It seems like putting lipstick on a pig, taking that old-as-the-hills, brick-shaped dry van and bolting on aerodynamic devices like side skirts, boat tails and scoops to reduce aerodynamic drag and fuel consumption. They are effective, but are such disguises the only way forward? Can or should the shape of the trailer be improved?
The short answers are “yes,” and “over my dead body.”
Tapering the rear of the trailer reduces drag; airflow management at the rear of the trailer is one of four critical areas of a tractor-trailer identified for aerodynamic improvements. Users, however, are wary of reduced cargo capacity, smaller or inconveniently positioned rear doors or complicated trailer loading that might result from changing the shape of the box.
The long answer is “yes, but it will likely take regulatory changes.” Changes to trailer design are, in fact, predicted in the new US Environmental Protection Agency’s Phase 2 greenhouse gas and fuel efficiency standards, which will be finalized in 2016.
“I suspect that the EPA change will result in changes to trailer shapes,” predicts Brian McAuliffe, a research officer in the aerodynamics laboratory, at the National Research Council Canada (NRC). He is also the thrust lead for the Enhanced Aerodynamics Performance thrust of the Fleet Forward 2020 program, which brings together experts and facilities from across NRC to offer technical R&D solutions to the transportation industry.
Under Fleet Forward 2020, NRC does aerodynamic testing and evaluations for OEMs and government regulators, and supports Canadian companies in the development of their technologies.
Currently, marketed trailer aerodynamic improvements fit into two main categories: bold shape changes like those seen in England, and North American successes in dolling up the pig without altering cubic volume or the rear doors. Possibly the most advanced expression of the technologies in the latter category is a Cummins-Peterbilt demonstration tractor-trailer, developed with support from the SuperTruck program, initiated by the U.S. Department of Energy.
In early 2014 Peterbilt Motors Company and Cummins announced that their SuperTruck managed 10.7 mpg in real-world driving conditions. Although they made many changes from tip to tail, including a lot of engine and transmission doctoring, Cummins and Peterbilt did not change the basic trailer shape. It did, however, push the designs of aerodynamic add-ons, big achievers and small, to wring more mileage out of the demonstration rig.
“A key goal of the project was to have no negative ripple-effects on a shipper’s operations. We set out to design a vehicle that can be seamlessly introduced into (fleets) without disrupting other areas of operations. Our research indicated that retaining the traditional box-van style of the trailer was essential to real-world adoption of the technologies we needed to develop,” explains Ken Damon, Peterbilt manager, vehicle performance group.
The real world has a way of putting a choke chain on innovation, although it can be persuaded to change.
Take two companies in Britain, the Cartwright Group and Don-Bur. They manufacture curvaceous trailers with rounded edges and sloping roofs that reduce drag and fuel consumption.
A sloping rear roof modifies the air wake, reducing suction at the rear of the trailer that causes aerodynamic drag.
Cartwright’s Cheetah has a conventional, straight-line roof at the front, but the rear half slopes down several inches.
Another of its designs slopes down at the front for smooth airflow from the cab roof and over the trailer. Cartwright reports fuel savings of up to 12% over a regular dry van.
Don-Bur’s Teardrop 2.0 trailer is tapered both in the front and at the rear. The company reports an 11.3% fuel saving and no loss – in fact, an increase – in cubic capacity.
Despite the acceptance of the Teardrop and Cheetah in the U.K., no such trailers grace our highways. The closest thing to them, and by close, I mean far, is the second version of a 2011 design collaboration among paper and packaging giant Cascades, trailer manufacturer Manac, FPInnovations and the University of Laval. This modified trailer sported a high-radius curve in the horizontal top front edge of the roof, rounded side edges up front, and a six-inch drop in the rear 10 feet of the roof. It failed to yield any fuel savings. Subsequently, however, Manac and Cascades built a second trailer, this time from scratch, that it has been road-testing since 2014 between Quebec and Ontario. Fuel records suggest a 3% fuel saving.
Those rounded front edges help reduce aerodynamic drag.
“Rounded corners in the front go a long ways. The wind is smoothly guided around the corner and stays attached to the vehicle,” McAuliffe says.
While not really changing the trailer shape, smoothing the trailer underbody may hold promise in reducing aerodynamic drag.
“My suspicion is that the biggest gains with current modern aero tractors are the underbody and base (back of the vehicle),” McAuliffe says.
A more radical idea is a variable-size trailer. A 2012 NRC technical report prepared for Transport Canada makes brief mention of a retractable trailer concept. Fully loaded, the trailer is a regular-sized dry van. But when it is less than full, the trailer can be partially collapsed to make it shorter.
Attributed to a British Columbia designer by the name of Brad Bennett, the upper walls and roof would winch up and down on an electric gear track assembly. Bennett reportedly claims that trucks, especially short-haul trucks, often travel from 15-50% empty over the distance of their trips.
This raises a tough question about trailer design.
“The challenging bit is how do you modify a box to be more aerodynamic but not to lose space and stay within the dimensions you are allowed,” asks Don Moore, executive director, Canadian Transportation Equipment Association. “Do we really know whether we are using all this space?”
Do carriers really need the full trailer volume? Is there an acceptable trade-off between volume, revenue and fuel cost?
“I would hope carriers have a pretty good grip on this,” Moore adds.
It is revealing that whenever designers are asked to sketch an aerodynamic trailer, they obligingly dash off a piece of truck porn straight from the pages of a 1960s Popular Mechanics magazine. Daimler, another SuperTruck program participant, did just that in a press release about its SuperTruck plans. Its concept drawing features a tractor shaped like a bottlenose dolphin’s head, and a smartly tapered trailer.
The overall effect is reminiscent of the Art Deco-style locomotive experiments of the 1930s.
In North America, however, these beauties have never been driven off the pages and into regular service. Daimler declined to discuss its trailer modifications for this article. The industry will have to wait till mid-2015 to hear the results of its testing, and whether its SuperTruck trailer deviates from that brick shape.
The early aerodynamic devices of the 1970s and 1980s met with resistance and the industry might not yet be willing to entertain changes in the dry box trailer shape. But GHG Phase 2 will include trailers. “There are a lot of discussions in the US between EPA and trailer manufacturers. From our perspective,” Moore says, “depending on what comes out of the GHG requirements, we are going to start seeing some changes.”
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