Antonov An-2 - Design and Development

Design and Development

The An-2 is used as a light utility transport, parachute drop aircraft, agricultural work and many other tasks suited to this large slow-flying biplane. Its slow flight and good field performance make it suited for short, unimproved fields, and some specialized variants have also been built for cold weather and other extreme environments. The Guinness Book of World Records states that the 45-year production run for the An-2 was for a time the longest ever, for any aircraft, but it was recently exceeded by the Lockheed C-130 Hercules.

The Antonov An-2 was designed to meet a 1947 Soviet Ministry of Forestry requirement for a replacement for the Polikarpov Po-2, which was used in large numbers in both agricultural and utility roles. Antonov designed a large single bay biplane of all-metal construction, with an enclosed cockpit and a cabin with room for seats accommodating twelve passengers. The first prototype, designated SKh-1, and powered by a Shvetsov ASh-21 radial engine, flew on 31 August 1947. The second prototype was fitted with a more powerful Shvetsov ASh-62 engine, which allowed the aircraft's payload to be significantly increased from 1,300 kg (2,870 lb) to 2,140 kg (4,720 lb), and in this form it was ordered into production.

By 1960 the USSR had produced over 5,000 units. Since 1960, most An-2s have been built at Poland's WSK factory in Mielec, with over 13,000 made there before full production ended in 1991. Limited production from parts stocks, as well as spares and maintenance coverage continued until 2001, when 4 aircraft were produced for Vietnam. China also builds the An-2 under license as the Shijiazhuang Y-5.

The An-2 was designed as a utility aircraft for use in forestry and agriculture. However, the basic airframe is highly adaptable and numerous variants have been developed. These include hopper-equipped versions for crop-dusting, scientific versions for atmospheric sampling, water-bombers for fighting forest-fires, flying ambulances, float-equipped seaplane versions, and lightly armed combat versions for dropping paratroops – Soviet paratroopers would practice low-level jumps into snowdrifts without parachutes. The most common version is the An-2T 12-seater passenger aircraft. All versions (other than the An-3) are powered by a 750 kW (1,000 hp) nine-cylinder Shvetsov ASh-62 radial engine, which was developed from the Wright R-1820. It uses 43 gallons of avgas per hour.

The An-2 has design features which make it suitable for operation in remote areas with unsurfaced airstrips:

• It has a pneumatic brake system (similar to those used on heavy road vehicles) to stop on short runways.
• It has an air line fitted to the compressor, so the pressure in the tires and shock absorbers can be adjusted without the need for special equipment.
• The batteries are large and easy to remove, so the aircraft does not need a ground power unit to supply power.
• There is no need for an external fuel pump to refuel the aircraft, as it has an onboard pump that allows the tanks to be filled from simple fuel drums.
• It has a minimum of complex systems. The crucial wing leading edge slats that give the aircraft its slow flight ability are fully automatic, being held closed by the airflow over the wings. Once the airspeed drops below 64 km/h (40 mph), the slats will extend because they are on elastic rubber springs.
• Take-off run: 170 m, landing run: 215 m (these numbers will of course vary depending on take-off/landing weight, outside air temperature, surface roughness, and headwind).

A note from the pilot's handbook reads: "If the engine quits in instrument conditions or at night, the pilot should pull the control column full aft and keep the wings level. The leading-edge slats will snap out at about 64 km/h (40 mph), and when the airplane slows to a forward speed of about 40 km/h (25 mph), the airplane will sink at about a parachute descent rate until the aircraft hits the ground."

The An-2 indeed has no stall speed quoted in the operating handbook. Pilots of the An-2 say one can fly the aircraft in full control at 30 mph (as a contrast, a modern Cessna four-seater light aircraft has a stall speed of around 50 mph). This slow stall speed makes it possible for the aircraft to fly backwards (if the aircraft is pointed into a headwind of, say, 35 mph (56 km/h), it will travel backwards at 5 mph (8.0 km/h) whilst under full control). (This is also possible with almost any other true Short Take Off and Landing (STOL) aircraft, but the Antonov has the distinction of being able to do the trick in the mildest headwind.)

Since the collapse of the Soviet Union and the Eastern European communist states, most airlines in these areas have been withdrawing their An-2s from service, as some of these aircraft are now over 40 years old and the production of avgas had decreased. Private operators are still using the planes, as their stability, capacity and slow-flying ability make them very popular, for instance for skydiving.

In the early 1980s Antonov experimented with a development of the An-2 powered by a modern turboprop engine. The unit used was a 1,450 horsepower (1,080 kW) Glushenkov engine, and aircraft fitted with this engine were fitted with a longer, more streamlined nose to accommodate it. See Antonov An-3 article for more information.

Whilst their high noise levels, increasing maintenance costs, high fuel consumption and unsophisticated nature (the pre-flight checks alone take between 30 and 40 minutes) make them obsolete for commercial service in Europe, the huge number of aircraft available means that prices are low (from as little as $30,000 for a serviceable example). This makes them ideal for the developing world, where their ability to carry large loads into short airstrips makes them assets to airlines on a budget. Many ex-Aeroflot An-2s work as regional airliners in Africa, Central and South America, Cuba and the Indian subcontinent.

North Korea has a number of the aircraft with wooden propellers and canvas wings on their variants (the Y-5 version license-built in China) giving them a low radar cross-section, and therefore a limited degree of "stealth". In a war they could possibly be used to parachute or deliver special forces troops behind enemy lines for sabotage operations.

The An-2's ability, looks and flying characteristics, and its status as "The World's Biggest single-engined production Biplane" mean that demand for the aircraft is increasing in the United States and Western Europe, where they are prized by collectors of classic aircraft, making the An-2 an increasingly common sight at airshows. However, in nearly all Western nations (the USA, Canada, the United Kingdom, France, etc.) one may not use the An-2 commercially (despite its obvious potential as a bush plane and parachute aircraft). This is because the aircraft has not been certified by the relevant national aviation authorities, which limits its use. These restrictions vary by country, but all prevent the An-2 being used for any 'for profit' purpose, with the exception of the United States, where An-2s imported since 1993 are limited to experimental certification & Title 14 Code of Federal Regulations, Part 21.191,21.193,21.195,91.313,91.319, but PZL-built An-2s are exempt from this restriction due to a bilateral agreement with Poland.