Convair XB-46
A medium jet bomber prototype built by Consolidated Vultee — Convair — for the 1944 Army Air Force competition that produced America's first jet bombers. Three prototypes and a static test airframe were ordered, but shrinking postwar budgets cut the programme to a single aircraft, completed without armament as a testbed after funds for the other two were redirected to the company's XA-44 project. It first flew on 2 April 1947 and handled well, yet the North American B-45 took the interim production contract and Boeing's swept-wing B-47 made the straight-wing design obsolete; the programme was cancelled in August 1947. The prototype flew on as a testbed until 1949, then served pneumatic-system trials in 1950. No example survives: the nose section sent to the Air Force Museum in 1951 apparently did not survive there, and the rest of the airframe was scrapped in February 1952.
Why It Mattered
The XB-46 was Consolidated Vultee's entry in the 1944 United States Army Air Force competition for a jet bomber, the contest that produced the first generation of American jet bombers. The Aviationist groups the four contenders as the 'Class of '47', since each first flew in 1947. The Air Force concluded that the rival B-45 could already do nearly everything the XB-46 promised, with more room to grow, and North American's bomber was further along and cheaper besides, taking the interim production contract in January 1947. Boeing's swept-wing XB-47 then reset expectations entirely, and the B-46 programme was cancelled in August 1947 as already obsolete. What remained of value was the single prototype itself, flown on as a testbed — including, in 1950, trials of the pneumatic control system that set the design apart.
Design Notes
The XB-46 paired a long, streamlined fuselage — Wikipedia describes its oval, torpedo-like form — with a straight, shoulder-mounted wing of high aspect ratio, 11.6. Four Chevrolet-built J35-C3 turbojets sat in two nacelles, paired under each wing, fed by flat oval intakes with S-shaped ducts. The wing carried Fowler flaps across more than 90 percent of its span, very small ailerons, and five perforated magnesium spoilers on each side. The design's most unusual feature was its flight controls: a pneumatic piping system transmitted the pilot's inputs and worked the aircraft's systems, where contemporaries used hydraulics, electrics or manual runs. The crew of three comprised two pilots in tandem under a single teardrop canopy, in a pressurised fighter-style cockpit, and a bombardier-navigator in a glazed nose. The slender fuselage proved a weakness, distorting under flight loads. The prototype flew unarmed; production aircraft were to add an Emerson tail turret with twin .50 calibre guns and an APG-27 remote sighting system, and to use more powerful J47 engines.
Operational History
Procurement began with a letter contract on 17 January 1945, and orders for three prototypes followed on 27 February; Vintage Aviation News adds that the contract also covered a static test airframe and cost more than $10 million. Postwar budget cuts then set the type against Convair's own forward-swept XA-44 attack project, and in June 1946 the Army Air Force agreed a substitution: one XB-46 completed as a stripped testbed, without armament or other equipment, and two XA-44s in place of the remaining bombers. The single aircraft, serial 45-59582, first flew on 2 April 1947, after a month of taxi testing, on a ninety-minute flight from the Convair plant at San Diego to Muroc Army Airfield; its pilot praised the handling. By September 1947 company and service pilots had flown 64 flights totalling 127 hours. The test pilots found stability and control excellent, but testing found trouble with engine de-icing and the cabin air system, vertical oscillations from resonance between wing and spoilers, and doubt over whether the three-man crew could escape in an emergency, since the exit relied on the pneumatic system holding the main door open against the slipstream. The programme had already been cancelled in August 1947; the aircraft was nonetheless accepted on 7 November and delivered on 12 November 1947. Further trials at Palm Beach Air Force Base from August 1948 to August 1949, on noise, tail vibration and stability and control, added 44 flying hours before the aircraft was withdrawn, support costs and a lack of spare parts having become prohibitive.
Afterlife
After a year sitting idle, the prototype was flown in July 1950 to Eglin Air Force Base, where its pneumatic system — unusual in an era of hydraulic and electrical actuation — was tested in the base's large climatic facility under the coldest conditions. That programme ended in November 1950, and the Air Force had no further use for the aircraft. On the 13th of January 1951, the Air Force sent the aircraft's nose to its museum at Wright-Patterson Air Force Base, but Wikipedia records that it appears not to have survived in the collection. The rest of the airframe was scrapped on 28 February 1952, and no example of the type survives. The Aviationist's verdict on the type — a sleek and beautiful aircraft that only looked fast — remains its most repeated epitaph.