Teen biz flies high. (Physical News).

High school pals Sean Frawley and Dan Getz share a passion for flying machines. But when they wanted to craft a toy ornithopter, a contraption that flies by flapping its wings, they found few build-it-yourself kits available. Far from discouraged, the Warwick Valley High students in Warwick, N.Y., spied a business opportunity: They invented their own ornithopter kit--based on a design by a 19th century French inventor--and launched the online Ornithopter Technologies. "I've always been fascinated by anything that flies," says Frawley.

Ornithopter Technologies' 50-centimeter (20-inch)-wide models are made of balsa wood and tissue paper, and powered by a twisted rubber band. You toss the ornithopter into the air--nose up--to make it fly. As the rubber band untwists, it forces the wings to flap up and down. Air exerts a normal (perpendicular) force on the wings that lifts the ornithopter up to 90 meters (300 feet) while propelling it forward.

By comparison, a real plane's thrust (forward motion) comes from its engine. The plane's lift (upward force) comes from wings designed as airfoils--surfaces curved so that air flows faster over the top than the bottom. Fast-moving air exerts less pressure (pushing force) than slow-moving air, so less pressure pushes above a plane's wing than below it. This creates an upward force on the wing, lifting the plane.

Since both Frawley and Getz leave for different colleges next year, their business plans are up in the air. "We've pretty much taken over my family's basement," Frawley says. "No way we'd be able to run this out of dorm rooms."