A DISCUSSION ON SIX-WHEELERS.
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Interesting Views Expressed in a Joint Meeting of the Institute of Transport and the I.A.E.
drAN Tuesday last there was a most interesting and wellkjattended joint meeting of the I.A.E. and the Institute of Transport at which Captain C. H. Kuhne gave a paper on "Military Transport Vehicles, Their Recent Developments and Commercial Significance." As was anticipated, the paper dealt particularly with the six-wheeler and emphasized the advantages of the type for commercial use at home.
Captain Kuhne said that all the unique advantages which made the six-wheeler so valuable as a military machine on rough country were almost equally valuable when the vehicle Came to be used on ordinary roads. Be .pointed out that the many Commercial applications and advantages of this type Of chassis all over the world were emphasized at the recent World Conference on Motor Transport Speaking of the remarkable adhesion obtained with six-wheeled chassis, Captain Kuhne described a test in which the medium-sized W.D. chassis on a hard, level road had been capable of hauling a number of laden lorries aggregating 81 tons in weight, a load representing 18 times the weight acting upon the driVing wheels of the vehicle which was hauling it
Considerable prominence was given in the paper to the arguments for and against the provision of a third differential between the two driving axles, and the author gave it as his opinion that for military and colonial purpOses such a differential would ruin the vehicle, whilst the experience of all users had gone to show that it was quite unnecessary. A development forecast by Captain Kuhne was a pneumatic tyre of oval section so as to permit of a greater wheelrim diameter, thus obviating the trouble at present experienced in cooling the brake drums.
. The discussion was opened by Mr. Legros, who dealt mainly with brakes, pointing out that if a third differential be used it is essential that all the brakes should take effect upon all four driving wheels. He also mentioned that the pedal pressure required was much too great for the comfort of the driver in a heavy six-wheeled chassis unless sonic arrangement of power or servo braking be adopted. General Gilbert, the Master-General of Ordnance, followed and described certain changes in administration which have taken place and which have resulted in centralizing experimental and research work. He paid a graceful tribute to Colonel Niblett for his work on the rigid-frame six-wheeler.
The meeting was attended by delegates from the Soeiety of Automotive Engineers (U.S.A.), and the secretary of that society, Mr. Clarkson, read a contribution by Mr. Horning, M.S.A.E., in which transport matters in America were interestingly described. He said that the rapid growth of road transport had originally led to an orgy of overloading and overspeeding in America, with the result that makers of vehicles had been forced into an all-round increase in engine sizes, the use of six-eylindered engines and, for freig,ht carrying, the development of six-whee ed chassis hauling trailers. The engine requirements for the latter were a power development of 75-80 h.p. at 1,000 r.p.rn., rising to 140-150 h.p. at 1,800 r.p.m.
The next speaker was G-'eneral Long, who, as the user of a big fleet of commercial vehicles, questioned whether the sixwheeler was worth buying commercially, as its first cost was higher than that of a four-wheeler, and the advantages which it offered for goods carrying were not, in his opinion, very great. General Long gave it as his opinion that the subsidy was useless for encouraging the six-wheeler, and asked why the War-Department aid not saY to the Ministry of Titansport, " You must tax a four-wheeler at £60 and the equivalent six-wheeler at only £30." This, said General Long, would be much more effective than the pre-sent subsidy scheme in persuading commercial users to employ six-wheelers—a view which was endorsed by Mr. Barford, who followed.
Major Hubbard, recently back from India, then gave the meeting an idea of the very successful trials which sixwheelers had been put through in that country. One particularly fine exploit was a run from Quetta to Karachi and back, a distance of 900 miles largely over camel tracks, with a temperature of 110 degrees in the shade, which was accomplished in three days for the outward journey and four days for the return journey.
In building commercial vehicles for India, said Major B40 Hubbard, it was essential to provide very large body accommodation, adequate engine power for the extremely long gradients which were met, and something special in the way of cooling systems. Mr. Shrapnell-Smith then made a racy speech, in which he said that on the score of more comfortable Tiding the six-wheeler claimed the attention of the passenger vehicle operator. He did not think that it would be practicable to persuade the Government to give the sixwheeler preferential taxation.
Colonel Hacking described conditions in Australia and >few Zealand and said that he believed the Australian Government was not only prepared to give the six-wheeler prefer-. ential taxation, but would also encourage it by means of a preferential tariff. Mr. Burford followed, and urged the need for standardization ; he suggested that the subsidy was much too limited in its scope.
Mr. Sydney Guy mentioned a number of very interesting points, including a test which he recently carried out on wheelspin, taking a four-wheeled and six-wheeled chassis with the same loads and gear ratios, each of which was run on pneumatic tyres up a straight gradient 250 yards in length, varying between 1 in 8 and 1 in 11. The revolutions of the front steering. wheels were taken as being correct (i.e., free from slip) and the revolutions of the driving wheels were counted. In the four-wheeler the driving wheel slipped four complete turns in 250 yards, whereas in the six-wheeler the slip amounted only to 11, turns.
Another test was then described by Mr. Watson, in which a loaded six-wheeler had been hauled by another vehicle through a draw-bar dynamometer. The tyres on one driving axle were let down until the preK.ure was only 20 lb., whilst those on the other driving axle were kept at 110 lb., but despite this big discrepancy the increase of tractive resistance above normal was only 8 per cent. Mr. Watson concludes that a third differential is quite unnecessary.
The meeting was enlivened by a most excellent film which showed six-wheeled vehicles extracting themselves from all sorts of difficult situations with consummate ease.