Flying is simple for objects that are lighter than the air around them, like a blimp or a helium balloon. They just float. Objects that are heavier than air, though, need some help. Below you will have a chance to design your own glider. To help you design your glider, it might help to think about the main forces acting on heavier-than-air flying objects:
Thrust. The force that propels objects forward is called thrust. Propellers and jet engines provide thrust for planes. A bird can create both lift and thrust by flapping its wings.
Drag. A plane experiences drag every time it flies. Drag is caused by air hitting the surface of a flying object, creating friction and slowing the object down. The force of drag operates in the opposite direction of thrust. Most objects that fly fast are streamlined in order to reduce drag.
Gravity. Objects near the Earth's surface are pulled downward by the Earth's gravitational field. If gravity were the only force operating, no object heavier than air would ever leave the ground.
Lift. Any force that operates upward against gravity can be called lift. For an object to rise, the lifting force must be greater than gravity. To hover in one place, like dragonflies and helicopters sometimes do, the upward force of lift must equal the downward force of gravity.
The wing of an airplane is curved on top to increase lift. A famous investigator named Daniel Bernoulli discovered that air flows faster over the top of a curved wing than below the wing. The faster air flow reduces air pressure above the wing, causing the wing to lift. That's why this is called The Bernoulli Effect.
As readers of Dragonfly magazine know, Paul MacCready won the first Kremer Prize, for building a human-powered airplane that could fly around a mile-long, figure-8 course. This was the first truly human-powered flight. Unlike a glider, the pilot provides the thrust by pedaling the craft like a bicycle.
A hang glider needs about 1.5 horsepower to stay airborne. Unfortunately, a strong bicyclist can only pedal at about half a horsepower (0.5 hp) for the 10 minutes needed to go around the Kremer course. Paul MacCready got the idea of tripling the size of the hang glider's wings without making the hang glider heavier. That way it would only take one-third the power to fly it. That equals about 0.37 horsepower--something a bicyclist/pilot could generate.
MacCready came up with the design of a new human-powered flying vessel. It was huge (30-meter wingspan), slow-flying (about 15 kilometers per hour, and light (25-34 kilograms). It would weigh about as much as a typical 10-year-old. The pilot pedals the aircraft like it was a bicycle. He called it the Gossamer Condor.
In August 1977, pilot Bryan Allen pedaled and piloted the Gossamer Condor to win the Kremer Prize for human-powered flight, the biggest cash prize in aviation! The Gossamer Condor now hangs in the National Air and Space Museum in Washington, D.C., next to the Wright Brothers' 1903 plane and Charles Lindbergh's Spirit of St. Louis, which he flew across the Atlantic Ocean in 1927.
Now that you have learned a bit about human-powered aircraft, it's time for you to design and test your craft right here on the Dragonfly Web pages. Here are some things to keep in mind:
Weight. Your pilot can only pedal at 0.37 horsepower. If your craft weighs too much, your pilot will not have enough strength to provide enough thrust.
Shape. The shape of the aircraft should do two things. First, it should reduce drag. The greater the surface on the front of the craft, the more drag. When it comes to reducing drag, the more streamlined the better. However, the second goal of the shape of the plane is to provide lift. Remember the Bernoulli effect? Well, a wing with a rounded top and a flat bottom will produce more lift. The longer the wing, the more lift. But, longer, fatter wings also produce more drag which will slow your aircraft down.
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