Indoor Booomerangs: Nonstandard Airfoil, Variable-Configuration
This is a device which when thrown returns to the thrower; the most familiar is the L-shaped Australian boomerang. All boomerangs employ an airfoil.* All others than the one described here employ roughly the conventional airfoil of an airplane wing: they have a cross-section thicker in the middle and thinner at the trailing edge. The airfoil of the device here is easier to fabricate, and can be cut from sheet cardboard.
In simplest form, this boomerang consists of a cross of two strips of light cardboard held perpendicular to each other by a rubber band looped from one over the other. The cardboard is of the type used in the backing of a pad of paper or a cereal box. Such cardboard has a grain; the two strips are cut lengthwise with the grain. For this weight of cardboard, 1 1/4" x 8 1/2" are good dimensions for each strip. The lift-producing airfoil is simply an upward curvature of the long axis of each blade. A cardboard sheet has a direction of warp which should be determined and used for the blade curvature. Each blade is gently bent upward from its center, so it is slightly and uniformly curved. The curve is gradual (not a sharp crease), to 1/4" - 1/2" at the blade tips. That is, when a blade is lying flat upward on a table, each tip is 1/4" - 1/2" above the center: |(. This warp generates all the lift needed. The two blades are assembled into a cross X with a rubber band. [The reader may find it helpful here to draw plan and elevation sketches of the micro-boomerang.]
Throwing: (1) Hold tip of one blade between thumb and forefinger, with blades curving to left. (For a right-hander, blades should curve toward them.) (2) Orient boomerang so that the side farthest from thrower forms an angle with the floor between vertical and 45 degrees. (3) Throw forward lightly, with an overhand motion, as a baseball is tossed. Aim for a spot slightly above the horizon. (4) As the boomerang is released, start it spinning rapidly with a sharp (downward) wrist flick.
When it leaves the right hand, the boomerang should be spinning counter-clockwise viewed from side nearest thrower. It should spin in a plane between vertical and 45 degrees with respect to the ground; it must not be spinning in a horizontal plane. The boomerang is easier to throw when sitting in a chair, because it tends to climb and hit the ceiling. [The reader may find it helpful here to sketch front, side, and overhead views of a stick-figure throwing the micro-boomerang.]
By sliding the two-bladed configuration from a cross to a T- or L-shape, the flight circle can be increased. By adding a third blade, configurations in the form of Z, H, U, J, Delta, etc. can be made that also return well. By adding a fourth blade, configurations in the form of #, M, etc. can be constructed that also work.
* J. Walker, Roundabout: The Physics of Rotation in the Everyday World (W. H. Freeman, 1985), chs. 9 & 10.
Copyright 1970, 2000, Christopher Cherniak