Which statement about parasite drag and induced drag with respect to airspeed is true?

• A. Parasite drag decreases with airspeed; induced drag decreases with airspeed.
• B. Parasite drag rises with airspeed; induced drag decreases with airspeed.
• C. Parasite drag rises with airspeed; induced drag decreases with airspeed.
• D. Parasite drag increases with airspeed; induced drag remains constant.

Answer: (C)

Two main sources of drag respond very differently to airspeed: parasite drag and induced drag. Parasite drag comes from all parts of the airplane that do not generate lift—fuselage, wings at non-lifting parts, wheels, antennas, and skin friction. This drag grows with dynamic pressure, so as speed increases (dynamic pressure rises with V^2), parasite drag increases roughly in proportion to V^2.

Induced drag arises from producing lift. It is tied to wingtip vortices and downwash that occur when the wing generates lift. For a given weight, increasing speed lets the wing achieve the required lift with a smaller lift coefficient, which weakens the vortices and downwash, causing induced drag to decrease roughly with 1/V^2.

So the true statement is that parasite drag rises with airspeed, while induced drag decreases with airspeed. This interplay is why total drag has a minimum at some intermediate speed, where lift-to-drag is optimized.