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Usually, when somebody tells you to "take a flying leap," they don't really expect you to fly. But you can if you know what you're doing and have a hang glider strapped on. Hang gliders work on the same principle as any winged aircraft. As the wings move forward, air is deflected above and below. The air traveling over the curved wing must travel farther--and faster--than the air below. When air speeds up, it drops in pressure, creating a low-pressure zone above the wing. This in turn gives the air traveling below greater relative pressure and the strength to push up the wing. To become airborne, a hang glider's airspeed must equal about 20 mph. Airspeed is a combination of the pilot's running speed and the speed of the wind coming toward the pilot. Many different combinations are possible. If a pilot is running at 20 mph, no wind is necessary. (But this is unlikely, since the world's fastest sprinters run only about 23 mph--without carrying hang gliders.) If the wind is blowing at 15 mph, the pilot need only run at 5 mph. A combination of a 10 mph wind with a 10mph run is considered ideal. As a wing lifts a glider up, gravity pulls it down. The two forces combine to create the gliding action, which is measured by the lift to drag (L/D) ratio. For instance, the average glider L/D ratio of 13:1 means that for every foot of drop, the glider sails 13 feet forward. However, pilots need to find constant upward forces to stay in the air for longer periods. Thermals, huge masses of rising warm air, are what hang gliders ride to stay aloft. These thermals are formed near Earth's surface and depend on warmth from the ground. Flat fields, dark pavement, and low lying towns create heat early in the day, while wooded areas heat up more slowly and stay warm longer. Ridge lift is another power source. When a ridge or a hill deflects wind upward, gliders can "catch the wave!" While suspended in the harness system, the pilot steers a hang glider by shifting his or her center of balance. Leaning forward and backward causes the glider to dive or climb. This motion changes the angle of attack and is used to take off and land, as well as to control speed during the flight. Shifting from side to side causes the glider to bank into turns. Pilots use a control bar to move their weight in relation to the wings. Other recommended equipment includes a helmet, parachute, variometer, and altimeter. Breaking gliding records is difficult, but designers are always trying to glide farther, faster, and higher. The new boomerang shaped SWIFT (swept wing with inboard flap) is capable of an incredible L/D ratio of 25:1 and has a top airspeed of 80 mph. How would the altitude of your launching point affect your flight and the equipment you would need? What sort of research could a pilot do before a flight to identify possible thermal locations? You've seen hang glider pilots running into the wind to take off. Hang gliders need a total airspeed of 20 mph to take off. How fast would a pilot have to run if there was no wind to run into? How fast if there was a 10 mph wind to run into? If the pilot was running 20 mph with a 10 mph wind coming from behind, would the glider take off?