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60-424: The Pratt & Whitney R-2800 Double Wasp is an American twin-row, 18-cylinder, air-cooled radial aircraft engine with a displacement of 2,800 cu in (46 L), and is part of the long-lived Wasp family of engines . The R-2800 saw widespread use in many important American aircraft during and after World War II . During the war years, Pratt & Whitney continued to develop new ideas to upgrade

120-412: A closed circuit carrying liquid coolant through channels in the engine block and cylinder head. A fluid in these channels absorbs heat and then flows to a heat exchanger or radiator where the coolant releases heat into the air (or raw water , in the case of marine engines ). Thus, while they are not ultimately cooled by the liquid, as the heat is exchanged with some other fluid like air, because of

180-430: A fluid is a function of its capacity and the difference in input and output temperatures. As the boiling point of water is reduced with lower pressure, and the water could not be efficiently pumped as steam, radiators had to have enough cooling power to account for the loss in cooling power as the aircraft climbed. The resulting radiators were quite large and caused a significant amount of aerodynamic drag . This placed

240-486: A great percentage of the heat generated, around 44%, escapes through the exhaust. Another 8% or so ends up in the oil , which itself has to be cooled in an oil cooler . This means less than half of the heat has to be removed through other systems. In an air-cooled engine, only about 12% of the heat flows out through the metal fins. Air cooled engines usually run noisier, however it provides more simplicity which gives benefits when it comes to servicing and part replacement and

300-536: A hammer. It was further investigated and described by Harry Ricardo during experiments carried out between 1916 and 1919 to discover the reason for failures in aircraft engines . Under ideal conditions the common internal combustion engine burns the fuel/air mixture in the cylinder in an orderly and controlled fashion. The combustion is started by the spark plug some 10 to 40 crankshaft degrees prior to top dead center (TDC), depending on many factors including engine speed and load. This ignition advance allows time for

360-458: A high thermal efficiency . Since the onset of knock is sensitive to the in-cylinder pressure, temperature and autoignition chemistry associated with the local mixture compositions within the combustion chamber, simulations which account for all of these aspects have thus proven most effective in determining knock operating limits and enabling engineers to determine the most appropriate operating strategy. The objective of knock control strategies

420-440: A horizontal fashion as a Flat engine , while vertical Straight-four engine have been used. Examples of past air-cooled road vehicles, in roughly chronological order, include: During the 1920s and 30s there was a great debate in the aviation industry about the merits of air-cooled vs. liquid-cooled designs. At the beginning of this period, the liquid used for cooling was water at ambient pressure. The amount of heat carried away by

480-456: A mixture of water and methanol into the carburetor to increase power for short periods. Several models of the R-2800s were fitted with ADI as standard equipment and were not given the W suffix. Few commercial aircraft used water injection. "A" Series: "B" Series: "C" Series "D" Series: "E" Series: The following is a partial list of aircraft that were powered by

540-405: A more complete mixing of fuel and air. Diesels actually do not suffer exactly the same "knock" as gasoline engines since the cause is known to be only the very fast rate of pressure rise, not unstable combustion. Diesel fuels are actually very prone to knock in gasoline engines but in the diesel engine there is no time for knock to occur because the fuel is only oxidized during the expansion cycle. In

600-550: Is a list of representative R-2800 variants, describing some of the mechanical changes made during development of the Double Wasp. Power ratings quoted are usually maximum "military" power that the engine could generate on takeoff and at altitude; 100 Octane fuel was used, unless otherwise noted. The R-2800 was developed and modified into a basic sequence of subtypes, "A" through "E" series, each of which indicated major internal and external modifications and improvements, such that

660-432: Is a short lag between the fuel being injected and combustion starting. By this time there is already a quantity of fuel in the combustion chamber which will ignite first in areas of greater oxygen density prior to the combustion of the complete charge. This sudden increase in pressure and temperature causes the distinctive diesel 'knock' or 'clatter', some of which must be allowed for in the engine design. Careful design of

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720-452: Is actually more efficient than deflagration, but is usually avoided due to its damaging effects on engine components.) If detonation is allowed to persist under extreme conditions or over many engine cycles, engine parts can be damaged or destroyed. The simplest deleterious effects are typically particle wear caused by moderate knocking, which may further ensue through the engine's oil system and cause wear on other parts before being trapped by

780-437: Is due to the travel of the flame front through the combustible fuel–air mix itself, and due to Rayleigh–Taylor instability (resulting from the hot, low-density combustion gasses expanding into the relatively cold and dense unburnt fuel–air mix) which rapidly stretches the burning zone into a complex of fingers of burning gas that have a much greater surface area than a simple spherical ball of flame would have (this latter process

840-408: Is enhanced and accelerated by any pre-existing turbulence in the fuel–air mixture). In normal combustion, this flame front moves throughout the fuel/air mixture at a rate characteristic for the particular mixture. Pressure rises smoothly to a peak, as nearly all the available fuel is consumed, then pressure falls as the piston descends. Maximum cylinder pressure is achieved a few crankshaft degrees after

900-499: Is in turbocharged Saab H engines , where a system called Automatic Performance Control was used to reduce boost pressure if it caused the engine to knock. Since the avoidance of knocking combustion is so important to development engineers, a variety of simulation technologies have been developed which can identify engine design or operating conditions in which knock might be expected to occur. This then enables engineers to design ways to mitigate knocking combustion whilst maintaining

960-441: Is less common in cold climates. As an aftermarket solution, a water injection system can be employed to reduce combustion chamber peak temperatures and thus suppress detonation. Steam (water vapor) will suppress knock even though no added cooling is supplied. Turbulence, as stated, has a very important effect on knock. Engines with good turbulence tend to knock less than engines with poor turbulence. Turbulence occurs not only while

1020-423: Is permanently monitoring the signal of one or more knock sensors (commonly piezoelectric sensor which are able to translate vibrations into an electric signal). If the characteristic pressure peak of a knocking combustion is detected the ignition timing is retarded by steps of a few degrees. If the signal normalizes indicating a controlled combustion the ignition timing is advanced again in the same fashion keeping

1080-422: Is to attempt to optimize the trade-off between protecting the engine from damaging knock events and maximizing the engine's output torque. Knock events are an independent random process. It is impossible to design knock controllers in a deterministic platform. A single time history simulation or experiment of knock control methods are not able to provide a repeatable measurement of controller's performance because of

1140-418: Is usually cheaper to be maintained. Many motorcycles use air cooling for the sake of reducing weight and complexity. Few current production automobiles have air-cooled engines (such as Tatra 815 ), but historically it was common for many high-volume vehicles. The orientation of the engine cylinders is commonly found in either single-cylinder or coupled in groups of two, and cylinders are commonly oriented in

1200-416: The air/fuel mixture in 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

1260-469: The flame front is subjected to a combination of heat and pressure for a certain duration (beyond the delay period of the fuel used), detonation may occur. Detonation is characterized by an almost instantaneous, explosive ignition of at least one pocket of fuel/air mixture outside of the flame front. A local shockwave is created around each pocket, and the cylinder pressure will rise sharply – and possibly beyond its design limits – causing damage. (Detonation

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1320-438: The "E" series engines had very few parts in common with the "A".. Pratt & Whitney's internal variant identification incorporated the series letter as part of the designation, for example Double Wasp S1A4-G ("A" series) and Double Wasp CB17 ("C" series). Data from White (Airlife) unless otherwise noted: The dash number for each military type (e.g.: -21 ) was allocated to identify the complete engine model in accordance with

1380-772: The 1900s. The first commercial production was by the New Way Motor Company of Lansing, Michigan, US. The company produced air-cooled engines in single and twin cylinders in both horizontal and vertical cylinder format. Subsequent to their initial production which was exported worldwide, other companies took up the advantages of this cooling method, especially in small portable engines. Applications include mowers, generators, outboard motors, pump sets, saw benches and auxiliary power plants and more. Engine knocking In spark-ignition internal combustion engines , knocking (also knock , detonation , spark knock , pinging or pinking ) occurs when combustion of some of

1440-922: The Corsair's naval rival, the Grumman F6F Hellcat , the US Army Air Forces' Republic P-47 Thunderbolt (which unusually, for single-engined aircraft, used a General Electric turbocharger ), the twin-engine Martin B-26 Marauder and Douglas A-26 Invader , as well as the first purpose-built twin-engine radar-equipped night fighter, the Northrop P-61 Black Widow . When the US entered the war in December 1941, designs advanced rapidly, and long-established engines such as

1500-474: The Double Wasp served with other countries well past the Korean War, some being retired as late as the latter part of the 1960s when the aircraft were replaced. Engines grow in power with development, but a major war demands the utmost performance from engines fitted to aircraft whose life in front-line service was unlikely to exceed 50 hours flying, over a period of only a month or two. In peacetime however,

1560-471: The Double Wasp was introduced with a smaller incremental power increase than was typical of earlier engines. Nevertheless, in 1941 the power output of production models increased to 2,100 hp (1,600 kW), and to 2,400 hp (1,800 kW) late in the war. Even more was coaxed from experimental models, with fan-cooled subtypes like the R-2800-57 producing 2,800 hp (2,100 kW), but in general

1620-598: The Duplex-Cyclone. The Double Wasp was more powerful than the world's only other modern 18-cylinder engine, the Gnome-Rhône 18L of 3,442 cu in (56.40 L). The Double Wasp was much smaller in displacement than either of the other 18-cylinder designs, and heat dissipation was a greater problem. To enable more efficient cooling, the usual practice of casting or forging the cylinder head cooling fins that had been effective enough for other engine designs

1680-690: The Light-Sport Aircraft ( LSA ) and ultralight aircraft market. Rotax uses a combination of air-cooled cylinders and liquid-cooled cylinder heads. Some small diesel engines, e.g. those made by Deutz AG and Lister Petter are air-cooled. Probably the only big Euro 5 truck air-cooled engine (V8 320 kW power 2100 N·m torque one) is being produced by Tatra . BOMAG part of the FAYAT group also utilizes an air cooled inline 6 cylinder motor, in many of their construction vehicles. Stationary or portable engines were commercially introduced early in

1740-573: The Navy underwriting air-cooled engine development at Pratt & Whitney and Wright Aeronautical . Most other groups, especially in Europe where aircraft performance was rapidly improving, were more concerned with the issue of drag. While air-cooled designs were common on light aircraft and trainers, as well as some transport aircraft and bombers , liquid-cooled designs remained much more common for fighters and high-performance bombers. The drag issue

1800-787: The R-2800 (and a few prototypes that utilized it at one point): Data from FAA TCDS Related development Comparable engines Related lists Air-cooled Air-cooled engines are widely seen in applications where weight or simplicity is the primary goal. Their simplicity makes them suited for uses in small applications like chainsaws and lawn mowers , as well as small generators and similar roles. These qualities also make them highly suitable for aviation use, where they are widely used in general aviation aircraft and as auxiliary power units on larger aircraft. Their simplicity, in particular, also makes them common on motorcycles . Most modern internal combustion engines are cooled by

1860-638: The R-2800 was a rather highly developed powerplant right from the beginning. The R-2800 powered several types of fighters and medium bombers during the war, including the US Navy's Vought F4U Corsair , with the XF4U-1 first prototype Corsair becoming the first airframe to fly (as originally designed) with the Double Wasp in its XR-2800-4 prototype version on May 29, 1940, and the first single-engine American fighter plane to exceed 400 mph (640 km/h) in level flight during October 1940. The R-2800 also powered

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1920-455: The US Navy used even (e.g.: -8). After 1940, however, in the interests of standardization, engines were sometimes built to a joint Army-Navy contract, in which case the engines used a common numeric suffix (e.g. the -10 was used by both Army and Navy aircraft.) The suffix W e.g.: -10W denotes a sub-series modified to use water injection . The "Anti-Detonant Injection" (ADI) system injected

1980-551: The Wright Cyclone and Double Wasp were re-rated on fuel of much higher octane rating ( anti-knock value) to give considerably more power. By 1944, versions of the R-2800 powering late-model P-47s (and other aircraft) had a rating (experimental) of 2,800 hp (2,100 kW) on 115-grade fuel with water injection. After World War II, the engine was used in the Korean War , and surplus World War II aircraft powered by

2040-636: The call was for reliability over a period of perhaps a dozen years, and the R-2800's reliability commended its use for long-range patrol aircraft and for the Douglas DC-6 , Martin 4-0-4 , and Convair 240 transports. The last two were twin-engine aircraft of size, passenger capacity, and high wing loading comparable to the DC-4 - itself usually powered by the R-2000 bored-out version of the Twin Wasp - and

2100-403: The combustion process to develop peak pressure at the ideal time for maximum recovery of work from the expanding gases. The spark across the spark plug's electrodes forms a small kernel of flame approximately the size of the spark plug gap. As it grows in size, its heat output increases, which allows it to grow at an accelerating rate, expanding rapidly through the combustion chamber. This growth

2160-439: The engine at its best possible operating point - the so-called ″knock limit″. Modern knock control-loop systems are able to adjust ignition timings for every cylinder individually. Depending on the specific engine the boost pressure is regulated simultaneously. This way performance is kept at its optimum while mostly eliminating the risk of engine damage caused by knock (e.g. when running on low octane fuel). An early example of this

2220-435: The engine is inhaling but also when the mixture is compressed and burned. Many pistons are designed to use "squish" turbulence to violently mix the air and fuel together as they are ignited and burned, which reduces knock greatly by speeding up burning and cooling the unburnt mixture. One example of this is all modern side valve or flathead engines . A considerable portion of the head space is made to come in close proximity to

2280-442: The engine's combustion chambers and cooling system as well as controlling the initial air intake temperature. The addition of tetraethyl lead (TEL), a soluble organolead compound added to gasoline, was common until it was discontinued for reasons of toxic pollution. Lead dust added to the intake charge will also reduce knock with various hydrocarbon fuels. Manganese compounds are also used to reduce knock with petrol fuel. Knock

2340-464: The engine, including water injection for takeoff in cargo and passenger planes and to give emergency power in combat. First run in 1937, near the time that the larger 3,347.9 cu in (54.862 L) competing 18-cylinder Wright Duplex-Cyclone 's development had been started in May of that year, the 2,804.5 cu in (45.958 L) displacement R-2800 was first-flown by 1940, one year before

2400-528: The first Constellations , which mostly used Wright Aeronautical's large Duplex-Cyclones. The Double Wasp still flies in restored vintage warbird aircraft displayed at air shows , and sees service worldwide on aircraft such as the Canadair CL-215 water-bomber. In addition, R-2800s continue to power Douglas DC-6 cargo and fuel-carrying aircraft in locations such as Alaska . A total of 125,334 R-2800 engines were produced between 1939 and 1960. This

2460-481: The gasoline engine the fuel is slowly oxidizing all the time while it is being compressed before the spark. This allows for changes to occur in the structure/makeup of the molecules before the very critical period of high temperature/pressure. Due to the large variation in fuel quality, atmospheric pressure and ambient temperature as well as the possibility of a malfunction, every modern combustion engine contains mechanisms to detect and prevent knocking. A control loop

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2520-414: The injector pump, fuel injector, combustion chamber, piston crown and cylinder head can reduce knocking greatly, and modern engines using electronic common rail injection have very low levels of knock. Engines using indirect injection generally have lower levels of knock than direct injection engines, due to the greater dispersal of oxygen in the combustion chamber and lower injection pressures providing

2580-401: The later C-series R-2800s with the two-piece gear reduction housings, on the "outboard" sides of the distributor casings. When the R-2800 was introduced in 1939, it was capable of producing 2,000 hp (1,500 kW), for a specific power value of 0.71 hp/cu in (32 kW/L). The design of conventional air-cooled radial engines had become so scientific and systematic by then that

2640-575: The liquid-coolant circuit they are known as liquid-cooled . In contrast, heat generated by an air-cooled engine is released directly into the air. Typically this is facilitated with metal fins covering the outside of the Cylinder Head and cylinders which increase the surface area that air can act on. Air may be force fed with the use of a fan and shroud to achieve efficient cooling with high volumes of air or simply by natural air flow with well designed and angled fins. In all combustion engines,

2700-506: The much smaller radiators and less fluid in the system, the weight and drag of these designs was well below contemporary air-cooled designs. On a weight basis, these liquid-cooled designs offered as much as 30% better performance. In the late- and post-war era, the high-performance field quickly moved to jet engines . This took away the primary market for late-model liquid-cooled engines. Those roles that remained with piston power were mostly slower designs and civilian aircraft. In these roles,

2760-455: The oil filter. Such wear gives the appearance of erosion, abrasion, or a "sandblasted" look, similar to the damage caused by hydraulic cavitation . Severe knocking can lead to catastrophic failure in the form of physical holes melted and pushed through the piston or cylinder head (i.e. rupture of the combustion chamber ), either of which depressurizes the affected cylinder and introduces large metal fragments, fuel, and combustion products into

2820-452: The oil system. Hypereutectic pistons are known to break easily from such shock waves. Detonation can be prevented by any or all of the following techniques: Because pressure and temperature are strongly linked, knock can also be attenuated by controlling peak combustion chamber temperatures by compression ratio reduction, exhaust gas recirculation , appropriate calibration of the engine's ignition timing schedule, and careful design of

2880-408: The optimum moment for the four-stroke cycle . The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. Knocking should not be confused with pre-ignition —they are two separate events. However, pre-ignition can be followed by knocking. The phenomenon of detonation

2940-413: The piston crown, making for much turbulence near TDC. In the early days of side valve heads this was not done and a much lower compression ratio had to be used for any given fuel. Also such engines were sensitive to ignition advance and had less power. Knocking is more or less unavoidable in diesel engines , where fuel is injected into highly compressed air towards the end of the compression stroke. There

3000-409: The piston passes TDC, so that the force applied on the piston (from the increasing pressure applied to the top surface of the piston) can give its hardest push precisely when the piston's speed and mechanical advantage on the crank shaft gives the best recovery of force from the expanding gases, thus maximizing torque transferred to the crankshaft. When unburned fuel–air mixture beyond the boundary of

3060-481: The radiator size by 50% compared to water cooled designs. The experiments were extremely successful and by 1932 the company had switched all future designs to this coolant. At the time, Union Carbide held a monopoly on the industrial process to make glycol, so it was initially used only in the US, with Allison Engines picking it up soon after. It was not until the mid-1930s that Rolls-Royce adopted it as supplies improved, converting all of their engines to glycol. With

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3120-454: The simplicity and reduction in servicing needs is far more important than drag, and from the end of the war on almost all piston aviation engines have been air-cooled, with few exceptions. As of 2020 , most of the engines manufactured by Lycoming and Continental are used by major manufacturers of light aircraft Cirrus , Cessna and so on. Other engine manufactures using air-cooled engine technology are ULPower and Jabiru , more active in

3180-539: The specification under which the engine was manufactured. Thus dash numbers did not necessarily indicate the sequence in which the engines were manufactured. For example: the -18W was a "C" series engine, built from 1945, whereas the -21 was a "B" series engine, built from 1943. Until 1940 the armed forces adhered strictly to the convention that engines built for the Army Air Forces used engine model numbers with odd numeric suffixes (e.g.: -5), while those built for

3240-458: The steam through tubes located just under the skin of the wings and fuselage, where the fast moving outside air condensed it back to water. While this concept was used on a number of record-setting aircraft in the late 1930s, it always proved impractical for production aircraft for a wide variety of reasons. In 1929, Curtiss began experiments replacing water with ethylene glycol in a Curtiss D-12 engine. Glycol could run up to 250 C and reduced

3300-427: The surface area of the fins. The twin distributors on the Double Wasp were prominently mounted on the upper surface of the forward gear reduction housing - with one of the pair of magnetos mounted between them on most models - and almost always prominently visible within a cowling, with the conduits for the spark plug wires emerging from the distributors' cases either directly forward or directly behind them, or on

3360-405: The two designs roughly equal in terms of power to drag, but the air-cooled designs were almost always lighter and simpler. In 1921, the US Navy , largely due to the efforts of Commander Bruce G. Leighton , decided that the simplicity of the air-cooled design would result in less maintenance workload, which was paramount given the limited working area of aircraft carriers . Leighton's efforts led to

3420-590: The volume of water required and the size of the radiator by as much as 30%, which opened the way to a new generation of high-powered, relatively low-drag liquid cooled inline engines such as the Rolls-Royce Merlin and Daimler-Benz DB601 , which had an advantage over the unpressurized early versions of the Jumo 211 . This also led to development work attempting to eliminate the radiator entirely using evaporative cooling , allowing it to turn to steam and running

3480-483: Was described in November 1914 in a letter from Lodge Brothers (spark plug manufacturers, and sons of Sir Oliver Lodge ) settling a discussion regarding the cause of "knocking" or "pinging" in motorcycles. In the letter they stated that an early ignition can give rise to the gas detonating instead of the usual expansion, and the sound that is produced by the detonation is the same as if the metal parts had been tapped with

3540-423: Was discarded, and instead, much thinner and closer-pitched cooling fins were machined from the solid metal of the cylinder-head forging. The fins were all cut at the same time by a gang of milling saws, automatically guided as it fed across the head in such a way that the bottom of the grooves rose and fell to make the roots of the fins follow the contour of the head, with the elaborate process substantially increasing

3600-493: Was upset by the 1929 introduction of the NACA cowl , which greatly reduced the drag of air-cooled engines in spite of their larger frontal area, and the drag related to cooling was at this point largely even. In the late 1920s into the 1930s, a number of European companies introduced cooling system that kept the water under pressure allowed it to reach much higher temperatures without boiling, carrying away more heat and thus reducing

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