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Brief history highlights of The Golden Age of Aviation and how air racing furthered Engine Development
One feature introduced late in World War I was reduction gears. Providing a reduction between the propeller and engine allowing the engine to be operated at its optimum speed for maximum output, and reduced the speed of the propeller shaft allowing for larger diameter propellers, slower turning speed and more efficient propellers could be developed.
In four stroke engines;during the induction stroke a combustable mixture of air and fuel is drawn into the cylinders of the engine. This mixture is supplied by a device known as a carburettor,a word derived from carburet, which means to combine an element with carbon. The carburettor combines fuel (a hydrocarbon) and air in the correct proportions to ensure satisfactory combustion. A mixture that is deficient in fuel is known as a lean mixture, one that has excess fuel is known as a rich mixture.
To obtain greater power output for aspirated engines, required additonal air-plus a balanced amount of fuel into the cylinders . Superchargers were adopted for aircraft engines, but normally it was not required to provide additional power at sea-level, but to pump more fuel/air mixture into the cylinders as the aircraft climbed, so that its service ceiling could be greatly increased. Unfortunately such refinements as reduction gears and superchargers carry penalties, they make an engine bigger and heavier, more complex, and need power from the engine to drive them. Initially the gains were minimal, but with growing experience and improving technology both of the devices became common place and valuable.
The Requirement for Bigger, Faster, Long range Airplanes Required New Engine Technology.
The Gnome rotary engine had dominated the field until World War I, but their fuel and oil consumption was high and the large rotating mass of engine produced a pronounced Gyroscopic effect, raising considerable complications when installed on fighter and long range aircraft. It was found to be impractical to build rotary engines in excess of 160hp.
This meant that the in-line and/or the radial engine would have to be developed as quickly as possible to satisfy the requirements for thousands of engines. The radial engine appeared to fit the bill for military usage: it was easier to maintain, it did not require a liquid cooling system (vulnerable to enemy fire) and was also lighter in weight relative to power output, and because of its short, single throw crankshaft, it would not suffer from crankshaft 'whip' and bearing trouble that was plagueing the in-line engines.
The in-line enthusiasts were quick to point out that the large frontal area of the radial engines meant excessive drag.
The radial engine had preceeded the Gnome rotary engine, but cooling problems prevented further development. Inevitably some water cooled engines were developed, but this was not the solution. It merely added to the disadvantages of radial engine and in-line engines.
The real answer was the cylinder design: particularly the shape, material and disposition of cooling fins so that would dissipate more heat into the airstream, and also the development of between-cylinder baffles ensured that the airstream was carried completely around the cylinder.
The designers of in-line engines had far more serious problems to resolve. It was not difficult to improve cooling, by using a water pump to speed circulation of the coolant and by attention to radiator design. But mechanical failures caused by crank shaft whip and the breakdown of bearings required complete redesign. This resulted in the design of Vee-type engines. This design meant that the crankshaft length was almost halved, reducing the tendancy to whip, and greatly increased reliability and longevity. It was the in-line engine that benefitted most from the demands of World War I. In Britain Rolls-Royce produced the Hawk, Falcon and Eagle, the latter was a Vee-12 with a maximum output of 360 hp. From Germany came a number of large-capacity six cylinder water cooled engines, but the most significant was the American Liberty, a water cooled Vee-12 of simple design intended for mass production after teething problems were overcome, it proved to be a reliable engine in the 400 hp class. Many successful designs such as the Hispano-Suiza were built under license in Britain, France and the United States, as were thousands of rotary engines. By the end of World War I many reliable engines in the 300-400 hp class had been designed.
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