A Mini Helicopter

A mini helicopter modeled on flying tree seeds could soon be flying overhead. Evan Ulrich and colleagues at the University of Maryland in College Park turned to the biological world for inspiration to build a scaled-down helicopter that could mimic the properties of full-size aircraft. The complex [blank] of full-size helicopters gets less efficient when shrunk, [blank] that standard mini helicopters expend most of their power simply fighting to stay stable in the air. The researchers realized that a simpler aircraft designed to stay stable passively would use much less power and reduce manufacturing costs to boot. It turns out that nature had [blank] them to it. The seeds of trees such as the maple have a single-blade structure that [blank] them to fly far away and drift safely to the ground. These seeds, known as samaras, need no engine to [blank] through the air, thanks to a process called autorotation. By analyzing the behavior of the samara with high-speed cameras, Ulrich and his team were able to copy its design. The samara copter is not the first single-winged helicopter- one was flown in 1952, and others have been attempted since - but it is the first to take advantage of the samara's autorotation. This allows Ulrich's vehicle to perform some neat tricks, such as falling safely to the ground if its motor fails or using vertical columns of air to stay aloft indefinitely. "We can turn off the motor and autorotate, which requires no power to sustain," says Ulrich.