The Boeing XP-7 was an attempt to adapt the PW-9 fighter to the new Curtiss Conqueror engine, and bore much the same relationship to the PW-9 as did the Curtiss P-6 to the Curtiss P-1.
The Army was interested in seeing how much the performance of the PW-9 fighter could be improved by the use of the Conqueror engine, and they ordered a single example on March 5, 1928. The last Boeing PW-9D off the production line (Ser No. 28-041) was experimentally fitted with a new 600-hp Curtiss V-1570-1 Conqueror engine and was redesignated XP-7 under the new system. The cowling had to be redesigned to contain the larger radiator, giving a shorter, deeper nose than that of the PW-9D. In addition, the new model incorporated an all-duralumin tailplane, a different type of tailskid, and a new control system for the ailerons.
The XP-7 was delivered to the Army on September 8, 1928, and began flight testing shortly thereafter. The Conqueror engine proved to be suitable for use in fighters, and an Air Corps specification was drawn up to cover the building of four service test P-7s. However, subsequent tests demonstrated that the performance of the XP-7 was not much better than that of the standard PW-9D, maximum speed being 168 mph at sea level as compared with 163 mph for the PW-9. Since Boeing's radial-engined XF4B-1 had already reached nearly 170 mph, it was concluded that the XP-7 project showed little promise and the Army cancelled its order for the four service-test P-7s. After the end of the tests, 28-041 was converted back to standard PW-9D configuration.
Performance of the XP-7 included a maximum speed of 167.5 mph at sea level and 163.5 mph at 5000 feet. Initial climb was 1867 ft/min, and an altitude of 10,000 feet could be attained in 7.1 minutes. The XP-7 had the same armament as did the PW-9D, namely one 0.50 cal. and one 0.30 cal machine gun mounted in the upper fuselage decking and synchronized to fire through the propeller arc. Weights were 2358 lbs empty, 3260 lbs. gross.