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Lockheed’s bid against McDonnell XF-88
The story of Lockheed’s bid against the McDonnell XF-88 began in 1946 when project engineers Don Palmer and Bill Ralston started work on the Model 090-32-01, with a contract from the USAAF awarded on 20 June for two prototypes (46-687 and 46-688). As explained by David Baker in his book US Air Power 1945–1990 Volume 1: US Fighters and Fighter-Bombers 1945-1949, the same team had been responsible for the P-80 and sifted test and wind tunnel results to inform a burgeoning series of ideas at Lockheed. Over the next year a wide range of concept studies emerged, more than 65 different designs including some extraordinary and bizarre configurations.
Unleashed from the conservative practices of war production, Lockheed’s design team came up with butterfly tails, W-shaped wings (the outer panels swept forwards), tri-engine configurations with engines on the wingtips and one in the vertical tail, and some that were simplified down to a single engine mounted in the fuselage and clean, thin and swept wings. At the time the USAAF was searching for an optimum specification to satisfy the requirement for a penetration fighter both as a bomber escort and for ground-attack roles.
Initial work on German research results
The basic requirement resulted in a rapidly changing list of specifications, at one time stipulating a combat range of up to 1,500 miles (2,413km) with time-to-height requirements of up to 50,000 (15,140m) in less than five minutes. But these specifications were fluid and moved up and down according to redefined operational requirements occurring at frequent intervals. Taking a broad approach, the Lockheed team decided not to be overly ambitious and to optimise maximum performance around available engines. They came up with Model 090-32-01 for which on 20 June 1946 the company received a contract for two prototypes (46-687 and 46-688).
At first, basing a lot of their initial work on German research results, the team designed a delta-wing configuration but reversed that decision after wind tunnel tests proved it to be impractical for the multi-role requirement. That forced compromise and the judgement favoured a simplified design with a slender fuselage and pointed nose and 35-degree sweptback wings.
Power would be provided by two 3,000lb (13.34kN) thrust axial-flow Westinghouse J34 turbojet engines, mounted side-by-side in the slender fuselage fed by lateral intakes. It had leading-edge slats, Fowler flaps and ailerons on the trailing edge and the pressurised cockpit incorporated an ejection seat beneath the bubble canopy. For combat the XF-90, as it was designated, would carry six 20mm cannon, high-velocity rockets and a bomb load of 2,000lb (907kg) with range extended by wingtip tanks.
The XF-90A: the first USAF jet with an afterburner
To satisfy stress levels for the ground-attack role, the XF-90 was to be fabricated primarily in 75ST aluminium for 15 percent greater strength than the more standard 24ST over heavy forgings and machined parts. But that increased the empty weight to about 50 percent greater than its rival, the McDonnell XF-88 and that low power/weight ratio virtually sealed its fate. This would not be the first time that a requirement combining interception and fighter roles with ground-attack duty doomed a design compromised by a multi-role concept.
The first flight of the first prototype took place on 3 June 1949 with Tony LeVier at the controls but, although putting up a credible show, it was too slow and sluggish due to the overweight condition. To improve performance, the second prototype was assigned the afterburning J34-WE-15 with a wet thrust of 4,200lb (18.7kN), designated XF-90A and this demonstrated a speed of 668mph (1,075km/hr) in level flight and Mach 1.12 in a dive. This was the first USAF jet equipped with afterburner and the first Lockheed project to exceed Mach 1 but an assessment judged it inferior to the F-86 which had already been in service for several years.
Lockheed worked up three alternative configurations with different engines including one with a single Allison J33-A-29 (Model 190-33-02), one with two Westinghouse J34-WE-2 engines (Model 290-34-03) or with a single General Electric J47-GE-21 engine (Model 390-35-02) but all options would have required substantial redesign of the fuselage and there was little value in that. The programme was abandoned in September 1950.
US Air Power 1945–1990 Volume 1: US Fighters and Fighter-Bombers 1945-1949 is published by Helion & Company and is available to order here.
Photo credit: U.S. Air Force
