Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the main advantage of a magneto ignition system over a battery ignition system for an aircraft reciprocating engine? |
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Definition
| A magneto has its own source of electrical energy, and it is not dependent upon the battery. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the function of the capacitor in a magneto? |
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Definition
| The capacitor minimizes arcing at the breaker points, and it speeds up the collapse of the primary current as the breaker points open. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is a compensated magneto cam, and on what kind of engine is one used? |
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Definition
| A compensated cam is a special cam used in magnetos mounted on high-performance radial engines. The cam has one lobe for each cylinder, and the lobes are ground in such a way that the breaker points open when the pistons in the different cylinders are the same linear distance from top center. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the significance of the numbers on the distributor of an aircraft magneto? |
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Definition
| These numbers are the sparking order of the magneto, not the firing order of the engine. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What happens in a magneto ignition system when the ignition switch is placed in the Off position? |
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Definition
| The primary circuit is connected to ground. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the reason for having a low-tension ignition system on some aircraft? |
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Definition
| Low-tension magnetos are used on aircraft that fly at high altitudes where there is a problem with flashover in the high-tension magneto distributor. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the basic difference between a low-tension magneto and a high-tension magneto? |
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Definition
| The low-tension ignition system has only one coil in the magneto, and it uses a carbon-brush-type distributor. Low voltage is distributed to high-tension transformers that are located on the heads of each cylinder. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is meant by an All Weather spark plug? |
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Definition
| A shielded spark plug that has a recess in the shielding in which a resilient grommet on the ignition lead forms a watertight seal. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is meant by the reach of a spark plug? |
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Definition
| The length of the threads on the spark plug that screw into the cylinder head. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the difference between a hot spark plug and a cold spark plug? |
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Definition
| A hot spark plug has a long path for the heat to travel between the nose core insulator and the spark plug shell. In a cold spark plug, the heat has a shorter distance to travel, and the spark plug operates cooler than a hot spark plug. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is checked when a magneto is internally timed? |
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Definition
| Internally timing a magneto consists of adjusting the breaker points so they will open at the instant the rotating magnet is in its E-gap position, and the distributor rotor is in the position to direct the high voltage to cylinder number one. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the purpose of a vernier coupling used on some aircraft magneto drives? |
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Definition
| Magnetos that are base mounted must have a vernier coupling between the magneto drive and the engine. This vernier coupling allows the magneto-to-engine timing to be varied in increments of less than one degree. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the advantage of fine-wire spark plugs over massive electrode spark plugs? |
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Definition
| Fine-wire spark plugs have a firing end that is more open than that of a massive electrode spark plug. The open firing end allows the gases that contain lead to be purged from the spark plug so they will not form solid lead contaminates. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
Why is it important that the spark plugs be kept in numbered holes in a tray when they are removed from an engine? |
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Definition
| Spark plugs tell a good deal about the internal condition of the cylinders from which they were taken. By knowing the cylinder from which each spark plug came, the mechanic can take the proper action when a spark plug indicates such conditions as detonation or overheating. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the purpose of staggered timing between the two magnetos on an aircraft engine? |
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Definition
| Engines in which the exhaust gas scavenging from the cylinders is uneven use staggered ignition timing. The spark plug nearest the exhaust valve, where the fuel-air mixture is diluted, fires before the spark plug on the intake side. By using staggered timing, the flame front caused by the two spark plugs will meet in the center of the piston. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
In what position should the ignition switch be placed when using a timing light on the magnetos? |
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Definition
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
Why is it important that a torque wrench always be used when installing spark plugs in an aircraft engine? |
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Definition
| If the spark plugs are not put in tight enough, there is the possibility of a poor seal, and if they are put in too tight, there is danger of cracking the insulation. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
Why are pressurized magnetos used on most reciprocating-engine-powered aircraft that fly at high altitudes? |
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Definition
| Pressurized air is a better insulator than less dense air. By pressurizing the distributors, the high voltage is kept from arcing across to the wrong electrode and causing vibration and loss of engine power. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What type of ignition system is used on most turbine engines? |
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Definition
| High-intensity, intermittent-duty, capacitor discharge ignition systems. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is meant by the E-gap in magneto timing? |
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Definition
| The E-gap angle is the position of the rotating magnet when the primary current flowing in the magneto coil is the greatest. The breaker points open when the rotating magnet is in its E-gap position. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What is the function of an impulse coupling? |
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Definition
| An impulse coupling is a spring-driven coupling between the magneto and the engine. When the engine is being started, the impulse coupling holds the rotating magnet until the piston passes over its top center position and starts down. The impulse coupling releases the magnet and the spring spins it fast so that it produces a hot and late spark. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What kind of gage should be used to measure the electrode gap in aircraft spark plugs? |
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Definition
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
How many igniters are used in most turbine engines? |
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Definition
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What are two types of ignition systems used in turbine engines? |
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Definition
| High-voltage systems and low-voltage systems. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
With which type of ignition system is a glow plug igniter used? |
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Definition
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
How is the strength of the magnet in a magneto checked? |
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Definition
| The magneto is put on a test stand and rotated at a specified speed. The breaker points are held open and the primary current is measured. The strength of the magnet determines the amount of primary current. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
In what position is the magnet in a magneto when the greatest change in flux density in the coil core takes place? |
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Definition
| It is a few degrees beyond its neutral position. When it is in this position, the breaker points open and the primary current is interrupted. The flux change in the coil core is the greatest. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
In what position is the magnet in a magneto when the breaker points begin to open? |
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Definition
| In its E-gap position, just a few degrees beyond its neutral position. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What malfunction in the ignition system would cause an aircraft reciprocating engine to continue to run after the ignition switch is placed in the Off position? |
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Definition
| The ignition switch is not grounding the magneto primary circuit. |
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Term
POWERPLANT IGNITION & STARTING SYSTEMS
What turns on the autoignition system in a turbo-prop engine? |
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Definition
| A torque pressure switch energizes the system when the engine stops producing torque. |
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