FAA Powerplant Written Practice Test

What does the primary coil do in a magneto system?

1. Amplifies the electrical current

2. Stores electrical energy

3. Creates a magnetic field

4. Distributes electrical charges

The correct answer is: Creates a magnetic field

In a magneto system, the primary coil plays a crucial role in creating a magnetic field. When current flows through the primary coil, it generates a magnetic field around it. This magnetic field is essential for the operation of the ignition system, particularly in generating the high voltage needed to ignite the fuel-air mixture in the combustion chamber. The creation of the magnetic field occurs due to the principles of electromagnetism, where an electric current produces a magnetic field around a conductor. In the magneto system, as the magneto rotates (typically driven by the engine), the changing magnetic field induces a voltage in the secondary coil, which ultimately results in the generation of a high-voltage spark discharge. This spark is what ignites the fuel in the engine, facilitating the combustion process. Understanding this function of the primary coil is important for recognizing how magnetos operate independently of external electrical power sources, which makes them reliable for aircraft engines. This independence is especially valuable in aviation because it ensures that the ignition system remains functional even if the aircraft’s electrical system fails.