This article should be split into multiple articles accessible from a disambiguation page.

A Pratt and Whitney turbofan engine for the F-15 Eagle is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine muffles noise and allows exhaust to escape. The mesh cover at the front of the engine (left of photo) prevents debris - or people - from being pulled into the engine by the huge volume of air rushing into the inlet.

A turbojet (jet) engine is a type of air-breathing internal combustion engine often used on aircraft. The principle of all jet engines is essentially the same; they accelerate a mass (air and combustion products) in one direction and, from Newton's third law of motion, the engine experiences thrust in the opposite direction. A Pratt and Whitney turbofan engine is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine cools the escaping exhaust gases and muffles the intense noise. ... A Pratt and Whitney turbofan engine is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine cools the escaping exhaust gases and muffles the intense noise. ... A colorized automobile engine An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. ... An aircraft is any machine capable of atmospheric flight. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... Sir Isaac Newton in Knellers 1689 portrait Sir Isaac Newton (25 December 1642 – 20 March 1727 by the Julian calendar in use in England at the time; or 4 January 1643 – 31 March 1727 by the Gregorian calendar) was an English physicist, mathematician, astronomer, philosopher, and alchemist who wrote... Newtons laws of motion are the three scientific laws which Isaac Newton discovered concerning the behaviour of moving bodies. ...

The engine draws air in at the front and compresses it. The air is combined with fuel, typically ignited by flame in the eddy of a flame holder, and burned as an atomized mixture. The combustion greatly increases the energy of the gases which are then exhausted out of the rear of the engine. The process is similar to a four-stroke cycle, with induction, compression, ignition and exhaust taking place continuously. The engine generates thrust because of the acceleration of the air through it—the equal and opposite force this acceleration produces is thrust. This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... For information on the band, see Fuel (band). ... A flame holder is a component of a jet engine designed to help keep continual combustion going. ... Combustion or burning is an exothermic reaction between a substance (the fuel) and a gas (the oxidizer) to release heat. ... Gas (actually as, part of the Gnu Binutils package) is the default Gcc Back-end. ... The four-stroke cycle of an internal combustion engine is the cycle most commonly used for automotive and industrial purposes today (cars and trucks, generators, etc). ... For the land-speed record breaking car, see ThrustSSC and Thrust2 For the computer game, see Thrust (computer game) Thrust is a reaction force described quantitatively by Newtons Second Law when a system expels or accelerates mass in one direction to propel a vehicle in the opposite direction. ... Acceleration is the time rate of change of velocity, and at any point on a v-t graph, it is given by the gradient of the tangent to that point In physics, acceleration (symbol: a) is defined as the rate of change (or time derivative) of velocity. ... In physics, a net force acting on a body causes that body to accelerate; that is, to change its velocity. ...

Jet engines take a relatively small mass of air and accelerate it by a large amount, whereas a propeller takes a large mass of air and accelerates it by a small amount. The high-speed exhaust of a jet engine makes it efficient at high speeds (especially supersonic speeds) and high altitudes. On slower aircraft and those required to fly short stages, a gas turbine-powered propeller engine, commonly known as a turboprop, is more common and much more efficient. Very small aircraft generally use conventional piston engines to drive a propeller but small turboprops are getting smaller as engineering technology improves. Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... A propeller can be seen as a rotating fin in water or a wing in air. ... Any speed over the speed of sound, which is approximately 343 m/s or 761 mph or 1,225 km/h at sea level, is said to be supersonic. ... The worlds first commercial, oil-free gas turbine is manufactured by Capstone. ... A propeller can be seen as a rotating fin in water or a wing in air. ... A Turboprop or turboshaft engine is a type of gas turbine. ... Components of a typical, four stroke cycle, DOHC piston engine. ...

The combustion efficiency of any given jet engine, like any internal combustion engine, is strongly influenced by the ratio of the compressed air's volume to the exhaust volume. In a turbine engine the compression of the air and the shape of the ducts passing into the ignition chamber prevents backflow from it and thus makes possible the continuous burning and propulsion process. Efficiency is the capability of acting or producing effectively with a minimum of waste, expense, or unnecessary effort. ... A colorized automobile engine An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. ... Volume (also called capacity) is a quantification of how much space an object occupies. ... WWII era ship propulsion turbine A turbine is a rotary engine that extracts energy from a fluid flow. ...

Modern turbojet engines are modular in concept and design. The central power-producing core, common to all jet engines, is called the gas generator (described above). To it are attached peripheral modules such as propeller reduction gearsets (turboprop/turboshaft), bypass fans, and afterburners. The kind of peripheral fitted is dependent on the aircraft design application.

History

Since the dawn of powered flight, the reciprocating piston engine in its different forms (rotary and static radial, aircooled and liquid-cooled inline) had been the only type of powerplant available to aircraft designers. This was understandable so long as low aircraft performance parameters were considered acceptable, and indeed inevitable. However, by approximately the late 1930s, engineers were beginning to realize that conceptually the piston engine was self-limiting in terms of the maximum performance which could be obtained from it; the limit was essentially one of propeller efficiency, which seemed to peak as blade tips approached supersonic radial velocity. If engine, and thus aircraft, performance was ever to increase beyond such a barrier, a way would have to be found to radically improve the design of the piston engine, or a wholly new type of powerplant would have to be conceived. The latter would prove to be the case. The gas turbine (turbojet, or simply jet) engine, as subsequently developed, would become almost as revolutionary to aviation as the Wright brothers' first flight. Components of a typical, four stroke cycle, DOHC piston engine. ... A propeller can be seen as a rotating fin in water or a wing in air. ... First flight, December 17, 1903. ...

The gas turbine was not an idea developed in the 1930s, the patent for a stationary turbine was granted to John Barber in England in 1791. The earliest attempts at jet engines were hybrid designs in which an external power source supplied the compression. In this system (called a thermojet by Secondo Campini) the air is first compressed by a fan driven by a conventional piston engine, then it is mixed with fuel and burned for jet thrust. Three known examples of this type of design were the Henri Coanda's Coanda-1910 aircraft, the much later Campini Caproni CC.2, and the Japanese Tsu-11 engine intended to power Ohka kamikaze planes towards the end of World War II. None were entirely successful and the CC.2 ended up being slower than the same design with a traditional engine and propeller combination. The worlds first commercial, oil-free gas turbine is manufactured by Capstone. ... A thermojet is a rudimentary type of jet engine. ... Secondo Campini (born August 28, 1904 in Bologna, died February 7, 1980 in Milan) was an Italian engineer and one of the pioneers of the jet engine. ... Henri Marie Coandă (June 7, 1886 - November 25, 1972) was a Romanian inventor, aerodynamics pioneer and the parent of the modern jet aircraft. ... The Coanda-1910 was an aircraft built by Romanian inventor Henri Coanda and exhibited by him at the Second International Aeronautical Exhibition in Paris around October 1910. ... A Italian Air Force Campini Caproni CC.2 in flight The Campini Caproni CC.2 (sometimes referred to as the N-1) was an early thermojet_powered aeroplane. ... The Tsu-11 was a primitive, thermojet-style jet engine produced in small numbers in Japan in the closing stages of World War II. It was principally designed to propel the Japanese Ohka flying bomb, a kamikaze weapon. ... The Yokosuka MXY-7 Ohka (桜花 cherry blossom) was a purpose-built kamikaze aircraft employed by Japan towards the end of World War II. The US gave the aircraft the Japanese name Baka (fool). It was a small flying bomb that was carried underneath a Mitsubishi G4M Betty bomber to... A kamikaze, a Mitsubishi Zero in this case, about to hit the USS Missouri. ... Mushroom cloud from the nuclear explosion over Nagasaki rising 18 km into the air. ...

Jet engine airflow simulation

The key to the useful jet engine was the gas turbine, used to extract energy to drive the compressor from the engine itself. The first gas turbine to successfully run self-sustaining was built in 1903 by Norwegian engineer Aegidius Elling. The first patents for jet propulsion were issued in 1917. Limitations in design and practical engineering and metallurgy prevented such engines reaching manufacture. The main problems were safety, reliability, weight and, especially, sustained operation. Jet Engine simulation from http://www. ... Jet Engine simulation from http://www. ... A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume. ...

On January 16, 1930 in England Frank Whittle submitted patents for his own design for a full-scale aircraft engine (granted in 1932). In 1935 Hans von Ohain started work on a similar design in Germany, seemingly unaware of Whittle's work. January 16 is the 16th day of the year in the Gregorian Calendar. ... 1930 is a common year starting on Wednesday. ... Royal motto: Dieu et mon droit (French: God and my right) Englands location within the UK Official language English de facto Capital London de facto Largest city London Area  - Total Ranked 1st UK 130,395 km² Population  - Total (2001)  - Density Ranked 1st UK 49,138,831 377/km² Religion... Sir Frank Whittle (June 1, 1907 - August 9, 1996) was a Royal Air Force officer who invented the jet engine in England while Hans von Ohain was inventing the same in Germany. ... Hans Joachim Pabst von Ohain (December 14, 1911-March 13, 1998) was one of the inventors of jet propulsion, along with Frank Whittle. ...

Ohain approached Ernst Heinkel, one of the larger aircraft industrialists of the day, who immediately saw the promise of the design. Heinkel had recently purchased the Hirth engine company, and Ohain and his master machinist Max Hahn were set up there as a new division of the Hirth company. They had their first HeS 1 engine running by September 1937. Unlike Whittle's design, Ohain used hydrogen as fuel, which he credits for the early success. Their subsequent designs culminated in the gasoline fuelled HeS 3 of 1,100 lbf (5 kN), which was fitted to Heinkel's simple and compact He 178 airframe and flown by Erich Warsitz in the early morning of August 27, 1939 from Marienehe aerodrome, an impressively short time for development. The He 178 was the world's first jetplane. Ernst Heinkel (January 24, 1888 - January 30, 1958) was a German aircraft designer and manufacturer. ... General Name, Symbol, Number Hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1 (IA), 1 , s Density, Hardness 0. ... The Heinkel He 178 was the worlds first aircraft to fly under turbojet power, and the first practical jet plane. ... Erich Warsitz († 12. ...

In England, Whittle had significant problems in finding funding for research, and the Air Ministry largely ignored it while they concentrated on more pressing issues. Using private funds he was able to get a test engine running in 1937, but this was very large and unsuitable for use in an aircraft. By 1939 work had progressed to the point where the engine was starting to look useful, and Whittle's Power Jets Ltd. started receiving Air Ministry money. In 1941 a flyable version of the engine called the W.1, capable of 1000 lbf (4 kN) of thrust, was fitted to the Gloster E28/39 airframe, and flew in May 1941. The Air Ministry was formerly a department of the United Kingdom Government, established in 1918 with the responsibility of managing the affairs of the (then newly formed) Royal Air Force. ... The Gloster E.28/39, (also referred to as the Gloster Whittle, Gloster Pioneer, or Gloster G.40) was the first jet engined aircraft to fly in the United Kingdom. ... Airframe is a novel by renowned author Michael Crichton first published in hardback edition in 1996 and as a paperback edition in 1997. ...

One problem with both of these early designs, which are called centrifugal-flow engines, was that the compressor works by "throwing" (accelerating) air outward from the central intake to the outer periphery of the engine where the air is then compressed by a divergent duct setup—converting velocity into pressure. The advantage was that such compressor designs were well understood in centrifugal superchargers but this leads to a very large cross section for the engine at rotational speeds that were usable at the time. A disadvantage was that the air flow had to be "bent" to flow rearwards through the combustion section and to the turbine and tailpipe. With improvements to bearings the shaft speed of the engine would increase and the diameter of the centrifugal compressor would reduce greatly. The shortness of this engine is an advantage. The strength of this type of compressor is an advantage over the later axial flow compressors that are still liable to foreign object damage (FOD in aviation parlance).

German Anselm Franz of Junkers' engine division (Junkers Motoren or Jumo) addressed this problem with the introduction of the axial-flow compressor. Essentially, this is a turbine in reverse. Air coming in the front of the engine is blown to the rear of the engine by a fan stage (convergent ducts), where it is crushed against a set of non-rotating blades called stators (divergent ducts). The process is nowhere near as powerful as the centrifugal compressor, so a number of these pairs of fans and stators are placed in series to get the needed compression. Even with all the added complexity, the resulting engine is much smaller in diameter. Jumo was assigned the next engine number, 4, and the result was the Jumo 004 engine. After many teething troubles, mass production of this engine started in 1944 as a powerplant for the world's first jet-fighter aircraft, the Messerschmitt Me 262. Because Hitler wanted a new bomber the Me 262 came too late to decisively impact Germany's position in World War II but it will be remembered as the first use of jet engines in service. After the end of the war the German Me 262 aircraft were extensively studied by the victorious allies and contributed to work on early Soviet and US jet fighters. Anselm Franz (1900-1994) was a pioneering jet engine engineer, known for the development of the Jumo 004 turbojet in Germany during World War II, and his work on turboshaft designs in the US after the war. ... For the Prussian/German landowning classes, see junker. The name Junkers is well known in connection with aircraft, which were produced under this name for the Luftwaffe during World War II. They were instrumental in many campaigns such as bombing Guernica and airborne landings on Crete with Ju 52, or... 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). ... The stator is the fixed part of a rotating machine. ... The Jumo 004 was the worlds first turbojet engine in production and operational use. ... The Messerschmitt Me 262 Schwalbe (Swallow) was the first operational jet powered aircraft. ... Mushroom cloud from the nuclear explosion over Nagasaki rising 18 km into the air. ...

British engines also were licensed widely in the US. Their most famous design, the Nene would also power the USSR's jet aircraft after a technology exchange. American designs wouldn't come fully into their own until the 1960s. The Rolls-Royce Nene was one of the earliest mass-produced jet engines, designed in 1944. ... Events and trends The 1960s was a turbulent decade of change around the world. ...

Types

There are a number of types of jet engines, all of which are based on the principle that air is compressed and used as an oxidizer for the fuel. Some examples are as follows:

CFM56-3 turbofan, lower half, side view. ... For the fictional method of interstellar travel, see Bussard ramjet. ... A Turboprop or turboshaft engine is a type of gas turbine. ... Turboshaft engines are a type of jet engine, differing from the similar turboprop largely in name and use -- turboshaft engines are used in helicopters, the name referring to the way the torque of the engine drives the power shaft at 90 degrees to the engine mounting. ... General Electric GE-36 unducted fan engine on a McDonnell Douglas MD-81 testbed An unducted fan, (abbreviated as UDF), or propfan, is a modified turbofan engine with the fan placed outside of the engine nacelle on the same axis as the compressor blades. ... A pulse jet engine is a very simple form of internal combustion engine wherein the combustion occurs in pulses and the propulsive effort is a reaction to the rearward flow of hot gasses. ... A pulse detonation engine, or PDE, is a type of aircraft engine that is designed primarily to be used in high-speed, high-altitude regimes. ... Deflagration is a process of subsonic combustion that usually propagates through thermoconductivity (hot burning material heats next layer of cold material and ignites it). ... Air-augmented rockets (also known as rocket-ejector, integral rocket ramjet, ramrocket, ducted rocket or ejector ramjets) use air collected during flight to use as additional working mass, leading to greater effective thrust for any given amount of fuel. ... A scramjet (supersonic combustion ramjet) is a variation of a ramjet where combustion of the fuel air mixture occurs at supersonic speeds. ... Mach number (Ma) is defined as a ratio of speed to the speed of sound in the medium in case. ... A turborocket is a type of aircraft engine combining elements of a jet engine and a rocket. ... The most fundamental reactions in chemistry are the redox processes. ... General Name, Symbol, Number Oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16 (VIA), 2, p Density, Hardness 1. ... Lox can stand for any of several things: Lox (salmon) - a type of salmon produce LOx (oxidizer) - liquid oxygen used as oxidizer in aerospace The Lox - was a Yonkers, NY-based rap trio This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the...

Turbojet

Whittle's and von Ohain's designs are classified as turbojets, the simplest kind of jet engine. In a turbojet all of the air passing through the engine goes through the combustion chambers. Generally turbojets are arranged around a central shaft, running the length of the engine, with the compressor and turbine connected to the shaft at opposite ends. In the middle of the engine is a combustion area, typically in the form of a number of individual "flame tubes" or "cans". The combustion area is either annular or can-annular in large modern engines with annular predominating. Simple turbojet engine airflow diagram, showing stages of intake, compression, combustion, and exhaust gas turbine operation. ... A combustion chamber is part of an engine in which fuel is burned. ... Compressor has several meanings: A gas compressor is a mechanical device that takes in a gas and increases its pressure by squeezing a volume of it into a smaller volume. ... WWII era ship propulsion turbine A turbine is a rotary engine that extracts energy from a fluid flow. ...

The compressor adds energy to the air flow, at the same time squeezing it into a smaller space (increasing its pressure), slowing it down, and increasing its temperature. Early jet engines had compression ratios as low as 5:1 (as do a lot of simple APUs and small propulsion turbines today); modern jet engines have compression ratios as high as 44:1, when operating at very high altitudes. These compression ratios are not comparable to those in a piston engine because the combustion process is continuous, as explained below. Higher compression ratios imply larger temperature rises; modern engines only achieve their high compression ratios at high altitude with very cold intake air (around –54 °C). When taking off in warmer air they run at lower compression ratios to keep the temperature of the compressed air within turbine temperature limits by bleeding air away from the compressor stages and dumping it overboard. As a result the engines are much less efficient when running at low altitudes. An Auxiliary Power Unit (APU) is a relatively small self-contained generator used in aircraft to start the main engines, usually with compressed air, and to provide electrical power while the aircraft is on the ground. ... Components of a typical, four stroke cycle, DOHC piston engine. ...

The burning process in the cans is significantly different from that in a piston engine. In the piston engine the burning gases are confined to a small volume and, as the fuel burns, the pressure increases dramatically. In a turbojet the air and fuel mixture passes, unconfined, through a can. As the mixture burns its volume increases dramatically and the pressure actually decreases (in the convergent duct) as the gases accelerate towards the rear of the engine.

In detail, the fuel-air mixture must be bought almost to a stop so that a stable flame can be maintained, this occurs just after the beginning of the combustion chamber. The aft part of this flame-front is allowed to progress rearward in the engine, this ensures that the rest of the fuel is burned as the flame becomes hotter when it leans out and, because of the shape of the combustion chamber the flow is accelerated rearwards. At the same time some pressure drop is unavoidable as it is the reason why the expanding gases travel out the rear of the engine rather than out the front. Less than 25% of the air is involved in combustion, in some engines as little as 12%, the rest acting as a reservoir to soak up the heating effect of the fuel burning.

Another difference between four-cycle engines and jet engines is that the peak flame temperature in a four-cycle engine is experienced only momentarily, and for a small portion of the entire cycle. The can in a jet engine is exposed to the peak flame temperature continuously, and operates at a pressure high enough that a stoichiometric fuel-air ratio would melt the can and everything downstream. Instead, jet engines run a very lean mixture, so lean that it would not normally support combustion. A central core of the flow is mixed with enough fuel to burn readily. The cans are carefully shaped to maintain a layer of fresh unburned air between the metal surfaces and the central core. This unburned air mixes into the burned gases to bring the temperature down to something the turbine can tolerate. In chemistry, stoichiometry is the study of the combination of elements in chemical reactions. ...

After the cans the gases are allowed to expand through the turbine. In the first stage the turbine is largely a reaction turbine (similar to a pelton wheel) and rotates because of the impact of the hot gas stream, later stages are convergent ducts that accelerate the gas rearward and gain energy from that process. Pressure drops and energy is transferred into the shaft. The turbine's rotational energy is used to drive the compressor to compress the intake air and some shaft power is extracted to drive accessories like fuel, oil and hydraulic pumps. The pressure drop through the turbine is much lower than the pressure rise through the compressor because the flow volume in the turbine is so much higher (because of the added fuel), which in turn is due to the higher temperature. In a turbojet almost two-thirds of all the power generated by burning fuel is used by the compressor to compress the air for the engine. Pelton wheel from Walchensee, Germany hydro power station A pelton wheel is one of the most efficient types of water wheel. ...

The efficiency of a jet engine is strongly dependent on the pressure drop through the turbine and nozzle. To achieve the largest possible drop, the engine operates at the highest possible compression ratio. Higher compression ratios imply higher compressor outlet temperatures and thus higher flame temperatures. The tolerable temperature limit is set by the turbine blades— usually the first stage. Modern turbine blades are single metal crystals with hollow interiors. Cooler air from the compressor is blown through the hollow interior of the blades. In a modern engine the turbine inlet temperature will typically be around 1700 °C, higher than the melting temperature of the blade material (around 1600 °C). Still higher temperature operation will require not only better materials but also some means of eliminating the oxides of nitrogen that form at such high combustion temperatures.

After the turbine, the gases are allowed to expand and accelerate further through the exhaust nozzle. In some turbojets the gases may actually transition to supersonic flow in the nozzle, in which case the nozzle will be a converging-diverging nozzle. A subsonic nozzle converges all the way to the end. Some supersonic military jets have variable nozzles that can change from subsonic to supersonic flow in different flight regimes.

Early German engines had serious problems controlling the turbine inlet temperature. Their early engines averaged only 10 hours of operation before failing—often with chunks of metal flying out the back of the engine when the turbine overheated. British engines tended to fare much better due to better metals. The Americans had the best materials because of their reliance on turbosupercharging in high altitude bombers of World War II. For a time some US jet engines included the ability to inject water into the engine to cool the compressed flow before combustion, usually during takeoff. The water would tend to prevent complete combustion and as a result the engine ran cooler again but the planes would take off leaving a huge plume of smoke. Mushroom cloud from the nuclear explosion over Nagasaki rising 18 km into the air. ...

Today these problems are much better handled but temperature still limits airspeeds in supersonic flight. At the very highest speeds the compression of the intake air raises the temperature to the point that the compressor blades will melt. At lower speeds better materials have increased the critical temperature and automatic fuel management controls have made it nearly impossible to overheat the engine.

Turbojets do not throttle efficiently. To operate well at all the compressor blades must turn at not less than 50 to 70% of the design maximum. At low throttle settings a great deal of power is wasted compressing a large fraction of the full-throttle airflow, only to expand it back again with relatively little temperature gain from the combustion chamber. Poor efficiency at low throttle settings helps to explain why turbines aren't used in cars—the engine would be burning a huge quantity of fuel even while sitting at a red light. In aircraft every bit of efficiency in running the compressor is needed. One common design technique is to use more than one turbine to drive the compressor stages at various speeds. Most such designs that use two stages are known as "two spool" engines. A few have used three stages with demonstrated efficiency gains. An airliner consuming 20 tons of fuel to fly from the east coast of the US to the west coast will gain much from a fractional increment in efficiency gain. An airliner on an 11 hour trip across the Pacific Ocean could reach Australia rather than New Zealand on a very small efficiency gain.

Turbofan

Main article: Turbofan CFM56-3 turbofan, lower half, side view. ...

If the propeller is better at low speeds, and the turbojet is better at 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). Turbofans essentially increase the size of the first-stage compressor to the point where they act as a ducted propeller (or fan) blowing air past the "core" of the engine. 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 propeller can be seen as a rotating fin in water or a wing in air. ...

Boeing 747 jet engine up close

This type of engine runs best from about 250 to 650 mph (400 to 1,000 km/h), which is why the turbofan is by far the most common type of engine in aviation. Image:Jet engine intake. ... Image:Jet engine intake. ...

The bypass ratio (the ratio of bypassed air mass to combustor air mass) is an important parameter for turbofans. Early turbofans (and most modern jet fighter engines) are low-bypass turbofans with bypass ratios less than 1. However, the "large mouthed" engines on almost all modern civilian jet aircraft are high-bypass turbofan engines which generally have bypass ratios of 3 or more. 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. ... 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. ... A high-bypass turbofan engine is a turbofan with a bypass ratio of at least 5. ...

Turbofans (especially high bypass engines) are fairly quiet. Noise from an aircraft jet engine comes from a number of sources, principally the fan blades and the jet efflux. The noise of a jet engine is strongly related to the speed of the air coming out the back: it varies with the eighth power of jet velocity. The final turbine of a turbofan extracts energy and thus velocity from the hot, fast, core air, and the bypass fan pumps that energy into a much larger mass of bypass air, so the result is a lower average velocity. Jet aircraft are often considered loud, but a conventional piston engine delivering the same power would be much louder.

Components

The components of a jet engine are standard across the different types of engines (noted above). The parts include:

• Air Induction
  For subsonic aircraft, the air intake to a jet engine presents no special difficulties, and consists essentially of an opening which is designed to minimise drag, as with any other aircraft component. However, the air reaching the compressor of a normal (not scramjet) jet engine must be travelling below the speed of sound, even for supersonic craft.
• Compressor Fan
  The compressor is the series of fans that are spaced very closely together. Each fan compresses the air a little more. Energy is derived from the exhaust fan (see below), passed along the shaft.
• Shaft
  This carries power from the exhaust fan to the compressor, and runs most of the length of the engine. There may be as many as three concentric shafts, rotating at independent speeds, with as many sets of exhaust fans and compressors. Other services, like a bleed of cool air, may also run down the shaft.
• Flame Cans or Flameholders or combustion chambers
  These are combustion chambers where fuel is continuously burned in the compressed air.
• Turbine fans or Exhaust fans
  These gather energy from the hot expanding air rushing out of the engine. This energy is used to drive the compressor through the shaft, or bypass fans, or props, or even (for a gas turbine-powered helicopter) converted entirely to rotational energy for use elsewhere.
• Afterburner (optional)
  (mainly military) Produces extra thrust by burning extra fuel, usually inefficiently, at the exhaust.
• Exhaust
  Air, once cooled and expanded, is vented out the back of the engine. Exhausts are designed to maximize thrust, since venting hot air does not provide nearly as much thrust as venting fast-moving cool air.
• Supersonic Nozzle
  The standard aerodynamic reference frame is attached to the aeroplane. Air must travel through the engine at subsonic speeds, to sustain operation of flow mechanics at the blades of the compressors and turbines. The supersonic nozzle is needed to convert the pressure and heat to velocity, and consequently momentum of the expelled air. A de Laval nozzle tapers down to a neck, accelerating the gas up to sonic speed, and then the nozzle opens out again. The hot gas thus expands and cools whilst pressing on the inside of the nozzle at a rearward facing angle. This accelerates the air even further; forming a powerful supersonic exhaust jet. The reaction on the inside of the nozzle multiplies the thrust up and accelerates the vehicle.

A flame holder is a component of a jet engine designed to help keep continual combustion going. ... The worlds first commercial, oil-free gas turbine is manufactured by Capstone. ... For other uses of afterburner, see Afterburner (disambiguation). ... A frame of reference in physics is a set of axes which enable an observer to measure the aspect, position and motion of all points in a system relative to the reference frame. ... A de Laval nozzle (or convergent-divergent nozzle, CD nozzle or con-di nozzle ) is a tube that is pinched in the middle, making an hourglass-shape. ...

Design considerations

The various components named above have constraints on how they are put together to generate the most efficiency or performance. Important here is air intake design, overall size, number of compressor stages (sets of blades), fuel type, number of exhaust stages, metallurgy of components, amount of bypass air used, where the bypass air is introduced, and many other factors. For instance, let's consider design of the air intake.

Air intake design

For aircraft travelling at supersonic speeds, a design complexity arises, since the air ingested by the engine must be below supersonic speed, otherwise the engine will "choke" and cease working. This subsonic air speed is achieved by passing the approaching air through a deliberately-generated shock wave (since one characteristic of a shock wave is that the air flowing through it is slowed). Therefore some means is needed to create a shockwave ahead of the intake. Any speed over the speed of sound, which is approximately 343 m/s or 761 mph or 1,225 km/h at sea level, is said to be supersonic. ...

The earliest types of supersonic aircraft featured a central shock cone, called an inlet cone, which was used to form the shock wave. This type of shock cone is clearly seen on the English Electric Lightning and MiG-21 aircraft, for example. The same approach can be used for air intakes mounted at the side of the fuselage, where a half cone serves the same purpose with a semicircular air intake, as seen on the F-104 Starfighter and BAC TSR-2. A more sophisticated approach is to angle the intake so that one of its edges forms a leading blade. A shockwave will form at this blade, and the air ingested by the engine will be behind the shockwave and hence subsonic. The Century series of US jets featured a number of variations on this approach, usually with the leading blade at the outer vertical edge of the intake which was then angled back inwards towards the fuselage. Typical examples include the Republic F-105 Thunderchief and F-4 Phantom. Later this evolved so that the leading edge was at the top horizontal edge rather than the outer vertical edge, with a pronounced angle downwards and rearwards. This approach simplified the construction of the intakes and permitted the use of variable ramps to control the airflow into the engine. Most designs since the early 1960s now feature this style of intake, for example the F-14 Tomcat, Panavia Tornado and Concorde. Introduction Inlet cones (sometimes called shock cones) are a component of some supersonic aircraft. ... The English Electric Lightning is a supersonic British fighter aircraft of the Cold War era, particularly remembered for its natural metal exterior that was used throughout much of its service life with the Royal Air Force and the Royal Saudi Air Force. ... Mikoyan-Gurevich MiG-21 (NATO reporting name Fishbed) is a fighter aircraft, originally built by the Mikoyan and Gurevich Design Bureau in the Soviet Union. ... The Lockheed F-104 Starfighter was the last of the day fighters, a high-performance supersonic interceptor aircraft capable of high speeds and climb rates. ... The British Aircraft Corporations TSR-2 was an ill-fated cold war project in the early 1960s to create what would, at that time, have been one of the most advanced aircraft in the world, with supercruise ability, and similar thrust and Mach 2+ performance to the Rockwell B... The Century series aircraft were a series of early US supersonic jet fighters built for the United States Air Force during the 1950s and early 1960s. ... The Republic F-105 Thunderchief was a single-seat, supersonic fighter-bomber used by the United States Air Force. ... The F-4 Phantom II (simply F-4 Phantom after 1990) is a two-place (tandem), supersonic, long-range, all-weather fighter-bomber built by McDonnell Douglas Corporation. ... Events and trends The 1960s was a turbulent decade of change around the world. ... Sailors prepare an F-14 Tomcat for flight on the aircraft carrier USS Abraham Lincoln, in support of Operation Iraqi Freedom (2003). ... IDS: RSAF Tornado IDS ADV: RAF Tornado F3 ECR: Luftwaffe Tornado ECR 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. ... The Aérospatiale-BAC Concorde supersonic transport (SST) was one of only two models of supersonic passenger airliners to have seen commercial service. ...

In one unusual instance (the SR-71), a variable air intake design was used to convert the engine from a turbojet to a ramjet, in flight. To get good efficiency over a wide range of speeds the Pratt & Whitney J58 could move a conical spike fore and aft within the engine nacelle, to keep the supersonic shock wave just in front of the inlet. In this manner, the airflow behind the shock wave, and more importantly, through the engine, was kept subsonic at all times. Additionally, and unusually for this engine, at high mach, the compressor for the J58 was unable to carry the high air flow entering the inlet without stalling its blades, and so the engine directed the excess air through 6 bypass pipes straight to the afterburner. At high speeds the engine actually obtained 80% of its thrust, versus 20% through the turbines itself, in this way. Essentially this allowed the engine to operate as a ramjet, and actually improving specific impulse (fuel efficiency) by 10-15%. The Lockheed SR-71, unofficially known as the Blackbird, is a long-range, advanced, strategic reconnaissance aircraft developed from the Lockheed A-12 and YF-12A aircraft by Lockheeds Skunk works, which was also responsible for the U-2 and many other advanced aircraft. ... Categories: Stub | Turbojet engines | Ramjet engines ... A cone is a basic geometrical shape: see cone (geometry). ... The specific impulse (commonly abbreviated Isp) of a propulsion system is the impulse (change in momentum) per unit weight/mass of propellant. ...

Finally, there is strong theoretical and experimental support for the idea that using a heat-exchanger to cool the air at the intake can increase the density of the air and thus reduce the necessary compression. This would create lower temperatures that permits lighter construction alloys to be used, reducing the engine's weight by several times. This leads to plausible designs like SABRE that might permit jet engined vehicles to be used to launch straight into space. For other uses, see Sabre (disambiguation). ...

See also

• Jetboat
• Spacecraft propulsion
• Supercharger
• Turbocharger

A jetboat is a boat propelled by a jet of water ejected from the back of the craft. ... A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi Spacecraft propulsion is used to change the velocity of spacecraft and artificial satellites, or in short, to provide delta-v. ... For other meanings, see supercharger (disambiguation) A supercharger (sometimes called a blower), a positive displacement or centrifugal pump, is a gas compressor used to pump air into the cylinders of an internal combustion engine. ... Turbocharger Cut-away A turbocharger is a device used in internal-combustion engines to increase the power output of the engine by increasing the mass of oxygen and fuel entering the engine. ...

External link

• Gas Turbine Builders' Resources (http://www.gtbuilder.com)
• Journey through a jet engine(flash) (http://www.rolls-royce.com/education/schools/journey02/flash.html)
• How Stuff Works article on how a Gas Turbine Engine works (http://travel.howstuffworks.com/turbine.htm)
• Influence of the Jet Engine on the Aerospace Industry (http://www.generalatomic.com/jetmakers/chapter15.html)