This section includes a brief description of the various aerodynamic components available. The generic term ‘container’ refers to the body (either fixed, such as a rigid body, or removable, such as an ISO container) within which the load is carried. Ensure that the features you choose are appropriate to the vehicle design and complementary to one another. Figure: highlights some of the most common features found on articulated and rigid vehicles.
Basic Vehicle Features: Basic features that influence the aerodynamics of a vehicle may be determined by vehicle specification, and must be considered when acquiring new or used vehicles.
- Cab/Container Gap Minimisation: Minimising the gap between the cab and trailer on articulated/drawbar vehicles is a simple way to improve aerodynamic performance. A large gap between an articulated tractor and trailer unit turns air downwards into the gap. This causes a change in pressure, increasing the total drag of the vehicle.
- Cab Front Edge Rounding: Vehicle drag can be reduced by rounding the front edge of the cab. The reduction you achieve will depend on the shape of the vehicle. With modern cabs, the side edges below windscreen level tend to be rounded.
- Cab/Container Height Equalisation: A closer match between cab and container heights will reduce the drag. Heights can be equalised by using deflectors or fairings, or by changing the body. Drag can be decreased further if a lower body is used, as this reduces the frontal area of the vehicle.
Truck Cab Features:
- Cab Roof Deflector: Fitted to a cab roof, this flat or contoured plate can be set at different angles to suit the body and is probably the most effective single add-on for vehicles using bodies of varying heights. The more the body extends, the more a well-adjusted deflector can offer potential benefits to reduce drag. If a trailer is not used, the drag on the cab will be much higher unless the deflector is lowered to its horizontal position.
- Cab Roof Fairing: This is the single most effective roof add-on when sized appropriately for the body, and may or may not be adjustable. Roof fairings are three-dimensional mouldings which fit on the cab roof and, if adjustable, can allow maximum savings with a range of differing body heights. Available as new or retrofit, fairings work by presenting the airflow with a smooth transition from the cab roof to the container.
- Cab Collar and Roof Fairing: This is either a fixed piece mounted on the front of the body or a rearward extension to a specific fixed roof fairing, available as new or retrofit. A collar makes the most effective transition between the cab and the body when used in conjunction with a suitable roof fairing, and it bridges the gap between the cab and the body along both sides and the roof.
- Cab Side-edge Turning Vanes: Usually located on the cab front edges below the windscreen level, these small extension pieces can reduce drag if they cover sharp edges and also help to reduce the build-up of road film and dirt. The feature needs to be specified when ordering a vehicle from new.
- Air Dam:Most modern vehicles come fitted with air dams, but they can also be retrofitted. Instead of allowing air to pass through the rough under-body, air dams divert air around the sides of the truck, thereby reducing the contribution of the vehicle under-body to the drag.
- Cab Side-edge Fairings: Cab side-edge fairings bridge the gap between the cab and body so are effective in reducing drag. Located at the sides of the rear cab edges, these fairings are available as new or retrofit.
- Tractor Side Panels: Tractor side panels cover the gap between the front and rear tractor wheels and can be fitted as new or retrofit. The panels reduce under-body drag by limiting the interaction of the airflow along the vehicle side with the vehicle chassis.
- Tractor Chassis Filler Panels: Tractor chassis filler panels have most effect on trucks with a large gap between the chassis members behind the cab. Available as new or retrofit, the panel is attached to the upper surface of the tractor chassis behind the cab.
- Chassis/Trailer Side Panels: These side panels cover the gaps next to the under-body on rigid vehicles or articulated trailers. Drag is reduced by limiting the interaction of the airflow along the vehicle side with the vehicle chassis. The panels are available as new or retrofit.
- Gap Seals or Vortex Stabilisers/Generators: A gap seal or vortex stabiliser/generator has the most impact on trucks with a large gap between cab and body. A gap seal is mounted on the front face of the body, extending forwards almost to the cab and vertically from the base of the body to the height of the cab. A vortex stabiliser is similar, but runs to just three-quarters of the cab height. Vortex stabilisers/generators can also be mounted on the cab collars. These features offer an effective alternative to cab side fairings on articulated vehicles.
- Container/Trailer Roof Tapering: Drag caused by the rear of a vehicle can be reduced by tapering the rear of the container or trailer.
- Trailer Roof Height Reduction: Drag can be reduced if the trailer height on articulated vehicles is lower than the tractor. However, the fuel efficiency benefit must be weighed against any loss in revenue resulting from having a smaller load space.
- Container Front Fairing: Container front fairings are mouldings around the edge of the front of the body or drawbar trailer. Fairings either are located around the perimeter of the container front or cover the entire container front above the level of the cab. The fairings encourage the airflow to stay attached at the front of the body roof and sides, thus reducing drag.
- Aerodynamic Sloping Front Roof Trailer: The aerodynamic sloping front roof trailer has been designed to improve the aerodynamic profile of articulated vehicles. The maximum potential internal load height is usually around 3.3 m, hence the lower foredeck is generally used for loose loads. These trailers usually come fitted with aerodynamic large radius cappings and glass reinforced plastic (GRP) skirts. An aerodynamic sloping roof needs to be specified when ordering a new trailer.
Ancillary (Add-on) Features
- Cab Roof Rim: This is a raised piece extending vertically from the front roof edge, and will be mainly beneficial for cabs which have sharp front roof edges. It also provides a good location to advertise an operator’s name, which is usually one of the main reasons for purchase.
- Cab Sun Visors: Sun visors can be specified in two designs and are added for driver comfort. One design extends out from just in front of the cab roof and, despite slight rounding of its edges, will increase the drag in nearly all circumstances. The second design is more rounded and extends over the top of the cab windscreen. This design rounds the front roof edge and can improve the aerodynamics of cabs with sharp front roof edges.
- Low-drag Mirrors: Rounding the front face of the mirrors can reduce drag, and the mirrors can also give the truck a smarter appearance.
- Additional Lights and Horns: These items will generally increase the drag of the truck, and are normally used only for cosmetic purposes. However, the negative impact can be limited if they are positioned back from the front edge of the cab.