Design work on the Mi-4 helicopter started in the second half of 1951 and the aircraft was flown in prototype form in August 1952. In appearance it closely resembled the contemporary Sikorsky S-55, but in terms of size and performance it equated with Sikorsky's later S-58. The Mi-4 was already in Soviet Air Force service by August 1953, when it was first seen publicly at the Tushino Aviation Day display, and it has since become the most widely built of all Soviet helicopters. Production is believed to have ceased around 1964, by which time several thousand had been built both in the Soviet Union and in China.
The Mi-4 was produced initially as a troop and assault transport helicopter for the Soviet armed forces. This version is characterised by circular cabin windows and a ventral fairing in which an observer can be stationed if required. Alternatively an additional fuel tank can be fitted in this position. One major difference between the Mi-4 and the S-55 is that the former has clamshell rear loading doors through which a maximum internal payload of 1600kg can be admitted. Typical military loads of the Mi-4 include 14 fully equipped troops, a GAZ-59 command vehicle, a 76mm anti-tank gun or 2 motorcycle combinations. Military Mi-4's have been exported to a number of air forces in the Soviet bloc, among the largest users being India, which has sixty, and Cuba, which has twenty-four.
From 1964 two civil versions of the Mi-4 were also built in considerable numbers. These were the Mi-4P (Passajirskii == passenger) and the Mi-4S (Selskokhoziaistvennii = rural economy). The Mi-4P is the standard version for Aeroflot, carrying 11 passengers normally or up to 16 in high density seating or, in the ambulance role, 8 stretchers and a medical attendant. The Mi-4P is distinguished by having square cabin windows, wheel spats and no ventral fairing; 100kg of baggage can be carried in addition to the normal passenger complement. The Mi-4S is normally used for agricultural operations, when it can be fitted with a 1000kg dust hopper or a 1600-l tank holding pesticide or fire-fighting chemical. All versions of the Mi-4 have provision for fitting inflatable pontoons in addition to the wheeled landing gear. A stripped-down Mi-4 established a number of speed-with-payload and payload-to-altitude records in 1956, and in more recent years both military and civil Mi-4's have performed a considerable amount of useful work in the Polar regions, their tasks including ice patrol and geological survey.
K.Munson "Helicopters And Other Rotorcraft Since 1907", 1968
The Mi-4 was the second Mil project to enter large-scale production. Several thousand have been built in both military and civil configurations, operating in the Soviet Union and various other countries. It has now been replaced in its original transport and antisubmarine roles by more modern, turbine-powered machines but many are still in service with support units.
The Mi-4 was first seen in public in August 1953, but it had made its first flight and entered production the year before. The first few years' output was exclusively for military use. In the basic version, NATO reporting name Hound-A, the Mi-4 is a transport helicopter, with a crew of two and provision for observer in a gondola beneath the forward fuselage. The engine is installed in the nose, leaving ample room in the cabin to accommodate up to 14 combat equipped troops, small vehicles or 1,600kg of supplies. Access to the cabin is facilitated by rear loading doors. A lot of these aircraft have been delivered to the VVS and a close support version was also produced, with a machine gun at the front of the gondola and rails for air-to-surface rockets on either side of the fuselage. The Mi-4 has also been used by the Soviet Naval Air Force for antisubmarine duties. In this version (Hound B), it has an under-nose search radar in front of the gondola, and a dipping sonar, which is stowed at the rear of the fuselage beneath the root of the tail boom when not in use. Another variant, designated Hound C, is designed for ECM and has broad lateral antennae and jamming apparatus. The Hound-A has been exported to virtually all the countries of the East European bloc and a number of others worldwide. Large numbers have also been produced in China.
A civil variant of the basic Mi-4 version has been produced for Aeroflot, for general use and freight transport; this was followed by the Mi-4P for passenger transport, which lacks the ventral gondola, and has a better finish and rectangular side windows in place of the round, military type. The Mi-4P, which went into regular service with Aeroflot in November 1958, can carry up to 11 passengers or eight stretchers and a medical attendant for ambulance duties. The special agricultural version is designated Mi-4S. It can carry a container in the cabin holding 1,000kg of solid insecticide or 1,600 liters in liquid form, plus dusting or spraying equipment. Although less common than the military one, the civil version has been used in various East European countries.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
Design of the Mil Mi-4, a conventional helicopter with about four times the capacity of the Mi-1, was initiated in 1951 and the first example was flown during May 1952. Produced initially for use by the Soviet armed forces in assault and troop transport roles, the Mi-4 'Hound-A' has clamshell rear doors to simplify the loading of vehicles and freight; alternatively, the cabin can accommodate up to 14 troops. Military Mi-4s are recognisable easily by having a ventral gondola which was intended originally for a navigator or observer, but can also house avionics equipment. Produced in large numbers for Soviet military use, the Mi-4 was also exported for service with more than 20 foreign air arms. A number remain in current use, and in more recent years conversions have been reported in Soviet use for ASW ('Hound-B') armed close support and ECM ('Hound-C'). From 1964 production of civil versions was initiated and combined civil/military production by Mil was estimated at 3,500 when production terminated in 1969. All versions can be equipped with inflatable pontoons which, mounted so that the landing wheels project below them, can be used for amphibious operations. The Mi-4 was also manufactured under licence in China, a total of about 1,000 built when production ended in 1979, and of which approximately two-thirds were for civil use.
Mi-4: basic military production version with clamshell rear doors; this configuration adopted also for civil cargo versions
Mi-4P: civil transport version used extensively by Aeroflot and seating eight to 11 passengers in furnished cabin; current major use in ambulance configuration carrying up to eight stretchers and a medical attendant
Mi-4S: basically an agricultural version with a large chemical container in the main cabin, but used also for fire-fighting operations Z-5: Chinese military version of the Mi-4, this being in service with both the army and navy
Xuanfeng: Chinese name for civil version of the Mi-4, at least one of which is flying with the PT6T-6 twin turbine engine
D.Donald "The Complete Encyclopedia of World Aircraft", 1997
Second challenge to OKB, this was dramatic leap in capability and resulted from Kremlin meeting of constructors September 1951 at which Stalin insisted on sudden great advance in Soviet helicopters. All backed away except Mil and Yakovlev; on following day these two were given one year to design, build and fly prototypes, Mil’s assignment being single-engined 12-passenger machine. Mil had prepared outline design beforehand which he produced at Kremlin; basically scaled-up rotors of Mi-1 with added fourth main rotor blade, and S-55 configuration. Rotor axis inclined forwards 5°. Fuselage light-alloy semi-monocoque with extensive use of magnesium. Engine installed at 25° in nose accessible through upper/lower hinged nose doors and left/right hinged side doors. Cooling fan and centrifugal clutch immediately to rear of engine, with inclined shaft between pilots to main gearbox. Separate cooling systems for oil radiator and hydraulics for flight control. Straight tail boom with adjustable stabilizers, deep skid/bumper and narrow fin carrying tail rotor on right, with three bakelite-ply blades. Main fuel tank welded aluminium, 960 lit, behind gearbox; optional aux tank 500 lit in hold or externally. Quad landing gear with pneumatic-braked mainwheels and castoring nosewheels, optional pontoons for water. Main hold 4.15m long, about 1.8m square section. Max internal load 1740kg including small vehicles loaded through left/right rear doors and clip-on ramps. Slung load to 1.3t. Alcohol de-icing of blades and windscreens as on Mi-1.
First flight delayed several weeks by blade flutter in ground-running from 14 April 1952. First flight May, Vinitsky assisted by Brovtsev. Remarkably few subsequent snags and NII testing completed before end of year.
Main production model military Mi-4T, with increased-diam main rotor, aluminium cargo floor, bulged circular windows with gun ports, ventral gondola for nav/observer, and tactical avionics. From 1954 Mi-4P civil variant with large rectangular windows, spatted wheels (often later removed), no gondola, and interior heated, soundproofed and equipped for ten passengers (each 20kg baggage)/wardrobe and toilet. Small batch of Mi-4L (Lyuks, de luxe) six-seaters. Some civil and mil equipped for casevac with eight stretchers and attendant. SKh multi-role ag variant for spraying (1600 lit) with wide sparaybars, dusting (1t) or forest fire-fighting.
Urgent development of improved metal blades 1954-60 culminating in dural blade with extruded spar and honeycomb box trailing sections. Magnesium fuselage skins replaced by aluminium, and better flight control and avionics.
April 1956 various records including 500km circuit at 187.254km/h, and later 1012kg lifted to 7575m. Main production continued with Mi-4A assault transport with A-12.7 with 200 rounds, 1740kg cargo or 14 troops; Mi-4S Salon VIP version (7315kg max) and, first flown 1962, Mi-4PL ASW version for AV-MF with four 250kg or six 100kg A/S bombs, chin radar (also fitted to various military variants), short but deeper gondola, towed MAD at rear and sonobuoys on external rack on right side. High altitude (2-speed supercharged) model 1965, Mi-4M tactical variant with gun turret and air/surface rockets 1968, and EW platform first seen 1977 with two pairs of lateral Yagi arrays and other aerials mainly for communications jamming. Production ceased 1964 at c3,200, of which c700 exported to 6 countries, plus 545 licence-built in China from 1959 as Z-5 with many changes. ASCC name "Hound".
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
NATO reporting name: Hound
TYPE: General purpose helicopter.
PROGRAMME: The Mi-4 was standard equipment in the Soviet armed forces, Aeroflot and with many other civil and military operators throughout the world. Several thousand were produced but only about 20 remain in service with the armed forces of the RFAS, fulfilling liaison duties.
Mi-4: Basic military version with underfuselage gondola for navigator. Production said to have started in 1952. Civil freight version is generally similar, with double clamshell rear-loading doors. Soviet films of military exercises, released in 1968, showed a close support version of the Mi-4, armed with a gun in the front of the underfuselage nacelle and air-to-surface rockets.
Mi-4L: Small batch of six-seat de luxe version; some equipped for medevac with eight stretchers and attendant.
Mi-4P: Passenger-carrying version, with seats for 8 to 11 passengers; entered service on Aeroflot's Simferopol' to Yalta route in the Crimea in November 1958. As an ambulance it can carry eight stretchers and a medical attendant. This version has square windows instead of the circular windows of the military version and has no underfuselage gondola. The wheels are often fitted with spats.
Mi-4S: Agricultural version. Large chemical container in main cabin, capacity 1,000kg of dust or 1,600 litres of spray. Container is fitted with mechanical distributor for dry chemicals, which are spread through bifurcated ducts by hydraulically actuated fan in duct which replaces the military ventral gondola. Liquids are sprayed from bars mounted aft of mainwheels. Rate of spread is up to 18 litres or 20kg/s, with swath width of 40 to 80m, at forward speed of 60km/h.
All versions to be fitted with two large inflatable pontoons, mounted so that the wheels of the landing gear protrude slightly beneath them, for amphibious operation.
In Spring 1965, details were given of a series of high-altitude tests made with an Mi-4 fitted with two-speed supercharger and all-metal main rotor. After engaging the second speed at 4,650m, the aircraft climbed to 8,000m. It was also operated at an airfield height of 5,000m.
DESIGN FEATURES: Four-blade main rotor with hydraulic servo-control and three-blade anti-torque rotor at starboard side of tailboom.
STRUCTURE: Main rotor blades were originally tapered, with steel spars and plywood covering; since 1961 they have been of constant-chord all-metal construction. All-metal semi-monocoque structure of pod and boom type, with provision for clamshell doors under the tailboom attachment point in freight-carrying version.
LANDING GEAR: Non-retractable four-wheel type. All units fitted with shock-absorbers. Nosewheels are fully castoring. Spats optional. Provision for fitting pontoons.
POWER PLANT: One 1,700hp ASh-82 V 18-cylinder air-cooled radial engine mounted in fuselage nose.
ACCOMMODATION: Crew of two on flight deck, with underfuselage gondola for observer in military version. Commercial version carries 8 to 16 passengers in heated, ventilated and soundproofed cabin, with door at rear on port side. Aft of cabin are a toilet, wardrobe and compartment for 100kg of baggage. Ambulance version carries eight stretchers and attendant. Freight version has clamshell rear doors. Military version carries up to 14 troops, 1,600kg of freight or vehicles such as a GAZ-69 'Jeep', 76mm anti-tank gun or two motorcycle/sidecar combinations.
ELECTRONICS AND EQUIPMENT: Radio and instrumentation for night and bad weather flying are standard equipment.
SYSTEMS: Liquid leading-edge de-icing system.
Jane's Helicopter Markets and Systems
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Technical data for Mi-4
Crew: 2, engine: 1 x ASh-82V pistone engine, rated at 1250kW, rotor diameter: 21.0m, length with rotors turning: 25.02m, height: 4.4m, fuselage width: 2.0m, take-off weight: 7550kg, empty weight: 5100kg, max speed: 185km/h, rate of climb: 5.6m/s, service ceiling: 5500m, hovering ceiling: 2000m, range with max fuel: 500km, payload: 1600kg