DESIGNING AND BUILDINC NE W.D. SPECIFICATION.
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THE SPECIFICATION (No. 11) of the War Department 30-cwt. lorry recently issued does not differ very widely frons that of 1922, which we published in our issue of August 1st of that year. With regard to the constructional details of the engine the specificaticn calls for a maximum swept out volume of 3,500 C.C. Suitable arrangements for preventing a gudgeon pin from scoring the cylinder are mentioned as essential. A large and efficient oil filter is to be fitted it such a position that it can be easily withdrawn for cleaning purposes without the loss ofthe bulk of the oil from •the crank chamber. A lubrication indicator is to be fitted within easy reach of the driver, so that he can " feel " whether the system is working. Test ceckz are aiso to be fitted to the engine sump. A positively driven 12-volt lighting dynamo, with two headlamps, two side and one tail lamp, is mentioned, bat this item is not essential in the case of vehicles which aro civilian-owned.
Piston Decarbonization Without Special Tools.
The following performances are specified as essen_ tial. Professor Dalby's Acceptance test, mentioned in appendix " D" of the specificseion, will be carried out on one or more engines of each batch. Arrangements for the decarbonization of piston tops and cylinders is made a special feature, and the removal of carbon has to be capable of being corn_ pletely carried out by one man in the specified time of five hours. The tools used in the operation must be only those normally carried on the vehicle. We notice that the use of special tools is condemned. This seems to us to be a very wise decision, as special tools are likely to get lost and without them a driver may be at a loss to know how to improvise a means of doing. a job. The removal and replacement of all caps of big-ends and main bearings has to be accomplished in five hours. (The number of men allowed is not mentioned.) We notice, in the specification of the ignition, that a hand control for advance and retard is mentioned as essential.
With regard to filet consumption, a performance is expected of one gallon per 12 miles, on 9. run of two hours' duration at an average speed. The cooling system is much the same as in the previous specification, excepting that no mention is made of the vehicles being expected to work in tropical climates, although provision for working in cold climates is still insisted upon. The bore of the tubes of the radiator has been reduced from in. to h. in. internal diameter. Straight vertical tubes, with tanks top and bottom, are specified. The coolmg system is expected satisfactorily to pass the following test :—The temperature of the water will be taken before and after the tests over rough ground, speed trials and hill-climbing, and it must not exceed 100 deg. F. above atmospheric temperature. The water circulating system, including radiator, is expected to withstand a pressure of 5 lb. to the square inch.
Non-Ferrous Metal for the Tank.
The petrol tank, we notice, is now specified to he made of non-ferrous metal, whilst, in the previous specification, " welded steel tanks, galvanized after making," were recommended. lead-coated -steel tanka being barred. It is interesting to know the reason for this (referred to later), as lead-coated steel has proved itself a very satisfactory material for tanks. The clutch is one of the components in which alteration in the specification has taken place. In each specification the plain cone type was admitted, but in the present one the use of leather for a lining is 'barred. The performance expected is that the clutch must permit the loaded vehicle to be started from a standstill on top gear on a level, hard road. With regard to the gearbox, no ratio of gears is mentioned in the present specification, but in the pre
viens one 35 to 1 was mentioned as a suggested ratio .for the lowest gear, and a ratio between top and bottom gears of about 5 to 1 was suggested. However, a high standard of performance is required, for the lorry, fully loaded, will be required to climb a, gradient of 1 in 4i, on a hard road without manipulation of the cluteh, the speed of approach having to approximate to the speed of the climb. The lorry must stop and restart on a gradient of 1 in 5 in both directions, and must climb an average gradient of 1-in 10 at a speed of 8 m.p h., on a hard road, for a distance of a quarter of a mile. The lorry, running on level roads, with good surfaces, must be capable of a speed of 30 m.p.h. for one mile, and of maintaining a speed of 2',3 m.p.h. for a period of two hours. Final transmission is specified as being of the fully enclosed type, without stay rods, but no mention is made as to whether any particular kinds of bevel gears will not be accepted. In the previous specification, double helical gears were not permitted, and the use of single helical gears would only be allowed after special consideration. Chains, as a drive for the final transmission, are still barred.
In the specification, the question of the class of universal joint to be used is left blank. In the previous specification, laminated „fabric or leather discs were mentioned as being preferred, but metal universal joints, if properly enclosed, could be used.
In specifying a " fully enclosed " rear axle, we take it that this does not apply to the propeller shaft, as, when flexib]e-fabric discs are used in the universal joints, it is not convenient to enclose them.
Road-wheel bearings are evidently left open to the discretion of the manufacturer. In the previous specification, taper roller bearings were mentioned as being. preferred, but plain. floating bush or ballbearing types would be accepted if approved.
British Pneumatic Tyres Demanded..
Road wheels are specified as being in accordance with the W.D. standard hub fitting, and to be suitable for tyres 34 ins. by 7 ins. or 38 ins. by 7 ins. The wheels are offset towards the centre of the vehicle, and are shown in Fig. B.P.733a. An alternative road-wheel equipment is provided for, however, which permits the substitution of standard W.V. wheels on mobilization. No mention is made of any special clearance for non-skid devices, such as chains, as in the earlier specification. Tyres are specified as being of the giant•Etraight-wall type, of apploved British make. The same size will be used for all four wheels. An alternative equipment, however, will be considered, provided that it can be changed to W.D. standard on mobilization. There is no mention of twin tyres being accepted, as in the previous specification. The outfit is to include a positively driven power inflator, which is to be an integral part of the design. Inflators operated by the pressure in the engine cylinders will not be accepted. The performance expected from this pump is that it shall be capable of inflating the tyre to the pressure specified by the makers in five minutes at the most. The vehicle must carry • a useful load of 30 cwt. The chassis weight is increased from 29 cwt. (as in the previous specification) to 35 cwt., but preference will be given to those makes which come below this latter figure.
A performance is, however, expected from the chassis, as regards frame distortion, as follows:— The effect of frame distortion on engine and gear control will be tested by jacking hp one liont wheel until the other is off the ground, with the vehicle fully loaded. During this test, it must be possible to operate the following without difficulty : (a) steering wheel ; (b) clutch ; (c) brakes ; (d) changespeed lever ; (e) engine starting handle ; (I) engine hand controls.
Capabilities Over Sand and Through Water.
Other severe tests are made over rough ground, which include running over sand 10 ins. deep .and ever unmetalled lanes. A watersplash, 18 ins, deep, with a hard bottom, has to be negotiated without affecting the running of the engine, magneto or carburetter. Oil lubrication is still preferred to grease, and this confirms an opinion we have expressed on many occasions. Taken as a whole, we do not think that manufacturers will have much cause for complaint concerning this modified specification, and more of them will be able to build to it with few departures from their standard practice, whilst no difficulty would seem to be created in complying with the various stipulations and suggestions, so as to enable a vehicle to qualify for the subsidy.
With regard to the performances demanded, in some instances the tests to be imposed seem rather severe. The 18-in. watersplash would be somewhat tiying to many vehicles, unless the engine and. gearbox were constructed as a unit. A great deal more latitude is allowed on several points than in the previous specification as regards the details of construction. On the other hand, the performances expected are more clearly set out. We think that this, perhaps, is a better plan than tying the designer too tightly to any particular form of construction. The specification really shows what should be aimed at rather than the means whereby that result is obtained.
Suggestions for Increasing Usefulness in Time of Warfare.
A few points occur to us as being likely to increase the usefulness of a vehicle when subjected to ihe very severe conditions prevailing in warfare. Some Of these suggestions might be worth consideration in future specifications.
We should have thought that the locking of the differential was worth while considering Vlrhen vehicles have to go over all sorts and conditicns of roads, as in war time. It might be said that no really satisfactory leek for differentials has been adopted for petrol vehicles yet, and this may be true to an extent, but we feel sure that, were some encouragement given to designers to produce such a device, we should not be very long before we had more than ene useful and quickly operated contrivance of The kind. More difficult things than this can be accomplished.
When vehicles are crowded together and subjected to extremely rough handling, as in war-time, one of the most vulnerable parts is the radiator, as, no matter how well protected, it is likely to become damaged. Should a change of radiators be needed it is usual to break the joint of the rubber hose, and this usually results in the :scrapping of this part. Unless a man is provided with a spare piece of hose, there is often delay. It has been suggested, and in many cases is standard practice, that the radiator be provided with suitable detachable flanges, so that the water pipes and their rubber hose need not he disturbed when removing a radiator.
Attention has been drawn to the danger of compensated brakes, in the event of one of the pull rods becoming useless through an accident. A device has recently been introduced for use in pleasure cars, whereby the compensating lever can be locked when once the correct compensation has been arrived at. By means of this very simple arrangement it would he possible for one side brake to be thrown out el action, without the complete failure of the brake result:ng. There seems to be no reason why the compensating device need be always in action after being once properly set. Some suggestions as to the best methods of carrying tools, spare parts and equipment, such as jack, tow lines, spades, etc., might be made. It is one thing to have the right tool, spare part or equipment with you when trouble happens on the load, but it is quite another thing to be able to find the implement quickly when wanted, and to be able to rely on it being in a satisfactory condition when found.
We have heard of the driver who " had a place for everything, and everything in its place." This sounds quite encouraging, but, when inquired into, it was found that it was all the same place, namely, one large tool box, in which all smaller parts were pounded to pieces by the larger and heavier articles. Cupboards with partitions labelled for the reception of certain articles have been found of the greatest value in keeping the more delicate parts from damage.
This arrangement also helps a kit inspection, as it can be seen at a glance whether any article is missing.
The following information may be of value to those who are interested in the production of vehicles which are intended to be in accordance with the specification. This information is not given as official, but it has been gathered from reliable sources.
In travelling through a watersplash, it has been .found, with most vehicles, that water has come through the radiator, and has caused trouble through getting to the fan belt, magneto and carburetter. We suggest that some device should be adopted whereby this might be prevented. A suggestion is made in our illustration where the number plate is shown to hinge, so as to he capable of being raised when the vehicle is passing through water. If baffles are fitted to the radiator to prevent undue cooling in cold climates, they might easily be made to perform the, double duty of baffle and shield for water. In the rapid inflation of large pneumatic tyres, it has been found that undue heat is often generated in the compressor. We understand that a watercooled pump would be welcomed, a position close to the engine being preferred. The pipes leading to the pump might be provided with a tap so that the water circulation to the pump is only in operation while the pump is in action. We understand that, although multi-plate clutches are not desired, there would be no objection to that class of multi-plate clutch in which the plates are not too thin and do not number more than seven. The clutch must, however, be one that works dry. Owing to the difficulty of keeping water from the magneto and carburetter, it is as well that these should be placed as high up as is conveniently possible.
. Although an undershield is specified; we understand that it may be possible for a vehicle to pass inspection without one, provided that every unit is properly protected from water \ entering it, and is so designed that, an undue leakage of oil is not possible. We feel sure that most of YJ those who have experienced the difficulty of keeping an undershield in order will welcome this.
The locking of the differential would, we understand, be welcomed, although it is not specified.
A spring device to which a drawbar for a• trailer can be attached would, we believe, be considered an 'advantage if made to act in both directions. The idea is that such a device permits of a rigid bar being used, which can push as well as pull.
We gather that the detachable wheel should not interfere with the brake drum, which should be permanently attached to the hub. In many cases, shackles, as • shown in our illustration_, have Proved more satisfactory than the ordinary hooks for towing, although we should have thought that hooks wOuld be quicker to deal with.
With regard to the length of wheelbase, we understand that as short a• base as is compatible with convenient use for civilian purposes would be preferred. Throwing the front wheels slightly backward, as is shown in our illustration, would be more acceptable than disposing them right in front of the chassis.
The barring of ferrous metal for the construction of petrol tanks may seem curious, as it is in common use and is found to be quite satisfactory. We understand, however, that, when such tanks have had to remain unused for long periods, rust has been found to form inside them, and for this reason non-ferrous metal should be used in their construction.
Our, illustrations of the chassis on the centre pages suggest the use of a pressed-steel pan to protect the underside of the flywheel and clutch from water when the vehicle is crossing a water-splash, but this is merely a suggestion put forward so as to permit dispensing with the undo rshl el ci which nowadays is favoured by few. The spring support. for the towing hook is, we believe, a proprietary idea, and, as perhaps ether suggestions included in our illustrations, is picked out as being an acceptable method of comply
with ing with the requirements of the War Department. In the wheel illustrated we show the form of the bolts and nuts adopted to ensure interchangeability.