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Minivan Kardboard Kammback boosts MPG +3.7% (6.6%, counting roof rack delete)
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While Trebuchet03 shows us how to do things by the book with CFD (computational fluid dynamics) to optimize a Kammback shape on his Jetta sedan, I employed the other kind of CFD on my brother's minivan:
Cardboard Fabrication with Ducttape :D This is a variation of Craig Vetter's CAD process: Cardboard Aided Design This was an A-B-A on road test under perhaps the most ideal conditions I've ever encountered on my favourite test road. No wind, no traffic, perfectly functioning cruise control :), tight distribution in the results. I'll post the full details later, but here's the skinny: Vehicle is a 2005 Pontiac Montana, long wheelbase version, 3.4L V6, automatic... http://ecomodder.com/imgs/montana-pa...boattail-2.jpg http://ecomodder.com/imgs/montana-pa...boattail-1.jpg (More photos below in post #20) This roughly slapped together Kammback, with fairly conservative angles (10 degree plan & roof taper), improved fuel economy by 3.7% in AAAA BB AA results. If you add in the initial roof rack removal I did to get to the clean roof, the total fuel economy improvement was +6.6%. That's significant, and hopefully may motivate some of you van/trucklet drivers. Absolutely nothing new here of course. Much attention has gone to studying and reducing the size of the wake behind trucks, since their cargo-carrying capability dictates a boxy profile with no taper at all. Researchers have known for decades that: Aerodynamic drag can be significantly reduced with trailer add-ons that reduce the wake and increase the base pressure. - Source: SAE 2000-01-2209 Edit: added the following, Nov 23... Details of the test... - Test speed: 88.5 km/h / 55 mph - Cruise control set once, cancelled with the brake pedal between runs; "resumed" for subsequent runs - Bidirectional averaged runs on a straight and nearly level test route; runs were abandoned & re-run where I was overtaken or caught up to another vehicle (aero interference) - Wind conditions were perfect: none! http://ecomodder.com/forum/attachmen...1&d=1227470567 A runs, average of all: 33.72 mpg (US) A runs, standard deviation (of average of bi-dir pairs): 0.35 mpg B runs, average: 34.975 mpg (US) B runs, standard deviation (of average of bi-dir pairs): 0.18 mpg Improvement of B over A: 1.255 mpg / 3.7% Roof racks on, Kammback off (one bi-dir run): 32.8 mpg (US) Improvement of B over roof racks: 2.175 mpg (US) / 6.6% |
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Is the rear hatch still functional? |
I don't see how it could raise ALL the way, but looks like it might go most of the way.
Fun project! |
Darin's amazing!
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Legal implications for the taillights? Most states have a visibility provision in the vehicle code... outlining exactly how much (area) of your taillight must be visible from a given angle... mostly rearward, but I believe they might have something to say about your blocking light from the side/rear-angle view. All in all, great work though.. and far less intelligence necessary to pull this off, making it a great mod in regard to effect vs. work/thought. We all like the thoughtless mods... like we don't have enough stress in our lives to add physical permutations of fluid dynamics and airflow based on a given scale to our schedules... roffle. All in all, a big :thumbup:.. can't wait for updates. |
Incredible result :thumbup:
The minivan is so long compare to the Kammback that I would have bet the difference was going to be non-measurable. It could be interesting to correlate the gain with the rear area reduction. It could also be interesting to see efficiency difference when the lower part of the Kammback is cut-out at the light level. (I will have to search again for an after-market cruise control available in France...) Denis. |
6% gas milage increase would be less 2mpg in that thing, thats hardly a deal to have to drive around with that on the back. I'm sorry but I dont feel 2mpg is enough of a savings to deal with that thing hanging off the back. you'd get better than 2mpg savings just driving ecostyle
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At $3 gas, 6750 highway miles/year*, 23 mpg = $58 savings. Less as gas drops, more as it increases obviously.
Another note: the speed of testing was just 89 km/h / 55 mph. Actual savings of course increase with speed. (* that's 45% of EPA's average annual distance of 15k miles total city+hwy) |
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This 6% is granted whoever drives, ecodriver or not. An ecodriver will have a 6% effort-less bonus, not negligible :cool: 15000 miles at 35mpg is 428 gallons 15000 miles at 33mpg is 455 gallons Result : 455 - 428 = 27 gallons free and 250 kg CO2 not sent to the atmosphere (see my sig). My son (and I if I'm always alive) will thank these efforts in 50 years. And this cardboard ecomod is only a test. Done in a more weather proof way, as metrompg and others know how to do it, it could be stealth. My white coroplast front grill block on my light grey car doesn't attire a lot of looks. Denis. |
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This was just a quick 'n' dirty test. A permanent version (my brother has no interest in one) would need proper lighting - lights brought out to the end of the addition is the obvious solution. |
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