What term describes the aerodynamic resistance due to the contact of moving air with the surface of an aircraft?

• A. Skin Friction Drag
• B. Form Drag
• C. Induced Drag
• D. Wave Drag

Answer: (A)

Skin friction drag is the aerodynamic resistance produced by the viscous interaction between moving air and the aircraft's surface. As air flows over the fuselage and wings, viscosity creates shear stresses in the boundary layer that act along the surface, converting part of the air’s kinetic energy into heat and producing drag parallel to the surface. This frictional component depends on surface area, roughness, speed (Reynolds number), and whether the boundary layer is laminar or turbulent.

The other types describe different drag sources: form drag comes from pressure differences around the body and flow separation, induced drag arises from the generation of lift and the resulting wingtip vortices, and wave drag appears from shock waves at high speeds in the transonic regime. The described resistance specifically due to air contacting the surface is skin friction drag.