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113-667: The General Electric GE9X is a high-bypass turbofan developed by GE Aerospace exclusively for the Boeing 777X . It first ran on the ground in April 2016 and first flew on March 13, 2018; it powered the 777-9's maiden flight in early 2020. It received its Federal Aviation Administration (FAA) type certificate on September 25, 2020. Derived from the General Electric GE90 with a larger fan, advanced materials like ceramic matrix composites (CMCs), and higher bypass and compression ratios, it

226-436: A general aviation aircraft and hundreds of millions of dollars for a commercial aircraft ; certification delays can cost millions of dollars and can decide a program's profitability. A type certificate (TC) is issued to signify the airworthiness of the approved design or "type" of an aircraft to be manufactured. The TC is issued by a regulatory authority, and once issued, the design cannot be changed unless at least part of

339-503: A carbon fiber composite fan case, first developed for the GEnx, to further reduce weight. The high pressure (HP) compressor is up to 2% more efficient. As the 129.5 in (329 cm) GE90 fan left little room to improve the bypass ratio, GE looked for additional efficiency by upping the overall pressure ratio from 40 to 60, focusing on boosting the high-pressure core's ratio from 19:1 to 27:1 by using 11 compressor stages instead of 9 or 10, and

452-434: 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

565-697: A different issue with the GE9X paused testing of the 777X. The GE9X increases fuel efficiency by 10% over the GE90. Its 61:1 overall pressure ratio should help provide a 5% lower thrust specific fuel consumption (TSFC) than the XWB-97 with maintenance costs comparable to the GE90-115B. The initial thrust of 105,000 lbf (470 kN) will be followed by 102,000 and 93,000 lbf (450 and 410 kN) derated variants. GE invested more than $ 2 billion for its development. Its nacelle

678-419: 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

791-410: 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

904-451: A given TC, each one need not be tested as rigorously but the confidence demonstrated by the TC is conferred, when the aircraft has been assigned a certificate of airworthiness (CoA). A CoA is issued for each aircraft that is properly registered if it conforms to its type design and ready for safe operation. The CoA is valid and the aircraft may be operated as long as it is maintained in accordance with

1017-426: 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

1130-416: 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

1243-572: 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 ,

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1356-516: A new variant may require re-certification. Again the basic process of type certifications is repeated (including maintenance programs). However, unaltered items from the basic design need not be retested. Normally, one or two of the original prototype fleet are remanufactured to the new proposed design. As long as the new design does not deviate too much from the original, static airframes do not need to be built. The resultant new prototypes are again subjected to flight tests. Upon successful completion of

1469-401: A proposed timetable of actions required for certification tests. With the application, the regulations to be applied will usually be frozen for this application for a given amount of time in order to avoid a situation where the applicant would have to change the design as a result of changed regulation. An initial design sample known as a prototype is built. This refers to either the aircraft,

1582-403: 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

1695-462: A routine A Check on the 747 testbed CF6 engines discovered fan-case corrosion and high pressure turbine airfoils on allowable limits. It first flew on March 13 with the previous design of the VSV lever arm. In early May, the first flight test phase of two was completed after 18 flights and 110 hours of run time; the GE9X high-altitude envelope was explored and its cruise performance evaluated. The second phase

1808-550: 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

1921-513: A third-generation, twin-annular pre-swirl (TAPS) combustor instead of the previous dual annular combustor. Able to endure hotter temperatures, ceramic matrix composites (CMC) are used in two combustor liners, two nozzles, and the shroud up from the CFM International LEAP stage 2 turbine shroud . CMCs are not used for the first-stage turbine blades, which have to endure extreme heat and centrifugal forces. These are improvements planned for

2034-473: 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

2147-421: 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

2260-496: 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

2373-704: 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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2486-438: Is 184 in (4,700 mm) wide. Most of the efficiency increase comes from the better propulsion efficiency of the higher-bypass-ratio fan. The bypass ratio is planned for 10:1. The fan is housed in 134 in (340 cm) diameter case. The GE9X has 16 blades , whereas the similarly sized GE90 has 22 and the smaller GEnx has 18. Having fewer fan blades reduces the engine weight, improves aerodynamic efficiency, and allows

2599-507: 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,

2712-410: 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

2825-470: Is drawn with inputs from tests results and also from initial customers' engineering departments. The proposed maintenance program is submitted to the regulators for comment and approval. After successful completion of ground and flight tests, along with an approved maintenance program, the prototype is approved, and the firm is granted the TC for the prototype (as understood that it should include all furnished equipment for its intended role). The legal term for

2938-430: 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,

3051-503: Is installed in a 174 in (440 cm) diameter nacelle, with 1.5 ft (0.46 m) of ground clearance. The engine and nacelle weighed 40,000 lb (18 t) with its new pylon and wing strengthening, compared to 17,000 lb (7.7 t) for the CF6-80C2s and its pylon. In February 2018, the GE9X's first flight was delayed by problems discovered in the high-pressure compressor (HPC) variable stator vanes (VSV) lever arms. Also

3164-413: 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

3277-420: 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

3390-405: Is tested, the flight tests may cover the whole world. Tests may also cover different environments - high and low altitude, freezing and hot climates, and so on, to confirm correct performance throughout the aircraft's design envelope . In parallel with aircraft testing, the applicant firm also draws up maintenance program to support continuous airworthiness after approval of the design. The program

3503-422: Is thus compromised. The regulators will now issue an airworthiness directive to the type certificate holder and to all owners globally. The directives normally consists of additional maintenance or design actions that are necessary to restore the type's airworthiness. Compliance is mandatory and thus if an operator does not comply with an AD, then the datum aircraft is not considered airworthy and further operation of

General Electric GE9X - Misplaced Pages Continue

3616-418: Is used to manufacture parts that would otherwise be impossible to make using traditional manufacturing processes. In August 2024, a first production bound engine will be delivered, with a new combustor liner design. Related development Comparable engines Related lists High-bypass turbofan The ratio of the mass-flow of air bypassing the engine core to the mass-flow of air passing through

3729-411: 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

3842-472: 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

3955-498: The Civil Aviation Administration of China (CAAC). When changes are needed to an airframe or on-board equipment, there are two options. One is to initiate a modification by the type design holder (manufacturer), and the other is to request a third party Supplemental type certificate (STC). The choice is determined by considering whether or not the change constitutes a new design (i.e. introduces risk not considered in

4068-677: 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

4181-493: The September 11 attacks . The certifying authority issues an AD when an unsafe condition is found to exist in a product (aircraft, aircraft engine, propeller, or appliance) of a particular type design. ADs are used by the certifying authority to notify aircraft owners and operators of unsafe conditions and to require their correction. ADs prescribe the conditions and limitations, including inspection, repair, or alteration under which

4294-412: The airworthiness of a particular category of aircraft, according to its manufacturing design ( type design ). Certification confirms that the aircraft of a new type intended for serial production is in compliance with applicable airworthiness requirements established by the national air law . For up to three seats, primary category aircraft certification costs around US$ 1 million, US$ 25 million for

4407-603: The flight envelope such as low altitudes; #5 ran an endurance test with rotors deliberately unbalanced to make the engine shake at the vibration limits allowed in service, a requirement for ETOPS certification; #6 did ingestion tests later in 2018; after LP turbine over-temperature tests, #7 did a second icing test phase in Winnipeg, Manitoba ; #8 did the triple redline FAA 150 h endurance test. Eight compliance engines, plus two spares, were required for 777-9 flight testing. A second phase, of 18 flights, began on December 10 to evaluate

4520-421: 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

4633-458: The 2017–2018 winter at Winnipeg, Manitoba . Simulated high-altitude conditions were used to test the GE9X for ice crystal icing (core icing) which was an issue for the GEnx . This testing improved the understanding of core icing as well as the more familiar rime ice . A design change required for the GEnx was the addition of bypass doors between the booster and high-pressure compressor which open into

General Electric GE9X - Misplaced Pages Continue

4746-420: The 777X first flight until January 2020. On January 25, 2020, the GE9X had its first flight on the 777X, flying for 3 hours and 52 minutes, before landing at Boeing Field. On September 28, GE announced its FAA type certificate, as eight test engines completed 8,000 cycles and 5,000 hours of running. ETOPS approval needed 3,000 ground-test cycles to be completed as a requirement for entry into service. In 2022,

4859-761: The A340-600 which is based on the Airbus A340-200 and the A340-300. Any additions, omissions or alterations to the aircraft's certified layout, built-in equipment, airframe and engines, initiated by any party other than the type certificate holder, need an approved supplementary ("supplemental" in FAA terminology) type certificate, or STC. The scope of an STC can be extremely narrow or broad. It could include minor modifications to passenger cabin items or installed instruments. More substantial modifications may involve engine replacement, as in

4972-659: The Blackhawk modifications to Cessna Conquest and Beechcraft King Air turboprops , or a complete role change for the aircraft, such as converting a B-17 or Stearman into an agricultural aircraft. STCs are applied due to either the type certificate holder's refusal (frequently due to economics) or its inability to meet some owners' requirements. STCs are frequently raised for out-of-production aircraft types conversions to fit new roles. Before STCs are issued, procedures similar to type certificate changes for new variants are followed, likely including thorough flight tests. STCs belong to

5085-496: The STC holder and are generally more restrictive than type certificate changes. The TC holder remains responsible for the continued integrity of the approved aircraft type design and must continue to be the focal point for resolving issues that may require corrective action. This requires the continued capability, or access to a capability, of providing appropriate technical solutions for service difficulties or mandatory corrective action. If

5198-399: The U.S. these sub-assemblies must meet requirements in the applicable Technical Standards Order (TSO). To meet those requirements the design documents are examined for compliance with the applicable Minimum Operating Performance Standards (MOPS) applicable to that sub-assembly. MOPS are published by expert industry groups such as: RTCA Inc., EUROCAE, and SAE. When aircraft are produced to meet

5311-464: 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

5424-464: The affected aircraft type would be unlawful , making the operator liable to legal action by the relevant national aviation authority, and rendering null-and-void any of the operator's insurance policies relating to the type, such as hull loss and accident third party coverage. ADs may also be raised with changes of the local or global aviation rules and requirements, e.g., the requirement to fit armored cockpit doors for all passenger airliners after

5537-422: 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

5650-409: 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

5763-456: The aircraft nacelle. A core engine was tested in the Evendale, Ohio , altitude test cell to check blade vibrations and engines 003, 004, and 007 were assembled in 2017, and the fourth engine was used for flight testing later in the year from Victorville, California . In 2018 ten compliance engines (including two spare engines) were needed for the four 777-9 flight-test aircraft. Type certification

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5876-493: The airflow path to reduce the chance of ice crystals entering the core. Design changes between FETT and second engine to test (SETT) addressed improvements required to meet efficiency goals: the minimum area in the duct between the HP turbine outlet and the LP turbine inlet was altered to set the operating line of the compressor, turbine and fan. The tip clearance at the front of the HP compressor

5989-411: The airworthiness certificate of their aircraft to remain valid. Other continuing airworthiness activities include additional tasks associated with the maintenance program and design changes to be accomplished via: Sometimes during service, the aircraft may encounter problems that may compromise the aircraft's safety, which are not anticipated or detected in prototype testing stages. The aircraft design

6102-472: The applicable airworthiness requirements and remains in a condition for safe operation throughout its operating life called continuing airworthiness . A maintenance program is issued by the aircraft operator and approved by the regulatory authority of the state of registry to maintain the airworthiness of the aircraft of the type owned by the operator. Maintenance tasks outlined in the maintenance program have to be scheduled and timely accomplished in order for

6215-407: The applicant design organisation submits documents to their local aviation regulating body, detailing how the proposed aircraft type design would fulfill the airworthiness requirements. After investigations by the regulator, the final approval of such documents (after the required comments and amendments in order to fulfill the laws), becomes the basis of the certification. The firm follows it and draws

6328-426: 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

6441-509: The bulletins and report the decision to the regulatory authority of the state of the aircraft registry. Sometimes SBs can become mandated by relevant ADs. Often the basic design is enhanced further by the type certificate holder. Major changes beyond the authority of the service bulletins require amendments to the type certificate. For example, increasing (or decreasing) an aircraft's flight performance, range and load carrying capacity by altering its systems, fuselage, wings or engines resulting in

6554-467: The certification program, the original type certificate is amended to include the new variant (normally denoted by a new model number additional to the original type designation). Typical examples are; the Boeing 737NG (737-600, 737-700, 737-800 and 737-900) which replaced the 737 Original family (737-100 and 737-200) and the 737 Classic family (737-300, 737-400 and 737-500) and the Airbus A340-500 and

6667-547: The core is referred to as 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

6780-400: The end of 2017. The initial 777X flight-test engines were shipped in 2018 for an initial 777-9 flight in early 2019. A quarter of the certification testing was done by May 2018: icing, crosswind /inlet distortion, inlet distortion , fan and booster blade vibrations, HP turbine blade vibrations and thermal survey . As it was larger than the GE90, the GE9X could only be installed under

6893-403: The end of January, the turbine case and rear frame strut were damaged during the blade out test and relevant components were redesigned. In early May, the flight test program was completed after 320 hours run time, during which high-altitude cruise fuel burn was established. Engines were modified to a final certifiable configuration standard before the maiden flight of the 777X, delayed beyond

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7006-445: 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

7119-571: The engine control software and hot-and-high performance and lasted until the first quarter of 2019 before FAA certification the same year. By then water ingestion, crosswind, blade-out, hailstone , bird ingestion and block or endurance testing had been completed. Flight tests were based in Victorville, California , and ranged as far as Seattle , Colorado Springs, Colorado , Fairbanks, Alaska , and Yuma, Arizona . By January 4, 2019, eight test flights and 55 hours of run time had been completed. At

7232-461: The engine design in terms of aerodynamic performance, mechanical system behavior and secondary air system heat management. The GE9X conducted icing tests in Winter 2017. The FETT was used for ground cold weather testing in natural icing conditions such as ground fog ; minor design changes using additive manufacturing were made within one month. Icing certification and evaluation finished during

7345-533: The engine has 65 CMC components, the most of any commercial aircraft engine at the time of its introduction. The compressor is designed with 3D aerodynamics and its first five stages are blisks , combined bladed-disk. The combustor is lean burning for greater efficiency and 30% NOx margin to CAEP/8. The compressor and high pressure turbine are made from powdered metal . The low-pressure turbine airfoils made of titanium aluminide (TiAl) are stronger, lighter, and more durable than nickel -based parts. 3D printing

7458-427: 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

7571-479: The engine's list price was US$ 41.4M. The first engine was expected to be ground-tested in 2016, with flight testing to begin in 2017 and certification happening in 2018. Because of the delays, the first flight test occurred in March 2018, with certification expected in late 2019. The first engine to test (FETT) completed its first run in April 2016. This engine completed 375 cycles in 335 hours run-time, which validated

7684-553: The engines or the propeller, depending on the basis of the certification. For the purpose of illustration, the discussion shall be limited to the aircraft. Normally a few prototypes are built, each subject to different tests. The prototypes are first used for ground and system tests. One of the prototypes (known as the "static airframe") is subject to destructive testing, i.e., the prototype is subject to stress beyond normal and abnormal operations until destruction. The test-results are compared with initial submitted calculations to establish

7797-516: 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

7910-494: 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

8023-519: The firm is now the "type certificate holder". Subsequently, the prototype now serves as a template for serial aircraft production and the aircraft rolling out of the factory should be identical to the prototype within the frames outlined in a TC data sheet, and each given a serial number (a "series aircraft"). As the aircraft enters into service, it is subject to operational wear and tear which may cause performance degradations. The set of processes by which an aircraft, engine, propeller or part complies with

8136-450: 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

8249-434: The first type design). If so, then type design holder must develop and approve a modification to the type design. If the regulatory authority agrees the change does not introduce new risk, the STC option is available. An STC is less expensive because the design change can be developed by a specialized design organization, a generally more flexible and efficient process than going through the original manufacturer. The STC defines

8362-496: 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

8475-429: 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

8588-452: The holder is no longer capable or if the TC is transferred to another holder a regulatory authority should take appropriate action in accordance with the national legislation. In the case of the TC being transferred to another holder the new holder shall be capable of fulfilling the TC holder responsibilities in following ADs and providing technical support to keep the type design current with the applicable airworthiness requirements, even after

8701-474: 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

8814-417: The low pressure (LP) fan and booster to spin faster to better match its speed with the LP turbine. The fan blades feature steel leading edges and fiberglass trailing edges to better absorb bird strikes with more flexibility than carbon fiber. Fourth generation carbon fiber composite materials, comprising the bulk of the fan blades, make them lighter, thinner, stronger, and more efficient. The GE9X also uses

8927-417: 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

9040-400: The next iteration of engine technology. The first-stage HP turbine shroud , the first- and second-stage HP turbine nozzles and the inner and outer combustor linings are made from CMC, only static components, operating 500 °F (260 °C) hotter than nickel alloys with some cooling. CMCs have twice the strength at one-third the weight of metal and require 59% less cooling. In total,

9153-525: 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

9266-452: The previously expected June 26 by a stator problem at the front of the 11-stage high-pressure compressor . Before certification, final tests included a full durability block test, replacing the usual "triple redline" test at maximum EGT and both rotor speeds, as modern high-bypass ratio engines cannot achieve all maximum conditions near sea level. The high-pressure compressor stator redesign delayed engine certification into autumn, which delayed

9379-587: The process for certification is repeated to cover the changes. The TC reflects a determination made by a regulatory authority that the type design is in compliance with airworthiness requirements. Examples of regulatory authorities are the United Kingdom's Civil Aviation Authority (CAA), the U.S. Federal Aviation Administration (FAA), the European Aviation Safety Agency (EASA), Transport Canada , Brazil’s Agência Nacional de Aviação Civil and

9492-456: The product design change, states how the modification affects the existing type design, and lists serial numbers of the aircraft affected. It also identifies the certification basis for regulatory compliance for the design change. The TC implies that aircraft manufactured according to the approved design can be issued an airworthiness certificate . To meet those requirements the aircraft and each sub-assembly must also be approved. For example, in

9605-477: The product may continue to be operated. With increasing in-service experience, the type certificate holder may find ways to improve the original design resulting in either lower maintenance costs or increased performance. These improvements (normally involving some alterations) are suggested through service bulletins to an aircraft owners/operators as optional (and may be extra cost) items. The owner/operator shall exercise their discretion whether or not to incorporate

9718-423: The production of the aircraft type has stopped but many out-of-production aircraft continue useful lives. STCs are also bound by the same rules. When the holder decides to stop supporting the aircraft type without the transfer of TC holder responsibilities, the TC is returned to the issuing regulatory authority and the remaining aircraft fleet can be grounded by the current states of registry until further decisions on

9831-467: 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

9944-689: The rules issued by the regulatory authority. The concept of a 'type certificate' was introduced by the "Air Navigation Regulations" published in May 1919 by the UK's Secretary of State for Air , Winston Churchill . The Buhl-Verville CA-3 Airster was the first aircraft to receive a type certificate in the US, (i.e. A.T.C. No. 1) issued by the Aeronautics Branch of the Department of Commerce on March 29, 1927. Initially,

10057-399: 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

10170-449: The smaller TF34 . More recent large high-bypass turbofans include the Pratt & Whitney PW4000 , the three-shaft Rolls-Royce Trent , the General Electric GE90 / GEnx and the GP7000 , produced jointly by GE and P&W. The Pratt & Whitney JT9D engine was the first high bypass ratio jet engine to power a wide-body airliner. Type certification A type certificate signifies

10283-502: 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

10396-454: 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

10509-520: 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

10622-497: 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

10735-665: 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

10848-428: 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

10961-425: 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

11074-445: 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

11187-453: 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

11300-476: 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

11413-418: 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

11526-416: The ultimate structural strength. Other prototypes will undergo other systems tests until the satisfaction of the regulators. With all ground tests completed, prototypes are made ready for flight tests. The flight tests are flown by specially approved flight test pilots who will fly the prototypes to establish the ultimate flight limits which should be within the airworthiness rules. If a long range airliner

11639-510: 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

11752-463: The wing on the Boeing 747-400 with its larger main gear struts and bigger tires and not the previous 747-100 GE testbed. The engine was tilted 5° more than the GE CF6 . Boeing built a specially designed pylon for the testbed. Suspended on a 19 ft (580 cm) strut, the fourth engine of the program began flight testing at the end of 2017. The engine, with a fan diameter of 134 in (340 cm),

11865-676: 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

11978-599: 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

12091-629: 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

12204-475: Was designed to improve fuel efficiency by 10% compared to the GE90. It is rated at 110,000 lbf (490 kN) of thrust, which is 5,000 lbf (20 kN) less than the GE90 highest thrust variant, the GE90-115, rated at 115,000 lbf (510 kN). In February 2012, GE announced studies on a more efficient derivative of the GE90, calling it the GE9X, to power both the -8 and -9 variants of the new Boeing 777X . It

12317-558: Was modified as a result of early running experience. SETT testing started on May 16, 2017, at Peebles, Ohio , 13 months after FETT; it was the first engine built to the finalized production standard for certification. During the FAA 150 hr block test, the variable stator vane (VSV) lever arm failed and its redesign led to a 3–month delay. SETT was followed by four more test engines by May 2018. The certification program began in May 2017. Eight additional engines were involved for certification, as well as one for ETOPS certification installed in

12430-553: Was planned for the fourth quarter of 2018. On November 10, 2017, a GE9X engine reached a record thrust of 134,300 lbf (597 kN) in Peebles, a new Guinness World Record breaking the GE90-115B 127,900 lbf (569 kN) record set in 2002. The block test engine ran at its operational limits, at triple red-line conditions: maximum fan speed, maximum core speed, and maximum exhaust gas temperature . Icing tests started in Winnipeg at

12543-484: Was scheduled to begin in the third quarter. By October 2018, half of the certification was completed, and eight development engines were used, mostly in Peebles, Ohio : #1 was stored; a fan blade was deliberately separated from the fan hub of #2 at takeoff thrust for the blade-out test; #3 was used for crosswind ground testing and cyclic and load testing of the thrust reverser cascade assembly; #4 explored boundaries of

12656-568: 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

12769-568: Was to feature the same 128 in (325 cm) fan diameter as the GE90-115B with thrust decreased by 15,800 lbf (70 kN) to a new rating of 99,500 lbf (443 kN) per engine. The engine for the 777-8X was to be derated to 88,000 lbf (390 kN). In 2013, the fan diameter was increased by 3.5 in (9 cm) to 132 in (335 cm). In 2014, the fan diameter was increased another 1.5 in (4 cm) to 133.5 in (339 cm), slightly increasing thrust from 102,000 to 105,000 lbf (450 to 470 kN). In 2016,

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