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tape prevents the fin from ever getting pushed sideways into the elevon’s path and hindering
its movement.
137.
Repeat for the second fin.
BALANCING
Correct fore-aft balance is achieved by adding lead to the nose area of the S-15. You can either melt
it yourself to the appropriate size and shape, use fishing sinkers beaten into shape with a hammer, or
make a slurry of lead shot mixed with epoxy glue.
For maximum effectiveness the lead should be positioned as far forward as possible but not so far
forward that it adversely affects the glider’s structural durability and/or the safety risk of impacts.
Please consult your local guidelines as to the minimum setback required for lead balance weight if
you intend to use the S-15 for competitive slope racing. It’s usually 1 1/2 inches (38mm) from the
wing’s leading edge and sometimes 2” (50mm) from the nose. Measurements are taken chord-wise
(direction of flight), not at right angles to the leading edge. Even if you don’t need it to comply with
competition rules and want to keep the glider’s weight to a minimum, we still recommend
maintaining AT LEAST a 30mm (1 3/16”) buffer of foam at the leading edge, preferably a little
more.
138.
Now it’s time for the most important step in the S-15’s construction; adjusting the
glider’s centre of gravity (CG), also known as its balance point. If the glider is not
accurately balanced it will not fly well and may not even fly at all. An incorrect centre of
gravity is one of the most common causes of poor flight performance so take extra care here.
During balance adjustment your glider must have everything already installed in place ready
to fly, namely the fins and pushrods.
139.
First, check that your glider is balanced side to side at the centre-line of the wing
(not necessarily always exactly at the panel join line). If required, you can embed a small
piece of lead into one of the wingtips towards the leading edge. If one wing half is
significantly heavier than the other the glider can have a tendency to roll one way better than
the other or consistently drop one wing tip when stalled (ie. one wing half is stalling
prematurely). Another sign that the wing is unbalanced (or warped) is when there is a
noticeable difference between the left and right elevon’s neutral trim position for straight
level flight.
140.
Now the very critical fore-aft balance. The S-15 has been designed to balance at
185mm (7 1/4”) back from the tip of the nose. Carefully measure this distance back from the
nose and clearly mark it with a pen on the bottom surface of the wing. Measure it again to
make sure it’s accurate.
141.
Now determine where your glider’s current balance point is. There are several ways
you can do this. Manufactured balancing stands are best but you can also make your own by
vertically mounting sticks of dowel into a base of wood with the dowel ends sharpened like
a screwdriver tip, or similar arrangements. As a next best option you can also use your
finger nail if you’re careful enough. The idea for all these methods is to accurately find the
distance back from the wing’s nose where it balances ie. where it is sitting horizontally and
can be made to tip forwards as easily as it can be made to tip backwards.
142.
Decide whether you’re going to add some of the lead immediately in front of the
battery pack or have it all positioned to either side of the battery pack.
