THE TROJAN AS A RIGID SIX-WHEELER.
If you've noticed an error in this article please click here to report it so we can fix it.
First Published Details of a Remarkable Conversion by which the 7-cwt. Trojan Van Chassis Can Carry Double its Normal Load and Traverse Trackless Country.
APID progress is being made in 1Annany directions with the development of the rigid-frame multi-wheeler, and there are many indications that this type of machine will shortly enjoy a well-merited popularity, not only in the case of the largest passenger and goods vehicles, but even in that of light models.
Spreading the load and braking and increasing the number of driving wheels present manifold advantages, including reduced wear on roads and tyres, improved riding—as the result of halving the frame lift for any particular rearspring deflection—decreases in the torsional stresses of the chassis and a greatly enhanced factor of safety of the vehicle as a whole. If required useful loads can be increased considerably without a proportionate rise in the chassis weight or engine power, and it has been proved in practice that the running costs of q six-wheeler compare favourably with those of an ordinary machine of similar load capacity, this being due partly to the. decreased Tolling resistance of the lightly laden tyres and partly to the saving of the losses due to the wheel spin which occurs when the drive is effected through two -wheels only.
As an example of what can be done with a rigid six-wheeler of compare
tively small size, we may instance the new Trojan chassis of this type which, with the same engine and a slightly lower gear ratio, can carry a total load of 16 cwt. in lieu of the useful load of 7 cwt. carried by the van, to which must, of course, be added the weight of the body in making a true comparison. In the case of the six-wheeler, the model illustrated, which is complete with a
platform giving 8 ft. ins, of loading space behind the driver's seat, has a total weight of 16 e.t.a.
The practicability and usefulness of such a chassis as this may possibly be questioned by some who havefl not fel-‘ lowed closely the deVelopment of special types of vehicle for particular purposes, such as that necessitating the occasional traversing of rough country, where the roads, if any exist, are little more than tracks and where, consequently, four driving wheels are essential. Certain classes of body, again, necessitate the provision of a long ,loading space, although the total load carried may be comparatively small.
Take, for instance, a caravan. Often an old lorry chassis is utilized as the motive unit, hut, as the tax has to be paid on the horse-power basis, this involves a large annual expenditure, and it would manifestly be cheaper to use a smaller-powered chassis, if this would provide the space necessary ; but the most important sphere for the new Trojan will, in our opinion, be in military transport and particularly for light ambulances, which could be employed under almost any road conditions. It might also be of value in certain branches of agricultural transport where vehicles are required to load direct from the fields or to carry fairly heavy loads over comparatively rough tracks.
Although the standard Trojan chassis is used as the basis of the six-wheeler, the new machine incorporates some features which have not before been included in multi-wheeler construction. For example, the Combined torque mid radius rods between the frame and the front axle of the bogie and between this tile and the rearmost, consist of spring leaves which are so arranged that they permit• free vertical movement of the axles, but offer strong resistance to rocking, as they are then stressed torsionally. This results in relieving the lower wheels of a large proportion of the load and throwing more on to the raised wheels, so that, if a wheel sink into soft ground or a pot-hole, the wheel secured to the other end of its live axle obtains an enhanced grip of the harder surface upon which it rests.
We will now describe in detail the
method of conversion. Starting from the forward end of the chassis, the first difference noted is that the front cantilever springs are carried outside the punt-like frame instead of inside. This increases the stability of the whole vehicle, as the spring base ia 6 ins. wider. Next,
an extra hand-brake lever is found to the right of the other levers; this controls expanding shoes in a brake drum secured to the rearmost wheel an the oft side, but, as in the case of the other two brakes, it acts on four wheels.
Towards the rear of the punt, and passing right through it, is the, main torqt:e tube which carries the engine, etc., and, normally, is extended to form the fulcrums of the rear cantilever springs, but in the six-wheeler acts as the anchorages for the forward radius and torque rods, which are carried back under the spring brackets of the front axle of the bogie. The second set of radius rods is pin-jointed to the forward axle and rigidly secured to that at the rear. By this arrangement all the driving and braking stresses are conveyed direct to the frame through these rods, instead of acting as usual through the fulcrums of the bogie springs. At the rear the suspension is by reversed semi-elliptic springs, mounted above and fulcruming on a cross-tube carried under a special extension frame, consisting of tapered ang,Ie-steel side members suitably braced and carrying the body platform. These springs have shackle links at each end which connect them to brackets bolted to the bogie axles and which are so shaped that they do not interfere with the spring movement, being first carried out and then bent in to bring the links practically vertical.
The position of the bogie front axle is such that the distance between it and the front axle is the same as in the ordinary van, i.e„ 8 ft., whilst the other bogie axle is 2 ft. 'S ins, behind the first, this, with the 28-in. by 21-in. Dunlop cushion tyres, allowing a space of 4 ins. between the bogie wheels at each side. The arrangement of the final drive is extremely simple, as the front axle of the bogie is driven in the normal way by a twin roller chain at the off side, whilst the other driving axle is connected to the first by a similar chain at the near side. As no differentials are employed, the drive is equally distributed over the four wheels, although, as explained earlier in the article, the actual wheel adhesion may vary according to the tilt of each axle.
No differences have been made in the engine and two-speed epicyclic gear, but the sprockets of the chain drive have been modified to reduce the gear ratio so that the vehicle has a speed of 20 m.p.h. at an engine speed of 1,500 r.p.m. The actual gear ratios are: Top; 6-1; low, 18-1; reverse, 252-1. We understand that the extra cost involved in the production of this interesting six-wheeler amounts to some f40 only.