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A « modern » Lockheed concept for an A-plane which shows an obvious similarity with the Convair designs of the fifties
Source : Lockheed)

Many articles were written during the fifties about A-planes and now we know that various aircraft manufacturers including Convair, Northrop and Lockheed  seriously studied the feasibility of such a concept .
As early as  1942 Enrico Fermi and the Manhattan Project group suggested to apply nuclear power to the propulsion of aircraft. In 1946 was initiated NEPA "Nuclear Energy for Propulsion of Aircraft" . Fairchild aircraft got the study contract but could not carry on due to the lack of data regarding the resistance of common engineering materials to radioactive radiations. In 1951 this program was superseded by a common  USAF and AEC (Atomic Energy Commission : the authority in charge of all A-projects in the SUSA at the time . They were the ones prohibiting looking into empty bomb bays) project) . At the time it was thought the nuclear rockets  (project Rover) and nuclear ramjets (project Pluto) would be easier to build than nuclear turbojets. Even with turbojets you got two options : the easy dirty way in which the air ingested via the intake goes through the reactor core : that's what is called the
« direct » method but the exhausted air is highly radioactive and therefore it was planned to use it only for high altitude cruise (with obvious disregard for the long term effects of this radioactive pollution) with the addition of a menagerie of odd solutions for the take-off and landing phase ( either auxiliary engines or « donkey » -booster- aircraft) . In the « indirect mode » the air stream is heated via a fluid which acts as a heat transfer system (either liquid metal or pressurized water) . It yields  slightly less power but it suppress (hem! Minimize would be more realistic?) radioactive pollution . Thus an indirect-system engine is okay for use during take-off and landing. (Again I emphasize that this was the thinking of the times, now it would be seriously reconsidered) . General Electric  got the contract for the "direct" engine development and  Pratt & Whitney for the "indirect" version
Convair  in this project was contracted for building the airframe which received the designation "X-6" and used many components from the largest bomber of the times : the  B36 . Indeed the reactor was believed to be bulky and weighty anti-radiation armor had to be installed generously around the reactor and around the crew compartment.  Then you could add another specification which stipulated that the crew compartment had to be the farthest away from the reactor as possible . This is why many designs are crane-necked. Only the first part of the project : testing the anti-radiation protection by carrying a live reactor aloft was actually tested aboard a specially modified B-36 renamed NB-36. The reactor aboard was activated but never linked to a propulsion system . The NB-36 flew from 1955 to 1957 .

General Electric did build various prototype direct-type nuclear engines but not one was declared airworthy and they were therefore limited to ground tests.  As for the indirect method pioneered by  Pratt& Whitney  it seems it got stuck in problems related to the heat-transfer fluid.

However the feasibility of an A-plane was perceived as
« obviously there » so more thinking got into the ergonomics of its operation , notably the difficulty associated with the ground infrastructure needed to cater for such aircraft . Moreover  in case of an flight accident, a major disaster on the ground underneath could be expected . Yet various crew pod ejection systems were conceived but even with this kind of system , the ejection procedure required first to stop the reactor before ejecting to avoid being roasted during the « just after ejection » phase. It was expected that cutting off the reactor could be executed in just a few  milliseconds!

Apparemently only Convair carried on until the end of the program , in view of the difficulties encountered the other aircraft manufacturers dropped  the ball well before 1961 .
It appears that the various experiments actually carried on, plus the actual deployment of atomic power plant in military vessels and civilian electrical power plants convinced everyone that the security constraints were irreconcilable with civilian vehicle operations and too massive in term of infrastructure requirements even for the military.
Actually A-planes were also killed by technological advances in missiles which rendered obsolete the concept of long-range manned bombers able to loiter for days or weeks along enemy borders.

Other countries arrived at the same conclusions . The British company Saunders-Roe  did offer a nuclear powered version of its giant seaplane Princess  but it was an obvious plot to keep afloat this design at a time when transatlantic seaplanes were getting obsolete. Proposal for a Sud-Aviation  SST do appear in the very early designs that were to crystallize into Concorde but they were quickly dropped .

According to their publications of the time the USSR had planned a giant seaplane weighting 1000 tons and equipped to carry 1000 passengers at 1000 Km/h . This monster was to come with 4 nuclear ...turboprops. In this design the heat-transfer fluid would have been liquid lead. The design bureau (OKB) responsible for this machine is unknown and it may have been just a propaganda device (or something from a Sci-Fi novel !)

In December 1958 Aviation Week  leaked out that the Soviets had an A-bomber already in the flying stage. It is today accepted that this
« leak » which used pictures of the  Miyasischiev "Bounder"  was a « direct or indirect » attempt to boost the American A-plane program on which the Congress was to appropriate (or not) funds in the coming days of this revelation.  Actually the only hardware to come out of this affair was … an Aurora model kit.. .

A few years later however  Tupolev did try to put an A-plane in the air with the  Tu-119.  A demonstrator Tu-95 LAL (Tu-119) was fitted with two NK 42 jet engines (chemical) and two NK44  nuclear  turbojets. This aircraft did a few test flights until 1962. It seems the anti-radiation protection was insufficient and the crew got irradiated. The project was dropped probably for the same reasons the American program had been.

Final design by  Convair. Early 60 (source : Convair via Airpower)

Convair also suggested a nuclear powered version of their B58 (source Convair)

Assuming that by construction an A-plane would HAVE to be huge , a Martin team proposed this "thing" called« Aldebaran » (The ship beside it is the USS America, ). This monster used a nuclear ramjet for propulsion. Welcome radioactive efflux ! If that kind of machine had been put into service we would all be glow in the dark with three arms and legs !  (source : via APR)

The only aircraft to actually fly in western countries with a live reactor aboard was the NB-36H (reserved rights)

Northrop offered this beautifull delta flying boat illustrated here by  Jo Kotula , an artist famous for his numerous Aurora boxarts. (photo : Northrop)

This one is Lockheed design  GL 232 of 1958  which was planed to use Pratt & Whitney indirect-type engine which was never finallized. This design lost out to the Convair design illustrated on top in what was called the CAMAL « Continuously Airborne Missile Launcher » competition

The first benefit of nuclear power was not speed but endurance , hence the first studies , attributed to the Soviets at the time , dealt with turboprops (with scimitar-shaped props to work efficiently at transonic speeds) (reserved rights)

A rather fanciful design for an atomic powered seaplane with three rotors and the improbable registration CCCP 1 (reserved rights)

This is more what the actual Soviet experimental A-plane looked (via José Fernadez)

And what a definitive version could have looked like : in red the reactor , in blue the jet engine, in green the crew compartment anti-radiation armor and a tank (water ? To act as an additionnal armor?) (via José Fernandez)

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