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The Convair XF-92

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This airplane was the world's first jet aircraft to fly using the radical delta-wing configuration pioneered by Germany's Dr. Alexander Lippisch during the 1930s.

                           

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Xf-92

Convair XF-92A

The Convair Model 7002 was completed in 1948 as a flying mock-up for the proposed delta wing  XP-92 interceptor. (In 1948 the Air Force changed the designation from P for pursuit to F for fighter). The XP-92 was to be powered with a new propulsion system that would consist of a ramjet engine with several small rockets inside the combustion chamber. It would have been a short range, Mach 1.65 interceptor with a flight time at altitude of 5.4 minutes. The Model 7002 was designed to investigate delta wing behavior at low and high subsonic speeds. When the XP-92's engine proved to impractical to build the project was shelved in 1948. Evan as the XP-92 program was ending, the Model 7002 was being prepared to fly. The 7002 was initially powered by an Allison J33-A-23 turbojet engine and later the J33-A-29 turbojet with afterburner. It was formally delivered to the Air Force on 14 May 1949 and named the XF-92. It was flown by Air Force test pilots until its nose gear collapsed on landing on October 14, 1953, ending its flying career. With the experience gained from the XF-92 program, Convair was able to win the competition for the "1954 Interceptor" program and to build the successful delta wing F-102.

Only one XF-92A was built; it was delivered to the Museum in 1969 from the University of the South, Sewanee, Tennessee.

SPECIFICATIONS
Span:
31 ft. 3 in.
Length: 42 ft. 5 in.
Height: 17 ft. 8 in.
Weight: 8,500 empty, 14,608 lbs. maximum
Armament: None
Engines: Allison J33-A-29 of 7,500 lbs. thrust with afterburner
Crew: One
Cost: $6,048,928

PERFORMANCE
Maximum speed:
715 mph / 624 knots
Cruising speed: 654 mph / 569 knots
Range: Not applicable
Service ceiling: 40,000 ft.   

COURTESY OF THE AIR FORCE MUSEUM

 

The History of The 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 nosewheel 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.s.t. 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.

Iniial 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 provide 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 is 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-92A:

Power-plant: 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:

  1. Fighters of the United States Air Force, Robert F. Dorr and David Donald, Temple Press Aerospace, 1990.
     
  2. The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.
     
  3. General Dynamics Aircraft and their Predecessors, John Wegg, Naval Institute Press, 1990.

By Joe Baugher

 

 

Chuck Yeager and the Convair FX-92A

             

The Convair model 7002, a delta winged turbojet airplane better known as the XF-92A was the first in a long line of American Delta Winged Aircraft. The F2Y, F-102, F-106 & B-58 Hustler were all based around the flight data acquired by the flight testing of the XF-92A.

Thomas Melvin Hemphill, the Preliminary Design Engineer and Project Engineer on the XF-92A, is featured in a March 1950 Skyways article that was published when the XF-92A was first introduced to the public by Hemphill and Convair. The plane was tested at Muroc by Pilots Sam Shannon and Bill Martin and others. General Chuck Yeager tested the plane for the Air Force. Nearly 80 tests flights were flown at Muroc/Edwards prior to the publication of the Skyways article. The XF-92A was built on a low cost budget with some parts scavenged from already existing planes.  In the annals of history, Hemphill has been largely overlooked with regard to the the XF-92A. It is with sincere thanks to the late Mr. Hemphill's daughter Zoe that this article has been brought to light.

The XF-92A was a single seat, jet propelled research fighter-type land plane. Characterized by a 60º delta wing and a large vertical tail, the wing platform of the XF-92A was an equilateral triangle with a span of 31’4”. With no separate horizontal tail surfaces, the elevons (combined elevator/aileron) provided the pitch and roll control for the aircraft. One of the more unusual aspects of the XF-92A was the hydraulically boosted controls. So sensitive were they, that when Colonel Al. Boyd asked Capt. Chuck Yeager “Now Chuck, what’s the technique on flying this airplane? Just how do I go about taking it off?” Yeager replied, “Well I’ll tell you sir. You get out there, you go rolling down the runway, and when that air-speed indicator indicates 180 (knots) you just blow a little on the stick. That’s all you have to do.”. Recalling some years later, Boyd said “I rolled down the runway to 180 and when I lifted the airplane off, I’ve never touched anything so sensitive in all my life. It was almost uncontrollable because the control system was so terribly sensitive”.

The initial flight testing of the 7002 was conducted by Convair chief experimental test pilot Ellis D. “Sam” Shannon. During taxi trials on June 9th 1948, the 7002 leapt off the lakebed to an altitude of some 10 to 15 feet at 180mph. Shannon kept the aircraft flying for around 40 seconds and covered a distance of around 2 miles before setting the aircraft back down on the lakebed.

Following this test, Convair technicians installed a more powerful Allison J-33-A-23 turbojet, a new tail pipe and tail-cone and a high speed canopy and windshield. The XP-92 project (from which the 7002 was born) was cancelled in June 1948, which freed the sole aircraft built from the constraints of development testing. This allowed it to embark on a pure delta platform research project. The Air Force re-designated the aircraft the XF-92A to distinguish it from the cancelled XP-92 (which would have been an experimental prototype fighter powered by a rocket). Convair resumed the contractor testing in September of 1948. Sam Shannon took the XF-92A up for its first flight on September 18th, 1948. The flight lasted for 18 minutes and was basically a pilot familiarization flight. Shannon immediately noticed that the control system was extremely sensitive and responded quickly to the most minute of control-stick deflections.

By the end of 1948, Shannon had made 10 flights in the XF-92A and another Convair pilot, Bill Martin joined the program and made his first flight on February 9th, 1949. Convair concluded the 1st phase of the flight testing on August 26th, 1949. In the 11 months of flight testing, the XF-92A made 47 flights, accumulating a total of 20 hours and 33 minutes of flying time in the hands of Shannon & Martin.

The Air Force conducted the second phase of the flight testing (stability & control). The primary pilot for this project was Capt. Chuck Yeager. Yeager made his first flight in the XF-92A on October 13th, 1949, almost exactly 2 years after he flew the Bell X-1 through the sound barrier for the worlds first supersonic flight. Maj. Frank “Pete” Everest joined Yeager on the project. Yeager & Everest both flew the aircraft through the speed of sound, all the while examining its stability & control characteristics during level flight, dives, sideslips & rolls. Yeager thought the XF-92A was a neat airplane to fly and later recalled, "The XF-92A was a step in the right direction in aircraft design. I flew it to supersonic speeds in a dive and had it as low as 67mph (in the landing pattern). The angle of attack was 44º. You just couldn’t stall the aircraft”.

Air Force pilots who made familiarization flights in the XF-92A were Lt. Col. Fred J. Ascani, Col. Albert Boyd, Lt. Col. Richard L. Johnson, Capt. J.E. Wolfe, Capt. Arthur “Kit” Murray and Maj. Jack Ridley.

The NACA’s Scott Crossfield made the 1st of his 25 flights (with the J-33-A-16 engine installed) on April 9th, 1953 with Chuck Yeager flying chase in an F-86 Sabre jet. Like all the other pilots who had flown the XF-92A, Crossfield found the controls to be sensitive. Crossfield’s last flight in the aircraft was made on October 14th, 1953. After touching down on the lakebed, the drogue ‘chute was deployed and jettisoned & Crossfield began to taxi back to the runway, as he slowed the plane near the end of its run, the XF-92A’s nose began to drop and it slewed around in a hard left turn. The plane settled on its nose, right landing gear & right wingtip. Crossfield crawled out of the cockpit after ascertaining that the aircraft was not about to turn over. Inspection showed that the nose strut attachment had failed during the taxi run and the cocked gear strut in turn caused the shock strut to buckle and fold up, slewing the plane around.

This was a rather ignominious end to the XF-92A’s flight career. During its 5 years of flying, the XF-92A had logged 119 flights with approximately 62 hours of flying time. The XF-92A is on permanent display at the USAF Museum, Dayton Ohio

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Three wind tunnel model tests 1944.

      THE ABOVE THREE PHOTOGRAPHS COURTESY OF GERALD LANDRY CALTECH

 

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One of five exeperimental  XF2Y-1 Convair 'SEA DART's.  Based on  the XF-92A airframe they were evaluated by the Navy in 1953, major problems prevented further development.  The only surviving "Sea Dart" is at the San Diego Aerospace Museum.  

 

PHOTOGRAPH COURTESY OF GERALD LANDRY   CALTECH

 

The Sea Dart test program began in December 1952 and ended in late 1957 with the three test aircraft performing over 300 test operations. All tests were conducted from the Convair San Diego Bay seaplane ramp. Four Convair engineering test pilots were involved, plus several Navy test pilots from the Naval Air Test Center, Patuxent River, Maryland.

Five Sea Dart aircraft were built. Only three were flown, with four aircraft still in existence today. The second aircraft crashed on 4 November 1954, and the last two aircraft were completed as airframes only, without the engines ever being installed.

 

XF2Y-1

  

Alexander M. Lippisch

The Delta Wing

More on the Delta Wing

A Wing For All Speeds

 

 

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