The NACA/NASA Full Scale Wind Tunnel

The Scene: A new wind tunnel, the NACA Full Scale Tunnel at the NACA Langley Memorial Aeronautical Laboratory, Hampton, Virginia The Time: May 27, 1931 The Action: A Navy Vought O3U-1 “Corsair II” –the whole airplane—is mounted in the wind tunnel. The airplane engine is turned on, and shortly the airplane is “flying” at 120 miles per hour. But, in reality, this airplane is standing still, and the air in the wind tunnel is blowing over it at 120 miles per hour. The significance: This is the first test carried out in the new National Advisory Committee for Aeronautics  (NACA), the precursor to NASA, Full Scale Tunnel (FST), not on a model of the airplane, but on the airplane itself. Here is the advantage of the FST–a whole airplane could be mounted in the cavernous test section, which is 9 meters (30 feet) high and 18 meters (60 feet) wide, thus eliminating the uncertainty associated with testing small models in small wind tunnels due to so-called “scale effects."

 

For the next 10 years, the Langley FST would be the largest wind tunnel in the world. It was a major factor in enhancing the world-wide presence of the United States in aeronautics. Moreover, for the next 78 years, virtually every American fighter airplane through the Lockheed Martin F-22 was tested in the FST. Of particular importance was the major series of tests called the “drag cleanup tests,” conducted during the period from 1938 to 1945. For these tests, a given airplane in its full operational configuration would be systematically stripped one-by-one of its external appendages, and rough contours smoothed over with putty, until just the smooth basic shape remained. The aerodynamic drag was measured at each stage, identifying the drag due to each item. In this fashion, those items causing the most drag were identified and modified so as to lower the overall drag of the airplane. These drag cleanup tests contributed to the increased speed of many U.S. airplanes during World War II. On March 6, 1943, a unique two-day test commenced in the tunnel; it was the most secret test ever conducted in the Full Scale Tunnel, and it has come to light only recently. The story began on June 4, 1942 when Japanese warplanes attacked the American military base at Dutch Harbor in the Aleutians. During this attack, a Japanese Mitsubishi Zero fighter had its oil line severed by ground fire, and the pilot had to make an emergency landing in what seemed to be a field of grass. The grass, however, concealed a bog covered with water and mud. The landing gear of the airplane dug in, the plane flipped over on its back, and the pilot was killed. The crashed airplane was spotted a month later by a U. S. Navy patrol airplane, and an inspection showed it to be salvageable. It was the first flyable Japanese Zero to fall into U.S. hands–a warplane of great value. The airplane was tested by the U.S. Navy at San Diego and at Anascostia in Washington, D.C. Then it was flown to the NACA Langley Memorial Laboratory for the installation of special instrumentation. It arrived at Langley about 3:00 pm on Friday, March 5, 1943 and was parked in plain sight on the Langley flight line. That night, under the cover of darkness, the Zero was secretly mounted in the Full Scale Tunnel, and for two days was tested under wraps. A special wind tunnel crew was sworn to absolute secrecy. When light dawned on Monday morning, the airplane was back at its original location on the flight line, as if nothing had happened. Existence of these secret tests came to light 67 years later when Joe Chambers, a previous director of the Full Scale Tunnel, interviewed some  of the retired Langley personnel who participated in these secret tests. No photographs of the Zero in the wind tunnel exist, and Chambers was unable to find the test results anywhere, so intense was the secrecy. But these tests underscored the value of the Full Scale Tunnel–nowhere else could a whole enemy airplane be flown into Langley Air Field on its way to Wright Field, rolled off the runway, spirited into the wind tunnel, tested in such an impromptu manner under the veil of the strictest secrecy, and have almost nobody know about for 67 years.

 

The post-war years at the NACA focused on high-speed aircraft in the flight range towards Mach 1. However, these aircraft had to take off and land at low speeds, and the Full Scale Tunnel was an ideal facility for such low-speed tests. Also, helicopter testing became more frequent in the Tunnel as well. In 1958 the NACA morphed into NASA, and the national space program went into full-tilt. Although space vehicles in low earth orbit travel at about 7,925 meters (26,000 feet) per second, and those intended to go the Moon and back enter the Earth’s atmosphere at 10,973 meters (36,000 feet) per second, these extreme hypersonic vehicles still have to land at low speeds, and once again the (now) NASA Langley Full Scale Tunnel became a workhorse for low-speed testing of the Air Force Dyna-Soar reentry glider, the Mercury Space Capsule, and the HL-10 lifting body. Also, during this period, free-flight testing of models commenced in the FST; this involved “flying” the models in the tunnel airstream by remote control. The large size of the Full Scale Tunnel test section facilitated such free-flight testing, which continued through the remainder of the FST days before demolition started. (Indeed, the National Air and Space Museum has in it collection a free-flight model of the futuristic Boeing X-48 blended wing body that was flown in the wind tunnel. It is currently on display in the How Things Fly gallery in the Museum in Washington, DC.) These free-flight tests were pioneering because they freed the model from any structural attachment to the tunnel such as being mounted on a force balance, and allowed the stability and control characteristics of the model to be tested and observed, unhindered by any fixed attachment. In the 1960s and '70s, there was  a great deal of interest in the aerodynamic characteristics of aircraft at very high angles of attack, and once again models were flown remotely in the Full Scale Tunnel at angles of attack of near 90 degrees in order to study such aerodynamic behavior. In 1985, The U.S. Department of the Interior designated the Langley Full Scale Tunnel as a National Historic Landmark. However, being such a landmark did not guarantee that the facility would be exempt from eventual demolition. In the early 1990s the pressure on NASA to reduce its wind tunnel inventory became overwhelming, and the director of Langley at that time, Paul Holloway, looked for a non-traditional way of preserving the Full Scale Tunnel. He found the answer in the form of nearby Old Dominion University. He approached Jim Cross, dean of Old Dominion’s College of Engineering, and encouraged him to submit a proposal to Langley for the college to take over the operation of the Full Scale Tunnel. Cross saw the opportunity to use the facility for some non-traditional aerodynamic testing. On August 19, 1997, Old Dominion University took over the operation of the Full Scale Tunnel. The tunnel became the largest university-operated tunnel in the world. Old Dominion University operated the tunnel from 1996 to 2009. During that time such non-traditional models including a reproduction of  the 1903 Wright Flyer by the Wright Experience and NASCAR  racers  were tested.

 

 

However, On September 4, 2009, the last test was run in the FST; the configuration tested was a Boeing X-48  blended wing body. Demolition started, and was completed by May 18, 2011, almost 80 years to the day after the facility was dedicated in 1931. Virtually the only artifact that remains from this historic tunnel is one of the two drive fans, acquired by the National Air and Space Museum. This fan assembly was installed in the Museum’s Boeing Milestones of Flight Hall in February 2015.

 

Reference: The definitive history of the FST is detailed in Cave of the Winds, by Joseph R. Chambers, NASA SP-2014-614, 2014. Joe Chambers was the Director of the FST from 1974 to 1981.