Trailer Talk

Some Aero Details Not So Obvious

Smoothing air flow saves fuel money, and every little bit adds up.

November 11, 2015

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Trailer portion of Freightliner's SuperTruck, displayed at the ATA expo last month, has large aero fairings and another so small you might not notice.  
Trailer portion of Freightliner's SuperTruck, displayed at the ATA expo last month, has large aero fairings and another so small you might not notice.

Trailer aerodynamics have become increasingly important in recent years as truck operators see that they can save fuel money. They’re so important that the federal government is paying several teams of truck and trailer makers to design concept rigs that show what’s possible in this area of science.

As far back as the 1980s I’ve written about various types of trailer aero fairings, from Nose Cones to TrailerTails and many brands of skirts and other appendages in between.

Here’s one I don’t recall writing about, at least not lately: the UnderTray and other products from SmartTruck. The company has posted a YouTube video depicting a tractor-trailer moving through the air at highway speed, with streamlines showing how the devices smooth air flow over the vehicle. Check it out here

This video leads to others on YouTube which further explain how the products work. In one of them, you’ll see lettering on a trailer proclaiming that the UnderTray was among HDT’s Top 20 picks in 2011. Of course I should’ve known that, but evidently my memory doesn’t reach back that far.

Also note the Diffuser, SmartTruck’s device mounted ahead of the rear underride guard that redirects air away from its vertical and horizontal members. These otherwise grab at the air and create drag. (Old timers still call this the “ICC bumper” because the old Interstate Commerce Commission required them, something I definitely don’t recall being a fact, but it’s part of trucking vocabulary.)

The trailer portion of Freightliner’s SuperTruck of course got large panels that improve air flow around corners, deep skirts to keep air away from the Strick van’s undercarriage and tandem, and a boat tail similar to a Trailer Tail, but home-made. One would expect all of those.

Leading edge of the rear underride guard's horizontal member has been curved to reduce air drag. Each corner of the member got this treatment.
Leading edge of the rear underride guard's horizontal member has been curved to reduce air drag. Each corner of the member got this treatment.

But, the underride guard also got attention. Daimler engineers affixed a piece of rolled sheet metal to each of the outer leading edges of the guard’s horizontal member. Those are not responsible for a whole lot of aerodynamic improvement, but represent the amount of detail work that went into the rig during its development. As the old saying goes, every little bit helps. 

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Author Bio

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Tom Berg

Senior Contributing Editor

Journalist since 1965, truck writer and editor since 1978. CDL-qualified; conducts road tests on new heavy-, medium- and light-duty tractors and trucks. Specializes in vocational and hybrid vehicles.

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