In the late 1930s - early 1940s, the main and practically the only tactical technique for attack aircraft was an attack from a horizontal flight at extremely low altitudes (from a low level flight). And in those days, and later - in the 1950s, when designing single-engine attack aircraft using the traditional scheme of their layout, the designers had to provide a fairly good forward-downward view. For airplanes with air-cooled engines, this problem has proven particularly intractable.
Experienced Il-20 attack aircraft
An overview in this direction is necessary so that the pilot can quickly and correctly assess the situation on the battlefield, identify targets, determine the countermeasures of enemy ground assets, select a target and maneuver for its attack, aim and manage to use the offensive weapons available on board as efficiently as possible. Since attack aircraft were often used as light bombers, a good view downward, directly under the aircraft, was also important to ensure accurate bombing.
The viewing angle of the TSh-2 attack aircraft (the most noticeable among our first armored attack aircraft) did not even reach one degree. When flying at an altitude of 15 m, the pilot could see targets ahead at a distance of at least 1000 meters. At the same time, firing from machine guns was completely excluded.
Creating the Su-6 aircraft, in order to obtain a more or less satisfactory forward-downward view, P. O. Sukhoi spent a long time looking for a place for the engine and carefully chose the contours of the engine hood.
S. V. Ilyushin, in order to improve visibility on BSh-2 (Il-2), had to raise the pilot's seat, lower the engine in relation to the axis of the aircraft, pay a lot of attention to the contours of the engine hood. As a result, it provided a forward-downward viewing angle of about 8 degrees.
All serial attack aircraft did not have a downward view under the plane at all. The exception was the Il-2, equipped with a special periscope, which, however, did not receive further distribution.
A way out of the situation was found using a delay in the time of dropping bombs, either with the help of special sights and temporary mechanisms, or by putting marks on the structural elements of the aircraft. Sometimes, in order to increase the effectiveness of the action of groups of Il-2 aircraft from low-level flight, it was necessary to make them "sighted" with the help of target designation aircraft for attack aircraft (STSUSH). In this capacity, SB, Pe-2 bombers, performing flight and searching for targets at medium altitudes, were used, and later - specially selected Il-2 crews. After the detection of the object of impact, the navigator or pilot of the STsUSH dropped bombs and thereby designated it.
In the early 1940s, the USSR made repeated attempts to create attack aircraft with an improved forward-downward view and the ability to fire at targets in this sector with mobile cannon and machine gun mounts. However, both the multipurpose single-seat aircraft of the battlefield "OPB" designed by SA Kocherigin, and the attack aircraft "BSh-MV" developed by the team of designers A. A. Arkhangelsky, G. M. Mozharovsky, I. V. Venevidov, and the armored attack aircraft "MSh" S. V. Ilyushin, using unconventional design solutions, did not go into the series.
Development of the Il-20 attack aircraft
IL-20 side design with a color option
Comparison of the viewing angles of Il-2 and Il-20 attack aircraft
They returned to work in this direction only after the end of the war. In accordance with the Decree of the USSR Council of Ministers of March 11, 1947 No. The Ilyushin Design Bureau was entrusted with the task of creating a new attack aircraft with slightly increased (compared to the Il-10) flight data, more powerful cannon and missile armament, improved visibility and armor. At the end of 1947, the designers completed the development of a single-engine armored two-seat attack aircraft with an MF-45sh liquid-cooled engine. The original layout scheme was used, which provided excellent forward-downward visibility. The cannon armament was also extraordinary. The draft design of the Il-20 MF-45sh aircraft was sent in February 1948 to the Air Force Research Institute.
The decree of the USSR Council of Ministers on the construction of prototypes of the Il-20 was adopted on June 12, 1948. The conclusion on the preliminary design was approved on June 19 of the same year by the chief engineer of the Air Force I. V. Markov. Engineer-major S. G. Frolov was appointed as the responsible executor for the aircraft. The mission of the attack aircraft was formulated as follows: "To suppress and destroy manpower and technical means on the battlefield and in the tactical depth of the enemy's location." It was proposed to make two projects with different options for offensive and defensive weapons.
According to the scheme, the first version of the aircraft was a low-wing aircraft with a liquid-cooled engine with a four-blade propeller with a diameter of 4.2 meters. The cockpit was located in an unusual way - directly above the engine - and was pushed forward to the limit. The front part of the cabin was set at an angle of 70 degrees. long windshield 100 mm thick. One end of it practically rested against the edge of the screw sleeve. This provided a forward-downward view in the 37-degree sector, and when diving at an angle of 40-45 degrees. the pilot could see targets almost directly under the plane. Oil and gas tanks were located behind the cockpit. Behind them was the gunner's cabin, remotely controlling a 23-mm cannon, located in a special mobile Il-VU-11 installation with a hydraulic drive and a mechanism for bypassing the cannon barrel along the contour of the fuselage and tail (in order to protect them from being hit by their own weapons).
Il-20 layout
Il-20 attack aircraft projections
The Il-VU-11 was designed by the Ilyushin Design Bureau. It provided large angles of fire in the upper part of the rear hemisphere: 80 degrees. - upward and 90 degrees. - to the right and to the left. The maximum speed of movement of the weapon in the mobile installation was 4-45 degrees / sec. Since the lower quarter of the hemisphere was not at all protected by the cannon installation, a cassette for 10 AG-2 aviation grenades was additionally placed below the fuselage, thereby organizing partial protection.
The tail unit was single-finned, the wing and horizontal unit were trapezoidal in plan. Water and oil coolers were located in the center section, the engine air intake - in the lower part of the fuselage, in the area of the front edge of the wing.
The cockpit and gunner, the engine, the fuel and lubrication systems, the cooling system were inside the armored box. The total weight of the metal armor was 1,840 kg, and the transparent armor was 169 kg. The cockpit had, in addition to the frontal, two side front bulletproof glasses 65 mm thick and rear bulletproof glass, also 65 mm. In the upper part of the cockpit, from the sides of the canopy, there were armor plates 10 mm thick; the sides of the cockpit, the rear bulkhead behind the pilot were 10 mm, and in the upper part - 15 mm. The shooter from behind and from above was protected by 100-mm bulletproof glass, a front upper sheet behind the gas tank and side 6-mm sheets, a lower armor sheet of the cab of 8 mm, upper and lower shielded armor with a thickness of 8 + 8 mm.
The armoring of the engine included an "armored trough" made of sheets with a thickness of 6, 8 and 12 mm, which protects it well from the front, from below and from the sides. The top sheet of the gas tank was 4 mm thick, the side sheets were 6 mm and the plates behind the tank were 10 mm, which completely covered it from those sides where there was no other armor protection. The radiators were covered from the sides with 4 mm sheets, a 6 mm radiator shield inside the "armored hole" of the engine, 8 mm thick lower armor plates, and two 10 mm radiator armor plates. As you can see, the booking was made extremely strong. It provided mainly protection against bullets of 12, 7 mm caliber and to a large extent - against projectiles of aviation 20-mm cannons. The thickness of the metal armor in comparison with the IL-10 increased by an average of 46%, and the transparent - by 59%. The offensive armament in the first version included two wing cannons of 23 mm caliber for firing forward in a dive or gliding, and two 23-mm cannons installed in the fuselage at an angle of 22 degrees. to the flight line - for firing at targets from low level flight. Normal bomb load was 400 kg, overload - 700 kg. Under the wing, in the reloading version, the suspension of four single-shot rocket guns ORO-132 was provided.
In the second version of the offensive armament, it was planned to use one 45 mm cannon, two 23 mm cannons and six ORO-132. The aircraft was equipped with advanced flight-navigation and radio communication equipment, thermal anti-icing system. This expanded the possibilities for its use in bad ones.
In the draft design, the second version of the defensive armament of the Il-20 aircraft was also developed. There, instead of the Il-VU-11 upper mount, they used the Il-KU-8 aft mobile cannon mount, located in the rear of the aircraft. It provided protection of the aircraft in the rear hemisphere from attacks by enemy fighters from all directions. In the Il-KU-8, the shooter was protected from behind by 100 mm bulletproof glass, from the sides - by 65 mm bulletproof glasses. The 10 mm thick armor curved along the contour of the rifle mount, the side 6-mm and rear 4-mm armor plates provided reliable protection for the shooter in this version.
The idea remained unfulfilled
Despite a number of original ideas, the preliminary design of the Il-20 was rejected as not complying with the decree of the USSR Council of Ministers and tactical and technical requirements. This concerned basic flight data and weapons.
The main drawback was the low flight speed of the aircraft, which turned out to be even lower than that of the serial Il-10. Offensive weapons also did not satisfy the customer.
It was noted that the firepower of the Il-20 is less than that of the Il-10. At the same time, it was possible to fire only from two cannons - either wing or fuselage. The expediency of using the latter was not in doubt, but a desire was expressed to have mobile installations. Along the way, let us say that the already existing by that time quite successful developments in this area G. M. Mozharovsky and I. V. Venevidov was not used. When loaded with PTAB, the bomb load was only 300 kg.
A significant increase in the midsection of the fuselage and its lateral surface led to a deterioration in the aerodynamics of the aircraft, an increase in the flight weight, and an increase in the possibility of being hit by enemy fire. Since the distribution of the armor installed on the aircraft was carried out over a large surface, the specialists of the Air Force Research Institute did not see an improvement in booking in comparison with the Il-10. The operation of the VMG has become extremely complicated due to irrational methods of approaching the motor and its units. For all work related to the removal of blocks or their covers, it was required to dismantle the engine itself from the aircraft. The mechanic had to perform all work on the motor in the upside down position. The pilot only got into the cockpit when the engine was not running. In an emergency escape, there was a danger of falling under the propeller.
The main positive factor was considered only an excellent forward-downward view (albeit only in a very narrow sector). The view to the sides and forward turned out to be the same as that of the IL-10.
The IL-20 model was presented to the model commission in July 1948. In the protocol, which was approved on July 21, 1948, the Air Force Commander-in-Chief, Air Marshal K. A. Vershinin, the motor was already called M-47. The model in the version with the Il-VU-11 was considered unfinished. The downward and sideward visibility turned out to be worse than on the Il-10. The cockpit was located too close to the propeller, which is unsafe when leaving it, and in an emergency landing, there is a high probability of damage to the cockpit by the propeller blades. There was no emergency reset of the flashlight and a protective anti-cabotage device. The layout made it difficult to operate.
Among the positive qualities were an excellent forward-downward view and the presence of guns shooting at an angle downward and making it possible to attack area targets from horizontal flight at altitudes from low-level flight to 700-800 meters.
The Air Force Commander did not consider it necessary to build the Il-20 until the final approval of the layout. However, the aircraft was manufactured in the first version. It had four movable 23-mm W-3 cannons designed by B. G. Shpitalny with 900 rounds of ammunition. The Il-VU-11 was equipped with a Sh-3 mobile cannon with an ammunition capacity of 200 rounds.
Factory tests began on November 20, 1948. The first flight in early December 1948 was made by pilot V. K. Kokkinaki. During the tests, the aircraft showed a maximum flight speed of only 515 km / h at an altitude of 2800 meters. Due to low flight data, failure to meet the requirements for armament and the lack of knowledge of the M-47 engine designed by M. R. Fleece work on the Il-20 in accordance with the Decree of the USSR Council of Ministers of May 14, 1949 was stopped.
The aircraft was examined by the Deputy Commander-in-Chief for Combat Training and noted the following shortcomings:
• the cockpit of the pilot and the gunner are separated by a gas tank;
• issues of diving have not been worked out;
• the effectiveness of extinguishing a fire in the area of the gas tank has not been ensured;
• installed four guns forward instead of six, and others.
S. V. Ilyushin worked on two more (besides those already discussed above) versions of the Il-20, with a layout like the Il-10, the flight data of which was obtained somewhat higher. But all this remained unfulfilled.
The last attempt to create an attack aircraft with an improved forward and downward view was the preliminary design of an armored two-seat attack aircraft Sh-218 with a powerful engine of the X-shaped M-251 scheme designed by S. M. Alekseev. But its performance was found to be unsatisfactory.
Thus, they could not get a good enough forward-down view from serial single-engine attack aircraft. In the Il-20 aircraft with the M-47 engine, this was achieved at the cost of losing in many other parameters, which did not allow the aircraft to be put into production. We can conclude that the hope to solve the problem of forward-downward visibility due to unconventional layouts of single-engine attack aircraft did not materialize.
