Text. AIRCRAFT SYSTEMS
Flight control systems
The flight control systems in most general aviation airplanes consist of the cockpit con-trols, cables, pulleys, and linkages connected to the movable control surfaces outside the airplane.
There are three primary and two sec-ondary flight control systems.
The primary flight control systems consist of the elevator, aileron, and rudder, which are essential in controlling the aircraft. The second-ary control systems consist of the trim tabs and wing flaps. The trim tabs enable the pilot to trim out control pressures, and the flaps enable the pilot to change the lifting characteristics of the wing and also to decrease the speed at which the wing stalls.
1. What does the primary flight control system consists of?
2. What are the components of the secondary flight control system?
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Electrical System
Electrical energy is required to operate navigation and communication radios, lights, and other airplane equipment.
Most airplanes are equipped with a di-rect-current (DC) electrical system and an alternating-current (AC) electrical system.
A basic airplane electrical system consists of the following components:
1. Generator. 2. Battery.
3. Master switch or battery switch.
4. Bus bar, fuses, and circuit breakers. 5. Voltage regulator.
6. Ammeter.
7. Starting motor.
8. Associated electrical wiring. 10. Accessories.
Engine-driven generators or alternators supply electric current to the electrical system and also maintain a sufficient electrical charge in the battery which is used primarily for starting.
Electrical energy stored in a battery provides a source of electricity for starting the engine and a limited supply of electricity for use in the event the generator fails.
Some airplanes are equipped with re-ceptacles to which external auxiliary power units (APU) can be connected to provide electrical energy for starting. These are very useful, especially during cold weather start-ing. Care must be exercised in starting en-gines using auxiliary power units when the battery is dead. If this is done, electrical energy will be forced into the dead battery, causing the battery to overheat and possibly explode, resulting in damage to the airplane.
A master switch is installed on air-planes to provide a means for the pilot to turn the electrical system "on" and "off." Turning the master switch "on" provides electrical energy to all the electrical equip-ment circuits with the exception of the igni-tion system.
Although additional electrical equipment may be found in some airplanes, the following lists the equipment most commonly found which uses the electrical system for its source of energy:
1. Position lights. 2. Landing lights. 3. Taxi lights.
4. Anticollision lights. 5. Interior cabin lights. 6. Instrument lights. 7. Radio equipment.
8. Turn indicator. 9. Fuel gauges.
10. Stall warning system. 11. Pitot heat.
Some airplanes are equipped with a bat-tery switch which controls the electrical power to the airplane in a manner similar to the mas-ter switch. In addition, a generator switch is installed which permits the pilot to exclude the generator from the electrical system in the event of generator failure. With the generator switch "off," the entire electrical load is placed on the battery. Therefore, all nonessential elec-trical equipment should be turned off to con-serve the energy stored in the battery.
A bus bar is used as a terminal in the air-plane electrical system to connect the main elec-trical system to the equipment using electricity as a source of power. This simplifies the wiring sys-tem and provides a common point from which voltage can be distributed throughout the system.
Fuses or circuit breakers are used in the electrical system to protect the circuits and equipment from electrical overload. Circuit breakers have the same function as a fuse but can be manually reset, rather than replaced, if an overload condition occurs in the electrical sys-tem.
An ammeter is an instrument used to mon-itor the performance of the airplane electrical sys-tem.
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An ammeter shows if the generator is producing an adequate supply of electrical power to the system by measuring the amperes of electricity. This instrument also indicates whether the battery is receiving an electrical charge.
A voltage regulator controls the rate of charge to the battery by stabilizing the electrical output which is usually slightly higher than the battery voltage.
An inverter is installed on airplanes to change direct current to alternating current.
1. What is electrical energy required for?
2. What are the basic electrical system components?
3. Does electrical system remain operative in case of generator failure? 4. Describe the purpose of circuit breakers.
5. What is the function of a voltage regulator?
Fuel System
The function of the fuel system is to provide a means of storing fuel in the air-plane and transferring this fuel to the air-plane engine. Fuel systems are classified ac-cording to the method used to furnish fuel to the engine from the fuel tanks. The two classifications are the "gravity feed" and the "fuel pump system."
The gravity feed system utilizes the force of gravity to transfer the fuel from the tanks to the engine. This system can be used on high-wing airplanes if the fuel tanks are installed in the wings. This places the fuel tanks above the carburetor and the fuel is gravity fed through the system and into the carburetor.
If the design of the airplane is such that gravity cannot be used to transfer fuel, fuel pumps are installed. This is true on low-wing airplanes where the fuel tanks in the wings are located below the carburetor.
Two fuel pump systems are used on most airplanes. The main pump system is engine driven and an auxiliary electric driven pump is provided for use in the event the en-gine pump fails. The auxiliary pump, com-monly known as the "boost pump," provides added reliability to the fuel system, and is also used as an aid in engine starting.
The electric auxiliary pump is controlled by a switch in the cockpit.
Most airplanes are designed to use space in the wings to mount fuel tanks. All tanks have filler openings which are covered by a cap. This system also includes lines connecting to the en-gine, fuel gauges indicating the pressure in the fuel lines, strainers, and vents which permit air to replace the fuel
Fuel overflow vents are provided to dis-charge fuel in the event the fuel expands because of high temperatures. Drain plugs or valves (sumps) are located at the bottom of the tanks from which water and other sediment can be drained from the tanks.
Fuel lines pass through a selector assembly lo-cated in the cockpit which provides a means for the pilot to turn the fuel "off," "on," or to select a par-ticular tank from which to draw fuel. The fuel selec-tor assembly may be a simple on/off valve, or a more complex arrangement which permits the pilot to select individual tanks or use all tanks at the same time.
Many airplanes are equipped with fuel strain-ers, called sumps, located at the low point in the fuel lines between the fuel selector and the carburetor. The sumps filter the fuel and trap water and sediment in a container which can be drained to remove foreign matter from the fuel.
1. What is the fuel system designed for? 2. How are fuel systems classified?
3. Where is fuel stored on the aircraft?
4. How is fuel delivered to the engine(s)? 5. Why is it necessary to filter the fuel?
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Oil System
Proper lubrication of the engine is es-sential to the extension of engine life and prevention of excessive maintenance.
The oil system provides a means of storing and circulating oil throughout the in-ternal components of the engine. Lubricating oil serves two purposes: (1) it furnishes a coating of oil over the surfaces of the moving parts, preventing direct metal-to-metal con-tact and the generation of heat, and (2) it ab-sorbs and dissipates, through the oil cooling system, part of the engine heat produced by the internal combustion process.
Usually the engine oil is stored in a sump at the bottom of the engine crankcase. An opening to the oil sump is provided through which oil can be added and a dip stick is provided to measure the oil level in the sump.
A pump forces oil from the sump to the various parts of the engine that require lubrication. The oil then drains back to the sump for recirculation.
Each engine is equipped with an oil pres-sure gauge and an oil temperature gauge which are monitored to determine that the oil system is functioning properly.
The oil pressure indication varies with the temperature of the oil. If the oil temperature is cold the pressure will be higher than if the oil is hot.
A loss of oil pressure is usually followed by engine failure. If this occurs while on the ground, the pilot must shut the engine down immediately; if in the air, land at a suitable emergency landing site.
It is important to check the oil level be-fore each flight. Starting a flight with an insuffi-cient oil supply can lead to serious conse-quences. The airplane engine will burn off a cer-tain amount of oil during operation, and begin-ning a flight when the oil level is low will usually result in an insufficient supply of oil before the flight terminates.
A more sophisticated aircraft is equipped with some other vital systems: hydraulic system, air condi-tioning and pressurization system, anti-icing (or de-icing) system, fire extinguishing system, and galley equipment
1. What is the function of the oil system? 2. What is a dipstick?
3. Why is a loss of oil pressure so dangerous?
4. Why is it important to check the oil level before each flight? 5. What is the function of a fuel selector assembly?
6. Where are usually fuel tanks mounted?
7. What is the function of an auxiliary electric driven pump?
Anti-icing system is designed to prevent ice formation on aircraft vital areas and permits aircraft operation without re-striction by icing conditions. The aircraft ice protection is provided by heating of critical areas (engine air intakes, leading edge, windshields, pitot tubes, static ports, etc) using hot air or electrical power.
Air conditioning and pressurization system provides maintaining the air in the pressurized compartments at the desired level of pressure, temperature and fresh-ness. The required bleed air for the system is supplied either by engine compressors or APU or a high pressure ground air supply unit.
The bleed air is cooled, conditioned and distri-buted to the individual compartments (flight compartment, passenger compartments and car-go compartments) and then discharged over-board through outflow valves.
Hydraulic system is designed to oper-ate undercarriage, wheel brakes, nose wheel steering, control surfaces, etc. This system is normally divided into at least two systems with maximum degree of independence. Each system comprises engine driven pumps, accumulators, valves, heat exchangers and filters. A non-inflammable liquid is the usual working fluid.
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1. What is anti-icing system designed for? 2. How is aircraft ice protection provided?
3. What is the function of air conditioning and pressurization system? 4. What is hydraulic system designed for?
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