NACA researcher examines a model mounted in the slotted test section of the tunnel. Caption title: "69739 Test Section of 16 FT High Speed Tunnel after Installation of Slotted Walls, 1951." Photograph published in Engineer in Charge: A History of the Langley Aeronautical Laboratory, 1917-1958 by James R. Hansen, page 330. Caption "Langley's development of slotted walls for wind tunnels- here seen installed in the 16 ft High Speed Tunnel- permitted, for the first time, a smooth transition from sub- to supersonic airflow. The advance is widely considered a benchmark in aeronautical research." Photograph published in Winds of Change, 75th Anniversary NASA publication, page 58, by James Schultz.
