Aircraft Electrical Systems

Question 1

How many alternators power an aircraft?

Answer 1

-Normally one
-Older aircraft have one generator

Question 2

What are batteries for in an aircraft?

Answer 2

-For starting and emergencies
-They can be disconnected from the system
-The are not needed in normal flight

Question 3

How are circuits protected?

Answer 3

-Circuit breakers
-Fuses on really old planes

Question 4

How are circuits completed?

Answer 4

-Through ground, which is the structure of the aircraft.
-It can be assumed that all ground are connected

Question 4

Aircraft use what type of electrical systems?

Answer 4

Single wire

Question 5

What two systems are aircraft circuits divided?

Answer 5

Power and Load

Question 6

What do power circuits connect to? and where can the power come from?

Answer 6

-Power circuits connect power to the bus.
-Power can come from a battery, generator, alternator, or a GPU.

Question 7

When an ammeter is wired to each end of a shunt it is not really an ammeter but a?

Answer 7

Micro voltmeter

Question 8

The shunt is a _____ with known_____. Therefore it will?

Answer 8

-conductor with known resistance.
-Drop a certain amount of voltage as power runs through it

Question 9

When alternator output is high or low?

Answer 9

-The voltage is at its peak
-The voltages is at its minimum

Question 10

Even though the ammeter is marked in amps its responding in?

Answer 10

Changes in voltage

Question 11

What is a zero-center ammeter?

Answer 11

To show at a glance whether the battery is being charged by the alternator or discharging because the alternator output is too low.

Question 12

When does a normally closed solenoid open?

Answer 12

When it is energized

Question 13

Why do alternators need to share the load?

Answer 13

One will take over and probably fail while the other one is doing nothing.

Question 14

How do you avoid excessive flow in a circuit?

Answer 14

By a device that will open the circuit

Question 15

Where are circuit breakers located any why?

Answer 15

-As near the source as possible
-They are protecting the aircraft wiring
-Individual components may have their own CB’s or fuses

Question 16

What are Current Limiters?

Answer 16

A type of slow blow fuse that allows a large amount of current to flow for a short length of time but opens if to much current flows for a long period

Question 17

Hot battery Bus

Answer 17

Has power any time a charged battery is installed

Question 18

Main battery Bus

Answer 18

Must be connected to the hot battery bus to get power or to ground power. Power for starting comes from this bus

Question 19

Power for starting comes from which bus?

Answer 19

Main battery bus

Question 20

Isolation Bus

Answer 20

-Also powered whenever the main battery bus is connected
-Connects the power of the 2 generators

Question 21

Generator Bus

Answer 21

How generator power gets to dual feed buses

Question 22

Dual Feed Bus

Answer 22

Divides load into multiple buses so that a fault doesn’t interrupt all power.

Question 23

Avionics Bus

Answer 23

Can be disconnected from the other power in the aircraft.

Question 24

What is a GCU?

Answer 24

Generator Control Unit-A line replaceable unit (LRU) that does more or less what you think, controls the generator. It can also control the connection of the generator through bus tie breakers (BTB), which are large circuit breakers that connect busses

Question 25

What is a BPCU?

Answer 25

A Bus Power Control Unit. Also, an LRU that monitors current throughout the aircraft. If it identifies a fault, it will signal the GCU which might open or close other bus ties

Question 26

What are current transformers?

Answer 26

Senses the amount of current in any wire using inductance. The BPCU will use it to identify a fault whenever the current amount is out of range

Question 27

What Bus system was used until the 80's on multi-engine aircraft?

Answer 27

Parallel bus systems

Question 28

How did a parallel bus system function?

Answer 28

All power is put on one bus, called the sync bus because the power had to be synchronized for phase and frequency. A third person on the flight deck, the flight engineer, did this.

Question 29

What is a good thing about a parallel bus?

Answer 29

That when one generator failed nothing had to be done and power simply came from the remaining generators

Question 30

What is a RAT?

Answer 30

Ram Air Turbine-turns an emergency generator and some also have hydraulic pumps

Question 31

What bus system is used on current aircraft?

Answer 31

Split Bus System- Reliant on computerized systems in aircraft to control power, and lot of other systems

Question 32

Do generators need to be synchronized on Split bus systems?

Answer 32

No-no two generators are ever on the same bus

Question 33

What happens on a split bus system if a generator fails?

Answer 33

The aircraft will have the remaining generator power both buses. When the APU generator comes on-line the airplane will disconnect the remaining generator from one bus and connect the APU to the bus of the failed generator

Question 34

What is a split parallel system?

Answer 34

Like flying to twin-engine aircraft next to each other.

Question 35

Do generators need to be synchronized on a split parallel system?

Answer 35

Yes for phase and frequency

Question 36

What happens if a generator fails on a split parallel system?

Answer 36

One side of the plane could be tied to the other side to keep system functioning.

Question 37

How is the circuit completed through the generator?

Answer 37

The ground from a load goes to the airframe and the ground from the generator pick up the return current.

Question 38

What is a single wire system?

Answer 38

A single wire goes from the bus to the load to the ground.

Question 39

How does a circuit breaker work?

Answer 39

It is made of two dissimilar metals that expand at different rates when heat is passed through them.

Question 40

What is a split bus relay?

Answer 40

When the avionics bus is separate from the main bus.

Question 41

NC

Answer 41

Normally Closed

Question 42

NO

Answer 42

Normally Open