Boeing A160 Hummingbird

The Boeing A160 Hummingbird, military designation YMQ-18A, was an unmanned helicopter built for long endurance and high altitude. Development began for DARPA at Frontier Systems under the engineer Abe Karem in 1998, with the Army and Navy funding it from 2003 and Boeing acquiring the company in May 2004. Its hingeless rotor blades, whose stiffness varies along their length, can change speed between 140 and 350 revolutions per minute through a two-speed transmission, a technique called optimum speed rotor technology that lets it fly on less fuel than a conventional helicopter. Early aircraft used modified Subaru piston engines and later ones a Pratt and Whitney PW207D turboshaft. The first hover was on 7 December 2001 and forward flight followed in January 2002. The goals were a 4,000 kilometre range, 24 hour endurance and 9,100 metre altitude, and the United States Army abandoned the project in December 2012.