show #1201

Peggy learns the basics of hang gliding, then goes for a ride. Segment length: 9:20

Contents

Insights & Connections


Vocabulary


Resources


Main activity


Try this

INSIGHTS & CONNECTIONS

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.

VOCABULARY

airspeed the speed at which a glider is passing through the air

altimeter instrument which measures altitude

angle of attack the angle at which a glider meets the air flowing over it. Decrease the angle of attack, and the glider dives and speeds up. Increasing the angle of attack slows the glider.

flare raising the nose of the glider sharply to stall forward motion and land

ground speed the speed at which the glider is passing over the ground. Ground speed is a result of airspeed and wind speed.

pitch movement which increases or decreases the angle of attack, controlled by shifting the pilot's weight forward and backward

roll side to side control movements to make the glider bank and turn

unstable air when air temperature drops rapidly at higher altitudes. This makes thermals rise more rapidly, offering more lift for gliders.

variometer instrument which measures altitude gains and losses

wind speed the speed at which the wind is passing over Earth

RESOURCES

Additional sources of information

General Aviation News & Flyer
8415 Steilacoom Boulevard
Tacoma, WA  98498
(800) 426-8538

Soaring Society of America, Inc.
PO Box E
Hobbs, NM  88241-1308
(505) 392-1177
(publishes Soaring magazine, Technical
Soaring quarterly, and a directory of 
soaring sites)

U.S. Hang Gliding Association
PO Box 8300
Colorado Springs, CO 
80933-8300
(719) 632-8300
(publishes Hang Gliding magazine. 
Can help you locate a hang gliding 
school or club in your area.)

MAIN ACTIVITY

In this activity, you'll make a model of the countryside and a simple glider. Then, using a blow dryer as a wind source, you'll recreate the air currents and thermals that a hang glider would encounter.

Materials

  1. Drop the pieces of paper just as they are to the floor from a height even with your chest. What happens? The air pressure below the paper is being released in random spurts. Now fold the pieces of paper in half to be 20 cm x 12.5 cm (8" x 5") and spread them open again. What happens now when you drop them, with the fold crease down? The fold is dividing air pressure equally on either side of it.
  2. Open the creased pieces of paper on a table and fold a long edge back about 2 cm (3/4"), creating a sort of lip. What happens when you drop the paper again? Keep folding this edge over onto itself, 2 cm at a time, and keep dropping it until you get a smooth gliding action. Why does this cause a forward motion? Can you figure out a way to calculate the lifttodrag ratio, using the measuring tape? (Remember the L/D definition--as the glider drops, how far does it move forward?) What thickness of paper has the best L/D ratio? Why?
  3. Using the blow dryer on a low, cool setting, turn your floor into a hang glider's paradise. Have a friend sit on the floor and hold the blow dryer even with a structure, while you fly your gliders over, around, and through your buildings and mountains. Create turbulence by shaking the blow dryer. Does a warmer setting cause different flight patterns? Create the ultimate thermal by pointing the blow dryer straight at the ceiling. Experiment using two blow dryers at once. Have fun!

(Hint: If you have trouble keeping the paper gliders aloft long enough to see the flight effects caused by your classroom countryside, try using air-filled balloons instead.)

TRY THIS!

The world records for distance in hang gliding are 488.49 km for men set by Larry Tudor in 1990, and 335.96 km for women set by Kari Castle in 1991. Matching these distances, where could you go if you were able to travel by hang glinder from your school?

TRY THIS!

Get a topographical map of your city, as well as an aerial photograph. Plan a flight over the city in a hang glider. Can you identify which parts of the city will have thermals rising from them and which will be cooler? What areas would you want to fly over at 8 a.m.? Noon? 6 p.m.?

TRY THIS!

Hang gliding pilots learn to "see" the air while they are flying. Stand outside on a breezy day. How many different ways can you determine what the air is doing? Pay attention to things such as how sound travels, how sun and shadows look on the ground, dust and blowing objects, plants and trees, etc. As you do this, can you anticipate what the wind will do next, even before you feel a shift in the breeze?

Newton's Apple is a production of KTCA Twin Cities Public Television. Made possible by a grant from 3M. Educational materials developed with the National Science Teachers Association.