Engine Electrical Sys-Powerplant
What is the ampere-hour rating of a storage battery that is designed to deliver 45 amperes for 2.5 hours?
112.5 ampere-hour.
Which Federal Aviation Regulation requirement prevents the use of automatic reset circuit breakers?
14 CFR Part 23.
What is a basic advantage of using AC for electrical power for a large aircraft?
AC systems operate at higher voltage than dc systems and therefore use less current and can use smaller and lighter weight wiring.
Aircraft electrical wire size is measured according to the
American Wire Gauge system.
How are the rotor windings of an aircraft alternator usually excited?
By a variable direct current.
Why is it unnecessary to flash the field of the exciter on a brushless alternator?
Permanent magnets are installed in the main field poles.
Electric motors are often classified according to the method of connecting the field coils and armature. Aircraft engine starter motors are generally of which type?
Series.
Why is a constant-speed drive used to control the speed of some aircraft engine-driven generators?
So that the frequency of the alternating current output will remain constant.
When selecting an electrical switch for installation in an aircraft circuit utilizing a direct current motor,
a derating factor should be applied.
When installing electrical wiring parallel to a fuel line, the wiring should be
above the fuel line.
The stationary field strength in a direct current generator is varied
according to the load requirements.
Generator voltage will not build up when the field is flashed and solder is found on the brush cover plate. These are most likely indications of
an open armature.
The time/current capacities of a circuit breaker or fuse must be
below those of the associated conductor.
(1) Alternators are rated in volt-amps, which is a measure of the apparent power being produced by the generator.(2) Alternating current has the advantage over direct current in that its voltage and current can easily be stepped up or down.Regarding the above statements,
both No. 1 and No. 2 are true.
(1) Electrical circuit protection devices are rated based on the amount of current that can be carried without overheating the wiring insulation.(2) A 'trip-free' circuit breaker makes it impossible to manually hold the circuit closed when excessive current is flowing.Regarding the above statements,
both No. 1 and No. 2 are true.
The generating system of an aircraft charges the battery by using
constant voltage and varying current.
One way that the automatic ignition relight systems are activated on gas turbine engines is by a
drop in compressor discharge pressure.
As the flux density in the field of a dc generator increases and the current flow to the system increases, the
force required to turn the generator increases.
The maximum number of terminals that may be connected to any one terminal stud in an aircraft electrical system is
four.
If a generator is malfunctioning, its voltage can be reduced to residual by actuating the
generator master switch.
Alternators (ac generators) that are driven by a constant-speed drive (CSD) mechanism are used to regulate the alternator to a constant
hertz output.
Aircraft that operate more than one generator connected to a common electrical system must be provided with
individual generator switches that can be operated from the cockpit during flight.
According to the electron theory of the flow of electricity, when a properly functioning dc alternator and voltage regulating system is charging an aircraft's battery, the direction of current flow through the battery
is into the negative terminal and out the positive terminal.
The constant current method of charging a ni-cad battery
is the method most effective in maintaining cell balance.
As a general rule, starter brushes are replaced when they are approximately
one-half their original length.
(1) Electrical wires larger than 10 gauge use uninsulated terminals.
only No. 1 is true.
(1) Most modern aircraft use circuit breakers rather than fuses to protect their electrical circuits.
only No. 1 is true.
A typical barrier type aircraft terminal strip is made of
paper-base phenolic compound.
In order to reduce the possibility of ground shorting the circuits when the connectors are separated for maintenance, the AN and MS electrical connectors should be installed with the
pin section on the ground side of the electrical circuit.
Aircraft copper electrical wire is coated with tin, silver, or nickel in order to
prevent oxidization.
The reason for flashing the field in a generator is to
restore correct polarity and/or residual magnetism to the field poles.
ON-OFF two position engine electrical switches should be installed
so the ON position is reached by a forward or upward motion.
A term commonly used when two or more electrical terminals are installed on a single lug of a terminal strip is
stacking.
Which Federal Aviation Regulation specifies that each resettable circuit protective device requires a manual operation to restore service after the device has interrupted the circuit?
14 CFR Part 23.
Which of the following Federal Aviation Regulations require that all aircraft using fuses as the circuit protective devices carry 'one spare set of fuses, or three spare fuses of each kind required
14 CFR Part 91.'?
The maximum allowable voltage drop between the generator and the bus bar is
2 percent of the regulated voltage.
(Refer to Figure 4.) In a 28-volt system, what is the maximum continuous current that can be carried by a single No. 10 copper wire 25 feet long, routed in free air?
35 amperes.
What is the frequency of most aircraft alternating current?
400 Hertz.
What speed must an eight-pole ac generator turn to produce 400-Hertz ac?
6,000 RPM.
How many hours will a 140 ampere-hour battery deliver 15 amperes?
9.33 hours.
What device is used to convert alternating current, which has been induced into the loops of the rotating armature of a dc generator, to direct current?
A commutator.
When does current flow through the coil of a solenoid-operated electrical switch?
Continually, as long as the control circuit is complete.
What type of electric motor is generally used with a direct-cranking engine starter?
Direct current, series-wound motor.
When installing an electrical switch, under which of the following conditions should the switch be derated from its nominal current rating?
Direct-current motor circuits.
What is the maximum number of bonding jumper wires that may be attached to one terminal grounded to a flat surface?
Four.
If the points in a vibrator-type voltage regulator stick in the closed position while the generator is operating, what will be the probable result?
Generator output voltage will increase.
What is the purpose of a reverse-current cutout relay?
It opens the main generator circuit whenever the generator voltage drops below the battery voltage.
What precaution is usually taken to prevent electrolyte from freezing in a lead acid battery?
Keep the battery fully charged.
What is the smallest terminal stud allowed for aircraft electrical power systems?
No. 10.
What type of lubricant may be used to aid in pulling electrical wires or cables through conduits?
Soapstone talc.
Which of the following aircraft circuits does NOT contain a fuse/circuit breaker?
Starter circuit.
Upon what does the output frequency of an ac generator (alternator) depend?
The speed of rotation and the number of field poles.
Which of the following is regulated in a generator to control its voltage output?
The strength of the field.
What are two types of AC motors that are used to produce a relatively high torque?
Three-phase induction and capacitor start.
How many basic types of circuit breakers are used in powerplant installation electrical systems?
Three.
What is used to polish commutators or slip rings?
Very fine sandpaper.
Bonding jumpers should be designed and installed in such a manner that they
provide a low electrical resistance in the ground circuit.
The part of a dc alternator power system that prevents reverse flow of current from the battery to the alternator is the
rectifier.
As the generator load is increased (within its rated capacity), the voltage will
remain constant and the amperage output will increase.
When the starter switch to the aircraft gas turbine engine starter-generator is energized and the engine fails to rotate, one of the probable causes would be the
starter solenoid is defective.
The most effective method of regulating aircraft direct current generator output is to vary, according to the load requirements, the
strength of the stationary field.
The resistance of the current return path through the aircraft is always considered negligible, provided the
structure is adequately bonded.
(Refer to Figure 4.) The following data concerning the installation of an electrical unit is known: current requirements for continuous operation -- 11 amperes; measured cable length -- 45 feet;
system voltage -- 28 volts (do not exceed 1 volt drop); cable in conduit and bundles. What is the minimum size copper electrical cable that may be selected? No. 12.
A certain direct current series motor mounted within an aircraft draws more amperes during start than when it is running under its rated load. The most logical conclusion that may be drawn is
the condition is normal for this type of motor.
A high surge of current is required when a dc electric motor is first started. As the speed of the motor increases,
the counter emf builds up and opposes the applied emf, thus reducing the current flow through the armature.
When a 28 volt, 75 ampere generator is installed on an aircraft, an electrical load analysis ground check is performed and it is determined that the battery is furnishing 57 amperes to the system, with all electrical equipment operating. This indicates
the load will be within the generator load limit.
Electrical switches are rated according to the
voltage and the current they can control.
Arcing at the brushes and burning of the commutator of a motor may be caused by
weak brush springs.
Electrical circuit protection devices are installed primarily to protect the
wiring.
