The Convair B-36 Peacemaker was a strategic bomber operated solely by the United States Air Force from 1949 to 1959. The B-36 was the largest mass-produced piston engine aircraft ever made. It had the longest wingspan of any combat aircraft ever built at 70.1 m (230 ft).
The B-36 was the first USAF bomber capable of delivering any of the nuclear weapons in the U.S. arsenal from inside its four bomb bays without aircraft modifications. With a range of 16,000 km (9,900 mi) and a maximum payload of 33,000 kg (73,000 lb), the B-36 was the USA's first bomber with an unrefueled intercontinental range. Until it was replaced by the jet powered Boeing B-52 Stratofortress, which first became operational in 1955, the B-36 was the primary nuclear weapons delivery vehicle of the Strategic Air Command (SAC), and the B-36 set the standard for range and payload for subsequent U.S. intercontinental bombers.
The B-36 was unusual in that all B-36s featured six 28-cylinder Pratt & Whitney R-4360 'Wasp Major' radial engines reverse mounted with their large three blade propellors pushing from behind the wings. This was done to minimise turbulence over the wings to increase lift. It also resulted in severe carburettor icing. Beginning with the B-36D, Convair added a pair of General Electric J47-19 jet engines suspended near the end of each wing. These were also retrofitted to all B-36Bs. Consequently, all B-36s were configured to have 10 engines, six radial propeller engines and four jet engines, leading to the Convair slogan of "six turning and four burning". Because of the carburettor icing problem referred to earlier, B-36 aircrews devised their own slogan of "two turning, two burning, two smoking, two choking, two unaccounted for". The B-36 had more engines than any other mass-produced aircraft. The jet pods greatly improved takeoff performance and dash speed over the target. In normal cruising flight, the jet engines were shut down to conserve fuel.
One interesting development of the B-36 was the NB-36H. The NB-36H was a B-36 which was modified to carry a 3 megawatt, operating nuclear reactor in its bomb bay. This aircraft tested shielding requirements for a planned nuclear fuelled jet aircraft, the Convair X-6. All the windows of the NB-36H were 300mm (12 inch) thick lead glass installed into a 1,100kg (12 ton) lead cockpit shield.
The X-6 would have been powered by General Electric X-39 engines (J47 engines modified to operate using thermal energy from the reactor), utilizing a P-1 reactor. In a nuclear powered jet engine, the reactor core was intended to be used as the heat source for the turbine, instead of burning jet fuel. The USAF pursued two different systems for nuclear-powered jet engines, the Direct Air Cycle concept which was assigned to General Electric, and Indirect Air Cycle which was assigned to Pratt & Whitney. The program was intended to develop and test nuclear powered jet engines for the Convair X-6, but the project was cancelled in 1961 before the X-6 prototype was built.
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