Electrical Start And Ignition Systems

Question 1

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

Answer 1

Visually inspect amount of wear groove remaining on brushes.

Question 2

What components of the starter generator require periodic inspection?

Answer 2

Commutator and brushes inspected for wear beyond limits.

Question 3

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

Answer 3

Both, field and armature.

Question 4

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

Answer 4

GPU, APU, compressed bleed air from running engine.

Question 5

When should ignition ideally occur?

Answer 5

Specific number of degrees determined by the manufacturer before piston reaches TDC on compression stroke.

Question 6

Why are dual magnetos used in engine ignition systems?

Answer 6

Improve combustion efficiency and redundancy for safety.

Question 7

Why is magneto timing so important for an engine to run properly?

Answer 7

Spark plug has to fire at specific time to produce required energy for spark at required time, magneto must be in e-gap position, breaker points must start to open and the distributor must be electrically aligned with particular cylinder.

Question 8

What function does a magneto perform?

Answer 8

Produces high voltage for spark to arc across spark plug gap.

Question 9

Name the components of a high tension magneto system.

Answer 9

Permanent multi-pole rotating magnet, soft iron core and pole shoes.

Question 10

Name the three main circuits of a high tension magneto system.

Answer 10

Magnetic, primary and secondary.

Question 11

What is an e-gap angle?

Answer 11

Point a few degrees past neutral position of rotating magnet where max 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

Capacitor.

Question 13

How does a magneto produce the high voltage required to fire a spark plug in the rotation cycle when the magnetic rotor is in the e-gap position?

Answer 13

Primary points open, interrupt current flow in primary circuit causing higher rate of flux change, introducing a pulse of high voltage in secondary coil.

Question 14

What is the p-lead and how does it function?

Answer 14

P-lead connects ignition switch to the primary circuit of magneto, when ignition switch is turned off p-lead on both magnetos are grounded, when the ignition switch is turned to the left position, right mag grounded.

Question 15

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

Answer 15

Used for internal mag timing and mag to engine timing, indicates exact instant magneto points open.

Question 16

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

Answer 16

High energy sparks clean off deposits on firing end.

Question 17

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

Answer 17

Allows the operation of the ignition system for given amount of time and 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/load meter indicate when connected to one battery positive lead to generator output lead?

Answer 19

One battery connection indicates charging or discharging, generator connection indicates current produced by the generator or electrical system.

Question 20

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

Answer 20

Generators paralleled.

Question 21

Where would you find generator rating and performance data?

Answer 21

Data plate attached to generator.

Question 22

How is the voltage of a dc generator controlled?

Answer 22

Varying field current strength.

Question 23

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

Answer 23

Three-phase alternator.

Question 24

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

Answer 24

Regulating voltage output of dc exciter.

Question 25

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

Answer 25

Frequency of alternator output.

Question 26

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

Answer 26

CSD's, IDG's and 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 components of direct cranking electric starter system an electric motor.

Answer 28

Reduction gears and automatic engaging and disengaging mechanism.

Question 29

Name three types of dc motors.

Answer 29

Series, shunt and compound.

Question 30

What type of dc motor commonly used for reciprocating engine starter and why?

Answer 30

Series wound motor because its high starting torque under load conditions.

Question 31

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

Answer 31

First a starter, then a generator while engine is running.

Question 32

What is the possible indication when a starter drags?

Answer 32

Dirty or worn starter commutator.

Question 33

Where would wire with high temperature insulation material be used?

Answer 33

When close to high temperature areas like exhaust stacks or heating ducts.

Question 34

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

Answer 34

American wire gauge AWG.

Question 35

How are wire sizes represented?

Answer 35

Numbered gauge size, smaller wires represented by larger numbers, smallest wire normally used in aircraft is 22 gauge.

Question 36

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

Answer 36

Not over one half inch.

Question 37

Why are wires bonded on powerplant installations?

Answer 37

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