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Past Issues

September 2005

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Wind deflectors

 

The dramatic increases in diesel prices over the last year have no doubt driven many transport operators into a state of near panic. With fuel costs accounting for around 33% of operating costs, their troubled sentiments are well founded especially given that diesel prices don't look set to decrease or stabilise any time soon and therefore, transporters need to look seriously at ways to cut fuel consumption. Green Band driving, reducing idling time and smart route planning are just some of the strategies used to achieve this. Another method is overcoming the often-overlooked problem of drag writes Paul Collings.

Let's face it, a truck isn't the most aerodynamic of vehicles," says Cameron Dudley-Owen, MD, Aero Truck, a Gauteng-based manufacturer of fibreglass Wind Management Systems, also known as wind deflectors. "Volume vans and articulated trailers in particular, have a substantial flat front-end that creates significant wind resistance which drives up fuel consumption."

Streamlining fleets
Dudley-Owen uses a flowing water analogy to explain his point: "Place a brick in a stream of water and you'll see the eddies of water that are created on the top, sides and rear of the brick. That's what happens to your average truck travelling at speed. 

"With an artic, wind passes over the cab roof and then hits the trailer bulkhead, creating eddies between the cab and trailer which produce significant drag and increased fuel consumption. On the other hand, if you placed a rounded pebble in the stream, you'd see the water passing smoothly over and around the pebble. In automotive terms, the pebble is a sports car. To create this effect on trucks, you need to effectively manage wind and resulting drag by streamlining the front, top, sides and rear of the vehicle." 

One only needs a basic understanding of physics to grasp the concept of aerodynamics and how it applies to moving trucks. The question is: Will a retrofitted wind deflector make any difference to fuel consumption on new trucks that have been put through extensive wind-tunnel tests and are fitted with components designed to optimise fuel consumption? 

Over the top
"Trucks are certainly a lot more aerodynamic and fuel efficient these days than they were twenty years ago," says Dudley-Owen. "The problem of drag arises when you fit a trailer or body that exceeds the height of the cab. Take a look around at volume vans of all sizes without deflectors and you'll see a gogga line on the bulkhead, showing clearly where the vacuum ends and where the wind and insects strike the trailer. A properly designed wind deflector will ensure the smooth movement of wind over the top of the trailer or van body." 

Dudley-Owen explains that while new cab designs are sleeker, bodies and trailers should also have rounded corners and edges. He adds that narrowing the gap between cab and trailer/body will also help reduce drag significantly, as will fitting an under-bumper dam, side skirts below the trailer/body and a rear-body roof taper to prevent a vacuum occurring behind the vehicle.
 

OEM buy-in
An interesting point is that certain Volvo, Scania and Freightliner models come fitted standard with air deflectors while other marques don't. 

"This is because vehicle height regulations differ from country to country," says Dudley-Owen. "In Sweden, for example, it's 4 metres. In South Africa it's 4.3 metres. The OE standard-fitted deflectors don't do the job effectively on a 4.3 metre bulkhead."

He adds that Nissan and Mercedes Benz supply Aero Truck with new models and facelifts to ensure a consistent design 'look and feel' between vehicle and the fibreglass wind management system. "Our systems are becoming increasingly popular with truck dealers who use them as a value-add to the sale," he says.

So who is buying wind deflectors in South Africa today? "Our main customer is the intermediate-size fleet owner running anything from small volume vans to long-haul artics. The corporate fleets have too much red tape to wade through to justify the purchase of a system, while the mid-size operation has a hands-on boss who realises the benefits of improved aerodynamics." 

Do the maths
And what benefits can a customer expect? "Firstly, for the skeptics, we offer a free 60-day trial on our units. With the correct driving style, i.e. taking the foot off the throttle a little to accommodate for the improved speed, the operator should see a fuel saving of between 6-8%. Our units sell for just under R10 000 and easily pay for themselves within the first year. Drivers will also benefit. Less drag means less driver fatigue."

There can be no denying that cutting fuel costs as much as possible is imperative to running a profitable transport operation these days. A wind management system costs relatively little compared to a truck's annual fuel bill. They are worth taking a look at.