What is the main objective of operating an engine at 'lean of peak'?

Operating an engine at 'lean of peak' refers to the fuel-air mixture being adjusted so that there is less fuel compared to air, positioning it just before the peak engine performance in terms of power output. The primary goal of this practice is to enhance fuel efficiency and economy. By using less fuel for the same amount of air, the engine can maintain a sufficient level of performance while consuming less fuel, which leads to better fuel economy.

This adjustment can reduce fuel expenditure without significantly sacrificing engine power or performance, making it particularly beneficial for long flights where fuel conservation is crucial. In addition to improving fuel efficiency, leaning the mixture can contribute to lower operational costs related to fuel expenses over time.

Maximizing horsepower output typically requires a richer fuel mixture, which would not align with the parameters of operating lean of peak. Increasing engine size does not pertain to fuel mixture settings but rather to physical dimensions and design of the engine itself. Reducing operational costs is a broader term that can apply in various contexts, but in this specific case, the main focus is on the direct improvement of fuel efficiency through the lean of peak operation.