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April 3-4, 2001
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It's a Bird, It's a Plane . . .
| Dreams of Flying Machines |
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Humans have long been fascinated with the notion of being able to rise from Earth by the power of flapping wings. Five hundred years ago, the Italian inventor and artist Leonardo da Vinci believed that if humans studied the wings of birds and copied their basic structure, we, too, would someday be able to fly like winged creatures. "A bird is an instrument working according to a mathematical law," wrote da Vinci. "It lies within the power of man to make this instrument with all its motions."
Da Vinci would have been pleased by the measure of success humans have achieved in terms of flight. We've created hang gliders, helicopters (also designed by da Vinci), and airplanes. We've circumnavigated the globe, broken the sound barrier, and traveled to the Moon. And yet, we have yet to perfect an ornithopter, a machine that can achieve liftoff and be propelled mainly by the power of flapping wings. There have been some limited successes with ornithopter flights over the centuries. The first working ornithopter was made in 1870 by Gustave Trouve. Thanks to the help of an internal combustion engine and gunpowder, it was able to fly 76 yards (70 meters). |
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| How Flight Works |
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For four years, Patricia Jones-Bowman has been testing an engine-driven flapping machine for University of Toronto researchers. While the craft has been able to achieve the necessary takeoff speeds of about 50 miles per hour, it's only been able to take little hops off the runway. Why is making an ornithopter that can fly so hard? Makers of ornithopters must overcome three basic problems. First, enough lift must be generated so that an ornithopter can rise from the ground. Then, that lift must be sustained to keep the object in flight. And finally, once in the air, the craft must be controlled. There are four scientific principles at work during flight: lift, gravity, thrust, and drag. Lift is an upward force, while gravity is a downward force. Thrust propels an object forward, while drag is a backward force. Earth's gravity pulls everything toward Earth. The heavier an object is, the harder it is to fly. The force that stops an object from falling to the ground is called lift. It is produced by air moving over the top of a surface—say the wing of a plane or a bird—more quickly than the air passing underneath. Fast-moving air creates less pressure, which means there is more pressure beneath the object, forcing it upward. Air moves faster over a cambered, or curved, surface than a flat surface. Thrust is the force that moves something forward through the air. Birds use muscle power to create forward thrust as well as upward lift; airplanes use engines. The air flowing over an object is slowed by the irregular surface of that object. This friction is called drag. Once in the air, a bird (and an ornithopter), must find a way to sustain lift and thrust, even when it is lifting up with its wings. To accomplish this, birds (and ornithopters) must constantly change their wing angle to take advantage of the rush of air. You can see why this is tricky and can lead to an unsteady environment in an ornithopter.
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| Flapping into the Future |
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Despite all the difficulties in creating a workable ornithopter, pilot Patricia Jones-Bowman is not deterred. She has created her own model of an ornithopter based on the skeleton of an ancient pterosaur and is convinced it will fly. Scientists are also continuing with their research. The U.S. military believes unmanned ornithopters could be very useful with surveillance tasks. Imagine a tiny ornithopter flying down a chimney to search for hostages, for example. To that end, the Department of Defense is working to create an ornithopter the size of a housefly. NASA research scientists are also attempting to create an ornithopter called an entomopter that would be used to survey the planet Mars.
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