"Larry Dighera" wrote in message
...

Given the "clean" design of the glider, the increase in parasitic
drag at higher speeds is probably insignificant compared to the "skin
friction drag" reduction.

I think so. Words for drag vary, and I've always used parasite drag to
include skin friction, but I think we mean the same thing.

For a laminar boundary layer, skin friction is proportional to Re^-0.5, and
for a turbulent boundary layer to Re^-0.2. If skin friction drag is about
2/3 of the total parasite drag (by which I mean skin friction + form drag),
which in turn is 1/2 the total drag at best glide, that would suggest that
the L/D should improve by between 1/15 and 1/6 of the increase in speed.
The data you quoted, with a 50% speed difference for a 2-3% difference in
L/D suggest something like the 1/15 expected of a turbulent boundary layer.

Julian