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58-433: This unorthodox design, first flying on 28 October 1949, was fitted with three General Electric J47 engines - an unusual number for a combat aircraft - two underneath the forward fuselage in pods, and one at the extreme tail with the intake at the base of the tailfin. The innovative, variable incidence wings, swept at 35° and with 6° anhedral , were equipped with leading edge slats and full-width flaps. Spoilers gave most of

116-416: A i r + m ˙ f ) V j − m ˙ a i r V {\displaystyle F_{N}=({\dot {m}}_{air}+{\dot {m}}_{f})V_{j}-{\dot {m}}_{air}V} where: If the speed of the jet is equal to sonic velocity the nozzle is said to be " choked ". If the nozzle is choked, the pressure at the nozzle exit plane

174-557: A compressor, a combustion chamber, and a turbine (that drives the compressor). The compressed air from the compressor is heated by burning fuel in the combustion chamber and then allowed to expand through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is accelerated to high speed to provide thrust. Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany , developed

232-539: A development of the gas turbine engine where an additional turbine is used to drive a rotating output shaft. These are common in helicopters and hovercraft. Turbojets were widely used for early supersonic fighters , up to and including many third generation fighters , with the MiG-25 being the latest turbojet-powered fighter developed. As most fighters spend little time traveling supersonically, fourth-generation fighters (as well as some late third-generation fighters like

290-585: A gas turbine to power an aircraft was filed in 1921 by Frenchman Maxime Guillaume . His engine was to be an axial-flow turbojet, but was never constructed, as it would have required considerable advances over the state of the art in compressors. In 1928, British RAF College Cranwell cadet Frank Whittle formally submitted his ideas for a turbojet to his superiors. In October 1929 he developed his ideas further. On 16 January 1930 in England, Whittle submitted his first patent (granted in 1932). The patent showed

348-542: A landing field, lengthening flights. The increase in reliability that came with the turbojet enabled three- and two-engine designs, and more direct long-distance flights. High-temperature alloys were a reverse salient , a key technology that dragged progress on jet engines. Non-UK jet engines built in the 1930s and 1940s had to be overhauled every 10 or 20 hours due to creep failure and other types of damage to blades. British engines, however, utilised Nimonic alloys which allowed extended use without overhaul, engines such as

406-413: A maximum load of 10,400 lb (4,700 kg), although the specified basic mission required only a 4,000 lb (1,814 kg) bombload. Eight 20 mm cannon mounted in the nose would have been installed in production aircraft. Crew was a pilot under a "fighter"-type bubble canopy and a Short-range navigation and bombing system (SHORAN) operator/navigator in a compartment located lower than and to

464-660: A night intruder/bomber to replace the Douglas A-26 Invader . The XB-51 was entered, as well as the Avro Canada CF-100 and English Electric Canberra ; the XB-51 and Canberra emerged from these as the favorites. Test flights showed the XB-51 to be highly maneuverable at low altitudes and substantially faster than the Canberra and faster than most fighter aircraft of the era. However, the XB-51's endurance

522-459: A second generation SST engine using the 593 core were done more than three years before Concorde entered service. They evaluated bypass engines with bypass ratios between 0.1 and 1.0 to give improved take-off and cruising performance. Nevertheless, the 593 met all the requirements of the Concorde programme. Estimates made in 1964 for the Concorde design at Mach 2.2 showed the penalty in range for

580-411: A significant impact on commercial aviation . Aside from giving faster flight speeds turbojets had greater reliability than piston engines, with some models demonstrating dispatch reliability rating in excess of 99.9%. Pre-jet commercial aircraft were designed with as many as four engines in part because of concerns over in-flight failures. Overseas flight paths were plotted to keep planes within an hour of

638-405: A small helicopter engine compressor rotates around 50,000 RPM. Turbojets supply bleed air from the compressor to the aircraft for the operation of various sub-systems. Examples include the environmental control system , anti-icing , and fuel tank pressurization. The engine itself needs air at various pressures and flow rates to keep it running. This air comes from the compressor, and without it,

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696-513: A turbojet application, where the output from the gas turbine is used in a propelling nozzle, raising the turbine temperature increases the jet velocity. At normal subsonic speeds this reduces the propulsive efficiency, giving an overall loss, as reflected by the higher fuel consumption, or SFC. However, for supersonic aircraft this can be beneficial, and is part of the reason why the Concorde employed turbojets. Turbojet systems are complex systems therefore to secure optimal function of such system, there

754-512: A turbojet engine is always subsonic, regardless of the speed of the aircraft itself. The intake has to supply air to the engine with an acceptably small variation in pressure (known as distortion) and having lost as little energy as possible on the way (known as pressure recovery). The ram pressure rise in the intake is the inlet's contribution to the propulsion system's overall pressure ratio and thermal efficiency . The intake gains prominence at high speeds when it generates more compression than

812-494: A turbojet is high enough at higher thrust settings to cause the nozzle to choke. If, however, a convergent-divergent de Laval nozzle is fitted, the divergent (increasing flow area) section allows the gases to reach supersonic velocity within the divergent section. Additional thrust is generated by the higher resulting exhaust velocity. Thrust was most commonly increased in turbojets with water/methanol injection or afterburning . Some engines used both methods. Liquid injection

870-487: 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"). Whittle later concentrated on the simpler centrifugal compressor only, for a variety of practical reasons. A Whittle engine was the first turbojet to run, the Power Jets WU , on 12 April 1937. It

928-413: Is a component of a turbojet used to divert air into the intake, in front of the accessory drive and to house the starter motor. An intake, or tube, is needed in front of the compressor to help direct the incoming air smoothly into the rotating compressor blades. Older engines had stationary vanes in front of the moving blades. These vanes also helped to direct the air onto the blades. The air flowing into

986-523: Is greater than atmospheric pressure, and extra terms must be added to the above equation to account for the pressure thrust. The rate of flow of fuel entering the engine is very small compared with the rate of flow of air. If the contribution of fuel to the nozzle gross thrust is ignored, the net thrust is: F N = m ˙ a i r ( V j − V ) {\displaystyle F_{N}={\dot {m}}_{air}(V_{j}-V)} The speed of

1044-573: Is modelled approximately by the Brayton cycle . The efficiency of a gas turbine is increased by raising the overall pressure ratio, requiring higher-temperature compressor materials, and raising the turbine entry temperature, requiring better turbine materials and/or improved vane/blade cooling. It is also increased by reducing the losses as the flow progresses from the intake to the propelling nozzle. These losses are quantified by compressor and turbine efficiencies and ducting pressure losses. When used in

1102-621: The F-111 and Hawker Siddeley Harrier ) and subsequent designs are powered by the more efficient low-bypass turbofans and use afterburners to raise exhaust speed for bursts of supersonic travel. Turbojets were used on Concorde and the longer-range versions of the Tu-144 which were required to spend a long period travelling supersonically. Turbojets are still common in medium range cruise missiles , due to their high exhaust speed, small frontal area, and relative simplicity. The first patent for using

1160-704: The Gloster Meteor , entered service in 1944, towards the end of World War II , the Me 262 in April and the Gloster Meteor in July. Only about 15 Meteor saw WW2 action but up to 1400 Me 262s were produced, with 300 entering combat, delivering the first ground attacks and air combat victories of jet planes. Air is drawn into the rotating compressor via the intake and is compressed to a higher pressure before entering

1218-588: The Heinkel HeS 3 ), or an axial compressor (as in the Junkers Jumo 004 ) which gave a smaller diameter, although longer, engine. By replacing the propeller used on piston engines with a high speed jet of exhaust, higher aircraft speeds were attainable. One of the last applications for a turbojet engine was Concorde which used the Olympus 593 engine. However, joint studies by Rolls-Royce and Snecma for

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1276-630: The Lockland facility (renamed to the Evendale facility) utilized vertical engine assembly to ensure compressor rotor balance and stability. The technological jump provided by the engine led to it becoming the most produced jet engine in aviation history, and established GE Aviation as a worldwide leader in jet propulsion. Overhaul life for the J47 ranged from 15 hours (in 1948) to a theoretical 1,200 hours (625 achievable in practice) in 1956. For example,

1334-527: The North American XB-70 Valkyrie , each feeding three engines with an intake airflow of about 800 pounds per second (360 kg/s). The turbine rotates the compressor at high speed, adding energy to the airflow while squeezing (compressing) it into a smaller space. Compressing the air increases its pressure and temperature. The smaller the compressor, the faster it turns. The (large) GE90-115B fan rotates at about 2,500 RPM, while

1392-488: The Rolls-Royce Welland and Rolls-Royce Derwent , and by 1949 the de Havilland Goblin , being type tested for 500 hours without maintenance. It was not until the 1950s that superalloy technology allowed other countries to produce economically practical engines. Early German turbojets had severe limitations on the amount of running they could do due to the lack of suitable high temperature materials for

1450-424: The Tu-144 , also used afterburners as does Scaled Composites White Knight , a carrier aircraft for the experimental SpaceShipOne suborbital spacecraft. Reheat was flight-trialled in 1944 on the W.2/700 engines in a Gloster Meteor I . The net thrust F N {\displaystyle F_{N}\;} of a turbojet is given by: F N = ( m ˙

1508-641: The X211 . The design based on the J47 became the X39 program. This system consisted of two modified J47 engines which, instead of combusting jet fuel, received their heated, compressed air from a heat exchanger that was part of the Heat Transfer Reactor Experiment (HTRE) reactor. The X-39 was successfully operated in conjunction with three different reactors, the HTRE-1, HTRE-2 and HTRE-3. Had

1566-608: The compressor , allowing fighter jets equipped with the engine to function at high altitudes, and in cold conditions such as the top of Mount Washington in New Hampshire's White Mountains , where the engine was first tested. The engine featured an electronically controlled afterburner , a system that dumped additional fuel into the combustor pipe 'behind' the engine, reheating the exhaust and producing significantly more thrust, although with greatly reduced efficiency and high fuel burn rates. The engine production process in

1624-678: The Air National Guard retired the jet-boosted KC-97Js. Despite this, these engines are still extensively utilized in F-86 Sabre jets owned by civilians, making them a common sight at air shows. The J47 design used experience from the TG-180/J35 engine which was described by Flight magazine in 1948 as the most widely used American-conceived turbojet. The turbojet featured a revolutionary anti-icing system where hollow frame struts allowed heated airflow to pass through from

1682-611: The B-57 – never reached the prototype stage, mainly because the many changes would have taken too long to implement and test, before it could be put into production. Flights by the XB-51 prototype, 46-685 , continued, for general research purposes, following the project's official cancellation by the USAF. A second prototype, 46-686 , which first flew in 1950, crashed during low-level aerobatics on 9 May 1952, killing pilot Major Neil H. Lathrop. 46-685 continued to fly, including an appearance in

1740-539: The J47-GE-23 was rated to run 225 hours time between overhauls . As installed on the F-86F, it experienced one in-flight shutdown every 33,000 hours in 1955 and 1956. Ground-based vehicles that used the engine include: In the 1950s, interest in the development of nuclear-powered aircraft led GE to experiment with two nuclear-powered gas turbine designs, one based on the J47, and another new and much larger engine called

1798-429: The XB-51 was not selected for procurement, it was decided that Martin would build 250 Canberras under license, under the designation B-57 . Furthermore, Martin's rotating bomb bay would be incorporated into production variants of the B-57. A "Super Canberra", incorporating other XB-51 features, such as swept wings and tail-planes, was also proposed. This aircraft – although it promised much better speed and performance than

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1856-464: The aircraft decreases the efficiency of the engine because it has been compressed, but then does not contribute to producing thrust. Compressor types used in turbojets were typically axial or centrifugal. Early turbojet compressors had low pressure ratios up to about 5:1. Aerodynamic improvements including splitting the compressor into two separately rotating parts, incorporating variable blade angles for entry guide vanes and stators, and bleeding air from

1914-410: The combustion chamber. Fuel is mixed with the compressed air and burns in the combustor. The combustion products leave the combustor and expand through the turbine where power is extracted to drive the compressor. The turbine exit gases still contain considerable energy that is converted in the propelling nozzle to a high speed jet. The first turbojets, used either a centrifugal compressor (as in

1972-432: The combustor and pass through to the turbine in a continuous flowing process with no pressure build-up. Instead, a small pressure loss occurs in the combustor. The fuel-air mixture can only burn in slow-moving air, so an area of reverse flow is maintained by the fuel nozzles for the approximately stoichiometric burning in the primary zone. Further compressed air is introduced which completes the combustion process and reduces

2030-421: The compressor enabled later turbojets to have overall pressure ratios of 15:1 or more. After leaving the compressor, the air enters the combustion chamber. The burning process in the combustor is significantly different from that in a piston engine . In a piston engine, the burning gases are confined to a small volume, and as the fuel burns, the pressure increases. In a turbojet, the air and fuel mixture burn in

2088-401: The compressor is passed through these to keep the metal temperature within limits. The remaining stages do not need cooling. In the first stage, the turbine is largely an impulse turbine (similar to a pelton wheel ) and rotates because of the impact of the hot gas stream. Later stages are convergent ducts that accelerate the gas. Energy is transferred into the shaft through momentum exchange in

2146-536: The compressor stage. Well-known examples are the Concorde and Lockheed SR-71 Blackbird propulsion systems where the intake and engine contributions to the total compression were 63%/8% at Mach 2 and 54%/17% at Mach 3+. Intakes have ranged from "zero-length" on the Pratt & Whitney TF33 turbofan installation in the Lockheed C-141 Starlifter , to the twin 65 feet (20 m) long, intakes on

2204-420: The concept independently into practical engines during the late 1930s. Turbojets have poor efficiency at low vehicle speeds, which limits their usefulness in vehicles other than aircraft. Turbojet engines have been used in isolated cases to power vehicles other than aircraft, typically for attempts on land speed records . Where vehicles are "turbine-powered", this is more commonly by use of a turboshaft engine,

2262-696: The film Toward the Unknown as the "Gilbert XF-120" fighter. The surviving prototype was en route to Eglin AFB to shoot additional footage when it crashed during takeoff, following a refueling stop in El Paso, Texas, on 25 March 1956. Data from U.S.Standard Aircraft Characteristics General characteristics Performance Armament Aircraft of comparable role, configuration, and era Related lists General Electric J47 The General Electric J47 turbojet (GE company designation TG-190)

2320-550: The fuselage, similar to the Boeing B-47 Stratojet , with outrigger wheels at the wingtips (originally proved on a modified Martin B-26 Marauder named "Middle River Stump Jumper"). The XB-51 was a large but aerodynamically "clean" design which incorporated nearly all major systems internally. The aircraft was fitted with a rotating bomb bay , a Martin trademark; bombs could also be carried externally up to

2378-475: The high-temperature materials used in their turbosuperchargers during World War II. Water injection was a common method used to increase thrust, usually during takeoff, in early turbojets that were thrust-limited by their allowable turbine entry temperature. The water increased thrust at the temperature limit, but prevented complete combustion, often leaving a very visible smoke trail. Allowable turbine entry temperatures have increased steadily over time both with

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2436-441: The introduction of superior alloys and coatings, and with the introduction and progressive effectiveness of blade cooling designs. On early engines, the turbine temperature limit had to be monitored, and avoided, by the pilot, typically during starting and at maximum thrust settings. Automatic temperature limiting was introduced to reduce pilot workload and reduce the likelihood of turbine damage due to over-temperature. A nose bullet

2494-401: The jet V j {\displaystyle V_{j}\;} must exceed the true airspeed of the aircraft V {\displaystyle V\;} if there is to be a net forward thrust on the airframe. The speed V j {\displaystyle V_{j}\;} can be calculated thermodynamically based on adiabatic expansion . The operation of a turbojet

2552-402: The opposite way to energy transfer in the compressor. The power developed by the turbine drives the compressor and accessories, like fuel, oil, and hydraulic pumps that are driven by the accessory gearbox. After the turbine, the gases expand through the exhaust nozzle producing a high velocity jet. In a convergent nozzle, the ducting narrows progressively to a throat. The nozzle pressure ratio on

2610-416: The program not been cancelled, these engines would have been used to power the proposed Convair X-6 . Data from Related development Comparable engines Related lists Turbojet The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle . The gas turbine has an air inlet which includes inlet guide vanes,

2668-483: The rear of the cockpit (only a small observation window was provided). Both crew members were provided with a pressurized, air conditioned environment, equipped with upward-firing ejection seats. The XB-51 was the first Martin aircraft equipped with ejection seats, these being of their own design. In 1950, the United States Air Force issued a new requirement based on early Korean War experience for

2726-459: The roll control and undersized ailerons provided feel for the pilot. The combination of variable incidence and slotted flaps gave a shorter takeoff run. Four 954 lb (4.24 kN) thrust Rocket-Assisted Take Off (RATO) bottles with a 14-second burn duration could be fitted to the rear fuselage to improve takeoff performance. Spectacular launches were a feature of later test flights. The main landing gear consisted of dual wheel sets in tandem in

2784-468: The supersonic airliner, in terms of miles per gallon, compared to subsonic airliners at Mach 0.85 (Boeing 707, DC-8) was relatively small. This is because the large increase in drag is largely compensated by an increase in powerplant efficiency (the engine efficiency is increased by the ram pressure rise which adds to the compressor pressure rise, the higher aircraft speed approaches the exhaust jet speed increasing propulsive efficiency). Turbojet engines had

2842-446: The temperature of the combustion products to a level which the turbine can accept. Less than 25% of the air is typically used for combustion, as an overall lean mixture is required to keep within the turbine temperature limits. Hot gases leaving the combustor expand through the turbine. Typical materials for turbines include inconel and Nimonic . The hottest turbine vanes and blades in an engine have internal cooling passages. Air from

2900-548: The thrust from a turbojet engine. It was flown by test pilot Erich Warsitz . The Gloster E.28/39 , (also referred to as the "Gloster Whittle", "Gloster Pioneer", or "Gloster G.40") made the first British jet-engined flight in 1941. It was designed to test the Whittle jet engine in flight, and led to the development of the Gloster Meteor. The first two operational turbojet aircraft, the Messerschmitt Me 262 and then

2958-412: The turbines would overheat, the lubricating oil would leak from the bearing cavities, the rotor thrust bearings would skid or be overloaded, and ice would form on the nose cone. The air from the compressor, called secondary air, is used for turbine cooling, bearing cavity sealing, anti-icing, and ensuring that the rotor axial load on its thrust bearing will not wear it out prematurely. Supplying bleed air to

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3016-471: The turbines. British engines such as the Rolls-Royce Welland used better materials giving improved durability. The Welland was type-certified for 80 hours initially, later extended to 150 hours between overhauls, as a result of an extended 500-hour run being achieved in tests. General Electric in the United States was in a good position to enter the jet engine business due to its experience with

3074-545: Was developed by General Electric from its earlier J35 . It first flew in May 1948. The J47 was the first axial-flow turbojet approved for commercial use in the United States. It was used in many types of aircraft, and more than 30,000 were manufactured before production ceased in 1956. It saw continued service in the US military until 1978. Packard built 3,025 of the engines under license. The J47's greatest advantage, as advertised,

3132-499: Was its array of features which were unavailable and unprecedented in any other engine. It was advertised as an 'all-weather engine' due to its anti-icing systems which allowed it to perform at high altitudes and extreme temperatures where other aircraft's performance suffered. Its development began without an explicit need for it, although this design was quickly purchased by the military for its many potential benefits. In 1978, J47s were formally withdrawn from active military duty when

3190-424: Was liquid-fuelled. Whittle's team experienced near-panic during the first start attempts when the engine accelerated out of control to a relatively high speed despite the fuel supply being cut off. It was subsequently found that fuel had leaked into the combustion chamber during pre-start motoring checks and accumulated in pools, so the engine would not stop accelerating until all the leaked fuel had burned off. Whittle

3248-451: Was significantly lower than that of the Canberra and this factor was decisive in its cancellation. In addition, a load limiting factor of only 3.67  g (36 m/s) meant that the general strength of the airframe was relatively low and would prevent tight turns while fully loaded. Additionally, the tandem main gear plus outriggers of the XB-51 were thought unsuitable for the requirement to fly from emergency forward airfields . While

3306-640: Was tested on the Power Jets W.1 in 1941 initially using ammonia before changing to water and then water-methanol. A system to trial the technique in the Gloster E.28/39 was devised but never fitted. An afterburner or "reheat jetpipe" is a combustion chamber added to reheat the turbine exhaust gases. The fuel consumption is very high, typically four times that of the main engine. Afterburners are used almost exclusively on supersonic aircraft , most being military aircraft. Two supersonic airliners, Concorde and

3364-485: Was unable to interest the government in his invention, and development continued at a slow pace. In Germany, Hans von Ohain patented a similar engine in 1935. His design, an axial-flow engine, as opposed to Whittle's centrifugal flow engine, was eventually adopted by most manufacturers by the 1950s. On 27 August 1939 the Heinkel He 178 , powered by von Ohain's design, became the world's first aircraft to fly using

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