Which drag is always present if lift is produced?

• A. Induced drag
• B. Profile drag
• C. Form drag
• D. Skin friction drag

Answer: (A)

Induced drag is the drag component that is inherently produced when lift is generated by a finite wing. When the wing creates lift, it deflects air downward and generates wingtip vortices and a downward flow (downwash). To conserve momentum, part of the lifting process must slow the aircraft’s forward motion along the flight path, which appears as a rearward, or drag, force. This induced drag increases with the amount of lift the wing is producing and decreases with higher speed or a longer (higher aspect ratio) wing, but it never goes to zero as long as lift exists.

Other forms of drag—skin friction and form (pressure) drag—are related to the surface roughness, shear forces, and the overall shape of the aircraft. They can be present even without lift and aren’t forced to appear solely because the wing is generating lift.