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Radial Engines - The Benefits

Updated on March 25, 2011

The Beauty of Radial Engines

When they try to start, the racket is beautiful. There is nothing more. An inline has a clean startup, just pumping away. A radial clatters and bangs. It's hard to decide whether it has genuinely started. Example below...

Sounds Like a Pratt & Whitney Radial, Sounds Good!


Does anyone feel the same?

Do you feel that poppet valves have overtaken the sleeve valve? I think that you will never get a prettier sound from a sleve valve as most large capacity poppet valves have never made it to sleeve valve technology, because sleeve valve was a new technology until the jet age.


Radial Engines on Wikipedia

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Radial engine in a cut-away view

Radial engine of a biplaneThe radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel. This configuration was very commonly used in large aircraft engines before most large aircraft started using turbine 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 rods' attachments to rings around the edge of the master rod. Four-stroke radials always have an odd number of cylinders per row, so that a consistent every-other-piston firing order 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 crank shaft revolution. This leads to an uneven firing order within the engine, and is not ideal. [1]

Most radial engines use overhead poppet valves driven by pushrods and lifters on a cam plate which is concentric with the crankshaft, with a few smaller radials, like the five-cylinder Kinner B-5, using individual camshafts within the crankcase for each cylinder. A few engines utilize sleeve valves instead, like the very reliable 14 cylinder Bristol Hercules (built up to 1970' under licence in France by SNECMA) and the powerful 18 cylinder Bristol Centaurus.

Contents [hide]

1 History

2 Radial versus inline debate

3 Multi-row radials

4 Modern radials

5 Diesel radials

6 Use in tanks

7 Model radial engines

8 See also

9 References

10 External links


A Continental radial engine, 1944

Pratt & Whitney R-1340 radial engine mounted in Sikorsky H-19 helicopterCharles Manly constructed a water-cooled 5-cylinder radial engine in 1901, a conversion of one of Stephen Balzer's rotary engines, for Langley's Aerodrome aircraft. Manly's engine produced 52 hp (39 kW) at 950 rpm.[2]

In 1903-04 Jacob Ellehammer used his experience constructing motorcycles to build the world's first air-cooled radial engine, a 3-cylinder engine which he used as the basis for a more powerful 5-cylinder model in 1907. This was installed in his triplane 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, 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.[3]

Another early radial engine was the 3-cylinder Anzani, originally built as a "semi-radial" W3 configuration design, one of which powered Louis Blériot's Blériot XI in his July 25, 1909 crossing of the English Channel. By 1914 Anzani had developed their range, their largest radial being a 20-cylinder engine of 200 hp (150 kW), with its cylinders arranged in four groups of five.[2] 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'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 9 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 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, 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.[2]

During the decade 1910-1920 the radial engine was largely overshadowed by its close relative, the rotary engine-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 (180 kW), 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. 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

1935 Monaco-Trossi, a rare example of automobile use.By 1918, the potential advantages of air-cooled radials over the water-cooled inline engine and air-cooled rotary engine that had powered World War I aircraft were well appreciated. While British designers had produced the ABC radial in 1917, they were unable to resolve its cooling problems, and it was not until the 1920s that the Bristol Aircraft Company produced reliable British radials.

In the US, NACA 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, 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.[4]

Wright's 225 hp (168 kW) J-5 Whirlwind radial engine of 1925 was widely acknowledged as "the first truly reliable aircraft engine".[5] Wright employed Giuseppe Mario Bellanca 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 was founded, with the P & W firm's initial offering, the Pratt & Whitney Wasp, 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 was considered to be falling behind in engine production, as they had not produced an inline engine, concentrating instead on radials. At that time inline engines were mostly air-cooled, and presented some cooling problems.[6]

Rolls Royce introduced the Merlin engine in 1933, which eventually powered the Spitfire and Hurricane fighters and the Lancaster heavy bomber, amongst others; the Merlin was also built in the US as the Packard V-1650. 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-38 Lightning and Messerschmitt Bf 109, but radial engines also saw service in the successful Mitsubishi Zero, P-47 Thunderbolt, F4U Corsair, F6F Hellcat, and Focke-Wulf Fw 190, while the late-war Hawker Sea Fury, 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 air arms had dedicated themselves to it because of its improved reliability for over-water flights and better power/weight ratio for aircraft carrier takeoffs. B

Radial Engines

About My Guest Author...

This article was written by my beloved husband Roger, who has extensive knowledge in this area. If you have any questions or comments about aeroplanes or their engines, please feel free to add them below. We'd love to hear from you!

Enter your comments or questions here...

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    • cattyjen profile imageAUTHOR


      7 years ago

      @anonymous: Sorry about the delay in replying, but I have not being paying attention recently! The reason is that in high powered radial engines, the two con rods do not directly oppose each other. Hope this helps. Regards Roger (Guest Author for Cattyjen).

    • profile image


      8 years ago

      why only there is an odd no. of cylinder in a raw in radial engine?.And also why and how firing order is performed?please explain in detail....

    • Pixelhound profile image


      9 years ago from west vancouver BC Canada

      I loved your lens great videos, I used to own a 1935 motorcycle built by the French company Gnome et Rhone it was very well engineered.


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