7/3/2012
Old Trailers Sport Aerodynamic Look
By Tom Berg, Senior Editor
Are truck and trailer aerodynamics new? Not exactly. Labatt's Streamliners like the one shown on the right were built in the 1930s and might be the most aerodynamic looking tractor-trailers ever produced.
Looks can be deceiving. Image and promotion of beer sales, not fuel savings, were why they existed.
"I don't believe aerodynamics played a big role in the design of these trucks," says Bill Johnston, executive director of the American Truck Historical Society. "While they are very streamlined in appearance, given the engines of the day and speed limits in many areas of 45-50 mph, reduced drag wouldn't make much difference. These trucks were designed during the Art Deco period and were more of an advertisement than anything else."
They make a good story, though. Count Alexis de Sakhnoffsky, a French-Polish industrial designer, penned the images under commission from Labatt executives. White Motor Co. of Canada custom-built the tractors, and Smith Bros. Motor Body Works of Toronto crafted the bodies. Several series were built, and one won a design award at the 1939 World's Fair in New York.
Tight fits
The rounded noses on semitrailers of the 1930s and '40s might have had an aero advantage because a rounded surface moves through the air easier than a flat one, but that's not why they were built that way, Johnston says.
The reason was tight clearance between trailers and tractors, something required to meet strict length limits at the time. Close coupling reduced overall length, and a round nose allowed sharp turns without the trailer corners hitting the cab. Short overall length limits were set by states in the East and Midwest, and short, tightly coupled rigs were all fleets could run.
In the West, where highways weren't so crowded, limits were far longer. "Everybody liked the looks of California trucks," Johnston recalls. "They had a 70-foot overall limit and were stretched out. But there was a trailer limit of 45 feet. That's why there was so much space between tractor and trailer."
Eventually, various states increased their length limits enough to allow a little more gap between tractors and trailers. In the 1950s, longer trailers with flat noses began appearing. Shippers liked the extra volume possible in square-nose trailers, and tractors used diesels with more horsepower and torque than old gasoline engines, so they could pull the trailers against the air. Diesels also used less fuel - which was cheap, anyway. A common limit was 55 feet overall with 40-foot trailers, something that stayed in force in some states until federal pre-emption in 1982.
Much has changed since then. A couple of Arab oil embargos caused fuel shortages and drove up fuel prices in the 1970s, which got truckers thinking about saving fuel. They started with tractors, but makers of trailers and truck bodies began offering rounded corners on the vehicles' noses. A radius of 6 inches at the front corners and leading edge of the roof was shown to deliver some fuel savings at highway speeds without losing interior cube.
In the early to mid '80s, federal and state lawmakers further stretched length limits, to where 53-foot semitrailers are now ubiquitous, and the old cabovers were replaced by long conventional-cab tractors. Fuel became increasingly expensive, causing truck builders and operators to look more seriously at aerodynamics as one way to save money. Smoother, aero-style tractors evolved. However, only in recent years did trailers begin getting extensive aero treatments.
Fleet acceptance
Fleet adoption of trailer aerodynamics has been slow. Many managers view side skirts and other equipment as things that add weight and cost and are subject to expensive damage.
What really pushed fleet people into it, suppliers say, were rules established a few years ago by California's Air Resources Board, which is determined to cut fuel use and reduce greenhouse gas emissions in the state. Long-haul fleets sending 53-foot trailers into California had to comply or face citations, so they began equipping them to meet minimum requirements. Usually this means a pair of side skirts and low-rolling-resistance tires that have been designated as such by the U.S. Department of Energy's SmartWay program.
The amount of fuel savings depends on individual operations, including how often trailers travel at speeds high enough for the devices to work. For some, the savings are negligible and the devices not worth their extra expense. For others, money savings were eye-opening, say suppliers of aero aids.
Side skirts have undergone a fast evolution, changing from more or less rigid panels to flexible pieces and mounts that bend when brushed or banged by obstacles, such as high rail crossings, then pop back into shape. Some operators look not only at performance but also styling, preferring to enhance their image by buying skirts with lines that complement those of the trailer.
Gap sealers could be considered a throwback to the close coupling of tractor-trailers in the old days of trucking. Sealers, whether vertical panels or bulbous appendages on the trailers' noses, keep air from intruding into the space where it's otherwise whipped into drag-inducing turbulence. Some products are rather new, but others have been on the market for years. Close coupling does some of what sealers do, if drivers are willing to keep sliding fifth wheels set forward.
Those who use the minimum amount of equipment on their trailers can save just a few percent in fuel. The most successful operations use multiple pieces, usually including side skirts, gap sealers, boat tails, wheel covers and wide-base single tires on lightweight wheels. Big-single tire-wheel combinations lower rolling resistance and save hundreds of pounds of tare weight, often enough to offset the aero devices' penalty in pounds. All these devices combine to save 10% or more at highway speeds, providing a reasonable and sometimes fast payback for the equipment investment.
More developments for trailers are on the way. The DOE is funding several Super Truck projects that aim to save even more fuel and reduce hydrocarbon emissions. Started several years ago, these projects are headed by truck manufacturers whose partners are makers of aero aids, tires and other equipment. Some involve trailer makers as full or partial partners.
Track testing of advanced equipment has shown drag reduction of up to 30%, and fleet road testing is seeking to find out if that converts to the expected 15% in fuel savings in real-world operations. Durability and repairability will be closely monitored in the fleet tests, participants say. Look for results to be published beginning late this year or into 2013, in time for truck and trailer builders to begin using them to meet upcoming fuel economy standards for heavy trucks.
Beyond the box
Designers of aero improvers have thus far been dealing almost exclusively with long box-type trailers - vans and reefers. What about shorter vans and flatbeds, tankers and dumps? Less-than-truckload fleets that run short pup trailers have become interested in aerodynamic devices and are running some, says one supplier. Meanwhile, work is being done on other trailer types.
Drop decks on electronics vans are easier to work with than full-height vans. Results might be only a couple percentage points, but they need less material for the fairings so the ROI will end up about the same. The same goes for drop-deck flatbeds. Flatbed operators in general tend to put a lot of miles on their trailers, so there's more potential for saving fuel.
The aero task is complicated, however, because most flatbeds have a high stance, requiring more material for side skirts. The vehicles have massive understructures, and some frames are bowed, like a bridge arch, so side skirts have to be custom shaped to fit a given frame and profile. Loads tied to flatbeds also vary in size and shape. Stacks of pipe might move through the air rather freely, but a large piece of machinery can upset air movement and interfere with what fairings are trying to do. Limited tests show results similar to vans, at 3% to 5%.
Dump trailers and truck bodies are changing from heavy outside braces to smooth, welded sides that offer less air resistance. Some are aluminum, some steel and some made of composites. These can be stronger and are easier to clean, and although builders do not officially claim fuel economy improvements, they point to customers who say tractors do use less fuel while pulling them.
Tankers would seem to be basically aerodynamic, but structural members and equipment boxes pull at the air, and long tractor-trailer gaps can cause turbulence and drag. A few builders have smoothed the profiles, and one supplier says he has done a drag-reducing nose wrap for a tanker builder. One fleet operator found that removing the traditional large fenders up front and replacing them with smaller fenders over the tractor's tandem reduces drag.
Most improvements to vans and reefers have been with add-ons. Should manufacturers make smoother trailers to begin with? In Europe, a trailer with a curved roof is being tested, notes one aero supplier.
How about covering the underside of the trailer body? This has been done with aluminum sheeting and hen plastic panels, and it can save fuel. But one can imagine how they would interfere with inspections and how salty moisture would get inside and fester, accelerating corrosion of frames and crossmembers. Rounding the profile of crossbeams might be a better solution. A Canadian flatbed manufacturer now offers a "monocoque" trailer with a smooth underside that claims to save fuel.
For now, the best way to improve the aerodynamic shape of trailers is to use add-ons. Fortunately, there are a lot of trailer aerodynamic improvers on the market with proven results. Go to www.epa.gov/smartway for a list of products.
From the June 2012 issue of HDT http://www.truckinginfo.com/news/news-detail.asp?news_id=77398&news_category_id=67&utm_source=Email&utm_medium=Enewsletter
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