A turboshaft engine is a form of gas turbine that is optimized to produce shaft horsepower rather than jet thrust . In concept, turboshaft engines are very similar to turbojets , with additional turbine expansion to extract heat energy from the exhaust and convert it into output shaft power. They are even more similar to turboprops , with only minor differences, and a single engine is often sold in both forms.
30-684: The Allison Model 250 , now known as the Rolls-Royce M250 , (US military designations T63 and T703 ) is a highly successful turboshaft engine family, originally developed by the Allison Engine Company in the early 1960s. The Model 250 has been produced by Rolls-Royce since it acquired Allison in 1995. In 1958, the Detroit Diesel Allison division of General Motors was chosen by the US Army to develop
60-513: A fixed ratio to provide either a gear reduction or increase in speed, sometimes in conjunction with a change in the orientation of the output shaft. Examples of such transmissions are used in helicopters and wind turbines . In the case of a wind turbine, the first stage of the gearbox is usually a planetary gear, to minimize the size while withstanding the high torque inputs from the turbine. Many transmissions – especially for transportation applications – have multiple gears that are used to change
90-604: A gas turbine engine. (Most tanks use reciprocating piston diesel engines.) The Swedish Stridsvagn 103 was the first tank to utilize a gas turbine as a secondary, high-horsepower "sprint" engine to augment its primary piston engine's performance. The turboshaft engines used in all these tanks have considerably fewer parts than the piston engines they replace or supplement, mechanically are very reliable, produce reduced exterior noise, and run on virtually any fuel: petrol (gasoline), diesel fuel , and aviation fuels. However, turboshaft engines have significantly higher fuel consumption than
120-473: A new light turbine engine to power a "Light Observation Aircraft" (LOA), to replace the Cessna O-1A Bird Dog . At this stage the US Army was unsure whether to have a fixed- or rotary-wing aircraft, so Allison was instructed to consider both applications. Design studies undertaken considered a wide range of possible mechanical configurations for the turboprop/turboshaft. These studies culminated in
150-453: Is connected to the compressor via the HP shaft. The combustion products continue to expand through the two-stage power turbine which generates shaft horsepower for the aircraft. A coaxial stub shaft connects the power turbine to a compact reduction gearbox, located inboard, between the centrifugal compressor and the exhaust/power turbine system. The exhaust stream then turns through 90 degrees to exit
180-475: Is connected to the engine via a torque converter (or a fluid coupling prior to the 1960s), instead of the friction clutch used by most manual transmissions and dual-clutch transmissions. A dual-clutch transmission (DCT) uses two separate clutches for odd and even gear sets . The design is often similar to two separate manual transmissions with their respective clutches contained within one housing, and working as one unit. In car and truck applications,
210-659: The Sikorsky CH-53E Super Stallion uses three General Electric T64 at 4,380 hp each. The first gas turbine engine considered for an armoured fighting vehicle, the GT 101 which was based on the BMW 003 turbojet, was tested in a Panther tank in mid-1944. The first turboshaft engine for rotorcraft was built by the French engine firm Turbomeca , led by its founder Joseph Szydlowski . In 1948, they built
240-445: The 'gas generator' and the 'power section'. The gas generator consists of the compressor , combustion chambers with ignitors and fuel nozzles , and one or more stages of turbine . The power section consists of additional stages of turbines, a gear reduction system, and the shaft output. The gas generator creates the hot expanding gases to drive the power section. Depending on the design, the engine accessories may be driven either by
270-457: The DCT functions as an automatic transmission, requiring no driver input to change gears. A continuously variable transmission (CVT) can change seamlessly through a continuous range of gear ratios . This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant RPM while
300-513: The HP shaft to supercharge a relatively low-pressure-ratio centrifugal compressor. The -C20B is typical, with an overall pressure ratio of 7.2:1, at an airflow of 3.45 lb/s (1.8 kg/s), with a power output, at the shaft, of 420 hp (310 kW). One of the latest versions of the Model 250 is the -C40, which has only a centrifugal compressor producing a pressure ratio of 9.2:1, at an airflow of 6.1 lb/s (2.8 kg/s), and develops, at
330-461: The Model 250: although air enters the intake/compression system in the conventional fashion, the compressed air leaving the centrifugal compressor diffuser is ported rearwards via two transfer pipes, which go around the outside of the turbine system, before the air is turned through 180 degrees at entry to the combustor. The combustion products expand axially forward through the two-stage (single-stage on early engines) high-pressure turbine section, which
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#1732801983585360-585: The T63, was selected for the US Army LOH in May 1965. The Model 250 powers a large number of helicopters, small aircraft and even a motorcycle ( MTT Turbine Superbike ). As a result, nearly 30,000 Model 250 engines have been produced, of which approximately 16,000 remain in service, making the Model 250 one of the highest-selling engines made by Rolls-Royce. Allison adopted a reverse-airflow engine configuration for
390-457: The clutch and/or shift between gears. Many early versions of these transmissions were semi-automatic in operation, such as Autostick , which automatically control only the clutch , but still require the driver's input to initiate gear changes. Some of these systems are also referred to as clutchless manual systems. Modern versions of these systems that are fully automatic in operation, such as Selespeed and Easytronic , can control both
420-401: The clutch operation and the gear shifts automatically, without any input from the driver. An automatic transmission does not require any input from the driver to change forward gears under normal driving conditions. The most common design of automatic transmissions is the hydraulic automatic, which typically uses planetary gearsets that are operated using hydraulics . The transmission
450-565: The diesel engines that are used in the majority of modern main battle tanks. Gear reduction A transmission (also called a gearbox ) is a mechanical device which uses a gear set —two or more gears working together—to change the speed, direction of rotation, or torque multiplication/reduction in a machine . Transmissions can have a single fixed-gear ratio, multiple distinct gear ratios , or continuously variable ratios. Variable-ratio transmissions are used in all sorts of machinery, especially vehicles. Early transmissions included
480-412: The driver to selecting either the next or previous gear, in a successive order. A semi-automatic transmission is where some of the operation is automated (often the actuation of the clutch), but the driver's input is required to move off from a standstill or to change gears. An automated manual transmission (AMT) is essentially a conventional manual transmission that uses automatic actuation to operate
510-472: The early mass-produced automobiles, the standard transmission design was manual : the combination of gears was selected by the driver through a lever (the gear stick ) that displaced gears and gear groups along their axes. Starting in 1939, cars using various types of automatic transmission became available in the US market. These vehicles used the engine's own power to change the effective gear ratio depending on
540-421: The engine in a radial direction through twin exhaust ducts, which form a V-shape seen in the front elevation. An important design feature of the Model 250 engine is its modular construction which greatly simplifies maintenance and repair activity. Also the unique reverse-flow design provides for ease of hot section maintenance. There are four modules: Earlier versions have seven axial compressor stages mounted on
570-406: The engine within its power band to produce optimal power, fuel efficiency , and smooth operation. Multiple gear ratios are also needed to provide sufficient acceleration and velocity for safe & reliable operation at modern highway speeds. ICEs typically operate over a range of approximately 600–7000 rpm, while the vehicle's speeds requires the wheels to rotate in the range of 0–1800 rpm. In
600-484: The first French-designed turbine engine, the 100-shp 782. Originally conceived as an auxiliary power unit , it was soon adapted to aircraft propulsion, and found a niche as a powerplant for turboshaft-driven helicopters in the 1950s. In 1950, Turbomeca used its work from the 782 to develop the larger 280-shp Artouste , which was widely used on the Aérospatiale Alouette II and other helicopters. This
630-452: The gas generator or by the power section. In most designs, the gas generator and power section are mechanically separate so they can each rotate at different speeds appropriate for the conditions, referred to as a ' free power turbine '. A free power turbine can be an extremely useful design feature for vehicles, as it allows the design to forgo the weight and cost of complex multiple-ratio transmissions and clutches . An unusual example of
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#1732801983585660-493: The load so as to keep the engine running close to its optimal rotation speed. Automatic transmissions now are used in more than 2/3 of cars globally, and on almost all new cars in the US. Most currently-produced passenger cars with gasoline or diesel engines use transmissions with 4–10 forward gear ratios (also called speeds) and one reverse gear ratio. Electric vehicles typically use a fixed-gear or two-speed transmission with no reverse gear ratio. The simplest transmissions used
690-449: The ratio of input speed (e.g. engine rpm) to the output speed (e.g. the speed of a car) as required for a given situation. Gear (ratio) selection can be manual, semi-automatic, or automatic. A manual transmission requires the driver to manually select the gears by operating a gear stick and clutch (which is usually a foot pedal for cars or a hand lever for motorcycles). Most transmissions in modern cars use synchromesh to synchronise
720-482: The right-angle drives and other gearing in windmills , horse -powered devices, and steam -powered devices. Applications of these devices included pumps , mills and hoists . Bicycles traditionally have used hub gear or Derailleur gear transmissions, but there are other more recent design innovations. Since the torque and power output of an internal combustion engine varies with its rpm , automobiles powered by ICEs require multiple gear ratios to keep
750-517: The shaft, 715 hp (533 kW). Data from The Instrumentation Design And Control of a T63-A-700 Gas Turbine Engine Related development Turboshaft Turboshaft engines are commonly used in applications that require a sustained high power output, high reliability, small size, and light weight. These include helicopters , auxiliary power units , boats and ships , tanks , hovercraft , and stationary equipment. A turboshaft engine may be made up of two major parts assemblies:
780-418: The speeds of the input and output shafts. However, prior to the 1950s, most cars used non-synchronous transmissions . A sequential manual transmission is a type of non-synchronous transmission used mostly for motorcycles and racing cars. It produces faster shift times than synchronized manual transmissions, through the use of dog clutches rather than synchromesh. Sequential manual transmissions also restrict
810-689: The testing of the first prototype engine, designated YT63-A-3, in April 1959. In 1960, the US Army settled for a rotary wing platform. The YT63-A-3 first flew in a variant of the Bell 47 helicopter in 1961. A modified version of the engine (YT63-A-5) with the exhaust pointing upwards (to avoid grass fires) soon followed. This version, rated at 250 hp, passed the Model Qualification Test in September 1962. The Hughes OH-6 design, powered by
840-763: The turboshaft principle is the Pratt & Whitney F135 -PW-600 turbofan engine for the STOVL Lockheed F-35B Lightning II – in conventional mode it operates as a turbofan, but when powering the Rolls-Royce LiftSystem , it switches partially to turboshaft mode to send 29,000 horsepower forward through a shaft and partially to turbofan mode to continue to send thrust to the main engine's fan and rear nozzle. Large helicopters use two or three turboshaft engines. The Mil Mi-26 uses two Lotarev D-136 at 11,400 hp each, while
870-452: The vehicle moves at varying speeds. CVTs are used in cars, tractors, side-by-sides , motor scooters, snowmobiles , bicycles, and earthmoving equipment . The most common type of CVT uses two pulleys connected by a belt or chain ; however, several other designs have also been used at times. Gearboxes are often a major source of noise and vibration in vehicles and stationary machinery. Higher sound levels are generally emitted when
900-655: Was following the experimental installation of a Boeing T50 turboshaft in an example of the Kaman K-225 synchropter on December 11, 1951, as the world's first-ever turboshaft-powered helicopter of any type to fly. The T-80 tank, which entered service with the Soviet Army in 1976, was the first tank to use a gas turbine as its main engine. Since 1980 the US Army has operated the M1 Abrams tank, which also has
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