Le vendredi 8 décembre 2017 14:08:56 UTC+1, Kiwi User a écritÂ*:
On Thu, 07 Dec 2017 21:40:48 -0800, Tango Whisky wrote:

Elevator always counts as non-lifting.

Obviously: In every man-carrying aircraft I know of (computer-stabilised
beasts like the F-22 excepted) the CG is in front of the wing's centre of
lift, so the tailplane *must* generate a downforce during stable, trimmed
flight.

No. (and by the ways, it's the neutral point which is important, not the center of lift of the wing).
What is important for stable flight is that the gradient of lift produced by the elevator over angle of attack is positive so that a pitching moment of the lift will be counter-balanced.
No if there is a gradient of lift over angle of attack for the elevator, the absolute value of the lift produced by the elevator will be zero for a defined angle of attack, negative below this angle, and positive above. the angle of attack for zero lift is a design parameter and is adjusted by chosing the fixed angle of the elevator in relation to the wing chord. Typically this angle is about -4°.

In any modern sailplane, you want to produce exactly zero lift at the elevator at max L/D speed, simply because this is were the elevator drag is minimum. As a consequence, the elevator will produce positive lift below max L/D speed, and negative lift above this speed.