I wasn't making a fixed/rotary distinction, just trying to confirm my understanding of the definition of induced drag (Since Nick asked the question).
So I went back to Prouty, and he defines it (Fig 1.2) as the 'horizontal' component of the lift vector. Since he was talking about the hover we can avoid arguments about what horizontal means. Wagtendonk seems to be working along the same lines (Fig 4-6).
My point is that as defined by Prouty, induced drag is simply a mechanical consequence of the definition of lift (ie. that force which is perpendicular to the local velocity) and the wing being tilted out of the horizontal plane.
Now I know the stuff about tip vortices and I'm sure that's an additional souce of lift induced drag, but coming back to my original point, the tip vortices (as I understand it) are not the only cause of induced drag.
To put it another way if you had no tip vortices (eg. by extending the wing through the walls of the wind tunnel) would an aerodynamicist still say that there is induced drag on a lift producing wing ?
Last edited by puntosaurus; 1st Dec 2007 at 04:25.