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. At neutral position

2. Full register

3. One-quarter rotation

4. Half register

The correct answer is: Full register

The position of the rotating magnet in a high tension magneto when the points first close is at "full register." This is significant because at full register, the magnetic field is maximally aligned with the induction coil, which is critical for producing a strong spark. When the points close, they interrupt the circuit, causing the magnetic field to collapse, which induces a high voltage in the ignition coil. If the magnet were positioned elsewhere, such as at the neutral position or any other point, the effectiveness of induced voltage would be compromised, leading to a weaker spark. Understanding the mechanics of the magneto operation helps clarify why the full register position is essential for efficient ignition system performance in aircraft engines. The timing of when the points close in relation to the magnet's position is therefore a crucial aspect of ignition timing and overall engine performance.