DIY





Making and Throwing a Boomerang

Throwing a boomerang and watching its flight can inspire the poetry of wonder. Making one yourself requires more persistence than poetry, but is worth the effort.

| July/August 1981

For pure grace and beauty—as well as for a stirring example of the wonder, symmetry, and constancy of nature's laws—the delicate, balanced, and bird-like flight of a boomerang is hard to beat. Even when the forces acting upon the device are explained and understood, its dramatic soaring is—as things controlled by nature tend to be—still, in essence, a mystery.

Once thrown, a "return" boomerang travels in a rising, circular flight. If the wielder is right-handed, it will fly up and around to his or her left (throwing a boomerang with the left hand reverses the circle), reaches its peak at a point about 45° from the line of the direction in which it was thrown, then begins a gradual, circling descent, and either glides gently to the ground or hovers for a few seconds before dropping. The commonly made comparison of its flight to that of a predatory bird is quite accurate. In fact, some primitive tribes, by throwing return boomerangs into the air while imitating a hawk's cry, are able to keep small birds on the ground and thus drive them into nets.

Generally, however, the return boomerang is used as a toy. It will typically weigh less than five ounces, and the angle of its limbs—each of which is no more than a foot long—can be as extreme as 90°. The approximately pound-and-a-half hunting versions, on the other hand, have gradual curves and overall lengths sometimes surpassing three feet. They can travel up to 250 yards in a straight line and are used by Australian aborigines for felling animals and birds.

How It Flies!

Return boomerangs operate on the principle of the airfoil. Their upper surfaces are curved, much like the top of an airplane's wing, while the undersides are flat. As one of these aerodynamic implements slices through space, the air flows faster over the greater surface area of the curved top, and (since, as the velocity of air increases, its pressure decreases) a partial vacuum is created. Therefore, the greater air pressure against the flat side pulls the boomerang up, around, and back to its starting point (the hunting boomerang is shaped to provide some lift in straight flight).



As the return boomerang leaves the thrower's hand, both its rotational and linear momentum are very strong. The airfoil principle is acting to move the device around to the left, but at first the linear momentum is great enough to resist this pull, and the device travels pretty much in a straight line. However, since linear velocity decreases much more quickly than does rotational velocity, the toy soon begins to circle. The whirling motion then causes the boomerang to tip over on its side so that it rises, still circling, like a bobsled going up and around a banked curve. Finally, the rotation slows so much that the air pressure can no longer hold the weight of the boomerang up, and the device begins to drop—though it continues to curve—until, if the throw is good, it lands near its starting point.

Most folks who aren't familiar with boomerangs assume that they're thrown sidearm, but that's not the case. When pitched in such a manner it will rise to a great height and then come crashing back down to the ground , sometimes even breaking apart on impact.






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