Opinions from Others.
Page 12
If you've noticed an error in this article please click here to report it so we can fix it.
Are Tractors Too Powerful?
The Editor, TEE COMMERCIAL 110TOR.
[1256] Sir,—" .Verax's" most-ingenuous letter [No. 1254] in your issue of the 16th inst. asks me further to explain the old traction-engine user's method of throwing the weight of the trailer on to the locomotive, as suggested by the writer for use with the fight tractor. Before doing so, it will, however, be necessary to refute " Yenta's" statement that the Broomand Wade tractor " was not sufficiently powerful to skid the driving wheels " in the War Office Trials of 1909.
" Yeraxis " own statement, viz., that "the Broom. and Wade tractor, which participated in the War Department Trials of 1909, as stated by Mr. Aveling, had a single-cylinder engine, stated to give 25 b.h.p,, and it is quite correct that less slip took place with its driving wheels than was the case with the Thornycroft tractor." His own statement, therefore, proves that the Broom and Wade tractor did have sufficient power to slip the driving wheels, but not so much as in the case of the Thornycroft tractor. The trouble, accordingly, is pot " are tractors too powerful "— since a 25 h.p. single-cylinder tractor can slip its wheels, but " how are we to increase the adhesion of the wheels of the tractor, so as to make full use of any power, however small, that it may be designed to develop ? " I consider that the more power the better, in the ease of a steam: tractor, and that this power "can be applied at the wheel rim" by the angularity of attachment of the load hauled.
In the old days of the road locomotive, the average driver never considered his locomotive " stalled " until ihe had made the smoke-box end of the boiler lift the fore-carriage and front axle from the road. When this happened, he began to consider if it would not he necessary to lighten the load. The reason the front end of the locomotive lifted was due to the angularity of the attachment of the load, the locomotive being a lever with the bind axle as centre, the load at the smoke-box end of the lever being less than the load at the tender end of the system. To overcome this difra culty, i.e., to lessen the load at the tender end of the lever, it will only be necessary to move the centre of the lever more towards the tender end, or. in other words, to attach the Toad as close as possible to the centre of the lever, which, in the case in question, is the hind axle of the locomotive.
My reason for dividing the tender is to avoid increase of the width of the tractor and to utilize the weight of the water in the tender to give increased adhesion, according to road-locomotive practice. If I have not made myself clear to " Verax," I should be very glad to submit to him—[T]irough our columns,
we hope.—En.]---a sketch and diagram showing the forces involved, and the advantages obtained by attaching the drawbar of the trailer to the main axle of the tractor at a suitable angle to secure the required result.
Measrs. Brainco's letter, following that from " Verax" in the same issue, makes some interesting references to a La France tractor-wagon. At the same time, I would venture to point out that the adoption of the tractor instead of the steam wagon in most instances is due to its capability to travel where a steam wagon would fail. if we increase the weight of the tractor by loading it, we have the same difficulties as those which are encountered with a steam wagon running on unmade roads. How many brickmakers have given up the steam wagon because of the impossibility of running a loaded one up to a building site ? The unloaded tractor, on the other hand, with its wire rope, can extricate itself out of any hole it may get into, and wind its trailer on to good ground. I reiterate, that the larger are the boiler and the engine of the steam tractor the more value is the machine to the purchaser, and that, without any great structural alteration in design of the tractors now On the road, they could be made to haul their eight tons without slipping by the simple means I have suggested.
have to thank" Verax " for this opportunity of ex plaining.—Yours faithfully, T. C. AVELING. 91, Canal Street, Birmingham.
A Challenge as to Resiliency The Editor, THE COMMERCIAL MOTOR.
[1257] Sir,—When people are at variance on a punciple, the real issue is often made clear by an analogy. The quality of the rubber insulation of an electric cable is the product of its durability multiplied by its electrical resistance. Conversely, the quality of a solid tire is its average mileage multiplied by resiliency, but, exactly as the resistance would never be measured except at the point when the cable is under water, so one must similarly consider resiliency at the point of maximum compression. Mechanically, it is certainly not in accordance with best modern practice to employ a pad of pure soft rubber when energy has to be constantly absorbed and a certain amount of heat thereby generated. It is well known, for example, that the tires on, say, a three-ton lorry, after a long non-stop run carrying a full load, will be quite warm. Pure rubber is unsuitable, .and has as a matter of fact been practically discarded in the electrical industry, largely owing to it tending to become soft under the influence of the latent heat that is generated in the heavier cables transmitting energy in bulk ; it also tends to become hard in winter.
The art of this manufacture is the correct blending of pure rubber with mineral matter, so as to produce a homogeneous mass, of maximum elasticity and greatest durability, which will retain these unique properties under "work." This is the reason that the best mechanical or electrical rubber contains added mineral matter.
The standard form of solid-band tire is already far too large an item and existing reliable working part of our present economical running costs to permit its principal advantages to be side-issued. It cannot be too clearly stated that resiliency, to be immediately effective, must be in the tread itself—at the point of contact with the road. No amount of " nursing" by pads of soft rubber or springs, either in the wheels or chassis, will in itself exclude the engine or load from the minimum of shock.—Yours truly,
LIGA TYRES, LTD. 26 Portugal Street, W.C.,