Army Pursuits the Biplane Period, 1920-1932
Curtiss P-6S, Curtiss Hawk, XP-10, XP-6D, XP-7, P-12's
However, Boeing had also completed a new design, Model 66, in July 1927. With an inverted 600-hp Packard 2A-1530 cooled by a radiator built into the juncture of lower wing and fuselage, this prototype was purchased by the Air Corps on January 27, 1928. Designated XP-8, that design was similar to the Navy’s F2B, but was handicapped by an unsatisfactory engine.
Although biplanes dominated the aviation picture, the Army and Boeing signed a $60,000 contract on June 13, 1928, for an XP-9 monoplane with a V-1570-15 engine, and strut-braced gull wings attached to the top of an all-metal stressed skin fuselage, the first since 1922. When the XP-9 was, at last, flown on November 18, 1930, the pilot called it “a menace” due to exceedingly poor vision and dangerous flying qualities.
When the Army ordered the Curtiss XP-10 biplane on June 18, 1928, the specification included an integral geared supercharger. This design’s top speed was expected to increase from 191 mph at sea level to 215 mph at 12,000 feet, with a 26,500-foot service ceiling, and have good maneuverability and pilot visibility as well. But when the XP-10 was completed in May 1930 at Garden City, only an unsupercharged sea-level V-1570-15 was installed. The XP-10 also featured plywood wings gulled into the fuselage, and wing surface radiators, but that cooling system was too vulnerable to bullet damage and tests were stopped in
October 1930 due to trouble with these coolers, which were not used again.
The next Curtiss design developed the familiar Hawk layout. The XP-11 was to be a P-6 with the experimental 600-hp Curtiss H-1640-1. That engine, flight-tested on the Thomas-Morse XP-13, was a failure, so the XP-11 project, together with a more advanced Curtiss XP-14 designed around that engine, was abandoned. Two of three P-11 airframes ordered in January 1929 were completed as P-6s, while the third became the YP-20.="images/5-50n.jpg" width="300" height="179" border="0" alt="CURTISS XP-6A racer">
Boeing P-12 series
First flown on April 11, 1929, the P-12 had a 450-hp R-1310-7 with cylinder fairings and the usual two guns in front of the pilot. Fabric covered the fuselage metal tube framework, but the tail surfaces and ailerons were of corrugated aluminum. Boeing designed its own airfoil section for the wooden wings, as it would for most future projects. The lone XP-12A displayed a deep NACA cowl, new Frise ailerons, and shorter landing gear, but was destroyed in a collision with a P-12 in May 1929 after only four flying hours.
The first air-cooled pursuits widely used by the Army were 90 P-12Bs ordered June 10, 1929, and delivered from February to May 1930 by rail, since Boeing then had no airfield for flyaway delivery. First flown May 30, the P-12B had the XP-12A’s ailerons and elevators, but omitted the cylinder fairings.