On Jan 28, 9:05*pm, wrote:
On Jan 28, 5:58*pm, DRN wrote:



On Jan 28, 1:59*pm, Mark Jardini wrote:

Sailplanes have of necessity a polar with min sink at speeds where
circles can be small enough to center thermals, and L/Dmax only a few
knots higher. Ballast is added to raise the L/D max perhaps 10Kts
higher.

What might a wing look like that was built for optimum L/D @
80-100Kts? What kind of L/D might be possible?

(will this winter never end?)

Mark J

Antares 20E max L/D is already up around 70 knots.
Still, there are a lot of compromises to make these
modern gliders thermal well...

See ya, Dave "YO electric"

If you think just in terms of wing loading, and ASW-27 needs about
14lbs/sq ft to get best L/D up to 80 kts and 18 lbs/sq ft to get it to
90 knots. Ignore aspect ratio, Reynolds number effects, etc and take
it back to wing area and you are talking about 62-79 sq ft. instead of
the 98 sq ft of the -27 and an aspect ratio of 31-39 instead of the 25
on the current -27. *Without doing the math, say that the aspect ratio
effect outweighs the Reynolds number effect by a little bit and you
get a 75-80 sq ft wing and an aspect ratio just above 30.

I'm guessing with current construction techniques you could build it,
but without some new airfoil innovation it might not climb very well.

9B

Oh, and I'd be surprised if you could get the max L/D much above the
mid 50s on a 15 M ship. Of course, you'd want to cruise it well above
the max L/D speed. Out west you might be able to imagine a glider
that could win races optimized around 14 lbs/sq ft, but I'd think even
western conditions might prove insufficient to support a glider with a
best L/D design point of 100 kts, since that implies cruise speeds
pretty considerably into triple digits and stall speeds and circling
radii that are pretty big.

9B