Aversion to "Lightweights"
Page 57
If you've noticed an error in this article please click here to report it so we can fix it.
EE article on the subject of lightweight buses by L. J. Cotton in your issue dated October 23, was icularly interesting and greatly enhanced by the use ;raphical methods of analysing performance. The )11 of specific tractive effort plotted against road d gave a comprehensive indication of the perforice of a vehicle, and it seems surprising that it is not i often seen, especially for purposes of comparison. stiniation of performance by evaluation of engine tie per ton is, as mentioned in the article, unfair to a .cle, such as the Leyland Tiger Cub, with a fastring engine. On the other hand, a comparison of :imum b.h.p. per ton, being unaffected by gear ratios, is that, with the weights quoted in the graphs, the al Tiger has a 7 per cent. higher power-weight ratio n both vehicles are empty, rising to 15 per cent. ier when fully laden.
t fact, the tractive-effort graphs show that the Royal T has, under all loading conditions, a higher pernance factor than_ the Tiger Cub over the following ortant speed ranges: 8-91, m.p.h., 12-17i m.p.h., :8i m.p.h., and 37-47 m.p.h. Rough calculations ;est that even if full use is made of all the Tiger ,'s combinations of gearbox and axle ratios, which as unlikely under normal conditions, the Royal :r's advantage over these speeds would be reduced not eliminated, except perhaps when both vehicles a empty. However, it is only fair to point out that unladen weights of actual vehicles are often more yurable to the performance of the lighter type of [de than those used as examples.
he use of lower alternative axle ratios would lily and for some conditions improve these results. Never, this procedure is available for both types of ;sis. For any vehicle, changes of overall gear ratio , assuming constant transmission efficiency,' only tiply tractive effort in inverse ratio to speed.
.s to the merits of lightweight construction as such, conservative outlook of many operators is due to rtisfactory experiences with lighter vehicles in the :. Trials over rough test tracks are very informative, to a point, but they cannot reproduce the effects of ES of operation in all weather conditions. Operators trally. need convincing that improvements in methods nanufacture are sufficient to give lightweight buses trouble-free and long life necessary to make savings 'uel consumption worthwhile.
: is true that most passengers are ignorant of the hanical details of the buses in which they ride. y are, however, capable of distinguishing a "tinny," ;), vehicle from a quiet one, and may tend to reduce travel to the minimum if new vehicles are noisier -1 their predecessors.
.educed thickness of panelling can, together with the acement of leathercloth by painted finishes for :tg panels, cause a tharked increase in drumming cts. These can largely nullify the value of a good inc mounting, and this was actually the case on a new icle with lightweight body on which I travelled :ntly.
'assengers in most districts have become accustomed .he smoothness of six-cylindered engines on effective ible mountings. Adoption of fouror five-cylindered ts, which are inherently less smooth running, must, therefore, adversely affect passenger comfort to some extent. It seems difficult to justify such a step, even for lightweight vehicles, for efficient direct-injection sixcylindered engines are now available with capacities as low as 51 litres. There seems little sense in making improvements in vehicle suspension, which is generally of a satisfactory standard, and at the same time allowing passengers to be subjected to more noise.
Greerfford, Middlesex. OBSERVER.
A Question of Averages
I READ with interest in The Commercial Motor dated November 13, the article entitled "Bonuses on Fuel Consumption," by S.T.R.
It says ". . . if during the four weeks of the month the lorry does 18 m.p.g., in one week, 21 mpg. for another and 22 m.p.g. for the other two weeks . the average weekly consumption for the period is 20.75 Surely, this can be true only provided that the weekly mileages are the same? It appears that the writer has taken "an average of an average" whereas the correct way must certainly be to take the whole month's mileage and divide, it by the total number of gallons used, Ventnor. E. I. CRINAUC. ,
A Live or Dead Load ?
A QUERY which has been the cause of numerous 1-1 arguments amongst my friends concerns the carrying of cattle. It is as follows: A driver of a cattletransporting motor vehicle is allowed to travel at 30 m.p.h. while carrying a live animal. Were this animal to die on the journey would the driver have to restrict the speed of the vehicle to 20 mph., as it would then be carrying deadweight?
Hampton-in-Arden, Warwicks. P. E. GIESS.
[This question is vague. The answer depends upon the circumstances, if the vehicle unladen weighs less than 3 tons, then it can travel at 30 m.p.h. whatever it be carrying. If it be over this weight, it is legally restricted to 20 m.p.h. even when carrying live cattle. A horsebox however, is permitted to run at 30 m.p.h. In the latter case there would not seem to be any question of having to lower the speed to 20 m.p.h. if the horse suddenly died. The first schedule to the Road Traffic Act, 1934, dealing with limits of speed, says that the maximum is 30 m.p.h. for a heavy motor car "if the vehicle is constructed or adapted for the conveyance of horses and their attendants and used solely for that purpose." It is not said definitely that the animals must be alive, but obviously dead horses would not require attendants. Any particular case would probably have to be treated on its merits—ED.]
IS it the Alpha and Omega ?
IN cate any readers are apprehensive of the two-pedal I control system fitted to the new Atkinson Alpha, they need not be. It has given satisfactory service for nearly 18 months experimentally and has seen normal bus service conditions abroad for many months on Leyland chassis.
Littleborough. • JOHN M. SIMPSON.