perhaps what Mr. Stine was implying was that at the small Reynolds numbers that typical 1/4A-B size BG/RG fly at, a thin flat plate is just as efficient as any potential airfoiled cross section.... which is true to a large degree....
recent research in MAV Micro Air Vehicles show that at low Rn, airfoil effciiency deteriorates rapidly ..
"For chord Reynolds numbers between 10,000 and
30,000, the boundary layer is completely laminar
and artificial tripping has not been successful. Experience
with hand-launched glider models indicates
that when the boundary layer separates it does not
reattach."
"The range 30,000 to 70,000 is of great interest
to MAV designers as well as model aircraft
builders. The choice of an airfoil section is very important
in this regime since relatively thick airfoils
(i.e., 6% and above) can have significant hysteresis
effects caused by laminar separation with transition
to turbulent flow. Also below chord Reynolds numbers
of about 50,000, the free shear layer after laminar
separation normally does not transition to turbulent
flow in time to reattach. Near the upper end of
this range, the critical Reynolds number can be decreased
by using boundary layer trips. Thin airfoil
sections (i.e., less than 6% thick) at the upper end
of this regime can exhibit reasonable performance."
I would guess that 1/4A-B size BR/G fly at 10,000-70,000 easily....