HAULING HEAVY LOADS OVER ROUGH COUNTRY.
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Details of an Entirely New F.W.D. RoadlessTraction Machine which will Draw Twelve-ton Loads and Carry Four Tons.
APARTICULARLY interesting type of cross-country machine, which combines the functions of a vehicle and tractor, has just been completed at its Slough works by the Four Wheel Drive Lorry Co., Ltd., 46, Charing Cross, London, S.W.1.
It is well known that a vehicle having Roadless-Traction tracks and frontwheel drive can be used successfully in situations where any other type of vehicle without front-wheel drive is almost inevitably stalled. For instance, if the front wheels sink into a fairly deep, narrow cut-ting, where the drive is at the rear only, the wheels are merely forced against the sides of the cutting, and if the attempt be persisted in something has to give ; whereas, with driven front wheels the pressure .against them of the drive from the tracks merely assists them in gaining a grip upon the opposing soil so that they can climb out.
There has, how
ever, been one important objection to the standard F.W.D.-Roadless-Traction machine, in that the driver and second man (if he be carried) are Perched above the engine, thus not only detracting from the appearance of the machine, but where such a machine may be employed for military uses, the added height makes it far more conspicuous. Therefore, one of the guiding principles in the -development of the latest product was to lower the driver and keep him alongside the engine, this applying also to the second man.
As the latest machine is Britishc36 built (in that it embodies considerably over the requisite 75 per cent. of British parts), it was not important to keep to the original American design, and alterations have been effected in almost every detail.
In considering the position of the driver it was found that if he were not moved inwards towards the centre line of the vehicle, the limit by which his position could be lowered was that which afforded sufficient clearance over the front wheel, but this was considered not
low enough, so the wh,ole engine was moved 7i ins, from the centre line of the chassis and raised 7 ins, to clear the front axle, it was also found necessary to design a special crankcase so that the oil pump would always be submerged and would continue to function with the vehicle at an angle of 30 degrees in any direction. The lower half of the crankcase also had to be offset to clear the front axle. To ensure better lubrication, a bigger oil pump was provided. This is double the standard size and also gives greater pressure.
Th3 engine is far more powerful than that employed on the original F.W.D., as it has cylinders of 5i-in. bore and 51-in. stroke.
To suit the altered position of the engine, a new fan gear had to be designed, and the Soleg carburetter, which is now employed as standard by the company, is equipped with a new inlet manifold having pockets giving a back surge which helps to feed the end cylinders. The carburetter is turned at an angle so that better accessibility is provided for the magneto. It has been. found with the new carburating arrangement that a tractor-lorry earrying 12 tons has a consumption of 1. gallon per 5.4 miles, whilst 8 m.p.g. is obtained on the 4-ton standard lorry. We cannot, at this stage, give the fuel consumption of the tractor.
To facilitate starting the Bosch magneto has an impulse device, and the hand-starting gear has been redesigned, consisting now of two shafts with a toggle device so arranged that the action of pushing in the starting-handle shaft engages the upper one, to which it is connected by a roller chain.
The power is conveyed from the engine through a clutch of the HeleShaw multiple-disc type, a Thermoid fabric joint being provided between the clutch and a new unit known as the re ducing gearbox. This unit not only serves to take the drive from the offset engine, but gives two ratios of gearing, these being 4-5 and 1-2. To effect this reduction the reducing gearbox has two large silent chains, both of which revolve while the clutch is engaged, but either of which can be brought into service by means of a sliding dog clutch. A further feature of this gearbox is that in an extension on the side of the ciise is carried a countershaft driven, by a roller chain mounted betweei the two silent chains. One end of this countershaft drives the air pump and the other end the dynamo.
The electric -starter is carried in a somewhat unusual manner in a deepflanged cross-member, the starter itself having a bracket at each side to support it.
The main gearbox is standard, except that the control for the differential locking gear is carried up to the driver's seat and is there operated by a lever conveniently situated between the driver's logs. To operate the lock, the driver drops the lever down to the floor ; this enables a tension spring to act through lever connections on the dogs of the locking gear, which engage so soon as the respective dogs come into alignment on cornering.
Rather than to have a high maximum speed it was thought by the company that by lowering the gear ratios a higher overall speed would be attained.
In oeder to obtain a larger lock on the front wheels the distance between the pivot centres of these was increased by ins, without affecting the spring centres. As a result of this alteration the tractor will turn in a eirele of 48 ft. diameter, whilst the front wheelsare still kept within the width of the back creeper tracks.
The front axle and shafts are entirely new, and the wheels are equipped with 40-in. by 8-in, pneumatic tyres. What would in the ordinary vehicle be the rear axle is bolted up solid to the frame. It has a new-type crown wheel and pinion of 100-ton tensile steel, the length of the teeth of which hag been Increased from Iii in. to 1; in.
Ilve.n the tracks are of new design, with east-steel idler arias and very large
roller bearings in all the rolless and idlers.
The whole frame was made in the coingamy's shops It has a new subframe for supporting the engine above its normal position in the main frame.
A standard • colonial-type radiator, similar to that on the tractor-lorry but with the front edge of the header chamfered off, gives a much greater cooling capacity and affords better vision to the driver.
The engine easing and dash are also new rind shaped to assist in permitting a good view of the "reed."
An unusual feature is that the petrol tank. which has a Capacity of about 45 gallons, with a smaller tank holding 2-2!,gallons let into the top of the main' tank for emergencies and to provide petrol on exceptional gradients, is carried in the front end of the-body.
The steering column is standard, but has been shortened and its Ake altered to snitthe new position.
So far as the brakes are concerned, instead of the external-contracting type of band brake on the rear wheels, much greater efficiency is afforded by the new interral-expanding shoes. The standard RCVS). feet brake has been retained.
All the pedal gearing has been redesigned. and the throttle and ignition controls are mounted on the side of the engine casing instead of on the steering
The machine is equipped with a winch of a netv vertical-shaft pattern, mounted between the frame side-members, just ahead of the rear axle, on four eaststeel brackets; whilst two steel plates carry the spindle.
The whole reduction for the winding gear is effected by a single-crown wheel. and pinion, the former having 104 teeth. The drive for this winch is taken off the top of the gearbox and actually affords two speeds through the reducing gearbox. The calculated pull on the cable is a little
over 5tons. .
One feature of the machine is the neat canopy, which is so arranged that it folds up, and by removing two pins it can be dropped, vertically so that it then lies below the height of the steering wheel..
To avoid fouling when crossing ditches the front axle has been carried forward, the axle centre being only 2 ft. 1 in. from the front of the frame.
The heeding dimensions of this interesting product are :—Wheelbase (from centre of bogie to centre of front wheel), 8 ft. OS ins.; overall height, 6 ft. 3 ins.; height, with canopy up, 7 ft. 9 ins. The speeds are 13 m.p.h.,
m.p.h: and 3+ m.p.h. on the upper ratios, and 8 m.p.h., 4 m.p.h. and 2 m.p.h. on the lower ratios, these being calculated at an engine speed of 1,30 r.p.m.
F. W.D.-Iloadless-Traction machines have been put through some very drastic tests, hauling heavy loads, and this new vehicle will not only carry 4 tons in its own body, but will also haul 12-ton usefnl loads across country—rather an astonishing performance I The drawbar pulls are 2,857 lb. on top gear. 4.000 lb. on second and 5,700 lb. on first, whilst the special low 'gear using the reducing box gives a pull of 8,100 lb.