How Weight Saving Can Incre, Lting Capacity in Double-deckers
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DOUBLE-DECK bus design has, of more recent years, set manufacturers some ticklish problems. The need for meeting the increased stresses resulting from more rapid acceleration and retardation, and for effecting a reduction in body weight to enable the maximum number of passengers to be carried, without exceeding legal axle-weight limits, arc problems which have called for the exercise of all the craft at the command of designers. That difficulties of this kind have been overcome within such fine limits is a tiibute to them.
A good example Of achievement .in. this direction is to be found in the steps that were taken in the development of the first two-axle 60-seater oil-engined vehicles now being supplied to Coventry Corporation.
Seating Problems at Peak Periods.
For a number of years the municipal transport department operated 60seater three-axle buses, but these were of standard composite construction based on six-cylinder petrol-engined chassis. More recently, the two-axle type, with a 55 or 56-seater body has been standardized, and this loss of seating capacity', although of little importance at normal periods, has presented a serious problem in dealing with intense peak periods and special works journeys.
Whereas it is usual for the operator when ordering a new vehicle to ask for particular items of fittings or furnishings, Mr. Ronald A. Fearnley. Coventry Transport Engineer, approached Transport Vehicles (Daimler), Ltd., and Brush Coachwork, Ltd., with the full appreciation that the first claim must be given to the proposition of increasing to 60 the seating capacity of the current type of vehicle, and regulating the question of furnishings accordingly. As the loaded bus was then up to the limit of its maximum weight, it was obvious that the weight of the five additional passengers would have to be compensated for by a corresponding reduction in weight of the vehicle itself. On the other hand, it was realized that no appreciable sacrifice could be made in the weight of essential equipment, or the method of construction. The balance, therefore, had to be struck by the elimination of the more superficial equipment or by the substitution of certain furnishings and fittings.
Having reached this stage, the question of tilt required special attention, because reduced weight of both chassis and body might influence the angle of tilt, Nevertheless, it was finally decided that, by the use of the shorter Daimler C.O.G.5 single-deck engine mounting in the double-deck chassis and the singledeck-type of dashboard and bonnet, more body space could be provided.
This, with a reduction of 2 ins, in plat form space, gave a total of 12i ins, i the lower saloon.
By closing up the seats to the repi lation spacing and working to fin limits, it was found possible to use tf total space thus afforded by providin a five-passenger seat backing on to th bulkhead and facing the reverse dire; tion. This increased the seatin capacity of the lower saloon to which, with 29 in the upper saloon. before, gave the required accommodation for 60 passengers.
By placing all five additional seats in the lower saloon and with certain reductions in weight in the upper saloon, this more than compensated for the loss of dead weight in tne chassis, so far as the tilt test was concerned. In fact, when the first vehicle was completed, the tilt showed even better results than before the adaptation was effected.
It was this question of weight reduction, however, that needed the most careful planning. Mr. Fearnley, with representatives of the two companies concerned, went through the zomplete specification of the vehicle, item by item, unlit 7 cwt.—equivalent to the weight of the five additional passengers—had been eliminated.
Transport Vehicles {Daimler), Ltd., promised to take off 3 cwt, from the z.hassis if Brush Coachwork, Ltd., was ible to account for the remaining 1 cwt. To begin with, a saving of cwt. in the weight of batteries was ffected by the adoption of 12-volt, nstead of 24-volt, electrical equipment.
Methods of Weight Saving.
A further hundredweight was saved )y• the use of standard wheels and yres, instead of the heavier type preritottsly favoured. The use of an Elekron casting for the gearbox, the dashKrard reduction previously referred to ind savings on other smaller items nade up the remaining hundredweight equired to be taken from the chassis. )espite the adoption of the single-deck ngine mounting, however, it was mind possible to continue the Daimler ninciple of the fully floating mounting s standard on the maker's C.O.G.5ype of chassis.
The reduction of weight from the iody presented a more complicated iroblem and the total of 4 cwt. had to ie reached by paring small amounts rom numerous items.
The largest saving was made by the ubstitution of a single-boarded roof of -in. thickness to the loWer saloon, Istead of the previous double-boarding ith white-lead packing. This ccounted for 84 IlaC The singleoarded roof was laid diagonally across ie vehicle to give equal strength and dditional bracing from corner to Drner.
A saving of 56 lb. was effected by ispensing with the double aluminium aliening of the side cove panels of the pper saloon, and a further 56 lb. by finishing the linoleaan at floor level, instead of carrying it 12 ins, up the sides .all around. The tubular-steelframe seats were each reduced by 1/ lb., giving another 45 lb. The interior double-panelling of the platform vestibule was replaced by Rexinecovered single-panelling, whilst the staircase stringers and risers were reduced from 18 to 20-gauge steel producing, together, another 38/ lb.
A further saving of 20 lb. each was effected by reducing the number of half-drop windows from six to four in both upper and lower saloons and by omitting a destination box on the off side of the upper saloon.
A farther total of more than 1/ cwt. was made up by many smaller items, such as a reduced number of roof ventilators, aluminium or duralumin fittings in place of those of stainless steel, reduced gauge handrails and so on which, although small individually, eventually reached the aggregate required.
So that the window lights should continue to be interchangeable with the present Stock, the extra 12/ ins, in interior body space was taken up at the sides by 6-in, quarter panels at the front and rear, those in the upper saloon being placed behind the first side window so as nbt to restrict forward visibility.
A curious effect of the finished vehicle is that, apart from the five additional seats, the layman would be unable to detect the difference between it and the 55-seater bus now operated at Coventry. So marked is the similarity from the exterior, in fact, that chromium mouldings are being placed around the front indicator of the new vehicles to enable inspectors to recognize them approaching.
A most interesting point arising from the construction of this 60-seater is that, when fully loaded, it weighs exactly the same as the 55-seater, so that its fuel consumption and general performance should be equal to the vehicle of smaller seating capacity. Upon reflection, this reveals the fact that 11 such vehicles provide the extra passenger accommodation of one 55-seater without adding to maintenance costs. This means that Coventry Transport Department is gaining an extra bus in every 12.