Aircraft Electrical Systems

Some electric motors have two sets of field windings wound in opposite directions so that the

motor can be operated in either direction

One purpose of a growler test is to determine the presence of

a shorted armature

What is the principal advantage of the series wound DC motor?

High starting torque

If a generator is equipped with a vibrator-type voltage regulator, the actual time the voltage regulator points remain open

depends on the load carried by the generator

What is a cause of generator brush arcing?

Low spring tension

The starting current of a series-wound DC motor, in passing through both the field and armature windings, produces a

high starting torque

Which motor would be most likely to have an armature brake?

Landing light retraction motor

The method most often used in overcoming the effect of armature reaction is through the use of

interpoles

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

strength of the magnetic field

The pole pieces or shoes used in a DC generator are a part of the

Field assembly

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

opposite the normal direction and through the shunt field in the normal direction

How does the magnetic brake used to stop rotation of an electric motor armature operate?

A friction brake is applied by a spring and released by a magnet

In a generator, what eliminates any possible sparking to the brush guides caused by the movement of the brushes within the holder?

The brush pigtail

A series-wound DC electric motor will normally require

more current at low RPM than at high RPM

The commutator of a generator

changes alternating current produced in the armature into direct current as it is taken from the armature

Which of the following is not one of the purposes of interpoles in a generator?

Reduce field strength

To test generator or motor armature windings for opens,

place armature in a growler and connect a 110V test light on adjacent segments; light should light

To what depth is the mica insulation between the commutator bars of a DC generator undercut?

Equal to the width of the mica

Which type of DC generator is not used as an airplane generator?

Series wound

During ground operation, aircraft generator cooling is usually accomplished by

an integral fan

Which of the following are the major parts of a DC motor?

Armature assembly, field assembly, brush

assembly, and end frame

(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

both 1 and 2 are true

If the positive field lead between a generator and a generator control panel breaks and is shorted while the engine is running, a voltmeter connected to generator out-put would indicate

residual voltage

What is a method used for restoring generator field residual magnetism?

Flash the fields

The inductor-type inverter output voltage is controlled by the

DC stator field current

When DC generators are operated in parallel to supply power for a single load, their controls include an equalizer circuit to assure that all generators share the load equally. The equalizer circuit operates by

increasing the output of the low generator and decreasing the output of the high generator until they are equal

What is the maximum amount of time a circuit can be in operation and still be an intermittent duty circuit?

Two minutes

The most common method of regulating the voltage output of a compound DC generator is to vary the

current flowing through the shunt field coils

If any one generator in a 24-volt DC system shows low voltage, the most likely cause is

an out-of-adjustment voltage regulator

How can the direction of rotation of a DC electric motor be changed?

Reverse the electrical connections to either the field or armature windings

How are generators rated?

Amperes at rated voltage

How is a shunt-wound DC generator connected?

Both fields are shunted across the armature

The poles of a generator are laminated to

reduce eddy current losses

Where is the generator rating and performance data located?

Stamped on the generator data plate

What is required when operating two aircraft AC generators in parallel?

Frequency and voltage must both be equal

How many cycles of AC voltage are produced in a six-pole alternator of the revolving-field type for each revolution of the rotor?

Three

What does a rectifier do?

Changes alternating current into direct current

When a diode is checked for an open circuit or a short circuit, it should be

disconnected from the circuit

When handling a high voltage capacitor in an elec trical circuit, be sure it

Is fully discharged before removing it from the circuit

The voltage output of an alternator may be regulated by controlling the

voltage output of the DC exciter

To help minimize radio interference a capacitor will largely eliminate and provide a steady direct current if the capacitor is connected to the generator in

Parallel

One advantage of using AC electrical power in aircraft is

greater ease in stepping the voltage up or down

The voltage in an AC transformer secondary that contains twice as many loops as the primary will be

greater and the amperage less than in the primary

The major advantages of alternating current (AC) over direct current (DC) is the fact that its current and voltage can easily be increased or decreased

by means of a transformer

Aircraft which operate only AC generators (alter-nators) as a primary source of electrical power normally provide current suitable for battery charging through the use of

a stepdown transformer and a rectifier

In an AC circuit with no phase lead or lag, which Is true?

Real power equals apparent power

What is the frequency of an alternator dependent upon?

RPM

What is the most accurate type of frequency measuring instrument?

Integrated circuit chip having a clock circuit

CSD generators are usually cooled by

Oil spray

A CSD unit drives a generator through the use of

a variable hydraulic pump and hydraulic motor

Integrated drive generators (IDG) employ a type of high output AC generator that utilizes

a brushless system to produce current

If the Integrated Drive Generator (IDG) scavenge oil filter is contaminated with metal, you should

remove and replace the IDG

When necessary during operation, CSD disconnect is usually accomplished by

a switch in the flight deck

A CSD unit that is disconnected in flight, due to a malfunction such as overtemperature, may be reconnected

only on the ground by maintenance personnel

A voltage regulator controls generator output by

varying current flow to generator field coil

Electric circuits are protected from overheating by

Fuses

In installations where the ammeter is in the generator or alternator lead, and the regulator system does not limit the maximum current that the generator or alternator can deliver, the ammeter can be redlined at what percent of the generator or alternator rating?

100

A circuit protection device called a current limiter is essentially a slow-blow fuse and is designed to be used in

heavy power circuits

Which of the following are considered circuit-pro-tective devices that are used in aircraft electrical systems?

Circuit breakers, fuses, and current limiters

What is the advantage of a circuit breaker when compared to a fuse?

It is resettable and reusable

What is the advantage of a current limiter?

It will take overload for a short period

In aircraft electrical systems, automatic reset circuit breakers

Should not be used as circuit protective devices

What is an important factor in selecting aircraft fuses?

Capacity matches the needs of the circuit

The circuit breaker in the instrument lighting system protects the

wiring from too much current

Why are the iron cores of most induction coils laminated?

To reduce the effects of eddy currents

A voltage regulator controls generator voltage by changing the

resistance of the generator field circuit

The overvoltage control automatically protects the generator system when excessive voltage is present by

opening the shunt field circuit

Residual voltage is a result of magnetism in the

Field shoes

Static inverters are electronic devices that change DC to AC with the

use of an oscillator

A battery-generator system provides direct cur-rent. On installations requiring alternating current from the battery-generator system, it is necessary to have

An inverter

Electric wire terminals for most aircraft applications must be what type?

Ring

The type of electric wire terminals used for most aircraft applications, in addition to providing good current carrying capabilities, are designed primarily

to prevent circuit failure due to terminal

disconnection

Aluminum wire must be stripped very carefully because

individual strands will break easily after being nicked

What is the appropriate method for installing pre-insulated terminal lugs and splices to electric wires?

Using a crimping tool to secure the terminal lug

Which of the following factors must be taken into consideration when determining the wire size to use for an aircraft installation?

Allowable power loss, permissible voltage drop, current carrying capability of the conductor, type of load

How should the splices be arranged if several are to be located in an electrical wire bundle?

Staggered along the length of the bundle

What is the minimum bend radius for an electrical wire bundle?

Ten times the outside diameter of the bundle

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

One

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

be limited as to the number of cables to minimize damage from a single electrical fault

What protection to wires and cables does conduit provide when used in aircraft installations?

Mechanical

Which of the following should be accomplished in the installation of aircraft wiring?

Locate the bundle above flammable fluid lines and securely clamp to structure

The primary considerations when selecting electric cable size are

current-carrying capacity and allowable voltage drop

Which of the following copper electrical cable sizes should be selected to replace a No. 6 aluminum electri. cal cable?

No.6

Which statement relating to electric wiring is true?

When attaching a terminal to the end of an electric cable, it should be determined that the strength of the cable-to-terminal joint is at least equal to the tensile strength of the cable itself

A circuit breaker is installed in an aircraft electrical system primarily to protect the

circuit and should be located as close to the source as possible

In the American Wire Gauge (AWG) system of numbers used to designate electrical wire sizes, the number assigned to a size is related to its

cross-sectional area

What should be used to protect wires from chafing when they must pass through bulkheads, firewalls ribs, etc.?

Suitable grommet

When considering an alteration, the criteria upon which the selection of electric cable size should be based are

current-carrying capacity and allowable voltage drop

If a wire is installed so that it comes in contact with some moving parts, what protection should be given the wire?

Pass through conduit

When adding a rheostat to a light circuit to control the light intensity, it should be connected in

series with the light

What is the color and orientation of the position (lights for navigation on civil airplanes?

Left side, red; right side, green; rear aft, white

The navigation lights of some aircraft consist of a single circuit controlled by a single switch which has an ON position and an OFF position, with no additional positions possible. This switch is referred to as a

single-pole, single-throw (SPST), two-position switch

Which of the following must be accomplished when installing an anticollision light?

Install a switch independent of the position light switch

(Refer to Figure 19) Upon completion of the landing gear extension cycle, the green light illuminated and the red light remained lit. What is the probable cause?

Short in the up limit switch

During inspection of an anticollision light installation for condition and proper operation, it should be determined that

the anticollision light can be operated independently of the position lights

What type of instrument is used for measuring very high values of resistance?

Megohmmeter

How can it be determined if a transformer winding has some of its turns shorted together?

The transformer will get hot in normal operation

Grounding is electrically connecting a conductive object to the primary structure. One purpose of grounding is to

prevent development of radio frequency potentials

Oil canning of the sides of aluminum or steel electrical junction boxes is considered to be

a shorting hazard

During inspection of the terminal strips of an aircraft electrical system, it should be determined that

the terminal studs are anchored against rotation