The leading edges of the empennage are capped with 1⁄8 × 1⁄4 balsa strips and rounded off. Elevators are joined with 1⁄4-inch dowel and attached to the stab with nylon flex hinges.
Like the real airplane, the model Minicab presented here is simple in construction and inexpensive to build. It uses 1⁄8-inch corru- gated cardboard as the primary building material, greatly reducing both building time and cost. The design makes use of card- board’s unique features in that it can be used in large sections and folded. For in- stance, the wing is built of three pieces of cardboard with cardboard ribs and a single spar. The tail surfaces and fuselage are pri- marily cardboard with little internal brac- ing required. The result is a low cost, fast building model that has good scale-like ap- pearance and can take plenty of punishment at the flying field.
Cardboard varies in weight, but any 1⁄8-inch corrugated stock will do. Sources include box manufacturers and local shopping centers where you can find stacks of discarded boxes. Look for cardboard with brown paper on one side and a white finished Kraft paper on the other side. The white paper on the outside of the model results in a smoother finish and neater appearance.
The model has a wingspan of 60 inches and a length of 39 inches. The bottom of the airfoil is flat with a curved upper surface, due to the scoring and folding technique employed. Engines of .40 to .50 size can be
The wing has a single spar, cardboard ribs. The folds between the leading edge and the spar help form the curved upper surface. Here the center section is complete and the spar has been glued into the outboard wing panel.
used. My model is powered by a .40 engine and has a flying weight of 74 ounces. This weight combined with the 539 square inch wing area results in a wing loading of 19.7 ounces per square foot. Its size and stability make it a good sport flying model.
Construction tips
Before we begin, take a look at these spe- cial tips for working with cardboard. Glue: A water-based glue, such as white glue or Titebond is recommended. I don’t recommend contact cement since parts can- not be shifted when gluing surfaces. Folding: I use a screening tool available
at any hardware store to score the fold lines. It consists of a handle with a 11⁄2-inch radius wheel at one end. Run this along a metal straightedge on the desired 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-grit sandpaper, fol- lowed by two coats of color dope. However, a wide variety of finishing materials may be used on the cardboard. Iron-on film covering can also be used. When using a plastic film, do not dope the surface to allow 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
Cut out all cardboard and wood parts, be- ing sure to note the direction of the corruga- tions. Score and fold cardboard parts as in- dicated on the plans. Empennage: The fin, rudder, stabilizer and elevator are each made from two pieces of cardboard laminated together cross-grain to give 1⁄4 inch thick surfaces. Add a 1⁄8 × 1⁄4 inch balsa strip to the fin leading edge and round off. Glue the rudder to the fin with its trailing edge offset a half inch to the outside of the flying circle. Add 1⁄8 × 1⁄4 inch balsa strips to the stabi-
lizer leading and trailing edges and round off. Glue the elevators to the 1⁄4-inch dowel. Add 1⁄8 × 1⁄4 inch balsa strips to the remain- der of the elevator leading edge and round off. Seal all raw edges with gummed paper tape. Hinge the elevators to the stabilizer with flex hinges at four places. Wing: The single wing spar is made in three pieces (one constant section center panel spar and a left and right outboard
The wing tips are balsa sanded to shape. The leadout guide (above) is made
of 1⁄8-inch ply. The 5⁄32-inch diameter wire main gear (at right) is attached to the 1⁄8-inch ply plate in the wing bottom with nylon gear clips. FLYING MODELS
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