tag:blogger.com,1999:blog-7494097266323039749.post258799271504241121..comments2016-01-14T07:47:50.763-08:00Comments on Training and Racing With a Power Meter Journal: A challenge to cycling aerodynamicistsHunterhttp://www.blogger.com/profile/10476979058435683579noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-7494097266323039749.post-6521114710064810972010-10-14T07:26:14.702-07:002010-10-14T07:26:14.702-07:00Hello Jim,
The approach that I used is described ...Hello Jim,<br /><br />The approach that I used is described in greater detail in this blog entry, to which I linked from the present one:<br /><br />http://www.trainingandracingwithapowermeter.com/2010/04/which-is-faster-cervelo-p2t-or-javelin.html<br /><br />As for changes in Crr with velocity, some experiments indicate that this may also occur with bicycle tires, but others do not support this conclusion. In any case, such non-linearities would appear to be quite small, and hence I have ignored them. <br /><br />Although I tested over a range of velocities, wind tunnel experiments have indicated that cyclists do not undergo any significant transition effects, i.e., as a whole our Cd (and hence CdA) is velocity-independent. <br /><br />OTOH, the Cd of a sphere would change very slightly (i.e., 5-10%) over the range of velocities and hence Reynolds numbers that I tested, so I took this into account when calculating the expected increase in drag.<br /><br />Hope this helps,<br /><br />AndyAndrew R. Coggan, Ph.D.https://www.blogger.com/profile/07152375621226680227noreply@blogger.comtag:blogger.com,1999:blog-7494097266323039749.post-70886977485416504152010-10-13T17:57:12.180-07:002010-10-13T17:57:12.180-07:00Dr. Coggan,
I'd like to know if I correctly u...Dr. Coggan,<br /><br />I'd like to know if I correctly understand the process. Forgive my question here, but I'm stuck with the first edition, so I don't quite get how you initially derive CdA from measurements. <br /><br />I'm assuming you measure the power and velocity from the SRM and then calculate from that the drag force due to wind by <br /><br />Pd = Dw*v<br /><br />where Pd is the Power required to overcome drag, Dw is the drag due to wind, and v is the velocity.<br /><br />From there you get<br /><br />Cd = [2Dw] / [pAv^2] <br /><br />where p is the air density, A is the frontal area, and v is velocity. Am I correct in this? If so, my follow-on question is whether you arrived at A by some type of direct measurement or by approximation.<br /><br />I assume that, regardless of the answer, the point is moot in this experiment because the CdA of the rider and bike remain constant and the effect of the ball is the experimental focus.<br /><br />For that, I assume that you begin with:<br />Ptotal = Pdrag + Prr <br /><br />Where Ptotal is the total power generated, Pdrag is the power required to overcome drag and Prr is the power required to overcome rolling resistance. The experiment then was to measure the change in power required to maintain a set speed, and then compare the measured change to that which was expected in calculations.<br /><br />The only thing you have to do is compare the change in Pdrag, as Prr is assumed constant. However, I've seen a couple of papers proposing that Crr is dependent on velocity. They focused on automotive applications, but could that have been the small factor that was still large enough to create the error discussed here?<br /><br />I also did not see you specify whether you maintained speed or power as the constant in your trial runs. Since you indicate the use of only one Reynolds number, I'm assuming you kept speed constant and used the increase in power to gauge the correlating increase in resistance. What is your opinion of how the experiment would have run if you'd maintained constant power? <br /><br />Thanks for the clarification. This was a fascinating read. <br /><br />Regards,<br />Jim GourleyJim Gourleyhttps://www.blogger.com/profile/02576213931649795833noreply@blogger.comtag:blogger.com,1999:blog-7494097266323039749.post-78718090238812357922010-10-13T07:37:35.834-07:002010-10-13T07:37:35.834-07:00Andy,
Hill's challenge stimulated a number of...Andy,<br /><br />Hill's challenge stimulated a number of experiments, but it wasn't until 1962 that Dennis F. Cain (1930-) and Robert E. Davies (1919-1993) were able to definitively demonstrate a change in ATP concentration during a single muscle contraction (1). What made this possible was the use of 1-fluoro-2,4-dinitrobenzene to irreversibly inhibit the Lohman reaction (i.e., rephosphorylation of ADP by PCr via creatine kinase). While this study really just confirmed what was already believed to be true, it (and Hill's challenge that stimulated it) was nonetheless important in pushing the field forward.<br /><br />1. Cain DF, Davies RE. Breakdown of adenosine triphosphate during a single contraction of working muscle. Biochem Biophys Res Commun 8:361–366, 1962.Andrew R. Coggan, Ph.D.https://www.blogger.com/profile/07152375621226680227noreply@blogger.comtag:blogger.com,1999:blog-7494097266323039749.post-27797592261608535862010-10-12T18:19:07.156-07:002010-10-12T18:19:07.156-07:00I don't know much about biochemistry, Andy. W...I don't know much about biochemistry, Andy. What was the outcome of the A.V. Hill challenge, if any? <br /><br />AndyF<br />http://andyfroncioni.comAndyFhttps://www.blogger.com/profile/13259576244930609088noreply@blogger.comtag:blogger.com,1999:blog-7494097266323039749.post-20418576836690809642010-10-12T17:47:34.499-07:002010-10-12T17:47:34.499-07:00Wow -- what a treat!
Characterizing the measur...Wow -- what a treat! <br /><br />Characterizing the measurement errors in aero testing can be quite a daunting task. Your careful approach to a very difficult problem is something I can use for my own testing.<br /><br />Thanks for posting this article!<br /><br />Andy Froncioni<br />http://andyfroncioni.comAndyFhttps://www.blogger.com/profile/13259576244930609088noreply@blogger.comtag:blogger.com,1999:blog-7494097266323039749.post-79430634231161272462010-10-12T15:00:21.093-07:002010-10-12T15:00:21.093-07:00Really interesting and very clearly explained. Th...Really interesting and very clearly explained. Thanks!Luke Moseleyhttps://www.blogger.com/profile/05717305032983411330noreply@blogger.com