FAA Powerplant Written Practice Test

How does a booster coil on a radial engine operate?

1. It works solely on electromagnetic energy

2. It requires no battery power

3. It operates off of battery power using a trailing finger in the distributor

4. It functions with solar energy

The correct answer is: It operates off of battery power using a trailing finger in the distributor

A booster coil on a radial engine is designed to enhance the ignition system's performance by increasing the voltage supplied to the spark plugs, particularly under conditions of high load or when starting the engine. This coil operates by relying on battery power, which is essential for its function. When the engine is cranked, the battery supplies electrical energy to the ignition system. The booster coil steps up this voltage, allowing a stronger spark to be produced at the spark plugs. This is particularly important in radial engines, where multiple cylinders may require increased ignition energy to ensure proper combustion across all cylinders, especially during tough starting conditions or when the engine is under load. The mention of a trailing finger in the distributor highlights how the ignition system organizes the flow of electricity to each cylinder in sequence, ensuring that the timing of the spark is correct. This coordination is crucial for the efficient operation of the engine. Other options, such as solely relying on electromagnetic energy or functioning without battery power, do not accurately describe the operational requirements of a booster coil. Similarly, solar power is not relevant to the functioning of a booster coil in this context, as it relies on traditional electrical sources to perform its role.