Discus Sprog Adjustment And Flight Testing - Aeros Discus 12 Owner's Manual

DISCUS SPROG ADJUSTMENT AND FLIGHT TESTING

The Discus uses outboard sprogs in combination with one transverse batten on each sprog. Each transverse batten spans
two top surface battens, so a total of four top surface battens are supported. The sprog system is the primary component of
the system, which provides pitch stability.
The function of the system is to support the trailing edge of the sail at low angles of attack, and thus provide a nose up
pitching moment. The sprogs are adjusted at the factory to their proper settings.
You can check this adjustment as follows:
SPROG MEASUREMENT
1. Fully set up glider on a reasonably level surface and set the VG to full tight.
2. Place three equal supports, about 1,7 m (5.5 ft) tall, under the each leading edge tube-cross tube junction and in place
behind the connection of rear bottom cables to a keel tube.
3. Tie a lightweight string tightly across the wing from the inner of the two supported battens on each sprog to the
corresponding batten on the other wing.
4. Press firmly on the end of each sprog supported batten and then release. Set the VG to full off and than to full tight
again. Measure the height of each thread relative to the top of the keel tube. The results should be as follows:
Batten Discus 125, Batten
# - # mm
7 - 7 *
8 - 8 *
5. Note that this method will not disclose sprogs that are asymmetric. If, after achieving the proper measurement, you have
a turn in the glider, which is only present at tighter VG settings, lower the sprog on the side the glider is turning towards, and
raise the other sprog by the same amount.
METHOD OF ADJUSTMENT
1. To adjust the sprog height, fully unzip the access
zipper to gain access to the sprog-LE tube connection
( ).
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2. Remove the sprog wire tang from the pin on the LE
tube, taking care to maintain the rotational alignment of the
sprog at its original setting.
3. At the front of the sprog there is a threaded adjuster.
To raise the sprog, turn the entire sprog counter clockwise.
To lower the sprog, turn it clockwise. One full turn raises or
lowers the sprogs end about 12 mm (1/2'').
4. Re-attach the sprog cable and press down firmly on
the rear end of the sprog to seat the cable before checking
the measurement again.
TEST FLIGHT
If the sprogs are set too low, it may cause a significant increase in trim speed and a reduction in pitch pressures at tighter
VG settings, and there will be a reduction in pitch stability at angles of attack below normal flight angles. This stability
reduction could increase the probability of a turbulence-induced tumble or other in-flight stability related loss of control. If the
sprogs are set too high, it may cause excessive pitch bar pressure at high speeds, and excessive roll control pressures, lag
in roll response.
Please be aware that flight-testing encompasses a very limited angle of attack range and that there is no correlation
between pitch stability in the flight test envelope and pitch stability in the extended angle of attack range that is investigated
on a test vehicle.
This test is best performed by a qualified test pilot, and, in any case, should be performed only in smooth air and with
caution.
Discus 148, Batten
# - # mm # - #
7 - 7 65 7 - 7
8 - 8 85 8 - 8
Discus 155,
Note: All figures are given with VG on only.
mm
Permissible range of thread heights relatively
to the top level of the keel tube is +/- 5 mm.
40
50
* - info coming with glider release.
15
Photo 32