Leading edges of empennage are capped with 1⁄8 × 1⁄4-inch balsa strips and rounded off (above). Elevators are joined with 1⁄4-inch diameter dowel and attached to the stab with flex nylon hinges. The wing (below) has
a single balsa spar, cardboard ribs and the leading edge folds to obtain the curved upper surface. Note the 1⁄8-inch ply spar joiners front and rear used to attach the outboard spars to the center wing spar.
AT A GLANCE Type:
Construction:
Wing span: Wing area: Length: Weight:
Wing loading:
Line length/diameter: Engine required: Prop:
C/L Sport Scale
cardboard with some balsa and ply
60 inches 508 sq. in. 42 inches 58 ounces
16.5 oz./sq.ft. 60 ft/.018 in.
.40–.50 two-stroke 9–6
used. My model is powered by a .40 engine and has a fully fueled flying weight of 58 ounces. This weight combined with the 508 square inch wing area results in a wing loading of 16.5 ounces/square foot. Its size makes it a very stable sport flying model.
Construction tips Before we begin, take a look at these spe-
cial tips for working with cardboard. Glue: Water base glue, such as white glue
or Titebond, is recommended. Contact ce- ment is not recommended since parts cannot be shifted when gluing surfaces. Folding: The scoring of the fold lines is
done with a screening tool available at any hardware store. It consists of a handle with a 11⁄2-inch radius wheel at one end, which is
FLYING MODELS
run along a metal straightedge on the fold line.
Finishing: Cardboard gives a solid sur-
face with no open areas to cover and is non- porous. The easiest finishing method is to give two coats of clear dope, sanding lightly between coats with #400 sandpaper, fol- lowed by two coats of color dope. However, a wide variety of finishing materials may be used on the cardboard. Coverings, such as Solarfilm, MonoKote and vinyl paper can be used. With any of these, it is recommended that the surface not be doped, which will re- sult in a better bond. Paper tape: All seams, joints and ex-
posed edges of the model are covered with strips of gummed paper tape. Obtain a one- inch wide roll from a stationary store. Sim- ply cut a thin strip to length, dip it in water and smooth it over the seam. Construction: Be sure to note the di- rection of the corrugations when cutting out the cardboard parts. Score and fold
cardboard parts as indicated on the plans. Empennage: The fin, rudder, stabilizer
and elevators are each made from two pieces of 1⁄8-inch cardboard laminated together cross grain to give 1⁄4-inch thick surfaces. Add a 1⁄8 × 1⁄4-inch balsa strip to the fin lead- ing edge and round off. Add 1⁄8 × 1⁄4-inch bal- sa strips to the stabilizer leading and trail- ing edges and round off. Glue the elevators to the 1⁄4-inch dowel. Add 1⁄8 × 1⁄4-inch balsa strips to the remainder of the elevator lead- ing edge and round off. Seal all raw edges with gummed paper tape. Hinge the eleva- tors to the stabilizer with flex hinges at four places. Wing: First note that the bottom of the
Bird Dog wing has no dihedral and is built flat on your work board. Begin construction by making the wing spar, which consists of three sections: a center section and a left and right outboard section. Each section of the spar is made from 1⁄4-inch balsa capped top and bottom with 1⁄4-inch square spruce
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