Form drag is caused by:

• A. Drag created because of the shape of a component or the aircraft.
• B. Drag due to skin friction on the surface.
• C. Drag due to wingtip vortices.
• D. Drag caused by airspeed.

Answer: (A)

Form drag comes from the pressure forces created by the object's shape as air flows around it. If a component or the whole aircraft has a blunt or less streamlined form, the flow separates earlier, creating a larger wake and a bigger pressure difference between the front and rear of the shape, which increases drag. A streamlined shape keeps the flow attached longer, reducing this pressure drag. Skin friction drag is due to viscous shear along the surface, and wingtip vortices create induced drag associated with lift. Drag that simply increases with airspeed isn’t a specific drag mechanism. So form drag is caused by the shape of a component or the aircraft.