At 19:01 27 March 2020, wrote:
Hi Michael,

indeed, SL12 includes a reference to turbulator tape in front of the
contro=
l surfaces. Especially in case of the rudder, this helps to reduce the
lack=
of rudder authority that most Astir. Turbulators on the suction side
in
fr=
ont of the ailerons also seem to improve aileron authority on some
gliders,=
like the ASK21.

However, the drawing that Grob released in the 80s and which the
Aerokurier=
article refers to, includes additional specifications for turbulator
tape
=
on the pressure side of the Eppler airfoil. These are not part of
SL12.
Whe=
n following these instructions, the tape will not be right in front of
the
=
aileron gap as shown in SL12. It will be a few centimetres further
upstream=
..

Regards
Christoph

I agree that the additional turbulator tape instructions which the
article refers to may bring some not so noticeable performance
increases. We have underwing turbulators installed in those
positions on our Twin 1's also, and absent side by side glide testing,
there is not much to notice. The handling was always a complaint
with the Twin 1's. and in this case, the addition of turbulators in
front of the control surfaces does help markedly, and the difference
is plain to see and feel. The rudder is most noticeable. Aileron
response is also better. I have even had success using it on the
upper stabilizer to enable more effective high speed nose-down
trim. Operators of Twin 1's that do not have the Z-tape installed
should try it. It doesn't cost much money, and I think the pilots
will be pleasantly surprised.

RO