Blake, I would read the Johnson report on the PIK and follow it
before I did any modifications to the wing of the PIK-20.
Doug

At 20:44 30 April 2015, Blake Seese 9V wrote:
On Thursday, April 30, 2015 at 12:19:05 PM UTC-6, Blake Seese
9V wrote:
Hello,
=20
Does anyone have any information on applying turbulator tape
to the
wings=
of a PIK 20 B? Can any improvement in performance or handling
be gained
fo=
r this airfoil?
=20
Thanks!
=20
3Y
Formerly 9V

All,

I found this on the web from Udo Rumpf:

The FX67 15%&17% was designed to be a naturally transitioning
airfoil. In
e=
arly wind tunnel test it looked to be a winner and was used on
some of the
=
first 15meter flapped gliders. As it turned out it was not as good
as the
d=
esigners hoped.

The FX67 has a steep pressure drop and a very pronounced
pressure
recovery,=
due to the high camber and the general layout of the airfoil. Also
the
sep=
aration bubble was not understood very well at that time. The
leading edge
=
is relatively sharp, which further makes the airfoil intolerant to
gusty
co=
nditions, like very turbulent thermals. The back 45% of the chord
is very
s=
ensitive for the turbulent flow to separate. That is why I think in
smooth
=
conditions that airfoil performance better.

The FX 67 15% Is used on the Mini Nimbus, Mosquito and our HP-
16s, '18s
and=
RS-15s.

The Pik20 and the LS3 use both the FX67-15%&17%

The Performance can be enhanced by first: making the airfoil
accurate in
bo=
th shape plus or minus 2.5% and waves within the .002"-.004"
tolerance and
=
second installing a turbulator on the top at about 52% chord. I
would use
3=
/16" cylinder dots about .040" high and spaced 1.25" apart.
Within 1.5"
dow=
n stream due to the 35 deg. wake the "top" surface will be awash
in
turbule=
nt attach flow, at higher speed the effect will take a little more
distance=
..