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| Aircraft propulsion |
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| Shaft engines: drivingpropellers,rotors,ducted fans orpropfans |
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Anaircraft engine, often referred to as anaero engine, is the power component of anaircraftpropulsion system. Aircraft using power components are referred to aspowered flight.[1] Most aircraft engines are eitherpiston engines orgas turbines, although a few have beenrocket powered and in recent years many smallUAVs have usedelectric motors.
The largest manufacturer ofturboprop engines forgeneral aviation is Pratt & Whitney.[2] General Electric announced its entry into the market in 2015.[2]
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For other configurations of aviation inline engine, such asX-engines,U-engines,H-engines, etc., seeInline engine (aeronautics).
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Rotary engines have the cylinders in a circle around the crankcase, as in a radial engine, (see above), but the crankshaft is fixed to the airframe and the propeller is fixed to the engine case, so that the crankcase and cylinders rotate. The advantage of this arrangement is that a satisfactory flow of cooling air is maintained even at low airspeeds, retaining the weight advantage and simplicity of a conventional air-cooled engine without one of their major drawbacks.The first practical rotary engine was theGnome Omega designed by the Seguin brothers and first flown in 1909. Its relative reliability and good power to weight ratio changed aviation dramatically.[12]
TheWankel is a type of rotary engine. TheWankel engine is about one half the weight and size of a traditionalfour-stroke cyclepiston engine of equal power output, and much lower in complexity. In an aircraft application, the power-to-weight ratio is very important, making the Wankel engine a good choice. Because the engine is typically constructed with an aluminium housing and a steel rotor, and aluminium 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 ofturbine engines. It was believed thatturbojet orturboprop 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 ofsports cars. The French companyCitroën had developed Wankel poweredRE-2 [fr]helicopter in 1970's.[13]
In modern times the Wankel engine has been used inmotor gliders where the compactness, light weight, and smoothness are crucially important.[14]
Starting in the 1930s attempts were made to produce a practicalaircraft diesel engine. In general, Diesel engines are more reliable and much better suited to running for long periods of time at medium power settings. The lightweight alloys of the 1930s were not up to the task of handling the much highercompression ratios of diesel engines, so they generally had poor power-to-weight ratios and were uncommon for that reason, although theClerget 14F Diesel radial engine (1939) has the same power to weight ratio as a gasoline radial. Improvements in Diesel technology in automobiles (leading to much better power-weight ratios), the Diesel's much better fuel efficiency and the high relative taxation of AVGAS compared to Jet A1 in Europe have all seen a revival of interest in the use of diesels for aircraft.[citation needed]Thielert Aircraft Engines converted Mercedes Diesel automotive engines, certified them for aircraft use, and became an OEM provider to Diamond Aviation for their light twin. Financial problems have plagued Thielert, so Diamond's affiliate — Austro Engine — developed the newAE300 turbodiesel, also based on a Mercedes engine.[15]
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A number of electrically powered aircraft, such as theQinetiQ Zephyr, have been designed since the 1960s.[16][17] Some are used as militarydrones.[18] InFrance in late 2007, a conventional light aircraft powered by an 18 kW electric motor using lithium polymer batteries was flown, covering more than 50 kilometers (31 mi), the first electric airplane to receive acertificate of airworthiness.[16]
On 18 May 2020, thePipistrel E-811 was the first electric aircraft engine to be awarded atype certificate byEASA for use ingeneral aviation. The E-811 powers thePipistrel Velis Electro.[19][11]
Many big companies, such as Siemens, are developing high performance electric engines for aircraft use, also, SAE shows new developments in elements as pure Copper core electric motors with a better efficiency. A hybrid system as emergency back-up and for added power in take-off is offered for sale by Axter Aerospace, Madrid, Spain.[20]
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The termadvanced technology engine refers to the modern generation of jet engines.[21]
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A rocket turbine engine is a combination of two types of propulsion engines: aliquid-propellant rocket and a turbine jet engine. Itspower-to-weight ratio is a little higher than a regular jet engine, and works at higher altitudes.[22]
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At the April 2018ILA Berlin Air Show,Munich-based research institutede:Bauhaus Luftfahrt presented a high-efficiency composite cycle engine for 2050, combining ageared turbofan with apiston engine core.The 2.87 m diameter, 16-blade fan gives a 33.7 ultra-highbypass ratio, driven by a geared low-pressure turbine but the high-pressure compressor drive comes from a piston-engine with two 10 piston banks without a high-pressure turbine, increasing efficiency with non-stationaryisochoric-isobaric combustion for higher peak pressures and temperatures.The 11,200 lb (49.7 kN) engine could power a 50-seatregional jet.[23]
Its cruiseTSFC would be 11.5 g/kN/s (0.406 lb/lbf/hr) for an overallengine efficiency of 48.2%, for a burner temperature of 1,700 K (1,430 °C), anoverall pressure ratio of 38 and a peak pressure of 30 MPa (300 bar).[24]Although engine weight increases by 30%,aircraft fuel consumption is reduced by 15%.[25]Sponsored by theEuropean Commission under Framework 7 projectLEMCOTEC, Bauhaus Luftfahrt,MTU Aero Engines andGKN Aerospace presented the concept in 2015, raising the overall engine pressure ratio to over 100 for a 15.2% fuel burn reduction compared to 2025 engines.[26]
On multi-engine aircraft, engine positions are numbered from left to right from the point of view of the pilot looking forward, so for example on a four-engine aircraft such as theBoeing 747, engine No. 1 is on the left side, farthest from the fuselage, while engine No. 3 is on the right side nearest to the fuselage.[27]
In the case of the twin-engineEnglish Electric Lightning, which has two fuselage-mounted jet engines one above the other, engine No. 1 is below and to the front of engine No. 2, which is above and behind.[28]
Refineries blend Avgas withtetraethyllead (TEL) to achieve these high octane ratings, a practice that governments no longer permit for gasoline intended for road vehicles. The shrinking supply of TEL and the possibility of environmental legislation banning its use have made a search for replacement fuels forgeneral aviation aircraft a priority for pilots’ organizations.[29]
Model aircraft typically usenitro engines (also known as "glow engines" due to the use of aglow plug) powered byglow fuel, a mixture ofmethanol,nitromethane, and lubricant. Electrically powered model airplanes[30] and helicopters are also commercially available. SmallmulticopterUAVs are almost always powered by electricity,[31][32] but larger gasoline-powered designs are under development.[33][34][35]
