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Radial Engines

A star among combustion engines

The unique visual appearance and incomparable sound of this engine is enthralling. Yet, radial engines are much more than just beautiful technology. Engineers love them for their uniform distribution of force and mass produced by cylinders that are arranged radially around the centred crankshaft. Thus, radial engines became one of the most popular engines in aircraft manufacturing, until they were replaced by jet engines. Large helicopters, such as the type Sikorski S-55, also use the reliable power of radial engines.

One of the few helicopters to incorporate a radial engine is the Sycamore. The legendary Bristol 171 Sycamore was the first helicopter completely developed and manufactured in Great Britain (maiden flight on 27 July1947). It features a 550 PS nine-cylinder Alvis-Leonides engine that was adjusted for helicopter application by using a special air-cooling system andmodified oil supply. The engine was also installed in fixed-wing airplanes, such as the British two-engined airplane Percival Prince, and the Twin Pioneer – a 1950s transport plane from the company, Scottish Aviation.

Once Flying Bulls’ newly acquired Sycamore helicopter arrived in Salzburg from Switzerland in spring 2010, the radial engine was submitted to Videoscope for inspection. The examination of the inside of the engine revealed heavy corrosion. It was then decided to replace the power unit with a structurally identical, recently overhauled unit. However, the new engine does not operate with a carburettor, but with single point injection (SPI), i.e. fuel is supplied to all nine cylinders through central injection.

Today, helicopters are almost exclusively fitted with turbines; smaller types, such as the Robinson R22/R44 or Schweizer 300 C, are powered by a Lycoming Boxer engine, and no longer by radial engines. Time is almost up for these gorgeous cylinder engine arrangements, although some enthusiasts still deal with this piece of aviation history – thus keeping it alive. The Sycamore was largely refurbished and rendered airworthy from 2010 to 2013, thanks to the profound know-how of the Flying Bulls specialists. On 16 October 2013, the Sycamore took off in Salzburg with the typical rich sound of its nine-cylinder radial engine.