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Rigids can be L " smooth 6
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How effective can aerodynamic rigids prove on typical multi-drop operations? CM talks to bodybuilders to find out.
Words: Steve Banner
Spend only a short amount of time on Britain's motorways and you will soon spot one of Don-Bur's distinctively-styled Teardrop trailers With a curved rooif, designed to cut aerodynamic drag to reduce fuel consumption, the trailers are producing an average 11% improvement on fuel for operators, claims the company. And if fuel consumption goes down, so do CO2 emissions As well as the tangible benefits it brings, running such a trailer is a public statement of the operator's commitment to being environmentally friendly.
"From that viewpoint, it's a marketing person's dream," says Don-Bur group marketing manager Richard Owens Yet while investing in aerodynamic treatments for your trailers and the tractor units that haul them makes economical sense if you are on trunking work covering mile after mile at reasonably-steady speeds, the benefits of doing so if you run a fleet of rigids seem less clear cut.
While some rigids spend a large chunk of their working lives on motorways, much of their time is inevitably spent on stop-start urban operations If you are grinding along at 5mph in traffic, all the spoilers, collars and side skirts in the world seem unlikely, on the face of it, to cut the amount of diesel you burn.
Such considerations have not, however, prevented Stoke-on-Trent's Don-Bur from producing a version of the Teardrop body for rigid chassis, or a number of operators from buying it. "We've built a significant quantity over the past two years," says Owens -It's difficult to validate any cut in fuel usage in an urban environment, but we would expect a saving of up to 8% if the vehicle is involved in long inter-city runs,he continues, "As far as purely urban work is concerned, you may find that driver training [to drive more efficiently] and cutting the vehicle's weight will have more of an impact than aerodynamics" Many rigids do face comparatively long runs from out-of-town distribution centres before commencing their urban delivery runs Concept Translating the Teardrop concept onto a rigid has not been easy, Owens admits "The required curve is difficult to achieve," he says "The length of a rigid's body compared with the length of a trailer means you risk ending up with something the shape of a bubble rather than the shape of a teardrop. Getting it right is an engineering challenge," adds Owens.
The optimum body length for a rigid Teardrop is 28ft: says Brian Moran. operations manager at The Delivery Co, the transport division of the PaperlinX group. Last year. he put eight Scania P320 6x2 26-tonne rigids into service with Teardrop curtainsider bodies and is pleased with their performance.
Five of them are fitted with single-deck bodies and are showing an average 9% to 9.5% improvement in fuel usage, he reports, while the three double-deckers are achieving an average 5% improvement. "The latter are slightly less aerodynamic than the former," he says.
"A single-decker operating out of our Ipswich depot achieved a 17% improvement, although the average for Ipswich is more like 12%," he adds.
The twin-deck Teardrops sit on low-slung chassis that give them an overall height of no more than 13ft, says Moran. "If we went to 1411, we'd be struggling to get to some of the places we need to go to becau.se of overhead obstructions," he says.
Efficiency
Keeping the height low contributes to the trailer's aerodynamic efficiency. Although buckleless curtains cheat the wind more than their buckled equivalents, Moran did not specify them. "They don't bring you that much of an aerodynamic benefit and they wouldn't suit our work," he observes, "We're pleased with our Teardrop Scanias and the drivers have taken to them too," he continues, "In fact, one of them took his to Truckfest."
However, fitting the streamlining package has increased their unladen weight, says Moran. "Our Teardrop 26-tonners are about 900kg heavier than the standard model," he says.
"However. I'm confident we can improve on this next time round by looking more carefully at the specifications."
The Scanias, which haul paper and plastics, are engaged in a pattern of multi-drop work that involves long motorway stints, so noticeable boosts in fuel efficiency are perhaps not surprising, despite the weight penalty.
Feedback from firms that have invested in Bevan Group's aerodynamic curved-roof Bevarr21 body for rigids indicates, however, that they are seeing cuts in diesel consumption averaging up to approximately 5%. even on urban runs, says business development manager Simon Lake.
"No matter what happens, it will always cut through the wind better than a straightforward box," he says.
Benefit
The Bevan2I built by the West Midlands company has the added benefit that its fuel-saving advantages arrive independently of driver behaviour, Lake points out. Regardless of how lightor heavy-footed the driver is on the accelerator pedal, aerodynamics will still bring a benefit.
Despite the complications imposed by the short body length of a rigid, streamlining a rigid is easier than streamlining a tractor unit/semi-trailer combination in one respect: with a rigid, the cab-top aerofoil that is invariably fitted will always be at the correct height to reduce wind drag in relation to the body, assuming it has been installed correctly, but a streamlined trailer may end up being coupled to a unit with a cab-lop moulding set at the wrong height, which would result in the aerodynamics being ruined.
As indicated by the figures from Millbrook, combining a curved roof with a cab top moulding and collar will aid fuel economy. Side skirts help too, but risk suffering damage on city-centre work or through careless forklift operatives.
Bear in mind that side skirts for a 7.5-tormer will cost you £125 per metre plus fitting, according to Kuda. With a site at Nedging Tye not far from Ipswich, it supplies a variety of aerodynamic aids.
A cab top spoiler plus collar will cost £750. falling to £495 if you want just the spoiler, says the him, excluding installation. Collars, spoilers and skirts should help you cut diesel usage by about 6%. depending on the work the rigid is on, says Kuda, stressing that such an improvement is difficult to quantify. A fall in diesel usage has to be balanced against the extra costs associated with the construction of an aerodynamic body. says Owens."But they add up to less than £1,000 as far as a Teardrop rigid is concerned," he states.
Costs
"The full treatment the 7.5-tonner tested at Millbrook would cost up to £2,000. excluding side skirts but including the curved roof, the collar for the cab and so on," says Bevan's Lake.