Modern-Aviation

Aircraft And Military Development & Applications

81-Lockheed Martin XF-90

The Lockheed Martin XF-90 was built in response to a United States Air Force requirement for a long-range penetration fighter and bomber escort. The same requirement produced the McDonnell XF-88 Voodoo. Lockheed received a contract for two prototype XP-90s. The design was developed by Willis Hawkins and the Skunk Works team under Kelly Johnson. Two prototypes were built. Developmental and political difficulties delayed the first flight until 3 June 1949, with Chief Test Pilot Tony LeVier at the controls. Performance of the design was considered inadequate due to being underpowered, and the XF-90 never entered production.

Maximum speed: 1,070 km/h (665 mph) Maiden flight: 03 Jun 1949 Length: 56.17 ft Wingspan: 40.03 ft Passengers: 1 Designers: Clarence Johnson · Willis Hawkins

One of the hottest looking fighters ever to be built, but not go into production was the Lockheed XF-90. It was the first U.S. built, swept-wing jet to be equipped with afterburners and wingtip fuel tanks as standard equipment and have fully adjustable vertical and horizontal stabilizers. Fowler flaps and leading-edge slats improved airflow over the wings, making the F-90 one of the pioneers in 35-degree swept-wing technology. In tests, the XF-90 exceeded Mach 1 fifteen times.

After World War II, the USAAF needed a “penetration fighter,” capable of escorting bombers to and from their targets. In 1945, the AAF issued a request for a fighter with a combat radius of about 900 miles. Competitors for the contract included McDonnell’s XP-88A, North American’s XP-86C, and Lockheed XP-90. (In 1948, the P designation for “pursuit,” was changed to F, for “fighter.”) Lockheed received a contract for two prototype XP-90s on June 20, 1946.

Despite its sleek appearance, the XF-90 was pretty much of a dog when it came to performance. The reason was that it was way overbuilt and way underpowered. The plane was expected to exceed the sound barrier, but very little was know at the time as to what would happen. The aluminum skin was built with a stronger 75ST aluminum rather than the standard 24ST aluminum alloy, plus a greater thickness to make it four times more stress-resistant than standard construction. Weighing more than a DC-3, it was built to withstand 12 Gs, making it 80 percent heavier than the F-86. Additionally, it was seriously underpowered with its two J34 Westinghouse engines providing a total thrust of only 6,000 lbs (2,721 kgs) required to push 27,200 lbs (12,338 kgs) of aircraft. The thrust/weight ratio was only 22%.

On May 17, 1950, as the test program was conducting power-on dives to work up to the sound barrier, the aircraft made a dive at fairly low altitude and disappeared in the haze. At that same moment, ground observers heard a tremendous boom. They thought the airplane had exploded but to their relief, the airplane had dived to Mach 1.12 and everything was fine. It went on to exceed the sound barrier a number of times, and the XF-90 handled fine with no structural problems.

The XF-90 was a precursor to the "missile with a man in it," the F-104 Starfighter. It caught the nation's attention with its sleek looking design and made for splashy advertising for Westinghouse engines and was featured on the 1953 September cover of the comic book Blackhawk. Thereafter, the young baby boomer generation would be mesmerized with the coming of the jet age and each new adventure of the pilot Blackhawk and his buddy Chuck. This was the atomic age, where children lived in fear of nuclear attack and were taught to hide under their desk in schools during air raid rehearsals. With his squadron of six sleek F-90Bs, Blackhawk and his fighters would keep the threat of the Red aggressors at bay.

Although Chuck Yeager had broken the sound barrier on October 14, 1947, it was too late to be of any help with the design of the XP-90. The ultimate winner of the competition was the McDonnell XF-88A Voodoo, and the XP-90 prototypes were left to an ignominious end. The first prototype was tested to destruction at the National Advisory Committee for Aeronautics Laboratory in Cleveland and became scrap. The second prototype was sent to the Nevada Proving Ground for use in a nuclear weapons test and was subjected to three nuclear blasts. The explosions severed the tail and blew the landing gear from the wing; the main wing structure was buckled and scorched.

In the late 1980s, the second prototype was recovered and decontaminated for preservation. It will be housed in the National Museum of the U.S. Air Force, near Dayton, Ohio. It is recognized for its importance played in the beginning of the cold war as an experiment in early atmospheric testing of atomic bombs. Its participation in three atmospheric atomic bomb tests helped in waging the cold war. The aircraft will be exhibited exactly as it sat, out in the desert for half a century.

Courtesy: Larry Dwyer. The Aviation History On-Line Museum. December 28, 2013

In response to a 1945 Army request for an advanced jet fighter, Lockheed proposed a jet powered initially by a Lockheed L-1000 axial flow turbojet, and then the General Electric J35. Further design refinements included using two Westinghouse J34 engines with afterburners. After data showed that a delta planform would not be suitable, the Lockheed Model 90 was built as a mockup in 1947 with swept wings.

The final design embodied much of the experience and shared the intake and low-wing layout of the previous P-80 Shooting Star, but with 35° sweptback wings, a sharply-pointed nose and two Westinghouse J34-WE-11 axial-flow turbojet engines, providing a total thrust of 6,200 lbf (27.6 kN), mounted side-by-side in the rear fuselage and fed by side-mounted air intakes. The wings had leading edge slats, Fowler flaps and ailerons on the trailing edge. The pressurized cockpit was fitted with an ejector seat and a bubble canopy. Proposed armament was six 20 mm (.79 in) cannons. The internal fuel was supplemented by wingtip-mounted tanks, bringing total fuel capacity to 1,665 gal (6,308 l). The use of 75ST aluminum rather than the then-standard 24ST aluminum alloy, along with heavy forgings and machined parts, resulted in an extremely well-constructed and sturdy airframe. However, these innovations also resulted in an aircraft with an empty weight more than 50 percent heavier than its competitors.

The first XF-90 used non-afterburning J34s, but these lacked the thrust for takeoff as rocket-assisted RATO were required for most of the first flights unless it carried a very low fuel load. The second (XF-90A) had afterburners installed which had been tested on an F-80 testbed. Even so, the aircraft remained underpowered.

General Characteristics
Crew: one
Length: 56 ft 2 in (17.12 m)
Wingspan: 40 ft 0 in (12.20 m)
Height: 15 ft 9 in (4.80 m)
Wing area: 345 ft² (32 m²)
Empty weight: 18,050 lb (8,204 kg)
Loaded weight: 27,200 lb (12,363 kg)
Max. takeoff weight: 31,060 lb (14,118 kg)
Powerplant: 2 × Westinghouse J34-WE-15 turbojets, 4,100 lbf (18.2 kN) each

Role: Fighter
Manufacturer: Lockheed
First flight: 3 June 1949
Status: Canceled
Number built: 2
Unit cost: US$5.1 million for the program

Performance
Maximum speed: 665 mph (1,064 km/h)
Range: 2,300 mi (3,680 km)
Service ceiling: 39,000 ft (11,890 m)
Rate of climb: 5,555 ft/min (28.2 m/s)
Wing loading: 79 lb/ft² (386 kg/m²)
Thrust/weight: 0.30

Armaments
6 × 20 mm (.79 in) cannons
8 × 5 in (127 mm) HVAR rockets
Up to 2,000 lb (907 kg) of bombs

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