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Ice protection
150
Fig. 13-4 Electrical ice protection.
forming, but the intermittently heated areas allow ice
to form, during their ’heat-off period. During the ’heaton’
period, adhesion of the ice is broken and it is then
removed by aerodynamic forces.
13. The cycling time of the intermittently heated
elements is arranged to ensure that the engine can
accept the amount of ice that collects during the
’heat-off’ period and yet ensure that the ’heat-on1
period is long enough to give adequate shedding,
without causing any run-back icing to occur behind
the heated areas.
14. A two-speed cycling system is often used to
accommodate the propeller and spinner requirements;
a ’fast’ cycle at the high air temperatures
when the water concentration is usually greater and
a ’slow’ cycle in the lower temperature range. A
typical cycling sequence chart is shown in fig, 13-5.
Ice protection
151
Fig. 13-5 Typical ice protection cyclic sequence.
Rolls-Royce RB211-524D4D
Bristol Proteus
Work began in September 1944 on the 4000
e.h.p. Proteus turbo-prop originally intended
to power the Bristol Brabazon 2 and
Saunders-Poe Princess. The Proteus first ran
in January 1947 and was later used to power
the Bristol Britannia at 4445 e.h.p. A
development of this engine, the Marine
Proteus, is used to power various patrol boats,
hovercraft and hydrofoils.
14: Fire protection
Contents Page
Introduction 153
Prevention of engine fire
ignition 153
External cooling and ventilation
Fire detection 154
Fire containment 156
Fire extinguishing 157
Engine overheat detection 157
INTRODUCTION
1. All gas turbine engines and their associated
installation systems incorporate features that
minimize the possibility of an engine fire. It is
essential, however, that if a failure does take place
and results in a fire, there is provision for the
immediate detection and rapid extinction of the fire,
and for the prevention of it spreading. The detection
and extinguishing systems must add as little weight
to the installation as possible.
PREVENTION OF ENGINE FIRE IGNITION
2. An engine/powerplant is designed to ensure that
the prevention of engine fire ignition is achieved as
far as possible. In most instances a dual failure is
necessary before a fire can occur.
3. Most of the potential sources of flammable fluids
are isolated from the ’hot end’ of the engine. External
fuel and oil system components and their associated
pipes are usually located around the compressor
casings, in a ’cool’ zone, and are separated by a
fireproof bulkhead from the combustion, turbine and
jet pipe area, or ’hot’ zone. The zones may be
ventilated, as described in para 8, to prevent the
accumulation of flammable vapours.
4. All pipes that carry fuel, oil or hydraulic fluid, are
made fire resistant/proof to comply with fire
regulations, and all electrical components and
connections are made explosion-proof. Sparking
caused by discharge of static electricity is prevented
by bonding all aircraft and engine components. This
gives electrical continuity between all the
components and makes them incapable of igniting
flammable vapour.
5. On some engines, tubes carrying flammable
fluids in ’hot areas’ of the engine are constructed with
a double skin. Should a fracture of the main fluid
carrying tube occur the outer skin will contain any
leakage, so preventing any possible fire ignition.
6. The power plant cowlings are provided with an
adequate drainage system to remove flammable
fluids from the nacelle, bay, or pod, and all seal
leakages from components are drained overboard at
a position such that fluid cannot re-enter the pod and
create a fire hazard.
7. Spontaneous ignition can be minimized on
aircraft flying at high Mach numbers by ducting
boundary layer bleed air around the engine.
153
However, if ignition should occur, this high velocity air
stream may have to be shut off, otherwise it would
increase the flame intensity and reduce the effectiveness
of the extinguishing system by rapid dispersal
of the extinguishant.
External cooling and ventilation
8. The engine bay or pod is usually cooled and
ventilated by atmospheric air being passed around
the engine and then vented overboard (fig. 14-1).
Convection cooling during ground running may be
provided by using an internal cooling outlet vent as
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