Which term is defined as drag caused by the friction of air moving over the aircraft structure, with the amount increasing directly with airspeed?

• A. Skin drag
• B. Induced drag
• C. Parasite drag
• D. Form drag

Answer: (C)

Drag caused by the friction of air moving over the aircraft surface is skin drag, also called skin friction drag. This is the portion of parasite drag that arises from viscous forces at the aircraft’s surface. As airspeed increases, the shear between the moving air and the surface grows, so skin drag increases with speed. Induced drag comes from lift and decreases as speed rises, while form drag stems from pressure differences around the shape and is not about surface friction. Parasite drag is the overall category that includes both skin friction drag and form drag, but the term that specifically describes friction on the surface is skin drag.