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8/3/2014 Aircraft engine - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Aircraft_engine 1/11
A Rolls-Royce Merlin installed in a preserved Avro
York
Part of a series on
Aircraft propulsion
Shaft engines :
driving propellers, rotors, ducted fans, or
propfans
Internal combustion engines:
Piston engine
Wankel engine
Turbines:
Turboprop
Turboshaft
External combustion engines:
Steam-powered
Reaction engines
Turbines:
Turbojet
Turbofan
Propfan
Rocket-powered
Motorjet
Pulsejet
Aircraft engineFrom Wikipedia, the free encyclopedia
An aircraft engine is the component of the propulsionsystem for an aircraft that generates mechanical power.Aircraft engines are almost always either lightweight pistonengines or gas turbines.
8/3/2014 Aircraft engine - Wikipedia, the free encyclopedia
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Ranger L-440 air-cooled, six-cylinder,
inverted, in-line engine used in
Fairchild PT-19
1926: Armstrong Siddeley Jaguar IV (S), the first series-produced supercharged engine for aircraft
use;[9][nb 1] two-row radial with a gear-driven centrifugal supercharger.
1930: Frank Whittle submitted his first patent for turbojet engine.
June 1939: Heinkel He 176 is the first successful aircraft to fly powered solely by a liquid-fueled rocket
engine.
August 1939: Heinkel HeS 3 turbojet propels the pioneering German Heinkel He 178 aircraft.
1940: Jendrassik Cs-1, the world's first run of a turboprop engine. It is not put into service.
1943 Daimler-Benz DB 670, first turbofan runs
1944: Messerschmitt Me 163B Komet, the world's first rocket-propelled combat aircraft deployed.
1945: First turboprop powered aircraft flies, a Gloster Meteor with two Rolls-Royce Trent engines.
1947: Bell X-1 rocket propelled aircraft exceeds the speed of sound.
1948: 100 shp 782, the first turboshaft engine to be applied to aircraft use; in 1950 used to develop the
larger 280 shp (210 kW) Turbomeca Artouste.
1949: Leduc 010, the world's first ramjet-powered aircraft flight.
1950: Rolls-Royce Conway, the world's first production turbofan, enters service.
1968: General Electric TF39 high bypass turbofan enters service delivering greater thrust and much better
efficiency.
2002: HyShot scramjet flew in dive.
2004: Hyper-X, the first scramjet to maintain altitude.
Shaft engines
Reciprocating (piston) engines
In-line engine
This type of engine has cylinders lined up in one row. It typically has aneven number of cylinders, but there are instances of three- and five-cylinder engines. The greatest advantage of an inline engine is that itallows the aircraft to be designed with a low frontal area to minimisedrag. If the engine crankshaft is located above the cylinders, it is called aninverted inline engine: this allows the propeller to be mounted high up toincrease ground clearance, enabling shorter landing gear. Thedisadvantages of an inline engine include a poor power-to-weight ratio,
because the crankcase and crankshaft are long and thus heavy. An in-line engine may be either air-cooled or liquid-cooled, but liquid-cooling is more common because it is difficult to get enough air-flow to cool the rear cylindersdirectly. Inline engines were common in early aircraft; one was used in the Wright Flyer, the aircraft that made thefirst controlled powered flight. However, the inherent disadvantages of the design soon became apparent, and theinline design was abandoned, becoming a rarity in modern aviation.
8/3/2014 Aircraft engine - Wikipedia, the free encyclopedia
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A Rolls-Royce Merlin V-12 Engine
A ULPower UL260i horizontally
opposed air-cooled aero engine
V-type engine
Cylinders in this engine are arranged in two in-line banks, typically tilted60-90 degrees apart from each other and driving a common crankshaft.The vast majority of V engines are water-cooled. The V design providesa higher power-to-weight ratio than an inline engine, while still providing asmall frontal area. Perhaps the most famous example of this design is the
legendary Rolls-Royce Merlin engine, a 27-litre (1649 in3) 60° V12engine used in, among others, the Spitfires that played a major role in theBattle of Britain.
Horizontally opposed engine
A horizontally opposed engine, also called a flat or boxer engine, has twobanks of cylinders on opposite sides of a centrally located crankcase.The engine is either air-cooled or liquid-cooled, but air-cooled versionspredominate. Opposed engines are mounted with the crankshafthorizontal in airplanes, but may be mounted with the crankshaft vertical inhelicopters. Due to the cylinder layout, reciprocating forces tend tocancel, resulting in a smooth running engine.
Opposed, air-cooled four- and six-cylinder piston engines are by far themost common engines used in small general aviation aircraft requiring upto 400 horsepower (300 kW) per engine. Aircraft that require more than400 horsepower (300 kW) per engine tend to be powered by turbineengines.
H configuration engine
An H configuration engine is essentially a pair of horizontally opposed engines placed together, with the twocrankshafts geared together.
Radial engine
This type of engine has one or more rows of cylinders arranged around a centrally located crankcase. Each rowgenerally has an odd number of cylinders to produce smooth operation. A radial engine has only one crank throwper row and a relatively small crankcase, resulting in a favorable power-to-weight ratio. Because the cylinderarrangement exposes a large amount of the engine's heat-radiating surfaces to the air and tends to cancelreciprocating forces, radials tend to cool evenly and run smoothly. The lower cylinders, which are under thecrankcase, may collect oil when the engine has been stopped for an extended period. If this oil is not cleared fromthe cylinders prior to starting the engine, serious damage due to hydrostatic lock may occur.
Most radial engines have the cylinders arranged evenly around the crankshaft, although some early engines,sometimes called semi-radials or fan configuration engines, had an uneven arrangement. The best known engine ofthis type is the Anzani engine, which was fitted to the Bleriot XI used for the first flight across the English Channel in1909. This arrangement had the drawback of needing a heavy counterbalance for the crankshaft, but was used toavoid the spark plugs oiling up.
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A Pratt & Whitney R-2800 engine
Le Rhone 9C rotary aircraft engine
In military aircraft designs, the large frontal area of the engine acted as an extra layer of armor for the pilot. Also air-cooled engines, without vulnerable radiators, are slightly less prone to battle damage, and on occasion wouldcontinue running even with one or more cylinders shot away. However, the large frontal area also resulted in anaircraft with an aerodynamically inefficient increased frontal area.
Rotary engine
Rotary engines have the cylinders in a circle around the crankcase, as in a radial engine, (see above), but thecrankshaft is fixed to the airframe and the propeller is fixed to the engine case, so that the crankcase and cylindersrotate. The advantage of this arrangement is that a satisfactory flow of cooling air is maintained even at lowairspeeds, retaining the weight advantage and simplicity of a conventional air-cooled engine without one of theirmajor drawbacks. The first practical rotary engine was the Gnome Omega designed by the Seguin brothers andfirst flown in 1909. Its relative reliability and good power to weight ratio
changed aviation dramatically. [10] Before the first World War mostspeed records were gained using Gnome-engined aircraft, and in theearly years of the war rotary engines were dominant in aircraft types forwhich speed and agility were paramount. To increase power, engineswith two rows of cylinders were built.
However, the gyroscopic effects of the heavy rotating engine producedhandling problems in aircraft and the engines also consumed largeamounts of oil since they used total loss lubrication, the oil being mixedwith the fuel and ejected with the exhaust gases. Castor oil was used forlubrication, since it is not soluble in petrol, and the resultant fumes werenauseating to the pilots. Engine designers had always been aware of themany limitations of the rotary engine so when the static style enginesbecame more reliable and gave better specific weights and fuelconsumption, the days of the rotary engine were numbered.
Turbine-powered
Turboprop
While military fighters require very high speeds, many civil airplanes donot. Yet, civil aircraft designers wanted to benefit from the high powerand low maintenance that a gas turbine engine offered. Thus was born theidea to mate a turbine engine to a traditional propeller. Because gasturbines optimally spin at high speed, a turboprop features a gearbox tolower the speed of the shaft so that the propeller tips don't reachsupersonic speeds. Often the turbines that drive the propeller areseparate from the rest of the rotating components so that they can rotateat their own best speed (referred to as a free-turbine engine). Aturboprop is very efficient when operated within the realm of cruisespeeds it was designed for, which is typically 200 to 400 mph (320 to640 km/h).
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Cutaway view of a Garrett TPE-331
turboprop engine showing the
gearbox at the front of the engine
A Rolls-Royce Model 250 turboshaft
engine common to many types of
helicopters
A General Electric J85-GE-17A
turbojet engine. This cutaway clearly
shows the 8 stages of axial
compressor at the front (left side of
the picture), the combustion
chambers in the middle, and the two
stages of turbines at the rear of the
engine.
Turboshaft engines are used primarily for helicopters and auxiliary power units. A turboshaft engine is similar inprinciple, but in a turboprop the propeller is supported by the engine and the engine is bolted to the airframe: in a
turboshaft, the engine does notprovide any direct physicalsupport to the helicopter'srotors. The rotor is connectedto a transmission which isbolted to the airframe, and theturboshaft engine drives thetransmission. The distinction isseen by some as slim, as insome cases aircraft companiesmake both turboprop andturboshaft engines based onthe same design.
Reaction engines
Reaction engines generate the thrust to propel an aircraft by ejecting the exhaust gases at high velocity from theengine, the resultant reaction of forces driving the aircraft forwards. The most common reaction propulsion enginesflown are turbojets, turbofans and rockets. Other types such as pulsejets, ramjets, scramjets and Pulse DetonationEngines have also flown. In jet engines the oxygen necessary for fuel combustion comes from the air, while rocketscarry oxygen in some form as part of the fuel load, permitting their use in space.
Jets
Turbojet
A turbojet is a type of gas turbine engine that was originally developedfor military fighters during World War II. A turbojet is the simplest of allaircraft gas turbines. It consists of a compressor to draw air in andcompress it, a combustion section where fuel is added and ignited, one ormore turbines that extract power from the expanding exhaust gases todrive the compressor, and an exhaust nozzle that accelerates the exhaustgases out the back of the engine to create thrust. When turbojets wereintroduced, the top speed of fighter aircraft equipped with them was atleast 100 miles per hour faster than competing piston-driven aircraft. Inthe years after the war, the drawbacks of the turbojet gradually becameapparent. Below about Mach 2, turbojets are very fuel inefficient andcreate tremendous amounts of noise. Early designs also respond veryslowly to power changes, a fact that killed many experienced pilots whenthey attempted the transition to jets. These drawbacks eventually led tothe downfall of the pure turbojet, and only a handful of types are still inproduction. The last airliner that used turbojets was the Concorde,whose Mach 2 airspeed permitted the engine to be highly efficient.
8/3/2014 Aircraft engine - Wikipedia, the free encyclopedia
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A cutaway of a CFM56-3 turbofan
engine
An XLR99
A turbofan engine is much the same as a turbojet, but with an enlarged fan at the front that provides thrust in muchthe same way as a ducted propeller, resulting in improved fuel-efficiency.Though the fan creates thrust like a propeller, the surrounding duct freesit from many of the restrictions that limit propeller performance. Thisoperation is a more efficient way to provide thrust than simply using thejet nozzle alone and turbofans are more efficient than propellers in thetrans-sonic range of aircraft speeds, and can operate in the supersonicrealm. A turbofan typically has extra turbine stages to turn the fan.Turbofans were among the first engines to use multiple spools—concentric shafts that are free to rotate at their own speed—to let theengine react more quickly to changing power requirements. Turbofansare coarsely split into low-bypass and high-bypass categories. Bypass airflows through the fan, but around the jet core, not mixing with fuel andburning. The ratio of this air to the amount of air flowing through the
engine core is the bypass ratio. Low-bypass engines are preferred for military applications such as fighters due tohigh thrust-to-weight ratio, while high-bypass engines are preferred for civil use for good fuel efficiency and lownoise. High-bypass turbofans are usually most efficient when the aircraft is traveling at 500 to 550 miles per hour(800 to 885 km/h), the cruise speed of most large airliners. Low-bypass turbofans can reach supersonic speeds,though normally only when fitted with afterburners.
Pulse jets
Pulse jets are mechanically simple devices that—in a repeating cycle—draw air through a no-return valve at thefront of the engine into a combustion chamber and ignited it. The combustion forces the exhaust gases out the backof the engine. It produces power as a series of pulses rather than as a steady output, hence the name. The onlyapplication of this type of engine was the German unmanned V1 flying bomb of World War II. Though the sameengines were also used experimentally for ersatz fighter aircraft, the extremely loud noise generated by the enginescaused mechanical damage to the airframe that was sufficient to make the idea unworkable.
Rocket
A few aircraft have used rocket engines for main thrust or attitudecontrol, notably the Bell X-1 and North American X-15. Rocket enginesare not used for most aircraft as the energy and propellant efficiency isvery poor except at high speeds, but have been employed for shortbursts of speed and takeoff. Rocket engines are very efficient only atvery high speeds, although they are useful because they produce verylarge amounts of thrust and weigh very little.
Newer engine types
Wankel engine
Another promising design for aircraft use was the Wankel rotary engine. The Wankel engine is about one half theweight and size of a traditional four-stroke cycle piston engine of equal power output, and much lower incomplexity. In an aircraft application, the power-to-weight ratio is very important, making the Wankel engine agood choice. Because the engine is typically constructed with an aluminium housing and a steel rotor, and aluminium
8/3/2014 Aircraft engine - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Aircraft_engine 8/11
Powerplant from a
Schleicher ASH 26e self-
launching motor glider,
removed from the glider and
mounted on a test stand for
maintenance at the Alexander
Schleicher GmbH & Co in
Poppenhausen, Germany.
Counter-clockwise from top
left: propeller hub, mast with
belt guide, radiator, Wankel
engine, muffler shroud.
expands more than steel when heated, a Wankel engine does not seize when overheated, unlike a piston engine.This is an important safety factor for aeronautical use. Considerable development of these designs started afterWorld War II, but at the time the aircraft industry favored the use of turbine engines. It was believed that turbojetor turboprop engines could power all aircraft, from the largest to smallest designs.The Wankel engine did not find many applications in aircraft, but was used byMazda in a popular line of sports cars. Recently, the Wankel engine has beendeveloped for use in motor gliders where the small size, light weight, and low
vibration are especially important.[11]
Wankel engines are becoming increasingly popular in homebuilt experimentalaircraft, due to a number of factors. Most are Mazda 12A and 13B engines,removed from automobiles and converted to aviation use. This is a very cost-effective alternative to certified aircraft engines, providing engines ranging from100 to 300 horsepower (220 kW) at a fraction of the cost of traditional engines.These conversions first took place in the early 1970s, and with hundreds or eventhousands of these engines mounted on aircraft, as of 10 December 2006 theNational Transportation Safety Board has only seven reports of incidentsinvolving aircraft with Mazda engines, and none of these is of a failure due todesign or manufacturing flaws. During the same time frame, they have reports ofseveral thousand reports of broken crankshafts and connecting rods, failedpistons and incidents caused by other components not found in the Wankelengines. Rotary engine enthusiasts refer to piston aircraft engines as"Reciprosaurs," and point out that their designs are essentially unchanged sincethe 1930s, with only minor differences in manufacturing processes and variation inengine displacement.
Diesel engine
Most aircraft engines use spark ignition, generally using gasoline as a fuel. Startingin the 1930s attempts were made to produce a compression ignition Diesel engine for aviation use. In general,Diesel engines are more reliable and much better suited to running for long periods of time at medium powersettings, which is why they are widely used in, for example, trucks and ships. The lightweight alloys of the 1930swere not up to the task of handling the much higher compression ratios of diesel engines, so they generally had poorpower-to-weight ratios and were uncommon for that reason, although the Clerget 14F Diesel radial engine (1939)has the same power to weight ratio as a gasoline radial. Improvements in Diesel technology in automobiles (leadingto much better power-weight ratios), the Diesel's much better fuel efficiency and the high relative taxation ofAVGAS compared to Jet A1 in Europe have all seen a revival of interest in the use of diesels for aircraft. ThielertAircraft Engines converted Mercedes Diesel automotive engines, certified them for aircraft use, and became anOEM provider to Diamond Aviation for their light twin. Financial problems have plagued Thielert, so Diamond's
affiliate — Austro Engine — developed the new AE300 turbodiesel, also based on a Mercedes engine.[12]
Competing new Diesel engines may bring fuel efficiency and lead-free emissions to small aircraft, representing thebiggest change in light aircraft engines in decades. Wilksch Airmotive build 2-stroke Diesel engine (same power toweight as a gasoline engine) for experimental aircraft: WAM 100 (100 hp), WAM 120 (120 hp) and WAM 160(160 hp)
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For very high supersonic/low hypersonic flight speeds inserting a cooling system into the air duct of a hydrogen jetengine permits greater fuel injection at high speed and obviates the need for the duct to be made of refractory oractively cooled materials. This greatly improves the thrust/weight ratio of the engine at high speed.
It is thought that this design of engine could permit sufficient performance for antipodal flight at Mach 5, or evenpermit a single stage to orbit vehicle to be practical. The hybrid air-breathing SABRE rocket engine is a pre-cooledengine under development.
Electric
About 60 electrically powered aircraft, such as the QinetiQ Zephyr, have been designed since the 1960s.[13][14]
Some are used as military drones.[15] In France in late 2007, a conventional light aircraft powered by an 18 kWelectric motor using lithium polymer batteries was flown, covering more than 50 kilometers (31 mi), the first electric
airplane to receive a certificate of airworthiness.[13]
Limited experiments with solar electric propulsion have been performed, notably the manned Solar Challenger andSolar Impulse and the unmanned NASA Pathfinder aircraft.
Fuel
All aviation fuel is produced to stringent quality standards to avoid fuel-related engine failures. Aviation standardsare much more strict than those for road vehicle fuel because an aircraft engine must meet a strictly defined level ofperformance under known conditions. These high standards mean that aviation fuel costs much more than fuel usedfor road vehicles.
Aircraft reciprocating (piston) engines are typically designed to run on aviation gasoline. Avgas has a higher octanerating than automotive gasoline to allow higher compression ratios, power output and efficiency at higher altitudes.Currently the most common Avgas is 100LL that refers to the octane rating (100 octane) and the lead content (LL= low lead).
Refineries blend Avgas with tetraethyllead (TEL) to achieve these high octane ratings, a practice that governmentsno longer permit for road vehicle gasoline. The shrinking supply of TEL and the possibility of environmentallegislation banning its use has made a search for replacement fuels for general aviation aircraft a priority for pilot's
organizations.[16]
Turbine engines and aircraft Diesel engines burn various grades of jet fuel. Jet fuel is a relatively heavy and lessvolatile petroleum derivative based on kerosene, but certified to strict aviation standards, with additional additives.
The History of Aircraft Power Plants Briefly Reviewed : From the " 7 lb. per h.p" Days to the " 1 lb. per h.p"
of To-day (http://www.flightglobal.com/pdfarchive/view/1935/1935%20-%201222.html)
"The Quest for Power" (http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%200959.html) a
1954 Flight article by Bill Gunston
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