Antonov An-70
a new generation tactical transport.

Polish article

Although plagued by lack of investment and the loss of the first prototype in a mid-air collision, the An-70 is proving to be a highly capable transport aircraft. So much so, as Paul Duffy reports in his analysis of Ukraine's latest aircraft, it is being considered by Germany for the Medium Military Transport Aircraft role.

"Antonov first entered the military transport scene in 1956 with its twin turboprop An-8. This was designed to carry either a tank or paratroops, and to offer the Soviet forces a similar capability to that of the Fairchild C-119, but less than that of the then new Lockheed C-130 Hercules. The An-8 soon proved itself, but a relatively small production of just 150 followed because the Soviet military authorities quickly sought a larger aircraft more capable of matching the performance of the growing numbers of Hercules entering service with the US Air Force and its allies. A little more than a year after the first flight of the An-8, its larger brother, the four-engined An-12, flew. This aircraft went on to become the standard military transport of the Soviet Union and its allies. It entered service in 1959, and remains in operation in substantial numbers even in the 21 st century. More than 1,300 were built in Russia and Uzbekistan.

Antonov has specialized in military transport ever since, and many of its aircraft have also been developed into civil versions. Based in the Ukrainian capital, Kiev, it is the only major design bureau of the former USSR to be situated outside Russia. While the Ukraine government is experiencing similar financial problems to those evident in Russia and the other former Soviet countries, it has allowed Antonov a greater freedom to find answers to its own problems. The company's general designer and chief executive, Piotr Balabuev, has done just that by using the fleet of aircraft the bureau inherited from the break-up of the Soviet Union. Most of these were the company's own design cargo aircraft, including six An-I 24-100s, the world's largest production aircraft, plus some An- 12s, -22s, -24s, -26s, -32s, -72s and the An-225, the sole example of the world's largest aircraft. With these, Antonov began to build a cargo airline in the late 1980s, working closely with the UK's Air Foyle. The commercial operations of the fleet have provided Antonov with the resources to design and build three new aircraft types which are currently in the flight test stage The other form Soviet design bureaux have not been as progressive: only Beriev, with the Be-200, and Tupolev, with the Tu-334, have managed to fly new transport types in the same period.

One of the new Antonovs is the An-70, (the other two are the An-38 and the An- 140) and both the aircraft and its story are remarkable.

It started when the Soviet Air Force (VVS) began to look for an An- 12 replacement in 1979. By then, the An- 12 had already been in service for 20 years. Production in the USSR had been completed by 1972, although a Chinese version, the Yuri Y-8, was produced until the mid1990s. About 1, 100 military versions of the An- 12 were delivered to the Soviet Air Force and the air forces of client states. A number of civil freighters were also delivered to Aeroflot and other airlines in countries with political and economic ties to the USSR.

Antonov was one of three design bureaux asked to submit proposals to the Soviet Ministry of Defence for the replacement, and the bureau's general designer Oleg Antonov asked his deputy Vasili Teplov to become chief designer for the work. However, detailed design requirements were not issued until 1987: Antonov's successor, Piotr Balabuev, confirmed Teplov as project leader.

Stringent requirements were laid down: the 30 years since the An-12 had been conceived had seen considerable advances, not only in aviation technology - annoured tanks and personnel camers had also grown in size, weight and capability. The new specifications required the aircraft to carry some 300 soldiers, or to airdrop 110 paratroops. It had to be able to lift bulky cargoes, including modem tanks, artillery and other military equipment and to have the ability to land and take off from short, soft strips. Short take off and landing (STOL) capability was regarded as essential. It was also required to have operating economics to a standard appropriate for the 2 1 st century, the first time this requirement had been sought in a Soviet military aircraft programme.

The new aircraft would also need to be adaptable in order to fill possible roles as a tanker, airborne early warning aircraft, and for patrol operations. From the start of 'serious' design, the Antonov team saw it as a possible replacement not only for the An- 12, but also for the C- 130 and the Transal I C. 160.

Configuration

Teplov and his team began by adopting a similar concept to that of the An- 12: a four-engined high wing design was considered necessary to allow operations from unpaved runways, including the grass strips or dirt tracks that would be needed for battlefield support. A wide body was dictated by the need to carry modem military armored vehicles, but the choice of engines was more difficult. For the first few years, money for the new aircraft came from the Soviet Union's central budget. This allowed a detailed study to be carried out in conjunction with a wide group of Soviet research bodies, and helped to decide on turboprops when research showed that the propeller wash could be used to advantage for short landings.

The research institutes involved in this work included the Central Aero and Hydrodynamics Institute (TsAGI), which carried out the detailed aerodynamic studies for the programme. The Central Institute of Aviation Motors (CLAM) helped to design and develop the engine requirements, and the Stupino Propeller Design Bureau (now called Aerosila) was given the task of designing the propellers and gearboxes for the new Antonov. An earlier Stupino design had allowed the Tupolev Tu-95 Bear and the world's first wide-body, the An-22, to fly at speeds considerably higher than was thought possible by Western specialists of the time. This was achieved by developing a gearbox that reduced the rotation rate, and by widening the chord of the propeller blades.

Materials were developed by other researchers: the All-Union Institute of Aviation Materials (VIAM) worked on the new composites and glass-fibers needed, while the All-Union Institute of Light Alloys (VILS) developed solutions to the metallic requirements.

Work undertaken by the Siberian Scientific Research Institute (SiBNIA) confirmed that the An-70 would be able to meet its operational life of 45,000 flight hours or 15,000 cycles.

Aerodynamic design

Teplov and his team teased that the aircraft's success depended on designing a wing that would be efficient at the relatively high cruise speed of Mach 0.68/0.70, whilst being capable of generating the high lift necessary for STOL operations. The early work was carried out in Kiev, using Antonov's own relatively basic wind tunnels. As the design was developed, the team transferred to Zhukovsky, near Moscow, where it could use TsAGI's facilities, which include some of the most advanced wind tunnels in the world. Using 22 purpose-built wing models, more than 12,000 hours of tests took place there before the final design was selected. Good low-speed performance has been achieved by the incorporation of an advanced multi-section flap and slat system.

TsAGI's wind tunnels were also used to develop the new Aerosila contra-rotating propeller, the l4ft 9in (4.5m) diameter SV-27. Each propeller has eight blades on the forward shaft, which turns anti- clockwise, and six on the rear shaft, which rotates clockwise.

A wide propeller chord, combined with a suitable engine gear ratio, ensures that the maximum airspeed required is achieved without the tip speed exceeding the critical Mach number for prop noise. The contra-rotating system also gives an excellent balance, and there is no tendency for asymmetric swing on takeoff or landing. The propeller pitch is fully variable and may be feathered.

A close study of the propeller wash, or 'propwash', showed it could be used to advantage for short field operations. With the propellers mounted just forward of the wing, a 'Coanda effect' results. This allows the flaps to maximize low speed lift, and with a glide slope angle of up to eight degrees, the threshold/ final approach speed drops to about 95kts (176km/h). Touchdown speed is as low as 76kts (140km/h). For a normal landing, final approach is at 132kts (245km/h). While the nominal full flaps setting is 65*, the outer portion lowers to 80' to take full advantage of the propwash. The propellers were deliberately mounted higher than the fuselage doors to allow an unimpeded exit for paratroop operations.

As was usual for the manufacture of large wings in the Soviet Union, that of the An-70 was constructed in the Tashkent aircraft production factory (TAPO). This had been the production entre for the An-22, and manufactured wings for-the An- 124 and -225. It is also where the Ilyushin II-76MF will be produced, which is expected to become a major rival to the An-70.

End of government investment

The Soviet Union was dissolved in December 1991 and with it ended the government's investment in the An-70 programme. However, most of the companies working on the project decided to continue as a partnership, and none have withdrawn.

The Soviet government selected the Ivchenko Motor Design Bureau, at Zaporozh'ye in the Ukraine, to develop the new engines. Led by Fiodor Muravchenko, it is now called the Progress Machine Building Design Bureau and works closely with the Motor Sich Zaporozh'ye production factory. One of the engine's requirements, which was satisfied early in the test programme, was that fuel bum should be at least 30% less than that of the best turbines in service at the time. Other partners include: Progress; Aerosila, the propeller designer, Elektroavtomatika, designer and producer of the avionics package; and Ufa Motors, the engine control manufacturer.

The VVS requirement called for a five-crew cockpit to include a pilot, co-pilot, engineer, navigator and radio operator. Elektroavtomatika developed a panel to give flight data, engine, system, and instrument information on six 77/8in (200mm) square screens. When Germany began to show interest in the An-70 for the Medium Military Transport Aircraft (MMTA) role, instead of the pan-European Future Large Aircraft (FLA) now being offered by Airbus as the A400M, Antonov took another look at the cockpit. For the MMTA role, the aircraft has been provisionally designated the An-7X, and has been audited for the German government by DASA. Its specialists concluded that it should not be difficult to reconfigure the cockpit for a three-crew operation, or even for two. It also concluded that there would be little risk in adapting the An-70 to meet the MMTA requirements. DASA also suggested that by adopting western production processes, weight savings of up to three tonnes could be achieved with a resultant increase in payload.

Flight control system

Antonov was the first aircraft designer/ manufacturer to introduce a fly-by-wire system on a transport aircraft; the An-124 Ruslan which made its first flight in 1982. It was, therefore, a logical choice for the control systems on the An-70, so Teplov's team developed what they term a 'second generation' system for the new transport. The system is not exactly the same as that used in the West, but in DASA:s audit, it was regarded as being equivalent. ('Equivalent' is a term used in certification issues to indicate that, although not directly in accordance with the airworthiness requirements of that country/ region's authorities, the system is satisfactory in terms of reliability and function and should meet all operational needs). Teplov has provided five systems to cater for failures - four are fly-by-wire, and the fifth is hydraulic. To reduce vulnerability to battle damage, the flying control surfaces - rudder and ailerons - have been divided into several sections, with three for the rudder and four for the flaps on each wing.

The Samara-made undercarriage assembly features three axles on each main unit, with two wheels on each axle, to reduce the footprint load (to 71lb/ft2 [5kg/cm2]) for operation from unprepared grass strips. Teplov says that this gives the An-70 an advantage over the FLA.

"Both aircraft could airdrop supplies or equipment to ground forces in battle conditions with equal accuracy. However, in many situations, the An-70 could land close by and allow surface delivery, if needed. In some situations, this could be a decisive factor."

As a design bureau, Antonov's task is not to build aircraft, but to take responsibility for its design and solve any problems arising during manufacture and operation. In Soviet times, a design bureau would only build an aircraft for test purposes: this meant that the prototypes, including the static and dynamic test examples, were built by the bureau, and all subsequent production examples were built in a designated production factory. Thus, Antonov built two prototype An-70s, one for flight test and the other for static tests. It entered into a commercial arrangement with two factories to manufacture production aircraft: Aviant in the Ukrainian capital, Kiev, and the Russian factory Aviakor, located in Samara.

The flight test aircraft was completed in autumn 1994, and following taxi trials and initial engine and systems tests, it made a successful first flight on December 16 that year. As was normal for Antonov first flights, this was simply a ferry from the design bureau's airstrip to the test center at Gostomel, a distance of some 13nm (25km).

Loss of first prototype

Financial shortages slowed down the flight programme, and the fourth flight did not take place until early February 1995. As was normal for an early test flight, the An-70 was accompanied on the sector by a chase 'plane, in this case an An-72. Weather was not ideal, and the two aircraft lost sight of each other and collided. The An-72, although damaged, landed safely but the prototype An-70 was destroyed and its seven crew killed.

A difficult time followed for the Ukrainian design bureau and its staff. Money continued to be scarce and the morale was low. Nevertheless, the first three flights had convinced Balabuev and Teplov that the design was a good one, and they fought to keep the programme alive. They consulted their partners in the project, and receiving full support from them all, decided to keep going.

TAPO Tashkent began the manufacture of a second wingset while Teplov and his team took the second An-70 fuselage, originally planned for static testing, and returned it to full flying specification. Another fuselage was subsequently constructed for the static test programme. Twenty-six months later, the An-70 was flying again, and the test work began in earnest.

Although the principal certification programme was for the military, Antonov decided to carry out a civil programme in parallel. With a great deal of commonality between the Soviet/Russian/Ukrainian military certification and the Avia Register of the MAK (Interstate Aviation Committee - (ARMAK), the new regulatory authority of the countries of the Commonwealth of Independent States) AP-25 programme, this made sense. The AP-25 rules were drawn up to correspond as closely as was practical with the West's Federal Airworthiness Requirement FAR-25 and Europe's Joint Airworthiness Requirement JAR-25. In fact, in order to cater for cold weather operations, AP-25 is more stringent in some respects than FAR/JAR-25.

On April 24, 1997, the second An-70 made its first flight and soon afterwards began the test programme. Antonov's own tests were conducted first, to prove that assembly and basic airworthiness were adequate; followed by certification test work. Antonov expects the full programme to require some 1,200 flight hours - financial strains on the company have meant that only about 200 hours had been completed by October 1999. However, this is expected to ease, as unofficial sources indicate that future customers have made some funding available. This may allow the completion of at least one production aircraft from both factories, and thus allow duee aircraft to take part in the test programme, which would shorten the elapsed time required considerably. Antonov expects the Russian/Ukrainian military tests, and those of the ARMAK, to be completed by the end of 2001, while Western approval should follow two years later.

Flight tests

So far, the flight tests have included handling characteristics, high incidence and stall tests, and take-off, climb, approach and landing tests. This last section includes investigation of STOL performance: approaches have been made at glide slope angles of up to 6*, and tests will continue up to 8*.

In the early tests, and with a take-off weight of 110 tons, a rate of climb of 4,900ft (1,493m) per minute was achieved. In landing trials, the STOL ground roll was just under 1,000ft (300m). So far, all trials have been made with 12 tons of test equipment on board, mounted on an upper deck which can also be used to carry troops or light cargo.

Fuel consumption during the trials has been measured at between 3 and 3.5 tonnes per hour, including take-off, climb, cruise and descent phases. In level flight at 16,000ft (5,000m), it is 3 ton - well under half the fuel bum of the rival Ilyushin Il-76TD. The cruise flight level in service is expected to be in the region of 26,000- 33,000ft (8-10,000m) and the maximum cruising altitude should be 39,000ft (12,000m): at these altitudes, the fuel bum should reduce even further.

Despite its use of propellers, the An-70 flies at speeds not much below those of turbojets. Cruise is in the 405-432kts (750-800km/h) range, only 27-54kts (50- 100km/h) lower than that of the Il-76.

At the time of writing (October 1999), the test programme was concentrating on ground handling and engine tests intended to prolong the service life. As both the airframe and the engines are new, Antonov and Progress are working as a team to achieve certification of their products. These include the many newly developed components and systems such as the avionics.

Antonov is also planning to develop a civil version of the An-70. With the International Civil Aviation Organization Chapter III regulations coming into force in 2001, most of the large fleet of Ilyushin Il-76 freighters serving with the airlines of the CIS countries will not be welcome in many western countries. While they will have no noise-related problems flying in their home regions, the loss of revenue from charter work to western Europe and the Americas will force some carriers to look for alternative aircraft. Antonov does not regard the An-70 as being a replacement for the Il-76, but admits it could fill some of the older aircraft's roles. In many cases, modem freighter needs are determined as much by cabin size as by payload weight and the 35 ton capacity of the new Antonov, combined with its wide, spacious cabin, afford it a number of advantages. Optional fits for the An-70T civil version include 12 ton-capacity loading cranes and roller floors.

A twin turboprop variant is also under consideration. Although this would have payload restrictions, it could be developed if Antonov finds customers for it.

The principal market for the An-70 will be military operators. Antonov calculates dig some 3,500 An-12s, C- I 30s and Transalls remain in service, and while the Ukrainian aircraft would not even be considered by some countries in the market for a replacement, it still leaves considerable opportunities. Antonov believes that the An-7X will be some 40% cheaper than the European A400M. For the 288 aircraft NATO requirement, this equates to eight to ten billion ECU/Euros, giving the An-70 a price tag not much higher than that of a similar number of C- 130.Js but offering a greater capability. The company is now planning a support programme for the export of An70/7Xs, building on experience it gained, in conjunction with Air Foyle and Rolls-Royce, when it offered the An- 124- 100M to the Royal Air Force. On the An-7X, the Antonov partners would work with western companies from Germany, France and Great Britain.

As a result of interest from other countries, the An-70 partners have formed the Medium Transport Aircraft International Consortium to market and support the aircraft.

The An-70 was conceived for the Soviet Air Force (VVS), although this has been succeeded by the air forces in the individual countries of the former Union. The largest of these is the Russian Air Force, but that country's economic difficulties are likely to mean that it can afford only small numbers of the An-70.

The major problem facing the An-70 is lack of finance. Piotr Balabuev has managed to keep the programme alive by carefully investing the design bureau's commercial earnings in new aircraft. However, to keep the programme running to schedule will require further funding, and this must be the design bureau's major priority for the next few years."

Antonov An-70 Specification

Powerplant: Four 14,000shp (10,440kW) Progress/Motor Sich D-27 propfans driving scimitarshaped, reversible-pitch Aerosila SV-27 l4ft 9in (4.49m) diameter, contra-rotating propellers, each with eight composite blades at the front and six at the rear.

Performance: Maximum speed: Mach 0.73. Normal cruise speed 405-432kts (750800km/h). Low altitude cruise speed 297kts (550km/h). Maximum range: (35 ton payload) 940nm (3,600km); (30 ton payload) 2,700nm (5,000km); (20 ton payload) 4,00nm (7,400km). Max operating altitude 39,370ft (12,000m).

Weights: Maximum take-off weight: 286,000lb (130,000kg). Empty weight: 145,500lb (66,000kg). Maximum payload: 103,600kg.

Dimensions: Length 133ft 0in (40.55m). Wingspan 144ft 61/2in (44.06m). Height: 53ft 13/4in (16.20m).

Accommodation: Three flight crew (two pilots and a flight engineer) plus loadmaster, although it can be converted for two-crew operation. Pressurized cargo compartment will accommodate a wide range of rigid or flexible pallets, containers, unpacked freight, wheeled or tracked vehicles or seat up to 170 troops."