S6A Streamer Duration Models
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 homemade 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 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.