Kraków 2007-08-22
235 Section 1974-04-26
OKB Sukhoi Su-20. Poland. History
The supersonic fighter-bomber with variable wing geometry. The first aircraft of this type in the Polish Army.
Variable wing geometry.
Before we begin discussing the Su-20 (Su-17) aircraft, let’s move to the famous parade in Domadiedovo, Moscow, on 1967-07-09. The parade was famous because this year marked the 50th anniversary of the communist revolution.
… The next three planes taking off were lined up in a single line, with increasing attractiveness. First, pilot V. Krizhanovsky takes off in the Su-7 BM, which we are already familiar with. Behind him, pilot A. Poltaranov takes off in the Su-7 BKL. This time with solid-fuel take-off accelerators, thanks to which the take-off run was much shorter. The third plane to take off is another plane from the Su-7 family. Behind the old ones is pilot E. K. Kukushev. The take-off is just as short as before, but there are no additional engines visible. Only in the air do the spectators notice that the plane has unusual wings. Their tips are movable. During take-off, they were spread wide. During flight, the pilot changes the geometry of the wings several times, and then lands. The commentator of the show informed that this is the first Soviet plane with variable wing geometry. Only after some time did we learn that it was an aircraft bearing the designation S-22 I, or Su-7 IG (izmeniajemaya geometrija).
At the beginning of the 1960s, the Sukhoi OKB began, on its own initiative, to study variable wing geometry. However, the work progressed relatively slowly. At the turn of 1964 and 1965, Soviet intelligence began to provide information about the new American TFX (F-111) aircraft. At that time, the Americans already had considerable experience in building aircraft with variable wing geometry. Let us recall; the X-5 and the Grumman XF-10 F-1 Jaguar, which was to be introduced into service. At that time, the Soviet authorities decided to finance this direction of work at the Sukhoi OKB and ordered the Mikoyan and Gurevich OKBs to start work on the MiG-23 aircraft in parallel.
In the Sukhoi OKB, after analysis, it was decided to use variable geometry in the design of the Su-7, otherwise designated S-22. This was dictated by the specifics of the fighter-bomber aviation operations. It was found that there was a need to improve flight characteristics at low speed. It should be noted that Sukhoi did not see the need to introduce variable geometry in fighter aircraft and, as it turned out, he was right.
The actions went towards reconstructing the wing itself, without changing its location relative to the fuselage. In May 1965, Pavel Osipovich Sukhoi, together with the head of the bureau’s design brigade, A. M. Polyakova, cooperating with the TSAGI, where the work was led by P. P. Krasilshchikov, presented the concept of the wing. It was divided into two parts. The part by the fuselage remained stationary. This allowed; leaving the main landing gear without major changes, the gunnery and the armament nodes in their previous places. Leaving a significant part of the wings stationary had the additional advantage that the displacement of the centre of pressure was small and within the entire range of the change in the sweep angle amounted to only 2% of the WCA. The movable part of the wings was 4 m long. In addition to the ailerons, it was also equipped with flaps, which can only be used with the minimum wing sweep. On the leading edge, retractable slats (front flaps) were installed, which resulted in improved aircraft manoeuvrability by increasing the permissible angles of attack from 17 degrees to 22 degrees. Space was also found there for internal fuel tanks. The change in the wing sweep angle takes place within the range of 30 degrees to 63 degrees.
An increase in the airfoil mass by 400 kg and a smaller amount of integral fuel in the wings would indicate that the range would be reduced. However, tunnel tests of the wing showed that in intermediate positions, close to 45 degrees, the range would even be slightly increased. This was the impetus for introducing a smooth change in the sweep angle, with the possibility of stopping at any point.
The wings are moved by two independent hydraulic systems connected by a synchronizer. Failure of one system only causes a decrease in the rotation speed.
S-22 I, also known as Su-7 IG. 1966.
Work on the S-22 I, also known as Su-7 IG (izmeniajemaja geometrija), began in full swing in May 1965. Nikoyal Georgievich Zyrin became the head of the team. The starting point was the Su-7 BM model used in the office for test flights until then. The rear of the fuselage came from the Su-7 BKL and a new wing was mounted on such a hybrid.
The reconstruction lasted from January to July 1966. After ground tests, the substantive council of the LII MAP, chaired by M. A. Galai, issued permission for the first flight. The first flight of the S-22 I (Su-7 IG) was performed by Vladimir S. Ilyushin on 1966-08-02. Thus, the aircraft became the first Soviet aircraft with variable wing geometry. Already in the first flight, the pilot made a change in geometry. The pilot found a slight moment of diving or climbing, eliminated by small movements of the control stick. After 20 minutes, the machine landed without problems in Zhukovsky. The aircraft was flown very intensively and without problems. Tests showed a significant improvement in flight characteristics at low speeds and altitudes and no deterioration in flight characteristics at high speeds.
New AL-21 engine developed in CCCP.
As a result of the Vietnam War, many components of General Electric J 79 engines were sent to CCCP. The Soviets decided to use this and create an engine that would allow a rapid increase in the flight parameters of Soviet combat aircraft, including the Su-17 aircraft. Work on the engine designated AL-21 F was carried out by engineer A. M. Lulka from 1965. The initial engine model was to develop a maximum thrust with afterburning of 1 x 87.25 kN, and its first prototype was ready for testing in 1966. From 1968, subsequent AL-21 F engines were used in prototypes of Su-24 aircraft.
A novelty was the movable first sections of the guide vanes in the compressor. Until then, such a solution had not been used in Soviet engines.
The engine had several defects, so in 1969, a decision was made to comprehensively modernize the engine. The work was completed by March 1970. The AL-21 F 3 engine was developed. The new engine received a larger compressor. Reliability was increased, the service life was extended and a thrust of 1 x 76.48 kN was obtained, and with afterburning 1 x 109.80 kN. The engine was adapted for flights at low altitudes.
In the first period of development and operation of the AL-21 F 3 engine, high-temperature titanium fires were a major problem. Finally, only in 1974, the engine successfully passed state tests and was approved for operation without major restrictions.
S-32 M / Su-17 M aircraft. 1971.
A new, smaller, lighter and more powerful engine (still single-flow) caused a thorough redesign of the Su-17 aircraft fuselage. The characteristic waist disappeared. The fuselage diameter decreased from 1.64 m to 1.55 m. The engine cooling grips changed their location. The service hatches were re-arranged. The fuel system has a capacity of 3,640 kg of aviation kerosene. The wing rotation synchronizer was improved, simplifying its construction by eliminating the cardan joints. The engine allowed the armament load to be increased to 4,000 kg. Therefore, two more armament attachment points were added, under the fuselage, with a load capacity of 500 kg each. To shorten the aircraft’s landing run, one new cruciform parachute with an area of 25 m2 was used, and the container was reduced.
The equipment was also modernized. The RSBN-2 S close-range navigation system was replaced by the RSBN-5 S. A new ARK-15 M radio compass. The Pion-GT-32 antenna set was moved from above to the rudder. All these changes did not increase the aircraft’s weight, on the contrary, the aircraft is 200 kg lighter.
After using a new AL-21 F 3 engine with a thrust of 1 x 76.48 kN, and with afterburning 1 x 109.80 kN, a new version of the aircraft was created, designated S-32 M (S-34). Two prototypes were built, designated S-32 M-1 and S-32 M-2. The first prototype made its first flight with pilot Ye. S. Soloviev, in December 1971. Probably on December 5, 1971. Factory tests were carried out quickly and both aircraft were sent to state tests.
The new engine significantly improved the aircraft’s performance. Compared to the Su-7 B, the payload almost doubled, reaching 4,000 kg, and the take-off and landing distance was halved. Compared to the Su-17, the range increased depending on the refueling variant by 145-165%.
In July 1972, the S-32 M-1 was lost. It was crashed by one of the military pilots during a familiarization flight. In the military, the aircraft was designated Su-17 M. The aircraft was initially accepted into service in 1973, and finally in November 1974. Production was carried out in the period 1971-1975, in the “51-61 and 67-73” series. The first aircraft entered service in 1972, mainly for the European part of the CCCP, including naval aviation. A total of 253 aircraft were built.
The production of the Su-17 and Su-17 M went on in parallel for some time, so some changes were introduced simultaneously on both types. For example, the first Su-17 M did not have a second pair of aerodynamic guide vanes on the center wing. The emergency air pressure receiver was still on the side, not on the boom. There was no angle of attack transmitter. It was similar with the armament. The changes were introduced gradually, during repairs. At the peak of production, the Kh-28 anti-radiation guided missiles were introduced into the armament. This is a large missile carried under the fuselage on the central beam PU-28 S. Detection and target indication of the passive homing head was provided by the Mietel-A equipment, carried in a container on the right inner beam under the wing. In addition, an additional type of PTB-800 fuel tanks was introduced to make the armament variants more flexible. Fuel can be refueled through the central throat on the back of the fuselage.
Su-7 BMK with a variable-geometry wing for export. 1973.
The decision to export the aircraft was not easy. Initially, it was planned to equip the Su-7 BMK aircraft with a modified wing. It was to allow it to carry 4,000 kg of cargo at 8 knots; two under the fuselage, six under the wings. The wings were to increase the capacity of the tanks by 330 kg. The aircraft was to be able to carry additional tanks, also under the wings. Probably PTB-1500. In 1973, the prototype of the aircraft was flown by V. A. Krechetov, but work on this was unexpectedly interrupted.
Su-20 (Su-17 MK). 1972
According to the plans, in February 1972, an export version of the Su-17 M designated as the Su-17 MK (Kommerchieskij) was ordered. The prototype took off on December 15, 1972, piloted by A. Isakov. The aircraft successfully passed state tests in January-December 1973 and was put into serial production. The first deliveries to the Middle East arrived in the first months of 1973, as the war, later called the “October War”, was approaching with great strides. Production was carried out in the period 1972-1976 and included 136 units, in the “62-66 and 74-76” series. The aircraft were exported to Egypt, Iraq, Poland and Syria. The Delta-N radio-command equipment disappeared from the aircraft’s cone, and the SRD-5 MK radio rangefinder was installed in its place, capable of cooperating with R-3 / R-13 air-to-air infrared guided missiles up to 4 pieces on APU-13 M under-wing beams. The Delta-NG equipment itself was placed in a gondola under the right inner node. The armament included UPK-23-250 gun gondolas with a GSz-23 cannon with a supply of 250 rounds. The Ch-28 and S-8 and S-25 n.p.r.s were completely excluded from the armament.
Combat use of the Su-17, Su-20.
The combat use of the Su-17 and Su-20 aircraft was significantly limited by weather conditions. A lower cloud base or poor visibility with a very simple navigation system often made it impossible to complete the task. Su-17 aircraft up to and including the Su-17 MK variant could be brought into the target area with some approximation, but the search for and attack had to be carried out in visual line of sight.
Su-20 R
In the mid-70s, for Su-20 (export) aircraft, KKR-1 reconnaissance pods (kompleksnoj razvedki container) were introduced. The pod has the dimensions; length 6.79 m, width 0.59 m, height 0.58 m, and with the beam 0.715 m, weight 780 kg. It is carried centrally under the fuselage. The pod allows vertical, perspective and panoramic photography of the terrain from low and medium altitudes in daylight conditions and from low altitudes, at night, as well as general radio-electronic reconnaissance from any altitude, at any time of day or night in “any weather conditions”. It consists of; AFA-39 camera (for vertical and perspective photography), PA-1 (panoramic), UA-47 (vertical at night), SFP-2 A flash cartridge ejector, 4 KDF-38 cassettes with FP-100 flash cartridges, BZ delay pulse block used to generate signals for opening the UA-47 camera shutter, SRS-9 Wiraz electronic reconnaissance stations, freon cooling system.
The Su-20 R aircraft with the KKR-1 container has a take-off weight of 15,610 kg, maximum speed depending on the flight altitude of 1,300 – 1,800 km/h. Range at an altitude of 200 m – 735 km or with two PTB-1 tanks 150 – 1,150 km. And range at an altitude of 10,000 m 1,400 km and 2,050 km respectively. The permissible overload of the aircraft in flight is 5g. Later, the KKR-1 pod was also installed on Su-22 aircraft.
Su-20 in the armament of the Polish Military Aviation.
Before we discuss the Polish Su-20 aircraft, let us move to the Parade Square in Warsaw on July 22, 1974.
…The people gathered around the Parade Square, on the occasion of the communist holiday of July 22, turned their heads towards the Saxon Garden at one point. Against the blue sky, five microscopic dots transformed into characteristic silhouettes from second to second. As they approached the capital, their speed increased. Five jets with great acceleration from horizontal flight entered vertical flight, leaving behind trails of exhaust fumes. Then, a change in wing geometry was demonstrated. These aircraft were the first fighter-bomber machines with variable wing geometry Su-20 in the Polish Army. These aircraft aroused great interest and at the same time brought another evolution in Polish Aviation.
Su-20 aircraft were also shown on television in July 1974, in a short film showing preparations for the July parade. The aircraft flying in a row demonstrated how to change the wing sweep angle. Even then, it was possible to observe that changing the sweep angle takes about 15 seconds. Years later, we learned that the pilots in this flight were: captain pilot Aleksander Zielenow, lieutenant pilot Ignacy Urbaniak, lieutenant pilot Jerzy Doliniec, captain pilot Mieczysław Kafel, captain pilot Stanisław Walczak and, as a backup pilot, lieutenant pilot Bogdan Likus.
The history of the purchase of Su-20 for Poland. At the beginning of the 70s, Polish politicians and military began to look for a successor to the Il-28 bombers. The last 6 Il-28 bombers were crossed out of the inventory in 1979, but for a whole decade the aircraft were of no combat value. CCCP offered us MiG-23 BN or Su-20 aircraft. Both aircraft with variable wing geometry. The offers were analyzed in terms of their usefulness in our aviation. According to Polish specialists, none of the offered aircraft met our requirements. But there was no other alternative. The choice fell on the Su-20, as a cheaper machine and to a large extent similar to the Su-7 aircraft of various varieties already used in Poland.
Su-20 deliveries to Poland. In the first days of 1974, a group of pilots and technicians left for Krasnodar to train on the new type of aircraft. Among the pilots were: Major Pilot Maciej Paszkowski – commander of the 7th Bomber-Reconnaissance Aviation Regiment from Powidz in 1974-1975, Second Lieutenant Pilot Bogdan Lis, Captain Tadeusz Kołodziejczyk and others. They were the first to perform independent flights on the Su-20 in Krasnodar. Due to bad weather conditions, the training was prolonged. During this training, during a flight on the Su-20, Captain Pilot Tadeusz Kołodziejczyk died.
The first 6 Su-20s were delivered to Poland in 1974. On April 26, 1974, the aircraft landed at the airport in Powidz. These aircraft received side numbers from 01 to 06, painted red. Of course, these were the ones that were shown to the public during the parade in Warsaw on July 22, 1974. We received the remaining aircraft only in 1976. A total of 25 were purchased. We did not buy the training and combat version, because the Su-7Us were still used in this role.
Unfortunately, before the main delivery was completed, on February 3, 1976, the first Su-20 aircraft was lost. The aircraft received the number 01. If the aircraft had survived until the side numbers were changed, it would have received the number 4241. A painful loss, because another pilot, Major (Capt.) Pilot Jerzy Doliniec, died. The crash occurred near the town of Kazimierz Biskupi. The cause was a technical failure of the equipment. The engine failed, which stopped working. In addition, the entire power supply failed and there were problems with the generators. The failure was the fault of the manufacturer, who admitted his guilt. Therefore, in place of the lost aircraft, the manufacturer delivered a new aircraft (1977). We received the aircraft on February 12, 1977. The aircraft received the nb 7125. We received the remaining 19 Su-20 aircraft in the summer of 1976. These aircraft received four-digit side numbers derived from the serial numbers, painted in red. At that time, the side numbers of the first 6 aircraft also changed.
In Poland, Su-20 aircraft became dual-purpose machines. On the one hand, they could effectively attack enemy objects in depth, and on the other hand, they could conduct active photo and radio-electronic reconnaissance, day and night. This second task was performed using a KKR-1 type underslung pod. The pods reached Poland later. It should not be forgotten that the Su-20 used in Poland was also a potential carrier of tactical nuclear weapons.
The Su-20 aircraft took part in their first joint exercises in 1976, during maneuvers codenamed “Shield-76”. Throughout their service in Poland, Su-20 aircraft were also operated from DOL (airport road sections).
In the 1980s, Polish pilots saved Su-20 aircraft from crashing three times, risking their own lives. On May 18, 1984, Captain Andrzej Pawul collided with a stork during the flight. The pilot suffered a facial injury from glass fragments and limited visibility. However, the pilot managed to land safely. On September 4, 1985, Captain Krzysztof Ryniecki. After firing a heavy S-24 missile, the engine pumped and the engine stalled. Despite the low altitude, the pilot managed to restart the engine and land safely at the airport. In 1988, the Su-20 aircraft with pilot Major Krzysztof Krzysztoforski was hit by lightning. The engine stalled. The pilot restarted the engine and landed safely at the airport.
Information from October 16, 1990, from a demonstration of Su-20 and Su-22 aircraft for Swedish officers. – “Su-20s used in Poland have excellent landing parameters. The master of short landings is captain Bogdan Juczyk. Before touchdown, at a height of 2 m, the pilot releases a braking parachute. The measured landing distance is only 350 m! At that time, American tests of the F-15 S / MTD aircraft gave a result of 450 m, without a braking parachute, and 380 m with the method used in Poland. The landing weight of the Su-20 aircraft is 11,000 kg, and the F-15 S / MTD aircraft – 13,000 kg.”
Written by Karol Placha Hetman