Zahlen, bitte! USAF-51-5712 – Aircraft with a nuclear core on board
In the pioneering days of nuclear technology, people even wanted to equip airplanes with atomic nuclei. However, this posed serious problems for the developers.
(Image: heise online)
A nuclear-powered airplane: nowadays, it sounds like a crazy idea from the computer game "Fallout", in which nuclear reactors were built into all kinds of 1950s technology. In the hot times of the Cold War, such an aircraft was actually the target of a research project.
From the planners' point of view, it had enormous strategic advantages: The limiting factor of an aircraft is primarily its fuel - it has to land again after a few hours. Nuclear-powered aircraft, on the other hand, could have remained in the air for longer and only had to land to replace the crew. At least that was the idea at the time.
Early thoughts on nuclear propulsion
Initial considerations were made as early as 1944 during the Manhattan Project. On 28 May 1946, the US Air Force launched a small research program called Nuclear Energy for the Propulsion of Aircraft (NEPA). The aim was to develop the basis for nuclear aircraft propulsion.
The basic research was successful and led to the Aircraft Nuclear Propulsion (ANP) program launched in 1951. Money was not so important – the Cold War and the fear that the Soviet Union had similar plans freed up resources and energy. The aim was to build two nuclear-powered prototypes known as the X-6.
In 1957, Kelley Johnson and F. A. Cleveland, two employees of Lockheed Aircraft Corporation, described the advantages of nuclear propulsion, especially for strategic bombers: "It appears that the strategic bomber will be the first candidate for nuclear propulsion, since its operation requires both high-speed and great endurance and offers inherent advantages over similar aircraft with chemical propulsion."
(Image: USAF)
Powerful bomber as the basis
The US aircraft manufacturer Convair was awarded the contract for the X-6, which was to be based on the B36 "Peacemaker" bomber. With its combination of six propellers and four jet engines, it offered sufficient thrust to transport heavy nuclear technology for tests. The conventional version was built in series from 1947 to 1954 in a total of 385 bombers. Two B36s were to be converted under the project name MX-1589: One for shielding tests, and the other to become a nuclear X-6 bomber.
Various manufacturers took care of the engine technology: General Electric developed direct-air turbojets. Pratt & Whitney, on the other hand, began developing indirect-air-circuit turbojets. Difference: In direct-air-circuit turbojets, ambient air is fed to the reactor via the compressor stage, heated by it and discharged again via the nozzle. In indirect air-circuit turbojets, there is another medium in between, which transports heat from the reactor to the air via a heat exchanger. While General Electric made great progress in development, Pratt & Whitney found it more difficult.
(Image: USAF)
A B-36H-20-CF, which bore the USAF serial number 51-5712, was converted as a test aircraft for the shielding. The aircraft was particularly suitable as it had previously been damaged in a tornado that passed over Carswell Air Force Base in September 1952: the nose, which would have had to be rebuilt for the conversion anyway, was damaged. The conversion began in 1955: no nuclear engines were installed yet - flight operations were purely conventional.
Installable reactor for test flights
A 1-megawatt ASTR reactor was installed, which was used to test the shielding against radioactive radiation in flight. The pilot, two nuclear engineers and one flight engineer did not have much space left after the shielded cabin was installed: the acrylic glass panel of the cockpit alone was 15 centimeters thick. The cockpit area was also protected with a 12-ton lead and rubber shield. Nine shield tanks filled with water were installed to further absorb radiation. The reactor, weighing almost 16 tons, was installed before take-off and removed again after landing.
Crew: 5 persons: Pilot, co-pilot, flight engineer and two nuclear engineers
Length: 49.38 meters
Wingspan: 70.1 meters
Height: 14.26 meters
Flight area: 443.3 square meters
Take-off mass: 163,000 kilograms
Maximum speed: approx. 628 km/h
Service ceiling: 12,200 meters
Engines: 6x Pratt & Whitney R-4360-53; 4x Generel Electric X-40
Test reactor: 1000 kW ASTR nuclear reactor, air-cooled
Flights: 47 (of which 21 with critical reactor)
Period: 1955 to 1957
Whereabouts: Scrapped in September 1958
The NTA completed 47 test flights and a total of 215 flight hours (21 flights and 81 hours with the reactor activated). Most of the test flights over New Mexico and Texas were accompanied by two escort aircraft: a Boeing B-50 for external recording of various flight data and a Boeing C-97 Stratofreighter with armed special forces on board to secure the crash site over a wide area in the event of an emergency landing.
Various problems stand in the way of propulsion
And although the tests were encouraging overall, the program was not under a good star: on the one hand, it was expensive, lengthy and poorly organized. It was also difficult to design the reactor small enough to provide the necessary power - not to mention the concerns about nuclear contamination in the event of a crash.
In addition, missile technology changed the focus: nuclear-tipped intercontinental missiles were much more promising for nuclear deterrence. As a result, no more X-6 aircraft were created in addition to the test vehicle for shielding. After no further funds were made available for testing, it was decided in 1958 to scrap the NB-36H. However, the ANP program continued.
(Image: USAF)
The emerging horror stories of Soviet nuclear bombers were not confirmed: although the Eastern Bloc also experimented with a converted Tupolev Tu-95LAL, they also struggled with the laboriously long development time, performance problems and strong environmental concerns.
On March 28, 1961, John F. Kennedy buried the ANP program in a speech with the words: "Almost 15 years and about $1 billion have already been invested in the development of a nuclear-powered aircraft, but the possibility of a militarily usable aircraft is still a long way off for the foreseeable future."
(mawi)
