Under the stated conditions, which combination produces the most lift?

• A. Low temperature, high pressure, and low humidity
• B. High temperature, low pressure, and high humidity
• C. Low temperature, low pressure, and high humidity
• D. High temperature, high pressure, and low humidity

Answer: (A)

Lift is directly tied to air density for a given rotor speed and geometry, because denser air provides more momentum exchange with the rotor blades. Air density increases when air is compressed (higher ambient pressure), when it is cooler (lower temperature makes the air denser), and when it is drier (humid air is less dense because water vapor has a lower molecular weight than dry air). So the combination that gives the densest air is low temperature, high pressure, and low humidity. With denser air, for the same rotor performance, you get more lift. The other options mix in higher temperatures, lower pressures, or higher humidity, each of which lowers density and reduces lift accordingly.