How do they make Boomerang?

>>Raw Materials

A wide variety of materials can be used to make a boomerang. Wood remains one of the most popular because it produces good results, is relatively inexpensive, and is easy to work. Generally preferred is aircraft-grade Finnish or Baltic birch plywood, which is laminated from skinny layers of wood. A 0.2-in (5-mm) thick sheet will have between five to 10 layers. To protect the wood from moisture, it is usually sealed with a polyurethane coating.

Polypropylene, acrylonitrile-butadiene-styrene (ABS) plastic, fiberglass, carbon fiber, and linen-phenolic resin are synthetic materials used for boomerangs laminates and Kevlar para-aramid fiber. Toy boomerangs made from urethane foam or cardboard can be used indoors.

>>Design

Because proper spinning action is crucial to the performance of a boomerang, some fundamental concepts must be followed during the design process. However, those essential elements leave a great deal of room for creativity, and boomerang makers frequently experiment with innovative shapes.

When creating a new pattern, the designer marks a point in the middle of a sheet of sturdy paper. This first guide mark denotes the center of gravity of the boomerang. As the designer continues to sketch the boomerang, they must balance the shape around the center of gravity point. The other important consideration is that the centerlines of each wing of the boomerang must generally point toward the center of gravity (i.e., within 10° in either direction). So the second set of guide marks the designer makes on the paper are the centerlines of the wings. Within the limitations set by the guide marks, the designer can then sketch as basic or whimsical design as desired.

After the design is completely drawn, the designer cuts it out from the sheet of paper. By hanging the pattern successively from the end of each wing, the designer can verify that the planned center of gravity has been adequately preserved. This will be true if the centerline of each wing hangs within 30° of vertical.

Serious designers who seek more precise methods can use more sophisticated techniques, including computer-aided design software.

>>The Manufacturing Process

The following description focuses on making a V-shaped plywood boomerang. Synthetic materials are worked similarly, but some generate dangerous dust or fumes when being cut or sanded. In this case, dust masks and protective clothing are essential.

Forming

1 The plywood sheet is checked for flatness. If it is not entirely flat, it is oriented so that the concave side will correspond to the top surface of the boomerang. This significantly increases the boomerang's strength, and it raises the wingtips slightly for better aerodynamics.
2 The pattern is placed on the plywood so that the wood grain runs across from the tip of one arm of the boomerang to the end of the other arm. The outline of the pattern is traced on the plywood with a pencil.
3 A scroll saw, jigsaw, coping saw, band-saw, or fret saw is used to cut the boomerang shape out of the plywood. This essential cutout is called the blank.

4 As an alternative to cutting a single-piece blank, two separate wings can be clipped, allowing a section of overlap where they will be joined. Using a router, half the thickness of this overlap section is cut away from each wing. The overlapping areas are joined with wood glue and clamped together until the joint hardens.
5 An outline is drawn on the top of the blank to show the areas shaped for the leading and trailing edges of the wings.

6 The profiles of the wings are shaped with a belt sander or by hand with a rasp or a plane. The top of the leading edge of each branch is decreased at a 45° angle, while the rear of the wing is angled down to leave a 0.04-0.08 in (1-2 mm) thick trailing edge. The bottom face of the leading edge is cut back slightly. The tips of the wings are shaped down to the same thickness as the trailing edge. The various layers of the plywood serve as contour lines that help the worker achieve uniform slopes.
7 A shallow section may also be cut out from the bottom surface of each wing. For example, this might consist of a 2-in (5-cm) long strip near the wing tip and behind the leading edge.

Finishing

8 Using progressively finer (80-250 grit) sandpaper, the surface of the boomerang is smoothed carefully with an orbital sander or by hand.
9 After spraying the surface with sanding sealer, fine steel wool is used to smooth the surface further. A coat of paint or wood stain is followed by one or more coats of the clear polyurethane finish.

Tuning

10 The boomerang is thrown several times to test its flight capabilities. Several types of adjustments may be made to tune the boomerang for better performance. For example, the wing profiles might be adjusted by additional sanding.
11 Another tuning technique is to bend the wings, raising their tips about 0.12 in (3 mm) above the vertex plane; this is called giving the boomerang a positive dihedral. It may be necessary to heat the boomerang to make it flexible enough to bend and make the adjustment permanent. This can be done with steam or even in a microwave oven.
12 Twisting the wings to raise or lower the leading edges can also affect the boomerang's performance.
13 Other tuning techniques include drilling holes through the wings, cutting slots in the leading edges of the wings, drilling shallow holes into the underside of the wings, and inserting lead or brass plugs to add weight.

>>Quality Control

Throughout the manufacturing process, the quality of the boomerang is periodically checked. Any unevenness in the boomerang, such as unequal sides or bumps, will take away from the aerodynamic design. Boomerangs are sanctioned by comities such as the World Boomerang Association and the United States Boomerang Association (USBA). These groups set the standards and rules that any boomerang competition must adhere to, such as safety, skill, and timing.

>>The Future

Boomerang innovations can be developed in two areas: materials and design. As new materials are created that are strong, durable, and lightweight, boomerang makers will try using them individually or in combination. For example, the boomerang that flew for more than 17 minutes consisted of a two-layer outer shell of carbon fibers and Kevlar; the body was filled with epoxy resin mixed with phenolic microballoons.

Two recent innovations suggest ways that designs can be modified to improve aerodynamics. One involved making the upper and lower surfaces of the trailing edges of a boomerang's wings slightly concave. Typically, these surfaces are flat or slightly convex. This design was used for the boomerang that set the current world record for distance. In the other example, a boomerang's wingtips were cut at an angle that made them perpendicular to imaginary lines leading to the center of rotation. Usually, the wingtips are perpendicular to the centerline of the wings. This modification was created by the holder of the unofficial MTA record.