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SAVINGS
They look smart and provide a convenient space for additional corporate promotion, but does the addition of roof deflectors, side skirts and cab fairings add anything to the performance of your truck? Well, the short answer, in theory, is an unequivocal yes. It's "in theory" because there are many variables which govern the relevance of such equipment. There can be instances when adornments such as these might be a complete waste of money—much depends on vehicle application. John Westrup is managing director of Hatcher Components, which has been manufacturing air management kits for the past 20 years. He says: This is big business now and, as far as we are concerned, it is split between supplying the OEMs and feeding
demand within the aftermarket. "We manufacture kits used in the UK by Mercedes-Benz, Volvo and Iveco Ford as dealerfit options," Westrup adds. "We also supply one of Renault's factories in France. Sales into the aftermarket have diminished because so much is available at the dealer. Most tractors are now fitted with at least a roof-mounted air deflector at the time of initial purchase."
Benefits
So what are the benefits? Surprisingly, Westrup reports that he is not often asked this question these days, which is perhaps just as well because it remains a grey area. The primary aim of an air management kit is to save fuel. The fact that trucks need to be built for maximum volume makes life difficult, but improve
ments can be made.
Reducing vehicle drag by smoothing the passage of air between the tractor and trailer, or the cab and the body on a rigid, will enable the vehicle to cut through the air more easily, so the engine works less hard and fuel is saved. Any vehicle with a body which extends above the height of the cab roof can benefit from this type of addition. Westrup adds: "It seems now the industry has accepted the genuine worth of this equipment, which makes our job a lot easier. But actually quantifying the results can be tricky because of the variables involved. Many factors—everything from load and driving style to vehicle application and weather—have a real effect and so the potential savings vary.
But I would suggest that a sav ing of perhaps 8% is a reasonable figure to
assume and,
N4, although this can never be guaranteed, I see this degree of improvement frequently out in the field." A roof spoiler and side screens are the normal constituents of an air management kit for a tractive unit. Side skirts can also be included, as can skirts for the trailer. There is a good range of products on the market and prices vary accordingly. Your main choice is whether to buy from a dealer or deal with an aftermarket specialist. Westrup advises: "There is a significant price difference between dealers and independent specialists, as you would expect. Undoubtedly the quality of the dealer-fit equipment will be superior, but whether or not this difference justifies the price discrepancy is a debatable point. "The specialist produced products often tend to be handmade and the quality of the finish and metalwork will usually be slightly inferior," he says. "But in terms of performance I believe the practical difference is negligible. Effectiveness varies little between the two ends of the price scale."
Management
Whether or not your vehicle actually needs an air management kit depends on your business. Aerodynamic additions only start to have an effect once the vehicle is moving at a reasonable speed, so this equipment will have little effect if the truck is used for multi-drop urban deliveries. Westrup believes that development has just about reached its practical peak as far as design technology is concerned. He says: "Changes nowadays tend to be driven by vehicle design. When a new cab is introduced then a modified aero kit is required as well. I've never seen revised kit designs appearing in between model changes."
Simple air deflectors or blades came first, back in the late seven ties. These were adjustable for rake, with the idea being that you set it to follow a line drawn between the front edge of the cab and the top of the body.
Westrup says: "We had one tested at MIRA in 1978, and the results indicated a fuel saving of an impressive 13.6% at a steady 8 okrnth. And the Streamliner deflector was combined with an auxiliary fuel tank which, coincidentally, filled the chassis area around the fifth wheel. Tests were carried out with and without this tank, and its presence was shown to contribute positively to fuel consumption levels."
Leyland followed this with a flared "3D" deflector which really set the trend for future design styles.
The present market is dominated by variations on this theme, although simpler blade-type deflectors are still available. These remain easy to fit, with many bolting on to a framework, similar to a car roof rack, which attaches to the cab gt it Lers.
The potential for much greater levels of aerodynam ic efficiency is limited by current truck design. Westrup explains: "The flatfronted, bonnetless styling provides a headache in aerodynamic terms. The Americans are lucky and their preference for bonneted tractors means much can be done to streamline the shape. Here we are restricted to roof spoilers and side skirts along the trailing edges of the cab. Even the latter is limited by the need for articulation and the variation in trailer being hauled.
"Over the years there have been many wonderful attempts at bridging the tractor-to-trailer gap with flexible panels and concertina sections, but none has been able to withstand the operating conditions," he says. "I'm sure there are other areas vdiere improvements could be made, but these would probably only happen at the expense of load space. For example, large radius corners on the trailer would do a lot to help, but would also significantly reduce the loading capacity within."
The biggest growth area at present is for skirting on trailers. Westrup reports; This is becoming big busi ness now, although I believe its effects in terms of fuel savings are minimal. The trend has been driven by the food industry where operators find it important for their vehicles to look smart and clean at all times. Trailer skirts hide most of the unsightly running gear and provide a significant cosmetic effect. Another advantage is that they contribute positively towards spray suppression."
Skirts
In practice there seems little to count against air management kits. They have no detrimental effect on the day-to-day running
of the vehicle and do not interfere with tractor coupling or vehicle maintenance. Perhaps the only slight disadvantage, particularly with trailer skirts, is their vulnerability to damage. All of them are constructed from GRP so a careless fork-lift truck operator can wreak havoc.
Judging by the large numbers of trucks now fitted with aero kits, it seems safe to assume that their virtues have been accepted. No longer are they regarded as a gimmick; quite the contrary. They represent a valuable aid to more cost-effective vehicle running, and one which will pay for itself.