Convair XB-46

The Convair B-46 officially originated back in 1944, at a time when the USAAF was already aware of German advances in the field of jet propulsion, especially as applied to the development of jet bombers. Alarmed by German developments, the War Department called for bids on a new family of jet-powered bombers, with gross weights ranging from 80,000 pounds to more than 200,000 pounds. An April 1944 specification called for a 1000-mile tactical radius, a maximum speed of 500 mph, and a 40,000 foot ceiling. These new aircraft were to be powered either by TG-180 or TG-190 engines which were then under development at General Electric. The TG-180 was eventually built by the Allison Division of General Motors as the J35, and the TG-190 was built by the General Electric company as the J47.

On November 6, 1944, Convair submitted a proposal for a fairly conventional design with a shoulder-mounted Davis wing and a slim well-streamlined fuselage. The aircraft was to be powered by four General Electric TG-180 axial-flow turbojets, paired in two underwing pod nacelles. The three crew members were to be housed in a pressurized cockpit. The pilot and copilot sat in tandem underneath a fighter-type bubble canopy, and the bombardier sat in the forward nose with a glazed nose section. Defensive armament consisted of two 0.50-inch machine guns in a remotely- controlled tail turret. Normal bomb load was 8000 pounds. The proposal was known as Model 109 by Convair.

Three prototypes of the Model 109 were ordered on February 27, 1945 under the designation XB-46. Serials were 45-59582/59584. At the same time, contracts were awarded to North American, Boeing, and Martin for the XB-45, XB-47, and XB-48 respectively.

The end of the Second World War resulted in the cancellation of many projects and the delay of others. However, the War Department felt that the development of a jet-powered bomber should still be pressed forward with the utmost speed, and the XB-45, XB-46, XB-47, and XB-48 contracts were left relatively unscathed. However, funds for two of the three XB-46s were diverted to Convair's XA-44 jet attack bomber project. In the event, the XA-44 design was converted to a light bomber design in December 1946 and redesignated XB-53. The XB-53 project was abandoned shortly thereafter.

In 1946, tensions between the USA and its erstwile Soviet ally were rising, and the USAAF concluded that it needed to field a jet-powered bomber as soon as possible. The USAAF decided that it could save some time if it skipped the competition that would ordinarily be held between the four bomber proposals and went ahead and reviewed the available designs to see which of them could be produced first. By that time, the XB-45 and XB-46 were nearing completion, but the XB-47 and XB-48 were still at least two more years away. The USAAF decided to appraise the XB-45 and XB-46 right away and choose one of them for immediate production. Any consideration of the XB-47 and XB-48 would be deferred until after they had flown. if either the XB-47 or XB-48 turned out at that time to be markedly superior to the plane that was then being produced, then that aircraft would be purchased and the currently-produced version would be phased out. This is indeed what happened when the XB-47 appeared.

The USAAF concluded that the Convair XB-46 would likely be inferior in performance to the North American XB-45 because of its higher weight, and that its thin, graceful fuselage would not be able to hold all the required radar equipment. Since the configuration of the XB-45 did not depart significantly from that of proven aircraft already in service and hence presented fewer risks, on August 2, 1946, the USAAF announced that they were going to endorse the immediate production of the B-45. Nevertheless, Convair would be permitted to complete a single XB-46 for test purposes, with essentially no chance of ever receiving a production contract for the type.

The sole XB-46 (45-59582) took to the air for the first time on April 2, 1947, with E. D. "Sam" Shannon and Bill Martin at the controls. The wing had nearly full-span Fowler-type flaps on the trailing edge, and roll control was achieved primarily by 20-foot long spoilers, the ailerons being only 6 feet long. The main undercarriage retracted into wells in the engine nacelles. The XB-46 was unusual in that it had a complete pneumatic system for the actuation of the undercarriage, bomb bay, crew doors, and brakes.

The B-46 program was officially cancelled by the USAF in August 1947, one year after the USAAF had endorsed the immediate production of the North American XB-45.

Company flight tests at Muroc were completed by September 1947 after 14 flights. The aircraft was re-engined with Allison J35-A-3 turbojets and then flown to Wright Field. The aircraft was accepted by the Air Force on November 7, 1947. The XB-46 was used in a variety of tests such as noise measurements and tail vibration investigations. Additional stability and control tests were carried out at West Palm Beach AFB in Florida between August 1948 and August 1949. However, these tests became increasingly more difficult to complete because of maintenance difficulties aggrivated by the lack of spare parts. Following completion of trials, the XB-46 was flown to Eglin Field in Florida in July of 1950 where a series of low temperature tests on the aircraft's pneumatic system were carried out in the base's climatic hangar. Following the completion of the climatic tests, the Air Force had no further need for the XB-46. The nose section was sent to the Air Force Museum at Wright-Patterson AFB in Ohio in early 1952. The remainder of the airframe was scrapped in February of 1952.

Specification of Convair XB-46:

Engines: Four 4000 lb.s.t. Allison-built General Electric J35-A-3 axial-flow turbojets. Performance: Maximum speed 545 mph at 15,000 feet, 491 mph at sea level. Cruising speed 439 mph at 35,000 feet. An altitude of 25,000 feet could be attained in 19 minutes. Service ceiling 40,000 feet. Range 2870 miles with 8000-pound bomb load. Maximum fuel capacity 6682 US gallons. Initial climb rate 2400 feet per minute at maximum takeoff weight. Weights: 48,000 pounds empty, 75,200 pounds combat, 94,400 pounds maximum take off. Dimensions: Wingspan 113 feet 0 inches, length 105 feet 9 inches, height 27 feet 11 inches, wing area 1285 square feet. Armament: Two 0.50-inch machine guns in tail turret. Space and structural provisions were made for an APG-27 remote control system with optics and radar sighting. Maximum bombload was 22,000 pounds.

Sources:

1. Post-World War II Bombers, 1945-1973, Marcelle Size Knaack, Office of Air Force History, 1988.
   
   
2. General Dynamics Aircraft and their Predecessors, John Wegg, Naval Institute Press, 1990.
   
   
3. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.