Right side view of US Army Sikorsky XR-4 helicopter [Vought-Sikorsky XR-4C, s/n 41-18874 , A19600307000], right side fuselage uncovered, on exhibit in the Smithsonian Institution Aircraft Building, 1961
Right side view of US Army Sikorsky XR-4 helicopter [Vought-Sikorsky XR-4C, s/n 41-18874 , A19600307000], right side fuselage uncovered, on exhibit in the Smithsonian Institution Aircraft Building, 1961