CRISIS-BORN FIGHTER PROJECTS, XP-48 TO XP-77
Fighter Projects begun in 1940-1941
General Arnold urged a new emphasis on pursuit tactics and plane development on November 14, 1939, admitting that previous views that bombers could not be defeated by fighters had “now been proven wholly untenable.” New pursuit requirements had to be established for World War Two.
Interceptor pursuit specification XC-622, dated November 27, 1939, called for a single-engine single-seater with a top speed at 15 to 20,000 feet of at least 425 mph. The “desired attainment” was 525 mph, which then seemed like a theoretical limit for propeller-driven planes. No more than seven minutes should be needed to climb to 20,000 feet, but endurance was limited to one and a half hours. At least four guns and six 20-pound bombs would be carried.
To find such fighter designs, Request for Data R40-C was circulated among potential fighter manufacturers on February 20, 1940. Replies from seven companies were opened April 15, 1940. The two designs considered most ready for construction were the Bell Model 13 and the Curtiss CP-40-2, both planned for the Continental XI-1430 inline engine. Designations XP-52 and XP-53 were assigned to these Bell and Curtiss projects. The Foreign Release Agreements made in April, releasing the P-39 and P-40 for export, obligated these companies to build new prototypes without cost to the Air Corps.d such fighter
Republic’s offering for the R40-C competition was the AP-12 with the proposed 2,350-hp Wright R-2160 Tornado engine enclosed behind the pilot, P-39 style, with an extension shaft and gear box driving contra-rotating propellers in the nose. Armament included a cannon and four machine-guns in the nose and two guns in the wings. While this very streamlined design was judged “the maximum that can be expected” from a conventional tractor arrangement, engine development would take over three years. Instead, Republic would develop the barrel-shaped AP-16, which became the XP-47B.
The highest marks of the R40-C evaluation made on May 15, 1940, were given to single-seaters with rearward-facing propellers and engines behind the pilot Fighters with pusher propellers offered advantages in drag reduction and a nose enhancing pilot visibility and heavy armament installations. Numerous structural complications presented themselves, however, and tricycle landing gear was a necessity.
Bell Aircraft’s Model 13B, the proposed P-39 replacement, had won only 532 of 1,000 merit points from R40-C, so this company switched its XP-52 program to the Model 16, a pusher arrangement. The XP-52 had tricycle landing gear, laminar flow airfoil wings, twin booms to support
the tail assembly, and a 1,600-hp Continental XI-1430-5 inline engine, cooled by a nose radiator and turning contra-rotating propellers. This specification, dated July 30, 1940, promised a 425-mph speed at 19,500 feet and an armament of two 20-mm and six .50-caliber guns.
As contract negotiations proceeded, Bell also offered a pusher interceptor on September 28 that had a 2000-hp Pratt & Whitney R-2800-23 cooled by air from a nose intake. This became the XP-59 on October 2, 1940, and by October 28 the Air Corps decided to abandon the XP-52. Two XP-59 prototypes ordered February 26, 1941, were to weigh 10,463 pounds each, do 450 mph at 22,000 feet, and have the XP-52’s armament
The XP-59 project was canceled on November 25, 1941, to relieve the load on Bell’s engineering staff and clear the way for the XP-59A jet and the XP-63. Both would go into production in 1943 as the Airacomet and the Kingcobra.
The three R40-C winners were designated the Vultee XP-54, with a Figure of Merit of 817 points; the Curtiss-Wright XP-55 with 770 points, and the Northrop XP-56, with 725 points. Preliminary engineering contracts were issued June 22, 1940.
The XP-54 and XP-56 single-seat pushers were to be powered by the Pratt & Whitney 2,200-hp liquid-cooled 24-cylinder X-l800-A3G (H-2600-1), but this engine was canceled on October 4, 1940, and other power plants had to be chosen for the actual prototypes.
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