Engine Electrical Systems

Question 1

Why is stranded wire used rather than solid wire in most power plant electrical systems?

Answer 1

Solid wire is likely to break when it is subjected to vibration.

Question 2

What two things must be considered in selection of wire size when making an electrical installation in an aircraft?

Answer 2

The current-carrying capability of the wire and the amount of voltage drop that is caused by current flowing through the wire.

Question 3

Why are the wires in certain electrical installations twisted together?

Answer 3

By twisting the wires together, the magnetic fields caused by current flowing in the wires are minimized.

Question 4

What is used to protect a wire bundle from chafing where it passes through a hole in a bulkhead or frame?

Answer 4

A grommet around the edges of the hole.

Question 5

How are electrical wires protected where they pass through an area of high temperature?

Answer 5

Wires passing through these areas are insulated with high temperature insulation, and the wires are enclosed in some type of protective conduit.

Question 6

What is the minimum separation that is allowed between a wire bundle and a fluid line that carries combustible fluid or oxygen?

Answer 6

A minimum of six inches.

Question 7

What is the significance of the color of the solderless connectors that are used on electrical wires?

Answer 7

The color of the insulation indicates the size of wire the connector will fit. Red terminals fit 22- through 18-gage wire, blue terminals fit 16- and 14-gage wire, and yellow terminals fit 12- and 10-gage wire.

Question 8

What is the maximum number of wire terminals that may be stacked on a single stud in a terminal strip?

Answer 8

Four.

Question 9

What is the purpose of the shielding that is used to encase some electrical wires?

Answer 9

Shielding intercepts radiated electromagnetic energy and carries it to ground so it will not interfere with any nearby sensitive electronic equipment.

Question 10

Why must a switch be derated if it is used in a circuit controlling a DC electric motor?

Answer 10

The initial current flowing into a DC electric motor is much higher than the current the motor uses after the armature begins to rotate. Because of this high inrush current, the controlling switches must be derated.

Question 11

What is used as the rectifier to produce direct current in a DC generator?

Answer 11

Brushes and a commutator.

Question 12

How does a vibrator-type voltage regulator control the output voltage of a DC generator?

Answer 12

The strength of the magnetic field produced in the voltage regulator relay is proportional to the generator output voltage. When the voltage rises above the regulated value, the relay pulls the contacts open and inserts a resistor in the generator field circuit.
The contacts vibrate open and closed, putting the resistor in and out of the field circuit to control the amount of voltage the generator produces.

Question 13

What is meant by paralleling the generators of a twin-engine aircraft?

Answer 13

Adjusting the voltage of the generators so they will share the electrical load equally.

Question 14

What is meant by flashing the field of a DC generator?

Answer 14

Restoring the residual magnetism to the frame of a generator by passing battery current through the field coils in the same direction it flows when the generator is producing current.

Question 15

What kind of rectifier is used in a DC alternator of the type that is used on most of the modern light airplanes?

Answer 15

A full-wave, three-phase rectifier made up of six sill-con diodes.

Question 16

What is used to maintain a constant frequency of the alternating current that is produced by an AC alternator driven by an aircraft turbine engine?

Answer 16

A hydraulic constant-speed drive unit between the engine and the alternator.

Question 17

What three things must be synchronized before a three-phase AC generator can be connected to a bus that is being served by another generator?

Answer 17

The voltage, frequency, and phase rotation of the generators.

Question 18

What must be done to reverse the direction of rotation of the armature of a DC electric motor?

Answer 18

The current flow must be reversed through the armature or the field windings, but not through both of them.

Question 19

Does a series-wound DC motor have a high or a low starting torque?

Answer 19

A high starting torque.

Question 20

Which aircraft electrical circuit does not normally contain a fuse or circuit breaker?

Answer 20

The starter motor circuit.

Question 21

When removing a battery from an aircraft, which connection should be removed first?

Answer 21

The ground connection must be disconnected first and connected last.

Question 22

What is meant by the effective voltage of sine wave alternating current?

Answer 22

The value of the alternating current that is needed to produce the same amount of heat as this value of direct current.

Question 23

What is a starter-generator that is used with many of the smaller gas turbine engines?

Answer 23

A single-engine-mounted component that serves as a starter for starting the turbine engine. When the engine is running, the circuitry can be shifted so it acts as a compound-wound generator.

Question 24

When should aircraft wiring be installed in a conduit?

Answer 24

When the wiring passes through an area in the aircraft where open wiring could likely be damaged, such as through a wheel well.