Aircraft Electrical Systems Flashcards
Good luck (lol)
What size generator must be used in an aircraft electrical system if the connected electrical load is 30 amps, and there is no way of monitoring the generator output?
When monitoring is not practical, the total continuously connected electrical load must be no more than 80% of the rated generator output. This would require a generator with a rating of 37.5 amps. Practically, a 40-amp generator would be installed
What is meant by paralleling the generators in a multi-engine aircraft?
Adjusting the voltage regulators so all the generators share the electrical load equally
What are the three types of voltage regulators used with aircraft generators?
- Vibrator-type
- Carbon-pile type
- Solid state-type
What is meant by “flashing” the field generator?
Restoring the residual magnetism to the frame of the generator. This is done by passing battery current through the field coils in the direction it normally flows when the generator is operating
What is meant by a trip-free circuit breaker?
A circuit breaker that cannot be closed while a fault exists, regardless of the position of the operating handle
What is meant by a slow-blow fuse?
A fuse that will allow more current than its rating to flow for a short period of time, but will open the circuit if more than its rate current continues to flow
What is the function of a fuse or circuit breaker in an aircraft electrical circuit?
It protects the wiring from an excess of current. It will open the circuit if enough current flows to heat the wire
What are the two principles upon which circuit breakers operate?
- Magnetic circuit breakers open a circuit when the current creates a strong enough magnetic field
- Thermal circuit breakers open a circuit when the current causes enough heat
What circuit in an aircraft electrical system is not required to have a circuit protective device?
The main circuit for starter motors, used during starting only
How does a vibrator-type voltage regulator maintain a constant voltage?
When the voltage rises above the desired value, an electromagnetic relay opens and inserts a resistor in the generator field circuit, decreasing the field current and lowering the generator output voltage
What two components are normally housed with a vibrator voltage regulator in a single-unit generator control?
- Current limiter
- Reverse-current cutout relay
What are the two types of inverters found in aircraft?
- Rotary inverters
- Static inverters
What is the purpose of an inverter?
To convert DC electricity to AC
How does a rotary inverter create AC voltage?
By using a DC motor to spin an AC generator
Where could you find the part number of a switch in an aircraft electrical system?
In the equipment table or bill of materials on the electrical circuit diagram for the aircraft
What is the main disadvantage of aluminum wire over copper wire for use in an aircraft electrical system?
Aluminum wire is more brittle than copper. It’s more subject to breakage when it’s nicked and subjected to vibration
What size aluminum wire would be proper to replace a piece of four-gauge copper wire?
Two-gauge. When you substitute aluminum wire for copper wire, use a wire that is two gauge numbers larger
What is the smallest size aluminum wire that is approved for use in aircraft electrical systems?
Six-gauge
Can you substitute aluminum wire for copper wire?
Yes. However, you must use aluminum wire two wire gauge sizes larger to carry the same current. Aluminum wire should never be used in runs of three feet or less, or in communication and navigation systems
Can a wire in free air carry the same current as wire in a bundle?
A wire by itself can hold a higher current than the same wire bundled with other wires. Always refer to an electrical wire size selection chart
What are common causes of wire failure in a crimped connector?
The wire was not inserted far enough into the connector and/or the connector was excessively crimped
What is one of the first things to check if an electrical component does not operate?
Always start with simple solutions and move to more complex. EX: If a light doesn’t function, is the system turned on, is the aircraft electrical system energized, or is the bulb burnt out?
What may be provided by the manufacturer to assist in troubleshooting?
Manufacturers often provide a troubleshooting logic chart
What are the four basic steps of troubleshooting?
- Know how the system should operate
- observe the way the system is operating
- Divide the system into smaller segments to isolate trouble
- Look for the obvious problem first
When routing a fluid line parallel to an electrical wire bundle, which should be on top?
The electrical wire bundle should be on top
What is the composition of 60/40 solder?
60% tin and 40% lead
What is the difference between soldering and brazing?
Soldering is a method of joining metal parts with a molten nonferrous alloy that melts at a temperature below 800 degrees F. Brazing is essentially the same except the brazing alloy melts at a temperature higher than 800 degrees F, but lower than the melting temperature of the metal used
Why must acid-core solder never be used on electrical wire?
The acid causes the wire to corrode
What determines the strength of a soldered joint?
The mechanical connection of the join, not the solder
Why are the solderless splices usually better than soldered splices in the wiring of an aircraft electrical system?
Soldered joints are usually stiff, and vibration can harden the wire and cause it to break. Solderless splices are designed to keep the joint flexible so vibration cannot cause the wire to break
What is an SPDT switch?
Single pole, double throw switch
If no specific instructions are available, which way should the operating handle of an electrical switch move to turn a component on?
Forward or upward
What color insulator on a preinsulated solderless connector indicates that the connector is proper for a 10-gauge wire
Yellow
How many splices are allowed in a single wire run?
One
What does the specific gravity of the electrolyte of a lead-acid battery indicate?
The amount of acid relative to the water in the electrolyte. This is an indication of the state of charge of the battery
What are the most likely causes of a battery with a distorted or swollen battery case?
The battery has been overcharged, causing overheating, or it could be caused by a plugged vent cap
On NiCd batteries, what is the minimum cell voltage at the end of the charge?
1.55 Volts
How is the state of charge determined on a NiCd battery?
The only accurate way to determine the state of charge of a NiCd battery is by measured discharge with a NiCd battery charger and following the manufacturer’s instructions
What could cause an AC electric motor to run too fast?
Excessive applied voltage or shorted field windings
What tool is used to check a motor or generator armature for shorts and opens under load conditions?
A growler
When using a growler, what indication will occur when a short exists between an armature segment?
When a metal blade is held over the armature and a short exists in a segment, the blade will begin to vibrate and “chatter”
How is the output voltage of an alternator controlled?
By varying the field current that excites the alternator
What instruments are used to monitor electrical system loads?
Ammeters and voltmeters
How would you identify a specific wire in a wire bundle
By the identification code marked on the wire
What tool would you use to determine the size of an unmarked wire?
A wire gauge
What colors are the navigation lights on the wingtips?
The left wingtip is red, right is green
Name several types of electrical devices that would be considered intermittent loads
- Landing gear
- Cowl and wing flap motors
- Radio transmitters
Why would it be necessary to analyze an electrical system before increasing the load on the system?
To determine that the generator capacity, wire size, and protective capacity will not be exceeded
What factors should be considered when determining the wire size for a particular application?
- The system voltage
- Permissible voltage drop
- Current to be carried
- Wire length
- Whether the load is continuous or intermittent
What is the relationship between the inside diameter of a conduit and the outside diameter of the wire bundle inside it?
The conduit must be 25% larger than the wire bundle
What is the maximum number of terminal lugs that can be placed on a single terminal strip stud?
Four
What is the proper length of a bonding jumper?
As short as practical, but long enough to allow free movement of the component
Under what conditions must a switch be derated from its nominal rating?
- When used with inductive circuits
- Circuits with high rush-in current
- And with DC motors
At what point do electric motors draw the most current?
When starting
Circuit breakers are designed to open before what condition occurs?
Before the wire emits smoke
At what point in a circuit should the protective device be located?
As close to the power source as possible
What type of circuit breaker may not be used in an aircraft?
An automatic resetting type
What part of an aircraft is identified by a white navigation light?
The tail
What could cause an AC electric motor to run too slowly?
Lack of lubrication, defective wiring, or low applied voltage
What should be done when making bonding or grounding connections between dissimilar materials?
Use a suitable washer so that any corrosion will occur on the washer
Prior to making a continuity check, what must be done to an electrical circuit?
The power must be turned off
