As the basis of the development of this single-rotor design are assumed the results of the theoretical, experimental and in-flight studies at OKB N.I.Kamov focused on the creation of the tail rotor or jet system of the compensation for reactionary torque of rotor and realization of azimuth guidance of single-screw helicopter. In the flight tests the research helicopter KA-26SS, equipped with the prototype of the tail boom of future helicopter with the jet system instead of two regular tail booms with the horizontal and vertical tail assembly, for these purposes was used.
The fuselage, tail boom, and chassis, of the carrier system KA-118 in appearance practically the same as in the single-screw single-engine helicopters of a similar class. A basic difference in the project was in the tail construction and the absence of traditional tail rotor. The absence of tail rotor leads to the decrease of aerodynamic drag of glider, which provides reaching high flight velocities (cruising and maximum). This single-rotor helicopter is less subjected to transverse vibrations, and it is also released of such deficiencies, connected with the presence of tail rotor as the possibility of entry into the vortex regime and the probability of destruction with hitting obstacles, that lead to flight accidents.
A basic difference in the helicopter KA-118 from the rotary-wing apparatus with the tail rotor consists of the power plant. It includes the main rotor gearbox, engine and their connecting shaft of transmission, and also ventilator installation with the drive from the main rotor gearbox. Ventilator installation is the source of excess air pressure, which along the channel in the tail boom will be given to the controlled jet nozzle. Tail boom is finished by vertical V-shaped tail assembly and fixed stabilizer.
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