On Thu, 16 Oct 2003 16:31:46 +0000, Robert Ehrlich
wrote:

He said that
one of the points where the manufacturers are trying to improve L/D, i.e. reduce
drag is by trying to have a neutral tail plane near the best L/D speed and
corresponding angle of attack, because this eliminates the induced drag due
to the tailplane lift. This implies, due to the instability of the main wing,
that the tailplane provides a down force at wing angles of attack lower than this
(neutral) angle (and so at higher speeds) and an up force at higher angles of attack,
i.e. at lower speeds.

This is common for all aircraft. You want to minimize drag at a
certain point of the envelope (best L/D, optimum cruise speed), so you
design your aircraft that the induced drag is 0 at this speed - and
induced drag = 0 means Cl = 0.


Bye
Andreas