. The steam-engine and other heat-motors. and intersecting OM, a perpendicular erected toBD at 0. The triangles OPT and CIA are similar, therefore ot=ai . 0T,=pXA[ Qp/ cr .. vi P*c/-Hence OT is the reqiured tangential pressure at this crank-position. 382 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. It is evident that connecting-rod positions will have to bedrawn for each crank-position in succession to determine a newpiston position and the corresponding net pressure, such as p. Bylaying off this pressure from the center of the shaft, on the crank-position, prolonged if necessary and drawing a para
. The steam-engine and other heat-motors. and intersecting OM, a perpendicular erected toBD at 0. The triangles OPT and CIA are similar, therefore ot=ai . 0T,=pXA[ Qp/ cr .. vi P*c/-Hence OT is the reqiured tangential pressure at this crank-position. 382 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. It is evident that connecting-rod positions will have to bedrawn for each crank-position in succession to determine a newpiston position and the corresponding net pressure, such as p. Bylaying off this pressure from the center of the shaft, on the crank-position, prolonged if necessary and drawing a parallel to thenew connecting-rod position as PfT was drawn, the tangentialpressure for the new crank-position will be indicated by thedistance between 0 and the point of intersection of the paralleland the line OM. It is not necessary to find the instantaneouscenter, as that is only necessary to prove the construction. The tangential pressures so found may be laid off in two ways:1. (Fig. 208.) At each point of division of the crank-circle. Fig. 208. lay off the tangential pressure radially—at right angles to itstrue position—from the center of the crank-pin. CT, for instance,is equal to OT. Join the points so found. The area enclosedby this line and the perimeter of the circle does not measure (Fig. 209.) A much more useful diagram is formed by recti-fying the path of the crank-pin—thus giving actual linear distance—and at each point of division on the rectified perimeter erectinga perpendicular equal to the tangential pressure at that areas then measure work and by means of a planimeter or by SPEED VARIATION CONTROL. 383 the method of ordinates we can obtain the excess or deficit ofwork—variation from the mean—that produces either positiveor negative acceleration. The importance of dividing the semicircles into equal parts isnow apparent, as it facilitates the rectification of the arcs. Accord-ing to Rankine the following method is accurate to nrW (
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