Electrical, Starting, + Ignition Systems

Question 1

How can the remaining service life of starter generator brushes be determined?

Answer 1

By visually inspecting the amount of wear groove remaining on the brushes.

Question 2

What components of the starter generator require periodic inspection?

Answer 2

Both commutator and brushes should be inspected for wear beyond operational limits.

Question 3

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

Answer 3

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

Question 4

What are possible sources of low pressure compressed air, used for starting jet transport aircraft equipped with air turbine starters?

Answer 4

Ground power unit.
Onboard auxiliary power unit.
Compressed bleed air from an already running engine.

Question 5

When should ignition ideally occur in a reciprocating engine?

Answer 5

A specific number of degrees before the piston reaches top dead center on the compression stroke.

Question 6

Why are dual magnetos used in the engine ignition system?

Answer 6

Improve combustion efficiency.
Provide redundancy for safety.

Question 7

Why is magneto timing so important?

Answer 7

The spark provided by the magneto must fire at a specific time for an engine to run properly.

Question 8

What function does a magneto perform?

Answer 8

It produces a high voltage that forces a spark to arc across a spark, plug gap.

Question 9

Name the components of a high tension magneto system:

Answer 9

A permanent multi-pole rotating magnet.
Soft iron core.
Pole shoes.

Question 10

Name the three circuits of a high tension magneto system:

Answer 10

Magnet.
Primary.
Secondary.

Question 11

What is a E gap angle?

Answer 11

A point a few degrees beyond the neutral position of a rotating magnet where maximum magnetic field stress exists.

Question 12

What reduces arcing in the points, and also aids the collapsing of the magnetic field in a magneto?

Answer 12

A capacitor

Question 13

How does a magneto produce the high voltage required to fire a spark plug?

Answer 13

In the rotation cycle, when the magnetic rotor is in the E gap position, the primary points open, which interrupts the current flow in the primary circuits causing a high rate of flux change in the core, and inducing a pulse of high voltage in the secondary coil.

Question 14

What is the P lead and how does it function?

Answer 14

The P lead connects the ignition switch to the primary circuit of the magneto. When the ignition switch is turned off the P leads on both magneto’s are grounded.

Question 15

What is a magneto timing light used for and what does it indicate?

Answer 15

It is used for both internal magneto timing and magneto to engine timing.
It indicates the exact instant the magneto points open.

Question 16

Why are turbine engine igniters generally not susceptible to carbon fouling?

Answer 16

The high energy sparks they produce, clean off any deposits on the firing end.

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 engine system for a given amount of time, and it is then followed by a minimum specified cooling down period.

Question 18

What are the three main components of a turbine engine ignition system?

Answer 18

Ignition exciters.
High tension leads.
Igniters.

Question 19

When the engine is operating, what does an ammeter or load meter indicate when connected to:
1) a battery positive lead?
2) generator output lead?

Answer 19

1) the ammeter indicates whether the battery is charging or discharging.

2) it indicates the current produced by the generator or electrical system load.

Question 20

What is done to ensure that each generator shares the load in a multiple generator system?

Answer 20

The generators are paralleled.

Question 21

Where would you find generator rating and performance data?

Answer 21

On the data plate attached to the generator.

Question 22

How is the voltage of a DC generator controlled?

Answer 22

By varying the field current strength.

Question 23

What is the most common type of alternator used in most aircraft AC systems?

Answer 23

The three phase alternator

Question 24

How does a voltage regulator control the voltage of an alternator?

Answer 24

By regulating the voltage output of the DC exciter.

Question 25

What does the speed of rotation in number of poles of an alternator determine?

Answer 25

The frequency of the alternator output

Question 26

What are some of the methods used to maintain 400 Hz alternator output frequency on large turbojet or turbofan engines?

Answer 26

Constant speed drives.
Integrated drive generators.
Variable speed constant frequency power systems.

Question 27

Name the major parts of a DC motor:

Answer 27

Armature.
Field.
Brushes.
Frame assembly.

Question 28

Name the components of a direct cranking electric starter system:

Answer 28

Electric motor.
Reduction gears.
Automatic engaging and disengaging mechanism.

Question 29

Name three types of DC motors:

Answer 29

Series.
Shunt.
Compound.

Question 30

What type of DC motor is commonly used for a reciprocating engine starter and why?

Answer 30

A series wound motor.
Because it has a high starting torque under heavy load conditions.

Question 31

What are the operating modes of a turbine engine starter generator?

Answer 31

It operates first as a starter, then as a generator once the engine is running.

Question 32

What is a possible indication when a starter drags?

Answer 32

A dirty or worn starter commutator.

Question 33

Where would wire with high temperature insulation material be used? 

Answer 33

When they run close to high temperature areas, such as exhaust stacks or heating ducts.

Question 34

What is the size standard for electrical wire used in US manufactured aircraft?

Answer 34

The American wire gauge (AWG)

Question 35

How are wire sizes represented?

Answer 35

By a numbered gauge size. Smaller wires are represented by larger numbers.

Question 36

What is the maximum slack allowed between the supports of a single wire or bundle installation?

Answer 36

Not over a half inch.

Question 37

Why are wires bonded on power plant installations?

Answer 37

To provide a current return path for electrical accessories, and to prevent static discharge.