FORT RUCKER, Ala. -- Before turbine engines took over the world of rotor-wing Aviation, a proof-of-concept system revolutionized helicopter flight with a radical new rotor design. The Lockheed CL-475 ...

Since helicopters appeared some 80 years ago, they’ve used a single high-speed tail rotor to counteract the torque of the main rotor, stabilizing the aircraft in flight. But that rotor is both the key ...