Questions - Aircraft Electrical System

Study Aid Questions

Fill in the Blanks

1. Ohm’s Law describes the basic ___________________ relationships of ____________________.

2. Materials with a resistance to current flow halfway between the best conductor and the best insulators are called ____________________. Their application is in the field of ___________________.

3. Almost all mechanical devices, such as _______________________ and ______________________, use electromagnetic induction to produce electrical power.

4. According to Fleming’s left hand rule the thumb represents _______________________, the index finger represents _______________________, and the middle finger denotes _________________.

5. DC systems that require AC current use a(n) _____________________ to make the switch from 24‐volt DC to 400 _________________________ current in order to operate specialty equipment.

6. _____________________ reactance and ______________________ reactance oppose current flow in AC circuits. They may also create a ________________ shift between voltage and current.

7. Capacitance of parallel plates is ___________________ proportional to the distance between the plates. Therefore, if the distance doubles the capacitance is ________________ by __________________.

8. In an AC circuit where there is no inductance or capacitance, _____________________ is equal to the _____________________ of the circuit.

9. Two main types of batteries include _________________ and ___________________. They are identified by the material used for the ____________________.

10. The emergency rate is the total ___________________load required to support the essential bus for ________________________ minutes.

11. Unlike lead‐acid batteries, the state of charge of a Ni‐Cad battery cannot be determined by measuring the specific gravity of the ____________________________ electrolyte. State of charge is found by measuring the _________________________ with a Ni‐Cad battery charger and following the ______________________________.

12. In a series wound DC generator, when load increases, the voltage ________________________. This is because the greater the current through the field coils to the external circuit, the ____________________ the induced EMF and the _________________________ the output voltage.

13. DC generator control systems are often referred to as voltage regulators or ______________________ They are designed to keep the generator ____________________ within limits for all flight condition.

14. DC alternators contain two major components including the ____________________ winding and the _____________________ winding. Using the process of ____________________ induction, voltage is produced and fed to the aircraft electrical ________________________ and current is produced to power any electrical _______________________.

15. A solid state regulator monitors DC alternator output ____________________ and controls alternator ___________________________ current.

16. Inverters are __________________ devices that convert DC power to __________________.DC power feeds power to an AC distribution ___________________ that can be either 26 or 115 volts.

17. Constant speed drives can either be an independent unit or mounted within the _________________. A dual CSD and alternator is known as a(n) ________________________.

18. AC alternator controls that measure the integrity of the electrical system include the _________________ (BPCU) and the __________________________ (GCU).

19. A warning horn, with the gear switch in the up position, sounds when the _____________________ is reduced past a certain threshold and when the gear squat switch is ________________________.

20. Due to inflight vibration and _________________, conductor wire should be _______________ to minimize fatigue breakage.

21. Insulation resistance can be measured with a _____________________ or insulation tester, although it may not give a true picture of the _________________ of the insulation.

22. The amount of current ___________________ is a function of the number of wires in the bundle and the _________________ of the total wire bundle capacity that is being used.

23. Circuit resistance can be determined by checking the ______________________ across the circuit. As long as this value does not exceed the limit set down by the manufacturer, the resistance value for the circuit is considered ___________________________.

24. There should be no more than ______________ splice(s) in any one wire segment between two connectors. Splices in bundles must be _____________________ as to minimize any increase in bundle size.

25. ________________ are devices that open and close circuits and they consist of one or more pair of contacts. Current is permitted to flow when these contacts ____________________.

Matching Questions

1. Match these diagram types with their descriptions below

a. wiring diagrams   b. block diagrams   c. pictorial diagrams   d. schematic diagrams{codeBox}

____  1. Picture of the components used instead of conventional electrical symbols
____  2. Indicates the location of components with respect to each other
____  3. Consists of blocks that represent several components
____  4. Illustrates principle of operation
____  5. Identifies each component within a system by its part and serial number
____  6. Aid in troubleshooting complex electrical systems

2. Match these switch types with their descriptions below.

a. switches   b. electromagnetic switches   c. current limiters{codeBox}

                1. Double‐pole single‐throw
                2. Relay

                3. Solenoid

                4. Fuse

                5. Toggle and rocker

                6. Circuit breaker

3 ‐ Match these switch types with the description or diagram below.

a. SPST   b. DPST   c. SPDT   d. DPDT{codeBox}

____  1. Switch is on in both positions
____  2. Activates two separate circuits at the same time
____  3. Switch routes current through either of the two paths
____  4. Turns two circuits ON & OFF with one lever
____  5. Open and closes a single circuit
____  6. May have a center “OFF” position





4 ‐ Match these aircraft lighting types with the descriptions below.

a. anti‐collision lights   b. position lights   c. landing and taxi lights   d. wing   e. inspection lights{codeBox}

____  1. Lights positioned in recessed areas of the wing designed to illuminate the ground
____  2. Rotating beam lights installed on the top of the fuselage or tail
____  3. Consists of one red, one green, and one white light
____  4. Lights that illuminate the leading edge of the wings
____  5. Has a white light located on the vertical stabilizer
____  6. Considered a safety light
____  7. Very powerful light directed by a parabolic reflector

5 ‐ Match these functions with their descriptions below..

a. Voltage Regulation   b. Overvoltage Protection   c. Parallel Gen. Operations   d. Over‐excitation Protection   e. Differential Voltage  f. Reverse Current Sensing{codeBox}

____  1. Ensures all generator voltage values are w/in a close tolerance before load is brought online
____  2. Adjusts the voltage regulation circuit to ensure all generators operate w/in limits
____  3. Adjusts field current to control generator output
____  4. Disconnects a generator from a bus in the event it becomes inoperative
____  5. Controls a generator that is out of limits due to a paralleled system failure
____  6. Opens the relay that controls the field excitation current

6 ‐ Place the order of sequence of these events from start to finish. (from a – f)

____  1. pilot exciter field creates a magnetic field and induces power in the pilot exciter field
____  2. via EMF, main alternator field generates power in the main armature
____  3. output of exciter armature is rectified
____  4. ACU receives power output from 1 of the armatures and sends it to the exciter field
____  5. output of main AC armature is 3 phase AC
____  6. exciter permanent magnet and armature start process

Knowledge Application Questions

1. A circuit with a 10Ω lamp and a 24 V DC battery has a current of how many amps?

2. What is the resistance of a lamp in a circuit with a 12 V DC battery and a current value of 3 amps?

3. What is the system voltage of a circuit with a resistance of 3.5Ω and a total current of 6.85A?

4. What is the effective value of the voltage if the peak value is 24V?

5. What is the peak value of the voltage if the effective voltage is 112V?

6. Referring to the diagram below; in an AC circuit with an inductance value of .175 Henrys and voltage of 110V at 60 cycles per second, what is the inductive reactance?


7. Referring to the diagram below, what is the impedance of the following circuit?


8. Referring to the diagram below and the relationship between impedance, resistance, and reactance, find the total impedance of the following circuit.


9. Referring to the diagram below; find the total impedance of the following circuit.


10. What is the equation for true power? ______________________________________

11. What is the unit for T.P.? _______________________________________________

12. Referring to the diagram below, what is the total impedance of the following parallel AC circuit?


13. What is the equation for apparent power? __________________________________

14. What is the unit for A.P.? _______________________________________________

15. Referring to the circuit diagram below, find TP, AP, and PF. (RT=5.6Ω )


16. Using below chart ‐ fig. 1; determine the wire size for the following conditions:
‐voltage source 115 volt, continuous operation
‐wire run of 160ft
‐10A load capacity

Figure 1 Conductor Chart – continuous flow

17. Using above chart ‐ fig. 1; determine the wire size considering the following:
‐voltage source 14V, continuous operation
‐wire run length of 7ft
‐7A load capacity

18. Using the below chart – fig. 2; determine the wire size considering the following:
‐Voltage 28V, intermittent flow ‐conduit
‐wire run of 24’ ‐10A load

Figure 2 Conductor Chart – intermittent flow

19. Using below chart ‐ fig. 3; What is the free air rating of a size 18 wire at an ambient temperature of 70°C and rated at 195°C?
195‐70=125, wire size 18

Figure 3 single copper wire in free air

20. Using above chart ‐ fig. 3; What is the free air rating of a #22 wire at an ambient temperature of 40°C and rated at 200°C?
200‐40=160, wire size 22

Multiple Choices Questions

1. Some electric motors have two sets of field windings wound in opposite directions so that the
a. speed of the motor can be more closely controlled.
b. motor can be operated in either direction.
c. power output of the motor can be more closely controlled.

2. One purpose of a growler test is to determine the presence of
a. an out of round commutator.
b. a broken field lead.
c. a shorted armature.

3. Electric wire terminals for most aircraft applications must be what type?
a. Ring.
b. Hook.
c. Slotted.

4. What is the principal advantage of the series wound dc motor?
a. Suitable for constant speed use.
b. High starting torque.
c. Low starting torque.

5. If a generator is equipped with a vibrator type voltage regulator, the actual time the voltage regulator points remain open
a. is controlled by the reverse current cutout relay point clearance.
b. depends on the load carried by the generator.
c. is increased when the external load is greater than the generator output.

6. What is a cause of generator brush arcing?
a. Low spring tension.
b. Carbon dust particles.
c. Seating brushes with No. 000 sandpaper.

7. When ac generators are operated in parallel, the
a. amperes and voltage must both be equal.
b. amperes and frequency must both be equal.
c. frequency and voltage must both be equal.

8. The starting current of a series wound dc motor, in passing through both the field and armature windings, produces a
a. low starting torque.
b. speed slightly higher when unloaded.
c. high starting torque.

9. Which motor would be most likely to have an armature brake?
a. Inverter drive motor.
b. Starter motor.
c. Landing light retraction motor.

10. The method most often used in overcoming the effect of armature reaction is through the use of
a. drum wound armatures in combination with a negatively connected series field.
b. interpoles.
c. shaded poles.

11. The only practical method of maintaining a constant voltage output from an aircraft generator under varying conditions of speed and load is to vary the
a. strength of the magnetic field.
b. number of conductors in the armature.
c. speed at which the armature rotates.

12. The pole pieces or shoes used in a dc generator are a part of the
a. armature assembly.
b. field assembly.
c. brush assembly.

13. How many cycles of ac voltage are produced in a six pole alternator of the revolving field type for each revolution of the rotor?
a. Six.
b. Four.
c. Three.

14. If the reverse current cutout relay contact points fail to open after the generator output has dropped below battery potential, current will flow through the generator armature
a. opposite the normal direction and through the shunt field in the normal direction.
b. in the normal direction and through the shunt field opposite the normal direction.
c. and the shunt field opposite the normal direction.

15. How does the magnetic brake used to stop rotation of an electric motor armature operate?
a. A friction brake is applied by a spring and released by a magnet.
b. A friction brake is applied by a magnet and released by a spring.
c. Centrifugal force releases a rotating brake cog from a stationary notch when the armature reaches a certain speed and magnetic force re engages the cog when the electrical power is turned off.

16. In a generator, what eliminates any possible sparking to the brush guides caused by the movement of the brushes within the holder?
a. Brush spring tension.
b. The brush pigtail.
c. Undercutting the mica on the commutator.

17. A series wound dc electric motor will normally require
a. more current at high RPM than at low RPM.
b. approximately the same current throughout its operating range of speed.
c. more current at low RPM than at high RPM.

18. The type of electric wire terminals used for most aircraft applications, in addition to providing good current carrying capabilities, are designed primarily
a. to prevent circuit failure due to terminal disconnection.
b. for permanent connection to the circuit.
c. for uncomplicated and rapid circuit connection and disconnection.

19. Aluminum wire must be stripped very carefully because
a. high resistance will develop in stripping nicks.
b. stripping nicks can cause short circuits.
c. individual strands will break easily after being nicked.

20. The commutator of a generator
a. changes direct current produced in the armature into alternating current as it is taken from the armature.
b. changes alternating current produced in the armature into direct current as it is taken from the armature.
c. reverses the current in the field coils at the proper time in order to produce direct current.

21. An ammeter in a battery charging system is for the purpose of indicating the
a. rate of current used to charge the battery.
b. amperage available for use.
c. total amperes being used in the airplane.

22. Which of the following is not one of the purposes of interpoles in a generator?
a. Reduce arcing at the brushes.
b. Reduce field strength.
c. Overcome armature reaction.

23. To test generator or motor armature windings for opens,
a. check adjacent segments on commutator with an ohmmeter on the high resistance scale.
b. use a 12/24V test light between the armature core segments and the shaft.
c. place armature in a growler and connect a 110V test light on adjacent segments; light should light.

24. What is the color and orientation of the position lights for navigation on civil airplanes?
a. Left side - white, right side - green, rear aft - red.
b. Left side - red, right side - green, rear aft - white.
c. Left side - green, right side - red, rear aft - white.

25. To what depth is the mica insulation between the commutator bars of a dc generator undercut?
a. Equal to twice the width of the mica.
b. Equal to the width of the mica.
c. One half the width of the mica.

26. A voltage regulator controls generator output by
a. introducing a resistance in generator-to-battery lead in the event of overload.
b. shorting out field coil in the event of overload.
c. varying current flow to generator field coil.

27. Which type of dc generator is not used as an airplane generator?
a. Compound wound.
b. Externally grounded.
c. Series wound.

28. What is the most accurate type of frequency measuring instrument?
a. Electrodynamometers using electromagnetic fields.
b. Integrated circuit chip having a clock circuit.
c. Electromagnets using one permanent magnet.

29. During ground operation, aircraft generator cooling is usually accomplished by
a. auxiliary air cooled through an air/fuel heat exchanger.
b. an integral fan.
c. an external motor-driven fan.

30. What does a rectifier do?
a. Changes direct current into alternating current.
b. Reduces voltage.
c. Changes alternating current into direct current.

31. What type of instrument is used for measuring very high values of resistance?
a. Shunt type ohmmeter.
b. Multimeter.
c. Megohmmeter.

32. When a diode is checked for an open circuit or a short circuit, it should be
a. checked with a milliamp ammeter.
b. in the circuit.
c. disconnected from the circuit.

33. When handling a high voltage capacitor in an electrical circuit, be sure it
a. is fully discharged before removing it from the circuit.
b. has at least a residual charge before removing it from the circuit.
c. has a full charge before removing it from the circuit.

34. Which of the following is most likely to cause thermal runaway in a nickel-cadmium battery?
a. Constant current charging of the battery to more than 100 percent of its capacity.
b. A high internal resistance condition.
c. Excessive current draw from the battery.

35. How can it be determined if a transformer winding has some of its turns shorted together?
a. The output voltage will be high.
b. The transformer will get hot in normal operation.
c. Measure the input voltage with an ohmmeter.

36. Which of the following are the major parts of a dc motor?
1. Armature assembly.
2. Field assembly.
3. Brush assembly.
4. Commutator.
5. Pole piece.
6. Rheostat.
7. End frame.

a. 2,3,4,5
b. 3,5,6,7
c. 1,2,3,7

37. (1) There are three basic types of dc motors; series, shunt, and compound.
(2) In the series motor, the field windings, consisting of relatively few turns of heavy wire, are connected in series with the armature winding.

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

38. For general electrical use in aircraft, the acceptable method of attaching a terminal to a wire is by
a. crimping.
b. soldering.
c. crimping and soldering

39. Which of the following factors must be taken into consideration when determining the wire size to use for an aircraft installation?
1. Mechanical strength.
2. Allowable power loss.
3. Ease of installation.
4. Resistance of current return path through the aircraft structure.
5. Permissible voltage drop.
6. Current carrying capability of the conductor.
7. Type of load (continuous or intermittent).

a. 1,2,4,5
b. 2,4,6,7
c. 2,5,6,7

40. When selecting hardware for attaching bonding connections to an aircraft structure, which of the following should be considered?
1. Mechanical strength.
2. Allowable power loss.
3. Ease of installation.
4. Permissible voltage drop.
5. Amount of current to be carried.
6. Type of load (continuous or intermittent).

a. 1,3,5
b. 1,2,3
c. 4,5,6

41. How should the splices be arranged if several are to be located in an electrical wire bundle?
a. Enclosed in a conduit.
b. Grouped together to facilitate inspection.
c. Staggered along the length of the bundle.

42. What is the minimum bend radius for an electrical wire bundle?
a. Ten times the outside diameter of the bundle.
b. Fifteen times the outside diameter of the bundle.
c. Five times the outside diameter of the bundle.

43. When approved, splices may be used to repair manufactured harnesses or installed wiring. The maximum number of splices permitted between any two connectors is
a. three.
b. two.
c. one.

44. AN/MS electrical connectors are specifically designed to meet
a. International Civil Aviation Organization (ICAO) standards.
b. Technical Standard Order (TSO) specifications.
c. military specifications.

45. The most common method of attaching a pin or socket to an individual wire in an MS electrical connector is by
a. crimping and soldering.
b. crimping.
c. soldering.

46. The pin section of an AN/MS connector is normally installed on
a. either side of a circuit (makes no difference).
b. the ground side of a circuit.
c. the power supply side of a circuit.

47. The voltage output of an alternator may be regulated by controlling the
a. voltage output of the dc exciter.
b. speed of the alternator.
c. resistance in the rotor windings.

48. If several long lengths of electrical cable are to be installed in rigid conduit, the possibility of damage to the cable as it is pulled through the conduit will be reduced by
a. applying a light coat of dielectric grease.
b. dusting the cable with powdered graphite.
c. dusting the cable with powdered soapstone.

49. Grounding is electrically connecting a conductive object to the primary structure. One purpose of grounding is to
a. prevent development of radio frequency potentials.
b. prevent current return paths.
c. allow static charge accumulation.

50. What is normally used to bond noncontinuous stainless steel aircraft components?
a. Aluminum jumpers.
b. Stainless steel jumpers.
c. Copper jumpers.

51. Aircraft fuse capacity is rated in
a. volts.
b. amperes.
c. ohms.

52. When adding a rheostat to a light circuit to control the light intensity, it should be connected in
a. parallel with the light.
b. series parallel with the light switch.
c. series with the light.

53. Circuits that must be operated only in an emergency or whose inadvertent activation could endanger a system frequently employ
a. guarded switches.
b. push-pull-type circuit breakers only (no switches).
c. spring-loaded to off toggle or rocker switches.

54. If one switch is used to control all navigation lights, the lights are most likely connected
a. parallel to each other and in series with the switch.
b. in series with each other and in series with the switch.
c. in series with each other and parallel to the switch.

55. Oil canning of the sides of aluminum or steel electrical junction boxes is considered to be
a. normal operation in vibration prone areas.
b. acceptable operation.
c. a shorting hazard.

56. Electric wiring installed in aircraft without special enclosing means (open wiring) offers the advantages of ease of installation, simple maintenance, and reduced weight. When bundling open wiring, the bundles should
a. be limited as to the number of cables to minimize damage from a single electrical fault.
b. include at least one shielded cable to provide good bonding of the bundle to the airframe.
c. be limited to a minimum bend radius of five times the bundle diameter to avoid excessive stresses on the cable insulation.

57. During inspection of the terminal strips of an aircraft electrical system, it should be determined that
a. only plain nuts and lockwashers have been used for terminal attachment to the studs.
b. only locknuts have been used for terminal attachment to the studs.
c. the terminal studs are anchored against rotation.

58. What protection to wires and cables does conduit provide when used in aircraft installations?
a. Mechanical.
b. Structural.
c. Electromagnetic.

59. Which of the following should be accomplished in the installation of aircraft wiring?
a. Provide adequate slack in the wire bundle to compensate for large changes in temperature.
b. Locate the bundle above flammable fluid lines and securely clamp to structure.
c. Support the bundle to structure and/ or solid fluid lines to prevent chafing damage.

60. If the (+) terminal of a voltmeter is connected to the (-) terminal of the source voltage and the (-) terminal of the meter is connected to the (+) terminal of the source voltage, the voltmeter will read
a. correctly.
b. low voltage.
c. backwards.

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