Last year, the Austrian engineering firm IAT21 set out to construct a flying machine that floated like a hummingbird, traveled as fast as a jet, was as quiet as a hot-air balloon, and was simple enough that a car mechanic could repair it. The company's working prototype, called D-Dalus, is roughly five feet by three feet square and can lift about 100 pounds. But the size and lift are not what's most impressive. A flying machine with no airfoil, rotor or jet propulsion can travel where most cannot: in very tight spaces and through terrible weather.