In this image taken in 1944, one of Langley Research Center's Sikorsky YR-4B/HNS-1 helicopters is seen in the 30 x 60 Full Scale Tunnel. A technician sets up camera equipment for stop-action rotor-blade photos. The Sikorsky Company built hundreds of R-4 helicopters during World War II. It was the first mass-produced helicopter.
Image Credit: NASA