Rare photographs of NASA's massive wind tunnels used to test aircraft, 1925-1990

All NASA craft will undergo full testing through one of the administration's 42 major wind tunnels and will be cleared for liftoff once all parameters are reached.

These wind tunnels range from only a few inches wide to cavernous enough to test full-size aircraft. Most of the time, large powerful fans suck air through the tube.

The object being tested is placed securely inside the tunnel so that it remains stationary. The object may be an aerodynamic test object such as a cylinder or airfoil, an individual component, a small model of a vehicle, or a full-size vehicle.

The air moving around a stationary object shows what would happen if the object was moving in the air. Wind speed can be studied in a variety of ways; The smoke or dye can be placed in the air and seen moving around the object.

The first wind tunnels were invented in the late 19th century, in the early days of aeronautical research, when many attempted to develop successful heavier-than-air flying machines.

The wind tunnel was seen as a means of reversing the general paradigm: instead of the wind remaining stationary and the object moving through it, the same effect would be achieved if the object remained stationary and the wind moved at speed.

In this way, a stationary observer can study the flying object in action and measure the aerodynamic forces being exerted on it.

In 1916 the US Navy built one of the largest wind tunnels in the world at the time at the Washington Navy Yard. The entrance was about 11 feet (3.4 m) in diameter and the discharge portion was 7 feet (2.1 m) in diameter. A 500 hp electric motor drives the paddle-type fan blades.

In 1931 the National Advisory Committee for Aeronautics (NACA) built a 30-foot-by-60-foot full-scale wind tunnel at the Langley Research Center in Langley, Virginia. The tunnel was powered by a pair of fans powered by 4,000 hp electric motors.

The layout was a double-return, closed-loop format and could accommodate many full-size real aircraft as well as scale models. The tunnel was eventually closed and, even though it was declared a National Historic Landmark in 1995, demolition began in 2010.

In 1941 the US built one of the largest wind tunnels at the time at Wright Field in Dayton, Ohio. This wind tunnel begins at 45 feet (14 m) and narrows to 20 feet (6.1 m) in diameter.

Two 40-foot (12 m) fans were powered by a 40,000 hp electric motor. Large scale aircraft models can be tested at airspeeds of 400 mph (640 km/h).

By the end of World War II, the US had built eight new wind tunnels, including the world's largest wind tunnel at Moffett Field near Sunnyvale, California, which could be used for full-size aircraft at speeds of less than 250 mph. was designed to test. Vertical wind tunnel at Wright Field, Ohio, where the air stream is upstream for testing models in spin conditions and concepts and engineering designs for the first primitive helicopters flown in America.

Later, special tunnels were developed to simulate subsonic, transsonic, supersonic and even hypersonic speeds – five times the speed of sound. Some tunnels can estimate the rapid heat of atmospheric re-entry, while others can test the effects of ice formation at high altitudes.

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