The Avro Lancaster is a British four-engined Second World War heavy bomber. It was designed and manufactured by Avro as a contemporary of the Handley Page Halifax, both bombers having been developed to the same specification, as well as the Short Stirling, all three aircraft being four-engined heavy bombers adopted by the Royal Air Force during the same wartime era; the Lancaster has its origins in the twin-engine Avro Manchester, developed during the late 1930s in response to the Air Ministry Specification P.13/36 for a capable medium bomber for "world-wide use". Developed as an evolution of the Manchester, the Lancaster was designed by Roy Chadwick and powered by four Rolls-Royce Merlins and in one version, Bristol Hercules engines, it first saw service with RAF Bomber Command in 1942 and as the strategic bombing offensive over Europe gathered momentum, it was the main aircraft for the night-time bombing campaigns that followed. As increasing numbers of the type were produced, it became the principal heavy bomber used by the RAF, the RCAF and squadrons from other Commonwealth and European countries serving within the RAF, overshadowing contemporaries such as the Halifax and Stirling.
A long, unobstructed bomb bay meant that the Lancaster could take the largest bombs used by the RAF, including the 4,000 lb, 8,000 lb and 12,000 lb blockbusters, loads supplemented with smaller bombs or incendiaries. The "Lanc", as it was known colloquially, became one of the most used of the Second World War night bombers, "delivering 608,612 long tons of bombs in 156,000 sorties"; the versatility of the Lancaster was such that it was chosen to equip 617 Squadron and was modified to carry the Upkeep "Bouncing bomb" designed by Barnes Wallis for Operation Chastise, the attack on German Ruhr valley dams. Although the Lancaster was a night bomber, it excelled in many other roles, including daylight precision bombing, for which some Lancasters were adapted to carry the 12,000 lb Tallboy and the 22,000 lb Grand Slam earthquake bombs; this was the largest payload of any bomber in the war. In 1943, a Lancaster was converted to become an engine test bed for the Metropolitan-Vickers F.2 turbojet. Lancasters were used to test other engines, including the Armstrong Siddeley Mamba and Rolls-Royce Dart turboprops and the Avro Canada Orenda and STAL Dovern turbojets.
Postwar, the Lancaster was supplanted as the main strategic bomber of the RAF by the Avro Lincoln, a larger version of the Lancaster. The Lancaster took on the role of long range anti-submarine patrol aircraft and air-sea rescue, it was used for photo-reconnaissance and aerial mapping, as a flying tanker for aerial refuelling and as the Avro Lancastrian, a long-range, high-speed, transatlantic passenger and postal delivery airliner. In March 1946, a Lancastrian of BSAA flew the first scheduled flight from the new London Heathrow Airport. In the 1930s, the Royal Air Force was interested in twin-engine bombers; these designs put limited demands on engine production and maintenance, both of which were stretched with the introduction of so many new types into service. Power limitations were so serious that the British invested in the development of huge engines in the 2,000 horsepower class in order to improve performance. During the late 1930s, none of these was ready for production. Both the United States and the Soviet Union were pursuing the development of bombers powered by arrangements of four smaller engines, the results of these projects proved to possess favourable characteristics such as excellent range and fair lifting capacity.
Accordingly, in 1936, the RAF decided to investigate the feasibility of the four-engined bomber. The origins of the Lancaster stem from a twin-engined bomber design, submitted in response to Specification P.13/36, formulated and released by the British Air Ministry during the mid 1930s. This specification had sought a new generation of twin-engined medium bombers suitable for "worldwide use". Further requirements of the specification included the use of a mid-mounted cantilever monoplane wing, all-metal construction. Various candidates were submitted for the specification by such manufacturers as Fairey, Boulton Paul, Handley Page and Shorts; the majority of these engines were under development at this point. In response, British aviation company Avro decided to submit their own design, designated the Avro 679, to meet Specification P.13/36. In February 1937, following consideration of the designs by the Air Ministry, Avro's design submission was selected along with Handley Page's bid being chosen as "second string".
Accordingly, during April 1937, a pair of prototypes of both designs were ordered. The resulting aircraft, named the Manchester, entered RAF service in November 1940. Although considered to be a capable aircraft in most areas, the Manchester proved to be underpowered and troubled by the unreliability of the Vulture engine; as a result, only 200 Manchesters were constructed and the
Direction finding, or radio direction finding, is the measurement of the direction from which a received signal was transmitted. This can refer to radio or other forms of wireless communication, including radar signals detection and monitoring. By combining the direction information from two or more suitably spaced receivers, the source of a transmission may be located via triangulation. Radio direction finding is used in the navigation of ships and aircraft, to locate emergency transmitters for search and rescue, for tracking wildlife, to locate illegal or interfering transmitters. RDF was important in combating German threats during both the World War II Battle of Britain and the long running Battle of the Atlantic. In the former, the Air Ministry used RDF to locate its own fighter groups and vector them to detected German raids. RDF systems can be used with any radio source, although long wavelengths require large antennas, are used only on ground-based systems; these wavelengths are used for marine radio navigation as they can travel long distances "over the horizon", valuable for ships when the line-of-sight may be only a few tens of kilometres.
For aerial use, where the horizon may extend to hundreds of kilometres, higher frequencies can be used, allowing the use of much smaller antennas. An automatic direction finder, which could be tuned to radio beacons called non-directional beacons or commercial AM radio broadcasters, was until a feature of most aircraft, but is now being phased out For the military, RDF is a key tool of signals intelligence; the ability to locate the position of an enemy transmitter has been invaluable since World War I, played a key role in World War II's Battle of the Atlantic. It is estimated that the UK's advanced "huff-duff" systems were directly or indirectly responsible for 24% of all U-Boats sunk during the war. Modern systems used phased array antennas to allow rapid beamforming for accurate results, are part of a larger electronic warfare suite. Early radio direction finders used mechanically rotated antennas that compared signal strengths, several electronic versions of the same concept followed. Modern systems use the comparison of phase or doppler techniques which are simpler to automate.
Early British radar sets were referred to as RDF, stated was a deception. In fact, the Chain Home systems used large RDF receivers to determine directions. Radar systems used a single antenna for broadcast and reception, determined direction from the direction the antenna was facing. Direction finding requires an antenna, directional. Many antenna designs exhibit this property. For example, a Yagi antenna has quite pronounced directionality, so the source of a transmission can be determined by pointing it in the direction where the maximum signal level is obtained. However, to establish direction to great accuracy requires more sophisticated technique. A simple form of directional antenna is the loop aerial; this consists of an open loop of wire on an insulating former, or a metal ring that forms the antenna elements itself, where the diameter of the loop is a tenth of a wavelength or smaller at the target frequency. Such an antenna will be least sensitive to signals that are normal to its face and most responsive to those meeting edge-on.
This is caused by the phase output of the transmitting beacon. The phase changing phase causes a difference between the voltages induced on either side of the loop at any instant. Turning the loop face on will not induce any current flow. Turning the antenna to obtain minimum signal will establish two possible directions from which the signal could be emanating; the NULL is used, as small angular deflections of the loop aerial near its null positions produce larger changes in current than similar angular changes near the loops max positions. For this reason, a null position of the loop aerial is used. To resolve the two direction possibilities, a sense antenna is used, the sense aerial has no directional properties but has the same sensitivity as the loop aerial. By adding the steady signal from the sense aerial to the alternating signal from the loop signal as it rotates, there is now only one position as the loop rotates 360° at which there is zero current; this acts as a phase ref point, allowing the correct null point to be identified, thus removing the 180° ambiguity.
A dipole antenna exhibits similar properties, is the basis for the Yagi antenna, familiar as the common VHF or UHF television aerial. For much higher frequencies still, parabolic antennas can be used, which are directional, focusing received signals from a narrow angle to a receiving element at the centre. More sophisticated techniques such as phased arrays are used for accurate direction finding systems called goniometers such as are used in signals intelligence. A helicopter based DF system was designed by ESL Incorporated for the U. S. Government as early as 1972. Single-channel DF uses a multi-antenna array with a single channel radio receiver; this approach to DF offers some drawbacks. Since it only uses one receiver and lower power consumption are benefits. Without the ability to look at each antenna more complex operations need to occur at the antenna in order to present the signal to the receiver; the two main categories that a single channel DF algorithm falls into are amplitude comparison and phase comparison.
Some algorithms can be hybrids of the two. The pseudo-doppler technique is a p
British Aerospace 146
The British Aerospace 146 is a short-haul and regional airliner, manufactured in the United Kingdom by British Aerospace part of BAE Systems. Production ran from 1983 until 2002. Manufacture of an improved version known as the Avro RJ began in 1992. A further-improved version with new engines, the Avro RJX, was announced in 1997, but only two prototypes and one production aircraft were built before production ceased in 2001. With 387 aircraft produced, the Avro RJ/BAe 146 is the most successful British civil jet airliner programme; the BAe 146/Avro RJ is a high-wing cantilever monoplane with a T-tail. It has four turbofan engines mounted on pylons underneath the wings, has retractable tricycle landing gear; the aircraft has quiet operation, has been marketed under the name Whisperjet. It sees wide usage at city-based airports such as London City Airport. In its primary role, it serves as a regional jet, short-haul airliner, or regional airliner, while examples of the type are in use as private jets.
The BAe 146/Avro RJ is in wide use with several European-based carriers such as CityJet. The largest operator of the type, Swiss Global Air Lines, retired its last RJ100 in August 2017; the BAe 146 was produced in -200 and -300 models. The equivalent Avro RJ versions are designated RJ70, RJ85, RJ100; the freight-carrying version carries the designation "QT", a convertible passenger-or-freight model is designated as "QC". A "gravel kit" can be fitted to aircraft to enable operations from unprepared airstrips. In August 1973, Hawker Siddeley launched a new 70-seat regional airliner project, the HS.146, to fill the gap between turboprop-powered airliners such as the Hawker Siddeley HS.748 and the Fokker F.27 and small jet airliners such as the BAC One-Eleven and Boeing 737. The chosen configuration had a high wing and a T-tail to give good short-field performance, while the aircraft was to be powered by four 6,500 lbf thrust Avco Lycoming ALF 502H turbofan engines. There were several reasons. A major factor would have been that no manufacturer was producing a 13,000-lbf-thrust-class high-bypass ratio turbofan engine at the time.
The programme was launched with backing from the UK government, which agreed to contribute 50% of the development costs in return for a share of the revenues from each aircraft sold. In October 1974, all work on the project was halted as a result of the world economic downturn resulting from the 1973 oil crisis. Low-key development proceeded, in 1978, British Aerospace, Hawker Siddeley's corporate successor, relaunched the project. British Aerospace marketed the aircraft as a quiet, low-consumption, turbofan aircraft, which would be effective at replacing the previous generation of turboprop-powered feeder aircraft; the first order for the BAe 146 was placed by Líneas Aéreas Privadas Argentinas in June 1981. Prior to the first flight, British Aerospace had forecast that the smaller 146-100 would outsell the 146-200 variant. By 1981, a large assembly line had been completed at British Aerospace's Hatfield site, the first completed aircraft flew that year followed by two more prototypes. Initial flight results showed climb performance.
In 1982, British Aerospace stated that the sale of a total 250 aircraft was necessary for the venture to break even. The BAe 146 received its Certificate of Airworthiness on 8 February 1983. Upon its launch into service, it was hailed as being "the world's quietest jetliner". Early production aircraft were built at Hatfield, a de Havilland factory; the Avro RJ family of aircraft was assembled at the Avro International BAE Systems Regional Aircraft Centre, at Woodford Aerodrome in Greater Manchester, England. Production of various sections of the aircraft was carried out at different BAE plants; the rear fuselage section was manufactured at BAE Systems' former Avro site at Chadderton, Greater Manchester. The centre fuselage section was manufactured at the Filton BAE site; the vertical stabilizer came from Brough, the engine pylons were made at Prestwick. The nose section was manufactured at Hatfield, where the assembly line for the early aircraft was located; some manufacturing was subcontracted outside the UK.
Due to the sales performance of the BAe 146, British Aerospace announced a development project in early 1991 to produce a new variant of the type, powered by two turbofan engines instead of four, offered to airlines as a regional jet aircraft. Dubbed the new regional aircraft, other proposed alterations from the BAe 146 included the adoption of a new enlarged wing and a lengthened fuselage. In 1993, the upgraded Avro RJ series superseded the BAe 146. Changes included the replacement of the original Lycoming ALF 502 turbofan engines by higher-thrust LF 507 turbofan engines, which were housed in redesigned nacelles; the Avro RJ series featured a modernised cockpit with EFIS replacing the analogue ADI, HSI, engine instrumentation. An arrangement between British Aerospace and Khazanah Nasional would have opened an Avro RJ production line in Malaysia, but this deal collapsed in 1997. In 2000, British Aerospace announced that it was to replace the Avro RJ series with a further-improved Avro RJX series.
Production of the Avro RJ ended with the final four aircraft being delivered in late 2003. British Ae
According to the International Civil Aviation Organization, a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a natural surface. In January 1919, aviation pioneer Orville Wright underlined the need for "distinctly marked and prepared landing places, the preparing of the surface of reasonably flat ground an expensive undertaking there would be a continuous expense for the upkeep." Runways are named by a number between 01 and 36, the magnetic azimuth of the runway's heading in decadegrees. This heading differs from true north by the local magnetic declination. A runway numbered 09 points east, runway 18 is south, runway 27 points west and runway 36 points to the north; when taking off from or landing on runway 09, a plane is heading around 90°. A runway can be used in both directions, is named for each direction separately: e.g. "runway 15" in one direction is "runway 33" when used in the other. The two numbers differ by 18.
For clarity in radio communications, each digit in the runway name is pronounced individually: runway one-five, runway three-three, etc.. A leading zero, for example in "runway zero-six" or "runway zero-one-left", is included for all ICAO and some U. S. military airports. However, most U. S. civil aviation airports drop the leading zero. This includes some military airfields such as Cairns Army Airfield; this American anomaly may lead to inconsistencies in conversations between American pilots and controllers in other countries. It is common in a country such as Canada for a controller to clear an incoming American aircraft to, for example, runway 04, the pilot read back the clearance as runway 4. In flight simulation programs those of American origin might apply U. S. usage to airports around the world. For example, runway 05 at Halifax will appear on the program as the single digit 5 rather than 05. If there is more than one runway pointing in the same direction, each runway is identified by appending left and right to the number to identify its position — for example, runways one-five-left, one-five-center, one-five-right.
Runway zero-three-left becomes runway two-one-right. In some countries, regulations mandate that where parallel runways are too close to each other, only one may be used at a time under certain conditions. At large airports with four or more parallel runways some runway identifiers are shifted by 1 to avoid the ambiguity that would result with more than three parallel runways. For example, in Los Angeles, this system results in runways 6L, 6R, 7L, 7R though all four runways are parallel at 69°. At Dallas/Fort Worth International Airport, there are five parallel runways, named 17L, 17C, 17R, 18L, 18R, all oriented at a heading of 175.4°. An airport with only three parallel runways may use different runway identifiers, such as when a third parallel runway was opened at Phoenix Sky Harbor International Airport in 2000 to the south of existing 8R/26L — rather than confusingly becoming the "new" 8R/26L it was instead designated 7R/25L, with the former 8R/26L becoming 7L/25R and 8L/26R becoming 8/26.
Runway designations may change over time because Earth's magnetic lines drift on the surface and the magnetic direction changes. Depending on the airport location and how much drift occurs, it may be necessary to change the runway designation; as runways are designated with headings rounded to the nearest 10°, this affects some runways sooner than others. For example, if the magnetic heading of a runway is 233°, it is designated Runway 23. If the magnetic heading changes downwards by 5 degrees to 228°, the runway remains Runway 23. If on the other hand the original magnetic heading was 226°, the heading decreased by only 2 degrees to 224°, the runway becomes Runway 22; because magnetic drift itself is slow, runway designation changes are uncommon, not welcomed, as they require an accompanying change in aeronautical charts and descriptive documents. When runway designations do change at major airports, it is changed at night as taxiway signs need to be changed and the huge numbers at each end of the runway need to be repainted to the new runway designators.
In July 2009 for example, London Stansted Airport in the United Kingdom changed its runway designations from 05/23 to 04/22 during the night. For fixed-wing aircraft it is advantageous to perform takeoffs and landings into the wind to reduce takeoff or landing roll and reduce the ground speed needed to attain flying speed. Larger airports have several runways in different directions, so that one can be selected, most nearly aligned with the wind. Airports with one runway are constructed to be aligned with the prevailing wind. Compiling a wind rose is in fact one of the preliminary steps taken in constructing airport runways. Note that wind direction is given as the direction the wind is coming from: a plane taking off from runway 09 faces east, into an "east wind" blowing from 090°. Runway dimensions vary from as small as 245 m long and 8 m wide in s
Battle of Singapore
The Battle of Singapore known as the Fall of Singapore, was fought in the South-East Asian theatre of World War II when the Empire of Japan invaded the British stronghold of Singapore—nicknamed the "Gibraltar of the East". Singapore was the major British military base in South-East Asia and was the key to British imperial interwar defence planning for South-East Asia and the South-West Pacific; the fighting in Singapore lasted from 8 to 15 February 1942, after the two months during which Japanese forces had advanced down the Malayan Peninsula. The campaign, including the final battle, was a decisive Japanese victory, resulting in the Japanese capture of Singapore and the largest British surrender in history. About 80,000 British and Australian troops in Singapore became prisoners of war, joining 50,000 taken by the Japanese in the earlier Malayan Campaign; the British prime minister, Winston Churchill, called it the "worst disaster" in British military history. During 1940 and 1941, the Allies had imposed a trade embargo on Japan in response to its continued campaigns in China and its occupation of French Indochina.
The basic plan for taking Singapore was worked out in July 1940. Intelligence gained in late 1940 – early 1941 did not alter the basic plan, but confirmed it in the minds of Japanese decision makers. On 11 November 1940, the German raider Atlantis captured the British steamer Automedon in the Indian Ocean, carrying papers meant for Air Marshal Sir Robert Brooke-Popham, the British commander in the Far East, which included much information about the weakness of the Singapore base. In December 1940, the Germans handed over copies of the papers to the Japanese; the Japanese had broken the British Army's codes and in January 1941, the Second Department of the Imperial Army had interpreted and read a message from Singapore to London complaining in much detail about the weak state of "Fortress Singapore", a message, so frank in its admission of weakness that the Japanese at first suspected it was a British plant, believing that no officer would be so open in admitting weaknesses to his superiors, only believed it was genuine after cross-checking the message with the Automedon papers.
As Japan's oil reserves were depleted by the ongoing military operations in China as well as industrial consumption, in the latter half of 1941, the Japanese began preparing a military response to secure vital resources if diplomatic efforts to resolve the situation failed. As a part of this process, the Japanese planners determined a broad scheme of manoeuvre that incorporated simultaneous attacks on the territories of Britain, The Netherlands and the United States; this would see landings in Malaya and Hong Kong as part of a general move south to secure Singapore, connected to Malaya by the Johor–Singapore Causeway, an invasion of the oil-rich area of Borneo and Java in the Dutch East Indies. In addition, strikes would be made against the United States naval fleet at Pearl Harbor, as well as landings in the Philippines, attacks on Guam, Wake Island and the Gilbert Islands. Following these attacks, a period of consolidation was planned, after which the Japanese planners intended to build up the defences of the territory, captured by establishing a strong perimeter around it stretching from the India–Burma frontier through to Wake Island, traversing Malaya, the Dutch East Indies, New Guinea and New Britain, the Bismarck Archipelago, the Marshall and Gilbert Islands.
This perimeter would be used to block Allied attempts to regain the lost territory and defeat their will to fight. The Japanese 25th Army invaded from Indochina, moving into northern Malaya and Thailand by amphibious assault on 8 December 1941; this was simultaneous with the Japanese attack on Pearl Harbor which precipitated the United States entry into the war. Thailand resisted, but soon had to yield; the Japanese proceeded overland across the Thai–Malayan border to attack Malaya. At this time, the Japanese began bombing strategic sites in Singapore; the Japanese 25th Army was resisted in northern Malaya by III Corps of the British Indian Army. Although the 25th Army was outnumbered by Allied forces in Malaya and Singapore, the Allies did not take the initiative with their forces, while Japanese commanders concentrated their forces; the Japanese were superior in close air support, armour, co-ordination and experience. While conventional British military thinking was that the Japanese forces were inferior, characterised the Malayan jungles as "impassable", the Japanese were able to use it to their advantage to outflank hastily established defensive lines.
Prior to the Battle of Singapore the most resistance was met at the Battle of Muar, which involved the Australian 8th Division and the Indian 45th Brigade, as the British troops left in the city of Singapore were garrison troops. At the start of the campaign, the Allied forces had only 164 first-line aircraft on hand in Malaya and Singapore, the only fighter type was the obsolete Brewster 339E Buffalo; these aircraft were operated by two Royal Australian Air Force, two Royal Air Force, one Royal New Zealand Air Force squadron. Major shortcomings included a slow rate of climb and the aircraft's fuel system which required the pilot to hand pump fuel if flying above 6,000 feet. In contrast, the Imperial Japanese Army Air Force was more numerous and better trained than the second-hand assortment of untrained pilots and inferior allied equipment remaining in Malaya and Singapore, their fighter aircraft were superior to the Allied fighters, which helped the Japanese to gain air supremacy. Although outnumbered and outclassed, the Buffalos were able to provide some resistance
Asphalt known as bitumen, is a sticky and viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, is classed as a pitch. Before the 20th century, the term asphaltum was used; the word is derived from the Ancient Greek ἄσφαλτος ásphaltos. The primary use of asphalt is in road construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete, its other main uses are for bituminous waterproofing products, including production of roofing felt and for sealing flat roofs. The terms "asphalt" and "bitumen" are used interchangeably to mean both natural and manufactured forms of the substance. In American English, "asphalt" is used for a refined residue from the distillation process of selected crude oils. Outside the United States, the product is called "bitumen", geologists worldwide prefer the term for the occurring variety. Common colloquial usage refers to various forms of asphalt as "tar", as in the name of the La Brea Tar Pits.
Occurring asphalt is sometimes specified by the term "crude bitumen". Its viscosity is similar to that of cold molasses while the material obtained from the fractional distillation of crude oil boiling at 525 °C is sometimes referred to as "refined bitumen"; the Canadian province of Alberta has most of the world's reserves of natural asphalt in the Athabasca oil sands, which cover 142,000 square kilometres, an area larger than England. The word "asphalt" is derived from the late Middle English, in turn from French asphalte, based on Late Latin asphalton, the latinisation of the Greek ἄσφαλτος, a word meaning "asphalt/bitumen/pitch", which derives from ἀ-, "without" and σφάλλω, "make fall"; the first use of asphalt by the ancients was in the nature of a cement for securing or joining together various objects, it thus seems that the name itself was expressive of this application. Herodotus mentioned that bitumen was brought to Babylon to build its gigantic fortification wall. From the Greek, the word passed into late Latin, thence into French and English.
In French, the term asphalte is used for occurring asphalt-soaked limestone deposits, for specialised manufactured products with fewer voids or greater bitumen content than the "asphaltic concrete" used to pave roads. The expression "bitumen" originated in the Sanskrit words jatu, meaning "pitch", jatu-krit, meaning "pitch creating" or "pitch producing"; the Latin equivalent is claimed by some to be gwitu-men, by others, subsequently shortened to bitumen, thence passing via French into English. From the same root is derived the Anglo-Saxon word cwidu, the German word Kitt and the old Norse word kvada. In British English, "bitumen" is used instead of "asphalt"; the word "asphalt" is instead used to refer to asphalt concrete, a mixture of construction aggregate and asphalt itself. Bitumen mixed with clay was called "asphaltum", but the term is less used today. In Australian English, the word "asphalt" is used to describe a mix of construction aggregate. "Bitumen" refers to the liquid derived from the heavy-residues from crude oil distillation.
In American English, "asphalt" is equivalent to the British "bitumen". However, "asphalt" is commonly used as a shortened form of "asphalt concrete". In Canadian English, the word "bitumen" is used to refer to the vast Canadian deposits of heavy crude oil, while "asphalt" is used for the oil refinery product. Diluted bitumen is known as "dilbit" in the Canadian petroleum industry, while bitumen "upgraded" to synthetic crude oil is known as "syncrude", syncrude blended with bitumen is called "synbit"."Bitumen" is still the preferred geological term for occurring deposits of the solid or semi-solid form of petroleum. "Bituminous rock" is a form of sandstone impregnated with bitumen. The oil sands of Alberta, Canada are a similar material. Neither of the terms "asphalt" or "bitumen" should be confused with coal tars. Tar is the thick liquid product of the dry distillation and pyrolysis of organic hydrocarbons sourced from vegetation masses, whether fossilized as with coal, or freshly harvested; the majority of bitumen, on the other hand, was formed when vast quantities of organic animal materials were deposited by water and buried hundreds of metres deep at the diagenetic point, where the disorganized fatty hydrocarbon molecules joined together in long chains in the absence of oxygen.
Bitumen occurs as a solid or viscous liquid. It may be mixed in with coal deposits. Bitumen, coal using the Bergius process, can be refined into petrols such as gasoline, bitumen may be distilled into tar, not the other way around; the components of asphalt include four main classes of compounds: Naphthene aromatics, consisting of hydrogenated polycyclic aromatic compounds Polar aromatics, consisting of high molecular weight phenols and carboxylic acids produced by partial oxidation of the material Saturated hydrocarbons. Most natural bitumens a
The Boeing 757 is a mid-size, narrow-body twin-engine airliner, designed and built by Boeing Commercial Airplanes. It is the manufacturer's largest single-aisle passenger aircraft and was produced from 1981 to 2004; the twinjet has a two-crew member glass cockpit, turbofan engines of sufficient power to allow takeoffs from short runways and higher altitudes, a conventional tail and, for reduced aerodynamic drag, a supercritical wing design. Intended to replace the smaller three-engine 727 on short and medium routes, the 757 can carry 200 to 295 passengers for a maximum of 3,150 to 4,100 nautical miles, depending on variant; the 757 was designed concurrently with a wide-body twinjet, the 767, owing to shared features, pilots can obtain a common type rating that allows them to operate both aircraft. The 757 was produced in two fuselage lengths; the original 757-200 entered service in 1983. The stretched 757-300, the longest narrow-body twinjet produced, began service in 1999. Passenger 757-200s have been modified to special freighter specification for cargo use, while military derivatives include the C-32 transport, VIP carriers, other multi-purpose aircraft.
Private and government operators have customized the 757 for research and transport roles. All 757s are powered by Rolls-Royce Pratt & Whitney PW2000 series turbofans. Eastern Air Lines and British Airways placed the 757 in commercial service in 1983; the narrow-body twinjet succeeded earlier single-aisle airliners, became used for short and mid-range domestic routes, shuttle services, transcontinental U. S. flights. After regulators granted approval for extended flights over water in 1986, airlines began using the aircraft for intercontinental routes. Major customers for the 757 included U. S. mainline carriers, European charter airlines, cargo companies. The airliner has recorded eight hull-loss accidents, including seven fatal crashes, as of September 2015. Production of the 757 ended in October 2004; the 757-200 was by far the most popular model, with 913 built. Diminished sales amid an airline industry trend toward smaller jetliners led Boeing to end production without a direct replacement, in favor of the 737 family.
The last 757 was delivered to Shanghai Airlines in November 2005. In July 2017, 666 of the narrow-body twinjets were in airline service. In the early 1970s, following the launch of the wide-body 747, Boeing began considering further developments of its narrow-body 727 trijet. Designed for short and medium length routes, the three-engined 727 was the best-selling commercial jetliner of the 1960s and a mainstay of the U. S. domestic airline market. Studies focused on improving the most successful 727 variant. Two approaches were considered: a stretched 727-300, an all-new aircraft code-named 7N7; the former was a cheaper derivative using the 727's existing technology and tail-mounted engine configuration, while the latter was a twin-engine aircraft which made use of new materials and improvements to propulsion technology which had become available in the civil aerospace industry. United Airlines provided input for the proposed 727-300, which Boeing was poised to launch in late 1975, but lost interest after examining development studies for the 7N7.
Although the 727-300 was offered to Braniff International Airways and other carriers, customer interest remained insufficient for further development. Instead, airlines were drawn to the high-bypass-ratio turbofan engines, new flight deck technologies, lower weight, improved aerodynamics, reduced operating cost promised by the 7N7; these features were included in a parallel development effort for a new mid-size wide-body airliner, code-named 7X7, which became the 767. Work on both proposals accelerated as a result of the airline industry upturn in the late 1970s. By 1978, development studies focused on two variants: a 7N7-100 with seating for 160, a 7N7-200 with room for over 180 seats. New features included a redesigned wing, under-wing engines, lighter materials, while the forward fuselage, cockpit layout, T-tail configuration were retained from the 727. Boeing planned for the aircraft to offer the lowest fuel burn per passenger-kilometer of any narrow-body airliner. On August 31, 1978, Eastern Air Lines and British Airways became the first carriers to publicly commit to the 7N7 when they announced launch orders totaling 40 aircraft for the 7N7-200 version.
These orders were signed in March 1979, when Boeing designated the aircraft as the 757. The shorter 757-100 was dropped; the 757 was intended to be more capable and more efficient than the preceding 727. The focus on fuel efficiency reflected airline concerns over operating costs, which had grown amid rising oil prices during the Yom Kippur War of 1973. Design targets included a 20 percent reduction in fuel consumption from new engines, plus an additional 10 percent from aerodynamic improvements, versus preceding aircraft. Lighter materials and new wings were expected to improve efficiency; the maximum take-off weight was set at 220,000 pounds, 10,000 pounds more than the 727. The 757's higher thrust-to-weight ratio allowed it to take off from short runways and serve airports in hot and high climates, offering better takeoff performance than that offered by competing aircraft. Competitors needed longer takeoff runs at airports at higher elevations, with higher ambient temperatures and thinner air.