FAA Powerplant Written Practice Test

Which statement about fuel/air ratios is correct?

1. The best power mixture is leaner than the best economy mixture

2. The best economy mixture is richer than the best power mixture

3. The mixture ratio that gives the best power is richer than the mixture that gives the best economy

4. Both mixtures have the same ratio

The correct answer is: The mixture ratio that gives the best power is richer than the mixture that gives the best economy

The correct understanding of fuel/air ratios is that the mixture ratio that delivers the best power is richer than the mixture that provides the best economy. In general, the best power mixture is richer, meaning it has a higher fuel content relative to air. This richer mixture ensures that there is enough fuel to produce maximum power, particularly during high-demand situations such as takeoff or climbing. By providing more fuel, combustion becomes more efficient, delivering the additional energy needed for increased power output. On the other hand, the best economy mixture is designed for optimal fuel efficiency, which occurs at a leaner fuel/air ratio. In this case, less fuel is used in relation to the amount of air, maximizing the distance traveled per gallon of fuel consumed, rather than maximizing power. Understanding this distinction between power and economy mixtures is crucial for pilots and engineers, as it affects performance, fuel consumption, and engine efficiency.