Lycoming XR-7755
Lycoming XR-7755 is the name of an aircraft engine that was developed between 1943 and 1945 by the American manufacturer Lycoming . The XR-7755 marked the height of the development of radial engines as aircraft engines .
technology
The XR-7755 was a four-stroke cycle - Otto engine , designed as a 36-cylinder series of radial engine with liquid cooling were arranged at the four 9-cylinder star behind the other (in series). As can be seen from the type designation, the displacement is 7755 cubic inches, which corresponds to almost 127 liters. The letters " X " stood for experimental , the " R " for radial in relation to the radial engine configuration.
In each cylinder head there was an overhead camshaft ( OHC valve control ) with two separate sets of cams per cylinder with different timing - one cam for the fuel-saving travel mode, the second for the power-intensive start mode. This switching of the valve timing effected by axial displacement of the camshaft.
The one-piece crankshaft was cranked four times - once for each of the four stars. As with the in-line four-cylinder, the offset angles of the individual cranks are 0 °, 180 °, 180 °, 0 °. In this way, uniform ignition intervals are achieved (one ignition per 20 ° crankshaft revolution). The engine was charged to improve altitude performance . This was achieved both by a radial charger driven by the crankshaft and by an additional turbocharger .
The aspired development goal of the four-valve four-stroke engine was 7000 PS (5150 kW). The absolute fuel consumption was just as huge: at 2600 rpm, at which 5000 hp were generated, the XR-7755 needed around 2200 liters of AvGas per hour. Still, the engine was quite efficient at 170 to 183 g / hp. Like all large and very powerful aircraft engines, it drove a pair of counter-rotating propellers, because a conventional single propeller otherwise required an impractically large diameter in order to be able to convert the large power into propulsion.
With the end of the Second World War , the development of the engine was stopped because the military no longer had any need.
The XR-7755 is the largest and most powerful aircraft piston engine ever built. Larger radial engines were and are only manufactured as marine engines by the Zvezda machine factory in Saint Petersburg . From the type family Zvezda TschN16 / 17 come 42-cylinder in-line radial engines as well as 56-cylinder in-line radial engines as well as double engines with 112 cylinders.
Technical specifications
- Type: four-valve, water-cooled 36-cylinder four-stroke gasoline engine (144 valves, OHC-controlled)
- Stroke: 171 mm
- Bore: 162 mm
- Displacement: 126.9 liters
- Power: 3680 kW (5000 hp ) at 2600 min -1
- maximum speed: 2700 min −1
- Length: 3050 mm
- Diameter: 1525 mm
- Mass: 2744 kg (dry)
Web links
- Lycoming XR-7755. The Aviation History On-Line Museum, October 12, 2013, accessed May 8, 2015 .
- Paul McBride: The XR-7755: The whole story. General Aviation News, April 20, 2007, accessed on May 8, 2015 (English): "Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming."