From Canadian Power Wiki
The Kamov Ka-31 (NATO reporting name 'Helix') is a military helicopter developed for the Soviet Navy and currently in service in Russia, China and India in the naval airborne early warning and control role.
As with all Kamov helicopters except the Ka-60/-62 family, the Ka-31 has co-axially mounted contra-rotating main rotors. The airframe of the Ka-31 is based on the Kamov Ka-27. One visually distinctive feature of the Ka-31 is the large antenna of the early-warning radar, which is either rotating or folded and stowed under the fuselage. The second is the reduction of the bulky electro-optical sensory suite beneath the cockpit. The landing gear retracts in order to prevent interference with the radar.