Questions and Answers - Aircraft Engine Electrical Systems

1. What device is used to convert alternating current, which has been induced into the loops of the rotating armature of a dc generator, to direct current?
a. A rectifier.
b. A commutator.
c. An inverter.

2. A certain direct current series motor mounted within an aircraft draws more amperes during start than when it is running under its rated load. The most logical conclusion that may be drawn is
a. the starting winding is shorted.
b. the brushes are floating at operating RPM because of weak brush springs.
c. the condition is normal for this type of motor.

3. The stationary field strength in a direct current generator is varied
a. by the reverse-current relay.
b. because of generator speed.
c. according to the load requirements.

4. What type of electric motor is generally used with a direct-cranking engine starter?
a. Direct current, shunt-wound motor.
b. Direct current, series-wound motor.
c. Synchronous motor.

5. Upon what does the output frequency of an ac generator (alternator) depend?
a. The speed of rotation and the strength of the field.
b. The speed of rotation, the strength of the field, and the number of field poles.
c. The speed of rotation and the number of field poles.

6. A high surge of current is required when a dc electric motor is first started. As the speed of the motor increases,
a. the counter emf decreases proportionally.
b. the applied emf increases proportionally.
c. the counter emf builds up and opposes the applied emf, thus reducing the current flow through the armature.

7. Alternators (ac generators) that are driven by a constantspeed drive (CSD) mechanism are used to regulate the alternator to a constant
a. voltage output.
b. amperage output.
c. hertz output.

8. What is used to polish commutators or slip rings?
a. Very fine sandpaper.
b. Crocus cloth or fine oilstone.
c. Aluminum oxide or garnet paper.

9. If a generator is malfunctioning, its voltage can be reduced to residual by actuating the
a. rheostat.
b. generator master switch.
c. master solenoid.

10. If the points in a vibrator-type voltage regulator stick in the closed position while the generator is operating, what will be the probable result?
a. Generator output voltage will decrease.
b. Generator output voltage will not be affected.
c. Generator output voltage will increase.

11. Why is a constant-speed drive used to control the speed of some aircraft engine-driven generators?
a. So that the voltage output of the generator will remain within limits.
b. To eliminate uncontrolled surges of current to the electrical system.
c. So that the frequency of the alternating current output will remain constant.

12. According to the electron theory of the flow of electricity, when a properly functioning dc alternator and voltage regulating system is charging an aircraft's battery, the direction of current flow through the battery
a. is into the negative terminal and out the positive terminal.
b. is into the positive terminal and out the negative terminal.
c. cycles back and forth with the number of cycles per second being controlled by the rotational speed of the alternator.

13. Aircraft that operate more than one generator connected to a common electrical system must be provided with
a. automatic generator switches that operate to isolate any generator whose output is less than 80 percent of its share of the load.
b. an automatic device that will isolate nonessential loads from the system if one of the generators fails.
c. individual generator switches that can be operated from the cockpit during flight.

14. The most effective method of regulating aircraft direct current generator output is to vary, according to the load requirements, the
a. strength of the stationary field.
b. generator speed.
c. number of rotating armature loops in use.

15. Electric motors are often classified according to the method of connecting the field coils and armature. Aircraft engine starter motors are generally of which type?
a. Compound.
b. Series.
c. Shunt (parallel).

16. As the generator load is increased (within its rated capacity), the voltage will
a. decrease and the amperage output will increase.
b. remain constant and the amperage output will increase.
c. remain constant and the amperage output will decrease.

17. As the flux density in the field of a dc generator increases and the current flow to the system increases, the
a. generator voltage decreases.
b. generator amperage decreases.
c. force required to turn the generator increases.

18. What is the purpose of a reverse-current cutout relay?
a. It eliminates the possibility of reversed polarity of the generator output current.
b. It prevents fluctuations of generator voltage.
c. It opens the main generator circuit whenever the generator voltage drops below the battery voltage.

19. Generator voltage will not build up when the field is flashed and solder is found on the brush cover plate. These are most likely indications of
a. an open armature.
b. excessive brush arcing.
c. armature shaft bearings overheating.

20. Why is it unnecessary to flash the field of the exciter on a brushless alternator?
a. The exciter is constantly charged by battery voltage.
b. Brushless alternators do not have exciters.
c. Permanent magnets are installed in the main field poles.

21. One way that the automatic ignition relight systems are activated on gas turbine engines is by a
a. drop in compressor discharge pressure.
b. sensing switch located in the tailpipe.
c. drop in fuel flow.

22. How are the rotor windings of an aircraft alternator usually excited?
a. By a constant ac voltage from the battery.
b. By a constant ac voltage.
c. By a variable direct current.

23. What precaution is usually taken to prevent electrolyte from freezing in a lead acid battery?
a. Place the aircraft in a hangar.
b. Remove the battery and keep it under constant charge.
c. Keep the battery fully charged.

24. What is the ampere-hour rating of a storage battery that is designed to deliver 45 amperes for 2.5 hours?
a. 1 12.5 ampere-hour.
b. 90.0 ampere-hour.
c. 45.0 ampere-hour.

25. How many hours will a 140 ampere-hour battery deliver 15 amperes?
a. 1.40 hours.
b. 9.33 hours.
c. 14.0 hours.

26. What is a basic advantage of using ac for electrical power for a large aircraft?

a. AC systems operate at higher voltage than dc systems and therefore use less current and can use smaller and lighter weight wiring.
b. AC systems operate at lower voltage than dc systems and therefore use less current and can use smaller and lighter weight wiring.
c. AC systems operate at higher voltage than dc systems and therefore use more current and can use smaller and lighter weight wiring.

27. What are two types of ac motors that are used to produce a relatively high torque?
a. Shaded pole and shunt field.
b. Shunt field and single phase.
c. Three-phase induction and capacitor start.

28. (1) Alternators are rated in volt-amps, which is a measure of the apparent power being produced by the generator.
(2) Alternating current has the advantage over direct current in that its voltage and current can easily be stepped up or down.

Regarding the above statements,
a. only No. 1 is true.
b. only No. 2 is true.
c. both No. 1 and No. 2 are true.

29. What is the frequency of most aircraft alternating current?
a. 115 Hertz.
b. 60 Hertz.
c. 400 Hertz.

30. The reason for flashing the field in a generator is to
a. restore correct polarity and/or residual magnetism to the field poles.
b. increase generator capacity.
c. remove excessive deposits.

31. The part of a dc alternator power system that prevents reverse flow of current from the battery to the alternator is the
a. reverse current relay.
b. voltage regulator.
c. rectifier.

32. The generating system of an aircraft charges the battery by using
a. constant current and varying voltage.
b. constant voltage and varying current.
c. constant voltage and constant current.

33. The constant current method of charging a ni-cad battery
a. will bring it up to fully charged in the shortest amount of time.
b. will lead to cell imbalance over a period of time.
c. is the method most effective in maintaining cell balance.

34. (Refer to figure 1) The following data concerning the installation of an electrical unit is known: current requirements for continuous operation - 11 amperes; measured cable length - 45 feet; system voltage – 28 volts (do not exceed 1 volt drop); cable in conduit and bundles. What is the minimum size copper electrical cable that may be selected?
a. No 10.
b. No 12.
c. No 14.

Figure 1. Electric Wire Chart

35. Which of the following aircraft circuits does NOT contain a fuse/circuit breaker?
a. Generator circuit.
b. Air-conditioning circuit.
c. Starter circuit.

36. The maximum number of terminals that may be connected to any one terminal stud in an aircraft electrical system is
a. two.
b. three.
c. four.

37. What is the maximum number of bonding jumper wires that may be attached to one terminal grounded to a flat surface?
a. Two.
b. Three.
c. Four.

38. As a general rule, starter brushes are replaced when they are approximately
a. one-half their original length.
b. one-third their original length.
c. two-thirds their original length.

39. When installing an electrical switch, under which of the following conditions should the switch be derated from its nominal current rating?
a. Conductive circuits.
b. Capacitive circuits.
c. Direct-current motor circuits.

40. The resistance of the current return path through the aircraft is always considered negligible, provided the
a. voltage drop across the circuit is checked.
b. generator is properly grounded.
c. structure is adequately bonded.

41. In order to reduce the possibility of ground shorting the circuits when the connectors are separated for maintenance, the AN and MS electrical connectors should be installed with the
a. socket section on the ground side of the electrical circuit.
b. pin section on the ground side of the electrical circuit.
c. pin section on the positive side of the electrical circuit.

42. When does current flow through the coil of a solenoid operated electrical switch?
a. Continually, as long as the aircraft's electrical system master switch is on.
b. Continually, as long as the control circuit is complete.
c. Only until the movable points contact the stationary points.

43. It is necessary to determine that the electrical load limit of a 28-volt, 75-amp generator, installed in a particular aircraft, has not been exceeded. By making a ground check, it is determined that the battery furnished 57 amperes to the system when all equipment that can continuously draw electrical power in flight is turned on. This type of load determination
a. can be made, but the load will exceed the generator load limit.
b. can be made, and the load will be within the generator load limit.
c. cannot be made on direct current electrical systems.

44. What type of lubricant may be used to aid in pulling electrical wires or cables through conduits?
a. Silicone grease.
b. Soapstone talc.
c. Rubber lubricant.

45. Which of the following is regulated in a generator to control its voltage output?
a. Speed of the armature.
b. Number of windings in the armature.
c. The strength of the field.

46. Bonding jumpers should be designed and installed in such a manner that they
a. are not subjected to flexing by relative motion of airframe or engine components.
b. provide a low electrical resistance in the ground circuit.
c. prevent buildup of a static electrical charge between the airframe and the surrounding atmosphere.

47. When the starter switch to the aircraft gas turbine engine starter-generator is energized and the engine fails to rotate, one of the probable causes would be the
a. power lever switch is defective.
b. undercurrent solenoid contacts are defective.
c. starter solenoid is defective.

48. Arcing at the brushes and burning of the commutator of a motor may be caused by
a. weak brush springs.
b. excessive brush spring tension.
c. low mica.

49. The maximum allowable voltage drop between the generator and the bus bar is
a. 1 percent of the regulated voltage.
b. 2 percent of the regulated voltage.
c. less than the voltage drop permitted between the battery and the bus bar.

50. ON-OFF two position engine electrical switches should be installed
a. so that the toggle will move in the same direction as the desired motion of the unit controlled.
b. under a guard.
c. so the ON position is reached by a forward or upward motion.

51. When selecting an electrical switch for installation in an aircraft circuit utilizing a direct current motor,
a. a switch designed for dc should be chosen.
b. a derating factor should be applied.
c. only switches with screw-type terminal connections should be used.

52. When installing electrical wiring parallel to a fuel line, the wiring should be
a. in metal conduit.
b. in a non-conductive fire-resistant sleeve.
c. above the fuel line.

53. (Refer to figure 2) In a 28-volt system, what is the maximum continuous current that can be carried by a single No. 10 copper wire 25 feet long, routed in free air?
a. 20 amperes.
b. 35 amperes.
c. 28 amperes.

Figure 2. Electric Wire Chart

54. What speed must an eight-pole ac generator turn to The frequency of AC produced by an AC generator is produce 400-Hertz ac?
a. 400 RPM.
b. 1,200 RPM.
c. 6000 RPM.

55. How many basic types of circuit breakers are used in powerplant installation electrical systems?
a. Two.
b. Three.
c. Four.

56. Which Federal Aviation Regulation specifies that each resettable circuit protective device requires a manual operation to restore service after the device has interrupted the circuit?
a. 14 CFR Part 23.
b. 14 CFR Part 43.
c. 14 CFR Part 91.

57. Which Federal Aviation Regulation requirement prevents the use of automatic reset circuit breakers?
a. 14 CFR Part 21.
b. 14 CFR Part 23.
c. 14 CFR Part 91.

58. The time/current capacities of a circuit breaker or fuse must be
a. above those of the associated conductor.
b. equal to those of the associated conductor.
c. below those of the associated conductor.

59. (1) Most modem aircraft use circuit breakers rather than fuses to protect their electrical circuits.
(2) Federal Aviation Regulations Part 23 requires that all electrical circuits incorporate some form of circuit protective device.

Regarding the above statements,
a. only No. 1 is true.
b. only No. 2 is true.
c. both No. 1 and No. 2 are true.

60. Electrical switches are rated according to the
a. voltage and the current they can control.
b. resistance rating of the switch and the wiring.
c. resistance and the temperature rating.

61. Electrical circuit protection devices are installed primarily to protect the
a. switches.
b. units.
c. wiring.

62. (1) Electrical circuit protection devices are rated based on the amount of current that can be carried without overheating the wiring insulation.
(2) A "trip-free" circuit breaker makes it impossible to manually hold the circuit closed when excessive current is flowing.

Regarding the above statements,
a. only No. 1 is true.
b. only No. 2 is true.
c. both No. 1 and No. 2 are true.

63. Which of the following Federal Aviation Regulations require that all aircraft using fuses as the circuit protective devices carry "one spare set of fuses, or three spare fuses of each kind required"?
a. FAR Part 23.
b. FAR Part 43.
c. FAR Part 91.

64. What is the smallest terminal stud allowed for aircraft electrical power systems?
a. No.6.
b. No.8.
c. No. 10.

65. A typical barrier type aircraft terminal strip is made of
a. paper-base phenolic compound.
b. polyester resin and graphite compound.
c. layered aluminum impregnated with compound.

66. A term commonly used when two or more electrical terminals are installed on a single lug of a terminal strip is
a. strapping.
b. stepping.
c. stacking.

67. (I) Electrical wires larger than 10 gauge use uninsulated terminals.
(2) Electrical wires smaller than 10 gauge use uninsulated terminals.

Regarding the above statements,
a. only No. 1 is true.
b. only No. 2 is true.
c. neither No. 1 nor No. 2 is true.

68. Aircraft electrical wire size is measured according to the
a. Military Specification system.
b. American Wire Gauge system.
c. Technical Standard Order system.

69. Aircraft copper electrical wire is coated with tin, silver, or nickel in order to
a. improve conductivity.
b. add strength.
c. prevent oxidization.

Powerplant Electrical Systems
Lacing and Tying Wire Bundles
Cutting & stripping Wire and Cable
Emergency Splicing Repairs
Connecting Terminal Lugs to Terminal Blocks
Bonding and Grounding
Connectors and Conduit
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