AerodynamicsQuestion 435 of 934

Where is interference drag the greatest?

  1. Where two surfaces run parallel to each other
  2. At the middle of a long, smooth fuselage skin
  3. Where two surfaces meet at perpendicular angles
  4. Along the trailing edge of a symmetrical wing tip
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Correct answer: Where two surfaces meet at perpendicular angles

The most interference drag is seen when two surfaces meet at perpendicular angles. Fairings reduce it.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 5: Aerodynamics of Flight — Interference Drag, page 103

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Questions last reviewed: 18 October 2026