Chapter 5 - The Era of High-Speed Flight

A High Pressure Tank Farm at Langley


[59] As NACA probed the hypersonic flight regime of missiles and spacecraft, a complete break with conventional facility design was necessary. Hypersonic testing requires very high temperature air at very high speeds, necessitating large pressure ratios and power inputs. Because of power limitations, short-duration runs typified the hypersonic tunnel. The traditional wind tunnel was not adaptable to this kind of operation, and a complete break with past tunnel design philosophy seemed necessary for the expeditious exploration of the hypersonic realm.

A different basic wind tunnel concept was developed at Langley in the late 1940s. It recognized that the general need in hypersonic experimentation was a supply of very hot, high-pressure air for short periods...


freeflight tunnel
Loading the gun in the Ames super-sonic freeflight tunnel.

Schematic drawing of the Ames supersonic free-flight tunnel.

Shadowgraph Shadowgraph of sabot separation.

image Diagram
Diagram of sabot operation.


[60] of time. This source of hot, pressurized air could be centralized and parceled out in bursts to individual test cells on demand. Diverse experiments could then be set up in the independent test cells without tying down a huge, expensive wind tunnel for days or even weeks.

Placed in operation in 1951, the Langley Gas Dynamics Laboratory consisted of a central tank farm capable of storing 19 000 cubic feet of air at 340 atmospheres pressure. At this pressure the air was 40 percent the density of water and weighed approximately 500 000 pounds. By feeding this air through several test cells into large vacuum tanks, pressure ratios at the beginning of an experiment could approach 10 000 to 1. No continuously operating tunnel could match that. To heat the air and prevent liquefaction in the test cells, huge steam and electric resistance heaters heated the air to 680° F and 1040° F, respectively.

The test cells of the Gas Dynamics Laboratory generally operated at speeds between Mach 1.5 and Mach 8.0. Typical test sections were approximately 20 inches. In later years, when models of various space craft had to be tested at reentry speeds, the facility substituted pure nitrogen and helium for air and provided this medium at 3500° F at pressures up to 340 atmospheres.