing is used for zones 1 and 2, while
a C02 system is provided for the gearbox compartment,
zone 3. A two-shot system is used and the warning lights,
buttons, and selector switches are mounted on the ceiling
fire-protection panel in the cockpit.
Thrust
Augmentation
The
thrust from a jet engine varies considerably with temperature
and airport altitude, and on a hot day  with
a temparature of 110 deg F, the reduction in jet thrust
can be as much as 16%. As this can be critical for take-off
conditions, where a possible engine failure has to be
taken into account, some means of thrust augmentation
has to be used.
Various
means of achieving the extra thrust were investigated,
and it was finally decided that injection of a water-methanol
mixture into the compressor inlet offered the best solution.
The predominant effect of this is to increase the mass
flow of air to the engine by increasing the air density
at the compressor inlet.
The
injection system itself is relatively simple, and has
few of the disadvantages of other forms of augmentation
such as, after-burning where the long sheets of flame
coming out of the tailcone are likely to cause alarm
to the passengers. The percentage increase in thrust
with rate of injection is shown in figure 12.
It
can be seen from the graph, that under tropical conditions,
to provide the static thrust which would be obtained
for take-off under standard I. C. A. N. conditions, it
is necessary to inject the mixture at a rate of 10 gals.
per minute.
A
tank is housed in each nacelle holding 66 gals. of water-methanol,
which is sufficient to supply each engine vdth the required
quantity for a period of three minutes.
Figure
13 shows the take-off distance for various gross weights
and temperatures.
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AVRO
C102 Jetliner
