Boeing B-52 Stratofortress XB-52

Boeing built two XB-52 airframes after winning the initial contract in June 1946. During a ground pressure test on 29 November 1951 the pneumatic system of one aircraft failed, damaging the wing trailing edge and requiring considerable repairs. The second airframe, modified with more operational equipment, flew first under the YB-52 designation on 15 April 1952; the XB-52 itself did not fly until 2 October 1952. Both prototypes were powered by experimental Pratt & Whitney YJ57-P-3 engines rated at 39 kN static thrust each. Development included 670 days of wind-tunnel work and 130 days of aerodynamic and aeroelastic testing.