How does humidity affect aircraft performance?

Humidity plays a significant role in aircraft performance primarily through its impact on air density. As humidity increases, the amount of water vapor in the air increases, which is less dense than the nitrogen and oxygen that make up the majority of dry air. This decrease in air density means that there are fewer air molecules in a given volume.

As a result, the lift generated by the wings of an aircraft is reduced because lift is directly related to air density; lower air density means a reduction in the amount of lift produced at the same airspeed. Additionally, engine performance is affected since most aircraft engines rely on a certain density of air to mix with fuel for combustion. Reduced air density means less oxygen is available for combustion, which leads to decreased engine performance.

Understanding how humidity diminishes air density clarifies why increased humidity reduces lift and engine performance in aviation.