On Jan 13, 4:18*am, Sparkorama
wrote:
jan;759730 Wrote:
Hi
If you look at the polar of a glider it is usually quite flat for a
moderately wide band of air speed and the best L/D is also flat. The
best L/D is probably the single best measure of the performance of a
glider. So for XC flying it is desirable to have a reasonable estimate
of the best L/D. When Dick Johnson used to do his evaluations of
gliders he found after proper sealing with tape of any joins and
polishing of the wings and surfaces that mostly he was unable to
duplicate the manufacturers claim for best L/Ds. What I attempted to
show in my original posting was that it is fairly easy to obtain a
reasonably accurate value of L/D for your glider as you usually fly it
- not necessarily prep'd for best performance. I used to use a L/D of
35 for the DG800B and Stemme and a L/D of 25 for the SparrowHawk. I
have only landed out once in the SparrowHawk and rarely have had to
push the button for the iron thermal on the motor gliders. I hope this
is useful.
Dave


Sounds like you have some very nice gliders, Dave! I'm pretty new to
soaring, but isn't the manufacturers L/D really a "best case" kind of
number, meaning when the moon is in the seventh house of aquarius and
all the elements are aligned in ultimate perfection? I've heard the L/D
can be dropped by all manner of things like water droplets on the wing,
bug splatter, and the stern look of a angry red-tailed hawk. Still, it's
good to know the real numbers. As it is, it looks like you can just
estimate that reality is a percentage (all three of yours are between 82
and 84%) of dreamland L/D numbers from manufacturers. Also, and I'm just
wondering here, since I don't really know, could it have something to do
with the way you fly? Or how much weight you're carrying? CG location?
Wouldn't there be many factors?

--
Sparkorama