The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is called a "star engine" in some other languages.
118-529: The Bristol Hercules is a 14-cylinder two-row radial aircraft engine designed by Sir Roy Fedden and produced by the Bristol Engine Company starting in 1939. It was the most numerous of their single sleeve valve ( Burt-McCollum , or Argyll , type) designs, powering many aircraft in the mid- World War II timeframe. The Hercules powered a number of aircraft types, including Bristol's own Beaufighter heavy fighter design, although it
236-415: A knock sensor that monitors if knock is being produced by the fuel being used. In modern computer-controlled engines, the ignition timing will be automatically altered by the engine management system to reduce the knock to an acceptable level. Octanes are a family of hydrocarbons that are typical components of gasoline. They are colorless liquids that boil around 125 °C (260 °F). One member of
354-411: A 14-cylinder twin-row version of the firm's 80 hp Lambda single-row seven-cylinder rotary, however reliability and cooling problems limited its success. Two-row designs began to appear in large numbers during the 1930s, when aircraft size and weight grew to the point where single-row engines of the required power were simply too large to be practical. Two-row designs often had cooling problems with
472-451: A 9-cylinder 980 cubic inch (16.06 litre) displacement diesel radial aircraft engine, the 225 horsepower (168 kW) DR-980 , in 1928. On 28 May 1931, a DR-980 powered Bellanca CH-300 , with 481 gallons of fuel, piloted by Walter Edwin Lees and Frederick Brossy set a record for staying aloft for 84 hours and 32 minutes without being refueled. This record stood for 55 years until broken by
590-685: A 9-cylinder radial diesel aero engine, was used in the M1A1E1 , while the Continental R975 saw service in the M4 Sherman , M7 Priest , M18 Hellcat tank destroyer , and the M44 self propelled howitzer . A number of companies continue to build radials today. Vedeneyev produces the M-14P radial of 360–450 hp (270–340 kW) as used on Yakovlev and Sukhoi aerobatic aircraft. The M-14P
708-678: A build-it-yourself kit. Verner Motor of the Czech Republic builds several radial engines ranging in power from 25 to 150 hp (19 to 112 kW). Miniature radial engines for model airplanes are available from O. S. Engines , Saito Seisakusho of Japan, and Shijiazhuang of China, and Evolution (designed by Wolfgang Seidel of Germany, and made in India) and Technopower in the US. Liquid cooling systems are generally more vulnerable to battle damage. Even minor shrapnel damage can easily result in
826-521: A civil-series engine developed from the Hercules 630. The Hercules 633 was the torquemeter version. The Hercules 638 and Hercules 672 , along with their torquemeter versions the Hercules 639 and Hercules 673 were developments of the Hercules 632. Hercules 634 – 1,690 hp (1,260 kW), a civil-series engine developed from the Hercules 630 with modified mounting ring and exhaust pipes for
944-399: A few French-built examples of the famous Blériot XI from the original Blériot factory — to a massive 20-cylinder engine of 200 hp (150 kW), with its cylinders arranged in four rows of five cylinders apiece. Most radial engines are air-cooled , but one of the most successful of the early radial engines (and the earliest "stationary" design produced for World War I combat aircraft)
1062-427: A five-cylinder engine the firing order is 1, 3, 5, 2, 4, and back to cylinder 1. Moreover, this always leaves a one-piston gap between the piston on its combustion stroke and the piston on compression. The active stroke directly helps compress the next cylinder to fire, making the motion more uniform. If an even number of cylinders were used, an equally timed firing cycle would not be feasible. As with most four-strokes,
1180-413: A flame wave initiate at the spark plug and then "travel in a fairly uniform manner across the combustion chamber" with the expanding gas mix pushing the piston throughout the entirety of the power stroke. A stable gasoline and air mix will combust when the flame wave reaches the molecules, adding heat at the interface. Knock occurs when a secondary flame wave forms from instability and then travels against
1298-440: A lighter fuel that's less prone to autoignition is a wise "insurance policy". For the same reasons, those lighter fuels which are better solvents are much less likely to cause any "varnish" or other fouling on the "backup" spark plugs. In almost all general aviation piston engines, the fuel mixture is directly controlled by the pilot, via a knob and cable or lever similar to (and next to) the throttle control. Leaning — reducing
SECTION 10
#17327799108721416-419: A loss of coolant and consequent engine overheating, while an air-cooled radial engine may be largely unaffected by minor damage. Radials have shorter and stiffer crankshafts, a single-bank radial engine needing only two crankshaft bearings as opposed to the seven required for a liquid-cooled, six-cylinder, inline engine of similar stiffness. While a single-bank radial permits all cylinders to be cooled equally,
1534-677: A number of experiments and modifications) enough cooling air to the rear. This basic concept was soon copied by many other manufacturers, and many late-WWII aircraft returned to the radial design as newer and much larger designs began to be introduced. Examples include the Bristol Centaurus in the Hawker Sea Fury , and the Shvetsov ASh-82 in the Lavochkin La-7 . For even greater power, adding further rows
1652-510: A power-to-weight ratio near that of contemporary gasoline engines and a specific fuel consumption of roughly 80% that for an equivalent gasoline engine. During WWII the research continued, but no mass-production occurred because of the Nazi occupation. By 1943 the engine had grown to produce over 1,000 hp (750 kW) with a turbocharger . After the war, the Clerget company was integrated in
1770-520: A process was discovered which used centrifugal casting to make the sleeves perfectly round. This final success arrived just before the start of the Second World War. In 1937 Bristol acquired a Northrop Model 8A-1, the export version of the A-17 attack bomber, and modified it as a testbed for the first Hercules engines. In 1939 Bristol developed a modular engine installation for the Hercules,
1888-420: A rear manifold. The Hercules 635 was the torquemeter version. Hercules 636 – a civil-series engine developed from the Hercules 630 with modified mounting ring and exhaust pipes for a rear manifold. The Hercules 637 was the torquemeter version. The Hercules 637-2 and Hercules 637-3 were further torquemeter developments. Hercules 730 – 2,040 hp (1,520 kW), a civil-series engine developed from
2006-486: A relatively low octane rating; the isomer iso-octane causes less knocking because it is more branched and combusts more smoothly. In general, branched compounds with a higher intermolecular force (e.g., London dispersion force for iso-octane) will have a higher octane rating, because they are harder to ignite. Octane isomers such as n-octane and 2,3,3-trimethylpentane have an octane rating of -20 and 106.1, respectively ( RON measurement). The large differences between
2124-648: A similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 lower than the RON, but there is no direct link between RON and MON. See the table below. In most countries in Europe, and in Australia and New Zealand,
2242-704: 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 series of three-cylinder methanol and gasoline-fueled model radial engines ranging from 0.90 cu.in. (15 cm ) to 4.50 cu.in. (75 cm ) in displacement, also all now available in spark-ignition format up to 84 cm displacement for use with gasoline. The German Seidel firm formerly made both seven- and nine-cylinder "large" (starting at 35 cm displacement) radio control model radial engines, mostly for glow plug ignition, with an experimental fourteen-cylinder twin-row radial being tried out -
2360-478: A single bank (or row) and an unusual double master connecting rod. Variants were built that could be run on either diesel oil or gasoline or mixtures of both. A number of powerhouse installations utilising large numbers of these engines were made in the U.S. Electro-Motive Diesel (EMD) built the "pancake" engines 16-184 and 16-338 for marine use. Zoche aero-diesels are a prototype radial design that have an even number of cylinders, either four or eight; but this
2478-492: A sleeve valve engine that would actually work by 1934, introducing their first sleeve-valve designs in the 750 horsepower (560 kilowatts) class Perseus and the 500 hp (370 kW) class Aquila that they intended to supply throughout the 1930s. Aircraft development in the era was so rapid that both engines quickly ended up at the low-power end of the military market and, in order to deliver larger engines, Bristol developed 14-cylinder versions of both. The Perseus evolved into
SECTION 20
#17327799108722596-681: A so-called " power-egg ", allowing the complete engine and cowling to be fitted to any suitable aircraft. A total of over 57,400 Hercules engines were built. Hercules I (1936) – 1,150 hp (860 kW), single-speed supercharger , run on 87 octane fuel. Hercules II (1938) – 1,375 hp (1,025 kW), single-speed supercharger, run on 87 octane fuel. Hercules III (1939) – 1,400 hp (1,000 kW), two-speed supercharger, run on either 87 or 100 octane fuel. Hercules IV (1939) – 1,380 hp (1,030 kW), single-speed supercharger, run on 87 octane fuel. Hercules V (1939) – 1,380 hp (1,030 kW), civil prototype derived from
2714-480: Is a measured and/or calculated rating of the fuel's ability to resist autoignition, the higher the octane of the fuel, the harder that fuel is to ignite and the more heat is required to ignite it. The result is that a hotter ignition spark is required for ignition. Creating a hotter spark requires more energy from the ignition system, which in turn increases the parasitic electrical load on the engine. The spark also must begin earlier in order to generate sufficient heat at
2832-493: Is a mixture of many hydrocarbons and often other additives). Octane ratings are not indicators of the energy content of fuels. (See Effects below and Heat of combustion ). They are only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced. Ethanol energy density can be compared with gasoline in heat-of-combustion tables. It
2950-599: Is also used by builders of homebuilt aircraft , such as the Culp Special , and Culp Sopwith Pup , Pitts S12 "Monster" and the Murphy "Moose" . 110 hp (82 kW) 7-cylinder and 150 hp (110 kW) 9-cylinder engines are available from Australia's Rotec Aerosport . HCI Aviation offers the R180 5-cylinder (75 hp (56 kW)) and R220 7-cylinder (110 hp (82 kW)), available "ready to fly" and as
3068-425: Is derived from testing the gasoline in ordinary multi-cylinder engines (rather than in a purpose-built test engine), normally at wide open throttle. This type of test was developed in the 1920s and is still reliable today. The original RdON tests were done in cars on the road, but as technology developed the testing was moved to chassis dynamometers with environmental controls to improve consistency. The evaluation of
3186-427: Is ignited only near the end of the compression stroke by electric spark plugs . Therefore, being able to compress the air/fuel mixture without causing detonation is important mainly for gasoline engines. Using gasoline with lower octane than an engine is built for may cause engine knocking and/or pre-ignition . The octane rating of aviation gasoline was extremely important in determining aero engine performance in
3304-412: Is not problematic, because they are two-stroke engines , with twice the number of power strokes as a four-stroke engine per crankshaft rotation. A number of radial motors operating on compressed air have been designed, mostly for use in model airplanes and in gas compressors. A number of multi-cylinder 4-stroke model engines have been commercially available in a radial configuration, beginning with
3422-411: Is possible for a fuel to have a Research Octane Number (RON) more than 100, because iso-octane is not the most knock-resistant substance available today. Racing fuels, avgas , LPG and alcohol fuels such as methanol may have octane ratings of 110 or significantly higher. Typical "octane booster" gasoline additives include MTBE , ETBE , iso-octane and toluene . Lead in the form of tetraethyllead
3540-435: Is the octane number of the fuel. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. A rating of 90 does not mean that the gasoline contains just iso-octane and heptane in these proportions, but that it has the same detonation resistance properties (generally, gasoline sold for common use never consists solely of iso-octane and heptane; it
3658-627: The Kawasaki Ki-100 and Yokosuka D4Y 3. In Britain, Bristol produced both sleeve valved and conventional poppet valved radials: of the sleeve valved designs, more than 57,400 Hercules engines powered the Vickers Wellington , Short Stirling , Handley Page Halifax , and some versions of the Avro Lancaster , over 8,000 of the pioneering sleeve-valved Bristol Perseus were used in various types, and more than 2,500 of
Bristol Hercules - Misplaced Pages Continue
3776-532: The Rutan Voyager . The experimental Bristol Phoenix of 1928–1932 was successfully flight tested in a Westland Wapiti and set altitude records in 1934 that lasted until World War II. 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 (390 kW) at 1910 rpm cruise power, with
3894-638: The SNECMA company and had plans for a 32-cylinder diesel engine of 4,000 hp (3,000 kW), but in 1947 the company abandoned piston engine development in favour of the emerging turbine engines. The Nordberg Manufacturing Company of the United States developed and produced a series of large two-stroke radial diesel engines from the late 1940s for electrical production, primarily at aluminum smelters and for pumping water. They differed from most radials in that they had an even number of cylinders in
4012-499: The Westland Lysander , Bristol Blenheim , and Blackburn Skua . In the years leading up to World War II, 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
4130-557: The four-stroke cycle . In a simple explanation, the forward moving wave of combustion that burns the hydrocarbon + oxygen mixture inside the cylinder like a wave that a surfer would wish to surf upon is violently disrupted by a secondary wave that has started elsewhere. The shock wave of these two separate waves creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential (incremental heating plus power loss) to completely destructive (detonation while one of
4248-423: The ideal gas law . Higher compression ratios necessarily add parasitic load to the engine, and are only necessary if the engine is being specifically designed to run on high-octane fuel. Aircraft engines run at relatively low speeds and are " undersquare ". They run best on lower-octane, slower-burning fuels that require less heat and a lower compression ratio for optimum vaporization and uniform fuel-air mixing, with
4366-533: The "headline" octane rating prominently displayed on the pump is the RON, but in Canada, the United States, and Mexico, the headline number is the simple mean or average of the RON and the MON, called the Anti-Knock Index ( AKI ), and often written on pumps as (R+M)/2 . AKI is also sometimes called PON (Pump Octane Number). Because of the 8 to 12 octane number difference between RON and MON noted above,
4484-551: The AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's sensitivity, and is not typically published for those countries that use the Anti-Knock Index labelling system. See the table in the following section for a comparison. Another type of octane rating, called Observed Road Octane Number ( RdON ),
4602-670: The American Pratt & Whitney company was founded, competing with Wright's radial engines. Pratt & Whitney's initial offering, the R-1340 Wasp , was test run later that year, beginning a line of engines over the next 25 years that included the 14-cylinder, twin-row Pratt & Whitney R-1830 Twin Wasp . More Twin Wasps were produced than any other aviation piston engine in the history of aviation; nearly 175,000 were built. In
4720-640: The American Evolution firm now sells the Seidel-designed radials, with their manufacturing being done in India. Octane rating An octane rating , or octane number , is a standard measure of a fuel 's ability to withstand compression in an internal combustion engine without causing engine knocking . The higher the octane number, the more compression the fuel can withstand before detonating. Octane rating does not relate directly to
4838-607: The American single-engine Vought F4U Corsair , Grumman F6F Hellcat , Republic P-47 Thunderbolt , twin-engine Martin B-26 Marauder , Douglas A-26 Invader , Northrop P-61 Black Widow , etc. The same firm's aforementioned smaller-displacement (at 30 litres), Twin Wasp 14-cylinder twin-row radial was used as the main engine design for the B-24 Liberator , PBY Catalina , and Douglas C-47 , each design being among
Bristol Hercules - Misplaced Pages Continue
4956-635: The Centaurus and rapid movement to the use of turboprops such as the Armstrong Siddeley Python and Bristol Proteus , which easily produced more power than radials without the weight or complexity. Large radials continued to be built for other uses, although they are no longer common. An example is the 5-ton Zvezda M503 diesel engine with 42 cylinders in 6 rows of 7, displacing 143.6 litres (8,760 cu in) and producing 3,942 hp (2,940 kW). Three of these were used on
5074-745: The German single-seat, single-engine Focke-Wulf Fw 190 Würger , and twin-engine Junkers Ju 88 . In Japan, most airplanes were powered by air-cooled radial engines like the 14-cylinder Mitsubishi Zuisei (11,903 units, e.g. Kawasaki Ki-45 ), Mitsubishi Kinsei (12,228 units, e.g. Aichi D3A ), Mitsubishi Kasei (16,486 units, e.g. Kawanishi H8K ), Nakajima Sakae (30,233 units, e.g. Mitsubishi A6M and Nakajima Ki-43 ), and 18-cylinder Nakajima Homare (9,089 units, e.g. Nakajima Ki-84 ). The Kawasaki Ki-61 and Yokosuka D4Y were rare examples of Japanese liquid-cooled inline engine aircraft at that time but later, they were also redesigned to fit radial engines as
5192-617: The Gnome and Le Rhône rotary powerplants, and Siemens-Halske built their own designs, including the Siemens-Halske Sh.III eleven-cylinder rotary engine , which was unusual for the period in being geared through a bevel geartrain in the rear end of the crankcase without the crankshaft being firmly mounted to the aircraft's airframe, so that the engine's internal working components (fully internal crankshaft "floating" in its crankcase bearings, with its conrods and pistons) were spun in
5310-457: The Hercules 100. The Hercules 103 was the torquemeter version. The Hercules 110 was a further development of the Hercules 101. Hercules 105 – 1,675 hp (1,249 kW), developed from the Hercules 101 with modified supercharger gears. Hercules 106 – 1,675 hp (1,249 kW), developed from the Hercules 101. The Hercules 107 was the torquemeter version. Hercules 120 – 1,715 hp (1,279 kW), high-altitude development of
5428-408: The Hercules 101. The Hercules 121 was the torquemeter version. The Hercules 200 was further modified version of the Hercules 120. Hercules 130 – 1,715 hp (1,279 kW), development of the Hercules 100. The Hercules 134 was a development with modified mounting ring and exhaust pipes for a rear manifold. Hercules 216 – 1,675 hp (1,249 kW), development of the Hercules 106 with
5546-412: The Hercules 230 and 630 with improved power section, the Hercules 731 was the torquemeter version. Hercules 732 – a civil-series engine developed from the Hercules 730 with modified mounting ring and exhaust pipes for a rear manifold. The Hercules 733 was the torquemeter version. Hercules 734 – 1,980 hp (1,480 kW), a civil-series engine developed from the Hercules 730. The Hercules 735
5664-416: The Hercules 230 for improved performance. The Hercules 233 was the torquemeter version. Hercules 234 – modified development of the Hercules 232. The Hercules 235 was the torquemeter version. The Hercules 238 was a military version of the Hercules 734 which itself was based on the Hercules 234. Hercules 260 – modified development of the Hercules 230 to suit reversible propellers . The Hercules 261
5782-408: The Hercules 230 power section and single speed supercharger. Applications: Hercules 230 – 1,925 hp (1,435 kW), development of the Hercules 130 with the re-designed power section and modified mounting ring and exhaust pipes for a rear manifold. The Hercules 270 was a development. The Hercules 231 and Hercules 271 were the torquemeter versions. Hercules 232 – modified development of
5900-937: The Hercules III. Hercules XI (1941) – 1,590 hp (1,190 kW), derived from the Hercules III, run on 100 octane fuel. Hercules XII – derived from the Hercules IV. Hercules XIV (1942) – 1,500 hp (1,100 kW), developed for the civil market and used by BOAC , run on 100 octane fuel. Hercules XVMT – 1,650 hp (1,230 kW), very high-altitude development of the Hercules II, single-speed supercharger with an auxiliary high-altitude turbo-supercharger . Hercules XVI (1942) – 1,615 hp (1,204 kW), two-speed supercharger, run on either 87 or 100 octane fuel. Hercules XVII (1943) – 1,615 hp (1,204 kW), two-speed supercharger locked in 'M' gear. Hercules XVIII – low-level development of
6018-445: The Hercules IV but not developed. Hercules VI (1941) – 1,615 hp (1,204 kW), two-speed supercharger, run on either 87 or 100 octane fuel. Hercules VII production cancelled. Hercules VIII – 1,650 hp (1,230 kW), very high-altitude version of the Hercules II, single-speed supercharger with an auxiliary high-altitude single-speed 'S' supercharger. Hercules X (1941) – 1,420 hp (1,060 kW), derived from
SECTION 50
#17327799108726136-624: The Hercules VI with cropped 12 in (300 mm) supercharger impellers . Hercules XIX (1943) – 1,725 hp (1,286 kW), a development of the Hercules XVII, the two-speed supercharger had cropped 12 in (300 mm) impellers locked in 'M' gear. Hercules XX – similar to the Hercules XIX. Hercules 36 – a development engine derived from the Hercules VI and Hercules XVI, run on 100 octane fuel. The Hercules 38
6254-528: The Hercules, and the Aquila into the Taurus . These smooth-running engines were largely hand-built, which was incompatible with the needs of wartime production. At that time, the tolerances were simply not sufficiently accurate to ensure the mass production of reliable engines. Fedden drove his teams mercilessly, at both Bristol and its suppliers, and thousands of combinations of alloys and methods were tried before
6372-513: The Japanese O.S. Max firm's FR5-300 five-cylinder, 3.0 cu.in. (50 cm ) 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 aeromodelling history. The rival Saito Seisakusho firm in Japan has since produced
6490-533: The Jupiter. Although other piston configurations and turboprops have taken over in modern propeller-driven aircraft , Rare Bear , which is a Grumman F8F Bearcat equipped with a Wright R-3350 Duplex-Cyclone radial engine, is still the fastest piston-powered aircraft . 125,334 of the American twin-row, 18-cylinder Pratt & Whitney R-2800 Double Wasp , with a displacement of 2,800 in (46 L) and between 2,000 and 2,400 hp (1,500-1,800 kW), powered
6608-758: The United Kingdom the Bristol Aeroplane Company was concentrating on developing radials such as the Jupiter, Mercury , and sleeve valve Hercules radials. Germany, Japan, and the Soviet Union started with building licensed versions of the Armstrong Siddeley, Bristol, Wright, or Pratt & Whitney radials before producing their own improved versions. France continued its development of various rotary engines but also produced engines derived from Bristol designs, especially
6726-404: The aircraft of World War II . The octane rating affected not only the performance of the gasoline, but also its versatility; the higher octane fuel allowed a wider range of lean to rich operating conditions. In spark ignition internal combustion engines , knocking (also knock , detonation , spark knock , pinging , or pinking ) occurs when combustion of some of the air/fuel mixture in
6844-504: The animated illustration, four cam lobes serve all 10 valves across the five cylinders, whereas 10 would be required for a typical inline engine with the same number of cylinders and valves. 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 Kinner B-5 and Russian Shvetsov M-11 , using individual camshafts within
6962-403: The available air) or "lean of peak" (less fuel, leaving some oxygen in the exhaust) as either will keep the fuel-air mixture from detonating prematurely. Because of the high cost of unleaded, high-octane avgas , and possible increased range before refueling, some general aviation pilots attempt to save money by tuning their fuel-air mixtures and ignition timing to run "lean of peak". Additionally,
7080-403: The axes of the cylinders are coplanar, the connecting rods cannot all be directly attached to the crankshaft unless mechanically complex forked connecting rods are used, none of which have been successful. Instead, 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
7198-460: The compression stroke, this liquid, being incompressible, stops piston movement. Starting or attempting to start the engine in such condition may result in a bent or broken connecting rod. Originally radial engines had one row of cylinders, but as engine sizes increased it became necessary to add extra rows. The first radial-configuration engine known to use a twin-row design was the 160 hp Gnôme "Double Lambda" rotary engine of 1912, designed as
SECTION 60
#17327799108727316-502: The crankcase and cylinders revolved with the propeller. It was similar in concept to the later radial, the main difference being that the propeller was bolted to the engine, and the crankshaft to the airframe. The problem of the cooling of the cylinders, a major factor with the early "stationary" radials, was alleviated by the engine generating its own cooling airflow. In World War I many French and other Allied aircraft flew with Gnome , Le Rhône , Clerget , and Bentley rotary engines,
7434-572: The crankcase for each cylinder. A few engines use sleeve valves such as the 14-cylinder Bristol Hercules and the 18-cylinder Bristol Centaurus , which are quieter and smoother running but require much tighter manufacturing tolerances . C. M. Manly constructed a water-cooled five-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 1903–1904 Jacob Ellehammer used his experience constructing motorcycles to build
7552-408: The crankshaft takes two revolutions to complete the four strokes of each piston (intake, compression, combustion, exhaust). The camshaft ring is geared to spin slower and in the opposite direction to the crankshaft. Its cam lobes are placed in two rows; one for the intake valves and one for the exhaust valves. The radial engine normally uses fewer cam lobes than other types. For example, in the engine in
7670-431: The crankshaft. The remaining pistons pin their connecting rods ' attachments to rings around the edge of the master rod. Extra "rows" of radial cylinders can be added in order to increase the capacity of the engine without adding to its diameter. Four-stroke radials have an odd number of cylinders per row, so that a consistent every-other-piston firing order can be maintained, providing smooth operation. For example, on
7788-413: The cylinder does not result from propagation of the flame front ignited by the spark plug , but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for
7906-419: The cylinders in two-row radials made it very difficult to utilise four valves per cylinder, consequently all non-sleeve valve two- and four-row radials were limited to the less efficient two-valve configuration. Also, as combustion chambers of sleeve-valve engines are uncluttered by valves, especially hot exhaust valves, so being comparatively smooth they allow engines to work with lower octane number fuels using
8024-421: The decreased air density at higher altitudes (such as Colorado) and temperatures (as in summer) requires leaning (reduction in amount of fuel per volume or mass of air) for the peak EGT and power (crucial for takeoff). The selection of octane ratings available at filling stations can vary greatly between countries. Due to its name, the chemical "octane" is often misunderstood as the only substance that determines
8142-482: The definition of octane rating. The following table lists octane ratings for various other fuels. Higher octane ratings correlate to higher activation energies : the amount of applied energy required to initiate combustion. Since higher octane fuels have higher activation energy requirements, it is less likely that a given compression will cause uncontrolled ignition, otherwise known as autoignition, self-ignition, pre-ignition, detonation, or knocking. Because octane
8260-597: The direct measurements required for research or motor octane numbers. An octane index can be of great service in the blending of gasoline. Motor gasoline, as marketed, is usually a blend of several types of refinery grades that are derived from different processes such as straight-run gasoline, reformate, cracked gasoline etc. These different grades are blended in amounts that will meet final product specifications. Most refiners produce and market more than one grade of motor gasoline, differing principally in their anti-knock quality. Being able to make sufficiently accurate estimates of
8378-486: The early 1920s Le Rhône converted a number of their rotary engines into stationary radial engines. 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 appreciated but were unrealized. British designers had produced the ABC Dragonfly radial in 1917, but were unable to resolve the cooling problems, and it
8496-507: The engine. Lighter and "thinner" fuel also has a lower specific heat , so the practice of running an engine "rich" to use excess fuel to aid in cooling requires richer and richer mixtures as octane increases. Higher-octane, lower-energy-dense "thinner" fuels often contain alcohol compounds incompatible with the stock fuel system components, which also makes them hygroscopic . They also evaporate away much more easily than heavier, lower-octane fuel which leads to more accumulated contaminants in
8614-401: The evaluation of the anti-knock quality of gasoline. Such substitute methods include FTIR, near infrared on-line analyzers, and others. Deriving an equation that can be used to calculate ratings accurately enough would also serve the same purpose, with added advantages. The term Octane Index is often used to refer to the use of an equation to determine a theoretical rating, in contradistinction to
8732-566: The fast Osa class missile boats . Another one was the Lycoming XR-7755 which was the largest piston aircraft engine ever built in the United States with 36 cylinders totaling about 7,750 in (127 L) of displacement and a power output of 5,000 horsepower (3,700 kilowatts). While most radial engines have been produced for gasoline, there have been diesel radial engines. Two major advantages favour diesel engines — lower fuel consumption and reduced fire risk. Packard designed and built
8850-630: The four-engine Boeing B-29 Superfortress and others. The Soviet Shvetsov OKB-19 design bureau was the sole source of design for all of the Soviet government factory-produced radial engines used in its World War II aircraft, starting with the Shvetsov M-25 (itself based on the American Wright Cyclone 9 's design) and going on to design the 41-litre displacement Shvetsov ASh-82 fourteen cylinder radial for fighters, and
8968-406: The fuel system. It is typically the hydrochloric acids that form due to that water and the compounds in the fuel that have the most detrimental effects on the engine fuel system components, as such acids corrode many metals used in gasoline fuel systems. During the compression stroke of an internal combustion engine, the temperature of the air-fuel mix rises as it is compressed, in accordance with
9086-449: The ignition spark coming as late as possible in order to extend the production of cylinder pressure and torque as far down the power stroke as possible. The main reason for using high-octane fuel in air-cooled engines is that it is more easily vaporized in a cold carburetor and engine and absorbs less intake air heat which greatly reduces the tendency for carburetor icing to occur. With their reduced densities and weight per volume of fuel,
9204-620: The largest-displacement production British radial from the Bristol firm to use sleeve valving, the Bristol Centaurus were used to power the Hawker Tempest II and Sea Fury . The same firm's poppet-valved radials included: around 32,000 of Bristol Pegasus used in the Short Sunderland , Handley Page Hampden , and Fairey Swordfish and over 20,000 examples of the firm's 1925-origin nine-cylinder Mercury were used to power
9322-447: The late-war Hawker Sea Fury and Grumman F8F Bearcat , two of the fastest production piston-engined aircraft ever built, using radial engines. Whenever a radial engine remains shut down for more than a few minutes, oil or fuel may drain into the combustion chambers of the lower cylinders or accumulate in the lower intake pipes, ready to be drawn into the cylinders when the engine starts. As the piston approaches top dead center (TDC) of
9440-446: The lifespan of engines. In 1927, Graham Edgar devised the method of using iso-octane and n-heptane as reference chemicals, in order to rate the knock resistance of a fuel with respect to this isomer of octane, thus the name "octane rating". By definition, the isomers iso-octane and n-heptane have an octane rating of 100 and 0, respectively. Because of its more volatile nature, n-heptane ignites and knocks readily, which gives it
9558-657: The lower of the two. One is referred to as the "aviation lean" rating, which for ratings up to 100 is the same as the MON of the fuel. The second is the "aviation rich" rating and corresponds to the octane rating of a test engine under forced induction operation common in high-performance and military piston aircraft. This utilizes a supercharger , and uses a significantly richer fuel/air ratio for improved detonation resistance. The most common currently used fuel, 100LL , has an aviation lean rating of 100 octane, and an aviation rich rating of 130. The RON/MON values of n- heptane and iso-octane are exactly 0 and 100, respectively, by
9676-487: The massive, 58-litre displacement Shvetsov ASh-73 eighteen-cylinder radial in 1946 - the smallest-displacement radial design from the Shvetsov OKB during the war was the indigenously designed, 8.6 litre displacement Shvetsov M-11 five cylinder radial. Over 28,000 of the German 42-litre displacement, 14-cylinder, two-row BMW 801 , with between 1,560 and 2,000 PS (1,540-1,970 hp, or 1,150-1,470 kW), powered
9794-445: The mixture from its maximum amount — must be done with knowledge, as some combinations of fuel mixture and throttle position (that produce the highest ) can cause detonation and/or pre-ignition , in the worst case destroying the engine within seconds. Pilots are taught in primary training to avoid settings that produce the highest exhaust gas temperatures, and run the engine either "rich of peak EGT " (more fuel than can be burned with
9912-479: The octane family, 2,2,4-Trimethylpentane (iso-octane), is used as a reference standard to benchmark the tendency of gasoline or LPG fuels to resist self-ignition. The octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and normal heptane that would have the same anti-knocking capability as the fuel under test. The percentage, by volume, of 2,2,4-trimethylpentane in that mixture
10030-401: The octane number by either of the two laboratory methods requires a special engine built to match the tests' rigid standards, and the procedure can be both expensive and time-consuming. The standard engine required for the test may not always be available, especially in out-of-the-way places or in small or mobile laboratories. These and other considerations led to the search for a rapid method for
10148-493: The octane rating (or octane number) of a fuel. This is an inaccurate description. In reality, the octane rating is defined as a number describing the stability and ability of a fuel to prevent an engine from unwanted combustions that occur spontaneously in the other regions within a cylinder (i.e., delocalized explosions from the spark plug). This phenomenon of combustion is more commonly known as engine knocking or self-ignition, which causes damage to pistons over time and reduces
10266-414: The octane rating of gasoline is not directly related to the power output of an engine. Using gasoline of a higher octane than an engine is designed for cannot increase its power output. Octane became well known in American popular culture in the 1960s, when gasoline companies boasted of "high octane" levels in their gasoline advertisements. The compound adjective "high-octane", meaning powerful or dynamic,
10384-404: The octane rating that will result from blending different refinery products is essential, something for which the calculated octane index is specially suited. Aviation gasolines used in piston aircraft engines common in general aviation have a slightly different method of measuring the octane of the fuel. Similar to an AKI, it has two different ratings, although it is usually referred to only by
10502-418: The octane ratings for the isomers show that the compound octane itself is clearly not the only factor that determines octane ratings, especially for commercial fuels consist of a wide variety of compounds. "Octane" is colloquially used in the expression "high-octane". The term is used to describe a powerful action because of the association with the concept of "octane rating". This is a misleading term, because
10620-548: The opposing direction to the crankcase and cylinders, which still rotated as the propeller itself did since it was still firmly fastened to the crankcase's frontside, as with regular umlaufmotor German rotaries. By the end of the war the rotary engine had reached the limits of the design, particularly in regard to the amount of fuel and air that could be drawn into the cylinders through the hollow crankshaft, while advances in both metallurgy and cylinder cooling finally allowed stationary radial engines to supersede rotary engines. In
10738-544: The other obvious benefit is that an aircraft with any given volume of fuel in the tanks is automatically lighter. And since many airplanes are flown only occasionally and may sit unused for weeks or months, the lighter fuels tend to evaporate away and leave behind fewer deposits such as "varnish" (gasoline components, particularly alkenes and oxygenates slowly polymerize into solids). Aircraft also typically have dual "redundant" ignition systems which are nearly impossible to tune and time to produce identical ignition timing, so using
10856-453: The path of the primary flame wave, thus depriving the power stroke of its uniformity and causing issues including power loss and heat buildup. The other rarely-discussed reality with high-octane fuels associated with "high performance" is that as octane increases, the specific gravity and energy content of the fuel per unit of weight are reduced. The net result is that to make a given amount of power , more high-octane fuel must be burned in
10974-466: The power output or the energy content of the fuel per unit mass or volume, but simply indicates the resistance to detonating under pressure without a spark. Whether or not a higher octane fuel improves or impairs an engine's performance depends on the design of the engine. In broad terms, fuels with a higher octane rating are used in higher-compression gasoline engines , which may yield higher power for these engines. The added power in such cases comes from
11092-595: The production leaders in all-time production numbers for each type of airframe design. The American Wright Cyclone series twin-row radials powered American warplanes: the nearly-43 litre displacement, 14-cylinder Twin Cyclone powered the single-engine Grumman TBF Avenger , twin-engine North American B-25 Mitchell , and some versions of the Douglas A-20 Havoc , with the massive twin-row, nearly 55-litre displacement, 18-cylinder Duplex-Cyclone powering
11210-415: The proper time for precise ignition. As octane, ignition spark energy, and the need for precise timing increase, the engine becomes more difficult to "tune" and keep "in tune". The resulting sub-optimal spark energy and timing can cause major engine problems, from a simple "miss" to uncontrolled detonation and catastrophic engine failure. Mechanically within the cylinder, stability can be visualized as having
11328-409: The rear bank of cylinders, but a variety of baffles and fins were introduced that largely eliminated these problems. The downside was a relatively large frontal area that had to be left open to provide enough airflow, which increased drag. This led to significant arguments in the industry in the late 1930s about the possibility of using radials for high-speed aircraft like modern fighters. The solution
11446-399: The results with those for mixtures of iso-octane and n-heptane. The compression ratio is varied during the test to challenge the fuel's antiknocking tendency, as an increase in the compression ratio will increase the chances of knocking. Another type of octane rating, called Motor Octane Number ( MON ), is determined at 900 rpm engine speed instead of the 600 rpm for RON. MON testing uses
11564-625: The same compression ratio. Conversely, the same octane number fuel may be utilised while employing a higher compression ratio, or supercharger pressure, thus attaining either higher economy or power output. The downside was the difficulty in maintaining sufficient cylinder and sleeve lubrication. Manufacturing was also a major problem. Sleeve valve engines, even the mono valve Fedden had elected to use, were extremely difficult to make. Fedden had experimented with sleeve valves in an inverted V-12 as early as 1927 but did not pursue that engine any further. Reverting to nine cylinder engines, Bristol had developed
11682-465: The same is not true for multi-row engines where the rear cylinders can be affected by the heat coming off the front row, and air flow being masked. A potential disadvantage of radial engines is that having the cylinders exposed to the airflow increases drag considerably. The answer was the addition of specially designed cowlings with baffles to force the air between the cylinders. The first effective drag-reducing cowling that didn't impair engine cooling
11800-600: The time. This reliance had a downside though: if the engines were mounted vertically, as in the M3 Lee and M4 Sherman , 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 , M2 Light Tank , M3 Stuart , M3 Lee , and LVT-2 Water Buffalo . The Guiberson T-1020 ,
11918-492: The ultimate examples of which reached 250 hp (190 kW) although none of those over 160 hp (120 kW) were successful. By 1917 rotary engine development was lagging behind new inline and V-type engines, which by 1918 were producing as much as 400 hp (300 kW), and were powering almost all of the new French and British combat aircraft. Most German aircraft of the time used water-cooled inline 6-cylinder engines. Motorenfabrik Oberursel made licensed copies of
12036-459: The valves is still open). Knocking should not be confused with pre-ignition —they are two separate events with pre-ignition occurring before the combustion event. However, pre-ignition is highly correlated with knock because knock will cause rapid heat increase within the cylinder eventually leading to destructive pre-detonation. Most engine management systems commonly found in automobiles today, typically electronic fuel injection (EFI), have
12154-481: The way the engine is designed to compress the air/fuel mixture, and not directly from the rating of the gasoline. In contrast, fuels with lower octane (but higher cetane numbers ) are ideal for diesel engines because diesel engines (also called compression-ignition engines) do not compress the fuel, but rather compress only air, and then inject fuel into the air that was heated by compression. Gasoline engines rely on ignition of compressed air and fuel mixture, which
12272-623: 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 and made a number of short free-flight hops. Another early radial engine was the three-cylinder Anzani , originally built as a W3 "fan" configuration, one of which powered Louis Blériot 's Blériot XI across the English Channel . Before 1914, Alessandro Anzani had developed radial engines ranging from 3 cylinders (spaced 120° apart) — early enough to have been used on
12390-433: Was a further development of the Hercules 36. Hercules 100 (1944) – 1,675 hp (1,249 kW), the first in a new sub-series of Hercules engines designed primarily for the impending post-war civil market. The entire series was split, some versions had standard epicyclic reduction gearing and parallel versions had a new torquemeter -type reduction gearing. Hercules 101 – 1,675 hp (1,249 kW), developed from
12508-512: Was carried out in the US, and demonstrated that ample airflow was available with careful design. This led to the R-4360 , which has 28 cylinders arranged in a 4 row corncob configuration. The R-4360 saw service on large American aircraft in the post- World War II period. The US and Soviet Union continued experiments with larger radials, but the UK abandoned such designs in favour of newer versions of
12626-683: Was developed in 1922 with Navy funding, and using aluminum cylinders with steel liners ran for an unprecedented 300 hours, at a time when 50 hours endurance was normal. At the urging of the Army and Navy the Wright Aeronautical Corporation bought Lawrance's company, and subsequent engines were built under the Wright name. The radial engines gave confidence to Navy pilots performing long-range overwater flights. Wright's 225 hp (168 kW) J-5 Whirlwind radial engine of 1925
12744-453: Was introduced with the BMW 801 14-cylinder twin-row radial. Kurt Tank designed a new cooling system for this engine that used a high-speed fan to blow compressed air into channels that carry air to the middle of the banks, where a series of baffles directed the air over all of the cylinders. This allowed the cowling to be tightly fitted around the engine, reducing drag, while still providing (after
12862-607: Was more commonly used on bombers . The Hercules also saw use in civilian designs, culminating in the 735 and 737 engines for such as the Handley Page Hastings C1 and C3 and Bristol Freighter . The design was also licensed for production in France by SNECMA . Shortly after the end of World War I, the Shell company, Asiatic Petroleum, commissioned Harry Ricardo to investigate problems of fuel and engines. His book
12980-483: Was not considered viable due to the difficulty of providing the required airflow to the rear banks. Larger engines were designed, mostly using water cooling although this greatly increased complexity and eliminated some of the advantages of the radial air-cooled design. One example of this concept is the BMW 803 , which never entered service. A major study into the airflow around radials using wind tunnels and other systems
13098-746: Was not until the 1920s that Bristol and Armstrong Siddeley produced reliable air-cooled radials such as the Bristol Jupiter and the Armstrong Siddeley Jaguar . In the United States the National Advisory Committee for Aeronautics (NACA) noted in 1920 that air-cooled radials could offer an increase in power-to-weight ratio and reliability; by 1921 the U.S. Navy had announced it would only order aircraft fitted with air-cooled radials and other naval air arms followed suit. Charles Lawrance 's J-1 engine
13216-486: Was once a common additive, but concerns about its toxicity have led to its use for fuels for road vehicles being progressively phased out worldwide beginning in the 1970s. The most common type of octane rating worldwide is the Research Octane Number ( RON ). RON is determined by running the fuel in a test engine at 600 rpm with a variable compression ratio under controlled conditions, and comparing
13334-465: Was published in 1923 as “The Internal Combustion Engine”. Ricardo postulated that the days of the poppet valve were numbered and that a sleeve valve alternative should be pursued. The rationale behind the single sleeve valve design was two-fold: to provide optimum intake and exhaust gas flow in a two-row radial engine, improving its volumetric efficiency and to allow higher compression ratios, thus improving its thermal efficiency . The arrangement of
13452-545: Was the Salmson 9Z series of nine-cylinder water-cooled radial engines that were produced in large numbers. Georges Canton and Pierre Unné patented the original engine design in 1909, offering it to the Salmson company; the engine was often known as the Canton-Unné. From 1909 to 1919 the radial engine was overshadowed by its close relative, the rotary engine , which differed from the so-called "stationary" radial in that
13570-709: Was the British Townend ring or "drag ring" which formed a narrow band around the engine covering the cylinder heads, reducing drag. The National Advisory Committee for Aeronautics studied the problem, developing the NACA cowling which further reduced drag and improved cooling. Nearly all aircraft radial engines since have used NACA-type cowlings. While inline liquid-cooled engines continued to be common in new designs until late in World War II , radial engines dominated afterwards until overtaken by jet engines, with
13688-460: Was the torquemeter version. Hercules 264 – 1,950 hp (1,450 kW), a development of the Hercules 260. The Hercules 265 was the torquemeter version. Hercules 268 – a further development of the Hercules 260. The Hercules 269 was the torquemeter version. Hercules 630 – 1,675 hp (1,249 kW), a civil development of the Hercules 100. The Hercules 631 was the torquemeter version. Hercules 632 – 1,690 hp (1,260 kW),
13806-399: Was the torquemeter version. The Hercules 238 was a military version of the civil Hercules 734. Hercules 736 – 2,040 hp (1,520 kW), a civil-series engine developed from the Hercules 730. The Hercules 737 was the torquemeter version. Radial engine The radial configuration was commonly used for aircraft engines before gas turbine engines became predominant. Since
13924-474: Was widely claimed as "the first truly reliable aircraft engine". Wright employed Giuseppe Mario Bellanca to design an aircraft to showcase it, and the result was the Wright-Bellanca WB-1 , which first flew later that year. The J-5 was used on many advanced aircraft of the day, including Charles Lindbergh 's Spirit of St. Louis , in which he made the first solo trans-Atlantic flight. In 1925
#871128