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 an all-weather spark plug?

Answer 2

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 3

What is meant by the reach of a spark plug?

Answer 3

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

Question 4

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

Answer 4

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 5

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

Answer 5

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 6

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

Answer 6

Spark plugs tell a good deal about the internal condition of the cylinders from which they were taken. By knowing they 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 7

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

Answer 7

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 or damaging the threads on the spark plug or the cylinder.

Question 8

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

Answer 8

A round wire gauge.

Question 9

What is a shower of sparks ignition system?

Answer 9

An ignition system that uses an induction vibrator to send pulsating DC into a set of retard breaker points on one of the magnetos. This provides a hot and retarded spark for starting the engine.

Question 10

What is an impulse coupling, and how does it work?

Answer 10

An impulse coupling is a spring-loaded coupling between a magneto shaft and the drive gear inside the engine. When the engine is rotated for starting, the impulse coupling locks the magnet so it cannot turn. The spring in the coupling winds up as the crankshaft continues to turn, and when the piston is near top center, the coupling releases and spins the magnet, producing a hot and retarded spark.

Question 11

What are the three distinct circuits in a magneto system?

Answer 11

-Magnetic circuit
-Primary electrical circuit
-Secondary electrical circuit

Question 12

What are the advantages of a solid-state magneto?

Answer 12

-No mechanical parts that wear
-Higher energy spark at low speeds
-No recurring inspection requirements

Question 13

What is the purpose of a FADEC system?

Answer 13

FADEC is a digital electronic fuel control for a gas turbine engine that is functioning during all engine operations, hence full authority. It includes the EEC and functions with the flight management computer. FADEC schedules the fuel to the nozzles in such a way that prevents overshooting power changes and over-temperature conditions. FADEC furnishes information to the EICAS.

Question 14

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

Answer 14

A starter-generator.

Question 15

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

Answer 15

They are light weight for the torque they produce.

Question 16

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

Answer 16

-APU
-GPU
-From a running engine

Question 17

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

Answer 17

The air shutoff and regulating valve.

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

What is the function of the capacitor in a magneto?

Answer 20

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

Question 21

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

Answer 21

The primary circuit is connected to ground.

Question 22

What is checked when a magneto is internally timed?

Answer 22

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 23

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

Answer 23

In the Both position.

Question 24

What is the E-gap in magneto timing?

Answer 24

The E-gap angle is the position of the rotating magnet where the primary current flowing is the magneto coil is the greatest. The breaker points open when the rotating magnet is in its E-gap position.

Question 25

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 25

The ignition switch is not grounding the magneto primary circuit.

Question 26

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

Answer 26

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

Question 27

How many igniters are used with most turbine eingines?

Answer 27

Two?

Question 28

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

Answer 28

-High-voltage systems
-Low-voltage systems

Question 29

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

Answer 29

A low-voltage system.

Question 30

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

Answer 30

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 measure. The strength of the magnet determines the amount of primary current.

Question 31

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

Answer 31

It’s 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 32

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

Answer 32

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

Question 33

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

Answer 33

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

Question 34

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

Answer 34

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

Question 35

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

Answer 35

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

Question 36

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

Answer 36

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.