Aircraft Systems

senses ventilation air temperature) turns on the fuel solenoid • Battery allowing fuel to spray into the burner chamber. Fuel mixes • Master/battery switch with air inside the chamber and is ignited by the spark plug, • Alternator/generator switch producing heat. • Bus bar, fuses, and circuit breakers The by-product, carbon monoxide, leaves the aircraft through • Voltage regulator the heater exhaust pipe. Air flowing over the outside of the burner chamber and inside the jacket of the heater absorbs • Ammeter/loadmeter the heat and carries it through ducts into the cabin. As the • Associated electrical wiring thermostat reaches its preset temperature, it turns off the fuel solenoid and stops the flow of fuel into the burner chamber. Engine-driven alternators or generators supply electric When ventilation air cools to the point that the thermostat current to the electrical system. They also maintain a again turns the fuel solenoid on, the burner starts again. sufficient electrical charge in the battery. Electrical energy stored in a battery provides a source of electrical power for This method of heat is very safe as an overheat switch is starting the engine and a limited supply of electrical power provided on all combustion heaters, which is wired into for use in the event the alternator or generator fails. the heater’s electrical system to shut off the fuel in the case of malfunction. In the unlikely event that the heater fuel Most DC generators do not produce a sufficient amount of solenoid, located at the heater, remains open or the control electrical current at low engine rpm to operate the entire switches fail, the remote fuel solenoid and/or fuel pump is electrical system. During operations at low engine rpm, the shut off by the mechanical overheat switch, stopping all fuel electrical needs must be drawn from the battery, which can flow to the system. quickly be depleted. As opposed to the fuel fired cabin heaters that are used Alternators have several advantages over generators. on most single-engine aircraft, it is unlikely for carbon Alternators produce sufficient current to operate the entire monoxide poisoning to occur in combustion heaters. electrical system, even at slower engine speeds, by producing Combustion heaters have low pressure in the combustion alternating current (AC), which is converted to DC. The tube that is vented through its exhaust into the air stream. The electrical output of an alternator is more constant throughout ventilation air on the outside of the combustion chamber is a wide range of engine speeds. of higher pressure than on the inside, and ram air increases the pressure on the outside of the combustion tube. In the Some aircraft have receptacles to which an external ground event a leak would develop in the combustion chamber, the power unit (GPU) may be connected to provide electrical higher-pressure air outside the chamber would travel into the energy for starting. These are very useful, especially chamber and out the exhaust. during cold weather starting. Follow the manufacturer’s recommendations for engine starting using a GPU. Bleed Air Heating Systems Bleed air heating systems are used on turbine-engine The electrical system is turned on or off with a master switch. aircraft. Extremely hot compressor bleed air is ducted into Turning the master switch to the ON position provides a chamber where it is mixed with ambient or re-circulated electrical energy to all the electrical equipment circuits air to cool the air to a useable temperature. The air mixture except the ignition system. Equipment that commonly uses is then ducted into the cabin. This type of system contains the electrical system for its source of energy includes: several safety features to include temperature sensors that • Position lights prevent excessive heat from entering the cabin, check valves to prevent a loss of compressor bleed air when • Anticollision lights starting the engine and when full power is required, and • Landing lights engine sensors to eliminate the bleed system if the engine • Taxi lights becomes inoperative. • Interior cabin lights Electrical System • Instrument lights Most aircraft are equipped with either a 14- or a 28-volt direct • Radio equipment current (DC) electrical system. A basic aircraft electrical • Turn indicator system consists of the following components: • Fuel gauges • Alternator/generator 7-30