1205 Aircraft Generators and Motors

How many amperes will a 28-volt generator be required to supply to a circuit containing five lamps in parallel, three of which have a resistance of 6 ohms each and two of which have a resistance of 5 ohms each?

25.23 amperes.

How much power must a 24-volt generator furnish to a system which contains the following loads? UNIT RATING One motor (75 percent efficient) 1/5 hp Three position lights 20 watts each One heating element 5 amp One anticollision light 3 amp (Note: 1 horsepower = 746 watts)

450 watts.

A 1-horsepower, 24-volt dc electric motor that is 80 percent efficient requires 932.5 watts. How much power will a 1-horsepower, 12-volt dc electric motor that is 75 percent efficient require? (Note: 1 horsepower = 746 watts)

994.6 watts.

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.

How are the rotor windings of an aircraft alternator usually excited?

By a variable direct current.

What does a rectifier do?

Changes alternating current into direct current.

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

Frequency and voltage must both be equal.

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 principal advantage of the series-wound dc motor?

High starting torque.

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

Landing light retraction motor.

What is a cause of generator brush arcing?

Low spring tension.

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.

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 (amperes) passing through the coil.

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.

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.

Why are the iron cores of most induction coils laminated?

To reduce the effects of eddy currents.

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

a brushless system to produce current.

One purpose of a growler test is to determine the presence

a shorted armature.

A CSD unit drives a generator through the use of

a variable hydraulic pump and hydraulic motor.

The stationary field strength in a direct current generator is varied

according to the load requirements.

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

alternating current to direct current.

An aircraft electrical circuit control relay is

an electronically operated switch.

During ground operation, aircraft generator cooling is usually accomplished by

an integral fan.

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

an out-of-adjustment voltage regulator.

(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.

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.

The inductor-type inverter output voltage is controlled by the

dc stator field current.

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.

Residual voltage is a result of magnetism in the

field shoes.

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.

If a generator is malfunctioning, its voltage can be reduced to residual by actuating the

force required to turn the generator increases.

The generator rating is usually found stamped on the

generator.

Alternators (ac generators) that are driven by a constant-speed drive (CSD) mechanism are used to regulate the alternator to a constant

hertz output.

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.

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.

A series-wound dc electric motor will normally require

more current at low RPM than at high RPM.

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.

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

opening the shunt field circuit.

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.

The part of a dc alternator power system that prevents reverse flow of current from the battery to the alternator is the

rectifier.

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

rectifiers which use the aircraft's ac generators as a source of power.

The poles of a generator are laminated to

reduce eddy current losses.

As the generator load is increased (within its rated capacity), the voltage will

remain constant and the amperage output will increase.

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.

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.

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

use of an oscillator.

A voltage regulator controls generator output by

varying current flow to generator field coil.

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

voltage output of the dc exciter.