Editing Hyper engine (section)

==Design and development==
Improvements in construction and lighter materials had already delivered some benefits on the way to higher [[power-to-weight ratio]]s. [[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 (physics)|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]].<ref name="Biermann">Biermann pp&nbsp;16, 17</ref>

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.<ref name="Taylor">Taylor p 64</ref>

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.<ref name="Bingham">Bingham pg 49</ref>

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&nbsp;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&nbsp;in<sup>3</sup> (20&nbsp;L), hoping the engine's smaller size would lead to reduced [[Parasitic drag#Form drag|drag]] and hence improved [[Range (aircraft)|range]].

===Hyper No. 1===

[[Samuel Dalziel Heron|Sam Heron]], head of development at [[Wright Field]] and a former colleague of Ricardo while Heron had been working at the [[Royal Aircraft Factory]], Farnborough, started working on the problem with a single-cylinder test engine that he converted to liquid cooling, using a [[Liberty L-12]] engine cylinder. He pushed the power to {{cvt|480|psi|MPa}} [[Mean effective pressure|brake mean effective pressure]], and the coolant temperature to {{convert|300|F|C|abbr=on|sigfig=2}} before reaching the magic numbers. By 1932, the USAAC's encouraging efforts led the Army to sign a development contract with [[Continental Motors Company]] for the continued development of the engine design. The contract limited Continental's role to construction and testing, leaving the actual engineering development to the Army.<ref name="White375">White p 375</ref>

Starting with the L-12-cylinder, they decreased the [[stroke (engine)|stroke]] from 7&nbsp;inches to 5&nbsp;inches to allow higher engine speeds, and then decreased the [[bore (engine)|bore]] from 5&nbsp;inches to 4.62&nbsp;inches, creating the 84&nbsp;in³ cylinder. This would be used in a V-12 engine of 1008&nbsp;in³ [[engine displacement|displacement]].<ref name="Balzer28">Balzer p.28</ref> They used the L-12's [[overhead camshaft]] to operate multiple valves of smaller size, which would improve charging and [[scavenging (automotive)|scavenging]] efficiency. Continental's first test engine, the single-cylinder Hyper No. 1, first ran in 1933.

They eventually determined that exhaust valves could run cooler when a hollow core filled with [[sodium#Metallic sodium|sodium]] is used—the sodium liquefies and considerably increases the heat transfer from the valve's head to its stem and then to the relatively cooler cylinder head where the liquid coolant picks it up.<ref name="Balzer28"/>

Liquid [[Internal combustion engine cooling|cooling systems]] at that time used plain water, which limited operating temperatures to about {{convert|180|F|C|abbr=on|-1}}. The engineers proposed using [[ethylene glycol]], which would allow temperatures up to {{convert|280|F|C|abbr=on|-1}}. At first they proposed using 100% glycol, but there was little improvement due to the lower [[heat capacity|specific heat]] of the glycol (about 2/3 that of water). They eventually determined that a 50/50 mixture (by volume) of water and glycol provided optimal heat removal.<ref name="Balzer28"/>

===Hyper No.2===

A second cylinder was added to Hyper No. 1 to make a horizontal opposed engine for evaluation of an horizontal opposed 12-cylinder engine. After running the modified engine with different combinations of cylinder bore and stroke, it was found that the high coolant temperature required to maintain the required output was impractical.  A third high-performance single-cylinder engine was then constructed with lower operating parameters.  This engine was designated "Hyper No. 2", and became the test bed for developing the cylinders that would become the O-1430-1.<ref name="Balzer28"/>

===Continental O/V/IV/XIV-1430===
{{main|Continental I-1430}}
[[File:Continental I-1430.jpg|thumb|IV-1430-9 in the [[National Museum of the United States Air Force]]]]
The Army apparently became concerned about the development of a suitable supercharger for high-altitude use, and for further development in 1934 they asked for a newer cylinder with slightly less performance and an increased volume of 118.8&nbsp;in<sup>3</sup> from its {{convert|5.5|in|mm|abbr=on}} bore and {{convert|5.0|in|mm|abbr=on}} stroke. This size cylinder would then be used in a 1,425&nbsp;in<sup>3</sup> 12-cylinder engine, delivering the same 1,000&nbsp;hp, with a performance of 0.7&nbsp;hp/in<sup>3</sup>. This placed its performance on a par with newer experimental engines from Europe like the [[Rolls-Royce Merlin|Rolls-Royce PV-12]], at least when running on the higher-octane fuels the Army planned to use.<ref name="White376">White p&nbsp;376</ref>

Another change was to the engine layout. The Army, convinced that future aircraft designs would use engines buried in the wings for additional streamlining, asked Continental to design a full-sized flat-horizontally opposed engine for installation inside a wing. The resulting engine was the Continental O-1430, which would require a ten-year development period which changed the layout to first an upright [[V12 engine|V-12 engine]] and later, an inverted V-12 engine before becoming reliable enough to be considered for full production as the Continental IV-1430 in 1943. By then other engines had already passed its 1,600&nbsp;hp (1,200&nbsp;kW) rating, and although the IV-1430 had a better power-to-weight ratio, there was little else to suggest setting up production in the middle of the war was worthwhile.<ref name="White376"/>

The project was eventually guided by the requirements in the "Request for data R40-C", which was included as a part of the Financial Year (FY) 1940 aircraft procurement program.