Which design feature is used to reduce interference drag?

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

Answer: (A)

Interference drag comes from the disturbed air where two components meet and flow around each other, creating sharp pressure changes and sometimes flow separation at the junction. A fairing is a streamlined cover placed at those junctions—like at wing-root, wheel wells, or between other adjoining parts—that smooths the transition and guides air smoothly around the intersection. By reducing the abrupt changes in direction and pressure, the flow encounters less disturbance, decreasing the interference drag produced by the junction.

Other drag types relate to different phenomena: form drag is all about the overall shape causing pressure drag, skin friction drag comes from viscous shear along the surface, and induced drag is tied to generating lift. Fairings specifically target the flow interaction at junctions, making them the design feature used to curb interference drag.