Chapter 3 - Through the Barnstorming Days to World War II

A Depression Bargain: The Full-Scale Tunnel


[22] The initial NACA Langley wind tunnel complex was complete by 1929-and it was churning out highquality aerodynamic research data. The Aeroplane of London stated in envious terms

The only people so far who have been able to get at something like accurate results from wind tunnel experiments are the workers at the experimental station at Langley Field.

Despite the praise from abroad, Langley wind tunnel designers saw a clearcut need for still another tunnel- a full-scale tunnel.

Although the small variable density tunnel gave aircraft designers confidence in scaling up test results from models, several research areas could be explored only with full-scale models or with the actual aircraft. To illustrate, how does the rotating propeller affect aircraft controllability? What interference effects are created by aircraft components ? Most important, drag penalties due to external struts, surface gaps, air leaks, engine cooling installation, and so on, can be [23] assessed best at full-scale sizes. Under the leadership of Smith J. De France, the design of the Full- Scale Wind Tunnel (FST) began at Langley in 1929, at the very start of the Depression. Using funds appropriated before the Depression, NACA was able to buy materials and labor at bargain prices. In addition, a large reservoir of talented but now unemployed aeronautical engineers became available to NACA.. As an interesting historical note, three members of the original FST staff-Smith J. De France, Abe Silverstein, and Harry J. Goett-eventually became NACA/NASA Center Directors.

The cavernous test section of the FST could accommodate a modest two-story house. It was 30 x 60 feet, with an open throat that facilitated the installation of full-size aircraft. Downstream, two propellers, each driven by a separate 4000-horsepower electric motor, circulated air through the test section at speeds between 25 and 118 mph. The air circuit similar to that of the earlier PRT, was of the doublereturn type; that is, the airflow from the dual propellers was split right and left into two streams. Doubling back between the test section and the building's wall, the streams reunited prior to the throat of the test section. Operational in the spring of 1931, the FST tunnel building (434 x 222 feet and 90 feet high) became a hard-to-ignore landmark at Langley.

When the drag tests in the FST indicated surprisingly large performance penalties from external struts and other exposed installations, a procession of military aircraft was dispatched to Langley for " drag cleanup tests." Here the drag penalties associated with various types of surface roughness, air scoops, antennas, and other surface excrescences were carefully measured in comparison to an aerodynamically smooth aircraft. Practically every highperformance aircraft used by the United States during World War II was checked out in the FST.

A strange hodgepodge of other vehicles also underwent aerodynamic tests in the FST because of its large size. Dirigibles, submarines, radar antennas, gliding parachutes, inflatable airplanes, and free-flying models were just a few of the vehicles and machines tested. So useful has the FST been to general aerodynamic research that it was completely rehabilitated after 46 years of active, useful life. In 1977, when the refurbished tunnel had been returned to operation, experiments were conducted on solutions to landing problems of the supersonic transport-a vehicle concept not even remotely envisioned by the original tunnel designers.

airship under test

 A scale model of an airship under test in the full-scale tunnel.