Airliner
An airliner is a type of aircraft for transporting passengers and air cargo. Such aircraft are most operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is defined as an aeroplane intended for carrying multiple passengers or cargo in commercial service; the largest of them are wide-body jets which are called twin-aisle because they have two separate aisles running from the front to the back of the passenger cabin. These are used for long-haul flights between airline hubs and major cities. A smaller, more common class of airliners is the single-aisle; these are used for short to medium-distance flights with fewer passengers than their wide-body counterparts. Regional airliners seat fewer than 100 passengers and may be powered by turbofans or turboprops; these airliners are the non-mainline counterparts to the larger aircraft operated by the major carriers, legacy carriers, flag carriers, are used to feed traffic into the large airline hubs. These regional routes form the spokes of a hub-and-spoke air transport model.
The lightest of short-haul regional feeder airliner type aircraft that carry a small number of passengers are called commuter aircraft, commuterliners and air taxis, depending on their size, how they are marketed, region of the world, seating configurations. The Beechcraft 1900, for example, has only 19 seats; when the Wright brothers made the world’s first sustained heavier-than-air flight, they laid the foundation for what would become a major transport industry. Their flight in 1903 was just 11 years before what is defined as the world’s first airliner; these airliners have had a significant impact on global society and politics. In 1913, Igor Sikorsky developed the first large multi-engine airplane, the Russky Vityaz, refined into the more practical Ilya Muromets with dual controls for a pilot plus copilot and a comfortable cabin with a lavatory, cabin heating and lighting; the large four-engine biplane was derived in a bomber aircraft, preceding subsequent transport and bomber aircraft.
Due to the onset of World War I, it was never used as a commercial airliner. It first flew on December 10, 1913 and took off for its first demonstration flight with 16 passengers aboard on February 25, 1914. In 1915, the first airliner was used by Elliot Air Service; the aircraft was a Curtiss JN 4, a small biplane, used in World War I as a trainer. It was used as a tour and familiarization flight aircraft in the early 1920s. In 1919, after World War I, the Farman F.60 Goliath designed as a long-range heavy bomber, was converted for commercial use into a passenger airliner. It could seat 14 passengers from 1919, around 60 were built. Several publicity flights were made, including one on 8 February 1919, when the Goliath flew 12 passengers from Toussus-le-Noble to RAF Kenley, near Croydon, despite having no permission from the British authorities to land. Another important airliner built in 1919 was the Airco DH.16. In March 1919, the prototype first flew at Hendon Aerodrome. Nine aircraft were built, all but one being delivered to the nascent airline, Aircraft Transport and Travel, which used the first aircraft for pleasure flying, on 25 August 1919, it inaugurated the first scheduled international airline service from London to Paris.
One aircraft was sold to the River Plate Aviation Company in Argentina, to operate a cross-river service between Buenos Aires and Montevideo. Meanwhile, the competing Vickers converted its successful WWI bomber, the Vickers Vimy, into a civilian version, the Vimy Commercial, it was redesigned with a larger-diameter fuselage, first flew from the Joyce Green airfield in Kent on 13 April 1919. The world's first all-metal transport aircraft was the Junkers F.13 from 1919, with 322 built. The Dutch Fokker company produced the Fokker F. II and the F. III; these aircraft were used by the Dutch airline KLM when it reopened an Amsterdam-London service in 1921. The Fokkers were soon flying to destinations across Europe, including Bremen, Brussels and Paris, they proved to be reliable aircraft. The Handley Page company in Britain produced the Handley Page Type W as the company's first civil transport aircraft, it housed two crew in 15 passengers in an enclosed cabin. Powered by two 450 hp Napier Lion engines, the prototype first flew on 4 December 1919, shortly after it was displayed at the 1919 Paris Air Show at Le Bourget.
It was the world's first airliner to be designed with an on-board lavatory. Meanwhile in France, the Bleriot-SPAD S.33 was a great success throughout the 1920s serving the Paris-London route, on continental routes. The enclosed cabin could carry four passengers with an extra seat in the cockpit. By 1921, aircraft capacity needed to be larger for the economics to remain favourable; the English company de Havilland, therefore built the 10-passenger DH.29 monoplane, while starting work on the design of the DH.32, an eight-seater biplane with a less powerful but more economical Rolls-Royce Eagle engine. Owing to the urgent need for more capacity, work on the DH.32 was stopped and the DH.34 biplane was designed, accommodating 10 passengers. The Fokker trimotor was an important and popular transport, manufactured under license in Europe and America. Throughout the 1920s, companies in Britain and France were at the forefront of the civil airliner industry considerably aided by governme
Grumman F-14 Tomcat
The Grumman F-14 Tomcat is an American supersonic, twin-engine, two-seat, twin-tail, variable-sweep wing fighter aircraft. It was the first such U. S. jet fighter with twin tails. The Tomcat was developed for the United States Navy's Naval Fighter Experimental program after the collapse of the F-111B project; the F-14 was the first of the American Teen Series fighters, which were designed incorporating air combat experience against MiG fighters during the Vietnam War. The F-14 first flew on 21 December 1970 and made its first deployment in 1974 with the U. S. Navy aboard USS Enterprise, replacing the McDonnell Douglas F-4 Phantom II; the F-14 served as the U. S. Navy's primary maritime air superiority fighter, fleet defense interceptor, tactical aerial reconnaissance platform into the 2000s; the Low Altitude Navigation and Targeting Infrared for Night pod system were added in the 1990s and the Tomcat began performing precision ground-attack missions. In the 1980s, F-14s were used as land-based interceptors by the Islamic Republic of Iran Air Force during the Iran–Iraq War, where they saw combat against Iraqi warplanes.
Iranian F-14s shot down at least 160 Iraqi aircraft during the war, while only 12 to 16 Tomcats were lost. The Tomcat was retired from the U. S. Navy's active fleet on 22 September 2006, having been supplanted by the Boeing F/A-18E/F Super Hornet; the F-14 remains in service with Iran's air force, having been exported to Iran in 1976. In November 2015, reports emerged of Iranian F-14s flying escort for Russian Tu-95 bombers on air strikes in Syria. Beginning in the late 1950s, the U. S. Navy sought a long-range, high-endurance interceptor to defend its carrier battle groups against long-range anti-ship missiles launched from the jet bombers and submarines of the Soviet Union; the U. S. Navy needed a Fleet Air Defense aircraft with a more powerful radar and longer range missiles than the F-4 Phantom II carried to intercept both enemy bombers and missiles; the Navy was directed to participate in the Tactical Fighter Experimental program with the U. S. Air Force by Secretary of Defense Robert McNamara.
McNamara wanted "joint" solutions to service aircraft needs to reduce development costs, had directed the Air Force to buy the F-4 Phantom II, developed for the Navy and Marine Corps. The Navy strenuously opposed the TFX as it feared compromises necessary for the Air Force's need for a low-level attack aircraft would adversely impact the aircraft's performance as a fighter. Weight and performance issues plagued the U. S. Navy F-111B would not be resolved to the Navy's satisfaction; the F-111 manufacturer General Dynamics partnered with Grumman on the Navy F-111B. With the F-111B program in distress, Grumman began studying alternatives. In 1966, the Navy awarded Grumman a contract to begin studying advanced fighter designs. Grumman narrowed down these designs to its 303 design. Vice Admiral Thomas F. Connolly, Deputy Chief of Naval Operations for Air Warfare, flew the developmental F-111A variant on a flight and discovered that it had difficulty going supersonic and had poor carrier landing characteristics.
He testified before Congress about his concerns against the official U. S. Department of the Navy position and, in May 1968, Congress stopped funding for the F-111B, allowing the Navy to pursue an answer tailored to its requirements; the name "Tomcat" was chosen to pay tribute to Admiral Connolly, as the nickname "Tom's Cat" had been used by the manufacturer, although the name followed the Grumman tradition of naming its fighter aircraft after felines. The F-111B had been designed for the long-range Fleet Air Defense interceptor role, but not for new requirements for air combat based on the experience of American aircraft against agile MiG fighters over Vietnam; the Navy studied the need for VFAX, an additional fighter, more agile than the F-4 Phantom for air-combat and ground-attack roles. Grumman continued work on its 303 design and offered it to the Navy in 1967, which led to fighter studies by the Navy; the company continued to refine the design into 1968. In July 1968, the Naval Air Systems Command issued a request for proposals for the Naval Fighter Experimental program.
VFX called for a tandem two-seat, twin-engined air-to-air fighter with a maximum speed of Mach 2.2. It would have a built-in M61 Vulcan cannon and a secondary close air support role; the VFX's air-to-air missiles would be either six AIM-54 Phoenix or a combination of six AIM-7 Sparrow and four AIM-9 Sidewinder missiles. Bids were received from General Dynamics, Ling-Temco-Vought, McDonnell Douglas and North American Rockwell. McDonnell Douglas and Grumman were selected as finalists in December 1968. Grumman was selected for the contract award in January 1969. Grumman's design reused the TF30 engines from the F-111B, though the Navy planned on replacing them with the Pratt & Whitney F401-400 engines under development for the Navy, along with the related Pratt & Whitney F100 for the USAF. Though lighter than the F-111B, it was still the largest and heaviest U. S. fighter to fly from an aircraft carrier, a consequence of the requirement to carry the large AWG-9 radar and AIM-54 Phoenix missiles and an internal fuel load of 16,000 lb.
Upon winning the contract for the F-14, Grumman expanded its Calverton, Long Island, New York facility for evaluating the aircraft. Much of the testing, including the first of many compressor stalls and multiple ejections, took place over Long Island Sound. In order to save time and forestall interference from Secretary McNamara, the Navy skipped the
Steel
Steel is an alloy of iron and carbon, sometimes other elements. Because of its high tensile strength and low cost, it is a major component used in buildings, tools, automobiles, machines and weapons. Iron is the base metal of steel. Iron is able to take on two crystalline forms, body centered cubic and face centered cubic, depending on its temperature. In the body-centered cubic arrangement, there is an iron atom in the center and eight atoms at the vertices of each cubic unit cell, it is the interaction of the allotropes of iron with the alloying elements carbon, that gives steel and cast iron their range of unique properties. In pure iron, the crystal structure has little resistance to the iron atoms slipping past one another, so pure iron is quite ductile, or soft and formed. In steel, small amounts of carbon, other elements, inclusions within the iron act as hardening agents that prevent the movement of dislocations that are common in the crystal lattices of iron atoms; the carbon in typical steel alloys may contribute up to 2.14% of its weight.
Varying the amount of carbon and many other alloying elements, as well as controlling their chemical and physical makeup in the final steel, slows the movement of those dislocations that make pure iron ductile, thus controls and enhances its qualities. These qualities include such things as the hardness, quenching behavior, need for annealing, tempering behavior, yield strength, tensile strength of the resulting steel; the increase in steel's strength compared to pure iron is possible only by reducing iron's ductility. Steel was produced in bloomery furnaces for thousands of years, but its large-scale, industrial use began only after more efficient production methods were devised in the 17th century, with the production of blister steel and crucible steel. With the invention of the Bessemer process in the mid-19th century, a new era of mass-produced steel began; this was followed by the Siemens–Martin process and the Gilchrist–Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron.
Further refinements in the process, such as basic oxygen steelmaking replaced earlier methods by further lowering the cost of production and increasing the quality of the final product. Today, steel is one of the most common manmade materials in the world, with more than 1.6 billion tons produced annually. Modern steel is identified by various grades defined by assorted standards organizations; the noun steel originates from the Proto-Germanic adjective stahliją or stakhlijan, related to stahlaz or stahliją. The carbon content of steel is between 0.002% and 2.14% by weight for plain iron–carbon alloys. These values vary depending on alloying elements such as manganese, nickel, so on. Steel is an iron-carbon alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction. Too little carbon content leaves iron quite soft and weak. Carbon contents higher than those of steel make a brittle alloy called pig iron. While iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel.
Common alloying elements include: manganese, chromium, boron, vanadium, tungsten and niobium. Additional elements, most considered undesirable, are important in steel: phosphorus, sulfur and traces of oxygen and copper. Plain carbon-iron alloys with a higher than 2.1% carbon content are known as cast iron. With modern steelmaking techniques such as powder metal forming, it is possible to make high-carbon steels, but such are not common. Cast iron is not malleable when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties. Certain compositions of cast iron, while retaining the economies of melting and casting, can be heat treated after casting to make malleable iron or ductile iron objects. Steel is distinguishable from wrought iron, which may contain a small amount of carbon but large amounts of slag. Iron is found in the Earth's crust in the form of an ore an iron oxide, such as magnetite or hematite. Iron is extracted from iron ore by removing the oxygen through its combination with a preferred chemical partner such as carbon, lost to the atmosphere as carbon dioxide.
This process, known as smelting, was first applied to metals with lower melting points, such as tin, which melts at about 250 °C, copper, which melts at about 1,100 °C, the combination, which has a melting point lower than 1,083 °C. In comparison, cast iron melts at about 1,375 °C. Small quantities of iron were smelted in ancient times, in the solid state, by heating the ore in a charcoal fire and welding the clumps together with a hammer and in the process squeezing out the impurities. With care, the carbon content could be controlled by moving it around in the fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily. All of these temperatures could be reached with ancient methods used since the Bronze Age. Since the oxidation rate of iron increases beyond 800 °C, it is important that smelting take place in a low-oxygen environment. Smelting, using carbon to reduce iro
General Electric CJ805
The General Electric CJ805 is a jet engine, developed by GE Aviation in the late 1950s. It differed only in detail, it was developed in two versions. The basic CJ805-3 was a turbojet and powered the Convair 880, while CJ805-23, a turbofan derivative, powered the Convair 990 airliners. Turbojet engines consist of a compressor at the front, a burner area, a turbine that powers the compressor. In order to reach practical compression ratios, compressors consist of multiple "stages", each further compressing the intake air. In the case of an axial flow design, the stages resemble fan disks or pinwheels, situated behind each other along a common shaft. One common problem in early jet engine designs was the phenomenon of "surging" or compressor stall; this occurs at low speeds when the airflow through the engine is small, or "off-design", conditions. It may occur when the airflow is not directly onto the front of the engine; as the air reaches the higher compression stages of the compressor, instabilities can form that, in extreme cases, can damage the engine.
One common solution found on early engines was the use of "bleed air", openings near the middle of the compressor stages that feed the air around the high-pressure section and into the burner. These are closed. Another solution to this problem is the use of variable stators or inlet vanes. In these designs, the angle of incidence of the stators at the front of the engine can be changed, allowing the degree of compression to be adjusted. At low speeds, the vanes are angled to lower the compression; this has the advantage of being more efficient than a bleed system because the entire compressor is used across the entire power range, but the disadvantage is significant mechanical complexity as each stator blade has to be independently rotated to the desired angles. Rolls-Royce abandoned it, they began development of multi-spool designs, a concept, selected by Pratt & Whitney. The variable stator was only selected by GE after a long internal debate on the best way to design an engine that would operate at speeds low enough for easy landings on an aircraft carrier all the way to Mach 2.
The J79 emerged as a powerful, lightweight design, GE began considering it as the basis for a high-power engine for commercial use. In 1952, Chapman Walker's design team at GE built a one-off prototype of a jet engine designed for transatlantic airliners, it used a single-stage fan powered by the same turbine shaft as the main engine compressor, as opposed to the Pratt & Whitney designs that were using a separate power shaft to run the fan. The GE design was not developed further. In 1955 Jack Parker took over GE's Aircraft Gas Turbine division, he hired Dixon Speas to begin interviewing executives at airlines to try to get a sense of the future market. Parker asked Speas to interview not the CEO's, but executives that might be the CEO by the time GE was ready to enter the civilian jet engine market. Parker and Neil Burgess, who ran the J79 program, spent a month meeting with AA, United, KLM, Swissair and SAS; the meetings demonstrated that those airlines that were flying propeller aircraft across the Atlantic were all looking to replace them with jets.
Around the same time, Convair was canvassing US carriers and found demand for a smaller jet aircraft for medium-range domestic routes. They began development of what would become the 880, approached Burgess to see if GE could develop a version of the J79 for this role. Burgess responded by sketching a version of the J79 with the afterburner removed and replaced by a thrust reverser, giving them an estimated unit price of $125,000 per engine; the 880's primary sales feature over the competing Douglas DC-8 and Boeing 707 was a higher cruise speed. This demanded more engine power from a lighter design, which led to a design like the J79. To gain experience with the engine in a civil setting, GE equipped a Douglas RB-66 with the new engine and flew simulated civil aviation routes out of Edwards Air Force Base; as development progressed, the 707 began to enter service, noise complains became a serious issue. There was a lawsuit, by residents around Newark airport, concerning the noise from existing propeller-driven aircraft such as the Super Constellation, Stratocruiser and DC-7C.
One way to reduce this problem is to mix cold air into the jet exhaust, accomplished on early engines with the addition of scalloped nozzles. This solution was adopted for the CJ805. Several airlines asked Convair for a larger version of the 880 with potential transatlantic range; such a design would be larger to hold more seating, as well has having to carry more fuel. To power it, a more powerful engine would be needed. By this time, the Rolls-Royce Conway was entering service, the Pratt & Whitney JT3D was following close behind; these designs both had twin-spool compressors, as opposed to using variable stators, the lower speed of the front, low-pressure, spool make it easy to power a fan. The problems RR and P&W had addressed with the two-spool system had been solved on the J79 with the variable stators, so in relative terms, the single compressor rotational speed was much faster than the low-pressure stage of these other engines; this meant. Instead, GE solved this problem with the addition of a separate fan system at the rear of the engine, powered by a new turbine stage.
The system was a bolt-on extension to the existing design and had no effect on the operation of the or
Afterburner
An afterburner is a component present on some jet engines those used on military supersonic aircraft. Its purpose is to provide an increase in thrust for supersonic flight and combat situations. Afterburning is achieved by injecting additional fuel into the jet pipe downstream of the turbine. Afterburning increases thrust without the weight of an additional engine, but at the cost of high fuel consumption and decreased fuel efficiency, limiting its practical use to short bursts. Pilots can activate and deactivate afterburners in-flight, jet engines are referred to as operating wet when afterburning is being used and dry when not. An engine producing maximum thrust wet is at maximum power, while an engine producing maximum thrust dry is at military power. Jet-engine thrust is governed by the general principle of mass flow rate. Thrust depends on two things: the mass of that gas. A jet engine can produce more thrust by either accelerating the gas to a higher velocity or by having a greater mass of gas exit the engine.
Designing a basic turbojet engine around the second principle produces the turbofan engine, which creates slower gas but more of it. Turbofans are fuel efficient and can deliver high thrust for long periods, but the design trade-off is a large size relative to the power output. Generating increased power with a more compact engine for short periods can be achieved using an afterburner; the afterburner increases thrust by accelerating the exhaust gas to a higher velocity. The temperature of the gas in the engine is highest just before the turbine, the ability for the turbine to withstand these temperatures is one of the primary restrictions on total dry engine thrust; this temperature is known as the Turbine Entry Temperature, one of the critical engine operating parameters. Because a combustion rate high enough to consume all the intake oxygen would create temperatures high enough to overheat the turbine, the flow of fuel must be restricted to an extent that fuel rather than oxygen becomes the limiting factor in the reaction, leaving some oxygen to flow past the turbine.
After passing the turbine, the gas expands at a near constant entropy, thus losing temperature. The afterburner injects fuel downstream of the turbine and reheats the gas; as a result of the temperature rise in the tailpipe, the gas is ejected through the nozzle at a higher velocity. The mass flow is slightly increased by the addition of the fuel. Afterburners produce markedly enhanced thrust as well as a visible flame at the back of the engine; this exhaust flame may show shock diamonds, which are caused by shock waves formed due to slight differences between ambient pressure and the exhaust pressure. These imbalances cause oscillations in the exhaust jet diameter over a short distance and cause visible banding where the pressure and temperature is highest. A similar type of thrust augmentation but using additional fuel burnt in a turbofan's cold bypass air only, instead of the combined cold and hot gas flows as in a conventional afterburning engine, is Plenum chamber burning, developed for the vectored thrust Bristol Siddeley BS100 engine for the Hawker Siddeley P.1154.
In this engine, where the cold bypass and hot core turbine airflows are split between two sets of nozzles and rear, in the same manner as the Rolls-Royce Pegasus, additional fuel and afterburning was applied to the front cold air nozzles only. This technique was developed to give greater thrust for take-off and supersonic performance in an aircraft similar to, but of higher weight, than the Hawker Siddeley Harrier. A jet engine afterburner is an extended exhaust section containing extra fuel injectors. Since the jet engine upstream will use little of the oxygen it ingests, additional fuel can be burned after the gas flow has left the turbines; when the afterburner is turned on, fuel is injected and igniters are fired. The resulting combustion process increases the afterburner exit temperature resulting in a steep increase in engine net thrust. In addition to the increase in afterburner exit stagnation temperature, there is an increase in nozzle mass flow, but a decrease in afterburner exit stagnation pressure.
The resulting increase in afterburner exit volume flow is accommodated by increasing the throat area of the propulsion nozzle. Otherwise, the upstream turbomachinery rematches; the first designs, e.g. Solar afterburners used on the F7U Cutlass, F-94 Starfire and F-89 Scorpion, had 2-position eyelid nozzles. Modern designs incorporate not only VG nozzles but multiple stages of augmentation via separate spray bars. To a first order, the gross thrust ratio is directly proportional to the root of the stagnation temperature ratio across the afterburner. Due to their high fuel consumption, afterburners are used as little as possible, they are used only when it is important to have as much thrust as possible. This includes during takeoff from short runways, assisting catapult launches from aircraft carriers, during air combat situations. A notable exception is the Whitney J58 engine used in the SR-71 Blackbird. In heat engines such as jet engines, efficiency is best when combustion is done at the highest pressure and temperature possible, expanded down to ambient pressure.
Since the exhaust gas has reduced oxygen due to previous combustion, since the fuel is not burning in a com
Turbofan
The turbofan or fanjet is a type of airbreathing jet engine, used in aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the turbo portion refers to a gas turbine engine which achieves mechanical energy from combustion, the fan, a ducted fan that uses the mechanical energy from the gas turbine to accelerate air rearwards. Thus, whereas all the air taken in by a turbojet passes through the turbine, in a turbofan some of that air bypasses the turbine. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust; the ratio of the mass-flow of air bypassing the engine core divided by 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. Most commercial aviation jet engines in use today are of the high-bypass type, most modern military fighter engines are low-bypass. Afterburners are not used on high-bypass turbofan engines but may be used on either low-bypass turbofan or turbojet engines.
Modern turbofans have either a smaller fan with several stages. An early configuration combined a low-pressure fan in a single rear-mounted unit. Turbofans were invented to circumvent an awkward feature of turbojets, that they were inefficient for subsonic flight. To raise the efficiency of a turbojet, the obvious approach would be to increase the burner temperature, to give better Carnot efficiency and fit larger compressors and nozzles. However, while that does increase thrust somewhat, the exhaust jet leaves the engine with higher velocity, which at subsonic flight speeds, takes most of the extra energy with it, wasting fuel. Instead, a turbofan can be thought of as a turbojet being used to drive a ducted fan, with both of those contributing to the thrust. Whereas all the air taken in by a turbojet passes through the turbine, in a turbofan some of that air bypasses the turbine; because the turbine has to additionally drive the fan, the turbine is larger and has larger pressure and temperature drops, so the nozzles are smaller.
This means. The fan has lower exhaust velocity, giving much more thrust per unit energy; the overall effective exhaust velocity of the two exhaust jets can be made closer to a normal subsonic aircraft's flight speed. In effect, a turbofan emits a large amount of air more whereas a turbojet emits a smaller amount of air, a far less efficient way to generate the same thrust; 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. The engine produces thrust through a combination of these two portions working together. Most commercial aviation jet engines in use today are of the high-bypass type, most modern military fighter engines are low-bypass. Afterburners are not used on high-bypass turbofan engines but may be used on either low-bypass turbofan or turbojet engines; the bypass ratio of a turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core.
A 10:1 bypass ratio, for example, means that 10 kg of air passes through the bypass duct for every 1 kg of air passing through the core. Turbofan engines are 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 is quoted for turboprop and unducted fan installations because their high propulsive efficiency gives them the overall efficiency characteristics of high bypass turbofans; this allows them to be shown together with turbofans on plots which show trends of reducing specific fuel consumption with increasing BPS. BPR can be quoted for lift fan installations where the fan airflow is remote from the engine and doesn't physically touch the engine core. Bypass provides a lower fuel consumption for the same thrust. If all the gas power from a gas turbine is converted to kinetic energy in a propelling nozzle, the aircraft 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.
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 seen with propellers and helicopter rotors by comparing disc loading and power loading. For example, 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 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 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 and low bpr turbojets. Low bpr has bee
Axial compressor
An axial compressor is a gas compressor that can continuously pressurize gases. It is a rotating, airfoil-based compressor in which the gas or working fluid principally flows parallel to the axis of rotation, or axially; this differs from other rotating compressors such as centrifugal compressor, axi-centrifugal compressors and mixed-flow compressors where the fluid flow will include a "radial component" through the compressor. The energy level of the fluid increases as it flows through the compressor due to the action of the rotor blades which exert a torque on the fluid; the stationary blades slow the fluid, converting the circumferential component of flow into pressure. Compressors are driven by an electric motor or a steam or a gas turbine. Axial flow compressors produce a continuous flow of compressed gas, have the benefits of high efficiency and large mass flow rate in relation to their size and cross-section, they do, require several rows of airfoils to achieve a large pressure rise, making them complex and expensive relative to other designs.
Axial compressors are integral to the design of large gas turbines such as jet engines, high speed ship engines, small scale power stations. They are used in industrial applications such as large volume air separation plants, blast furnace air, fluid catalytic cracking air, propane dehydrogenation. Due to high performance, high reliability and flexible operation during the flight envelope, they are used in aerospace engines. Axial compressors consist of stationary components. A shaft drives a central drum, retained by bearings, which has a number of annular airfoil rows attached in pairs, one rotating and one stationary attached to a stationary tubular casing. A pair of rotating and stationary airfoils is called a stage; the rotating airfoils known as blades or rotors, accelerate the fluid. The stationary airfoils known as stators or vanes, convert the increased rotational kinetic energy into static pressure through diffusion and redirect the flow direction of the fluid, preparing it for the rotor blades of the next stage.
The cross-sectional area between rotor drum and casing is reduced in the flow direction to maintain an optimum Mach number using variable geometry as the fluid is compressed. As the fluid enters and leaves in the axial direction, the centrifugal component in the energy equation does not come into play. Here the compression is based on diffusing action of the passages; the diffusing action in stator converts absolute kinetic head of the fluid into rise in pressure. The relative kinetic head in the energy equation is a term that exists only because of the rotation of the rotor; the rotor reduces the relative kinetic head of the fluid and adds it to the absolute kinetic head of the fluid i.e. the impact of the rotor on the fluid particles increases its velocity and thereby reduces the relative velocity between the fluid and the rotor. In short, the rotor increases the absolute velocity of the fluid and the stator converts this into pressure rise. Designing the rotor passage with a diffusing capability can produce a pressure rise in addition to its normal functioning.
This produces greater pressure rise per stage which constitutes a rotor together. This is the reaction principle in turbomachines. If 50% of the pressure rise in a stage is obtained at the rotor section, it is said to have a 50% reaction; the increase in pressure produced by a single stage is limited by the relative velocity between the rotor and the fluid, the turning and diffusion capabilities of the airfoils. A typical stage in a commercial compressor will produce a pressure increase of between 15% and 60% at design conditions with a polytropic efficiency in the region of 90–95%. To achieve different pressure ratios, axial compressors are designed with different numbers of stages and rotational speeds; as a rule of thumb we can assume that each stage in a given compressor has the same temperature rise. Therefore, at the entry, temperature to each stage must increase progressively through the compressor and the ratio / entry must decrease, thus implying a progressive reduction in stage pressure ratio through the unit.
Hence the rear stage develops a lower pressure ratio than the first stage. Higher stage pressure ratios are possible if the relative velocity between fluid and rotors is supersonic, but this is achieved at the expense of efficiency and operability; such compressors, with stage pressure ratios of over 2, are only used where minimizing the compressor size, weight or complexity is critical, such as in military jets. The airfoil profiles are turning. Although compressors can be run at other conditions with different flows, speeds, or pressure ratios, this can result in an efficiency penalty or a partial or complete breakdown in flow. Thus, a practical limit on the number of stages, the overall pressure ratio, comes from the interaction of the different stages when required to work away from the design conditions; these “off-design” conditions can be mitigated to a certain extent by providing some flexibility in the compressor. This is achieved through the use of adjustable stators or with valves that can bleed fluid from the main flow between stages.
Modern jet engines use a series of compressors. The law of moment of momentum states that the sum of the moments of external forces acting on a fluid, temporarily occupying th
