An H engine is a piston engine comprising two separate flat engines (complete with separate crankshafts), most often geared to a common output shaft. The name "H engine" is due to the engine blocks resembling a letter "H" when viewed from the front. The most successful "H" engine in this form was the Napier Dagger and its derivatives. The name was also applied to engines of the same basic layout, but rotated through 90 degrees—most famously the Napier Sabre series. A variation on the "H" theme were the Fairey Prince (H-16) & Fairey P.24 Monarch , where the two engines retained separate drives, driving Contra-rotating propellers through separate concentric shafts. Although successful, they only existed in prototype form.
33-477: The Napier Sabre is a British H-24-cylinder , liquid-cooled , sleeve valve , piston aero engine , designed by Major Frank Halford and built by D. Napier & Son during World War II . The engine evolved to become one of the most powerful inline piston aircraft engines in the world, developing from 2,200 hp (1,600 kW) in its earlier versions to 3,500 hp (2,600 kW) in late-model prototypes. The first operational aircraft to be powered by
66-470: A consequence the reliability of the Vulture when it entered service was very poor. Apart from delivering significantly less than the designed power, the Vulture suffered from frequent failures of the connecting rod big end bearings, which was found to be caused by a breakdown in lubrication, and also from heat dissipation problems. Rolls-Royce were initially confident that they could solve the problems, but
99-583: A few units were produced in early 1939. Any development planned was interrupted by World War II and subsequent years of austerity. Wooler built a motorcycle prototype with a similar configuration to the Brough Superior Golden Dream and exhibited it at the British International Motor Show at Earls Court Exhibition Centre in 1948 and again in 1951. This was replaced by a flat-four engined prototype at
132-469: A new sleeve problem appeared in 1944 when aircraft were operating from Normandy soil with its abrasive, gritty dust. Quality control proved to be inadequate, engines were often delivered with improperly cleaned castings, broken piston rings and machine cuttings left inside the engine. Mechanics were overworked trying to keep the Sabres running and during cold weather they had to run them every two hours during
165-419: A study on the concept of the sleeve valve engine. In it, he wrote that traditional poppet valve engines would be unlikely to produce much more than 1,500 hp (1,100 kW), a figure that many companies were eyeing for next generation engines. To pass this limit, the sleeve valve would have to be used, to increase volumetric efficiency , as well as to decrease the engine's sensitivity to detonation, which
198-424: Is a relatively rare layout, with its main use being in aircraft engines during the 1930s and 1940s. The 1966 Lotus 43 Formula One car used a BRM 16-cylinder H engine, and an 8-cylinder H engine was used for powerboat racing in the 1970s. The benefits of an H engine are the ability to share common parts with the flat engine upon which it is based, and the good engine balance which results in less vibration (which
231-508: Is difficult to achieve in many other types of four-cylinder engines). However, H engines are relatively heavy and have a high centre of gravity. The latter is not only due to the second crankshaft being located near the top of the engine, but also the engine must be high enough off the ground to allow clearance underneath for the exhaust pipes . The U engine layout uses a similar concept, placing two straight engines side-by-side. The British Racing Motors (BRM) H-16 Formula One engine won
264-583: The Hawker Typhoon and its derivative, the Hawker Tempest . Without the advanced supercharger, the engine's performance over 20,000 ft (6,100 m) fell off rapidly and pilots flying Sabre-powered aircraft, were generally instructed to enter combat only below this altitude. At low altitude, both planes were formidable. As air superiority over Continental Europe was slowly gained, Typhoons were increasingly used as fighter-bombers , notably by
297-713: The Hawker Typhoon , which was powered by the Napier Sabre . The cancellation caused the abandonment of the Vulture-engined version of the Vickers Warwick bomber. The only aircraft type designed for the Vulture to go into production was the twin-engined Avro Manchester . When the engine reliability problems became clear, the Avro team persuaded the Air Ministry that switching to a four-Merlin version of
330-677: The RAF Second Tactical Air Force . The Tempest became the principal destroyer of the V-1 flying bomb ( Fieseler Fi 103 ), since it was the fastest of all the Allied fighters at low levels. Later, the Tempest destroyed about 20 Messerschmitt Me 262 jet aircraft. Development continued and the later Sabre VII delivered 3,500 hp (2,600 kW) with a new supercharger. By the end of World War II, there were several engines in
363-488: The Rolls-Royce Peregrine , were fairly standard designs, with two cylinder banks arranged in a V form and with a displacement of 21 litres (1,300 cu in). The Vulture was, in effect, two Peregrines joined by a new crankcase turning a new crankshaft, producing an X engine configuration with a displacement of 42 litres (2,600 cu in). The Vulture used cylinders of the same bore and stroke as
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#1732772843027396-665: The Rolls-Royce Vulture and the Bristol Centaurus failed as the next generation of high power engines and to keep Napier in the aero-engine industry. The first Sabre engines were ready for testing in January 1938, although they were limited to 1,350 hp (1,010 kW). By March, they were passing tests at 2,050 hp (1,530 kW) and by June 1940, when the Sabre passed the Air Ministry 's 100-hour test,
429-666: The Supermarine Schneider Trophy competitors in 1923 and 1927, as well as several land speed record cars. By the late 1920s, the Lion was no longer competitive and work started on replacements. Napier followed the Lion with two H-block designs: the H-16 Rapier and the H-24 Dagger . The H-block has a compact layout, consisting of two horizontally opposed engines, one atop or beside the other. Since
462-514: The 1953 show. German firm Konig, who specialised in racing outboard motors, built a few 1000cc H-8s in the 1970s, which were basically two of their VC500 flat fours mounted one above the other, with the direction of rotation reversed on one of them. Each half of the engine was a water cooled 2-stroke with rotating disc valve driven by a toothed belt via two 45/90 degree pulleys, plus two siamesed expansion chamber exhausts, fed by two single choke carbs. Both cylinders at each end of each engine fired at
495-492: The 1966 US Grand Prix in a Lotus 43 driven by Jim Clark. It was also used by the unsuccessful 1966 BRM P83 car driven by Graham Hill and Jackie Stewart. As a racing-car engine it was hampered by a high center of gravity , and it was heavy and complex, with gear-driven twin overhead cams for each of four cylinder heads, two gear-coupled crankshafts, and mechanical fuel injection. The Brough Superior Golden Dream motorcycle, first shown in 1938. A 1,000 cc H-4 design and
528-612: The Dagger as the basis. The layout of the H-block, with its inherent balance and the Sabre's relatively short stroke, allowed it to run at a higher rate of rotation, to deliver more power from a smaller displacement, provided that good volumetric efficiency could be maintained (with better breathing), which sleeve valves could do. The Napier company decided first to develop a large 24 cylinder liquid–cooled engine, capable of producing at least 2,000 hp (1,500 kW) in late 1935. Although
561-708: The Peregrine, but the cylinder spacing was increased to accommodate a longer crankshaft, necessary for extra main bearings and wider crankpins . The engine suffered from an abbreviated development period because Rolls-Royce suspended Vulture development in 1940 during the Battle of Britain to concentrate on the Merlin, which powered the RAF's two main fighters, the Hawker Hurricane and Supermarine Spitfire , and as
594-603: The Sabre were the Hawker Typhoon and Hawker Tempest ; the first aircraft powered by the Sabre was the Napier-Heston Racer , which was designed to capture the world speed record. Other aircraft using the Sabre were early prototype and production variants of the Blackburn Firebrand , the Martin-Baker MB 3 prototype and a Hawker Fury prototype. The rapid introduction of jet engines after
627-488: The Vulture design meant that the engines were derated to around 1,450 to 1,550 hp in service by limiting the maximum rpm . Although several new aircraft designs had been planned to use the Vulture, work on the engine's design ended in 1941 as Rolls-Royce concentrated on their more successful Merlin design. Another 24-cylinder engine, the Napier Sabre , proved more successful after a lengthy development period. The supercharged Rolls-Royce Kestrel and its derivative,
660-464: The company continued with the opposed H layout of the Dagger, this new design positioned the cylinder blocks horizontally and it was to use sleeve valves. All of the accessories were grouped conveniently above and below the cylinder blocks, rather than being at the front and rear of the engine, as in most contemporary designs. The Air Ministry supported the Sabre programme with a development order in 1937 for two reasons: to provide an alternative engine if
693-476: The company was purchased by the English Electric Company , which ended the supercharger project immediately and devoted the whole company to solving the production problems, which was achieved quickly. By 1944, the Sabre V was delivering 2,400 horsepower (1,800 kilowatts) consistently and the reputation of the engine started to improve. This was the last version to enter service, being used in
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#1732772843027726-545: The company's much smaller Merlin was already nearing the same power level as the Vulture's original specification, in part because of its accelerated development in 1940, and so production of the Vulture was discontinued after only 538 had been built. The Vulture had been intended to power the Hawker Tornado interceptor but with the cancellation of Vulture development, Hawker abandoned the Tornado and concentrated on
759-485: The competing Rolls-Royce company, which had its own agenda. In 1944, Rolls-Royce produced a similar design prototype called the Eagle . Napier seemed complacent and tinkered with the design for better performance. In 1942, it started a series of projects to improve its high-altitude performance, with the addition of a three-speed, two-stage supercharger , when the basic engine was still not running reliably. In December 1942,
792-478: The cylinders are opposed, the motion in one is balanced by the motion on the opposing side, eliminating both first order and second order vibration. In these new designs, Napier chose air cooling but in service, the rear cylinders proved to be impossible to cool properly, which made the engines unreliable. During the 1930s, studies showed the need for engines capable of developing one horsepower per cubic inch of displacement (about 45 kW/ litre ). Such power output
825-626: The first production versions were delivering 2,200 hp (1,600 kW) from their 2,238 cubic inch (37 litre) displacements. By the end of the year, they were producing 2,400 hp (1,800 kW). The contemporary 1940 Rolls-Royce Merlin II was generating just over 1,000 hp (750 kW) from a 1,647 cubic inch (27 litre) displacement. Problems arose as soon as mass production began. Prototype engines had been hand-assembled by Napier craftsmen and it proved to be difficult to adapt it to assembly-line production techniques. The sleeves often failed due to
858-416: The night so that the engine oil would not congeal and prevent the engine from starting the next day. These problems took too long to remedy and the engine gained a bad reputation. To make matters worse, mechanics and pilots unfamiliar with the different nature of the engine, tended to blame the Sabre for problems that were caused by not following correct procedures. This was exacerbated by the representatives of
891-490: The same power class. The Pratt & Whitney R-4360 Wasp Major four-row, 28-cylinder radial produced 3,000 hp (2,200 kW) at first and later types produced 3,800 hp (2,800 kW), but these required almost twice the displacement in order to do so, 4,360 cubic inches (71 litres). Note: The engine has been used in many aircraft, including two mass-produced fighters. Data from Lumsden Comparable engines Related lists H engine The H engine
924-547: The same time, hence the siamesed exhausts for each pair. Subaru has marketed its flat-four and flat-six engines as "H4" and "H6" respectively. The letter "H" in this case refers to "horizontally-opposed", an alternative term for flat engines ; these engines can also be said to look like a "H" or conjoined "H"s, albeit from the top and in schematic form. The Saab H engine is a straight-four engine produced from 1981 to 2009. The letter "H" represents "high compression". Rolls-Royce Vulture The Rolls-Royce Vulture
957-601: The war led to the quick demise of the Sabre, as there was less need for high power military piston aero engines and because Napier turned its attention to developing turboprop engines such as the Naiad and Eland . Prior to the Sabre, Napier had been working on large aero engines for some time. Its most famous was the Lion , which had been a very successful engine between the World Wars and in modified form had powered several of
990-600: The way they were manufactured from chrome-molybdenum steel, leading to seized cylinders, which caused the loss of the sole prototype Martin-Baker MB 3 . The Ministry of Aircraft Production was responsible for the development of the engine and arranged for sleeves to be machined by the Bristol Aeroplane Company from its Taurus engine forgings. These nitrided austenitic steel sleeves were the result of many years of intensive sleeve development, experience that Napier did not have. Air filters had to be fitted when
1023-426: Was a British aero engine developed shortly before World War II that was designed and built by Rolls-Royce Limited . The Vulture used the unusual " X-24 " configuration, whereby four cylinder blocks derived from the Rolls-Royce Peregrine were joined by a common crankshaft supported by a single crankcase . The engine was originally designed to produce around 1,750 horsepower (1,300 kW ) but problems with
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1056-550: Was needed to propel aircraft large enough to carry large fuel loads for long range flights. A typical large engine of the era, the Pratt & Whitney R-1830 Twin Wasp , developed about 1,200 hp (890 kW) from 1,830 cubic inches (30 litres), so an advance of some 50 per cent would be needed. This called for radical changes and while many companies tried to build such an engine, none succeeded. In 1927, Harry Ricardo published
1089-491: Was prevalent with the poor quality, low-octane fuels in use at the time. Halford had worked for Ricardo 1919–1922 at its London office and Halford's 1923 office was in Ladbroke Grove, North Kensington, only a few miles from Ricardo, while Halford's 1929 office was even closer (700 yards), and while in 1927 Ricardo started work with Bristol Engines on a line of sleeve-valve designs, Halford started work with Napier, using
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