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XP-92

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Status: Operational 1948. Thrust: 52.90 kN (11,892 lbf). Gross mass: 6,620 kg (14,590 lb).

Originally it was planned the operational aircraft would be boosted by 6 x 900 kgf RL-11 liquid rocket engines, but the airplane never flew in this configuration.

Convair XF-92A by Joe Baugher

In August of 1945, the USAAF announced a competition for a supersonic interceptor capable of reaching an altitude of 50,000 feet in four minutes and capable of achieving a maximum speed of 700 mph. A tall order for 1945!

A team from Consolidated Vultee Aircraft Corporation (better known as Convair) won the competition in May of 1946. The Convair design proposal was for a ramjet-powered aircraft with wing sweep of 45 degrees. The designation XP-92 was assigned to the project.

However, wind tunnel testing indicated that there would be problems with wing tip stalling at low angles of attack and with lateral control problems. Consequently, the Convair team went back to some wartime German research by Dr. Alexander Lippisch, who had been an early pioneer in delta wings.

The Convair team decided to adapt their aircraft to a delta-winged configuration. The aircraft that they eventually came up with was an interceptor with a delta wing and a V-shaped butterfly tail. It was to be powered by a single 1560-lb.st. Westinghouse J30-WE-1 turbojet plus no less than six 2000-lb.st liquid-fueled rocket engines. The P-92 was envisaged as a very fast point-defense interceptor with range and endurance being sacrificed for all-out performance.

In order to speed development of the P-92, in November 1946 the USAAF authorized Convair to build a delta-winged research aircraft to prove out the concept. This aircraft was given the company designation of Model 7-002. A USAF serial number of 46-682 was assigned. In order to save time and money, extensive use was made of existing aircraft components where feasible. The main undercarriage was taken from a North American FJ-1 Fury, the nose wheel was taken from a Bell P-63 Kingcobra, the engine and hydraulics were taken from a Lockheed P-80 Shooting Star, the ejector seat and cockpit canopy were taken from the cancelled Convair XP-81, and the rudder pedals were taken from a BT-13 trainer. The delta wing planform required that "elevons" be developed to replace the traditional elevators and ailerons. All flight controls were hydraulically-activated and were irreversible.

Construction was well underway when Vultee Field was closed down in the summer of 1947. The airframe was then transferred out to Convair's plant in San Diego for completion. The airframe was completed in the autumn of 1947, and in December it was shipped without an engine to NACA's Ames Aeronautical Laboratory at Moffett Field near Sunnyvale for wind-tunnel testing. After the wind-tunnel testing was completed, the airframe was returned to San Diego, where it was installed with a 4250 lb.st. Allison J33-A-21 turbojet.

The Model 7-002 was then taken out to Muroc Dry Lake (later Edwards AFB) in April of 1948. Tests were at first limited solely to taxiing and high speed ground runs, although a short hop was made on June 9, 1948. In the meantime, the USAF finally came to the conclusion that the F-92 point-defense interceptor concept was not a very practical idea, and decided to cancel the program. However, the idea of a delta-winged aircraft was sufficiently interesting that the USAF decided to continue on with the flight testing of the Model 7-002, even though no production was envisaged. The Model 7-002 aircraft was assigned the designation XF-92A.

A 5200 lb.st. J33-A-23 engine was installed before the official flight testing began. The XF-92A officially took to the air for the first time on September 18, 1948, Sam Shannon being the pilot. The XF-92A was the world's first true delta-winged aircraft to fly.

Initial flight testing was performed by Sam Shannon and Bill Martin. They found the controls to be extremely sensitive. Initial testing was completed by August 26, 1949. The XF-92A was then turned over to USAF test pilots Capt. Charles E "Chuck" Yeager and Maj. Frank K. "Pete" Everest, who did most of the test flying with the aircraft until the end of the year. The XF-92A was easy to land and was extremely stable at speeds of Mach 0.9. However, the XF-92A could not exceed the speed of sound in level flight and could only exceed Mach 1.0 in a dive, this being done at least once with Major Everest as the pilot.

In 1951, the XF-92A was refitted with an Allison J33-A-29 engine with afterburner, offering a thrust of 7500 lb.st. The re-engined XF-92A was flown by Chuck Yeager for the first time on July 20, 1951. However, there was very little improvement in performance. In addition, there were maintenance problems with this engine and only 21 flights were made during the next 19 months.

A further engine change was made to the 8400 lb.st. J33-A-16, and on April 9, 1953, the test pilot A. Scott Crossfield began a series of flights on behalf of NACA. These tests indicated a violent pitch-up tendency during high-speed turns. Wing fences were added which partially alleviated this problem.

On October 14, 1953, the XF-92A suffered a nose wheel collapse during a high-speed taxiing run. The damage was sufficiently severe that the XF-92A had to be withdrawn from service. Although the XF-92A never produced a useful combat aircraft, it nevertheless provided a lot of valuable data on delta wing aircraft, and was instrumental in the development of the later F-102 and F-106 delta-winged interceptors.

Following the withdrawal of the XF-92A from test-flying work, it was eventually disposed of as a static exhibit, and was parked outside to weather away. It was rescued from this fate by the USAF in 1962 and was currently in storage awaiting exhibit at the USAF museum at Wright-Patterson AFB. I was there in June of 1992, but it was still not yet on display.

Specification of the XF-92:

One Allison J33-A-29 turbojet, 5900 lb.st. dry and 7500 lb.st. with afterburner. Dimensions: wingspan 31 feet 4 inches, length 42 feet 6 inches, height 17 feet 9 inches, wing area 425 square feet. Weights: 9078 pounds empty, 14,608 pounds gross. Maximum speed: 718 mph at sea level, 655 mph at 35,000 feet. Climb to 35,000 feet in 4.3 minutes, service ceiling 50,750 feet. The XF-92A was never fitted with any armament.

Sources:

Fighters of the United States Air Force, Robert F. Dorr and David Donald, Temple Press Aerospace, 1990.

The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.

General Dynamics Aircraft and their Predecessors, John Wegg, Naval Institute Press, 1990.