Ka-27 "Helix-A" Helicopters (Unusual Aircraft Collection)

These strange-looking helicopters are Russian navy Ka-27s, which received the NATO reporting name "Helix-A".

The Ka-27 has the same contra-rotating rotor design of other helicopters designed by Kamov, such as the Ka-50 Black Shark and the Ka-226 Sergei.   Although it's more complex mechanically than traditional single rotor designs, there are several major advantages.   The biggest benefit of having two rotors turning in opposite directions is that the torque created by one rotor is cancelled out by the torque created by the other rotor.   When the rotor on an ordinary helicopter turns, the torque makes the body of the helicopter turn in the opposite direction.   Normally this is counteracted by the tail rotor pushing back to keep the helicopter's fuselage from spinning, however this uses up to 30% of the total engine power.

A helicopter like the Ka-27 which doesn't need a tail rotor can use this power to carry heavier loads, to climb higher or faster, or to fly forwards faster.   Another advantage of not having a tail rotor is that it's safer - quite a few helicopter accidents happen when the tail rotor hits an object or a person on the ground.   Another benefit is that the helicopter can be made more compact, allowing it to operate where there isn't much space, for instance landing on city streets, or on a ship.   This advantage is the major reason why Kamov was successful making naval helicopters, while other Russian manufacturers like Mil built land-based helicopters like the Mi-6 "Hook" and Mi-10 "Harke".