Two designs found in:
APPLICATION OF ATOMIC ENGINES IN AVIATION(PRIMENENIYE ATOMNYKH DVIGATELEY v AVIATSII)By G. N. Nesterenko. A. L Sobolev, Yu. N. SushkovMilitary Press of the Ministry of Defense of the USSRMoscow, 1957
as republished in translated form in:
HEARING BEFORE THESUBCOMMITTEE ON RESEARCH AND DEVELOPMENTOF THE JOINT COMMITTEE ON ATOMIC ENERGY CONGRESS OF THE UNITED STATESEIGHTY-SIXTH CONGRESSFIRST SESSIONON THEAIRCRAFT NUCLEAR PROPULSION PROGRAMJULY 23, 1959Printed for the use of the Joint Committee on Atomic Energy
« More within reach at present may be the creation of an atomic helicopter of large carrying capacity. In this design, vertical take-off and landing could be ensured with a reactor of considerably less power than in a regular aircraft with vertical take-off. The rotors of a helicopter, rotating at low speed, develop a sea-level thrust exceeding the weight of the helicopter with engines of a power below that of the rapidly rotating propellers of regular aircraft with vertical take-off. It is true that the extremely large lifting rotor interferes with high speeds in horizontal flight. When the rotating rotor is in the streamline flow of the ambient air around the rotating rotor in horizontal flight, the considerable difference in the speeds of the blade which, at the given moment, is moving against the airflow (forward) and that of the blade moving with the flow (rearward) causes a helicopter to begin losing stability at a speed of about 300 km/hr and creates the risk of nose-over and crash. The speed at which stability is lost is known as the critical speed of a helicopter; at present, it is impossible to exceed this speed.
Despite the comparatively low horizontal flying speeds and the limited critical speeds, helicopters built in the USSR have been widely applied thanks to their advantages on take-off and landing. The celling and range of modern helicopters with chemical fuels are small. The development of a helicopter with an atomic power plant will permit a significant increase in range and to extend the area of usefulness of helicopters in general. Heavy atomic helicopters will make it possible to carry freight and passengers over enormous distances, without need to refuel at airfields and, for that matter, without the need for airfields at all.
Even more attractive is the concept of an atomic convertiplane. This is a combined type of aircraft capable of taking off and landing vertically on small areas. In flight, the engines are able to rotate from the vertical to the horizontal position, and the convertiplane is able to develop significantly greater speeds in horizontal flight than the customary type of helicopter. The installation of atomic turboprop engines will make it possible for a convertiplane to fly any desired distance and to land at any point on the surface of the earth. It would be within the power of such an aircraft to carry an expedition from Moscow to the Antarctic or any other distant point on the surface of the earth within a single day, to fly around the world within 24 hours, and rapidly to transport passengers, emergency freight, mail, etc. to any desired distance. Moreover, this will require no intermediate landing fields, bases, or fuel depots, nor will the vast expenditures for the construction of intermediate landing fields be necessary or the cost of delivering hundreds and thousands of tons of chemical fuels to such airfields. »