Aircraft Electrical Systems Notes

Aircraft Generator Cooling

• Aircraft generators are cooled by an integral fan during ground operation.

Voltage Regulator Functionality

• A low voltage reading in a 24-volt DC system could indicate an out-of-adjustment voltage regulator.

Generator Field Coil Continuity

• When testing a generator field coil with an ohmmeter, a series field coil should show very low resistance due to the few turns of heavy wire.

Circuit Overheating Protection

• Fuses or circuit breakers protect electrical circuits from overheating.

Function of Static Inverters

• Static inverters convert DC to AC using an oscillator to create the appropriate frequency and waveform.

Intermittent Duty Circuits

• An intermittent duty circuit may operate for a maximum of two minutes.

Reverse Current Cutout Relay

• If a relay fails to open when generator output drops below battery potential, current will flow oppositely through the generator armature.

Electrical Junction Boxes in Fire Zones

• Stainless steel is recommended for junction boxes in fire zones.

Wire Size Determination Factors

• Consideration for wire size includes permissible voltage drop, allowable power loss, current-carrying capability, and type of load.

Bonding Stainless Steel Components

• Copper jumpers are recommended to bond noncontinuous stainless steel components to avoid corrosion.

Lubrication of Electrical Cable

• To minimize damage when pulling cables through rigid conduit, dusting them with powdered soapstone is effective.

Navigation Lights Wiring

• If navigation lights are controlled by one switch, they are likely connected in parallel with each other and in series with the switch.

Restoring Residual Magnetism

• Flashing the fields can restore residual magnetism in a generator by passing DC through the field coils.

Types of Switch Configurations

• A switch that requires manual holding in the ON position should be a single-pole, single-throw (SPST) normally open switch.

Purpose of Laminated Poles

• Laminating generator poles reduces eddy current losses.

Circuit Control Relays

• An aircraft electrical circuit control relay functions as an electronically operated switch.

Series Wound Generator Usage

• Series-wound DC generators are typically not employed in aircraft due to regulation challenges.

Handling High-Voltage Capacitors

• Ensure that high-voltage capacitors are fully discharged before removal from circuits to avoid electric shock.

Voltage Drop Calculations

• Voltage drop in No. 18 copper wire over 50 feet carrying 12.5 amperes is calculated as:

  VD = RLA = 0.00644 imes 50 imes 12.5 = 4.025 ext{ volts}

Automatic Reset Circuit Breakers

• They should not be trusted as circuit protection devices according to 14 CFR Part 23 requirements.

Constant Speed Drive (CSD) Disconnect

• This is usually controlled by a switch located in the cockpit.

Thermal Runaway in Batteries

• Excessive current draw can cause thermal runaway in nickel-cadmium batteries, leading to overheating and failure.

Purpose of Rectifiers

• Rectifiers convert alternating current (AC) to direct current (DC).

Routing Coaxial Cables

• Cables should be routed as directly as possible in installations.

Navigation Lights Color Codes

• Navigation lights: left - red, right - green, rear - white.

Protection for Wires Near Moving Parts

• Wires that may contact moving parts should be passed through conduit for protection.

Single-Pole, Double-Throw (SPDT) Switch Functionality

• Indicates number of circuits completed through the switch: an SPDT switch can select one of two paths.

Alteration Criteria for Electric Cable Size

• Current-carrying capacity and voltage drop considerations are crucial for electric cable size selection in alterations.

Transformer Winding Short Testing

• Heat generation during normal operation can indicate shorted transformer windings.

Circuit Breakers Purpose

• Designed to protect electrical circuits by installed as close to the source as possible.

Emergency Circuits

• Guarded switches are typically used for circuits that only operate during emergencies.

Minimum Bend Radius for Wire Bundles

• Should be at least ten times the outside diameter of the bundle.

Constant-Speed Drive (CSD) Mechanics

• CSD units maintain generator speed by utilizing a variable hydraulic system.

Types of DC Motors

• Three basic types: series, shunt, compound.

Role of Pole Pieces in DC Generators

• Pole pieces are part of the field assembly in a generator.

Function of Ammeters

• Ammeters indicate the rate of current charging a battery in the circuit.

Anticollision Light Requirements

• Must function independently from position lights.

Radio Interference Minimization

• Capacitors connected in parallel with AC generators help eliminate radio noise.

Parallel Operation of AC Generators

• Frequency and voltage of connected AC generators must be equal.

Splice Configuration

• Required splices within wire bundles should be staggered along the bundle's length.

Voltmeter Connection

• Must be connected in parallel with the load to measure voltage correctly.

Grounding in Electrical Systems

• Grounding helps stabilize electrical systems and prevent radio signals.

Advantages of Alternating Current (AC)

• AC voltage can be easily modified using transformers, unlike direct current (DC).