The L-39 was developed by Aero Vodochody, the famous Czech aircraft company founded in 1919 that specialized in production of military light combat jets. In the times of the Czechoslovak Socialist Republic, the company had evolved into a conglomerate of aircraft factories that were focused on hydraulics, avionics, motors, besides the final product. Czechoslovakia, a relatively small country, could produce various sporting airplanes, such as Moravan Otrokovice's ZLINs, and sailplanes. The number of aircraft per capita in Czechoslovakia was exceptional.
The L-39 Albatross succeeds the L-29 Maya/Delfin. L-39 ALBATROS light training jet aircraft is a development of the well-tried L-29 DELFÍN. It is designed for initial and advanced training. This elegant looking jet trainer has been in service with numerous air forces for many years and has even become a common sight at air shows. Several modified and upgraded versions have been developed since 1968, known as L-39C, L-39V, L-39ZA, L-39MS and L-39ZO. The armed weapons-trainer variant is designated the L-39ZA, and a close-support and ground-attack version is designated the L-39ZO.
A low-wing aircraft with tandem seating and a classic all-metal airframe, it is equipped with a three-point hydraulically operated retractable landing-gear. Trapezoidal wings have fuel tanks on their tips. The wing has double-slotted flaps with a takeoff deflection of 25° and landing deflection of 44°. The fuselage consists of two construction parts - the forward and the rear one. The rear fuselage and tail are removable. The electronic equipment and oxygen system are located in a dielectric nose cover. In L-39, the canopy of the cockpit is hinged to the right. In newer development types L-59 (originally L-39MS) and L-139 it is hinged hydraulically upwards to the rear.
The power plant is an Al-25TL by-pass double-shaft turbojet engine with max. static thrust of 16.87 kN. The engine is started by a Saphire 5 single-shaft gas turbine. The types with maximum takeoff weight of 5,700 kg are equipped with a more powerful DV-2 engine with max. thrust of 21.57 kN. There is a classic mechanical control system with power transmission over levers and pull rods from both pilot posts.
The electrical equipment is powered by the main generator (9 kW) from an accumulator enabling autonomous operation. The electrical net includes inverters (115 V and 3x36 V). Radio equipment of the aircraft consists of radio, communication, radionavigation and identification devices. For the training of landing and approach, a RSBN-5S close navigation system and ILS landing system are used. The aircraft is also equipped with the RKL-41 radio compass, RV-5 radio altimeter, MRP-56PS marker and an identification device.
In Febuary 1964 the Czechoslovak Ministry of Defense issued a preliminary technical specification for a new trainer aircraft to replace the L-29. A developement team, headed by the Chief Designer Jan Vlcek and the Chief of Preliminary Design Karel Dlouhy of Aero, had already been looking at a number of perspective replacements. It was necessary then to respect the reccomendations of the "Main Customer" - ie: Soviet Union (who eventually ended up getting over 2/3 of the production!) There was no possibility to manufacture such an aircraft without an obligation about it's future acquistion. Over the next couple of years, military jet trainers became the main topic within the Czechoslovak aviation industry.
It was decided that the prototypes were to be equipped with modified AI-25 turbofans - AI-25's originally powering the Yak-40. The company responsible for the AI-25W modification was Motorlet in Jinonice and VZLU in Letnany were tasked with developing the VS-1 ejection seat. A milestone in the production was the flight of prototype L-39 X-02, flown by Rudolf Duchon from the Aero airfield on 4 November 1968. It was followed by ten pre-production aircraft.
The flight tests showed that the L-39 had excellent flight characteristics with the aerodynamically smooth design. Some problems were incounted with the powerplant and engine intakes, which had to be modified, resulting in the cross-section being enlarged. Three prototypes were flown and the next two airframes underwent ground testing. The advanced Enviroment Control System (ECS) was developed and tested, the next protype already with the final design of air intakes was used for testing of an engine starter driven by the Saphir 5 air turbine of French design, thus providing the aircraft with full capability of being independant of ground power sources.
As a final powerplant of the L-39, the AI-25TL turbofan was selected, produced by Progress in the Ukraine, which became the exclusive engine supplier. In 1971 the AI-25TL was tested on the second and seventh prototypes, together with other modifications. In the same year, preperation was made for the series production at Aero and the aircraft was officially named "Albatros". The first aircraft of the preproduction (zero) series were handed over to the Czechoslovak Airforce on 28 March 1972.
Extensive testing continued along side the beginning of series production, resulting in some systems modifications. The L-39 X-07 prototype completed the next phase of military and contractor tests by the summer of '72, and a year later it passed State Verification tests in the Soviet Union, therefore complying with the requirements for deployment to Soviet military academies.
The Czech Republic tried to sell its famous L-39 to Australia. The plane's technical characteristics and price fully met the demands of the customer. However, the L-39's major competitor, the British Aerospace Hawk 200 came out on top after the British government exerted pressure on Canberra.
As the new versions of "Thirty Nines" began to appear in 1977, the basic version was retitled L-39C. It is equipped with mostly equipment of Soviet origin. It was the standard jet trainer for the Soviet Union, and Czechoslavakia from 1971 to 1973. The aircraft is the standard jet trainer for former Warsaw Pact countries. The L-39 was exported to 16 countries. The newest recipients of these aircraft are: Afghanistan, Algeria, Bulgaria, Cuba, Ethiopia, Iraq, Libya, Nigeria, Romania, Syria, and Vietnam. From 1971 to 1999 a total of 2921 units of L-39/59 family were delivered and unrivalled more than 4 million flight hours were flown at users all over the world.
A contract for delivery of 12 new L-39C jet trainers was signed by Aero Vodochody in Sana´a, Yemen Republic capital, at the end of February 1999. The contract, which is result of several years intensive negotiations, covers also delivery of spare parts, logistics, pilot and ground crew training and service support.
The new generation of L-39s brought a wide range of innovations. Among them is a new Williams engine with great traction, fixed avionics and, most importantly — from the glider's perspective — the so-called 'wet wing'. The point is that the aircraft's wing structure is used as a reservoir for fuel.
Over the years, different versions were built. The L-39C version has two wing pods, L-39ZA and L-39ZO have reinforced wings with four underwing stations on which they can carry bombs, rockets, or two short-range air-to-air missiles. The L-39MS has higher performance and modern electronic equipment and avionics.
- L 39C: Standard aircraft for basic and advanced training
- L 39V: Single-seat aircraft for target towing. Used by Czech and East German Air Forces. Only eight built. On request of the Czechoslovak Airforce, a single seat L-39V target towing modification was developed. The rear unpressurized cockpit of the eighth prototype, tested since 1972, was equipped with a winch device driven by a ram-air turbine, located in a pod under the fuselage. The KT-04 target was developed by Letov; and procedures for take off and target retrieval were also developed and tested.
- L 39ZO: Training and multipurpose light attack aircraft with underfuselage gun pod and four hardpoints und reinforced wing. First flown on 25 August 1975, a potential for the L-39ZO aircraft was distinguished very soon and therefore in 1973 developement an armed version was started, especially because of the export ability to the countries of the "Third World". This modification was able to be used for advanced weapons training by placing an extra hardpoint under each wing - therefore increasing the number of hardpoints to four. The modification with four hardpoints on the reinforced wing and with ability to carry two external droptanks on inboard pylons, got airborne for the first time on 25 June 1975 as the ninth prototype was designated the L-39ZO. A year later the ninth and tenth prototypes concluded combined contractual and verification tests.
- L 39ZA: Trainer and light attack aircraft with impoved avionics. First flown in September 1976. This version remained on offer for a time, but as of 2012 is not in production. L-39ZA is equipped with a sight with a camera gun and a two-barrel 23mm quick-firing Gsh-23 gun, which is installed under the fuselage. Besides training tasks, it can also be used for tactical air surveillance. Following on from development of the L-39ZO, in 1976 the ninth and tenth prototypes were engaged in tests of the GSh-23 twin barreled machine gun and designated L-39ZA's. These two prototypes were complemented by the eleventh L-39 prototype X-11 on 16 May 1977. This was the first aircraft to be shown in the West at the 32nd Paris Air Salon in the same year. The L-39ZA can also be utilized for reconnaissance.
- L 39ZA/ART: Version for Thailand with avionics supplied by Elbit of Israel.
- L-39MS: Featured important advances designed for enhanced performance and a broader combat envelope to include light attack/COIN (counterinsurgency) and limited air and ground defense operations. Armament is similar, but includes an option of four external fuel drop tanks. For export, this model was given the designation.
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