Which variables influence lift in the lift equation L = 1/2 ρ V^2 S Cl?

• A. air density ρ, velocity V, wing area S, coefficient of lift Cl
• B. air density ρ, velocity V, wing area S, coefficient of drag Cd
• C. air density ρ, velocity V, wing area S, Reynolds number Re
• D. air density ρ, velocity V, wing area S, Mach number M

Answer: (B)

Lift in the basic equation comes from the dynamic pressure acting over the wing area and scaled by how effectively the wing generates lift. The four factors that appear directly in L = 1/2 ρ V^2 S Cl are air density, speed, wing area, and the lift coefficient. Air density determines how much air mass is interacting with the wing; faster speeds increase the dynamic pressure (V^2), boosting lift; a larger wing area provides more surface to generate lift; and the lift coefficient encapsulates the wing’s shape and angle of attack, reflecting how effectively the wing converts the flow into lift. The drag coefficient is about drag, not lift, so it does not appear in this lift expression. Reynolds number and Mach number influence the flow and thus Cl in real situations, but they are not separate multiplicative terms in the simple lift formula.