Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...

to cool them in order to keep the engine within operating temperatures. In all combustion engines, a great percentage of the heat generated (around 44%) escapes through the exhaust, not through the metal fins of an air-cooled engine (12%). About 8% of the heat energy is transferred to the

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

, which although primarily meant for

lubrication Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubric ...

, also plays a role in heat dissipation via a

cooler A cooler, portable ice chest, ice box, cool box, chilly bin (in New Zealand), or esky ( Australia) is an insulated box used to keep food or drink cool. Ice cubes are most commonly placed in it to help the contents inside stay cool. Ice packs a ...

. ''Air-cooled engines'' are used generally in applications which would not suit

liquid cooling Liquid cooling refers to cooling by means of the convection or circulation of a liquid. Examples of liquid cooling technologies include: * Cooling by convection or circulation of coolant, including water cooling * Liquid cooling and ventilati ...

, as such modern air-cooled engines are used in

motorcycles A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...

general aviation aircraft General aviation (GA) is defined by the International Civil Aviation Organization (ICAO) as all civil aviation aircraft operations with the exception of commercial air transport or aerial work, which is defined as specialized aviation services ...

, lawn mowers, generators,

outboard motor An outboard motor is a propulsion system for boats, consisting of a self-contained unit that includes engine, gearbox and propeller or jet drive, designed to be affixed to the outside of the transom. They are the most common motorised method ...

s, pump sets, saw benches and

auxiliary power unit An auxiliary power unit (APU) is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft and naval ships as well as some large land vehicles. Aircraft APUs generally produce 115& ...

Introduction

Most modern

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

s are cooled by a closed circuit carrying liquid

coolant A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosi ...

through channels in the engine block and cylinder head, where the coolant absorbs heat, to a

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...

radiator Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics. A radiator is always ...

where the coolant releases heat into the air (or

raw water Raw water is water found in the environment that has not been treated and does not have any of its minerals, ions, particles, bacteria, or parasites removed. Raw water includes rainwater, ground water, water from infiltration wells, and water fro ...

, in the case of

marine engine An inboard motor is a marine propulsion system for boats. As opposed to an outboard motor where an engine is mounted outside the hull of the craft, an ''inboard motor'' is an engine enclosed within the hull of the boat, usually connected to a pr ...

s). Thus, while they are not ''ultimately'' cooled by the liquid, because of the liquid-coolant circuit they are known as ''water-cooled''. In contrast, heat generated by an air-cooled engine is released directly into the air. Typically this is facilitated with metal

fins A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

covering the outside of the Cylinder Head and

cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an ...

s which increase the surface area that air can act on. Air may be force fed with the use of a fan and shroud to achieve efficient cooling with high volumes of air or simply by natural air flow with well designed and angled fins. In all combustion engines, a great percentage of the heat generated (around 44%) escapes through the exhaust, not through either a liquid cooling system nor through the metal fins of an air-cooled engine (12%). About 8% of the heat energy finds its way into the

, which although primarily meant for

, also plays a role in heat dissipation via a

. Air cooled engines usually run noisier, however it provides more simplicity which gives benefits when it comes to servicing and part replacement and is usually cheaper to be maintained.

Applications

Road vehicles

Many

motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle Steering, steered by a Motorcycle handlebar, handlebar. Motorcycle design varies greatly to suit a range of different purposes: Long-distance ...

s use air cooling for the sake of reducing weight and complexity. Few current production automobiles have air-cooled engines (such as

Tatra 815 The Tatra 815 is a truck family, produced by Czech company Tatra. It uses the traditional tatra concept of rigid backbone tube and swinging half-axles giving independent suspension. The vehicles are available in 4x4, 6x6, 8x8, 10x8, 10x10, 1 ...

), but historically it was common for many high-volume vehicles. The orientation of the engine cylinders is commonly found in either single-cylinder or coupled in groups of two, and cylinders are commonly oriented in a horizontal fashion as a

Flat engine A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, ...

, while vertical

Straight-four engine A straight-four engine (also called an inline-four) is a four-cylinder piston engine where cylinders are arranged in a line along a common crankshaft. The vast majority of automotive four-cylinder engines use a straight-four layout (with the ...

have been used. Examples of past air-cooled road vehicles, in roughly chronological order, include: * Franklin (1902-1934) * New Way (1905) - limited production run out from the "CLARKMOBILE" *

Chevrolet Series M Copper-Cooled The 1923 Chevrolet Series M Copper-Cooled was an automobile made to be completely air-cooled by Chevrolet in 1923. It was designed by Charles F. Kettering, head engineer of Delco, the General Motors research division wing in Dayton, Ohio. The ...

(1921-1923) (very few built), Chapter 5, "The copper-cooled engine" * Tatra all-wheel-drive military trucks *

Tatra 11 The Tatra T11 is an automobile that was produced from 1923 through 1927. It was the first Tatra model to use the unique combination of major components that are still in use on the trucks produced by Tatra to this day. Origins Hans Ledwinka crea ...

(1923-1927) and subsequent models *

Tatra T77 The Czechoslovakian Tatra 77 (T77) is by many considered to be the first serial-produced, truly aerodynamically-designed automobile. It was developed by Hans Ledwinka and Paul Jaray, the Zeppelin aerodynamic engineer. Launched in 1934, the Tatra 7 ...

(1934-1938) *

Tatra T87 The Tatra 87 (T87) is a car built by Czechoslovak manufacturer Tatra. It was powered by a rear-mounted 2.9-litre air-cooled 90-degree overhead cam V8 engine that produced 85 horsepower and could drive the car at nearly . It is ranked among the ...

(1936-1950) *

Tatra T97 The Tatra 97 (T97) is a Czechoslovak mid-size car built by Tatra in Kopřivnice, Moravia from 1936 to 1939. History The Tatra 97 was designed to complement two full-size cars in the Tatra range: the Tatra 77 launched in 1934 and the Tatra 87 l ...

(1936-1939) * Tatra T600 Tatraplan (1946-1952) *

Tatra T603 The Tatra 603 is a large rear-engined luxury car which was produced by the Czechoslovak company Tatra from 1956 to 1975. It was a continuation of the series of Tatra streamlined sedans which began with the Tatra 77. In Socialist Czechoslovakia ...

(1955-1975) *

Tatra T613 The Tatra 613 is a large luxury rear wheel driven car with rear-mounted air-cooled engine manufactured by Czechoslovak manufacturer Tatra from 1974 until 1996 as a replacement for the Tatra 603 series. It featured an all-new body styled by Vign ...

(1974-1996) *

Tatra T700 The Tatra 700 is a rear-engined luxury car released in 1996 by the Czech car maker Tatra. It was essentially a heavily restyled version of the Tatra 613 model it replaced. It is one of the last production cars with an air-cooled engine. The ...

(1996-1999) *

Crosley Crosley was a small, independent American manufacturer of subcompact cars, bordering on microcars. At first called the Crosley Corporation and later Crosley Motors Incorporated, the Cincinnati, Ohio, firm was active from 1939 to 1952, int ...

(1939-1945) * The East German

Trabant Trabant () is a series of small cars produced from 1957 until 1991 by former East German car manufacturer VEB Sachsenring Automobilwerke Zwickau. In total, four different models were made, the Trabant 500, Trabant 600, Trabant 601, and the Tr ...

(1957-1991) *

Trabant 500 The Trabant P 50 (), also known as the Trabant 500, is the first series production model of the East German Trabant series, made by VEB Sachsenring Automobilwerke Zwickau. It was produced from 1957 until 1962; in total, 131,495 units were built (i ...

(1957-1962) * Trabant 600 (1962-1965) *

Trabant 601 The Trabant 601 (or Trabant P601 series) was a Trabant model produced by VEB Sachsenring in Zwickau, Saxony. It was the third generation of the model, built for the longest production time, from 1964 to 1990. As a result, it is the best-known Tra ...

(1964-1989) * ZAZ Zaporozhets (1958-1994) *

Fiat 500 The Fiat 500 ( it, Cinquecento, ) is a rear-engined, four-seat, small city car that was manufactured and marketed by Fiat Automobiles from 1957 until 1975 over a single generation in two-door saloon and two-door station wagon bodystyles. Launc ...

(1957-1975) *

Fiat 126 The Fiat 126 (Type 126) is a four-passenger, rear-engine, city car manufactured and marketed by Fiat over a twenty-eight year production run from 1972 until 2000, over a single generation. Introduced by Fiat in October 1972 at the Turin Auto Show ...

(1972-1987) *

Porsche 356 The Porsche 356 is a sports car that was first produced by Austrian company Porsche Salzburg, Porsche Konstruktionen GesmbH (1948–1949), and then by German company Porsche, Dr. Ing. h. c. F. Porsche GmbH (1950–1965). It was Porsche's first ...

(1948-1965) *

Porsche 911 The Porsche 911 (pronounced ''Nine Eleven'' or in german: Neunelfer) is a two-door 2+2 high performance rear-engined sports car introduced in September 1964 by Porsche AG of Stuttgart, Germany. It has a rear-mounted flat-six engine and ori ...

(1964-1998) * Porsche 912 (1965-1969, 1976) * VW-Porsche 914 (1969-1976) * The

Volkswagen Beetle The Volkswagen Beetle—officially the Volkswagen Type 1, informally in German (meaning "beetle"), in parts of the English-speaking world the Bug, and known by many other nicknames in other languages—is a two-door, rear-engine economy car, ...

, Type 2, SP2,

Karmann Ghia The Volkswagen Karmann Ghia is a sports car marketed in 2+2 coupe (1955–1974) and 2+2 convertible (1957–1974) body styles by Volkswagen. Internally designated the Type 14, the Karmann Ghia combined the chassis and mechanicals of the Type 1 ( ...

, and Type 3 all utilized the same air-cooled engine (1938-2013) with various displacements * Volkswagen Type 2 (T3) (1979–1982) * Volkswagen Type 4 (1968-1974) * Volkswagen Gol (G1) (1980-1986) *

Toyota U engine The Toyota U engine is a series of flat engines produced by Toyota. The original version of this engine was produced in the 1960s and 1970s in flat-twin configuration. The engine series was extended in 2012 for the engine derived from the Subaru f ...

(1961-1976) *

Chevrolet Corvair The Chevrolet Corvair is a compact car manufactured by Chevrolet for model years 1960–1969 in two generations. A response to the Volkswagen Beetle, it remains the only American-designed, mass-produced passenger car with a Rear-engine design, ...

(1960-1969) *

Citroën 2CV The Citroën 2CV (french: link=no, deux chevaux(-vapeur), , lit. "two steam horse(power)s", meaning "two ''taxable'' horsepower") is an air-cooled front-engine, front-wheel-drive, economy family car, introduced at the 1948 Paris Mondial d ...

(1948-1990) (Featured a high pressure oil cooling system, and used a fan bolted to the crankshaft end) * Citroën GS and GSA * Honda 1300 (1969-1973) *

NSU Prinz The NSU Prinz (Prince) is an automobile which was produced in West Germany by the NSU Motorenwerke AG from 1958 to 1973. NSU Prinz I, II & III The first post-war NSU car, the Prinz I, was launched at the Frankfurt Motor Show in September 1957 a ...

* Royal Enfield Motorcycles (India): The 350cc and 500cc Twinspark motorcycle engines are air-cooled *

Oltcit Club The Oltcit Club was a supermini produced between 1984 and 1988 and developed in co-operation by Citroën of France and Oltcit, a joint venture company with the Romanian government. They were powered by the air-cooled engines from the Citroën ...

(1981–1995)T13/653, G11/631 and VO36/630 *

Demak Dzm 200 2015 Demak is on the north coast of Central Java province, on the island of Java, Indonesia. * Demak, Demak, modern-day large town * Demak Sultanate, sixteenth century sultanate * Demak Regency Demak ( jv, ꦢꦼꦩꦏ꧀) is a regency located in th ...

Aviation

Most aviation

piston engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common feat ...

s are air-cooled. While water cooled engines were widely used from the early days of flight, air cooled engines were the dominant choice in aircraft. Following the Second World War, turbojets and jet turbine powered aircraft have come to dominate flight regimes where water cooled piston engines offered the advantage of reduced drag. Today, piston engines are mostly used in slower general aviation aircraft where the greater drag produced by air cooled engines is not a major disadvantage. Therefore, most aero engines produced today are of the air cooled variety. Today, most of the engines currently (2005) manufactured by Lycoming and Continental are used by major manufacturers of light aircraft Cirrus,

Cessna Cessna () is an American brand of general aviation aircraft owned by Textron Aviation since 2014, headquartered in Wichita, Kansas. Originally, it was a brand of the Cessna Aircraft Company, an American general aviation aircraft manufacturing ...

and so on. Other engine manufactures using air-cooled engine technology are

ULPower ULPower Aero Engines is a Belgian company which manufactures engines specifically designed for light aircraft/rotorcraft use. History In 2001 the founding partners of ULPower were asked to fix an issue with a Jabiru engine fitted into a helico ...

and Jabiru, more active in the Light-Sport Aircraft ( LSA) and

ultralight aircraft Ultralight aviation (called microlight aviation in some countries) is the flying of lightweight, 1- or 2-seat fixed-wing aircraft. Some countries differentiate between weight-shift control and Aircraft flight control system, conventional three-a ...

market.

Rotax Rotax is the brand name for a range of internal combustion engines developed and manufactured by the Austrian company BRP-Rotax GmbH & Co KG (until 2016 BRP-Powertrain GmbH & Co. KG), in turn owned by the Canadian Bombardier Recreational Produc ...

uses a combination of air-cooled cylinders and liquid-cooled cylinder heads.

Diesel engines

Some small diesel engines, e.g. those made by

Deutz AG Deutz AG is a German internal combustion engine manufacturer, based in Porz, Cologne, Germany. History The company was founded by Nicolaus Otto, the inventor of the four-stroke internal combustion engine, and his partner Eugen Langen on 31 ...

and Lister Petter are air-cooled. Probably the only big Euro 5 truck air-cooled engine (V8 320 kW power 2100 N·m torque one) is being produced by Tatra.

Stationary or portable engines

Stationary or portable engines were commercially introduced early in the 1900s. The first commercial production was by the New Way Motor Company of Lansing, Michigan, US. The company produced air-cooled engines in single and twin cylinders in both horizontal and vertical cylinder format. Subsequent to their initial production which was exported worldwide, other companies took up the advantages of this cooling method, especially in small portable engines. Applications include mowers, generators, outboard motors, pump sets, saw benches and auxiliary power plants and more.

Introduction

Applications

Road vehicles

Aviation

Diesel engines

Stationary or portable engines

References

Bibliography

Cited sources

Further reading