Engine electrical

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

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.

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

rectifier.

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.

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.

What is the frequency of most aircraft alternating current?

400 Hertz.

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.

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

By a variable direct current.

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.

(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.

Upon what does the output frequency of an ac generator (alternator) depend?

The speed of rotation and the number of field poles.

What are two types of ac motors that are used to produce a relatively high torque?

Three-phase induction and capacitor start.

What is used to polish commutators or slip rings?

Very fine sandpaper.

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.

(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.

One way that the automatic ignition relight systems are activated on gas turbine engines is by a

drop in compressor discharge pressure.

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.

How many hours will a 140 ampere-hour battery deliver 15 amperes?

9.33 hours.

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.

What type of electric motor is generally used with a direct-cranking engine starter?

Direct current, series-wound motor.

What precaution is usually taken to prevent electrolyte from freezing in a lead acid battery?

Keep the battery fully charged.

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.

Which of the following aircraft circuits does NOT contain a fuse/circuit breaker?

Starter circuit.

The generating system of an aircraft charges the battery by using

constant voltage and varying current.

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

remain constant and the amperage output will increase.

The reason for flashing the field in a generator is to

restore correct polarity and/or residual magnetism to the field poles

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.