Aircraft Electrical System Flashcards
Some electric motors have two sets of field windings wound in opposite directions so that the
motor can be operated in both directions
One purpose of a growler test is to determine the presence of
a shorted armature
Electric wire terminals for must 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 point remain open
depends on the load carried by the regulator
What is the cause of generator brush arcing?
Low spring tension
When ac generators are operated in parallel, the
frequency and voltage must be both be equal
The starting current of a series wound dc motor in passing through 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 DC generators 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 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 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 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 purpose 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 100V test light on adjacent segments; light should 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
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 flows 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 into 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
is fully charged before removing it from 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?
The transformer will get hot in normal operation
Which of the following are the major parts of a dc motor?
Armature assembly, field assembly, brush assembly and end frame
No.1 There are three basic types of DC motors; series shunt and compound
2. In the series motor, the field windings, consistings of relatively few turns of heavy wire, are connected in series with the armature winding
Both No.1 and No.2 are true
What is the appropriate method for installing pre-insulated terminal plugs and splices to electrical 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
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
How should the splices be arranged if several are to be located in an electrical wire bundle?
Staggered across the length of the bundle
What is the minimum bend radius for an electrcial 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
Electrical connectors used in aircraft assemblies should meet which of the following specifications?
Military Specifications (MS)
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 pulled through the conduit will be reduced by
dusting the cable 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 id 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 of steel electrical junction boxes is considered to be
a shorting hazard
Electric wiring installed in aircraft without special enclosing means (open wiring) offers the advantage 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 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 the contact closed
Aircraft electrical junction boxes located in a fire zone are usually constructed of
stainless steel
To help minimize radio interference in 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 of some aircraft consist of single circuit controlled by a single switch which has as ON and OFF position, with no additional position possible. This switch is referred to as a
single pole, single throw (SPST), two position switch
Electric circuits are protected from over heating by
fuses
How should co axial cable be 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 rating relating to electrical 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 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
A circuit breaker is installed in an aircraft electrical system to 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 a 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
Which of the following are considered circuit protective devices that are used in aircraft electrical systems?
Circuit breakers, fuses and current limiters
If a wire is installed so that it comes into contact with some moving parts, what protection should be given to 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 allowable voltage drop for a No. 18 copper wire 50 feet long to carry 12.5 amps, continuous operation?
Use formula VD=RLA
VD = Voltage drop
R = Resistance per ft = .00644
L = Length of wire
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 breakers compared to a fuse?
It is resettable and resusble
What is the advantage of a current limiter?
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?
Suitable grommet
In aircraft electrical system, automatic circuit breakers
should not be used as circuit protective devices
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
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 stopping voltage going up or down
Why are the iron cores of most induction coils laminated?
To reduce the effects of eddy currents
Certain transport aircraft us AC 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 aircrafts 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
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 major advantages of alternating currents (AC) over direct current is the fact that its current and voltage can be easily be increased and 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 numbers of turn of wire in the coil and the amount of current (amps) 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
When DC generators are operated in parallel and to supply power for a single load, their controls include an equalizer circuit to assure that all generators share the load equally. The equaliser 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
Static inverters are electronic devices that change DC to AC with the
use of an oscillator
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 rectifier
During inspection of an anti collision light for condition and proper operation, it should be determined that
the anti-collision light can be operated independently of the position light
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 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
An aircraft electrical circuit control relay is
an electrically operated switch
A relay is
a 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 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
What is the frequency of an alternator dependent upon
RPM
Where is the generator rating and performance data located?
reduce eddy current losses
Residual voltage is a result of magnetism in the
fieldn 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 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 Generators (IDG) scavenge filter is contaminated with pieces of metal you should
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 malfunction such as over temp may be reconnected
only on the ground by maintenance personnel
