Over time, several devices and new aerodynamic shapes have been introduced to the trailer market in order to overcome aerodynamic drag, thus increasing fuel efficiency and reducing greenhouse gas emissions. Aerodynamic drag is the force that impacts on the movement of an object. A 20% reduction in aerodynamic drag can reduce fuel usage by approximately 6% at 50 km/h and 10% at 80 km/h. Improving the aerodynamics of a trailer can include a range of changes to the design – from streamlining the trailer’s shape; adding skirts, boat tails or air deflectors; to alignment and pneumatics. The addition of a trapped vortex, attached flow shaping to the front of the trailer, an undercarriage skirt, vortex strakes at the top and sides of the trailer, a boat tail and the patented Teardrop Trailer developed by Don-Bur Bodies and Trailers in the UK can all offer significant fuel savings.
To further increase efficiency, the gap between the truck and trailer should also be taken into account, especially in terms of distance, seals, extensions and air deflectors.
Most of the aerodynamic options that are currently available offer a quick return on investment with minimal impact on day to day operations, and little to no maintenance.
Approximately two metres in length, a boat tail is a tapering protrusion that is mounted to the rear of the trailer to offer dramatically improved aerodynamics and a 7.5% reduction in fuel consumption as shown in tests conducted by PART (Platform for Aerodynamic Road Transport) in Holland. These tests included wind tunnel experiments and computer simulations using small scale models.
To provide further evidence, an articulated vehicle was driven for one year with a boat tail and one year without in order to determine the realistic fuel savings that could be expected. Boat tails of various lengths were tested, and it was found that the optimum length was two metres. PART aims to reduce fuel consumption in the road transport industry by improving aerodynamics. It hopes to achieve a 20 percent reduction in fuel consumption and CO2 emissions by 2020.
Canadian based Transtex Composite is one such company that has developed a boat tail as well as undercarriage skirt. Transtex Composite supplies the market with a range of aerodynamic products and specialises in improving the aerodynamic properties of vehicles and transport equipment.
The National Research Council of Canada (NRC) conducted tests in 2006 using 1:10 scale models to test the concept of trailer skirts, boat tails and gap closure. It determined that these devices could be used alone or together to provide fuel savings. And low costs to install these devices and the increasing cost of fuel, make each of these economically viable options to reduce fuel consumption. NRC also found that a lower skirt provided better performance, as has been stated by many manufacturers. The length of the trailer did not hinder the performance of the skirts, as this device works by sheltering the trailer bogey.
NRC conducted these tests in a closed wall, closed return, atmospheric wind tunnel with a test section that was 9.14 metres high and wide, and 22.5 metres long. The maximum speed tested was 200 km/h with a turbulence level of 0.5 percent.
Trailer skirts by Laydon Composites Ltd, also in Canada were tested at the Goodyear proving grounds. Constructed from impact resistant ABS plastic and rubber, the Laydon trailer skirt was tested on a 53 foot trailer and Goodyear consistently measured a fuel saving of up to 6.3% on the test track in Texas.
In addition, Solus Solutions and Technologies in Virginia, United States has developed the Mini-Skirt. This patent-pending device has a controlled vortex to generate an upwash field that is captured by an inboard vertical panel therefore providing greater fuel savings than traditional trailer skirts. Solus claims that it offers fuel savings of up to 6% for ground clearances of up to 20 inches. Full scaled models of trailers fitted with the Solus Mini-Skirt were tested in wind tunnel experiments.
Ever-changing wind speeds and characteristics can impact a vehicle’s aerodynamic resistance, so creating a shape that can respond well to all wind speeds and directions is important.
The patented Teardrop Trailer concept offers fuel savings as well as greater load capacity. Don-Bur claims that this innovative design uses 10% less fuel and 10% extra volume. It produces 20% less fleet CO2 emissions, equating to approximately six tonnes per annum per trailer.
In producing this concept, Don-Bur wanted to achieve not only fuel savings, but also a cost-effective product with a quick return on investment. The trailer needed to be compatible with existing fleets, achieve a generous cubic capacity that would not alter existing payload capacities or loading methods and offer an aesthetically appealing design – and it seems that Don-Bur has ticked each of these boxes.
As the Teardrop Trailer needed to achieve significant fuel savings independent of other aerodynamic devices, trials were undertaken in comparison to prime mover and trailer combinations fitted with full aerodynamic devices. It was shown that the total resistant drag force on the Teardrop Trailer at 90 km/h was 35.7% less than a standard trailer, despite the increase in height. The aerodynamic effect increases as speed increases.
The streamlined shape of the Teardrop Trailer minimises any turbulence caused by a rapid change in object shape or surface direction. Main areas that cause turbulence on a prime mover and trailer combination are the gap between the truck and trailer, the front bulkhead, beneath the chassis and the large area of turbulence towards the rear of the combination.
Don-Bur has likened the design of the Teardrop Trailer to the perfect aerodynamic lines of a teardrop, which significantly reduces the co-efficient of drag by utilizing a specially designed continuous full-length curve along the roof. The roofline begins at 3.8 – 4 metres at the front of the trailer before gradually curving upwards and then tapering towards the rear.
The front bulkhead has a slight forward lean which reduces gap turbulence, with large radius rails to further minimise vortex effects.
The Teardrop trailer is available as a box van or curtain-sider and is currently used by a number of large fleets throughout the UK