CFM56-3 turbofan, lower half, side view.

Boeing 747 jet engine up close

The turbofan is a type of airplane engine which has evolved from the axial-flow turbojet engine, essentially by increasing the relative size of the Low Pressure (LP) Compressor to the point where some (or in some cases, most) of the air exiting the unit actually bypasses the core (or gas generator). This bypass air either expands through a separate propelling nozzle, or is mixed with the hot gases leaving the Low Pressure (LP) Turbine, before expanding through a Mixed Stream Propelling Nozzle. A mounted CFM56 turbofan on display at MIT. . © 2005 joseph barillari File links The following pages link to this file: Turbofan CFM International CFM56 Categories: GFDL images ... A mounted CFM56 turbofan on display at MIT. . © 2005 joseph barillari File links The following pages link to this file: Turbofan CFM International CFM56 Categories: GFDL images ... CFM International CFM-56 series engines is a family of high-bypass turbofan engines made by CFM International and has a thrust range from 18,500 to 34,000 lbf (82 kN to 151 kN). ... Image:Jet engine intake. ... Image:Jet engine intake. ... Fixed-wing aircraft is a term used to refer to what are more commonly known as aeroplanes in Commonwealth English (excluding Canada) or airplanes in North American English. ... An engine is something that produces some effect from a given input. ... The axial flow compressor is an improvement on the centrifugal compressor previously used in turbine engines,though small and micro turbines use centrifugal compressors with relative advantages (in terms of pressure ratios achieveable per stage of compression). ... Jet engine diagram Turbojets are the simplest and oldest kind of general purpose jet engine. ...

If the turboprop is better at moderate flight speeds and the turbojet is better at very high speeds, it might be imagined that at some speed range in the middle a mixture of the two is best. Such an engine is the turbofan (originally termed bypass turbojet by the inventors at Rolls Royce). Another term used is ducted fan. A diagram showing how a turboprop works. ... Rolls-Royce is a set of companies, all deriving from the British automobile and aero-engine manufacturing company founded by Henry Royce and C.S. Rolls in 1906. ... A ducted fan is an arrangement of a propeller-driven aircraft where the propeller is mounted inside the fuselage, within a duct. ...

The difference between a ducted fan and a propeller is that the duct slows the air before it arrives at the fan. As both propeller and fan blades must operate subsonically to be efficient, ducted fans allow efficient operation at higher vehicle speeds. A ducted fan is an arrangement of a propeller-driven aircraft where the propeller is mounted inside the fuselage, within a duct. ... This article needs a complete rewrite for the reasons listed on the talk page. ...

Depending on specific thrust (i.e. net thrust/intake airflow), ducted fans operate best from about 250 to 1300 mph (400 to 2000 km/h), which is why turbofans are the most common type of engine for aviation use today.

In a turbofan, the LP Compressor is often called a fan. Civil turbofans usually have a single fan stage, whereas most military turbofans have multi-stage fans.

Bypass ratio (the ratio of bypassed air mass to combustor air mass) is a parameter often used for classifying turbofans, although specific thrust is a better parameter. In aeronautical engineering, and jet engine design in particular, bypass ratio is a common measurement that compares the amount of air deliberately blown past the engine to that moving through the core. ...

The noise of any type of jet engine is strongly related to the velocity of the exhaust gases. High bypass ratio (i.e. low specific thrust) turbofans are relatively quiet compared to turbojets and low bypass ratio (i.e. high specific thrust) turbofans. A low specific thrust engine has a low jet velocity almost by definition, as the following approximate equation for net thrust implies:

Fn = m * (Vjfe - Va)

where:

m intake mass flow

Vjfe fully expanded jet velocity (in the exhaust plume)

Va aircraft flight velocity

Rearranging the above equation, specific thrust is given by:

Fn/m = (Vjfe - Va)

So for zero flight velocity, specific thrust is directly proportional to jet velocity.

Jet aircraft are often considered loud, but a conventional piston engine or a turboprop engine delivering the same power would be much louder. (NASA has a web page with details on jet noise.) A diagram showing how a turboprop works. ... NASA Logo Listen to this article · (info) This audio file was created from the revision dated 2005-09-01, and does not reflect subsequent edits to the article. ...

Low-bypass turbofans

Early turbojet engines were very fuel-inefficient, as their overall pressure ratio and turbine inlet temperature were severely limited by the technology available at the time. Improved materials, and the introduction of twin compressors such as in the Pratt & Whitney JT3C engine, increased the overall pressure ratio and thus the thermodynamic efficiency of engines, but led to a poor propulsive efficiency, as pure turbojets have a low mass flow, high velocity exhaust. Jet engine diagram Turbojets are the simplest and oldest kind of general purpose jet engine. ... The Pratt & Whitney JT3C was a turbojet engine of the 1950s. ... This article needs to be cleaned up to conform to a higher standard of quality. ...

The original low-bypass turbofan engines were designed to improve propulsive efficiency by reducing the exhaust speed to a value closer to aircraft speeds. The Rolls-Royce Conway, the first turbofan, had a bypass ratio of 0.3, similar to the modern General Electric F404 fighter engine. Civil turbofan engines of the 1960s, such as the Pratt & Whitney JT8D and the Rolls-Royce Spey had bypass ratios close to unity. Since the 1970s, most jet fighter engines have been low-bypass turbofans with a mixed exhaust andafterburners – the first afterburning turbofan was the Pratt & Whitney TF30. A few low-bypass ratio military turbofans (e.g. F404) have Variable Inlet Guide Vanes, with piano-style hinges, to direct air onto the first rotor stage. This improves the fan surge margin in the mid-flow range. The Rolls-Royce Conway was the first by-pass engine to go into service in the world. ... A turbofan engine with afterburner. ... The Pratt & Whitney JT8D is a low-bypass turbofan jet engine, introduced by Pratt & Whitney in February 1964 with the inaugural flight of Boeings 727. ... The Spey is a low-bypass turbofan engine from Rolls-Royce that has been in widespread service for over 30 years. ... This article provides extensive lists of events and significant personalities of the 1970s. ... A fighter aircraft is a military aircraft designed primarily for attacking other aircraft, as opposed to a bomber, which is designed to attack ground targets, primarily by dropping bombs. ... For other uses of afterburner, see Afterburner (disambiguation). ... The TF-30, produced by Pratt & Whitney was the worlds first afterburning turbofan. ...

Imagine a retrofit situation where a new low bypass ratio, mixed exhaust, turbofan is replacing an old turbojet, in a particular military application. Say the new engine is to have the same airflow and net thrust (i.e. same specific thrust) as the one it is replacing. A bypass flow can only be introduced if the turbine inlet temperature is allowed to increase, to compensate for a correspondingly smaller core flow. Improvements in turbine cooling/material technology would facilitate the use of a higher turbine inlet temperature, despite increases in cooling air temperature, resulting from a probable increase in overall pressure ratio.

Efficiently done, the resulting turbofan would probably operate at a higher nozzle pressure ratio than the turbojet, but with a lower exhaust temperature to retain datum 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).

Modern low-bypass military turbofans include the Pratt & Whitney F119, the Eurojet EJ200 and the General Electric F110, all of which feature a mixed exhaust, afterburner and variable area propelling nozzle. Non-afterburning engines include the Rolls-Royce/Turbomeca Adour and the unmixed, vectored thrust, Rolls-Royce Pegasus. The Pratt & Whitney F119-PW-100 with integrated vectorable thrust nozzles. ... Categories: Stub | Turbofan engines ... The F110 is an afterburning turbofan produced by General Electric. ... RAF Jaguars Adour The Adour jet engine is a two-shaft turbofan developed by Rolls-Royce/Turbomeca, a joint subsidiary of Rolls-Royce (UK) and Turbomeca (France). ... Rolls-Royce Pegasus The Rolls Royce Pegasus is a turbofan engine manufactured by Rolls-Royce plc. ...

High-bypass turbofan engines

The introduction of variable compressor stators enabled high pressure ratio compressors to work surge-free at all throttle settings. This innovation made its debut in the General Electric J79, a single-shaft turbojet for supersonic military aircraft. When variable stators were combined with multiple compressors, dramatic increases in overall pressure ratio became possible. Higher turbine inlet temperatures (through improvements in turbine cooling/material technology) enabled relatively small mass flow gas generators to be employed, thus making high-bypass turbofan engines feasible, with bypass ratios of 5 or more. The General Electric J79 was a turbojet engine built for use in a variety of fighter aircraft and bomber aircraft. ... Jet engine diagram Turbojets are the simplest and oldest kind of general purpose jet engine. ... This page is about high speed motion of bodies such as airplanes through air or other fluids. ... Military aircraft are airplanes used in warfare. ...

The first high-bypass turbofan engine was the General Electric TF39, built to power the Lockheed C-5 Galaxy military transport aircraft. The civil General Electric CF6 engine used a related design. Other high-bypass turbofans are the Pratt & Whitney JT9D, the three-shaft Rolls-Royce RB211 and the CFM International CFM56. More recent large high-bypass turbofans include the Pratt & Whitney PW4000, the three-shaft Rolls-Royce Trent and the General Electric GE90. The General Electric TF39 and CF6 family of high-bypass turbofan engines are the most popular large aircraft turbines in the world, powering civil and military widebodies from a variety of manufacturers. ... The Lockheed SR-71, remarkably advanced for its time and unsurpassed in many areas of performance The Lockheed U-2 first flew in 1955 providing much needed intelligence on Soviet bloc countries Lockheed Corporation was an aerospace company founded in 1912 which merged with Martin Marietta in 1995 to form... The Lockheed C-5 Galaxy is one of the largest aircraft in the world. ... The General Electric TF39 and CF6 family of high-bypass turbofan engines are the most popular large aircraft turbines in the world, powering civil and military widebodies from a variety of manufacturers. ... The Pratt & Whitney JT9D engine is the first high-bypass-ratio engine to power a wide-bodied aircraft. ... Rolls-Royce RB211 engine The Rolls Royce RB.211 family is a family of high-bypass turbofan aircraft engines made by Rolls-Royce capable of generating 37,400 to 60,600 pound (166 to 270 kN) thrust. ... CFM56-3 CFM International CFM-56 series engines is a family of high-bypass turbofan engines made by CFM International and has a thrust range from 18,500 to 34,000 lbf (82 kN to 151 kN). ... The Pratt & Whitney PW4000 is a family of high-bypass turbofan aircraft engines with certified thrust ranging from 52,000 to 99,040 lbf (230 to 440 kN). ... Rolls-Royce Trent 900 on A380 prototype Rolls Royce Trent is a family of high-bypass turbofan engine manufactured by Rolls-Royce, developments of the famous RB211 with thrust ratings spanning between 53,000 to 95,000 lbf (236 to 423 kN). ... NASA GE90 airflow simulation General Electric GE90 is a family of high-bypass turbofan engines built by General Electric for the Boeing 777, with thrust ranging from 74,000 to 115,000 lbf (329 to 512 kN). ...

The tremendously higher thrust provided by high-bypass turbofan engines also made civil wide-body aircraft practical and economical. In addition to the vastly increased thrust, these engines are also generally quieter. This is not so much due to the higher bypass ratio, but as to the use of low pressure ratio, single stage, fans, which significantly reduce specific thrust and, thereby, jet velocity. The combination of a higher overall pressure ratio and turbine inlet temperature improves thermal efficiency. This, together with a lower specific thrust (better propulsive efficiency), leads to a lower specific fuel consumption. Wide-body Virgin Atlantic Airbus A340-300 A wide-body aircraft is a large airliner with a fuselage diameter of about 5 to 6 metres and twin aisles. ...

For reasons of fuel economy, and also of reduced noise, almost all of today's jet airliners are powered by high-bypass turbofans. Although modern military aircraft tend to use low bypass ratio turbofans, military transport aircraft (e.g. C17 ) mainly use high bypass ratio turbofans (or turboprops) for fuel efficiency.

The Soviet Union's engine technology was less advanced than the West's and its first wide-body aircraft, the Ilyushin Il-86, was powered by low-bypass engines. The Yakovlev Yak-42, a medium-range, rear-engined aircraft seating up to 120 passengers was the first Soviet aircraft to use high-bypass engines. Il-86 of Pulkovo Aviation Enterprise at St. ... The three engined Yakovlev Yak-42 was designed as a replacement for the twin engined Tupolev Tu-134 jet. ...

Technical Discussion

1) Specific Thrust (net thrust/intake airflow) is an important parameter for turbofans and jet engines in general. Imagine a fan (driven by an appropriately sized electric motor) operating within a pipe, which is connected to a propelling nozzle. Fairly obviously, the higher the Fan Pressure Ratio (discharge pressure/inlet pressure), the higher the jet velocity and the corresponding specific thrust. Now imagine we replace this set-up with an equivalent turbofan - same airflow and same fan pressure ratio. Obviously, the core of the turbofan must produce sufficient horsepower to drive the fan via the Low Pressure (LP) Turbine. If we choose a low (HP) Turbine Inlet Temperature for the gas generator, the core airflow needs to be relatively high to compensate. The corresponding bypass ratio is therefore relatively low. If we raise the Turbine Inlet Temperature, the core airflow can be smaller, thus increasing bypass ratio. Raising turbine inlet temperature tends to increase thermal efficiency and, therefore, improve fuel efficiency.

2) Naturally, as altitude increases there is a decrease in air density and, therefore, the net thrust of an engine. There is also a flight speed effect, termed Thrust Lapse Rate. Consider the equation for net thrust again:

Fn = m * (Vjfe - Va)

With a high specific thrust (e.g. fighter) engine, the jet velocity is relatively high, so intuitively one can see that increases in flight velocity have less of an impact upon net thrust than a medium specific thrust (e.g. trainer) engine, where the jet velocity is lower. The impact of thrust lapse rate upon a low specfic thrust (e.g. civil) engine is even more severe. At high flight speeds, high specific thrust engines can pick-up net thrust through the ram rise in the intake, but this effect tends to diminish at supersonic speeds because of shock wave losses.

3) Thrust growth on civil turbofans is usually obtained by increasing fan airflow, thus preventing the jet noise becoming too high. However, the larger fan airflow requires more horsepower from the core. This can be achieved by raising the Overall Pressure Ratio (combustor inlet pressure/intake delivery pressure) to induce more airflow into the core and by increasing turbine inlet temperature. Together, these parameters tend to increase core thermal efficiency and improve fuel efficiency.

Recent developments in blade technology

The turbine blades in a turbofan engine are subject to high heat and stress, and require special fabrication. New material construction methods and material science have allowed blades, which were originally polycrystalline (regular metal), to be made from lined up metallic crystals and more recently mono-crystalline blades, which can operate at higher temperatures with less distortion. WWII era steam turbine used for ship propulsion. ... Materials science includes those parts of chemistry and physics that deal with the properties of materials. ... A polycrystalline material is made of several smaller crystallites. ...

Turbofan engine manufacturers

The turbofan engine market is dominated by General Electric, Rolls-Royce plc and Pratt & Whitney, in order of market share. General Electric Aircraft Engines (GEAE) is the top supplier of aircraft engines in the world and offers engines for the majority of commercial aircraft. ... Rolls-Royce plc (also known as Rolls-Royce Aero Engines) is the second-largest aircraft engine maker in the world, behind General Electrics GE Aircraft Engines division. ... Pratt & Whitney is an American owned aircraft engine manufacturer whose products are widely used in both civil and military aircraft. ...

General Electric

GE Aircraft Engines, part of the General Electric Conglomerate, currently has the largest share of the turbofan engine market. Through joint ventures CFM International and Engine Alliance, they have created the very successful CFM56 series and the new GP7200. General Electric Aircraft Engines (GEAE) is the top supplier of aircraft engines in the world and offers engines for the majority of commercial aircraft. ... The General Electric Company, or GE, NYSE: GE is a multinational technology and services company. ... Categories: Stub | Aircraft engine manufacturers | General Electric subsidiaries ... The Engine Alliance, a 50/50 joint venture between General Electric and Pratt & Whitney, was formed in August 1996 to develop, manufacture, sell, and support a family of modern technology engines for new high-capacity, long-range aircraft. ... CFM56-3 CFM International CFM-56 series engines is a family of high-bypass turbofan engines made by CFM International and has a thrust range from 18,500 to 34,000 lbf (82 kN to 151 kN). ... Categories: Stub | Turbofan engines ...

Rolls-Royce

Rolls-Royce plc is the second largest manufacturer of turbofans and is most noted for their RB211 and Trent series, as well as their joint venture engines for the Airbus A320 and Boeing MD-90 families (IAE V2500), the Panavia Tornado (Turbo-Union RB199) and the Boeing 717 (BR700). As owners of the Allison Engine Company, their engines power the C-130 Hercules and several Embraer regional jets. Rolls-Royce plc (also known as Rolls-Royce Aero Engines) is the second-largest aircraft engine maker in the world, behind General Electrics GE Aircraft Engines division. ... Rolls-Royce RB211 engine The Rolls Royce RB.211 family is a family of high-bypass turbofan aircraft engines made by Rolls-Royce capable of generating 37,400 to 60,600 pound (166 to 270 kN) thrust. ... Rolls-Royce Trent 900 on A380 prototype Rolls Royce Trent is a family of high-bypass turbofan engine manufactured by Rolls-Royce, developments of the famous RB211 with thrust ratings spanning between 53,000 to 95,000 lbf (236 to 423 kN). ... The Airbus A320 is a short to medium range commercial passenger aircraft manufactured by Airbus. ... The McDonnell Douglas DC-9 (initially known as the Douglas DC-9) is a family of twin-engine, single-aisle jet airliners, first manufactured in 1965 and subsequently, in greatly modified form, under a succession of different names. ... Categories: Stub | Turbofan engines ... The Panavia Tornado is a jet engine fighter-bomber jointly developed as the Multi-role combat aircraft - or MRCA - by Italy, Germany and the United Kingdom. ... RB199s of Tornado F3 The Turbo Union RB199 is an aircraft jet engine designed and built jointly by Rolls-Royce, MTU and FiatAvio (now Avio). ... 717 in new Boeing Colors AirTran Airways 717 at BWI The twinjet Boeing 717 is Boeing Commercial Airplanes smallest commercial airliner intended for the 100-seat market. ... The BR700 family of engines was developed by BMW and Rolls-Royce plc through the joint venture company BMW Rolls-Royce to power regional and corporate jets. ... The Allison Engine Company was an aircraft engine manufacturer that was acquired by Rolls-Royce in 1995. ... A United States Air Force C-130 Hercules The Lockheed C-130 Hercules is a four-engine turboprop aircraft that serves as the main tactical airlifter for military forces worldwide. ... Embraer, the Empresa Brasileira de Aeronáutica S.A. is a Brazilian company, founded on August 19, 1969, by the Brazilian government. ...

Pratt & Whitney

Pratt & Whitney is behind GE and Rolls-Royce, the JT9D has the proud distinction of being chosen by Boeing to power the original 747 "Jumbo jet". Pratt & Whitney is an American owned aircraft engine manufacturer whose products are widely used in both civil and military aircraft. ... The Pratt & Whitney JT9D engine is the first high-bypass-ratio engine to power a wide-bodied aircraft. ... The Boeing Company NYSE: BA is the leading American aircraft and aerospace manufacturer, headquartered in Chicago, Illinois, with its largest production facilities in Everett, Washington, near Seattle, Washington. ... Singapore Airlines Boeing 747-412. ...

Extreme bypass jet engines

In the 1970's Rolls-Royce/SNECMA tested a M45SD-02 turbofan fitted with variable pitch fan blades to improve handling at ultra low fan pressure ratios and to provide thrust reverse down to zero aircraft speed. The engine was aimed at ultra quiet STOL aircraft operating from city center airports.

In a bid for increased efficiency with speed, a development of the turbofan and turboprop , known as a propfan engine, was created that had an unducted fan. The fan blades are situated outside of the duct, so that it appears like a turboprop with wide scimitar-like blades. Both General Electric and Pratt & Whitney/Allison demonstrated propfan engines in the 1980's. Excessive cabin noise and relatively cheap jet fuel prevented the engines being put into service. General Electric GE-36 UDF Unducted Fan engine on a McDonnell Douglas MD-81 testbed A propfan is a modified turbofan engine, with the fan placed outside of the engine nacelle on the same axis as the compressor blades. ...

Other meanings

The Unicode standard includes a turbofan character, #274B, in the dingbats range. Its official name is "HEAVY EIGHT TEARDROP-SPOKED PROPELLER ASTERISK = turbofan". In appropriately-configured browsers, it should appear in quotes here: "❋"; In computing, Unicode provides an international standard which has the goal of providing the means to encode the text of every document people want to store on computers. ... A dingbat is a ornament or spacer used in typesetting, sometimes more formally known as a printers ornament. The term supposedly originated as onomatopoeia in old style metal-type print shops, where extra space around text or illustrations would be filled by dinging an ornament into the space...