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67-441: The JT8D is an axial-flow front turbofan engine incorporating a two-spool design. There are two coaxially-mounted independent rotating assemblies: one rotating assembly for the low pressure compressor (LPC) which consists of the first six stages (i.e. six pairs of rotating and stator blades, including the first two stages which are for the bypass turbofan), driven by the second (downstream) turbine (which consists of three stages); and

134-402: A polytropic efficiency in the region of 90–95%. To achieve different pressure ratios, axial compressors are designed with different numbers of stages and rotational speeds. As a rule of thumb we can assume that each stage in a given compressor has the same temperature rise (Delta T). Therefore, at the entry, temperature (Tstage) to each stage must increase progressively through the compressor and

201-500: A $ 1.2–1.4 billion development in 7–8 years. Aerion received 50 letters-of-intent before enlarging the design as the Aerion AS2 in 2014. Powered by two Pratt & Whitney JT8D -219 engines, the $ 80 million aircraft was to transport 8–12 passengers up to Mach 1.6 and up to 4,000 nmi (7,400 km). Aerion abruptly announced on May 21, 2021 that it will be shutting down due to inability to raise capital. In 2003, Aerion commenced

268-458: A $ 250,000 deposit. By 2010, the company claimed 50 letters-of-intent . By then, Aerion sought a joint venture with a business aircraft manufacturer for deliveries five to six years later. In March 2012, UK-based Indigo Lyon joined Swiss ExecuJet Aviation Group as sales agents outside North America . By October 2013, the company expected flight testing to begin in 2019, to reach market in 2021. Aerion believes that their design will find

335-589: A composite supersonic natural laminar flow wing, with existing Pratt & Whitney JT8D -219 engine for a 40,800 kg (90,000 lb) gross-weight. When necessary, it could also cruise efficiently just below the speed of sound at Mach .95-.99. If produced, it would allow practical non-stop travel from Europe to North America and back within one business day. The Aerion SBJ's key enabling technology, supersonic natural Laminar flow, has been conclusively demonstrated in transonic wind tunnel tests and in supersonic flight tests conducted in conjunction with NASA . In

402-429: A compressor is defined according to its design. But in actual practice, the operating point of the compressor deviates from the design- point which is known as off-design operation. from equation (1) and (2) The value of ( tan ⁡ β 2 + tan ⁡ α 1 ) {\displaystyle (\tan \beta _{2}+\tan \alpha _{1})\,} doesn't change for

469-482: A good estimate of their performance can be made before they are first run on a rig. The compressor map shows the complete running range, i.e. off-design, of the compressor from ground idle to its highest corrected rotor speed, which for a civil engine may occur at top-of-climb, or, for a military combat engine, at take-off on a cold day. Not shown is the sub-idle performance region needed for analyzing normal ground and in-flight windmill start behaviour. The performance of

536-474: A high-speed aircraft. Real work on axial-flow engines started in the late 1930s, in several efforts that all started at about the same time. In England, Hayne Constant reached an agreement with the steam turbine company Metropolitan-Vickers (Metrovick) in 1937, starting their turboprop effort based on the Griffith design in 1938. In 1940, after the successful run of Whittle's centrifugal-flow design, their effort

603-445: A market, despite the US ban on supersonic flight, whereas Gulfstream views the ban as prohibitive. In 2014, the design was updated as the Aerion AS2 , with length and takeoff weight increased to accommodate customer requests. The $ 80 million aircraft would transport 8–12 passengers up to Mach 1.6 and up to 4,000 nmi (7,400 km). It would have a conventional aluminium fuselage and

670-686: A new version of the engine, the JT8D-200 series. Designed to be quieter, cleaner, more efficient, yet more powerful than earlier models, the -200 Series power-plant was re-engineered with a significantly higher bypass ratio (1.74 to 1) covering the 18,500 to 21,700 pound-force (82 to 97 kN) thrust range and powering the McDonnell Douglas MD-80 series . This increase was achieved by increasing bypass fan diameter from 39.9 inches (101 cm) to 49.2 inches (125 cm) and reducing fan pressure ratio (from 2.21 to 1.92). Overall engine pressure ratio

737-427: A number of papers in the early 1920s claimed that a practical axial-flow turbojet engine would be impossible to construct. Things changed after A. A. Griffith published a seminal paper in 1926, noting that the reason for the poor performance was that existing compressors used flat blades and were essentially "flying stalled ". He showed that the use of airfoils instead of the flat blades would increase efficiency to

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804-401: A practical limit on the number of stages, and the overall pressure ratio, comes from the interaction of the different stages when required to work away from the design conditions. These “off-design” conditions can be mitigated to a certain extent by providing some flexibility in the compressor. This is achieved normally through the use of adjustable stators or with valves that can bleed fluid from

871-408: A reaction turbine) could have its action reversed to act as an air compressor, calling it a turbo compressor or pump. His rotor and stator blading described in one of his patents had little or no camber although in some cases the blade design was based on propeller theory. The machines, driven by steam turbines, were used for industrial purposes such as supplying air to blast furnaces. Parsons supplied

938-418: A rise in pressure. The relative kinetic head in the energy equation is a term that exists only because of the rotation of the rotor. The rotor reduces the relative kinetic head of the fluid and adds it to the absolute kinetic head of the fluid i.e., the impact of the rotor on the fluid particles increases their velocity (absolute) and thereby reduces the relative velocity between the fluid and the rotor. In short,

1005-558: A search for a large aerospace partner, including Bombardier Aerospace and Dassault Aviation . The SBJ project was unveiled at the 2004 NBAA convention, backed by US billionaire Robert Bass , with introduction targeted at 2011 for a $ 1.2–1.4 billion development cost, anticipating a 250–300 aircraft civil market over 10 years. Aerion then planned wind tunnel testing in the second half of 2005, before partnerships and detailed design. Global Express lead designer John Holding joined Aerion in 2008 to lead advanced design. Each customer put

1072-466: A second rotating assembly for the high-pressure compressor (HPC) section, which has seven stages. The high-pressure compressor is driven by the first (upstream) turbine, which has a single stage. The front-mounted bypass fan has two stages. The annular discharge duct for the bypass fan runs along the full length of the engine, so that both the fan air and exhaust gases can exit through the same nozzle. This arrangement allows some noise attenuation, in that

1139-437: A single compressor stage may be shown by plotting stage loading coefficient ( ψ {\displaystyle \psi \,} ) as a function of flow coefficient ( ϕ {\displaystyle \phi \,} ) Stage pressure ratio against flow rate is lower than for a no-loss stage as shown. Losses are due to blade friction, flow separation , unsteady flow and vane-blade spacing. The performance of

1206-484: A single large compressor spinning at a single speed. Later designs added a second turbine and divided the compressor into low-pressure and high-pressure sections, the latter spinning faster. This two-spool design, pioneered on the Bristol Olympus , resulted in increased efficiency. Further increases in efficiency may be realised by adding a third spool, but in practice the added complexity increases maintenance costs to

1273-415: A stage is obtained at the rotor section, it is said to have a 50% reaction. The increase in pressure produced by a single stage is limited by the relative velocity between the rotor and the fluid, and the turning and diffusion capabilities of the airfoils. A typical stage in a commercial compressor will produce a pressure increase of between 15% and 60% (pressure ratios of 1.15–1.6) at design conditions with

1340-446: A test rig, a higher delivery pressure at a particular speed can be caused momentarily by burning too-great a step-jump in fuel which causes a momentary blockage until the compressor increases to the speed which goes with the new fuel flow and the surging stops. Suppose the initial operating point D ( m ˙ , P D {\displaystyle {\dot {m}},P_{D}\,} ) at some rpm N. On decreasing

1407-468: A wide range of operating points till stalling. Also α 1 = α 3 {\displaystyle \alpha _{1}=\alpha _{3}\,} because of minor change in air angle at rotor and stator, where α 3 {\displaystyle \alpha _{3}\,} is diffuser blade angle. Representing design values with (') for off-design operations (from eq. 3 ): for positive values of J, slope of

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1474-403: Is a gas compressor that can continuously pressurize gases . It is a rotating, airfoil -based compressor in which the gas or working fluid principally flows parallel to the axis of rotation, or axially. This differs from other rotating compressors such as centrifugal compressor , axi-centrifugal compressors and mixed-flow compressors where the fluid flow will include a "radial component" through

1541-408: Is calculated through degree of reaction . Therefore, Greitzer used a Helmholtz resonator type of compression system model to predict the transient response of a compression system after a small perturbation superimposed on a steady operating condition. He found a non-dimensional parameter which predicted which mode of compressor instability, rotating stall or surge, would result. The parameter used

1608-401: Is given by the equation: Power consumed by an ideal moving blade, P is given by the equation: Change in enthalpy of fluid in moving blades: Therefore, which implies, Isentropic compression in rotor blade , Therefore, which implies Degree of Reaction , The pressure difference between the entry and exit of the rotor blade is called reaction pressure . The change in pressure energy

1675-640: Is publicized as being half the cost of the competing 707 re-engine powerplant, the CFM International CFM56 , for reasons of geometrical and balance similarity to the engine it is replacing and the associated relative up-front wing modification costs of the two choices. The proposed Aerion SBJ supersonic business jet , previously under development, was to use a pair of JT8D-219 engines for sustained supersonic flight. More than 14,000 JT8D engines have been produced, totaling more than one-half billion hours of service, with more than 350 operators, making it

1742-404: Is reduced in the flow direction to maintain an optimum Mach number axial velocity as the fluid is compressed. As the fluid enters and leaves in the axial direction, the centrifugal component in the energy equation does not come into play. Here the compression is fully based on diffusing action of the passages. The diffusing action in the stator converts the absolute kinetic head of the fluid into

1809-412: Is simply no "perfect" compressor for this wide range of operating conditions. Fixed geometry compressors, like those used on early jet engines, are limited to a design pressure ratio of about 4 or 5:1. As with any heat engine , fuel efficiency is strongly related to the compression ratio , so there is very strong financial need to improve the compressor stages beyond these sorts of ratios. Additionally

1876-419: Is undesirable. The following explanation for surging refers to running a compressor at a constant speed on a rig and gradually reducing the exit area by closing a valve. What happens, i.e. crossing the surge line, is caused by the compressor trying to deliver air, still running at the same speed, to a higher exit pressure. When the compressor is operating as part of a complete gas turbine engine, as opposed to on

1943-453: The J30 . As Griffith had originally noted in 1929, the large frontal size of the centrifugal compressor caused it to have higher drag than the narrower axial-flow type. Additionally the axial-flow design could improve its compression ratio simply by adding additional stages and making the engine slightly longer. In the centrifugal-flow design the compressor itself had to be larger in diameter, which

2010-475: The Royal Aircraft Establishment . Other early jet efforts, notably those of Frank Whittle and Hans von Ohain , were based on the more robust and better understood centrifugal compressor which was widely used in superchargers . Griffith had seen Whittle's work in 1929 and dismissed it, noting a mathematical error, and going on to claim that the frontal size of the engine would make it useless on

2077-563: The JSTARS more time on station due to the engine's 17% greater fuel efficiency. However these plans were cancelled after the single conversion when the decision was taken to retire the platform. NATO originally planned to re-engine their fleet of E-3 Sentry AWACS aircraft, however again this was cancelled after the decision was taken to retire the E-3 platform in preference for the E-7 Wedgetail. The -219

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2144-522: The United States, both Lockheed and General Electric were awarded contracts in 1941 to develop axial-flow engines, the former a pure jet , the latter a turboprop. Northrop also started their own project to develop a turboprop, which the US Navy eventually contracted in 1943. Westinghouse also entered the race in 1942, their project proving to be the only successful one of the US efforts, later becoming

2211-693: The benefits of high efficiency and large mass flow rate , particularly in relation to their size and cross-section. They do, however, require several rows of airfoils to achieve a large pressure rise, making them complex and expensive relative to other designs (e.g. centrifugal compressors). Axial compressors are integral to the design of large gas turbines such as jet engines , high speed ship engines, and small scale power stations. They are also used in industrial applications such as large volume air separation plants, blast furnace air, fluid catalytic cracking air, and propane dehydrogenation . Due to high performance, high reliability and flexible operation during

2278-520: The blade-profile leads to reduced compression and drop in engine power. Negative stall is negligible compared to the positive stall because flow separation is least likely to occur on the pressure side of the blade. In a multi-stage compressor, at the high pressure stages, axial velocity is very small. Stalling value decreases with a small deviation from the design point causing stall near the hub and tip regions whose size increases with decreasing flow rates. They grow larger at very low flow rate and affect

2345-413: The burner can's perimeter in such a way that the burning fuel is held near the can's centerline. There are nine combustion chambers positioned in a can-annular arrangement. Each chamber has three air inlet hole sizes: the smallest is for cooling, the medium is for burning and the largest for forming an air blanket. In response to environmental concerns that began in the 1970s, the company began developing

2412-400: The compressed air to slow down before entering one of the engine's nine burner cans. Again, there are two bosses to extract 13th stage air for anti-icing, de-icing of fuel, and airframe (cabin pressurization) use. Not all the compressed air enters the burner cans at the fuel-ignition point; some bypasses the can completely and cools the first turbine stage, and some is gradually introduced into

2479-436: The compressor faces a wide variety of operating conditions. On the ground at takeoff the inlet pressure is high, inlet speed zero, and the compressor spun at a variety of speeds as the power is applied. Once in flight the inlet pressure drops, but the inlet speed increases (due to the forward motion of the aircraft) to recover some of this pressure, and the compressor tends to run at a single speed for long periods of time. There

2546-460: The compressor may stall if the inlet conditions change abruptly, a common problem on early engines. In some cases, if the stall occurs near the front of the engine, all of the stages from that point on will stop compressing the air. In this situation the energy required to run the compressor drops suddenly, and the remaining hot air in the rear of the engine allows the turbine to speed up the whole engine dramatically. This condition, known as surging,

2613-424: The compressor size, weight or complexity is critical, such as in military jets. The airfoil profiles are optimized and matched for specific velocities and turning. Although compressors can be run at other conditions with different flows, speeds, or pressure ratios, this can result in an efficiency penalty or even a partial or complete breakdown in flow (known as compressor stall and pressure surge respectively). Thus,

2680-454: The compressor. In a rotor with blades moving say towards right. Let some blades receives flow at higher incidence, this blade will stop positively. It creates obstruction in the passage between the blade to its left and itself. Thus the left blade will receive the flow at higher incidence and the blade to its right with decreased incidence. The left blade will experience more stall while the blade to its right will experience lesser stall. Towards

2747-435: The compressor. The energy level of the fluid increases as it flows through the compressor due to the action of the rotor blades which exert a torque on the fluid. The stationary blades slow the fluid, converting the circumferential component of flow into pressure. Compressors are typically driven by an electric motor or a steam or a gas turbine. Axial flow compressors produce a continuous flow of compressed gas, and have

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2814-440: The compressor. An analysis is made of rotating stall in compressors of many stages, finding conditions under which a flow distortion can occur which is steady in a traveling reference frame, even though upstream total and downstream static pressure are constant. In the compressor, a pressure-rise hysteresis is assumed. It is a situation of separation of air flow at the aero-foil blades of the compressor. This phenomenon depending upon

2881-578: The compressor. Due to this back flow, pressure in pipe will decrease because this unequal pressure condition cannot stay for a long period of time. Though valve position is set for lower flow rate say point G but compressor will work according to normal stable operation point say E, so path E-F-P-G-E will be followed leading to breakdown of flow, hence pressure in the compressor falls further to point H( P H {\displaystyle P_{H}\,} ). This increase and decrease of pressure in pipe will occur repeatedly in pipe and compressor following

2948-402: The curve is negative and vice versa. In the plot of pressure-flow rate the line separating graph between two regions- unstable and stable is known as the surge line . This line is formed by joining surge points at different rpms. Unstable flow in axial compressors due to complete breakdown of the steady through flow is termed as surging. This phenomenon affects the performance of compressor and

3015-416: The cycle E-F-P-G-H-E also known as the surge cycle. This phenomenon will cause vibrations in the whole machine and may lead to mechanical failure. That is why left portion of the curve from the surge point is called unstable region and may cause damage to the machine. So the recommended operation range is on the right side of the surge line. Stalling is an important phenomenon that affects the performance of

3082-402: The entire blade height. Delivery pressure significantly drops with large stalling which can lead to flow reversal. The stage efficiency drops with higher losses. Non-uniformity of air flow in the rotor blades may disturb local air flow in the compressor without upsetting it. The compressor continues to work normally but with reduced compression. Thus, rotating stall decreases the effectiveness of

3149-553: The first commercial axial flow compressor for use in a lead smelter in 1901. Parsons' machines had low efficiencies, later attributed to blade stall, and were soon replaced with more efficient centrifugal compressors. Brown Boveri & Cie produced "reversed turbine" compressors, driven by gas turbines, with blading derived from aerodynamic research which were more efficient than centrifugal types when pumping large flow rates of 40,000 cu.ft. per minute at pressures up to 45 p.s.i. Because early axial compressors were not efficient enough

3216-477: The flight envelope, they are also used in aerospace rocket engines , as fuel pumps and in other critical high volume applications. Axial compressors consist of rotating and stationary components. A shaft drives a central drum which is retained by bearings inside of a stationary tubular casing. Between the drum and the casing are rows of airfoils, each row connected to either the drum or the casing in an alternating manner. A pair of one row of rotating airfoils and

3283-442: The flow-rate at same rpm along the characteristic curve by partial closing of the valve, the pressure in the pipe increases which will be taken care by increase in input pressure at the compressor. Further increase in pressure till point P (surge point), compressor pressure will increase. Further moving towards left keeping rpm constant, pressure in pipe will increase but compressor pressure will decrease leading to back air-flow towards

3350-480: The inlet pressure and temperature. Similar units exist throughout the engine to check temperatures and pressures. At the 13th (i.e. the final) compressor stage, air is bled out and used for anti-icing. The amount is controlled by the Pressure Ratio Bleed Control sense signal (PRBC). The diffuser case at the aft end of the compressor houses the 13th stage. Its increasing cross-sectional area allows

3417-410: The main flow between stages (inter-stage bleed). Modern jet engines use a series of compressors, running at different speeds; to supply air at around 40:1 pressure ratio for combustion with sufficient flexibility for all flight conditions. The law of moment of momentum states that the sum of the moments of external forces acting on a fluid which is temporarily occupying the control volume is equal to

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3484-558: The most popular of all low-bypass turbofan engines ever produced. Regular production ended in 1985, but some replacement engines were produced for military aircraft in 2011. Mainline airline use of the JT8D continued until 2020 when Delta Air Lines retired their MD-88 fleet early due to the COVID-19 pandemic . Data from Related development Comparable engines Related lists Axial compressor#Spools An axial compressor

3551-622: The need for hush kits, enhanced short field performance, and steeper and faster climb rates with roughly a 10% reduction in fuel burn for extended range. Pratt & Whitney, in a joint venture with Seven Q Seven (SQS) and Omega Air, developed the JT8D-219 as a re-engine powerplant for Boeing 707 -based aircraft. Northrop Grumman used the -219 to re-engine one of the United States Air Force's fleet of 19 Joint Surveillance Target Attack Radar System ( E-8 Joint STARS ) aircraft, which would allow

3618-515: The net change of angular momentum flux through the control volume. The swirling fluid enters the control volume at radius, r 1 {\displaystyle r_{1}\,} , with tangential velocity, V w 1 {\displaystyle V_{w1}\,} , and leaves at radius, r 2 {\displaystyle r_{2}\,} , with tangential velocity, V w 2 {\displaystyle V_{w2}\,} . Rate of change of momentum, F

3685-470: The next row of stationary airfoils is called a stage. The rotating airfoils, also known as blades or rotors, accelerate the fluid in both the axial and circumferential directions. The stationary airfoils, also known as vanes or stators, convert the increased kinetic energy into static pressure through diffusion and redirect the flow direction of the fluid to prepare it for the rotor blades of the next stage. The cross-sectional area between rotor drum and casing

3752-490: The point of negating any economic benefit. That said, there are several three-spool engines in use, perhaps the most famous being the Rolls-Royce RB211 , used on a wide variety of commercial aircraft. Aerion SBJ The Aerion SBJ was a supersonic business jet project designed by American firm Aerion Corporation . Unveiled in 2004, the designer sought a joint venture with a business aircraft manufacturer for

3819-469: The point where a practical jet engine was a real possibility. He concluded the paper with a basic diagram of such an engine, which included a second turbine that was used to power a propeller . Although Griffith was well known due to his earlier work on metal fatigue and stress measurement, little work appears to have started as a direct result of his paper. The only obvious effort was a test-bed compressor built by Hayne Constant , Griffith's colleague at

3886-484: The ratio (Delta T)/(Tstage) entry must decrease, thus implying a progressive reduction in stage pressure ratio through the unit. Hence the rear stage develops a significantly lower pressure ratio than the first stage. Higher stage pressure ratios are also possible if the relative velocity between fluid and rotors is supersonic, but this is achieved at the expense of efficiency and operability. Such compressors, with stage pressure ratios of over 2, are only used where minimizing

3953-401: The right stalling will decrease whereas it will increase towards its left. Movement of the rotating stall can be observed depending upon the chosen reference frame. From an energy exchange point of view axial compressors are reversed turbines. Steam-turbine designer Charles Algernon Parsons , for example, recognized that a turbine which produced work by virtue of a fluid's static pressure (i.e.

4020-403: The rotor increases the absolute velocity of the fluid and the stator converts this into pressure rise. Designing the rotor passage with a diffusing capability can produce a pressure rise in addition to its normal functioning. This produces greater pressure rise per stage which constitutes a stator and a rotor together. This is the reaction principle in turbomachines . If 50% of the pressure rise in

4087-587: The rotor speed, Helmholtz resonator frequency of the system and an "effective length" of the compressor duct. It had a critical value which predicted either rotating stall or surge where the slope of pressure ratio against flow changed from negative to positive. Axial compressor performance is shown on a compressor map , also known as a characteristic, by plotting pressure ratio and efficiency against corrected mass flow at different values of corrected compressor speed. Axial compressors, particularly near their design point are usually amenable to analytical treatment, and

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4154-453: The still-hot fast-moving turbine exhaust is shrouded in much-cooler and slower-moving air (from the bypass fan) before interacting with ambient air. Thus, the JT8D noise levels were significantly reduced from previous non-turbofan engines, although the low bypass ratio meant that, compared to subsequently developed turbofans, high noise levels were still produced. Within the fan inlet case, there are anti-icing air bosses and probes to sense

4221-566: The summer of 2010, an Aerion-designed calibration fixture was tested aboard a NASA F-15 B. The experiments were intended to influence future laminar flow airfoil manufacturing standards for surface quality and assembly tolerances. A second test surface was flown during the first half of 2013, its design guided by the 2010 test. The new test surface was designed to provide large extents of laminar flow and be shaped so boundary layer instabilities grow relatively slowly and smoothly. These characteristics should facilitate good boundary layer imaging of

4288-421: Was a major problem on early engines and often led to the turbine or compressor breaking and shedding blades. For all of these reasons, axial compressors on modern jet engines are considerably more complex than those on earlier designs. All compressors have an optimum point relating rotational speed and pressure, with higher compressions requiring higher speeds. Early engines were designed for simplicity, and used

4355-460: Was also increased from 15.4 to 21.0. Since entering service in 1980, more than 2,900 of the -200 series engines have been produced. The JT8D-217 and -219 engine(s) were tested in 2001 and were deemed suitable replacements for the old TF33 engines on military and commercial aircraft as part of the Super 27 re-engining program. The updated engines offer reduced (Stage-3) noise compliance standards without

4422-426: Was much more difficult to fit properly into a thin and aerodynamic aircraft fuselage (although not dissimilar to the profile of radial engines already in widespread use). On the other hand, centrifugal-flow designs remained much less complex (the major reason they "won" in the race to flying examples) and therefore have a role in places where size and streamlining are not so important. In the jet engine application,

4489-461: Was re-designed as a pure jet, the Metrovick F.2 . In Germany, von Ohain had produced several working centrifugal engines, some of which had flown including the world's first jet aircraft ( He 178 ), but development efforts had moved on to Junkers ( Jumo 004 ) and BMW ( BMW 003 ), which used axial-flow designs in the world's first jet fighter ( Messerschmitt Me 262 ) and jet bomber ( Arado Ar 234 ). In

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