Flight Test Files: B-47A Stratojet

Boeing B-47A (NACA 150) shown on the ramp near NACA High-Speed Flight Research Station at South Base of Edwards Air Force Base, California, in 1953. Image via NASA


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.

NACA Aircraft Fleet on lakebed D 558 II and B 47A Stratojet
In 1954 this photo of two swept wing airplanes was taken on the ramp of NACA High-Speed Flight Research Station. The Douglas D-558-ll is a research aircraft while the Boeing B-47A Stratojet is a production bomber and very different in size. Both contributed to the studies for swept back wing research.

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.

B 47A Stratojet on ramp with pilots and crew
In 1954 after a research flight in the Boeing B-47A Stratojet Crew Chief Wilbur McClenaghan (center) asks of the pilots if there are any “squawks” that should be taken care of before the next flight. Pilots are Joe Walker on the viewer’s left and Stanley Butchart on the right. Data system technician Merle Curtis, in coveralls, is busy checking the airdata head mounted on the nose boom with the help of Instrumentation Crew Chief Raymond Langley. The door to the cockpit area is open showing a view of the ladder that folds down to be used by the pilots to enter and leave the area. Image via NASA

Photos and historical information by Armstrong Flight Research Center

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