Cheshire-based Cartwright Group has launched a new aerodynamic semi-trailer, which it claims has the ability to slash fuel bills by 16%. The Cheetah Aero System was developed in conjunction with TNT Express, the Department of Energy and the Transport Research Laboratory. TNT has just taken delivery of 86 of them following a successful year-long trial in which it slashed its annual carbon emissions by 13 tonnes.
Commenting on the new trailer, which shows a 42% total reduction in drag coefficient compared with a regular trailer, director John Cartwright explains that it incorporates many innovative aerodynamic features. Cartwright has been experimenting with aerodynamic aids for the past 15 years, and some of those used on the Cheetah have previously been included on other customers' trailers. However, this is the first time that all have been offered in one package.
He says one of the most important features is a specially-designed cab roof fairing, which together with the cab collars, results in significant improvements. The underside of the trailer has been tidied-up, producing a smoother surface. "Everything that doesn't need to be there has been moved out of the way," says Cartwright. The trailer's forward edges have been rounded-off, while the rear of the roof features an aerodynamic scoop to channel air and reduce turbulence.
Although bespoke tapered skirts have been fitted around the trailer, the decision was made not to cover the wheels. This, according to Cartwright, was done for safety reasons. He explains that covering the wheels can cause the brakes to heat up and can result in a fire. Likewise, there are no side-skirts on the tractor - as this has been shown in wind-tunnels to do nothing to improve the aerodynamics.
Although barely visible in these pictures, the sides of the TNT trailers have been tapered towards the top by 40mm on each side. This enhances the aerodynamic effect, but is only possible because TNT carries loose loads. With pallets, a more subtle tapering would be required. Cartwright explains that unlike some other aerodynamic trailers with radically different shapes, the Cheetah has the advantage of being standard height. He says no part of the roofline protrudes above the cab - keeping drag to a minimum. "If you start changing the shape of a trailer, you can't carry as much product," he says. "The Cheetah is a commercially viable trailer. After all, we aren't designing Formula One cars are we?"