{"id":1561,"date":"2010-11-28T22:24:00","date_gmt":"2010-11-28T21:24:00","guid":{"rendered":"https:\/\/medianbox.fr\/wordpress\/?p=1561"},"modified":"2014-08-13T22:41:53","modified_gmt":"2014-08-13T20:41:53","slug":"cyclisme-laerodynamisme-a-velo","status":"publish","type":"post","link":"https:\/\/medianbox.fr\/wordpress\/?p=1561","title":{"rendered":"MeDiaN@Sports &#8211; \u00ab L&rsquo;A\u00e9rodynamisme \u00e0 v\u00e9lo \u00bb"},"content":{"rendered":"<h3>Pr\u00e9sentation g\u00e9n\u00e9rale<\/h3>\n<p>Dans ce pr\u00e9c\u00e9dent <a title=\"Cyclisme : &quot;V\u00e9lo et \u00e9quation du mouvement&quot;\" href=\"https:\/\/medianbox.fr\/wordpress\/?p=1323\" target=\"_blank\">article<\/a>, nous avons vu que l&rsquo;\u00e9quation g\u00e9rant le mouvement d&rsquo;un cycliste peut s&rsquo;\u00e9crire sous la forme suivante :<\/p>\n<p style=\"text-align: center;\"><img src='https:\/\/s0.wp.com\/latex.php?latex=C_%7Bm%7D+%3D+K%5Cddot%7B%5Ctheta_%7Bp%7D+%7D+%2B+%5Cleft+%28+%5Clambda_%7B1%7D%2B2.+%5Clambda_%7B2%7Dt+%5Cright+%29+%5Cdot%7B%5Ctheta_%7Bp%7D%7D+%2B+%5Cleft+%28M_%7Btot%7D+%5Cright+%29+.g.a.t.sin%28%5Calpha%29&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='C_{m} = K\\ddot{\\theta_{p} } + \\left ( \\lambda_{1}+2. \\lambda_{2}t \\right ) \\dot{\\theta_{p}} + \\left (M_{tot} \\right ) .g.a.t.sin(\\alpha)' title='C_{m} = K\\ddot{\\theta_{p} } + \\left ( \\lambda_{1}+2. \\lambda_{2}t \\right ) \\dot{\\theta_{p}} + \\left (M_{tot} \\right ) .g.a.t.sin(\\alpha)' class='latex' \/><br \/>\nAvec <img src='https:\/\/s0.wp.com\/latex.php?latex=K%3Da%5E%7B2%7D.t%5E%7B2%7D+%5Cleft+%28+M%2B2.+%5Cleft+%28M_%7B1%7D%2BM_%7B2%7D+%5Cright%29+%2B+m_%7BP%7D+%2B+2.+m_%7Bp%7D%2BM_%7BCycliste%7D+%5Cright%29%2B0%2C13%5E%7B2%7D+%5Cleft+%28m_%7BP%7D+%2B+2.+m_%7Bp%7D+%5Cright%29+&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='K=a^{2}.t^{2} \\left ( M+2. \\left (M_{1}+M_{2} \\right) + m_{P} + 2. m_{p}+M_{Cycliste} \\right)+0,13^{2} \\left (m_{P} + 2. m_{p} \\right) ' title='K=a^{2}.t^{2} \\left ( M+2. \\left (M_{1}+M_{2} \\right) + m_{P} + 2. m_{p}+M_{Cycliste} \\right)+0,13^{2} \\left (m_{P} + 2. m_{p} \\right) ' class='latex' \/><br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=M_%7Btot%7D+%3D+%5Cleft+%28M%2BM_%7B1%7D%2BM_%7B2%7D%2Bm_%7BP%7D%2B2m_%7Bp%7D%2BM_%7BCycliste%7D+%5Cright+%29+&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='M_{tot} = \\left (M+M_{1}+M_{2}+m_{P}+2m_{p}+M_{Cycliste} \\right ) ' title='M_{tot} = \\left (M+M_{1}+M_{2}+m_{P}+2m_{p}+M_{Cycliste} \\right ) ' class='latex' \/><br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=%5Calpha+%3D+Arctan+%28%5Cfrac%7BDenivele%7D%7B100%7D%29&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='\\alpha = Arctan (\\frac{Denivele}{100})' title='\\alpha = Arctan (\\frac{Denivele}{100})' class='latex' \/><br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=t%3D%5Cfrac%7BNdents_%7Bplateau%7D+%7D%7BNdents_%7Bpignon%7D%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='t=\\frac{Ndents_{plateau} }{Ndents_{pignon}}' title='t=\\frac{Ndents_{plateau} }{Ndents_{pignon}}' class='latex' \/><\/p>\n<p style=\"text-align: left;\">Cette \u00e9quation est cependant insuffisante pour repr\u00e9senter la r\u00e9alit\u00e9 car elle n\u00e9glige l&rsquo;ensemble des actions ext\u00e9rieures s&rsquo;opposant pourtant \u00e0 l&rsquo;avancement du cycliste. Pour obtenir une mod\u00e9lisation plus pr\u00e9cise, il faudra donc prendre en compte un certain nombre d&rsquo;actions suppl\u00e9mentaire et en particulier celles dues \u00e0 l&rsquo;air.<\/p>\n<h2>R\u00e9sistance a\u00e9rodynamique<\/h2>\n<h3 style=\"padding-left: 30px;\">P\u00e9n\u00e9tration dans l&rsquo;air<\/h3>\n<h4 style=\"padding-left: 60px;\">Mod\u00e9lisation math\u00e9matique<\/h4>\n<p style=\"padding-left: 60px;\">La r\u00e9sistance a\u00e9rodynamique est l&rsquo;action exerc\u00e9e par l&rsquo;air sur le cycliste lorsque celui-avance. Pouvant \u00eatre favorable ou d\u00e9favorable, sa valeur est proportionnelle au carr\u00e9 de la vitesse relative du cycliste par rapport au vent.<\/p>\n<p style=\"padding-left: 60px;\">Bien que la d\u00e9termination pr\u00e9cise des ph\u00e9nom\u00e8nes a\u00e9rodynamique soit extr\u00eamement complexe, on peut cependant obtenir une id\u00e9e de cette r\u00e9sistance gr\u00e2ce \u00e0 la formule ci-dessous:<\/p>\n<p style=\"text-align: center; padding-left: 60px;\"><img src='https:\/\/s0.wp.com\/latex.php?latex=R_%7BC_%7Bx%7D%7D%3D+%5Cfrac%7B1%7D%7B2%7D.%5Crho+.S.C_%7Bx%7D.V%5E%7B2%7D_%7Ba%7D%3D+%5Cfrac%7B1%7D%7B2%7D.%5Crho+.S.C_%7Bx%7D.%28V_%7Bvent%7D%2B%5Cdot%7B%5Cxi+%7D%29%5E%7B2%7D+&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='R_{C_{x}}= \\frac{1}{2}.\\rho .S.C_{x}.V^{2}_{a}= \\frac{1}{2}.\\rho .S.C_{x}.(V_{vent}+\\dot{\\xi })^{2} ' title='R_{C_{x}}= \\frac{1}{2}.\\rho .S.C_{x}.V^{2}_{a}= \\frac{1}{2}.\\rho .S.C_{x}.(V_{vent}+\\dot{\\xi })^{2} ' class='latex' \/><br \/>\navec <img src='https:\/\/s0.wp.com\/latex.php?latex=%5Crho&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='\\rho' title='\\rho' class='latex' \/> la masse volumique de l&rsquo;air;<br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=S&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='S' title='S' class='latex' \/> la surface frontale du cycliste;<br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=C_%7Bx%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='C_{x}' title='C_{x}' class='latex' \/> le coefficient de p\u00e9n\u00e9tration dans l&rsquo;air du cycliste (environ 0.9);<br \/>\net <img src='https:\/\/s0.wp.com\/latex.php?latex=V_%7Bvent%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='V_{vent}' title='V_{vent}' class='latex' \/> vitesse du vent est compt\u00e9e positivement lorsqu&rsquo;il est oppos\u00e9 \u00e0 la vitesse d&rsquo;avancement<\/p>\n<h4 style=\"text-align: left; padding-left: 60px;\">Param\u00e8tres influents <img src='https:\/\/s0.wp.com\/latex.php?latex=R_%7BC_%7Bx%7D%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='R_{C_{x}}' title='R_{C_{x}}' class='latex' \/><\/h4>\n<h5 style=\"text-align: left; padding-left: 90px;\">Les conditions atmosph\u00e9riques (<img src='https:\/\/s0.wp.com\/latex.php?latex=%5Crho&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='\\rho' title='\\rho' class='latex' \/>)<\/h5>\n<p style=\"padding-left: 90px;\">La masse volumique de l&rsquo;air d\u00e9pend de plusieurs facteurs qui sont l&rsquo;humidit\u00e9, la temp\u00e9rature et la pression atmosph\u00e9rique qui varie avec l&rsquo;altitude. Dans les conditions normales, on peut approcher la masse volumique de l&rsquo;air gr\u00e2ce \u00e0 la formule suivante :<\/p>\n<p style=\"padding-left: 90px; text-align: center;\"><img src='https:\/\/s0.wp.com\/latex.php?latex=%5Crho+%28H_%7Bg%7D+%2C%5Ctheta%2C+p+%29%3D%5Cfrac+%7B1%7D+%7B287%2C06+%28%5Ctheta+%2B273%2C15%29%7D+%28p+-+230%2C617.H_%7Bg%7D+.+exp%28%5Cfrac%7B17.5043.%5Ctheta%7D%7B241.2%2B%5Ctheta+%7D%29%29&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='\\rho (H_{g} ,\\theta, p )=\\frac {1} {287,06 (\\theta +273,15)} (p - 230,617.H_{g} . exp(\\frac{17.5043.\\theta}{241.2+\\theta }))' title='\\rho (H_{g} ,\\theta, p )=\\frac {1} {287,06 (\\theta +273,15)} (p - 230,617.H_{g} . exp(\\frac{17.5043.\\theta}{241.2+\\theta }))' class='latex' \/><\/p>\n<p style=\"padding-left: 90px; text-align: left;\">A 20\u00b0C et \u00e0 pression normale, on consid\u00e8re souvent que <img src='https:\/\/s0.wp.com\/latex.php?latex=%5Crho_%7B20%7D%3D1.204kg%2Fm%5E3&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='\\rho_{20}=1.204kg\/m^3' title='\\rho_{20}=1.204kg\/m^3' class='latex' \/><\/p>\n<h5 style=\"padding-left: 90px; text-align: left;\">La taille et la position du cycliste, la g\u00e9om\u00e9trie de son mat\u00e9riel (<img src='https:\/\/s0.wp.com\/latex.php?latex=S+et+C_%7Bx%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='S et C_{x}' title='S et C_{x}' class='latex' \/>)<\/h5>\n<p style=\"padding-left: 90px;\">Le <img src='https:\/\/s0.wp.com\/latex.php?latex=C_%7Bx%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='C_{x}' title='C_{x}' class='latex' \/> est le coefficient de p\u00e9n\u00e9tration dans l&rsquo;air de l&rsquo;ensemble Cycliste+V\u00e9lo. Il diff\u00e8re suivant la position du cycliste et l&rsquo;incidence du vent. Cependant, on peut consid\u00e9rer que 0,95 est une bonne approximation de ce coefficient dans la majorit\u00e9 des cas.<\/p>\n<p style=\"padding-left: 90px;\">S est la surface frontale de l&rsquo;ensemble cycliste+V\u00e9lo. Cette surface peut \u00eatre d\u00e9termin\u00e9e assez facilement en utilisant un appareil photo num\u00e9rique et le logiciel The Gimp (voir ce <a title=\"Mesurer la surface d'un objet avec The GIMP\" href=\"https:\/\/medianbox.fr\/wordpress\/?p=1727\" target=\"_blank\">tuto<\/a>). Voici ce que l&rsquo;on obtient dans mon cas.<\/p>\n<p style=\"padding-left: 90px; text-align: center;\"><a href=\"https:\/\/medianbox.fr\/wordpress\/?attachment_id=1605\" rel=\"attachment wp-att-1605\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1605\" title=\"SCx1\" src=\"https:\/\/medianbox.fr\/wordpress\/wp-content\/uploads\/2010\/11\/SCx1.png\" alt=\"\" width=\"458\" height=\"358\" srcset=\"https:\/\/medianbox.fr\/wordpress\/wp-content\/uploads\/2010\/11\/SCx1.png 572w, https:\/\/medianbox.fr\/wordpress\/wp-content\/uploads\/2010\/11\/SCx1-300x234.png 300w\" sizes=\"auto, (max-width: 458px) 100vw, 458px\" \/><\/a><\/p>\n<p style=\"padding-left: 90px; text-align: left;\">On peut aussi noter que les positions en contre la montre et\/ou des tri-athl\u00e8tes permettent d&rsquo;atteindre des SCx de l&rsquo;ordre de 0,25.<\/p>\n<h5 style=\"padding-left: 90px; text-align: left;\">Du vent apparent<\/h5>\n<p style=\"padding-left: 120px;\">Le vent apparent est la vitesse du vent par rapport au cycliste. Il d\u00e9pend de la vitesse propre du vent, de son incidence et de la vitesse du cycliste.<\/p>\n<p style=\"padding-left: 120px;\">Ainsi, <img src='https:\/\/s0.wp.com\/latex.php?latex=V_%7Ba%7D%5E%7B2%7D%3D%28V_%7Bvent%7D.+cos%28i%29%2BV%7BCycliste%7D%29%5E%7B2%7D%3D%28V_%7Bvent%7D.cos%28i%29%2B%5Cdot%7B%5Cxi+%7D%29%5E%7B2%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='V_{a}^{2}=(V_{vent}. cos(i)+V{Cycliste})^{2}=(V_{vent}.cos(i)+\\dot{\\xi })^{2}' title='V_{a}^{2}=(V_{vent}. cos(i)+V{Cycliste})^{2}=(V_{vent}.cos(i)+\\dot{\\xi })^{2}' class='latex' \/><\/p>\n<p style=\"padding-left: 120px; text-align: center;\"><a href=\"https:\/\/medianbox.fr\/wordpress\/?attachment_id=1617\" rel=\"attachment wp-att-1617\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1617\" title=\"vent apparent1\" src=\"https:\/\/medianbox.fr\/wordpress\/wp-content\/uploads\/2010\/11\/vent-apparent1.png\" alt=\"\" width=\"430\" height=\"199\" srcset=\"https:\/\/medianbox.fr\/wordpress\/wp-content\/uploads\/2010\/11\/vent-apparent1.png 537w, https:\/\/medianbox.fr\/wordpress\/wp-content\/uploads\/2010\/11\/vent-apparent1-300x139.png 300w\" sizes=\"auto, (max-width: 430px) 100vw, 430px\" \/><\/a><\/p>\n<h4 style=\"padding-left: 60px;\">Conclusion<\/h4>\n<p style=\"text-align: left; padding-left: 90px;\">La r\u00e9sistance d\u00fb \u00e0 l&rsquo;air ramen\u00e9e au p\u00e9dalier est finalement donn\u00e9e par la relation :<\/p>\n<p style=\"text-align: center; padding-left: 60px;\"><strong><img src='https:\/\/s0.wp.com\/latex.php?latex=+R_%7BC_%7Bx%7D%7D%3D+%5Cfrac%7B1%7D%7B2%7D.%5Crho+.S.C_%7Bx%7D.%28V_%7Bvent%7D.cos%28i%29%2Ba.t.%5Cdot%7B%5Ctheta_%7Bp%7D%7D%29%5E%7B2%7D+&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt=' R_{C_{x}}= \\frac{1}{2}.\\rho .S.C_{x}.(V_{vent}.cos(i)+a.t.\\dot{\\theta_{p}})^{2} ' title=' R_{C_{x}}= \\frac{1}{2}.\\rho .S.C_{x}.(V_{vent}.cos(i)+a.t.\\dot{\\theta_{p}})^{2} ' class='latex' \/><\/strong><\/p>\n<p style=\"text-align: center; padding-left: 60px;\"><strong><br \/>\n<\/strong><\/p>\n<h3 style=\"padding-left: 30px;\">Friction de l&rsquo;air<\/h3>\n<p style=\"padding-left: 60px;\">Lorsque qu&rsquo;un v\u00e9lo avance, le frottement de l&rsquo;air sur celui-ci ainsi que les ph\u00e9nom\u00e8ne a\u00e9rodynamique qu&rsquo;il g\u00e9n\u00e8re (tra\u00een\u00e9e, d\u00e9pression,&#8230;) agissent comme un frein \u00e0 cet l&rsquo;avancement. L&rsquo;essentiel de ces pertes sont en r\u00e9alit\u00e9 g\u00e9n\u00e9r\u00e9es par la rotation des roues et c&rsquo;est pourquoi les fabricants proposent de plus en plus des roues dites a\u00e9rodynamique (jantes hautes, r\u00e9duction du nombre de rayons, rayons profil\u00e9s,&#8230;).<\/p>\n<p style=\"padding-left: 60px;\">Ces roues peuvent alors \u00eatre caract\u00e9ris\u00e9es par un coefficient qui d\u00e9finit leur efficacit\u00e9 de friction (Cf=0.0027 pour des roues standards avec des pneus 700x23C).<\/p>\n<p style=\"padding-left: 60px;\">La r\u00e9sistance due \u00e0 la friction de l&rsquo;air peut \u00eatre approxim\u00e9e gr\u00e2ce \u00e0 la relation ci-dessous :<\/p>\n<p style=\"padding-left: 60px; text-align: center;\"><strong><img src='https:\/\/s0.wp.com\/latex.php?latex=+R_%7Bfriction_%7Bair%7D%7D%3D+C_%7Bf%7D.%28V_%7Bvent%7D.cos%28i%29%2Ba.t.%5Cdot%7B%5Ctheta_%7Bp%7D%7D%29%5E%7B2%7D+&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt=' R_{friction_{air}}= C_{f}.(V_{vent}.cos(i)+a.t.\\dot{\\theta_{p}})^{2} ' title=' R_{friction_{air}}= C_{f}.(V_{vent}.cos(i)+a.t.\\dot{\\theta_{p}})^{2} ' class='latex' \/><\/strong><\/p>\n<h2>Conclusion<\/h2>\n<p>La prise en compte de l&rsquo;a\u00e9rodynamisme nous permet d&rsquo;accro\u00eetre la pr\u00e9cision de l&rsquo;\u00e9quation du mouvement \u00e9tablie pr\u00e9c\u00e9demment. Celle ci devient d\u00e9sormais :<\/p>\n<p style=\"text-align: center;\"><img src='https:\/\/s0.wp.com\/latex.php?latex=C_%7Bm%7D+%3D+K%5Cddot%7B%5Ctheta_%7Bp%7D+%7D+%2B+%5Cleft+%28+%5Clambda_%7B1%7D%2B2.+%5Clambda_%7B2%7Dt+%5Cright+%29+%5Cdot%7B%5Ctheta_%7Bp%7D%7D+%2B+%5Cleft+%28M_%7Btot%7D+%5Cright+%29+.g.a.t.sin%28%5Calpha%29+%2B+C_%7Baero_%7Bp%7D%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='C_{m} = K\\ddot{\\theta_{p} } + \\left ( \\lambda_{1}+2. \\lambda_{2}t \\right ) \\dot{\\theta_{p}} + \\left (M_{tot} \\right ) .g.a.t.sin(\\alpha) + C_{aero_{p}}' title='C_{m} = K\\ddot{\\theta_{p} } + \\left ( \\lambda_{1}+2. \\lambda_{2}t \\right ) \\dot{\\theta_{p}} + \\left (M_{tot} \\right ) .g.a.t.sin(\\alpha) + C_{aero_{p}}' class='latex' \/><br \/>\nAvec <img src='https:\/\/s0.wp.com\/latex.php?latex=K%3Da%5E%7B2%7D.t%5E%7B2%7D+%5Cleft+%28+M%2B2.+%5Cleft+%28M_%7B1%7D%2BM_%7B2%7D+%5Cright%29+%2B+m_%7BP%7D+%2B+2.+m_%7Bp%7D%2BM_%7BCycliste%7D+%5Cright%29%2B0%2C13%5E%7B2%7D+%5Cleft+%28m_%7BP%7D+%2B+2.+m_%7Bp%7D+%5Cright%29+&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='K=a^{2}.t^{2} \\left ( M+2. \\left (M_{1}+M_{2} \\right) + m_{P} + 2. m_{p}+M_{Cycliste} \\right)+0,13^{2} \\left (m_{P} + 2. m_{p} \\right) ' title='K=a^{2}.t^{2} \\left ( M+2. \\left (M_{1}+M_{2} \\right) + m_{P} + 2. m_{p}+M_{Cycliste} \\right)+0,13^{2} \\left (m_{P} + 2. m_{p} \\right) ' class='latex' \/><br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=M_%7Btot%7D+%3D+%5Cleft+%28M%2BM_%7B1%7D%2BM_%7B2%7D%2Bm_%7BP%7D%2B2m_%7Bp%7D%2BM_%7BCycliste%7D+%5Cright+%29+&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='M_{tot} = \\left (M+M_{1}+M_{2}+m_{P}+2m_{p}+M_{Cycliste} \\right ) ' title='M_{tot} = \\left (M+M_{1}+M_{2}+m_{P}+2m_{p}+M_{Cycliste} \\right ) ' class='latex' \/><br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=%5Calpha+%3D+Arctan+%28%5Cfrac%7BDenivele%7D%7B100%7D%29&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='\\alpha = Arctan (\\frac{Denivele}{100})' title='\\alpha = Arctan (\\frac{Denivele}{100})' class='latex' \/><br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=t%3D%5Cfrac%7BNdents_%7Bplateau%7D+%7D%7BNdents_%7Bpignon%7D%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='t=\\frac{Ndents_{plateau} }{Ndents_{pignon}}' title='t=\\frac{Ndents_{plateau} }{Ndents_{pignon}}' class='latex' \/><br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=C_%7Baero_%7Bp%7D%7D%3Dt.C_%7Baero_%7Broues%7D%7D%3Da.t.R_%7Baero%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='C_{aero_{p}}=t.C_{aero_{roues}}=a.t.R_{aero}' title='C_{aero_{p}}=t.C_{aero_{roues}}=a.t.R_{aero}' class='latex' \/><br \/>\n<img src='https:\/\/s0.wp.com\/latex.php?latex=R_%7Baero%7D%3DR_%7BC_%7Bx%7D%7D%2BR_%7Bfriction_%7Bair%7D%7D%3D%28%5Cfrac%7B1%7D%7B2%7D%5Crho.S.C_%7Bx%7D%2BC_%7Bf%7D%29.%28V_%7BVent%7D.cos%28i%29%2Ba.t.%5Cdot%7B%5Ctheta_%7Bp%7D%7D%29%5E%7B2%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='R_{aero}=R_{C_{x}}+R_{friction_{air}}=(\\frac{1}{2}\\rho.S.C_{x}+C_{f}).(V_{Vent}.cos(i)+a.t.\\dot{\\theta_{p}})^{2}' title='R_{aero}=R_{C_{x}}+R_{friction_{air}}=(\\frac{1}{2}\\rho.S.C_{x}+C_{f}).(V_{Vent}.cos(i)+a.t.\\dot{\\theta_{p}})^{2}' class='latex' \/><\/p>\n<h3>Mais aspirons \u00e0 aller plus loin&#8230;<\/h3>\n<p style=\"text-align: justify;\">Tout cycliste ayant d\u00e9j\u00e0 rouler en groupe a pu constater l&rsquo;importance de l&rsquo;aspiration a\u00e9rodynamique\u00a0 dans ce sport. Le placement dans un peloton et la capacit\u00e9 du coureur \u00e0 s&rsquo;abriter dans les roues permet ainsi une \u00e9conomie \u00e9nerg\u00e9tique importante non n\u00e9gligeable qui pourra faire la diff\u00e9rence en fin de parcours. La litt\u00e9rature fait ainsi souvent \u00e9tat d&rsquo;un gain possible de 30% en fonction des conditions.<\/p>\n<p style=\"text-align: justify;\">L&rsquo;objectif de ce paragraphe est de faire appara\u00eetre un facteur de correction <img src='https:\/\/s0.wp.com\/latex.php?latex=k_%7Bcorr%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='k_{corr}' title='k_{corr}' class='latex' \/> dans l&rsquo;\u00e9quation qui prendra en compte l&rsquo;aspiration dont pourra profiter le cycliste lors d&rsquo;une cyclosportive par exemple.<\/p>\n<p style=\"text-align: justify;\">L&rsquo;id\u00e9e \u00e9tant d&rsquo;affiner le r\u00e9sultat sans dispositif autre que le compteur, la d\u00e9termination du coefficient correcteur se fera sur la base du raisonnement ci-dessous :<br \/>\n&#8211; Le gain maximum attribuer \u00e0 l&rsquo;aspiration est d&rsquo;environ 30%. Nous pouvons donc supposer qu&rsquo;une sortie en groupe r\u00e9aliser \u00e0 100% dans les roues permet au coureur de r\u00e9duire de 30% l&rsquo;\u00e9nergie d\u00e9pens\u00e9e pour vaincre les forces a\u00e9rodynamiques.<br \/>\n&#8211; A l&rsquo;inverse, un sortie \u00e0 2 o\u00f9 les cyclistes prennent les relais \u00e0 part \u00e9gale permettra \u00e0 chacun de s&rsquo;abriter 50% du temps seulement.<\/p>\n<p style=\"text-align: justify;\">Le facteur correcteur <img src='https:\/\/s0.wp.com\/latex.php?latex=k_%7Bcorr%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='k_{corr}' title='k_{corr}' class='latex' \/> est donc fonction du temps passer \u00e0 s&rsquo;abriter par rapport au temps totale de la sortie et pourra s&rsquo;\u00e9crire :<\/p>\n<p style=\"text-align: center;\"><img src='https:\/\/s0.wp.com\/latex.php?latex=k_%7Bcorr%7D+%3D+1-%5Cfrac%7Bt_%7Babrite%7D%7D%7B100%7D%2A0.3&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='k_{corr} = 1-\\frac{t_{abrite}}{100}*0.3' title='k_{corr} = 1-\\frac{t_{abrite}}{100}*0.3' class='latex' \/> o\u00f9 <img src='https:\/\/s0.wp.com\/latex.php?latex=t_%7Babrite%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='t_{abrite}' title='t_{abrite}' class='latex' \/> est le pourcentage de temps pass\u00e9 dans les roues.<\/p>\n<p style=\"text-align: center;\">Par cons\u00e9quent, si <img src='https:\/\/s0.wp.com\/latex.php?latex=t_%7Babrite%7D+%3D+100&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='t_{abrite} = 100' title='t_{abrite} = 100' class='latex' \/>%, <img src='https:\/\/s0.wp.com\/latex.php?latex=k_%7Bcorr%7D+%3D+0.7&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='k_{corr} = 0.7' title='k_{corr} = 0.7' class='latex' \/><br \/>\nsi <img src='https:\/\/s0.wp.com\/latex.php?latex=t_%7Babrite%7D+%3D+0&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='t_{abrite} = 0' title='t_{abrite} = 0' class='latex' \/>%, <img src='https:\/\/s0.wp.com\/latex.php?latex=k_%7Bcorr%7D+%3D+1&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='k_{corr} = 1' title='k_{corr} = 1' class='latex' \/><\/p>\n<p style=\"text-align: left;\">L&rsquo;\u00e9quation tenant compte de l&rsquo;aspiration est donc :<\/p>\n<p style=\"text-align: center;\"><img src='https:\/\/s0.wp.com\/latex.php?latex=C_%7Bm%7D+%3D+K%5Cddot%7B%5Ctheta_%7Bp%7D+%7D+%2B+%5Cleft+%28+%5Clambda_%7B1%7D%2B2.+%5Clambda_%7B2%7Dt+%5Cright+%29+%5Cdot%7B%5Ctheta_%7Bp%7D%7D+%2B+%5Cleft+%28M_%7Btot%7D+%5Cright+%29+.g.a.t.sin%28%5Calpha%29+%2B+k_%7Bcorr%7D.C_%7Baero_%7Bp%7D%7D&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='C_{m} = K\\ddot{\\theta_{p} } + \\left ( \\lambda_{1}+2. \\lambda_{2}t \\right ) \\dot{\\theta_{p}} + \\left (M_{tot} \\right ) .g.a.t.sin(\\alpha) + k_{corr}.C_{aero_{p}}' title='C_{m} = K\\ddot{\\theta_{p} } + \\left ( \\lambda_{1}+2. \\lambda_{2}t \\right ) \\dot{\\theta_{p}} + \\left (M_{tot} \\right ) .g.a.t.sin(\\alpha) + k_{corr}.C_{aero_{p}}' class='latex' \/><\/p>\n<p style=\"text-align: left;\">Cette \u00e9quation nous permet d&rsquo;\u00e9crire quelques remarques int\u00e9ressantes :<\/p>\n<p style=\"text-align: justify;\">La r\u00e9sistance a\u00e9rodynamique varie suivant le carr\u00e9 de la vitesse. Cette r\u00e9sistance augmente par cons\u00e9quent avec la vitesse de fa\u00e7on exponentielle. L&rsquo;aspiration pouvant permettre de r\u00e9duire ces pertes de 30%, il est primordiale de savoir s&rsquo;abriter correctement lors d&rsquo;une sortie en groupe pour maximiser ses performances.<\/p>\n<p style=\"text-align: left;\">Lorsque le vent nous arrive de cot\u00e9 (i=90\u00b0 ou i=270\u00b0), sa participation \u00e0 la r\u00e9sistance \u00e0 l&rsquo;avancement est th\u00e9oriquement nulle puisque cos(i)=0. Si i est entre 90\u00b0 et 270\u00b0, cos(i)&lt;0 : le vent devient moteur.<\/p>\n<p style=\"text-align: left;\">La position du cycliste sur son v\u00e9lo est fondamentale : le fait de passer d&rsquo;une position bras tendu \u00e0 une position a\u00e9ro permet en effet de r\u00e9duire son SCx de pr\u00e8s de 24% (<img src='https:\/\/s0.wp.com\/latex.php?latex=%5Cfrac%7B%280.41-0.31%29%7D%7B0.41%7D%2A100&#038;bg=121315&#038;fg=ffffff&#038;s=0' alt='\\frac{(0.41-0.31)}{0.41}*100' title='\\frac{(0.41-0.31)}{0.41}*100' class='latex' \/>) et de r\u00e9duire d&rsquo;autant les pertes a\u00e9ro.<\/p>\n<p style=\"text-align: left;\">Les conditions climatiques ne sont pas sans incidence sur les pertes a\u00e9rodynamique.En effet celles-ci sont d&rsquo;autant plus faibles que la temp\u00e9rature est \u00e9lev\u00e9e, que la pression est faible (altitude) et que le taux d&rsquo;hygrom\u00e9trie est grand.<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Approximation de l&rsquo;\u00e9quation du mouvement d&rsquo;un v\u00e9lo montant une pente en ligne droite et en prenant en compte l&rsquo;a\u00e9rodynamisme.<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"ngg_post_thumbnail":0,"footnotes":""},"categories":[60],"tags":[],"class_list":["post-1561","post","type-post","status-publish","format-standard","hentry","category-mediansports"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>MeDiaN@Sports - \u00ab L&#039;A\u00e9rodynamisme \u00e0 v\u00e9lo \u00bb - MeDiaN@Tour<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/medianbox.fr\/wordpress\/?p=1561\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"MeDiaN@Sports - \u00ab L&#039;A\u00e9rodynamisme \u00e0 v\u00e9lo \u00bb - MeDiaN@Tour\" \/>\n<meta property=\"og:description\" content=\"Approximation de l&#039;\u00e9quation du mouvement d&#039;un v\u00e9lo montant une pente en ligne droite et en prenant en compte l&#039;a\u00e9rodynamisme.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/medianbox.fr\/wordpress\/?p=1561\" \/>\n<meta property=\"og:site_name\" content=\"MeDiaN@Tour\" \/>\n<meta property=\"article:published_time\" content=\"2010-11-28T21:24:00+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2014-08-13T20:41:53+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/medianbox.fr\/wordpress\/wp-content\/uploads\/2010\/11\/SCx1.png\" \/>\n<meta name=\"author\" content=\"MeDiaN\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"\u00c9crit par\" \/>\n\t<meta name=\"twitter:data1\" content=\"MeDiaN\" \/>\n\t<meta name=\"twitter:label2\" content=\"Dur\u00e9e de lecture estim\u00e9e\" \/>\n\t<meta name=\"twitter:data2\" content=\"7 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/medianbox.fr\\\/wordpress\\\/?p=1561#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/medianbox.fr\\\/wordpress\\\/?p=1561\"},\"author\":{\"name\":\"MeDiaN\",\"@id\":\"https:\\\/\\\/medianbox.fr\\\/wordpress\\\/#\\\/schema\\\/person\\\/e1cba8e776ddbc5e91ef69e134732c6d\"},\"headline\":\"MeDiaN@Sports &#8211; 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