n Your Opinion
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'A Convenient Hypothesis'
I WOULD like to refer to the report by P. A. C. Brockington (COMMERCIAL MOTOR, June 24) on the eleventh Congress of the Federation Internationale des Societes d'Ingenieurs des Techniques de l'Automobile at Munich, when he described part of a paper by Dr. Gorge, of MAN.
This paper concerned the effects of rigidity of structure on the handling, rolling and swaying, and road holding of commercial vehicles with particular respect to tankers. This hypothesis evidently does not apply to the tractive units of articulated lorries.
The wheelbase, little more than that of a fair-sized car, and heavy cross-section chassis members must be one of the most rigid moving structures produced by MAN for transport, short of a locomotive or a tank. Anyone who has been on test with an uncoupled tractive unit will never forget the incredible rocking-horse effect. Dr. Gorge's hypothesis has steered well clear of these units.
Mr. R. B. Daniell mentions centrifugal force in his letter (August 12). Every non-Newtonian student of mechanics knows that this is a force acting in a straight line (inertia) and that if it be multiplied by the distance between the kingpin and the front axle and the sine of the angle (originally acute) between the centre lines of the two parts of the machine, one has the value of the couple tending to rotate the tractive unit, The couple resisting rotation, on the other hand, is pathetically small and is found by multiplying the same straight-line force by the same sine value and the ridiculously short horizontal distance between the kingpin and the rear axle (mean position).
It is true that the resisting couple also increases as the sine of the angle, but so does the difference between the couples, and this is what produces the angular acceleration.
As the jack-knife increases so does the angle, hence the sine value and also the couple producing it, which is why the driver doesn't stand a "cat in hell's" chance of correcting it.
It is quite obvious that if the kingpin or turntable were situated at equal distances from either axle the couples tending and resisting would be equal and that jack-knifing would not occur.
R. W. MASTERS, Leeds 17.
I WAS interested to read A. J. P. Wilding's articles in COMMERCIA MOTOR of July 22 and 29 regarding shortage of spare parts. I particular, I was surprised that such an issue is being made regardin the non-availability of cab parts.
We operate a considerable number of both Albion and Leylan. vehicles within the group, and about a year ago we experience. similar difficulties in obtaining front wings and aprons. As a result our engineer developed cab parts out of glass fibre. Since this tim these parts have been modified and have reached perfection.
Leyland's attention was drawn to our new project some Si: months ago, and on their recommendation we are now supplyim operators in this country and overseas with glass-fibre aprons am front wings.
Needless to say, we are rapidly expanding our production of thesi parts, and are in the process of developing similar parts for Dodg4 vehicles.
W. RHODES Director, Rhodes Transport Ltd., Chesterfield
AT LONG last COMMERCIAL MOTOR has taken another step tc make the journal more attractive to the modern fleet operator After giving the journal a "face lift" earlier this year you have now included a special monthly feature to deal with the problems oflighl vans and cars.
As a fleet operator with a majority of such vehicles I congratulate COMMERCIAL MOTOR on this new venture, and I am sure that all my colleagues in the transport profession will join me in a vote of thanks to those who have had the initiative to introduce it. Good luck, and may you go from strength to strength. F. H. WOODWARD, Manager, Transport Services. The Plessey Company Ltd.