Parasitic drag

[3][1]: 641–642 [4]: 19 It is named as such because it is not useful, in contrast with lift-induced drag which is created when an airfoil generates lift.

Form drag depends on the longitudinal section[clarification needed] of the body.

A prudent choice of body profile is essential for a low drag coefficient.

Interference drag is greater when two surfaces meet at perpendicular angles, and can be minimised by the use of fairings.

Skin friction is caused by viscous drag in the boundary layer around the object.

The boundary layer at the front of the object is usually laminar and relatively thin, but becomes turbulent and thicker towards the rear.

The position of the transition point from laminar to turbulent flow depends on the shape of the object.

There are two ways to decrease friction drag: the first is to shape the moving body so that laminar flow is possible.

The second method is to increase the length and decrease the cross-section of the moving object as much as practicable.

To do so, a designer can consider the fineness ratio, which is the length of the aircraft divided by its diameter at the widest point (L/D).