Hello Scott:

Along with Eric Greenwell's very good suggestion, here are a few other
considerations. If you are designing for FAR part 103, then your
weight constraints and therefore structural considerations will drive
your design more than subtle aero concerns. From a practical
standpoint, the thicker sections will give you greater freedom in the
design process.

Here are the opposite ends of the spectrum in the current state of the
art for sub 155 lb. empty structures:

Carbon Dragon @ 145 lbs. Root section nominally 18% at root but
actually increased to 21% over a short section of the span for
structural reasons. 13% tips, highly tailored aerodynamically due to
large q-differential across span at very slow circling speeds.

SparrowHawk at circa 153 lbs. With pre-preg carbon construction and
excellent engineering, able to use relatively thin and very slippery
sections for the R-numbers throughout. Not practical for most
homebuilders to take this route. If you like this design approach, it
is very well executed and you might consider buying one as they are
reasonably priced.

Best Regards,
Gary Osoba

Eric Greenwell wrote in message ...
Scott wrote:
If one were to design their own sailplane, which airfoil would be a good
choice for low drag and fairly low speed (ie, an ultralight part 103
sailplane for exampl)? In other words, is a thicker airfoil (more lift)
better at slow speeds or a thinner airfoil (less drag)? Which type would
give the best glide ratio with all other things being equal?

Have you read Fundamentals of Sailplane Design? That'd be a good place
to start if you haven't. Join the Sailplane Homebuilder's Associaton at
the same time (buy the book from them, too).

Thicker and thinner don't mean much; instead, you need to be talking
about the characteristics you want, such stall speeds, desired L/D at
max and cruise speeds, wing loadings, construction (wood and fabric,
carbon, or ?) and so on. Theennn you can start asking about the airfoil!