Earlier, Ron Wanttaja wrote:

...Nor do you see many canard sailplanes,
which place the highest demands on aerodynamics.

The way it's been explained to me, the wake of the canard surface
interacts with the wing flow field so as to make it difficult to
arrive at reasonable compromises for both low- and high-speed flight.
Also, the tip vortex from the canard does things to the wing flow
fields that are hard to compensate for at any speed.

The only canard sailplane I know of, the Rutan Solitaire, had
performance that was whelming at best. Although it won the SHA
sailplane design contest that year, only two or three were ever built.
I believe that none are regularly operated.

Getting near the bounds of this topic, (but I suspect that Jay is
gonna like this one), NASA has done analysis that suggests that there
are substantial gains to be found in joined wing designs. Basically,
the main wing sweeps back and then turns up at a winglet. The
horizontal stabilizer sweeps forward, and joins smoothly to the top of
the winglet. This type of design has potential for low drag and good
strength-to-weight ratios. However, there is relatively little in the
way of real-world validation of these theories. For more information,
see the several technical papers on the topic by Ilan Kroo.

Thanks, and best regards

Bob K.
http://www.hpaircraft.com/hp-24