Questions - 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.

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