Jeppesen Chapter 8 - Electrical, Starting, and Ignition Systems (37 items)

Question 1

Q1. How can the remaining service life of starter-generator brushes be determined?

Answer 1

A1. By visually inspecting the amount of wear groove remaining on the brushes.

Question 2

Q3. Between field and armature windings in starter-generators, which ordinarily receive current for operation in the start mode?

Answer 2

A3. Generally, both field and armature receive current for operation in the start mode.

Question 3

Q4. What are possible sources of low pressure compressed air used for starting jet transport aircraft equipped with air turbine starters?

Answer 3

A4. A ground power unit (GPU), an on-board auxiliary power unit (APU), compressed bleed air from an already running engine.

Question 4

Q5. When should ignition ideally occur?

Answer 4

A5. A specific number of degrees (as determined by the manufacturer) before the piston reaches top dead center on the compression stroke.

Question 5

Q6. Why are dual magnetos used in the engine ignition system?

Answer 5

A6. To improve combustion efficiency, and provide redundancy for safety.

Question 6

Q7. Why is magneto timing so important?

Answer 6

A7. 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. If any of these requirements are not correctly adjusted, the engine will run rough or may not run at all. When preparing a magneto for installation, first the internal timing must be correctly adjusted , then the magneto-to-engine timing is adjusted.

Question 7

Q8. What function does a magneto perform?

Answer 7

A8. It produces a high voltage that forces a spark to arc across a spark plug gap.

Question 8

Q9. Name the components of a high tension magneto system.

Answer 8

A9. A permanent multipole rotating magnet, soft iron core, and pole shoes.

Question 9

Q10. Name the three main circuits of a high tension magneto system.

Answer 9

A10. Magnetic, Primary, and Secondary.

Question 10

Q11. What is an E-Gap angle?

Answer 10

A11. It is a point a few degrees beyond the neutral position of a rotating magnet where maximum magnetic field stress exists.

Question 11

Q12. What reduces arcing in the points and also aids the collapsing of the magnetic field in a magneto?

Answer 11

A12. A capacitor.

Question 12

Q13. How does a magneto produce the high voltage required to fire a spark plug?

Answer 12

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 circuit causing a high rate of flux change in the core, and inducing a pulse of high voltage in the secondary coil

Question 13

Q14. What is the P-lead and how does it function?

Answer 13

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 visa versa.

Question 14

Q15. What is a magneto timing light used for, and what does it indicate?

Answer 14

A15. It is used for both internal magneto timing and magneto-to-engine timing, and indicates the exact instant the magneto points open.

Question 15

Q16. Why are turbine engine igniters generally not susceptible to carbon fouling?

Answer 15

A16. Because the high energy sparks they produce clean off any deposits on the firing end.

Question 16

Q17. What is the function of a duty cycle in relation to a turbine engine ignition system?

Answer 16

A17. 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 17

Q18. What are three main components of a turbine engine ignition system?

Answer 17

A18. Ignition exciters, high tension leads, igniters.

Question 18

Q19. When the engine operating, what does an ammeter / load-meter indicate when connected to: 1.Battery positive lead? 2.Generator output lead?

Answer 18

When connected to the battery positive lead, the ammeter indicates whether the battery is charging or discharging. When connected to the generator output lead, it indicates the current produced by the generator, or electrical system load.

Question 19

Q20. What is done to ensure that each generator shares the load in a multiple generator system?

Answer 19

A20. The generators are paralleled.

Question 20

Q21. Where would you find generator rating and performance data?

Answer 20

A21. On the data plate attached to each generator.

Question 21

Q22. How is the voltage of a DC generator controlled?

Answer 21

A22. By varying the field current strength.

Question 22

Q23. What is the most common type of alternator used in most aircraft AC systems?

Answer 22

A23. The three phase alternator.

Question 23

Q24. How does a voltage regulator control the voltage of an alternator?

Answer 23

A24. By regulating the voltage output of the DC exciter.

Question 24

Q25. What does the speed of rotation and number of poles of an alternator determine?

Answer 24

A25. The frequency of the alternator output.

Question 25

Q26. What are some of the methods used to maintain 400 Hertz alternator output frequency on a large turbojet or turbofan engines?

Answer 25

A26. Constant Speed Drives, Integrated Drive Generators, and Variable-speed constant frequency (VSCF) power systems.

Question 26

Q27. Name the major parts of a DC motor.

Answer 26

A27. The armature, field, brushes, and frame assembly.

Question 27

Q28. Name the components of a direct cranking electric starter system.

Answer 27

A28. (1)Electric motor, (2)reduction gears, (3)and an automatic engaging and disengaging system.

Question 28

Q29. Name three types of DC motors.

Answer 28

A29. Series, Shunt, and Compound.

Question 29

Q30. What type of DC motor is commonly used for a reciprocating engine starter and why?

Answer 29

A30. A series wound motor is commonly used because it has a high starting torque under heavy load conditions.

Question 30

Q31. What are the operating modes of a turbine engine starter generator?

Answer 30

A31. It operates first as a starter, then as a generator once the engine is running.

Question 31

Q32. What is a possible indication when a starter drags?

Answer 31

A32. A dirty or worn commutator.

Question 32

Q33. Where would wire with high temperature insulation material be used?

Answer 32

A33. When they run close to high temperature areas such as exhaust stacks or heating stacks.

Question 33

Q34. What is the size standard for electrical wire used in US manufactured aircraft?

Answer 33

A34. The American Wire Gauge (AWG).

Question 34

Q35. How are wire sizes represented?

Answer 34

A35. By a numbered gauge size. The smaller wires are represented by larger numbers. The smallest size wire normally used in aircraft is 22-gauge

Question 35

Q36. What is the maximum slack allowed between the supports of a single wire or bundle installation?

Answer 35

A36. Not over 1/2 inch

Question 36

Q37. Why are wires bonded on powerplant installations?

Answer 36

A37. To provide current return path for electrical accessories, and to prevent static discharge.

Question 37

Q2. What components of the starter-generator require periodic inspection?

Answer 37

A2. Both commutator and brushes should be inspected for wear beyond operational limits.