Title: Flying on Nuclear - The Superpowers Quest for a Nuclear Powered Bomber
Authors: Raul Colon
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Having tackled the reactor, transfer mechanism, and shielding problems, the program moved it to the aircraft design stage. By late 1951, the program was heavily involved in the acquisition of a test-bed type aircraft for the initial trials of the configuration. The only proven airframe large enough to carry the massive reactor and Heat Transfer system was the Convair’s B-36 Peacekeeper Bomber. The Peacemaker started to enter front line service with the U.S. Air Force in late 1948 and at the time of the nuclear powered program, was the Strategic Air Command (SAC) main nuclear deterrent platform. The B-36 was indeed massive. The dimensions are impressive even today. A wingspan of 230ft, a length of 162ft 1in, high of 46ft 8in, and a wind area of 4,772sq ft. This bomber maximum take-off weight was an amazing 410,000lbs; which is why the program managers selected the B-36. A service ceiling of 39,900ft and a climb rate of 2,220ft per minute were also pluses in the selection process. Once the testing aircraft had been identified, the next phase would commence at once; the conversion of the B-36 into an experimental aircraft. The main modification made to the original B-36 airframe was on the nose cone section. The original crew and avionics cabin was replaced by a massive 11tons structure lined with lead, and rubber. Water tanks were also placed in the aft section of the frame to absorb any escaping radiation.

The other section of the plane that underwent significant modifications was the rear-internal bomb bay. Internal cross sections were remove as well as many of the bomb carrying rafts in order to make space for the nuclear reactor power plant. These alterations made it possible for the aircraft to receive a new call sign designation. It is from this moment on that this sole B-36 Peacemaker, number 51-5712, sample would be called Nuclear Test Aircraft-36. A further call sign change was made when the nuclear powered plant was installed on the aircraft. Thus the NB-36 “Crusader” was born. Identifying the aircraft was the radioactivity symbol painted on the tailfin. The R-1, one standing for the energy it would generate, a megawatt; reactor installed on the aircraft was a liquid-sodium cooled power plant winched up into the plane’s bomb bay at a dedicated pit on Convair’s Fort Worth plant every time the NB-36 was scheduled to take to the air. When the NB-36 landed, the R-1 was removed for research purposes. The original B-36 was powered by six Pratt & Whitney 3600hp, R4360-53 radial piston engines, supplemented by four General Electric 54000lb thrust J47-19 turbojets. After conversion, the engines were removed and a new configuration was incorporated. The NB-36 now had four GE J47 nuclear converted piston engines generating 3,800hp augmented by four 23.13Kn turbojets generating 5,200lb of thrust. Each of the engines utilized the Direct-Cycle Configuration for power conversion. The NB-36 was designed from the beginning, to be propelled to the air with a conventional chemical mixture, and then the crew would switch on the reactor after achieving the necessary heat requirements on its core. On landing approaches, the aircraft would switch back to chemical mixture. This procedure was implemented in order to minimize the possibility of a major radiation leak in case of a crash landing.

The NB-36 made 47 recorded flights between the summer of 1955 and the fall of 1957. All these tests were made operating the NB-36 with conventional chemical power. The R-1 reactor was turned-on on many of these flights, not to actually power the aircraft, but to test and collect data on the feasibility of a sustained nuclear reaction on a moving platform. All the data collected by these tests showed the program managers that the possibility of using a nuclear power plant to provide an aircraft with unlimited operational range was indeed at their disposal at this time. Impressive as the taxi and flight testing were for the NB-36, the complete concept of a nuclear powered aircraft was made irrelevant by advances in conventional aircraft and engine design and the public concern about the dangers of flying a nuclear reactor over their homeland. In the end, after expending no less than 469,350,000 millions on the nuclear powered program and having a concept aircraft flying, the U.S. Air Force shelf the program in the late 1960s, thus ending any major attempt by the United States to utilizing nuclear propulsion to impulse an aircraft in combat.

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