Fourth Generation Fighter Trainer
Developing the L-39MS and L-59 Super Albatros
The advent of the fourth generation of fighters with their glass cockpit technology, fly by wire control systems and digital engine management systems required a trainer that could ready the student pilot for the advances he would find when he progressed to such aircraft as the MIG-29, Su-27 and F-16.
By the middle of the 1970s, prototypes of fourth generation fighter aircraft were flying in countries all over the world. The end of the decade would see a number in service, most notably the F-15 and F-16 in the US, followed only a few years later by their equivalents in the Soviet Union, the Su-27 and MIG-29. All these aircraft were extremely agile, had advanced management systems and avionics, the information from which was conveyed to the pilot on Head Up Displays (HUDS) and Multi Function Displays (MFDS) in the cockpit. The age of the ‘glass cockpit’ had arrived and provided pilots with all the performance, tactical, mission and threat information they needed in a modern electronic warfare environment. Coupled to this, most of the new generation of fighters had fly by wire control systems and advanced aerodynamics which meant flying them was a very different experience to flying those aircraft they replaced. Aero was quick to recognise that the gap between the existing trainer aircraft and the front line they were supposed to be preparing pilots for was growing again, so the L-39MS programme was begun in order curb this trend and produce a trainer that would allow students to make the transition to the new combat aircraft with relative ease. The Soviet Air Force was also interested in an improved trainer, citing increased power and performance along with such features as a computerised integrated weapons delivery and navigation system among its prime requirements for such an aircraft. The need for a more powerful engine was addressed in a bi-lateral agreement between the Soviet Union and Czechoslovakia to develop and produce a new turbofan of superior performance to the existing AI-25 design.
The Ivchenko-progress Design Bureau and Engine Manufacturing Plant in the Ukraine was to design and develop the engine, which would then be produced by the new Slovak engine manufacturer that had recently been built in Povázská Bystrica, Povazské Strojárne Letecké Motory (PSLM). Unusually for a military engine, the new design had a single stage fan, more typical in civil applications. Known as the DV-2, the new engine produced one third more thrust than the earlier AI-25, developing 4850lb (2200kg) as opposed to 3800lb (1724kg) in the original engine. The first engine was run in static tests during 1984, and later during the engine development a modified L-39 fuselage with the DV-2 fitted to it was mounted in the bomb bay of a Tupolev Tu-16 twin engined bomber flying testbed in order to perform flight tests. The greater power would offset the increased weight of the additional systems the new version of the trainer would require and would have the additional benefit of giving the new version improved performance and handling closer to that of the new generation of fighters. The project became known as the L-39MS. Aside from the engine and its mounts, there were many other extensive changes to the airframe which, although the initial plan had been to maintain a high degree of commonality with the L-39, essentially made the new version of the aircraft a new design in many respects. The cockpit canopy changed to a single piece design hinged at the rear and hydraulically operated, which, in the event of an emergency, was jettisoned using rockets. Inside the cockpit, the ejection seats were changed as well, the VS-2 ‘zero-zero’ seat being fitted in pace of the earlier VS-1. The avionics changed significantly with MFDS in the instrument panel and a head up display to more closely resemble the new generation of fighters, and included a new integrated navigation and communications suite, all developed in Prague’s Výzkumný a zkuśební letecký ústav, VZLÚ or Aeronautical Research and Test Institute. The wing was strengthened to cope with the increased aircraft weight and to enable greater loads to be carried on the underwing pylons to expand the new version’s abilities as a weapons trainer and light attack aircraft. To monitor the health of the airframe and its systems, a diagnostic system was developed to track a wide variety of parameters and report their status, enabling engineers to maintain awareness of the overall condition of the aircraft in service. For the first time in the development of the L-39, the flight control system was changed from the simple direct linkage mechanical system the aircraft had been fitted with since the beginning. The ailerons and elevator were now hydraulically operated by irreversible actuators, partly due to the more advanced flight characteristics the increase in engine power imbued in the aircraft, and partly to give the new version similar handling characteristics to the new generation of fighters. This would ease the transition between types for the students as they would already be used to flying with powered controls. The first L-39MS was the X-21 prototype, which had all of the airframe, avionics and system changes but was still powered by the AI-25TL turbofan. This made its first flight in 1983 before the DV-2 engine was ready to allow the flight test programme of the many upgrades to begin. The first of the L-39MS prototypes to fly fitted with the DV-2 engine was the X-22, which got airborne on September 30, 1986. This was followed by two more prototypes, the X-24 on June 26 1987 and the X-25 on October 6 the same year. Considerable flight testing was required, the prototypes often flying with their rear cockpits full of telemetry and recording equipment to monitor the performance of the aircraft and its new systems. By 1989, the first pre-production aircraft was completed, making its first flight on October 1 and beginning a series of military flight trials for the Czechoslovak Air Force with the identifying number 0001. In 1992, five L-39MS trainers were built for the
BELOW: As part of the flight tests for the Ivchenko-progress DV-2, an L-39MS fuselage fitted with the engine was suspended in the bomb bay of a Tupolev Tu-16 flying laboratory from the Russian LII. Pavel Kucˇera
ABOVE: The increased power of the L-39MS with the DV-2 engine is obvious in this shot of 0006 of the Czechoslovak Air Force loaded with the under nose cannon, rocket pods and air-to-air missiles. Pavel Kucˇera
ABOVE: A Pslm-built Ivchenko-progress DV-2 turbofan on display in the Museum of Aviation, Košice, Slovakia. www.leteckemotory.cz ABOVE RIGHT: Still powered by the AI-25TL turbofan, the X-21 prototype of the L-39MS was the first to fly in 1983. Note the single piece cockpit canopy hinged at the rear. Pavel Kucˇera RIGHT: The third L-39MS prototype, the X-24, first flew on June 26, 1987. Note the rear cockpit is full of recording and telemetry equipment. Pavel Kucˇera