Boeing XP-9

Last revised June 6, 1998

The XP-9 was Boeing's first monoplane fighter design. Bearing the company designation Model 96, it was designed to Army Specification X-1623A which was issued on May 24, 1928. The Model 96 was designated XP-9 by the Army when a contract for one example was signed on May 29, 1928. The serial number was 28-386. The XP-9 was actually the first Boeing monoplane to start through the factory, but various delays postponed the delivery date from April 1929 to September 1930, so it was not the first actually to fly, having been beaten into the air by the new Model 200 Monomail.

The construction of the XP-9 was entirely new to Boeing. The fuselage was a semi-monocoque structure of sheet dural over metal formers for the portion aft of the rear undercarriage struts and welded steel tubing from that point forward to the engine. The tail surfaces of the XP-9 were identical to those of the contemporary P-12/F4B. The shoulder-mounted, externally-braced monoplane wing had a conventional two-spar structure with a metal framework and fabric covering. Power was supplied by a 600 hp Curtiss SV-1570-15 Conqueror liquid-cooled engine with supercharging. A chin-type radiator was mounted underneath the engine. A 0.50-cal machine gun was mounted on each side of the fuselage, firing through tunnels mounted just below the engine cylinder blocks. In addition, two 122-lb or five 25-lb bombs could be carried.

Upon completion, the XP-9 was delivered by rail to the Army Test Centre at Wright Field. It made its first flight there on November 18, 1930. Flight tests of the XP-9 by the Army were rather disappointing. Visibility from the cockpit was extremely poor. The plane suffered with such a large number of serious instability problems that it frightened even the most experienced Army pilots, who dubbed it a menace. Controllability was improved somewhat by replacing the P-12-like corrugated metal vertical tail with a larger design. However, this was not sufficient to overcome the basic shortcomings of the design, and the Army chose not to order the XP-9 into production. The Army was in fact so dissatisfied with the XP-9 that they did not even exercise their option for five Y1P-9 monoplanes to be built under the P-12D contract. In August 1931, the Army relegated the XP-9 to use as a non-flying instructional airframe. Only 15 flying hours had been completed.

Performance included a maximum speed of 213 mph and an initial climb rate of 2560 ft/min. An altitude of 5000 feet could be reached in 2.3 minutes, and service ceiling was 26,800 feet. Range was 425 miles. Weights were 2669 lbs. empty, 3623 lb gross.


  1. Boeing Aircraft since 1916, Peter M. Bowers, Naval Institute Press, 1989.

  2. The American Fighter, Enzo Angellucci and Peter Bowers, Orion Books, 1987.