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25 juin 2012 1 25 /06 /juin /2012 04:36

John Logie Baird

John Logie Baird FRSE (13 August 1888 – 14 June 1946)[1] was a Scottish[2] engineer and inventor of the world's first practical, publicly demonstrated television system, and also the world's first fully electronic colour television tube. HP G62-a70SQ Keyboard 

Although Baird's electromechanical system was eventually displaced by purely electronic systems (such as those of Vladimir Zworykin, Marconi-EMI and Philo Farnsworth), Baird's early successes demonstrating working television broadcasts and his colour and cinema television work earn him a prominent place in television's invention. HP G62-a70SV Keyboard 

In 2002, Logie Baird was ranked number 44 in the list of the "100 Greatest Britons" following a UK-wide vote.[3] In 2006, Logie Baird was also named as one of the 10 greatest Scottish scientists in history, having been listed in the National Library of Scotland's 'Scottish Science Hall of Fame'.[4] The "Baird" brand name was first owned by Thorn-EMI and was sold off to a small Chinese manufacturer when Thorn-EMI was dissolved. HP G62-a74SS Keyboard 

Although the development of television was the result of work by many inventors, Baird was a prominent pioneer and made major advances in the field. Particularly in Britain, many historians credit Baird with being the first to produce a live, HP G62-a75ER Keyboard 

moving, greyscaletelevision image from reflected light. Baird achieved this, where other inventors had failed, by obtaining a better photoelectric cell and improving the signal conditioningfrom the photocell and the video amplifier. HP G62-a75SS Keyboard 

Between 1902 and 1907, Arthur Korn invented and built the first successful signal-conditioning circuits for image transmission. The circuits overcame the image-destroying lag effect that is part of selenium photocells. Korn's compensation circuit allowed him to send still pictures by telephone or wireless between countries and even over oceans, HP G62-a80ER Keyboard 

while his circuit operated without benefit of electronic amplification.[5] Korn's success at transmitting halftone still images suggested that such compensation circuits might work in television. Baird was the direct beneficiary of Korn's research and success.[6][7] HP G62-a80ES Keyboard 

In his first attempts to develop a working television system, Baird experimented with the Nipkow disk. Paul Nipkow had invented this scanning disc system in 1884.[8]Television historian Albert Abramson calls Nipkow's patent "the master television patent."[9] Nipkow's work is important because Baird and many others chose to develop it into a broadcast medium. HP G62-a80SV Keyboard 

In early 1923, and in poor health, Baird moved to 21 Linton Crescent, Hastings, on the south coast of England and later rented a workshop in Queen's Arcade in the town. Baird built what was to become the world's first working television set using items including an old hatbox and a pair of scissors, HP G62-a82ER Keyboard 

some darning needles, a few bicycle light lenses, a used tea chest, and sealing wax and glue that he purchased.[10] In February 1924, he demonstrated to the Radio Times that a semi-mechanical analogue television system was possible by transmitting moving silhouette images. HP G62-a83ER Keyboard 

In July of the same year, he received a 1000-volt electric shock, but survived with only a burnt hand. His landlord, a Mr Tree, asked him to quit his workshop and he moved to upstairs rooms in Soho, London, where he made a technical breakthrough. HP G62-a84ER Keyboard 

Baird gave the first public demonstration of moving silhouette images by television at Selfridges department store in London in a three-week series of demonstrations beginning on 25 March 1925. HP G62-a84SS Keyboard 

In his laboratory on 2 October 1925, Baird successfully transmitted the first television picture with a greyscale image: the head of a ventriloquist's dummy nicknamed "Stooky Bill" in a 30-line vertically scanned image, at five pictures per second.[11]HP G62-a85EM Keyboard 

Baird went downstairs and fetched an office worker, 20-year-old William Edward Taynton, to see what a human face would look like, and Taynton became the first person to be televised in a full tonal range.[12] Looking for publicity, Baird visited the Daily Express newspaper to promote his invention. HP G62-a85ES Keyboard 

The news editor was terrified: he was quoted by one of his staff as saying: "For God's sake, go down to reception and get rid of a lunatic who's down there. He says he's got a machine for seeing by wireless! Watch him — he may have a razor on him."[13] HP G62-a90SS Keyboard

On 26 January 1926, Baird repeated the transmission for members of the Royal Institution and a reporter from The Times in his laboratory at 22 Frith Street in the Soho district of London.[14] By this time, he had improved the scan rate to 12.5 pictures per second. It was the first demonstration of a television system that could broadcast live moving images with tone graduation. HP G62-b00SA Keyboard

He demonstrated the world's first colour transmission on 3 July 1928, using scanning discs at the transmitting and receiving ends with three spirals of apertures, each spiral with a filter of a different primary colour; and three light sources at the receiving end, with a commutator to alternate their illumination. That same year he also demonstrated stereoscopic television. HP G62-b01ET Keyboard

In 1932, Baird was the first person in Britain to demonstrate ultra-short wave transmission. (Today, we refer to "ultra short waves" as the VHF band.) Contrary to some reports, these transmissions were far from the first VHF telecasts. HP G62-b01SG Keyboard

In 1931, the US Federal Radio Commission allocated VHF television bands. From 1931 to 1933, station W9XD in Milwaukee, Wisconsin transmitted some of the first VHF television signals. The station's 45-line, triply interlaced pictures used theU. A. Sanabria television technology.[15] HP G62-b01SL Keyboard


In 1927, Baird transmitted a long-distance television signal over 438 miles (705 km) of telephone line between London and Glasgow; Baird transmitted the world's first long-distance television pictures to the Central Hotel at Glasgow Central Station.[16] HP G62-b02ET Keyboard

This transmission was Baird's response to a 225-mile, long-distance telecast between stations of AT&T Bell Labs. The Bell stations were in New York and Washington, DC. The earlier telecast took place in April 1927, a month before Baird's demonstration.[9] HP G62-b02SD Keyboard

Baird then set up the Baird Television Development Company Ltd, which in 1928 made the first transatlantic television transmission, from London to Hartsdale, New York, and the first television programme for the BBC. In November 1929, Baird and Bernard Natan established France's first television company, HP G62-b02SG Keyboard

Télévision-Baird-Natan. He televised the first live transmission of the Epsom Derby in 1931. He demonstrated a theatre television system, with a screen two feet by five feet (60 cm by 150 cm), in 1930 at the London Coliseum, Berlin, Paris, and Stockholm.[17] By 1939 he had improved his theatre projection system to televise a boxing match on a screen 15 ft (4.6 m) by 12 ft (3.7 m).[18] HP G62-b02SL Keyboard

From 1929 to 1932, the BBC transmitters were used to broadcast television programmes using the 30-line Baird system, and from 1932 to 1935, the BBC also produced the programmes in their own studio at 16 Portland Place. On 3 November 1936, HP G62-b03ET Keyboard

from Alexandra Palace located on the high ground of the north London ridge, the BBC began alternating Baird 240-line transmissions with EMI's electronic scanning system which had recently been improved to 405 lines after a merger with Marconi. HP G62-b03SG Keyboard

The Baird system at the time involved an intermediate film process, where footage was shot on cinefilm which was rapidly developed and scanned. HP G62-b03SD Keyboard

The trial was due to last 6 months but the BBC were forced to cease broadcasts with the Baird system in February 1937, due to a disastrous fire in the Baird studio. It was becoming apparent to the BBC that the Baird system would ultimately fail due in large part to the lack of mobility of the Baird system's cameras, with their developer tanks, hoses, and cables.[19] HP G62-b03SL Keyboard

Baird's television systems were replaced by the electronic television system developed by the newly formed company EMI-Marconi under Isaac Shoenberg, which had access to patents developed by Vladimir Zworykin and RCA. HP G62-b04ET Keyboard

Similarly, Philo T. Farnsworth's electronic "Image Dissector" camera was available to Baird's company via a patent-sharing agreement. However, the Image Dissector camera was found to be lacking in light sensitivity, requiring excessive levels of illumination. Baird used the Farnsworth tubes instead to scan cinefilm, HP G62-b04SD Keyboard

in which capacity they proved serviceable though prone to dropouts and other problems. Farnsworth himself came to London to Baird's Crystal Palace laboratories in 1936, but was unable to fully solve the problem; the fire that burned Crystal Palace to the ground later that year further hampered the Baird company's ability to compete.[20] HP G62-b04SL Keyboard

Baird made many contributions to the field of electronic television after mechanical systems had taken a back seat. In 1939, he showed colour television using acathode ray tube in front of which revolved a disc fitted with colour filters, a method taken up by CBS and RCA in the United States. HP G62-b05EG Keyboard

In 1941, he patented and demonstrated a system of three-dimensional television at a definition of 500 lines. On 16 August 1944, he gave the world's first demonstration of a fully electronic colour television display. His 600-line colour system used triple interlacing, HP G62-b05EO Keyboard

using six scans to build each picture.[21][22] In 1943, the Hankey Committee was appointed to oversee the resumption of television broadcasts after the war. Baird persuaded them to make plans to adopt his proposed 1000-line Telechrome electronic colour system as the new post-war broadcast standard. HP G62-b05ET Keyboard

The picture quality on this system would have been comparable to today's HDTV. The Hankey Committee's plan lost all momentum partly due to the challenges of postwar reconstruction. The monochrome 405-line standard remained in place until 1985 in some areas, HP G62-b05EW Keyboard

and it was three decades until the introduction of the 625-line system in 1964 and (PAL) colour in 1967. A demonstration of large screen three-dimensional television by the BBC was reported in March 2008, over 60 years after Baird's demonstration. HP G62-b05SD Keyboard

Other inventions

Some of Baird's early inventions were not fully successful. In his twenties he tried to create diamonds by heating graphite and shorted out Glasgow's electricity supply. Later Baird perfected a glass razor which was rust-resistant, but shattered. HP G62-b05SL Keyboard

Inspired by pneumatic tyres he attempted to make pneumatic shoes, but his prototype contained semi-inflated balloons which burst. He also invented a thermal undersock (the Baird undersock), which was moderately successful. Baird suffered from cold feet, and after a number of trials, he found that an extra layer of cotton inside the sock provided warmth.[10] HP G62-b05SW Keyboard

Baird's numerous other developments demonstrated his particular talent at invention. He was a visionary and began to dabble with electricity. In 1928, he developed an early video recording device, which he dubbed Phonovision. HP G62-b06ED Keyboard

The system consisted of a large Nipkow disk attached by a mechanical linkage to a conventional 78-rpm record-cutting lathe. The result was a disc that could record and play back a 30-line video signal. Technical difficulties with the system prevented its further development, HP G62-b06EG Keyboard

but some of the original phonodiscs have been preserved, and have since been restored by Donald McLean, a Scottish electrical engineer.[23] Baird's other developments were in fibre-optics, radio direction finding, infrared night viewing and radar. HP G62-b06ET Keyboard

There is discussion about his exact contribution to the development of radar, for his wartime defence projects have never been officially acknowledged by the UK government. According to Malcolm Baird, his son, what is known is that in 1926 Baird filed a patent for a device that formed images from reflected radio waves, HP G62-b06SG Keyboard

a device remarkably similar to radar, and that he was in correspondence with the British government at the time. The radar contribution is in dispute. HP G62-b06SL Keyboard

According to some experts, Baird's "noctovision" is not radar. Unlike radar (except Doppler radar), Noctovision is incapable of determining the distance to the scanned subject. Noctovision also cannot determine the coordinates of the subject in three-dimensional space.[24] HP G62-b07EG Keyboard

Later years

From December 1944 until his death two years later, Baird lived at a house in Station Road, Bexhill-on-Sea, East Sussex, immediately north of the station itself.[25] Baird died in Bexhill on 14 June 1946 after a stroke in February of that year. HP G62-b07ET Keyboard

The old house was demolished in 2007. The Sea Road-Station Road skyline now features a new block of 51 flats on the site, renamed "Baird Court".HP G62-b07EO Keyboard

John Logie Baird is buried with his mother, father and wife in Helensburgh Cemetery.

A jet engine is a reaction engine that discharges a fast moving jet which generates thrust by jet propulsion in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, and pulse jets. In general, most jet engines are internal combustion engines[1] but non-combusting forms also exist. HP G62-b07SL Keyboard

In common parlance, the term jet engine loosely refers to an internal combustion airbreathing jet engine (a duct engine). These typically consist of an engine with a rotary (rotating) air compressor powered by a turbine ("Brayton cycle"), with the leftover power providing thrust via a propelling nozzle. These types of jet engines are primarily used by jet aircraft for long distance travel. HP G62-b08EG Keyboard

Early jet aircraft used turbojet engines which were relatively inefficient for subsonic flight. Modern subsonic jet aircraft usually use high-bypass turbofan engines which offer high speed with fuel efficiency comparable (over long distances) to piston and propeller aeroengines.[2] HP G62-b08ET Keyboard

Jet engines can be dated back to the invention of the aeolipile before the first century AD. This device used steam power directed through two nozzles to cause a sphere to spin rapidly on its axis. So far as is known, it was not used for supplying mechanical power, and the potential practical applications of this invention were not recognized. It was simply considered a curiosity. HP G62-b08SL Keyboard

Jet propulsion only took off, literally and figuratively, with the invention of the gunpowder-powered rocket by the Chinese in the 13th century as a type offireworks, and gradually progressed to propel formidable weaponry. However, although very powerful, at reasonable flight speeds rockets are very inefficient and so jet propulsion technology stalled for hundreds of years. HP G62-b09ED Keyboard

The earliest attempts at airbreathing jet engines were hybrid designs in which an external power source first compressed air, which was then mixed with fuel and burned for jet thrust. In one such system, called a thermojet by Secondo Campini but more commonly, motorjet, HP G62-b09ET Keyboard

the air was compressed by a fan driven by a conventional piston engine. Examples of this type of design were the Caproni Campini N.1, and the Japanese Tsu-11 engine intended to power Ohka kamikaze planes towards the end of World War II. HP G62-b09EZ Keyboard

None were entirely successful and the N.1 ended up being slower than the same design with a traditional engine and propellercombination. HP G62-b09SA Keyboard

Even before the start of World War II, engineers were beginning to realize that the piston engine was self-limiting in terms of the maximum performance which could be attained; the limit was due to issues related to propeller efficiency,[3]HP G62-b10EH Keyboard

which declined as blade tips approached the speed of sound. If engine, and thus aircraft, performance were 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 developed. HP G62-b10EK Keyboard

This was the motivation behind the development of the gas turbine engine, commonly called a "jet" engine, which would become almost as revolutionary to aviation as the Wright brothers' first flight. HP G62-b10EM Keyboard

The key to a practical jet engine was the gas turbine, used to extract energy from the engine itself to drive the compressor. 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. HP G62-b10EP Keyboard

The first gas turbine to successfully run self-sustaining was built in 1903 by Norwegian engineer Ægidius Elling. Limitations in design and practical engineering and metallurgy prevented such engines reaching manufacture. The main problems were safety, reliability, weight and, especially, sustained operation. HP G62-b10EV Keyboard

In 1928, RAF College Cranwell cadet [5] Frank Whittle formally submitted his ideas for a turbo-jet to his superiors. In October 1929 he developed his ideas further.[6] On 16 January 1930 in England, Whittle submitted his first patent (granted in 1932).[7]HP G62-b10EW Keyboard

The patent showed a two-stage axial compressor feeding a single-sided centrifugal compressor. Practical axial compressors were made possible by ideas from A.A.Griffith in a seminal paper in 1926 ("An Aerodynamic Theory of Turbine Design"). HP G62-b10SA Keyboard

Whittle would later concentrate on the simpler centrifugal compressor only, for a variety of practical reasons. Whittle had his first engine running in April 1937. It was liquid-fuelled, and included a self-contained fuel pump. Whittle's team experienced near-panic when the engine would not stop, accelerating even after the fuel was switched off. HP G62-b10SD Keyboard

It turned out that fuel had leaked into the engine and accumulated in pools, so the engine would not stop until all the leaked fuel had burned off. Whittle was unable to interest the government in his invention, and development continued at a slow pace. HP G62-b10SG Keyboard

In 1935 Hans von Ohain started work on a similar design in Germany, apparently unaware of Whittle's work.[8] His first device was strictly experimental and could only run under external power, but he was able to demonstrate the basic concept. HP G62-b10SI Keyboard

Ohain was then introduced to 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. HP G62-b10SJ Keyboard

They had their first HeS 1 centrifugal engine running by September 1937. Unlike Whittle's design, Ohain used hydrogen as fuel, supplied under external pressure. Their subsequent designs culminated in the gasoline-fuelled HeS 3 of 1,100 lbf (5 kN), HP G62-b10SK Keyboard

which was fitted to Heinkel's simple and compact He 178airframe and flown by Erich Warsitz in the early morning of August 27, 1939, from Rostock-Marienehe aerodrome, an impressively short time for development. The He 178 was the world's first jet plane.[9] HP G62-b10SO Keyboard

Austrian Anselm Franz of Junkers' engine division (Junkers Motoren or "Jumo") introduced the axial-flow compressor in their jet engine. Jumo was assigned the next engine number in the RLM 109-0xx numbering sequence for gas turbine aircraft powerplants, "004",HP G62-b10SP Keyboard

and the result was the Jumo 004 engine. After many lesser technical difficulties were solved, mass production of this engine started in 1944 as a powerplant for the world's first jet-fighter aircraft, the Messerschmitt Me 262 (and later the world's first jet-bomber aircraft, HP G62-b10SQ Keyboard

the Arado Ar 234). A variety of reasons conspired to delay the engine's availability, causing the fighter to arrive too late to improve Germany's position in World War II. Nonetheless, it will be remembered as the first use of jet engines in service. HP G62-b10ST Keyboard

Meanwhile, in Britain the Gloster E28/39 had its maiden flight on 15 May 1941 and the Gloster Meteor finally entered service with the RAF in July 1944. HP G62-b10SV Keyboard

Following the end of the war the German jet aircraft and jet engines were extensively studied by the victorious allies and contributed to work on early Soviet and US jet fighters. The legacy of the axial-flow engine is seen in the fact that practically all jet engines on fixed wing aircraft have had some inspiration from this design. HP G62-b10SW Keyboard

By the 1950s the jet engine was almost universal in combat aircraft, with the exception of cargo, liaison and other specialty types. HP G62-b11EK Keyboard

By this point some of the British designs were already cleared for civilian use, and had appeared on early models like the de Havilland Comet and Avro Canada Jetliner. By the 1960s all large civilian aircraft were also jet powered, leaving the piston engine in low-cost niche roles such as cargo flights. HP G62-b11ER Keyboard

The efficiency of turbojet engines was still rather worse than piston engines but by the 1970s, with the advent of high bypass turbofan jet engines, an innovation not foreseen by the early commentators such as Edgar Buckingham, at high speeds and high altitudes that seemed absurd to them, fuel efficiency was about the same as the best piston and propeller engines.[2] HP G62-b11ET Keyboard


Jet engines are usually used as aircraft engines for jet aircraft. They are also used for cruise missiles and unmanned aerial vehicles.

In the form of rocket engines they are used for fireworks, model rocketry, spaceflight, and military missiles. HP G62-b11SA Keyboard

Jet engines have also been used to propel high speed cars, particularly drag racers, with the all-time record held by arocket car. A turbofan powered car ThrustSSC currently holds the land speed record. HP G62-b12EK Keyboard

Jet engine designs are frequently modified for non-aircraft applications, as industrial gas turbines. These are used in electrical power generation, for powering water, natural gas, or oil pumps, and providing propulsion for ships and locomotives. HP G62-b12ER Keyboard

Industrial gas turbines can create up to 50,000 shaft horsepower. Many of these engines are derived from older military turbojets such as the Pratt & Whitney J57 and J75 models. There is also a derivative of the P&W JT8D low-bypass turbofan that creates up to 35,000 HP. HP G62-b12SA Keyboard

Commonly aircraft are propelled by airbreathing jet engines. Most airbreathing jet engines that are in use are turbofan jet engines which give good efficiency at speeds just below the speed of sound. HP G62-b12SL Keyboard

Gas turbines are rotary engines that extract energy from a flow of combustion gas. They have an upstream compressor coupled to a downstream turbine with a combustion chamber in-between. In aircraft engines, those three core components are often called the "gas generator."[10] There are many different variations of gas turbines, but they all use a gas generator system of some type. HP G62-b12ST Keyboard


A turbojet engine is a gas turbine engine that works by compressing air with an inlet and a compressor (axial, centrifugal, or both), mixing fuel with the compressed air, burning the mixture in the combustor, and then passing the hot, high pressure air through a turbine and a nozzle. HP G62-b13EA Keyboard

The compressor is powered by the turbine, which extracts energy from the expanding gas passing through it. The engine converts internal energy in the fuel to kinetic energy in the exhaust, producing thrust. All the air ingested by the inlet is passed through the compressor, combustor, and turbine, unlike the turbofan engine described below.[11] HP G62-b13EO Keyboard


A turbofan engine is a gas turbine engine that is very similar to a turbojet. Like a turbojet, it uses the gas generator core (compressor, combustor, turbine) to convert internal energy in fuel to kinetic energy in the exhaust. Turbofans differ from turbojets in that they have an additional component, a fan. Like the compressor, the fan is powered by the turbine section of the engine. HP G62-b13ER Keyboard

Unlike the turbojet, some of the flow accelerated by the fan bypasses the gas generator core of the engine and is exhausted through a nozzle. The bypassed flow is at lower velocities, but a higher mass, making thrust produced by the fan more efficient than thrust produced by the core. Turbofans are generally more efficient than turbojets at subsonic speeds, but they have a larger frontal area which generates more drag.[12] HP G62-b13SA Keyboard

There are two general types of turbofan engines, low bypass and high bypass. Low bypass turbofans have a bypass ratio of around 2:1 or less, meaning that for each kilogram of air that passes through the core of the engine, two kilograms or less of air bypass the core.[citation needed]HP G62-b13SL Keyboard

Low bypass turbofans often used a mixed exhaust nozzle meaning that the bypassed flow and the core flow exit from the same nozzle.[13] High bypass turbofans have larger bypass ratios, sometimes on the order of 5:1 or 6:1. These turbofans can produce much more thrust than low bypass turbofans or turbojets because of the large mass of air that the fan can accelerate, and are often more fuel efficient than low bypass turbofans or turbojets.[citation needed] HP G62-b13ST Keyboard

Turboprop engines are jet engine derivatives, still gas turbines, that extract work from the hot-exhaust jet to turn a rotating shaft, which is then used to produce thrust by some other means. While not strictly jet engines in that they rely on an auxiliary mechanism to produce thrust, turboprops are very similar to other turbine-based jet engines, and are often described as such. HP G62-b14ER Keyboard

In turboprop engines, a portion of the engines' thrust is produced by spinning a propeller, rather than relying solely on high-speed jet exhaust. As their jet thrust is augmented by a propeller, turboprops are occasionally referred to as a type of hybrid jet engine. HP G62-b14SO Keyboard

While many turboprops generate the majority of their thrust with the propeller, the hot-jet exhaust is an important design point, and maximum thrust is obtained by matching thrust contributions of the propeller to the hot jet.[14]Turboprops generally have better performance than turbojets or turbofans at low speeds where propeller efficiency is high, but become increasingly noisy and inefficient at high speeds.[15] HP G62-b14ST Keyboard

Turboshaft engines are very similar to turboprops, differing in that nearly all energy in the exhaust is extracted to spin the rotating shaft, which is used to power machinery rather than a propeller, they therefore generate little to no jet thrust and are often used to power helicopters.[13] HP G62-b15EL Keyboard

A propfan engine (also called "unducted fan", "open rotor", or "ultra-high bypass") is a jet engine that uses its gas generator to power an exposed fan, similar to turboprop engines. Like turboprop engines, propfans generate most of their thrust from the propeller and not the exhaust jet. HP G62-b15ER Keyboard

The primary difference between turboprop and propfan design is that the propeller blades on a propfan are highly swept to allow them to operate at speeds around Mach 0.8, which is competitive with modern commercial turbofans. HP G62-b15ET Keyboard

These engines have the fuel efficiency advantages of turboprops with the performance capability of commercial turbofans.[16] While significant research and testing (including flight testing) has been conducted on propfans, no propfan engines have entered production. HP G62-b15EV Keyboard

Ram powered

Ram powered jet engines are airbreathing engines similar to gas turbine engines and they both follow the Brayton cycle. Gas turbine and ram powered engines differ, however, in how they compress the incoming airflow. Whereas gas turbine engines use axial or centrifugal compressors to compress incoming air, HP G62-b15SA Keyboard

ram engines rely only on air compressed through the inlet or diffuser.[17] Ram powered engines are considered the most simple type of air breathing jet engine because they can contain no moving parts.[18] HP G62-b15SL Keyboard

Ramjets are the most basic type of ram powered jet engines. They consist of three sections; an inlet to compressed oncoming air, a combustor to inject and combust fuel, and a nozzle expel the hot gases and produce thrust. Ramjets require a relatively high speed to efficiently compress the oncoming air, HP G62-b15SV Keyboard

so ramjets cannot operate at a standstill and they are most efficient at supersonic speeds. A key trait of ramjet engines is that combustion is done at subsonic speeds. The supersonic oncoming air is dramatically slowed through the inlet, HP G62-b15SW Keyboard

where it is then combusted at the much slower, subsonic, speeds.[17]The faster the oncoming air is, however, the less efficient it becomes to slow it to subsonic speeds. Therefore ramjet engines are limited to approximately Mach 5.[19] HP G62-b16EA Keyboard


Scramjets are mechanically very similar to ramjets. Like a ramjet, they consist of an inlet, a combustor, and a nozzle. The primary difference between ramjets and scramjets is that scramjets do not slow the oncoming airflow to subsonic speeds for combustion, they use supersonic combustion instead. The name "scramjet" comes from "supersonic combusting ramjet." HP G62-b16ER Keyboard

Since scramjets use supersoni

c combustion they can operate at speeds above Mach 6 where traditional ramjets are too inefficient. Another difference between ramjets and scramjets comes from how each type of engine compresses the oncoming air flow: HP G62-b16SA Keyboard

while the inlet provides most of the compression for ramjets, the high speeds at which scramjets operate allow them to take advantage of the compression generated by shock waves, primarily oblique shocks.[20] HP G62-b16SO Keyboard

Very few scramjet engines have ever been built and flown. In May 2010 the Boeing X-51 set the endurance record for the longest scramjet burn at over 200 seconds.[21] HP G62-b16ST Keyboard

Non-continuous combustion

The rocket engine uses the same basic physical principles as the jet engine for propulsion via thrust, but is distinct in that it does not require atmospheric air to provide oxygen; the rocket carries all components of the reaction mass. HP G62-b17EL Keyboard

This type of engine is used for launching satellites, space exploration and manned access, and permitted landing on the moonin 1969. HP G62-b17ER Keyboard

Rocket engines are used for high altitude flights as they have a lack of reliance on atmospheric oxygen and this allows them to operate at arbitrary altitudes, or anywhere where very high accelerations are needed since rocket engines themselves have a very high thrust-to-weight ratio. HP G62-b17SA Keyboard

However, the high exhaust speed and the heavier, oxidizer-rich propellant results in far more propellant use than turbofans although, even so, at extremely high speeds they become energy-efficient.

An approximate equation for the net thrust of a rocket engine is: HP G62-b17ST Keyboard

All jet engines are reaction engines that generate thrust by emitting a jet of fluid rearwards at relatively high speed. The forces on the inside of the engine needed to create this jet give a strong thrust on the engine which pushes the craft forwards. HP G62-b18EL Keyboard

Jet engines make their jet from propellant from tankage that is attached to the engine (as in a 'rocket') as well as in duct engines (those commonly used on aircraft) by ingesting an external fluid (very typically air) and expelling it at higher speed. HP G62-b18EO Keyboard

Propelling nozzle

The propelling nozzle is the key component of all jet engines as it creates the exhaust jet. Propelling nozzles turn pressurized, slow moving, usually hot gas, into lower pressure, fast moving, colder gas by adiabatic expansion.[23] HP G62-b18EO Keyboard

Propelling nozzles can be subsonic, sonic, or supersonic,[24] but in normal operation nozzles are usually sonic or supersonic. Nozzles operate to constrict the flow, and hence help raise the pressure in the engine, and physically the nozzles are very typically convergent, HP G62-b18ER Keyboard

or convergent-divergent. Convergent-divergent nozzles can give supersonic jet velocity within the divergent section, whereas in a convergent nozzle the exhaust fluid cannot exceed the speed of sound of the gas within the nozzle. HP G62-b18SA Keyboard


The motion impulse of the engine is equal to the fluid mass multiplied by the speed at which the engine emits this mass: where is the fluid mass per second and is the exhaust speed. In other words, a vehicle gets the same thrust if it outputs a lot of exhaust very slowly, HP G62-b18ST Keyboard

or a little exhaust very quickly. (In practice parts of the exhaust may be faster than others, but it is the average momentum that matters, and thus the important quantity is called the effective exhaust speed - here. HP G62-b19ER Keyboard

However, when a vehicle moves with certain velocity , the fluid moves towards it, creating an opposing ram drag at the intake:

Most types of jet engine have an intake, which provides the bulk of the fluid exiting the exhaust. Conventional rocket motors, however, do not have an intake, the oxidizer and fuel both being carried within the vehicle. Therefore, HP G62-b19SL Keyboard

rocket motors do not have ram drag; the gross thrust of the nozzle is the net thrust of the engine. Consequently, the thrust characteristics of a rocket motor are different from that of an air breathing jet engine, and thrust is independent of speed. HP G62-b19SO Keyboard

The jet engine with an intake duct is only useful if the velocity of the gas from the engine, , is greater than the vehicle velocity, , as the net engine thrust is the same as if the gas were emitted with the velocity . So HP G62-b19ST Keyboard

HP G62-b20EB Keyboardthe thrust is actually equal to

Cycle efficiency

In addition to propulsive efficiency, another factor is cycle efficiency; essentially a jet engine is typically a form of heat engine. Heat engine efficiency is determined by the ratio of temperatures that are reached in the engine, in this case at the entry to the propulsive nozzle, to the temperature thatHP G62-b20EH Keyboard

Cycle efficiency is highest in rocket engines (~60+%), as they can achieve extremely high combustion temperatures and can have very large, energy efficient nozzles. Cycle efficiency in turbojet and similar is nearer to 30%, the practical combustion temperatures and nozzle efficiencies are much lower. HP G62-b20EI Keyboard

Consumption of fuel or propellant

A closely related (but different) concept to energy efficiency is the rate of consumption of propellant mass. Propellant consumption in jet engines is measured by Specific Fuel Consumption, Specific impulse or Effective exhaust velocity. HP G62-b20EP Keyboard

They all measure the same thing. Specific impulse and effective exhaust velocity are strictly proportional, whereas specific fuel consumption is inversely proportional to the others. HP G62-b20ES Keyboard

For airbreathing engines such as turbojets energy efficiency and propellant (fuel) efficiency are much the same thing, since the propellant is a fuel and the source of energy. In rocketry, the propellant is also the exhaust, and this means that a high energy propellant gives better propellant efficiency but can in some cases actually can give lower energy efficiency. HP G62-b20EV Keyboard

It can be seen that the subsonic turbofans such as General Electric's CF6 uses a lot less fuel to generate thrust for a second than Concorde's turbojet, the 593. However, since energy is force times distance and the distance per second is greater for Concorde, HP G62-b20EW Keyboard

the actual power generated by the engine for the same amount of fuel is higher for Concorde at Mach 2 cruise than the CF6. The Concorde's engines are more efficient for thrust per mile, indeed, the most efficient ever.[31] HP G62-b20SA Keyboard

Thrust-to-weight ratio

The thrust to weight ratio of jet engines of similar principles varies somewhat with scale, but mostly is a function of engine construction technology. Clearly for a given engine, the lighter the engine, the better the thrust to weight is, the less fuel is used to compensate for drag due to the lift needed to carry the engine weight, or to accelerate the mass of the engine. HP G62-b20SC Keyboard

As can be seen in the following table, rocket engines generally achieve very much higher thrust to weight ratios than duct engines such as turbojet and turbofan engines. HP G62-b20SG Keyboard

This is primarily because rockets almost universally use dense liquid or solid reaction mass which gives a much smaller volume and hence the pressurisation system that supplies the nozzle is much smaller and lighter for the same performance. HP G62-b20SJ Keyboard

Duct engines have to deal with air which is 2-3 orders of magnitude less dense and this gives pressures over much larger areas, and which in turn results in more engineering materials being needed to hold the engine together and for the air compressor. HP G62-b20SO Keyboard

Propeller engines are useful for comparison. They accelerate a large mass of air but by a relatively small maximum change in speed. This low speed limits the maximum thrust of any propeller driven airplane. However, because they accelerate a large mass of air, propeller engines, such as turboprops, can be very efficient. HP G62-b20SQ Keyboard

On the other hand, turbojets accelerate a much smaller mass of the air and burned fuel, but they emit it at the much higher speeds possible with a de Laval nozzle. This is why they are suitable for supersonic and higher speeds. HP G62-b20SS Keyboard

Low bypass turbofans have the mixed exhaust of the two air flows, running at different speeds (c1 and c2). The thrust of such engine is

where m1 and m2 are the air masses, being blown from the both exhausts. Such engines are effective at lower speeds, than the pure jets, but at higher speeds than the turboshafts and propellers in general. For instance, at the 10 km altitude, HP G62-b20SV Keyboard

turboshafts are most effective at about Mach 0.4 (0.4 times the speed of sound), low bypass turbofans become more effective at about Mach 0.75 and turbojets become more effective than mixed exhaust engines when the speed approaches Mach 2-3. HP G62-b20SW Keyboard

Rocket engines have extremely high exhaust velocity and thus are best suited for high speeds (hypersonic) and great altitudes. At any given throttle, the thrust and efficiency of a rocket motor improves slightly with increasing altitude (because the back-pressure falls thus increasing net thrust at the nozzle exit plane), HP G62-b21EC Keyboard

whereas with a turbojet (or turbofan) the falling density of the air entering the intake (and the hot gases leaving the nozzle) causes the net thrust to decrease with increasing altitude. Rocket engines are more efficient than even scramjets above roughly Mach 15.[44] HP G62-b21EO Keyboard

With the exception of scramjets, jet engines, deprived of their inlet systems can only accept air at around half the speed of sound. The inlet system's job for transonic and supersonic aircraft is to slow the air and perform some of the compression. HP G62-b21ER Keyboard

The limit on maximum altitude for engines is set by flammability- at very high altitudes the air becomes too thin to burn, or after compression, too hot. For turbojet engines altitudes of about 40 km appear to be possible, whereas for ramjet engines 55 km may be achievable. Scramjets may theoretically manage 75 km.[45] Rocket engines of course have no upper limit. HP G62-b21SA Keyboard

At more modest altitudes, flying faster compresses the air in at the front of the engine, and this greatly heats the air. The upper limit is usually thought to be about Mach 5-8, as above about Mach 5.5, HP G62-b21SL Keyboard

the atmospheric nitrogen tends to react due to the high temperatures at the inlet and this consumes significant energy. The exception to this is scramjets which may be able to achieve about Mach 15 or more[citation needed], as they avoid slowing the air, and rockets again have no particular speed limit. HP G62-b22ER Keyboard


Noise is due to shockwaves that form when the exhaust jet interacts with the external air. The intensity of the noise is proportional to the thrust as well as proportional to the fourth power of the jet velocity.[citation needed]HP G62-b22SL Keyboard

HP G62-b23SO Keyboard

Generally then, the lower speed exhaust jets emitted from engines such as high bypass turbofans are the quietest, whereas the fastest jets, such as rockets and turbojets and ramjets are the loudest. HP G62-b22ST Keyboard

Although some variation in jet speed can often be arranged from a jet engine (such as by throttling back and adjusting the nozzle) it is difficult to vary the jet speed from an engine over a very wide range. HP G62-b23ER Keyboard

Engines for supersonic vehicles such as Concorde, military jets and rockets need to have supersonic exhaust to support their top speeds, making them especially noisy even at low speed. HP G62-b23ET Keyboard


An engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematicsand ingenuity to develop solutions for technical problems. Engineers design materials, structures and systems while considering the limitations imposed by practicality, HP G62-b23SA Keyboard

safety and cost.[1][2] The word engineer is derived from the Latinroots ingeniare ("to contrive, devise") and ingenium ("cleverness").[3][4] HP G62-b23SL Keyboard

Engineers are grounded in applied sciences, and their work in research and development is distinct from the basic research focus of scientists.[2] The work of engineers forms the link between scientific discoveries and their subsequent applications to human needs.[1] HP G62-b23SL Keyboard


Engineers develop new technological solutions. During the engineering design process, the responsibilities of the engineer may include defining problems, conducting and narrowing research, analyzing criteria, finding and analyzing solutions, and making decisions. HP G62-b24EO Keyboard

Much of an engineer's time is spent on researching, locating, applying, and transferring information.[5] Indeed, research suggests engineers spend 56% of their time engaged in various different information behaviours, including 14% actively searching for information.[6] HP G62-b24ER Keyboard

Engineers must weigh different design choices on their merits and choose the solution that best matches the requirements. Their crucial and unique task is to identify, understand, and interpret the constraints on a design in order to produce a successful result. HP G62-b24ET Keyboard

Engineers apply techniques of engineering analysis in testing, production, or maintenance. Analytical engineers may supervise production in factories and elsewhere, determine the causes of a process failure, and test output to maintain quality. HP G62-b24SA Keyboard

They also estimate the time and cost required to complete projects. Supervisory engineers are responsible for major components or entire projects. Engineering analysis involves the application of scientific analytic principles and processes to reveal the properties and state of the system, HP G62-b24SL Keyboard

device or mechanism under study. Engineering analysis proceeds by separating the engineering design into the mechanisms of operation or failure, analyzing or estimating each component of the operation or failure mechanism in isolation, and re-combining the components. They may analyse risk.[7][8][9][10] HP G62-b24ST Keyboard

Many engineers use computers to produce and analyze designs, to simulate and test how a machine, structure, or system operates, to generate specifications for parts, to monitor the quality of products, and to control the efficiency of processes. HP G62-b25ER Keyboard

Specialization and management

Most engineers specialize in one or more engineering disciplines.[1] Numerous specialties are recognized by professional societies, and each of the major branches of engineering has numerous subdivisions. Civil engineering, for example, HP G62-b25ES Keyboard

includes structural and transportation engineering, and materials engineering includes ceramic, metallurgical, and polymer engineering. Engineers also may specialize in one industry, such as motor vehicles, or in one type of technology, such as turbines or semiconductor materials.[1] HP G62-b25SA Keyboard

Several recent studies have investigated how engineers spend their time; that is, the work tasks they perform and how their time is distributed among these. Research[11][12] suggests that there are several key themes present in engineers’ work: (1) technical work (i.e., the application of science to product development); HP G62-b25SC Keyboard

(2) social work (i.e., interactive communication between people); (3) computer-based work; (4) information behaviours. Amongst other more detailed findings, a recent work sampling study[12] found that engineers spend 62.92% of their time engaged in technical work, 40.37% in social work, and 49.66% in computer-based work. Furthermore, HP G62-b25SG Keyboard

there was considerable overlap between these different types of work, with engineers spending 24.96% of their time engaged in technical and social work, 37.97% in technical and non-social, 15.42% in non-technical and social, and 21.66% in non-technical and non-social. HP G62-b25SO Keyboard

Engineering is also an information intensive field, with research finding that engineers spend 55.8% of their time engaged in various different information behaviours, including 14.2% actively seeking information from other people (7.8%) and information repositories such as documents and databases (6.4%)[11]. HP Pavilion dv5z-1200 CTO Keyboard

The time engineers spend engaged in such activities is also reflected in the competencies required in engineering roles. In addition to engineers’ core technical competence, research has also demonstrated the critical nature of their personal attributes, project management skills, and cognitive abilities to success in the role[13]. HP Pavilion DV6-1000 Keyboard

Engineers have obligations to the public, their clients, employers and the profession. Many engineering societies have established codes of practice and codes of ethics to guide members and inform the public at large. Each engineering discipline and professional society maintains a code of ethics, HP Pavilion DV6-1000 cto Keyboard

which the members pledge to uphold. Depending on their specializations, engineers may also be governed by specific statute, whistleblowing, product liability laws, and often the principles of business ethics.[14][15][16] HP Pavilion DV6-1000eg Keyboard

Some graduates of engineering programs in North America may be recognized by the Iron Ring or Engineer's Ring, a ring made of iron or stainless steel that is worn on the little finger of the dominant hand. This tradition began in 1925 in Canada withThe Ritual of the Calling of an Engineer, HP Pavilion DV6-1000et Keyboard

where the ring serves as a symbol and reminder of the engineer's obligations for the engineering profession. In 1972, the practice was adopted by several colleges in the United States including members of the Order of the Engineer. HP Pavilion DV6-1001tx Keyboard


Main article: Engineering education

Most engineering programs involve a concentration of study in an engineering specialty, along with courses in both mathematics and the physical and life sciences. Many programs also include courses in general engineering. A design course, HP Pavilion DV6-1001xx Keyboard

sometimes accompanied by a computer or laboratory class or both, is part of the curriculum of most programs. Often, general courses not directly related to engineering, such as those in the social sciences or humanities, also are required. HP Pavilion DV6-1002tx Keyboard

Graduate training is essential for engineering faculty positions and some research and development programs, but is not required for the majority of entry-level engineering jobs. Many experienced engineers obtain graduate degrees in engineering or business administration to learn new technology and broaden their education. Numerous high-level executives in government and industry began their careers as engineers. HP Pavilion DV6-1003tx Keyboard

Accreditation is the process by which engineering program are evaluated by an external body to determine if applicable standards are met. The Washington Accordserves as an international accreditation agreement for academic engineering degrees, recognizing the substantial equivalency in the standards set by many major national engineering bodies. HP Pavilion DV6-1004tx Keyboard

In the United States, post-secondary degree programs in engineering are accredited by the Accreditation Board for Engineering and Technology. In much of Europe and the Commonwealth professional accreditation is provided by Engineering Institutions, such as the Institution of Civil Engineers,the Institution of Mechanical Engineers or the Institution of Engineering and Technology from the United Kingdom. HP Pavilion DV6-1005ea Keyboard


Main article: Regulation and licensure in engineering

In many countries, engineering tasks such as the design of bridges, electric power plants, industrial equipment, machine design and chemical plants, must be approved by a licensed professional engineer. Most commonly titled Professional Engineer is a license to practice and is indicated with the use of post-nominal letters; PE or P.Eng. HP Pavilion DV6-1005ez Keyboard

These are common in North America, European Engineer (Eur Ing) in Europe. The practice of engineering in the UK is not a regulated profession other than the control of the titles of Chartered Engineer (CEng) and Incorporated Engineer (IEng). HP Pavilion DV6-1005tx Keyboard

The title CEng is in use in much of theCommonwealth. Many engineers in the UK also include semi skilled trades to engineering technicians. This is seen by some as a misuse of the title, giving a false image of the profession. A growing movement in the UK is to legally protect the title 'Engineer' so that only professional engineers can use it, a DirectGov petition,[17] has been started to further this cause. HP Pavilion DV6-1006tx Keyboard

In the United States, licensure is generally attainable through combination of education, pre-examination (Fundamentals of Engineering exam), examination (Professional Engineering Exam),[18] and engineering experience (typically in the area of 5+ years). HP Pavilion DV6-1007tx Keyboard

Each state tests and licenses Professional Engineers. Currently most states do not license by specific engineering discipline, but rather provide generalized licensure, and trust engineers to use professional judgement regarding their individual competencies; HP Pavilion DV6-1008tx Keyboard

this is the favoured approach of the professional societies. Despite this, however, at least one of the examinations required by most states is actually focused on a particular discipline; candidates for licensure typically choose the category of examination which comes closest to their respective expertise. HP Pavilion DV6-1009el Keyboard

In Canada, the profession in each province is governed by its own engineering association. For instance, in the Province of British Columbia an engineering graduate with four or more years of post graduate experience in an engineering-related HP Pavilion DV6-1009tx Keyboard

field and passing exams in ethics and law will need to be registered by the Association for Professional Engineers and Geoscientists (APEGBC)[19] in order to become a Professional Engineer and be granted the professional designation of P.Eng allowing one to practice engineering. HP Pavilion DV6-1010ea Keyboard

In Continental Europe, Latin America, Turkey and elsewhere the title is limited by law to people with an engineering degree and the use of the title by others is illegal. In Italy, the title is limited to people who both hold an engineering degree and have passed a professional qualification examination (Esame di Stato). HP Pavilion DV6-1010ed Keyboard

In Portugal, professional engineer titles and accredited engineering degrees are regulated and certified by the Ordem dos Engenheiros. In the Czech Republic, the title "engineer" (Ing.) is given to people with a (masters) degree in chemistry, HP Pavilion DV6-1010ef Keyboard

technology or economics for historical and traditional reasons. In Greece, the academic title of "Diploma Engineer" is awarded after completion of the five-year engineering study course and the title of "Certified Engineer" is awarded after completion of the four-year course of engineering studies at a Technological Educational Institute (TEI). HP Pavilion DV6-1010et Keyboard


The perception of engineering varies across countries and continents. In the United States, continental western Europe, eastern Europe, Asia, the Middle East, Latin American and Canada engineering and engineers are held in very high esteem. HP Pavilion DV6-1010tx Keyboard

British school children in the 1950s were brought up with stirring tales of 'the Victorian Engineers', chief amongst whom were the Brunels, theStephensons, Telford and their contemporaries. In Canada, a 2002 study by the Ontario Society of Professional Engineers revealed that engineers are the third most respected professionals behind doctors and pharmacists.[20]HP Pavilion DV6-1011tx Keyboard

In the Indian subcontinent, Russiaand China, engineering is one of the most sought after undergraduate courses, inviting thousands of applicants to show their ability in highly competitive entrance examinations. In Egypt, the educational system makes engineering the second-most-respected profession in the country (after medicine); HP Pavilion DV6-1012el Keyboard

engineering colleges at Egyptian universities require extremely high marks on the General Certificate of Secondary Education (Arabic: الثانوية العامةal-Thānawiyyah al-`Āmmah)—on the order of 97 or 98%—and are thus considered (with colleges of medicine, natural science, and pharmacy) to be among the "pinnacle colleges" (كليات القمةkullīyāt al-qimmah). HP Pavilion DV6-1012tx Keyboard

The definition of what engineering is varies across countries. In the UK "engineering" is defined as an industry sector consisting of employers and employees loosely termed as "engineers" who range from semi skilled trades to chartered engineers. HP Pavilion DV6-1013ea Keyboard

In the US and Canada, engineering is defined as a regulated profession whose practice and practitioners are licensed and governed by law. In some English speaking countries engineering has been seen as a somewhat dry, uninteresting field in popular culture and has also been thought to be the domain of nerds.[21] For example, the cartoon character Dilbert is an engineer. HP Pavilion DV6-1013tx Keyboard

Inscience fiction, engineers are often portrayed as highly knowledgeable and respectable individuals who understand the overwhelming future technologies often portrayed in the genre. Several Star Trek characters are engineers. HP Pavilion DV6-1014el Keyboard

One difficulty in increasing public awareness of the profession is that average people, in the typical run of ordinary life, do not ever have any personal dealings with engineers, even though they benefit from their work every day. By contrast, it is common to visit a doctor at least once a year, the accountant at tax time, the pharmacist for drugs, and, occasionally, even a lawyer. HP Pavilion DV6-1014tx Keyboard

In companies and other organizations in the UK there is a tendency to undervalue people with advanced technological and scientific skills compared to celebrities, fashion practitioners, entertainers and managers. In his book The Mythical Man-Month,[22] HP Pavilion DV6-1016el Keyboard

Fred Brooks Jr says that managers think of senior people as "too valuable" for technical tasks, and that management jobs carry higher prestige. He tells how some laboratories, such as Bell Labs, abolish all job titles to overcome this problem: HP Pavilion DV6-1016ez Keyboard

a professional employee is a "member of the technical staff." IBM maintain a dual ladder of advancement; the corresponding managerial and engineering / scientific rungs are equivalent. Brooks recommends that structures need to be changed; the boss must give a great deal of attention to keeping his managers and his technical people as interchangeable as their talents allow. HP Pavilion DV6-1018el Keyboard

HP Pavilion DV6-1020ec Keyboard

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