Air flowing around the fuselage collides with air flowing over the wing, merging into a current of air different from the two original currents. This is most observed when two surfaces meet at perpendicular angles. This is describing which drag type?

• A. Induced drag
• B. Parasite drag
• C. Interference drag
• D. Skin friction drag

Answer: (C)

Interference drag is caused by the way airflow around neighboring surfaces interacts and disturbs the local flow field. When air flows around the fuselage meets air flowing over the wing, their wakes collide and merge into a new current, altering pressure distribution at the junction. This interaction creates extra drag specifically at where the surfaces meet, especially at right angles, because the disrupted flow is not simply the sum of the two streams but a combined, less efficient pattern. Induced drag relates to lift-generated vortices, not the flow interaction between adjacent surfaces. Skin friction and other parasite drag forms describe viscous or form drag along surfaces, but the described phenomenon centers on the interference of the two flow fields.