Lesson 10: Aircraft Electrical Systems

Aircraft Electrical Systems

• A circuit must have at least three parts.

Aircraft Electrical Systems

• A circuit must have at least three parts.

• The source

Aircraft Electrical Systems

• A circuit must have at least three parts.

• The source

• The electron transportation and distribution system

Aircraft Electrical Systems

• A circuit must have at least three parts.

• The source

• The electron transportation and distribution system

• The load (Where the work is done)

Series And Parallel Circuits

• Series Circuit

• All electrons must flow through all active components.

• The amount of voltage dropped across the filament is always less than the total.

• Voltage drop depends on the amount of resistance of the individual load.

Series And Parallel Circuits

• Parallel Circuit

• A portion of the electrons flow through each filament.

• The amount of voltage drop is equal to the total voltage produced by the source.

Voltage And Current Measuring Instruments

• Current and voltage are the most commonly measured variables.

• Voltmeters

• Ammeters

Voltage And Current Measuring Instruments

• Voltmeters (Parallel)

• Measures current but indicates values of voltage.

• Indicates electrical system condition.

Voltage And Current Measuring Instruments

• Ammeters

• Measures current flow

• Battery is charging when electrons are flowing from the positive terminal.

• This would be a positive indication.

The Aircraft Electrical System

The Aircraft Electrical System

• Source

• 12 volt battery with the negative terminal connected to the airframe (negative ground).

• Master solenoid

• Master switch

The Aircraft Electrical System

• The Starter Circuit

• Starter switch circuit (control circuit)

• Starter solenoid circuit (motor circuit)

• The master switch/solenoid circuit must also be connected.

The Aircraft Electrical System

• The Busbar

• Rigid point that is a convenient place to terminate many wires neatly and safely.

• Connected to the positive terminal of the battery, when the master switch is on.

• Same electrical potential as the battery.

• Circuit breakers are often mounted.

The Aircraft Electrical System

• The Alternator

• The alternator switch completes a circuit to the voltage regulator.

• The voltage regulator samples the system voltage and increases or decreases the field voltage which limits alternator output.

The Aircraft Electrical System

• Ammeters And Loadmeter In The Circuit

• Installed between the master solenoid and the busbar.

• Senses the amount and direction of current flow in the battery circuit.

• Installed between A terminal of the alternator and the busbar.

• Senses current flow (in one direction), or output, of the alternator (loadmeter).

Ignition Systems

Battery Ignition System

Magnetos

• Completely independent of the electrical system of the airplane.

• Primary current is interrupted by a set of breaker points, and high voltage for the spark plugs comes from the voltage step-up in the magneto coil.

• Rotating Magnet Magneto

Rotating Magnet Magneto

Rotating Magnet Magneto

• Resultant Flux (E-gap)

• Maximum current is flowing several degrees after neutral.

Rotating Magnet Magneto

Rotating Magnet Magneto

• Dual Magnetos

• High-tension Magnetos

• Low-tension Magnetos

High-tension Magneto

Low-tension Magneto

Rotating Magnet Magneto

• Aids To Starting

• Magnetos provide a good, hot spark at idle, at cruise, and at high speed.

• But not when the engine is turning slowly during start.

» Impulse Coupling

Impulse coupling

• A small spring-loaded coupling between the magneto shaft and the engine drive gear.

Impulse coupling

Vibrator starting system“Shower of Sparks”

• Pulsating DC from the induction vibrator is directed into the magneto coil.