FAA Powerplant Written Practice Test

What is the typical firing order on a 4 cylinder opposed aircraft engine?

1. Opposed cylinders from the rear to the front

2. Opposed cylinders from the front to the rear

3. Sequentially in a clockwise direction

4. Randomly with no specific order

The correct answer is: Opposed cylinders from the rear to the front

The typical firing order for a 4-cylinder opposed aircraft engine is indeed from the rear to the front. This firing order is designed to balance engine operations and minimize vibrations. In an opposed (or horizontally opposed) engine configuration, the cylinders are arranged in two banks, with each bank positioned opposite each other. Firing from the rear to the front helps ensure that the power strokes of the cylinders occur in a manner that creates a counterbalance, thereby enhancing engine smoothness and efficiency. This setup reduces the overall weight of the engine while maintaining effective power delivery and mechanical simplicity. The effective arrangement so produced ensures that forces generated by the firing of one cylinder are offset by the forces generated by the opposite cylinder. Firing in a random order or without a specific sequence, as suggested by some alternatives, would lead to unbalanced forces within the engine, likely resulting in increased vibration and wear. In contrast to the sequential arrangement of the cylinders, including options that suggest a clockwise method, which is generally not applicable to opposed engines due to the inherent design structure, emphasizes the importance of a systematic approach to firing order in maintaining the optimal functionality of the engine.