S T1 T2 L1 L2 L3 C2 C3 C1 R1 R2 R3 R4 Off S1 On L R Both Off L R Grd L R L In Switch Retard Switch Retard breaker Main  breaker Main  breaker Starting vibrator Magneto switch Left magneto Right magneto V1 Figure 4-30.  High-tension retard breaker magneto and starting vibrator circuit.  the impulse coupling in light aircraft. This system uses an  additional breaker to obtain retarded sparks for starting. The  starting vibrator is also adaptable to many helicopter ignition  systems. A schematic diagram of an ignition system using  the retard breaker magneto and starting vibrator concept is  shown in  Figure 4-30 . magneto begin to open. The interrupted surges of current from  the vibrator can still find a path to ground through the retard  breaker points, which do not open until the retarded firing  position of the engine is reached. At this point in crankshaft  travel, the retard points open. Since the main breaker points  are still open, the magneto primary coil is no longer shorted,  and current produces a magnetic field around T1. With the magneto switch in the both position and the starter  switch S1 in the on position, starter solenoid L3 and coil L1  are energized, closing relay contacts R4, R1, R2, and R3. R3  connects the right magneto to ground, keeping it inoperative  during starting operation. Electrical current flows from the  battery through R1, vibrator points V1, coil L2, through both  the retard breaker points, through R2, and the main breaker  points of the left magneto to ground. Each time the vibrator points V1 open, current flow through  V1 is interrupted. The collapsing field about T1 cuts through  the magneto coil secondary and induces a high-voltage surge  of energy used to fire the spark plug. Since the V1 points are  opening and closing rapidly and continuously, a shower of  sparks is furnished to the cylinders when both the main and  retard breaker points are open. After the engine begins to accelerate, the manual starter switch  is released, causing L1 and L3 to become deenergized. This  action causes both the vibrator and retard breaker circuits to  become inoperative. It also opens relay contact R3, which  removes the ground from the right magneto. Both magnetos  now fire at the normal running advanced degree position of  crankshaft rotation before top dead center piston position. The energized coil L2 opens vibrator points V1, interrupting  the current flow through L2. The magnetic field about L2  collapses, and vibrator points V1 close again. Once more,  current flows through L2, and again V1 vibrator points open.  This process is repeated continuously, and the interrupted  battery current flows to ground through the main and retard  breaker points of the left magneto. Since relay R4 is closed, the starter is energized and the engine  crankshaft is rotated. When the engine reaches its normal  advance firing position, the main breaker points of the left  This system, which is in limited use, is designed for light  aircraft reciprocating engines. A typical system consists of a  Low-Tension Retard Breaker Vibrator 4-19