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B-52G Nuclear Engine Flying Testbed
In 1946, The Department of Defense (DoD) initiated a joint project between the Atomic Energy Commission (AEC) and the Air Force known as the Aircraft Nuclear Propulsion (ANP) Program. As told by Tony Landis, Air Force Materiel Command History Office, in the article Flashback: Boeing B-52G Nuclear Engine Testbed, based on requirements established by the DoD, the ANP program, known also as the Manned Aircraft Nuclear Propulsion Program, was to develop a nuclear-powered airplane for military purposes. The reactor and related shielding were the responsibility of the AEC while the Air Force was responsible for the airframe, turbomachinery and auxiliary components.
The reason for pursuing the ANP program was to provided new approaches to the propulsion of manned aircraft by the use of nuclear fission as the power source, thereby overcoming the limitations of range and endurance of chemically-powered aircraft. The ultimate objective being the development of a militarily useful aircraft that could be used for strategic and reconnaissance purposes.
As explained by Scott Lowther in his book Boeing B-47 Stratojet & B-52 Stratofortress Origins and Evolution, General Electric spent years working on nuclear engine designs. By the time President John F Kennedy cancelled the programme in 1961, the company had two nuclear jet engines in advanced development: the XMA-1 used a single reactor integrated with two X211 turbojets, and the XNJ140E married a reactor to a single jet engine. Both systems were direct air cycle designs; both attached the compressors as close as possible to the front of the reactor and the turbines as close as possible to the back.
30,000lb of shielding
Consequently these looked like turbojets with very fat combustors, rather than complex assemblies of pipes and engines and reactors.
While GE had tested the X21 1 turbojet components at operational conditions for the XMA-1 engine, it had then cancelled that engine in favour of the XNJ140E which seemed to hold more promise. Unfortunately, by the time of overall programme cancellation, that engine had not yet made it to hardware stage. GE had, however, drawn up details of how to test the engine. The Air Force had planned on using the Convair NX2 aircraft as a multi-engine demonstrator, an all-new aircraft configuration meant to demonstrate a practical tactical weapons system configuration. But GE felt that the B-52G could serve as a single-engine demonstrator.
The company studied several configurations, placing the XNJ140E-1 engine inside the rear fuselage or on top of it, but eventually it was concluded that hanging it in a special nacelle off the left side of the rear fuselage was the most practical option The result seemed to mirror the Canadair CL-52, with a similarly outsized nacelle seemingly clumsily nailed to the rear of the aircraft, making it appear ill-balanced. As the engine assembly weighed 60,000lb, it certainly seems remarkable that the B-52G did not end up tail heavy- though the additional 30,000lb of shielding required for the cockpit would have provided some counter balance.
Creation of ozone
Additional studies suggested that the B-52G could take a second XNJ140E-1 nacelle on the other side; two of these nuclear engines would allow the aircraft to shut down all four of its conventional J57 jet engines (the other four having been removed) and fly on purely nuclear power. Illustrations of this two-engine configuration are not currently available.
An interesting detail was pointed out: the crew’s oxygen supply would need to be located in a low-radiation area of the aircraft… not because gamma rays of neutrons from the reactor would ‘activate’ the oxygen and make it radioactive, but because the radiation would spark the creation of ozone (03)- chemically toxic to the crew. Other concerns were raised regarding some of the standard materials used in the B-52: elastomers in hoses, tyres, wires and seals, along with semiconductors and lubricants and hydraulic fluids would be negatively affected by radiation. These problems were not as well understood a decade earlier, but now they were known issues to be addressed.
The cockpit as shown looks unchanged but would have had to be completely new – a heavily shielded bunker like that of the Convair NB-36H.
Boeing B-47 Stratojet & B-52 Stratofortress Origins and Evolution is published by Mortons Books and is available to order here.
Photo credit: U.S. Air Force
