Coaxial helicopter propellers are not often used in modern helicopter engineering. The only helicopters with this propeller design, in serial production - Russian Ka, including the famous Ka-52 Alligator. But what explains the rarity of using a coaxial screw circuit?
As is known, the most common in world and domestic helicopter industry is a scheme with one main rotor and an open tail rotor, which is intended to compensate for the reactive moment from the rotor. After all, he "spins" the helicopter in the direction, opposite to the rotation of the rotor.
The undoubted advantage of the steering scheme is structural simplicity, relatively low maintenance and repair costs. But losing the tail rotor, the helicopter loses control and crashes.
Coaxial screw pattern less common, but its use allows you to make the helicopter more tenacious and, respectively, more adapted to combat missions. Interesting, that the use of a coaxial circuit is the result of the work of Soviet and Russian designers.
The first domestic coaxial helicopter was introduced in 1948 year. It was a Ka-8 "Irkutian", released by the Kamov design bureau in triplicate. Then released Ka-10 and Ka-15. The last helicopter became the first product of Kamov Design Bureau, entered into serial production. So in the Soviet Union began the serial production of helicopters with a coaxial propeller scheme.
Unlike the classic single-screw design, putting a coaxial circuit into practice is much more difficult. Experts call it one of the most outstanding achievements of Russian helicopter industry. But the complexity in the design and execution is offset by the undoubted advantages of the coaxial scheme.
At first, coaxial helicopters are smaller, high compactness, which increases angular speeds and makes the machine more maneuverable. In particular, such a helicopter is capable of performing “funnel” figures, "Oblique loop", which can not carry the helicopters of the classical scheme with the tail rotor.
Secondly, coaxial helicopters have greater combat survivability due to the lack of a tail rotor with its gearbox and drives. At the same time, it is easier for a helicopter to maneuver near the ground or other surface, on which he can sit.
Thirdly, coaxial helicopters have higher load factor, i.e. the ratio of payload to total flight weight.
Such characteristics of coaxial helicopters determined the specifics of their use.. Coaxial helicopters are much more efficient as deck-based helicopters, they can be used in mountainous regions with their difficult meteorological conditions. So, Ka-50 was actively used during the hostilities in the North Caucasus.
In the same time, coaxial helicopters, for all their undeniable merits, there are certain disadvantages. The most significant minus for their mass production is the high cost.. According to experts, Mi-28 is inferior to coaxial Ka-52 in almost all characteristics, but the cost of the latter is much higher, and it's about millions of dollars.
Experts also note the complexity of the coaxial helicopter control system, significant vibration risk, insufficient road stability, danger of collision of blades rotating in opposite directions.
Currently, the main modern coaxial attack helicopter attack helicopter is the Ka-52 Alligator. These combat vehicles have been successfully tested in Syria., showing good performance in an unusual climate for Russia. Helicopters Ka-52 are part of the army aviation, and deck aviation of the Russian Navy.
Ilya Polonsky
