Aircraft Electrical Flashcards
Some electric motors have two sets of field windings wound in opposite directions so that the —
Motor can be operated in neither direction
One purpose of a growler test is to determine the presence of
A shorted armature
Electric wire terminals for most aircraft applications must be what type?
Ring
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
When ac generators are operated in parallel, the —
Frequency and voltage must be both equal
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
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
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 to 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 release 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 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
The commutator of a generator
Changes alternating current produced in the armature into direct current as it is taken from the
armature
An ammeter in a battery charging system is for the purpose of indicating the
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
To test generator or motor armature windings for opens,
A place armature in a growler and connect a 110v test light on adjacent segments; light should light.
What is the color and orientation of the position lights for navigation on civil airplanes?
ans. Left side – red , right side – green, rear aft – white
To what depth is the mica insulation between the commutator bars of a dc generator undercut?
Equal to the width of the mica
A voltage regulator controls generator output by
Varying current flow to generator field coil
Which type of dc generator is not used as an airplane generator?
Series wound
What is the most accurate type of frequency-measuring instrument?
Integrated circuit chip having a clock circuit
During ground operation, aircraft generator cooling is usually accomplished by
An integral fan
What does a rectifier do?
Changes alternating current to direct current
What type of instrument is used for measuring very high values of resistance?
Megohmmeter
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 electrical circuit, be sure it
It is fully discharge before removing it from the circuit
Which of the following is most likely to cause thermal runaway in a nickel-cadmium battery?
Excessive current draw from the battery
How can it be determined if a transformer winding has some of its turns shorted together?
Transformer will get hot in normal operation
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.
1,2,3,7
(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 no. 1 and no. 2 are true
For general electrical use in aircraft, the acceptable method of attaching a terminal to a wire is by
Crimping
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).
2,5,6,7
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).
1, 3, 5
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
AN/MS electrical connectors are specifically designed to meet
Military specification
The most common method of attaching a pin or socket to an individual wire in an MS electrical
connector is by
Crimping
The pin section of an AN/MS connector is normally installed on
The ground side of a circuit
The voltage output of an alternator may be regulated by controlling the
Voltage output of the dc exciter
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 soapstone
Grounding is electrically connecting a conductive object to the primary structure. One purpose of
grounding is to
Prevent development of radio frequency potentials
What is normally used to bond non-continuous stainless steel aircraft components?
Copper jumpers
Aircraft fuse capacity is rated in
Amperes
When adding a rheostat to a light circuit to control the light intensity, it should be connected in
series with the light
Circuits that must be operated only in an emergency or whose inadvertent activation could endanger a
system frequently employ
Guarded switches
If one switch is used to control all navigation lights, the lights are most likely connected
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
A shorting hazard
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
During inspection of the terminal strips of an aircraft electrical system, it should be determined that
The terminal studs are anchored against rotation
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
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
Backwards
When using the voltage drop method of checking circuit resistance, the
Input voltage must be maintained at a constant value
The nominal rating of electrical switches refers to continuous
Current rating with contacts closed
Aircraft electrical junction boxes located in a fire zone are usually constructed of
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
The primary considerations when selecting electric cable size are
Current carrying capacity and allowable voltage drop
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
Electric circuits are protected from overheating by means of
Fuses
How does the routing of coaxial cables differ from the routing of electrical wiring?
Coaxial cable are routed as directly as possible
Which of the following copper electrical cable sizes should be selected to replace a No. 6 aluminum
electrical cable?
No. 6
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
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.
Bonding connections should be tested for
Resistance value
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 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
How should a voltmeter be connected?
In parallel with the load
A circuit protection device called a current limiter is essentially a slow-blow fuse and is designed to be
used in
Heavy power circuits
If it is necessary to use an electrical connector where it may be exposed to moisture, the mechanic
should
Use a special moisture proof type
The three kinds of circuit-protection devices used most commonly in aircraft circuits are
Circuit breakers, fuses, 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?
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
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 = .00644 / L = Length of wires
A = Amperes
4v
What is the purpose of the selection of derated switches for known continuous load current
applications?
To obtain reasonable switch efficiency and service life
What is the advantage of a circuit breaker when compared to a fuse?
Resettable and reusable
What is the advantage of a current limiter?
It will take overload for a short period
Where electric cables must pass through holes in bulkheads, formers, ribs, firewalls, etc., the wires
should be protected from chafing by
Using a suitable grommet
In aircraft electrical systems, automatic reset circuit breakers
Should not be used as protective devices
A certain switch is described as a single-pole, double-throw switch (SPDT). The throw of a switch
indicates the number of
Circuits each pole can complete through the switch
When considering an alteration, the criteria upon which the selection of electric cable size should be
based are
Current carrying and allowable voltage drop
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
One advantage of using ac electrical power in aircraft is
Greater ease in stepping the voltage up or down
Why are the iron cores of most induction coils laminated?
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 generators, the
batteries are kept charged by
Rectifiers which use the aircraft’s ac generator 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
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
Residual voltage
What is a method used for restoring generator field residual magnetism?
Flash the fields
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
Which of the following must be accomplished when installing an anti-collision light?
Install a switch independent of the position light switch
The inductor-type inverter output voltage is controlled by the
Dc stator field current
When using an ohmmeter to check the continuity of a generator field coil, the coil should
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 amount of current (ampere) passing through the coil
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
What is the maximum amount of time a circuit can be in operation and still be an intermittent duty
circuit?
Two minutes
(Refer to Figure 18.) Which of the batteries are connected together incorrectly?
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 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
How can the direction of rotation of a dc electric motor be changed?
Reverse the electrical connections to either the field or armature windings
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 step down transformer and a rectifier
During inspection of an anti-collision light installation for condition and proper operation, it should be
determined that
The anti-collision light can be operated independently of the position lights
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 manufacturer
A battery-generator system provides direct current. On installations requiring alternating current from
the battery-generator system, it is necessary to have
An inverter
A relay is
Magnetically operated switch
The purpose of a rectifier in an electrical system is to change
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
In an ac circuit with no phase lead or lag, which is true?
Real power equals apparent power
How are generators rated?
Amperes and 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 by eddy current losses
What is the frequency of an alternator dependent upon?
Rpm
The generator rating is usually found stamped on the
Generator
Residual voltage is a result of magnetism in the
Field shoes
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 not open
CSD driven 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 IDG scavenge oil filter is contaminated with chunks or pieces of metal
Remove and replace the IDG
When necessary during operation, CSD disconnect is usually accomplished by
A switch in the cockpit
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
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
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
