Design and development
The Il-12 was developed as a private venture by the Ilyushin Design Bureau from autumn 1943 and was intended as a replacement for the Lisunov Li-2, a license-produced version of the Douglas DC-3. The new aircraft followed a classical layout for a twin-engine transport, with a metallic structure, monoplane wings, a conventional tail section. One major improvement over the Li-2 design was the tricycle landing gear, which allowed better visibility when taxiing and landing. Initially the Il-12 was designed for 29 passengers in a pressurized fuselage, with projected maximum range is assumed of 5,000 kilometers at a cruising speed 400 kph. The aircraft was to use four M-88B engines already proven in use on the Ilyushin Il-4.
However, during development, the M-88B engines had to be replaced by two ACh-31 diesel engines (each producing 1,500 hp). The plans for a pressurized fuselage were abandoned and the number of passengers reduced to 27. The Il-12 made its maiden flight on 15 August 1945. It was soon decided to re-engine the aircraft with Shvetsov ASh-82 radial engines with the revised aircraft flying on 9 January 1946.
The Il-12 was found to have problems with vibration during testing, having poor engine out characteristics and requiring a strut under the rear fuselage to prevent tipping during loading due to center-of-gravity problems. Further problems was the use of magnesium near the engines which in case of engine fire could cause an uncontrolled fire, damaging the wing structure. (This was later revealed by a crash of an Ilyushin Il-12 near Voronezh which killed all on board, following an engine fire. Subsequently, as a result of the accident investigation, the magnesium was replaced by aluminium alloys and the fire extinguishing system was redesigned.) However, once these problems were resolved, factory test pilots praised the quality of the new aircraft, which contributed to the decision to launch the Il-12 in series production.
The fuselage of the Il-12 had a considerable volume, and was equipped with eight rectangular windows on each side. The crew consisted of three and the aircraft could transport 32 soldiers, 32 parachutists or cargo. There was also a civil version, which although designed to carry up to 32 passengers, was limited in Aeroflot service to 21, with normally only 18 carried. At that passenger load, it meant that use of the Il-12 for passenger use was un-economic.
A total of 663 Il-12s were manufactured. The aircraft was later improved into the Ilyushin Il-14.