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Artic wind drag trial shows fuE savings possible at speed

7th February 1975
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Page 63, 7th February 1975 — Artic wind drag trial shows fuE savings possible at speed
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IN EXCLUSIVE TRIALS carried out last week by Commercial Motor at the Motor Industry Research Association's proving ground near Nuneaton, it was shown that a wind drag reducer could bring down fual bills by over 10 per cent on a high artic van.

The result of the tests bears out the findings of an earlier experiment staged for the press by the importer of the American-made Airshield equipment, CT(London) Ltd, using two identical rigid box-vans (CM December13 1974).

Our test outfit was provided by Golden Wonder Ltd, whose transport manager, Mr Don Boote, is noted for his enterprise in pioneering vehicle innovations aimed at locating fleet operating efficiency. Golden Wonder's maxim m-length Ford York Freightmaster artic vans are nearly 3.65m (12ft) h gh overall. The front bulkhead of the t ailer van protrudes just about 1.5 m( in) above the domed roof of the tractor ab.

Dime sional details of the test outfit a D 1614 tractive unit (a Ford SVO special) coupled to a 12.3m (40ft 6in) long tr iler were supplied to CT, which elected to 1.04 m (41in) -high deflect° from the range ^available to provide the right kind of airflow over and aro nd the front of the trailer.

Whe an Airshield installation is fitted t an artic, the central fin or "vortex stabilizer", which helps to neutralize the rearward drag co ponent of side winds, is attached to I trailer, rather than forming an integ support for the main deflector on roof of the cab. This means that mi ancillary bracketry is called for support the Airshield on the roof o tractor cab nine pieces of hardwa in fact, without counting nuts, bolts a so on.

A firm anchorage for the deflectol obviously vital, and CT is curren working on standard fitting procedtu for the cabs of all vehicles curren going into service in Britain. It necessary to pick up on the ME support frame of the roof — integra welded on a steel cab, but often time runners in the low-volume type of grp design.

There is more to the aerodynamics of the Airshield system than meets the eye.

As viewed from the side, the deflector is much more vertical than one would expect it to be. This is explained by the fact that a vortex of air builds up in front of the Airshield at its base which itself creates a deflecting barrier — or ramp -to divert the main airstream just over the front edge of the trailer van's roof.

For mixed fleets of van and flat platform trailers the artic deflector can be arranged to hinge back to a near horizontal position so that its own drag effect is avoided when the trailer or its load is no higher than cab roof level.

Because of Golden Wonder's nonstandard trailer kingpin position — specified in order to maximize load space length — the cab grp is unusually small and the grp wedge-section Air shield trailer fin selected was only 450 mm (18in) -deep from front to back. For most UK artics a 600mm (24in -deep fin is recommended.

It was decided to measure fuel consumption at steady speeds of 64 and 80km /h (40 and 50mph) and at full throttle, around the MIRA high-speed banked track. The 64km/ h (40 mph) run was representative of traffic-free A-road running while the 80km/h (50mph) test was considered to be typical of motorway working, where drivers are diligent enough to hold down their speeds to a predetermined level in the interests of fuel economy. Just how realistic such a comparison is will vary from one fleet to another. • The full-throttle run, however, represented the effect of fitting an Airshield deflector on a vehicle whose driver • keeps his foot hard on the accelerator.

Consequently, our measured average speed reflects the benefits of stream lining on journey times as well as on fuel consumption. The full-throttle lap speeds were, in fact, increased by no less than 8.6km /h (5.4mph) or 9.7 per cent from 89km /II (55.4mph) to 97km/ h (60.8mph), so that an all-motorway 320km (200 mile haul could theoretically be completed 20 mm faster.

In practice the advantages of the Airshield equipment are dependent to a considerable extent on gvw. While over an essentially level route, like the MIRA track, rolling resistence is constant, the undulations on a long motorway haul will have the effect of building up momentum to relieve the engine of some of its work on upgrades. And the additional horsepower needed to push an unstreamlintd artic through the air compared with an equivalent deflector equipped outfit is likely to be a larger percentage on a lightly laden com bination. Golden Wonder is to monitor its fuel figures on the same vehicle on motorway running (laden in one direction only) with potato crisps and/or peanuts between the company's depots at Corby, Northants and Barnsley, Yorks.

Round the MIRA circuit formerly an airfield — the reduction in drag from fitting the Airshield device ought to give fuel savings of a similar order, whether the artic van is empty or laden, Accordingly, for simplicity, all our fuel measurement tests were carried out with the outfit unladen, weighing 7.95 tonnes (7 tons 171/2 cwt).

Wind speed was not a significant. factor on the day of the test, varying between 5 and .14km / h (9mph), southerly, as recorded by the indicator on MIR A's control tower. Ambient temperature was 6°C (43°F).

Our test procedure involved driving for 32km (20 miles) at a constant indicated speed and then at full throttle; the Ford's speedometer was later calibrated using M IR A's milepost markers and was shown to be about 3.5 per cent fast at 96km I h (60 mph). The whole procedure was repeated with the Airshield removed, but with its attachment brackets, on cab roof and trailer bulkhead, in place.

Results are summarized in the table below: Fuel consumed was measured through an American-made digital meter in the cab of the Ford. It can be seen that impressive though the fuel savings are through fitting the Airshield, an even more dramatic improvement in consumption is implied by a reduction in cruising speed. Easing off the throttle on the non-streamlin outfit just enough to bring the avera speed down from 89 to 80km/ h (55.4 50mph) will give a 27 per cent boost the mpg figure. And slackening off t cruising speed down to 64km ( 40 mph) — from full throttle — can gi almost 60 per cent more mileage frc each gallon of fuel.

By fitting the Airshield equipme and successfully persuading drivers keep their speed down to 64km (40mph) — probably an impossibil without the use of road speed govern( — motorway fuel bills could be slash in half.

In order to keep the benefits streamlining in prespective, it should remembered that the average vi bodied artic spends much of its ti plying ordinary A-class trunk roa where the density of traffic inevital brings down travelling speeds, throu both legal and circumstantial c( straints. The extra fuel burned wt accelerating away from roundabouts from other obstructions to free trai flow will have the effect of reducing • margin of benefit.

Mr Boote was suitably gratified w the results of our MIRA tests, an seems likely that in due course so kind of wind drag reducing equipmi will be fitted to the whole of the Golc Wonder fleet, which includes rigid a drawbar outfits, all with high, fl fronted bodywork.

We hope to report in CM on • company's lOng-term findings with test outfit in a few weeks' time.

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