As which parameter increases, induced drag decreases?

• A. Altitude
• B. Airspeed
• C. Weight
• D. Mach number

Answer: (B)

Induced drag is the part of drag caused by the wing producing lift, and it is most directly affected by how much lift the wing must generate. In steady level flight the lift must equal the aircraft’s weight. As airspeed increases, the wing can generate the same lift with a smaller lift coefficient, because lift is proportional to 1/2 ρ V^2 S CL. Since CL decreases with speed, the strength of the wingtip vortices—and thus the induced drag—decreases. In short, higher airspeed means less induced drag.

Raising altitude, increasing weight, or changing Mach can affect overall flight conditions and total drag, but they don’t produce the same consistent inverse relationship with induced drag that increasing airspeed does.