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The Lockheed XF-90, shown in flight with test pilot Tony Levier in the cockpit, seemed the epitome of a supersonic jet, but never lived up to its looks.

Style Over Substance

By Robert Gutmann
1/25/2018 • Aviation History Magazine

Lockheed’s XF-90 embodied the rakish appearance of an early jet fighter, but its sleek exterior hid a host of shortcomings.

Created by the famous Lockheed “Skunk Works” and heavily publicized as the U.S. Air Force’s next fighter, the futuristic XF-90 seemed to epitomize what a supersonic fighter ought to look like. It was the first Air Force jet to be equipped with afterburners and the first Lockheed aircraft to exceed the speed of sound. With its bulging air intakes, twin jet pipes, swept wings and tail surfaces, pointed nose and wingtip fuel tanks, the XF-90 captured the public’s imagination.

Westinghouse, which manufactured the engines, featured the XF-90 in its corporate advertising. The creators of the popular Blackhawk comic book series adopted the XF-90 as its hero’s jet fighter of choice. Automakers of the day adopted styling cues from the rakish-looking airplane, including sweptback tail fins, faux jet intakes, bulbous “bullet” fairings and twin exhaust pipes. Oldsmobiles even came with a hood ornament inspired by the XF-90.

What the many admirers of the sleek XF-90 did not realize was that the aircraft was a dog. Grossly overweight and underpowered, built to fulfill an Air Force specification that was virtually impossible to satisfy, it proved to be one of the Skunk Works’ rare failures.

The XP-90, as it was originally designated, was one of three prototypes from three different companies that were designed to fulfill a U.S. Army Air Forces request in the autumn of 1945 for a “penetration fighter.” That was the USAAF’s new term for a fighter capable of escorting long-range bombers and establishing air superiority over enemy territory—a jet-powered equivalent to World War II’s North American P-51 Mustang.

The design parameters for the new penetration fighter—supersonic speed, a combat radius of 900 miles and armament of no less than six 20mm cannons—were very difficult to meet at that time. Nevertheless, three designs were selected for proto­type development. North American’s XF-93 was a larger and bulkier development of its F-86 Sabre, with a pointed nose and side air intakes. It was powered by a single 7,250-pound-thrust Pratt & Whitney J48 turbojet, a license-built version of the British Rolls-Royce Tay jet engine. McDonnell submitted the XF-88, a completely original design powered by two Westinghouse J34 turbo­jets rated at 3,000 pounds’ thrust each. Although never accepted for series production, it became the predecessor of the highly successful F-101 Voodoo. 

The third design, Lock­heed’s XF-90, was essentially an enlarged, twin-engine F-80 Shooting Star with swept wings and tail surfaces, powered by a pair of turbojets mounted side-by-side in the fuselage. Lockheed originally intended to install its L-1000 axial-flow turbojets, which it had begun developing in 1942, but the company’s preoccupation with wartime production eventually led it to abandon the project. In any case the USAAF granted a higher priority to General Electric and Westinghouse, whose jet engines were much further along in development. As a result the XF-90, like the XF-88, was powered by Westinghouse J34s.

The XF-90 was a striking-looking airplane, but it concealed some serious shortcomings beneath its sleek aluminum skin, not all of which were attributable to Lockheed. For example, in an era when jet engines were notorious gas-guzzlers and inflight refueling had yet to be perfected, the prospective penetration fighters had to be large enough to carry sufficient fuel to satisfy the 900-mile combat radius requirement. The XF-90 was 56 feet 2 inches long with a 40-foot wingspan—very large for a single-seat fighter of the day. Even then, wingtip fuel tanks—the first on any Air Force fighter—were necessary to accommodate enough fuel for the fighter’s long-range missions.

There was also the challenge of exceeding the sound barrier, yet to be accomplished when the XF-90 was being designed. Nobody knew exactly how much stress the airplane would be subjected to, but it was expected to be a great deal. As a result the airframe was fabricated out of 75ST aluminum, which had greater tensile strength than the normal 24ST variety. In addition, all the structural parts and the skin were fashioned from thicker-gauge aluminum, fastened together with half-inch-diameter rivets. These structural elements made the XF-90 strong enough to withstand 12 Gs, but it also resulted in a single-seat fighter that weighed as much as a Douglas DC-3. 

Furthermore, the XF-90 was designed prior to National Advisory Com­mittee of Aeronautics (NACA) engineer Richard T. Whitcomb’s discovery of the aerodynamic “area rule,” the application of which led to a fuselage configuration that significantly reduced transonic drag. Without the benefits of that innovation, the XF-90 had a difficult time exceeding the sound barrier, even in a dive.

Two XF-90 prototypes were built, the first of which made its maiden flight on June 3, 1949. Because it was not equipped with the specified afterburners, however, it could not even leave the runway without the assistance of RATO (rocket assisted takeoff) units unless it was carrying a reduced fuel load. The second prototype, which did have afterburners, at least managed to get airborne without external assistance.

The XF-90 eventually did break the sound barrier, but only just, and only in a dive. Nevertheless, the aircraft proved too underpowered to win a production contract, placing third after the competing XF-88 and XF-93. In fact, a fly-off between the three prospective fighters demonstrated that the entire penetration fighter concept was unrealistic. Consequently, production orders for the F-88 and F-93 were soon canceled. In any event, by then the Air Force was becoming convinced its new bomber, the Boeing B-47 Stratojet, performed so well that it would require no escort.

Lockheed’s Skunk Works engineers learned valuable lessons from the failure of the XF-90. Their next fighter, the F-104 Starfighter, proved to be far more successful.

In 1953 the first XF-90 prototype was transferred to NACA for static testing, during the course of which it was destroyed. The second prototype had a more spectacular fate. Sent to a nuclear test site in the Nevada desert in 1952, its super-strong airframe survived no less than three nuclear bomb blasts. In 2003 the surprisingly intact remains of the second XF-90 were recovered and brought to the National Museum of the U.S. Air Force in Dayton, Ohio, for decontamination. The museum plans to exhibit it as a demonstration of the effects of a nuclear blast. 

 

This feature appears in the March 2018 issue of Aviation History. Subscribe here.

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