2. In addition to the basic airframe and rotating components,
must be incorporated into the airframe.
These may be necessary for the operation of the helicopter,
or may be special requirements for the type of work that is
being done with the helicopter.
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3. 3
Fuel system
Electrical system,
Ventilating system
Possibly heating and air
conditioning
4. The fuel system is usually made up of one or more tanks.
Fuel systems are normally force feed because there would be few places that the fuel could be
located for a gravity feed system.
The Bell4 7, however, is the exception to the rule because it does use a gravity system to deliver
fuel to the engine.
The Bell 206 would be more typical of a fuel system found in a light turbine helicopter.
This fuel system incorporates a single bladder type fuel cell, located below and aft of the rear
passenger seat.
Installed in the fuel cell are two boost pumps, an upper and lower indicating unit, and a solenoid
operated sump drain.
The two boost pumps are interconnected to supply fuel through a common line.
These pumps are typical submersible centrifugal pumps.
Both of these pumps are identical and are provided with screens over the inlets.
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5. The outlet ports join to form a single line to the engine.
Before these lines join, a check valve is located in each line, so one pump does not cycle fuel
through the other, in case of pump failure.
Either pump can supply sufficient fuel. A pump failure would immediately be indicated because a
pressure switch is located in the outlet port of each pump.
A shutoff valve is incorporated into the single line.
This is an electrically operated valve.
The fuel then passes through a fuel filter unit.
This is equipped with a bypass caution light which operates on the differential of pressure.
The fuel then proceeds to the engine filter unit before entering the engine (Fig. 10-21).
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6. BOOST PUMP -PRESSURE ENGINE Fig. 10-21 Schematic of the Be/1206 fuel system.
Additional provisions are made in the system for a fuel pressure gauge, vent system, and fuel
quantity indicator.
This is all quite similar to what might be found in any fixed-wing aircraft.
A fuel selector is not necessary because only one tank is involved.
Where more than one tank is employed, this selector system would also be found.
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7. The electrical systems are also quite similar to what might be found in a fixed-wing aircraft or
light turbine powered aircraft.
However, the turbine powered helicopters will utilize starter-generators and quite often two
batteries rather than one for assuring good starts.
Nickel-cadmium batteries are used almost exclusively.
This is because electrical assist from ground power units are almost never available for starts.
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8. In recent years, a few helicopters have started to use "environmental control units'' (ECU).
These are air cycle machines which furnish either hot or cool air.
Fig. 10-22 shows a typical combustion heater and ventilating system.
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