Sanding or Waxing - PIK 20 Question

"Maule Driver" wrote in message
news
Udo Rumpf wrote:
I am always surprised when I read comments about sensitivity to rain
or water and I agree water that pearls on the wing surface will have
a negative effect on "all airfoil shapes". When was the last time you
flew
through rain and where it mattered in regards to getting home or not.
Either one is cut off and one has to land in any case or one escapes
a light and short duration shower and waits it out. I have no interest
in how my airfoil performs when exposed to water.

In my limited experience, you are generally correct. But the PIK20b in my
experience is *particularly* sensitive to water.

I flew the PIK in a number of eastern US contests. We didn't fly in much
rain but one particular encounter in the mid-80s captured my attention.
I pulled up into a thermal just as a light sprinkle of rain hit. I
stalled out of the pull up! This is the only time I can remember stalling
accidently in any conditions.

It didn't at first occur to me that the rain and the stall were related
but it soon became apparent that I wasn't flying the same sailplane I was
flying before the rain.

I didn't make it home that day and landed at an airport. The anemic
Citabria was sent from Dansville to pick me up at Grand Canyon airport (NY
State). We started the tow just as another light sprinkle fell. The
Citabria lifted off in its normally anemic way but I couldn't get the
unballasted PIK off the ground. I rolled off into the grass at the end.
Anyone familiar with Grand Canyon (in the mid-80s) knows the reason for
the name. Fortunately the ground falls away quickly and I became
airborne.

I would suggest that the PIK is a notable exception to your conclusion.


On hind sight I should have realized how bad "moisture" is on the FX 67
airfoil

I had done experiments with this airfoil under the assumption
that it was only related the way it was constructed, as in the HP
technique,
I used turbulators successfully on the top surface to counter some of the
ills of that airfoil.
Wing dropping on take off for one, as well as in landing mode when the
glider with this airfoil
showed stall behaviour well before the stall speed was reached.

One other experiment I conducted, installing a .040" wire, tape down along
the span
about 5% from the leading edge. My surprise was It climbed much better but
the cruise was no better then a K6 which made sense to me.

It seems everything has be just dead on with this airfoil shape for it to
perform to it potential.
One glider I know of is the LS3, which has done just that I never heard of
any complains.
Regards
Udo