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Aviation History
1947
1947 - 0005.PDF
JANUARY 2ND, 1947 FLIGHT load on the engine is at once increased and thus the r.p.m. tend to fall, and (although the boost value does not change) immediately this happens the constant-speed unit regu- lates the blade pitch to finer angles, say 30 and 28 deg., allowing the engine to speed-up to its original figure of 2,100 r.p.m. On the other hand, should the pilot start diving, the load on the engine is relieved, the "revs" tend to soar and the blade pitch is consequently coarsened until the engine r.p.m. are brought back to their selected figure. As the time-lag between enghve r.p.m. change and corrective action is very small, engine speed and boost pressure remain virtually constant. The actual power output of the engine is thus maintained at a determined value, irrespec- tive of the attitude of the machins, although naturally OPERATING LINKAGE from the engine. Meshing with the driving g^ar is an idler gear mounted on a short hollow shaft incorporating a non- return valve through which engine oil enters the unit. These gear wheels form the pump which feeds oil, via ducts in the casing, into the interior of the hollow driving- gear shaft, from which two outlets give access to the oil pipes connecting to the airscrew tubes. Inside the hollow gear shaft is the piston valve which has lands upon it and is moved by the centrifugal governor, so determining to which oil tube the high-pressure oil shall he fed. When the piston valve is in a central position IIOIIJ -outlets are blanked-off by the lands, and the high-pressure oil from the pump is by-passed back through a relief valve to the suction side of the pump. The centrifugal governor consists of two L-shaped fly- BEARING DRIVING PIN ASSEMBLY TRANSLATION BEARING UNIT The design and construction of theRoto/ 15 Geg. pitch range six-blade contra-rotating airscrew are clearly shewn m this special "Flight" cut- away drawing. How the movement of the sliding cylinder is transmitted through the operating links and translation bear- ing for pitch-change motion can easily be followed. the speed of flight is dependent upon attitude. When climbing, L for instance, the engine would be \\ .turning over at the same speed for •s*8HfJ~same boost, thus producing the same power as for level flight, but due to the finer blade pitch which permits this condition, the aircraft will not be pullett through the air for so great a distance per revolution of the airscrew, and thus the climbing speed will be lower. Constant-speed Unit The constant-speed unit is mounted on and driven by the engine, and is composed of three main elements, viz., a gear-type oil pump, a centrifugal governor, and a piston valve, all of which are housed in a three-part casing. The gear-type pump is also the drive for the centrifugal governor and comprises a driving gear mounted on a long hollow shaft, one end of which is splined to transmit the drive weights, the lower arms of which bear against the outer race of a ball bearing mounted on the end of the, piston valve. On the other side of the ball bearing is a flange against which bears a, coil spring to compensate the centri- fugal movement of the fly-weights. Above the spring is a sleeve along which are cut racking teeth to mesh with a toothed segment controlled from the pilot's cockpit. Thus, according to the position to which the segment is turned, the tension of the coil spring is either lessened or increased in order to balanGe the centrifugal moment of the fly-weights, and so determine the position of the piston valve and the consequent distribution of the oil to the
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