. Railroad construction. Theory and practice . 757° §263. Straight frog-rail. Curved switch-rail. ° § frog-rail. Straightswitch-rail. ° §265. Straight frog-rail. Straight switch-rail. ° This shows that the effect of using straight frog-rails andstraight switch-rails is to sharpen the curve and shorten the leadin each case separately, and that the combined effect is stillgreater. The effect of the straight switch-rails is especiallymarked in reducing the length of lead, and therefore Eq. 78 to80, although having the advantage of ext
. Railroad construction. Theory and practice . 757° §263. Straight frog-rail. Curved switch-rail. ° § frog-rail. Straightswitch-rail. ° §265. Straight frog-rail. Straight switch-rail. ° This shows that the effect of using straight frog-rails andstraight switch-rails is to sharpen the curve and shorten the leadin each case separately, and that the combined effect is stillgreater. The effect of the straight switch-rails is especiallymarked in reducing the length of lead, and therefore Eq. 78 to80, although having the advantage of extreme simplicity, can-not be used for point-switches without material error. Theeffect of the straight frog-rail is less, and since it can be mate-rially reduced by bending the free end of the frog-rails, the in-fluence of this feature is frequently ignored, the frog-rails areassumed to be curved, and Eq. 85 and 86 are used. (See § 276for a further discussion of this point.) 2^7. Dimensions for a turnout from the OUTER side of a curved. track. In this demonstration the switch-rails will ,be consideredas uniformly circular from the switch-points to the frog-point. 278 RAILROAD CONSTRUCTION. § 267. In the triangle FCD (Fig. 141) we have{FC-^CD) :(FC-CD) i(FDC + DFC) .tan i(FDC-DFC);but i(FDC + DFO = 90° - id and i(FDC-DFC)=iF. Also, FC-^CD=2R and FC-CD=g; .*. 2R :g y cot ^6 : tan Ji^:: cot Ji^ : tan J/?; .-. tani^ = ^ (91) Also, OF : FC :: sin 6 : sin 0; but 5i^=7, = 2(i^ + ig)sinJ^ (93) Tf the curvature of the main track is very sharp or the frogangle unusually small, F may be less than 6; in which case thecenter 0 will be on the same side of the main track as C. will become (by calling r= —r and changing the signs) (._i,)=(J2 + i,^^._^;-l- (94) If we call d the degree of curve corresponding to the radiusr, and D the degree of curve corresponding to the radius R, alsod the degree of curve of a turnout from a straight track (the frogangle F being the sam
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