Chapter 5 - The Era of High-Speed Flight

NACA's First Hypersonic Tunnels


[56] So formidable were the design problems of hypersonic tunnels in 1945 that Langley, under the leadership of John V. Becker, chose to build a pilot model first. It was small, with an 11-inch test section, and powered by releasing the air in a 50-atmosphere pressure tank through the nozzle and test section into a vacuum receiving tank. With high pressure on one side and very low pressure on the other, pressure ratios up to several thousand could be maintained for about 100 seconds. An electrical resistance heater raised the air temperature in the settling chamber to...


drawing of the pilot hypersonic tunnel

 [57] In 1945 Langley built a pilot hypersonic tunnel with an 11-inch test section. To reach high pressure ratios, air from a pressure tank was blown through the test section into an evacuated tank.


....900° F to forestall liquefaction of the expanding air in the nozzle. This pilot model was small but flexible-and it worked. The whole apparatus would have fit easily inside an average house.

In 1946 Alfred J. Eggers of Ames began designing a 10 x 14-inch continuous-flow hypersonic tunnel with provisions for varying the Mach number. For power, the pressurizing pumps from the adjacent 12-foot pressure tunnel forced air through electrical heaters, into the nozzle, and finally into a battery of vacuum pumps. The key to varying the Mach number continuously lay in a variable-geometry nozzle and diffuser located downstream from the test section. The role of the diffuser was to control the location and strength of the so-called normal shock that would parasitically consume considerable tunnel power. Coaxing this tunnel up to hypersonic Mach numbers was much like tuning a musical instrument. The secret was to start the tunnel at a low Mach setting with the power-consuming normal shock located far down in the diffuser. Then, with the tunnel running, the nozzle and diffuser throats were narrowed down,thereby increasing the test Mach number but without changing the losses in the power-consuming shock wave located in the diffuser. In the process the Mach number in the test section was increased and the power efficiency of the whole tunnel maximized. As with the Langley blowdown tunnel, the Ames facility was a place to learn more about hypersonic flow and how to design better tunnels in the future.