The performance of some gliders is badly effected by wet wings. PIK 20,
Kestrel 17 and 19, Grob 103 spring to mind but there are others. The
Kestrel and PIK have a Wortman Section and the Grob an Eppler. All these
gliders suffer from very high sink with wet wings. Other gliders are not
so badly effected, the ASW17 would climb in rain. It very much depends on
the wing section as the ASW17 has a different Wortman Section.

Whatever the performance issues I would agree with the rule that a winch
launch should not be undertaken with wet wings, doing so could result in
you being served by undertakers.

At 15:11 29 April 2009, Chris Reed wrote:
Geoff Vincent wrote:

My experience with wet wings (DG-300 and PIK 20B) when winch launching
is that the droplets disappear from the wing surface long before you
enter rotation and to all intents and purposes the launch is normal.
Both above-mentioned gliders had a well polished surface finish
though.

The British Gliding Association advice is never to winch launch with wet

wings. From memory of Steve Longland's book (effectively part II of the

BGA Instructor's Manual), your minimum winch speed is calculated as 1.5

x Vs (free flight), to allow a safe margin over the increased stall
speed on the winch caused by the weight of cable + pull of winch. If wet

wings increase the stall speed by, say, 15% (for my Open Cirrus it's
15-20%), the safe winch launch window is much smaller.

For my aircraft the normal launch window is 90-110 kph (50-59 kt). With
wet wings, the free flight stall speed rises from 60kph to 69kph (say 70

for ease of calculation), and 1.5 x this is 105kph. Max winch speed
remains the same, so I now have a safe window of only 5 kph (3 kt)!

It might be that the rain in the Southern hemisphere runs off wings
quicker, but I'm not taking chances on that if I get the opportunity to

fly there!