Aero Vodochody L-39 Albatros

16 Apr 2018

In 1964, Czechoslovak aircraft manufacturer Aero Vodochody embarked on a new design project to meet the specified requirements for a "C-39" (C for cvičný – trainer), setting up a design team under the leadership of Jan Vlček and the Aero L-39 Albatros was born.  

Aero L-39 Albatros

This aircraft was to serve as a replacement for the Aero L-29 Delfín, an early jet-powered trainer, as a principal training aircraft. Vlcek envisioned the type, a twin-seat single-engine aircraft, being adopted as the primary trainer throughout the Warsaw Pact nations.

Aero L-29 Delfín

On 4 November 1969, the L-39 (under the designation "Prototype X-02" – the second airframe to be built) conducted its maiden flight, for which it was piloted by Rudolf Duchoň, the factory's test pilot. Serial production of the initial model of the L-39, designated L-39C, commenced in 1971.

 In 1972, the L-39 Albatros was formally recognized by the majority of the countries comprising the Warsaw Pact as their preferred primary trainer, after which point, sizable orders from military customers throughout the bloc proceeded, many of which were from the Soviet Air Forces. In 1974, the first L-39 trainer entered service with the Czechoslovak Air Force.

Several specialised variants of the base L-39 design were quickly introduced. In 1972, a purpose-built target tug variant, the L-39V, conducted its initial flight.  In 1975, the first L-39ZO training/light combat model, which was equipped with four underwing hardpoints as well as a strengthened wing and modified landing gear, performed its first flight.

L-39V

In 1977, the first L-39ZA light combat variant, which was fitted with a single Gryazev-Shipunov GSh-23 cannon mounted underneath the fuselage in addition to the four hardpoints and strengthening of the L-39ZO, made its maiden flight.

Roughly 200 L-39s were being sold each year upon the jet trainer market during the late 1980s. According to the Stockholm International Peace Research Institute, in 1993, the total export orders gained for the L-39 represented 80 per cent of the value of all Czech military product export sales made for that year. During the 1990s, shortly following the dissolution of the Soviet Union and the end of the Cold War, Aero Vodochody decided to develop versions of the Albatros equipped with Western-sourced avionics, engines, and weapon systems.  Around the same time, Aero Vodochody formed an active partnership with Elbit Systems of Israel, under which a number of L-39s were delivered to Elbit to be equipped with modern electronics and on-board systems before being re-exported to end users such as the Royal Thai Air Force.

Sales of the L-39 declined during the 1990s. This downturn has been attributed to the loss of the captive Warsaw Pact trainer market, to which a substantial proportion of the total aircraft manufactured had been historically sold to; allegations about Czechoslovak banks being unable to finance the defence industry and inaction on the part of the Czechoslovak government; and concerns over the quality of manufacturing standards. In 1996, production of the L-39 came to an end. Since the end of production, Aero Vodochody has developed several improved variants of the L-39 to take its place, and has continued extensive support and overhaul operations for existing L-39 customers.

One of the replacements for the L-39 Albatros was the Aero L-159 Alca, a modernised version of the L-39. Originally, Aero Vodochody had intended to develop the L-159 in partnership with Elbit, but the Czech Ministry of Defence instead selected Rockwell Collins to partner on the program.

L-159

The limited success of the L-159 led Aero to announce at the 2014 Farnborough Airshow that it was developing an upgraded version of the L-39, designated L-39NG, to compete with the Alenia Aermacchi M-346 and British Aerospace Hawk.

Alenia Aermacchi M-346

British Aerospace Hawk

The L-39NG replaces the AI-25 turbofan with a Williams FJ44 engine; the airframe is modified, the wingtip fuel tanks being eliminated, and a new suite of avionics will be provided. First flight of the L-39NG was in September 2015, with deliveries starting in 2020.

L-39NG

The L-39 Albatros was designed to be a cost-effective jet-powered trainer aircraft, which is also capable of performing ground attack missions. For operational flexibility, simplicity, and affordability, the majority of on-board systems have been simplified to avoid incurring high levels of maintenance, as well as to minimize damage caused by mishandling when flown by inexperienced air crew. It could be readily flown from austere airstrips such as frozen lakebeds, enabled through the rugged design of the landing gear and favourable low landing speeds. The aircraft's flying qualities are reportedly simple, which is made easier by way of a rapid throttle response, making it easier for students who had never previously flown before to successfully control.  As a training platform, the L-39 itself comprised part of a comprehensive system which also used flight simulators and mobile ground test equipment.

The low-set, straight wing has a double-taper planform, 2½-deg dihedral from the roots, a relatively low aspect ratio, and 100 litres (26 US gal; 22 imp gal) fuel tanks permanently attached to the wingtips. The trailing edge has double-slotted trailing edge flaps inboard of mass-balanced ailerons; the flaps are separated from the ailerons by small wing fences.  An automatic trimming system was present, the flaps and the trim system being connected in order to counteract the potentially large pitch changes that would otherwise be generated by vigorous movements of the flaps. The tall, swept vertical tail has an inset rudder. Variable-incidence horizontal stabilizers with inset elevators are mounted at the base of the rudder and over the exhaust nozzle. Side-by-side airbrakes are located under the fuselage ahead of the wing's leading edge. The flaps, landing gear, wheel brakes and air brakes are powered by a hydraulic system. Controls are pushrod-actuated and have electrically powered servo tabs on the ailerons and rudder. Operational g-force limits at 4,200 kilograms (9,300 lb) are +8/-4 g.

A long, pointed nose leads back to the tandem cockpit, in which the student and instructor sit on Czech-built VS-1 ejection seats under individual canopies, which are opened manually and are hinged on the right.

 

The rear seat, typically used by the instructor, is elevated slightly to readily enable observation and guidance of the student's actions in the forward position. The design of the cockpit, panel layout and many of its fittings resemble or are identical in function to those of other commonly-used Soviet aircraft; for example, the procedure for deploying the ejection seat is exactly the same as for the Mikoyan MiG-29. The cockpit is highly pressurized, requiring the air crew to wear oxygen masks only when flying in excess of 23,000 feet.  A gyro gunsight for weapon-aiming purposes is typically present in the forward position only.

A single turbofan engine, an Ivchenko AI-25TL (made in the Soviet Union) is positioned in the rear fuselage, fed through shoulder-mounted, semi-circular air intakes (fitted with splitter plates) just behind the cockpit and the tailpipe below the horizontal tailplane. The engine has a time between overhaul (TBO) of 1,000 flight hours; however, it is allegedly cheaper than the majority of turbine engines to overhaul. Five rubber bag fuel tanks are located in the fuselage behind the cockpit. Several heavy radio units are typically installed in an aft avionics bay; these are often removed on civilian-operated aircraft and replaced with a 70-gallon fuel tank. Additional fuel tanks can be fitted in the rear cockpit position and externally underneath the wings; the tip-tanks can also be expanded for a greater fuel capacity.

The aircraft is fitted with a hydraulically-actuated retractable nosewheel undercarriage which is designed to allow operation from grass airfields. The main landing gear legs retract inward into wing bays while the nose gear retracts forward.

 

The basic L-39C trainer has provision for two underwing pylons for drop tanks or practice weapons, but these are not usually fitted. It can be armed with a pair of K-13 missiles to provide a basic air defence capability.  Light-attack variants have four underwing hardpoints for ground attack stores, while the ZA variant also has an under fuselage gun pod.  Mock UB-16 rocket pods can also be installed for visual appearance only.

While newer versions are now replacing older L-39s in service, thousands remain in active service as trainers, and many are finding new homes with private warbird owners all over the world. It has been claimed that the L-39's desirability stems from the fact that it is "the only available second-generation jet trainer". This trend is particularly evident in the United States, where their $200,000–$300,000 price puts them in range of moderately wealthy pilots looking for a fast, agile personal jet.  Their popularity led to a purely L-39 Jet class being introduced at the Reno Air Races in 2002, though it has since been expanded to include other, similar aircraft.

L-39 at the Reno Air Races

 

General characteristics

 

Crew: 2

Length: 12.13 m (39 ft 9½ in)

Wingspan: 9.46 m (31 ft 0½ in)

Height: 4.77 m (15 ft 7¾ in)

Wing area: 18.8 m² (202 ft²)

Airfoil: NACA 64A012 mod

Empty weight: 3,455 kg (7,617 lb)

Max. takeoff weight: 4,700 kg (10,362 lb)

Powerplant: 1 × Ivchenko AI-25TL turbofan, 16.87 kN (3,792 lbf)

 

Performance

 

Never exceed speed: Mach 0.80 (609 mph, 980 km/h)

Maximum speed: 750 km/h (405 knots, 466 mph) at 5,000 m (16,400 ft)

Range: 1,100 km (593 nmi, 683 mi) (internal fuel)

1,750 km, (944 nmi, 1,087 mi) (internal and external fuel)

Endurance: 2 hr 30 min (internal fuel), 3 hr 50 min (internal and external fuel)

Service ceiling: 11,000 m (36,100 ft)

Rate of climb: 21 m/s (4,130 ft/min)

Wing loading: 250.0 kg/m² (51.3 lb/ft²)

Thrust/weight: 0.37

Climb to 5,000 m (16,400 ft): 5 min

Take-off roll: 530 m (1,740 ft)

Landing roll: 650 m (2,140 ft)

 

Armament

 

Up to 284 kg (626 lb) of stores on two external hardpoints

 

 

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