Earlier, D.A.L wrote:

I have noticed that several articles
on glider performance refer to
adding/modifying the wing root to
get better performance. Can anyone
refer me to further info on wing root
fairing design and or mods to
improve performance.

Wing fuselage junction fillets are often a pretty troublesome
aspect of glider design. The way I understand it, they
are usually developed either empirically, using tuft
testing, or using lots of CFD computing horsepower.

On the other hand, it seems to be one of those aspects
where you get some points just for trying. Dick Schreder
developed the HP-18 side-of-body junction by eye, and
seemed to have gotten it pretty close on the first
try. The only thing I would have done differently would
be to adjust the fillet trailing edge slightly so that
it lines up at the -5 flap setting instead of 0.

There are some references in Thomas' _Fundamentals
of Sailplane Design_, but the book itself is pretty
skimpy regarding developing junction fillets for existing
sailplanes. Small radii near the leading edge, big
radius at the bac, that sort of thing.

One of the cites in Thomas is to a study by Mark Maughmer
at Penn State. If you can get in touch with him, he
might be able to give you some reasonable guidelines.
Another cite is to Dick Johnson's 1979 compendium of
flight test articles; you can get most of those off
of the SSA Web server.

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