Aerodynamic streamline template - online tool (view streamlined extension on any car)

[aerohead]

Originally Posted by Vekke

Why arent this or the other clearer templates pictures in use on the template tool?

The architecture of the 'template' is a function of ground clearance,and exactly where the location of the roof apex occurs.It's completely based upon ground reflection.
Without this context,the 'template' is useless.
Use of the 'template' as presented, prevents any confusion about it's methodology.

[aerohead]

Sorry for not linking, but surfing the web I came across this UFO:
Carlisle ARINC 791 SATCOM

[Vekke]

Tool uses the old template could somebody update the AST-II version of the template to the tool.

[aerohead]

Originally Posted by Vekke

Tool uses the old template could somebody update the AST-II version of the template to the tool.

I'd help if I could, but I've never had anything to do with creating this thread.

[dremd]

Do any of you guys have thoughts on how to use the template regarding Tesla model X fixed rear spoiler? I am considering building a hitch mounted cargo box/ boat tail. Does the spoiler stick out into airflow above template, or does it define part of the template? I kinda want it to define the template so I get additional height inside the storage box/ boat tail. Completely planning on blocking tail lights and license plate just run trailer lights and secondary license plate bracket. Good news about stuff like this is on a Model X is I’m unlikely to make it any uglier.

[freebeard]

The template is a generic solution and your Model X is a specific case. It lacks the semicircular cross section the template wants.

I'd start with Mair.

[aerohead]

here's my 'two-cents' :
1) While all streamlined profiles originate from bodies of revolution, their performance is NOT strictly limited to bodies of 'circular' cross-section.
2) Streamline profiles simply provide a super-velocity deceleration ramp, free of any adverse pressure gradient, which, if otherwise present, would trigger premature flow separation, and attendant higher pressure drag.
3) The AST-III ought to perform satisfactorily for the Model X, as it's original pop-up, three-position, rear deck spoiler's tearing edge appears to intersect the imaginary contour defined by the AST-III.
4) This is true of all Tesla passenger cars, especially the generation- II Roadster.
5) Following Franz von Holzhausen's development of the Model X rear slope, one observes three 'contours' with each following contour correcting aerodynamic 'sins' of it's preceding contour.
6) The backlight 'droops' to 24-degrees, which for a 40.7% roofline, well exceeds W. A. Mair's 22-degree downslope angle maximum recommendation.
7) Aside from all US NAVY torpedoes respecting Mair's 22-degrees, one also observes that all PGA & WPGA regulation golf balls happen to demonstrate flow separation at, or very-near 22-degrees slope angle, beyond which the boundary layer throws in the towel and leaves town.
8) The Von Mises inflexion sculpted into the Model X's deck relaxes the 24-degrees, down to 19-degrees.
9) The tearing edge of the pop-up spoiler further relaxes the 19-degree departure angle of the deck down to 12-degrees, which happens to coincide with the imaginary contour of the AST-III.
10) A fully-streamlined Model X would be 294-inches in length, vs 197- inches.
11) A 24" tail extension affixed to cargo platform would net a 221-" body length.
12) Rendering a fineness-ratio of 3.31969.
13) This is MORE 'slender' than:
* IONIQ 6, Cd 0.21
* Tesla Model S Plaid, Cd 0.208
* Lucid Air, Cd 0.20
* Mercedes-Benz EQS, Cd 0.20
* Rovomobil CAD, Cd 0.196
* VW XL1, Cd 0.189
* Lightyear 0, Cd 0.175
14) The 'elongated' Model X's ultimate Cd would be contingent upon plan-taper, and diffuser geometry, however, it would reside within Cd 0.21, to Cd 0.175 territory.
15) Aero wheels would enhance the boat-tails' performance.
16) Rear skirts would also enhance the tail's performance [ Lightyear's partial rear skirts provide a Cd 0.0033 ( 1.9% ) drag reduction, and additional 15-km range ]
Full rear skirts on the SAAB 9.3 sedan generated a Cd 0.016 ( 6.42% ) drag reduction.

[ERTW]

I have a question about which template is correct; the web app, or the jpeg in this thread? Refer to the Aston Martin Vantage pics. Web app in white, forum template in green.



Designers have been scaling the template to the leading edge of the bumper to good effect. the GM Precept concept had 0.175 in "production" state, and was a bit lower with some cleaned up details (around 0.157). It only contends with the air that's being pushed up over the car - it's not exactly in ground effect.



The Model Y does this as well. I think a box extending from the back would stop any downwash from the back screen and clean up the flow.

[aerohead]

https://ecomodder.com/forum/showthre...rt-c-9287.html

Originally Posted by ERTW

I have a question about which template is correct; the web app, or the jpeg in this thread? Refer to the Aston Martin Vantage pics. Web app in white, forum template in green.
Attachment 34467
Attachment 34468

Designers have been scaling the template to the leading edge of the bumper to good effect. the GM Precept concept had 0.175 in "production" state, and was a bit lower with some cleaned up details (around 0.157). It only contends with the air that's being pushed up over the car - it's not exactly in ground effect.
Attachment 34469
Attachment 34470

The Model Y does this as well. I think a box extending from the back would stop any downwash from the back screen and clean up the flow.
Attachment 34471

1) Both the 'green' and 'white' contour comparisons for the Aston Martin are 'correct', as far as proper use of the templates go.
2) As there are AST- Parts A, B, and C, they're only useful if among the three, at least one of them happens to coincide with the transition zone of some OEM roofline contour / silhouette, from the roof apex rearwards.
3) The full vehicle height alignment, from the road surface to the roof apex, as with the Vantage, is the only 'proper' application of the tool.
4) We're striving to establish the effective fineness ratio of the vehicle, in the context of the ground reflection technique, developed by Ludwig Prandtl and Edmund Rumpler, as this is related to the drag minimum possible at this ratio.
5) Mechanical Engineering did an article on the development of the GM, PNGV 'Precept' concept, contributed by the team members who developed the car. They attribute Cd 0.163 to the actual 1:1- scale car.
6) I don't have the Tesla Model Y blueprint with me today. With the optional, carbon-fiber rear spoiler installed, the spoiler's tearing edge happens to intersect the contour of the AST, version 'C', which has the most aggressive down-slope of the three.
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I've lost my source for posting images, and awaiting an acquaintance's finishing her Masters in Design. She's going to help me come back up to speed on sharing the dimensional analysis materials.
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Here is the original AST, which illustrates how a vehicle is analyzed in mirror image with ground reflection.
The image ended up at the top of the page.
If you'll look at the bottom row of illustrations, the table, that's 4th from the left depicts what the air 'sees' when your passing by. The above ground, and 'underground' bodies.
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The drag table to the left of the 'mirrored' VW Beetle is from Sighard Hoerner's 1965 book, AERODYNAMIC DRAG. You can see that the lowest drag known occurs at a fineness-ratio of 2.5:1, and Cd 0.04.
All three ASTs are based on the 2.5:1 length divided by diameter streamline body of revolution.
The 'half-bodies' generated from the 'full body' all have Cd 0.08, with ground clearance. When wheels are added, the drag climbs to Cd 0.12.
When extremely 'tight', full, swept wheel fairings are added, the drag falls to below Cd 0.09.
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As to why those who use ASTs to compare only the a vehicles' 'greenhouse', I'd be speculating.
On a LeMans Prototype ( LMP ) type race car, or supercar, in which the width of the greenhouse constitutes only a fraction of the vehicle's overall body width, the designer may be treating this structure merely as a 'blister canopy', as if it originated from a much 'smaller' car, and is then just glommed onto the main body, conserving frontal projected area. Don't know.