On Thu, 17 Jun 2004 05:12:08 GMT, "Gldcomp"
wrote:


Situation at low speeds:
Don't forget that the center of pressure (CP) moves forward with
rising AoA, creating a nose-up momentum - and this needs to be
encountered by the tail (wich is therefore creating lift at speeds
below the speed of max. L/D). And vice versa.

Correction : The tail is generating LESS negative lift.

Nope.
As Bert has been pointing out repeatedly - for a typical powered plane
setup this might be correct, but not for a glider.

BTW: The tail of a powered plane is also designed not to deliver any
lift at the typical cruise condition of this plane (speed, wing
loading, CG, density altitude).



Just take a look at the AoA of the tail:

AoA_tail = (AoA_wing) - (longitudinal dihedral)

with longitudinal dihedral typically being 1.5 degrees.


Grab one of the available airfoil simulators (e.g.
http://www.mh-aerotools.de/airfoils/javafoil.htm), use a symmetrical
tail airfoil with a, say, 5 degrees upwards elevator deflection, and
simulate it at a typical AoA of about 5 degrees (simulating a wing
AoA of 6.5 degrees for a typical thermalling situation).

Voila - you'll see that that the lift vector of the tail points in the
same direction as the wing's one, despite the upwards-deflected
elevator.





Bye
Andreas