Special class of ground attack ('Stormovik' in Russian classification - A.S.) aircraft, specialized for attack of ground targets from extremely low altitude always attracted attention of aviators. It was developed in a variety of different projects starting as early as 1912.
After the Civil War (1917- 1922 - A.S.) special squad of "boevick"'s (exactly - fighter, AS) was created within outnumbered Soviet VVS under special order of "Narcomvoenmor" (people's commissar of military and naval - AS). This detachment became a prototype for future stormovik detachments. It was armed with ordinary R-1 reconnaissance aircrafts. New practical operation methods vere summarized in late 1927 in the first issue of "Lessons (Nastavlenija ?) of attack aviation".
Design of specialized stormovik started from hammering out TTT. Those were developed by 1st section of Science-Technical commetee of VVS command. This section was lead (since 1926) by young VVS academy graduate S.V.Ilyushin. First experimental planes were TSh-1, TSh-2 and TSh-3. Those were not a complete mess, but suffered from heavy passive external 'hanged' armor (adding 400-900kg) and weak engines of 20th-30th. As a result this class of stormoviks had no chance for recognition.
At the same time military experts worldwide raised opinion that stormovik should be a multi-purpose aircraft, or aircraft of so called combined type. It supposed to serve as a recco, light bomber and just 2-seat escort fighter.
Multi-purpose weakly armored attackers were under specially intensive development in the USA (Valgi A-11(?), Nortrop A-17 Nomad, Curtiss A-18 Shrike) and Great Britain (Fairey "Battle"). Main efforts of German aircraft were concentrated on dive bombers (Junkers Ju-87 'Stuka' and Heinkel He-118).
In the beginning of 1936 in Soviet Union several design bureaus initiated creation of multi-purpose aircrafts. There was a contest between design bureaus lead by D.P. Grigorovich, S.A. Kocherigin, I.G. Neman, N.N. Polikarpov and P.O. Sukhoi. This secret project was named 'Ivanov'. Polikarpov's team also was busy with building new dive bomber VIT-1. S.V.Ilyushin, formally in charge for design, building and production of his first military aircraft DB-3, did not take official part in this job. Nevertheless, he started his own research of armored stormovik parameters and design.
S.V.Ilyushin charged himself with extremely complicated task. But at the moment a lot of aviation innovations were already available : powerful liquid cooling engine (A.A. Mikulin), rapid aviation guns (B.G. Shpitalny), aircraft based rocket missiles designed by RNII, 'stampable' geterogenic aviation armor with high hardness of an external layer (S.G. Kishkin, N.M.Silijarov) and transparent aviation armor (B.V. Efremov, N.M. Gudimov).
At last at January 1938 designer came to government with proposal for realization of his project : two-seat (pilot and gunner) armored stormovik, with combat efficiency outclassing aircrafts created under 'Ivanov' project.
Armored stormovik of S.V.Ilyushin TsKB-55 was a two-seat low wing monoplane with retractable gears. In flight main gears were semi-hidden in wing nacells. Aircraft planned to have single AM-35 liquid cooling engine with take off power 993kW (1350hp), developed by A.A. Mikulin team. The key design solution was slick armor fuselage, protecting all important components: crew, engine, gas and oil systems. Armored fuselage was actively included into stress distribution scheme. Front section carried load of engine, reductor (gear box) and cooling system. Central section was loaded with crew, rear defence gun turret, wings and tail section.
It was the first case in the USSR when clear armor K-4 was used on stormovik. Frontal sections of pilot canopy were made of this armor. Parts of aircraft not protected by armor where designed to survive severe combat damages: Tail section had active skin supported with stringers, wing and tailplane had 2 spars, tail fin was a single piece with fuselage. Fact that main gears were not completely hidden in wing nacells allowed to ground aircraft with minimal damage on any unleveled opening without main gear extraction. Weight-saving loaded armoring provided sufficient room for heavy powerful attack armament.
Originally planed armament was 5 ShKAS 7.62mm machine guns, including 4 fixed in wing and one for rear defence on a turret. Bombs (400kg) were located in 4 inner wing bays, where bombs were partially shielded by armor. There were special armor shields in front of them. In overloaded option additional 200kg of bombs could be attached under the wings (on wing stinger separating bomb bays).
State commission tests of BSh-2 (TsKB-55 #2) started at April 1, 1940. General conclusion of military experts was positive, but some weak point were cleared. Those were : low speed on ground level (326km/h) and restricted pilot's view (by huge engine).
On the final stage of refinement S.V.Ilyushin received suggestion to rebuild aircraft into single-seater, to install two PTB-23 (designer Ja.G. Gaubin) 23mm guns and two ShKAS machine guns, also enforcing armoring of aircraft.
Aircraft TsKB-55 #1 was urgently rebuilt. It received a new designation TsKB-57. The first test flight took place at October 12, 1940 under supervision of V.K.Kokkinaki. He was one who completed factory tests in extremely compressed period - only 40 flight days. He mentioned that aircraft flight control is extremely simple and has no 'peculiarities'. Maximum speed reached on ground level was 423km/h and on ceiling altitude - 437km/h, quite high for 1940.
Stalin's directive to start mass production of aircraft was signed in November designated Il-2, and under this designation it came to state approval test.
The first mass-production Il-2 was produced in March 1940, as short as in 3 months after documentation was received by factory. During production period aircraft artillery was improved after arriving of powerful 23mm gun VJa-23 (designed by A.A. Volkov and S.Ja. Jartcev). Projectiles of this gun penetrated 25mm steel armor from distance 400m. It was those guns Il-2 passed state approval tests.
Design efforts in Germany completed in 1939 ( Spring) with creation of experimental planes Focke-Wulf Fw 189 'Uhu'/'Rama (Frame)' (converted from (in)famous reconnaissater by redesigning of the central nacell) and Henschel Hs 129.
Both were significantly weaker than Il-2 by their armament, flight characteristics and design concept.
Il-2 obtained its combat trial on July 1, 1941 near town of Bobrujsk and Berezina river. Dependability, firepower, invulnerability for handgun (and generally small anti-aircraft gun) fire made Il-2 a weapon of terror, just in hands of unskilled pilots. Combat experience instantly highlighted also one significant disadvantage (predicted long ago by S.V.Ilyushin) - vulnerability from fighter attacks from rear hemisphere. Starting form the very first days of war design bureau received numerous suggestions from combat pilots to install remotely controlled machine gun or gunner's cockpit for rear protection, as it was done on experimental TsKB-55.
In July 1941 in 4 months after start of mass production, factory produced about 300 Il-2's/month. But rapid advance of enemy ground troops endangered production facilities of Il-2 and specially engines. It became necessary in extremely short time to investigate possibility to accommodate aircraft for air-cooling engine M-82, manufactured far behind front lines. As soon as September 8, 1941 test-pilot V.K. Kokkinaki made the first test of Il-2 with new engine, and within 8 days completed factory test program.
Evacuation delayed state commission tests, which took place in February-March 1942. Those test confirmed factory results. At that time production of both Il-2 and AM-38 engine had full steam on new built factories.
At the same time it became clear that armor-shielded liquid-cooling engine is better solution that unprotected air-cooling engine, despite its better survivability in case of combat damage. Despite Il-4 (Il-2M82) with M-82 engine was recommended for mass production, only one experiment aircraft was built.
So option of rear gunner cockpit with defence weapon was developed with minimal changes in aircraft design. Flight weight was increased only by 270 kg.
In March 1942 2-seat Il-2 came under factory tests. If was found that maximum speed of aircraft significantly decreased. Stormovik became more tough to control, specially during take-off and landing. AM-38 required to became more powerful. Fortunately, team of A.A. Mikulin solved this problem very quickly.
Two-seater Il-2's with new AM-38 meet first combat on Central Front October 30, 1942 during attack of enemy airfield near Smolensk. High combat efficiency of two-seaters was noticed instantly. Just during combat tests period gunners shot down 7 Bf 109 and repelled numerous fighter attacks.
Starting January 1943 airforce started to receive IL-2 with improved supercharged AM-38F engine, what further improved speed, maneuverability and take-off/landing performance. New engine had take-off power 1250kW (1700hp), which could be increased in combat for a short period up to 1309kW (1780hp).
The second cockpit lead to Center of gravity shift back (~3.5%) and degrading of longitudinal static stability. This unpleasant effect was eliminated by increase of wing sweep to 15°. But mass production of Il-2 with swept leading edge ('arrow') wing started only in the late 1943.
Other direction of Il-2 modifications was gaining of its attack firepower. Starting at the end of 1941 Ilyushin's OKB (Osoboe Konstruktorskoe Bureau, Special Design Bureau - AS) studied options of installing two 37mm guns Sh-37 (B.G. Shpitalnyj) on single-seat Il-2. But this modification failed to became wide-used because low reliability of Sh-37 guns. In addition, low placing relatively to aircraft center of gravity lead to 'dives' during fire and to lower fire accuracy.
In March-April 1943 2-seater Il-2 with AM-38F was tried with modest 37mm NS-37 guns developed by A.E. Nudelman team. This modification was tested in combat in Kursk Battle in July 1943. High efficiency was demonstrated during operations against enemy tanks and motorized infantry during this battle. Captured Nazi soldiers confirmed that their forces suffered heavy losses from aircrafts with 'big gun'. Il-2 with NS-37 was able to destroy famous German Tigers with its gunfire...
Rocket armament was also modified. Starting 1942 Il-2 was equipped with rocket missiles RBS-82 or RBS-132 (with armor-piercing warhead and powerful rocket engine) for more efficient destruction of enemy tanks. Efficiency of armored vehicle destruction with Il-2 gained dramatically after introducing of compact anti-tank bombs PTAB-2.5(-1.5) with cumulative action, developed by I.A. Larionov. Up to 192 such bombs could be housed in four cassettes, installed in bomb bays. If hits target, PTAB was able to burn through 70mm armor. Those bombs were tested first time during same Kursk Battle. During first five days attackers from 291th storm division destroyed and damaged 422 enemy tanks.
There vere more modifications of Il-2. For artillery spotting and reconnaissance Il-2KR was used starting summer 1943. It had same design and arming, but had modified cockpit equipment, fuel system and armoring.
In 1943 small series of trainers UIl-2 were manufactured with re-equipped rear cockpit, allowing to correct pilot's errors.
Il-2 had unique design as no other aircraft in service during WWII. No any other country had such a weapon. Developed in Germany (at the same time as Il-2) armored attacker Henschel Hs 129 at the moment of German attack against USSR was not in combat ready conditions. Moreover, Luftwaffe command relied completely on dive bomber Junkers Ju-87 'Stuka' and did not make any attempts to replace it until 1941. Reason for this overconfidence was that this plane did very well during blitz-campaigns on the West Front. In early period of Great Patriotic War it was a big mess for Soviet Union also. But later heavy losses of 'Stuka's in USSR forced Germany to accelerate development of Hs 129.
Starting early 1942 small amount of those aircrafts participated in combat. Despite well armored cockpit, engines of Hs 129 were vulnerable, and general flight performance was quite poor. Together with absence of defence weapons it resulted that Hs 129 (869 produced) was almost completely eliminated by Soviet fighters. At the same time Soviet industry supplied army with 36163 Il-2's...
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