Powerplant: H - Ignition And Starting Systems

Front 1

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

Back 1

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

Front 2

What is the function of the capacitor in a magneto?

Back 2

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

Front 3

What is a compensated magneto cam, and on what kind of engine is one used?

Back 3

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.

Front 4

What is the significance of the numbers on the distributor of an aircraft magneto?

Back 4

These numbers are the sparking order of the magneto, not the firing order of the engine.

Front 5

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

Back 5

The primary circuit is connected to ground.

Front 6

What is the reason for having a low–tension ignition system on some aircraft?

Back 6

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.

Front 7

What is the basic difference between a low–tension magneto and a high–tension magneto?

Back 7

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.

A high–tension magneto produces high voltage in the magneto coil, and it is sent to the correct spark plug by the built–in high–voltage distributor.

Front 8

What is meant by an All Weather spark plug?

Back 8

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

Front 9

What is meant by the reach of a spark plug?

Back 9

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

Front 10

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

Back 10

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.

Front 11

What is checked when a magneto is internally timed?

Back 11

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.

Front 12

What is the purpose of a vernier coupling used on some aircraft magneto drives?

Back 12

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.

Front 13

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

Back 13

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.

Front 14

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

Back 14

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.

Front 15

What is the purpose of staggered timing between the two magnetos on an aircraft engine?

Back 15

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.

Front 16

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

Back 16

In the Both position.

Front 17

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

Back 17

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.

Front 18

Why are pressurized magnetos used on most reciprocating–engine–powered aircraft that fly at high altitudes?

Back 18

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.

Front 19

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

Back 19

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

Front 20

What is meant by the E–gap in magneto timing?

Back 20

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.

Front 21

What is the function of an impulse coupling?

Back 21

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.

Front 22

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

Back 22

A round wire gage.

Front 23

How many igniters are used in most turbine engines?

Back 23

Two

Front 24

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

Back 24

High–voltage systems and low–voltage systems.

Front 25

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

Back 25

A low–voltage system.

Front 26

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

Back 26

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.

Front 27

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

Back 27

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.

Front 28

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

Back 28

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

Front 29

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?

Back 29

The ignition switch is not grounding the magneto primary circuit.

Front 30

What turns on the autoignition system in a turbo–prop engine?

Back 30

A torque pressure switch energizes the system when the engine stops producing torque.

Front 31

What kind of equipment is used to test an ignition harness for a recip enigne?

Back 31

High–voltage electrical leakage detector

Front 32

Why is it important that a torque wrench always be used when installing spark–plugs?

Back 32

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 isulation

Front 33

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

Back 33

Starter–generator

Front 34

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

Back 34

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

Front 35

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

Back 35

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

Front 36

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

Back 36

Battery voltage is too low to supply enough current to hold the relay engaged

Front 37

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

Back 37

They are light weight for the torque they produce

Front 38

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

Back 38

APU, GPU or from a running engine

Front 39

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

Back 39

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

Front 40

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

Back 40

Air shutoff and regulating valve

Front 41

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

Back 41

It has a self–contained lube system with the oil held in the starter housing

Front 42

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

Back 42

Magnetic chip detectors