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General A&P Oral > Aircraft Electrical Systems > Flashcards

Aircraft Electrical Systems Flashcards

1
Q

What size generator must be used in an aircraft electrical system if the connected electrical load is 30 amps, and there is now way of monitoring the generator output?

A

When monitoring is not practical, the total continuously connected electrical load must be no more that 80% of the rated generator output. This would require a generator with a rating of 37.5 amps. Practically, a 40-amp generator would be installed.

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2
Q

What is meant by “flashing” the field of a generator?

A

Restoring the residual magnetism to the frame of the generator. This is done by passing battery current through the field coils in the direction it normally flows when the generator is operating.

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3
Q

What is meant by paralleling the generators in a multi-engine aircraft?

A

Adjusting the voltage regulators so all the generators share the electrical load equally.

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4
Q

What are three types of voltage regulators ued with aircraft generators?

A

Vibrator-type, carbon-pile type, and solid state-type.

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5
Q

How many electrical phases are in an aircraft alternators?

A

Three

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6
Q

What is the advantage of using AC power over DC power?

A

AC voltages can be stepped up to higher voltages, which means that current goes down and smaller wires can be used to save weight. The voltage is stepped back down at the point of use.

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7
Q

What is the frequency of AC voltage used in aircraft?

A

400 Hz.

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8
Q

What is a starter-generator?

A

A starter-generator is a generator and a starter combined into a single unit.

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9
Q

How many sets of field windings are contained in a starter-generator?

A

There are two sets of field windings. One field is used to start the engine and one is used for the generation of electrical power.

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10
Q

How does a constant speed drive (CSD) unit maintain a constant output frequency of the AC generator?

A

By maintaining a constant speed of the generator as the engine speed varies.

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11
Q

What is an integrated drive generator (IDG)?

A

When a constant speed drive (CSD_ is combined within the alternator housing, the assembly is known as an IDG.

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12
Q

What is meant a trip-free circuit breaker?

A

A circuit breaker than cannot be closed while a fault exists, regardless of the position of the operating handle.

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13
Q

What is meant by a slow-blow fuse?

A

A fuse that will allow more current than its rating to flow for a short period of time, be will open the circuit if more than its rated current continues to flow.

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14
Q

What is the function of a fuse or circuit breaker in an aircraft electrical circuit?

A

It protects the wiring from an excess of current. It will open the circuit if enough current flows to heat the wire.

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15
Q

What are two principles upon which circuit breakers operate?

A

Magnetic circuit breakers open a circuit when the current creates a strong enough magnetic field. Thermal circuit breakers open a circuit when the current causes enough heat.

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16
Q

What circuit in an aircraft electrical system is not required to have a circuit protective device?

A

The main circuit for starter motors, used during starting only.

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17
Q

Is an automatic-reset circuit breaker approved for aircraft electrical circuits?

A

No a manual operation is needed to restore service after the circuit breaker has tripped.

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18
Q

How does a vibrator-type voltage regulator maintain a constant voltage?

A

When the voltage rises above the desired value, an electromagnetic relay opens and inserts a resistor in the generator field current and lowering the generator output voltage.

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19
Q

What two components are normally housed with a vibrator voltage regulator in a single-unit generator control

A

A current limiter and a reverse-current cutout relay?

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20
Q

What are the two types of inverters found in aircraft?

A

Rotary inverters and static inverters.

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21
Q

Wat is the purpose of an inverter?

A

To convert DC electricity into AC electricity.

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22
Q

How does a rotary inverter create AC voltage?

A

By using a DC motor to spin an AC generator?

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23
Q

Where could you find the part number of a switch in an aircraft electrical system?

A

In the equipment table or bill of materials on the electrical circuit diagram for the aircraft.

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24
Q

What is the main disadvantage of aluminum wire over copper wire for use in an aircraft electrical system?

A

Aluminum wire is more brittle that copper. It is more subject to breakage when it is nicked or when it is subjected to vibration.

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25
Q

What size aluminum wire would be proper to replace a piece of four-gauge copper?

A

Two-gauge. When you substitute aluminum wire for copper wire, use a wire that is two gauge numbers larger.

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26
Q

What is the smallest size aluminum wire that is approved for use in an aircraft electrical system?

A

Six-gauge.

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27
Q

Can you substitute aluminum wire for copper wire?

A

Yes. However, you must use aluminum wire two wire gauge sizes larger to carry the same current. Aluminum wire should never be used runs of three feet or less, or in communication and navigation systems.

28
Q

Can wire in free air carry the same current as wire in a bundle?

A

Wire in free air may be used to a higher current level than the same size wire in a bundle. Always refer to an electrical wire size selection chart.

29
Q

What are common causes of wire failure in a crimped connector?

A

The wire was not inserted far enough into the connector and/or the connector was excessively crimped.

30
Q

What is one of the first things to check if an electrical component does not operate?

A

Always start with simple solutions and move to more complex, is the component turned on? Is power available? For example, if a light doesn’t function is the system turned on, is the aircraft electrical system energized, or is the bulb burnt out?

31
Q

What may be provided by the manufacturer to assist in trouble shooting?

A

Manufacturers often provide a trouble shooting logic chart.

32
Q

What are the four basic steps of trouble shooting?

A

Know how the system should operate, Observe the way the system is operating. Divide the system into smaller segments to isolate trouble. Look for the obvious problem first.

33
Q

When routing a fluid line parallel to an electrical wire bundle, which should be on top?

A

The electrical wire bundle should be on top.

34
Q

Why must a switch be derated if it used in a circuit that supplies incandescent lamps?

A

The high-inrush current caused by the low resistance of the cold filaments requires that the switched be derated.

35
Q

What is the purpose of aircraft wire shielding?

A

To eliminate electromagnetic interference by applying a metallic covering to the wire.

36
Q

In aircraft that are of aluminum construction, what is one of the primary design elements for lightning protection?

A

The use of bonding or grounding straps between all major components and flight controls on the airplane.

37
Q

How are composite aircraft protected from the damage of lightning strikes?

A

By using a conductive copper for aluminum mesh in the outer layers of the composite structure.

38
Q

What is the purpose of grounding straps on an instrument panel?

A

To ensure electrical continuity from the panel to the airframe for proper system operation and to reduce the potential for EMI.

39
Q

What are the colors and positions of aircraft position lights?

A

Left-Red
Right-Green
Aft-White

40
Q

What is the purpose of wing inspection lights?

A

To permit visual detection of ice formation on wing leading edges while flying at night.

41
Q

What two things must you take into consideration when selecting the wire size to use in an aircraft electrical system installation?

A

The current carrying capability of the wire and the voltage drop caused by the current flowing through the wire.

42
Q

What is the maximum number of wires that should be connected to any single stud in a terminal strip?

A

Four.

43
Q

How is a wire bundle protected from chafing where the bundle goes through a hole in a fuselage frame or bulkhead?

A

The edges of the hole are covered with a flexible grommet, and the bundle is secured to the structure with a cushioned clamp.

44
Q

What kind of clamp is used to secure a wire bundle to the aircraft structure?

A

A cushioned clamp.

45
Q

What is the composition of 60/40 solder?

A

60%tin and 40%lead.

46
Q

What is the difference between soldering and brazing?

A

Soldering is a method of joining metal parts with a molten nonferrous alloy that melts at a temperature below 800°F. Brazing is essentially the same except the brazing alloy melts at a temperature higher than 800 but lower than the melting temperature of the metal on which it is used.

47
Q

Why must acid-core solder never be used on electrical wire?

A

The acid causes the wire to corrode.

48
Q

What determines the strength of a soldered joint?

A

The mechanical connection of the joint, not the solder.

49
Q

Why are solderless splices usually better than soldered splices in the wring of an aircraft electrical system?

A

Soldered joints are usually stiff, and vibration can harden the wire and cause it to break. Solderless splices are designed to keep the joint flexible so vibration cannot cause the wire to break.

50
Q

What is a SPDT switch?

A

A single-pole, double-throw switch.

51
Q

If no specific instructions are available, which way should the operating handle of a n electrical switch move to turn a component on?

A

Forward or upward.

52
Q

What color insulator on a preinsulated solderless connector indicates that the connector is proper for a 10-gauge?

A

Yellow.

53
Q

How many splices are allowed in a single wire run?

A

One.

54
Q

When checking an electrical circuit for proper operation, what are the most efficient measurements (voltage, current, or resistance)?

A

Voltage measurements are usually the quickest way to verify the completeness of the circuit by measuring the voltage at various points through the circuit.

55
Q

What does the specific gravity of the electrolyte of a lead-acid aircraft battery indicate?

A

The amount of acid relative to the water in the electrolyte. This is an indication of the state of charge of the battery.

56
Q

What are the most likely causes of a battery with a distorted or swollen battery case?

A

The battery has been overcharged or over-discharged, causing overheating, or it could be caused by a plugged vent cap.

57
Q

On Ni-Cad batteries, what is the minimum cell voltage at the end of the charge?

A

1.55 volts.

58
Q

How is the state of charged determined on a Ni-Cad battery?

A

The only accurate way to determine the state of charge on a Ni-Cad battery is by a measured discharge with a Ni-cad battery charger and following the manufacturer’s instructions.

59
Q

What are the risks associated with testing and troubleshooting electrical systems or components?

A

Incorrect procedures during testing and troubleshooting can lead to damage of components and systems, or even personal injury. Always follow the manufacturer’s procedures for testing and troubleshooting.

60
Q

What are the risks associated with connecting or disconnecting external power?

A

There is a risk that system switches or controls have been moved while the power is off. Connecting power could cause the systems to move. Before connecting power, confirm the position of landing gear controls and flap position levers.

61
Q

What care should be taken when working on energized circuits or systems?

A

An energized system may begin to operate or move unexpectedly while working on the system. Follow the maintenance manual procedures for adjusting or servicing energized circuits and systems.

62
Q

What risks are associated with performing maintenance in areas containing wires and wire bundles?

A

If the bundles are exposed, it may be easy to inadvertently catch on a wire or bundle with a tool or support equipment, such as step ladders. Take care to avoid and protect wires and wire bundles when working in these areas.

63
Q

What risk are associated with routing and securing wires and wire bundles?

A

Misrouted wires can interfere with other systems or become damaged by surrounding structure and components. To mitigate these risks, route wires and wire bundles with sufficient clearance from any moving components and any structure where chafing could occur. Use proper standoffs and cushioned clamps to maintain clearance and chafe protection.

64
Q

What are the risks of using the incorrect wire size in a circuit?

A

A wire size that is too small will not be able to handle the current and may melt or catch fire. Correct usage of wire sizing charts is critical when determining wire sizes.

65
Q

When replacing a wire terminal, why is it important to select the correct size and follow proper installation procedures?

A

Incorrect terminals or poor installation can cause the connection to fail. Always follow terminal size and installation procedures, including the use of approved or recommended tools for the installation.

66
Q

What are the risk associated with soldering wire connections?

A

Soldered connections are stiff and can become brittle, causing premature failure. When required, soldered connections must be done correctly and supported to prevent movement of the wires.

67
Q

What are the risk associated with incorrect soldering practices?

A

A cold solder joint will result in poor connection and early failure. Excessive heat during soldering can damage other wires and components. Excessive solder can cause bridging to other wires or terminals or too much solder in the wire is prone to becoming brittle. Follow professional soldering practices to prevent premature failure of the solder connection.

General A&P Oral (28 decks)

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