A SIX-WHEELER WITH TRACKING WHEELS.
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A Vehicle of New Design which Does Not Grind its Tyres when Cornering and which Appears to Gain in Fuel Economy from that Fact.
TE have for some time watched with interest the V V progress of a new development in six-wheelers which is the production of Mr. Holly Whitby, of H.
Whitby and Co., Ltd., High Street, Ponders End, Enfield, Middlesex. Mr. Whitby has the double advantage of being a practical engineer and, for some years, of having conducted the business of haulage contractor. The six-wheeler he has produced, although resembling what is known as the rigid-frame type, must be put in a separate category as, when a departure is made from a straight course, shown in Fig. 1, the centre pair of wheels take up a new position so that there i3 no grinding of the tyres. This will be seen in the diagrammatic view, Fig. 2, and in the photograph, Fig. 4, in both of which it will be seen that, as soon as the front wheels divert the frame from a straight course, the central axle automatically moves to a position where its axial line approximately extends to the centre point around which the vehicle is turning. This action is not produced by means of any connection between the axles and the steering wheels, which might make the steering hard. It is an entirely auto-matte action produced by the central -and rearmost axles being mounted on the beams (B) which lie under the springs and act as a parallelogram as shown in Fig. 2, diverting the course of the central wheels as soon as any departure from a straight line is made, thus automatically bringing their angle to approximately half that of the steering wheels.
The design appears to have overcome the defect that is present in all rigid-frame six-wheelers, namely, when not running in a straight line, there must be a certain amount of grinding of the tyres. The overcoming, in this case, of this defect is not accomplished by the introduction of complication, but merely by allowing the central axle to have free castor action, swinging from its ball-joint on the torque tube and providing vertical pivot action at the point where the side beams (B) join the springs and where they join the axles at At and A2, the movement of the frame as it is steered in either direction causing the central axle to assume an angle that is midway (approximately)
between that of the steering wheels and the rear axle.
The joints where the beams join the axles at Al and
A2 are of such a kind that the
wheels can follow uneven ground in the usual manner Of rigid-frame six-wheelers, whilst the joints where the springs are connected to the beams (II) have horizontal and vertical pivots, but do not admit of any rolling motion, the only additions to the usual construction of the rigid-frame six-wheeler being the pivot (A) with vertical axis under the spring, and the sliding movement permitted at Al,. the usual universal joints where the beams connect to the axles being all that is required to enable the correct alignment of the central axle to take place.
We were given some figures relating to the economy in fuel consumption of these vehicles in comparison with another type of six-wheeler carrying a load of 9 tons S cwt. from Ware to Isleworth, but not having been able to check them ourselves, we do not propose to give them here. The economy claimed, however, was said to be so marked that it induced us to make a trial, the result of which points to the fact that some appreciable economy must be effected by the use of the arrangement of self-alig,nieg axles.
Following our usual practice of not accepting responsibility for figures unless they are obtained under our supervision, we checked the petrol consumption of one of the vehicles of this type with solid tyres under the following conditions :—A private car mileometer was carefully checked against reliable milestones for 10 miles ; we thea went to the malt houses at Ware, where John Page, Junr., a haulage contractor of Ware, was loading up with 9 tons of malt and 8 cwt. of sacks. We then saw the tank filled with ordinary No. 3 commercial petrol and measured its height when standing on level ground. A run was made under ordinary traffic conditions to Watney's brewery at Isleworth, a trip of 37-i miles. 'A large part of the run was through traffic, as the
journey was taken between 11 o'clock and 1 o'clock midday. The consumption worked out at slightly better than a gallon per 6 miles. This figure could, no doubt, be considerably improved upon.
Among other advantages claimed for this type is the rather important one that a more even distribution of the wheels is possible than with the ordinary rigid-frame Six-wheeler, as the central axle can be placed in a more forward position than is possible with an axle that cannot alter its course. It is necessary to have .such axles close together in order to minimize tyre grinding. A further advantage is that when drawing away from a kerb, the body does not sweep over the pavement, even if it has a long overhang. Our illustration Fig. 5 shows a vehicle close up • to a kerb,' whilst Fig. 6 shows the position of the same vehicle when it _had moved forward 3 ft. The black lines in Fig. 4 indicate the relative alignment of the central axle with the rear when cornering sharply.
Up to the present, six of these vehicles have been constructed, some of which have been running on regular work for 18 months in the hands of haulage contractors who have bought them, in two cases a repeat order being given. The combined mileage to date of the six vehicles is 100,000 miles.
Although the tracking of the wheels when travelling in a forward direction appears to be perfect, the tracking, when reversing, is not so perfect. as grinding of the tyres thentakes place, but in all probability this is no more than would be the case with an ordinary rigid-frame six-wheeler. We understand that Mi. Whitby has patented the arrangement in most of the important countries and is open to consider any proposals for the production of such vehicles on a larger scale.