Archive digitization



Aviation and Diplomacy

Frank Piasecki

NATO 1949-2009 Projekt ekspozycji w Muzeum Lotnictwa Polskiego w Krakowie



Polish Aviation Museum

31-864 Kraków,
al. Jana Pawła II 39
phone: (12) 640 99 60,
(12) 642 40 70
e-mail: info@muzeumlotnictwa.pl

a cultural institution of the Malopolska Region

Małopolska – Kraków Region


Patronage

Kraków Airport







Aeroplane: Sukhoi Su-20 (NATO: Fitter-C)

Sukhoi Su-20 (NATO: Fitter-C)
USSR
fighter-bomber
1973



  • Technical data


Span (maximum wing sweep) 10.03 m
Length (with air pressure receiver) 18.73 m
Take-off weight (maximum) 18120 kg
Maximum speed (without external stores) 2230 km/h
Ceiling 15200 m
Range 2500 km
Armament see text
Powerplant :
AL-21F3, rated at 11,200 kG of thrust.

 

By the end of the 1950's, the stormy development of aviation technology was connected with increasing aircraft speed and ceiling with the cost of extending take off and landing distances and a drop in manoeuvrability. Therefore building high quality long runways, became necessary. Such objects, however, became very sensitive to enemy air attacks. The destruction of even a small part of runway could make take off and landings difficult, or even paralyse them.
The OKB-1 Sukhoi Experimental and Construction Works coped with problems of improving the Su-7 fighter-bomber and its follow up derivatives.
The flexible geometrical wing configuration could save many problems on the Su-7 however designers were aware that applying such a configuration would cause significant aerodynamic and technical difficulties. By the mid 1960's, the Soviet Air Force set the standards for a new, multi-role frontal aircraft. The machine needed to feature supersonic, low altitude cruising speed, short take off and landing on runways of 1000 - 1200m length and a 700 - 800km operational radius with a one tonne bomb load.
The variable wing configuration could make its designing easier. The work on the new aircraft, named the S-221, started in May 1965. To speed up the program, the front part of the Su-7BM and the rear part of the Su-7BKL were used. The wing was divided into two parts - one fixed, attached to the fuselage and the movable outer wing, suspended on a special rotary joint attached to the fixed wing section. The outer wing was equipped with slats coupled with flaps. It significantly improved flight characteristics at low speeds and low angle of wing sweep adjustments. The one problem to solve was the construction of the fluid drives for changing the wing sweep, steering the high-lift devices and synchronising wing position.
Changes in the airframe construction increased its total mass to 400kg and decreased the fuel load 400 litres.
In August 1966, the S-221 flew for the first time. Intensified tests started, gradually introducing the necessary changes. In November 1967, the decision to start the Su-17 (the S-32) production fell.
Radio and navigation systems, as well as aiming devices, were applied.
The armament, similar to that of the Su-7BKL, consisted of two 30mm cannons buried at the wing roots. The external stores consisted of six hard points capable of carrying up to 2500kg (including a nuclear bomb). In 1973, air-to-surface guided Ch-23 missiles enriched the aircraft's armament (it required a special radio commanding guidance system). The Su-17 was produced until 1975. It was a step forward in comparison with the Su-7 however the unsolved problem with the gas-guzzling Al.-7 engine, resulting in a short range, remained.
In 1972, production of the new, Su-17 (S-32) derivative started. It entered service in the same year. The aircraft was powered with the modern and economical AL.-21F engine, designed by A. I .Lyulka. The design was based on the "captured" American J-79 turbojet engine. The Al.-21F, caused changes in construction in the fuselage and inspection hatches. The flexible wing mechanism was improved and the fuel load increased.
In 1975, the central fuelling was introduced, significantly speeding-up the flight readiness. The external load was increased to 4000kg.
The armament consisted of various bombs (including nuclear), unguided and guided missiles (the Ch-23 missile guiding station was placed in the intake cone, similar to those used on other Su aircraft). New ground attack armament was introduced: cluster bombs, unguided R-8 and guided Ch-28 missiles, which were used for fighting enemy radar stations. Production of the Su-17M ended 1976.
In 1972, a proposal came of producing the Su-17 export version under the commercial name, the Su-20. Its prototype, named the S-32 was flown in December 1972.
Two derivatives were envisaged:
- The "A" derivative (practically the same Su-17M, was envisaged for the Warsaw Pact members)
- The "B" impoverished derivative, with the Su-7BMK equipment and armament for other operators.
The Su-20 was capable of carrying four infra-red guided R-3S or R-13 rockets (the Su-17 didn't carry them). The radio range finder was placed in the intake cone. The guidance of the air-to-air Ch-23 missile was done with the help of a transmitter placed in a container hanged under the wing, close to the fuselage.
The only Su-20 operator was Poland, which bought 26 aircraft. The first aircraft came in 1974 and the next delivery took place in 1976. The 27th aircraft came to Poland in 1977, as compensation of the aircraft loss due to the producer's fault. Part of the aircraft was equipped with a camera placed in the ventral part of the fuselage, behind the nose wheel bay. This version was unofficially known as the Su-20R. The last examples of the Su-20 were withdrawn from service in 1997. It was the first flexible geometry wing aircraft to enter the Polish Air force.

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Dofinansowano ze środków Ministra Kultury i Dziedzictwa Narodowego
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