Landracing Forum
Tech Information => Aerodynamics => Topic started by: gasblender37 on March 27, 2015, 10:12:45 AM
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I am looking for drag coefficients for the different bodies used in the modified roadster classes.
Thanks,
Skip
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I'd guess that between 1923 and 1938 Ford (the most-popular make used) didn't do too many aero tests on their sub-sub-sonic roadster bodies -- which usually went down the road with a big top up.
And, as for use in Modified Roadsters, their aero probably depended on the shape of the builder's body fashioned from the firewall forward. Hardly any two are alike.
If someone gave you a clue on their body, it probably wouldn't apply to someone else's same-year body -- and not be reliable to use for comparisons to other years only.
You've also gotta look at Streamliners -- where there are hardly any restrictions -- and notice that almost all of them are also unique. (I'm not much help here, am I?)
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I think the closest shape to a 30's style roadster that there has been any aerodynamic testing on would be the Lotus 7 @ about 0.7.
Anything you chose is not likely to be much better, and it will definitely have a larger frontal area, but for estimates, I think that number would likely get you close.
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Even thou you may not like the look of them, get pictures of RO Yales Contrivance modifieds. You'll be chasing him anyway. To me they a bu-- ugly but I'm not in modified. One thing to consider is how the air leaves the design not only the hole it punches in the air...Good Luck..
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Al I can say is............
F R O N T A L
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Somewhere on this website there was this list by Dr Mayf, or Prof Mayf, that lists all sorts of drag coefficients. Maybe someone remembers how to get it. I forgot.
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Somewhere on this website there was this list by Dr Mayf, or Prof Mayf, that lists all sorts of drag coefficients. Maybe someone remembers how to get it. I forgot.
Close! http://www.mayfco.com/tbls.htm (http://www.mayfco.com/tbls.htm) :-D
Mike
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Besides frontal area, the grille shell is important. It is the most prominent front end feature. In the applications I've seen, the grille area is blocked so it acts somewhat like a flat plate. You want the minimum size and a round transition from front surface to side to promote flow attachment along the sides and top. Some of the roadster grilles seem to have rounder edges than others.
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in modified roadster (the class he asked about) I believe you can make any kind of nose you like, forward of the firewall. "streamlining ahead of and including the cowl (4.I.1) is permitted" 2014 rulebook
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Back to square one -- he's looking for the drag coefficients on the various Roadster BODIES.
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For Fords a 23 shoul be better than a 26/27 and on up......Contrivance is a 23
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in modified roadster (the class he asked about) I believe you can make any kind of nose you like, forward of the firewall. "streamlining ahead of and including the cowl (4.I.1) is permitted" 2014 rulebook
In the words of Rick Perry: "Oops". In the future I'll read the OP's post and rules book more closely. Thanks.
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In re: reading the rulebook more closely: Now you have a better idea of why I always suggest buying at least three copies of the rulebook -- station one by your easy chair, one in the shop/garage, and one on the back of the toilet. Whenever you're sitting down or working on the race vehicle -- read, read, and then read some more. :-D
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I picked up my copy at the GG event and ordered 2 more when I sent in my test and tune entry the other day
yep the rule book controls our lives almost!!!!!!!!!
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Re: the link in Reply#6. Does anybody know the legitimacy of drag coefficients in that table? The intro says they were derived by a "computer program"- whatever that means? It isn't clear to me what data they were based on.
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Back to square one -- he's looking for the drag coefficients on the various Roadster BODIES.
Thanks Stan,
Your right. I guess I should have asked what are the frontal areas of the various Roadster BODIES in stead of the drag coefficients :dhorse:
Thanks,
Skip
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If you read the text on Dr. Mayfields table page he says the data comes from a computer program called "cartest" available on the web.
I have no info on that program but that should give you a search key to find out more info about the program.
Looks like the source should be here:
http://www.cartestsoftware.com/index.php
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Please post the aero info for the old classic cars and hot rods if you find it.
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"Cartest" website doesn't even give a hint where the drag coefficient data originates. :?
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... Please post the aero info for the old classic cars and hot rods if you find it...
The only thing that comes to my mind, is an article one of the engineer-editors (Don Franciso maybe?) wrote in Hot Rod back in '53 or '54 (need to dig it out sometime). He showed a short list of "representative" vehicle types with ballpark drag coefficients. The only one I recall was drop-tank lakesters, at about 0.9 Cd.
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Here are a couple of sites that show some Cd's:
http://en.wikipedia.org/wiki/Automobile_drag_coefficient
The one above is mostly recent street vehicles, but it also shows JCB DieselMax and Goldenrod
There's more at:
http://en.wikipedia.org/wiki/Automotive_aerodynamics
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... http://en.wikipedia.org/wiki/Automobile_drag_coefficient...
A couple things of interest there-
> Typical Formula 1 car 0.7- 1.1
> Summers Brothers' Goldenrod 0.117