IL-14 development history
IL-12 for IL-14 as DC-2 for DC-3
The year was 1943, amidst the still raging World War 2 soviet airplane designer Sergey Ilyushin commenced the project for development of IL-12 - a modern civil passenger airplane to replace Li-2 (DC-3) when the war will finally end. This project had to become the first one in the successful line of civil airplanes designed by Ilyushin Design Bureau. One of the main peculiarities of the project was a complete absence of any predetermined technical requirements for such an airplane. Paramount were maximum safety and comfort of the flight for the passengers. Passenger capacity, commercial loads and range had to be greater than those of Li-2.
Originally Ilyushin planned to equip his IL-12 with four engines of M-88 family (1200 hp), that proved to be efficient on IL-4 long-range bombers. However first flight of an experimental IL-12 in August 1945 was performed using two new liquid-cooled diesel engines ACh-31 (1500 hp), designed by Alexey Charomsky. Unfortunately several test flights showed the need for significant improvements to the diesel engines before they would be able to meet the required performance specifications for civil aircraft engines. All that added to uncertainty for the future of the airplane - there was a risk to miss the planned deadlines of state trials and the start of commercial operation of IL-12 on USSR airlines.
At this critical moment Sergey Ilyushin decided for the only one available alternative - to replace the yet “raw” ACh-31 diesel engines by gasoline engines already widely operated during the long war years. Correctly believing that a faultless operation of a powerplant is one of the primary prerequisites of flight safety, Ilyushin opted for a unique Perm “star” - extensively used on soviet fighters La-5, La-7 and TU-2 bomber air-cooled radial engine ASh-82FN (1700 hp) created by a Design Bureau from Perm (now OJSC Aviadvigatel). Performance characteristics of this engine designed by Arkady Shvetsov were close to those prescribed for civil aircraft engines and the absence of liquid cooling provided for significantly easier operational maintenance and quicker preflights, especially under winter conditions.
ASh-82FN (named M-82FNV till April 1, 1944) - a modification of ASh-82 (M-82) engine. New engine was different from the original through the use of direct fuel injection and improved supercharger. Engine prototypes undergone state trials in the end of 1942. From January 1943 ASh-82FN has been serially produced on Factories #19 and #29.
It is worth to mention that the advisability of equipping the new passenger plane with Shvetsov “stars” has been confirmed through aerodynamical test of IL-12 models by TsAGI (Central Aerohydrodynamic Institute). These tests confirmed that replacement of diesel engines by engines from Perm does not adversely affect the aerodynamics of the perspective airplane.
In January 1946 test pilots brothers Konstantin and Vladimir Kokkinaki took the first experimental IL-12 with ASh-82FN engines into the air. The following test flights clearly showed that Ilyushin Design Bureau managed to create a modern high-speed airliner, that noticeably outmatched by all performance numbers the Soviet Li-2 and American C-47. Ensuing years of operation on Aeroflot lines demonstrated high potential for modernization of this unique for its time airplane.
Praises to IL-12 from factory test pilots, their certainty in the reliability of the plane and its engines contributed to the decision to start serial production even before the beginning of state trials. This allowed to speed up the production of the new passenger airliner and strengthening of domestic civil aviation transportation system. By the way already on May 1, 1947 a wing of IL-12 participated in an aerial parade over Red square.
June 1947 marked the start of the regular flights of IL-12 on main airlines of Aeroflot with passengers on board. Pilots very positively reviewed the airplane noting the comfort of the pilot cabin, stability of the new aircraft while taking off and landing under normal conditions as well as with sidewind, high thrust-to-weight ratios and climb speeds easing quick penetration of weather, reliability of the engines in icing conditions.
Starting from 1948 IL-12 was actively involved in international transportation. First route was Moscow - Sofia. Later to its regular destinations added capitals of European and Asian states: Prague and Ulan-Bator, Teheran and Budapest, cities in China, Poland and many others. By 1956 IL-12 already was the workhorse for Polar aviation of Glavsevmorput`, and only two years later become the first Soviet airplane to fly over the South pole.
Regular commercial flights of IL-12 started in just 1,5 year after first flight of the prototype with ASh-82FN engines. Six months later IL-12s had flown over 4 mln. km., made more than 5000 landings. For the first time our civil aviation witnessed a new airliner to be put into operation at such a fast pace.
IL-14 - mastering single engine take-off
Right after the end of IL-12 state trials Ilyushin Design Bureau challenged to resolve a then new to the international aircraft manufacturing problem of a continued take-off of a twin-engine airplane after an engine-out during the takeoff roll or shortly after becoming airborne.
The new IL-14 was resembling the IL-12 in terms of general design, aerodynamics and equipment, while having larger size and take-off weight. A new wing has been designed for IL-14, the split flaps were exchanged for slotted flaps which significantly increased the aerodynamical quality with lowered flaps at airspeeds ranging from take-off up to 175 km/h. That allowed the airplane to shorten the takeoff roll and have better climb rates. Further decrease in parasite drag has been achieved through shorter time needed to raise gear and to feather propellers. While keeping the same arrangement of the passenger cabin as in IL-12 with 18 passenger seats, the new plane had much more forward center-of-gravity range - 12-19% MAC (compared to 19-22% MAC for IL-12), what significantly enhanced stability on ground and allowed to discard the ground tail support.
Initially Sergey Ilyushin had plans to install on IL-14 two ASh-73 (2400 hp) engines designed by Arkady Shvetsov, most powerful domestic piston engines at the time. The increased thrust-to-weight ratio should have given the airplane an ability to continue take-off in case of failure of one of the engines at airspeeds greater than V2 (in case of not enough remaining runway available for aborted take-off), and an increase in passenger number up to 48 which provided for better economic efficiency of the new plane compared to IL-12.
Although the perspectives of IL-14 with ASh-73 engines seemed bright, the project never came to life. And the reason was - too powerful engines, as the high asymmetric thrust of one engine in case of an engine-out on take-off made it complicated to maintain direction of flight. This significant yawing moment required all control surfaces to be more effective at low airspeeds and at the same time to remain not too heavy on control inputs.
Meanwhile the work on the IL-14 project continued. After all aerodynamical improvements, implementation of new type of flaps and other innovations the calculations for the upgraded airplane suggested that it should be able to reliably take off on one engine in all possible scenarios if merely 50 HP were added to the ASh-82FN engines. As the result Arkady Shvetsov offered to Sergey Ilyushin a different engine - ASh-82T.
Take-off power of the new engine from Perm, designed in 1949 based on ASh-83 engine increased up to 1900 hp. It was available up to altitudes of 400-500 meters, significantly improving the operational safety of IL-14 at high-altitude airfields and at high air temperatures.
ASh-82T had rather low brake specific fuel consumption at cruise power - 200-220 g/(hp*h). It's design features include reduction gear with the self aligning pinion for load balancing on satellite gear transmission, and mechanism for balancing the forces of inertia of the second order, and valve seat inserts. In contrast to ASh-82FN and ASh-21 the ASh-83 engine was started not by compressed air but with the use of an electric-inertia starter of combined action, same as ASh-73TK engines. At the same time there was an improvement program put in place to enhance the reliability of the engine and to increase its TBO up to 500 hours (later increased up t0 1200 hours). ASh-82T has been mass produced in USSR till 1953 and in some neighboring soviet countries - till 1977-1978.
First flight of an experimental IL-14 with ASh-82FN took place on July 13, 1950 under command of Vladimir Kokkinaki. The flight went on for only 15 minutes due to excessive temperature in heat exchangers of the air heating system.
For the second experimental IL-14, that received the name IL-14P, there were both a new exhaust and an air heating systems designed, combined into one unit, and to enhance the control characteristics at low airspeeds the vertical stabilizer and rudder were increased by 17% in square footage. The pilots outside field of view was improved by increasing the size of the forward and side windows.
Regular commercial flights on IL-14P with ASh-82T engines started in November 1954. At that time period these planes were used for special government flights. In 1955 as part of the soviet government delegation visits to India, Burma and Afghanistan ten IL-14Ps covered 22500 km each. There wasn’t a single failure of airplane equipment, including ASh-82T, during these flights. And further operation of IL-14P on Aeroflot airlines confirmed the high safety and reliability levels of the type, achieved largely through immaculate performance of its engines.
IL-14P has been manufactured in 14 modifications in USSR, Czechoslovakia and East Germany, has been operated till the beginning of 1990s on regular airlines in Cuba, Guinea, Egypt, India, Poland, Mongolia, Yugoslavia, Hungary, Romania, China and many other countries. For a long period IL-14s were extensively used by scientific expeditions on North and South poles, operated in a variety of climatic zones - all that proved the high quality of the airframe and engines design, their outstanding flying, technical and economical characteristics.