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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=DE link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>Hi Michael,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>I add a little graphic about stiffness:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><img width=1024 height=664 id="Bild_x0020_1" src="cid:image001.jpg@01D0C45C.23F5EFE0" alt=Bild></span><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>The graph was taken from the web but it shows very clear that the stiffness of an I beam and a H beam are in different directions.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>I beam stiffness is perpendicular to the crank, H beam parallel to the crank axis.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>There are 3 major forces in a rod:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>Pulling at TDC<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>Compression at LDC<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>And bending from the rotation<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>For the first two forces the area of the rod is the important factor. The shape is not important.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>For the bending forces the shape gets important.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>If you attach a rope to a wall, take the other end in your hand and moving your hand quick up and down (like a crank stroke) the rope will swing up and down too and shows a bended line. A rod is like this rope and gets bended caused by the rotation of the crank.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>For the stiffness of the rod beam the orientation if the beam design is very mandatory. Like a beam in a building there is a strong axis and a weak axis.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>The top graph shows how the “I = stiffness value” is affected by the orientation of the H or I.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>That means an I rod can bear more bending forces than a H rod. An that leads to a better resistance of an I rod against fatigue.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>Crank flexing is there but compared to the 3 main forces so small that it doesn’t influent the total result.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>If it would, then all engines would suffer from many bearing failures because at least to transfer the flexing from the crank journal to the rod beam the only contact way would be the bearing and that means the bearing gets forces on its edge and it would bear this for long and fail quickly.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>I had a look to the Manly rod catalogue.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>All I-beam rods seem to bear higher power than the H-beam ones by same or lower weight. I think that is a clear statement of a rod designer who builds both types. The H-beam is the cheap brother of the I-beam and fails earlier on heavy use is my guess from all I have learned in the last few days.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>But I’m open for other thoughts.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>Cheers<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>Chris<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'>Von:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> Michael Porter [mailto:mdporter@dfn.com] <br><b>Gesendet:</b> Mittwoch, 22. Juli 2015 00:19<br><b>An:</b> MadMarx<br><b>Betreff:</b> Re: [Fot] Racing rod design<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On 7/21/2015 11:24 AM, MadMarx wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>Hi Guys,</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>In US forums I found an interesting opinion:</span><o:p></o:p></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>H-beam rods are for low rev high torque engine (turbo, compressor)</span><o:p></o:p></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'>I-beam are for medium torque engines with high revs</span><o:p></o:p></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></blockquote><p class=MsoNormal><br>It's going to depend upon four variables--Young's modulus for the specific material used, the section modulus of the shape used, the mass and the finish treatment. In a piston engine, the peak bending load is going to be at the point of highest downward pressure on the piston combined with the largest angular deflection of the rod from perpendicular. That's going to be somewhere around 75-90 deg. of rotation after TDC on the power stroke. <br><br>If all other variables are the same, then section modulus matters, and generally, what determines the section modulus with regard to bending is the beam strength and resistance to torsional deflection (even though the rod runs in only one plane, torsional deflection has to be considered since the crank throws are heaving up and down and bending the crank between the mains under both varying piston pressure and inertial forces, and those forces are translated to the rod at roughly 90 deg. to the plane of rod rotation).<br><br>For that reason, I think the H-beam rod would have a lower stiffness in the vector approximately 90 deg from its plane of rotation, as compared to an I-beam, all other things being equal. With forces parallel to the plane of rotation, the H-beam ought to be stiffer. So, maybe, the difference is not exactly rpm, but how the crankshaft behaves at that rpm. If it's twisting and bending, the rods will be subject to twisting and bending loads more or less normal to the plane of rotation--the vector where the H-beam has the least beam strength, in addition to the expected bending loads parallel to the plane of rotation.<br><br>With a theoretically perfect crankshaft, one that does not deflect under load, the H-beam rod would be stronger and less prone to deflection in all cases, I'm presuming, because its section modulus would be higher, and its beam strength higher in the plane of rotation. It might be that the H-beam is still actually superior in all cases, if properly finished, is no heavier, is of the best material and is not subjected to bending/torsional loads beyond its limits angular to the plane of rotation. But, to know for sure, one would need to know the actual section modulus of the specific shapes to be compared, and to have some idea of the crankshaft behavior at the speeds required. And, it would probably be helpful to do some detailed analysis of the failure mode of the rod in question. Signs of fatigue from torsional flexing or side bending loads would be helpful to know, and would inform any decision about what to buy next.<br><br><br>Cheers, Chris.<br><br><br><br><br><br><o:p></o:p></p><pre>-- <o:p></o:p></pre><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre>Michael Porter<o:p></o:p></pre><pre>Roswell, NM<o:p></o:p></pre><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre>Never let anyone drive you crazy when you know it's within walking distance....<o:p></o:p></pre></div></body></html>