Ignition and Starting Systems

Question 1

What is the main advantage of a magneto ignition system over a battery ignition system for an aircraft reciprocating engine?

Answer 1

A magneto has its own source of electrical energy, and is not dependent upon the battery.

Question 2

What is the function of the capacitor in a magneto?

Answer 2

The capacitor minimizes arcing at the breaker points, and it speeds up the collapse of the primary current as the breaker points open.

Question 3

What happens in a magneto ignition system when the ignition switch is placed in the Off position?

Answer 3

The primary circuit is connected to ground.

Question 4

What is checked when a magneto is internally timed?

Answer 4

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 position to direct the high voltage to cylinder number one.

Question 5

In what position should the ignition switch be placed when using a timing light on the magnetos?

Answer 5

In the Both position.

Question 6

What type of ignition system is used on most turbine engines?

Answer 6

High-intensity, intermittent-duty, capacitor discharge ignition systems.

Question 7

What is the E-gap in magneto timing?

Answer 7

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.

Question 8

What is the function of an impulse coupling?

Answer 8

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.

Question 9

How many igniters are used with most turbine engines?

Answer 9

Two.

Question 10

What are two types of ignition systems used in turbine engines?

Answer 10

High-voltage systems and low-voltage systems.

Question 11

With which type of turbine-engine ignition system is a glow plug igniter used?

Answer 11

A low-voltage system.

Question 12

How is the strength of the magnet in a magneto checked?

Answer 12

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.

Question 13

In what position is the magnet in a magneto, when the greatest change in flux density in the coil core takes place?

Answer 13

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.

Question 14

In what position is the magnet in a magneto when the breaker points begin to open?

Answer 14

In its E-gap position, just a few degrees beyond its neutral position.

Question 15

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?

Answer 15

The ignition switch is not grounding the magneto primary circuit.

Question 16

What kind of equipment is used to test an ignition harness for a reciprocating engine?

Answer 16

A high-voltage electrical leakage detector.

Question 17

What is an All-Weather spark plug?

Answer 17

A shielded spark plug that has a recess in the shielding in which a resilient grommet on the ignition lead forms a watertight seal.

Question 18

What is meant by the reach of a spark plug?

Answer 18

The length of the threads on the spark plug that screw into the cylinder head.

Question 19

What is the difference between a hot spark plug and a cold spark plug?

Answer 19

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.

Question 20

What is the advantage of fine-wire spark plugs over massive electrode spark plugs?

Answer 20

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.

Question 21

Why is it important that the spark plugs be kept in numbered holes in a tray when they are removed from an engine?

Answer 21

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.

Question 22

Why is it important that a torque wrench always be used when installing spark plugs in an aircraft engine?

Answer 22

If the spark plugs are not put in tight enough, there is the possibility of a poor seal; if they are put in too tight, there is danger of cracking the insulation.

Question 23

What kind of gage should be used to measure the electrode gap in aircraft spark plugs?

Answer 23

A round wire gage.

Question 24

What kind of electric starting system is used on many of the smaller turbine engines?

Answer 24

A starter-generator.

Question 25

What happens when the start switch for a turbine engine with a starter-generator is placed in the START position?

Answer 25

a. Current flows into the starter relay which closes and actuates the ignition exciter.
b. Current flows through the series motor coils of the starter generator and rotates the engine until it starts.

Question 26

What happens when the start switch for a turbine engine with a starter-generator is placed in the RUN position?

Answer 26

a. The starter relay opens, shutting off current to the ignition exciter and the motor windings in the starter-generator.
b. The generator field relay is closed connecting the voltage regulator to the starter-generator.
c. The output of the generator flows to the bus through the generator circuit breaker.

Question 27

What is indicated if the starter relay chatters rather than locks in, when the start switch is placed in the START position?

Answer 27

The battery voltage is too low to supply enough current to hold the relay engaged.

Question 28

Why are air-turbine starters superior to electric starters for large turbine engines?

Answer 28

They are light weight for the torque they produce.

Question 29

Where does an air-turbine starter get its air for starting the engines on a jet transport airplane?

Answer 29

From an APU, GPU, or from a running engine.

Question 30

What is the purpose of the shear section in an air-turbine drive shaft?

Answer 30

If the ratchet mechanism fails to release and the engine drives the starter to a speed higher than its design speed, the shear section will break and disconnect the starter from the engine.

Question 31

What prevents too high an air pressure from overspeeding an air-turbine starter?

Answer 31

The air shutoff and regulating valve.

Question 32

Where does an air-turbine starter get it lubricating oil?

Answer 32

It has a self-contained lubrication system with the oil held in the starter housing.

Question 33

What device in an air-turbine starter warns a technician if there are any metal chips or particles in the oil?

Answer 33

Magnetic chip detectors warn of any metal contamination in the oil.