The Ka-25 (NATO name “Hormone”) is a naval helicopter produced by Kamov.
The Hormone first took flight in 1963 and was officially introduced in 1972.
The Ka-25 was developed from it’s predecessor, the Ka-20 “Harp”.
The primary role the Ka-25 was created for is anti-submarine warfare. The need for anti-submarine helicopters was high in the 1950s on both the Soviet and US sides of the cold war.
The compact design of the Ka-20 was seen as an ideal springboard and certainly much faster than designing something from scratch. It’s compactness was crucial to the requirement for a ship-borne helicopter that would operate from the deck.
Early demonstrators lacked many of the key elements such as corrosion resistance, but were needed quickly for proof-of-concept purposes. The first complete prototypes were equipped with many advancements for the time, such as anti-corrosion, aluminum alloy rotor blades, automated blade folding and, hydraulic controls and alcohol de-icing.
This was a twin-engine helicopter, which is a common design for overwater operations. These were free-turbine units that had electrically de-iced inlets and plain lateral exhausts with no efforts to mask their infrared signature. They both drove the main gearbox directly as well as the cooling system for said gearbox.
For the time the materials were also quite advanced. It used a stressed-skin duralumin skin with rivets that were flush. There was also limited use of bonded honeycomb sandwich panels.
Notably, as with almost all Kamov helicopters, the Ka-25 used a coaxial twin rotor design, which means that it did not require an anti-torque rotor. Instead, the tri-fin tail boom acts as a stabilizer when dipping sonar equipment or during autorotation.
While production only ran from 1965-1977, the total number of units built is estimated at an impressive 460.