Re: Astrir turbulator tapes

[[email protected]]

Hi Ruediger,

there is a drawing from Grob, specifying the turbulator location for the single-seaters as follows (distances measured on the pressure side of the wing from the trailing edge to the trailing edge of the tape):

Wing root: 360mm
Inboard end of the aileron: 300mm
Wing tip: 178mm

Twin I and II twoseaters receive the tape only at the ailerons with the following dimensions:
4300mm from the wing tip: 380mm
Inboard end of the aileron: 370mm
Wing tip: 208mm

Unfortunately, these locations are not included in the service letters from LTB Lindner.

The tapes do not significantly improve the performance - perhaps 1 or 2 points, you won't notice that. But they remove the seperation bubble from the ailerons and improve the airflow there. You will notice that the glider becomes more stable in a turn. You will also need less aileron input for corrections and the aileron in general is a bit more responsive.

Best
Christoph

[Michael Opitz]

At 07:27 27 March 2020, wrote:
>Hi Ruediger,
>
>there is a drawing from Grob, specifying the turbulator location for
the
>si=
>ngle-seaters as follows (distances measured on the pressure side
of the
>win=
>g from the trailing edge to the trailing edge of the tape):
>
>Wing root: 360mm
>Inboard end of the aileron: 300mm
>Wing tip: 178mm
>
>Twin I and II twoseaters receive the tape only at the ailerons with
the
>fol=
>lowing dimensions:
>4300mm from the wing tip: 380mm
>Inboard end of the aileron: 370mm
>Wing tip: 208mm
>
>Unfortunately, these locations are not included in the service
letters
>from=
> LTB Lindner.
>
>The tapes do not significantly improve the performance - perhaps
1 or 2
>poi=
>nts, you won't notice that. But they remove the seperation bubble
from the
>=
>ailerons and improve the airflow there. You will notice that the
glider
>bec=
>omes more stable in a turn. You will also need less aileron input for
>corre=
>ctions and the aileron in general is a bit more responsive.
>
>Best
>Christoph


Christoph,

Please re-read Lindner SL-12. It plainly states that all control
surface seals including the rudder may have the Z-Tape installed
just in front of the gap seals. In the case of the rudder, IMO, it
greatly increases the effectiveness of that control surface,
especially at low speeds like on initial take-off roll, etc.. The
drawings you refer to may be for possible increased performance
due to dealing with the laminar separation bubble where the
Z-tape is extended beyond the ends of the ailerons, but it is not
the same as where the service letter basically allows all Grob
glider types to have sealed control surfaces with optional Z-Tape
included.

RO

[[email protected]]

Hi Michael,

indeed, SL12 includes a reference to turbulator tape in front of the control 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 front 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. When 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

[Michael Opitz]

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