John,

I'm not sure that I'm understanding what you said in your note, so let
me try to rephrase, then tell me if I'm getting it...

You are suggesting that because of spiral instability that the inboard
aileron must be deflected downward (to stop overbanking), leading to
increased drag. Another way to counteract this overbanking tendency is
to use the glider's dihedral by initiating a slip. (Dihedral rolls the
glider level if slightly slipped). This eliminates the costly drag at
the wing tip for less costly drag at the tail. Do I have this right?

If this is the case, it would require a larger slip (10 - 20 degrees),
since the slip must be extended to the wings. In the previous model,
we've kept the wings coordinated by compensating for the displacement
of the yaw string from the cg. Therefore, we saw no dihedral effects.
Has this been discussed previously?

(John Firth) wrote in message ...
Todd is quite right about the exagerated slip shown by the yaw string.
AS for slipping in turns, deliberately, I think the reason is to
counter the spiral instability; if you use opposite aileron input to
counter the bankinbg tendency then the inboard aileron (downward deflection)
will stall earlier then the outboard one; the objective is to fly as
slowly as possible for min. turn radius so leave the ailerons neutral
and slip to hold the bank angle.
Made a big difference in the Std Libelle. in circling speed.
John Firth
an old no longer bold soaring pilot.

Measured with a cad-program, for a turn radius of 30 m, the thread angle
should be 3.6 degrees, if the distance of the thread from cg is 2 m. Tighter
turn, wider angle. How precisely you can keep your thread in a 3-4 degree
angle?

The typical canopy shape causes the airflow to split which
appears to amplify the yaw string angle for small slip
angles.
Todd Pattist - "WH" Ventus C
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