Chapter 5 - The Era of High-Speed Flight

The Ames Unitary Plan Wind Tunnel Complex


[66] The best-laid plans change in the face of hard realities, and the Ames Unitary Plan tunnel was no exception. The initial plan called for a single tunnel with an 8-foot test section that had both transonic and supersonic capability. This could not be, for two reasons: (1) differing test section size requirements and (2) vastly different compressor requirements. At transonic speeds, for example, the frontal area of the model being tested should be only 1 percent or less of the test section area for good results; however, at high Mach numbers, as the shock waves slope downstream more nearly parallel to the aircraft axis, smaller test sections for the same size model are very satisfactory. In the matter of the wind tunnel compressor, a single-stage fan suffices up to about Mach 1.2, but higher speeds demand multistage compressors with thousands of blades. No single tunnel can properly cover the entire range of aircraft and missile flight.


drawing of shock wave calculations

[67] The length of the so-called test rhombus in a supersonic tunnel increases at higher Mach numbers as wall-reflected shock waves cross the axis farther downstream. A model of a given size can be tested in smaller tunnels at higher Mach numbers.


Consequently, the Ames Unitary Plan Wind Tunnel, under the guidance of Ralph Huntsberger, became in effect three separate test sections driven by a giant centralized power plant consisting of four tandem-coupled, variable-speed electric motors capable of 180 000 horsepower on a continuous basis and 240000 horsepower for 30 minutes. The transonic test section spanned 11 x 11- feet, while the two supersonic sections were somewhat smaller: 9 x 7-feet and 8 x 7-feet. A 3-stage compressor drove the transonic legs; an 11-stage compressor, the two supersonic legs. Giant valves 20 feet in diameter and weighing 250 tons shunted the centrally supplied air from one supersonic leg to another. Although construction of this impressive complex was finished in 1955, a blade failure in a compressor delayed full facility operation with the transonic leg until late 1957.

The west coast segment of the aerospace industry quickly capitalized on the nearby Ames facilities. The famed Boeing fleet of commercial transports and the Douglas DC-8, DC-9, and DC-10 were all tested at great length. Cruise efficiencies were improved and landing performance enhanced. These craft went on to dominate the world commercial aircraft market. In addition, practically all modern military aircraft, such as the F-111 fighter, the C-5A transport, and the B-1 bomber, went through the Ames Unitary Plan tunnels. Indeed, it is not overstating the importance of the tunnels to claim that almost all high-performance U.S. aircraft flying today or about to fly have been tested at Ames. In later years, almost all NASA manned space vehicles, including the Space Shuttle, were tested in the Ames Unitary Plan tunnel complex.