sisu1a wrote:
I don't recall ever seeing an estimate of the performance loss in a
glider as a function of yaw string deflection. Does anyone know what it is?
Ultimately, I'm wondering how much attention should be paid to
deflections of, say, 1/8", 1/4", 1/2", etc., on the usual 4"-5" long yaw
string.
Without actually 'calibrating' your yawstring with a slip/skid ball
for your particular ship and installation first, I don't think such
specifically meaningful data can't really be derived, and it will vary
somewhat from ship to ship (at least type to type...) so would not be
universally applicable.
Since a straight yawstring in a turn does not mean perfect
coordination in all ships, and in fact indicates a skidding turn on
some due to crossflow effects on canopies as well as the position of
the string being forward of the C/G ( wait are you just being funny
and I took the bait, hmmm 
the yawstring calibration card would
be nice to have, even if it's just committed to memory.
Mostly, I was thinking of straight flight. Circling is more complicated,
and aerodynamic efficiency is generally a lower priority to proper
positioning.
Reread 'Circling The Holighaus Way' by Johnson for a much better
explanation than mine...
http://www.owp.us/Johnson/CirclingTheHolighausWay.pdf
Unfortunately, the article doesn't offer any estimate of performance
loss. As far as avoiding stalling or spinning (one of the reasons given
for a slipping turn while circling), I have to fight with my ASH 26 E to
make it do either in a turn; in fact, at my normal 35 to 45 degree range
of bank, it won't. So, maybe the newer gliders don't respond as well to
a slipping turn as the older gliders. The flight manual doesn't mention
doing it, either. Perhaps, being a flapped glider, where the flaps work
differentially with the ailerons, that eliminates the advantage of the
slipping turn.
But, if anyone has estimates of the performance loss/gain versus yaw
string defection in circling flight, I'd love to see those, too.
--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes"
http://tinyurl.com/y739x4
* Sections on Mode S, TPAS, ADS-B, Flarm, more
* "A Guide to Self-launching Sailplane Operation" at
www.motorglider.org