Glider wing profiles (and now also those on the elevator) are designed to
provide a maximum of laminar flow distance over the chord line. For that
reason, they are quite prone to the laminar flow to separate from the wing
surface and form a "separation bubble" that than attaches itself again to the
wing some ways down the stream lines and change to turbulent. The net effect
is, that a substantial drag increase in noticed. In order to avoid the
separation bubble, turbuators (either blow holes in the wing supplied with ram
air or zig-zag tape) are employed to change the air flow to turbulent in a
forced manner. Overall, the wing will have less drag over most of the gliders
speed range. Gliders are flown very slow (40-45 knots) in thermals and quite
fast (80-110 knots) wnen "running" between thermals. Over this speed range a
marked reduction in drag is noticeable. At the VNE speed of around 150 knots,
they will increase the overall drag.
These days, turbulators also appear near the trailing edge of the rudder and on
the inside and outside of winglets on gliders.
With wind tunnel or oil flow testing it could be determined if laminar flow
separation exists for the Europa wing. Here in the US, Dr. Richard Johnson has
devised some clever in-flight testing methods for gliders to determine the
overall drag over the speed range. He is well known here to determine the
effectiveness for turbulators at different locations of the wing. His methods
might not be applicable to testing the Europa, the power lever messes things
up...
Herb
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