AA

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.
  • 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: 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).