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112-461: The project traces its origins to a 1990 requirement to replace the aging Aero L-39 jet trainers, which were reaching the end of their service lives. The Aero L-29 had originally been selected as a Warsaw Pact standard trainer in 1961, in preference to the Yak-30 and PZL TS-11 Iskra . It started to be replaced in 1974 by the greatly updated L-39, powered by the new Ivchenko AI-25 engine. By 1990

224-580: A Strela-2 MANPADS fired by Doku Zavgayev 's pro-Russian militia. The pilot, Col. Ali Musayev and the co-pilot Dedal Dadayev were killed. One of the main reasons that prompted the first Su-25 air raids that destroyed the Chechen air force on the ground, and started the Russian intervention , was preparations being made by Dudayev's air force, which had been spotted by reconnaissance Sukhoi Su-24 MRs. There were fears that these aircraft could slow or deter

336-403: 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 that is designed to allow operation from grass airfields. The main landing gear legs retract inward into wing bays while

448-830: A considerable number of L-39 trainers, having transferred the bulk of their training activities onto the Czechoslovak aircraft. During the American-led invasion of Iraq in 2003, on 14 April 2003, a pair of United States Navy McDonnell Douglas F/A-18 Hornets attacked several L-29 and L-39 aircraft on the ground at an airfield near the city of Tikrit ; these had been believed to have been modified to perform as delivery platforms for weapons. Libya acquired some 180 L-39ZOs around 1978, which served at Sabha and Okba Ben Nafi flying schools along with Yugoslav-made G-2 Galeb for advanced jet training and Italian-made SF.260s (for primary training). The L-39s were deployed during

560-434: A corresponding increase in pressure and temperature in the exhaust duct which in turn cause a higher gas speed from the propelling nozzle (and higher KE and wasted fuel). Although the engine would use less fuel to produce a pound of thrust, more fuel is wasted in the faster propelling jet. In other words, the independence of thermal and propulsive efficiencies, as exists with the piston engine/propeller combination which preceded

672-419: A discordant nature known as "buzz saw" noise. All modern turbofan engines have acoustic liners in the nacelle to damp their noise. They extend as much as possible to cover the largest surface area. The acoustic performance of the engine can be experimentally evaluated by means of ground tests or in dedicated experimental test rigs. In the aerospace industry, chevrons are the "saw-tooth" patterns on

784-410: 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,

896-486: A drone being brought down by a heat-seeking missile fired from a MiG-29 . A UN investigation also concluded that the footage was authentic and that the drone was shot down by a Russian MiG-29 using a Vympel R-73 heat seeking missile. The Taliban Air Force had managed to obtain around five L-39C aircraft from the remnants of the former Democratic Republic of Afghanistan Air Force ; with foreign technical support and pilots, these were placed into combat operations during

1008-606: 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. In September 2012, there were 255 L-39s registered with the U.S. Federal Aviation Administration and four registered with Transport Canada . Several display teams use the L-39 such as the Patriots Jet Team (6 L-39s),

1120-410: A fixed total applied fuel:air ratio, the total fuel flow for a given fan airflow will be the same, regardless of the dry specific thrust of the engine. However, a high specific thrust turbofan will, by definition, have a higher nozzle pressure ratio, resulting in a higher afterburning net thrust and, therefore, a lower afterburning specific fuel consumption (SFC). However, high specific thrust engines have

1232-426: A high dry SFC. The situation is reversed for a medium specific thrust afterburning turbofan: i.e., poor afterburning SFC/good dry SFC. The former engine is suitable for a combat aircraft which must remain in afterburning combat for a fairly long period, but has to fight only fairly close to the airfield (e.g. cross border skirmishes). The latter engine is better for an aircraft that has to fly some distance, or loiter for

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1344-416: A higher nozzle pressure ratio than the turbojet, but with a lower exhaust temperature to retain net thrust. Since the temperature rise across the whole engine (intake to nozzle) would be lower, the (dry power) fuel flow would also be reduced, resulting in a better specific fuel consumption (SFC). Some low-bypass ratio military turbofans (e.g. F404 , JT8D ) have variable inlet guide vanes to direct air onto

1456-590: A long time, before going into combat. However, the pilot can afford to stay in afterburning only for a short period, before aircraft fuel reserves become dangerously low. The first production afterburning turbofan engine was the Pratt & Whitney TF30 , which initially powered the F-111 Aardvark and F-14 Tomcat . Low-bypass military turbofans include the Pratt & Whitney F119 , the Eurojet EJ200 ,

1568-495: 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  [ cs ] . 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

1680-403: A pure-jet of the same thrust, and jet noise is no longer the predominant source. Turbofan engine noise propagates both upstream via the inlet and downstream via the primary nozzle and the by-pass duct. Other noise sources are the fan, compressor and turbine. Modern commercial aircraft employ high-bypass-ratio (HBPR) engines with separate flow, non-mixing, short-duct exhaust systems. Their noise

1792-563: A range of countries across the world both as a trainer and a light-attack aircraft. Since the 1990s, it has also become popular among civilian operators. By the end of the century, in excess of 2,800 L-39s had served with over 30 air forces. Several derivatives of the L-39 Albatros were developed. During the 1980s, Aero Vodochody used it as the basis for the L-59 Super Albatros , an enlarged and updated model. Furthermore,

1904-569: A static thrust of 4,320 lb (1,960 kg), and had a bypass ratio of 6:1. The General Electric TF39 became the first production model, designed to power the Lockheed C-5 Galaxy military transport aircraft. The civil General Electric CF6 engine used a derived design. Other high-bypass turbofans are the Pratt & Whitney JT9D , the three-shaft Rolls-Royce RB211 and the CFM International CFM56 ; also

2016-473: A turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. A bypass ratio of 6, for example, means that 6 times more air passes through the bypass duct than the amount that passes through the combustion chamber. Turbofan engines are usually described in terms of BPR, which together with overall pressure ratio, turbine inlet temperature and fan pressure ratio are important design parameters. In addition BPR

2128-421: A turbojet engine uses all of the engine's output to produce thrust in the form of a hot high-velocity exhaust gas jet, a turbofan's cool low-velocity bypass air yields between 30% and 70% of the total thrust produced by a turbofan system. The thrust ( F N ) generated by a turbofan depends on the effective exhaust velocity of the total exhaust, as with any jet engine, but because two exhaust jets are present

2240-496: A turbojet even though an extra turbine, a gearbox and a propeller are added to the turbojet's low-loss propelling nozzle. The turbofan has additional losses from its greater number of compressor stages/blades, fan and bypass duct. Froude, or propulsive, efficiency can be defined as: η f = 2 1 + V j V a {\displaystyle \eta _{f}={\frac {2}{1+{\frac {V_{j}}{V_{a}}}}}} where: While

2352-704: A turbojet which accelerates a smaller amount more quickly, which is a less efficient way to generate the same thrust (see the efficiency section below). The ratio of the mass-flow of air bypassing the engine core compared to the mass-flow of air passing through the core is referred to as the bypass ratio . Engines with more jet thrust relative to fan thrust are known as low-bypass turbofans , those that have considerably more fan thrust than jet thrust are known as high-bypass . Most commercial aviation jet engines in use are high-bypass, and most modern fighter engines are low-bypass. Afterburners are used on low-bypass turbofans on combat aircraft. The bypass ratio (BPR) of

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2464-553: Is a high-performance jet trainer designed and produced by Aero Vodochody in the Czech Republic . In addition to performing basic and advanced pilot training, it has also flown combat missions in a light-attack role. Unusually, the aircraft never received a NATO reporting name . The L-39 Albatros was designed during the 1960s as a successor to the Aero L-29 Delfín , an early jet-powered principal training aircraft. Performing its maiden flight on 4 November 1968, it became

2576-434: Is a type of airbreathing jet engine that is widely used in aircraft propulsion . The word "turbofan" is a combination of references to the preceding generation engine technology of the turbojet and the additional fan stage. It consists of a gas turbine engine which achieves mechanical energy from combustion, and a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all

2688-507: Is best suited to high supersonic speeds. If it is all transferred to a separate big mass of air with low kinetic energy, the aircraft is best suited to zero speed (hovering). For speeds in between, the gas power is shared between a separate airstream and the gas turbine's own nozzle flow in a proportion which gives the aircraft performance required. The trade off between mass flow and velocity is also seen with propellers and helicopter rotors by comparing disc loading and power loading. For example,

2800-410: Is considerable potential for reducing fuel consumption for the same core cycle by increasing BPR.This is achieved because of the reduction in pounds of thrust per lb/sec of airflow (specific thrust) and the resultant reduction in lost kinetic energy in the jets (increase in propulsive efficiency). If all the gas power from a gas turbine is converted to kinetic energy in a propelling nozzle, the aircraft

2912-430: Is due to the speed, temperature, and pressure of the exhaust jet, especially during high-thrust conditions, such as those required for takeoff. The primary source of jet noise is the turbulent mixing of shear layers in the engine's exhaust. These shear layers contain instabilities that lead to highly turbulent vortices that generate the pressure fluctuations responsible for sound. To reduce the noise associated with jet flow,

3024-413: Is quoted for turboprop and unducted fan installations because their high propulsive efficiency gives them the overall efficiency characteristics of very high bypass turbofans. This allows them to be shown together with turbofans on plots which show trends of reducing specific fuel consumption (SFC) with increasing BPR. BPR can also be quoted for lift fan installations where the fan airflow is remote from

3136-420: Is sufficient core power to drive the fan. A smaller core flow/higher bypass ratio cycle can be achieved by raising the inlet temperature of the high-pressure (HP) turbine rotor. To illustrate one aspect of how a turbofan differs from a turbojet, comparisons can be made at the same airflow (to keep a common intake for example) and the same net thrust (i.e. same specific thrust). A bypass flow can be added only if

3248-411: Is very fuel intensive. Consequently, afterburning can be used only for short portions of a mission. Unlike in the main engine, where stoichiometric temperatures in the combustor have to be reduced before they reach the turbine, an afterburner at maximum fuelling is designed to produce stoichiometric temperatures at entry to the nozzle, about 2,100 K (3,800 °R; 3,300 °F; 1,800 °C). At

3360-564: The Battle of Aleppo , launching several strikes upon rebel-held positions. It has been claimed the L-39 was the first fixed-wing aircraft to be employed against the rebels. In February 2013, insurgents successfully captured a number of intact L-39s, along with their support equipment, after raiding and later taking over the Al-Jarrah airbase. In late 2013, reports emerged of claims by Islamist fighters that they had successfully flown two of

3472-720: The Breitling Jet Team (7 L-39s) and the Black Diamond Jet Team (5 L-39s). There are also several L-39s that have been made available for private jet rides by various operators in Australia, Czech Republic , France , Germany , Spain and the US. These L-39s are mostly in private hands, but some also belong to government agencies, such as those in Vyazma , Russia . In March 2018 there were five L-39s on

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3584-479: The Bristol Olympus , and Pratt & Whitney JT3C engines, increased the overall pressure ratio and thus the thermodynamic efficiency of engines. They also had poor propulsive efficiency, because pure turbojets have a high specific thrust/high velocity exhaust, which is better suited to supersonic flight. The original low-bypass turbofan engines were designed to improve propulsive efficiency by reducing

3696-806: The Chadian-Libyan conflict , mainly to Ouadi Doum air base. During the final Chadian offensive in March 1987, the Chadians captured Ouadi Doum along with several aircraft (11 L-39s included) and Soviet SAM systems and tanks. A Chadian report to the UN , reported the aforementioned capture on 11 L-39s and the destruction (or downing) of at least four of them. In the midst of that conflict, on 21 April 1983, three LARAF Ilyushin Il-76 TDs and one Lockheed C-130 Hercules landed at Manaus Airport , Brazil after one of

3808-779: The First Nagorno-Karabakh War in the 1980s and early 1990s. A number of these were reportedly shot down by air defenses employed by the Nagorno-Karabakh Defense Army . In September 2015, Aero Vodochody sought a large order for the latest model of the L-39 to Azerbaijan; by this point, Azerbaijan had a total of 24 airworthy L-39s remaining in service. The newly de facto independent Chechen Republic of Ichkeria found itself with dozens of L-39s (as well as several L-29s, three MiG-17s, two MiG-15UTIs, helicopters and other transport and civilian aircraft) left at Khankala and Kalinovskaya airbases by

3920-702: The General Electric F110 , the Klimov RD-33 , and the Saturn AL-31 , all of which feature a mixed exhaust, afterburner and variable area propelling nozzle. To further improve fuel economy and reduce noise, almost all jet airliners and most military transport aircraft (e.g., the C-17 ) are powered by low-specific-thrust/high-bypass-ratio turbofans. These engines evolved from the high-specific-thrust/low-bypass-ratio turbofans used in such aircraft in

4032-582: The Mikoyan MiG-29 . The cockpit is partially pressurized, requiring the air crew to wear oxygen masks 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-25 TL (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

4144-675: The Mikoyan MiG-AT , Yakovlev Yak-130 (then known as the Yak-UTS), the Myasischev M-200 and the S-54. Most of these designs were typical trainers; they were built to be docile in handling, low cost in operation, and were essentially all-new in design. Sukhoi decided to take a different approach, and develop a true high-performance design closer to a fighter than a trainer. Advances in aerodynamics and flight controls allowed even

4256-491: 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; allegations about Czechoslovak banks being unable to finance the defense industry and inaction on the part of the Czechoslovak government; and concerns over

4368-468: The Russian Air Force in 1991, the newly formed service found itself with hundreds of L-39 aircraft, the majority of which were surplus to their training requirements. According to author Stephan Wilkinson, by 2005, Russia was seeking to potentially sell up to 800 of their L-39s, which were receiving only a basic level of maintenance once per month while their fate was being decided. Starting in

4480-529: The Soviet Air Force in 1992. Most of these, however, were reportedly abandoned or not in flyable condition, but during the August–November 1994 conflict between nationalist and pro-Russian forces L-39s were deployed and were possibly one of the few air attack (and possibly reconnaissance) elements on Dzhokar Dudayev 's forces. At least one was reported as shot down near Goragorsk on October 4 by

4592-559: The War in Abkhazia (1992–1993) , Abkhaz separatist forces received several L-39s from Russia and Chechnya, which were used in combat against Georgian forces. On 10 January 1993, an Abkhaz L-39 was shot down by a Russian SA-11 Buk during a friendly-fire incident. The pilot, Oleg Chanba, who was commander of the Abkhaz separatist air force, was killed during the incident. On 1 April 1993, during

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4704-463: The Warsaw Pact nations. 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. During 1972, the L-39 Albatros was formally recognized by the majority of

4816-520: The bypass ratio . The engine produces thrust through a combination of these two portions working together. Engines that use more jet thrust relative to fan thrust are known as low-bypass turbofans ; conversely those that have considerably more fan thrust than jet thrust are known as high-bypass . Most commercial aviation jet engines in use are of the high-bypass type, and most modern fighter engines are low-bypass. Afterburners are used on low-bypass turbofan engines with bypass and core mixing before

4928-522: 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

5040-421: The 1960s. Modern combat aircraft tend to use low-bypass ratio turbofans, and some military transport aircraft use turboprops . Low specific thrust is achieved by replacing the multi-stage fan with a single-stage unit. Unlike some military engines, modern civil turbofans lack stationary inlet guide vanes in front of the fan rotor. The fan is scaled to achieve the desired net thrust. The core (or gas generator) of

5152-657: 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 onboard systems before being re-exported to end users such as

5264-668: 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. The first flight of the L-39 Skyfox was in December 2018, and final military type certification was granted by the Czech Military Aviation Authority in 2022. The first production L-39NG is expected to fly by the end of 2022. The L-39 Albatros

5376-624: The Il-76s developed technical problems while crossing the Atlantic Ocean . The aircraft were then searched by the Brazilian authorities: instead of medical supplies – as quoted in the transport documentation – the crate of the first of 17 L-39s bound for Nicaragua together with arms and parachutes, to support the country's war against US-backed Contras , were found. The cargo was impounded for some time before being returned to Libya, while

5488-598: The L-159 in partnership with Elbit, but the Czech Ministry of Defense instead selected Rockwell Collins to partner on the program. 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 ( Skyfox ), to compete with the Alenia Aermacchi M-346 and British Aerospace Hawk . The L-39 Skyfox replaces

5600-513: The L-39 lineage would be extended to the L-139, a prototype L-39 fitted with a Western-sourced Garrett TFE731 engine. A combat-oriented development of the aircraft, designated as the L-159 ALCA , entered production in 1997, and has since been procured by a range of export customers. Production of the original L-39 came to an end during the mid-1990s, orders having declined substantially following

5712-452: The L-39V, conducted its initial flight. During 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. 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

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5824-528: The Russian air and ground campaign, as well as the capability of several aircraft to conduct kamikaze attacks on Russian nuclear power plants (specifically via means of the ejection seat in most aircraft, notably the L-39, by filling them with explosives to act as improvised cruise missiles). Iraq became the first export customer for the L-39 Albatros. By mid 1970, the Iraqi Air Force had procured

5936-581: The S-56, essentially an S-55 adapted for carrier use. The design was deliberately tailored for the Admiral Kuznetsov , and was designed to fit into a 10 by 3 by 3 meter space, making it one of the most compact naval fighters ever designed. The small size, especially vertically, opened the possibility of adding another internal deck between the two existing aircraft decks in the Kuznetsov , increasing

6048-554: The Soviet Air Force had about 1,000 L-39s on force, when the new Czech Republic stated they would no longer be supplying spares. The Soviet Air Force's commander-in-chief, Air Marshal Yefimov, issued a statement on the issue on 20 April 1990. On 25 June 1990 the first official RFP document was issued for the Uchebno-Trenirovochnyi Samolyot (UTS) program. Four companies responded with designs,

6160-875: The UTS contract, and Sukhoi started looking for other markets. Sukhoi then modified the design to allow it to mount the same radar as the Su-27, the Phazotron Sokol . Shown in June 1997, the S-55 was a lighter, shorter-range fighter that complemented the Su-27 in the same way the F-16 complements the F-15. Designed as a low-cost fighter, primarily for export, the S-55 was nevertheless a very advanced design compared to similar fighters that were "up-converted" from trainers. Sukhoi also produced

6272-464: The aerospace industry has sought to disrupt shear layer turbulence and reduce the overall noise produced. Fan noise may come from the interaction of the fan-blade wakes with the pressure field of the downstream fan-exit stator vanes. It may be minimized by adequate axial spacing between blade trailing edge and stator entrance. At high engine speeds, as at takeoff, shock waves from the supersonic fan tips, because of their unequal nature, produce noise of

6384-422: The afterburner, raising the temperature of exhaust gases by a significant degree, resulting in a higher exhaust velocity/engine specific thrust. The variable geometry nozzle must open to a larger throat area to accommodate the extra volume and increased flow rate when the afterburner is lit. Afterburning is often designed to give a significant thrust boost for take off, transonic acceleration and combat maneuvers, but

6496-409: The afterburner. Modern turbofans have either a large single-stage fan or a smaller fan with several stages. An early configuration combined a low-pressure turbine and fan in a single rear-mounted unit. The turbofan was invented to improve the fuel consumption of the turbojet. It achieves this by pushing more air, thus increasing the mass and lowering the speed of the propelling jet compared to that of

6608-404: The air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust . The ratio of the mass-flow of air bypassing the engine core to the mass-flow of air passing through the core is referred to as

6720-563: The attack on civilian targets in Sokhumi , Georgian forces managed to damage an L-39, which fell into the sea. In the spring of 2008, a number of Georgian drones were shot down by Abkhazian separatist forces over the Abkhazia region. The Abkhazian separatist forces claimed that one of its missile-equipped L-39s had shot down a Georgian Hermes 450 unmanned reconnaissance drone. Footage released later by Georgian authorities clearly shows

6832-474: The average stage loading and to maintain LP turbine efficiency. Reducing core flow also increases bypass ratio. Bypass ratios greater than 5:1 are increasingly common; the Pratt & Whitney PW1000G , which entered commercial service in 2016, attains 12.5:1. Further improvements in core thermal efficiency can be achieved by raising the overall pressure ratio of the core. Improvements in blade aerodynamics can reduce

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6944-586: The captured L-39s. In October 2014, the Syrian Government claimed that at least two rebel-held L-39s had been airworthy and had recently been destroyed by Syrian Air Force aircraft. According to Reuters , by 2014, the L-39 had allegedly become one of the favoured platforms of the Syrian Air Force for performing ground attack missions due to its slower speed and higher agility over other aircraft in its inventory. In December 2015, following

7056-1015: The civilian register in New Zealand . One registered as an L-39 and four others registered as L-39C . Since 2004, the Defence & MRO Division of Aero Vodochody has performed a general maintenance, repair and modernisation program of civil-operated L-39s, as well as performing the demilitarisation of ex-military aircraft. Services offered to civil operators include life-extension programs, support for civil registration/certification, training of ground/flight crew, logistics and analysis, customization, routine inspection, condition-based maintenance support, and providing general expertise/consultancy work. Data from Jane's All The World's Aircraft 1988–89 , Aero Vodochody General characteristics Performance Armament Related development Aircraft of comparable role, configuration, and era Turbofan A turbofan or fanjet

7168-426: The cockpit and the tailpipe below the horizontal tailplane. The engine has a time between overhaul (TBO) of 1,000 flight hours; 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

7280-627: 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,

7392-556: The downing. 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

7504-678: The early 1990s, the Russian Air Force has pursued the development of a domestically built jet trainer, for which the Yakovlev Yak-130 was selected; the Yak-130 shall eventually replace the L-39 in Russian service within its operational roles. On 24 February 2022, a Ukrainian L-39 from the 39th Tactical Aviation Brigade (Ukraine) piloted by Dmytro Kolomiyets was shot down by a Russian aircraft in Khmelnytskyi during

7616-679: The end of the Cold War . At the Farnborough Airshow in July 2014, Aero Vodochody announced the launch of the L-39NG , an upgraded and modernised version of the L-39; this programme is set to produce new-build aircraft alongside the extensive rebuilding of existing aircraft. In 2023, production of the L-39NG resumed under the name Skyfox , with 34 aircraft on order. In 1964, the Czechoslovak aircraft manufacturer Aero Vodochody embarked on

7728-448: The engine and doesn't flow past the engine core. Considering a constant core (i.e. fixed pressure ratio and turbine inlet temperature), core and bypass jet velocities equal and a particular flight condition (i.e. Mach number and altitude) the fuel consumption per lb of thrust (sfc) decreases with increase in BPR. At the same time gross and net thrusts increase, but by different amounts. There

7840-427: The engine must generate enough power to drive the fan at its rated mass flow and pressure ratio. Improvements in turbine cooling/material technology allow for a higher (HP) turbine rotor inlet temperature, which allows a smaller (and lighter) core, potentially improving the core thermal efficiency. Reducing the core mass flow tends to increase the load on the LP turbine, so this unit may require additional stages to reduce

7952-458: The exhaust velocity to a value closer to that of the aircraft. The Rolls-Royce Conway , the world's first production turbofan, had a bypass ratio of 0.3, similar to the modern General Electric F404 fighter engine. Civilian turbofan engines of the 1960s, such as the Pratt & Whitney JT8D and the Rolls-Royce Spey , had bypass ratios closer to 1 and were similar to their military equivalents. The first Soviet airliner powered by turbofan engines

8064-494: The fan nozzle. The amount of energy transferred depends on how much pressure rise the fan is designed to produce (fan pressure ratio). The best energy exchange (lowest fuel consumption) between the two flows, and how the jet velocities compare, depends on how efficiently the transfer takes place which depends on the losses in the fan-turbine and fan. The fan flow has lower exhaust velocity, giving much more thrust per unit energy (lower specific thrust ). Both airstreams contribute to

8176-450: The first fan rotor stage. This improves the fan surge margin (see compressor map ). Since the 1970s, most jet fighter engines have been low/medium bypass turbofans with a mixed exhaust, afterburner and variable area exit nozzle. An afterburner is a combustor located downstream of the turbine blades and directly upstream of the nozzle, which burns fuel from afterburner-specific fuel injectors. When lit, large volumes of fuel are burnt in

8288-466: The first trainer aircraft in the world to be equipped with a turbofan powerplant. Quantity production of the L-39 Albatros proceeded in 1971; one year later, it was formally recognized by the majority of the Warsaw Pact countries as their preferred primary trainer. Accordingly, thousands of L39s would be produced for various military customers in Eastern Europe. Additionally, it was exported to

8400-406: 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

8512-625: The four hardpoints and strengthening of the L-39ZO, made its maiden flight. According to aerospace publication Flight International , roughly 200 L-39s were being sold each year in 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

8624-496: The fuel used to move the aircraft forwards. A turbofan harvests that wasted velocity and uses it to power a ducted fan that blows air in bypass channels around the rest of the turbine. This reduces the speed of the propelling jet while pushing more air, and thus more mass. The other penalty is that combustion is less efficient at lower speeds. Any action to reduce the fuel consumption of the engine by increasing its pressure ratio or turbine temperature to achieve better combustion causes

8736-429: The gross thrust of the engine. The additional air for the bypass stream increases the ram drag in the air intake stream-tube, but there is still a significant increase in net thrust. The overall effective exhaust velocity of the two exhaust jets can be made closer to a normal subsonic aircraft's flight speed and gets closer to the ideal Froude efficiency . A turbofan accelerates a larger mass of air more slowly, compared to

8848-474: The hot nozzle to convert to kinetic energy. Turbofans represent an intermediate stage between turbojets , which derive all their thrust from exhaust gases, and turbo-props which derive minimal thrust from exhaust gases (typically 10% or less). Extracting shaft power and transferring it to a bypass stream introduces extra losses which are more than made up by the improved propulsive efficiency. The turboprop at its best flight speed gives significant fuel savings over

8960-664: The later stages of the 1996–2001 phase of the Afghan civil war against the Northern Alliance . In early 2001, only two of these reportedly remained operational. Following the United States invasion of Afghanistan in 2001, a number of L-39s were inducted into the Afghan Air Force . A number of L-39s, along with older L-29s, were used extensively by Azeri forces to perform ground attack missions during

9072-417: The mechanical power produced by the turbine. In a bypass design, extra turbines drive a ducted fan that accelerates air rearward from the front of the engine. In a high-bypass design, the ducted fan and nozzle produce most of the thrust. Turbofans are closely related to turboprops in principle because both transfer some of the gas turbine's gas power, using extra machinery, to a bypass stream leaving less for

9184-421: The most advanced fighters have docile handling suitable for transition training, while at the same time the older generation aircraft had handling so different from modern aircraft that it gave them limited utility. Given their extensive experience with upgraded versions of the original Su-27, Sukhoi chose to use much of this design in the new trainer. Versions with one AL-31 or two smaller engines were studied, with

9296-530: 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 defense capability. Light-attack variants have four underwing hardpoints for ground attack stores, while the ZA variant also has an underfuselage gun pod . Mock UB-16 rocket pods can also be installed for visual appearance only. During

9408-539: The number of extra compressor stages required, and variable geometry stators enable high-pressure-ratio compressors to work surge-free at all throttle settings. The first (experimental) high-bypass turbofan engine was the AVCO-Lycoming PLF1A-2, a Honeywell T55 turboshaft-derived engine that was first run in February 1962. The PLF1A-2 had a 40 in diameter (100 cm) geared fan stage, produced

9520-532: The opening hours of the Russian invasion of Ukraine . On 9 August 2022, Dmytro Kolomiyets was posthumously awarded with the Order of the Gold Star . On 25 August 2023, two Ukrainian L-39s collided during a combat mission over Zhytomyr , killing three pilots. Among those killed was combat pilot Andrii Pilshchykov , an Order of Courage recipient more commonly known by his callsign "Juice", who had become famous in

9632-519: 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

9744-467: The required thrust still maintained by increasing the mass accelerated. A turbofan does this by transferring energy available inside the engine, from the gas generator, to a ducted fan which produces a second, additional mass of accelerated air. The transfer of energy from the core to bypass air results in lower pressure and temperature gas entering the core nozzle (lower exhaust velocity), and fan-produced higher pressure and temperature bypass-air entering

9856-414: 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

9968-482: 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 a jet aircraft before to successfully control. As a training platform, the L-39 itself comprised part of a comprehensive system that also used flight simulators and mobile ground test equipment. The low-set, straight wing has

10080-399: The same helicopter weight can be supported by a high power engine and small diameter rotor or, for less fuel, a lower power engine and bigger rotor with lower velocity through the rotor. Bypass usually refers to transferring gas power from a gas turbine to a bypass stream of air to reduce fuel consumption and jet noise. Alternatively, there may be a requirement for an afterburning engine where

10192-454: The securing of the Kweiris airbase by government forces, the resumption of ground-attack missions by L-39s in the vicinity of Aleppo commenced shortly thereafter. On 26 December 2017, a Syrian L-39 was shot down near Hama airport. On 3 March 2020, a Syrian Arab Army Air Force L-39 was shot down by a Turkish Air Force F-16 over Idlib province. Both Syrian and Turkish forces confirmed

10304-458: The single-engine version favoured throughout. The design that emerged appeared to be a Su-33 with a fuselage plug removed behind the cockpit, giving it a cross-section similar to other advanced trainers of the era. The first design study, shown publicly not long afterwards, was upgraded and improved during 1992. A new version, with airframe enlarged by approximately 25 per cent, was revealed at 1996 Farnborough Air Show . The Yak-130 eventually won

10416-502: The sole requirement for bypass is to provide cooling air. This sets the lower limit for BPR and these engines have been called "leaky" or continuous bleed turbojets (General Electric YJ-101 BPR 0.25) and low BPR turbojets (Pratt & Whitney PW1120). Low BPR (0.2) has also been used to provide surge margin as well as afterburner cooling for the Pratt & Whitney J58 . Propeller engines are most efficient for low speeds, turbojet engines for high speeds, and turbofan engines between

10528-454: The speed of the propelling jet has to be reduced because there is a price to be paid in producing the thrust. The energy required to accelerate the gas inside the engine (increase in kinetic energy) is expended in two ways, by producing a change in momentum ( i.e. a force), and a wake which is an unavoidable consequence of producing thrust by an airbreathing engine (or propeller). The wake velocity, and fuel burned to produce it, can be reduced and

10640-536: The technology and materials available at the time. The first turbofan engine, which was only run on a test bed, was the German Daimler-Benz DB 670 , designated the 109-007 by the German RLM ( Ministry of Aviation ), with a first run date of 27 May 1943, after the testing of the turbomachinery using an electric motor, which had been undertaken on 1 April 1943. Development of the engine

10752-497: The thrust equation can be expanded as: F N = m ˙ e v h e − m ˙ o v o + B P R ( m ˙ c ) v f {\displaystyle F_{N}={\dot {m}}_{e}v_{he}-{\dot {m}}_{o}v_{o}+BPR\,({\dot {m}}_{c})v_{f}} where: The cold duct and core duct's nozzle systems are relatively complex due to

10864-494: The total number of fighters that could be carried by two to three times. The S-56 was also offered to the Indian Navy in 1999, but was not purchased. General characteristics Performance Armament (light fighter versions) a variety of bombs rockets and missiles on external hardpoints Related development Aircraft of comparable role, configuration, and era Aero L-39 The Aero L-39 Albatros

10976-673: The trailing edges of some jet engine nozzles that are used for noise reduction . The shaped edges smooth the mixing of hot air from the engine core and cooler air flowing through the engine fan, which reduces noise-creating turbulence. Chevrons were developed by GE under a NASA contract. Some notable examples of such designs are Boeing 787 and Boeing 747-8  – on the Rolls-Royce Trent 1000 and General Electric GEnx engines. Early turbojet engines were not very fuel-efficient because their overall pressure ratio and turbine inlet temperature were severely limited by

11088-410: The transports were permitted to return to their country. During the 1990s and 2000s, Libya made multiple attempts to get components and services for its air force in spite of an embargo placed upon the country by United Nations Security Council Resolution 748 ; by 2001, only half of Libya's L-39s were serviceable as a consequence. Following the dissolution of the Soviet Union and the formation of

11200-428: The turbine inlet temperature is not too high to compensate for the smaller core flow. Future improvements in turbine cooling/material technology can allow higher turbine inlet temperature, which is necessary because of increased cooling air temperature, resulting from an overall pressure ratio increase. The resulting turbofan, with reasonable efficiencies and duct loss for the added components, would probably operate at

11312-425: The turbojet uses the gas from its thermodynamic cycle as its propelling jet, for aircraft speeds below 500 mph there are two penalties to this design which are addressed by the turbofan. Firstly, energy is wasted as the propelling jet is going much faster rearwards than the aircraft is going forwards, leaving a very fast wake. This wake contains kinetic energy that reflects the fuel used to produce it, rather than

11424-445: The turbojet, is lost. In contrast, Roth considers regaining this independence the single most important feature of the turbofan which allows specific thrust to be chosen independently of the gas generator cycle. The working substance of the thermodynamic cycle is the only mass accelerated to produce thrust in a turbojet which is a serious limitation (high fuel consumption) for aircraft speeds below supersonic. For subsonic flight speeds

11536-453: The turbojet. This is done mechanically by adding a ducted fan rather than using viscous forces. A vacuum ejector is used in conjunction with the fan as first envisaged by inventor Frank Whittle . Whittle envisioned flight speeds of 500 mph in his March 1936 UK patent 471,368 "Improvements relating to the propulsion of aircraft", in which he describes the principles behind the turbofan, although not called as such at that time. While

11648-476: The two flows may combine within the ducts, and share a common nozzle, which can be fitted with afterburner. Most of the air flow through a high-bypass turbofan is lower-velocity bypass flow: even when combined with the much-higher-velocity engine exhaust, the average exhaust velocity is considerably lower than in a pure turbojet. Turbojet engine noise is predominately jet noise from the high exhaust velocity. Therefore, turbofan engines are significantly quieter than

11760-418: The two. Turbofans are the most efficient engines in the range of speeds from about 500 to 1,000 km/h (270 to 540 kn; 310 to 620 mph), the speed at which most commercial aircraft operate. In a turbojet (zero-bypass) engine, the high temperature and high pressure exhaust gas is accelerated when it undergoes expansion through a propelling nozzle and produces all the thrust. The compressor absorbs

11872-510: The use of two separate exhaust flows. In high bypass engines, the fan is situated in a short duct near the front of the engine and typically has a convergent cold nozzle, with the tail of the duct forming a low pressure ratio nozzle that under normal conditions will choke creating supersonic flow patterns around the core . The core nozzle is more conventional, but generates less of the thrust, and depending on design choices, such as noise considerations, may conceivably not choke. In low bypass engines

11984-536: The west for his articulate appeals early in the war for allies to supply F-16s to Ukraine. The Syrian Arab Air Force has operated a number of armed L-39ZA light attack variants. Since the early stages of the Syrian civil war , the Syrian Air Force's L-39 aircraft have been routinely deployed in counter-insurgency operations against various rebel ground forces, a number of these aircraft have also been shot down by ground fire. They were first used operationally during

12096-701: The world, with an experience base of over 10 million service hours. The CF700 turbofan engine was also used to train Moon-bound astronauts in Project Apollo as the powerplant for the Lunar Landing Research Vehicle . A high-specific-thrust/low-bypass-ratio turbofan normally has a multi-stage fan behind inlet guide vanes, developing a relatively high pressure ratio and, thus, yielding a high (mixed or cold) exhaust velocity. The core airflow needs to be large enough to ensure there

12208-614: Was abandoned with its problems unsolved, as the war situation worsened for Germany. Later in 1943, the British ground tested the Metrovick F.3 turbofan, which used the Metrovick F.2 turbojet as a gas generator with the exhaust discharging into a close-coupled aft-fan module comprising a contra-rotating LP turbine system driving two co-axial contra-rotating fans. Improved materials, and the introduction of twin compressors, such as in

12320-660: Was derived from the General Electric J85/CJ610 turbojet 2,850 lbf (12,700 N) to power the larger Rockwell Sabreliner 75/80 model aircraft, as well as the Dassault Falcon 20 , with about a 50% increase in thrust to 4,200 lbf (19,000 N). The CF700 was the first small turbofan to be certified by the Federal Aviation Administration (FAA). There were at one time over 400 CF700 aircraft in operation around

12432-466: 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 onboard 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

12544-587: Was the Tupolev Tu-124 introduced in 1962. It used the Soloviev D-20 . 164 aircraft were produced between 1960 and 1965 for Aeroflot and other Eastern Bloc airlines, with some operating until the early 1990s. The first General Electric turbofan was the aft-fan CJ805-23 , based on the CJ805-3 turbojet. It was followed by the aft-fan General Electric CF700 engine, with a 2.0 bypass ratio. This

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