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63-509: The Short SC.7 Skyvan (nicknamed the "Flying Shoebox") is a British 19-seat twin- turboprop aircraft first flown in 1963, that was manufactured by Short Brothers of Belfast , Northern Ireland . Featuring a basic rugged design and STOL capabilities, it was used in small numbers by airlines, and also by some smaller air forces. In more recent years the remaining examples were mostly used for short-haul freight and skydiving . The Short 330 and Short 360 are regional airliners developed from

126-414: A calculation of the mass of natural gas—which often contains carbon dioxide ( CO 2 ), nitrogen ( N 2 ), and various alkanes —includes the mass of the carbon dioxide, nitrogen and all alkanes in determining the value of m fuel . For pure octane the stoichiometric mixture is approximately 15.1:1, or λ of 1.00 exactly. In naturally aspirated engines powered by octane, maximum power

189-406: A constant-speed propeller increase their pitch as aircraft speed increases. Another benefit of this type of propeller is that it can also be used to generate reverse thrust to reduce stopping distance on the runway. Additionally, in the event of an engine failure, the propeller can be feathered , thus minimizing the drag of the non-functioning propeller. While the power turbine may be integral with

252-416: A large amount of air by a small degree than a small amount of air by a large degree, a low disc loading (thrust per unit disc area) increases the aircraft's energy efficiency , and this reduces the fuel use. Propellers work well until the flight speed of the aircraft is high enough that the airflow past the blade tips reaches the speed of sound. Beyond that speed, the proportion of the power that drives

315-497: A richer mixture (lower air–fuel ratio) is used to produce cooler combustion products (thereby utilizing evaporative cooling ), and so avoid overheating of the cylinder head , and thus prevent detonation. The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required. For pure octane fuel,

378-575: A test-bed not intended for production. It first flew on 20 September 1945. From their experience with the Trent, Rolls-Royce developed the Rolls-Royce Clyde , the first turboprop engine to receive a type certificate for military and civil use, and the Dart , which became one of the most reliable turboprop engines ever built. Dart production continued for more than fifty years. The Dart-powered Vickers Viscount

441-448: Is The stoichiometric mixture fraction is related to λ (lambda) and Φ (phi) by the equations assuming In industrial fired heaters , power plant steam generators, and large gas-fired turbines , the more common terms are percent excess combustion air and percent stoichiometric air. For example, excess combustion air of 15 percent means that 15 percent more than the required stoichiometric air (or 115 percent of stoichiometric air)

504-429: Is a turbine engine that drives an aircraft propeller . A turboprop consists of an intake , reduction gearbox , compressor , combustor , turbine , and a propelling nozzle . Air enters the intake and is compressed by the compressor. Fuel is then added to the compressed air in the combustor, where the fuel-air mixture then combusts . The hot combustion gases expand through the turbine stages, generating power at

567-544: Is being used. A combustion control point can be defined by specifying the percent excess air (or oxygen) in the oxidant , or by specifying the percent oxygen in the combustion product. An air–fuel ratio meter may be used to measure the percent oxygen in the combustion gas, from which the percent excess oxygen can be calculated from stoichiometry and a mass balance for fuel combustion. For example, for propane ( C 3 H 8 ) combustion between stoichiometric and 30 percent excess air (AFR mass between 15.58 and 20.3),

630-408: Is frequently reached at AFRs ranging from 12.5 to 13.3:1 or λ of 0.850 to 0.901. The air-fuel ratio of 12:1 is considered as the maximum output ratio, whereas the air-fuel ratio of 16:1 is considered as the maximum fuel economy ratio. Fuel–air ratio is commonly used in the gas turbine industry as well as in government studies of internal combustion engine , and refers to the ratio of fuel to

693-482: Is normally a constant-speed (variable pitch) propeller type similar to that used with larger aircraft reciprocating engines , except that the propeller-control requirements are very different. Due to the turbine engine's slow response to power inputs, particularly at low speeds, the propeller has a greater range of selected travel in order to make rapid thrust changes, notably for taxi, reverse, and other ground operations. The propeller has 2 modes, Alpha and Beta. Alpha

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756-494: Is sacrificed in favor of shaft power, which is obtained by extracting additional power (beyond that necessary to drive the compressor) from turbine expansion. Owing to the additional expansion in the turbine system, the residual energy in the exhaust jet is low. Consequently, the exhaust jet produces about 10% of the total thrust. A higher proportion of the thrust comes from the propeller at low speeds and less at higher speeds. Turboprops have bypass ratios of 50–100, although

819-404: Is the mode for all flight operations including takeoff. Beta, a mode typically consisting of zero to negative thrust, is used for all ground operations aside from takeoff. The Beta mode is further broken down into 2 additional modes, Beta for taxi and Beta plus power. Beta for taxi as the name implies is used for taxi operations and consists of all pitch ranges from the lowest alpha range pitch, all

882-440: Is therefore independent of) both mass and molar values for the fuel and the oxidizer. Consider, for example, a mixture of one mole of ethane ( C 2 H 6 ) and one mole of oxygen ( O 2 ). The fuel–oxidizer ratio of this mixture based on the mass of fuel and air is and the fuel-oxidizer ratio of this mixture based on the number of moles of fuel and air is Clearly the two values are not equal. To compare it with

945-616: The P-3 Orion , and the C-130 Hercules military transport aircraft. The first turbine-powered, shaft-driven helicopter was the Kaman K-225 , a development of Charles Kaman 's K-125 synchropter , which used a Boeing T50 turboshaft engine to power it on 11 December 1951. December 1963 saw the first delivery of Pratt & Whitney Canada's PT6 turboprop engine for the then Beechcraft 87, soon to become Beechcraft King Air . 1964 saw

1008-830: The Piper Meridian , Socata TBM , Pilatus PC-12 , Piaggio P.180 Avanti , Beechcraft King Air and Super King Air . In April 2017, there were 14,311 business turboprops in the worldwide fleet. Between 2012 and 2016, the ATSB observed 417 events with turboprop aircraft, 83 per year, over 1.4 million flight hours: 2.2 per 10,000 hours. Three were "high risk" involving engine malfunction and unplanned landing in single‑engine Cessna 208 Caravans , four "medium risk" and 96% "low risk". Two occurrences resulted in minor injuries due to engine malfunction and terrain collision in agricultural aircraft and five accidents involved aerial work: four in agriculture and one in an air ambulance . Jane's All

1071-590: The Tupolev Tu-114 can reach 470 kn (870 km/h; 540 mph). Large military aircraft , like the Tupolev Tu-95 , and civil aircraft , such as the Lockheed L-188 Electra , were also turboprop powered. The Airbus A400M is powered by four Europrop TP400 engines, which are the second most powerful turboprop engines ever produced, after the 11 MW (15,000 hp) Kuznetsov NK-12 . In 2017,

1134-401: The oxygen content of combustion air should be specified because of different air density due to different altitude or intake air temperature, possible dilution by ambient water vapor , or enrichment by oxygen additions. An air-fuel ratio meter monitors the air–fuel ratio of an internal combustion engine . Also called air–fuel ratio gauge , air–fuel meter , or air–fuel gauge , it reads

1197-647: The Astazou engines with Garrett AiResearch TPE331 turboprops of 715 shp (533 kW). A total of 149 Skyvans (including the two prototypes) were produced before production ended in 1986. Skyvans served widely in both military and civilian operations, and the type remained in service in 2009 with a number of civilian operators, and in military service in Guyana and Oman. Skyvans continue to be used in limited numbers for air-to-air photography and for skydiving operations. In 1970, Questor Surveys of Toronto Canada converted

1260-643: The Miles proposal, Short rejected the Caravan. They developed their own design for a utility all-metal aircraft which was called the Short SC.7 Skyvan . The Skyvan is a twin-engined all-metal, high-wing monoplane, with a braced, high aspect ratio wing, and an unpressurised , square-section fuselage with twin fins and rudders . It was popular with freight operators compared to other small aircraft because of its large rear door for loading and unloading freight. Its fuselage resembles

1323-519: The Soviet Union had the technology to create the airframe for a jet-powered strategic bomber comparable to Boeing's B-52 Stratofortress , they instead produced the Tupolev Tu-95 Bear, powered with four Kuznetsov NK-12 turboprops, mated to eight contra-rotating propellers (two per nacelle) with supersonic tip speeds to achieve maximum cruise speeds in excess of 575 mph, faster than many of

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1386-485: The World's Aircraft . 2005–2006. Fuel mixture In an internal combustion engine or industrial furnace, the air–fuel ratio is an important measure for anti-pollution and performance-tuning reasons. If exactly enough air is provided to completely burn all of the fuel ( stoichiometric combustion ), the ratio is known as the stoichiometric mixture , often abbreviated to stoich . Ratios lower than stoichiometric (where

1449-452: The air. Air–fuel equivalence ratio, λ (lambda), is the ratio of actual AFR to stoichiometry for a given mixture. λ  = 1.0 is at stoichiometry, rich mixtures λ  < 1.0, and lean mixtures λ  > 1.0. There is a direct relationship between λ and AFR. To calculate AFR from a given λ , multiply the measured λ by the stoichiometric AFR for that fuel. Alternatively, to recover λ from an AFR, divide AFR by

1512-467: The air–fuel equivalence ratio (defined previously) as follows: The relative amounts of oxygen enrichment and fuel dilution can be quantified by the mixture fraction , Z, defined as where Y F,0 and Y O,0 represent the fuel and oxidizer mass fractions at the inlet, W F and W O are the species molecular weights, and v F and v O are the fuel and oxygen stoichiometric coefficients, respectively. The stoichiometric mixture fraction

1575-497: The air–fuel ratio with an air–fuel ratio meter . In the typical air to natural gas combustion burner, a double-cross limit strategy is employed to ensure ratio control. (This method was used in World War II). The strategy involves adding the opposite flow feedback into the limiting control of the respective gas (air or fuel). This assures ratio control within an acceptable margin. There are other terms commonly used when discussing

1638-422: The combustion process is completed in approximately 2 milliseconds at an engine speed of 6,000  revolutions per minute (100 revolutions per second, or 10 milliseconds per revolution of the crankshaft. For a four-stroke engine this would mean 5 milliseconds for each piston stroke, and 20 milliseconds to complete one 720 degree Otto cycle ). This is the time that elapses from the spark plug firing until 90% of

1701-417: The compressor intake is at the aft of the engine, and the exhaust is situated forward, reducing the distance between the turbine and the propeller. Unlike the small-diameter fans used in turbofan engines, the propeller has a large diameter that lets it accelerate a large volume of air. This permits a lower airstream velocity for a given amount of thrust. Since it is more efficient at low speeds to accelerate

1764-459: The control system. The turboprop system consists of 3 propeller governors , a governor, and overspeed governor, and a fuel-topping governor. The governor works in much the same way a reciprocating engine propeller governor works, though a turboprop governor may incorporate beta control valve or beta lift rod for beta operation and is typically located in the 12 o'clock position. There are also other governors that are included in addition depending on

1827-539: The detonation of the fuel-air mix while approaching or shortly after maximum cylinder pressure is possible under high load (referred to as knocking or pinging), specifically a "pre-detonation" event in the context of a spark-ignition engine model. Such detonation can cause serious engine damage as the uncontrolled burning of the fuel-air mix can create very high pressures in the cylinder. As a consequence, stoichiometric mixtures are only used under light to low-moderate load conditions. For acceleration and high-load conditions,

1890-399: The equivalence ratio, we need to determine the fuel–oxidizer ratio of ethane and oxygen mixture. For this we need to consider the stoichiometric reaction of ethane and oxygen, This gives Thus we can determine the equivalence ratio of the given mixture as or, equivalently, as Another advantage of using the equivalence ratio is that ratios greater than one always mean there is more fuel in

1953-412: The exhaust gas. The fuel–air equivalence ratio , Φ (phi), of a system is defined as the ratio of the fuel-to-oxidizer ratio to the stoichiometric fuel-to-oxidizer ratio. Mathematically, where m represents the mass, n represents a number of moles, subscript st stands for stoichiometric conditions. The advantage of using equivalence ratio over fuel–oxidizer ratio is that it takes into account (and

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2016-493: The first jet aircraft and comparable to jet cruising speeds for most missions. The Bear would serve as their most successful long-range combat and surveillance aircraft and symbol of Soviet power projection through to the end of the 20th century. The USA used turboprop engines with contra-rotating propellers, such as the Allison T40 , on some experimental aircraft during the 1950s. The T40-powered Convair R3Y Tradewind flying-boat

2079-546: The first deliveries of the Garrett AiResearch TPE331 , (now owned by Honeywell Aerospace ) on the Mitsubishi MU-2 , making it the fastest turboprop aircraft for that year. In contrast to turbofans , turboprops are most efficient at flight speeds below 725 km/h (450 mph; 390 knots) because the jet velocity of the propeller (and exhaust) is relatively low. Modern turboprop airliners operate at nearly

2142-528: The first of two Skyvan 3s for aerial geological survey work. The Collier Mosquito Control District uses Skyvans for aerial spraying. Skyvan G-BEOL starred in the film Kingsman Secret Service as the aircraft trainee kingsmen skydived from. Skyvans still active in 2022–2024 include Data from Jane's Civil and Military Upgrades 1994-95 General characteristics Performance Related development Aircraft of comparable role, configuration, and era Related lists Turboprop A turboprop

2205-434: The fuel is in excess) are considered "rich". Rich mixtures are less efficient, but may produce more power and burn cooler. Ratios higher than stoichiometric (where the air is in excess) are considered "lean". Lean mixtures are more efficient but may cause higher temperatures, which can lead to the formation of nitrogen oxides . Some engines are designed with features to allow lean-burn . For precise air–fuel ratio calculations,

2268-455: The fuel's stoichiometric rate by measuring the exhaust gas composition and controlling fuel volume. Vehicles without such controls (such as most motorcycles until recently, and cars predating the mid-1980s) may have difficulties running certain fuel blends (especially winter fuels used in some areas) and may require different carburetor jets (or otherwise have the fueling ratios altered) to compensate. Vehicles that use oxygen sensors can monitor

2331-423: The fuel–air mix is combusted, typically some 80 degrees of crankshaft rotation later. Catalytic converters are designed to work best when the exhaust gases passing through them are the result of nearly perfect combustion. A perfectly stoichiometric mixture burns very hot and can damage engine components if the engine is placed under high load at this fuel–air mixture. Due to the high temperatures at this mixture,

2394-399: The fuel–oxidizer mixture than required for complete combustion (stoichiometric reaction), irrespective of the fuel and oxidizer being used—while ratios less than one represent a deficiency of fuel or equivalently excess oxidizer in the mixture. This is not the case if one uses fuel–oxidizer ratio, which takes different values for different mixtures. The fuel–air equivalence ratio is related to

2457-558: The gas generator section, many turboprops today feature a free power turbine on a separate coaxial shaft. This enables the propeller to rotate freely, independent of compressor speed. Alan Arnold Griffith had published a paper on compressor design in 1926. Subsequent work at the Royal Aircraft Establishment investigated axial compressor-based designs that would drive a propeller. From 1929, Frank Whittle began work on centrifugal compressor-based designs that would use all

2520-455: The gas power produced by the engine for jet thrust. The world's first turboprop was designed by the Hungarian mechanical engineer György Jendrassik . Jendrassik published a turboprop idea in 1928, and on 12 March 1929 he patented his invention. In 1938, he built a small-scale (100 Hp; 74.6 kW) experimental gas turbine. The larger Jendrassik Cs-1 , with a predicted output of 1,000 bhp,

2583-424: The mixture of air and fuel in internal combustion engines. Mixture is the predominant word that appears in training texts, operation manuals, and maintenance manuals in the aviation world. Air–fuel ratio is the ratio between the mass of air and the mass of fuel in the fuel–air mix at any given moment. The mass is the mass of all constituents that compose the fuel and air, whether combustible or not. For example,

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2646-406: The model, such as an overspeed and fuel topping governor on a Pratt & Whitney Canada PT6 , and an under-speed governor on a Honeywell TPE331 . The turboprop is also distinguished from other kinds of turbine engine in that the fuel control unit is connected to the governor to help dictate power. To make the engine more compact, reverse airflow can be used. On a reverse-flow turboprop engine,

2709-657: The most widespread turboprop airliners in service were the ATR 42 / 72 (950 aircraft), Bombardier Q400 (506), De Havilland Canada Dash 8 -100/200/300 (374), Beechcraft 1900 (328), de Havilland Canada DHC-6 Twin Otter (270), Saab 340 (225). Less widespread and older airliners include the BAe Jetstream 31 , Embraer EMB 120 Brasilia , Fairchild Swearingen Metroliner , Dornier 328 , Saab 2000 , Xian MA60 , MA600 and MA700 , Fokker 27 and 50 . Turboprop business aircraft include

2772-588: The original SC.7. In 1958 , Short was approached by F.G. Miles Ltd (successor company to Miles Aircraft ) which was seeking backing to produce a development of the Hurel-Dubois Miles HDM.106 Caravan design with a high aspect ratio wing similar to that of the Hurel-Dubois HD.31 . Short acquired the design and data gathered from trials of the Miles Aerovan based HDM.105 prototype. After evaluating

2835-487: The oxidation reaction is: Any mixture greater than 14.7:1 is considered a lean mixture ; any less than 14.7:1 is a rich mixture – given perfect (ideal) "test" fuel (gasoline consisting of solely n - heptane and iso-octane ). In reality, most fuels consist of a combination of heptane, octane, a handful of other alkanes , plus additives including detergents, and possibly oxygenators such as MTBE ( methyl tert -butyl ether ) or ethanol / methanol . These compounds all alter

2898-416: The pilot not being able to see out of the rear of the aircraft for backing and the amount of debris reverse stirs up, manufacturers will often limit the speeds beta plus power may be used and restrict its use on unimproved runways. Feathering of these propellers is performed by the propeller control lever. The constant-speed propeller is distinguished from the reciprocating engine constant-speed propeller by

2961-403: The point of exhaust. Some of the power generated by the turbine is used to drive the compressor and electric generator . The gases are then exhausted from the turbine. In contrast to a turbojet or turbofan , the engine's exhaust gases do not provide enough power to create significant thrust, since almost all of the engine's power is used to drive the propeller. Exhaust thrust in a turboprop

3024-494: The propeller that is converted to propeller thrust falls dramatically. For this reason turboprop engines are not commonly used on aircraft that fly faster than 0.6–0.7 Mach , with some exceptions such as the Tupolev Tu-95 . However, propfan engines, which are very similar to turboprop engines, can cruise at flight speeds approaching 0.75 Mach. To maintain propeller efficiency across a wide range of airspeeds, turboprops use constant-speed (variable-pitch) propellers. The blades of

3087-477: The propeller. This allows for propeller strike or similar damage to occur without damaging the gas generator and allowing for only the power section (turbine and gearbox) to be removed and replaced in such an event, and also allows for less stress on the start during engine ground starts. Whereas a fixed shaft has the gearbox and gas generator connected, such as on the Honeywell TPE331 . The propeller itself

3150-446: The propulsion airflow is less clearly defined for propellers than for fans. The propeller is coupled to the turbine through a reduction gear that converts the high RPM /low torque output to low RPM/high torque. This can be of two primary designs, free-turbine and fixed. A free-turbine turboshaft found on the Pratt & Whitney Canada PT6 , where the gas generator is not connected to

3213-585: The same speed as small regional jet airliners but burn two-thirds of the fuel per passenger. Compared to piston engines, their greater power-to-weight ratio (which allows for shorter takeoffs) and reliability can offset their higher initial cost, maintenance and fuel consumption. As jet fuel can be easier to obtain than avgas in remote areas, turboprop-powered aircraft like the Cessna Caravan and Quest Kodiak are used as bush airplanes . Turboprop engines are generally used on small subsonic aircraft, but

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3276-409: The shape of a railroad boxcar for simplicity and efficiency. Construction started at Sydenham Airport in 1960, and the first prototype first flew on 17 January 1963, powered by two Continental piston engines. Later in 1963, the prototype was re-engined with the intended Turbomeca Astazou II turboprop engines of 520 shp (390 kW); the second prototype (the first Series 2 Skyvan)

3339-480: The standard mounting 52 and 67 mm ( 2 + 1 ⁄ 16 and 2 + 5 ⁄ 8  in) diameters, as other types of car 'gauges'. These usually have 10 or 20 LEDs. Analogue 'needle' style gauges are also available. In theory, a stoichiometric mixture has just enough air to completely burn the available fuel. In practice, this is never quite achieved, due primarily to the very short time available in an internal combustion engine for each combustion cycle. Most of

3402-432: The stoichiometric AFR for that fuel. This last equation is often used as the definition of λ : Because the composition of common fuels varies seasonally, and because many modern vehicles can handle different fuels when tuning, it makes more sense to talk about λ values rather than AFR. Most practical AFR devices actually measure the amount of residual oxygen (for lean mixes) or unburnt hydrocarbons (for rich mixtures) in

3465-420: The stoichiometric ratio, with most of the additives pushing the ratio downward (oxygenators bring extra oxygen to the combustion event in liquid form that is released at the time of combustions; for MTBE -laden fuel, a stoichiometric ratio can be as low as 14.1:1). Vehicles that use an oxygen sensor or other feedback loops to control fuel to air ratio (lambda control), compensate automatically for this change in

3528-443: The voltage output of an oxygen sensor , sometimes also called AFR sensor or lambda sensor. The original narrow-band oxygen sensors became factory installed standard in the late 1970s and early 1980s. In recent years a newer and much more accurate wide-band sensor, though more expensive, has become available. Most stand-alone narrow-band meters have 10 LEDs and some have more. Also common, narrow band meters in round housings with

3591-410: The way down to zero pitch, producing very little to zero-thrust and is typically accessed by moving the power lever to a beta for taxi range. Beta plus power is a reverse range and produces negative thrust, often used for landing on short runways where the aircraft would need to rapidly slow down, as well as backing operations and is accessed by moving the power lever below the beta for taxi range. Due to

3654-504: Was destroyed in a bombing raid. In 1941, the engine was abandoned due to war, and the factory converted to conventional engine production. The first mention of turboprop engines in the general public press was in the February 1944 issue of the British aviation publication Flight , which included a detailed cutaway drawing of what a possible future turboprop engine could look like. The drawing

3717-522: Was initially fitted with Turbomeca Astazou X turboprop engines of 666 shp (497 kW) but subsequently the initial production version was powered by Turbomeca Astazou XII turboprop engines of 690 shp (510 kW). In 1967, it was found that the Astazou XII was temperature limited at high altitudes. Consequently, in 1968, production switched to the Skyvan Series 3 aircraft, which replaced

3780-686: Was operated by the U.S. Navy for a short time. The first American turboprop engine was the General Electric XT31 , first used in the experimental Consolidated Vultee XP-81 . The XP-81 first flew in December 1945, the first aircraft to use a combination of turboprop and turbojet power. The technology of Allison's earlier T38 design evolved into the Allison T56 , used to power the Lockheed Electra airliner, its military maritime patrol derivative

3843-629: Was produced and tested at the Ganz Works in Budapest between 1937 and 1941. It was of axial-flow design with 15 compressor and 7 turbine stages, annular combustion chamber. First run in 1940, combustion problems limited its output to 400 bhp. Two Jendrassik Cs-1s were the engines for the world's first turboprop aircraft – the Varga RMI-1 X/H . This was a Hungarian fighter-bomber of WWII which had one model completed, but before its first flight it

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3906-593: Was the first turboprop aircraft of any kind to go into production and sold in large numbers. It was also the first four-engined turboprop. Its first flight was on 16 July 1948. The world's first single engined turboprop aircraft was the Armstrong Siddeley Mamba -powered Boulton Paul Balliol , which first flew on 24 March 1948. The Soviet Union built on German World War II turboprop preliminary design work by Junkers Motorenwerke, while BMW, Heinkel-Hirth and Daimler-Benz also worked on projected designs. While

3969-481: Was very close to what the future Rolls-Royce Trent would look like. The first British turboprop engine was the Rolls-Royce RB.50 Trent , a converted Derwent II fitted with reduction gear and a Rotol 7 ft 11 in (2.41 m) five-bladed propeller. Two Trents were fitted to Gloster Meteor EE227 — the sole "Trent-Meteor" — which thus became the world's first turboprop-powered aircraft to fly, albeit as

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