FAA Powerplant Written Practice Test

What is the typical fuel/oil ratio for a two-stroke cycle light sport aircraft engine?

1. 25:1

2. 40:1

3. 50:1

4. 100:1

The correct answer is: 50:1

The typical fuel/oil ratio for a two-stroke cycle light sport aircraft engine is often around 50:1. This ratio indicates that for every 50 parts of fuel, there is 1 part of oil mixed in. Two-stroke engines require oil mixed with the fuel for lubrication since they do not have a separate lubrication system like four-stroke engines. The 50:1 ratio provides an adequate amount of oil to ensure proper lubrication, performance, and prevention of engine wear, while minimizing the amount of oil that could produce excessive smoke and emissions. Higher ratios, such as 100:1, may not provide sufficient lubrication, leading to increased wear and the potential for engine failure. Conversely, lower ratios like 25:1 or 40:1 might be suitable for other applications or older engines but are typically not necessary for modern light sport aircraft engines, which are designed to operate efficiently at the 50:1 ratio.