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Old September 28th 20, 04:18 PM posted to rec.aviation.soaring
Michael Opitz
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Posts: 318
Default Grob Twin Astir getting

At 14:12 28 September 2020, Kenn Sebesta wrote:
@Steve, that's a great description, I'll go try it with the other
direction. My natural slip tendency is to bank left because I'm right
handed-- it's easier and more accurate for me to push left than

pull right.

It happens in lots of gliders, particularly older generation

trainers, at
least learning in Australia it was part of sideslip approach training.
Puchatek's are great for it.

It's also in the flight manual (see page 27)

The side-slip is quite controllable and, if needed,
this manoeuvre can be used for steeper approaches.
It is effective by using a 15 degrees angle of sideslip and should

be
finished of a safe hight (98 km/h;
54 kts; 61 mph). Rudder effect reversal have not
been observed.
17 th march 1982
FLIGHT MANUAL GROB G 103 27
The temporary control force to overcome the
force reversal or rudder lock is calculated
approximately 5 to 6 daN (rudder pressure).
The aileron does not change its force direction, rather it returns

independently from the
full deflected position.
Rudder lock can be relieved without pilot input on the rudder.

After
moving the aileron
into neutral position, the Sailplane rolls out
of the Slip into wing level position. Thereafter the rudder frees

itself
from the full
deflected position and the force reversal is
relieved. Using this method to end the Slip
the Sailplane does not adopt unusual flight
attitudes and deviates only slightly from its original flight course.


That's an excellent reference. It certainly describes what I see, but

it's
not in our POH
(http://www.franconiasoaring.org/pdf-

files/Flight%20Manual%20Grob%20103%20Astir%20FH%20Rev%2
09.pdf).
I wonder why not?


You have a Twin Astir (I) first generation. The above quote is
probably from a Twin II manual. Twin I's have a center hinged
rudder with no factory seals. IIRC, Twin II's have a side hinged
rudder with a tape seal on the hinge side.

The rudder on the Twin I can be made noticeably more effective by
adding seals with Z tape running just in front of the rudder gap IAW
LTB Lindner (Grob certificate holder) Service Letter SL-12.

http://www.ltb-lindner.com/service-letter.html

Putting seals and Z tape on a Twin Astir rudder costs little in time
or materials and yields much better rudder efficacy. I assume that
your glider does not yet have this mod, so get it done ASAP. You
won't be sorry, and you won't be complaining about a small and
ineffective rudder anymore.

RO

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