Feature Story

Boeing Wind Tunnel blows strong for nearly 70 years

On Dec. 17, 1947, the 44th anniversary of the Wright brothers' historic first flight of a powered aircraft at Kitty Hawk, N.C., another flight took place at Seattle's Boeing Field that ranks as one of the most important in aviation. Boeing's B-47 Stratojet bomber flew for the first time that day -- and changed the shape of jet aircraft.

The B-47 was America's, and arguably the world's, first large swept-wing jet. Seemingly forgotten in history, the Stratojet's revolutionary design was the first to pair swept wings with jet engines suspended from the wings in podded nacelles. Discovered in the Boeing High Speed Wind Tunnel in 1945, this basic design is still the model for all jets built today by Boeing, Airbus and others. For Boeing, the journey to become the pioneer of large swept-wing jets began in April 1939 when the company hired famed test pilot Edmund T. "Eddie" Allen to head its new Flight and Research organization. A respected scientist, Allen was accorded the freedom to do whatever was necessary to advance Boeing's flight research efforts -- and that included building a private wind tunnel. At the time aircraft manufacturers did not have their own wind tunnels and the fierce competition to use the few operated by NACA (forerunner of NASA) and a handful of universities resulted in Boeing falling behind the competition. Allen championed the idea of a company-owned wind tunnel, capable of near-transonic (approaching the speed of sound) speeds. The estimated cost of $1 million represented a huge risk for Boeing at the time. But it also was a great opportunity, and in August 1941 Boeing President, Phil Johnson authorized construction of a high-speed wind tunnel capable of speeds of Mach .9 (625 mph, or 1,000 kilometers per hour).

The B-47 was the first full design tested in the new wind tunnel. The swept-wing concept had first come to Boeing in May 1945 by way of a letter sent from Germany by the company's leading aerodynamicist, George Schairer, who was serving on Air Force Gen. "Hap" Arnold's Scientific Advisory Group. That group was tasked with securing German aircraft and rocket research. Boeing engineers subsequently saw dramatic results during wind tunnel tests of Schairer's swept-wing data, but they also discovered that the wings had to remain "clean" to achieve the high-speed benefits. And this presented a problem since the standard design for multi-engine airplanes at the time was to mount the engines on the wings. As he puzzled over the problem during a train ride back from Wright Field, Ohio (today known as Wright-Patterson AFB), Boeing Chief Engineer Ed Wells came up with the idea of engine pods mounted off the wings. The concept was tested in the Boeing wind tunnel by mounting model engine nacelles on the end of a pole (the "broomstick" test) and moving the nacelles around the wing until the optimal position was discovered -- forward and below the wing.

These discoveries all came together in the Boeing wind tunnel as the optimal design for a subsonic jet -- and resulted in the revolutionary XB-47 that rolled out of Boeing Plant 2 in September 1947 -- only two years after Schairer sent his note from Germany.

Just as building their own low-speed wind tunnel was critical to the success of the Wright brothers, so too was the wind tunnel key to success for Boeing and the B-47. Improved over the years, the now-transonic wind tunnel has tested some of the best-known airplanes in aviation history and continues its work today with jets such as the 737 MAX. Boeing was fortunate that a leader arrived at the right time to set a course for success by not only pioneering the organization that continues today as Boeing Test & Evaluation but also insisting the company build its own wind tunnel. The Edmund T. Allen Memorial Aeronautical Laboratories are named in his honor.