Wills Wing Ultra Sport 135, Owner'S Service Manual

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Ultra Sport Stability Systems
Several design features of the Ultra Sport determine the glider's degree of stability in pitch:
a. The combination of wing sweep and spanwise twist.
b. Reflex in the root section, the degree of which is determined by the lengths of the kingpost, control
bar, and front to rear top and bottom wires, by the shape of the root battens.
c. Reflex support bridles running from the kingpost to the trailing edge at the number four, five, six,
and seven (and eight on the 166) battens.
d. The shape of the preformed battens and the internal fabric ribs, and adjustment of the internal
velcro attachments which define the airfoil.
e. A bridle compensation system on the 135 and 166 that is linked to the VG activation mechanism.
Correct attachment and proper adjustment of the reflex support bridles are critical to providing ad-
equate stability at low angles of attack, particularly those below the normal operating range.
Ultra Sport Reflex Bridle Adjustment and Flight Testing
Bridles are an integral part of a system to provide pitch stability on the Ultra Sport. The Ultra Sport
147 uses four reflex support bridle lines per side (8 total) and the 166 uses five reflex support lines per
side (10 total). These lines run from a ring which connects at the top of the kingpost through grommets
in the sail to a ball retainer on the underside of the trailing edge. Their function is to support the
trailing edge of the sail at low angles of attack, and thus provide a nose up pitching moment.
The variable geometry system on the Ultra Sport 147 functions by moving the center hinge connection
of the crossbar assembly aft along the keel, thus pushing the leading edges outward and increasing the
airframe nose angle. The variable geometry system on the Ultra Sport 166 functions by activating
levers mounted at the outboard end of each crossbar to achieve the same result. Both mechanisms
result in increased spanwise sail tension and a reduction in spanwise twist.
Depending on the VG mechanism, two possible effects result from engaging the VG which contribute
to a tightening of the bridle lines. The first, which occurs on both the 147 and 166, is a flattening of
the upward curve of the trailing edge of the sail. The second, which occurs only on the 147, is a
downward folding of the wings around the axis of the keel, which occurs because the airframe nose
angle widens, but the bottom side wires do not get longer.
Although the Ultra Sport 166 is only subject to the first effect, the bridle tightening from this effect is
more pronounced because the VG range is much wider. As a result, the Ultra Sport 166 is equipped
with a bridle compensation system which adjusts bridle length corresponding to VG setting.
Bridle measurement
As a preliminary check of the bridle adjustment, you can measure the effective bridle length settings.
The glider must be fully assembled to measure the bridles. Set the glider to VG loose. At each bridle
station batten, stretch a thread tightly across the trailing edge connecting the bridle station batten with
the corresponding batten on the other side, (four threads on the 147, five on the 166.) Each thread
should end in a loop which is looped over the batten tip, and each thread should be tensioned so that the