In typical airplane operations, when is the mixture control usually set to rich?

The mixture control is typically set to rich during takeoff to ensure the engine receives the optimal fuel-air mixture for maximum power and performance. At full throttle, the engine requires a rich fuel mixture to produce the necessary horsepower for takeoff, especially since this is a critical phase of flight where maximum performance is essential for a safe and efficient climb.

While the mixture may be adjusted during other phases of flight, such as leaning for fuel efficiency during cruise, rich settings for takeoff help to prevent engine issues that could arise from running too lean. Additionally, at lower altitudes, the density of the air is higher, which allows more fuel to be mixed with the air for combustion. This rich setting helps to facilitate a strong and reliable climb out during this critical phase of flight.