What is induced drag?

What is induced drag?

• A. The primary drag produced by skin friction
• B. The undesirable but unavoidable byproduct of lift. Increases in direct proportion to the increase in angle of attack
• C. Drag caused by crosswinds
• D. The total drag at maximum speed

Answer: (B)

Induced drag is the drag that arises as a byproduct of generating lift. When a wing produces lift, air spills around the tips, creating wingtip vortices. These vortices generate a downwash behind the wing, effectively increasing the angle of attack the wing sections must behave as if they have. To maintain the same lift, the wing must work harder, which shows up as a resisting force—that is, drag. The amount of induced drag increases as you demand more lift, which happens when you raise the angle of attack or increase the lift coefficient. In subsonic flight, this drag decreases with speed because higher speed means the wing can generate the same lift at a lower angle of attack. It’s also more noticeable on short, low‑aspect‑ratio wings, where wingtip effects are stronger. So, the description that it’s an undesirable byproduct of lift, rising with increases in angle of attack, captures why induced drag exists and how it behaves.

Induced drag is the drag that arises as a byproduct of generating lift. When a wing produces lift, air spills around the tips, creating wingtip vortices. These vortices generate a downwash behind the wing, effectively increasing the angle of attack the wing sections must behave as if they have. To maintain the same lift, the wing must work harder, which shows up as a resisting force—that is, drag.

The amount of induced drag increases as you demand more lift, which happens when you raise the angle of attack or increase the lift coefficient. In subsonic flight, this drag decreases with speed because higher speed means the wing can generate the same lift at a lower angle of attack. It’s also more noticeable on short, low‑aspect‑ratio wings, where wingtip effects are stronger.

So, the description that it’s an undesirable byproduct of lift, rising with increases in angle of attack, captures why induced drag exists and how it behaves.