FAA Powerplant Written Practice Test

What is the approximate position of the rotating magnet in a high tension magneto when the points first close?

1. Full register

2. Half register

3. Quarter register

4. Neutral position

The correct answer is: Full register

In a high tension magneto, the rotating magnet's position when the points first close is crucial for the timing of the ignition system. At this moment, the magnetic flux begins to change rapidly, which induces a sufficient voltage in the secondary winding of the magneto. When the points close, the rotating magnet is in a position known as "full register." This is the point where the magnetic field is at its maximum strength, effectively allowing the maximum amount of magnetic lines of flux to link with the coil windings. This alignment ensures efficient induction of high voltage, which is necessary for sparking the ignition. When considering other positions, such as half register or quarter register, these would not allow for the optimal magnetic coupling necessary for maximum voltage generation at the point of closure. The neutral position typically refers to the point where there is no magnetic effect on the winding, which is not suitable for ignition timing. Thus, full register is key to ensuring that ignition occurs effectively and at the right moment in the engine cycle.