Quote:
Originally Posted by brad walton
Sail plane pilots have debated waxed vs. unwaxed vs. very light crosshatch pattern on wing surfaces. My recollection is a light crosshatch sanding with 400 wet/dry sandpaper produced a measurable increase in the amount of laminar flow.
Recall also a smooth golf ball won't carry as far as a dimpled ball.
A little orange peel in the paint surface may actually be beneficial.
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All true above, but don't start sanding yet. High performance gliders (fiberglass) are covered with gelcoat that is contoured and sanded by hand for hundreds of hours to an extreme tolerance of less than .003" deviation (wing).
Gelcoat and water/humidity don't mix and because it cost over 25K$ to refinish we wax it. Less than 3 do not because they believe the slight improvement in performance gives them an edge racing. So they sand with 4' aluminum sanding blocks and check the wings profile with a wave gauge to achieve <.003. A lot.
Everyone else waxes the **** out of it to ward off the devil.
Because smooth is sticky, we apply turbulator strips spanwise on the underside 'near' the trailing edge to help with airflow separation . Location is determined by wind tunnel testing. Why new glider = 160K$ +++
What improves our glider performance more, and I plan to apply this to my 14, is we do everything we can to reduce/eliminate/control where cockpit air escapes or leaks. Canopy and wing roots (via fuselage spar openings) escape are very high drag producers.
So, we seal the best we can by glueing material over openings, attaching flexible boots to pushrods , thin foam to canopy frames.
Most important is we give the air inside a place it wants to go, the tail. An exit as far back as possible in the belly so the escaping air does not impact a tail surface. A NACA vent perhaps. This means louvers in the aft cabin bulkhead.
Or go slow....less drag.
Hank
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