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Old 01-21-2019, 04:48 PM   #101 (permalink)
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Thinking of the rear undertray, I have a front-wheel drive vehicle with a box-beam rear axle. The axle is quite visible under the rear bumper. Would it be better to have the undertray below the axle[s travel] or above it with a teardrop profile added to the axle?

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Old 01-21-2019, 05:09 PM   #102 (permalink)
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Quote:
Originally Posted by freebeard View Post
Thinking of the rear undertray, I have a front-wheel drive vehicle with a box-beam rear axle. The axle is quite visible under the rear bumper. Would it be better to have the undertray below the axle[s travel] or above it with a teardrop profile added to the axle?
Sounds like my Insight - torsion beam rear axle. I went under the axle with the undertray (pic in video), using a steel frame to support the ABS sheet. In the case of the Insight, that also allowed me to incorporate a diffuser.
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Old 01-24-2019, 02:13 PM   #103 (permalink)
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Old 01-26-2019, 02:41 PM   #104 (permalink)
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Old 01-26-2019, 04:51 PM   #105 (permalink)
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The car shown in my profile pic lost 5mph of top speed after the ad hoc repairs after a collision. I think it was mostly from the elephant-ear fenders, not the always-popped-up headlights. That left headlight was like sighting down a laser pointer driving at night, but the whole nose from the A-pillar forward was replaced eventually.

Since we have OP and aerohead together in the thread, what do you think of this? It's the Theoretical Template, truncated with an exponential bell for a difusser.



The thinking is that the curved bottom edge would form vortexes that implode the wake compared to a straight edge.

The thinking on the Dasher was to put a kick-up in the undertray and have a wing on the axle that would apply to unsprung weight directly, but it's too complicated by the exhaust and gas tank.
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Old 01-26-2019, 06:17 PM   #106 (permalink)
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Since we have OP and aerohead together in the thread, what do you think of this? It's the Theoretical Template, truncated with an exponential bell for a difusser.


(
To be honest, I wouldn't know. The more I researched the subject, the less that I think people can tell just by looking. I read paper after paper where the engineers were surprised by the test results - whether that testing was in a wind tunnel or on the road. Maybe CFD at this stage? (And then take that as a 'best guess' rather than a definitive answer.)
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Old 01-27-2019, 08:20 PM   #107 (permalink)
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I just finished reading my copy of the book. Excellent job. This book could be more accurately titled "The Ecomodders Aerodynamic Bible".

I now know why my wheel covers did not affect the gas mileage.

My air dam also did not affect the gas mileage. I now know how to find out why, and then what to do about it. Full disclosure: The old air dam was made of brittle plastic and was in several pieces held together with Gorilla tape. There should be room for drag reduction.

My 100% grille block has never caused overheating, even on a long upgrade at 91 deg F with the AC running. I think I should look further into that also. There's room to further reduce drag.

He did miss one thing. The PNGV - Partnership for a New Generation of Vehicles, where GM, Ford, and Chrysler built full size cars capable of 72 to 80 MPG.
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Old 01-27-2019, 08:25 PM   #108 (permalink)
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Thanks for the praise.

He didn't miss the PNGV cars - he couldn't find any technical information on those cars' aerodynamics. (If there's any around, I'd love to see it.)
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Old 01-30-2019, 01:08 PM   #109 (permalink)
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Pngv

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Thanks for the praise.

He didn't miss the PNGV cars - he couldn't find any technical information on those cars' aerodynamics. (If there's any around, I'd love to see it.)
The only thing I've seen was in a circa 1999 Mechanical Engineering magazine,from an engineering student at the University of New Mexico,Las Cruces' campus,Central Plant.
It covered the development of the General Motors 'Precept' PNGV concept.
This car was bench-marked against an EV 1 test mule(Cd 0.197 according to GM),and at full-scale,in the Warren,Michigan,full-scale wind tunnel,recorded Cd 0.168,or 0.163,I'll have to check.
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Old 01-30-2019, 05:33 PM   #110 (permalink)
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GM PRECEPT and siblings

In my fanny pack I've got a small notepad,and in it found a note about the PRECEPT,listing Cd 0.163.
GM/AeroVironment had claimed Cd 0.19 for the 1987 IMPACT.
GM EV1 @ Cd 0.197.
GM EV1/Impact LSR,modified speed record car,Ft.Stockton,Texas,1993,@ Cd 0.14.
GM ULTRALITE concept,1991-2 @ Cd 0.192
GM CITATION-IV concept,1984,@ Cd 0.185 (running prototype)
GM CITATION-III concept,1983 @ Cd 0.14 (non-operative glider)
GM/AeroVironment SunRaycer (body only-no wheels) @ Cd 0.089
GM SunRaycer,World Solar Challenge,1987,@ Cd 0.125 (original claim)
GM SunRaycer as per Bob Boniface,@ Cd 0.143 (perhaps crosswind averaged Cd)
GM 'EPCOT' car (EPCOT CENTER Florida),@ Cd 0.23

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