During steady, level cruise, the lift equals which quantity?

• A. Lift equals weight
• B. Lift equals drag
• C. Weight equals thrust
• D. CL is constant

Answer: (A)

In steady, level cruise the forces in the vertical direction balance, so the lift produced by the wings must equal the aircraft’s weight. This is why lift equals weight: the aircraft is not accelerating upward or downward, so the upward lift exactly cancels the downward weight. Lift depends on air density, velocity, wing area, and the lift coefficient, L = 1/2 ρ V^2 S CL, and the flight condition adjusts speed and angle of attack to set CL so that L matches W. Drag is balanced by thrust in the horizontal direction, not by lift, and CL does not have to be constant for steady level flight.