The Early Days
Charles 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.
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.
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. 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.
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.
The Wasp Major, a four-row radial.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 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, was a 28-cylinder 4-row radial engine used in many large aircraft designs in the post-World War II 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 5,000 horsepower (3,700 kW). 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 also built a limited number of 'Zvezda' 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 10,000 hp (7,500 kW) at 2,000 rpm. They were used on fast attack craft, such as Osa class missile boats.
Wed, Sep 21 2011 12:32 AM
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