8-Foot High Speed Tunnel (HST)

Interior view of the slotted throat test section installed in the 8-Foot High Speed Tunnel (HST) in 1950. The slotted region is about 160 inches in length. In this photograph, the sting-type model support is seen straight on. In a NASA report, the test section is described as follows: The test section of the Langley 8-foot transonic tunnel is dodecagonal in cross section and has a cross-sectional area of about 43 square feet. Longitudinal slots are located between each of the 12 wall panels to allow continuous operation through the transonic speed range. The slots contain about 11 percent of the total periphery of the test section. Six of the twelve panels have windows in them to allow for schlieren observations. The entire test section is enclosed in a hemispherical shaped chamber. John Becker noted that the tunnel s final achievement was the development and use in routine operations of the first transonic slotted throat. The investigations of wing-body shapes in this tunnel led to Whitcomb s discovery of the transonic area rule. James Hansen described the origins of the the slotted throat as follows: In 1946 Langley physicist Ray H. Wright conceived a way to do transonic research effectively in a wind tunnel by placing slots in the throat of the test section. The concept for what became known as the slotted-throat or slotted-wall tunnel came to Wright not as a solution to the chronic transonic problem, but as a way to get rid of wall interference (i.e., the mutual effect of two or more meeting waves or vibrations of any kind caused by solid boundaries) at subsonic speeds. For most of the year before Wright came up with this idea, he had been trying to develop a theoretical understanding of wall interference in the 8-Foot HST, which was then being repowered for Mach 1 capability. When Wright presented these ideas to John Stack, the response was enthusiastic but neither Wright nor Stack thought of slotted-throats as a solution to the transonic problem, only the wall interference problem. It was an accidental discovery which showed that slotted throats might solve the transonic problem. Most engineers were skeptical but Stack persisted. Initially, plans were to modify the 16-Foot tunnel but in the spring of 1948, Stack announced that the 8-Foot HST would also be modified. As Hansen notes: The 8-Foot HST began regular transonic operations for research purposes on 6 October 1950. The concept was a success and led to plans for a new wind tunnel which would be known as the 8-Foot Transonic Pressure Tunnel. -- Published in U.S., National Advisory Committee for Aeronautics, Characteristics of Nine Research Wind Tunnels of the Langley Aeronautical Laboratory, 1957, pp. 17, 22 James R. Hansen, Engineer in Charge, NASA SP-4305, p. 454 and Chapter 11, The Slotted Tunnel and the Area Rule.