S-67 Blackhawk flight demonstrator is seen in this picture alongside the S-71 full-scale mockup. The S-67 was a considerably larger aircraft with its 61 ft five-blade main rotor compared to the 52 ft four-blade S-71 rotor.
Sikorsky S-67 Blackhawk was a private-venture, prototype attack helicopter built in 1970 with Sikorsky Aircraft research and development (R&D) funds. A tandem, two-seat aircraft designed around the dynamic drive and rotor systems of the Sikorsky S-61, it was designed to serve as an attack helicopter or to transport up to 8 troops into combat. The lone S-67 prototype crashed while conducting a low-level aerobatic demonstration at the Farnborough Airshow in September 1974.