The Boeing YP-29 was an attempt to produce a modernized version of the highly successful P-26 pursuit aircraft.
The YP-29 originated as the Boeing company's Model 264 project. The Model 264 was a new and more advanced fighter design developed at company expense in the interval between the appearance of the XP-936 (P-26 prototype, company designation of Model 248) and the delivery of the first P-26A (Model 266) to the Army. The new model was initiated as a private venture by Boeing in collaboration with the Army, in which the company agreed to construct three prototypes under a bailment contract.
Basically, the Model 264 was an updated and modernized P-26. It differed from the P-26 in having fully-cantilever wings and a retractable undercarriage. The undercarriage was similar to that which appeared on the Monomail, in which the main landing gear wheels retracted backwards about halfway into the wings. The fuselage and the tail unit were basically the same as those of the P-26. The engine was the tried and true Pratt & Whitney R-1340 Wasp air-cooled radial, basically the same type of engine which powered the P-26. The aircraft had the same armament as did the P-26A, namely one 0.30-cal and one 0.50 cal machine guns mounted in the fuselage sides and firing between the cylinder heads of the radial engine.
The first Model 264 to leave the Boeing factory featured a narrow sliding cockpit enclosure that was essentially a transparent continuation of the pilot's oversize protective headrest all the way to the windshield frame. The engine was the Pratt & Whitney R-1340-31 Wasp of 550 hp, essentially identical to the engine which powered the engine. However, the radial engine was enclosed in a full NACA cowling rather than being surrounded by the narrow Townend ring that was used on the P-26.
The airplane made its maiden flight on January 20, 1934 and was flown to Wright Field for Army testing 5 days later. The plane was originally tested by the Army on a bailment contract under the experimental military designation of XP-940. During testing, the XP-940 achieved a maximum speed of 220 mph at 10,000 feet. The gross weight was 3814 pounds.
Upon testing of the XP-940, the Army decided on June 29, 1934 to buy it and its two sister ships. The pursuit designation of P-29 was assigned. In the meantime, the XP-940 had been returned to the factory in March for modifications. The Army did not like the narrow cockpit enclosure, feeling that it restricted pilot vision too much. Consequently, Boeing replaced the narrow sliding cockpit enclosure by a standard open cockpit installation, but the distinctive long headrest that extended all the way to the tail was retained. The engine was replaced by a 600 hp Pratt & Whitney R-1340-35. The full NACA engine cowling that had been originally used was replaced by a drag ring similar to that which appeared on the P-26A.
The modified XP-940 was returned to the Army in April of 1934. The newly-configured plane flew for the first time on June 4, 1934. Later that June, when the Army purchased the airplane outright, it was assigned the designation YP-29A and given a serial number of 34-24. It eventually became just plain P-29A after an engine change to a 600 hp Pratt & Whitney R-1340-27 in place of the R-1340-35.
The cleaner design of the YP-29A resulted in a plane which was 16 mph faster than the P-26A, but the greater weight cut down on the ceiling and the maneuverability, and the Army cancelled an intended P-29A order. The three prototypes were subsequently used strictly for experimental purposes.
As mentioned earlier, the military was displeased with the narrow cockpit enclosure of the XP-940. The second Model 264 ordered by the Army was completed with a large and roomy glasshouse enclosure around the cockpit. In addition, the tailwheel was housed in a different fairing. The engine was the 600 hp Pratt and Whitney R-1340-35, enclosed in an anti-drag ring. The plane was delivered to the Army on September 4, 1934 under the designation YP-29 with a serial number of 34-23. Despite its earlier Army designation and serial number, it was actually the second Model 264 to fly. Weights were 2509 lbs. empty, 3518 lbs. gross. Maximum speed was 250 mph at 10,000 feet. Initial climb was 1600 feet per minute. Service ceiling was 26,000 feet, and absolute ceiling was 26,700 feet. Range was 800 miles. This new cockpit enclosure satisfied the requirement for pilot protection at 250 mph operating speeds. Nevertheless, the landing speed of the YP-29 was considered too high for Army operational use.
Because of the increased landing speed of the new monoplane design, the YP-29 was returned to the factory for the installation of wing flaps. Following service testing by the Army and Boeing, which included trials with controllable pitch propellers, the service test designation was dropped and changed to plain P-29 after the engine was changed to a Pratt & Whitney R-1340-39.
The third Model 264 was completed as YP-29B with an open cockpit configuration similar to that of the YP-29A. The serial number was 34-25. It was delivered to the USAAC on October 11, 1934. The only outward differences between it and the YP-29A were the addition of a one-piece wing flap similar to that of the YP-29, an additional one degree of dihedral in the wing, and an oleo tail wheel assembly similar to that of the YP-29. The YP-29B was sent to Chanute Field in Illinois for service testing. It was eventually redesignated just plain P-29B.