Quote:
Originally Posted by Cd
So - Aerohead, what would happen if I created a nearly exact duplicate of the Aptera rear end from the end of my car's roofline ? ( 1993 Civic hatchback - same as the AeroCivic )
The curve of the Aptera swoops down out of the curve of the template and sweeps back again to the shape towards the end of the tail.
It would certainly shorten the overal length to use the Aptera shape.
While I have your attention, I'd also like to ask you how you had / have your front wheel covers installed on your truck.
It appears as though they have no rollers like the AeroCivic. Does the tire just rub against to backside ?
What keeps them in place ?
Have they been removed recently ? If so, why ?
- Thanks
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1) First, the Morelli form, with 4-wheels, has no discernible aerodynamic advantage over a K-form, fastback, as championed by W.H. Hucho (It's Cd can never be lower than 0.16 ).
2) Only a '3-wheeled' Morelli form would have an edge ( 1992, MIT Aztec solar race car / 2022 Aptera ).
3) The Morelli form is derived from a 1947 NACA ( NASA) 2-dimensional, mathematical algorithm which Professor Alberto Morelli studied into the weeds at the Turin Polytechnic Institute.
4) No 'styling' is involved in the Morelli form.
5) No 'committees' were involved in the Morelli.
6) Only Morelli and Sergio Pininfarina had anything to say about the Morelli form.
7) Every detail of every square-millimeter of a Morelli form's surface is generated mathematically.
8) There are serious ground clearance constraints imposed on Morelli forms.
9) There are serious body 'camber' constraints imposed on Morelli forms.
10) Geometrically, a 1993, HONDA CIVIC hatchback forebody possesses none of the architectural parameters necessary as the prerequisites to create the 'SOURCE' flow which allows an Aptera's aft-body 'SINK' flow to exist.
11) Aerodynamically, this really is an 'apples & oranges' situation.
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12) Hucho's only recommendation for low-drag revolved around ' a half-body, which forms a complete body of revolution together with its mirror image-produced through reflection from the roadway.' (This IS, by definition, the AST ).
13) The lowest drag streamline body of revolution has a Cd 0.04, which is satisfied by the AST.
14) This body of revolution produces a half-body of Cd 0.08.
15) Adding wheels pushes the Cd to 0.13.
16) Integration of the wheels into the body allows for a Cd which approaches 0.08, in ground proximity ( Hucho, page- 201, 2nd-Edition ).
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Until someone can provide 'better' solutions to those DIY'ers without access to industry-grade CFD or a full-scale wind tunnel, I'll remain an advocate of the K-form, fastback, based on the 2.5:1 fineness ratio streamline body.
Goro Tamai, of MIT, wrote in his 'The Leading Edge', that those without access to CFD or wind tunnel, would want to limit ( solar race car ) aft-body contours to within a 'rule-of-thumb, 17-degrees, to 20-degrees of the free stream flow.
23-degrees is Buchheim et al.'s limit.
W.A.Mair advocated for 22-degrees.
Hucho did not dispute Mair.
EPA said 22-degrees.
All dimpled golf balls experience flow separation @ 22-degrees.
Douglas Aircraft Corporation ( US NAVY Aviator ground school text ) flow imaging revealed an attachment limit @ 22-degrees.
I'm a chicken when involving hundreds of man-hours of member's time on complex, compound-curve fabrication that, they'd probably like to get 'right' the first time, so I'll remain a 22-degree maximum advocate.