On 2/22/2011 12:11 PM, noel.wade wrote:
Just to throw my voice into the mix - my DG-300 was retrofitted with
(factory-supplied) winglets...

The difference in L/D is so small with most winglets, that even if its
working correctly it would be hard to notice... Like others have said
- its "almost as good as" an equal improvement in span. What's the L/
D difference between a good 15-meter ship and a good 16-meter ship?
Very little.

No one can notice the difference between 40 and 42 in L/D. You might be
able to measure it with very careful measurements, but "notice" it? No.

However, I do notice an improvement in slow-speed handling with my
winglets on. This is where I believe a lot of people derive benefit
from them: Improved airflow over the wing at slow speeds and while
turning can directly translate into better thermalling performance,
both in reduced drag and in improved aileron control/authority.

Noel echos my experience, and it's not just in flight, but on the ground
roll, too. It makes a glider less likely to drop a wing at the start of
takeoff, or near the end of the rollout.

I retrofitted factory winglets to my ASH 26E. Besides the above, I could
see (and confirm with photographs), that the wingtips were higher in
flight with the winglets than without, evidence that the winglets had
shifted the lift distribution outwards. I have no idea if the cruise L/D
was changed.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)