Engine | R-2800 Overhaul Manual |
Description of the Front Section, Reduction Gearing, and Torque Indicating System
The front case incorporates a recessed liner at its front end which supports the propeller shaft thrust bearing. The propeller shaft thrust bearing is a ball bearing which has a split inner race and supports the front end of the propeller shaft, transmitting the thrust of the propeller from the propeller shaft, transmitting the thrust of the propeller from the propeller shaft to the crankcases. A boss is provided in the front case for installation and support of the governor oil transfer tube, and a mounting pad is provided for a torque indicator oil pressure
transfer cover. In the R-2800-42W engine, bosses are provided in the front case for the installation and support of two governor oil transfer tubes which carry oil to the propeller shaft oil transfer bearing (Fig 2-2) (Fig 2-4). Six circular, steel lined recesses are located in the rear of the front case to house six torque indicator pistons. A bracket secured to the rear side of the front part of the front case positions the propeller shaft oil transfer bearing.
The propeller reduction ratio is 20:9, and the reduction gearing is of the spur planetary type. The reduction drive fixed gear is an internal spur ring gear with diagonal splines on its outside diameter, which mesh with splines machined in the reduction drive fixed gear support secured to the rear face of the front case. Six reduction drive fixed gear retainers bolted to the support hold the fixed gear in place. A coupling splined to the front end of the crankshaft mates with internal splines in the reduction drive gear and transmits power from the crankshaft to the
drive gear (Fig 2-5). In the R-2800-42W engines, the reduction drive gear is splined and locked to the coupling with three retaining screws
. Teeth on the outside diameter of the drive gear mesh with 15 reduction drive pinions housed in the reduction drive pinion cage, which is integral with the propeller shaft. The reduction drive pinion races are held in the cage by pinion shafts. Each pinion mates with the teeth on the inside diameter of the fixed gear.
The torque indicating system makes possible the accurate measurement of the actual power output to the propeller when the airplane is in flight. As the reduction drive fixed gear moves forward on the diagonal splines in its outside diameter in response to the torque applied to the propeller shaft by the crankshaft through the reduction drive gear, the forward thrust of the reduction drive fixed gear is counterbalanced by pressure oil operating on the gear through the six torque indicator pistons. Each piston carries two oil seal rings, is fitted on its rear end with a slipper bearing which maintains contact with the fixed gear, and is retained in its recess by a cover. Oil pressure is supplied by the booster section of the oil pump located in the bottom of the front case, to the master piston, which by its own movement meters the flow of oil to itself and the five other pistons in direct proportion to the varying load applied to the six pistons through the reduction drive fixed gear. Thus, the reduction drive fixed gear is always balanced by oil pressure acting against the front side of the pistons. The oil pressure acting on the torque indicator pistons also acts, through a cored passage and external tubes, on a gage in the airplane. By calculating the oil pressure acting on the torque pistons together with the engine rpm and a previously determined torque constant, the pilot can determine the horsepower being delivered to the propeller.
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