AF Aircraft Electrical Systems

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

speed of the motor can be more closely controlled.
power output of the motor can be more closely controlled.
motor can be operated in either direction.

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

an out-of-round commutator.
a broken field lead.
a shorted armature.

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

Slotted.
Hook.
Ring.

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

High starting torque.
Suitable for constant speed use.
Low 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.
is controlled by the reverse-current cutout relay point clearance.
is increased when the external load is greater than the generator output.

What is a cause of generator brush arcing?

Seating brushes with No. 000 sandpaper.
Carbon dust particles.
Low spring tension.

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

Amperes and frequency must both be equal.
Frequency and voltage must both be equal.
Amperes and voltage must both be equal.

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

low starting torque.
spread slightly higher when unloaded.
high starting torque.

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

Starter motor.
Landing light retraction motor.
Inverter drive motor.

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

interpoles.
shaded poles.
drum-wound armatures in combination with a negatively connected series field.

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.
number of conductors in the armature.
speed at which the armature rotates.

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

armature assembly.
field assembly.
brush assembly.

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

Four.
Three.
Six.

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

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

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

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.
A friction brake is applied by a magnet and released by a spring.
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.
Brush spring tension.
Undercutting the mica on the commutator.

A series-wound DC electric motor will normally require

more current at high RPM than at low RPM.
approximately the same current throughout its operating range of speed.
more current at low RPM than at high RPM.

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.
for uncomplicated and rapid circuit connection and disconnection.
for permanent connection to the circuit.

Aluminum wire must be stripped very carefully because

high resistance will develop in stripping nicks.
stripping nicks can cause short circuits.
individual strands will break easily after being nicked.

The commutator of a generator

changes direct current produced in the armature into alternating current as it is taken from the artmature.
changes alternating current produced in the armature into direct current as it is taken from the armature.
reverses the current in the field coils as the proper time in order to produce direct current.

An ammeter in a battery charging system is for the purpose of indicating the

amperage available for use.
total amperes being used in the airplane.
rate of current used to charge the battery

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

Reduce field strength.
Overcome armature reaction.
Reduce arcing at the brushes.

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.
check adjacent segments on commutator with an ohmmeter on the high resistance scale.
use a 12.24V test light between the armature core segments and the shaft.

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

Left side, green; right side, red; rear left, white.
Left side, red; right side, green; rear aft, white.
Left side, white; right side, green; read aft, red.

A voltage regulator controls generator output by

introducing a resistance in generator-to-battery lead in the event of overload.
shorting out field coil in the event of overload.
varying current flow to generator field coil.

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

Externally grounded.
Series wound.
Compound wound.

What is the most accurate type of frequency measuring instrument?

Integrated circuit chip having a clock circuit.
Electrodynamometers using electromagnetic fields.
Electromagnets using one permanent magnet.

During ground operation, aircraft generator cooling is usually accomplished by

auxiliary air cooled through an air/fuel heat exchanger.
an integral fan.
an external motor-driven fan.

What does a rectifier do?

Changes direct current into alternating current.
Changes alternating current into direct current.
Reduces voltage.

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

Megohmmeter.
Short-type ohmmeter.
Multimeter.

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

One-half the width of the mica.
Equal to twice the width of the mica.
Equal to the width of the mica.

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

in the circuit.
checked with a milliamp ammeter.
disconnected from the circuit.

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

has a full charge before removing it from the circuit.
has at least a residual charge before removing it from the circuit.
is fully discharged before removing it from the circuit.

Which of the following is most likely to cause thermal runaway in a nickel-cadmium battery?

A high internal resistance condition.
Excessive current draw from the battery.
Constant current charging of the battery to more than 100 percent of its capacity.

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

Measure the input voltage with an ohmmeter.
The output voltage will be high.
The transformer will get hot in normal ooperation.

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

Armature assembly, field assembly, brush assembly, and end frame.
Field assembly, brush assembly, commutator, and pole piece.
Brush assembly, pole piece, rheostat, and end frame.

(1) There are three basic types of DC motors; series, short, 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,

only 1 is true.
only 2 is true.
both 1 and 2 are true.

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.
Soldering the terminal lug to the end of the wire.
Soldering the exposed wire prior to crimping on 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 fo the conductor, type of load.
Mechanical strength, allowable power loss, resistance of current return path through the aircraft structure, type of load.
Allowable power loss, resistance of current path through the aircraft structure, type of load.

When selecting hardware for attaching bonding connections to an aircraft structure, which of the following should be considered?

Mechanical strength, ease of installation, amount of current to be carried.
Permissible voltage drop, amount of current to be carried, type of load.
Mechanical strength, allowable power loss, ease of installation.

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

Staggered along the length of the bundle.
Grouped together to facilitate inspection.
Splicing within wire bundles is not permitted.

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

Ten times the outside diameter of the bundle.
Five times the outside diameter of the bundle.
Fifteen 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 connections is

one.
two.
three.

Electrical connectors used in aircraft assemblies should meet which of the following specifications?

Parts Manufacturer Approval (PMA).
Military Specifications (MS).
Society of Electrical Specifications (SES).

The most common method of attaching a pin or socket to an individual wire in an MS electrical connector is by

crimping.
soldering.
crimping and soldering.

The pin section of an AN/MS connector is normally installed on

the power supply side of a circuit.
the ground side of a circuit.
either side of a circuit (makes no difference).

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

speed of the alternator.
voltage output of the DC exciter.
resistance in the rotor windings.

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

dusting the cable with powdered graphite.
dusting the cable with powdered soapstone.
applying a light coat of dielectric grease.

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

prevent current return paths.
allow static charge accumulation.
prevent development of radio frequency potentials.

What is normally used to bond noncontinuous stainless steel aircraft components?

Stainless steel jumpers.
Copper jumpers.
Aluminum jumpers.

Aircraft fuse capacity is rated in

volts.
ohms.
amperes.

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

parallel with the light.
series with the light.
series parallel with the light switch.

Circuits that must be operated only in an emergency or whose inadvertent activation could endanger a system frequently employ

guarded switches.
push-pull-type circuit breakers only (no switches).
spring-loaded to off toggle or rocker switches.

If one switch is used to control all navigation lights, the lights are most likely connected

in series with each other and parallel to the switch.
in series with each other and in series with the switch.
parallel to each other and in series with the switch.

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

normal operation in vibration prone areas.
a shorting hazard.
acceptable operation.

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.
include at least one shielded cable to provide good bonding of the bundle to the airframe.
be limited to a minimum bend radius of five times the bundle diameter to avoid excessive stresses on the cable insulation.

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

only locknuts have been used for terminal attachment to the studs.
the terminal studs are anchored against rotation.
only plain nuts and lockwashers have been used for terminal attachment to the studs.

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

Elecromagnetic.
Mechanical.
Structural.

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

Support the bundle to structure and/or solid fluid lines to prevent chafing damage.
Provide adequate slack in the wire bundle to compensate for large changes in temperature.
Locate the bundle above flammable fluid lines and securely clamp to structure.

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

correctly.
low voltage.
backwards.

When using the voltage drop method of checking circuit resistance, the

input voltage must be maintained at a constant value.
output voltage must be maintained at a constant value.
input voltage must be varied.

The nominal rating of electrical switches refers to continuous

current rating with the contacts open.
voltage rating with the contacts closed.
current rating with the contacts closed.

Aircraft electrical junction boxes located in a fire zone are usually constructed of

aluminum sheets.
carbon steel.
stainless steel.

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.
series.
series/parallel.

The primary considerations when selecting electric cable size are

current carrying capacity and allowable voltage drop.
the voltage and amperage of the load it must carry.
the system voltage and cable length.

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

double-pole, single-throw (DPST), two-position switch.
single-pole, double-throw (SPDT), two-position switch.
single-pole, single-throw (SPST), two-position switch.

Electric circuits are protected from overheating by

thermocouples.
AN/MS connections.
fuses.

How should a coaxial cable be routed?

Parallel with stringers or ribs.
Perpendicular to stringers or ribs.
As directly as possible.

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

No. 4.
No. 6.
No. 8.

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?

50.
75.
100.

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 twice the tensile strength of the cable.
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.
All electric cable splices should be covered with soft insulating tubing (spaghetti) for mechanical protection against external abrasion.

Bonding connections should be tested for

resistance value.
amperage value.
reactance.

What kind of switch should you install in a single wire circuit that required the switch to be manually held in the ON position?

Single-pole, single-throw (SPST), two-position formally open (NO).
Single-pole, single-throw (SPST), single-position.
Single-pole, double-throw (SPDT), single-position normally open (NO).

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.
circuit and should be located as close to the unit as possible.
electrical unit in the circuit and should be located as close to the source as possible.

How should a voltmeter be connected?

In series with the source.
In parallel with the load.
In series with the load.

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

400 cycle AC circuits.
heavy power circuits.
starter-generator circuits.

If it is necessary to use an electrical connector where it may be exposed to moisture, the mechanic should

coat the connector with grease.
use a special moisture-proof type.
spray the connector with varnish or zinc-chromate.

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

Circuit breaker, relays, and current limiters.
Circuit breakers, fuses, and current limiters.
Circuit breakers, capacitors, and current limiters.

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

Wrap with soft wire solder into a shield.
Wrap with friction tape.
Pass through conduit.

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

combined resistance and current-carrying capacity.
current-carrying capacity.
cross-sectional area.

What is the voltage drop for a No. 18 copper wire 50 feet long to carry 12.5 amperes, continuous operation?

Use the formula VD = RLA

VD = Voltage drop
R = Resistance per ft. = .00844
L = Length of wire
A = Amperes

1/2V.
1V.
4V.

What is the purpose of the selection of derated switches for known continuous load current applications?

To calculate the voltage drop across the circuit.
To prevent short circuits in the motor field windings.
To obtain reasonable switch efficiency and service life.

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

It is easily replaced.
It controls current flow.
It is resettable and reusable.

What is the advantage of a current limiter?

It breaks circuit quickly.
It can be reset easily.
It will take overload for a short period.

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

Aerodynamic duct tape.
Suitable grommet.
Plastic spiral wrap.

In aircraft electrical systems, automatic reset circuit breakers

should not be used as circuit protective devices.
are useful where only temporary overloads are normally encountered.
must be used in all circuits essential to safe operation of the aircraft.

A certain switch is described as a single-pole double-throw (SPDT) switch. The throw of a switch indicates the number of

circuits each pole can complete through the switch.
terminals at which current can enter or leave the switch.
places at which the operating device (toggle, plunger, etc.) will come to rest and at the same time open or close a circuit.

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

applied voltage and allowable voltage drop.
current-carrying capacity and allowable voltage drop.
current-carrying capacity and applied voltage.

What is an important factor in selecting aircraft fuses?

The current exceeds a predetermined value..
The voltage rating should be lower than the maximum circuit voltage.
Capacity matches the needs of the circuit.

The circuit breaker in the instrument lighting system protects the

lights from too much current.
wiring from too much current.
wiring from too much voltage.

One advantage of using AC electrical power in aircraft is

that AC electrical motors can be reversed while D motors cannot.
greater ease in stepping the voltage up or down.
that the effective voltage is 1:41 times the maximum instantaneous voltage; therefore, less power input is required.

Why are the iron cores of most induction coils laminated?

To reduce the core reluctance.
To increase the core permeability.
To reduce the effects of eddy currents.

Certain transport aircraft use AC electrical power for all normal operation and battery furnished DC electrical power for standby emergency use. In aircraft of this type that operate no DC generations, the batteries are kept charged by

inverters which use the aircraft’s AC generations as a source of power.
alterations which use the aircraft’s generators as a source of power.
rectifiers which use the aircraft’s AC generators as a source of power.

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.
greater and the amperage greater than in the primary.
less and the amperage greater than in the primary.

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 output would indicate

zero voltage.
residual voltage.
normal voltage.

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

Flash the fields.
Reseat the brushes.
Energize the armature.

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

by means of an inverter.
by means of a rectifier.
by means of a transformer.

Which of the following must be accomplished when installing an anti-collision light?

Install a switch independent of the position light switch.
Use shielded electrical cable to assure fail-safe operation.
Connect the anti-collision light to the aircraft position light switch.

The inductor-type inverter output voltage is controlled by the

number of poles and the speed of the motor.
voltage regulator.
DC stator field current.

When using an ohmmeter to check the continuity of a generator field coil, the coil should

be removed from the generator housing.
show high resistance when the meter prods are connected to the terminals of the coil.
show very low resistance if it is a series field coil.

The strength of the core of an electromagnet depends upon the material from which it is constructed and which of the following?

The number of turns of wire in the coil and the applied voltage.
The number of turns of wire in the coil and the amount of current (amperes) passing through the coil.
The size (cross section) and the number of turns of wire in the coil and the applied voltage.

A voltage regulator controls generator voltage by changing the

resistance in the generator output circuit.
current in the generator output circuit.
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.
opening and resetting the field control relay.
breaking a circuit to the top coil of the field control relay.

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 to equal the output of the high generator.
decreasing the output of the high generator to equal the output of the low generator.
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?

Three minutes.
Two minutes.
One minute.

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.
total effective field strength by changing the reluctance of the magnetic circuit.
resistance of the series field circuit.

Refer to Figure 18. Which of the batteries are connected together incorrectly?

1.
2.
3.

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 down limit switch.
Short in the gear safety switch.
Short in the up limit switch.

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

an out-of-adjustment voltage regulator.
shorted or grounded wiring.
a defective reverse current cutout relay.

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

Interchange the wires which connect the motor to the external power source.
Reverse the electrical connections to either the field or armature windings.
Rotate the positive brush one commutator segment.

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

use of an oscilitator.
properties of an exclusive OR gate.
input from an amplifier control by integrated circuits.

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

a stepdown transformer and a rectifier.
an inverter and a voltage-dropping resistor.
a dynamotor with a half-wave DC output.

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

electrical or mechanical interconnections are provided so that the anti-collision light will operate at all times that the position light switch is in the ON position.
an appropriately rated fuse is in position at the light to protect the connecting wiring against electrical faults.
the anti-collision light can be operated independently of the position lighs.

Major adjustments on equipment such as regulators, contactors, and inverters are best accomplished outside the airplane on test benches with necessary instruments and equipment. Adjustment procedure should be as outlined by

the equipment manufactuer.
the FAA.
aircraft technical orders.

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

a transformer.
an inverter.
a variable resistor between the battery and gnerator.

An aircraft electrical circuit control relay is

an electrically operated switch.
a device which converts electrical energy to kinetic energy.
any conductor which receives electrical energy and passes it on with little or no resistance.

The purpose of a rectifier in an electrical system is to change

the frequency of alternating current.
direct current to alternating current.
alternating current to direct current.

What is the ratio of turns between the primary coil winding and the secondary coil winding of a transformer designed to triple its input voltage?

Primary will have one-third as many turns as its secondary.
Primary will have twice as many turns as its secondary.
Primary will have three times as many turns as its secondary.

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

Real power is zero.
Real power is greater than apparent power.
Real power equals apparent power.

How are generators rated?

Watts at rated voltage.
Amperes at rated voltage.
The impedance at rated voltage.

How is a shunt-wound DC generator connected?

One field is shunted across the other.
Both fields are shunted across the armature.
The field and armature are shunted with a capacitor.

The poles of a generator are laminated to

reduce flux losses.
increase flux concentration.
reduce eddy current losses.

What is the frequency of an alternator dependent upon?

Voltage.
RPM.
Current.

Where is the generator rating and performance data located?

In the pilot operating handbook.
Stamped on the generator data plate.
In the aircraft maintenance manual.

Residual voltage is a result of magnetism in the

field windings..
field shoes.
armature.

In troubleshooting an electrical circuit, if an ohmmeter is properly connected across a circuit component and some value of resistance is read,

the component has continuity and is open.
either the component or the circuit is shorted.
the component has continuity and is not open.

CSD generators are usually cooled by

oil spray.
an integral fan.
both ram air and an integral fan.

A CSD unit drives a generator through the use of

a synchronous electric motor.
an infinitely variable mechanical gearing system.
a variable hydraulic pump and hydraulic motor.

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

brushes and slip rings to carry generated DC exciter current to the rotating field.
battery current to excite the field.
a brushless system to produce current.

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

do an oil analysis to diagnose the problem.
remove and replace the IDG.
replace the oil and filter at 25 hour intervals.

When necessary during operation, CSD disconnect is usually accomplished by

a switch in the cockpit.
circuit breaker activation.
a shear section in the input shaft.

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

automatically if the temperature falls back into the normal operating range.
manually by the flightcrew.
only on the ground by maintenance personnel.

AF Aircraft Electrical Systems

Jon K

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