The Kellett XR-8 (later redesignated XH-8) was a helicopter built in the United States during World War II. It was a two-seat machine intended to demonstrate the feasibility of a twin-rotor system, and while it accomplished this, it also demonstrated a number of problems that prevented further development of this particular design.
Read more about Kellett XR-8: Design and Development, Operational History, Variants, Specifications (XR-8)