Quote:
Originally Posted by jimepting
Are you sure of this Phil. I have not seen wind tunnel smoke or tell tail data which would indicate separation. From the work that 3 Wheeler did, I though the rear met the template, if indeed that is an indicator. The rear most portion is only about 18 deg by my measurement. Could it have a Cd=.25 if it had separation?  |
I'm not scientifically sure,but I'll explain my comment.
*Honda's wind tunnel photo of the smoke trace over the Insight is shot from about the cowl position and at about door handle height.
* From Honda's technical drawing,some of the roofline is obscured in the photo.
*The smoke trace is more 'flattering',than if compared to a shot taken at 100-meters,closer to true-length.
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*From Honda's drawing,the departure angle at the roof terminus is 14-degrees.
*Jaray's pumpkin seed of 1921 had this angle at 32% 'Template' aft-body,for Cd 0.13 for his car.
* VW's 2009 1-liter car also uses it @ 32% for a Cd 0.195 car.
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* At 32%,Mair limits the boat tail to 13-degrees.
* Lay was at 12.5-degrees @ 32% and fetched Cd 0.12 for his car.
* Kamm used 13.5-degrees " ".
* The Kamm-Jaray model was 12-degrees.
* GM Sunraycer,10-degrees
* "template",12-degrees
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* Insight gets Cd 0.25 @ 34% aft-body
* 1999-2005 AUDI A-2 3-Liter gets Cd 0.25 @ 29% aft-body
* 1987 Renault Vesta-II gets Cd 0.187 @ 28.5% aft-body ( Vesta is a 'Template' aft-body form.
* New Beetle is Cd 0.38 @ 28% aft-body
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It appears that the shallower 'template' tangent angles are providing lower Cd's per body length which would be in accord with Hucho,who defined the 'template',and it suggests that separation is the culprit.
The Insight I&II are close.Same for Prius.
I don't think Toyota or Honda considered that folks like us would be picking up where they left off,so they might leave a little on the table,as Toyota's styling chief has eluded to.
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I am convinced that boat tail performance is absolutely dependent upon perfect onset flow and these tangent angles are of the upmost importance.
I'm not comfortable recommending anything less than the 'Template'.And I do believe that anything 'below' it is risking separation which is antithetical to streamlining.Again,I'm leaning on Hucho's words.
Sorry for the long answer,but the question merits the distance.