Streamlining against harsh wind: aerodynamics in commercial vehicles
Aerodynamics offer considerable potential for lowering fuel consumption and emissions in trucks and buses. Almost 40 percent of the total energy expended to keep a 40 ton truck moving at a constant speed of 85 km/h on a flat road section is to overcome air resistance alone.
Strict limits are however imposed on the aerodynamic improvements that can be made to trucks by manufacturers due to the legal requirements governing length and height. When developing the current TGS and TGX truck series, MAN was able to improve the air resistance by four percent compared to the TGA predecessor model through aerodynamic streamlining. Taking these existing general requirements into account, the best possible aerodynamic performance of the conventional front-drive truck has therefore already been achieved. If the legal requirements were to change, the air resistance of trucks could be significantly reduced.
MAN Truck & Bus presented an aerodynamically-optimised semitrailer truck at the IAA 2010 in Hanover based on the flow topology of a dolphin. The tractor which has been extended by 80 centimetres together with the semitrailer, increased in height by 20 centimetres and has a truncated rear end, achieves a sensationally low cW value of 0.30.
With the bus, the aerodynamics engineers have a much higher degree of design freedom as in this case the entire vehicle can be crafted from the front round to the side through to the rear as a form-locking unit. The NEOPLAN Starliner and Cityliner coaches are striking examples of this. The air resistance coefficients of cW = 0.36 or 0.35 already compare favourably with those of a passenger car.
This means that, compared to a conventional bus design, up to 10 percent fuel can be saved on long-distance routes at a constant speed of 100 km/h. A coach can therefore save around 1800 litres of diesel and 4.7 tons of CO2 for an annual mileage of 60,000 km.
