Aircraft

16AE206 Aircraft system and instruments prepared by 3/9/2020 1 R.Vijayakumar AP/Aero Basics

• Wherever there is an electric field there is an accompanying magnetic field • Electromagnetic induction • Transformer action

16AE206 Aircraft system and instruments prepared by 3/9/2020 2 R.Vijayakumar AP/Aero Ignition system- engine

• It must deliver high tension spark at each at the correct at predetermined timing.

Battery ignition ignition

16AE206 Aircraft system and instruments prepared by 3/9/2020 3 R.Vijayakumar AP/Aero Battery Ignition System

• Similar to the ignition system of automobiles • A rotated by the engine disrupts the flow of current in the primary circuit. This collapsing magnetic field inducers a high voltage at the . • This voltage is directed to the

16AE206 Aircraft system and instruments prepared by 3/9/2020 4 R.Vijayakumar AP/Aero Magneto Ignition System A magneto is an engine driven AC generator It works on the principle of mutual induction Engine rotates a permanent magnet surrounded by an electric coil. This rotation induces an electric current in the coil windings.  At correct time the current is stopped & magnetic field collapses in the secondary winding and the resultant induced current is carried to the spark plug. The spark Jumps the electrodes starting ignition.

16AE206 Aircraft system and instruments prepared by 3/9/2020 5 R.Vijayakumar AP/Aero Magneto Ignition System

• High tension magneto

• Low tension magneto

16AE206 Aircraft system and instruments prepared by 3/9/2020 6 R.Vijayakumar AP/Aero High Tension Magneto

Magnetic circuit Primary electrical circuit

Secondary electrical circuit

16AE206 Aircraft system and instruments prepared by 3/9/2020 7 R.Vijayakumar AP/Aero Magnetic circuit

permanent multi-pole rotating magnet, a soft iron core, and pole shoes

16AE206 Aircraft system and instruments prepared by 3/9/2020 8 R.Vijayakumar AP/Aero Magnetic density

 It is subjected to an increasing and decreasing magnetic field  A change in polarity each 90° of magnet travel

16AE206 Aircraft system and instruments prepared by 3/9/2020 9 R.Vijayakumar AP/Aero Primary electrical circuit

 consists of a set of breaker contact points, a condenser, and an insulated coil.  Coil consists of few turns of copper wire  Capacitor is wired parallel to breaker points  Primary circuit is completed when breaker points are in contact  Condenser is to avoid arcing when opening circuit

16AE206 Aircraft system and instruments prepared by 3/9/2020 10 R.Vijayakumar AP/Aero Breaker contact points

breaker points with condenser opens to interrupt the flow of current in the primary coil, causing an extremely rapid change in flux linkages. The resultant high-voltage in the secondary winding discharges across the gap in the spark plug. They automatically open & close the primary circuit at correct time in relation to piston position.

16AE206 Aircraft system and instruments prepared by 3/9/2020 11 R.Vijayakumar AP/Aero Secondary Electrical Circuit

• They contains the secondary windings of the coil, rotor, distributor cap, ignition lead, and spark plug. • secondary coil is made up of a winding containing approximately 13,000 turns of fine, insulated wire • distributor numbers represent the magneto sparking order

16AE206 Aircraft system and instruments prepared by 3/9/2020 12 R.Vijayakumar AP/Aero Magneto inherent problems

• Moisture is a good conductor of electricity • If absorbed by the no conducting material in the magneto, such as distributor blocks, distributor fingers, and coil cases can create an electrical circuit. • The high-voltage current that normally arcs across the air gaps of the distributor can flash across a wet insulating surface to ground or misfire the spark plug called flash over and causes misfiring of the cylinder. • This causes pre-ignition, to prevent this coils ,condensers, are waxed. • This causes carbon tracking

16AE206 Aircraft system and instruments prepared by 3/9/2020 13 R.Vijayakumar AP/Aero Ignition harness

• The ignition harness consists of several ignition leads. Ignition leads are insulated wires that that carries the electrical energy from the magneto to the spark plug. • It provides an electrical path to spark plug as well it shields the system from external magnetic fields.

16AE206 Aircraft system and instruments prepared by 3/9/2020 14 R.Vijayakumar AP/Aero Low Tension Magneto

In early years, it was difficult  Low voltage is generated in magneto to provide insulators that  This low voltage is increased by could contain the high-voltage transformer action of secondary coil. all weather and radio-  Ignition lead will have short length equipped aircraft have ignition  Distributor uses brush type contact wires enclosed in shielding to so flash over is avoided  high-voltage is present only in short prevent radio noise due to leads between the transformer and high-voltages. spark plug

16AE206 Aircraft system and instruments prepared by 3/9/2020 15 R.Vijayakumar AP/Aero Spark plug

Its function is to create a spark that will ignite the fuel air mixture Spark plugs operate at extreme temperatures, electrical pressures, and very high cylinder pressures.

16AE206 Aircraft system and instruments prepared by 3/9/2020 16 R.Vijayakumar AP/Aero Different types of Spark plug

 Hot plugs have a long insulator nose that creates a long heat transfer path  Cold plugs have a relatively short insulator to provide a rapid transfer of heat to the cylinderhead.  High compression engine will have cold spark plug  Low compression engine will have hot spark plug

16AE206 Aircraft system and instruments prepared by 3/9/2020 17 R.Vijayakumar AP/Aero Problems associated with spark plug

• Lead fouling • Carbon fouling • Electrode erosion • Graphite Fouling of Spark Plugs

16AE206 Aircraft system and instruments prepared by 3/9/2020 18 R.Vijayakumar AP/Aero Turbine engine Ignition system

 Capacitor-type , Consists of 2 independent ignition units operating from low voltage DC power(aircraft battery/permanent magnet generator)

air is ducted to the exciter box flows around the igniter lead and goes to nacelle.

 Typical ignition system includes two exciter units, two transformers, two intermediate ignition leads, and two high tension leads

16AE206 Aircraft system and instruments prepared by 3/9/2020 19 R.Vijayakumar AP/Aero Turbine engine Ignition system

There is no timing of ignition Once engine is started the ignition system is switched off However continues ignition is used in critical flight modes such as take off and landing, emergency situations. A continuous series of sparks isproduced until the engine starts

16AE206 Aircraft system and instruments prepared by 3/9/2020 20 R.Vijayakumar AP/Aero 16AE206 Aircraft system and instruments prepared by 3/9/2020 21 R.Vijayakumar AP/Aero  filter that prevents noise voltage from being induced into the aircraft electrical system  DC Motor driving the multilobe cam and single lobe cam are operated by this low V  When the breaker opens, the flow of current stops, and the collapse of the field induces a voltage in the secondary of the transformer  When capacitor is charged, contactor is closed by lobe mechanical action  A portion of the charge flows through the primary of the triggering transformer and the capacitor  This current induces a high-voltage in the secondary, which ionizes the gap at the spark igniter

16AE206 Aircraft system and instruments prepared by 3/9/2020 22 R.Vijayakumar AP/Aero