A typical S6A model is shown on the following plan. It includes a
fiberglass body, a nose cone made from plastic or fiberglass, balsa fins,
an external shockcord, a pleated streamer, and an ejection plug.
S6A bodies are typically handmade from fiberglass and a laminating epoxy.
A 30 mm mandrel with a boattail shape is commonly used. The mandrel is
typically made from aluminum, steel, or a plastic. The basic process
involves coating the mandrel with a release agent, applying the fiberglass
and epoxy resin to the mandrel, squeegeeing off the excess resin, allowing
the epoxy to cure, then removing the resulting airframe from the mandrel.
The making of bodies in this way is definitely an art, and a lot of
esoteric building techniques have been developed to refine the basic
process. One popular refinement involves using tissue or Mylar in
combination with the fiberglass, which gives a nice look to the finished
bird. Some modelers even omit the fiberglass entirely, preferring to use
vellum or drafting paper to make their S6A bodies. This yields competitive
models while minimizing the need for special tooling and materials.
Many materials have been tried for S6A nose cones, including balsa, foam,
fiberglass, and plastic. Currently, the most popular materials seem to
be
fiberglass and vacuum-formed plastic. Fiberglass nose cones are usually
made over a nose cone-shaped male or a female mold. The mold is coated
with a release agent, fiberglass and epoxy resin are applied to the mold,
the epoxy is allowed to cure, and the resulting nose cone is then removed
from the mold. Vacuum-formed plastic cones are made by heating a piece
of
sheet plastic and forming it over a nose cone-shaped male mandrel using
a
vacuum. Some modelers have made miniature vacuum-forming machines using
nothing more than an oven, a frame to hold sheets of plastic, and air
plenum box hooked up to a vacuum cleaner. Since 92 nearly all of the 30
mm
nose cones used in S6A and other events by the U.S. Team have been made
by
the same man, who spent many hours perfecting his art of vacuum-forming.
Fins for S6A models are pretty conventional and are usually made from
balsa
or G10 glass board stock. Balsa is usually chosen over G10 for its low
mass. For a lightweight and smooth finish, balsa fins are sometimes
finished with epoxy, occasionally in combination with tissue or fiberglass.
Such fins are usually coated with epoxy and clamped between flat plates
or
placed in a vacuum bag to yield a smooth finish.
Streamers these days are typically made from Mylar. Such streamers are
usually pleated by hand, which tends to cause the streamer to flap
violently on the way down, increasing the drag and extending the flight
duration. The folds in such streamers are often ironed-in with a small
iron or a Monokote iron. Note that unlike NAR competition, streamers used
in S6A are allowed to attached the streamer in two places at one end of
the
streamer, i.e. a "yoke." Some think this method of streamer attachment
is
advantageous because it tends to yield better flapping action.
Ejection plugs are commonly used with S6A models because of the large
volume enclosed by the 30 mm Big Berthas of today. These plugs are nothing
more than circular pieces of Styrofoam that slide into the model in place
of wadding, protecting the streamer from hot ejection gases and also
facilitating deployment. Some modelers use a hot wire to cut these plugs
out from sheets of foam, though an easier and quicker method is to spin
a
piece of fiberglass tubing on a drill press and use the rotating fiberglass
tube to "burn" out plugs from sheets of foam. Such foam plugs
fit nicely
into the 30 mm bodies and actually suffer little or no damage from the
ejection charge if the fit of the plug is good. Some competitors use
ejection plugs made from cup-shaped pieces of foil.
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