Alexander Mladenov introduces the L-39NG jet trainer, a major upgrade of the big-selling Aero Vodochody Albatros family
The L-39NG (New Generation) is the latest model offered by Aero Vodochody of the Czech Republic, widely known as a manufacturer of dependable and affordable jet trainers and light attack aircraft. After more than a decade of flat business without any new aircraft sales, the company is at last set to return to growth in its core business.
In the early 2010s, the company, also known simply as Aero, adopted a pragmatic approach of not continuing with the development of all-new jet trainers for the highly competitive global jet trainer market. Instead, its management decided to strengthen its weakened position in its specific market niche by accommodating the needs of existing operators.
The L-39 continues to give sterling service worldwide and has plenty of upgrade opportunities. As a result, Aero launched the L-39NG deep upgrade project, presented for the first time at the Farnborough Airshow in July 2014. The project is funded on a 50/50 basis by Aero and the Czech arms export agency Omnipol, which is also responsible for marketing.
A Great Legacy
The L-39 has the distinction of being the jet trainer produced in the largest numbers in the world. Designed in the 1970s as a standard advanced jet trainer for the Warsaw Pact nations, more than 3,000 examples were built, with a worldwide proliferation in the 1980s and 1990s. This figure also includes the slightly improved L-59 derivative sold to Egypt and Tunisia and the radically improved light attack version, the L-159, ordered by the Czech Air Force and also sold to the Iraqi Air Force and US company Draken International.
Legacy Albatros derivatives are widely known as excellent trainers, with superb handling performance and rugged design featuring a sturdy and simple wide-track undercarriage with low-pressure tyres and engine air inlets situated above the wing to prevent foreign object damage.
Most of the aircraft built between the early 1970s and the late 1990s are still flying in the fleets of no fewer than 46 military operators worldwide, while civilian-registered examples fly in some 15 countries, including with four civil jet display teams. The total flight time amassed by the global Albatros fleet has exceeded five million hours, with aircraft flown in all climatic conditions. These vary from dry desert to humid jungle and from salty marine to dry and cold environments, where the L-39’s rugged design invariably demonstrates good reliability.
The L-39NG upgrade programme has been divided into two phases to ensure a new life for the omnipresent L-39 and make the aircraft more attractive by boosting its performance, improving economics of operation and offering all-new cockpit avionics with an electronic flight information system (EFIS).
The first phase incorporates replacing the engine and introducing new avionics. It is intended to attract a proportion of existing customers who feel happy operating their older L-39s, but sooner or later will need either to consider a replacement or select an option for a comprehensive upgrade and life extension. The second phase involves offering newly built L-39NGs to new customers looking to purchase highly capable yet affordable jet trainers.
The NG upgrade package was developed by Aero’s design office to address these needs and grab a potentially big share of markets where Aero has little or no chance of selling its new L-159B high-performance trainer and light attack aircraft due to its much higher price tag. The L-39NG’s two upgrade phases can be implemented simultaneously or separately, depending on customers’ needs and budget. When adopting both phases, they will get a virtually new jet trainer at a price that Aero advertises as affordable. A newly built airframe comes with a 15,000-hour total service life, enough for at least 30 years of use, combining performance and reliability with economy of operation and maintenance.
Wingspan: 9.56m (31ft 4in)
Length, overall: 12.03m (39ft 6in)
Height: 4.77m (15ft 6in)
Empty weight: 3,100kg (6,834lb)
Max take-off weight: 5,600–6,000kg (12,346– 13,228lb)
Max internal fuel: 1,200–1,450kg (2,646–3,197lb)
Max payload on external stores: 1,050- 1,650kg (2,315-3,637lb)
Max speed: 420kts (778km/h)
Range on internal fuel: 1,400nm (2,590km)
Rate of climb at sea level: 4,500ft/min (23m/s)
Design load factor: +8/-4G
According to Jakub Broz, an Aero marketing manager for defence and MRO businesses, phase one of the L-39NG upgrade can be offered to interested customers right now, while phase two (which features a newly produced airframe) can be offered in 2017 at the earliest.
The scope of activities in this phase includes the replacement of the existing Ukrainianmade Motor Sich AI-25TL turbofan engine with the US-made Williams International FJ44-4M. In addition, phase one may include the integration of an all-new flight/navigation avionics suite supplied by US company Genesys Aerosystems, originally designed for installation on civil aircraft, together with a head-up display built by the Czech company SPEEL Praha.
The FJ44-4M, featuring dualchannel full authority digital engine control and delivering enhanced speed, range and endurance, is a militarised and higher-rated derivative of a very popular turbofan family. Originally designed for powering light business jets, the total flight time of the FJ44 model family has exceeded ten million hours, with no fewer than 4,600 units now in operation worldwide, which demonstrates superb reliability.
The new engine is set to address the shortcomings of the L-39’s antiquated AI-25PL engine and the Saphir-5 auxiliary power unit (APU) used for engine startup. The AI-25TL is no longer considered to be fuel efficient and has a very long response time for transitioning from idle to the maximum power setting, while its time between overhauls is limited to 750 hours. In addition, there is only one authorised overhaul centre, at the manufacturer Motor Sich’s premises in Zaporozhya, Ukraine.
The FJ44-4M is already proven on military aircraft, as it has been used to power the upgraded twin-engine Saab 105 and the new single-engine Leonardo (formerly Alenia Aermacchi) M-345 jet trainers. Equipped with an electrical starter, the new engine features roughly the same maximum thrust rating as the AI-25TL, delivering 3,790lb (16.87kN). The FJ44-4M, however, is lighter and boasts a much better response time of transitioning from idle to maximum power setting of between three and five seconds, compared to 9 to 12 seconds for the AI-25TL.
The FJ44-4M is a twin-spool design, featuring a single-stage fan, three-stage axial low-pressure compressor stages and one centrifugal high-pressure compressor stage in addition to one high-pressure turbine stage and two low-pressure turbine stages. Its fuel consumption is claimed to be 15% less than that of the AI-25TL, and it is much more resistant to compressor surges. The engine weighs 305kg (670lb) and the total weight saving from the AI-25TL when installed on the L-39NG amounts to about 160kg (353lb). This is possible thanks to the combination of the lighter engine and the removal of the Saphir-5 APU, which is used to supply compressed air for the AI-25TL’s start-up. The FJ44-4J’s integration on the L-39NG utilises the existing AI-25TL mounts on the fuselage, and its installation requires only minor airframe modifications.
The FJ44-4M is operated on-condition and its service life exceeds 10,000 hours. The engine is not required to undergo overhauls at fixed intervals like the AI-25TL; instead it only has to be cycled through four weeklong inspections during its heavy maintenance and it is also free from calendar service life limitations. By comparison, the AI-25TL’s overhaul at Motor-Sich takes four to six months as a rule. Furthermore, the FJ44-4M can be serviced by a network of more than 70 maintenance centres worldwide, and Williams International also offers a lifetime warranty under an engine maintenance programme called TAP Blue. This plan covers all types of scheduled and unscheduled maintenance against a fixed price per flight hour paid by the customer, including repairs in case of foreign object damage. The FJ44-4M is not controlled by the International Traffic in Arms Regulation (ITAR), so Aero will be able to offer it to existing customers worldwide without restrictions.
During intense operations, the FJ44-4M would justify the L-39’s re-engining, as the combined savings from the lower fuel consumption and reduced maintenance requirements will recover the initial investment in re-engining the aircraft in a relatively short period. However, Aero is still reluctant to release any information on the price of the L-39’s re-engining with the FJ44- 4M and the subsequent return on investment in various usage cases.
The first flight of an L-39NG prototype powered by the FJ44-4M, but retaining the old airframe, took place on September 14, 2015, from Aero’s Odolena Voda facility near Prague. According to Broz, pilot comments after the first sortie were extremely positive, as the re-engined Albatros demonstrated a much better performance. The first L-39NG prototype, wearing the serial 2626, is a former Ukrainian Air Force L-39C bought back by Aero Vodochody for use as a company development aircraft.
New Avionics Suite
In addition to the new engine, phase one of the L-39NG upgrade includes the option for integrating an all-new avionics suite combined with airframe and systems life extension.
The new avionics suite with a modular core is supplied by Genesys Aerosystems, formerly S-TEC and Chelton Flight Systems. Being a non-ITAR product, the lightweight and highly capable EFIS incorporates three 6 x 8in (152 x 203mm) IDU-680 colour displays in each cockpit in portrait format, arranged side by side. However, the prototype aircraft featured only one IDU-680 and one smaller IDU-450 display (5 x 4in/127 x 102mm) in the front cockpit in addition to the new Czech-made head-up display.
The three IDU-680s are interchangeable and each can be divided into two smaller displays, offering each pilot a total of six displays. The displays are night vision googles (NVG) compatible. The 3D synthetic vision includes Highway in the Sky functionality, which shows three-dimensional terrain, obstacles and traffic on the primary flight display (PFD).
The display on the left side is used to show a moving map with the planned route superimposed on it, together with tactical situation information and simulation of the employment of various sensors and weapons. The central display is used as a PFD for the presentation of all necessary flight/navigation data, as well as the 3D synthetic vision, while the display on the right shows the information from the engine information and crew alerting system.
The all-new avionics suite conceived for the L-39NG also integrates a GPS module, an attitude reference and heading system and an air data system. In addition, it features a Czech-developed embedded virtual training system to simulate air-to-air radars and a tactical situation display.
Phase Two: New Airframe
The first L-39NG prototype is to be joined by a second, which is scheduled to take to the air for the first time in 2017. A set of more extensive features is offered in the second phase of the L-39NG upgrade. The first of these is the introduction of a comprehensively redesigned, newly built airframe, which will be lighter and more durable than the existing design. It also features an all-new wing design with integral fuel tanks (the so-called ‘wet wing’), which means the aircraft lacks the characteristic fixed wingtip tanks used on all old versions of the L-39. Removing the wingtip tanks will reduce wing loading and allow an increase in the roll rate. The fuselage has a smaller diameter cross-section due to the smaller diameter of the new engine. The fuselage will see some use of composites, mainly in areas affected by vibration. The combination of the all-new wing and the extensively redesigned fuselage also creates less drag, so the L-39NG will boast better aerodynamic performance. The all-new wing features four pylons for external stores in addition to one pylon under the fuselage; each pylon is rated at 375kg (827lb). The wing pylons are ‘wet’, or plumbed to carry external fuel tanks.
The other changes to be introduced in phase two include single-point refuelling, increased-volume fuel tanks, NVGcompatible lighting in both cockpits, VS-2 zero-zero ejection seats and a single-piece canopy for improved pilot visibility and better bird strike protection. The aircraft will also receive a new debriefing system and a health and usage monitoring system.
According to Jakub Broz, the first new airframe will be built in 2017, and the first flight of the phase two L-39NG is set for late 2017 or early 2018, with the first deliveries of newly built aircraft in 2019 at the earliest.
In mid-September 2016, Aero reported the completion of the first phase of the L-39NG’s development effort, centred on the new engine and avionics integration. The test work included exploration of the entire flight envelope, including flight with up to 8.5g manoeuvring loads. The testing has also encompassed evaluation of the functionality of the newly installed Genesys Aerosystems avionics suite.
The main marketing points to attract new customers highlighted by Aero include the ability to use the existing L-39 aircraft up to the end of its extended airframe service life while avoiding the difficulties associated with the maintenance of the AI-25TL engine, combined with lower and predictable maintenance costs. There is also a possibility to adopt a ‘support by the hour’ programme that fully covers the L-39NG’s scheduled maintenance, all unscheduled maintenance events (such as damage, leakages or broken items) and foreign object damage (such as bird strike or stone hit).
Despite the mass use of legacy L-39 versions worldwide, the prospective market for the NG upgrade could be a modest one. No fewer than 700 L-39s continue in operation today or are held in long-term storage, good for a subsequent return to flight operations. However, the vast majority of these aircraft are assigned to the fleets of several big operators in countries that will never consider the NG upgrade, such as Russia and Ukraine, while once-big fleets in Libya and Syria are non-existent or unreachable. In addition, many of the existing L-39 operators in Third World countries are financially constrained and struggle to keep their fleets in serviceable condition with limited budgets, so investing in a serious upgrade could be far beyond their financial reach. It will be a pretty good success for Aero if it manages to collect 100 to 120 orders in the medium term. The company itself expects the size of the future NG market to amount to 120 aircraft in the first four or five years. Aero sources say that the eventual production rate will reach 15 aircraft a year.
While there are no firm orders yet, some expressions of keen interest from potential customers have been made, and these could be converted into upgrade contracts in the foreseeable future. The Czech state-owned company LOM Praha was the first potential customer who claimed interest in re-engining its fleet of eight L-39s. The company manages a military flight training centre at Pardubice in the Czech Republic mainly to train pilots for the Czech Air Force, and it seems entirely natural for it to emerge as the launch customer. The second potential customer in Europe that has expressed strong interest in the L-39NG is the Breitling Jet Team of France, which flies aerobatic displays with a fleet of seven L-39Cs.
Draken International of Lakeland, Florida, is the principal US partner in the L-39NG programme. It has concluded an agreement with Aero to undertake the upgrade works on aircraft purchased by operators in the Americas. According to the clauses of the exclusive partnership with Aero Vodochody, Draken International is also the official distributor of L-39NG and L-159 in the Americas, offered to both military and civil customers. At the same time, Aero continues with its marketing efforts in other parts of the world, where potential customers could be found among existing Albatros operators.
The chief advantage of the L-39NG is the superb flight and systems performance that is offered at an affordable price, rendering the aircraft a worthy competitor to more modern designs that are beyond the reach of budgetconstrained operators. That is why the L-39NG could be a consideration for countries with limited procurement budgets where the L-39 has been well-established in service; the NG will be the most cost-effective solution for the next two to three decades.
L-39 MAIN VERSIONS OVERVIEW
The first prototype of the Albatros made its maiden flight on November 4, 1968, at Aero’s factory airfield in Odolena Voda near Prague. The flight test programme saw the use of four prototypes, while the first production-standard L-39s were delivered to the-then Czechoslovakian Air Force in March 1972. The new type was used to replace the L-29 Delfin and the MiG-15UTI in the basic and advanced training roles for fast-jet pilots. It was provided with two underwing pylons for UB-16-57U 16-round 57mm rocket packs, practice bombs weighing up to 100kg (220lb) or I-318 heat-seeking air-to-air training rounds. Later, this initial version was redesigned as the L-39C (C denoting Cviceni, or training).
The L-39C production tally, including the sub-variants, amounted to 2,280 examples. The main customer was the Soviet Air Force (which took 2,080 aircraft between 1973 and 1991) and it was also sold to Afghanistan, Algeria, Cuba, Ethiopia, Vietnam, Yemen and Iraq. After the break-up of the Soviet Union in 1991, Russia inherited the biggest L-39C fleet, while Ukraine also got a sizeable inventory and subsequently sold on a significant proportion of it. Former Soviet L-39Cs were also delivered to or inherited by military operators in the former Soviet republics of Azerbaijan, Belarus, Kazakhstan, Kyrgyzstan and Lithuania. The latest L-39C operator is the South Sudan Air Force, which is reported to have received two former Ukrainian aircraft in 2016. A large number of second-hand L-39Cs were sold to civilian operators and private owners around the world, mainly in the United States, Canada and Western Europe.
The L-39ZO (ZO denoting Zagrantcny Obchod, or armed) was the second mass production version. It was designed to offer enhanced weapons training capabilities and be used as a light attack aircraft; a total of 347 were built. It comes equipped with four underwing pylons for carrying a total of 1,100kg (2,425lb) of external stores, but otherwise retained the L-39C’s basic design. The inboard pylon pair is also plumbed for external fuel tanks. The L-39ZO prototype made its maiden flight on June 25, 1975. Iraq was the launch customer for this version, receiving its first aircraft in 1977. The L-39ZO was also delivered to East Germany, Libya and Syria. Later, former Libyan aircraft were delivered to Egypt and Uganda, while former East German examples were donated to Hungary.
The L-39ZA was the third version of the Albatros launched into mass production. It has further enhanced weapons training capabilities and features a strengthened undercarriage to support the increased take-off weight, including 1,100kg (2,425lb) of underwing stores. It also introduced a provision for an under-nose gun pack containing a GSh-23L 23mm twin-barrel cannon with a 3,000rpm rate of fire and 250 rounds. Two prototypes were involved in the L-39ZA’s test programme, with the first taking to the air for the first time on September 29, 1976. A total of 265 L-39ZAs were built between 1980 and 1997.
The first production-standard L-39ZAs were delivered to the Czechoslovakian Air Force in 1980, and this version remained in production in the 1980s and 1990s. Original export customers included Algeria, Bangladesh, Bulgaria, Nigeria, Romania, Syria and Thailand. Later, second-hand aircraft were sold to Cambodia (ex-Czech examples), Uganda (ex-Bulgarian), Lithuania (ex-Czech) and Slovakia (which inherited aircraft belonging to the former Czechoslovakian Air Force, also including L-39ZAs and L-39Cs).
The L-39MS (MS denoting Modernised, Super) is the fourth production-standard Albatros derivative, with considerably enhanced performance, new equipment, a new powerplant and a refined structure. Developed as a higher-performance trainer in the early 1980s, it introduced the new PS/ZMK DV-2 turbofan rated at 4,850lb (21.57kN), a strengthened fuselage for operations at a higher take-off weight as well as hydraulically actuated flight controls and VS-2 zero-zero ejection seats. The first prototype, powered by the DV-2 engine, made its maiden flight on September 30, 1986. Externally, the L-39MS can be easily distinguished from the L-39ZA thanks to its more pointed nose, larger wingtip tanks and the upwards/backwards-opening, single-piece canopy. A batch of six pre-series L-39MS aircraft was delivered to the Czechoslovakian Air Force, with the first example taken on strength in 1991; upon the dissolution of Czechoslovakia in 1993, four were retained by the Czech Air Force and two were inherited by the Slovak Air Force.
Under the new designation L-59 (assigned in 1991), the L-39MS was also sold to two export customers, Egypt (49) and Tunisia (12), which took their first jets in 1993 and 1995 respectively.