From: Jay Novak <[EMAIL PROTECTED]> Date: 2006/08/04 Fri PM 06:27:27 CDT To: [email protected] Subject: RE: [F500] Torque at 150 MPH
Excelent comment Jay, Chris S Well Chuck, anyone who actually knows the answer to your question will not say what the answer is. Thanks ... Jay Novak -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Chuck Voboril Sent: Thursday, August 03, 2006 10:00 PM To: [email protected] Subject: Re: [F500] Torque at 150 MPH Mark(Red Doggie?), I sent another post after that that corrected the ft-lbs to pounds on the Newtons, but you are right, I dropped rho somehow and didn't multiply it on my spreadsheet. So air density was 1 and not 1.2 kg/m^3 and Newtons were 20% low. One (me) can be fooled into believing that in steady state one only needs energy to keep the car there at a steady speed. When it finally dawned upon me that it would only be true for an instant, I realized that power is involved since energy is used over time. You put it very well "Force applied over a distance is work, and work per time is power. Power determines speed, maximum power determines top speed." 'course now that we have had this conversation, probably no one will take the bait in my last post to reveal what happened when they tried clutching with a falling RPM curve (to top end on the torque peak). I think that it was Q that was supposed to have tried that. Chuck >From: Mark Osterbrink <[EMAIL PROTECTED]> >Reply-To: [email protected] >To: [email protected] >Subject: Re: [F500] Torque at 150 MPH >Date: Wed, 02 Aug 2006 20:06:24 -0400 > >You were supposed to do it with LESS than 72 hp :) >In short, at any speed you are traveling over a distance in a time. While >you travel that distance, you are applying a force to overcome drag. Force >applied over a distance is work, and work per time is power. Power >determines speed, maximum power determines top speed. > >You have the drag equation right, but have a few errors from there. >1/2*CD*A*rho*V^2 = 0.5*0.6*0.5*1.2*67.056^2 = 809 N of drag force. >Newtons don't convert to foot-pounds, but would convert to pounds force >(675N is about 151 lb). >809 Newtons at 67 m/s = 54273 Watts, or 72.78 hp >Can't go that fast with that car with less than 72 hp. >Your example (72 hp @ 2500 RPM, 1.0 gearing and 10.1" tire radius) gets you >there within rounding errors, but that's because you started with the 72 hp >limit I gave you. > >If we take your 151 ft*lbf assumption, and apply it to 50 hp instead of 72 >you can see the problem. 151 ft*lb at 1739 RPM is 50 hp. 151 ft*lb times >the 1.0 gear ratio divided by the 10.1" radius gives us 809 N of force, so >we have enough force. But 1739 RPM times 1.0 gear ratio times 10.1" times >2pi only give us 104 MPH. If we change the gearing to give us 150 MPH, we >only have 556 N - not enough grunt. Can't get there with only 50 HP. > >Like I said, power is what's important, torque was invented to confuse and >misdirect :) > > > >Chuck Voboril wrote: >>Red Doggie, >> >>Don't really need a steam engine afterall. >> >>Assuming zero acceleration at steady state speed (and no mistakes in the >>SI vs English conversions) >> >>Using classic equation for drag force in Newtons using your Cd, frontal >>area, density of the medium, and speed in m/s. >>N=1/2*Cd*A*rho*v^2 >> >>I came up with 675.4 Newtons SI which converts to 151 ft-lbs. English >> >> >>Then, a motor which produces 72 HP at 2500 RPM will have the required 151 >>ft-lbs. >> >>10.1" radius tires, 1:1 gearing at 2500 rpm >>speed(MPH)=RPM*tire radius/(168*gearing) >> >> >>You do have a very valid point that HP cannot be ignored. >>It is totally tied to HP and RPM. >>However, since RPM was free, I used it to my advantage. > > >-- >No virus found in this outgoing message. >Checked by AVG Free Edition. >Version: 7.1.394 / Virus Database: 268.10.5/405 - Release Date: 8/1/2006 > >________________________________ >FormulaCar Magazine - A Proud Supporter of Formula 500 >The Official Publication of Junior Formula Car Racing >Subscribe Today! www.formulacarmag.com or 519-624-2003 >_________________________________ > > > >_______________________________________________ >F500 mailing list - [email protected] >To unsubscribe or change options please visit: >http://f500.org/mailman/listinfo/f500 >*** Please, DO NOT send unsubscribe requests to the mailing list! *** ________________________________ FormulaCar Magazine - A Proud Supporter of Formula 500 The Official Publication of Junior Formula Car Racing Subscribe Today! www.formulacarmag.com or 519-624-2003 _________________________________ _______________________________________________ F500 mailing list - [email protected] To unsubscribe or change options please visit: http://f500.org/mailman/listinfo/f500 *** Please, DO NOT send unsubscribe requests to the mailing list! *** ________________________________ FormulaCar Magazine - A Proud Supporter of Formula 500 The Official Publication of Junior Formula Car Racing Subscribe Today! www.formulacarmag.com or 519-624-2003 _________________________________ _______________________________________________ F500 mailing list - [email protected] To unsubscribe or change options please visit: http://f500.org/mailman/listinfo/f500 *** Please, DO NOT send unsubscribe requests to the mailing list! *** ________________________________ FormulaCar Magazine - A Proud Supporter of Formula 500 The Official Publication of Junior Formula Car Racing Subscribe Today! www.formulacarmag.com or 519-624-2003 _________________________________ _______________________________________________ F500 mailing list - [email protected] To unsubscribe or change options please visit: http://f500.org/mailman/listinfo/f500 *** Please, DO NOT send unsubscribe requests to the mailing list! ***
