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Towards Square One in Tipper Design
Page 89
Page 90
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P. A. C. BROCKINGTON TALKS TO THREE TOP TIPPER DESIGNERS AND DISCOVERS THAT THE CONSTRUCTION AND USE REGULATIONS OFFER DOUBTFUL BENEFITS AT HIGH COST TO TIPPER OPERATORS. TECHNICALLY there is no objection to uprating the gross weight of four-wheel tippers from 14 to 16 tons. However, because of the additional weight of the heavier chassis, tipping gear and body, the maximum payload advantage will be only about a ton and in some cases will not exceed 14 cwt., whilst the extra cost will vary between E7011 and 11,000 according to the make A chassis.
The 22-ton gross, six-wheel rigid tipper is a doubtful starter in the C and U stakes necause the higher rating will afford a myload increase on average of not more :han 5 cwt. and at best about 10 cwt. The txtra 6 tons on the gross loading cornmred with a 16-ton four-wheeler could, therefore, yield a payload increase of ittle more than a ton. Because of their )oor manceuvrability and " unmanagetble" body length, plated eight-wheelers n any category are entirely unsuitable as ipping chassis, and body-length lifficulties are also unfavourable to :mploying uprated semi-trailer tipping mtfits. A workable solution to the tipper )roblem might, however. be provided by txploiting the jack-knife principle of Iperation.
These comments on tipping problems :mated by the new regulations summarize he conclusions of Mr, W. Meats, of felehoist Ltd., Cheltenham, and are in .lose accord with the views of Mr. L. :enton, of Welford Engineering Oldbury) Ltd., Tipton, Staffs, who points o the obvious inference that the regulaions were introduced with little regard o the requirements of tipper operators. dr. Fenton observes that, although the egulations enable trunking lorries to be nioduced to carry a greater payload with treater safety, they will encourage weight :aring of tipping lorries and the building :f vehicles with a reduced margin of afety. Moreover, enforcement of the egulations will be more difficult.
According to Mr. Fenton, the height ,f the body is an all-important factor in he load-carrying capacities of tipcated ipping vehicles, a high body reducing he payload advantage in the case of a laximum-load four-wheeler by at least 5 cwt. In general agreement with Mr. Meats, Mr. Fenton gives 15 cwt. to one ton as the normal range of payload increase for a vehicle of this type built to a satisfactory standard of safety and 0004800 as the extra cost, compared with a 14-ton gross machine. The allowable increase in rear-axle weight of 9 to 10 tons is regarded as a valuable concession in its application to 14-ton gross machines, the rear axle of vehicles in the existing category being frequently overloaded, The additional weight involved in stiffening the frame structure of a lowheight body is an unavoidable necessity. but one which represents economic use of a weigh( increment compared with the loss of payload resulting from employing a high body to contain a bulkier load. Regarding 22-ton rigid six-wheelers, Mr. Fenton draws attention to the penalty created by the obligatory wheelbase of Ig ft., which virtually precludes the use of a trailing axle because the necessary increase in weight well to the rear of the live axle would reduce traction to an unacceptable extent. The appeal of the six-wheeler has been perpetuated by licence considerations and by the reluctance of many operators to purchase eight-wheelers on the score of cost. Strengthening the chassis of an uprated 22-ton-gross machine and using a heavier tipping gear and body would reduce the payload advantage to well under one ton. and the vehicle would be uneconomic operationally unless it were specially designed, and used, to carry a bulk load.
Dealing with the potential of the 28ton-gross eight-wheeler, Mr. Fenton gives the maximum payload advantage as two tons. which would apply to a low-bodied vehicle, and an advantage of, say, one ton if ,a high body were employed, the additional cost of the vehicle being about £1,000.
In Mr. Fenton's opinion,. uprated trailer outfits are unacceptable economically for normal loads, mainly because of the greater weight of the longer bodies, of the strengthened chassis and of the more robust tipping gears. A tractor and fourwheel-in-line, 20-ton outfit can be built, he claims, to carry a payload of 15 tons, whereas it would be difficult to obtain a payload in excess of 14 tons with a 22-ton-gross machine.
Although the 28-ton-gross outfit offers a nominal increase in useful load of four tons to 18 tons, in practice it would be difficult to obtain a payload of 16 tons. The operator would, therefore, have to pay about £5,500 to £6,000 for a machine that would carry one ton more than a four-wheel-in-line outfit costing approximately £3,000.
Both Mr. Meats and Mr. Fenton observe that the application of a minimum power-to-weight ratio (of say 10 b.h.p. per ton) solely to plated vehicles could negative any payload gains nominally provided by the regulations. it would then be a case of returning to Square One and paying out a large sum of money to run heavier vehicles capable of carrying the same payload.
In a review of tipping-gear problems. with particular reference to the new regulations. Mr. Fenton observes that elevating the long bodies of high-grossweight tipping vehicles of the rigid or articulated type to an angle of 450 involves structural requirements that are extremely difficult to provide. A 30 ft. body equipped with front-mounted gears would require base rams of 7 in. diameter and top rams of 3 in. diameter, and this ANould not ensure safe tipping in the case
of sticky loads. Fitting a stabilizer increases weight and is not necessarily desirable, on the score that it ties the body too rigidly to the vehicle chassis frame, which is subject to severe deflection when the vehicle is operating on uneven ground. Ideally the vehicle should be equipped with hydraulically-operated stabilizing jacks, which drivers could be instructed to use intelligently. The alternative of employing a front-of-body gear in conjunction with an under-body type might be considered.
Weighbridge problems would be aggravated by the use of longer vehicles, in Mr. Fenton's opinion, because in a typical case the weighbridge attendant refuses to weigh each axle separately, particularly if there is a queue. Answering questions in his capacity as chief draughtsman of Edbro Ltd., Mr. R. G. Webster specifically mentions the fact that the new regulations allow a width of 8 ft. 21. in. This could help in obtaining better door hinging arrangements on dropsided tipper bodies, where previously little room was available on vehicles having wide base tyres to get within legal width and obtain proper slide-door clearances with the door dropped.
He, too, agrees that artics come out better, and bearing in mind the fact that Edbro experience on semi-trailer tippers in Europe, Canada and the United States over a good number of years has shown that a 23 ft. body length is the maximum for safe operation (apart from a few specialized applications) he stresses the point that with such vehicles it is essential for both chassis and body to he extremely rigid, particularly from a torsional point of view.
But,. going into some detail on the question of rigid tippers, Mr. Webster prophesies that the light production fourwheel tipper is still going to be a popular machine--a situation that will not be rationalized until plating is brought in for all trucks. He thinks that the light 20-ton g.v.w. six-wheel tipper is also going to be a popular machine, and the 22-ton six-wheel tipper may also be useful for bulk haulage tipping---but it is bound to be a heavier machine. '
With eight-wheelers he suggests that the 23 ft,-wheelbase 26-tonner could be a proposition with body lengths or around 22 ft. Apart from this, he agrees with the views expressed by Mr. Meats of Telehoist that it is very doubtful if the 28-ton eight-wheeler is a practical proposition " as a normal trunk, let alone a tipper ".