For more than three decades, the $250,000 Sikorsky Prize has been dangling over the head's of engineering students just out of their reach. To claim the prize, you just have to build a human-powered helicopter that can hover at a height of about 10 feet for a full minute while staying inside a 13-foot box. Sounds simple enough, but it's actually a very difficult achievement. NPR visits the University of Maryland to see a team of students who have their eyes on the Sikorsky Prize.