Has Weight Too Saving Gone Far?
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How Discriminate Pruning of the Standard Product
Could Show a Saving in Weight of More Than a Ton
THE double-deck bus, an almost exclusively British product, remained supreme for town or city
service, said Mr. Copestake. It could carry 27 per cent, more people and occupied 10 per cent. less street space than the orthodox single-decker.
To give the same service with singledeckers, 27 per cent, greater fleet strength would be required, with a corresponding increase in platform and maintenance staffs and garage accommodation. Experiments were proceeding with single-deckers of high standing capacity, but Mr. Copestake believed that their use would be limited to specialized routes and that for town and city services the double-decker would continue as the basic type
The "Lightweight" Bus
One of the chief topics discussed by operators and vehicle makers during the past few years had been concerned with weight, and from these talks had been evolved the loosely called lightweight bus. Mr. Copestake felt that the name was unfortunate, as he did not think that a lightweight bus, using the word in its true sense, was desired.
In the early 'thirties, the weight of double-deckers was limited to 10 tons gross, which restricted the designer to all unladen weight of between 6 tons 2 cwt. and 6 tons 18 cwt., usually proportioned to approximately 60 per cent. for the chassis and 40 per cent, for the body. In 1936, the gross-weight limit was increased to 101 tons, and in 1941 to 11 tons, and again in 1946 to 12 tons.
With this concession, operators pressed the vehicle makers to use h eav ler sections. Larger engines, 24volt electrical equipment and larger tyres naturally followed. Then came the increase in overall length from 26 ft. to 27 ft. and overall width to 8 ft.
Fuel was the most important item of
increased operating costs, and how far fuel economy could be effected as weight was reduced was, the speaker thought, a question that could be answered only by closely controlled service tests and by running comparable vehicles over the same routes and under identical conditions.
Reliable large-scale tests had shown that double-deck vehicles, confined to city routes, could yield an improvement of 8.38 m.p.g. to 8.76 m.p.g. (0.45 per cent.) by reducing laden weight from 11 tons 15 cwt. to 11 tons 4 cwt. OA per cent.).
A Foolhardy Policy
Whilst it could be accepted that a reduction in weight could lower fuel costs, it seemed foolhardy to prune 2 tons from a vehicle having a 15-year expectancy of life and reduce its economic life to 10 years.
Experience with . pre-war vehicles showed that at the end of five years, allmetal bodies required, on an average, 450 man-hours for structural repairs, whereas the post-war vehicle at the same age did not call for such repairs. How far, then, was it possible to go with vehicle-weight reduction and still obtain an estimated life of 15 years?
Most present-day designs of bulkhead is I 3 had been influenced by the pre-war failures and were, it was considered, reinforced to an unnecessary degree, when it was remembered that the troubles were partly caused by other factors.
Front bulkheads in tight alloy had been produced to weigh as little as 120 lb., compared with the steel versions, which varied in weight from 200 lb. to 320 lb. A promising method of reducing the weight and cost of wheel-arches was to use one of the corrosion-resisting aluminium alloys.
Mr. Copestake could see no reason why the interior stress skins or truss panels should not be of aluminium, instead of steel. This would result in a saving of about 200 lb. per vehicle. A change of gauge for the exterior panels of the upper tittioon from 18 to 19 s.w.g. would save 20 lb. per body, If the timber fillets and packings to which the panels, ceilings and so on were attached could be eliminated, about 2 cwt. could be saved.
Plywood for Floors
The floors of a double-deck vehicle made up a fair portion of the total weight, and a good-quality resin-bonded plywood might be employed in place of tongued-and-grooved boards.
In the upper saloon, the floor extended to the full width of the vehicle, but about 16 per cent. of it was not used, as it was under the side covings. A typical example of such a floor would weigh about 330 lb., but if the unnecessary 9 in of board OTT each side were omitted about 60 lb. would be saved.
Linoleum was the most popular floor cox ering, but by using 4-in, material in place of the normal 3/16-in, linoleum, a reduction of 80 lb. could be achieved.
The high-backed double passenger seat weighed about 37 lb. By reducing the cushion and squab boards and using alternative fillings, each seat had been reduced by 6 lb., the total saving being in the region of 14 cwt. per vehicte.
Thirty-two-ounce toughened glass was commonly used in all positions, except the windscreen. The weight was approximately 400 lb. per bus. If a 26-oz. toughened glass could be produced to the accurate limits required for rubber glazing, it would be quite satisfactory and would reduce the weight of glass to 325 lb..
Replacing Stainless Steel
Whilst appreciating the fine service given by stainless steel for handrails, stanchions, the top rails of seat frames and so on, aluminium alloy was offered as an alternative. This would cut the cost by about £20 per vehicle and the weight by nearly 40 lb.
To try to reduce chassis weight was quite different from cutting body weight. To attempt any major weight-saving on the chassis frame was tempting providence, Mr. Copestake said. The thickness of the members of some chassis could possibly be reduced by 1/32 in., but heavier local reinforcement at the front and over the wheel-arches might be necessary.
Many of the brackets, adaptor plates and so on attached to the frame could be lightened. Light-alloy for dumb irons, spring brackets, engine and gearbox-mounting brackets could yield a large saving. Front-axle weight varied on different makes of vehicle performing the same function, and if the lightest components were adopted, some makers could save as much as If cwt. Similarly, about 1 cwt. could be pared off the rear axle. A further cwt. could possibly be removed by using a light-alloy spring bracket and brake carrier assembly.
The increased fuel consumption of vehicles with fluid couplings and epicyclic gearboxes was often decried, but in a large number of cases there were variables which could easily affect the results. Tests were proceeding in Birmingham with six buses having frictionplate clutches and constant-mesh gearboxes, and six of the same type with fluid couplings and epicyclic gearboxes. The results so far had shown only a small saving in favour of the buses with plate clutches.
Further weight reductions had been achieved in the standard layout by using aluminium in place of cast-iron for the flywheel end-cover and by employing Elektron for the gearcase. In the first case the saving was cwt. and in the second 45 lb.
Reducing Engine Size
Body weight could, on the figures quoted by lowered by 11 cwt. and the chassis by 6 cwt. This permitted the engine capacity to be reduced without impairing the b.h.p.-weight ratio.
A reduction in engine weight of about 14 cwt. could be achieved and as 12-volt starting equipment was adequate, a further 1 cwt. saving was possible. Were the road springs rated so that shock absorbers were unnecessary, another I cwt. might be removed.
The modern double-decker could be reduced to an all-up weight of 10Itons without departing from present-day standards of finish, performance, maintenance and ultimate life.