What is the primary concern when establishing the firing order for an opposed engine?

The primary concern when establishing the firing order for an opposed engine is to provide for balance and eliminate vibration to the greatest extent possible. In opposed engines, which typically have a configuration where cylinders are arranged in two horizontal rows, the timing of the power impulses (the events that occur when fuel is ignited) must be optimized to ensure smooth operation.

If the firing order is not thoughtfully designed to balance the impulses from each cylinder, it can lead to uneven forces acting on the engine structure, which can cause excessive vibration. Vibration not only affects the performance of the engine but can also lead to mechanical failures over time. Thus, selecting a firing order that promotes balance across the engine is critical for reliability, longevity, and passenger comfort, as well as for the overall performance of the aircraft.

Strategies to achieve this balance often involve spacing out the firing events in such a way that the opposing cylinder pairs produce counteracting forces, leading to reduced vibrations and a smoother engine operation.