electrical system

Question 1

what are the types of current

Answer 1

direct
alternating

Question 2

what is direct current (DC)

Answer 2

constant direction of electron flow produced by batteries

Question 3

what is alternating current (AC)

Answer 3

flow of electrons that reverse periodically, produced by generators or alternators

Question 4

what are capacitors

Answer 4

components that can store electrical charge (DC) and allow AC to move through them

Question 5

when a wire is moved through a magnetic field, what is produced?

Answer 5

a current

Question 6

what is static electricity

Answer 6

an imbalance of electrical charge that remains in or on the surface of material until its able to equalise

Question 7

how is static electricity formed?

Answer 7

charge builds up until the voltage difference between the object and its surroundings is enough to produce a current through a resistive insulator to an oppositely charged item
– think lightning

Question 8

how are metal aircraft affected by lightning?

Answer 8

• lightning is conducted by airframe
• puncture holes may be made on entry and exit points on skin
• wingtips may be blown off
• DOES NOT IMPACT STRUCTURAL INTEGRITY

Question 9

how are glass-reinforced plastic (GRP) aircraft affected by lightning?

Answer 9

• not a good conductor
• probably explode

Question 10

how are wood aircraft affected by lightning

Answer 10

not good conductors
probably ignite

Question 11

how is aircraft equipment affected by lightning?

Answer 11

some nav. equipment (ADF) will give inaccurate readings near a thunderstorm
- compass, comms radios, nav equipment also damaged

Question 12

what are the characteristics of an aircraft battery

Answer 12

• usually 12V or 24V
• battery capacity measured in ampere-hours (AH)
• location varies

Question 13

what is the capacity of batteries in parallel

Answer 13

sum of battery capacities

Question 14

what is the overall system voltage of batteries in series

Answer 14

sum of battery voltage
– capacity is the same (as batteries in series need to have equal AH ratings)

Question 15

what do charging devices produce

Answer 15

AC

Question 16

what kind of current do most light aircraft use

Answer 16

DC

Question 17

how is AC converted to DC

Answer 17

using rectifiers, lumpy AC smoothed to DC with capacitance

Question 18

what is a generator made of

Answer 18

magnets and coils of wire

Question 19

what do generators do

Answer 19

produce electricity whenever shaft of generator is rotated

Question 20

generators wont produce electricity under a certain …

Answer 20

rpm

Question 21

generators are powered by:

Answer 21

either engine or air

Question 22

how are generators and an alternator different

Answer 22

alternator doesnt use magnets

Question 23

how is the magnetic field produced in an alternator

Answer 23

by field windings (coil of wires) that need a source of electricity to produce a magnetic field

Question 24

how do alternators produce power

Answer 24

rotary motion of shaft = electrical power
– need a source of power to start electrical generation

Question 25

why use an alternator rather than a generator?

Answer 25

alternator produces more power

Question 26

can alternators be turned on and off?

Answer 26

technically yes - if an engine is hand started with a flat battery, no power will be produced as alternator doesnt have field winding activated -- implies that alternators can be turned on and off by pilot controlling power to field winding

Question 27

why are solenoids used

Answer 27

some devices need a high current, but its unsafe for current to be sent through switches -- slave device used

Question 28

how do solenoids/relays work?

Answer 28

a small current used to operate a switch within the solenoid/relay that then allows a large current to flow through switch to device

Question 29

what does the master switch operate

Answer 29

operates the battery solenoid that connects battery power to power bus inside aircraft

Question 30

what is a power bus

Answer 30

a strip of metal onto which connections are made - must carry high current and low resistance

Question 31

what is a fuse

Answer 31

a piece of wire that melts if a current above the fuses rating is detecting -- breaks circuit and removes power

Question 32

how do circuit breakers work

Answer 32

by a mechanical action based on the principle circuit breaker pops open and breaks the circuit

Question 33

what is the max. amount of times a fuse or circuit breaker should be reset after tripping

Answer 33

once

Question 34

what is the battery used for

Answer 34

starting and a backup supply of electricity in case of generator or alternator failure

Question 35

what are the generator and alternator used for

Answer 35

to provide electrical power for normal operation and top up charging current to aircraft battery

Question 36

how does the starter motor start

Answer 36

- when pilot starts engine, a solenoid operates - solenoid closes its contacts allowing a high current to pass from battery to starter for engine to turn

Question 37

how does the starter motor work after starting

Answer 37

it has a special gear cog and spring arrangement called a BENDIX - when starter motor turns, the bendix operates and pushes out a small rotating cog to engage with flywheel cogs to turn the engine - once engine starts, pilot releases starter mechanism and bendix withdraws from flywheel cogs and small cog (starter motor) stops rotating

Question 38

what does the starter warning light indicate

Answer 38

if bendix cog has disengaged from flywheel or not

Question 39

why should engine cranking be limited to 10s

Answer 39

prevent battery or starter motor overheating

Question 40

what should you be careful of when starting the engine

Answer 40

very high current is drawn by starter motor -- takes a huge toll on battery especially in cold temps