One experimental machine, the "Model 347", was a prototype for a second-generation CH program. The program was initiated in 1969 and involved a rebuild of an existing CH-program featuring a fuselage stretch; four-bladed rotors; a taller rear rotor pylon; and elements borrowed from the Soviet Mil organization's heavy lift helicopters, including detachable wings to improve range and payload and a "booth" that could be extended from under the nose to house a pilot for control of crane loads.

Initial flight was on 27 May 1970. The machine was later fitted with a fly-by-wire flight control system, and was run through evaluations for several years in the early 1970s.