Single Engine Aircraft Electrical Systems

Question 1

What is Direct Current (DC)?

Answer 1

the flow of electricity in one direction

Question 2

what is Alternating Current (AC)?

Answer 2

flow of electricity which changes direction

Question 3

what systems typically use DC? (11)

Answer 3

• Lights
• Radios
• Transponders
• Starter Motor
• Altitude and heading reference system
• Multi-function display
• Turn indicator
• Oil T and P gauge
• Trim
• Flaps
• Alternator (to initially power the electromagnet)

Question 4

what does the battery do in a typical electrical circuit system?

Answer 4

it’s simply a container for storing electrical energy. When the terminals of the battery are connected to a complete electrical circuit a current will flow unless the circuit is broken. (battery is flat)

Question 5

how does the battery work in an electrical circuit?

Answer 5

the negative terminal of the battery has a surplus of electrons and the positions have protons with a shortage of electrons.

when placed in a circuit a load (like a lightbulb) is applied and then the free electrons will form from the negative terminal through the load to the positive.

Question 6

how is battery life determined?

Answer 6

based on its capacity and the current amperage being drawn from it.

Question 7

what is the typical battery fitted onto the aircraft?

Answer 7

a lead-acid type or a nickel-cadmium (NiCad) battery.

Question 8

what is the function of a bus bar?

Answer 8

it is the main conductor and the main distributor of power.

Question 9

how does a bus bar work?

Answer 9

electrical power is supplied to the bus bar by the alternator or generator and the battery using a bus isolation circuit breaker.

the electrical power is then distributed to the circuits and the electrical components that require power.

Question 10

what type of equipment must be run at all times independent of the master switch?

Answer 10

clock, oil pressure switch and flight hour recorder.

Question 11

the alternator or generator has the capacity to do what?

Answer 11

produce a higher voltage than that required by the aircraft system.

Question 12

what does a voltage regulator do?

Answer 12

control or regulate the generated voltage produced by the alternator or generator.

Question 13

what do overvoltage protectors and relays do?

Answer 13

guard against malfunction of the regulator.

Question 14

what does a voltmeter do?

Answer 14

indicate the voltage.

Question 15

what does an overvoltage light do?

Answer 15

indicate whenever the alternator does not provide power, but the battery does.

Question 16

what are the advantages of an alternator?

Answer 16

lighter then a generator and produces the same amount of power

Question 17

what are the disadvantages of an alternator?

Answer 17

needs power to get the electromagnet started meaning it uses power from the battery.

Question 18

what does an alternator do?

Answer 18

provide the aircraft with electrical power. mechanically driven by the engine and will produce power whenever the engine is running.

Question 19

what are the advantages of a generator?

Answer 19

does not need power to get the electromagnet excited.

Question 20

what are the disadvantages of a generator?

Answer 20

• heavier and larger than an alternator for the same amount of power produced
• produce less current per RPM and so are less suited for low RPM situations.

Question 21

what does a generator do?

Answer 21

same as an alternator by providing the aircraft with electrical power but is self-sustaining.

Question 22

what does an ammeter do?

Answer 22

measures the amount of electrical current in amperes (amps) flowing at a specific place within the circuit.

Question 23

what are the two types of ammeters?

Answer 23

left zero ammeter and centre-zero ammeter.

Question 24

what does the left-zero ammeter do?

Answer 24

measures only the output of the alternator or generator.

It graduated from zero amperes on the left-hand side of the scale and the reading increased to a maximum at the right hand side of the scale.

Question 25

what does the left-zero ammeter indicate?

Answer 25

only the load being placed on the alternator/generator.

with the number of loads determined by how many electrical services are on and how much power they demand.

Question 26

what are the indications of the left zero ammeter?

Answer 26

• With battery switch ON and engine not running or with the engine running and alternator switch OFF. it reads zero
• in normal operating with the engine running and alternator ON. the ammeter will show the alternator output. the amount of current flowing from the alternator to the electrical services and the battery.

Question 27

what does the centre-zero ammeter do?

Answer 27

measures the flow of current (amperage) either into our out of the battery.

Question 28

current going into the battery is what?

Answer 28

charge and the ammeter needle will deflect to the right of the centre towards the + side

Question 29

current going out of the battery is what?

Answer 29

discharge and the ammeter needle will deflect to the left of the centre towards the - side.

Question 30

no current flow either into or out of the battery is shown how?

Answer 30

by the needle being in the centre position.

Question 31

with the battery switch ON and no alternator output, the ammeter will indicate what?

Answer 31

a discharge from the battery with the amount of discharge being indicated depending on the number of circuits in operation and their consumption.

Question 32

what does the master switch do?

Answer 32

controls all of the circuits in teh aircraft electrical system.

Question 33

why must the master switch be turned ON?

Answer 33

for any of the electrical services to receive power or for the battery to be recharged when the engine is running.

Question 34

when should the master switch be turned OFF?

Answer 34

after stopping the engine to prevent the battery from discharging by the powering the electrical equipment which will still be connected.

Question 35

in an aircraft with an alternator installed the master switch is a split switch. what does each switch do?

Answer 35

• one half operates the battery switch (or master relay for electrical systems) which connects battery power to the bus bar.
• one half, the alternator switch, energies the alternator. connects the alternator field to the bus bar thus providing the alternator with battery power for field excitation.

Question 36

if either switch has to be turned OFF in flight what should be considered?

Answer 36

consider terminating the flight.

Question 37

can the switches be turned on separately?

Answer 37

yes

Question 38

which switch can be turned off separately?

Answer 38

the alternator switch as switching the battery OFF will automatically switch the alternator off.

Question 39

what do fuses, circuit breakers and overload switches do?

Answer 39

used to protect equipment from any electrical current overload.

Question 40

what happens if there’s an electrical overload or short-circuit?

Answer 40

fuse-wire will melt or blow or a circuit breaker will pop and break the circuit so no current can flow through it.

Question 41

overload switches are combined what?

Answer 41

ON/OFF switches and overload protectors.

Question 42

when will overload switches turn themselves off?

Answer 42

if they experience an electrical overload.

the pilot can switch them back on like a resettable circuit breaker.