As others have indicated, a bit of an error in terminology in FE's explanation (my error: that should be LD's explanation). Correct for where 'Induced' should have been used instead of 'Parasite' and it would be more correct.
All objects in a moving fluid (or moving through a fluid) - including air - experience 'drag'. Drag is the term used to describe forces that act in opposition to the direction of motion.
The total amount of drag experienced is conventionally divided into two major categories:
'Induced' drag: A retarding force caused as a by-product of producing 'Lift' ie it is induced by producing lift. Nothing is free so causing a force to be produced must have a cost somewhere; and
'Parasite' drag: The remainder of the drag experienced by the body. This is present even when no lift is being produced. Parasite drag, in turn, is subdivided into several components:
'Form' drag: relates to the frontal area being shoved through the fluid.
'Skin friction': Any fluid flowing past a surface experiences frictional forces.
'Intersection drag': Where surfaces intersect they interfere with the ability of the air to flow around the body. In a sense the other surface 'blocks' where the fluid would have gone in order to allow space for the first surface to move through.
Last edited by Tinstaafl; 7th Feb 2004 at 20:10.