In March of 1943, the Consolidated Aircraft Corporation merged with Vultee Aircraft Incorporated, forming the Consolidated Vultee Aircraft Corporation. The name of the new merged corporation was often abbreviated to *Convair*, although that name did not get officially registered as a trademark until 1954.
One of the first products of this new merged corporation was the XP-81 mixed-power escort fighter. The primary drawback of most early jet fighters was their high fuel consumption, leading to a relatively limited range and a rather short endurance as compared to piston-engined fighters. In 1943, the USAAF was interested in figuring out a way to couple the improved performance offered by jet propulsion with the long endurance that was demanded by the Pacific campaign, and issued a requirement for a long range escort fighter to be powered by a combination of turboprop and jet engine. The turboprop engine would be used for cruising flight, with the turbojet engine being turned on for takeoff and for high speed flight. The specification called for a 1250-mile operating range and a maximum speed of 500 mph.
Charles R. 'Jack' Irvine, Vultee's chief designer and chief test pilot Frank W. Davis collaborated with the USAAF and came up with an all-metal cantilever low-winged monoplane powered by an experimental General Electric TG-100 (later redesignated XT31) turboprop mounted in the nose and provided with a ventral exhaust, as well as by an Allison-built J33-GE-5 turbojet in the rear fuselage fed by a pair of dorsal intakes. A retractable tricycle undercarriage was fitted. The pressurized cockpit was housed underneath a bubble canopy. The project bore the company designation of Model 102.
Convair began detailed design work on the Model 102 on January 5, 1944. The USAAF ordered two prototypes of the design from Convair on February 11, 1944. The designation XP-81 was applied, and the serials were 44-91000 and 44-91001. The contract was subsequently modified to include thirteen service-test YP-81s. The YP-81 was to have been powered by the lighter and more powerful TG-110 turboprop, the wing was to have been moved aft ten inches, and an armament of six 0.5-inch machine guns or six 20-mm cannon was to have been fitted.
The TG-100 turboprop engine encountered an extensive series of teething troubles and was not yet available when the XP-81 (44-91000) was ready for its first flight. A Packard Merlin V-1560-7 power package from a P-51D Mustang was supplied in its place. A P-38J-style beard radiator inlet was mounted below the propeller spinner. The Merlin-powered XP-81 was trucked to Muroc Dry Lake, where it was flown for the first time on February 11, 1945. The handling proved to be exceptionally good. However, the directional stability was marginal and a 15-inch fin extension and a short ventral fin were added. The second XP-81 was fitted at the factory with a rounded fin extension and a long ventral fin.
In the meantime, the war against Japan had progressed to the point where the capture of such islands as Guam and Saipan had largely eliminated the need for long-range, high-speed escort fighters. The 13 pre-production YP-81s were cancelled shortly before V-J Day, but work continued on the two XP-81s.
The first XP-81 was flown back to Vultee Field to be fitted with the TG-100, but the work was not finished until after V-J Day. The first flight with the TG-100 took place on December 21, 1945. The TG-100 was supposed to deliver 2300 e.h.p, but actually delivered only 1400 e.h.p. Consequently, the performance of the turboprop-powered XP-81 was no better than that of the Merlin-powered version. In addition, excess propeller vibration and persistent oil leaks became important problems.
The XP-81 program was officially terminated on May 9, 1947. Both prototypes were redesignated ZXF-81 in 1948, indicating a testbed status. In 1949, they were both stripped of useful parts and placed on a photographic and bombing range at Edwards AFB. The remains of both machines were stored for a long time at the Flight Test Museum at Edwards. They have now been moved to the USAF Museum at Wright Patterson AFB for eventual restoration and display.
Specification of the XP-81:
One 2300 ehp General Electric XT31-GE-1 (TG-100) turboprop and one 3750 lb.st. Allison J33-GE-5 turbojet. Proposed armament (never fitted) was six 0.50-inch machine guns or 6 20-mm cannon and two 1600-pound bombs. Weights were 12,755 pounds empty, 19,500 pounds loaded, 24,650 pounds maximum overload. Dimensions were wingspan 50 feet 6 inches, 44 feet 10 inches, height 14 feet 0 inches, 425 square feet wing area. The following estimated performance figures were based on an assumption of a full 2300 hp output from the turboprop: Maximum speed, 478 mph at sea level, 507 mph at 30,000 feet. Range 2500 miles at 275 mph at 25,000 feet. Initial climb rate was 5300 feet per minute. Service ceiling was 35,500 feet.