An aircraft engine is the component of the propulsion system for an
aircraft that generates mechanical power.
Aircraft engines are almost
always either lightweight piston engines or gas turbines, except for
small multicopter UAVs which are almost always electric aircraft.
1 Manufacturing industry
2 Development history
3 Shaft engines
3.1 Reciprocating (piston) engines
3.1.1 In-line engine
3.1.2 V-type engine
3.1.3 Horizontally opposed engine
3.1.4 H configuration engine
3.1.5 Radial engine
3.1.6 Rotary engine
4 Reaction engines
4.2 Pulse jets
5 Newer engine types
5.2 Diesel engine
5.3 Precooled jet engines
7 See also
10 External links
See also: List of aircraft engines
In commercial aviation, the major players in the manufacturing of
turbofan engines are Pratt & Whitney, General Electric,
CFM International (a joint venture of Safran Aircraft
Engines and General Electric). A major entrant into the market
launched in 2016 when
Aeroengine Corporation of China was formed by
organizing smaller companies engaged in designing and manufacturing
aircraft engines into a new state owned behemoth of 96,000
In general aviation, the dominant manufacturer of turboprop engines
has been Pratt & Whitney. General Electric announced in 2015
entrance into the market.
Wright vertical 4-cylinder engine
See also: Timeline of jet power
John Stringfellow made a steam engine for a 10-foot wingspan
model aircraft which achieved the first powered flight, albeit with
1903: Charlie Taylor built an inline aeroengine for the Wright Flyer
Manly-Balzer engine sets standards for later radial engines.
Léon Levavasseur produces a successful water-cooled V8 engine
for aircraft use.
René Lorin patents a design for the ramjet engine.
Louis Seguin designed the Gnome Omega, the world's first rotary
engine to be produced in quantity. In 1909 a Gnome powered Farman III
aircraft won the prize for the greatest non-stop distance flown at the
Grande Semaine d'Aviation
Grande Semaine d'Aviation setting a world record for endurance
of 180 kilometres (110 mi).
1910: Coandă-1910, an unsuccessful ducted fan aircraft exhibited at
Paris Aero Salon, powered by a piston engine. The aircraft never flew,
but a patent was filed for routing exhaust gases into the duct to
1914: Auguste Rateau suggests using exhaust-powered compressor – a
turbocharger – to improve high-altitude performance; not accepted
after the tests
1917-18 - The Idflieg-numbered R.30/16 example of the Imperial German
Zeppelin-Staaken R.VI heavy bomber becomes the
earliest known supercharger-equipped aircraft to fly, with a Mercedes
D.II straight-six engine in the central fuselage driving a
Brown-Boveri mechanical supercharger for the R.30/16's four Mercedes
Sanford Alexander Moss picks up Rateau's idea and creates the
first successful turbocharger
Armstrong Siddeley Jaguar
Armstrong Siddeley Jaguar IV (S), the first series-produced
supercharged engine for aircraft use;[nb 1] two-row radial with a
gear-driven centrifugal supercharger.
Frank Whittle submitted his first patent for a turbojet engine.
Heinkel He 176
Heinkel He 176 is the first successful aircraft to fly
powered solely by a liquid-fueled rocket engine.
Heinkel HeS 3
Heinkel HeS 3 turbojet propels the pioneering German
Heinkel He 178
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 modified Gloster
Meteor with two Rolls-Royce Trent engines.
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,
General Electric TF39
General Electric TF39 high bypass turbofan enters service
delivering greater thrust and much better efficiency.
HyShot scramjet flew in dive.
2004: NASA X-43, the first scramjet to maintain altitude.
Ranger L-440 air-cooled, six-cylinder, inverted, in-line engine used
in Fairchild PT-19
Reciprocating (piston) engines
Main article: reciprocating engine
Main article: Straight engine
In this entry, for clarity, the term "inline engine" refers only to
engines with a single row of cylinders, as used in automotive
language, but in aviation terms, the phrase "inline engine" also
covers V-type and opposed engines (as described below), and is not
limited to engines with a single row of cylinders. This is typically
to differentiate them from radial engines. A straight engine typically
has an even number of cylinders, but there are instances of three- and
five-cylinder engines. The greatest advantage of an inline engine is
that it allows the aircraft to be designed with a low frontal area to
minimise drag. If the engine crankshaft is located above the
cylinders, it is called an inverted inline engine: this allows the
propeller to be mounted high up to increase ground clearance, enabling
shorter landing gear. The disadvantages 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 cylinders directly.
Inline engines were common in early aircraft; one was used in the
Wright Flyer, the aircraft that made the first controlled powered
flight. However, the inherent disadvantages of the design soon became
apparent, and the inline design was abandoned, becoming a rarity in
For other configurations of aviation inline engine, such as X-engines,
U-engines, H-engines, etc., see Inline engine (aeronautics).
Rolls-Royce Merlin V-12 Engine
Main article: V engine
Cylinders in this engine are arranged in two in-line banks, typically
tilted 60-90 degrees apart from each other and driving a common
crankshaft. The vast majority of V engines are water-cooled. The V
design provides a higher power-to-weight ratio than an inline engine,
while still providing a small frontal area. Perhaps the most famous
example of this design is the legendary
Rolls-Royce Merlin engine, a
27-litre (1649 in3) 60° V12 engine used in, among others, the
Spitfires that played a major role in the Battle of Britain.
Horizontally opposed engine
Main article: Flat engine
ULPower UL260i horizontally opposed air-cooled aero engine
A horizontally opposed engine, also called a flat or boxer engine, has
two banks of cylinders on opposite sides of a centrally located
crankcase. The engine is either air-cooled or liquid-cooled, but
air-cooled versions predominate. Opposed engines are mounted with the
crankshaft horizontal in airplanes, but may be mounted with the
crankshaft vertical in helicopters. Due to the cylinder layout,
reciprocating forces tend to cancel, resulting in a smooth running
engine. Opposed-type engines have high power-to-weight ratios because
they have a comparatively small, lightweight crankcase. In addition,
the compact cylinder arrangement reduces the engine’s frontal area
and allows a streamlined installation that minimizes aerodynamic drag.
These engines always have an even number of cylinders, since a
cylinder on one side of the crankcase “opposes” a cylinder on the
Opposed, air-cooled four- and six-cylinder piston engines are by far
the most common engines used in small general aviation aircraft
requiring up to 400 horsepower (300 kW) per engine.
require more than 400 horsepower (300 kW) per engine tend to be
powered by turbine engines.
H configuration engine
Main article: H engine
An H configuration engine is essentially a pair of horizontally
opposed engines placed together, with the two crankshafts geared
A Pratt & Whitney R-2800 engine
Main article: Radial engine
This type of engine has one or more rows of cylinders arranged around
a centrally located crankcase. Each row generally has an odd number of
cylinders to produce smooth operation. A radial engine has only one
crank throw per row and a relatively small crankcase, resulting in a
favorable power-to-weight ratio. Because the cylinder arrangement
exposes a large amount of the engine's heat-radiating surfaces to the
air and tends to cancel reciprocating forces, radials tend to cool
evenly and run smoothly. The lower cylinders, which are under the
crankcase, may collect oil when the engine has been stopped for an
extended period. If this oil is not cleared from the cylinders prior
to starting the engine, serious damage due to hydrostatic lock may
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 of this type is the Anzani engine, which was fitted to
Bleriot XI used for the first flight across the
English Channel in
1909. This arrangement had the drawback of needing a heavy
counterbalance for the crankshaft, but was used to avoid the spark
plugs oiling up.
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 would continue running even with one or
more cylinders shot away. However, the large frontal area also
resulted in an aircraft with an aerodynamically inefficient increased
Le Rhone 9C rotary aircraft engine
Main article: Rotary engine
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 the
Gnome Omega designed by the
Seguin brothers and first flown in 1909. Its relative reliability and
good power to weight ratio changed aviation dramatically.  Before
the first World War most speed records were gained using Gnome-engined
aircraft, and in the early years of the war rotary engines were
dominant in aircraft types for which speed and agility were paramount.
To increase power, engines with two rows of cylinders were built.
However, the gyroscopic effects of the heavy rotating engine produced
handling problems in aircraft and the engines also consumed large
amounts of oil since they used total loss lubrication, the oil being
mixed with the fuel and ejected with the exhaust gases.
Castor oil was
used for lubrication, since it is not soluble in petrol, and the
resultant fumes were nauseating to the pilots.
Engine designers had
always been aware of the many limitations of the rotary engine so when
the static style engines became more reliable and gave better specific
weights and fuel consumption, the days of the rotary engine were
Cutaway view of a Garrett TPE-331 turboprop engine showing the gearbox
at the front of the engine
Main article: Turboprop
While military fighters require very high speeds, many civil airplanes
do not. Yet, civil aircraft designers wanted to benefit from the high
power and low maintenance that a gas turbine engine offered. Thus was
born the idea to mate a turbine engine to a traditional propeller.
Because gas turbines optimally spin at high speed, a turboprop
features a gearbox to lower the speed of the shaft so that the
propeller tips don't reach supersonic speeds. Often the turbines that
drive the propeller are separate from the rest of the rotating
components so that they can rotate at their own best speed (referred
to as a free-turbine engine). A turboprop is very efficient when
operated within the realm of cruise speeds it was designed for, which
is typically 200 to 400 mph (320 to 640 km/h).
Allison Model 250
Allison Model 250 turboshaft engine common to many types of
Main article: Turboshaft
Turboshaft engines are used primarily for helicopters and auxiliary
power units. A turboshaft engine is similar to a turboprop in
principle, 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 not provide any direct physical support to the helicopter's
rotors. The rotor is connected to a transmission which is bolted to
the airframe, and the turboshaft engine drives the transmission. The
distinction is seen by some as slim, as in some cases aircraft
companies make both turboprop and turboshaft engines based on the same
Main article: Jet engine
Reaction engines generate the thrust to propel an aircraft by ejecting
the exhaust gases at high velocity from the engine, the resultant
reaction of forces driving the aircraft forwards. The most common
reaction propulsion engines flown are turbojets, turbofans and
rockets. Other types such as pulsejets, ramjets, scramjets and pulse
detonation engines have also flown. In jet engines the oxygen
necessary for fuel combustion comes from the air, while rockets carry
oxygen in some form as part of the fuel load, permitting their use in
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.
Main article: Turbojet
A turbojet is a type of gas turbine engine that was originally
developed for military fighters during World War II. A turbojet is the
simplest of all aircraft gas turbines. It consists of a compressor to
draw air in and compress it, a combustion section where fuel is added
and ignited, one or more turbines that extract power from the
expanding exhaust gases to drive the compressor, and an exhaust nozzle
that accelerates the exhaust gases out the back of the engine to
create thrust. When turbojets were introduced, the top speed of
fighter aircraft equipped with them was at least 100 miles per hour
faster than competing piston-driven aircraft. In the years after the
war, the drawbacks of the turbojet gradually became apparent. Below
about Mach 2, turbojets are very fuel inefficient and create
tremendous amounts of noise. Early designs also respond very slowly to
power changes, a fact that killed many experienced pilots when they
attempted the transition to jets. These drawbacks eventually led to
the downfall of the pure turbojet, and only a handful of types are
still in production. The last airliner that used turbojets was the
Concorde, whose Mach 2 airspeed permitted the engine to be highly
A cutaway of a CFM56-3 turbofan engine
Main article: Turbofan
A turbofan engine is much the same as a turbojet, but with an enlarged
fan at the front that provides thrust in much the same way as a ducted
propeller, resulting in improved fuel-efficiency. Though the fan
creates thrust like a propeller, the surrounding duct frees it from
many of the restrictions that limit propeller performance. This
operation is a more efficient way to provide thrust than simply using
the jet nozzle alone, and turbofans are more efficient than propellers
in the transsonic range of aircraft speeds and can operate in the
supersonic realm. 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 the engine react more quickly to changing power
requirements. Turbofans are coarsely split into low-bypass and
high-bypass categories. Bypass air flows through the fan, but around
the jet core, not mixing with fuel and burning. 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 to high thrust-to-weight ratio, while high-bypass
engines are preferred for civil use for good fuel efficiency and low
noise. 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.
Main article: Pulsejet
Pulse jets are mechanically simple devices that—in a repeating
cycle—draw air through a no-return valve at the front of the engine
into a combustion chamber and ignited it. The combustion forces the
exhaust gases out the back of the engine. It produces power as a
series of pulses rather than as a steady output, hence the name. The
only application of this type of engine was the German unmanned V1
flying bomb of World War II. Though the same engines were also used
experimentally for ersatz fighter aircraft, the extremely loud noise
generated by the engines caused mechanical damage to the airframe that
was sufficient to make the idea unworkable.
Main article: Rocket engine
A few aircraft have used rocket engines for main thrust or attitude
control, notably the
Bell X-1 and North American X-15. Rocket engines
are not used for most aircraft as the energy and propellant efficiency
is very poor, but have been employed for short bursts of speed and
takeoff. Where fuel/propellant efficiency is of lesser concern, rocket
engines can be useful because they produce very large amounts of
thrust and weigh very little.
Newer engine types
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,
Wankel engine, muffler shroud.
Another promising design for aircraft use was the
Wankel engine is about one half the weight and size of a
traditional four-stroke cycle piston 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
after World War II, but at the time the aircraft industry favored the
use of turbine engines. It was believed that turbojet or turboprop
engines could power all aircraft, from the largest to smallest
Wankel engine did not find many applications in aircraft,
but was used by
Mazda in a popular line of sports cars. The French
Citroën had developed
Wankel powered RE-2 (fr)
helicopter in 1970's.
In modern times the
Wankel engine has been used in motor gliders where
the compactness, light weight, and smoothness are crucially
The now-defunct Staverton-based firm MidWest designed and produced
single- and twin-rotor aero engines, the MidWest AE series. These
engines were developed from the motor in the Norton Classic
motorcycle. The twin-rotor version was fitted into ARV Super2s and the
Rutan Quickie. The single-rotor engine was put into a Chevvron motor
glider and into the Schleicher ASH motor-gliders. After the demise of
MidWest, all rights were sold to Diamond of Austria, who have since
developed a MkII version of the engine.
As a cost-effective alternative to certified aircraft engines some
Wankel engines, removed from automobiles and converted to aviation
use, have been fitted in homebuilt experimental aircraft.
with outputs ranging from 100 horsepower (75 kW) to 300
horsepower (220 kW) can be a fraction of the cost of traditional
engines. Such conversions first took place in the early
1970s; and as of 10 December 2006 the National
Transportation Safety Board has only seven reports of incidents
involving aircraft with
Mazda engines, and none of these is of a
failure due to design or manufacturing flaws.
Aircraft diesel engine
Most aircraft engines use spark ignition, generally using gasoline as
a fuel. Starting in the 1930s attempts were made to produce a
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 power settings, which is why they are
widely used in, for example, trucks and ships. The lightweight alloys
of the 1930s were not up to the task of handling the much higher
compression ratios of diesel engines, so they generally had poor
power-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 (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.
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 new AE300
turbodiesel, also based on a Mercedes engine. Competing new Diesel
engines may bring fuel efficiency and lead-free emissions to small
aircraft, representing the biggest change in light aircraft engines in
decades. Wilksch Airmotive build 2-stroke
Diesel engine (same power to
weight as a gasoline engine) for experimental aircraft: WAM 100
(100 hp), WAM 120 (120 hp) and WAM 160 (160 hp)
Precooled jet engines
Main article: Precooled jet engine
For very high supersonic/low hypersonic flight speeds, inserting a
cooling system into the air duct of a hydrogen jet engine permits
greater fuel injection at high speed and obviates the need for the
duct to be made of refractory or actively 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 even permit a single
stage to orbit vehicle to be practical. The hybrid air-breathing SABRE
rocket engine is a pre-cooled engine under development.
A number of electrically powered aircraft, such as the QinetiQ Zephyr,
have been designed since the 1960s. Some are used as military
France 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 a certificate of
Limited experiments with solar electric propulsion have been
performed, notably the manned
Solar Challenger and
Solar Impulse and
NASA Pathfinder aircraft.
Many big companies, 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. 
Small multicopter UAVs are almost always powered by electric motors.
Aircraft reciprocating (piston) engines are typically designed to run
on aviation gasoline.
Avgas has a higher octane rating than automotive
gasoline to allow higher compression ratios, power output, and
efficiency at higher altitudes. Currently the most common
100LL. This refers to the octane rating (100 octane) and the lead
content (LL = low lead, relative to the historic levels of lead in
pre-regulation Avgas).
Avgas with tetraethyllead (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 for general aviation aircraft a
priority for pilots’ organizations.
Turbine engines and aircraft Diesel engines burn various grades of jet
Jet fuel is a relatively less volatile petroleum derivative
based on kerosene, but certified to strict aviation standards, with
additional additives.
Model aircraft typically use nitro engines (also known as "glow
engines" due to the use of a glow plug) powered by glow fuel, a
mixture of methanol, nitromethane, and lubricant. Electrically powered
model airplanes and helicopters are also commercially available.
Small multicopter UAVs are almost always powered by
electricity, but larger gasoline-powered designs are under
development.  
Aircraft diesel engine
Aircraft engine position number
List of aircraft engines
United States military aircraft engine designations
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