Aircraft Electrical Diagram
Power Generation, I
Most aircraft require some form of electrical power to operate navigation-, taxi-, landing-, strobe lights, one or more COM and NAV radio's, transponder, intercom and other electronic systems.
The electrical system consist of a battery and an alternator or generator on older aircraft. All of this is connected through several meters (kilometers in large aircraft) of wire.
All matter on earth is made up from molecules and they consist of atoms. Atoms are made of electrons, protons and neutrons. Electricity is about the flow of electrons attracted to protons and repelled by other electrons.
Magnetism can and is used to generate electricity needed to operate lights, radio's and navigation equipment on board aircraft.
We will take a quick look where and how aircraft use magnetism and how this energy can be stored for later use.
Magnetism Basics
Described by Aristotle to Thales in a discussion around 600 BCE and used in India by surgeon Sushruta for surgical purposes. In 1819 professor Hans Christian Oersted noted the relation ship of electricity and magnetism as he discovered that an electrical current could influence a compass.
Magnetism enables certain materials (iron based) to attract (opposite poles) or repel (equal poles) each other. It is widely used in aircraft in applications as the compass, alternators/generators, starter motors, navigation and instruments.
Magnetic material consist of minute particles each having a north and a south pole and they are aligned in one direction. Non magnetized material have the same particles: they are only not aligned but in random order.
A magnetic field exists around a magnet, this can be shown with a compass (also a small magnet which aligns itself with the magnetic field of the earth). This magnetic field is called flux and it can be 'guided' by using soft iron. Soft iron has a permeability (comparable with electrical conductivity) which is some 1000 times higher than air, and this property is used in relays and motors.
Temporary
Some materials are magnetized without difficulty, they also loose this property with the same ease. Soft iron is known for this. Which makes them very suitable for temporary magnets to be used in for example: relays, solenoid switches and electromagnets.
Permanent
Other materials are not so easily magnetized (hard iron, steel) but when they are magnetized they will not loose that property that easy. They can be used as a permanent magnet. You will need to hammer or heat them to make them loose their magnetic field.
In an aircraft you will normally find permanent magnets in engines as iron detector (Rotax), compasses or generators and temporary magnets in alternators, electromagnets, relays, etc.
Electromagnets
An electromagnet is basically an insulated wire wound a number of turns around a piece of iron. If you send a current through that coil a magnetic field is created proportional to the amount turns in de winding and the current in the coil. Put differently: the strength of the magnetic field that is created depends on the current, windings and permeability of the core.
It works in reverse too: move a magnet through a coil and electricity is generated.
When switching off a current through an electromagnet an inductive voltage spike is created. The reason is that a large coiled inductor resists changes in the current through its windings. And any change (switching off), will result the energy stored in the coil, to be returned to the electrical circuit with reversed polarity.
To protect the electronics of the aircraft this inverse voltage spike needs to be dampened. This can be done by a capacitor or a diode. A good example is a engine starter relay or any other type of coil which is switched on or off.
