FAA Powerplant Written Practice Test

If an aircraft engine has 9 cylinders, what can be deduced about its firing order?

1. 1-3-5-7-9-2-4-6-8

2. 1-2-3-4-5-6-7-8-9

3. 1-4-6-8-2-5-7-3-9

4. 1-3-5-2-4-6-8-7-9

The correct answer is: 1-3-5-7-9-2-4-6-8

The correct answer is a specific firing order commonly used in radial engines, particularly in a 9-cylinder engine configuration. This order, 1-3-5-7-9-2-4-6-8, ensures that the engine runs smoothly and balances the forces exerted throughout the engine cycle. In engines with multiple cylinders, the firing order is designed to evenly distribute the power strokes and maintain balance in the crankshaft, which helps to minimize vibrations and enhance overall performance. A common approach in radial engines is to have every cylinder in an alternating sequence to achieve a harmonious operation. In this case, the proposed firing order accommodates the 9-cylinder layout by allowing the engine to operate in a well-structured firing pattern that supports reliability and efficiency. Other options may not follow the configurations needed for proper power delivery or could lead to imbalances that can cause vibrations, increased wear, or even engine failure. The chosen order effectively illustrates the principles of smooth operation in this specific engine design.