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Boomerangs | |
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Introduction
Most of us are familiar with the boomerang, the wonderful stick that returns when you throw it. However, most of us don't know the history of the boomerang. To understand why a boomerang returns, we must look at the shape of the boomerang, the aerodynamics and the physics. Finally, the correct way to throw the boomerang will be discussed. History The boomerang is often thought of as a weapon. However, the boomerang has mostly been a recreational toy. The real weapon used by the Aborigines was the killer-stick. The killer-stick is similar to a boomerang. But, one major difference - the killer-stick does not return to the thrower.
The killer-stick looks similar to a modern day airfoil. This stick actually flew through the air at high speeds. It rotates through the air, much like the discus and frisbee of today. The killer-stick could be thrown very far and with great accuracy (on target). The boomerang is smaller and lighter than a killer-stick. It looks more like a "swept-back" wing. The boomerang was not used to kill game, but was used to hunt birds. When a flock of birds was spotted, an Aboriginal hunter imitated (copied) the call of a hawk. the hunter would then throw the boomerang above the birds. The birds, thinking it was a hawk, would swoop down to elude (escape) and fly directly into the waiting nets of the hunter. The boomerang would return to the hunter. Shape
Look at the figures. The boomerang has a leading wing and a trailing wing connected at the elbow. The leading edge strikes the air first as the boomerang rotates. The angle between the wings is 105 to 110 degrees. There are right-handed and left-handed boomerangs. Aerodynamics As the boomerang flies through the air, each wing produces lift. Remember, Bernoulli's principle is that the air moves faster over the upper surface than the air moving over the lower surface. The difference in pressure causes lift. The boomerang is thrown with a spin in a similar manner as the discus and frisbee. This spin has two effects on the boomerang, as it travels through the air. The first being a stabilizing force known as gyroscopic stability. This was discussed before in the discus and frisbee sections. The second effect of the spin results in the curved (turning) flight of the boomerang.
The turning force comes from the unequal air speed of the spinning wings. The boomerang is spinning and moving forward. Thus, the forward moving wing experiences more lift than the retreating (backward moving) wing. The retreating wing then becomes the forward wing. The net result is a force which turns the boomerang.
Another way of demonstrating the principle is to compare the spinning boomerang to spinning bike wheels. Boomerang: It is thrown with a spin, with a slight tilt from vertical. This causes the boomerang to continually turn until it returns to the thrower (complete circle). Bicycle: As the wheels spin forward a rider (with "no hands" on the handle bars) leans slightly from the vertical. The bicycle will turn in a complete circle. Unlike the bicycle the boomerang will lay down flat (in the air), from vertical, as it returns to the thrower. How long a boomerang stays in the air is determined by the force with which it is thrown, and the amount of spin at launch. As with anything flying through the air, a boomerang is subject to drag and its own weight. The drag slows the boomerang down, thereby limiting the flight time. However, given enough spin and initial velocity (speed) the boomerang might circle above the throwers head a few times before landing. Throwing
Now that we have a good understanding of how a boomerang works, we should also know how to properly throw a boomerang for many happy returns. A boomerang is launched almost vertically (see figure). The angle depends on the speed of the wind. If a boomerang were to be launched horizontally, it would begin to climb until the wings stalled. At this point, the boomerang would simply fall to the ground. The boomerang is also thrown at an angle to the wind. The thrower starts by facing the wind and turns about 50 degrees to his right or left, depending on whether the thrower is right or left handed. With the proper angle to the wind, the boomerang will return to you as planned. The boomerang is such a simple device and yet it relies on complex aerodynamics and physics. Thanks to our understanding of the boomerang, more shapes have been explored:
No matter what the shape is, the principles are the same and the boomerang returns to the thrower.
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