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Road and workshop
Page 42
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Loads and forces (29)
• Last week I discussed higher speeds now being achieved by "'heavies" and the almost certain loss over the side of anything loose on the platform or loosely assembled. A trip down any of the motorways will clearly indicateanother hazard of increasing frequency. I refer to regular traces of shattered windscreens, either in a neat pile on a layby where a driver has personally cleared the blind or shattered screen himself, or thinly spread over several yards of road, where he has had it cleaned out for him by flying objects.
While it is true that you will see an equal number of both features, screen failures in the main originate from an impact of some kind. A few failures are caused by hitting a bump or hole, when a screen already biased in its frame will shatter, but all too often something arrives out of the blue from the opposing traffic across the reservation. By the time the unfortunate driver has realized what has happened, the culprit has gone and could rarely know what had happened.
A main cause of many screen black-outs is without doubt small debris such as coal, coke, light gravel and builders" materials, either from an open tipper or one very loosely sheeted-down. Most users of motorways have experienced something like a shower of hail on their car roof when closing up on or overtaking an open-topped tipper. While there is no particular risk when both are going in the same direction, it needs only a strong side wind or a fast curve, and opposing traffic is facing material arriving at around 100 mph.
One of my associates can confirm that a 1;in. piece of soft coke does not burst on impact with a screen, but goes on straight through. Most readers will remember that, during the summer, a flying brick shattered the screen of a car, killing the passenger. In this particular instance, it is not too clear whether the brick came from the load or was, in fact, held between the rear twins and thrown backwards. One thing is certain, however, and this is that the brick was not falling but travelling almost horizontally. The hail of gravel and other debris that wind pressure can lift from a tipper is a very real problem and can no longer be ignored. In many instances, open-topped tippers have a piled-up load with only a loosely tied sheet over the top. This sheet soon flaps free and if air can gain access at the front at gale force, material streams from the load.
Possibly one factor that tends to be overlooked is the tipper itself, as in the past it was never a particularly fast vehicle. Its differential ratio was usually suited to dealing with rough and heavy ground and it did not venture too far from base. Now, however, distance is no object, material is being delivered 300 miles by tipping vehicles and, while many of the special powdered regular consignments travel by tanker or tipping container that spill nothing, the general purpose tipper is still open-topped. Further, the speed of most of these recent tippers is equal to that of any other vehicle, and 60 mph is achieved with ease. In long-distance work using tipper equipment it is expected that full use will be made of motorway running. In my own case, where vehicles are needed with tipping bodies, it is expected that I will provide machinery suitable for site operations but at the same time able to keep up with traffic on motorways as required. This means seeking out the best axle ratio and quite often using two-speed axle or overdrive.
However, in the light of high-speed running with open-topped tipping vehicles, it is imperative that all tippers for use on fast roads be fitted with an ample supply of rope hooks right round the body and at least 2ft below the top of it. A good quality heavy sheet should be made up specially eyeletted and capable of being lashed down securely all round the body in such a way that neither can air gain entry or debris be spilled.
Tests have shown that almost any loose material will travel undisturbed at high speed Where care is taken to sheet correctly, and I find the best way to guarantee a good seal for the sheet is to bolt on all round the body, about 1ft from the top, a light 21n. by 2in, timber rail, suitably rounded to save sheet damage.