:: wikimiki.org ::

Turboprop

Turboprop

A Turboprop (Turbo-propeller) or turboshaft engine is a type of gas turbine. It differs from a Turbojet in that the design is optimized to produce rotating shaft power to drive a propeller, instead of thrust from the exhaust gas. Basically, a turbojet consists of an intake, compressor, combustor, turbine and a propelling nozzle. Air drawn into the intake is compressed by the compressor. Fuel is burnt with the compressed air in the combustor. The hot combustion gases expand through the turbine, to provide power to the compressor. Further expansion of the gases occurs in the propelling nozzle; the high velocity jet produced providing forward thrust. In a turboprop much of the jet thrust is sacrificed in favor of shaftpower, which is obtained by extracting additional power (to that necessary to drive the compressor) from the turbine expansion process. Whilst the power turbine may be integral with the compressor turbine, most turboprops today feature a Free Power Turbine, on a separate coaxial shaft. This enables the propeller to rotate freely, independent of compressor speed. Owing to the additional expansion in the turbine system, the residual energy in the jet is fairly low (<10% of total thrust, including that of the propeller). Because the propeller is very much larger in diameter than the power turbine, the tip speed of the propeller can become supersonic. Consequently, to prevent this, a speed reduction gearbox is inserted between the power turbine and propeller shafts. The gearbox is part of the engine, whereas in a turboshaft the (helicopter) rotor reduction gearbox is remote from the engine. Turboprops are very efficient at modest flight speeds (below 450mph), because the jet velocity of the propeller (and exhaust) is relatively low. Consequently, small commuter aircraft and military transports tend to feature turboprop engines. Although turboprops are used in some General Aviation applications, their high price deters more widespread acceptance. While most modern turbojet and turbofan engines use axial-flow compressors, turboprop engines usually contain at least one stage of centrifugal compression, because of the small size of the engines. centrifugal compression Propellers lose efficiency as aircraft speed increases, which is why turboprops are not used on higher-speed aircraft. However, turboprops are far more efficient than piston-driven propeller engines. The worlds first Turboprop was the 'Jendrassik CS-1' designed by Gyorgy Jendrassik. It was produced and flown briefly in Czecho-Slovakia between 1939 and 1942. The aircraft it was fitted to was the Varga XG/XH twin-engined Recconaisance bomber. Not surprisingly the engines proved very unreliable. For more info. visit "Podklady", a Czech Aircraft drawing site (Czech text). Jendrassik had also produced a small scale turboprop of 75 kW in 1937. (Added By Peter Butt 03/12/05) The first British turboprop engine was the Rolls-Royce RB.50 Trent, a converted Derwent II fitted with reduction gear and a Rotol 7' 11" five-bladed propeller. Two Trents were fitted to Gloster Meteor EE227 - the sole "Trent-Meteor" - which became the first relataively reliable turboprop powered aircraft. From their experience with the Trent, Rolls-Royce developed the Dart, which became one of the most reliable turbprop engines ever built. Dart production continued for more than fifty years. For info on Trent go to Rolls-Royce Heritage Trust) The first American Turboprop was the General-Electric T-31. A European consortium is currently developing the 11000shp TP400-D6 turboprop for the A400M military transport. The engine is all-axial and has a two shaft core, with a free power turbine mounted on a third coaxial shaft. Residual thrust on a turboshaft is avoided by: a) further expansion in the turbine system and/or b) truncating and turning the exhaust through 90degrees, to produce two opposing jets. Apart from the above and the remote location of the gearbox, there is very little difference between a turboprop and a turboshaft.

External links

- [http://Innodyn.com Innodyn]
- [http://tanks45.tripod.com/Jets45/Histories/Trent/Trent.htm Gloster Trent-Meteor] Category:Gas turbines Category:Aircraft engines Category:Jet engines

Gas turbine

, and foil bearings. ]] A gas turbine is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.) Energy is added to the gas stream in the combustor, where air is mixed with fuel and ignited. Combustion increases the temperature, velocity and volume of the gas flow. This is directed through a diffuser (nozzle) over the turbine's blades, spinning the turbine and powering the compressor. Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks.

Theory of operation

Gas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isentropically, combustion occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure. In practise, friction and turbulence cause: a) non-isentropic compression - for a given overall pressure ratio, the compressor delivery temperature is higher than ideal b) non-isentropic expansion - although the turbine temperature drop necessary to drive the compressor is unaffected, the associated pressure ratio is greater, which decreases the expansion available to provide useful work. a) a pressure loss in the combustor - reduces the expansion available to provide useful work. Image:Brayton cycle.png As with all cyclic heat engines, higher combustion temperature means greater efficiency. The limiting factor is the ability of the steel, ceramic, or other materials that make up the engine to withstand heat and pressure. Considerable engineering goes into keeping the turbine parts cool. Most turbines also try to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchangers that pass exhaust heat to the compressed air, prior to combustion. Combined cycle designs pass waste heat to steam turbine systems. And combined heat and power (co-generation) uses waste heat for hot water production. Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple turbines might have one moving part: the shaft/compressor/turbine/alternator-rotor assembly (see image above), not counting the fuel system. More sophisticated turbines may have multiple shafts (spools), hundreds of turbine blades, movable stator blades, and a vast system of complex piping, combustors and heat exchangers. As a general rule, the smaller the engine the faster the shaft/s rotate, to maintain tip speed: Jet engines operate around 10,000 rpm and micro turbines around 100,000 rpm. Thrust bearings and journal bearings are a critical part of design. Traditionally, they have been hydrodynamic oil bearings, or oil-cooled ball bearings. This is giving way to hydrodynamic foil bearings, which have become common place in micro turbines and APU’s (auxiliary power units.)

Jet engines

See jet engine page.

Gas turbines for electrical power production

jet engine of 60% in combined cycle configurations.]] Industrial gas turbines range in size from truck-mounted mobile plants to enormous, complex systems. The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated building. They can be particularly efficient—up to 60 percent—when waste heat from the gas turbine is recovered by a conventional steam turbine in a combined cycle configuration. Simple cycle gas turbines in the power industry require smaller capital investment than combined cycle gas, coal or nuclear plants and can be designed to generate small or large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for baseload plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Large simple cycle gas turbines may produce several hundred megawatts of power and approach 40 percent thermal efficiency.

Micro turbines

thermal efficiency Also known as:
- Turbo alternators
- Gensets
- MicroTurbine® (registered trademark of Capstone Turbine Corporation)
- Turbogenerator® (registered tradename of Honeywell Power Systems, Inc.) Micro turbines are becoming wide spread for distributed power and combined heat and power applications. They range from handheld units producing less than a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts. Part of their success is due to advances in electronics, which allow unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows, for example, the generator to be integrated with the turbine shaft, and to double as the starter motor. Micro turbine systems have many advantages over piston engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. However, piston engine generators are quicker to respond to changes in output power requirement. They accept most commercial fuels, such as natural gas, propane, diesel and kerosene. The are also able to produce renewable energy when fueled with biogas from landfills and sewage treatment plants. Micro turbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator. Recuperators are difficult to design and manufacture because they operate under high pressure and temperature differentials. Exhaust heat can be used for water heating, drying processes or absorption chillers, which create cold for air conditioning from heat energy instead of electric energy. Typical micro turbine efficiencies are 25 to 35 percent. When in a combined heat and power cogeneration system, efficiencies of greater than 80 percent are commonly achieved.

Auxiliary power units

Auxiliary power units (APUs) are small gas turbines designed for auxiliary power of larger machines, usually aircraft. They are well suited for supplying compressed air for aircraft ventilation (with an appropriate compressor design), start-up power for larger jet engines, and electrical and hydraulic power. (These are not to be confused with the auxiliary propulsion units, also abbreviated APUs, aboard the gas-turbine-powered Oliver Hazard Perry-class guided-missile frigates. The Perrys' APUs are large electric motors that provide maneuvering help in close waters, or emergency backup if the gas turbines are not working.)

Gas turbines in vehicles

Gas turbines are used on ships, locomotives, helicopters, and in tanks. A number of experiments have been conducted with gas turbine powered automobiles. In 1950, designer F. R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum. Rover and the BRM Formula One team joined forces to produce a gas turbine powered coupe, which entered the 1963 24 hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km) and had a top speed of 142 mph (229 km/h). American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. [http://www.aardvark.co.nz/pjet/chrysler.shtml A history of Chrysler turbine cars]. In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator. Gas turbines offer a high-powered engine in a very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of rpms and powers needed in vehicle applications. Also, turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small turbines are rarities. It is also worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important. Their use in hybrids reduces the second problem. Capstone currently lists on their website a version of their turbines designed for installation in hybrid vehicles. The MTT Turbine SUPERBIKE appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a jet engine - specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 283kW (380shp). Speed-tested to 365km/h or 227mph (according to some stories, the testing team ran out of road during the test), it holds the Guinness World Records for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000. Use of gas turbines in military tanks has been more successful. In the 1950s, a Conqueror heavy tank was experimentally fitted with a Parsons 650-hp gas turbine, and they have been used as auxiliary power units in several other production models. Today, the Soviet/Russian T-80 and U.S. M1 Abrams tanks use gas turbine engines. See tank for more details. Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See Gas turbine-electric locomotive for more information.

Naval use

Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti) was commissioned in 1961. The first U.S. gas-turbine powered ships were the U.S. Coast Guard's Hamilton-class High Endurance Cutters the first of which (USCGC Hamilton) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry-class frigates, Spruance-class and Arleigh Burke-class destroyers, and Ticonderoga-class guided missile cruisers. USS Makin Island, a modified Wasp-class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines.

Amateur gas turbines

A popular hobby is to construct a gas turbine from an automotive turbocharger. A combustion chamber is fabricated and plumbed between the compressor and turbine. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. Several small companies manufacture small turbines and parts for the amateur. See external links for resources.

Advances in technology

Gas turbine technology has steadily advanced since its inception and continues to evolve; research is active in producing ever smaller gas turbines. Computer design, specifically CFD and finite element analysis along with material advances, has allowed higher compression ratios and temperatures, more efficient combustion, better cooling of engine parts and reduced emissions. Additionally, compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system. On another front, microelectronics and power switching technology have enabled commercially viable micro turbines for distributed and vehicle power. An excellent example is the Capstone line of micro turbines, which do not require an oil system and can run unattended for months on end.

External links

- [http://web.mit.edu/aeroastro/www/labs/GTL/gtl_about.html MIT Gas Turbine Laboratory]
- [http://www.memagazine.org/backissues/october97/features/turbdime/turbdime.html MIT Microturbine research]
- [http://www.sciencemuseum.org.uk/collections/treasures/margas.asp First Marine Gas Turbine 1947] Amateur groups and small manufacturers
- [http://groups.yahoo.com/group/DIYGasTurbines DIY Gas Turbines Yahoo Group]
- [http://www.power.alstom.com/home/equipment___systems/turbines/gas_turbines/7323.EN.php?languageId=EN&dir=/home/equipment___systems/turbines/gas_turbines/ ALSTOM Gas Turbines]
- [http://www.nyethermodynamics.com Nye Thermodynamics Corporation]
- [http://www.Innodyn.com Innodyn]
- [http://www.m-dot.com/page8.html M-Dot Microturbines] Large turbine manufacturers
- [http://www.rolls-royce.com/energy/products/oilgas/gasturb.jsp Rolls-Royce Gas Turbines]
- [http://www.mpshq.com/products_gasturbines.htm Mitsubishi Gas Turbines]
- [http://www.gepower.com/prod_serv/products/gas_turbines_cc/en/index.htm GE Gas Turbines]
- [http://www.siemenswestinghouse.com/en/gasturbinesitem/index.cfm Siemens Gas Turbines]
- [http://lmz.frinet.org/centere.htm LMZ Gas Turbines (Russia)]
- [http://www.ivchenko-progress.com/ Ivchenko-Progress (Ukraine)]
- [http://www.avid.ru/ Perm motors (Russia)]
- [http://www.microturbine.com/ Capstone Microturbines]
- [http://mysolar.cat.com/cda/layout Solar Turbines] Category:Engines Category:Turbines Category:Gas turbines Category:Marine propulsion ja:ガスタービンエンジン

Turbojet

:For the transportation company, see TurboJET. TurboJET Turbojets are the simplest and oldest kind of general purpose jet engine. Two different engineers, Frank Whittle in Britain and Hans von Ohain in Germany, developed the concept during the late '30's. Fighter aircraft, fitted with turbojet engines, first entered service in 1944, towards the end of WW2. A turbojet engine is used primarily to propel aircraft. Air is drawn into the rotating compressor via the intake and is compressed to a higher pressure before entering the combustion chamber. Fuel is mixed with the compressed air and ignited by flame in the eddy of a flame holder. This combustion process significantly raises the temperature of the gas. Hot combustion products leaving the combustor expand through the turbine, where power is extracted to drive the compressor. Although this expansion process reduces the turbine exit gas temperature and pressure, both parameters are usually still well above ambient conditions. The gas stream exiting the turbine expands to ambient pressure via the propelling nozzle, producing a high velocity jet in the exhaust plume. If the jet velocity exceeds the aircraft flight velocity, there is a net forward thrust upon the airframe. Modern jet engines are mainly turbofans, where some (if not most) of the air entering the intake bypasses the combustor. Although ramjet engines are simpler in design (virtually no moving parts), they are incapable of operating at low flight speeds.

Air intake

Preceding the compressor is the air intake (or inlet), which is designed to recover, as efficiently as possible, the ram pressure of the streamtube approaching the intake. Downstream of the intake, air enters the compression system.

Compressor

The compressor, which rotates at very high speed, adds energy to the airflow, at the same time squeezing it into a smaller space, thereby increasing its pressure and temperature (try rapidly pumping on a bicycle pump - it will quickly become very warm!). Several types of compressor are used in turbojets and gas turbines in general: axial, centrifugal, axial-centrifugal, double-centrifugal, etc. Early turbojet compressors had overall pressure ratios as low as 5:1 (as do a lot of simple auxiliary power units and small propulsion turbojets today). Aerodynamic improvements, plus splitting the compression system into two separate units and/or fitting variable stators, enabled later turbojets to have overall pressure ratios of 15:1 or more. In comparison, modern civil turbofan engines have overall pressure ratios as high as 44:1 or more. After leaving the compression system, the compressed air enters the combustor.

Combustor

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 dramatically. In a turbojet the air and fuel mixture passes, unconfined, through the combustion chamber. As the mixture burns its temperature increases dramatically, the pressure actually decreasing a few percent. In detail, the fuel-air mixture must be brought almost to a stop so that a stable flame can be maintained, this occurs just after the beginning of the combustion chamber. The aft part of this flame front is allowed to progress rearward in the engine. This ensures that the rest of the fuel is burned as the flame becomes hotter when it leans out, and because of the shape of the combustion chamber the flow is accelerated rearwards. Some pressure drop is unavoidable, as it is the reason why the expanding gases travel out the rear of the engine rather than out the front. Less than 25% of the air is involved in combustion, in some engines as little as 12%, the rest acting as a reservoir to soak up the heating effect of the fuel burning. Another difference between piston engines and jet engines is that the peak flame temperature in a piston engine is experienced only momentarily, and for a small portion of the entire cycle. The combustor in a jet engine is exposed to the peak flame temperature continuously and operates at a pressure high enough that a stoichiometric fuel-air ratio would melt the can and everything downstream. Instead, jet engines run a very lean mixture, so lean that it would not normally support combustion. A central core of the flow is mixed with enough fuel to burn readily. The cans are carefully shaped to maintain a layer of fresh unburned air between the metal surfaces and the central core. This unburned air mixes into the burned gases to bring the temperature down to something the turbine can tolerate.

Turbine

Hot gases leaving the combustor are allowed to expand through the turbine. In the first stage the turbine is largely a reaction 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 rearward and gain energy from that process. Pressure drops, and energy is transferred into the shaft. The turbine's rotational energy is used primarily to drive the compressor. Some shaft power is extracted to drive accessories, like fuel, oil, and hydraulic pumps. Because of its significantly higher entry temperature, the turbine pressure ratio is much lower than that of the compressor. In a turbojet almost two thirds of all the power generated by burning fuel is used by the compressor to compress the air for the engine.

Nozzle

After the turbine, the gases are allowed to expand through the exhaust nozzle to atmospheric pressure, producing a high velocity jet in the exhaust plume. In a convergent nozzle, the ducting narrows progressively to a throat. The nozzle pressure ratio on a turbojet is usually high enough for the expanding gases to reach Mach 1.0 and choke the throat. Normally the flow will go supersonic in the exhaust plume, external to the engine. If, however, a convergent-divergent nozzle is fitted, the divergent (increasing flow area) section allows the gases to reach supersonic velocity within the nozzle itself. This is slightly more efficient on thrust, than using a convergent nozzle. There is, however, the added weight and complexity, since the con-di nozzle must be fully variable, to cope basically with engine throttling.

Net thrust

Below is an approximate equation for calculating the net thrust of a turbojet:

F_n = m \cdot (V_ - V_a)

where:

m =

intake mass flow

V_ =

fully expanded jet velocity (in the exhaust plume)

V_a =

= aircraft flight velocity Whilst the m
- V_jfe term represents the nozzle gross thrust, the m
- V_a term represents the ram drag of the intake. Obviously, the jet velocity must exceed that of the flight velocity if there is to be a net forward thrust on the airframe.

Cycle improvements

Increasing the overall pressure ratio of the compression system raises the combustor entry temperature. Therefore, at a fixed fuel flow and airflow, there is an increase in turbine inlet temperature. Although the higher temperature rise across the compression system, implies a larger temperature drop over the turbine system, the nozzle temperature is unaffected, because the same amount of heat is being added to the system. There is, however, a rise in nozzle pressure, because overall pressure ratio increases faster than the turbine expansion ratio. Consequently, net thrust increases, whilst specific fuel consumption (fuel flow/net thrust) decreases. So turbojets can be made more fuel efficient by raising overall pressure ratio and turbine inlet temperature in unison. However, better turbine materials and/or improved vane/blade cooling are required to cope with increases in both turbine inlet temperature and compressor delivery temperature. Increasing the latter requires better compressor materials.

Early designs

Early German engines had serious problems controlling the turbine inlet temperature. Their early engines averaged only ten hours of operation before failing—often with chunks of metal flying out the back of the engine when the turbine overheated. British engines tended to fare better due to better metals. The Americans had the best materials because of their reliance on turbosupercharging in high altitude bombers of World War II. For a time some US jet engines included the ability to inject water into the engine to cool the compressed flow before combustion, usually during takeoff. The water would tend to prevent complete combustion and as a result the engine ran cooler again, but the planes would takeoff leaving a huge plume of smoke. Today these problems are much better handled, but temperature still limits airspeeds in supersonic flight. At the very highest speeds, the compression of the intake air raises the temperature to the point that the compressor blades will melt. At lower speeds, better materials have increased the critical temperature, and automatic fuel management controls have made it nearly impossible to overheat the engine.

Turboshaft

Turboshaft engines and jet engines use a gas turbine to produce power. While jet engines use mostly the produced thrust power, turboshaft engines use mostly shaft power. A turboshaft used to drive a propeller is commonly called turboprop. But turboshaft engines are also used in helicopters, ships, tanks and locomotives. The name itself is most common for helicopter engines. The first true turboshaft engine was built by the French engine firm Turbomeca, led by the founder, Joseph Szydlowski. In 1948 they built the first French-designed turbine engine, the 100shp 782. In 1950 this work was used to develop the larger 280shp Artouste, which was widely used on the Aérospatiale Alouette and other helicopters. The distinct whine of the Artouste is familiar to all those who have watched a 1967 UK television series The Prisoner, since an Alouette was featured in many of the episodes. Note that Artouste is also the name of an unrelated English design, the Blackburn Artouste. Major efforts were underway in the United States and England to build similar engines. In the US Anselm Franz followed the same principles of simplicity that he used to develop the Jumo 004 in Germany, producing the T53 engine at Lycoming in 1953, and following this with the larger T55. General Electric beat his design into operation with their T58 series. Today almost all engines are built so that power-take-off is independent of engine speed. This has two advantages: (1) it allows a helicopter rotor or propeller to spin at any speed instead of being geared directly to the turbine, and (2) it allows the engine to be split into two sections, the "hot section" containing the majority of the engine, and the separate power-take-off, allowing the hot-section to be removed for easier maintenance. This leads to slightly larger engines—compare the Pratt & Whitney PT-6 and similar models from Garrett Systems, for instance—but for the speed ranges served by these engines it is considered to be unimportant. Today practically all smaller turbine engines come in both turboprop and turboshaft versions, differing primarily in their accessory systems. Category:Gas turbines Category:Aircraft engines

Helicopter

]] , a four seat development of the R22]] A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors (propellers). Helicopters are classified as rotary-wing aircraft to distinguish them from conventional fixed-wing aircraft. The word helicopter is derived from the Greek words helix (spiral) and pteron (wing). The engine-driven helicopter was invented by the Slovak inventor Jan Bahyl. The first stable, fully-controllable helicopter placed in production was invented by Igor Sikorsky. Compared to conventional fixed-wing aircraft, helicopters are much more complex, more expensive to buy and operate, relatively slow, have shorter range and restricted payload. The compensating advantage is maneuverability: helicopters can hover in place, reverse, and above all take off and land vertically. Subject only to refuelling facilities and load/altitude limitations, a helicopter can travel to any location, and land anywhere with enough space (a diameter of length 1.5 times the rotor disk).

Applications

Helicopters have many uses, both military and civil, including troop transportation, infantry support, firefighting, [http://www.tropicaled.com/helicopter2.htm shipboard operations], business transportation, casualty evacuation (including MEDEVAC, and air/sea/mountain rescue), police and civilian surveillance, carrying goods (some helicopters can carry slung loads, accommodating awkwardly shaped items), or as a mount for still, film or television cameras. Helicopters suffer from significantly higher operating and maintenance costs compared with fixed wing aircraft. The costs are due to inherent mechanical complexity and greater power requirements for a given gross weight. For these reasons, helicopters are not economically viable for commercial transportation. Speed and range limitations also constrain commercial applications.

History

police] Since around 400 BC the Chinese had a flying top that was used as a children's toy. This toy eventually made its way to Europe via trade and has been depicted in a 1463 European painting. Incidentally, the Wright brothers as children were given a rubber-band-powered version of this toy invented by Alphonse Penaud and were very much fascinated by it and built their own copies. "Pao Phu Tau" was a 4th century book in China that described some of the ideas in a rotary wing aircraft. The first somewhat practical idea of a human carrying helicopter was first conceived by Leonardo da Vinci around 1490, but it was not until after the invention of the powered aeroplane in the 20th century that actual models were produced. Developers such as Jan Bahyl, Oszkár Asbóth, Louis Breguet, Paul Cornu, Emile Berliner, Ogneslav Kostovic Stepanovic and Igor Sikorsky pioneered this type of aircraft, with Juan de la Cierva introducing the first practical autogiro in 1923 that was to be the basis for the modern helicopter. A flight of the first fully controllable helicopter was demonstrated by Raúl Pateras de Pescara 1916 in Buenos Aires, Argentina. The German Focke-Wulf Fw 61 was the first practical helicopter. It first flew in 1934. The Bell 47 designed by Arthur Young was the first helicopter to be licensed (in March 1946) for use in the United States. Reliable helicopters capable of stable hover flight were developed decades after fixed wing aircraft. This is largely due to higher engine power density requirements when compared with fixed wing aircraft. Igor Sikorsky is reported to have delayed his own helicopter research until suitable engines were commercially available. Improvements in fuels and engines during the first half of the 20th century were a critical factor in helicopter development. The availability of lightweight turboshaft engines in the second half of the 20th century led to the development of larger, faster, and higher performance helicopters. Turboshaft engines are the preferred powerplant for all but the smallest and least expensive helicopters today.

Generating lift

A conventional aircraft is able to fly because the forward motion of its angled wings forces air downwards, creating an opposite reaction called lift that forces the wings upwards. A helicopter uses exactly the same method, except that instead of moving the entire aircraft, only the wings themselves are moved, in a circular motion. The helicopter's rotor can simply be regarded as rotating wings (hence the military appellation of "rotary wing aircraft"). lift

Conventional layout

There are several possible design layouts for arranging a helicopter's rotors. The most common design is the Sikorsky-layout, which is used by approximately 95% of all helicopters manufactured to date. It is as follows: turning the rotor generates lift but it also applies a reverse torque to the vehicle, which would spin the helicopter fuselage in the opposite direction to the rotor. At low speeds, the most common way to counteract this torque is to have a smaller vertical propeller mounted at the rear of the aircraft called a tail rotor. This rotor creates thrust which is in the opposite direction from the torque generated by the main rotor. When the thrust from the tail rotor is sufficient to cancel out the torque from the main rotor, the helicopter will not rotate around the main rotor shaft. The world's largest and smallest series-produced helicopters follow this principle. The Mil Mi-26 can lift 27 metric tons, the Robinson R22 has a crew of two and a gross weight of 1300 lbs (590 kg). Almost all civilian helicopters have the main rotor and tail rotor system. The world's fastest helicopter, the Westland Lynx can perform aerobatic loops and rolls with this conventional rotor system. aerobatic (Poland)]] Sometimes the blades of a tail rotor are not separated by the same angle, but laid out in an X-shape, which is supposed to reduce the noise levels for military use (e.g. AH-64 Apache). If the tail rotor is shrouded (i.e., a fan embedded in the vertical tail) it is called a fenestron. The fenestron rotor system on the model EC120 helicopter uses a shaft driven system and gearbox to turn the fan. It is less efficient but the advantages are that less noise is generated, it's safer for people that may walk near it and there is less chance of the blades being damaged by objects because it's shrouded, unlike the traditional tail rotor. Other helicopters use a Notar (an acronym meaning no tail rotor) design: they blow air through a long slot along the tail boom, utilizing the Coanda effect to produce forces to counter the torque. Notars adjust thrust by opening and closing a sliding circular cover near the end of the tail boom. The amount of power required to prevent a helicopter from spinning is significant. A tail rotor can use up to 30% of the engine's power, and this power does not help the helicopter produce lift or forward motion. To reduce this waste during cruise, the vertical stabilizer is often angled to produce a force which helps counter the main rotor torque. At high speeds, it is possible for the vertical stabilizer to counteract the entire torque, leaving more power available for forward flight. This is commonly known as slip-streaming and can make hovering turns difficult on windy days. Another reason for the angled vertical stabilizer is to make it possible to stage a successful high-speed, run-on landing, in case of the tail rotor failure or damage. Many military helicopters, especially attack types, have short wings called stub wings to add lift during forward motion. They are also used as external mounts for weapons. In extreme cases, such as that of the Mil Mi-24, the wings are large enough to obstruct airflow down from the rotors, making the helicopter all but unable to hover.

Alternative layouts

Mil Mi-24]] There are alternatives to Sikorsky's layout, which save the weight of a tail boom and rotor. Such designs use two rotors which turn in opposite directions, or contra-rotate. All of these systems are designed for the same purpose: to produce a net rotational speed of zero. These methods introduce even more mechanical complexity to the design and are usually relegated to specialized helicopter types. The co-axial design, where rotors are mounted on top of each other at the top of the fuselage and share a common main axle complex, was first built by Theodore von Karman and Asbóth Oszkár in 1918 and later became the hallmark of soviet Kamov design bureau (see for example the Kamov Ka-50 "Hokum"). Co-axial helicopters in flight are highly resistant to side-winds, which makes them suitable for shipboard use, even without a rope-pulley landing system. Another example is the Kamov Ka-26, a successful crop duster aircraft. The Kaman system of intermeshing rotors, which was developed in Nazi Germany for a small anti-submarine warfare helicopter, features two main rotors on separate, obliquely mounted axles. The contra-rotating rotors are located on top of the fuselage, close to each other. During the Cold War the American Kaman company started to produce similar helicopters for USAF firefighting purposes. Kamans have high stability and powerful lifting capability, thus the latest Kaman V-Max model is a dedicated sky crane design, used for construction works. In the flying-waggon or tandem rotor system (sometimes called "flying banana" for the peculiar shape of early U.S. examples), the two main rotors are located at the front and rear extremity of a long, boxy fuselage that resembles a railway wagon. A prime example is the Boeing CH-47 Chinook, that can carry 14 tons of payload. Waggon helicopters are practical for military logistical purposes, because entry and unloading is easily facilitated via the unobstructed front and rear ramps. The rotors and turbines are located very high on top of the fuselage, making them less sensitive to damage and dirt. The main drawback of a waggon is limited agility in air and the need for a highly trained crew, as the large main rotors have long outreach beyond the fuselage and may easily hit nearby obstacles (in 2001, a South Korean army CH-47 Chinook crashed onto a bridge for that reason while being shown live on TV). A helicopter built by Juan de la Cierva had three main rotors. These were placed at the corners of an equilateral triangle and all turned the same direction. equilateral triangle In the cross system, the rotary wing aircraft resembles a traditional fixed-wing airplane, with the two main rotors mounted at the extremities of its wings. Such helicopters are rare, because structural integrity of the wings is difficult to maintain against the amplified resonance of far off-board rotor-turbine units. The 1930s German FW-61 helicopter was built to such design. The world's largest ever helicopter, the Soviet Mil-V-12 prototype, was a cross of two Mil Mi-6 turbine-rotor units built onto a modified Antonov cargo plane. The U.S. V-22 Osprey tilting rotorcraft is similar, although its nacelles can be rotated, and shares some of the inherent technical problems of a cross system. nacelleA recent development in helicopter technology is the NOTAR system, which stands for NO TAil Rotor. The NOTAR eliminates the tail rotor by conducting high-velocity air through the tail boom. The NOTAR system was developed in the United States and is used exclusively by McDonnel Douglas Helicopters, or MD Helicopters. The most unusual design is the roto-rocket principle, where the single main rotor draws power not from the shaft, but from its own wingtip jet nozzles, which are either pressurized from a fuselage-mounted gas turbine or have their own pulsejet combustion chambers. Although this method is simple and eliminates precession, development of such helicopters ceased soon, because their extreme noise levels preclude both military and civilian use.

Controlling flight

Useful flight requires that an aircraft be controlled in all three dimensions (see flight dynamics). In a fixed-wing aircraft, this is easy: small movable surfaces are adjusted to change the aircraft's shape so that the air rushing past pushes it in the desired direction. In a helicopter, however, there often isn't enough airspeed for this method to be practical. flight dynamics, an aerodynamically restyled F28 for the corporate market.]] For rotation about the vertical axis (yaw) the anti-torque system is used. Varying the pitch of the tail rotor alters the sideways thrust produced. Dual-rotor helicopters have a differential between the two rotor transmissions that can be adjusted by an electric or hydraulic motor to transmit differential torque and thus turn the helicopter. Yaw controls are usually operated with anti-torque pedals, on the floor in the same place as a fixed-wing aircraft's rudder pedals. For pitch (tilting forward and back) or roll (tilting sideways) the angle of attack of the main rotor blades is altered or cycled during the rotation creating a differential of lift at different points of the rotary wing. More lift at the rear of the rotary wing will cause the aircraft to pitch forward, a increase on the left will cause a roll to the right and so on. Helicopters maneuver with three flight controls besides the pedals. The collective pitch control lever controls the collective pitch, or angle of attack, of the helicopter blades altogether, that is, equally throughout the 360 degree plane-of-rotation of the main rotor system. When the angle of attack is increased, the blade produces more lift. The collective control is usually a lever at the pilot's left side, near his leg. Simultanously increasing the collective and adding power with the throttle causes a helicopter to rise. angle of attack] The throttle controls the absolute power produced by the engine that is connected to the rotor by a transmission. The throttle control is a twist grip on the collective control. RPM control is critical to proper operation for several reasons. Helicopter rotors are designed to operate at a specific RPM. If the RPM is too low, rapid descent with power, known as settling with power could result. If the RPM is too high, damage to the main rotor hub from excessive forces could result. In general, RPM must be maintained within a tight tolerance, usually a few percent. In many piston-powered helicopters, the pilot must manage the engine and rotor RPM. The pilot manipulates the throttle to maintain rotor RPM and therefore regulates the effect of drag on the rotor system. Turbine engined helicopters, and some piston helicopters, use servo-feedback loop in their engine controls to maintain rotor RPM and relieves the pilot of routine responsibility for that task. The cyclic changes the pitch of the blades cyclically, causing the lift to vary across the plane of the rotor disk. This variation in lift causes the rotor disk to tilt, and the helicopter to move during hover flight or change attitude in forward flight. The cyclic is similar to a joystick and is usually positioned in front of the pilot. The cyclic controls the angle of the stationary section of the swashplate, which in turn controls the angle of the rotating section of the swashplate. The rotating section rotates with the rotor and is connected to blade pitch horns through pitch links, one link for each blade. When the swashplate is not tilted, the blades are all at the collective angle. When it is tilted, the links give a pitch-up at some azimuthal angle and a pitch-down at the opposite angle, hence creating a sinusoidal variation in blade angle of attack. This causes the helicopter to tilt in the same direction as the cyclic. If the pilot pushes the cyclic forward, then the helicopter tilts forward, and the rotor produces a thrust in the forward direction. angle of attack] As a helicopter moves forward, the rotor blades on one side move at rotor tip speed plus the aircraft speed and is called the advancing blade. As the blade swings to the other side of the helicopter, it moves at rotor tip speed minus aircraft speed and is called the retreating blade. To compensate for the added lift on the advancing blade and the decreased lift on the retreating blade, the angle of attack of the blades is regulated as the blade spins around the helicopter. The angle of attack is increased on the retreating blade to produce more lift, compensating for the slower airspeed over the blade. And the angle of attack is decreased on the advancing blade to produce less lift, compensating for the faster airspeed over the blade. If the angle of attack of any wing, including rotor blades, is too high, the airflow above the wing separates causing instant loss of lift and increase in drag. This condition is called aerodynamic stall. On a helicopter, this can happen in any of three ways. #As helicopter speed increases, the advancing blades approach the speed of sound and generate shock waves that disrupt the airflow over the blade causing loss of lift. #As helicopter speeds increase, the retreating blade experiences lower relative airspeeds and the controls compensate with higher angle of attack. With a low enough relative airspeed and a high enough angle of attack, aerodynamic stall is inevitable. This is called retreating blade stall. #Any low rotor RPM flight condition accompanied by increasing collective pitch application will cause aerodynamic stall. stall AH.1 (XV134), now on the UK Civil Register.]] Helicopters are powered aircraft, but they can still fly without power by using the momentum in the rotors and using downward motion to force air through the rotors. The main rotor acts like a "windmill" and turns. This technique is known as autorotation. A transmission connects the main rotor to the tail rotor so that all flight controls are available after engine failure. Autorotation can allow a pilot to make an emergency landing if the engine failure occurs while the helicopter is traveling high enough or fast enough. (see Height-velocity diagram). A very peculiar feature of the cyclic is that the lift is made to occur 90 degrees of rotation before the direction of tilt. This is because when one tries to tilt a spinning object (like a rotor), it moves at right angles to the direction of the force. This is called "gyroscopic precession". So control forces on the rotor are rotated 90 degrees before the desired motion. For example, forward motion requires less lift at the front of the disk and more lift at the rear of the disk, so the pilot pushes the cyclic forward. The helicopter's control linkages rotate the pitching forces 90 degrees backwards against the rotor spin, to push on the sides of the rotor rather than its front and back. It took inventors many years to recognize precession, and to learn how to arrange the cyclic's control system to overcome it.

Stability

Fixed wing aircraft are designed to be inherently stable. If a gust of wind or a nudge to one of the controls causes a fixed wing aircraft to pitch, roll, or yaw, the aerodynamic design of the aircraft will tend to correct the motion, and the aircraft will return to its original attitude. A small, fixed wing aircraft can be stable enough that a pilot can let go of the controls while looking at a map or dealing with a radio, and the plane will generally stay on course. precession In contrast, helicopters are very unstable. Simply hovering requires continuous, active corrections from the pilot. When a hovering helicopter is nudged in one direction by a gust of wind, it will tend to continue in that direction, and the pilot must adjust the cyclic to correct the motion. Hovering a helicopter has been compared to balancing yourself while standing on a large beach ball. Adjusting one flight control on a helicopter almost always has an effect that requires an adjustment of the other controls. Moving the cyclic forward causes the helicopter to move forward, but will also cause a reduction in lift, which will require extra collective for more lift. Increasing collective will reduce rotor RPM, requiring an increase in throttle to maintain constant rotor RPM. Changing collective will also cause a change in torque, which will require the pilot to adjust the foot pedals. Small helicopters can be so unstable that it may be impossible for the pilot to ever let go of the cyclic while in flight. While fixed-wing aircraft are generally designed so pilots sit on the left side of the aircraft, freeing up their right hand for dealing with radios, engine controls, and the like, helicopters are generally designed so pilots sit on the right side of the aircraft so they can keep their right hand (usually the strong hand) on the cyclic at all times, leaving the radios and engine controls for their left hand (usually the weaker hand).

Limitations

precession The single most obvious limitation of the helicopter is its slow speed. The current record is around 400 km/h set by the Westland Lynx. There are several reasons why a helicopter cannot fly as fast as a fixed wing aircraft.
- When the helicopter is at rest, the outer tips of the rotor travel at a speed determined by the length of the blade and the RPM. In a moving helicopter, however, the speed of the blades relative to the air depends on the speed of the helicopter as well as on their rotational velocity. The airspeed of the forward-going rotor blade is much higher than that of the helicopter itself. It is possible for this blade to exceed the speed of sound, and thus produce vastly increased drag and vibration. It is theoretically possible to have spiralling rotors, similar in principle to variable-pitch swept wings, which could exceed the speed of sound, but no presently known materials are light enough, strong enough, and flexible enough to construct them.
- Most rotors are not rigid. Because the advancing blade has higher airspeed than the retreating blade, a perfectly rigid blade would generate more lift on that side and tip the aircraft over. In consequence, rotor blades are designed to "flap" - lift and twist in such a way that the advancing blade flaps up and develops a smaller angle of attack, thus producing less lift than a rigid blade would. Conversely, the retreating blade flaps down, develops a higher angle of attack, and generates more lift. At high speeds, the force on the rotors is such that they "flap" excessively and the retreating blade can reach too high an angle and stall. In some designs the hub is rigid. The blades are made from composites which can bend without breaking. Fully rigid rotors exist and create very responsive helicopters. In most such designs, the lift is varied cyclically and according to the speed of the helicopter. The adjustment is either by adjusting the angle of attack of the blades, or by engine-powered vacuum devices that suck air into the blades, adjusting the lift. speed of sound) twin rotor helicopter had a large cargo door and external hoist, and was used as personnel/paratroop transport, casualty evacuation, and for lifting large loads. The Belvedere had a production run of only 26 and went into RAF service in 1961.]]
- Rotorhead design is a limiting factor on many helicopters. Low or negative-G situations encountered in a semi-rigid system will result in blade flapping down until it hits the tail boom or other airframe structure, followed by rotor separation, causing a crash.
- Helicopters are susceptible to potentially disastrous vortex ring effects. In these, the downward wind from the rotor causes a circular vortex to form around the rotor. If this ring is augmented by terrain, wind, rain, or sea spray, the helicopter can lose enough lift to experience settling with power and hit the ground. During the closing years of the 20th century designers began working on helicopter noise reduction. Urban communities have often expressed great dislike of noisy aircraft, and police and passenger helicopters can be unpopular. The redesigns followed the closure of some city heliports and government action to constrain flight paths in national parks and other places of natural beauty. Helicopters vibrate. An unadjusted helicopter can easily vibrate so much that it will shake itself apart. To reduce vibration, all helicopters have rotor adjustments for height and pitch. Most also have vibration dampers for height and pitch. Some also use mechanical feedback systems to sense and counter vibration. Usually the feedback system uses a mass as a "stable reference" and a linkage from the mass operates a flap to adjust the rotor's angle of attack to counter the vibration. Adjustment is difficult in part because measurement of the vibration is hard. The most common adjustment measurement system is to use a stroboscopic flash lamp, and observe painted markings or coloured reflectors on the underside of the rotor blades. The traditional low-tech system is to mount coloured chalk on the rotor tips, and see how they mark a linen sheet.

Landing

On a ship

angle of attack] A helo deck is a helicopter pad on the deck of a ship, usually located on the stern and always clear of obstacles that would prove hazardous to a helicopter landing. In the U.S. Navy it is commonly and properly referred to as the flight deck. In the Royal Navy, landing on is usually achieved by lining up slightly astern and on the port quarter, as the ship steams into the wind and the aircraft captain slides across and over the deck. Shipboard landing for some helicopters is assisted though use of a haul-down device that involves attachment of a cable to a probe on the bottom of the aircraft prior to landing. Tension is maintained on the cable as the helicopter descends which assists the pilot with accurate positioning of the aircraft on the deck; once on deck locking beams close on the probe, locking the aircraft to the flight deck. This device was pioneered by the Royal Canadian Navy and was called "Beartrap". The U.S. Navy implementation of this device, based on Beartrap, is called the "RAST" system (for Recovery Assist, Secure and Traverse) and is an integral part of the LAMPS MK III (SH-60B) weapons system.

Hazards of helicopter flight

As with any moving vehicle, operation outside of safe regimes could result in loss of control, structural damage, or fatality. For helicopters the hazards are particularly acute since they are flying at relatively low altitude, with little time to react to a sudden event. The following is a list of some of the potential hazards:
- Retreating blade stall
- Settling with power
- Ground resonance
- Low-G condition
- Operating within the shaded area of the height-velocity diagram
- Vortex ring state, a problem the V-22 Osprey was associated with Each of these conditions is potentially fatal and recovery might not be possible. For this reason, good pilotage demands operation within safe flight regimes and avoiding hazardous conditions at all costs.

Helicopter models and identification

V-22 Osprey In identifying conventional helicopters during flight it is helpful to know that when viewed from below, the rotor of a French, Russian, Soviet or Ukrainian designed helicopter rotates counter-clockwise, whilst that of a helicopter built in Italy, the UK or the USA rotates clockwise (see list of helicopter models). Some companies, notably Schweizer in the USA, are developing remotely-controlled variants of light helicopters for use in future battlefields. [http://rotomotion.com/ Rotomotion] is currently selling a line of small (less than 50 kg) rotorcraft UAVs, including an all electric helicopter. Hybrid types that combine features of helicopters and fixed wing designs include the experimental Fairey Rotodyne of the 1950s and the Bell Boeing Osprey, which is on order by the U.S. Marine Corps and will be the first mass produced tilt-rotor aircraft to enter service. A helicopter should not be mistaken for an autogyro, which is a historical predecessor of the helicopter that gains lift from an unpowered rotor. Some common nicknames for helicopters are "copter", "chopper", "whirlybird", "windmill", "helo" (common U.S. Navy usage) or "paraffin budgie" (the latter term being mostly used in the UK offshore oil industry).

External links

- : "Aircraft, especially aircraft of the direct lift amphibian type and means of construction and operating the same"
- [http://www.helis.com/ Helicopter history]
- [http://centennialofflight.com/history/helicopter.html Helicopter history]
- [http://www.aerospaceweb.org/design/helicopter/history.shtml Image of a Chinese flying top]
- [http://www.centennialofflight.gov/essay/Rotary/early_20th_century/HE2.htm Helicopter development in the early 20th century]
- [http://www.centennialofflight.gov/essay/Dictionary/helicopter/DI27.htm Description of a helicopter]
- [http://www.heli-szene.de/ Helicopter pictures and videos (in German)]
- [http://www.mh-53pavelow.com/ Sikorsky MH-53J/M PAVE LOW helicopter]

References

- Thicknesse P, Jones A et al, Military Rotorcraft, 2nd edition, 2000, Brassey's World Military Technology series, Shirvenham UK, xvi + 160pp, ISBN 1857533259
- Wragg D, Helicopters at War: A pictorial history, 1983, Robert Hale Ltd, London UK, 283pp, ISBN 0709008589
- ko:헬리콥터 ja:ヘリコプター nb:Helikopter

Turbojet

Air intake

Compressor

Combustor

Turbine

Nozzle

Net thrust

Below is an approximate equation for calculating the net thrust of a turbojet:

F_n = m \cdot (V_ - V_a)

where:

m =

intake mass flow

V_ =

fully expanded jet velocity (in the exhaust plume)

V_a =

Cycle improvements

Early designs

Axial-flow compressor

: axial compressor

Rolls-Royce plc

Rolls-Royce plc is the second-largest aircraft engine maker in the world, behind General Electric's GE Aircraft Engines division. Rolls-Royce was nationalised in 1971 by which time aircraft engines had long been the most significant part of the business. The automobile company was separated in 1973 and the present Rolls-Royce plc was re-privatised in 1987.

History

The Rolls-Royce company was founded in 1906 by Henry Royce and C.S. Rolls and produced its first aircraft engine in 1914. Around half the aircraft engines used by the Allies in WW1 were made by Rolls-Royce. By the late 1920s, aero engines made up most of Rolls-Royce's business. Henry Royce's last design was the Merlin aero engine, which came out in 1935 although he had died in 1933. This was a development subsequent to the R engine, which had powered a record-breaking Supermarine S6B seaplane to almost 400mph in the 1931 Schneider Trophy.) The Merlin was a powerful V12 engine, and was fitted into many World War II aircraft: the British Hawker Hurricane, Supermarine Spitfire, De Havilland Mosquito (twin-engined), Avro Lancaster (4-engine), Vickers Wellington (2-engine); it also transformed the American P-51 Mustang into possibly the best fighter of its time, its Merlin engine built by Packard under license. Over 160,000 Merlin engines were produced. In the post-World War II period Rolls-Royce made significant advances in gas turbine engine design and manufacture. The Dart and Tyne turboprop engines were particularly important enabling airlines to cut journey times within several continents whilst jet airliners were introduced on longer services. The Dart engine was used in Argosy, Avro 748, Friendship, Herald and Viscount aircraft, whilst the more powerful Tyne powered the Atlantic, Transall, Vanguard and the SRN-4 hovercraft. Many of these turboprops are still in service. Amongst the jet engines of this period was the RB163 Spey which powers the Trident, BAC 1-11, Grumman Gulfstream II and Fokker F28. During the late 50's and 60's there was a significant rationalisation of the British aero-engine manufacturers, culminating in the merger of Rolls-Royce and Bristol Siddeley in 1966 (Bristol Siddeley had itself resulted from the merger of Armstrong-Siddeley and Bristol in 1959). Bristol, with its principal factory at Filton, near Bristol, had a strong base in military engines, including the Olympus, which was chosen for Concorde.

Nationalisation & separation

Having been selected as the sole engine for the Lockheed L-1011 (Tristar) Rolls-Royce committed heavily to the RB211 engine. Development of the RB211 was hampered by considerable problems and on February 4, 1971 Rolls-Royce was declared bankrupt. To save the company Edward Heath's government nationalized it. The automotive division was separated from the aircraft engine division in 1973 as Rolls-Royce Motors.

Privatisation & expansion

Rolls-Royce plc was privatized in 1987 under Margaret Thatcher. Following this return to the private sector Rolls Royce has gone from strength to strength. The 1980s saw the introduction of a policy to offer an engine on every civil aircraft type with the company now powering 17 different airliners (and their variants) compared to General Electric's 14 and Pratt & Whitney's 10. In 1990 BMW and Rolls-Royce established the BMW Rolls-Royce joint venture to produce the BR700 range of engines for regional and corporate jets. Rolls-Royce acquired the Allison Engine Company in 1995 from General Motors. This brought four new engine types into the Rolls-Royce civil engine portfolio on seven platforms and several light aircraft applications. Allison is now known as Rolls-Royce Corporation, part of Rolls-Royce North America, which also includes the former Cooper Rolls joint venture which became wholly owned after Rolls-Royce bought out the share owned by Cooper Cameron Corporation, which had inherited it on being split off from Cooper Industries. This acquisition included virtually all of Cooper's remaining presence in its Mount Vernon, Ohio birthplace. In 1996 Rolls-Royce and Airbus signed a Memorandum of Understanding specifiying the Trent 900 as the engine of choice for the then A3XX. Rolls-Royce has established a leading position in the corporate and regional airline sector through the development of the Tay engine, the Allison acquisition and the consolidation of the BMW Rolls-Royce joint venture. In 1999 BMW Rolls-Royce was renamed Rolls-Royce Deutschland and in 2000 this group became a 100% owned subsidiary of Rolls-Royce plc. On April 6, 2004 Boeing announced that it had selected both Rolls-Royce and General Electric to power its new 787. Rolls-Royce submitted the Trent 1000, a further development of that series. GE's offering is the GENX, a development of the GE90.

Current operations

See List of Rolls-Royce engines for details of applications and past engines Rolls-Royce's aerospace business makes commercial and military gas turbine engines for military, airline, and corporate aircraft customers worldwide. In the U.S., the company makes engines for regional and corporate jets, helicopters, and turboprop aircraft. Rolls-Royce also constructs and installs power generation systems and is one of the world's largest makers of marine propulsion systems. Its core gas turbine technology has created one of the broadest product ranges of aero-engines in the world, with 50,000 engines in service with 500 airlines, 2,400 corporate and utility operators and more than 100 armed forces, powering both fixed- and rotary-wing aircraft.

Civil Aerospace

Defence Aerospace

Combat aircraft

- Adour (with Turbomeca)
- EJ200 (as part of Eurojet)
- F136 (with General Electric) General Electric
- Pegasus
- RB199 (as part of Turbo-Union)
- Spey

Helicopters

- AE 1107C-Liberty
- Gem
- Model 250 turboshaft
- MTR390 (with MTU and Turbomeca)
- RTM322 (with Turbomeca)
- T800 (with Honeywell)

Transport market

- AE 1107C-Liberty
- AE 2100
- Model 250 turboprop
- T56
- Tay
- TP400-D6 (as part of Europrop International)

Trainer market

- Adour (with Turbomeca)
- FJ44 (with Williams International)
- Model 250 turboprop
- Viper

Tactical market

- AE 1107C-Liberty
- AE 2100
- AE 3007
- BR710
- Model 250 turboprop
- Spey
- T56
- T800 (with Honeywell)
- Tay

Unmanned aerial vehicle market

- AE 3007
- Model 250 turboshaft
- Viper

Marine

Gas turbines

- Allison 501
- MT30
- MT50
- Spey
- WR-21 (with Northrop Grumman)

Diesel engines

- Bergen series
- Crossley Pielstick

Waterjets

- Kamewa Waterjets

Submarine

- PWR1 Reactor
- PWR2 Reactor

External links

- [http://www.rolls-royce.com Rolls-Royce]
- [http://civil.rolls-royce.com Civil Aerospace at Rolls-Royce]
- [http://defence.rolls-royce.com Defence Aerospace at Rolls-Royce]
- [http://marine.rolls-royce.com Marine Solutions at Rolls-Royce]
- [http://energy.rolls-royce.com Energy Generation at Rolls-Royce]
- [http://history.rolls-royce.com History at Rolls-Royce]
- [http://education.rolls-royce.com Education at Rolls-Royce]
- [http://careers.rolls-royce.com Careers at Rolls-Royce]
- [http://www.thejetengine.com The Jet Engine - A book by Rolls-Royce] Category:Aircraft engine manufacturers Category:Engineering companies of the United Kingdom Category:Aerospace companies of the United Kingdom Category:Companies traded on the London Stock Exchange

Rolls-Royce Trent

Rolls Royce Trent is a family of high-bypass turbofan engines manufactured by Rolls-Royce. All are developments of the famous RB211 with thrust ratings spanning between 53,000 to 95,000 lb_f (236 to 423 kN). The name has also been used for a number of previous designs.

Earlier designations

RB211 "Trent" was the name originally given by Rolls-Royce to the world's first turboprop engine (right). It was based on a concept provided by Sir Frank Whittle and derived by mating a five-bladed propeller driven through a reduction gearbox onto the company's Derwent II turbojet. It first flew on an experimental Gloster Meteor aircraft in the middle 1940s. The designation was reused again in the 1960s for the RB203 bypass turbofan which was designed to replace the Spey. It was the first three-spool engine, forerunner of the RB211 series. It was rated at 9980 lb_f (44.4 kN).

Present designation

The current Trent is the development of the three-shaft RB211 family of engines. By 1987, a variant of the RB211, the RB211-524L, had been developed to such an extent that it bore little resemblance to the original RB211, other than the three-shaft layout. Rolls-Royce decided that the 524L would be the basis of a new engine family, and so the newest Trent was born. Rolls-Royce had started naming their engines after British rivers in 1942—a practice which was revived for the Trent after a 30-year gap. The Trent's advanced layout provides lighter weight and better performance compared to the original RB211 and other comparable competing engines. It features the wide-chord fan and single crystal high-pressure turbine blades inherited from later generations of the RB211, but with improved performance and durability. The core turbomachinery is brand new, giving better performance, noise and pollution levels. In fact, it was seen fit to be retrofitted to the RB211-524G/HT for improved performance compared to the original 524G and 524H. The Trent's advanced layout allows it to be fully scalable to the widest range of thrust of any current generation large turbofans. Airbus gives all Rolls-Royce engined planes the designator "4"; eg. A330-342 or A380-841.

History

By the early 1990's, Rolls-Royce RB211 had 15 to 20 percent market share of the big commercial turbofans; however, GE and Pratt and Whitney were still way out in front. In the late 1980's the huge growth of ETOPS capable airliner twinjets led to demands for higher thrust rated turbofans. The option to Rolls-Royce was either to update the RB211 or risk exiting the big turbofan business; the result was, of course, that the RB211 was redeveloped into the Trent. The new Trent family spawned derivatives capable of powering a wide range of airliners. The initial variant, Trent 600, was to power the McDonnell Douglas MD-11 with British Caledonian as its launch customer. The subsequent takeover of British Caledonian by British Airways led to its cancellation, and later as the trijet itself suffered poor sales the Trent 600 was put on ice. Then with the launch of Airbus A330, the Trent 700 was launched with initial customer, Cathay Pacific in March 1995. The Trent 700 was selected by many A330 customers and later went on to become the primary engine for the A330. The Trent 800 for the Boeing 777 was also launched by Cathay Pacific. However, initially, Rolls-Royce had difficulty selling the engine. A further blow came in form of a big General Electric GE90 order from British Airways, traditionally a Rolls-Royce customer. The breakthrough came when the company won orders from Singapore Airlines, previously a staunch Pratt & Whitney customer, for its 34 Boeing 777s; this was when sales really took off and large North American orders from American Airlines and Delta Air Lines for their 777 fleets soon followed. Since then the Trent has risen to become the market leader for the 777 and has established a reputation for being a very reliable engine with good after-sales support; British Airways returned to Rolls-Royce for its second batch of 777s. Soon after in 1997, the Trent 500 was chosen to power the long-range quad-engined Airbus A340-500/-600 family. It entered service with Virgin Atlantic Airways' A340-600 in mid-2002 and with Air Canada's ultra-long range A340-500 in 2003. This was followed by the 70,000 to 80,000 pound (310 to 360 kN) thrust Trent 900, which was the launch engine for the Airbus A380. The latest in the family is Trent 1000, which was launched on the back of All Nippon Airways' order for 50 Boeing 787s. Currently it is the leading engine for the 787. Trent's market share has wildly exceeded early Rolls-Royce market projections and has currently garnered more sales than its competitors (GE and Pratt & Whitney) combined, capturing more than 50% of the market. Trent's excellent design has also been adapted for marine and industrial applications. The huge revenue generated from sales has also propelled Rolls-Royce's market position to the second biggest engine manufacturer in the world.

Triple-spool advantages

The Rolls-Royce RB211 and Trent use a triple-spool design rather than the more common twin-spool design. Although inherently more complex than a typical twin-spool design, the superiority of this design shows at higher thrust ratings by the total improvement achieved. Excellent development progress from the original RB211-22 to the current Trents has turned Rolls-Royce's higher thrust turbofans into performance leaders in their respective thrust rating classes, which translates into a market leadership figure of excess of 50% of all total widebody orders in 2004. As thrust rating increases, the high-pressure compressor increases in length resulting in a more complex airflow which increases the probability of airflow instability and compressor stall. Twin-spool engines require complex airflow control devices to prevent this but the triple-spool design gets around this problem by splitting the high pressure compressor into two, thereby increasing the total number of engine compressors to three. Each compressor is now allowed to rotate at its own optimum speed, making the engine's airflow very stable over a wide range of speeds. A triple-spool design features a higher compression ratio as compared to a twin-spool design making it generally shorter and lighter. The Trent, for example, is lighter than its General Electric GE90 equivalent. A lower individual spool rotation speed leads to a reduced parts count resulting in longer life and reduced maintenance costs. Most importantly, the triple-spool design allows design flexibility by simply resizing the compressors and turbines to accommodate different thrust ratings. The Trent's broad spread of thrust ratings spans 56,000 to 107,000 lbf (249 to 476 kN) and may be increased to 110,000 lbf (489 kN). By comparison, Pratt & Whitney's PW4000 series engines have a range of 56,000 to 90,000 lb_f (249 to 400 kN), GE's CF6-80 a range of 56,000 to 68,000 lb_f (249 to 302 kN) and GE90 a range of 84,000 to 115,000 lb_f (374 to 512 kN). This flexibility allowed Rolls-Royce to offer engines earlier than others for newer aircraft such as the Boeing's Next Generation 747, 777-200LR, 777-300ER and the 787 and Airbus' A340-500/600, A350 and A380.

Variants

Trent 500 Series

The Trent 500 family was designed to power the Airbus A340-500 and A340-600. It comes in 2 thrust ratings: 53,000 and 56,000 lb_f (236 to 249 kN). The Trent 500 features a Trent 700 wide-chord fan together with a core scaled from the Trent 800. The Trent 500 series is the most reliable member of the Trent family. It features the lowest maintenance costs for its ultra-long range class application; two Trent 556s fitted on an Airbus A340-500/600 are cheaper to maintain than one General Electric GE90-115 fitted on a Boeing 777.

Trent 600 Series

The Trent 600 family is designed to power future Boeing 747 aircraft developments. It is actually a refinement of the original RB211-524L. According to Rolls Royce, it performs better than any current 747 engine.

Trent 700 Series

The Trent 700 family was designed to power the Airbus A330. It features a fan with a diameter of 2.47 m and comes in 2 thrust ratings, 67,500 and 71,000 lb_f (300 to 316 kN). It first entered service on Cathay Pacific A330s in March, 1995.

Trent 800 Series

The Trent 800 family is designed to power the Boeing 777. It powers the 777-200, 777-200ER, and 777-300 variants. It is available with thrust ratings spanning 75,000 to 95,000 lb_f (334 to 423 kN). The hollow titanium wide-chord fan is 2.89 m in diameter. The engine is one of the lightest in its class; a Trent-powered Boeing 777 weighs up to 3.6 metric tons less than General Electric and Pratt & Whitney-powered versions. The Trent 800 was the first engine to be certified for ETOPS (Extended range over-water operations by twin engine aircraft) at entry into service. Since that time it has become a class leader for reliability, regularly returning a basic engine dispatch reliability of 99.9% which was a factor in securing 80% of installations on 777s since the start of 1997 and over 2 million flying hours since 1996.

Trent 8104

Originally designed for the 777-200LR and 777-300ER (both part of the 777X project), this engine comes in two thrust ratings, 104,000 and 114,000 lb_f (463 to 507 kN), and has been tested up to 117,000 lb_f (520 kN). Rolls-Royce offered the 8104 to Boeing earlier than other manufacturers. Boeing had a requirement that the participating engine developer assume a risk-sharing role on the overall 777X project. Rolls-Royce was unwilling to do so, and thus Boeing chose advanced developments of the GE90, the GE90-110B and GE90-115B. This relegated the 8104 to the role of demonstrator engine. It featured swept-back fan blades and a host of new technologies such as contra-rotating spools.

Trent 900 Series

The Trent 900 family is designed to power the Airbus A380, for which it is the launch engine. It comes in two thrust ratings, 70,000 and 76,000 lb_f (311 and 338 kN) but is capable of achieving 84,000 lb_f (374 kN). It features a significant amount of technology inherited from the 8104 demonstrator including its 2.95 m diameter swept-back fan. It is also the first member of the Trent family to feature a contra-rotating HP spool and uses the core of the very reliable Trent 500. It is the only A380 engine that can be transported on a Boeing 747 freighter. Airbus A380 Engine controls is provided by Hamilton Sundstrand, a United Technologies (UTC) company. UTC is also the parent company of Pratt & Whitney, who, with GE Aircraft Engines, is partnering to produce the Engine Alliance GP7200, the other engine available for the A380. This kind of cooperation among competitors is prevalent in the aircraft market as it provides for risk sharing among them and diversity in source countries, a significant factor in an airlines' choice of airframe and powerplant. The Trent 900 made its maiden flight on May 17 2004 on Airbus' A340-300 testbed, replacing the port inner CFM56-5 and dwarfing the remaining engines. A380 customers which have selected the Trent include Virgin Atlantic, Qantas, Singapore Airlines (already the largest Trent operator), Lufthansa and Malaysia Airlines.

Trent 1000 Series

On April 6, 2004 Boeing announced that it had selected two engine partners for the 787, Rolls-Royce and General Electric. Initially, Boeing toyed with the idea of sole sourcing the powerplant for the 787, with GE being the most likely candidate. However potential customers demanded choices and Boeing relented. For the first time in commercial aviation, both engine types will have a standard interface with the aircraft, allowing any 787 to be fitted with either a GE or Rolls-Royce engine at any time. Engine interchangeability makes the 787 a far more flexible asset to airlines, allowing them to change from one manufacturer's engine to the other's in light of any future engine developments which conform more closely to their operating profile. The engine market for the 787 is estimated to be $40 billion USD over the next 25 years. The Trent 1000 (as well as GE's GEnx) are both evolutionary derivatives of existing designs, whereas the Pratt & Whitney engine was to be an all-new design. The technology found in the Trent 8104 demonstrator is used extensively. The Trent 1000 is a bleedless design, with power take-off from the intermediate-pressure spool instead of the high-pressure spool found in other members of the Trent family, to fulfill the Boeing requirements of a "more-electric" engine. A 112-inch diameter swept-back fan, with a smaller diameter hub to help maximize airflow, was specified. Bypass ratio has been increased over previous variants by suitable adjustments to the core flow. Contra-rotating the IP and HP spools improves IP turbine efficiency, while use of more monolithic parts reduces the parts count for lower maintenance costs. A tiled combustor is featured. The first run of the Trent 1000 is expected in early 2006. In June 2004, the first public engine selection was made by

Turboprop

External links

Gas turbine

Theory of operation

Jet engines

Gas turbines for electrical power production

Micro turbines

Auxiliary power units

Gas turbines in vehicles

Naval use

Amateur gas turbines

Advances in technology

See also

Further reading

External links

Turbojet

Air intake

Compressor

Combustor

Turbine

Nozzle

Net thrust

Cycle improvements

Early designs

See also

Turboshaft

Helicopter

Applications

History

Generating lift

Conventional layout

Alternative layouts

Controlling flight

Stability

Limitations

Landing

On a ship

Hazards of helicopter flight

Helicopter models and identification

See also

External links

References

Turbojet

Air intake

Compressor

Combustor

Turbine

Nozzle

Net thrust

Cycle improvements

Early designs

See also

Axial-flow compressor

Rolls-Royce plc

History

Nationalisation & separation

Privatisation & expansion

Current operations

Civil Aerospace

Airlines

Regional aircraft

Helicopters

Defence Aerospace

Combat aircraft

Helicopters

Transport market

Trainer market

Tactical market

Unmanned aerial vehicle market

Marine

Gas turbines

Diesel engines

Waterjets

Submarine

External links

Rolls-Royce Trent

Earlier designations

Present designation

History

Triple-spool advantages