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The hyper engine was a 1930s study project by the United States Army Air Corps (USAAC) to develop a high-performance aircraft engine that would be equal to or better than the aircraft and engines then under development in Europe. The project goal was to produce an engine that was capable of delivering 1 hp/in3 (46 kW/L) of engine displacement for a weight of less than 1 lb/hp delivered. The ultimate design goal was an increased power-to-weight ratio suitable for long-range airliners and bombers. At the time, no production engine could come close to the requirements, although this milestone had been met by special modified or purpose-built racing engines such as the Napier Lion and Rolls-Royce R. A typical large engine of the era, the Pratt & Whitney R-1830 Twin Wasp radial developed about 1,200 hp (895 kW) from 1,830 in3 (30 L) so an advance of at least 50% would be needed. Simply scaling up an existing design would not solve the problem. While it would have increased the total available power, it would not have any significant effect on the power-to-weight ratio; for that, more radical changes were needed.〔White p 211〕 Several engines were built as part of the hyper program, but for a variety of reasons none of these saw production use. Air-cooled engines from a variety of US companies were delivering similar power ratings by the early 1940s, and the licensed production of the Rolls-Royce Merlin as the Packard V-1650 provided hyper-like performance from an inline while the Allison V-1710 did the same from a US design, one produced as a private effort outside the hyper program. ==Design and development== Improvements in construction and lighter materials had already delivered some benefits on the way to higher power-to-weight ratios. Aluminum was being introduced in place of steel as the quality and strength of aluminum alloys improved during the 1930s; this lowered engine weight noticeably, but not enough to achieve a 50% overall improvement. To reach that goal, the power of the engine would also need to be increased. Power is a combination of energy and the rate it is delivered, so to improve the power-to-weight ratio, one would need to increase the operating pressures of the engine, the operating speed, or a combination of both. Further gains could be made by eliminating losses like friction, combustion inefficiencies and scavenging losses, delivering more of the theoretical power to the propeller.〔Biermann pp 16, 17〕 The USAAC engineers determined that it would study all three improvements. Before long, they concluded that increasing the combustion temperature and scavenging efficiency promised the greatest increases of all of the possibilities. To meet that goal, increasing engine speed seemed to be the most attractive solution. However, there were a number of practical problems that were impeding progress in these areas. Increasing the compression ratio is an easy change that improves the mean effective pressure (MEP), but leads to engine knocking from inconsistent detonation. Uncontrolled, knock can damage the engine and was a major block on the way to improved power settings. This change would also increase the operating temperatures, which presented a problem with the valves. Valves were already reaching temperatures that would cause pre-ignition of the fuel as it flowed past them. Increasing operational speed is also, theoretically, a simple change to the engine design. However, at high operating speeds the valves do not completely close before the cam opens them again, a problem called "valve float". Valve float allows gases in the cylinder to escape through the partially open valve, reducing the engine efficiency. Increasing valve spring pressure to close the valves faster led to rapid cam wear and increased friction, reducing overall performance by more than any horsepower gained.〔Taylor p 64〕 As valves were a key issue in both approaches to improved performance, they had been a major area of research in the 1920s and 30s. In the UK, Harry Ricardo had written an influential paper on the sleeve valve system for exactly these reasons, claiming it was the only way forward. He had some success in selling this idea, most notably to Bristol Aeroplane Company Engines, where Roy Fedden became "a believer". Ricardo's friendly competitor, Frank Halford, designed his own sleeve valve engine with Napier & Son, another prominent British engine maker.〔Bingham pg 49〕 The USAAC was not so convinced that the sleeve valve was the only solution. Ironically it was one of Ricardo's papers on the sleeve valve design that led to the USAAC's hyper engine efforts. In one late 1920s paper he claimed that the 1 hp/in³ goal was impossible to achieve with poppet valve type engines. The USAAC engineering team at Wright Field decided to test this claim by beating it. They proposed an engine of about 1200 cubic inches (20 L), hoping the engine's smaller size would lead to reduced drag and hence improved range. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hyper engine」の詳細全文を読む スポンサード リンク
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