TYPE: Twin-turbine multipurpose military helicopter.
PROGRAMME: Originated from an urgent requirement placed in 1958. Prototype flew 1961; shown in Soviet Aviation Day flypast, Tushino Airport, Moscow, July 1961, carrying two dummy Air-to-Surface Missiles (ASMs not fitted to production aircraft); about 140 built 1966 to 1973, of which 65 remain operational with Russian Navy.
Ka-25B ("Hormone-A"): 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").
Ka-25BShZ: Equipped to tow minesweeping gear.
Ka-25Ts ("Hormone-B"): Special electronics version, providing over-the-horizon target acquisition for ship-launched cruise missiles.
Ka-25PL: Version developed to replace Ka-25B as ship-based anti-submarine helicopter.
Ka-25PS ("Hormone-C"): Search and rescue version with special role equipment, including hoist.
OPERATORS: Versions of the Ka-25 are in service with the armed forces of the following countries: India (5); Russian Federation (65); Syria (5); Ukraine (18); and Vietnam (5).
Following details apply to Ka-25PL:
DESIGN FEATURES: Use of folding three-blade coaxial rotors, requiring no tail rotor, and triple tail fins ensures compact stowed overall dimensions on board ship; engines above cabin and external mounting of operational equipment and auxiliary fuel leaves interior uncluttered.
POWER PLANT: Two 671kW Glushenkov GTD-3F turboshafts, mounted side by side above cabin, forward of rotor driveshaft, on early aircraft. Later aircraft have 738kW GTD-3BM turboshafts. Independent fuel supply to each engine. Provision for carrying external fuel tank on each side of cabin.
ACCOMODATION: Pilot and co-pilot side by side on flight deck, with rearward-sliding door on each side. Entry to main cabin is via a rearward-sliding door to rear of main landing gear on port side. Cabin large enough to contain 12 folding seats for passengers.
AVIONICS: Equipment available for all versions includes autopilot, navigational system, radio compass, radio communications, lighting system for all-weather operation by day or night, and hoist mounted above cabin door. IFF antennae (NATO 'Odd Rods') above nose and alongside central tail fin. Dipping sonar housed in compartment at rear of main cabin, immediately forward of tailboom, and search radar (NATO 'Short Horn') in flat-bottom undernose radome (diameter 1.25 m; 4 ft 1 in) on anti-submarine version, which can have a canister of sonobuoys mounted externally aft of the starboard main landing gear. Most aircraft have a cylindrical housing for ESM above the tailboom, with a shallow blister fairing to the rear of the cylindrical housing. Similar housing under rear of cabin for datalink equipment.
EQUIPMENT: Cylindrical container on each side of lower fuselage for markers, smoke generators or beacons. The port side container has been seen housing reconnaissance cameras.
ARMAMENT: Doors under the fuselage of some aircraft enclose a weapons bay for two 450mm ASW torpedoes, nuclear or conventional depth charges and other stores.
Jane's Aircraft Upgrades, 2001
A major milestone in the history of the naval combat shipboard and carrier-borne aviation was the Ka-25 helicopter. 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. This was the first dedicated combat helicopter designed in our country. The emergence of the Ka-25 was inseparably connected with the creation of the ocean-going Navy and with ensuring a reliable anti-submarine defence. It was designed for destroying atomic submarines. The State acceptance trials of the Ka-25 were completed in 1968.
All in all, 18 different modifications of the Ka-25 were designed and built, i.e. 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. The Ka-25PL was exported to India, Syria, Bulgaria, Vietnam and Yugoslavia. 12 Soviet Navy Ka-25BTs took part in minesweeping operations in the Suez Gulf.
For the Ka-25 the OKB developed a co-axial rotor system which was fully up to the latest achievements of scientific knowledge and to the technologies currently in use in the country. In subsequent co-axial helicopter types only minor changes were made to some elements of the rotor system to improve their design, production technologies and maintainability. The co-axial helicopter's aerodynamically symmetrical layout, coupled with the autopilot, sophisticated avionics suite and good handling qualities, enabled one pilot to fulfil long-endurance combat tasks under any weather conditions.
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. They achieved this by skilfully joining the efforts of a large number of cooperating enterprises. During prototype construction the designers - for the first time in OKB history - had to adapt it to the ship. One of the big problems was the fact that space on a ship is extremely limited and every square metre has to be used to the full. The company's specialists were well aware of that - and achieved an excellent result: 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 rotor-craft's dimensions for hangar stowage during cruise, the designers created an electromechanical rotor blade folding system. This made the helicopter quite compact; e.g., overall length with the blades folded was only 11.0m.
Even in retrospective, with our present-day knowledge, one cannot help feeling respect for the specialists and leaders who assumed responsibility for the implementation of the shipboard combat helicopter concept. Inevitably, there were sceptics at the time among Ministry of Aviation Industry, Air Force and Navy officials who though it impossible to cut through the interdepartmental bureaucratic red tape. Moreover, critics questioned the soundness of the co-axial helicopter layout. And yet, Kamov and his co-workers succeeded in constructing a rotorcraft that laid the foundation for a large-scale introduction of co-axial helicopters into service.
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 reliability of the Ka-25 during shipboard operations was amply demonstrated during numerous sea and ocean cruises in which Kamov specialists participated. 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 well-known ASW cruisers "Moskva" and "Leningrad". The Ka-25 passed this test with flying colours.
The Ka-25 ensured the navigation of ships in the Polar North, operating from the nuclear-powered icebreaker "Sibir". As a rule, ice patrol and guidance of ships through icefields was conducted under adverse weather conditions with limited visibility. At the time, this complicated task could only be tackled by the Ka-25 fitted with modern avionics, including a 360° search radar. It should be noted that the Ka-25 was the first extremely compact co-axial helicopter in the world to accommodate a powerful search radar and ensure its effective operation. The Ka-25 is undoubtedly a unique helicopter. Quite a few features put into effect by the OKB's specialists in the process of its design can be described as "a world's first".
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.
G.Kuznetsov "OKB Kamov - 50 years", 1999
To meet a Soviet Naval Air Force specification in the late fifties for an antisubmarine helicopter for ship or shore-based use, the Kamov bureau developed a helicopter powered by twin turbines installed side-by-side above the cabin, which drove two three-bladed coaxial, contra-rotating rotors as on their other aircraft. It was first seen at the Tushino air display in July 1961 and was assigned the NATO reporting name Harp. The prototype may have been designated Ka-20.
The Harp was characterized by a large radome under the nose and a fairing beneath the tail boom. The armament consisted of two fixed machine guns in the nose and two small air-to-surface missiles (probably dummies) at the sides of the fuselage. The production version, designated Ka-25, differed from the prototype only in minor details, and was assigned the code name Hormone. About 460 were built between 1966 and 1975. They have replaced the piston-engined Mi-4s in the Soviet Navy and Naval Air Force and a few have been exported to Syria, India and Yugoslavia.
NATO now recognises two distinct variants of the Ka-25. The first, designated Hormone-A, is 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). 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. Some models have been seen with different types of fairings, probably containing submarine detection apparatus. Some have big hatches beneath the fuselage, enclosing a bay for antisubmarine torpedoes, nuclear depth charges or other types of weapons (probably air-to-surface guided missiles).
The second variant of the Ka-25, designated Hormone-B, has special electronic equipment for target spotting and guidance of surface-to-surface missiles. It has a larger more spherical radome under the nose and a cylindrical radome under the rear of the cabin. This variant has no ventral loading doors.
The Ka-25 normally has a crew of two pilots and two or three ASW equipment operators, but it also has secondary capability for troop transport, as the cabin is large enough to accommodate 12. Each of the four landing gear wheels can be enclosed by an inflatable pontoon surmounted by flotation bottles. This guarantees buoyancy if the aircraft is forced to ditch.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
Urgent demand for ASW shipboard helo in 1958 won easily by compact Kamov coaxial design, with many other advantages. First prototype, called Ka-20, merely test vehicle for turboshaft engines mounted above fuselage, gearbox and rotors, shown Tushino 1961 with dummy missiles (ASCC reporting name "Harp"). 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, main cabin 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.
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. Cockpit for two pilots, options include 12 tip-up cabin seats, rescue hoist, external fuel drum each side as alternative to containers for cameras, flares, smoke floats or beacons. Total production 1966-75 about 460 in three versions:
Ka-25BSh: ASW version. I/J-band search radar with 360° 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, upgradedEW 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".
Ka-25K (probably Ka-25Ts): OTH targeting version for feeding guidance data to cruise missiles launched by surface warships and submarines. 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. ASCC "Hormone-B".
Ka-25K: Unrelated to previous, 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.
Ka-25PS: SAR and transport version, 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. Painted white/red. Replaced by Ka-27PS. ASCC "Hormone-C".
Bill Gunston "The Osprey's Encyclopedia of Russian Aircraft", 2000
- About 400 aircraft, known in the West as 'Hormone-A', '-B' and '-C, were built.
- The Soviet Union constructed four 'Kiev'-class carriers which used 'Hormones' for anti-submarine warfare.
- This family of helicopters began with the Ka-20 'Harp', first flown in 1960.
- Not normally armed, the Ka-25 can carry bombs, depth charges or torpedoes.
- Only the 'Hormone-B' has retractable landing gear which can be lifted out of the scanning beam of the nose radar.
- The 'Hormone' is cluttered inside and does not give its crew room to stand.