Even on a laminar flow wing the airflow tends to break away at some point. This
always causes turbulence, and, therefore, drag. It has been found that (some,
maybe all but I'm not sure) aerofoils benefit from controlling the point at
which this breakaway occurs. The resultant drag is then lower. The turbulator
strip (a long, thin strip of plastic about half and inch wide with a serrated
trailing edge) is the means to achieve controlled breakaway. I have not come
across one on the lower wing section - they are usually on the top wing at
about the three quarter chord position.
Taping up all the joints reduces parasitic, interference drag. I can't recollect
by what percentage - but it's *de rigeur* - something that no serious,
glass-ship owner would omit to do before flying. The lower performance the
glider, the less advantage there is. I suspect that the thing up the front of
the Europa responsible for the noise would negate most of the benefits.
Alan Jackson (week days in Bristol, weekends in Northants.)
PS Given the already clean aerodynamics of the Europa, I was somewhat surprised
to find that the motorglider wing design has an L/D of only 24:1. The now rather
ancient and slow (60-65 knot cruise) Ventures (ex ATC version of the
Motorfalke in tube, wood and fabric) are rated at 22:1 and not terribly useful
for soaring (I know, I've tried!). The Grob 109 has an L/D of well over 30:1...
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