Originally from an urgent requirement placed in 1958, in the 1960s it became clear that from the Ka-20 helicopter Kamov’s bureau, under chief engineer Barshevsky, had developed the standard ship-based machine of the Soviet fleets, replacing the Mi-4. Designated Ka-25 and allotted the new Western code name of “Hormone”, it was in service in at least five major versions, with numerous sub-types, including the Hormone A (ship-based ASW), Hormone B (over-the-horizon-targetting) and Hormone C (SAR). The air-to-surface missiles carried by the Ka-20 demonstrator did not appear on the Ka-25. The most obvious external differences between Harp and Hormone are a strengthening of the undercarriage, with the addition of a second strut, and a slight redesign of the vertical tail surfaces.
For the first time, Kamov designers fitted a rotary-wing aircraft with a mission avionics suite and weapons system which allowed the helicopter to navigate above water surface devoid of any reference points and fulfill the task of locating and destroying a submarine, both in manual and automatic mode. During prototype construction the designers - for the first time in OKB history - had to adapt it to the ship. The Ka-25's take-off weight increased 5-fold compared to that of the Ka-15 for an increase in dimensions by a factor of only 1.6. To reduce the rotorcraft's dimensions for hangar stowage during cruise, the designers created an electromechanical rotor blade folding system. This made the helicopter quite compact with the overall length with the blades folded was only 11.0m.
Powered by two GTD-3F turboshaft engines developed by V.A.Glushenkov, the Ka-25 first flew in 1961 with test pilot D.K.Yefremov at the controls. The Ka-25 was shown in Soviet Aviation Day flypast, Tushino Airport, Moscow, July 1961, carrying two dummy Air-to-Surface Missiles (ASMs not fitted to production aircraft), entering active service in 1965.
The engines are above the cabin and external mounting of operational equipment and auxiliary fuel leaves the interior uncluttered. Two 671kW Glushenkov GTD-3F turboshafts, mounted side by side above cabin, forward of rotor driveshaft, were on early aircraft and later aircraft have 738kW GTD-3BM turboshafts. There is independent fuel supply to each engine, and provision for carrying external fuel tanks on each side of cabin.
Equipment includes an autopilot tailored to deck operations and hover, twin-gyro platform and Doppler, duplicated HF, VHF, UHF, night lighting plus strobe, radio compass, radar altimeter, IFF and four passive RWRs.
Definitive Ka-25 prototypes incorporated anti-corrosion structure, cabin housing mission equipment. NII testing 1963-69. Rotors with lubricated hinges and aluminium blades with nitrogen-pressure crack warning, hydraulic control, alcohol deicing and auto blade folding. Forward-facing electrically heated inlets, lateral plain (no IR protection) exhausts, and rear drive to rotors and to large cooling fan for oil radiator served by circular aft-facing inlet above rear fuselage. Airframe entirely dural stressed-skin, mainly flush-riveted but incorporating some bonding and sandwich panels. Main fuselage devoted to payload; side-by-side dual control nose cockpit with sliding door on each side. Entry to main cabin is via a rearward-sliding door to rear of main landing gear on port side. The main cabin is 1.5m wide, 1.25m high and 3.95m long with sliding door on left and access at front to cockpit, and much of underfloor volume occupied by left right groups of tanks filled by left-side pressure connection. Cable fairing along right side of cabin. Short boom for tailplane with elevators and central fin and toed-in tip fins carrying rudders. Latter used mainly in autorotation, yaw control by pedals applying differential collective; mixer box holds total rotor thrust constant to reduce workload eg landing on pitching deck. Rotors not designed for negative-g. Two castoring front wheels (tyres 400x150) on vertical short strut with rear brace pivoted to fuselage to swing up and out to rear out of radar FOV. Two sprag-braked main wheels (600x180) each on vertical strut able to swing vertically on parallel V-struts pivoted to fuselage for same reason; landing loads reacted by diagonal shock retraction strut. Each wheel fitted for rapid-inflation buoyancy collar.
The Ka-25's flight test programme revealed that each type of warship had its peculiarities as far as pitching and rolling characteristics and airflow over the deck were concerned. Development of methods of helicopter landings on ships of different categories in daytime and at night with the ship under way and at rest, as well as water landing techniques, was accomplished by test pilots V.M.Yevdokimov and N.P.Bezdetnov. They conducted a large amount of test work with a view to evaluating the automatic engine control system, mastering single-engine piloting techniques and making engine-out landings in autorotation mode without a landing run.
The State acceptance trials of the Ka-25 were completed in 1968.
At its own initiative, the OKB made an attempt to build a civil derivative of the Ka-25 - the Ka-25K intended for cargo and passenger transportation and for flying crane operations. In 1967 the Ka-25K prototype was successfully demonstrated in the static display and in flight at the Le Bourget / Paris Air Show in 1967. It had an extensively glazed gondola under the nose (in place of the fairing for the search radar of the military version), with a rearward-facing operator's cockpit suspended under the forward fuselage for controlling the machine during operations with slung loads. A hatch was provided in the cabin floor for a cable to be lowered by winch. The cabin could take either a maximum load of 2000kg, 12 passengers or four stretchers and an attendant.
The engines, a pair of 900shp Glushenkov GTD-3 turboshafts, are mounted side-by- side forward of the transmission.
Design work on the Ka-25K was led by deputy chief designer I.A.Ehrlikh; the leading designer was S.V.Mikheyev. Although intended primarily as a flying crane, the Ka-25K can also be used as a conventional transport helicopter. In this role the chin gondola is removed, and the load is accommodated in the large hold. The floor has nine lash-down points for freight, which can be loaded through a sliding door in the left side.
Alternatively, up to 12 passengers can be carried on tip-up seats along the sides of the hold.
This variant was not put into production or service.
Ka-25Ts Hormone B
Two versions of the helicopter were designed in parallel: the Ka-25PL and the Ka-25Ts. The former is a submarine hunter equipped with weapons, the latter is a reconnaissance platform tasked with seeking out surface targets and designating them to the powerful artillery and rockert weapons placed on ships and at coastal bases. The airframe, rotor system and powerplant of these helicopters were designed with a maximum degree of commonality.
The Ka-25PL was exported to India, Syria, Bulgaria, Vietnam and Yugoslavia.
The Ka-25Ts ("Hormone-B") special electronics version provides over-the-horizon target acquisition for ship-launched cruise missiles including SS-N-3B (NATO "Shaddock") from "Kresta I" cruisers, SS-N-12 ("Sandbox") from "Kiev" and "Slava" class cruisers, SS-N-19 ("Shipwreck") from battle cruisers Kirov and Frunze, and SS-N-22 ("Sunburn") from "Sovremenny" class destroyers. "Kiev" and "Kirov" class ships each carry three "Hormone-Bs", other classes one; larger undernose radome (NATO "Big Bulge") than Ka-25BSh, with spherical undersurface; cylindrical radome under rear cabin for datalink; when radar operates, all landing gear wheels can retract upward to minimise interference to emissions; cylindrical fuel container each side of lower fuselage.
The four landing wheels are each surrounded by a buoyancy bag ring which can be swiftly inflated by the gas bottles just above it. The traditional Kamov layout with superimposed coaxial rotors redu-ces disc diameter, and automatic blade folding is provided for stowage in small hangars. The four -legged landing gear is specially tailo-red to operation from pitching decks, each leg having an optional quick-infl-ating flotation bag. The rear legs can be raised vertically, on their pivoted bracing struts, to lift the wheels out of the vision of the search radar always fitted under the nose.
NATO recognises two distinct variants of the Ka-25, and two radars have been identif-ied. The smaller type is carried by the Hormone-A variant on ASW missions; this model also has a towed MAD bird, dipping sonar, electro-optical sensor (and possibly others), and an optional right-side box of sonobuoys. Basically a ship-based and antisubmarine version operating from cruisers of the Kresta and Kara classes, Moskva and Leningrad carrier/cruisers and Kiev and Minsk ASW cruisers. The Moskva and Leningrad carrier/cruisers can carry about 18 Ka-25s; the larger Kiev and Minsk, about 30. Those of the Kara class carry three and the Kresta four (Kresta I) or five (Kresta II). Some models have been seen with different types of fairings. Some have big hatches beneath the fuselage, enclosing a bay for antisubmarine torpedoes, nuclear depth charges or other types of weapons.
A larger radar is fitted to the Hormone-B for electronic countermeasures, which is believed to be able to guide the SS-N-12 'Sandbox' cruise missile fired from friendly surface ships and, especially, submarines. Many other equipment items include a cylindrical container under the rear of the cabin and a streamlined pod under the tail.
Hormone-A has a search radar in a large fairing under the nose, and a towed magnetic anomaly detector (MAD), while a dipping sonar is housed in a compartment at the rear of the cabin. The helicopter also has electro-optical sensors.
The Hormone-B has no ventral loading doors.
The first ocean cruise of the Ka-25 took place in April-September 1967. The helicopter operated from the flight deck of the "Tobol" mothership, having logged 100 flight hours during the cruise. Deployment of helicopters on ships - both singly and in groups - was subjected to a very stringent testing on ships of various types, including the ASW cruisers "Moskva" and "Leningrad".
The Ka-25 ensured the navigation of ships in the Polar North, operating from the nuclear-powered icebreaker "Sibir". At the time, this task could only be tackled by the Ka-25 fitted with modern avionics, including a 360 degree search radar.
In 1982 Ka-25s were seen with-out flotation gear but with a long ventral box housing (it is believed) a long wire-guided torpedo. All Ka-25s have a large cabin normally provided with 12 folding seats additional to those for the crew of two pilots plus three sys-tems operators. About 460 of all variants were built by 1975, and the type continued to play an important part in Soviet naval operations in 1989, operat-ing from destroyers, cruisers, helicop-ter carriers (18 are believed to be car-ried on each of the two ships Moskva and Leningrad) and aircraft carriers (Kiev and Minsk each accommodate 16 'Hormone-A' and three 'Hormone-B' helicopters). Ka-25s were used aboard the Kresta and Kara class cruisers and from shore bases.
The type has also been exported for ship- and land-based op-erations.
The Hormone-C search-and-rescue helicopter is based on the 'Hormone-A' without the latter's mission equipment. The Ka-25C was utilised in vertical replenishment as well as search and rescue operations.
In all, 18 different modifications of the Ka-25 were designed and built, including the Ka-25PL basic ASW version, the Ka-25Ts over-the-horizon (OTH) targeting version, the Ka-25PS SAR version, the Ka-25BT mine countermeasures version, the civil Ka-25K flying crane etc.
Versions of the Ka-25 were in service with the armed forces of India (5), Russian Federation (65), Syria (5), Ukraine (18), Vietnam (5), and Yugoslavia.
12 Soviet Navy Ka-25BTs took part in minesweeping operations in the Suez Gulf.
Total production 1966-75 about 460.
As early as 1968, when N.I.Kamov was still alive, the OKB joined the competition of design studies for an Army assault/transport helicopter. The Kamov contender was a derivative of the Ka-25 designated Ka-25F featuring a redesigned fuselage and skid undercarriage. The armament comprised a 23-mm GSh-23 cannon with 400 rounds in a chin turret, six UB-16-57 rocket pods with 57-mm unguided rockets, six "Falanga" (Solifuge) anti-tank guided missiles, and bombs. The Ka-25F project received a positive appraisal from the Air Force's research institutes but lost out to the competing Mi-24 helicopter.
Ship-based anti-submarine helicopter, operated from former Soviet Navy missile frigates, cruisers, helicopter carriers and carrier/cruisers of "Kiev" class; major shortcoming is lack of automatic hover capability, preventing night and adverse weather use of dipping sonar. Replaced progressively by Ka-27PL ("Helix-A").
ASW version. I/J-band search radar with 360 degree scan in flat-bottom radome under nose, box for three vertical sonobuoys can be clipped aft on right side. Oka-2 dipping sonar at aft end of fuselage on centerline or (seldom fitted) APM-60 MAD sensor in pod on pylon under tail, large ESM receiver drum above boom with optional ADF sense blister immediately to rear, EO viewing port under boom, upgraded EW suite. Weapon bay 0.9m wide under centerline, initially with two bulged doors, later as largely external rectangular box, tailored mainly to two AS torpedoes (originally 450mm calibre) with wire reel on left side of fuselage; alternatively nuclear or conventional depth charges or other stores, max 1.9t. Replaced in CIS Navy by Ka-27PL, but serves with India, former Yugoslavia, Syria and Vietnam. ASCC "Hormone-A".
Equipped to tow minesweeping gear.
Version developed to replace Ka-25B as ship-based anti-submarine helicopter.
Search and rescue version with special role equipment, including hoist. No weapon bay, radar as BSh, normal equipment includes winch, 12 seats, provision for stretchers and aux tanks; options include nose quad Yagi antenna for homing receiver, ESM, searchlight and loudspeaker. Replaced by Ka-27PS.
Special electronics version, providing over-the-horizon target acquisition for ship-launched cruise missiles. ASW and ESM equipment and weapon bay omitted, internal fuel increased, OTH targeting and cruise-missile guidance radar with large elliptical (instead of rectangular) scanner reflector in bulged radome, secure data link to surface fleet including small antenna in vertical cylinder under rear centerline of fuselage.
Single civil prototype (SSSR-21110) 1966 with gondola under lengthened nose for controlling 2t slung load; elec-deiced blades, option 12 passenger seats. No ASCC name.
Engines: 2 x Glushenkov GTD-3F turboshaft, 662kW / 900-shp
Rotor diameter: 15.74m / 51.64 ft
Fuselage length: 9.75m / 32 ft
Fuselage width: 12.35 ft
Height: 5.37 m / 17.61 ft
Max take-off weight: 7100kg / 16,500 lb
Empty weight: 4100kg
Max speed: 220km/h / 113 kts
Cruising speed: 200km/h
Service ceiling: 3500m / 11,500 ft
Range: 400km / 217 nm
Internal payload: 1500kg
External payload: 2000kg
Engines: 2 x Glushenkov GTD-313M free-turbine turboshaft, 900 hp.
Main rotor diameter (both) 51 ft 8 in (15.75 m)
Fuselage length, about 34 ft (10.36 m)
Height 17 ft 8 in (5.4 m)
EmptyWeight: about 11,023 lb (5000 kg)
Maxi-mum loaded weight 16,535 lb (7500 kg)
Maximum speed 120 mph (193 kph)
Service ceiling, about 11 000 ft (3350 m)
Range with external tanks 650 km (405 miles)
Armament: one or two 400 mm AS torpedoes nuclear or other stores, internal.
Engines: 2 x GTD-3F turboshaft, 728kW
Rotor diameter: 15.74m
Fuselage length: 9.75m
Max take-off weight: 7200kg
Empty weight: 4765kg
Max speed: 220km/h
Cruising speed: 180km/h
Service ceiling: 3500m
KA-25Ts Hormone B