Radial engine
Overview
The radial engine is a reciprocating type
Reciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

 internal combustion
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

 engine configuration
Engine configuration
Engine configuration is an engineering term for the layout of the major components of a reciprocating piston internal combustion engine. These components are the cylinders and crankshafts in particular but also, sometimes, the camshaft....

 in which the cylinder
Cylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...

s point outward from a central crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 like the spokes on a wheel. This configuration was very commonly used in large aircraft engines before most large aircraft started using turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

 engines.

In a radial engine, the pistons are connected to the crankshaft with a master-and-articulating-rod assembly. One piston, the uppermost one in the animation, has a master rod with a direct attachment to the crankshaft.
Encyclopedia
The radial engine is a reciprocating type
Reciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

 internal combustion
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

 engine configuration
Engine configuration
Engine configuration is an engineering term for the layout of the major components of a reciprocating piston internal combustion engine. These components are the cylinders and crankshafts in particular but also, sometimes, the camshaft....

 in which the cylinder
Cylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...

s point outward from a central crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 like the spokes on a wheel. This configuration was very commonly used in large aircraft engines before most large aircraft started using turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

 engines.

In a radial engine, the pistons are connected to the crankshaft with a master-and-articulating-rod assembly. One piston, the uppermost one in the animation, has a master rod with a direct attachment to the crankshaft. The remaining pistons pin their connecting rod
Connecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....

s' attachments to rings around the edge of the master rod. Four-stroke
Four-stroke cycle
A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.There are two...

 radials always have an odd number of cylinders per row, so that a consistent every-other-piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

 firing order
Firing order
The firing order is the sequence of power delivery of each cylinder in a multi-cylinder reciprocating engine.This is achieved by sparking of the spark plugs in a gasoline engine in the correct order, or by the sequence of fuel injection in a Diesel engine...

 can be maintained, providing smooth operation. This is achieved by the engine taking two revolutions of the crankshaft to complete the four strokes, (intake, compression, power, exhaust), which means the firing order is 1,3,5,2,4 and back to cylinder 1 again. This means that there is always a two-piston gap between the piston on its power stroke and the next piston to fire (i.e., the piston on compression). If an even number of cylinders was used, the firing order would be something similar to 1,3,5,2,4,6, which leaves a three-piston gap between firing pistons on the first crankshaft revolution, and only a one-piston gap on the second crankshaft revolution. This leads to an uneven firing order within the engine, and is not ideal.
The protoype radial Zoche aero-diesels (below) have an even number of cylinders, either four or eight; but this is not problematic, because they are two-stroke engines, with twice the number of power strokes as a four-stroke engine.

Most radial engines use overhead poppet valve
Poppet valve
A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...

s driven by pushrods and lifter
Tappet
A tappet is the noise made by a worn cam follower, however the term is widely used to represent the cam follower itself. In mechanical engineering it is a projection which imparts a linear motion to some other component within an assembly...

s on a cam plate which is concentric with the crankshaft, with a few smaller radials, like the five-cylinder Kinner B-5
Kinner B-5
|-See also:-References:* http://www.oldengine.org/members/diesel/Duxford/usaero4.htm-External links:...

, using individual camshafts within the crankcase for each cylinder. A few engines utilize sleeve valve
Sleeve valve
The sleeve valve is a type of valve mechanism for piston engines, distinct from the usual poppet valve. Sleeve-valve engines saw use in a number of pre-World War II luxury cars and in USA in the Willys-Knight car and light truck...

s instead, like the very reliable 14-cylinder Bristol Hercules
Bristol Hercules
|-See also:-Bibliography:*Gunston, B. Classic World War II Aircraft Cutaways. Osprey. ISBN 1-85532-526-8*Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9...

 (built up to 1970 under licence in France by SNECMA) and the powerful 18-cylinder Bristol Centaurus
Bristol Centaurus
|-See also:-Bibliography:*Bridgman, L, Jane's Fighting Aircraft of World War II. Crescent. ISBN 0-517-67964-7*Gunston, Bill. Development of Piston Aero Engines. Cambridge, England. Patrick Stephens Limited, 2006. ISBN 0-7509-4478-1...

.

History

C. M. Manly constructed a water-cooled five-cylinder radial engine in 1901, a conversion of one of Stephen Balzer's rotary engine
Rotary engine
The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it...

s, for Langley
Samuel Pierpont Langley
Samuel Pierpont Langley was an American astronomer, physicist, inventor of the bolometer and pioneer of aviation...

's Aerodrome aircraft. Manly's engine produced 52 hp at 950 rpm.

In 1903-04 Jacob Ellehammer
Jacob Ellehammer
Jacob Christian Hansen Ellehammer was a Danish watchmaker and inventor born in Bakkebølle, Denmark. He is remembered chiefly for his contributions to powered flight....

 used his experience constructing motorcycles to build the world's first air-cooled radial engine, a three-cylinder engine which he used as the basis for a more powerful five-cylinder model in 1907. This was installed in his triplane
Triplane
A triplane is a fixed-wing aircraft equipped with three vertically-stacked wing planes. Tailplanes and canard foreplanes are not normally included in this count, although they may occasionally be.-Design principles:...

 and made a number of short free-flight hops. During 1908-9, Ellehammer developed another engine, which had six cylinders arranged in two rows of three. His engines had a very good power-to-weight ratio
Power-to-weight ratio
Power-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources...

, but his aircraft designs suffered from his lack of understanding of control. If he had concentrated on his engines, he might have become a successful manufacturer.

Another early radial engine was the three-cylinder Anzani
Anzani
Anzani was an engine manufacturer founded by the Italian Alessandro Anzani , which produced proprietary engines for aircraft, cars, boats, and motorcycles in factories in Britain, France and Italy.-Overview:...

, originally built as a "semi-radial" W3 configuration design, one of which powered Louis Blériot
Louis Blériot
Louis Charles Joseph Blériot was a French aviator, inventor and engineer. In 1909 he completed the first flight across a large body of water in a heavier-than-air craft, when he crossed the English Channel. For this achievement, he received a prize of £1,000...

's Blériot XI
Blériot XI
The Blériot XI is the aircraft in which, on 25 July 1909, Louis Blériot made the first flight across the English Channel made in a heavier-than-air aircraft . This achievement is one of the most famous accomplishments of the early years of aviation, and not only won Blériot a lasting place in...

 in his July 25, 1909 crossing of the English Channel
English Channel
The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...

. By 1914 Anzani had developed their range, their largest radial being a 20-cylinder engine of 200 hp, with its cylinders arranged in four groups of five. One of the three-cylinder "fully radial", 120º cylinder angle Anzani powerplants still exists today, in fully running condition, in the nose of Old Rhinebeck Aerodrome
Old Rhinebeck Aerodrome
The Old Rhinebeck Aerodrome is a museum of World War I aircraft and antique automobiles that is located in Red Hook, New York, USA.-History:The aerodrome was the creation of Cole Palen, who was partially inspired by the Shuttleworth Collection in England. He regularly flew many of the aircraft...

's restored and flyable 1909 vintage Blériot XI. There is also another running Anzani at Brodhead airfield to go on a replica Blériot XI.

Radial engines are regarded as being air-cooled almost by definition—so that it is interesting that one of the most successful of the early radial engines was the Salmson 9Z series of nine-cylinder water-cooled radial engines that were produced in large numbers during the First World War. Georges Canton and Pierre Unné patented the original engine design in 1909, offering it to the Salmson
Salmson
Salmson was a French engineering company, initially in the automobile and aeroplane manufacturing area,turning to pump manufacturing in the 1960s.-History:...

 company—and the engine was often known as the Canton-Unné.

The radial engine was not developed at this time in Germany: two radial engines were made there before World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

, but the Germans seemed to lose faith in the type under war conditions, or it may have been that insistence on standardization ruled out any but proven engine types.

During the decade 1910-1920 the radial engine was largely overshadowed by its close relative, the rotary engine
Rotary engine
The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it...

—which differed from the so-called "stationary" radial in that the whole engine revolved with the propeller. In WWI, many French and other Allied aircraft flew with Bentley, Clerget, Gnome and Le Rhone rotary engines, the ultimate examples of which produced about 240 hp, with the Germans either making close copies of the Gnome and Le Rhone powerplants built by the Oberursel firm, or, late in the war, using the unique Siemens eleven-cylinder rotary engine
Siemens-Halske Sh.III
Siemens-Halske's Sh.III was an 11-cylinder, air-cooled rotary engine developed in Germany during World War I, similar to the Sh.I.-Design:It shared with its predecessor the unusual design feature of having its internal workings rotating in a clockwise direction as seen from "nose-on", within the...

. By the end of the war the rotary engine was already essentially obsolete, being superseded as a type by rapid development of true radials.

Radial versus inline debate

By 1918, the potential advantages of air-cooled radials over the water-cooled inline engine
Inline engine (aviation)
In aviation, an inline engine means any reciprocating engine with banks rather than rows of cylinders, including straight engines, flat engines, V engines and H engines, but excluding radial engines and rotary engines....

 and air-cooled rotary engine
Rotary engine
The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it...

 that had powered World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 aircraft were well appreciated. While British designers had produced the ABC Dragonfly
ABC Dragonfly
-Bibliography:* Bruce, J.M. "Sopwith Snipe...:...the RAF's First Fighter. . " Air Enthusiast International Volume 6 Number 6, June 1974. Bromley, UK: Fine Scroll....

 radial in 1917, they were unable to resolve its cooling problems, and it was not until the 1920s that the Bristol Aeroplane Company
Bristol Aeroplane Company
The Bristol Aeroplane Company, originally the British and Colonial Aeroplane Company, was both one of the first and one of the most important British aviation companies, designing and manufacturing both airframes and aero engines...

 and Armstrong Siddeley
Armstrong Siddeley
Armstrong Siddeley was a British engineering group that operated during the first half of the 20th century. It was formed in 1919 and is best known for the production of luxury motor cars and aircraft engines.-Siddeley Autocars:...

 produced reliable British radials such as the Bristol Jupiter
Bristol Jupiter
The Bristol Jupiter was a British nine-cylinder single-row piston radial engine built by the Bristol Aeroplane Company. Originally designed late in World War I and known as the Cosmos Jupiter, a lengthy series of upgrades and developments turned it into one of the finest engines of its era.The...

 and the Armstrong Siddeley Jaguar.

In the US, NACA
NACA
- Organizations :* National Advisory Committee for Aeronautics, the forerunner of the U.S. federal agency NASA* National Association for Campus Activities, an organization for programmers of university and college activities...

 noted in 1920 that air-cooled radials could offer ship-based aircraft an increase in the power-to-weight ratio and reliability, and by 1921 the US Navy had announced it would only order aircraft fitted with air-cooled radials. Charles Lawrance's J-1 engine
Lawrance J-1
The Lawrance J-1 was an engine developed by Charles Lanier Lawrance and used in American aircraft in the early 1920s. It was a 9-cylinder, air-cooled radial design.-Development:...

, developed in 1922 with Navy funding, and using aluminium cylinders with steel liners, ran for an unprecedented 300 hours, at a time when 50 hours endurance was acceptable for liquid-cooled engines. At the urging of the Army and Navy the Wright Aeronautical Corporation bought Lawrance's company, and subsequent engines were known as Wright Radials. The radial engines gave confidence to Navy pilots performing long-range overwater flights, and their increased performance meant that carrier-based aircraft could hold their own against land-based aircraft in combat.

Wright's 225 hp J-5 Whirlwind radial engine of 1925 was widely acknowledged as "the first truly reliable aircraft engine". Wright employed Giuseppe Mario Bellanca
Giuseppe Mario Bellanca
Giuseppe Mario Bellanca was an Italian-American airplane designer and builder who created the first enclosed cabin monoplane in the United States in 1922. This aircraft is now on display at the National Air & Space Museum's Steven F. Udvar-Hazy Center.-Biography:He was born on March 19, 1886 in...

 to design an aircraft to showcase it, and the result was the Wright-Bellanca 1, or WB-1, which was first flown in the latter part of that year. The J-5 was used on many advanced aircraft of the day, including Charles Lindbergh's Ryan NYP with which he made the first solo Atlantic flight.

In 1925, the American rival firm to Wright's radial engine production efforts, Pratt & Whitney
Pratt & Whitney
Pratt & Whitney is a U.S.-based aerospace manufacturer with global service operations. It is a subsidiary of United Technologies Corporation . Pratt & Whitney's aircraft engines are widely used in both civil aviation and military aviation. Its headquarters are in East Hartford, Connecticut, USA...

 was founded, with the P & W firm's initial offering, the Pratt & Whitney Wasp
Pratt & Whitney R-1340
|-See also:* Pratt & Whitney Wasp series* Pratt & Whitney R-985 Wasp Junior* Pratt & Whitney R-1535 Twin Wasp Junior* Pratt & Whitney R-1830 Twin Wasp-Bibliography:...

, being test run later in that year, the start of production for the many models of Pratt & Whitney radial engines that were to appear during the second quarter of the 20th century, among them the 14-cylinder, twin row Pratt & Whitney R-1830 Twin Wasp, possibly the most-produced aviation engine of any single design, with a total production quantity of nearly 175,000 engines.

By 1929, it was considered by some that inline engines would completely displace air-cooled radials, and the Bristol Aeroplane Company
Bristol Aeroplane Company
The Bristol Aeroplane Company, originally the British and Colonial Aeroplane Company, was both one of the first and one of the most important British aviation companies, designing and manufacturing both airframes and aero engines...

 was considered to be falling behind in engine production, as they had not produced an inline engine, concentrating instead on radials such as the Jupiter and Mercury
Bristol Mercury
|-See also:-Bibliography:* Bridgman, L, Jane's fighting aircraft of World War II. Crescent. ISBN 0-517-67964-7* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9...

. At that time inline engines were mostly air-cooled, and presented some cooling problems.

Rolls-Royce introduced the Merlin engine
Rolls-Royce Merlin
The Rolls-Royce Merlin is a British liquid-cooled, V-12, piston aero engine, of 27-litre capacity. Rolls-Royce Limited designed and built the engine which was initially known as the PV-12: the PV-12 became known as the Merlin following the company convention of naming its piston aero engines after...

 in 1933, which eventually powered the Supermarine Spitfire
Supermarine Spitfire
The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...

 and Hawker Hurricane
Hawker Hurricane
The Hawker Hurricane is a British single-seat fighter aircraft that was designed and predominantly built by Hawker Aircraft Ltd for the Royal Air Force...

 fighters and the Avro Lancaster
Avro Lancaster
The Avro Lancaster is a British four-engined Second World War heavy bomber made initially by Avro for the Royal Air Force . It first saw active service in 1942, and together with the Handley Page Halifax it was one of the main heavy bombers of the RAF, the RCAF, and squadrons from other...

 heavy bomber, amongst others; the Merlin was also built in the US as the Packard V-1650
Packard V-1650
The Packard V-1650 was a liquid cooled 27 litre 60° V12 piston aircraft engine variant of the Rolls-Royce Merlin produced under licence by the Packard Motor Car Company...

. By 1938 liquid-cooled inline aircraft engines had been successfully developed in the US by the automobile industry, with the backing of the US Army. Many notable fighter aircraft of World War II were powered by inline engines, including the Supermarine Spitfire, P-51 Mustang
P-51 Mustang
The North American Aviation P-51 Mustang was an American long-range, single-seat fighter and fighter-bomber used during World War II, the Korean War and in several other conflicts...

, P-38 Lightning
P-38 Lightning
The Lockheed P-38 Lightning was a World War II American fighter aircraft built by Lockheed. Developed to a United States Army Air Corps requirement, the P-38 had distinctive twin booms and a single, central nacelle containing the cockpit and armament...

 and Messerschmitt Bf 109
Messerschmitt Bf 109
The Messerschmitt Bf 109, often called Me 109, was a German World War II fighter aircraft designed by Willy Messerschmitt and Robert Lusser during the early to mid 1930s...

, but radial engines also saw service in the successful Mitsubishi Zero
A6M Zero
The Mitsubishi A6M Zero was a long-range fighter aircraft operated by the Imperial Japanese Navy Air Service from 1940 to 1945. The A6M was designated as the , and also designated as the Mitsubishi A6M Rei-sen and Mitsubishi Navy 12-shi Carrier Fighter. The A6M was usually referred to by the...

, P-47 Thunderbolt
P-47 Thunderbolt
Republic Aviation's P-47 Thunderbolt, also known as the "Jug", was the largest, heaviest, and most expensive fighter aircraft in history to be powered by a single reciprocating engine. It was heavily armed with eight .50-caliber machine guns, four per wing. When fully loaded, the P-47 weighed up to...

, F4U Corsair
F4U Corsair
The Vought F4U Corsair was a carrier-capable fighter aircraft that saw service primarily in World War II and the Korean War. Demand for the aircraft soon overwhelmed Vought's manufacturing capability, resulting in production by Goodyear and Brewster: Goodyear-built Corsairs were designated FG and...

, F6F Hellcat
F6F Hellcat
The Grumman F6F Hellcat was a carrier-based fighter aircraft developed to replace the earlier F4F Wildcat in United States Navy service. Although the F6F resembled the Wildcat, it was a completely new design powered by a 2,000 hp Pratt & Whitney R-2800. Some tagged it as the "Wildcat's big...

, and Focke-Wulf Fw 190
Focke-Wulf Fw 190
The Focke-Wulf Fw 190 Würger was a German Second World War single-seat, single-engine fighter aircraft designed by Kurt Tank in the late 1930s. Powered by a radial engine, the 190 had ample power and was able to lift larger loads than its well-known counterpart, the Messerschmitt Bf 109...

, while the late-war Hawker Sea Fury
Hawker Sea Fury
The Hawker Sea Fury was a British fighter aircraft developed for the Royal Navy by Hawker during the Second World War. The last propeller-driven fighter to serve with the Royal Navy, it was also one of the fastest production single piston-engined aircraft ever built.-Origins:The Hawker Fury was an...

, one of the fastest production single piston-engined aircraft ever built, used a radial engine. Until the development of the jet engine, bombers, transport aircraft, and airliners commonly used radial engines. Factors influencing the choice of radial over inline were the larger radial engine displacements available, the reliability of the engine, and the maintenance simplicity. Additionally, the larger total frontal area of these aircraft meant the radial engine's large frontal profile was less detrimental in proportion to smaller aircraft designs.

The radial was popular largely due to its simplicity, and most navy
Navy
A navy is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions...

 air arms
Naval aviation
Naval aviation is the application of manned military air power by navies, including ships that embark fixed-wing aircraft or helicopters. In contrast, maritime aviation is the operation of aircraft in a maritime role under the command of non-naval forces such as the former RAF Coastal Command or a...

 had dedicated themselves to it because of its improved reliability for over-water flights and better power/weight ratio for aircraft carrier
Aircraft carrier
An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...

 takeoffs. Being liquid-cooled, inline engines require the added weight and complexity of cooling systems and are generally more vulnerable to battle damage. Damage to an inline engine could result in a loss of coolant and consequent engine seizure, while an air-cooled radial could take damage but continue to operate. Additionally, radials offered higher mechanical efficiency than inline engines, as they had shorter and stiffer crankshafts, a five-cylinder radial needing only two crankshaft bearings as opposed to the seven required for a six-cylinder inline engine. The shorter crankshaft also produced less vibration and hence higher reliability. Another advantage of the air-cooled radial is that all cylinders receive equal cooling airflow, and most radial-engined aircraft designed since the 1930s were fitted with NACA cowling
NACA cowling
The NACA cowling is a type of aerodynamic fairing used to streamline radial engines for use on airplanes and developed by the National Advisory Committee for Aeronautics in 1927...

s to further improve cooling and reduce drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

. Also, by being flat, radial engines resulted in shorter aircraft with better landing visibility (very important for carrier landings).

The inline engine's major advantage was a smaller frontal area compared to radial engines. This made it possible to build more streamlined designs and, for single-engine aircraft, could improve the pilot's forward visibility. In addition, being liquid-cooled offered greater options for both engine and radiator placement. For example, the P-39 Airacobra mounted the engine behind the pilot to allow the large M4 cannon
M4 cannon
The 37 mm Automatic Gun, M4, known as the T9 during development, was a 37 mm autocannon designed by John Browning and used in the Bell P-39 Airacobra and P-63 Kingcobra fighters, as well as experimentally on other designs. It provided interceptors with a weapon that could shoot down any...

 to be mounted in the front of the aircraft, while the Spitfire incorporated an underwing radiator design which offset cooling drag by using the cooling air to generate thrust.

Multi-row radials

Originally radial engines had one row of cylinders, but as engine sizes increased it became necessary to add extra rows. The first known radial-configuration engine to ever use a twin-row design was the 160 hp Gnôme "Double Lambda" rotary engine of 1912, designed as a 14-cylinder twin-row version of the firm's 80 hp Lambda
Gnome Lambda
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6....

 single-row seven-cylinder rotary, with only the German Oberursel U.III clone of the Double Lambda reproducing the Gnome Double Lambda's twin-row design before the end of World War I. Most stationary radial engines did not exceed two rows, but the largest displacement radial engine ever built in quantity, the Pratt & Whitney R-4360 Wasp Major, nicknamed corncob
Corncob
A corncob is the central core of a maize ear.The corn plant's ear is also considered a "cob" or "pole" but it is not fully a "pole" until the ear is shucked, or removed from the plant material around the ear...

, was a 28-cylinder 4-row radial engine used in many large aircraft designs in the post-World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 period. The Lycoming R-7755 was the largest piston-driven aircraft engine ever produced; with 36 cylinders totaling about 7,750 in³ (127 L) of displacement and a power output of 5000 hp. It was originally intended to be used in the "European bomber" that eventually emerged as the Convair B-36. Only two examples were built before the project was terminated in 1946. The USSR
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 also built a limited number of 'Zvezda
JSC Zvezda M503
The Zvezda M503 was a maritime 6 row, 42 cylinder diesel radial engine built in the 1970s by the Soviet Union. Its primary use was in Soviet missile boats, which used three of these engines....

' engines with up to 56 cylinders, which were even larger in displacement than the Lycoming R-7755. The 112-cylinder diesel boat engines featuring 16 rows with 7 banks of cylinders, bore of 160 mm (6.3 in), stroke of 170 mm (6.7 in), and total displacement of 383 liters (23,931 in³). The engine produced 10000 hp at 2,000 rpm
Revolutions per minute
Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...

. They were used on fast attack craft, such as Osa class missile boat
Osa class missile boat
The Project 205 Tsunami, more commonly known by their NATO reporting name Osa, are a class of missile boats developed for the Soviet Navy in the early 1960s. The Osas are probably the most numerous class of missile boats ever built, with over 400 vessels constructed for both the Soviet Navy and for...

s.

Modern radials

At least five companies build radials today. Vedeneyev
Vedeneyev
|-See also:- References :* YAK-55M Operator Handbook* M14 Log books...

 engines produces the M-14P model, 360 hp (up to 450 hp) radial used on Yakovlev
Yakovlev
The Yak Aircraft Corporation is a Russian aircraft designer and manufacturer...

s, and Sukhoi
Sukhoi
Sukhoi Company is a major Russian aircraft manufacturer, headquartered in Begovoy District, Northern Administrative Okrug, Moscow, famous for its fighters...

 Su-26 and Su-29 aerobatic aircraft. The M-14P has also found great favor among builders of experimental aircraft, such as the Culp's Special, and Culp's Sopwith Pup http://culpsspecialties.com, Pitts
Pitts Special
The Pitts Special is a series of light aerobatic biplane designed by Curtis Pitts. It has accumulated many competition wins since its first flight in 1944...

 S12 "Monster" and the Murphy "Moose". 110 hp
Rotec R2800
The Rotec R2800 is a seven-cylinder radial engine built by Rotec Engineering PTY LTD in Australia. The R2800 was Rotec's first engine offering when they first opened their doors in 2000. In 2005, Rotec released a more powerful variant, the Rotec R3600 which basically adds two more cylinders for a...

 7-cylinder and 150 hp
Rotec R3600
The Rotec R3600 is a nine-cylinder radial engine built by Rotec Engineering PTY LTD in Australia. Initially released in 2005, it was a followup of the 7-cylinder Rotec R2800 released five years earlier. Both this engine and its smaller cousin have been frequently used as both replacement engines...

 9-cylinder engines are available from Australia's Rotec Engineering. HCI Aviation http://www.hciaviation.com/ offers the R180 5-cylinder (75 hp) and R220 7-cylinder (110 hp), available "ready to fly" and as a build-it-yourself kit. Verner Motor, from the Czech Republic, now builds several radial engines. Models range in power from 71 hp to 172 hp. http://www.vernermotor.com/ Miniature radial engines for model airplane use are also available from Seidel in Germany, OS and Saito Seisakusho of Japan, and Technopower in the USA. The Saito firm is known for making three different sizes of 3-cylinder radials, as well as a 5-cylinder example, as the Saito firm is a specialist in making a large line of miniature four-stroke engines for model use in both methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

-burning glow plug
Glow plug (model engine)
A glow plug is a device, similar to a spark plug, used to help ignite the fuel in the very small internal combustion engines typically used in model aircraft, model cars and similar applications...

 and gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

-fueled spark plug ignition
Spark plug
A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.Spark plugs have an insulated central electrode which is connected by...

 engine formats.

Diesel radials

While most radial engines have been produced for gasoline fuels, there have been instances of diesel fueled engines. The Bristol Phoenix
Bristol Phoenix
|-See also:-Bibliography:*Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9...

 of 1928-1932 was successfully tested in aircraft and the Nordberg Manufacturing Company of the US developed and produced a series of large radial diesel engines from the 1940s.

To reduce the danger of engine fires, in 1932 the French company Clerget developed the 14D, a 14-cylinder two-stroke diesel radial engine. After a series of improvements, in 1938 the 14F2 model produced 520 hp at 1910 rpm cruise power, with a power-to-weight ratio near that of contemporary gasoline engines and a specific fuel consumption
Brake specific fuel consumption
Brake Specific Fuel Consumption is a measure of fuel efficiency within a shaft reciprocating engine.It is the rate of fuel consumption divided by the power produced. It may also be thought of as power-specific fuel consumption, for this reason...

 of .365 lb/hp/hour. During WWII the research continued, but no engines were mass-produced because of the Nazi occupation, and by 1943 the engine had grown to produce over 1000 hp with a turbocharger. After the war, the Clerget company was integrated in the SNECMA
Snecma
Snecma is a major French manufacturer of engines for commercial and military aircraft, and for space vehicles. The name is an acronym for Société Nationale d'Étude et de Construction de Moteurs d'Aviation .In 2005, the Snecma group, which included Snecma ,...

 company and had plans for a 32-cylinder diesel engine of 4000 hp, but in 1947 the company abandoned piston engine development in favor of work on the emerging turbine engines.

The Nordberg engines were initially designed for electricity production in aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 smelters. They differed from the norm of radial design by using two opposite cylinders as a double master instead of the more usual single master rod, and managed to run perfectly circular. The engine design also permitted even numbers of cylinders in a single row with the cylinders being fired in consecutive order. The engines were a two-stroke design and were also available in a dual-fuel gas/diesel model. A number of powerhouse installations utilising large numbers of these engines were made in the US.

Packard designed and built a diesel radial aircraft engine, the DR-980, in 1928. It was a 9-cylinder radial engine displacing 980 cubic inches and rated to produce 225 hp. On 28 May 1931, a Bellanca CH-300
Bellanca CH-300
-References:NotesCitationsBibliography* Szurovy, Geza. Bushplanes. St. Paul, Minnesota: Zenith Press, 2004. ISBN 0-7603-1478-0.* Taylor, Michael J.H. Jane's Encyclopedia of Aviation. London: Studio Editions, 1989, p. 149.-External links:* *...

 fitted with a DR-980, piloted by Walter Edwin Lees
Walter Edwin Lees
Walter Edwin Lees was an early American aviator who set a flight endurance record in 1931.-Biography:He was born in 1887 in Janesville, Wisconsin, and attended the University of Wisconsin–Madison. He made his first solo flight on November 14, 1912, near St. Louis, Missouri...

 and Frederick Brossy
Frederick Brossy
Frederic A. Brossy set the flight endurance record with Walter Edwin Lees on May 28, 1931.-Biography:He was born in 1902 to Francis E. Brossy. In 1931 he was an ensign in reserve squadron VN-9RD9 at the Naval Reserve Aviation Base in Grosse Ile, Michigan. Walter Edwin Lees was a lieutenant in the...

, set a record for staying aloft for 84 hours and 32 minutes without being refueled. This record was not broken until 55 years later by the Rutan Voyager.

The Zoche outfit in Germany have produced a prototype range of radial air-cooled two-stroke diesel aero-engines
Aircraft engine
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...

, comprising a V-twin, a single-row cross-4 and a double-row cross-8. A Zoche engine has run successfully in wind tunnel tests , but Zoche seem barely closer to production than they were a decade ago. Experimental engine manufacturers seem to experience difficulties in proceeding beyond the prototype stage.

Compressed air radials

A number of radial motors operating on compressed air have been designed, mostly for use in model airplanes, or simply as a building project. Radial compressed air engines include Liney Machine Halo 5, Mike Smyth SF376, Taiyo UTAM4, ... They have also been used in gas compressors.

Use in tanks

In the years leading up to WWII, as the need for armored vehicles was realized, designers were faced with the problem of how to power the vehicles, and turned to using aircraft engines, among them radial types. The radial aircraft engines provided greater power-to-weight ratios and were more reliable than conventional inline vehicle engines available at the time. This reliance had a downside though: if the engines were mounted vertically as in the M3 Lee
M3 Lee
The Medium Tank M3 was an American tank used during World War II. In Britain the tank was called "General Lee", named after Confederate General Robert E. Lee, and the modified version built with a new turret was called the "General Grant", named after U.S. General Ulysses S. Grant.Design commenced...

 and M4 Sherman
M4 Sherman
The M4 Sherman, formally Medium Tank, M4, was the primary tank used by the United States during World War II. Thousands were also distributed to the Allies, including the British Commonwealth and Soviet armies, via lend-lease...

, their comparatively large diameter gave the tank a higher silhouette than designs using inline engines.

The Continental R-670, a 7-cylinder radial aero engine which first flew in 1931, became a widely used tank powerplant, being installed in the M1 Combat Car
M1 Combat Car
The M1 Combat Car was a light tank used by the U.S. Cavalry in late 1930s. After the Spanish Civil War, most armies, including the U.S. Army, realized that they needed "gun" armed tanks and not vehicles armed merely with machine guns...

, M2 Light Tank
M2 Light Tank
The Light Tank M2 was an American pre-World War II light tank that saw combat with the US Marine Corps 1st Tank Battalion on Guadalcanal in 1942, during World War II. Its service with the 1st Tank Battalion during the Pacific War was its only U.S...

, M3 Stuart, M3 Lee
M3 Lee
The Medium Tank M3 was an American tank used during World War II. In Britain the tank was called "General Lee", named after Confederate General Robert E. Lee, and the modified version built with a new turret was called the "General Grant", named after U.S. General Ulysses S. Grant.Design commenced...

, LVT-2 Water Buffalo
Landing Vehicle Tracked
The Landing Vehicle Tracked was a class of amphibious vehicles introduced by the United States Navy, Marine Corps and Army during World War II. Originally intended solely as cargo carriers for ship to shore operations, they rapidly evolved into assault troop and fire support vehicles as well...

.

The Guiberson T-1020, a 9-cylinder radial diesel aero engine, was used in the M1A1E1, M2, and M3, while the Continental R975 saw service in the M4 Sherman
M4 Sherman
The M4 Sherman, formally Medium Tank, M4, was the primary tank used by the United States during World War II. Thousands were also distributed to the Allies, including the British Commonwealth and Soviet armies, via lend-lease...

, M7 Priest
M7 Priest
The 105 mm Howitzer Motor Carriage M7 was an American self-propelled artillery vehicle produced during World War II. It was given the official service name 105 mm Self Propelled Gun, Priest by the British Army, due to the pulpit-like machine gun ring, and following on from the Bishop and...

, M18 Hellcat
M18 Hellcat
The 76 mm Gun Motor Carriage M18 was an American tank destroyer of World War II. The manufacturer, Buick, gave it the nickname "Hellcat" and it was the fastest tracked armored fighting vehicle during the war with a top speed up to 60 mph. Hellcat crews took advantage of the vehicle's...

 tank destroyer
Tank destroyer
A tank destroyer is a type of armored fighting vehicle armed with a gun or missile launcher, and is designed specifically to engage enemy armored vehicles...

, and the M44 self-propelled howitzer.

Model radial engines

A number of multi-cylinder 4-stroke model engine
Model engine
In radio-controlled modeling, a model engine is an internal combustion engine used to power a radio-controlled aircraft, radio-controlled car, radio-controlled boat, free flight and control line aircraft, and tether car models also use these engines....

s have been commercially available in a radial configuration, beginning with the Japanese O.S. Max
O.S. Max
O.S. Engines is a Japanese model engine manufacturer.The company was founded in 1936 by machinist Shigeo Ogawa for the production of model steam engines...

 firm's FR5-300 five-cylinder, 3.0 cu.in. (50 cm3) displacement "Sirius" radial in 1986. The American 'Technopower' firm had made smaller-displacement five- and seven-cylinder model radial engines as early as 1976, but the OS firm's engine was the first mass-produced radial engine design in aeromodeling history. The rival Saito Seisakusho firm in Japan has since produced a similarly sized five-cylinder radial four-stroke model engine of their own as a direct rival to the OS design, with Saito also creating a trio of three-cylinder radial engines ranging from 0.90 cu.in. (15 cm3) to 4.50 cu.in. (75 cm3) in displacement. The German Seidel firm has made both seven- and nine-cylinder "large" (starting at 70 cm3 displacement) radio control model radial engines, mostly for glow plug ignition, with an experimental fourteen-cylinder twin-row radial being tried out.

See also

  • Kinner B-5
    Kinner B-5
    |-See also:-References:* http://www.oldengine.org/members/diesel/Duxford/usaero4.htm-External links:...

  • List of aircraft engines
  • Rotary engine
    Rotary engine
    The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it...

  • Technopower
  • Vedeneyev
    Vedeneyev
    |-See also:- References :* YAK-55M Operator Handbook* M14 Log books...

  • Warner Scarab
    Warner Scarab
    |-See also:-References:*-External links:*...

  • Zvezda M503, a 42-cylinder Soviet missile boat diesel radial engine.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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