FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1951
1951 - 2537.PDF
FLIGHT, 21 December 1951 ATOMIC-POWERED AIRCRAFT Some of the Problems now being Tackled in America: Basic Research Completed THE American Air Force and the Atomic EnergyCommission recently issued a statement concerningatomic-powered aircraft. This announced that the basic research on an atomic engine for aircraft had been completed, proving the feasibility of the project, and deter- mining its general design. But, continued the report, there were still some vital, complex problems which remained to be resolved before such a power plant could be made, installed and flown. At the. General Electric Company's Lockland, Cincinnati, gas-turbine factory, efforts were being made to find the solutions, and contracts had been awarded to the company for the subsequent manufacture of the atomic engine. Some details of the unit have been given by Dr. Miles C. Leverett, who has been working on the project since its early days. Fuel, in the form either of uranium-235 or plutonium-239, would be distributed throughout the reactor, and tubes or pipes would ensure the flow of coolant which captured the reactor's heat—its usable form of energy. The absorbing rods for controlling the reactor, continued Dr. Leverett, could be inserted or withdrawn; if, in their original position, the rods were absorbing that number of neutrons which made the reactor most critical, i.e. with the power neither rising nor falling, then withdrawal would create a slight excess of neutrons in the reactor, and the power would start to increase. Deeper insertion of the rods would decrease power, since more neutrons would then be absorbed and, as a result, the chain reaction would gradually die. Exact control of the reactor action was vital, first because there was a remote possibility of the unit becoming a low-grade atomic bomb, but, more important, because it might build up such heat that it could melt or disintegrate. Another problem was the best way of using the reactor heat; one method under consideration was the adoption of turbine- driven propellers actuated by steam generated in the reactor. A second suggestion was that the reactor should directly or indirectly take the place of the combustion chamber of a conventional turbojet engine. Variation of one of these basic ideas would probably be used for heat-utilization in the final nuclear engine. Combating Radiation Shielding the aircraft's crew from the gamma and beta rays given off by the reactor was a considerable problem. The requirements, said Dr. Leverett, were dictated by the two basic radiations which it was desired to stop. The neutrons were slowed down most effectively by light atoms, and for this reason a satisfactory shield would contain hydrogen atoms. Gamma rays, on the other hand, were degraded in energy and were stopped by heavy elements, such as lead. It was clear that the most suitable combination would be to have both light and heavy elements arranged in the most strategic fashion. The solution to this problem was very complicated. It was further stated that another major headache was radiation damage to substances other than the human anatomy. Constant exposure to radiation caused some of these substances (which might be used as coolant for the engine) to lose their ability to conduct heat, and some just decomposed. Even outside the area of the most intense radiation, ordinary oil or grease would become like tar, or possibly solidify. Electrical insulation also broke down and disintegrated after long exposure to radiation. Concerning the use of fuel. Dr. Leverett said that the chain reaction would continue in the reactor only so long as there was present a certain minimum quantity of fissionable material known as the critical mass. As soon as the reaction had consumed so much fissionable material that the mass dropped very slightly below the critical mass, the chain reaction died and could not be started again with adding more fissionable material. This made it necessary to remove the remaining fuel from the reactor, purify it and prepare it for re-use. With reference to actual fuel weight, it was stated that one pound of uranium-235 will, on undergoing fission, liberate heat equivalent to the energy liberated by burning 1,700,000 pounds of petrol. Thus, fuel economy was of no concern to the pilot of an atomic-powered aircraft. It had frequently been explained that such a machine could fly round the world non-stop for about as long as the crew could withstand the strain of the flight. For a flight round the world at the Equator, and under cover of darkness, the aircraft would require a minimum top speed of 1,000 m.p.h., whilst, at the latitude of the United States, such a mission would require a speed of about 750 m.p.h. Structural problems of an airframe for an atomic power plant were also reviewed by Dr. Leverett. It was probable that the aircraft would have swept-back wings, and be of a size between those of the Boeing B-50 and B-36. It was estimated that the necessary shielding apparatus for the crew would weigh between 50 and 100 tons, but this would take the place of the fuel load weight on a conventional machine, at least as far as size and strength in design were concerned, since the atomic fuel would weigh only a few pounds at most. Weight Distribution The existence of a large concentrated weight, such as the shield and the reactor, and its accommodation, made necessary considerable structural re-design of the airframe. In conventional aircraft, the weight was usually distributed over the wing and throughout the fuselage; concentrating the weight in the fuselage greatly increased wing bending moments. Although the aircraft would require heavy forgings inside the wing and fuselage structure, the outward appearance of the machine would not necessarily be affected. It had been suggested that the shield itself could be used to give strength to the airframe; this would appear to be a potential solution offering so many advantages as to make it virtually certain to be adopted. The very fact that only a small amount of the atomic fuel was consumed in flight meant that the gross landing weight of a nuclear aircraft would be approximately the same as the take-off weight. This gave rise to a new set of possibly serious problems. Firstly, the landing gear had to be strong enough to take this higher landing weight. Secondly, the landing speed was increased, and a possible change in landing attitude might necessitate further modi- fications in the landing gear, or in the tail clearance-angle requirements. Recent extensive research on high-speed flying-boat hulls carried out by Cpnvair, the company making the first atomic aircraft's airframe, might offer a solution to this problem, by the possible conversion of the design from a land-based to a water-based type. TURBINE FUELS BECAUSE the steadily increasing demand for aviation kerosineis likely to lead to a world shortage, the use in the near future of low-grade petrol in many jet aircraft is foreseen. No technical difficulties are likely to arise, though slight reduction in perform- ance is to be expected. In America, where petrol is frequently used in place of kerosine as jet fuel, an improved blend, bearing the designation JP-4, is shortly to be introduced by the Air Force. It will help to reduce the risk of boiling at high altitude from which the current higher- vapour-pressure fuel is said to suffer. The main disadvantage of any such change lies in increased fire-risk, though recent news reports do suggest that crash-fires, at any rate, are almost as likely with kerosine as with petrol. In many instances, no doubt, ignition of lubricating oil—always a serious factor in initiating crash-fires—has been responsible.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
