W.D. ENCOURAGEMENT OF THE SIX-WHEELER.
Page 51
Page 52
Page 53
If you've noticed an error in this article please click here to report it so we can fix it.
ONE OF the most important announcements ever issued by the War Department in connection with the co-ordination of military and civilian requirements in respect of transport was made a few days ago, when the War Department scheme for subsidized mechanical transport was extended to include that most interesting and eminently practicable machine, the rigid-frame six-wheeler, the subsidy offered being E40 per annum for three years, and the model being that known officially as the W.D. type medium six-wheeled lorry.
In some quarters doubts have been expressed as to the benefits conferred by previous subsidies, and the success of the results obtained from them. In our opinion, they not only do much to help the user in his selection of a vehicle, but, what is more, they popularize types which have proved successful, and the W.D. requirements have been such that they permit little doubt of a user obtaining a thoroughly satisfactory machine if hepurchases a subsidy model, for the specifications to which they have been built have ensured efficiency and good design.
The pre-war subsidy did not really have sufficient time to enable the fall benefits conferred by It to be
. reaped by manufacturers, users and the W.D. itself, but the post-war specification for a 30-cwt. vehicle suitable for running-on pneumatic tyres has, in our opinion, been an undoubted success, which is proved by the fact that full advantage was taken of the number of vehicles which could be subsidized in any particular year. Apart from this, the scheme did much to popularize the employment of pneumatic tyres on commercial vehicles.
We believe that the W.D. is most wise to select the medium-type vehicle for the subsidy. Incidentally, the specification is much more generous than was the case with the old 30-cwt. one. Only the essentials are now insisted upon; in other cases, the W.D. states its preference, but this does not necessarily mean that deviations will cause a vehicle to be rejected.
One important point is that no engine size is given; Instead a certain factor of performance is required. Similarly, with the bogie, this is preferably to be of the W.D. pattern, but if this pattern can be improved upon, well and good.
The specification is the result of experiments carried out over a long period with a view to producing a vehicle capable of putting up a reasonable crosscountry performance, whilst combining the maximum of efficiency as an ordinary commercial vehicle for use on roads. It is equipped with pneumatic tyres, and capable of transporting heavier loads than the ordinary four-wheeled vehicle of similar dimensions and power. By reason of its special gearing and construction it is capable of travelling fast with a normal load and
of towing a loaded trailer at slower speeds. In addition to these excellent features, it is most economical in fuel consumption and maintenance. Already the leading manufacturers of commercial vehicles are building this type of vehicle, and full information regarding it may be obtained by applying to the Chief Inspector of Subsidized Transport, 14-16, Grosvenor Gardens, London, S.W.1. Specifications and technical information will also be supplied to all chassis manufacturers on application to the Under-Secretary of State, War Office, London, S.W.1.
One of the reasons why we consider the W.D. is correct in subsidizing the six-wheeler having a fairly large load capacity, is that this should more readily appeal to the commercial user than a vehicle of this type carrying, say, 25-30 cwt., where the full advantages of the multi-wheeler are not quite so • apparent as is the case with the heavier model. The actual specification is wide enough to permit the building of sixwheelers which, in civilian service, should be able to carry with ease and efficiency loads of from four to five tons, and such vehicles should make a strong appeal to the civilian user, for the features embodied in their design, and in particular the semi-bogie arrangement of the two axles at the rear, confer undoubted advantages over four-wheeled vehicles of similar load capacity.
The special features indorporated in the construction are two driving axles under the load, a form of suspension of these axles which gives free articulation and maximum adhesion between the wheels and the ground, pneumatic tyres, a particularly wide range of gear to enable reasonably high speeds on the road and high tractive effort on bad surfaces, and a satisfactory degree of ground clearance under all conditions.
The W.D. special design for the suspension and transmission lay-out of the semi-bogie has been protected by patent application within the Empire. This has been done to place all British manufacturers on equal terms with regard to this special item, In that it is equally available to all of them if they wish to use it.
We have, on many occasions, drawn attention to the many advantages conferred by the employment of more wheels than four if these be arranged suitably; in fact, The Cornmeicial Motor was the first journal to• realize its potentialities, and it has consistently, advised makers to turn their attention to it, and users to ask for It. We inaugurated this campaign in 1921, and in face of much opposition and criticism from people who could not then recognize the benefits conferred. The wonderful progress which has been made since that time has shown that we were completely justified in the attitude we adopted. Six-wheeled passenger vehicles are now either in employment or are being ordered for use in many parts C29
of the country, some as the result Of expeXienCe already obtained with such vehicles, and we have no doubt that in a very short time there will be a big dernand for vehicles of this type designed expressly for the carrying of goods. We believe that they will not only save money to their users, but will do much towards the relief of expenditure on the roads.
For the information of our readers we will give a précis Of the specification which, it should be noted, is number 30. This must not be looked upon as a full specification, and those who wish this must apply for It as previously advised.
Engine.
Professor Dalby's test will be carried out on one or more engines of each batch, the fuel employed being No. 3 petrol. The curve for power, torque and petrol consumption must be planned out and furnished to the inspecting officer. All other engines will have a two hours' test under full load, and at a piston speed of 1,000 ft. per minute, followed by 10 mins, at various speeds up to 1,400 np.m. until the peak of the horse-power curve is passed. The b.h.p. must not be less than that calculated by dividing the revolutions by 40.
Decarbonization of piston top and cylinder head must be effected by one man in five hours with ordinary tools. A similar period is allowed for big-end and main bearings .examination, including the removal and replacement of caps.
Points in the construction include arrangements for the prevention of cylinder scoring by loose gudgeon pins, means for adjusting timing chains, an easily accessible and large oil filter, which it is desirable to be able to withdraw with:. out involving a big loss of oil. The .driver must be able to feel the lubrication indicator to see if the system be working. A high-level cock and a level indicator are tequired on the sump. Electric light is necessary and the dynamo must be driven positively—not by a belt. The throttle must automatically elose if it becomes disconnected.
With regard to the ignition, this must be by h.t, magneto, of an approved make, with hand control for advance and retard, and the flywheel must be clearly marked with a fixed pointer to facilitate ignition timing.
For the starting handle a locking device is required to keep the handle vertical when not in use. Folding or detachable handles will not be accepted.
Petrol consumption is not to be greater than one gallon per nine miles, and when under test no coasting Will be permitted.
Cooling System.
This must be easy to drain entirely. The temperature should not exceed 100 degrees Fehr. above atmospheric temperature at the radiator top immediately before and after tests on rough ground and those concerned with speed and hill-climbing. The system must withstand an internal pressure of 5 lb. per sq. in. Provision must be made to reduce the cooling capacity. The drain cock must be of not less than 4-in. bore and not subject to accidental opening. A. vertical tube type with detachable header and bottom tanks, with tubes not less than Ton. in., is preferred. Preference is given to a hinged cap with screw adjustment without loose parts and with an opening of 2i ins. area. A copper gauze strainer of 50 mesh is necessary. The fin. overflow pipe must be baffled and a stout bar or tube at least 14 ins. in diameter must protect the radiator.
Petrol System.
This must give an adequate supply on all gradients inchided in the specification and on any road camber, even when the tank is nearly empty. It must provide enough for 120 miles without replenishment. The tank must be of non-ferrous metal and feed solely by gravity, a two-way cock retaining 2-1, gallons in normal position, releasing this
in the third position. It is preferred that the cap be identical with that on the radiator. A removable copper gauze strainer of 200-mesh is necessary; also an accessible, and easily cleaned filter between the tank and carburetter.
Clutch.
This must permit the loaded vehicle to start from a
standstill on top gear on level road. Multiple disc or leather-faced clutches will not be accepted. A clutch stop must be provided.
Gearbox.
The factor of performance must not be less than 55 for negotiating bad surfaces or extreme gradients. The formula for this factor is given in an appendix (not reproduced). In addition the loaded vehicle must start in forward or reverse gear on a gradient of 1 in 5, climb an average gradient of 1 in 10 at not less than 5 m.p.h. for a quarter of a mite, maintain an average speed of 20 m.p.h. for five hours on a selected route, including gradients not exceeding 1 in 15, and cover one mile from a flying start at, at least, 30 m.p.h. on the level. On speed trials the governor gear, when fitted, may be removed, Gradients, are measured as the ratio of the vertical rise to the equivalent horizontal. distance.
At least four speeds forward and one reverse of normal ratite; are required for ordinary road use. Gate change is essential, with a safety catch for reverse. With a subsidiary reducing gear, a separate lever must lie provided. Uiilesg the slots are marked clearly and are in view of the driver, a legible diagram must be fitted to the dash. A combined mileometer and speedometer positively driven from the transmission and mounted on the dash is necessary. No speedometer need be fitted to civilian-owned vehicles enrolled under the scheme, but the gearbox must provide a positive speedometer drive if required.
The gearbox must be fitted with a test plug or cock for the oil, or, -preferably, provided with, a filler . orifice through which the level can be seen, this being so placed that the box cannot be overfilled. The sliding-type box is preferred.
Final Transmission.
Rear axles must be fully -enclosed and without tie rods. It is preferred that the oil level cant be seen and the filler so placed that the easing cannot be overfilled. Chain drive is not acceptable.
Universal Joints.
All joints behind the gearbox must be of the all-metal type. Adequate and unfailing lubrication is essential.
Jack Platforms.
It is desirable that front and rear axles should have suitable platforms near the ends to receive the head of a jack. These platforms will not be less then lei ins, from the ground with all tyres removed.
Wheels.
Vehicles bought by the War Department will he fitted with twin wheels on each driven hub, and single wheels on the front hubs, all to take 36-in. by 6-in. pneumatics, the wheels to be 24 ins., with 6-in, rims, with an offeet of 4.25 ins, and a bore of 221 mm.; the nave thickness is to be 11 mm., and eight stud holes on a pitch circle diameter. of 275 mm. are required, the studs and nuts to be standard W.D. taper-seat pattern. Provided the hubs and clearances enable this equipment to be fitted, the vehicles may be accepted for subsidy on alternative wheel and tyre equipments., e.g., 36-in. by 6-in., 34-in. by 7-1m, 28-in. by 7-in., etc., singles on all wheels at the discretion of the Q.I.S.T. It should be noted, however, that the factor of performance will, therefore, be calculated in all cases on the basis of the 86-in. tyre.
Tyre Pump.
This must be capable of inflating to the correct pressure in five. minutes, air to be free of all traces of oil. It must be positively driven as an integral part of the design.'
Steering.
The turning circle must not exceed 50 ft. in diameter. It wilt be determined on level hard ground for both locks and will be taken as the outside clegmeter of the circle made by the track of the steering wheels. Stops must be provided to prevent the tyres of the front wheels fouling any part of the chassis.
Chassis.
The effect of frame distortion will be tested with the vehicle loaded by jacking up one front wheel until the other is off the ground. Tests on reugh ground will be conducted to test overheating of the water and articulation and adhesion of the driving wheels. They will include trials on soft sand tiP to 10 ins, deep, wet clay land and bog, rough natural heather and gravel land with gradients up to 1 in 3. The vehicles will also be driven through water 18 ins, deep, and this must not affect running.
It is considered that the ratio of the commercial useful load, on home roads, to the chassis weight should be from 1.2 to 1.4. The vehicles will, however, be considered to be 'within the scope of the specification when the ratio of the usefulW.D. load of 3 tons to the chassis weight is not less than 0.9. This indicates a maximum (diesels weight of about 65 cwt.
It is preferred that fitted and driven bolts be used in place of rivets throughout the eheSsis for parts liable to replacement.
The minimum road clearance must be 10i ins.
A new feature of this specification is that the W.D. sprung towing gear is not essential, but the rear end of the frame must be so designed that it can be attached without
drilling fresh hales or distoibing any other part of the ci assis. The engine and gearbox units must be mounted Ilk a three-point suspension system.
The maximum overall width must not exceed 7 ft. 6 ins., and the track of the front wheels at the point of ground contact must not be lees than the track of the inner tyres, or greater than the track of the outer tyres. It is preferred that it should not be 6 ine, greater than the track of the inner tyres.
Towing loops of W.D. pattern must he ,provided at each end. The chassis frame must be braced against horizontal distortion due to a direct or diagonal pull in any direction up to 20 degrees with the longitudinal axis.
The suspension of the driving axles must give free relative movement of the driving wheels, according to the limits given I under one of our illustrations, without disturbing the eauklity of weight distribution. It is also essential that this equality should not be disturbed by any conditions of torque, tractive effort or braking effort.
Stops must be fitted TO limit finally the movement of the axles,. upwards by rubber or spring buffers on the side members, and downwards by suitable straps encircling the axles and dependent from the side members..
An important clause is that in order to obtain adequate body space with reasonable wheelbase, there is no objection to the driver being enclosed in a forward position or alongside the ermine, provided that accessibility is perraitted, and . the general' layout approved.
Chassis bought by the War.Department must be of such dimensions as to carry a W.D. pattern cab and body, the main dimensions of Which are given in one of the illustrations, but it is realized that with subsidized vehicles longer bodies may be required, and it is hoped that by extending the length of the side members so that reduction of them will be a simple matter of cutting off the surplus ends without structural alterations, the maker may be able to meet without difficulty the requirements of the commercial user and the War Department.
Control.
The pressure and range of travel of the pedals must permit easy control bya driver of average height and strength. Clutch pedal on left, brake pedal on right, and foot accelerator are required. Brake levers must pull on and be well away from the change-speed lever. It is preferred that the levers for throttle and ignition move forward to increase speed and operate over a rack or an equivalent arrangement.
Brakes.
Each brake must smoothly and effectively stop and hold a loaded vehicle on a gradient of 1 in 5 in each direction. The design must permit the continuous application of one brake only for half a mile on the average gradient of 1 in 12, and at not less than 8 m.p.h., with the gear lever in neutral. Each brake to be capable of adjustment, without tools, in five minutes. It is preferred that brakes operating on drums on the driving wheels be compensated. They must not be operated by wires or chains.
Body.
In the ease of civilian-owned vehicles, the following stipulations will apply :—Only goods-carrying vehicles of reasonable weight will be accepted. There must be no internal fixtures rendering them unsuitable for bulk loads. With a lorry, sides and hinged tailboard not less than 18 ins, high must be provided. They may be detachable. It is preferred that with a van body the internal height. should be not less than 5 ft. and not more than 6 ft., .
Lubrication.
Oil lubrication throughout the chaeeis is essential, and high-pressure. rigid-nozzle guns, such us the Enots Autoram and Tecalemit Zerk, are preferred.
A full set of cloth process tracings of drawings with leading dimensions must be supplied. The list is given in the specification. In addition, an illustrated handbook for the driver's instruction, and including a lubricating chart, must be provided with each chassis.
• Equipment.
All standard tools, jack, etc., will be supplied by the War Department. Particulars are included in the appendix.
The makers will be required to supply special -lords and ecuipment additional to these.