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109-434: The Rolls-Royce Pegasus is a British turbofan engine originally designed by Bristol Siddeley . It was manufactured by Rolls-Royce plc . The engine is not only able to power a jet aircraft forward, but also to direct thrust downwards via swivelling nozzles . Lightly loaded aircraft equipped with this engine can manoeuvre like a helicopter . In particular, they can perform vertical takeoffs and landings . In US service,

218-564: A Hiduminium aluminium alloy engine; this model cost £950. Car production continued at a reduced rate throughout 1940, and a few were assembled in 1941. The week that World War II ended in Europe, Armstrong Siddeley introduced its first post-war models; these were the Lancaster four-door saloon and the Hurricane drophead coupe . The names of these models echoed the names of aircraft produced by

327-579: A 2-stage fan and used the Orpheus 6 core. Although the fan was overhung, inlet guide vanes were still incorporated. The HP spool comprised a 7-stage compressor driven by a single-stage turbine. A 2-stage LP turbine drove the fan. There was no plenum at fan exit, but 4 thrust-vectoring nozzles were fitted. Further development of the engine then proceeded in tandem with the aircraft, the Hawker P.1127 . The aircraft first flew (tethered hover) on 21 October 1960, powered by

436-727: A common gearbox, and could be found on the Fairey Gannet . The Python turboprop powered the Westland Wyvern strike aircraft. Further development of the Mamba removed the reduction gearbox to give the Adder turbojet . Another pioneer in the production of the RAE engine design was Metrovick , who started with a design known as the Metrovick F.2 . This engine never entered production, and Metrovick turned to

545-419: 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

654-422: A few degrees of nozzle movement to get the aircraft moving forward quickly enough to produce lift from the wing, and that even at a 15-degree angle the aircraft accelerated very well. The pilot simply had to move the nozzle control forward slowly. During transition from horizontal back to vertical the pilot would simply slow to roughly 200 knots and turn the nozzles downward, allowing the engine thrust to take over as

763-410: 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

872-426: 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

981-416: 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

1090-659: A larger design, the Beryl, and then to an even larger design, the Sapphire . Armstrong Siddeley later took over the Sapphire design, and it went on to be one of the most successful 2nd generation jet engines, competing with the better-known Rolls-Royce Avon . The company went on to develop an engine – originally for unmanned Jindivik target drones – called the Viper . This product was further developed by Bristol Siddeley and, later, Rolls-Royce and

1199-572: 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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1308-401: 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 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

1417-403: 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

1526-451: A simple thrust vectoring system that uses four swiveling nozzles, giving the Harrier thrust both for lift and forward propulsion, allowing for STOVL flight. Combustion system is an annular combustor with ASM low-pressure vaporising burners. Engine starting was by a top-mounted packaged combined gas turbine starter/ APU . The front nozzles, which are made of steel, are fed with air from

1635-550: 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

1744-427: A subsidiary with J. D. Siddeley as managing director. In 1927, Armstrong Whitworth merged its heavy engineering interests with Vickers to form Vickers-Armstrongs . At this point, J. D. Siddeley brought Armstrong Siddeley and Armstrong Whitworth Aircraft into his control. In 1928, Armstrong Siddeley Holdings bought Avro from Crossley Motors . Also that year Siddeley partnered with Walter Gordon Wilson , inventor of

1853-473: 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

1962-421: 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

2071-496: 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

2180-704: 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

2289-563: A while as an aircraft engine division within Rolls-Royce. In June 1972, Rolls-Royce (1972) Ltd sold all the stock of spares plus all patents, specifications, drawings, catalogues and the name of Armstrong Siddeley Motors Ltd to the Armstrong Siddeley Owners Club Ltd. This meant that "Armstrong Siddeley" and "A-S Sphinx Logo" are trademarks and copyright of the Armstrong Siddeley Owners Club Ltd. The "Siddeley" name survived

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2398-400: A while longer in aviation, through Hawker Siddeley Aviation and Hawker Siddeley Dynamics. In 1977 they joined with others to become British Aerospace (BAe) which with further mergers is now BAE Systems . The first car produced from the union was a fairly massive machine, a 5-litre 30 hp . A smaller 18 hp appeared in 1922 and a 2-litre 14 hp was introduced in 1923. 1928 saw

2507-619: A year, and in New Zealand, Armstrong Siddeley Car Club in New Zealand Inc. publish Sphinx-NZ monthly. Throughout the 1920s and 1930s, Armstrong Siddeley produced a range of low- and mid-power aircraft radial engines , all named after big cats . They also produced a tiny 2-cylinder engine called the Ounce , another name for the snow leopard , for ultralight aircraft. The company started work on their first gas turbine engine in 1939, following

2616-507: 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,

2725-410: 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

2834-430: 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,

2943-413: 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

3052-420: 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

3161-424: 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 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

3270-411: 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

3379-472: 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

Rolls-Royce Pegasus - Misplaced Pages Continue

3488-677: 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

3597-771: The Gloster Aircraft Company and Air Training Services – Hawker Siddeley , a famous name in British aircraft production. Armstrong Whitworth Aircraft and Armstrong Siddeley Motors became subsidiaries of Hawker Siddeley, with Sopwith himself becoming the new chairman of Armstrong Siddeley Motors. At this time, there remained an "unbroken business association" between the Siddeley family and the Middleton-Joy family who were manufactures of Filtrate Oil and had enjoyed considerable success in car-racing rallies. Armstrong Siddeley

3706-521: The Hawker Siddeley Group (the name adopted by the company in 1935) during the war. These cars all used a 2-litre six-cylinder (16 hp) engines, increased to 2.3-litre (18 hp) engines in 1949. From 1949 to 1952 two commercial variants of the 18 hp Whitleys were produced, primarily for export. The Utility Coupé was a conventional coupe utility style vehicle, while the Station Coupé

3815-450: The pre-selector gearbox , to create Improved Gears Ltd, which later became Self-Changing Gears – the gearbox that should be credited with enabling the marketing tagline "Cars for the daughters of gentlemen". Armstrong Siddeley manufactured luxury cars, aircraft engines, and later, aircraft. In 1935, J. D. Siddeley's interests were purchased for £2 million by aviation pioneer Tommy Sopwith , owner of Hawker Aircraft , to form – along with

3924-399: The "baby Sapphire" heralded the beginning of the end for Armstrong Siddeley, it was because Jaguar had launched the unitary-construction 2.4 saloon in 1955, which was quicker, significantly cheaper, and much better-looking than the 234 and 236. The last new model produced by Armstrong Siddeley was 1958's Star Sapphire, with a 4-litre engine, and automatic transmission . The Armstrong Siddeley

4033-492: The 1930s by the introduction of a range of six-cylinder cars with ohv engines, though a four-cylinder 12 hp was kept in production until 1936. In 1932 - or thereabouts, a line of special, rather more sporty designs was started which resulted in the Rally Tourer series. The aim was to help shake off the somewhat pedestrian image of what was in fact a rather advanced product. Of the 16 rally tourers built, many were used by

4142-421: 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

4251-552: The BE53/3 (Pegasus 2). Free hover was achieved on 19 November of the same year. Transition to wing-borne flight occurred in 1961. Later versions of the P.1127 were fitted with the Pegasus 3 and eventually the Pegasus 5. The Pegasus 5 was also used in the Kestrel , a refinement of the P.1127, of which nine were built for a Tripartite evaluation exercise. The Kestrel was subsequently developed into

4360-582: The Company. A related engine design, the 39,500 lbf (with reheat ) Bristol Siddeley BS100 for a supersonic VTOL fighter (the Hawker Siddeley P.1154 ) was not developed to production as the aircraft project was cancelled in 1965. A non-vectored 26,000 lb thrust derivative of the Pegasus running on liquid hydrogen , the RB.420, was designed and offered in 1970 in response to a NASA requirement for an engine to power

4469-480: The Harrier combat aircraft. By the time the Pegasus 5/2 was built, both the fan and HP compressor had been zero-staged and 2nd stage added to the HP turbine. The flight testing and engine development received no government funding; the plane's funding came entirely from Hawker. The first engines had barely enough thrust to lift the plane off the ground due to weight growth problems. Flight tests were initially conducted with

Rolls-Royce Pegasus - Misplaced Pages Continue

4578-447: The LP compressor, and the rear nozzles, which are of Nimonic with hot (650 °C) jet exhaust. The airflow split is about 60/40 front/back. The nozzles are rotated using motorcycle chains driven by air motors powered by air from the HP compressor. The nozzles rotate through a range of 98.5 degrees. The engine is mounted in the centre of the Harrier and as a result, it was necessary to remove

4687-525: The Orpheus core, improving the overall pressure ratio, creating what is now considered a conventional turbofan configuration. For a year Bristol designed the engine in isolation, with little feedback from the various airframe manufacturers furnished with data. However, in May 1957 the team received a supportive letter from Sydney Camm of Hawker Aviation stating they were looking for a Hawker Hunter replacement. The aircraft designer, Ralph Hooper , suggested having

4796-732: The UK, Australia, New Zealand, the Netherlands and Germany. Armstrong Siddeley Owners Club Ltd has members worldwide and many members of the ASCC in Australia are resident overseas. In the United Kingdom, ASOC publishes a monthly members magazine Sphinx . In Australia, the Armstrong Siddeley Car Club publishes Southern Sphinx six times a year. In the Netherlands, ASOC Dutch also publishes six times

4905-464: 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

5014-422: 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

5123-441: 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 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

5232-545: The aircraft slowed and the wings stopped producing lift. The RAF was not much of a convert to the VTOL idea, and described the whole project as a toy and a crowd pleaser . The first prototype P1127 made a very heavy landing at the Paris Air Show in 1963. Series manufacture and design and development improvement to the Pegasus to produce ever-higher thrusts were continued by Bristol engines beyond 1966, when Rolls-Royce Ltd bought

5341-422: The aircraft tethered, with the first free hover achieved on 19 November 1960. The first transition from static hover to conventional flight was achieved on 8 September 1961. It was originally feared that the aircraft would have difficulty transitioning between level and vertical flight, but during testing it was found to be extremely simple. Testing showed that because of the extreme power-to-weight ratio it only took

5450-426: 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

5559-582: The blower scrolls. Although the idea of vectoring the thrust was quite novel, the engine proposed was considered to be far too heavy. As a result, an engineer at Bristol Engine Company , Gordon Lewis , began in 1956 to study alternative engine concepts, using, where possible, existing engine components from the Orpheus and Olympus engine series. The work was overseen by the Technical Director Stanley Hooker . One concept which looked promising

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5668-464: The company's first 15 hp six; 1929 saw the introduction of a 12 hp vehicle. This was a pioneering year for the marque, during which it first offered the Wilson preselector gearbox as an optional extra; it became standard issue on all cars from 1933. In 1930 the company marketed four models, of 12, 15, 20, and 30 hp, the last costing £1450. The company's rather staid image was endorsed during

5777-465: The company's name to The Siddeley-Deasy Motor Car Company Limited. Siddeley's name had been added to the product's radiator earlier in 1912. His cars began to use the slogan "As silent as the Sphinx", sporting a Sphinx as a bonnet mascot. In April 1919, Siddeley-Deasy was bought out by Armstrong Whitworth Development Company of Newcastle upon Tyne and in May 1919 became Armstrong Siddeley Motors Ltd,

5886-521: The design pioneered at the Royal Aircraft Establishment by Alan Arnold Griffith . Known as the "ASX" for "Armstrong Siddeley eXperimental", the original pure-turbojet design was later adapted to drive a propeller, resulting in the "ASP". From then on, AS turbine engines were named after snakes . The Mamba and Double Mamba were turboprop engines, the latter being a complex piece of engineering with two side-by-side Mambas driving through

5995-445: 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

6104-572: The engine is designated F402 . Originally the Bristol Siddeley Pegasus, the engine powers all versions of the Harrier family of multi-role military aircraft . Rolls-Royce licensed Pratt & Whitney to build the Pegasus for US built versions. However Pratt & Whitney never completed any engines, with all new build being manufactured by Rolls-Royce in Bristol, England. The Pegasus was also

6213-427: 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

6322-578: The engine or aircraft from the Ministry of Defence . Fortunately, engine development was financially supported to the tune of 75% from the Mutual Weapons Development Program , Verdon Smith of Bristol Siddeley Engines Limited (BSEL), which Bristol Engines had by then become on its merger with Armstrong Siddeley , quickly agreeing to pay the remainder. The first prototype engine (one of two BE53/2s built), ran on 2 September 1959 and featured

6431-416: 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 the fan nozzle. The amount of energy transferred depends on how much pressure rise

6540-516: 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

6649-573: The fan and core compressor because the fan did not supercharge the core compressor. Although the BE.52 was a self-contained power plant and lighter than Wibault's concept, the BE.52 was still complicated and heavy. As a result, work on the BE.53 concept started in February 1957. In the BE.53 the Olympus stages were fitted close to the Orpheus stages; thus simplifying the inlet ducting. The Olympus stages now supercharged

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6758-411: 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

6867-450: 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

6976-474: The four thrust vectoring nozzles (originally suggested by Lewis), with hot gases from the rear two. Further joint discussions helped to refine the engine design. The 1957 Defence White Paper , which focused on missiles, and not crewed aircraft – which were declared 'obsolete' - was not good news, because it precluded any future government financial support for development of not already extant crewed combat aircraft. This prevented any official financial support for

7085-483: 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 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

7194-400: 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 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

7303-443: 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 the required thrust still maintained by increasing the mass accelerated. A turbofan does this by transferring energy available inside

7412-429: 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

7521-409: 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 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

7630-474: 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

7739-468: The mass-flow of air bypassing the engine core to the mass-flow of air passing through 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

7848-417: 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

7957-474: 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

8066-439: The older 2.3-litre six-cylinder engine). The Sapphire 346 sported a bonnet mascot in the shape of a sphinx with namesake Armstrong Siddeley Sapphire jet engines attached. The 234 and 236 Sapphires might have looked to some of marque's loyal customers like a radical departure from the traditional Armstrong Siddeley appearance. However, in truth, they were simply too conservative in a period of rapidly developing automotive design. If

8175-490: The operating limits are determined by jet pipe temperature. To enable the engine speed and hence thrust to be increased for take-off, water is sprayed into the combustion chamber and turbine to keep the blade temperature down to an acceptable level. Water for the injection system is contained in a tank located between the bifurcated section of the rear (hot) exhaust duct. The tank contains up to 500 lb (227 kg, 50 imperial gallons ) of distilled water. Water flow rate for

8284-411: The owners or senior directors, and were entered into various rallies, achieving some good results and making for good publicity. Only one of those 16 special cars is now known to exist: a 1933, Long-15 Rally Tourer which, according to the records, shared the same body as the 20 hp version (which had a slightly longer bonnet). In 1933, the 5-litre six-cylinder Siddeley Special was announced, featuring

8393-532: The planned engine for a number of aircraft projects, among which were the prototypes of the German Dornier Do 31 VSTOL military transport project. Michel Wibault , the French aircraft designer, had the idea to use vectored thrust for vertical take-off aircraft. This thrust would come from four centrifugal blowers shaft driven by a Bristol Orion turboprop , the exhaust from each blower being vectored by rotating

8502-530: The production of cars, aircraft engines, gearboxes for tanks and buses, rocket and torpedo motors, and the development of railcars. Company mergers and takeovers with Hawker Aviation and Bristol Aero Engines saw the continuation of the car production which ceased in August 1960. The company was absorbed into the Rolls-Royce conglomerate which was interested in the aircraft and aircraft engine business. Eventually,

8611-442: The projected Space Shuttle on its return flight through the atmosphere. In the event, NASA chose a shuttle design using a non-powered gliding return. The Pegasus vectored-thrust turbofan is a two-shaft design with three low pressure (LP) and eight high pressure (HP) compressor stages driven by two LP and two HP turbine stages respectively. It is the first turbofan to have the fan ahead of the LP shaft front bearing. This eliminated

8720-414: The propulsion of aircraft", in which he describes the principles behind the turbofan, although not called as such at that time. While 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

8829-685: The range was extended with the introduction of a 3-cylinder engine rated at 33 bhp (25 kW). The engines were built at Armstrong Siddeley's factory at Walnut Street in Leicester until that factory closed in August 1957. Production was transferred to the factory of Armstrong Siddeley ( Brockworth ) Ltd in Gloucestershire and in 1958 to the factory of Petters Limited at Staines, Middlesex. The engines built by Petters were designated AS1, AS2 and AS3 to distinguish them from that company's other products. Production ended in 1962 when Petters introduced

8938-485: The remaining spares and all motor car interests were sold to the Armstrong Siddeley Owners Club Ltd, which now owns the patents, designs, copyrights and trademarks, including the name Armstrong Siddeley. Considered "an elegant car appropriate for royal use", the "Armstrong Siddeley Saloon" was used by the Prince of Wales (later King Edward VIII) during his 1930 tour of Uganda . The Siddeley Autocar Company, of Coventry ,

9047-425: The required turbine temperature reduction is approximately 35   gpm (imperial gallons per minute) for a maximum duration of approximately 90 seconds. The quantity of water carried is sufficient for and appropriate to the particular operational role of the aircraft. Selection of water injection engine ratings (Lift Wet/Short Lift Wet) results in an increase in the engine speed and jet pipe temperature limits beyond

9156-414: The requirement for bearing-support struts in front of the fan and the icing hazard that goes with them. Unusually the LP and HP spools rotate in opposite directions which significantly reduces the gyroscopic effects which would otherwise cause aircraft control problems at low aircraft speeds. LP and HP blades are made from titanium. The fan is a transonic design and airflow is 432 lb/s. The engine employs

9265-437: The respective dry (non-injected) ratings (Lift Dry/Short Lift Dry). Upon exhausting the available water supply in the tank, the limits are reset to the 'dry' levels. A warning light in the cockpit provides advance warning of water depletion to the pilot. Pegasus engines are on public display at the following museums: Data from Related development Comparable engines Related lists Turbofan The ratio of

9374-399: 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

9483-599: 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. Armstrong Siddeley Aircraft engines Merged with Bristol Aero Engines (1960) became Bristol Siddeley Armstrong Siddeley

9592-502: 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

9701-520: 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

9810-497: 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

9919-665: 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

10028-428: 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

10137-476: 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

10246-418: 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

10355-510: 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

10464-424: The wing to change the powerplant after mounting the fuselage on trestles. The change took a minimum of eight hours, although using the proper tools and lifting equipment this could be accomplished in less than four. The maximum take-off thrust available from the Pegasus engine is limited, particularly at the higher ambient temperatures, by the turbine blade temperature. As this temperature cannot reliably be measured,

10573-676: 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

10682-449: Was a British engineering group that operated during the first half of the 20th century. It was formed in 1919 and is best known for the production of luxury vehicles and aircraft engines . The company was created following the purchase by Armstrong Whitworth of Siddeley-Deasy , a manufacturer of luxury motor cars that were marketed to the top echelon of society. After the merge of companies, this focus on quality continued throughout in

10791-521: Was a casualty of the 1960 merger with Bristol; the last car left the Coventry factory in 1960. Cars produced by Armstrong Siddeley had designations that came from the tax horsepower rating of their engines. Limousine, landaulette A feature of many of their later cars was the option of an electrically controlled pre-selector gearbox. Like many British cars of this era, there are active owners' clubs supporting their continued use in several countries, e.g.

10900-403: Was a single-cylinder engine producing 5 bhp (3.7 kW) at 900 rpm and a twin-cylinder version. Each cylinder had a capacity of 988 cm (60.2 cubic inches). The power output and speed was progressively increased. By the end of 1954 the single-cylinder engine was rated at 11 bhp (8.2 kW) at 1800 rpm and the twin-cylinder engine 22 bhp (16 kW) at the same speed. In 1955

11009-498: 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

11118-529: Was appointed general manager. Without the consent of the Vickers brothers Siddeley added his own name to the Wolseley nameplate but it was dropped on his departure. In 1909, J. D. Siddeley resigned from Wolseley and in 1910, he took on management of The Deasy Motor Car Manufacturing Company, Limited. The shareholders were so pleased with his success in that post that on 7 November 1912 they unanimously agreed to change

11227-629: 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

11336-412: Was effectively a dual cab vehicle, although it still retained only two doors. However, it did have two rows of seating to accommodate up to four adults and the doors were larger to allow better access to the rear. From 1953 the company produced the Sapphire, with a 3.4-litre six-cylinder engine. In 1956, the model range was expanded with the addition of the 234 (a 2.3-litre four-cylinder) and the 236 (with

11445-490: Was founded by John Davenport Siddeley (1866–1953) in 1902. Its products, made for him by a Vickers subsidiary, were heavily based on Peugeots using many Peugeot parts and fitted with English-built bodies. J. D. Siddeley was appointed London sales manager of Vickers Limited's subsidiary Wolseley in early 1905 at the same time as Wolseley purchased the goodwill and patent rights of his Siddeley car. A few months later Herbert Austin left to form his own business and Siddeley

11554-404: Was merged with the aircraft engine business of Bristol Aeroplane Company (Bristol Aero Engines) to form Bristol Siddeley as part of an ongoing rationalisation under government influence of the British aircraft and aircraft engine manufacturers. Armstrong Siddeley produced their last cars in 1960. Bristol Siddeley and Rolls-Royce merged in 1966, the latter subsuming the former which remained for

11663-481: Was sold in great numbers over many years. A range of rocket motors were also produced, including the Snarler and Stentor . The rocket development complemented that of Bristol, and Bristol Siddeley would become the leading British manufacturer of rocket engines for missiles. In 1946 Armstrong Siddeley produced their first diesel engines . They were medium-speed engines for industrial and agricultural use. Initially there

11772-568: 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

11881-458: Was the BE52, which initially used the Orpheus 3 as the engine core and, on a separate coaxial shaft, the first two stages of an Olympus 21 LP compressor, which acted as a fan, delivering compressed air to two thrust vectoring nozzles at the front of engine. At this point in the design exercise, the exhaust from the LP turbine discharged through a conventional rear nozzle. There were separate intakes for

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