Current to primary coil is controlled by a switch in the Cockpit known as a MAGNETO SWITCH
When switch is OFF
Primary circuit is grounded (circuit closed) – NO spark
When switch is ON
Primary circuit is opened – Spark takes place
Spark takes place when contact beaker points are just opening (as opened).
Should the grounding wire be broken circuit will always be open & spark will take place if propeller is related, Irrespective of the position of the Magneto switch.
A/c system has Dual Magneto system everything is duplicated except fro the Rotating Magnets.
Dual Magneto system gives (1) Better safety (2) Better Fuel Combustion.
During flight switch is at both position.
Both – Both Magnetos circuit open – Both Magneto gives spark
Left – Left Magnetos open right Magnetos closed – Left Magneto gives spark only
Right – Right Magnetos open left Magnetos closed – Right Magneto gives spark only
OFF – Both Magnetos closed – Both Magnetos gives no spark
Dead Cut Check – is done at low rpm to check continuity of the Magneto circuit.
Magnetos Drop Check – is done at high rpm to check Maximum drop of Magnetos (Magnetos Serviceability Check) & also to check Grounding wire of each Magnetos.
Left Magneto Check
Both to Right – Drop is observed, If no rpm drop, Left Grounding wire is broken
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Right Magneto Check
Both to Left – Drop is observed, If no drop in rpm, Right Grounding wire is broken
Impulse Coupling – Momentarily rotates the Magnetos to assist start
Before Engine Starts Impulse Coupling
1. It momentarily rotates the Magnetos
2. It Delays the spark to take place in the Power Stroke.
After Engine starts, Impulse Coupling
1) Advances the spark earlier & earlier as rpm increase
Low Tension Booster Coil – current is drawn from Battery & is fed to the Primary of Magneto during starting.
High Tension Booster Coil – separate Primary & Secondary. It draws current from Battery for Primary during starting & it’s Secondary provides the Spark to the Spark Plug.
Distributor – Controls the Spark to different Cylinders.