A little while back, we began a series of articles looking at the air-test work which NASA and its forebear, the N.A.C.A., conducted at their facility in the Mojave Desert, located within the massive military test complex now known as Edwards Air Force Base. The civilian-run organization has often conducted its aerospace tests with active-duty military aircraft on bailment, with data shared back and forth to either help the U.S. aerospace industry, or the military itself.
One series of tests involved B-47A Stratojet 49-1900, the first example of the revolutionary, though twitchy, nuclear bomber to roll off Boeing’s production line in Witchita, Kansas. As the Dryden Archives record… NACA High-Speed Flight Research Station obtained this B-47A Stratojet (labeled NACA 150) to study the characteristics of a large, flexible swept-wing aircraft in 1953.
NACA laboratories had an interest in B-47A NACA 150; Langley Memorial Laboratory wished to study the impact of aeroelasticity upon structural loads and Ames Aeronautical Laboratory, the impact of aeroelasticity upon dynamic stability. Operation of the aircraft from either Center was not practical because of runway length. Accordingly B-47A NACA 150 went on secondment to the NACA High-Speed Flight Research Station at Edwards, where it flew from May 1953 to 1957.
In earlier decades, the response to control-surface motions had been fairly well established for a relatively rigid airplane by flight test and theory. However, by the mid 1950s, the desire to increase the range and speed of large airplanes led to swept-back wings of high aspect ratio, thin airfoils, and fuselages with high fineness ratios (i.e. long and thin). All of these factors tend to increase the flexibility of the structure and the associated aeroelastic effects which were becoming of greater importance in problems of static and dynamic stability and control. The dynamic effects were especially important in the design of automatic control systems, because structural modes could introduce instabilities which would not arise with a rigid airplane.
The B-47A Stratojet did not have any apparent problems when it arrived at NACA but the testing revealed some serious design deficiencies; in particular, buffeting problems limited the plane’s speeds and certain lift values. The B-47A testing resulted in reports that gave engineers and design teams around the country access to reliable information on the dynamic behavior and response characteristics that could be expected of large, flexible, swept-wing airplanes, such as the Boeing KC-135 and the B-707 transport. Thus the flight test experiences with NACA 150 proved to be hugely influential in future large aircraft design and safe operation.
Photos and historical information by Armstrong Flight Research Center
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Born in Milan, Italy, Moreno moved to the U.S. in 1999 to pursue a career as a commercial pilot. His aviation passion began early, inspired by his uncle, an F-104 Starfighter Crew Chief, and his father, a military traffic controller. Childhood adventures included camping outside military bases and watching planes at Aeroporto Linate. In 1999, he relocated to Atlanta, Georgia, to obtain his commercial pilot license, a move that became permanent. With 24 years in the U.S., he now flies full-time for a Part 91 business aviation company in Atlanta. He is actively involved with the Commemorative Air Force, the D-Day Squadron, and other aviation organizations. He enjoys life with his supportive wife and three wonderful children.
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