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Old 08-03-2014, 12:23 AM   #21 (permalink)
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Here's a link to a thread with a post by Bondo about his patent (8,408,626) on reducing drag on semi trailers: http://ecomodder.com/forum/showthrea...-20744-11.html. They must be in production by someone because I've seen 2 or 3 going down the road in the last six months. Course, it wasn't until I found his post that I read the patent and understood how they worked. The first one I saw, I actually thought it was some kind of weather shield for unloading on an uncovered dock in the rain, sigh. Just couldn't put "aerodynamics" and "18 wheeler" together mentally :-).

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Old 08-03-2014, 08:04 AM   #22 (permalink)
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AirFlow BulletTruck Project
http://ecomodder.com/forum/showthrea...tml#post289346
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Old 08-03-2014, 04:06 PM   #23 (permalink)
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Thanks, Nemo, for the BulletTruck link, great stuff there. I also wanted to give a link to an article at another site: Getting Better Fuel Mileage (Trucks) • Speed Talk. This site is primarily oriented towards building drag race engines but there is a lot of discussion about engine efficiency and some aero. One interesting tidbit from this article is the comment that cab to trailer front spacing needs to be under 24" and ideally 15-18". By 24" the drag has risen noticeably, and at 48" the drag is the same as two independent vehicles. Has anyone seen any other guidelines on this? That poster doesn't give a reference.
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Old 08-04-2014, 08:34 AM   #24 (permalink)
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I saw one of these the other day on the freeway and snapped a photo (attached).

Foldable tail extension!
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Old 08-04-2014, 12:14 PM   #25 (permalink)
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Old 08-04-2014, 12:41 PM   #26 (permalink)
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If those drawings are to scale it looks like when the gap is one tire diameter the Cd has risen about 40% of the total loss, and at 1/2 a tire diameter the Cd has only risen 12% of the total loss. So if the tires are 36" tall (my guess, too lazy to go look), that would be a gap of 18" for the 12% of the total loss, and 36" for the 40% of total loss, which compares pretty well with the 24" max guideline in the article I linked. Thanks, freebeard.
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Old 08-04-2014, 06:04 PM   #27 (permalink)
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spacing

Quote:
Originally Posted by ijames View Post
Thanks, Nemo, for the BulletTruck link, great stuff there. I also wanted to give a link to an article at another site: Getting Better Fuel Mileage (Trucks) • Speed Talk. This site is primarily oriented towards building drag race engines but there is a lot of discussion about engine efficiency and some aero. One interesting tidbit from this article is the comment that cab to trailer front spacing needs to be under 24" and ideally 15-18". By 24" the drag has risen noticeably, and at 48" the drag is the same as two independent vehicles. Has anyone seen any other guidelines on this? That poster doesn't give a reference.
Here's one study

Here's one from GM illustrating the effect of gap-fillers





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Last edited by aerohead; 08-04-2014 at 06:19 PM.. Reason: add table
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Old 08-05-2014, 11:40 PM   #28 (permalink)
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Oops, need to correct a mistake I made in post #21 above - the patent by Bondo I listed is for his aerodynamic pickup truck bed extender. The patent on reducing drag on 18 wheelers with the box extension and vortex generators is by William Basford, number 6,959,958. Sorry bout that.

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