IS THE MOTORBUS TOP-HEAVY?
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By "The Inspector."
THERE CAN HAVE been few occasions On which two consecutive issues of THE COMMERCIAL MOTOR have each included a large-sized illustration showing a three-ton lorry turned over on its side. The last two issues, however, I notice include such pictures. Last week it was of a Maudslay, evidently capsized on account of the driver " taking the bank" at the 'side of the road during his hurried journey away from the Front during a recent phase of the great German offensive. In the .previous issue the incapacitated vehicle was a Leyland, and in this instance the text makes it clear that the machine had turned over because it had been charged.by a light railway locomotive. .
These two instances, coming so close together, are ,effective reminders of the relative infrequency of similar happenings, taking into account the enormous numbers of motor vehicles of all kinds which now use the roads and tracks of the world. Short of falling down an embankment, or some equally remarkable interruption to its more normal progress, it is indee4 very seldom that a motor vehicle capsizes. I have in my own experience known of some terrific collisionsin some of which eases two Motor vehicles have been concerned, whilst, in others, obstacles as wide apart in nature as a charging lion in East Africa and a peaceful milk cart in East London have been encountered. In very exceptional instances have I known the machine to turn right over.
When first the motorbus was seen on the streets of London, and many of the readers-of THE COMMERCIAL MOTOR will recall the extraordinary interest that these early corners aroused, the invariable criticism that was first of all heard was that, they were dangerously top-heavy. They were, of course, much 'bulkier and considerably higher than the old horsed buses which they displaced, and I doubt whether even to-day many people have been effectively convinced that the motorb-us is indeed more stable than the. old horsed bus. With the many millions of miles of running which the London motorbus services have recorded, I believe I win correct in saying that the numbers of occasions on which double-deck buses love oyerturned on their sides could be counted on the fingers of One hand..
0 There was within thelast few weeks a serious mishap of this nature on the Hendon-Golders Green road.
In several instances, of tha circumstances of which I happen to be aware, there have followed heated discussions as to the cause of the overturning, but such discussion never proved -Co be very illuminating.. 1 do remember, however, :that, in one of the earlier instances, the Editor of THE COMMERCEAL•MOTOR was asked to give his -expert opinion as to the stability of the motorbus structure as a whole. From published particulars of the report which he furnished, it was evident that the actual centre of gravity of a bus loaded at the top and empty inside, was very little above the top line of the frame of the chassis, and that is a circumstance of which the ordinary nontechnical member of the public is unaware, and as to which, if he were told, he would, at the mere evidence of his eye, certainly preve sceptical. It has, fon some while past; been established in certain tests —I believe they were carried out by Tilling's, although I am not quite sure on that point—that the critical angle of an ordinary unloaded motorbus is no less than 45 degrees from the vertical. The normal stability of the motorbus is, therefore, an undoubted fact, and this makes it all the more remarkable that a, heavy Army lorry loaded, or, at any rate, partly loaded,such as that shown in the picture of tie overturned Leyland, should have been pushed right over by,the locomotive of a light military railway.
It is very difficult to reduce happenings of this sort to terms of accurate mathematical expression, and, as a matter of fact, I suppose their production would be one for very abstruse consideration. It certainly appears to he a fact that a stable structure of considerable size can be overturned with relative facility by a much lighter object, if the blow causing the trouble happen to take place in some particularly critical manner and direction. This must have been so in the case of the Leyland referred to. I remember quite -well, some years ago, watching a hansom cab— a type which admittedly had its centre of gravity unduly high—mount a low kerb of not more than 6 ins, elevation with one wheel and, then, instead of bumping down into the road, as one would expect, particularly taking into a,cceunt the camber of all roads towards the kerb, it proceeded on the one wheel, with the uplifted one gradually getting higher and higher until at about 20 yards distance the whole contrivance, horse, cab and driver, to say nothing of the highly-divertedpassenger inside, turned over on its side with a crash. I was inn position to observe the whole happening quite closely, and I must admit to having been quite puzzled as to how it was that the cab did not quickly recoveritself.
On another occasion, 1 remember seeing an early type of lofty (I suppose-it was of about 30-cwt. capacity), coming round a wide sweep at a street corner, and, With its near front wheel striking a horsed milk-. cart standing by the side of the kerb, it turned completely over in a direction away from the milk-cart. Incidentally, the milk-cart was distributed well over the roadway, together with some ten or fifteen gallons of the precious fluid. That was another case in which it was very difficult to arrive at a conclusion as to the reason of the overturn. As a matter of fact, I do not think that the majority of us need to puzzle our heads with' suCh problems in dynamics, but it is at least assuring to realize that on balance the motor vehicle itself is a remarkably stable structure. It appears to be only in exceptional circumstances, and for reasons that are seldom ascertainable, that such a thing is likely to happen. . The jury has had great difficulty in making up its mind as to the cause of the recent lIendon smash. If the motor vehicle as a type were not inherently stable, there would certainly be many thousands of much more serious accidents in dangerously slippery weather than there are.
In this connection, I wonder how many of the readers of THE COMMERCIAL MOTOR have at some time or another been inveigled into a discussion as to the side on which a, racing car would turn turtle when taking corners at high speed ? It used to be a favourite problem upon which to invite opinions.