The Light Van Problem and How it Must
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Page 9
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Be Tackled.
Some Suggestions as to Desirable Capacity, Power and Type oi Construction.
(Continued from page 8.)
In the course of our investigations into the problem which is the subject-matter of the present .series of articles, we have,it may be recalled, gone into the pros and cons of ,the..case for the substitution of small motor vehicles.forcycle carriers in considerable detail. We haveindicated 'those numerous employments of the latter, whichwe, without prejudice, fairly say cannot at present be superseded by automobile means. By this process of elimination we have been enabled clearly to indicate other distinct grades of employment for cycle carriers which may be properly challenged by the smallest industrial-motor units.
In our last instalment, we went on to investigate the possibilities of the supersession of the one-horsed cart, as distinct from tradesmen's other light vehicles. We have dealt with the one-horse van on munermis occasions in other issues.
The Need for Clever Design.
We had. thus reached that stage in our consideration of the subject in which we had become convinced that these various classes of employment -called for motor-vehicle construction of a very special kind, it will not be inappropriate for us, in this connection, to quote from the concluding paragraph which we wrote last week under the present heading : "We wish to urge, it will be seen, that the energies of designers and manufacturers chould be bent upon the production of really cheap mociels--cheap but good, of course It is strictly necessary to be able to suggest to the obstinate customer of the tradesman class a vehicle of which at least he can think on something of a plane with his horse, his harness, and his cart."
Now, that is the whole crux of the situation, so far as the problem concerns the manufacturer and the designer, and we may devote the present instalment of this article to the setting down of certain broad general lines of design upon which we consider manufacturers may very well concentrate, in order to cater for the light-van user.
The Parcelcar is an Established Type.
At the moment, we do not desire further to discuss the design of the three-wheeled parcelcar or to criticise it. This is a type which has the recommendation of several years of hard practical service behind it, and it has been prayed, in spite of much preliminary criticism of a destructive nature, to serve very well many requirements of the storekeeper and of the larger tradesman, What Some Users Prefer.
The parcelear is quite properly grouped with the light van as a class of delivery plant of similar load-carrying capacity, but there is a distinction which will be obvious to most of our readers. The light van will have to be a design which will more closely approximate the needs of those who do not find in the parcelcar, in its normally developed form of construction, just what they would wish in respect of stability under all ciremnstance.s, n14 accessibility of components, protection and comfort for the driver, and appearance. And, it must be remembered, there is a considerable proportion of users which prefers a four-wheeler.
Points like these, and certain others which will occur to those who have the matter under consideration, must be largely answered by the individual. As we have said, the pareelcar serves well in certain classes of service. But there is also a rapidly-growing demand for the light van proper.
To Carry Up to 7 cwt.
Now, as to type and constructional details. First of all, we must decide as to the load-carrying capacity for which the machine is to be sold, and two courses are open to the designer, as with all other commercial models. He must either sell the machine as of load capacity considerably ,below that which he anticipates will be frequently carried, or he must sell it with the description of its intended capacity in this respect, with the stipulation that no guarantee will be given if overloading is to be authorized on any occasion.
The light van itself may be fairly classified to include all four-wheeler industrial models which have a load-carrying capacity of nothing greater than 10 cwt. The happy mean, we consider, will be attained with a machine which will carry at the utmost 7 cwt. net load. This, from our investigation of the subject would appear to be providing for the requirements of a very large body of tradesmen and similar would-he users. The light van mast also be a small van ; it must require little storage room.
The Speed and Power Desirable.
We will assume the net load capacity at something between 6 and 7 cwt. then, and we shall require to attain speeds on the flat at times of as much as 25 miles an hour. Moreover, we must be able, with full load on board, to climb gradients of I in 10 at a reasonable speed and without overdoing the engine. We do not think it necessary to provide for heavier work than that with the standard model.
The weight of the chassis should not be in excess of 10 cwt,. and something considerably less than this
will, with certain designs, be found quite practicable. A two-cylinder, water-cooled engine should suffice for the power unit, and probably a bore of 3:; ins, and a stroke of 41 ins, will be about the best proportions for it. A leather-to-metal cone clutch is the simplest form for this component, and the cheapest to maintain and to replace. A simple sliding three-speedand-reverse gearbox, with a propeller shaft drive to a worm-driven back axle appeals to us as a cheap, simple, efficient and hard-wearing drive.
Some Framework Suggestions.
It is probable that rolled channel-steel framing will be found to be the best for this class of work. Tubular flanged cross members may be usefully em bodied. The points to be considered in respect of framework are : strength, cheapness, simplicity of repair, and ease of attachment for springs, brackete, and fittings.
There should be one transverse frame member amidships, on which to anchor the rear portion of the gearbox, and another at the back end of the frame. The front one can well be formed either by the bending round arid butting of the channel side members, or by the making of the side members and the front cross member of one piece, bent like a big IT. Four long semi-elliptic Springs should be provided.
A Large Radiator. Unit Assembly.
Now, with regard to engine detail, we should be inclined to spend a little money on a thoroughly adequate radiator, and, the therrno-syphon cooling being proportioned on ample lines, a fan and pump could be dispensed with. The cylinders should be east with ample water jackets. As the engine is a two-cylinder model, adjustable ignition will be advisable. No adjustment need be provided on the valve tappets. Lubrication should be good enough on the splash system, suitable oil channels being cast in the crank chamber both transversely and longitudinally. The crankcase can conveniently be bolted by extensions to the gearbox case, in order to save the, cost of alignment in erecting. Three-point suspension is secured in this way, although the principal advantage obtained is that the power units can be erected in large numbers separately and dropped fully equipped into the frames.
A quite simple form of leather-disc universal joint could be used on the forward end of the propeller shaft. The worm geareasa could be made a cheap job in malleable cast-iron, and, taking everything into consideration, it would be best to design the worm on top of the wheel in alignment with the gearbox.
A Spur.gear Differential and Its Shafts.
There is probably little to be gained by the adoption of any form of differential other than one of the spur-gear class; the differential should not be ei!minated for economy's sake. The efficiency of the sour-gear type is slightly higher than flat of the bevel-gear pattern, and the cost is rather lower in respect of the former. The differential shafts should be of the floating pattern, enclosed ie mild steel tubes, the latter .being brazed into the worm-gear easing; swaged tubes are expensive and screwing is liable to weaken the structure. These tubes, of eonrse, should take the weight only, the differential shafts being responsible for the driving and braking
torque— the latter often by far the greater. Steel pressings for the back-axle casings, of course, are an available and probable alternative if huge numbers of these units are to be put through ; the worm housing in such construction requires very careful design and workmanship.
Brakes and Wheels.
With regard to brakes, both foot and hand-actuated sets shoula engage on steel drums bolted to the rear eoad wheels. There is little reason why these should
not, operate on the inner and outer surfaces, respectively, of the same drum on each side. The most satisfactory road wheels will probably be found to be of the wooden artillery type. The wire wheel, of course, has much to recommend it with regard to strength, but there is the great objection that it will probably not be found to be kept in such good or such clean condition as the wooden one in industrial service. It has seldom been adopted for cabs, it is well to recall.
Ball bearings sitouki be used in all four hubs, and in this connection we would suggest also the use of bail bearings for the crankshaft of the small engine, and, of course, in the gearbox and back axle. We are not putting a great deal of power into this machine, and, therefore, it is important that as much of it as possible should get through to the tires of the back wheels.
Some Suggested Overall Dimensions.
The size of the road wheels may be 25 ins, all round, the wheelbase perhaps 7 ft. or 7 ft. 6 ins., and the track from 3 ft. 8 ins, to a ft. A suitable body might be of the following sizes: length, 4 ft. ; width, 3 ft. 6 ins. to 4 ft, ; and height, 4 ft. 8 ins, outside sizes. With regard to the steering gear, the Ackermann type, of coarse, will be adopted, and a worm, with a complete worm wheel, affording four adjustments, will probably be found economical. This latter refinement is a very useful one, which can be effected in this ease at no very great extra cost.
'Ike front transverse steering tube should be positioned behind the front axle, the latter being of stamped I-section steel. The anchorage of the steering column should be so designed as to enable the rake to be easily adjusted, so that the standard chassis can more readily accommodate various special ts'pes of bodies if necessary.
The petrol tank may be cheaply and effectively placed on the dashboard, and, by the use of suitable brackets, also carrying the lamps, the dash may be suitably stiffened and the tank supported firmly and cheaply ; no screen is necessary.
To Sell at £150 or Less.
We have only attempted to indicate the broad general lines on which we consider a machine of this type may well be constructed, but we have in our possession certain schemes for little vehicles, of this class, which it should be possible to sell in considerable numbers and at reasonable profit for .something in the neighbourhood of £150, and this price should include three lamps and a small but adequate tool kit.
It is agreat point to remember that the prospective tradesman-owner, who is a business man himself, is likely to appreciate the soundness of a definite offer for a certain figure. He is certainly more than inclined to be irritated by the suggestion of a number of additional fittings that should' be purchased—need,less to say—at additional cost.
In our next issue we shall publish a fully-illustrated description of a first-class example of light-van construction, which is just being put upon the market at less than the above figure. We shall also write briefly of the probable costs of running. We may conclude bv reminding users—manufacturers will know it, of course—that the problem of the production of a simple and cheap small van is a very di fferent one for the man who is out to make, shall we say, one a week, to that with which the bigoutput factory is fated. These are considerations for the individual producer. We can usefully do no more than to indicate the general trend of requirements as revealed by our extensive inquiries and careful observation.
We shall be hapny to enter into correspondence with any responsible parties who are contemplating this class of manufacture, with a view to placing our own experience and information, so far as possible, at their disnosal. We shall welcome inquiries of the kind, and do our hest to satisfy them.
fro be concluded.)