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Consult the appropriate Manufacturers Maintenance Publication

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Warning

In the above figure, all switches and relays are in the normal "OFF" position. These diagrams illustrate the electrical operations of the magneto circuits . 

They are not to be used for installation purposes.

 

Starting Vibrator with Relay

 

With the ignition switch in the "BOTH" position and the start switch S1 in the ON position, starter solenoid L3 and coil L1 are energized, closing their relay contacts R1, R2 and R3. Relay contact R2 connects to the right magneto to ground, rendering it inoperative during starting (this is why the magneto swtich is placed in the BOTH position for starting). Battery current flows through vibrator points V1, coil L2, through retard contact of left magneto to ground as well as through relay contact R1 and through main cointact assembly to ground. A magnetic field around coil L2 produced from this current causes vibrator points V1 to open. Current stops flowing through coil L2 causing the magnetic field to collapse and vibrator points V1 to re-close. This allows coil L2 to energize and vibrator points V1 again to open. This interupted battery current will be carried to ground through the main and retard contact assemblies.

 

When the engine reaches its normal advance firing position, the main breaker assembly of the left magneto opens. However, vibrator current is still carried to ground through the retard contact assembly, which does not open until the starting retard position of the engine is reached. When the retard contact assembly opens (main contact assembly  is still open), vibrator current flows through the primary of transfomer T1 (magneto coil) producing a magnetic field around the coil. as the vibrator points V1 open, current flow through the primary of transformer T1 ceases. This induces a high voltage in the seconday which fires the spark plug. A shower of sparks is therefore produced at the spark plug due to this opening and closing of the vibrator points V1 while the main and retard contact assmblies are open.

 

When the engine fires and begins to increase in speed, the starter switch is released and in turn relay coil L1 and Starter soleniod L3 are energized. this opens the virbator and retard contact assmbly cicuits, rendering them inoperative. The right magneto is no longer grounded and thus both magnetos are simultaneously firing in  full advance.

Test, Repair, Inspect and Overhaul Bendix and Slick aircraft magnetos