Ignition and Starting Systems

Question 1

What is the purpose of a magneto?

Answer 1

To produce a high voltage that forces a spark to arc across a spark plug gap

Question 2

What are the three major circuits of a high tension magneto system?

Answer 2

Magnetic, primary, and secondary

Question 3

What are the components of a high tension magnetic circuit?

Answer 3

A permanent multipole rotating magnet, soft iron core, and pole shoes.

Question 4

In terms of the engine crankshaft position, when does the ignition event occur?

Answer 4

A specified number of crankshaft degrees before top dead center on the compression stroke.

Question 5

Where is the E-gap position in a magneto?

Answer 5

A few degrees past magnetic neutral.

Question 6

What happens when a magnetic rotor is in the E-gap position and the primary breaker points open?

Answer 6

The flow of current in the primary circuit stops and a high rate of flux change occurs in the core, inducing a pulse of high voltage in the secondary circuit and the spark plugs fire.

Question 7

What is the purpose of the capacitor in a magneto?

Answer 7

Prevents arcing at the points and aids in rapid collapse of the magnetic field.

Question 8

When an ignition switch is off in a magneto system, what is the condition of the ground circuit?

Answer 8

The circuit to ground is completed.

Question 9

What is the purpose of using two magnetos in an engines ignition system?

Answer 9

System redundancy and improved combustion efficiency.

Question 10

Which magneto is grounded when the magneto switch is selected to the right magneto?

Answer 10

The left magneto is grounded.

Question 11

What are the three events required to fire a spark plug in a cylinder when its piston is in the prescribed position?

Answer 11

Magneto is in the E-gap position, breaker points are opening, and the distributor is aligned with that cylinder.

Question 12

What does a magneto timing light indicate?

Answer 12

It indicates the exact instant the magneto points open.

Question 13

What is the main concern when preparing a magneto for installation?

Answer 13

Internal timing

Question 14

Are turbine engine spark igniters generally susceptible to carbon fouling?

Answer 14

No, because the high energy sparks they produce clean off any deposits that form on the firing end.

Question 15

The remaining service life of the brushes typically used in many start generators can be determined by visual inspection of what?

Answer 15

The amount of wear groove remaining on the brushes

Question 16

What are typically the three main components of turbine engine ignition systems?

Answer 16

Ignition exciters, high tension leads, and igniters

Question 17

What is the function of a duty cycle in relation to a turbine engine ignition system?

Answer 17

A duty cycle allows the operation of the ignition system for a given amount of time, to be followed by a minimum specified cooling down period.

Question 18

Name three sources of high volume, low pressure compressed air commonly used for starting jet transport aircraft equipped with air turbine starters.

Answer 18

The APU, a GPU, and compressor bleed air from an already running engine.

Question 19

Between field and armature windings in starter generators, which ordinarily receive current for operation in the start mode?

Answer 19

Generally, both the field and the armature receive current for operation in the start mode.

Question 20

What are the two parts of a starter-generator that commonly require periodic inspection to ensure that they do not wear beyond operational limits?

Answer 20

The commutator and brushes