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Wright R-4090 Cyclone
 
Wright-R4090-01
 
During the 1940s, Wright Aeronautical Corporation was constantly in competition with Pratt & Whitney for new engine designs required for civil and military aircraft. Utilising the Wright R-3350 as a basis, Wright developed a 22-cylinder engine (Wright model no. 792C22AA), using R-3350 cylinders arranged as a two-row radial engine with 11 cylinders per row.
 
The air-cooled R-4090 was rated to deliver 3,000 hp (2,200 kW) at 2,800 rpm for take-off, from a total displacement of 4,092 cu in (67.06 l), with a compression ratio of 6.85:1. Improved performance was expected from the R-4090 if it was proceeded with. A two-speed single-stage supercharger helped maintain rated power to higher altitudes.
 
Wright-R4090-02
 
The core of the engine was a forged steel crankcase which enclosed the three piece two-throw crankshaft. The three-piece crankshaft was built up through the two one-piece master connecting rods. Ten articulating rods were attached to each master rod. The cylinders were arranged equally around the crankcase, with each row off-set by 16.3636° to ensure cooling airflow. The cylinders had 3,900 sq in (2.52 sq m) of cooling fin area. Each cylinder’s hemispherical combustion chamber had two valves; the exhaust valve was sodium-cooled. It appears that the .333 to 1 propeller gear reduction was provided by Wright’s standard, multi-pinion planetary gear system.
 
Wright-R4090-03
 
Accessories similar to other Cyclone engines were arranged around the rear face of the crankcase and a 0.333:1 planetary reduction gearbox at the front. The supercharger and accessory drive section was very similar to that used on the R-3350 engine. However, the supercharger had a 14 in (356 mm) impeller and gear ratios of 5 to 1 and 7 to 1.
 
Wright-R4090-04
Rear view of the R-4090 showing the supercharger and accessory
drive section which is very similar to that found on the R-3350.
 
Although there are no records of failings of the R-4090, the engine was abandoned to allow development of the R-3350 Cyclone 18 series. It is doubtful that the engine ever flew. Perhaps three R-4090 engines were completed: two XR-4090-1 engines with a single propeller shaft and one XR-4090-3 engine with a coaxial shaft for contra-rotating propellers. The XR-4090-3 weighed an additional 30 lb (13.6 kg) for a total of 3,260 lb (1,478 kg). In addition, the XR-4090-3 was to have a two-speed nose case to maximize propeller and engine speed efficiency for maximum power and cruise power.
 
Ultimately, the R-4090 Cyclone 22 was abandoned so that more resources could be used for the R-3350 Cyclone 18.
 
Variants:
 
XR-4090-1
(790C22AA1), drove a single propeller.
 
R-4090-3
(792C22AA), drove a contra-rotating propeller shaft and was intended to have a two-speed reduction gearbox to maximise efficiency in cruising flight.
 
XR-4090-1
Type: Air-cooled 22 cylinder two-row radial piston engine
Bore: 6.125 in (155.6 mm)
Stroke: 6.3125 in (160.3 mm)
Displacement: 4,092 cu in (67.06 l)
Length: 91 in (2,300 mm)
Diameter: 58 in (1,500 mm)
Dry weight: 3,230 lb (1,470 kg)
Fuel type: Gasoline
Power output: 3,000 hp (2,200 kW) at 2,800 rpm for take-off
Compression ratio: 6.85:1
Supercharger: 14 in (360 mm) diameter impeller, single-stage two-speed supercharger; gear ratios: of 5 to 1 and 7 to 1.
Reduction gear: 0.333:1 planetary reduction gearbox
 
 
 
 
 


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