Aero L-39 Albatros L-39V

The L-39V was born of a very specific Czechoslovak training need: an aircraft able to tow an aerial target at which fighter pilots and anti-aircraft gunners could fire live rounds. The letter V stands for «vlečná», towing. In 1970, while the L-39 was going through intensive testing, the Ministry of National Defence set out requirements for a target-towing aircraft, and the answer was to adapt the trainer itself. The aircraft was conceived together with the target it would tow, the KT-04, which was presented as part of the L-39 training system.

The first L-39V was built in 1972 as the X-08 prototype, powered by an AI-25TL engine, and was completed around June that year. For reeling the cable, the designers chose to reuse, with some changes, the system that had already proved itself on the towing versions of the MiG-15. The towing and cable-cutting equipment passed ground tests in late August and early September 1972, and flight testing, delayed by modifications, began in October 1972. According to valka.cz, 45 test flights were flown, about three quarters of them with the target in tow, and X-08 was also used to study wing behaviour at minimum speeds. In early 1973 its engine was replaced, the de-icing system was tested on it and a Czechoslovak-made Safír 5 air generator was fitted. From July to September 1973 it went through military trials with the KT-04; after these were assessed, both aircraft and target were modified, and supplementary trials of the cable-cutting device took place between July and September 1974.

The differences from the standard L-39 went deep. The aircraft was a single-seater: the former rear cockpit housed a drum with a 5 mm steel cable, driven through a reduction gear by a small L-03 ram-air turbine hung under the fuselage. That turbine, with a forty-blade rotor, had been designed in the 1950s by Bohuslav Listoň's team and was made at the Malešice aircraft repair works. Behind it sat the emergency cable cutter, first mechanical and later hydraulic, and cable guides were fitted under the fuselage. The cockpit was neither pressurised nor sealed, the aircraft lacked part of the navigation equipment (the RSBN-5S system, for example, was not installed), load factors were limited to between −3 and +6 g, and the initial climb rate of 21 m/s was 1 m/s lower than that of the L-39C. The aircraft wore a conspicuous yellow and white scheme, with blue-edged national insignia and a grey-green band ahead of the cockpit.

The KT-04 was developed between 1969 and 1971 by Jan Franc's group at Rudý Letov at the request of the Czechoslovak air force; its first flights were made in 1971 behind a MiG-15. It was an all-metal unpowered glider with a span of 5.3 m, a length of 4.9 m and a take-off weight of 110 kg, cleared to 600 km/h, whose electronics recorded rounds passing close to the target and relayed the results to ground scoring equipment. Series production began in 1974 after the military trials and, according to the Kunovice aviation museum, ran from 1975 to 1985, with more than 300 targets built. Take-off was unusual: the target, sitting on a jettisonable trolley, was hooked on 100 to 150 m behind the L-39V, which stayed on the ground until about 210 km/h (against about 150 km/h for other versions) and climbed more steeply; once the tug was about 80 m up, the target released itself from the trolley, which dropped onto the runway and deployed its braking parachute. In flight the cable could be paid out to 1.5 km, and the target followed the tug's path a few tens of metres below it. Because it had so little drag, the target tended to catch up with the aircraft if the pilot throttled back sharply or extended the airbrakes, so a device released it if the cable stayed slack for more than five seconds. When firing ended, the turbine reeled the cable in until the target was 150 m behind, a sliding ring released the hook, and the KT-04 came down by parachute onto an inflatable bag that cushioned the landing.

Eight L-39Vs were built in all, every one in 1976 as part of the 7th production series, with construction numbers ending in 0705, 0715, 0720, 0725, 0730, 0735, 0740 and 0745. The Czechoslovak air force used six from 1976 (0720, 0725, 0730, 0735, 0740 and 0745). The first targets and tugs served with the 5th squadron of the 5th Fighter Regiment at Plzeň-Líně; four flew briefly with the 1st Fighter Regiment at Planá near České Budějovice, and in the early 1980s they moved to a special training squadron of the Košice military aviation college. They also operated from Malacky-Kuchyňa, home of an air firing range. When the federation split on 1 January 1993, four went to Slovakia and two to the Czech Republic. In Slovakia they served as reserve aircraft for the «Biele Albatrosy» aerobatic team; in 2001 the two still flying moved to Sliač, where by 2005 KT-04 targets had been towed only three times, always with 0745, and both aircraft (0745 and 0730) were used for routine training flights in the colours of that since-disbanded team. According to valka.cz, 0720 and 0735 are displayed at the Vyškov museum of aviation and ground equipment.

The other two, 0705 and 0715, passed from Czechoslovak service to East Germany's National People's Army, where they carried the numbers 170 and 171: the first was taken over on 30 May 1980 and the second in June 1981, and both flew with the target-towing unit at Peenemünde. After reunification they received the Luftwaffe registrations 28+48 and 28+49 on 30 October 1990. 28+48 was repainted and handed over to the Luftwaffe Museum at Berlin-Gatow on 29 March 1995; 28+49 went first to the company Aerotec and later to the aviation technology museum at Rothenburg, near the Polish border.