8 Electrical, Starting, And Ignition Systems

Question 1

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

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

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

Answer 3

Both field and armature.

Question 4

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 an already running engine.

Question 5

5. When should ignition ideally occur?

Answer 5

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

Question 6

6. Why are dual magnetos used in the engine ignition system?

Answer 6

To improve combustion efficiency and provide redundancy for safety.

Question 7

7. Why is magneto timing so important?

Answer 7

For an engine to run properly, the spark plug in a cylinder has to fire at a specific time. To produce the required energy for the spark at the required time, the magneto must be in the E gap position, the breaker points must start to open, and the distributor must be electrically aligned with the particular cylinder.

Question 8

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

9. Name the components of a high tension magneto system.

Answer 9

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

Question 10

10. Name the 3 main circuits of a high tension magneto system.

Answer 10

Magnetic, primary, and secondary.

Question 11

11. What is an E gap angle?

Answer 11

It is a point a few degrees beyond the neutral position of a rotating magnet where max magnetic field stress exists.

Question 12

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

Answer 12

Capacitor.

Question 13

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 E gap position, the primary points open, which interrupts the current flow in the primary circuit causing a high rate of flux change in the core, and inducing a pulse of high voltage in the secondary coil.

Question 14

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 magnetos are grounded. When the ignition switch is turned to the left position, the right magneto is grounded, so that only the left magneto operates, and vise versa.

Question 15

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, and indicates the exact instant the magneto points open.

Question 16

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

Answer 16

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

Question 17

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, and is then followed by a minimum specified cooling down period.

Question 18

18. What are the 3 main components of a turbine engine ignition system?

Answer 18

Ignition exciters, high tension leads, igniters.

Question 19

19. When the engine is operating, what does an ammeter/load meter indicate when connected to: battery positive lead and generator output lead?

Answer 19

Charging or discharging.
Current produced by the generator or electrical system load.

Question 20

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

21. Where would you find generator rating and performance data?

Answer 21

On the data plate attached to the generator.

Question 22

22. How is the voltage of a DC generator controlled?

Answer 22

By varying the field current strength.

Question 23

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

Answer 23

3 phase alternator.

Question 24

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

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

Answer 25

The frequency of the alternator output.

Question 26

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

Answer 26

Constant speed drives, integrated drive generators, and variable speed constant frequency power systems.

Question 27

27. Name the major parts of a DC motor.

Answer 27

The armature, field, brushes, and frame assembly.

Question 28

28. Name the components of a direct cranking electric starter system.

Answer 28

An electric motor, reduction gears, and an auto engaging/disengaging mechanism.

Question 29

29. Name 3 types of DC motors.

Answer 29

Series, shunt, compound.

Question 30

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

Answer 30

A series wound motor is commonly used because it has a high starting torque under heavy load conditions.

Question 31

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

Answer 31

First as a starter, then as a generator once the engine is running.

Question 32

32. What is a possible indication when a starter drags?

Answer 32

A dirty or worn starter commutator.

Question 33

33. Where would wire with high temp insulation material be used?

Answer 33

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

Question 34

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

Answer 34

AWG

Question 35

35. How are wire sizes represented?

Answer 35

By a numbered gauge size. The smaller wires are represented by larger numbers. The smallest size wire normally used in aircraft is 22AWG.

Question 36

36. What is the max slack allowed between the supports of a single wire or bundle installation?

Answer 36

Not over half inch.

Question 37

37. Why are wires bonded on powerplant installations?

Answer 37

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