Almost all Yak-28Bs with outdated RBP-3 radar sight were handed over to the customer for combat training. At the same time, a maximum speed was guaranteed within 1600 … 1700 km / h, a practical ceiling of 14 … 15 km and a flight range without hanging tanks of 1550 km. As it is easy to see, in terms of all the main characteristics, the machine "did not reach" the requirements of the decree of January 5, 1959, But much more important from the point of view of the Air Force turned out to be the discrepancy between the modern requirements of the composition of the onboard instrumentation, navigation and sighting equipment. Thus, OKB-115 fell into the "zugzwang" - it had a ready-made aircraft, put into production, but the required "filling" for it was absent. There were two options for the "stuffing": the "Lotos" radio rangefinder station (DBS-S) and the new autonomous onboard radar station "Initiative".
The Initiative was a completely perfect device, but it was distinguished by extremely low reliability. However, "Lotus" also required some refinement. The leadership of the GKAT found a way out: for a while, the Irkutsk aircraft plant was loaded with the release of a simple training version of the Yak-28U, which lacked complex electronic devices. In the meantime, the refinement of the Yak-28L variant with the Lotos system continued hastily. Flight tests of the aircraft were carried out in the period from September 30, 1960 to January 14, 1961. Engineers Leonov and Yu. V. Petrov, pilots V. M. Volkov and V. G. Mukhin, navigator N. M. Shipovsky, and on state tests - engineers S. I. Blatov and A. I. Lobanov, pilots S. G. Dedukh, L. M. Kuvshinov and V. E. Khomyakov. The main drawback of the car was the deteriorated view of the front hemisphere from the navigator's cabin. Despite some remarks, on November 27, 1961, the Yak-28L aircraft was adopted by the Air Force.
On the Yak-28L aircraft of the later series, the power plant consisted of two R11AF2-300 turbojet engines with a thrust of 6100 kgf at afterburner. Armament consisted of bombs of caliber from 100 to 3000 kg. Yak-28L was never officially adopted, and the release of this modification was limited to 111 copies.
In 1960, another modification of the bomber, the Yak-28I, entered factory tests. Factory tests were carried out by test pilots V. M. Volkov, V. G. Mukhin, navigator N. M. Shipovsky, leading engineers M. I. Leonov and R. S. Petrov. The aircraft was equipped with an integrated armament control system consisting of an Initiative-2 radar, an OPB-116 optical sight and an AP-28K autopilot. In comparison with the RPB-3, the new radar had a greater detection range and better resolution and, on the whole, was not inferior to the best world models of that time. It was thanks to its good characteristics that this radar subsequently became one of the most widespread in the USSR and was used on 12 types of aircraft. The crew with its help could search and attack point moving targets at any time of the day and in adverse weather conditions. Compared to OPB-115, OPB-116 possessed increased accuracy, increased field of view, better resolution and allowed bombing from altitudes of 2000-20000 m at a flight speed of 800-1700 km / h. Automatic data entry into the sight was provided from an altitude of 3500 m, and before that it was carried out only manually.
To place the radar in the fuselage, an insert was made in the cockpit area. On the prototype, the nose cone was glazed in a new way, which improved the view from the navigator's cockpit. To increase stability in flight, the height of the crests at the root of the wing was increased. Initially, the Yak-28I prototype, like the experienced Yak-28L, was tested with the R-11AF-300 engines. In the process of revision, the car was equipped with R-11AF2-300 in modernized gondolas, which were distinguished by a circular section of the inlet and an elongated front part.
It was on this plane that the new power plant was tested. The problem of unstable operation of the compressor, typical for the R-11F-300, was solved by modifying the first stage blades. The elements of the anti-icing system of the new air inlet worked at the Yak-25 flying laboratory. The Yak-28I was put into serial production even before the end of testing and fine-tuning of the Initiative-2 station. When the aircraft began to operate in units, a significant deviation of the characteristics of the station from those recorded in the technical specifications was revealed. During control bombing, the errors exceeded the standard. Factory military representatives immediately stopped accepting the bombers. The brewing scandal forced the Minister of the Aviation Industry P. V. Dementyev to take emergency measures. Yakovlev with a large team, chief designers and specialists in the navigation system, optical sight, radar, etc., as well as representatives of the relevant research institutes were invited to the airfield, where the tests and development of the new "Initiative" were carried out. In an effort to quickly understand the causes of the identified defects, work began with ground checks. When they gave nothing, flight experiments were allowed on a production aircraft. However, even at this stage, it was not possible to advance in research. They had to equip the KZA bomber, carry out a whole complex of flight research and development work, which lasted for almost a year and became, in fact, the first serious study of the supersonic bombing system in the USSR.
A significant contribution to the refinement of the Yak-28I bombing system was made by employees of the Scientific Research Institute of Aviation Systems (NIIAS). It was thanks to them that it was possible to find out that errors in determining the ballistic characteristics of bombs, measuring airspeed, instrumental errors of instruments, as well as neglect of external conditions when bombs leave the bomb bay, have a significant effect on accuracy. 1969 conducted special flight tests of the serial Yak-28I in order to study the possibility of bombing in the climb mode without modifying the sighting system. The tests were carried out at altitudes from 400 to 3200 m. From May 6 to June 18, 1970, the Yak-28L No. 3921204 was tested with a modified NR-23 artillery gun (lead pilot Major II Shirochenko). Earlier firing from a cannon in long bursts at high altitudes disrupted the operation of the power plant. Tests have shown that the improvements made made it possible to fire in bursts of up to 15-20 shots at altitudes of more than 8000 m.
Tests of the aircraft with the aim of further improving it continued for many years. So, from March 20 to April 4, 1962, the State Research Institute of the Air Force conducted joint state tests of the Yak-28 serial bomber No. 1900304 with an RPB-3 sight and improved take-off and landing characteristics (in fact, it was a Yak-28B, but in the documentation sometimes the index "B" went down). Improvements to the aircraft were carried out at OKB-115 in order to reduce the length of the takeoff and run. In the rear part of the fuselage, between frames 34 and 37, attachment points for two starting powder accelerators SPRD-118 were installed. In addition, instead of non-braking wheels, KT-82 brake wheels were installed on the front landing gear (they were installed on all production aircraft, starting with this number) and a brake parachute release machine was introduced. Unlike the Yak-28L, the fuel reserve was reduced by 755 kg, and at the maximum take-off weight - by 995 kg. The tests were carried out by test pilots of the Air Force GKNII Yu. M. Sukhov and V. V. Dobrovolsky. After their completion, the improvements were introduced into the series.
223 Yak-28I aircraft were built, which were officially accepted into service. In total, the combat units received about 350 shock Yak-28 of various modifications.
During 1964-1965. In the OKB-115, on the basis of the Yak-28I, a carrier aircraft was designed for the K-28P weapon system, which included two X-28 anti-radar missiles and control equipment. In 1965, they completed the preliminary design, prepared the documentation and began building an experimental Yak-28N aircraft (carrier) by modifying the serial Yak-28I. Its factory tests began in the same year. The missiles were suspended from launchers under the wing consoles. The radar detection equipment was located at the site of the Initiative radar. In addition to the suspensions, the car externally differed in the guidance station antennas attached to the right engine nacelle. Despite the tests carried out, the Yak-28N was not introduced into the series, but the X-28 itself subsequently found application on Su-17M2 fighter bombers and Su-24 bombers.
From September to October 1969, factory tests of the Yak-28IM aircraft, equipped with four underwing pylons for additional weapons, were carried out. The prototype was built by modifying the serial Yak-28I # 4940503. Joint state tests of the bomber were carried out in 1973. By that time, the Su-17 and Su-24, equipped with a wide range of weapons, were launched into large-scale production, and there was no point in continuing to expand the combat capabilities of the Yak-28.
In general, over the years of production, 111 Yak-28L and 223 Yak-28I were produced. In general, we can conclude that A. S. Yakovlev managed to achieve the adoption of a machine that did not fully satisfy the Air Force command in terms of its qualities, although on the whole it met the world requirements of that time. According to all the main flight data, the strike version of the Yak-28 did not reach the specified TTT values by 10 … 15%, especially in terms of the flight range. For the sake of fairness, it should be noted that there really was no real alternative to the "twenty-eighth" in the version of a front-line bomber. And over time, after eliminating childhood illnesses and gaining positive operating experience, the Air Force Main Command took the side of OKB-115, seeking to expand the production of the Yak-28I, which the USSR State Planning Committee categorically objected to.
In the late fifties - early sixties of the last century, the Yakovlev Design Bureau developed several projects of combat aircraft, which were the development of the Yak-25 - Yak-28 family. The development of the Yak-32 aircraft was brought to the draft design, signed by A. S. Yakovlev May 25, 1959 Provided for the installation of engines VK-13 or AL-7F1. Flight weight: normal 23,500 kg, with outboard tanks 27,000 kg. The maximum speed is 2500 km / h, the service ceiling is 21000 m, the flight range is 2600 km with 7% fuel remaining. It was this version of the machine that aroused the greatest interest among the Air Force command, which turned to A. S. Yakovlev and the leadership of the GKAT with a proposal to design, first of all, a front-line bomber with the data indicated above, and only later to develop a reconnaissance aircraft on its basis. Taught by the bitter experience of fine-tuning radar bomber sights, the lack of readiness of which prevented the adoption of the aircraft for service and caused conflicts with the Air Force, Yakovlev reacted without enthusiasm to the ideas of K. A. Vershinin. The full-scale development of the Yak-32 never began.
The next development by OKB-115 was the Yak-34 reconnaissance bomber, the speed of which was planned to be increased to 3000 km / h, and the service ceiling - to 21000 … 22000 m with a flight range of 3400 km (2200 km at a speed of 2500 km / h). Obviously, the transition to speeds of the order of 3000 km / h required a transition to new structural materials - steel and titanium. At that time, the Mikoyan OKB-155 began to develop a car with close LTD. Already without much hope, in March 1962, OKB-115 proposed a variant of the Yak-34R with P21-300 (P21A-300) engines. The deadline for flight tests is the fourth quarter of 1965. But the development of the future MiG-25 has advanced so far among competitors that the Yak-34R project remained unclaimed. At this OKB A. S. Yakovleva actually stopped trying to create new front-line reconnaissance aircraft and bombers. The team faced new challenges related to the development of vertical take-off and landing aircraft, as well as passenger cars.
To be continued.
the article uses schemes from the site "Russian Power"
