All NASA craft must undergo complete testing through one of the administration’s 42 major wind tunnels and it’s cleared for liftoff once all the parameters are reached.
These wind tunnels range from just a few inches wide to cavernous enough to test full-sized aircraft. Most of the time, large powerful fans suck air through the tube.
The object being tested is held securely inside the tunnel so that it remains stationary. The object can be an aerodynamic test object such as a cylinder or an airfoil, an individual component, a small model of the vehicle, or a full-sized vehicle.
The air moving around the stationary object shows what would happen if the object was moving through the air. The motion of the air can be studied in different ways; smoke or dye can be placed in the air and can be seen as it moves around the object.
The earliest wind tunnels were invented towards the end of the 19th century, in the early days of aeronautic research, when many attempted to develop successful heavier-than-air flying machines.
The wind tunnel was envisioned as a means of reversing the usual paradigm: instead of the air standing still and an object moving at speed through it, the same effect would be obtained if the object stood still and the air moved at speed past it.
In that way, a stationary observer could study the flying object in action and could measure the aerodynamic forces being imposed on it.
The US Navy in 1916 built one of the largest wind tunnels in the world at that time at the Washington Navy Yard. The inlet was almost 11 feet (3.4 m) in diameter and the discharge part was 7 feet (2.1 m) in diameter. A 500 hp electric motor drove 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 Langley Research Center in Langley, Virginia. The tunnel was powered by a pair of fans driven 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 constructed one of the largest wind tunnels at that time at Wright Field in Dayton, Ohio. This wind tunnel starts at 45 feet (14 m) and narrows to 20 feet (6.1 m) in diameter.
Two 40-foot (12 m) fans were driven by a 40,000 hp electric motor. Large-scale aircraft models could 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 largest one in the world at Moffett Field near Sunnyvale, California, which was designed to test full-size aircraft at speeds of less than 250 mph and a vertical wind tunnel at Wright Field, Ohio, where the wind stream is upwards for the testing of models in spin situations and the concepts and engineering designs for the first primitive helicopters flown in the US.
Later on, specialized tunnels were developed to simulate subsonic, transsonic, supersonic and even hypersonic speeds — five times the speed of sound. Some tunnels can approximate the fiery heat of atmospheric re-entry, while others can test the effects of ice buildup at high altitudes.
(Photo credit: NASA / Wikimedia Commons).